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Sample records for rapid glacial retreat

  1. 2017 Rapid Retreat Of Thwaites Glacier

    Science.gov (United States)

    Milillo, P.; Rignot, E. J.; Mouginot, J.; Scheuchl, B.

    2017-12-01

    We employ data from the second generation of SAR systems e.g. the Italian COSMO- SkyMed (CSK) constellation and the German TanDEM-X (TDX) formation to monitor grounding line retreat using short repeat-time interferometry and accurate InSAR DEM on Thwaites glacier in the Amundsen Sea Embayment (ASE), West Antarctica. The ASE is a marine-based ice sheet with a retrograde bed containing enough ice to raise global sea level by 120 cm. Several studies have inferred the mechanical properties of portions of ASE using observationally constrained numerical models, but these studies offer only temporal snapshots of basal mechanics owing to a dearth of observational time series. Prior attempts of grounding lines mapping have been limited because few space-borne SAR missions offer the short-term repeat pass capability required to map the differential vertical displacement of floating ice at tidal frequencies with sufficient detail to resolve grounding line boundaries in areas of fast ice deformation. Using 1-day CSK repeat pass data and TDX DEMs, we collected frequent, high-resolution grounding line measurements of Thwaites glaciers spanning 2015-2017. We compare the results with ERS data spanning 1996-2011, and Sentinel-1a 2014-2015 data. Between 2011 and 2017 we observe a maximum retreat of 5-7 km across the main Thwaites glacier tongue and Thwaites Eastern ice shelf (TEIS) corresponding to an increased retreat rate of 0.5 km/yr. Grounding line retreat has been fueled by the enhanced intrusion of warm, salty, subsurface ocean water of circumpolar deep water origin onto the continental shelf, beneath the floating ice shelf, to reach the glacier grounding zone and melt it from below at rates varying from 50 to 150 m/yr. The retreat rate varies depending on the magnitude of ice melt by the ocean, the rate of ice thinning and the shape of the glacier surface and bed topography.

  2. Timing of Glacial Lake Missoula Outburst Floods and the southwestern Cordilleran Ice Sheet retreat.

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    Hendy, I. L.; Bervid, H. D.; Carlson, A. E.

    2017-12-01

    Glacial Lake Missoula formed when the Purcell Trench Lobe dammed the Clark Fork River in Montana and catastrophically collapsed repeatedly through the last glacial period as the southern Cordilleran Ice Sheet advanced and retreated. A well-dated 50-kyr jumbo piston core MD02-2496 (48.97˚ N, 127.04˚ W, water depth of 1243 m) collected from the continental slope 75 km off Vancouver Island contains evidence of these floods. The in-situ bulk elemental composition of the 35-m core was determined at 1 mm intervals using an ITRAX X-ray Fluorescence (XRF) Core Scanner (Cox Analytical Instruments) at the Sediment Geochemistry Lab of the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University. With 40 mixed planktonic foraminifera and bulk organic carbon 14C ages, the core provides a high-resolution resolution record of glaciomarine sedimentation during deglaciation. A series of >81 layers of fine-grained sediments with ancient (K/Ar ages of 300 Ma and eNd of -8) shale-like (high Rb counts) composition can be found between 19.6 and 9.2 m below coretop. These layers are interspersed by coarser grained, young (K/Ar ages of 100 Ma and eNd of -3) sediments containing ice-rafted debris (IRD). The composition and age of the layers indicates the sediments originated in Glacial Lake Missoula and were transported by ocean currents 250 miles north along the west coast of North America. The flood layers begin at 19.5 ka with five thin (5 cm thick) appear after 19.3 ka. At 17.1 ka, IRD concentrations increase from 50 grains g-1 from 16.5-16.35 ka, except in flood layers, as the Juan de Fuca Strait deglaciated. Another 16 flood layers occur from 16.3-15.65 ka; however, the base and top of these layers are diffuse rather than abrupt like earlier flood layers suggesting enhanced mixing between flood and melt waters. The final flood layers from 14.9-14.5 ka are thin (Lake Missoula flood sedimentation changed during the advance and retreat of the Cordilleran Ice Sheet.

  3. Evidence for slow late-glacial ice retreat in the upper Rangitata Valley, South Island, New Zealand

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    Shulmeister, J.; Fink, D.; Winkler, S.; Thackray, G. D.; Borsellino, R.; Hemmingsen, M.; Rittenour, T. M.

    2018-04-01

    A suite of cosmogenic radionuclide ages taken from boulders on lateral and latero-terminal moraines in the Rangitata Valley, eastern South Island, New Zealand demonstrates that relatively thick ice occupied valley reaches inland of the Rangitata Gorge until c. 21 ka. Thereafter ice began to thin, and by c. 17 ka it had retreated 33 km up-valley of the Rangitata Gorge to the Butler-Brabazon Downs, a structurally created basin in the upper Rangitata Valley. Despite its magnitude, this retreat represents a minor ice volume reduction from 21 ka to 17 ka, and numerous lateral moraines preserved suggest a relatively gradual retreat over that 4 ka period. In contrast to records from adjacent valleys, there is no evidence for an ice-collapse at c. 18 ka. We argue that the Rangitata record constitutes a more direct record of glacial response to deglacial climate than other records where glacial dynamics were influenced by proglacial lake development, such as the Rakaia Valley to the North and the major valleys in the Mackenzie Basin to the south-west. Our data supports the concept of a gradual warming during the early deglaciation in the South Island New Zealand.

  4. Retarded deglaciation of north-Spitsbergen fjords during the last glacial - an example of bathymetric controls on the dynamics of retreating glaciers

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    Forwick, M.; Vorren, T. O.; Hass, H.; Vogt, C. M.

    2012-12-01

    North and west Spitsbergen fjords acted as pathways for fast-flowing ice streams during the last glacial (e.g. Ottesen et al., 2005). The deglaciation of west Spitsbergen fjords occurred stepwise and the ice retreat terminated around 11,200 cal. years BP (calendar years before the present; e.g. Forwick & Vorren, 2009, 2011, and references therein; Baeten et al., 2010). However, the deglaciation dynamics and chronology of north Spitsbergen fjords still remain poorly understood. We present swath-bathymetry, high-resolution seismic data and two sediment cores from the approx. 110 km long, N-S oriented Wijdefjorden-Austfjorden fjord system, the largest fjord system on northern Spitsbergen. The data indicate that - as in the fjords on west Spitsbergen - multiple halts and/or readvances interrupted the retreat of the ice front during the final phase of the last glacial. However, even though the study area and several west Spitsbergen fjords are fed by the same glacier source (the ice field Lomonosovfonna), the final deglaciation of Wijdefjorden-Austfjorden took place after 9300 cal. years BP, i.e. at least approx. 2000 years later than in the west. We assume that the retarded deglaciation in the north is mainly related to the fjord bathymetry, i.e. a more than 35 km wide and up to 60 m high area in the central parts of the study area (approx. 45 km beyond the present fjord head) that acted as pinning point for the grounded glacier. Multiple, relatively large and partly stacked moraine ridges and sediment wedges are suggested to reflected that the ice front retreated slowly across this shallow area and that repeated readvances interrupted this retreat. The absence of larger sediment wedges in the deeper parts between the shallow area and the fjord head may indicate that the final retreat occurred relatively rapid. References: Baeten, N.J., Forwick, M., Vogt, C. & Vorren, T.O., 2010. Late Weichselian and Holocene sedimentary environments and glacial activity in

  5. Modeling subglacial sediment discharge in 1-dimension: comparison with measurments and implications for glacial retreat

    Science.gov (United States)

    Delaney, I. A.; Werder, M.; Farinotti, D.

    2017-12-01

    In recent decades increased sedimentation rates have been observed in reservoirs downstream of some retreating glaciers. This material either originates from slopes recently exposed by glacier retreat and no longer stabilized by ice, or subglacially, where pressurized melt water transports sediments from the glacier bed. Some evidence suggests that recently exposed periglacial areas can stablize relatively quickly and in some catchments provides a smaller precentage of the total sediment compared to the subglacial environment. As a result, in order predict and forecast sediment yield from glaciated catchments as glaciers thin and thier hydrology evolves, a subglacial sediment transport model must be implemented. Here a simple 1-dimensional glacio-hydraulic model uses the Darcy-Weissbach relationship to determine shear-stress of presurized water on the glacier bed. This is coupled with a sediment transport relationship to determine quantity of discharged material from the glacier snout. Several tuning factors allow calibration and the model to reproduces processes known to occur subglacially, including seasonal evolution of sediment expulsion and deposition of sediment on adverse slopes of overdeepenings. To asses the model's application to real glaciers, sediment flux data has been collected from Gornergletscher, Aletschgletscher and Griesgletscher in the Swiss Alps over time-scales of up to decades. By calibrating to these data, the skill of the model in recreating sediment trends and volumes is assesed. The outputs capture annual erosion quanities relatively well, however, challenges exist in capturing inter-annual variations in sediment discharge. Many of the model's short comings relate to caputuring the spatial distribution of sediment throughout the glacier bed, which is particularing difficult in 1-dimension. However, this work suggests that a simple models can be used to predict subglacial sediment transport with reasonable ability. Additionally, further

  6. Linking Backbarrier Lacustrine Stratigraphy with Spatial Dynamics of Shoreline Retreat in a Rapidly Subsiding Region of the Mississippi River Delta

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    Dietz, M.; Liu, K. B.; Bianchette, T. A.; Yao, Q.

    2017-12-01

    The shoreline along the northern Gulf of Mexico is rapidly retreating as coastal features of abandoned Mississippi River delta complexes erode and subside. Bay Champagne is located in the Caminada-Moreau headland, a region of shoreline west of the currently active delta that has one of the highest rates of retreat and land loss. As a result, this site has transitioned from a stable, circular inland lake several kilometers from the shore to a frequently perturbed, semi-circular backbarrier lagoon, making it ideal to study the environmental effects of progressive land loss. Analyses of clastic layers in a series of sediment cores collected at this site over the past decade indicate the lake was less perturbed in the past and has become increasingly more sensitive to marine incursion events caused by tropical cyclones. Geochemical and pollen analyses of these cores also reveal profound changes in environmental and chemical conditions in Bay Champagne over the past century as the shoreline has retreated. Through relating stratigraphy to spatial changes observed from satellite imagery, this study attempts to identify the tipping point at which Bay Champagne began the transition from an inland lake to a backbarrier environment, and to determine the rate at which this transition occurred. Results will be used to develop a model of the environmental transition experienced by a rapidly retreating coastline and to predict how other regions of the Mississippi River deltaic system could respond to future shoreline retreat.

  7. Reconstructing the evolution of a deep seated rockslide (Marzell) and its response to glacial retreat based on historic and remote sensing data

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    Fey, Christine; Wichmann, Volker; Zangerl, Christian

    2017-12-01

    In this study a combination of different topographic data from historic topographic maps and remote sensing is used to reconstruct and monitor the behaviour of the high alpine ice contact rockslide system Marzell and its response to glacial debuttressing in the Eastern Alps. Topographic data from archives (historical topographic maps, national glacier inventories, aerial images, orthoimages and ALS data) and data from monitoring campaigns (geodetic measurements, terrestrial laser scanning and UAV imaging campaigns) are processed to georeferenced images and/or elevation data, respectively. The data from different data sources is compiled and analysed with the aim to i) reconstruct the extent, thickness and volume changes of the glacier since 1893 and ii) to analyse the rockslide deformation evolution by extracting information about the displacement direction, dip angle, velocity and partial failure of rockslide slabs since 1951. The rockslide is compound of different rockslide slabs which move downwards as rigid blocks along basal shear zones. The analyses and interpretation of the data suggest a rotational type of rockslide failure mechanisms. The rockslide activity correlates with the ice volume loss at the adjacent part of the glacier. In the period between 1971 and 1997 the annual average rockslide activity was about 0.05 m/a and the annual average ice thickness loss was 0.1 m/a. Since the end of the last century the annual average ice thickness loss increased dramatically to 5 m/a. In that period the rockslide activity accelerated. The highest rockslide activity (up to 1.5 m/a) was observed in the 2000s when half of the slope toe was exposed because of glacier retreat. Since 2010 a deceleration of the rockslide can be observed. In the vicinity of the rockslide the glacier almost disappeared and lost 99.88% of its ice volume between 1893 and 2014. The geomorphological and geological information gathered about the rockslide evolution and the glacier retreat form

  8. Tracking millennial-scale Holocene glacial advance and retreat using osmium isotopes: Insights from the Greenland ice sheet

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    Rooney, Alan D.; Selby, David; Llyod, Jeremy M.; Roberts, David H.; Luckge, Andreas; Sageman, Bradley B.; Prouty, Nancy G.

    2016-01-01

    High-resolution Os isotope stratigraphy can aid in reconstructing Pleistocene ice sheet fluctuation and elucidating the role of local and regional weathering fluxes on the marine Os residence time. This paper presents new Os isotope data from ocean cores adjacent to the West Greenland ice sheet that have excellent chronological controls. Cores MSM-520 and DA00-06 represent distal to proximal sites adjacent to two West Greenland ice streams. Core MSM-520 has a steadily decreasing Os signal over the last 10 kyr (187Os/188Os = 1.35–0.81). In contrast, Os isotopes from core DA00-06 (proximal to the calving front of Jakobshavn Isbræ) highlight four stages of ice stream retreat and advance over the past 10 kyr (187Os/188Os = 2.31; 1.68; 2.09; 1.47). Our high-resolution chemostratigraphic records provide vital benchmarks for ice-sheet modelers as we attempt to better constrain the future response of major ice sheets to climate change. Variations in Os isotope composition from sediment and macro-algae (seaweed) sourced from regional and global settings serve to emphasize the overwhelming effect weathering sources have on seawater Os isotope composition. Further, these findings demonstrate that the residence time of Os is shorter than previous estimates of ∼104 yr.

  9. Large-scale glacitectonic deformation in response to active ice sheet retreat across Dogger Bank (southern central North Sea) during the Last Glacial Maximum

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    Phillips, Emrys; Cotterill, Carol; Johnson, Kirstin; Crombie, Kirstin; James, Leo; Carr, Simon; Ruiter, Astrid

    2018-01-01

    High resolution seismic data from the Dogger Bank in the central southern North Sea has revealed that the Dogger Bank Formation records a complex history of sedimentation and penecontemporaneous, large-scale, ice-marginal to proglacial glacitectonic deformation. These processes led to the development of a large thrust-block moraine complex which is buried beneath a thin sequence of Holocene sediments. This buried glacitectonic landsystem comprises a series of elongate, arcuate moraine ridges (200 m up to > 15 km across; over 40-50 km long) separated by low-lying ice marginal to proglacial sedimentary basins and/or meltwater channels, preserving the shape of the margin of this former ice sheet. The moraines are composed of highly deformed (folded and thrust) Dogger Bank Formation with the lower boundary of the deformed sequence (up to 40-50 m thick) being marked by a laterally extensive décollement. The ice-distal parts of the thrust moraine complex are interpreted as a "forward" propagating imbricate thrust stack developed in response to S/SE-directed ice-push. The more complex folding and thrusting within the more ice-proximal parts of the thrust-block moraines record the accretion of thrust slices of highly deformed sediment as the ice repeatedly reoccupied this ice marginal position. Consequently, the internal structure of the Dogger Bank thrust-moraine complexes can be directly related to ice sheet dynamics, recording the former positions of a highly dynamic, oscillating Weichselian ice sheet margin as it retreated northwards at the end of the Last Glacial Maximum.

  10. Microscale soil structure development after glacial retreat - using machine-learning based segmentation of elemental distributions obtained by NanoSIMS

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    Schweizer, Steffen; Schlueter, Steffen; Hoeschen, Carmen; Koegel-Knabner, Ingrid; Mueller, Carsten W.

    2017-04-01

    Soil organic matter (SOM) is distributed on mineral surfaces depending on physicochemical soil properties that vary at the submicron scale. Nanoscale secondary ion mass spectrometry (NanoSIMS) can be used to visualize the spatial distribution of up to seven elements simultaneously at a lateral resolution of approximately 100 nm from which patterns of SOM coatings can be derived. Existing computational methods are mostly confined to visualization and lack spatial quantification measures of coverage and connectivity of organic matter coatings. This study proposes a methodology for the spatial analysis of SOM coatings based on supervised pixel classification and automatic image analysis of the 12C, 12C14N (indicative for SOM) and 16O (indicative for mineral surfaces) secondary ion distributions. The image segmentation of the secondary ion distributions into mineral particle surface and organic coating was done with a machine learning algorithm, which accounts for multiple features like size, color, intensity, edge and texture in all three ion distributions simultaneously. Our workflow allowed the spatial analysis of differences in the SOM coverage during soil development in the Damma glacier forefield (Switzerland) based on NanoSIMS measurements (n=121; containing ca. 4000 particles). The Damma chronosequence comprises several stages of soil development with increasing ice-free period (from ca. 15 to >700 years). To investigate mineral-associated SOM in the developing soil we obtained clay fractions (2.2 g cm3). We found increased coverage and a simultaneous development from patchy-distributed organic coatings to more connected coatings with increasing time after glacial retreat. The normalized N:C ratio (12C14N: (12C14N + 12C)) on the organic matter coatings was higher in the medium-aged soils than in the young and mature ones in both heavy and light mineral fraction. This reflects the sequential accumulation of proteinaceous SOM in the medium-aged soils and C

  11. Hillslope failure and paraglacial reworking of sediments in response to glacier retreat, Fox Valley, New Zealand.

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    McColl, Samuel T.; Fuller, Ian C.; Anderson, Brian; Tate, Rosie

    2017-04-01

    Climate and glacier fluctuations influence sediment supply to glacier forelands, which in turn influences down-valley hazards to infrastructure and tourism within glacier forelands. At Fox Glacier, one of New Zealand's most iconic and popular glaciers, rapid retreat has initiated a range of hillslope and valley floor responses, that present a cascade of hazards and changes that need to be carefully managed. Fox Glacier has retreated many kilometres historically, with 2.6 km of retreat since the mid-20th century, and a phase of rapid retreat of 50-340 m per year since 2009. To study the system response to past and ongoing glacial retreat at the Fox valley, morphological changes are being observed using time-lapse photography and the annual collection of high-resolution digital elevation models (DEMs) and orthophoto mosaics. The DEMs are being produced using Structure from Motion photogrammetry from UAV/RPAS and helicopter platforms, and are being used, along with manual ground surveying, to produce ground surface change models (DoDs; DEMs of Difference) and sediment budgets for the valley. Results from time-lapse photography and DoDs show that glacial retreat has initiated destabilisation and (mostly chronic) mass movement of surficial glacial sediments on the valley slopes near the glacier terminus. Alluvial fans farther down valley are actively growing, reworking glacial and landslide sediments from tributary catchments. These paraglacial sediments being delivered to the proglacial river from the glacier terminus and alluvial fans are driving aggradation of the valley floor of decimetres to metres per year and maintaining a highly dynamic braid plain. Valley floor changes also include the melting of buried dead ice, which are causing localised subsidence at the carpark and one of the alluvial fans. The unstable slopes and active debris fans, aggrading and highly active river channel, ground subsidence, add to the spectacle but also the hazards of the Fox valley

  12. Dating glacimarine sediments from the continental shelf in the Amundsen Sea using a multi-tool box: Implications for West Antarctic ice-sheet extent and retreat during the last glacial cycle

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    Hillenbrand, C. D.; Smith, J.; Klages, J. P.; Kuhn, G.; Maher, B.; Moreton, S.; Wacker, L.; Frederichs, T.; Wiers, S.; Jernas, P.; Anderson, J. B.; Ehrmann, W. U.; Graham, A. G. C.; Gohl, K.; Larter, R. D.

    2016-02-01

    Satellite data and in-situ measurements show that today considerable mass loss is occurring from the Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS). The observational record only spans the past four decades, and until recently the long-term context of the current deglaciation was poorly constrained. This information is, however, crucial for understanding WAIS dynamics, evaluating the role of forcing mechanisms for ice-sheet melting, and testing and calibrating ice-sheet models that attempt to predict future WAIS behavior and its impact on global sea level. Over the past decade several multinational marine expeditions and terrestrial fieldwork campaigns have targeted the Amundsen Sea shelf and its hinterland to reconstruct the WAIS configuration during the Last Glacial Maximum (LGM) and its subsequent deglacial history. The resulting studies succeeded in shedding light on the maximum WAIS extent at the LGM and the style, pattern and speed of its retreat and thinning thereafter. Despite this progress, however, significant uncertainties and discrepancies between marine and terrestrial reconstructions remain, which may arise from difficulties in dating sediment cores from the Antarctic shelf, especially their deglacial sections. Resolving these issues is crucial for understanding the WAIS' contribution to post-LGM sea-level rise, its sensitivity to different forcing mechanisms and its future evolution. Here we present chronological constraints on WAIS advance in the Amundsen Sea and its retreat from 20 ka BP into the Holocene that were obtained by various techniques, such as 14C dating of large ( 10 mg) and small (sample aliquots of calcareous microfossils, 14C dating of acid-insoluble organic matter combusted at low (300 °C) and high (800 °C) temperatures and dating of sediment cores by using geomagnetic paleointensity. We will compare the different age constraints and discuss their reliability, applicability and implications for WAIS history.

  13. Benthic Trophic Interactions in an Antarctic Shallow Water Ecosystem Affected by Recent Glacier Retreat.

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    Francesca Pasotti

    Full Text Available The western Antarctic Peninsula is experiencing strong environmental changes as a consequence of ongoing regional warming. Glaciers in the area are retreating rapidly and increased sediment-laden meltwater runoff threatens the benthic biodiversity at shallow depths. We identified three sites with a distinct glacier-retreat related history and different levels of glacial influence in the inner part of Potter Cove (King George Island, South Shetland Islands, a fjord-like embayment impacted since the 1950s by a tidewater glacier retreat. We compared the soft sediment meio- and macrofauna isotopic niche widths (δ13C and δ15N stable isotope analysis at the three sites to investigate possible glacier retreat-related influences on benthic trophic interactions. The isotopic niches were locally shaped by the different degrees of glacier retreat-related disturbance within the Cove. Wider isotopic niche widths were found at the site that has become ice-free most recently, and narrower niches at the older ice-free sites. At an intermediate state of glacier retreat-related disturbance (e.g. via ice-growler scouring species with different strategies could settle. The site at the earliest stage of post-retreat development was characterized by an assemblage with lower trophic redundancy. Generally, the isotopic niche widths increased with increasing size spectra of organisms within the community, excepting the youngest assemblage, where the pioneer colonizer meiofauna size class displayed the highest isotopic niche width. Meiofauna at all sites generally occupied positions in the isotopic space that suggested a detrital-pool food source and/or the presence of predatory taxa. In general ice scour and glacial impact appeared to play a two-fold role within the Cove: i either stimulating trophic diversity by allowing continuous re-colonization of meiofaunal species or, ii over time driving the benthic assemblages into a more compact trophic structure with

  14. Benthic Trophic Interactions in an Antarctic Shallow Water Ecosystem Affected by Recent Glacier Retreat.

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    Pasotti, Francesca; Saravia, Leonardo Ariel; De Troch, Marleen; Tarantelli, Maria Soledad; Sahade, Ricardo; Vanreusel, Ann

    2015-01-01

    The western Antarctic Peninsula is experiencing strong environmental changes as a consequence of ongoing regional warming. Glaciers in the area are retreating rapidly and increased sediment-laden meltwater runoff threatens the benthic biodiversity at shallow depths. We identified three sites with a distinct glacier-retreat related history and different levels of glacial influence in the inner part of Potter Cove (King George Island, South Shetland Islands), a fjord-like embayment impacted since the 1950s by a tidewater glacier retreat. We compared the soft sediment meio- and macrofauna isotopic niche widths (δ13C and δ15N stable isotope analysis) at the three sites to investigate possible glacier retreat-related influences on benthic trophic interactions. The isotopic niches were locally shaped by the different degrees of glacier retreat-related disturbance within the Cove. Wider isotopic niche widths were found at the site that has become ice-free most recently, and narrower niches at the older ice-free sites. At an intermediate state of glacier retreat-related disturbance (e.g. via ice-growler scouring) species with different strategies could settle. The site at the earliest stage of post-retreat development was characterized by an assemblage with lower trophic redundancy. Generally, the isotopic niche widths increased with increasing size spectra of organisms within the community, excepting the youngest assemblage, where the pioneer colonizer meiofauna size class displayed the highest isotopic niche width. Meiofauna at all sites generally occupied positions in the isotopic space that suggested a detrital-pool food source and/or the presence of predatory taxa. In general ice scour and glacial impact appeared to play a two-fold role within the Cove: i) either stimulating trophic diversity by allowing continuous re-colonization of meiofaunal species or, ii) over time driving the benthic assemblages into a more compact trophic structure with increased

  15. Rapid global ocean-atmosphere response to Southern Ocean freshening during the last glacial.

    Science.gov (United States)

    Turney, Chris S M; Jones, Richard T; Phipps, Steven J; Thomas, Zoë; Hogg, Alan; Kershaw, A Peter; Fogwill, Christopher J; Palmer, Jonathan; Bronk Ramsey, Christopher; Adolphi, Florian; Muscheler, Raimund; Hughen, Konrad A; Staff, Richard A; Grosvenor, Mark; Golledge, Nicholas R; Rasmussen, Sune Olander; Hutchinson, David K; Haberle, Simon; Lorrey, Andrew; Boswijk, Gretel; Cooper, Alan

    2017-09-12

    Contrasting Greenland and Antarctic temperatures during the last glacial period (115,000 to 11,650 years ago) are thought to have been driven by imbalances in the rates of formation of North Atlantic and Antarctic Deep Water (the 'bipolar seesaw'). Here we exploit a bidecadally resolved 14 C data set obtained from New Zealand kauri (Agathis australis) to undertake high-precision alignment of key climate data sets spanning iceberg-rafted debris event Heinrich 3 and Greenland Interstadial (GI) 5.1 in the North Atlantic (~30,400 to 28,400 years ago). We observe no divergence between the kauri and Atlantic marine sediment 14 C data sets, implying limited changes in deep water formation. However, a Southern Ocean (Atlantic-sector) iceberg rafted debris event appears to have occurred synchronously with GI-5.1 warming and decreased precipitation over the western equatorial Pacific and Atlantic. An ensemble of transient meltwater simulations shows that Antarctic-sourced salinity anomalies can generate climate changes that are propagated globally via an atmospheric Rossby wave train.A challenge for testing mechanisms of past climate change is the precise correlation of palaeoclimate records. Here, through climate modelling and the alignment of terrestrial, ice and marine 14 C and 10 Be records, the authors show that Southern Ocean freshwater hosing can trigger global change.

  16. Glacial Meltwater Contirbutions to the Bow River, Alberta, Canada

    Science.gov (United States)

    Bash, E. A.; Marshall, S. J.; White, E. C.

    2009-12-01

    Assessment of glacial melt is critical for water resource management in areas which rely on glacier-fed rivers for agricultural and municipal uses. Changes in precipitation patterns coupled with current glacial retreat are altering the glacial contribution to river flow in areas such as the Andes of South America and the high ranges of Asia, as well as the Rockies of Western Canada. Alberta’s Bow River has its headwaters in the eastern slopes of the Canadian Rockies and contributes to the Nelson drainage system feeding into Hudson Bay. The Bow River basin contains several population centers, including the City of Calgary, and is heavily taxed for agricultural use. The combined effects of rapid glacial retreat in the Canadian Rockies, higher drought frequency, and increased demand are likely to heighten water stress in Southern Alberta. However, there has been little focus to date on the extent and importance of glacial meltwater in the Bow River. The Bow River contains 74.5 km2 of glacier ice, which amounts to only 0.29% of the basin. While this number is not high compared to some glacierized areas, Hopkinson and Young (1998) report that in dry years, glacier melt can provide up to 50% of late summer flows at a station in the upper reaches of the river system. We extend this work with an assessment of monthly and annual glacial contributions to the Bow River farther downstream in Calgary. Our analysis is based on mass balance, meteorological, and hydrological data that has been collected at the Haig Glacier since 2001. This data is used in conjunction with glacier coverage and hypsometric data for the remainder of the basin to estimate seasonal snow and glacial meltwater contributions to the Bow River from the glacierized fraction of the catchment. The results of this study show the percentage of total flow attributed to glacial melt to be highly variable. Glacier runoff contributes up to an order of magnitude more water to the Bow River per unit area of

  17. Differences in Bacterial Diversity and Communities Between Glacial Snow and Glacial Soil on the Chongce Ice Cap, West Kunlun Mountains.

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    Yang, Guang Li; Hou, Shu Gui; Le Baoge, Ri; Li, Zhi Guo; Xu, Hao; Liu, Ya Ping; Du, Wen Tao; Liu, Yong Qin

    2016-11-04

    A detailed understanding of microbial ecology in different supraglacial habitats is important due to the unprecedented speed of glacier retreat. Differences in bacterial diversity and community structure between glacial snow and glacial soil on the Chongce Ice Cap were assessed using 454 pyrosequencing. Based on rarefaction curves, Chao1, ACE, and Shannon indices, we found that bacterial diversity in glacial snow was lower than that in glacial soil. Principal coordinate analysis (PCoA) and heatmap analysis indicated that there were major differences in bacterial communities between glacial snow and glacial soil. Most bacteria were different between the two habitats; however, there were some common bacteria shared between glacial snow and glacial soil. Some rare or functional bacterial resources were also present in the Chongce Ice Cap. These findings provide a preliminary understanding of the shifts in bacterial diversity and communities from glacial snow to glacial soil after the melting and inflow of glacial snow into glacial soil.

  18. Impact of glaciers retreat on highland Andean wetlands and communities: lessons from the upper Cachi catchment (Ayacucho, Peru)

    Science.gov (United States)

    Angulo, Oscar; Biévre Bert, De

    2017-04-01

    The vulnerability of water resources under climate change scenarios in Peru is generally regarded to be connected to a diminished availability of water due to retreating glaciers. However, the impact of glacier retreat goes much beyond a decline of glacial water reserves. This article argues that another important impact is the extreme erosion in areas where glaciers have recently melted, as well as the accumulation of erosion material in highland wetlands located downslope. As a direct consequence of these changes highland Andean communities which depend on these ecosystems are affected in socio-economic terms as they find themselves forced to alter ancestral dynamics and traditional practices of land and water use. This quickly leads to a vicious cycle of risks and threats. In such a context a possibility to adapt to glacial retreat should be to protect areas affected by glacial melt in order to enable a rapid development of protective vegetation cover. In the upper catchment of the Cachi River interesting experiences of protection and water harvesting exist that could be extended to other high vulnerability areas for the benefit of highland populations as well as downstream water users, such as the irrigation system of Cachi and the city of Ayacucho.

  19. Low-δD hydration rinds in Yellowstone perlites record rapid syneruptive hydration during glacial and interglacial conditions

    Science.gov (United States)

    Bindeman, Ilya N.; Lowenstern, Jacob B.

    2016-01-01

    of glacial ice. Cooling calculations, combined with the observed high water diffusion coefficients noted for 60–150 °C, suggest that if sufficient hot water or steam is available, any rhyolite flow greater than ~5 m thick can develop the observed ~250-µm hydration rinds within the expected timescale of cooling (weeks–years). As the process of hydration involves shattering of 30- to 100-µm-thick slivers to expose unhydrated rhyolite glass, the time required for hydration may be even shorter. Rapid hydration and formation of relatively thick-walled glass shards allow perlites to provide a snapshot view of the meteoric water (and thus climate) at the time of initial alteration. Perlites retain their initial hydration D/H signal better than thin-walled ash, which in contrast hydrates over many thousands of years with time-averaged precipitation.

  20. 20th-century glacial-marine sedimentation in Vitus Lake, Bering Glacier, Alaska, U.S.A.

    Science.gov (United States)

    Molnia, B.F.; Post, A.; Carlson, P.R.

    1996-01-01

    Vitus Lake, the ice-marginal basin at the southeastern edge of Bering Glacier, Alaska, U.S.A., is a site of modern, rapid, glacial-marine sedimentation. Rather than being a fresh-water lake, Vitus Lake is a tidally influenced, marine to brackish embayment connected to the Pacific Ocean by an inlet, the Seal River. Vitus Lake consists of five deep bedrock basins, separated by interbasinal highs. Glacial erosion has cut these basins as much as 250 m below sea level. High-resolution seismic reflection surveys conducted in 1991 and 1993 of four of Vitus Lake's basins reveal a complex, variable three-component acoustic stratigraphy. Although not fully sampled, the stratigraphy is inferred to be primarily glacial-marine units of (1) basal contorted and deformed glacial-marine and glacial sediments deposited by basal ice-contact processes and submarine mass-wasting; (2) acoustically well-stratified glacial-marine sediment, which unconformably overlies the basal unit and which grades upward into (3) acoustically transparent or nearly transparent glacial-marine sediment. Maximum thicknesses of conformable glacial-marine sediment exceed 100 m. All of the acoustically transparent and stratified deposits in Vitus Lake are modern in age, having accumulated between 1967 and 1993. The basins where these three-part sequences of "present-day" glacial-marine sediment are accumulating are themselves cut into older sequences of stratified glacial and glacial-marine deposits. These older units outcrop on the islands in Vitus Lake. In 1967, as the result of a major surge, glacier ice completely filled all five basins. Subsequent terminus retreat, which continued through August 1993, exposed these basins, providing new locations for glacial-marine sediment accumulation. A correlation of sediment thicknesses measured from seismic profiles at specific locations within the basins, with the year that each location became ice-free, shows that the sediment accumulation at some locations

  1. Gigantic landslides versus glacial deposits: on origin of large hummock deposits in Alai Valley, Northern Pamir

    Science.gov (United States)

    Reznichenko, Natalya

    2015-04-01

    As glaciers are sensitive to local climate, their moraines position and ages are used to infer past climates and glacier dynamics. These chronologies are only valid if all dated moraines are formed as the result of climatically driven advance and subsequent retreat. Hence, any accurate palaeoenvironmental reconstruction requires thorough identification of the landform genesis by complex approach including geomorphological, sedimentological and structural landform investigation. Here are presented the implication of such approach for the reconstruction of the mega-hummocky deposits formation both of glacial and landslide origin in the glaciated Alai Valley of the Northern Pamir with further discussion on these and similar deposits validity for palaeoclimatic reconstructions. The Tibetan Plateau valleys are the largest glaciated regions beyond the ice sheets with high potential to provide the best geological record of glacial chronologies and, however, with higher probabilities of the numerous rock avalanche deposits including those that were initially considered of glacial origin (Hewitt, 1999). The Alai Valley is the largest intermountain depression in the upper reaches of the Amudarja River basin that has captured numerous unidentified extensive hummocky deposits descending from the Zaalai Range of Northern Pamir, covering area in more than 800 km2. Such vast hummocky deposits are usually could be formed either: 1) glacially by rapid glacial retreat due to the climate signal or triggered a-climatically glacial changes, such as glacial surge or landslide impact, or 2) during the landslide emplacement. Combination of sediment tests on agglomerates forming only in rock avalanche material (Reznichenko et al., 2012) and detailed geomorphological and sedimentological descriptions of these deposits allowed reconstructing the glacial deposition in the Koman and Lenin glacial catchments with identification of two gigantic rock avalanches and their relation to this glacial

  2. The sensitivity of the Greenland Ice Sheet to glacial-interglacial oceanic forcing

    Science.gov (United States)

    Tabone, Ilaria; Blasco, Javier; Robinson, Alexander; Alvarez-Solas, Jorge; Montoya, Marisa

    2018-04-01

    Observations suggest that during the last decades the Greenland Ice Sheet (GrIS) has experienced a gradually accelerating mass loss, in part due to the observed speed-up of several of Greenland's marine-terminating glaciers. Recent studies directly attribute this to warming North Atlantic temperatures, which have triggered melting of the outlet glaciers of the GrIS, grounding-line retreat and enhanced ice discharge into the ocean, contributing to an acceleration of sea-level rise. Reconstructions suggest that the influence of the ocean has been of primary importance in the past as well. This was the case not only in interglacial periods, when warmer climates led to a rapid retreat of the GrIS to land above sea level, but also in glacial periods, when the GrIS expanded as far as the continental shelf break and was thus more directly exposed to oceanic changes. However, the GrIS response to palaeo-oceanic variations has yet to be investigated in detail from a mechanistic modelling perspective. In this work, the evolution of the GrIS over the past two glacial cycles is studied using a three-dimensional hybrid ice-sheet-shelf model. We assess the effect of the variation of oceanic temperatures on the GrIS evolution on glacial-interglacial timescales through changes in submarine melting. The results show a very high sensitivity of the GrIS to changing oceanic conditions. Oceanic forcing is found to be a primary driver of GrIS expansion in glacial times and of retreat in interglacial periods. If switched off, palaeo-atmospheric variations alone are not able to yield a reliable glacial configuration of the GrIS. This work therefore suggests that considering the ocean as an active forcing should become standard practice in palaeo-ice-sheet modelling.

  3. Glacial flour in lacustrine sediments: Records of alpine glaciation in the western U.S.A. during the last glacial interval

    Science.gov (United States)

    Rosenbaum, J. G.; Reynolds, R. L.

    2010-12-01

    glacial-age sediments, but cosmogenic dating (by Laabs et al.) of highly resistant quartzite boulders provide ages from terminal moraines in the Bear River drainage. Glacial flour appears abruptly at ~26 cal ka in Bear Lake, whereas it is present at the base of the Upper Klamath Lake core (~37 cal ka). Both glacial flour records (1) contain millennial-scale variations (uncertainties in chronology prevent precise correlation of these features), (2) attain maxima circa 19 cal ka, and (3) rapidly decline beginning prior to 18 cal ka. At Bear Lake the age of the decline in glacial flour coincides with cosmogenic exposure ages (18.1 - 18.7 ka) of terminal moraines in the upper Bear River valley. This concurrence supports the interpretation that the maximum amount and subsequent decrease in glacial flour are indicative of maximum glacial extent and glacial retreat, respectively, and more generally that increases and decreases in rock flour in these lake sediments represent waxing and waning of glaciers. Laabs, B,J.C., et al., 2007, Chronology of the last glacial maximum in the upper Bear River basin, Utah, Arctic and Alpine Research, v. 39, p. 537 - 548.

  4. The response of southern California ecosystems to Younger Dryas-like rapid climate change: Comparison of glacial terminations 1 and 5.

    Science.gov (United States)

    Heusser, L. E.; Hendy, I. L.

    2015-12-01

    The Younger Dryas is a well-known rapid climatic cooling that interrupted the Marine Isotope Stage (MIS) 1-2 deglacial warming of Termination 1. This cool event has been associated with ice sheet readvance, meridional overturning, circulation changes, and southward movement of the Intertropical Convergence Zone. In Southern California, the Younger Dryas has been associated with cooler SST, low marine productivity, a well-ventilated oxygen minimum zone, and a wetter climate. Similar rapid cooling events have been found at other terminations including Termination 5 at the MIS 11-12 deglaciation (~425 Ka) identified by ice rafting events in the North Atlantic. Here we present new pollen census data from a unique suite of cores taken from the sub-oxic sediments of Santa Barbara Basin (MV0508-15JC, MV0805-20JC, MV0508-33JC, 29JC and 21JC). These short cores, collected on a truncated anticline within SBB, provide the opportunity to examine the response of southern California terrestrial and marine ecosystems to rapid climate change during the MIS 11-12 deglaciation (Termination 5), which is identified by a bioturbated interval within a sequence of laminated sediments. During Termination 1, changes in Southern California precipitation are reflected in pollen- based reconstructions Southern California vegetation. The high precipitation of glacial montane-coniferous assemblages of pine (Pinus) and Juniper (Juniperus/Calocedrus) transitions into interglacial drought, as expresssed by arid oak (Quercus)/chaparral vegetation. The Younger Dryas interrupts the transition as a high-amplitude pulse in pine associated with increased Gramineae (grass). Termination 5 differs, as the high precipitation of glacial montane-coniferous assemblages do not transition into arid oak/chaparral vegetation. However, a Younger Dryas-like rapid climate event was associated with increased pine and grass.

  5. Knickpoint formation, rapid propagation, and landscape response following coastal cliff retreat at last-interglacial sea-level highstand: Kaua'i, Hawai'i

    Science.gov (United States)

    Lamb, Michael; Mackey, Ben; Scheingross, Joel; Farley, Ken

    2013-04-01

    The propagation of knickpoints through a landscape is recognized as a highly efficient mechanism of channel incision, and exerts a first-order control in communicating changes in base level throughout a landscape. However, few settings allow reconstruction of the long-term rate of knickpoint retreat. Here, we use cosmogenic 3He exposure dating of olivine within basalt to document the retreat rate of a waterfall in Ka'ula'ula Valley, a small catchment on the Na Pali coast of Kaua'i, Hawai'i. We constrained the exposure age of 18 features (in-channel boulders, stable boulders on terraces, and in-channel bedrock) along the length of the channel that allow us to discriminate between models of knickpoint propagation. Cosmogenic exposure ages are oldest near the coast (120 ka) and systematically decrease with upstream distance towards the waterfall (waterfall has migrated 4 km up valley over the past 120 ka at an average rate of 33 mm/yr. Steady-state vertical erosion appears to dominate upstream of the waterfall, where the channel has incised ~100 m into the original surface of the shield volcano. Our results indicate the lateral rate of knickpoint retreat exceeds rates of vertical channel incision by three orders of magnitude, and that knickpoints may be the primary driver of relief generation in Hawaiian catchments. Submarine landslides have been proposed as the cause of knickpoints in Kaua'i streams; however, the bathymetry off the northwest Kaua'i coast lacks evidence for large submarine flank collapse. Alternatively, we propose substantial cliff erosion during the last interglacial sea-level highstand generated a waterfall at the coast, which has subsequently propagated inland. Superimposing Kaua'i's subsidence history and Pleistocene sea level fluctuations indicate that the only time waves could have eroded cliffs at Ka'ula'ula Valley's entrance over the past 1.5 Ma was during the last interglacial, ~130-120 ka. Knickpoint generation during sea level high stands

  6. The paradox of a long grounding during West Antarctic Ice Sheet retreat in Ross Sea.

    Science.gov (United States)

    Bart, Philip J; Krogmeier, Benjamin J; Bart, Manon P; Tulaczyk, Slawek

    2017-04-28

    Marine geological data show that the West Antarctic Ice Sheet (WAIS) advanced to the eastern Ross Sea shelf edge during the Last Glacial Maximum (LGM) and eventually retreated ~1000 km to the current grounding-line position on the inner shelf. During the early deglacial, the WAIS deposited a voluminous stack of overlapping grounding zone wedges (GZWs) on the outer shelf of the Whales Deep Basin. The large sediment volume of the GZW cluster suggests that the grounding-line position of the paleo-Bindschadler Ice Stream was relatively stationary for a significant time interval. We used an upper bound estimate of paleo-sediment flux to investigate the lower bound duration over which the ice stream would have deposited sediment to account for the GZW volume. Our calculations show that the cluster represents more than three millennia of ice-stream sedimentation. This long duration grounding was probably facilitated by rapid GZW growth. The subsequent punctuated large-distance (~200 km) grounding-line retreat may have been a highly non-linear ice sheet response to relatively continuous external forcing such as gradual climate warming or sea-level rise. These findings indicate that reliable predictions of future WAIS retreat may require incorporation of realistic calculations of sediment erosion, transport and deposition.

  7. Chronology of fast climatic changes during the last glacial period; Chronologie des variations climatiques rapides pendant la derniere periode glaciaire

    Energy Technology Data Exchange (ETDEWEB)

    Bard, E.; Rostek, F.; Menot-Combes, G. [Cerege, UMR 6635 et College de France, 13 - Aix-en-Provence (France)

    2006-01-15

    The history of the glacial climate is punctuated by events occurring at the scale of a human life. They are characterised by temperature changes of large amplitude, simultaneously in Greenland and the North Atlantic. These events affected not only the surface hydrology, but also the deep circulation of this oceanic basin. A by-product of the obvious correspondence between Dansgaard-Oeschger and Heinrich in the polar ice and marine sediments is to allow, by correlation, the construction of a calendar chronology for the marine records. This chronostratigraphic approach was validated by means of radiocarbon dating of deep-sea sediments raised on the Iberian Margin. Our study also contributes to the international effort of calibration of the radiocarbon time scale by providing significant results in the interval between 33000 and 41000 years calendar BP. (authors)

  8. Glacial cycles

    DEFF Research Database (Denmark)

    Kaufmann, R. K.; Juselius, Katarina

    We use a statistical model, the cointegrated vector autoregressive model, to assess the degree to which variations in Earth's orbit and endogenous climate dynamics can be used to simulate glacial cycles during the late Quaternary (390 kyr-present). To do so, we estimate models of varying complexity...... and compare the accuracy of their in-sample simulations. Results indicate that strong statistical associations between endogenous climate variables are not enough for statistical models to reproduce glacial cycles. Rather, changes in solar insolation associated with changes in Earth's orbit are needed...... to simulate glacial cycles accurately. Also, results suggest that non-linear 10 dynamics, threshold effects, and/or free oscillations may not play an overriding role in glacial cycles....

  9. Ice/Bedrock Feedbacks as a Principle Contributor to Glacial-Interglacial Oscillations

    Science.gov (United States)

    Kimmel, J.; Lee, K.; Jackson, C. H.

    2014-12-01

    Since the mid-Pleistocene, the oscillation between glacial and interglacial climate states occurs with a period of approximately 100 kyr. Each cycle is comprised of a slow glaciation with a subsequent rapid deglaciation. While the solar forcing is clearly an important driver for these transitions, the power spectrum of the solar forcing is quite different from the subsequent climate response and, in general, does not have a noticeable correlation with global ice volume. Instead, previous studies have shown that internal climate processes and their interactions (e.g., CO2, water vapor, isostatic bed response) play a significant role in producing these global climate cycles. The rapid retreat of large ice sheets at the start of an interglacial is often attributed to the interaction between surface and atmospheric processes. While calving is thought to amplify this retreat, it is not typically considered a principle driver of the ice sheet response. Our study investigates the potential for ice/bedrock feedbacks to be a principle contributor in shaping the glacial-interglacial climate oscillation -- particularly the rapid deglaciation that precedes an interglacial. The ice sheet model we develop includes a piecewise linear ice/bedrock feedback while atmospheric and surface processes are taken to be as simple as possible. Due to the long timescale of the bedrock response and the rapid mass loss due to calving, the model ice sheet exhibits rapid deglaciation from a stable maximum when it retreats through an overdeepening. However, ice sheet advance is also shown to be as rapid unless a more complex bedrock response is considered. In particular, we show that a forebulge created by the displacement of the mantle adds a new stable branch to the volume/equilibrium line bifurcation diagram that results in slower growth of the ice sheet during glaciation.

  10. Murdoch Retreats from China

    Institute of Scientific and Technical Information of China (English)

    Jessy Zhang

    2006-01-01

    @@ News Corp's Asian flagship enterprise Star Group announced in early June it would sell a 19.9 percent stake in Phoenix Satellite Television to China Mobile. This move is widely interpreted as a signal that Rudolf Murdoch, the helmsman of News Corp,might have lost his patience and could eventually retreat from the Chinese media market.

  11. In Review (Geology): Alpine Landscape Evolution Dominated by Cirque Retreat

    Science.gov (United States)

    Oskin, Michael; Burbank, Doug

    2005-01-01

    Despite the abundance in alpine terrain of glacially dissected landscapes, the magnitude and geometry of glacial erosion can rarely be defined. In the eastern Kyrgyz Range, a widespread unconformity exhumed as a geomorphic surface provides a regional datum with which to calibrate erosion. As tectonically driven surface uplift has progressively pushed this surface into the zone of ice accumulation, glacial erosion has overprinted the landscape. With as little as 500 m of incision into rocks underlying the unconformity, distinctive glacial valleys display their deepest incision adjacent to cirque headwalls. The expansion of north-facing glacial cirques at the expense of south-facing valleys has driven the drainage divide southwards at rates up to 2 to 3 times the rate of valley incision. Existing ice-flux-based glacial erosion rules incompletely model expansion of glacial valleys via cirque retreat into the low-gradient unconformity remnants. Local processes that either directly sap cirque headwalls or inhibit erosion down-glacier appear to control, at least initially, alpine landscape evolution.

  12. Deglacial history of the Pensacola Mountains, Antarctica from glacial geomorphology and cosmogenic nuclide surface exposure dating

    Science.gov (United States)

    Bentley, M. J.; Hein, A. S.; Sugden, D. E.; Whitehouse, P. L.; Shanks, R.; Xu, S.; Freeman, S. P. H. T.

    2017-02-01

    The retreat history of the Antarctic Ice Sheet is important for understanding rapid deglaciation, as well as to constrain numerical ice sheet models and ice loading models required for glacial isostatic adjustment modelling. There is particular debate about the extent of grounded ice in the Weddell Sea embayment at the Last Glacial Maximum, and its subsequent deglacial history. Here we provide a new dataset of geomorphological observations and cosmogenic nuclide surface exposure ages of erratic samples that constrain the deglacial history of the Pensacola Mountains, adjacent to the present day Foundation Ice Stream and Academy Glacier in the southern Weddell Sea embayment. We show there is evidence of at least two glaciations, the first of which was relatively old and warm-based, and a more recent cold-based glaciation. During the most recent glaciation ice thickened by at least 450 m in the Williams Hills and at least 380 m on Mt Bragg. Progressive thinning from these sites was well underway by 10 ka BP and ice reached present levels by 2.5 ka BP, and is broadly similar to the relatively modest thinning histories in the southern Ellsworth Mountains. The thinning history is consistent with, but does not mandate, a Late Holocene retreat of the grounding line to a smaller-than-present configuration, as has been recently hypothesized based on ice sheet and glacial isostatic modelling. The data also show that clasts with complex exposure histories are pervasive and that clast recycling is highly site-dependent. These new data provide constraints on a reconstruction of the retreat history of the formerly-expanded Foundation Ice Stream, derived using a numerical flowband model.

  13. Bathymetry and retreat of Southeast Greenland glaciers from Operation IceBridge and Ocean Melting Greenland data

    Science.gov (United States)

    Millan, R.; Rignot, E. J.; Morlighem, M.; Bjork, A. A.; Mouginot, J.; Wood, M.

    2017-12-01

    Southeast Greenland has been one of the largest contributors to ice mass loss in Greenland in part because of significant changes in glacier dynamics. The leading hypothesis for the changes in glacier dynamics is that enhanced thermal forcing from the ocean has dislodged a number of glaciers from their anchoring positions and some of them retreated rapidly along a reverse bed. The glaciers response has been observed to vary significantly from one fjord to the next, but until now there was not enough data to understand or interpret these changes. In particular, there was no data on glacier bed topography and seafloor bathymetry in the fjords. Here we present the results of new fjord mapping by the NASA Ocean Melting Greenland mission combined with a recent high-resolution airborne gravity survey by NASA Operation IceBridge. We combine these data with a reconstruction of the bed using a mass conservation approach upstream extending into the glacial fjords for the first time. In the fjord and along the ice-ocean transition, we employ a 3D inversion of gravity data to infer the bed elevation along a set of 9 survey boxes spanning south of Helheim Glacier to the southern tip of Southeast Greenland. We combine the results with an analysis of the glacier front history since the 1930's and Conductivity Temperature Depth data obtained in the fjord by OMG in 2016. The data reveals bed elevations several 100-m deeper than previously thought, for almost all the glaciers, up to 500 m for some of them. For many glaciers, the bed profiles help to completely understand the history of retreat of the glaciers. For instance, glaciers stranded on sills have been stable; glaciers on a reverse slope have retreated rapidly; and glaciers with a normal slope have retreated slowly. The mapping also helps document the extent of the marine portion of the glacier basins. In many of the fjords, we document the presence of warm, salty Atlantic Water which fuels large melt rates. We employ

  14. Post-Glacial and Paleo-Environmental History of the West Coast of Vancouver Island

    Science.gov (United States)

    Dallimore, A.; Enkin, R. J.

    2005-12-01

    Annually laminated sediments in anoxic fjords are potentially ideal paleoclimate recorders, particularly once proxy measurements for atmospheric, oceanographic and sedimentological conditions have been calibrated. On the west coast of Canada, these sediments also record the changing environment as glaciers retreated from this area about 12 ka y BP. In Effingham Inlet, a 40 m core taken from the French ship the Marion Dufresne as part of the international IMAGES/PAGES program, gives evidence of an isolation basin at maximum glacial isostatic rebound and lowest paleo-sea level followed by eustatic sea level rise about 10 ka y BP. The Late Pleistocene record also marks dramatic changes in glacial sedimentary source and transport. Excellent chronological control is provided by complementary yet independent dating methods including radiocarbon dates on both plants and shells, identification of the Mazama Ash, varve counting and paleomagnetic, paleosecular variation correlations in the lower, pro-glacial section of the core which does not contain organic material. Paleoenvironmental evidence from this core provides information on immediate post-glacial conditions along the coast and rapid climatic changes throughout the Holocene, with implications for the possibility of early human migration routes and refugia.

  15. Glacial morphology and depositional sequences of the Antarctic Continental Shelf

    Science.gov (United States)

    ten Brink, Uri S.; Schneider, Christopher

    1995-01-01

    Proposes a simple model for the unusual depositional sequences and morphology of the Antarctic continental shelf. It considers the regional stratal geometry and the reversed morphology to be principally the results of time-integrated effects of glacial erosion and sedimentation related to the location of the ice grounding line. The model offers several guidelines for stratigraphic interpretation of the Antarctic shelf and a Northern Hemisphere shelf, both of which were subject to many glacial advances and retreats. -Authors

  16. River piracy and drainage basin reorganization led by climate-driven glacier retreat

    Science.gov (United States)

    Shugar, Daniel H.; Clague, John J.; Best, James L.; Schoof, Christian; Willis, Michael J.; Copland, Luke; Roe, Gerard H.

    2017-04-01

    River piracy--the diversion of the headwaters of one stream into another one--can dramatically change the routing of water and sediment, with a profound effect on landscape evolution. Stream piracy has been investigated in glacial environments, but so far it has mainly been studied over Quaternary or longer timescales. Here we document how retreat of Kaskawulsh Glacier--one of Canada's largest glaciers--abruptly and radically altered the regional drainage pattern in spring 2016. We use a combination of hydrological measurements and drone-generated digital elevation models to show that in late May 2016, meltwater from the glacier was re-routed from discharge in a northward direction into the Bering Sea, to southward into the Pacific Ocean. Based on satellite image analysis and a signal-to-noise ratio as a metric of glacier retreat, we conclude that this instance of river piracy was due to post-industrial climate change. Rapid regional drainage reorganizations of this type can have profound downstream impacts on ecosystems, sediment and carbon budgets, and downstream communities that rely on a stable and sustained discharge. We suggest that the planforms of Slims and Kaskawulsh rivers will adjust in response to altered flows, and the future Kaskawulsh watershed will extend into the now-abandoned headwaters of Slims River and eventually capture the Kluane Lake drainage.

  17. Phylogeographic insights into cryptic glacial refugia.

    Science.gov (United States)

    Provan, Jim; Bennett, K D

    2008-10-01

    The glacial episodes of the Quaternary (2.6 million years ago-present) were a major factor in shaping the present-day distributions of extant flora and fauna, with expansions and contractions of the ice sheets rendering large areas uninhabitable for most species. Fossil records suggest that many species survived glacial maxima by retreating to refugia, usually at lower latitudes. Recently, phylogeographic studies have given support to the existence of previously unknown, or cryptic, refugia. Here we summarise many of these insights into the glacial histories of species in cryptic refugia gained through phylogeographic approaches. Understanding such refugia might be important as the Earth heads into another period of climate change, in terms of predicting the effects on species distribution and survival.

  18. Glacial Influences on Solar Radiation in a Subarctic Sea.

    Science.gov (United States)

    Understanding macroscale processes controlling solar radia­tion in marine systems will be important in interpreting the potential effects of global change from increasing ultraviolet radiation (UV) and glacial retreat. This study provides the first quantitative assessment of UV i...

  19. Process-based modelling of fluvial system response to rapid climate change: 2. application to the River Maas (The Netherlands) during the Last Glacial-Interglacial Transition

    NARCIS (Netherlands)

    Bogaart, P.W.; Balen, van R.T.; Kasse, C.; Vandenberghe, J.

    2003-01-01

    A comprehensive process-based numerical model of catchment hydrology and alluvial channel dynamics is applied to the evolution of the river Maas during the Last Glacial-Interglacial Transition. Palaeo-climatological reconstructions based on a number of climatic and environmental proxies are combined

  20. Ultra-high resolution pollen record from the northern Andes reveals rapid shifts in montane climates within the last two glacial cycles

    Directory of Open Access Journals (Sweden)

    M. H. M. Groot

    2011-03-01

    Full Text Available Here we developed a composite pollen-based record of altitudinal vegetation changes from Lake Fúquene (5° N in Colombia at 2540 m elevation. We quantitatively calibrated Arboreal Pollen percentages (AP% into mean annual temperature (MAT changes with an unprecedented ~60-year resolution over the past 284 000 years. An age model for the AP% record was constructed using frequency analysis in the depth domain and tuning of the distinct obliquity-related variations to the latest marine oxygen isotope stacked record. The reconstructed MAT record largely concurs with the ~100 and 41-kyr (obliquity paced glacial cycles and is superimposed by extreme changes of up to 7 to 10° Celsius within a few hundred years at the major glacial terminations and during marine isotope stage 3, suggesting an unprecedented North Atlantic – equatorial link. Using intermediate complexity transient climate modelling experiments, we demonstrate that ice volume and greenhouse gasses are the major forcing agents causing the orbital-related MAT changes, while direct precession-induced insolation changes had no significant impact on the high mountain vegetation during the last two glacial cycles.

  1. Glacier Change, Supraglacial Debris Expansion and Glacial Lake Evolution in the Gyirong River Basin, Central Himalayas, between 1988 and 2015

    Directory of Open Access Journals (Sweden)

    Sheng Jiang

    2018-06-01

    Full Text Available Himalayan glacier changes in the context of global climate change have attracted worldwide attention due to their profound cryo-hydrological ramifications. However, an integrated understanding of the debris-free and debris-covered glacier evolution and its interaction with glacial lake is still lacking. Using one case study in the Gyirong River Basin located in the central Himalayas, this paper applied archival Landsat imagery and an automated mapping method to understand how glaciers and glacial lakes interactively evolved between 1988 and 2015. Our analyses identified 467 glaciers in 1988, containing 435 debris-free and 32 debris-covered glaciers, with a total area of 614.09 ± 36.69 km2. These glaciers decreased by 16.45% in area from 1988 to 2015, with an accelerated retreat rate after 1994. Debris-free glaciers retreated faster than debris-covered glaciers. As a result of glacial downwasting, supraglacial debris coverage expanded upward by 17.79 km2 (24.44%. Concurrent with glacial retreat, glacial lakes increased in both number (+41 and area (+54.11%. Glacier-connected lakes likely accelerated the glacial retreat via thermal energy transmission and contributed to over 15% of the area loss in their connected glaciers. On the other hand, significant glacial retreats led to disconnections from their proglacial lakes, which appeared to stabilize the lake areas. Continuous expansions in the lakes connected with debris-covered glaciers, therefore, need additional attention due to their potential outbursts. In comparison with precipitation variation, temperature increase was the primary driver of such glacier and glacial lake changes. In addition, debris coverage, size, altitude, and connectivity with glacial lakes also affected the degree of glacial changes and resulted in the spatial heterogeneity of glacial wastage across the Gyirong River Basin.

  2. Greenland's 20th Century retreat illuminated - great spatial variability with strong connections to subglacial topography and fjord bathymetry

    Science.gov (United States)

    Bjork, A. A.; Kjeldsen, K. K.; Boeckel, M. V.; Korsgaard, N. J.; Fenty, I. G.; Khan, S. A.; Mouginot, J.; Morlighem, M.; Rignot, E. J.; Dowdeswell, J. A.; Kjaer, K. H.

    2017-12-01

    Mass loss acceleration from the Greenland Ice Sheet is a dominant contributor in recent global sea-level rise, and has been for several decades. While ice sheet wide mass loss has recently been documented from the end of the Little Ice Age (c. 1900 CE) to the 1980s, the detailed changes during this period remain poorly known. In this study, we map glacier margins of Greenland's 310 largest outlet glaciers in order to get the full picture of the 20th Century mass loss. We take advantage of the rich history of aerial photography over Greenland and combine photos from archives in Denmark, Norway, United Kingdom, and United States. We supplement the historical aerial photographs with declassified US spy satellite imagery and recent satellite imagery to document glacial retreat and advance on a decadal scale. With recent advances in bathymetry mapping and subglacial topography mapping, we are able to show that spatial differences in retreat throughout the last 100 years are largely controlled by the underlying topography. Our study further highlights hotspots of past rapid mass loss in Greenland, and discusses implications for periods of regional stability and advance.

  3. Extensive Holocene ice sheet grounding line retreat and uplift-driven readvance in West Antarctica

    Science.gov (United States)

    Kingslake, J.; Scherer, R. P.; Albrecht, T.; Coenen, J. J.; Powell, R. D.; Reese, R.; Stansell, N.; Tulaczyk, S. M.; Whitehouse, P. L.

    2017-12-01

    The West Antarctic Ice Sheet (WAIS) reached its Last Glacial Maximum (LGM) extent 29-14 kyr before present. Numerical models used to project future ice-sheet contributions to sea-level rise exploit reconstructions of post-LGM ice mass loss to tune model parameterizations. Ice-sheet reconstructions are poorly constrained in areas where floating ice shelves or a lack of exposed geology obstruct conventional glacial-geological techniques. In the Weddell and Ross Sea sectors, ice-sheet reconstructions have traditionally assumed progressive grounding line (GL) retreat throughout the Holocene. Contrasting this view, using three distinct lines of evidence, we show that the GL retreated hundreds of kilometers inland of its present position, before glacial isostatic rebound during the Mid to Late Holocene caused the GL to readvance to its current position. Evidence for retreat and readvance during the last glacial termination includes (1) widespread radiocarbon in sediment cores recovered from beneath ice streams along the Siple and Gould Coasts, indicating marine exposure at least 200 km inland of the current GL, (2) ice-penetrating radar observations of relic crevasses and other englacial structures preserved in slow-moving grounded ice, indicating ice-shelf grounding and (3) an ensemble of new ice-sheet simulations showing widespread post-LGM retreat of the GL inland of its current location and later readvance. The model indicates that GL readvance across low slope ice-stream troughs requires uplift-driven grounding of the ice shelf on topographic highs (ice rises). Our findings highlight ice-shelf pinning points and lithospheric response to unloading as drivers of major ice-sheet fluctuations. Full WAIS collapse likely requires GL retreat well beyond its current position in the Ronne and Ross Sectors and linkage via Amundsen Sea sector glaciers.

  4. The character and mechanism of glacial variation in the peripheral Tibetan Plateau

    Science.gov (United States)

    Yi, S.; Wang, Q.; Sun, W.

    2016-12-01

    Global warming has accelerated glacier retreat in the peripheral Tibetan Plateau. Our study demonstrates consistent glacier variation in time series constructed by laser altimetry and space gravimetry in these regions. It largely enhances reliability of glacier changes and narrows down significant inconsistent in previous studies. The glacial melt is roughly weakening from southeast to northwest: from Nyenchen Tanglha to Himalaya then to Pamir even a positive gain in the Western Kunlun. A sharp melt of glacier on Nyenchen Tanglha is primarily caused by high temperature and rapid rise rather than decreasing in annual precipitation as previously thought. Glaciers on Hindu Kush, Karakoram and Western Kun even Pamir are less affect by slow rise of local temperature.

  5. Phylogeography and post-glacial recolonization in wolverines (Gulo gulo from across their circumpolar distribution.

    Directory of Open Access Journals (Sweden)

    Joanna Zigouris

    Full Text Available Interglacial-glacial cycles of the Quaternary are widely recognized in shaping phylogeographic structure. Patterns from cold adapted species can be especially informative - in particular, uncovering additional glacial refugia, identifying likely recolonization patterns, and increasing our understanding of species' responses to climate change. We investigated phylogenetic structure of the wolverine, a wide-ranging cold adapted carnivore, using a 318 bp of the mitochondrial DNA control region for 983 wolverines (n=209 this study, n=774 from GenBank from across their full Holarctic distribution. Bayesian phylogenetic tree reconstruction and the distribution of observed pairwise haplotype differences (mismatch distribution provided evidence of a single rapid population expansion across the wolverine's Holarctic range. Even though molecular evidence corroborated a single refugium, significant subdivisions of population genetic structure (0.01< ΦST <0.99, P<0.05 were detected. Pairwise ΦST estimates separated Scandinavia from Russia and Mongolia, and identified five main divisions within North America - the Central Arctic, a western region, an eastern region consisting of Ontario and Quebec/Labrador, Manitoba, and California. These data are in contrast to the nearly panmictic structure observed in northwestern North America using nuclear microsatellites, but largely support the nuclear DNA separation of contemporary Manitoba and Ontario wolverines from northern populations. Historic samples (c. 1900 from the functionally extirpated eastern population of Quebec/Labrador displayed genetic similarities to contemporary Ontario wolverines. To understand these divergence patterns, four hypotheses were tested using Approximate Bayesian Computation (ABC. The most supported hypothesis was a single Beringia incursion during the last glacial maximum that established the northwestern population, followed by a west-to-east colonization during the Holocene. This

  6. Phylogeography and post-glacial recolonization in wolverines (Gulo gulo) from across their circumpolar distribution.

    Science.gov (United States)

    Zigouris, Joanna; Schaefer, James A; Fortin, Clément; Kyle, Christopher J

    2013-01-01

    Interglacial-glacial cycles of the Quaternary are widely recognized in shaping phylogeographic structure. Patterns from cold adapted species can be especially informative - in particular, uncovering additional glacial refugia, identifying likely recolonization patterns, and increasing our understanding of species' responses to climate change. We investigated phylogenetic structure of the wolverine, a wide-ranging cold adapted carnivore, using a 318 bp of the mitochondrial DNA control region for 983 wolverines (n=209 this study, n=774 from GenBank) from across their full Holarctic distribution. Bayesian phylogenetic tree reconstruction and the distribution of observed pairwise haplotype differences (mismatch distribution) provided evidence of a single rapid population expansion across the wolverine's Holarctic range. Even though molecular evidence corroborated a single refugium, significant subdivisions of population genetic structure (0.01< ΦST <0.99, P<0.05) were detected. Pairwise ΦST estimates separated Scandinavia from Russia and Mongolia, and identified five main divisions within North America - the Central Arctic, a western region, an eastern region consisting of Ontario and Quebec/Labrador, Manitoba, and California. These data are in contrast to the nearly panmictic structure observed in northwestern North America using nuclear microsatellites, but largely support the nuclear DNA separation of contemporary Manitoba and Ontario wolverines from northern populations. Historic samples (c. 1900) from the functionally extirpated eastern population of Quebec/Labrador displayed genetic similarities to contemporary Ontario wolverines. To understand these divergence patterns, four hypotheses were tested using Approximate Bayesian Computation (ABC). The most supported hypothesis was a single Beringia incursion during the last glacial maximum that established the northwestern population, followed by a west-to-east colonization during the Holocene. This pattern is

  7. Rapid melting dynamics of an alpine glacier with repeated UAV photogrammetry

    Science.gov (United States)

    Rossini, Micol; Di Mauro, Biagio; Garzonio, Roberto; Baccolo, Giovanni; Cavallini, Giuseppe; Mattavelli, Matteo; De Amicis, Mattia; Colombo, Roberto

    2018-03-01

    Glacial retreat is a major problem in the Alps, especially over the past 40 years. Unmanned aerial vehicles (UAVs) can provide an unparalleled opportunity to track the spatiotemporal variations in rapidly changing glacial morphological features related to glacial dynamics. The objective of this study is to evaluate the potential of commercial UAV platforms to detect the evolution of the surface topography and morphology of an alpine glacier over a short time scale through the repeated acquisition of high-resolution photogrammetric data. Two high-resolution UAV surveys were performed on the ablation region of the Morteratsch Glacier (Swiss Alps) in July and September 2016. First, structure-from-motion (SfM) techniques were applied to create orthophotos and digital surface models (DSMs) of the glacial surface from multi-view UAV acquisitions. The geometric accuracy of DSMs and orthophotos was checked using differential global navigation satellite system (dGNSS) ground measurements, and an accuracy of approximately 17 cm was achieved for both models. High-resolution orthophotos and DSMs made it possible to provide a detailed characterization of rapidly changing glacial environments. Comparing the data from the first and the second campaigns, the evolution of the lower part of the glacier in response to summer ablation was evaluated. Two distinct processes were revealed and accurately quantified: an average lowering of the surface, with a mean ice thinning of 4 m, and an average horizontal displacement of 3 m due to flowing ice. These data were validated through a comparison of different algorithms and approaches, which clearly showed the consistency of the results. The melt rate spatial patterns were then compared to the glacial brightness and roughness maps derived from the September UAV acquisition. The results showed that the DSM differences describing the glacial melt rates were inversely related to the glacial brightness. In contrast, a positive but weaker

  8. Exceptional retreat of Novaya Zemlya's marine-terminating outlet glaciers between 2000 and 2013

    Directory of Open Access Journals (Sweden)

    J. R. Carr

    2017-09-01

    Full Text Available Novaya Zemlya (NVZ has experienced rapid ice loss and accelerated marine-terminating glacier retreat during the past 2 decades. However, it is unknown whether this retreat is exceptional longer term and/or whether it has persisted since 2010. Investigating this is vital, as dynamic thinning may contribute substantially to ice loss from NVZ, but is not currently included in sea level rise predictions. Here, we use remotely sensed data to assess controls on NVZ glacier retreat between 1973/76 and 2015. Glaciers that terminate into lakes or the ocean receded 3.5 times faster than those that terminate on land. Between 2000 and 2013, retreat rates were significantly higher on marine-terminating outlet glaciers than during the previous 27 years, and we observe widespread slowdown in retreat, and even advance, between 2013 and 2015. There were some common patterns in the timing of glacier retreat, but the magnitude varied between individual glaciers. Rapid retreat between 2000 and 2013 corresponds to a period of significantly warmer air temperatures and reduced sea ice concentrations, and to changes in the North Atlantic Oscillation (NAO and Atlantic Multidecadal Oscillation (AMO. We need to assess the impact of this accelerated retreat on dynamic ice losses from NVZ to accurately quantify its future sea level rise contribution.

  9. Changes in Glaciers and Glacial Lakes and the Identification of Dangerous Glacial Lakes in the Pumqu River Basin, Xizang (Tibet

    Directory of Open Access Journals (Sweden)

    Tao Che

    2014-01-01

    Full Text Available Latest satellite images have been utilized to update the inventories of glaciers and glacial lakes in the Pumqu river basin, Xizang (Tibet, in the study. Compared to the inventories in 1970s, the areas of glaciers are reduced by 19.05% while the areas of glacial lakes are increased by 26.76%. The magnitudes of glacier retreat rate and glacial lake increase rate during the period of 2001–2013 are more significant than those for the period of the 1970s–2001. The accelerated changes in areas of the glaciers and glacial lakes, as well as the increasing temperature and rising variability of precipitation, have resulted in an increased risk of glacial lake outburst floods (GLOFs in the Pumqu river basin. Integrated criteria were established to identify potentially dangerous glacial lakes based on a bibliometric analysis method. It is found, in total, 19 glacial lakes were identified as dangerous. Such finding suggests that there is an immediate need to conduct field surveys not only to validate the findings, but also to acquire information for further use in order to assure the welfare of the humans.

  10. Observations and modeling of fjord sedimentation during the 30 year retreat of Columbia Glacier, AK

    Science.gov (United States)

    Love, Katherine B; Hallet, Bernard; Pratt, Thomas L.; O'Neel, Shad

    2016-01-01

    To explore links between glacier dynamics, sediment yields and the accumulation of glacial sediments in a temperate setting, we use extensive glaciological observations for Columbia Glacier, Alaska, and new oceanographic data from the fjord exposed during its retreat. High-resolution seismic data indicate that 3.2 × 108 m3 of sediment has accumulated in Columbia Fjord over the past three decades, which corresponds to ~5 mm a−1 of erosion averaged over the glaciated area. We develop a general model to infer the sediment-flux history from the glacier that is compatible with the observed retreat history, and the thickness and architecture of the fjord sediment deposits. Results reveal a fivefold increase in sediment flux from 1997 to 2000, which is not correlated with concurrent changes in ice flux or retreat rate. We suggest the flux increase resulted from an increase in the sediment transport capacity of the subglacial hydraulic system due to the retreat-related steepening of the glacier surface over a known subglacial deep basin. Because variations in subglacial sediment storage can impact glacial sediment flux, in addition to changes in climate, erosion rate and glacier dynamics, the interpretation of climatic changes based on the sediment record is more complex than generally assumed.

  11. Lake sediment-based Late Holocene glacier reconstruction reveals medieval retreat and two-phase Little Ice Age on subantarctic South Georgia

    Science.gov (United States)

    van der Bilt, W. G. M.; Bakke, J.; Werner, J.; Paasche, O.; Rosqvist, G. N.; Vatle, S. S.

    2016-12-01

    Southern Ocean climate is rapidly changing. Yet beyond the instrumental period (± 100 years), our comprehension of climate variability in the region is restricted by a lack of high-resolution paleoclimate records. Alpine glaciers, ubiquitous on Southern Ocean islands, may provide such data as they rapidly respond to climate shifts, recording attendant changes in extent by variations in glacial erosion. Rock flour, the fine-grained fraction of this process, is suspended in meltwater streams and transfers this signal to the sediments of downstream lakes, continuously recording glacier history. Here, we use this relationship and present the first reconstruction of the Late Holocene (1250 cal. yr BP - present) glacier history of the Southern Ocean island of South Georgia, using sediments from the glacier-fed Middle Hamberg lake. Variations are resolved on multi-centennial scales due to robust chronological control. To fingerprint a glacial erosion signal, we employed a set of routinely used physical, geochemical and magnetic parameters. Using Titanium counts, validated against changes in sediment density and grain size distribution, we continuously reconstruct glacier variations over the past millennium. Refining local moraine evidence and supporting evidence from other Southern Hemisphere sites, this study shows a progressive diminishing of consecutive Late Holocene advances. These include a two-stage Little Ice Age, in agreement with other Southern Hemisphere glacier evidence. The presented record furthermore captures an unreported retreat phase behind present limits around 500 cal. yr BP.

  12. Modeling the evolution of the Laurentide Ice Sheet from MIS 3 to the Last Glacial Maximum: an approach using sea level modeling and ice flow dynamics

    Science.gov (United States)

    Weisenberg, J.; Pico, T.; Birch, L.; Mitrovica, J. X.

    2017-12-01

    The history of the Laurentide Ice Sheet since the Last Glacial Maximum ( 26 ka; LGM) is constrained by geological evidence of ice margin retreat in addition to relative sea-level (RSL) records in both the near and far field. Nonetheless, few observations exist constraining the ice sheet's extent across the glacial build-up phase preceding the LGM. Recent work correcting RSL records along the U.S. mid-Atlantic dated to mid-MIS 3 (50-35 ka) for glacial-isostatic adjustment (GIA) infer that the Laurentide Ice Sheet grew by more than three-fold in the 15 ky leading into the LGM. Here we test the plausibility of a late and extremely rapid glaciation by driving a high-resolution ice sheet model, based on a nonlinear diffusion equation for the ice thickness. We initialize this model at 44 ka with the mid-MIS 3 ice sheet configuration proposed by Pico et al. (2017), GIA-corrected basal topography, and mass balance representative of mid-MIS 3 conditions. These simulations predict rapid growth of the eastern Laurentide Ice Sheet, with rates consistent with achieving LGM ice volumes within 15 ky. We use these simulations to refine the initial ice configuration and present an improved and higher resolution model for North American ice cover during mid-MIS 3. In addition we show that assumptions of ice loads during the glacial phase, and the associated reconstructions of GIA-corrected basal topography, produce a bias that can underpredict ice growth rates in the late stages of the glaciation, which has important consequences for our understanding of the speed limit for ice growth on glacial timescales.

  13. Lateglacial geomorphology in the Tweedsmuir Hills, Scotland - Implications for retreat patterns, glacier reconstruction and chronology.

    Science.gov (United States)

    Pearce, D.; Rea, B.; McDougall, D.

    2012-04-01

    Lateglacial landform assemblage indicates more extensive glaciation than previously envisaged, with both a transection ice-mass and icefield coexisting, reflecting different topographic controls. Interestingly, a geomorphic pattern is observable in more than one valley, which is interpreted as a synchronous recession of the outlet glaciers and a rapid deglaciation towards the summits. Whilst two landsystems have been mapped the second poses interesting problems regarding extent and timing of glaciation. The Loch Skene site has been traditionally associated with a small valley glacier. However, it appears to feed ice into a lower valley which exhibits a landform assemblage typical of Lateglacial deglaciation in Scotland. It is tentatively proposed that the Loch Skene glacier represents a retreat phase prior to complete deglaciation rather than the Younger Dryas maximum.

  14. Glacial lakes of the Central and Patagonian Andes

    Science.gov (United States)

    Wilson, Ryan; Glasser, Neil F.; Reynolds, John M.; Harrison, Stephan; Anacona, Pablo Iribarren; Schaefer, Marius; Shannon, Sarah

    2018-03-01

    The prevalence and increased frequency of high-magnitude Glacial Lake Outburst Floods (GLOFs) in the Chilean and Argentinean Andes suggests this region will be prone to similar events in the future as glaciers continue to retreat and thin under a warming climate. Despite this situation, monitoring of glacial lake development in this region has been limited, with past investigations only covering relatively small regions of Patagonia. This study presents new glacial lake inventories for 1986, 2000 and 2016, covering the Central Andes, Northern Patagonia and Southern Patagonia. Our aim was to characterise the physical attributes, spatial distribution and temporal development of glacial lakes in these three sub-regions using Landsat satellite imagery and image datasets available in Google Earth and Bing Maps. Glacial lake water volume was also estimated using an empirical area-volume scaling approach. Results reveal that glacial lakes across the study area have increased in number (43%) and areal extent (7%) between 1986 and 2016. Such changes equate to a glacial lake water volume increase of 65 km3 during the 30-year observation period. However, glacial lake growth and emergence was shown to vary sub-regionally according to localised topography, meteorology, climate change, rate of glacier change and the availability of low gradient ice areas. These and other factors are likely to influence the occurrence of GLOFs in the future. This analysis represents the first large-scale census of glacial lakes in Chile and Argentina and will allow for a better understanding of lake development in this region, as well as, providing a basis for future GLOF risk assessments.

