WorldWideScience

Sample records for polar ice streams

  1. Stochastic ice stream dynamics.

    Science.gov (United States)

    Mantelli, Elisa; Bertagni, Matteo Bernard; Ridolfi, Luca

    2016-08-09

    Ice streams are narrow corridors of fast-flowing ice that constitute the arterial drainage network of ice sheets. Therefore, changes in ice stream flow are key to understanding paleoclimate, sea level changes, and rapid disintegration of ice sheets during deglaciation. The dynamics of ice flow are tightly coupled to the climate system through atmospheric temperature and snow recharge, which are known exhibit stochastic variability. Here we focus on the interplay between stochastic climate forcing and ice stream temporal dynamics. Our work demonstrates that realistic climate fluctuations are able to (i) induce the coexistence of dynamic behaviors that would be incompatible in a purely deterministic system and (ii) drive ice stream flow away from the regime expected in a steady climate. We conclude that environmental noise appears to be crucial to interpreting the past behavior of ice sheets, as well as to predicting their future evolution.

  2. Polar bears and sea ice habitat change

    Science.gov (United States)

    Durner, George M.; Atwood, Todd C.; Butterworth, Andy

    2017-01-01

    The polar bear (Ursus maritimus) is an obligate apex predator of Arctic sea ice and as such can be affected by climate warming-induced changes in the extent and composition of pack ice and its impacts on their seal prey. Sea ice declines have negatively impacted some polar bear subpopulations through reduced energy input because of loss of hunting habitats, higher energy costs due to greater ice drift, ice fracturing and open water, and ultimately greater challenges to recruit young. Projections made from the output of global climate models suggest that polar bears in peripheral Arctic and sub-Arctic seas will be reduced in numbers or become extirpated by the end of the twenty-first century if the rate of climate warming continues on its present trajectory. The same projections also suggest that polar bears may persist in the high-latitude Arctic where heavy multiyear sea ice that has been typical in that region is being replaced by thinner annual ice. Underlying physical and biological oceanography provides clues as to why polar bear in some regions are negatively impacted, while bears in other regions have shown no apparent changes. However, continued declines in sea ice will eventually challenge the survival of polar bears and efforts to conserve them in all regions of the Arctic.

  3. Seasonal ice dynamics of the Northeast Greenland Ice Stream

    DEFF Research Database (Denmark)

    Vijay, Saurabh; Khan, Shfaqat Abbas; Simonsen, Sebastian Bjerregaard

    2018-01-01

    and temporal details. This study focus on the Northeast Greenland Ice Stream (NEGIS), which consists of three main outlets, 79 North glacier (79N), Zachariae Isstrøm (ZI) and Storstrømmen Glacier (SG). While both 79 North and Storstrømmen have floating tongues, Zachariae Isstrøm is mostly grounded...

  4. Switch of flow direction in an Antarctic ice stream.

    Science.gov (United States)

    Conway, H; Catania, G; Raymond, C F; Gades, A M; Scambos, T A; Engelhardt, H

    2002-10-03

    Fast-flowing ice streams transport ice from the interior of West Antarctica to the ocean, and fluctuations in their activity control the mass balance of the ice sheet. The mass balance of the Ross Sea sector of the West Antarctic ice sheet is now positive--that is, it is growing--mainly because one of the ice streams (ice stream C) slowed down about 150 years ago. Here we present evidence from both surface measurements and remote sensing that demonstrates the highly dynamic nature of the Ross drainage system. We show that the flow in an area that once discharged into ice stream C has changed direction, now draining into the Whillans ice stream (formerly ice stream B). This switch in flow direction is a result of continuing thinning of the Whillans ice stream and recent thickening of ice stream C. Further abrupt reorganization of the activity and configuration of the ice streams over short timescales is to be expected in the future as the surface topography of the ice sheet responds to the combined effects of internal dynamics and long-term climate change. We suggest that caution is needed when using observations of short-term mass changes to draw conclusions about the large-scale mass balance of the ice sheet.

  5. Destabilization of the Northeast Greenland Ice Stream

    DEFF Research Database (Denmark)

    Korsgaard, N. J.; Khan, Shfaqat Abbas; Kjaer, K. H.

    . Here, we reveal that the Northeast Greenland Ice Stream (NEGIS), which extends more than 600 km into the interior of the ice sheet, is now undergoing dynamic thinning after more than a quarter of a century of stability. This sector of the GrIS is of particular interest in sea level projections, because...... the glacier flows into a large submarine basin with a negative bed slope near the grounding line. Our findings unfold the next step in mass loss of the GrIS as we show a heightened risk of rapid sustained loss from Northeast Greenland on top of the thinning in Southeast and Northwestern Greenland....

  6. How dynamic are ice-stream beds?

    Science.gov (United States)

    Davies, Damon; Bingham, Robert G.; King, Edward C.; Smith, Andrew M.; Brisbourne, Alex M.; Spagnolo, Matteo; Graham, Alastair G. C.; Hogg, Anna E.; Vaughan, David G.

    2018-05-01

    Projections of sea-level rise contributions from West Antarctica's dynamically thinning ice streams contain high uncertainty because some of the key processes involved are extremely challenging to observe. An especially poorly observed parameter is sub-decadal stability of ice-stream beds, which may be important for subglacial traction, till continuity and landform development. Only two previous studies have made repeated geophysical measurements of ice-stream beds at the same locations in different years, but both studies were limited in spatial extent. Here, we present the results from repeat radar measurements of the bed of Pine Island Glacier, West Antarctica, conducted 3-6 years apart, along a cumulative ˜ 60 km of profiles. Analysis of the correlation of bed picks between repeat surveys shows that 90 % of the bed displays no significant change despite the glacier increasing in speed by up to 40 % over the last decade. We attribute the negligible detection of morphological change at the bed of Pine Island Glacier to the ubiquitous presence of a deforming till layer, wherein sediment transport is in steady state, such that sediment is transported along the basal interface without inducing morphological change to the radar-sounded basal interface. Given the precision of our measurements, the upper limit of subglacial erosion observed here is 500 mm a-1, far exceeding erosion rates reported for glacial settings from proglacial sediment yields, but substantially below subglacial erosion rates of 1.0 m a-1 previously reported from repeat geophysical surveys in West Antarctica.

  7. Promoting Diversity Through Polar Interdisciplinary Coordinated Education (Polar ICE)

    Science.gov (United States)

    McDonnell, J. D.; Hotaling, L. A.; Garza, C.; Van Dyk, P. B.; Hunter-thomson, K. I.; Middendorf, J.; Daniel, A.; Matsumoto, G. I.; Schofield, O.

    2017-12-01

    Polar Interdisciplinary Coordinated Education (ICE) is an education and outreach program designed to provide public access to the Antarctic and Arctic regions through polar data and interactions with the scientists. The program provides multi-faceted science communication training for early career scientists that consist of a face-to face workshop and opportunities to apply these skills. The key components of the scientist training workshop include cultural competency training, deconstructing/decoding science for non-expert audiences, the art of telling science stories, and networking with members of the education and outreach community and reflecting on communication skills. Scientists partner with educators to provide professional development for K-12 educators and support for student research symposia. Polar ICE has initiated a Polar Literacy initiative that provides both a grounding in big ideas in polar science and science communication training designed to underscore the importance of the Polar Regions to the public while promoting interdisciplinary collaborations between scientists and educators. Our ultimate objective is to promote STEM identity through professional development of scientists and educators while developing career awareness of STEM pathways in Polar science.

  8. Subglacial hydrology and the formation of ice streams.

    Science.gov (United States)

    Kyrke-Smith, T M; Katz, R F; Fowler, A C

    2014-01-08

    Antarctic ice streams are associated with pressurized subglacial meltwater but the role this water plays in the dynamics of the streams is not known. To address this, we present a model of subglacial water flow below ice sheets, and particularly below ice streams. The base-level flow is fed by subglacial melting and is presumed to take the form of a rough-bedded film, in which the ice is supported by larger clasts, but there is a millimetric water film which submerges the smaller particles. A model for the film is given by two coupled partial differential equations, representing mass conservation of water and ice closure. We assume that there is no sediment transport and solve for water film depth and effective pressure. This is coupled to a vertically integrated, higher order model for ice-sheet dynamics. If there is a sufficiently small amount of meltwater produced (e.g. if ice flux is low), the distributed film and ice sheet are stable, whereas for larger amounts of melt the ice-water system can become unstable, and ice streams form spontaneously as a consequence. We show that this can be explained in terms of a multi-valued sliding law, which arises from a simplified, one-dimensional analysis of the coupled model.

  9. Patterned basal seismicity shows sub-ice stream bedforms

    Science.gov (United States)

    Barcheck, C. G.; Tulaczyk, S. M.; Schwartz, S. Y.

    2017-12-01

    Patterns in seismicity emanating from the bottom of fast-moving ice streams and glaciers may indicate localized patches of higher basal resistance— sometimes called 'sticky spots', or otherwise varying basal properties. These seismogenic basal areas resist an unknown portion of the total driving stress of the Whillans Ice Plain (WIP), in West Antarctica, but may play an important role in the WIP stick-slip cycle and ice stream slowdown. To better understand the mechanism and importance of basal seismicity beneath the WIP, we analyze seismic data collected by a small aperture (micro-earthquakes in Dec 2014, and we compare the resulting map of seismicity to ice bottom depth measured by airborne radar. The number of basal earthquakes per area within the network is spatially heterogeneous, but a pattern of two 400m wide streaks of high seismicity rates is evident, with >50-500 earthquakes detected per 50x50m grid cell in 2 weeks. These seismically active streaks are elongated approximately in the ice flow direction with a spacing of 750m. Independent airborne radar measurements of ice bottom depth from Jan 2013 show a low-amplitude ( 5m) undulation in the basal topography superposed on a regional gradient in ice bottom depth. The flow-perpendicular wavelength of these low-amplitude undulations is comparable to the spacing of the high seismicity bands, and the streaks of high seismicity intersect local lows in the undulating basal topography. We interpret these seismic and radar observations as showing seismically active sub-ice stream bedforms that are low amplitude and elongated in the direction of ice flow, comparable to the morphology of mega scale glacial lineations (MSGLs), with high basal seismicity rates observed in the MSGL troughs. These results have implications for understanding the formation mechanism of MSGLS and well as understanding the interplay between basal topographic roughness, spatially varying basal till and hydrologic properties, basal

  10. Ice-Shelf Flexure and Tidal Forcing of Bindschadler Ice Stream, West Antarctica

    Science.gov (United States)

    Walker, Ryan T.; Parizek, Bryron R.; Alley, Richard B.; Brunt, Kelly M.; Anandakrishnan, Sridhar

    2014-01-01

    Viscoelastic models of ice-shelf flexure and ice-stream velocity perturbations are combined into a single efficient flowline model to study tidal forcing of grounded ice. The magnitude and timing of icestream response to tidally driven changes in hydrostatic pressure and/or basal drag are found to depend significantly on bed rheology, with only a perfectly plastic bed allowing instantaneous velocity response at the grounding line. The model can reasonably reproduce GPS observations near the grounding zone of Bindschadler Ice Stream (formerly Ice Stream D) on semidiurnal time scales; however, other forcings such as tidally driven ice-shelf slope transverse to the flowline and flexurally driven till deformation must also be considered if diurnal motion is to be matched

  11. Sodium, Iodine and Bromine in Polar Ice Cores

    DEFF Research Database (Denmark)

    Maffezzoli, Niccolo

    Abstract: This research focuses on sodium, bromine and iodine in polar ice cores, with the aim of reviewing and advancing their current understanding with additional measurements and records, and investigating the connections of these tracers with sea ice and their feasibility as sea ice indicators...... with a description of the main analytic al techniques used to measure ionic and elemental species in ice cores. Chapter 4 introduces sodium, bromine and iodine with a theoretical perspective and a particular focus on their connections with sea ice. Some of the physical and chemical properties that are believed...... back trajectory analyses of the past 17 years. The results identify the aerosol source area influencing the Renland ice cap, a result necessary for the interpretation of impurity records obtained from the ice core. Chapter 6 reviews the published ice/snow measurements of bromine and iodine at polar...

  12. Polar Ice Caps: a Canary for the Greenland Ice Sheet

    Science.gov (United States)

    Honsaker, W.; Lowell, T. V.; Sagredo, E.; Kelly, M. A.; Hall, B. L.

    2010-12-01

    Ice caps are glacier masses that are highly sensitive to climate change. Because of their hypsometry they can have a binary state. When relatively slight changes in the equilibrium line altitude (ELA) either intersect or rise above the land the ice can become established or disappear. Thus these upland ice masses have a fast response time. Here we consider a way to extract the ELA signal from independent ice caps adjacent to the Greenland Ice Sheet margin. It may be that these ice caps are sensitive trackers of climate change that also impact the ice sheet margin. One example is the Istorvet Ice Cap located in Liverpool Land, East Greenland (70.881°N, 22.156°W). The ice cap topography and the underlying bedrock surface dips to the north, with peak elevation of the current ice ranging in elevation from 1050 to 745 m.a.s.l. On the eastern side of the ice mass the outlet glaciers extending down to sea level. The western margin has several small lobes in topographic depressions, with the margin reaching down to 300 m.a.s.l. Topographic highs separate the ice cap into at least 5 main catchments, each having a pair of outlet lobes toward either side of the ice cap. Because of the regional bedrock slope each catchment has its own elevation range. Therefore, as the ELA changes it is possible for some catchments of the ice cap to experience positive mass balance while others have a negative balance. Based on weather observations we estimate the present day ELA to be ~1000 m.a.s.l, meaning mass balance is negative for the majority of the ice cap. By tracking glacier presence/absence in these different catchments, we can reconstruct small changes in the ELA. Another example is the High Ice Cap (informal name) in Milne Land (70.903°N, 25.626°W, 1080 m), East Greenland. Here at least 4 unconformities in ice layers found near the southern margin of the ice cap record changing intervals of accumulation and ablation. Therefore, this location may also be sensitive to slight

  13. Sea ice classification using dual polarization SAR data

    International Nuclear Information System (INIS)

    Huiying, Liu; Huadong, Guo; Lu, Zhang

    2014-01-01

    Sea ice is an indicator of climate change and also a threat to the navigation security of ships. Polarimetric SAR images are useful in the sea ice detection and classification. In this paper, backscattering coefficients and texture features derived from dual polarization SAR images are used for sea ice classification. Firstly, the HH image is recalculated based on the angular dependences of sea ice types. Then the effective gray level co-occurrence matrix (GLCM) texture features are selected for the support vector machine (SVM) classification. In the end, because sea ice concentration can provide a better separation of pancake ice from old ice, it is used to improve the SVM result. This method provides a good classification result, compared with the sea ice chart from CIS

  14. Polar Sea Ice Monitoring Using HY-2A Scatterometer Measurements

    Directory of Open Access Journals (Sweden)

    Mingming Li

    2016-08-01

    Full Text Available A sea ice detection algorithm based on Fisher’s linear discriminant analysis is developed to segment sea ice and open water for the Ku-band scatterometer onboard the China’s Hai Yang 2A Satellite (HY-2A/SCAT. Residual classification errors are reduced through image erosion/dilation techniques and sea ice growth/retreat constraint methods. The arctic sea-ice-type classification is estimated via a time-dependent threshold derived from the annual backscatter trends based on previous HY-2A/SCAT derived sea ice extent. The extent and edge of the sea ice obtained in this study is compared with the Special Sensor Microwave Imager/Sounder (SSMIS sea ice concentration data and the Sentinel-1 SAR imagery for verification, respectively. Meanwhile, the classified sea ice type is compared with a multi-sensor sea ice type product based on data from the Advanced Scatterometer (ASCAT and SSMIS. Results show that HY-2A/SCAT is powerful in providing sea ice extent and type information, while differences in the sensitivities of active/passive products are found. In addition, HY-2A/SCAT derived sea ice products are also proved to be valuable complements for existing polar sea ice data products.

  15. Monstrous Ice Cloud System in Titan's Present South Polar Stratosphere

    Science.gov (United States)

    Anderson, Carrie; Samuelson, Robert; McLain, Jason; Achterberg, Richard; Flasar, F. Michael; Milam, Stefanie

    2015-11-01

    During southern autumn when sunlight was still available, Cassini's Imaging Science Subsystem discovered a cloud around 300 km near Titan's south pole (West, R. A. et al., AAS/DPS Abstracts, 45, #305.03, 2013); the cloud was later determined by Cassini's Visible and InfraRed Mapping Spectrometer to contain HCN ice (de Kok et al., Nature, 514, pp 65-67, 2014). This cloud has proven to be only the tip of an extensive ice cloud system contained in Titan's south polar stratosphere, as seen through the night-vision goggles of Cassini's Composite InfraRed Spectrometer (CIRS). As the sun sets and the gloom of southern winter approaches, evidence is beginning to accumulate from CIRS far-IR spectra that a massive system of nitrile ice clouds is developing in Titan's south polar stratosphere. Even during the depths of northern winter, nothing like the strength of this southern system was evident in corresponding north polar regions.From the long slant paths that are available from limb-viewing CIRS far-IR spectra, we have the first definitive detection of the ν6 band of cyanoacetylene (HC3N) ice in Titan’s south polar stratosphere. In addition, we also see a strong blend of nitrile ice lattice vibration features around 160 cm-1. From these data we are able to derive ice abundances. The most prominent (and still chemically unidentified) ice emission feature, the Haystack, (at 220 cm-1) is also observed. We establish the vertical distributions of the ice cloud systems associated with both the 160 cm-1 feature and the Haystack. The ultimate aim is to refine the physical and possibly the chemical relationships between the two. Transmittance thin film spectra of nitrile ice mixtures obtained in our Spectroscopy for Planetary ICes Environments (SPICE) laboratory are used to support these analyses.

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

    Science.gov (United States)

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

    2018-06-01

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

  17. Sea-ice indicators of polar bear habitat

    Directory of Open Access Journals (Sweden)

    H. L. Stern

    2016-09-01

    Full Text Available Nineteen subpopulations of polar bears (Ursus maritimus are found throughout the circumpolar Arctic, and in all regions they depend on sea ice as a platform for traveling, hunting, and breeding. Therefore polar bear phenology – the cycle of biological events – is linked to the timing of sea-ice retreat in spring and advance in fall. We analyzed the dates of sea-ice retreat and advance in all 19 polar bear subpopulation regions from 1979 to 2014, using daily sea-ice concentration data from satellite passive microwave instruments. We define the dates of sea-ice retreat and advance in a region as the dates when the area of sea ice drops below a certain threshold (retreat on its way to the summer minimum or rises above the threshold (advance on its way to the winter maximum. The threshold is chosen to be halfway between the historical (1979–2014 mean September and mean March sea-ice areas. In all 19 regions there is a trend toward earlier sea-ice retreat and later sea-ice advance. Trends generally range from −3 to −9 days decade−1 in spring and from +3 to +9 days decade−1 in fall, with larger trends in the Barents Sea and central Arctic Basin. The trends are not sensitive to the threshold. We also calculated the number of days per year that the sea-ice area exceeded the threshold (termed ice-covered days and the average sea-ice concentration from 1 June through 31 October. The number of ice-covered days is declining in all regions at the rate of −7 to −19 days decade−1, with larger trends in the Barents Sea and central Arctic Basin. The June–October sea-ice concentration is declining in all regions at rates ranging from −1 to −9 percent decade−1. These sea-ice metrics (or indicators of habitat change were designed to be useful for management agencies and for comparative purposes among subpopulations. We recommend that the National Climate Assessment include the timing of sea-ice retreat and advance in

  18. Sea-ice indicators of polar bear habitat

    Science.gov (United States)

    Stern, Harry L.; Laidre, Kristin L.

    2016-09-01

    Nineteen subpopulations of polar bears (Ursus maritimus) are found throughout the circumpolar Arctic, and in all regions they depend on sea ice as a platform for traveling, hunting, and breeding. Therefore polar bear phenology - the cycle of biological events - is linked to the timing of sea-ice retreat in spring and advance in fall. We analyzed the dates of sea-ice retreat and advance in all 19 polar bear subpopulation regions from 1979 to 2014, using daily sea-ice concentration data from satellite passive microwave instruments. We define the dates of sea-ice retreat and advance in a region as the dates when the area of sea ice drops below a certain threshold (retreat) on its way to the summer minimum or rises above the threshold (advance) on its way to the winter maximum. The threshold is chosen to be halfway between the historical (1979-2014) mean September and mean March sea-ice areas. In all 19 regions there is a trend toward earlier sea-ice retreat and later sea-ice advance. Trends generally range from -3 to -9 days decade-1 in spring and from +3 to +9 days decade-1 in fall, with larger trends in the Barents Sea and central Arctic Basin. The trends are not sensitive to the threshold. We also calculated the number of days per year that the sea-ice area exceeded the threshold (termed ice-covered days) and the average sea-ice concentration from 1 June through 31 October. The number of ice-covered days is declining in all regions at the rate of -7 to -19 days decade-1, with larger trends in the Barents Sea and central Arctic Basin. The June-October sea-ice concentration is declining in all regions at rates ranging from -1 to -9 percent decade-1. These sea-ice metrics (or indicators of habitat change) were designed to be useful for management agencies and for comparative purposes among subpopulations. We recommend that the National Climate Assessment include the timing of sea-ice retreat and advance in future reports.

  19. The role of the margins in ice stream dynamics

    Science.gov (United States)

    Echelmeyer, Keith; Harrison, William

    1993-07-01

    At first glance, it would appear that the bed of the active ice stream plays a much more important role in the overall force balance than do the margins, especially because the ratio of the half-width to depth for a typical ice stream is large (15:1 to 50:1). On the other hand, recent observations indicate that at least part of the ice stream is underlain by a layer of very weak till (shear strength about 2 kPa), and this weak basal layer would then imply that some or all of the resistive drag is transferred to the margins. In order to address this question, a detailed velocity profile near Upstream B Camp, which extends from the center of the ice stream, across the chaotic shear margin, and onto the Unicorn, which is part of the slow-moving ice sheet was measured. Comparison of this observed velocity profile with finite-element models of flow shows several interesting features. First, the shear stress at the margin is on the order of 130 kPa, while the mean value along the bed is about 15 kPa. Integration of these stresses along the boundaries indicates that the margins provide 40 to 50 percent, and the bed, 60 to 40 percent of the total resistive drag needed to balance the gravitational driving stress in this region. (The range of values represents calculations for different values of surface slope.) Second, the mean basal stress predicted by the models shows that the entire bed cannot be blanketed by the weak till observed beneath upstream B - instead there must be a distribution of weak till and 'sticky spots' (e.g., 85 percent till and 15 percent sticky spots of resistive stress equal to 100 kPa). If more of the bed were composed of weak till, then the modeled velocity would not match that observed. Third, the ice must exhibit an increasing enhancement factor as the margins are approached (E equals 10 in the chaotic zone), in keeping with laboratory measurements on ice under prolonged shear strain. Also, there is either a narrow zone of somewhat stiffer ice (E

  20. Geomorphology and till architecture of terrestrial palaeo-ice streams of the southwest Laurentide Ice Sheet: A borehole stratigraphic approach

    Science.gov (United States)

    Norris, Sophie L.; Evans, David J. A.; Cofaigh, Colm Ó.

    2018-04-01

    A multidimensional study, utilising geomorphological mapping and the analysis of regional borehole stratigraphy, is employed to elucidate the regional till architecture of terrestrial palaeo-ice streams relating to the Late Wisconsinan southwest Laurentide Ice Sheet. Detailed mapping over a 57,400 km2 area of southwestern Saskatchewan confirms previous reconstructions of a former southerly flowing ice stream, demarcated by a 800 km long corridor of megaflutes and mega-scale glacial lineations (Ice Stream 1) and cross cut by three, formerly southeast flowing ice streams (Ice Streams 2A, B and C). Analysis of the lithologic and geophysical characteristics of 197 borehole samples within these corridors reveals 17 stratigraphic units comprising multiple tills and associated stratified sediments overlying preglacial deposits, the till thicknesses varying with both topography and distance down corridor. Reconciling this regional till architecture with the surficial geomorphology reveals that surficial units are spatially consistent with a dynamic switch in flow direction, recorded by the cross cutting corridors of Ice Streams 1, 2A, B and C. The general thickening of tills towards lobate ice stream margins is consistent with subglacial deformation theory and variations in this pattern on a more localised scale are attributed to influences of subglacial topography including thickening at buried valley margins, thinning over uplands and thickening in overridden ice-marginal landforms.

  1. DMSP SSM/I Daily and Monthly Polar Gridded Bootstrap Sea Ice Concentrations

    Data.gov (United States)

    National Aeronautics and Space Administration — DMSP SSM/I Daily and Monthly Polar Gridded Bootstrap Sea Ice Concentrations in polar stereographic projection currently include Defense Meteorological Satellite...

  2. The isotopic composition of methane in polar ice cores

    Science.gov (United States)

    Craig, H.; Chou, C. C.; Welhan, J. A.; Stevens, C. M.; Engelkemeir, A.

    1988-01-01

    Air bubbles in polar ice cores indicate that about 300 years ago the atmospheric mixing ratio of methane began to increase rapidly. Today the mixing ratio is about 1.7 parts per million by volume, and, having doubled once in the past several hundred years, it will double again in the next 60 years if current rates continue. Carbon isotope ratios in methane up to 350 years in age have been measured with as little as 25 kilograms of polar ice recovered in 4-meter-long ice-core segments. The data show that: (1) in situ microbiology or chemistry has not altered the ice-core methane concentrations, and (2) that the carbon-13 to carbon-12 ratio of atmospheric CH4 in ice from 100 years and 300 years ago was about 2 per mil lower than at present. Atmospheric methane has a rich spectrum of isotopic sources: the ice-core data indicate that anthropogenic burning of the earth's biomass is the principal cause of the recent C-13H4 enrichment, although other factors may also contribute.

  3. Microstructural Location and Composition of Impurities in Polar Ice Cores, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set contains measurements of impurities and ions in three polar ice cores: the Vostok 5G ice core and the Byrd ice core from Antarctica, and the Greenland...

  4. ICESat's First Year of Measurements Over the Polar Ice Sheets

    Science.gov (United States)

    Shuman, C. A.

    2004-05-01

    NASA's Ice, Cloud and Land Elevation Satellite (ICESat) mission was developed to measure changes in elevation of the Greenland and Antarctic ice sheets. Its primary mission goal is to significantly refine estimates of polar ice sheet mass balance. Obtaining precise, spatially dense, ice sheet elevations through time is the first step towards this goal. ICESat data will then enable study of associations between observed ice changes and dynamic or climatic forcing factors, and thus enable improved estimation of the present and future contributions of the ice sheets to global sea level rise. ICESat was launched on January 12, 2003 and acquired science data from February 20th to March 29th with the first of the three lasers of the Geoscience Laser Altimeter System (GLAS). Data acquisition with the second laser began on September 25th and continued until November 18th, 2003. For one-year change detection, the second laser is scheduled for operation from approximately February 17th to March 20th, 2004. Additional operational periods will be selected to 1) enable periodic measurements through the year, and 2) to support of other NASA Earth Science Enterprise missions and activities. To obtain these precise ice sheet elevations, GLAS has a 1064 nm wavelength laser operating at 40 Hz with a designed range precision of about 10 cm. The laser footprints are about 70 m in diameter on the Earth's surface and are spaced every 172 m along-track. The on-board GPS receiver enables radial orbit determinations to an accuracy better than 5 cm. The star-tracking attitude-determination system will enable laser footprints to be located to 6 m horizontally when attitude calibration is completed. The orbital altitude averages 600 km at an inclination of 94 degrees with coverage extending from 86 degrees N and S latitude. The spacecraft attitude can be controlled to point the laser beam to within 50 m of surface reference tracks over the ice sheets and to point off-nadir up to 5 degrees to

  5. Ice stream behaviour and deglaciation of the Scandinavian Ice Sheet in the Kuittijärvi area, Russian Karelia

    Directory of Open Access Journals (Sweden)

    Juha-Pekka Lunkka

    2008-01-01

    Full Text Available Glacial landforms of the Lake Kuittijärvi area, Russian Karelia, which covers an area of more than 7000 km^2, were studied in detail using aerial photography and satellite imagery methods and on-site field observations. This was done to reconstruct a detailed historyof Scandinavian ice sheet behaviour in the Lake Kuittijärvi area. The results indicate that the Lake Tuoppajärvi sub-ice stream (TIS that formed the northern part of the Kuusamo-White Sea ice stream and the Lake Kuittijärvi sub-ice stream (KIS, which was part of theNorthern Karelian ice stream, operated in the area during the last deglaciation. Subglacially formed lineation patterns associated with other indicative landforms such as end moraines and esker ridges indicate a clear age relationship between the ice streams’ activity and that the KIS was active after the linear landforms were created by the TIS. It is estimated that deglaciation of the TIS from the Kalevala end moraine to the Lake Pääjärvi end moraine took place between ca. 11 300 – 10 900 calendar years ago. It seems that the terminus of the KIS marker by the Kalevala end moraine was also formed around 11 300 calendar years ago but the KIS remained active longer than the TIS. Both of these sub-ice streams terminated into a glacial lake that was part of a larger White Sea Basin ice lake.

  6. Ice condensation on sulfuric acid tetrahydrate: Implications for polar stratospheric ice clouds

    Directory of Open Access Journals (Sweden)

    T. J. Fortin

    2003-01-01

    Full Text Available The mechanism of ice nucleation to form Type 2 PSCs is important for controlling the ice particle size and hence the possible dehydration in the polar winter stratosphere. This paper probes heterogeneous ice nucleation on sulfuric acid tetrahydrate (SAT. Laboratory experiments were performed using a thin-film, high-vacuum apparatus in which the condensed phase is monitored via Fourier transform infrared spectroscopy and water pressure is monitored with the combination of an MKS baratron and an ionization gauge. Results show that SAT is an efficient ice nucleus with a critical ice saturation ratio of S*ice = 1.3 to 1.02 over the temperature range 169.8-194.5 K. This corresponds to a necessary supercooling of 0.1-1.3 K below the ice frost point. The laboratory data is used as input for a microphysical/photochemical model to probe the effect that this heterogeneous nucleation mechanism could have on Type 2 PSC formation and stratospheric dehydration. In the model simulations, even a very small number of SAT particles (e.g., 10-3 cm-3 result in ice nucleation on SAT as the dominant mechanism for Type 2 PSC formation. As a result, Type 2 PSC formation is more widespread, leading to larger-scale dehydration. The characteristics of the clouds are controlled by the assumed number of SAT particles present, demonstrating that a proper treatment of SAT is critical for correctly modeling Type 2 PSC formation and stratospheric dehydration.

  7. Polar Stereographic Valid Ice Masks Derived from National Ice Center Monthly Sea Ice Climatologies, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — These valid ice masks provide a way to remove spurious ice caused by residual weather effects and land spillover in passive microwave data. They are derived from the...

  8. Bringing Society to a Changing Polar Ocean: Polar Interdisciplinary Coordinated Education (ICE)

    Science.gov (United States)

    Schofield, O.

    2015-12-01

    Environmental changes in the Arctic and Antarctic appear to be accelerating and scientists are trying to understand both the patterns and the impacts of change. These changes will have profound impact on humanity and create a need for public education about these critical habitats. We have focused on a two-pronged strategy to increase public awareness as well as enable educators to discuss comfortably the implications of climate change. Our first focus is on entraining public support through the development of science documentaries about the science and people who conduct it. Antarctic Edge is a feature length award-winning documentary about climate change that has been released in May 2015 and has garnered interest in movie theatres and on social media stores (NetFlix, ITunes). This broad outreach is coupled with our group's interest assisting educators formally. The majority of current polar education is focused on direct educator engagement through personal research experiences that have impact on the participating educators' classrooms. Polar Interdisciplinary Coordinated Education (ICE) proposes to improve educator and student engagement in polar sciences through exposure to scientists and polar data. Through professional development and the creation of data tools, Polar ICE will reduce the logistical costs of bringing polar science to students in grades 6-16. We will provide opportunities to: 1) build capacity of polar scientists in communicating and engaging with diverse audiences; 2) create scalable, in-person and virtual opportunities for educators and students to engage with polar scientists and their research through data visualizations, data activities, educator workshops, webinars, and student research symposia; and 3) evaluate the outcomes of Polar ICE and contribute to our understanding of science education practices. We will use a blended learning approach to promote partnerships and cross-disciplinary sharing. This combined multi-pronged approach

  9. Changes on the ice plain of Ice Stream B and Ross Ice Shelf

    Science.gov (United States)

    Shabtaie, Sion

    1993-01-01

    During the 1970's and 1980's, nearly 200 stations from which accurate, three dimensional position fixes have been obtained from TRANSIT satellites were occupied throughout the Ross Ice Shelf. We have transformed the elevations obtained by satellite altimetry to the same geodetic datum, and then applied a second transformation to reduce the geodetic heights to elevations above mean sea level using the GEM-10C geoidal height. On the IGY Ross Ice Shelf traverse between Oct. 1957 and Feb. 1958, an accurate method of barometric altimetry was used on a loop around the ice shelf that was directly tied to the sea at both ends of the travel route, thus providing absolute elevations. Comparisons of the two sets of data at 32 station pairs on floating ice show a mean difference of 0 +/- 1 m. The elevation data were also compared with theoretical values of elevations for a hydrostatically floating ice shelf. The mean difference between theoretical and measured values of elevations is -2 +/- 1 m.

  10. Crevasse-squeeze ridge corridors: Diagnostic features of late-stage palaeo-ice stream activity

    Science.gov (United States)

    Evans, David J. A.; Storrar, Robert D.; Rea, Brice R.

    2016-04-01

    A 200-km-long and 10-km-wide linear assemblage of till-filled geometrical ridges on the bed of the Maskwa palaeo-ice stream of the late Wisconsinan southwest Laurentide Ice Sheet are interpreted as crevasse-squeeze ridges (CSR) developed during internal flow unit reorganization, immediately prior to ice stream shutdown. Ridge orientations are predominantly orientated WNW-ESE, with a subordinate WSW-ENE alignment, both indicative of ice fracture development transverse to former ice stream flow, as indicated by NNE-SSW aligned MSGL. Subglacial till injection into basal and/or full depth, mode I and II crevasses occurred at the approximate centreline of the ice stream, in response to extension and fracturing. Landform preservation indicates that this took place during the final stages of ice streaming, immediately prior to ice stream shutdown. This linear zone of ice fracturing therefore likely represents the narrowing of the fast-flowing trunk, similar to the plug flow identified in some surging valley glaciers. Lateral drag between the final active flow unit and the slower moving ice on either side is likely recorded by the up-ice bending of the CSR limbs. The resulting CSR corridor, here related to an individual ice stream flow unit, constitutes a previously unreported style of crevasse infilling and contrasts with two existing CSR patterns: (1) wide arcuate zones of CSRs related to widespread fracturing within glacier surge lobes; and (2) narrow concentric arcs of CSRs and recessional push moraines related to submarginal till deformation at active temperate glacier lobes.

  11. Ross Ice Shelf airstream driven by polar vortex cyclone

    Science.gov (United States)

    Schultz, Colin

    2012-07-01

    The powerful air and ocean currents that flow in and above the Southern Ocean, circling in the Southern Hemisphere's high latitudes, form a barrier to mixing between Antarctica and the rest of the planet. Particularly during the austral winter, strong westerly winds isolate the Antarctic continent from heat, energy, and mass exchange, bolstering the scale of the annual polar ozone depletion and driving the continent's record-breaking low temperatures. Pushing through this wall of high winds, the Ross Ice Shelf airstream (RAS) is responsible for a sizable amount of mass and energy exchange from the Antarctic inland areas to lower latitudes. Sitting due south of New Zealand, the roughly 470,000-square-kilometer Ross Ice Shelf is the continent's largest ice shelf and a hub of activity for Antarctic research. A highly variable lower atmospheric air current, RAS draws air from the inland Antarctic Plateau over the Ross Ice Shelf and past the Ross Sea. Drawing on modeled wind patterns for 2001-2005, Seefeldt and Cassano identify the primary drivers of RAS.

  12. Arctic amplification: does it impact the polar jet stream?

    Directory of Open Access Journals (Sweden)

    Valentin P. Meleshko

    2016-10-01

    Full Text Available It has been hypothesised that the Arctic amplification of temperature changes causes a decrease in the northward temperature gradient in the troposphere, thereby enhancing the oscillation of planetary waves leading to extreme weather in mid-latitudes. To test this hypothesis, we study the response of the atmosphere to Arctic amplification for a projected summer sea-ice-free period using an atmospheric model with prescribed surface boundary conditions from a state-of-the-art Earth system model. Besides a standard global warming simulation, we also conducted a sensitivity experiment with sea ice and sea surface temperature anomalies in the Arctic. We show that when global climate warms, enhancement of the northward heat transport provides the major contribution to decrease the northward temperature gradient in the polar troposphere in cold seasons, causing more oscillation of the planetary waves. However, while Arctic amplification significantly enhances near-surface air temperature in the polar region, it is not large enough to invoke an increased oscillation of the planetary waves.

  13. Ice-dammed lateral lake and epishelf lake insights into Holocene dynamics of Marguerite Trough Ice Stream and George VI Ice Shelf, Alexander Island, Antarctic Peninsula

    Science.gov (United States)

    Davies, Bethan J.; Hambrey, Michael J.; Glasser, Neil F.; Holt, Tom; Rodés, Angél; Smellie, John L.; Carrivick, Jonathan L.; Blockley, Simon P. E.

    2017-12-01

    We present new data regarding the past dynamics of Marguerite Trough Ice Stream, George VI Ice Shelf and valley glaciers from Ablation Point Massif on Alexander Island, Antarctic Peninsula. This ice-free oasis preserves a geological record of ice stream lateral moraines, ice-dammed lakes, ice-shelf moraines and valley glacier moraines, which we dated using cosmogenic nuclide ages. We provide one of the first detailed sediment-landform assemblage descriptions of epishelf lake shorelines. Marguerite Trough Ice Stream imprinted lateral moraines against eastern Alexander Island at 120 m at Ablation Point Massif. During deglaciation, lateral lakes formed in the Ablation and Moutonnée valleys, dammed against the ice stream in George VI Sound. Exposure ages from boulders on these shorelines yielded ages of 13.9 to 9.7 ka. Following recession of the ice stream, George VI Ice Shelf formed in George VI Sound. An epishelf lake formed at 15-20 m asl in Ablation and Moutonnée valleys, dated from 9.4 to 4.6 ka, suggesting that the lake was stable and persistent for some 5000 years. Lake-level lowering occurred after this, with the lake level at 12 m at 3.1 ± 0.4 ka and at 5 m asl today. A readvance of the valley glaciers on Alexander Island at 4.4 ± 0.7 ka is recorded by valley glacier moraines overlying epishelf lake sediments. We speculate that the glacier readvance, which occurred during a period of warmth, may have been caused by a dynamic response of the glaciers to a lowering in surface elevation of George VI Ice Shelf.

  14. Stick-slip Cycles and Tidal Modulation of Ice Stream Flow

    Science.gov (United States)

    Lipovsky, B.; Dunham, E. M.

    2016-12-01

    The reactivation of a single dormant Antarctic ice stream would double the continent's mass imbalance. Despite importance of understanding the likelihood of such an event, direct observation of the basal processes that lead to the activation and stagnation of streaming ice are minimal. As the only ice stream undergoing stagnation, the Whillans Ice Plain (WIP) occupies a central role in our understanding of these subglacial processes. Complicating matters is the observation, from GPS records, that the WIP experiences most of its motion during episodes of rapid sliding. These sliding events are tidally modulated and separated by 12 hour periods of quiescence. We conduct numerical simulations of ice stream stick-slip cycles. Our simulations include rate- and state-dependent frictional sliding, tidal forcing, inertia, upstream loading in a cross-stream, thickness-averaged formulation. Our principal finding is that ice stream motion may respond to ocean tidal forcing with one of two end member behaviors. In one limit, tidally modulated slip events have rupture velocities that approach the shear wave speed and slip events have a duration that scales with the ice stream width divided by the shear wave speed. In the other limit, tidal modulation results in ice stream sliding velocities with lower amplitude variation but at much longer timescales, i.e. semi-diurnal and longer. This latter behavior more closely mimics the behavior of several active ice streams (Bindschadler, Rutford). We find that WIP slip events exist between these two end member behaviors: rupture velocities are far below the inertial limit yet sliding occurs only episodically. The continuum of sliding behaviors is governed by a critical ice stream width over which slip event nucleate. When the critical width is much longer than the ice stream width, slip events are unable to nucleate. The critical width depends on the subglacial effective pressure, ice thickness, and frictional and elastic constitutive

  15. ispace's Polar Ice Explorer: Commerically Exploring the Poles of the Moon

    Science.gov (United States)

    Calzada-Diaz, A.; Acierno, K.; Rasera, J. N.; Lamamy, J.-A.

    2018-04-01

    This work provides the background, rationales, and scientific objectives for the ispace Polar Ice Explorer Project, an ISRU exploratory mission that aims to provide data about the lunar polar environment.

  16. Polar bear and walrus response to the rapid decline in Arctic sea ice

    Science.gov (United States)

    Oakley, K.; Whalen, M.; Douglas, David C.; Udevitz, Mark S.; Atwood, Todd C.; Jay, C.

    2012-01-01

    The Arctic is warming faster than other regions of the world due to positive climate feedbacks associated with loss of snow and ice. One highly visible consequence has been a rapid decline in Arctic sea ice over the past 3 decades - a decline projected to continue and result in ice-free summers likely as soon as 2030. The polar bear (Ursus maritimus) and the Pacific walrus (Odobenus rosmarus divergens) are dependent on sea ice over the continental shelves of the Arctic Ocean's marginal seas. The continental shelves are shallow regions with high biological productivity, supporting abundant marine life within the water column and on the sea floor. Polar bears use sea ice as a platform for hunting ice seals; walruses use sea ice as a resting platform between dives to forage for clams and other bottom-dwelling invertebrates. How have sea ice changes affected polar bears and walruses? How will anticipated changes affect them in the future?

  17. Measurements of acetylene in air extracted from polar ice cores

    Science.gov (United States)

    Nicewonger, M. R.; Aydin, M.; Montzka, S. A.; Saltzman, E. S.

    2016-12-01

    Acetylene (ethyne) is a non-methane hydrocarbon emitted during combustion of fossil fuels, biofuels, and biomass. The major atmospheric loss pathway of acetylene is oxidation by hydroxyl radical with a lifetime estimated at roughly two weeks. The mean annual acetylene levels over Greenland and Antarctica are 250 ppt and 20 ppt, respectively. Firn air measurements suggest atmospheric acetylene is preserved unaltered in polar snow and firn. Atmospheric reconstructions based on firn air measurements indicate acetylene levels rose significantly during the twentieth century, peaked near 1980, then declined to modern day levels. This historical trend is similar to that of other fossil fuel-derived non-methane hydrocarbons. In the preindustrial atmosphere, acetylene levels should primarily reflect emissions from biomass burning. In this study, we present the first measurements of acetylene in preindustrial air extracted from polar ice cores. Air from fluid and dry-drilled ice cores from Summit, Greenland and WAIS-Divide Antarctica is extracted using a wet-extraction technique. The ice core air is analyzed using gas chromatography and high-resolution mass spectrometry. Between 1400 to 1800 C.E., acetylene levels over Greenland and Antarctica varied between roughly 70-120 ppt and 10-30 ppt, respectively. The preindustrial Greenland acetylene levels are significantly lower than modern levels, reflecting the importance of northern hemisphere fossil fuel sources today. The preindustrial Antarctic acetylene levels are comparable to modern day levels, indicating similar emissions in the preindustrial atmosphere, likely from biomass burning. The implications of the preindustrial atmospheric acetylene records from both hemispheres will be discussed.

