WorldWideScience

Sample records for rapid glacial retreat

  1. Holocene Glacial Retreat at Walgreen Coast, West Antarctica

    Science.gov (United States)

    Lindow, J.; Johnson, J.; Castex, M.; Wittmann, H.; Smith, J.; Lisker, F.; Gohl, K.; Spiegel, C.

    2012-12-01

    The Walgreen Coast of West Antarctica represents one of the most rapidly changing sectors of the West Antarctic Ice Sheet (WAIS). With the fastest ice streams in the whole Antarctic, the WAIS is characterised by rapid thinning and grounding line retreat. Airborne and satellite-based short-term observations show a doubling of the negative net mass balance between 1996-2006 (Rignot et al., 2008). Furthermore, because the WAIS is largely grounded below sea level, continued inland thinning and grounding line retreat could result in rapid ice sheet collapse, which would raise global sea level by between 3-5 m. However, due to remoteness and challenging accessibility, onshore data is limited to a few isolated nunataks making it difficult to assess the long-term evolution of the glacial dynamics along Walgreen Coast. To address this we present new data from two key areas of the Walgreen Coast; the Kohler Range and the Pine Island Bay. Our 10Be surface exposure ages from erratic boulders in the Kohler Range are the first and reveal that this area became ice-free between 8.3 and 12.3 ka. This implies a long-term thinning rate of 3.3 cm/yr and agrees with similar data published from glaciers eastward. Our ages are also consistent with recent deglaciation models which suggest strong thinning after 15 ka and off-shore sediments shows a concurrent lateral ice-shelf front retreat. Our results suggest an ice-cover at least 300 m thicker in the Kohler Range during the early Holocene and that subsequent average thinning occurred on rates one order of magnitude slower than recent satellite measurements show. This implies that the recent trend in ice-sheet thinning results from a recent dynamic changes rather than a response to long-term thinning. To further constrain the lateral deglaciation history along the eastern Walgreen Coast, namely the Pine Island Glacier, we collected additional samples from a chain of islands, located flow-parallel and downstream of the ice-shelf front. We

  2. Glacial Retreat and Associated Glacial Lake Hazards in the High Tien Shan

    Science.gov (United States)

    Smith, T. T.

    2013-12-01

    A number of studies have identified glacial retreat throughout the greater Himalayan region over the past few decades, but the Karakorum region remains an anomaly with large stagnating or advancing glaciers. The glacial behavior in the Tien Shan is still unclear, as few studies have investigated mass balances in the region. This study focuses on the highest peaks of the Tien Shan mountain range, in the region of Jengish Chokusu along the Kyrgyzstan-China-Kazakhstan border. In a first step, a 30-year time series of Landsat imagery (n=27) and ASTER imagery (n=10) was developed to track glacial growth and retreat in the region. Using a combination of spectral and topographic information, glacial outlines are automatically delineated. As several important glaciers in the study region contain medium to high levels of debris cover, our algorithm also improves upon current methods of detecting debris-covered glaciers by using topography, distance weighting methods, river networks, and additional spectral data. Linked to glacial retreat are glacial lake outburst floods (GLOFs) that have become increasingly common in High Mountain Asia over the last few decades. As glaciers retreat, their melt water is often trapped by weakly bonded moraines. These moraines have been known to fail due to overtopping caused by surge waves created by avalanches, rockslides, or glacial calving. A suite of studies throughout High Mountain Asia have used remotely-sensed data to monitor the formation and growth of glacial lakes. In a second step of the work, lake-area changes over the past 15 years were tracked monthly and seasonally using dense Landsat/ASTER coverage (n=30) with an automatic procedure based on spectral and topographic information. Previous work has identified GLOFs as a significant process for infrastructural damage in the southern Tien Shan/northern Pamir, as well as in the better studied Himalaya region. Lake identification and quantification of lake-growth rates is a valuable

  3. Retreat patterns and dynamics of the Sentralbankrenna glacial system, central Barents Sea

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    Esteves, Mariana; Bjarnadóttir, Lilja R.; Winsborrow, Monica C. M.; Shackleton, Calvin S.; Andreassen, Karin

    2017-08-01

    The Barents Sea Ice Sheet (BSIS) is a good palaeo-analogue for the present day West Antarctic Ice Sheet. Both were marine-based ice sheets, particularly vulnerable to ocean warming and sea-level rise. Understanding the BSIS ice dynamics and patterns of retreat since the Last Glacial Maximum (LGM) is useful in developing our knowledge of spatial and temporal variations during marine-based ice sheet retreat. While the western margins of the Barents Sea have been extensively studied, few studies have focused on the central regions, which hosted key ice stream tributaries and major ice domes and divides. Presenting a new high-resolution (5 m) bathymetric dataset, this glacial geomorphological study focuses on the Sentralbankrenna palaeo-glacial system in the central Barents Sea. A large number of grounding zone wedges, mega-scale glacial lineations and areas with tunnel valleys and palaeo-subglacial basins were identified. These form the basis for a six-stage reconstruction of ice stream retreat through deglaciation since the LGM. In reconstructing the retreat of the Sentralbankrenna Ice Stream, we document the rapid but highly spatially variable pattern of retreat of a marine-based ice sheet margin. The presence of several tunnel valleys and interconnected palaeo-subglacial basin systems indicates an abundance of meltwater, likely to have been stored and released through several discharge events, significantly influencing the ice stream margin dynamics. This study provides insight into the behaviour and dynamics of ice during the late stages of the BSIS deglaciation within the central Barents Sea, increasing our understanding of grounding line processes.

  4. Heterotrophic microbial communities use ancient carbon following glacial retreat.

    Science.gov (United States)

    Bardgett, Richard D; Richter, Andreas; Bol, Roland; Garnett, Mark H; Bäumler, Rupert; Xu, Xinliang; Lopez-Capel, Elisa; Manning, David A C; Hobbs, Phil J; Hartley, Ian R; Wanek, Wolfgang

    2007-10-22

    When glaciers retreat they expose barren substrates that become colonized by organisms, beginning the process of primary succession. Recent studies reveal that heterotrophic microbial communities occur in newly exposed glacial substrates before autotrophic succession begins. This raises questions about how heterotrophic microbial communities function in the absence of carbon inputs from autotrophs. We measured patterns of soil organic matter development and changes in microbial community composition and carbon use along a 150-year chronosequence of a retreating glacier in the Austrian Alps. We found that soil microbial communities of recently deglaciated terrain differed markedly from those of later successional stages, being of lower biomass and higher abundance of bacteria relative to fungi. Moreover, we found that these initial microbial communities used ancient and recalcitrant carbon as an energy source, along with modern carbon. Only after more than 50 years of organic matter accumulation did the soil microbial community change to one supported primarily by modern carbon, most likely from recent plant production. Our findings suggest the existence of an initial stage of heterotrophic microbial community development that precedes autotrophic community assembly and is sustained, in part, by ancient carbon.

  5. The history of retreat dynamics of Petermann Glacier inferred from submarine glacial landforms

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    Jakobsson, M.; Hogan, K.; Mayer, L. A.; Mix, A. C.; Jerram, K.; Mohammad, R.; Stranne, C.; Eriksson, B.

    2016-12-01

    Preserved submarine glacial landforms produced at the base and margin of ice sheets and outlet glaciers comprise records of past ice dynamics complementary to modern glaciological process studies. The Petermann 2015 Expedition on the Swedish icebreaker Oden systematically mapped approximately 3100 km2 of the seafloor in Petermann Fjord and the adjacent Hall Basin of Nares Strait, northwest Greenland, with an EM122 (12 kHz) multibeam and SBP120 (2-7 kHz) chirp sub-bottom profiler. Complete, overlapping mapping coverage permitted compilation of a high-quality (15x15m) digital terrain model (DTM). In addition, the seafloor at the margin of one of the smaller outlet glaciers draining into the Petermann Fjord and selected shallow areas along the coast were mapped using a small survey boat (RV Skidbladner), equipped with an EM2040 (200-300 kHz) multibeam. High-resolution (2 x 2 m) DTMs were compiled from the RV Skidbladner surveys. The seafloor morphology of Petermann Fjord and adjacent Hall Basin is dominated by a stunning glacial landform record comprising the imprints of Petermann Glacier's retreat dynamics since the Last Glacial Maximum (LGM). The entrance to Petermann Fjord consists of a prominent bathymetric sill formed by a large well-develop grounding zone wedge that undoubtedly represents a stability point during the glacier's retreat history. The deepest entrance to the fjord is 443 m and located on the southern side of this grounding zone wedge. Outside of this grounding zone wedge in Hall Basin, less well developed grounding zones appears to be present. The landform assemblage in between the grounding zones, in particular the lack of retreat ridges, may signify a leap-frog behavior of the glacier's retreat; rapid break-up and disintegration of the outlet glacier causing retreat back to the next stability point dictated by the local bedrock geology. While numerous classical glacial landforms characteristic for fast flowing ice streams are identified, the

  6. Historical aerial imagery reveals rapid frontal retreat following the 1920’s warming in southeast Greenland

    DEFF Research Database (Denmark)

    Bjørk, Anders Anker; Kjær, Kurt H.; Korsgaard, Niels Jákup

    in the similarity of the retreat following the early century warming and the latest decade, with a majority of the 132 glaciers exhibiting larger retreat rates in the early period. Furthermore, during the mid century cooling glaciers in southeast Greenland showed a surprisingly rapid response to the cooling......The Greenland ice sheet (GIS) is undergoing massive changes in its frontal positions, velocity structure, and overall mass balance. Since 2000, marine and terrestrial terminating glaciers in southeast Greenland have experienced dramatic frontal retreat and dynamic thinning in response to increased...... demonstrate decadal sensitivity to temperature changes with rapid retreat following the early century warming (1919-1932) and glacial advance during a minor, but profound mid century cooling (1955-1972) succeeded by the present warming again leading to massive retreat. One significant finding lies...

  7. Ice stream reorganization and glacial retreat on the northwest Greenland shelf

    Science.gov (United States)

    Newton, A. M. W.; Knutz, P. C.; Huuse, M.; Gannon, P.; Brocklehurst, S. H.; Clausen, O. R.; Gong, Y.

    2017-08-01

    Understanding conditions at the grounding-line of marine-based ice sheets is essential for understanding ice sheet evolution. Offshore northwest Greenland, knowledge of the Last Glacial Maximum (LGM) ice sheet extent in Melville Bugt was previously based on sparse geological evidence. This study uses multibeam bathymetry, combined with 2-D and 3-D seismic reflection data, to present a detailed landform record from Melville Bugt. Seabed landforms include mega-scale glacial lineations, grounding-zone wedges, iceberg scours, and a lateral shear margin moraine, formed during the last glacial cycle. The geomorphology indicates that the LGM ice sheet reached the shelf edge before undergoing flow reorganization. After retreat of 80 km across the outer shelf, the margin stabilized in a mid-shelf position, possibly during the Younger Dryas (12.9-11.7 ka). The ice sheet then decoupled from the seafloor and retreated to a coast-proximal position. This landform record provides an important constraint on deglaciation history offshore northwest Greenland.

  8. Kame deltas provide evidence for a new glacial lake and suggest early glacial retreat from central Lower Michigan, USA

    Science.gov (United States)

    Schaetzl, Randall J.; Lepper, Kenneth; Thomas, Sarah E.; Grove, Leslie; Treiber, Emma; Farmer, Alison; Fillmore, Austin; Lee, Jordan; Dickerson, Bethany; Alme, Kayleigh

    2017-03-01

    In association with an undergraduate Honors Seminar at Michigan State University, we studied two small kame deltas in north-central Lower Michigan. These recently identified deltas provide clear evidence for a previously unknown proglacial lake (Glacial Lake Roscommon) in this large basin located in an interlobate upland. Our first goal was to document and characterize the geomorphology of these deltas. Because both deltas are tied to ice-contact ridges that mark the former position of the retreating ice margin within the lake, our second goal was to establish the age of one of the deltas, thereby constraining the timing of ice retreat in this part of Michigan, for which little information currently exists. Both deltas are composed of well-sorted fine and medium sands with little gravel, and have broad, nearly flat surfaces and comparatively steep fronts. Samples taken from the upper 1.5 m of the deltas show little spatial variation in texture, aside from a general fining toward their outer margins. Gullies on the outer margins of both deltas probably postdate the formation of the deltas proper; we suggest that they formed by runoff during a permafrost period, subsequent to lake drawdown. We named the ice lobe that once covered this area the Mackinac Lobe, because it had likely advanced into the region across the Mackinac Straits area. Five of six optically stimulated luminescence (OSL) ages from one of the deltas had minimal scatter and were within ± 1000 years of one another, with a mean age of 23.1 ± 0.4 ka. These ages suggest that the Mackinac Lobe had started to retreat from the region considerably earlier than previously thought, even while ice was near its maximum extent in Illinois and Indiana, and the remainder of Michigan was ice-covered. This early retreat, which appears to coincide with a short-lived warm period indicated from the Greenland ice core, formed an "opening" that was at least occasionally flooded. Thick and deep, fine-textured deposits

  9. Linking permafrost distribution, glacial retreat and colluvial sediment dynamics in the Saldur River basin, Eastern Italian Alps

    Science.gov (United States)

    Brardinoni, Francesco; Sosio, Rosanna; Scotti, Riccardo; Cavalli, Marco; Comiti, Francesco; Mair, Volkmar

    2014-05-01

    In the last three decades generalized atmospheric temperature rise has produced rapid glacial retreat and permafrost degradation in high mountain environments of the European Alps. While it is widely recognized that these changes can impart general instability to mountain slopes (i.e., several projects have documented single case studies of high magnitude-low frequency, catastrophic slope failures), to our knowledge, there appears to be little empirical data available for investigating the spatial distribution of mass-wasting intensity through time in high mountain areas in relation to permafrost degradation and deglaciation patterns. This is a critical shortcoming. Understanding and quantifying the influence of similar transient conditions on mass-wasting processes holds critical long-term implications on the overall sediment flux reshaping mountain landscapes (e.g., post-LGM landscape evolution), as well as more practical short-term applications on water quality issues, damage control/prevention to infrastructure, and reservoir siltation, to mention some. In this contribution we present an integrated approach that aims to: (i) document the spatial distribution of mass-wasting activity and sediment production in the Saldur River basin (97 km^2); (ii) detect causal linkages between mass-wasting intensity, the potential spatial distribution of discontinuous permafrost, and patterns of glacier retreat; and (iii) identify source-to-sink colluvial sedimentary pathways as modulated by the spatial organization of glacial and periglacial landforms. To these ends, we map rock glaciers, protalus ramparts and moraines, and compile a field- and air photo-based multi-temporal (1959-2012) inventory of colluvial sediment sources. We then combine these data with two historical datasets of debris flow and landslide events (both implemented and maintained by the Autonomous Province of Bolzano) and analyse mass-wasting spatial distribution and intensity in relation to proximity of

  10. Ice sheet retreat dynamics inferred from glacial morphology of the central Pine Island Bay Trough, West Antarctica

    Science.gov (United States)

    Jakobsson, Martin; Anderson, John B.; Nitsche, Frank O.; Gyllencreutz, Richard; Kirshner, Alexandra E.; Kirchner, Nina; O'Regan, Matthew; Mohammad, Rezwan; Eriksson, Björn

    2012-03-01

    Pine Island Glacier drains portions of the West Antarctic Ice Sheet into the Amundsen Sea. During the Last Glacial Maximum the glacier extended nearly 500 km from its present location onto the outer continental shelf. Unusually restricted sea-ice cover during the austral summer of 2010 allowed for a systematic multibeam swath-bathymetric and chirp sonar survey of the mid-shelf section of Pine Island Trough. The mapped glacial landforms reveal new information about the paleo-Pine Island Ice Stream's dynamic retreat from the mid-shelf area and confirm previous suggestion of a retreat in distinct steps. The periods of grounding line stability during the overall retreat phase are marked by sediment accumulations, i.e. grounding zone wedges. These wedges are here mapped in sufficient detail to characterize spatial dimensions and estimate the volume of deposited sediment. Considering a range of sediment flux rates from the paleo-Pine Island Ice Stream we estimate that the largest and most clearly defined grounding zone wedge, located at about 73°S in the surveyed area, took between 600 and 2000 years to form. The ice stream retreated landward of this wedge before 12.3 cal ka BP. The swath-bathymetric imagery of landforms in Pine Island Trough includes glacial features that suggest that retreat between periods of grounding line stability may be associated with episodes of ice shelf break-up. The depths of grounding line wedges decrease in a landward direction, from 740 to 670 m, and record elevation of the grounding line as it stepped landward. In all, the grounding line elevation varied by only ˜80 m over a distance of just over 100 km, implying a low ice sheet profile during retreat. Finally, we revisited seismic reflection profile NB9902, acquired along Pine Island Trough in 1999, in combination with the newly acquired swath-bathymetric imagery from 2010. Together these data show that the ice stream paused during its retreat to form grounding zone wedges at an area

  11. Evidence of macroalgal colonization on newly ice-free areas following glacial retreat in Potter Cove (South Shetland Islands), Antarctica.

    Science.gov (United States)

    Quartino, María Liliana; Deregibus, Dolores; Campana, Gabriela Laura; Latorre, Gustavo Edgar Juan; Momo, Fernando Roberto

    2013-01-01

    Climate warming has been related to glacial retreat along the Western Antarctic Peninsula. Over the last years, a visible melting of Fourcade Glacier (Potter Cove, South Shetland Islands) has exposed newly ice-free hard bottom areas available for benthic colonization. However, ice melting produces a reduction of light penetration due to an increase of sediment input and higher ice impact. Seventeen years ago, the coastal sites close to the glacier cliffs were devoid of macroalgae. Are the newly ice-free areas suitable for macroalgal colonization? To tackle this question, underwater video transects were performed at six newly ice-free areas with different degree of glacial influence. Macroalgae were found in all sites, even in close proximity to the retreating glacier. We can show that: 1. The complexity of the macroalgal community is positively correlated to the elapsed time from the ice retreat, 2. Algae development depends on the optical conditions and the sediment input in the water column; some species are limited by light availability, 3. Macroalgal colonization is negatively affected by the ice disturbance, 4. The colonization is determined by the size and type of substrate and by the slope of the bottom. As macroalgae are probably one of the main energy sources for the benthos, an expansion of the macroalgal distribution can be expected to affect the matter and energy fluxes in Potter Cove ecosystem.

  12. Evidence of macroalgal colonization on newly ice-free areas following glacial retreat in Potter Cove (South Shetland Islands, Antarctica.

    Directory of Open Access Journals (Sweden)

    María Liliana Quartino

    Full Text Available Climate warming has been related to glacial retreat along the Western Antarctic Peninsula. Over the last years, a visible melting of Fourcade Glacier (Potter Cove, South Shetland Islands has exposed newly ice-free hard bottom areas available for benthic colonization. However, ice melting produces a reduction of light penetration due to an increase of sediment input and higher ice impact. Seventeen years ago, the coastal sites close to the glacier cliffs were devoid of macroalgae. Are the newly ice-free areas suitable for macroalgal colonization? To tackle this question, underwater video transects were performed at six newly ice-free areas with different degree of glacial influence. Macroalgae were found in all sites, even in close proximity to the retreating glacier. We can show that: 1. The complexity of the macroalgal community is positively correlated to the elapsed time from the ice retreat, 2. Algae development depends on the optical conditions and the sediment input in the water column; some species are limited by light availability, 3. Macroalgal colonization is negatively affected by the ice disturbance, 4. The colonization is determined by the size and type of substrate and by the slope of the bottom. As macroalgae are probably one of the main energy sources for the benthos, an expansion of the macroalgal distribution can be expected to affect the matter and energy fluxes in Potter Cove ecosystem.

  13. Heterogeneous glacial lake changes and links of lake expansions to the rapid thinning of adjacent glacier termini in the Himalayas

    Science.gov (United States)

    Song, Chunqiao; Sheng, Yongwei; Wang, Jida; Ke, Linghong; Madson, Austin; Nie, Yong

    2017-03-01

    Glacier mass loss in the Himalayas has far-reaching implications for the alteration of regional hydrologic regimes, an increased risk of glacial lake outburst, downstream water resource abundance, and contributions to sea level rise. However, the mass losses of Himalayan glaciers are not well understood towing to the scarcity of observations and the heterogeneous responses of Himalayan glaciers to climate change and local factors (e.g., glacier surge, interacting with proglacial lakes). In particular, there is a lack of understanding on the unique interactions between moraine-dammed glacial lakes and their effects on debris cover on valley glacier termini. In this study, we examined the temporal evolution of 151 large glacial lakes across the Himalayas and then classified these glacial lakes into three categories: proglacial lakes in contact with full or partial debris-covered glaciers (debris-contact lakes), ice cliff-contact lakes, and non-glacier-contact lakes. The results show that debris-contact lakes experienced a dramatic areal increase of 36.5% over the years 2000 to 2014, while the latter two categories of lakes remained generally stable. The majority of lake expansions occurred at the glacier front without marked lake level rises. This suggests that the rapid expansion of these debris-contact lakes can be largely attributed to the thinning of debris-covered ice as caused by the melting of glacial fronts and the subsequent glacial retreat. We reconstructed the height variations of glacier fronts in contact with 57 different proglacial lakes during the years 2000 to 2014. These reconstructed surface elevation changes of debris-covered, lake-contact glacier fronts reveal significant thinning trends with considerable lowering rates that range from 1.0 to 9.7 m/y. Our study reveals that a substantial average ice thinning of 3.9 m/y occurred at the glacier fronts that are in contact with glacial lakes.

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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

  18. Rapid ocean-atmosphere response to Southern Ocean freshening during the last glacial period

    Science.gov (United States)

    Turney, Christian; Jones, Richard; Phipps, Steven; Thomas, Zoë; Hogg, Alan; Kershaw, Peter; Fogwill, Christopher; Palmer, Jonathan; Bronk Ramsey, Christopher; Adolphi, Florian; Muscheler, Raimund; Hughen, Konrad; Staff, Richard; Grosvenor, Mark; Golledge, Nicholas; Rasmussen, Sune; Hutchinson, David; Haberle, Simon; Lorrey, Andrew; Boswijk, Gretel

    2017-04-01

    Contrasting Greenland and Antarctic temperature trends during the late last glacial period (60,000 to 11,703 years ago) are thought to be driven by imbalances in the rate of formation of North Atlantic and Antarctic Deep Water (the 'bipolar seesaw'), with cooling in the north leading the onset of warming in the south. Some events, however, appear to have occurred independently of changes in deep water formation but still have a southern expression, implying that an alternative mechanism may have driven some global climatic changes during the glacial. Testing these competing hypotheses is challenging given the relatively large uncertainties associated with correlating terrestrial, marine and ice core records of abrupt change. Here we exploit a bidecadally-resolved 14C calibration dataset obtained from New Zealand kauri (Agathis australis) to undertake high-precision alignment of key climate datasets spanning 28,400 to 30,400 years ago. We observe no divergence between terrestrial and marine 14C datasets implying limited impact of freshwater hosing on the Atlantic Meridional Overturning Circulation (AMOC). However, an ice-rafted debris event (SA2) in Southern Ocean waters appears to be associated with dramatic synchronous warming over the North Atlantic and contrasting precipitation patterns across the low latitudes. Using a fully coupled climate system model we undertook an ensemble of transient meltwater simulations and find that a southern salinity anomaly can trigger low-latitude temperature changes through barotropic and baroclinic oceanic waves that are atmospherically propagated globally via a Rossby wave train, consistent with contemporary modelling studies. Our results suggest the Antarctic ice sheets and Southern Ocean dynamics may have contributed to some global climatic changes through rapid ocean-atmospheric teleconnections, with implications for past (and future) change.

  19. A rapidly growing moraine-dammed glacial lake on Ngozumpa Glacier, Nepal

    Science.gov (United States)

    Thompson, Sarah S.; Benn, Douglas I.; Dennis, Kathryn; Luckman, Adrian

    2012-04-01

    Moraine-dammed glacial lakes are becoming increasingly common in the Himalaya as a result of glacier mass loss, causing concern about glacier lake outburst flood risk. In addition to extant lakes, the potential exists for many more to form, as more glaciers ablate down to the level of potential moraine dams. In this paper, we document the recent rapid growth of, a moraine-dammed lake on Ngozumpa Glacier, Nepal. Using a combination of ground-based mapping and sonar surveys, aerial photographs (< 1 m resolution), and ASTER imagery (15 m resolution), processes and rates of lake expansion have been determined. The lake first formed between 1984 and 1992 when collapse of an englacial conduit allowed water to accumulate at the level of a gap in the lateral moraine, ~km from the glacier terminus. Lake growth was initially slow, but since 2001 it has undergone exponential growth at an average rate of 10% y-1. In 2009, the lake area was 300,000 m2, and its volume was at least 2.2 million m3. Calving, subaqueous melting, and melting of subaerial ice faces all contribute to the expansion of the lake; but large-scale, full-height slab calving is now the dominant contributor to growth. Comparison with other lakes in the region indicate that lake growth will likely continue unchecked whilst the spillway remains at its current level and may attain a volume of hundreds of millions of cubic metres within the next few decades.

  20. The early rise and late demise of New Zealand's last glacial maximum.

    Science.gov (United States)

    Rother, Henrik; Fink, David; Shulmeister, James; Mifsud, Charles; Evans, Michael; Pugh, Jeremy

    2014-08-12

    Recent debate on records of southern midlatitude glaciation has focused on reconstructing glacier dynamics during the last glacial termination, with different results supporting both in-phase and out-of-phase correlations with Northern Hemisphere glacial signals. A continuing major weakness in this debate is the lack of robust data, particularly from the early and maximum phase of southern midlatitude glaciation (∼30-20 ka), to verify the competing models. Here we present a suite of 58 cosmogenic exposure ages from 17 last-glacial ice limits in the Rangitata Valley of New Zealand, capturing an extensive record of glacial oscillations between 28-16 ka. The sequence shows that the local last glacial maximum in this region occurred shortly before 28 ka, followed by several successively less extensive ice readvances between 26-19 ka. The onset of Termination 1 and the ensuing glacial retreat is preserved in exceptional detail through numerous recessional moraines, indicating that ice retreat between 19-16 ka was very gradual. Extensive valley glaciers survived in the Rangitata catchment until at least 15.8 ka. These findings preclude the previously inferred rapid climate-driven ice retreat in the Southern Alps after the onset of Termination 1. Our record documents an early last glacial maximum, an overall trend of diminishing ice volume in New Zealand between 28-20 ka, and gradual deglaciation until at least 15 ka.

  1. Historical aerial imagery reveals rapid frontal retreat following the 1920’s warming in southeast Greenland

    DEFF Research Database (Denmark)

    Bjørk, Anders Anker; Kjær, Kurt H.; Korsgaard, Niels Jákup

    , indicating that stabilization and subsequent advance can occur with a short cooling period. Marine terminating glaciers originating from the GIS experienced the largest frontal fluctuations often out of sync with local glaciers and ice caps indicating a larger coherence with ocean temperatures, whereas local...... glaciers and ice caps and GIS terrestrial terminating glaciers shows frontal fluctuations closely related to the air temperature.......The Greenland ice sheet (GIS) is undergoing massive changes in its frontal positions, velocity structure, and overall mass balance. Since 2000, marine and terrestrial terminating glaciers in southeast Greenland have experienced dramatic frontal retreat and dynamic thinning in response to increased...

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

    Science.gov (United States)

    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

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

    Directory of Open Access Journals (Sweden)

    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

  4. Episodic Neoglacial expansion and rapid 20th century retreat of a small ice cap on Baffin Island, Arctic Canada, and modeled temperature change

    Directory of Open Access Journals (Sweden)

    S. L. Pendleton

    2017-11-01

    Full Text Available Records of Neoglacial glacier activity in the Arctic constructed from moraines are often incomplete due to a preservation bias toward the most extensive advance, often the Little Ice Age. Recent warming in the Arctic has caused extensive retreat of glaciers over the past several decades, exposing preserved landscapes complete with in situ tundra plants previously entombed by ice. The radiocarbon ages of these plants define the timing of snowline depression and glacier advance across the site, in response to local summer cooling. Erosion rapidly removes most dead plants that have been recently exposed by ice retreat, but where erosive processes are unusually weak, dead plants may remain preserved on the landscape for decades. In such settings, a transect of plant radiocarbon ages can be used to construct a near-continuous chronology of past ice margin advance. Here we present radiocarbon dates from the first such transect on Baffin Island, which directly dates the advance of a small ice cap over the past two millennia. The nature of ice expansion between 20 BCE and ∼ 1000 CE is still uncertain, but episodic advances at ∼ 1000 CE, ∼ 1200, and  ∼ 1500 led to the maximum Neoglacial dimensions ~ 1900 CE. We employ a two-dimensional numerical glacier model calibrated using the plant radiocarbon ages ice margin chronology to assess the sensitivity of the ice cap to temperature change. Model experiments show that at least ∼ 0.44 °C of cooling over the past 2 kyr is required for the ice cap to reach its 1900 CE margin, and that the period from ∼ 1000 to 1900 CE must have been at least 0.25° C cooler than the previous millennium, results that agree with regional temperature reconstructions and climate model simulations. However, significant warming since 1900 CE is required to explain retreat to its present position, and, at the same rate of warming, the ice cap will disappear before 2100 CE.

  5. The state and their implication of Himalayan glacial lake changes from satellite observations

    Science.gov (United States)

    Nie, Y.; Sheng, Y.; Liu, Q.; Liu, L.; Liu, S.; Zhang, Y.; Song, C.

    2015-12-01

    Glacial lake outburst floods (GLOFs)generally result in catastrophic damages and fatalities. The Himalayas, the world's highest mountains hosting large number of glaciers, have frequently suffered from GLOFs events in the past decades. Climatic warming-induced melting and retreating glaciers make glacial lakes expand obviously and urge the potential risk of GLOFs in Himalayas. However, our knowledge on the state of glacial lakes in the entire Himalayas is still limited. This study conducts a systematically satellite-based inventory to firstly reveal the evolution complex, regional difference and causes of Himalayan glacial lake changes in the whole Himalayas. Hundreds of Landsat images and Google Earth high resolution imagery were employed to extract the extents of glacial lakes at four epochs (circa1990, circa 2000, circa 2005 and circa 2010). Object-oriented mapping method was used to automatically map the lakes. In association with published glacier data (e.g., China Glacier Inventory, Randolph and GLIMS Glacier data), visual inspections and iterative checks for individual lake guarantee the accuracy of our results. This study demonstrates the spatial and topographic distributions, differences, heterogeneity of glacial lake changes and their causes. Our results show that Himalayan glacial lakes present a rapidly expanding state in general. Both disappeared lakes and new-formed lakes were observed, however, pre-existing glacial lakes contributed most to the total areal expansion. Himalayan glacial lakes appeared a clear altitudinal difference between north side and south side of main range. Evolutions of glacial lakes between eastern, western and central Himalaya were different, and the most rapidly expanding areas need to be more concerned. Climatic and geomorphic controls result in the heterogeneity of glacial lake changes. This study will help assess the potential risk of GLOFs and promote the public awareness of glacial disasters in high mountain areas.

  6. Tidal pumping - missing factor in glacial bays evolution?

    Science.gov (United States)

    Szczucinski, Witold; Moskalik, Mateusz; Dominiczak, Aleksander

    2017-04-01

    Most of the glaciers worldwide are subjected to rapid retreat. It is particularly well visible in Svalbard, where tidewater glaciers after the termination of the Little Ice Age often resulted in formation of new glacial bays. These bays are specific environments, characterised by high sediment accumulation rates, seasonal formation of sea-ice cover and common presence of icebergs. They are usually separated from the rest of the fjord by shallow (e.g. submerged moraine) or narrow passages. Although hostile, these bays also host unique ecosystems, with particular importance as feeding grounds for seals and sea birds. Among factors considered in development of such environments the role of tides is usually neglected or assumed as constant. Here we would like to stress the increasing role of tides in development of glacial bays ecosystems, as well as for import and burial of organic carbon in the bays. We present a model of tide development and results on present day conditions from Brepolen bay in Hornsund (southern Spitsbergen). On the basis of ADCP and CTD surveys we present the modern conditions and water exchange rates between the glacial bay and the fjord. Analysis of archival satellite images, aerial photographs and historical maps was used to map the change in glacial bay area. Finally simple modeling allow to identify a linear increase in tidal pumping magnitude (water exchange due to tides) with increasing glacial bay area due to glaciers retreat. We discuss it in context of potential consequences for bay oceanography, ecology and sedimentation. With fast glacier retreat and rapid grow of glacial bays one may expect the following effects of increasing tidal pumping: enhanced water exchange with the central part of the fjord, increasing salinity, facilitating colonisation by new species (e.g. import of juvenile forms of benthic species), increased input of marine organic carbon into setting suitable for its burial (high sediment accumulation rate in glacial

  7. 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.

  8. Differential timing of C4 plant decline and grassland retreat during the penultimate deglaciation

    Science.gov (United States)

    He, Juan; Jia, Guodong; Li, Li; Wang, Pinxian

    2017-09-01

    Compound-specific stable carbon isotope composition of terrestrial leaf wax n-alkyl lipids (δ13Calk) was measured in sediments from the northern South China Sea (SCS), allowing assessment of vegetation change in the source area within the penultimate glacial cycle during 60-160 kyr. Our δ13Calk record suggested a prominent vegetation contrast between the glacial and the interglacial, with more C4 plant developing during the glaciation and a rapid decline during the glacial termination. This deglacial change in δ13Calk was attributed to an increase in humidity caused by the enhancement of the East Asian Summer Monsoon (EASM). However, the inferred deglacial C4 decline lagged by 4 kyr behind the grass retreat inferred from published pollen record. We argue that the time discrepancy in the two terrestrial plant proxies may have resulted from their differential responses to regional climate change, with grass community structure more sensitive to temperature rise and plant photosynthetic pathway more sensitive to humidity increase. Therefore, an earlier penultimate deglacial warming relative to humidity increase can be inferred from the lead of grass retreat relative to C4 decline, which implies that EASM may be delayed during the deglacial warming.

  9. Do Higher Sea-cliff Retreat Rates Imply Faster Sea-cliff Retreat?

    Science.gov (United States)

    Mushkin, A.; Katz, O.; Porat, N.

    2015-12-01

    Inland retreat of sea cliffs in response to post LGM (last glacial maximum) sea-level rise is an ongoing process that affects coastal environments and communities worldwide. Here, we examine a globally recurring pattern where reported sea-cliff retreat rates since the 20th century often appear to exceed longer-term millennial-scale ('background') rates that rarely exceed ~0.1 m/yr. Focusing on Israel's 30-km-long Mediterranean 'Sharon' sea-cliff as a case study we demonstrate that such apparent increase in rates may also reflect a widely acknowledged sampling bias in geologic rate estimates inferred from observation time windows ('Tobs') shorter than process episodicity. We show that this possible bias leads to an ambiguity in conventional rate estimates obtained by averaging observed retreat distances over Tobs, and that as a result despite ubiquitous and robust observations of cliff retreat since the 20th century (e.g., aerial photographs) recent/current retreat rates for many of the world's episodically retreating sea cliffs remain essentially unknown. To address this present limitation in our ability to detect and quantify recent changes in sea-cliff retreat rates we use airborne LiDAR to measure the continuous wave-driven volumetric erosion of collapsed material from the cliff base as an effective upper-bound constraint for the m/yr rate of episodic retreat of the cliff itself. We find that while conventional retreat rate estimates since the 20th century along the Sharon sea cliff artefactually increase up to several m/yr as an inverse function of Tobs, the LiDAR-constrained retreat rates are not susceptible to this sampling bias, are comparable to the cliff's background retreat rate of 0.03-0.07 m/yr since the mid Holocene and thus indicate no recent acceleration in retreat. This ability to unambiguously constrain sea-cliff retreat rates with annual to decadal-scale observations directly impacts the global-scale push to quantify, better understand and

  10. Rapid retreat of the East Asian summer monsoon in the middle Holocene and a millennial weak monsoon interval at 9 ka in northern China

    Science.gov (United States)

    Dong, Jinguo; Shen, Chuan-Chou; Kong, Xinggong; Wu, Chung-Che; Hu, Hsun-Ming; Ren, Haojia; Wang, Yi

    2018-01-01

    Knowledge of hydroclimatic dynamics in the East Asian monsoon region during the Holocene was hindered by few absolutely-dated and decadally-resolved proxy records in northern China. Here we present replicated carbonate δ18O records of six stalagmites with sub-decadal to multi-decadal resolutions from the Lianhua cave to reveal a detailed evolution of the East Asian Summer Monsoon (EASM) intensity in northern China since 11.5 thousand years before present (ka BP, before 1950 CE). Our composite record shows that solar forcing dominated hydroclimatic changes regionally, including an intensified monsoon at the Holocene Optimum from the termination of Younger Dryas to 6.5 ka BP, and a subsequent multi-millennial weakening monsoon, that agrees with cave records in central and southern China. However, the EASM has retreated southwards more rapidly than the Indian summer monsoon after ∼6.5 ka BP, resulting in aridity conditions occurring at 4.0 ka BP in northern China, which is almost 2000-year earlier than that in central and southern China. This north-south asynchroneity is likely related to the different regional responses among the coupling of the EASM, Indian summer monsoon, the solar forcing, and the differences in thermal forcing due to complex geographical configurations. In addition, a relative enrichment of 1‰ in 18O data of the Lianhua record from 9.5 to 8.1 ka BP shows that the Holocene Optimum was punctuated by a millennial-long weakening monsoon interval, which is not registered among previous cave records in central and southern China. The fresh water-induced cold climate conditions in the North Atlantic region could create stronger East Asian winter monsoon, and induce a weakened EASM and a southward shift of rain belt in northern China. Therefore, it shall not be surprised that there are strong heterogeneities among regional hydroclimatic conditions across monsoonal China, given the complex interplay between external and internal forcing mechanisms

  11. Modelling the dynamics of palaeo ice-stream retreat in Marguerite Bay, Antarctica

    Science.gov (United States)

    Jamieson, S. S.; Vieli, A.; Livingstone, S. J.; Stokes, C. R.; O'Cofaigh, C.; Hillenbrand, C.

    2010-12-01

    The aim is to use numerical models of ice stream behaviour to understand the processes that triggered and controlled the retreat of the Marguerite Bay palaeo ice stream after the Last Glacial Maximum (LGM). This is important because at present a number of marine-based ice streams in Antarctica are rapidly losing mass. Given the consequences of this mass loss for future sea-level rise, it is crucial to improve our understanding and predictive abilities of grounding line retreat of marine-based ice streams. Because contemporary records of grounding line retreat are very short (decades) and may not be representative of behaviour on century or millennial timescales, we focus on the longer-term post-LGM retreat dynamics of the palaeo ice stream as recorded in the marine-geophysical record. Our approach combines numerical modelling with geomorphological mapping in order to understand the processes that triggered and controlled the hypothesized rapid retreat of the Marguerite Bay palaeo ice-stream. Here we describe the numerical model, modelling approach and results of sensitivity testing to understand the behaviour of the Marguerite Bay palaeo ice stream. High-resolution bathymetric data of the Marguerite Bay area has enabled detailed geomorphological mapping and provides a record of grounding line retreat. These mapping data, set into a chronological framework of deglaciation, are used to constrain a 1-dimensional flowline model of the Marguerite palaeo- ice-stream. The numerical model includes basal, lateral and longitudinal stresses and a robust treatment of grounding-line motion through the use of a constantly adjusting spatial grid. We subject the model to a range of external forcing including changes in sea-level, temperature and accumulation in order to reproduce the geomorphological evidence and therefore understand the dynamics of ice stream retreat in this area. We find that slow-downs or re-stabilisations of the grounding line occur in areas of reverse bed

  12. Glacial geomorphology of the northwestern Weddell Sea, eastern Antarctic Peninsula continental shelf: Shifting ice flow patterns during deglaciation

    Science.gov (United States)

    Campo, Jennifer M.; Wellner, Julia S.; Domack, Eugene; Lavoie, Caroline; Yoo, Kyu-Cheul

    2017-03-01

    During the Last Glacial Maximum, grounded ice from the expanded Antarctic Peninsula Ice Sheet extended across the continental shelf. Grounded and flowing ice created a distinctive array of glacial geomorphic features on the sea floor, which were then exposed as the ice sheet retreated. The recent disintegration of the northern parts of the Larsen Ice Shelf (Larsen A and B) have permitted acquisition of marine geophysical data in previously inaccessible and unmapped areas. We present a reconstruction of the evolving ice-flow path and ice sheet geometry of the eastern Antarctic Peninsula, with particular focus paid to newly surveyed areas that shed light on the dynamics of a marine-terminating glacial geomorphic environment, where ice shelves play a major role in grounding line stability. Shifting flow directions were mapped in several areas, including across the Seal Nunataks, which divide Larsen A and B, and offshore of Larsen C, indicating flow reorientation that reflects the changing ice sheet geometry as retreat neared the modern coastline. The measured flow indicators in this area reveal comparatively high elongation ratios (> 20), indicating rapid ice flow. Evidence of possible previous ice-shelf collapses are noted near the shelf break, further illustrating the critical, protective effect that ice shelves impart to marine-terminating glacial environments. Modern ice retreat is governed in part by reorganization of flow patterns accompanying grounding line movement; such reorganizations happened in the past and can aid understanding of modern processes.

  13. 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.

    2016-11-01

    Hydration of silicic volcanic glass forms perlite, a dusky, porous form of altered glass characterized by abundant "onion-skin" fractures. The timing and temperature of perlite formation are enigmatic and could plausibly occur during eruption, during post-eruptive cooling, or much later at ambient temperatures. To learn more about the origin of natural perlite, and to fingerprint the hydration waters, we investigated perlitic glass from several synglacial and interglacial rhyolitic lavas and tuffs from the Yellowstone volcanic system. Perlitic cores are surrounded by a series of conchoidal cracks that separate 30- to 100-µm-thick slivers, likely formed in response to hydration-induced stress. H2O and D/H profiles confirm that most D/H exchange happens together with rapid H2O addition but some smoother D/H variations may suggest separate minor exchange by deuterium atom interdiffusion following hydration. The hydrated rinds (2-3 wt% H2O) transition rapidly (within 30 µm, or by 1 wt% H2O per 10 µm) to unhydrated glass cores. This is consistent with quenched "hydration fronts" where H2O diffusion coefficients are strongly dependent on H2O concentrations. The chemical, δ18O, and δD systematics of bulk glass records last equilibrium between 110 and 60 °C without chemical exchange but with some δ18O exchange. Similarly, the δ18O of water extracted from glass by rapid heating suggests that water was added to the glass during cooling at 400 °C) experimental data. The thick hydration rinds in perlites, measuring hundreds of microns, preserve the original D/H values of hydrating water as a recorder of paleoclimate conditions. Measured δD values in perlitic lavas are -150 to -191 or 20-40 ‰ lower than glass hydrated by modern Yellowstone waters. This suggests that Yellowstone perlites record the low-δD signature of glacial ice. Cooling calculations, combined with the observed high water diffusion coefficients noted for 60-150 °C, suggest that if sufficient hot

  14. 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

    hundreds of microns, preserve the original D/H values of hydrating water as a recorder of paleoclimate conditions. Measured δD values in perlitic lavas are −150 to −191 or 20–40 ‰ lower than glass hydrated by modern Yellowstone waters. This suggests that Yellowstone perlites record the low-δD signature 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.

  15. 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

  16. 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.

  17. Quaternary Glacial Mapping in Western Wisconsin Using Soil Survey Information

    Science.gov (United States)

    Oehlke, Betsy M.; Dolliver, Holly A. S.

    2011-01-01

    The majority of soils in the western Wisconsin have developed from glacial sediments deposited during the Quaternary Period (2.6 million years before present). In many regions, multiple advances and retreats have left a complex landscape of diverse glacial sediments and landforms. The soils that have developed on these deposits reflect the nature…

  18. Ocean forcing of Ice Sheet retreat in central west Greenland from LGM to the early Holocene

    Science.gov (United States)

    Jennings, Anne E.; Andrews, John T.; Ó Cofaigh, Colm; Onge, Guillaume St.; Sheldon, Christina; Belt, Simon T.; Cabedo-Sanz, Patricia; Hillaire-Marcel, Claude

    2017-08-01

    Three radiocarbon dated sediment cores from trough mouth fans on the central west Greenland continental slope were studied to determine the timing and processes of Greenland Ice Sheet (GIS) retreat from the shelf edge during the last deglaciation and to test the role of ocean forcing (i.e. warm ocean water) thereon. Analyses of lithofacies, quantitative x-ray diffraction mineralogy, benthic foraminiferal assemblages, the sea-ice biomarker IP25, and δ18 O of the planktonic foraminifera Neogloboquadrina pachyderma sinistral from sediments in the interval from 17.5-10.8 cal ka BP provide consistent evidence for ocean and ice sheet interactions during central west Greenland (CWG) deglaciation. The Disko and Uummannaq ice streams both retreated from the shelf edge after the last glacial maximum (LGM) under the influence of subsurface, warm Atlantic Water. The warm subsurface water was limited to depths below the ice stream grounding lines during the LGM, when the GIS terminated as a floating ice shelf in a sea-ice covered Baffin Bay. The deeper Uummannaq ice stream retreated first (ca. 17.1 cal ka BP), while the shallower Disko ice stream retreated at ca. 16.2 cal ka BP. The grounding lines were protected from accelerating mass loss (calving) by a buttressing ice shelf and by landward shallowing bathymetry on the outer shelf. Calving retreat was delayed until ca. 15.3 cal ka BP in the Uummannaq Trough and until 15.1 cal ka BP in the Disko Trough, during another interval of ocean warming. Instabilities in the Laurentide, Innuitian and Greenland ice sheets with outlets draining into northern Baffin Bay periodically released cold, fresh water that enhanced sea ice formation and slowed GIS melt. During the Younger Dryas, the CWG records document strong cooling, lack of GIS meltwater, and an increase in iceberg rafted material from northern Baffin Bay. The ice sheet remained in the cross-shelf troughs until the early Holocene, when it retreated rapidly by calving and strong

  19. 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.

  20. Do Higher 20th Century Sea-cliff Retreat Rates Necessarily Imply Recent Acceleration in Sea-cliff Retreat?

    Science.gov (United States)

    Mushkin, Amit; Katz, Oded; Porat, Naomi

    2017-04-01

    Inland retreat of sea cliffs in response to post LGM (last glacial maximum) sea-level rise is an ongoing process that affects coastal environments and communities worldwide. Here, we examine a globally recurring pattern where reported sea-cliff retreat rates since the 20th century often appear to exceed longer-term millennial-scale ('background') rates that rarely exceed 0.1 m/yr. Focusing on Israel's 30-km-long Mediterranean 'Sharon' sea-cliff as a case study we demonstrate that such apparent increase in rates may also reflect a widely acknowledged sampling bias in geologic rate estimates inferred from observation time windows ('OTW') shorter than process episodicity. We show that this possible bias leads to an ambiguity in conventional rate estimates obtained by averaging observed retreat distances over OTW, and that as a result despite ubiquitous and robust observations of cliff retreat since the 20th century (e.g., aerial photographs) recent/current retreat rates for many of the world's episodically retreating sea cliffs remain essentially unknown. To address this present limitation in our ability to detect and quantify recent changes in sea-cliff retreat rates we use airborne LiDAR to measure the continuous wave-driven volumetric erosion of collapsed material from the cliff base as an effective upper-bound constraint for the m/yr rate of episodic retreat of the cliff itself. We find that while conventional retreat rate estimates since the 20th century along the Sharon sea cliff artefactually increase up to several m/yr as an inverse function of OTW, the LiDAR-constrained retreat rates are not susceptible to this sampling bias, are comparable to the cliff's background retreat rate of 0.03-0.07 m/yr since the mid Holocene and thus indicate no recent acceleration in retreat. This ability to unambiguously constrain sea-cliff retreat rates with annual to decadal-scale observations directly impacts the global-scale push to quantify, better understand and ultimately

  1. ACL Research Retreat VI

    NARCIS (Netherlands)

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

    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

  2. Glacial seismology

    Science.gov (United States)

    Aster, R. C.; Winberry, J. P.

    2017-12-01

    Seismic source and wave propagation studies contribute to understanding structure, transport, fracture mechanics, mass balance, and other processes within glaciers and surrounding environments. Glaciogenic seismic waves readily couple with the bulk Earth, and can be recorded by seismographs deployed at local to global ranges. Although the fracturing, ablating, melting, and/or highly irregular environment of active glaciers can be highly unstable and hazardous, informative seismic measurements can commonly be made at stable proximal ice or rock sites. Seismology also contributes more broadly to emerging studies of elastic and gravity wave coupling between the atmosphere, oceans, solid Earth, and cryosphere, and recent scientific and technical advances have produced glaciological/seismological collaborations across a broad range of scales and processes. This importantly includes improved insight into the responses of cryospheric systems to changing climate and other environmental conditions. Here, we review relevant fundamental physics and glaciology, and provide a broad review of the current state of glacial seismology and its rapidly evolving future directions.

  3. Sensitivity of palaeo-ice-stream retreat patterns to ice-ocean interactions and topography: a test of the marine ice sheet instability hypothesis

    Science.gov (United States)

    Jamieson, S.; Vieli, A.; Livingstone, S. J.; O'Cofaigh, C.; Stokes, C. R.; Hillenbrand, C.

    2011-12-01

    The aim is to understand the long-term controls on marine ice stream retreat. Short-term observations combined with modelling are helping decipher the controls driving contemporary mass loss via dynamic thinning and grounding-line retreat. However, ice-stream response times are likely to be longer than the timescales for which contemporary observations are available. We therefore focus on century to millenial timescales by investigating the retreat of Marguerite Bay palaeo-ice stream in Antarctica after the LGM. Our approach is to use high-resolution mapping of glacial landforms on the sea floor to constrain a numerical ice stream model. Mapped positions of grounding-zone wedges indicate that the palaeo-ice stream paused multiple times during its rapid retreat over a bed that deepens inland. The geomorphic record not only questions the marine ice sheet instability hypothesis but also provides geometrical and dynamical constraints for retreat experiments using numerical ice stream models. To understand the controls on the retreat pattern in Marguerite Bay, we test the sensitivity of the ice stream to a range of forcing regimes using a 1-dimensional numerical flow-line model that incorporates basal, lateral and longitudinal stresses and a self-refining grid scheme. Ice-ocean interactions are incorporated via a fixed-length ice shelf, the inclusion of an ice-ocean boundary condition and the calculation of ocean-driven melt. We test modelled retreat sensitivity to a range of external forcing patterns including sea-level, temperature, accumulation and ocean-driven melt. In addition, the importance of the topographic setting of the ice drainage basin is also examined. We find that the modelled ice stream naturally re-creates the pauses observed in the geomorphic record and that the pattern of palaeo-grounding-line retreat in Marguerite Bay can only be achieved within the chronological timeframe by including ocean-driven melt. Sensitivity tests indicate that the

  4. 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.

  5. Across the southern Andes on fin: glacial refugia, drainage reversals and a secondary contact zone revealed by the phylogeographical signal of Galaxias platei in Patagonia.

    Science.gov (United States)

    Zemlak, Tyler S; Habit, Evelyn M; Walde, Sandra J; Battini, Miguel A; Adams, Emily D M; Ruzzante, Daniel E

    2008-12-01

    We employed DNA sequence variation at two mitochondrial (control region, COI) regions from 212 individuals of Galaxias platei (Pisces, Galaxiidae) collected throughout Patagonia (25 lakes/rivers) to examine how Andean orogeny and the climatic cycles throughout the Quaternary affected the genetic diversity and phylogeography of this species. Phylogenetic analyses revealed four deep genealogical lineages which likely represent the initial division of G. platei into eastern and western lineages by Andean uplift, followed by further subdivision of each lineage into separate glacial refugia by repeated Pleistocene glacial cycles. West of the Andes, refugia were likely restricted to the northern region of Patagonia with small relicts in the south, whereas eastern refugia appear to have been much larger and widespread, consisting of separate northern and southern regions that collectively spanned most of Argentinean Patagonia. The retreat of glacial ice following the last glacial maximum allowed re-colonization of central Chile from nonlocal refugia from the north and east, representing a region of secondary contact between all four glacial lineages. Northwestern glacial relicts likely followed pro-glacial lakes into central Chilean Patagonia, whereas catastrophic changes in drainage direction (Atlantic --> Pacific) for several eastern palaeolakes were the likely avenues for invasions from the east. These mechanisms, combined with evidence for recent, rapid and widespread population growth could explain the extensive contemporary distribution of G. platei throughout Patagonia.

  6. Glacial cycles

    DEFF Research Database (Denmark)

    Kaufmann, R. K.; Juselius, Katarina

    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......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...

  7. 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.

  8. 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.

  9. Regional and global forcing of glacier retreat during the last deglaciation.

    Science.gov (United States)

    Shakun, Jeremy D; Clark, Peter U; He, Feng; Lifton, Nathaniel A; Liu, Zhengyu; Otto-Bliesner, Bette L

    2015-08-21

    The ongoing retreat of glaciers globally is one of the clearest manifestations of recent global warming associated with rising greenhouse gas concentrations. By comparison, the importance of greenhouse gases in driving glacier retreat during the most recent deglaciation, the last major interval of global warming, is unclear due to uncertainties in the timing of retreat around the world. Here we use recently improved cosmogenic-nuclide production-rate calibrations to recalculate the ages of 1,116 glacial boulders from 195 moraines that provide broad coverage of retreat in mid-to-low-latitude regions. This revised history, in conjunction with transient climate model simulations, suggests that while several regional-scale forcings, including insolation, ice sheets and ocean circulation, modulated glacier responses regionally, they are unable to account for global-scale retreat, which is most likely related to increasing greenhouse gas concentrations.

  10. Effects of tectonism on glacial and paraglacial processes- a New Zealand case study

    Science.gov (United States)

    Shulmeister, J.

    2012-04-01

    The mountains of South Island, New Zealand, are the product of plate interactions between the Indo-Australian and Pacific Plates. The Southern Alps of New Zealand are aligned along the oblique strike-slip Alpine Fault and connect the opposite facing subduction zones of the Puysegur Trough to the South and the Hikurangi Margin to the North. These mountains are characterised by rapid uplift and equally rapid erosion due to a combination of plentiful orographic precipitation and highly fractured bedrock. Consequently, landslides are the dominant erosional process in these landscapes, rather than soil diffusion. The combination of high erosion and high precipitation rates provide exceptional sediment supply to New Zealand mountain glacier valleys mostly in the form of mass movement deposits provided from the valley slopes. Unlike most glaciated mountainous regions, a significant percentage of the precipitation falls as rain and even in winter there is substantial water flow in the lower reaches of the modern glaciers. Similar conditions would have prevailed during full glacial times. The exceptional sediment supply generated by the rapid uplift and erosion modifies the bahaviour of the glaciers as follows; 1. New Zealand glaciers advance behind substantial ice contact fans. These fans are built by rivers that emerge from the front of the glacier. Despite substantial sediment supply from screes and shallow landslides, most material rapidly reaches the glacier base and is transported and reworked in sub-glacial drainages. The ice contact fans and their distal braid plains are the main product of glacial sedimentation. Terminal moraines are a very minor component of the system as they have low preservation potential on ice margins dominated by year round fluvial reworking. Lateral moraines are usually largely stratified. These moraines are much more substantial than terminal moraines because they aggrade as the glacier advances and are abandoned when the glacier begins to

  11. Heterogeneous Status of Glacial Terminal-Contacted Lakes in Himalayas Due to Different Geomorphology and Glacier Characters

    Science.gov (United States)

    Liu, Q.; Nie, Y.; Liu, S.