  15. Power grid control in retreat

    International Nuclear Information System (INIS)

    Morch, Stein

    2000-01-01

    Bilateral grid control that obstructs free trade of electricity is in retreat. Negotiations on opening the Skagerrak cables are in progress. The EU, national authorities, network companies with system responsibility, market actors, electricity exchanges all push for quick opening of the grid. At present, free trade of electricity is hindered not so much by physical bottlenecks in the grid as by market actors possessing control and bilateral agreements. The article discusses current bilateral agreements and how they might affect the possibility of a free trade of electricity in Europe

  16. Neoglacial Antarctic sea-ice expansion driven by mid-Holocene retreat of the Ross Ice Shelf.

    Science.gov (United States)

    Bendle, J. A.; Newton, K.; Mckay, R. M.; Crosta, X.; Etourneau, J.; Anya, A. B.; Seki, O.; Golledge, N. R.; Bertler, N. A. N.; Willmott, V.; Schouten, S.; Riesselman, C. R.; Masse, G.; Dunbar, R. B.

    2017-12-01

    Recent decades have seen expanding Antarctic sea-ice coverage, coeval with thinning West Antarctic Ice Sheet (WAIS) ice shelves and the rapid freshening of surface and bottom waters along the Antarctic margin. The mid-Holocene Neoglacial transition represents the last comparable baseline shift in sea-ice behaviour. The drivers and feedbacks involved in both the recent and Holocene events are poorly understood and characterised by large proxy-model mismatches. We present new records of compound specific fatty acid isotope analyses (δ2H-FA), highly-branched isoprenoid alkenes (HBIs) TEX86L temperatures, grain-size, mass accumulations rates (MARs) and image analyses from a 171m Holocene sediment sequence from Site U1357 (IODP leg 318). In combination with published records we reconstruct Holocene changes in glacial meltwater, sedimentary inputs and sea-ice. The early Holocene (11 to 10 ka) is characterised by large fluctuations in inputs of deglacial meltwater and sediments and seismic evidence of downlapping material from the south, suggesting a dominating influence from glacial retreat of the local outlet glaciers. From 10 to 8 ka there is decreasing meltwater inputs, an onlapping drift and advection of material from the east. After ca. 8 ka positively correlated δ2H-FA and MARs infer that pulses of glacial melt correlate to stronger easterly currents, driving erosion of material from upstream banks and that the Ross Ice Shelf (RIS) becomes a major influence. A large mid-Holocene meltwater pulse (preceded by warming TEX86L temperatures) is evident between ca. 6 to 4.5 ka, culminating in a rapid and permanent increase in sea-ice from 4.5 ka. This is coeval with cosmogenic nuclide evidence for a rapid thinning of the Antarctic ice sheet during the mid-Holocene (Hein et al., 2016). We suggest this represents a final major pulse of deglaciation from the Ross Ice Shelf, which initiates the Neoglacial, driving cool surface waters along the coast and greater sea

  17. Modelling Waterfall Retreat in Heterogenous Bedrock

    Science.gov (United States)

    Attal, M.; Hodge, R. A.; Williams, R.; Baynes, E.

    2016-12-01

    Bedrock rivers are the mediators of environmental change through mountainous landscapes. In response to an increase in uplift rate for example, a "knickpoint" (often materialised as a waterfall) will propagate upstream, separating a domain downstream where the river and its adjacent hillslopes have steepened in response to the change from a "relict" domain upstream which is adjusted to the conditions before the change (Crosby and Whipple 2006). Many studies assume that knickpoint propagation rate scales with drainage area, based on the stream power theory. However, recent studies in a range of locations have found no obvious relationship between knickpoint retreat rate and drainage area, potentially resulting from the stream power law neglecting (i) the influence of sediment on the processes associated with waterfall migration and (ii) thresholds for bedrock detachment (Cook et al. 2013; Mackey et al. 2014; DiBiase et al. 2015; Baynes et al. 2015; Brocard et al. 2016). In this study, we develop a 1D model of waterfall retreat in horizontally bedded bedrock with varying joint spacing. In the model, knickpoint migration is based on two rules: a waterfall will start migrating once the threshold flow depth (a function of knickpoint height and joint spacing) has been exceeded (Lamb and Dietrich 2009), and the migration rate will then be a function of the water-depth-to-waterfall-height ratio, based on experimental results by Baynes (2015). Using a hydrograph based on a Poisson rectangular pulse rainfall simulator (Tucker and Bras 2001), we demonstrate the importance of structure in controlling the speed at which waterfalls migrate but also their number and the length over which they are distributed (Fig. 1). The model is applied to the Jökulsá á Fjöllum, NE Iceland, where rapid migration of waterfalls as a result of discrete events has been identified (Baynes et al. 2015), using new constraints on joint spacing derived from high resolution lidar survey of the gorge

  18. Endodontic retreatment decisions: no consensus.

    Science.gov (United States)

    Aryanpour, S; Van Nieuwenhuysen, J P; D'Hoore, W

    2000-05-01

    The objectives of the present study were to: (i) evaluate the consensus, if any, amongst dental schools, students and their instructors managing the same clinical cases, all of which involved endodontically treated teeth; and (ii) determine the predominant proposed treatment option. Final year students, endodontic staff members and instructors of 10 European dental schools were surveyed as decision makers. Fourteen different radiographic cases of root canal treated teeth accompanied by a short clinical history were presented to them in a uniform format. For each case the decision makers were requested to: (i) choose only one out of nine treatment alternatives proposed, from 'no treatment' to 'extraction' via 'retreatment' and 'surgery' (ii) assess on two 5-point scales: the difficulty of making a decision, and the technical complexity of the retreatment procedure. The results indicate wide inter- and also intra-school disagreements in the clinical management of root canal treated teeth. Analysis of variance showed that the main source of variation was the 'school effect', explaining 1.8% (NS) to 18.6% (P < 0.0001) of the treatment variations. No other factor explained as much variance. Decision difficulty was moderately correlated to technical complexity (Pearsons' r ranging from 0.19 to 0.35, P < 0.0001). No clear consensus occurred amongst and within dental schools concerning the clinical management of the 14 cases. The lack of consensus amongst schools seems to be due mainly to chance or uncertainty, but can be partly explained by the 'school effect'.

  19. Temperature under the Tongue: A paleotemperature record of the Drygalksi Ice Tongue with improved chronology of ice retreat

    Science.gov (United States)

    Subt, C.; Rosenheim, B. E.; Lee, J. I.; Yoo, K. C.; Browne, I. M.; Shevenell, A.

    2017-12-01

    The Ross Embayment is among the most well-studied regions in Antarctica. Despite the relative abundance of data, the style and forcing of deglaciation of the Ross Sea sector following the Last Glacial Maximum (LGM; 23-19 ka) is challenging due to the region's considerable size, complex geometry, and the difficulties in dating Antarctic glaciomarine sedimentary sequences. Ross Sea sediments indicate a dynamic glacial retreat in the western Ross Sea, whereas regional glacial systems may have retreated and advanced multiple times during the last deglaciation. Two marine sediment cores collected near the Drygalski Ice Tongue in the western Ross Sea during 2012 and 2015 Korea Polar Research Institute (KOPRI) expeditions reveal a sequence of alternating diatomaceous muds and oozes interbedded with diamict, which suggest dynamic post-LGM grounded ice retreat in the Ross Sea. Dynamic retreat is hypothesized to have been driven by rising sea levels and warmer ocean waters on the continental shelf, thus a record of upper ocean temperatures should reflect this. Here we present the first post-LGM upper ocean temperature record from the Ross Sea, developed using the TEX86 (tetraether index of lipids consisting of 86 carbons) paleothermometer. To overcome the difficulties of dating these sediments using traditional methods, we apply specialized Ramped PyrOx 14C dating for sediments with high proportions of relict carbon . This technique is particularly well-suited for the post-LGM retreat sedimentary sequences from Antarctic margins because it allows for separation of autochthonous and relict material for dating. By combining organic paleothermometry and state-of-the-art chronologic techniques, we gain a more thorough understanding of upper ocean temperatures in the Ross Sea during the last deglaciation, and their implications for ice retreat.

  20. Low post-glacial rebound rates in the Weddell Sea due to Late Holocene ice-sheet readvance.

    OpenAIRE

    Bradley, S.L.; Hindmarsh, R.C.A.; Whitehouse, P.L.; Bentley, M.J.; King, M.A.

    2015-01-01

    Many ice-sheet reconstructions assume monotonic Holocene retreat for the West Antarctic Ice Sheet, but an increasing number of glaciological observations infer that some portions of the ice sheet may be readvancing, following retreat behind the present-day margin. A readvance in the Weddell Sea region can reconcile two outstanding problems: (i) the present-day widespread occurrence of seemingly stable ice streams grounded on beds that deepen inland; and (ii) the inability of models of glacial...

  1. Decadal-scale climate drivers for glacial dynamics in Glacier National Park, Montana, USA

    Science.gov (United States)

    Pederson, Gregory T.; Fagre, Daniel B.; Gray, Stephen T.; Graumlich, Lisa J.

    2004-06-01

    Little Ice Age (14th-19th centuries A.D.) glacial maxima and 20th century retreat have been well documented in Glacier National Park, Montana, USA. However, the influence of regional and Pacific Basin driven climate variability on these events is poorly understood. We use tree-ring reconstructions of North Pacific surface temperature anomalies and summer drought as proxies for winter glacial accumulation and summer ablation, respectively, over the past three centuries. These records show that the 1850's glacial maximum was likely produced by ~70 yrs of cool/wet summers coupled with high snowpack. Post 1850, glacial retreat coincides with an extended period (>50 yr) of summer drought and low snowpack culminating in the exceptional events of 1917 to 1941 when retreat rates for some glaciers exceeded 100 m/yr. This research highlights potential local and ocean-based drivers of glacial dynamics, and difficulties in separating the effects of global climate change from regional expressions of decadal-scale climate variability.

  2. Reconstruction of Last Glacial to early Holocene monsoon variability from relict lake sediments of the Higher Central Himalaya, Uttrakhand, India

    DEFF Research Database (Denmark)

    Juyal, N.; Pant, R.K.; Basavaiah, N.

    2009-01-01

    .5 ka and after14.5–13 ka. The Last Glacial phase ended with the deposition of outwash gravel dated at 11 ka indicating glacial retreat and the onset of Holocene condition. Additionally, centennial scale fluctuations between 16.5 ka and 12.7 ka in the magnetic and geochemical data are seen. A close...... instability in higher northern latitudes. However, centennial scale abrupt changes are attributed to the result of albedo changes on the Himalaya and Tibetan plateau....

  3. Salt Marshes as Monitors of Late Holocene Outlet Glacier Retreat

    Science.gov (United States)

    Wake, L. M.; Woodroffe, S.; Long, A. J.; Milne, G. A.

    2014-12-01

    New proxy sea-level records extracted from salt marshes in the vicinity of Jakobshavn Isbrae (Pakitsoq; 69.51°N, 50.74°W) and at previous sites in central western Greenland (Sisimiut; 66.47°N, 53.61°W and Aasiaat; 68.69°N, 52.88°W) are analyzed with respect to their ability to act as proximal tide gauges detecting mass balance changes in nearby outlet glaciers associated with the transition from the Little Ice Age ("LIA", 1400-1850AD) to the Industrial Period (>1850AD). Data at Pakitsoq demonstrate that sea-level rose at a rate of 3.5 ±1.7 mm/yr prior to 1850AD and slowed to 0.3 ±0.6mm/yr thereafter, producing a slowdown in sea level of 3.2 ± 1.8 mm/yr. A similar slowdown, occurring at 1600AD, is observed at Aasiaat and Sisimiut. We interpret these observed changes using a glacial isostatic adjustment model of sea-level change truncated at degree and order 4096, with an aim to determine if the sea-level data can be used to place constraints on changes in Jakobshavn Isbrae and/or Kangiata Nunaata Sermia (Nuuk fjord) during this period. Modelled sea level at Pakitsoq is insensitive to the location of thickening (thinning) associated with grounding line advance (retreat) and the rate of advance and retreat but is sensitive to the change point in time between periods of growth associated with LIA expansion (sea level rise) and the onset of 19th century recession (sea level fall) of Jakobshavn Isbrae. We conclude that the change in sea-level rate observed at Pakitsoq circa 1850AD marks the onset of post LIA retreat of this outlet glacier. Conversely, the modelled sea-level response to the retreat of Kangiata Nunaata Sermia from its LIA maximum at ca. 1761AD is below the detection threshold of the salt marsh record at Sisimiut.

  4. Glacial rebound and crustal stress in Finland

    International Nuclear Information System (INIS)

    Lambeck, K.; Purcell, A.

    2003-11-01

    The last ice age of Fennoscandinavia continues to have geological repercussions across Finland despite the last ice having retreated almost 10,000 years ago: land uplift, shoreline retreat, and the stress state of the crust continues to evolve. This report focusses on the glacial rebound signals for Finland and the Gulf of Bothnia and explores the consequences of the ongoing deformation. The rebound signals include the geological evidence as well as instrumental observations: the tide gauge and lake-level measurements of the past century, the changes in geodetic levels recorded in the repeat levelling surveys of the region and the direct measurement of crustal deformation (radial and horizontal) using high-precision space-geodesy measurements. These signals provide constraints on the Earth's rheology, its elasticity and viscosity, and the glacial history of the region. Once observationally constrained, the rebound models are used to predict both the ongoing evolution of shorelines and the changing state of stress within the crust. This report covers: (i) A review of glacial rebound modelling for Scandinavia (Sections 2 and 3). (ii) Review of observational evidence relating to sea-level change and crustal rebound (Section 4). (iii) New earth and ice-sheet model results from the inversion of the geological evidence for sea-level change, including models of shoreline evolution (Sections 5 and 6). (iv) Earth-model results from the inversion of the geodetic evidence for sea-level change (Section 7). (v) Development of crustal stress models for past and present stress states (Section 8). (vi) Conclusions and recommendations (Section 9). Specific conclusions reached pertain to: (i) Thickness of ice cover over Scandinavia since the Last Glacial Maximum, particularly for the Lateglacial period. (ii) Sea-level change and shoreline evolution for the Baltic area since the time the region became ice-free for the last time. (iii) The predicted rates of present-day crustal

  5. Cooperative Spatial Retreat for Resilient Drone Networks.

    Science.gov (United States)

    Kang, Jin-Hyeok; Kwon, Young-Min; Park, Kyung-Joon

    2017-05-03

    Drones are broadening their scope to various applications such as networking, package delivery, agriculture, rescue, and many more. For proper operation of drones, reliable communication should be guaranteed because drones are remotely controlled. When drones experience communication failure due to bad channel condition, interference, or jamming in a certain area, one existing solution is to exploit mobility or so-called spatial retreat to evacuate them from the communication failure area. However, the conventional spatial retreat scheme moves drones in random directions, which results in inefficient movement with significant evacuation time and waste of battery lifetime. In this paper, we propose a novel spatial retreat technique that takes advantage of cooperation between drones for resilient networking, which is called cooperative spatial retreat (CSR). Our performance evaluation shows that the proposed CSR significantly outperforms existing schemes.

  6. Glacier retreat and associated sediment dynamics in proglacial areas: a case study from the Silvretta Alps, Austria

    Science.gov (United States)

    Felbauer, Lucia; Pöppl, Ronald

    2016-04-01

    Global warming results in an ongoing retreat of glaciers in the Alps, leaving behind large amounts of easily erodible sediments. In addition, the debuttressing of rock-walls and the decay of permafrost in the high mountain regions facilitates mass movements of potential disastrous consequences, such as rock falls, landslides and debris flows. Therefore, it is highly important to quantify the amount of sediments that are supplied from the different compartments and to investigate how glacial retreat influences sediment dynamics in proglacial areas. In the presented work glacier retreat and associated sediment dynamics were investigated in the Kromer valley (Silvretta Alps, Austria) by analyzing remote sensing data. Glacial retreat from the period of 1950 to 2012 was documented by interpreting aerial photographs. By digitizing the different stages of the glaciers for six time frames, changes in glacier area and length were mapped and quantified. In order to identify, characterize and quantify sediment dynamics in the proglacial areas a high resolution DEM of difference (DoD) between 2007 and 2012 was created and analyzed, further differentiating between different zones (e.g. valley bottom, hillslope) and types of geomorphic processes (e.g. fluvial, gravitational). First results will be presented at the EGU General Assembly 2016.

  7. Climate Change and Glacier Retreat: Scientific Fact and Artistic Opportunity

    Science.gov (United States)

    Fagre, D. B.

    2008-12-01

    Mountain glaciers continue to retreat rapidly over most of the globe. In North America, at Glacier National Park, Montana, recent research results from Sperry Glacier (2005-2007) indicate negative mass balances are now 3-4 times greater than in the 1950s. A geospatial model of glacier retreat in the Blackfoot-Jackson basin suggested all glaciers would be gone by 2030 but has proved too conservative. Accelerated glacier shrinkage since the model was developed has mirrored an increase in actual annual temperature that is almost twice the rate used in the model. The glaciers in Glacier National Park are likely to be gone well before 2030. A variety of media, curricula, and educational strategies have been employed to communicate the disappearance of the glaciers as a consequence of global warming. These have included everything from print media and television coverage to podcasts and wayside exhibits along roads in the park. However, a new thrust is to partner with artists to communicate climate change issues to new audiences and through different channels. A scientist-artist retreat was convened to explore the tension between keeping artistic products grounded in factually-based reality while providing for freedom to express artistic creativity. Individual artists and scientists have worked to create aesthetic and emotional images, using painting, poetry, music and photography, to convey core messages from research on mountain ecosystems. Finally, a traveling art exhibit was developed to highlight the photography that systematically documents glacier change through time. The aim was to select photographs that provide the most compelling visual experience for an art-oriented viewer and also accurately reflect the research on glacier retreat. The exhibit opens on January 11, 2009

  8. Alaska Harbor Seal Glacial Surveys

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Floating glacial ice serves as a haul-out substrate for a significant number (10-15%) of Alaskan harbor seals, and thus surveying tidewater glacial fjords is an...

  9. Glacial conditions in the Red Sea

    Science.gov (United States)

    Rohling, Eelco J.

    1994-10-01

    In this paper, results from previous studies on planktonic foraminifera, δ18O, and global sea level are combined to discuss climatic conditions in the Red Sea during the last glacial maximum (18,000 B.P.). First, the influence of 120-m sea level lowering on the exchange transport through the strait of Bab-el-Mandab is considered. This strait is the only natural connection of the Red Sea to the open ocean. Next, glacial Red Sea outflow salinity is estimated (about 48 parts per thousand) from the foraminiferal record. Combined, these results yield an estimate of the glacial net water deficit, which appears to have been quite similar to the present (about 2 m yr-1). Finally, budget calculation of δ18O fluxes suggests that the glacial δ18O value of evaporation was about 50% of the present value. This is considered to have resulted from substantially increased mean wind speeds over the glacial Red Sea, which would have caused a rapid drop in the kinematic fractionation factor for 18O. The sensitivity of the calculated values for water deficit and isotopic fractionation to the various assumptions and estimates is evaluated in the discussion. Improvents are to be expected especially through research on the glacial salinity contrast between the Red Sea and Gulf of Aden. It is argued, however, that such future improvement will likely result in a worsening of the isotopic discrepancy, thus increasing the need for an additional mechanism that influenced fractionation (such as mean wind speed). This study demonstrates the need for caution when calculating paleosalinities from δ18O records under the assumption that the modern S∶δ18O relation has remained constant through time. Previously overlooked factors, such as mean wind speed, may have significantly altered that relation in the past.

  10. Extreme beach retreat history inferred from cut-and-fill beach deposits at Moruya, SE Australia

    Science.gov (United States)

    Tamura, T.; Woodroffe, C. D.; Oliver, T.; Cunningham, A. C.

    2017-12-01

    A sequence of beach ridges often records a `cut and fill', where the fair-weather swash accretion of beach sand is punctuated by storm erosion. The detailed chronology of the sequence is thus a clue to decipher past storm events and associated beach erosion, but has not been explored much. Here we explore the potential of such a sequence to detect past extreme retreats in Bengello Beach at Moruya, southeastern Australia. Beach monitoring since 1972 reveals that Bengello beach has shown a typical cut and fill, in which the beach retreats several tens of meters in relation to storms and recovers within a following few years. A storm event caused extreme retreat up to 50 m in 1974. Since then, no retreat exceeded 30 m. The beach monitoring highlights the sporadic nature of the prograded beach deposits; they can only be preserved as stratigraphic records during rapid beach recovery following a large retreat deeper than the beach profile envelope. Thus, ages of the preserved beach deposits roughly correspond to timings of large retreat. Optically-stimulated luminescence (OSL) ages were determined for beach deposits at 5-10 m intervals along a shore-normal transect from the modern foredune to beach ridge 120 m inland. The most landward sample was dated as 510 yr, indicating that the net progradation rate is 0.24 m/yr, concordant with both the long- and short-term rates since the mid Holocene and 1972, respectively. Other ages show four events of retreat around 350, 180, 130 and 90 yr, and also reflect the beach scarp resulting from the 1974 event. The retreat of each event is given by the distance between the shoreline position prior to storm erosion and relevant gap in OSL age. The position of the pre-storm shoreline is estimated by assuming a constant rate of the net progradation of 0.24 m/yr, as with long- and short-term rates. The retreat of the four events is then determined as 45-55 m, similar to the 1974 event. In summary, extreme beach retreats, including that in

  11. Cosmogenic evidence for limited local LGM glacial expansion, Denton Hills, Antarctica

    Science.gov (United States)

    Joy, Kurt; Fink, David; Storey, Bryan; De Pascale, Gregory P.; Quigley, Mark; Fujioka, Toshiyuki

    2017-12-01

    The geomorphology of the Denton Hills provides insight into the timing and magnitude of glacial retreats in a region of Antarctica isolated from the influence of the East Antarctic ice sheet. We present 26 Beryllium-10 surface exposure ages from a variety of glacial and lacustrine features in the Garwood and Miers valleys to document the glacial history of the area from 10 to 286 ka. Our data show that the cold-based Miers, Joyce and Garwood glaciers retreated little since their maximum positions at 37.2 ± 6.9 (1σ n = 4), 35.1 ± 1.5 (1σ, n = 3) and 35.6 ± 10.1 (1σ, n = 6) ka respectively. The similar timing of advance of all three glaciers and the lack of a significant glacial expansion during the global LGM suggests a local LGM for the Denton Hills between ca. 26 and 51 ka, with a mean age of 36.0 ± 7.5 (1σ, n = 13) ka. A second cohort of exposure ages provides constraints to the behaviour of Glacial Lake Trowbridge that formerly occupied Miers Valley in the late Pleistocene. These data show active modification of the landscape from ∼20 ka until the withdrawal of ice from the valley mouths, and deposition of Ross Sea Drift, at 10-14 ka.

  12. Climate Change Adaptation Decision Making for Glacial Lake Outburst Floods From Palcacocha Lake in Peru

    Science.gov (United States)

    Cuellar, A. D.; McKinney, D. C.

    2014-12-01

    Climate change has accelerated glacial retreat in high altitude glaciated regions of Peru leading to the growth and formation of glacier lakes. Glacial lake outburst floods (GLOF) are sudden events triggered by an earthquake, avalanche into the lake or other shock that causes a sudden outflow of water. These floods are catastrophic because of their sudden onset, the difficulty predicting them, and enormous quantity of water and debris rapidly flooding downstream areas. Palcacocha Lake in the Peruvian Andes has experienced accelerated growth since it burst in 1941 and threatens the major city of Huaraz and surrounding communities. Since the 1941 flood stakeholders have advocated for projects to adapt to the increasing threat posed by Palcacocha Lake. Nonetheless, discussions surrounding projects for Palcacocha have not included a rigorous analysis of the potential consequences of a flood, probability of an event, or costs of mitigation projects. This work presents the first step to rationally analyze the risks posed by Palcacocha Lake and the various adaptation projects proposed. In this work the authors use decision analysis to asses proposed adaptation measures that would mitigate damage in downstream communities from a GLOF. We use an existing hydrodynamic model of the at-risk area to determine how adaptation projects will affect downstream flooding. Flood characteristics are used in the HEC-FIA software to estimate fatalities and injuries from an outburst flood, which we convert to monetary units using the value of a statistical life. We combine the monetary consequences of a GLOF with the cost of the proposed projects and a diffuse probability distribution for the likelihood of an event to estimate the expected cost of the adaptation plans. From this analysis we found that lowering the lake level by 15 meters has the least expected cost of any proposal despite uncertainty in the effect of lake lowering on flooding downstream.

  13. Decision Making Methodology to Mitigate Damage From Glacial Lake Outburst Floods From Imja Lake in Nepal

    Science.gov (United States)

    McKinney, D. C.; Cuellar, A. D.

    2015-12-01

    Climate change has accelerated glacial retreat in high altitude glaciated regions of Nepal leading to the growth and formation of glacier lakes. Glacial lake outburst floods (GLOF) are sudden events triggered by an earthquake, moraine failure or other shock that causes a sudden outflow of water. These floods are catastrophic because of their sudden onset, the difficulty predicting them, and enormous quantity of water and debris rapidly flooding downstream areas. Imja Lake in the Himalaya of Nepal has experienced accelerated growth since it first appeared in the 1960s. Communities threatened by a flood from Imja Lake have advocated for projects to adapt to the increasing threat of a GLOF. Nonetheless, discussions surrounding projects for Imja have not included a rigorous analysis of the potential consequences of a flood, probability of an event, or costs of mitigation projects in part because this information is unknown or uncertain. This work presents a demonstration of a decision making methodology developed to rationally analyze the risks posed by Imja Lake and the various adaptation projects proposed using available information. In this work the authors use decision analysis, data envelopement analysis (DEA), and sensitivity analysis to assess proposed adaptation measures that would mitigate damage in downstream communities from a GLOF. We use an existing hydrodynamic model of the at-risk area to determine how adaptation projects will affect downstream flooding and estimate fatalities using an empirical method developed for dam failures. The DEA methodology allows us to estimate the value of a statistical life implied by each project given the cost of the project and number of lives saved to determine which project is the most efficient. In contrast the decision analysis methodology requires fatalities to be assigned a cost but allows the inclusion of uncertainty in the decision making process. We compare the output of these two methodologies and determine the

  14. Preservation potential of subtle glacial landforms based on detailed mapping of recently exposed proglacial areas: application of unmanned aerial vehicle (UAV) and structure-from-motion (SfM)

    Science.gov (United States)

    Ewertowski, Marek; Evans, David; Roberts, David; Tomczyk, Aleksandra; Ewertowski, Wojciech

    2016-04-01

    Ongoing glacier retreat results in the continuous exposure of proglacial areas. Such areas contain invaluable information about glacial process-form relationships manifest in specific landform assemblages. However, preservation potential of freshly exposed glacial landforms is very low, as proglacial terrains are one of the most dynamic parts of the landscape. Therefore, rapid mapping and geomorphological characterisation of such areas is important from a glaciological and geomorphological point of view for proper understanding and reconstruction of glacier-landform dynamics and chronology of glacial events. Annual patterns of recession and relatively small areas exposed every year, mean that the performing of regular aerial or satellite survey is expensive and therefore impractical. Recent advances in technology enables the development of low-cost alternatives for traditional aerial surveys. Small unmanned aerial vehicles (UAV) can be used to acquire high-resolution (several cm) low-altitude photographs. The UAV-based photographs can be subsequently processed through the structure-from-motion process to generate detailed orthophotomaps and digital elevation models. In this study we present case studies from the forelands of various glaciers on Iceland and Svalbard representing different types of proglacial landscapes: Fláajökull (annual push moraines); Hofellsjökul (bedrock bedforms and push moraines); Fjallsjökull (marginal drainage network); Rieperbreen (crevasse squeeze ridges and longitudinal debris stripes); Ayerbreen (transverse debris ridges); Foxfonna (longitudinal debris stripes);Hørbyebreen (geometric ridge network); Nordenskiöldbreen (fluted till surface); Ebbabreen (controlled moraine complex). UAV campaigns were conducted using a low-cost quadcopter platform. Resultant orthophotos and DEMs enabled mapping and assessment of recent glacial landscape development in different types of glacial landsystems. Results of our study indicate that

  15. Andean glacial lakes and climate variability since the last glacial maximum

    Directory of Open Access Journals (Sweden)

    1995-01-01

    á registrada en la estratigrafía de varios lagos, incluyendo el Lago Titicaca. Los niveles de los lagos estaban subiendo y había neoglaciación en el Holoceno superior después de la fase de sequía en el Holoceno medio. Sediment cores from glacial lakes in the tropical-subtropical Andes provide a nearly continuous record of late glacial and Holocene paleoclimates. Basal radiocarbon dates from lakes and peats suggest that the last glacial maximum significantly predated the global maximum at 18 14C kyr BP. Most lakes have basal radiocarbon ages of <13 14C kyr BP, implying that there was a late-Pleistocene phase of glaciation that may have culminated about 14 14C kyr BP. Late glacial advances are recorded in several sediment records from lakes and by 10 14C kyr BP glaciers had retreated to within their modern limits. Mid-Holocene aridity is recorded in the stratigraphy from a number of lakes including Lago Titicaca. This phase of aridity was followed by rising lake levels and neoglaciation in the late Holocene.

  16. Gravity measurements in southeastern Alaska reveal negative gravity rate of change caused by glacial isostatic adjustment

    Science.gov (United States)

    Sun, W.; Miura, S.; Sato, T.; Sugano, T.; Freymueller, J.; Kaufman, M.; Larsen, C. F.; Cross, R.; Inazu, D.

    2010-12-01

    For the past 300 years, southeastern Alaska has undergone rapid ice-melting and land uplift attributable to global warming. Corresponding crustal deformation (3 cm/yr) caused by the Little Ice Age retreat is detectable with modern geodetic techniques such as GPS and tidal gauge measurements. Geodetic deformation provides useful information for assessing ice-melting rates, global warming effects, and subcrustal viscosity. Nevertheless, integrated geodetic observations, including gravity measurements, are important. To detect crustal deformation caused by glacial isostatic adjustment and to elucidate the viscosity structure in southeastern Alaska, Japanese and U.S. researchers began a joint 3-year project in 2006 using GPS, Earth tide, and absolute gravity measurements. A new absolute gravity network was established, comprising five sites around Glacier Bay, near Juneau, Alaska. This paper reports the network's gravity measurements during 2006-2008. The bad ocean model in this area hindered ocean loading correction: Large tidal residuals remain in the observations. Accurate tidal correction necessitated on-site tidal observation. Results show high observation precision for all five stations: day ice thickness changes. A gravity bias of about -13.2 ± 0.1 mGal exists between the Potsdam and current FG5 gravity data.

  17. Damage to root dentin during retreatment procedures

    NARCIS (Netherlands)

    Shemesh, H.; Roeleveld, A.C.; Wesselink, P.R.; Wu, M.K.

    2011-01-01

    Introduction: The aim of this study was to explore the influence of retreatment procedures on the appearance of defects on the root canal walls. Methods: Two hundred mandibular premolars were divided into 4 groups. One group was left unprepared. The rest of the teeth were prepared with ProTaper

  18. Little Ice Age advance and retreat of Glaciar Jorge Montt, Chilean Patagonia

    Directory of Open Access Journals (Sweden)

    A. Rivera

    2012-03-01

    Full Text Available Glaciar Jorge Montt (48°20' S/73°30' W, one of the main tidewater glaciers of the Southern Patagonian Icefield (SPI, has experienced the greatest terminal retreat observed in Patagonia during the past century, with a recession of 19.5 km between 1898 and 2011. This retreat has revealed trees laying subglacially until 2003. These trees were dated using radiocarbon, yielding burial ages between 460 and 250 cal yrs BP. The presence of old growth forest during those dates indicates that Glaciar Jorge Montt was upvalley of its present position before the commonly recognized Little Ice Age (LIA period in Patagonia. The post-LIA retreat was most likely triggered by climatically induced changes during the 20th century; however, Glaciar Jorge Montt has responded more dramatically than its neighbours. The retreat of Jorge Montt opened a 19.5 km long fjord since 1898, which reaches depths in excess of 390 m. The bathymetry is well correlated with glacier retreat rates, suggesting that dynamic responses of the glacier are at least partially connected to near buoyancy conditions at the ice front, resulting in high calving fluxes, accelerating thinning rates and rapid ice velocities.

  19. Weathering During Glacial-Interglacial Cycles Based on Pb Isotopes at Orphan Knoll, NW Atlantic

    Science.gov (United States)

    Flynn, S. N.; Martin, E. E.

    2017-12-01

    Seawater Pb isotopes extracted from FeMn oxyhydroxide coatings on deep sea sediments preserve a record of regional variations in continental weathering intensity. Crocket et al. (2012) documented a distinct increase in seawater Pb isotopes across Termination I (TI) at IODP Sites U1302/03 on Orphan Knoll in the NW Atlantic which they attributed to an increase in weathering intensity associated with ice sheet retreat. Deglaciation during Termination II (TII) was more rapid than TI due to higher insolation forcing and elevated CO2 levels. This rapid warming followed Heinrich Stadial 11 (HS11) cooling and circulation changes, but was not interrupted by a Younger Dryas-type reversal in warming. In this study, Pb isotopic data from leachates of the Sites U1302/03 are used to test whether changes in weathering are a feature of terminations and whether differences in the character of the termination translate to differences in the weathering response. We analyzed the clay/silt fraction to minimize preformed FeMn oxyhydroxides associated with IRD. All three Pb isotopic systems display similar patterns. Seawater 206Pb/204Pb values are 19.5 during MIS 6, reach a minimum of 18.7 during HS11, increase in < 1 ky to 20.6 in MIS 5e, and then vary between 19.9 - 20.5 across MIS 5e-d. In comparison to the TI study (Crocket et al., 2009), the TII HS is defined by a minimum in Pb isotopes that suggests suppressed chemical weathering during cooling and ice sheet advance. The increase in 206Pb/204Pb during TII indicates a rapid increase in weathering at high latitudes following glacial retreat. This result is consistent with a negative shift in ɛNd values during TII observed farther south on Bermuda Rise and interpreted as increased weathering of old continental material (Deaney et al. 2017). Future research on TII at Orphan Knoll includes analyses of detrital Pb isotopes to isolate the impact of changes in source material versus weathering intensity on seawater Pb isotopes, and

  20. Microbial assemblages in soil microbial succession after glacial retreat in Svalbard (High Arctic)

    Czech Academy of Sciences Publication Activity Database

    Kaštovská, Klára; Elster, Josef; Stibal, Marek; Šantrůčková, H.

    2005-01-01

    Roč. 50, č. 3 (2005), s. 396-407 ISSN 0095-3628 Institutional research plan: CEZ:AV0Z6005908 Keywords : microbial assemblages * deglaciated soil * Svalbard Subject RIV: EF - Botanics Impact factor: 2.674, year: 2005

  1. Floating like a cork: The importance of glacial isostasy in the deglaciation progress in Iceland

    Science.gov (United States)

    Norddahl, H.; Ingolfsson, O.

    2016-12-01

    Being positioned on top of a hotspot and between two spreading ocean plates explains rheological structure of Iceland and the properties of a 30-35 km thick lithosphere, possibly with high proportion of partial melt, on top of a low viscous asthenosphere below Iceland, in the middle of the North Atlantic Ocean. Rapid variations in glacier loading on the Iceland crust have been proved to generate more or less an instantaneous depression or uplift of the crust and, thus, uphold both temporal and spacial glacio-isostatic equilibrium. Formation of a shoreline requires at least temporal equilibrium between glacial isostasy and eustasy. Eminent raised shorelines - found throughout Iceland - were formed during two separate but consecutive culmination of climatically induced glacier re-advance and consequent transgression of relative sea-level in Younger Dryas and Preboreal times (12.0 and 11.3 kcal BP). A Marine Limit shoreline in W Iceland was formed at 14.7 kcal BP, subsequent to a collapse-like retreat of the marine based part of the Icelandic Ice Sheet (IIS) and just prior to the onset of the Bølling warming, i.e. during a period of anticipated rapid isostatic uplift. A temporary glacio-isostatic equilibrium at that time is best explained by changes in the mode of deglaciation generating dynamic changes within the Ice Sheet itself, changes that resulted in reduced rates of mass-loss and glacio-isostatic uplift to such a degree that a temporal quasi-equilibrium between eustatic rise and isostatic uplift was established. Formation of well-developed raised shoreline is generally regarded as a deglaciation proxy signaling large ice volume changes. Formation of the ML shoreline in W Iceland during the rapid climatic improvement at the beginning of the Bølling/Allerød Interstadial underlines the importance of, beside the geological data, also to take into consideration physical properties of both the lithosphere and asthenosphere in each location.

  2. Retreatments after multifocal intraocular lens implantation: an analysis

    Directory of Open Access Journals (Sweden)

    Gundersen KG

    2016-03-01

    Full Text Available Kjell Gunnar Gundersen,1 Sarah Makari,2 Steffen Ostenstad,1 Rick Potvin2 1Ifocus Eye Clinic, Haugesund, Norway; 2Science in Vision, Akron, NY, USA Purpose: To determine the incidence and etiology of required retreatment after multifocal intraocular lens (IOL implantation and to evaluate the methods and clinical outcomes of retreatment.Patients and methods: A retrospective chart review of 416 eyes of 209 patients from one site that underwent uncomplicated cataract surgery with multifocal IOL implantation. Biometry, the IOL, and refractive data were recorded after the original implantation, with the same data recorded after retreatment. Comments related to vision were obtained both before and after retreatment for retreated patients.Results: The multifocal retreatment rate was 10.8% (45/416 eyes. The eyes that required retreatment had significantly higher residual refractive astigmatism compared with those who did not require retreatment (1.21±0.51 D vs 0.51±0.39 D, P<0.01. The retreatment rate for the two most commonly implanted primary IOLs, blended bifocal (10.5%, 16/152 and bilateral trifocal (6.9%, 14/202 IOLs, was not statistically significantly different (P=0.12. In those requiring retreatment, refractive-related complaints were most common. Retreatment with refractive corneal surgery, in 11% of the eyes, and piggyback IOLs, in 89% of the eyes, was similarly successful, improving patient complaints 78% of the time.Conclusion: Complaints related to ametropia were the main reasons for retreatment. Residual astigmatism appears to be an important determinant of retreatment rate after multifocal IOL implantation. Retreatment can improve symptoms for a high percentage of patients; a piggyback IOL is a viable retreatment option. Keywords: piggyback IOL, Sulcoflex, toric, STAAR, symptoms, astigmatism

  3. Glacial Features (Point) - Quad 168 (EPPING, NH)

    Data.gov (United States)

    University of New Hampshire — The Glacial Features (Point) layer describes point features associated with surficial geology. These glacial features include, but are not limited to, delta forsets,...

  4. Technology Retreats and the Politics of Social Media

    Directory of Open Access Journals (Sweden)

    Adam Fish

    2017-04-01

    Full Text Available This essay examines weeklong technology retreats in Silicon Valley. These retreats embody digital healthism, which I define as the discourse that promotes the self-regulation of digital consumption for personal health. I argue that the self-regulation advanced by digital healthism insufficiently addresses the politics of media refusal. Technology retreats channel frustrations about social media use into opportunities for personal and corporate growth instead of political activism. I consider how technology retreats might participate in a dialogue about the regulation of social media platforms and companies by states. Evidence for these claims come from ethnographic research with the founders of a technology retreat in Silicon Valley.

  5. Effect of Topography on Subglacial Discharge and Submarine Melting During Tidewater Glacier Retreat

    Science.gov (United States)

    Amundson, J. M.; Carroll, D.

    2018-01-01

    To first order, subglacial discharge depends on climate, which determines precipitation fluxes and glacier mass balance, and the rate of glacier volume change. For tidewater glaciers, large and rapid changes in glacier volume can occur independent of climate change due to strong glacier dynamic feedbacks. Using an idealized tidewater glacier model, we show that these feedbacks produce secular variations in subglacial discharge that are influenced by subglacial topography. Retreat along retrograde bed slopes (into deep water) results in rapid surface lowering and coincident increases in subglacial discharge. Consequently, submarine melting of glacier termini, which depends on subglacial discharge and ocean thermal forcing, also increases during retreat into deep water. Both subglacial discharge and submarine melting subsequently decrease as glacier termini retreat out of deep water and approach new steady state equilibria. In our simulations, subglacial discharge reached peaks that were 6-17% higher than preretreat values, with the highest values occurring during retreat from narrow sills, and submarine melting increased by 14% for unstratified fjords and 51% for highly stratified fjords. Our results therefore indicate that submarine melting acts in concert with iceberg calving to cause tidewater glacier termini to be unstable on retrograde beds. The full impact of submarine melting on tidewater glacier stability remains uncertain, however, due to poor understanding of the coupling between submarine melting and iceberg calving.

  6. New details about the LGM extent and subsequent retreat of the West Antarctic Ice Sheet from the easternmost Amundsen Sea Embayment shelf

    Science.gov (United States)

    Klages, J. P.; Hillenbrand, C. D.; Kuhn, G.; Smith, J. A.; Graham, A. G. C.; Nitsche, F. O.; Frederichs, T.; Arndt, J. E.; Gebhardt, C.; Robin, Z.; Uenzelmann-Neben, G.; Gohl, K.; Jernas, P.; Wacker, L.

    2017-12-01

    In recent years several previously undiscovered grounding-zone wedges (GZWs) have been described within the Abbot-Cosgrove palaeo-ice stream trough on the easternmost Amundsen Sea Embayment shelf. These GZWs document both the Last Glacial Maximum (LGM; 26.5-19 cal. ka BP) grounding-line extent and the subsequent episodic retreat within this trough that neighbors the larger Pine Island-Thwaites trough to the west. Here we combine bathymetric, seismic, and geologic data showing that 1) the grounding line in Abbot Trough did not reach the continental shelf break at any time during the last glacial period, and 2) a prominent stacked GZW constructed from six individual wedges lying upon another was deposited 100 km upstream from the LGM grounding-line position. The available data allow for calculating volumes for most of these individual GZWs and for the entire stack. Sediment cores were recovered seawards from the outermost GZW in the trough, and from the individual wedges of the stacked GZW in order to define the LGM grounding-line extent, and provide minimum grounding-line retreat ages for the respective positions on the stacked GZW. We present implications of a grounded-ice free outer shelf throughout the last glacial period. Furthermore, we assess the significance of the grounding-line stillstand period recorded by the stacked GZW in Abbot Trough for the timing of post-LGM retreat of the West Antarctic Ice Sheet from the Amundsen Sea Embayment shelf.

  7. Patterns of retreatment with radiotherapy in a large academic centre

    International Nuclear Information System (INIS)

    Khor, Richard; Ball, David; Duchesne, Gillian; Bressel, Mathias; Tai, Keen Hun; Tedesco, Jo; Gill, Suki; Fitzpatrick, Claire; Foroudi, Farshad; Rose, William

    2013-01-01

    To characterise retreatment rates with radiotherapy at a large multifacility academic radiotherapy centre and assess the effect of distance on retreatment rate. Electronic administrative records were reviewed for patients receiving radiotherapy between 1998 and 2010 at regional and metropolitan facilities. Course-level data were reconstructed from electronic administrative databases. Intent of therapy, treatment dates and diagnosis were available for analysis. Retreatment characteristics were derived, including proportion of patients receiving retreatment, proportion of total radiotherapy prescriptions dedicated to retreatment and retreatment per treating facility. Travel distance for each patient to their treatment centre was estimated, and retreatment rates were reported as a function of increasing distance. A total of 48,200 patients were treated with 66,277 treatment courses during the study period. Retreatment courses constituted 25.2% of all courses prescribed. During the study period, 20.4% of all patients received at least one treatment course. Of these, the average number of retreatment courses prescribed was 1.84. Patients treated with radical intent had a retreatment rate of 13% compared with 45% for those treated initially with palliative intent. Retreatment rates in individual tumour sites ranged from 1.3 to 44.4%. The retreatment rate for those living less than 100km from treatment facility was 24.8%, and 20.5% for those living more than 100km from treatment centre (P<0.001) Retreatment accounted for over one quarter of radiotherapy courses, with the rate influenced by casemix and follow-up duration. With increasing distance from treatment centre, a decrease in retreatment rate was observed.

  8. Enhancing rates of erosion and uplift through glacial perturbations

    Science.gov (United States)

    Norton, Kevin; Schlunegger, Fritz; Abbühl, Luca

    2010-05-01

    Research over the past decade has shown that the pattern of modern rock uplift in the Swiss Alps correlates with both long-term (thermochronometers) and short-term (cosmogenic nuclide-derived denudation rates, sediment loads, lake fills) measures of erosion. This correlation has been attributed alternately to isostatic causes (compensation to erosion and/or glacial unloading) and tectonic forces (ongoing collision and partial delamination). Of these potential driving forces, only isostatic compensation to erosion fits all available structural, geodetic, and flexural models. We explore this uplift-erosion relationship by analyzing river channel steepness for Alpine rivers. Zones of oversteepening, and hence enhanced stream power, are associated with glacial erosion and deposition during LGM and earlier glaciations, resulting in the focusing of erosion into the inner gorges which connect hanging tributary valleys to the main glacial trunk valley. These inner gorges are transient zones in which fluvial and hillslope processes are in the process of re-adjusting this glacially perturbed landscape. Bedrock properties also play a major role in the response time of these adjustments. Glacially generated knickzones are located within 5 km of the trunk stream in the Rhone valley where resistant lithologies dominate (gneiss), whereas the knickzones have migrated as much as 10 km or further in the less resistant rocks (buendnerschists) of the Rhine valley. We suggest that the rock uplift pattern is controlled by surface denudation as set by the glacial-interglacial history of the Alps. Rapid, focused erosion results in rapid rock uplift rates in the Central Swiss Alps, where glaciers were most active. An interesting ramification of this reasoning is that in the absence of glacial perturbation, both rock uplift rates and denudation rates would be substantially lower in this isostatically compensated mountain belt.

  9. Reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the Laurentide Ice Sheet

    Science.gov (United States)

    Margold, Martin; Stokes, Chris R.; Clark, Chris D.

    2018-06-01

    This paper reconstructs the deglaciation of the Laurentide Ice Sheet (LIS; including the Innuitian Ice Sheet) from the Last Glacial Maximum (LGM), with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides. We build on a recent inventory of Laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the LIS, which we depict in a series of palaeogeographic maps. Results show that the drainage network at the LGM was similar to modern-day Antarctica. The majority of the ice streams were marine terminating and topographically-controlled and many of these continued to function late into the deglaciation, until the ice sheet lost its marine margin. Ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build-up, peak-phase and collapse of the Cordilleran-Laurentide ice saddle. The south-eastern marine margin in Atlantic Canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the LGM. In contrast, the ice streams draining towards the north-western and north-eastern marine margins in the Beaufort Sea and in Baffin Bay appear to have remained stable throughout most of the Late Glacial, and some of them continued to function until after the Younger Dryas (YD). The YD influenced the dynamics of the deglaciation, but there remains uncertainty about the response of the ice sheet in several sectors. We tentatively ascribe the switching-on of some major ice streams during this period (e.g. M'Clintock Channel Ice Stream at the north-west margin), but for other large ice streams whose timing partially overlaps with the YD, the drivers are less clear and ice-dynamical processes, rather than effects of climate and surface mass balance are viewed as more likely drivers. Retreat

  10. Earth's glacial record and its tectonic setting

    Science.gov (United States)

    Eyles, N.

    1993-09-01

    Glaciations have occurred episodically at different time intervals and for different durations in Earth's history. Ice covers have formed in a wide range of plate tectonic and structural settings but the bulk of Earth's glacial record can be shown to have been deposited and preserved in basins within extensional settings. In such basins, source area uplift and basin subsidence fulfill the tectonic preconditions for the initiation of glaciation and the accomodation and preservation of glaciclastic sediments. Tectonic setting, in particular subsidence rates, also dictates the type of glaciclastic facies and facies successions that are deposited. Many pre-Pleistocene glaciated basins commonly contain well-defined tectonostratigraphic successions recording the interplay of tectonics and sedimentation; traditional climatostratigraphic approaches involving interpretation in terms of either ice advance/retreat cycles or glacio-eustatic sea-level change require revision. The direct record of continental glaciation in Earth history, in the form of classically-recognised continental glacial landforms and "tillites", is meagre; it is probable that more than 95% of the volume of preserved "glacial" strata are glacially-influenced marine deposits that record delivery of large amounts of glaciclastic sediment to offshore basins. This flux has been partially or completely reworked by "normal" sedimentary processes such that the record of glaciation and climate change is recorded in marine successions and is difficult to decipher. The dominant "glacial" facies in the rock record are subaqueous debris flow diamictites and turbidites recording the selective preservation of poorly-sorted glaciclastic sediment deposited in deep water basins by sediment gravity flows. However, these facies are also typical of many non-glacial settings, especially volcanically-influenced environments; numerous Archean and Proterozoic diamictites, described in the older literature as tillites, have no

  11. The last glacial maximum

    Science.gov (United States)

    Clark, P.U.; Dyke, A.S.; Shakun, J.D.; Carlson, A.E.; Clark, J.; Wohlfarth, B.; Mitrovica, J.X.; Hostetler, S.W.; McCabe, A.M.

    2009-01-01

    We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level ???14.5 ka.

  12. Summary of the RHIC Retreat 2008

    Energy Technology Data Exchange (ETDEWEB)

    Pilat,F.; Brennan, M.; Brown, K.; Fischer, W.; Montag, C.

    2008-08-01

    The main goal of the RHIC Retreat is to review last run's performance and prepare for the next. As always though we also discussed the longer term goals and plans for the facility to put the work in perspective and in the right priority. A straw-man plan for the facility was prepared for the DOE that assumes 30 cryoweek and running 2 species per year. The plan outlines RHIC operations for 2008-2012 and integrates well accelerator and detector upgrades to optimize the physics output with high luminosities. The plans includes guidance from the PAC and has been reviewed by DOE.

  13. Summary of the RHIC Retreat 2008

    International Nuclear Information System (INIS)

    Pilat, F.; Brennan, M.; Brown, K.; Fischer, W.; Montag, C.

    2008-01-01

    The main goal of the RHIC Retreat is to review last run's performance and prepare for the next. As always though we also discussed the longer term goals and plans for the facility to put the work in perspective and in the right priority. A straw-man plan for the facility was prepared for the DOE that assumes 30 cryoweek and running 2 species per year. The plan outlines RHIC operations for 2008-2012 and integrates well accelerator and detector upgrades to optimize the physics output with high luminosities. The plans includes guidance from the PAC and has been reviewed by DOE

  14. Drainage of ice-dammed lakes and glacier retreat - a link

    DEFF Research Database (Denmark)

    Kjeldsen, Kristian Kjellerup; Kjaer, K. H.; Rysgaard, Søren

    2011-01-01

    surface freshwater run-off is found in the top of the water column in the fjord while sub-glacial meltwater is entrained deeper in the water column. The latter is highly important as this colder buoyant freshwater is pushed to the water surface followed by a compensating deeper landward current bringing...... in the fjord. The large quantity of buoyant freshwater changed the osmotic pressure and pushed redfish to the water surface causing them to die from divers disease. Further investigation suggested that three ice-dammed lakes adjacent to the Narssap Sermia glacier had drained within the previous year. Analysis......-30 times the volume of an ice-dammed lake prior to drainage. The warm water influx in turn causes the glacier to retreat and to gradually become thinner which feeds back to an increase in drainage events of ice-dammed lakes over time. On a larger scale the feedback mechanism between the drainage of lakes...

  15. A preliminary structural analysis of the pattern of post-glacial faults in Northern Sweden

    International Nuclear Information System (INIS)

    Talbot, C.

    1986-10-01

    The post-glacial kinematics inferred from the structures suggest horizontal NW or WNW compression with lateral relief to the NE at depth below surficial upward relief. These kinematics are sufficiently similar to the kinematics throughout Europe north of the Alps to suspect the neotectonic motion of the Eurasian lithospheric plate over the last 38 or even 58 (+/- 2)Ma as the causative force. Large displacements appear to have occurred within a hundred years or so of the last ice retreating from any particular part of northern Scandinavia. This suggests a sudden relief during glacial unloading (and melting of ground water) of plate tectonic forces accumulated during glacial loading. Recent earthquakes in the region display similar kinematics to the post-glacial fractures on a regional scale but indications of ground movement along the forested fault scarps in the lifetime of the trees is observed at only a few localities. Only geodetic strain measurements or small-earthquake monitoring will resolve whether current ductile or seismic motion is occuring along the most obvious post-glacial scarps. Such investigations are under way. (orig./DG)

  16. Efficacy of ProTaper universal retreatment files in removing filling materials during root canal retreatment.

    Science.gov (United States)

    Giuliani, Valentina; Cocchetti, Roberto; Pagavino, Gabriella

    2008-11-01

    The aim of this study was to evaluate the efficacy of the ProTaper Universal System rotary retreatment system and of Profile 0.06 and hand instruments (K-file) in the removal of root filling materials. Forty-two extracted single-rooted anterior teeth were selected. The root canals were enlarged with nickel-titanium (NiTi) rotary files, filled with gutta-percha and sealer, and randomly divided into 3 experimental groups. The filling materials were removed with solvent in conjunction with one of the following devices and techniques: the ProTaper Universal System for retreatment, ProFile 0.06, and hand instruments (K-file). The roots were longitudinally sectioned, and the image of the root surface was photographed. The images were captured in JPEG format; the areas of the remaining filling materials and the time required for removing the gutta-percha and sealer were calculated by using the nonparametric one-way Kruskal-Wallis test and Tukey-Kramer tests, respectively. The group that showed better results for removing filling materials was the ProTaper Universal System for retreatment files, whereas the group of ProFile rotary instruments yielded better root canal cleanliness than the hand instruments, even though there was no statistically significant difference. The ProTaper Universal System for retreatment and ProFile rotary instruments worked significantly faster than the K-file. The ProTaper Universal System for retreatment files left cleaner root canal walls than the K-file hand instruments and the ProFile Rotary instruments, although none of the devices used guaranteed complete removal of the filling materials. The rotary NiTi system proved to be faster than hand instruments in removing root filling materials.

  17. A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum

    Science.gov (United States)

    Bentley, Michael J.; Ó Cofaigh, Colm; Anderson, John B.; Conway, Howard; Davies, Bethan; Graham, Alastair G. C.; Hillenbrand, Claus-Dieter; Hodgson, Dominic A.; Jamieson, Stewart S. R.; Larter, Robert D.; Mackintosh, Andrew; Smith, James A.; Verleyen, Elie; Ackert, Robert P.; Bart, Philip J.; Berg, Sonja; Brunstein, Daniel; Canals, Miquel; Colhoun, Eric A.; Crosta, Xavier; Dickens, William A.; Domack, Eugene; Dowdeswell, Julian A.; Dunbar, Robert; Ehrmann, Werner; Evans, Jeffrey; Favier, Vincent; Fink, David; Fogwill, Christopher J.; Glasser, Neil F.; Gohl, Karsten; Golledge, Nicholas R.; Goodwin, Ian; Gore, Damian B.; Greenwood, Sarah L.; Hall, Brenda L.; Hall, Kevin; Hedding, David W.; Hein, Andrew S.; Hocking, Emma P.; Jakobsson, Martin; Johnson, Joanne S.; Jomelli, Vincent; Jones, R. Selwyn; Klages, Johann P.; Kristoffersen, Yngve; Kuhn, Gerhard; Leventer, Amy; Licht, Kathy; Lilly, Katherine; Lindow, Julia; Livingstone, Stephen J.; Massé, Guillaume; McGlone, Matt S.; McKay, Robert M.; Melles, Martin; Miura, Hideki; Mulvaney, Robert; Nel, Werner; Nitsche, Frank O.; O'Brien, Philip E.; Post, Alexandra L.; Roberts, Stephen J.; Saunders, Krystyna M.; Selkirk, Patricia M.; Simms, Alexander R.; Spiegel, Cornelia; Stolldorf, Travis D.; Sugden, David E.; van der Putten, Nathalie; van Ommen, Tas; Verfaillie, Deborah; Vyverman, Wim; Wagner, Bernd; White, Duanne A.; Witus, Alexandra E.; Zwartz, Dan

    2014-09-01

    A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse 1a. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community.

  18. The potential for retreating alpine glaciers to alter alpine ecosystems in the Colorado Front Range

    Science.gov (United States)

    Hall, E.; Baron, J.

    2013-12-01

    Glaciers are retreating at an unprecedented rate. In mid-latitude alpine ecosystems the presence of glaciers and rock glaciers govern rates and ecology of alpine and sub-alpine ecosystems. Changes in the thermal environment due to the loss of isothermal habitat and inputs from glacier melt chemistry are altering alpine ecosystems in unpredictable ways. In particular, glacier may be a source of nitrogen that is altering alpine ecosystem dynamics. Loch Vale Watershed (LVWS) located within Rocky Mountain National Park. LVWS contains a surface glacier (Andrew's glacier) and a rock glacier (Taylor's glacier) at the headwater of each of the two drainages within the watershed. We collected precipitation from a National Atmospheric Deposition Site and surface water from multiple alpine lakes and streams during a particularly high and low snow year in the Colorado Front Range. We also sampled stream and lake sediments at each site to analyze the associated microbial community. Concentrations of nitrate and ammonium, relative abundance of amoA (the gene responsible for a key step in the microbial nitrification pathway), and the dual isotope signal to nitrate all point to snow melt as a key deliverer of nitrogen to ecosystems along the Colorado Front Range. However, late summer surface water chemistry is isotopically similar to the chemistry of glacial ice. This suggests that retreating glacier may be an additional source of N to alpine ecosystems and have the potential to alter microbial community composition, biogeochemical rate processes, and ecosystem function. These dynamics are most likely not unique to the Colorado Front Range and should be globally distributed as glaciers continue to retreat in high altitude ecosystems around the world.

  19. Glacier Retreat in the Southern Peruvian Andes: Climate Change, Environmental Impacts, Human Perception and Social Response

    Science.gov (United States)

    Orlove, B.

    2007-12-01

    This paper presents results from recent environmental and anthropological research near glacierized areas in the department of Cusco, Peru, home to the well-known Quelccaya Ice Cap and to the peak of Ausangate (6384 m). Glaciers in the region are in negative mass balance, losing volume and area, with upslope movement of the glacier fronts. Somewhat paradoxically, flows in many streams close to the glaciers are reduced, particularly in the dry season, due to a shift in the seasonal distribution of melting, to increased evaporation and to increased percolation into newly-exposed sands and gravels. Associated with this reduction in flow is a desiccation of some anthropogenic and natural wetlands, reducing the availability of dry season forage to wild (vicuna) and domesticated (alpaca, llama) ruminants. Interviews and ethnographic observations with local populations of Quechua-speaking herders at elevations of 4500-5200 meters provide detailed comments on these changes. They have an extensive vocabulary of terms for glacial features associated with retreat. They link this treat with environmental factors (higher temperatures, greater winds that deposit dust on lower portions of glaciers) and with religious factors (divine punishment for human wrong-doing, failure of humans to respect mountain spirits). They describe a variety of economic and extra-economic impacts of this retreat on different spatial, social and temporal scales. Though they face other issues as well (threats of pollution from new mining projects, inadequacy of government services), glacier retreat is their principal concern. Many herders express extreme distress over this unprecedented threat to their livelihoods and communities, though a few propose responses - out-migration, the formation of an association of neighboring communities, development of irrigation works - that could serve as adaptations.

  20. Improved age constraints for the retreat of the Irish Sea Ice Stream

    Science.gov (United States)

    Smedley, Rachel; Chiverrell, Richard; Duller, Geoff; Scourse, James; Small, David; Fabel, Derek; Burke, Matthew; Clarke, Chris; McCarroll, Danny; McCarron, Stephen; O'Cofaigh, Colm; Roberts, David

    2016-04-01

    BRITICE-CHRONO is a large (> 45 researchers) consortium project working to provide an extensive geochronological dataset constraining the rate of retreat of a number of ice streams of the British-Irish Ice Sheet following the Last Glacial Maximum. When complete, the large empirical dataset produced by BRITICE-CHRONO will be integrated into model simulations to better understand the behaviour of the British-Irish Ice Sheet in response to past climate change, and provide an analogue for contemporary ice sheets. A major feature of the British-Irish Ice Sheet was the dynamic Irish Sea Ice Stream, which drained a large proportion of the ice sheet and extended to the proposed southern limit of glaciation upon the Isles of Scilly (Scourse, 1991). This study will focus on a large suite of terrestrial samples that were collected along a transect of the Irish Sea basin, covering the line of ice retreat from the Isles of Scilly (50°N) in the south, to the Isle of Man (54°N) in the north; a distance of 500 km. Ages are determined for both the eastern and western margins of the Irish Sea using single-grain luminescence dating (39 samples) and terrestrial cosmogenic nuclide dating (10 samples). A Bayesian sequence model is then used in combination with the prior information determined for deglaciation to integrate the geochronological datasets, and assess retreat rates for the Irish Sea Ice Stream. Scourse, J.D., 1991. Late Pleistocene stratigraphy and palaeobotany of the Isles of Scilly. Philosophical Transactions of the Royal Society of London B334, 405 - 448.

  1. Glacial and Quaternary geology of the northern Yellowstone area, Montana and Wyoming

    Science.gov (United States)

    Pierce, Kenneth L.; Licciardi, Joseph M.; Krause, Teresa R.; Whitlock, Cathy

    2014-01-01

    This field guide focuses on the glacial geology and paleoecology beginning in the Paradise Valley and progressing southward into northern Yellowstone National Park. During the last (Pinedale) glaciation, the northern Yellowstone outlet glacier flowed out of Yellowstone Park and down the Yellowstone River Valley into the Paradise Valley. The field trip will traverse the following Pinedale glacial sequence: (1) deposition of the Eightmile terminal moraines and outwash 16.5 ± 1.4 10Be ka in the Paradise Valley; (2) glacial recession of ~8 km and deposition of the Chico moraines and outwash 16.1 ± 1.7 10Be ka; (3) glacial recession of 45 km to near the northern Yellowstone boundary and moraine deposition during the Deckard Flats readjustment 14.2 ± 1.2 10Be ka; and (4) glacial recession of ~37 km and deposition of the Junction Butte moraines 15.2 ± 1.3 10Be ka (this age is a little too old based on the stratigraphic sequence). Yellowstone's northern range of sagebrush-grasslands and bison, elk, wolf, and bear inhabitants is founded on glacial moraines, sub-glacial till, and outwash deposited during the last glaciation. Floods released from glacially dammed lakes and a landslide-dammed lake punctuate this record. The glacial geologic reconstruction was evaluated by calculation of basal shear stress, and yielded the following values for flow pattern in plan view: strongly converging—1.21 ± 0.12 bars (n = 15); nearly uniform—1.04 ± 0.16 bars (n = 11); and strongly diverging—0.84 ± 0.14 bars (n = 16). Reconstructed mass balance yielded accumulation and ablation each of ~3 km3/yr, with glacial movement near the equilibrium line altitude dominated by basal sliding. Pollen and charcoal records from three lakes in northern Yellowstone provide information on the postglacial vegetation and fire history. Following glacial retreat, sparsely vegetated landscapes were colonized first by spruce parkland and then by closed subalpine forests. Regional fire activity

  2. Glacial lakes in Austria - Distribution and formation since the Little Ice Age

    Science.gov (United States)

    Buckel, J.; Otto, J. C.; Prasicek, G.; Keuschnig, M.

    2018-05-01

    Glacial lakes constitute a substantial part of the legacy of vanishing mountain glaciation and act as water storage, sediment traps and sources of both natural hazards and leisure activities. For these reasons, they receive growing attention by scientists and society. However, while the evolution of glacial lakes has been studied intensively over timescales tied to remote sensing-based approaches, the longer-term perspective has been omitted due a lack of suitable data sources. We mapped and analyzed the spatial distribution of glacial lakes in the Austrian Alps. We trace the development of number and area of glacial lakes in the Austrian Alps since the Little Ice Age (LIA) based on a unique combination of a lake inventory and an extensive record of glacier retreat. We find that bedrock-dammed lakes are the dominant lake type in the inventory. Bedrock- and moraine-dammed lakes populate the highest landscape domains located in cirques and hanging valleys. We observe lakes embedded in glacial deposits at lower locations on average below 2000 m a.s.l. In general, the distribution of glacial lakes over elevation reflects glacier erosional and depositional dynamics rather than the distribution of total area. The rate of formation of new glacial lakes (number, area) has continuously accelerated over time with present rates showing an eight-fold increase since LIA. At the same time the total glacier area decreased by two-thirds. This development coincides with a long-term trend of rising temperatures and a significant stepping up of this trend within the last 20 years in the Austrian Alps.

  3. Dissolved organic matter export in glacial and non-glacial streams along the Gulf of Alaska

    Science.gov (United States)

    Hood, E. W.; Scott, D.; Jeffery, A.; Schreiber, S.; Heavner, M.; Edwards, R.; D'Amore, D. V.; Fellman, J.

    2009-12-01

    The Gulf of Alaska drainage basin contains more than 75,000 km2 of glaciers, many of which are rapidly thinning and receding. We are using a paired watershed approach to evaluate how changes in glacier ecosystems will impact the export dissolved organic matter (DOM) into the Gulf of Alaska. Our primary study watersheds, Lemon Creek and Montana Creek, are similar in size, bedrock lithology and elevation range and extend from near sea level to the margin or interior of the Juneau Icefield. Lemon Creek has a glacial coverage of ~60%, while Montana Creek is free of glacier ice. Our goal is to evaluate seasonal differences in the quantity, chemical character and reactivity of DOM being exported from these watersheds to downstream near-shore marine ecosystems. In addition, we are monitoring a variety of physical parameters that influence instream DOM metabolism in both watersheds. Our initial results from the 2009 runoff season indicate that concentrations of dissolved organic carbon (DOC) are substantially higher in the non-glacial watershed. However, fluorescence analyses indicate that DOM from the glacier watershed has a higher protein and lower humic material content compared to DOM from the non-glacial watershed. After the spring snowmelt season, physical parameters between the two watersheds diverged, with higher streamflow and turbidity as well as colder water temperatures in the glacial watershed. Although our previous yield calculations show significantly higher DOC fluxes from the forested watershed, our results here suggest that glacier watersheds may be an important source of labile carbon to the near shore marine ecosystem. The contrast in the physical habitat between the two rivers (e.g glacier stream = cold, low light penetration, unstable substrate) supports the hypothesis that that in-stream DOM processing is limited within glacier dominated rivers, therefore delivering a higher percentage of labile DOM downstream.

  4. Submarine glacial landforms on the Bay of Fundy–northern Gulf of Maine continental shelf

    Science.gov (United States)

    Todd, B.J.; Shaw, J.; Valentine, Page C.

    2016-01-01

    The Bay of Fundy–northern Gulf of Maine region surrounds the southern part of Nova Scotia, encompassing, from west to east, the Bay of Fundy, Grand Manan Basin, German Bank, Browns Bank, Northeast Channel and northeastern Georges Bank (Fig. 1a, b). During the last glacial maximum (c. 24–20 14C ka BP), the SE margin of the Laurentide Ice Sheet (LIS) occupied the study area, the rest of the Gulf of Maine and the continental Scotian Shelf off Atlantic Canada (see Dyke et al. 2002, fig. 1; Shaw et al. 2006, fig. 8; Hundert & Piper 2008, fig. 16). Early mapping of the glaciated region on the Scotian Shelf using side-scan sonar imagery and seismic-reflection profiles revealed topographic features interpreted to be recessional moraines indicative of retreat of the LIS (King et al. 1972; King 1996). Subsequently, multibeam sonar seafloor mapping of local-scale glacial landforms on the inner Scotian Shelf off Halifax, Nova Scotia (Fig. 1b) provided further information on the dynamics of the advance and retreat of the ice sheet (Loncarevic et al.1994). Interpretation of seismic-reflection profiles across Georges Bank revealed that the surficial sediment is a veneer of glacial debris transported to Georges Bank by the LIS during the late Pleistocene from continental areas to the north (Shepard et al. 1934; Knott & Hoskins 1968; Schlee 1973; Twichell et al. 1987; Fader et al. 1988). Recent high-resolution multibeam sonar surveys of German Bank and the Bay of Fundy mapped a complex of ice-advance and ice-retreat features attributed to the activity of the LIS (Todd et al. 2007; Todd & Shaw 2012).

  5. A multi-decadal remote sensing study on glacial change in the North Patagonia Ice Field Chile

    Science.gov (United States)

    Tetteh, Lucy Korlekwor

    Glaciers in the North Patagonian Ice Fields are temperate glaciers and can be studied to understand the dynamics of climate change. However, the ice field has been neglected in mass balance studies. In this study, multi decadal study of glacial mass balance, glacier retreat and glacial lake expansion in the North Patagonia were studied. Landsat (TM, ETM+ and 8) and ASTER images were used. San Quintin glacier experienced the highest retreat. Demarcation of glacier lakes boundaries indicated an increase in glacial lake area an addition of 4 new glacial lakes. Nef glacier recorded the highest mass gain of 9.91 plus or minus 1.96 m.w.e.a.-1 and HPN-4 glacier recorded the highest mass loss of -8.9 plus or minus 1.96 m.w.e.a. -1. However, there is a high uncertainty in the elevation values in the DEM due to the rugged nature of the terrain and presence of the heavy snow cover.

  6. Predicting future glacial lakes in Austria using different modelling approaches

    Science.gov (United States)

    Otto, Jan-Christoph; Helfricht, Kay; Prasicek, Günther; Buckel, Johannes; Keuschnig, Markus

    2017-04-01

    Glacier retreat is one of the most apparent consequences of temperature rise in the 20th and 21th centuries in the European Alps. In Austria, more than 240 new lakes have formed in glacier forefields since the Little Ice Age. A similar signal is reported from many mountain areas worldwide. Glacial lakes can constitute important environmental and socio-economic impacts on high mountain systems including water resource management, sediment delivery, natural hazards, energy production and tourism. Their development significantly modifies the landscape configuration and visual appearance of high mountain areas. Knowledge on the location, number and extent of these future lakes can be used to assess potential impacts on high mountain geo-ecosystems and upland-lowland interactions. Information on new lakes is critical to appraise emerging threads and potentials for society. The recent development of regional ice thickness models and their combination with high resolution glacier surface data allows predicting the topography below current glaciers by subtracting ice thickness from glacier surface. Analyzing these modelled glacier bed surfaces reveals overdeepenings that represent potential locations for future lakes. In order to predict the location of future glacial lakes below recent glaciers in the Austrian Alps we apply different ice thickness models using high resolution terrain data and glacier outlines. The results are compared and validated with ice thickness data from geophysical surveys. Additionally, we run the models on three different glacier extents provided by the Austrian Glacier Inventories from 1969, 1998 and 2006. Results of this historical glacier extent modelling are compared to existing glacier lakes and discussed focusing on geomorphological impacts on lake evolution. We discuss model performance and observed differences in the results in order to assess the approach for a realistic prediction of future lake locations. The presentation delivers

  7. Retreatment Rates Among Endometriosis Patients Undergoing Hysterectomy or Laparoscopy.

    Science.gov (United States)

    Soliman, Ahmed M; Du, Ella Xiaoyan; Yang, Hongbo; Wu, Eric Q; Haley, Jane C

    2017-06-01

    Hysterectomy and laparoscopy are the two most common surgical options used to treat women with endometriosis, yet the disease may still recur. This study aimed to determine the long-term retreatment rates among endometriosis patients in the United States who received either hysterectomy or laparoscopy. Patients aged 18-49 years with endometriosis who underwent hysterectomy or laparoscopy were identified in the Truven Health MarketScan claims database (2004-2013). The retreatment rate up to 8 years after the initial surgery was estimated using Kaplan-Meier survival analysis. The relative risk of retreatment among patients with hysterectomy versus laparoscopy was assessed using a Cox proportional hazard model. A total of 24,915 patients with endometriosis who underwent hysterectomy and 37,308 patients with endometriosis who underwent laparoscopy were identified. The estimated retreatment rates were 3.3%, 4.7%, and 5.4% in the 2nd, 5th, and 8th year following hysterectomy, respectively, while the rates following laparoscopy were 15.8%, 27.5%, and 35.2%, respectively. The hazard ratio of retreatment was 0.157 (95% confidence interval [CI]: 0.146-0.169) comparing hysterectomy to laparoscopy. In the sensitivity analysis, which expanded the definition of retreatment by including medical treatments, the retreatment rate increased by a factor of 11-14 for the hysterectomy cohort and by a factor of 2-4 for the laparoscopy cohort, and the hazard ratio of retreatment rate for hysterectomy versus laparoscopy was 0.490 (95% CI: 0.477-0.502). Our study results indicated that the disease retreatment rate after laparoscopy is high among patients with endometriosis; even hysterectomy does not guarantee freedom from retreatment.

  8. Glacial evolution in King George and Livingston Islands (Antarctica) since the Last Glacial Maximum based on cosmogenic nuclide dating and glacier surface reconstruction - CRONOANTAR project

    Science.gov (United States)

    Ruiz Fernández, Jesús; Oliva, Marc; Fernández Menéndez, Susana del Carmen; García Hernández, Cristina; Menéndez Duarte, Rosa Ana; Pellitero Ondicol, Ramón; Pérez Alberti, Augusto; Schimmelpfennig, Irene

    2017-04-01

    CRONOANTAR brings together researchers from Spain, Portugal, France and United Kingdom with the objective of spatially and temporally reconstruct the deglaciation process at the two largest islands in the South Shetlands Archipelago (Maritime Antarctica), since the Global Last Glacial Maximum. Glacier retreat in polar areas has major implications at a local, regional and even planetary scale. Global average sea level rise is the most obvious and socio-economically relevant, but there are others such as the arrival of new fauna to deglaciated areas, plant colonisation or permafrost formation and degradation. This project will study the ice-free areas in Byers and Hurd peninsulas (Livingston Island) and Fildes and Potter peninsulas (King George Island). Ice-cap glacier retreat chronology will be revealed by the use of cosmogenic isotopes (mainly 36Cl) on glacially originated sedimentary and erosive records. Cosmogenic dating will be complemented by other dating methods (C14 and OSL), which will permit the validation of these methods in regions with cold-based glaciers. Given the geomorphological evidences and the obtained ages, a deglaciation calendar will be proposed and we will use a GIS methodology to reconstruct the glacier extent and the ice thickness. The results emerging from this project will allow to assess whether the high glacier retreat rates observed during the last decades were registered in the past, or if they are conversely the consequence (and evidence) of the Global Change in Antarctica. Acknowledgements This work has been funded by the Spanish Ministry of Economy, Industry and Competitiveness (Reference: CTM2016-77878-P).

  9. Late-Quaternary glacial to postglacial sedimentation in three adjacent fjord-lakes of the Québec North Shore (eastern Canadian Shield)

    Science.gov (United States)

    Poiré, Antoine G.; Lajeunesse, Patrick; Normandeau, Alexandre; Francus, Pierre; St-Onge, Guillaume; Nzekwe, Obinna P.

    2018-04-01

    High-resolution swath bathymetry imagery allowed mapping in great detail the sublacustrine geomorphology of lakes Pentecôte, Walker and Pasteur, three deep adjacent fjord-lakes of the Québec North Shore (eastern Canada). These sedimentary basins have been glacio-isostatically uplifted to form deep steep-sided elongated lakes. Their key geographical position and limnogeological characteristics typical of fjords suggest exceptional potential for long-term high-resolution paleoenvironmental reconstitutions. Acoustic subbottom profiles acquired using a bi-frequency Chirp echosounder (3.5 & 12 kHz), together with cm- and m-long sediment core data, reveal the presence of four acoustic stratigraphic units. The acoustic basement (Unit 1) represents the structural bedrock and/or the ice-contact sediments of the Laurentide Ice Sheet and reveals V-shaped bedrock valleys at the bottom of the lakes occupied by ice-loaded sediments in a basin-fill geometry (Unit 2). Moraines observed at the bottom of lakes and in their structural valleys indicate a deglaciation punctuated by short-term ice margin stabilizations. Following ice retreat and their isolation, the fjord-lakes were filled by a thick draping sequence of rhythmically laminated silts and clays (Unit 3) deposited during glaciomarine and/or glaciolacustrine settings. These sediments were episodically disturbed by mass-movements during deglaciation due to glacial-isostatic rebound. AMS 14C dating reveal that the transition between deglaciation of the lakes Pentecôte and Walker watersheds and the development of para- and post-glacial conditions occurred around 8000 cal BP. The development of the lake-head river delta plain during the Holocene provided a constant source of fluvial sediment supply to the lakes and the formation of turbidity current bedforms on the sublacustrine delta slopes. The upper sediment succession (i.e., ∼4-∼6.5 m) consists of a continuous para-to post-glacial sediment drape (Unit 4) that contains

  10. Retreating academics: creating spaces for the scholarship of ...

    African Journals Online (AJOL)

    , this paper explores particular spaces created to support academic engagement in the scholarship of teaching and learning: the space of writing retreats. The metaphor of 'tapestry' is used to capture the development of a complex conceptual ...