  18. A tale of two polar bear populations: Ice habitat, harvest, and body condition

    Science.gov (United States)

    Rode, Karyn D.; Peacock, Elizabeth; Taylor, Mitchell K.; Stirling, Ian; Born, Erik W.; Laidre, Kristin L.; Wiig, Øystein

    2012-01-01

    One of the primary mechanisms by which sea ice loss is expected to affect polar bears is via reduced body condition and growth resulting from reduced access to prey. To date, negative effects of sea ice loss have been documented for two of 19 recognized populations. Effects of sea ice loss on other polar bear populations that differ in harvest rate, population density, and/or feeding ecology have been assumed, but empirical support, especially quantitative data on population size, demography, and/or body condition spanning two or more decades, have been lacking. We examined trends in body condition metrics of captured bears and relationships with summertime ice concentration between 1977 and 2010 for the Baffin Bay (BB) and Davis Strait (DS) polar bear populations. Polar bears in these regions occupy areas with annual sea ice that has decreased markedly starting in the 1990s. Despite differences in harvest rate, population density, sea ice concentration, and prey base, polar bears in both populations exhibited positive relationships between body condition and summertime sea ice cover during the recent period of sea ice decline. Furthermore, females and cubs exhibited relationships with sea ice that were not apparent during the earlier period (1977–1990s) when sea ice loss did not occur. We suggest that declining body condition in BB may be a result of recent declines in sea ice habitat. In DS, high population density and/or sea ice loss, may be responsible for the declines in body condition.

  19. Rapid grounding line migration induced by internal variability of a marine-terminating ice stream

    Science.gov (United States)

    Robel, A.; Schoof, C.; Tziperman, E.

    2013-12-01

    Numerous studies have found significant variability in the velocity of ice streams to be a prominent feature of geomorphologic records in the Siple Coast (Catania et al. 2012) and other regions in West Antarctica (Dowdeswell et al. 2008). Observations indicate that grounding line position is strongly influenced by ice stream variability, producing rapid grounding line migration in the recent past (Catania et al. 2006) and the modern (Joughin & Tulaczyk 2002). We analyze the interaction of grounding line mass flux and position in a marine-terminating ice stream using a stretch-coordinate flowline model. This model is based on that described in Schoof (2007), with a mesh refined near the grounding line to ensure accurate resolution of the mechanical transition zone. Here we have added lateral shear stress (Dupont & Alley 2005) and an undrained plastic bed (Tulaczyk et al. 2000). The parameter dependence of ice stream variability seen in this model compares favorably to both simpler (Robel et al. 2013) and more complex (van der Wel et al. 2013) models, though with some key differences. We find that thermally-induced internal ice stream variability can cause very rapid grounding line migration even in the absence of retrograde bed slopes or external forcing. Activation waves propagate along the ice stream length and trigger periods of rapid grounding line migration. We compare the behavior of the grounding line due to internal ice stream variability to changes triggered externally at the grounding line such as the rapid disintegration of buttressing ice shelves. Implications for Heinrich events and the Marine Ice Sheet Instability are discussed.

  20. A Microbial Community in Sediments Beneath the Western Antarctic Ice Sheet, Ice Stream C (Kamb)

    Science.gov (United States)

    Skidmore, M.; Han, S.; Foo, W.; Bui, D.; Lanoil, B.

    2004-12-01

    In 2000, an ice-drilling project focusing on the "sticky spot" of Ice Stream C recovered cores of sub-glacial sediments from beneath the Western Antarctic Ice Sheet. We have characterized several chemical and microbiological parameters of the sole intact sediment core. Pore waters extracted from these sediments were brackish and some were supersaturated with respect to calcite. Ion chromatography demonstrated the presence of several organic acids at low, but detectable, levels in the pore water. DAPI direct cell counts were approximately 107 cells g-1. Aerobic viable plate counts were much lower than direct cell counts; however, they were two orders of magnitude higher on plates incubated at low temperature (4 ° C; 3.63 x 105 CFU ml-1) than at higher temperatures (ca. 22° C; 1.5 x 103 CFU ml-1); no colonies were detected on plates incubated anaerobically at either temperature. 16S rDNA clone library analysis indicates extremely limited bacterial diversity in these samples: six phylogenetic clades were detected. The three dominant bacterial phylogenetic clades in the clone libraries (252 clones total) were most closely related to Thiobacillus thioparus (180 clones), Polaromonas vacuolata (34 clones), and Gallionella ferruginea (35 clones) and their relatives; one clone each represented the other three phylogenetic clades (most closely related to Ralstonia pickettii, Lysobacter antibioticus, and Xylella fastidiosa, respectively). These sequences match closely with sequences previously obtained from other subglacial environments in Alaska, Ellesmere Island, Canada and New Zealand. Implications of this microbial community to subglacial chemistry and microbial biogeography will be discussed.

  1. Solid and gaseous inclusions in the EDML deep ice core: origins and implications for the physical properties of polar ice

    Science.gov (United States)

    Faria, S. H.; Kipfstuhl, S.; Garbe, C. S.; Bendel, V.; Weikusat, C.; Weikusat, I.

    2010-12-01

    The great value of polar deep ice cores stems mainly from two essential features of polar ice: its crystalline structure and its impurities. They determine the physical properties of the ice matrix and provide proxies for the investigation of past climates. Experience shows that these two essential features of polar ice manifest themselves in a multiscale diversity of dynamic structures, including dislocations, grain boundaries, solid particles, air bubbles, clathrate hydrates and cloudy bands, among others. The fact that these structures are dynamic implies that they evolve with time through intricate interactions between the crystalline structure, impurities, and the ice flow. Records of these interactions have been carefully investigated in samples of the EPICA deep ice core drilled in Dronning Maud Land, Antarctica (75°S, 0°E, 2882 m elevation, 2774.15 m core length). Here we show how the distributions of sizes and shapes of air bubbles correlate with impurities and the crystalline structure, how the interaction between moving grain boundaries and micro-inclusions changes with ice depth and temperature, as well as the possible causes for the abrupt change in ice rheology observed in the MIS6-MIS5e transition. We also discuss how these observations may affect the flow of the ice sheet and the interpretation of paleoclimate records. Micrograph of an EDML sample from 555m depth. One can identify air bubbles (dark, round objects), microinclusions (tiny defocused spots), and a grain boundary pinned by a bubble. The width of the image is 700 micrometers.

  2. Projected polar bear sea ice habitat in the Canadian Arctic Archipelago.

    Directory of Open Access Journals (Sweden)

    Stephen G Hamilton

    Full Text Available Sea ice across the Arctic is declining and altering physical characteristics of marine ecosystems. Polar bears (Ursus maritimus have been identified as vulnerable to changes in sea ice conditions. We use sea ice projections for the Canadian Arctic Archipelago from 2006 - 2100 to gain insight into the conservation challenges for polar bears with respect to habitat loss using metrics developed from polar bear energetics modeling.Shifts away from multiyear ice to annual ice cover throughout the region, as well as lengthening ice-free periods, may become critical for polar bears before the end of the 21st century with projected warming. Each polar bear population in the Archipelago may undergo 2-5 months of ice-free conditions, where no such conditions exist presently. We identify spatially and temporally explicit ice-free periods that extend beyond what polar bears require for nutritional and reproductive demands.Under business-as-usual climate projections, polar bears may face starvation and reproductive failure across the entire Archipelago by the year 2100.

  3. Projected polar bear sea ice habitat in the Canadian Arctic Archipelago.

    Science.gov (United States)

    Hamilton, Stephen G; Castro de la Guardia, Laura; Derocher, Andrew E; Sahanatien, Vicki; Tremblay, Bruno; Huard, David

    2014-01-01

    Sea ice across the Arctic is declining and altering physical characteristics of marine ecosystems. Polar bears (Ursus maritimus) have been identified as vulnerable to changes in sea ice conditions. We use sea ice projections for the Canadian Arctic Archipelago from 2006 - 2100 to gain insight into the conservation challenges for polar bears with respect to habitat loss using metrics developed from polar bear energetics modeling. Shifts away from multiyear ice to annual ice cover throughout the region, as well as lengthening ice-free periods, may become critical for polar bears before the end of the 21st century with projected warming. Each polar bear population in the Archipelago may undergo 2-5 months of ice-free conditions, where no such conditions exist presently. We identify spatially and temporally explicit ice-free periods that extend beyond what polar bears require for nutritional and reproductive demands. Under business-as-usual climate projections, polar bears may face starvation and reproductive failure across the entire Archipelago by the year 2100.

  4. A one stop website for sharing sea ice, ocean and ice sheet data over the polar regions

    Science.gov (United States)

    Chen, Z.; Cheng, X.; Liu, J.; Hui, F.; Ding, Y.

    2017-12-01

    The polar regions, including the Arctic and Antarctic, are changing rapidly. Our capabilities to remotely monitor the state of the polar regions are increasing greatly. Satellite and airborne technologies have been deployed and further improvements are underway. Meanwhile, various algorithms have been developed to retrieve important parameters to maximize the effectiveness of available remote sensing data. These technologies and algorithms promise to greatly increase our understanding of variations in sea ice, ocean and ice sheet. However, so much information is scattered out there. It is challenging to find exactly what you are looking for by just searching it through the network. Therefore, we try to establish a common platform to sharing some key parameters for the polar regions. A group of scientists from Beijing Normal University and University at Albany developed a website as a "one-stop shop" for the current state of the polar regions. The website provides real-time (or near real-time) key parameters derived from a variety of operational satellites in an understandable, accessible and credible way. Three types of parameter, which are sea ice, ocean and ice sheet respectively, are shown and available to be downloaded in the website. Several individual parameters are contained in a specific type of parameter. The parameters of sea ice include sea ice concentration, sea ice thickness, melt pond, sea ice leads and sea ice drift. The ocean parameters contain sea surface temperature and sea surface wind. Ice sheet balance, ice velocity and some other parameters are classified into the type of ice sheet parameter. Some parameters are well-calibrated and available to be obtained from other websites, such as sea ice concentration, sea ice thickness sea surface temperature. Since these parameters are retrieved from different sensors, such as SSMI, AMSR2 etc., data format, spatial resolution of the parameters are not unified. We collected and reprocessed these

  5. Analytical solutions for the surface response to small amplitude perturbations in boundary data in the shallow-ice-stream approximation

    Directory of Open Access Journals (Sweden)

    G. H. Gudmundsson

    2008-07-01

    Full Text Available New analytical solutions describing the effects of small-amplitude perturbations in boundary data on flow in the shallow-ice-stream approximation are presented. These solutions are valid for a non-linear Weertman-type sliding law and for Newtonian ice rheology. Comparison is made with corresponding solutions of the shallow-ice-sheet approximation, and with solutions of the full Stokes equations. The shallow-ice-stream approximation is commonly used to describe large-scale ice stream flow over a weak bed, while the shallow-ice-sheet approximation forms the basis of most current large-scale ice sheet models. It is found that the shallow-ice-stream approximation overestimates the effects of bed topography perturbations on surface profile for wavelengths less than about 5 to 10 ice thicknesses, the exact number depending on values of surface slope and slip ratio. For high slip ratios, the shallow-ice-stream approximation gives a very simple description of the relationship between bed and surface topography, with the corresponding transfer amplitudes being close to unity for any given wavelength. The shallow-ice-stream estimates for the timescales that govern the transient response of ice streams to external perturbations are considerably more accurate than those based on the shallow-ice-sheet approximation. In particular, in contrast to the shallow-ice-sheet approximation, the shallow-ice-stream approximation correctly reproduces the short-wavelength limit of the kinematic phase speed given by solving a linearised version of the full Stokes system. In accordance with the full Stokes solutions, the shallow-ice-sheet approximation predicts surface fields to react weakly to spatial variations in basal slipperiness with wavelengths less than about 10 to 20 ice thicknesses.

  6. Evidence of unfrozen liquids and seismic anisotropy at the base of the polar ice sheets

    Science.gov (United States)

    Wittlinger, Gérard; Farra, Véronique

    2015-03-01

    We analyze seismic data from broadband stations located on the Antarctic and Greenland ice sheets to determine polar ice seismic velocities. P-to-S converted waves at the ice/rock interface and inside the ice sheets and their multiples (the P-receiver functions) are used to estimate in-situ P-wave velocity (Vp) and P-to-S velocity ratio (Vp/Vs) of polar ice. We find that the polar ice sheets have a two-layer structure; an upper layer of variable thickness (about 2/3 of the total thickness) with seismic velocities close to the standard ice values, and a lower layer of approximately constant thickness with standard Vp but ∼25% smaller Vs. The lower layer ceiling corresponds approximately to the -30 °C isotherm. Synthetic modeling of P-receiver functions shows that strong seismic anisotropy and low vertical S velocity are needed in the lower layer. The seismic anisotropy results from the preferred orientation of ice crystal c-axes toward the vertical. The low vertical S velocity may be due to the presence of unfrozen liquids resulting from premelting at grain joints and/or melting of chemical solutions buried in the ice. The strongly preferred ice crystal orientation fabric and the unfrozen fluids may facilitate polar ice sheet basal flow.

  7. Interannual observations and quantification of summertime H2O ice deposition on the Martian CO2 ice south polar cap

    Science.gov (United States)

    Brown, Adrian J.; Piqueux, Sylvain; Titus, Timothy N.

    2014-01-01

    The spectral signature of water ice was observed on Martian south polar cap in 2004 by the Observatoire pour l'Mineralogie, l'Eau les Glaces et l'Activite (OMEGA) ( Bibring et al., 2004). Three years later, the OMEGA instrument was used to discover water ice deposited during southern summer on the polar cap ( Langevin et al., 2007). However, temporal and spatial variations of these water ice signatures have remained unexplored, and the origins of these water deposits remains an important scientific question. To investigate this question, we have used observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter (MRO) spacecraft of the southern cap during austral summer over four Martian years to search for variations in the amount of water ice. We report below that for each year we have observed the cap, the magnitude of the H2O ice signature on the southern cap has risen steadily throughout summer, particularly on the west end of the cap. The spatial extent of deposition is in disagreement with the current best simulations of deposition of water ice on the south polar cap (Montmessin et al., 2007). This increase in water ice signatures is most likely caused by deposition of atmospheric H2O ice and a set of unusual conditions makes the quantification of this transport flux using CRISM close to ideal. We calculate a ‘minimum apparent‘ amount of deposition corresponding to a thin H2O ice layer of 0.2 mm (with 70% porosity). This amount of H2O ice deposition is 0.6–6% of the total Martian atmospheric water budget. We compare our ‘minimum apparent’ quantification with previous estimates. This deposition process may also have implications for the formation and stability of the southern CO2 ice cap, and therefore play a significant role in the climate budget of modern day Mars.

  8. Effects of a controlled under-ice oil spill on invertebrates of an arctic and a subarctic stream

    Energy Technology Data Exchange (ETDEWEB)

    Miller, M.C.; Stout, J.R.; Alexander, V.

    1986-01-01

    The short-term drift of macroinvertebrates is documented following two controlled oil spills placed under ice in an arctic (Imnavait Creek) and subarctic (Poker-Caribou Creek) stream just as ice covered the water in early winter. No mortality was observed, but several species responded by differentially drifting from the oil-impacted areas during the following days. In the arctic stream, Trichotanypus posticalis (Diptera) showed a significant increase in drift for the first few days. There was also an overall increase in drift of total organisms post spill. Phaenospectra sp. 1, the numerical dominant, decreased its nocturnal drifting compared with the upstream control station in the 5 days post spill. In the subarctic stream, Skwala sp. 1 (Plecoptera), Prosimulium sp. 1 (Simulidae) and Pseudodiamesa sp. 1 showed significant increase din drift post spill. Among the species of benthic invertebrates sampled with a Hess sampler (WILDCO, Saginaw, Mich.), only the density of Nemoura sp. 1 declined significantly post spill. Polar ordinations using percent difference showed that the oil-treated stations separated from the control stations in both the drift and the Hess bottom samples. Colonization of artificial substrates in Imnavait Creek during the winter following the spill was almost non-existent. In Poker-Caribou Creek much colonization took place over the winter with significantly more occurring on unoiled rocks as compared with oiled rocks.

  9. Ice Motion and Topography Near Margin Areas of Kamb Ice Stream, Antarctica, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set includes ice motion and topography measurements that were taken by measuring movement and altitude of poles set in the West Antarctic Ice Shelf. The...

  10. Dual HF radar study of the subauroral polarization stream

    Directory of Open Access Journals (Sweden)

    R. A. Makarevich

    2008-01-01

    Full Text Available The dual HF radars comprising the Tasman International Geophysical Environment Radar (TIGER system often observe localized high-velocity F-region plasma flows (≥1500 m/s in the midnight sector (20:00–02:00 MLT at magnetic latitudes as low as Λ=60° S. The flow channels exhibit large variability in the latitudinal extent and electric field strength, and are similar to the subauroral polarization stream or SAPS, a plasma convection feature thought to be related to the polarization electric field due to the charge separation during substorm and storm development. In this study, the 2-D plasma drift velocity within the channel is derived for each of the two TIGER radars from the maximum velocities measured in all 16 radar beams within the latitudinally narrow channel, and the time variation of the subauroral electric field is examined near substorm onset. It is demonstrated that the flow channel often does not have a clear onset, rather it manifests differently in different phases of its evolution and can persist for at least two substorm cycles. During the growth phase the electric fields within the flow channel are difficult to distinguish from those of the background auroral convection but they start to increase near substorm onset and peak during the recovery phase, in contrast to what has been reported previously for auroral convection which peaks just before the substorm onset and falls sharply at the substorm onset. The response times to substorm onset range from −5 to +40 min and show some dependence on the substorm location with longer delays observed for substorms eastward of the radars' viewing area. The propagation velocity of the high-velocity region is also investigated by comparing the observations from the two closely-spaced TIGER radars. The observations are consistent with the notion that the polarization electric field is established with the energetic ions drifting westward and equatorward from the initial substorm

  11. The efficiency of mechanisms driving Subauroral Polarization Streams (SAPS

    Directory of Open Access Journals (Sweden)

    H. Wang

    2011-07-01

    Full Text Available We have investigated the seasonal and diurnal variation of SAPS (Subauroral Polarization Streams occurrence based on 3663 SAPS events identified in DMSP ion drift observations in the Northern Hemisphere during July 2001 and June 2003. Their relationships with high latitude convection electric field, substorm, and ionospheric conductivity have been addressed. SAPS occurrences show a clear seasonal and diurnal variation with the occurrence rates varying by a factor of 5. It is found that the convection electric field might play a dominant role in association with SAPS occurrence. Peak convection electric fields mark the occurrence maximum of SAPS. Substorm might play a secondary role related to SAPS occurrence. It account for the secondary maximum in SAPS occurrence rate during December solstice. Our work demonstrates that the substorm induced electric field can develop SAPS during relatively low global convection. Somewhat low fluxtube-integrated conductivity is favorable for SAPS to develop. Another topic is the temporal relationship between SAPS and substorm phases. SAPS can occur at substorm onset, substorm expansion and recovery phases. Most probably SAPS tend to occur 60 min/45 min after substorm onset during quiet/more disturbed geomagnetic activity, respectively. This indicates that enhanced global convection helps SAPS to develop quicker during substorms. The peak plasma velocity of SAPS is increased on average only by 5–10 % by the substorm process.

  12. Greenhouse gas mitigation can reduce sea-ice loss and increase polar bear persistence

    Science.gov (United States)

    Amstrup, Steven C.; Deweaver, E.T.; Douglas, David C.; Marcot, B.G.; Durner, George M.; Bitz, C.M.; Bailey, D.A.

    2010-01-01

    On the basis of projected losses of their essential sea-ice habitats, a United States Geological Survey research team concluded in 2007 that two-thirds of the worlds polar bears (Ursus maritimus) could disappear by mid-century if business-as-usual greenhouse gas emissions continue. That projection, however, did not consider the possible benefits of greenhouse gas mitigation. A key question is whether temperature increases lead to proportional losses of sea-ice habitat, or whether sea-ice cover crosses a tipping point and irreversibly collapses when temperature reaches a critical threshold. Such a tipping point would mean future greenhouse gas mitigation would confer no conservation benefits to polar bears. Here we show, using a general circulation model, that substantially more sea-ice habitat would be retained if greenhouse gas rise is mitigated. We also show, with Bayesian network model outcomes, that increased habitat retention under greenhouse gas mitigation means that polar bears could persist throughout the century in greater numbers and more areas than in the business-as-usual case. Our general circulation model outcomes did not reveal thresholds leading to irreversible loss of ice; instead, a linear relationship between global mean surface air temperature and sea-ice habitat substantiated the hypothesis that sea-ice thermodynamics can overcome albedo feedbacks proposed to cause sea-ice tipping points. Our outcomes indicate that rapid summer ice losses in models and observations represent increased volatility of a thinning sea-ice cover, rather than tipping-point behaviour. Mitigation-driven Bayesian network outcomes show that previously predicted declines in polar bear distribution and numbers are not unavoidable. Because polar bears are sentinels of the Arctic marine ecosystem and trends in their sea-ice habitats foreshadow future global changes, mitigating greenhouse gas emissions to improve polar bear status would have conservation benefits throughout

  13. Greenhouse gas mitigation can reduce sea-ice loss and increase polar bear persistence.

    Science.gov (United States)

    Amstrup, Steven C; Deweaver, Eric T; Douglas, David C; Marcot, Bruce G; Durner, George M; Bitz, Cecilia M; Bailey, David A

    2010-12-16

    On the basis of projected losses of their essential sea-ice habitats, a United States Geological Survey research team concluded in 2007 that two-thirds of the world's polar bears (Ursus maritimus) could disappear by mid-century if business-as-usual greenhouse gas emissions continue. That projection, however, did not consider the possible benefits of greenhouse gas mitigation. A key question is whether temperature increases lead to proportional losses of sea-ice habitat, or whether sea-ice cover crosses a tipping point and irreversibly collapses when temperature reaches a critical threshold. Such a tipping point would mean future greenhouse gas mitigation would confer no conservation benefits to polar bears. Here we show, using a general circulation model, that substantially more sea-ice habitat would be retained if greenhouse gas rise is mitigated. We also show, with Bayesian network model outcomes, that increased habitat retention under greenhouse gas mitigation means that polar bears could persist throughout the century in greater numbers and more areas than in the business-as-usual case. Our general circulation model outcomes did not reveal thresholds leading to irreversible loss of ice; instead, a linear relationship between global mean surface air temperature and sea-ice habitat substantiated the hypothesis that sea-ice thermodynamics can overcome albedo feedbacks proposed to cause sea-ice tipping points. Our outcomes indicate that rapid summer ice losses in models and observations represent increased volatility of a thinning sea-ice cover, rather than tipping-point behaviour. Mitigation-driven Bayesian network outcomes show that previously predicted declines in polar bear distribution and numbers are not unavoidable. Because polar bears are sentinels of the Arctic marine ecosystem and trends in their sea-ice habitats foreshadow future global changes, mitigating greenhouse gas emissions to improve polar bear status would have conservation benefits throughout

  14. Black carbon aerosols and the third polar ice cap

    Energy Technology Data Exchange (ETDEWEB)

    Menon, Surabi; Koch, Dorothy; Beig, Gufran; Sahu, Saroj; Fasullo, John; Orlikowski, Daniel

    2010-04-15

    Recent thinning of glaciers over the Himalayas (sometimes referred to as the third polar region) have raised concern on future water supplies since these glaciers supply water to large river systems that support millions of people inhabiting the surrounding areas. Black carbon (BC) aerosols, released from incomplete combustion, have been increasingly implicated as causing large changes in the hydrology and radiative forcing over Asia and its deposition on snow is thought to increase snow melt. In India BC emissions from biofuel combustion is highly prevalent and compared to other regions, BC aerosol amounts are high. Here, we quantify the impact of BC aerosols on snow cover and precipitation from 1990 to 2010 over the Indian subcontinental region using two different BC emission inventories. New estimates indicate that Indian BC emissions from coal and biofuel are large and transport is expected to expand rapidly in coming years. We show that over the Himalayas, from 1990 to 2000, simulated snow/ice cover decreases by {approx}0.9% due to aerosols. The contribution of the enhanced Indian BC to this decline is {approx}36%, similar to that simulated for 2000 to 2010. Spatial patterns of modeled changes in snow cover and precipitation are similar to observations (from 1990 to 2000), and are mainly obtained with the newer BC estimates.

  15. Slow-slip events on the Whillans Ice Plain, Antarctica, described using rate-and-state friction as an ice stream sliding law

    Science.gov (United States)

    Lipovsky, Bradley Paul; Dunham, Eric M.

    2017-04-01

    The Whillans Ice Plain (WIP), Antarctica, experiences twice daily tidally modulated stick-slip cycles. Slip events last about 30 min, have sliding velocities as high as ˜0.5 mm/s (15 km/yr), and have total slip ˜0.5 m. Slip events tend to occur during falling ocean tide: just after high tide and just before low tide. To reproduce these characteristics, we use rate-and-state friction, which is commonly used to simulate tectonic faulting, as an ice stream sliding law. This framework describes the evolving strength of the ice-bed interface throughout stick-slip cycles. We present simulations that resolve the cross-stream dimension using a depth-integrated treatment of an elastic ice layer loaded by tides and steady ice inflow. Steady sliding with rate-weakening friction is conditionally stable with steady sliding occurring for sufficiently narrow ice streams relative to a nucleation length. Stick-slip cycles occur when the ice stream is wider than the nucleation length or, equivalently, when effective pressures exceed a critical value. Ice streams barely wider than the nucleation length experience slow-slip events, and our simulations suggest that the WIP is in this slow-slip regime. Slip events on the WIP show a sense of propagation, and we reproduce this behavior by introducing a rate-strengthening region in the center of the otherwise rate-weakening ice stream. If pore pressures are raised above a critical value, our simulations predict that the WIP would exhibit quasi-steady tidally modulated sliding as observed on other ice streams. This study validates rate-and-state friction as a sliding law to describe ice stream sliding styles.

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

    Science.gov (United States)

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

    2016-04-01

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

  17. Perspectives for DNA studies on polar ice cores

    DEFF Research Database (Denmark)

    Hansen, Anders J.; Willerslev, E.

    2002-01-01

    Recently amplifiable ancient DNA was obtained from a Greenland ice core. The DNA revealed a diversity of fungi, plants, algae and protists and has thereby expanded the range of detectable organic material in fossil glacier ice. The results suggest that ancient DNA can be obtained from other ice c...

  18. The Big Science Questions About Mercury's Ice-Bearing Polar Deposits After MESSENGER

    Science.gov (United States)

    Chabot, N. L.; Lawrence, D. J.

    2018-05-01

    Mercury’s polar deposits provide many well-characterized locations that are known to have large expanses of exposed water ice and/or other volatile materials — presenting unique opportunities to address fundamental science questions.

  19. Survival and breeding of polar bears in the southern Beaufort Sea in relation to sea ice

    Science.gov (United States)

    Regehr, E.V.; Hunter, C.M.; Caswell, H.; Amstrup, Steven C.; Stirling, I.

    2010-01-01

    1. Observed and predicted declines in Arctic sea ice have raised concerns about marine mammals. In May 2008, the US Fish and Wildlife Service listed polar bears (Ursus maritimus) - one of the most ice-dependent marine mammals - as threatened under the US Endangered Species Act. 2. We evaluated the effects of sea ice conditions on vital rates (survival and breeding probabilities) for polar bears in the southern Beaufort Sea. Although sea ice declines in this and other regions of the polar basin have been among the greatest in the Arctic, to date population-level effects of sea ice loss on polar bears have only been identified in western Hudson Bay, near the southern limit of the species' range. 3. We estimated vital rates using multistate capture-recapture models that classified individuals by sex, age and reproductive category. We used multimodel inference to evaluate a range of statistical models, all of which were structurally based on the polar bear life cycle. We estimated parameters by model averaging, and developed a parametric bootstrap procedure to quantify parameter uncertainty. 4. In the most supported models, polar bear survival declined with an increasing number of days per year that waters over the continental shelf were ice free. In 2001-2003, the ice-free period was relatively short (mean 101 days) and adult female survival was high (0 ∙ 96-0 ∙ 99, depending on reproductive state). In 2004 and 2005, the ice-free period was longer (mean 135 days) and adult female survival was low (0 ∙ 73-0 ∙ 79, depending on reproductive state). Breeding rates and cub litter survival also declined with increasing duration of the ice-free period. Confidence intervals on vital rate estimates were wide. 5. The effects of sea ice loss on polar bears in the southern Beaufort Sea may apply to polar bear populations in other portions of the polar basin that have similar sea ice dynamics and have experienced similar, or more severe, sea ice declines. Our findings

  20. Survival and breeding of polar bears in the southern Beaufort Sea in relation to sea ice.

    Science.gov (United States)

    Regehr, Eric V; Hunter, Christine M; Caswell, Hal; Amstrup, Steven C; Stirling, Ian

    2010-01-01

    1. Observed and predicted declines in Arctic sea ice have raised concerns about marine mammals. In May 2008, the US Fish and Wildlife Service listed polar bears (Ursus maritimus) - one of the most ice-dependent marine mammals - as threatened under the US Endangered Species Act. 2. We evaluated the effects of sea ice conditions on vital rates (survival and breeding probabilities) for polar bears in the southern Beaufort Sea. Although sea ice declines in this and other regions of the polar basin have been among the greatest in the Arctic, to date population-level effects of sea ice loss on polar bears have only been identified in western Hudson Bay, near the southern limit of the species' range. 3. We estimated vital rates using multistate capture-recapture models that classified individuals by sex, age and reproductive category. We used multimodel inference to evaluate a range of statistical models, all of which were structurally based on the polar bear life cycle. We estimated parameters by model averaging, and developed a parametric bootstrap procedure to quantify parameter uncertainty. 4. In the most supported models, polar bear survival declined with an increasing number of days per year that waters over the continental shelf were ice free. In 2001-2003, the ice-free period was relatively short (mean 101 days) and adult female survival was high (0.96-0.99, depending on reproductive state). In 2004 and 2005, the ice-free period was longer (mean 135 days) and adult female survival was low (0.73-0.79, depending on reproductive state). Breeding rates and cub litter survival also declined with increasing duration of the ice-free period. Confidence intervals on vital rate estimates were wide. 5. The effects of sea ice loss on polar bears in the southern Beaufort Sea may apply to polar bear populations in other portions of the polar basin that have similar sea ice dynamics and have experienced similar, or more severe, sea ice declines. Our findings therefore are

  1. Ice Stream Slowdown Will Drive Long-Term Thinning of the Ross Ice Shelf, With or Without Ocean Warming

    Science.gov (United States)

    Campbell, Adam J.; Hulbe, Christina L.; Lee, Choon-Ki

    2018-01-01

    As time series observations of Antarctic change proliferate, it is imperative that mathematical frameworks through which they are understood keep pace. Here we present a new method of interpreting remotely sensed change using spatial statistics and apply it to the specific case of thickness change on the Ross Ice Shelf. First, a numerical model of ice shelf flow is used together with empirical orthogonal function analysis to generate characteristic patterns of response to specific forcings. Because they are continuous and scalable in space and time, the patterns allow short duration observations to be placed in a longer time series context. Second, focusing only on changes that are statistically significant, the synthetic response surfaces are used to extract magnitude and timing of past events from the observational data. Slowdown of Kamb and Whillans Ice Streams is clearly detectable in remotely sensed thickness change. Moreover, those past events will continue to drive thinning into the future.

  2. Increased Land Use by Chukchi Sea Polar Bears in Relation to Changing Sea Ice Conditions.

    Science.gov (United States)

    Rode, Karyn D; Wilson, Ryan R; Regehr, Eric V; St Martin, Michelle; Douglas, David C; Olson, Jay

    2015-01-01

    Recent observations suggest that polar bears (Ursus maritimus) are increasingly using land habitats in some parts of their range, where they have minimal access to their preferred prey, likely in response to loss of their sea ice habitat associated with climatic warming. We used location data from female polar bears fit with satellite radio collars to compare land use patterns in the Chukchi Sea between two periods (1986-1995 and 2008-2013) when substantial summer sea-ice loss occurred. In both time periods, polar bears predominantly occupied sea-ice, although land was used during the summer sea-ice retreat and during the winter for maternal denning. However, the proportion of bears on land for > 7 days between August and October increased between the two periods from 20.0% to 38.9%, and the average duration on land increased by 30 days. The majority of bears that used land in the summer and for denning came to Wrangel and Herald Islands (Russia), highlighting the importance of these northernmost land habitats to Chukchi Sea polar bears. Where bears summered and denned, and how long they spent there, was related to the timing and duration of sea ice retreat. Our results are consistent with other studies supporting increased land use as a common response of polar bears to sea-ice loss. Implications of increased land use for Chukchi Sea polar bears are unclear, because a recent study observed no change in body condition or reproductive indices between the two periods considered here. This result suggests that the ecology of this region may provide a degree of resilience to sea ice loss. However, projections of continued sea ice loss suggest that polar bears in the Chukchi Sea and other parts of the Arctic may increasingly use land habitats in the future, which has the potential to increase nutritional stress and human-polar bear interactions.

  3. Increased Land Use by Chukchi Sea Polar Bears in Relation to Changing Sea Ice Conditions.

    Directory of Open Access Journals (Sweden)

    Karyn D Rode

    Full Text Available Recent observations suggest that polar bears (Ursus maritimus are increasingly using land habitats in some parts of their range, where they have minimal access to their preferred prey, likely in response to loss of their sea ice habitat associated with climatic warming. We used location data from female polar bears fit with satellite radio collars to compare land use patterns in the Chukchi Sea between two periods (1986-1995 and 2008-2013 when substantial summer sea-ice loss occurred. In both time periods, polar bears predominantly occupied sea-ice, although land was used during the summer sea-ice retreat and during the winter for maternal denning. However, the proportion of bears on land for > 7 days between August and October increased between the two periods from 20.0% to 38.9%, and the average duration on land increased by 30 days. The majority of bears that used land in the summer and for denning came to Wrangel and Herald Islands (Russia, highlighting the importance of these northernmost land habitats to Chukchi Sea polar bears. Where bears summered and denned, and how long they spent there, was related to the timing and duration of sea ice retreat. Our results are consistent with other studies supporting increased land use as a common response of polar bears to sea-ice loss. Implications of increased land use for Chukchi Sea polar bears are unclear, because a recent study observed no change in body condition or reproductive indices between the two periods considered here. This result suggests that the ecology of this region may provide a degree of resilience to sea ice loss. However, projections of continued sea ice loss suggest that polar bears in the Chukchi Sea and other parts of the Arctic may increasingly use land habitats in the future, which has the potential to increase nutritional stress and human-polar bear interactions.

  4. Can polar bears use terrestrial foods to offset lost ice-based hunting opportunities?

    OpenAIRE

    Rode, Karyn D.; Robbins, Charles T.; Nelson, Lynne; Amstrup, Steven C.

    2015-01-01

    Increased land use by polar bears (Ursus maritimus) due to climate‐change‐induced reduction of their sea‐ice habitat illustrates the impact of climate change on species distributions and the difficulty of conserving a large, highly specialized carnivore in the face of this global threat. Some authors have suggested that terrestrial food consumption by polar bears will help them withstand sea‐ice loss as they are forced to spend increasing amounts of time on land. Here, we evaluate the nutriti...

  5. Statistical characterization of the Sub-Auroral Polarization Stream (SAPS)

    Science.gov (United States)

    Kunduri, B.; Baker, J. B.; Ruohoniemi, J. M.; Erickson, P. J.; Coster, A. J.; Oksavik, K.

    2017-12-01

    The Sub-Auroral Polarization Stream (SAPS) is a narrow region of westward directed plasma convection typically observed in the dusk-midnight sector equatorward of the main auroral oval. SAPS plays an important role in mid-latitude space weather dynamics and has a controlling influence on the evolution of large-scale plasma features, such as Storm Enhanced Density (SED) plumes. In this study, data from North American mid-latitude SuperDARN radars collected between January 2011 and December 2014 have been used to compile a database of SAPS events for statistical analysis. We examine the dependence of SAPS velocity magnitude and direction on geomagnetic activity and magnetic local time. The lowest speed limit and electric fields observed during SAPS are discussed and histograms of SAPS velocities for different Dst bins and MLAT-MLT locations are presented. We find significant differences in SAPS characteristics between periods of low and high geomagnetic activity, suggesting that SAPS are driven by different mechanisms during storm and non-storm conditions. To further explore this possibility, we have characterized the SAPS location and peak speed relative to the ionospheric trough specified by GPS Total Electron Content (TEC) data from the MIT Haystack Madrigal database. A particular emphasis is placed on identifying the extent to which the location, structure, and depth of the trough may play a controlling influence on SAPS speeds during storm and non-storm periods. The results are interpreted in terms of the current paradigm for active thermosphere-ionosphere feedback being an important component of SAPS physics.

  6. Can polar bears use terrestrial foods to offset lost ice-based hunting opportunities?

    Science.gov (United States)

    Rode, Karyn D.; Robbins, Charles T.; Nelson, Lynne; Amstrup, Steven C.

    2015-01-01

    Increased land use by polar bears (Ursus maritimus) due to climate-change-induced reduction of their sea-ice habitat illustrates the impact of climate change on species distributions and the difficulty of conserving a large, highly specialized carnivore in the face of this global threat. Some authors have suggested that terrestrial food consumption by polar bears will help them withstand sea-ice loss as they are forced to spend increasing amounts of time on land. Here, we evaluate the nutritional needs of polar bears as well as the physiological and environmental constraints that shape their use of terrestrial ecosystems. Only small numbers of polar bears have been documented consuming terrestrial foods even in modest quantities. Over much of the polar bear's range, limited terrestrial food availability supports only low densities of much smaller, resident brown bears (Ursus arctos), which use low-quality resources more efficiently and may compete with polar bears in these areas. Where consumption of terrestrial foods has been documented, polar bear body condition and survival rates have declined even as land use has increased. Thus far, observed consumption of terrestrial food by polar bears has been insufficient to offset lost ice-based hunting opportunities but can have ecological consequences for other species. Warming-induced loss of sea ice remains the primary threat faced by polar bears.

  7. Airborne geophysics for mesoscale observations of polar sea ice in a changing climate

    Science.gov (United States)

    Hendricks, S.; Haas, C.; Krumpen, T.; Eicken, H.; Mahoney, A. R.

    2016-12-01

    Sea ice thickness is an important geophysical parameter with a significant impact on various processes of the polar energy balance. It is classified as Essential Climate Variable (ECV), however the direct observations of the large ice-covered oceans are limited due to the harsh environmental conditions and logistical constraints. Sea-ice thickness retrieval by the means of satellite remote sensing is an active field of research, but current observational capabilities are not able to capture the small scale variability of sea ice thickness and its evolution in the presence of surface melt. We present an airborne observation system based on a towed electromagnetic induction sensor that delivers long range measurements of sea ice thickness for a wide range of sea ice conditions. The purpose-built sensor equipment can be utilized from helicopters and polar research aircraft in multi-role science missions. While airborne EM induction sounding is used in sea ice research for decades, the future challenge is the development of unmanned aerial vehicle (UAV) platform that meet the requirements for low-level EM sea ice surveys in terms of range and altitude of operations. The use of UAV's could enable repeated sea ice surveys during the the polar night, when manned operations are too dangerous and the observational data base is presently very sparse.

  8. Conservation status of polar bears (Ursus maritimus) in relation to projected sea-ice declines

    Science.gov (United States)

    Laidre, K. L.; Regehr, E. V.; Akcakaya, H. R.; Amstrup, S. C.; Atwood, T.; Lunn, N.; Obbard, M.; Stern, H. L., III; Thiemann, G.; Wiig, O.

    2016-12-01

    Loss of Arctic sea ice due to climate change is the most serious threat to polar bears (Ursus maritimus) throughout their circumpolar range. We performed a data-based sensitivity analysis with respect to this threat by evaluating the potential response of the global polar bear population to projected sea-ice conditions. We conducted 1) an assessment of generation length for polar bears, 2) developed of a standardized sea-ice metric representing important habitat characteristics for the species; and 3) performed population projections over three generations, using computer simulation and statistical models representing alternative relationships between sea ice and polar bear abundance. Using three separate approaches, the median percent change in mean global population size for polar bears between 2015 and 2050 ranged from -4% (95% CI = -62%, 50%) to -43% (95% CI = -76%, -20%). Results highlight the potential for large reductions in the global population if sea-ice loss continues. They also highlight the large amount of uncertainty in statistical projections of polar bear abundance and the sensitivity of projections to plausible alternative assumptions. The median probability of a reduction in the mean global population size of polar bears greater than 30% over three generations was approximately 0.71 (range 0.20-0.95. The median probability of a reduction greater than 50% was approximately 0.07 (range 0-0.35), and the probability of a reduction greater than 80% was negligible.

  9. Co-distribution of seabirds and their polar cod prey near the ice edge in southern Baffin Bay

    DEFF Research Database (Denmark)

    LeBlanc, Mathieu; Gauthier, S; Mosbech, Anders

    species, and age-1 polar cod found in bird stomachs were likely individuals associated to ice. At a large scale of hundreds of kilometers, seabirds and age-0 polar cod were more abundant in ice-covered habitats (30 to 100% ice concentration). At medium and small scale of 12.5 and 1 km respectively...

  10. Increased Arctic sea ice drift alters adult female polar bear movements and energetics.

    Science.gov (United States)

    Durner, George M; Douglas, David C; Albeke, Shannon E; Whiteman, John P; Amstrup, Steven C; Richardson, Evan; Wilson, Ryan R; Ben-David, Merav

    2017-09-01

    Recent reductions in thickness and extent have increased drift rates of Arctic sea ice. Increased ice drift could significantly affect the movements and the energy balance of polar bears (Ursus maritimus) which forage, nearly exclusively, on this substrate. We used radio-tracking and ice drift data to quantify the influence of increased drift on bear movements, and we modeled the consequences for energy demands of adult females in the Beaufort and Chukchi seas during two periods with different sea ice characteristics. Westward and northward drift of the sea ice used by polar bears in both regions increased between 1987-1998 and 1999-2013. To remain within their home ranges, polar bears responded to the higher westward ice drift with greater eastward movements, while their movements north in the spring and south in fall were frequently aided by ice motion. To compensate for more rapid westward ice drift in recent years, polar bears covered greater daily distances either by increasing their time spent active (7.6%-9.6%) or by increasing their travel speed (8.5%-8.9%). This increased their calculated annual energy expenditure by 1.8%-3.6% (depending on region and reproductive status), a cost that could be met by capturing an additional 1-3 seals/year. Polar bears selected similar habitats in both periods, indicating that faster drift did not alter habitat preferences. Compounding reduced foraging opportunities that result from habitat loss; changes in ice drift, and associated activity increases, likely exacerbate the physiological stress experienced by polar bears in a warming Arctic. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

  11. Snow and Ice Applications of AVHRR in Polar Regions: Report of a Workshop

    Science.gov (United States)

    Steffen, K.; Bindschadler, R.; Casassa, G.; Comiso, J.; Eppler, D.; Fetterer, F.; Hawkins, J.; Key, J.; Rothrock, D.; Thomas, R.; hide

    1993-01-01

    The third symposium on Remote Sensing of Snow and Ice, organized by the International Glaciological Society, took place in Boulder, Colorado, 17-22 May 1992. As part of this meeting a total of 21 papers was presented on snow and ice applications of Advanced Very High Resolution Radiometer (AVHRR) satellite data in polar regions. Also during this meeting a NASA sponsored Workshop was held to review the status of polar surface measurements from AVHRR. In the following we have summarized the ideas and recommendations from the workshop, and the conclusions of relevant papers given during the regular symposium sessions. The seven topics discussed include cloud masking, ice surface temperature, narrow-band albedo, ice concentration, lead statistics, sea-ice motion and ice-sheet studies with specifics on applications, algorithms and accuracy, following recommendations for future improvements. In general, we can affirm the strong potential of AVHRR for studying sea ice and snow covered surfaces, and we highly recommend this satellite data set for long-term monitoring of polar process studies. However, progress is needed to reduce the uncertainty of the retrieved parameters for all of the above mentioned topics to make this data set useful for direct climate applications such as heat balance studies and others. Further, the acquisition and processing of polar AVHRR data must become better coordinated between receiving stations, data centers and funding agencies to guarantee a long-term commitment to the collection and distribution of high quality data.

  12. Conservation status of polar bears (Ursus maritimus) in relation to projected sea-ice declines

    Science.gov (United States)

    Regehr, Eric V.; Laidre, Kristin L.; Akçakaya, H. Resit; Amstrup, Steven C.; Atwood, Todd C.; Lunn, Nicholas J.; Obbard, Martyn E.; Stern, Harry; Thiemann, Gregory W.; Wiig, Øystein

    2016-01-01

    Loss of Arctic sea ice owing to climate change is the primary threat to polar bears throughout their range. We evaluated the potential response of polar bears to sea-ice declines by (i) calculating generation length (GL) for the species, which determines the timeframe for conservation assessments; (ii) developing a standardized sea-ice metric representing important habitat; and (iii) using statistical models and computer simulation to project changes in the global population under three approaches relating polar bear abundance to sea ice. Mean GL was 11.5 years. Ice-covered days declined in all subpopulation areas during 1979–2014 (median −1.26 days year−1). The estimated probabilities that reductions in the mean global population size of polar bears will be greater than 30%, 50% and 80% over three generations (35–41 years) were 0.71 (range 0.20–0.95), 0.07 (range 0–0.35) and less than 0.01 (range 0–0.02), respectively. According to IUCN Red List reduction thresholds, which provide a common measure of extinction risk across taxa, these results are consistent with listing the species as vulnerable. Our findings support the potential for large declines in polar bear numbers owing to sea-ice loss, and highlight near-term uncertainty in statistical projections as well as the sensitivity of projections to different plausible assumptions.