    2014-12-01

    Widespread expanding of glacial lakes around the Himalayas, which has led (or will lead) to hazard risks in their downstream valleys due to the potential glacial outburst flood (GLOF), has been widely reported during the past decades. Among all type of glacial lakes, those lakes contacted with the terminals of modern glaciers are generally found experienced most remarkable area increases. That is mostly due to the coupled processes, such as calving, between the lake growths and ice tongue retreats. Thermal absorption and convection of lake water are important for calving at the ice cliff or sub-marine melting under the supra-ponded water bodies. Currently, many larger moraine dammed lakes, e. g., Imja Tsho (Nepal) and Longbasaba Lake (China), are observed undergoing remarkable growths and synchronically with the rapid ice margin collapses due to calving. Some newly formed and rapidly growing supraglacial lakes are also identified on the debris-covered region of Himalayan glaciers, e. g., the Rongbuk Glacier (China), Ngozumpa Glacier (Nepal) and Thorthormi Glacier (Butan), which are speculated to experience accelerated expanding in the near future and finally developing as bigger terminal-calving lakes. However, not all such lake-glacier systems present the same scenes. After experienced the phases of rapid lake growth and terminal retreat, despite the contacting and calving still existing, the positions of the calving lines may be balanced by the positive advances of the ice tongue. We have observed several lakes with stagnation of growth or even shrinkage in lake area as the advance of the calving ice margin. The heterogeneous status of these ice-contacted glacial lakes are mainly due to the different local geomorphology (e. g., slope, lake-basin shape and valley aspect) and glacier characters (e. g., debris cover, velocity and mass balance). These related factors are important for both the prediction of lake and glacier changes and the evaluation of GLOF hazards

  12. Continued retreat of Thwaites Glacier, West Antarctica, controlled by bed topography and ocean circulation

    Science.gov (United States)

    Seroussi, H.; Nakayama, Y.; Larour, E.; Menemenlis, D.; Morlighem, M.; Rignot, E.; Khazendar, A.

    2017-06-01

    The Amundsen Sea sector is experiencing the largest mass loss, glacier acceleration, and grounding line retreat in Antarctica. Enhanced intrusion of Circumpolar Deep Water onto the continental shelf has been proposed as the primary forcing mechanism for the retreat. Here we investigate the dynamics and evolution of Thwaites Glacier with a novel, fully coupled, ice-ocean numerical model. We obtain a significantly improved agreement with the observed pattern of glacial retreat using the coupled model. Coupled simulations over the coming decades indicate a continued mass loss at a sustained rate. Uncoupled simulations using a depth-dependent parameterization of sub-ice-shelf melt significantly overestimate the rate of grounding line retreat compared to the coupled model, as the parameterization does not capture the complexity of the ocean circulation associated with the formation of confined cavities during the retreat. Bed topography controls the pattern of grounding line retreat, while oceanic thermal forcing impacts the rate of grounding line retreat. The importance of oceanic forcing increases with time as Thwaites grounding line retreats farther inland.

  13. Patterns of retreatment by radiotherapy.

    Science.gov (United States)

    Barton, M B; Allen, S; Delaney, G P; Hudson, H M; Hao, Z; Allison, R W; van der Linden, Y M

    2014-10-01

    To describe patterns of treatment for those who receive more than one episode of megavoltage radiotherapy (retreatment) by cancer type for better service planning and benchmarking. Institutional databases of all patients who received their first megavoltage radiotherapy for any type of cancer at the Liverpool and Macarthur Cancer Therapy Centres (LM), New South Wales, Australia, Royal Brisbane and Women's Hospital (RBWH), Queensland, Australia and Radiotherapeutic Institution Friesland (RIF), Leeuwarden, the Netherlands, over the period 1991-2009 were examined. Radiotherapy retreatment was defined as any radiotherapy episode, to any body site, after an initial episode of radiotherapy, for the same cancer diagnosis. The total retreatment rate was defined as the number of retreatment episodes of radiotherapy divided by the number of cases in the cohort. In total, 62,270 patients (RBWH 38581, LM 9654, RIF 14035) received 77,762 episodes of radiotherapy, giving a total retreatment rate of 0.25; 52,351 patients (84%) received only one episode of treatment and 9919 (16%) received two or more episodes of treatment. Overall retreatment rates for LM, RBWH and RIF were 0.24, 0.25 and 0.26, respectively. For the five most common cancer types treated, the median time between treatment episodes was longest for breast cancer (11.3 months), then head and neck cancer (9.7 months), colorectal cancer (7.2 months), prostate cancer (4.4 months) and lung cancer (4.1 months). Ninety-one per cent of all fractions were delivered in the first episode of treatment. The retreatment rate was very similar between the three facilities, suggesting agreement about the indications for retreatment. Copyright © 2014 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

  14. Submarine glacial landforms record Late Pleistocene ice-sheet dynamics, Inner Hebrides, Scotland

    Science.gov (United States)

    Dove, Dayton; Arosio, Riccardo; Finlayson, Andrew; Bradwell, Tom; Howe, John A.

    2015-09-01

    streamlined landforms suggest partial stabilization of the HIS prior to the ice sheet retreating to more isolated, topographically confined troughs and basins. Retreat from the shelf towards, and back into the Inner Hebrides may have been rapid due the prevalence of overdeepened troughs. Within the near-shore fjord-like troughs and deeps, basin-aligned streamlined landforms indicate the subsequent flow of thinner topographically partitioned ice masses, and overprinted moraines record further ice margin retreat, potentially along tide-water margins. This work provides the first geomorphological constraints for this large marine-influenced sector of the former BIIS. We also shed new light on the glacial geomorphic record found at the transition from terrestrial to marine continental-shelf settings, and examine the interplay between substrate geology, bed topography/bathymetry, and grounding-line positions - relationships which are important for characterizing contemporary marine ice sheet margins.

  15. A millennial-scale record of tidewater glacier advance and retreat, SW Greenland.

    Science.gov (United States)

    Pearce, Danni; Mair, Doug; Rea, Brice; Schofield, Ed; Lea, James; Barr, Iestyn; Kamenos, Nick; Schoenrock, Kate

    2017-04-01

    Tidewater glaciers (TWGs) exert a major control on the short- and long-term mass balance of the Greenland Ice Sheet (GrIS) and have experienced widespread retreat over the last century. However, in many cases inferences on their dynamics, prior to this, are poorly constrained due to a lack of observations and paucity of mapped or mappable deglacial geomorphology. Especially lacking is evidence associated with TWG advance during the Little Ice Age (LIA, AD c. 1300 to 1850). Such data are crucial for numerical model calibration and validation in order to more confidently forward model ice sheet dynamics and projection future sea-level rise. Therefore, empirical data constraints from the palaeo-record, that span such timescales (decadal to millennial), are essential. Kangiata Nunaata Sermia (KNS) is the most dynamic TWG in SW Greenland, located c. 100 km inland from Nuuk, at the head of Godthabsfjord. KNS has received considerable research attention over the last decade but glacial geomorphological and numerical dating investigations have been limited. However, the adjacent topography and geomorphology presents a unique opportunity to reconstruct the advance and retreat dynamics over the LIA. We present detailed glacial geomorphological mapping for KNS, which followed a morphostratigraphic approach, using a combination of aerial photos, Landsat, a DEM and field mapping. This identified a three landsystems, which are associated with the LIA, pre-LIA and neoglacial. From the mapping inferences on rapid changes in meltwater routing have been inferred. When KNS reached its LIA maximum (c. 1761), the calving front was c. >22 km further along the fjord than present and a number of ice-dammed lakes were formed. We present new 14C dating from peat underlying lake sediments associated with an ice-dammed lake and buried palaeosols resulting from meltwater re-routing over topographic spillways. The ages support an early and rapid LIA advance phase, with advance rates being

  16. 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.

  17. Projecting 21st century coastal cliff retreat in Southern California

    Science.gov (United States)

    Limber, P. W.; Barnard, P.; Erikson, L. H.; Vitousek, S.

    2016-12-01

    In California, sea level is expected to rise over 1 m by 2100, with extreme projections approaching 3 m. Sea level rise (SLR) increases the frequency, severity, and duration of wave impacts on coastal cliffs, potentially accelerating cliff retreat rates. To assess the future risk to cliff-top infrastructure, densely populated Southern California cities like Los Angeles and San Diego require estimates of coastal retreat over long time (multi-decadal) and large spatial (>100 km) scales. We developed a suite of eight coastal cliff retreat models, ranging in complexity from empirical 1-D representations of cliff response to wave impacts to more intricate 2-D process-based models integrated with artificial neural networks. The ensemble produces a comprehensive estimate of time-averaged coastal cliff retreat with uncertainty, is applicable to different geological environments, and is flexible in application depending on processing power, available data, and/or available time (e.g. if processing power and time are limited, the fast 1-D models can be used as a `rapid assessment' tool). Global-to-local nested wave models provided the hindcasts (1980-2010) and forecasts (2010-2100) used to force the models, and waves were applied in combination with eight SLR scenarios ranging from 0.25 m to 2 m. In the more detailed models, tides, non-tidal residuals, and storm surge were included for the hindcast and forecast periods. For model calibration, a new automated cliff edge extraction routine was used to estimate historical cliff retreat rates from LiDAR data. Initial model application to Southern California suggests that 1 m of SLR during the 21st century will cause cliff retreat rates to increase on average by over 50% relative to historical rates. Model results also demonstrate how small-scale, episodic cliff failure events can coalesce through time into spatially uniform, long-term cliff retreat signals.

  18. Ocean forcing of glacier retreat in the western Antarctic Peninsula.

    Science.gov (United States)

    Cook, A J; Holland, P R; Meredith, M P; Murray, T; Luckman, A; Vaughan, D G

    2016-07-15

    In recent decades, hundreds of glaciers draining the Antarctic Peninsula (63° to 70°S) have undergone systematic and progressive change. These changes are widely attributed to rapid increases in regional surface air temperature, but it is now clear that this cannot be the sole driver. Here, we identify a strong correspondence between mid-depth ocean temperatures and glacier-front changes along the ~1000-kilometer western coastline. In the south, glaciers that terminate in warm Circumpolar Deep Water have undergone considerable retreat, whereas those in the far northwest, which terminate in cooler waters, have not. Furthermore, a mid-ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat. We conclude that changes in ocean-induced melting are the primary cause of retreat for glaciers in this region. Copyright © 2016, American Association for the Advancement of Science.

  19. Glacial landforms and relicts in the high mountains of Taiwan

    Science.gov (United States)

    Chu, H.-T.

    2009-04-01

    Glacial landforms and relicts in the high mountains of Taiwan Hao-tsu Chu Central Geological Survey, MOEA, Taiwan ROC Glacial landforms and relicts are well preserved in the high mountains of Taiwan although substantial orographic precipitation, periglacial, earthquakes, and surface erosion processes have been active ever since the retreat of the last glaciations. Variations of glacial landforms and relicts in the northern, central, and southern areas of Taiwan are attributed mainly to differences in lithology. Cirque glaciers and rectilinear trough valleys are distinctive glacial landforms in the Hseuhshan (3884m) and the Nanhutashan (3742m) area, respectively, in north-central Taiwan. Both of these areas are composed of hard and durable thick layers of meta-sandstone, meta-conglomerate, and quartzite with minor slate. Diagnostic glacial landform and glacial erosional features of streamlined bodies and striated moraines are widely distributed in the high ground above 3300m of the Hohuanshan (3416m) area and the Shangyang Shan (3496m) - Sanchar Shan (3602m) area, respectively in north-central and southern Taiwan. These two areas are mainly composed of weaker rocks of slate, schist with minor meta-sandstones. Whereas in central Taiwan, in the Mount Yushan (3952m) area, limited glacial landforms of polished and striated bedrock surface was found. The preservation of geomorphic surfaces with glacial erosional forms is highly favorable near or at the top of drainage divide where the effect of stream headward erosion, mass wasting, and surface creeping are not obvious.

  20. Deglaciation of the Appalachian Plateau, northeastern Pennsylvania—till shadows, till knobs forming “beaded valleys”: Revisiting systematic stagnation-zone retreat

    Science.gov (United States)

    Braun, Duane D.

    2006-04-01

    Glacial retreat from valleys in the moderate relief (300-500 m) Small Lakes Section of the Appalachian Plateau in northeastern Pennsylvania was characterized by episodic deposition of till in a series of knobs that formed "beaded valleys". Individual valleys have a north to south series of till knobs alternating with wetlands or lakes at a spacing of one to five kilometers. Outcrop and well data, while small and few in any individual knob, when put together from the more than 1000 knobs mapped in region, show that the till knobs are typically 30 to 50 m thick. The knobs are cored by subglacial till (lodgment-deformation till) with a wedge of supraglacial till (flow or re-sedimented till) on the south sides, push structures in the interiors and north sides, and an overall veneer of "colluviated till" that thickens downslope on all sides. Glaciofluvial deposits are scarce, usually appearing as thin lenses on the flank of the knobs. The knobs are interpreted to be the periglacially and post-glacially modified remnants of recessional moraines. Individual till knobs were rapidly deposited in a few decades, probably through layer by layer stacking of deformation till and till block melanges. Active ice shearing over inactive ice could form an adverse slope where rapid till deposition could take place. The ice retreated systematically in a stagnation-zone retreat mode, with active ice leaving till knobs and 1-5 km wide stagnant-zone ice leaving the lake basins between the knobs. The till knobs can be connected from valley to valley, in lines perpendicular to the southwesterly ice flow, to delineate ice margin positions across the region. Valleys transverse to ice flow have "till shadows", 30 to 50 m thick till deposits on the north or lee side of the valley. "One-sided" post-glacial bedrock gorges with bedrock on the south side and till on the north side, are ubiquitous in "till shadow" valleys and form as the stream incises down the bedrock-till contact. Till outcrops in

  1. Chronology and dynamics of the Amundsen Gulf Ice Stream in Arctic Canada during the last glacial-interglacial transition

    Science.gov (United States)

    Lakeman, T. R.; MacLean, B.; Blasco, S.; Bennett, R.; Hughes Clarke, J. E.

    2012-04-01

    An extensive ice stream of the Laurentide ice sheet occupied Amundsen Gulf during the Last Glacial Maximum. The grounded ice stream extended northwestward to the margin of the inner shelf in the Beaufort Sea and to a depth of 450 metres. This glacier was one of the largest ice streams to emanate into the Arctic Ocean during the last glaciation and, as such, exerted a primary influence on the dynamics of the northwest Laurentide Ice Sheet. Ice stream retreat from its maximum position began prior to 13,000 cal yr BP. The pattern of extensive sole marks or glacial flutings on the seabed and on the adjacent mainland and islands confirms the direction of flow was from southeast to northwest. In the Gulf these features are imprinted primarily on subglacial sediment deposits. The bathymetry of the Gulf and known extent of the ice stream on land indicates the ice was at least 700 m thick. A series of moraines at the mouth of the Gulf mark temporary positions of the retreating ice stream margin. Early stages of ice retreat may have been associated with meltwater discharge under the ice stream as evidenced by current erosion associated with some sole marks or glacial flutings. Melting at the leading edge of the ice stream resulted in calving of icebergs and the generation of keel-scour marks in the seabed. Retreat of the ice stream was relatively rapid as indicated by thin and spatially discontinuous deglacial glaciomarine sediment in the Gulf. Furthermore, an expansive database of deglacial radiocarbon ages from eastern Banks Island, western Victoria Island, and the adjacent Arctic mainland, indicates that the ice stream had retreated fully from the Gulf by 12,500 cal yr BP. The lack of Holocene sediment draping the sole marks or flutings, and outcrops of exposed bedrock and glaciomarine sediment indicate very low sedimentation rates since ice retreat. The thin veneer of recent fine sediment that has been deposited discontinuously on the seabed in the Gulf indicates little

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

    Science.gov (United States)

    Carr, J. Rachel; Bell, Heather; Killick, Rebecca; Holt, Tom

    2017-09-01

    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.

  3. 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.

  4. The Greenland Ice Sheet-ocean interaction in the past two glacial cycles.

    Science.gov (United States)

    Tabone, Ilaria; Robinson, Alexander; Álvarez-Solas, Jorge; Montoya, Marisa

    2017-04-01

    Observations suggest that during the last decades the Greenland Ice Sheet (GrIS) has lost a huge amount of ice, significantly contributing to current sea level rise. A portion of this intensified ice discharge is connected to the observed acceleration of Greenland's marine-terminating glaciers, which recent studies directly attribute to increasing North Atlantic temperatures, triggering melting of the GrIS outlet glaciers, grounding-line retreat, enhanced ice discharge into the ocean and potentially contributing to current sea level changes. Analysis of the past GrIS evolution is crucial for a better understanding of its current behavior and its sensitivity to future climate variations. Reconstructions suggest that in glacial times the GrIS expanded up to the continental shelf, while warmer interglacial climates led to its rapid retreat, triggering a fast discharge of ice into the ocean. In this work the response of the GrIS to past climate changes, in particular glacial cycles, has been studied using a three-dimensional hybrid ice-sheet/ice-shelf model. The model features the capability to simulate ice sheets, ice shelves and ice streams as it applies both the Shallow Ice Approximation (SIA), in grounded areas of the ice sheet moving under slow, deformational flow, and the Shallow Shelf Approximation (SSA), in ice shelves and ice streams. This has allowed us to assess the effect of the variation of oceanic temperatures on the GrIS evolution throughout the two last glacial cycles through changes in submarine melting, an aspect that has not been investigated up to now. The results show a very high-sensitivity of the GrIS to the changing oceanic properties, among which oceanic temperature and heat flux variations are found to be the main drivers of the GrIS expansion and retreat throughout the past climates. This work therefore confirms that the ice-ocean interaction is a crucial factor driving Greenland's marine-terminating ice adjustments and highlights the need

  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. Hasty retreat of glaciers in the Palena province of Chile

    Science.gov (United States)

    Paul, F.; Mölg, N.; Bolch, T.

    2013-12-01

    . Typically, these glaciers lost contact to the accumulation areas of tributaries and now consist of an ablation area only. Furthermore, numerous pro-glacial lakes formed or expanded rapidly, increasing the local hazard potential. On the other hand, some glaciers located on or near to (still active) volcanoes have also advanced in the same time period. Observed trends in temperature (decreasing) are in contrast to the observed strong glacier shrinkage.

  7. 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.

  8. The writing retreat: a high-yield clinical faculty development opportunity in academic writing.

    Science.gov (United States)

    Cable, Christian T; Boyer, Debra; Colbert, Colleen Y; Boyer, Edward W

    2013-06-01

    The need for consistent academic productivity challenges junior clinician-scholars, who often lack the aptitude to ensure efficient production of manuscripts. To solve this problem, an academic division of a major medical center developed an off-site writing retreat. The purpose of the retreat was not to teach writing skills, but to offer senior mentor assistance with a focus on the elements of manuscript writing. The retreat paired senior faculty members with junior staff. Senior faculty identified manuscript topics and provided real-time writing and editing supervision. Team-building exercises, midcourse corrections, and debriefing interviews were built into the retreat. The number of manuscripts and grant proposals generated during the 2008-2011 retreats was recorded, and the program was evaluated by using unstructured debriefing interviews. An average of 6 to 7 faculty members and fellows participated in each retreat. During the past 4 years, participants produced an average of 3 grant proposals and 7 manuscripts per retreat. After the writing retreat, each fellow and junior faculty member produced an average of 4 scholarly products per year, compared to fewer than 2 for prior years' retreats. Participant feedback indicated the success of the retreat resulted from protected time, direct mentorship by the scholars involved, and pairing of authors, which allows for rapid production of manuscripts and accelerated the editing process. More than 80% of mentors returned each year to participate. The writing retreat is a feasible, effective strategy to increase scholarship among faculty, acceptable to mentees and mentors, and sustainable over time.

  9. 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

  10. 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.

  11. 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.

  12. 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

  13. GLOF, Glacial Lake Mapping an ESA DUE Innovator 2 Project

    Science.gov (United States)

    Wiesmann, Andreas; Strozzi, Tazio; Kaab, Andreas

    2010-12-01

    Glacier lake outbursts have repeatedly been the cause of major fatal events and damage in, for instance, the Himalayas, Central Asia, Andes, Caucasus, and the European Alps. The related hazards may even currently increase due to climate change as glaciers worldwide retreat and leave under certain circumstances glacier lakes behind. As a particularly far-reaching glacier- related hazard, glacier lake outburst floods may have devastating impact on populated areas that are located far downstream of the source area. Glacial lakes are often located in inaccessible areas, or can only be accessed with a substantial effort and cost to investigate their condition. While e.g. in Switzerland a network is setup to monitor glacier changes and help prevent glacial hazards, large and inaccessible areas e.g. in the Pamir and Himalayan mountains cannot be easily monitored from ground and air. Spaceborne remote sensing data are therefore a valuable and important information source to collect information on glacial lakes in these areas.

  14. Glacier retreat in New Zealand during the Younger Dryas stadial.

    Science.gov (United States)

    Kaplan, Michael R; Schaefer, Joerg M; Denton, George H; Barrell, David J A; Chinn, Trevor J H; Putnam, Aaron E; Andersen, Bjørn G; Finkel, Robert C; Schwartz, Roseanne; Doughty, Alice M

    2010-09-09

    Millennial-scale cold reversals in the high latitudes of both hemispheres interrupted the last transition from full glacial to interglacial climate conditions. The presence of the Younger Dryas stadial (approximately 12.9 to approximately 11.7 kyr ago) is established throughout much of the Northern Hemisphere, but the global timing, nature and extent of the event are not well established. Evidence in mid to low latitudes of the Southern Hemisphere, in particular, has remained perplexing. The debate has in part focused on the behaviour of mountain glaciers in New Zealand, where previous research has found equivocal evidence for the precise timing of increased or reduced ice extent. The interhemispheric behaviour of the climate system during the Younger Dryas thus remains an open question, fundamentally limiting our ability to formulate realistic models of global climate dynamics for this time period. Here we show that New Zealand's glaciers retreated after approximately 13 kyr bp, at the onset of the Younger Dryas, and in general over the subsequent approximately 1.5-kyr period. Our evidence is based on detailed landform mapping, a high-precision (10)Be chronology and reconstruction of former ice extents and snow lines from well-preserved cirque moraines. Our late-glacial glacier chronology matches climatic trends in Antarctica, Southern Ocean behaviour and variations in atmospheric CO(2). The evidence points to a distinct warming of the southern mid-latitude atmosphere during the Younger Dryas and a close coupling between New Zealand's cryosphere and southern high-latitude climate. These findings support the hypothesis that extensive winter sea ice and curtailed meridional ocean overturning in the North Atlantic led to a strong interhemispheric thermal gradient during late-glacial times, in turn leading to increased upwelling and CO(2) release from the Southern Ocean, thereby triggering Southern Hemisphere warming during the northern Younger Dryas.

  15. Quantitative interpretation of atmospheric carbon records over the last glacial termination

    Science.gov (United States)

    KöHler, Peter; Fischer, Hubertus; Munhoven, Guy; Zeebe, Richard E.

    2005-12-01

    The glacial/interglacial rise in atmospheric pCO2 is one of the best known changes in paleoclimate research, yet the cause for it is still unknown. Forcing the coupled ocean-atmosphere-biosphere box model of the global carbon cycle BICYCLE with proxy data over the last glacial termination, we are able to quantitatively reproduce transient variations in pCO2 and its isotopic signatures (δ13C, Δ14C) observed in natural climate archives. The sensitivity of the Box model of the Isotopic Carbon cYCLE (BICYCLE) to high or low latitudinal changes is comparable to other multibox models or more complex ocean carbon cycle models, respectively. The processes considered here ranked by their contribution to the glacial/interglacial rise in pCO2 in decreasing order are: the rise in Southern Ocean vertical mixing rates (>30 ppmv), decreases in alkalinity and carbon inventories (>30 ppmv), the reduction of the biological pump (˜20 ppmv), the rise in ocean temperatures (15-20 ppmv), the resumption of ocean circulation (15-20 ppmv), and coral reef growth (iron fertilization in the Southern Ocean together with a breakdown in Southern Ocean stratification, the latter caused by rapid sea ice retreat, trigger the onset of the pCO2 increase. After these events the reduced North Atlantic Deep Water (NADW) formation during the Heinrich 1 event and the subsequent resumption of ocean circulation at the beginning of the Bølling-Allerød warm interval are the main processes determining the atmospheric carbon records in the subsequent time period of Termination I. We further deduce that a complete shutdown of the NADW formation during the Younger Dryas was very unlikely. Changes in ocean temperature and the terrestrial carbon storage are the dominant processes explaining atmospheric δ13C after the Bølling-Allerød warm interval.

  16. The last ice-sheet advance and retreat across the Antarctic continental shelf: Synchrony or diachrony?

    Science.gov (United States)

    Hillenbrand, C.; Livingstone, S. J.; O'Cofaigh, C.; Stokes, C. R.; Vieli, A.; Jamieson, S.; Smith, J.; Kuhn, G.; Melles, M.; Graham, A. G.; Larter, R. D.

    2012-12-01

    Over the last few decades, numerous studies from various sectors of the Antarctic continental shelf have reconstructed the spatial extent of grounded ice-sheet advance during the last glacial period and the timing of its retreat. Most reconstructions were based on the bathymetric mapping of subglacial bedforms on the seabed and the palaeoenvironmental interpretation and dating of sub-seafloor sediments in cores. In addition, surface exposure age dating on rocks from the hinterland using cosmogenic isotopes and ice-sheet models were used to constrain the last ice-sheet advance and retreat. Different regional reconstructions provided consistent results for several study areas. In contrast, recent circum-Antarctic reviews that compiled the spatial and temporal information about maximum ice-sheet advance and retreat from these regional studies came to conflicting conclusions regarding i) the maximum extent of grounded ice, and ii) the synchronous/diachronous behaviour of the northern and southern hemispheric ice sheets and the individual drainage sectors within the Antarctic Ice Sheet, respectively. Resolving these conflicts is essential for identifying the main drivers of Antarctic ice-sheet retreat, evaluating the contribution of Antarctic ice-sheet melting to global sea-level rise over the last ~20 ka, understanding the dynamics of individual drainage sectors within the Antarctic Ice Sheet, and locating possible glacial refuges for benthic organisms on the Antarctic shelf. Here we will present examples of circum-Antarctic reconstructions and discuss possible reasons for conflicting conclusions. In some cases, apparent discrepancies can simply be explained by the ambiguity of terms such as "Last Glacial Maximum", which can refer either to a particular time slice (e.g. 23-19 ka BP) or to the time when grounded ice reached its last maximum extent in a particular sector of the Antarctic continental shelf, and "deglaciation", which can refer either to the time of

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

    Science.gov (United States)

    Pederson, G.T.; Fagre, D.B.; Gray, S.T.; Graumlich, L.J.

    2004-01-01

    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. Copyright 2004 by the American Geophysical Union.

  18. Geomorphic signature of an Antarctic palaeo-ice stream: implications for understanding subglacial processes and grounding line retreat

    Science.gov (United States)

    Livingstone, S. J.; Jamieson, S.; Vieli, A.; O'Cofaigh, C.; Stokes, C. R.; Hillenbrand, C.

    2010-12-01

    deformation till at the grounding-line during still-stands (Alley et al. 1989), are well documented, yet poorly understood phenomena. We present evidence of four previously unreported GZWs on the outer continental shelf of Marguerite Bay occuring within a zone that has undergone catastrophic grounding line retreat (Kilfeather et al. 2010). This suggests that GZWs can form relatively rapidly, while the localised nature and close association of these features with mega-scale glacial lineations is in keeping with a dynamic sedimentary system characterised by hierarchies of sediment transport. Preliminary modelling results are also presented that use the geomorphological evidence to constrain numerical simulations of the Marguerite Bay palaeo-ice stream system. Modelling output is then compared with both the known retreat style as recorded by geomorphological mapping and the deglacial chronology.

  19. Early and abrupt retreat of the Laurentide Ice Sheet margin from the Mackenzie River valley, southern Northwest Territories

    Science.gov (United States)

    Margold, Martin; Froese, Duane G.; Gosse, John C.; Yang, Guang; McKenna, Jillian; Hidy, Alan J.

    2017-04-01

    The detachment of the Laurentide Ice Sheet margin from the Canadian Cordillera opened the present-day drainage route of the Mackenzie River to the Arctic Ocean and an ice-free corridor that allowed for migration of species between Beringia and the mid-latitudes of North America. The existing ice-margin chronology depicts the southern reach of the Mackenzie River between 61 and 63° N as glaciated until about 13 ka, representing the last portion of the Laurentide Ice Sheet margin abutting the eastern foot of the Cordillera. A substantial retreat of the ice sheet margin in this region has been suggested to have occurred during the subsequent Younger Dryas cold period, despite the fact that in many other regions ice masses stabilised or even re-grew at this time. However, until now, deglacial chronometry for this region and the western LIS margin is sparse and consists mostly of minimum-limiting macrofossil and bulk C-14 ages from organics materials overlying glacial sediment. With the aim to bring new data on the deglaciation history of the Mackenzie River valley, we collected samples for Be-10 exposure dating from glacial erratic boulders in the southern Franklin Mountains that bound the Mackenzie River valley from the east. The sampling elevations ranged between 1480 and 800 m a.s.l., however, the measured ages show only a weak correlation with elevation. Instead, 10 out of 12 measured samples cluster tightly around 15 ka, with the remaining two samples likely containing Be-10 inherited from previous periods of exposure. Our results thus indicate a pre-Younger Dryas rapid down-wasting of the ice sheet surface, which we infer was accompanied by an ice margin retreat to the southeast. The southern reach of the Mackenzie River valley at the eastern foot of the Cordillera was, according to our results, ice free shortly after 15 ka, with the prospect that the ice-free corridor might have opened significantly earlier than hitherto anticipated. Further research is

  20. 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.

  1. Cooperative Spatial Retreat for Resilient Drone Networks

    National Research Council Canada - National Science Library

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

    2017-01-01

    ... 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...

  2. 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

  3. Postglacial trends of hillslope development in two glacially formed mountain valleys in western Norway

    Science.gov (United States)

    Laute, K.; Beylich, A. A.

    2012-04-01

    Although rockfall talus slopes occur in all regions where rock weathering products accumulate beneath rock faces and cliffs, they are particularly common in glacially formed mountain landscapes. The retreat of glacier ice from glaciated valleys which have probably experienced oversteepening of rock slopes by glacial erosion causes paraglacial destabilization of the valley sidewalls related to stress-relief, unloading, frost weathering and / or degradation of mountain permafrost. Large areas of the Norwegian fjord landscapes are occupied by hillslopes which are owned by the influences of the glacial inheritance of the last glacial maximum (LGM). This study focuses on Postglacial trends of hillslope development in two glacially formed mountain valleys in western Norway (Erdalen and Bødalen). The research is part of a doctoral thesis, which is integrated in the Norwegian Research Council (NFR) funded SedyMONT-Norway project within the ESF TOPO-EUROPE SedyMONT (Timescales of sediment dynamics, climate and topographic change in mountain landscapes) Programme. The main aspects addressed in this study are: (i) the spatio-temporal variability of denudative slope processes over the Holocene and (ii) the Postglacial modification of the glacial relief. The applied process-based approach includes detailed geomorphological fieldmapping combined with terrestrial laser scans (LIDAR) of slope deposits in order to identify possible deposition processes and their spatial variability, relative dating techniques (tree rings and lichens) to analyze subrecent temporal variations, detailed surface mapping with additional geophysical subsurface investigations to estimated regolith thicknesses as well as CIR- and orthophoto delineation combined with GIS and DEM computing for calculating estimates of average valley-wide rockwall retreat rates. Results show Holocene rockwall retreat rates for the two valleys which are in a comparable range with other estimates of rockwall retreat rates in

  4. 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.

  5. Recent acceleration in coastal cliff retreat rates on the south coast of Great Britain.

    Science.gov (United States)

    Hurst, Martin D; Rood, Dylan H; Ellis, Michael A; Anderson, Robert S; Dornbusch, Uwe

    2016-11-22

    Rising sea levels and increased storminess are expected to accelerate the erosion of soft-cliff coastlines, threatening coastal infrastructure and livelihoods. To develop predictive models of future coastal change we need fundamentally to know how rapidly coasts have been eroding in the past, and to understand the driving mechanisms of coastal change. Direct observations of cliff retreat rarely extend beyond 150 y, during which humans have significantly modified the coastal system. Cliff retreat rates are unknown in prior centuries and millennia. In this study, we derived retreat rates of chalk cliffs on the south coast of Great Britain over millennial time scales by coupling high-precision cosmogenic radionuclide geochronology and rigorous numerical modeling. Measured (10)Be concentrations on rocky coastal platforms were compared with simulations of coastal evolution using a Monte Carlo approach to determine the most likely history of cliff retreat. The (10)Be concentrations are consistent with retreat rates of chalk cliffs that were relatively slow (2-6 cm⋅y(-1)) until a few hundred years ago. Historical observations reveal that retreat rates have subsequently accelerated by an order of magnitude (22-32 cm⋅y(-1)). We suggest that acceleration is the result of thinning of cliff-front beaches, exacerbated by regional storminess and anthropogenic modification of the coast.

  6. Holocene Climate Variability and Glacial History in a Southern Patagonia Tidewater Glacier System, Marinelli Fjord, Chile

    Science.gov (United States)

    Boyd, B.; Anderson, J.; Wellner, J. S.

    2006-12-01

    The inland passage of Chile to the Antarctic Peninsula comprises the most continuous latitudinal transect of alpine glaciers and ice caps in the Southern Hemisphere and provides an excellent natural laboratory to study climate variability in the Holocene. Marinelli Fjord is one of six tidewater glacier systems being studied as a part of a large international study of glacial erosion, continental denudation and climate variability in the Southern Hemisphere. Marinelli Fjord, located at 54°20'S, 69°35'W, is fed from the Cordillera Darwin Icefield, via the Marinelli and Ainsworth Glaciers in the southern most reaches of South America. This system is currently considered to be in a temperate climatic regime, but may represent a more transitional system between temperate and sub-polar during the Last Glacial Maximum. A comprehensive data set of high resolution seismic, cores, swath bathymetry and single channel seismic was collected in Marinelli Fjord during the 2005 field season via the Nathaniel B. Palmer. The integration of lithostratigraphy, high-resolution seismic stratigraphy and radiocarbon stratigraphy are being used to determine climate variability and establish the glacial history within the fjord. Data indicate that sedimentation rates are highly variable throughout the fjord, ranging from 2.65cm/yr for areas most proximal to the ice-front and 0.065cm/yr for the outer basin. Coupled radiocarbon stratigraphy with lithostratigraphy indicates that there was a major retreat in the position of Marinelli Glacier near 12,000 ybp. This is manifested as a distinct change in lithofacies from ice-proximal glaciomarine to ice-distal glaciomarine, and a decrease in sedimentation rate. This is evidence for the first major post-Last Glacial Maximum glacial retreat into the fjord and is most likely directly linked to the clearing of grounded ice from the Straights of Magellan. Following the post-LGM retreat at 12,000 ybp, Marinelli Glacier retreated further into the inner

  7. Summary of the RHIC Retreat 2007

    Energy Technology Data Exchange (ETDEWEB)

    Pilat,F.; Gardner, C.; Montag, C.; Roser, T.

    2008-08-01

    The RHIC Retreat 2007 took place on July 16-17 2007 at the Foxwoods Resort in CT, about 3 weeks after the end of the RHIC Run-7. The goal of the Retreat is traditionally to plan the upcoming run in the light of the results from the previous one, by providing a snapshot of the present understanding of the machine and a forum for free and frank discussion. A particular attention was paid to the challenge of increasing the time at store, and the related issue of system reliability. An interesting Session covered all new developments aimed to improve the machine performance and luminosity. In Section 2 we summarize the results from Run-7 for RHIC and the injectors and discuss the present objectives of the RHIC program and performance. Sections 3-6 are summaries of the Retreat sessions focused on preparation for deuteron gold and polarized protons, respectively, machine availability and new developments.

  8. Early warning method of Glacial Lake Outburst Floods based on temperature and rainfall

    Science.gov (United States)

    Liu, Jingjing; Su, Pengcheng; Cheng, Zunlan

    2017-04-01

    Glacial lake outburst floods (GLOFs) are serious disasters in glacial areas. At present, glaciers are retreating while glacial lake area and the outburst risk increases due to the global warming. Therefore, the research of early warning method of GLOFs is important to prevent and reduce the disasters. This paper provides an early warning method using the temperature and rainfall as indices. The daily growth rate of positive antecedent accumulative temperature and the antecedent thirty days accumulative precipitation are calculated for 21 events of GLOF before 2010, based on data from the 21 meteorological stations nearby. The result shows that all the events are above the curve, TV = -0.0193RDC + 3.0018, which can be taken as the early warning threshold curve. This has been verified by the GLOF events in the Ranzeaco glacial lake on 2013-07-05.

  9. 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...

  10. The North American Late Wisconsin ice sheet and mantle viscosity from glacial rebound analyses

    Science.gov (United States)

    Lambeck, Kurt; Purcell, Anthony; Zhao, S.

    2017-02-01

    model (LW-6) is characterized by multiple ice domes from at least ∼17-18 ka onwards. The resolution for earlier periods is largely constrained by global ice volume considerations. The two principal domes are over southern Nunavut (the Keewatin Dome) and over Québec-Labrador, both of ≥3500 m thickness, separated by an ice ridge some 1500 m lower than the domes, the latter a requirement imposed by the gradient information. Over western Canada ice thickness gradients east of the Cordilleras are partly constrained by the shoreline data for former Lake McConnell (as is the lateglacial ice thickness of the Keewatin dome) and indicate that any ice-free corridor between the Laurentian and Cordilleran components is unlikely to have existed before ∼13ka. Reconstructions of the glacial lakes are consistent with the locations and timing of the observational evidence for the four major lake systems with the likely drainage routes identified. The evolution of the LW-6 ice-volume function, expressed as equivalent sea level, is characterized by a rapid decrease in ice volume from ∼15 to 14.5 ka, corresponding to the Bølling-Allerød period, in the main from rapid ice retreat along the southern margin, with further contributions from drainage through the St Lawrence River valley and from ice retreat from the major northern straits and gulfs, but not Hudson Strait where the rsl data point to late removal of ice (after 10 ka). The contribution of the drainage of the lakes to global sea level rise is small, earth's rotation axis.

  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. Roof Shield for Advance and Retreat Mining

    Science.gov (United States)

    Lewis, E. V.

    1985-01-01

    Shield sections change their configuration to suit mining mode. Articulation cylinders raise rear shield to advance position, and locking cylinders hold it there. To change to retreat position articulation cylinders lower shield. Locking pins at edge of outermost shield plate latch shield to chock base. Shield accommodates roof heights ranging from 36 to 60 inches (0.9 to 1.52 meters).

  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. The chronology of the Last Glacial Maximum and deglacial events in central Argentine Patagonia

    Science.gov (United States)

    Hein, Andrew S.; Hulton, Nicholas R. J.; Dunai, Tibor J.; Sugden, David E.; Kaplan, Michael R.; Xu, Sheng

    2010-05-01

    This paper evaluates the chronology of the last glacial cycle and deglaciation in the Lago Pueyrredón valley of central Patagonia, 47.5° S, Argentina. The valley was a major outlet of the former Patagonian Ice Sheet and the moraines that record its fluctuations are an important proxy record of climate change in southern South America. Such moraines are well-preserved in the Lago Pueyrredón valley owing in part to the semi-arid environment east of the mountain front. Here, we provide the first direct chronology for the age of the "Rio Blanco" moraine system by utilizing cosmogenic-nuclide surface exposure ages. Boulders on the moraines give 10Be exposure ages that indicate the Last Glacial Maximum (LGM) maximum extent occurred by 27-25 ka. Subsequent advances occurred at 23-22 ka, 20-18 ka, and ca. 18-17 ka. Initial deglaciation began after ca. 18-17 ka and was interrupted as evidenced by the Lago Columna moraines up-valley. Subsequently the outlet glaciers occupying both the Lago Pueyrredón basin (Chilean name: Lago Cochrane) and the Lago Buenos Aires basin (Chilean name: Lago General Carrera) to the north, rapidly retreated more than 80 km at around 16.5-15 ka. The timing of the LGM maximum extent and the onset of deglaciation occurred broadly synchronously throughout Patagonia. Deglaciation resulted in a series of interconnected glacier-dammed lakes in the region that initially drained toward the Atlantic Ocean and later drained to the Pacific Ocean as a consequence of disintegrating ice in the Andes.

  15. Hasty retreat of glaciers in northern Patagonia

    Science.gov (United States)

    Paul, Frank; Mölg, Nico

    2014-05-01

    decline (area and thickness loss). Some glaciers retreated more than 3 km over this time period or even disappeared completely. Typically, these glaciers lost contact to the accumulation areas of tributaries and melted away as dead ice. Furthermore, numerous proglacial lakes formed or expanded rapidly, increasing the local hazard potential. On the other hand, some glaciers located on or near to (still active) volcanoes have also slightly advanced over the same time period. Observed trends in temperature (decreasing) are in contrast to the observed strong glacier shrinkage, indicating that also other factors must play a role.

  16. The last North American ice sheet and mantle viscosity from glacial rebound analyses.

    Science.gov (United States)

    Lambeck, Kurt; Purcell, Anthony; Zhao, Jason

    2017-04-01

    This abstract presents new results for both earth (E-6) and ice-sheet (LW-6) parameters from the inversion of North American geological evidence for relative sea-level change (rsl) and tilting of palaeo-lake shorelines, complemented with loose constraints from observations of present-day radial crustal displacement across North America. The resulting earth response function is representative of the sub-continental mantle conditions with 3-layer effective mantle parameters (lithospheric thickness H and upper- and lower-mantle viscosities ηum and ηum) of H=102 (85-120) km, ηum =5.1x1020 (3.5-7.5)x1020, ηlm=1.3x1022 (0.8-2.8)x1022 (95% limits). The difference between ηum and the comparable estimate of for ocean mantle is statistically significant. An important new constraint on the interior of the ice model is provided by shoreline gradient information from Glacial Lakes McConnell, Agassiz, Algonquin and Ojibway and require multiple ice domes from at least 17-18 ka onwards with principal domes are over southern Nunavut (the Keewatin Dome) and over Québec-Labrador, both of 3500 m thickness, separated by an ice ridge across Ontario and northern Manitoba some 1500 m lower than the domes. The North American ice sheet volume before 17 ka remains poorly constrained from the North American analyses alone. Reconstructions of the glacial lakes are consistent with the locations and timing of the observational evidence for the four major lake systems with the likely drainage routes identified. The evolution of the LW-6 ice-volume function, expressed as equivalent sea level, is characterized by a rapid decrease in ice volume from 15-14.5 ka, corresponding to the Bølling-Allerød period, in the main from rapid ice retreat along the southern margin, with further contributions from drainage through the St Lawrence River valley and the major northern straits and gulfs, but not Hudson Strait where the rsl data point to late removal of ice (after 10 ka). The contribution of the

  17. Retreat of the Southwest Labrador Sector of the Laurentide Ice Sheet During the Last Termination

    Science.gov (United States)

    Lowell, T. V.; Kelly, M. A.; Fisher, T. G.; Barnett, P. J.; Howley, J. A.; Zimmerman, S. R. H.

    2016-12-01

    Large ice sheets are suspected to have played a major role in forcing the transitions from glacial to interglacial conditions, known as terminations. To improve the understanding of the role of the Laurentide Ice Sheet in the last termination, we present a chronology of ice sheet recession from just subsequent to end of the Last Glacial Maximum (LGM) to the early Holocene. We focus on the retreat of the southwest Labrador Sector of the ice sheet in northern Minnesota and adjacent Ontario. Multiple moraines in this region mark an overall pattern of ice recession interrupted by stillstands and/or minor readvances. Radiocarbon and 10Be ages from 50 sites along this 400 km-long transect indicate that the oldest moraine complex, the Vermillion moraine, formed at 17.0 ka. Subsequently, the ice margin retreated with minor standstills until the Dog Lake moraine was deposited between 12.7 and 12.3 ka. Recession from the Dog Lake moraine began by 12.3 ka the ice margin receded 150 km to the north-northeast by 10.7 ka. In general, the radiocarbon and 10Be ages define a pattern of near-continuous ice sheet retreat. Deposition of the Vermillion and Dog Lake moraines occurred at the beginning of Heinrich stadials 1 ( 17.5-14.5 ka) and 0 ( 12.9-11.7 ka), respectively, but ice recession occurred throughout the remainder of these stadials. This pattern is different from climate conditions registered by Greenland ice cores which show cold conditions from the end of the LGM until the Bølling warming at 14.5 ka, and throughout the Younger Dryas ( 12.9-11.7 ka). We suggest that the pattern of ice sheet recession is more similar to mountain glaciers in the southern mid-latitudes and tropics, and that Heinrich stadials may have been characterized by warming at least in the summertime that influenced near global ice recession.

  18. Skillful seasonal forecasts of Arctic sea ice retreat and advance dates in a dynamical forecast system

    Science.gov (United States)

    Sigmond, M.; Reader, M. C.; Flato, G. M.; Merryfield, W. J.; Tivy, A.

    2016-12-01

    The need for skillful seasonal forecasts of Arctic sea ice is rapidly increasing. Technology to perform such forecasts with coupled atmosphere-ocean-sea ice systems has only recently become available, with previous skill evaluations mainly limited to area-integrated quantities. Here we show, based on a large set of retrospective ensemble model forecasts, that a dynamical forecast system produces skillful seasonal forecasts of local sea ice retreat and advance dates - variables that are of great interest to a wide range of end users. Advance dates can generally be skillfully predicted at longer lead times ( 5 months on average) than retreat dates ( 3 months). The skill of retreat date forecasts mainly stems from persistence of initial sea ice anomalies, whereas advance date forecasts benefit from longer time scale and more predictable variability in ocean temperatures. These results suggest that further investments in the development of dynamical seasonal forecast systems may result in significant socioeconomic benefits.

  19. 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.

  20. Pleistocene glacial evolution of Fuentes Carrionas (Cantabrian Range, NW Spain)

    Science.gov (United States)

    Pellitero, Ramon

    2014-05-01

    Fuentes Carrionas is a massif situated at the N of Spain, between Castilla y Leon and Cantabria regions. It is the second highest mountain massif of the Cantabrian Range after Picos de Europa, with peaks over 2500 m.a.s.l. and valleys well over 1000 m.a.s.l. Fuentes Carrionas was glaciated during Quaternary, and even during the Holocene and as far as Little Ice Age the presence of glaciers, or at least permafrost is controversial. Results from glacial geomorphology analysis of Fuentes Carrionas Massif are presented. Based on the interpretation of glacial landforms, glacial evolution since the Last Glacial Maximum until Pleistocene deglaciation is described. Four different glacial equilibrium phases are identified, the last one divided into two pulsations. Deglaciation process took place between 36 ka BP and 11 ka BP. Local Last Glacial Maximum is dated back to 36-38 ka. BP, therefore earlier than LGM. Glaciers reached 15 km. long and occupied valleys down to 1250 m.a.s.l. during this phase. By European LGM (20-18 ka.BP) glaciers had substantially retreated to fronts about 1700 m.a.s.l. A final stage with two marked pulsations shows only small glaciers located at cirques above 2000 m.a.s.l. and, finally, only small cirque glaciers at North and Northeast orientation above 2200 m.a.s.l. Both these phases have been correlated to Oldest and Younger Dryas, although no dates have been done yet. A palaeoenvironmental reconstruction is proposed, based on ELA (Equilibrium Line Altitude) rise. ELA has been calculated with the AAR method and 0.67 ratio. This reconstruction shows that temperatures ranged between 9°C and 10°C lower than present ones at the end of Pleistocene, depending on a precipitations variation between 30% higher and 20% lower than current ones. Further research will focus on these retreat phases, especially on Younger Dryas identification and reconstruction for this site and the rest of Cantabrian Range.

  1. Kelp genes reveal effects of subantarctic sea ice during the Last Glacial Maximum

    OpenAIRE

    Fraser, Ceridwen I.; Nikula, Raisa; Spencer, Hamish G.; Waters, Jonathan M.

    2009-01-01

    The end of the Last Glacial Maximum (LGM) dramatically reshaped temperate ecosystems, with many species moving poleward as temperatures rose and ice receded. Whereas reinvading terrestrial taxa tracked melting glaciers, marine biota recolonized ocean habitats freed by retreating sea ice. The extent of sea ice in the Southern Hemisphere during the LGM has, however, yet to be fully resolved, with most palaeogeographic studies suggesting only minimal or patchy ice cover in subantarctic waters. H...

  2. Glacial landforms identified in high-resolution bathymetry indicate past Greenland ice sheet dynamics in Melville Bay, northeast Baffin Bay

    Science.gov (United States)

    Slabon, Patricia; Dorschel, Boris; Jokat, Wilfried; Myklebust, Reidun; Hebbeln, Dierk; Gebhardt, Catalina

    2017-04-01

    The maximum glacial extent of the Greenland Ice Sheet (GIS) and its advance and retreat across the continental shelf are crucial to better understand past ice-sheet dynamics and to predict its future development in times of climate change. Analyses of distribution and shape of glacial landforms are, thus, used to interpret information on ice-stream advances and retreats across the shelf. This study focuses on the past dynamics of the northwest GIS across the Greenland continental shelf. The research area is located in the Melville Bay, northeast Baffin Bay. Our interpretations base on analyses of high-resolution swath-bathymetric data acquired in 2010 and 2015 with the research vessels RV Polarstern and RV Maria S. Merian. The bathymetric data provide information along and across the axes of the major cross-shelf troughs of Melville Bay, allowing us to reconstruct the ice-sheet dynamics between the shelf edge and the present-day coast. The results of the analyses show glacial landforms that document former dynamics of the Greenland Ice Sheet (GIS). Moraines at the shelf edge give evidence for the maximum GIS extent. Grounding-zone wedges (GZWs), till lobes and glacial lineations define a pattern of variable ice-stream retreat in the individual cross-shelf troughs. Slow ice-stream retreat occurred in the northern cross-shelf trough compared to more episodic retreats in the central and southern cross-shelf troughs of Melville Bay. Periods of ice sheet grounding-zone stabilizations are indicated by large GZW-complexes on the mid- to inner shelf. Finally, the northwest GIS retreated across the inner continental shelf before 8.41 ka BP as revealed by an age-dated geological sample. Furthermore, on inter-trough banks, evidence has been found for minor ice-stream activity on localized ice domes. The glacial landforms across the northwest Greenland continental shelf, thus, host records of varying and discontinuous ice-sheet retreats since the last glacial maximum.

  3. New radiometric and geomorphologic evidences of a last glacial maximum older than 18 ka in SW European mountains: the example of Redes Natural Park (Cantabrian Mountains, NW Spain)

    Science.gov (United States)

    Sánchez, Montserrat Jiménez; Arquer, Pedro Farias

    The first numerical age determinations from radiocarbon dating establish the chronology of glacial events in Redes Natural Park (Cantabrian Mountain, NW Spain). A core drilled in an ice-dammed deposit provided a minimum age of 28 990 ± 230 years BP for the maximum glacial expansion (phase I). Another core from a cirque bottom-fill provided organic sediment with 20 640 ± 300 years BP, a minimum age for the first glacial retreat (phase II). Radiometric dating of proglacial deposits interpreted as synchronous with the last glacial maximum phase in neighbouring Comella basin (Picos de Europa), yield ages of 40 480 ± 820 years BP. The chronological data presented in this work are consistent with the model of glacier evolution established in the Pyrénées, with a glacial maximum phase for the last glacial period older than 18 ka.

  4. 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

  5. Quaternary geology of the Boston area: Glacial events from Lake Charles to Lake Aberjona

    Science.gov (United States)

    Stone, Byron D.; Lane, John W.

    2014-01-01

    The multiple-glacial and glaciomarine Quaternary history of the Boston, Massachusetts area has been known generally since the earliest studies of the then newly recognized glacial deposits described by Prof. Louis Agassiz in the late1840’s and fossil marine shells in the drift in the 1850’s. Attention then turned to possible glacial erosional effects on the preglacial bedrock physiography, as related to rock units and structure, and to the challenges of defining useful physical and lithic characteristics of the drift by Prof. W.O. Crosby and others, 1880-1900. The problems of deducing the relative stratigraphic order among such small, fossil-barren surficial sedimentary deposits, and extending knowledge gained from studies of postulated ancient glacial lakes to a regional understanding of the history of many lakes during the retreat of the ice sheet required field work and use of geologic maps. With the advent of modern topographic maps in the 1880’s, the early period of discovery included field studies of glacial lake deposits in local river basins in the Boston region, basins that drain northward, thereby creating glacial lake basins dammed by the ice margin as it retreated to the north. Guided by M.I.T. and Harvard professors W.O. Crosby, N.S. Shaler, J.B. Woodworth, W.M. Davis, and others in the 1880-1920 period, the first Quaternary glacial stratigraphers were students (e.g. Crosby and Grabau, 1896, Clapp, 1905, Fuller 1905, Goldthwaite 1906, Grabau, 1906, Taylor, Tight).

  6. Late Quaternary Advance and Retreat of an East Antarctic Ice Shelf System: Insights from Sedimentary Beryllium-10 Concentrations

    Science.gov (United States)

    Guitard, M. E.; Shevenell, A.; Domack, E. W.; Rosenheim, B. E.; Yokoyama, Y.

    2014-12-01

    Observed retreat of Antarctica's marine-based glaciers and the presence of warm (~2°C) modified Circumpolar Deep Water on Antarctica's continental shelves imply ocean temperatures may influence Antarctic cryosphere stability. A paucity of information regarding Late Quaternary East Antarctic cryosphere-ocean interactions makes assessing the variability, timing, and style of deglacial retreat difficult. Marine sediments from Prydz Bay, East Antarctica contain hemipelagic siliceous mud and ooze units (SMO) alternating with glacial marine sediments. The record suggests Late Quaternary variability of local outlet glacier systems, including the Lambert Glacier/Amery Ice Shelf system that drains 15% of the East Antarctic Ice Sheet. We present a refined radiocarbon chronology and beryllium-10 (10Be) record of Late Quaternary depositional history in Prydz Channel, seaward of the Amery Ice Shelf system, which provides insight into the timing and variability of this important outlet glacier system. We focus on three piston cores (NBP01-01, JPC 34, 35, 36; 750 m water depth) that contain alternating SMO and granulated units uninterrupted by glacial till; the record preserves a succession of glacial marine deposits that pre-date the Last Glacial Maximum. We utilize the ramped pyrolysis preparatory method to improve the bulk organic carbon 14C-based chronology for Prydz Channel. To determine if the SMO intervals reflect open water conditions or sub-ice shelf advection, we measured sedimentary 10Be concentrations. Because ice cover affects 10Be pathways through the water column, sedimentary concentrations should provide information on past depositional environments in Prydz Channel. In Prydz Channel sediments, 10Be concentrations are generally higher in SMO units and lower in glacial units, suggesting Late Quaternary fluctuations in the Amery Ice Shelf. Improved chronologic constraints indicate that these fluctuations occurred on millennial timescales during the Last Glacial

  7. Sea ice breakup and marine melt of a retreating tidewater outlet glacier in northeast Greenland (81 degrees N)

    DEFF Research Database (Denmark)

    Bendtsen, Jorgen; Mortensen, John; Lennert, Kunuk

    2017-01-01

    Rising temperatures in the Arctic cause accelerated mass loss from the Greenland Ice Sheet and reduced sea ice cover. Tidewater outlet glaciers represent direct connections between glaciers and the ocean where melt rates at the ice-ocean interface are influenced by ocean temperature and circulation...... glacier is a floating ice shelf with near-glacial subsurface temperatures at the freezing point. Melting from the surface layer significantly influenced the ice foot morphology of the glacier terminus. Hence, melting of the tidewater outlet glacier was found to be critically dependent on the retreat....... However, few measurements exist near outlet glaciers from the northern coast towards the Arctic Ocean that has remained nearly permanently ice covered. Here we present hydrographic measurements along the terminus of a major retreating tidewater outlet glacier from Flade Isblink Ice Cap. We show...