  11. Cooperative Spatial Retreat for Resilient Drone Networks †

    Science.gov (United States)

    Kang, Jin-Hyeok; Kwon, Young-Min; Park, Kyung-Joon

    2017-01-01

    Drones are broadening their scope to various applications such as networking, package delivery, agriculture, rescue, and many more. For proper operation of drones, reliable communication should be guaranteed because drones are remotely controlled. When drones experience communication failure due to bad channel condition, interference, or jamming in a certain area, one existing solution is to exploit mobility or so-called spatial retreat to evacuate them from the communication failure area. However, the conventional spatial retreat scheme moves drones in random directions, which results in inefficient movement with significant evacuation time and waste of battery lifetime. In this paper, we propose a novel spatial retreat technique that takes advantage of cooperation between drones for resilient networking, which is called cooperative spatial retreat (CSR). Our performance evaluation shows that the proposed CSR significantly outperforms existing schemes. PMID:28467390

  12. Formation and interpretation of eskers beneath retreating ice sheets

    Science.gov (United States)

    Creyts, T. T.; Hewitt, I.

    2017-12-01

    The retreat of the ice sheets during the Pleistocene left large and spectacular subglacial features exposed. Understanding these features gives us insight into how the ice sheets retreated, how meltwater influenced retreat, and can help inform our understanding of potential future rates of ice sheet retreat. Among these features, eskers, long sinuous ridges primarily composed of clastic sediments, lack a detailed explanation of how surface melt rates and ice sheet retreat rates influence their growth and spatial distribution. Here, we develop a theory for esker formation based on the initial work of Rothlisberger modified for sediment transport and inclusion of surface meltwater forcing. The primary subglacial ingredients include water flow through subglacial tunnels with the addition of mass balances for sediment transport. We show how eskers when water flow slows below a critical stress for sediment motion. This implies that eskers are deposited in a localized region near the snout of the ice sheet. Our findings suggest that very long eskers form sequentially as the ice front retreats. The position of the esker follows the path of the channel mouth through time, which does not necessarily coincide with the instantaneous route of the feeding channel. However, in most cases, we expect those locations to be similar. The role of surface meltwater and the climatology associated with the forcing is crucial to the lateral spacing of the eskers. We predict that high surface melt rates lead to narrower catchments but that the greater extent of the ablation area means that channels are likely larger. At the same time, for a given channel size (and hence sediment flux), the size of a deposited esker depends on a margin retreat rate. Hence, the size of the eskers is related delicately to the balance between surface melt rates and margin retreat rates. We discuss how our theory can be combined with observed esker distributions to infer the relationship between these two rates

  13. Low post-glacial rebound rates in the Weddell Sea due to Late Holocene ice-sheet readvance

    Science.gov (United States)

    Bradley, Sarah L.; Hindmarsh, Richard C. A.; Whitehouse, Pippa L.; Bentley, Michael J.; King, Matt A.

    2015-03-01

    Many ice-sheet reconstructions assume monotonic Holocene retreat for the West Antarctic Ice Sheet, but an increasing number of glaciological observations infer that some portions of the ice sheet may be readvancing, following retreat behind the present-day margin. A readvance in the Weddell Sea region can reconcile two outstanding problems: (i) the present-day widespread occurrence of seemingly stable ice streams grounded on beds that deepen inland; and (ii) the inability of models of glacial isostatic adjustment to match present-day uplift rates. By combining a suite of ice loading histories that include a readvance with a model of glacial isostatic adjustment we report substantial improvements to predictions of present-day uplift rates, including reconciling one problematic observation of land sinking. We suggest retreat behind present grounding lines occurred when the bed was lower, and isostatic recovery has since led to shallowing, ice sheet re-grounding and readvance. The paradoxical existence of grounding lines in apparently unstable configurations on reverse bed slopes may be resolved by invoking the process of unstable advance, in accordance with our load modelling.

  14. Monitoring of Bashkara glacial lakes (the Central Caucasus) and modelling of their potential outburst.

    Science.gov (United States)

    Krylenko, I.; Norin, S.; Petrakov, D.; Tutubalina, O.; Chernomorets, S.

    2009-04-01

    In recent decades due to glacier retreat the glacial lakes in the Central Caucasus, as well as in other high-mountainous areas of the world, have expanded intensively. As result the risk of lake outbursts and destructive floods is raising. In this paper we present one of the most potentially hazardous lakes of this region - a group of glacial lakes near the Bashkara glacier in the upper Adylsu river valley, to the southeast of Mt. Elbrus. Total area of these lakes is about 100,000m2, and a total volume exceeds 1,000,000 m3. The biggest of them - the Bashkara lake has formed in late 1930s - early 1940s and the small Lapa lake has appeared in the end of 1980s. The Bashkara lake outburst occurred twice in the end of 1950s and produced devastating debris flows of ca. 2 million m3. We have monitored these lakes since 1999. Our work includes detailed field research: constant measurements of water level during warm period, annually repeated bathymetric surveys, geodetic surveys, observations on dam condition and some special measurements (i.e. water temperature distribution, current velocity). Also we use aerial and satellite images to obtain data about dynamic of areas for the lakes. From 2001 to 2006 years volume of the Lapa lake has increased 5 times (from 30,000 m3 to 140,000 m3), the Bashkara lake in this period was quasi-stable. In 2006-2008 volume of the Lapa lake has decreased due to sedimentation, however, rapid growth of water level in Bashkara lake (more than 20 sm. per day) has suddenly begun. As a result, volume of the Bashkara lake exceeded 1,000000 m3 in July 2008 whereas in 2001 -2007 year it was about 800,000 m3. Previous maximum of water level was exceeded on 3,5 m, moraine dam with ice core was overtopped and overflow has started. Thus, Bashkara glacier lakes are unstable and risk of outburst is increasing. To assess parameters and zones of potential outburst flood in the Adylsu River valley we have carried out hydrodynamic simulation. Two computer

  15. Assessment of Apical Extrusion of Debris during Endodontic Retreatment with 3 Rotary Nickel-Titanium Retreatment Systems and Hand Files

    Directory of Open Access Journals (Sweden)

    Gkampesi S.

    2016-03-01

    Full Text Available Aim: to evaluate the amount of debris extruded apically as well as the time needed for removal of root canal filling material using ProTaper, MTwo, REndo NiTi rotary retreatment systems and hand files.

  16. The Last Glacial in Northern Iceland: geothermal and permafrost controls

    Science.gov (United States)

    Gudmundsson, A.; van Vliet-Lanoë, B.; Bourgeois, O.; Dauteuil, O.; Embry, J. C.; Guillou, H.; Schneider, J. L.

    2003-04-01

    This paper provides arguments for a multi-advance model of Weichselian glaciation-deglaciation of Northern Iceland considering the influence of the geothermal gradient and of the ice sheds on the different ice-stream outlets. This paper is based on morphological mapping , SPOT images analysis high resolution stratigraphy, palaeopedology, tephra petrography and Ar/K dating. The Last Glaciation Maximum has a limited extend in Northern Iceland, with cold-based characteristics, except in sectors of high thermal gradient which supported low profile ice streams, a main difference with MIS6. Ice sheet building started from MIS 5d with a limited extent. At MIS 5b the thickness of the ice is enough to enable the activity of the eastern hyalocastite ridge in the NVZ. The maximal extent is reached abruptly at the boundary stage 3/2, probably in relation with increased precipitation, with development of H3, followed by a drastic retreat, controlled by very low precipitation rate and cold-based glaciers. This period is responsible for long periglacial morphogenesis inland, on the nunataks and ice free areas, and for starved sedimentation on the shelf and in the fjords. From 17 ka or H2, precipitation rose again and a second maximal extent, the Fnjoskadalur Stadial, the so-called "Old Dryas", in retreat from the former one. The main deglaciation took place at the onset of the Bölling. A late glacial pulse of minimal intensity occurred with the Younger Dryas. The Pre-Boreal stadial is extremely limited in the North of Iceland in relation with the lower and colder conditions compared to the south coast inflenced by the Irminger current.

  17. Modulation of Sea Ice Melt Onset and Retreat in the Laptev Sea by the Timing of Snow Retreat in the West Siberian Plain

    Science.gov (United States)

    Crawford, A. D.; Stroeve, J.; Serreze, M. C.; Rajagopalan, B.; Horvath, S.

    2017-12-01

    As much of the Arctic Ocean transitions to ice-free conditions in summer, efforts have increased to improve seasonal forecasts of not only sea ice extent, but also the timing of melt onset and retreat. This research investigates the potential of regional terrestrial snow retreat in spring as a predictor for subsequent sea ice melt onset and retreat in Arctic seas. One pathway involves earlier snow retreat enhancing atmospheric moisture content, which increases downwelling longwave radiation over sea ice cover downstream. Another pathway involves manipulation of jet stream behavior, which may affect the sea ice pack via both dynamic and thermodynamic processes. Although several possible connections between snow and sea ice regions are identified using a mutual information criterion, the physical mechanisms linking snow retreat and sea ice phenology are most clearly exemplified by variability of snow retreat in the West Siberian Plain impacting melt onset and sea ice retreat in the Laptev Sea. The detrended time series of snow retreat in the West Siberian Plain explains 26% of the detrended variance in Laptev Sea melt onset (29% for sea ice retreat). With modest predictive skill and an average time lag of 53 (88) days between snow retreat and sea ice melt onset (retreat), West Siberian Plains snow retreat is useful for refining seasonal sea ice predictions in the Laptev Sea.

  18. Rapid Late Holocene glacier fluctuations reconstructed from South Georgia lake sediments using novel analytical and numerical techniques

    Science.gov (United States)

    van der Bilt, Willem; Bakke, Jostein; Werner, Johannes; Paasche, Øyvind; Rosqvist, Gunhild

    2016-04-01

    The collapse of ice shelves, rapidly retreating glaciers and a dramatic recent temperature increase show that Southern Ocean climate is rapidly shifting. Also, instrumental and modelling data demonstrate transient interactions between oceanic and atmospheric forcings as well as climatic teleconnections with lower-latitude regions. Yet beyond the instrumental period, a lack of proxy climate timeseries impedes our understanding of Southern Ocean climate. Also, available records often lack the resolution and chronological control required to resolve rapid climate shifts like those observed at present. Alpine glaciers are found on most Southern Ocean islands and quickly respond to shifts in climate through changes in mass balance. Attendant changes in glacier size drive variations in the production of rock flour, the suspended product of glacial erosion. This climate response may be captured by downstream distal glacier-fed lakes, continuously recording glacier history. Sediment records from such lakes are considered prime sources for paleoclimate reconstructions. Here, we present the first reconstruction of Late Holocene glacier variability from the island of South Georgia. Using a toolbox of advanced physical, geochemical (XRF) and magnetic proxies, in combination with state-of-the-art numerical techniques, we fingerprinted a glacier signal from glacier-fed lake sediments. This lacustrine sediment signal was subsequently calibrated against mapped glacier extent with the help of geomorphological moraine evidence and remote sensing techniques. The outlined approach enabled us to robustly resolve variations of a complex glacier at sub-centennial timescales, while constraining the sedimentological imprint of other geomorphic catchment processes. From a paleoclimate perspective, our reconstruction reveals a dynamic Late Holocene climate, modulated by long-term shifts in regional circulation patterns. We also find evidence for rapid medieval glacier retreat as well as a

  19. Regional Analysis of the Hazard Level of Glacial Lakes in the Cordillera Blanca, Peru

    Science.gov (United States)

    Chisolm, Rachel E.; Jhon Sanchez Leon, Walter; McKinney, Daene C.; Cochachin Rapre, Alejo

    2016-04-01

    The Cordillera Blanca mountain range is the highest in Peru and contains many of the world's tropical glaciers. This region is severely impacted by climate change causing accelerated glacier retreat. Secondary impacts of climate change on glacier retreat include stress on water resources and the risk of glacial lake outburst floods (GLOFs) from the many lakes that are forming and growing at the base of glaciers. A number of GLOFs originating from lakes in the Cordillera Blanca have occurred over the last century, several of which have had catastrophic impacts on cities and communities downstream. Glaciologists and engineers in Peru have been studying the lakes of the Cordillera Blanca for many years and have identified several lakes that are considered dangerous. However, a systematic analysis of all the lakes in the Cordillera Blanca has never before been attempted. Some methodologies for this type of systematic analysis have been proposed (eg. Emmer and Vilimek 2014; Wang, et al. 2011), but as yet they have only been applied to a few select lakes in the Cordillera Blanca. This study uses remotely sensed data to study all of the lakes of the Glacial Lake Inventory published by the Glaciology and Water Resources Unit of Peru's National Water Authority (UGRH 2011). The objective of this study is to assign a level of potential hazard to each glacial lake in the Cordillera Blanca and to ascertain if any of the lakes beyond those that have already been studied might pose a danger to nearby populations. A number of parameters of analysis, both quantitative and qualitative, have been selected to assess the hazard level of each glacial lake in the Cordillera Blanca using digital elevation models, satellite imagery, and glacier outlines. These parameters are then combined to come up with a preliminary assessment of the hazard level of each lake; the equation weighting each parameter draws on previously published methodologies but is tailored to the regional characteristics

  20. Comparison of the amount of apical debris extrusion associated with different retreatment systems and supplementary file application during retreatment process.

    Science.gov (United States)

    Çiçek, Ersan; Koçak, Mustafa Murat; Koçak, Sibel; Sağlam, Baran Can

    2016-01-01

    The type of instrument affects the amount of debris extruded. The aim of this study was to compare the effect of retreatment systems and supplementary file application on the amount of apical debris extrusion. Forty-eight extracted mandibular premolars with a single canal and similar length were selected. The root canals were prepared with the ProTaper Universal system with a torque-controlled engine. The root canals were dried and were obturated using Gutta-percha and sealer. The specimens were randomly divided into four equal groups according to the retreatment procedures (Group 1, Mtwo retreatment files; Group 2, Mtwo retreatment files + Mtwo rotary file #30 supplementary file; Group 3, ProTaper Universal retreatment (PTUR) files; and Group 4, PTUR files + ProTaper F3 supplementary file). The extruded debris during instrumentation were collected into preweighed Eppendorf tubes. The amount of apically extruded debris was calculated by subtracting the initial weight of the tube from the final weight. Three consecutive weights were obtained for each tube. No statistically significant difference was found in the amount of apically extruded debris between Groups 1 and 3 (P = 0.590). A significant difference was observed between Groups 1 and 2 (P file significantly increased the amount of apically extruded debris.

  1. Investigating the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle

    Directory of Open Access Journals (Sweden)

    S. Bonelli

    2009-07-01

    Full Text Available A 2.5-dimensional climate model of intermediate complexity, CLIMBER-2, fully coupled with the GREMLINS 3-D thermo-mechanical ice sheet model is used to simulate the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle and to investigate the ice sheets responses to both insolation and atmospheric CO2 concentration. This model reproduces the main phases of advance and retreat of Northern Hemisphere ice sheets during the last glacial cycle, although the amplitude of these variations is less pronounced than those based on sea level reconstructions. At the last glacial maximum, the simulated ice volume is 52.5×1015 m3 and the spatial distribution of both the American and Eurasian ice complexes is in reasonable agreement with observations, with the exception of the marine parts of these former ice sheets.
    A set of sensitivity studies has also been performed to assess the sensitivity of the Northern Hemisphere ice sheets to both insolation and atmospheric CO2. Our results suggest that the decrease of summer insolation is the main factor responsible for the early build up of the North American ice sheet around 120 kyr BP, in agreement with benthic foraminifera δ18O signals. In contrast, low insolation and low atmospheric CO2 concentration are both necessary to trigger a long-lasting glaciation over Eurasia.

  2. The future of ice sheets and sea ice: between reversible retreat and unstoppable loss.

    Science.gov (United States)

    Notz, Dirk

    2009-12-08

    We discuss the existence of cryospheric "tipping points" in the Earth's climate system. Such critical thresholds have been suggested to exist for the disappearance of Arctic sea ice and the retreat of ice sheets: Once these ice masses have shrunk below an anticipated critical extent, the ice-albedo feedback might lead to the irreversible and unstoppable loss of the remaining ice. We here give an overview of our current understanding of such threshold behavior. By using conceptual arguments, we review the recent findings that such a tipping point probably does not exist for the loss of Arctic summer sea ice. Hence, in a cooler climate, sea ice could recover rapidly from the loss it has experienced in recent years. In addition, we discuss why this recent rapid retreat of Arctic summer sea ice might largely be a consequence of a slow shift in ice-thickness distribution, which will lead to strongly increased year-to-year variability of the Arctic summer sea-ice extent. This variability will render seasonal forecasts of the Arctic summer sea-ice extent increasingly difficult. We also discuss why, in contrast to Arctic summer sea ice, a tipping point is more likely to exist for the loss of the Greenland ice sheet and the West Antarctic ice sheet.

  3. The health impact of residential retreats: a systematic review.

    Science.gov (United States)

    Naidoo, Dhevaksha; Schembri, Adrian; Cohen, Marc

    2018-01-10

    Unhealthy lifestyles are a major factor in the development and exacerbation of many chronic diseases. Improving lifestyles though immersive residential experiences that promote healthy behaviours is a focus of the health retreat industry. This systematic review aims to identify and explore published studies on the health, wellbeing and economic impact of retreat experiences. MEDLINE, CINAHL and PsychINFO databases were searched for residential retreat studies in English published prior to February 2017. Studies were included if they were written in English, involved an intervention program in a residential setting of one or more nights, and included before-and-after data related to the health of participants. Studies that did not meet the above criteria or contained only descriptive data from interviews or case studies were excluded. A total of 23 studies including eight randomised controlled trials, six non-randomised controlled trials and nine longitudinal cohort studies met the inclusion criteria. These studies included a total of 2592 participants from diverse geographical and demographic populations and a great heterogeneity of outcome measures, with seven studies examining objective outcomes such as blood pressure or biological makers of disease, and 16 studies examining subjective outcomes that mostly involved self-reported questionnaires on psychological and spiritual measures. All studies reported post-retreat health benefits ranging from immediately after to five-years post-retreat. Study populations varied widely and most studies had small sample sizes, poorly described methodology and little follow-up data, and no studies reported on health economic outcomes or adverse effects, making it difficult to make definite conclusions about specific conditions, safety or return on investment. Health retreat experiences appear to have health benefits that include benefits for people with chronic diseases such as multiple sclerosis, various cancers, HIV

  4. Geoarchaeological response to landscape changes of the Greek continental shelf since the Last Glacial Maximum

    Science.gov (United States)

    Kapsimalis, Vasilios; Pavlopoulos, Kosmas; Panagiotopoulos, Ioannis

    2010-05-01

    An overview of geological, sedimentological, palaeoclimatic, archaeological and mythological data is presented in order to detect the geomorphological changes of the Aegean and Ionian shelves during the last sea-level transgression, and comprehend the consequent prehistoric human adaptations. The irregular rise of sea level since the Last Glacial Maximum forced the Palaeolithic human to abandon its settlements located near the old (lower) coastlines and to move landward in new positions. Commonly, the coastline movement was very slow causing no significant impact on human activities; however in some cases, the transgression was very prompt causing human migration towards highlands. In some very gentle-dipped and wide regions, e.g. the North Aegean plateau, the sea-level rise caused a rapid coastline retreat (in some extreme case as fast as 10 m/yr) and inundation of an extended surface area. However, at the same time, in the steep parts of the Greek shelf, e.g. the Kyparissiakos Gulf and Crete, the coastline advanced landwards with a slow motion (commonly, a few cm/yr) covering small areas. In addition, coastal regions with particular geomorphologic characteristics, e.g. coastal paleo-lakes protected by a sill (gulfs of Corinth, Amvrakikos, Pagasitikos Evvoikos, Saronikos), were deluged by the sea during different periods and under different intensity, depending on the elevation of the sill and the manner of its overflow. Although the presence of Palaeolithic human in the Greek mainland has been confirmed by several archaeological excavations, there is no certain evidence for human settlement in the deep parts of Greek shelf. However, many archaeologists have suggested that some of Palaeolithic people lived on the shelf, when the sea level was lower than its present position. Nevertheless, some potential Palaeolithic migration routes can be indicated taking into account (a) the palaeogeographic reconstruction of Greek shelf over the Last Quaternary; (b

  5. Obsidian hydration dates glacial loading?

    Science.gov (United States)

    Friedman, I; Pierce, K L; Obradovich, J D; Long, W D

    1973-05-18

    Three different groups of hydration rinds have been measured on thin sections of obsidian from Obsidian Cliff, Yellowstone National Park, Wyoming. The average thickness of the thickest (oldest) group of hydration rinds is 16.3 micrometers and can be related to the original emplacement of the flow 176,000 years ago (potassium-argon age). In addition to these original surfaces, most thin sections show cracks and surfaces which have average hydration rind thicknesses of 14.5 and 7.9 micrometers. These later two hydration rinds compare closely in thickness with those on obsidian pebbles in the Bull Lake and Pinedale terminal moraines in the West Yellowstone Basin, which are 14 to 15 and 7 to 8 micrometers thick, respectively. The later cracks are thought to have been formed by glacial loading during the Bull Lake and Pinedale glaciations, when an estimated 800 meters of ice covered the Obsidian Cliff flow.

  6. Glacier retreat of the Tian Shan and its impact on the urban growth and environment evaluated from satellite remote sensing data

    Science.gov (United States)

    Fu, B. H.; Guo, Q.; Yan, F.; Zhang, J.; Shi, P. L.; Ayinuer, M.; Xue, G. L.

    2017-07-01

    The retreat of mountain glaciers, notably in high Asia, provides evidence for the rise of global temperature. The mass balance is vital for the health of a glacier. If the amount of frozen precipitation in the accumulation zone exceeds the quantity of glacial ice loss due to melting or lies in the ablation zone, the glacier will advance. Conversely, if the accumulation is less than the ablation, the glacier will retreat. Glaciers in retreat will have negative mass balances, and if they do not reach an equilibrium between accumulation and ablation, will eventually disappear. Long-term changes of the mountain glaciers in the Tian Shan, Central Asia, are not well constrained. Analyses of satellite remote sensing data combined with the ground observations reveal a 37.5% decline of glaciered area from 1989 to 2014 in No.1 Glacier, the headwaters of the Urumqi River basin, Chinese Tian Shan, which could be linked to increased summer melting. The results show that the area of glaciers was reduced from 31.55 km2 in 18 August 1989 to 28.66 km2 in 24 August 1994 and 19.74 km2 in 31 August 2014. The glacier area was reduced by 0.47 km2/per year in recent 25 years since 1989, and the annual reduction was 1.5%. Meanwhile, the urban area of Urumqi, the biggest city of Xinjiang Uygur Autonomous Region, increased from 156 km2 in 1989 to 555 km2 in 2014. Correspondingly, the population of permanent residents increased from 1.06 million in 1989 to 3.53 million in 2014. We suggest that the decline of glacier area is driven primarily by summer melting and, possibly, linked to the combined effects of the global rise in temperatures and black carbon/CO2 emission from coal-fired power plants, cement plants and petroleum chemical plants from the nearby Urumqi and surrounding regions. The continuing retreat of glaciers will have a number of different quantitative impacts. Populations in the arid Central Asia regions are heavily dependent on snow and glacier melt for their irrigation and

  7. Landmark Study Reveals Antarctic Glacier's Long History of Retreat

    OpenAIRE

    Kuska, Dale M.

    2016-01-01

    Faculty Showcase Archive Article Approved for public release; distribution is unlimited. A major study, released in late November in the journal “Nature,” reveals the history of retreat of the massive Pine Island Glacier (PIG) in western Antarctica, widely considered one of the largest contributors to global sea-level rise.

  8. Glacial evolution of the Ampato Volcanic Complex (Peru)

    Science.gov (United States)

    Alcalá, J.; Palacios, D.; Zamorano, J. J.; Vázquez, L.

    2009-04-01

    .O. (1990): Recent glacial history and paleoclimate of the Peruvian - Bolivian Andes. Quaternary Science Reviews, 9: 137-152. Seltzer, G. O.; Rodbell, D. T; Baker, P. A.; Fritz, S. C.; Tapia, P. M.; Rowe, H.D.; y Dunbar, R. B. (2002): Early warming of Tropical South America at the Last Glacial-Interglacial Transition. Science, 296: 1.685-1.686. Smith, J. A.; Seltzer, G.O.; Rodbell, R.T.; y Klein, A.R. (2005): Regional synthesis of last glacial maximum snowlines in the tropical Andes, South America. Quaternary International, 138: 145 -167. Zech, R.; Kull, CH.; Kubik, P. W. y Veit, H. (2007): Exposure dating of Late Glacial and pre-LGM moraines in the Cordon de Doña Rosa, Northern/Central Chile (31° S). Climate of the Past, 3: 1-14. Zech, R.; Kull, CH.; Kubik, P. W. y Veit, H. (2007): LGM and Late Glacial glacier advances in the Cordillera Real and Cochabamba (Bolivia) deduced from 10Be surface exposure dating. Climate of the Past, 3: 623-635. Zreda, M., J. England, F. Phillips, D. Elmore, and P. Sharma, (1999): Unblocking the Nares Strait by Greenland and Ellesmere ice-sheet retreat 10,000 years ago, Nature, 398: 139-142.

  9. Emerging Glacial Lakes in the Cordillera Blanca, Peru: A Case Study at Arteson Glacier

    Science.gov (United States)

    Chisolm, R. E.; Mckinney, D. C.; Gomez, J.; Voss, K.

    2012-12-01

    Tropical glaciers are an essential component of the water resources systems in the mountainous regions where they are located, and a warming climate has resulted in the accelerated retreat of Andean glaciers in recent decades. The shrinkage of Andean glaciers influences the flood risk for communities living downstream as new glacial lakes have begun to form at the termini of some glaciers. As these lakes continue to grow in area and volume, they pose an increasing risk of glacial lake outburst floods (GLOFs). Ice thickness measurements have been a key missing link in studying the tropical glaciers in Peru and how climate change is likely to impact glacial melt and the growth of glacial lakes. Ground penetrating radar (GPR) has rarely been applied to glaciers in Peru to measure ice thickness, and these measurements can tell us a lot about how a warming climate will affect glacier mass balance. This study presents GPR data taken in July 2012 at the Arteson glacier in the Cordillera Blanca, Peru. A new lake has begun to form at the terminus of the Arteson glacier, and this lake has key features, including overhanging ice and loose rock likely to create landslides, that could trigger a catastrophic GLOF if the lake continues to grow. This new lake is part of a series of three lakes that have formed below the Arteson glacier. The two lower lakes, Artesonraju and Paron, are much larger so that if there were an avalanche or landslide into the new lake below Arteson glacier, the impact could potentially be more catastrophic than a GLOF from one single lake. Estimates of how the lake mass balance is likely to evolve due to the retreating glacier are key to assessing the flood risk from this dynamic three-lake system. Because the glacier mass balance and lake mass balance are closely linked, the ice thickness measurements and measurements of the bed slope of the Arteson glacier and underlying bedrock give us a clue to how the lake is likely to evolve. GPR measurements of

  10. Holocene glacial fluctuations in southern South America

    Science.gov (United States)

    Reynhout, S.; Sagredo, E. A.; Kaplan, M. R.; Aravena, J. C.; Martini, M. A.; Strelin, J. A.; Schaefer, J. M.

    2016-12-01

    Understanding the timing and magnitude of former glacier fluctuations is critical to decipher long-term climatic trends and to unravel both natural cycles and human impact on the current glacial behavior. Despite more than seven decades of research efforts, a unifying model of Holocene glacial fluctuations in Southern South America remains elusive. Here, we present the state-of-the-art regarding the timing of Holocene glacial fluctuation in southern Patagonia-Tierra del Fuego, with a focus on a new generation of high-resolution radiocarbon and 10Be surface exposure dating chronologies. Recently acquired evidence suggest that after receding from advanced Late Glacial positions, Patagonian glaciers were for the most part close to, or even behind, present ice margins during the Early Holocene. On the other hand, emerging chronologies indicate that in some areas there were extensive expansions (century scale?) that punctuated the warm interval. Subsequently, we have evidence of multiple millennial timescale glacial advances starting in the middle Holocene. Several glacial maxima are defined by moraines and other landforms from 7000 years ago to the 19th century, with a gap sometime between 4,500 and 2,500 years ago. The last set of advances began around 800-600 years ago. Although glacial activity is documented in Patagonia at the same time as the European Little Ice Age, the extent of these glacial events are less prominent than those of the mid-Holocene. The causes that may explain these glacial fluctuations remain elusive. Finally, we discuss ongoing efforts to better define the timing and extent of Holocene glaciations in southern South America, and to establish the basis to test competing hypothesis of regional Holocene climate variability.

  11. A century of ice retreat on Kilimanjaro: the mapping reloaded

    Directory of Open Access Journals (Sweden)

    N. J. Cullen

    2013-03-01

    Full Text Available A new and consistent time series of glacier retreat on Kilimanjaro over the last century has been established by re-interpreting two historical maps and processing nine satellite images, which removes uncertainty about the location and extent of past and present ice bodies. Three-dimensional visualization techniques were used in conjunction with aerial and ground-based photography to facilitate the interpretation of ice boundaries over eight epochs between 1912 and 2011. The glaciers have retreated from their former extent of 11.40 km2 in 1912 to 1.76 km2 in 2011, which represents a total loss of about 85% of the ice cover over the last 100 yr. The total loss of ice cover is in broad agreement with previous estimates, but to further characterize the spatial and temporal variability of glacier retreat a cluster analysis using topographical information (elevation, slope and aspect was performed to segment the ice cover as observed in 1912, which resulted in three glacier zones being identified. Linear extrapolation of the retreat in each of the three identified glacier assemblages implies the ice cover on the western slopes of Kilimanjaro will be gone before 2020, while the remaining ice bodies on the plateau and southern slopes will most likely disappear by 2040. It is highly unlikely that any body of ice will be present on Kilimanjaro after 2060 if present-day climatological conditions are maintained. Importantly, the geo-statistical approach developed in this study provides us with an additional tool to characterize the physical processes governing glacier retreat on Kilimanjaro. It remains clear that, to use glacier response to unravel past climatic conditions on Kilimanjaro, the transition from growth to decay of the plateau glaciers must be further resolved, in particular the mechanisms responsible for vertical cliff development.

  12. Treatment philosophy and retreatment rates following piezoelectric lithotripsy.

    Science.gov (United States)

    Fegan, J; Camp, L A; Wilson, W T; Miller, G L; Preminger, G M

    1993-01-01

    Second generation lithotriptors offer the advantage of anesthesia-free fragmentation of renal and ureteral calculi but they frequently require multiple treatments to attain a stone-free status. However, excessive single lithotripsy sessions or multiple treatments may be associated with significant damage to the kidney. For some clinicians a common treatment philosophy involves evaluation of serial plain abdominal films every 24 hours after lithotripsy and immediate retreatment of all patients with incomplete fragmentation. To avoid unnecessary retreatments and, thus, minimize potential renal damage, we prospectively evaluated 100 patients undergoing lithotripsy on a Wolf Piezolith 2300 device. Patients were routinely treated with 4,000 shocks at 1,100 bar. Serial plain abdominal films were obtained at 1 day and 2 weeks after lithotripsy. The need for retreatment was determined by the plain abdominal film results. Additional therapy was considered necessary if there was no stone fragmentation or if residual fragments measured greater than 4 mm. Of the patients whose plain abdominal film at 24 hours indicated the need for a repeat treatment 43% were stone-free on the 2-week film. Thus, these patients were spared an unnecessary treatment by allowing adequate time for the stone fragments to pass spontaneously. Our data suggest that repeat treatments on second generation lithotriptors should not be performed within 24 hours. Rather, the patient should be reevaluated at least 1 to 2 weeks later to avoid unnecessary retreatment with the attendant potential for renal injury. In addition, when comparing the retreatment rates of various lithotriptors, one should also consider the treatment philosophy used at the particular institution and the timing of the radiographic studies used to determine the stone-free status.

  13. Spiral computed tomography assessment of the efficacy of different rotary versus hand retreatment system.

    Science.gov (United States)

    Mittal, Neelam; Jain, Jyoti

    2014-01-01

    The purpose of this study was to evaluate the efficacy of nickel-titanium rotary retreatment systems versus stainless steel hand retreatment system with or without solvent for gutta-percha removal during retreatment. Sixty extracted human mandibular molar teeth with single canal in a distal root was prepared with ProTaper rotary nickel-titanium files and obturated with gutta-percha and sealer. The teeth were randomly divided into six groups of 10 specimens in each groups. The volume of filling material before and after retreatment were evaluated in cm(3) using the computed tomography (CT) scanner proprietary software. Maximum amount of filling material removed during retreatment with ProTaper retreatment system with solvent and minimum with hand retreatment system with solvent. None of the technique was 100% effective in removing the filling materials, but the ProTaper retreatment system with solvent was better.

  14. A Glacial Perspective on the Impact of Heinrich Stadials on North Atlantic Climate

    Science.gov (United States)

    Bromley, G. R.; Putnam, A. E.; Rademaker, K. M.; Balter, A.; Hall, B. L.

    2017-12-01

    The British Isles contain a rich geologic record of Late Pleistocene ice sheet behaviour in the NE North Atlantic basin. We are using cosmogenic 10Be surface-exposure dating, in conjunction with detailed glacial-geomorphic mapping, to reconstruct the timing and nature of cryospheric change - and thus climate variability - in northern Scotland since the Last Glacial Maximum. Our specific focus is Heinrich Stadial 1 (18,300-14,700 years ago), arguably the most significant abrupt climate event of the last glacial cycle and a major feature in global palaeoclimate records. Such constraint is needed because of currently conflicting models of how these events impact terrestrial environments and a recent hypothesis attributing this disparity to enhanced seasonality in the North Atlantic basin. To date, we have measured 10Be in > 30 samples from glacial erratics located on moraines deposited by the British Ice Sheet as it retreated from the continental shelf to its highland source regions. Our preliminary results indicate that the stadial was characterised by widespread deglaciation driven by atmospheric warming, a pattern that is suggestive of pronounced seasonality. Additionally, we report new exposure ages from moraines deposited during a subsequent phase of alpine glaciation (known locally as the Loch Lomond Readvance) that has long been attributed to the Younger Dryas stadial. With the growing focus on the full expression of stadials, and the inherent vulnerability of Europe to shifts in North Atlantic climate, developing the extant record of terrestrial glaciation and comparing these data to marine records is a critical step towards understanding the drivers of abrupt climate change.

  15. Glacial and periglacial environment monitoring in Aosta Valley - Northwestern Italian Alps

    Science.gov (United States)

    Motta, Elena; Cremonese, Edoardo; Morra di Cella, Umberto; Pogliotti, Paolo; Vagliasindi, Marco

    2010-05-01

    Aosta Valley is a small alpine region of about 3.300 km2 located in the NW Italy, on the southern side of the Alps and surrounded by the highest Alpine peaks such as Mont Blanc (4810m), Mont Rose (4634m) and Cervino (4478m), More than 50% of the territory has an elevation above 2000 metres asl. High mountain, glacial and periglacial environments cover a significant part of the territory. As the cryosphere is strongly sensitive to climate change, global warming effects are particularly evident in this alpine region, and they often affect environment and social and economic life, thus representing a key issue for politicians and people working and living in the valley. Among these effects, some of the most important are the decrease of water storage due to glaciers retreat and the increasing natural hazards as a consequence of rapid environmental dynamics. Hence the importance of monitoring glacial and periglacial environment, in order to quantify effects of climate change, to detect new dynamics and to manage consequences on the environment and the social life. In Aosta Valley the understanding of these phenomena is carried out by means of several actions, both at a regional scale and on specific representative sites. A multi-temporal analysis of aerial photographs, orthophotos and satellite imagery allows to detect glaciers evolution trend at a regional scale. All this information is collected in a Regional Glacier inventory, according to the World Glaciers Inventory standard and recommendations. Analysis of the information collected in the Inventory show that the total area presently covered by glaciers is about 135 km2; area changes occurred in the past has been about -44.3 km2, and -17 km2. between 1975 and 2005. Glacier inventory also gathers - for each of the about 200 glaciers - morphological data, information about events and photos both historical and present. Glacier mass balance (the difference resulting from the mass gained by the glacier through the

  16. Magnetic and mineralogical properties of central Baffin Bay sediments since the Last Glacial Maximum

    Science.gov (United States)

    Simon, Q.; St-Onge, G.; Hillaire-Marcel, C.

    2011-12-01

    different proxies tend to demonstrate the establishment of the modern Baffin Bay oceanic circulation that followed the deglaciation and the opening of Lancaster Sound, Jones Sound and Nares Strait, and the onset of the Western Greenland Current. These data provide strong marine evidence of 1) increasing supplies of sedimentary material coming from the rapid retreat of ice streams in the northern part of Baffin Bay starting at 16 ka and 2) the ice-margin dynamics (Innuitian vs. Greenland ice sheets) since the LGM. The study enables to document these sedimentological changes with regard to regional and Northern Hemisphere climatic variability, and highlights the importance of Baffin Bay for the establishment of modern oceanic circulation.

  17. Rapid sedimentation and overpressure in shallow sediments of the Bering Trough, offshore southern Alaska

    Science.gov (United States)

    Daigle, Hugh; Worthington, Lindsay L.; Gulick, Sean P. S.; Van Avendonk, Harm J. A.

    2017-04-01

    Pore pressures in sediments at convergent margins play an important role in driving chemical fluxes and controlling deformation styles and localization. In the Bering Trough offshore Southern Alaska, extreme sedimentation rates over the last 140 kyr as a result of glacial advance/retreats on the continental shelf have resulted in elevated pore fluid pressures in slope sediments overlying the Pamplona Zone fold and thrust belt, the accretionary wedge resulting from subduction of the Yakutat microplate beneath the North American Plate. Based on laboratory experiments and downhole logs acquired at Integrated Ocean Drilling Program Site U1421, we predict that the overpressure in the slope sediments may be as high as 92% of the lithostatic stress. Results of one-dimensional numerical modeling accounting for changes in sedimentation rate over the last 130 kyr predicted overpressures that are consistent with our estimates, suggesting that the overpressure is a direct result of the rapid sedimentation experienced on the Bering shelf and slope. Comparisons with other convergent margins indicate that such rapid sedimentation and high overpressure are anomalous in sediments overlying accretionary wedges. We hypothesize that the shallow overpressure on the Bering shelf/slope has fundamentally altered the deformation style within the Pamplona Zone by suppressing development of faults and may inhibit seismicity by focusing faulting elsewhere or causing deformation on existing faults to be aseismic. These consequences are probably long-lived as it may take several million years for the excess pressure to dissipate.

  18. Recent glacier retreat and lake formation in the Querecocha watershed, Cordillera Blanca, Peru

    Science.gov (United States)

    López Moreno, J.; Valero-Garces, B.; Revuelto, J.; Azorín-Molina, C.; Bazo, J.; Cochachin, A.; Fontaneda, S.; Mark, B. G.

    2013-12-01

    In the Andes, and specifically in the Peruvian mountains a marked decrease of the glaciated area has occurred since the end of the Little Ice Age, and it has been accelerated since the last decades of the 20th century. As a result of the glacier retreat new pro-glaciar lakes are originated, and often the area and volume of existing ones increases. The study of these newly-formed lakes and their recent evolution may provide a better understanding of the hydrological and geomorphological evolution of deglaciated areas, and a better evaluation of the risk of glacial lakes outburst floods (GLOFS). In this work, we use 26 annual Landsat Thematic Mapper images from 1975 to 2010 to determine changes of the glaciated surface, snow line elevation and lakes formation in the headwaters of the Querecocha watershed in Cordillera Blanca (Perú). We also present the information derived from 10 short sediment cores (up to 50 cm long) retrieved along several transects in Yanamarey Lake. Both data sets inform of the sediment yield and lake development in recently deglaciated environments of the Andes. Results demonstrate that only one third of the surface covered by ice in 1975 remained in 2010. In this period, snowline has shifted up more than 100 meters in elevation in both, Yanamarey North and South areas respectively. At the same time, new lakes have been formed very quickly in these deglaciated areas. Preliminary 137Cs dating of Yanamarey sediment core indicates that at least the top 50 cm of the lake sequence deposited after 1960. This is coherent with the Landsat image of 1975 that showed the current surface of the lake still covered by ice. The high sediment rate (> 1 cm/yr) in the lake demonstrates the very high sediment yield in these geomorphically active settings. The sediment cores are composed of cm-thick sequences defined by grain-size (silt-clay) common in proglacial lakes reflecting the variability of hydrological response associated to the glacier retreat in the

  19. Glacial greenhouse-gas fluctuations controlled by ocean circulation changes.

    Science.gov (United States)

    Schmittner, Andreas; Galbraith, Eric D

    2008-11-20

    Earth's climate and the concentrations of the atmospheric greenhouse gases carbon dioxide (CO(2)) and nitrous oxide (N(2)O) varied strongly on millennial timescales during past glacial periods. Large and rapid warming events in Greenland and the North Atlantic were followed by more gradual cooling, and are highly correlated with fluctuations of N(2)O as recorded in ice cores. Antarctic temperature variations, on the other hand, were smaller and more gradual, showed warming during the Greenland cold phase and cooling while the North Atlantic was warm, and were highly correlated with fluctuations in CO(2). Abrupt changes in the Atlantic meridional overturning circulation (AMOC) have often been invoked to explain the physical characteristics of these Dansgaard-Oeschger climate oscillations, but the mechanisms for the greenhouse-gas variations and their linkage to the AMOC have remained unclear. Here we present simulations with a coupled model of glacial climate and biogeochemical cycles, forced only with changes in the AMOC. The model simultaneously reproduces characteristic features of the Dansgaard-Oeschger temperature, as well as CO(2) and N(2)O fluctuations. Despite significant changes in the land carbon inventory, CO(2) variations on millennial timescales are dominated by slow changes in the deep ocean inventory of biologically sequestered carbon and are correlated with Antarctic temperature and Southern Ocean stratification. In contrast, N(2)O co-varies more rapidly with Greenland temperatures owing to fast adjustments of the thermocline oxygen budget. These results suggest that ocean circulation changes were the primary mechanism that drove glacial CO(2) and N(2)O fluctuations on millennial timescales.

  20. Decadal-scale coastal cliff retreat in southern and central California

    Science.gov (United States)

    Young, Adam P.

    2018-01-01

    Airborne LiDAR data collected in 1998 and 2009-2010 were used to measure coastal cliff erosion and retreat between the Mexico/California border and Bodega Head, California. Cliff erosion was detected along 44% of the 595 km of shoreline evaluated, while the remaining cliffs were relatively stable. The mean cliff top retreat rate was 0.12 m/yr, while mean retreat averaged over the entire cliff face was 0.04 m/yr. The maximum cliff top and face retreat rates were 4.2 and 3.8 m/yr, respectively. Historical ( 1930s to 1998) and recent retreat rates were significantly inversely correlated for areas with large historical or recent cliff retreat, such that locations with elevated historical retreat had low levels of recent retreat and locations with elevated recent retreat were preceded by low rates of historical retreat. The strength of this inverse correlation increased with cliff change magnitudes up to r2 of 0.91 for cliff top retreat rates > 2.9 m/yr. Mean recent retreat rates were 52-83% lower than mean historical retreat rates. Although beaches can protect cliffs against wave-driven erosion, cliffs fronted by beaches retreated 49% more than cliffs without beaches. On average, unarmored cliff faces retreated 0.05 m/yr between 1998 and 2009-2010, about three times faster than artificially armored cliffs. Alongshore metrics of wave-cliff impact, precipitation, and cliff hardness were generally not well correlated with recent cliff changes. A cliff hazard metric is used to detect cliff steepening and areas prone to future cliff top failures.

  1. Rituximab Retreatment in Rheumatoid Arthritis in a Real-life Cohort

    DEFF Research Database (Denmark)

    Chatzidionysiou, Katerina; Lie, Elisabeth; Lukina, Galina

    2017-01-01

    of 800 patients qualified for the second analysis: 616 were retreated on flare and 184 at fixed interval. For the first retreatment, the fixed-interval retreatment group yielded significantly better results than the on-flare group (estimated marginal mean DAS28 = 3.8, 95% CI 3.6-4.1 vs 4.6, 95% CI 4.......5-4.7, p leads to further clinical improvement after the first course of RTX. A fixed-interval retreatment strategy seems to be more effective than on-flare retreatment....

  2. Can shrubs help to reconstruct historical glacier retreats?

    International Nuclear Information System (INIS)

    Buras, Allan; Hallinger, Martin; Wilmking, Martin

    2012-01-01

    In the 21st century, most of the world’s glaciers are expected to retreat due to further global warming. The range of this predicted retreat varies widely as a result of uncertainties in climate and glacier models. To calibrate and validate glacier models, past records of glacier mass balance are necessary, which often only span several decades. Long-term reconstructions of glacier mass balance could increase the precision of glacier models by providing the required calibration data. Here we show the possibility of applying shrub growth increments as an on-site proxy for glacier summer mass balance, exemplified by Salix shrubs in Finse, Norway. We further discuss the challenges which this method needs to meet and address the high potential of shrub growth increments for reconstructing glacier summer mass balance in remote areas. (letter)

  3. Radial Flow Effects On A Retreating Rotor Blade

    Science.gov (United States)

    2014-05-01

    birds , marine life and even insect wings. In some cases such as helicopters, wind turbines and compres- sors, dynamic stall becomes the primary...on dynamic stall and reverse flow as applied to a helicopter rotor in forward flight and a wind turbine operating at a yaw angle. While great...occurring on a retreating blade with a focus on dynamic stall and reverse flow as applied to a helicopter rotor in forward flight and a wind turbine

  4. Periodicity in a Conceptual Model of Glacial Cycles in the Absence of Milankovitch Forcing

    Science.gov (United States)

    Hahn, J.; Walsh, J.; Widiasih, E.; McGehee, R.

    2015-12-01

    Previously, McGehee and Widiasih coupled Budyko's Energy Balance Model with dynamics of a latitudinal ice-line incorporating the albedo feedback effect. They reduced this model to a two-dimensional equation of global mean temperature and a latitudinal ice-line. With this conceptual model, we now include dynamics of the ablation and accumulation of ice, to form a three-dimensional system that partitions the regions of the Earth latitudinally into an accumulation zone, ablation zone, and ice-free zone. Motivated by the findings of Abe-Ouchi et al that the fast retreat of ice-sheets is due to an increased rate of ablation via the effects of delayed isostatic rebound, we incorporate a simple switching mechanism to the model which increases the rate of ablation during periods of glacial retreat. This forms a discontinuous system of the Earth's temperature and ice-volume in which we find a stable periodic orbit. This can be interpreted as a intrinsic cycling of the Earth's climate in the absence of Milankovitch forcing.

  5. The Holocene history of Nares Strait: Transition from glacial bay to Arctic-Atlantic throughflow

    Science.gov (United States)

    Jennings, Anne E.; Sheldon, Christina; Cronin, Thomas M.; Francus, Pierre; Stoner, Joseph; Andrews, John

    2011-01-01

    Retreat of glacier ice from Nares Strait and other straits in the Canadian Arctic Archipelago after the end of the last Ice Age initiated an important connection between the Arctic and the North Atlantic Oceans, allowing development of modern ocean circulation in Baffin Bay and the Labrador Sea. As low-salinity, nutrient-rich Arctic Water began to enter Baffin Bay, it contributed to the Baffin and Labrador currents flowing southward. This enhanced freshwater inflow must have influenced the sea ice regime and likely is responsible for poor calcium carbonate preservation that characterizes the Baffin Island margin today. Sedimentologic and paleoceanographic data from radiocarbon-dated core HLY03-05GC, Hall Basin, northern Nares Strait, document the timing and paleoenvironments surrounding the retreat of waning ice sheets from Nares Strait and opening of this connection between the Arctic Ocean and Baffin Bay. Hall Basin was deglaciated soon before 10,300 cal BP (calibrated years before present) and records ice-distal sedimentation in a glacial bay facing the Arctic Ocean until about 9,000 cal BP. Atlantic Water was present in Hall Basin during deglaciation, suggesting that it may have promoted ice retreat. A transitional unit with high ice-rafted debris content records the opening of Nares Strait at approximately 9,000 cal BP. High productivity in Hall Basin between 9,000 and 6,000 cal BP reflects reduced sea ice cover and duration as well as throughflow of nutrient-rich Pacific Water. The later Holocene is poorly resolved in the core, but slow sedimentation rates and heavier carbon isotope values support an interpretation of increased sea ice cover and decreased productivity during the Neoglacial period.

  6. Last Glacial Maximum Salinity Reconstruction

    Science.gov (United States)

    Homola, K.; Spivack, A. J.

    2016-12-01

    It has been previously demonstrated that salinity can be reconstructed from sediment porewater. The goal of our study is to reconstruct high precision salinity during the Last Glacial Maximum (LGM). Salinity is usually determined at high precision via conductivity, which requires a larger volume of water than can be extracted from a sediment core, or via chloride titration, which yields lower than ideal precision. It has been demonstrated for water column samples that high precision density measurements can be used to determine salinity at the precision of a conductivity measurement using the equation of state of seawater. However, water column seawater has a relatively constant composition, in contrast to porewater, where variations from standard seawater composition occur. These deviations, which affect the equation of state, must be corrected for through precise measurements of each ion's concentration and knowledge of apparent partial molar density in seawater. We have developed a density-based method for determining porewater salinity that requires only 5 mL of sample, achieving density precisions of 10-6 g/mL. We have applied this method to porewater samples extracted from long cores collected along a N-S transect across the western North Atlantic (R/V Knorr cruise KN223). Density was determined to a precision of 2.3x10-6 g/mL, which translates to salinity uncertainty of 0.002 gms/kg if the effect of differences in composition is well constrained. Concentrations of anions (Cl-, and SO4-2) and cations (Na+, Mg+, Ca+2, and K+) were measured. To correct salinities at the precision required to unravel LGM Meridional Overturning Circulation, our ion precisions must be better than 0.1% for SO4-/Cl- and Mg+/Na+, and 0.4% for Ca+/Na+, and K+/Na+. Alkalinity, pH and Dissolved Inorganic Carbon of the porewater were determined to precisions better than 4% when ratioed to Cl-, and used to calculate HCO3-, and CO3-2. Apparent partial molar densities in seawater were

  7. Latest Pleistocene and Holocene glacial events in the Colonia valley, Northern Patagonia Icefield, southern Chile

    Science.gov (United States)

    Nimick, David A.; Mcgrath, Daniel; Mahan, Shannon; Friesen, Beverly A.; Leidich, Jonathan

    2016-01-01

    The Northern Patagonia Icefield (NPI) is the primary glaciated terrain worldwide at its latitude (46.5–47.5°S), and constraining its glacial history provides unique information for reconstructing Southern Hemisphere paleoclimate. The Colonia Glacier is the largest outlet glacier draining the eastern NPI. Ages were determined using dendrochronology, lichenometry, radiocarbon, cosmogenic 10Be and optically stimulated luminescence. Dated moraines in the Colonia valley defined advances at 13.2 ± 0.95, 11.0 ± 0.47 and 4.96 ± 0.21 ka, with the last being the first constraint on the onset of Neoglaciation for the eastern NPI from a directly dated landform. Dating in the tributary Cachet valley, which contains an ice-dammed lake during periods of Colonia Glacier expansion, defined an advance at ca. 2.95 ± 0.21 ka, periods of advancement at 810 ± 49 cal a BP and 245 ± 13 cal a BP, and retreat during the intervening periods. Recent Colonia Glacier thinning, which began in the late 1800s, opened a lower-elevation outlet channel for Lago Cachet Dos in ca. 1960. Our data provide the most comprehensive set of Latest Pleistocene and Holocene ages for a single NPI outlet glacier and expand previously developed NPI glacial chronologies.

  8. Development of Petrov glacial-lake system (Tien Shan and outburst risk assessment

    Directory of Open Access Journals (Sweden)

    I. A. Torgoev

    2013-01-01

    Full Text Available Global climate warming causes an intensive melting and retreat of glaciers in the Tien Shan mountains. Melting water of glaciers causes overfilling of high mountain lakes. The increase of the surface and volume of the Petrov Lake accompanied with the decrease of stability of the dam represents an extremely dangerous situation that can produce a natural disaster. Failure can happen due to erosion, a buildup of water pressure, an earthquake or if a large enough portion of a glacier breaks off and massively displaces the waters in a glacial lake at its base. In case of the lake dam rupture, flooding of a disposal site of highly toxic tailing from the gold mine Kumtor is a threat. If this happens, the toxic waste containing cyanides would contaminate a large area in the Naryn (Syrdarya river basin. Even if the flooding of the disposal site does not occur, the damage after lake dam fracture will be immense due to the glacial lake outburst flood may be a devastating mudslide. In order to prevent or reduce the risk of this event we recommend performing engineering surveys for the development and implementation of the project for the controlled reduction of water level in the Blue Bay of the Petrov Lake to a safe volume.

  9. Little Ice Age glacial geomorphology and sedimentology of Portage Glacier, South-Central Alaska

    Directory of Open Access Journals (Sweden)

    Carlos Córdova

    2009-06-01

    Full Text Available The study of glacial landforms and deposits is important, as it isdifficult to observe processes under modern glaciers and ice-sheets. Thus landscapes and sediments that are the product of present glaciation can give insight into processes that occurred during Pleistocene times. This study investigates the genesis of little ice age glacial landforms present in Portage Glacier, South-Central Alaska. The present day moraine morphology and sedimentology in Portage Glacier valley reveals the presence of two types of till and moraines. The clast-rich sandy diamicton present on the 1852 moraine is interpreted to be a basal till indicating this feature is a pushmoraine representing an advance or a standstill position of Portage Glacier in 1852. The moderately sorted gray sandy boulder gravel present on the 1900 and 1922 moraines is interpreted to be an ice-marginal deposit (ablation till with a mixture of supraglacial and glaciofluvial sediments deposited by slumping and stream sortingprocesses. All of these features are interpreted to be ablation moraines representing glacier retreat and moraine building in 1900 and1922.

  10. Potentially dangerous glacial lakes in Kyrgyzstan - Research overview of 2004-2015

    Science.gov (United States)

    Jansky, Bohumir; Yerokhin, Sergey; Sobr, Miroslav; Engel, Zbynek; Cerny, Michal; Falatkova, Kristyna; Kocum, Jan; Benes, Vojtech

    2016-04-01

    Global warming causes intensive melting and retreat of glaciers in most of high mountains all over the world. This process is also evident in the mountain regions of central Tien Shan. Glacier melt water affects changes in hydrological regime of water streams and causes overfilling of high mountain lake basins. The dams of many lakes are very unstable and can burst open. To determine the degree of such risk, it is necessary to analyse the genesis of lakes, to characterize the morphology of the lake basins and to know the particularities of their hydrological regime. According to the latest inventory within territory of Kyrgyzstan, a total of 1328 lakes have been identified as potentially dangerous, 12 lakes are considered as currently dangerous, other 25 feature high potential hazard. Since 1952 more than 70 disastrous cases of lake outburst have been registered. The hazardous alpine lakes are studied in Kyrgyzstan systematically since 1966. Since 2004, Czech-Kyrgyz research team has been operating in Kyrgyzstan in the field of dangerous glacial lakes. Projects were focused primarily on high-mountain glacial lakes risk assessment, propositions of risk mitigation measures, establishment of permanent research station near one of the studied glacier complexes, preparation of risk analysis for selected endangered valleys, evaluation of climatic and hydrological data and glacier development within observed regions. The most significant portion of data and information has been gathered during field work, complemented by satellite image analysis and surveillance flights over the monitored sites.

  11. DECOVALEX III/BENCHPAR PROJECTS. The Thermal-Hydro-Mechanical Responses to a Glacial Cycle and their Potential Implications for Deep Geological Disposal of Nuclear Fuel Waste in a Fractured Crystalline Rock Mass. Report of BMT3/WP4

    Energy Technology Data Exchange (ETDEWEB)

    Chan, T.; Stanchell, F.W. [Atomic Energy of Canada Ltd, Toronto (Canada); Christiansson, R. [Swedish Nuclear Fuel and Waste Management Co., Figeholm (Sweden); Boulton, G.S. [Univ. of Edinburgh (United Kingdom). School of GeoSciences; Eriksson, L.O.; Vistrand, P.; Wallroth, T. [Chalmers Univ. of Technology, Goeteborg (Sweden). Dept. of Geology; Hartikainen, J. [Helsinki Univ. of Technology (Finland). Inst. of Mathematics; Jensen, M.R. [0ntario Power Generation, Toronto (Canada); Mas lvars, D. [Royal Inst. of Technology, Stockholm (Sweden). Land and Water Resources engineering

    2005-02-15

    A number of studies related to past and on-going deep repository performance assessments have identified glaciation/deglaciation as major future events in the next few hundred thousand years capable of causing significant impact on the long term performance of the repository system. Benchmark Test 3 (BMT3) of the international DECOVALEX III project has been designed to provide an illustrative example that explores the mechanical and hydraulic response of a fractured crystalline rock mass to a period of glaciation. The primary purpose of this numerical study is to investigate whether transient events associated with a glacial cycle could significantly influence the performance of a deep geological repository in a crystalline shield setting. A conceptual site-scale (tens of kilometres) hydro-mechanical (HM) model was assembled based primarily on site-specific litho-structural, hydrogeological and geomechanical data from the Whiteshell Research Area in the Canadian Shield, with simplification and generalization. Continental glaciological modelling of the Laurentide ice sheet through the last glacial cycle lasting approximately 100,000 years suggests that this site was glaciated at about 60 ka and between about 22.5 ka and 11 ka before present with maximum ice sheet thickness reaching 2,500 m and maximum basal water pressure head reaching 2000 m. The ice-sheet/drainage model was scaled down to generate spatially and temporally variable hydraulic and mechanical glaciated surface boundary conditions for site-scale subsurface HM modelling and permafrost modelling. Under extreme periglacial conditions permafrost was able to develop down to the assumed 500-m repository horizon. Two- and three-dimensional coupled HM finite-element simulations indicate: during ice-sheet advance there is rapid rise in hydraulic head, high transient hydraulic gradients and high groundwater velocities 2-3 orders of magnitude higher than under nonglacial conditions; surface water recharges deeper

  12. DECOVALEX III/BENCHPAR PROJECTS. The Thermal-Hydro-Mechanical Responses to a Glacial Cycle and their Potential Implications for Deep Geological Disposal of Nuclear Fuel Waste in a Fractured Crystalline Rock Mass. Report of BMT3/WP4

    International Nuclear Information System (INIS)

    Chan, T.; Stanchell, F.W.; Christiansson, R.; Boulton, G.S.; Mas lvars, D.

    2005-02-01

    A number of studies related to past and on-going deep repository performance assessments have identified glaciation/deglaciation as major future events in the next few hundred thousand years capable of causing significant impact on the long term performance of the repository system. Benchmark Test 3 (BMT3) of the international DECOVALEX III project has been designed to provide an illustrative example that explores the mechanical and hydraulic response of a fractured crystalline rock mass to a period of glaciation. The primary purpose of this numerical study is to investigate whether transient events associated with a glacial cycle could significantly influence the performance of a deep geological repository in a crystalline shield setting. A conceptual site-scale (tens of kilometres) hydro-mechanical (HM) model was assembled based primarily on site-specific litho-structural, hydrogeological and geomechanical data from the Whiteshell Research Area in the Canadian Shield, with simplification and generalization. Continental glaciological modelling of the Laurentide ice sheet through the last glacial cycle lasting approximately 100,000 years suggests that this site was glaciated at about 60 ka and between about 22.5 ka and 11 ka before present with maximum ice sheet thickness reaching 2,500 m and maximum basal water pressure head reaching 2000 m. The ice-sheet/drainage model was scaled down to generate spatially and temporally variable hydraulic and mechanical glaciated surface boundary conditions for site-scale subsurface HM modelling and permafrost modelling. Under extreme periglacial conditions permafrost was able to develop down to the assumed 500-m repository horizon. Two- and three-dimensional coupled HM finite-element simulations indicate: during ice-sheet advance there is rapid rise in hydraulic head, high transient hydraulic gradients and high groundwater velocities 2-3 orders of magnitude higher than under nonglacial conditions; surface water recharges deeper

  13. The glacial cycles and cosmic rays

    CERN Document Server

    Kirkby, Jasper; Müller, R A

    2004-01-01

    The cause of the glacial cycles remains a mystery. The origin is widely accepted to be astronomical since paleoclimatic archives contain strong spectral components that match the frequencies of Earth's orbital modulation. Milankovitch insolation theory contains similar frequencies and has become established as the standard model of the glacial cycles. However, high precision paleoclimatic data have revealed serious discrepancies with the Milankovitch model that fundamentally challenge its validity and re-open the question of what causes the glacial cycles. We propose here that the ice ages are initially driven not by insolation cycles but by cosmic ray changes, probably through their effect on clouds. This conclusion is based on a wide range of evidence, including results presented here on speleothem growth in caves in Austria and Oman, and on a record of cosmic ray flux over the past 220 kyr obtained from the 10Be composition of deep-ocean sediments.

  14. Links between Patagonian Ice Sheet fluctuations and Antarctic dust variability during the last glacial period (MIS 4-2)

    Science.gov (United States)

    Kaiser, Jérôme; Lamy, Frank

    2010-06-01

    Antarctic and Greenland ice-core records reveal large fluctuations of dust input on both orbital and millennial time-scales with potential global climate implications. At least during glacial periods, the Antarctic dust fluctuations appear to be largely controlled by environmental changes in southern South America. We compare dust flux records from two Antarctic ice-cores to variations in the composition of the terrigenous supply at ODP Site 1233 located off southern Chile and known to record fluctuations in the extent of the northern part of the Patagonian ice-sheet (NPIS) during the last glacial period (Marine Isotope Stage, MIS, 4 to 2). Within age uncertainties, millennial-scale glacial advances (retreats) of the NPIS correlate to Antarctic dust maxima (minima). In turn, NPIS fluctuations were closely related to offshore sea surface temperature (SST) changes. This pattern suggests a causal link involving changes in temperature, in rock flour availability, in latitudinal extensions of the westerly winds and in foehn winds in the southern Pampas and Patagonia. We further suggest that the long-term trend of dust accumulation is partly linked to the sea-level related changes in the size if the Patagonian source area due to the particular morphology of the Argentine shelf. We suggest that sea-level drops at the beginning of MIS 4 and MIS 2 were important for long-term dust increases, while changes in the Patagonian dust source regions primarily control the early dust decrease during the MIS 4/3 transition and Termination 1.

  15. Recent glacier retreat and climate trends in Cordillera Huaytapallana, Peru

    Science.gov (United States)

    López-Moreno, J. I.; Fontaneda, S.; Bazo, J.; Revuelto, J.; Azorin-Molina, C.; Valero-Garcés, B.; Morán-Tejeda, E.; Vicente-Serrano, S. M.; Zubieta, R.; Alejo-Cochachín, J.

    2014-01-01

    We analyzed 19 annual Landsat Thematic Mapper images from 1984 to 2011 to determine changes of the glaciated surface and snow line elevation in six mountain areas of the Cordillera Huaytapallana range in Peru. In contrast to other Peruvian mountains, glacier retreat in these mountains has been poorly documented, even though this is a heavily glaciated area. These glaciers are the main source of water for the surrounding lowlands, and melting of these glaciers has triggered several outburst floods. During the 28-year study period, there was a 55% decrease in the surface covered by glaciers and the snowline moved upward in different regions by 93 to 157 m. Moreover, several new lakes formed in the recently deglaciated areas. There was an increase in precipitation during the wet season (October-April) over the 28-year study period. The significant increase in maximum temperatures may be related to the significant glacier retreat in the study area. There were significant differences in the wet season temperatures during El Niño (warmer) and La Niña (colder) years. Although La Niña years were generally more humid than El Niño years, these differences were not statistically significant. Thus, glaciers tended to retreat at a high rate during El Niño years, but tended to be stable or increase during La Niña years, although there were some notable deviations from this general pattern. Climate simulations for 2021 to 2050, based on the most optimistic assumptions of greenhouse gas concentrations, forecast a continuation of climate warming at the same rate as documented here. Such changes in temperature might lead to a critical situation for the glaciers of the Cordillera Huaytapallana, and may significantly impact the water resources, ecology, and natural hazards of the surrounding areas.

  16. Risk factors for tuberculosis treatment failure, default, or relapse and outcomes of retreatment in Morocco.

    Science.gov (United States)

    Dooley, Kelly E; Lahlou, Ouafae; Ghali, Iraqi; Knudsen, Janine; Elmessaoudi, My Driss; Cherkaoui, Imad; El Aouad, Rajae

    2011-02-28

    Patients with tuberculosis require retreatment if they fail or default from initial treatment or if they relapse following initial treatment success. Outcomes among patients receiving a standard World Health Organization Category II retreatment regimen are suboptimal, resulting in increased risk of morbidity, drug resistance, and transmission.. In this study, we evaluated the risk factors for initial treatment failure, default, or early relapse leading to the need for tuberculosis retreatment in Morocco. We also assessed retreatment outcomes and drug susceptibility testing use for retreatment patients in urban centers in Morocco, where tuberculosis incidence is stubbornly high. Patients with smear- or culture-positive pulmonary tuberculosis presenting for retreatment were identified using clinic registries in nine urban public clinics in Morocco. Demographic and outcomes data were collected from clinical charts and reference laboratories. To identify factors that had put these individuals at risk for failure, default, or early relapse in the first place, initial treatment records were also abstracted (if retreatment began within two years of initial treatment), and patient characteristics were compared with controls who successfully completed initial treatment without early relapse. 291 patients presenting for retreatment were included; 93% received a standard Category II regimen. Retreatment was successful in 74% of relapse patients, 48% of failure patients, and 41% of default patients. 25% of retreatment patients defaulted, higher than previous estimates. Retreatment failure was most common among patients who had failed initial treatment (24%), and default from retreatment was most frequent among patients with initial treatment default (57%). Drug susceptibility testing was performed in only 10% of retreatment patients. Independent risk factors for failure, default, or early relapse after initial treatment included male gender (aOR = 2.29, 95% CI 1

  17. Geochemical Weathering in Glacial and Proglacial Environments

    Science.gov (United States)

    Tranter, M.

    2003-12-01

    It seems counterintuitive that chemical erosion in glaciated regions proceeds at rates comparable to those of temperate catchments with comparable specific runoff (Anderson et al., 1997). All the usual factors that are associated with elevated rates of chemical weathering ( Drever, 1988, 1994), such as water, soil, and vegetation, are either entirely absent or absent for much of the year. For example, glaciated regions are largely frozen for significant periods each year, the residence time of liquid water in the catchment is low ( Knight, 1999), there are thin, skeletal soils at best, and vegetation is either absent or limited ( French, 1997). Other chapters in this volume have highlighted how these factors are important in other, more temperate and tropical environments. Even so, chemical erosion rates in glaciated terrain are usually near to or greater than the continental average ( Sharp et al., 1995; Wadham et al., 1997; Hodson et al., 2000). This is because glaciated catchments usually have high specific runoff, there are high concentrations of freshly comminuted rock flour, which is typically silt sized and coated with microparticles, and adsorbed organic matter or surface precipitates that may hinder water-rock interactions are largely absent ( Tranter, 1982). In short, the rapid flow of water over fine-grained, recently crushed, reactive mineral surfaces maximizes both the potential rates of chemical weathering and chemical erosion.A range of both lab- and field-based studies of glacial chemical weathering have been undertaken, mainly on the smaller glaciers of Continental Europe (e.g., Brown et al., 1993a, b), Svalbard (e.g., Hodson et al., 2002), and North America (e.g., Anderson et al., 2000). The field-based studies typically generate hydrographs of glacier runoff, which show a characteristic diurnal cycle during summer in low latitudes ( Figure 1), and more subdued diurnal cycles at high latitudes (Figure 2 and Figure 3). The concentration of ions in

  18. Retreatment of Recurrent Cystic Craniopharyngioma With Chromic Phosphorus P 32

    Science.gov (United States)

    Kumar, P.P.; Good, R.R.; Skultety, F.M.; Jones, E.O.; Chu, W.K.

    1986-01-01

    A cystic craniopharyngioma in a two-year-old boy recurred six months after surgery and postoperative external-beam radiotherapy. Successful retreatment was accomplished with radioisotope injection of 0.5 mCi of chromic phosphorus P 32 into the intracranial cyst, which delivered approximately 300.00 Gy to the cyst wall. The patient's symptoms were relieved, and he is without evidence of disease or cystic fluid accumulation four years after intracavitary 32P irradiation. ImagesFigure 1Figure 2Figure 3 PMID:3735454

  19. The solutions to your problems in endodontic retreatment and microsurgery

    Directory of Open Access Journals (Sweden)

    Leslie Ang

    2016-06-01

    How to find the 4th canal in the upper Second molars in 60% of your patients, How to find the 4th canal in the upper First molars in 90% of your patients, How to retreat canals root filled with metal posts, fiber posts, gutta percha, hard canal cement & thermafils, How to remove fractured posts and posts cemented with resin cements. Understand why and how to perform Endodontic Surgery: How to treat large periapical lesions microsurgically, How to use the latest Ultrasonic technology under the Surgical Operating Microscope in all forms of microsurgery, Learn about the modern concepts in transplants, apicoectomies and intentional replantations.

  20. Got Dating: Outcomes of a Teen 4-H Relationship Retreat

    Directory of Open Access Journals (Sweden)

    Naomi Brower

    2012-03-01

    Full Text Available To support youth in developing healthy relationships, state and county staff collaborated to offer a statewide overnight teen retreat to teach health relationship skills. Evaluation of 64 youth participants from rural and urban counties found significant increases in posttest knowledge of relationship skills for both male and female youth. Youth also reported that the content was very helpful and worth repeating. Program success may be attributed to addressing the interesting and needed subject of dating relationships as well as involvement of state ambassador and collegiate 4-H members as teachers. Implications and replication suggestions are outlined.

  1. A first look at the ACER-SST dataset: Mapping the spatio-temporal variability of sea-surface temperatures in the last Glacial and the Holocene

    Science.gov (United States)

    Rehfeld, Kira; Laepple, Thomas; Bassinot, Franck; Daniau, Anne-Laure; Desprat, Stéphanie; Kim, Jung-Hyun; Fernanda Sánchez-Goñi, Maria; Harrison, Sandy

    2016-04-01

    Climate in the last Glacial was characterized by abrupt and large-scale changes around cold Heinrich-Events and warm Dansgaard-Oeschger excursions in the Northern high latitudes. The global repercussions of these periods of rapid dynamics are, to date, unconstrained. Here, we present a first statistical analysis of the global multi-proxy ACER (Abrupt Climate Changes and Environmental Responses) sea surface temperature dataset, spanning the last 80 thousand years, to investigate the spatial footprints of glacial climate dynamics. In a first step we evaluate the spatial and temporal variability throughout the Glacial period, and contrast them with that during the Holocene. In a second step we investigate to which extent a temporal synchroneity of extreme events during the Glacial is detectable in the proxy records, and analyze the reversibility of Glacial dynamics.

  2. Spiral computed tomography assessment of the efficacy of different rotary versus hand retreatment system

    OpenAIRE

    Neelam Mittal; Jyoti Jain

    2014-01-01

    Aims: The purpose of this study was to evaluate the efficacy of nickel-titanium rotary retreatment systems versus stainless steel hand retreatment system with or without solvent for gutta-percha removal during retreatment. Materials and Methods: Sixty extracted human mandibular molar teeth with single canal in a distal root was prepared with ProTaper rotary nickel-titanium files and obturated with gutta-percha and sealer. The teeth were randomly divided into six groups of 10 specimens in ...

  3. A ~20,000 year history of glacial variability in the tropical Andes recorded in lake sediments from the Cordillera Blanca, Peru

    Science.gov (United States)

    Stansell, N.; Rodbell, D. T.; Moy, C. M.

    2010-12-01

    Pro-glacial lake sediments from the Cordillera Blanca, Peru contain continuous records of climate variability spanning the Last Glacial Maximum to present day. Here we present results from two alpine lake basins in the Queshgue Valley (9.8°S, 77.3°W) that contain high-resolution records of clastic sediment deposition for the last ~20,000 years. Radiocarbon-dated sediment cores were scanned at 0.5 to 1.0 cm resolution using a profiling x-ray fluorescence scanner for major and minor element distributions. In addition, we measured down-core variations in magnetic susceptibility, organic carbon, biogenic silica and calcium carbonate. Samples of bedrock and sediments from glacial moraines in the Queshgue watershed were analyzed using an ICP-MS in order to fingerprint and trace the source of glacial sediments deposited in the lakes. The bedrock is dominated by a combination of granodiorite with high Sr concentrations and meta-sedimentary rocks with high Zr values. Because the glacial sediments proximal to the modern glacier terminus are composed mostly of the granodiorite end-member, we interpret changes in Sr and clastic sediment concentrations in the lake sediment profiles as proxies for past glacial variability. Preliminary results indicate that glaciers retreated soon after ~14,500 cal yr BP and remained less extensive during the remaining late Glacial Stage and early Holocene. Gradually increasing clastic sediments through the middle and late Holocene indicate that glaciers became progressively larger, or more erosive towards present day. However, this overall Holocene trend of increasing glacier extent was interrupted by multiple periods of centennial- to millennial-scale ice margin retreat. For example, relative peaks in clastic sediments occurred from ~14,500 to 6000, 5600 to 5000, 4600 to 4200, 3600 to 3200, 2800 to 2700, 2400 to 2200, 1750 to 1550, 1100 to 900 cal yr BP, and during the Little Ice Age (~700 to 50 cal yr BP), while periods of low clastic

  4. Restoration and recovery of hurricane-damaged mangroves using the knickpoint retreat effect and tides as dredging tools.

    Science.gov (United States)

    Bashan, Yoav; Moreno, Manuel; Salazar, Bernardo G; Alvarez, Leonardo

    2013-02-15

    In 2001, a hurricane moved a large sand dune, blocking the sole outlet channel of a mangrove. In the absence of daily tidal flow, the two ponds containing the mangrove vegetation evaporated, the secondary drainage channels were lost, and a salt crust formed on the bed of the ponds. The mangrove lost most of its trees and the remaining suffered from osmotic shock that led to defoliation. Restoration involved creating a knickpoint retreat (waterfall retreat effect) and tidal flow as a dredging mechanism to restore the outlet and form secondary channels in the ponds. During a very low tide, we deepened the mouth of the outlet channel by 1 m below high tide level to form a small waterfall when high tides receded. During successive tides, this one-step knickpoint deteriorated and formed a series of low rapids. With a steep gradient, the rapids retreated upstream into the ponds, first reopening the outlet channel and then carving new secondary channels in the pond mud flat. The excavation process of the outlet channel was repeated three times and was sufficient to effectively improve the hydrology of the entire pond system; allowing adequate flooding and draining of the mangrove ponds. Hydrology analysis tested by the Engelund-Hansen sediment transport formula established that the output of sediment from the ecosystem is greater than the input of sand into the mangroves. This is keeping the main channel continuously open. After eight years, tidal flow continues to keep the channels open; the salt crust has disappeared; the trees have recovered, and a large area of new vegetation has emerged. Copyright © 2012 Elsevier Ltd. All rights reserved.

  5. Modeled seasonality of glacial abrupt climate events

    NARCIS (Netherlands)

    Flueckiger, J.; Knutti, R.; White, J.W.C.; Renssen, H.

    2008-01-01

    Greenland ice cores, as well as many other paleo-archives from the northern hemisphere, recorded a series of 25 warm interstadial events, the so-called Dansgaard-Oeschger (D-O) events, during the last glacial period. We use the three-dimensional coupled global ocean-atmosphere-sea ice model

  6. Glacial Cycles and ice-sheet modelling

    NARCIS (Netherlands)

    Oerlemans, J.

    1982-01-01

    An attempt is made to simulate the Pleistocene glacial cycles with a numerical model of the Northern Hemisphere ice sheets. This model treats the vertically-integrated ice flow along a meridian, including computation of bedrock adjustment and temperature distribution in the ice. Basal melt water is

  7. Expanding Greenland’s Glacial Record

    DEFF Research Database (Denmark)

    Bjørk, Anders Anker

    . On order to expand the glacial history of Greenland, this thesis explores physical and geological archives for evidence of the glaciers’ past response to climatic variations. Using aerial photographs, the dynamic history of the Greenland Ice Sheet is extended back to 1900 C.E. Glacier changes covering...

  8. Scientific retreats with 'speed dating': networking to stimulate new interdisciplinary translational research collaborations and team science.

    Science.gov (United States)

    Ranwala, Damayanthi; Alberg, Anthony J; Brady, Kathleen T; Obeid, Jihad S; Davis, Randal; Halushka, Perry V

    2017-02-01

    To stimulate the formation of new interdisciplinary translational research teams and innovative pilot projects, the South Carolina Clinical and Translational Research (SCTR) Institute (South Carolina Clinical and Translational Science Award, CTSA) initiated biannual scientific retreats with 'speed dating' networking sessions. Retreat themes were prioritized based on the following criteria; cross-cutting topic, unmet medical need, generation of novel technologies and methodologies. Each retreat begins with an external keynote speaker followed by a series of brief research presentations by local researchers focused on the retreat theme, articulating potential areas for new collaborations. After each session of presentations, there is a 30 min scientific 'speed dating' period during which the presenters meet with interested attendees to exchange ideas and discuss collaborations. Retreat attendees are eligible to compete for pilot project funds on the topic of the retreat theme. The 10 retreats held have had a total of 1004 participants, resulted in 61 pilot projects with new interdisciplinary teams, and 14 funded projects. The retreat format has been a successful mechanism to stimulate novel interdisciplinary research teams and innovative translational research projects. Future retreats will continue to target topics of cross-cutting importance to biomedical and public health research. Copyright © 2016 American Federation for Medical Research.

  9. The retreat of the world's mountain glaciers during recent decades

    International Nuclear Information System (INIS)

    Francou, B.; Vincent, Ch.