  13. Conservation status of polar bears (Ursus maritimus) in relation to projected sea-ice declines.

    Science.gov (United States)

    Regehr, Eric V; Laidre, Kristin L; Akçakaya, H Resit; Amstrup, Steven C; Atwood, Todd C; Lunn, Nicholas J; Obbard, Martyn; Stern, Harry; Thiemann, Gregory W; Wiig, Øystein

    2016-12-01

    Loss of Arctic sea ice owing to climate change is the primary threat to polar bears throughout their range. We evaluated the potential response of polar bears to sea-ice declines by (i) calculating generation length (GL) for the species, which determines the timeframe for conservation assessments; (ii) developing a standardized sea-ice metric representing important habitat; and (iii) using statistical models and computer simulation to project changes in the global population under three approaches relating polar bear abundance to sea ice. Mean GL was 11.5 years. Ice-covered days declined in all subpopulation areas during 1979-2014 (median -1.26 days year -1 ). The estimated probabilities that reductions in the mean global population size of polar bears will be greater than 30%, 50% and 80% over three generations (35-41 years) were 0.71 (range 0.20-0.95), 0.07 (range 0-0.35) and less than 0.01 (range 0-0.02), respectively. According to IUCN Red List reduction thresholds, which provide a common measure of extinction risk across taxa, these results are consistent with listing the species as vulnerable. Our findings support the potential for large declines in polar bear numbers owing to sea-ice loss, and highlight near-term uncertainty in statistical projections as well as the sensitivity of projections to different plausible assumptions. © 2016 The Authors.

  14. White-beaked dolphins trapped in the ice and eaten by polar bears

    Directory of Open Access Journals (Sweden)

    Jon Aars

    2015-06-01

    Full Text Available Polar bears (Ursus maritimus depend on sea ice, where they hunt ice-associated seals. However, they are opportunistic predators and scavengers with a long list of known prey species. Here we report from a small fjord in Svalbard, Norwegian High Arctic, a sighting of an adult male polar bear preying on two white-beaked dolphins (Lagenorhynchus albirostris on 23 April 2014. This is the first record of this species as polar bear prey. White-beaked dolphins are frequent visitors to Svalbard waters in summer, but have not previously been reported this far north in early spring. We suggest they were trapped in the ice after strong northerly winds the days before, and possibly killed when forced to surface for air at a small opening in the ice. The bear had consumed most parts of one dolphin. When observed he was in the process of covering the mostly intact second dolphin with snow. Such caching behaviour is generally considered untypical of polar bears. During the following ice-free summer and autumn, at least seven different white-beaked dolphin carcasses were observed in or near the same area. We suggest, based on the area and the degree to which these dolphins had decayed, that they were likely from the same pod and also suffered death due to entrapment in the ice in April. At least six different polar bears were seen scavenging on the carcasses.

  15. New marine geophysical and sediment record of the Northeast Greenland Ice Stream.

    Science.gov (United States)

    Callard, L.; Roberts, D. H.; O'Cofaigh, C.; Lloyd, J. M.; Smith, J. A.; Dorschel, B.

    2017-12-01

    The NE Greenland Ice Stream (NEGIS) drains 16% of the Greenland Ice Sheet (GrIS) and has a sea-level equivalent of 1.1-1.4 m. Stabilised by two floating ice shelves, 79N and Zachariae Isstrom, until recently it has shown little response to increased atmospheric and oceanic warming. However, since 2010 it has experienced an accelerated rate of grounding line retreat ( 4 km) and significant ice shelf loss that indicates that this sector of the GrIS is now responding to current oceanic and/or climatic change and has the potential to be a major contributor to future global sea-level rise. The project `NEGIS', a collaboration between Durham University and AWI, aims to reconstruct the history of the NE Greenland Ice Stream from the Last Glacial Maximum (LGM) to present using both onshore and offshore geological archives to better understand past ice stream response to a warming climate. This contribution presents results and interpretations from an offshore dataset collected on the RV Polarstern, cruises PS100 and PS109 in 2016 and 2017. Gravity and box cores, supplemented by swath bathymetric and sub-bottom profiler data, were acquired and initial core analysis including x-radiographs and MSCL data logging has been performed. Data collection focused principally in the Norske Trough and the area directly in front of the 79N ice shelf, a sub-ice shelf environment as recently as two years ago. On the outer shelf streamlined subglacial bedforms, grounding-zone wedges and moraines as well as overconsolidated subglacial tills, record an extensive ice sheet advance to the shelf edge. On the inner shelf and in front of the 79N ice shelf, deep, glacially-eroded bedrock basins are infilled with stratified sediment. The stratified muds represent deglacial and Holocene glacimarine sedimentation, and capture the recent transition from sub-ice shelf to shelf free conditions. Multiproxy palaeoenvironmental reconstructions, including foraminifera and diatom analysis, and radiocarbon

  16. Firn thickness variations across the Northeast Greenland Ice Stream margins indicating nonlinear densification rates

    Science.gov (United States)

    Riverman, K. L.; Anandakrishnan, S.; Alley, R. B.; Peters, L. E.; Christianson, K. A.; Muto, A.

    2013-12-01

    Northeast Greenland Ice Stream (NEGIS) is the largest ice stream in Greenland, draining approximately 8.4% of the ice sheet's area. The flow pattern and stability mechanism of this ice stream are unique to others in Greenland and Antarctica, and merit further study to ascertain the sensitivity of this ice stream to future climate change. Geophysical methods are valuable tools for this application, but their results are sensitive to the structure of the firn and any spatial variations in firn properties across a given study region. Here we present firn data from a 40-km-long seismic profile across the upper reaches of NEGIS, collected in the summer of 2012 as part of an integrated ground-based geophysical survey. We find considerable variations in firn thickness that are coincident with the ice stream shear margins, where a thinner firn layer is present within the margins, and a thicker, more uniform firn layer is present elsewhere in our study region. Higher accumulation rates in the marginal surface troughs due to drift-snow trapping can account for some of this increased densification; however, our seismic results also highlight enhanced anisotropy within the firn and upper ice column that is confined to narrow bands within the shear margins. We thus interpret these large firn thickness variations and abrupt changes in anisotropy as indicators of firn densification dependent on the effective stress state as well as the overburden pressure, suggesting that the strain rate increases nonlinearly with stress across the shear margins. A GPS strain grid maintained for three weeks across both margins observed strong side shearing, with rapid stretching and then compression along particle paths, indicating large deviatoric stresses in the margins. This work demonstrates the importance of developing a high-resolution firn densification model when conducting geophysical field work in regions possessing a complex ice flow history; it also motivates the need for a more

  17. From cyclic ice streaming to Heinrich-like events: the grow-and-surge instability in the Parallel Ice Sheet Model

    Directory of Open Access Journals (Sweden)

    J. Feldmann

    2017-08-01

    Full Text Available >Here we report on a cyclic, physical ice-discharge instability in the Parallel Ice Sheet Model, simulating the flow of a three-dimensional, inherently buttressed ice-sheet-shelf system which periodically surges on a millennial timescale. The thermomechanically coupled model on 1 km horizontal resolution includes an enthalpy-based formulation of the thermodynamics, a nonlinear stress-balance-based sliding law and a very simple subglacial hydrology. The simulated unforced surging is characterized by rapid ice streaming through a bed trough, resulting in abrupt discharge of ice across the grounding line which is eventually calved into the ocean. We visualize the central feedbacks that dominate the subsequent phases of ice buildup, surge and stabilization which emerge from the interaction between ice dynamics, thermodynamics and the subglacial till layer. Results from the variation of surface mass balance and basal roughness suggest that ice sheets of medium thickness may be more susceptible to surging than relatively thin or thick ones for which the surge feedback loop is damped. We also investigate the influence of different basal sliding laws (ranging from purely plastic to nonlinear to linear on possible surging. The presented mechanisms underlying our simulations of self-maintained, periodic ice growth and destabilization may play a role in large-scale ice-sheet surging, such as the surging of the Laurentide Ice Sheet, which is associated with Heinrich events, and ice-stream shutdown and reactivation, such as observed in the Siple Coast region of West Antarctica.

  18. Design and Operation of Automated Ice-Tethered Profilers for Real-Time Seawater Observations in the Polar Oceans

    National Research Council Canada - National Science Library

    Toole, J; Proshutinsky, A; Krishfield, R; Doherty, K; Frye, Daniel E; Hammar, T; Kemp, J; Peters, D; Heydt, K. von der

    2006-01-01

    An automated, easily-deployed Ice-Tethered Profiler (ITP) has been developed for deployment on perennial sea ice in polar oceans to measure changes in upper ocean temperature and salinity in all seasons...

  19. Persistent Tracers of Historic Ice Flow in Glacial Stratigraphy near Kamb Ice Stream, West Antarctica

    OpenAIRE

    Holschuh, Nicholas; Christianson, Knut; Conway, Howard; Jacobel, Robert W.; Welch, Brian C.

    2018-01-01

    Variations in properties controlling ice flow (e.g., topography, accumulation rate, basal friction) are recorded by structures in glacial stratigraphy. When anomalies that disturb the stratigraphy are fixed in space, the structures they produce advect away from the source, and can be used to trace flow pathways and reconstruct ice-flow patterns of the past. Here we provide an example of one of these persistent tracers: a prominent unconformity in the glacial layering that originates at Mt. Re...

  20. Mechanisms of basal ice formation in polar glaciers: An evaluation of the apron entrainment model

    Science.gov (United States)

    Fitzsimons, Sean; Webb, Nicola; Mager, Sarah; MacDonell, Shelley; Lorrain, Regi; Samyn, Denis

    2008-06-01

    Previous studies of polar glaciers have argued that basal ice can form when these glaciers override and entrain ice marginal aprons that accumulate adjacent to steep ice cliffs. To test this idea, we have studied the morphology, structure, composition, and deformation of the apron and basal ice at the terminus of Victoria Upper Glacier in the McMurdo dry valleys, which are located on the western coast of the Ross Sea at 77°S in southern Victoria Land, Antarctica. Our results show that the apron has two structural elements: an inner element that consists of strongly foliated ice that has a steep up-glacier dip, and an outer element that lacks a consistent foliation and has a down-glacier, slope-parallel dip. Although strain measurements show that the entire apron is deforming, the inner element is characterized by high strain rates, whereas relatively low rates of strain characterize the outer part of the apron. Co-isotopic analyses of the ice, together with analysis of solute chemistry and sedimentary characteristics, show that the apron is compositionally different from the basal ice. Our observations show that aprons may become deformed and partially entrained by advancing glaciers. However, such an ice marginal process does not provide a satisfactory explanation for the origin of basal ice observed at the ice margin. Our interpretation of the origin of basal ice is that it is formed by subglacial processes, which are likely to include deformation and entrainment of subglacial permafrost.

  1. Microbial processes at the beds of glaciers and ice sheets: a look at life below the Whillans Ice Stream

    Science.gov (United States)

    Mikucki, J.; Campen, R.; Vancleave, S.; Scherer, R. P.; Coenen, J. J.; Powell, R. D.; Tulaczyk, S. M.

    2017-12-01

    Groundwater, saturated sediments and hundreds of subglacial lakes exist below the ice sheets of Antarctica. The few Antarctic subglacial environments sampled to date all contain viable microorganisms. This is a significant finding because microbes are known to be key in mediating biogeochemical cycles. In sediments, microbial metabolic activity can also result in byproducts or direct interactions with sediment particles that influence the physical and geochemical characteristics of the matrix they inhabit. Subglacial Lake Whillans (SLW), a fresh water lake under the Whillans Ice Stream that drains into the Ross Sea at its grounding zone, was recently sampled as part of the NSF-funded Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project. Sediments from both SLW and its grounding zone contain microbial taxa related to iron, sulfur, nitrogen and methane oxidizers. In addition to molecular data, biogeochemical measurements and culture based experiments on Whillans sediments support the notion that the system is chemosynthetic with energy derived in part by cycling inorganic compounds. Etch pitting and mineral precipitates on fossil sponge spicules suggest that spicules may also provide microbial nutrients in these environments. Perhaps the most widespread microbial process that affects sediment structure and mineral weathering is the production of extra polymeric substances (EPS). Several phylogenetic groups detected in Whillans sediments are known to produce EPS and we have observed its production in pure cultures enriched directly from these sediments. Our data sheds light on how microbial life persists below the Antarctic Ice Sheet despite extended isolation in icy darkness, and how these microbes may be shaping their environment.

  2. Data assimilation of surface altimetry on the North-Easter Ice Stream using the Ice Sheet System Model (ISSM)

    Science.gov (United States)

    Larour, Eric; Utke, Jean; Morlighem, Mathieu; Seroussi, Helene; Csatho, Beata; Schenk, Anton; Rignot, Eric; Khazendar, Ala

    2014-05-01

    Extensive surface altimetry data has been collected on polar ice sheets over the past decades, following missions such as Envisat and IceSat. This data record will further increase in size with the new CryoSat mission, the ongoing Operation IceBridge Mission and the soon to launch IceSat-2 mission. In order to make the best use of these dataset, ice flow models need to improve on the way they ingest surface altimetry to infer: 1) parameterizations of poorly known physical processes such as basal friction; 2) boundary conditions such as Surface Mass Balance (SMB). Ad-hoc sensitivity studies and adjoint-based inversions have so far been the way ice sheet models have attempted to resolve the impact of 1) on their results. As for boundary conditions or the lack thereof, most studies assume that they are a fixed quantity, which, though prone to large errors from the measurement itself, is not varied according to the simulated results. Here, we propose a method based on automatic differentiation to improve boundary conditions at the base and surface of the ice sheet during a short-term transient run for which surface altimetry observations are available. The method relies on minimizing a cost-function, the best fit between modeled surface evolution and surface altimetry observations, using gradients that are computed for each time step from automatic differentiation of the ISSM (Ice Sheet System Model) code. The approach relies on overloaded operators using the ADOLC (Automatic Differentiation by OverLoading in C++) package. It is applied to the 79 North Glacier, Greenland, for a short term transient spanning a couple of decades before the start of the retreat of the Zachariae Isstrom outlet glacier. Our results show adjustments required on the basal friction and the SMB of the whole basin to best fit surface altimetry observations, along with sensitivities each one of these parameters has on the overall cost function. Our approach presents a pathway towards assimilating

  3. Invariant polar bear habitat selection during a period of sea ice loss.

    Science.gov (United States)

    Wilson, Ryan R; Regehr, Eric V; Rode, Karyn D; St Martin, Michelle

    2016-08-17

    Climate change is expected to alter many species' habitat. A species' ability to adjust to these changes is partially determined by their ability to adjust habitat selection preferences to new environmental conditions. Sea ice loss has forced polar bears (Ursus maritimus) to spend longer periods annually over less productive waters, which may be a primary driver of population declines. A negative population response to greater time spent over less productive water implies, however, that prey are not also shifting their space use in response to sea ice loss. We show that polar bear habitat selection in the Chukchi Sea has not changed between periods before and after significant sea ice loss, leading to a 75% reduction of highly selected habitat in summer. Summer was the only period with loss of highly selected habitat, supporting the contention that summer will be a critical period for polar bears as sea ice loss continues. Our results indicate that bears are either unable to shift selection patterns to reflect new prey use patterns or that there has not been a shift towards polar basin waters becoming more productive for prey. Continued sea ice loss is likely to further reduce habitat with population-level consequences for polar bears. © 2016 The Author(s).

  4. High contributions of sea ice derived carbon in polar bear (Ursus maritimus tissue.

    Directory of Open Access Journals (Sweden)

    Thomas A Brown

    Full Text Available Polar bears (Ursus maritimus rely upon Arctic sea ice as a physical habitat. Consequently, conservation assessments of polar bears identify the ongoing reduction in sea ice to represent a significant threat to their survival. However, the additional role of sea ice as a potential, indirect, source of energy to bears has been overlooked. Here we used the highly branched isoprenoid lipid biomarker-based index (H-Print approach in combination with quantitative fatty acid signature analysis to show that sympagic (sea ice-associated, rather than pelagic, carbon contributions dominated the marine component of polar bear diet (72-100%; 99% CI, n = 55, irrespective of differences in diet composition. The lowest mean estimates of sympagic carbon were found in Baffin Bay bears, which were also exposed to the most rapidly increasing open water season. Therefore, our data illustrate that for future Arctic ecosystems that are likely to be characterised by reduced sea ice cover, polar bears will not only be impacted by a change in their physical habitat, but also potentially in the supply of energy to the ecosystems upon which they depend. This data represents the first quantifiable baseline that is critical for the assessment of likely ongoing changes in energy supply to Arctic predators as we move into an increasingly uncertain future for polar ecosystems.

  5. High contributions of sea ice derived carbon in polar bear (Ursus maritimus) tissue.

    Science.gov (United States)

    Brown, Thomas A; Galicia, Melissa P; Thiemann, Gregory W; Belt, Simon T; Yurkowski, David J; Dyck, Markus G

    2018-01-01

    Polar bears (Ursus maritimus) rely upon Arctic sea ice as a physical habitat. Consequently, conservation assessments of polar bears identify the ongoing reduction in sea ice to represent a significant threat to their survival. However, the additional role of sea ice as a potential, indirect, source of energy to bears has been overlooked. Here we used the highly branched isoprenoid lipid biomarker-based index (H-Print) approach in combination with quantitative fatty acid signature analysis to show that sympagic (sea ice-associated), rather than pelagic, carbon contributions dominated the marine component of polar bear diet (72-100%; 99% CI, n = 55), irrespective of differences in diet composition. The lowest mean estimates of sympagic carbon were found in Baffin Bay bears, which were also exposed to the most rapidly increasing open water season. Therefore, our data illustrate that for future Arctic ecosystems that are likely to be characterised by reduced sea ice cover, polar bears will not only be impacted by a change in their physical habitat, but also potentially in the supply of energy to the ecosystems upon which they depend. This data represents the first quantifiable baseline that is critical for the assessment of likely ongoing changes in energy supply to Arctic predators as we move into an increasingly uncertain future for polar ecosystems.

  6. Invariant polar bear habitat selection during a period of sea ice loss

    Science.gov (United States)

    Wilson, Ryan R.; Regehr, Eric V.; Rode, Karyn D.; St Martin, Michelle

    2016-01-01

    Climate change is expected to alter many species' habitat. A species' ability to adjust to these changes is partially determined by their ability to adjust habitat selection preferences to new environmental conditions. Sea ice loss has forced polar bears (Ursus maritimus) to spend longer periods annually over less productive waters, which may be a primary driver of population declines. A negative population response to greater time spent over less productive water implies, however, that prey are not also shifting their space use in response to sea ice loss. We show that polar bear habitat selection in the Chukchi Sea has not changed between periods before and after significant sea ice loss, leading to a 75% reduction of highly selected habitat in summer. Summer was the only period with loss of highly selected habitat, supporting the contention that summer will be a critical period for polar bears as sea ice loss continues. Our results indicate that bears are either unable to shift selection patterns to reflect new prey use patterns or that there has not been a shift towards polar basin waters becoming more productive for prey. Continued sea ice loss is likely to further reduce habitat with population-level consequences for polar bears.

  7. Cl-36 in polar ice, rainwater and seawater

    Science.gov (United States)

    Finkel, R. C.; Nishiizumi, K.; Elmore, D.; Ferraro, R. D.; Gove, H. E.

    1980-01-01

    Concentrations of the cosmogenic radioisotope Cl-36 in Antarctic ice, rain, and an upper limit of the seawater value are determined using van de Graaff accelerator high energy mass spectrometry. Cl-36 concentrations in Antarctic ice range between 2.5 to 8.7 x 10 to the 6th atoms Cl-36/kg, while those concentrations in samples collected at the Alan Hills ice field locations where meteorites have been brought to the surface by glacial flow and ablation are found to vary by more than a factor of three. This variation is attributed either to the effects of atmospheric mixing and scavenging or to radioactive decay in old ice. The Cl-36 concentration found in a present sample of rainwater is much lower than that reported in samples collected in the early 1960's, suggesting the occurrence of a decrease in the concentration of atmospheric Cl-36 derived from nuclear weapons tests over this time period.

  8. Minimum and Maximum Potential Contributions to Future Sea Level Rise from Polar Ice Sheets

    Science.gov (United States)

    Deconto, R. M.; Pollard, D.

    2017-12-01

    New climate and ice-sheet modeling, calibrated to past changes in sea-level, is painting a stark picture of the future fate of the great polar ice sheets if greenhouse gas emissions continue unabated. This is especially true for Antarctica, where a substantial fraction of the ice sheet rests on bedrock more than 500-meters below sea level. Here, we explore the sensitivity of the polar ice sheets to a warming atmosphere and ocean under a range of future greenhouse gas emissions scenarios. The ice sheet-climate-ocean model used here considers time-evolving changes in surface mass balance and sub-ice oceanic melting, ice deformation, grounding line retreat on reverse-sloped bedrock (Marine Ice Sheet Instability), and newly added processes including hydrofracturing of ice shelves in response to surface meltwater and rain, and structural collapse of thick, marine-terminating ice margins with tall ice-cliff faces (Marine Ice Cliff Instability). The simulations improve on previous work by using 1) improved atmospheric forcing from a Regional Climate Model and 2) a much wider range of model physical parameters within the bounds of modern observations of ice dynamical processes (particularly calving rates) and paleo constraints on past ice-sheet response to warming. Approaches to more precisely define the climatic thresholds capable of triggering rapid and potentially irreversible ice-sheet retreat are also discussed, as is the potential for aggressive mitigation strategies like those discussed at the 2015 Paris Climate Conference (COP21) to substantially reduce the risk of extreme sea-level rise. These results, including physics that consider both ice deformation (creep) and calving (mechanical failure of marine terminating ice) expand on previously estimated limits of maximum rates of future sea level rise based solely on kinematic constraints of glacier flow. At the high end, the new results show the potential for more than 2m of global mean sea level rise by 2100

  9. The formation of multiple layers of ice particles in the polar summer mesopause region

    Directory of Open Access Journals (Sweden)

    H. Li

    2016-01-01

    Full Text Available This paper presents a two-dimensional theoretical model to study the formation process of multiple layers of small ice particles in the polar summer mesosphere as measured by rockets and associated with polar mesosphere summer echoes (PMSE. The proposed mechanism primarily takes into account the transport processes induced by gravity waves through collision coupling between the neutral atmosphere and the ice particles. Numerical solutions of the model indicate that the dynamic influence of wind variation induced by gravity waves can make a significant contribution to the vertical and horizontal transport of ice particles and ultimately transform them into thin multiple layers. Additionally, the pattern of the multiple layers at least partially depends on the vertical wavelength of the gravity wave, the ice particle size and the wind velocity. The results presented in this paper will be helpful to better understand the occurrence of multiple layers of PMSE as well as its variation process.

  10. A High-Resolution Continuous Flow Analysis System for Polar Ice Cores

    DEFF Research Database (Denmark)

    Dallmayr, Remi; Goto-Azuma, Kumiko; Kjær, Helle Astrid

    2016-01-01

    of Polar Research (NIPR) in Tokyo. The system allows the continuous analysis of stable water isotopes and electrical conductivity, as well as the collection of discrete samples from both inner and outer parts of the core. This CFA system was designed to have sufficiently high temporal resolution to detect...... signals of abrupt climate change in deep polar ice cores. To test its performance, we used the system to analyze different climate intervals in ice drilled at the NEEM (North Greenland Eemian Ice Drilling) site, Greenland. The quality of our continuous measurement of stable water isotopes has been......In recent decades, the development of continuous flow analysis (CFA) technology for ice core analysis has enabled greater sample throughput and greater depth resolution compared with the classic discrete sampling technique. We developed the first Japanese CFA system at the National Institute...

  11. C-band Joint Active/Passive Dual Polarization Sea Ice Detection

    Science.gov (United States)

    Keller, M. R.; Gifford, C. M.; Winstead, N. S.; Walton, W. C.; Dietz, J. E.

    2017-12-01

    A technique for synergistically-combining high-resolution SAR returns with like-frequency passive microwave emissions to detect thin (Radar (SAR) is high resolution (5-100m) but because of cross section ambiguities automated algorithms have had difficulty separating thin ice types from water. The radiometric emissivity of thin ice versus water at microwave frequencies is generally unambiguous in the early stages of ice growth. The method, developed using RADARSAT-2 and AMSR-E data, uses higher-ordered statistics. For the SAR, the COV (coefficient of variation, ratio of standard deviation to mean) has fewer ambiguities between ice and water than cross sections, but breaking waves still produce ice-like signatures for both polarizations. For the radiometer, the PRIC (polarization ratio ice concentration) identifies areas that are unambiguously water. Applying cumulative statistics to co-located COV levels adaptively determines an ice/water threshold. Outcomes from extensive testing with Sentinel and AMSR-2 data are shown in the results. The detection algorithm was applied to the freeze-up in the Beaufort, Chukchi, Barents, and East Siberian Seas in 2015 and 2016, spanning mid-September to early November of both years. At the end of the melt, 6 GHz PRIC values are 5-10% greater than those reported by radiometric algorithms at 19 and 37 GHz. During freeze-up, COV separates grease ice (cross-pol/co-pol SAR ratio corrects for COV deficiencies. In general, the dual-sensor detection algorithm reports 10-15% higher total ice concentrations than operational scatterometer or radiometer algorithms, mostly from ice edge and coastal areas. In conclusion, the algorithm presented combines high-resolution SAR returns with passive microwave emissions for automated ice detection at SAR resolutions.

  12. Martian North Polar Water-Ice Clouds During the Viking Era

    Science.gov (United States)

    Tamppari, L. K.; Bass, D. S.

    2000-01-01

    The Viking Orbiters determined that the surface of Mars' northern residual cap consists of water ice. Observed atmospheric water vapor abundances in the equatorial regions have been related to seasonal exchange between reservoirs such as the polar caps, the regolith and between different phases in the atmosphere. Kahn modeled the physical characteristics of ice hazes seen in Viking Orbiter imaging limb data, hypothesizing that ice hazes provide a method for scavenging water vapor from the atmosphere and accumulating it into ice particles. Given that Jakosky found that these particles had sizes such that fallout times were of order one Martian sol, these water-ice hazes provided a method for returning more water to the regolith than that provided by adsorption alone. These hazes could also explain the rapid hemispheric decrease in atmospheric water in late northern summer as well as the increase during the following early spring. A similar comparison of water vapor abundance versus polar cap brightness has been done for the north polar region. They have shown that water vapor decreases steadily between L(sub s) = 100-150 deg while polar cap albedo increases during the same time frame. As a result, they suggested that late summer water-ice deposition onto the ice cap may be the cause of the cap brightening. This deposition could be due to adsorption directly onto the cap surface or to snowfall. Thus, an examination of north polar waterice clouds could lend insight into the fate of the water vapor during this time period. Additional information is contained in the original extended abstract.

  13. Properties of horizontally oriented ice crystals observed by polarization lidar over summit, Greenland

    Directory of Open Access Journals (Sweden)

    Neely Ryan R.

    2018-01-01

    Full Text Available A source of error in microphysical retrievals and model simulations is the assumption that clouds are composed of only randomly oriented ice crystals. This assumption is frequently not true, as evidenced by optical phenomena such as parhelia. Here, observations from the Cloud, Aerosol and Polarization Backscatter Lidar at Summit, Greenland are utilized along with other sensors and beam imaging to examine the properties of horizontally oriented ice crystals and the environment conditions in which they occur.

  14. Tropical tales of polar ice: evidence of Last Interglacial polar ice sheet retreat recorded by fossil reefs of the granitic Seychelles islands

    Science.gov (United States)

    Dutton, Andrea; Webster, Jody M.; Zwartz, Dan; Lambeck, Kurt; Wohlfarth, Barbara

    2015-01-01

    In the search for a record of eustatic sea level change on glacial-interglacial timescales, the Seychelles ranks as one of the best places on the planet to study. Owing to its location with respect to the former margins of Northern Hemisphere ice sheets that wax and wane on orbital cycles, the local-or relative-sea level history is predicted to lie within a few meters of the globally averaged eustatic signal during the Last Interglacial period. We have surveyed and dated Last Interglacial fossil corals to ascertain peak sea level and hence infer maximum retreat of polar ice sheets during this time interval. We observe a pattern of gradually rising sea level in the Seychelles between ˜129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 ± 1.7 m higher than present. After accounting for thermal expansion and loss of mountain glaciers, this sea-level budget would require ˜5-8 m of polar ice sheet contribution, relative to today's volume, of which only ˜2 m came from the Greenland ice sheet. This result clearly identifies the Antarctic ice sheet as a significant source of melt water, most likely derived from one of the unstable, marine-based sectors in the West and/or East Antarctic ice sheet. Furthermore, the establishment of a +5.9 ± 1.7 m eustatic sea level position by 128.6 ± 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand.

  15. Research progress of anti-icing/deicing technologies for polar ships and offshore platforms

    Directory of Open Access Journals (Sweden)

    XIE Qiang

    2017-01-01

    Full Text Available The polar regions present adverse circumstances of high humidity and strong air-sea exchange. As such, the surfaces of ships and platforms (oil exploiting and drilling platforms serving in polar regions can easily be frozen by ice accretion, which not only affects the operation of the equipment but also threatens safety. This paper summarizes the status of the anti-icing/deicing technologies of both China and abroad for polar ships and offshore platforms, and introduces the various effects of ice accretion on polar ships and offshore platforms, and the resulting safety impacts. It then reviews existing anti-icing/deicing technologies and methods of both China and abroad, including such active deicing methods as electric heating, infrared heating and ultrasonic guided wave deicing, as well as such passive deicing methods as super hydrophobic coating, sacrificial coating, aqueous lubricating layer coating and low cross-link density (with interfacial slippage coating, summarizes their applicability to polar ships and offshore platforms, and finally discusses their advantages/disadvantages.

  16. Disintegration of a marine-based ice stream - evidence from the Norwegian Channel, north-eastern North Sea

    Science.gov (United States)

    Morén, Björn M.; Petter Sejrup, Hans; Hjelstuen, Berit O.; Haflidason, Haflidi; Schäuble, Cathrina; Borge, Marianne

    2014-05-01

    The Norwegian Channel Ice Stream repeatedly drained large part of the Fennoscandian Ice Sheet through Mid and Late Pleistocene glacial stages. During parts of Marine Isotope Stages 2 and 3, glacial ice from Fennoscandia and the British Isles coalesced in the central North Sea and the Norwegian Channel Ice Stream reached the shelf edge on multiple occasions. Through the last decades a large amount of acoustic and sediment core data have been collected from the Norwegian Channel, providing a good background for studies focussing on stability- and development-controlling parameters for marine-based ice streams, the retreat rate of the Norwegian Channel Ice Stream, and the behaviour of the Fennoscandian Ice Sheet. Further, this improved understanding can be used to develop more accurate numerical climate models and models which can be used to model ice-sheet behaviour of the past as well as the future. This study presents new acoustic records and data from sediment cores which contribute to a better understanding of the retreat pattern and the retreat rate of the last ice stream that occupied the Norwegian Channel. From bathymetric and TOPAS seismic data, mega-scale glacial lineations, grounding-zone wedges, and end moraines have been mapped, thereby allowing us to reconstruct the pro- and subglacial conditions at the time of the creation of these landforms. It is concluded that the whole Norwegian Channel was deglaciated in just over 1 000 years and that for most of this time the ice margin was located at positions reflected by depositional grounding-zone wedges. Further work will explore the influence of channel shape and feeding of ice from western Norwegian fjords on this retreat pattern through numerical modelling.

  17. Exospheric transport restrictions on water ice in lunar polar traps

    Science.gov (United States)

    Hodges, R. R., Jr.

    1991-01-01

    There is little doubt that at least 10 exp 17 g of water has accreted on the moon as a result of the reduction of ferric iron at the regolith surface by solar wind protons, the vaporization of chondrites, and perhaps comet impacts. Lacking an efficient escape mechanism, most of this water (or its progeny) is probably on the moon now. If the water were to have migrated to permanently shaded cold traps near the lunar poles, ice deposts with densities greater than 1000 g/sq cm would cover the traps, providing accessible resources. However, exospheric transport considerations suggest that the actual amount of water ice in the cold traps is probably too small to be of practical interest. The alternative is global assimilation of most of the water into the regolith, a process that must account for about 30 micromoles of water per gram of soil.

  18. Accelerated Prediction of the Polar Ice and Global Ocean (APPIGO)

    Science.gov (United States)

    2014-09-30

    APPIGO) Eric Chassignet Center for Ocean-Atmosphere Prediction Studies (COAPS) Florida State University PO Box 3062840 Tallahassee, FL 32306...PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Florida Atlantic University,Center for Ocean-Atmosphere Prediction Studies (COAPS),PO Box 3062840...Cavalieri, D. J., C. I. Parkinson , P. Gloersen, and H. J. Zwally. 1997. Arctic and Antarctic Sea Ice Concentrations from Multichannel Passive-Microwave

  19. Reduced body size and cub recruitment in polar bears associated with sea ice decline

    Science.gov (United States)

    Rode, Karyn D.; Amstrup, Steven C.; Regehr, Eric V.

    2010-01-01

    Rates of reproduction and survival are dependent upon adequate body size and condition of individuals. Declines in size and condition have provided early indicators of population decline in polar bears (Ursus maritimus) near the southern extreme of their range. We tested whether patterns in body size, condition, and cub recruitment of polar bears in the southern Beaufort Sea of Alaska were related to the availability of preferred sea ice habitats and whether these measures and habitat availability exhibited trends over time, between 1982 and 2006. The mean skull size and body length of all polar bears over three years of age declined over time, corresponding with long‐term declines in the spatial and temporal availability of sea ice habitat. Body size of young, growing bears declined over time and was smaller after years when sea ice availability was reduced. Reduced litter mass and numbers of yearlings per female following years with lower availability of optimal sea ice habitat, suggest reduced reproductive output and juvenile survival. These results, based on analysis of a long‐term data set, suggest that declining sea ice is associated with nutritional limitations that reduced body size and reproduction in this population.

  20. Greenhouse gas mitigation can reduce sea-ice loss and increase polar bear persistence

    Science.gov (United States)

    Steven C. Amstrup; Eric T. DeWeaver; David C. Douglas; Bruce G. Marcot; George M. Durner; Cecilia M. Bitz; David A. Bailey

    2010-01-01

    On the basis of projected losses of their essential sea-ice habitats, a United States Geological Survey research team concluded in 2007 that two-thirds of the world's polar bears (Ursus maritimus) could disappear by mid-century if business-as-usual greenhouse gas emissions continue. That projection, however, did not consider the possible...

  1. Movements of female polar bears (Usrus maritimus) in the East Greenland pack ice

    DEFF Research Database (Denmark)

    Wiig, Øystein; Born, Erik W.; Pedersen, Leif Toudal

    2003-01-01

    The movements of two adult female polar bears (Ursus maritimus) in East Greenland and the Greenland Sea area were studied by use of satellite telemetry between the fall of 1994 and the summer of 1998. One female was tracked for 621 days, the other for 1,415 days. During this time the females used...... for a closer monitoring of the effects of this change on the East Greenland polar bear population....... movement rates varied between 0.32 and 0.76km/h. Both bears had very large home ranges (242,000 and 468,000 km(2)) within the dynamic pack ice of the Greenland Sea. The facts that the bears made extensive use of the offshore sea ice and that there is a marked reduction of the Greenland Sea ice call...

  2. Earthquake-induced deformations on ice-stream landforms in Kuusamo, eastern Finnish Lapland

    Science.gov (United States)

    Sutinen, Raimo; Hyvönen, Eija; Middleton, Maarit; Airo, Meri-Liisa

    2018-01-01

    Kuusamo in eastern Finnish Lapland is characterized by ice-streamlined landforms as well as clusters of historical and recent earthquakes (Mw landslides, earth flows as well as kettle holes (craters), on the fluted surfaces within the Kuusamo ice-stream fan. We found these deformations to be a common feature on the Archean granitoid gneisses and within a 20 km wide and NW-SE oriented corridor between the major intrusives, the Iivaara nepheline syenite and the Näränkävaara gabbro. Of the paleolandslides, liquefaction morphologies were generally developed on the distal slopes (1.3-2.8%; 0.75-1.6°) of the streamlined forms. Sedimentary anisotropy, obtained with azimuthal electrical conductivity (σa; skin depth down to 3-6 m), of the deformed flutes significantly deviated from the non-deformed (clean) ones. The fields of the Pulju moraine, a subglacial landform, formed a grounding zone for the ice-streaming SW of the paleolandslide cluster. We therefore propose that both subglacial and postglacial earthquake-induced landforms are present in Kuusamo. No PGFs could be verified in the Kuusamo area, yet gravity, airborne magnetic, and LiDAR morphological lineaments suggest that the old Paleoproterozoic structures have been reactivated as strike-slip faults, due to the lithospheric plate stresses and glacio-isostatic adjustment (GIA).

  3. Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline.

    Science.gov (United States)

    Bromaghin, Jeffrey F; Mcdonald, Trent L; Stirling, Ian; Derocher, Andrew E; Richardson, Evan S; Regehr, Eric V; Douglas, David C; Durner, George M; Atwood, Todd; Amstrup, Steven C

    2015-04-01

    In the southern Beaufort Sea of the United States and Canada, prior investigations have linked declines in summer sea ice to reduced physical condition, growth, and survival of polar bears (Ursus maritimus). Combined with projections of population decline due to continued climate warming and the ensuing loss of sea ice habitat, those findings contributed to the 2008 decision to list the species as threatened under the U.S. Endangered Species Act. Here, we used mark-recapture models to investigate the population dynamics of polar bears in the southern Beaufort Sea from 2001 to 2010, years during which the spatial and temporal extent of summer sea ice generally declined. Low survival from 2004 through 2006 led to a 25-50% decline in abundance. We hypothesize that low survival during this period resulted from (1) unfavorable ice conditions that limited access to prey during multiple seasons; and possibly, (2) low prey abundance. For reasons that are not clear, survival of adults and cubs began to improve in 2007 and abundance was comparatively stable from 2008 to 2010, with ~900 bears in 2010 (90% CI 606-1212). However, survival of subadult bears declined throughout the entire period. Reduced spatial and temporal availability of sea ice is expected to increasingly force population dynamics of polar bears as the climate continues to warm. However, in the short term, our findings suggest that factors other than sea ice can influence survival. A refined understanding of the ecological mechanisms underlying polar bear population dynamics is necessary to improve projections of their future status and facilitate development of management strategies.

  4. Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline

    Science.gov (United States)

    Bromaghin, Jeffrey F.; McDonald, Trent L.; Stirling, Ian; Derocher, Andrew E.; Richardson, Evan S.; Regehr, Eric V.; Douglas, David C.; Durner, George M.; Atwood, Todd C.; Amstrup, Steven C.

    2015-01-01

    In the southern Beaufort Sea of the United States and Canada, prior investigations have linked declines in summer sea ice to reduced physical condition, growth, and survival of polar bears (Ursus maritimus). Combined with projections of population decline due to continued climate warming and the ensuing loss of sea ice habitat, those findings contributed to the 2008 decision to list the species as threatened under the U.S. Endangered Species Act. Here, we used mark–recapture models to investigate the population dynamics of polar bears in the southern Beaufort Sea from 2001 to 2010, years during which the spatial and temporal extent of summer sea ice generally declined. Low survival from 2004 through 2006 led to a 25–50% decline in abundance. We hypothesize that low survival during this period resulted from (1) unfavorable ice conditions that limited access to prey during multiple seasons; and possibly, (2) low prey abundance. For reasons that are not clear, survival of adults and cubs began to improve in 2007 and abundance was comparatively stable from 2008 to 2010, with ~900 bears in 2010 (90% CI 606–1212). However, survival of subadult bears declined throughout the entire period. Reduced spatial and temporal availability of sea ice is expected to increasingly force population dynamics of polar bears as the climate continues to warm. However, in the short term, our findings suggest that factors other than sea ice can influence survival. A refined understanding of the ecological mechanisms underlying polar bear population dynamics is necessary to improve projections of their future status and facilitate development of management strategies.

  5. Stormtime Simulations of Sub-Auroral Polarization Streams (SAPS)

    Science.gov (United States)

    Huba, J.; Sazykin, S. Y.; Coster, A. J.

    2017-12-01

    We present simulation results from the self-consistently coupled SAMI3/RCM code on the impact of geomagnetic storms on the ionosphere/plasmasphere system with an emphasis on the development of sub-auroral plasma streams (SAPS). We consider the following storm events: March 31, 2001, March 17, 2013, March 17, 2015, September 3, 2012, and June 23, 2015. We compare and contrast the development of SAPS for these storms. The main results are the development of sub-auroral (< 60 degrees) low-density, high-speed flows (1 - 2 km/s). Additionally, we discuss the impact on plasmaspheric dynamics. We compare our model results to data (e.g., Millstone Hill radar, GPS TEC).

  6. Estimation of Melt Pond Fractions on First Year Sea Ice Using Compact Polarization SAR

    Science.gov (United States)

    Li, Haiyan; Perrie, William; Li, Qun; Hou, Yijun

    2017-10-01

    Melt ponds are a common feature on Arctic sea ice. They are linked to the sea ice surface albedo and transmittance of energy to the ocean from the atmosphere and thus constitute an important process to parameterize in Arctic climate models and simulations. This paper presents a first attempt to retrieve the melt pond fraction from hybrid-polarized compact polarization (CP) SAR imagery, which has wider swath and shorter revisit time than the quad-polarization systems, e.g., from RADARSAT-2 (RS-2). The co-polarization (co-pol) ratio has been verified to provide estimates of melt pond fractions. However, it is a challenge to link CP parameters and the co-pol ratio. The theoretical possibility is presented, for making this linkage with the CP parameter C22/C11 (the ratio between the elements of the coherence matrix of CP SAR) for melt pond detection and monitoring with the tilted-Bragg scattering model for the ocean surface. The empirical transformed formulation, denoted as the "compact polarization and quad-pol" ("CPQP") model, is proposed, based on 2062 RS-2 quad-pol SAR images, collocated with in situ measurements. We compared the retrieved melt pond fraction with CP parameters simulated from quad-pol SAR data with results retrieved from the co-pol ratio from quad-pol SAR observations acquired during the Arctic-Ice (Arctic-Ice Covered Ecosystem in a Rapidly Changing Environment) field project. The results are shown to be comparable for observed melt pond measurements in spatial and temporal distributions. Thus, the utility of CP mode SAR for melt pond fraction estimation on first year level ice is presented.