  8. Sea ice breakup and marine melt of a retreating tidewater outlet glacier in northeast Greenland (81°N)

    DEFF Research Database (Denmark)

    Bendtsen, Jørgen; Mortensen, John; Lennert, Kunuk

    2017-01-01

    Rising temperatures in the Arctic cause accelerated mass loss from the Greenland Ice Sheet and reduced sea ice cover. Tidewater outlet glaciers represent direct connections between glaciers and the ocean where melt rates at the ice-ocean interface are influenced by ocean temperature and circulation...... glacier is a floating ice shelf with near-glacial subsurface temperatures at the freezing point. Melting from the surface layer significantly influenced the ice foot morphology of the glacier terminus. Hence, melting of the tidewater outlet glacier was found to be critically dependent on the retreat....... However, few measurements exist near outlet glaciers from the northern coast towards the Arctic Ocean that has remained nearly permanently ice covered. Here we present hydrographic measurements along the terminus of a major retreating tidewater outlet glacier from Flade Isblink Ice Cap. We show...

  9. Stratigraphy, optical dating chronology (IRSL) and depositional model of pre-LGM glacial deposits in the Hope Valley, New Zealand

    Science.gov (United States)

    Rother, Henrik; Shulmeister, James; Rieser, Uwe

    2010-02-01

    A 110 m thick succession of glacial valley fill is described from Poplars Gully, central South Island, New Zealand. The section consists of eight lithofacies assemblages that represent different stages of ice occupation in the valley. Basal sediments record an ice retreat phase followed by a glacial re-advance which deposited mass flow diamictons and till. A subsequent ice retreat from the site is indicated by the stratigraphic transition from till to thick glacio-fluvial gravels. This is followed by a probably short-lived glacier re-advance that caused folding and thrusting of proglacial sediments. Final glacial retreat from the valley led to the formation of a large proglacial lake. In total, Poplars Gully holds evidence for two major ice advances, separated by a glacial retreat that resulted in complete ice evacuation from the lower Hope Valley. Infrared stimulated luminescence (IRSL) dating on ice-proximal sediments from Poplars Gully yielded six ages between 181 and 115 ka BP. Our stratigraphic logging and dating results show that the fill sequence was not, as previously thought, deposited in association with ice advances during the Last Glacial Maximum (LGM) nor indeed during the last glacial cycle. LGM glaciers later overran the fill but we find that the older glacial sequences are considerably more voluminous than those deposited during the last glacial cycle. We also show that the mid-Pleistocene glaciers carved a much deeper valley trough than did glaciers during the LGM. Taken together these features are likely to reflect a significant difference in the magnitude of successive Pleistocene glaciations in the valley, with the mid-Pleistocene ice advances having been considerably larger than those of the last glacial cycle. The recognition of the in-situ survival of extensive pre-MIS 5 (Marine Isotope Stage) deposits in valley troughs that were later occupied by LGM glaciers represents a new feature in the Quaternary stratigraphy of the Southern Alps. The

  10. Tropical ocean-atmospheric forcing of Late Glacial and Holocene glacier fluctuations in the Cordillera Blanca, Peru

    Science.gov (United States)

    Stansell, Nathan D.; Licciardi, Joseph M.; Rodbell, Donald T.; Mark, Bryan G.

    2017-05-01

    Evaluating the timing and style of past glacier fluctuations in the tropical Andes is important for our scientific understanding of global environmental change. Terrestrial cosmogenic nuclide ages on moraine boulders combined with 14C-dated clastic sediment records from alpine lakes document glacial variability in the Cordillera Blanca of Peru during the last 16 ka. Late Glacial ice extents culminated at the start of the Antarctic Cold Reversal and began retracting prior to the Younger Dryas. Multiple moraine crests dating to the early Holocene mark brief readvances or stillstands that punctuated overall retreat of the Queshque Valley glacier terminus during this interval. Glaciers were less extensive during the middle Holocene before readvancing during the latest Holocene. These records suggest that tropical Atlantic and Pacific ocean-atmospheric processes exerted temporally variable forcing of Late Glacial and Holocene glacial changes in the Peruvian Andes.

  11. 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,...

  12. Glacial Features (Point) - Quad 169 (NEWMARKET, 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,...

  13. Decade-scale coastal bluff retreat from LiDAR data: Lake Erie coast of Pennsylvania, USA

    Science.gov (United States)

    Foyle, A. M.; Naber, M. D.

    2010-12-01

    Bluff retreat is a significant problem along many parts of the southern Great Lakes coastline of the United States. On the Pennsylvania coast of Lake Erie, where semi-consolidated clay-rich glacial till sequences overlie bedrock, erosion of the bluffs results in a permanent loss of fine-grained sediment from the coastal zone. Bluff retreat is of concern to coastal property owners and regulators because evaluating landslide hazards and developing regulations on coastal development must account for spatial and temporal variability in coastal retreat. Bluff retreat also contributes to temporary degradation in coastal water quality. The goal of this pilot study is to evaluate medium-term spatial variability in bluff retreat magnitudes and rates along a sector of the Pennsylvania coast. Newly available high resolution LiDAR data cover a one-decade time frame (1998-2007) and permit mapping of the bluff-crest position on two comparable, high-quality data sets. In contrast, long-term coastal change analyses typically involve comparison of a recent LiDAR data set with an older, lower-resolution data set developed from either field measurements, T-sheets, or aerial photography. While the older data can have much larger inherent errors than the LiDAR data, they become less significant over the longer time frames involved. The 6 km, geologically homogeneous, coastal bluff site is characterized by ~20 m of unlithified Pleistocene glacial tills and lake plain sediments overlying a 3-4 m ledge of near-horizontal Devonian shale and sandstone bedrock. Bluff slopes range from 35-90 degrees, beaches are narrow to non-existent, and the coast is frequently protected by ground-freeze and a lake ice shelf during winter. DEMs, hillshades, and slope and contour maps were generated from the bare-earth 1998 and 2007 LiDAR data, and checked against 2005 aerial ortho-photography. Maps were analyzed at a scale of 1:120 in ArcGIS and the bluff crest was identified primarily by the visual

  14. Modeling the retreat of the Jakobshavn Glacier from the LIA and into the future

    Science.gov (United States)

    Steiger, Nadine; Hestnes Nisancioglu, Kerim; Åkesson, Henning; Maghami Nick, Faezeh

    2017-04-01

    Many marine-terminating glaciers on Greenland have experienced rapid retreat and acceleration during the last decades, coinciding with increased air and ocean temperatures. Destabilized marine-terminating glaciers have been capable of discharging vast amounts of ice into the ocean, contributing significantly to sea-level rise. In order to conduct prospective simulations of the glaciers' development and their future contribution to sea-level rise, it is crucial to understand the dynamics and triggers of the past retreat, as well as the relative importance of the external forcing versus fjord geometry. Using an idealized numerical flowband model1,2, we are able to reproduce the documented retreat of the Jakobshavn Glacier, western Greenland, since the Little Ice Age (LIA). Based on the results from the hindcast experiments, we investigate the relative role of climate forcing and fjord geometry on glacier stability and assess the potential for non-linear retreat in the coming 200 years. References: [1] Nick et al. 2009, Nature Geoscience, doi:10.1038/ngeo394. [2] Nick et al. 2013, Nature, doi:10.1038/nature12068

  15. Automatically detecting Himalayan Glacial Lake Outburst Floods in LANDSAT time series

    Science.gov (United States)

    Veh, Georg; Korup, Oliver; Roessner, Sigrid; Walz, Ariane

    2017-04-01

    More than 5,000 meltwater lakes currently exist in the Himalayas, and some of them have grown rapidly in past decades due to glacial retreat. This trend might raise the risk of Glacial Lake Outburst Floods (GLOFs), which have caused catastrophic damage and several hundred fatalities in historic time. Yet the growing number and size of Himalayan glacial lakes have no detectable counterpart in increasing GLOF frequency. Only 35 events are documented in detail since the 1950s, mostly in the Himalayas of Eastern Nepal and Bhutan. Observations are sparse in the far eastern and totally missing in the northwestern parts of the mountain belt. The GLOF record is prone to a censoring bias, such that mainly larger floods or flood impacts have been registered. Thus, establishing a more complete record and learning from past GLOFs is essential for hazard assessment and regional planning. To detect previously unreported GLOFs in the Himalayas, we developed an automated processing chain for generating GLOF related surface-cover time series from LANDSAT data. We downloaded more than 5,000 available LANDSAT TM, ETM+ and OLI images from 1987 to present. We trained a supervised machine-learning classifier with >4,000 randomly selected image pixels and topographic variables derived from digital topographic data (SRTM and ALOS DEMs), defining water, sediment, shadow, clouds, and ice as the five main classes. We hypothesize that GLOFs significantly decrease glacial lake area while increasing the amount of sediment cover in the channel network downstream simultaneously. Thus we excluded shadows, clouds, and lake ice from the analysis. We derived surface cover maps from the fitted model for each satellite image and compiled a pixelwise time-series stack. Customized rule sets were applied to systematically remove misclassifications and to check for a sediment fan in the flow path downstream of the former lake pixels. We verified our mapping approach on thirteen GLOFs documented in the

  16. Benevolent theory: moral treatment at the York Retreat.

    Science.gov (United States)

    Charland, Louis C

    2007-03-01

    The York Retreat is famous in the history of nineteenth-century psychiatry because of its association with moral treatment. Although there exists a substantial historical literature on the evolution of moral treatment at the Retreat, several interpretive problems continue to obscure its unique therapeutic legacy. The nature of moral treatment as practised at the Retreat will be clarified and discussed in a historical perspective. It will be argued that moral treatment at the Retreat was primarily a matter of affective conditioning guided by 'benevolent theory'.

  17. Glacier ice-surface lowering in the Altai Mountains of western Mongolia during the last glacial termination

    Science.gov (United States)

    Norris, N. R.

    2016-12-01

    The Altai Mountains of western Mongolia preserve an exceptional record of mountain glacier retreat during the last glacial termination ( 18,000 - 11,000 yrs ago). Extra-polar glaciers are highly sensitive to changes in atmospheric temperature. Therefore, a reconstruction of the character and rate of glacier retreat in the Tsagaan Gol valley reveals past climate conditions in Inner Asia. This research will help place contemporary interior Asian climate change into context. Here, we present 10Be surface exposure dates from an elevation profile of glacial-erratic boulders mantling an ice-molded bedrock feature located within the local last glacial maximum limit. On the basis of these dates, we reconstruct a chronology of ice-surface lowering of the former glacier system. The glaciated valleys of the western Altai Mountains are also culturally significant due to the presence of petroglyphs carved in glacially polished bedrock surfaces. This chronology of glacier recession reveals the earliest possible date of human occupation in the valley. The data reported here are part of a larger research effort to develop a chronology of glacial behavior from the outermost terminal moraines to the margin of extant glaciers in the high mountains of western Mongolia, using cosmogenic exposure age dating techniques.

  18. Oceanographic gradients and seabird prey community dynamics in glacial fjords

    Science.gov (United States)

    Arimitsu, Mayumi L.; Piatt, John F.; Madison, Erica N.; Conaway, Jeff; Hillgruber, N.

    2012-01-01

    Glacial fjord habitats are undergoing rapid change as a result of contemporary global warming, yet little is known about how glaciers influence marine ecosystems. These ecosystems provide important feeding, breeding and rearing grounds for a wide variety of marine organisms, including seabirds of management concern. To characterize ocean conditions and marine food webs near tidewater glaciers, we conducted monthly surveys of oceanographic variables, plankton, fish and seabirds in Kenai Fjords, Alaska, from June to August of 2007 and 2008. We also measured tidal current velocities near glacial features. We found high sediment load from glacial river runoff played a major role in structuring the fjord marine ecosystem. Submerged moraines (sills) isolated cool, fresh, stratified and silt-laden inner fjord habitats from oceanic influence. Near tidewater glaciers, surface layers of turbid glacial runoff limited availability of light to phytoplankton, but macrozooplankton were abundant in surface waters, perhaps due to the absence of a photic cue for diel migration. Fish and zooplankton community structure varied along an increasing temperature gradient throughout the summer. Acoustic measurements indicated that low density patches of fish and zooplankton were available in the surface waters near glacial river outflows. This is the foraging habitat occupied most by Kittlitz's murrelet (Brachyramphus brevirostris), a rare seabird that appears to be specialized for life in glacially influenced environments. Kittlitz's murrelets were associated with floating glacial ice, and they were more likely to occur near glaciers, in deeper water, and in areas with high acoustic backscatter. Kittlitz's murrelet at-sea distribution was limited to areas influenced by turbid glacial outflows, and where prey was concentrated near the surface in waters with low light penetration. Tidewater glaciers impart unique hydrographic characteristics that influence marine plankton and fish

  19. Glacial Lake Outburst Flood Risk in Himachal Pradesh, India: An Integrative and Anticipatory Approach to Inform Adaptation Planning

    Science.gov (United States)

    Allen, Simon; Linsbauer, Andreas; Huggel, Christian; Singh Randhawa, Surjeet

    2016-04-01

    Most research concerning the hazard from glacial lake outburst floods (GLOFs) has focused on the threat from lakes that have formed over the past century, and which continue to expand rapidly in response to recent warming of the climate system. However, attention is shifting towards the anticipation of future hazard and risk associated with new lakes that will develop as glaciers continue to retreat and dramatically different landscapes are uncovered. Nowhere will this threat be more pronounced than in the Himalaya, where the majority of the world's glaciers are found, and where the dynamics of nature interact closely with livelihoods and anthropogenic resources. Using the Indian Himalayan state of Himachal Pradesh (HP) as a case study, we combine a suite of GIS-based approaches to: 1)Implement a large-scale automated GLOF risk assessment within an integrative climate risk framework that recognizes both physical and socio-economic determining factors. 2)Expand the assessment beyond the current situation, to provide early anticipation of emerging GLOF hazard as new lakes form in response to further retreat of the Himalayan glaciers. Results clearly demonstrate a significant future increase in relative GLOF hazard levels across most Thesils of HP (administrative units), as the overall potential for GLOFs being triggered from mass movement of ice and rock avalanches increases, and as new GLOF paths affect additional land areas. Across most Thesils, the simulated increase in GLOF frequency is an order of magnitude larger than the simulated increase in GLOF affected area, as paths from newly formed glacial lakes generally tend to converge downstream within existing flood channels. In the Thesil of Kullu for example, we demonstrate a 7-fold increase in the probability of GLOF occurrence, and a 3-fold increase in the area affected by potential GLOF paths. In those situations where potential GLOFs from new lakes will flow primarily along existing flood paths, any

  20. 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.

  1. 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

  2. Glacial geology of the Shingobee River headwaters area, north-central Minnesota

    Science.gov (United States)

    Melchior, Robert C.

    2014-01-01

    During middle and late Wisconsin time in the Shingobee River headwaters area, the Laurentide Wadena lobe, Hewitt and Itasca phases, produced terminal and ground moraine along with a variety of associated glacial features. The stratigraphic record is accessible and provides details of depositional mode as well as principal glacial events during the advance and retreat of middle and late Wisconsin ice tongues. Geomorphic features such as tunnel valleys, stream terraces, and postglacial stream cuts formed by erosional events persist to the present day. Middle Wisconsin Hewitt phase deposits are the oldest and include drumlins, ground moraine, boulder pavements, and outwash. Together, these deposits suggest a wet-based, periodically surging glacier in a subpolar thermal state. Regional permafrost and deposition from retreating ice are inferred between the end of the Hewitt phase and the advance of late Wisconsin Itasca phase ice. Itasca phase glaciation occurred as a contemporaneous pair of adjacent ice tongues whose contrasting moraine styles suggest independent flow modes. The western (Shingobee) portion of the Itasca moraine contains composite ridges, permafrost phenomena, hill-hole pairs, and debris flows. By contrast, eastern (Onigum) moraine deposits generally lack glaciotectonic features and consist almost exclusively of mud and debris flows. Near the end of the Itasca phase, large-scale hill-hole pairs developed in the Shingobee division, and debris flows from the Onigum division blocked the preexisting Shingobee tunnel valley to form glacial lake Willobee. Postglacial streams formed deep valleys as glacial lake Willobee catastrophically drained. Dates based on temperature trends in Greenland ice cores are proposed for prominent glacial events in the Shingobee area. This report proposes that Hewitt phase glaciation occurred between 27.2 and 23.6 kiloannum and Itasca phase glaciation between 22.8 and 14.7 kiloannum. Des Moines lobe (Younger Dryas) glaciation

  3. Hydrologically-induced slow-down as a mechanism for tidewater glacier retreat

    Science.gov (United States)

    Hewitt, Ian

    2017-04-01

    Outlet glaciers flowing into the ocean often terminate at a calving front, whose position is sensitively determined by the balance between ice discharge and calving/terminus-melting. Rapid retreat of tidewater glaciers can be initiated when the front is perturbed from a preferred pinning point, particularly when the glacier sits in an overdeepened trough. This is believed to make certain areas of ice sheets particularly vulnerable to ice loss. A number of factors may cause a previously stable front position to become unstable, including changes in buttressing provided by an ice shelf, and changes in ocean temperature. Another possibility is that initial retreat is induced by a reduction in the supply of ice from the interior of the ice sheet. Such a reduction can naturally arise from an increase in surface melting and runoff (in the absence of accumulation changes), and this may be amplified if more efficient meltwater routing reduces basal lubrication, as has been observed in some areas of the Greenland ice sheet. Since the initiation of rapid retreat often results in an increase of ice discharge at the front (due to increased ice thickness), such a process may not be easy to detect. In this study, I employ a simplified model of an outlet glacier and its frontal behaviour to examine the extent to which hydrologically induced slow-down of the feeding ice sheet may induce (or help to induce) calving front retreat. The model builds on earlier parameterisations of grounding line fluxes, and assumes that calving occurs according to a criterion that keeps the front close to the flotation thickness. The glacier bed is assumed to be plastic. This allows for a transparent identification of the different forcing terms affecting margin position. We conclude that hydrologically-induced slow-down of ice sheets is likely to have a more significant effect on mass loss than hydrologically-induced speed-up.

  4. 10Be dating of late Pleistocene megafloods and Cordilleran Ice Sheet retreat in the northwestern United States

    Science.gov (United States)

    Balbas, Andrea M.; Barth, Aaron M.; Clark, Peter U.; Clark, Jorie; Caffee, Marc A.; O'Connor, Jim E.; Baker, Victor R.; Konrad, Kevin; Bjornstad, Bruce

    2017-01-01

    During the late Pleistocene, multiple floods from drainage of glacial Lake Missoula further eroded a vast anastomosing network of bedrock channels, coulees, and cataracts, forming the Channeled Scabland of eastern Washington State (United States). However, the timing and exact pathways of these Missoula floods remain poorly constrained, thereby limiting our understanding of the evolution of this spectacular landscape. Here we report cosmogenic 10Be ages that directly date flood and glacial features important to understanding the flood history, the evolution of the Channeled Scabland, and relationships to the Cordilleran Ice Sheet (CIS). One of the largest floods occurred at 18.2 ± 1.5 ka, flowing down the northwestern Columbia River valley prior to blockage of this route by advance of the Okanogan lobe of the CIS, which dammed glacial Lake Columbia and diverted later Missoula floods to more eastern routes through the Channeled Scabland. The Okanogan and Purcell Trench lobes of the CIS began to retreat from their maximum extent at ca. 15.5 ka, likely in response to onset of surface warming of the northeastern Pacific Ocean. Upper Grand Coulee fully opened as a flood route after 15.6 ± 1.3 ka, becoming the primary path for later Missoula floods until the last ones from glacial Lake Missoula at 14.7 ± 1.2 ka. The youngest dated flood(s) (14.0 ± 1.4 ka to 14.4 ± 1.3 ka) came down the northwestern Columbia River valley and were likely from glacial Lake Columbia, indicating that the lake persisted for a few centuries after the last Missoula flood.

  5. Student leadership retreat focusing on a commitment to excellence.

    Science.gov (United States)

    Janke, Kristin K; Traynor, Andrew P; Sorensen, Todd D

    2009-05-27

    To design and evaluate a student leadership retreat focused on: leadership regardless of position or title, the need for passionate commitment to excellence, the importance of teamwork, and the value of self-reflection. Students in their second, third, and fourth year of a doctor of pharmacy (PharmD) program were invited to participate in an off-campus leadership retreat that combined organized learning activities and social/networking opportunities. Retreat content utilized didactic, experiential, and self-directed learning activities. Forty-two students participated in the retreat and were surveyed pre- and post-retreat. A student-led group evaluation and course evaluations were also utilized. Responses on the post-retreat evaluation suggested an increased belief in their ability to influence change and an enhanced awareness of the role of self-reflection in creating excellence in the profession. An off-campus overnight retreat has value in challenging student perceptions about leadership and promoting reflection on their personal role in leading change within the profession Continued exploration and development of this format is warranted for commitment to excellence programming and also for additional leadership topics and audiences.

  6. Some additional observations for understanding the glacial history and neotectonics of the Venezuelan Andes and Bocono fault

    Science.gov (United States)

    Wesnousky, S. G.; Arenguren, R.; Rengifo, M.; Owen, L. A.; Caffee, M. W.

    2011-12-01

    To quantify the glacial history and neotectonics of the Venezuelan Andes we report 23 cosmogenic surface exposure ages from moraines of the Sierra Nevada de Merida, 6 ages from an offset fan along the flanks of the Andes, and several OSL ages of glacial outwash deposits. Rocks from the La Victoria and Los Zerpas moraines yield ages of 16.5±1.6 ka and 16.9±1.3 ka, respectively. About 25 km to the west in the drainage basin of the Rio Mucujun, rocks on the crest of the La Culata moraine show ages of 15.2 ± 0.9 kyr and 15.1 ± 1.1 kyr, respectively. A large La Culata inset moraine, situated upstream from the terminus of moraine deposits gives an age of 14.2 ± 1.0 kyr. Previously documented offsets of the La Victoria and Los Zerpas moraines by a strand of the Bocono fault are ~100m, suggesting a latest Pleistocene slip rate of about ~6 mm/yr, less than the total right-lateral slip across the Bocono fault of 12±2 mm/yr interpreted by others from geodesy. Surface exposure ages for boulders from a fan that is truncated, abandoned, and uplifted ~120 m above stream grade by a southeast dipping thrust fault along the northwestern flank of the Andes at Tucanizon show large scatter and range to about 110 kyr. The observations place an initial upper limit of about 1 mm/yr on the late Pleistocene uplift of the Andes. The outwash of the glaciers that produced the moraines of La Culata was transported down the Rio Mucujun to its confluence with the Rio Chama where it produced valley fill deposits with a surface at 100 m heights and greater above the Rio Chama. The largest and highest remnant of this surface is that upon which the major city of Merida is located. Initial dating of sediments within the fill deposits with optical stimulated luminescence suggests that the final aggradation of valley fill deposits on which the Meseta is formed occurred quite rapidly over a period of about 5 to 6 kyr and that the surface was initially incised and abandoned 30 ky ago, some 15 kyr

  7. Endodontic procedures for retreatment of periapical lesions.

    Science.gov (United States)

    Del Fabbro, Massimo; Corbella, Stefano; Sequeira-Byron, Patrick; Tsesis, Igor; Rosen, Eyal; Lolato, Alessandra; Taschieri, Silvio

    2016-10-19

    When primary root canal therapy fails, periapical lesions can be retreated with or without surgery. Root canal retreatment is a non-surgical procedure that involves removal of root canal filling materials from the tooth, followed by cleaning, shaping and obturating of the canals. Root-end resection is a surgical procedure that involves exposure of the periapical lesion through an osteotomy, surgical removal of the lesion, removal of part of the root-end tip, disinfection and, commonly, retrograde sealing or filling of the apical portion of the remaining root canal. This review updates one published in 2008. To assess effects of surgical and non-surgical therapy for retreatment of teeth with apical periodontitis.To assess effects of surgical root-end resection under various conditions, for example, when different materials, devices or techniques are used. We searched the following electronic databases: the Cochrane Oral Health Trials Register (to 10 February 2016), the Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 1), MEDLINE Ovid (1946 to 10 February 2016) and Embase Ovid (1980 to 10 February 2016). We searched the US National Registry of Clinical Trials (ClinicalTrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform for ongoing trials (to 10 February 2016). We placed no restrictions regarding language and publication date. We handsearched the reference lists of the studies retrieved and key journals in the field of endodontics. We included randomised controlled trials (RCTs) involving people with periapical pathosis. Studies could compare surgery versus non-surgical treatment or could compare different types of surgery. Outcome measures were healing of the periapical lesion assessed after one-year follow-up or longer; postoperative pain and discomfort; and adverse effects such as tooth loss, mobility, soft tissue recession, abscess, infection, neurological damage or loss of root sealing material

  8. The grounding-zone wedge inventory on the Amundsen Sea Embayment shelf, West Antarctica: formation processes and significance for establishing reliable post-LGM retreat chronologies

    Science.gov (United States)

    Klages, Johann P.; Hillenbrand, Claus-Dieter; Larter, Robert D.; Graham, Alastair G. C.; Smith, James A.; Gohl, Karsten; Kuhn, Gerhard

    2017-04-01

    Grounding-zone wedges (GZW) have been mapped on the sea floor in various sectors of formerly glaciated continental shelf around Antarctica. In most cases, these wedges record periods of grounding-line stillstands during ice-sheet retreat following the Last Glacial Maximum ( 26-19 ka BP). The presence of GZWs along the axis of a palaeo-ice stream trough therefore indicates a style of episodic retreat of the grounding line from its LGM to modern position. However, information about their composition and internal structure is sparse, and precise chronological constraints for both the onset and duration of stillstands they represent are still lacking. Consequently, the role of grounding-zone wedge formation in modulating post-LGM ice-sheet retreat cannot be reliably quantified. This information is vital, however, for calculating reliable retreat rates during the past, which are essential for evaluating and understanding the significance of modern retreat rates. Here we present the currently known inventory of GZWs on the continental shelf of the Amundsen Sea Embayment (ASE), West Antarctica, and introduce newly acquired data from one particular middle shelf GZW revealing the first information of its internal structure and composition. We will also discuss geological preconditions at the ice sheet bed that led to GZW formation. Furthermore, we will present our approach to i) reliably date the onset of GZW development, and ii) constrain the duration of these stillstands, including better estimations for subglacial sediment delivery rates. This knowledge will help refine available post-LGM retreat chronologies, which, in turn, serve as a basis for validating and improving ice-sheet models in an area where these are urgently needed.

  9. 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

  10. Assessment of Potentially Dangerous Glacial Lakes in Chinese Himalayas

    Science.gov (United States)

    Xiaojun, Yao; Shiyin, Liu; Xin, Wang

    2010-05-01

    Glacial lake outburst floods (GLOFs) are catastrophic discharges of water resulting primarily from melting glaciers. In the face of global warming, most Himalayan glaciers have been retreating at a rate that ranges from a few meters to several tens of meters per year, resulting in an increase in the number and size and size of glacial lakes and a concomitant increase in the threat of GLOFs. In the past 50 years, 16 GLOF events which were reported in Tibet had caused the loss of human lives as well as severe damage to local infrastructure. Based on the combination of temperature and precipitation of these 14 failed moraine-dammed lakes, the climatic background could be classified into 4 types, that is, warm-wet, warm-arid, cold-wet and near common weather condition. Under different climatic background types, the outburst mechanisms can be further divided into 5 types and 21 modes based on the analysis of 31 failed moraine-dammed lakes documented all over the world. As to a potentially dangerous moraine-dammed lake, all possible breach modes under each climatic background are firstly described and its qualitative possibilities are given by experts, then the decision-making trees are formed and the breach probability of the potentially dangerous moraine-dammed lake can be calculate. The breaching probabilities of the 143 potentially dangerous moraine-dammed lakes were calculated one by one using the decision-making trees model in Chinese Himalayas. The calculating results show that there are 44 lakes with very high breaching probability, 47 lakes with high breaching probability, 24 lakes with median breaching probability, 24 lakes with low breaching probability, 4 lakes with very low breaching probability. The 91 lakes with very high and high breaching probability rate should be requested in the next steps of detailed assessment and should be took into account in local infrastructure construction, such as road, hydropower station and residential plan, etc. Key words

  11. Supraglacial rock avalanches and their effect on glacial deposition

    Science.gov (United States)

    Reznichenko, N.; Davies, T. R. H.; Shulmeister, J.; Winkler, S.

    2012-04-01

    Although rock avalanches occur commonly in glaciated valleys, it is only recently that their effects on the regime and final deposits of debris-covered glaciers have been recognized. The supraglacially-emplaced rock avalanche deposits are distinct features on glacial surfaces due to their different sedimentology and greater depth than other debris covers. The metre-scale thickness and large areal extent of these deposits significantly impact the glacier mass balance by preventing ice-surface ablation (Reznichenko et al., 2011). These effects are often neglected in estimating the total change of glacial mass balance and its response to the catastrophic event. A supraglacial rock avalanche deposit can cause a glacier to form a moraine that will not reflect any current climate forcing. It is likely that only larger rock avalanche events (with respect to the size of the glacier) will result in a significant glacial response (e.g. advance or cessation of retreat). However, all supraglacially transported rock avalanche sediment will be recycled into moraines. The climatic signals extracted from the moraine chronologies of such glaciers may consequently have significant errors. The specific sedimentary characteristics of rock avalanche sediment such as agglomerates produced under high stress conditions (Reznichenko et al., in press) can be used to identify moraines that may have been formed from rock avalanche effect. Reznichenko, N.V., Davies, T.R.H. and Alexander, D.J., 2011. Effects of rock avalanches on glacier behaviour and moraine formation. Geomorphology, v. 132, is.3-4, p. 327-338 Reznichenko, N.V., Davies, T.R.H., Shulmeister, J. and Larsen S.H. Accepted. A new technique for identifying rock-avalanche-sourced sediment in moraines and some paleoclimatic implications. Geology.

  12. Re-treatment after full-course radiotherapy: is it a viable option?

    Energy Technology Data Exchange (ETDEWEB)

    Stewart, F.A. [Netherlands Cancer Inst., Amsterdam (Netherlands). Div. of Experimental Therapy

    1999-07-01

    Re-irradiation of previously treated areas may become necessary for recurrent cancer, new primary tumours (common in head and neck cancer patients), or nodal and metastatic disease. Factors that should be taken into account in the decision to re-treat include: (1) Previously treated volume (how much overlap is there with new treatment fields) and dose fractionation schedule; (2) which critical tissues or organs are at risk; (3) how much time has elapsed since first treatment; (4) whether there are any practical alternatives to re-irradiation? Rapidly proliferating tissues generally recover well from the initial radiotherapy and will tolerate re-irradiation to almost full doses. Some slowly proliferating tissues are also capable of partial proliferative and functional recovery, although this takes several months and some residual damage remains. Preclinical data demonstrate that re-irradiation with reduced doses is possible in lung and spinal cord after intervals of 3-6 months. Other slowly proliferating organs, e.g. the kidneys, do not appear to be capable of recovery, even after low, subtolerance doses. The largest clinical experience of re-irradiation is for head and neck cancers. A review of this literature reveals that the most frequent normal tissue complication seen is trismus (lockjaw), which occurs in 16 to 30% of re-treated cases, with lower incidences of soft tissue or bone necrosis and fibrosis. Myelitis is rarely reported, even in the re-treatment situation. In general the highest incidence of local control for the lowest incidence of serious complications is achieved for combinations of external beam and brachytherapy, and for small, well-differentiated, new primary tumours rather than recurrent disease. Re-treatment with total doses <55 Gy gives very poor local control rates. Re-treatment schedules with curative intent require a high re-treatment dose, which is accompanied by an increased risk of normal tissue damage. To minimize serious complications

  13. 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

  14. Centennial glacier retreat as categorical evidence of regional climate change

    Science.gov (United States)

    Roe, Gerard H.; Baker, Marcia B.; Herla, Florian

    2017-02-01

    The near-global retreat of glaciers over the last century provides some of the most iconic imagery for communicating the reality of anthropogenic climate change to the public. Surprisingly, however, there has not been a quantitative foundation for attributing the retreats to climate change, except in the global aggregate. This gap, between public perception and scientific basis, is due to uncertainties in numerical modelling and the short length of glacier mass-balance records. Here we present a method for assessing individual glacier change based on the signal-to-noise ratio, a robust metric that is insensitive to uncertainties in glacier dynamics. Using only meteorological and glacier observations, and the characteristic decadal response time of glaciers, we demonstrate that observed retreats of individual glaciers represent some of the highest signal-to-noise ratios of climate change yet documented. Therefore, in many places, the centennial-scale retreat of the local glaciers does indeed constitute categorical evidence of climate change.

  15. 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 ...

  16. Rituximab Retreatment for Low-Tumor Burden Follicular Lymphoma

    Science.gov (United States)

    A summary of results from a randomized clinical trial of patients with low–tumor burden follicular lymphoma that compared maintenance therapy with rituximab versus retreatment with rituximab only when there was evidence of disease progression.

  17. Parallel retreat of rock slopes underlain by alternation of strata

    Science.gov (United States)

    Imaizumi, Fumitoshi; Nishii, Ryoko; Murakami, Wataru; Daimaru, Hiromu

    2015-06-01

    Characteristic landscapes (e.g., cuesta, cliff and overhang of caprock, or stepped terrain) formed by differential erosion can be found in areas composed of variable geology exhibiting different resistances to weathering. Parallel retreat of slopes, defined as recession of slopes without changes in their topography, is sometimes observed on slopes composed of multiple strata. However, the conditions needed for such parallel retreat have not yet been sufficiently clarified. In this study, we elucidated the conditions for parallel retreat of rock slopes composed of alternating layers using a geometric method. In addition, to evaluate whether various rock slopes fulfilled the conditions for parallel retreat, we analyzed topographic data obtained from periodic measurement of rock slopes in the Aka-kuzure landslide, central Japan. Our geometric analysis of the two-dimensional slopes indicates that dip angle, slope gradient, and erosion rate are the factors that determine parallel retreat conditions. However, dip angle does not significantly affect parallel retreat conditions in the case of steep back slopes (slope gradient > 40°). In contrast, dip angle is an important factor when we consider the parallel retreat conditions in dip slopes and gentler back slopes (slope gradient toppling, but spatial distribution of the erosion rate measured by airborne LiDAR scanning and terrestrial laser scanning (TLS) roughly fulfills parallel retreat conditions. The Aka-kuzure landslide is characterized by repetition of steep sandstone cliffs and gentle shale slopes that form a stepped topography. The inherent resistance of sandstone to weathering is greater than that of shale. However, the vertical erosion rate within the sandstone was higher than that within the shale, due to direct relationship between slope gradient and vertical erosion rate in the Aka-kuzure landslide.

  18. Increasing Resident Wellness Through a Novel Retreat Curriculum.

    Science.gov (United States)

    Cornelius, Angela; Cornelius, Brian G; Edens, Mary Ann

    2017-07-28

    Background Because of their arduous schedules, residents are susceptible to burnout, fatigue, and depression. In 2015, the Accreditation Council for Graduate Medical Education (ACGME) launched a campaign to foster physician wellness, in response to the suicides of three residents during the previous year. The campaign calls for strategies to developing resiliency, identify problems, and promote well-being. One of the suggested methods to promote well-being was a residency retreat. Objective To implement a novel retreat curriculum that emphasizes team building between residents and faculty, with which residents expressed high satisfaction. Methods We created an "Amazing Race" style retreat involving five activity stations set up in a neighborhood park in which 25 of our 34 residents participated. These stations implemented team building, faculty-resident bonding and resident-resident bonding. An anonymous survey was administered to the 25 participating emergency medicine (EM) residents after the retreat, of whom 21 returned the survey. The survey consisted of questions to assess the resident's perception of the team building activities, their satisfaction with each of the five activity stations and overall retreat satisfaction. Results Of the 25 residents who participated in the retreat, 21 (84%) returned the post-retreat survey (one participant returned a survey leaving the ranking questions incomplete). This low-cost event received high satisfaction ratings in regard to team-building, resident bonding, and faculty-resident bonding. Conclusions This novel retreat proved to be a low-cost and easily implemented activity with which the residents expressed high levels of satisfaction.

  19. Glacial Lake Expansion in the Central Himalayas by Landsat Images, 1990–2010

    Science.gov (United States)

    Nie, Yong; Liu, Qiao; Liu, Shiyin

    2013-01-01

    Glacial lake outburst flood (GLOF) is a serious hazard in high, mountainous regions. In the Himalayas, catastrophic risks of GLOFs have increased in recent years because most Himalayan glaciers have experienced remarkable downwasting under a warming climate. However, current knowledge about the distribution and recent changes in glacial lakes within the central Himalaya mountain range is still limited. Here, we conducted a systematic investigation of the glacial lakes within the entire central Himalaya range by using an object-oriented image processing method based on the Landsat Thematic Mapper (TM) or Enhanced Thematic Mapper (ETM) images from 1990 to 2010. We extracted the lake boundaries for four time points (1990, 2000, 2005 and 2010) and used a time series inspection method combined with a consistent spatial resolution of Landsat images that consistently revealed lake expansion. Our results show that the glacial lakes expanded rapidly by 17.11% from 1990 to 2010. The pre-existing, larger glacial lakes, rather than the newly formed lakes, contributed most to the areal expansion. The greatest expansions occurred at the altitudinal zones between 4800 m and 5600 m at the north side of the main Himalayan range and between 4500 m and 5600 m at the south side, respectively. Based on the expansion rate, area and type of glacial lakes, we identified 67 rapidly expanding glacial lakes in the central Himalayan region that need to be closely monitored in the future. The warming and increasing amounts of light-absorbing constituents of snow and ice could have accelerated the melting that directly affected the glacial lake expansion. Across the main central Himalayas, glacial lakes at the north side show more remarkable expansion than those at the south side. An effective monitoring and warning system for critical glacial lakes is urgently needed. PMID:24376778

  20. Glacial Lake Expansion in the Central Himalayas By Landsat Images, 1990-2010

    Science.gov (United States)

    Nie, Y.; Liu, Q.; Liu, S.

    2014-12-01

    Glacial lake outburst flood (GLOF) is a serious hazard in high, mountainous regions. In the Himalayas, catastrophic risks of GLOFs have increased in recent years because most Himalayan glaciers have experienced remarkable downwasting under a warming climate. However, current knowledge about the distribution and recent changes in glacial lakes within the central Himalaya mountain range is still limited. Here, we conducted a systematic investigation of the glacial lakes within the entire central Himalaya range by using an object-oriented image processing method based on the Landsat Thematic Mapper (TM) or Enhanced Thematic Mapper (ETM) images from 1990 to 2010. We extracted the lake boundaries for four time points (1990, 2000, 2005 and 2010) and used a time series inspection method combined with a consistent spatial resolution of Landsat images that consistently revealed lake expansion. Our results show that the glacial lakes expanded rapidly by 17.11% from 1990 to 2010. The pre-existing, larger glacial lakes, rather than the newly formed lakes, contributed most to the areal expansion. The greatest expansions occurred at the altitudinal zones between 4800 m and 5600 m at the north side of the main Himalayan range and between 4500 m and 5600 m at the south side, respectively. Based on the expansion rate, area and type of glacial lakes, we identified 67 rapidly expanding glacial lakes in the central Himalayan region that need to be closely monitored in the future. The warming and increasing amounts of light-absorbing constituents of snow and ice could have accelerated the melting that directly affected the glacial lake expansion. Across the main central Himalayas, glacial lakes at the north side show more remarkable expansion than those at the south side. An effective monitoring and warning system for critical glacial lakes is urgently needed.

  1. Glacial lake expansion in the central Himalayas by Landsat images, 1990-2010.

    Directory of Open Access Journals (Sweden)

    Yong Nie

    Full Text Available Glacial lake outburst flood (GLOF is a serious hazard in high, mountainous regions. In the Himalayas, catastrophic risks of GLOFs have increased in recent years because most Himalayan glaciers have experienced remarkable downwasting under a warming climate. However, current knowledge about the distribution and recent changes in glacial lakes within the central Himalaya mountain range is still limited. Here, we conducted a systematic investigation of the glacial lakes within the entire central Himalaya range by using an object-oriented image processing method based on the Landsat Thematic Mapper (TM or Enhanced Thematic Mapper (ETM images from 1990 to 2010. We extracted the lake boundaries for four time points (1990, 2000, 2005 and 2010 and used a time series inspection method combined with a consistent spatial resolution of Landsat images that consistently revealed lake expansion. Our results show that the glacial lakes expanded rapidly by 17.11% from 1990 to 2010. The pre-existing, larger glacial lakes, rather than the newly formed lakes, contributed most to the areal expansion. The greatest expansions occurred at the altitudinal zones between 4800 m and 5600 m at the north side of the main Himalayan range and between 4500 m and 5600 m at the south side, respectively. Based on the expansion rate, area and type of glacial lakes, we identified 67 rapidly expanding glacial lakes in the central Himalayan region that need to be closely monitored in the future. The warming and increasing amounts of light-absorbing constituents of snow and ice could have accelerated the melting that directly affected the glacial lake expansion. Across the main central Himalayas, glacial lakes at the north side show more remarkable expansion than those at the south side. An effective monitoring and warning system for critical glacial lakes is urgently needed.

  2. 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.

  3. 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).

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

    Science.gov (United States)

    Zhao, Chen; King, Matt A.; Watson, Christopher S.; Barletta, Valentina R.; Bordoni, Andrea; Dell, Matthew; Whitehouse, Pippa L.

    2017-09-01

    Rapid regional warming in the Antarctic Peninsula has led to the significant retreat and eventual collapse of several major ice shelves since the 1970s, triggering the subsequent acceleration and thinning of their feeding glaciers. The Wordie Ice Shelf, lying off the west coast of the Antarctic Peninsula, has undergone long-term disintegration since the 1960s with a substantial calving event occurring around 1989, followed by continuous steady retreat and its almost-complete disappearance. The dynamic response of the upstream glaciers to the ice shelf collapse and the response of the solid Earth to the associated mass loss are not fully understood. To quantify the mass loss from the system, we generated a digital elevation model (DEM) using airborne vertical and oblique imagery from 1966 and compared it to a DEM derived from 2008 SPOT data. This analysis reveals lowering over that time of approximately 60 m at the front of Fleming Glacier. Using IceBridge and ICESat-2/GLAS data spanning 2002-2014, we show an increased rate of mean ice-surface lowering, with rates post-2008 more than twice those of 2002-2008. We use these load change data as a basis for the simulation of viscoelastic solid Earth 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 the Fleming Glacier, after the application of elastic and plate tectonic corrections, point away from Marguerite Bay rather than the present glacier front. This suggests

  5. 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 (debris flows or significant flood waves which could locally interfere with people or structures. Flood waves could possibly travel for long distances to the major valleys - albeit they would likely only incur rising water levels in already existing streambeds down there.

  6. Glacial Lake Growth and Associated Glacier Dynamics: Case Study from the Himalayas, Andes, Alaska and New Zealand

    Science.gov (United States)

    Binger, D. J.; Haritashya, U. K.; Kargel, J. S.; Shugar, D. H.

    2016-12-01

    Glacial lake growth and associated glacier dynamics: Case study from the Himalayas, Andes, Alaska and New Zealand David J. Binger1, Umesh K. Haritashya1 and Jeffrey S. Kargel21University of Dayton, Dayton, OH 2University of Arizona, Tucson, AZ As a result of climate change most of the world's alpine glaciers are undergoing measurable retreat and dynamic changes. The result of accelerated melting has led to the formation and growth of potentially dangerous glacial lakes. In this study, alpine glaciers and associated lakes from the Himalayas, Andes, Alaska and New Zealand, showing similar geomorphological settings were analyzed to compare differences in regional proglacial lake growth and its relationship with glacier dynamics. Specifically, we analyzed the surface area growth of the lakes, retreat of glacier terminus, changes in glacier velocity, surface temperature and potential glacial lake outburst flood triggers. Using Landsat and ASTER satellite images, Cosi - Corr software, and in house thermal mapping, 10 glaciers were analyzed and compared. Results show a substantial increase in proglacial lake surface area, accelerated velocity and significant calving of the glaciers. Glacier surface temperatures varied by location, with some remaining constant and others 2°C - 4°C increases; although increased surface temperature did not always show a direct correlation with increasing retreat rate. Lakes with high rates of surface area growth paired with glaciers with increased velocity and calving could prove to be unsustainable and lead to an increased risk for glacial lake outburst floods. Overall, result show the changing dynamics of the alpine glaciers in different mountain regions and the growth of their proglacial lakes.

  7. Glacial landscape evolution on Hall Peninsula, Baffin Island, since the Last Glacial Maximum: insights into switching glacial dynamics and thermo-mechanical conditions

    Science.gov (United States)

    Johnson, C. L.; Ross, M.

    2012-12-01

    channelized zones (GTZ 2) suggests a switch from warm to cold-based conditions over large areas while warm-based conditions prevailed within the channelized flow zone. This record may reflect the transition from LGM (thick warm-based ice) to thinner topographically-controlled ice, with cold-based patches, during early deglaciation. The catchment zones of the channelized system locally extended into the central area of Hall Peninsula (GTZ 3) which is reflected in till dispersal patterns and the striation record. The retreat of the LIS was later marked by southeastward readvances and/or surges (GTZ 4) and short-lived glacial lakes whose location requires ice to be maintained over GTZ 1. Thin cold-based ice remaining over GTZ 1 may explain the preservation of the inferred LGM landscape in that zone during deglacial events. The glacial landscape of Hall Peninsula reflects the effect of a switch from uniform warm-based ice and laterally extensive erosive basal sliding during LGM to a channelized flow during deglaciation and intervening cold-based zones. The change in basal thermo-mechanical conditions and the geometry of the channelized flow system may be precursor controlling factors to the development and shape of post LIS ice caps in this part of the Canadian Arctic.

  8. Knickpoint Retreat: the Role of Channel Self-Organisation

    Science.gov (United States)

    Baynes, E.; Lague, D.; Attal, M.

    2016-12-01

    Landscape connectivity occurs through the valley network, and the action of rivers within these valleys controls both landscape morphology, and landscape response to tectonic or climatic change. Such response to transient forcing is manifested in bedrock river profiles through migrating `knickzones' or `knickpoints', that separate a downstream reach, broadly in equilibrium with the new conditions and an upstream reach which is yet to adjust. Knickpoints therefore mark a dynamic boundary location within mountain landscapes, yet the complexities of the mechanisms of knickpoint retreat are often ignored in studies of landscape evolution. We carried out a series of box flume experiments (65 cm long, 30 cm wide), to explore the importance of mean discharge and substrate strength on the form and migration of knickpoints in a cohesive homogenous substrate. The retreat rate of knickpoints is independent of mean discharge, with knickpoints retreating faster through a weaker substrate. Despite an order of magnitude increase in discharge during our experiments, the bed shear stress remains almost constant due to a self-regulatory response of channel width to higher discharge, leading to no change in the upstream retreat rate of the waterfalls. These experiments challenge the established assumption in models of landscape evolution that a simple relationship exists between knickpoint retreat and discharge/drainage area, and we hypothesise that the correlation between knickpoint retreat and drainage area identified in some landscapes is caused by increasing bedload flux (the `tools' for erosion) with drainage area. Knickpoint retreat modelling approaches should therefore be re-evaluated, and greater attention paid to the role of bedload flux and connectivity between river channels and hillslopes.

  9. A new remote hazard and risk assessment framework for glacial lakes in the Nepal Himalaya

    OpenAIRE

    Rounce, DR; McKinney, DC; Lala, JM; Byers, AC; Watson, CS

    2016-01-01

    Glacial lake outburst floods (GLOFs) pose a significant threat to downstream communities and infrastructure due to their potential to rapidly unleash stored lake water. The most common triggers of these GLOFs are mass movement entering the lake and/or the self-destruction of the terminal moraine due to hydrostatic pressures or a buried ice core. This study initially uses previous qualitative and quantitative assessments to understand the hazards associated with eight glacial...

  10. Glaciers, Glacial lakes and Glacial Lake Outburst Floods in the Koshi Basin

    Science.gov (United States)

    Shrestha, F.; Gao, X.; Khanal, N. R.; Maharjan, S. B.; Bajracharya, S. R.; Shrestha, R. B.; Lizong, W.; Mool, P. K.

    2016-12-01

    Glacier is a vital water resources for mountain communities. Recession in glacier area either increased the glacial lake size or develop a new lake. The consequences of these changes in lake has become one of the major issue in the management of GLOF risk. This paper presents the distribution of, and changes in, glaciers, glacial lakes in the Koshi basin and also looks at past GLOF events that have occurred in the basin and their distance of impact. Data on the number of glaciers and glacial lakes and their areas were generated for the years 1977, 1990, 2000, and 2010 using Landsat images. The study revealed that there were a total of 845 glaciers (Nepal side) and 2,168 glacial lakes (Nepal and China side) with a total area of 1,103 km2 and 127.608 km2 in 2010. The number of glacier increased by 15% (109) and area decreased by 26% (396 km2) over 33 years. In case of glacier lakes, the number and area increased from 1,160 to 2,168 and from 94.444 km2 to 127.608 km2 during 33 years with an overall growth rates of 86.9% and 35.1%. A large number of glacial lakes are small in size (≤ 0.1 km2). End moraine dammed lakes with area ≥ 0.1 km2 were selected to analyse the change characteristics of glacial lakes. The results show that there were 134 lakes ≥ 0.1 km2 in 2010; these lakes had a total area of 43.06 km2 in 1997, increased to 64.35 km2 in 2010. The distribution of lakes on the north side of the Himalayas (in China) was three times higher than on the south side of the Himalayas (in Nepal). Comparing the mean growth rate in area and length for the 33 years, the growth rate on the north side was found to be a little slower than that on the south side. This relationship did not hold true for length change in the different periods. The study identified 42 rapidly growing large lakes that are dangerous in terms of GLOF risk. In the past, 18 GLOF events have been reported. The downstream distance impacted by those events was up to 90 km. Among them, 13 GLOF events

  11. Benefits of Attending a Weekend Childhood Cancer Survivor Family Retreat.

    Science.gov (United States)

    Bashore, Lisa; Bender, Joyce

    2017-09-01

    To explore the long-term benefits to families of childhood cancer survivors who attended a weekend childhood cancer survivor family retreat. Descriptive-qualitative study including families who had attended the weekend retreat at least once but not in the past 12 months, and who attend a large pediatric hematology and oncology cancer survivorship program in Texas. A semistructured interview guide was used during three audio-taped focus groups to explore the benefits of having attended a weekend retreat. Descriptive qualitative analysis was used to analyze the focus groups' transcripts. Seven families participated in the focus groups, and the themes identified were reconnecting (with others or family), putting life in perspective, and changing outlook on life. Retreats offer families of cancer survivors opportunities to reconnect with others and their own family members in a therapeutic environment. These reconnections in a therapeutic environment enriched the families' positive outlooks on life and changed their perspectives. Families of childhood cancer survivors report a lack of support following the completion of therapy. Retreats in a nonclinical therapeutic setting optimize family-perceived support, relationship building, and reconnecting survivor families. © 2017 Sigma Theta Tau International.

  12. Forecasting Stability or Retreat in Emerging Democratic Regimes

    Directory of Open Access Journals (Sweden)

    Snigdha Dewal

    2013-05-01

    Full Text Available Drawing on the literatures on elite transitions, factionalism and the new institutionalism, this paper hypothesizes that the stability of partially democratic and emerging democratic regimes is dependent on the willingness of elites to make credible commitments to cooperate and comply with democratic rules. That willingness (or lack thereof can be signaled by the presence of cooperative or conflict-precipitating events and actions in the periods around elections. We identify and analyze a variety of intra-elite interactions and demonstrate that conflict-precipitating events significantly increase the odds of a democratic retreat in the months before or just after an election, while cooperative events can balance them and prevent retreat. Using event data collected from 40 low- and middle-income countries for two-year periods around national elections between 1991 and 2007 we show that the imbalance of conflict-precipitating over cooperative events is far greater in cases of retreat from democracy. Furthermore, international intervention and pressure had a negative relationship with democratic stability. A logistic regression model accurately identified democratic retreat in 79 percent of the cases examined. Factor analysis revealed several common patterns of intra-elite conflict that can lead to democratic retreat, or conversely, patterns of cooperative events that bolster democratic consolidation. Finally, the data strongly argues for a model of democratic development that depends on open-ended elite maneuvering and the emergence of elite agreements, rather than a model where strong prior institutional constraints determine elite actions.

  13. Beyond debuttressing: Mechanics of paraglacial rock slope damage during repeat glacial cycles

    Science.gov (United States)

    Grämiger, Lorenz M.; Moore, Jeffrey R.; Gischig, Valentin S.; Ivy-Ochs, Susan; Loew, Simon

    2017-04-01

    Cycles of glaciation impose mechanical stresses on underlying bedrock as glaciers advance, erode, and retreat. Fracture initiation and propagation constitute rock mass damage and act as preparatory factors for slope failures; however, the mechanics of paraglacial rock slope damage remain poorly characterized. Using conceptual numerical models closely based on the Aletsch Glacier region of Switzerland, we explore how in situ stress changes associated with fluctuating ice thickness can drive progressive rock mass failure preparing future slope instabilities. Our simulations reveal that glacial cycles as purely mechanical loading and unloading phenomena produce relatively limited new damage. However, ice fluctuations can increase the criticality of fractures in adjacent slopes, which may in turn increase the efficacy of fatigue processes. Bedrock erosion during glaciation promotes significant new damage during first deglaciation. An already weakened rock slope is more susceptible to damage from glacier loading and unloading and may fail completely. We find that damage kinematics are controlled by discontinuity geometry and the relative position of the glacier; ice advance and retreat both generate damage. We correlate model results with mapped landslides around the Great Aletsch Glacier. Our result that most damage occurs during first deglaciation agrees with the relative age of the majority of identified landslides. The kinematics and dimensions of a slope failure produced in our models are also in good agreement with characteristics of instabilities observed in the field. Our results extend simplified assumptions of glacial debuttressing, demonstrating in detail how cycles of ice loading, erosion, and unloading drive paraglacial rock slope damage.

  14. The drainage and glacial history of the Still River Valley, southwestern Connecticut

    Science.gov (United States)

    Thompson, Woodrow B.

    1971-01-01

    The Still River is located in southwestern Connecticut. From its origin on the New York border, it passes through Danbury and flows northward to its junction with the Housatonic River in New Milford. Interpretation of the Still River's history is based on its surficial geology and bedrock topography. High bedrock surfaces to the south, east, and west of the river show that its preglacial direction was probably to the north. The Still River has developed along the easily eroded Inwood Marble as a subsequent tributary to the Housatonic. Pleistocene glaciation left a variety of deposits in the Still Valley. The oldest of these is the 'lower' till, of either Illinoian or Altonian age. This till unit is overlain in turn by the Woodfordian 'upper' till. The upper till has basal and ablation facies. Ice-contact deposits formed in the fringing stagnation zone of the last retreating ice sheet. As the glacier withdrew along the Still Valley, preglacial Lake Danbury was impounded against the highlands to the south. Glacial retreat opened progressively lower outlets for this lake. Its final stage was contained by a till (?) barrier at the Housatonic Gorge in New Milford. Filling of the lake by glacial outwash was soon followed by downcutting of the dam and establishment of the modern Housatonic and Still River channels.

  15. Seismic Stratigraphy of Ice Sheet Advance-Retreat Cycles on the Sabrina Coast Continental Shelf, East Antarctica

    Science.gov (United States)

    Frederick, B. C.; Gulick, S. P. S.; Saustrup, S.; Fernandez-Vasquez, R. A.; Domack, E. W.; Lavoie, C.; Blankenship, D. D.; Leventer, A.; Shevenell, A.