    2009-01-01

    Glaciers have become essential tools for measuring changes in the global environment. Here, we analyze glacier evolution during the last few decades and we wonder whether the observed retreat remains in the range of glacier fluctuations since the mid-Holocene. The main fluctuations experienced by glaciers during the last millenniums, and particularly during the Little Ice Age (-1300 A.D. to ∼1860 A.D.), are presented succinctly. The recent 1960-2005 period, well documented both by ground and remote sensing observations, shows important disparities between different massifs concerning the timing and the magnitude of glacier fluctuations, which depend on regional climatic conditions. The links between glacier mass balance evolution and climate is clear when approached from an energy balance but the variables commonly considered are only temperature and precipitation. The strong correlation existing between these variables and the mass balance evolution makes it possible to simulate glaciers in the future in function of distinct climatic scenarios. Modeling glacier retreat for the 21. century is an important goal because it will allow the impacts on water resource and sea level to be assessed. (authors)

  10. The Efficacy of the WaveOne Reciprocating File System versus the ProTaper Retreatment System in Endodontic Retreatment of Two Different Obturating Techniques.

    Science.gov (United States)

    Jorgensen, Ben; Williamson, Anne; Chu, Rene; Qian, Fang

    2017-06-01

    This ex vivo study aimed to evaluate the efficacy of retreating GuttaCore (Dentsply Tulsa Dental Specialties, Tulsa, OK) and warm vertically condensed gutta-percha in moderately curved canals with 2 different systems: ProTaper Universal Retreatment (Dentsply Tulsa Dental) and WaveOne (Dentsply Tulsa Dental). Eighty mesial roots of mandibular molars were used in this study. The mesiobuccal canals in each sample were prepared to length with the WaveOne Primary file (Dentsply Tulsa Dental). The canals were obturated with either a warm vertical approach or with GuttaCore and divided into 4 retreatment groups with the same mean root curvature: warm vertical retreated with ProTaper, warm vertical retreated with WaveOne, GuttaCore retreated with ProTaper, and GuttaCore retreated with WaveOne. The warm vertical groups were obturated using a continuous-wave technique of gutta-percha compaction, and the GuttaCore groups were obturated according to the manufacturer's instructions. After allowing sealer to set, each specimen was retreated with either the ProTaper Universal Retreatment files D1, D2, or D3 or with the WaveOne Primary file to the predetermined working length. The time taken to reach the working length was recorded. Instrument fatigue and failure were also evaluated. The post hoc 2-sample t tests showed that the overall mean total time taken to reach the working length for the warm vertical groups was significantly greater than that observed for the GuttaCore groups (mean = 87.11 vs 60.16 seconds, respectively), and the overall mean total time taken to reach the working length for WaveOne was significantly greater than that observed for ProTaper (99.09 vs 48.18 seconds, respectively). Two-way analysis of variance showed a significant main effect for both the type of experiment groups (F 1,76  = 15.32, P = .0002) and the type of retreatments (F 1,76  = 54.67, P file underwent more separations than the ProTaper files. The WaveOne Primary file underwent

  11. Luminescence dating of paleolake deltas and glacial deposits in Garwood Valley, Antarctica: Implications for climate, Ross ice sheet dynamics, and paleolake duration

    Science.gov (United States)

    Levy, Joseph S.; Rittenour, Tammy M.; Fountain, Andrew G.; O'Connor, Jim E.

    2017-01-01

    The formation of perched deltas and other lacustrine deposits in the McMurdo Dry Valleys of Antarctica is widely considered to be evidence of valley-filling lakes dammed by the grounded Ross Sea ice sheet during the local Last Glacial Maximum, with lake drainage interpreted as a record of grounding line retreat. We used luminescence dating to determine the age of paleolake deltas and glacial tills in Garwood Valley, a coastal dry valley that opens to the Ross Sea. Luminescence ages are stratigraphically consistent with radiocarbon results from algal mats within the same delta deposits but suggest radiocarbon dates from lacustrine carbonates may overestimate deposit ages by thousands of years. Results suggest that late Holocene delta deposition into paleolake Howard in Garwood Valley persisted until ca. 3.5 ka. This is significantly younger than the date when grounded ice is thought to have retreated from the Ross Sea. Our evidence suggests that the local, stranded ice-cored till topography in Garwood Valley, rather than regional ice-sheet dynamics, may have controlled lake levels for some McMurdo Dry Valleys paleolakes. Age control from the supraglacial Ross Sea drift suggests grounding and up-valley advance of the Ross Sea ice sheet into Garwood valley during marine oxygen isotope stage (MIS) 4 (71–78 ka) and the local Last Glacial Maximum (9–10 ka). This work demonstrates the power of combining luminescence dating with existing radiocarbon data sets to improve understanding of the relationships among paleolake formation, glacial position, and stream discharge in response to climate change.

  12. Probabilistic estimation of dune retreat on the Gold Coast, Australia

    Science.gov (United States)

    Palmsten, Margaret L.; Splinter, Kristen D.; Plant, Nathaniel G.; Stockdon, Hilary F.

    2014-01-01

    Sand dunes are an important natural buffer between storm impacts and development backing the beach on the Gold Coast of Queensland, Australia. The ability to forecast dune erosion at a prediction horizon of days to a week would allow efficient and timely response to dune erosion in this highly populated area. Towards this goal, we modified an existing probabilistic dune erosion model for use on the Gold Coast. The original model was trained using observations of dune response from Hurricane Ivan on Santa Rosa Island, Florida, USA (Plant and Stockdon 2012. Probabilistic prediction of barrier-island response to hurricanes, Journal of Geophysical Research, 117(F3), F03015). The model relates dune position change to pre-storm dune elevations, dune widths, and beach widths, along with storm surge and run-up using a Bayesian network. The Bayesian approach captures the uncertainty of inputs and predictions through the conditional probabilities between variables. Three versions of the barrier island response Bayesian network were tested for use on the Gold Coast. One network has the same structure as the original and was trained with the Santa Rosa Island data. The second network has a modified design and was trained using only pre- and post-storm data from 1988-2009 for the Gold Coast. The third version of the network has the same design as the second version of the network and was trained with the combined data from the Gold Coast and Santa Rosa Island. The two networks modified for use on the Gold Coast hindcast dune retreat with equal accuracy. Both networks explained 60% of the observed dune retreat variance, which is comparable to the skill observed by Plant and Stockdon (2012) in the initial Bayesian network application at Santa Rosa Island. The new networks improved predictions relative to application of the original network on the Gold Coast. Dune width was the most important morphologic variable in hindcasting dune retreat, while hydrodynamic variables, surge and

  13. Writing Retreat Increases Productivity And Community For Women Geoscientists

    Science.gov (United States)

    O'Connell, S.; Holmes, M.

    2011-12-01

    Five, weeklong geoscientist writing retreats have been completed with an NSF ADANCE PAID grant. During the five nights and four and a half days, eight to twenty-four academics have gathered in a rural setting outside of Boston to get to focus on writing papers and proposals while getting to know each other. Participants range in age and experience from graduate students to emeritus professors. Over twenty papers and proposals acknowledge their production, in part to this writing retreat. Impact extends beyond papers as informal mentoring and discussions at meals and in the evenings centers on succeeding in academia. Research and teaching are foremost in the conversation. Post-docs learn strategies for applying for jobs and grants, and senior professors discuss strategies for working with academic administrations, running departments and mentoring students. They also learn new technologies and perspectives from younger participants. Particularly helpful are discussions on work-life balance. Networking opportunities extend beyond the retreat as participants join each other at their home institutions to give seminars, develop research projects and mentor each other's students. All weeks follow the same format. Participants arrive Sunday and meet during an evening welcome reception. Monday is devoted to writing. Tuesday a writing coach is available. In the morning, using examples from the scientific literature, she discusses strategies and techniques for writing clearly at a group session. During the afternoon, participants work with the coach individually or in small groups to improve their own writing projects. Wednesday evening a skill session is offered on a topic of interest. These have included undergraduate research, NSF funding, productive techniques for dealing with conflict, and generational characteristics and attitudes, which can hamper communication. A Thursday evening wrap-up session prepares participants for Friday's departure. We believe that this model

  14. The amount of glacial erosion of the bedrock

    International Nuclear Information System (INIS)

    Paasse, Tore

    2004-11-01

    The purpose of this study is to estimate an upper bound for the average erosion of fresh bedrock that can reasonably be expected during a glacial period or a single glaciation. The study is based on the assumption that classic sediments, formed by Scandinavian ice erosion during the Quaternary period, still exist within the formerly glaciated area or its periphery. The volume of these sediments thus constitutes the maximum average glacial erosion of bedrock within this area. This volume is calculated by estimating the thickness of the minerogenic Quaternary from well data in Sweden and Denmark and from seismic measurements in adjacent sea areas. The average thickness of the Quaternary deposits and other reogolith in the investigated area was estimated to 16 m. Assuming that the whole volume is the result of glacial erosion of fresh bedrock this corresponds to 12 m depth. However, a great part of the sediments may consist of glacially redistributed Tertiary regolith. As the amount of Tertiary regolith is uncertain the estimated maximum average glacial erosion rate in fresh bedrock is uncertain, and assuming that the total sediment volume is the result of glacial erosion leads to an overestimation of the glacial erosion depth. Considering this, the average glacial erosion during a full glacial period has been estimated to between 0.2 m and 4 m. If the extremes in the made assumptions are excluded the glacial erosion during a glacial cycle can be estimated to about 1 m

  15. The amount of glacial erosion of the bedrock

    Energy Technology Data Exchange (ETDEWEB)

    Paasse, Tore [Geological Survey of Sweden, Uppsala (Sweden)

    2004-11-01

    The purpose of this study is to estimate an upper bound for the average erosion of fresh bedrock that can reasonably be expected during a glacial period or a single glaciation. The study is based on the assumption that classic sediments, formed by Scandinavian ice erosion during the Quaternary period, still exist within the formerly glaciated area or its periphery. The volume of these sediments thus constitutes the maximum average glacial erosion of bedrock within this area. This volume is calculated by estimating the thickness of the minerogenic Quaternary from well data in Sweden and Denmark and from seismic measurements in adjacent sea areas. The average thickness of the Quaternary deposits and other reogolith in the investigated area was estimated to 16 m. Assuming that the whole volume is the result of glacial erosion of fresh bedrock this corresponds to 12 m depth. However, a great part of the sediments may consist of glacially redistributed Tertiary regolith. As the amount of Tertiary regolith is uncertain the estimated maximum average glacial erosion rate in fresh bedrock is uncertain, and assuming that the total sediment volume is the result of glacial erosion leads to an overestimation of the glacial erosion depth. Considering this, the average glacial erosion during a full glacial period has been estimated to between 0.2 m and 4 m. If the extremes in the made assumptions are excluded the glacial erosion during a glacial cycle can be estimated to about 1 m.

  16. Simple tool for the rapid, automated quantification of glacier advance/retreat observations using multiple methods

    Science.gov (United States)

    Lea, J.

    2017-12-01

    The quantification of glacier change is a key variable within glacier monitoring, with the method used potentially being crucial to ensuring that data can be appropriately compared with environmental data. The topic and timescales of study (e.g. land/marine terminating environments; sub-annual/decadal/centennial/millennial timescales) often mean that different methods are more suitable for different problems. However, depending on the GIS/coding expertise of the user, some methods can potentially be time consuming to undertake, making large-scale studies problematic. In addition, examples exist where different users have nominally applied the same methods in different studies, though with minor methodological inconsistencies in their approach. In turn, this will have implications for data homogeneity where regional/global datasets may be constructed. Here, I present a simple toolbox scripted in a Matlab® environment that requires only glacier margin and glacier centreline data to quantify glacier length, glacier change between observations, rate of change, in addition to other metrics. The toolbox includes the option to apply the established centreline or curvilinear box methods, or a new method: the variable box method - designed for tidewater margins where box width is defined as the total width of the individual terminus observation. The toolbox is extremely flexible, and has the option to be applied as either Matlab® functions within user scripts, or via a graphical user interface (GUI) for those unfamiliar with a coding environment. In both instances, there is potential to apply the methods quickly to large datasets (100s-1000s of glaciers, with potentially similar numbers of observations each), thus ensuring large scale methodological consistency (and therefore data homogeneity) and allowing regional/global scale analyses to be achievable for those with limited GIS/coding experience. The toolbox has been evaluated against idealised scenarios demonstrating its accuracy, while feedback from undergraduate students who have trialled the toolbox is that it is intuitive and simple to use. When released, the toolbox will be free and open source allowing users to potentially modify, improve and expand upon the current version.

  17. Relative timing of last glacial maximum and late-glacial events in the central tropical Andes

    Science.gov (United States)

    Bromley, Gordon R. M.; Schaefer, Joerg M.; Winckler, Gisela; Hall, Brenda L.; Todd, Claire E.; Rademaker, Kurt M.

    2009-11-01

    Whether or not tropical climate fluctuated in synchrony with global events during the Late Pleistocene is a key problem in climate research. However, the timing of past climate changes in the tropics remains controversial, with a number of recent studies reporting that tropical ice age climate is out of phase with global events. Here, we present geomorphic evidence and an in-situ cosmogenic 3He surface-exposure chronology from Nevado Coropuna, southern Peru, showing that glaciers underwent at least two significant advances during the Late Pleistocene prior to Holocene warming. Comparison of our glacial-geomorphic map at Nevado Coropuna to mid-latitude reconstructions yields a striking similarity between Last Glacial Maximum (LGM) and Late-Glacial sequences in tropical and temperate regions. Exposure ages constraining the maximum and end of the older advance at Nevado Coropuna range between 24.5 and 25.3 ka, and between 16.7 and 21.1 ka, respectively, depending on the cosmogenic production rate scaling model used. Similarly, the mean age of the younger event ranges from 10 to 13 ka. This implies that (1) the LGM and the onset of deglaciation in southern Peru occurred no earlier than at higher latitudes and (2) that a significant Late-Glacial event occurred, most likely prior to the Holocene, coherent with the glacial record from mid and high latitudes. The time elapsed between the end of the LGM and the Late-Glacial event at Nevado Coropuna is independent of scaling model and matches the period between the LGM termination and Late-Glacial reversal in classic mid-latitude records, suggesting that these events in both tropical and temperate regions were in phase.

  18. An improved active contour model for glacial lake extraction

    Science.gov (United States)

    Zhao, H.; Chen, F.; Zhang, M.

    2017-12-01

    Active contour model is a widely used method in visual tracking and image segmentation. Under the driven of objective function, the initial curve defined in active contour model will evolve to a stable condition - a desired result in given image. As a typical region-based active contour model, C-V model has a good effect on weak boundaries detection and anti noise ability which shows great potential in glacial lake extraction. Glacial lake is a sensitive indicator for reflecting global climate change, therefore accurate delineate glacial lake boundaries is essential to evaluate hydrologic environment and living environment. However, the current method in glacial lake extraction mainly contains water index method and recognition classification method are diffcult to directly applied in large scale glacial lake extraction due to the diversity of glacial lakes and masses impacted factors in the image, such as image noise, shadows, snow and ice, etc. Regarding the abovementioned advantanges of C-V model and diffcults in glacial lake extraction, we introduce the signed pressure force function to improve the C-V model for adapting to processing of glacial lake extraction. To inspect the effect of glacial lake extraction results, three typical glacial lake development sites were selected, include Altai mountains, Centre Himalayas, South-eastern Tibet, and Landsat8 OLI imagery was conducted as experiment data source, Google earth imagery as reference data for varifying the results. The experiment consequence suggests that improved active contour model we proposed can effectively discriminate the glacial lakes from complex backgound with a higher Kappa Coefficient - 0.895, especially in some small glacial lakes which belongs to weak information in the image. Our finding provide a new approach to improved accuracy under the condition of large proportion of small glacial lakes and the possibility for automated glacial lake mapping in large-scale area.

  19. Comparative evaluation of debris extruded apically by using, Protaper retreatment file, K3 file and H-file with solvent in endodontic retreatment

    Directory of Open Access Journals (Sweden)

    Chetna Arora

    2012-01-01

    Full Text Available Aim: The aim of this study was to evaluate the apical extrusion of debris comparing 2 engine driven systems and hand instrumentation technique during root canal retreatment. Materials and Methods: Forty five human permanent mandibular premolars were prepared using the step-back technique, obturated with gutta-percha/zinc oxide eugenol sealer and cold lateral condensation technique. The teeth were divided into three groups: Group A: Protaper retreatment file, Group B: K3, file Group C: H-file with tetrachloroethylene. All the canals were irrigated with 20ml distilled water during instrumentation. Debris extruded along with the irrigating solution during retreatment procedure was carefully collected in preweighed Eppendorf tubes. The tubes were stored in an incubator for 5 days, placed in a desiccator and then re-weighed. Weight of dry debris was calculated by subtracting the weight of the tube before instrumentation and from the weight of the tube after instrumentation. Data was analyzed using Two Way ANOVA and Post Hoc test. Results : There was statistically significant difference in the apical extrusion of debris between hand instrumentation and protaper retreatment file and K3 file. The amount of extruded debris caused by protaper retreatment file and K3 file instrumentation technique was not statistically significant. All the three instrumentation techniques produced apically extruded debris and irrigant. Conclusion: The best way to minimize the extrusion of debris is by adapting crown down technique therefore the use of rotary technique (Protaper retreatment file, K3 file is recommended.

  20. Efficacy of two rotary retreatment systems in removing Gutta-percha and sealer during endodontic retreatment with or without solvent: A comparative in vitro study.

    Science.gov (United States)

    Bhagavaldas, Moushmi Chalakkarayil; Diwan, Abhinav; Kusumvalli, S; Pasha, Shiraz; Devale, Madhuri; Chava, Deepak Chowdary

    2017-01-01

    The aim of this in vitro study was to compare the efficacy of two retreatment rotary systems in the removal of Gutta-percha (GP) and sealer from the root canal walls with or without solvent. Forty-eight extracted human mandibular first premolars were prepared and obturated with GP and AH Plus sealer. Samples were then randomly divided into four groups. Group I was retreated with MtwoR rotary system without solvent, Group II was retreated with MtwoR rotary system with Endosolv R as the solvent, Group III with D-RaCe rotary system without solvent, and Group IV with D-RaCe rotary system and Endosolv R solvent. The cleanliness of canal walls was determined by stereomicroscope (×20) and AutoCAD software. Kruskal-Wallis test and Mann-Whitney U-test were used to compare the data. Results showed that none of the retreatment systems used in this study was able to completely remove the root canal filling material. D-RaCe with or without solvent showed significantly ( P > 0.05) less filling material at all levels compared to MtwoR with/without solvent. Within the limitation of the current study, D-RaCe rotary retreatment system is more effective in removing filling material from root canal walls when compared to MtwoR rotary retreatment system.

  1. Glacial lakes in South Tyrol: distribution, evolution and potential for GLOFs

    Science.gov (United States)

    Schug, Marie-Claire; Mergili, Martin

    2017-04-01

    All over the world glaciers are currently retreating, leading to the formation or growth of glacial lakes. Some of these lakes are susceptible to sudden drainage. In order to assess the danger of glacial lake outburst floods (GLOFs) in South Tyrol in the Italian Alps, we present (i) an inventory of lakes, (ii) an analysis of the development of selected glacial lakes since 1945, and (iii) the susceptibility to and the possible impact areas of GLOFs. The inventory includes 1010 lakes that are larger than 250 m2 at an elevation above 2000 m asl, most of them of glacial origin. These lakes are mapped manually from orthophotos. Apart from collecting information on the spatial distribution of these lakes, the inventory lists dam material, glacier contact, and further parameters. 89% of the lakes in the investigation area are impounded by bedrock, whereas 93% of the lakes are detached from the associated glacier. The majority of lakes is small to medium sized (selected lakes are analyzed in detail in the field and from multi-temporal orthophotos, including the development of lake size and surroundings in the period since 1945. The majority of the selected lakes, however, was first recorded on orthophotos from the early 1980s. Eight of ten lakes grew significantly in that period. But when the lakes detached from the glacier until the early 2000s, the growth slowed down or ceased. Based on the current development of the selected lakes we conclude that the close surroundings of these lakes have stabilised and the lakes' susceptibility to an outburst has thus decreased. We further conduct broad-scale analyses of the susceptibility of the mapped lakes to GLOFs, and of the potential reach of possible GLOFs. The tool r.glachaz is used to determine the potentially dangerous lakes. Even though some few lakes require closer attention, the overall susceptibility to GLOFs in South Tyrol is relatively low, as most lakes are impounded by bedrock. In some cases, GLOFs caused by impact

  2. Patients' perceptions, treatment need, and complexity of orthodontic re-treatment

    NARCIS (Netherlands)

    Ren, Yijin; Boxum, Christo; Sandham, John

    The aim of the present study was to investigate the subjective perception and objective treatment need and complexity of patients seeking orthodontic re-treatment. One hundred subjects (66 females, 34 males, age 26.7+/-8.2 years) seeking re-treatment were asked to complete a questionnaire which was

  3. Quantification of glacial effects on radionuclide transport: transport sensitivity studies for SKI's SITE-94

    International Nuclear Information System (INIS)

    King-Clayton, L.M.; Smith, P.A.; Dverstorp, B.

    1996-01-01

    Site-scale radionuclide transport calculations have been carried out for a hypothetical deep repository at the Aespoe site, southeast Sweden. The work complements and utilizes results from regional-scale, variable density flow modelling in which the groundwater flow field is time-dependent, reflecting the impact of climate evolution over the next 130,000 years at the site. The climate evolution and its impacts are qualitatively described in the Central Climate Change Scenario, which specifies a hypothetical evolution of the local climate over the period modelled, including the periodic development of permafrost conditions and ice sheet advance and retreat. The work summarised here is complementary to the transport calculations undertaken as part of the SKI SITE-94 performance assessment project, with the specific objective of quantifying the impact of transient changes in flow direction and magnitude. The spatial evolution of 79 Se and 129 I contaminant plumes, released from the hypothetical repository under the influence of time-dependent (step-wise varying) head boundary conditions associated with ice sheet and permafrost development, is compared with that of a steady-state Base Case based on continuing present-day conditions. The results indicate that temporal changes in flow conditions due to future climate changes can have a significant effect on the transport of radionuclides from a source at depth. A case with high sub-ice sheet recharge and taliks (ie. gaps in the permafrost), creating groundwater fluxes up to an order of magnitude greater than the Base Case, has the greatest impact on radionuclide flux out of the geosphere, with a maximum 79 Se flux of over three orders of magnitude greater than that of the Base Case. The maximum 129 I flux is nearer one order of magnitude greater than the Base Case. In all cases modelled with time dependent boundary conditions, the greatest radionuclide fluxes occur towards the end of the main glacial periods (periods

  4. Factors contributing to the surgical retreatment of mandibular fractures

    Directory of Open Access Journals (Sweden)

    João Gualberto de Cerqueira Luz

    2013-06-01

    Full Text Available The purpose of this retrospective study was to evaluate contributing factors in patients requiring surgical retreatment of mandibular fractures. Of all the patients with mandibular fractures who were treated using internal fixation at a trauma hospital over a seven-year period, 20 patients (4.7% required a second surgery and thus composed the “reoperated” group. The control group comprised 42 consecutive patients with mandibular fractures who were treated at the same clinic and who healed without complications. Medical charts were reviewed for gender, age, substance abuse history, dental condition, etiology, location of fracture, degree of fragmentation, fracture exposure, teeth in the fracture line, associated facial fractures, polytrauma, time elapsed between trauma and initial treatment, surgical approach and fixation system. Statistical analyses were performed using the Statistical Package for Social Sciences (SPSS version 20.0; descriptive statistics and the chi-squared test were used to determine differences between groups. Significant differences in substance abuse (p = 0.006, dental condition (p < 0.001, location of fracture (p = 0.010, degree of fragmentation (p = 0.003 and fracture exposure (p < 0.001 were found. With regard to age and time elapsed between trauma and initial treatment, older patients (31.4 years, SD = 11.1 and a delay in fracture repair (19.1 days, SD = 18.7 were more likely to be associated with reoperation. It was concluded that substance abuse, age, dental condition, location of fracture, degree of fragmentation, fracture exposure and the time between trauma and initial treatment should be considered contributing factors to the occurrence of complications that require surgical retreatment of mandibular fractures.

  5. Are glacials "dry" - and in what sense?

    Science.gov (United States)

    Scheff, J.; Seager, R.; Coats, S.; Liu, H.

    2016-12-01

    Glacial maxima during the Pleistocene are generally thought to be arid on land, with a few regional exceptions. Recent work on future climate change, however, has found that different wetness-related variables have opposite-signed responses over large portions of the continents, belying simple ideas of local "drying" or "wetting" with global temperature change in models. Here, we show that this behavior extends to simulations of the Last Glacial Maximum as well: the continents are modeled to have generally wetter topsoils and higher values of standard climate-wetness metrics in the LGM than in the preindustrial, as well as generally lower precipitation and ubiquitously lower photosynthesis (likely driven by the low CO2), with the streamflow response falling in between. Is this model-derived view of the LGM an accurate one? Using a large community pollen and plant-fossil compilation, we confirm that LGM grasslands and open woodlands grew at many sites of present potential forest, seasonal or dry forests at many sites of present potential rain- or seasonal forests, and so forth, while changes in the opposite sense were extremely few and spatially confined. We show that this strongly resembles the simulated photosynthesis changes, but not the simulated streamflow or soil moisture changes. Meanwhile, published LGM lake-level estimates resemble the simulated streamflow changes, but not the photosynthesis changes. Thus, the last glacial does not appear to be systematically "dry" outside the high latitudes, but merely carbon-starved. Similarly, local findings of reduced or more open vegetation at the LGM (e.g. from pollen, carbon isotopes, or dustiness) do not indicate local "aridity" unless corroborating hydrological proxies are also found. Finally, this work suggests that glacial-era evidence of open vegetation with high lake levels (as in the eastern Mediterranean) is not odd or paradoxical, but entirely consistent with climate model output.

  6. Timing of maximum glacial extent and deglaciation from HualcaHualca volcano (southern Peru), obtained with cosmogenic 36Cl.

    Science.gov (United States)

    Alcalá, Jesus; Palacios, David; Vazquez, Lorenzo; Juan Zamorano, Jose

    2015-04-01

    Andean glacial deposits are key records of climate fluctuations in the southern hemisphere. During the last decades, in situ cosmogenic nuclides have provided fresh and significant dates to determine past glacier behavior in this region. But still there are many important discrepancies such as the impact of Last Glacial Maximum or the influence of Late Glacial climatic events on glacial mass balances. Furthermore, glacial chronologies from many sites are still missing, such as HualcaHualca (15° 43' S; 71° 52' W; 6,025 masl), a high volcano of the Peruvian Andes located 70 km northwest of Arequipa. The goal of this study is to establish the age of the Maximum Glacier Extent (MGE) and deglaciation at HualcaHualca volcano. To achieve this objetive, we focused in four valleys (Huayuray, Pujro Huayjo, Mollebaya and Mucurca) characterized by a well-preserved sequence of moraines and roches moutonnées. The method is based on geomorphological analysis supported by cosmogenic 36Cl surface exposure dating. 36Cl ages have been estimated with the CHLOE calculator and were compared with other central Andean glacial chronologies as well as paleoclimatological proxies. In Huayuray valley, exposure ages indicates that MGE occurred ~ 18 - 16 ka. Later, the ice mass gradually retreated but this process was interrupted by at least two readvances; the last one has been dated at ~ 12 ka. In the other hand, 36Cl result reflects a MGE age of ~ 13 ka in Mollebaya valley. Also, two samples obtained in Pujro-Huayjo and Mucurca valleys associated with MGE have an exposure age of 10-9 ka, but likely are moraine boulders affected by exhumation or erosion processes. Deglaciation in HualcaHualca volcano began abruptly ~ 11.5 ka ago according to a 36Cl age from a polished and striated bedrock in Pujro Huayjo valley, presumably as a result of reduced precipitation as well as a global increase of temperatures. The glacier evolution at HualcaHualca volcano presents a high correlation with

  7. Submarine glacial landforms and interactions with volcanism around Sub-Antarctic Heard and McDonald Islands

    Science.gov (United States)

    Picard, K.; Watson, S. J.; Fox, J. M.; Post, A.; Whittaker, J. M.; Lucieer, V.; Carey, R.; Coffin, M. F.; Hodgson, D.; Hogan, K.; Graham, A. G. C.

    2017-12-01

    Unravelling the glacial history of Sub-Antarctic islands can provide clues to past climate and Antarctic ice sheet stability. The glacial history of many sub-Antarctic islands is poorly understood, including the Heard and McDonald Islands (HIMI) located on the Kerguelen Plateau in the southern Indian Ocean. The geomorphologic development of HIMI has involved a combination of construction via hotspot volcanism and mechanical erosion caused by waves, weather, and glaciers. Today, the 2.5 km2 McDonald Islands are not glacierised; in contrast, the 368 km2 Heard Island has 12 major glaciers, some extending from the summit of 2813 m to sea level. Historical accounts from Heard Island suggest that the glaciers were more extensive in the 1850s to 1870s, and have retreated at least 12% (33.89 km2) since 1997. However, surrounding bathymetry suggests a much more extensive previous glaciation of the HIMI region that encompassed 9,585 km2, likely dating back at least to the Last Glacial Maximum (LGM) ca. 26.5 -19 ka. We present analyses of multibeam bathymetry and backscatter data, acquired aboard RV Investigator in early 2016, that support the previous existence of an extensive icecap. These data reveal widespread ice-marginal and subglacial features including moraines, over-deepened troughs, drumlins and crag-and-tails. Glacial landforms suggest paleo-ice flow directions and a glacial extent that are consistent with previously documented broad scale morphological features. We identify >660 iceberg keel scours in water depths ranging from 150 - 530 m. The orientations of the iceberg keel scours reflect the predominantly east-flowing Antarctic Circumpolar Current and westerly winds in the region. 40Ar/39Ar dating of volcanic rocks from submarine volcanoes around McDonald Islands suggests that volcanism and glaciation coincided. The flat-topped morphology of these volcanoes may result from lava-ice interaction or erosion by glaciers post eruption during a time of extensive ice

  8. Modelling end-glacial earthquakes at Olkiluoto

    International Nuclear Information System (INIS)

    Faelth, B.; Hoekmark, H.

    2011-02-01

    The objective of this study is to obtain estimates of the possible effects that post-glacial seismic events in three verified deformation zones (BFZ100, BFZ021/099 and BFZ214) at the Olkiluoto site may have on nearby fractures in terms of induced fracture shear displacement. The study is carried out by use of large-scale models analysed dynamically with the three dimensional distinct element code 3DEC. Earthquakes are simulated in a schematic way; large planar discontinuities representing earthquake faults are surrounded by a number of smaller discontinuities which represent rock fractures in which shear displacements potentially could be induced by the effects of the slipping fault. Initial stresses, based on best estimates of the present-day in situ stresses and on state-of-the-art calculations of glacially-induced stresses, are applied. The fault rupture is then initiated at a pre-defined hypocentre and programmed to propagate outward along the fault plane with a specified rupture velocity until it is arrested at the boundary of the prescribed rupture area. Fault geometries, fracture orientations, in situ stress model and material property parameter values are based on data obtained from the Olkiluoto site investigations. Glacially-induced stresses are obtained from state-of-the-art ice-crust/mantle finite element analyses. The response of the surrounding smaller discontinuities, i.e. the induced fracture shear displacement, is the main output from the simulations

  9. Incidence, outcomes, and risk factors for retreatment after wavefront-optimized ablations with PRK and LASIK.

    Science.gov (United States)

    Randleman, J Bradley; White, Alfred J; Lynn, Michael J; Hu, Michelle H; Stulting, R Doyle

    2009-03-01

    To analyze and compare retreatment rates after wavefront-optimized photorefractive keratectomy (PRK) and LASIK and determine risk factors for retreatment. A retrospective chart review was performed to identify patients undergoing PRK or LASIK with the wavefront-optimized WaveLight platform from January 2005 through December 2006 targeted for a piano outcome and to determine the rate and risk factors for retreatment surgery in this population. Eight hundred fifty-five eyes were analyzed, including 70 (8.2%) eyes with hyperopic refractions and 785 (91.8%) eyes with myopic refractions. After initial treatment, 72% of eyes were 20/20 or better and 99.5% were 20/40 or better. To improve uncorrected visual acuity, 54 (6.3%) eyes had retreatments performed. No significant differences in retreatment rates were noted based on age (P = .15), sex (P = .8), eye (P = .3), PRK versus LASIK (P = 1.0), room temperature (P = .1) or humidity (P = .9), and no correlation between retreatment rate and month or season of primary surgery (P = .4). There was no correlation between degree of myopia and retreatment rate. Eyes were significantly more likely to undergo retreatment if they were hyperopic (12.8% vs 6.0%, P = .006) or had astigmatism > or = 1.00 diopter (D) (9.1% vs 5.3%, P = .04). Retreatment rate was 6.3% with the WaveLight ALLEGRETTO WAVE excimer laser. This rate was not influenced by age, sex, corneal characteristics, or environmental factors. Eyes with hyperopic refractions or astigmatism > or = 1.00 D were more likely to undergo retreatment.

  10. New glacial evidences at the Talacasto paleofjord (Paganzo basin, W-Argentina) and its implications for the paleogeography of the Gondwana margin

    Science.gov (United States)

    Aquino, Carolina Danielski; Milana, Juan Pablo; Faccini, Ubiratan Ferrucio

    2014-12-01

    The Talacasto paleovalley is situated in the Central Precordillera of San Juan, Argentina, where upper Carboniferous-Permian rocks (Paganzo Group) rest on Devonian sandstones of the Punta Negra Formation. This outcrop is an excellent example of a glacial valley-fill sequence that records at least two high-frequency cycles of the advance and retreat of a glacier into the valley. The paleocurrent analysis shows transport predominantly to the south, indicating that at this site the ice flow differs from the other nearby paleovalleys. Evidence of the glacial origin of this valley can be seen in the glacial striae on the valley's sides, as well as the U-shape of the valley, indicated by very steep locally overhanging valley walls. Deglaciation is indicated by a set of retransported conglomerates deposited in a shallow-water environment followed by a transgressive succession, which suggests eustatic rise due to meltwater input to the paleofjord. The complete sedimentary succession records distinct stages in the evolution of the valley-fill, represented by seven stratigraphical units. These units are identified based on facies associations and their interpreted depositional setting. Units 1 to 5 show one cycle of deglaciation and unit 6 marks the beginning of a new cycle of glacier advance which is characterized by different types of glacial deposits. All units show evidence of glacial influence such as dropstones and striated clasts, which indicates that the glaciers were always present in the valley or in adjacent areas during sedimentation. The Talacasto paleofjord provides good evidence of the Late Paleozoic Gondwana glaciation in western Argentina and examples of sedimentary successions which have been interpreted as being deposited by a confined wet-based glacier in advance and retreat cycles, with eventual release of icebergs into the basin. The outcrop is also a key for reconstructing the local glacial paleogeography, and it suggests a new interpretation that is

  11. Post-glacial recolonization of the Great Lakes region by the common gartersnake (Thamnophis sirtalis) inferred from mtDNA sequences.

    Science.gov (United States)

    Placyk, John S; Burghardt, Gordon M; Small, Randall L; King, Richard B; Casper, Gary S; Robinson, Jace W

    2007-05-01

    Pleistocene events played an important role in the differentiation of North American vertebrate populations. Michigan, in particular, and the Great Lakes region, in general, were greatly influenced by the last glaciation. While several hypotheses regarding the recolonization of this region have been advanced, none have been strongly supported. We generated 148 complete ND2 mitochondrial DNA (mtDNA) sequences from common gartersnake (Thamnophis sirtalis) populations throughout the Great Lakes region to evaluate phylogeographic patterns and population structure and to determine whether the distribution of haplotypic variants is related to the post-Pleistocene retreat of the Wisconsinan glacier. The common gartersnake was utilized, as it is believed to have been one of the primary vertebrate invaders of the Great Lakes region following the most recent period of glacial retreat and because it has been a model species for a variety of evolutionary, ecological, behavioral, and physiological studies. Several genetically distinct evolutionary lineages were supported by both genealogical and molecular population genetic analyses, although to different degrees. The geographic distribution of the majority of these lineages is interpreted as reflecting post-glacial recolonization dynamics during the late Pleistocene. These findings generally support previous hypotheses of range expansion in this region.

  12. Changing Groundwater and Lake Storage in the Americas from the Last Glacial Maximum to the Present Day

    Science.gov (United States)

    Callaghan, K. L.; Wickert, A. D.; Michael, L.; Fan, Y.; Miguez-Macho, G.; Mitrovica, J. X.; Austermann, J.; Ng, G. H. C.

    2017-12-01

    Groundwater accounts for 1.69% of the globe's water storage - nearly the same amount (1.74%) that is stored in ice caps and glaciers. The volume of water stored in this reservoir has changed over glacial-interglacial cycles as climate warms and cools, sea level rises and falls, ice sheets advance and retreat, surface topography isostatically adjusts, and patterns of moisture transport reorganize. During the last deglaciation, over the past 21000 years, all of these factors contributed to profound hydrologic change in the Americas. In North America, deglaciation generated proglacial lakes and wetlands along the isostatically-depressed margin of the retreating Laurentide Ice Sheet, along with extensive pluvial lakes in the desert southwest. In South America, changing patterns of atmospheric circulation caused regional and time-varying wetting and drying that led to fluctuations in water table levels. Understanding how groundwater levels change in response to these factors can aid our understanding of the effects of modern climate change on groundwater resources. Using a model that incorporates temporally evolving climate, topography (driven by glacial isostatic adjustment), ice extent, sea level, and spatially varying soil properties, we present our estimates of changes in total groundwater storage in the Americas over the past 21000 years. We estimate depth to water table at 500-year intervals and at a 30-arcsecond resolution. This allows a comparative assessment of changing groundwater storage volumes through time. The model has already been applied to the present day and has proven successful in estimating modern groundwater depths at a broad scale (Fan et al., 2013). We also assess changing groundwater-fed lakes, and compare model-estimated lake sizes and locations to paleorecords of these lakes. Our data- and model-integrated look back at the terminal Pleistocene provides an estimate of groundwater variability under extreme climate change. Preliminary results

  13. CO{sub 2} and N{sub 2}O emissions in a soil chronosequence at a glacier retreat zone in Maritime Antarctica

    Energy Technology Data Exchange (ETDEWEB)

    Thomazini, A., E-mail: andre.thz@gmail.com [Department of Plant Production, Federal University of Espírito Santo, 29500-000 Alegre, Espírito Santo (Brazil); Mendonça, E.S., E-mail: eduardo.mendonca@ufes.br [Department of Plant Production, Federal University of Espírito Santo, 29500-000 Alegre, Espírito Santo (Brazil); Teixeira, D.B., E-mail: daniel.dbt@hotmail.com [FCAV/UNESP, Via de Acesso, Prof. Paulo Donato Castellane s/n, 14884-900 Jaboticabal, SP (Brazil); Almeida, I.C.C., E-mail: ivancarreiro@yahoo.com.br [Instituto Federal do Norte de Minas Gerais, Fazenda São Geraldo, s/n km. 06, 39480-000 Januária, Minas Gerais (Brazil); La Scala, N., E-mail: lascala@fcav.unesp.br [FCAV/UNESP, Via de Acesso, Prof. Paulo Donato Castellane s/n, 14884-900 Jaboticabal, SP (Brazil); Canellas, L.P., E-mail: lucianocanellas@gmail.com [UENF — Universidade Estadual do Norte Fluminense Darcy Ribeiro, Núcleo de Desenvolvimento de Insumos Biológicos para a Agricultura (NUDIBA), Av. Alberto Lamego, 2000, Campos dos Goytacazes 28013-602, Rio de Janeiro (Brazil); Spokas, K.A., E-mail: kurt.Spokas@ars.usda.gov [USDA-ARS, Soil and Water Management Unit, University of Minnesota — St. Paul, MN 55108 (United States); Milori, D.M.B.P., E-mail: debora.milori@embrapa.br [Embrapa Instrumentation Brazilian Agricultural Research Corporation, São Carlos, SP (Brazil); Turbay, C.V.G., E-mail: cturbay@gmail.com [Department of Geology, Federal University of Espírito Santo, 29500-000 Alegre, Espírito Santo (Brazil); and others

    2015-07-15

    Studies of C cycle alterations are extremely important to identify changes due to climate change, especially in the polar ecosystem. The objectives of this study were to (i) examine patterns of soil CO{sub 2}-C and N{sub 2}O-N emissions, and (ii) evaluate the quantity and quality of soil organic matter across a glacier retreat chronosequence in the Maritime Antarctica. Field measurements were carried out during January and February 2010 (summer season) along a retreating zone of the White Eagle Glacier, at King George Island, Maritime Antarctica. Soil samples (0–10 cm) were collected along a 500-m transect at regular intervals to determine changes in soil organic matter. Field CO{sub 2}-C emission measurements and soil temperature were carried out at regular intervals. In addition, greenhouse gas production potentials were assessed through 100 days laboratory incubations. Soils exposed for a longer time tended to have greater concentrations of soluble salts and possess sandier textures. Total organic C (3.59 g kg{sup −1}), total N (2.31 g kg{sup −1}) and labile C (1.83 g kg{sup −1}) tended to be lower near the glacier front compared with sites away from it, which is correlated with decreasing degree of humification of the soil organic matter with exposure time. Soil CO{sub 2}-C emissions tended to increase with distance from the glacier front. On average, the presence of vegetation increased CO{sub 2}-C emissions by 440%, or the equivalent of 0.633 g of CO{sub 2}-C m{sup −2} h{sup −1}. Results suggest that newly exposed landsurfaces undergo soil formation with increasing labile C input from vegetation, accompanied by increasing soil CO{sub 2}-C emissions. Despite the importance of exposure time on CO{sub 2}-C production and emissions, there was no similar trend in soil N{sub 2}O-N production potentials as a function of glacial retreat. For N{sub 2}O, instead, the maximum production occurred in sites with the first stages of vegetation growth

  14. Evidence of a low-latitude glacial buzzsaw: Progressive hypsometry reveals height-limiting glacial erosion in tropical mountain belts

    Science.gov (United States)

    Cunningham, M.; Stark, C. P.; Kaplan, M. R.; Schaefer, J. M.; Winckler, G.

    2017-12-01

    It has been widely demonstrated that glacial erosion limits the height of mid-latitude mountain ranges—a phenomenon commonly referred to as the "glacial buzzsaw." The strength of the buzzsaw is thought to diminish, or die out completely, at lower latitudes, where glacial landscapes occupy only a small part of mountain belts affected by Pleistocene glaciation. Here we argue that glacial erosion has actually truncated the rise of many tropical orogens. To elicit signs of height-limiting glacial erosion in the tropics, we employ a new take on an old tool: we identify transient geomorphic features by tracking the evolution of (sub)catchment hypsometry with increasing elevation above base level, a method we term "progressive hypsometry." In several tropical mountain belts, including the Central Range of Taiwan, the Talamanca of Costa Rica, the Finisterres of Papua New Guinea, and the Rwenzoris of East Africa, progressive hypsometry reveals transient landscapes perched at various elevations, but the highest of these transient features are consistently glacial landscapes near the lower limit of late-Pleistocene glacial equilibrium line altitude (ELA) fluctuation. We attribute this pattern to an efficient glacial buzzsaw. In many cases, these glacial landscapes are undergoing contemporary destruction by headward propagating, fluvially-driven escarpments. We deduce that a duel between glacial buzzcutting and fluvially-driven scarp propagation has been ongoing throughout the Pleistocene in these places, and that the preservation potential of tropical glacial landscapes is low. To this end, we have identified possible remnants of glacial landscapes in the final stages of scarp consumption, and use 3He surface exposure age dating of boulders and bedrock surfaces in two of these landscapes to constrain major geomorphic activity to before the onset of the Last Glacial Maximum. Our work points to a profound climatic influence on the evolution of these warm, tectonically active

  15. Safety of BTZ retreatment for patients with low-grade peripheral neuropathy during the initial treatment.

    Science.gov (United States)

    Vidisheva, Aleksandra P; Wang, James; Spektor, Tanya M; Bitran, Jacob D; Lutzky, Jose; Tabbara, Imad A; Ye, Joseph Z; Ailawadhi, Sikander; Stampleman, Laura V; Steis, Ronald G; Moezi, Mehdi M; Swift, Regina A; Maluso, Tina M; Udd, Kyle A; Eshaghian, Shahrooz; Nassir, Youram; Berenson, James R

    2017-10-01

    Neuropathy is an important complication that may limit treatment options for patients with multiple myeloma. Previous studies have focused on treatment efficacy and have shown that retreatment with bortezomib (BTZ) is an effective treatment option. The goal of this study was to focus on the clinical manifestations of peripheral neuropathy (PN) and to retrospectively compare the incidence and severity of PN between the initial BTZ regimen and upon retreatment. Furthermore, this study evaluated how certain factors affect BIPN, which will help determine what conditions should be considered prior to retreatment. Charts were reviewed from 93 patients who were retreated with a BTZ-containing regimen after previously being treated with this drug. Among the patients who developed PN, most patients in the study had low-grade neuropathy during the initial BTZ treatment (n = 52, 68%). The results showed no evidence of cumulative toxicity, and there was no significant difference in the incidence and severity of PN upon retreatment. Factors such as the presence of baseline PN, number of prior treatments, dose of BTZ, and comorbidities did not increase the severity of PN upon retreatment. The lapse of time between the two regimens also did not affect the severity of PN. The results suggest that retreatment with BTZ may be a feasible option, without additional risks of PN, for MM patients even with peripheral neuropathy during their initial treatment with this drug.

  16. Enhancing the research and publication efforts of health sciences librarians via an academic writing retreat.

    Science.gov (United States)

    Bullion, John W; Brower, Stewart M

    2017-10-01

    This case study describes the South Central Chapter of the Medical Library Association (SCC/MLA) initiative to develop an academic writing retreat for members who sought the necessary time and support to advance their research projects toward publication. SCC/MLA staged a dedicated writing retreat to coincide with the organization's 2012, 2013, and 2014 annual meetings. Each cohort met over two days to write and to workshop their peers' manuscripts. Organizers distributed an online survey one month after each retreat to evaluate attendees' perceptions. Three years' worth of writing retreats yielded fourteen peer-reviewed articles and one book chapter. Participants indicated that the retreat helped them meet or exceed their writing goals by offering protected time and a setting conducive to productivity. The format of the retreat is cost effective and easily adaptable for fellow professionals who wish to organize a formal event as a conference offering or simply support a writing group at their home institutions. In SCC/MLA, the retreat revitalized interest in writing and demystified the scholarly publication process.

  17. Is raised helicobacter pylori antibody titre enough to decide retreatment

    International Nuclear Information System (INIS)

    Bibi, S.; Ahmed, W.; Arif, A.; Alam, S.E.

    2011-01-01

    Background: Helicobacter pylori infection causes a rise in its antibodies which take almost a year to come to baseline following successful eradication treatment. Checking these values in between a year may give falsely high values and many patients may thus be over treated. Aims: To serially determine Helicobacter pylori antibody titres in patients after giving them triple therapy for H. pylori eradication and see how these values drop over time. Study type, Settings and duration: Longitudinal study conducted in Department of Gastroenterology and Hepatology, Pakistan Medical Research Council, Research Centre, Jinnah Post Graduate Medical Centre, Karachi, from May 2006 to April 2010. Subjects and Methods: Over the period of four years, 186 patients who were found positive for campylobacter like organism test during endoscopy were further tested for anti H. pylori IgG titre before being treated for H. pylori. Patients were given triple therapy comprising of Omeprazole (20 mg twice daily), Amoxicillin (1 gm twice daily) and Clarythromycin (500 mg twice daily) for a week and were followed at 1, 3, 6 and 12 months to check symptomatic relief and they were tested again for H.Pylori antibody titres. Data was collected on pre-designed proforma which included patient's demography, symptoms and diagnosis. Results: Out of 186 patients who had a positive campylobacter like organism test, 173 patients consented to participate in the study. Serology for H.Pylori was positive in 119(68%) cases. A decline in mean antibody titres was observed as 11%, 21.5%, 54.7% and 59.2% at 1, 3, 6 and 12 months respectively. Conclusions: Sensitivity of serology for diagnosing H. pylori infection is good but using these as a tool for monitoring response to treatment is doubtful. A slow drop in H.pylori antibodies was seen over 12 months and therefore, physicians are cautioned not to retreat the already treated cases till about one year post treatment. Policy message: H. pylori antibodies should

  18. Impact of Basal Conditions on Grounding-Line Retreat

    Science.gov (United States)

    Koellner, S. J.; Parizek, B. R.; Alley, R. B.; Muto, A.; Holschuh, N.; Nowicki, S.

    2017-12-01

    current grounding-line position. Mixed rheology beds tend to mimic the retreat of the higher-exponent bed, a behavior enhanced over bumps as the stabilizing ridges tap into ice from local valleys. Thus, accounting for variable basal conditions in ice-sheet model projections is critical for improving both the timing and magnitude of retreat.

  19. Role of CO2 and Southern Ocean winds in glacial abrupt climate change

    Directory of Open Access Journals (Sweden)

    M. Montoya

    2012-06-01

    Full Text Available The study of Greenland ice cores revealed two decades ago the abrupt character of glacial millennial-scale climate variability. Several triggering mechanisms have been proposed and confronted against growing proxy-data evidence. Although the implication of North Atlantic deep water (NADW formation reorganisations in glacial abrupt climate change seems robust nowadays, the final cause of these reorganisations remains unclear. Here, the role of CO2 and Southern Ocean winds is investigated using a coupled model of intermediate complexity in an experimental setup designed such that the climate system resides close to a threshold found in previous studies. An initial abrupt surface air temperature (SAT increase over the North Atlantic by 4 K in less than a decade, followed by a more gradual warming greater than 10 K on centennial timescales, is simulated in response to increasing atmospheric CO2 levels and/or enhancing southern westerlies. The simulated peak warming shows a similar pattern and amplitude over Greenland as registered in ice core records of Dansgaard-Oeschger (D/O events. This is accompanied by a strong Atlantic meridional overturning circulation (AMOC intensification. The AMOC strengthening is found to be caused by a northward shift of NADW formation sites into the Nordic Seas as a result of a northward retreat of the sea-ice front in response to higher temperatures. This leads to enhanced heat loss to the atmosphere as well as reduced freshwater fluxes via reduced sea-ice import into the region. In this way, a new mechanism that is consistent with proxy data is identified by which abrupt climate change can be promoted.

  20. Impact of ice melting on distribution of particulate sterols in glacial fjords of Chilean Patagonia

    Science.gov (United States)

    Gutiérrez, Marcelo H.; Riquelme, Pablo; Pantoja, Silvio

    2016-04-01

    We analyzed variability in abundance and composition of sterols in waters of the fjord adjacent to glacier Jorge Montt, one of the fastest retreated glaciers in Patagonian Icefields. The study was carried out between August 2012 and November 2013 under different meltwater scenarios. Distribution of sterols in surface and bottom waters was determined by Gas Chromatography coupled to Mass Spectrometry. Sterol concentration ranged from 18 to 1726 ng/L in surface and bottom waters and was positive correlated with chlorophyll-a concentration. Under high melting conditions in austral summer, surface meltwaters showed high concentrations of sterols and were dominated by methylene-cholesterol, a representative sterol of centric diatoms. In the area near open ocean and in austral autumn, winter and spring in proglacial fjord, lower sterol concentrations in surface waters were accompanied by other microalgae sterols and an increase in relative abundance of plant sterols, evidencing a different source of organic matter. In autumn, when high meltwater flux was also evidenced, presence of stanols and an uncommon tri-unsaturated sterol suggests influence of meltwaters in composition of sterols in the downstream fjord. We conclude that ice melting can modify sterol composition by setting conditions for development of a singular phytoplankton population able to thrive in surface meltwater and by carrying glacier organic matter into Patagonian glacial fjords. In projected ice melting scenario, these changes in organic matter quantity and quality can potentially affect availability of organic substrates for heterotrophic activity and trophic status of glacial fjords. This research was funded by COPAS Sur-Austral (PFB-31)

  1. A mechanism for overdeepenings of glacial valleys and fjords

    OpenAIRE

    Herman F.; Beaud F.; Champagnac J.-D.; Lemieux J.-M.; Sternai P.

    2011-01-01

    Most glacial erosion models assume that erosion rates are proportional to ice sliding velocity. While recent studies have shown that water plays a major role in modulating sliding velocities the impact it might have on erosion rates is still unclear. Here we incorporate subglacial hydrology into a glacial erosion model that is based on a sliding rule. Our results explicitly highlight that adding subglacial hydrology has profound impacts on the temporal and spatial patterns of glacial erosion....

  2. Modeled post-glacial landscape evolution at the southern margin of the Laurentide Ice Sheet: hydrological connection of uplands controls the pace and style of fluvial network expansion

    Science.gov (United States)

    Lai, J.; Anders, A. M.

    2017-12-01

    Landscapes of the US Midwest were repeatedly affected by the southern margin of the Laurentide Ice Sheet during the Quaternary. Glacial processes removed pre-glacial relief and left constructional landforms including low-relief till plains and high-relief moraines. As the ice retreated, meltwater was collected in subglacial or proglacial lakes and outburst floods of glacial lakes episodically carved deep valleys. These valleys provided the majority of post-glacial landscape relief. However, a significant fraction of the area of low-relief till plains was occupied by closed depressions and remained unconnected to these meltwater valleys. This area is referred to as non-contributing area (NCA) because it does not typically contribute surface runoff to stream networks. Decreasing fractions of NCA on older glacial landscape surfaces suggests that NCA becomes integrated into external drainage networks over time. We propose that this integration could occur via two different paths: 1) through capture of NCA as channel heads propagate into the upland or, 2) through erosion of a channel along a flow path that, perhaps intermittently, connects NCA to the external drainage network. We refer the two cases as "disconnected" and "connected" cases since the crucial difference between them is the hydrological connectivity on the upland. We investigate the differences in the evolution of channel networks and morphology in low relief landscapes under disconnected and connected drainage regimes through numerical simulations of fluvial and hillslope processes. We observe a substantially faster evolution of the channel network in the connected case than in the disconnected case. Modeled landscapes show that channel network in the connected case has longer, more sinuous channels. We also find that the connected case removes lower amounts of total mass than the disconnected case when the same degree of channel integration is achieved. Observed landscapes in US Midwest are more

  3. Simulation of the last glacial cycle with a coupled climate ice-sheet model of intermediate complexity

    Directory of Open Access Journals (Sweden)

    A. Ganopolski

    2010-04-01

    Full Text Available A new version of the Earth system model of intermediate complexity, CLIMBER-2, which includes the three-dimensional polythermal ice-sheet model SICOPOLIS, is used to simulate the last glacial cycle forced by variations of the Earth's orbital parameters and atmospheric concentration of major greenhouse gases. The climate and ice-sheet components of the model are coupled bi-directionally through a physically-based surface energy and mass balance interface. The model accounts for the time-dependent effect of aeolian dust on planetary and snow albedo. The model successfully simulates the temporal and spatial dynamics of the major Northern Hemisphere (NH ice sheets, including rapid glacial inception and strong asymmetry between the ice-sheet growth phase and glacial termination. Spatial extent and elevation of the ice sheets during the last glacial maximum agree reasonably well with palaeoclimate reconstructions. A suite of sensitivity experiments demonstrates that simulated ice-sheet evolution during the last glacial cycle is very sensitive to some parameters of the surface energy and mass-balance interface and dust module. The possibility of a considerable acceleration of the climate ice-sheet model is discussed.

  4. Extinction and ecological retreat in a community of primates

    Energy Technology Data Exchange (ETDEWEB)

    Crowley, B. E.; Godfrey, L. R.; Guilderson, T. P.; Zermeno, P.; Koch, P. L.; Dominy, N. J.

    2012-05-23

    The lemurs of Madagascar represent a prodigious adaptive radiation. At least 17 species ranging from 11 to 160 kg have become extinct during the past 2000 years. The effect of this loss on contemporary lemurs is unknown. The concept of competitive release favours the expansion of living species into vacant niches. Alternatively, factors that triggered the extinction of some species could have also reduced community-wide niche breadth. Here, we use radiocarbon and stable isotope data to examine temporal shifts in the niches of extant lemur species following the extinction of eight large-bodied species. We focus on southwestern Madagascar and report profound isotopic shifts, both from the time when now-extinct lemurs abounded and from the time immediately following their decline to the present. Unexpectedly, the past environments exploited by lemurs were drier than the protected (albeit often degraded) riparian habitats assumed to be ideal for lemurs today. Neither competitive release nor niche contraction can explain these observed trends. We develop an alternative hypothesis: ecological retreat, which suggests that factors surrounding extinction may force surviving species into marginal or previously unfilled niches.

  5. Paludification and forest retreat in northern oceanic environments.

    Science.gov (United States)

    Crawford, R M M; Jeffree, C E; Rees, W G

    2003-01-01

    Examination of temperature variations over the past century for Europe and the Arctic from northern Norway to Siberia suggests that variations in the North Atlantic Oscillation are associated with an increase in oceanicity in certain maritime regions. A southward depression of the tree line in favour of wet heaths, bogs and wetland tundra communities is also observed in northern oceanic environments. The physiological basis for this change in ecological succession from forest to bog is discussed in relation to the long-term effects of flooding on tree survival. The heightened values currently detected in the North Atlantic Oscillation Index, together with rising winter temperatures, and increased rainfall in many areas in northern Europe, presents an increasing risk of paludification with adverse consequences for forest regeneration, particularly in areas with oceanic climates. Climatic warming in oceanic areas may increase the area covered by bogs and, contrary to general expectations, lead to a retreat rather than an advance in the northern limit of the boreal forest. High water-table levels are not automatically detrimental to forest survival as can be seen in swamp, bottom land and mangrove forests. Consequently, the inhibitory effects of flooding on tree survival and regeneration in northern regions should not be uncritically accepted as merely due to high water levels. Evidence is discussed which suggests that physiological and ecological factors may interact to inhibit forest regeneration in habitats where there is a risk of prolonged winter-flooding combined with warmer winters and cool moist summers.

  6. Species-wide phylogeography of North American mule deer (Odocoileus hemionus): cryptic glacial refugia and postglacial recolonization.

    Science.gov (United States)

    Latch, Emily K; Heffelfinger, James R; Fike, Jennifer A; Rhodes, Olin E

    2009-04-01

    Quaternary climatic oscillations greatly influenced the present-day population genetic structure of animals and plants. For species with high dispersal and reproductive potential, phylogeographic patterns resulting from historical processes can be cryptic, overshadowed by contemporary processes. Here we report a study of the phylogeography of Odocoileus hemionus, a large, vagile ungulate common throughout western North America. We examined sequence variation of mitochondrial DNA (control region and cytochrome b) within and among 70 natural populations across the entire range of the species. Among the 1766 individual animals surveyed, we recovered 496 haplotypes. Although fine-scale phylogenetic structure was weakly resolved using phylogenetic methods, network analysis clearly revealed the presence of 12 distinct haplogroups. The spatial distribution of haplogroups showed a strong genetic discontinuity between the two morphological types of O. hemionus, mule deer and black-tailed deer, east and west of the Cascade Mountains in the Pacific Northwest. Within the mule deer lineage, we identified several haplogroups that expanded before or during the Last Glacial Maximum, suggesting that mule deer persisted in multiple refugia south of the ice sheets. Patterns of genetic diversity within the black-tailed deer lineage suggest a single refugium along the Pacific Northwest coast, and refute the hypothesis that black-tailed deer persisted in one or more northern refugia. Our data suggest that black-tailed deer recolonized areas in accordance with the pattern of glacial retreat, with initial recolonization northward along a coastal route and secondary recolonization inland.

  7. Relative sea-level changes and crustal movements in Britain and Ireland since the Last Glacial Maximum

    Science.gov (United States)

    Shennan, Ian; Bradley, Sarah L.; Edwards, Robin

    2018-05-01

    The new sea-level database for Britain and Ireland contains >2100 data points from 86 regions and records relative sea-level (RSL) changes over the last 20 ka and across elevations ranging from ∼+40 to -55 m. It reveals radically different patterns of RSL as we move from regions near the centre of the Celtic ice sheet at the last glacial maximum to regions near and beyond the ice limits. Validated sea-level index points and limiting data show good agreement with the broad patterns of RSL change predicted by current glacial isostatic adjustment (GIA) models. The index points show no consistent pattern of synchronous coastal advance and retreat across different regions, ∼100-500 km scale, indicating that within-estuary processes, rather than decimetre- and centennial-scale oscillations in sea level, produce major controls on the temporal pattern of horizontal shifts in coastal sedimentary environments. Comparisons between the database and GIA model predictions for multiple regions provide potentially powerful constraints on various characteristics of global GIA models, including the magnitude of MWP1A, the final deglaciation of the Laurentide ice sheet and the continued melting of Antarctica after 7 ka BP.

  8. The role of Southern Ocean mixing and upwelling in glacial-interglacial atmospheric CO2 change

    International Nuclear Information System (INIS)

    Watson, Andrew J.; Naveira Garabato, Alberto C.

    2006-01-01

    Decreased ventilation of the Southern Ocean in glacial time is implicated in most explanations of lower glacial atmospheric CO 2 . Today, the deep (>2000 m) ocean south of the Polar Front is rapidly ventilated from below, with the interaction of deep currents with topography driving high mixing rates well up into the water column. We show from a buoyancy budget that mixing rates are high in all the deep waters of the Southern Ocean. Between the surface and 2000 m depth, water is upwelled by a residual meridional overturning that is directly linked to buoyancy fluxes through the ocean surface. Combined with the rapid deep mixing, this upwelling serves to return deep water to the surface on a short time scale. We propose two new mechanisms by which, in glacial time, the deep Southern Ocean may have been more isolated from the surface. Firstly, the deep ocean appears to have been more stratified because of denser bottom water resulting from intense sea ice formation near Antarctica. The greater stratification would have slowed the deep mixing. Secondly, subzero atmospheric temperatures may have meant that the present-day buoyancy flux from the atmosphere to the ocean surface was reduced or reversed. This in turn would have reduced or eliminated the upwelling (contrary to a common assumption, upwelling is not solely a function of the wind stress but is coupled to the air/sea buoyancy flux too). The observed very close link between Antarctic temperatures and atmospheric CO 2 could then be explained as a natural consequence of the connection between the air/sea buoyancy flux and upwelling in the Southern Ocean, if slower ventilation of the Southern Ocean led to lower atmospheric CO 2 . Here we use a box model, similar to those of previous authors, to show that weaker mixing and reduced upwelling in the Southern Ocean can explain the low glacial atmospheric CO 2 in such a formulation

  9. Interhemispheric correlation of late pleistocene glacial events.

    Science.gov (United States)

    Lowell, T V; Heusser, C J; Andersen, B G; Moreno, P I; Hauser, A; Heusser, L E; Schlüchter, C; Marchant, D R; Denton, G H

    1995-09-15

    A radiocarbon chronology shows that piedmont glacier lobes in the Chilean Andes achieved maxima during the last glaciation at 13,900 to 14,890, 21,000, 23,060, 26,940, 29,600, and >/=33,500 carbon-14 years before present ((14)C yr B.P.) in a cold and wet Subantarctic Parkland environment. The last glaciation ended with massive collapse of ice lobes close to 14,000(14)C yr B.P., accompanied by an influx of North Patagonian Rain Forest species. In the Southern Alps of New Zealand, additional glacial maxima are registered at 17,720(14)C yr B.P., and at the beginning of the Younger Dryas at 11,050 (14)C yr B. P. These glacial maxima in mid-latitude mountains rimming the South Pacific were coeval with ice-rafting pulses in the North Atlantic Ocean. Furthermore, the last termination began suddenly and simultaneously in both polar hemispheres before the resumption of the modern mode of deep-water production in the Nordic Seas. Such interhemispheric coupling implies a global atmospheric signal rather than regional climatic changes caused by North Atlantic thermohaline switches or Laurentide ice surges.

  10. Modeled seasonality of glacial abrupt climate events

    Energy Technology Data Exchange (ETDEWEB)

    Flueckiger, Jacqueline [Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO (United States); Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zuerich, Zurich (Switzerland); Knutti, Reto [Institute for Atmospheric and Climate Science, ETH Zuerich, Zurich (Switzerland); White, James W.C. [Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO (United States); Renssen, Hans [Vrije Universiteit Amsterdam, Faculty of Earth and Life Sciences, Amsterdam (Netherlands)

    2008-11-15

    Greenland ice cores, as well as many other paleo-archives from the northern hemisphere, recorded a series of 25 warm interstadial events, the so-called Dansgaard-Oeschger (D-O) events, during the last glacial period. We use the three-dimensional coupled global ocean-atmosphere-sea ice model ECBILT-CLIO and force it with freshwater input into the North Atlantic to simulate abrupt glacial climate events, which we use as analogues for D-O events. We focus our analysis on the Northern Hemisphere. The simulated events show large differences in the regional and seasonal distribution of the temperature and precipitation changes. While the temperature changes in high northern latitudes and in the North Atlantic region are dominated by winter changes, the largest temperature increases in most other land regions are seen in spring. Smallest changes over land are found during the summer months. Our model simulations also demonstrate that the temperature and precipitation change patterns for different intensifications of the Atlantic meridional overturning circulation are not linear. The extent of the transitions varies, and local non-linearities influence the amplitude of the annual mean response as well as the response in different seasons. Implications for the interpretation of paleo-records are discussed. (orig.)

  11. The St. Ignatius Jesuit Retreat and Training Centre: Cultivating Ecological Awareness and Connection with the Earth

    Science.gov (United States)

    Groen, Janet

    2017-01-01

    This chapter focuses on the role of religiously based spirituality in cultivating environmental awareness and citizenship by examining an adult environmental education program offered at the Ignatius Jesuit Centre, a religious retreat center in Guelph, Canada.

  12. Late Proterozoic glacially controlled shelf sequences in western Mali (west Africa)

    Science.gov (United States)

    Deynoux, M.; Prousti, J. N.; Simon, B.

    The Late Proterozoic deposits of the Bakoye Group (500 m) in western Mali constitute a remarkable example of a glacially influenced sedimentary record on an epicratonic platform. They are composed of alternating marine and continental formations which represent accumulation in a basin located in the vicinity of upland areas covered by ice sheets. One of these formations (the Ba4 Formation), which is the focus of this study, is composed of three major units. The basal Unit 1 is made up of carbonaceous coarse to fine grained sandstones which are organized in fining upward sequences and which comprise lenticular diamictite intercalations. This Unit is considered to represent the fore slope gravity flows of a subaqueous ice-cootact fan fed by meltwater streams (≪glacioturbidites≫). Unit 2 is made up of coarse to fine grained sandstones in a highly variable association of facies. This Unit is characterized by the abundance of wave ripples associated with convolute beddings. planar or wavy beddings and tabular or hummocky crossbeddings in a general shallowing upward trend. It also comprises evidence of gravity processes including debris flows and large slumped sandstone bodies. Unit 2 represents the progressive filling of the Ba4 basin and reflects the combined effect of glacially induced eustatism and isostacy during a phase of glacial retreat. The basal part of Unit 3 is made up of a succession (a few meters thick) of conglomerates, diamictites, sandstones, siltstones or carbonates lying on an erosional unconformity marked by periglacial frost wedges. The upper part of Unit 3 is thicker (100-150 m) and onlaps on these basal facies with a succession of sandstone bars exhibiting swaley and hummocky crossbeddings, large cut and fill structures, and planar laminations. Unit 3 is strongly transgressive, the lower shoreface and backshore deposits include algal mats and are onlapped by sand ridges emplaced in a high energy upper to middle shoreface environment. Overall

  13. Reliable Refuge: Two Sky Island Scorpion Species Select Larger, Thermally Stable Retreat Sites.

    Science.gov (United States)

    Becker, Jamie E; Brown, Christopher A

    2016-01-01

    Sky island scorpions shelter under rocks and other surface debris, but, as with other scorpions, it is unclear whether these species select retreat sites randomly. Furthermore, little is known about the thermal preferences of scorpions, and no research has been done to identify whether reproductive condition might influence retreat site selection. The objectives were to (1) identify physical or thermal characteristics for retreat sites occupied by two sky island scorpions (Vaejovis cashi Graham 2007 and V. electrum Hughes 2011) and those not occupied; (2) determine whether retreat site selection differs between the two study species; and (3) identify whether thermal selection differs between species and between gravid and non-gravid females of the same species. Within each scorpion's habitat, maximum dimensions of rocks along a transect line were measured and compared to occupied rocks to determine whether retreat site selection occurred randomly. Temperature loggers were placed under a subset of occupied and unoccupied rocks for 48 hours to compare the thermal characteristics of these rocks. Thermal gradient trials were conducted before parturition and after dispersal of young in order to identify whether gravidity influences thermal preference. Vaejovis cashi and V. electrum both selected larger retreat sites that had more stable thermal profiles. Neither species appeared to have thermal preferences influenced by reproductive condition. However, while thermal selection did not differ among non-gravid individuals, gravid V. electrum selected warmer temperatures than its gravid congener. Sky island scorpions appear to select large retreat sites to maintain thermal stability, although biotic factors (e.g., competition) could also be involved in this choice. Future studies should focus on identifying the various biotic or abiotic factors that could influence retreat site selection in scorpions, as well as determining whether reproductive condition affects thermal

  14. Investigating the Impact of Ecological Succession on Fluxes of Halogenated Volatile Organic Compounds (HVOCs) from Retreating Glacier Forefields

    Science.gov (United States)

    Macdonald, M.; Young, D.; O'Doherty, S.; Wadham, J.

    2017-12-01

    The Arctic is one of the fastest warming regions of the Earth, with temperature increases of +7oC projected by 2100 under a mitigation emission scenario. These climate perturbations are forecast to cause the retreat of extensive glacial systems across Canada, Greenland, Svalbard and the Russian Arctic. This will reveal new proglacial land surfaces for microbial colonisation, ultimately succeeding to tundra over decades to centuries. A relatively unexplored dimension to these changes is their impact upon the emission and consumption of halogenated volatile organic compounds (HVOCs) from proglacial land surfaces. HVOCs are involved in several important atmospheric processes such as ozone destruction and aerosol formation and despite considerable research, uncertainties remain in the natural cycles of some of these compounds. Here, we investigated the influence of biological process on the fluxes of HVOCs from recently (chambers on surfaces spanning recently-exposed sediments, to approx. 100 yr old tundra in front of Midtre Lovenbreen glacier, Svalbard. In-field analysis of a suite of HVOCs was conducted using a GCMS (gas chromatograph mass spectrometer) with a custom-built pre-concentration system. HVOC concentrations were evaluated with reference to biological (e.g. cell numbers) and physio-chemical (e.g. water content) parameters of the land surface, in order to assess the importance of the microbial community on the net flux. Significant rates of consumption of some HVOC species and production of others was detected. Further laboratory incubations supported the findings in the field. Proglacial surfaces are, therefore, a previously unrecognised sink and source of various HVOCs that have the potential to increase in importance with projected future climate change.

  15. Alpine glacial topography and the rate of rock column uplift

    DEFF Research Database (Denmark)

    Pedersen, Vivi Kathrine; Egholm, D.L.; Nielsen, S.B.

    2010-01-01

    The present study investigates the influence of alpine glacial erosion on the morphology and relief distribution of mountain regions associated with varying rock column uplift rates. We take a global approach and analyse the surface area distribution of all mountain regions affected by glacial er...

  16. Effects of glacial meltwater on corrosion of copper canisters

    International Nuclear Information System (INIS)

    Ahonen, L.; Vieno, T.

    1994-08-01

    The composition of glacial meltwater and its reactions in the bedrock are examined. The evidences that there are or should be from past intrusions of glacial meltwater and oxygen deep in the bedrock are also considered. The study is concluded with an evaluation of the potential effects of oxygenated meltwater on the corrosion of copper canisters. (46 refs., 3 figs., 2 tabs.)

  17. Retreatment of Exudative Age-Related Macular Degeneration after Loading 3-Monthly Intravitreal Ranibizumab.

    Science.gov (United States)

    Sugiyama, Atsushi; Sakurada, Yoichi; Honda, Shigeru; Miki, Akiko; Matsumiya, Wataru; Yoneyama, Seigo; Kikushima, Wataru; Iijima, Hiroyuki

    2018-01-01

    The aim of this study was to investigate the clinical implications of required retreatment after 3-monthly intravitreal ranibizumab (IVR) injections followed by as-needed reinjections up to 5 years in eyes with exudative age-related macular degeneration (AMD). A retrospective cohort study was conducted for 165 treatment-naïve eyes from 165 patients with exudative AMD. Visual changes were investigated in terms of the required retreatments. Retreatment-free proportions were 37.0, 23.7, 16.6, 12.1, and 10.5% at 12, 24, 36, 48, and 60 months, respectively. Visual changes were significantly better in eyes which did not require retreatment at every yearly checkpoint within the 5 years. A multivariate logistic regression analysis revealed that requirement of additional IVR treatments in the first 12-24 months was associated with the T allele (risk allele) of ARMS2 A69S (p = 0.010 and 0.015, respectively). Cox regression analysis revealed that older age (p = 0.046) and the T allele of ARMS2 A69S (p = 0.036) were associated with required retreatment within the 5-year follow-up period. Age and the T allele of ARMS2 A69S are the risk factors requiring retreatments, leading to poor visual change in eyes with exudative AMD following the initial 3-monthly IVR. © 2017 S. Karger AG, Basel.

  18. A method for selecting potential geosites. The case of glacial geosites in the Chablais area (French and Swiss Prealps)

    Science.gov (United States)

    Perret, Amandine; Reynard, Emmanuel

    2014-05-01

    stages of the glacial retreat since the Last Glacial Maximum. From a spatial point of view, the objective was to show the different types of glacial remnants, but also some landforms related to deglaciation processes. Finally, 32 glacial and associated geosites were selected. Each geosite was submitted to a full evaluation process, including basis information, description, explanation of morphogenesis and an evaluation of values assigned to geosites. This assessment, first qualitative, provided valuable information concerning their intrinsic interest and their management. A numerical evaluation was also assessed to classify geosites and define an order of priority for their touristic promotion. It is worth to be noted that each selected points of interest can in fact be qualified as a geosite, using a clear method of selection. In this study, the numerical evaluation is not a mean to select geosites but a way to rank one geosite to another. Some geosites can be abandoned if intrinsic values are too low. Despite a well-defined protocol, the subjectivity and authors' choices are part of the selection process and inventory. This fact is certainly not a weakness. It must be considered whenever such inventory is made. Reference Martin, S. (2012). Valoriser le géopatrimoine par la médiation indirecte et la visualisation des objets géomorphologiques (Thèse de doctorat). Université de Lausanne, Lausanne. Reynard E., Fontana G., Kozlik L., Scapozza C. (2007). A method for assessing the scientific and additional values of geomorphosites, Geographica Helvetica, 62(3), 148-158. Reynard, E., Perret, A., Grangier, L., & Kozlik, L. (2012). Methodological approach for the assessment, protection, promotion and management of geoheritage. EGU General Assembly, Vienna.

  19. Giant seafloor craters formed by hydrate-controlled large-scale methane expulsion from the Arctic seafloor after ice sheet retreat

    Science.gov (United States)

    Andreassen, K.; Hubbard, A.; Patton, H.; Vadakkepuliyambatta, S.; Winsborrow, M.; Plaza-Faverola, A. A.; Serov, P.

    2017-12-01

    Large-scale methane releases from thawing Arctic gas hydrates is a major concern, yet the processes and fluxes involved remain elusive. We present geophysical data indicating two contrasting processes of natural methane emissions from the seafloor of the northern Barents Sea, Polar North Atlantic. Abundant gas flares, acoustically imaged in the water column reveal slow, gradual release of methane bubbles, a process that is commonly documented from nearby areas, elsewhere in the Arctic and along continental margins worldwide. Conversely, giant craters across the study area indicate a very different process. We propose that these are blow-out craters, formed through large-scale, abrupt methane expulsion induced when gas hydrates destabilized after the Barents Sea Ice Sheet retreated from the area. The data reveal over 100 giant seafloor craters within an area of 440 km2. These are up to 1000 m in diameter, 30 m deep and with a semi-circular to elliptical shape. We also identified numerous large seafloor mounds, which we infer to have formed by the expansion of gas hydrate accumulations within the shallow subsurface, so-called gas hydrate pingos. These are up to 1100 m wide and 20 m high. Smaller craters and mounds < 200 m wide and with varying relief are abundant across the study site. The empirical observations and analyses are combined with numerical modelling of ice sheet, isostatic and gas hydrate evolution and indicate that during glaciation, natural gas migrating from underlying hydrocarbon reservoirs was stored as subglacial gas hydrates. On ice sheet retreat, methane from these hydrate reservoirs and underlying free gas built up and abruptly released, forming the giant mounds and craters observed in the study area today. Petroleum basins are abundant beneath formerly and presently glaciated regions. We infer that episodes of subglacial sequestration of gas hydrates and underlying free gas and subsequent abrupt expulsions were common and widespread throughout

  20. Glacial isostatic uplift of the European Alps

    Science.gov (United States)

    Mey, Jürgen; Scherler, Dirk; Wickert, Andrew D.; Egholm, David L.; Tesauro, Magdala; Schildgen, Taylor F.; Strecker, Manfred R.

    2016-01-01

    Following the last glacial maximum (LGM), the demise of continental ice sheets induced crustal rebound in tectonically stable regions of North America and Scandinavia that is still ongoing. Unlike the ice sheets, the Alpine ice cap developed in an orogen where the measured uplift is potentially attributed to tectonic shortening, lithospheric delamination and unloading due to deglaciation and erosion. Here we show that ∼90% of the geodetically measured rock uplift in the Alps can be explained by the Earth’s viscoelastic response to LGM deglaciation. We modelled rock uplift by reconstructing the Alpine ice cap, while accounting for postglacial erosion, sediment deposition and spatial variations in lithospheric rigidity. Clusters of excessive uplift in the Rhône Valley and in the Eastern Alps delineate regions potentially affected by mantle processes, crustal heterogeneity and active tectonics. Our study shows that even small LGM ice caps can dominate present-day rock uplift in tectonically active regions. PMID:27830704

  1. Quaternary glacial stratigraphy and chronology of Mexico

    Science.gov (United States)

    White, Sidney E.