  7. Influence of the Gulf Stream on the Barents Sea ice retreat and Eurasian coldness during early winter

    International Nuclear Information System (INIS)

    Sato, Kazutoshi; Inoue, Jun; Watanabe, Masahiro

    2014-01-01

    Abnormal sea-ice retreat over the Barents Sea during early winter has been considered a leading driver of recent midlatitude severe winters over Eurasia. However, causal relationships between such retreat and the atmospheric circulation anomalies remains uncertain. Using a reanalysis dataset, we found that poleward shift of a sea surface temperature front over the Gulf Stream likely induces warm southerly advection and consequent sea-ice decline over the Barents Sea sector, and a cold anomaly over Eurasia via planetary waves triggered over the Gulf Stream region. The above mechanism is supported by the steady atmospheric response to the diabatic heating anomalies over the Gulf Stream region obtained with a linear baroclinic model. The remote atmospheric response from the Gulf Stream would be amplified over the Barents Sea region via interacting with sea-ice anomaly, promoting the warm Arctic and cold Eurasian pattern. (letter)

  8. Efficient meltwater drainage through supraglacial streams and rivers on the southwest Greenland ice sheet.

    Science.gov (United States)

    Smith, Laurence C; Chu, Vena W; Yang, Kang; Gleason, Colin J; Pitcher, Lincoln H; Rennermalm, Asa K; Legleiter, Carl J; Behar, Alberto E; Overstreet, Brandon T; Moustafa, Samiah E; Tedesco, Marco; Forster, Richard R; LeWinter, Adam L; Finnegan, David C; Sheng, Yongwei; Balog, James

    2015-01-27

    Thermally incised meltwater channels that flow each summer across melt-prone surfaces of the Greenland ice sheet have received little direct study. We use high-resolution WorldView-1/2 satellite mapping and in situ measurements to characterize supraglacial water storage, drainage pattern, and discharge across 6,812 km(2) of southwest Greenland in July 2012, after a record melt event. Efficient surface drainage was routed through 523 high-order stream/river channel networks, all of which terminated in moulins before reaching the ice edge. Low surface water storage (3.6 ± 0.9 cm), negligible impoundment by supraglacial lakes or topographic depressions, and high discharge to moulins (2.54-2.81 cm⋅d(-1)) indicate that the surface drainage system conveyed its own storage volume every drainage to true outflow from the ice edge. However, Isortoq discharges tended lower than runoff simulations from the Modèle Atmosphérique Régional (MAR) regional climate model (0.056-0.112 km(3)⋅d(-1) vs. ∼0.103 km(3)⋅d(-1)), and when integrated over the melt season, totaled just 37-75% of MAR, suggesting nontrivial subglacial water storage even in this melt-prone region of the ice sheet. We conclude that (i) the interior surface of the ice sheet can be efficiently drained under optimal conditions, (ii) that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and (iii) that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater export from the ice sheet to the ocean.

  9. Past climate changes derived from isotope measurements in polar ice cores

    International Nuclear Information System (INIS)

    Beer, J.; Muscheler, R.; Wagner, G.; Kubik, P.K.

    2002-01-01

    Measurements of stable and radioactive isotopes in polar ice cores provide a wealth of information on the climate conditions of the past. Stable isotopes (δ 18 O, δD) reflect mainly the temperature, whereas δ 18 O of oxygen in air bubbles reveals predominantly the global ice volume and the biospheric activity. Cosmic ray produced radioisotopes (cosmogenic nuclides) such as 10 Be and 36 Cl record information on the solar variability and possibly also on the solar irradiance. If the flux of a cosmogenic nuclide into the ice is known the accumulation rate can be derived from the measured concentration. The comparison of 10 Be from ice with 14 C from tree rings allows deciding whether observed 14 C variations are caused by production or system effects. Finally, isotope measurements are very useful for establishing and improving time scales. The 10 Be/ 36 Cl ratio changes with an apparent half-life of 376,000 years and is therefore well suited to date old ice. Significant abrupt changes in the records of 10 Be, 36 Cl from ice and of δ 18 O from atmospheric oxygen representing global signals can be used to synchronize ice and sediment cores. (author)

  10. Buried CO2 Ice traces in South Polar Layered Deposits of Mars detected by radar sounder

    Science.gov (United States)

    Castaldo, L.; Mège, D.; Orosei, R.; Séjourné, A.

    2014-12-01

    SHARAD (SHAllow RADar) is the subsurface sounding radar provided by the Italian Space Agency (ASI) as a facility instrument to NASA's 2005 Mars Reconnaissance Orbiter (MRO). The Reduced Data Record of SHARAD data covering the area of the South Polar Layered Deposits (SPLD), has been used. The elaboration and interpretation of the data, aimed to estimate electromagnetic properties of surface layers, has been performed in terms of permittivity. The theory of electromagnetic scattering from fractal surfaces, and the estimation of geometric parameters from topographic data by Mars Orbiter Laser Altimeter (MOLA) which was one of five instruments on board the Mars Global Surveyor (MGS) spacecraft, has been used. A deep analysis of inversion has been made on all Mars and extended to the South Polar Caps in order to extract the area with a permittivity constant of CO2 ice. Several corrections have been applied to the data, moreover the calibration of the signal requires the determination of a constant that takes into account the power gain due to the radar system and the surface in order to compensate the power losses due to the orbitographic phenomena. The determination of regions with high probability of buried CO2 ice in the first layer of the Martian surface, is obtained extracting the real part of the permittivity constant of the CO2 ice (~2), estimated by other means. The permittivity of CO2ice is extracted from the Global Permittivity Map of Mars using the global standard deviation of itself as following: ɛCO2ice=ɛCO2ice+ Σ (1)where Σ=±std(ɛMapMars)/2Figure 1(a) shows the south polar areas where the values of the permittivity point to the possibility of a CO2 ice layer. Figure 1(b) is the corresponding geologic map. The comparison between the two maps indicates that the area with probable buried CO2 overlaps Hesperian and Amazonian polar units (Hp, Hesperian plains-forming deposits marked by narrow sinuous, anabranching ridges and irregular depressions, and

  11. Breaking the Ice: Strategies for Future European Research in the Polar Oceans - The AURORA BOREALIS Concept

    Science.gov (United States)

    Lembke-Jene, L.; Biebow, N.; Wolff-Boenisch, B.; Thiede, J.; European Research Icebreaker Consortium

    2011-12-01

    Research vessels dedicated to work in polar ice-covered waters have only rarely been built. Their history began with Fritjof Nansen's FRAM, which he used for his famous first crossing of the Arctic Ocean 1893-1896. She served as example for the first generation of polar research vessels, at their time being modern instruments planned with foresight. Ice breaker technology has developed substantially since then. However, it took almost 80 years until this technical advance also reached polar research, when the Russian AKADEMIK FEDEROV, the German POLARSTERN, the Swedish ODEN and the USCG Cutter HEALY were built. All of these house modern laboratories, are ice-breakers capable to move into the deep-Arctic during the summer time and represent the second generation of dedicated polar research vessels. Still, the increasing demand in polar marine research capacities by societies that call for action to better understand climate change, especially in the high latitudes is not matched by adequate facilities and resources. Today, no icebreaker platform exists that is permanently available to the international science community for year-round expeditions into the central Arctic Ocean or heavily ice-infested waters of the polar Southern Ocean around Antarctica. The AURORA BOREALIS concept plans for a heavy research icebreaker, which will enable polar scientists around the world to launch international research expeditions into the central Arctic Ocean and the Antarctic continental shelf seas autonomously during all seasons of the year. The European Research Icebreaker Consortium - AURORA BOREALIS (ERICON-AB) was established in 2008 to plan the scientific, governance, financial, and legal frameworks needed for the construction and operation of this first multi-nationally owned and operated research icebreaker and polar scientific drilling platform. By collaborating together and sharing common infrastructures it is envisioned that European nations make a major contribution to

  12. New Techniques for Radar Altimetry of Sea Ice and the Polar Oceans

    Science.gov (United States)

    Armitage, T. W. K.; Kwok, R.; Egido, A.; Smith, W. H. F.; Cullen, R.

    2017-12-01

    Satellite radar altimetry has proven to be a valuable tool for remote sensing of the polar oceans, with techniques for estimating sea ice thickness and sea surface height in the ice-covered ocean advancing to the point of becoming routine, if not operational, products. Here, we explore new techniques in radar altimetry of the polar oceans and the sea ice cover. First, we present results from fully-focused SAR (FFSAR) altimetry; by accounting for the phase evolution of scatterers in the scene, the FFSAR technique applies an inter-burst coherent integration, potentially over the entire duration that a scatterer remains in the altimeter footprint, which can narrow the effective along track resolution to just 0.5m. We discuss the improvement of using interleaved operation over burst-more operation for applying FFSAR processing to data acquired by future missions, such as a potential CryoSat follow-on. Second, we present simulated sea ice retrievals from the Ka-band Radar Interferometer (KaRIn), the instrument that will be launched on the Surface Water and Ocean Topography (SWOT) mission in 2021, that is capable of producing swath images of surface elevation. These techniques offer the opportunity to advance our understanding of the physics of the ice-covered oceans, plus new insight into how we interpret more conventional radar altimetry data in these regions.

  13. Genomic Evidence of Widespread Admixture from Polar Bears into Brown Bears during the Last Ice Age.

    Science.gov (United States)

    Cahill, James A; Heintzman, Peter D; Harris, Kelley; Teasdale, Matthew D; Kapp, Joshua; Soares, Andre E R; Stirling, Ian; Bradley, Daniel; Edwards, Ceiridwen J; Graim, Kiley; Kisleika, Aliaksandr A; Malev, Alexander V; Monaghan, Nigel; Green, Richard E; Shapiro, Beth

    2018-05-01

    Recent genomic analyses have provided substantial evidence for past periods of gene flow from polar bears (Ursus maritimus) into Alaskan brown bears (Ursus arctos), with some analyses suggesting a link between climate change and genomic introgression. However, because it has mainly been possible to sample bears from the present day, the timing, frequency, and evolutionary significance of this admixture remains unknown. Here, we analyze genomic DNA from three additional and geographically distinct brown bear populations, including two that lived temporally close to the peak of the last ice age. We find evidence of admixture in all three populations, suggesting that admixture between these species has been common in their recent evolutionary history. In addition, analyses of ten fossil bears from the now-extinct Irish population indicate that admixture peaked during the last ice age, whereas brown bear and polar bear ranges overlapped. Following this peak, the proportion of polar bear ancestry in Irish brown bears declined rapidly until their extinction. Our results support a model in which ice age climate change created geographically widespread conditions conducive to admixture between polar bears and brown bears, as is again occurring today. We postulate that this model will be informative for many admixing species pairs impacted by climate change. Our results highlight the power of paleogenomics to reveal patterns of evolutionary change that are otherwise masked in contemporary data.

  14. Sea ice-atmospheric interaction: Application of multispectral satellite data in polar surface energy flux estimates

    Science.gov (United States)

    Steffen, Konrad; Key, J.; Maslanik, J.; Schweiger, A.

    1993-01-01

    This is the third annual report on: Sea Ice-Atmosphere Interaction - Application of Multispectral Satellite Data in Polar Surface Energy Flux Estimates. The main emphasis during the past year was on: radiative flux estimates from satellite data; intercomparison of satellite and ground-based cloud amounts; radiative cloud forcing; calibration of the Advanced Very High Resolution Radiometer (AVHRR) visible channels and comparison of two satellite derived albedo data sets; and on flux modeling for leads. Major topics covered are arctic clouds and radiation; snow and ice albedo, and leads and modeling.

  15. Estimation of degree of sea ice ridging based on dual-polarized C-band SAR data

    Science.gov (United States)

    Gegiuc, Alexandru; Similä, Markku; Karvonen, Juha; Lensu, Mikko; Mäkynen, Marko; Vainio, Jouni

    2018-01-01

    For ship navigation in the Baltic Sea ice, parameters such as ice edge, ice concentration, ice thickness and degree of ridging are usually reported daily in manually prepared ice charts. These charts provide icebreakers with essential information for route optimization and fuel calculations. However, manual ice charting requires long analysis times, and detailed analysis of large areas (e.g. Arctic Ocean) is not feasible. Here, we propose a method for automatic estimation of the degree of ice ridging in the Baltic Sea region, based on RADARSAT-2 C-band dual-polarized (HH/HV channels) SAR texture features and sea ice concentration information extracted from Finnish ice charts. The SAR images were first segmented and then several texture features were extracted for each segment. Using the random forest method, we classified them into four classes of ridging intensity and compared them to the reference data extracted from the digitized ice charts. The overall agreement between the ice-chart-based degree of ice ridging and the automated results varied monthly, being 83, 63 and 81 % in January, February and March 2013, respectively. The correspondence between the degree of ice ridging reported in the ice charts and the actual ridge density was validated with data collected during a field campaign in March 2011. In principle the method can be applied to the seasonal sea ice regime in the Arctic Ocean.

  16. Consequences of long-distance swimming and travel over deep-water pack ice for a female polar bear during a year of extreme sea ice retreat

    Science.gov (United States)

    Durner, George M.; Whiteman, J.P.; Harlow, H.J.; Amstrup, Steven C.; Regehr, E.V.; Ben-David, M.

    2011-01-01

    Polar bears (Ursus maritimus) prefer to live on Arctic sea ice but may swim between ice floes or between sea ice and land. Although anecdotal observations suggest that polar bears are capable of swimming long distances, no data have been available to describe in detail long distance swimming events or the physiological and reproductive consequences of such behavior. Between an initial capture in late August and a recapture in late October 2008, a radio-collared adult female polar bear in the Beaufort Sea made a continuous swim of 687 km over 9 days and then intermittently swam and walked on the sea ice surface an additional 1,800 km. Measures of movement rate, hourly activity, and subcutaneous and external temperature revealed distinct profiles of swimming and walking. Between captures, this polar bear lost 22% of her body mass and her yearling cub. The extraordinary long distance swimming ability of polar bears, which we confirm here, may help them cope with reduced Arctic sea ice. Our observation, however, indicates that long distance swimming in Arctic waters, and travel over deep water pack ice, may result in high energetic costs and compromise reproductive fitness.

  17. Continental-scale transport of sediments by the Baltic Ice Stream elucidated by coupled grain size and Nd provenance analyses

    Science.gov (United States)

    Boswell, Steven M.; Toucanne, Samuel; Creyts, Timothy T.; Hemming, Sidney R.

    2018-05-01

    We introduce a methodology for determining the transport distance of subglacially comminuted and entrained sediments. We pilot this method on sediments from the terminal margin of the Baltic Ice Stream, the largest ice stream of the Fennoscandian Ice Sheet during the Last Glacial Maximum. A strong correlation (R2 = 0.83) between the εNd and latitudes of circum-Baltic river sediments enables us to use εNd as a calibrated measure of distance. The proportion of subglacially transported sediments in a sample is estimated from grain size ratios in the silt fraction (investigations of Fennoscandinavian erosion, and is consistent with rapid ice flow into the Baltic basins prior to the Last Glacial Maximum. The methodology introduced here could be used to infer the distances of glacigenic sediment transport from Late Pleistocene and earlier glaciations.

  18. Water on Mars: Inventory, distribution, and possible sources of polar ice

    Science.gov (United States)

    Clifford, S. M.

    1992-01-01

    Theoretical considerations and various lines of morphologic evidence suggest that, in addition to the normal seasonal and climatic exchange of H2O that occurs between the Martian polar caps, atmosphere, and mid to high latitude regolith, large volumes of water have been introduced into the planet's long term hydrologic cycle by the sublimation of equatorial ground ice, impacts, catastrophic flooding, and volcanism. Under the climatic conditions that are thought to have prevailed on Mars throughout the past 3 to 4 b.y., much of this water is expected to have been cold trapped at the poles. The amount of polar ice contributed by each of the planet's potential crustal sources is discussed and estimated. The final analysis suggests that only 5 to 15 pct. of this potential inventory is now in residence at the poles.

  19. What About Sea Ice? People, animals, and climate change in the polar regions: An online resource for the International Polar Year and beyond

    Science.gov (United States)

    Renfrow, S.; Meier, W. N.; Wolfe, J.; Scott, D.; Leon, A.; Weaver, R.

    2005-12-01

    Decreasing Arctic sea ice has been one of the most noticeable changes on Earth over the past quarter-century. The years 2002 through 2005 have had much lower summer sea ice extents than the long-term (1979-2000). Reduced sea ice extent has a direct impact on Arctic wildlife and people, as well as ramifications for regional and global climate. Students, educators, and the general public want and need to have a better understanding of sea ice. Most of us are unfamiliar with sea ice: what it is, where it occurs, and how it affects global climate. The upcoming International Polar Year will provide an opportunity for the public to learn about sea ice. Here, we provide an overview of sea ice, the changes that the sea ice is undergoing, and information about the relation between sea ice and climate. The information presented here is condensed from the National Snow and Ice Data Center's new 'All About Sea Ice' Web site (http://www.nsidc.org/seaice/), a comprehensive resource of information for sea ice.

  20. Methanesulfonic acid (MSA) migration in polar ice: data synthesis and theory

    Science.gov (United States)

    Osman, Matthew; Das, Sarah B.; Marchal, Olivier; Evans, Matthew J.

    2017-11-01

    Methanesulfonic acid (MSA; CH3SO3H) in polar ice is a unique proxy of marine primary productivity, synoptic atmospheric transport, and regional sea-ice behavior. However, MSA can be mobile within the firn and ice matrix, a post-depositional process that is well known but poorly understood and documented, leading to uncertainties in the integrity of the MSA paleoclimatic signal. Here, we use a compilation of 22 ice core MSA records from Greenland and Antarctica and a model of soluble impurity transport in order to comprehensively investigate the vertical migration of MSA from summer layers, where MSA is originally deposited, to adjacent winter layers in polar ice. We find that the shallowest depth of MSA migration in our compilation varies over a wide range (˜ 2 to 400 m) and is positively correlated with snow accumulation rate and negatively correlated with ice concentration of Na+ (typically the most abundant marine cation). Although the considered soluble impurity transport model provides a useful mechanistic framework for studying MSA migration, it remains limited by inadequate constraints on key physico-chemical parameters - most notably, the diffusion coefficient of MSA in cold ice (DMS). We derive a simplified version of the model, which includes DMS as the sole parameter, in order to illuminate aspects of the migration process. Using this model, we show that the progressive phase alignment of MSA and Na+ concentration peaks observed along a high-resolution West Antarctic core is most consistent with 10-12 m2 s-1 values previously estimated from laboratory studies. More generally, our data synthesis and model results suggest that (i) MSA migration may be fairly ubiquitous, particularly at coastal and (or) high-accumulation regions across Greenland and Antarctica; and (ii) can significantly change annual and multiyear MSA concentration averages. Thus, in most cases, caution should be exercised when interpreting polar ice core MSA records, although records

  1. Remotely Operated Vehicles under sea ice - Experiences and results from five years of polar operations

    Science.gov (United States)

    Katlein, Christian; Arndt, Stefanie; Lange, Benjamin; Belter, Hans Jakob; Schiller, Martin; Nicolaus, Marcel

    2016-04-01

    The availability of advanced robotic technologies to the Earth Science community has largely increased in the last decade. Remotely operated vehicles (ROV) enable spatially extensive scientific investigations underneath the sea ice of the polar oceans, covering a larger range and longer diving times than divers with significantly lower risks. Here we present our experiences and scientific results acquired from ROV operations during the last five years in the Arctic and Antarctic sea ice region. Working under the sea ice means to have all obstacles and investigated objects above the vehicle, and thus changes several paradigms of ROV operations as compared to blue water applications. Observations of downwelling spectral irradiance and radiance allow a characterization of the optical properties of sea ice and the spatial variability of the energy partitioning across the atmosphere-ice-ocean boundary. Our results show that the decreasing thickness and age of the sea ice have led to a significant increase in light transmission during summer over the last three decades. Spatially extensive measurements from ROV surveys generally provide more information on the light field variability than single spot measurements. The large number of sampled ice conditions during five cruises with the German research icebreaker RV Polarstern allows for the investigations of the seasonal evolution of light transmittance. Both, measurements of hyperspectral light transmittance through sea ice, as well as classification of upward-looking camera images were used to investigate the spatial distribution of ice-algal biomass. Buoyant ice-algal aggregates were found to be positioned in the stretches of level ice, rather than pressure ridges due to a physical interaction of aggregate-buoyancy and under-ice currents. Synchronous measurements of sea ice thickness by upward looking sonar provides crucial additional information to put light-transmittance and biological observations into context

  2. Implications of basal micro-earthquakes and tremor for ice stream mechanics: Stick-slip basal sliding and till erosion

    Science.gov (United States)

    Barcheck, C. Grace; Tulaczyk, Slawek; Schwartz, Susan Y.; Walter, Jacob I.; Winberry, J. Paul

    2018-03-01

    The Whillans Ice Plain (WIP) is unique among Antarctic ice streams because it moves by stick-slip. The conditions allowing stick-slip and its importance in controlling ice dynamics remain uncertain. Local basal seismicity previously observed during unstable slip is a clue to the mechanism of ice stream stick-slip and a window into current basal conditions, but the spatial extent and importance of this basal seismicity are unknown. We analyze data from a 2010-2011 ice-plain-wide seismic and GPS network to show that basal micro-seismicity correlates with large-scale patterns in ice stream slip behavior: Basal seismicity is common where the ice moves the least between unstable slip events, with small discrete basal micro-earthquakes happening within 10s of km of the central stick-slip nucleation area and emergent basal tremor occurring downstream of this area. Basal seismicity is largely absent in surrounding areas, where inter-slip creep rates are high. The large seismically active area suggests that a frictional sliding law that can accommodate stick-slip may be appropriate for ice stream beds on regional scales. Variability in seismic behavior over inter-station distances of 1-10 km indicates heterogeneity in local bed conditions and frictional complexity. WIP unstable slips may nucleate when stick-slip basal earthquake patches fail over a large area. We present a conceptual model in which basal seismicity results from slip-weakening frictional failure of over-consolidated till as it is eroded and mobilized into deforming till.

  3. IceCube Polar Virtual Reality exhibit: immersive learning for learners of all ages

    Science.gov (United States)

    Madsen, J.; Bravo Gallart, S.; Chase, A.; Dougherty, P.; Gagnon, D.; Pronto, K.; Rush, M.; Tredinnick, R.

    2017-12-01

    The IceCube Polar Virtual Reality project is an innovative, interactive exhibit that explains the operation and science of a flagship experiment in polar research, the IceCube Neutrino Observatory. The exhibit allows users to travel from the South Pole, where the detector is located, to the furthest reaches of the universe, learning how the detection of high-energy neutrinos has opened a new view to the universe. This novel exhibit combines a multitouch tabletop display system and commercially available virtual reality (VR) head-mounted displays to enable informal STEM learning of polar research. The exhibit, launched in early November 2017 during the Wisconsin Science Festival in Madison, WI, will study how immersive VR can enhance informal STEM learning. The foundation of this project is built upon a strong collaborative effort between the Living Environments Laboratory (LEL), the Wisconsin IceCube Particle Astrophysics Center (WIPAC), and the Field Day Laboratory groups from the University of Wisconsin-Madison campus. The project is funded through an NSF Advancing Informal STEM Learning (AISL) grant, under a special call for engaging students and the public in polar research. This exploratory pathways project seeks to build expertise to allow future extensions. The plan is to submit a subsequent AISL Broad Implementation proposal to add more 3D environments for other Antarctic research topics and locations in the future. We will describe the current implementation of the project and discuss the challenges and opportunities of working with an interdisciplinary team of scientists and technology and education researchers. We will also present preliminary assessment results, which seek to answer questions such as: Did users gain a better understanding of IceCube research from interacting with the exhibit? Do both technologies (touch table and VR headset) provide the same level of engagement? Is one technology better suited for specific learning outcomes?

  4. ACTIVITY OF LICHENS UNDER THE INFLUENCE OF SNOW AND ICE (18th Symposium on Polar Biology)

    OpenAIRE

    Ludger, KAPPEN; Burkhard, SCHROETER

    1997-01-01

    A major aim of our investigations is to explain the adaptation of vegetation to the peculiar environmental conditions in polar regions. Our concept describes the main limiting and favorable factors influencing photosynthetic production of cryptogams, mainly lichens. Snow and ice-usually stress factors to the activity of plants-can be effectively used by lichens because of their poikilohydrous nature. Light, the basic driving force for photosynthetic activity, may be deleterious under certain ...

  5. Implications of 36Cl exposure ages from Skye, northwest Scotland for the timing of ice stream deglaciation and deglacial ice dynamics

    Science.gov (United States)

    Small, David; Rinterknecht, Vincent; Austin, William E. N.; Bates, Richard; Benn, Douglas I.; Scourse, James D.; Bourlès, Didier L.; Hibbert, Fiona D.

    2016-10-01

    Geochronological constraints on the deglaciation of former marine based ice streams provide information on the rates and modes by which marine based ice sheets have responded to external forcing factors such as climate change. This paper presents new 36Cl cosmic ray exposure dating from boulders located on two moraines (Glen Brittle and Loch Scavaig) in southern Skye, northwest Scotland. Ages from the Glen Brittle moraines constrain deglaciation of a major marine terminating ice stream, the Barra-Donegal Ice Stream that drained the former British-Irish Ice Sheet, depending on choice of production method and scaling model this occurred 19.9 ± 1.5-17.6 ± 1.3 ka ago. We compare this timing of deglaciation to existing geochronological data and changes in a variety of potential forcing factors constrained through proxy records and numerical models to determine what deglaciation age is most consistent with existing evidence. Another small section of moraine, the Scavaig moraine, is traced offshore through multibeam swath-bathymetry and interpreted as delimiting a later stillstand/readvance stage following ice stream deglaciation. Additional cosmic ray exposure dating from the onshore portion of this moraine indicate that it was deposited 16.3 ± 1.3-15.2 ± 0.9 ka ago. When calculated using the most up-to-date scaling scheme this time of deposition is, within uncertainty, the same as the timing of a widely identified readvance, the Wester Ross Readvance, observed elsewhere in northwest Scotland. This extends the area over which this readvance has potentially occurred, reinforcing the view that it was climatically forced.

  6. Ice processes affect habitat use and movements of adult cutthroat trout and brook trout in a Wyoming foothills stream

    Science.gov (United States)

    Lindstrom, J.W.; Hubert, W.A.

    2004-01-01

    Habitat use and movements of 25 adult cutthroat trout Oncorhynchus clarkii and 25 adult brook trout Salvelinus fontinalis from fall through winter 2002-2003 were assessed by means of radiotelemetry in a 7-km reach of a Rocky Mountains foothills stream. Temporal dynamics of winter habitat conditions were evaluated by regularly measuring the features of 30 pools and 5 beaver Castor canadensis ponds in the study reach. Groundwater inputs at three locations raised mean daily water temperatures in the stream channel during winter to 0.2-0.6??C and kept at least 250 m of the downstream channel free of ice, but the lack of surface ice further downstream led to the occurrence of frazil ice and anchor ice in pools and unstable habitat conditions for trout. Pools in segments that were not affected by groundwater inputs and beaver ponds tended to be stable and snow accumulated on the surface ice. Pools throughout the study reach tended to become more stable as snow accumulated. Both cutthroat trout and brook trout selected beaver ponds as winter progressed but tended to use lateral scour pools in proportion to their availability. Tagged fish not in beaver ponds selected lateral scour pools that were deeper than average and stable during winter. Movement frequencies by tagged fish decreased from fall through winter, but some individuals of both species moved during winter. Ice processes affected both the habitat use and movement patterns of cutthroat trout and brook trout in this foothills stream.

  7. Polarization difference due to nonrandomly oriented ice particles at millimeter/submillimeter waveband

    International Nuclear Information System (INIS)

    Xie Xinxin; Miao Jungang

    2011-01-01

    This paper presents polarized signature due to oriented circular columnar and planar ice crystals at millimeter/submillimeter (mm/sub-mm) waveband. DDSCAT 6.1 and RT4 code package are employed for scattering properties and radiative transfer simulations, respectively, at the three estimated window frequencies (150, 220 and 340 GHz) of FengYun-4 (FY-4). We use empirical formulas to describe realistic sizes of planar and columnar particles and assume that ice particles are in Gamma-size distribution in this study. A 'resonance' feature of polarized signals as a function of median mass diameter is notably found for horizontally oriented columns and blunt plates at the frequency of 340 GHz; however, there is no promising resonance characteristic for horizontally aligned plates with empirical sizes at the three window channels of FY-4. The position of the resonance peak is related to particle aspect ratio, frequency and ice water path (IWP), and it moves to a shorter median mass diameter when the particle aspect ratio decreases or IWP in clouds increases. Considering that particle canting angle distribution (Gaussian distribution in this study), polarization difference, as well as the brightness temperature difference between clear and cloudy sky, decreases rapidly when particles gradually change from horizontally oriented to randomly oriented. The upwelling brightness temperature is insensitive to particle size and shape but sensitive to particle orientation, the difference of brightness temperature between horizontal and random orientation up to 6 K, whereas polarized signature is quite sensitive to particle microphysics as well as orientation; polarized measurements thereby could benefit retrieval of cloud microphysical parameters.

  8. A study of the decontamination procedures used for chemical analysis of polar deep ice cores

    Directory of Open Access Journals (Sweden)

    Takayuki Miyake

    2009-11-01

    Full Text Available We investigated the decontamination procedures used on polar deep ice cores before chemical analyses such as measurements of the concentrations of iron species and dust (microparticles. We optimized cutting and melting protocols for decontamination using chemically ultraclean polyethylene bags and simulated ice samples made from ultrapure water. For dust and ion species including acetate, which represented a high level of contamination, we were able to decrease contamination to below several μg l^ for ion concentrations and below 10000 particles ml^ for the dust concentration. These concentration levels of ion species and dust are assumed to be present in the Dome Fuji ice core during interglacial periods. Decontamination of the ice core was achieved by cutting away approximately 3 mm of the outside of a sample and by melting away approximately 30% of a sample's weight. Furthermore, we also report the preparation protocols for chemical analyses of the 2nd Dome Fuji ice core, including measurements of ion and dust concentrations, pH, electric conductivity (EC, and stable isotope ratios of water (δD and δO, based on the results of the investigation of the decontamination procedures.

  9. Organic molecules in the polar ice: from chemical analysis to environmental proxies

    Science.gov (United States)

    Barbante, Carlo; Zennaro, Piero; Giorio, Chiara; Kehrwald, Natalie; Benton, Alisa K.; Wolff, Eric W.; Kalberer, Markus; Kirchgeorg, Torben; Zangrando, Roberta; Barbaro, Elena; Gambaro, Andrea

    2015-04-01

    The molecular and isotopic compositions of organic matter buried in ice contains information that helps reconstruct past environmental conditions, evaluate histories of climate change, and assess impacts of humans on ecosystems. In recent years novel analytical techniques were developed to quantify molecular compounds in ice cores. As an example, biomass burning markers, including monosaccharide anhydrides, lightweight carboxylic acids, lignin and resin pyrolysis products, black carbon, and charcoal records help in reconstructing past fire activity across seasonal to millennial time scales. Terrestrial biomarkers, such as plant waxes (e.g. long-chain n-alkanes) are also a promising paleo vegetation proxy in ice core studies. Polycyclic aromatic hydrocarbons are ubiquitous pollutants recently detected in ice cores. These hydrocarbons primarily originate from incomplete combustion of organic matter and fossil fuels (e.g. diesel engines, domestic heating, industrial combustion) and therefore can be tracers of past combustion activities. In order to be suitable for paloeclimate purposes, organic molecular markers detected in ice cores should include the following important features. Markers have to be stable under oxidizing atmospheric conditions, and ideally should not react with hydroxyl radicals, during their transport to polar regions. Organic markers must be released in large amounts in order to be detected at remote distances from the sources. Proxies must be specific, in order to differentiate them from other markers with multiple sources. The extraction of glaciochemical information from ice cores is challenging due to the low concentrations of some impurities, thereby demanding rigorous control of external contamination sources and sensitive analytical techniques. Here, we review the analysis and use of organic molecules in ice as proxies of important environmental and climatic processes.

  10. Irish Ice Sheet dynamics during deglaciation of the central Irish Midlands: Evidence of ice streaming and surging from airborne LiDAR

    Science.gov (United States)

    Delaney, Catherine A.; McCarron, Stephen; Davis, Stephen

    2018-04-01

    High resolution digital terrain models (DTMs) generated from airborne LiDAR data and supplemented by field evidence are used to map glacial landform assemblages dating from the last glaciation (Midlandian glaciation; OI stages 2-3) in the central Irish Midlands. The DTMs reveal previously unrecognised low-amplitude landforms, including crevasse-squeeze ridges and mega-scale glacial lineations overprinted by conduit fills leading to ice-marginal subaqueous deposits. We interpret this landform assemblage as evidence for surging behaviour during ice recession. The data indicate that two separate phases of accelerated ice flow were followed by ice sheet stagnation during overall deglaciation. The second surge event was followed by a subglacial outburst flood, forming an intricate esker and crevasse-fill network. The data provide the first clear evidence that ice flow direction was eastward along the eastern watershed of the Shannon River basin, at odds with previous models, and raise the possibility that an ice stream existed in this area. Our work demonstrates the potential for airborne LiDAR surveys to produce detailed paleoglaciological reconstructions and to enhance our understanding of complex palaeo-ice sheet dynamics.

  11. United States Naval Academy Polar Science Program's Visual Arctic Observing Buoys; The IceGoat

    Science.gov (United States)

    Woods, J. E.; Clemente-Colon, P.; Nghiem, S. V.; Rigor, I.; Valentic, T. A.

    2012-12-01

    The U.S. Naval Academy Oceanography Department currently has a curriculum based Polar Science Program (USNA PSP). Within the PSP there is an Arctic Buoy Program (ABP) student research component that will include the design, build, testing and deployment of Arctic Buoys. Establishing an active, field-research program in Polar Science will greatly enhance Midshipman education and research, as well as introduce future Naval Officers to the Arctic environment. The Oceanography Department has engaged the USNA Ocean Engineering, Systems Engineering, Aerospace Engineering, and Computer Science Departments and developed a USNA Visual Arctic Observing Buoy, IceGoat1, which was designed, built, and deployed by midshipmen. The experience gained through Polar field studies and data derived from these buoys will be used to enhance course materials and laboratories and will also be used directly in Midshipman independent research projects. The USNA PSP successfully deployed IceGoat1 during the BROMEX 2012 field campaign out of Barrow, AK in March 2012. This buoy reports near real-time observation of Air Temperature, Sea Temperature, Atmospheric Pressure, Position and Images from 2 mounted webcams. The importance of this unique type of buoy being inserted into the U.S. Interagency Arctic Buoy Program and the International Arctic Buoy Programme (USIABP/IABP) array is cross validating satellite observations of sea ice cover in the Arctic with the buoys webcams. We also propose to develop multiple sensor packages for the IceGoat to include a more robust weather suite, and a passive acoustic hydrophone. Remote cameras on buoys have provided crucial qualitative information that complements the quantitative measurements of geophysical parameters. For example, the mechanical anemometers on the IABP Polar Arctic Weather Station at the North Pole Environmental Observatory (NPEO) have at times reported zero winds speeds, and inspection of the images from the NPEO cameras have showed

  12. Comparison of Single and Dual Polarized Envisat Asar Data with Laser Scanner Data of Saa Ice Freeboard in Fram Strait

    DEFF Research Database (Denmark)

    Pedersen, Leif Toudal; Kloster, Kjell; Hvidegaard, Sine Munk

    2005-01-01

    In this project we have produced co-registered datasets of laser scanner and ENVISAT ASAR AP data. A comparison of ENVISAT ASAR Alternate Polarization (AP) mode (HH+VV) backscatter coefficient values and polarization ratios with ice freeboard height measured with the KMS laser scanner is made. Th...

  13. A Closer Look at Some of Mercury's North Polar Deposits: Three Craters that Could Have Extensive Surface Ice but Don't?

    Science.gov (United States)

    Chabot, N. L.; Neumann, G. A.; Ernst, C. M.; Mazarico, E. M.; Shread, E. E.

    2018-05-01

    We investigate three of Mercury's north polar craters that are predicted from their thermal conditions to be conducive to the presence of extensive water ice at the surface, but that may lack such ice.

  14. Dependence of the cross polar cap potential saturation on the type of solar wind streams

    OpenAIRE

    Nikolaeva, N. S.; Yermolaev, Yu. I.; Lodkina, I. G.

    2013-01-01

    We compare of the cross polar cap potential (CPCP) saturation during magnetic storms induced by various types of the solar wind drivers. By using the model of Siscoe-Hill \\citep{Hilletal1976,Siscoeetal2002a,Siscoeetal2002b,Siscoeetal2004,Siscoe2011} we evaluate criteria of the CPCP saturation during the main phases of 257 magnetic storms ($Dst_{min} \\le -50$ nT) induced by the following types of the solar wind streams: magnetic clouds (MC), Ejecta, the compress region Sheath before MC ($Sh_{M...

  15. Influence of Arctic Sea Ice Extent on Polar Cloud Fraction and Vertical Structure and Implications for Regional Climate

    Science.gov (United States)

    Palm, Stephen P.; Strey, Sara T.; Spinhirne, James; Markus, Thorsten

    2010-01-01

    Recent satellite lidar measurements of cloud properties spanning a period of 5 years are used to examine a possible connection between Arctic sea ice amount and polar cloud fraction and vertical distribution. We find an anticorrelation between sea ice extent and cloud fraction with maximum cloudiness occurring over areas with little or no sea ice. We also find that over ice!free regions, there is greater low cloud frequency and average optical depth. Most of the optical depth increase is due to the presence of geometrically thicker clouds over water. In addition, our analysis indicates that over the last 5 years, October and March average polar cloud fraction has increased by about 7% and 10%, respectively, as year average sea ice extent has decreased by 5% 7%. The observed cloud changes are likely due to a number of effects including, but not limited to, the observed decrease in sea ice extent and thickness. Increasing cloud amount and changes in vertical distribution and optical properties have the potential to affect the radiative balance of the Arctic region by decreasing both the upwelling terrestrial longwave radiation and the downward shortwave solar radiation. Because longwave radiation dominates in the long polar winter, the overall effect of increasing low cloud cover is likely a warming of the Arctic and thus a positive climate feedback, possibly accelerating the melting of Arctic sea ice.

  16. The Influence of Arctic Sea Ice Extent on Polar Cloud Fraction and Vertical Structure and Implications for Regional Climate

    Science.gov (United States)

    Palm, Stephen P.; Strey, Sara T.; Spinhirne, James; Markus, Thorsten

    2010-01-01

    Recent satellite lidar measurements of cloud properties spanning a period of five years are used to examine a possible connection between Arctic sea ice amount and polar cloud fraction and vertical distribution. We find an anti-correlation between sea ice extent and cloud fraction with maximum cloudiness occurring over areas with little or no sea ice. We also find that over ice free regions, there is greater low cloud frequency and average optical depth. Most of the optical depth increase is due to the presence of geometrically thicker clouds over water. In addition, our analysis indicates that over the last 5 years, October and March average polar cloud fraction has increased by about 7 and 10 percent, respectively, as year average sea ice extent has decreased by 5 to 7 percent. The observed cloud changes are likely due to a number of effects including, but not limited to, the observed decrease in sea ice extent and thickness. Increasing cloud amount and changes in vertical distribution and optical properties have the potential to affect the radiative balance of the Arctic region by decreasing both the upwelling terrestrial longwave radiation and the downward shortwave solar radiation. Since longwave radiation dominates in the long polar winter, the overall effect of increasing low cloud cover is likely a warming of the Arctic and thus a positive climate feedback, possibly accelerating the melting of Arctic sea ice.

  17. The Contribution of Water Ice Clouds to the Water Cycle in the North Polar Region of Mars: Preliminary Analysis

    Science.gov (United States)

    Bass, D. S.; Tamppari, L. K.

    2000-01-01

    While it has long been known that Mars' north residual polar cap and the Martian regolith are significant sources of atmospheric water vapor, the amount of water vapor observed in the northern spring season by the Viking Mars Atmospheric Water Detector instrument (MAWD) cannot be attributed to cap and regolith sources alone. Kahn suggested that ice hazes may be the mechanism by which additional water is supplied to the Martian atmosphere. Additionally, a significant decrease in atmospheric water vapor was observed in the late northern summer that could not be correlated with the return of the cold seasonal C02 ice. While the detection of water ice clouds on Mars indicate that water exists in Mars' atmosphere in several different phases, the extent to which water ice clouds play a role in moving water through the Martian atmosphere remains uncertain. Work by Bass et. al. suggested that the time dependence of water ice cap seasonal variability and the increase in atmospheric water vapor depended on the polar cap center reaching 200K, the night time saturation temperature. Additionally, they demonstrated that a decrease in atmospheric water vapor may be attributed to deposition of water ice onto the surface of the polar cap; temperatures were still too warm at this time in the summer for the deposition of carbon dioxide. However, whether water ice clouds contribute significantly to this variability is unknown. Additional information is contained in original extended abstract.

  18. Movement of a female polar bear (Ursus maritimus) in the Kara Sea during the summer sea-ice break-up.

    Science.gov (United States)

    Rozhnov, V V; Platonov, N G; Naidenko, S V; Mordvintsev, I N; Ivanov, E A

    2017-01-01

    The polar bear movement trajectory in relation to onset date of the sea-ice break-up was studied in the coastal zone of the Taimyr Peninsula, eastern part of the Kara Sea, using as an example a female polar bear tagged by a radio collar with an Argos satellite transmitter. Analysis of the long-term pattern of ice melting and tracking, by means of satellite telemetry, of the female polar bear who followed the ice-edge outgoing in the north-eastern direction (in summer 2012) suggests that direction of the polar bear movement depends precisely on the direction of the sea-ice cover break-up.

  19. The relevance of grain dissection for grain size reduction in polar ice: insights from numerical models and ice core microstructure analysis

    Science.gov (United States)

    Steinbach, Florian; Kuiper, Ernst-Jan N.; Eichler, Jan; Bons, Paul D.; Drury, Martyn R.; Griera, Albert; Pennock, Gill M.; Weikusat, Ilka

    2017-09-01

    The flow of ice depends on the properties of the aggregate of individual ice crystals, such as grain size or lattice orientation distributions. Therefore, an understanding of the processes controlling ice micro-dynamics is needed to ultimately develop a physically based macroscopic ice flow law. We investigated the relevance of the process of grain dissection as a grain-size-modifying process in natural ice. For that purpose, we performed numerical multi-process microstructure modelling and analysed microstructure and crystallographic orientation maps from natural deep ice-core samples from the North Greenland Eemian Ice Drilling (NEEM) project. Full crystallographic orientations measured by electron backscatter diffraction (EBSD) have been used together with c-axis orientations using an optical technique (Fabric Analyser). Grain dissection is a feature of strain-induced grain boundary migration. During grain dissection, grain boundaries bulge into a neighbouring grain in an area of high dislocation energy and merge with the opposite grain boundary. This splits the high dislocation-energy grain into two parts, effectively decreasing the local grain size. Currently, grain size reduction in ice is thought to be achieved by either the progressive transformation from dislocation walls into new high-angle grain boundaries, called subgrain rotation or polygonisation, or bulging nucleation that is assisted by subgrain rotation. Both our time-resolved numerical modelling and NEEM ice core samples show that grain dissection is a common mechanism during ice deformation and can provide an efficient process to reduce grain sizes and counter-act dynamic grain-growth in addition to polygonisation or bulging nucleation. Thus, our results show that solely strain-induced boundary migration, in absence of subgrain rotation, can reduce grain sizes in polar ice, in particular if strain energy gradients are high. We describe the microstructural characteristics that can be used to

  20. The Relevance of Grain Dissection for Grain Size Reduction in Polar Ice: Insights from Numerical Models and Ice Core Microstructure Analysis

    Directory of Open Access Journals (Sweden)

    Florian Steinbach

    2017-09-01

    Full Text Available The flow of ice depends on the properties of the aggregate of individual ice crystals, such as grain size or lattice orientation distributions. Therefore, an understanding of the processes controlling ice micro-dynamics is needed to ultimately develop a physically based macroscopic ice flow law. We investigated the relevance of the process of grain dissection as a grain-size-modifying process in natural ice. For that purpose, we performed numerical multi-process microstructure modeling and analyzed microstructure and crystallographic orientation maps from natural deep ice-core samples from the North Greenland Eemian Ice Drilling (NEEM project. Full crystallographic orientations measured by electron backscatter diffraction (EBSD have been used together with c-axis orientations using an optical technique (Fabric Analyser. Grain dissection is a feature of strain-induced grain boundary migration. During grain dissection, grain boundaries bulge into a neighboring grain in an area of high dislocation energy and merge with the opposite grain boundary. This splits the high dislocation-energy grain into two parts, effectively decreasing the local grain size. Currently, grain size reduction in ice is thought to be achieved by either the progressive transformation from dislocation walls into new high-angle grain boundaries, called subgrain rotation or polygonisation, or bulging nucleation that is assisted by subgrain rotation. Both our time-resolved numerical modeling and NEEM ice core samples show that grain dissection is a common mechanism during ice deformation and can provide an efficient process to reduce grain sizes and counter-act dynamic grain-growth in addition to polygonisation or bulging nucleation. Thus, our results show that solely strain-induced boundary migration, in absence of subgrain rotation, can reduce grain sizes in polar ice, in particular if strain energy gradients are high. We describe the microstructural characteristics that can be

  1. Future sea ice conditions in Western Hudson Bay and consequences for polar bears in the 21st century.

    Science.gov (United States)

    Castro de la Guardia, Laura; Derocher, Andrew E; Myers, Paul G; Terwisscha van Scheltinga, Arjen D; Lunn, Nick J

    2013-09-01

    The primary habitat of polar bears is sea ice, but in Western Hudson Bay (WH), the seasonal ice cycle forces polar bears ashore each summer. Survival of bears on land in WH is correlated with breakup and the ice-free season length, and studies suggest that exceeding thresholds in these variables will lead to large declines in the WH population. To estimate when anthropogenic warming may have progressed sufficiently to threaten the persistence of polar bears in WH, we predict changes in the ice cycle and the sea ice concentration (SIC) in spring (the primary feeding period of polar bears) with a high-resolution sea ice-ocean model and warming forced with 21st century IPCC greenhouse gas (GHG) emission scenarios: B1 (low), A1B (medium), and A2 (high). We define critical years for polar bears based on proposed thresholds in breakup and ice-free season and we assess when ice-cycle conditions cross these thresholds. In the three scenarios, critical years occur more commonly after 2050. From 2001 to 2050, 2 critical years occur under B1 and A2, and 4 under A1B; from 2051 to 2100, 8 critical years occur under B1, 35 under A1B and 41 under A2. Spring SIC in WH is high (>90%) in all three scenarios between 2001 and 2050, but declines rapidly after 2050 in A1B and A2. From 2090 to 2100, the mean spring SIC is 84 (±7)% in B1, 56 (±26)% in A1B and 20 (±13)% in A2. Our predictions suggest that the habitat of polar bears in WH will deteriorate in the 21st century. Ice predictions in A1B and A2 suggest that the polar bear population may struggle to persist after ca. 2050. Predictions under B1 suggest that reducing GHG emissions could allow polar bears to persist in WH throughout the 21st century. © 2013 John Wiley & Sons Ltd.