    2014-12-01

    2D multichannel seismic (MCS), multibeam and CHIRP data were collected as part of the recent R/V Nathaniel B. Palmer (NBP1402) cruise to investigate the marine record of cryosphere-ocean dynamics on the continental shelf between the Dalton Ice Tongue and Totten Glacier systems. Outlet glaciers and ice shelves along this coastline drain a catchment area extending across the Aurora Subglacial Basin (ASB) whose topography lies below sea level and contains an ice volume of approximately 6.9m of sea level rise equivalent. Analysis of over 750km of high-resolution MCS data has revealed the preservation of extensive tilted fluvial-deltaic shelf sedimentation and the first evidence of polythermal glacial advance in this region with well-preserved subglacial meltwater channels and tunnel valley systems. This expansive fluvial to glacial sedimentary section is separated by a regional unconformity from a series of irregular, localized unconformities preserved in an otherwise seismically transparent facies. We interpret these transparent facies as subglacial diamictites deposited over several glacial cycles. Detailed seismic stratigraphic analysis of the glacial sequences above the regional unconformity identified at least 4 glacial cycles illustrated by grounding zone wedge moraine deposits recorded in both MCS and multibeam bathymetric data. Distinct differences were evident in the stratigraphic architecture of polar versus polythermal glaciations including greater preservation of till deposits above the regional unconformity proximal to the exposed bedrock boundary and the present-day ice front. Sedimentary sequence preservation here appears dictated by the geometry of local ice advance and allied basement structure controls. Integration of marine geology, high resolution CHIRP and multibeam bathymetry data with MCS sequence geometry and acoustic facies mapping has led to improved constraints on rates, styles and patterns of glacial retreat. Such improvements to deformable

  16. Managed Retreat: A Global Analysis of Drivers, Barriers, and Outcomes

    Science.gov (United States)

    Hino, M.; Mach, K. J.; Field, C. B.

    2016-12-01

    Managed retreat is the strategic relocation of structures or abandonment of land to reduce natural hazard risk. Although managed retreat is a potentially important climate change adaptation option, it has not yet been deployed or studied as extensively as traditional protection or accommodation measures such as levees and beach nourishment. Its application faces numerous social and legal challenges that complicate its integration into a risk-management portfolio. However, a deeper understanding of its potential future use is urgently needed given the projected scope of climate-induced displacement in the coming decades. We evaluate the drivers, barriers, and outcomes of 27 recent cases of managed retreat that have resettled 1.6-2.7 million people. The examples originate in 19 countries, occur in pre- and post-disaster settings, and address flooding, erosion, earthquakes, and tsunamis. A model based on two key factors—who benefits from retreat and who initiates it—organizes the diverse set of cases into four quadrants and provides a structure for deeper analysis of case-specific complexities. Different sociopolitical features, such as the distribution of power, strength of governance, and attachment to place, emerge as particularly influential in each quadrant. The model acts as a point of departure for unpacking these complexities. By integrating these wide-ranging examples, the model enables a broader understanding of the landscape of managed retreat and the underlying social dynamics. It provides insight on how such dimensions can be incorporated into decision-making in a changing climate, advancing consideration and potential implementation of retreat.

  17. Sea ice breakup and marine melt of a retreating tidewater outlet glacier in northeast Greenland (81°N).

    Science.gov (United States)

    Bendtsen, Jørgen; Mortensen, John; Lennert, Kunuk; K Ehn, Jens; Boone, Wieter; Galindo, Virginie; Hu, Yu-Bin; Dmitrenko, Igor A; Kirillov, Sergei A; Kjeldsen, Kristian K; Kristoffersen, Yngve; G Barber, David; Rysgaard, Søren

    2017-07-10

    Rising temperatures in the Arctic cause accelerated mass loss from the Greenland Ice Sheet and reduced sea ice cover. Tidewater outlet glaciers represent direct connections between glaciers and the ocean where melt rates at the ice-ocean interface are influenced by ocean temperature and circulation. However, few measurements exist near outlet glaciers from the northern coast towards the Arctic Ocean that has remained nearly permanently ice covered. Here we present hydrographic measurements along the terminus of a major retreating tidewater outlet glacier from Flade Isblink Ice Cap. We show that the region is characterized by a relatively large change of the seasonal freshwater content, corresponding to ~2 m of freshwater, and that solar heating during the short open water period results in surface layer temperatures above 1 °C. Observations of temperature and salinity supported that the outlet glacier is a floating ice shelf with near-glacial subsurface temperatures at the freezing point. Melting from the surface layer significantly influenced the ice foot morphology of the glacier terminus. Hence, melting of the tidewater outlet glacier was found to be critically dependent on the retreat of sea ice adjacent to the terminus and the duration of open water.

  18. 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.

  19. Wisconsinan and early Holocene glacial dynamics of Cumberland Peninsula, Baffin Island, Arctic Canada

    Science.gov (United States)

    Margreth, Annina; Gosse, John C.; Dyke, Arthur S.

    2017-07-01

    Three glacier systems-an ice sheet with a large marine-based ice stream, an ice cap, and an alpine glacier complex-coalesced on Cumberland Peninsula during the Late Wisconsinan. We combine high-resolution mapping of glacial deposits with new cosmogenic nuclide and radiocarbon age determinations to constrain the history and dynamics of each system. During the Middle Wisconsinan (Oxygen Isotope Stage 3, OIS-3) the Cumberland Sound Ice Stream of the Laurentide Ice Sheet retreated well back into Cumberland Sound and the alpine ice retreated at least to fiord-head positions, a more significant recession than previously documented. The advance to maximal OIS-2 ice positions beyond the mouth of Cumberland Sound and beyond most stretches of coastline remains undated. Partial preservation of an over-ridden OIS-3 glaciomarine delta in a fiord-side position suggests that even fiord ice was weakly erosive in places. Moraines formed during deglaciation represent stillstands and re-advances during three major cold events: H-1 (14.6 ka), Younger Dryas (12.9-11.7 ka), and Cockburn (9.5 ka). Distinctly different responses of the three glacial systems are evident, with the alpine system responding most sensitively to Bølling-Allerød warming whereas the larger systems retreated mainly during Pre-Boreal warming. While the larger ice masses were mainly influenced by internal dynamics, the smaller alpine glacier system responded sensitively to local climate effects. Asymmetrical recession of the alpine glacier complex indicates topoclimatic control on deglaciation and perhaps migration of the accumulation area toward moisture source.

  20. Using a maximum simplicity paleoclimate model to simulate millennial variability during the last four glacial periods

    Science.gov (United States)

    Siddall, Mark; Stocker, Thomas F.; Blunier, Thomas; Spahni, Renato; McManus, Jerry F.; Bard, Edouard

    2006-12-01

    Many studies have documented the existence of millennial-scale variability in the Earth system during the last glacial period. An increasing number of studies document the occurrence of similar millennial variability during glacial periods previous to the last one. Here we use the simplest possible thermal-bipolar seesaw model to consider this variability for the last four glacial periods. We invert this model and use the high-pass filtered Vostok stable isotope records to make a first, tentative, attempt to estimate high-latitude N. Hemisphere temperature variability over the last four glacial periods, beyond the reach of Greenland ice-core records. The model result is compared against the Vostok methane record, which shows rapid variations in parallel to Greenland temperature records during the last glacial period. A further comparison is carried out against the planktonic oxygen isotope of north Atlantic core ODP 980. There is agreement between the records on the existence of similar millennial-scale variability during the last three glacial periods with very similar characteristics to the variability during the last glacial cycle.

  1. 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

    Recent years investigations have suggested that the circulation of warm seawater along the coast of Greenland play an important role for the mass balance of the Greenland Ice Sheet. A key driving force for the circulation is the contribution of meltwater in the inner parts of fjord systems where ......, the circulation of water masses and the retreat of tidewater glaciers may suggest a speedup of the melting of the Greenland Ice Sheet.......Recent years investigations have suggested that the circulation of warm seawater along the coast of Greenland play an important role for the mass balance of the Greenland Ice Sheet. A key driving force for the circulation is the contribution of meltwater in the inner parts of fjord systems where...... 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...

  2. Towards an improved inventory of Glacial Lake Outburst Floods in the Himalayas

    Science.gov (United States)

    Veh, Georg; Walz, Ariane; Korup, Oliver; Roessner, Sigrid

    2016-04-01

    The retreat of glaciers in the Himalayas and the associated release of meltwater have prompted the formation and growth of thousands of glacial lakes in the last decades. More than 2,200 of these lakes have developed in unconsolidated moraine material. These lakes can drain in a single event, producing potentially destructive glacial lake outburst floods (GLOFs). Only 44 GLOFs in the Himalayas have been documented in more detail since the 1930s, and evidence for a change, let alone an increase, in the frequency of these flood events remains elusive. The rare occurrence of GLOFs is counterintuitive to our hypothesis that an increasing amount of glacial lakes has to be consistent with a rising amount of outburst floods. Censoring bias affects the GLOF record, such that mostly larger floods with commensurate impact have been registered. Existing glacial lake inventories are also of limited help for the identification of GLOFs, as they were created in irregular time steps using different methodological approach and covering different regional extents. We discuss the key requirements for generating a more continuous, close to yearly time series of glacial lake evolution for the Himalayan mountain range using remote sensing data. To this end, we use sudden changes in glacial lake areas as the key diagnostic of dam breaks and outburst floods, employing the full archive of cloud-free Landsat data (L5, L7 and L8) from 1988 to 2015. SRTM and ALOS World 3D topographic data further improve the automatic detection of glacial lakes in an alpine landscape that is often difficult to access otherwise. Our workflow comprises expert-based classification of water bodies using thresholds and masks from different spectral indices and band ratios. A first evaluation of our mapping approach suggests that GLOFs reported during the study period could be tracked independently by a significant reduction of lake size between two subsequent Landsat scenes. This finding supports the feasibility

  3. Wringing the last drop of optically stimulated luminescence response for accurate dating of glacial sediments

    Science.gov (United States)

    Medialdea, Alicia; Bateman, Mark D.; Evans, David J.; Roberts, David H.; Chiverrell, Richard C.; Clark, Chris D.

    2017-04-01

    BRITICE-CHRONO is a NERC-funded consortium project of more than 40 researchers aiming to establish the retreat patterns of the last British and Irish Ice Sheet. For this purpose, optically stimulated luminescence (OSL) dating, among other dating techniques, has been used in order to establish accurate chronology. More than 150 samples from glacial environments have been dated and provide key information for modelling of the ice retreat. Nevertheless, luminescence dating of glacial sediments has proven to be challenging: first, glacial sediments were often affected by incomplete bleaching and secondly, quartz grains within the sediments sampled were often characterized by complex luminescence behaviour; characterized by dim signal and low reproducibility. Specific statistical approaches have been used to over come the former to enable the estimated ages to be based on grain populations most likely to have been well bleached. This latest work presents how issues surrounding complex luminescence behaviour were over-come in order to obtain accurate OSL ages. This study has been performed on two samples of bedded sand originated on an ice walled lake plain, in Lincolnshire, UK. Quartz extracts from each sample were artificially bleached and irradiated to known doses. Dose recovery tests have been carried out under different conditions to study the effect of: preheat temperature, thermal quenching, contribution of slow components, hot bleach after a measuring cycles and IR stimulation. Measurements have been performed on different luminescence readers to study the possible contribution of instrument reproducibility. These have shown that a great variability can be observed not only among the studied samples but also within a specific site and even a specific sample. In order to determine an accurate chronology and realistic uncertainties to the estimated ages, this variability must be taken into account. Tight acceptance criteria to measured doses from natural, not

  4. Iceland Dust Storms Linked to Glacial Outwash Deposits and to Sub-Glacial Flood (Jökulhlaup) Events

    Science.gov (United States)

    Prospero, J. M.; Arnalds, Ó.; Olafsson, H.; Bullard, J.; Hodgkins, R.

    2008-12-01

    two major glaciers, Mýrdalsjökull and Vatnajökull, the latter being the largest glacier in Europe. In our presentation we review the Iceland dust aerosol data and show the relationship to these six satellite- captured dust outbreaks along with other environmental data associated with these events. We point out that the synoptic events associated with these dust outbreaks could carry dust into the high latitudes and to Europe. We also note that glaciers on Iceland have been retreating in recent decades and that this trend is expected to continue with changing climate. Thus dust activity from newly-exposed glacial deposits will most likely increase in the future on Iceland and possibly from other glacial terrains in the Arctic.

  5. Hazard and Risk of Glacial Lake Outburst Floods in the Nepal Himalayas

    Science.gov (United States)

    Rounce, David; McKinney, Daene

    2016-04-01

    As the climate changes and glaciers continue to melt, the number of glacial lakes and the size of these lakes is rapidly increasing. These glacial lakes are contained by terminal moraines composed of debris, soil, and sometimes ice, which are susceptible to fail catastrophically and cause a glacial lake outburst flood (GLOF). Understanding the hazard and risk associated with these lakes is important for downstream communities and other stakeholders, e.g., hydroelectric companies. Unfortunately, existing methods that are used to assess GLOF hazards yield conflicting classifications, which leads to confusion amongst the stakeholders who these studies are meant to assist. This study assesses existing methods on potentially dangerous glacial lakes in Nepal and uses these methods to develop an objective and holistic risk & action framework that may be used to assist and prioritize risk-mitigation actions.

  6. MECHANISM OF GULLY-HEAD RETREAT - A STUDY AT ...

    African Journals Online (AJOL)

    Osondu

    Near vertical and overhanging slope of considerable height develop tension cracks leading to mass failure and gully head retreat. Number of instability factors is operating at the gully heads and no linear relation can be established between these factors and gully erosion. Key words: Tension crack, Mass failure, Gully head ...

  7. Geophysical monitoring of coastal erosion and cliff retreat of ...

    African Journals Online (AJOL)

    Michael.Machutchon

    From the laser scanning datasets it has been calculated that a nett erosional trend exists for the study area with sediment moving towards the north. In the western portion of the study area, where a coastal road has been undercut and complete failure has occurred, the progress of cliff retreat has been accurately measured ...

  8. MECHANISM OF GULLY-HEAD RETREAT - A STUDY AT ...

    African Journals Online (AJOL)

    Osondu

    erosion. Key words: Tension crack, Mass failure, Gully head retreat, Geotechnical properties. Introduction. Gully erosion, caused by the instability of the channel or gully-heads and gully-walls, is a serious problem in lateritic environments and is responsible for the destruction of agricultural land and structures such as roads,.

  9. Jumpstarting Junior Faculty Motivation and Performance with Focused Writing Retreats

    Science.gov (United States)

    Girardeau, Laura; Rud, A. G.; Trevisan, Michael S.

    2014-01-01

    Faculty members are critical assets to universities, and large losses to institutions occur if they are not successful. Although institutions value publications and grants in the tenure process, newer professors receive little guidance in writing for these endeavors. Faculty writing retreats help apprentice professors in the craft of writing;…

  10. Scientists Discover New Possibilities at Scientific Investigators Retreat | Poster

    Science.gov (United States)

    By Nancy Parrish, Staff Writer; photos by Richard Frederickson, Staff Photographer Scientists who attended the 2015 NCI Intramural Scientific Investigators Retreat on Jan. 13 had a chance to discuss research results with other investigators from across the National Cancer Institute. And this year, they could also explore new possibilities for the future of their research.

  11. The challenge of re-treatment pulmonary tuberculosis at two ...

    African Journals Online (AJOL)

    Background With an annual tuberculosis (TB) incidence of about 350 cases per 100,000 of the population, Uganda is a high burden country. Moreover, it is evident that some TB patients have been treated for a previous episode of the disease. Objective To highlight the burden of re-treatment pulmonary TB and examine ...

  12. Geophysical monitoring of coastal erosion and cliff retreat of ...

    African Journals Online (AJOL)

    Geophysical monitoring of coastal erosion and cliff retreat of Monwabisi Beach, False Bay, South Africa. ... Conventional beach profile data were acquired using a differential global positioning system (DGPS) in April 2014 and LiDAR data were acquired in November 2014. From the laser scanning datasets it has been ...

  13. Modeling the cliff retreat response to base-level change in layered rocks, Colorado Plateau, USA

    Science.gov (United States)

    Ward, D.; Sheehan, C.

    2015-12-01

    The retreat of cliffs is an important mode of erosion in layered rocks of variable strength. For example, the iconic Colorado Plateau landscapes of Grand Canyon, Canyonlands, and Monument Valley owe their unique forms to this process. These landscapes are the end result of incision by trunk streams followed by cliff retreat. Local interactions between stochastic rockfall and first-order channels draining a cliff regulate the cliff retreat response to a base-level fall. However, nonlinear transport dynamics, steep slopes, and variable rock strength challenge the modeling of landscape evolution in these settings. Here, we employ structure-from-motion photogrammetry to generate high-resolution DTMs of a natural experiment site on the Colorado Plateau. The site features a simple, sandstone-over-shale stratigraphy with a continuous gradient in cliffband height and evidence for an ongoing transient response to base level fall. The terrain data inform a high-resolution (dx=5 m), 2D numerical model of cliffband erosion. The model simulates the interaction of three primary processes: fluvial erosion and sediment transport; hillslope transport of regolith, including shallow landsliding; and rockfall from resistant units. Crucially, the model allows us to modify stratigraphy arbitrarily to examine the landscape response to parameters such as thickness, spacing, and dip of resistant units. Results indicate that the contrast in fluvial erodibility sets the pattern of emergence of cliffs as a resistant layer is exhumed, while the difference in weathering rates across rock types sets the rate at which cliffs emerge. Once rockfall begins, erosion rates are modified by the thickness of the resistant layer, which sets the volume of rockfall debris reaching the channels below the cliff. The modeling highlights the need for process-based understanding of the conditions for cliff failure by rockfall and redistribution of the debris in very steep, rapidly-eroding landscapes.

  14. Modelling grounding line retreat during deglaciation of the Western Fennoscandian Ice Sheet using ISSM

    Science.gov (United States)

    Åkesson, Henning; Morlighem, Mathieu; Nisancioglu, Kerim H.; Svendsen, John Inge; Mangerud, Jan

    2017-04-01

    Recent marine-based ice mass loss in Greenland and Antarctica has been broadly attributed to increased air temperatures and warmer ocean conditions. However, these changes display considerable spatial and temporal heterogeneity, suggesting that topographic factors are modulating the response. To elucidate factors important for decadal and longer time scales, the relatively short observational record needs to be complemented by studies of past marine-based mass changes. Large-scale ice sheet models are however too coarse to accurately resolve grounding line migration, marine-terminating glacier acceleration and ice shelf collapse on paleo-time scales. Here we study regional marine ice sheet changes during deglaciation of the Fennoscandian Ice Sheet in SW Norway, with similar topography to Greenland. With coastal mountains deeply incised by fjords extending far inland, this area provides clues to responsible processes and rates of future mass loss from the Greenland Ice Sheet, and associated contribution to sea level. We use the state-of-the-art ice sheet model ISSM to transiently simulate the entire deglaciation from 18 to 11 ka, including the readvance during Younger Dryas. Grounding line migration is tracked highly accurately within the adaptive finite-element model mesh. We use proxies, geomorphological data, and exposure dating of ice thickness and marginal changes to provide three-dimensional constraints on ice sheet thinning and retreat. We find that the modelled outermost ice sheet margin is largely insensitive to ocean warming, and that ice shelf collapse has a minor effect on upstream flow. Instead, considerable surface mass balance changes are required to trigger retreat. Once initiated, grounding line retreat is rapid, paced by fjord topography and submarine melt rate. We discuss the implications of our findings in context of deglaciation of the Laurentide and Eurasian Ice Sheets, as well as recent mass loss and potential future marine ice sheet

  15. 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.

  16. 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

  17. Glacial influence and stream macroinvertebrate biodiversity under climate change: Lessons from the Southern Alps.

    Science.gov (United States)

    Lencioni, Valeria

    2017-12-06

    The aim of this work was to highlight the main ecological predictors driving invertebrate distribution in eight glacier-fed streams in the Southern Alps. Thirty-five sites belonging to four stream types were sampled monthly during the ablation season of one, two or three years between 1996 and 2014. Taxa from glacial (kryal and glacio-rhithral) and non-glacial (kreno-rhithral and lake outlet) sites were separated by canonical correspondence analysis (CCA) along a glacial influence gradient and a hydrological-altitudinal gradient. High glacial influence was associated mainly with low maximum water temperature (Tmax), high Glacial Index (calculated as a function of glacier area and distance from the glacier), and the abundance of Diamesa species (D. steinboecki, D. goetghebueri, D. zernyi, and D. latitarsis). Change-point analysis and Threshold Indicator Taxa Analysis confirmed the CCA results in identifying these Diamesa species as the taxa with the strongest preference for high percent glacier cover in the catchment (change point~30%) and low Tmax (change point~6°C). Temporal changes in community structure were highlighted in seven sites fed by glaciers under different retreat rates. Where the rate was faster and the remaining glacier smaller (≪1km2), the most cold-stenothermal kryal inhabitant, D. steinboecki, almost disappeared or survived only as brachypterous populations, whereas other Diamesinae (Pseudokiefferiella parva), Orthocladiinae (e.g. Eukiefferiella, Orthocladius), Limoniidae, Baetidae, Nemouridae, and non-insect taxa (e.g. Oligochaeta, Hydracarina) became more abundant. Upstream migration was observed in Diamesa spp. which conquered new stream reaches left free by the retreating glacier, and euriecious taxa which colonized reaches with ameliorated environmental conditions, no longer the exclusive habitat of Diamesa spp. Co-occurrence of stochastic and deterministic assembly processes seem to drive spatio-temporal changes in these invertebrate

  18. 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

  19. Glacial effects limiting mountain height.

    Science.gov (United States)

    Egholm, D L; Nielsen, S B; Pedersen, V K; Lesemann, J-E

    2009-08-13

    The height of mountain ranges reflects the balance between tectonic rock uplift, crustal strength and surface denudation. Tectonic deformation and surface denudation are interdependent, however, and feedback mechanisms-in particular, the potential link to climate-are subjects of intense debate. Spatial variations in fluvial denudation rate caused by precipitation gradients are known to provide first-order controls on mountain range width, crustal deformation rates and rock uplift. Moreover, limits to crustal strength are thought to constrain the maximum elevation of large continental plateaus, such as those in Tibet and the central Andes. There are indications that the general height of mountain ranges is also directly influenced by the extent of glaciation through an efficient denudation mechanism known as the glacial buzzsaw. Here we use a global analysis of topography and show that variations in maximum mountain height correlate closely with climate-controlled gradients in snowline altitude for many high mountain ranges across orogenic ages and tectonic styles. With the aid of a numerical model, we further demonstrate how a combination of erosional destruction of topography above the snowline by glacier-sliding and commensurate isostatic landscape uplift caused by erosional unloading can explain observations of maximum mountain height by driving elevations towards an altitude window just below the snowline. The model thereby self-consistently produces the hypsometric signature of the glacial buzzsaw, and suggests that differences in the height of mountain ranges mainly reflect variations in local climate rather than tectonic forces.

  20. 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.

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

    DEFF Research Database (Denmark)

    Chatzidionysiou, Katerina; Lie, Elisabeth; Lukina, Galina

    2017-01-01

    OBJECTIVE: Several aspects of rituximab (RTX) retreatment in rheumatoid arthritis (RA) need to be further elucidated. The aim of this study was to describe the effect of repeated courses of RTX on disease activity and to compare 2 retreatment strategies, fixed-interval versus on-flare retreatment...

  2. Attack or retreat: contrasted defensive tactics used by Cyprian honeybee colonies under attack from hornets.

    Science.gov (United States)

    Papachristoforou, Alexandros; Rortais, Agnès; Sueur, Jérôme; Arnold, Gérard

    2011-02-01

    This study describes the tactics used by Cyprian honeybees (Apis mellifera cypria) to defend their colonies against hornet (Vespa orientalis orientalis) attacks. We use simulated hornet attacks and a combination of video recordings and image analysis to reveal, for the first time, contrasted intra-subspecies defensive tactics that operate at the colony level during predation. In some colonies, when attacked, the numbers of guards at the hive entrance increases rapidly to attack, engulf, and kill invading hornets. In other colonies, guards avoid conflicts with hornets by retreating gradually and by forming a defensive line of honeybees at the hive entrance. Retreater colonies have propolis walls at the hive entrances with small apertures that are too narrow to allow the hornet to access the hive and that therefore reinforces entrance protection. On the contrary, attacker colonies have propolis walls with large openings through which the hornet can pass; these bees block the hornet's access by intensively guarding the hive entrance. We experimentally destroy propolis walls to test whether colonies consistently rebuild walls with the same intrinsic characteristics and we also monitor the survival rate of each anti-predator tactic after massive natural predation by hornets. Copyright © 2010 Elsevier B.V. All rights reserved.

  3. The timing and cause of glacial advances in the southern mid-latitudes during the last glacial cycle based on a synthesis of exposure ages from Patagonia and New Zealand

    Science.gov (United States)

    Darvill, Christopher M.; Bentley, Michael J.; Stokes, Chris R.; Shulmeister, James

    2016-10-01

    Glacier advances in the southern mid-latitudes during the last glacial cycle (ca. 110-10 ka) were controlled by changes in temperature and precipitation linked to several important ocean-climate systems. As such, the timing of glacial advance and retreat can yield important insights into the mechanisms of Southern Hemisphere climate change. This is particularly important given that several recent studies have demonstrated significant glacial advances prior to the global Last Glacial Maximum (gLGM) in Patagonia and New Zealand, the cause of which are uncertain. The recent increase in chronological studies in these regions offers the opportunity to compare regional trends in glacial activity. Here, we compile the first consistent 10Be exposure-dating chronologies for Patagonia and New Zealand to highlight the broad pattern of mid-latitude glacial activity over the last glacial cycle. Our results show that advances or still stands culminated at 26-27 ka, 18-19 ka and 13-14 ka in both Patagonia and New Zealand and were broadly synchronous, but with an offset between regions of up to 900 years that cannot be explained by age calculation or physically plausible erosion differences. Furthermore, there is evidence in both regions for glacial advances culminating from at least 45 ka, during the latter half of Marine Isotope Stage (MIS) 3. Glacial activity prior to the gLGM differed from the large Northern Hemisphere ice sheets, likely due to favourable Southern Hemisphere conditions during late MIS 3: summer insolation reached a minimum, seasonality was reduced, winter duration was increasing, and sea ice had expanded significantly, inducing stratification of the ocean and triggering northward migration of oceanic fronts and the Southern Westerly Winds. Glacial advances in Patagonia and New Zealand during the gLGM were probably primed by underlying orbital parameters. However, the precise timing is likely to have been intrinsically linked to migration of the coupled ocean

  4. An inventory of glacial lakes in the Austrian Alps

    Science.gov (United States)

    Buckel, Johannes; Otto, Jan-Christoph; Keuschnig, Markus; Götz, Joachim

    2016-04-01

    The formation of lakes is one of the consequences of glacier retreat due to climate change in mountain areas. Numerous lakes have formed in the past few decades in many mountain regions around the globe. Some of these lakes came into focus due to catastrophic hazard events especially in the Himalayas and the Andes. Glacial lake development and lifetime is controlled by the complex interplay of glacier dynamics, geomorphological process activity and geological boundary conditions. Besides the hazard potential new lakes in formerly glaciated areas will significantly contribute to a new landscape setting and to changing geomorphologic, hydrologic and ecologic conditions at higher alpine altitudes. We present an inventory of high alpine lakes in the Austrian Alps located above an altitude of 1700 m asl. Most of these lakes are assumed to be of glacial origin, but other causes for development, like mass movements are considered as well. The inventory is a central part of the project FUTURELAKES that aims at modelling the potential development of glacial lakes in Austria (we refer to the presentation by Helfricht et al. during the conference for more details on the modelling part). Lake inventory data will serve as one basis for model validation since modelling is performed on different time steps using glacier inventory data. The purpose of the lake inventory is to get new insights into boundary conditions for lake formation and evolution by analysing existing lake settings. Based on these information the project seeks to establish a model of lake sedimentation after glacier retreat in order to assess the potential lifetime of the new lakes in Austria. Lakes with a minimum size of 1000 m² were mapped using multiple aerial imagery sources. The dataset contains information on location, geometry, dam type, and status of sedimentation for each lake. Additionally, various geologic, geomorphic and morphometric parameters describe the lake catchments. Lake data is related to

  5. Glacial Features (Point) - Quad 170 (PORTSMOUTH, NH-ME)

    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,...

  6. Glacial Features (Point) - Quad 202 (NEWBURYPORT EAST, MA-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,...

  7. Microbial formation of labile organic carbon in Antarctic glacial environments

    Science.gov (United States)

    Smith, H. J.; Foster, R. A.; McKnight, D. M.; Lisle, J. T.; Littmann, S.; Kuypers, M. M. M.; Foreman, C. M.

    2017-04-01

    Roughly six petagrams of organic carbon are stored within ice worldwide. This organic carbon is thought to be of old age and highly bioavailable. Along with storage of ancient and new atmospherically deposited organic carbon, microorganisms may contribute substantially to the glacial organic carbon pool. Models of glacial microbial carbon cycling vary from net respiration to net carbon fixation. Supraglacial streams have not been considered in models although they are amongst the largest ecosystems on most glaciers and are inhabited by diverse microbial communities. Here we investigate the biogeochemical sequence of organic carbon production and uptake in an Antarctic supraglacial stream in the McMurdo Dry Valleys using nanometre-scale secondary ion mass spectrometry, fluorescence spectroscopy, stable isotope analysis and incubation experiments. We find that heterotrophic production relies on highly labile organic carbon freshly derived from photosynthetic bacteria rather than legacy organic carbon. Exudates from primary production were utilized by heterotrophs within 24 h, and supported bacterial growth demands. The tight coupling of microbially released organic carbon and rapid uptake by heterotrophs suggests a dynamic local carbon cycle. Moreover, as temperatures increase there is the potential for positive feedback between glacial melt and microbial transformations of organic carbon.

  8. Microbial formation of labile organic carbon in Antarctic glacial environments

    Science.gov (United States)

    Smith, H.J.; Foster, R.; McKnight, D.M.; Lisle, John T.; Littmann, S.; Kuypers, M.M.M.; Foreman, C.M.

    2017-01-01

    Roughly six petagrams of organic carbon are stored within ice worldwide. This organic carbon is thought to be of old age and highly bioavailable. Along with storage of ancient and new atmospherically deposited organic carbon, microorganisms may contribute substantially to the glacial organic carbon pool. Models of glacial microbial carbon cycling vary from net respiration to net carbon fixation. Supraglacial streams have not been considered in models although they are amongst the largest ecosystems on most glaciers and are inhabited by diverse microbial communities. Here we investigate the biogeochemical sequence of organic carbon production and uptake in an Antarctic supraglacial stream in the McMurdo Dry Valleys using nanometre-scale secondary ion mass spectrometry, fluorescence spectroscopy, stable isotope analysis and incubation experiments. We find that heterotrophic production relies on highly labile organic carbon freshly derived from photosynthetic bacteria rather than legacy organic carbon. Exudates from primary production were utilized by heterotrophs within 24 h, and supported bacterial growth demands. The tight coupling of microbially released organic carbon and rapid uptake by heterotrophs suggests a dynamic local carbon cycle. Moreover, as temperatures increase there is the potential for positive feedback between glacial melt and microbial transformations of organic carbon.

  9. 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.

  10. Glacial Debutressing and Displacement History of the Driest Rockslide (Central Alps, Switzerland)

    Science.gov (United States)

    Vogler, Matthias; Loew, Simon; Glueer, Franziska; Grämiger, Lorenz

    2016-04-01

    Only few studies have been performed, where the physical interactions between a retreating valley glacier and rock slope movements have been recorded and analyzed in detail. The Driest landslide, situated at the current tongue of the Great Aletsch Glacier in the Swiss Alps, offers a unique case study, because the history of the Great Aletsch Glacier has been studied in great detail by various researchers and the Driest landslide displacements can be unraveled for similar time windows. In this paper we focus on the most recent observation period, i.e. the rockslide and glacier history since the Little Ice Age, when the entire Driest landslide was covered by the glacial ice. Our kinematic model of the Driest landslide, based on field mapping and photogrammetric analyses, was confirmed by displacement vector data from two robotic total stations recording daily displacements of 12 reflectors positioned within the instability. The rockslide basal rupture plane is a compound sliding surface composed of a steeply dipping head scarp, a presumably moderately steep central section, and an upward directed daylighting frontal section. This rupture plane geometry is structurally conditioned by a regional fault in the head scarp area and a rotating Alpine foliation in the toe area. The most recent displacement history of this old rotational rockslide has been unraveled by lichenometry (i.e. systematic mapping of greenish Rhizocarpon Geographicum diameters) in the deepest part of the head scarp, calibrated with dendrochronologic data. Depending on the lichen profile position within the head scarp area, different displacement time histories of the Driest landslide can be developed and correlated with glacial ice elevations as recorded by multiple aerial images and historical documents. Whereas displacement rates before 1991 were in the order of 1 cm/year, significantly higher displacement rates ranging between 7 and 13 cm/year are recorded in the head scarp area for the period

  11. Last Glacial Maximum in Poland

    Science.gov (United States)

    Marks, Leszek

    2002-01-01

    The Last Glacial Maximum (LGM) in Poland is represented by the Leszno Phase and occurred after 21 ka radiocarbon years. In turn the deglacial Poznań Phase is estimated at 18.4 ka, the Pomeranian Phase at 15.2 ka, the Gardno Phase at about 14.0-13.8 ka, the Słupsk Bank Phase at 13.5-13.2 ka and the Southern Middle Bank Phase at 12.7-12.5 ka BP. The ice sheet limit at LGM was not synchronous everywhere in Poland but occurred as several major and minor ice lobes that reflected a stream-like structure of the ice body that radiated southwards from the Baltic Basin. Meltwater runoff during the LGM created a complex system of sandur trains and ice-marginal spillways, with numerous intervening proglacial lakes.

  12. Glacial Isostatic Adjustment in Antarctica

    Science.gov (United States)

    Whitehouse, P. L.

    2014-12-01

    In order to determine the distribution of present-day ice mass change across the Antarctic Ice Sheet it is first necessary to remove the geodetic signal of past ice mass change. This signal arises due to the ongoing process of Glacial Isostatic Adjustment (GIA), which has traditionally been estimated by modelling the response of the Earth system to ice-sheet changes during a glacial cycle. Reconstructions of ice-sheet change are typically based on field observations relating to past ice extent and thickness, although a more recent approach has involved the use of ice-sheet models, and even coupled ice-sheet - GIA models, to reconstruct the ice-sheet history in areas where field constraints are sparse. Both methods have their limitations and in this presentation I will highlight the advantages of each and compare recently-published models to assess our current state of knowledge in the field of Antarctic GIA. I will also briefly discuss the motivation behind active areas of model development, which include the consideration of lateral variations in Earth structure and feedbacks between solid Earth, ice sheet and ocean processes. Finally, I will assess the suitability of the various data sets that are used to constrain or test Antarctic GIA models, and I will explain how combinations of data are being used to isolate the GIA signal independently of traditional modelling assumptions. Despite the clear benefits of this approach for the purposes of quantifying present-day ice mass change, it is still crucial to be able to model how GIA processes will evolve in the future. The motivation for this goal is provided by recent modelling studies, which suggest that GIA processes will be modified by, and are capable of influencing, the future dynamics of the Antarctic Ice Sheet.

  13. Pathological organizations and psychic retreats in eating disorders.

    Science.gov (United States)

    Kadish, Yael Adira

    2012-04-01

    A set of characteristic symptoms allow for the relatively straightforward diagnosis of eating disorders. Simultaneously and paradoxically, underlying the eating disorders are a wide variety of personality organizations/disorders, stretching from the neurotic to the borderline and narcissistic, and even to conditions approaching psychosis. This paper will argue that the inherent commonalities can be ascribed to pathological organizations of a similar nature and quality, operational across the spectrum of eating disorders and functioning in a particular, sadomasochistic way. The typical forms that eating disorders take are based on the specific ways that food and the body are used, that is, symptom manifestation. These distinctive symptom manifestations appear to be related to Steiner's (1982, 1993) notion of a psychic retreat. Pathological organizations and psychic retreats are latent until called upon either sporadically or continuously. When activated, these defensive structures operate like a complex psychic skeleton around which the unique psychodynamics of each patient become rearranged and thereby transformed.

  14. Assessing Glacial Lake Outburst Flood Hazard in the Nepal Himalayas using Satellite Imagery and Hydraulic Models

    Science.gov (United States)

    Rounce, D.; McKinney, D. C.

    2015-12-01

    The last half century has witnessed considerable glacier melt that has led to the formation of large glacial lakes. These glacial lakes typically form behind terminal moraines comprising loose boulders, debris, and soil, which are susceptible to fail and cause a glacial lake outburst flood (GLOF). These lakes also act as a heat sink that accelerates glacier melt and in many cases is accompanied by rapid areal expansion. As these glacial lakes continue to grow, their hazard also increases due to the increase in potential flood volume and the lakes' proximity to triggering events such as avalanches and landslides. Despite the large threat these lakes may pose to downstream communities, there are few detailed studies that combine satellite imagery with hydraulic models to present a holistic understanding of the GLOF hazard. The aim of this work is to assess the GLOF hazard of glacial lakes in Nepal using a holistic approach based on a combination of satellite imagery and hydraulic models. Imja Lake will be the primary focus of the modeling efforts, but the methods will be developed in a manner that is transferable to other potentially dangerous glacial lakes in Nepal.

  15. Intermittent glacial sliding velocities explain variations in long-timescale denudation

    Science.gov (United States)

    Yanites, Brian J.; Ehlers, Todd A.

    2016-09-01

    Quantifying controls on glacial erosion over geologic timescales is central to understanding the role of Cenozoic climate change on the development of modern mountain belts, yet the mechanisms that produce the distinct relief and topography visible in glaciated regions remain poorly constrained. We test the hypothesis that commonly assumed glacial sliding parameterizations control denudation rates over geologic timescales. We do this by modeling glacier dynamics over a glacial-interglacial cycle and compare with a dense dataset of (U-Th)/He thermochronometer derived denudation rates from the southern Coast Mountains, BC. Results indicate zones of rapid Quaternary erosion correspond to locations where the model predicts the highest averaged sliding velocities. The results are consistent with the hypothesis that sliding influences the rate of glacial erosion. Regression between sliding predicted by the model and erosion rates shows a statistically significant correlation (r2 = 0.6). The coefficient of the regression (10-5) is smaller than previous estimates based on data from much shorter timescales. The model results also reveal that for a specific location, active subglacial sliding, and hence erosion, occurs for only ∼10-20% of a glacial-interglacial cycle, suggesting high temporal variations in erosion rates. This intermittency of erosion requires instantaneous erosion rates to be greater than long term averages, explaining how timescale averaging can impact estimates of glacial erosion rates.

  16. 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.

  17. Scientific Investigators Retreat Brings Like Minds Together | Poster

    Science.gov (United States)

    Scientists throughout NCI gathered at the 2016 Intramural Scientific Investigators Retreat on Jan. 12, at the Ronald Reagan Building and International Trade Center, to discuss the results of their research with fellow investigators. Several researchers who have made significant advances toward the goal of eliminating the threat of cancer spoke to a packed auditorium of like-minded experts. Speaker topics included the role genetics play in the risk of breast cancer, using fiberglass to...

  18. [Re-treatments of recurrence after pelvic floor repair surgery].

    Science.gov (United States)

    Fan, S X; Wang, F M; Lin, L S; Song, Y F

    2017-06-25

    Objective: To analyze re-treatments of recurrence after the pelvic floor repair surgery. Methods: The protocol and the effect of re-treatments were investigated by reviewing and analyzing the clinical data of 81 recurrent patients (grade Ⅱ and above), who had received the pelvic floor repair surgery from January 2011 to January 2016. Pelvic organ prolapse quantitation system (POP-Q) and two questionnaires about quality of life [pelvic floor distress inventory-short form 20 (PFDI-20) and pelvic floor impact questionnaire short form (PFIQ-7)] were used to evaluate objective and subjective efficacy, respectively. Results: Among 81 recurrent patients who were followed up for a median of 35 months (10- 69 months), 78 cases (with prolapse up to grade Ⅲ or Ⅳ) were treated by surgical operation with both objective cure rate and subjective satisfaction being 100% (78/78); 3 cases (with grade Ⅱ prolapse) were treated by pelvic floor electrical stimulation biofeedback, and 1 case among the three cases had the vaginal foreign body sensation, the subjective satisfaction was 2/3. The methods of surgical operation for the 78 recurrent patients included: total pelvic floor reconstructive surgery (55 cases; 3 of which involve trachelectomy), anterior pelvic reconstructive surgery (2 cases), posterior pelvic reconstructive surgery (3 cases), Y-mesh sacral colpopexy (2 cases), colpocleisis (11 cases), vaginal hysterectomy combined posterior fornix forming (3 cases), and vaginal hysterectomy combined posterior pelvic reconstructive surgery(2 cases). Conclusion: The extent of recurrence, the recurrent site and complications must be carefully considered and evaluated for re-treatments of recurrence after pelvic floor repair surgery, and then an appropriately individualized re-treatment protocol could be designed for each of the patients.

  19. A dynamic retreat model for the North Sea Lobe of the British and Irish Ice sheet from the Vale of Pickering, UK

    Science.gov (United States)

    Eddey, Laura; Bateman, Mark D.; Livingstone, Stephen J.; Lee, Jonathan R.

    2017-04-01

    During the Last Glaciation, a large proglacial lake occupied the Vale of Pickering in North Yorkshire, UK. The lake was bounded to the east by ice in the North Sea and to the west by ice in the Vale of York. Until recently, the duration, extent and evolution of Glacial Lake Pickering in response to changes in ice sheet dynamics was uncertain (e.g. Livingstone et al 2012). New research using glacial geomorphological mapping from high-resolution LiDAR and NextMap data combined with luminescence dating has shown that ice may have extended into the Vale of Pickering much earlier and in several advance/retreat stages, leaving a series of subtle moraines. This is also supported through several stages of lake development, reflected in historical and recently recovered boreholes. These results indicate a much earlier onset of glaciation of the North Sea Lobe of the British and Irish Ice Sheet in the region and a longer and more dynamic history. As such this work has important implications for understanding the wider glacial and deglacial history of the North Sea Basin. Livingstone, S.J., Evans, D.J.A., Cofaigh, C.O. et al. (6 more authors) (2012) Glaciodynamics of the central sector of the last British-Irish Ice Sheet in Northern England. Earth Science Reviews, 111 (1-2). 25 - 55.

  20. Retreatment Predictions in Odontology by means of CBR Systems.

    Science.gov (United States)

    Campo, Livia; Aliaga, Ignacio J; De Paz, Juan F; García, Alvaro Enrique; Bajo, Javier; Villarubia, Gabriel; Corchado, Juan M

    2016-01-01

    The field of odontology requires an appropriate adjustment of treatments according to the circumstances of each patient. A follow-up treatment for a patient experiencing problems from a previous procedure such as endodontic therapy, for example, may not necessarily preclude the possibility of extraction. It is therefore necessary to investigate new solutions aimed at analyzing data and, with regard to the given values, determine whether dental retreatment is required. In this work, we present a decision support system which applies the case-based reasoning (CBR) paradigm, specifically designed to predict the practicality of performing or not performing a retreatment. Thus, the system uses previous experiences to provide new predictions, which is completely innovative in the field of odontology. The proposed prediction technique includes an innovative combination of methods that minimizes false negatives to the greatest possible extent. False negatives refer to a prediction favoring a retreatment when in fact it would be ineffective. The combination of methods is performed by applying an optimization problem to reduce incorrect classifications and takes into account different parameters, such as precision, recall, and statistical probabilities. The proposed system was tested in a real environment and the results obtained are promising.

  1. Retreatment Predictions in Odontology by means of CBR Systems

    Science.gov (United States)

    Campo, Livia; Aliaga, Ignacio J.; García, Alvaro Enrique; Villarubia, Gabriel; Corchado, Juan M.

    2016-01-01

    The field of odontology requires an appropriate adjustment of treatments according to the circumstances of each patient. A follow-up treatment for a patient experiencing problems from a previous procedure such as endodontic therapy, for example, may not necessarily preclude the possibility of extraction. It is therefore necessary to investigate new solutions aimed at analyzing data and, with regard to the given values, determine whether dental retreatment is required. In this work, we present a decision support system which applies the case-based reasoning (CBR) paradigm, specifically designed to predict the practicality of performing or not performing a retreatment. Thus, the system uses previous experiences to provide new predictions, which is completely innovative in the field of odontology. The proposed prediction technique includes an innovative combination of methods that minimizes false negatives to the greatest possible extent. False negatives refer to a prediction favoring a retreatment when in fact it would be ineffective. The combination of methods is performed by applying an optimization problem to reduce incorrect classifications and takes into account different parameters, such as precision, recall, and statistical probabilities. The proposed system was tested in a real environment and the results obtained are promising. PMID:26884749

  2. Glacial flutings in bedrock, an observation in East Greenland

    DEFF Research Database (Denmark)

    Funder, Svend Visby

    1978-01-01

    and 5 m in height and occur between 50 and 250 m above sea level inthe gently sloping lowland area adjacent to the fjord. They were probably formed beneath the lateral part of the former Harefjord-Glacier which receded rapidly in the fjord and exposed the area at c. 7500 years BP. Large scale glacial...... flutings have not been recorded before in Greenland, but seem to be of common occurrence in parts of North America. They have probably been formed near the margin of actively moving glaciers, and secondary flow in the basal ice may have played an important role...

  3. 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.

  4. Mapping Glacial Lake Changes in Mountain Areas of Central Asia with Landsat Imagery during 1990-2010

    Science.gov (United States)

    LI, Junli; Chen, Xi; Bao, Anming

    2014-05-01

    Central Asia is one of the world most vulnerable areas responding to global change. Glacier lakes in alpine regions remain sensitive to climatic change and fluctuate with temperature and precipitation variations. Study shows that glaciers in Central Asia have retreated dramatically, leading to the expansion of the existing glacial lakes and the emergence of many new glacial lakes. The existence of these lakes increases the possibility of outburst flood during the ice melting season, which can bring a disaster to the downstream area. Mapping glacial lakes and monitoring their changes would improve our understanding of regional climate change and glacier related hazards. Glacial lakes in Central Asia are mainly located at the Tianshan Mountains, the Altai Mountains and Kunlun Mountains with average elevation more than 1500 meters. Most of these lakes are supplied with the glaciers and snowmelt water during the summer seasons. Satellite remote sensing provides an efficient and objective tool to analyse the status and variations of glacial lakes. The increased availability of remote sensing sensors with appropriate spatial and temporal resolutions, broad coverage makes lake investigations more feasible and cost-effective. The paper intends to map glacier lake changes in the Tianshan Mountains, the Altai Mountains and Kunlun Mountains with Landsat imagery. About 400 scenes of Landsat images in circa 1990, circa 2000 and 2010 are used to map the glacial lakes over the Central Asia, and the temporal processes and spatial patterns of these lake changes are also analysed, so as to find the relations between lake changes and region climate change. Over 12 000 glacial lakes were mapped in circa 2010, and the most of them are located the Altai Mountains and the Tianshan Mountains. The result shows that the numbers and areas of the glacial lakes in the Altai Mountain remain stable. The Tianshan Mountain have experienced changes in the last two decades, and about a half number

  5. First approaches towards modelling glacial hazards in the Mount Cook region of New Zealand’s Southern Alps

    OpenAIRE

    Allen, S.; Schneider, D.; Owens, I F

    2009-01-01

    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...

  6. Global glacier dynamics during the last ten Pleistocene glacial cycles: assessing patterns, similarities and contrasts between different cold stages

    Science.gov (United States)

    Hughes, Philip; Gibbard, Philip

    2017-04-01

    Glacier mass balance is directly influenced by summer temperatures and precipitation. The timing of glacier advance and retreat depends on the interplay of these two variables and global patterns vary depending on the relative changes in summer temperatures and precipitation, especially winter precipitation in the case of mid-latitude glaciers. Glaciers are known to have reached their maximum extents at a range of times during the last glacial cycle (Weichselian/Wisconsinan Stage, etc.). Some reached their maximum in Marine Isotope Stage (MIS) 2 close to the global Last Glacial Maximum (LGM) when global sea levels were at their lowest. Some sectors of the largest mid-latitude ice sheets in the Northern Hemisphere (Laurentide, British-Irish, SE Fennoscandian) appear to have reached their maximum extent around this time and these ice sheets probably dominated the global sea-level signal at the LGM. Other ice sheets and large ice caps reached their maximum extent before this, many achieving their maximum in MIS 3, 4 or earlier (New Zealand, Patagonia, East Antarctica, Himalaya-Tibet, Cordilleran, Alaska, SW Fennoscandia). In northern Eurasia, the Barents-Kara ice sheet reached its maximum extent early in the last glacial cycle (late MIS 5). Improvements in geochronology offer the opportunity to assess these variations and to compare them with earlier, Middle Pleistocene glaciations, some of which were the most extensive recorded in the Quaternary. The global patterns of glaciation observed for the last glacial cycle, one of the longest recorded in the Pleistocene, provide a template for understanding previous glacial cycles. The pattern of ice build-up, advances and retreats can be linked to glacier size, proximity to the major oceans (continentality) and also to changes in global solar radiation receipt at different latitudes. Whilst glacier growth is modulated by variations in solar radiation, it is the feedback mechanisms between glacier size and climatic

  7. A Late-Glacial sedimentary sequence at KIlkeel, Northern Ireland: implications for the glaciation of the Irish Sea Basin

    Science.gov (United States)

    Merritt, Jon; Roberson, Sam; Cooper, Mark

    2017-04-01

    This paper re-evaluates the nature and timing of a Late-Glacial ice sheet re-advance in the north western sector of the Irish Sea basin. The sedimentary archive in the region records the collapse of the Irish Sea Ice Stream, a major outlet glacier of the British-Irish Ice Sheet. The region documents the interplay between southerly flowing Scottish ice, ice flowing southeast from Lough Neagh and locally sourced Mournes ice. We present the results of sedimentological analysis of a glacigenic sequence exposed in a modern cliff section 3 km long between Derryoge and Kilkeel, Co. Down, Northern Ireland. The interaction between an advancing ice-sheet outlet lobe and rapidly changing sea levels are examined using facies analysis and micromorphology. The section is composed of four lithofacies associations (LAs). These are, from the base, a laminated, fossiliferous and deformed silt (LA1) at least 4.5 m thick that contains lenses of diamicton and discontinuous rafts of sandy gravel. Marine shells form the axis of a fold hinge, part of a lightly tectonised channel fill within the raft. LA1 is overlain by a sandy diamict (LA2) up to 14 m thick containing mainly local clasts with some of northern provenance. Within LA2 are wide channel structures infilled by laminated clayey silts (LA2b). These form deposits up to 14 m thick and contain small-scale folds, discrete shear zones and ball-and-pillow structures. LA2b forms a lithofacies association with LA2, consisting of a lower subfacies of sheared and deformed silts, overlain by sandy diamicton, capped by a striated boulder pavement. These are interpreted to represent retreat/advance cycles of a marine terminating ice margin. Up to five such cycles are identified. LA2 is widely punctuated by fissures and conduits infilled by loose sands and gravels. These are inferred to be emplaced by subglacial meltwater during the final stages of ice sheet advance. Covering both LA2 and LA2b, LA3 is a unit of glaciofluvial outwash, composed

  8. Climatic vs. tectonic control on glacial relief

    Science.gov (United States)

    Prasicek, Günther; Herman, Frederic; Robl, Jörg

    2017-04-01

    The limiting effect of a climatically-induced glacial buzz-saw on the height of mountain ranges has been extensively discussed in the geosciences. The buzz-saw concept assumes that solely climate controls the amount of topography present above the equilibrium line altitude (ELA), while the rock uplift rate plays no relevant role. This view is supported by analyses of hypsometric patterns in orogens worldwide. Furthermore, numerical landscape evolution models show that glacial erosion modifies the hypsometry and reduces the overall relief of mountain landscapes. However, such models often do not incorporate tectonic uplift and can only simulate glacial erosion over a limited amount of time, typically one or several glacial cycles. Constraints on glacial end-member landscapes from analytical, time-independent models are widely lacking. Here we present a steady-state solution for a glacier equilibrium profile in an active orogen modified from the mathematical conception presented by Headley et al. (2012). Our approach combines a glacial erosion law with the shallow ice approximation, specifically the formulations of ice sliding and deformation velocities and ice flux, to calculate ice surface and bed topography from prescribed specific mass balance and rock uplift rate. This solution allows the application of both linear and non-linear erosion laws and can be iteratively fitted to a predefined gradient of specific mass balance with elevation. We tested the influence of climate (fixed rock uplift rate, different ELAs) and tectonic forcing (fixed ELA, different rock uplift rates) on steady-state relief. Our results show that, similar to fluvial orogens, both climate and rock uplift rate exert a strong influence on glacial relief and that the relation among rock uplift rate and relief is governed by the glacial erosion law. This finding can provide an explanation for the presence of high relief in high latitudes. Headley, R.M., Roe, G., Hallet, B., 2012. Glacier

  9. A fresh look at glacial foods

    Science.gov (United States)

    Colman, Steven M.

    2002-01-01

    Over the last 20 years, it has become clear that ice ages are characterized by glacial as well as climatic instability on millennial time scales. In his Perspective, Colman highlights two recent papers investigating the role of glacial meltwater and continental drainage in this instability. The results suggest a fundamental instability feedback between ocean circulation and ice sheet dynamics and provides an explanation for why instability was greatest at times of intermediate ice volume.

  10. 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.

  11. Quaternary glacial geomorphosites from the Cantabrian Mountains (northern Iberian Peninsula): the Redes Natural Reservation and Picos de Europa Regional Park

    Science.gov (United States)

    Rodríguez-Rodríguez, Laura; Jiménez-Sánchez, Montserrat; José Domínguez-Cuesta, María

    2013-04-01

    The Cantabrian Mountains is a mountain range 480 km-long and up to 2,648 m altitude (Torre Cerredo Peak) trending parallel to the Cantabrian Coastline between Pyrenees and the northwest corner of the Iberian Peninsula (~43oN 5oW). This mountain range is an outstanding area to research the climatic patterns across South Europe during the Quaternary glaciations since well-preserved glacial features evidence the occurrence of past mountain glaciations in a climatic environment marked by the transition from a maritime climate (Atlantic) to Mediterranean one across the mountain range. The available studies in the Cantabrian Mountains stand that the regional glacial maximum recorded here is prior to ca 38, and that glaciers were in some locations remarkably retreated by the time of the global Last Glacial Maximum (Jiménez-Sánchez et al., in press; Serrano et al., in press). This study is focused on an area about 800 km2 that includes 36 peaks over 2,000 m (Pico Mampodre; 2,192 m) and partially covers the Redes Natural Reservation and Picos de Europa Regional Park. A geomorphologic database in ArcGIS was produced for this area as a previous step to reconstruct in detail the extent, flow pattern and chronology of the former glaciers (PhD under progress). Here we present a selection of 18 glacial geomorphosites classified according to genetic criteria in sites that show: (i) a nicely preserved moraine sequence recording the transition from glacial to periglacial conditions; (ii) glacial erosion features; (iii) glacial and ice related deposits (like moraines, ice-dammed deposits, erratic boulders or fluvio-glacial deposits); (iv) slope instability related to glacial debuttressing (complex landslides and rock avalanches); and (v) the interaction between the landscape and human activity. The interest of the geomorphosites is supported by its good quality of preservation, allowing its use as a basis to reconstruct the glacial and paraglacial processes in this region during

  12. Understanding the glacial methane cycle

    Science.gov (United States)

    Hopcroft, Peter O.; Valdes, Paul J.; O'Connor, Fiona M.; Kaplan, Jed O.; Beerling, David J.