    The volcano Iztaccihuatl in central Mexico was glaciated twice during the middle Pleistocene, once probably in pre-Illinoian (or pre-Bull Lake) time, and once in late Illinoian (or Bull Lake) time. Glaciation during the late Pleistocene was restricted to the late Wisconsin (or Pinedale). A maximum advance and one readvance are recorded in the early part, and one readvance in the latter part. Three or four small neoglacial advances occurred during the Holocene. Two other volcanoes nearby, Ajusco and Malinche, have a partial record of late Pleistocene and Holocene glaciations. Three others, Popocatépetl, Pico de Orizaba, and Nevado de Toluca, have a full Holocene record of three to five glacial advances during Neoglaciation.

  2. Glacial refugia and post-glacial colonization patterns in European bryophytes

    OpenAIRE

    Kyrkjeeide, Magni Olsen; Stenøien, Hans K.; Flatberg, Kjell Ivar; Hassel, Kristian

    2014-01-01

    Most species are assumed to have survived south or east of the ice sheet covering northern Europe during the last glacial maximum. Molecular and macrofossil evidence suggests, however, that some species may have survived in ice-free areas in Scandinavia. In plants, inbreeding and vegetative growth are associated with low genetic load and enhanced survival in small, isolated populations. These characteristics are often found in bryophytes, possibly allowing them to survive extreme conditions i...

  3. Small scale tests on the progressive retreat of soil slopes

    Science.gov (United States)

    Voulgari, Chrysoula; Utili, Stefano; Castellanza, Riccardo

    2015-04-01

    In this paper, the influence due to the presence of cracks on the morphologic evolution of natural cliffs subject to progressive retreat induced by weathering is investigated through small scale laboratory tests. Weathering turns hard rocks into soft rocks that maintain the structure of the intact rocks, but are characterised by higher void ratios and reduced bond strengths; soft rocks are transformed into granular soils generally called residual soils. A number of landslides develop in slopes due to weathering which results in the progressive retrogression of the slope face and the further degradation within the weathering zone. Cracks, that are widely present, can be a result of weathering and they can cause a significant decrease in their stability, as they provide preferential flow channels which increase the soil permeability and decrease the soil strength. The geological models employed until now are mainly empirical. Several researchers have tried to study the stability of slopes through experimental procedures. Centrifuge modelling is widely used to investigate the failure of slopes. Small scale tests are also an important approach, in order to study the behaviour of a slope under certain conditions, such as the existence of water, as they allow the observation of the infiltration processes, the movement of the weathering front, deformation and failure. However, the deformation response of a slope subject to weathering is not yet thoroughly clarified. In this work, a set of experiments were conducted to investigate weathering induced successive landslides. Weathering was applied to the slope model by wetting the slope crest through a rainfall simulator device. The moisture content of the soil during the tests was monitored by soil moisture sensors that were buried inside the slope model. High resolution cameras were recording the behaviour of the slope model. GeoPIV was used to analyse the frames and obtain the deformations of the slope model during the

  4. A late glacial record of ice-sheet dynamics and melt supply recovered in the sediments of IODP Expedition 347 in the Baltic Sea

    Science.gov (United States)

    Passchier, Sandra; Jensen, Jørn Bo; Kenzler, Michael; Johnson, Sean; Andrén, Thomas; Barker Jørgensen, Bo

    2015-04-01

    Modern observations of increased surface ablation, meltwater routing to the bed, and increases in glacial speeds point to feedbacks between ice-sheet dynamics, melt supply, and subglacial discharge. Paleorecords have the potential to explore the decadal to centennial variability of these systems, but until recently such records were short and discontinuous in ice-proximal settings and underutilized for this specific purpose. The Integrated Ocean Drilling Program Expedition 347 in the Baltic Sea recovered annually laminated sediments that document the dynamics of the Scandinavian Ice Sheet. Hydraulic piston cores recovered from Sites M0060, M0063, M0064, and M0065 allow us to reconstruct a nearly complete record of ca. 6000 years in ice retreat history at annual to decadal resolution between ca. 17 and 11ka. The late glacial successions of these four IODP drillsites comprise of a till or proglacial fluvioglacial sediment overlain by variable thicknesses of well-laminated deglacial successions within several high-recovery holes. As the Scandinavian Ice Sheet retreated from the western Baltic Sea, and to the North, the ice-sheet's grounding line migrated across the four sites and deposited overlapping sections of high-resolution ice-proximal to ice-distal successions. Laser particle size results from Sites M0060 and M0063, and inspection of line-scan images, show shifts in sedimentary facies and lithologies that were not recognized during initial visual core description. For example, at Site M0060 in the Kattegat, ice-rafting fluxes in silty clays decrease upward and are negligible in the overlying varved succession. These characteristics are interpreted as ice retreat within a calving bay environment from ca. 17ka onward, followed by distal glacial marine deposition from sediment plumes governed by meltwater discharge. Moreover, at Site M0063 in the Baltic Sea, laser particle size distributions record an abrupt shift from interlaminated clayey silt to laminated clay

  5. Modeling Antarctic Ice Sheet retreat in warm climates: a historical perspective.

    Science.gov (United States)

    Pollard, D.; Deconto, R. M.; Gasson, E.

    2016-12-01

    Early modeling of Antarctic Ice Sheet size vs. climate focused on asymmetry between retreat and growth, with much greater warming needed to cause retreat from full ice cover, due to Height Mass Balance Feedback and albedo feedback. This led to a long-standing model-data conflict, with models needing 1000 to2000 ppmv atmospheric CO2 to produce retreat from full size, vs. proxy data of large ice fluctuations despite much lower CO2 since the Miocene.Subsequent modeling with marine ice physics found that the West Antarctic Ice Sheet could undergo repeated warm-period collapses with realistic past forcing. However, that yields only 3 to 7 m equivalent sea-level rise above modern, compared to 10 to 20 m or more suggested by some geologic data. Large subglacial basins in East Antarctica could be vulnerable to the same processes,but did not retreat in most models due to narrower and shallower sills.After recent modifications, some ice sheet models were able to produce warm-period collapse of major East Antarctic basins, with sea-level rise of up to 15 m. The modifications are (i) hydrofracturing by surface melt, and structural failure of ice cliffs, or (ii) numerical treatment at the grounding line. In these models, large retreat occurs both for past warmintervals, and also for future business-as-usual scenarios.Some interpretations of data in the late Oligocene and Miocene suggest yet larger fluctuations, between 50 to 100% of modern Antarctic size. That would require surface-melt driven retreat of some terrestrial East Antarctic ice, despite the hysteresis issue raised above. A recent study using a coupled climate-ice sheet model found that with a finer climate gridand more frequent coupling exchange, substantial retreat of terrestrial Antarctica can occur with 500 to 840 ppmv CO2, much lower than in earlier models. This will allow meaningful interactions between modeling and deeper-time geologic interpretations since the late Oligocene.

  6. Variability, trends, and predictability of seasonal sea ice retreat and advance in the Chukchi Sea

    Science.gov (United States)

    Serreze, Mark C.; Crawford, Alex D.; Stroeve, Julienne C.; Barrett, Andrew P.; Woodgate, Rebecca A.

    2016-10-01

    As assessed over the period 1979-2014, the date that sea ice retreats to the shelf break (150 m contour) of the Chukchi Sea has a linear trend of -0.7 days per year. The date of seasonal ice advance back to the shelf break has a steeper trend of about +1.5 days per year, together yielding an increase in the open water period of 80 days. Based on detrended time series, we ask how interannual variability in advance and retreat dates relate to various forcing parameters including radiation fluxes, temperature and wind (from numerical reanalyses), and the oceanic heat inflow through the Bering Strait (from in situ moorings). Of all variables considered, the retreat date is most strongly correlated (r ˜ 0.8) with the April through June Bering Strait heat inflow. After testing a suite of statistical linear models using several potential predictors, the best model for predicting the date of retreat includes only the April through June Bering Strait heat inflow, which explains 68% of retreat date variance. The best model predicting the ice advance date includes the July through September inflow and the date of retreat, explaining 67% of advance date variance. We address these relationships by discussing heat balances within the Chukchi Sea, and the hypothesis of oceanic heat transport triggering ocean heat uptake and ice-albedo feedback. Developing an operational prediction scheme for seasonal retreat and advance would require timely acquisition of Bering Strait heat inflow data. Predictability will likely always be limited by the chaotic nature of atmospheric circulation patterns.

  7. Psychological effects of a one-month meditation retreat on experienced meditators: the role of nonattachment

    Directory of Open Access Journals (Sweden)

    Jesus Montero-Marin

    2016-12-01

    Full Text Available Background. There are few studies devoted to assessing the impact of meditation-intensive retreats on the well-being, positive psychology and personality of experienced meditators. We aimed to assess whether a 1-month Vipassana retreat: a would increase mindfulness and well-being; b would increase prosocial personality traits; and c whether psychological changes would be mediated and/or moderated by non-attachment.Method. A controlled, non-randomized, pre-post-intervention trial was used. The intervention group was a convenience sample (n=19 of experienced meditators who participated in a 1-month Vipassana meditation retreat. The control group (n=19 comprised matched experienced meditators who did not take part in the retreat. During the retreat, the mean duration of daily practice was 8-9 hours, the diet was vegetarian and silence was compulsory. The Experiences Questionnaire (EQ, Non-Attachment Scale (NAS, Positive and Negative Affect Schedule (PANAS, Satisfaction With Life Scale (SWLS, Temperament Character Inventory Revised (TCI-R-67, Five Facets Mindfulness Questionnaire (FFMQ, Self-Other Four Immeasurables (SOFI and the MINDSENS Composite Index were administered. ANCOVAs and linear regression models were used to assess pre-post changes and mediation/moderation effects.Results. Compared to controls, retreatants showed increases in non-attachment, observing, MINDSENS, positive-affect, balance-affect and cooperativeness; and decreases in describing, negative-others, reward-dependence and self-directedness. Non-attachment had a mediating role in decentring, acting aware, non-reactivity, negative-affect, balance-affect and self-directedness; and a moderating role in describing and positive others, with both mediating and moderating effects on satisfaction with life.Conclusions. A 1-month Vipassana meditation retreat seems to yield improvements in mindfulness, well-being and personality, even in experienced meditators. Non-attachment might

  8. Fossil Coral Records of ENSO during the Last Glacial Period

    Science.gov (United States)

    Partin, J. W.; Taylor, F. W.; Shen, C. C.; Edwards, R. L.; Quinn, T. M.; DiNezro, P.

    2017-12-01

    Only a handful of paleoclimate records exist that can resolve interannual changes, and hence El Nino/Southern Oscillation (ENSO) variability, during the last glacial period, a time of altered mean climate. The few existing data suggest reduced ENSO variability compared to the Holocene, possibly due to a weaker zonal sea surface temperature gradient across the tropical Pacific and/or a deeper thermocline in the eastern tropical Pacific. Our goal is to add crucial data to this extremely limited subset using sub-annually resolved fossil corals that grew during this time period to reconstruct ENSO. We seek to recover fossil corals from Vanuatu, SW Pacific (16°S, 167°E) with the objective of using coral δ18O to reconstruct changes in the ENSO during and near the Last Glacial Maximum (LGM). Modern δ18O coral records from Vanuatu show a high degree of skill in capturing ENSO variability, making it a suitable site for reconstructing ENSO variability. We have custom designed and are building a drill system that can rapidly core many 0-25 m holes resulting in much more meters of penetration than achieved by previous land-based reef drilling. As the new drill system is extremely portable and can be quickly relocated by workers without landing craft or vehicles, it is time and cost efficient. Because the proposed drilling sites have uplifted extremely fast, 7 mm/year, the LGM shoreline has been raised from 120-140 m depth to within a depth range of 10 below to 20 m above present sea level. This enables all the drilling to be within the time range of interest ( 15-25 ka). A last advantage is that the LGM corals either are still submersed in seawater or emerged only within the last 2000 years at the uplift rate of 7 mm/yr. This greatly reduces the chances of disruption of the original climate signal because sea water is less diagenetically damaging than meteoric water in the mixed, phreatic, or vadose zones. LGM coral records will enable us to compare the proxy variability

  9. Use of multi-criteria decision analysis to identify potentially dangerous glacial lakes.

    Science.gov (United States)

    Kougkoulos, Ioannis; Cook, Simon J; Jomelli, Vincent; Clarke, Leon; Symeonakis, Elias; Dortch, Jason M; Edwards, Laura A; Merad, Myriam

    2018-04-15

    Glacial Lake Outburst Floods (GLOFs) represent a significant threat in deglaciating environments, necessitating the development of GLOF hazard and risk assessment procedures. Here, we outline a Multi-Criteria Decision Analysis (MCDA) approach that can be used to rapidly identify potentially dangerous lakes in regions without existing tailored GLOF risk assessments, where a range of glacial lake types exist, and where field data are sparse or non-existent. Our MCDA model (1) is desk-based and uses freely and widely available data inputs and software, and (2) allows the relative risk posed by a range of glacial lake types to be assessed simultaneously within any region. A review of the factors that influence GLOF risk, combined with the strict rules of criteria selection inherent to MCDA, has allowed us to identify 13 exhaustive, non-redundant, and consistent risk criteria. We use our MCDA model to assess the risk of 16 extant glacial lakes and 6 lakes that have already generated GLOFs, and found that our results agree well with previous studies. For the first time in GLOF risk assessment, we employed sensitivity analyses to test the strength of our model results and assumptions, and to identify lakes that are sensitive to the criteria and risk thresholds used. A key benefit of the MCDA method is that sensitivity analyses are readily undertaken. Overall, these sensitivity analyses lend support to our model, although we suggest that further work is required to determine the relative importance of assessment criteria, and the thresholds that determine the level of risk for each criterion. As a case study, the tested method was then applied to 25 potentially dangerous lakes in the Bolivian Andes, where GLOF risk is poorly understood; 3 lakes are found to pose 'medium' or 'high' risk, and require further detailed investigation. Copyright © 2017 Elsevier B.V. All rights reserved.

  10. Risk Factors for Retreatment Following Myopic LASIK with Femtosecond Laser and Custom Ablation for the Treatment of Myopia.

    Science.gov (United States)

    Kruh, Jonathan N; Garrett, Kenneth A; Huntington, Brian; Robinson, Steve; Melki, Samir A

    2017-01-01

    To identify risks factors for retreatment post-laser in situ keratomeliusis (LASIK). A retrospective chart review from December 2008 to September 2012 identified 1,402 patients (2,581 eyes) that underwent LASIK treatment for myopia with the Intralase™ FS, STAR S4 IR™ Excimer Laser, and WaveScan WaveFront™ technology. In this group, 83 patients were retreated. All charts were reviewed for preoperative age, gender, initial manifest refraction spherical equivalent (MRSE), total astigmatism, and iris registration. Increased incidence rates of retreatment post-LASIK were preoperative age >40 years (p -3.0 D (p = 0.02), and astigmatism >1D (p = 0.001). Iris registration capture did not significantly reduce the retreatment rate (p = 0.12). Risk factors for retreatment included preoperative age >40 years, initial MRSE > -3.0 D, and astigmatism >1D. There was no difference in retreatment rate for patients based on gender or iris registration capture.

  11. Late Ordovician (Ashgillian) glacial deposits in southern Jordan

    Science.gov (United States)

    Turner, Brian R.; Makhlouf, Issa M.; Armstrong, Howard A.

    2005-11-01

    The Late Ordovician (Ashgillian) glacial deposits in southern Jordan, comprise a lower and upper glacially incised palaeovalley system, occupying reactivated basement and Pan-African fault-controlled depressions. The lower palaeovalley, incised into shoreface sandstones of the pre-glacial Tubeiliyat Formation, is filled with thin glaciofluvial sandstones at the base, overlain by up to 50 m of shoreface sandstone. A prominent glaciated surface near the top of this palaeovalley-fill contains intersecting glacial striations aligned E-W and NW-SE. The upper palaeovalley-fill comprises glaciofluvial and marine sandstones, incised into the lower palaeovalley or, where this is absent, into the Tubeiliyat Formation. Southern Jordan lay close to the margin of a Late Ordovician terrestrial ice sheet in Northwest Saudi Arabia, characterised by two major ice advances. These are correlated with the lower and upper palaeovalleys in southern Jordan, interrupted by two subsidiary glacial advances during late stage filling of the lower palaeovalley when ice advanced from the west and northwest. Thus, four ice advances are now recorded from the Late Ordovician glacial record of southern Jordan. Disturbed and deformed green sandstones beneath the upper palaeovalley-fill in the Jebel Ammar area, are confined to the margins of the Hutayya graben, and have been interpreted as structureless glacial loessite or glacial rock flour. Petrographic and textural analyses of the deformed sandstones, their mapped lateral transition into undeformed Tubeiliyat marine sandstones away from the fault zone, and the presence of similar sedimentary structures to those in the pre-glacial marine Tubeiliyat Formation suggest that they are a locally deformed facies equivalent of the Tubeiliyat, not part of the younger glacial deposits. Deformation is attributed to glacially induced crustal stresses and seismic reactivation of pre-existing faults, previously weakened by epeirogenesis, triggering sediment

  12. Transcending Gender: Female Non-Buddhists’ Experiences of the Vipassanā Meditation Retreat

    Directory of Open Access Journals (Sweden)

    Brooke Schedneck

    2018-03-01

    Full Text Available Female non-Buddhists have been writing detailed descriptions of their personal experiences in vipassanā meditation retreats since the 1960s. These memoirists relate to the English-speaking world their experience of the retreat process and self-transformations. Early memoirists traveled Asia in order to learn and practice vipassanā meditation. These memoirs are as much about the meditation practice itself as living in an Asian culture. The mindfulness craze, beginning in the late 2000s, brought with it increased awareness of vipassanā practice. At this time we see a renewed interest in recording vipassanā retreat experiences, but these are even more personal and not concerned with travel, as many vipassanā meditation retreats are now available outside of Asia. I consider four female memoirists: Marie Byles and Jane Hamilton-Smith, writing in the 1960s and 1970s, and Raji Lukkoor, and Jennifer Howd, whose memoirs appeared in 2010 and 2014, respectively. These women’s writings demonstrate that, although non-Buddhist female meditators understand vipassanā meditation as a nongendered practice, it is still an embodied, gendered experience. Each of these women has different reactions to the female gender on the retreat, from outrage at gender discrimination to acceptance of it, from judgment of female teachers and meditators to revealing a more feminine self.

  13. Orthograde endodontic retreatment of teeth with individual cast posts: Report of two cases

    Directory of Open Access Journals (Sweden)

    Ramić Bojana

    2012-01-01

    Full Text Available Introduction. The failure of primary endodontic treatment is manifested by various clinical symptoms following endodontic therapy or, more frequently, by the development of chronic inflammatory process in the apex region without any subjective symptoms. In case of unfavorable outcome of the primary endodontic treatment, orthograde endodontic retreatment is the method of choice for a prolonged therapy. Outline of Cases. Two female patients, 47 and 44 years old, were presented at the Dental Clinic of Vojvodina for endodontic retreatment of teeth 22, 23 and 13, within the repeated prosthetic restoration. Intraradicular individual cast posts were removed using ultrasonic instruments. Remains of gutta-percha were removed by engine driven rotary re-treatment files, root canals were shaped and cleaned using the crown-down technique, and obturated with gutta-percha and epoxy-resin-based sealer using the lateral compaction technique. Conclusion. When there are metal posts or broken instruments in the root canal, the use of ultrasonic instruments is considered a safe method characterized by negligible tooth substance loss and minimal root damage causing fractures and perforations, and the entire procedure is effective and predictable. Non-surgical orthograde endodontic retreatment, when properly performed in accessible and penetrable root canals, achieves a high cure rate, good and lasting results and eliminates the need for radical procedures, such as apical surgery or tooth extraction. When nonsurgical endodontic retreatment is done, treated teeth must be restored by full coronal coverage as soon as possible, to prevent coronal leakage or fracture.

  14. Wastewater retreatment and reuse system for agricultural irrigation in rural villages.

    Science.gov (United States)

    Kim, Minyoung; Lee, Hyejin; Kim, Minkyeong; Kang, Donghyeon; Kim, Dongeok; Kim, YoungJin; Lee, Sangbong

    2014-01-01

    Climate changes and continuous population growth increase water demands that will not be met by traditional water resources, like surface and ground water. To handle increased water demand, treated municipal wastewater is offered to farmers for agricultural irrigation. This study aimed to enhance the effluent quality from worn-out sewage treatment facilities in rural villages, retreat effluent to meet water quality criteria for irrigation, and assess any health-related and environmental impacts from using retreated wastewater irrigation on crops and in soil. We developed the compact wastewater retreatment and reuse system (WRRS), equipped with filters, ultraviolet light, and bubble elements. A pilot greenhouse experiment was conducted to evaluate lettuce growth patterns and quantify the heavy metal concentration and pathogenic microorganisms on lettuce and in soil after irrigating with tap water, treated wastewater, and WRRS retreated wastewater. The purification performance of each WRRS component was also assessed. The study findings revealed that existing worn-out sewage treatment facilities in rural villages could meet the water quality criteria for treated effluent and also reuse retreated wastewater for crop growth and other miscellaneous agricultural purposes.

  15. A model ensemble for projecting multi‐decadal coastal cliff retreat during the 21st century

    Science.gov (United States)

    Limber, Patrick; Barnard, Patrick; Vitousek, Sean; Erikson, Li

    2018-01-01

    Sea cliff retreat rates are expected to accelerate with rising sea levels during the 21st century. Here we develop an approach for a multi‐model ensemble that efficiently projects time‐averaged sea cliff retreat over multi‐decadal time scales and large (>50 km) spatial scales. The ensemble consists of five simple 1‐D models adapted from the literature that relate sea cliff retreat to wave impacts, sea level rise (SLR), historical cliff behavior, and cross‐shore profile geometry. Ensemble predictions are based on Monte Carlo simulations of each individual model, which account for the uncertainty of model parameters. The consensus of the individual models also weights uncertainty, such that uncertainty is greater when predictions from different models do not agree. A calibrated, but unvalidated, ensemble was applied to the 475 km‐long coastline of Southern California (USA), with 4 SLR scenarios of 0.5, 0.93, 1.5, and 2 m by 2100. Results suggest that future retreat rates could increase relative to mean historical rates by more than two‐fold for the higher SLR scenarios, causing an average total land loss of 19 – 41 m by 2100. However, model uncertainty ranges from +/‐ 5 – 15 m, reflecting the inherent difficulties of projecting cliff retreat over multiple decades. To enhance ensemble performance, future work could include weighting each model by its skill in matching observations in different morphological settings

  16. Scientific Retreats with ‘Speed Dating’: Networking to Stimulate New Interdisciplinary Translational Research Collaborations and Team Science

    Science.gov (United States)

    Alberg, Anthony J.; Brady, Kathleen T.; Obeid, Jihad S.; Davis, Randal; Halushka, Perry V.

    2016-01-01

    To stimulate the formation of new interdisciplinary translational research teams and innovative pilot projects, the South Carolina Clinical & Translational Research (SCTR) Institute (South Carolina Clinical and Translational Science Award, CTSA) initiated biannual scientific retreats with “speed dating” networking sessions. Retreat themes were prioritized based on the following criteria; cross-cutting topic, unmet medical need, generation of novel technologies and methodologies. Each retreat commences with an external keynote speaker followed by a series of brief research presentations by local researchers focused on the retreat theme, articulating potential areas for new collaborations. After each session of presentations, there is a 30 minute scientific “speed dating” period during which the presenters meet with interested attendees to exchange ideas and discuss collaborations. Retreat attendees are eligible to compete for pilot project funds on the topic of the retreat theme. The 10 retreats held have had a total of 1004 participants, resulted in 61 pilot projects with new interdisciplinary teams, and 14 funded projects. The retreat format has been a successful mechanism to stimulate novel interdisciplinary research teams and innovative translational research projects. Future retreats will continue to target topics of cross-cutting importance to biomedical and public health research. PMID:27807146

  17. Measuring Surface Deformation in Glacier Retreated Areas Based on Ps-Insar - Geladandong Glacier as a Case Study

    Science.gov (United States)

    Mohamadi, B.; Balz, T.

    2018-04-01

    Glaciers are retreating in many parts of the world as a result of global warming. Many researchers consider Qinghai-Tibetan Plateau as a reference for climate change by measuring glaciers retreat on the plateau. This retreat resulted in some topographic changes in retreated areas, and in some cases can lead to geohazards as landslides, and rock avalanches, which is known in glacier retreated areas as paraglacial slope failure (PSF). In this study, Geladandong biggest and main glacier mass was selected to estimate surface deformation on its glacier retreated areas and define potential future PSF based on PS-InSAR technique. 56 ascending and 49 descending images were used to fulfill this aim. Geladandong glacier retreated areas were defined based on the maximum extent of the glacier in the little ice age. Results revealed a general uplift in the glacier retreated areas with velocity less than 5mm/year. Obvious surface motion was revealed in seven parts surround glacier retreated areas with high relative velocity reached ±60mm/year in some parts. Four parts were considered as PSF potential motion, and two of them showed potential damage for the main road in the study area in case of rock avalanche into recent glacier lakes that could result in glacier lake outburst flooding heading directly to the road. Finally, further analysis and field investigations are needed to define the main reasons for different types of deformation and estimate future risks of these types of surface motion in the Qinghai-Tibetan Plateau.

  18. Regional Geomorphological Conditions Related to Recent Changes of Glacial Lakes in the Issyk-Kul Basin, Northern Tien Shan

    Directory of Open Access Journals (Sweden)

    Mirlan Daiyrov

    2018-03-01

    Full Text Available To assess the current state of glacial lakes, we examine the seasonal lake-area changes of 339 glacial lakes in the Teskey and Kungoy Ranges of the Issyk-Kul Basin, Kyrgyzstan, during 2013–2016 based on optical satellite images (Landsat7/ETM+ and 8/OLI. The glacial lakes are classified into six types based on their seasonal variations in area: stable, increasing, decreasing, appearing, vanishing, and short-lived. We then track the number of each type in a given year and examine how each number changes from one year to the next. We find that many appearing, vanishing, and short-lived types occurred in both mountain ranges, having a large variability in number that is not directly related to the local short-term summer temperature anomaly, nor to precipitation or glacier recession. However, those in the Teskey Range vary significantly more than those in the Kungoy Range. To determine if the changing number and distribution of the various lake types may be due to changes in ground ice, we apply differential interferometric synthetic aperture radar (DInSAR analysis using ALOS-2/PALSAR-2 for the debris landforms behind which glacial lakes appear. In the Teskey Range, ground ice occurs in 413 out of a total of 930 debris landforms, whereas in the Kungoy Range, ground ice occurs in 71 out of 180. In zones with predominant glacier-retreat during 1971–2010 (from Corona KH-4B and ALOS/PRISM, the Teskey Range had 180 new lake depressions as potential lake-basins, whereas the Kungoy Range had just 22. Existing depressions also expanded when melting ice produced subsidence. Such subsidence, together with debris landforms containing ground ice and ice tunnels, appear to cause the observed large number variability. In particular, the deposition of ice and debris by tunnel collapse or the freezing of storage water in a debris landform may close-off an ice tunnel, causing a lake to appear. Subsequent re-opening via melting of such blockage would produce

  19. Abiotic landscape and vegetation patterns in the Netherlands during the Weichselian Late Glacial

    NARCIS (Netherlands)

    Hoek, W.Z.

    2000-01-01

    The Late Glacial landscape of the Netherlands was a landscape with changing geomorphology and vegetation. Glacial, eolian and fluvial processes in the time before the Late Glacial initially had formed the main landscape types that still existed during the Late Glacial. In these landscape types,

  20. Glacial cycles: exogenous orbital changes vs. endogenous climate dynamics

    Science.gov (United States)

    Kaufmann, R. K.; Juselius, K.

    2010-04-01

    We use a statistical model, the cointegrated vector autoregressive model, to assess the degree to which variations in Earth's orbit and endogenous climate dynamics can be used to simulate glacial cycles during the late Quaternary (390 kyr-present). To do so, we estimate models of varying complexity and compare the accuracy of their in-sample simulations. Results indicate that strong statistical associations between endogenous climate variables are not enough for statistical models to reproduce glacial cycles. Rather, changes in solar insolation associated with changes in Earth's orbit are needed to simulate glacial cycles accurately. Also, results suggest that non-linear dynamics, threshold effects, and/or free oscillations may not play an overriding role in glacial cycles.

  1. Inverse vertical migration and feeding in glacier lanternfish (Benthosema glaciale)

    KAUST Repository

    Dypvik, Eivind; Klevjer, Thor A.; Kaartvedt, Stein

    2011-01-01

    lanternfish (Benthosema glaciale) were mainly distributed below ~200 m and displayed three different diel behavioral strategies: normal diel vertical migration (NDVM), inverse DVM (IDVM) and no DVM (NoDVM). The IDVM group was the focus of this study

  2. Breakup of last glacial deep stratification in the South Pacific

    Science.gov (United States)

    Basak, Chandranath; Fröllje, Henning; Lamy, Frank; Gersonde, Rainer; Benz, Verena; Anderson, Robert F.; Molina-Kescher, Mario; Pahnke, Katharina

    2018-02-01

    Stratification of the deep Southern Ocean during the Last Glacial Maximum is thought to have facilitated carbon storage and subsequent release during the deglaciation as stratification broke down, contributing to atmospheric CO2 rise. Here, we present neodymium isotope evidence from deep to abyssal waters in the South Pacific that confirms stratification of the deepwater column during the Last Glacial Maximum. The results indicate a glacial northward expansion of Ross Sea Bottom Water and a Southern Hemisphere climate trigger for the deglacial breakup of deep stratification. It highlights the important role of abyssal waters in sustaining a deep glacial carbon reservoir and Southern Hemisphere climate change as a prerequisite for the destabilization of the water column and hence the deglacial release of sequestered CO2 through upwelling.

  3. Radioiodine uptake following iodine-131 therapy for Graves' disease: an early indicator of need for retreatment

    International Nuclear Information System (INIS)

    Carpentier, W.R.; Gilliland, P.F.; Piziak, V.K.; Petty, F.C.; McConnell, B.G.; Verdonk, C.A.; Ibarra, J.D.; Thompson, J.Q.

    1989-01-01

    Forty-five patients with Graves' disease were studied prospectively to determine if 24-hour I-131 uptake measurements alone or in combination with serum thyroid hormone levels at six weeks would determine the necessity for retreatment of the thyrotoxicosis. All patients with an I-131 uptake greater than 30% at six weeks required retreatment. No patient with an I-131 uptake of less than 15% required retreatment. Patients with uptakes between 15% and 30% were variable. An elevated free thyroxin index at 6 weeks is not helpful to determine which patients will remain thyrotoxic. Patients with a free thyroxin index within the normal range at six weeks can be predicted to be euthyroid by 12 weeks if their 24-hour I-131 uptake is between 15% and 30% and to be hypothyroid if their 24-hour I-131 uptake is below 15%. There was no difference between patient groups treated initially with antithyroid medication and those who were not

  4. Retreatment of Chronic Hepatitis C Infection with Telaprevir: Preliminary Results in Turkey

    Directory of Open Access Journals (Sweden)

    Orhan Yıldız

    2015-09-01

    Full Text Available Background: The use of pegylated interferon alpha and ribavirin (PegIFN/RBV for the retreatment of chronic hepatitis C virus (HCV infection without a sustained virological response (SVR prior to PegIFN/RBV treatment has resulted in low success rates. Aims: To investigate the efficacy and safety of telaprevir (TVR in combination with PegIFN/RBV in patients infected with HCV genotypes 1 and 4 who were previously treated with PegIFN/RBV and failed to achieve SVR. Study Design: Multi-center, retrospective, cross-sectional study. Methods: The study included 111 patients: 80 prior relapsers, 25 prior null responders, and six prior partial responders to PegIFN/RBV treatment. The patients were given TVR/PegIFN/RBV for 12 weeks, followed by a 12-week PegIFN/RBV treatment; virological response results were assessed at weeks 4, 12, and 24. Treatment was discontinued in patients with HCV RNA >1000 IU/mL at week 4 or with negative RNA results at week 4 but >1000 IU/mL at week 12. Rapid virological response (RVR, early virological response (EVR, extended rapid virological response (eRVR, and virological response at 24th week of treatment were evaluated. The side effects of combination therapy and the rates of treatment discontinuation were investigated. Results: The mean age of the patients was 56.02±9.96 years and 45.9% were male. Ninety-one percent of the patients were infected with viral genotype 1, 69.6% with the interleukin (IL 28B genotype CT and 20.2% were cirrhotic. The RVR rate was 86.3% in prior relapsers, 56% in prior null responders, and 50% in prior partial responders (p=0.002. EVR rates in those groups were 91.3%, 56%, and 83.3%, respectively (p<0.001. eRVR rates were 83.8% in prior relapsers, 48% in prior null responders, and 50% in prior partial responders (<0.001. The virological response at the 24th week of treatment was found to be the highest in prior relapsers (88.8%; it was 56% in prior null responders and 66.7% in prior partial

  5. Crustal deformation associated with glacial fluctuations in the eastern Chugach Mountains, Alaska

    Science.gov (United States)

    Sauber, Jeanne; Plafker, George; Molnia, Bruce F.; Bryant, Mark A.

    2000-04-01

    The changes of the solid Earth in south central Alaska in response to two major glacial fluctuations on different temporal and spatial scales have been estimated and we evaluated their influence on the stress state and ongoing tectonic deformation of the region. During the recent (1993-1995) Bering Glacier surge, a large transfer of ice from the Bagley Ice Field to the Bering Glacier terminus region occurred. We estimated the elastic displacement of the solid Earth due to ice mass redistribution from Global Positioning System (GPS) measurements at sites near the surging glacier. We can account for these displacements by transfer of an ice volume of about 14 km3 from the surge reservoir area to the terminus region. We examined the background seismicity (ML ≥ 2.5) before, during, and after the surge. We found that the occurrence of small earthquakes (ML ≤ 4.0) in the surge reservoir region increased during the surge time interval possibly in response to a decrease in ice mass. This suggests that a small decrease in the vertical stress, σ3, could be enough to modulate the occurrence of small, shallow earthquakes in this dominantly thrust fault setting. During this century the southern Alaska coastal glaciers have been undergoing an overall decrease in volume. Based on our compilation of changes in the extent and thickness of the coastal glaciers between the Malaspina and Bering, we calculated surface displacements due to the Earth's viscoelastic response to annual thinning and to the cumulative retreat over the last 100 years. The uplift of the region due to an average annual thinning rate of 1-6 m/yr in the ablation region is 1-12 mm/yr. For our reference model with a viscosity of 5×1019 Pa s for depths between ≈ 40 and 200 km the total viscoelastic response due to the retreat over the last century may be as much as a couple of meters within the coastal ablation zone near Icy Bay. The maximum decrease in σv between 0 and 10 km was ≈ 1.0 MPa, which is

  6. Foreland sedimentary record of Andean mountain building during advancing and retreating subduction

    Science.gov (United States)

    Horton, Brian K.

    2016-04-01

    As in many ocean-continent (Andean-type) convergent margins, the South American foreland has long-lived (>50-100 Myr) sedimentary records spanning not only protracted crustal shortening, but also periods of neutral to extensional stress conditions. A regional synthesis of Andean basin histories is complemented by new results from the Mesozoic Neuquén basin system and succeeding Cenozoic foreland system of west-central Argentina (34-36°S) showing (1) a Late Cretaceous shift from backarc extension to retroarc contraction and (2) an anomalous mid-Cenozoic (~40-20 Ma) phase of sustained nondeposition. New detrital zircon U-Pb geochronological results from Jurassic through Neogene clastic deposits constrain exhumation of the evolving Andean magmatic arc, retroarc thrust belt, foreland basement uplifts, and distal eastern craton. Abrupt changes in sediment provenance and distal-to-proximal depositional conditions can be reconciled with a complex Mesozoic-Cenozoic history of extension, post-extensional thermal subsidence, punctuated tectonic inversion involving thick- and thin-skinned shortening, alternating phases of erosion and rapid accumulation, and overlapping igneous activity. U-Pb age distributions define the depositional ages of several Cenozoic stratigraphic units and reveal a major late middle Eocene-earliest Miocene (~40-20 Ma) hiatus in the Malargüe foreland basin. This boundary marks an abrupt shift in depositional conditions and sediment sources, from Paleocene-middle Eocene distal fluviolacustrine deposition of sediments from far western volcanic sources (Andean magmatic arc) and subordinate eastern cratonic basement (Permian-Triassic Choiyoi igneous complex) to Miocene-Quaternary proximal fluvial and alluvial-fan deposition of sediments recycled from emerging western sources (Malargüe fold-thrust belt) of Mesozoic basin fill originally derived from basement and magmatic arc sources. Neogene eastward advance of the fold-thrust belt involved thick

  7. Glacial ocean circulation and stratification explained by reduced atmospheric temperature

    OpenAIRE

    Jansen, Malte F.

    2016-01-01

    To understand climatic swings between glacial and interglacial climates we need to explain the observed fluctuations in atmospheric carbon dioxide (CO2), which in turn are most likely driven by changes in the deep ocean circulation. This study presents a model for differences in the deep ocean circulation between glacial and interglacial climates consistent with both our physical understanding and various proxy observations. The results suggest that observed changes in ocean circulation and s...

  8. Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier.

    Science.gov (United States)

    Smith, J A; Andersen, T J; Shortt, M; Gaffney, A M; Truffer, M; Stanton, T P; Bindschadler, R; Dutrieux, P; Jenkins, A; Hillenbrand, C-D; Ehrmann, W; Corr, H F J; Farley, N; Crowhurst, S; Vaughan, D G

    2017-01-05

    The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line-which marks the boundary between grounded ice and floating ice shelf-is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreat is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Thus our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.

  9. Low post-glacial rebound rates in the Weddell Sea due to Late Holocene ice-sheet readvance

    Science.gov (United States)

    Bradley, Sarah L.; Hindmarsh, Richard C. A.; Whitehouse, Pippa; Bentley, Michael J.; King, Matt

    2014-05-01

    The Holocene deglaciation of West Antarctica resulted in widespread ice surface lowering. While many ice-sheet reconstructions generally assume a monotone Holocene retreat for the West Antarctica Ice sheet (WAIS) [Ivins et al., 2013; Peltier, 2004; Whitehouse et al., 2012], an increasing number of glaciological observations infer it is readvancing, following retreat behind the present-day margin[Siegert et al., 2013]. We will show that a readvance in the Weddell Sea region can reconcile two outstanding problems: (i) the present-day widespread occurrence of seemingly stable ice-streams grounded on beds that deepen inland in apparent contradiction to theory [Schoof, 2007]; and (ii) the inability of models of Glacial Isostatic Adjustment (GIA) to match present-day uplift rates [Whitehouse et al., 2012]. Combining a suite of ice loading histories that include a readvance with a model of GIA provides significant improvements to predictions of present-day uplift rates, and we are able to reproduce previously unexplained observations of subsidence in the southern sector of the Weddell Sea. We hypothesize that retreat behind present grounding lines occurred when the bed was lower, and isostatic recovery led to shallowing, ice sheet re-grounding and readvance. We will conclude that some sections of the current WAIS grounding line that are theoretically unstable, may be advancing and that the volume change of the WAIS may have been more complex in the Late Holocene than previously posited. This revised Holocene ice-loading history would have important implications for the GIA correction applied to Gravity Recovery and Climate Experiment (GRACE) data, likely resulting in a reduction in the GIA correction and a smaller estimate of present-day ice mass loss within the Weddell Sea region of the WAIS. Ivins, E. R., T. S. James, J. Wahr, E. J. O. Schrama, F. W. Landerer, and K. M. Simon (2013), Antarctic contribution to sea level rise observed by GRACE with improved GIA correction

  10. Glacial Survival of Boreal Trees in Northern Scandinavia

    DEFF Research Database (Denmark)

    Parducci, L; Jørgensen, Tina; Tollefsrud, M M

    2012-01-01

    It is commonly believed that trees were absent in Scandinavia during the last glaciation and first recolonized the Scandinavian Peninsula with the retreat of its ice sheet some 9000 years ago. Here, we show the presence of a rare mitochondrial DNA haplotype of spruce that appears unique to Scandi......It is commonly believed that trees were absent in Scandinavia during the last glaciation and first recolonized the Scandinavian Peninsula with the retreat of its ice sheet some 9000 years ago. Here, we show the presence of a rare mitochondrial DNA haplotype of spruce that appears unique...

  11. Lake sediment multi-taxon DNA from North Greenland records early post-glacial appearance of vascular plants and accurately tracks environmental changes

    DEFF Research Database (Denmark)

    Epp, L. S.; Gussarova, C.; Boessenkool, S.

    2015-01-01

    temperatures. Lake sediments contain DNA paleorecords of the surrounding ecosystems and can be used to retrieve a variety of organismal groups from a single sample. In this study, we analyzed vascular plant, bryophyte, algal (in particular diatom) and copepod DNA retrieved from a sediment core spanning...... phases, and distinct temporal changes in plant presence were recovered. The plant DNA was mostly in agreement with expected vegetation history, but very early occurrences of vascular plants, including the woody Empetrum nigrum, document terrestrial vegetation very shortly after glacial retreat. Our study...... core. Our DNA record was stratigraphically coherent, with no indication of leaching between layers, and our cross-taxon comparisons were in accordance with previously inferred local ecosystem changes. Authentic ancient plant DNA was retrieved from nearly all layers, both from the marine and the limnic...

  12. The retreat of mountain glaciers: what can satellites tell us?

    International Nuclear Information System (INIS)

    Berthier, E.

    2008-01-01

    Mountain glaciers are one of the best indicators of climate change and their rapid wastage make them a strong contributor to sea level rise. The estimated 160,000 mountain glaciers are spread all around the globe and remain difficult to access. Consequently, only a limited number (about 50 glaciers) are regularly monitored in the field. Today, high resolution satellite optical images are combined to some advanced methodologies to survey their fast and alarming evolution. (author)

  13. The glacial record of New Zealand's Southern Alps

    Science.gov (United States)

    Schaefer, J. M.; Denton, G.; Lowell, T.; Anderson, B.; Rinterknecht, V.; Schlosser, P.; Ivy-Ochs, S.; Kubik, P.; Schluechter, C.; Chinn, T.; Barrell, D.; Lifton, N.; Jull, T.

    2004-12-01

    We present detailed mapping and surface exposure dating using in-situ Be-10 and C-14 of the moraine set of Lake Pukaki, New Zealand's Southern Alps, spanning from the penultimate glaciation, over several Last Glacial Maximum (LGM) moraines, the late glacial event to Holocene glacial advances. New Zealand, a mountain ridge in the middle of the Southern Ocean, has one of the best preserved moraine records world-wide, offering the opportunity to reconstruct amplitude and timing of climate changes from Southern mid-latitudes, an area where paleoclimate data is scarce. The extensive mapping effort by G. Denton and colleagues (http://wyvern.gns.cri.nz/website/csigg/) provides a unique background for sample selection for Surface Exposure Dating. Our extensive data set (>40 samples analyzed so far) indicate that (i) the LGM in New Zealand terminated clearly prior to the Boelling/Alleroed warming, (ii) the late glacial advance is within uncertainties consistent with the timing of the Younger Dryas cold reversal; (iii) there occurred an early Holocene glacial event of the same amplitude than the Little Ice Age. This latter event is the first Holocene glacial event from the Southern Hemisphere dated by in-situ Be-10 and C-14.

  14. Contrasting evidence of Holocene ice margin retreat, south-western Greenland

    DEFF Research Database (Denmark)

    Levy, L. B.; Larsen, N. K.; Davidson, T. A.

    2017-01-01

    Constraining the Greenland Ice Sheet's (GrIS) response to Holocene climate change provides calibrations for ice sheet models that hindcast past ice margin fluctuations. Ice sheet models predict enhanced ice retreat in south-western Greenland during the middle Holocene; however, few geological...... observations corroborating the extensive retreat are available. We present new data from lake sediment cores from the Isua region, south-western Greenland, which provide constraints on Holocene fluctuations of the GrIS margins. Our data indicate that the main GrIS margin was 30 km west of its present...

  15. 3D Modeling of Glacial Erratic Boulders in the Haizi Shan Region, Eastern Tibetan Plateau

    Science.gov (United States)

    Sheriff, M.; Stevens, J.; Radue, M. J.; Strand, P.; Zhou, W.; Putnam, A. E.

    2017-12-01

    The focus of our team's research is to study patterns of glacier retreat in the Northern and Southern Hemispheres at the end of the last ice age. Our purpose is to search for what caused this great global warming. Such information will improve understanding of how the climate system may respond to the human-induced buildup of fossil carbon dioxide. To reconstruct past glacier behavior, we sample boulders deposited by glaciers to find the rate of ancient recession. Each sample is tested to determine the age of the boulder using 10Be cosmogenic-nuclide dating. My portion of this research focuses on creating 3D models of the sampled boulders. Such high-resolution 3D models afford visual inspection and analysis of each boulder in a virtual reality environment after fieldwork is complete. Such detailed virtual reconstructions will aid post-fieldwork evaluation of sampled boulders. This will help our team interpret 10Be dating results. For example, a high-resolution model can aid post-fieldwork observations, and allow scientists to determine whether the rock has been previously covered, eroded, or moved since it was deposited by the glacier, but before the sample was collected. Also a model can be useful for recognizing patterns between age and boulder morphology. Lastly, the models can be used for those who wish to review the data after publication. To create the 3D models, I will use Hero4 GoPro and Canon PowerShot digital cameras to collect photographs of each boulder from different angles. I will then process the digital imagery using `structure-from-motion' techniques and Agisoft Photoscan software. All boulder photographs will be synthesized to 3D and based on a standardized scale. We will then import these models into an environment that can be accessed using cutting-edge virtual reality technology. By producing a virtual archive of 3D glacial boulder reconstructions, I hope to provide deeper insight into geological processes influencing these boulders during and

  16. A new concept for glacial geological investigations of surges, based on High-Arctic examples (Svalbard)

    Science.gov (United States)

    Lønne, Ida

    2016-01-01

    Svalbard is a key area for the investigation of glacial surges, and almost two centuries worth of field observations exists from this region. Studies have shown that the course of a surge and the associated formation of landforms are strongly influenced by basinal factors, and that the broad range of variables involved can hamper interpretations and comparisons. Based on a review of surges in Svalbard, a new concept for glacial geological investigations has been developed that combines ice-flows, ice-front movements, and morphostratigraphy. The concept is comprised of the following four elements: 1) classification based on the configuration and characteristics of the receiving basin, 2) division of the surge cycle into six stages, 3) guidelines for morphological mapping, and 4) use of an allostratigraphic approach for interpreting ice-front movements. In this context, delineation of the active phase is critical, which include the history of terminus movements, and four main categories of receiving basins are recognized. These are (A) terrestrial basins with deformable substrates, (B) terrestrial basins with poorly deformable substrates, (C) shallow water basins, and (D) deep water basins. The ice-front movement history is reconstructed by coupling information from the proglacial moraines (syn-surge), the supraglacial moraines (post-surge), and the associated traces of meltwater to the surge stages (I-VI). This approach has revealed a critical relationship between the termination of the active phase and three morphological elements, namely, the maximum ice-front position, the maximum moraine extent and the youngest proglacial moraine, which are unique for each of the basins A-D. The concept is thus a novel and more precise approach for mapping the active phase and the active phase duration, as shown by the ∼12-year long surge of Fridtjovbreen, where stage I was 30 months (inception), stage II was 54 months (ice-front advance), stage III was 12 months (stillstand

  17. Organic carbon in glacial fjords of Chilean Patagonia

    Science.gov (United States)

    Pantoja, Silvio; Gutiérrez, Marcelo; Tapia, Fabián; Abarzúa, Leslie; Daneri, Giovanni; Reid, Brian; Díez, Beatriz

    2016-04-01

    The Southern Ice Field in Chilean Patagonia is the largest (13,000 km2) temperate ice mass in the Southern hemisphere, yearly transporting ca. 40 km3 of freshwater to fjords. This volume of fresh and cold water likely affects adjacent marine ecosystems by changing circulation, productivity, food web dynamics, and the abundance and distribution of planktonic and benthic organisms. We hypothesize that freshwater-driven availability of inorganic nutrient and transport of organic and inorganic suspended matter, as well as microbes, become a controlling factor for productivity in the fjord associated with the Baker river and Jorge Montt glacier. Both appear to be sources of silicic acid, but not of nitrate and particulate organic carbon, especially during summer, when surface PAR and glacier thawing are maximal. In contrast to Baker River, the Jorge Montt glacier is also a source of dissolved organic carbon towards a proglacial fjord and the Baker Channel, indicating that a thorough chemical description of sources (tidewater glacier and glacial river) is needed. Nitrate in fiord waters reaches ca. 15 μM at 25 m depth with no evidence of mixing up during summer. Stable isotope composition of particulate organic nitrogen reaches values as low as 3 per mil in low-salinity waters near both glacier and river. Nitrogen fixation could be depleting δ15N in organic matter, as suggested by the detection at surface waters of nif H genes belonging to diazotrophs near the Montt glacier. As diazotrophs have also been detected in other cold marine waters (e.g. Baltic Sea, Arctic Ocean) as well as glaciers and polar terrestrial waters, there is certainly a potential for both marine and freshwater microbes to contribute and have a significant impact on the Patagonian N and C budgets. Assessing the impact of freshwater on C and N fluxes and the microbial community structure in Patagonian waters will allow understanding future scenarios of rapid glacier melting. This research was funded

  18. Volcanic CO2 Emissions and Glacial Cycles: Coupled Oscillations

    Science.gov (United States)

    Burley, J. M.; Huybers, P. J.; Katz, R. F.

    2016-12-01

    Following the mid-Pleistocene transition, the dominant period of glacial cycles changed from 40 ka to 100 ka. It is broadly accepted that the 40 ka glacial cycles were driven by cyclical changes in obliquity. However, this forcing does not explain the 100 ka glacial cycles. Mechanisms proposed for 100 ka cycles include isostatic bed depression and proglacial lakes destabilising the Laurentide ice sheet, non-linear responses to orbital eccentricity, and Antarctic ice sheets influencing deep-ocean stratification. None of these are universally accepted. Here we investigate the hypothesis that variations in volcanic CO2 emissions can cause 100 ka glacial cycles. Any proposed mechanism for 100 ka glacial cycles must give the Earth's climate system a memory of 10^4 - 10^5years. This timescale is difficult to achieve for surface processes, however it is possible for the solid Earth. Recent work suggests volcanic CO2 emissions change in response to glacial cycles [1] and that there could be a 50 ka delay in that response [2]. Such a lagged response could drive glacial cycles from 40 ka cycles to an integer multiple of the forcing period. Under what conditions could the climate system admit such a response? To address this, we use a simplified climate model modified from Huybers and Tziperman [3]. Our version comprises three component models for energy balance, ice sheet growth and atmospheric CO2 concentration. The model is driven by insolation alone with other components varying according to a system of coupled, differential equations. The model is run for 500 ka to produce several glacial cycles and the resulting changes in global ice volume and atmospheric CO2 concentration.We obtain a switch from 40 ka to 100 ka cycles as the volcanic CO2 response to glacial cycles is increased. These 100 ka cycles are phase-locked to obliquity, lasting 80 or 120 ka. Whilst the MOR response required (in this model) is larger than plausible estimates based on [2], it illustrates the

  19. Coupled ice sheet - climate simulations of the last glacial inception and last glacial maximum with a model of intermediate complexity that includes a dynamical downscaling of heat and moisture

    Science.gov (United States)

    Quiquet, Aurélien; Roche, Didier M.

    2017-04-01

    Comprehensive fully coupled ice sheet - climate models allowing for multi-millenia transient simulations are becoming available. They represent powerful tools to investigate ice sheet - climate interactions during the repeated retreats and advances of continental ice sheets of the Pleistocene. However, in such models, most of the time, the spatial resolution of the ice sheet model is one order of magnitude lower than the one of the atmospheric model. As such, orography-induced precipitation is only poorly represented. In this work, we briefly present the most recent improvements of the ice sheet - climate coupling within the model of intermediate complexity iLOVECLIM. On the one hand, from the native atmospheric resolution (T21), we have included a dynamical downscaling of heat and moisture at the ice sheet model resolution (40 km x 40 km). This downscaling accounts for feedbacks of sub-grid precipitation on large scale energy and water budgets. From the sub-grid atmospheric variables, we compute an ice sheet surface mass balance required by the ice sheet model. On the other hand, we also explicitly use oceanic temperatures to compute sub-shelf melting at a given depth. Based on palaeo evidences for rate of change of eustatic sea level, we discuss the capability of our new model to correctly simulate the last glacial inception ( 116 kaBP) and the ice volume of the last glacial maximum ( 21 kaBP). We show that the model performs well in certain areas (e.g. Canadian archipelago) but some model biases are consistent over time periods (e.g. Kara-Barents sector). We explore various model sensitivities (e.g. initial state, vegetation, albedo) and we discuss the importance of the downscaling of precipitation for ice nucleation over elevated area and for the surface mass balance of larger ice sheets.

  20. Reconceptualizing Leadership in Migrant Communities: Latina/o Parent Leadership Retreats as Sites of Community Cultural Wealth

    Science.gov (United States)

    Nava, Pedro E.; Lara, Argelia

    2016-01-01

    This article examines how the Education Leadership Foundation (a leadership development community based organization) in partnership with the Migrant Education Program use parent retreats for building leadership, and skill development of migrant farm-working families. Utilizing cooperative and community responsive practices, these retreats build…

  1. Timing, cause and impact of the late Eocene stepwise sea retreat from the Tarim Basin (west China)

    NARCIS (Netherlands)

    Bosboom, R.|info:eu-repo/dai/nl/322947359; Dupont-Nivet, G.|info:eu-repo/dai/nl/313092559; Grothe, A.|info:eu-repo/dai/nl/338017712; Brinkhuis, H.|info:eu-repo/dai/nl/095046097; Villa, G.; Mandic, O.; Stoica, M.; Kouwenhoven, T.J.|info:eu-repo/dai/nl/191377406; Huang, W.; Yang, W.; Guo, Z.

    2014-01-01

    A vast shallow epicontinental sea extended across Eurasia and was well-connected to the Western Tethys before it retreated westward and became isolated as the Paratethys Sea. However, the palaeogeography and the timing of this westward retreat are too poorly constrained to determine potential wider

  2. Microfabric and Structures in Glacial Ice

    Science.gov (United States)

    Monz, M.; Hudleston, P. J.

    2017-12-01

    Similar to rocks in active orogens, glacial ice develops both structures and fabrics that reflect deformation. Crystallographic preferred orientation (CPO), associated with mechanical anisotropy, develops as ice deforms, and as in rock, directly reflects the conditions and mechanisms of deformation and influences the overall strength. This project aims to better constrain the rheologic properties of natural ice through microstructural analysis and to establish the relationship of microfabric to macroscale structures. The focus is on enigmatic fabric patterns found in coarse grained, "warm" (T > -10oC) ice deep in ice sheets and in valley glaciers. Deformation mechanisms that produce such patterns are poorly understood. Detailed mapping of surface structures, including bedding, foliation, and blue bands (bubble-free veins of ice), was done in the ablation zone of Storglaciären, a polythermal valley glacier in northern Sweden. Microstructural studies on samples from a transect across the ablation zone were carried out in a cold room. Crystal size was too large for use of electron backscattered diffraction to determine CPO, therefore a Rigsby universal stage, designed specifically for ice, was used. In thick and thin sections, recrystallized grains are locally variable in both size (1mm-7cm in one thin section) and shape and clearly reflect recrystallization involving highly mobile grain boundaries. Larger crystals are often branching, and appear multiple times throughout one thin section. There is a clear shape preferred orientation that is generally parallel with foliation defined by bubble alignment and concentration. Locally, there appears to be an inverse correlation between bubble concentration and smoothness of grain boundaries. Fabric in samples that have undergone prolonged shear display roughly symmetrical multimaxima patterns centered around the pole to foliation. The angular distances between maxima suggest a possible twin relationship that may have

  3. Quaternary sedimentation of the Alaskan Beaufort shelf: Influence of regional tectonics, fluctuating sea levels, and glacial sediment sources

    Science.gov (United States)

    Dinter, D.A.

    1985-01-01

    The offshore stratigraphy of the Quaternary Gubik Formation of Arctic Alaska has been studied on high-resolution seismic profiles with a maximum sub-seafloor penetration of about 100 m. In general, marine transgressive subunits of the Gubik Formation are wedge-shaped on the shelf, thickening slightly seaward to the shelf break, beyond which they are offset by landslides and slumps. Beneath the eastern third of the Alaskan Beaufort shelf, active folding has created two persistent structural depressions, the Eastern and Western Wedge Terranes, in which the wedge morphology is especially well developed. The youngest transgressive marine wedge, which was deposited in such a way as to fill these depressions, leaving a generally flat present-day shelf surface, is inferred to be late Wisconsin or younger in age because it overlies a prominent disconformity interpreted to have been formed during the late Wisconsin glacial sea-level minimum. The thickness of this youngest wedge, Unit A, locally exceeds 40 m on the outer shelf, yet apparently relict gravel deposits collected from its seabed surface indicate that the depositional rate is presently quite low on the middle and outer shelf. Lithologies of the gravels are exotic to Alaska, but similar to suites exposed in the Canadian Arctic Islands. These observations suggest a depositional scenario in which the retreating Laurentide Ice Sheet shed sediment-laden icebergs from the Canadian Arctic Islands into the Arctic Ocean following the late Wisconsin glacial maximum. These bergs were then rafted westward by the Beaufort Gyre and grounded on the Alaskan shelf by northeasterly prevailing winds. Especially large numbers of bergs accumulated in the wedge terrane embayments-created as sea level rose-and melted there, filling the embayments with their sedimentary cargo. As glacial retreat slowed, depositional rates on the shelf dwindled. This mode of deposition in the Alaskan Beaufort wedge terranes may be typical of early post-glacial

  4. Reconstruction of a glacial lake outburst flood (GLOF) in the Engaño Valley, Chilean Patagonia: Lessons for GLOF risk management.

    Science.gov (United States)

    Anacona, Pablo Iribarren; Mackintosh, Andrew; Norton, Kevin

    2015-09-15

    Floods from moraine-dammed lake failures can have long standing effects not only on riverine landscapes but also on mountain communities due to the high intensity (i.e. great depth and high velocities) and damaging capacity of glacial lake outburst floods (GLOFs). GLOFs may increase in frequency as glaciers retreat and new lakes develop and there is an urgent need to better understand GLOF dynamics and the measures required to reduce their negative outcomes. In Patagonia at least 16 moraine-dammed lakes have failed in historic time, however, data about GLOF dynamics and impacts in this region are limited. We reconstruct a GLOF that affected a small village in Chilean Patagonia in March 1977, by semi structured interviews, interpretation of satellite images and 2D hydraulic modelling. This provides insight into the GLOF dynamics and the planning issues that led to socioeconomic consequences, which included village relocation. Modelling shows that the water released by the GLOF was in the order of 12-13 × 10(6)m(3) and the flood lasted for about 10h, reaching a maximum depth of ~1.5m in Bahía Murta Viejo, ~ 26 km from the failed lake. The lake had characteristics in common with failed lakes worldwide (e.g. the lake was in contact with a retreating glacier and was dammed by a narrow-steep moraine). The absence of land-use planning and the unawareness of the GLOF hazard contributed to the village flooding. The Río Engaño GLOF illustrates how small-scale and short-distance migration is a reasonable coping strategy in response to a natural hazard that may increase in frequency as atmospheric temperature rises and glaciers retreat. Copyright © 2015 Elsevier B.V. All rights reserved.

  5. Late Pleistocene glacial fluctuations in Cordillera Oriental, subtropical Andes

    Science.gov (United States)

    Martini, Mateo A.; Kaplan, Michael R.; Strelin, Jorge A.; Astini, Ricardo A.; Schaefer, Joerg M.; Caffee, Marc W.; Schwartz, Roseanne

    2017-09-01

    The behavior of subtropical glaciers during Middle to Late Pleistocene global glacial maxima and abrupt climate change events, specifically in Earth's most arid low-latitude regions, remains an outstanding problem in paleoclimatology. The present-day climate of Cordillera Oriental, in arid northwestern Argentina, is influenced by shifts in subtropical climate systems, including the South American Summer Monsoon. To understand better past glacier-subtropical climates during the global Last Glacial Maximum (LGM, 26.5-19 ka) and other time periods, we combined geomorphic features with forty-two precise 10Be ages on moraine boulders and reconstructed paleo-equilibrium line altitudes (ELA) at Nevado de Chañi (24°S) in the arid subtropical Andes. We found a major glacial expansion at ∼23 ± 1.6 ka, that is, during the global LGM. Additional glacial expansions are observed before the global LGM (at ∼52-39 ka), and after, at 15 ± 0.5 and 12 ± 0.6 ka. The ∼15 ka glacial event was found on both sides of Chañi and the ∼12 ka event is only recorded on the east side. Reconstructed ELAs of the former glaciers exhibit a rise from east to west that resembles the present subtropical climate trajectory from the Atlantic side of the continent; hence, we infer that this climate pattern must have been present in the past. Based on comparison with other low-latitude paleoclimate records, such as those from lakes and caves, we infer that both temperature and precipitation influenced past glacial occurrence in this sector of the arid Andes. Our findings also imply that abrupt deglacial climate events associated with the North Atlantic, specifically curtailed meridional overturning circulation and regional cooling, may have had attendant impacts on low subtropical Southern Hemisphere latitudes, including the climate systems that affect glacial activity around Nevado de Chañi.

  6. Variaciones glaciales durante el Holoceno en Patagonia Central, Aisén, Chile: evidencias geomorfológicas Holocene glacial variations in Central Patagonia, Aisén, Chile: geomorphological evidences

    Directory of Open Access Journals (Sweden)

    María Mardones

    2011-07-01

    en la temperatura y precipitación atmosférica.During the Holocene, the patagonian glaciers were characterized by geomorphologically registered advances and retreats. This paper presents the geomorphological evolution and evidences of Holocene glacial advances within a segment in Central Patagonia Cordillera. This area will be used as a reference for studying the postglacial paleoclimatic evolution in the southernmost part of South America. The study area is the río Blanco basin (45°30'S, located in Central Patagonia (Aisén Region, Chile. Radiometric dating of organic sediments, within terminal moraines, provides preliminary data of two glacial advances. The first one is represented by the Lake Elizalde frontal moraine, which yielded a 14C age of 9.370±50 years BP (10,700 to 10,480 cal. yr BP. According to this chronological age, this glacial event took place in the Early Holocene. This glacial advance, being 100 to 200 years older than that observed immediately south of the study area, on the eastern edge of General Carrera Lake (or Buenos Aires Lake, in Argentina and approximately 100 years younger than the event recorded in the Puerto Banderas I moraine (Argentino Lake, 50°S. These results show that the behavior patterns of the Central Patagonia glaciers differ from that observed both in the Lake District (41°S, Chile and in the Magallanes District (54°S, Chile, where there are no traces of glacial readvancement recorded during the Early Holocene. After a major retreat to the west, a more recent glacial advance occurred in the Quetro river valley (a tributary river of the Blanco river, at an age prior to 2.250±40 BP (2.340 to 2.150 cal. yr BP, comparable to the cold stage of the Middle Neoglacial, interpreted to have occurred in different parts of Patagonia. Confronting these results with previously published pollen records, we postulate that the cause of both glacier fluctuations are regional variations in the atmospheric temperature and precipitations.

  7. ACL Research Retreat VI : An update on ACL injury risk and prevention

    NARCIS (Netherlands)

    R.J. Schmitz; M. Collins; D.A. Padua; Anne Benjaminse; A.M. Chaudhari; S.J. Schultz

    2012-01-01

    It has been well recognized that multiple factors, whether individually or in combination, contribute to noncontact anterior cruciate ligament (ACL) injury. The ongoing mission of the ACL Research Retreat is to bring clinicians and researchers together to present and discuss the most recent advances

  8. Comparison of retreatment ability of full-sequence reciprocating instrumentation and 360° rotary instrumentation.

    Science.gov (United States)

    Capar, Ismail Davut; Gok, Tuba; Orhan, Ezgi

    2015-12-01

    The purpose of the present study was to investigate the amount of root canal filling material after root canal filling removal with 360° rotary instrumentation or reciprocating motion with the same file sequence. Root canals of the 36 mandibular premolars were shaped with ProTaper Universal instruments up to size F2 and filled with corresponding single gutta-percha cone and sealer. The teeth were assigned to two retreatment groups (n = 18): group 1 360° rotational motion and group 2 reciprocating motion of ATR Tecnika motors (1310° clockwise and 578° counterclockwise). Retreatment procedure was performed with ProTaper Universal retreatment files with a sequence of D1-3 and ProTaper Universal F3 instruments. Total time required to remove filling material were recorded. Remaining filling material was examined under stereomicroscope at ×8 magnification. The data were analysed statistically using the Mann-Whitney U test, and testing was performed at 95 % confidence level (p  0.05) in terms of remaining filling material. The total time required for retreatment was shorter in 360° rotational motion group compared to reciprocating motion group (p instruments with reciprocating motion of ATR motor and conventional rotary motion have similar efficacy in root canal filling removal.

  9. From Retreat to Re-engagement: The New American Foreign Policy ...

    African Journals Online (AJOL)

    From Retreat to Re-engagement: The New American Foreign Policy for ... that the re-engagement with Sub-Saharan Africa, is based on US perception of threats ... in the subordination of the region to the world's only superpower and its allies.

  10. The use of social Stegodyphus spider retreats as nest-lining by pale ...

    African Journals Online (AJOL)

    The pale chanting-goshawk (Melierax canorus) incorporates silk nests (hereafter 'retreats') of the social spider Stegodyphus dumicola (Araneae: Eresidae) in the construction of the nest-lining of their own nests. This study investigates whether pale chanting-goshawks in the Little Karoo, South Africa, show a preference for ...

  11. Late Eocene sea retreat from the Tarim Basin (west China) and concomitant Asian paleoenvironmental change

    NARCIS (Netherlands)

    Bosboom, R.E.; Dupont-Nivet, G.; Houben, A.J.P.; Brinkhuis, H.; Villa, G.; Mandic, O.; Stoica, M.; Zachariasse, W.J.; Guo, ZJ.; Li, CX.; Krijgsman, W.

    2011-01-01

    The Paleogene sediments of the southwest Tarim Basin along the West Kunlun Shan in western China include the remnants of the easternmost extent of a large epicontinental sea. This shallow sea once extended across the Eurasian continent before it retreated westward and eventually separated as the

  12. Linking Tarim Basin sea retreat (west China) and Asian aridification in the late Eocene

    NARCIS (Netherlands)

    Bosboom, R.; Dupont-Nivet, G.; Grothe, A.; Brinkhuis, H.; Villa, G.; Mandic, O.; Stoica, M.; Huang, W.; Yang, W.; Guo, Z.; Krijgsman, W.

    2014-01-01

    The Tarim Basin in western China formed the easternmost margin of a shallow epicontinental sea that extended across Eurasia and was well connected to the western Tethys during the Paleogene. Climate modelling studies suggest that the westward retreat of this sea from Central Asia may have been as

  13. Soil development along a glacial chronosequence (Pré de Bar glacier, NW Italy)

    Science.gov (United States)

    Letey, Stéphanie; Freppaz, Michele; Filippa, Gianluca; Stanchi, Silvia; Cerli, Chiara; Pogliotti, Paolo; Zanini, Ermanno

    2010-05-01

    After the maximum expansion phase of the Little Ice Age, soils located in proglacial areas in the Italian Alps evolved over a time span of about 190 years. In the future, as a consequence of climate change, additional areas will become ice-free and therefore subject to pedogenesis. In such conditions, ice retreat time and topography are expected to play a major role among soil formation factors. Due to extreme environmental characteristics, soil evolution will be rather slow, and heavily influenced by severe soil loss phenomena (e.g. water erosion due to extreme rainfall event and snowmelt, avalanche erosion). We investigated the soil formation along a glacial chronosequence of an Alpine glacier foreland. The Pré de Bar glacier is located in North West Italy (Aosta Valley Region), in the Mont Blanc massif, between 3750 and 2150 m a.s.l. and it covers an area of 340 ha. The glacier was chosen because of the availability of old photographs documenting the glacier retreat phases starting from 1820. At the present time, the cumulative retreat length of the Pré de Bar glacier has reached 1600 m. Along this length, sampling sites were established at 6 successional stages from 6 to 189 years since deglaciation, from 2100 to 1880 m a.s.l.. Soil profiles were opened and sampled according to diagnostic horizons, then they were characterized by means of standard chemical and physical methods. Moreover, as recently deglaciated soils, characterized by incipient pedogenesis, may be particularly vulnerable from the physical point of view, the Atterberg Limits (LL, Liquid Limit; and PL, Plastic Limit) and the WAS (Water Aggregate Stability) index were determined, as indicators of soil physical quality. Soil samples were also subjected to organic matter density fractionation to assess the role of organic C in structure development. All the analyzed soils were classified as Lythic Cryorthents (higher elevation) or Typic Cryorthents (lower elevation) (USDA - Soil Taxonomy), with

  14. Investigations into localized re-treatment of the retina with a 3-nanosecond laser.

    Science.gov (United States)

    Chidlow, Glyn; Plunkett, Malcolm; Casson, Robert J; Wood, John P M

    2016-08-01

    Subvisual retinal lasers necessarily cause clinically invisible lesions, hence, they could intentionally or inadvertently be targeted at precisely the same or an overlapping location during repeat laser treatment. Herein, we investigated the structural integrity and cellular responses of localized re-treatment using a nanosecond laser (2RT) currently in trials for early age-related macular degeneration. Rats were randomly assigned to one of five groups: sham, subvisual 2RT, subvisual 2RT re-treatment, visual effect 2RT, visual effect 2RT re-treatment. Re-treatment groups were lasered on days 0 and 21; single laser groups were only lasered on day 21. All rats were euthanized at day 28 and eyes were then dissected and processed for immunohistochemistry. For re-treatment, the laser was targeted at precisely the same locations on both delivery occasions. Analytical endpoints included monitoring of retinal vascular integrity overlying lesions, investigation into any potential choroidal neovascularization, assessment of the RPE, quantification of collateral injury to photoreceptors or other neuronal classes, and delineation of glial reactivity. Repeat laser administration to rats caused ostensibly identical retinal-RPE-choroid responses to those obtained in age-matched rats that received only a single application. Specifically, 7 days after treatment, RPE cells were re-populating lesion sites. No obvious consistent differences were evident between the single and repeat laser groups. Moreover, repeat laser caused no (measurable) additive injury to photoreceptors or other retinal neuronal classes from single laser treatment. In re-lasered animals, there was no increase in microglial activity overlying and adjacent to lesion sites relative to single lasered rats. Finally, there was no evidence of choroidal neovascularization after repeat laser treatment. The overall results provide a measure of confidence that re-treatment of patients with 2RT should not provide any

  15. Continuing evidence for poorer treatment outcomes for single male patients: Retreatment data from RTOG 97-14

    International Nuclear Information System (INIS)

    Konski, Andre; DeSilvio, Michelle; Hartsell, William; Watkins-Bruner, Deborah; Coyne, James; Scarantino, Charles; JanJan, Nora

    2006-01-01

    Purpose: The specific aim of this study was to evaluate outcome differences by gender and partner status for patients treated on Radiation Therapy Oncology Group (RTOG) protocol 97-14. Methods and Materials: RTOG 97-14 randomized patients with metastatic breast or prostate cancer to bone to receive 8 Gy in 1 fraction or 30 Gy in 10 fractions. Retreatment rates and overall survival were made based upon gender, marital status, and Karnofsky Performance Status (KPS). The cumulative incidence method was used to estimate retreatment time at 36 months from enrollment, and Gray's test was used to test for treatment differences within the same groupings. Marital status, gender, KPS, and treatment were variables tested in a univariate Cox model evaluating the time to retreatment. Results: Married men and women and single women receiving 30 Gy had significantly longer time to retreatment, p = 0.0067, p = 0.0052, and p = 0.0009 respectively. We failed to show a difference in retreatment rates over time in single men receiving either 30 Gy or 8 Gy. Univariate analysis of the entire group determined patients receiving 30 Gy in 10 fractions significantly less likely to receive retreatment, p < 0.0001, with a trend toward single patients less likely to be re-treated, p = 0.07. Conclusion: Non-disease-related variables, such as social support, might influence the results of clinical trials with subjective endpoints such as retreatment rates. The statistically nonsignificant difference in the 36-month retreatment rates observed in single male patients receiving 8 Gy may be a result of inadequate social support systems in place to facilitate additional care. Patients receiving 8 Gy in a single fraction had significantly higher retreatment rates compared with patients receiving 30 Gy in 10 fractions

  16. Retreat of Stephenson Glacier, Heard Island, from Remote Sensing and Field Observations

    Science.gov (United States)

    Mitchell, W.; Schmieder, R.

    2017-12-01

    Heard Island (Australian sub-Antarctic territory, 53 S, 73.5 E) is a volcanic island mantled in glaciers, and a UNESCO World Heritage Site both for its geology and ecology. Lying to the south of the Antarctic Convergence, the changes in response to climate seen on Heard Island are likely to be a bellwether for areas further south. Beginning in 1999, American satellites (Landsat 7, EO-1, and Landsat 8) have produced images of the island on a roughly weekly basis. Although the island is often shrouded in clouds, clear images of at least portions of the island are plentiful enough to create a nearly-annual record of the toe of Stephenson Glacier. During this period, Stephenson Glacier retreated by nearly 5 km, and lost 50% of its area. As a result of this retreat, a portion of the glacier now could be classified as a separate glacier. Additionally, in 2016, terrestrial photographs of Stephenson Glacier were taken during a three-week expedition to Heard Island, which accessed the Stephenson Glacier area by boat via the proglacial Stephenson Lagoon. During that work, sonar indicated some depths in the lagoon exceeding 100 m. Much of the loss in glacier length and area occurred during the mid- and late-2000s, with retreat rates slowing toward 2017. At this time, the glacier has retreated so that the main toe is not far from the base of a tall ice falls, while another toe—perhaps now a separate glacier—is land-based. This type of retreat pattern, fast over water and slower on land, is typical of other tidewater glaciers. Further monitoring of Stephenson Glacier and other glaciers on Heard Island will continue using Landsat 8.

  17. Evaluation of apically extruded debris during root canal retreatment with several NiTi systems.

    Science.gov (United States)

    Dincer, A N; Er, O; Canakci, B C

    2015-12-01

    To compare the amount of debris extruded apically during root canal retreatment using ProTaper, Mtwo and Reciproc instruments with hand H-files. In total, 60 freshly extracted human mandibular incisor teeth were used. All root canals were prepared with a Reciproc R25 file than filled with Gutta-percha and AH Plus sealer using cold lateral condensation before being assigned randomly to four groups (n = 15 each). In group 1, root fillings were removed with the Protaper Universal retreatment system; ProTaper Universal F3 and F4 instruments were used for the final preparation. In group 2, root fillings were removed with the Mtwo retreatment system; Mtwo size 30, .06 taper, size 35, .06 taper and size 40, .06 taper files were used for the final preparation. In group 3, root fillings were removed with Reciproc R25 instruments; Reciproc R40 instruments were used for the final preparation. In group 4, the root fillings were removed with Gates Glidden burs and sizes 35, 30 and 25 H-files; for final preparation, a size 40 H-file was used. Glass vials were used for debris collection. The vials were weighed before and after Gutta-percha removal. Additionally, the times required for the retreatment procedures were recorded. Data were analysed statistically using one-way analysis of variance. The Reciproc system produced significantly smaller amounts of apical extruded debris than the other groups (P ProTaper groups. The ProTaper and Reciproc groups required significantly less time than the Mtwo and H-file groups (P hand filing. Use of the ProTaper and Reciproc instruments required less time for retreatment procedures than use of the Mtwo or H-file. © 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd.

  18. Stability of therapeutic retreatment of corneal wavefront customized ablation with the SCHWIND CAM: 4-year data.

    Science.gov (United States)

    Aslanides, Ioannis M; Kolli, Sai; Padroni, Sara; Padron, Sara; Arba Mosquera, Samuel

    2012-05-01

    To evaluate the long-term outcomes of aspheric corneal wavefront ablation profiles for excimer laser retreatment. Eighteen eyes that had previously undergone LASIK or photorefractive keratectomy (PRK) were retreated with LASIK using the corneal wavefront ablation profile. Custom Ablation Manager (SCHWIND eye-tech-solutions, Kleinostheim, Germany) software and the ESIRIS flying spot excimer laser system (SCHWIND) were used to perform the ablations. Refractive outcomes and wavefront data are reported up to 4 years after retreatment. Pre- and postoperative data were compared with Student t tests and (multivariate) correlation tests. P<.05 was considered statistically significant. A bilinear correlation of various postoperative wavefront aberrations versus planned correction and preoperative aberration was performed. Mean manifest refraction spherical equivalent (MRSE) before retreatment was -0.38±1.85 diopters (D) and -0.09±0.22 D at 6 months and -0.10±0.38 D at 4 years postoperatively. The reduction in MRSE was statistically significant at both postoperative time points (P<.005). Postoperative aberrations were statistically lower (spherical aberration P<.05; coma P<.005; root-mean-square higher order aberration P<.0001) at 4 years postoperatively. Distribution of the postoperative uncorrected distance visual acuity (P<.0001) and corrected distance visual acuity (P<.01) were statistically better than preoperative values. Aspheric corneal wavefront customization with the ESIRIS yields visual, optical, and refractive results comparable to those of other wavefront-guided customized techniques for the correction of myopia and myopic astigmatism. The corneal wavefront customized approach shows its strength in cases where abnormal optical systems are expected. Systematic wavefront customized corneal ablation appears safe and efficacious for retreatment cases. Copyright 2012, SLACK Incorporated.