  2. Increasing nest predation will be insufficient to maintain polar bear body condition in the face of sea ice loss.

    Science.gov (United States)

    Dey, Cody J; Richardson, Evan; McGeachy, David; Iverson, Samuel A; Gilchrist, Hugh G; Semeniuk, Christina A D

    2017-05-01

    Climate change can influence interspecific interactions by differentially affecting species-specific phenology. In seasonal ice environments, there is evidence that polar bear predation of Arctic bird eggs is increasing because of earlier sea ice breakup, which forces polar bears into nearshore terrestrial environments where Arctic birds are nesting. Because polar bears can consume a large number of nests before becoming satiated, and because they can swim between island colonies, they could have dramatic influences on seabird and sea duck reproductive success. However, it is unclear whether nest foraging can provide an energetic benefit to polar bear populations, especially given the capacity of bird populations to redistribute in response to increasing predation pressure. In this study, we develop a spatially explicit agent-based model of the predator-prey relationship between polar bears and common eiders, a common and culturally important bird species for northern peoples. Our model is composed of two types of agents (polar bear agents and common eider hen agents) whose movements and decision heuristics are based on species-specific bioenergetic and behavioral ecological principles, and are influenced by historical and extrapolated sea ice conditions. Our model reproduces empirical findings that polar bear predation of bird nests is increasing and predicts an accelerating relationship between advancing ice breakup dates and the number of nests depredated. Despite increases in nest predation, our model predicts that polar bear body condition during the ice-free period will continue to decline. Finally, our model predicts that common eider nests will become more dispersed and will move closer to the mainland in response to increasing predation, possibly increasing their exposure to land-based predators and influencing the livelihood of local people that collect eider eggs and down. These results show that predator-prey interactions can have nonlinear responses to

  3. Prospects for reconstructing paleoenvironmental conditions from organic compounds in polar snow and ice

    Science.gov (United States)

    Giorio, Chiara; Kehrwald, Natalie; Barbante, Carlo; Kalberer, Markus; King, Amy C. F.; Thomas, Elizabeth R.; Wolff, Eric W.; Zennaro, Piero

    2018-03-01

    Polar ice cores provide information about past climate and environmental changes over periods ranging from a few years up to 800,000 years. The majority of chemical studies have focused on determining inorganic components, such as major ions and trace elements as well as on their isotopic fingerprint. In this paper, we review the different classes of organic compounds that might yield environmental information, discussing existing research and what is needed to improve knowledge. We also discuss the problems of sampling, analysis and interpretation of organic molecules in ice. This review highlights the great potential for organic compounds to be used as proxies for anthropogenic activities, past fire events from different types of biomass, terrestrial biogenic emissions and marine biological activity, along with the possibility of inferring past temperature fluctuations and even large-scale climate variability. In parallel, comprehensive research needs to be done to assess the atmospheric stability of these compounds, their ability to be transported long distances in the atmosphere, and their stability in the archive in order to better interpret their fluxes in ice cores. In addition, specific decontamination procedures, analytical methods with low detection limits (ng/L or lower), fast analysis time and low sample requests need to be developed in order to ensure a good time resolution in the archive.

  4. Prospects for reconstructing paleoenvironmental conditions from organic compounds in polar snow and ice

    Science.gov (United States)

    Giorio, Chiara; Kehrwald, Natalie; Barbante, Carlo; Kalberer, Markus; King, Amy C.F.; Thomas, Elizabeth R.; Wolff, Eric W.; Zennaro, Piero

    2018-01-01

    Polar ice cores provide information about past climate and environmental changes over periods ranging from a few years up to 800,000 years. The majority of chemical studies have focused on determining inorganic components, such as major ions and trace elements as well as on their isotopic fingerprint. In this paper, we review the different classes of organic compounds that might yield environmental information, discussing existing research and what is needed to improve knowledge. We also discuss the problems of sampling, analysis and interpretation of organic molecules in ice. This review highlights the great potential for organic compounds to be used as proxies for anthropogenic activities, past fire events from different types of biomass, terrestrial biogenic emissions and marine biological activity, along with the possibility of inferring past temperature fluctuations and even large-scale climate variability. In parallel, comprehensive research needs to be done to assess the atmospheric stability of these compounds, their ability to be transported long distances in the atmosphere, and their stability in the archive in order to better interpret their fluxes in ice cores. In addition, specific decontamination procedures, analytical methods with low detection limits (ng/L or lower), fast analysis time and low sample requests need to be developed in order to ensure a good time resolution in the archive.

  5. Thermal behavior and ice-table depth within the north polar erg of Mars

    Science.gov (United States)

    Putzig, Nathaniel E.; Mellon, Michael T.; Herkenhoff, Kenneth E.; Phillips, Roger J.; Davis, Brian J.; Ewer, Kenneth J.; Bowers, Lauren M.

    2014-02-01

    We fully resolve a long-standing thermal discrepancy concerning the north polar erg of Mars. Several recent studies have shown that the erg's thermal properties are consistent with normal basaltic sand overlying shallow ground ice or ice-cemented sand. Our findings bolster that conclusion by thoroughly characterizing the thermal behavior of the erg, demonstrating that other likely forms of physical heterogeneity play only a minor role, and obviating the need to invoke exotic materials. Thermal inertia as calculated from orbital temperature observations of the dunes has previously been found to be more consistent with dust-sized materials than with sand. Since theory and laboratory data show that dunes will only form out of sand-sized particles, exotic sand-sized agglomerations of dust have been invoked to explain the low values of thermal inertia. However, the polar dunes exhibit the same darker appearance and color as that of dunes found elsewhere on the planet that have thermal inertia consistent with normal sand-sized basaltic grains, whereas Martian dust deposits are generally lighter and redder. The alternative explanation for the discrepancy as a thermal effect of a shallow ice table is supported by our analysis of observations from the Mars Global Surveyor Thermal Emission Spectrometer and the Mars Odyssey Thermal Emission Imaging System and by forward modeling of physical heterogeneity. In addition, our results exclude a uniform composition of dark dust-sized materials, and they show that the thermal effects of the dune slopes and bright interdune materials evident in high-resolution images cannot account for the erg's thermal behavior.

  6. Thermal behavior and ice-table depth within the north polar erg of Mars

    Science.gov (United States)

    Putzig, Nathaniel E.; Mellon, Michael T.; Herkenhoff, Kenneth E.; Phillips, Roger J.; Davis, Brian J.; Ewer, Kenneth J.; Bowers, Lauren M.

    2014-01-01

    We fully resolve a long-standing thermal discrepancy concerning the north polar erg of Mars. Several recent studies have shown that the erg’s thermal properties are consistent with normal basaltic sand overlying shallow ground ice or ice-cemented sand. Our findings bolster that conclusion by thoroughly characterizing the thermal behavior of the erg, demonstrating that other likely forms of physical heterogeneity play only a minor role, and obviating the need to invoke exotic materials. Thermal inertia as calculated from orbital temperature observations of the dunes has previously been found to be more consistent with dust-sized materials than with sand. Since theory and laboratory data show that dunes will only form out of sand-sized particles, exotic sand-sized agglomerations of dust have been invoked to explain the low values of thermal inertia. However, the polar dunes exhibit the same darker appearance and color as that of dunes found elsewhere on the planet that have thermal inertia consistent with normal sand-sized basaltic grains, whereas Martian dust deposits are generally lighter and redder. The alternative explanation for the discrepancy as a thermal effect of a shallow ice table is supported by our analysis of observations from the Mars Global Surveyor Thermal Emission Spectrometer and the Mars Odyssey Thermal Emission Imaging System and by forward modeling of physical heterogeneity. In addition, our results exclude a uniform composition of dark dust-sized materials, and they show that the thermal effects of the dune slopes and bright interdune materials evident in high-resolution images cannot account for the erg’s thermal behavior.

  7. Comparison of CO/sub 2/ measurements by two laboratories on air from bubbles in polar ice

    Energy Technology Data Exchange (ETDEWEB)

    Barnola, J.M.; Raynaud, D.; Neftel, A.; Oeschger, H.

    1983-06-02

    The CO/sub 2/ content of air enclosed in bubbles in polar ice has been reported by two laboratories (in Grenoble and Bern) to be representative of the atmospheric CO/sub 2/ concentration at the time the ice was formed. Such ice core studies indicate lower concentrations in ice formed at the end of the ice age, around 18,000 yr BP, and several explanations have been proposed for such a change. Both laboratories are currently measuring various ice cores in order to determine the pre-AD 1850 CO/sub 2/ level in the atmosphere, which relates to the partitioning of anthropogenic CO/sub 2/ among the atmospheric, biospheric and oceanic reservoirs. The two laboratories use different ice cores and different analytical procedures and, therefore, there is a need to know to what extent the measurements are quantitatively comparable. The results are presented of a comparison between the two laboratories based on measurements from the same ice core sections, which indicate that the measurements can be compared with great confidence. The results suggest that the mean CO/sub 2/ level recorded by Antartic ice for the period 800-2500 yr BP is about 260 p.p.m.v.

  8. Azimuthal Structure of the Sand Erg that Encircles the North Polar Water-Ice Cap

    Science.gov (United States)

    Teodoro, L. A.; Elphic, R. C.; Eke, V. R.; Feldman, W. C.; Maurice, S.; Pathare, A.

    2011-12-01

    The sand erg that completely encircles the perennial water-ice cap that covers the Martian north geographic pole displays considerable azimuthal structure as seen in visible and near-IR images. Much of this structure is associated with the terminations of the many steep troughs that cut spiral the approximately 3 km thick polar ice cap. Other contributions come from the katabatic winds that spill over steep-sided edges of the cap, such as what bounds the largest set of dunes that comprise Olympia Undae. During the spring and summer months when these winds initiate from the higher altitudes that contain sublimating CO2 ice, which is very cold and dry, heat adiabatically when they compress as they lose altitude. These winds should then remove H2O moisture from the uppermost layer of the sand dunes that are directly in their path. Two likely locations where this desiccation may occur preferentially is at the termination of Chasma Boreale and the ice cap at Olympia Undae. We will search for this effect by sharpening the spatial structure of the epithermal neutron counting rates measured at northern high latitudes using the Mars Odyssey Neutron Spectrometer (MONS). The epithermal range of neutron energies is nearly uniquely sensitive to the hydrogen content of surface soils, which should likely be in the form of H2O/OH molecules/radicals. We therefore convert epithermal counting rates in terms of Water-Equivalent-Hydrogen, WEH. However, MONS counting-rate data have a FWHM of ~550 km., which is sufficiently broad to prevent a close association of WEH variability with images of geological features. In this study, we reduce spurious features in the instrument smeared neutron counting rates through deconvolution. We choose the PIXON numerical deconvolution technique for this purpose. This technique uses a statistical approach (Pina 2001, Eke 2001), which is capable of removing spurious features in the data in the presence of noise. We have previously carried out a detailed

  9. Effects of earlier sea ice breakup on survival and population size of polar bears in western Hudson Bay

    Science.gov (United States)

    Regehr, E.V.; Lunn, N.J.; Amstrup, Steven C.; Stirling, I.

    2007-01-01

    Some of the most pronounced ecological responses to climatic warming are expected to occur in polar marine regions, where temperature increases have been the greatest and sea ice provides a sensitive mechanism by which climatic conditions affect sympagic (i.e., with ice) species. Population-level effects of climatic change, however, remain difficult to quantify. We used a flexible extension of Cormack-Jolly-Seber capture-recapture models to estimate population size and survival for polar bears (Ursus maritimus), one of the most ice-dependent of Arctic marine mammals. We analyzed data for polar bears captured from 1984 to 2004 along the western coast of Hudson Bay and in the community of Churchill, Manitoba, Canada. The Western Hudson Bay polar bear population declined from 1,194 (95% CI = 1,020-1,368) in 1987 to 935 (95% CI = 794-1,076) in 2004. Total apparent survival of prime-adult polar bears (5-19 yr) was stable for females (0.93; 95% CI = 0.91-0.94) and males (0.90; 95% CI = 0.88-0.91). Survival of juvenile, subadult, and senescent-adult polar bears was correlated with spring sea ice breakup date, which was variable among years and occurred approximately 3 weeks earlier in 2004 than in 1984. We propose that this correlation provides evidence for a causal association between earlier sea ice breakup (due to climatic warming) and decreased polar bear survival. It may also explain why Churchill, like other communities along the western coast of Hudson Bay, has experienced an increase in human-polar bear interactions in recent years. Earlier sea ice breakup may have resulted in a larger number of nutritionally stressed polar bears, which are encroaching on human habitations in search of supplemental food. Because western Hudson Bay is near the southern limit of the species' range, our findings may foreshadow the demographic responses and management challenges that more northerly polar bear populations will experience if climatic warming in the Arctic continues as

  10. Subauroral Polarization Streams (SAPS) Duration as Determined From Van Allen Probe Successive Electric Drift Measurements

    Science.gov (United States)

    Lejosne, Solène; Mozer, F. S.

    2017-09-01

    We examine a characteristic feature of the magnetosphere-ionosphere coupling, namely, the persistent and latitudinally narrow bands of rapid westward ion drifts called the subauroral polarization streams (SAPS). Despite countless works on SAPS, information relative to their durations is lacking. Here we report on the first statistical analysis of more than 200 near-equatorial SAPS observations based on more than 2 years of Van Allen Probe electric drift measurements. First, we present results relative to SAPS radial locations and amplitudes. Then, we introduce two different ways to estimate SAPS durations. In both cases, SAPS activity is estimated to last for about 9 h on average. However, our estimates for SAPS duration are limited either by the relatively long orbital periods of the spacecraft or by the relatively small number of observations involved. Fifty percent of the events fit within the time interval [0;18] hours.

  11. Massive CO2 Ice Deposits Sequestered in the South Polar Layered Deposits of Mars

    Science.gov (United States)

    Phillips, Roger J.; Davis, Brian J.; Tanaka, Kenneth L.; Byrne, Shane; Mellon, Michael T.; Putzig, Nathaniel E.; Haberle, Robert M.; Kahre, Melinda A.; Campbell, Bruce A.; Carter, Lynn M.; Smith, Isaac B.; Holt, John W.; Smrekar, Suzanne E.; Nunes, Daniel C.; Plaut, Jeffrey J.; Egan, Anthony F.; Titus, Timothy N.; Seu, Roberto

    2011-01-01

    Shallow Radar soundings from the Mars Reconnaissance Orbiter reveal a buried deposit of carbon dioxide (CO2) ice within the south polar layered deposits of Mars with a volume of 9500 to 12,500 cubic kilometers, about 30 times that previously estimated for the south pole residual cap. The deposit occurs within a stratigraphic unit that is uniquely marked by collapse features and other evidence of interior CO2 volatile release. If released into the atmosphere at times of high obliquity, the CO2 reservoir would increase the atmospheric mass by up to 80%, leading to more frequent and intense dust storms and to more regions where liquid water could persist without boiling.

  12. Leveraging scientific credibility about Arctic sea ice trends in a polarized political environment.

    Science.gov (United States)

    Jamieson, Kathleen Hall; Hardy, Bruce W

    2014-09-16

    This work argues that, in a polarized environment, scientists can minimize the likelihood that the audience's biased processing will lead to rejection of their message if they not only eschew advocacy but also, convey that they are sharers of knowledge faithful to science's way of knowing and respectful of the audience's intelligence; the sources on which they rely are well-regarded by both conservatives and liberals; and the message explains how the scientist arrived at the offered conclusion, is conveyed in a visual form that involves the audience in drawing its own conclusions, and capsulizes key inferences in an illustrative analogy. A pilot experiment raises the possibility that such a leveraging-involving-visualizing-analogizing message structure can increase acceptance of the scientific claims about the downward cross-decade trend in Arctic sea ice extent and elicit inferences consistent with the scientific consensus on climate change among conservatives exposed to misleadingly selective data in a partisan news source.

  13. Cold-Based Glaciation on Mercury: Accumulation and Flow of Ice in Permanently-Shadowed Circum-Polar Crater Interiors

    Science.gov (United States)

    Fastook, J. L.; Head, J. W.

    2018-05-01

    Examining the potential for dynamic flow of ice deposits in permanently-shadowed craters, it is determined that the cold environment of the polar craters yields very small velocities and deformation is minimal on a time scale of millions of years.

  14. Polarized Raman spectroscopic study of relaxed high density amorphous ices under pressure.

    Science.gov (United States)

    Suzuki, Yoshiharu; Tominaga, Yasunori

    2010-10-28

    We have made high density amorphous ice (HDA) by the pressure-induced amorphization of hexagonal ice at 77 K and measured the volume change on isobaric heating in a pressure range between 0.1 and 1.5 GPa. The volume of HDA on heating below ∼0.35 GPa increases, while the volume of HDA on heating above ∼0.35 GPa decreases. The polarized OH-stretching Raman spectra of the relaxed HDAs are compared with that of the unannealed HDA. The relaxed HDAs are prepared at 0.2 GPa at 130 K and 1.5 GPa at 160 K. It is found that the relatively strong totally symmetric OH-stretching vibration mode around 3100 cm(-1) exists in the depolarized reduced Raman spectrum χ(VH)(") of the unannealed HDA and that its intensity rapidly decreases by relaxation. The χ(VH)(") profiles of the relaxed HDA are similar to those of liquid water. These results indicate that the HDA reaches a nearly equilibrium state by annealing and the intrinsic state of HDA relates to a liquid state. The pressure-volume curve of the relaxed HDA at 140 K seems to be smooth in the pressure range below 1.5 GPa.

  15. SEA-LEVEL RISE. Sea-level rise due to polar ice-sheet mass loss during past warm periods.

    Science.gov (United States)

    Dutton, A; Carlson, A E; Long, A J; Milne, G A; Clark, P U; DeConto, R; Horton, B P; Rahmstorf, S; Raymo, M E

    2015-07-10

    Interdisciplinary studies of geologic archives have ushered in a new era of deciphering magnitudes, rates, and sources of sea-level rise from polar ice-sheet loss during past warm periods. Accounting for glacial isostatic processes helps to reconcile spatial variability in peak sea level during marine isotope stages 5e and 11, when the global mean reached 6 to 9 meters and 6 to 13 meters higher than present, respectively. Dynamic topography introduces large uncertainties on longer time scales, precluding robust sea-level estimates for intervals such as the Pliocene. Present climate is warming to a level associated with significant polar ice-sheet loss in the past. Here, we outline advances and challenges involved in constraining ice-sheet sensitivity to climate change with use of paleo-sea level records. Copyright © 2015, American Association for the Advancement of Science.

  16. The effect of the external medium on the gravity-induced polarity of cytoplasmic streaming in Chara corallina (Characeae)

    Science.gov (United States)

    Staves, M. P.; Wayne, R.; Leopold, A. C.

    1997-01-01

    Gravity induces a polarity of cytoplasmic streaming in vertical internodal cells of Chara such that the downwardly directed stream moves faster than the upwardly directed stream. In order to determine whether the statolith theory (in which intracellular sedimenting particles are responsible for gravity sensing) or the gravitational pressure theory (in which the entire protoplast acts as the gravity sensor) best explain the gravity response in Chara internodal cells, we controlled the physical properties of the external medium, including density and osmolarity, with impermeant solutes and examined the effect on the polarity of cytoplasmic streaming. As the density of the external medium is increased, the polarity of cytoplasmic streaming decreases and finally disappears when the density of the external medium is equal to that of the cell (1015 kg/m3). A further increase in the density of the external medium causes a reversal of the gravity response. These results are consistent with the gravitational pressure theory of gravity sensing since the buoyancy of the protoplast is dependent on the difference between the density of the protoplast and the external medium, and are inconsistent with the statolith theory since the buoyancy of intracellular particles are unaffected by changes in the external medium.

  17. IOCCG Report Number 16, 2015 Ocean Colour Remote Sensing in Polar Seas . Chapter 2; The Polar Environment: Sun, Clouds, and Ice

    Science.gov (United States)

    Comiso, Josefino C.; Perovich, Don; Stamnes, Knut; Stuart, Venetia (Editor)

    2015-01-01

    The polar regions are places of extremes. There are months when the regions are enveloped in unending darkness, and months when they are in continuous daylight. During the daylight months the sun is low on the horizon and often obscured by clouds. In the dark winter months temperatures are brutally cold, and high winds and blowing snow are common. Even in summer, temperatures seldom rise above 0degC. The cold winter temperatures cause the ocean to freeze, forming sea ice. This sea ice cover acts as a barrier limiting the transfer of heat, moisture, and momentum between the atmosphere and the ocean. It also greatly complicates the optical signature of the surface. Taken together, these factors make the polar regions a highly challenging environment for optical remote sensing of the ocean.

  18. Correlation of Ice-Rafted Detritus in South Atlantic Sediments with Climate Proxies in Polar Ice over the Last Glacial Period

    Directory of Open Access Journals (Sweden)

    Sharon L. Kanfoush

    2013-03-01

    Full Text Available Previous study identified 6–7 millennial-scale episodes of South Atlantic ice-rafted sediment deposition (SA events during the glaciation. Questions remain, however, regarding their origin, significance for sea-ice and/or Antarctic ice-sheet dynamics, and relationship to climate. Here I correlate sediment core (TTN057–21 SA events to Greenland and Antarctic ice using two independent methods, stable isotopes and geomagnetic paleointensity, placing SA events in the context of polar climate change in both hemispheres. Marine isotopic stage (MIS 3 SA events generally coincided with Greenland interstadials and with cooling following Antarctic warm events (A1-A4. This anti-phase behavior is best illustrated when SA0 coincided with both the Antarctic Cold Reversal and Bolling-Allerod warming in Greenland. Moreover, SA events coincide with sea-level rises during the deglaciation (mwp1A and MIS 3 (30.4, 38.3, 43.7, 51.5 ka, implying unpinning of grounded Weddell Sea region ice masses discharged debris-laden bergs that had a chilling effect on South Atlantic surface temperatures.

  19. The influence of firn air transport processes and radiocarbon production on gas records from polar firn and ice

    DEFF Research Database (Denmark)

    Buizert, Christo

    Air bubbles found in polar ice cores preserve a record of past atmospheric composition up to 800 kyr back in time. The composition of the bubbles is not identical to the ancient atmosphere, as it is influenced by processes prior to trapping, within the ice sheet itself, and during sampling...... does not vanish completely in the lock-in zone, as is commonly assumed. Six state-of-the-art firn air transport models are tuned to the NEEM site; all models successfully reproduce the data within a 1 Gaussian distribution. We present the first intercomparison study of firn air models, where we...

  20. Global Pattern of The Evolutions of the Sub-Auroral Polarization Streams

    Science.gov (United States)

    He, F.; Zhang, X.; Wang, W.; Wan, W.

    2017-12-01

    Due to the spatial and temporal limitations of the in-situ measurements from the low altitude polar orbiting satellites or the ionospheric scan by incoherent scatter radars, the global configuration and evolution of SAPS are still not very clear. Here, we present multi-satellite observations of the evolution of subauroral polarization streams (SAPS) during the main phase of a server geomagnetic storm occurred on 31 March 2001. DMSP F12 to F15 observations indicate that the SAPS were first generated in the dusk sector at the beginning of the main phase. Then the SAPS channel expanded towards the midnight and moved to lower latitudes as the main phase went on. The peak velocity, latitudinal width, latitudinal alignment, and longitudinal span of the SAPS channels were highly dynamic during the storm main phase. The global evolution of the SAPS corresponds well with that of the region-2 field-aligned currents, which are mainly determined by the azimuthal pressure gradient of the ring current. Further studies on 37 storms and 30 isolated substorms indicate that the lifetime of the SAPS channel was proportional to the period of time for southward interplanetary magnetic field (IMF). The SAPS channel disappeared after northward turning of the IMF. During the recovery phase, if the IMF kept northward, no SAPS channel was generated, if the IMF turned to southward again, however, SAPS channel will be generated again with lifetime proportional to the duration of the southward IMF. During isolated substorms, the SAPS channel was also controlled by IMF. The SAPS channel was generated after substorm onset and the peak drift velocity of the SAPS channel achieved its maximum during the recovery phase of the substorm. It is suggested that, SAPS channel were mainly controlled by IMF, more works should be done with observations or simulations of investigate the global patterns of the SAPS and the magnetosphere-ionosphere couplings.

  1. Ice Velocity Variations of the Polar Record Glacier (East Antarctica Using a Rotation-Invariant Feature-Tracking Approach

    Directory of Open Access Journals (Sweden)

    Tingting Liu

    2017-12-01

    Full Text Available In this study, the ice velocity changes from 2004 to 2015 of the Polar Record Glacier (PRG in East Antarctica were investigated based on a feature-tracking method using Landsat-7 enhanced thematic mapper plus (ETM+ and Landsat-8 operational land imager (OLI images. The flow field of the PRG curves make it difficult to generate ice velocities in some areas using the traditional normalized cross-correlation (NCC-based feature-tracking method. Therefore, a rotation-invariant parameter from scale-invariant feature transform (SIFT is introduced to build a novel rotation-invariant feature-tracking approach. The validation was performed based on multi-source images and the making earth system data records for use in research environments (MEaSUREs interferometric synthetic aperture radar (InSAR-based Antarctica ice velocity map data set. The results indicate that the proposed method is able to measure the ice velocity in more areas and performs as well as the traditional NCC-based feature-tracking method. The sequential ice velocities obtained present the variations in the PRG during this period. Although the maximum ice velocity of the frontal margin of the PRG and the frontal iceberg reached about 900 m/a and 1000 m/a, respectively, the trend from 2004 to 2015 showed no significant change. Under the interaction of the Polar Times Glacier and the Polarforschung Glacier, both the direction and the displacement of the PRG were influenced. This impact also led to higher velocities in the western areas of the PRG than in the eastern areas. In addition, elevation changes and frontal iceberg calving also impacted the ice velocity of the PRG.

  2. A gas extraction system for the measurement of carbon dioxide and carbon isotopes in polar ice cores

    International Nuclear Information System (INIS)

    Steig, E.

    1992-06-01

    Knowledge of the distribution of Carbon 13 in the glacial ocean, atmosphere, and biosphere is important to understanding the causes of glacial/interglacial changes in atmospheric CO 2 levels. Although deep-ocean Carbon 13 values are well-constrained by ocean sediment studies, model-based estimates of changes in the carbon budget for the biosphere and atmosphere vary considerably. Measurement of atmospheric Carbon 13 in CO 2 in ice cores will provide additional constraints on this budget and will also improve estimates of changes in the ocean surface layer Carbon 13. Direct measurement of ancient atmospheric Carbon 13 can be accomplished through polar ice core studies. A gas-extraction line for ice cores has been designed and constructed with particular attention to the specific difficulties of measuring Carbon 13 in CO 2 . The ice is shaved, rather than crushed, to minimize fractionation effects resulting from gas travel through long air-paths in the ice. To minimize the risk of isotopic contamination and fractionation within the vacuum line, CO 2 is separated immediately from the air; the CO 2 concentration is then measured by a simple pressure/volume comparison rather than by gas chromatography or spectroscopy. Measurements from Greenland ice core samples give an average value of 280±2 ppM CO 2 for preindustrial samples, demonstrating that the extraction system gives accurate, precise determinations Of CO 2 concentrations. Measurement of δ 13 C from polar ice samples has not been achieved at this time. However, results on standard air samples demonstrate a precision for δ 13 C of less than 0.2 per-thousand at the 95% confidence level

  3. Web-based Tools for Educators: Outreach Activities of the Polar Radar for Ice Sheet Measurements (PRISM) Project

    Science.gov (United States)

    Braaten, D. A.; Holvoet, J. F.; Gogineni, S.

    2003-12-01

    The Radar Systems and Remote Sensing Laboratory at the University of Kansas (KU) has implemented extensive outreach activities focusing on Polar Regions as part of the Polar Radar for Ice Sheet Measurements (PRISM) project. The PRISM project is developing advanced intelligent remote sensing technology that involves radar systems, an autonomous rover, and communications systems to measure detailed ice sheet characteristics, and to determine bed conditions (frozen or wet) below active ice sheets in both Greenland and Antarctica. These measurements will provide a better understanding of the response of polar ice sheets to global climate change and the resulting impact the ice sheets will have on sea level rise. Many of the research and technological development aspects of the PRISM project, such as robotics, radar systems, climate change and exploration of harsh environments, can kindle an excitement and interest in students about science and technology. These topics form the core of our K-12 education and training outreach initiatives, which are designed to capture the imagination of young students, and prompt them to consider an educational path that will lead them to scientific or engineering careers. The K-12 PRISM outreach initiatives are being developed and implemented in a collaboration with the Advanced Learning Technology Program (ALTec) of the High Plains Regional Technology in Education Consortium (HPR*TEC). ALTec is associated with the KU School of Education, and is a well-established educational research center that develops and hosts web tools to enable teachers nationwide to network, collaborate, and share resources with other teachers. An example of an innovative and successful web interface developed by ALTec is called TrackStar. Teachers can use TrackStar over the Web to develop interactive, resource-based lessons (called tracks) on-line for their students. Once developed, tracks are added to the TrackStar database and can be accessed and modified

  4. An Auroral Boundary-Oriented Model of Subauroral Polarization Streams (SAPS)

    Science.gov (United States)

    Landry, R. G.; Anderson, P. C.

    2018-04-01

    An empirical model of subauroral polarization stream (SAPS) electric fields has been developed using measurements of ion drifts and particle precipitation made by the Defense Meteorological Satellite Program from 1987 to 2012 and Dynamics Explorer 2 as functions of magnetic local time (MLT), magnetic latitude, the auroral electrojet index (AE), hemisphere, and day of year. Over 500,000 subauroral passes are used. This model is oriented in degree magnetic latitude equatorward of the aurora and takes median values instead of the mean to avoid the contribution of low occurrence frequency subauroral ion drifts so that the model is representative of the much more common, latitudinally broad, low-amplitude SAPS field. The SAPS model is in broad agreement with previous statistical efforts in the variation of the SAPS field with MLT and magnetic activity level, although the median field is weaker. Furthermore, we find that the median SAPS field is roughly conjugate in both hemispheres for all seasons, with a maximum in SAPS amplitude and width found for 1800-2000 MLT. The SAPS amplitude is found to vary seasonally only from about 1800-2000 MLT, maximizing in both hemispheres during equinox months. Because this feature exists despite controlling for the AE index, it is suggested that this is due to a seasonal variation in the flux tube averaged ionospheric conductance at MLT sectors where it is more likely that one flux tube footprint is in darkness while the other is in daylight.

  5. What to eat now? Shifts in polar bear diet during the ice-free season in western Hudson Bay

    Science.gov (United States)

    Gormezano, Linda J; Rockwell, Robert F

    2013-01-01

    Under current climate trends, spring ice breakup in Hudson Bay is advancing rapidly, leaving polar bears (Ursus maritimus) less time to hunt seals during the spring when they accumulate the majority of their annual fat reserves. For this reason, foods that polar bears consume during the ice-free season may become increasingly important in alleviating nutritional stress from lost seal hunting opportunities. Defining how the terrestrial diet might have changed since the onset of rapid climate change is an important step in understanding how polar bears may be reacting to climate change. We characterized the current terrestrial diet of polar bears in western Hudson Bay by evaluating the contents of passively sampled scat and comparing it to a similar study conducted 40 years ago. While the two terrestrial diets broadly overlap, polar bears currently appear to be exploiting increasingly abundant resources such as caribou (Rangifer tarandus) and snow geese (Chen caerulescens caerulescens) and newly available resources such as eggs. This opportunistic shift is similar to the diet mixing strategy common among other Arctic predators and bear species. We discuss whether the observed diet shift is solely a response to a nutritional stress or is an expression of plastic foraging behavior. PMID:24223286

  6. Inverted Basal Shear Stress of Antarctic and Greenland Ice Streams and Glaciers, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set includes basal shear distributions inferred from surface observations - surface ice velocities (Joughin et al., 2010, Rignot et al., 2011), bed and...

  7. Ice at the Interface: Atmosphere-Ice-Ocean Boundary Layer Processes and Their Role in Polar Change---Workshop Report

    Energy Technology Data Exchange (ETDEWEB)

    Hunke, Elizabeth C. [Los Alamos National Laboratory

    2012-07-23

    The atmosphere-ocean boundary layer in which sea ice resides includes many complex processes that require a more realistic treatment in GCMs, particularly as models move toward full earth system descriptions. The primary purpose of the workshop was to define and discuss such coupled processes from observational and modeling points of view, including insight from both the Arctic and Antarctic systems. The workshop met each of its overarching goals, including fostering collaboration among experimentalists, theorists and modelers, proposing modeling strategies, and ascertaining data availability and needs. Several scientific themes emerged from the workshop, such as the importance of episodic or extreme events, precipitation, stratification above and below the ice, and the marginal ice zone, whose seasonal Arctic migrations now traverse more territory than in the past.

  8. What drove the methane cycle in the past - evidence from carbon isotopic data of methane enclosed in polar ice cores

    OpenAIRE

    Möller, Lars

    2013-01-01

    During the last glacial cycle, greenhouse gas concentrations fluctuated on decadal and longer timescales. Concentrations of methane, as measured in polar ice cores, show a close connection with Northern Hemisphere temperature variability, but the contribution of the various methane sources and sinks to changes in concentration is still a matter of debate. This thesis assess changes in methane cycling over the past 160,000 years by measurements of the carbon isotopic composition d13C of methan...

  9. 10Be and δ2H in polar ice cores as a probe of the solar variability's influence on climate

    International Nuclear Information System (INIS)

    Raisbeck, G.M.; Yiou, F.; Jouzel, J.; Domaine Univ., 38 - St-Martin-d'Heres; Petit, J.R.

    1990-01-01

    By using the technique of accelerator mass spectrometry, it is now possible to measure detailed profiles of cosmogenic (cosmic ray produced) 10 Be in polar ice cores. Recent work has demonstrated that these profiles contain information on solar activity, via its influence on the intensity of galactic cosmic rays arriving in the Earth's atmosphere. It has been known for some time that, as a result of temperature-dependent fractionation effects, the stable isotope profiles δ 2 O and δ 2 H in polar ice cores contain palaeoclimate information. Thus by comparing the 10 Be and stable isotope profiles in the same ice core, one can test the influence of solar variability on climate, and this independent of possible uncertainties in the absolute chronology of the records. We present here the results of such a comparison for two Antarctic ice cores; one from the South Pole, covering the past ca. 1000 years, and one from Dome C, covering the past ca. 3000 years. (author)

  10. Trials and Tribulations of Fluorescent Dissolved Organic Matter Chemical Interpretations: A case study of polar ice cores

    Science.gov (United States)

    D'Andrilli, J.

    2017-12-01

    Excitation emission matrix fluorescence spectroscopy is widely applied for rapid dissolved organic matter (DOM) characterization in aquatic systems. Fluorescent DOM surveys are booming, not only as a central focus in aquatic environments, but also as an important addition to interdisciplinary research (e.g., DOM analysis in concert with ice core paleoclimate reconstructions, stream metabolism, hydrologic regimes, agricultural developments, and biological activity), opening new doors, not just for novelty, but also for more challenges with chemical interpretations. Recently, the commonly used protein- versus humic-like classifications of DOM have been ineffective at describing DOM chemistry in various systems (e.g., ice cores, wastewaters, incubations/engineered). Moreover, the oversimplification of such classifications used to describe fluorescing components, without further scrutiny, has become commonplace, ultimately producing vague reporting. For example, West Antarctic ice core DOM was shown to contain fluorescence in the low excitation/emission wavelength region, however resolved fluorophores depicting tyrosine- and tryptophan-like DOM were not observed. At first, as literature suggested, we reported this result as protein-like, and concluded that microbial contributions were dominant in deep ice. That initial interpretation would disintegrate the conservation paradigm of atmospheric composition during deposition, the crux of ice core research, and contradict other lines of evidence. This begged the question, "How can we describe DOM chemistry without distinct fluorophores?" Antarctic ice core DOM was dominated by neither tyrosine- nor tryptophan-like fluorescence, causing "unusual" looking fluorescent components. After further examination, deep ice DOM was reported to contain fluorescent species most similar to monolignols and tannin-like phenols, describing the precursors of lignin from low carbon producing environments, consistent with marine sediment

  11. Snow Grain Size Retrieval over the Polar Ice Sheets with the Ice, Cloud and Land Elevation Satellite (ICESat) Observations

    Science.gov (United States)

    Yang, Yuekui; Marshak, Alexander; Han, Mei; Palm, Stephen P.; Harding, David J.

    2016-01-01

    Snow grain size is an important parameter for cryosphere studies. As a proof of concept, this paper presents an approach to retrieve this parameter over Greenland, East and West Antarctica ice sheets from surface reflectances observed with the Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud, and land Elevation Satellite (ICESat) at 1064 nanometers. Spaceborne lidar observations overcome many of the disadvantages in passive remote sensing, including difficulties in cloud screening and low sun angle limitations; hence tend to provide more accurate and stable retrievals. Results from the GLAS L2A campaign, which began on 25 September and lasted until 19 November, 2003, show that the mode of the grain size distribution over Greenland is the largest (approximately 300 microns) among the three, West Antarctica is the second (220 microns) and East Antarctica is the smallest (190 microns). Snow grain sizes are larger over the coastal regions compared to inland the ice sheets. These results are consistent with previous studies. Applying the broadband snow surface albedo parameterization scheme developed by Garder and Sharp (2010) to the retrieved snow grain size, ice sheet surface albedo is also derived. In the future, more accurate retrievals can be achieved with multiple wavelengths lidar observations.

  12. High-speed solar wind streams and polar mesosphere winter echoes at Troll, Antarctica

    Directory of Open Access Journals (Sweden)

    S. Kirkwood

    2015-06-01

    Full Text Available A small, 54 MHz wind-profiler radar, MARA, was operated at Troll, Antarctica (72° S, 2.5° E, continuously from November 2011 to January 2014, covering two complete Antarctic winters. Despite very low power, MARA observed echoes from heights of 55–80 km (polar mesosphere winter echoes, PMWE on 60% of all winter days (from March to October. This contrasts with previous reports from radars at high northern latitudes, where PWME have been reported only by very high power radars or during rare periods of unusually high electron density at PMWE heights, such as during solar proton events. Analysis shows that PWME at Troll were not related to solar proton events but were often closely related to the arrival of high-speed solar wind streams (HSS at the Earth, with PWME appearing at heights as low as 56 km and persisting for up to 15 days following HSS arrival. This demonstrates that HSS effects penetrate directly to below 60 km height in the polar atmosphere. Using local observations of cosmic-noise absorption (CNA, a theoretical ionization/ion-chemistry model and a statistical model of precipitating energetic electrons associated with HSS, the electron density conditions during the HSS events are estimated. We find that PMWE detectability cannot be explained by these variations in electron density and molecular-ion chemistry alone. PWME become detectable at different thresholds depending on solar illumination and height. In darkness, PWME are detected only when the modelled electron density is above a threshold of about 1000 cm−3, and only above 75 km height, where negative ions are few. In daylight, the electron density threshold falls by at least 2 orders of magnitude and PWME are found primarily below 75 km height, even in conditions when a large proportion of negative ions is expected. There is also a strong dawn–dusk asymmetry with PWME detected very rarely during morning twilight but often during evening twilight. This behaviour cannot be

  13. High-speed solar wind streams and polar mesosphere winter echoes at Troll, Antarctica

    Energy Technology Data Exchange (ETDEWEB)

    Kirkwood, S.; Belova, E. [Swedish Institute of Space Physics, Kiruna (Sweden). Polar Atmospheric Research; Osepian, A. [Polar Geophysical Institute, Murmansk (Russian Federation); Lee, Y.S. [Korea Astronomy and Space Science Institute, Daejeon (Korea, Republic of)

    2015-10-01

    A small, 54 MHz wind-profiler radar, MARA, was operated at Troll, Antarctica (72 S, 2.5 E), continuously from November 2011 to January 2014, covering two complete Antarctic winters. Despite very low power, MARA observed echoes from heights of 55-80 km (polar mesosphere winter echoes, PMWE) on 60% of all winter days (from March to October). This contrasts with previous reports from radars at high northern latitudes, where PWME have been reported only by very high power radars or during rare periods of unusually high electron density at PMWE heights, such as during solar proton events. Analysis shows that PWME at Troll were not related to solar proton events but were often closely related to the arrival of high-speed solar wind streams (HSS) at the Earth, with PWME appearing at heights as low as 56 km and persisting for up to 15 days following HSS arrival. This demonstrates that HSS effects penetrate directly to below 60 km height in the polar atmosphere. Using local observations of cosmic-noise absorption (CNA), a theoretical ionization/ion-chemistry model and a statistical model of precipitating energetic electrons associated with HSS, the electron density conditions during the HSS events are estimated. We find that PMWE detectability cannot be explained by these variations in electron density and molecular-ion chemistry alone. PWME become detectable at different thresholds depending on solar illumination and height. In darkness, PWME are detected only when the modelled electron density is above a threshold of about 1000 cm{sup -3}, and only above 75 km height, where negative ions are few. In daylight, the electron density threshold falls by at least 2 orders of magnitude and PWME are found primarily below 75 km height, even in conditions when a large proportion of negative ions is expected. There is also a strong dawn-dusk asymmetry with PWME detected very rarely during morning twilight but often during evening twilight. This behaviour cannot be explained if PMWE

  14. Large-Scale Structure and Dynamics of the Sub-Auroral Polarization Stream (SAPS)

    Science.gov (United States)

    Baker, J. B. H.; Nishitani, N.; Kunduri, B.; Ruohoniemi, J. M.; Sazykin, S. Y.

    2017-12-01

    The Sub-Auroral Polarization Stream (SAPS) is a narrow channel of high-speed westward ionospheric convection which appears equatorward of the duskside auroral oval during geomagnetically active periods. SAPS is generally thought to occur when the partial ring current intensifies and enhanced region-2 field-aligned currents (FACs) are forced to close across the low conductance region of the mid-latitude ionospheric trough. However, recent studies have suggested SAPS can also occur during non-storm periods, perhaps associated with substorm activity. In this study, we used measurements from mid-latitude SuperDARN radars to examine the large-scale structure and dynamics of SAPS during several geomagnetically active days. Linear correlation analysis applied across all events suggests intensifications of the partial ring current (ASYM-H index) and auroral activity (AL index) are both important driving influences for controlling the SAPS speed. Specifically, SAPS flows increase, on average, by 20-40 m/s per 10 nT of ASYM-H and 10-30 m/s per 100 nT of AL. These dependencies tend to be stronger during the storm recovery phase. There is also a strong local time dependence such that the strength of SAPS flows decrease by 70-80 m/s for each hour of local time moving from dusk to midnight. By contrast, the evidence for direct solar wind control of SAPS speed is much less consistent, with some storms showing strong correlations with the interplanetary electric field components and/or solar wind dynamic pressure, while others do not. These results are discussed in the context of recent simulation results from the Rice Convection Model (RCM).