    2017-02-01

    Atmospheric methane (CH4) varied with climate during the Quaternary, rising from a concentration of 375 p.p.b.v. during the last glacial maximum (LGM) 21,000 years ago, to 680 p.p.b.v. at the beginning of the industrial revolution. However, the causes of this increase remain unclear; proposed hypotheses rely on fluctuations in either the magnitude of CH4 sources or CH4 atmospheric lifetime, or both. Here we use an Earth System model to provide a comprehensive assessment of these competing hypotheses, including estimates of uncertainty. We show that in this model, the global LGM CH4 source was reduced by 28-46%, and the lifetime increased by 2-8%, with a best-estimate LGM CH4 concentration of 463-480 p.p.b.v. Simulating the observed LGM concentration requires a 46-49% reduction in sources, indicating that we cannot reconcile the observed amplitude. This highlights the need for better understanding of the effects of low CO2 and cooler climate on wetlands and other natural CH4 sources.

  13. Origin and Distribution Of Glacial Lakes: A Case Study In Tista Basin, India

    Science.gov (United States)

    Kulkarni, A. V.

    2015-12-01

    Himalayan glaciers are experiencing retreat due to changes in the temperature and precipitation pattern. Retreating glaciers depending upon the underlying bed topography can cause lake formation near terminus. Therefore formation and draining of lakes in the glaciated terrain of Himalaya is commonly observed. However, few lakes became stable under suitable geomorphologic conditions and grow sufficiently large to threaten population and infrastructure in downstream. In this investigation changes in glacial lakes in Tista basin were studied using satellite images for a period between 1989 and 2010. The Tista basin in Sikkim covers approximately 7096 sq km area and the total glaciated area is 501± 29 sq km. During the period of investigation the lake area is increased from 6.6 ± 0.8 km2 to 9.6 ± 1.1 km2 due to formation of new lakes and also due to expansion of existing lake. Out of 23 lakes, 16 showed variable increase in area. We have also observed formation of stable proglacial lake due to coalescence of small supra glacial lakes on Changsang and South Lhonak Glacier. The size of lake near South Lhonak Glacier was increased from 18 to 126 ha from 1978 to 2014 (Figure). Therefore detail field investigations were carried out to understand volume and extent of ice in end moraine. The water volume was estimated as 53 million m3 using bathymetric survey and ice at the core of terminal moraines was mapped using resistivity survey. These investigations suggests a possibility of catastrophic outburst flood, if moraine dam breached under extreme weather conditions. Therefore, mitigation strategy is needed to improve safety of people living in the region. In addition, numerous remote sensing based investigations have mapped more than 300 lakes in the glaciated terrain in India, therefore, a national program to monitor glacier lakes and strategy to mitigate possible disaster is needed. Figure: Expansion of the lake near South Lhonak glacier from year 1990 to 2014.

  14. Evolution of supra-glacial ponds on a debris-covered Chamlang South Glacier, Nepal Himalaya to a potentially dangerous glacial lake

    Science.gov (United States)

    Lamsal, D.; Sawagaki, T.; Watanabe, T.; Sakai, A.

    2013-12-01

    A number of moraine dammed glacial lakes have been developed in the Himalayan region since 1950s as a result of melting and retreat of debris-covered glaciers. Such glacial lakes sometimes produce devastating glacier lake outburst floods (GLOFs) which are often several times bigger than normal climatic floods. In Nepal Himalaya, about a score glacial lakes have been identified as ';potentially dangerous' largely relying on remote sensing image analyses. Chamlang South Glacier Lake in the Eastern Nepal Himalaya, which evolved from few tiny supra-glacial ponds in 1960s on debris-covered Chamlang South Glacier into a large glacial lake is one among them. Moreover, the lake has been repeatedly cited as a potentially dangerous lake for a glacial lake outburst flood (GLOF) and also regarded as one of the most highly prioritized critical lakes in Nepal Himalaya. However, detailed investigation of the lake either by field survey or remote sensing has not been carried out on Chamlang South Glacier/Glacier Lake hitherto. We carried out surface area and bathymetric mappings of the lake, detailed topographic mappings of moraine dam complex and surrounding of the glacial lake, and field assessment to examine the development of Chamlang South Glacier Lake, and to assess its prospect of GLOF and potential volume of water to be released from the lake in the event of dam breach. High-resolution Corona KH-4A and Advanced Land Observing Satellite (ALOS) PRISM stereo-data taken in 1964 and 2006 respectively were processed to generate digital terrain models (DTMs). Surface area of supra-glacial ponds in 1964 was 0.040 km2 which grew to 0.636 km2 by 1992 and reached 0.864 km2 by 2000 and virtually stopped expanding thereafter. Produced bathymetric map revealed the lake to be 87 m deep (maximum) and volume of water contained in the lake was calculated to be ~35.6 × 106 m3. Extensive surface lowering as high as 156.9 m, and average surface lowering by 2.2 m/year is found. All topographic

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

    OpenAIRE

    Damodar Lamsal; Takanobu Sawagaki; Teiji Watanabe; Alton C. Byers

    2016-01-01

    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 (0.0...

  16. 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.

  17. 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.

  18. 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.

  19. The influence of glacial meltwater on alpine aquatic ecosystems: a review.

    Science.gov (United States)

    Slemmons, Krista E H; Saros, Jasmine E; Simon, Kevin

    2013-10-01

    The recent and rapid recession of alpine glaciers over the last 150 years has major implications for associated aquatic communities. Glacial meltwater shapes many of the physical features of high altitude lakes and streams, producing turbid environments with distinctive hydrology patterns relative to nival systems. Over the past decade, numerous studies have investigated the chemical and biological effects of glacial meltwater on freshwater ecosystems. Here, we review these studies across both lake and stream ecosystems. Focusing on alpine regions mainly in the Northern Hemisphere, we present examples of how glacial meltwater can affect habitat by altering physical and chemical features of aquatic ecosystems, and review the subsequent effects on the biological structure and function of lakes and streams. Collectively or separately, these factors can drive the overall distribution, diversity and behavior of primary producers, triggering cascading effects throughout the food web. We conclude by proposing areas for future research, particularly in regions where glaciers are soon projected to disappear.

  20. The Carbon Cycle as the Main Determinant of Glacial-Interglacial Periods

    CERN Document Server

    de la Cuesta, Diego Jiménez; Núñez, Darío; Rumbos, Beatriz; Vergara-Cervantes, Carlos

    2013-01-01

    An intriguing problem in climate science is the existence of Earth's glacial cycle. We show that it is possible to generate these periodic changes in climate by means of the Earth's carbon cycle as the main source factor. The carbon exchange between the Ocean, the Continent and the Atmosphere is modeled by means of a Lotka-Volterra three species system and the resulting atmospheric carbon cycle is used as the unique radiative forcing mechanism. It is shown that the carbon dioxide and temperature paths that are thus obtained have the same qualitative structure as the 100 kyr glacial-interglacial cycles depicted by the Vostok ice core data, reproducing the asymmetries of rapid heating--slow cooling, and short interglacial--long glacial ages.

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

    OpenAIRE

    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 Grah...

  2. Hazard Assessment of Glacial Lake Outburst Flood and Potential of ICTs for Coping: A Case of Eastern Himalaya of Nepal

    Science.gov (United States)

    Bhattarai, D. R.

    2015-12-01

    Retreat of glaciers and formation of glacial lakes in Nepal Himalaya have been reported to be related with the temperature rise in the region. Glacier Lake Outburst Floods (GLOF) are the growing climate induced hazards in the Himalaya. GLOF has increased the vulnerability of community and fragile ecosystem in the mountain valleys. This study has analyzed the potential impacts from GLOF in the highland of eastern Nepal and the potential role of Information Communication Technologies (ICT) to cope with such impacts. I analyzed the trend of climatic pattern (temperature and precipitation) of the Eastern Himalaya Region of Nepal available from the Department of Hydrology and Meteorology, Government of Nepal, and prepared the latest location map of the glacial lakes using google earth and ArcGIS applications in the highland of the Kanchanjungha Conservation Area of the region. Tiptala glacial lake, located at an elevation of 4950 m, within the conservation area, was selected for the GLOF hazard assessment. I used semi-structured questionnaire survey and key informants' interviews in the community in order to assess the potential hazard of GLOF. With the varying sizes, 46 glacial lakes were located in the region, which covers over 2.57 sq. km in total. Though the larger portion of the downstream area of the Tiptala glacial lake fall in the remote location away from major residential area, few villages, major pasture lands for Yaks, foot trails, and several bridges across the Tamor River below the lake are in risk of GLOF. Poor access due to extreme geographical remoteness and capacity to afford the modern technologies in the community are the major limiting factor to the knowledge and information about the climate change and related impacts. Modern ICTs has high potential to reduce the risk of climate related hazards in the remote area by information dissemination and awareness.

  3. A Palaeohydrological Shift during Neogene East Antarctic Ice Sheet Retreat

    Science.gov (United States)

    Rees-Owen, R. L.; Newton, R.; Ivanovic, R. F.; Francis, J.; Tindall, J. C.; Riding, J. B.

    2015-12-01

    The East Antarctic Ice Sheet is an important driver of global climate, playing a particular role in governing albedo and atmospheric circulation (eg. Singh et al., 2013). Recent evidence from marine sediment and terrestrial glaciovolcanic sequences suggests that the EAIS underwent periodic retreat and collapse in response to warmer climates during the late Neogene (14 to 3 million years ago). Mummified prostrate trees recovered from palaeosols at Oliver Bluffs in the Beardmore Glacier region, Transantarctic Mountains (85° S), represent a rare insight into the terrestrial palaeoclimate during one of these periods of retreat. Prostrate trees are an understudied but useful tool for interrogating endmember (e.g. periglacial) environments at high altitudes and latitudes. We present exciting new palaeoclimate data from the sequence at Oliver Bluffs. δ18O analysis of tree ring cellulose suggests that Antarctic summer palaeoprecipitation was enriched relative to today (-25 to -5‰ for ancient, -35 to -20‰ for modern); consistent with our isotope-enabled general circulation model simulations. The MBT/CBT palaeothermometer gives a summer temperature of 3-6ºC, consistent with other palaeobotanical climate indices. These geological and model data have wide-ranging implications for our understanding of the hydrological cycle during this time period. We present data suggesting that changes in moisture recycling and source region indicate a markedly different hydrological cycle.

  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. A new remote hazard and risk assessment framework for glacial lakes in the Nepal Himalaya

    Science.gov (United States)

    Rounce, David R.; McKinney, Daene C.; Lala, Jonathan M.; Byers, Alton C.; Watson, C. Scott

    2016-08-01

    Glacial lake outburst floods (GLOFs) pose a significant threat to downstream communities and infrastructure due to their potential to rapidly unleash stored lake water. The most common triggers of these GLOFs are mass movement entering the lake and/or the self-destruction of the terminal moraine due to hydrostatic pressures or a buried ice core. This study initially uses previous qualitative and quantitative assessments to understand the hazards associated with eight glacial lakes in the Nepal Himalaya that are widely considered to be highly dangerous. The previous assessments yield conflicting classifications with respect to each glacial lake, which spurred the development of a new holistic, reproducible, and objective approach based solely on remotely sensed data. This remote hazard assessment analyzes mass movement entering the lake, the stability of the moraine, and lake growth in conjunction with a geometric GLOF to determine the downstream impacts such that the present and future risk associated with each glacial lake may be quantified. The new approach is developed within a hazard, risk, and management action framework with the aim that this remote assessment may guide future field campaigns, modeling efforts, and ultimately risk-mitigation strategies. The remote assessment was found to provide valuable information regarding the hazards faced by each glacial lake and results were discussed within the context of the current state of knowledge to help guide future efforts.

  6. 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 (F1,76 = 15.32, P = .0002) and the type of retreatments (F1,76 = 54.67, P < .0001). Also, the WaveOne Primary file underwent more separations than the ProTaper files. The

  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. 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.

  9. 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.

  10. Sources of glacial moisture in Mesoamerica

    Science.gov (United States)

    Bradbury, J.P.

    1997-01-01

    Paleoclimatic records from Mesoamerica document the interplay between Atlantic and Pacific sources of precipitation during the last glacial stage and Holocene. Today, and throughout much of the Holocene, the entire region receives its principal moisture in the summer from an interaction of easterly trade winds with the equatorial calms. Glacial records from sites east of 95?? W in Guatemala, Florida, northern Venezuela and Colombia record dry conditions before 12 ka, however. West of 95?? W, glacial conditions were moister than in the Holocene. For example, pollen and diatom data show that Lake Pa??tzcuaro in the central Mexican highlands was cool, deep and fresh during this time and fossil pinyon needles in packrat middens in Chihuahua, Sonora, Arizona, and Texas indicate cooler glacial climates with increased winter precipitation. Cold Gulf of Mexico sea-surface temperatures and reduced strength of the equatorial calms can explain arid full and late glacial environments east of 95?? W whereas an intensified pattern of winter, westerly air flow dominated hydrologic balances as far south as 20?? N. Overall cooler temperatures may have increased effective moisture levels during dry summer months in both areas. ?? 1997 INQUA/ Elsevier Science Ltd.

  11. The glacial relief in the Leaota Mountains

    Directory of Open Access Journals (Sweden)

    George MURĂTOREANU

    2008-05-01

    Full Text Available The presence of glacial relief in the Romanian medium height massifs is still controversial. The medium height mountains, such as theLeaota Mountains (in the Bucegi group, with maximum altitudes of almost 2000 m andmedium altitudes of approximately 1250 m, can display traces of glacial relief dating from theUpper Pleistocene. The aim of this article is to provide evidence about the presence of theglacial morphology in the northern part of the Leaota Peak, the main orographic node in themassif with the same name. Thus, on the basis of field observations, of topographical mapanalysis and by using the geographic information systems which made possible a detailedmorphometric analysis, I was able to gather evidence proving the existence of a glacial cirquein the Leaota Mountains. The arguments put forward in this article show that the glacial reliefis represented in the Leaota Mountains through a small-size suspended glacial cirque, whichdisplays all the morphologic elements proving the existence of glaciation in this massif.

  12. Hydrothermal iron flux variability following rapid sea level changes

    National Research Council Canada - National Science Library

    Middleton, Jennifer L; Langmuir, Charles H; Mukhopadhyay, Sujoy; McManus, Jerry F; Mitrovica, Jerry X

    2016-01-01

    .... Mir sediments reveal sixfold to eightfold increases in hydrothermal iron and copper deposition during the Last Glacial Maximum, followed by a rapid decline during the sea level rise associated with deglaciation...

  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. Numerical model of the glacially-induced intraplate earthquakes and faults formation

    Science.gov (United States)

    Petrunin, Alexey; Schmeling, Harro

    2016-04-01

    According to the plate tectonics, main earthquakes are caused by moving lithospheric plates and are located mainly at plate boundaries. However, some of significant seismic events may be located far away from these active areas. The nature of the intraplate earthquakes remains unclear. It is assumed, that the triggering of seismicity in the eastern Canada and northern Europe might be a result of the glacier retreat during a glacial-interglacial cycle (GIC). Previous numerical models show that the impact of the glacial loading and following isostatic adjustment is able to trigger seismicity in pre-existing faults, especially during deglaciation stage. However this models do not explain strong glaciation-induced historical earthquakes (M5-M7). Moreover, numerous studies report connection of the location and age of major faults in the regions undergone by glaciation during last glacial maximum with the glacier dynamics. This probably imply that the GIC might be a reason for the fault system formation. Our numerical model provides analysis of the strain-stress evolution during the GIC using the finite volume approach realised in the numerical code Lapex 2.5D which is able to operate with large strains and visco-elasto-plastic rheology. To simulate self-organizing faults, the damage rheology model is implemented within the code that makes possible not only visualize faulting but also estimate energy release during the seismic cycle. The modeling domain includes two-layered crust, lithospheric mantle and the asthenosphere that makes possible simulating elasto-plastic response of the lithosphere to the glaciation-induced loading (unloading) and viscous isostatic adjustment. We have considered three scenarios for the model: horizontal extension, compression and fixed boundary conditions. Modeling results generally confirm suppressing seismic activity during glaciation phases whereas retreat of a glacier triggers earthquakes for several thousand years. Tip of the glacier

  15. Deglaciation and post-glacial environmental evolution in the Western Massif of Picos de Europa

    Science.gov (United States)

    Ruiz-Fernández, Jesús; Oliva, Marc; García, Cristina; López-Sáez, José Antonio; Gallinar, David; Geraldes, Miguel

    2014-05-01

    This study examines the process of deglaciation of the Western Massif of Picos de Europa through field work, geomorphological mapping, sedimentary records and absolute datings of 14C. This massif has several peaks over 2,400 m a.s.l. (Peña Santa de Castilla, 2,596 m; Torre Santa María, 2,486 m; Torre del Mediu, 2,467 m). It is composed mainly by Carboniferous limestones. This area has been intensively affected by karstic dissolution, Quaternary glaciers and fluvio-torrential processes (Miotke, 1968; Moreno et al, 2010; Ruiz-Fernández et al, 2009; Ruiz-Fernández, 2013). At present day, periglacial processes are active at the highest elevations (Ruiz-Fernández, 2013). We have identified four main glacial stages regarding the deglaciation of the massif: (i) maximum advance corresponding to the Last Glaciation, (ii) retreat and stabilization after the maximum advance, (iii) Late Glacial, and (iv) Little Ice Age. Sedimentological studies also contribute data to the understanding of the chronological framework of these environmental changes. The datings of the bottom sediments in two long sequences (8 and 5.4 m) provided a minimum age of 18,075 ± 425 cal BP for the maximum advance stage and 11,150 ± 900 cal BP for retreat and stabilization in the phase following the maximum advance. The ongoing analyses of these sequences at very high resolution will provide new knowledge about the environmental conditions prevailing since the deglaciation of the massif. References Miotke, F.D. (1968). Karstmorphologische studien in der glazial-überformten Höhenstufe der Picos de Europa, Nordspanien. Hannover, Selbtverlag der Geografischen Gessellschaft, 161 pp. Moreno, A., Valero, B.L., Jiménez, M., Domínguez, M.J., Mata, M.P., Navas, A., González, P., Stoll, H., Farias, P., Morellón, M., Corella, J.P. & Rico, M. (2010). The last deglaciation in the Picos de Europa National Park (Cantabrian Mountains, Northern Spain). Journal of Quaternary Science, 25 (7), 1076-1091. Ruiz

  16. Comparative Evaluation of Stress developed on Rotary Retreatment Instruments during Retrieval of Gutta-percha.

    Science.gov (United States)

    Sihivahanan, Dhanasekaran; Reddy, T Vinay Kumar; Thomas, Anchu Rachel; Senthilnathan, Natarajan; Sivakumar, Murali; Shivanna, Sushmita

    2017-06-01

    The aim of the study is to compare the maximum stress distribution on the rotary retreatment instruments within the root canal at cervical, middle, and the apical one-third during retreatment of gutta-percha. A human mandibular premolar was scanned, and three-dimensional geometry of the root was reconstructed using finite element analysis (FEA) software package (ANSYS). The basic model was kept unchanged; tooth models were created using the same dimensions and divided into two groups as follows: Group I: ProTaper Universal retreatment system and group II: Mtwo rotary retreatment system. The stress distribution on the surface and within the retreatment files was analyzed numerically in the FEA package (ANSYS). The FEA analysis revealed that the retreatment instruments received the greatest stress in the cervical third, followed by the apical third and the middle third. The stress generated on the ProTaper Universal retreatment system was less when compared with the Mtwo retreatment files. The study concludes that the retreatment instruments undergo higher stress in the cervical third region, and further in vivo and in vitro studies are necessary to evaluate the relationship between instrument designs, stress distribution, residual stresses after use, and the torsional fracture of the retreatment instrument. The stress developed on the rotary retreatment instruments during retrieval of gutta-percha makes the instrument to get separated. There is no instrument system, i.e., suitable for all clinical situations and it is important to understand how the structural characteristics could influence the magnitude of stresses on the instrument to prevent its fracture in use.

  17. 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

  18. 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

  19. Compounding Hazards Facing Nepalese Villages due to Glacial Lake Thulagi, Extreme Monsoons, and Landslides

    Science.gov (United States)

    Leonard, Gregory; Kargel, Jeffrey; Regmi, Dhananjay

    2014-05-01

    Thulagi Tsho is listed by ICIMOD as among the most hazardous glacial lakes in Nepal. The listing is warranted by the physiography and downstream vulnerabilities. Tal Village—along a major trekking route—and a hydroelectric dam and reservoir are notably at risk due to the potential for a glacier lake outburst flood (GLOF), an extreme summer monsoon, extreme spring snowmelt, landslides, and rockfalls. Tal is downstream from Thulagi Lake just a couple meters above river level, and ordinary monsoons already cause an approach toward flood conditions, according to residents. A high flood stage due to an extreme monsoon or unusually rapid springtime melting of a thick winter snowpack could be catastrophic. Two significant mass movements occurred recently in Tal, one having buried some structures in the village in June 2012. In a favorable note, satellite image analysis shows that Thulagi Lake has slowed its elongation in the last couple years. Furthermore, any tsunami or other flood surge would have to traverse and erode a wide end moraine in order to generate a GLOF. On the other hand, remote sensing and field observations show that wasting of Thulagi Glacier has debuttressed the northern lateral moraine, which is slipping toward the growing lake and the thinning/retreating glacier. The landslip itself is not necessarily a bad thing: it is causing a loss of gravitational potential energy of the lateral moraine, and if that process continues gradually, it will result in diminished instability. However, the debuttressing and moraine slip signifies that the moraines are unstable. Will a rapid mass movement dump into the lake? Triggers could include seismicity, extreme rainfall, or a small landslip. The risk of a serious GLOF exceeds that of Imja Lake due to Thulagi Lake's large hydrographic head and the shape of its downstream end, which could funnel and amplify a potential tsunami generated by a large mass movement into the lake. A moraine collapse into the lake would

  20. Late Quaternary Glacier Retreat in the Mongolian Altai

    Science.gov (United States)

    Bader, N. E.; Carson, R. J.; Wegmann, K. W.; Frankel, K. L.; Bayasgalan, A.; Dundon, K. M.; Ladig, K. L.; Leary, R. J.; Matzinger, G. R.; Seymour, A. M.

    2008-12-01

    The glaciated Mongolian Altai range preserves moraine complexes and other landforms from extensive late Pleistocene glaciations. We studied ancient and modern glacial features in six valleys draining into the Delüün Valley (47.905°N, 90.724°E) in Mongolia's far western Bayan-Ölgiy province. Moraines were assigned relative ages based on morphology and boulder frequency. For example, in the Altai Mountains along the Mongolia-China border west of the Delüün Valley, modern glaciers sit upvalley of Last Glacial Maximum (LGM) moraines that contain abundant large granitic erratic boulders and impound Chigertey Gol; in older, more rounded moraines about 8 km down-valley, most of the granitic boulders are weathered and wind-abraded down to ground level. We observed no evidence for glacial deposits older than LGM in valleys draining the western flank of the tectonically active Khukh Serkhyn Mountains along the east side of the Delüün Valley. Cosmogenic 10Be ages will help further establish the timing of moraine deposition. Recent changes in glaciers in the Khukh Serkhyn Mountains were identified using maps derived from 1963 aerial photographs and our own 2008 field observations. We used the toe-to-summit altitude method to establish the equilibrium-line elevation (ELA) of the mountain glaciers during the time each moraine complex was deposited. Between the LGM and 1963, the ELA rose from about 3200 m to at least 3700 m; currently the ELA is probably higher than 4000 m. Areal extent of the glaciers west of the Khukh Serkhyn drainage divide decreased from approximately 112 km2 during the LGM to about 7 km2 in 1963 to about 4 km2 today. This represents an order of magnitude increase in the mean loss rate of glacial area since 1963, compared to the mean loss rate since the LGM. If the present rate of loss continues, these glaciers will disappear by about 2075. The loss of mountain glaciers in the Mongolian Altai will reduce the availability of summer meltwater to local

  1. North Atlantic warming and the retreat of Greenland's outlet glaciers.

    Science.gov (United States)

    Straneo, Fiammetta; Heimbach, Patrick

    2013-12-05

    Mass loss from the Greenland ice sheet quadrupled over the past two decades, contributing a quarter of the observed global sea-level rise. Increased submarine melting is thought to have triggered the retreat of Greenland's outlet glaciers, which is partly responsible for the ice loss. However, the chain of events and physical processes remain elusive. Recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes, multidecadal natural ocean variability and a long-term increase in the North Atlantic's upper ocean heat content since the 1950s all contributed to a warming of the subpolar North Atlantic. This led, in conjunction with increased runoff, to enhanced submarine glacier melting. Future climate projections raise the potential for continued increases in warming and ice-mass loss, with implications for sea level and climate.

  2. GPCR Retreat 2014: a good view leads to many discoveries!

    Science.gov (United States)

    Chidiac, Peter; Hébert, Terence E

    2015-06-01

    The GPCR gods smiled on us last year as the 15th Annual GPCR Retreat was held last October 2nd-4th in Bromont, Québec. The fall colors were at their peak and the meeting attendees were also in fine form. The program was one of the best we have seen at any GPCR-related meeting in years and there was a great deal of excitement about new methodological approaches to understanding receptor biology, new concepts in GPCR signaling and a continued emphasis on translation of these discoveries. This year was also the first year we opened the meeting with a short course on biased agonism and how to measure and analyze it.

  3. Living at the margin of the retreating Fennoscandian Ice Sheet

    DEFF Research Database (Denmark)

    Möller, Per; Östlund, Oluf; Barnekow, Lena

    2013-01-01

    total 6 m2) are interpreted as resulting from short-stay hunter-gatherer camps. Radiocarbon dating on burnt bones suggest an age of occupancy at ~10,700 cal. yr BP, which is more or less contemporary with 'Komsa Phase' sites on the north coast of Norway (~300-360 km northwards). The Aareavaara site...... in the Ancylus Lake with highest shorelines formed at ~170 m a.s.l. The hunter-gatherer camp sites at Aareavaara were thus, both in time and space, located in close proximity to the retreating ice sheet margin, but also in a waterfront location, in fact on an island in the Ancylus Lake. Our pollen data suggest...

  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. An analysis of the long term hydrological dynamics of the Careser, a rapidly retreating Alpine glacier.

    Science.gov (United States)

    Stella, Elisa; Meneghetti, Erica; Cainelli, Oscar; Bellin, Alberto

    2017-04-01

    Alpine glaciers are shrinking at a relentless pace, as an effect of the increasing temperature and the concomitant reduction of snowfall that the Alpine region experienced in the last 40 years. The impact of these changes is relevant, given the importance of the Alps from ecological and economical points of view. While the ubiquitous reduction of glaciers mass through the Alps has been reported in a number of studies, its effect on streamflow is less studied, mainly because much less data are available on streamflow emerging from glaciers. In the present work we analyze a long streamflow time series, recorded since the 70s, in the Careser creek emerging from the Careser Glacier, which mass has been monitored since 1920, first discontinuously and then continuously from 1967. Because of these long-term observations, the Careser has been classified as one of the reference glaciers by the World Glacier Monitoring Service, which provides balances data every two years. We performed a comprehensive analysis of multiscale variations of precipitation, temperature, water discharge and glacier mass. In addition we explored the correlations between streamflow and climatic drivers at monthly and subdaily scales. We observed significant changes in the timing of streamflow, with anticipated snow melting and a reduction of summer runoff, while at the annual scale the increase of ice-melting offsets runoff reduction caused by less winter precipitation falling as snow. In fact, in most years since the 1990 ice melts from beginning of May to October, thereby causing a dramatic reduction of the glacier volume. However, in the last years the significant reduction of the glacier surface, attenuated this tendency to increase the total annual runoff volume. At the sub-daily scale we observed a progressive increase of the difference between the maximum and minimum water discharge. Overall the hydrological regime changes significantly as an effect of the rise in temperature and the lower winter snowfall, which increased the importance of ice melting as source of streamflow with respect to snow melting, which was still the primary source of streamflow in the 70s.

  6. Impact of different file systems on the amount of apically extruded debris during endodontic retreatment.

    Science.gov (United States)

    Uzunoglu, Emel; Turker, Sevinc Aktemur

    2016-01-01

    The goal of present study was to determine the effect of different nickel-titanium file systems on the amount of apically extruded debris during endodontic retreatment: D-RaCe retreatment systems, EdgeFile XR retreatment rotary files, and Reciproc R40. Thirty-six single-rooted prepared mandibular premolar teeth were filled with Gutta-percha and AH Plus sealer. The teeth were then randomly assigned into three groups (n = 12) for retreatment. The endodontic retreatment was performed as follows: D-RaCe, EdgeFile XR, Reciproc 40. Debris extruded apically during the retreatment was collected into preweighed Eppendorf tubes. An incubator was used to store tubes at 70(°) C for 5 days. The initial weight was subtracted from final weight of the Eppendorf tubes to calculate the weight of the dry extruded debris for each group. The data obtained were evaluated using Welch analysis of variance and Games-Howell post-hoc tests (P endodontic retreatment, number, and taper of files might have an influence on the amount of apically extruded debris during endodontic retreatment.

  7. Outcome of orthograde endodontic retreatment--A two-year follow-up.

    Science.gov (United States)

    Nesković, Jelena; Zivković, Slavoljub; Medojević, Milica; Maksimović, Milos

    2016-01-01

    Endodontic retreatment is a complex intervention that requires detailed analysis of possible reasons for failure, and flawless practical execution of the procedure. The aim of the study was to assess the outcome of endodontic retreatment based on clinical and radiographic criteria after a two-year observation period. Clinical study included 49 teeth indicated for endodontic retreatment based on periapical index (PAI). All teeth were divided into two groups. Group I comprised teeth without any periapical lesion (PAI score of 1 and 2) while Group II consisted of teeth with visible periapical radiolucency (PAI score of 3, 4, and 5). Endodontic retreatment was completed in two visits with inter-appointment medication of 2% chlorhexidine and calcium hydroxide for two weeks. Outcome of endodontic retreatment was evaluated 12-24 months after final obturation. Endodontic retreatment was successful in 93.3% in Group I after 24 months. In Group II, successful treatment and complete healing was found in 52.9% of teeth, whereas 14.7% of teeth showed only partial healing. However, clinical symptomatology was not present in any of the cases. Considering the absence of clinical signs and subjective symptoms, retreatment was successful in 67.6% of cases where chronic periapical inflammation was present. Endodontic retreatment was successful in high percentage in teeth with and without periapical lesions.

  8. 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

  9. Teacher Retreating: The Little Known Behavior That Impacts Teaching and Learning

    Science.gov (United States)

    Ratcliff, Nancy J.; Carroll, Kimberly L.; Hunt, Gilbert H.

    2014-01-01

    This paper discusses findings from four years of observational research examining classroom climate. Specifically, findings that focused on one powerful teacher behavior (teacher retreating) were examined. These data indicated that teacher retreating was negatively correlated to the amount of instructional interaction occurring between students…

  10. Glacial conditioning of stream position and flooding in the braid plain of the Exit Glacier foreland, Alaska

    Science.gov (United States)

    Curran, Janet H.; Loso, Michael G.; Williams, Haley B.

    2017-09-01

    Flow spilling out of an active braid plain often signals the onset of channel migration or avulsion to previously occupied areas. In a recently deglaciated environment, distinguishing between shifts in active braid plain location, considered reversible by fluvial processes at short timescales, and more permanent glacier-conditioned changes in stream position can be critical to understanding flood hazards. Between 2009 and 2014, increased spilling from the Exit Creek braid plain in Kenai Fjords National Park, Alaska, repeatedly overtopped the only access road to the popular Exit Glacier visitor facilities and trails. To understand the likely cause of road flooding, we consider recent processes and the interplay between glacier and fluvial system dynamics since the maximum advance of the Little Ice Age, around 1815. Patterns of temperature and precipitation, the variables that drive high streamflow via snowmelt, glacier meltwater runoff, and rainfall, could not fully explain the timing of road floods. Comparison of high-resolution topographic data between 2008 and 2012 showed a strong pattern of braid plain aggradation along 3 km of glacier foreland, not unexpected at the base of mountainous glaciers and likely an impetus for channel migration. Historically, a dynamic zone follows the retreating glacier in which channel positions shift rapidly in response to changes in the glacier margin and fresh morainal deposits. This period of paraglacial adjustment lasts one to several decades at Exit Glacier. Subsequently, as moraine breaches consolidate and lock the channel into position, and as the stream regains the lower-elevation valley center, upper-elevation surfaces are abandoned as terraces inaccessible by fluvial processes for timescales of decades to centuries. Where not constrained by these terraces and moraines, the channel is free to migrate, which in this aggradational setting generates an alluvial fan at the breach of the final prominent moraine. The position of

  11. Response to Edwards' comments on Origin of British and Irish mammals: disparate post-glacial colonisation and species introductions

    Science.gov (United States)

    Montgomery, W. I.; Provan, J.

    2014-12-01

    We are most grateful to Dr Edwards for her lucid summary of recent, calibrated dates for giant Irish deer, red deer, reindeer and brown bear in Irish deposits during the period before and after the Last Glacial Maximum (LGM). Montgomery et al. (2014) dealt largely with the period after the LGM because the physical evidence suggests Ireland was completely covered by ice for at least part of the period between 28 ka and 23 ka (Clark et al., 2012; O'Cofaigh et al., 2012) when Ireland would not have supported any terrestrial mammals. The earliest it was possible for re-colonisation of these species to occur after LGM was probably during the rapid retreat of ice after 23 ka and before 15 ka when the Irish Sea became a complete barrier to terrestrial mammals between Britain and Ireland. There are no dates for any of the four species during the LGM and only one for giant Irish deer (BM-1794, date 18,761-18,034 cal. BP) which is from a site close to the present coast just south of Dublin, between LGM and completion of the Irish Sea, suggesting that conditions generally remained unsuitable for even cold-adapted mammals for many millennia after LGM. Edwards (2014) indicates clearly that all four species are well represented after Ireland became an island although giant Irish deer struggle to make it into the Holocene and the red deer record is broken and perhaps influenced by people (Carden et al., 2012). The sudden reappearance of large mammals around 13-15 ka is consistent with re-colonisation from cryptic refugia lying to the south and west of present day Ireland. The relatively short periods of warming and cooling during the Older and Younger Dryas respectively, followed by warming in the Holocene and the arrival of Mesolithic and Neolithic people remain the major events in the history of Irish mammals until the late 19th Century to the present during which many mammals species have been introduced (Montgomery et al., 2014). Whilst events prior to the LGM are important

  12. 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

  13. 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.

  14. Glacial isostatic uplift of the European Alps

    NARCIS (Netherlands)

    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

  15. Late glacial aridity in southern Rocky Mountains

    Energy Technology Data Exchange (ETDEWEB)

    Davis, O.K.; Pitblado, B.L. [Univ. of Arizona, Tucson, AZ (United States)

    1995-09-01

    While the slopes of the present-day Colorado Rocky Mountains are characterized by large stands of subalpine and montane conifers, the Rockies of the late glacial looked dramatically different. Specifically, pollen records suggest that during the late glacial, Artemisia and Gramineae predominated throughout the mountains of Colorado. At some point between 11,000 and 10,000 B.P., however, both Artemisia and grasses underwent a dramatic decline, which can be identified in virtually every pollen diagram produced for Colorado mountain sites, including Como Lake (Sangre de Cristo Mountains), Copley Lake and Splains; Gulch (near Crested Butte), Molas Lake (San Juan Mountains), and Redrock Lake (Boulder County). Moreover, the same pattern seems to hold for pollen spectra derived for areas adjacent to Colorado, including at sites in the Chuska Mountains of New Mexico and in eastern Wyoming. The implications of this consistent finding are compelling. The closest modem analogues to the Artemisia- and Gramineae-dominated late-glacial Colorado Rockies are found in the relatively arid northern Great Basin, which suggests that annual precipitation was much lower in the late-glacial southern Rocky Mountains than it was throughout the Holocene.

  16. Critical insolation-CO2 relation for diagnosing past and future glacial inception

    Science.gov (United States)

    Ganopolski, Andrey; Winkelmann, Ricarda; Schellnhuber, Hans Joachim

    2016-04-01

    Past rapid growth of Northern Hemisphere continental ice sheets, which terminated rather stable and warm climate periods, is generally attributed to reduced summer insolation in boreal latitudes (Milanković , 1941; Hays et al., 1976, Paillard, 1998). Yet pertinent summer insolation is near to its minimum at present (Berger and Loutre, 2002), and there are no signs of a new ice age (Kemp et al., 2011). This challenges our scientific understanding of the mechanisms driving glacial cycles and our ability to predict the next glacial inception (Masson-Delmotte et al., 2013). Here we propose a fundamental functional relationship between boreal summer insolation and global CO2 concentration, which explains the beginning of the past eight glacial cycles and can anticipate future periods when glacial inception may occur again. Using a simulations ensemble generated by an Earth system model of intermediate complexity constrained by paleoclimatic data, we show that glacial inception was narrowly missed before the beginning of the Industrial Revolution. This can be explained by the combined effect of relatively high late-Holocene CO2 concentration and low orbital eccentricity of the Earth (Loutre and Berger, 2003). Additionally, our analysis shows that even in the absence of human perturbations no significant buildup of ice sheets would occur within the next several thousand years and that the current interglacial would likely last for another 50,000 years. However, moderate anthropogenic cumulative CO2 emissions of 1000 to 1500 GtC may already postpone the next glacial inception by at least 100,000 years (Archer and Ganopolski, 2005; Paillard, 2006). Our simulations demonstrate that under natural conditions alone the Earth system would be expected to stay in the delicate interglacial climate state, steering clear of both large-scale glaciation of the Northern Hemisphere and its complete deglaciation, for an unusually long time.

  17. Comparative study of apically extruded debris using one manual and two rotary instrumentation techniques for endodontic retreatment

    Directory of Open Access Journals (Sweden)

    Alper Kustarci

    2012-03-01

    Conclusion: All retreatment techniques produced extruded debris during endodontic retreatment; however, both rotary NiTi systems were associated with less apical extrusion than manual instrumentation with Hedström files.

  18. Potential flood volume of Himalayan glacial lakes

    Directory of Open Access Journals (Sweden)

    K. Fujita

    2013-07-01

    Full Text Available Glacial lakes are potentially dangerous sources of glacial lake outburst floods (GLOFs, and represent a serious natural hazard in Himalayan countries. Despite the development of various indices aimed at determining the outburst probability, an objective evaluation of the thousands of Himalayan glacial lakes has yet to be completed. In this study we propose a single index, based on the depression angle from the lakeshore, which allows the lakes to be assessed using remotely sensed digital elevation models (DEMs. We test our approach on five lakes in Nepal, Bhutan, and Tibet using images taken by the declassified Hexagon KH-9 satellite before these lakes experienced an outburst flood. All five lakes had a steep lakefront area (SLA, on which a depression angle was steeper than our proposed threshold of 10° before the GLOF event, but the SLA was no longer evident after the events. We further calculated the potential flood volume (PFV; i.e., the maximum volume of floodwater that could be released if the lake surface was lowered sufficiently to eradicate the SLA. This approach guarantees repeatability to assess the possibility of GLOF hazards because it requires no particular expertise to carry out, though the PFV does not quantify the GLOF risk. We calculated PFVs for more than 2000 Himalayan glacial lakes using visible band images and DEMs of ASTER data. The PFV distribution follows a power-law function. We found that 794 lakes did not have an SLA, and consequently had a PFV of zero, while we also identified 49 lakes with PFVs of over 10 million m3, which is a comparable volume to that of recorded major GLOFs. This PFV approach allows us to preliminarily identify and prioritize those Himalayan glacial lakes that require further detailed investigation on GLOF hazards and risk.

  19. Potential flood volume of Himalayan glacial lakes

    Science.gov (United States)

    Fujita, K.; Sakai, A.; Takenaka, S.; Nuimura, T.; Surazakov, A. B.; Sawagaki, T.; Yamanokuchi, T.

    2013-07-01

    Glacial lakes are potentially dangerous sources of glacial lake outburst floods (GLOFs), and represent a serious natural hazard in Himalayan countries. Despite the development of various indices aimed at determining the outburst probability, an objective evaluation of the thousands of Himalayan glacial lakes has yet to be completed. In this study we propose a single index, based on the depression angle from the lakeshore, which allows the lakes to be assessed using remotely sensed digital elevation models (DEMs). We test our approach on five lakes in Nepal, Bhutan, and Tibet using images taken by the declassified Hexagon KH-9 satellite before these lakes experienced an outburst flood. All five lakes had a steep lakefront area (SLA), on which a depression angle was steeper than our proposed threshold of 10° before the GLOF event, but the SLA was no longer evident after the events. We further calculated the potential flood volume (PFV); i.e., the maximum volume of floodwater that could be released if the lake surface was lowered sufficiently to eradicate the SLA. This approach guarantees repeatability to assess the possibility of GLOF hazards because it requires no particular expertise to carry out, though the PFV does not quantify the GLOF risk. We calculated PFVs for more than 2000 Himalayan glacial lakes using visible band images and DEMs of ASTER data. The PFV distribution follows a power-law function. We found that 794 lakes did not have an SLA, and consequently had a PFV of zero, while we also identified 49 lakes with PFVs of over 10 million m3, which is a comparable volume to that of recorded major GLOFs. This PFV approach allows us to preliminarily identify and prioritize those Himalayan glacial lakes that require further detailed investigation on GLOF hazards and risk.

  20. Radionuclide transport during glacial cycles: Comparison of two different approaches for handling flow transients

    Science.gov (United States)

    Selroos, J.-O.; Cheng, H.; Painter, S.; Vidstrand, P.

    2012-04-01

    We investigate the effect of future, transient ice sheet movement and permafrost development on transport of radionuclides from a proposed repository site in Sweden using numerical groundwater flow and radionuclide transport modelling. Specifically, two different transport approaches are compared. Both approaches utilize simulations of the groundwater flow field of several future climate regimes. The groundwater flow modelling comprises a transient simulation of glacial advance and retreat. The different climate regimes are identified as steady-state snap-shots in time during the glacial advance/retreat and are used as time epochs with constant characteristics in the subsequent transport modelling. The first transport approach uses steady-state particle trajectories representing temperate climate conditions, but modifies the transport velocity along the trajectories according to the flow ratio at repository depth between the other climate regimes and the temperate regime. The second approach uses the time epochs in a pseudo-transient fashion, where particle tracking is performed in each individual flow field representing a given time epoch. The transport code MARFA (Painter and Mancillas, 2009) is used for both cases. MARFA uses a particle-based Monte Carlo method to simulate the transport of radionuclides in a sparsely fractured geological medium. The algorithm uses non-interacting particles to represent packets of radionuclide mass. These particles are moved through the system according to rules that mimic the underlying physical transport and retention processes. The physical processes represented in MARFA include advection, longitudinal dispersion, Fickian diffusion into an infinite or finite rock matrix, equilibrium sorption, decay, and in-growth. The set of times required for particles to pass through the geological barrier are used to reconstruct discharge rates. Two different climate sequences are analyzed. First, a simplified sequence consisting of

  1. Penultimate and last glacial oceanographic variations in the Bering Sea on millennial timescales: Links to North Atlantic climate

    Science.gov (United States)

    Ovsepyan, E. A.; Ivanova, E. V.; Lembke-Jene, L.; Max, L.; Tiedemann, R.; Nürnberg, D.

    2017-05-01

    We present high-resolution multi-proxy records from a marine sediment core (SO201-2-85KL) from the western Bering Sea to assess orbital- and millennial-scale paleoceanographic conditions during two last glacial intervals, including both terminations. Based on changes in foraminiferal assemblages, grain-size content and previously published TOC and δ13C records, we reconstruct variations in sea-surface biological productivity, intermediate-water oxygenation and sea-ice conditions during the last 180 kyr. Our data demonstrate remarkable differences between the penultimate (MIS 6) and last (MIS 4-2) glacial. Relatively high sea surface bioproductivity and reduced sea-ice cover are reconstructed for the penultimate glacial interval, whereas low bioproductivity and expanded sea-ice cover appear to be typical for the last glacial. Millennial-scale changes in intermediate water ventilation are inferred from faunal records for the middle part of the penultimate glacial. High-amplitude environmental variability during the penultimate glacial time in the Bering Sea resembles the well-known Dansgaard-Oeschger oscillations, and roughly corresponds to similar rapid climatic fluctuations found in North Atlantic records. The Termination II and I intervals display a similar succession of high-bioproductivity events, being more pronounced during the penultimate glacial-interglacial transition, probably due to the different orbital configuration. During the late phase of Termination II, two short intervals, characterized by high sea surface bioproductivity and low oxygen content of bottom waters, resemble the Bølling and Allerød warmings, whereas an episode with low bioproductivity occurs in between, similar to the Older Dryas. Our results provide support for a close circumpolar coupling between high-latitude environments on millennial timescales at least since the penultimate glacial.

  2. Abrupt climate and vegetation variability of eastern Anatolia during the last glacial

    Science.gov (United States)

    Pickarski, N.; Kwiecien, O.; Langgut, D.; Litt, T.

    2015-11-01

    Detailed analyses of the Lake Van pollen, Ca / K ratio, and stable oxygen isotope record allow the identification of millennial-scale vegetation and environmental changes in eastern Anatolia throughout the last glacial (~ 111.5-11.7 ka BP). The climate of the last glacial was cold and dry, indicated by low arboreal pollen (AP) levels. The driest and coldest period corresponds to Marine Isotope Stage (MIS) 2 (~ 28-14.5 ka BP), which was dominated by highest values of xerophytic steppe vegetation. Our high-resolution multi-proxy record shows rapid expansions and contractions of tree populations that reflect variability in temperature and moisture availability. These rapid vegetation and environmental changes can be related to the stadial-interstadial pattern of Dansgaard-Oeschger (DO) events as recorded in the Greenland ice cores. Periods of reduced moisture availability were characterized by enhanced occurrence of xerophytic species and high terrigenous input from the Lake Van catchment area. Furthermore, the comparison with the marine realm reveals that the complex atmosphere-ocean interaction can be explained by the strength and position of the westerlies, which are responsible for the supply of humidity in eastern Anatolia. Influenced by the diverse topography of the Lake Van catchment, more pronounced DO interstadials (e.g., DO 19, 17-16, 14, 12 and 8) show the strongest expansion of temperate species within the last glacial. However, Heinrich events (HE), characterized by highest concentrations of ice-rafted debris (IRD) in marine sediments, cannot be separated from other DO stadials based on the vegetation composition in eastern Anatolia. In addition, this work is a first attempt to establish a continuous microscopic charcoal record for the last glacial in the Near East. It documents an immediate response to millennial-scale climate and environmental variability and enables us to shed light on the history of fire activity during the last glacial.

  3. 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

  4. A conceptual model for glacial cycles and the middle Pleistocene transition

    Science.gov (United States)

    Daruka, István; Ditlevsen, Peter D.

    2016-01-01

    Milankovitch's astronomical theory of glacial cycles, attributing ice age climate oscillations to orbital changes in Northern-Hemisphere insolation, is challenged by the paleoclimatic record. The climatic response to the variations in insolation is far from trivial. In general the glacial cycles are highly asymmetric in time, with slow cooling from the interglacials to the glacials (inceptions) and very rapid warming from the glacials to the interglacials (terminations). We shall refer to this fast-slow dynamics as the "saw-tooth" shape of the paleoclimatic record. This is non-linearly related to the time-symmetric variations in the orbital forcing. However, the most pronounced challenge to the Milankovitch theory is the middle Pleistocene transition (MPT) occurring about one million years ago. During that event, the prevailing 41 kyr glacial cycles, corresponding to the almost harmonic obliquity cycle were replaced by longer saw-tooth shaped cycles with a time-scale around 100 kyr. The MPT must have been driven by internal changes in climate response, since it does not correspond to any apparent changes in the orbital forcing. In order to identify possible mechanisms causing the observed changes in glacial dynamics, it is relevant to study simplified models with the capability of generating temporal behavior similar to the observed records. We present a simple oscillator type model approach, with two variables, a temperature anomaly and a climatic memory term. The generalization of the ice albedo feedback is included in terms of an effective multiplicative coupling between this latter climatic memory term (representing the internal degrees of freedom) and the external drive. The simple model reproduces the temporal asymmetry of the late Pleistocene glacial cycles and suggests that the MPT can be explained as a regime shift, aided by climatic noise, from a period 1 frequency locking to the obliquity cycle to a period 2-3 frequency locking to the same obliquity

  5. Uncertainty in the Himalayan energy–water nexus: estimating regional exposure to glacial lake outburst floods

    OpenAIRE

    Schwanghart, Wolfgang; Worni, Raphael; Huggel, Christian; Stoffel, Markus; Korup, Oliver

    2016-01-01

    Himalayan water resources attract a rapidly growing number of hydroelectric power projects (HPP) to satisfy Asia’s soaring energy demands. Yet HPP operating or planned in steep, glacier-fed mountain rivers face hazards of glacial lake outburst floods (GLOFs) that can damage hydropower infrastructure, alter water and sediment yields, and compromise livelihoods downstream. Detailed appraisals of such GLOF hazards are limited to case studies, however, and a more comprehensive, systematic analysi...

  6. Re-treatment profiles during long-term maintenance therapy in a periodontal practice in Norway.

    Science.gov (United States)

    Fardal, Oystein; Linden, Gerard J

    2005-07-01

    Periodontal therapy coupled with active maintenance has been shown to be effective in maintaining periodontal health, however, the question of re-treatment is rarely alluded to in the literature. To quantify the type and extent of re-treatment in a group of patients who had completed a definitive course of periodontal treatment in a Norwegian specialist periodontal practice. The study also investigated factors associated with the provision of periodontal surgery as a re-treatment modality. A consecutive group of patients who had comprehensive periodontal treatment, which included periodontal surgery, and were subsequently maintained for between 10 and 17 years were studied. One hundred and one patients with an average age at reassessment of 59.4 (standard deviation (SD) 9.0) years were studied. The average length of the review period was 13.1 (SD 1.9) years. In addition to routine maintenance, 50 patients had further re-treatment and 40 of those who were re-treated had periodontal surgery in the study period. Logistic regression showed that independent predictors of surgical re-treatment, with the effects adjusted for other variables in the model, were uncertain or poor prognosis at baseline, erratic or poor post baseline compliance and a family history of periodontal disease. Considerable amounts of re-treatment, including in many cases extensive non-surgical treatment or periodontal surgery, were provided for patients who had surgical periodontal treatment and were subsequently maintained for least 10 years in a specialist periodontal practice.

  7. Short-term sea cliff failure events accumulate into long-term cliff retreat signals

    Science.gov (United States)

    Limber, Patrick; Palaseanu-Lovejoy, Monica; Danielson, Jeffrey; Barnard, Patrick

    2017-04-01

    Sea cliff retreat is an episodic process, where sudden landslide events punctuate longer periods of relative cliff stability. Understanding sea cliff behavior is key to defining coastal hazard zones or projecting future retreat due to sea level rise (SLR), when present. But, predicting when a particular landslide will occur, or how large it will be, is exceptionally difficult. As a result, rates of sea cliff retreat are often time-averaged over many individual landslides during a given time interval. Time averaging of episodic processes like cliff retreat has several drawbacks, however. For one, the mean erosion or retreat rate can be heavily biased by the time interval over which it is measured, especially over short time scales (e.g. double during the next century. Now, we can estimate with uncertainty 1) how such rate changes will potentially increase annual landslide probabilities and shorten recurrence intervals, 2) how long-term rates emerge from the accumulation of individual, instantaneous landslide events, and 3) the minimum time scale over which time-averaged retreat rates are representative of the long-term cliff retreat signal.

  8. [Effectiveness of short course intermittent regimen on different categories of retreated patients with pulmonary tuberculosis].

    Science.gov (United States)

    Wang, X; Dai, Y; Cao, J

    2001-08-01

    To evaluate the efficacy of short course intermittent regimen in the different categories of retreated patients with tuberculosis. 303 retreated patients with smear-positive pulmonary tuberculosis were recruited for the study. They were divided into three groups based on the history of tuberculosis and anti-tuberculosis treatment. 87 were in relapse group, 21 in failure group (failure after the initial treatment) and 195 in other retreatment group. Sputum Mycobacterium tuberculosis culture and drug susceptibility test were conducted before treatment. The same retreatment regimen (2-3H3R3Z3E3S3/5-6H3R3E3) was employed for all three groups of patients. Drug resistance and the outcomes of three groups of retreatment tuberculosis were analysed. The drug resistance rates and efficacy of retreatment showed no statistical difference among three groups (P > 0.05). In other retreatment group, the drug resistant rate in patients who received anti-TB drugs for more than 12 months (79.5%) was significantly higher than those for less than 12 months (59.8%, 0.01 short course intermittent regimen.

  9. 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.

  10. 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.

  11. Weichselian stratigraphy, geomorphology and glacial dynamics in southern Finnish Lapland

    Directory of Open Access Journals (Sweden)

    Pertti Sarala

    2005-01-01

    Full Text Available Quaternary stratigraphy and geomorphology were investigated by using aerial photo interpretation, digital elevation models and stratigraphical studies in southern Finnish Lapland. The development of glacial morphology was examined by reconstructing glacial flow patterns and subglacial conditions with emphasis on glacial dynamics. By comparing the climate history and available chronological data the ice-sheet development during the Weichselian was modelled in the area. Also, the Quaternary lithostratigraphy with descriptions, formalnames and type sections of the Peräpohja Group was proposed. Glacial morphology with clear indication of glacial flow directions represents two Weichselian glacial advances in the area of southern Finnish Lapland. The older, northwest-southeast oriented glacial movement was seen as a drumlin field and was preserved under a later cold-based ice sheet. A west-east oriented landform assemblage of ribbed moraines, drumlins and flutings mainly indicated the younger glacial phase. Of the age of ice sheet development during the Weichselian two alternative interpretations have been presented:In the first model, the first glacial advance occurred during the Early Weichselian and was followed by interstadial about 85–74 ka ago. The Middle and Late Weichselian glaciation was continuously covering southern Finnish Lapland after that. The second model includes a new interpretation, in which the first glacial advance that reached the area is connected to the beginning of the Middle Weichselian. Ice-free interstadial occurred about 50–30 ka ago before the Late Weichselian glacial advance, when the Weichselian maximum wasreached.

  12. Growing educational differentials in the retreat from marriage among Korean men.

    Science.gov (United States)

    Park, Hyunjoon; Lee, Jae Kyung

    2017-08-01

    Applying discrete-time hazard models to person-year data constructed from 1% microdata sample of 2010 Korean Census, we explore how men's education affects their transition to first marriage, and how the relationship between education and marriage has changed across three 10-year birth cohorts of Korean men born from 1946 to 1975. Drawing on Oppenheimer's theory of marriage and review of changing educational and economic contexts of Korean men, we develop a hypothesis on growing educational differentials in marriage. We find that the high educated delay marriage until later ages but catch up to the extent to which they are eventually more likely to marry than the low educated. There is a continued trend across cohorts toward the delay and avoidance of marriage at all educational levels. However, the trend of retreat from marriage has been more substantial for men with high school or less education compared to men with a university degree, leading to growing educational gaps over time in marriage. Among the three cohorts, the youngest cohort, among which low educated men's economic prospects have particularly deteriorated due to rapid educational expansion and economic crisis, shows most pronounced decline in marriage. Copyright © 2016 Elsevier Inc. All rights reserved.