  19. The Role of Silence at the Retreats of a Buddhist Community

    Directory of Open Access Journals (Sweden)

    Orsolya Huszár

    2016-12-01

    Full Text Available The purpose of the study is to establish that the definition of silence as simply an absence of something or as the background of communication proves to be inadequate in a number of communicative instances. The interpretation of silence is culturally determined, and the underappreciation of its role is typical in low-context Western cultures; this is also evinced by the neglect of the topic in the literature. The present study will describe the communicative functions of silence through the findings of field work conducted at the retreats of a Buddhist community in Hungary, providing empirical input for the relevant theoretical constructs. The research findings show that silence is accorded a central role in essentially every component of the retreat (meditations, relaxation, ceremonies, teachings, small-group sharings, meals and rest; and while each event at the retreat focuses primarily on a different specific function of communication, the entire retreat does involve the linkage, affecting, revelational and – to a certain extent – activating functions (to follow the five-element typology of J. Vernon Jensen, as well as – to a lesser extent – the judgmental function. The research also shows that it requires time for individuals in a low-context culture to recognize the “point” of silence – something that the retreats provide the right opportunity for. In fact, the insights the individuals arrived at through these occasions could be put to use in their daily lives, helping their problem-solving and social relationships and in general improving their quality of life.

  20. Re-treatment tuberculosis cases categorised as "other": are they properly managed?

    Directory of Open Access Journals (Sweden)

    Hannock Tweya

    Full Text Available BACKGROUND: Although the World Health Organization (WHO provides information on the number of TB patients categorised as "other", there is limited information on treatment regimens or treatment outcomes for "other". Such information is important, as inappropriate treatment can lead to patients remaining infectious and becoming a potential source of drug resistance. Therefore, using a cohort of TB patients from a large registration centre in Lilongwe, Malawi, our study determined the proportion of all TB re-treatment patients who were registered as "other", and described their characteristics and treatment outcomes. METHODS: This retrospective observational study used routine program data to determine the proportion of all TB re-treatment patients who were registered as "other" and describe their characteristics and treatment outcomes between January 2006 and December 2008. RESULTS: 1,384 (12% of 11,663 TB cases were registered as re-treatment cases. Of these, 898 (65% were categorised as "other": 707 (79% had sputum smear-negative pulmonary TB and 191 (21% had extra pulmonary TB. Compared to the smear-positive relapse, re-treatment after default (RAD and failure cases, smear-negative "other" cases were older than 34 years and less likely to have their HIV status ascertained. Among those with known HIV status, "other" TB cases were more likely to be HIV positive. Of TB patients categorised as "other", 462 (51% were managed on the first-line regimen with a treatment success rate of 63%. CONCLUSION: A large proportion of re-treatment patients were categorised as "other". Many of these patients were HIV-infected and over half were treated with a first-line regimen, contrary to national guidelines. Treatment success was low. More attention to recording, diagnosis and management of these patients is warranted as incorrect treatment regimen and poor outcomes could lead to the development of drug resistant forms of TB.

  1. Optimal tuning of a GCM using modern and glacial constraints

    Energy Technology Data Exchange (ETDEWEB)

    Gregoire, Lauren J.; Valdes, Paul J.; Payne, Antony J.; Kahana, Ron [University of Bristol, School of Geographical Sciences, Bristol (United Kingdom)

    2011-08-15

    In climate models, many parameters used to resolve subgrid scale processes can be adjusted through a tuning exercise to fit the model's output to target climatologies. We present an objective tuning of a low resolution Atmosphere-Ocean General Circulation Model (GCM) called FAMOUS where ten model parameters are varied together using a Latin hypercube sampling method to create an ensemble of 100 models. The target of the tuning consists of a wide range of modern climate diagnostics and also includes glacial tropical sea surface temperature. The ensemble of models created is compared to the target using an Arcsin Mielke score. We investigate how the tuning method used and the addition of glacial constraints impact on the present day and glacial climates of the chosen models. Rather than selecting a single configuration which optimises the metric in all the diagnostics, we obtain a subset of nine 'good' models which display great differences in their climate but which, in some sense, are all better than the original configuration. In those simulations, the global temperature response to last glacial maximum forcings is enhanced compared to the control simulation and the glacial Atlantic Ocean circulation is more in agreement with observations. Our study demonstrates that selecting a single 'optimal' configuration, relying only on present day constraints may lead to misrepresenting climates different to that of today. (orig.)

  2. Glacial ocean circulation and stratification explained by reduced atmospheric temperature.

    Science.gov (United States)

    Jansen, Malte F

    2017-01-03

    Earth's climate has undergone dramatic shifts between glacial and interglacial time periods, with high-latitude temperature changes on the order of 5-10 °C. These climatic shifts have been associated with major rearrangements in the deep ocean circulation and stratification, which have likely played an important role in the observed atmospheric carbon dioxide swings by affecting the partitioning of carbon between the atmosphere and the ocean. The mechanisms by which the deep ocean circulation changed, however, are still unclear and represent a major challenge to our understanding of glacial climates. This study shows that various inferred changes in the deep ocean circulation and stratification between glacial and interglacial climates can be interpreted as a direct consequence of atmospheric temperature differences. Colder atmospheric temperatures lead to increased sea ice cover and formation rate around Antarctica. The associated enhanced brine rejection leads to a strongly increased deep ocean stratification, consistent with high abyssal salinities inferred for the last glacial maximum. The increased stratification goes together with a weakening and shoaling of the interhemispheric overturning circulation, again consistent with proxy evidence for the last glacial. The shallower interhemispheric overturning circulation makes room for slowly moving water of Antarctic origin, which explains the observed middepth radiocarbon age maximum and may play an important role in ocean carbon storage.

  3. Recent changes in Imja Glacial Lake and its damming moraine in the Nepal Himalaya revealed by in situ surveys and multi-temporal ASTER imagery

    Energy Technology Data Exchange (ETDEWEB)

    Fujita, Koji; Sakai, Akiko; Nuimura, Takayuki [Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601 (Japan); Yamaguchi, Satoru [Snow and Ice Research Center, National Research Institute for Earth Science and Disaster Prevention, Nagaoka 940-0821 (Japan); Sharma, Rishi R [Department of Hydrology and Meteorology, Ministry of Environment, Science and Technology, Babar Mahal, Kathmandu (Nepal)

    2009-10-15

    Changes in the area and bathymetry of Imja Glacial Lake and in the elevation of its damming moraine, Khumbu region, Nepal Himalaya are investigated. Previously reported changes in the lake area have been updated by multi-temporal ASTER images, which revealed a decreased expansion rate after 2000. A provisional expansion of the lake observed in 2004, from which some studies concluded an accelerated lake expansion due to global warming, has, from 2005, subsided to the glacier surface. Bathymetric changes for the period 1992-2002 that were first obtained for Himalayan glacial lakes suggest that the melting of debris-covered ice beneath the lake is insignificant in terms of the increase in lake volume, and that the retreat of a glacier in contact with the lake by calving is essential for the lake's expansion. Changes in the height of a damming moraine for the period 2001-2007 suggest a continuous surface lowering near the lake, though the lowering rates are smaller than those for the period 1989-1994.

  4. The Arctic: Glacial Refugium or Area of Secondary Contact? Inference from the Population Genetic Structure of the Thick-Billed Murre (Uria lomvia), with Implications for Management.

    Science.gov (United States)

    Tigano, Anna; Damus, Martin; Birt, Tim P; Morris-Pocock, Jamie A; Artukhin, Yuri B; Friesen, Vicki L

    2015-01-01

    Quaternary glaciations affected the distribution of many species. Here, we investigate whether the Arctic represented a glacial refugium during the Last Glacial Maximum or an area of secondary contact following the ice retreat, by analyzing the genetic population structure of the thick-billed murre (Uria lomvia), a seabird that breeds throughout the North Atlantic, North Pacific and Arctic Oceans. The thick-billed murre is a species of socio-economic importance and faces numerous threats including hunting, oil pollution, gill netting, and climate change. We compared variation in the mitochondrial DNA (mtDNA) control region (n = 424), supplemented by 4 microsatellite loci (n = 445), among thick-billed murres sampled throughout their range. MtDNA data indicated that colonies comprise 4 genetically differentiated groups (Φst = 0.11-0.81): 1) Atlantic Ocean plus New Siberian Islands region, 2) Cape Parry, 3) Chukchi Sea, and 4) Pacific Ocean. Microsatellite variation differed between Atlantic and Pacific populations. Otherwise, little substructure was found within either ocean. Atlantic and Pacific populations appear to have been genetically isolated since the last interglacial period and should be considered separate evolutionary significant units for management. The Chukchi Sea and Cape Parry appear to represent areas of secondary contact, rather than arctic refugial populations. © The American Genetic Association 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  5. Recent changes in Imja Glacial Lake and its damming moraine in the Nepal Himalaya revealed by in situ surveys and multi-temporal ASTER imagery

    International Nuclear Information System (INIS)

    Fujita, Koji; Sakai, Akiko; Nuimura, Takayuki; Yamaguchi, Satoru; Sharma, Rishi R

    2009-01-01

    Changes in the area and bathymetry of Imja Glacial Lake and in the elevation of its damming moraine, Khumbu region, Nepal Himalaya are investigated. Previously reported changes in the lake area have been updated by multi-temporal ASTER images, which revealed a decreased expansion rate after 2000. A provisional expansion of the lake observed in 2004, from which some studies concluded an accelerated lake expansion due to global warming, has, from 2005, subsided to the glacier surface. Bathymetric changes for the period 1992-2002 that were first obtained for Himalayan glacial lakes suggest that the melting of debris-covered ice beneath the lake is insignificant in terms of the increase in lake volume, and that the retreat of a glacier in contact with the lake by calving is essential for the lake's expansion. Changes in the height of a damming moraine for the period 2001-2007 suggest a continuous surface lowering near the lake, though the lowering rates are smaller than those for the period 1989-1994.

  6. Glacial history of the European marine mussels

    NARCIS (Netherlands)

    Smietanka, B.; Burzynski, A.; Hummel, H.; Wenne, R.

    2014-01-01

    Mussels of the genus Mytilus have been used to assess the circumglacial phylogeography of the intertidal zone. These mussels are representative components of the intertidal zone and have rapidly evolving mitochondrial DNA, suitable for high resolution phylogeographic analyses. In Europe, the three

  7. The Downstream Fate of Glacial Runoff and Groundwater in the Cordillera Blanca, Peru

    Science.gov (United States)

    McKenzie, J. M.; Gordon, R.; Chavez, D.; Maharaj, L.; Baraer, M.; Mark, B. G.; Lautz, L. K.

    2013-12-01

    Rapid glacier recession in the Cordillera Blanca, Peru, is raising concerns about current and future water resources for the inhabitants of the Rio Santa watershed. Glacier meltwater buffers stream discharge throughout the range, reducing the variability of annual runoff and maintaining stream flows during the dry season. Groundwater is also an important component of dry season runoff as it can contribute as much as 50-70% to outflow in some Rio Santa tributaries. A better understanding of groundwater dynamics in high elevation watersheds is needed, including quantification of recharge, subsurface processes, and available storage. We present the results from recent groundwater studies in the Cordillera Blanca where numerous investigative techniques have been used, including ground penetrating radar, hydraulic conductivity measurements, tracer tests, and hydrochemical mixing models. Our research focuses primarily on the low-relief pampa valley floors across which glacial-melt derived rivers flow. Across the Cordillera, these valley systems cover approximately 65 km2 and are comprised of unconsolidated glacial, talus, and lacustrine deposits and wetlands. The valleys commonly have buried, permeable, talus aquifers that are overlain by relatively impermeable, glaciolacustrine deposits. Glaciofluvial outwash deposits also act as aquifers (hydraulic conductivity of 10-4 m/s). The travel time of water stored in these systems is generally less than 3-4 years and the maximum observed dry season groundwater velocity is 60 cm/day. While groundwater represents an important component of dry season water resources source of water in the Cordillera Blanca, it is also potentially vulnerable to climate change including changes in the precipitation regime and decrease in glacially derived recharge.

  8. The glacial inception as recorded in the NorthGRIP Greenland ice core: timing, structure and associated abrupt temperature changes

    Energy Technology Data Exchange (ETDEWEB)

    Landais, Amaelle [UMR CEA-CNRS, CEA Saclay, IPSL/Laboratoire des Sciences du Climat et de l' Environnement, Gif-sur -Yvette (France); Hebrew University, Institute of Earth Sciences, Givat Ram, Jerusalem (Israel); Masson-Delmotte, Valerie; Jouzel, Jean; Minster, Benedicte [UMR CEA-CNRS, CEA Saclay, IPSL/Laboratoire des Sciences du Climat et de l' Environnement, Gif-sur -Yvette (France); Raynaud, Dominique [LGGE, UMR CNRS-UJF, St Martin d' Heres (France); Johnsen, Sigfus [University of Copenhagen, Department of Geophysics, Copenhagen (Denmark); Huber, Christof; Leuenberger, Markus; Schwander, Jakob [University of Bern, Physics Institute, Bern (Switzerland)

    2006-02-01

    The mechanisms involved in the glacial inception are still poorly constrained due to a lack of high resolution and cross-dated climate records at various locations. Using air isotopic measurements in the recently drilled NorthGRIP ice core, we show that no evidence exists for stratigraphic disturbance of the climate record of the last glacial inception ({proportional_to}123-100 kyears BP) encompassing Dansgaard-Oeschger events (DO) 25, 24 and 23, even if we lack sufficient resolution to completely rule out disturbance over DO 25. We quantify the rapid surface temperature variability over DO 23 and 24 with associated warmings of 10{+-}2.5 and 16{+-}2.5 C, amplitudes which mimic those observed in full glacial conditions. We use records of {delta}{sup 18}O of O{sub 2} to propose a common timescale for the NorthGRIP and the Antarctic Vostok ice cores, with a maximum uncertainty of 2,500 years, and to examine the interhemispheric sequence of events over this period. After a synchronous North-South temperature decrease, the onset of rapid events is triggered in the North through DO 25. As for later events, DO 24 and 23 have a clear Antarctic counterpart which does not seem to be the case for the very first abrupt warming (DO 25). This information, when added to intermediate levels of CO{sub 2} and to the absence of clear ice rafting associated with DO 25, highlights the uniqueness of this first event, while DO 24 and 23 appear similar to typical full glacial DO events. (orig.)

  9. EFFICACY OF PROTAPER NEXT AND PROTAPER UNIVERSAL RETREATMENT SYSTEMS IN REMOVING GUTTA-PERCHA IN CURVED ROOT CANALS DURING ROOT CANAL RETREATMENT

    Directory of Open Access Journals (Sweden)

    Taha ÖZYÜREK

    2017-04-01

    Full Text Available Purpose: The aim of this study was to compare the cleanliness of root canal walls after retreatment using ProTaper Next (PTN, ProTaper Universal Retreatment (PTR nickel-titanium (NiTi systems and Hedström hand files in curved mesial canals of mandibular molar teeth and the time required for gutta-percha and sealer removal. Materials and Methods: Ninety mandibular molar teeth with curved mesial roots were instrumented up to #35.04 with Mtwo NiTi rotary instruments and obturated using the continuous wave of condensation technique. Removal of gutta-percha and sealer was performed using one of the following: PTN and PTR NiTi systems and Hedström hand files. Samples were placed on the VistaScan phosphor plates in the mesio-distal direction and the radiographs were taken. The digital radiographs were analyzed using AutoCAD software. Also, the total time required for gutta-percha removal was calculated by a chronometer. Results: The total retreatment time was significantly shorter in the PTN and PTR groups compared with the manual group (p<0.05. There was a significant difference between the groups according to the total residual gutta-percha and sealer (p<0.05. The PTN and PTR groups left significantly less gutta-percha and sealer remnant than the manual group (p<0.001. Conclusion: Within the limitations of this study, the PTN and PTR groups showed less residual gutta-percha and sealer than the manual group. The NiTi rotary systems were significantly faster than the manual group in the time required for gutta-percha and sealer removal.

  10. Efficacy of protaper next and protaper universal retreatment systems in removing gutta-percha in curved root canals during root canal retreatment.

    Science.gov (United States)

    Ozyurek, Taha; Ozsezer-Demiryurek, Ebru

    2017-01-01

    The aim of this study was to compare the cleanliness of root canal walls after retreatment using ProTaper Next (PTN), ProTaper Universal Retreatment (PTR) nickel-titanium (NiTi) systems and Hedström hand files in curved mesial canals of mandibular molar teeth and the time required for gutta-percha and sealer removal. Ninety mandibular molar teeth with curved mesial roots were instrumented up to #35.04 with Mtwo NiTi rotary instruments and obturated using the continuous wave of condensation technique. Removal of gutta-percha and sealer was performed using one of the following: PTN and PTR NiTi systems and Hedström hand files. Samples were placed on the VistaScan phosphor plates in the mesio-distal direction and the radiographs were taken. The digital radiographs were analyzed using AutoCAD software. Also, the total time required for gutta-percha removal was calculated by a chronometer. The total retreatment time was significantly shorter in the PTN and PTR groups compared with the manual group (p<0.05). There was a significant difference between the groups according to the total residual gutta-percha and sealer (p<0.05). The PTN and PTR groups left significantly less gutta-percha and sealer remnant than the manual group (p<0.001). Within the limitations of this study, the PTN and PTR groups showed less residual gutta-percha and sealer than the manual group. The NiTi rotary systems were significantly faster than the manual group in the time required for gutta-percha and sealer removal.

  11. The Diabetic Foot Attack: "'Tis Too Late to Retreat!"

    Science.gov (United States)

    Vas, Prashanth R J; Edmonds, Michael; Kavarthapu, Venu; Rashid, Hisham; Ahluwalia, Raju; Pankhurst, Christian; Papanas, Nikolaos

    2018-03-01

    The "diabetic foot attack" is one of the most devastating presentations of diabetic foot disease, typically presenting as an acutely inflamed foot with rapidly progressive skin and tissue necrosis, at times associated with significant systemic symptoms. Without intervention, it may escalate over hours to limb-threatening proportions and poses a high amputation risk. There are only best practice approaches but no international protocols to guide management. Immediate recognition of a typical infected diabetic foot attack, predominated by severe infection, with prompt surgical intervention to debride all infected tissue alongside broad-spectrum antibiotic therapy is vital to ensure both limb and patient survival. Postoperative access to multidisciplinary and advanced wound care therapies is also necessary. More subtle forms exist: these include the ischemic diabetic foot attack and, possibly, in a contemporary categorization, acute Charcot neuroarthropathy. To emphasize the importance of timely action especially in the infected and ischemic diabetic foot attack, we revisit the concept of "time is tissue" and draw parallels with advances in acute myocardial infarction and stroke care. At the moment, international protocols to guide management of severe diabetic foot presentations do not specifically use the term. However, we believe that it may help increase awareness of the urgent actions required in some situations.

  12. Overdeepening development in a glacial landscape evolution model with quarrying

    DEFF Research Database (Denmark)

    Ugelvig, Sofie Vej; Egholm, D.L.; Iverson, Neal R.

    In glacial landscape evolution models, subglacial erosion rates are often related to basal sliding or ice discharge by a power-law. This relation can be justified when considering bed abrasion, where rock debris transported in the basal ice drives erosion. However, the relation is not well...... supported when considering models for quarrying of rock blocks from the bed. Field observations indicate that the principal mechanism of glacial erosion is quarrying, which emphasize the importance of a better way of implementing erosion by quarrying in glacial landscape evolution models. Iverson (2012...... around the obstacles. The erosion rate is quantified by considering the likelihood of rock fracturing on topographic bumps. The model includes a statistical treatment of the bedrock weakness, which is neglected in previous quarrying models. Sliding rate, effective pressure, and average bedslope...

  13. ESR Dating Research of Glacial Tills in Tibetan Plateau

    Science.gov (United States)

    Bi, W.; Yi, C.

    2016-12-01

    In recent years, Quaternary Glacial-chronology has been made remarkable progress in the Tibetan Platean(TP) with the development of several numeric dating techniques, such as cosmogenic nuclides(NC), optically stimulated luminescence(OSL) and 14C. In constrast, the dating of Quaternary glacial tills in 100,000 years even more than million-year has been a challenge, just because the techniques has defects themselves and the sediments were stransformed during the geological and geomorphology progress later. Electron Spin Resonance(ESR) has been becoming one of the key methods of Quaternary Glacial-chronology with wide range of dating, expecially for the sample older than 100,000 years up to million-year scale. The accurate measurement of equivalent dose significantly impacts on accuracy and reliability of ESR dating method. Therefore, the study of the mechanisms of resetting processes is fundamental for accurate and reliable ESR dating. To understand the mechanism and characteristics of quartz ESR signal resetting of different samples, a series of laboratory simulation and field observation studies were carried out, which made lots of important breakthrough. But the research in quartz ESR signal of moraines is less and the test of ESR dating method is still in the qualitative investigation. Therefor, we use ESR dating and study on the mechanism and characteristics of quartz ESR signals in tills in the Tibetan Platean. In the adjust method of Modern, the quartz ESR signals in Modern glacial tills represent residual values which can be adjusted signals in the older glacial tills. As a consequence, ESR dating of the quartz in moraines needs to be explored in deep with building models to adjust ages which are measured by ESR dating. Therefore, ESR dating will become the trusted one of the cross dating methods in Quaternary Glacial-chronology with the adjust mothod improving the accuracy of ESR dating ages.

  14. Reasons for Retreatment of Amalgam and Composite Restorations among the Patients Referring to Tabriz Faculty of Dentistry

    Directory of Open Access Journals (Sweden)

    Siavash Savadi Oskoee

    2007-06-01

    Full Text Available

    Background and aims. Retreatment of existing restorations not only requires a lot of money and time but also there is a danger of weakening tooth structure and irritating the pulp. Since awareness of the reasons for the retreatment of teeth will save the teeth from possible future failure, the aim of this study was to assess the reasons for retreatment of amalgam and composite restorations in patients referring to Tabriz Faculty of Dentistry.

    Materials and methods. In this descriptive study, the subjects had previously received an amalgam or a composite restoration in the Operative Department by dental students and were judged to need retreatment in their second visit. A total of 300 defective teeth were selected by simple random sampling method. The data was collected through examination and questionnaires and analyzed using chi-square test.

    Results. There was a statistically significant association between the type of the restorative material and the reason for retreatment (p=0.001.

    Conclusion. Although the reasons for the retreatment of amalgam and composite restorations were different, recurrent caries was the main reason for the retreatment for both restorative materials.

  15. Habitat selection in a rocky landscape: experimentally decoupling the influence of retreat site attributes from that of landscape features.

    Directory of Open Access Journals (Sweden)

    Benjamin M Croak

    Full Text Available Organisms selecting retreat sites may evaluate not only the quality of the specific shelter, but also the proximity of that site to resources in the surrounding area. Distinguishing between habitat selection at these two spatial scales is complicated by co-variation among microhabitat factors (i.e., the attributes of individual retreat sites often correlate with their proximity to landscape features. Disentangling this co-variation may facilitate the restoration or conservation of threatened systems. To experimentally examine the role of landscape attributes in determining retreat-site quality for saxicolous ectotherms, we deployed 198 identical artificial rocks in open (sun-exposed sites on sandstone outcrops in southeastern Australia, and recorded faunal usage of those retreat sites over the next 29 months. Several landscape-scale attributes were associated with occupancy of experimental rocks, but different features were important for different species. For example, endangered broad-headed snakes (Hoplocephalus bungaroides preferred retreat sites close to cliff edges, flat rock spiders (Hemicloea major preferred small outcrops, and velvet geckos (Oedura lesueurii preferred rocks close to the cliff edge with higher-than-average sun exposure. Standardized retreat sites can provide robust experimental data on the effects of landscape-scale attributes on retreat site selection, revealing interspecific divergences among sympatric taxa that use similar habitats.

  16. Glacial modification of granite tors in the Cairngorms, Scotland

    Science.gov (United States)

    Hall, A.M.; Phillips, W.M.

    2006-01-01

    A range of evidence indicates that many granite tors in the Cairngorms have been modified by the flow of glacier ice during the Pleistocene. Comparisons with SW England and the use of a space-time transformation across 38 tor groups in the Cairngorms allow a model to be developed for progressive glacial modification. Tors with deeply etched surfaces and no, or limited, block removal imply an absence of significant glacial modification. The removal of superstructure and blocks, locally forming boulder trains, and the progressive reduction of tors to stumps and basal slabs represent the more advanced stages of modification. Recognition of some slabs as tor stumps from which glacial erosion has removed all superstructure allows the original distribution of tors to be reconstructed for large areas of the Cairngorms. Unmodified tors require covers of non-erosive, cold-based ice during all of the cold stages of the Middle and Late Pleistocene. Deformation beneath cold-based glacier ice is capable of the removal of blocks but advanced glacial modification requires former wet-based glacier ice. The depth of glacial erosion at former tor sites remains limited largely to the partial or total elimination of the upstanding tor form. Cosmogenic nuclide exposure ages (Phillips et al., 2006) together with data from weathering pit depths (Hall and Phillips, 2006), from the surfaces of tors and large erratic blocks require that the glacial entrainment of blocks from tors occurred in Marine Isotope Stages (MIS) 4-2, 6 and, probably, at least one earlier phase. The occurrence of glacially modified tors on or close to, the main summits of the Cairngorms requires full ice cover over the mountains during these Stages. Evidence from the Cairngorms indicates that tor morphology can be regarded as an important indicator of former ice cover in many formerly glaciated areas, particularly where other evidence of ice cover is sparse. Recognition of the glacial modification of tors is important

  17. Glacial Fluctuation in the Source Region of the Yangtze River

    International Nuclear Information System (INIS)

    Shengyi, Gao; Qingsong, Fan; Xi, Cao; Li, Ma

    2014-01-01

    Glaciers in the source region of the Yangtze River are not only water resources but also important energy and environmental resources. Glacial fluctuation is an important component of the study of changes in the natural environment, including climate change. We investigated the glaciers in the source region of the Yangtze River, and analyzed the fluctuations using multi-temporal remote sensing data. The trend in glacial fluctuation and the factors that influence it were determined. The results have implications for water resource management and environmental conservation in the Yangtze River region

  18. Late-Glacial radiocarbon- and palynostratigraphy in the Swiss Plateau

    International Nuclear Information System (INIS)

    Ammann, B.; Lotter, A.F.

    1989-01-01

    A detailed Late-Glacial radiocarbon stratigraphy for the Swiss Plateau has been established on the basis of over 90 accelerator 14 C dates on terrestrial plant macrofossils. A comparison of the radiocarbon ages derived from terrestrial, telmatic and limnic material at different sites on the Swiss Plateau yields a proposal for modifying the zonation system of Welten for the Late-Glacial. By retaining the limits of chronozones and by refining the palynostratigraphic criteria for the limits of biozones, a separation between chrono- and biozonation at the beginning of the Boelling and the Younger Dryas becomes obvious. 54 refs

  19. Decision logic for retreatment of asymptomatic lung cancer recurrence based on positron emission tomography findings

    International Nuclear Information System (INIS)

    Frank, Albert; Lefkowitz, David; Jaeger, Stanley; Gobar, Lisa; Sunderland, John; Gupta, Naresh; Scott, Walter; Mailliard, James; Lynch, Henry; Bishop, John; Thorpe, Patricia; Dewan, Naresh

    1995-01-01

    Purpose: The purpose of the study was to determine if Positron emission tomography (PET) 2-[F-18] fluoro-2-deoxy-D-glucose (FDG) imaging could detect subclinical local lung cancer recurrence and whether retreatment of such recurrence was feasible and beneficial. Methods and Materials: Twenty patients with biopsy proven lung cancer were studied with Positron emission tomography for the purpose of detecting subclinical lung cancer recurrence over a period of 4.25 years. All patients were treated with external radiation as part or all of their therapy. Twenty patients had baseline PET and computed tomography (CT) studies for comparison with later studies. Surviving patients had a total of 40 sequential PET scans and 35 CT scans. The follow-up interval ranged from 5 to 40 months posttreatment. The differential uptake ratio (DUR) was determined for regions of interest of increased FDG uptake. Results: The median DUR value of the 20 baseline PET studies was 5.59. The DUR value of greater than 3 was empirically selected as being positive for tumor detection. On baseline studies, PET had a 100% correlation with the CT findings in regard to detection of the site of primary tumor involvement. Four of 20 patients showed areas of discordance in the mediastinal and hilar areas on initial PET and CT studies. Seven of 17 patients showed discordant posttreatment PET-CT findings. Two false positive PET studies were due to radiation pneumonitis and one to macrophage glycolysis in tumor necrosis. For detection of asymptomatic tumor recurrence, analysis of sequential PET and CT studies, biopsy results, and the patient's clinical course suggested that PET had a sensitivity of 100%, specificity of 89.3%, and accuracy of 92.5%. Computerized Tomography was found to have a sensitivity of 67%, specificity of 85%, and accuracy of 82% for detection of such early-stage recurrence. Five patients went on to have retreatment with external irradiation based upon the PET evidence. Four retreated

  20. Means of Slope Retreat on the Na Pali Cliffs, Kauai, Hawaii

    Science.gov (United States)

    Osborn, G.; Sheardown, A.; Blay, C.

    2016-12-01

    The spectacular, 500 to 600 m high, deeply grooved escarpment referred to as the Na Pali cliffs, on the northwest coast of Kauai, requires a substrate competent enough to hold up high steep cliffs yet erodible enough to allow generation of wide, deep grooves. These opposing tendencies are afforded by weathering of originally strong basalt that keeps pace with erosion. The fluted cliffs maintain a rather consistent slope angle, generally 50-60°, whether they are close to the shoreline or have retreated some distance from it, indicating that the slopes are retreating parallel to themselves. Previous literature promotes groundwater sapping or waterfall-plunge-pool erosion as the chief means of valley-head retreat, but there is no evidence that either concept provides a general explanation for retreat of the fluted cliffs. The eroding cliffs maintain steepness because as much rock is eroded at the base as at the top, and transported sediment is washed completely out of the gully system. The thin-bedded basalts exposed in the steep flutes are decomposed into irregularly alternating fine sediment of low to moderate cohesion and thoroughly fractured beds or lenses of solid but chemically weathered rock, and covered with a veneer of sparse grass. Erosion proceeds by episodic removal of thin grass-covered surficial sheets of the weathering products. Some of this process may be facilitated by shallow mass movement, but probably most of the work is done by overland and channelized flow during intense rainstorms. The Na Pali coast experiences one-hour rainfalls of 2-2.5 inches (1 year recurrence interval) and 5-6 inches (100 year recurrence interval); experiments by others on basaltic soils in Molokai suggest such rain is more than enough to generate erosion-inducing overland flow. Between the deep grooves and the shoreline are slopes with lesser drainage densities and lesser slope angles. The rocks here are not distinguished from the rocks above in previous literature, and

  1. Evidence of a high-Andean, mid-Holocene plant community: An ancient DNA analysis of glacially preserved remains.

    Science.gov (United States)

    Gould, Billie A; León, Blanca; Buffen, Aron M; Thompson, Lonnie G

    2010-09-01

    Around the world, tropical glaciers and ice caps are retreating at unprecedented rates because of climate change. In at least one location, along the margin of the Quelccaya Ice Cap in southeastern Peru, ancient plant remains have been continually uncovered since 2002. We used genetic analysis to identify plants that existed at these sites during the mid-Holocene. • We examined remains between 4576 and 5222 yr old, using PCR amplification, cloning, and sequencing of a fragment of the chloroplast trnL intron. We then matched these sequences to sequences in GenBank. • We found evidence of at least five taxa characteristic of wetlands, which occur primarily at lower elevations in the region today. • A diverse community most likely existed at these locations the last time they were ice-free and thus has the potential to reestablish with time. This is the first genetic analysis of vegetation uncovered by receding glacial ice, and it may become one of many as ancient plant materials are newly uncovered in a changing climate.

  2. Transport sensitivity studies for SITE-94: Time-dependent site-scale modelling of future glacial impact

    International Nuclear Information System (INIS)

    King-Clayton, L.; Smith, Paul

    1996-10-01

    The report details the methodology and preliminary results from the modelling of radionuclide transport from a hypothetical repository based at the Aespoe site in Sweden. The work complements and utilizes the results from regional-scale, variable density flow modelling by Provost, in which the groundwater flow field is time dependent, reflecting the impact of climate evolution over the next 130,000 years. The climate evolution include development of permafrost conditions and ice sheet advance and retreat. The results indicate that temporal changes in flow conditions owing to future climate changes have a significant effect on the transport of radionuclides from a repository. In all cases modelled with time-dependent boundary conditions, the greatest radionuclide fluxes occur towards the end of the main glacial periods, and correspond to periods of high groundwater discharge at the margin of the modelled ice sheets. Fluxes to the biosphere may, for limited periods (2000 years or less), be three times higher than those from the near field. The study provides a quantitative way of illustrating the possible effects of future glaciations on radionuclide transport from the repository. Such effects are likely to be significant in any potential siting area predicted to be affected by future periods of ice cover. 8 refs, 22 tabs, 119 figs

  3. Changes in Hydrologic Conditions and Greenhouse Gas Emissions in Circumpolar Regions due to Climate Change Induced Permafrost Retreat

    Energy Technology Data Exchange (ETDEWEB)

    Whiticar, M. J. [School of Earth and Ocean Sciences, University of Victoria, Victoria (Canada); Bhatti, J.; Startsev, N. [Northern Forestry Centre, St Edmonton, AB (Canada)

    2013-07-15

    Thawing permafrost peatlands substantially influence Canadian northern ecosystems by changing the regional hydrology and mobilizing the vast carbon (C) reserves that results in increased greenhouse gas (GHGs) emissions to the atmosphere. With permafrost distribution controlled largely by topography and climate, our International polar y ear (IPY) study intensively monitored the local C cycling processes and GHG fluxes associated with different hydrologic and permafrost environments at 4 sites along a climatic gradient extending from the Isolated patches permafrost Zone (northern alberta), to the continuous permafrost Zone (Inuvik, NWT). Each site encompasses a local gradient from upland forest and peat plateau to collapse scar. Our multi-year measurements of peatland profiles and flux chambers for CH{sub 4} and CO{sub 2} concentrations and stable isotope ratios indicate processes, including methanogenesis, methanotrophy, transport and emission that control the distribution of these GHGs. These relationships are modulated by fluctuating local soil water and corresponding ecosystem conditions. The gas geochemistry shows that significant surface CH{sub 4} production occurs by both hydrogenotrophic and acetoclastic methanogenesis in submerged, anaerobic peats, e.g., collapse scars, whereas methane oxidation is restricted to aerobic, drier environments, e.g., upland sites and peat-atmosphere interface. The most active methanogenesis and emissions are in areas of actively thawing permafrost contrasting with sites under continuous permafrost. This degree of methanogenesis is being amplified by the increased rate of Arctic warming and the rapid retreat of permafrost in canada's arctic (approximately. 2.5 km/a). (author)

  4. Retreatment and outcomes of recurrent intracranial vertebral artery dissecting aneurysms after stent assisted coiling: a single center experience.

    Directory of Open Access Journals (Sweden)

    Ying Song

    Full Text Available The retreatment of recurrent intracranial vertebral artery dissecting aneurysms (VADAs after stent assisted coiling (SAC has not yet been studied. The purpose of this study was to evaluate the strategies and outcomes for retreatment of recurrent VADAs after SAC.Between September 2009 and November 2013, six consecutive patients presenting with recurrent intracranial VADAs after SAC were enrolled in this study. They were all male with age ranging from 29 to 54 years (mean age, 46.2 years. The procedures of treatments and angiographic and clinical follow-up were reviewed retrospectively. Retreatment modalities were selected individually according to the characteristics of recurrence. The outcomes of retreatment were evaluated by angiographic and clinical follow-up.Six patients with recurrent intracranial VADAs after SAC were retreated, with second SAC in three patients, coil embolization, double overlapping stents placement and endovascular occlusion with aneurysm trapping in one patient, respectively. Immediate angiographic outcomes of retreatment were: complete occlusion in three patients, nearly complete occlusion in two patients, and contrast medium retention in dissecting aneurysm in one patient. All cases were technically successful. No complications related to endovascular procedures occurred. Angiographic follow-up was available in all five patients treated with second SAC or double overlapping stents, which was complete occlusion in four patients, obliteration of parent artery in one patient, showing no recurrence at 4-11 months (mean: 8.6 months. Clinical follow-up was performed in all six patients at 11-51 months after initial endovascular treatment and at 9-43 months after retreatment. The mRS of last clinical follow-up was excellent in five patients and mild disability in only one patient.Endovascular retreatment is feasible and effective for recurrent intracranial VADAs after SAC. Individualized strategies of retreatment should be

  5. MEASURING SURFACE DEFORMATION IN GLACIER RETREATED AREAS BASED ON PS-INSAR – GELADANDONG GLACIER AS A CASE STUDY

    Directory of Open Access Journals (Sweden)

    B. Mohamadi

    2018-04-01

    Full Text Available Glaciers are retreating in many parts of the world as a result of global warming. Many researchers consider Qinghai-Tibetan Plateau as a reference for climate change by measuring glaciers retreat on the plateau. This retreat resulted in some topographic changes in retreated areas, and in some cases can lead to geohazards as landslides, and rock avalanches, which is known in glacier retreated areas as paraglacial slope failure (PSF. In this study, Geladandong biggest and main glacier mass was selected to estimate surface deformation on its glacier retreated areas and define potential future PSF based on PS-InSAR technique. 56 ascending and 49 descending images were used to fulfill this aim. Geladandong glacier retreated areas were defined based on the maximum extent of the glacier in the little ice age. Results revealed a general uplift in the glacier retreated areas with velocity less than 5mm/year. Obvious surface motion was revealed in seven parts surround glacier retreated areas with high relative velocity reached ±60mm/year in some parts. Four parts were considered as PSF potential motion, and two of them showed potential damage for the main road in the study area in case of rock avalanche into recent glacier lakes that could result in glacier lake outburst flooding heading directly to the road. Finally, further analysis and field investigations are needed to define the main reasons for different types of deformation and estimate future risks of these types of surface motion in the Qinghai-Tibetan Plateau.

  6. Rapid climate variability during warm and cold periods in polar regions and Europe

    DEFF Research Database (Denmark)

    Masson-Delmotte, V.; Landais, A.; Combourieu-Nebout, N.

    2005-01-01

    Typical rapid climate events punctuating the last glacial period in Greenland, Europe and Antarctica are compared to two rapid events occurring under warmer conditions: (i) Dansgaard-Oeschger event 25, the first abrupt warming occurring during last glacial inception; (ii) 8.2 ka BP event, the only...... rapid cooling recorded during the Holocene in Greenland ice cores and in Ammersee, Germany. The rate of warming during previous warmer interglacial periods is estimated from polar ice cores to 1.5 °C per millennium, without abrupt changes. Climate change expected for the 21st century should however...

  7. Assessment of glacial lake development and prospects of outburst susceptibility: Chamlang South Glacier, eastern Nepal Himalaya

    Directory of Open Access Journals (Sweden)

    Damodar Lamsal

    2016-01-01

    Full Text Available Chamlang South Tsho has been identified as one of the six high-priority glacial lakes in terms of glacial lake outburst flood (GLOF danger in Nepal Himalaya, despite the fact that no detailed investigations of the lake had been hitherto undertaken. We conducted detailed mapping of the lake and its surroundings along with field surveys in October 2009 to determine the developmental history of Chamlang South Tsho and to assess its potential for GLOF. The lake expanded rapidly between 1964 (0.04 km2 and 2000 (0.86 km2 and has been stable ever since. Future lake expansion is improbable as its sides are confined by relatively stable landforms. The lake is 87-m deep with a water volume of approximately 34.9–35.6 × 106 m3. Hanging glaciers on the steep surrounding mountain slopes and prominent seepage water in the terminal moraine dam could be potential triggers for a future outburst flood. Additionally, the debris-covered dead-ice dam, which is higher than the lake water level, is narrow and low; therefore, it could be overtopped easily by surge waves. Furthermore, the pronounced difference in elevation between the lake and the base of the terminal moraine dam makes the lake susceptible for a large flood.

  8. Could brown bears (Ursus arctos) have survived in Ireland during the Last Glacial Maximum?

    Science.gov (United States)

    Leonard, Saoirse A; Risley, Claire L; Turvey, Samuel T

    2013-08-23

    Brown bears are recorded from Ireland during both the Late Pleistocene and early-mid Holocene. Although most of the Irish landmass was covered by an ice sheet during the Last Glacial Maximum (LGM), Irish brown bears are known to have hybridized with polar bears during the Late Pleistocene, and it is suggested that the Irish brown bear population did not become extinct but instead persisted in situ through the LGM in a southwestern ice-free refugium. We use historical population modelling to demonstrate that brown bears are highly unlikely to have survived through the LGM in Ireland under any combination of life-history parameters shown by living bear populations, but instead would have rapidly become extinct following advance of the British-Irish ice sheet, and probably recolonized Ireland during the end-Pleistocene Woodgrange Interstadial from a closely related nearby source population. The time available for brown bear-polar bear hybridization was therefore restricted to narrow periods at the beginning or end of the LGM. Brown bears would have been extremely vulnerable to extinction in Quaternary habitat refugia and required areas substantially larger than southwestern Ireland to survive adverse glacial conditions.

  9. A synthesis of post-glacial diatom records from Lake Baikal

    Science.gov (United States)

    Bradbury, J. Platt; Bezrukova, E.; Chernyaeva, G.; Colman, S.M.; Khursevich, G.; King, J.W.; Likoshway, Ye. V.

    1994-01-01

    glacial periods, the deep basin sediments of Lake Baikal are dominated by rapidly deposited clastics entering from large rivers with possibly glaciated headwaters. On the sublacustrine Academician Ridge (depth = 300 m), however, detailed analysis of the diatom biostratigraphy indicates that diastems (hiatuses of minor duration) and (or) highly variable rates of accumulation complicate paleolimnologic and paleoclimatic reconstructions from these records.

  10. Glacial Erosion Driven by Seasonal Shifts in Meltwater Drainage

    Science.gov (United States)

    Ugelvig, S. V.; Egholm, D. L.

    2017-12-01

    Subglacial erosion processes, like abrasion and quarrying, have been studied for decades. While models for abrasion clearly points to sliding speed as a primary control on abrasion rates, quarrying rates are thought to be governed by more complex combinations of sliding speed, effective pressure, bedrock slope and short-term water pressure fluctuations. Early models for quarrying focused on the deviatoric stress needed for growth of small isolated cracks in otherwise homogeneous intact bedrock. The rate-limiting factor for quarrying was thus the subcritical crack growth. Later studies have included effects of pre-existing fractures in the bedrock that weaken the rock. Here the strength distribution in the rock is based on the assumption that larger rock bodies have lower strength, because they have a higher probability of containing a weak fracture. However, this approach has been hampered by the assumption of steady-state cavity configuration. Here we attempt to combine previous model efforts in a model that tracks the temporal evolution of cavities while including a statistical treatment of bedrock strength. Using a two-dimensional finite-difference model, we simulate the spatial and temporal evolution of the hydrological system at the base of a glacier, while simultaneously computing rates of abrasion and quarrying. Cavity lengths and channel cross-sections evolve through time, which allow us to study how temporal shifts in ice-bed contact area and deviatoric stress influence quarrying rates over the course of a year. Furthermore, we use the temporal evolution of contact area between ice and bed to predict basal sliding speed and scale abrasion rates. Our results suggest that ice-bed contact area is a key variable in controlling sliding speed and rates of glacial erosion on seasonal time scales, where the subglacial drainage system reorganizes to accommodate the variations in surface melt rates. However, on diurnal timescales cavities and channels cannot adjust

  11. Rapid ice unloading in the Fleming Glacier region, southern Antarctic Peninsula, and its effect on bedrock uplift rates

    DEFF Research Database (Denmark)

    Zhao, Chen; King, Matt A.; Watson, Christopher S.

    2017-01-01

    deformation. We subtract modeled elastic deformation rates, and a suite of modeled viscous rates, from GPS-derived three-dimensional bedrock velocities at sites to the south of Fleming Glacier to infer properties of Earth rheology. Assuming the pre-breakup bedrock uplift was positive due to post-Last Glacial...... Maximum (LGM) ice retreat, our viscoelastic-corrected GPS uplift rates suggest upper mantle viscosities are >2×1019 Pas and likely >1×1020 Pas in this region, 1–2 orders of magnitude greater than previously found for the northern Antarctic Peninsula. Horizontal velocities at the GPS site nearest...

  12. The Multitrophic Effects of Climate Change and Glacier Retreat in Mountain Rivers.

    Science.gov (United States)

    Fell, Sarah C; Carrivick, Jonathan L; Brown, Lee E

    2017-10-01

    Climate change is driving the thinning and retreat of many glaciers globally. Reductions of ice-melt inputs to mountain rivers are changing their physicochemical characteristics and, in turn, aquatic communities. Glacier-fed rivers can serve as model systems for investigations of climate-change effects on ecosystems because of their strong atmospheric-cryospheric links, high biodiversity of multiple taxonomic groups, and significant conservation interest concerning endemic species. From a synthesis of existing knowledge, we develop a new conceptual understanding of how reducing glacier cover affects organisms spanning multiple trophic groups. Although the response of macroinvertebrates to glacier retreat has been well described, we show that there remains a relative paucity of information for biofilm, microinvertebrate, and vertebrate taxa. Enhanced understanding of whole river food webs will improve the prediction of river-ecosystem responses to deglaciation while offering the potential to identify and protect a wider range of sensitive and threatened species.

  13. Increasing Research Productivity and Professional Development in Psychology With a Writing Retreat.

    Science.gov (United States)

    Stanley, Ian H; Hom, Melanie A; Chu, Carol; Joiner, Thomas E

    2017-09-01

    Writing is a core feature of the training requirements and career demands of psychology faculty members and graduate students. Within academic psychology, specifically, writing is vital for the generation of scientific knowledge through manuscripts and grant applications. Although resources exist regarding how to improve one's writing skills, few models have been described regarding how to promote a culture of writing productivity that realizes tangible deliverables, such as manuscripts and grant applications. In this article, we discuss the rationale, model, and initial outcome data of a writing retreat developed and implemented to increase research productivity among psychology faculty and trainees. We also review best practices for conducting writing retreats and identify key areas for future SoTL on advancing writing.

  14. Ice flow models and glacial erosion over multiple glacial–interglacial cycles

    OpenAIRE

    Headley, R. M.; Ehlers, T. A.

    2015-01-01

    Mountain topography is constructed through a variety of interacting processes. Over glaciological timescales, even simple representations of glacial-flow physics can reproduce many of the distinctive features formed through glacial erosion. However, detailed comparisons at orogen time and length scales hold potential for quantifying the influence of glacial physics in landscape evolution models. We present a comparison using two different numerical models for glacial flow ov...

  15. Soft-Cliff Retreat, Self-Organized Critical Phenomena in the Limit of Predictability?

    Science.gov (United States)

    Paredes, Carlos; Godoy, Clara; Castedo, Ricardo

    2015-03-01

    The coastal erosion along the world's coastlines is a natural process that occurs through the actions of marine and subaerial physico-chemical phenomena, waves, tides, and currents. The development of cliff erosion predictive models is limited due to the complex interactions between environmental processes and material properties over a wide range of temporal and spatial scales. As a result of this erosive action, gravity driven mass movements occur and the coastline moves inland. Like other studied earth natural and synthetically modelled phenomena characterized as self-organized critical (SOC), the recession of the cliff has a seemingly random, sporadic behavior, with a wide range of yearly recession rate values probabilistically distributed by a power-law. Usually, SOC systems are defined by a number of scaling features in the size distribution of its parameters and on its spatial and/or temporal pattern. Particularly, some previous studies of derived parameters from slope movements catalogues, have allowed detecting certain SOC features in this phenomenon, which also shares the recession of cliffs. Due to the complexity of the phenomenon and, as for other natural processes, there is no definitive model of recession of coastal cliffs. In this work, various analysis techniques have been applied to identify SOC features in the distribution and pattern to a particular case: the Holderness shoreline. This coast is a great case study to use when examining coastal processes and the structures associated with them. It is one of World's fastest eroding coastlines (2 m/yr in average, max observed 22 m/yr). Cliffs, ranging from 2 m up to 35 m in height, and made up of glacial tills, mainly compose this coast. It is this soft boulder clay that is being rapidly eroded and where coastline recession measurements have been recorded by the Cliff Erosion Monitoring Program (East Riding of Yorkshire Council, UK). The original database has been filtered by grouping contiguous

  16. Panretinal photocoagulation versus intravitreal injection retreatment pain in high-risk proliferative diabetic retinopathy

    Directory of Open Access Journals (Sweden)

    Célia Regina Farias de Araújo Lucena

    2013-02-01

    Full Text Available PURPOSE: To compare pain related to intravitreal injection and panretinal photocoagulation in the management of patients with high-risk proliferative diabetic retinopathy. METHODS: Prospective study including patients with high-risk proliferative diabetic retinopathy and no prior laser treatment randomly assigned to receive panretinal photocoagulation (PRP group or panretinal photocoagulation plus intravitreal ranibizumab (PRPplus group. In all patients, panretinal photocoagulation was administered in two sessions (weeks 0 and 2, and intravitreal ranibizumab was administered at the end of the first laser session in the PRPplus group. Retreatment was performed at weeks 16 and 32 if active new vessels were detected at fluorescein angiography. Patients in the PRPplus group received intravitreal ranibizumab and patients in the PRP group received 500-µm additional spots per quadrant of active new vessels. After the end of retreatment, a 100-degree Visual Analog Scale was used for pain score estimation. The patient was asked about the intensity of pain during the whole procedure (retinal photocoagulation session or intravitreal ranibizumab injection. Statistics for pain score comparison were performed using a non-parametric test (Wilcoxon rank sums. RESULTS: Seventeen patients from PRPplus and 14 from PRP group were evaluated for pain scores. There were no significant differences between both groups regarding gender, glycosylated hemoglobin and disease duration. Mean intravitreal injection pain (±SEM was 4.7 ± 2.1 and was significantly lower (p<0.0001 than mean panretinal photocoagulation pain (60.8 ± 7.8. Twelve out of 17 patients from the PRPplus group referred intensity pain score of zero, while the minimal score found in PRP group was found in one patient with 10.5. CONCLUSION: In patients with high-risk proliferative diabetic retinopathy who needed retreatment for persistent new vessels, there was more comfort for the patient when retreatment

  17. Postoperative Pain after Endodontic Retreatment Using Rotary or Reciprocating Instruments: A Randomized Clinical Trial.

    Science.gov (United States)

    Comparin, Daniel; Moreira, Edson Jorge Lima; Souza, Erick M; De-Deus, Gustavo; Arias, Ana; Silva, Emmanuel João Nogueira Leal

    2017-07-01

    The aim of this randomized clinical trial was to evaluate the influence of rotary or reciprocating retreatment techniques on the incidence, intensity, duration of postoperative pain, and medication intake. After power analysis calculations, 65 patients who needed endodontic retreatment were randomly assigned to 1 of 2 groups according to the instrumentation system used: Mtwo (VDW, Munich, Germany) or Reciproc (VDW). Retreatments were performed in a single visit by an endodontic specialist. Participants were asked to rate the incidence and intensity of the postoperative pain on a verbal rating scale 24, 48, and 72 hours after treatment. Patients were also asked to record the number of prescribed analgesic medication tablets (ibuprofen 400 mg) taken. A logistic regression analysis was used to assess both the incidence and duration of pain. Differences in the intensity of pain were analyzed using the ordinal (linear) chi-square test, and the Mann-Whitney U test was used to assess differences in the intake of analgesic medication between groups. No statistically significant difference was found among the 2 groups in relation to postoperative pain or analgesic medication intake at the 3 time points assessed (P > .05). Multivariate analysis showed a significantly higher incidence of pain after 24 hours when preoperative pain was present and a significantly longer duration of pain for men than women independently of the retreatment technique used. The reciprocating system and the continuous rotary system were found to be equivalent regarding the incidence, intensity, duration of postoperative pain, and intake of analgesic medication. Copyright © 2017 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  18. Comparison of cyclic fatigue resistance of three different rotary nickel-titanium instruments designed for retreatment.

    Science.gov (United States)

    Inan, Ugur; Aydin, Cumhur

    2012-01-01

    A number of rotary nickel-titanium (NiTi) systems have been developed to provide better, faster, and easier cleaning and shaping of the root canal system, and recently, rotary NiTi systems designed for root canal retreatment have been introduced. Because the main problem with the rotary NiTi files is fracture, the aim of this study was to compare the cyclic fatigue resistance of 3 different rotary NiTi systems designed for root canal retreatment. Total of 60 instruments of 3 different rotary NiTi systems designed for root canal retreatment were used in this study. Twenty R-Endo R3, 20 ProTaper D3, and 20 Mtwo R (Retreatment) 25.05 instruments were tested. Cyclic fatigue testing of instruments was performed by using a device that allowed the instruments to rotate freely inside an artificial canal. Each instrument was rotated until fracture occurred, and the number of cycles to fracture for each instrument was calculated. Representative samples were also evaluated under a scanning electron microscope to confirm the fracture was flexural. Data were analyzed by using 1-way analysis of variance test. R-Endo R3 instruments showed better cyclic fatigue resistance than ProTaper D3 and Mtwo R 25.05 instruments, and the difference was statistically significant (P instruments were more resistant to fatigue failure than ProTaper D3 and Mtwo R 25.05. Copyright © 2012 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  19. Endodontic retreatment: clinical comparison of reciprocating systems versus rotary system in disinfecting root canals.

    Science.gov (United States)

    Martinho, Frederico C; Freitas, Lilian F; Nascimento, Gustavo G; Fernandes, Aleteia M; Leite, Fabio R M; Gomes, Ana P M; Camões, Izabel C G

    2015-07-01

    This clinical study was conducted to compare the effectiveness of single-file reciprocating systems and rotary systems in removing endotoxins and cultivable bacteria in endodontic retreatment. Thirty endodontically treated teeth with post-treatment apical periodontitis were selected. The specimens were divided into three groups according to the system used: WaveOne (n = 10), Reciproc instrument (n = 10), and ProTaper Universal Retreatment system (n = 10). Samples were collected before and after chemomechanical preparation. The irrigation was performed by using 2.5% sodium hypochlorite. A chromogenic limulus amebocyte lysate assay test was used to quantify endotoxins. Culture techniques were used to determine bacterial colony-forming unit counts. At baseline, endotoxins and cultivable bacteria were recovered from 100% of the root canal samples in a median value of 5.84 EU/mL and 4.98 × 10(3) CFU/mL, respectively. After CMP, no differences were found in the median percentage values of endotoxin reduction achieved with reciprocating systems-WaveOne [94.11%] and Reciproc [93.29%] and with rotary systems-ProTaper [94.98%] (P > 0.05). Both single-file reciprocating systems [WaveOne (98.27%) and Reciproc (99.54%)] and rotary system [ProTaper (98.73%)] were effective in reducing bacterial load (P > 0.05). Moreover, no differences were found among the systems tested. The Reciproc and WaveOne reciprocating systems were as effective as the ProTaper system for removal of endotoxins and bacteria in endodontic retreatment. All systems tested were effective to remove cultivable bacteria and endotoxin in endodontic retreatment. As no differences among systems were observed, it is possible to suggest that clinicians should choose the preferred technique to perform endodontic.

  20. Processes controlling the retreat of the Isles Dernieres, a Louisiana barrier-island chain

    Science.gov (United States)

    Dingler, John R.; Reiss, Thomas E.

    1991-01-01

    The Isles Dernieres is a low-lying, transgressive barrier-island chain situated about 150 km west of the modern Mississippi delta. Much of the Isles Dernieres consists of highly dissected salt-marsh muds that lie at or slightly above sea level and are covered by a veneer of sand along the shoreline facing the Gulf of Mexico. Maximum berm elevations are generally less than 1.5 m above mean sea level. Since the mid-1800s, the initial island has been fragmented into four islands, and the beach face has retreated landward at a rate of more than 10 m/yr. The dominant processes controlling degradation of the chain are cold fronts that pass through the area several times each year and occasional hurricanes. Beach surveys over a 2-year period on the Isles Dernieres document irreversible beach-face retreat in conjunction with multiple cold fronts and one major hurricane (Gilbert). Although both the hurricane and the cold fronts caused the island to erode, the erosional patterns of the two storm types differed from each other. During the two years, over 60 cold fronts collectively caused about 37 m of beach-face retreat, whereas Gilbert itself produced more than 40 m of retreat. A major difference between the two storm types was in the percentage of washover sand produced by each. Commonly, the cold fronts did not create enough of a storm surge to overtop the berm, so most of the material removed from the beach face must have moved offshore or alongshore. Gilbert, in contrast, inundated the study site, and essentially all the sand removed from the beach face moved to the backshore.

  1. The Glacial-Interglacial summer monsoon recorded in southwest Sulawesi speleothems: Evidence for sea level thresholds driving tropical monsoon strength

    Science.gov (United States)

    Kimbrough, A. K.; Gagan, M. K.; Dunbar, G. B.; Krause, C.; Di Nezio, P. N.; Hantoro, W. S.; Cheng, H.; Edwards, R. L.; Shen, C. C.; Sun, H.; Cai, B.; Rifai, H.

    2016-12-01

    Southwest Sulawesi lies within the Indo-Pacific Warm Pool (IPWP), at the center of atmospheric convection for two of the largest circulation cells on the planet, the meridional Hadley Cell and zonal Indo-Pacific Walker Circulation. Due to the geographic coincidence of these circulation cells, southwest Sulawesi serves as a hotspot for changes in tropical Pacific climate variability and Australian-Indonesian summer monsoon (AISM) strength over glacial-interglacial (G-I) timescales. The work presented here spans 386 - 127 ky BP, including glacial terminations IV ( 340 ky BP) and both phases of TIII (TIII 248 ky BP and TIIIa 217 ky BP). This record, along with previous work from southwest Sulawesi spanning the last 40 kyr, reveals coherent climatic features over three complete G-I cycles. The multi-stalagmite Sulawesi speleothem δ18O record demonstrates that on G-I timescales, the strength of the AISM is most sensitive to changes in sea level and its impact on the regional distribution of land and shallow ocean. Stalagmite δ18O and trace element (Mg/Ca) data indicate a rapid increase in rainfall at glacial terminations and wet interglacials. TIV, TIII, TIIIa, and TI are each characterized by an abrupt 3‰ decrease in δ18O that coincides with sea level rise and flooding of the Sunda and Sahul shelves. Strong evidence for a sea level (flooding/exposure) threshold is found throughout the southwest Sulawesi record. This is most clearly demonstrated over the period 230 - 212 ky BP (MIS 7d-7c), when a sea level fall to only -80 to -60 m for 10 kyr results in a weakened AISM and glacial conditions, followed by a full termination. Taken together, both glaciations and glacial terminations imply a sea level threshold driving the AISM between two primary levels of intensity (`interglacial' & `glacial'). These massive, sea-level driven shifts in AISM strength are superimposed on precession-scale variability associated with boreal fall insolation at the equator, indicating

  2. Geometric dependency of Tibetan lakes on glacial runoff

    NARCIS (Netherlands)

    Phan Hien, V.; Lindenbergh, R.C.; Menenti, M.

    2013-01-01

    The Tibetan Plateau is an essential source of water for Southeast Asia. The runoff from its ~34 000 glaciers, which occupy an area of ~50 000 km2, feeds Tibetan lakes and major Asian rivers like the Indus and Brahmaputra. Reported glacial shrinkage likely has an impact on the runoff. Unfortunately,

  3. Inherent characteristics of sawtooth cycles can explain different glacial periodicities

    NARCIS (Netherlands)

    Omta, A.W.; Kooi, B.W.; van Voorn, G.A.K.; Rickaby, R.E.M; Follows, M.J.

    2016-01-01

    At the Mid-Pleistocene Transition about 1 Ma, the dominant periodicity of the glacial-interglacial cycles shifted from ~40 to ~100 kyr. Here, we use a previously developed mathematical model to investigate the possible dynamical origin of these different periodicities. The model has two variables,

  4. Inherent characteristics of sawtooth cycles can explain different glacial periodicities

    NARCIS (Netherlands)

    Omta, Anne Willem; Kooi, Bob W.; Voorn, van G.A.K.; Rickaby, Rosalind E.M.; Follows, Michael J.

    2016-01-01

    At the Mid-Pleistocene Transition about 1 Ma, the dominant periodicity of the glacial-interglacial cycles shifted from ~40 to ~100 kyr. Here, we use a previously developed mathematical model to investigate the possible dynamical origin of these different periodicities. The model has two

  5. Testing Hypotheses About Glacial Cycles Against the Observational Record

    DEFF Research Database (Denmark)

    Kaufmann, Robert; Juselius, Katarina

    2013-01-01

    We estimate an identified cointegrated vector autoregression (CVAR) model of the climate system to test hypotheses about the physical mechanisms that may drive glacial cycles during the late Pleistocene. Results indicate that a permanent doubling of CO2 generates a 11.1oC rise in Antarctic...

  6. Glacial isostatic stress shadowing by the Antarctic ice sheet

    Science.gov (United States)

    Ivins, E. R.; James, T. S.; Klemann, V.

    2005-01-01

    Numerous examples of fault slip that offset late Quaternary glacial deposits and bedrock polish support the idea that the glacial loading cycle causes earthquakes in the upper crust. A semianalytical scheme is presented for quantifying glacial and postglacial lithospheric fault reactivation using contemporary rock fracture prediction methods. It extends previous studies by considering differential Mogi-von Mises stresses, in addition to those resulting from a Coulomb analysis. The approach utilizes gravitational viscoelastodynamic theory and explores the relationships between ice mass history and regional seismicity and faulting in a segment of East Antarctica containing the great Antarctic Plate (Balleny Island) earthquake of 25 March 1998 (Mw 8.1). Predictions of the failure stress fields within the seismogenic crust are generated for differing assumptions about background stress orientation, mantle viscosity, lithospheric thickness, and possible late Holocene deglaciation for the D91 Antarctic ice sheet history. Similar stress fracture fields are predicted by Mogi-von Mises and Coulomb theory, thus validating previous rebound Coulomb analysis. A thick lithosphere, of the order of 150-240 km, augments stress shadowing by a late melting (middle-late Holocene) coastal East Antarctic ice complex and could cause present-day earthquakes many hundreds of kilometers seaward of the former Last Glacial Maximum grounding line.

  7. Atlantic Meridional Overturning Circulation During the Last Glacial Maximum.

    NARCIS (Netherlands)

    Lynch-Stieglitz, J.; Adkins, J.F.; Curry, W.B.; Dokken, T.; Hall, I.R.; Herguera, J.C.; Hirschi, J.J.-M.; Ivanova, E.V.; Kissel, C.; Marchal, O.; Marchitto, T.M.; McCave, I.N.; McManus, J.F.; Mulitza, S.; Ninnemann, U.; Peeters, F.J.C.; Yu, E.-F.; Zahn, R.

    2007-01-01

    The circulation of the deep Atlantic Ocean during the height of the last ice age appears to have been quite different from today. We review observations implying that Atlantic meridional overturning circulation during the Last Glacial Maximum was neither extremely sluggish nor an enhanced version of

  8. 76 FR 50476 - Application To Export Electric Energy; Glacial Energy of Texas, Inc.

    Science.gov (United States)

    2011-08-15

    ... DEPARTMENT OF ENERGY [OE Docket No. EA-382] Application To Export Electric Energy; Glacial Energy... Application. SUMMARY: Glacial Energy of Texas, Inc. (Glacial) has applied for authority to transmit electric... for authority to transmit electric energy from the United States to Mexico for five years as a power...

  9. Postoperative pain after endodontic retreatment: single- versus two-visit treatment.

    Science.gov (United States)

    Yoldas, Oguz; Topuz, Aysin; Isçi, A Sehnaz; Oztunc, Haluk

    2004-10-01

    The purpose of this clinical study was to determine the effect of 1- or 2-visit root canal treatment on the postoperative pain in the retreatment cases. Two hundred eighteen cases that required retreatment were included in the study. Obturated and unfilled canal space and the status of periapical tissues were evaluated according to the PAI index. The patients were subcategorized in regard to the presence or the absence of preoperative pain. Approximately half of each category was treated in 1 appointment. After removing the previous root canal obturation materials and biomechanic preparation of root canals, the teeth in the 1-visit group were obturated at the first appointment by using AH 26 sealer and laterally compacted gutta-percha, and those in the 2-visit group were medicated with calcium hydroxide-chlorhexidine combination and then closed with a temporary filling material. One week after the initial appointment, patients were asked about the occurrence of postoperative pain. The level of discomfort was rated as no pain, mild pain, moderate pain, or severe pain (flare-up). Data were statistically analyzed using the chi-squared and Fischer exact tests. Eight patients from the 1-visit group and 2 patients from the 2-visit group had flare-ups. There was a statistical difference between the groups (P endodontic treatment with intracanal medication was found to be effective in reducing postoperative pain of previously symptomatic teeth and decreased the number of flare-ups in all retreatment cases.

  10. Prevalence of multidrug resistance among retreatment pulmonary tuberculosis cases in a tertiary care hospital, Hyderabad, India

    Directory of Open Access Journals (Sweden)

    Subhakar Kandi

    2013-01-01

    Full Text Available Background: India is one of the high tuberculosis (TB burden countries in the world. India ranks second in harboring multi drug resistant (MDR-TB cases. About 50,000 of MDR cases are recorded in retreatment pulmonary TB cases. This study was conducted in a tertiary care facility (Government General and Chest Hospital in Hyderabad, India. Objectives: Toassess: Proportion of the TB patients having MDR-TB at the initiation of retreatment regimen; the prevalence of isoniazid (INH resistance in this geographical area. Materials and Methods: An analytical, observational, prospective cohort study of patients attending the out-patient department from December 2010 to March 2011. Results: Sputum samples from 100 patients were subjected to acid fast bacilli (AFB culture and drug sensitivity testing. Of these, 28 (28% were MDR-TB, 42 (42% were non-MDR-TB and 39% being INH resistance. Conclusions: In conclusion, one third of the retreatment pulmonary TB cases attending a tertiary care institute for TB will be MDR-TB at the initiation of treatment and there is a need to include ethambutol in the continuation phase of new TB case treatment in view of high INH resistance.

  11. Skin-deep diagnosis: affective bias and zebra retreat complicating the diagnosis of systemic sclerosis.

    Science.gov (United States)

    Miller, Chad S

    2013-01-01

    Nearly half of medical errors can be attributed to an error of clinical reasoning or decision making. It is estimated that the correct diagnosis is missed or delayed in between 5% and 14% of acute hospital admissions. Through understanding why and how physicians make these errors, it is hoped that strategies can be developed to decrease the number of these errors. In the present case, a patient presented with dyspnea, gastrointestinal symptoms and weight loss; the diagnosis was initially missed when the treating physicians took mental short cuts and used heuristics as in this case. Heuristics have an inherent bias that can lead to faulty reasoning or conclusions, especially in complex or difficult cases. Affective bias, which is the overinvolvement of emotion in clinical decision making, limited the available information for diagnosis because of the hesitancy to acquire a full history and perform a complete physical examination in this patient. Zebra retreat, another type of bias, is when a rare diagnosis figures prominently on the differential diagnosis but the physician retreats for various reasons. Zebra retreat also factored in the delayed diagnosis. Through the description of these clinical reasoning errors in an actual case, it is hoped that future errors can be prevented or inspiration for additional research in this area will develop.

  12. Interest in health promotion among Korean American Seventh-day Adventists attending a religious retreat.

    Science.gov (United States)

    Jo, Angela M; Maxwell, Annette E; Choi, Sunhye; Bastani, Roshan

    2012-01-01

    Little is known about interest in faith-based health promotion programs among Asian American populations. Among the Christian denominations, the Seventh-day Adventist (SDA) church is known to place a strong doctrinal emphasis on health. To understand appropriate ways to develop and implement health promotion programs and to conduct research among Korean American SDAs. We collaborated with the North American Division of Korean SDA Churches which sponsors annual week-long religious retreats for their church members. We developed and administered a 10-page questionnaire at their 2009 retreat in order to assess socio-demographic and church characteristics, religiosity, perceived relationship between health and religion, and interest and preferences for church-based health promotion programs. Overall, 223 participants completed our survey (123 in Korean and 100 in English). The sample consisted of regular churchgoers who were involved in a variety of helping activities, and many holding leadership positions in their home churches. The vast majority was interested in receiving health information at church (80%) in the form of seminars, cooking classes and workshops (50-60%). Fewer respondents were interested in support groups (27%). Some interests and preferences differed between English and Korean language groups. Korean American SDA church retreat participants from a large geographic area are very interested in receiving health information and promoting health at their churches and can potentially serve as "agents of influence" in their respective communities.

  13. Seabed Gradient Controlling Onshore Transport Rates of Surf Sand during Beach Retreat by Sea Level Rise

    Science.gov (United States)

    Lee, Hee Jun; Yi, Hi-Il

    2018-03-01

    A simple relationship is proposed for the onshore transport rates of surf-zone sand to evaluate the beach retreat caused by sea level rise. It suggests that the preservation potential of surf sand is proportional inversely to the seabed gradient during beach retreat. According to this relationship, the erosional remnants of surf sand would be more readily developed on a gentler shelf collectively as transgressive sand sheets. This finding may explain the previous studies regarding the Korean shelves that proposed that the Holocene transgressive sand sheets (HTSS) occur not in the steep eastern shelf but in the gentle western shelf. In line with such presence/absence of the HTSS are the results from some coastal seismic profiles obtained in the present study. The profiles indicate that sand deposits are restricted within the nearshore in the eastern coast, whereas they are persistently traceable to the offshore HTSS in the western coast. Tide is proven to have a negligible influence on the total duration of surf-zone processes. This study may be useful in predicting the consequences of the beach retreat that takes place worldwide as sea levels rise as a result of global warming.

  14. Cost-effectiveness of retreatment with varenicline after failure with or relapse after initial treatment for smoking cessation

    Directory of Open Access Journals (Sweden)

    Lieven Annemans

    2015-01-01

    Conclusion: This analysis suggests that in the long term, varenicline retreatment is a dominant intervention, meaning both greater health gains and greater costs saved, over other possible interventions and therefore should be considered as a standard option.

  15. Treatment and retreatment with omalizumab in chronic spontaneous urticaria: Real life experience with twenty-five patients

    Directory of Open Access Journals (Sweden)

    Murat Türk

    2018-01-01

    Conclusions: Omalizumab has high efficacy in both the treatment and retreatment of CSU; however, relapse rates after discontinuation are high. Autoimmune markers may be helpful in predicting treatment response and relapse.

  16. Efficacy and safety of bortezomib-based retreatment at the first relapse in multiple myeloma patients: A retrospective study.

    Science.gov (United States)

    Oriol, Albert; Giraldo, Pilar; Kotsianidis, Ioannis; Couturier, Catherine; Olie, Robert; Angermund, Ralf; Corso, Alessandro

    2015-08-01

    Multiple myeloma remains incurable and retreatment with available therapies is of substantial interest. This retrospective observational study included data from 35 patients treated initially and at the first relapse with bortezomib-containing regimens. Bortezomib retreatment provided a similar depth and time to response as first-line therapy; however, as could be expected, the duration of response was shorter with retreatment. The tolerability profile was similar with bortezomib as the first- and second-line therapy, with no evidence of cumulative toxicity. These findings support bortezomib retreatment after a treatment-free interval of ≥6 months in patients who achieved at least a partial response to the first-line bortezomib-based therapy.

  17. The retreatment of carboplatin via high-dose intraperitoneal chemotherapy in patients with a history of a hypersensitivity reaction

    NARCIS (Netherlands)

    Kerkhof, M.H.; Ruiz Zapata, A.M.; Bril, H.; Bleeker, M.C.G.; Belien, J.A.M.; Stoop, R.; Helder, M.N.

    2014-01-01

    A hypersensitivity reaction attributed to platinum-based chemotherapy is a relatively common occurrence. Hyperthermic intraperitoneal chemotherapy potentially facilitates the safe retreatment of platinum therapy following this complication. We describe 3 ovarian cancer patients who were successfully

  18. Call for papers: SAJHE special issue 'Re-imagining writing retreats for academic staff in higher education'

    Directory of Open Access Journals (Sweden)

    Guest Editors

    2016-06-01

    Full Text Available Call for papers for an upcoming special issue of the South African Journal of Higher Education (SAJHE in 2016: ‘Re-imagining writing retreats for academic staff in higher education’.

  19. Influence of glacial meltwater on global seawater δ234U

    Science.gov (United States)

    Arendt, Carli A.; Aciego, Sarah M.; Sims, Kenneth W. W.; Das, Sarah B.; Sheik, Cody; Stevenson, Emily I.

    2018-03-01

    We present the first published uranium-series measurements from modern Greenland Ice Sheet (GrIS) runoff and proximal seawater, and investigate the influence of glacial melt on global seawater δ234U over glacial-interglacial (g-ig) timescales. Climate reconstructions based on closed-system uranium-thorium (U/Th) dating of fossil corals assume U chemistry of seawater has remained stable over time despite notable fluctuations in major elemental compositions, concentrations, and isotopic compositions of global seawater on g-ig timescales. Deglacial processes increase weathering, significantly increasing U-series concentrations and changing the δ234U of glacial meltwater. Analyses of glacial discharge from GrIS outlet glaciers indicate that meltwater runoff has elevated U concentrations and differing 222Rn concentrations and δ234U compositions, likely due to variations in subglacial residence time. Locations with high δ234U have the potential to increase proximal seawater δ234U. To better understand the impact of bulk glacial melt on global seawater δ234U over time, we use a simple box model to scale these processes to periods of extreme deglaciation. We account for U fluxes from the GrIS, Antarctica, and large Northern Hemisphere Continental Ice Sheets, and assess sensitivity by varying melt volumes, duration and U flux input rates based on modern subglacial water U concentrations and compositions. All scenarios support the hypothesis that global seawater δ234U has varied by more than 1‰ through time as a function of predictable perturbations in continental U fluxes during g-ig periods.

  20. Millennial-scale variability during the last glacial in vegetation records from North America

    Science.gov (United States)

    Jiménez-Moreno, Gonzalo; Anderson, R. Scott; Desprat, S.; Grigg, L.D.; Grimm, E.C.; Heusser, L.E.; Jacobs, Brian F.; Lopez-Martinez, C.; Whitlock, C.L.; Willard, D.A.

    2010-01-01

    High-resolution pollen records from North America show that terrestrial environments were affected by Dansgaard-Oeschger (D-O) and Heinrich climate variability during the last glacial. In the western, more mountainous regions, these climate changes are generally observed in the pollen records as altitudinal movements of climate-sensitive plant species, whereas in the southeast, they are recorded as latitudinal shifts in vegetation. Heinrich (HS) and Greenland (GS) stadials are generally correlated with cold and dry climate and Greenland interstadials (GI) with warm-wet phases. The pollen records from North America confirm that vegetation responds rapidly to millennial-scale climate variability, although the difficulties in establishing independent age models for the pollen records make determination of the absolute phasing of the records to surface temperatures in Greenland somewhat uncertain. ?? 2009 Elsevier Ltd.

  1. Late Glacial to Early Holocene socio-ecological responses to climatic instability within the Mediterranean basin

    Science.gov (United States)

    Fernández-López de Pablo, Javier; Jones, Samantha E.; Burjachs, Francesc

    2018-03-01

    The period spanning the Late Glacial and the Early Holocene (≈19-8.2 ka) witnessed a dramatic sequence of climate and palaeoenvironmental changes (Rasmussen et al., 2014). Interestingly, some of the most significant transformations ever documented in human Prehistory took place during this period such as the intensification of hunter-gatherer economic systems, the domestication process of wild plants and animals, and the spread of farming across Eurasia. Understanding the role of climate and environmental dynamics on long-term cultural and economic trajectories, as well as specific human responses to episodes of rapid climate change, still remains as one of the main challenges of archaeological research (Kintigh et al., 2014).

  2. Flow and transport processes in a macroporous subsurface-drained glacial till soil

    DEFF Research Database (Denmark)

    Villholth, Karen G.; Jensen, Karsten Høgh

    1998-01-01

    disturbance and compaction of the soil surface. Hypothetically introducing fully surface-connected macropores into the calibrated model resulted in a 22% increase in the loss of solute to the drain, indicating the significance of the hydraulic conditions at the soil surface and the model specification thereof......The experimental results from a field-scale tracer experiment in a subsurface-drained glacial till soil were analyzed by the application of a single/dual porosity model (MACRO), optionally accounting for concurrent and interacting flow and transport in the bulk soil porosity as well...... concentration. The exchange was overpredicted and too rapid when the soil aggregate size (distance between macropores) obtained from an image analysis of soil cores was used in the model. On this basis, the model assumption of instant equilibration of the solute across the matrix porosity, disregarding small...

  3. Glacial and oceanic history of the polar North Atlantic margins: An overview

    DEFF Research Database (Denmark)

    Elverhøj, A.; Dowdeswell, J.; Funder, S.V.