  15. Innovative optical spectrometers for ice core sciences and atmospheric monitoring at polar regions

    Science.gov (United States)

    Grilli, Roberto; Alemany, Olivier; Chappellaz, Jérôme; Desbois, Thibault; Faïn, Xavier; Kassi, Samir; Kerstel, Erik; Legrand, Michel; Marrocco, Nicola; Méjean, Guillaume; Preunkert, Suzanne; Romanini, Daniele; Triest, Jack; Ventrillard, Irene

    2015-04-01

    In this talk recent developments accomplished from a collaboration between the Laboratoire Interdisciplinaire de Physique (LIPhy) and the Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE) both in Grenoble (France), are discussed, covering atmospheric chemistry of high reactive species in polar regions and employing optical spectrometers for both in situ and laboratory measurements of glacial archives. In the framework of an ANR project, a transportable spectrometer based on the injection of a broadband frequency comb laser into a high-finesse optical cavity for the detection of IO, BrO, NO2 and H2CO has been realized.[1] The robust spectrometer provides shot-noise limited measurements for as long as 10 minutes, reaching detection limits of 0.04, 2, 10 and 200 ppt (2σ) for the four species, respectively. During the austral summer of 2011/12 the instrument has been used for monitoring, for the first time, NO2, IO and BrO at Dumont d'Urville Station at East of Antarctica. The measurements highlighted a different chemistry between East and West coast, with the halogen chemistry being promoted to the West and the OH and NOx chemistry on the East.[2] In the framework of a SUBGLACIOR project, an innovative drilling probe has been realized. The instrument is capable of retrieving in situ real-time vertical profiles of CH4 and δD of H2O trapped inside the ice sheet down to more than 3 km of depth within a single Antarctic season. The drilling probe containing an embedded OFCEAS (optical-feedback cavity-enhanced absorption spectroscopy) spectrometer will be extremely useful for (i) identify potential sites for investigating the oldest ice (aiming 1.5 Myrs BP records for resolving a major climate reorganization called the Mid-Pleistocene transition occurred around 1 Myrs ago) and (ii) providing direct access to past temperatures and climate cycles thanks to the vertical distribution of two key climatic signatures.[3] The spectrometer provides detection

  16. Ultra-Wideband Radiometry Remote Sensing of Polar Ice Sheet Temperature Profile, Sea Ice and Terrestrial Snow Thickness: Forward Modeling and Data Analysis

    Science.gov (United States)

    Tsang, L.; Tan, S.; Sanamzadeh, M.; Johnson, J. T.; Jezek, K. C.; Durand, M. T.

    2017-12-01

    The recent development of an ultra-wideband software defined radiometer (UWBRAD) operating over the unprotected spectrum of 0.5 2.0 GHz using radio-frequency interference suppression techniques offers new methodologies for remote sensing of the polar ice sheets, sea ice, and terrestrial snow. The instrument was initially designed for remote sensing of the intragalcial temperature profile of the ice sheet, where a frequency dependent penetration depth yields a frequency dependent brightness temperature (Tb) spectrum that can be linked back to the temperature profile of the ice sheet. The instrument was tested during a short flight over Northwest Greenland in September, 2016. Measurements were successfully made over the different snow facies characteristic of Greenland including the ablation, wet snow and percolation facies, and ended just west of Camp Century during the approach to the dry snow zone. Wide-band emission spectra collected during the flight have been processed and analyzed. Results show that the spectra are highly sensitive to the facies type with scattering from ice lenses being the dominant reason for low Tbs in the percolation zone. Inversion of Tb to physical temperature at depth was conducted on the measurements near Camp Century, achieving a -1.7K ten-meter error compared to borehole measurements. However, there is a relatively large uncertainty in the lower part possibly due to the large scattering near the surface. Wideband radiometry may also be applicable to sea ice and terrestrial snow thickness retrieval. Modeling studies suggest that the UWBRAD spectra reduce ambiguities inherent in other sea ice thickness retrievals by utilizing coherent wave interferences that appear in the Tb spectrum. When applied to a lossless medium such as terrestrial snow, this coherent oscillation turns out to be the single key signature that can be used to link back to snow thickness. In this paper, we report our forward modeling findings in support of instrument

  17. The wide-spread presence of rib-like patterns in basal shear of ice streams detected by surface data inversion

    Science.gov (United States)

    Sergienko, O. V.

    2013-12-01

    The direct observations of the basal conditions under continental-scale ice sheets are logistically impossible. A possible approach to estimate conditions at the ice - bed interface is from surface observations by means of inverse methods. The recent advances in remote and ground-based observations have allowed to acquire a wealth observations from Greenland and Antarctic ice sheets. Using high-resolution data sets of ice surface and bed elevations and surface velocities, inversions for basal conditions have been performed for several ice streams in Greenland and Antarctica. The inversion results reveal the wide-spread presence of rib-like spatial structures in basal shear. The analysis of the hydraulic potential distribution shows that these rib-like structures co-locate with highs of the gradient of hydraulic potential. This suggests that subglacial water plays a role in the development and evolution of the basal shear ribs.

  18. Ice Water Classification Using Statistical Distribution Based Conditional Random Fields in RADARSAT-2 Dual Polarization Imagery

    Science.gov (United States)

    Zhang, Y.; Li, F.; Zhang, S.; Hao, W.; Zhu, T.; Yuan, L.; Xiao, F.

    2017-09-01

    In this paper, Statistical Distribution based Conditional Random Fields (STA-CRF) algorithm is exploited for improving marginal ice-water classification. Pixel level ice concentration is presented as the comparison of methods based on CRF. Furthermore, in order to explore the effective statistical distribution model to be integrated into STA-CRF, five statistical distribution models are investigated. The STA-CRF methods are tested on 2 scenes around Prydz Bay and Adélie Depression, where contain a variety of ice types during melt season. Experimental results indicate that the proposed method can resolve sea ice edge well in Marginal Ice Zone (MIZ) and show a robust distinction of ice and water.

  19. Reconstructing the post-LGM decay of the Eurasian Ice Sheets with Ice Sheet Models; data-model comparison and focus on the Storfjorden (Svalbard) ice stream dynamics history

    Science.gov (United States)

    Petrini, Michele; Kirchner, Nina; Colleoni, Florence; Camerlenghi, Angelo; Rebesco, Michele; Lucchi, Renata G.; Forte, Emanuele; Colucci, Renato R.

    2017-04-01

    The challenge of reconstructing palaeo-ice sheets past growth and decay represent a critical task to better understand mechanisms of present and future global climate change. Last Glacial Maximum (LGM), and the subsequent deglaciation until Pre-Industrial time (PI) represent an excellent testing ground for numerical Ice Sheet Models (ISMs), due to the abundant data available that can be used in an ISM as boundary conditions, forcings or constraints to test the ISMs results. In our study, we simulate with ISMs the post-LGM decay of the Eurasian Ice Sheets, with a focus on the marine-based Svalbard-Barents Sea-Kara Sea Ice Sheet. In particular, we aim to reconstruct the Storfjorden ice stream dynamics history by comparing the model results with the marine geological data (MSGLs, GZWs, sediment cores analysis) available from the area, e.g., Pedrosa et al. 2011, Rebesco et al. 2011, 2013, Lucchi et al. 2013. Two hybrid SIA/SSA ISMs are employed, GRISLI, Ritz et al. 2001, and PSU, Pollard&DeConto 2012. These models differ mainly in the complexity with which grounding line migration is treated. Climate forcing is interpolated by means of climate indexes between LGM and PI climate. Regional climate indexes are constructed based on the non-accelerated deglaciation transient experiment carried out with CCSM3, Liu et al. 2009. Indexes representative of the climate evolution over Siberia, Svalbard and Scandinavia are employed. The impact of such refined representation as opposed to the common use of the NGRIP δ18O index for transient experiments is analysed. In this study, the ice-ocean interaction is crucial to reconstruct the Storfjorden ice stream dynamics history. To investigate the sensitivity of the ice shelf/stream retreat to ocean temperature, we allow for a space-time variation of basal melting under the ice shelves by testing two-equations implementations based on Martin et al. 2011 forced with simulated ocean temperature and salinity from the TraCE-21ka coupled

  20. The Particle Habit Imaging and Polar Scattering probe PHIPS: First Stereo-Imaging and Polar Scattering Function Measurements of Ice Particles

    Science.gov (United States)

    Abdelmonem, A.; Schnaiter, M.; Schön, R.; Leisner, T.

    2009-04-01

    Cirrus clouds impact climate by their influence on the water vapour distribution in the upper troposphere. Moreover, they directly affect the radiative balance of the Earth's atmosphere by the scattering of incoming solar radiation and the absorption of outgoing thermal emission. The link between the microphysical properties of ice cloud particles and the radiative forcing of the clouds is not as yet well understood and the influence of the shapes of ice crystals on the radiative budget of cirrus clouds is currently under debate. PHIPS is a new experimental device for the stereo-imaging of individual cloud particles and the simultaneous measurement of the polar scattering function of the same particle. PHIPS uses an automated particle event triggering system that ensures that only those particles are captured which are located in the field of view - depth of field volume of the microscope unit. Efforts were made to improve the resolution power of the microscope unit down to about 3 µm and to facilitate a 3D morphology impression of the ice crystals. This is realised by a stereo-imaging set up composed of two identical microscopes which image the same particle under an angular viewing distance of 30°. The scattering part of PHIPS enables the measurement of the polar light scattering function of cloud particles with an angular resolution of 1° for forward scattering directions (from 1° to 10°) and 8° for side and backscattering directions (from 18° to 170°). For each particle the light scattering pulse per channel is stored either as integrated intensity or as time resolved intensity function which opens a new category of data analysis concerning details of the particle movement. PHIPS is the first step to PHIPS-HALO which is one of the in situ ice particle and water vapour instruments that are currently under development for the new German research aircraft HALO. The instrument was tested in the ice cloud characterisation campaign HALO-02 which was conducted

  1. Assessment of RISAT-1 and Radarsat-2 for Sea Ice Observations from a Hybrid-Polarity Perspective

    Directory of Open Access Journals (Sweden)

    Martine M. Espeseth

    2017-10-01

    Full Text Available Utilizing several Synthetic Aperture Radar (SAR missions will provide a data set with higher temporal resolution. It is of great importance to understand the difference between various available sensors and polarization modes and to consider how to homogenize the data sets for a following combined analysis. In this study, a uniform and consistent analysis across different SAR missions is carried out. Three pairs of overlapping hybrid- and full-polarimetric C-band SAR scenes from the Radar Imaging Satellite-1 (RISAT-1 and Radarsat-2 satellites are used. The overlapping Radarsat-2 and RISAT-1 scenes are taken close in time, with a relatively similar incidence angle covering sea ice in the Fram Strait and Northeast Greenland in September 2015. The main objective of this study is to identify the similarities and dissimilarities between a simulated and a real hybrid-polarity (HP SAR system. The similarities and dissimilarities between the two sensors are evaluated using 13 HP features. The results indicate a similar separability between the sea ice types identified within the real HP system in RISAT-1 and the simulated HP system from Radarsat-2. The HP features that are sensitive to surface scattering and depolarization due to volume scattering showed great potential for separating various sea ice types. A subset of features (the second parameter in the Stokes vector, the ratio between the HP intensity coefficients, and the α s angle were affected by the non-circularity property of the transmitted wave in the simulated HP system across all the scene pairs. Overall, the best features, showing high separability between various sea ice types and which are invariant to the non-circularity property of the transmitted wave, are the intensity coefficients from the right-hand circular transmit and the linear horizontal receive channel and the right-hand circular on both the transmit and the receive channel, and the first parameter in the Stokes vector.

  2. Range contraction and increasing isolation of a polar bear subpopulation in an era of sea-ice loss.

    Science.gov (United States)

    Laidre, Kristin L; Born, Erik W; Atkinson, Stephen N; Wiig, Øystein; Andersen, Liselotte W; Lunn, Nicholas J; Dyck, Markus; Regehr, Eric V; McGovern, Richard; Heagerty, Patrick

    2018-02-01

    Climate change is expected to result in range shifts and habitat fragmentation for many species. In the Arctic, loss of sea ice will reduce barriers to dispersal or eliminate movement corridors, resulting in increased connectivity or geographic isolation with sweeping implications for conservation. We used satellite telemetry, data from individually marked animals (research and harvest), and microsatellite genetic data to examine changes in geographic range, emigration, and interpopulation connectivity of the Baffin Bay (BB) polar bear ( Ursus maritimus ) subpopulation over a 25-year period of sea-ice loss. Satellite telemetry collected from n  = 43 (1991-1995) and 38 (2009-2015) adult females revealed a significant contraction in subpopulation range size (95% bivariate normal kernel range) in most months and seasons, with the most marked reduction being a 70% decline in summer from 716,000 km 2 (SE 58,000) to 211,000 km 2 (SE 23,000) ( p  Bears in the 2000s were less likely to leave BB, with significant reductions in the numbers of bears moving into Davis Strait (DS) in winter and Lancaster Sound (LS) in summer. Harvest recoveries suggested both short and long-term fidelity to BB remained high over both periods (83-99% of marked bears remained in BB). Genetic analyses using eight polymorphic microsatellites confirmed a previously documented differentiation between BB, DS, and LS; yet weakly differentiated BB from Kane Basin (KB) for the first time. Our results provide the first multiple lines of evidence for an increasingly geographically and functionally isolated subpopulation of polar bears in the context of long-term sea-ice loss. This may be indicative of future patterns for other polar bear subpopulations under climate change.

  3. Looking Through the Ice: Searching for Past and Present Habitable Zones in the Martian North Polar Region Using MOLA DEMs

    Science.gov (United States)

    Payne, M. C.; Farmer, J. D.

    2002-12-01

    Hydrothermal systems have been acknowledged as important gateways to accessing a potential subsurface biology (extant or extinct) on Mars. Groundwater circulation, sustained for up to one billion years by large plutonic bodies (as modeled by previous authors), might well be capable of tapping into a deep subsurface biosphere and subsequently carrying members of microbial communities to the surface. Hence, future robotic missions with near surface drilling capabilities may be able to unearth cryopreserved biosignatures, or perhaps extant organisms, in the midst of the hydrothermal system itself. Digital Elevation Models (DEMs) constructed from Mars Orbiter Laser Altimeter (MOLA) data have proved to be a valuable tool in the search for potential habitable zones for extant and extinct life, and the detection of possible hydrothermal systems on Mars. When formatted for use in a Geographical Information Systems (GIS) software package such as ESRI's ArcView, MOLA data can be used to compose DEMs. Those DEMs can, in turn, be used to create contour maps, to allow profiling through features of interest, and to generate hillshaded views, which provide an image-like perspective of a selected area. Furthermore, DEMs eliminate many problems associated with photographic images such as over-/underexposure, poor focus, and albedo values too high or low for optimal observations. During this study, DEMs were used in the analysis of several regions north of 70° N latitude, in the Martian north polar cap and polar cap margin. The regions were selected during a Viking image survey that concentrated on the location of surface expressions of potential magma-ice interactions, and hence past or present hydrothermal activity. Specific features sought included individual volcanoes and volcanic fields, as well as pseudocrater fields, subglacial volcanic constructs (such as tuyas and tindar ridges), fluvial channels and outwash plains (indicative of j”kulhlaup flooding events), possible

  4. Radar Interferometry Studies of the Mass Balance of Polar Ice Sheets

    Science.gov (United States)

    Rignot, Eric (Editor)

    1999-01-01

    The objectives of this work are to determine the current state of mass balance of the Greenland and Antarctic Ice Sheets. Our approach combines different techniques, which include satellite synthetic-aperture radar interferometry (InSAR), radar and laser altimetry, radar ice sounding, and finite-element modeling. In Greenland, we found that 3.5 times more ice flows out of the northern part of the Greenland Ice Sheet than previously accounted for. The discrepancy between current and past estimates is explained by extensive basal melting of the glacier floating sections in the proximity of the grounding line where the glacier detaches from its bed and becomes afloat in the ocean. The inferred basal melt rates are very large, which means that the glaciers are very sensitive to changes in ocean conditions. Currently, it appears that the northern Greenland glaciers discharge more ice than is being accumulated in the deep interior, and hence are thinning. Studies of temporal changes in grounding line position using InSAR confirm the state of retreat of northern glaciers and suggest that thinning is concentrated at the lower elevations. Ongoing work along the coast of East Greenland reveals an even larger mass deficit for eastern Greenland glaciers, with thinning affecting the deep interior of the ice sheet. In Antarctica, we found that glaciers flowing into a large ice shelf system, such as the Ronne Ice Shelf in the Weddell Sea, exhibit an ice discharge in remarkable agreement with mass accumulation in the interior, and the glacier grounding line positions do not migrate with time. Glaciers flowing rapidly into the Amudsen Sea, unrestrained by a major ice shelf, are in contrast discharging more ice than required to maintain a state of mass balance and are thinning quite rapidly near the coast. The grounding line of Pine Island glacier (see diagram) retreated 5 km in 4 years, which corresponds to a glacier thinning rate of 3.5 m/yr. Mass imbalance is even more negative

  5. Comparison of fabric analysis of snow samples by Computer-Integrated Polarization Microscopy and Automatic Ice Texture Analyzer

    Science.gov (United States)

    Leisinger, Sabine; Montagnat, Maurine; Heilbronner, Renée; Schneebeli, Martin

    2014-05-01

    Accurate knowledge of fabric anisotropy is crucial to understand the mechanical behavior of snow and firn, but is also important for understanding metamorphism. Computer-Integrated Polarization Microscopy (CIP) method used for the fabric analysis was developed by Heilbronner and Pauli in the early 1990ies and uses a slightly modified traditional polarization microscope for the fabric analysis. First developed for quartz, it can be applied to other uniaxial minerals. Up to now this method was mainly used in structural geology. However, it is also well suited for the fabric analysis of snow, firn and ice. The method is based on the analysis of first- order interference colors images by a slightly modified optical polarization microscope, a grayscale camera and a computer. The optical polarization microscope is featured with high quality objectives, a rotating table and two polarizers that can be introduced above and below the thin section, as well as a full wave plate. Additionally, two quarter-wave plates for circular polarization are needed. Otherwise it is also possible to create circular polarization from a set of crossed polarized images through image processing. A narrow band interference filter transmitting a wavelength between 660 and 700 nm is also required. Finally a monochrome digital camera is used to capture the input images. The idea is to record the change of interference colors while the thin section is being rotated once through 180°. The azimuth and inclination of the c-axis are defined by the color change. Recording the color change through a red filter produces a signal with a well-defined amplitude and phase angle. An advantage of this method lies in the simple conversion of an ordinary optical microscope to a fabric analyzer. The Automatic Ice Texture Analyzer (AITA) as the first fully functional instrument to measure c-axis orientation was developed by Wilson and other (2003). Most recent fabric analysis of snow and firn samples was carried

  6. Using the tracer-dilution discharge method to develop streamflow records for ice-affected streams in Colorado

    Science.gov (United States)

    Capesius, Joseph P.; Sullivan, Joseph R.; O'Neill, Gregory B.; Williams, Cory A.

    2005-01-01

    Accurate ice-affected streamflow records are difficult to obtain for several reasons, which makes the management of instream-flow water rights in the wintertime a challenging endeavor. This report documents a method to improve ice-affected streamflow records for two gaging stations in Colorado. In January and February 2002, the U.S. Geological Survey, in cooperation with the Colorado Water Conservation Board, conducted an experiment using a sodium chloride tracer to measure streamflow under ice cover by the tracer-dilution discharge method. The purpose of this study was to determine the feasibility of obtaining accurate ice-affected streamflow records by using a sodium chloride tracer that was injected into the stream. The tracer was injected at two gaging stations once per day for approximately 20 minutes for 25 days. Multiple-parameter water-quality sensors at the two gaging stations monitored background and peak chloride concentrations. These data were used to determine discharge at each site. A comparison of the current-meter streamflow record to the tracer-dilution streamflow record shows different levels of accuracy and precision of the tracer-dilution streamflow record at the two sites. At the lower elevation and warmer site, Brandon Ditch near Whitewater, the tracer-dilution method overestimated flow by an average of 14 percent, but this average is strongly biased by outliers. At the higher elevation and colder site, Keystone Gulch near Dillon, the tracer-dilution method experienced problems with the tracer solution partially freezing in the injection line. The partial freezing of the tracer contributed to the tracer-dilution method underestimating flow by 52 percent at Keystone Gulch. In addition, a tracer-pump-reliability test was conducted to test how accurately the tracer pumps can discharge the tracer solution in conditions similar to those used at the gaging stations. Although the pumps were reliable and consistent throughout the 25-day study period

  7. STREAM

    DEFF Research Database (Denmark)

    Godsk, Mikkel

    This paper presents a flexible model, ‘STREAM’, for transforming higher science education into blended and online learning. The model is inspired by ideas of active and collaborative learning and builds on feedback strategies well-known from Just-in-Time Teaching, Flipped Classroom, and Peer...... Instruction. The aim of the model is to provide both a concrete and comprehensible design toolkit for adopting and implementing educational technologies in higher science teaching practice and at the same time comply with diverse ambitions. As opposed to the above-mentioned feedback strategies, the STREAM...... model supports a relatively diverse use of educational technologies and may also be used to transform teaching into completely online learning. So far both teachers and educational developers have positively received the model and the initial design experiences show promise....

  8. An Ultra-Wideband, Microwave Radar for Measuring Snow Thickness on Sea Ice and Mapping Near-Surface Internal Layers in Polar Firn

    Science.gov (United States)

    Panzer, Ben; Gomez-Garcia, Daniel; Leuschen, Carl; Paden, John; Rodriguez-Morales, Fernando; Patel, Azsa; Markus, Thorsten; Holt, Benjamin; Gogineni, Prasad

    2013-01-01

    Sea ice is generally covered with snow, which can vary in thickness from a few centimeters to >1 m. Snow cover acts as a thermal insulator modulating the heat exchange between the ocean and the atmosphere, and it impacts sea-ice growth rates and overall thickness, a key indicator of climate change in polar regions. Snow depth is required to estimate sea-ice thickness using freeboard measurements made with satellite altimeters. The snow cover also acts as a mechanical load that depresses ice freeboard (snow and ice above sea level). Freeboard depression can result in flooding of the snow/ice interface and the formation of a thick slush layer, particularly in the Antarctic sea-ice cover. The Center for Remote Sensing of Ice Sheets (CReSIS) has developed an ultra-wideband, microwave radar capable of operation on long-endurance aircraft to characterize the thickness of snow over sea ice. The low-power, 100mW signal is swept from 2 to 8GHz allowing the air/snow and snow/ ice interfaces to be mapped with 5 c range resolution in snow; this is an improvement over the original system that worked from 2 to 6.5 GHz. From 2009 to 2012, CReSIS successfully operated the radar on the NASA P-3B and DC-8 aircraft to collect data on snow-covered sea ice in the Arctic and Antarctic for NASA Operation IceBridge. The radar was found capable of snow depth retrievals ranging from 10cm to >1 m. We also demonstrated that this radar can be used to map near-surface internal layers in polar firn with fine range resolution. Here we describe the instrument design, characteristics and performance of the radar.

  9. Assessment of diffusive isotopic fractionation in polar firn, and application to ice core trace gas records

    DEFF Research Database (Denmark)

    Buizert, C.; Sowers, T.; Blunier, T.

    2013-01-01

    During rapid variations of the atmospheric mixing ratio of a trace gas, diffusive transport in the porous firn layer atop ice sheets and glaciers alters the isotopic composition of that gas relative to the overlying atmosphere. Records of past atmospheric trace gas isotopic composition from ice...... cores and firn need to be corrected for this diffusive fractionation artifact. We present a novel, semi-empirical method to accurately estimate the magnitude of the diffusive fractionation in the ice core record. Our method (1) consists of a relatively simple analytical calculation; (2) requires only...... commonly available ice core data; (3) is not subject to the uncertainties inherent to estimating the accumulation rate, temperature, close-off depth and depth-diffusivity relationship back in time; (4) does not require knowledge of the true atmospheric variations, but uses the smoothed records obtained...

  10. Near-Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Sea Ice Concentrations

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set provides a near-real-time (NRT) map of sea ice concentrations for both the Northern and Southern Hemispheres. The near-real-time passive microwave...

  11. The Large Scale Distribution of Water Ice in the Polar Regions of the Moon

    Science.gov (United States)

    Jordan, A.; Wilson, J. K.; Schwadron, N.; Spence, H. E.

    2017-12-01

    For in situ resource utilization, one must know where water ice is on the Moon. Many datasets have revealed both surface deposits of water ice and subsurface deposits of hydrogen near the lunar poles, but it has proved difficult to resolve the differences among the locations of these deposits. Despite these datasets disagreeing on how deposits are distributed on small scales, we show that most of these datasets do agree on the large scale distribution of water ice. We present data from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO), LRO's Lunar Exploration Neutron Detector (LEND), the Neutron Spectrometer on Lunar Prospector (LPNS), LRO's Lyman Alpha Mapping Project (LAMP), LRO's Lunar Orbiter Laser Altimeter (LOLA), and Chandrayaan-1's Moon Mineralogy Mapper (M3). All, including those that show clear evidence for water ice, reveal surprisingly similar trends with latitude, suggesting that both surface and subsurface datasets are measuring ice. All show that water ice increases towards the poles, and most demonstrate that its signature appears at about ±70° latitude and increases poleward. This is consistent with simulations of how surface and subsurface cold traps are distributed with latitude. This large scale agreement constrains the origin of the ice, suggesting that an ancient cometary impact (or impacts) created a large scale deposit that has been rendered locally heterogeneous by subsequent impacts. Furthermore, it also shows that water ice may be available down to ±70°—latitudes that are more accessible than the poles for landing.

  12. Constraining the thickness of polar ice deposits on Mercury using the Mercury Laser Altimeter and small craters in permanently shadowed regions

    Science.gov (United States)

    Deutsch, Ariel N.; Head, James W.; Chabot, Nancy L.; Neumann, Gregory A.

    2018-05-01

    . For Mercury's polar deposits, we argue that Case I of the small craters predating the emplacement of the ice deposits is more likely, given other geologic evidence that suggests that these ice deposits are relatively young. Using the ice thickness estimates from Case I to calculate the total amount of water ice currently contained in Mercury's polar deposits results in a value of ∼1014-1015 kg. This is equivalent to ∼100-1000 km3 ice in volume. This volume of water ice is consistent with delivery via micrometeorite bombardment, Jupiter-family comets, or potentially a single impactor.

  13. Water Vapor, Temperature, and Ice Particles in Polar Mesosphere as Measured by SABER/TIMED and OSIRIS/Odin Instruments

    Science.gov (United States)

    Feofilov, A. G.; Petelina, S. V.; Kutepov, A. A.; Pesnell, W. D.; Goldberg, R. A.

    2009-01-01

    Although many new details on the properties of mesospheric ice particles that farm Polar Mesospheric Clouds (PMCs) and also cause polar mesospheric summer echoes have been recently revealed, certain aspects of mesospheric ice microphysics and dynamics still remain open. The detailed relation between PMC parameters and properties of their environment, as well as interseasonal and interhemispheric differences and trends in PMC properties that are possibly related to global change, are among those open questions. In this work, mesospheric temperature and water vapor concentration measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite are used to study the properties of PMCs with respect to the surrounding atmosphere. The cloud parameters, namely location, brightness, and altitude, are obtained from the observations made by the Optical Spectrograph and Infrared Imager System (OSIRIS) on the Odin satellite. About a thousand of simultaneous common volume measurements made by SABER and OSIRIS in both hemispheres from 2002 until 2008 are used. The correlation between PMC brightness (and occurrence rate) and temperatures at PMC altitudes and at the mesopause is analysed. The relation between PMC parameters, frost point temperature, and gaseous water vapor content in and below the cloud is also discussed. Interseasonal and interhemispheric differences and trends in the above parameters, as well as in PMC peak altitudes and mesopause altitudes are evaluated.

  14. Additions and corrections to the absorption coefficients of CO2 ice: Applications to the Martian south polar cap

    International Nuclear Information System (INIS)

    Calvin, W.M.

    1990-01-01

    Reflectance spectra of carbon dioxide frosts were calculated using the optical constants provided by Warren (1986) for the wavelength region 2-6 μm. In comparing these calculated spectra to spectra of frosts observed in the laboratory and on the surface of Mars, problems in the optical constants presented by Warren (1986) became apparent. Absorption coefficients for CO 2 ice have been derived using laboratory reflectance measurements and the Hapke (1981) model for calculating diffuse reflectance. This provides approximate values in regions where no data were previously available and indicates where corrections to the compilation by Warren (1986) are required. Using these coefficients to calculate the reflectance of CO 2 ice at varying grain sizes indicates that a typical Mariner polar cap spectrum is dominated by absorptions due to CO 2 frost or ice at grain sizes that are quite large, probably of the order of millimeters to centimeters. There are indications of contamination of water frost or dust, but confirmation will require more precise absorption coefficients for solid CO 2 than can be obtained from the method used here

  15. Modelling the climate and surface mass balance of polar ice sheets using RACMO2 - Part 2: Antarctica (1979-2016)

    Science.gov (United States)

    Melchior van Wessem, Jan; van de Berg, Willem Jan; Noël, Brice P. Y.; van Meijgaard, Erik; Amory, Charles; Birnbaum, Gerit; Jakobs, Constantijn L.; Krüger, Konstantin; Lenaerts, Jan T. M.; Lhermitte, Stef; Ligtenberg, Stefan R. M.; Medley, Brooke; Reijmer, Carleen H.; van Tricht, Kristof; Trusel, Luke D.; van Ulft, Lambertus H.; Wouters, Bert; Wuite, Jan; van den Broeke, Michiel R.

    2018-04-01

    We evaluate modelled Antarctic ice sheet (AIS) near-surface climate, surface mass balance (SMB) and surface energy balance (SEB) from the updated polar version of the regional atmospheric climate model, RACMO2 (1979-2016). The updated model, referred to as RACMO2.3p2, incorporates upper-air relaxation, a revised topography, tuned parameters in the cloud scheme to generate more precipitation towards the AIS interior and modified snow properties reducing drifting snow sublimation and increasing surface snowmelt. Comparisons of RACMO2 model output with several independent observational data show that the existing biases in AIS temperature, radiative fluxes and SMB components are further reduced with respect to the previous model version. The model-integrated annual average SMB for the ice sheet including ice shelves (minus the Antarctic Peninsula, AP) now amounts to 2229 Gt y-1, with an interannual variability of 109 Gt y-1. The largest improvement is found in modelled surface snowmelt, which now compares well with satellite and weather station observations. For the high-resolution ( ˜ 5.5 km) AP simulation, results remain comparable to earlier studies. The updated model provides a new, high-resolution data set of the contemporary near-surface climate and SMB of the AIS; this model version will be used for future climate scenario projections in a forthcoming study.

  16. Antioxidant responses in the polar marine sea-ice amphipod Gammarus wilkitzkii to natural and experimentally increased UV levels

    International Nuclear Information System (INIS)

    Krapp, Rupert H.; Bassinet, Thievery; Berge, Jorgen; Pampanin, Daniela M.; Camus, Lionel

    2009-01-01

    Polar marine surface waters are characterized by high levels of dissolved oxygen, seasonally intense UV irradiance and high levels of dissolved organic carbon. Therefore, the Arctic sea-ice habitat is regarded as a strongly pro-oxidant environment, even though its significant ice cover protects the ice-associated (=sympagic) fauna from direct irradiation to a large extent. In order to investigate the level of resistance to oxyradical stress, we sampled the sympagic amphipod species Gammarus wilkitzkii during both winter and summer conditions, as well as exposed specimens to simulated levels of near-natural and elevated levels of UV irradiation. Results showed that this amphipod species possessed a much stronger antioxidant capacity during summer than during winter. Also, the experimental UV exposure showed a depletion in antioxidant defences, indicating a negative effect of UV exposure on the total oxyradical scavenging capacity. Another sympagic organism, Onisimus nanseni, was sampled during summer conditions. When compared to G. wilkitzkii, the species showed even higher antioxidant scavenging capacity.

  17. Role of polar anticyclones and mid-latitude cyclones for Arctic summertime sea-ice melting

    Science.gov (United States)

    Wernli, Heini; Papritz, Lukas

    2018-02-01

    Annual minima in Arctic sea-ice extent and volume have been decreasing rapidly since the late 1970s, with substantial interannual variability. Summers with a particularly strong reduction of Arctic sea-ice extent are characterized by anticyclonic circulation anomalies from the surface to the upper troposphere. Here, we investigate the origin of these seasonal circulation anomalies by identifying individual Arctic anticyclones (with a lifetime of typically ten days) and analysing the air mass transport into these systems. We reveal that these episodic upper-level induced Arctic anticyclones are relevant for generating seasonal circulation anomalies. Sea-ice reduction is systematically enhanced during the transient episodes with Arctic anticyclones and the seasonal reduction of sea-ice volume correlates with the area-averaged frequency of Arctic anticyclones poleward of 70° N (correlation coefficient of 0.57). A trajectory analysis shows that these anticyclones result from extratropical cyclones injecting extratropical air masses with low potential vorticity into the Arctic upper troposphere. Our results emphasize the fundamental role of extratropical cyclones and associated diabatic processes in establishing Arctic anticyclones and, in turn, seasonal circulation anomalies, which are of key importance for understanding the variability of summertime Arctic sea-ice melting.

  18. Glacially-megalineated limestone terrain of Anticosti Island, Gulf of St. Lawrence, Canada; onset zone of the Laurentian Channel Ice Stream

    Science.gov (United States)

    Eyles, Nick; Putkinen, Niko

    2014-03-01

    Anticosti is a large elongate island (240 km long, 60 km wide) in eastern Canada within the northern part of a deep water trough (Gulf of St. Lawrence) that terminates at the Atlantic continental shelf edge. The island's Pleistocene glaciological significance is that its long axis lay transverse to ice from the Quebec and Labrador sectors of the Laurentide Ice Sheet moving south from the relatively high-standing Canadian Shield. Recent glaciological reconstructions place a fast-flowing ice stream along the axis of the Gulf of St. Lawrence but supporting geologic evidence in terms of recognizing its hard-bedded onset zone and downstream streamlined soft bed is limited. Anticosti Island consists of gently southward-dipping limestone plains composed of Ordovician and Silurian limestones (Vaureal, Becscie and Jupiter formations) with north-facing escarpments transverse to regional ice flow. Glacial deposits are largely absent and limestone plains in the higher central plateau of the island retain a relict apparently ‘preglacial’ drainage system consisting of deeply-incised dendritic bedrock valleys. In contrast, the bedrock geomorphology of the lower lying western and eastern limestone plains of the island is strikingly different having been extensively modified by glacial erosion. Escarpments are glacially megalineated with a distinct ‘zig-zag’ planform reflecting northward-projecting bullet-shaped ‘noses’ (identified as rock drumlins) up to 2 km wide at their base and 4 km in length with rare megagrooved upper surfaces. Drumlins are separated by southward-closing, funnel-shaped ‘through valleys’ where former dendritic valleys have been extensively altered by the streaming of basal ice through gaps in the escarpments. Glacially-megalineated bedrock terrain such as on the western and eastern flanks of Anticosti Island is elsewhere associated with the hard-bedded onset zones of fast flowing ice streams and provides important ground truth for the

  19. A new method based on low background instrumental neutron activation analysis for major, trace and ultra-trace element determination in atmospheric mineral dust from polar ice cores

    Energy Technology Data Exchange (ETDEWEB)

    Baccolo, Giovanni, E-mail: giovanni.baccolo@mib.infn.it [Graduate School in Polar Sciences, University of Siena, Via Laterina 8, 53100, Siena (Italy); Department of Environmental Sciences, University of Milano-Bicocca, P.zza della Scienza 1, 20126, Milano (Italy); INFN, Section of Milano-Bicocca, P.zza della Scienza 3, 20126, Milano (Italy); Clemenza, Massimiliano [INFN, Section of Milano-Bicocca, P.zza della Scienza 3, 20126, Milano (Italy); Department of Physics, University of Milano-Bicocca, P.zza della Scienza 3, 20126, Milano (Italy); Delmonte, Barbara [Department of Environmental Sciences, University of Milano-Bicocca, P.zza della Scienza 1, 20126, Milano (Italy); Maffezzoli, Niccolò [Centre for Ice and Climate, Niels Bohr Institute, Juliane Maries Vej, 30, 2100, Copenhagen (Denmark); Nastasi, Massimiliano; Previtali, Ezio [INFN, Section of Milano-Bicocca, P.zza della Scienza 3, 20126, Milano (Italy); Department of Physics, University of Milano-Bicocca, P.zza della Scienza 3, 20126, Milano (Italy); Prata, Michele; Salvini, Andrea [LENA, University of Pavia, Pavia (Italy); Maggi, Valter [Department of Environmental Sciences, University of Milano-Bicocca, P.zza della Scienza 1, 20126, Milano (Italy); INFN, Section of Milano-Bicocca, P.zza della Scienza 3, 20126, Milano (Italy)

    2016-05-30

    Dust found in polar ice core samples present extremely low concentrations, in addition the availability of such samples is usually strictly limited. For these reasons the chemical and physical analysis of polar ice cores is an analytical challenge. In this work a new method based on low background instrumental neutron activation analysis (LB-INAA) for the multi-elemental characterization of the insoluble fraction of dust from polar ice cores is presented. Thanks to an accurate selection of the most proper materials and procedures it was possible to reach unprecedented analytical performances, suitable for ice core analyses. The method was applied to Antarctic ice core samples. Five samples of atmospheric dust (μg size) from ice sections of the Antarctic Talos Dome ice core were prepared and analyzed. A set of 37 elements was quantified, spanning from all the major elements (Na, Mg, Al, Si, K, Ca, Ti, Mn and Fe) to trace ones, including 10 (La, Ce, Nd, Sm, Eu, Tb, Ho, Tm, Yb and Lu) of the 14 natural occurring lanthanides. The detection limits are in the range of 10{sup −13}–10{sup −6} g, improving previous results of 1–3 orders of magnitude depending on the element; uncertainties lies between 4% and 60%. - Highlights: • A new method based on neutron activation for the multi-elemental characterization of atmospheric dust entrapped in polar ice cores is proposed. • 37 elements were quantified in μg size dust samples with detection limits ranging from 10{sup −13} to 10{sup −6} g. • A low background approach and a clean analytical protocol improved INAA performances to unprecedented levels for multi-elemental analyses.

  20. Evaluation and Improvement of Polar WRF simulations using the observed atmospheric profiles in the Arctic seasonal ice zone

    Science.gov (United States)

    Liu, Z.; Schweiger, A. J. B.

    2016-12-01

    We use the Polar Weather Research and Forecasting (WRF) model to simulate atmospheric conditions during the Seasonal Ice Zone Reconnaissance Survey (SIZRS) over the Beaufort Sea in the summer since 2013. With the 119 SIZRS dropsondes in the18 cross sections along the 150W and 140W longitude lines, we evaluate the performance of WRF simulations and two forcing data sets, the ERA-Interim reanalysis and the Global Forecast System (GFS) analysis, and explore the improvement of the Polar WRF performance when the dropsonde data are assimilated using observation nudging. Polar WRF, ERA-Interim, and GFS can reproduce the general features of the observed mean atmospheric profiles, such as low-level temperature inversion, low-level jet (LLJ) and specific humidity inversion. The Polar WRF significantly improves the mean LLJ, with a lower and stronger jet and a larger turning angle than the forcing, which is likely related to the lower values of the boundary layer diffusion in WRF than in the global models such as ECMWF and GFS. The Polar WRF simulated relative humidity closely resembles the forcing datasets while having large biases compared to observations. This suggests that the performance of Polar WRF and its forecasts in this region are limited by the quality of the forcing dataset and that the assimilation of more and better-calibrated observations, such as humidity data, is critical for their improvement. We investigate the potential of assimilating the SIZRS dropsonde dataset in improving the weather forecast over the Beaufort Sea. A simple local nudging approach is adopted. Along SIZRS flight cross sections, a set of Polar WRF simulations are performed with varying number of variables and dropsonde profiles assimilated. Different model physics are tested to examine the sensitivity of different aspects of model physics, such as boundary layer schemes, cloud microphysics, and radiation parameterization, to data assimilation. The comparison of the Polar WRF runs with

  1. The Relevance of Grain Dissection for Grain Size Reduction in Polar Ice : Insight from Numerical Models and Ice Core Microstructure Analysis

    NARCIS (Netherlands)

    Steinbach, F.; Kuiper, E.N.; Eichler, J.; Bons, P. D.; Drury, M. R.; Griera, A.; Pennock, G.M.; Weikusat, I.

    2017-01-01

    The flow of ice depends on the properties of the aggregate of individual ice crystals, such as grain size or lattice orientation distributions. Therefore, an understanding of the processes controlling ice micro-dynamics is needed to ultimately develop a physically based macroscopic ice flow law. We

  2. Determination of heavy metals in polar snow and ice by laser-excited atomic fluorescence spectrometry

    International Nuclear Information System (INIS)

    Bolshov, M.A.; Boutron, C.F.

    1994-01-01

    The new laser-excited atomic fluorescence spectrometry technique offers unrivalled sensitivity for the determination of trace metals in a wide variety of samples. This has allowed the direct determination of Pb, Cd and Bi in Antarctic and Greenland snow and ice down to the sub pg/g level. (authors). 11 refs., 2 figs

  3. Software Design Description for the Polar Ice Prediction System (PIPS) Version 3.0

    Science.gov (United States)

    2008-11-05

    ice area with respect to x and y real trc- tracer at geometric center of cell real trx , try- limited derivative of tracer with respect to x and y...yp1 real xp2, yp2 real xp3, yp3 integer iflux, jflux real aic, aix, aiy real aiflx real trc, trx , try real atflx 95 PIPS 3.0 SDD Subroutine

  4. Getting around Antarctica: new high-resolution mappings of the grounded and freely-floating boundaries of the Antarctic ice sheet created for the International Polar Year

    Directory of Open Access Journals (Sweden)

    R. Bindschadler

    2011-07-01

    Full Text Available Two ice-dynamic transitions of the Antarctic ice sheet – the boundary of grounded ice features and the freely-floating boundary – are mapped at 15-m resolution by participants of the International Polar Year project ASAID using customized software combining Landsat-7 imagery and ICESat/GLAS laser altimetry. The grounded ice boundary is 53 610 km long; 74 % abuts to floating ice shelves or outlet glaciers, 19 % is adjacent to open or sea-ice covered ocean, and 7 % of the boundary ice terminates on land. The freely-floating boundary, called here the hydrostatic line, is the most landward position on ice shelves that expresses the full amplitude of oscillating ocean tides. It extends 27 521 km and is discontinuous. Positional (one-sigma accuracies of the grounded ice boundary vary an order of magnitude ranging from ±52 m for the land and open-ocean terminating segments to ±502 m for the outlet glaciers. The hydrostatic line is less well positioned with errors over 2 km. Elevations along each line are selected from 6 candidate digital elevation models based on their agreement with ICESat elevation values and surface shape inferred from the Landsat imagery. Elevations along the hydrostatic line are converted to ice thicknesses by applying a firn-correction factor and a flotation criterion. BEDMAP-compiled data and other airborne data are compared to the ASAID elevations and ice thicknesses to arrive at quantitative (one-sigma uncertainties of surface elevations of ±3.6, ±9.6, ±11.4, ±30 and ±100 m for five ASAID-assigned confidence levels. Over one-half of the surface elevations along the grounded ice boundary and over one-third of the hydrostatic line elevations are ranked in the highest two confidence categories. A comparison between ASAID-calculated ice shelf thicknesses and BEDMAP-compiled data indicate a thin-ice bias of 41.2 ± 71.3 m for the ASAID ice thicknesses. The relationship between the seaward offset of the hydrostatic line

  5. Getting around Antarctica: New High-Resolution Mappings of the Grounded and Freely-Floating Boundaries of the Antarctic Ice Sheet Created for the International Polar Year

    Science.gov (United States)

    Bindschadler, R.; Choi, H.; Wichlacz, A.; Bingham, R.; Bohlander, J.; Brunt, K.; Corr, H.; Drews, R.; Fricker, H.; Hall, M.; hide

    2011-01-01

    Two ice-dynamic transitions of the Antarctic ice sheet - the boundary of grounded ice features and the freely-floating boundary - are mapped at 15-m resolution by participants of the International Polar Year project ASAID using customized software combining Landsat-7 imagery and ICESat/GLAS laser altimetry. The grounded ice boundary is 53 610 km long; 74% abuts to floating ice shelves or outlet glaciers, 19% is adjacent to open or sea-ice covered ocean, and 7% of the boundary ice terminates on land. The freely-floating boundary, called here the hydrostatic line, is the most landward position on ice shelves that expresses the full amplitude of oscillating ocean tides. It extends 27 521 km and is discontinuous. Positional (one-sigma) accuracies of the grounded ice boundary vary an order of magnitude ranging from +/- 52m for the land and open-ocean terminating segments to +/- 502m for the outlet glaciers. The hydrostatic line is less well positioned with errors over 2 km. Elevations along each line are selected from 6 candidate digital elevation models based on their agreement with ICESat elevation values and surface shape inferred from the Landsat imagery. Elevations along the hydrostatic line are converted to ice thicknesses by applying a firn-correction factor and a flotation criterion. BEDMAP-compiled data and other airborne data are compared to the ASAID elevations and ice thicknesses to arrive at quantitative (one-sigma) uncertainties of surface elevations of +/-3.6, +/-9.6, +/-11.4, +/-30 and +/-100m for five ASAID-assigned confidence levels. Over one-half of the surface elevations along the grounded ice boundary and over one-third of the hydrostatic line elevations are ranked in the highest two confidence categories. A comparison between ASAID-calculated ice shelf thicknesses and BEDMAP-compiled data indicate a thin-ice bias of 41.2+/-71.3m for the ASAID ice thicknesses. The relationship between the seaward offset of the hydrostatic line from the grounded ice

  6. NASA IceBridge and PolarTREC - Education and Outreach Partnership

    Science.gov (United States)

    Bartholow, S.; Warburton, J.; Beck, J.; Woods, J. E.