  13. Ocean-driven thinning enhances iceberg calving and retreat of Antarctic ice shelves

    Science.gov (United States)

    Liu, Yan; Moore, John C.; Cheng, Xiao; Gladstone, Rupert M.; Bassis, Jeremy N.; Liu, Hongxing; Wen, Jiahong; Hui, Fengming

    2015-01-01

    Iceberg calving from all Antarctic ice shelves has never been directly measured, despite playing a crucial role in ice sheet mass balance. Rapid changes to iceberg calving naturally arise from the sporadic detachment of large tabular bergs but can also be triggered by climate forcing. Here we provide a direct empirical estimate of mass loss due to iceberg calving and melting from Antarctic ice shelves. We find that between 2005 and 2011, the total mass loss due to iceberg calving of 755 ± 24 gigatonnes per year (Gt/y) is only half the total loss due to basal melt of 1516 ± 106 Gt/y. However, we observe widespread retreat of ice shelves that are currently thinning. Net mass loss due to iceberg calving for these ice shelves (302 ± 27 Gt/y) is comparable in magnitude to net mass loss due to basal melt (312 ± 14 Gt/y). Moreover, we find that iceberg calving from these decaying ice shelves is dominated by frequent calving events, which are distinct from the less frequent detachment of isolated tabular icebergs associated with ice shelves in neutral or positive mass balance regimes. Our results suggest that thinning associated with ocean-driven increased basal melt can trigger increased iceberg calving, implying that iceberg calving may play an overlooked role in the demise of shrinking ice shelves, and is more sensitive to ocean forcing than expected from steady state calving estimates. PMID:25733856

  14. Arctic cyclone water vapor isotopes support past sea ice retreat recorded in Greenland ice.

    Science.gov (United States)

    Klein, Eric S; Cherry, J E; Young, J; Noone, D; Leffler, A J; Welker, J M

    2015-05-29

    Rapid Arctic warming is associated with important water cycle changes: sea ice loss, increasing atmospheric humidity, permafrost thaw, and water-induced ecosystem changes. Understanding these complex modern processes is critical to interpreting past hydrologic changes preserved in paleoclimate records and predicting future Arctic changes. Cyclones are a prevalent Arctic feature and water vapor isotope ratios during these events provide insights into modern hydrologic processes that help explain past changes to the Arctic water cycle. Here we present continuous measurements of water vapor isotope ratios (δ(18)O, δ(2)H, d-excess) in Arctic Alaska from a 2013 cyclone. This cyclone resulted in a sharp d-excess decrease and disproportional δ(18)O enrichment, indicative of a higher humidity open Arctic Ocean water vapor source. Past transitions to warmer climates inferred from Greenland ice core records also reveal sharp decreases in d-excess, hypothesized to represent reduced sea ice extent and an increase in oceanic moisture source to Greenland Ice Sheet precipitation. Thus, measurements of water vapor isotope ratios during an Arctic cyclone provide a critical processed-based explanation, and the first direct confirmation, of relationships previously assumed to govern water isotope ratios during sea ice retreat and increased input of northern ocean moisture into the Arctic water cycle.

  15. Outcomes of Holmium Laser Enucleation of the Prostate in the Re-Treatment Setting.

    Science.gov (United States)

    Marien, Tracy; Kadihasanoglu, Mustafa; Tangpaitoon, Teerayut; York, Nadya; Blackburne, Andrew T; Abdul-Muhsin, Haidar; Borofsky, Michael S; Krambeck, Amy E; Humphreys, Mitchell R; Lingeman, James E; Miller, Nicole L

    2017-06-01

    Holmium laser enucleation of the prostate can also be applied in the re-treatment setting when other benign prostatic hyperplasia therapies fail. We compared outcomes in men who underwent holmium laser enucleation of the prostate in the primary vs the re-treatment setting. We retrospectively reviewed the records of 2,242 patients who underwent holmium laser enucleation of the prostate at a total of 4 academic hospitals between 2003 and 2015. Patient demographics, and operative and perioperative outcomes were compared between re-treatment and primary holmium laser enucleation of the prostate. Of the 360 of 2,242 men (16%) who underwent re-treatment holmium laser enucleation of the prostate the procedure was done for residual urinary symptoms in 71%. The most common primary procedure was transurethral resection of the prostate in 42% of cases. Mean time between prior benign prostatic hyperplasia surgery and re-treatment was 68 months (range 1 to 444). There were no significant differences in age, prostate size, AUA (American Urological Association) symptom score or average flow rate between the cohorts. Perioperatively, re-treatment holmium laser enucleation of the prostate was associated with significantly shorter operative time, reduced blood loss, lower specimen weight and shorter length of stay. The AUA symptom score improved in both groups, although it remained higher in men who underwent re-treatment (6.5 vs 5.0, p enucleation of the prostate performed in the re-treatment setting were no different from those in the primary setting. While re-treatment was associated with an increased likelihood of clot retention, urethral stricture and higher AUA symptom score, these minimal differences must be considered against the overall favorable symptom improvement across both cohorts. Copyright © 2017 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

  16. Interaction between glacier and glacial lake in the Bhutan, Himalaya

    Science.gov (United States)

    Tsutaki, S.; Fujita, K.; Yamaguchi, S.; Sakai, A.; Nuimura, T.; Sugiyama, S.; Komori, J.; Takenaka, S.; Tshering, P.

    2012-12-01

    Recession of mountain glaciers in the Himalayas has been reported in the context of global warming. Associated with the glacier retreat, supraglacial lakes have been formed on the termini of debris-covered glaciers. Although it has been said that lake-terminating glaciers flow faster than land-terminating glaciers, observational evidence was scarce. We observationally investigated the influence of the presence/absence of glacial lakes on changes in surface elevation through glacier dynamics in two debris-covered glaciers, Thorthormi Glacier (land-terminating) and Lugge Glacier (lake-terminating), in the Lunana region, the Bhutan Himalaya. We surveyed the surface elevation of debris-covered areas of the two glaciers in 2004 and 2011 by a differential GPS. Change in surface elevation of the lake-terminating Lugge Glacier was much more negative than that of the land-terminating Thorthormi Glacier. Considering almost flat slope and location at lower elevation, however, larger ice thinning rate of the Thorthormi Glacier should have been expected than the Lugge Glacier. We measured surface flow speed of the two glaciers during 2009-2010 by multitemporal orthorectified The Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) images of ALOS. Surface flow speed of the Thorthormi Glacier was faster in the upper reaches and reduced toward the downstream. In contrast, the flow speed at the Lugge Glacier measured in the same periods was greatest at the lower most part. Observed spatial distribution of surface flow speed at both glaciers are evaluated by a two-dimensional numerical flow model. The model shows that contribution of basal sliding to surface flow velocity is large in the lower part of both glaciers. Particularly in the Thorthormi Glacier, approximately 100% of surface flow velocity attribute to basal sliding. Calculated emergence velocity at the Thorthormi Glacier is larger than that at the Lugge Glacier. This result suggests that decreasing in flow

  17. Two-signed feedback of cross-isthmus moisture transport on glacial overturning controlled by the Atlantic warm pool

    NARCIS (Netherlands)

    Boer, H.J. de; Roche, D.M.; Renssen, H.; Dekker, S.C.

    2011-01-01

    This paper studies the control of the Atlantic Warm Pool (AWP) on atmospheric moisture transport across the Central American isthmus as a potential feedback on rapid glacial climate fluctuations. Defined as a region of the Atlantic with surface temperatures above 28.5 °C, the modern AWP expands from

  18. 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.

  19. The 20th Annual Prostate Cancer Foundation Scientific Retreat report.

    Science.gov (United States)

    Miyahira, Andrea K; Simons, Jonathan W; Soule, Howard R

    2014-06-01

    The 20th Annual Prostate Cancer Foundation (PCF) Scientific Retreat was held from October 24 to 26, 2013, in National Harbor, Maryland. This event is held annually for the purpose of convening a diverse group of leading experimental and clinical researchers from academia, industry, and government to present and discuss critical and emerging topics relevant to prostate cancer (PCa) biology, and the diagnosis, prognosis, and treatment of PCa patients, with a focus on results that will lend to treatments for the most life-threatening stages of this disease. The themes that were highlighted at this year's event included: (i) mechanisms of PCa initiation and progression: cellular origins, neurons and neuroendocrine PCa, long non-coding RNAs, epigenetics, tumor cell metabolism, tumor-immune interactions, and novel molecular mechanisms; (ii) advancements in precision medicine strategies and predictive biomarkers of progression, survival, and drug sensitivities, including the analysis of circulating tumor cells and cell-free tumor DNA-new methods for liquid biopsies; (iii) new treatments including epigenomic therapy and immunotherapy, discovery of new treatment targets, and defining and targeting mechanisms of resistance to androgen-axis therapeutics; and (iv) new experimental and clinical epidemiology methods and techniques, including PCa population studies using patho-epidemiology. © 2014 Wiley Periodicals, Inc.

  20. 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.

  1. Geomorphic and shallow-acoustic investigation of an Antarctic Peninsula fjord system using high-resolution ROV and shipboard geophysical observations: Ice dynamics and behaviour since the Last Glacial Maximum

    Science.gov (United States)

    García, Marga; Dowdeswell, J. A.; Noormets, R.; Hogan, K. A.; Evans, J.; Ó Cofaigh, C.; Larter, R. D.

    2016-12-01

    Detailed bathymetric and sub-bottom acoustic observations in Bourgeois Fjord (Marguerite Bay, Antarctic Peninsula) provide evidence on sedimentary processes and glacier dynamics during the last glacial cycle. Submarine landforms observed in the 50 km-long fjord, from the margins of modern tidewater glaciers to the now ice-distal Marguerite Bay, are described and interpreted. The landforms are grouped into four morpho-sedimentary systems: (i) glacial advance and full-glacial; (ii) subglacial and ice-marginal meltwater; (iii) glacial retreat and neoglaciation; and (iv) Holocene mass-wasting. These morpho-sedimentary systems have been integrated with morphological studies of the Marguerite Bay continental shelf and analysed in terms of the specific sedimentary processes and/or stages of the glacial cycle. They demonstrate the action of an ice-sheet outlet glacier that produced drumlins and crag-and-tail features in the main and outer fjord. Meltwater processes eroded bedrock channels and ponds infilled by fine-grained sediments. Following the last deglaciation of the fjord at about 9000 yr BP, subsequent Holocene neoglacial activity involved minor readvances of a tidewater glacier terminus in Blind Bay. Recent stillstands and/or minor readvances are inferred from the presence of a major transverse moraine that indicates grounded ice stabilization, probably during the Little Ice Age, and a series of smaller landforms that reveal intermittent minor readvances. Mass-wasting processes also affected the walls of the fjord and produced scars and fan-shaped deposits during the Holocene. Glacier-terminus changes during the last six decades, derived from satellite images and aerial photographs, reveal variable behaviour of adjacent tidewater glaciers. The smaller glaciers show the most marked recent retreat, influenced by regional physiography and catchment-area size.

  2. Pleistocene environments and glacial history of the northern North Sea

    Science.gov (United States)

    Reinardy, Benedict; Hjelstuen, Berit; Petter Sejrup, Hans; Augedal, Hans; Jørstad, Arild

    2017-04-01

    advances. A thick till unit overlain by a sand layer in the study area was deposited by grounded ice during the Last Glacial Maximum and subsequent drainage of an ice dammed lake in the southern North Sea during the last deglaciation (MIS2) of the study area. This study shows that much of the Quaternary age sediments within the northern North Sea were deposited relatively rapidly during short periods of time probably leaving significant hiatuses within the stratigraphic record. This finding has implications for previous studies that use a chronological framework assuming a relatively continuous sedimentation rate and record for the Early Pleistocene within the North Sea.

  3. Efficacy of passive ultrasonic irrigation in removing root filling material during endodontic retreatment

    National Research Council Canada - National Science Library

    Carina MICHELON; Marina FRIGHETTO; Pauline Mastella LANG; Mariana De Carlo BELLO; Rafael PILLAR; Geraldo Fagundes SERPA; Carlos Alexandre Souza BIER

    Abstract Introduction The aim of endodontic retreatment is to remove the previous root filling materials completely to allow for the subsequent steps of cleaning, canal shaping and filling replacement...

  4. 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.

  5. The retreat of multiculturalism in the liberal state: theory and policy.

    Science.gov (United States)

    Joppke, Christian

    2004-06-01

    This article discusses a recent retreat of multiculturalism in the liberal state. This retreat has occurred both at the level of theory and policy. With the help of some recent liberal critiques of multiculturalism, the first part maps out some shortcomings of the notion of minority integration through cultural recognition, particularly with respect to immigrants. The second part discusses a retreat from multiculturalism policies in three states that had been prominently committed to them: Australia, the Netherlands, and Britain. This practical retreat of multiculturalism is due to a variety of factors, their importance differing across cases: the chronic lack of public support for multiculturalism policies; inherent deficits and failures of multiculturalism policies, especially in socio-economic respect; and a new assertiveness of the liberal state to impose liberal principles.

  6. Contributions of a retreat weekend to the healing and coping of cancer patients' relatives.

    Science.gov (United States)

    Arnaert, Antonia; Gabos, Theresa; Ballenas, Vincent; Rutledge, Robert D H

    2010-02-01

    Relatives play a key role in the daily support and care of cancer patients. This role, however, can negatively affect relatives physically, psychologically, emotionally, and spiritually, challenging their health and well-being. Consequently, this could inhibit relatives' abilities to continue in their roles as caregivers. Although various studies have examined different interventions for the relatives of cancer patients, no formal research has been published on the role that retreat weekends play in their cancer journeys. In this qualitative study we used semistructured interviews to explore the experiences of 8 relatives who attended a "Skills for Healing Retreat Weekend" in Ontario, Canada. The findings indicate that the retreat, in bringing people together to partake in discussions and activities, fostered a sense of community among the participants. The retreat also had enduring effects, contributing to relatives' ongoing processes of healing as well as providing them with strategies for coping in their roles as caregivers.

  7. Hydrography and circulation in the northwestern Bay of Bengal during the retreat of southwest monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Murty, V.S.N.; Sarma, Y.V.B.; Babu, M.T.; Rao, D.P.

    The distribution of temperature and salinity in the upper 500 m of the northwestern Bay of Bengal, adjoining the East Coast of India, during the retreat of southwest monsoon (September) of 1983 is presented. This study reveals coastal upwelling...

  8. Simulations of cataclysmic outburst floods from Pleistocene Glacial Lake Missoula

    Science.gov (United States)

    Denlinger, Roger P.; O'Connell, D. R. H.

    2009-01-01

    Using a flow domain that we constructed from 30 m digital-elevation model data of western United States and Canada and a two-dimensional numerical model for shallow-water flow over rugged terrain, we simulated outburst floods from Pleistocene Glacial Lake Missoula. We modeled a large, but not the largest, flood, using initial lake elevation at 1250 m instead of 1285 m. Rupture of the ice dam, centered on modern Lake Pend Oreille, catastrophically floods eastern Washington and rapidly fills the broad Pasco, Yakima, and Umatilla Basins. Maximum flood stage is reached in Pasco and Yakima Basins 38 h after the dam break, whereas maximum flood stage in Umatilla Basin occurs 17 h later. Drainage of these basins through narrow Columbia gorge takes an additional 445 h. For this modeled flood, peak discharges in eastern Washington range from 10 to 20 × 106 m3/s. However, constrictions in Columbia gorge limit peak discharges to 6 m3/s and greatly extend the duration of flooding. We compare these model results with field observations of scabland distribution and high-water indicators. Our model predictions of the locations of maximum scour (product of bed shear stress and average flow velocity) match the distribution of existing scablands. We compare model peak stages to high-water indicators from the Rathdrum-Spokane valley, Walulla Gap, and along Columbia gorge. Though peak stages from this less-than-maximal flood model attain or exceed peak-stage indicators along Rathdrum-Spokane valley and along Columbia gorge, simulated peak stages near Walulla Gap are 10–40 m below observed peak-stage indicators. Despite this discrepancy, our match to field observations in most of the region indicates that additional sources of water other than Glacial Lake Missoula are not required to explain the Missoula floods.

  9. 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

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

    Directory of Open Access Journals (Sweden)

    Jamie E Becker

    Full Text Available 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

  11. Developing a service marketing strategy for wellness tourism company : Case study: Golden Retreats

    OpenAIRE

    Falck, Jenni

    2013-01-01

    Idea for this thesis arose when author was practicing yoga with the main owner of Golden Retreats in Mexico, where she owns a yoga studio. After variable conversations and mutual interest towards marketing and yoga, decision of the marketing strategy focused research was made. Purpose of this thesis was to understand the mix of suitable marketing strategies for wellness tourism business by approaching the subject by case-study about Golden Retreats. The research questions focused of findi...

  12. Outcomes of HIV-infected patients treated for recurrent tuberculosis with the standard retreatment regimen.

    Science.gov (United States)

    McGreevy, J; Jean Juste, M A; Severe, P; Collins, S; Koenig, S; Pape, J W; Fitzgerald, D W

    2012-06-01

    The Groupe Haitien d'Etude du Sarcome de Kaposi et des Infections Opportunistes (the GHESKIO AIDS and TB Center) in Port-au-Prince, Haiti. To measure the effectiveness of the standard TB retreatment regimen (2HRZES/1HRZE/5HRE) in human immunodeficiency virus (HIV) infected adults. Cohort study. Of 1318 HIV-infected patients with access to antiretroviral therapy following World Health Organization guidelines, 56 were diagnosed with recurrent pulmonary TB and retreated with the standard retreatment regimen: 10 patients (18%) died during retreatment, 3 (5%) defaulted, and 2 (4%) failed treatment. Forty-one patients (73%) achieved retreatment 'success' (cure, treatment completed). Of these, 8 (20%) died during follow-up, 5 (12%) were lost, and 5 (12%) had a second recurrence of TB. Only 26 (46%) of the 56 patients remained alive, in care, and TB-free after a median of 36 months of follow-up. HIV-infected patients treated for recurrent TB with the standard retreatment regimen have high mortality and poor long-term outcomes.

  13. 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.

  14. A regional approach for modeling cliff retreat rate: The Makhteshim Country, Israel

    Science.gov (United States)

    Finzi, Yaron; Harlev, Noam

    2016-10-01

    Cliff retreat rate significantly affect the evolution of landforms and cliff stability. Cliff retreat studies also provide intriguing clues regarding past geomorphic conditions and environmental changes. We hereby present a model to calculate cliff retreat rate based on spatial data of cliff structure and morphology. The model is applied to numerous cliffs in the arid Makhteshim Country, Israel, and results are calibrated using published rates of two local cliffs. The calculated retreat rates confirm previous assertions that the crater cliffs are receding very slowly, but reveal that the rates vary significantly along the cliffs (1-18 cm ky- 1). Results also provide first estimates of retreat rates of other major cliffs in the region including fast retreat rates at the Sede Zin cliff (300-600 cm ky- 1). The proposed model provides a robust analysis to account for local cliff-talus morphology and yields rate estimates representative of current conditions rather than a long-term (geologic) average rate. Results presented constitute important new insights into regional geomorphic processes and on the stability of specific cliff sections within the study area.

  15. Altitudinal dynamics of glacial lakes under changing climate in the Hindu Kush, Karakoram, and Himalaya ranges

    Science.gov (United States)

    Ashraf, Arshad; Naz, Rozina; Iqbal, Muhammad Bilal

    2017-04-01

    The environmental challenges posed by global warming in the Himalayan region include early and rapid melting of snow and glaciers, creation of new lakes, and expansion of old ones posing a high risk of glacial lakes outburst flood (GLOF) hazard for downstream communities. According to various elevation ranges, 3044 lakes were analyzed basinwide in the Hindu Kush-Karakoram-Himalaya (HKH) ranges of Pakistan using multisensor remote sensing data of the 2001-2013 period. An overall increase in glacial lakes was observed at various altitudinal ranges between 2500 and 5500, m out of which noticeable change by number was within the 4000-4500 m range. The analysis carried out by glacial-fed lakes and nonglacial-fed lakes in different river basins indicated variable patterns depending on the geographic location in the HKH region. The correlation analysis of parameters like lake area, expansion rate, and elevation was performed with 617 glacial lakes distributed in various river basins of the three HKH ranges. Lake area (2013) and elevation showed a negative relationship for all basins except Hunza, Shigar, and Shyok. The correlation between the expansion rate of lakes and elevation was on the positive side for Swat, Gilgit, Shigar, and Shingo basins-a situation that may be attributed to the variable altitudinal pattern of temperature and precipitation. In order to explore such diverse patterns of lake behavior and relationship with influential factors in the HKH, detailed studies based on using high resolution image data coupled with in situ information are a prerequisite. Although an increase in lake area observed below 3500 m would be favorable for water resource management, but could be alarming in context of glacial flood hazards that need to be monitored critically on a long-term basis.

  16. Biogeochemical drivers of microbial community convergence across actively retreating glaciers

    Energy Technology Data Exchange (ETDEWEB)

    Castle, Sarah C.; Nemergut, Diana R.; Grandy, A. Stuart; Leff, Jonathan W.; Graham, Emily B.; Hood, Eran; Schmidt, Steven K.; Wickings, Kyle; Cleveland, Cory C.

    2016-10-01

    The ecological processes that influence biogeographical patterns of microorganisms are actively debated. To investigate how such patterns emerge during ecosystem succession, we examined the biogeochemical drivers of bacterial community assembly in soils over two environmentally distinct, recently deglaciated chronosequences separated by a distance of more than 1,300 kilometers. Our results show that despite different geographic, climatic, and soil chemical and physical characteristics at the two sites, soil bacterial community structure and decomposer function converged during plant succession. In a comparative analysis, we found that microbial communities in early succession soils were compositionally distinct from a group of diverse, mature forest soils, but that the differences between successional soils and mature soils decreased from early to late stages of succession. Differences in bacterial community composition across glacial sites were largely explained by pH. However, successional patterns and community convergence across sites were more consistently related to soil organic carbon and organic matter chemistry, which appeared to be tightly coupled with bacterial community structure across both young and mature soils.

  17. 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)

  18. Subduction zone decoupling/retreat modeling explains south Tibet (Xigaze) and other supra-subduction zone ophiolites and their UHP mineral phases

    Science.gov (United States)

    Butler, Jared P.; Beaumont, Christopher

    2017-04-01

    The plate tectonic setting in which proto-ophiolite 'oceanic' lithosphere is created remains controversial with a number of environments suggested. Recent opinions tend to coalesce around supra-subduction zone (SSZ) forearc extension, with a popular conceptual model in which the proto-ophiolite forms during foundering of oceanic lithosphere at the time of spontaneous or induced onset of subduction. This mechanism is favored in intra-oceanic settings where the subducting lithosphere is old and the upper plate is young and thin. We investigate an alternative mechanism; namely, decoupling of the subducting oceanic lithosphere in the forearc of an active continental margin, followed by subduction zone (trench) retreat and creation of a forearc oceanic rift basin, containing proto-ophiolite lithosphere, between the continental margin and the retreating subduction zone. A template of 2D numerical model experiments examines the trade-off between strength of viscous coupling in the lithospheric subduction channel and net slab pull of the subducting lithosphere. Three tectonic styles are observed: 1) C, continuous subduction without forearc decoupling; 2) R, forearc decoupling followed by rapid subduction zone retreat; 3) B, breakoff of subducting lithosphere followed by re-initiation of subduction and in some cases, forearc decoupling (B-R). In one case (BA-B-R; where BA denotes backarc) subduction zone retreat follows backarc rifting. Subduction zone decoupling is analyzed using frictional-plastic yield theory and the Stefan solution for the separation of plates containing a viscous fluid. The numerical model results are used to explain the formation of Xigaze group ophiolites, southern Tibet, which formed in the Lhasa terrane forearc, likely following earlier subduction and not necessarily during subduction initiation. Either there was normal coupled subduction before subduction zone decoupling, or precursor slab breakoff, subduction re-initiation and then decoupling

  19. Fracture Resistance of Endodontically Retreated Roots After Retreatment Using Self-Adjusting File, Passive Ultrasonic Irrigation, Photon-Induced Photoacoustic Streaming, or Laser.

    Science.gov (United States)

    Kamalak, Aliye; Uzun, Ismail; Arslan, Hakan; Keleş, Ali; Doğanay, Ezgi; Keskin, Cangül; Akçay, Merve

    2016-10-01

    Additional cleaning techniques and devices are required to remove maximum amount of residual filling material, which might limit disinfection of root canal system during retreatment. This study aimed to compare fracture resistance of roots when self-adjusting file (SAF), photon-induced photoacoustic streaming (PIPS), passive ultrasonic irrigation (PUI), erbium-doped yttrium aluminum garnet (Er:YAG), or neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers are applied following the use of retreatment files in endodontics. A total of 117 human mandibular canine teeth of similar dimensions were selected and divided into nine groups (n = 13). Aside from control, instrumented, and only-prepared groups, 91 teeth were remaining, of which 13 were assigned to the only-filling group and final 78 to retreatment, thus R-Endo file, R-Endo+SAF, R-Endo+PUI, R-Endo+Er:YAG laser, R-Endo+Nd:YAG laser, and R-Endo+PIPS. The fracture strengths of the retreatment groups were lower than control, instrumented, and only-filling groups (p  0.05). Further cleaning methods using SAF, PIPS, Er:YAG laser, Nd:YAG laser, or PUI did not decrease the fracture resistance when compared with the R-Endo group.

  20. 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.

  1. Near Real-Time Monitoring of Glacial Lake Imja (Khumbu-Everest Region)

    Science.gov (United States)

    Lichtenegger, Juerg; Raj Gurung, Deo; Mool, Pradeep Kumar; Bigot, Jean-Charles

    2010-12-01

    The fast shrinking of glaciers in high mountain areas of the world favours the formation of water bodies within the dead ice area behind the end-moraines. In the past some glacial lakes have burst their natural dams, causing floods and considerable damage down-streams. The necessity to monitor glacial lakes has been recognized. Due to the extreme remoteness as well as high cloudiness of the Himalayas satellite-born imaging radar are proposed. The aim of the study is to provide frequently and rapidly an up-to-date perimeter of the lake, for the 2007/2010 years' period. The interpretation of single images is often difficult due to a rough water surface masking the lake border. Superimposing successive images give satisfactory results. Single-look complex data pairs processed to DInSAR-fringes reveal movements on the terminal moraine area and on parts of the steep lateral moraines. The hazard assessment needs to consider such findings.

  2. Assessing glacial lake outburst flood risk

    Science.gov (United States)

    Kougkoulos, Ioannis; Cook, Simon; Jomelli, Vincent; Clarke, Leon; Symeonakis, Elias

    2017-04-01

    Glaciers across the world are thinning and receding in response to atmospheric warming. Glaciers tend to erode subglacial basins and deposit eroded materials around their margins as lateral-frontal terminal moraines. Recession into these basins and behind impounding moraines causes meltwater to pond as proglacial and supraglacial lakes. Consequently, there has been a general trend of increasing number and size of these lakes associated with glacier melting in many mountainous regions around the globe, in the last 30 years. Glacial lake outburst floods (GLOFs) then may occur where the glacial lake dam (ice, rock, moraine, or combination thereof) is breached, or overtopped, and thousands of people have lost their lives to such events in the last few decades, especially in the Andes and in the Himalaya. Given the ongoing and arguably increasing risk posed to downstream communities, and infrastructure, there has been a proliferation of GLOF studies, with many seeking to estimate GLOF hazard or risk in specific regions, or to identify 'potentially dangerous glacial lakes'. Given the increased scientific interest in GLOFs, it is timely to evaluate critically the ways in which GLOF risk has been assessed previously, and whether there are improvements that can be made to the ways in which risk assessment is achieved. We argue that, whilst existing GLOF hazard and risk assessments have been extremely valuable they often suffer from a number of key shortcomings that can be addressed by using different techniques as multi-criteria decision analysis and hydraulic modelling borrowed from disciplines like engineering, remote sensing and operations research.

  3. Late-glacial of southern South America

    Science.gov (United States)

    Heusser, C. J.

    Overall trends in late-glacial paleoenvironments of southern South America are interpretable from the pollen stratigraphy of radiocarbon dated sections of mires in Tierra del Fuego (55°S), the Chilotan archipelago (42-43°S), and the Chilean Lake District (39-41°S). In Tierra del Fuego, southern beech ( Nothofagus) and shrub and herb taxa (Gramineae, Empetrum, Acaena, Gunnera, Compositae and Cyperaceae) serve as indicators of the changing climate; in the Chilotan archipelago and in the Chilean Lake District, southern beech and other trees (species of Myrtaceae, Podocarpus, Prumnopitys, Pseudopanax and Weinmannia) suffice as indices of climatic change. Pollen records from each of these regions, although in need of greater dating control, indicate climatic sequences that are broadly similar. The records, however, are not regionally consistent in all aspects and differ in their indicator value with the implication of fossil beetle evidence. Attempts at correlation can be unsatisfactory at times and can stem inter alia from the different ecophysiological responses of both plants and beetles to environmental pressures. These differences, which affect the timing of reproduction and migration, may result in the variable occurrence of different species in the records. The broad implication of the pollen data is that following a glacial readvance culminating at about 15,000-14,500 BP, late-glacial climate was generally warmer during intervals before 13,000 and between 12,000 and 11,000 BP, and was cooler between 13,000 and 12,000 and from 11,000 to 10,000 BP.

  4. Glacial history of the North Atlantic marine snail, Littorina saxatilis, inferred from distribution of mitochondrial DNA lineages.

    Directory of Open Access Journals (Sweden)

    Marina Panova

    Full Text Available The North Atlantic intertidal gastropod, Littorina saxatilis (Olivi, 1792, exhibits extreme morphological variation between and within geographic regions and has become a model for studies of local adaptation; yet a comprehensive analysis of the species' phylogeography is lacking. Here, we examine phylogeographic patterns of the species' populations in the North Atlantic and one remote Mediterranean population using sequence variation in a fragment of the mitochondrial cytochrome b gene (607 bp. We found that, as opposed to many other rocky intertidal species, L. saxatilis has likely had a long and continuous history in the Northwest Atlantic, including survival during the last glacial maximum (LGM, possibly in two refugia. In the Northeast Atlantic, several areas likely harboured refugial populations that recolonized different parts of this region after glacial retreat, resulting in strong population structure. However, the outlying monomorphic Venetian population is likely a recent anthropogenic introduction from northern Europe and not a remnant of an earlier wider distribution in the Mediterranean Sea. Overall, our detailed phylogeography of L. saxatilis adds an important piece to the understanding of Pleistocene history in North Atlantic marine biota as well as being the first study to describe the species' evolutionary history in its natural range. The latter contribution is noteworthy because the snail has recently become an important model species for understanding evolutionary processes of speciation; thus our work provides integral information for such endeavours.

  5. Expanding Greenland’s Glacial Record

    DEFF Research Database (Denmark)

    Bjørk, Anders Anker

    Mass loss from the Greenland Ice Sheet and adjecent glaciers and ice caps has accelerated within the last decades, and these changes are accurately observed using a variety of different data products. However, the observational era is relatively short offering little insight into past dynamics....... 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...

  6. Glacial lakes in the Indian Himalayas--from an area-wide glacial lake inventory to on-site and modeling based risk assessment of critical glacial lakes.

    Science.gov (United States)

    Worni, Raphael; Huggel, Christian; Stoffel, Markus

    2013-12-01

    Glacial lake hazards and glacial lake distributions are investigated in many glaciated regions of the world, but comparably little attention has been given to these topics in the Indian Himalayas. In this study we present a first area-wide glacial lake inventory, including a qualitative classification at 251 glacial lakes >0.01 km(2). Lakes were detected in the five states spanning the Indian Himalayas, and lake distribution pattern and lake characteristics were found to differ significantly between regions. Three glacial lakes, from different geographic and climatic regions within the Indian Himalayas were then selected for a detailed risk assessment. Lake outburst probability, potential outburst magnitudes and associated damage were evaluated on the basis of high-resolution satellite imagery, field assessments and through the use of a dynamic model. The glacial lakes analyzed in the states of Jammu and Kashmir and Himachal Pradesh were found to present moderate risks to downstream villages, whereas the lake in Sikkim severely threatens downstream locations. At the study site in Sikkim, a dam breach could trigger drainage of ca. 16×10(6)m(3) water and generate maximum lake discharge of nearly 7000 m(3) s(-). The identification of critical glacial lakes in the Indian Himalayas and the detailed risk assessments at three specific sites allow prioritizing further investigations and help in the definition of risk reduction actions. Copyright © 2012 Elsevier B.V. All rights reserved.

  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. The last glacial termination on the eastern flank of the central Patagonian Andes (47 ° S)

    Science.gov (United States)

    Henríquez, William I.; Villa-Martínez, Rodrigo; Vilanova, Isabel; De Pol-Holz, Ricardo; Moreno, Patricio I.

    2017-07-01

    Few studies have examined in detail the sequence of events during the last glacial termination (T1) in the core sector of the Patagonian Ice Sheet (PIS), the largest ice mass in the Southern Hemisphere outside of Antarctica. Here we report results from Lago Edita (47°8' S, 72°25' W, 570 m a.s.l.), a small closed-basin lake located in a valley overridden by eastward-flowing Andean glaciers during the Last Glacial Maximum (LGM). The Lago Edita record shows glaciolacustrine sedimentation until 19 400 yr BP, followed by organic sedimentation in a closed-basin lake and a mosaic of cold-resistant hygrophilous conifers and rainforest trees, along with alpine herbs between 19 400 and 11 000 yr BP. Our data suggest that the PIS retreated at least ˜ 90 km from its LGM limit between ˜ 21 000 and 19 400 yr BP and that scattered, low-density populations of cold-resistant hygrophilous conifers, rainforest trees, high-Andean and steppe herbs thrived east of the Andes during the LGM and T1, implying high precipitation levels and southern westerly wind (SWW) influence at 47° S. The conifer Podocarpus nubigena increased between 14 500 and 13 000 yr BP, suggesting even stronger SWW influence during the Antarctic Cold Reversal, after which it declined and persisted until 11 000 yr BP. Large increases in arboreal pollen at ˜ 13 000 and ˜ 11 000 yr BP led to the establishment of forests near Lago Edita between 10 000 and 9000 yr BP, suggesting a rise in the regional tree line along the eastern Andean slopes driven by warming pulses at ˜ 13 000 and ˜ 11 000 yr BP and a subsequent decline in SWW influence at ˜ 11 000 yr BP. We propose that the PIS imposed a regional cooling signal along its eastern, downwind margin through T1 that lasted until the separation of the northern and southern Patagonian ice fields along the Andes during the Younger Dryas period. We posit that the withdrawal of glacial and associated glaciolacustrine environments through T1 provided a route for the

  9. Kelp genes reveal effects of subantarctic sea ice during the Last Glacial Maximum.

    Science.gov (United States)

    Fraser, Ceridwen I; Nikula, Raisa; Spencer, Hamish G; Waters, Jonathan M

    2009-03-03

    The end of the Last Glacial Maximum (LGM) dramatically reshaped temperate ecosystems, with many species moving poleward as temperatures rose and ice receded. Whereas reinvading terrestrial taxa tracked melting glaciers, marine biota recolonized ocean habitats freed by retreating sea ice. The extent of sea ice in the Southern Hemisphere during the LGM has, however, yet to be fully resolved, with most palaeogeographic studies suggesting only minimal or patchy ice cover in subantarctic waters. Here, through population genetic analyses of the widespread Southern Bull Kelp (Durvillaea antarctica), we present evidence for persistent ice scour affecting subantarctic islands during the LGM. Using mitochondrial and chloroplast genetic markers (COI; rbcL) to genetically characterize some 300 kelp samples from 45 Southern Ocean localities, we reveal a remarkable pattern of recent recolonization in the subantarctic. Specifically, in contrast to the marked phylogeographic structure observed across coastal New Zealand and Chile (10- to 100-km scales), subantarctic samples show striking genetic homogeneity over vast distances (10,000-km scales), with a single widespread haplotype observed for each marker. From these results, we suggest that sea ice expanded further and ice scour during the LGM impacted shallow-water subantarctic marine ecosystems more extensively than previously suggested.

  10. A post-glacial relative sea-level curve from Fiordland, New Zealand

    Science.gov (United States)

    Dlabola, E. K.; Wilson, G. S.; Gorman, A. R.; Riesselman, C. R.; Moy, C. M.

    2015-08-01

    The modern fjords of southwest New Zealand were previously stranded lakes isolated from the Tasman Sea by bedrock and moraine sills following the retreat of glaciers at the Last Glacial Maximum. The isolated lake basins were subsequently inundated with sea water when sea-level rise overtopped the sills. A record of the lacustrine-to-marine environmental transition is preserved in the fjord basin sediments and is identified in two New Zealand fjords with high-resolution seismic data and paleoenvironmental analysis of sediment cores. Seismic data are used to constrain the maximum sill depth and microfossil assemblages are used to track the lacustrine-to-marine transition. Chronology is based on fourteen radiocarbon ages. A relative sea-level curve for Fiordland, New Zealand is constructed based on sill depths and age constraints on the marine incursion. The sea-level curve allows insights into estimated uplift rates for Fiordland during the Holocene. From a lowstand of at least 107 mbsl 14,750 yr ago, these data reveal a stepwise transgression. Meltwater Pulse 1b is identified between 12,400 and 11,400 yr ago, with a second acceleration in sea-level rise observed 9700 yr ago. This record contributes a new sea-level curve for a mid-latitude (45°S) Southern Hemisphere location as well as new evidence for Meltwater Pulse 1b.

  11. Interhemispheric correlation of late pleistocene glacial events

    Energy Technology Data Exchange (ETDEWEB)

    Lowell, T.V. [Univ. of Cincinnati, OH (United States); Heusser, C.J. [Clinton Woods, Tuxedo, NY (United States); Andersen, B.G. [Univ. of Oslo (Norway)] [and others

    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 {ge}33,500 carbon-14 years before present ({sup 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 {sup 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 {sup 14}C yr B.P., and at the beginning of the Younger Dryas at 11,050 {sup 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. 51 refs., 3 figs., 1 tab.

  12. 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.; Schluchter, C.; Marchant, D. R.; Denton, G. H.

    1995-09-01

    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 (14C 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 14C 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 14C yr B.P., and at the beginning of the Younger Dryas at 11,050 14C 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.

  13. Geothermal activity helps life survive glacial cycles.

    Science.gov (United States)

    Fraser, Ceridwen I; Terauds, Aleks; Smellie, John; Convey, Peter; Chown, Steven L

    2014-04-15

    Climate change has played a critical role in the evolution and structure of Earth's biodiversity. Geothermal activity, which can maintain ice-free terrain in glaciated regions, provides a tantalizing solution to the question of how diverse life can survive glaciations. No comprehensive assessment of this "geothermal glacial refugia" hypothesis has yet been undertaken, but Antarctica provides a unique setting for doing so. The continent has experienced repeated glaciations that most models indicate blanketed the continent in ice, yet many Antarctic species appear to have evolved in almost total isolation for millions of years, and hence must have persisted in situ throughout. How could terrestrial species have survived extreme glaciation events on the continent? Under a hypothesis of geothermal glacial refugia and subsequent recolonization of nongeothermal regions, we would expect to find greater contemporary diversity close to geothermal sites than in nongeothermal regions, and significant nestedness by distance of this diversity. We used spatial modeling approaches and the most comprehensive, validated terrestrial biodiversity dataset yet created for Antarctica to assess spatial patterns of diversity on the continent. Models clearly support our hypothesis, indicating that geothermally active regions have played a key role in structuring biodiversity patterns in Antarctica. These results provide critical insights into the evolutionary importance of geothermal refugia and the history of Antarctic species.

  14. Geothermal activity helps life survive glacial cycles

    Science.gov (United States)

    Fraser, Ceridwen I.; Terauds, Aleks; Smellie, John; Convey, Peter; Chown, Steven L.

    2014-01-01

    Climate change has played a critical role in the evolution and structure of Earth’s biodiversity. Geothermal activity, which can maintain ice-free terrain in glaciated regions, provides a tantalizing solution to the question of how diverse life can survive glaciations. No comprehensive assessment of this “geothermal glacial refugia” hypothesis has yet been undertaken, but Antarctica provides a unique setting for doing so. The continent has experienced repeated glaciations that most models indicate blanketed the continent in ice, yet many Antarctic species appear to have evolved in almost total isolation for millions of years, and hence must have persisted in situ throughout. How could terrestrial species have survived extreme glaciation events on the continent? Under a hypothesis of geothermal glacial refugia and subsequent recolonization of nongeothermal regions, we would expect to find greater contemporary diversity close to geothermal sites than in nongeothermal regions, and significant nestedness by distance of this diversity. We used spatial modeling approaches and the most comprehensive, validated terrestrial biodiversity dataset yet created for Antarctica to assess spatial patterns of diversity on the continent. Models clearly support our hypothesis, indicating that geothermally active regions have played a key role in structuring biodiversity patterns in Antarctica. These results provide critical insights into the evolutionary importance of geothermal refugia and the history of Antarctic species. PMID:24616489

  15. Total Water Storage Change in Cameroon: Calculation, Variability and Link with Onset and Retreat Dates of the Rainy Season

    Directory of Open Access Journals (Sweden)

    Guy Merlin Guenang

    2016-11-01

    Full Text Available Total water storage change (TWSC was calculated using CRU (Climatic Research Unit monthly gridded data for the period 1962–1993 over Cameroon. Investigations were conducted to link its annual cycle with both the beginning and the end of the rainy season. A method was derived as an alternative to determine onset and retreat dates of the rainy season. Two methods were used for the calculation of TWSC. The first method used potential evapotranspiration (PET from the Thornthwaite formula (PET T H and the second, CRU gridded PET data estimated from the Penman–Monteith formula (PET P M . A comparative study of the corresponding TWSC, namely TWSC T H and TWSC P M , respectively, was done. According to the preliminary results, the study area is classified as humid below latitude 8 ∘ N and semiarid above. The results of the spatial and temporal variations showed a close correlation between the two methods, but with a slight gap between their different values, those of TWSC P M being larger and fluctuating less. The annual cycles of TWSC and PR generally showed similar patterns, and their intensities decreased from the southern part of the area (Equatorial forest zone to the northern part (Sahelian zone. For mean T W S C = 0 , two different points were identified: the first and the second corresponding dates matching the onset and retreat months of the rainy season, respectively, except in the arid area (Sahelian zone, where only the retreat month of the rainy season was perfectly determined. The delay observed in the determination of rainfall onset date in that area is assigned to PET formulas that are defined only for humid areas and to the influence of high temperature just before the beginning of the rainy season, promoting the rapid evaporation of soil water immediately after the first rains. Application of the same method ( T W S C = 0 for the individual year showed similar performances. Although TWSC is always negative in Zone 3 and positive

  16. Effectiveness of traditional meditation retreats: A systematic review and meta-analysis.

    Science.gov (United States)

    Khoury, Bassam; Knäuper, Bärbel; Schlosser, Marco; Carrière, Kimberly; Chiesa, Alberto

    2017-01-01

    An increasing number of studies are investigating traditional meditation retreats. Very little, however, is known about their effectiveness. To evaluate the effectiveness of meditation retreats on improving psychological outcomes in general population. A systematic review of studies published in journals or as dissertations in PSYCINFO, PUBMED, CINAHL or Web of Science from the first available date until October 22, 2016. A total of 20 papers (21 studies, N=2912) were included. Effect-size estimates of outcomes combined suggested that traditional meditation retreats are moderately effective in pre-post analyses (n=19; Hedge's g=0.45; 95% CI [0.35, 0.54], pmeditation styles. Results suggested large effects on measures of anxiety, depression and stress, and moderate effects on measures of emotional regulation and quality of life. As to potential mechanisms of actions, results showed large effects on measures of mindfulness and compassion, and moderate effects on measures of acceptance. In addition, changes in mindfulness levels strongly moderated clinical effect sizes. However, heterogeneity was significant among trials, probably due to differences in study designs, types and duration of the retreats and assessed outcomes, limiting therefore the implications of the results. Meditation retreats are moderately to largely effective in reducing depression, anxiety, stress and in ameliorating the quality of life of participants. Copyright © 2016 Elsevier Inc. All rights reserved.

  17. Evaluation of a team-building retreat to promote nursing faculty cohesion and job satisfaction.

    Science.gov (United States)

    Birx, Ellen; Lasala, Kathleen B; Wagstaff, Mark

    2011-01-01

    With the growing global shortage of nursing faculty, there is increased need to develop and evaluate strategies to promote nursing faculty job satisfaction. Using quantitative and qualitative research methods, a team-building faculty retreat including challenge course activities was evaluated to determine its effects on group cohesion and job satisfaction. Mean Job in General scores for the sample (n = 29) at the start of the study were comparable with national norms for employees with graduate degrees. There were statistically significant increases in Job in General scores and group cohesion scores from pretest to posttest on the day of the retreat. However, the positive changes were not maintained at the end of the semester when follow-up data were gathered. Content analysis of the retreat day reflections revealed the following themes: getting to know each other better, seeing commonalities and differences, spending time together, developing trust, and working as a group. Several themes were identified in the end of the semester reflections: getting to know each other, feeling closer as a group, setting a friendlier tone for the semester, and that the retreat was a positive experience. Based on these findings, we recommend the use of a faculty retreat with challenge course activities to promote nursing faculty cohesion and job satisfaction. However, follow-up activities are recommended to maintain positive results over time. 2011 Elsevier Inc. All rights reserved.

  18. 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 < 0.05). Both continuous rotation and reciprocating motion showed similar effectiveness in terms of root canal filling material removal. Using ProTaper Universal retreatment instruments with reciprocating motion of ATR motor and conventional rotary motion have similar efficacy in root canal filling removal.

  19. 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.

  20. Influence of solvents on the bond strength of resin sealer to intraradicular dentin after retreatment

    Directory of Open Access Journals (Sweden)

    Marcelo PALHAIS

    Full Text Available Abstract This study evaluated the removal of filling material with ProTaper Universal Rotary Retreatment system (PTR combined with solvents and the influence of solvents on the bond strength (PBS of sealer to intraradicular dentin after canal reobturation. Roots were endodontically treated and distributed to five groups (n = 12. The control group was not retreated. In the four experimental groups, canals were retreated with PTR alone or in combination with xylol, orange oil, and eucalyptol. After filling material removal, two specimens of each group were analysed by SEM and µCT to verify the presence of filling remnants on root canal walls. The other roots were reobturated and sectioned in 1-mm-thick dentin slices that were subjected to the push-out test. Data were analysed by two-way ANOVA and Tukey’s test (α = 0.05. SEM and µCT analysis revealed that all retreatment techniques left filling remnants on canal walls. The control group (3.47 ± 1.21 presented significantly higher (p 0.05, and differed significantly from the group with eucalyptol (1.89 ± 0.63. The solvents reduced the PBS of the sealer to dentin and no retreatment technique promoted complete removal of filling material.

  1. 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...

  2. Light attenuation characteristics of glacially-fed lakes

    Science.gov (United States)

    Rose, Kevin C.; Hamilton, David P.; Williamson, Craig E.; McBride, Chris G.; Fischer, Janet M.; Olson, Mark H.; Saros, Jasmine E.; Allan, Mathew G.; Cabrol, Nathalie

    2014-07-01

    Transparency is a fundamental characteristic of aquatic ecosystems and is highly responsive to changes in climate and land use. The transparency of glacially-fed lakes may be a particularly sensitive sentinel characteristic of these changes. However, little is known about the relative contributions of glacial flour versus other factors affecting light attenuation in these lakes. We sampled 18 glacially-fed lakes in Chile, New Zealand, and the U.S. and Canadian Rocky Mountains to characterize how dissolved absorption, algal biomass (approximated by chlorophyll a), water, and glacial flour contributed to attenuation of ultraviolet radiation (UVR) and photosynthetically active radiation (PAR, 400-700 nm). Variation in attenuation across lakes was related to turbidity, which we used as a proxy for the concentration of glacial flour. Turbidity-specific diffuse attenuation coefficients increased with decreasing wavelength and distance from glaciers. Regional differences in turbidity-specific diffuse attenuation coefficients were observed in short UVR wavelengths (305 and 320 nm) but not at longer UVR wavelengths (380 nm) or PAR. Dissolved absorption coefficients, which are closely correlated with diffuse attenuation coefficients in most non-glacially-fed lakes, represented only about one quarter of diffuse attenuation coefficients in study lakes here, whereas glacial flour contributed about two thirds across UVR and PAR. Understanding the optical characteristics of substances that regulate light attenuation in glacially-fed lakes will help elucidate the signals that these systems provide of broader environmental changes and forecast the effects of climate change on these aquatic ecosystems.

  3. Contrasting scaling properties of interglacial and glacial climates

    Science.gov (United States)

    Ditlevsen, Peter; Shao, Zhi-Gang

    2017-04-01

    Understanding natural climate variability is essential for assessments of climate change. This is reflected in the scaling properties of climate records. The scaling exponents of the interglacial and the glacial climates are fundamentally different. The Holocene record is monofractal, with a scaling exponent H˜0.7. On the contrary, the glacial record is multifractal, with a significantly higher scaling exponent H˜1.2, indicating a longer persistence time and stronger nonlinearities in the glacial climate. The glacial climate is dominated by the strong multi-millennial Dansgaard-Oeschger (DO) events influencing the long-time correlation. However, by separately analysing the last glacial maximum lacking DO events, here we find the same scaling for that period as for the full glacial period. The unbroken scaling thus indicates that the DO events are part of the natural variability and not externally triggered. At glacial time scales, there is a scale break to a trivial scaling, contrasting the DO events from the similarly saw-tooth-shaped glacial cycles. Ref: Zhi-Gang Shao and Peter Ditlevsen, Nature Comm. 7, 10951, 2016

  4. 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.

  5. Glacial-interglacial vegetation change in the Zambezi catchment

    Science.gov (United States)

    Dupont, L. M.; Kuhlmann, H.

    2017-01-01

    Changes in the environment are thought to have had strong impact on human evolution. The pollen record of GeoB9311, retrieved offshore of the Zambezi River mouth, indicates glacial-interglacial changes in the vegetation of southern East Africa with enhanced forests in the coastal area during interglacials, more Afromontane forest and ericaceous bushland during glacials and an increase in mopane woodland during the transitional periods. C4 swamps, probably with papyrus, might have spread during the more humid phases of the glacial, while mangroves responded sensitively to changes in sea level. The spread of open ericaceous bushland and Afromontane forest during glacials is found for most of Southern Africa with the exception of the extreme south and southwest regions. In contrast to the western part of the continent, forest and woodland in East Africa did not completely disappear during the glacial. It seems that on a regional scale climatic perturbations of the vegetation are less severe than in West Africa.

  6. Late-Post-Glacial Tilt of the Lake Ladoga - Gulf of Finland Region and Rheology Models

    Science.gov (United States)

    Amantov, Aleksey; Amantova, Marina; Fjeldskaar, Willy

    2017-04-01

    Numerous Earth rheology models attempt to explain features of late- and post-glacial isostatic adjustment of Fennoscandia. An area of specific interest is the peripheral areas to the former ice sheet. We used geological-geomorphological observations of relevant elements of the Lake Ladoga - Eastern Gulf of Finland for verification of our modeling studies. New revised glaciation- deglaciation were tested together with thin ice model scenario, with only 10-11 000 years total last ice-age duration on largest highs. On this basis we expect an uplift pattern which differ from what is generally usually assumed, with more distinct northern trend eastward from the Ladoga basin, and subsidence in the Lake Onega region. Hydro-isostasy (HI) was a very noticeable factor in the post-glacial adjustment, both in local and regional scale. The local one is connected with water load changes of the Baltic-Ladoga system. Its details are extremely important for the verification of Earth rheology parameters. Gulf of Finland and Ladoga regions have probably experienced several dramatic water level changes, and expected HI pattern was sophisticated. In the modeling we have incorporated drops of large local ice lakes. Another one due to ice sheet retreat in Sweden probably happened 13000 cal. BP, with smaller influence due to posterior readvance and Baltic Ice Lake water rise untill the final drop at 11600 cal. BP. The minimum water level in the region from the model culminated 10800 cal. BP, with expected extensive dry land areas in south-eastern parts of the basin. Ancyllus Lake transgression could have two peaks, with another deep level fall in both separated basins at culmination of Baltic Ancyllus Lake regression 8700-8900 cal. BP. This could be synchronous with the known most pronounced largest sea level fall in Great Lakes of North America, being also caused by global climatic changes. Final dramatic changes influenced south-eastern Ladoga, with transgression and final drop took

  7. Rare Carboniferous and Permian glacial and non-glacial bryophytes and associated lycophyte megaspores of the Paraná Basin, Brazil: A new occurrence and paleoenvironmental considerations

    Science.gov (United States)

    Ricardi-Branco, Fresia; Rohn, Rosemarie; Longhim, Marcia Emilia; Costa, Juliana Sampaio; Martine, Ariel Milani; Christiano-de-Souza, Isabel Cortez

    2016-12-01

    Fossil bryophytes are rare because their preservation is compromised by the presence of a thin cuticle (if any) and a lack of lignin. Except for the occurrence of one bryophyte in the glacial Dwyka Group of the Karoo Basin, the other rare Late Paleozoic records in Gondwana are notably from the Paraná Basin in Southeast/South Brazil. Four bryophyte sites (including a newly discovered one) were found in the lower part of the thick Permo-Carboniferous glacial succession of the Itararé Group, and one was found in the Guadalupian Teresina Formation, which was roughly assigned to an epeiric sea (or "lake") dominated by a warm, semi-arid climate. This study describes the fossils from the new occurrence from the Itararé Group and discusses the context in which the bryophyte beds originated in the basin. The new samples confirm that all of the bryophytes of the Itararé Group can be classified as Dwykea araroii Ricardi-Branco et al. (a possible pleurocarp) and are associated with the lycophyte megaspore Sublagenicula brasiliensis (Dijkstra) Dybová-Jachowicz. In the much younger Teresina Formation, the bryophytes are Yguajemanus yucapirus Cristiano-de-Souza et al. and Capimirinus riopretensis Cristiano-de-Souza et al., and abundant charophytes and rare dwarf lycophyte stems and bracts are present in the same layers. Although the two stratigraphic units represent distinct paleoenvironments and climates, they seem to share some characteristics: a) the bryophyte assemblages were transported very little; b) they were deposited in very calm environments; c) they were the main components (along with some lycophytes) of local or poorly diversified regional vegetation. The low number of species, which is characteristic of opportunistic communities, can be explained by local or regional conditions that would have been stressful for the vascular plants in other areas. During the deposition of the Itararé Group, the main control was probably the cold climate in addition to a

  8. 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

  9. The value of initial cavitation to predict re-treatment with pulmonary tuberculosis.

    Science.gov (United States)

    Huang, Qiusheng; Yin, Yongmei; Kuai, Shougang; Yan, Yan; Liu, Jun; Zhang, YingYing; Shan, Zhongbao; Gu, Lan; Pei, Hao; Wang, Jun

    2016-05-06

    Pulmonary cavitation is the classic hallmark of pulmonary tuberculosis (PTB) and is the site of very high mycobacterial burden associated with antimycobacterial drug resistance and treatment failure. The objective of this study was to investigate the relationship between re-treatment PTB and initial pulmonary cavitation coordinated with other clinical factors. We conducted a case-control study of 291 newly diagnosed cases of pulmonary TB in The Infectious Hospital of Wuxi from Dec 2009 to Dec 2011 with complete follow-up information until December 31st of 2014. 68 patients were followed-up with PTB re-treatment; the rest of the PTB patients (n = 223) had completed anti-TB treatment, and cured without re-treatment were selected as controls. The univariate analysis [hazard ratio (HR) 1.885, 95 % CI 1.170-3.035, P = 0.009] and the multivariable analysis (HR 2.242, 95 % CI 1.294-3.882, P = 0.004) demonstrated that the initial pulmonary cavitation was a prognostic predictor for TB re-treatment. Additionally, the re-treatment rates in PTB patients with cavitation and no-cavitation were 27.1 and 15.5 %, respectively, with significant difference (log-rank test; P = 0.010). Other factors, age of ≥60 and history of smoking, were also prognostic variables. Initial pulmonary cavitation of chest X-ray was a significant predictor for PTB re-treatment.