    1998-01-01

    Greenland Icc Sheet, in thc Late Pliocene as compared with the t...liddlejLate Miocene. The Svalbard-Barents Sea margin is characterised by major prograding fans, built mainly of stacked debris flows. These fans are interpreted as products of rapid sediment delivery from fast-llowing ice streams reaching...... the shelf break during full glacial conditions. Such major submarine fans are not found north of the Scorcsby Suml Fan off East Greenland, where ice seldom reached the shelf break, sedimentation rates were relatively low and sediment transport appears to have becn localised in several major deep......-sca submarine channel systems. Fcw debris flows are present and more uniform, acoustically-stratified scdiments predominate. In general, the Greenland Ice Sheet has been more stable than those on the European North Atlantic margin, which rcflect greater variability in heat and moisture transfer at timescale...

  4. Efficacy of reciprocating and rotary NiTi instruments for retreatment of curved root canals assessed by micro-CT.

    Science.gov (United States)

    Rödig, T; Reicherts, P; Konietschke, F; Dullin, C; Hahn, W; Hülsmann, M

    2014-10-01

    To compare the efficacy of reciprocating and rotary NiTi-instruments in removing filling material from curved root canals using micro-computed tomography. Sixty curved root canals were prepared and filled with gutta-percha and sealer. After determination of root canal curvatures and radii in two directions as well as volumes of filling material, the teeth were assigned to three comparable groups (n = 20). Retreatment was performed using Reciproc, ProTaper Universal Retreatment or Hedström files. Percentages of residual filling material and dentine removal were assessed using micro-CT imaging. Working time and procedural errors were recorded. Statistical analysis was performed by variance procedures. No significant differences amongst the three retreatment techniques concerning residual filling material were detected (P > 0.05). Hedström files removed significantly more dentine than ProTaper Universal Retreatment (P  0.05). Reciproc and ProTaper Universal Retreatment were significantly faster than Hedström files (P = 0.0001). No procedural errors such as instrument fracture, blockage, ledging or perforation were detected for Hedström files. Three perforations were recorded for ProTaper Universal Retreatment, and in both NiTi groups, one instrument fracture occured. Remnants of filling material were observed in all samples with no significant differences between the three techniques. Hedström files removed significantly more dentine than ProTaper Universal Retreatment, but no significant differences between both NiTi systems were detected. Procedural errors were observed with ProTaper Universal Retreatment and Reciproc. © 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd.

  5. Tropical tales of polar ice: evidence of Last Interglacial polar ice sheet retreat recorded by fossil reefs of the granitic Seychelles islands

    Science.gov (United States)

    Dutton, Andrea; Webster, Jody M.; Zwartz, Dan; Lambeck, Kurt; Wohlfarth, Barbara

    2015-01-01

    In the search for a record of eustatic sea level change on glacial-interglacial timescales, the Seychelles ranks as one of the best places on the planet to study. Owing to its location with respect to the former margins of Northern Hemisphere ice sheets that wax and wane on orbital cycles, the local-or relative-sea level history is predicted to lie within a few meters of the globally averaged eustatic signal during the Last Interglacial period. We have surveyed and dated Last Interglacial fossil corals to ascertain peak sea level and hence infer maximum retreat of polar ice sheets during this time interval. We observe a pattern of gradually rising sea level in the Seychelles between ˜129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 ± 1.7 m higher than present. After accounting for thermal expansion and loss of mountain glaciers, this sea-level budget would require ˜5-8 m of polar ice sheet contribution, relative to today's volume, of which only ˜2 m came from the Greenland ice sheet. This result clearly identifies the Antarctic ice sheet as a significant source of melt water, most likely derived from one of the unstable, marine-based sectors in the West and/or East Antarctic ice sheet. Furthermore, the establishment of a +5.9 ± 1.7 m eustatic sea level position by 128.6 ± 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand.

  6. Overall response rates to radiation therapy for patients with painful uncomplicated bone metastases undergoing initial treatment and retreatment

    International Nuclear Information System (INIS)

    Bedard, Gillian; Hoskin, Peter; Chow, Edward

    2014-01-01

    Introduction: Radiation therapy has been shown to successfully palliate bone metastases. A number of systematic reviews and large clinical trials have reported response rates for initial treatment and retreatment. Objective: To determine overall response rates of patients with painful uncomplicated bone metastases undergoing initial treatment and retreatment. Methods: Intent-to-treat and evaluable patient statistics from a systematic review of palliative radiotherapy trials for initial treatment of bone metastases and a randomized clinical trial of retreatment were pooled and analyzed to determine the overall response rates for patients receiving initial treatment and retreatment. Results: In the intent-to-treat calculation, 71–73% of patients had an overall response to radiation treatment and in the evaluable patient population; 85–87% of patients did so. Response rates varied slightly whether patients underwent single or multiple fractions in initial treatment or retreatment. Conclusions: Single and multiple fraction radiation treatment yielded very similar overall response rates. Patients treated with a single fraction for both initial and repeat radiation experience almost identical overall response to those patients treated with multiple fraction treatment. It is therefore recommended that patients with uncomplicated painful bone metastases be treated with a single 8 Gy fraction of radiation at both the initial treatment and retreatment

  7. To evaluate and compare the efficacy, cleaning ability of hand and two rotary systems in root canal retreatment.

    Science.gov (United States)

    Shivanand, Sunita; Patil, Chetan R; Thangala, Venugopal; Kumar, Pabbati Ravi; Sachdeva, Jyoti; Krishna, Akash

    2013-05-01

    To evaluate and compare the efficacy, cleaning ability of hand and two rotary systems in root canal retreatment. Sixty extracted premolars were retreated with following systems: Group -ProTaper Universal retreatment files, Group 2-ProFile system, Group 3-H-file. Specimens were split longitudinally and amount of remaining gutta-percha on the canal walls was assessed using direct visual scoring with the aid of stereomicroscope. Results were statistically analyzed using ANOVA test. Completely clean root canal walls were not achieved with any of the techniques investigated. However, all three systems proved to be effective for gutta-percha removal. Significant difference was found between ProTaper universal retreatment file and H-file, and also between ProFile and H-file. Under the conditions of the present study, ProTaper Universal retreatment files left significantly less guttapercha and sealer than ProFile and H-file. Rotary systems in combination with gutta-percha solvents can perform superiorly as compared to the time tested traditional hand instrumentation in root canal retreatment.

  8. Risk and resilience in the late glacial: A case study from the western Mediterranean

    Science.gov (United States)

    Barton, C. Michael; Aura Tortosa, J. Emili; Garcia-Puchol, Oreto; Riel-Salvatore, Julien G.; Gauthier, Nicolas; Vadillo Conesa, Margarita; Pothier Bouchard, Geneviève

    2018-03-01

    The period spanning the Last Glacial Maximum through early Holocene encompasses dramatic and rapid environmental changes that offered both increased risk and new opportunities to human populations of the Mediterranean zone. The regional effects of global climate change varied spatially with latitude, topography, and distance from a shifting coastline; and human adaptations to these changes played out at these regional scales. To better understand the spatial and temporal dynamics of climate change and human social-ecological-technological systems (or SETS) during the transition from full glacial to interglacial, we carried out a meta-analysis of archaeological and paleoenvironmental datasets across the western Mediterranean region. We compiled information on prehistoric technology, land-use, and hunting strategies from 291 archaeological assemblages, recovered from 122 sites extending from southern Spain, through Mediterranean France, to northern and peninsular Italy, as well as 2,386 radiocarbon dates from across this region. We combine these data on human ecological dynamics with paleoenvironmental information derived from global climate models, proxy data, and estimates of coastlines modeled from sea level estimates and digital terrain. The LGM represents an ecologically predictable period for over much of the western Mediterranean, while the remainder of the Pleistocene was increasingly unpredictable, making it a period of increased ecological risk for hunter-gatherers. In response to increasing spatial and temporal uncertainty, hunter-gatherers reorganized different constituents of their SETS, allowing regional populations to adapt to these conditions up to a point. Beyond this threshold, rapid environmental change resulted in significant demographic change in Mediterranean hunter-gatherer populations.

  9. Rapid evolution of the paraglacial Moosfluh rock slope instability (Swiss Alps) captured by Sentinel-1

    Science.gov (United States)

    Manconi, Andrea; Glueer, Franziska; Loew, Simon

    2017-04-01

    The Great Aletsch Region (GAR, Swiss Alps) has undergone to several cycles of glacial advancement and retreat, which have deeply affected the evolution of the surrounding landscape. Currently, this region is one of the places where the effects of climate change can be strikingly observed, as the Aletsch glacier is experiencing a remarkable retreat with rates in the order of 50 meters every year. In particular, a deep-seated slope instability located in the area called "Moosfluh" has shown during the past 20 years evidences of a slow but progressive increase of surface displacement. The moving mass associated to the Moosfluh rockslide affects an area of about 2 km2 and entails a volume estimated in the order of 150-200 Mm3. In the late summer 2016, an unusual acceleration of the Moosfluh rockslide was observed. Compared to previous years, when ground deformations were in the order of few centimeters, in the period September-October 2016 maximum velocities have reached locally 1 m/day. Such a critical evolution resulted in an increased number of local rock failures and caused the generation of several deep tensile cracks, hindering the access to hiking paths visited by tourists. Moreover, surface deformations have also affected the Moosfluh cable car station, located near the crest of the unstable slope. In this critical framework, the information available on ground was not enough to disentangle the spatial extent of the most active region. To investigate that, we have processed a number of Sentinel-1 SAR images acquired over the GAR. We paired images with maximum temporal baseline spanning 12 and 24 days, in order to preserve the highest possible interferometric coherence over the target area. Secondly, by stacking surface displacements obtained from the differential interferograms, we have increased the signal-to-noise ratio to produce velocity maps of the Moosfluh landslide over the period of interest. This approach has allowed us to constrain the lateral borders

  10. Fish Scale Evidence for Rapid Post Glacial Colonization of an Atlantic Coastal Pond

    Science.gov (United States)

    Daniels, R. A.; Peteet, Dorothy

    1996-01-01

    Fish scales from the sediment of Allamuchy Pond, New Jersey, USA, indicate that fishes were present in the pond within 400 years of the time of the first deposition of organic material, at approximately 12,600 yrs BP. The earliest of the scales, from a white sucker, Catostomus commersoni, appears in sediment dated 12,260 +/- 220 yrs BP. Presence of scales in sediment deposited before I 0,000 yrs BP indicates that Atlantic salmon, Salmo salar, sunfish, Lepomis sp., and yellow perch, Perca flavescens, also were early inhabitants of the pond. The timing of the arrival of each of these fishes suggests that they migrated out from Atlantic coastal refugia. A minnow scale, referred to Phoxininae, was also retrieved; it could not be matched to any cyprinid currently found in northeastern North America. The species present historically in this pond are from five families found currently in ponds throughout the Northeast and sugoest that the lentic palaeo-enviromnent was similar to present mid-elevation or high-latitude lentic systems.

  11. Sediment core and glacial environment reconstruction - a method review

    Science.gov (United States)

    Bakke, Jostein; Paasche, Øyvind

    2010-05-01

    Alpine glaciers are often located in remote and high-altitude regions of the world, areas that only rarely are covered by instrumental records. Reconstructions of glaciers has therefore proven useful for understanding past climate dynamics on both shorter and longer time-scales. One major drawback with glacier reconstructions based solely on moraine chronologies - by far the most common -, is that due to selective preservation of moraine ridges such records do not exclude the possibility of multiple Holocene glacier advances. This problem is true regardless whether cosmogenic isotopes or lichenometry have been used to date the moraines, or also radiocarbon dating of mega-fossils buried in till or underneath the moraines themselves. To overcome this problem Karlén (1976) initially suggested that glacial erosion and the associated production of rock-flour deposited in downstream lakes could provide a continuous record of glacial fluctuations, hence overcoming the problem of incomplete reconstructions. We want to discuss the methods used to reconstruct past glacier activity based on sediments deposited in distal glacier-fed lakes. By quantifying physical properties of glacial and extra-glacial sediments deposited in catchments, and in downstream lakes and fjords, it is possible to isolate and identify past glacier activity - size and production rate - that subsequently can be used to reconstruct changing environmental shifts and trends. Changes in average sediment evacuation from alpine glaciers are mainly governed by glacier size and the mass turnover gradient, determining the deformation rate at any given time. The amount of solid precipitation (mainly winter accumulation) versus loss due to melting during the ablation-season (mainly summer temperature) determines the mass turnover gradient in either positive or negative direction. A prevailing positive net balance will lead to higher sedimentation rates and vice versa, which in turn can be recorded in downstream

  12. The Glacial BuzzSaw, Isostasy, and Global Crustal Models

    Science.gov (United States)

    Levander, A.; Oncken, O.; Niu, F.

    2015-12-01

    The glacial buzzsaw hypothesis predicts that maximum elevations in orogens at high latitudes are depressed relative to temperate latitudes, as maximum elevation and hypsography of glaciated orogens are functions of the glacial equilibrium line altitude (ELA) and the modern and last glacial maximum (LGM) snowlines. As a consequence crustal thickness, density, or both must change with increasing latitude to maintain isostatic balance. For Airy compensation crustal thickness should decrease toward polar latitudes, whereas for Pratt compensation crustal densities should increase. For similar convergence rates, higher latitude orogens should have higher grade, and presumably higher density rocks in the crustal column due to more efficient glacial erosion. We have examined a number of global and regional crustal models to see if these predictions appear in the models. Crustal thickness is straightforward to examine, crustal density less so. The different crustal models generally agree with one another, but do show some major differences. We used a standard tectonic classification scheme of the crust for data selection. The globally averaged orogens show crustal thicknesses that decrease toward high latitudes, almost reflecting topography, in both the individual crustal models and the models averaged together. The most convincing is the western hemisphere cordillera, where elevations and crustal thicknesses decrease toward the poles, and also toward lower latitudes (the equatorial minimum is at ~12oN). The elevation differences and Airy prediction of crustal thickness changes are in reasonable agreement in the North American Cordillera, but in South America the observed crustal thickness change is larger than the Airy prediction. The Alpine-Himalayan chain shows similar trends, however the strike of the chain makes interpretation ambiguous. We also examined cratons with ice sheets during the last glacial period to see if continental glaciation also thins the crust toward

  13. Evaluation of apically extruded debris during root canal retreatment with two different rotary systems followed by a self-adjusting file.

    Science.gov (United States)

    Cakici, Fatih; Cakici, Elif B; Küçükekenci, Funda Fundaoglu

    2016-02-01

    To compare the amount of apically extruded debris during root canal retreatment using ProTaper retreatment system (Dentsply Maillefer, Ballaigues, Switzerland), ProTaper retreatment system with Self-Adjusting File (SAF) system (ReDent-Nova, Ra'anana, Israel), Mtwo retreatment system (VDW, Munich, Germany), Mtwo retreatment system with SAF instruments. In total, 72 extracted human mandibular incisor teeth were used. All root canals were prepared with ProTaper universal (Dentsply Maillefer) up to F2 file and filled with gutta percha and AH plus sealer using cold lateral condensation before being assembled randomly into 4 groups (n = 18 each). Root canal filling materials were removed using the ProTaper retreatment system, the ProTaper retreatment system followed by SAF system, Mtwo retreatment system and Mtwo retreatment system followed by SAF system. Debris extruded apically during the removal of canal filling material was collected into preweighed Eppendorf tubes. The tubes were then stored in an incubator at 70°C for 5 days. The weight of the dry extruded debris was established by subtracting the preretreatment and postretreatment weight of the Eppendorf tubes for each group. The data obtained were analyzed using Kruskal-Wallis test. All retreatment techniques caused the apical extrusion of debris. There was no significant difference between the groups statistically (p>0.05). The results of this study showed that SAF system after Mtwo retreatment system and ProTaper retreatment system for improving retreatment has no significant effect on the amount of debris extruded apically.

  14. The timing and cause of glacial activity during the last glacial in central Tibet based on 10Be surface exposure dating east of Mount Jaggang, the Xainza range

    Science.gov (United States)

    Dong, Guocheng; Zhou, Weijian; Yi, Chaolu; Fu, Yunchong; Zhang, Li; Li, Ming

    2018-04-01

    Mountain glaciers are sensitive to climate change, and can provide valuable information for inferring former climates on the Tibetan Plateau (TP). The increasing glacial chronologies indicate that the timing of the local Last Glacial Maximum (LGM) recorded across the TP is asynchronous, implying different local influences of the mid-latitude westerlies and Asian Summer Monsoon in triggering glacier advances. However, the well-dated sites are still too few, especially in the transition zone between regions controlled by the two climate systems. Here we present detailed last glacial chronologies for the Mount Jaggang area, in the Xainza range, central Tibet, with forty-three apparent 10Be exposure-ages ranging from 12.4 ± 0.8 ka to 61.9 ± 3.8 ka. These exposure-ages indicate that at least seven glacial episodes occurred during the last glacial cycle east of Mount Jaggang. These include: a local LGM that occurred at ∼61.9 ± 3.8 ka, possibly corresponding to Marine Isotope Stage 4 (MIS 4); subsequent glacial advances at ∼43.2 ± 2.6 ka and ∼35.1 ± 2.1 ka during MIS 3; one glacial re-advance/standstill at MIS3/2 transition (∼29.8 ± 1.8 ka); and three glacial re-advances/standstills that occurred following MIS 3 at ∼27.9 ± 1.7 ka, ∼21.8 ± 1.3 ka, and ∼15.1 ± 0.9 ka. The timing of these glacial activities is roughly in agreement with North Atlantic millennial-scale climate oscillations (Heinrich events), suggesting the potential correlations between these abrupt climate changes and glacial fluctuations in the Mount Jaggang area. The successively reduced glacial extent might have resulted from an overall decrease in Asian Summer Monsoon intensity over this timeframe.

  15. Was the Sun especially active at the end of the late glacial epoch?

    Science.gov (United States)

    Alekseeva, Liliya

    mother,'' who takes human souls to the World of dead. At the beginning of glacial-sheet degradation, people lived by hunting for wild reindeer. The animal moved to high latitudes behind the edge of the thawing glacial sheet, and the people followed the main object of their hunting. Thus, they went in the direction of their mythological World of dead. As they unexpectedly discovered the enchanting eye-catcher of northern lights, they should assume that they encountered the border of the World of dead. Emotional experience gained from such direct contact with the World of dead, as also from the narratives about the fascinating and spectacular view of this World seen by their own eyes, was recorded in the cosmological myths. Later, the descendants of the hunters scattered over the drying earth, which rapidly became overgrown with forest. The relics of their cosmological myths persist as a cultural phenomenon. Thus, the cultural inheritance looks like evidence of high auroral and solar activity at the epoch when the glacial sheet was thawing. If so, we deal with a mirror reflection of the correlation between the space weather and climate known for Maunder's minimum.

  16. Quantifying Regional Vegetation Changes in China During Three Contrasting Warming Intervals since the Last Glacial Maximum

    Science.gov (United States)

    Li, Q.; Wu, H.; Yu, Y.; Sun, A.; Luo, Y.

    2017-12-01

    Reconstructing patterns of past vegetation change on a large-scale facilitates a better understanding of the interactions and feedbacks between climate change and the terrestrial biosphere. In addition, reducing the uncertainty in predictions of vegetation change under global warming highlights the importance of reconstructing vegetation patterns during past warming intervals. Here, we present a quantitative regional vegetation reconstruction for China during three intervals: Last Glacial Maximum (LGM, 18±2 14C kyr B.P.), early Holocene (8.5±0.5 14C kyr B.P.), and mid-Holocene (6±0.5 14C kyr B.P.). The biomization method, based on 249 pollen records, was used for the reconstructions. The results demonstrate that during the LGM, steppe and desert expanded eastwards and southwards, reaching the present-day temperate deciduous forest (TEDE) zone, and dominated northern China. In contrast, the forest in Eastern China underwent a substantial southwards retreat and the percentage of forest-type sites was at a minimum. In addition, the warm mixed forest (WAMF) and TEDE shifted southwards of 10° N relative to the present-day, and tropical seasonal rain forest (TSFO) was almost absent. At the same time, the forest-steppe boundary shifted southwards to near the middle and lower reaches of Yangtze River. For the early Holocene and mid-Holocene, the TSFO, WAMF, and TEDE shifted northwards by 2-5° relative to today, and the percentage of forest sites increased and reached a maximum in the mid-Holocene. The slight expansion of forest from the early Holocene to the mid-Holocene caused the forest-steppe boundary to shift northwestwards to near the present-day 300 mm isohyet by the mid-Holocene. Our results also indicate that climatic warming since the LGM, which strengthened the East Asian summer monsoon, favored the development of forest in China. This is potentially an important finding for evaluating the possible response of forest in China to future global warming.

  17. The distribution of glacial erratics in the Northeast Atlantic

    International Nuclear Information System (INIS)

    Huggett, Q.

    1985-01-01

    A detailed study of all the available information on glacial erratics has been carried out. This has included an examination of 288 dredge hauls, 1164 sediment cores and 176 camera runs. Sufficient data have now been collected to provide an estimate of the impact risk of a point projectile with a glacial erratic, down to oxygen isotope stage 5 (127,000 years) in three areas of the North East Atlantic. 1. Porcupine seabight (50 deg N, 14 deg W) 0.460%; 2. King's Trough Flank (42 deg N, 24 deg W) 0.502%; 3. Great Meteor East (31 deg N, 25 deg W) 0.015%. These estimates are for all erratics larger than 1.5 cm diameter and apply only down to oxygen isotope stage 5. If estimates are required at greater depths than this, it is proposed that a detailed study of a long core should be undertaken. (author)

  18. Long-term cliff retreat and erosion hotspots along the central shores of the Monterey Bay National Marine Sanctuary

    Science.gov (United States)

    Moore, Laura J.; Griggs, Gary B.

    2002-01-01

    Quantification of cliff retreat rates for the southern half of Santa Cruz County, CA, USA, located within the Monterey Bay National Marine Sanctuary, using the softcopy/geographic information system (GIS) methodology results in average cliff retreat rates of 7–15 cm/yr between 1953 and 1994. The coastal dunes at the southern end of Santa Cruz County migrate seaward and landward through time and display net accretion between 1953 and 1994, which is partially due to development. In addition, three critically eroding segments of coastline with high average erosion rates ranging from 20 to 63 cm/yr are identified as erosion ‘hotspots’. These locations include: Opal Cliffs, Depot Hill and Manresa. Although cliff retreat is episodic, spatially variable at the scale of meters, and the factors affecting cliff retreat vary along the Santa Cruz County coastline, there is a compensation between factors affecting retreat such that over the long-term the coastline maintains a relatively smooth configuration. The softcopy/GIS methodology significantly reduces errors inherent in the calculation of retreat rates in high-relief areas (e.g. erosion rates generated in this study are generally correct to within 10 cm) by removing errors due to relief displacement. Although the resulting root mean squared error for erosion rates is relatively small, simple projections of past erosion rates are inadequate to provide predictions of future cliff position. Improved predictions can be made for individual coastal segments by using a mean erosion rate and the standard deviation as guides to future cliff behavior in combination with an understanding of processes acting along the coastal segments in question. This methodology can be applied on any high-relief coast where retreat rates can be measured.

  19. Comparison of 5468 retreatments after laser in situ keratomileusis by lifting the flap or performing photorefractive keratectomy on the flap.

    Science.gov (United States)

    Ortega-Usobiaga, J; Llovet-Osuna, F; Katz, T; Djodeyre, M R; Druchkiv, V; Bilbao-Calabuig, R; Baviera, J

    2018-02-01

    To assess visual outcomes of retreatment after laser in situ keratomileusis (LASIK) by lifting the flap or performing photorefractive keratectomy (PRK) on the flap, as well as to establish whether there was an increased risk of epithelial ingrowth (EIG) when LASIK and lifting of the flap are separated by a long time interval and to determine the incidence of corneal haze after PRK. Retrospective study of 4077 patients (5468 eyes) who underwent LASIK and subsequent retreatment were reviewed in order to study their visual results and identify cases of EIG and corneal haze. Enhancements included 5196 eyes from 3876 patients that were retreated by lifting the flap, and 272 eyes from 201 patients that were retreated by PRK on the flap. No statistically significant differences were found between the retreatments in terms of predictability, efficacy, and safety. A total of 704 cases of EIG were found after lifting the flap, for which surgical cleansing was necessary in 70. Surgical cleansing decreased the efficacy index when compared with patients with EIG who did not need cleansing (P=.01). Differences in terms of safety and predictability were not statistically significant. The incidence of corneal haze after ablation of the surface of the previous flap was 14.34%, although none of these cases were clinically relevant. Visual outcomes were similar between patients who were retreated by lifting the flap and those who underwent PRK. The incidence of EIG when the flap was lifted was 13.55%. The incidence of EIG increases with the time elapsed between the primary procedure and retreatment. Copyright © 2017 Sociedad Española de Oftalmología. Publicado por Elsevier España, S.L.U. All rights reserved.

  20. Psychological Effects of a 1-Month Meditation Retreat on Experienced Meditators: The Role of Non-attachment.

    Science.gov (United States)

    Montero-Marin, Jesus; Puebla-Guedea, Marta; Herrera-Mercadal, Paola; Cebolla, Ausias; Soler, Joaquim; Demarzo, Marcelo; Vazquez, Carmelo; Rodríguez-Bornaetxea, Fernando; García-Campayo, Javier

    2016-01-01

    Background: There are few studies devoted to assessing the impact of meditation-intensive retreats on the well-being, positive psychology, and personality of experienced meditators. We aimed to assess whether a 1-month Vipassana retreat: (a) would increase mindfulness and well-being; (b) would increase prosocial personality traits; and (c) whether psychological changes would be mediated and/or moderated by non-attachment. Method: A controlled, non-randomized, pre-post-intervention trial was used. The intervention group was a convenience sample ( n = 19) of experienced meditators who participated in a 1-month Vipassana meditation retreat. The control group ( n = 19) comprised matched experienced meditators who did not take part in the retreat. During the retreat, the mean duration of daily practice was 8-9 h, the diet was vegetarian and silence was compulsory. The Experiences Questionnaire (EQ), Non-attachment Scale (NAS), Positive and Negative Affect Schedule (PANAS), Satisfaction With Life Scale (SWLS), Temperament Character Inventory Revised (TCI-R-67), Five Facets Mindfulness Questionnaire (FFMQ), Self-Other Four Immeasurables (SOFI) and the MINDSENS Composite Index were administered. ANCOVAs and linear regression models were used to assess pre-post changes and mediation/moderation effects. Results: Compared to controls, retreatants showed increases in non-attachment, observing, MINDSENS, positive-affect, balance-affect, and cooperativeness; and decreases in describing, negative-others, reward-dependence and self-directedness. Non-attachment had a mediating role in decentring, acting aware, non-reactivity, negative-affect, balance-affect and self-directedness; and a moderating role in describing and positive others, with both mediating and moderating effects on satisfaction with life. Conclusions: A 1-month Vipassana meditation retreat seems to yield improvements in mindfulness, well-being, and personality, even in experienced meditators. Non-attachment might

  1. Glacial cycles:exogenous orbital changes vs. endogenous climate dynamics

    OpenAIRE

    Kaufmann, R. K.; Juselius, Katarina

    2010-01-01

    We use a statistical model, the cointegrated vector autoregressive model, to assess the degree to which variations in Earth's orbit and endogenous climate dynamics can be used to simulate glacial cycles during the late Quaternary (390 kyr-present). To do so, we estimate models of varying complexity and compare the accuracy of their in-sample simulations. Results indicate that strong statistical associations between endogenous climate variables are not enough for statistical models to reproduc...

  2. Uncovering the glacial history of the Irish continental shelf (Invited)

    Science.gov (United States)

    Dunlop, P.; Benetti, S.; OCofaigh, C.

    2013-12-01

    In 1999 the Irish Government initiated a €32 million survey of its territorial waters known as the Irish National Seabed Survey (INSS). The INSS is amongst the largest marine mapping programmes ever undertaken anywhere in the world and provides high-resolution multibeam, backscatter and seismic data of the seabed around Ireland. These data have been used to provide the first clear evidence for extensive glaciation of the continental shelf west and northwest of Ireland. Streamlined drumlins on the mid to outer shelf record former offshore-directed ice flow towards the shelf edge and show that the ice sheet was grounded in a zone of confluence where ice flowing onto the shelf from northwest Ireland merged with ice flowing across the Malin Shelf from southwest Scotland. The major glacial features on the shelf are well developed nested arcuate moraine systems that mark the position of the ice sheet margin and confirm that the former British Irish Ice Sheet was grounded as far as the shelf edge around 100 km offshore of west Donegal at the last glacial maximum. Distal to the moraines, on the outermost shelf, prominent zones of iceberg plough marks give way to the Barra/Donegal fan and a well developed system of gullies and canyons which incise the continental slope. Since 2008 several scientific cruises have retrieved cores from the shelf and slope to help build a more detailed understanding of glacial events in this region. This presentation will provide an overview of the glacial history of the Irish shelf and will discuss ongoing research programmes that are building on the initial research findings to produce a better understanding of the nature and timing of ice sheet events in this region.

  3. The INTIMATE event stratigraphy of the last glacial period

    Science.gov (United States)

    Olander Rasmussen, Sune; Svensson, Anders

    2015-04-01

    The North Atlantic INTIMATE (INtegration of Ice-core, MArine and TErrestrial records) group has previously recommended an Event Stratigraphy approach for the synchronisation of records of the Last Termination using the Greenland ice core records as the regional stratotypes. A key element of these protocols has been the formal definition of numbered Greenland Stadials (GS) and Greenland Interstadials (GI) within the past glacial period as the Greenland expressions of the characteristic Dansgaard-Oeschger events that represent cold and warm phases of the North Atlantic region, respectively. Using a recent synchronization of the NGRIP, GRIP, and GISP2 ice cores that allows the parallel analysis of all three records on a common time scale, we here present an extension of the GS/GI stratigraphic template to the entire glacial period. In addition to the well-known sequence of Dansgaard-Oeschger events that were first defined and numbered in the ice core records more than two decades ago, a number of short-lived climatic oscillations have been identified in the three synchronized records. Some of these events have been observed in other studies, but we here propose a consistent scheme for discriminating and naming all the significant climatic events of the last glacial period that are represented in the Greenland ice cores. In addition to presenting the updated event stratigraphy, we make a series of recommendations on how to refer to these periods in a way that promotes unambiguous comparison and correlation between different proxy records, providing a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations. The work presented is a part of a newly published paper in an INTIMATE special issue of Quaternary Science Reviews: Rasmussen et al., 'A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-core records: refining and extending the INTIMATE event

  4. Glacially striated, soft sediment surfaces on late Paleozoic tillite at São Luiz do Purunã, PR

    Directory of Open Access Journals (Sweden)

    Ivo Trosdtorf Jr.

    2005-06-01

    Full Text Available Striae and furrows found on the upper surfaces of three stratigraphically superposed decimetric beds of late Paleozoic lodgement tillite of the Itararé Subgroup in the northern Paraná Basin were engraved by ploughing of clasts and possibly also ice protuberances at the base of the glacier, on unconsolidated to partially consolidated sediment. Associated features indicate that the rheology of the bed varied from stiff during lodgement to soft and deformable during ploughing. Poor drainage of meltwater at the glacier-bed interface may have contributed to lower the strength of sediment to deformation. The deformed interval was probably generated during a single glacial phase or advance of a glacier grounding in a marine or lacustrine water body. Changes in the dynamics of the glacier involving slow and fast flow were correlated respectively with alternation of deposition and erosion. The proposed model is analogous to that of lodgement till complexes from the Pleistocene of the northern hemisphere. Retreat of the glacier was probably fast, followed by settling of muds on top of the upper striated and furrowed surface, and progradation of deltaic sands during post-glacial time.Estrias e sulcos encontrados sobre três camadas decimétricas, estratigraficamente superpostas, de tilito de alojamento neopaleozóico do Subgrupo Itararé, na porção norte da Bacia do Paraná, foram formados por aração de clastos e, possivelmente, por protuberâncias de gelo, na base da geleira. Feições associadas indicam que a reologia do sedimento variou de rígido, durante o alojamento, a inconsolidado e deformável durante a aração. A baixa drenagem da água de degelo na interface geleira-substrato pode ter contribuído para reduzir a resistência do sedimento à deformação. A sucessão acima foi gerada provavelmente durante uma única fase glacial ou avanço de geleira sobre corpo de água marinho ou lacustre. Mudanças na dinâmica da geleira envolvendo

  5. Evaluation of image-guided helical tomotherapy for the retreatment of spinal metastasis

    International Nuclear Information System (INIS)

    Mahan, Stephen L.; Ramsey, Chester R.; Scaperoth, Daniel D.; Chase, Daniel J.; Byrne, Thomas E.

    2005-01-01

    Introduction: Patients with vertebral metastasis that receive radiation therapy are typically treated to the spinal cord tolerance dose. As such, it is difficult to successfully deliver a second course of radiation therapy for patients with overlapping treatment volumes. In this study, an image-guided helical tomotherapy system was evaluated for the retreatment of previously irradiated vertebral metastasis. Methods and Materials: Helical tomotherapy dose gradients and maximum cord doses were measured in a cylindrical phantom for geometric test cases with separations between the planning target volume (PTV) and the spinal cord organ at risk (OAR) of 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm. Megavoltage computed tomography (CT) images were examined for their ability to localize spinal anatomy for positioning purposes by repeat imaging of the cervical spine in an anthropomorphic phantom. In addition to the phantom studies, 8 patients with cord compressions that had received previous radiation therapy were retreated to a mean dose of 28 Gy using conventional fractionation. Results and Discussion: Megavoltage CT images were capable of positioning an anthropomorphic phantom to within ±1.2 mm (2σ) superior-inferiorly and within ±0.6 mm (2σ) anterior-posteriorly and laterally. Dose gradients of 10% per mm were measured in phantom while PTV uniformity indices of less than 11% were maintained. The calculated maximum cord dose was 25% of the prescribed dose for a 10-mm PTV-to-OAR separation and 71% of the prescribed dose for a PTV-to-OAR separation of 2 mm. Eight patients total have been treated without radiation-induced myelopathy or any other adverse effects from treatment. Conclusions: A technique has been evaluated for the retreatment of vertebral metastasis using image-guided helical tomotherapy. Phantom and patient studies indicated that a tomotherapy system is capable of delivering dose gradients of 10% per mm and positioning the patient within 1.2 mm without the use of

  6. Risk factors for treatment default among re-treatment tuberculosis patients in India, 2006.

    Science.gov (United States)

    Jha, Ugra Mohan; Satyanarayana, Srinath; Dewan, Puneet K; Chadha, Sarabjit; Wares, Fraser; Sahu, Suvanand; Gupta, Devesh; Chauhan, L S

    2010-01-25

    Under India's Revised National Tuberculosis Control Programme (RNTCP), >15% of previously-treated patients in the reported 2006 patient cohort defaulted from anti-tuberculosis treatment. To assess the timing, characteristics, and risk factors for default amongst re-treatment TB patients. For this case-control study, in 90 randomly-selected programme units treatment records were abstracted from all 2006 defaulters from the RNTCP re-treatment regimen (cases), with one consecutively-selected non-defaulter per case. Patients who interrupted anti-tuberculosis treatment for >2 months were classified as defaulters. 1,141 defaulters and 1,189 non-defaulters were included. The median duration of treatment prior to default was 81 days (25%-75% interquartile range 44-117 days) and documented retrieval efforts after treatment interruption were inadequate. Defaulters were more likely to have been male (adjusted odds ratio [aOR] 1.4, 95% confidence interval [CI] 1.2-1.7), have previously defaulted anti-tuberculosis treatment (aOR 1.3 95%CI 1.1-1.6], have previous treatment from non-RNTCP providers (AOR 1.3, 95%CI 1.0-1.6], or have public health facility-based treatment observation (aOR 1.3, 95%CI 1.1-1.6). Amongst the large number of re-treatment patients in India, default occurs early and often. Improved pre-treatment counseling and community-based treatment provision may reduce default rates. Efforts to retrieve treatment interrupters prior to default require strengthening.

  7. Interference of partial visual analysis of root filling quality and apical status on retreatment decisions

    Directory of Open Access Journals (Sweden)

    Renata Dornelles Morgental

    2012-04-01

    Full Text Available OBJECTIVE: The presence of periapical radiolucency has been used as a criterion for endodontic treatment failure. However, in addition to the inherent limitations of radiographic examinations, radiographic interpretations are extremely subjective. Thus, this study investigated the effect of partial analysis of root filling quality and periapical status on retreatment decisions by general dentists. MATERIAL AND METHODS: Twelve digitalized periapical radiographs were analyzed by 10 observers. The study was conducted at three time points at 1-week intervals. Radiographs edited with the Adobe Photoshop CS4 software were analyzed at three time points: first, only root filling quality was analyzed; second, only the periapical areas of the teeth under study were visualized; finally, observers analyzed the unedited radiographic image. Spearman ’s coefficient was used to analyze the correlations between the scores assigned when the periapical area was not visible and when the unedited radiograph was analyzed, as well as between the scores assigned when root fillings where not visible and when the unedited radiograph was analyzed. Sensitivity, specificity, positive and negative predictive values between partial images and unedited radiographs were also used to analyze retreatment decisions. The level of significance was set at 5%. RESULTS: The visualization of the root filling on the unedited radiograph affected the interpretation of the periapical status and the technical quality of the fillings has a greater influence on the general dentist’s decision to prescribe endodontic retreatment than the periapical condition. CONCLUSION: In order to make endodontic diagnosis, radiographic interpretation process should not only emphasize technical aspects, but also consider biological factors.

  8. Contributions of culture and antimicrobial susceptibility tests to the retreatment of patients with pulmonary tuberculosis

    Directory of Open Access Journals (Sweden)

    Bruno Horta Andrade

    2013-08-01

    Full Text Available Introduction This study evaluated the efficacy of retreatment of pulmonary tuberculosis (TB with regard to treatment outcomes and antimicrobial susceptibility testing (ST profiles. Methods This retrospective cohort study analyzed 144 patients treated at a referral hospital in Brazil. All of them had undergone prior treatment, were smear-positive for TB and received a standardized retreatment regimen. Fisher's 2-tailed exact test and the χ2 test were used; RRs and 95% CIs were calculated using univariate and multivariate binary logistic regression. Results The patients were cured in 84 (58.3% cases. Failure was associated with relapsed treatment and abandonment (n=34. Culture tests were obtained for 103 (71.5% cases; 70 (48.6% had positive results. ST results were available for 67 (46.5% cases; the prevalence of acquired resistance was 53.7%. There were no significant differences between those who achieved or not therapeutic success (p=0.988, despite being sensitive or resistant to 1 or more drugs. Rifampicin resistance was independently associated with therapeutic failure (OR: 4.4, 95% CI:1.12-17.37, p=0.034. For those cases in which cultures were unavailable, a 2nd model without this information was built. In this, return after abandonment was significantly associated with retreatment failure (OR: 3.59, 95% CI:1.17-11.06, p=0.026. Conclusions In this cohort, the general resistance profile appeared to have no influence on treatment outcome, except in cases of rifampicin resistance. The form of reentry was another independent predictor of failure. The use of bacterial culture identification and ST in TB management must be re-evaluated. The recommendations for different susceptibility profiles must also be improved.

  9. Efficacy of Different Nickel-Titanium Instruments in Removing Gutta-percha during Root Canal Retreatment.

    Science.gov (United States)

    Özyürek, Taha; Demiryürek, Ebru Özsezer

    2016-04-01

    The aim of this study was to compare the cleanliness of root canal walls after retreatment using ProTaper Next (PTN; Dentsply Maillefer, Ballaigues, Switzerland), Twisted File Adaptive (TFA; Axis/SybronEndo, Orange, CA), Reciproc (PRC; VDW, Munich, Germany), and ProTaper Universal retreatment (PTR, Dentsply Maillefer) nickel-titanium systems and the time required for gutta-percha and sealer removal. Eighty human maxillary central incisors with single and straight root canals were instrumented up to #40.02 with manual K-files (Dentsply Maillefer) and obturated using the continuous wave of condensation technique. Removal of the gutta-percha and sealer was performed using 1 of the following nickel-titanium systems: PTN, TFA, RPC, or PTR. The teeth were sectioned, and digital images were captured. The photographs were analyzed using AutoCAD software (Autodesk, San Rafael, CA). Also, the total time required for gutta-percha removal was calculated by a chronometer. The total retreatment time was significantly shorter in the PTR group compared with the other groups (P < .05). There was a significant difference between the groups according to the total residual gutta-percha and sealer (P < .05). The PTN and PTR groups left significantly less gutta-percha and sealer remnant than the TFA and RPC groups (P < .05). Within the limitations of this study, the PTN and the PTR groups showed less residual gutta-percha and sealer than the TFA and RPC groups. The time required for gutta-percha and sealer removal was similar for all the groups, except for the PTR group. Copyright © 2016 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  10. Deformed glacial deposits of Passamaquoddy Bay area, New Brunswick

    International Nuclear Information System (INIS)

    Kumarapeli, S.

    1990-03-01

    The New Brunswick-Maine border area, centred around Passamaquoddy Bay, is characterized by a distinctly higher level of seismic activity compared with the very low level background activity of the region. In this same general area, post-glacial deformation including faulting, has been observed in glaciofluvial and ice contact deposits and the possibility that these structures may in some way related to neotectonic movements in the area has been suggested. A study was undertaken to document these structures and to investigate their origin. The studies show that structures related to collapse of sediments due to melting of buried ice masses are the most prominent post-depositional structures in the glacial sediments. A second group of structures includes failure phenomena such as slumping. These require the action of a mechanism leading to reduction of sediment strength which could be achieved by seismic shaking. However, such failure phenomena could also be brought about by non-seismic processes, thus a unique interpretation of the origin of these structures is difficult, if not impossible. Since seismic shaking is the most effective, regionally extensive trigger of a broad group of failure phenomena in soft sediments, the related structures are usually spread over a large area, but are restricted to a very short time gap. Although the establishment of such space and time relationships may be feasible, for example in extensive lake deposits, it is difficult to do so in patchy laterally variable deposits such as the glacial deposits in Passamaquoddy Bay area

  11. Nutrient biogeochemistry of the eastern Arabian Sea during the southwest monsoon retreat

    Digital Repository Service at National Institute of Oceanography (India)

    George, R; Muraleedharan, K.R; Martin, G.D.; Sabu, P.; Gerson, V.J.; Dineshkumar, P.K.; Nair, S.M.; Chandramohanakumar, N.; Nair, K.K.C.

    and adjoining southeastern Arabian Sea. Curr Sci 96:364–375 Jyothibabu R, Madhu NV, Jayalakshmi KV, Balachandran KK, Shiyas CA, Martin GD, Nair KKC (2006) Impact of freshwater influx on microzooplankton mediated food web in a tropical estuary (Cochin backwaters... ARTICLE Nutrient biogeochemistry of the eastern Arabian Sea during the southwest monsoon retreat Rejomon George • K. R. Muraleedharan • G. D. Martin • P. Sabu • Vijay John Gerson • P. K. Dineshkumar • S. M. Nair • N. Chandramohanakumar • K. K. C. Nair...

  12. Management of curved root canals in endodontics: clinical case of retreatment

    International Nuclear Information System (INIS)

    Meneses Guzman, Jose Pablo

    2005-01-01

    The management of curved root canals in endodontics therapy has required time, patience and skill of the operator, and lots collaboration by the patient. Proper cleaning, disinfection, conformation and root canal filling, in most cases, has prevented the appearance of lesions of bacterial origin to apical or maintenance of these lesions in teeth that are portrayed level. A clinical case is described of retreatment of a first mandibular molar by conventional endodontic treatment with their respective steps, to achieve signs of tissue repair at the apical level. (author) [es

  13. The 20th century retreat of ice caps in Iceland derived from airborne SAR

    DEFF Research Database (Denmark)

    Magnússon, Eyjólfur; Björnsson, Helgi; Dall, Jørgen

    2005-01-01

    with the Danish airborne EMISAR radar system. Polarimetric and interferometric SAR data reveal the margins of the present ice caps as well as a series of terminal moraines in the fore field. These moraines date back to the maximum Neoglacial extent at the end of the 19th century and the outermost allow...... of the surges in W-Vatnajokull in the 20th century are observed in the SAR data including the most recent surges in the 1990s. Interestingly no push moraines were observed in front of the surge advance, but the moraines appear when the glaciers start retreating. We estimate that the collective decrease...

  14. Yoga Retreat : Grafiikan työstäminen Facebook peliin

    OpenAIRE

    Kälviäinen, Jenna

    2013-01-01

    In the thesis the process of graphic design of Facebook games is discussed. The Author got an opportunity to work as a graphic designer for Gajatri Studios in their first video game project called Yoga Retreat. Experiences from the project, the decisions made and the problems faced were analyzed in detail. In the theory section the history of Facebook in general was explored and the question of how Facebook became one of the most well-known websites of the Internet was discussed as well as...

  15. Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier

    OpenAIRE

    Smith, J.A.; Andersen, T.J.; Shortt, M.; Gaffney, A.M.; Truffer, M.; Stanton, T.P.; Bindschadler, R.; Dutrieux, P.; Jenkins, A.; Hillenbrand, C.-D.; Ehrmann, W.; Corr, H.F.J.; Farley, N.; Crowhurst, S.; Vaughan, D.G.

    2016-01-01

    The article of record as published may be found at http://dx.doi.org/10.1038/nature20136 The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line—which marks the boundary between grounded ice and floating ice shelf—is underway. Under...

  16. Comparison of the amount of apically extruded debris produced by four retreatment techniques: an ex vivo study

    Directory of Open Access Journals (Sweden)

    Cristiane Ferreira Alfenas

    2017-12-01

    Full Text Available Objective: the aim of this study was to compare the amount of apically extruded debris during the removal of root canal filling material using nickel-titanium rotary retreatment instruments and Hedström files. Material and Methods: sixty mandibular incisors with a single canal were instrumented and obturated by cold lateral compaction. For retreatment, specimens were randomly divided into four groups (n = 15: Hedström files with or without solvent; D-RaCe system and Mtwo retreatment system. Debris extruded apically during the removal of canal filling material was collected into preweighed Eppendorf tubes. The tubes were then stored in an incubator at 70°C for 5 days. The weight of the dry extruded debris was established by subtracting the preretreatment and postretreatment weight of the Eppendorf tubes for each group. The mean weights of extruded material were analyzed by one-way ANOVA. Results: the results showed that all retreatment techniques caused apical extrusion of debris, but no statistically significant difference was observed between groups (p>0.05. Conclusion: under the conditions of this study, all retreatment techniques caused apical debris extrusion.

  17. Non-surgical retreatment of a failed apicoectomy without retrofilling using white mineral trioxide aggregate as an apical barrier.

    Science.gov (United States)

    Stefopoulos, Spyridon; Tzanetakis, Giorgos N; Kontakiotis, Evangelos G

    2012-01-01

    Root-end resected teeth with persistent apical periodontitis are usually retreated surgically or a combination of non-surgical and surgical retreatment is employed. However, patients are sometimes unwilling to be subjected to a second surgical procedure. The apical barrier technique that is used for apical closure of immature teeth with necrotic pulps may be an alternative to non-surgically retreat a failed apicoectomy. Mineral trioxide aggregate (MTA) has become the material of choice in such cases because of its excellent biocompatibility, sealing ability and osseoinductive properties. This case report describes the non-surgical retreatment of a failed apicoectomy with no attempt at retrofilling of a maxillary central incisor. White MTA was used to induce apical closure of the wide resected apical area. Four-year follow-up examination revealed an asymptomatic, fully functional tooth with a satisfactory healing of the apical lesion. White MTA apical barrier may constitute a reliable and efficient technique to non-surgically retreat teeth with failed root-end resection. The predictability of such a treatment is of great benefit for the patient who is unwilling to be submitted to a second surgical procedure.

  18. Investigating glacial mass balance variability around the Prince Gustav Channel

    Science.gov (United States)

    Royston, Samantha; Gudmundsson, Hilmar; Clarke, Lucy; Fox, Adrian

    2015-04-01

    Glaciers on the Antarctic Peninsula have shown a varied response to recent climatic change. Most commonly, AP tidewater glaciers have retreated at the calving front and their flow rate has accelerated, increasing the contribution to sea level rise. Here, we utilise the results from a new photogrammetric technique that unlocks the archives of aerial photography from the 1940's to present, to investigate the driving mechanisms of glacier mass change on the AP over this period. Surface DEMs at different epochs have been derived using the new technique for a number of individual glacier basins. A higher-order vertically-integrated ice stream model is used to investigate the driving mechanisms of change for the area around the Prince Gustav Channel, incorporating basins covered by the new datasets. The Prince Gustav Ice Shelf collapsed in January 1995, followed by significant frontal retreat and speed up of its tributary glaciers. Additionally, significant changes have been observed for non-tributary glaciers such as Whisky Glacier on James Ross Island. Here, we investigate the sensitivity of this region's glaciers to ice shelf collapse, atmospheric and oceanic variability.

  19. Simulating the vegetation response in western Europe to abrupt climate changes under glacial background conditions

    Directory of Open Access Journals (Sweden)

    M.-N. Woillez

    2013-03-01

    Full Text Available The last glacial period has been punctuated by two types of abrupt climatic events, the Dansgaard–Oeschger (DO and Heinrich (HE events. These events, recorded in Greenland ice and in marine sediments, involved changes in the Atlantic Meridional Overturning Circulation (AMOC and led to major changes in the terrestrial biosphere. Here we use the dynamical global vegetation model ORCHIDEE to simulate the response of vegetation to abrupt changes in the AMOC strength. We force ORCHIDEE offline with outputs from the IPSL_CM4 general circulation model, in which the AMOC is forced to change by adding freshwater fluxes in the North Atlantic. We investigate the impact of a collapse and recovery of the AMOC, at different rates, and focus on Western Europe, where many pollen records are available for comparison. The impact of an AMOC collapse on the European mean temperatures and precipitations simulated by the GCM is relatively small but sufficient to drive an important regression of forests and expansion of grasses in ORCHIDEE, in qualitative agreement with pollen data for an HE event. On the contrary, a run with a rapid shift of the AMOC to a hyperactive state of 30 Sv, mimicking the warming phase of a DO event, does not exhibit a strong impact on the European vegetation compared to the glacial control state. For our model, simulating the impact of an HE event thus appears easier than simulating the abrupt transition towards the interstadial phase of a DO. For both a collapse or a recovery of the AMOC, the vegetation starts to respond to climatic changes immediately but reaches equilibrium about 200 yr after the climate equilibrates, suggesting a possible bias in the climatic reconstructions based on pollen records, which assume equilibrium between climate and vegetation. However, our study does not take into account vegetation feedbacks on the atmosphere.

  20. Integrated hazard assessment of Cirenmaco glacial lake in Zhangzangbo valley, Central Himalayas

    Science.gov (United States)

    Wang, Weicai; Gao, Yang; Iribarren Anacona, Pablo; Lei, Yanbin; Xiang, Yang; Zhang, Guoqing; Li, Shenghai; Lu, Anxin

    2018-04-01

    Glacial lake outburst floods (GLOFs) have recently become one of the primary natural hazards in the Himalayas. There is therefore an urgent need to assess GLOF hazards in the region. Cirenmaco, a moraine-dammed lake located in the upstream portion of Zhangzangbo valley, Central Himalayas, has received public attention after its damaging 1981 outburst flood. Here, by combining remote sensing methods, bathymetric survey and 2D hydraulic modeling, we assessed the hazard posed by Cirenmaco in its current status. Inter-annual variation of Cirenmaco lake area indicates a rapid lake expansion from 0.10 ± 0.08 km2 in 1988 to 0.39 ± 0.04 km2 in 2013. Bathymetric survey shows the maximum water depth of the lake in 2012 was 115 ± 2 m and the lake volume was calculated to be 1.8 × 107 m3. Field geomorphic analysis shows that Cirenmaco glacial lake is prone to GLOFs as mass movements and ice and snow avalanches can impact the lake and the melting of the dead ice in the moraine can lower the dam level. HEC-RAS 2D model was then used to simulate moraine dam failure of the Cirenmaco and assess GLOF impacts downstream. Reconstruction of Cirenmaco 1981 GLOF shows that HEC-RAS can produce reasonable flood extent and water depth, thus demonstrate its ability to effectively model complex GLOFs. GLOF modeling results presented can be used as a basis for the implementation of disaster prevention and mitigation measures. As a case study, this work shows how we can integrate different methods to GLOF hazard assessment.

  1. Late glacial multiproxy evidence of vegetation development and environmental change at Solova, southeastern Estonia

    Directory of Open Access Journals (Sweden)

    Amon, Leeli

    2010-06-01

    Full Text Available Reinvestigation of the late glacial Solova (Remmeski basin, based on plant macro­fossil and diatom record, AMS 14C chronology and sediment composition (loss-on-ignition and magnetic susceptibility data, provided information on vegetation history and palaeoenvironmental and palaeoclimatic changes since the time of the deglaciation of the area around 14 000 cal yr BP. The chronology of the sequence is based on seven AMS dates on terrestrial macrofossils, providing evidence of rapid sedimentation in between 14 000 and 13 500 cal yr BP. Loss-on-ignition data show a clear short-lived warming episode centred to 13 800 cal yr BP, tentatively correlated with the GI-1c warming of the event stratigraphy of the Last Termination in the North Atlantic region, which suggests that at least parts of the Haanja Heights were ice-free by 14 000 cal yr BP. Macrofossil evidence indicates Betula nana–Dryas octopetala-dominated open tundra communities with Saxifraga on dry ground, and Carex sp. and Juncus on wet ground at that time. The first evidence of the postglacial presence of tree birch (Betula pendula in Estonia is dated back to 13 500 cal yr BP. However, conifer remains were not found in the late glacial sediment sequence of Solova Bog. The late-Allerød (GI-1a organic deposits, which are quite typical of other parts of Estonia and indicate general warming, are missing at Solova, most probably due to a hiatus in sedimentation in this very small and shallow upland basin.

  2. Subdivision of Glacial Deposits in Southeastern Peru Based on Pedogenic Development and Radiometric Ages

    Science.gov (United States)

    Goodman, Adam Y.; Rodbell, Donald T.; Seltzer, Geoffrey O.; Mark, Bryan G.

    2001-07-01

    The Cordillera Vilcanota and Quelccaya Ice Cap region of southern Peru (13°30‧-14°00‧S; 70°40‧-71°25‧W) contains a detailed record of late Quaternary glaciation in the tropical Andes. Quantification of soil development on 19 moraine crests and radiocarbon ages are used to reconstruct the glacial history. Secondary iron and clay increase linearly in Quelccaya soils and clay accumulates at a linear rate in Vilcanota soils, which may reflect the semicontinuous addition of eolian dust enriched in secondary iron to all soils. In contrast, logarithmic rates of iron buildup in soils in the Cordillera Vilcanota reflect chemical weathering; high concentrations of secondary iron in Vilcanota tills may mask the role of eolian input to these soils. Soil-age estimates from extrapolation of field and laboratory data suggest that the most extensive late Quaternary glaciation occurred >70,000 yr B.P. This provides one of the first semiquantitative age estimates for maximum ice extent in southern Peru and is supported by a minimum-limiting age of ∼41,520 14C yr B.P. A late glacial readvance culminated ∼16,650 cal yr B.P. in the Cordillera Vilcanota. Following rapid deglaciation of unknown extent, an advance of the Quelccaya Ice Cap occurred between ∼13,090 and 12,800 cal yr B.P., which coincides approximately with the onset of the Younger Dryas cooling in the North Atlantic region. Moraines deposited <394 cal yr B.P. in the Cordillera Vilcanota and <300 cal yr B.P. on the west side of the Quelccaya Ice Cap correlate with Little Ice Age moraines of other regions.

  3. [Test your decision-making. When to do endodontic retreatment? Results of a study].

    Science.gov (United States)

    Aryanpour, S; D'Hoore, W; Van Nieuwenhuysen, J P

    2000-01-01

    The goals of this survey were to determine the most frequent therapeutic option and to evaluate the consensus among a sample of Belgian practitioners managing the same simulated cases of root treated teeth. On average, conservative options (nonsurgical retreatment 35.27% and no retreatment 29.61%) are the most selected alternatives. Surgical options and extraction respectively constitute 21.18% and 13% of the treatment propositions. As expected, the presence of radiographic and/or clinical signs resulted in a more aggressive attitude, but the presence of symptoms does not seem to be a valid reason for reintervention. The results of the study demonstrate considerable interindividual variations in clinical management of root treated teeth, regardless of personal factors, such as gender, years of experience and graduation institution. Even if a consensus appears within a group of professionals, it is not necessarily applied by a majority of practitioners; this contributes certainly to the explanation of the geographical or institutional variations noted in the medical practices.

  4. Comparison of different retreatment techniques and root canal sealers: a scanning electron microscopic study

    Directory of Open Access Journals (Sweden)

    Neslihan Simsek

    2014-05-01

    Full Text Available The aim of this study was to evaluate the effectiveness of two retreatment techniques, in terms of the operating time and scanning electron microscopy (SEM results, in removing three different root canal sealers from root canals that were previously filled with gutta-percha. Sixty extracted single-rooted human premolars were divided into three groups and filled with iRoot SP, MM Seal, and AH Plus sealers, along with gutta-percha, through a lateral compaction technique. Root canal fillings of the samples were removed by ESI ultrasonic tips or R-Endo files. The time to reach the working length was recorded. Longitudinally sectioned samples were examined under SEM magnification. Each picture was evaluated in terms of the residual debris. Data were statistically analyzed with the Kruskall-Wallis test. No statistically significant differences were found in terms of operating time (p>0.05. Significant differences in the number of debris-free dentinal tubules were found among the root canal thirds, but this finding was not influenced by the experimental group (p < 0.05. Resin sealer tags were observed inside the dentinal tubules in the MM Seal group. Under the conditions of this study, it may be established that there was no difference among the sealers and retreatment techniques.

  5. LASIK and PRK in hyperopic astigmatic eyes: is early retreatment advisable?

    Science.gov (United States)

    Frings, Andreas; Richard, Gisbert; Steinberg, Johannes; Druchkiv, Vasyl; Linke, Stephan Johannes; Katz, Toam

    2016-01-01

    To analyze the refractive and keratometric stability in hyperopic astigmatic laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) during the first 6 months after surgery. This retrospective cross-sectional study included 97 hyperopic eyes; 55 were treated with LASIK and 42 with PRK. Excimer ablation for all eyes was performed using the ALLEGRETTO excimer laser platform using a mitomycin C for PRK and a mechanical microkeratome for LASIK. Keratometric and refractive data were analyzed during three consecutive follow-up intervals (6 weeks, 3 months, and 6 months). The corneal topography was obtained using Scheimpflug topography, and subjective refractions were acquired by expert optometrists according to a standardized protocol. After 3 months, mean keratometry and spherical equivalent were stable after LASIK, whereas PRK-treated eyes presented statistically significant (P1 D occurred. The optical zone diameter did not correlate with the development of regression. After corneal laser refractive surgery, keratometric changes are followed by refractive changes and they occur up to 6 months after LASIK and for at least 6 months after PRK, and therefore, caution should be applied when retreatment is planned during the 1st year after surgery because hyperopic refractive regression can lead to suboptimal visual outcome. Keratometric and refractive stability is earlier achieved after LASIK, and therefore, retreatment may be independent of late regression.

  6. Effect of retreating sea ice on Arctic cloud cover in simulated recent global warming

    Directory of Open Access Journals (Sweden)

    M. Abe

    2016-11-01

    Full Text Available This study investigates the effect of sea ice reduction on Arctic cloud cover in historical simulations with the coupled atmosphere–ocean general circulation model MIROC5. Arctic sea ice has been substantially retreating since the 1980s, particularly in September, under simulated global warming conditions. The simulated sea ice reduction is consistent with satellite observations. On the other hand, Arctic cloud cover has been increasing in October, with about a 1-month lag behind the sea ice reduction. The delayed response leads to extensive sea ice reductions because the heat and moisture fluxes from the underlying open ocean into the atmosphere are enhanced. Sensitivity experiments with the atmospheric part of MIROC5 clearly show that sea ice reduction causes increases in cloud cover. Arctic cloud cover increases primarily in the lower troposphere, but it decreases in the near-surface layers just above the ocean; predominant temperature rises in these near-surface layers cause drying (i.e., decreases in relative humidity, despite increasing moisture flux. Cloud radiative forcing due to increases in cloud cover in autumn brings an increase in the surface downward longwave radiation (DLR by approximately 40–60 % compared to changes in clear-sky surface DLR in fall. These results suggest that an increase in Arctic cloud cover as a result of reduced sea ice coverage may bring further sea ice retreat and enhance the feedback processes of Arctic warming.

  7. Nonsurgical endodontic retreatment of fused teeth with transposition: a case report

    Directory of Open Access Journals (Sweden)

    Miguel Agostinho Beco Pinto Cardoso

    2016-05-01

    Full Text Available Tooth transposition is a disorder in which a permanent tooth develops and erupts in the normal position of another permanent tooth. Fusion and gemination are developmental disturbances presenting as the union of teeth. This article reports the nonsurgical retreatment of a very rare case of fused teeth with transposition. A patient was referred for endodontic treatment of her maxillary left first molar in the position of the first premolar, which was adjacent to it on the distobuccal side. Orthopantomography and periapical radiography showed two crowns sharing the same root, with a root canal treatment and an associated periapical lesion. Tooth fusion with transposition of a maxillary molar and a premolar was diagnosed. Nonsurgical endodontic retreatment was performed. At four yr follow-up, the tooth was asymptomatic and the radiolucency around the apical region had decreased, showing the success of our intervention. The diagnosis and treatment of fused teeth require special attention. The canal system should be carefully explored to obtain a full understanding of the anatomy, allowing it to be fully cleaned and obturated. Thermoplastic techniques were useful in obtaining hermetic obturation. A correct anatomical evaluation improves the set of treatment options under consideration, leading to a higher likelihood of esthetically and functionally successful treatment.

  8. Late effects of radiation on the lumbar spinal cord of guinea pigs: Re-treatment tolerance

    International Nuclear Information System (INIS)

    Mason, K.A.; Withers, H.R.; Chiang, Chi-Shiun

    1993-01-01

    Using a guinea pig model of lumbar myelopathy, various factors affecting the tolerance of spinal cord to irradiation were assessed: (a) extent of initial injury; (b) time interval between priming and test doses; and (c) animal age at the time of initial radiation treatment. A 3 cm section of lumbar spinal cord of guinea pigs was irradiated with fractionated doses of 4.5 Gy gamma rays given as 9 fractions per week. Guinea pigs were primed with 9 x 4.5 Gy in 7 days which is 60% of the ED 50 for a continuous course of treatment. After 28 or 40 weeks, animal were retreated with 6-14 fractions of 4.5 Gy. Animals were observed for 2 years following the priming dose and both the incidence and latency of myelopathy recorded. Young adult guinea pigs (8 wk old) showed both a decreased radiation tolerance and latency compared to old individuals (40 wk old). At 28 or 40 wk after 9 x 4.5 Gy, only about 8% of the initial injury was remembered in young adult guinea pigs. The amount of residual injury was dependent on the initial damage as a proportion of the tolerance dose. The spinal cord shows a greater capacity for long-term recovery than generally appreciated and re-treatment doses clinically prescribed may be lower than necessary. 8 refs., 3 figs., 2 tabs

  9. Periodic isolation of the southern coastal plain of South Africa and the evolution of modern humans over late Quaternary glacial to interglacial cycles

    Science.gov (United States)

    Compton, J. S.

    2012-04-01

    Humans evolved in Africa, but where in Africa and by what mechanisms remain unclear. The evolution of modern humans over the last million years is associated with the onset of major global climate fluctuations, glacial to interglacial cycles, related to the build up and melting of large ice sheets in the Northern Hemisphere. During interglacial periods, such as today, warm and wet climates favored human expansion but during cold and dry glacial periods conditions were harsh and habitats fragmented. These large climate fluctuations periodically expanded and contracted African ecosystems and led to human migrations to more hospitable glacial refugia. Periodic isolation of relatively small numbers of humans may have allowed for their rapid evolutionary divergence from the rest of Africa. During climate transitions these divergent groups may have then dispersed and interbred with other groups (hybridization). Two areas at the opposite ends of Africa stand out as regions that were periodically isolated from the rest of Africa: North Africa (the Maghreb) and the southern coastal plain (SCP) of South Africa. The Maghreb is isolated by the Sahara Desert which periodically greens and is reconnected to the rest of Africa during the transition from glacial to interglacial periods. The SCP of South Africa is isolated from the rest of Africa by the rugged mountains of the Cape Fold Belt associated with inedible vegetation and dry climates to the north. The SCP is periodically opened when sea level falls by up to 130 m during glacial maxima to expose the present day submerged inner continental shelf. A five-fold expansion of the SCP receiving more rainfall in glacial periods may have served as a refuge to humans and large migratory herds. The expansive glacial SCP habitat abruptly contracts, by as much as one-third in 300 yr, during the rapid rise in sea level associated with glacial terminations. Rapid flooding may have increased population density and competition on the SCP to

  10. Role of assesssment for retreatment with transarterial chemoembolization score in decision of retreatment with trans-arterial chemo-embolization sessions in patients with hepatocellular carcinoma

    International Nuclear Information System (INIS)

    Abbasi, A.H.; Abid, S.; Haq, T.U.; Awan, S.

    2017-01-01

    Background: The objective behind this study was to determine that Assessment for Re-treatment with Transarterial chemoembolization (ART) score is really applicable in patients with hepatocellular carcinoma. Methods: A cross sectional observational study was conducted on all patients with hepatocellular carcinoma of intermediate stage and undergone ≥2 Transarterial chemoembolization. ART score was assessed before and after each session of Transarterial chemoembolization. Multi-logistic regression analysis was performed to compare the final outcome of patients with ART score of ≥2.5 into groups with two and more than two Trans-arterial chemo-embolization sessions. Results: A total of 100 HCC patients were recruited for final analysis. Our study participants consisted of total 100 HCC patients. Mean Child Pugh score was 6.1±0.95. In our study, most of the study participants (n=63) had ART score of less than 1.5 as compared to ART score >2.5 (n=37). A significant proportion of patients with ART score of 2.5, p-value<0.001. Patients with ART score of more than 2.5 did not show any survival benefit after having 3rd or 4th Trans-arterial chemo-embolization session, p=0.47. Conclusions: Our study findings suggest that those HCC patients who receive multiple sessions of TACE with a low ART score have more favourable outcomes with increased survival rate. (author)

  11. Radioiodine uptake following iodine-131 therapy for Graves' disease: an early indicator of need for retreatment

    Energy Technology Data Exchange (ETDEWEB)

    Carpentier, W.R.; Gilliland, P.F.; Piziak, V.K.; Petty, F.C.; McConnell, B.G.; Verdonk, C.A.; Ibarra, J.D.; Thompson, J.Q.

    1989-01-01

    Forty-five patients with Graves' disease were studied prospectively to determine if 24-hour I-131 uptake measurements alone or in combination with serum thyroid hormone levels at six weeks would determine the necessity for retreatment of the thyrotoxicosis. All patients with an I-131 uptake greater than 30% at six weeks required retreatment. No patient with an I-131 uptake of less than 15% required retreatment. Patients with uptakes between 15% and 30% were variable. An elevated free thyroxin index at 6 weeks is not helpful to determine which patients will remain thyrotoxic. Patients with a free thyroxin index within the normal range at six weeks can be predicted to be euthyroid by 12 weeks if their 24-hour I-131 uptake is between 15% and 30% and to be hypothyroid if their 24-hour I-131 uptake is below 15%. There was no difference between patient groups treated initially with antithyroid medication and those who were not.

  12. A cosmogenic 10Be chronology for the local last glacial maximum and termination in the Cordillera Oriental, southern Peruvian Andes: Implications for the tropical role in global climate

    Science.gov (United States)

    Bromley, Gordon R. M.; Schaefer, Joerg M.; Hall, Brenda L.; Rademaker, Kurt M.; Putnam, Aaron E.; Todd, Claire E.; Hegland, Matthew; Winckler, Gisela; Jackson, Margaret S.; Strand, Peter D.

    2016-09-01

    Resolving patterns of tropical climate variability during and since the last glacial maximum (LGM) is fundamental to assessing the role of the tropics in global change, both on ice-age and sub-millennial timescales. Here, we present a10Be moraine chronology from the Cordillera Carabaya (14.3°S), a sub-range of the Cordillera Oriental in southern Peru, covering the LGM and the first half of the last glacial termination. Additionally, we recalculate existing 10Be ages using a new tropical high-altitude production rate in order to put our record into broader spatial context. Our results indicate that glaciers deposited a series of moraines during marine isotope stage 2, broadly synchronous with global glacier maxima, but that maximum glacier extent may have occurred prior to stage 2. Thereafter, atmospheric warming drove widespread deglaciation of the Cordillera Carabaya. A subsequent glacier resurgence culminated at ∼16,100 yrs, followed by a second period of glacier recession. Together, the observed deglaciation corresponds to Heinrich Stadial 1 (HS1: ∼18,000-14,600 yrs), during which pluvial lakes on the adjacent Peruvian-Bolivian altiplano rose to their highest levels of the late Pleistocene as a consequence of southward displacement of the inter-tropical convergence zone and intensification of the South American summer monsoon. Deglaciation in the Cordillera Carabaya also coincided with the retreat of higher-latitude mountain glaciers in the Southern Hemisphere. Our findings suggest that HS1 was characterised by atmospheric warming and indicate that deglaciation of the southern Peruvian Andes was driven by rising temperatures, despite increased precipitation. Recalculated 10Be data from other tropical Andean sites support this model. Finally, we suggest that the broadly uniform response during the LGM and termination of the glaciers examined here involved equatorial Pacific sea-surface temperature anomalies and propose a framework for testing the viability

  13. Seismic facies and stratigraphy of the Cenozoic succession in McMurdo Sound, Antarctica: Implications for tectonic, climatic and glacial history

    Science.gov (United States)

    Fielding, C.R.; Whittaker, J.; Henrys, S.A.; Wilson, T.J.; Nash, T.R.

    2007-01-01

    A new stratigraphic model is presented for the evolution of the Cenozoic Victoria Land Basin of the West Antarctic Rift, based on integration of seismic reflection and drilling data. The Early Rift phase (?latest Eocene to Early Oligocene) comprises wedges of strata confined by early extensional faults, and which contain seismic facies consistent with drainage via coarse-grained fans and deltas into discrete, actively subsiding grabens and half-grabens. The Main Rift phase (Early Oligocene to Early Miocene) comprises a lens of strata that thickens symmetrically from the basin margins into a central depocenter, and in which stratal events pass continuously over the top of the Early Rift extensional topography. Internal seismic facies and lithofacies indicate a more organized, cyclical shallow marine succession, influenced increasingly upward by cycles of glacial advance and retreat into the basin. The Passive Thermal Subsidence phase (Early Miocene to ?) comprises an evenly distributed sheet of strata that does not thicken appreciably into the depocentre, with more evidence for clinoform sets and large channels. These patterns are interpreted to record accumulation under similar environmental conditions but in a regime of slower subsidence. The Renewed Rifting phase (? to Recent, largely unsampled by coring thus far) has been further divided into 1, a lower interval, in which the section thickens passively towards a central depocentre, and 2. an upper interval, in which more dramatic thickening patterns are complicated by magmatic activity. The youngest part of the stratigraphy was accumulated under the influence of flexural loading imposed by the construction of large volcanic edifices, and involved minimal sediment supply from the western basin margin, suggesting a change in environmental (glacial) conditions at possibly c. 2 Ma.

  14. Numerical investigations of subglacial hydrology as a direct and indirect driver of glacial erosion

    OpenAIRE

    Beaud, Flavien

    2017-01-01

    Glaciers shape high altitude and latitude landscapes in numerous ways. Erosion associated with glacial processes can limit the average height of mountain ranges, while creating the greatest relief on Earth and shaping the highest mountain peaks, but glaciers can also shield pre-existing topography. Glacial erosion processes, though still enigmatic, are central to the evolution of landscapes, particularly since the onset of the Pleistocene. Glacial erosion comprises three fundamental processes...

  15. Climate change and the global pattern of moraine-dammed glacial lake outburst floods

    Directory of Open Access Journals (Sweden)

    S. Harrison

    2018-04-01

    Full Text Available Despite recent research identifying a clear anthropogenic impact on glacier recession, the effect of recent climate change on glacier-related hazards is at present unclear. Here we present the first global spatio-temporal assessment of glacial lake outburst floods (GLOFs focusing explicitly on lake drainage following moraine dam failure. These floods occur as mountain glaciers recede and downwaste. GLOFs can have an enormous impact on downstream communities and infrastructure. Our assessment of GLOFs associated with the rapid drainage of moraine-dammed lakes provides insights into the historical trends of GLOFs and their distributions under current and future global climate change. We observe a clear global increase in GLOF frequency and their regularity around 1930, which likely represents a lagged response to post-Little Ice Age warming. Notably, we also show that GLOF frequency and regularity – rather unexpectedly – have declined in recent decades even during a time of rapid glacier recession. Although previous studies have suggested that GLOFs will increase in response to climate warming and glacier recession, our global results demonstrate that this has not yet clearly happened. From an assessment of the timing of climate forcing, lag times in glacier recession, lake formation and moraine-dam failure, we predict increased GLOF frequencies during the next decades and into the 22nd century.

  16. Arctic Ocean sea ice cover during the penultimate glacial and the last interglacial.

    Science.gov (United States)

    Stein, Ruediger; Fahl, Kirsten; Gierz, Paul; Niessen, Frank; Lohmann, Gerrit

    2017-08-29

    Coinciding with global warming, Arctic sea ice has rapidly decreased during the last four decades and climate scenarios suggest that sea ice may completely disappear during summer within the next about 50-100 years. Here we produce Arctic sea ice biomarker proxy records for the penultimate glacial (Marine Isotope Stage 6) and the subsequent last interglacial (Marine Isotope Stage 5e). The latter is a time interval when the high latitudes were significantly warmer than today. We document that even under such warmer climate conditions, sea ice existed in the central Arctic Ocean during summer, whereas sea ice was significantly reduced along the Barents Sea continental margin influenced by Atlantic Water inflow. Our proxy reconstruction of the last interglacial sea ice cover is supported by climate simulations, although some proxy data/model inconsistencies still exist. During late Marine Isotope Stage 6, polynya-type conditions occurred off the major ice sheets along the northern Barents and East Siberian continental margins, contradicting a giant Marine Isotope Stage 6 ice shelf that covered the entire Arctic Ocean.Coinciding with global warming, Arctic sea ice has rapidly decreased during the last four decades. Here, using biomarker records, the authors show that permanent sea ice was still present in the central Arctic Ocean during the last interglacial, when high latitudes were warmer than present.

  17. Climate change and the global pattern of moraine-dammed glacial lake outburst floods

    Science.gov (United States)

    Harrison, Stephan; Kargel, Jeffrey S.; Huggel, Christian; Reynolds, John; Shugar, Dan H.; Betts, Richard A.; Emmer, Adam; Glasser, Neil; Haritashya, Umesh K.; Klimeš, Jan; Reinhardt, Liam; Schaub, Yvonne; Wiltshire, Andy; Regmi, Dhananjay; Vilímek, Vít

    2018-04-01

    Despite recent research identifying a clear anthropogenic impact on glacier recession, the effect of recent climate change on glacier-related hazards is at present unclear. Here we present the first global spatio-temporal assessment of glacial lake outburst floods (GLOFs) focusing explicitly on lake drainage following moraine dam failure. These floods occur as mountain glaciers recede and downwaste. GLOFs can have an enormous impact on downstream communities and infrastructure. Our assessment of GLOFs associated with the rapid drainage of moraine-dammed lakes provides insights into the historical trends of GLOFs and their distributions under current and future global climate change. We observe a clear global increase in GLOF frequency and their regularity around 1930, which likely represents a lagged response to post-Little Ice Age warming. Notably, we also show that GLOF frequency and regularity - rather unexpectedly - have declined in recent decades even during a time of rapid glacier recession. Although previous studies have suggested that GLOFs will increase in response to climate warming and glacier recession, our global results demonstrate that this has not yet clearly happened. From an assessment of the timing of climate forcing, lag times in glacier recession, lake formation and moraine-dam failure, we predict increased GLOF frequencies during the next decades and into the 22nd century.

  18. Treatment and retreatment with omalizumab in chronic spontaneous urticaria: Real life experience with twenty-five patients.

    Science.gov (United States)

    Türk, Murat; Yılmaz, İnsu; Bahçecioğlu, Sakine Nazik

    2018-01-01

    Previous data have shown the high efficacy of omalizumab in chronic spontaneous urticaria (CSU). However, factors that may be effective on the response to therapy, relapse rates after drug discontinuation, and efficacy of retreatment remain unclear. This study aimed to determine the efficacy of omalizumab in CSU refractory to conventional therapy, to identify possible factors affecting treatment response and relapse, and also to evaluate the efficacy of retreatment on relapsed disease. The data of CSU patients treated with 300 mg/month omalizumab for at least 3 months were retrospectively analyzed. In order to evaluate the efficacy of treatment and retreatment, baseline and follow-up concomitant medication score (CMS) and urticaria activity score (UAS) were calculated. Possible factors affecting treatment response and relapse were identified. Twenty-five patients were included. The median duration of omalizumab therapy was 6 (6-12) months. Of the patients with baseline UAS 6 (5.5-6) and CMS 13 (10-15), 8 (32%) had complete response (UAS = 0) and 2 (8%) were non-responders after 3 months of therapy. None of the complete responders were positive for IgG-anti-TPO. After discontinuation of omalizumab therapy, 11 (61%) patients experienced relapse and 10 of them received retreatment with omalizumab. Half of the patients had complete response, and half had partial response (UAS = 1-4) after retreatment. No treatment related adverse events were documented. Omalizumab has high efficacy in both the treatment and retreatment of CSU; however, relapse rates after discontinuation are high. Autoimmune markers may be helpful in predicting treatment response and relapse. Copyright © 2017 Japanese Society of Allergology. Production and hosting by Elsevier B.V. All rights reserved.

  19. Effect of Endodontic Retreatment on Push-out Bond Strength and Quality of Fiber Postbonding Interface of Resin Cements.