    2015-12-01

    PolarTREC-Teachers and Researchers Exploring and Collaborating, a teacher professional development program, began with the International Polar Year in 2004 and continues today in the United States. PolarTREC has worked specifically with OIB for 3 years and looking forward to ongoing collaboration. PolarTREC brings U.S. K­12 educators and polar researchers together through an innovative teacher research experience model. Participating teachers spend 3-6 weeks in the field with research teams conducting surveys and collecting data on various aspects of polar science. During their experience, teachers become research team members filling a variety of roles on the team. They also fulfill a unique role of public outreach officer, conducting live presentations about their field site and research as well as journaling, answering questions, and posting photos. Working with OIB has opened up the nature of science for the participating teachers. In developing the long-term relationship with OIB teams, teachers can now share (1) the diversity of training, backgrounds, and interests of OIB scientists, (2) identify the linkages between Greenlandic culture and community and cryospheric science and evidence of climate change, (3) network with Danish and Greenlandic educators on the mission (4) gain access to the full spectrum of a science project - development, implementation, analysis, networking, and dissemination of information. All aspects help these teachers become champions of NASA science and educational leaders in their communities. Evaluation data shows that PolarTREC has clearly achieved it goals with the OIB partnership and suggests that linking teachers and researchers can have the potential to transform the nature of science education. By giving teachers the content knowledge, pedagogical tools, confidence, understanding of science in the broader society, and experiences with scientific inquiry, participating teachers are using authentic scientific research in their

  7. Semiempirical self-consistent polarization description of bulk water, the liquid-vapor interface, and cubic ice.

    Science.gov (United States)

    Murdachaew, Garold; Mundy, Christopher J; Schenter, Gregory K; Laino, Teodoro; Hutter, Jürg

    2011-06-16

    We have applied an efficient electronic structure approach, the semiempirical self-consistent polarization neglect of diatomic differential overlap (SCP-NDDO) method, previously parametrized to reproduce properties of water clusters by Chang, Schenter, and Garrett [ J. Chem. Phys. 2008 , 128 , 164111 ] and now implemented in the CP2K package, to model ambient liquid water at 300 K (both the bulk and the liquid-vapor interface) and cubic ice at 15 and 250 K. The SCP-NDDO potential retains its transferability and good performance across the full range of conditions encountered in the clusters and the bulk phases of water. In particular, we obtain good results for the density, radial distribution functions, enthalpy of vaporization, self-diffusion coefficient, molecular dipole moment distribution, and hydrogen bond populations, in comparison to experimental measurements. © 2011 American Chemical Society

  8. Polar bears (Ursus maritimus mating during late June on the pack ice of northern Svalbard, Norway

    Directory of Open Access Journals (Sweden)

    Thomas G. Smith

    2015-03-01

    Full Text Available Polar bears are seasonal breeders and typically mate from late March to early May. Implantation is, however, delayed until autumn, which can allow plasticity in the date of mating. As for other seasonal breeders, a rapid return to estrus after the loss of dependent offspring can be expected, even into the summer. A few earlier observations and dissections of dead animals suggest that polar bears are able to mate in summer. We report on a mating incident on 29 June 2014, the first documented mating this late in the season among wild polar bears. The female had lost her dependent cub during the period prior to the mating event. We speculate that she lost this cub late in the mating season, entered estrus and successfully mated in late June.

  9. Magnetization reversal of ferromagnetic nanoparticles induced by a stream of polarized electrons

    Energy Technology Data Exchange (ETDEWEB)

    Kozhushner, M.A.; Gatin, A.K.; Grishin, M.V.; Shub, B.R. [Semenov Institute of Chemical Physics of RAS, 4, Kosygin Street, Moscow 119991 (Russian Federation); Kim, V.P.; Khomutov, G.B. [Faculty of Physics, Lomonosov Moscow State University, Lenin Gory 1-2, Moscow 119991 (Russian Federation); Ilegbusi, O.J. [University of Central Florida, 4000 Central Florida Boulevard, Orlando, FL 32816-2450 (United States); Trakhtenberg, L.I. [Semenov Institute of Chemical Physics of RAS, 4, Kosygin Street, Moscow 119991 (Russian Federation)

    2016-09-15

    The remagnetization of ferromagnetic Fe{sub 3}O{sub 4} nanoparticles of several thousand cubic nanometers by spin-polarized current is investigated. For this purpose, magnetite nanoparticles are synthesized and deposited on a conductive nonmagnetic substrate. The remagnetization is conducted in high-vacuum scanning tunneling microscope (STM). The STM tip from magnetized iron wire constitutes one electrode while the ferromagnetic nanoparticle on the graphite surface represents the second electrode. The measured threshold value of remagnetization current (I{sub thresh}=9 nA) is the lowest value of current at which remagnetization occurs. The change in nanoparticle magnetization is detected by the effect of giant magnetic resistance, specifically, the dependence of the weak polarized current (Ipolarized current on magnetic moment of small ferromagnetic nanoclusters. The peculiarities of size dependence of the observed effects are explained. - Highlights: • Ferromagnetic nanoparticle in STM with ferromagnetic tip. • Change of the direction of nanoparticle magnetization by current I>I{sub cr}=9 nA. • GMR effect used to control change of magnetization.

  10. NON-RACEMIC AMINO ACID PRODUCTION BY ULTRAVIOLET IRRADIATION OF ACHIRAL INTERSTELLAR ICE ANALOGS WITH CIRCULARLY POLARIZED LIGHT

    International Nuclear Information System (INIS)

    De Marcellus, Pierre; Nuevo, Michel; Danger, Gregoire; Deboffle, Dominique; Le Sergeant d'Hendecourt, Louis; Meinert, Cornelia; Filippi, Jean-Jacques; Meierhenrich, Uwe J.; Nahon, Laurent

    2011-01-01

    The delivery of organic matter to the primitive Earth via comets and meteorites has long been hypothesized to be an important source for prebiotic compounds such as amino acids or their chemical precursors that contributed to the development of prebiotic chemistry leading, on Earth, to the emergence of life. Photochemistry of inter/circumstellar ices around protostellar objects is a potential process leading to complex organic species, although difficult to establish from limited infrared observations only. Here we report the first abiotic cosmic ice simulation experiments that produce species with enantiomeric excesses (e.e.'s). Circularly polarized ultraviolet light (UV-CPL) from a synchrotron source induces asymmetric photochemistry on initially achiral inter/circumstellar ice analogs. Enantioselective multidimensional gas chromatography measurements show significant e.e.'s of up to 1.34% for ( 13 C)-alanine, for which the signs and absolute values are related to the helicity and number of CPL photons per deposited molecule. This result, directly comparable with some L excesses measured in meteorites, supports a scenario in which exogenous delivery of organics displaying a slight L excess, produced in an extraterrestrial environment by an asymmetric astrophysical process, is at the origin of biomolecular asymmetry on Earth. As a consequence, a fraction of the meteoritic organic material consisting of non-racemic compounds may well have been formed outside the solar system. Finally, following this hypothesis, we support the idea that the protosolar nebula has indeed been formed in a region of massive star formation, regions where UV-CPL of the same helicity is actually observed over large spatial areas.

  11. Communicating polar science to the general public: sharing the social media experience of @OceanSeaIceNPI

    Science.gov (United States)

    Rösel, Anja; Pavlov, Alexey K.; Granskog, Mats A.; Gerland, Sebastian; Meyer, Amelie; Hudson, Stephen R.; King, Jennifer; Itkin, Polona; Cohen, Lana; Dodd, Paul; de Steur, Laura

    2016-04-01

    The findings of climate science need to be communicated to the general public. Researchers are encouraged to do so by journalists, policy-makers and funding agencies and many of us want to become better science communicators. But how can we do this at the lab or small research group level without specifically allocated resources in terms of funds and communication officers? And how do we sustain communication on a regular basis and not just during the limited lifetime of a specific project? One of the solutions is to use the emerging platform of social media, which has become a powerful and inexpensive tool for communicating science to different target audiences. Many research institutions and individual researchers are already advanced users of social media, but small research groups and labs remain underrepresented. The group of oceanographers, sea ice and atmospheric scientists at the Norwegian Polar Institute (@OceanSeaIceNPI( will share our experiences developing and maintaining researcher-driven outreach for over a year through Instagram, Twitter and Facebook. We will present our solutions to some of the practical considerations such as identifying key target groups, defining the framework for sharing responsibilities and interactions within the research group, and choosing an up-to-date and appropriate social medium. By sharing this information, we aim to inspire and assist other research groups and labs in conducting their own effective science communication.

  12. Fine-Scale Layering of Mars Polar Deposits and Signatures of Ice Content in Nonpolar Material From Multiband SHARAD Data Processing

    Science.gov (United States)

    Campbell, Bruce A.; Morgan, Gareth A.

    2018-02-01

    The variation of Shallow Radar (SHARAD) echo strength with frequency reveals material dielectric losses and polar layer properties. Loss tangents for Elysium and Amazonis Planitiae deposits are consistent with volcanic flows and sediments, while the Medusae Fossae Formation, lineated valley fill, and lobate debris aprons have low losses consistent with a major component of water ice. Mantling materials in Arcadia and Utopia Planitiae have higher losses, suggesting they are not dominated by ice over large fractions of their thickness. In Gemina Lingula, there are frequent deviations from a simple dependence of loss on depth. Within reflector packets, the brightest reflectors are often different among the frequency subbands, and there are cases of reflectors that occur in only the high- or low-frequency echoes. Many polar radar reflections must arise from multiple thin interfaces, or single deposits of appropriate thickness, that display resonant scattering behaviors. Reflector properties may be linked to climate-controlled polar dust deposition.

  13. Use of water stable isotopes in climatology and paleoclimatology illustrated from polar ice cores studies

    International Nuclear Information System (INIS)

    Jouzel, J.; Lorius, C.

    1994-01-01

    The isotopic content of ancient waters (deuterium and oxygen 18) gives a key access to past climatic changes. An essentially linear relationship exists between the isotopic content of a precipitation and the temperature of the site (at least for medium and high latitudes). This link between water isotope atmospheric cycle and climate is presented through various isotopic models and illustrated from the deuterium profile obtained along the Vostok ice core in East Antarctica. This 2 km record which covers a full glacial-interglacial cycle (160000 years) confirms the existence of a link between insolation changes and climate (Milankovitch theory). It shows also that the greenhouse effect has played a role in glacial-interglacial changes in amplifying this orbital forcing. (authors). 10 figs., 23 refs

  14. Longer ice-free seasons increase the risk of nest depredation by polar bears for colonial breeding birds in the Canadian Arctic.

    Science.gov (United States)

    Iverson, Samuel A; Gilchrist, H Grant; Smith, Paul A; Gaston, Anthony J; Forbes, Mark R

    2014-03-22

    Northern polar regions have warmed more than other parts of the globe potentially amplifying the effects of climate change on biological communities. Ice-free seasons are becoming longer in many areas, which has reduced the time available to polar bears (Ursus maritimus) to hunt for seals and hampered bears' ability to meet their energetic demands. In this study, we examined polar bears' use of an ancillary prey resource, eggs of colonial nesting birds, in relation to diminishing sea ice coverage in a low latitude region of the Canadian Arctic. Long-term monitoring reveals that bear incursions onto common eider (Somateria mollissima) and thick-billed murre (Uria lomvia) nesting colonies have increased greater than sevenfold since the 1980s and that there is an inverse correlation between ice season length and bear presence. In surveys encompassing more than 1000 km of coastline during years of record low ice coverage (2010-2012), we encountered bears or bear sign on 34% of eider colonies and estimated greater egg loss as a consequence of depredation by bears than by more customary nest predators, such as foxes and gulls. Our findings demonstrate how changes in abiotic conditions caused by climate change have altered predator-prey dynamics and are leading to cascading ecological impacts in Arctic ecosystems.

  15. Observation of atomic oxygen O(1S) green-line emission in the summer polar upper mesosphere associated with high-energy (≥30 keV) electron precipitation during high-speed solar wind streams

    Science.gov (United States)

    Lee, Young-Sook; Kwak, Young-Sil; Kim, Kyung-Chan; Solheim, Brian; Lee, Regina; Lee, Jaejin

    2017-01-01

    The auroral green-line emission at 557.7 nm wavelength as arising from the atomic oxygen O(1S → 1D) transition typically peaks at an altitude of 100 km specifically in the nightside oval, induced by auroral electrons within an energy range of 100 eV-30 keV. Intense aurora is known as being suppressed by sunlight in summer daytime but usually occurs in low electrical background conductivity. However, in the present study in summer (July) sunlit condition, enhancements of O(1S) emission rates observed by using the Wind Imaging Interferometer/UARS were frequently observed at low altitudes below 90 km, where ice particles are created initially as subvisible and detected as polar mesosphere summer echoes, emerging to be an optical phenomenon of polar mesospheric clouds. The intense O(1S) emission occurring in summer exceeds those occurring in the daytime in other seasons both in occurrence and in intensity, frequently accompanied by occurrences of supersonic neutral velocity (300-1500 m s-1). In the mesosphere, ion motion is controlled by electric field and the momentum is transferred to neutrals. The intense O(1S) emission is well associated with high-energy electron precipitation as observed during an event of high-speed solar wind streams. Meanwhile, since the minimum occurrences of O(1S) emission and supersonic velocity are maintained even in the low precipitation flux, the mechanism responsible is not only related to high-energy electron precipitation but also presumably to the local conditions, including the composition of meteoric-charged ice particles and charge separation expected in extremely low temperatures (<150 K).

  16. Predicting Clear-Sky Reflectance Over Snow/Ice in Polar Regions

    Science.gov (United States)

    Chen, Yan; Sun-Mack, Sunny; Arduini, Robert F.; Hong, Gang; Minnis, Patrick

    2015-01-01

    Satellite remote sensing of clouds requires an accurate estimate of the clear-sky radiances for a given scene to detect clouds and aerosols and to retrieve their microphysical properties. Knowing the spatial and angular variability of clear-sky albedo is essential for predicting clear-sky radiance at solar wavelengths. The Clouds and the Earth's Radiant Energy System (CERES) Project uses the nearinfrared (NIR; 1.24, 1.6 or 2.13 micrometers), visible (VIS; 0.63 micrometers) and vegetation (VEG; 0.86 micrometers) channels available on the Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) to help identify clouds and retrieve their properties in both snow-free and snow-covered conditions. Thus, it is critical to have reliable distributions of clear-sky albedo for all of these channels. In CERES Edition 4 (Ed4), the 1.24-micrometer channel is used to retrieve cloud optical depth over snow/ice-covered surfaces. Thus, it is especially critical to accurately predict the 1.24-micrometer clear-sky albedo alpha and reflectance rho for a given location and time. Snow albedo and reflectance patterns are very complex due to surface texture, particle shapes and sizes, melt water, and vegetation protrusions from the snow surface. To minimize those effects, this study focuses on the permanent snow cover of Antarctica where vegetation is absent and melt water is minimal. Clear-sky albedos are determined as a function of solar zenith angle (SZA) from observations over all scenes determined to be cloud-free to produce a normalized directional albedo model (DRM). The DRM is used to develop alpha(SZA=0 degrees) on 10 foot grid for each season. These values provide the basis for predicting r at any location and set of viewing & illumination conditions. This paper examines the accuracy of this approach for two theoretical snow surface reflectance models.

  17. The evolution of the englacial temperature distribution in the superimposed ice zone of a polar ice cap during a summer season

    NARCIS (Netherlands)

    Greuell, W.; Oerlemans, J.

    1989-01-01

    The aim of the present investigation was to provide more insight into the processes affecting the evolution of the englacial temperature distribution at a non-temperate location on a glacier. Measurements were made in the top 10 m of the ice at the summit of Laika Ice Cap (Canadian Arctic)

  18. Behavioural and physiological responses of brook trout Salvelinus fontinalis to midwinter flow reduction in a small ice-free mountain stream.

    Science.gov (United States)

    Krimmer, A N; Paul, A J; Hontela, A; Rasmussen, J B

    2011-09-01

    This study presents an experimental analysis of the effects of midwinter flow reduction (50-75%, reduction in discharge in 4 h daily pulses) on the physical habitat and on behaviour and physiology of overwintering brook trout Salvelinus fontinalis in a small mountain stream. Flow reduction did not result in significant lowering of temperature or formation of surface or subsurface ice. The main findings were (1) daily movement by S. fontinalis increased (c. 2·5-fold) during flow reduction, but was limited to small-scale relocations (reduced during flow reduction. (3) Although both experimental and reference fish did lose mass and condition during the experiment, no effects of flow reduction on stress indicators (blood cortisol or glucose) or bioenergetics (total body fat, water content or mass loss) were detected, probably because access to the preferred type of cover remained available. Like other salmonids, S. fontinalis moves little and seeks physical cover during winter. Unlike many of the more studied salmonids, however, this species overwinters successfully in small groundwater-rich streams that often remain ice-free, and this study identifies undercut banks as the critical winter habitat rather than substratum cover. © 2011 The Authors. Journal of Fish Biology © 2011 The Fisheries Society of the British Isles.

  19. Evidence for Surface Water Ice in the Lunar Polar Regions Using Reflectance Measurements from the Lunar Orbiter Laser Altimeter and Temperature Measurements from the Diviner Lunar Radiometer Experiment

    Science.gov (United States)

    Fisher, Elizabeth A.; Lucey, Paul G.; Lemelin, Myriam; Greenhagen, Benjamin T.; Siegler, Matthew A.; Mazarico, Erwan; Aharonson, Oded; Williams, Jean-Pierre; Hayne, Paul O.; Neumann, Gregory A.; hide

    2017-01-01

    We find that the reflectance of the lunar surface within 5 deg of latitude of theSouth Pole increases rapidly with decreasing temperature, near approximately 110K, behavior consistent with the presence of surface water ice. The North polar region does not show this behavior, nor do South polar surfaces at latitudes more than 5 deg from the pole. This South pole reflectance anomaly persists when analysis is limited to surfaces with slopes less than 10 deg to eliminate false detection due to the brightening effect of mass wasting, and also when the very bright south polar crater Shackleton is excluded from the analysis. We also find that south polar regions of permanent shadow that have been reported to be generally brighter at 1064 nm do not show anomalous reflectance when their annual maximum surface temperatures are too high to preserve water ice. This distinction is not observed at the North Pole. The reflectance excursion on surfaces with maximum temperatures below 110K is superimposed on a general trend of increasing reflectance with decreasing maximum temperature that is present throughout the polar regions in the north and south; we attribute this trend to a temperature or illumination-dependent space weathering effect (e.g. Hemingway et al. 2015). We also find a sudden increase in reflectance with decreasing temperature superimposed on the general trend at 200K and possibly at 300K. This may indicate the presence of other volatiles such as sulfur or organics. We identified and mapped surfaces with reflectances so high as to be unlikely to be part of an ice-free population. In this south we find a similar distribution found by Hayne et al. 2015 based on UV properties. In the north a cluster of pixels near that pole may represent a limited frost exposure.

  20. Evidence for surface water ice in the lunar polar regions using reflectance measurements from the Lunar Orbiter Laser Altimeter and temperature measurements from the Diviner Lunar Radiometer Experiment

    Science.gov (United States)

    Fisher, Elizabeth A.; Lucey, Paul G.; Lemelin, Myriam; Greenhagen, Benjamin T.; Siegler, Matthew A.; Mazarico, Erwan; Aharonson, Oded; Williams, Jean-Pierre; Hayne, Paul O.; Neumann, Gregory A.; Paige, David A.; Smith, David E.; Zuber, Maria T.

    2017-08-01

    We find that the reflectance of the lunar surface within 5° of latitude of the South Pole increases rapidly with decreasing temperature, near ∼110 K, behavior consistent with the presence of surface water ice. The North polar region does not show this behavior, nor do South polar surfaces at latitudes more than 5° from the pole. This South pole reflectance anomaly persists when analysis is limited to surfaces with slopes less than 10° to eliminate false detection due to the brightening effect of mass wasting, and also when the very bright south polar crater Shackleton is excluded from the analysis. We also find that south polar regions of permanent shadow that have been reported to be generally brighter at 1064 nm do not show anomalous reflectance when their annual maximum surface temperatures are too high to preserve water ice. This distinction is not observed at the North Pole. The reflectance excursion on surfaces with maximum temperatures below 110 K is superimposed on a general trend of increasing reflectance with decreasing maximum temperature that is present throughout the polar regions in the north and south; we attribute this trend to a temperature or illumination-dependent space weathering effect (e.g. Hemingway et al., 2015). We also find a sudden increase in reflectance with decreasing temperature superimposed on the general trend at 200 K and possibly at 300 K. This may indicate the presence of other volatiles such as sulfur or organics. We identified and mapped surfaces with reflectances so high as to be unlikely to be part of an ice-free population. In this south we find a similar distribution found by Hayne et al. (2015) based on UV properties. In the north a cluster of pixels near that pole may represent a limited frost exposure.

  1. Copepods in ice-covered seas—Distribution, adaptations to seasonally limited food, metabolism, growth patterns and life cycle strategies in polar seas

    Science.gov (United States)

    Conover, R. J.; Huntley, M.

    1991-07-01

    While a seasonal ice cover limits light penetration into both polar seas for up to ten months a year, its presence is not entirely negative. The mixed layer under sea ice will generally be shallower than in open water at the same latitude and season. Ice forms a substrate on which primary production can be concentrated, a condition which contrasts with the generally dilute nutritional conditions which prevail in the remaining ocean. The combination of a shallow, generally stable mixed layer with a close proximity to abundant food make the under-ice zone a suitable nursery for both pelagic and benthic species, an upside-down benthos for opportunistic substrate browsers, and a rich feeding environment for species often considered to be neritic in temperate environments. Where the ice cover is not continuous there may be a retreating ice edge that facilitates the seasonal production of phytoplankton primarily through increased stability from the melt water. Ice edge blooms similarly encourage secondary production by pelagic animals. Pseudocalanus acuspes, which may be the most abundant and productive copepod in north polar latitudes, initiates growth at the start of the "spring bloom" of epontic algae, reaching sexual maturity at breakup or slightly before. In the Southern Hemisphere, the small neritic copepod Paralabidocera antarctica and adult krill have been observed to utilize ice algae. Calanus hyperboreus breeds in the dark season at depth and its buoyant eggs, slowly developing on the ascent, reach the under-ice layer in April as nauplii ready to benefit from the primary production there. On the other hand, C. glacialis may initiate ontogenetic migrations and reproduction in response to increased erosion of ice algae due to solar warming and melting at the ice-water interface. While the same species in a phytoplankton bloom near the ice edge reproduces actively, those under still-consolidated ice nearby can have immature gonads. Diel migration and diel feeding

  2. Ice Lens Formation, Frost Heave, Thin Films, and the Importance of the Polar H2O Reservoir at High Obliquity

    Science.gov (United States)

    Zent, A. P.; Sizemore, H. G.; Rempel, A. W.

    2011-01-01

    Several lines of evidence indicate that the volume of shallow ground ice in the martian high latitudes exceeds the pore volume of the host regolith. Boynton et al. found an optimal fit to the Mars Odyssey Gamma Ray Spectrometer (GRS) data at the Phoenix landing site by modeling a buried layer of 50-75% ice by mass (up to 90% ice by volume). Thermal and optical observations of recent impact craters in the northern hemisphere have revealed nearly pure ice. Ice deposits containing only 1-2% soil by volume were excavaged by Phoenix. One hypothesis for the origin of this excess ice is that it developed in situ by a mechanism analogous to the formation of terrestrial ice lenses and needle ice. Problematically, terrestrial soil-ice segregation is driven by freeze/thaw cycling and the movement of bulk water, neither of which are expected to have occurred in the geologically recent past on Mars. If however ice lens formation is possible at temperatures less than 273 K, there are possible implications for the habitability of Mars permafrost, since the same thin films of unfrozen water that lead to ice segregation are used by terrestrial psychrophiles to metaboluze and grow down to temperatures of at least 258 K.

  3. Constraining the Depth of Polar Ice Deposits and Evolution of Cold Traps on Mercury with Small Craters in Permanently Shadowed Regions

    Science.gov (United States)

    Deutsch, Ariel N.; Head, James W.; Neumann, Gregory A.; Chabot, Nancy L.

    2017-01-01

    Earth-based radar observations revealed highly reflective deposits at the poles of Mercury [e.g., 1], which collocate with permanently shadowed regions (PSRs) detected from both imagery and altimetry by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft [e.g., 2]. MESSENGER also measured higher hydrogen concentrations at the north polar region, consistent with models for these deposits to be composed primarily of water ice [3]. Enigmatic to the characterization of ice deposits on Mercury is the thickness of these radar-bright features. A current minimum bound of several meters exists from the radar measurements, which show no drop in the radar cross section between 13- and 70-cm wavelength observations [4, 5]. A maximum thickness of 300 m is based on the lack of any statistically significant difference between the height of craters that host radar-bright deposits and those that do not [6]. More recently, this upper limit on the depth of a typical ice deposit has been lowered to approximately 150 m, in a study that found a mean excess thickness of 50 +/- 35 m of radar-bright deposits for 6 craters [7]. Refining such a constraint permits the derivation of a volumetric estimate of the total polar ice on Mercury, thus providing insight into possible sources of water ice on the planet. Here, we take a different approach to constrain the thickness of water-ice deposits. Permanently shadowed surfaces have been resolved in images acquired with the broadband filter on MESSENGER's wide-angle camera (WAC) using low levels of light scattered by crater walls and other topography [8]. These surfaces are not featureless and often host small craters (less than a few km in diameter). Here we utilize the presence of these small simple craters to constrain the thickness of the radar-bright ice deposits on Mercury. Specifically, we compare estimated depths made from depth-to-diameter ratios and depths from individual Mercury Laser Altimeter (MLA

  4. Comparisons of Simulated and Observed Sub-Auroral Polarization Stream (SAPS) during the 17 March 2013 Storm

    Science.gov (United States)

    Chen, M.; Lemon, C.; Sazykin, S. Y.; Wolf, R.; Anderson, P. C.

    2016-12-01

    Sub-Auroral Polarization Streams (SAPS), characterized by large subauroral E x B velocities that span from dusk to the early morning sector for high magnetic activity, result from strong magnetosphere-ionosphere coupling. We investigate how electron and ion precipitation and the ionospheric conductance affect the simulated development of the SAPS electric field for the 17 March 2013 storm. Our approach is to use the magnetically and electrically self-consistent Rice Convection Model - Equilibrium (RCM-E) of the inner magnetosphere to simulate the SAPS. We use parameterized rates of whistler-generated electron pitch-angle scattering from Orlova and Shprits [JGR, 2014] that depend on equatorial radial distance, magnetic activity (Kp), and magnetic local time (MLT) outside the simulated plasmasphere. Inside the plasmasphere, parameterized scattering rates due to hiss [Orlova et al., GRL, 2014] are used. Ions are scattered at a fraction of strong pitch-angle scattering where the fraction is scaled by epsilon, the ratio of the gyroradius to the field-line radius of curvature, when epsilon is greater than 0.1. The electron and proton contributions to the auroral conductance in the RCM-E are calculated using the empirical Robinson et al. [JGR, 1987] and Galand and Richmond [JGR, 2001] equations, respectively. The "background" ionospheric conductance is based on parameters from the International Reference Ionosphere [Bilitza and Reinisch, JASR, 2008] but modified to include the effect of specified ionospheric troughs. Parameterized simulations will aid in understanding the underlying physical process. We compare simulated precipitating particle energy flux and E x B velocities with DMSP observations where SAPS are observed during the 17 March 2013 storm. Analysis of discerpancies between the simulation results and data will aid us in assessing needed improvements in the model.

  5. On the relationship of polar mesospheric cloud ice water content, particle radius and mesospheric temperature and its use in multi-dimensional models

    Directory of Open Access Journals (Sweden)

    E. J. Jensen

    2009-11-01

    Full Text Available The distribution of ice layers in the polar summer mesosphere (called polar mesospheric clouds or PMCs is sensitive to background atmospheric conditions and therefore affected by global-scale dynamics. To investigate this coupling it is necessary to simulate the global distribution of PMCs within a 3-dimensional (3-D model that couples large-scale dynamics with cloud microphysics. However, modeling PMC microphysics within 3-D global chemistry climate models (GCCM is a challenge due to the high computational cost associated with particle following (Lagrangian or sectional microphysical calculations. By characterizing the relationship between the PMC effective radius, ice water content (iwc, and local temperature (T from an ensemble of simulations from the sectional microphysical model, the Community Aerosol and Radiation Model for Atmospheres (CARMA, we determined that these variables can be described by a robust empirical formula. The characterized relationship allows an estimate of an altitude distribution of PMC effective radius in terms of local temperature and iwc. For our purposes we use this formula to predict an effective radius as part of a bulk parameterization of PMC microphysics in a 3-D GCCM to simulate growth, sublimation and sedimentation of ice particles without keeping track of the time history of each ice particle size or particle size bin. This allows cost effective decadal scale PMC simulations in a 3-D GCCM to be performed. This approach produces realistic PMC simulations including estimates of the optical properties of PMCs. We validate the relationship with PMC data from the Solar Occultation for Ice Experiment (SOFIE.

  6. Snow nitrate photolysis in polar regions and the mid-latitudes: Impact on boundary layer chemistry and implications for ice core records

    Science.gov (United States)

    Zatko, Maria C.

    The formation and recycling of nitrogen oxides (NOx=NO+NO 2) associated with snow nitrate photolysis has important implications for air quality and the preservation of nitrate in ice core records. This dissertation examines snow nitrate photolysis in polar and mid-latitude regions using field and laboratory based observations combined with snow chemistry column models and a global chemical transport model to explore the impacts of snow nitrate photolysis on boundary layer chemistry and the preservation of nitrate in polar ice cores. Chapter 1 describes how a global chemical transport model is used to calculate the photolysis-driven flux and redistribution of nitrogen across Antarctica, and Chapter 2 presents similar work for Greenland. Snow-sourced NOx is most dependent on the quantum yield for nitrate photolysis as well as the concentration of photolabile nitrate and light-absorbing impurities (e.g., black carbon, dust, organics) in snow. Model-calculated fluxes of snow-sourced NOx are similar in magnitude in Antarctica (0.5--7.8x108 molec cm-2 s -1) and Greenland (0.1--6.4x108 molec cm-2 s-1) because both nitrate and light-absorbing impurity concentrations in snow are higher (by factors of 2 and 10, respectively) in Greenland. Snow nitrate photolysis influences boundary layer chemistry and ice-core nitrate preservation less in Greenland compared to Antarctica largely due to Greenland's proximity to NOx-source regions. Chapter 3 describes how a snow chemistry column model combined with chemistry and optical measurements from the Uintah Basin Winter Ozone Study (UBWOS) 2014 is used to calculate snow-sourced NOx in eastern Utah. Daily-averaged fluxes of snow-sourced NOx (2.9x10 7--1.3x108 molec cm-2 s-1) are similar in magnitude to polar snow-sourced NO x fluxes, but are only minor components of the Uintah Basin boundary layer NOx budget and can be neglected when developing ozone reduction strategies for the region. Chapter 4 presents chemical and optical

  7. Demography of an apex predator at the edge of its range: impacts of changing sea ice on polar bears in Hudson Bay.

    Science.gov (United States)

    Lunn, Nicholas J; Servanty, Sabrina; Regehr, Eric V; Converse, Sarah J; Richardson, Evan; Stirling, Ian

    2016-07-01

    Changes in the abundance and distribution of wildlife populations are common consequences of historic and contemporary climate change. Some Arctic marine mammals, such as the polar bear (Ursus maritimus), may be particularly vulnerable to such changes due to the loss of Arctic sea ice. We evaluated the impacts of environmental variation on demographic rates for the Western Hudson Bay (WH), polar bear subpopulation from 1984 to 2011 using live-recapture and dead-recovery data in a Bayesian implementation of multistate capture-recapture models. We found that survival of female polar bears was related to the annual timing of sea ice break-up and formation. Using estimated vital rates (e.g., survival and reproduction) in matrix projection models, we calculated the growth rate of the WH subpopulation and projected population responses under different environmental scenarios while accounting for parametric uncertainty, temporal variation, and demographic stochasticity. Our analysis suggested a long-term decline in the number of bears from 1185 (95% Bayesian credible interval [BCI] = 993-1411) in 1987 to 806 (95% BCI = 653-984) in 2011. In the last 10 yr of the study, the number of bears appeared stable due to temporary stability in sea ice conditions (mean population growth rate for the period 2001-2010 = 1.02, 95% BCI = 0.98-1.06). Looking forward, we estimated long-term growth rates for the WH subpopulation of ~1.02 (95% BCI = 1.00-1.05) and 0.97 (95% BCI = 0.92-1.01) under hypothetical high and low sea ice conditions, respectively. Our findings support previous evidence for a demographic linkage between sea ice conditions and polar bear population dynamics. Furthermore, we present a robust framework for sensitivity analysis with respect to continued climate change (e.g., to inform scenario planning) and for evaluating the combined effects of climate change and management actions on the status of wildlife populations. © 2016 by the Ecological Society of

  8. Demography of an apex predator at the edge of its range: impacts of changing sea ice on polar bears in Hudson Bay

    Science.gov (United States)

    Lunn, Nicholas J.; Servanty, Sabrina; Regehr, Eric V.; Converse, Sarah J.; Richardson, Evan S.; Stirling, Ian

    2016-01-01

    Changes in the abundance and distribution of wildlife populations are common consequences of historic and contemporary climate change. Some Arctic marine mammals, such as the polar bear (Ursus maritimus), may be particularly vulnerable to such changes due to the loss of Arctic sea ice. We evaluated the impacts of environmental variation on demographic rates for the Western Hudson Bay (WH), polar bear subpopulation from 1984 to 2011 using live-recapture and dead-recovery data in a Bayesian implementation of multistate capture–recapture models. We found that survival of female polar bears was related to the annual timing of sea ice break-up and formation. Using estimated vital rates (e.g., survival and reproduction) in matrix projection models, we calculated the growth rate of the WH subpopulation and projected population responses under different environmental scenarios while accounting for parametric uncertainty, temporal variation, and demographic stochasticity. Our analysis suggested a long-term decline in the number of bears from 1185 (95% Bayesian credible interval [BCI] = 993–1411) in 1987 to 806 (95% BCI = 653–984) in 2011. In the last 10 yr of the study, the number of bears appeared stable due to temporary stability in sea ice conditions (mean population growth rate for the period 2001–2010 = 1.02, 95% BCI = 0.98–1.06). Looking forward, we estimated long-term growth rates for the WH subpopulation of ~1.02 (95% BCI = 1.00–1.05) and 0.97 (95% BCI = 0.92–1.01) under hypothetical high and low sea ice conditions, respectively. Our findings support previous evidence for a demographic linkage between sea ice conditions and polar bear population dynamics. Furthermore, we present a robust framework for sensitivity analysis with respect to continued climate change (e.g., to inform scenario planning) and for evaluating the combined effects of climate change and management actions on the status of wildlife populations.

  9. AMSR-E/Aqua Daily L3 25 km Tb and Sea Ice Concentration Polar Grids V002

    Data.gov (United States)

    National Aeronautics and Space Administration — The AMSR-E/Aqua Level-3 25 km daily sea ice product includes 6.9 - 89.0 GHz TBs and sea ice concentration averages (daily, ascending, and descending) on a 25 km...

  10. Initial Results from Radiometer and Polarized Radar-Based Icing Algorithms Compared to In-Situ Data

    Science.gov (United States)

    Serke, David; Reehorst, Andrew L.; King, Michael

    2015-01-01

    In early 2015, a field campaign was conducted at the NASA Glenn Research Center in Cleveland, Ohio, USA. The purpose of the campaign is to test several prototype algorithms meant to detect the location and severity of in-flight icing (or icing aloft, as opposed to ground icing) within the terminal airspace. Terminal airspace for this project is currently defined as within 25 kilometers horizontal distance of the terminal, which in this instance is Hopkins International Airport in Cleveland. Two new and improved algorithms that utilize ground-based remote sensing instrumentation have been developed and were operated during the field campaign. The first is the 'NASA Icing Remote Sensing System', or NIRSS. The second algorithm is the 'Radar Icing Algorithm', or RadIA. In addition to these algorithms, which were derived from ground-based remote sensors, in-situ icing measurements of the profiles of super-cooled liquid water (SLW) collected with vibrating wire sondes attached to weather balloons produced a comprehensive database for comparison. Key fields from the SLW-sondes include air temperature, humidity and liquid water content, cataloged by time and 3-D location. This work gives an overview of the NIRSS and RadIA products and results are compared to in-situ SLW-sonde data from one icing case study. The location and quantity of super-cooled liquid as measured by the in-situ probes provide a measure of the utility of these prototype hazard-sensing algorithms.

  11. Millennial and sub-millennial scale climatic variations recorded in polar ice cores over the last glacial period

    DEFF Research Database (Denmark)

    Capron, E.; Landais, A.; Chappellaz, J.

    2010-01-01

    Since its discovery in Greenland ice cores, the millennial scale climatic variability of the last glacial period has been increasingly documented at all latitudes with studies focusing mainly on Marine Isotopic Stage 3 (MIS 3; 28–60 thousand of years before present, hereafter ka) and characterized...... that when ice sheets are extensive, Antarctica does not necessarily warm during the whole GS as the thermal bipolar seesaw model would predict, questioning the Greenland ice core temperature records as a proxy for AMOC changes throughout the glacial period....

  12. High-precision dual-inlet IRMS measurements of the stable isotopes of CO2 and the N2O / CO2 ratio from polar ice core samples

    Directory of Open Access Journals (Sweden)

    T. K. Bauska

    2014-11-01

    Full Text Available An important constraint on mechanisms of past carbon cycle variability is provided by the stable isotopic composition of carbon in atmospheric carbon dioxide (δ13C-CO2 trapped in polar ice cores, but obtaining very precise measurements has proven to be a significant analytical challenge. Here we describe a new technique to determine the δ13C of CO2 at very high precision, as well as measuring the CO2 and N2O mixing ratios. In this method, ancient air is extracted from relatively large ice samples (~400 g with a dry-extraction "ice grater" device. The liberated air is cryogenically purified to a CO2 and N2O mixture and analyzed with a microvolume-equipped dual-inlet IRMS (Thermo MAT 253. The reproducibility of the method, based on replicate analysis of ice core samples, is 0.02‰ for δ13C-CO2 and 2 ppm and 4 ppb for the CO2 and N2O mixing ratios, respectively (1σ pooled standard deviation. Our experiments show that minimizing water vapor pressure in the extraction vessel by housing the grating apparatus in a ultralow-temperature freezer (−60 °C improves the precision and decreases the experimental blank of the method to −0.07 ± 0.04‰. We describe techniques for accurate calibration of small samples and the application of a mass-spectrometric method based on source fragmentation for reconstructing the N2O history of the atmosphere. The oxygen isotopic composition of CO2 is also investigated, confirming previous observations of oxygen exchange between gaseous CO2 and solid H2O within the ice archive. These data offer a possible constraint on oxygen isotopic fractionation during H2O and CO2 exchange below the H2O bulk melting temperature.

  13. Spectral dependence of backscattering coefficient of mixed phase clouds over West Africa measured with two-wavelength Raman polarization lidar: Features attributed to ice-crystals corner reflection

    Science.gov (United States)

    Veselovskii, I.; Goloub, P.; Podvin, T.; Tanre, D.; Ansmann, A.; Korenskiy, M.; Borovoi, A.; Hu, Q.; Whiteman, D. N.

    2017-11-01

    The existing models predict that corner reflection (CR) of laser radiation by simple ice crystals of perfect shape, such as hexagonal columns or plates, can provide a significant contribution to the ice cloud backscattering. However in real clouds the CR effect may be suppressed due to crystal deformation and surface roughness. In contrast to the extinction coefficient, which is spectrally independent, consideration of diffraction associated with CR results in a spectral dependence of the backscattering coefficient. Thus measuring the spectral dependence of the cloud backscattering coefficient, the contribution of CR can be identified. The paper presents the results of profiling of backscattering coefficient (β) and particle depolarization ratio (δ) of ice and mixed-phase clouds over West Africa by means of a two-wavelength polarization Mie-Raman lidar operated at 355 nm and 532 nm during the SHADOW field campaign. The lidar observations were performed at a slant angle of 43 degree off zenith, thus CR from both randomly oriented crystals and oriented plates could be analyzed. For the most of the observations the cloud backscatter color ratio β355/β532 was close to 1.0, and no spectral features that might indicate the presence of CR of randomly oriented crystals were revealed. Still, in two measurement sessions we observed an increase of backscatter color ratio to a value of nearly 1.3 simultaneously with a decrease of the spectral depolarization ratio δ355/δ532 ratio from 1.0 to 0.8 inside the layers containing precipitating ice crystals. We attribute these changes in optical properties to corner reflections by horizontally oriented ice plates.

  14. Bathymetry and ocean properties beneath Pine Island Glacier revealed by Autosub3 and implications for recent ice stream evolution (Invited)

    Science.gov (United States)

    Jenkins, A.; Dutrieux, P.; McPhail, S.; Perrett, J.; Webb, A.; White, D.; Jacobs, S. S.

    2009-12-01

    The Antarctic ice sheet, which represents the largest of all potential contributors to sea level rise, appears to be losing mass at a rate that has accelerated over recent decades. Ice loss is focussed in a number of key drainage basins where dynamical changes in the outlet glaciers have led to increased discharge. The synchronous response of several independent glaciers, coupled with the observation that thinning is most rapid over their floating termini, is generally taken as an indicator that the changes have been driven from the ocean. Some of the most significant changes have been observed on Pine Island Glacier, where thinning, acceleration and grounding line retreat have all been observed, primarily through satellite remote sensing. Even during the relatively short satellite record, rates of change have been observed to increase. Between 20th and 30th January 2009 the Autosub3 autonomous underwater vehicle was deployed from host ship RVIB Nathaniel B Palmer on six sorties into the ocean cavity beneath Pine Island Glacier. Total track length was 887 km (taking 167 hours) of which 510 km (taking 94 hours) were beneath the glacier. Some of the main aims were to map both the seabed beneath and the underside of the glacier and to investigate how warm Circumpolar Deep Water (CDW) flows beneath Pine Island Glacier and determines its melt rate. Among the instruments carried by Autosub-3 were a Seabird CTD, with dual conductivity and temperature sensors plus a dissolved oxygen sensor and a transmissometer, a multi-beam echosounder that could be configured to look up or down, and two Acoustic Doppler Current Profilers (ADCPs): an upward-looking 300 kHz instrument and a downward-looking 150 kHz instrument, providing a record of ice draft and seabed depth along the vehicle track. The ADCP data reveal an apparently continuous ridge with an undulating crest that extends across the cavity about 30km in from the current ice front. This topographic feature blocks CDW inflow

  15. Modelling the climate and surface mass balance of polar ice sheets using RACMO2 - Part 1: Greenland (1958-2016)

    Science.gov (United States)

    Noël, Brice; van de Berg, Willem Jan; Melchior van Wessem, J.; van Meijgaard, Erik; van As, Dirk; Lenaerts, Jan T. M.; Lhermitte, Stef; Kuipers Munneke, Peter; Smeets, C. J. P. Paul; van Ulft, Lambertus H.; van de Wal, Roderik S. W.; van den Broeke, Michiel R.