  10. Comparative assessment of the incidence of vertical root fractures between conventional versus surgical endodontic retreatment.

    Science.gov (United States)

    Karygianni, L; Krengel, M; Winter, M; Stampf, S; Wrbas, K T

    2014-11-01

    Vertical root fractures (VRFs) are a common cause of tooth loss. Little evidence exists though, relating the incidence of VRFs to the type of endodontic retreatment. This retrospective study aimed at evaluating the impact of conventional versus surgical endodontics on root canal-filled teeth with VRFs. Over a period of 13 years, 200 endodontically retreated teeth from 192 patients with VRFs were extracted and further examined. VRFs were assessed in relation to age, gender, tooth group, clinical signs, extension on the root surface, patency, as well as type of endodontic retreatment and restoration. Statistical analysis was conducted using a Cox PH Model, Chi-squared, Wilcoxon rank-sum, and Log rank tests at a significance level of 5 %. The majority of teeth with VRFs (62.31 %) had undergone the combination of conventional root canal retreatment and apical surgery. Women (64.06 %) presented VRFs more frequently than men (35.94 %) at the mean age of 51.1 and 55.1 years, respectively. Maxillary first (17.5 %) and second (16.5 %) premolars, restored by a resin-based material without a post (56.28 %) were more susceptible to VRFs. Apically initiated (84.1 %) VRFs could be diagnosed more easily on radiographs. The type of endodontic treatment strongly correlated with VRFs. The prevalence of VRFs in teeth having undergone both conventional and surgical endodontic retreatment could be attributed, among others, to additive dentin damage related to the aforementioned endodontic procedures. The possible involvement of endodontic retreatment in the multifactorial etiology of VRFs needs to be taken into consideration in clinical practice.

  11. Uncertainty in Greenland glacial isostatic adjustment

    DEFF Research Database (Denmark)

    Milne, G. A.; Lecavalier, B.; Kjeldsen, K. K.

    It is well known that the interpretation of geodetic data in Greenland to constrain recent ice mass changes requires knowledge of isostatic land motion associated with past changes in the ice sheet. In this talk we will consider a variety of factors that limit how well the signal due to past mass...... of the ice history with a focus on the past few thousand years. In particular, we will show predictions of contemporary land motion and gravity changes due to loading changes following the Little Ice Age computed using a new reconstruction of ice thickness changes based largely on empirical data. A primary...... changes (commonly referred to as glacial isostatic adjustment (GIA)) can be defined. Predictions based on a new model of Greenland GIA will be shown. Using these predictions as a reference, we will consider the influence of plausible variations in some key aspects of both the Earth and ice load components...

  12. Control of glacial quarrying by bedrock joints

    Science.gov (United States)

    Hooyer, Thomas S.; Cohen, Denis; Iverson, Neal R.

    2012-06-01

    A principal assumption of models that describe bedrock quarrying by glaciers is that cracks in the bed are small and isolated. These cracks are assumed to grow slowly in response to glacial loading to eventually delimit the areas of quarried surfaces. If this assumption is correct, then quarried-surface orientations will be controlled by orientations of principal stresses in the bed associated with sliding and resultant ice-bed separation downglacier from rock ledges and roches moutonnées, rather than by orientations of joints that predate glacial loading. To test this hypothesis, we compared orientations of quarried surfaces and preglacial joints in nine recently deglaciated forefields of glaciers in Canada and Switzerland with different bedrock lithologies and bedforms. In all but one forefield, quarried surfaces and major joint sets are coincident, with orientations of quarried surfaces bearing no systematic relationship to sliding direction other than their obvious tendency to not face upglacier. A difference in sliding direction of 64° between two areas of one glacier forefield had no effect on the orientation of quarried surfaces, with the same joint set exploited in both areas. These observations motivate a new characterization of subglacial bedrock that differs from that of existing quarrying models. The bed is idealized as a group of rock blocks separated by preglacial joints. Slow crack growth necessary for quarrying would be confined to small bodies of rock (bridges) that connect the faces of joints. This model of the bed does not allow it to be treated as an intact elastic solid with hydraulically isolated cracks as is usually assumed, which would have a profound influence on characterization of quarrying mechanics.

  13. Glacial onset predated Late Ordovician climate cooling

    Science.gov (United States)

    Pohl, Alexandre; Donnadieu, Yannick; Le Hir, Guillaume; Ladant, Jean-Baptiste; Dumas, Christophe; Alvarez-Solas, Jorge; Vandenbroucke, Thijs R. A.

    2016-06-01

    The Ordovician glaciation represents the acme of one of only three major icehouse periods in Earth's Phanerozoic history and is notorious for setting the scene for one of the "big five" mass extinction events. Nevertheless, the mechanisms that drove ice sheet growth remain poorly understood and the final extent of the ice sheet crudely constrained. Here using an Earth system model with an innovative coupling method between ocean, atmosphere, and land ice accounting for climate and ice sheet feedback processes, we report simulations portraying for the first time the detailed evolution of the Ordovician ice sheet. We show that the emergence of the ice sheet happened in two discrete phases. In a counterintuitive sequence of events, the continental ice sheet appeared suddenly in a warm climate. Only during the second act, and set against a background of decreasing atmospheric CO2, followed steeply dropping temperatures and extending sea ice. The comparison with abundant sedimentological, geochemical, and micropaleontological data suggests that glacial onset may have occurred as early as the Middle Ordovician Darriwilian, in agreement with recent studies reporting third-order glacioeustatic cycles during the same period. The second step in ice sheet growth, typified by a sudden drop in tropical sea surface temperatures by ˜8°C and the further extension of a single, continental-scale ice sheet over Gondwana, marked the onset of the Hirnantian glacial maximum. By suggesting the presence of an ice sheet over Gondwana throughout most of the Middle and Late Ordovician, our models embrace the emerging paradigm of an "early Paleozoic Ice Age."

  14. Rift in Antarctic Glacier: a Unique Chance to Study Ice Shelf Retreat

    Science.gov (United States)

    Howat, Ian M.; Jezek, Ken; Studinger, Michael; Macgregor, Joseph A.; Paden, John; Floricioiu, Dana; Russell, Rob; Linkswiler, Matt; Dominguez, Roseanne T.

    2012-01-01

    It happened again, but this time it was caught in the act. During the last week of September 2011 a large transverse rift developed across thefloating terminus of West Antarcticas PineIsland Glacier, less than 5 years after its lastlarge calving event, in 2007 (Figure 1). PineIsland Glaciers retreat has accelerated substantiallyin the past 2 decades, and it is nowlosing 50 gigatons of ice per year, or roughly 25 of Antarcticas total annual contributionto sea level rise [Rignot et al., 2008]. The glaciers recent accelerated retreat is likely triggered by ocean warming and increased submarine melting. As such, it is of significant interest to glaciologists and of heightened societal relevance.

  15. Retreatability of two endodontic sealers, EndoSequence BC Sealer and AH Plus: a micro-computed tomographic comparison.

    Science.gov (United States)

    Oltra, Enrique; Cox, Timothy C; LaCourse, Matthew R; Johnson, James D; Paranjpe, Avina

    2017-02-01

    Recently, bioceramic sealers like EndoSequence BC Sealer (BC Sealer) have been introduced and are being used in endodontic practice. However, this sealer has limited research related to its retreatability. Hence, the aim of this study was to evaluate the retreatability of two sealers, BC Sealer as compared with AH Plus using micro-computed tomographic (micro-CT) analysis. Fifty-six extracted human maxillary incisors were instrumented and randomly divided into 4 groups of 14 teeth: 1A, gutta-percha, AH Plus retreated with chloroform; 1B, gutta-percha, AH Plus retreated without chloroform; 2A, gutta-percha, EndoSequence BC Sealer retreated with chloroform; 2B, gutta-percha, EndoSequence BC Sealer retreated without chloroform. Micro-CT scans were taken before and after obturation and retreatment and analyzed for the volume of residual material. The specimens were longitudinally sectioned and digitized images were taken with the dental operating microscope. Data was analyzed using an ANOVA and a post-hoc Tukey test. Fisher exact tests were performed to analyze the ability to regain patency. There was significantly less residual root canal filling material in the AH Plus groups retreated with chloroform as compared to the others. The BC Sealer samples retreated with chloroform had better results than those retreated without chloroform. Furthermore, patency could be re-established in only 14% of teeth in the BC Sealer without chloroform group. The results of this study demonstrate that the BC Sealer group had significantly more residual filling material than the AH Plus group regardless of whether or not both sealers were retreated with chloroform.

  16. 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

    2017-10-19

    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.

  17. Automated reconstruction of drainage basins and water discharge to the sea through glacial cycles

    Science.gov (United States)

    Wickert, Andrew

    2015-04-01

    Over glacial cycles, ice masses and their geophysical impacts on surface topography dramatically changed drainage patterns and river discharges. These changes impacted meltwater discharge to the ocean, geomorphology, and climate. As the river systems'the threads that tied the ice sheets to the sea'were stretched, severed, and rearranged during deglaciation, they also shrank and swelled with the pulse of meltwater inputs and proglacial lake dynamics. Here I present a general method to compute past river flow paths, drainage basin geometries, and river discharges. I automate these calculations within GRASS GIS to take advantage of rapid solution techniques for drainage networks in an open-source and compute-cluster-ready environment. I combine modern topography and bathymetry with ice sheet reconstructions from the last glacial cycle and a global glacial isostatic adjustment model to build digital elevation models of the past Earth surface. I then sum ice sheet mass balance with computed precipitation and evapotranspiration from a paleoclimate general circulation model to produce grids of water input. I combine these topographic and hydrologic inputs to compute past river networks and discharges through time. These paleodrainage reconstructions connect ice sheets, sea level, and climate models to fluvial systems, which in turn generate measurable terrace and sedimentary records as they carry physical, compositional, and isotopic signatures of ice sheet melt and landscape change through their channels and to the sea. Therefore, this work provides a self-consistent paleogeographic framework within which models and geologic records may be quantitatively compared to build new insights into past glacial systems.

  18. A Glacial Chronology of the Strait of Magellan

    Science.gov (United States)

    Peltier, C.; Kaplan, M. R.; Schaefer, J. M.; Soteres, R.; Sagredo, E. A.; Aravena, J. C.

    2016-12-01

    In order to address the fundamental question of when and why Ice Age climates begin and end in South America and the Southern Hemisphere, robust glacial chronologies are needed. As previous studies have demonstrated, well-preserved glacial deposits left by large ice sheet lobes adjacent to the Strait of Magellan (52°S; Chile) in southernmost South America provide a unique opportunity to reconstruct the timing and structure of at least the last two glaciations and terminations. We apply precise 10Be surface exposure dating of glacially deposited moraine boulders, along with detailed geomorphic mapping of the area. Here we present new results for a sequence of six moraine sets at the Strait of Magellan that span 18-28 ka and 60-70 ka showing that boulders from the outermost moraine ridge dated thus far are marine isotope stage (MIS) 4 in age. This coincides with a glacial maximum in New Zealand's Southern Alps (44°S), providing evidence for a hemispheric-scale full glacial maximum during MIS-4, similar in size to MIS-2. Inboard the MIS-4 moraine, mapping and dating of several moraines fringing the Strait of Magellan area will afford us insight into the fine structure of the local Last Glacial Maximum and its regional, hemispheric and inter-hemispheric significance. Establishment of such detailed glacier records in southernmost South America and throughout the Southern Hemisphere will help to test proposed mechanisms for the last two glacial maxima and their terminations.

  19. Biogeochemistry of glacial runoff along the Gulf of Alaska

    Science.gov (United States)

    Hood, E.; Scott, D.; Vermilyea, A.; Stubbins, A.; Raymond, P.; Spencer, R.

    2012-04-01

    Glaciers and ice sheets represent the second largest reservoir of water in the global hydrologic system and glacier ecosystems cover 10% of the Earth, however the biogeochemistry of glacier discharge has not been well characterized. Preliminary investigations have shown that runoff from glaciers can be an important contributor of dissolved organic carbon (DOC) and macro- and micro- nutrients such as P and Fe to downstream aquatic ecosystems. There is also mounting evidence that glacier ecosystems may be a source of anthropogenically derived constituents such as fossil fuel combustion by-products and persistent organic pollutants that are deposited in precipitation and released in melting glacier ice. As a result, it is critical to develop our understanding of glacial biogeochemistry, particularly in near-shore marine ecosystems along glacially-dominated coastal margins that receive large volumes of glacial runoff. To examine the spatial and temporal variability in the biogeochemical properties of glacial runoff, we sampled snow, ice melt, and glacial runoff at the Mendenhall Glacier near Juneau, Alaska during the summer of 2012. Mendenhall Glacier extends from near-sea level to >1700 m.a.s.l. and encompasses ~120 km2 of the 3900 km2 Juneau Icefield. The main sub-glacial drainage channel was sampled weekly throughout the glacier melt season (May-October) for a suite of physical (temperature, conductivity, suspended sediment) and biogeochemical (C, N, P, Fe and trace metals) parameters. In addition, we did opportunistic sampling of snow in the glacier accumulation zone and supra-glacial meltwater streams on the glacier surface. We also analyzed particulate and dissolved Hg in glacial runoff to quantify the export of Hg to downstream aquatic ecosystems. Preliminary results show that concentrations of dissolved organic carbon in snow, ice melt, and sub-glacial runoff were typically low (isotopes (13C and 14C), fluorescence spectrophotometry, and electrospray ionization

  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. Microorganism penetration in dentinal tubules of instrumented and retreated root canal walls. In vitro SEM study

    Directory of Open Access Journals (Sweden)

    Saad Al-Nazhan

    2014-11-01

    Full Text Available Objectives This in vitro study aimed to investigate the ability of Candida albicans (C. albicans and Enterococcus faecalis (E. faecalis to penetrate dentinal tubules of instrumented and retreated root canal surface of split human teeth. Materials and Methods Sixty intact extracted human single-rooted teeth were divided into 4 groups, negative control, positive control without canal instrumentation, instrumented, and retreated. Root canals in the instrumented group were enlarged with endodontic instruments, while root canals in the retreated group were enlarged, filled, and then removed the canal filling materials. The teeth were split longitudinally after canal preparation in 3 groups except the negative control group. The teeth were inoculated with both microorganisms separately and in combination. Teeth specimens were examined by scanning electron microscopy (SEM, and the depth of penetration into the dentinal tubules was assessed using the SMILE view software (JEOL Ltd. Results Penetration of C. albicans and E. faecalis into the dentinal tubules was observed in all 3 groups, although penetration was partially restricted by dentin debris of tubules in the instrumented group and remnants of canal filling materials in the retreated group. In all 3 groups, E. faecalis penetrated deeper into the dentinal tubules by way of cell division than C. albicans which built colonies and penetrated by means of hyphae. Conclusions Microorganisms can easily penetrate dentinal tubules of root canals with different appearance based on the microorganism size and status of dentinal tubules.

  3. Iceland rising : Solid Earth response to ice retreat inferred from satellite radar interferometry and visocelastic modeling

    NARCIS (Netherlands)

    Auriac, A.; Spaans, K.H.; Sigmundsson, F.; Hooper, A.; Schmidt, P.; Lund, B.

    2013-01-01

    A broad uplift occurs in Iceland in response to the retreat of ice caps, which began circa 1890. Until now, this deformation signal has been measured primarily using GPS at points some distance away from the ice caps. Here, for the first time we use satellite radar interferometry (interferometric

  4. 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 ...

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

    NARCIS (Netherlands)

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

    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

  6. 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

  7. 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

  8. Results of cohort analysis by category of tuberculosis retreatment cases in Morocco from 1996 to 2003.

    Science.gov (United States)

    Ottmani, S E; Zignol, M; Bencheikh, N; Laâsri, L; Chaouki, N; Mahjour, J

    2006-12-01

    To analyse treatment outcomes by subcategory of tuberculosis (TB) retreatment cases. All TB patients treated with the Category II regimen from 1996 to 2003 in Morocco were enrolled in this retrospective study. For each cohort, the retreatment outcome data were analysed as a whole and by the following sub-categories: 1) cases who relapsed after one course of anti-tuberculosis treatment; 2) cases who failed the Category I regimen; and 3) cases who interrupted one course of anti-tuberculosis treatment. The study population included 14 635 retreatment patients, among whom 81.7% were TB relapse cases, 5.2% had failed the Category I regimen and 13.1% were defaulters. The average treatment success rates were respectively 74.8% (range 71.8-76.6), 58.0% (range 52.4-74.0) and 51.4% (range 46.4-55.6) among relapse, failure and default cases. Failure and default rates were significantly higher (P < 0.001) among patients who failed Category I treatment and among those who defaulted, respectively. TB cases who fail the Category I regimen should systematically receive drug susceptibility testing, while defaulters should be given support to improve treatment adherence. Stratified cohort analysis by subcategory of retreatment has been shown to be useful for evaluating the performance of TB control programmes.

  9. Partial flap during laser In-situ Keratomileusis: Pathogenesis and timing of retreatment

    Directory of Open Access Journals (Sweden)

    Rao Srinivas

    2000-01-01

    Full Text Available Purpose: To report the timing of retreatment and clinical outcomes in patients with a partial corneal flap during laser in-situ keratomileusis (LASIK, and to describe the causes of this complication. Methods: Retrospective review of case records of four patients (4 eyes who had a partial corneal flap during LASIK. Results: The mean age of the four patients was 23 ± 4.7 years, and mean preoperative spherical equivalent (SE refraction was -9.1 ± 3.1D (range, -5.5 to -13D. A 160 μm corneal flap was attempted during the initial treatment. Retreatment with a 180 μm corneal flap was performed at a mean of 5.1 ± 1.6 weeks (range, 4 to 7.5 weeks after the initial procedure. There were no intraoperative complications during retreatment. Post-LASIK mean SE refraction was -1.0 ± 1.1D (range, +0.38 to -2.0D, after a mean follow up of 19 ± 15.7 weeks (range, 7 to 42 weeks. Best spectacle-corrected visual acuity decreased in one eye from 6/5 to 6/6 and was maintained in the others. Conclusion: LASIK retreatment can be performed as early as one month after a partial flap, if the refraction is stable and a thicker corneal flap is created.

  10. The Benefits and Challenges of Academic Writing Retreats: An Integrative Review

    Science.gov (United States)

    Kornhaber, Rachel; Cross, Merylin; Betihavas, Vasiliki; Bridgman, Heather

    2016-01-01

    The immediate drivers to increase publication outputs in higher education are government and research funding, organisational status, performance expectations and personal career aspirations. Writing retreats are one of a range of strategies used by universities to boost publication output. The aims of this integrative review were to synthesise…

  11. Mechanism of Gully-Head Retreat - A Study at Ganganir Danga ...

    African Journals Online (AJOL)

    Height and slope of gully heads, width at top and base of the gully head were monitored. Geotechnical properties of soil like cohesion and angle of internal frication, bulk density were measured to estimate shear stress and shear strength at gully head. Linear retreat of the gully heads was monitored by pegging technique.

  12. Southern Ocean warming and Wilkes Land ice sheet retreat during the mid-Miocene

    NARCIS (Netherlands)

    Sangiorgi, F.; Bijl, P.K.; Passchier, S.; Salzmann, U.; Schouten, S.; McKay, R.M.; Cody, R.D.; Pross, J.; van de Flierdt, T.; Bohaty, S.M.; Levy, R.; Williams, T.; Escutia, C.; Brinkhuis, H.

    2018-01-01

    Observations and model experiments highlight the importance of ocean heat in forcing icesheet retreat during the present and geological past, but past ocean temperature data arevirtually missing in ice sheet proximal locations. Here we document paleoceanographicconditions and the (in)stability of

  13. Influences of glacial melt and permafrost thaw on the age of dissolved organic carbon in the Yukon River basin

    Science.gov (United States)

    Aiken, George R.; Spencer, Robert G.M.; Striegl, Robert G.; Schuster, Paul F.; Raymond, Peter A.

    2014-01-01

    Responses of near-surface permafrost and glacial ice to climate change are of particular significance for understanding long-term effects on global carbon cycling and carbon export by high-latitude northern rivers. Here we report Δ14C-dissolved organic carbon (DOC) values and dissolved organic matter optical data for the Yukon River, 15 tributaries of the Yukon River, glacial meltwater, and groundwater and soil water end-member sources draining to the Yukon River, with the goal of assessing mobilization of aged DOC within the watershed. Ancient DOC was associated with glacial meltwater and groundwater sources. In contrast, DOC from watersheds dominated by peat soils and underlain by permafrost was typically enriched in Δ14C indicating that degradation of ancient carbon stores is currently not occurring at large enough scales to quantitatively influence bulk DOC exports from those landscapes. On an annual basis, DOC exported was predominantly modern during the spring period throughout the Yukon River basin and became older through summer-fall and winter periods, suggesting that contributions of older DOC from soils, glacial meltwaters, and groundwater are significant during these months. Our data indicate that rapidly receding glaciers and increasing groundwater inputs will likely result in greater contributions of older DOC in the Yukon River and its tributaries in coming decades.

  14. Effects of catastrophic draining of Wisconsinian glacial lakes on the continental shelf; an example from Block Island Sound, RI

    Science.gov (United States)

    Klotsko, S.; Driscoll, N. W.

    2013-12-01

    After the last glacial maximum (~21 kya) runoff from the Laurentide ice sheet was trapped behind terminal moraines, creating large glacial lakes along the New York-southern New England coast. These lakes drained catastrophically from east to west, with Lake Block Island Sound (occupying current Block Island Sound, RI; BIS) draining ~ 16 kya. Glacial Lake Connecticut, located in current Long Island Sound just south of BIS, drained through Block Island Sound approximately 500 years later. This catastrophic draining created large, 100-meter deep depressions on the shelf as waters flowed through a low in the moraine called ';The Race'. These depressions have remained open through the transgression, with exposure to swift modern tidal currents in the region. In 1999, the two easternmost, more circular features were mapped using high-resolution seismic CHIRP data. These data show several geologic units, including bedrock, glacial lake varved deposits, and modern sediment. The modern sediment can be seen prograding towards the eastern depression, but is hindered by a local topographic high, preventing the depression from being filled. We postulate that the depressions were not filled in with sediment during the transgression because they were filled with ice and are now drowned kettle holes. Another possibility is the transgression across the shelf was too rapid for sediment to fill in such large depressions.

  15. Glacial bottleneck and postglacial recolonization of a seed parasitic weevil, Curculio hilgendorfi, inferred from mitochondrial DNA variation.

    Science.gov (United States)

    Aoki, K; Kato, M; Murakami, N

    2008-07-01

    Climatic changes during glacial periods have had a major influence on the recent evolutionary history of living organisms, even in the warm temperate zone. We investigated phylogeographical patterns of a weevil Curculio hilgendorfi (Curculionidae), a host-specific seed predator of Castanopsis (Fagaceae) growing in the broadleaved evergreen forests in Japan. We examined 2709 bp of mitochondrial DNA for 204 individuals collected from 62 populations of the weevil. Four major haplogroups were detected, in southwestern and northeastern parts of the main islands and in central and southern parts of the Ryukyu Islands. The demographic population expansion was detected for the two groups in the main islands but not for the Ryukyu groups. The beginning time of the expansion was dated to 39,000-59,000 years ago, which is consistent with the end of the last glacial period. Our data also demonstrated that the southwestern population of the main islands has experienced a more severe bottleneck and more rapid population growth after glacial ages than the northeastern population. At least three refugial areas in the main islands were likely to have existed during the last glacial periods, one of which had not previously been recognized by analyses of intraspecific chloroplast DNA variation of several plant species growing in the broadleaved evergreen forests. Our results represent the first phylogeographical and population demographic analysis of an insect species associated with the broadleaved evergreen forests in Japan, and reveal more detailed postglacial history of the forests.

  16. Slowing down the retreat of the Morteratsch glacier, Switzerland, by artificially produced summer snow

    Science.gov (United States)

    Oerlemans, Johannes; Keller, Felix; Haag, Martin

    2017-04-01

    Many large valley glaciers in the world are retreating at historically unprecedented rates. Also in the Alps, where warming over the past decades has been more than twice as large as the global mean, all major glaciers have retreated over distances of several kilometers over the past hundred years. The Morteratsch Glacier, Pontresina, Switzerland, is a major touristic attraction. Due to strong retreat the lowest part of the glacier is getting out of sight from the gravel road that provided direct access to the glacier front. The Community of Pontresina has commissioned a preparatory study to find out if it is possible to slow down the retreat of the Morteratsch Glacier in an environmentally friendly way. In this article we report on the outcome of such a study, based on a modelling approach. Our analysis is based on a 20- year weather station record from the lower part of the glacier, combined with calculations with an ice flow model. This model has been carefully calibrated against the historical glacier length record, to ensure an optimal initial state for projections into the future. We arrive at the conclusion that producing summer snow in the ablation zone over a larger area (typically 0.5 to 1 km ^2) is the best option, and may have a significant effect on the rate of retreat on a timescale of decades. We consider three scenarios of climate change: (i) no change, (ii) a rise of the Equilibrium Line Altitude (ELA) by 1 m/yr, and (iii) a rise of the ELA by 2 m/yr. Projections of glacier length are done until the year 2100. It takes about 10 years before snow deposition in the higher ablation zone starts to affect the position of the glacier snout. The difference in glacier length between the snow and no-snow experiments becomes 400 to 500 m within two decades.

  17. Repeated large-scale retreat and advance of Totten Glacier indicated by inland bed erosion.

    Science.gov (United States)

    Aitken, A R A; Roberts, J L; van Ommen, T D; Young, D A; Golledge, N R; Greenbaum, J S; Blankenship, D D; Siegert, M J

    2016-05-19

    Climate variations cause ice sheets to retreat and advance, raising or lowering sea level by metres to decametres. The basic relationship is unambiguous, but the timing, magnitude and sources of sea-level change remain unclear; in particular, the contribution of the East Antarctic Ice Sheet (EAIS) is ill defined, restricting our appreciation of potential future change. Several lines of evidence suggest possible collapse of the Totten Glacier into interior basins during past warm periods, most notably the Pliocene epoch, causing several metres of sea-level rise. However, the structure and long-term evolution of the ice sheet in this region have been understood insufficiently to constrain past ice-sheet extents. Here we show that deep ice-sheet erosion-enough to expose basement rocks-has occurred in two regions: the head of the Totten Glacier, within 150 kilometres of today's grounding line; and deep within the Sabrina Subglacial Basin, 350-550 kilometres from this grounding line. Our results, based on ICECAP aerogeophysical data, demarcate the marginal zones of two distinct quasi-stable EAIS configurations, corresponding to the 'modern-scale' ice sheet (with a marginal zone near the present ice-sheet margin) and the retreated ice sheet (with the marginal zone located far inland). The transitional region of 200-250 kilometres in width is less eroded, suggesting shorter-lived exposure to eroding conditions during repeated retreat-advance events, which are probably driven by ocean-forced instabilities. Representative ice-sheet models indicate that the global sea-level increase resulting from retreat in this sector can be up to 0.9 metres in the modern-scale configuration, and exceeds 2 metres in the retreated configuration.

  18. Cosmogenic 36Cl glacial chronologies of the Mount Geyikdaǧ (Southern Turkey)

    Science.gov (United States)

    Ciner, Attila; Akif Sarıkaya, Mehmet; Yıldırım, Cengiz

    2017-04-01

    We report the timing of advances of glaciers during the Late Pleistocene in the Mount Geyikdaǧ (36.53oN, 32.10oE, 2877 m), situated in the central Taurus Mountains of Turkey. Several piedmont glaciers originated from the Geyikdaǧ ice cap (˜40 km2), situated between 2350-2650 m above sea level (a.s.l.) and deeply carved the north-facing hill slopes before reaching the Namaras Valley (2000-2050 m a.s.l). The hummocky moraines resulted from in-situ deposition of stagnant glacier ice where debris cover was heterogeneously distributed on the glacier surface. Boulders from hummocky, disintegration, lateral and terminal moraines from the Namaras, Susam, Çimi and Güneycik valleys (1750-2200 m a.s.l.) were dated by terrestrial cosmogenic nuclide (TCN) 36Cl surface exposure dating. A total of seventy-four boulder ages indicate at least four phases of deglaciation during the Late Pleistocene. Our results indicate that during the Last Glacial Maximum (LGM), glaciers reached their maximum positions at 20.4±4.4 ka and 19.5±2.5 ka ago (1σ; ka = 1000 calendar years). This date is in accordance with the local glacial maximum, represented by piedmont glaciers (18.0±1.1 ka) in the northern side of the mountain. Glaciers started to retreat after the LGM and shortly stabilized or re-advanced three times before they completely vanished out. The first stage ended between 17.1±3.8 ka and 14.2±1.5 ka ago during the Late-glacial. Later, glaciers re-advanced during the Younger Dryas stadial (between 12.7±2.1 ka and 11.6±1.3 ka ago). The last glaciation occurred during the Holocene 8.9±1.2 ka and 5.2±1.0 ka ago. Later, glaciers mostly vanished from the study area, but a few rock glaciers developed during the Late Holocene. Additionally, from a well-preserved moraine loop and a rock glacier inside that loop, we also obtained contrasting TCN 36Cl inventories. We measured 4 samples from each landform and obtained the weighted average ages of 5.3±1.2 ka and 11.8±1.5 ka for the

  19. Radiocarbon chronology of the late-glacial Puerto Bandera moraines, Southern Patagonian Icefield, Argentina

    Science.gov (United States)

    Strelin, J. A.; Denton, G. H.; Vandergoes, M. J.; Ninnemann, U. S.; Putnam, A. E.

    2011-09-01

    We report radiocarbon dates that constrain the timing of the deposition of the late-glacial Puerto Bandera moraine system alongside the western reaches of Lago Argentino adjacent to the Southern Patagonian Icefield. Close maximum-limiting radiocarbon ages ( n = 11) for glacier advance into the outer moraines, with a mean value of 11,100 ± 60 14C yrs BP (12,990 ± 80 cal yrs BP), were obtained from wood in deformation (soft) till exposed beneath flow and lodgment till in Bahía del Quemado on the northeast side of Brazo Norte (North Branch) of western Lago Argentino. Other exposures of this basal deformation till in Bahía del Quemado reveal incorporated clasts of peat, along with larger inclusions of deformed glaciofluvial and lacustrine deposits. Radiocarbon dates of wood included in these reworked peat clasts range from 11,450 ± 45 14C yrs BP to 13,450 ± 150 14C yrs BP (13,315 ± 60 to 16,440 ± 340 cal yrs BP). The implication is that, during this interval, glacier fronts were situated inboard of the Puerto Bandera moraines, with the peat clasts and larger proglacial deposits being eroded and then included in the basal till during the Puerto Bandera advance. Minimum-limiting radiocarbon ages for ice retreat come from basal peat in cores sampled in spillways and depressions generated during abandonment of the Puerto Bandera moraines. Glacier recession and subsequent plant colonization were initiated close behind different frontal sectors of these moraines prior to: 10,750 ± 75 14C yrs BP (12,660 ± 70 cal yrs BP) east of Brazo Rico, 10,550 ± 55 14C yrs BP (12,490 ± 80 cal yrs BP) in Peninsula Avellaneda, and 10,400 ± 50 14C yrs BP (12,280 ± 110 cal yrs BP) in Bahía Catalana. In addition, a radiocarbon date indicates that by 10,350 ± 45 14C yrs BP (12,220 ± 110 cal yrs BP), the Brazo Norte lobe (or former Upsala Glacier) had receded well up the northern branch of Lago Argentino, to a position behind the Herminita moraines. Furthermore, glacier termini

  20. Aquifers of Alluvial and Glacial Origin - Direct Download

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This data set represents the extent of the alluvial and glacial aquifers north of the southern-most line of glaciation. Aquifers are shown in the States of Maine,...

  1. Surficial Geology - 24K - Surficial and Glacial Materials

    Data.gov (United States)

    Vermont Center for Geographic Information — The surficial geologic materials data at a scale of 1:24,000 depict types of unconsolidated surficial and glacial materials overlying bedrock in Vermont. Data is...

  2. Circulation and oxygenation of the glacial South China Sea

    Science.gov (United States)

    Li, Dawei; Chiang, Tzu-Ling; Kao, Shuh-Ji; Hsin, Yi-Chia; Zheng, Li-Wei; Yang, Jin-Yu Terence; Hsu, Shih-Chieh; Wu, Chau-Ron; Dai, Minhan

    2017-05-01

    Degree of oxygenation in intermediate water modulates the downward transferring efficiency of primary productivity (PP) from surface water to deep water for carbon sequestration, consequently, the storage of nutrients versus the delivery and sedimentary burial fluxes of organic matter and associated biomarkers. To better decipher the PP history of the South China Sea (SCS), appreciation about the glacial-interglacial variation of the Luzon Strait (LS) throughflow, which determines the mean residence time and oxygenation of water mass in the SCS interior, is required. Based on a well-established physical model, we conducted a 3-D modeling exercise to quantify the effects of sea level drop and monsoon wind intensity on glacial circulation pattern, thus, to evaluate effects of productivity and circulation-induced oxygenation on the burial of organic matter. Under modern climatology wind conditions, a 135 m sea-level drop results in a greater basin closeness and a ∼24% of reduction in the LS intermediate westward throughflow, consequently, an increase in the mean water residence time (from 19.0 to 23.0 years). However, when the wind intensity was doubled during glacial low sea-level conditon, the throughflow restored largely to reach a similar residence time (18.4 years) as today regardless its closeness. Comparing with present day SCS, surface circulation pattern in glacial model exhibits (1) stronger upwelling at the west off Luzon Island, and (2) an intensified southwestward jet current along the western boundary of the SCS basin. Superimposed hypothetically by stronger monsoon wind, the glacial SCS conditions facilitate greater primary productivity in the northern part. Manganese, a redox sensitive indicator, in IMAGES core MD972142 at southeastern SCS revealed a relatively reducing environment in glacial periods. Considering the similarity in the mean water residence time between modern and glacial cases, the reducing environment of the glacial southeastern SCS

  3. Reconstructing the last glacial and deglacial ice sheets

    Science.gov (United States)

    It has been over a decade since publication of the CLIMAP [Denton and Hughes, 1981] global reconstruction of ice sheets at the last glacial maximum for the CLIMAP Project. To an extent never envisaged at the time, this reconstruction has been used by groups worldwide as boundary-condition input for general circulation models (GCMs) and other numerical experiments to reconstruct glacial-maximum atmospheric and oceanic circulation. Other GCM experiments based on rough approximations of ice-sheet size through the deglacial interval also have been run [Kutzbach and Guetter, 1986], and the climatic output has in turn been compared against ground-truth data such as vegetation and lake levels [COHMAP, 1988].Recently, several results have provided fresh impetus for updating the CLIMAP reconstruction: coral reef data [Fairbanks, 1989] placing sea level near -120 m at the last glacial maximum at Barbados, which also provide a deglacial record of sea level; U-series dates on these corals [Bard et al., 1990] showing that 14C chronologies are anomalously young through the deglaciation, which place the last glacial maximum at 21,000-20,000 years ago; major improvements [Tushingham and Peltier, 1991] in iteratively matching hypothesized ice-sheet thickness histories based on an independent model of the Earth's visco-elasticity to radiometrically dated sea-level rebound histories; and glacial and marine geological fieldwork by many scientists. These findings provide significant new constraints on the past size of the ice sheets at the last glacial maximum and throughout deglaciation. As an added impetus, the NATO Paleoclimate Modeling Intercomparison Project (PMIP) has called for an updated reconstruction of glacial-maximum ice sheets. Their objective is to compare the performance of GCMs when tested on a realistic (glacial) world having ice-sheet boundary conditions very different from today's.

  4. Modeling glacial flow on and onto Pluto's Sputnik Planitia

    OpenAIRE

    Umurhan, O. M.; A. D. Howard; Moore, J. M.; Earle, A. M.; Binzel, R. P.; Stern, S. A.; Schenk, P. M.; R. A. Beyer; White, O.L.; NImmo, F.; W. B. McKinnon; Ennico, K.; Olkin, C. B.; Weaver, H. A.; Young, L.A.

    2016-01-01

    Observations of Pluto's surface made by the New Horizons spacecraft indicates present-day nitrogen ice glaciation in and around the basin known as Sputnik Planum. Motivated by these observations, we have developed an evolutionary glacial flow model of solid nitrogen ice taking into account its published thermophysical and rheologies properties. This model assumes that glacial ice layers flow laminarly and have low aspect ratios which permits a vertically integrated mathematical formulation. W...

  5. 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

    2018-02-01

    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.

  6. Posterior Reversible Encephalopathy Syndrome Associated with Sorafenib and Successful Retreatment.

    Science.gov (United States)

    Laruelle, Marie; Filleul, Bertrand; Duprez, Thierry; Machiels, Jean-Pascal

    2016-02-05

    Posterior reversible encephalopathy syndrome (PRES) is a clinical and radiological syndrome characterized by acute hypertension, headache, decreased level of consciousness, visual disturbances and seizures associated with characteristic neuroimaging changes indicative of vasogenic edema of the posterior cerebral white matter. Several medical conditions have been associated with PRES including hypertensive encephalopathy and eclampsia. The use of cytotoxic and immunosuppressant drugs, such as those which target vascular endothelial growth factor (VEGF), have also been implicated. We report here the case of a 71-year-old woman with metastatic clear cell renal carcinoma who developed PRES 3 months after commencing sorafenib. Elevated blood pressure (BP) was recorded, and MRI of the brain) of the brain showed asymmetric areas of increased signal intensity within the supratentorial white matter suggestive of PRES. Clinical and radiological features rapidly improved with BP control and discontinuation of sorafenib. Sorafenib was resumed with no sign of PRES recurrence. The present case report supports the hypothesis that, in selected patients, the re-introduction of anti-VEGF therapies after PRES is feasible. © 2016 S. Karger AG, Basel.

  7. A 500-year dual stable isotope tree ring chronology of a Late Glacial cooling event

    Science.gov (United States)

    Pauly, Maren; Helle, Gerhard; Büntgen, Ulf; Friedrich, Michael; Heinrich, Ingo; Kromer, Bernd; Nievergelt, Daniel; Reinig, Frederick; Riedel, Frank; Sookdeo, Adam; Treydte, Kerstin; Wacker, Lukas; Brauer, Achim

    2017-04-01

    A recent discovery of over 250 subfossil pine trees in Zürich (dated 14 000 - 11 000 cal BP) has provided the opportunity to study the inconsistent warming transition from the last ice age to the current interglacial. This period (the Late Glacial) has been extensively studied through the development of mostly non-tree ring palaeoclimate proxy records due to the intrigue of numerous prominent climate oscillations. However, such existing (lake sediment and ice core) records often lack the temporal resolution required to interpret rapid environmental changes. Tree rings can help to resolve such events due to their high resolution (annually-resolved) growth banding and absolute dating potential. Moreover, the analysis of stable isotopes can strongly improve the climate signal implemented in tree-ring width. Since numerous environmental conditions are all integrated in the rather simple ring-width series, measurements of chemical tree responses (via stable isotopes) can greatly refine the climate-growth-dynamics. In this study, we are developing a well replicated 500-year annually resolved dual stable isotope (δ18O, δ13C) chronology from tree-ring cellulose, in an effort to reconstruct the environmental dynamics of a short-term Late Glacial cooling event (13 950 - 13 450 cal BP) in an otherwise naturally warming world. We will present and discuss the biological response to this rapid climate oscillation in the face of low atmospheric CO2 concentrations and other site conditions without any human fingerprint.

  8. 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

  9. High-resolution sub-ice-shelf seafloor records of twentieth century ungrounding and retreat of Pine Island Glacier, West Antarctica

    Science.gov (United States)

    Davies, D.; Bingham, R. G.; Graham, A. G. C.; Spagnolo, M.; Dutrieux, P.; Vaughan, D. G.; Jenkins, A.; Nitsche, F. O.

    2017-09-01

    Pine Island Glacier Ice Shelf (PIGIS) has been thinning rapidly over recent decades, resulting in a progressive drawdown of the inland ice and an upstream migration of the grounding line. The resultant ice loss from Pine Island Glacier (PIG) and its neighboring ice streams presently contributes an estimated ˜10% to global sea level rise, motivating efforts to constrain better the rate of future ice retreat. One route toward gaining a better understanding of the processes required to underpin physically based projections is provided by examining assemblages of landforms and sediment exposed over recent decades by the ongoing ungrounding of PIG. Here we present high-resolution bathymetry and sub-bottom-profiler data acquired by autonomous underwater vehicle (AUV) surveys beneath PIGIS in 2009 and 2014, respectively. We identify landforms and sediments associated with grounded ice flow, proglacial and subglacial sediment transport, overprinting of lightly grounded ice-shelf keels, and stepwise grounding line retreat. The location of a submarine ridge (Jenkins Ridge) coincides with a transition from exposed crystalline bedrock to abundant sediment cover potentially linked to a thick sedimentary basin extending upstream of the modern grounding line. The capability of acquiring high-resolution data from AUV platforms enables observations of landforms and understanding of processes on a scale that is not possible in standard offshore geophysical surveys.

  10. 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.

  11. 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.

  12. 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

  13. 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

  14. 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

  15. Glacial survival of boreal trees in northern Scandinavia

    DEFF Research Database (Denmark)

    Parducci, Laura; Jørgensen, Tina; Tollefsrud, Mari Mette

    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...

  16. Should precise numerical dating overrule glacial geomorphology?

    Science.gov (United States)

    Winkler, Stefan

    2016-04-01

    Numerical age dating techniques, namely different types of terrestrial cosmogenic nuclide dating (TCND), have achieved an impressive progress in both laboratory precision and regional calibration models during the past few decades. It is now possible to apply precise TCND even to young landforms like Late Holocene moraines, a task seemed hardly achievable just about 15 years ago. An increasing number of studies provide very precise TCND ages for boulders from Late Holocene moraines enabling related reconstruction of glacier chronologies and the interpretation of these glacial landforms in a palaeoclimatological context. These studies may also solve previous controversies about different ages assigned to moraines obtained by different dating techniques, for example relative-age dating techniques or techniques combining relative-age dating with few fixed points derived from numerical age dating. There are a few cases, for example Mueller Glacier and nearby long debris-covered valley glacier in Aoraki/Mt.Cook National Park (Southern Alps, New Zealand), where the apparent "supremacy" of TCND-ages seem to overrule glacial geomorphological principles. Enabled by a comparatively high number of individual boulders precisely dated by TCND, moraine ridges on those glacier forelands have been primarily clustered on basis of these boulder ages rather than on their corresponding morphological position. To the extreme, segments of a particular moraine complex morphologically and sedimentologically proven to be formed during one event have become split and classified as two separate "moraines" on different parts of the glacier foreland. One ledge of another moraine complex contains 2 TCND-sampled boulders apparently representing two separate "moraines"-clusters of an age difference in the order of 1,500 years. Although recently criticism has been raised regarding the non-contested application of the arithmetic mean for calculation of TCND-ages for individual moraines, this

  17. Offshore records of late to post-glacial environments, western Scotland.

    Science.gov (United States)

    McIntyre, Kate; Howe, John; Bradwell, Tom; Shimmield, Tracy

    2010-05-01

    During the Younger Dryas stadial (GS-1) of 12.8-11.5 ka BP, a substantial ice cap was present over much of western Scotland. Outlet glaciers drained westward from the main ice cap to the coast via the numerous fjord basins which indent Scotland's west coast. Onshore evidence for the Scottish Younger Dryas ice cap is manifest in landscape features such as moraines, eskers, erratics and till/outwash deposits, while the deglacial records preserved in the submarine geomorphology and sediments of the fjord basins have until quite recently been neglected, as a result of their relative inaccessibility. Here we present new data from seismic and multibeam sonar surveys carried out in Loch Linnhe and the Sound of Sleat, supported by sedimentological data and 14C dating from gravity cores. In Loch Linnhe, numerous features have been revealed, including numerous recessional moraines, roches moutonees, pockmarks resulting from gas/fluid escape at the seabed and possibly fault-related, deep current-scouring around topographic highs, and a large outwash fan south of the Corran Narrows, presumed to relate to glacier retreat during the last deglaciation. An abrupt change in sedimentary properties in a gravity core taken from the survey area has been radiocarbon-dated to 10,455 +/- 74 cal y BP, possibly representing the transition from glaciomarine to full marine conditions in the loch. The more limited survey in the Sound of Sleat reveals a substantial end moraine outside the mouth of Loch Hourn, suggesting a 2.5 km seaward extension of the presently mapped Younger Dryas glacial limit in this area. Radiocarbon dating suggests full marine conditions were established in this loch by 11.2 ka BP.

  18. Late-Glacial History of Lago Argentino, Argentina, and Age of the Puerto Bandera Moraines

    Science.gov (United States)

    Strelin, Jorge A.; Malagnino, Eduardo C.

    2000-11-01

    In the west-central part of Lago Argentino, the Puerto Bandera moraines are clearly detached from longer, more prominent moraines of the last glaciation and from shorter and smaller Neoglacial moraines. Scientists have long speculated about the age of the Puerto Bandera moraines. Detailed geomorphologic studies in the western area of Lago Argentino, including stratigraphic profiles at Bahı´a del Quemado in the northern branch (Brazo Norte), indicate that the Puerto Bandera moraines were deposited by three pulses of ice. Each of the three pulses is represented by single moraine ridges and belts of tightly arranged ridges. The timing of the three glacier advances was established by radiocarbon dating, including data published by John Mercer. The oldest moraine system, formed during the Puerto Bandera I substade, was deposited ca. 13,000 14C yr B.P. Moraines of the Puerto Bandera II substade were deposited ca. 11,000 14C yr B.P. The youngest moraine system was deposited during a minor readvance, shortly before 10,390 C14 yr B.P., and thus appears to have occurred some time during the European Younger Dryas interval. After this third substade, the ice tongues retreated into the interior branches of Lago Argentino and have remained there since. Evidence found at Bahı´a del Quemado, together with data provided by other authors, attests to a significant climatic change by the middle Holocene, which we believe occurred during the Herminita advance, the first Holocene glacial readvance recognized within the area.

  19. 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.

  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. A ground penetrating radar investigation of a glacial-marine ice- contact delta, Pineo Ridge, eastern coastal Maine

    Science.gov (United States)

    Tary, A.K.; Duncan, M. FitzGerald; Weddle, T.K.

    2007-01-01

    In eastern coastal Maine, many flat-topped landforms, often identified as glacial-marine deltas, are cultivated for blueberry production. These agriculturally valuable features are not exploited for aggregate resources, severely limiting stratigraphic exposure. Coring is often forbidden; where permissible, coarse-grained surficial sediments make coring and sediment retrieval difficult. Ground penetrating radar (GPR) has become an invaluable tool in an ongoing study of the otherwise inaccessible subsurface morphology in this region and provides a means of detailing the large-scale sedimentary structures comprising these features. GPR studies allow us to reassess previous depositional interpretations and to develop alternative developmental models. The work presented here focuses on Pineo Ridge, a large, flat-topped ice-marginal glacial-marine delta complex with a strong linear trend and two distinct landform zones, informally termed East Pineo and West Pineo. Previous workers have described each zone separately due to local morphological variation. Our GPR work further substantiates this geomorphic differentiation. East Pineo developed as a series of deltaic lobes prograding southward from an ice-contact margin during the local marine highstand. GPR data do not suggest postdepositional modification by ice-margin re-advance. We suggest that West Pineo has a more complex, two-stage depositional history. The southern section of the feature consists of southward-prograding deltaic lobes deposited during retreat of the Laurentide ice margin, with later erosional modification during marine regression. The northern section of West Pineo formed as a series of northward-prograd- ing deltaic lobes as sediment-laden meltwater may have been diverted by the existing deposits of the southern section of West Pineo. ?? 2007 The Geological Society of America. All rights reserved.

  2. Evolutionary, multi-scale analysis of river bank line retreat using continuous wavelet transforms: Jamuna River, Bangladesh

    OpenAIRE

    Mount, Nick J.; Tate, Nicholas J.; Sarker, Maminul H.; Thorne, Colin R.

    2013-01-01

    In this study continuous wavelet transforms are used to explore spatio-temporal patterns of multi-scale bank line retreat along a 204 km reach of the Jamuna River, Bangladesh. A sequence of eight bank line retreat series, derived from remotely-sensed imagery for the period 1987-1999, is transformed using the Morlet mother wavelet. Bank erosion is shown to operate at several characteristic spatial and temporal scales. Local erosion and bank line retreat are shown to occur in short, well def...

  3. 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.

  4. Of ice and water: Quaternary fluvial response to glacial forcing

    Science.gov (United States)

    Cordier, Stéphane; Adamson, Kathryn; Delmas, Magali; Calvet, Marc; Harmand, Dominique

    2017-06-01

    Much research, especially within the framework of the Fluvial Archives Group, has focused on river response to climate change in mid-latitude non-glaciated areas, but research into the relationships between Quaternary glacial and fluvial dynamics remains sparse. Understanding glacial-fluvial interactions is important because glaciers are able to influence river behaviour significantly, especially during glacial and deglacial periods: (1) when they are located downstream of a pre-existing fluvial system and disrupt its activity, leading to hydrographical, hydrosedimentary and isostatic adjustments, and (2) when they are located upstream, which is a common scenario in mid-latitude mountains that were glaciated during Pleistocene cold periods. In these instances, glaciers are major water and sediment sources. Their role is particularly significant during deglaciation, when meltwater transfer towards the fluvial system is greatly increased while downstream sediment evacuation is influenced by changes to glacial-fluvial connectivity and basin-wide sediment storage. This means that discharge and sediment flux do not always respond simultaneously, which can lead to complex fluvial behaviour involving proglacial erosion and sedimentation and longer-term paraglacial reworking. These processes may vary spatially and temporally according to the position relative to the ice margin (ice-proximal versus ice-distal). With a focus on the catchments of Europe, this paper aims to review our understanding of glacial impacts on riversystem behaviour. We examine the methods used to unravel fluvial response to 'glacial forcing', and propose a synthesis of the behaviour of glacially-fed rivers, opening perspectives for further research.

  5. Endodontic retreatment behaviour: the influence of disease concepts and personal values.

    Science.gov (United States)

    Reit, C; Kvist, T

    1998-09-01

    To explain dentists' variation in endodontic retreatment decision making a praxis concept (PC) has been generated. PC assumes that practitioners operate along a health continuum. Various periapical conditions are then perceived as different stages on a continuous health scale, based on their radiographic appearance. PC suggests that an individual's placement of a cut-off point for retreatment on the health continuum to a large extent is dependent on the agent's personal values. In the present study value judgements (utilities) concerning two periapical health states in endodontically treated teeth were investigated among 82 dental students. The two methods used to elicit utilities, a Visual Analogue Scale (VAS) and the Standard Gamble (SG), produced large inter- and intra-individual variations. VAS frequently generated lower utility values. The results obtained in the study satisfy a necessary criterion for the validity of PC and strengthen the position of the theory.

  6. 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.

  7. 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.

  8. 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

  9. Outcome of orthograde retreatment after failed apicoectomy: use of a mineral trioxide aggregate apical plug.

    Science.gov (United States)

    Mente, Johannes; Leo, Meltem; Michel, Annemarie; Gehrig, Holger; Saure, Daniel; Pfefferle, Thorsten

    2015-05-01

    This controlled, single-center historic cohort study project evaluates treatment outcomes of a nonsurgical treatment approach after failed apicoectomy. The treatment outcomes of nonsurgical retreatment after a failed apicoectomy were evaluated clinically and radiographically. The study cohort consisted of teeth that had received primary root canal treatment and subsequent apicoectomy elsewhere before the patients presented with post-treatment disease. Orthograde retreatment and obturation using an apical mineral trioxide aggregate plug was performed by postgraduate students and endodontic specialists in 25 cases between 2004 and 2012. Pre-, intra-, and postoperative information and the potential effect on the retreatment outcome were evaluated and statistically analyzed using the chi-square test. Twenty-two patients with 23 teeth attended the follow-up examinations (recall rate = 92%). The follow-up periods ranged from 12 to 102 months (median = 35 months). Twenty teeth (87%) were classified as "success," and 3 teeth were considered (17%) "failure." The chi-square test confirmed that the preoperative factor "number of roots" had a statistically significant effect on treatment outcome (odds ratio = 0.08; 95% confidence interval, 0-1.76; P = .03). The factor "tooth location" was of borderline significance (odds ratio = 0.1; 95% confidence interval, 0-2.14; P = .05). The results of the present study suggest that orthograde retreatment combined with orthograde placement of an apical mineral trioxide aggregate plug is a promising long-term treatment option for teeth with postsurgical pathosis. The success rates were higher for single-rooted teeth. The use of cone-beam computed tomographic imaging in cases of inconclusive periapical radiographs is recommended to minimize the risk of misinterpretation when assessing treatment outcome. Copyright © 2015 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  10. Plasticity of visual attention in Isha yoga meditation practitioners before and after a 3-month retreat

    Directory of Open Access Journals (Sweden)

    Claire eBraboszcz

    2013-12-01

    Full Text Available Meditation has lately received considerable interest from cognitive neuroscience. Studies suggest that daily meditation leads to long lasting attentional and neuronal plasticity. We present changes related to the attentional systems before and after a 3 month intensive meditation retreat. We used 3 behavioral psychophysical tests - a Stroop task, an attentional blink task, and a global-local letter task - to assess the effect of Isha yoga meditation on attentional resource allocation. 82 Isha yoga practitioners were tested at the beginning and at the end of the retreat. Our results showed an increase in correct responses specific to incongruent stimuli in the Stroop task. Congruently, a positive correlation between previous meditation experience and accuracy to incongruent Stroop stimuli was also observed at baseline. We also observed a reduction of the attentional blink. Unexpectedly, a negative correlation between previous meditation experience and attentional blink performance at baseline was observed. Regarding spatial attention orientation as assessed using the global-local letter task, participants showed a bias toward local processing. Only slight differences in performance were found pre- vs. post- meditation retreat. Previous meditation experience influenced the Stroop and attentional blink tasks in opposite directions – for the Stroop task congruent with the improvements seen after the retreat whereas for the attentional blink previous experience correlated negatively with performance. Biasing towards the local stimuli in the global-local task and negative correlation of previous meditation experience with attentional blink performance is consistent with Isha practices being more focused-attention practices. Given the relatively small effect sizes and the absence of a control group, our results do not allow clear support nor rejection of the hypothesis of meditation-driven neuronal plasticity in the attentional system for Isha yoga

  11. A Weeklong Meditation Retreat Decouples Behavioral Measures of the Alerting and Executive Attention Networks.

    Directory of Open Access Journals (Sweden)

    James C Elliott

    2014-02-01

    Full Text Available Previous studies have examined the influence of meditation on three functionally different components of attention: executive control, alerting, and orienting. These studies have consistently found that meditation training improves both executive attention and alerting, but there has not been a consistent and clear effect of meditation training on orienting. In addition, while previous studies have shown that the functional coupling of the alerting and executive networks increases the processing of task irrelevant stimuli, it is unknown if participating in a meditation retreat can decouple these components of attention and lead to improved performance. The current study investigated the influence of a week-long intensive meditation retreat on three components of attention by randomly assigning participants to either pre- or postretreat testing groups. A modified attention network test (ANT was used. Executive attention was measured as the difference in response time between congruent and incongruent task irrelevant flankers (conflict effect. Reflexive and volitional orienting were measured by manipulating cue validity and stimulus onset asynchrony. The coupling of executive attention and alerting was measured by examining flanker interference as a function of the SOA of an alerting cue. The meditation retreat improved task based indices of executive attention, but not reflexive or volitional orienting. There was clear behavioral evidence of coupling between executive attention and alerting in the preretreat group, as the conflict effect peaked when an alerting cue was presented 300 ms before the target. Importantly, there was no increase in the conflict effect for the postretreat group. This is consistent with the notion that the retreat decoupled the executive and alerting networks. These results suggest that previously reported improvements in the executive and alerting networks after meditation training might be mediated by the same

  12. The importance of microsonics concept for optimization of endodontic retreatment outcome: a case report

    OpenAIRE

    Cláudia Fernandes de Magalhães Silveira; Carlos Eduardo Fontana; Felipe Davini; Roberta Aranha de Araújo Arruda; Carlos Eduardo da Silveira Bueno

    2012-01-01

    Introduction: During the past few decades, the endodontic treatment has benefited from the development of new techniques and devices, which have improved the outcome and predictability. Important attributes such as the operating microscope and ultrasonics have found indispensable applications in a number of dental procedures in endodontics. Objective and case report: This study describes a case of endodontic retreatment of a maxillary first molar in which the second mesiobuccal canal could be...