    Science.gov (United States)

    Pelegrine, Rina Andréa; Paulillo, Luís Alexandre Maffei Sartini; Kato, Augusto Shoji; Fontana, Carlos Eduardo; Pinheiro, Sérgio Luiz; De Martin, Alexandre Sigrist; Bueno, Carlos Eduardo da Silveira

    2016-01-01

    The aim of this study is to evaluate the impact of endodontic retreatment on push-out bond strength and dentin interface of two resin cements used for fiber postcementation during endodontic retreatment. The root canals of 40 extracted human canines were prepared, obturated and divided into four groups (n = 10). Gutta-percha was partially removed and fiber posts were immediately cemented in groups 1 and 2 using Panavia F with ED Primer and RelyX™ U200, respectively. In groups 3 and 4, the root canal access was sealed with temporary restorative cement, specimens were stored for 30 days, endodontically retreated, and fiber posts were cemented using the resin cements applied to groups 1 and 2, respectively. Push-out tests and scanning electron microscopy analyses of different areas were performed. Data from push-out bond strengths were analyzed by one-way analysis of variance and Tukey's tests. Higher bond strength values were detected in the apical third for group 1 than group 3 (p 0.05). Comparisons between different thirds in the same group revealed a higher bond strength in the apical third for group 1. Scanning electron microscopy showed formation of hybrid layer and extensive resin tags in group 1. No hybrid layer was observed in groups 2 and 4. Endodontic retreatment had adverse effects on the push-out bond strength and dentinal interface of Panavia F with ED Primer when used for fiber postcementation specifically in the apical third, but not on RelyX™ U200. A significant interaction was detected between endodontic retreatment and resin cement, which indicated that endodontic retreatment might adversely affect the push-out bond strength and dentinal interface of Panavia F with ED Primer when used for fiber postcementation specifically in the apical third.

  20. Climate change and diverse dimensions of glacial lake outburst floods (GLOFs): Lake Palcacocha case study, Peru

    Science.gov (United States)

    Emmer, Adam; Walker-Crawford, Noah; Carey, Mark; Huggel, Christian; Verheyen, Roda; Wallimann-Helmer, Ivo

    2017-04-01

    Post-Little Ice Age (LIA) climate change has led to worldwide glacier retreat, formation and evolution of glacial lakes, occasionally followed by glacier lake outburst floods (GLOFs). Hundreds of GLOFs are documented throughout the 20th and 21st century, of which a certain number that caused massive downstream destruction and up to thousands of lives lost. Management of GLOF hazards and risks has typically been a local concern, focusing on the implementation of specific technical and engineering measures. Recently, however, researchers have realized that the complexity of both the risks and the socio-environmental context requires a broader understanding and response beyond the more typical local perception and management. The growing cumulative greenhouse gas (GHG) emissions, for instance, increase the anthropogenic contribution to glacier retreat, lake formation and growth and eventually to GLOF. GLOF hazard and risk management is inherently linked to the global scale from this perspective. It implies that additional important dimensions enter the debate, including ethical and legal questions about the responsibility for damage and loss due to GLOFs. Here we analyze the conditions at an emblematic case in Peru's Cordillera Blanca, which has made international headlines repeatedly since it first generated one of the world's most deadly GLOFs in 1941 to its present-day growth and instability. Situated upstream from the regional center of Huaráz (population ˜120,000), Lake Palcacocha has attracted significant attention in recent years within Peru and at an international level. Perspectives on Palcacocha lack truly cross-disciplinary research, missing more comprehensive insight. This contribution is unique for its analysis of diverse dimensions, which also provide a framework for other GLOF hazard, risk, and climate-related studies. The main aim of this constribution is to understand the links between them, their drivers and inhibitors. Four dimensions were studied

  1. Glacial hazards: communicating the science and managing the risk

    Science.gov (United States)

    Reynolds, J. M.

    2009-04-01

    The recession of glaciers worldwide has received huge media coverage over the last few years in association with the issue of climate change. Young people at schools and colleges are increasingly aware of the environmental pressures due to ‘global warming'. Yet simultaneously, there appears to be an increasing move away from studying science both at pre-university and undergraduate levels. One of the oft cited reasons is that students cannot see the application of the subjects being taught them. Glacial hazards are one of the most obvious adverse effects of climate change, with many, often poor, communities in remote mountain areas being the most affected by frequently devastating Glacial Lake Outburst Floods (GLOFs). When students are exposed to examples of these hazards and the science behind them, many become enthused by the subject and want to study it further. There has been a huge increase in the number of students selecting projects on glacial hazards as well as a large increase in the number of institutions offering to teach modules on this subject. In an effort to provide a basic visualisation, Peter Kennett has taken the principle of GLOFs and developed a cheap but highly visual demonstration of the potentially devastating effect of melting ice within a moraine leading to subsidence and subsequent dam failure. This is available on www.earthlearningidea.com as ‘Dam burst danger - modelling the collapse of a natural dam in the mountains - and the disaster that might follow'. Furthermore, the methods by which glacial hazards are assessed provide excellent applications of geophysics, geology, geography (physical and Human), engineering, mathematics, and glaciology. By exploring the potential vulnerability of communities downstream, the applications can be extended to include sociology, economics, geopolitics and even psychology. Glacial hazards have been the subject of presentations to the Earth Science Teachers Association (ESTA) in the UK to demonstrate

  2. Scottish landform examples : The Cairngorms - a pre-glacial upland granite landscape

    OpenAIRE

    Hall, A.M.; Gillespie, M.R.; Thomas, C.W.; Ebert, K.

    2013-01-01

    The Cairngorm massif in NE Scotland (Figure 1) is an excellent example of a preglacial upland landscape formed in granite. Glacial erosion in the mountains has been largely confined to valleys and corries (Rea, 1998) and so has acted to dissect a pre-existing upland (Figure 2). Intervening areas of the massif experienced negligible glacial erosion due to protective covers of cold-based ice (Sugden, 1968) and preserve a wide range of pre-glacial and non-glacial landforms and reg...

  3. Creating a specialist protein resource network: a meeting report for the protein bioinformatics and community resources retreat

    DEFF Research Database (Denmark)

    Babbitt, Patricia C.; Bagos, Pantelis G.; Bairoch, Amos

    2015-01-01

    During 11–12 August 2014, a Protein Bioinformatics and Community Resources Retreat was held at the Wellcome Trust Genome Campus in Hinxton, UK. This meeting brought together the principal investigators of several specialized protein resources (such as CAZy, TCDB and MEROPS) as well as those from...... protein databases from the large Bioinformatics centres (including UniProt and RefSeq). The retreat was divided into five sessions: (1) key challenges, (2) the databases represented, (3) best practices for maintenance and curation, (4) information flow to and from large data centers and (5) communication...

  4. Efficacy of Different Methods for Removing Root Canal Filling Material in Retreatment - An In-vitro Study.

    Science.gov (United States)

    Kasam, Swetha; Mariswamy, Annapoorna Ballagere

    2016-06-01

    Although success of endodontic therapy has significantly improved in the last few decades due to the introduction of novel materials and techniques, failures of endodontic therapy requiring re-treatment still comprise a significant percentage of patients requiring root canal treatment. To evaluate and compare the effective removal of gutta percha and sealer, amount of apical debris extrusion and time required for gutta percha removal using various endodontic files. Total 48 extracted mandibular premolars were mounted on acrylic blocks and endodontic procedure was carried out using size 40 K file and obturated using guttapercha and zinc oxide eugenol sealer. After one month storage, samples were decoronated, mounted on screw capped vials and subjected to removal of obturated material by four instruments: H files, safe sided H files, protaper universal retreatment rotary system and ultrasonic retreatment tip, grouped as 1, 2, 3, and 4 respectively. Only 2mm of obturated material from the coronal part was removed using no. 3 Gates Glidden drill, guttapercha was softened with a drop of xylene for 2 mins for each canal and retreatment was performed. The retreatment procedure was said to be complete when no visible debris were observed on the instrument flutes. The samples split into two halves and examined under stereomicroscope, photographed, assessed using AUTOCAD software and percentage of remaining filling material in coronal, middle, apical thirds of the canal was calculated in mm(2). Retreatment time was recorded in seconds and apically extruded debris was assessed by microbalance in grams for each tooth. The data was analyzed by using descriptive statistics, ANOVA and Scheffe's post hoc test through SPSS for windows (v 16.0). The ultrasonic retreatment tip had less percentage of residual guttapercha/sealer, shorter mean operating time and little apical extrusion with a significant difference (p<0.05) between the other groups. All techniques retained guttapercha

  5. Climate Stability: Pathway to understand abrupt glacial climate shifts

    Science.gov (United States)

    Zhang, X.; Knorr, G.; Barker, S.; Lohmann, G.

    2017-12-01

    Glacial climate is marked by abrupt, millennial-scale climate changes known as Dansgaard-Oeschger (DO) cycles that have been linked to variations in the Atlantic meridional overturning circulation (AMOC). The most pronounced stadial coolings, Heinrich Stadials (HSs), are associated with massive iceberg discharges to the North Atlantic. This motivates scientists to consider that the North Atlantic freshwater perturbations is a common trigger of the associated abrupt transitions between weak and strong AMOC states. However, recent studies suggest that the Heinrich ice-surging events are triggered by ocean subsurface warming associated with an AMOC slow-down. Furthermore, the duration of ice-rafting events does not systematically coincide with the beginning and end of the pronounced cold conditions during HSs. In this context, we show that both, changes in atmospheric CO2 and ice sheet configuration can provide important control on the stability of the AMOC, using a coupled atmosphere-ocean model. Our simulations reveal that gradual changes in Northern Hemisphere ice sheet height and atmospheric CO2 can act as a trigger of abrupt glacial/deglacial climate changes. The simulated global climate responses—including abrupt warming in the North Atlantic, a northward shift of the tropical rain belts, and Southern Hemisphere cooling related to the bipolar seesaw—are generally consistent with empirical evidence. We further find that under a delicate configuration of atmospheric CO2 and ice sheet height the AMOC can be characterized by a self-oscillation (resonance) feature (Hopf Bifucation) with a 1000-year cycle that is comparable with observed small DO events during the MIS 3. This provides an alternative explanation for millennial-scale DO variability during glacial periods.

  6. Pyrite sulfur isotopes reveal glacial-interglacial environmental changes

    Science.gov (United States)

    Pasquier, Virgil; Sansjofre, Pierre; Rabineau, Marina; Revillon, Sidonie; Houghton, Jennifer; Fike, David A.

    2017-06-01

    The sulfur biogeochemical cycle plays a key role in regulating Earth’s surface redox through diverse abiotic and biological reactions that have distinctive stable isotopic fractionations. As such, variations in the sulfur isotopic composition (δ34S) of sedimentary sulfate and sulfide phases over Earth history can be used to infer substantive changes to the Earth’s surface environment, including the rise of atmospheric oxygen. Such inferences assume that individual δ34S records reflect temporal changes in the global sulfur cycle; this assumption may be well grounded for sulfate-bearing minerals but is less well established for pyrite-based records. Here, we investigate alternative controls on the sedimentary sulfur isotopic composition of marine pyrite by examining a 300-m drill core of Mediterranean sediments deposited over the past 500,000 y and spanning the last five glacial-interglacial periods. Because this interval is far shorter than the residence time of marine sulfate, any change in the sulfur isotopic record preserved in pyrite (δ34Spyr) necessarily corresponds to local environmental changes. The stratigraphic variations (>76‰) in the isotopic data reported here are among the largest ever observed in pyrite, and are in phase with glacial-interglacial sea level and temperature changes. In this case, the dominant control appears to be glacial-interglacial variations in sedimentation rates. These results suggest that there exist important but previously overlooked depositional controls on sedimentary sulfur isotope records, especially associated with intervals of substantial sea level change. This work provides an important perspective on the origin of variability in such records and suggests meaningful paleoenvironmental information can be derived from pyrite δ34S records.

  7. Glacial-interglacial atmospheric CO2 change: a possible

    Directory of Open Access Journals (Sweden)

    L. C. Skinner

    2009-09-01

    Full Text Available So far, the exploration of possible mechanisms for glacial atmospheric CO2 drawdown and marine carbon sequestration has tended to focus on dynamic or kinetic processes (i.e. variable mixing-, equilibration- or export rates. Here an attempt is made to underline instead the possible importance of changes in the standing volumes of intra-oceanic carbon reservoirs (i.e. different water-masses in influencing the total marine carbon inventory. By way of illustration, a simple mechanism is proposed for enhancing the marine carbon inventory via an increase in the volume of relatively cold and carbon-enriched deep water, analogous to modern Lower Circumpolar Deep Water (LCDW, filling the ocean basins. A set of simple box-model experiments confirm the expectation that a deep sea dominated by an expanded LCDW-like watermass holds more CO2, without any pre-imposed changes in ocean overturning rate, biological export or ocean-atmosphere exchange. The magnitude of this "standing volume effect" (which operates by boosting the solubility- and biological pumps might be as large as the contributions that have previously been attributed to carbonate compensation, terrestrial biosphere reduction or ocean fertilisation for example. By providing a means of not only enhancing but also driving changes in the efficiency of the biological- and solubility pumps, this standing volume mechanism may help to reduce the amount of glacial-interglacial CO2 change that remains to be explained by other mechanisms that are difficult to assess in the geological archive, such as reduced mass transport or mixing rates in particular. This in turn could help narrow the search for forcing conditions capable of pushing the global carbon cycle between glacial and interglacial modes.

  8. Greenland's glacial fjords and their role in regional biogeochemical dynamics.

    Science.gov (United States)

    Crosby, J.; Arndt, S.

    2017-12-01

    Greenland's coastal fjords serve as important pathways that connect the Greenland Ice Sheet (GrIS) and the surrounding oceans. They export seasonal glacial meltwater whilst being significant sites of primary production. These fjords are home to some of the most productive ecosystems in the world and possess high socio-economic value via fisheries. A growing number of studies have proposed the GrIS as an underappreciated yet significant source of nutrients to surrounding oceans. Acting as both transfer routes and sinks for glacial nutrient export, fjords have the potential to act as significant biogeochemical processors, yet remain underexplored. Critically, an understanding of the quantitative contribution of fjords to carbon and nutrient budgets is lacking, with large uncertainties associated with limited availability of field data and the lack of robust upscaling approaches. To close this knowledge gap we developed a coupled 2D physical-biogeochemical model of the Godthåbsfjord system, a sub-Arctic sill fjord in southwest Greenland, to quantitatively assess the impact of nutrients exported from the GrIS on fjord primary productivity and biogeochemical dynamics. Glacial meltwater is found to be a key driver of fjord-scale circulation patterns, whilst tracer simulations reveal the relative nutrient contributions from meltwater-driven upwelling and meltwater export from the GrIS. Hydrodynamic circulation patterns and freshwater transit times are explored to provide a first understanding of the glacier-fjord-ocean continuum, demonstrating the complex pattern of carbon and nutrient cycling at this critical land-ocean interface.

  9. Last Glacial vegetation and climate change in the southern Levant

    Science.gov (United States)

    Miebach, Andrea; Chen, Chunzhu; Litt, Thomas

    2015-04-01

    Reconstructing past climatic and environmental conditions is a key task for understanding the history of modern mankind. The interaction between environmental change and migration processes of the modern Homo sapiens from its source area in Africa into Europe is still poorly understood. The principal corridor of the first human dispersal into Europe and also later migration dynamics crossed the Middle East. Therefore, the southern Levant is a key area to investigate the paleoenvironment during times of human migration. In this sense, the Last Glacial (MIS 4-2) is particularly interesting to investigate for two reasons. Firstly, secondary expansions of the modern Homo sapiens are expected to occur during this period. Secondly, there are ongoing discussions on the environmental conditions causing the prominent lake level high stand of Lake Lisan, the precursor of the Dead Sea. This high stand even culminated in the merging of Lake Lisan and Lake Kinneret (Sea of Galilee). To provide an independent proxy for paleoenvironmental reconstructions in the southern Levant during the Last Glacial, we investigated pollen assemblages of the Dead Sea/Lake Lisan and Lake Kinneret. Located at the Dead Sea Transform, the freshwater Lake Kinneret is nowadays connected via the Jordan with the hypersaline Dead Sea, which occupies Earth's lowest elevation on land. The southern Levant is a transition area of three different vegetation types. Therefore, also small changes in the climate conditions effect the vegetation and can be registered in the pollen assemblage. In contrast to the Holocene, our preliminary results suggest another vegetation pattern during the Last Glacial. The vegetation belt of the fragile Mediterranean biome did no longer exist in the vicinity of Lake Kinneret. Moreover, the vegetation was rather similar in the whole study area. A steppe vegetation with dwarf shrubs, herbs, and grasses predominated. Thermophilous elements like oaks occurred in limited amounts. The

  10. Knickpoint formation and retreat: stairway to heaven or pathway to declivity

    Science.gov (United States)

    Rengers, Francis; Tucker, Gregory

    2016-04-01

    The importance of knickpoints in shaping fluvial systems has been observed in laboratory settings, small experimental plots, and at the landscape scale. By creating a step in a river's longitudinal profile, knickpoints can shield upstream tributaries from a much lower base level, and therefore represent a buffer in the energy transfer of a stream system. Knickpoints are located at a transition point between the potential energy of material stored upstream and the kinetic energy of erosion processes and sediment transport below the knickpoint. We hypothesize that the long-term persistence of a discrete, retreating knickpoint requires a balance between the fluvial erosion of the feature, and sedimentation rates downstream. Here we present the results of a short-term (four year) study of knickpoint morphology in a natural gully system to better constrain the conditions necessary to preserve distinct knickpoints over time. We monitored knickpoint erosion using time-lapse photography, repeat terrestrial lidar, soil moisture monitoring, and rainfall-runoff measurements. Our results indicate that shallow subsurface hydrology leads to knickpoint erosion via mass failure, and produces a stable and predictable morphological signature of knickpoint erosion (amphitheater shaped heads). We generalized these observations into a numerical model of erosion/sedimentation to understand the geomorphic legacy of knickpoints in deeply incised gullies. Modeling showed that knickpoints can maintain an incisional step for hundreds to thousands of years when knickpoints retreat via mass failure and sediment is removed from the knickpoint base by fluvial scour. To test simulations of long-term stability generated by the numerical model, we used Optically Stimulated Luminesence to date alluvial deposits at existing gully knickpoints. This geochronological dating confirmed that gully knickpoints have been active in our study area for hundreds to thousands of years, particularly during drought

  11. First approaches towards modelling glacial hazards in the Mount Cook region of New Zealand's Southern Alps

    Directory of Open Access Journals (Sweden)

    S. K. Allen

    2009-03-01

    Full Text Available Flood and mass movements originating from glacial environments are particularly devastating in populated mountain regions of the world, but in the remote Mount Cook region of New Zealand's Southern Alps minimal attention has been given to these processes. Glacial environments are characterized by high mass turnover and combined with changing climatic conditions, potential problems and process interactions can evolve rapidly. Remote sensing based terrain mapping, geographic information systems and flow path modelling are integrated here to explore the extent of ice avalanche, debris flow and lake flood hazard potential in the Mount Cook region. Numerous proglacial lakes have formed during recent decades, but well vegetated, low gradient outlet areas suggest catastrophic dam failure and flooding is unlikely. However, potential impacts from incoming mass movements of ice, debris or rock could lead to dam overtopping, particularly where lakes are forming directly beneath steep slopes. Physically based numerical modeling with RAMMS was introduced for local scale analyses of rock avalanche events, and was shown to be a useful tool for establishing accurate flow path dynamics and estimating potential event magnitudes. Potential debris flows originating from steep moraine and talus slopes can reach road and built infrastructure when worst-case runout distances are considered, while potential effects from ice avalanches are limited to walking tracks and alpine huts located in close proximity to initiation zones of steep ice. Further local scale studies of these processes are required, leading towards a full hazard assessment, and changing glacial conditions over coming decades will necessitate ongoing monitoring and reassessment of initiation zones and potential impacts.

  12. An inventory of historical glacial lake outburst floods in the Himalayas based on remote sensing observations and geomorphological analysis

    Science.gov (United States)

    Nie, Yong; Liu, Qiao; Wang, Jida; Zhang, Yili; Sheng, Yongwei; Liu, Shiyin

    2018-05-01

    Glacial lake outburst floods (GLOFs) are a unique type of natural hazard in the cryosphere that may result in catastrophic fatalities and damages. The Himalayas are known as one of the world's most GLOF-vulnerable zones. Effective hazard assessments and risk management require a thorough inventory of historical GLOF events across the Himalayas, which is hitherto absent. Existing studies imply that numerous historical GLOF events are contentious because of discrepant geographic coordinates, names, or outburst time, requiring further verifications. This study reviews and verifies over 60 historical GLOF events across the Himalayas using a comprehensive method that combines literature documentations, archival remote sensing observations, geomorphological analysis, and field investigations. As a result, three unreported GLOF events were discovered from remote sensing images and geomorphological analysis. Eleven suspicious events were identified and suggested to be excluded. The properties of five outburst lakes, i.e., Degaco, Chongbaxia Tsho, Geiqu, Lemthang Tsho, and a lake on Tshojo Glacier, were corrected or updated. A total of 51 GLOF events were verified to be convincing, and these outburst lakes were classified into three categories according to their statuses in the past decades, namely disappeared (12), stable (30), and expanding (9). Statistics of the verified GLOF events show that GLOF tended to occur between April and October in the Himalayas. We suggest that more attention should be paid to rapidly expanding glacial lakes with high possibility of repetitive outbursts. This study also demonstrates the effectiveness of integrating remote sensing and geomorphic interpretations in identifying and verifying GLOF events in remote alpine environments. This inventory of GLOFs with a range of critical attributes (e.g., locations, time, and mechanisms) will benefit the continuous monitoring and prediction of potentially dangerous glacial lakes and contribute to

  13. Predicting Land-Ice Retreat and Sea-Level Rise with the Community Earth System Model

    Energy Technology Data Exchange (ETDEWEB)

    Lipscomb, William [Los Alamos National Laboratory

    2012-06-19

    Coastal stakeholders need defensible predictions of 21st century sea-level rise (SLR). IPCC assessments suggest 21st century SLR of {approx}0.5 m under aggressive emission scenarios. Semi-empirical models project SLR of {approx}1 m or more by 2100. Although some sea-level contributions are fairly well constrained by models, others are highly uncertain. Recent studies suggest a potential large contribution ({approx}0.5 m/century) from the marine-based West Antarctic Ice Sheet, linked to changes in Southern Ocean wind stress. To assess the likelihood of fast retreat of marine ice sheets, we need coupled ice-sheet/ocean models that do not yet exist (but are well under way). CESM is uniquely positioned to provide integrated, physics based sea-level predictions.

  14. Attempts to retreat from a dead-ended long capillary by backward swimming in Paramecium

    Directory of Open Access Journals (Sweden)

    Itsuki eKunita

    2014-06-01

    Full Text Available We have observed how the ciliate Paramecium attempts to retreat from the dead-end of a long capillary that is too narrow for turning. After many trial-and-error episodes of short-term backward swimming (SBS, which is the conventional avoidance behavior exhibited in free swimming when an obstacle is faced, long-term backward swimming (LBS that lasted five to ten times longer was developed. LBS may have a beneficial effect for complete withdrawal from the capillary space, although in our experiment it was impossible for the organism to do so due to the capillary length. In order to identify a physically possible mechanism for LBS, we propose model equations for the membrane potential of Hodgkin-Huxley type, which describe the control of ciliary movement. The physiological implications and physical mechanism of the development of LBS are discussed.

  15. Impacts of Aerosols on the Retreat of the Sierra Nevada Glaciers in California

    Science.gov (United States)

    El-Askary, H. M.; Li, J.; Ta, T. N.; Jong, A.; Zhang, X.

    2015-12-01

    Natural dust aerosol is an active component of the climate system and plays multiple roles in physical climate and bio-geo-chemical exchanges between the atmosphere, land surface and ocean. Aerosol deposition on snow is amongst the different causes of glacier retreat around the world as well as the reduction of snow albedo. We have observed a long range transport of dust and pollution aerosols from China to the U.S. In this paper we compared summer and winter seasons glacier changes between 2000 and 2013, and how the dust aerosol change over this 13 years. Multiple images, acquired from Landsat-5 TM, Landsat-7 ETM+ and Landsat-8 OLI were used in the study. The change detection analysis was employed to identify the glacier changes for two seasons. The results suggest that the glacier decreased dramatically over 13 years in both seasons.

  16. Retreatment of failed regenerative endodontic of orthodontically treated immature permanent maxillary central incisor: a case report

    Directory of Open Access Journals (Sweden)

    Musaed Fahad Al-Tammami

    2017-02-01

    Full Text Available A revascularization procedure was shown to be the best alternative therapy for immature teeth with necrotic pulp and apical infection. A 12 year old female with a history of trauma to her upper central incisor and a sinus tract was referred for endodontic treatment. She was an active orthodontic patient and had undergone regenerative endodontic treatment for the past 2 years. Clinical examination revealed no response to sensibility, percussion, and palpation tests. The preoperative radiograph showed an open apex and apical rarefaction. The case was diagnosed as previously treated tooth with asymptomatic apical periodontitis. Regenerative endodontic retreatment was performed, and the case was followed for 3 years. Clinical, radiographic, and cone-beam computed tomography follow-up examination revealed an asymptomatic tooth, with evidence of periapical healing and root maturation.

  17. Glacitectonic deformation around the retreating margin of the last Irish ice sheet

    Science.gov (United States)

    Knight, J.

    2008-12-01

    Evidence for ice-marginal glacitectonic shunting and deformation of bedrock slabs is described from three sites around the west coast of Ireland. These sites (Brandon Bay, County Kerry; Pigeon Point, County Mayo; Inishcrone, County Sligo) are all locations where the late Devensian ice margin retreated on land and was confined to within limestone bedrock embayments. At these sites, flat-lying bedrock slabs (bedrock slabs have been variously stacked, rotated, deformed into open folds, and brecciated. Separating the bedrock slabs is either a thin layer (bedrock that shows internal folding; or a thicker (bedrock fractures and bedding planes and away from the ice margin, and that bedrock slabs were moved in part by hydraulic lift as well as thrust-style ice-marginal tectonics. The presence of a mosaic of warm and frozen ice-bed patches, in combination with strong geologic control and meltwater generation from behind the ice margin, can help explain formation of these unusual bedrock slab features.

  18. Do Wellness Tourists Get Well? An Observational Study of Multiple Dimensions of Health and Well-Being After a Week-Long Retreat.

    Science.gov (United States)

    Cohen, Marc M; Elliott, Fiona; Oates, Liza; Schembri, Adrian; Mantri, Nitin

    2017-02-01

    Wellness retreats use many complementary and alternative therapies within a holistic residential setting, yet few studies have evaluated the effect of retreat experiences on multiple dimensions of health and well-being, and no published studies have reported health outcomes in wellness tourists. To assess the effect of a week-long wellness-retreat experience in wellness tourists. A longitudinal observational study with outcomes assessed upon arrival and departure and 6 weeks after the retreat. A rural health retreat in Queensland, Australia. A holistic, 1-week, residential, retreat experience that included many educational, therapeutic, and leisure activities and an organic, mostly plant-based diet. Multiple outcome measures were performed upon arrival and departure and 6 weeks after the retreat. These included anthropometric measures, urinary pesticide metabolites, a food and health symptom questionnaire, the Five Factor Wellness Inventory, the General Self Efficacy questionnaire, the Pittsburgh Insomnia Rating Scale, the Depression Anxiety Stress Scale, the Profile of Mood States, and the Cogstate cognitive function test battery. Statistically significant improvements (p effects and assess the value and relevance of retreat experiences to clinicians and health insurers.

  19. A comparative evaluation of efficacy of protaper universal rotary retreatment system for gutta-percha removal with or without a solvent

    Directory of Open Access Journals (Sweden)

    M Sita Ram Kumar

    2012-01-01

    Full Text Available Aim: The aim was to evaluate and compare the efficacy of ProTaper Universal rotary retreatment system with or without solvent and stainless steel hand files for endodontic filling removal from root canals and also to compare retreatment time for each system. Materials and Methods: Thirty extracted mandibular premolars with single straight canals were endodontically treated. Teeth were divided into three major groups, having 10 specimens each. Removal of obturating material in group 1 by stainless steel hand files with RC Solve, group 2 by ProTaper Universal retreatment instruments and group 3 by ProTaper Universal retreatment instruments along with RC solve was done. Retreatment was considered complete for all groups when no filling material was observed on the instruments. The retreatment time was recorded for each tooth. All specimens were grooved longitudinally in a buccolingual direction. The split halves were examined under a stereomicroscope and images were captured and analyzed. The remaining filling debris area ratios were considered for statistical analysis. Results: With ANOVA test, statistical analysis showed that there was statistically no significant difference regarding the amount of filling remnants between the groups (P < 0.05. Differences between the means of groups are statistically significant regarding the retreatment time. Conclusion: Irrespective of the technique used, all the specimens had some remnants on the root canal wall. ProTaper Universal retreatment system files alone proved to be faster than the other experimental groups.

  20. Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias mountains, Alaska

    Digital Repository Service at National Institute of Oceanography (India)

    Gulick, S.P.S.; Jaeger, J.M.; Mix, A.C.; Asahi, H.; Bahlburg, H.; Belanger, C.L.; Berbel, G.B.B.; Childress, L.; Cowan, E.; Drab, L.; Forwick, M.; Fukumura, A.; Ge, S.; Gupta, S.M.; Kioka, A.; Konno, S.; LeVay, L.J.; Marz, C.; Matsuzaki, K.M.; McClymont, E.L.; Moy, C.; Muller, J.; Nakamura, A.; Ojima, T.; Ribeiro, F.R.; Ridgway, K.D.; Romero, O.E.; Slagle, A.L.; Stoner, J.S.; St-Onge, G.; Suto, I.; Walczak, M.D.; Worthington, L.L.; Bailey, I.; Enkelmann, E.; Reece, R.; Swartz, J.M.

    the onset of quasi-periodic (~100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2–0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50–80%. Such a rapid net mass loss explains apparent...

  1. Glacial sequence stratigraphy reveal the Weichselian glacial history of the SE sector of the Eurasian Ice Sheet

    Science.gov (United States)

    Räsänen, Matti

    2016-04-01

    Reconstructions of the last Weichselian glacial cycle 117,000-11,700 years (kyr) ago propose that S Finland, adjacent Russia and the Baltic countries in the SE sector of the Eurasian Ice Sheet (EIS), were glaciated during the Middle Weichselian time [marine isotope stage (MIS) 4, 71-57 kyr ago] and that this glaciation was preceded in S Finland by an Early Weichselian interstadial (MIS 5c, 105-93 kyr ago) with pine forest. Here glacial sequence stratigraphy (Powell and Cooper 2002) is applied to isolated Late Pleistocene onshore outcrop sections in S Finland. The analysed sedimentary records have traditionally been investigated, interpreted and published separately by different authors without an attempt to a methodologically more systematic survey. By putting new field data and old observations into a regional sequence stratigraphic framework it is shown how previously unnoticed regularities can be found in the lithofacies and fossil successions. It is shown that the proposed Middle Weichselian glaciation or the pine dominated interstadial did not take place at all (Räsänen et al. 2015). The one Late Weichselian glaciation (MIS 2, 29-11 kyr ago) at the SE sector of EIS was preceded in S Finland by a nearly 90 kyr long still poorly known non-glacial period, featuring tundra with permafrost and probably birch forest. The new Middle Weichselian paleoenvironmental scenario revises the configuration and hydrology of the S part of EIS and gives new setting for the evolution of Scandinavian biota. References Powell, R. D., and Cooper, J. M., 2002, A glacial sequence stratigraphic model for temperate, glaciated continental shelves, in Dowdeswell, J. A., and Cofaig, C. Ó. eds., Glacier-Influenced Sedimentation on High-Latitude Continental Margins: The Geological Society of London, London, Geological Society London, Special Publication v. 203, p. 215-244. Räsänen, M.E., Huitti, J.V., Bhattarai, S. Harvey, J. and Huttunen, S. 2015, The SE sector of the Middle

  2. Glacial loess or shoreface sands: a re-interpretation of the Upper Ordovician (Ashgillian) glacial Ammar Formation, Southern Jordan

    Science.gov (United States)

    Turner, B. R.; Makhlouf, I. M.; Armstrong, H. A.

    2003-04-01

    Upper Ordovician (Ashgillian) glacial deposits of the Ammar Formation, Southern Jordan, comprise locally deformed, structureless fine sandstone, incised by glacial channels filled by braided outwash plain sandstones and transgressive marine mudstones. The structureless sandstones, previously interpreted as a glacial rock flour or loessite derived from the underlying undisturbed sandstones, differ significantly from typical loessite and contain hitherto unrecognised sedimentary structures, including hummocky cross-stratification. The sandstones, which grade laterally and vertically into stratigraphically equivalent undeformed marginal marine sandstones, are interpreted as a deformed facies of the underlying sandstones, deposited in a similar high energy shoreface environment. Although deformation of the shoreface sandstones was post-depositional, the origin of the deformation, and its confinement to the Jebel Ammar area is unknown. Deformation due to the weight of the overlying ice is unlikely as the glaciofluvial channels are now thought to have been cut by tunnel valley activity not ice. A more likely mechanism is post-glacial crustal tectonics. Melting of ice caps is commonly associated with intraplate seismicity and the development of an extensional crustal stress regime around the perimeter of ice caps; the interior is largely aseismic because the weight of the ice supresses seismic activity and faulting. Since southern Jordan lay close to the ice cap in Saudi Arabia it may have been subjected to postglacial seismicity and crustal stress, which induced ground shaking, reduced overburden pressure, increased hydrostatic pressure and possibly reactivation of existing tectonic faults. This resulted in liquefaction and extensive deformation of the sediments, which show many characteristics of seismites, generated by earthquake shocks. Since the glaciation was a very short-lived event (0.2-1 Ma), deglaciation and associated tectonism triggering deformation, lasted

  3. Selective embolization of unruptured intracranial aneurysms is associated with low retreatment rate

    Energy Technology Data Exchange (ETDEWEB)

    Bandeira, Alexandra; Raphaeli, Guy [Erasme University Hospital, Department of Radiology, Neuroradiology Section, Brussels (Belgium); Erasme University Hospital, Interventional Neuroradiology Fellows, Brussels (Belgium); Baleriaux, Danielle [Erasme University Hospital, Department of Radiology, Neuroradiology Section, Brussels (Belgium); Bruneau, Michael; Witte, Olivier De [Erasme University Hospital, Neurosurgery, Brussels (Belgium); Lubicz, Boris [Erasme University Hospital, Department of Radiology, Neuroradiology Section, Brussels (Belgium); Hopital Erasme, Service de Radiologie, Brussels (Belgium)

    2010-02-15

    To report long-term imaging findings of 101 patients with 129 unruptured intracranial aneurysms (UIA) treated by embolization. A retrospective review of our prospectively maintained database identified all patients with an UIA treated by embolization with coils only and with a minimal 12-month imaging follow-up. The clinical charts, procedural data, and angiographic results were reviewed. Between March 2004 and June 2009, 101 patients with 129 UIA were identified (71 women/30 men, mean age = 51.4 years). Ninety-four aneurysms (73%) were large (10-25 mm), and 35 (27%) were small (<10 mm). Aneurysms mean size was 10.7 mm (median, 9 mm; range 3-22 mm); 87 UIA (67.5%) had a small neck (<4 mm or neck/sac ratio < 0.7), and 42 (32.5%) had a wide neck ({>=}4 mm or neck/sac ratio {>=} 0.7). Selective coiling with bare/coated coils was performed in 125 cases and four cases, respectively. The balloon-assisted technique was used in 47 cases (36.4%). Only one patient experienced a symptomatic complication (thromboembolism) and kept a slight hemiparesis. Immediate results included 77 complete occlusions (59.7%), 45 neck remnants (34.9%), and 7 incomplete occlusions (5.4%). Mean imaging follow-up of 32 months showed 104 stable occlusions (80.6%), 12 further thrombosis (9.3%), 7 major recanalizations (5.4%), and 6 minor recanalizations (4.7%). Retreatment was required in seven wide-necked and/or large aneurysms including four treated with coated coils. No bleeding occurred during follow-up. Selective embolization of UIA is associated with stable long-term anatomical results and low retreatment rate. (orig.)

  4. "Managed Retreat" in Response to Superstorm Sandy: The Oakwood Beach Story

    Science.gov (United States)

    Tirone, J.

    2017-12-01

    This presentation shares lessons learned from firsthand experience of the home buyout process in New York City after Superstorm Sandy. Many have described Sandy as "the perfect storm" from a meteorological perspective, but it was also the perfect storm from a government-buyout perspective. For a buyout to work in New York City, with its high property values and dense housing and population, many conditions had to be in place before the storm. Before Sandy hit, Oakwood Beach on Staten Island had already had enough. Hurricane Isaac flooded streets and basements in 2010, followed by Hurricane Irene in 2011. Many residents of this multi-generational neighborhood had just finished fixing their homes. A few years before, a brush fire spread through the invasive and highly flammable Phragmites reeds, destroying a protective berm installed by the Army Corps of Engineers in 2000 and threatening to damage many homes. An aerial view would show how these homes incredulously sat in the middle of a marsh, a marsh designated as part of the Bluebelt wetlands storm water management system by New York City's Department of Environmental Protection. Even more incredulously, while New York City was buying up unimproved lots to expand the Bluebelt to improve drainage for inland homes, the City was also issuing building permits to developers - sometimes for lots directly in the Bluebelt's path. Welcome to Staten Island, where the political influence of developers made any effort to retreat from the waterfront especially difficult and contentious. Before the storm, no one knew what a buyout was, never mind how to go about seeking one. For the most part, this included local officials. Managed retreat is typically understood as a top-down directive, but in this case the buyout plan was initiated from the bottom up by eight ordinary citizens who used research, trust, and networking to get their voices heard and, against all odds, to drive a highly successful State-supported buyout program.

  5. Cohort Trends in Premarital First Births: What Role for the Retreat From Marriage?

    Science.gov (United States)

    Wu, Lawrence L.; Shafer, Emily Fitzgibbons

    2015-01-01

    We examine cohort trends in premarital first births for U.S. women born between 1920 and 1964. The rise in premarital first births is often argued to be a consequence of the retreat from marriage, with later ages at first marriage resulting in more years of exposure to the risk of a premarital first birth. However, cohort trends in premarital first births may also reflect trends in premarital sexual activity, premarital conceptions, and how premarital conceptions are resolved. We decompose observed cohort trends in premarital first births into components reflecting cohort trends in (1) the age-specific risk of a premarital conception taken to term; (2) the age-specific risk of first marriages not preceded by such a conception, which will influence women’s years of exposure to the risk of a premarital conception; and (3) whether a premarital conception is resolved by entering a first marriage before the resulting first birth (a “shotgun marriage”). For women born between 1920–1924 and 1945–1949, increases in premarital first births were primarily attributable to increases in premarital conceptions. For women born between 1945–1949 and 1960–1964, increases in premarital first births were primarily attributable to declines in responding to premarital conceptions by marrying before the birth. Trends in premarital first births were affected only modestly by the retreat from marriages not preceded by conceptions—a finding that holds for both whites and blacks. These results cast doubt on hypotheses concerning “marriageable” men and instead suggest that increases in premarital first births resulted initially from increases in premarital sex and then later from decreases in responding to a conception by marrying before a first birth. PMID:24072609

  6. Glacial geology of the upper Wairau Valley, Marlborough, New Zealand

    International Nuclear Information System (INIS)

    McCalpin, J.P.

    1992-01-01

    Late Pleistocene glaciers in the upper Wairau Valley deposited four groups of moraines inferred to represent one Waimean ice advance, two Otiran ice advances, and an advance of early Aranuian age. The Waimean and early Otiran glaciers advanced into Tarndale Valley, deposited terminal moraines, and shed outwash down both the Alma River and Travellers Valley. The middle Otiran glacier terminated in northern Tarndale Valley and shed outwash from the southern part of its terminus down the Alma River. The north side of the terminus abutted a large ice-dammed lake in the Wairau Gorge, and fan-deltas graded to an old shore level at an elevation of 1040 m. Well-preserved moraines at the mouths of four glaciated tributaries may be middle Otiran recessional, or late Otiran terminal moraines. The latest ice advance extended 11 km down the upper Wairau Valley and deposited a subdued moraine at Island Gully. The composite chronology of the latest glacial advance based on 10 radiocarbon ages suggests it occurred between about 9.5 and 10.2 ka. This age span is similar to that of early Aranuian glacial advances dated by other workers in the Southern Alps, and may reflect Younger Dryas cooling. (author). 22 refs., 10 figs., 3 tabs

  7. Linking microbial diversity and functionality of arctic glacial surface habitats.

    Science.gov (United States)

    Lutz, Stefanie; Anesio, Alexandre M; Edwards, Arwyn; Benning, Liane G

    2017-02-01

    Distinct microbial habitats on glacial surfaces are dominated by snow and ice algae, which are the critical players and the dominant primary colonisers and net producers during the melt season. Here for the first time we have evaluated the role of these algae in association with the full microbial community composition (i.e., algae, bacteria, archaea) in distinct surface habitats and on 12 glaciers and permanent snow fields in Svalbard and Arctic Sweden. We cross-correlated these data with the analyses of specific metabolites such as fatty acids and pigments, and a full suite of potential critical physico-chemical parameters including major and minor nutrients, and trace metals. It has been shown that correlations between single algal species, metabolites, and specific geochemical parameters can be used to unravel mixed metabolic signals in complex communities, further assign them to single species and infer their functionality. The data also clearly show that the production of metabolites in snow and ice algae is driven mainly by nitrogen and less so by phosphorus limitation. This is especially important for the synthesis of secondary carotenoids, which cause a darkening of glacial surfaces leading to a decrease in surface albedo and eventually higher melting rates. © 2016 The Authors. Environmental Microbiology published by Society for Applied Microbiology and John Wiley & Sons Ltd.

  8. Rapid Holocene thinning of outlet glaciers followed by readvance in the western Ross Embayment, Antarctica

    Science.gov (United States)

    Jones, R. S.; Whitmore, R.; Mackintosh, A.; Norton, K. P.; Eaves, S.; Stutz, J.

    2017-12-01

    Investigating Antarctic deglaciation following the LGM provides an opportunity to better understand patterns, mechanisms and drivers of ice sheet retreat. In the Ross Sea sector, geomorphic features preserved on the seafloor indicate that streaming East Antarctic outlet glaciers once extended >100 km offshore of South Victoria Land prior to back-stepping towards their modern configurations. In order to adequately interpret the style and causes of this retreat, the timing and magnitude of corresponding ice thickness change is required. We present new constraints on ice surface lowering from Mawson Glacier, an outlet of the East Antarctic Ice Sheet that flows into the western Ross Sea. Surface-exposure (10Be) ages from samples collected in elevation transects above the modern ice surface reveal that rapid thinning occurred at 5-8 ka, broadly coeval with new ages of grounding-line retreat at 6 ka and rapid thinning recorded at nearby Mackay Glacier at 7 ka. Our data also show that a moraine formed near to the modern ice margin of Mawson Glacier at 0.8 ka, which, together with historical observations, indicates that glaciers in this region readvanced during the last thousand years. We argue that 1) the accelerated thinning of outlet glaciers was driven by local grounding-line retreat through overdeepened basins during the early-mid Holocene, and 2) the glaciers subsequently readvanced, possibly linked to late Holocene sea-ice expansion, before retreating to their current positions. Our work demonstrates that these outlet glaciers were closely coupled to environmental and topography-induced perturbations near their termini throughout the Holocene.

  9. Causes of strong ocean heating during glacial periods

    Science.gov (United States)

    Zimov, N.; Zimov, S. A.

    2013-12-01

    During the last deglaciation period, the strongest climate changes occurred across the North Atlantic regions. Analyses of borehole temperatures from the Greenland ice sheet have yielded air temperature change estimates of 25°C over the deglaciation period (Dahl-Jensen et al. 1998). Such huge temperature changes cannot currently be explained in the frames of modern knowledge about climate. We propose that glacial-interglacial cycles are connected with gradual warming of ocean interior waters over the course of glaciations and quick transport of accumulated heat from ocean to the atmosphere during the deglaciation periods. Modern day ocean circulation is dominated by thermal convection with cold waters subsiding in the Northern Atlantic and filling up the ocean interior with cold and heavy water. However during the glaciation thermal circulation stopped and ocean circulation was driven by 'haline pumps' -Red and Mediterranean seas connected with ocean with only narrow but deep straights acts as evaporative basins, separating ocean water into fresh water which returns to the ocean surface (precipitation) and warm but salty, and therefore heavy, water which flows down to the ocean floor. This haline pump is stratifying the ocean, allowing warmer water locate under the colder water and thus stopping thermal convection in the ocean. Additional ocean interior warming is driven by geothermal heat flux and decomposition of organic rain. To test the hypothesis we present simple ocean box model that describes thermohaline circulation in the World Ocean. The first box is the Red and Mediterranean sea, the second is united high-latitude seas, the third is the ocean surface, and the fourth the ocean interior. The volume of these water masses and straight cross-sections are taken to be close to real values. We have accepted that the exchange of water between boxes is proportional to the difference in water density in these boxes, Sun energy inputs to the ocean and sea surface

  10. The role of bank collapse on tidal creek ontogeny: A novel process-based model for bank retreat

    Science.gov (United States)

    Gong, Zheng; Zhao, Kun; Zhang, Changkuan; Dai, Weiqi; Coco, Giovanni; Zhou, Zeng

    2018-06-01

    Bank retreat in coastal tidal flats plays a primary role on the planimetric shape of tidal creeks and is commonly driven by both flow-induced bank erosion and gravity-induced bank collapse. However, existing modelling studies largely focus on bank erosion and overlook bank collapse. We build a bank retreat model coupling hydrodynamics, bank erosion and bank collapse. To simulate the process of bank collapse, a stress-deformation model is utilized to calculate the stress variation of bank soil after bank erosion, and the Mohr-Coulomb failure criterion is then applied to evaluate the stability of the tidal creek bank. Results show that the bank failure process can be categorized into three stages, i.e., shear failure at the bank toe (stage I), tensile failure on the bank top (stage II), and sectional cracking from the bank top to the toe (stage III). With only bank erosion, the planimetric shapes of tidal creeks are funneled due to the gradually seaward increasing discharge. In contrast to bank erosion, bank collapse is discontinuous, and the contribution of bank collapse to bank retreat can reach 85%, highlighting that the expansion of tidal creeks can be dominated by bank collapse process. The planimetric shapes of tidal creeks are funneled with a much faster expansion rate when bank collapse is considered. Overall, this study makes a further step toward more physical and realistic simulation of bank retreat in estuarine and coastal settings and the developed bank collapse module can be readily included in other morphodynamic models.

  11. Dry-season retreat and dietary shift of the dart-poison frog Dendrobates tinctorius (Anura: Dendrobatidae)

    NARCIS (Netherlands)

    Born, M.; Bongers, F.; Poelman, E.H.; Sterck, F.J.

    2010-01-01

    Dry-season retreat and dietary shift of the dart-poison frog Delldrobates tillCtOrillS (Anura: Dendrobatidae). Seasonal rainfall affects tropical forest dynamics and behavior of species that are part of these ecosystems. TIle positive correlation between amphibian ac tivity pattems and rainfall has

  12. Potential to induce dentinal cracks during retreatment procedures of teeth treated with “Russian red”: An ex vivo study

    Directory of Open Access Journals (Sweden)

    Eglė Nedzinskienė

    2017-01-01

    Conclusions: Retreatment methods had a damaging effect on the root dentin of teeth previously treated with resorcinol–formaldehyde resin. At magnification ×16, the efficacy of using the dye for the detection of cracks was higher than detection without the dye.

  13. From networking to next-working: how an academic department "retreated" and advanced at the same time.

    Science.gov (United States)

    Yager, Joel; Kenna, Heather; Hantke, Mindy

    2015-04-01

    Department-wide retreats conducted at periods of transition can enrich and benefit academic departments in several ways. Here, the authors describe the organization, conduct, and immediate outcomes of a department-wide retreat in a university department of psychiatry intended to (1) foster networking and communication among faculty who often work in "silos" and (2) invite the faculty to provide "internal consultations" regarding aspirational strategic goals and recommendations for short-term actionable tactics to address these goals. The retreat featured an evening networking and socializing poster session followed by a day-long event consisting of small group and large group interactive sessions. Participants were 120 faculty members including 44 new and younger faculty members who prepared and presented posters about themselves and their work. A variety of aspirational goals and specific recommendations for follow-up emerged from small groups were discussed in plenary sessions and were subsequently summarized and distributed to the faculty to be addressed by ongoing workgroups. Immediate informal feedback suggests that conducting and acting on recommendations ensuing from academic department retreats can foster at least a short-term sense of shared community and purpose, network faculty, identify commonly held values and aspirational goals, and potentially stimulate formation of innovative affinity groups and collaborations. Longer-term workgroup efforts and outcome assessments are required to assess the enduring results and value of such undertakings.

  14. Creating a specialist protein resource network: a meeting report for the protein bioinformatics and community resources retreat

    NARCIS (Netherlands)

    Babbitt, P.C.; Bagos, P.G.; Bairoch, A.; Bateman, A.; Chatonnet, A.; Chen, M.J.; Craik, D.J.; Finn, R.D.; Gloriam, D.; Haft, D.H.; Henrissat, B.; Holliday, G.L.; Isberg, V.; Kaas, Q.; Landsman, D.; Lenfant, N.; Manning, G.; Nagano, N.; Srinivasan, N.; O'Donovan, C.; Pruitt, K.D.; Sowdhamini, R.; Rawlings, N.D.; Saier, M.H., Jr.; Sharman, J.L.; Spedding, M.; Tsirigos, K.D.; Vastermark, A.; Vriend, G.

    2015-01-01

    During 11-12 August 2014, a Protein Bioinformatics and Community Resources Retreat was held at the Wellcome Trust Genome Campus in Hinxton, UK. This meeting brought together the principal investigators of several specialized protein resources (such as CAZy, TCDB and MEROPS) as well as those from

  15. Differences in the clinical-epidemiological profile between new cases of tuberculosis and retreatment cases after default

    Directory of Open Access Journals (Sweden)

    Aylana de Souza Belchior

    Full Text Available Abstract OBJECTIVE To identify the socioeconomic and clinical-epidemiological factors related to tuberculosis in new cases and retreatment cases. METHOD Comparative study with 126 patients, of which 42 were retreatment cases after default attended in a reference center, and 84 were new cases completing the first treatment and treated in Basic Health Units. The collection of primary data was through interview, and of secondary data by records of the Notifiable Diseases Information System. Comparative analysis between the two groups. RESULTS The new cases differ from retreatment cases regarding educational level. The clinical-epidemiological profile shows a significant difference in relation to performance of the tuberculin skin test, and the HIV test result (positive in favor of new cases. In relation to performance of sputum culture and the result (positive of the first sputum smear of the first and second samples, in favor of retreatment cases. CONCLUSION The two groups are significantly different in clinical and epidemiological characteristics that show the access to exams.

  16. Retreatment of patients with treatment failure of direct-acting antivirals: Focus on hepatitis C virus genotype 1b.

    Science.gov (United States)

    Kanda, Tatsuo; Nirei, Kazushige; Matsumoto, Naoki; Higuchi, Teruhisa; Nakamura, Hitomi; Yamagami, Hiroaki; Matsuoka, Shunichi; Moriyama, Mitsuhiko

    2017-12-14

    The recent development of direct-acting antiviral agents (DAAs) against hepatitis C virus (HCV) infection could lead to higher sustained virological response (SVR) rates, with shorter treatment durations and fewer adverse events compared with regimens that include interferon. However, a relatively small proportion of patients cannot achieve SVR in the first treatment, including DAAs with or without peginterferon and/or ribavirin. Although retreatment with a combination of DAAs should be conducted for these patients, it is more difficult to achieve SVR when retreating these patients because of resistance-associated substitutions (RASs) or treatment-emergent substitutions. In Japan, HCV genotype 1b (GT1b) is founded in 70% of HCV-infected individuals. In this minireview, we summarize the retreatment regimens and their SVR rates for HCV GT1b. It is important to avoid drugs that target the regions targeted by initial drugs, but next-generation combinations of DAAs, such as sofosbuvir/velpatasvir/voxilaprevir for 12 wk or glecaprevir/pibrentasvir for 12 wk, are proposed to be potential solution for the HCV GT1b-infected patients with treatment failure, mainly on a basis of targeting distinctive regions. Clinicians should follow the new information and resources for DAAs and select the proper combination of DAAs for the retreatment of HCV GT1b-infected patients with treatment failure.

  17. Late Post-glacial Sea Level Rise and Its Effects On Human Activity In Asia

    Science.gov (United States)

    Oppenheimer, S. J.

    Three rapid post-glacial sea-level rises flooded coastlines with large continental shelves. The last of these, shortly before the interglacial optimum c.7,500BP, not only changed coastal Neolithic societies, but may also have stimulated maritime skills. Two Asian examples explore these aspects. First, during the Mid-Holocene, the Arabian Gulf transgressed as far inland as Ur probably laying down Woolley's famous Ur Flood silt layer between 7,000-5,500 BP. Stratigraphy and dating suggests the phase of rapid sea level rise immediately preceded the start of the 'Ubaid pottery period. Red-slipped Uruk pottery and copper items then appear from about 6,000BP, but above Woolley's silt layer. The Sumerian King Lists also record a major upheaval and dynastic change after 'the Flood'. Second, the final flooding of the Sunda shelf in Southeast Asia was followed by a maritime extension of human occupation from Northern Melanesia south into the Solomon Islands 6,000 years ago. Simultaneously, further west on the north coast of New Guinea, new archaeological assemblages ap- pear beneath a silt layer left by a pro-grading 6,000 year-old inland sea. The presence of arboriculture items such as betel nuts and the contemporary arrival of dogs and pigs in the same region suggests intrusion from Southeast Asia. This supports Solheim's suggestion that rapid sea-level rise on the eastern edge of the Sunda Shelf stimulated maritime skills and invention in Southeast Asia. This may have provided the initial stimulus to the first maritime expansion that was later to colonise the whole Pacific.

  18. Reconciling deep calibration and demographic history: bayesian inference of post glacial colonization patterns in Carcinus aestuarii (Nardo, 1847 and C. maenas (Linnaeus, 1758.

    Directory of Open Access Journals (Sweden)

    Ilaria A M Marino

    Full Text Available A precise inference of past demographic histories including dating of demographic events using bayesian methods can only be achieved with the use of appropriate molecular rates and evolutionary models. Using a set of 596 mitochondrial cytochrome c oxidase I (COI sequences of two sister species of European green crabs of the genus Carcinus (C. maenas and C. aestuarii, our study shows how chronologies of past evolutionary events change significantly with the application of revised molecular rates that incorporate biogeographic events for calibration and appropriate demographic priors. A clear signal of demographic expansion was found for both species, dated between 10,000 and 20,000 years ago, which places the expansions events in a time frame following the Last Glacial Maximum (LGM. In the case of C. aestuarii, a population expansion was only inferred for the Adriatic-Ionian, suggestive of a colonization event following the flooding of the Adriatic Sea (18,000 years ago. For C. maenas, the demographic expansion inferred for the continental populations of West and North Europe might result from a northward recolonization from a southern refugium when the ice sheet retreated after the LGM. Collectively, our results highlight the importance of using adequate calibrations and demographic priors in order to avoid considerable overestimates of evolutionary time scales.

  19. Glacial wetland distribution and methane emissions estimated from PMIP2 climate simulations

    NARCIS (Netherlands)

    Weber, S.L.; Drury, A.J.; Toonen, W.H.J.; Weele, M. van

    2010-01-01

    The interglacial–glacial decrease in atmospheric methane concentration is often attributed to a strong decline in the wetland source. This seems consistent with the extreme coldness and vastly expanded ice sheets. Here we analyse coupled model simulations for the last glacial maximum from the

  20. Last Glacial Maximum CO2 and d13C successfully reconciled

    NARCIS (Netherlands)

    Bouttes, N.; Paillard, D.; Roche, D.M.V.A.P.; Brovkin, V.; Bopp, L.

    2011-01-01

    During the Last Glacial Maximum (LGM, ∼21,000 years ago) the cold climate was strongly tied to low atmospheric CO2 concentration (∼190 ppm). Although it is generally assumed that this low CO2 was due to an expansion of the oceanic carbon reservoir, simulating the glacial level

  1. Weak oceanic heat transport as a cause of the instability of glacial climates

    NARCIS (Netherlands)

    Colin de Verdière, A.; Raa, L. te

    2010-01-01

    The stability of the thermohaline circulation of modern and glacial climates is compared with the help of a two dimensional ocean-atmosphere-sea ice coupled model. It turns out to be more unstable as less freshwater forcing is required to induce a polar halocline catastrophy in glacial climates. The

  2. Widespread secondary contact and new glacial refugia in the halophilic rotifer Brachionus plicatilis in the Iberian Peninsula.

    Science.gov (United States)

    Campillo, Sergi; Serra, Manuel; Carmona, María José; Gómez, Africa

    2011-01-01

    Small aquatic organisms harbour deep phylogeographic patterns and highly structured populations even at local scales. These patterns indicate restricted gene flow, despite these organisms' high dispersal abilities, and have been explained by a combination of (1) strong founder effects due to rapidly growing populations and very large population sizes, and (2) the development of diapausing egg banks and local adaptation, resulting in low effective gene flow, what is known as the Monopolization hypothesis. In this study, we build up on our understanding of the mitochondrial phylogeography of the halophilic rotifer Brachionus plicatilis in the Iberian Peninsula by both increasing the number of sampled ponds in areas where secondary contact is likely and doubling sample sizes. We analyzed partial mitochondrial sequences of 252 individuals. We found two deep mitochondrial DNA lineages differing in both their genetic diversity and the complexity of their phylogeographic structure. Our analyses suggest that several events of secondary contact between clades occurred after their expansion from glacial refugia. We found a pattern of isolation-by-distance, which we interpret as being the result of historical colonization events. We propose the existence of at least one glacial refugium in the SE of the Iberian Peninsula. Our findings challenge predictions of the Monopolization hypothesis, since coexistence (i.e., secondary contact) of divergent lineages in some ponds in the Iberian Peninsula is common. Our results indicate that phylogeographic structures in small organisms can be very complex and that gene flow between diverse lineages after population establishment can indeed occur.

  3. Widespread secondary contact and new glacial refugia in the halophilic rotifer Brachionus plicatilis in the Iberian Peninsula.

    Directory of Open Access Journals (Sweden)

    Sergi Campillo

    Full Text Available Small aquatic organisms harbour deep phylogeographic patterns and highly structured populations even at local scales. These patterns indicate restricted gene flow, despite these organisms' high dispersal abilities, and have been explained by a combination of (1 strong founder effects due to rapidly growing populations and very large population sizes, and (2 the development of diapausing egg banks and local adaptation, resulting in low effective gene flow, what is known as the Monopolization hypothesis. In this study, we build up on our understanding of the mitochondrial phylogeography of the halophilic rotifer Brachionus plicatilis in the Iberian Peninsula by both increasing the number of sampled ponds in areas where secondary contact is likely and doubling sample sizes. We analyzed partial mitochondrial sequences of 252 individuals. We found two deep mitochondrial DNA lineages differing in both their genetic diversity and the complexity of their phylogeographic structure. Our analyses suggest that several events of secondary contact between clades occurred after their expansion from glacial refugia. We found a pattern of isolation-by-distance, which we interpret as being the result of historical colonization events. We propose the existence of at least one glacial refugium in the SE of the Iberian Peninsula. Our findings challenge predictions of the Monopolization hypothesis, since coexistence (i.e., secondary contact of divergent lineages in some ponds in the Iberian Peninsula is common. Our results indicate that phylogeographic structures in small organisms can be very complex and that gene flow between diverse lineages after population establishment can indeed occur.

  4. The glacially overdeepened trough of the Salzach Valley, Austria: Bedrock geometry and sedimentary fill of a major Alpine subglacial basin

    Science.gov (United States)

    Pomper, Johannes; Salcher, Bernhard C.; Eichkitz, Christoph; Prasicek, Günther; Lang, Andreas; Lindner, Martin; Götz, Joachim

    2017-10-01

    Overdeepened valleys are unambiguous features of glacially sculpted landscapes. They result from erosion at the bed of the glacier and their size and shape is determined by ice dynamics and the characteristics of the underlying bedrock. Major overdeepened valleys representing vertical bedrock erosion of several hundreds of meters are characteristic features of many trunk valleys in the formerly glaciated parts of the Alpine mountain belt. The thick sedimentary fill usually hinders attempts to unravel bedrock geometry, formation history and fill characteristics. Based on reflection seismic data and core-logs from multiple deep drillings we construct a detailed bedrock model of the Lower Salzach Valley trough, one of the largest overdeepened valleys in the European Alps. The analysed overdeepened structure characterized by a strongly undulating topography. Two reaches of enhanced erosion can be identified and are suggested to be related to variations in bedrock erodibility and a triple glacier confluence. The sedimentary fill shows clear characteristics of rapid infilling and subaqueous fan delta deposits indicate a strong influence of tributary streams. Associated surface lowering of the valley floor had a major impact on tributary stream incision but also on the available ice accumulation area at subsequent glaciations. The extent to which fills of earlier glaciations have been preserved from erosion during the last glacial maximum remains ambiguous and demands further exploration. To our knowledge the presented bedrock model is one of the best defined of any major overdeepened trunk valley.

  5. Root Canal Retreatment menggunakan Kombinasi Kalsium Hidroksida dan Chlorhexidine sebagai Medikamen Intra Kanal Insisivus Sentral Kiri Maksila

    Directory of Open Access Journals (Sweden)

    Andina Novita Sari

    2014-12-01

    retreatment dengan cleaning dan shaping ulang yang baik dengan menggunakan medikasi intrakanal berupa kombinasi kalsium hidroksida dan chlorhexidine 2% diharapkan mempunyai efek antimikroba yang sinergis untuk mencapai kesuksesan root canal retreatment.   Root Canal Retreatment Using Calcium Hydroxide as Intra Canal Medicament On The Maxillary Left Incisor. Enterococcus faecalis bacteria is most abundant in the root canal infection treated endodontically. Chlorhexidine has a broad antibacterial spectrum and has been used as an endodontic irrigant and intracanal medication. Chlorhexidine has a bactericidal and fungicidal effect as chlorhexidine absorbed into the bacterial cell surface and cause damage to the integrity of the cell membrane. Calcium hydroxide is a biocompatible, antimicrobial agents with high pH effects and stimulates hard tissue formation. A mixture of calcium hydroxide and chlorhexidine is used to control bacteria Enterococcus faecalis alternative. The purpose of this case report is to report on the success of root canal treatment in the left maxillary central incisor with acute periapical periodontitis using a combination of calcium hydroxide and chlorhexidine as intracanal A 24 years old female patient presents with left upper central incisor tooth ache since 4 years ago. The tooth was hurt to percussion, but normal to pulpation as well as the mobility. The tooth has a history of previous trauma and broken 6 years ago and has performed endodontic treatment. Radiographic examination showed obturation teeth 21 are not hermetic with periapical radiolucency in diffuse boundaries, widening of the periodontal ligament and the dissolution of the lamina dura. Root canal re-treatment using a combination of calcium hydroxide and chlorhexidine as intracanal medicaments were performed. In conclussion, the root canal cleaning and shaping retreatment can be performed using a combination of calcium hydroxide and chlorhexidine as intracanal

  6. Healing the heart: a randomized pilot study of a spiritual retreat for depression in acute coronary syndrome patients.

    Science.gov (United States)

    Warber, Sara L; Ingerman, Sandra; Moura, Vera L; Wunder, Jenna; Northrop, Alyssa; Gillespie, Brenda W; Durda, Kate; Smith, Katherine; Rhodes, Katherine S; Rubenfire, Melvyn

    2011-01-01

    Depression is associated with increased risk of cardiovascular morbidity and mortality in coronary heart disease. Numerous conventional and complementary therapies may address depression. Few involving spirituality have been tested. The aim of this study was to compare the effects of a nondenominational spiritual retreat, Medicine for the Earth (MFTE), on depression and other measures of well-being six- to 18-months post acute coronary syndrome (ACS). A randomized controlled pilot study of MFTE, Lifestyle Change Program (LCP), or usual cardiac care (control) was conducted in Southeastern Michigan. ACS patients were recruited via local and national advertising (n = 58 enrolled, 41 completed). The four-day MFTE intervention included guided imagery, meditation, drumming, journal writing, and nature-based activities. The four-day LCP included nutrition education, exercise, and stress management. Both retreat groups received follow-up phone coaching biweekly for three months. Validated self-report scales of depression, spiritual well-being, perceived stress, and hope were collected at baseline, immediately post-retreat, and at three and six months. Depression was not significantly different among groups (P = .21). However, the MFTE group had the highest depression scores at baseline and had significantly lower scores at all postintervention time points (P ≤ .002). Hope significantly improved among MFTE participants, an effect that persisted at three- and six-month follow-up (P = .014). Although several measures showed improvement in all groups by six months, the MFTE group had immediate improvement post-retreat, which was maintained. This pilot study shows that a nondenominational spiritual retreat, MFTE, can be used to increase hope while reducing depression in patients with ACS. Copyright © 2011 Elsevier Inc. All rights reserved.

  7. Thermal study on the impurity effect on thermodynamic stability of the glacial phase in triphenyl phosphite-triphenyl phosphate system

    International Nuclear Information System (INIS)

    Tanabe, Ikue; Takeda, Kiyoshi; Murata, Katsuo

    2005-01-01

    To investigate the impurity effect on thermodynamic stability of the glacial phase, an apparently amorphous metastable phase observed in triphenyl phosphite (TPP), the differential scanning calorimetry (DSC) was carried out in the temperature range 120-350 K for binary mixtures between TPP and triphenyl phosphate (TPPO). Heating up from the glassy liquid, supercooled liquid phase transformed into glacial phase below the crystallization temperature for all the samples with x < 0.2, where x denotes the mole fraction of TPPO. Both transformation temperatures from liquid to glacial and from glacial to crystal increased and temperature range that glacial phase appears narrowed with the content of TPPO. The peak intensity of exothermic effect due to the transformation from liquid to glacial becomes larger whereas that from glacial to crystal reduced. The kinetic and thermodynamic stabilities were discussed for liquid and glacial phases based on the DSC results

  8. Thermal study on the impurity effect on thermodynamic stability of the glacial phase in triphenyl phosphite-triphenyl phosphate system

    Energy Technology Data Exchange (ETDEWEB)

    Tanabe, Ikue [Department of Chemistry, Naruto University of Education, Naruto, Tokushima 772-8502 (Japan); Takeda, Kiyoshi [Department of Chemistry, Naruto University of Education, Naruto, Tokushima 772-8502 (Japan)]. E-mail: takeda@naruto-u.ac.jp; Murata, Katsuo [Department of Chemistry, Naruto University of Education, Naruto, Tokushima 772-8502 (Japan)

    2005-06-15

    To investigate the impurity effect on thermodynamic stability of the glacial phase, an apparently amorphous metastable phase observed in triphenyl phosphite (TPP), the differential scanning calorimetry (DSC) was carried out in the temperature range 120-350 K for binary mixtures between TPP and triphenyl phosphate (TPPO). Heating up from the glassy liquid, supercooled liquid phase transformed into glacial phase below the crystallization temperature for all the samples with x < 0.2, where x denotes the mole fraction of TPPO. Both transformation temperatures from liquid to glacial and from glacial to crystal increased and temperature range that glacial phase appears narrowed with the content of TPPO. The peak intensity of exothermic effect due to the transformation from liquid to glacial becomes larger whereas that from glacial to crystal reduced. The kinetic and thermodynamic stabilities were discussed for liquid and glacial phases based on the DSC results.

  9. Kisameet Glacial Clay: an Unexpected Source of Bacterial Diversity.

    Science.gov (United States)

    Svensson, Sarah L; Behroozian, Shekooh; Xu, Wanjing; Surette, Michael G; Li, Loretta; Davies, Julian

    2017-05-23

    Widespread antibiotic resistance among bacterial pathogens is providing the impetus to explore novel sources of antimicrobial agents. Recently, the potent antibacterial activity of certain clay minerals has stimulated scientific interest in these materials. One such example is Kisameet glacial clay (KC), an antibacterial clay from a deposit on the central coast of British Columbia, Canada. However, our understanding of the active principles of these complex natural substances is incomplete. Like soils, clays may possess complex mixtures of bacterial taxa, including the Actinobacteria , a clade known to be rich in antibiotic-producing organisms. Here, we present the first characterization of both the microbial and geochemical characteristics of a glacial clay deposit. KC harbors surprising bacterial species richness, with at least three distinct community types. We show that the deposit has clines of inorganic elements that can be leached by pH, which may be drivers of community structure. We also note the prevalence of Gallionellaceae in samples recovered near the surface, as well as taxa that include medically or economically important bacteria such as Actinomycetes and Paenibacillus These results provide insight into the microbial taxa that may be the source of KC antibacterial activity and suggest that natural clays may be rich sources of microbial and molecular diversity. IMPORTANCE Identifying and characterizing the resident microbial populations (bacteria, viruses, protozoa, and fungi) is key to understanding the ecology, chemistry, and homeostasis of virtually all sites on Earth. The Kisameet Bay deposit in British Columbia, Canada, holds a novel glacial clay with a history of medicinal use by local indigenous people. We previously showed that it has potent activity against a variety of antibiotic-resistant bacteria, suggesting it could complement our dwindling arsenal of antibiotics. Here, we have characterized the microbiome of this deposit to gain insight

  10. Evolution of high-Arctic glacial landforms during deglaciation

    Science.gov (United States)

    Midgley, N. G.; Tonkin, T. N.; Graham, D. J.; Cook, S. J.

    2018-06-01

    Glacial landsystems in the high-Arctic have been reported to undergo geomorphological transformation during deglaciation. This research evaluates moraine evolution over a decadal timescale at Midtre Lovénbreen, Svalbard. This work is of interest because glacial landforms developed in Svalbard have been used as an analogue for landforms developed during Pleistocene mid-latitude glaciation. Ground penetrating radar was used to investigate the subsurface characteristics of moraines. To determine surface change, a LiDAR topographic data set (obtained 2003) and a UAV-derived (obtained 2014) digital surface model processed using structure-from-motion (SfM) are also compared. Evaluation of these data sets together enables subsurface character and landform response to climatic amelioration to be linked. Ground penetrating radar evidence shows that the moraine substrate at Midtre Lovénbreen includes ice-rich (radar velocities of 0.17 m ns-1) and debris-rich (radar velocities of 0.1-0.13 m ns-1) zones. The ice-rich zones are demonstrated to exhibit relatively high rates of surface change (mean thresholded rate of -4.39 m over the 11-year observation period). However, the debris-rich zones show a relatively low rate of surface change (mean thresholded rate of -0.98 m over the 11-year observation period), and the morphology of the debris-rich landforms appear stable over the observation period. A complex response of proglacial landforms to climatic warming is shown to occur within and between glacier forelands as indicated by spatially variable surface lowering rates. Landform response is controlled by the ice-debris balance of the moraine substrate, along with the topographic context (such as the influence of meltwater). Site-specific characteristics such as surface debris thickness and glaciofluvial drainage are, therefore, argued to be a highly important control on surface evolution in ice-cored terrain, resulting in a diverse response of high-Arctic glacial landsystems

  11. Southern westerly winds: a pacemaker of Holocene glacial fluctuations in Patagonia?

    Science.gov (United States)

    Sagredo, E. A.; Reynhout, S.; Kaplan, M. R.; Patricio, M. I.; Aravena, J. C.; Martini, M. A.; Schaefer, J. M.

    2017-12-01

    A well-resolved glacial chronology is crucial to compare sequences of glacial/climate events within and between regions, and thus, to unravel mechanisms underlying past climate changes. Important efforts have been made towards understanding the Holocene climate evolution of the Southern Andes; however, the timing, patterns and causes of glacial fluctuations during this period still remain elusive. Recent advances in terrestrial cosmogenic nuclide surface exposure dating, together with the establishment of a Patagonian 10Be production rate, have opened new possibilities for establishing high-resolution glacial chronologies at centennial/decadal scale. Here we present a 10Be surface exposure chronology of fluctuations of a small, climate-sensitive mountain glacier at Mt. Fitz Roy area (49.3°S), spanning from the last glacial termination to the present. Thirty new 10Be ages show glacial advances and moraine building events at 17.1±0.9 ka, 13.5±0.5 ka, 10.2±0.7 ka or 9.9±0.5 ka, 6.9±0.2 ka, 6.1±0.3 ka, 4.5±0.2 ka and 0.5±0.1 ka. Similar to the pattern observed in New Zealand, this sequence features progressively less extensive glacial advances during the late-glacial and early Holocene, followed by advances of roughly similar extent during the mid- to late-Holocene. We suggest that while the magnitude of Holocene glacial fluctuations in Patagonia is modulated by SH summer insolation ("modulator"), the specific timing of these glacial events is influenced by centennial-scale shifts of the Southern Westerly Winds ("pacemaker").

  12. Wetland methane emissions during the Last Glacial Maximum estimated from PMIP2 simulations: climate, vegetation and geographic controls

    NARCIS (Netherlands)

    Weber, S.L.; Drury, A.J.; Toonen, W.H.J.; Weele, M. van

    2010-01-01

    It is an open question to what extent wetlands contributed to the interglacial‐glacial decrease in atmospheric methane concentration. Here we estimate methane emissions from glacial wetlands, using newly available PMIP2 simulations of the Last Glacial Maximum (LGM) climate from coupled

  13. Genetic signature of Last Glacial Maximum regional refugia in a circum-Antarctic sea spider

    Science.gov (United States)

    Soler-Membrives, Anna; Linse, Katrin; Miller, Karen J.; Arango, Claudia P.

    2017-10-01

    The evolutionary history of Antarctic organisms is becoming increasingly important to understand and manage population trajectories under rapid environmental change. The Antarctic sea spider Nymphon australe, with an apparently large population size compared with other sea spider species, is an ideal target to look for molecular signatures of past climatic events. We analysed mitochondrial DNA of specimens collected from the Antarctic continent and two Antarctic islands (AI) to infer past population processes and understand current genetic structure. Demographic history analyses suggest populations survived in refugia during the Last Glacial Maximum. The high genetic diversity found in the Antarctic Peninsula and East Antarctic (EA) seems related to multiple demographic contraction-expansion events associated with deep-sea refugia, while the low genetic diversity in the Weddell Sea points to a more recent expansion from a shelf refugium. We suggest the genetic structure of N. australe from AI reflects recent colonization from the continent. At a local level, EA populations reveal generally low genetic differentiation, geographically and bathymetrically, suggesting limited restrictions to dispersal. Results highlight regional differences in demographic histories and how these relate to the variation in intensity of glaciation-deglaciation events around Antarctica, critical for the study of local evolutionary processes. These are valuable data for understanding the remarkable success of Antarctic pycnogonids, and how environmental changes have shaped the evolution and diversification of Southern Ocean benthic biodiversity.

  14. Late-glacial and Holocene history of changes in Quelccaya Ice Cap, Peru

    Science.gov (United States)

    Kelly, M. A.; Lowell, T. V.; Schaefer, J. M.; Finkel, R. C.

    2008-12-01

    Quelccaya Ice Cap in the southeastern Peruvian Andes (~13-14° S latitude) is an icon for climate change. Its rapidly receding outlet, Qori Kalis Glacier, has been monitored since the 1970's. Cores from Quelccaya Ice Cap provide high-resolution information about temperature and precipitation during the past 1,500 years. We extend the understanding of past changes in Quelccaya Ice Cap based on mapping and dating of glacial moraines and associated deposits. Our results include fifty 10Be ages of moraines and bedrock as well as twenty-nine 14C ages of organic material associated with moraines. These results form the basis of a chronology of changes in Quelccaya Ice Cap from ~16,000 yr BP to late Holocene time. Results from 10Be and 14C dating indicate that Quelccaya Ice Cap experienced a significant advance at 12,700-11,400 yr BP. Subsequent to this advance, the ice margin deposited at least three recessional moraine sets. Quelccaya Ice Cap receded to near its present-day margin by ~10,000 yr BP. Neoglacial advances began by ~3,000 yr BP and culminated with a maximum advance during the Little Ice Age. This chronology fits well with prior work which indicates a restricted Quelccaya Ice Cap during middle Holocene time. Moreover, the overlap between moraine and ice core data for the last 1,500 years provides a unique opportunity to assess the influences of temperature and precipitation on past ice cap extents.

  15. Last glacial megafaunal death assemblage and early human occupation at Lake Menindee, southeastern Australia

    Science.gov (United States)

    Cupper, Matthew L.; Duncan, Jacqui

    2006-09-01

    The Tedford subfossil locality at Lake Menindee preserves a diverse assemblage of marsupials, monotremes and placental rodents. Of the 38 mammal taxa recorded at the site, almost a third are of extinct megafauna. Some of the bones are articulated or semi-articulated and include almost complete skeletons, indicating that aeolian sediments rapidly buried the animals following death. New optical ages show the site dates to the early part of the last glacial (55,700 ± 1300 yr weighted mean age). This is close to the 51,200-39,800 yr Australia-wide extinction age for megafauna suggested by Roberts et al. [2001, Science 292:1888-1892], but like all previous researchers, we cannot conclusively determine whether humans were implicated in the deaths of the animals. Although an intrusive hearth at the site dating to 45,100 ± 1400 yr ago is the oldest evidence of human occupation of the Darling River, no artifacts were identified in situ within the sub-fossil-bearing unit. Non-anthropogenic causes, such as natural senescence or ecosystem stress due to climatic aridity, probably explain the mortality of the faunal assemblage at Lake Menindee.

  16. Paleoclimatic implications of glacial<