  13. Bank retreat study of a meandering river reach case study: River Irwell

    OpenAIRE

    Duran, R.; Beevers, L; Crosato, A.; Wright, N.

    2010-01-01

    Lack of data is often considered a limitation when undertaking morphological studies. This research deals with morphological studies of small rivers experiencing bank erosion processes when only limited data are available. A reach of the meandering gravel-bed river Irwell (United Kingdom) is taken as a case study in order to analyze the bank retreat process that is endangering the stability of structures located in the area. Two models of different complexity are applied. The first is a physi...

  14. The effect of reciprocation versus rotational movement on the incidence of root defects during retreatment procedures.

    Science.gov (United States)

    Üstün, Y; Topçuoğlu, H S; Düzgün, S; Kesim, B

    2015-10-01

    To compare the incidence of dentinal defects caused by reciprocating and rotary techniques during retreatment procedures. One hundred and twenty extracted mandibular premolars with single canals were selected. Twenty teeth were left unprepared. The root canals in the remaining 100 teeth were prepared with K-files up to size 35 and filled with Gutta-percha and AH Plus sealer using a passive cold lateral compaction technique. Twenty canals were filled and received no further treatment. Eighty teeth were divided into four groups (n = 20 in each) to undergo the removal of the root filling. In groups 1 and 2, the root filling was removed using ProTaper Retreatment files and Reciproc files, respectively, and the canals were not refilled. In groups 3 and 4, the root filling was removed using ProTaper Retreatment files and Reciproc files, respectively, and the canals were then refilled using a conventional cold lateral compaction technique. The roots were sectioned horizontally at 3, 6 and 9 mm from the root apex and observed under a stereomicroscope at 20× magnification. Defects were categorized as no defect, incomplete defect and fracture. The differences between the groups were analysed using the chi-square exact test (P = 0.05). No defects were observed in the unprepared and filled groups, in contrast to the experimental groups. In the coronal thirds, groups 2 and 4 had more dentinal defects than groups 1 and 3 (P 0.05). Both nickel-titanium systems were associated with dentinal defects during retreatment procedures in extracted premolar teeth. © 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd.

  15. Cohort Trends in Premarital First Births: What Role for the Retreat From Marriage?

    OpenAIRE

    England, Paula; WU, LAWRENCE L.; Shafer, Emily Fitzgibbons

    2013-01-01

    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 ob...

  16. Climate change and glacier retreat drive shifts in an Antarctic benthic ecosystem.

    Science.gov (United States)

    Sahade, Ricardo; Lagger, Cristian; Torre, Luciana; Momo, Fernando; Monien, Patrick; Schloss, Irene; Barnes, David K A; Servetto, Natalia; Tarantelli, Soledad; Tatián, Marcos; Zamboni, Nadia; Abele, Doris

    2015-11-01

    The Antarctic Peninsula (AP) is one of the three places on Earth that registered the most intense warming in the last 50 years, almost five times the global mean. This warming has strongly affected the cryosphere, causing the largest ice-shelf collapses ever observed and the retreat of 87% of glaciers. Ecosystem responses, although increasingly predicted, have been mainly reported for pelagic systems. However, and despite most Antarctic species being benthic, responses in the Antarctic benthos have been detected in only a few species, and major effects at assemblage level are unknown. This is probably due to the scarcity of baselines against which to assess change. We performed repeat surveys of coastal benthos in 1994, 1998, and 2010, analyzing community structure and environmental variables at King George Island, Antarctica. We report a marked shift in an Antarctic benthic community that can be linked to ongoing climate change. However, rather than temperature as the primary factor, we highlight the resulting increased sediment runoff, triggered by glacier retreat, as the potential causal factor. The sudden shift from a "filter feeders-ascidian domination" to a "mixed assemblage" suggests that thresholds (for example, of tolerable sedimentation) and alternative equilibrium states, depending on the reversibility of the changes, could be possible traits of this ecosystem. Sedimentation processes will be increasing under the current scenario of glacier retreat, and attention needs to be paid to its effects along the AP.

  17. 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.

  18. [Renal lithiasis, can we predict the need for retreatment in retrograde intrarenal surgery (RIRS)?

    Science.gov (United States)

    Palmero-Martí, José Luis; Panach-Navarrete, Jorge; Valls-González, Lorena; Ganau-Ituren, Amparo; Pastor-Lence, Juan Carlos; Benedicto-Redón, Antonio

    2017-06-01

    To analyze the predictive factors for retreatment in RIRS to achieve complete lithiasis resolution. Retrospective comparative study analyzing 298 cases of RIRS performed in our center over a 3 year period. The cohort was divided in two groups: Resolution in one operation or more than one, evaluating homogeneicity for age and gender. We compared the folowing variables: Hounsfield units, body mass index (BMI), number of stones, size, (on the case of multiple stones, larger stone size), side, location in the kidney and stone biochemistry. Bivariant statistical analysis by Student's t and Chi square tests, and multivariate analysis by binary logistic regression. ROC curves were made to set cutting points for relationship between quantitative variables. The groups were homogeneous for both age and gender (p>0.05). 260 (87.25%) patients required one treatment only and 38 (12.75%) more than one. Among the study variables, the only one that showed differences between the groups wa stone size, being the mean size 18 mm in the single treatment group and 26 mm in the more than one treatment group (Difference between mean values -8.27, 95%CI: -5,91 - -10.63, plithiasis. The largest stone size is related with the need of retreatments, so it must be taken into consideration specially over 2 cm. In our series, for every extra millimeter in size the probability of retreatment increased 1.14 times, demonstrating the importance of size in this context.

  19. 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

    2017-11-01

    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.

  20. Comparative sem evaluation of three solvents used in endodontic retreatment: an ex vivo study

    Directory of Open Access Journals (Sweden)

    Miriam F. Zaccaro Scelza

    2008-02-01

    Full Text Available This study compared, by scanning electron microscopy (SEM, the efficacy of three solvents on the removal of filling materials from dentinal tubules during endodontic retreatment. Forty human maxillary canines with straight canals were prepared according to a crown-down technique and enlarged to a#30 apical file size, before obturation with gutta-percha and a zinc-oxide-eugenol based sealer. The samples were stored for 3 months before being randomly assigned to four groups: chloroform (n=10, orange oil (n=10, eucalyptol (n=10 and control (n=10. Solvents were applied to a reservoir created on the coronal root third using Gates Glidden drills. The total time for retreatment using the solvents was 5 minutes per tooth. Following retreatment the roots were split longitudinally for SEM evaluation. SEM images were digitized, analyzed using Image ProPlus 4.5 software, and the number of dentinal tubules free of filling material from the middle and apical thirds was recorded. No significant difference was found among the solvent groups regarding the number of dentinal tubules free of root filling remnants in the middle and apical root thirds (p>0.05. However, the control group had fewer dentinal tubules free of filling material (p<0.05. Under the tested conditions, it may be concluded that there was no significant difference among the solvents used to obtain dentinal tubules free of filling material remnants.

  1. 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.

  2. Plasticity of visual attention in Isha yoga meditation practitioners before and after a 3-month retreat

    Science.gov (United States)

    Braboszcz, Claire; Cahn, B. Rael; Balakrishnan, Bhavani; Maturi, Raj K.; Grandchamp, Romain; Delorme, Arnaud

    2013-01-01

    Meditation has lately received considerable interest from cognitive neuroscience. Studies suggest that daily meditation leads to long lasting attentional and neuronal plasticity. We present changes related to the attentional systems before and after a 3 month intensive meditation retreat. We used three behavioral psychophysical tests - a Stroop task, an attentional blink task, and a global-local letter task-to assess the effect of Isha yoga meditation on attentional resource allocation. 82 Isha yoga practitioners were tested at the beginning and at the end of the retreat. Our results showed an increase in correct responses specific to incongruent stimuli in the Stroop task. Congruently, a positive correlation between previous meditation experience and accuracy to incongruent Stroop stimuli was also observed at baseline. We also observed a reduction of the attentional blink. Unexpectedly, a negative correlation between previous meditation experience and attentional blink performance at baseline was observed. Regarding spatial attention orientation as assessed using the global-local letter task, participants showed a bias toward local processing. Only slight differences in performance were found pre- vs. post- meditation retreat. Biasing toward the local stimuli in the global-local task and negative correlation of previous meditation experience with attentional blink performance is consistent with Isha practices being focused-attention practices. Given the relatively small effect sizes and the absence of a control group, our results do not allow clear support nor rejection of the hypothesis of meditation-driven neuronal plasticity in the attentional system for Isha yoga practice. PMID:24376429

  3. Evaluating Object-Based Image Analysis on Glacial Micromorphology

    Science.gov (United States)

    Chin, K. S.; Sjogren, D. B.

    2007-12-01

    Micromorphology has recently been applied more in analyzing glacial sediments at a microscopic level. It provides additional information and details that may help to explain glacial processes in areas where macro- scale observations cannot yield sufficient information. However, the process of interpreting thin sections has been very subjective, and reaching general consensus about glacial processes is difficult. Remote sensing technology is increasingly helpful in the development and advancement of many sciences; the concepts that lie behind the technology in object cognition used in other fields, such as landscape ecology, can be applied to micromorphology. Similar to what has been done to landscape ecology in the past, automating the process of interpreting objects in glacial sediments may potentially simplify and decrease the subjectivity of the process. Definiens Professional 5 is an object-based image analysis program that imitates human cognitive methods; it is used in this study to identify objects apart from background matrices in multiple thin section images of glacial sediments. The program's initial results proved that more work was needed to be done for better results, but overall the software produced promising results. The method is repeatable and continues to generate consistent results with no bias or ambiguity, so the application of this method to micromorphology and other areas alike will be valuable.

  4. Glacial lake mapping with very high resolution satellite SAR data

    Science.gov (United States)

    Strozzi, T.; Wiesmann, A.; Kääb, A.; Joshi, S.; Mool, P.

    2012-08-01

    Floods resulting from the outbursts of glacial lakes are among the most far-reaching disasters in high mountain regions. Glacial lakes are typically located in remote areas and space-borne remote sensing data are an important source of information about the occurrence and development of such lakes. Here we show that very high resolution satellite Synthetic Aperture Radar (SAR) data can be employed for reliably mapping glacial lakes. Results in the Alps, Pamir and Himalaya using TerraSAR-X and Radarsat-2 data are discussed in comparison to in-situ information, and high-resolution satellite optical and radar imagery. The performance of the satellite SAR data is best during the snow- and ice-free season. In the broader perspective of hazard management, the detection of glacial lakes and the monitoring of their changes from very high-resolution satellite SAR intensity images contributes to the initial assessment of hazards related to glacial lakes, but a more integrated, multi-level approach needs also to include other relevant information such as glacier outlines and outline changes or the identification of unstable slopes above the lake and the surrounding area, information types to which SAR analysis techniques can also contribute.

  5. Somma-Vesuvius ground deformation over the last glacial cycle

    Science.gov (United States)

    Marturano, Aldo; Aiello, Giuseppe; Barra, Diana

    2013-04-01

    Vertical ground movements at Somma-Vesuvius during the last glacial cycle have been inferred from micropalaeontological and petrochemical analyses of rock samples from boreholes drilled at the archaeological sites of Herculaneum and Pompeii as well as on the apron of the volcano and the adjacent Sebeto and Sarno Valleys. Opposing movements occurred during the periods preceding and following the Last Glacial Maximum (LGM). The uplift began 20 ka ago with marine deposits rising several tens of metres up to 25 m a.s.l., recovering previous subsidence which occurred during the Late glacial period, suggesting a strict connection between volcano-tectonic and glacial cycles. Here we present the analysis of deposits predating the LGM, which confirms subsidence of the Campanian Plain where Mt. Somma-Vesuvius is located, shows variable surface loading effects and highlights the volcano-tectonic stages experienced by the volcano. The self-balancing mechanism of the volcanic system, evolving towards an explosive, subaerial activity 60 ka ago, is testified to by a large ground oscillation in phase with sea level change during the last glacial cycle.

  6. Spawning distribution of sockeye salmon in a glacially influenced watershed: The importance of glacial habitats

    Science.gov (United States)

    Young, Daniel B.; Woody, C.A.

    2007-01-01

    The spawning distribution of sockeye salmon Oncorhynchus nerka was compared between clear and glacially turbid habitats in Lake Clark, Alaska, with the use of radiotelemetry. Tracking of 241 adult sockeye salmon to 27 spawning locations revealed both essential habitats and the relationship between spawn timing and seasonal turbidity cycles. Sixty-six percent of radio-tagged sockeye salmon spawned in turbid waters (???5 nephelometric turbidity units) where visual observation was difficult. Spawning in turbid habitats coincided with seasonal temperature declines and associated declines in turbidity and suspended sediment concentration. Because spawn timing is heritable and influenced by temperature, the observed behavior suggests an adaptive response to glacier-fed habitats, as it would reduce embryonic exposure to the adverse effects of fine sediments. ?? Copyright by the American Fisheries Society 2007.

  7. First approaches towards modelling glacial hazards in the Mount Cook region of New Zealand's Southern Alps

    Science.gov (United States)

    Allen, S. K.; Schneider, D.; Owens, I. F.

    2009-03-01

    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.

  8. 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.

  9. 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’.

  10. A 70-year record of outlet glacier retreat in northern Greenland

    Science.gov (United States)

    Hill, Emily; Carr, Rachel; Stokes, Chris; Gudmundsson, Hilmar

    2017-04-01

    Over the past two decades, the Greenland Ice Sheet (GrIS) has undergone accelerated mass loss increasing its contribution to sea level rise. This is partly attributed to increased mass loss from dynamic marine-terminating outlet glaciers. Despite marine-terminating outlet glaciers in northern Greenland draining 40% of the ice sheet by area, they are comparatively less well-studied than other regions of the ice sheet (e.g. central west or south-east). This region could be susceptible to marine-ice sheet instability due to large proportions of the bedrock rested below sea level and is also unique in the presence of large floating ice tongues. Here, we use a range of satellite imagery sources, accompanied by historical maps, to examine multi-decadal front position changes at 21 outlet glaciers in northern Greenland between 1948 and 2016. We accompany these terminus changes, with annual records of ice velocity, climate-ocean forcing data, and glacier-specific factors (e.g. fjord-width and basal topography) to understand the dominant forcing on glacier dynamics in the region. Over the last 70 years, there has been a clear pattern of glacier retreat in northern Greenland. This is particularly notable during the last two decades, where 62% of our study glaciers showed accelerated retreat. This was most notable at Humboldt, Tracy, Hagen Brae, C. H. Ostenfeld and Petermann Glaciers, and in the case of the latter three glaciers, this involved substantial retreat of their floating ice tongues (> 10 km). Alongside retreat, several study glaciers underwent simultaneous velocity increases. However, the collapse of floating ice tongues did not always result in increased velocity. Similar to other regions of the ice sheet, recent glacier retreat in the northern regions of the Greenland Ice Sheet could be linked to climatic-oceanic forcing, but at this stage this remains largely unknown. This response to external forcing is further complicated by the presence of glacier

  11. Retreatment with bortezomib alone or in combination for patients with multiple myeloma following an initial response to bortezomib.

    Science.gov (United States)

    Sood, Raman; Carloss, Harry; Kerr, Robert; Lopez, Jose; Lee, Martin; Druck, Mark; Walters, Ian B; Noga, Stephen J

    2009-10-01

    This clinical trial was conducted to determine the safety and efficacy of bortezomib retreatment in patients with multiple myeloma (MM) who had previously responded to bortezomib. Patients with progressive MM who had previously tolerated bortezomib as a single agent or in combination with other drugs, with a minimum of partial response (PR; >or=50% M-protein reduction) for >or=4 months, who had not received intervening MM therapy, were retreated with bortezomib (days 1, 4, 8, and 11 of a 21-day cycle) with a starting dose being the dose at which the patient ended the initial treatment. Patients were allowed to receive bortezomib on retreatment in combination with dexamethasone, thalidomide, or doxorubicin. Thirty-two patients received bortezomib retreatment (most with added dexamethasone). The median treatment-free interval (last dose of initial bortezomib treatment to first dose of retreatment) was 9.9 (range 2.5-34.0) months. The median duration of retreatment was 2.8 (<1-7.9) months; median total duration of bortezomib treatment was 6.7 (2.5-19.8) months. Based on the investigators' assessment of best response, the overall response rate (complete plus PR) was 50%. The median time from start of retreatment to progressive disease (PD) was 6.6 (95% confidence interval: 5.1-9.6) months. Thirteen patients (41%) experienced PN; bortezomib-related SAEs were reported in four patients. Retreatment with bortezomib alone or in combination is effective and well tolerated in patients with MM who have responded to their initial bortezomib treatment. (c) 2009 Wiley-Liss, Inc.

  12. 21st century Himalayan hydropower: Growing exposure to glacial lake outburst floods?

    Science.gov (United States)

    Schwanghart, Wolfgang; Worni, Raphael; Huggel, Christian; Stoffel, Markus; Korup, Oliver

    2014-05-01

    . Everest and Lulana regions of Nepal and Bhutan, respectively. Together with the dense, cascading sequence of hydropower stations along several river networks in these areas, the combination of GLOFs and artificial reservoirs in steep terrain may result in increasing threats to downstream communities. Hydropower stations are infrastructural investments with minimum design lives of several decades, and our results suggest that their planning should be orchestrated with projected changes in glacier response to future climate change. Our data underline the preponderance of glacial lakes in areas with high glacial retreat rates and a commensurate exposure of hydropower stations to GLOFs. To ensure sustainable water resources use at minimum risk implications for on-site downstream communities, potential changes in GLOF hazard should be taken seriously when planning hydropower stations in the Hindu Kush-Himalaya.

  13. Glacial geology of the Hellas region on Mars

    Science.gov (United States)

    Kargel, Jeffrey S.; Strom, Robert G.; Johnson, Natasha

    1991-01-01

    A glacial geologic interpretation was recently presented for Argyre, which is herein extended to Hellas. This glacial event is believed to constitute an important link in a global cryohydric epoch of Middle Amazonian age. At glacial maximum, ice apparently extended far beyond the regions of Argyre and Hellas, and formed what is termed as the Austral Ice Sheet, an agglomeration of several ice domes and lobes including the Hellas Lobe. It is concluded that Hellas was apparently heavily glaciated. Also glaciation was young by Martian standards (Middle Amazonian), and ancient by terrestrial standards. Glaciation appears to have occurred during the same period that other areas on Mars were experiencing glaciation and periglacial activity. Glaciation seems to have occurred as a geological brief epoch of intense geomorphic activity in an era characterized by long periods of relative inactivity.

  14. 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.

  15. Provenance of glacial tills in Ong Valley, Antarctica, inferred from quartz cathodoluminescence imaging, zircon U/Pb dating, and trace element geochemistry

    Science.gov (United States)

    Edwards, K. L.; Padilla, A. J.; Evans, A.; Morgan, D. J.; Balco, G.; Putkonen, J.; Bibby, T.

    2014-12-01

    An issue for interpreting exposure ages using cosmogenic nuclides is prior exposure (inheritance), especially for stable nuclides such as Ne-21. In this study we examine the reliability of provenance as a possible tool for determining the degree to which inheritance is an issue for a given sample. We use zircon U/Pb ages, quartz cathodoluminescence imaging, and trace element geochemistry from Antarctic glacial drifts and compare these to zircon, quartz, and trace elements from local bedrock in order to determine the drifts' origins. This is potentially useful in Ong Valley in the Central Transantarctic Mountains, and likely elsewhere in Antarctica, as Antarctic glacial sediments are only derived either from sources that lie beneath the ice, where it likely had little prior exposure to cosmic rays, or from the relatively small amount of local, exposed bedrock, which would have inherited nuclides. Thus, sediment provenance is likely correlated with its inherited nuclide inventory. The bedrock of Ong Valley is composed of granite (Hope Granite, Granite Harbour Intrusives) and gneiss, and contains three glacial drifts. We collected samples from these three drifts and the surrounding bedrock. Cosmogenic nuclide dating using Ne-21 provides exposure ages for the quartz that can be used to constrain the timing of the glacier's retreat from the three sites. The accuracy of these three exposure ages depends on the prior (or inherited) exposure of the sediment and its sources. The use of the use of multiple methods for determining provenance allows us to compare the results and see if they reach the same conclusion. If cathodoluminescence imaging proves to be a reliable method for establishing provenance it would provide complementary information for cosmogenic nuclide dating, especially because quartz is significantly more abundant and we would be obtaining coupled provenance information and exposure ages from a single mineral.

  16. 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

    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......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...

  17. Glacial melt content of water use in the tropical Andes

    Science.gov (United States)

    Buytaert, Wouter; Moulds, Simon; Acosta, Luis; De Bièvre, Bert; Olmos, Carlos; Villacis, Marcos; Tovar, Carolina; Verbist, Koen M. J.

    2017-11-01

    Accelerated melting of glaciers is expected to have a negative effect on the water resources of mountain regions and their adjacent lowlands, with tropical mountain regions being among the most vulnerable. In order to quantify those impacts, it is necessary to understand the changing dynamics of glacial melting, but also to map how glacial meltwater contributes to current and future water use, which often occurs at considerable distance downstream of the terminus of the glacier. While the dynamics of tropical glacial melt are increasingly well understood and documented, major uncertainty remains on how the contribution of tropical glacial meltwater propagates through the hydrological system, and hence how it contributes to various types of human water use in downstream regions. Therefore, in this paper we present a detailed regional mapping of current water demand in regions downstream of the major tropical glaciers. We combine these maps with a regional water balance model to determine the dominant spatiotemporal patterns of the contribution of glacial meltwater to human water use at an unprecedented scale and resolution. We find that the number of users relying continuously on water resources with a high (>25%) long-term average contribution from glacial melt is low (391 000 domestic users, 398 km2 of irrigated land, and 11 MW of hydropower production), but this reliance increases sharply during drought conditions (up to 3.92 million domestic users, 2096 km2 of irrigated land, and 732 MW of hydropower production in the driest month of a drought year). A large proportion of domestic and agricultural users are located in rural regions where climate adaptation capacity tends to be low. Therefore, we suggest that adaptation strategies should focus on increasing the natural and artificial water storage and regulation capacity to bridge dry periods.

  18. Geometric dependency of Tibetan lakes on glacial runoff

    Directory of Open Access Journals (Sweden)

    V. H. Phan

    2013-10-01

    Full Text Available 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, accurate quantification of glacial changes is difficult over the high-relief Tibetan Plateau. However, it has recently been shown that it is possible to directly assess water level changes of a significant number of the ~900 Tibetan lakes with an area over 1 km2. This paper exploits different remote sensing products to create drainage links between Tibetan glaciers, lakes and rivers. The results allow us to differentiate between lakes with and without outlet. In addition, we introduce the notion of geometric dependency of a lake on glacial runoff, defined as the ratio between the total area of glaciers draining into a lake and the total area of the lake catchment. We determined these dependencies for all ~900 sufficiently large Tibetan lakes. To do so, we combined three remote sensing products: the CAREERI glacier mask product, a lake mask product based on the MODIS MOD44W water product and the HydroSHEDS river network product derived from Shuttle Radar Topography Mission (SRTM elevation data. Using a drainage network analysis, we determined all drainage links between glaciers and lakes. The results show that 25.3% of the total glacier area directly drains into one of 244 Tibetan lakes. The results also give the geometric dependency of each lake on glacial runoff. For example, there are ten lakes with direct glacial runoff from at least 240 km2 of glacier. Three case studies, including one of the well-studied Nam Tso Lake, demonstrate how the geometric dependency of a lake on glacial runoff can be directly linked to hydrological processes.

  19. Modelling last glacial cycle ice dynamics in the Alps

    Science.gov (United States)

    Seguinot, Julien; Jouvet, Guillaume; Huss, Matthias; Funk, Martin; Preusser, Frank

    2017-04-01

    The European Alps, cradle of pioneer glacial studies, are one of the regions where geological markers of past glaciations are most abundant and well-studied. Such conditions make the region ideal for testing numerical glacier models based on approximated ice flow physics against field-based reconstructions, and vice-versa. Here, we use the Parallel Ice Sheet Model (PISM) to model the entire last glacial cycle (120-0 ka) in the Alps, with a horizontal resolution of 1 km. Climate forcing is derived using present-day climate data from WorldClim and the ERA-Interim reanalysis, and time-dependent temperature offsets from multiple paleo-climate proxies, among which only the EPICA ice core record yields glacial extent during marine oxygen isotope stages 4 (69-62 ka) and 2 (34-18 ka) in agreement to geological reconstructions. Despite the low variability of this Antarctic-based climate forcing, our simulation depicts a highly dynamic ice cap, showing that alpine glaciers may have advanced many times over the foreland during the last glacial cycle. Cumulative basal sliding, a proxy for glacial erosion, is modelled to be highest in the deep valleys of the western Alps. Finally, the Last Glacial Maximum advance, often considered synchronous, is here modelled as a time-transgressive event, with some glacier lobes reaching their maximum as early as 27 ka, and some as late as 21 ka. Modelled ice thickness is about 900 m higher than observed trimline elevations, yet our simulation predicts little erosion at high elevation due to cold ice conditions.

  20. Quantifying the ocean's role in glacial CO2 reductions

    Directory of Open Access Journals (Sweden)

    R. Ohgaito

    2012-03-01

    Full Text Available A series of Last Glacial Maximum (LGM marine carbon cycle sensitivity experiments is conducted to test the effect of different physical processes, as simulated by two atmosphere-ocean general circulation model (AOGCM experiments, on atmospheric pCO2. One AOGCM solution exhibits an increase in North Atlantic Deep Water (NADW formation under glacial conditions, whereas the other mimics an increase in Antarctic Bottom Water (AABW associated with a weaker NADW. None of these sensitivity experiments reproduces the observed magnitude of glacial/interglacial pCO2 changes. However, to explain the reconstructed vertical gradient of dissolved inorganic carbon (DIC of 40 mmol m−3 a marked enhancement in AABW formation is required. Furthermore, for the enhanced AABW sensitivity experiment the simulated stable carbon isotope ratio (δ13C decreases by 0.4‰ at intermediate depths in the South Atlantic in accordance with sedimentary evidence. The shift of deep and bottom water formation sites from the North Atlantic to the Southern Ocean increases the total preformed nutrient inventory, so that the lowered efficiency of Southern Ocean nutrient utilization in turn increases atmospheric pCO2. This change eventually offsets the effect of an increased abyssal carbon pool due to stronger AABW formation. The effects of interhemispheric glacial sea-ice changes on atmospheric pCO2 oppose each other. Whereas, extended sea-ice coverage in the Southern Hemisphere reduces the air-sea gas exchange of CO2 in agreement with previous theoretical considerations, glacial advances of sea-ice in the Northern Hemisphere lead to a weakening of the oceanic carbon uptake through the physical pump. Due to enhanced gas solubility associated with lower sea surface temperature, both glacial experiments generate a reduction of atmospheric pCO2 by about 20–23 ppmv. The sensitivity experiments presented here demonstrate the presence of compensating effects of different physical

  1. Preglacial surface remnants and Quaternary glacial regimes in northwestern Sweden

    Science.gov (United States)

    Kleman, Johan; Stroeven, Arjen P.

    1997-05-01

    We present a detailed map of the distribution of preglacial surface remnants in the Kebnekaise region of northwestern Sweden. In this mountain area we discern four important large-scale geomorphological units, each representing a specific set of erosional agents and formative conditions. These are: (i) intact preglacial surface remnants, characterized by gentle slopes, round summits, wide shallow valleys, and an absence of rock basins; (ii) preglacial surface remnants showing signs of minor glacial erosion and deposition; (iii) glacially scoured surfaces, including glacial troughs; (iv) deep fluvial valleys cut into the preglacial surface. The pattern of glacial erosion is explained as the result of three specific modes of glaciation known to have existed during the last 120,000 years, and inferred to have repeatedly prevailed during the last 2.75 million years: cirque glaciation, mountain ice sheets, and Fennoscandian ice sheets. A deep-ocean oxygen-isotope record of foraminifera from the North Atlantic (DSDP 607) was used to infer the temporal extent of these modes of glaciation during the last 2.75 million years. We interpret the preglacial landscape preservation and the pattern of glacial erosion in terms of the configuration, the basal thermal regime, and the duration of such glaciation events. The average subglacial thermal regime of both ice sheet types was frozen on the uplands and melting in the main valleys, where outlet glaciers and ice-streams formed. The pre-glacial landscape is best preserved at intermediate elevations, low enough not to have been covered by cirque glaciers, and apparently high enough not to have experienced melted-bed conditions and subglacial erosion during ice sheet overriding events. In a narrow high-relief zone along the elevation axis, interglacial fluvial erosion was morphologically important. The absence of glacial erosion on uplands in this zone allowed fluvial erosion to commence on the same locations during each ice

  2. 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

  3. 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.

  4. Climate Events and Cycles During the Last Glacial-Interglacial Transition

    Science.gov (United States)

    Lee, Eun Hee; Lee, Dae-Young; Park, Mi-Young

    2017-09-01

    During the last glacial-interglacial transition, there were multiple intense climatic events such as the Bølling-Allerød warming and Younger Dryas cooling. These events show abrupt and rapid climatic changes. In this study, the climate events and cycles during this interval are examined through wavelet analysis of Arctic and Antarctic ice-core 18O and tropical marine 14C records. The results show that periods of 1383-1402, 1029-1043, 726-736, 441-497 and 202-247 years are dominant in the Arctic region, whereas periods of 1480, 765, 518, 311, and 207 years are prominent in the Antarctic TALDICE. In addition, cycles of 1019, 515, and 209 years are distinct in the tropical region. Among these variations, the de Vries cycle of 202-209 years, correlated with variations in solar activity, was detected globally. In particular, this cycle shows a strong signal in the Antarctic between about 13,000 and 10,500 yr before present (BP). In contrast, the Eddy cycle of 1019-1043 years was prominent in Greenland and the tropical region, but was not detected in the Antarctic TALDICE records. Instead, these records showed that the Heinrich cycle of 1480 year was very strong and significant throughout the last glacial-interglacial interval.

  5. Arid and Humid Fluctuations in Mediterranean Iberia Since the Last Glacial Maximum Reconstructed From Lake Records

    Science.gov (United States)

    Valero-Garces, B. L.; Gonzalez-Samperiz, P.; Navas, A.; Delgado-Huertas, A.; Gonzalez-Barrios, A.; Machin, J.; Mata, P.

    2001-12-01

    In the Mediterranean regions of the Iberian Peninsula, vegetational and hydrological changes for the Last Glacial Cycle have responded more to effective moisture than to temperature fluctuations. The geographical location of the Iberian Peninsula at the southern edge of the westerlies explains the singularity of its climate and the dependence of North Atlantic, Mediterranean and Tropical influences. Discrepancies in the paleorecords, the lack of continuous paleoclimatic reconstructions, a scarcity of multiproxy studies, and inadequate age control have hindered our understanding of Iberian paleoclimate variability since the Last Glacial Maximum. We apply a variety of hydrologically-sensitive tools to selected lake core records to identify the main rapid arid/humid transitions and to characterize the century and millennium-long arid periods since the LGM. We reconstruct relative lake level curves for from alpine and saline lake sites along a N-S transect from the Pyrenees to the Ebro valley (NE Spain) based on sedimentary facies, elemental and isotope geochemistry, combined with a low-resolution pollen stratigraphy. Deglaciation in the southern Pyrenees occurred earlier than in the Alpine and Scandinavian regions, with a maximum ice extent before 30 kyr and a modest glacial re-advance during the global LGM. Vegetational refugia occurred during the LGM in the central Ebro valley, and there are evidences for large moisture fluctuations afterwards. A number of century-scale arid periods during full glacial, Lateglacial and Holocene have been identified. The Early Holocene was the most humid period in both regions, the Pyrenees and the Ebro valley. More paleotransects with better chronologies across Iberian will provide the needed records to solve these controversies. Cores have been retrieved from relatively deeper lakes in southern Spain (Zoñar, Cordoba province), and the Iberian Range (Taravilla) and detailed analyses and dating are in progress. The paleoclimate

  6. Simulating the last glacial-interglacial transition with a coupled atmosphere-ocean-ice sheet model

    Science.gov (United States)

    Mikolajewicz, Uwe; Ziemen, Florian

    2015-04-01

    One of the major challenges in climate modeling is the simulation of glacial-interglacial transitions. A few models of intermediate complexity have been successful in simulating the last termination. Complex atmosphere-ocean general circulation models have been shown to be able to yield realistic climate changes with prescribed ice sheets. Here we presents results from a first attempt to simulate a substantial part of the last glacial cycle with an AOGCM coupled interactively with a state-of-the-art ice sheet model. The ECHAM5/MPIOM AOGCM has been interactively coupled to the dynamical ice sheet model PISM. The latter is run for most of the northern hemisphere with a horizontal resolution of 20 km. An earlier version of this model ( Ziemen et al. 2014) has been applied to a steady state simulation of the last glacial maximum (LGM). The model was integrated from the late Glacial into the Holocene using insolation and greenhouse gas concentrations as transient forcing. Land sea mask and ocean topography are fixed at LGM conditions, river routing and surface elevation for the atmospheric model component are calculated interactively depending on the simulated ice sheets. To make these long simulations feasible, the atmosphere is accelerated by a factor of 10 relative to the other model components using a periodically-synchronous coupling technique. A mini-ensemble with different initial conditions has been run. In all simulation the northern hemispheric deglaciation starts between 18 and 17 kyr BP, consistent with the onset of global warming. The model produces Heinrich event like variability as part of its internal variability. These rapid ice discharge events have a strong impact on the North Atlantic meridional overturning circulation (NAMOC). During the peak deglaciation the NAMOC is collapsed (with a few short interruptions) for several thousand years, which is longer than the estimates from reconstructions. This seems to be an artifact due to keeping ocean

  7. A large thermogenic-methane release event in the SW Barents Sea, during the Last Glacial Maximum. Indications from numerical modelling and seismic reflection data

    Science.gov (United States)

    Anka, Z.; Rodrigues, E.; di Primio, R.; Ostanin, I.; Stoddart, D.; Horsfield, B.

    2011-12-01

    The Barents Sea, located in the Norwegian Artic area, has undergone a series of tectonic, paleoceanographic and paleo-climatic events during the Cenozoic, which most likely have caused the redistribution and leakage of hydrocarbons accumulations (Ohm et al., 2008). (Dimakis et al., 1998). Present-day under-filled accumulations are known to have leaked in the past providing a source of hydrocarbons, mostly thermogenic methane. However, the timing, extent and driving factors for this event are largely unconstrained. We built a 3D basin model of the Hammerfest Basin in the SW Barents Sea, in order to quantify the masses of liquid and gaseous hydrocarbons generated, accumulated and eventually leaked from the reservoirs during the evolution of the basin. Particular emphasis was placed on analysing the fate of leaked volumes within the dynamics of Plio-Quaternary glacial cycles and formation or destabilization of gas hydrate deposits. The model was calibrated with maturity and temperature well data and reconstructs, with large degree of accuracy, the composition and volume of the hydrocarbons, particularly the gaseous phase present in the main reservoirs. Our results predict the development of overpressures in the reservoirs due to the ice loading of the basin during the glacial periods. Pressure fluctuations derived from cyclic loading-unloading during the glacial-interglacial periods reached up to 5 MPa. The under-filled nature of the present-day accumulations would result from leakage events during the episodes of glacial retreat, in the transition from glacial to interglacial periods. Considerations of the gas hydrate stability conditions in the basin during the time span between 1.00Ma and ≈11,500 years indicate that the leaking thermogenic methane was probably trapped as gas hydrate deposits during the glacial events and then released at once upon hydrate destabilisation during the Last Glacial Maximun (LGM). These results are supported by the presence of km

  8. 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

  9. Glacial meltwater impounding: Evidence from the late Quaternary ...

    Indian Academy of Sciences (India)

    Glacial meltwater impounding: Evidence from the late. Quaternary glaciogenic sediments in the Sangla valley, district Kinnaur, Himachal Pradesh, India. R K Ganjoo1∗ and M N Koul2. 1Department of Geology, University of Jammu, Jammu 180 006, India. 2Department of Geography, University of Jammu, Jammu 180 006, ...

  10. Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks.

    Science.gov (United States)

    Torres, Mark A; Moosdorf, Nils; Hartmann, Jens; Adkins, Jess F; West, A Joshua

    2017-08-15

    Connections between glaciation, chemical weathering, and the global carbon cycle could steer the evolution of global climate over geologic time, but even the directionality of feedbacks in this system remain to be resolved. Here, we assemble a compilation of hydrochemical data from glacierized catchments, use this data to evaluate the dominant chemical reactions associated with glacial weathering, and explore the implications for long-term geochemical cycles. Weathering yields from catchments in our compilation are higher than the global average, which results, in part, from higher runoff in glaciated catchments. Our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals. To evaluate the effects of glacial weathering on atmospheric pCO2, we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon (DIC) generated by weathering reactions. Compared with nonglacial weathering, glacial weathering is more likely to yield alkalinity/DIC ratios less than 1, suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of CO2 to the atmosphere. Back-of-the-envelope calculations indicate that oxidative fluxes could change ocean-atmosphere CO2 equilibrium by 25 ppm or more over 10 ky. Over longer timescales, CO2 release could act as a negative feedback, limiting progress of glaciation, dependent on lithology and the concentration of atmospheric O2 Future work on glaciation-weathering-carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals.

  11. 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 South-East Asia. The run-off from its ~ 34 000 glaciers, which occupy an area of ~ 50 000 km2, feed Tibetan lakes and major Asian rivers like Indus and Brahmaputra. Reported glacial shrinkage likely has its impact on the run-off. Unfortunately,

  12. 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,

  13. What is the phase space of the last glacial inception?

    Science.gov (United States)

    Bahadory, Taimaz; Tarasov, Lev

    2017-04-01

    Would the ice and climate pattern of glacial inception changed much with small tweaks to the initial Eemian climate state? Given the very limited available geological constraints, what is the range of potential spatio-temporal patterns of ice sheet inception and associated climate? What positive and negative feedbacks between ice, atmospheric and ocean circulation, and vegetation dominate glacial inception? As a step towards answering these questions, we examine the phase space of glacial inception in response to a subset of uncertainties in a coupled 3D model through an ensemble of simulations. The coupled model consists of the GSM (Glacial Systems Model) and LOVECLIM earth systems model of intermediate complexity. The former includes a 3D ice sheet model, asynchronously coupled glacio isostatic adjustment, surface drainage solver, and permafrost resolving bed thermal model. The latter includes an ocean GCM, atmospheric component, dynamic/thermodynamic seaice, and simplified dynamical vegetation. Our phase space exploration probes uncertainties in: initial conditions, downscaling and upscaling, the radiative effect of clouds, snow and ice albedo, precipitation parameterization, and freshwater discharge. The probe is constrained by model fit to present day climate and LGM climate.

  14. Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks

    Science.gov (United States)

    Torres, Mark A.; Moosdorf, Nils; Hartmann, Jens; Adkins, Jess F.; West, A. Joshua

    2017-08-01

    Connections between glaciation, chemical weathering, and the global carbon cycle could steer the evolution of global climate over geologic time, but even the directionality of feedbacks in this system remain to be resolved. Here, we assemble a compilation of hydrochemical data from glacierized catchments, use this data to evaluate the dominant chemical reactions associated with glacial weathering, and explore the implications for long-term geochemical cycles. Weathering yields from catchments in our compilation are higher than the global average, which results, in part, from higher runoff in glaciated catchments. Our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals. To evaluate the effects of glacial weathering on atmospheric pCO2, we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon (DIC) generated by weathering reactions. Compared with nonglacial weathering, glacial weathering is more likely to yield alkalinity/DIC ratios less than 1, suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of CO2 to the atmosphere. Back-of-the-envelope calculations indicate that oxidative fluxes could change ocean-atmosphere CO2 equilibrium by 25 ppm or more over 10 ky. Over longer timescales, CO2 release could act as a negative feedback, limiting progress of glaciation, dependent on lithology and the concentration of atmospheric O2. Future work on glaciation-weathering-carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals.

  15. 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.

  16. Groundwater quality in the glacial aquifer system, United States

    Science.gov (United States)

    Stackelberg, Paul E.

    2017-12-07

    Groundwater provides nearly 50 percent of the Nation’s drinking water. To help protect this vital resource, the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Project assesses groundwater quality in aquifers that are important sources of drinking water (Burow and Belitz, 2014). The glacial aquifer system constitutes one of the important areas being evaluated.

  17. Glacial-interglacial changes in the surface water characteristics of ...

    Indian Academy of Sciences (India)

    Globigerinoides ruber) from a deep sea sediment core (GC-1) in the Andaman Sea show high glacial-to-Holocene 180 amplitude of 2.1% which is consistent with previously published records from this marginal basin and suggest increased ...

  18. 76 FR 50476 - Application To Export Electric Energy; Glacial Energy of Texas, Inc.

    Science.gov (United States)

    2011-08-15

    ... franchised service area. The electric energy that Glacial proposes to export to Mexico would be ] surplus... Application To Export Electric Energy; Glacial Energy of Texas, Inc. AGENCY: Office of Electricity Delivery.... (Glacial) has applied for authority to transmit electric energy from the United States to Mexico pursuant...

  19. 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

  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. 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

    2017-06-23

    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.

  2. Efficacy of passive ultrasonic irrigation in removing root filling material during endodontic retreatment

    Directory of Open Access Journals (Sweden)

    Carina MICHELON

    Full Text Available Abstract Introduction The aim of endodontic retreatment is to remove the previous root filling materials completely to allow for the subsequent steps of cleaning, canal shaping and filling replacement. Objective To evaluate the efficacy of passive ultrasonic irrigation (PUI in the removal of residual root filling material after removing the bulk of the root filling with nickel-titanium rotary instruments. Material and method Eighteen mesial isthmus-containing roots of human mandibular molars were prepared and filled. The root canal filling was removed with the ProTaper Retreatment system and K-files. The specimens were randomized into 2 groups (n = 9, both irrigated with 2.5% NaOCl and 17% EDTA. In the conventional group, an irrigation syringe was used. In the PUI group, the PUI technique was used. The roots were sectioned longitudinally and evaluated under stereomicroscopy. Student’s t test was used to compare groups and the general linear model was used to compare the apical, cervical, and middle root thirds within each group, in regard to the percentages of remaining residual filling material. Result There was no statistically significant intergroup difference, irrespective of which root third was evaluated (P > 0.05. In the PUI group, the apical third showed a significantly higher percentage of residual filling material, in comparison with the cervical (P = 0.038 and middle (P = 0.029 thirds. Conclusion The PUI technique was not more effective than the conventional irrigation technique in removing residual root filling material during endodontic retreatment in root canals with a complex anatomy.

  3. 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.

  4. Efficacy and safety of retreatment with nivolumab in metastatic melanoma patients previously treated with nivolumab.

    Science.gov (United States)

    Nomura, Motoo; Otsuka, Atsushi; Kondo, Tomohiro; Nagai, Hiroki; Nonomura, Yumi; Kaku, Yo; Matsumoto, Shigemi; Muto, Manabu

    2017-11-01

    Nivolumab is a monoclonal antibody directed against programmed death-1 that has been shown to improve survival in patients with metastatic melanoma. However, the efficacy of nivolumab and other agents in melanoma remains limited. The objective of this study was to evaluate the efficacy and safety of retreatment with nivolumab in metastatic melanoma patients who previously progressed on nivolumab. A retrospective review was performed on eight consecutive metastatic melanoma patients retreated with nivolumab who progressed on previous nivolumab. These patients received nivolumab 2 mg/kg every 3 weeks. Best responses to each treatment were assessed using RECIST 1.1. Of eight metastatic melanoma patients, three patients received chemotherapy before first nivolumab. The median first nivolumab treatment period was 4.1 months. During first nivolumab, 3 (37.5%) patients achieved a partial response and 3 (37.5%) patients achieved stable disease as their best response. First nivolumab was discontinued due to disease progression in seven patients and grade 3 colitis in 1 patient. Patients were subsequently treated with ipilimumab (n = 6), vemurafenib (n = 1), or no other medical treatment (n = 1). The median treatment period between first and second nivolumab was 3.0 months. Four patients received radiation therapy between first and second nivolumab. The median second nivolumab treatment period was 4.3 months. Among the eight patients who received second nivolumab, 2 (25%) patients achieved a partial response and 3 (37.5%) patients achieved stable disease as their best response. Second nivolumab was discontinued due to disease progression in seven patients. One patient continues to receive second nivolumab. Among the four patients treated with ipilimumab and radiotherapy between first and second nivolumab, the response rate was 50% and the disease control rate was 75%. This study showed that retreatment with nivolumab is an option for select metastatic melanoma

  5. Incidence of Dentinal Defects and Vertical Root Fractures after Endodontic Retreatment and Mechanical Cycling.

    Science.gov (United States)

    De Carlo Bello, Mariana; Pillar, Rafael; Mastella Lang, Pauline; Michelon, Carina; Abreu da Rosa, Ricardo; Souza Bier, Carlos Alexandre

    2017-01-01

    The aim of this study was to evaluate the incidence of dentinal defects and vertical root fractures (VRFs) after endodontic retreatment and mechanical cycling (MC). Two hundred mandibular premolars were selected. Forty teeth were left unprepared (control group). The remaining 160 root canals were prepared with ProTaper instruments and filled by using two different techniques [eighty with lateral compaction (LC) and eighty with single-cone (SC)]. Forty canals from each group (LC and SC) received no further treatment. The remaining eighty teeth were divided into two groups (LCR and SCR) ( n =40) in order to undergo the removal of the root filling, re-preparation and refilling with lateral compaction and single-cone, respectively. All of the teeth were subjected to MC (1000000 cycles, 130 N, 2.2 Hz and 37 ° C). The roots were sectioned at 3, 6 and 9 mm from the apex and observed under 20× magnification. The defects were classified as: no defect, VRF and other defects . Statistical analysis was performed using the Fisher's Exact test and the Chi -Squared tests ( α =0.05). MC alone did not promote any other defects or VRFs. Experimental groups presented higher dentinal defects than the control group ( P =0.021). Retreatment groups did not present a higher amount of dentinal defects than the groups that were subjected to the first treatment ( P >0.05). Endodontic treatment and retreatment, regardless of the filling technique and MC, did not influence the occurrence of dentinal defects or VRFs in the human premolars.

  6. 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.

  7. Nonsurgical Endodontic Retreatment of Maxillary Second Molar with Two Palatal Root Canals: A Case Report

    Directory of Open Access Journals (Sweden)

    Mahsa Eskandarinezhad

    2012-04-01

    Full Text Available Successful endodontic treatment requires thorough knowledge regarding each root canal system of any tooth and probability of extra canals should be considered. Second maxillary molar with two palatal root canals is not frequent and its incidence reported in literatures is about 0.4–2%. The present case report describes non-surgical retreatment of maxillary second molar with two palatal root canals. Radiographic interpretation is difficult in this region; so, very careful examination of pulpal space and using supportive devices such as loupe and operating microscope is recommended to discover any unusual anatomic features like extra canals.

  8. Management of Post Endodontic Retreatment Pain With Low Level Laser Therapy.

    Science.gov (United States)

    Asnaashari, Mohammad; Ashraf, Hengameh; Daghayeghi, Amir Houshang; Mojahedi, Seyed Masoud; Azari-Marhabi, Saranaz

    2017-01-01

    Introduction: Pharmacotherapy with analgesics and non-steroidal anti-inflammatory drugs has been traditionally used to relief post-operative pain of endodontic treatments. However, due to the side effects reported for these drugs, some efforts have been made to decrease the post-operative pain of the endodontic treatments through laser irradiation. The present study aimed to evaluate the effects of low level laser therapy (LLLT) on the reduction of pain after root canal retreatment. Methods: In this clinical trial, 61 patients requiring endodontic retreatments in posterior teeth were selected. A single visit endodontic retreatment was performed. After biomechanical preparation, low level laser was irradiated to the buccal and lingual mucosa overlying the apices of the target tooth in the experimental group. In the control group patients received placebo laser to eliminate the probable psychological effects of laser. Laser irradiation was done with a single dose of 808 nm wavelength (Whitening Lase II- Laser DMC, Samsung, Korea) with 100 mW power, and dose of 70 J/cm2 for 80 seconds. Pain severity was recorded before, immediately after and 4, 8, 12, 24 and 48 hours after the treatment by visual analogue scale (VAS). The pain scores were statistically analyzed by chi-square test between 2 groups. The effects of different variables on the post-operative pain experience were also studied by means of Logistic regression. Results: Pain scores decreased significantly through time until 48 hours after treatment. No significant differences were observed between the 2 modalities regarding pain scores at any time. According to regression analysis, pain severity scores were lower in the laser-irradiated specimens than control groups (OR = 5.69); however, this difference was not statistically significant. Consumption of analgesics after the treatment had significant effect in decreasing post-operative pain experience (OR = 56) while factors of age, gender, laser irradiation

  9. Oncology Nurse Retreat: A Strength-Based Approach to Self-Care and Personal Resilience
.

    Science.gov (United States)

    Kuglin Jones, Ann

    2017-04-01

    Oncology nurses are at high risk for burnout and compassion fatigue. Self-care is an essential element that oncology nurses should incorporate into their daily lives but, instead, is often deprioritized. As a result, nurses do not seek out educational opportunities that focus on self-care or personal growth. This article describes the curriculum that was developed for an oncology nurse retreat that promoted self-care and building personal resilience using tools that could be adapted for use with patients and families.
.

  10. Surgical management of an endodontic retreatment failure of a mandibular first molar

    Directory of Open Access Journals (Sweden)

    Kinjal M Gathani

    2016-01-01

    Full Text Available One of the common endodontic iatrogenic mishaps is the extrusion of obturation material which has a negative effect on the long-term prognosis of the tooth. Surgical endodontics has enabled us to save teeth with persistent infections and extrusions when orthograde treatment has been unsuccessful. Apicoectomy of the molars is not frequently performed even though its success rate can reach that of anteriors and premolars. This case report describes the orthograde and surgical management of a mandibular first molar with external root resorption, instrument separation in the canal, and extruded obturation material, which had been unresponsive to endodontic retreatment.

  11. Investigators Retreat: A Forum to Bridge Frederick and Bethesda Cancer Research | Poster

    Science.gov (United States)

    By Andrea Frydl, Contributing Writer Nearly 700 researchers, scientists, and laboratory technicians convened in the Ronald Reagan Building and International Trade Center in Washington, DC, for the 2014 NCI Intramural Scientific Investigators Retreat on Jan. 14. The event featured presentations and posters exploring topics in cancer research from KRAS signaling to animal care. One of the highlights of the event was a presentation made by Valerie Beral, Ph.D., from University of Oxford, discussing “Rosalind Franklin and Cancer in Women.” 

  12. Perception of approaching and retreating floor-projected shapes in a large, immersive, multimedia learning environment.

    Science.gov (United States)

    Dolgov, Igor; Birchfield, David A; McBeath, Michael K; Thornburg, Harvey; Todd, Christopher G

    2009-04-01

    Perception of floor-projected moving geometric shapes was examined in the context of the Situated Multimedia Arts Learning Laboratory (SMALLab), an immersive, mixed-reality learning environment. As predicted, the projected destinations of shapes which retreated in depth (proximal origin) were judged significantly less accurately than those that approached (distal origin). Participants maintained similar magnitudes of error throughout the session, and no effect of practice was observed. Shape perception in an immersive multimedia environment is comparable to the real world. One may conclude that systematic exploration of basic psychological phenomena in novel mediated environments is integral to an understanding of human behavior in novel human-computer interaction architectures.

  13. 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.

  14. The Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient

    Science.gov (United States)

    Dowdeswell, Julian A.; Canals, Miquel; Jakobsson, Martin; Todd, Brian J.; Dowdeswell, Evelyn K.; Hogan, Kelly A.

    2017-04-01

    Twenty years ago, the international marine community brought together a first Atlas of Acoustic Images of the high-latitude geo-marine environment (Davies et al. 1997). The present Atlas is a new attempt to summarize the state of knowledge of high-latitude glacier-influenced systems, focusing on HR imagery derived from multibeam swath bathymetry and novel 2D and 3D seismic reflection tools. These new-generation techniques, aided by accurate global positioning, have revolutionized the imaging of the seafloor and subseafloor over the past two decades and have now been deployed widely in polar and subpolar waters, providing vast quantities of new data. It is, therefore, timely to provide a compilation of the variety of submarine glacial and related landforms, together with their stratigraphic setting where possible, for scientific, technological, environmental and economic reasons. The glacial imprint on the modern seabed and palaeo-shelf surfaces, buried in glacial-sedimentary depocentres, can now be imaged better than ever before using the above techniques, providing novel insights into present and past environmental conditions and sedimentary architecture. The understanding of polar regions and their changing ice cover is of enhanced significance as they are both a key driver of global change and important responders to it. Finally, industry is increasingly interested on the dimensions and architecture of glacial sedimentary depocentres on present and past continental shelves because of the hydrocarbon potential of some glacial-sedimentary systems. The Atlas consists of a comprehensive series of over 180 contributions that describe, illustrate and discuss the full variability of landforms found on the high-latitude, glacier-influenced systems, and is organised in terms of their positions on a continental margin into those from: (1) fjords, (2) continental shelves and plateaus, and (3) the deep margin and basins beyond. The Atlas has been published by the Geological

  15. 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

    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...... as in the macropores. The model analysis showed that macropore flow is essential in describing the observed transport phenomenon on a short as well as a longer time scale. The diffusive exchange of solute between the matrix and the macropores was very sensitive and critical for the model prediction of the drainage...... 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...

  16. Early last glacial intra-interstadial climate variability recorded in a Sardinian speleothem

    Science.gov (United States)

    Columbu, Andrea; Drysdale, Russell; Capron, Emilie; Woodhead, Jon; De Waele, Jo; Sanna, Laura; Hellstrom, John; Bajo, Petra

    2017-08-01

    Chemical and physical proxy data from a precisely dated early last glacial (∼113-110 ka, MIS5d) Sardinian stalagmite reveal a sub-millennial-scale, cool-dry climate event centered at 112.0 +0.52/-0.59 ka, followed by a rapid return to warm-wet conditions at 111.76 +0.43/-0.45 ka. Comparison with regional speleothem records and the palaeotemperature proxy record from the NGRIP ice core (Greenland) suggests that this event corresponds to Greenland Interstadial (GI) 25b and 25a, an intra-interstadial climate oscillation within GI-25, according to the recent Greenland stratigraphic framework. The speleothem age is in reasonable agreement (within 0.8 kyr) with that of the corresponding event in Greenland based on the GICC05modelext ice chronology but is older by about 3.7 kyr than the Greenland age based on the AICC2012 chronology.

  17. 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.