    2018-03-01

    We evaluate modelled Greenland ice sheet (GrIS) near-surface climate, surface energy balance (SEB) and surface mass balance (SMB) from the updated regional climate model RACMO2 (1958-2016). The new model version, referred to as RACMO2.3p2, incorporates updated glacier outlines, topography and ice albedo fields. Parameters in the cloud scheme governing the conversion of cloud condensate into precipitation have been tuned to correct inland snowfall underestimation: snow properties are modified to reduce drifting snow and melt production in the ice sheet percolation zone. The ice albedo prescribed in the updated model is lower at the ice sheet margins, increasing ice melt locally. RACMO2.3p2 shows good agreement compared to in situ meteorological data and point SEB/SMB measurements, and better resolves the spatial patterns and temporal variability of SMB compared with the previous model version, notably in the north-east, south-east and along the K-transect in south-western Greenland. This new model version provides updated, high-resolution gridded fields of the GrIS present-day climate and SMB, and will be used for projections of the GrIS climate and SMB in response to a future climate scenario in a forthcoming study.

  16. Sea Ice Ecosystems

    Science.gov (United States)

    Arrigo, Kevin R.

    2014-01-01

    Polar sea ice is one of the largest ecosystems on Earth. The liquid brine fraction of the ice matrix is home to a diverse array of organisms, ranging from tiny archaea to larger fish and invertebrates. These organisms can tolerate high brine salinity and low temperature but do best when conditions are milder. Thriving ice algal communities, generally dominated by diatoms, live at the ice/water interface and in recently flooded surface and interior layers, especially during spring, when temperatures begin to rise. Although protists dominate the sea ice biomass, heterotrophic bacteria are also abundant. The sea ice ecosystem provides food for a host of animals, with crustaceans being the most conspicuous. Uneaten organic matter from the ice sinks through the water column and feeds benthic ecosystems. As sea ice extent declines, ice algae likely contribute a shrinking fraction of the total amount of organic matter produced in polar waters.

  17. Sedimentary and rock magnetic signatures and event scenarios of deglacial outburst floods from the Laurentian Channel Ice Stream

    Science.gov (United States)

    Leng, Wei; von Dobeneck, Tilo; Bergmann, Fenna; Just, Janna; Mulitza, Stefan; Chiessi, Cristiano M.; St-Onge, Guillaume; Piper, David J. W.

    2018-04-01

    Eastern Canadian margin sediments bear testimony to several catastrophic deglacial meltwater discharges from the retreating Laurentide Ice Sheet. The reddish-brown plumite layers deposited on the levees of the Laurentian Fan valleys have been recognized as indications of multiple outburst floods between Heinrich events 2 and 1. Five event layers have been consistently recorded in three new gravity cores retrieved on the SW Grand Banks slope and comply with the previously published Laurentian Fan core MD95-2029. The apparently huge extent of these outburst plumes around the Laurentian Fan as well as their causes and consequences are investigated in this study using physical properties, rock magnetic and grain-size analyses, together with seismoacoustic profiling. We provide the first detailed 14C ages of the outburst event sequence and discuss their recurrence intervals in the context of regional ice retreat. Compared to the hemipelagic interlayers, event layers have overall uniform and systematic changes of rock-magnetic properties. Hematite contents increase over time and proximally while magnetite grain sizes fine upwards and spatially away from the fan. Based on the sediment composition and load, we argue that these plumites were formed by recurrent erosion of glacial mud deposits in the Laurentian Channel by meltwater outbursts. Three alternative glaciological scenarios are evaluated: in each case, the provenance of the transported sediment is not an indicator of the precise source of the meltwater.

  18. Sulfur mass loading of the atmosphere from volcanic eruptions: Calibration of the ice core record on basis of sulfate aerosol deposition in polar regions from the 1982 El Chichon eruption

    Science.gov (United States)

    Sigurdsson, Haraldur; Laj, Paolo

    1990-01-01

    Major volcanic eruptions disperse large quantities of sulfur compound throughout the Earth's atmosphere. The sulfuric acid aerosols resulting from such eruptions are scavenged by snow within the polar regions and appear in polar ice cores as elevated acidity layers. Glacio-chemical studies of ice cores can, thus, provide a record of past volcanism, as well as the means for understanding the fate of volcanic sulfur in the atmosphere. The primary objectives of this project are to study the chemistry and physical properties of volcanic fallout in a Greenland Ice Core in order to evaluate the impact of the volcanic gases on the atmospheric chemistry and the total atmospheric mass of volcanic aerosols emitted by major volcanic eruptions. We propose to compare the ice core record to other atmospheric records performed during the last 10 years to investigate transport and deposition of volcanic materials.

  19. Robust Exploration and Commercial Missions to the Moon Using LANTR Propulsion and In-Situ Propellants Derived From Lunar Polar Ice (LPI) Deposits

    Science.gov (United States)

    Borowski, Stanley K.; Ryan, Stephen W.; Burke, Laura M.; McCurdy, David R.; Fittje, James E.; Joyner, Claude R.

    2017-01-01

    Since the 1960s, scientists have conjectured that water icecould survive in the cold, permanently shadowed craters located at the Moons poles Clementine (1994), Lunar Prospector (1998),Chandrayaan-1 (2008), and Lunar Reconnaissance Orbiter (LRO) and Lunar CRater Observation and Sensing Satellite(LCROSS) (2009) lunar probes have provided data indicating the existence of large quantities of water ice at the lunar poles The Mini-SAR onboard Chandrayaan-1discovered more than 40 permanently shadowed craters near the lunar north pole that are thought to contain 600 million metric tons of water ice. Using neutron spectrometer data, the Lunar Prospector science team estimated a water ice content (1.5 +-0.8 wt in the regolith) found in the Moons polar cold trap sand estimated the total amount of water at both poles at 2 billion metric tons Using Mini-RF and spectrometry data, the LRO LCROSS science team estimated the water ice content in the regolith in the south polar region to be 5.6 +-2.9 wt. On the basis of the above scientific data, it appears that the water ice content can vary from 1-10 wt and the total quantity of LPI at both poles can range from 600 million to 2 billion metric tons NTP offers significant benefits for lunar missions and can take advantage of the leverage provided from using LDPs when they become available by transitioning to LANTR propulsion. LANTR provides a variablethrust and Isp capability, shortens burn times and extends engine life, and allows bipropellant operation The combination of LANTR and LDP has performance capability equivalent to that of a hypothetical gaseousfuel core NTR (effective Isp 1575 s) and can lead to a robust LTS with unique mission capabilities that include short transit time crewed cargo transports and routine commuter flights to the Moon The biggest challenge to making this vision a reality will be the production of increasing amounts of LDP andthe development of propellant depots in LEO, LLO and LPO. An industry

  20. The Effect of Sub-Auroral Polarization Streams (SAPS) on Ionosphere and Thermosphere during 2015 St. Patrick's Day storm: Global Ionosphere-Thermosphere Model (GITM) Simulations

    Science.gov (United States)

    Guo, J.; Deng, Y.; Zhang, D.; Lu, Y.; Sheng, C.

    2017-12-01

    Sub-Auroral Polarization Streams (SAPS) are incorporated into the non-hydrostatic Global Ionosphere-Thermosphere Model (GITM), revealing the complex effects on neutral dynamics and ion-neutral coupling processes. The intense westward ion stream could enhance the neutral zonal wind within the SAPS channel. Through neutral dynamics the neutrals then divide into two streams, one turns poleward and the other turns equatorward, forming a two-cell pattern in the SAPS-changed wind. The significant Joule heating induced by SAPS also leads to traveling atmospheric disturbances (TAD) accompanied by traveling ionospheric disturbances (TID), increasing the total electron content (TEC) by 2-8 TECu in the mid-latitude ionosphere. We investigate the potential causes of the reported poleward wind surge during the St. Patrick's Day storm in 2015. It is confirmed that Coriolis force on the westward zonal wind can contribute the poleward wind during post-SAPS interval. In addition, the simulations imply that the sudden decrease of heating rate within auroral oval could result in a TAD propagating equatorward, which could also be responsible for the sudden poleward wind surge. This study highlights the complicated effects of SAPS on ion-neutral coupling and neutral dynamics.

  1. Millennial and sub-millennial scale climatic variations recorded in polar ice cores over the last glacial period

    Directory of Open Access Journals (Sweden)

    E. Capron

    2010-06-01

    Full Text Available Since its discovery in Greenland ice cores, the millennial scale climatic variability of the last glacial period has been increasingly documented at all latitudes with studies focusing mainly on Marine Isotopic Stage 3 (MIS 3; 28–60 thousand of years before present, hereafter ka and characterized by short Dansgaard-Oeschger (DO events. Recent and new results obtained on the EPICA and NorthGRIP ice cores now precisely describe the rapid variations of Antarctic and Greenland temperature during MIS 5 (73.5–123 ka, a time period corresponding to relatively high sea level. The results display a succession of abrupt events associated with long Greenland InterStadial phases (GIS enabling us to highlight a sub-millennial scale climatic variability depicted by (i short-lived and abrupt warming events preceding some GIS (precursor-type events and (ii abrupt warming events at the end of some GIS (rebound-type events. The occurrence of these sub-millennial scale events is suggested to be driven by the insolation at high northern latitudes together with the internal forcing of ice sheets. Thanks to a recent NorthGRIP-EPICA Dronning Maud Land (EDML common timescale over MIS 5, the bipolar sequence of climatic events can be established at millennial to sub-millennial timescale. This shows that for extraordinary long stadial durations the accompanying Antarctic warming amplitude cannot be described by a simple linear relationship between the two as expected from the bipolar seesaw concept. We also show that when ice sheets are extensive, Antarctica does not necessarily warm during the whole GS as the thermal bipolar seesaw model would predict, questioning the Greenland ice core temperature records as a proxy for AMOC changes throughout the glacial period.

  2. Numerical simulation of flow and melting characteristics of seawater-ice crystals two-phase flow in inlet straight pipe of shell and tube heat exchanger of polar ship

    Science.gov (United States)

    Xu, Li; Huang, Chang-Xu; Huang, Zhen-Fei; Sun, Qiang; Li, Jie

    2018-05-01

    The ice crystal particles are easy to enter into the seawater cooling system of polar ship together with seawater when it sails in the Arctic. They are easy to accumulate in the pipeline, causing serious blockage of the cooling pipe. In this study, the flow and melting characteristics of ice particles-seawater two-phase flow in inlet straight pipe of shell-and-tube heat exchanger were numerically simulated by using Eulerian-Eulerian two-fluid model coupled with the interphase heat and mass transfer model. The influences of inlet ice packing factor, ice crystal particle diameter, and inlet velocity on the distribution and melting characteristics of ice crystals were investigated. The degree of asymmetry of the distribution of ice crystals in the cross section decreases gradually when the IPF changes from 5 to 15%. The volume fractions of ice crystals near the top of the outlet cross section are 19.59, 19.51, and 22.24% respectively for ice packing factor of 5, 10 and 15%. When the particle diameter is 0.5 mm, the ice crystals are gradually stratified during the flow process. With particle diameters of 1.0 and 2.0 mm, the region with the highest volume fraction of ice crystals is a small circle and the contours in the cloud map are compact. The greater the inlet flow velocity, the less stratified the ice crystals and the more obvious the turbulence on the outlet cross section. The average volume fraction of ice crystals along the flow direction is firstly rapidly reduced and then stabilized after 300 mm.

  3. A natural ice boom

    Energy Technology Data Exchange (ETDEWEB)

    Hopper, H.R. [Manitoba Hydro, Winnipeg, MB (Canada)

    1998-10-01

    Planning for ice jams and ice movements are critical on the Nelson River in northern Manitoba in designing cofferdams. Experience on the St. Lawrence River demonstrated the possibility of exercising some control over ice action by judicious placement of log booms or ice control structures. The success of experiments with man-made controls led to field tests in which an ice sheet of sufficient magnitude and competence was introduced into the open water stream of the Nelson River. The ice sheet was subsequently jammed in a narrow channel, thereby creating a natural ice bridge or boom upstream of a proposed hydro development. Under favourable conditions, this boom would initiate the progression of the ice cover from its location upstream, cutting off the downstream reach from the ice producing potential of the upstream reach. Although ice would still be generated downstream, the length of the reach between the ice boom and the development site would be short enough that ice jamming at the development site would never occur. Although problems in blasting prevented the introduction of a competent ice sheet into the main stream of the river at the location chosen, sufficient confidence in the theory was gained to warrant further consideration. 4 refs., 1 tab., 10 figs.

  4. Geomagnetic reversals, polar ice and cosmic spherules: some recent measurements with a small dedicated accelerator mass-spectrometry facility

    International Nuclear Information System (INIS)

    Raisbeck, G.M.; Yiou, F.

    1987-01-01

    We have developed techniques for measuring the cosmogenic isotopes 10 Be (half-life 1.5 Ma) and 26 Al (716 ka) by using a small (ca. 2.2 MV) dedicated accelerator mass spectrometer facility. Three recent applications of such measurements are as follows. 1. 10 Be has been measured in marine-sediment cores at levels corresponding to three recent geomagnetic reversals. We observe an increase in 10 Be production at each of these times. The results give information on the form and length of the geomagnetic intensity changes during a reversal, and the level at which magnetic remanence is acquired in the sediments. 2. 10 Be has been measured over a 2083 m ice core, corresponding to the last climatic cycle, recovered from Vostok, Antarctica. The results suggest that the precipitation rate during the last Ice Age was about half of its present rate. There are also some indications of fairly rapid 10 Be production changes. 3. 10 Be and 26 Al have been measured in 'cosmic spherules' (small round objects, ca. 500 μm diameter) recovered in deep-sea sediments and in melt lakes on Greenland ice. The results confirm an extraterrestrial origin for such objects, as well as indicating that the parent bodies of most of them were irradiated in space as small (less than 1 cm) objects. These spherules thus very probably represent cometary debris. (author)

  5. Polarized Radiative Transfer of a Cirrus Cloud Consisting of Randomly Oriented Hexagonal Ice Crystals: The 3 x 3 Approximation for Non-Spherical Particles

    Science.gov (United States)

    Stamnes, S.; Ou, S. C.; Lin, Z.; Takano, Y.; Tsay, S. C.; Liou, K.N.; Stamnes, K.

    2016-01-01

    The reflection and transmission of polarized light for a cirrus cloud consisting of randomly oriented hexagonal columns were calculated by two very different vector radiative transfer models. The forward peak of the phase function for the ensemble-averaged ice crystals has a value of order 6 x 10(exp 3) so a truncation procedure was used to help produce numerically efficient yet accurate results. One of these models, the Vectorized Line-by-Line Equivalent model (VLBLE), is based on the doubling- adding principle, while the other is based on a vector discrete ordinates method (VDISORT). A comparison shows that the two models provide very close although not entirely identical results, which can be explained by differences in treatment of single scattering and the representation of the scattering phase matrix. The relative differences in the reflected I and Q Stokes parameters are within 0.5 for I and within 1.5 for Q for all viewing angles. In 1971 Hansen showed that for scattering by spherical particles the 3 x 3 approximation is sufficient to produce accurate results for the reflected radiance I and the degree of polarization (DOP), and he conjectured that these results would hold also for non-spherical particles. Simulations were conducted to test Hansen's conjecture for the cirrus cloud particles considered in this study. It was found that the 3 x 3 approximation also gives accurate results for the transmitted light, and for Q and U in addition to I and DOP. For these non-spherical ice particles the 3 x 3 approximation leads to an absolute error 2 x 10(exp -6) for the reflected and transmitted I, Q and U Stokes parameters. Hence, it appears to be an excellent approximation, which significantly reduces the computational complexity and burden required for multiple scattering calculations.

  6. Measurements of the spin structure of the nucleon using SPHICE: A strongly polarized hydrogen and deuterium ice target

    International Nuclear Information System (INIS)

    Babusci, D.; Blecher, M.; Breuer, M.; Caracappa, A.; Commeaux, C.; Didelez, J.; Fan, Q.; Giordano, G.; Hicks, K.; Hoblit, S.; Hoffmann-Rothe, P.; Honig, A.; Kistner, O.C.; Khandaker, M.; Li, Z.; Lucas, M.A.; Matone, G.; Miceli, L.; Preedom, B.M.; Rigney, M.; Sandorfi, A.M.; Schaerf, C.; Thorn, C.E.

    1995-01-01

    Frozen-spin HD polarized targets operating between 0.4 and 4K, used with cold-transfer (4K) techniques, provide great configurational flexibility. Their long depolarization times under target usage conditions assure reasonable match between polarization production and usage times, for weakly ionizing beam fluxes, and the very long relaxation times at fields above 7T (∼1 yr.) provide an economical storage mode and open-quote open-quote off-the-shelf close-quote close-quote availability. copyright 1995 American Institute of Physics

  7. Enantiomeric excesses induced in amino acids by ultraviolet circularly polarized light irradiation of extraterrestrial ice analogs: A possible source of asymmetry for prebiotic chemistry

    International Nuclear Information System (INIS)

    Modica, Paola; De Marcellus, Pierre; D'Hendecourt, Louis Le Sergeant; Meinert, Cornelia; Meierhenrich, Uwe J.; Nahon, Laurent

    2014-01-01

    The discovery of meteoritic amino acids with enantiomeric excesses of the L-form (ee L ) has suggested that extraterrestrial organic materials may have contributed to prebiotic chemistry and directed the initial occurrence of the ee L that further led to homochirality of amino acids on Earth. A proposed mechanism for the origin of ee L in meteorites involves an asymmetric photochemistry of extraterrestrial ices by UV circularly polarized light (CPL). We have performed the asymmetric synthesis of amino acids on achiral extraterrestrial ice analogs by VUV CPL, investigating the chiral asymmetry transfer at two different evolutionary stages at which the analogs were irradiated (regular ices and/or organic residues) and at two different photon energies (6.6 and 10.2 eV). We identify 16 distinct amino acids and precisely measure the L-enantiomeric excesses using the enantioselective GC × GC-TOFMS technique in five of them: α-alanine, 2,3-diaminopropionic acid, 2-aminobutyric acid, valine, and norvaline, with values ranging from ee L = –0.20% ± 0.14% to ee L = –2.54% ± 0.28%. The sign of the induced ee L depends on the helicity and the energy of CPL, but not on the evolutionary stage of the samples, and is the same for all five considered amino acids. Our results support an astrophysical scenario in which the solar system was formed in a high-mass star-forming region where icy grains were irradiated during the protoplanetary phase by an external source of CPL of a given helicity and a dominant energy, inducing a stereo-specific photochemistry.

  8. Polar Stratigraphy

    Science.gov (United States)

    1999-01-01

    These three images were taken on three different orbits over the north polar cap in April 1999. Each shows a different part of the same ice-free trough. The left and right images are separated by a distance of more than 100 kilometers (62 miles). Note the similar layers in each image.

  9. ROCK and RHO Playlist for Preimplantation Development: Streaming to HIPPO Pathway and Apicobasal Polarity in the First Cell Differentiation.

    Science.gov (United States)

    Alarcon, Vernadeth B; Marikawa, Yusuke

    2018-01-01

    In placental mammalian development, the first cell differentiation produces two distinct lineages that emerge according to their position within the embryo: the trophectoderm (TE, placenta precursor) differentiates in the surface, while the inner cell mass (ICM, fetal body precursor) forms inside. Here, we discuss how such position-dependent lineage specifications are regulated by the RHOA subfamily of small GTPases and RHO-associated coiled-coil kinases (ROCK). Recent studies in mouse show that activities of RHO/ROCK are required to promote TE differentiation and to concomitantly suppress ICM formation. RHO/ROCK operate through the HIPPO signaling pathway, whose cell position-specific modulation is central to establishing unique gene expression profiles that confer cell fate. In particular, activities of RHO/ROCK are essential in outside cells to promote nuclear localization of transcriptional co-activators YAP/TAZ, the downstream effectors of HIPPO signaling. Nuclear localization of YAP/TAZ depends on the formation of apicobasal polarity in outside cells, which requires activities of RHO/ROCK. We propose models of how RHO/ROCK regulate lineage specification and lay out challenges for future investigations to deepen our understanding of the roles of RHO/ROCK in preimplantation development. Finally, as RHO/ROCK may be inhibited by certain pharmacological agents, we discuss their potential impact on human preimplantation development in relation to fertility preservation in women.

  10. Decadal ecosystem response to an anomalous melt season in a polar desert in Antarctica.

    Science.gov (United States)

    Gooseff, Michael N; Barrett, John E; Adams, Byron J; Doran, Peter T; Fountain, Andrew G; Lyons, W Berry; McKnight, Diane M; Priscu, John C; Sokol, Eric R; Takacs-Vesbach, Cristina; Vandegehuchte, Martijn L; Virginia, Ross A; Wall, Diana H

    2017-09-01

    Amplified climate change in polar regions is significantly altering regional ecosystems, yet there are few long-term records documenting these responses. The McMurdo Dry Valleys (MDV) cold desert ecosystem is the largest ice-free area of Antarctica, comprising soils, glaciers, meltwater streams and permanently ice-covered lakes. Multi-decadal records indicate that the MDV exhibited a distinct ecosystem response to an uncharacteristic austral summer and ensuing climatic shift. A decadal summer cooling phase ended in 2002 with intense glacial melt ('flood year')-a step-change in water availability triggering distinct changes in the ecosystem. Before 2002, the ecosystem exhibited synchronous behaviour: declining stream flow, decreasing lake levels, thickening lake ice cover, decreasing primary production in lakes and streams, and diminishing soil secondary production. Since 2002, summer air temperatures and solar flux have been relatively consistent, leading to lake level rise, lake ice thinning and elevated stream flow. Biological responses varied; one stream cyanobacterial mat type immediately increased production, but another stream mat type, soil invertebrates and lake primary productivity responded asynchronously a few years after 2002. This ecosystem response to a climatic anomaly demonstrates differential biological community responses to substantial perturbations, and the mediation of biological responses to climate change by changes in physical ecosystem properties.

  11. Transient Conditions at the Ice/bed Interface Under a Palaeo-ice Stream Derived from Numerical Simulation of Groundwater Flow and Sedimentological Observations in a Drumlin Field, NW Poland

    Science.gov (United States)

    Hermanowski, P.; Piotrowski, J. A.

    2017-12-01

    Evacuation of glacial meltwater through the substratum is an important agent modulating the ice/bed interface processes. The amount of meltwater production, subglacial water pressure, flow patterns and fluxes all affect the strength of basal coupling and thus impact the ice-sheet dynamics. Despite much research into the subglacial processes of past ice sheets which controlled sediment transport and the formation of specific landforms, our understanding of the ice/bed interface remains fragmentary. In this study we numerically simulated, using finite difference and finite element codes, groundwater flow pattern and fluxes during an ice advance in the Stargard Drumlin Field, NW Poland to examine the potential influence of groundwater drainage on the landforming processes. The results are combined with sedimentological observations of the internal composition of the drumlins to validate the outcome of the numerical model. Our numerical experiments of groundwater flow suggest a highly time-dependent response of the subglacial hydrogeological system to the advancing ice margin. This is manifested as diversified areas of downward- and upward-oriented groundwater flows whereby the drumlin field area experienced primarily groundwater discharge towards the ice sole. The investigated drumlins are composed of (i) mainly massive till with thin stringers of meltwater sand, and (ii) sorted sediments carrying ductile deformations. The model results and sedimentological observations suggest a high subglacial pore-water pressure in the drumlin field area, which contributed to sediment deformation intervening with areas of basal decoupling and enhanced basal sliding.

  12. Following the south polar cap recession as viewed by OMEGA/MEX using automatic detection of H2O and CO2 ices.

    Science.gov (United States)

    Schmidt, F.; Doute, S.; Schmitt, B.

    In order to understand Mars' current climate it is necessary to detect, characterize and monitor CO2 and H2O at the surface (permanent and seasonal icy deposits) and in the atmosphere (vapor and clouds). Here we will focus on the South Seasonal Polar Cap (SSPC) whose recession was previously observed with different techniques : from earth in the visible range with HST [James 1996], or from MGS spacecraft with MOC images [Benson 2005], in the thermal IR range by the TES [Kieffer 2000], in the near infrared by OMEGA/MEX [Langevin submitted]. The time and space evolutions of the SSPC is a major annual climatic signal both at the global and the regional scales. In particular the measurement of the temporal and spatial distributions of CO2 constrains exchange processes between both surface and atmosphere. This exchange may involve preponderant species : H2O, CO2 and dust. In this work we will apply a new detection technique : "wavanglet" in order to follow the recession of the SSPC thanks to OMEGA/MEX observations. This method was especially developed in the goal to classify a huge dataset, such OMEGA ones. We propose to use "wavanglet" as a supervised automatic classification method that identifies spectral features and classifies the image in spectrally homogeneous units. Additionally we will evaluate quantitative detection limits of "wavanglet" based on synthetic dataset simulating OMEGA spectra in typical situation of the SSPC. This detection limit will be discussed in terms of abundance for H2O and CO2 ices in order to improve the interpretation of the classification. Finally we will present the recession of the SSPC using "wavanglet" and we will compare the results with those of earlier investigation. An interpretation of the similarities and disagreements between those maps will be done.

  13. Modeling the heating and melting of sea ice through light absorption by microalgae

    Science.gov (United States)

    Zeebe, Richard E.; Eicken, Hajo; Robinson, Dale H.; Wolf-Gladrow, Dieter; Dieckmann, Gerhard S.

    1996-01-01

    In sea ice of polar regions, high concentrations of microalgae are observed during the spring. Algal standing stocks may attain peak values of over 300 mg chl a m-2 in the congelation ice habitat. As of yet, the effect of additional heating of sea ice through conversion of solar radiation into heat by algae has not been investigated in detail. Local effects, such as a decrease in albedo, increasing melt rates, and a decrease of the physical strength of ice sheets may occur. To investigate the effects of microalgae on the thermal regime of sea ice, a time-dependent, one-dimensional thermodynamic model of sea ice was coupled to a bio-optical model. A spectral one-stream model was employed to determine spectral attenuation by snow, sea ice, and microalgae. Beer's law was assumed to hold for every wavelength. Energy absorption was obtained by calculating the divergence of irradiance in every layer of the model (Δz = 1 cm). Changes in sea ice temperature profiles were calculated by solving the heat conduction equation with a finite difference scheme. Model results indicate that when algal biomass is concentrated at the bottom of congelation ice, melting of ice resulting from the additional conversion of solar radiation into heat may effectively destroy the algal habitat, thereby releasing algal biomass into the water column. An algal layer located in the top of the ice sheet induced a significant increase in sea ice temperature (ΔT > 0.3 K) for snow depths less than 5 cm and algal standing stocks higher than 150 mg chl a m-2. Furthermore, under these conditions, brine volume increased by 21% from 181 to 219 parts per thousand, which decreased the physical strength of the ice.

  14. Glacier seismology: eavesdropping on the ice-bed interface

    Science.gov (United States)

    Walter, F.; Röösli, C.

    2015-12-01

    Glacier sliding plays a central role in ice dynamics. A number of remote sensing and deep drilling initiatives have therefore focused on the ice-bed interface. Although these techniques have provided valuable insights into bed properties, they do not supply theorists with data of sufficient temporal and spatial resolution to rigorously test mathematical sliding laws. As an alternative, passive seismic techniques have gained popularity in glacier monitoring. Analysis of glacier-related seismic sources ('icequakes') has become a useful technique to study inaccessible regions of the cryosphere, including the ice-bed interface. Seismic monitoring networks on the polar ice sheets have shown that ice sliding is not only a smooth process involving viscous deformation and regelation of basal ice layers. Instead, ice streams exhibit sudden slip episodes over their beds and intermittent phases of partial or complete stagnation. Here we discuss new and recently published discoveries of basal seismic sources beneath various glacial bodies. We revisit basal seismicity of hard-bedded Alpine glaciers, which is not the result of pure stick-slip motion. Sudden changes in seismicity suggest that the local configuration of the subglacial drainage system undergoes changes on sub daily time scales. Accordingly, such observations place constraints on basal resistance and sliding of hard-bedded glaciers. In contrast, certain clusters of stick-slip dislocations associated with micro seismicity beneath the Greenland ice sheet undergo diurnal variations in magnitudes and inter event times. This is best explained with a soft till bed, which hosts the shear dislocations and whose strength varies in response to changes in subglacial water pressure. These results suggest that analysis of basal icequakes is well suited for characterizing glacier and ice sheet beds. Future studies should address the relative importance between "smooth" and seismogenic sliding in different glacial environments.

  15. AMSR-E/Aqua Daily L3 12.5 km Tb, Sea Ice Conc., & Snow Depth Polar Grids V002

    Data.gov (United States)

    National Aeronautics and Space Administration — The AMSR-E/Aqua Level 3 12.5 km daily sea ice product includes 18.7 - 89.0 GHz TBs, sea ice concentration averages (asc & desc), and 5-day snow depth over sea...

  16. Ionization and NO production in the polar mesosphere during high-speed solar wind streams. Model validation and comparison with NO enhancements observed by Odin-SMR

    Energy Technology Data Exchange (ETDEWEB)

    Kirkwood, S.; Belova, E. [Swedish Institute of Space Physics, Kiruna (Sweden). Polar Atmospheric Research; Osepian, A. [Polar Geophysical Institute, Murmansk (Russian Federation); Urban, J.; Perot, K. [Chalmers Univ. of Technology, Gothenburg (Sweden). Dept. of Radio and Space Science; Sinha, A.K. [Indian Institute of Geomagnetism, Navi Mumbai (India)

    2015-09-01

    Precipitation of high-energy electrons (EEP) into the polar middle atmosphere is a potential source of significant production of odd nitrogen, which may play a role in stratospheric ozone destruction and in perturbing large-scale atmospheric circulation patterns. High-speed streams of solar wind (HSS) are a major source of energization and precipitation of electrons from the Earth's radiation belts, but it remains to be determined whether these electrons make a significant contribution to the odd-nitrogen budget in the middle atmosphere when compared to production by solar protons or by lower-energy (auroral) electrons at higher altitudes, with subsequent downward transport. Satellite observations of EEP are available, but their accuracy is not well established. Studies of the ionization of the atmosphere in response to EEP, in terms of cosmic-noise absorption (CNA), have indicated an unexplained seasonal variation in HSS-related effects and have suggested possible order-of-magnitude underestimates of the EEP fluxes by the satellite observations in some circumstances. Here we use a model of ionization by EEP coupled with an ion chemistry model to show that published average EEP fluxes, during HSS events, from satellite measurements (Meredith et al., 2011), are fully consistent with the published average CNA response (Kavanagh et al., 2012). The seasonal variation of CNA response can be explained by ion chemistry with no need for any seasonal variation in EEP. Average EEP fluxes are used to estimate production rate profiles of nitric oxide between 60 and 100 km heights over Antarctica for a series of unusually well separated HSS events in austral winter 2010. These are compared to observations of changes in nitric oxide during the events, made by the sub-millimetre microwave radiometer on the Odin spacecraft. The observations show strong increases of nitric oxide amounts between 75 and 90 km heights, at all latitudes poleward of 60 S, about 10 days after the

  17. Ionization and NO production in the polar mesosphere during high-speed solar wind streams. Model validation and comparison with NO enhancements observed by Odin-SMR

    International Nuclear Information System (INIS)

    Kirkwood, S.; Belova, E.; Urban, J.; Perot, K.

    2015-01-01

    Precipitation of high-energy electrons (EEP) into the polar middle atmosphere is a potential source of significant production of odd nitrogen, which may play a role in stratospheric ozone destruction and in perturbing large-scale atmospheric circulation patterns. High-speed streams of solar wind (HSS) are a major source of energization and precipitation of electrons from the Earth's radiation belts, but it remains to be determined whether these electrons make a significant contribution to the odd-nitrogen budget in the middle atmosphere when compared to production by solar protons or by lower-energy (auroral) electrons at higher altitudes, with subsequent downward transport. Satellite observations of EEP are available, but their accuracy is not well established. Studies of the ionization of the atmosphere in response to EEP, in terms of cosmic-noise absorption (CNA), have indicated an unexplained seasonal variation in HSS-related effects and have suggested possible order-of-magnitude underestimates of the EEP fluxes by the satellite observations in some circumstances. Here we use a model of ionization by EEP coupled with an ion chemistry model to show that published average EEP fluxes, during HSS events, from satellite measurements (Meredith et al., 2011), are fully consistent with the published average CNA response (Kavanagh et al., 2012). The seasonal variation of CNA response can be explained by ion chemistry with no need for any seasonal variation in EEP. Average EEP fluxes are used to estimate production rate profiles of nitric oxide between 60 and 100 km heights over Antarctica for a series of unusually well separated HSS events in austral winter 2010. These are compared to observations of changes in nitric oxide during the events, made by the sub-millimetre microwave radiometer on the Odin spacecraft. The observations show strong increases of nitric oxide amounts between 75 and 90 km heights, at all latitudes poleward of 60 S, about 10 days after the

  18. Accuracy and precision of polar lower stratospheric temperatures from reanalyses evaluated from A-Train CALIOP and MLS, COSMIC GPS RO, and the equilibrium thermodynamics of supercooled ternary solutions and ice clouds

    Science.gov (United States)

    Lambert, Alyn; Santee, Michelle L.

    2018-02-01

    We investigate the accuracy and precision of polar lower stratospheric temperatures (100-10 hPa during 2008-2013) reported in several contemporary reanalysis datasets comprising two versions of the Modern-Era Retrospective analysis for Research and Applications (MERRA and MERRA-2), the Japanese 55-year Reanalysis (JRA-55), the European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-I), and the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (NCEP-CFSR). We also include the Goddard Earth Observing System model version 5.9.1 near-real-time analysis (GEOS-5.9.1). Comparisons of these datasets are made with respect to retrieved temperatures from the Aura Microwave Limb Sounder (MLS), Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Global Positioning System (GPS) radio occultation (RO) temperatures, and independent absolute temperature references defined by the equilibrium thermodynamics of supercooled ternary solutions (STSs) and ice clouds. Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations of polar stratospheric clouds are used to determine the cloud particle types within the Aura MLS geometric field of view. The thermodynamic calculations for STS and the ice frost point use the colocated MLS gas-phase measurements of HNO3 and H2O. The estimated bias and precision for the STS temperature reference, over the 68 to 21 hPa pressure range, are 0.6-1.5 and 0.3-0.6 K, respectively; for the ice temperature reference, they are 0.4 and 0.3 K, respectively. These uncertainties are smaller than those estimated for the retrieved MLS temperatures and also comparable to GPS RO uncertainties (bias 0.7 K) in the same pressure range. We examine a case study of the time-varying temperature structure associated with layered ice clouds formed by orographic gravity waves forced by flow over the Palmer Peninsula and

  19. Polar bears at risk

    Energy Technology Data Exchange (ETDEWEB)

    Norris, S.; Rosentrater, L.; Eid, P.M. [WWF International Arctic Programme, Oslo (Norway)

    2002-05-01

    Polar bears, the world's largest terrestrial carnivore, spend much of their lives on the arctic sea ice. This is where they hunt and move between feeding, denning, and resting areas. The world population, estimated at 22,000 bears, is made up of 20 relatively distinct populations varying in size from a few hundred to a few thousand animals. About 60 per cent of all polar bears are found in Canada. In general, the status of this species is stable, although there are pronounced differences between populations. Reductions in the extent and thickness of sea ice has lead the IUCN Polar Bear Specialist Group to describe climate change as one of the major threats facing polar bears today. Though the long-term effects of climate change will vary in different areas of the Arctic, impacts on the condition and reproductive success of polar bears and their prey are likely to be negative. Longer ice-free periods resulting from earlier break-up of sea ice in the spring and later formation in the fall is already impacting polar bears in the southern portions of their range. In Canada's Hudson Bay, for example, bears hunt on the ice through the winter and into early summer, after which the ice melts completely, forcing bears ashore to fast on stored fat until freeze-up in the fall. The time bears have on the ice to hunt and build up their body condition is cut short when the ice melts early. Studies from Hudson Bay show that for every week earlier that ice break-up occurs, bears will come ashore 10 kg lighter and in poorer condition. It is likely that populations of polar bears dividing their time between land and sea will be severely reduced and local extinctions may occur as greenhouse gas emissions continue to rise and sea ice melts. Expected changes in regional weather patterns will also impact polar bears. Rain in the late winter can cause maternity dens to collapse before females and cubs have departed, thus exposing occupants to the elements and to predators. Such

  20. Autonomous Sea-Ice Thickness Survey

    Science.gov (United States)

    2016-06-01

    the conductivity of an infinitely thick slab of sea ice. Ice thickness, Hice, is then obtained by subtracting the height of the ...Thickness Survey of Sea Ice Runway” ERDC/CRREL SR-16-4 ii Abstract We conducted an autonomous survey of sea -ice thickness using the Polar rover Yeti...efficiency relative to manual surveys routinely con- ducted to assess the safety of roads and runways constructed on the sea ice. Yeti executed the

  1. Sea-ice deformation state from synthetic aperture radar imagery - Part I: comparison of C- and L-band and different polarization

    DEFF Research Database (Denmark)

    Dierking, Wolfgang; Dall, Jørgen

    2007-01-01

    configuration and ice conditions. Optical imagery of sufficient quality for comparison is available only in a very few cases. To characterize the deformation state, the areal fraction of deformation features and the average distance between these features are evaluated. The values obtained for both parameters...... negligible. In comparison to optical images, it was observed that deformed-ice areas can be distinguished from level ice over their whole length and extension at L-band, whereas at C-band, often, only prominent parts are visible....

  2. Ice Sheets & Ice Cores

    DEFF Research Database (Denmark)

    Mikkelsen, Troels Bøgeholm

    Since the discovery of the Ice Ages it has been evident that Earth’s climate is liable to undergo dramatic changes. The previous climatic period known as the Last Glacial saw large oscillations in the extent of ice sheets covering the Northern hemisphere. Understanding these oscillations known....... The first part concerns time series analysis of ice core data obtained from the Greenland Ice Sheet. We analyze parts of the time series where DO-events occur using the so-called transfer operator and compare the results with time series from a simple model capable of switching by either undergoing...

  3. Ice, Ice, Baby!

    Science.gov (United States)

    Hamilton, C.

    2008-12-01

    The Center for Remote Sensing of Ice Sheets (CReSIS) has developed an outreach program based on hands-on activities called "Ice, Ice, Baby". These lessons are designed to teach the science principles of displacement, forces of motion, density, and states of matter. These properties are easily taught through the interesting topics of glaciers, icebergs, and sea level rise in K-8 classrooms. The activities are fun, engaging, and simple enough to be used at science fairs and family science nights. Students who have participated in "Ice, Ice, Baby" have successfully taught these to adults and students at informal events. The lessons are based on education standards which are available on our website www.cresis.ku.edu. This presentation will provide information on the activities, survey results from teachers who have used the material, and other suggested material that can be used before and after the activities.

  4. High-precision GPS autonomous platforms for sea ice dynamics and physical oceanography

    Science.gov (United States)

    Elosegui, P.; Wilkinson, J.; Olsson, M.; Rodwell, S.; James, A.; Hagan, B.; Hwang, B.; Forsberg, R.; Gerdes, R.; Johannessen, J.; Wadhams, P.; Nettles, M.; Padman, L.

    2012-12-01

    Project "Arctic Ocean sea ice and ocean circulation using satellite methods" (SATICE), is the first high-rate, high-precision, continuous GPS positioning experiment on sea ice in the Arctic Ocean. The SATICE systems collect continuous, dual-frequency carrier-phase GPS data while drifting on sea ice. Additional geophysical measurements also collected include ocean water pressure, ocean surface salinity, atmospheric pressure, snow-depth, air-ice-ocean temperature profiles, photographic imagery, and others, enabling sea ice drift, freeboard, weather, ice mass balance, and sea-level height determination. Relatively large volumes of data from each buoy are streamed over a satellite link to a central computer on the Internet in near real time, where they are processed to estimate the time-varying buoy positions. SATICE system obtains continuous GPS data at sub-minute intervals with a positioning precision of a few centimetres in all three dimensions. Although monitoring of sea ice motions goes back to the early days of satellite observations, these autonomous platforms bring out a level of spatio-temporal detail that has never been seen before, especially in the vertical axis. These high-resolution data allows us to address new polar science questions and challenge our present understanding of both sea ice dynamics and Arctic oceanography. We will describe the technology behind this new autonomous platform, which could also be adapted to other applications that require high resolution positioning information with sustained operations and observations in the polar marine environment, and present results pertaining to sea ice dynamics and physical oceanography.

  5. Study of mixed phase clouds over west Africa: Ice-crystal corner reflection effects observed with a two-wavelength polarization lidar

    Directory of Open Access Journals (Sweden)

    Veselovskii Igor

    2018-01-01

    Full Text Available Lidar sounding is used for the analysis of possible contribution of the corner reflection (CR effect to the total backscattering in case of ice crystals. Our study is based on observations of mixed phase clouds performed during the SHADOW campaign in Senegal. Mie-Raman lidar allows measurements at 355 nm and 532 nm at 43 dg. off-zenith angle, so the extinction and backscattering Ångström exponents can be evaluated. In some measurements we observed the positive values of backscattering Ångström exponent, which can be attributed to the corner reflection by horizontally oriented ice plates.

  6. A simple holistic hypothesis for the self-destruction of ice sheets

    Science.gov (United States)

    Hughes, T.

    2011-07-01

    Ice sheets are the only components of Earth's climate system that can self-destruct. This paper presents the quantitative force balance for bottom-up modeling of ice sheets, as first presented qualitatively in this journal as a way to quantify ice-bed uncoupling leading to self-destruction of ice sheets ( Hughes, 2009a). Rapid changes in sea level and climate can result if a large ice-sheet self-destructs quickly, as did the former Laurentide Ice Sheet of North America between 8100 and 7900 BP, thereby terminating the last cycle of Quaternary glaciation. Ice streams discharge up to 90 percent of ice from past and present ice sheets. A hypothesis is presented in which self-destruction of an ice sheet begins when ubiquitous ice-bed decoupling, quantified as a floating fraction of ice, proceeds along ice streams. This causes ice streams to surge and reduce thickness by some 90 percent, and height above sea level by up to 99 percent for floating ice, so the ice sheet undergoes gravitational collapse. Ice collapsing over marine embayments becomes floating ice shelves that may then disintegrate rapidly. This floods the world ocean with icebergs that reduce the ocean-to-atmosphere heat exchange, thereby triggering climate change. Calving bays migrate up low stagnating ice streams and carve out the accumulation zone of the collapsed ice sheet, which prevents its recovery, decreases Earth's albedo, and terminates the glaciation cycle. This sequence of events may coincide with a proposed life cycle of ice streams that drain the ice sheet. A first-order treatment of these life cycles is presented that depends on the longitudinal force balance along the flowbands of ice streams and gives a first approximation to ice-bed uncoupling at snapshots during gravitational collapse into ice shelves that disintegrate, thereby removing the ice sheet. The stability of the Antarctic Ice Sheet is assessed using this bottom-up approach.

  7. Balance of the West Antarctic Ice Sheet

    Science.gov (United States)

    2002-01-01

    For several decades, measurements of the West Antarctic Ice Sheet showed it to be retreating rapidly. But new data derived from satellite-borne radar sensors show the ice sheet to be growing. Changing Antarctic ice sheets remains an area of high scientific interest, particularly in light of recent global warming concerns. These new findings are significant because scientists estimate that sea level would rise 5-6 meters (16-20 feet) if the ice sheet collapsed into the sea. Do these new measurements signal the end of the ice sheet's 10,000-year retreat? Or, are these new satellite data simply much more accurate than the sparse ice core and surface measurements that produced the previous estimates? Another possibility is that the ice accumulation may simply indicate that the ice sheet naturally expands and retreats in regular cycles. Cryologists will grapple with these questions, and many others, as they examine the new data. The image above depicts the region of West Antarctica where scientists measured ice speed. The fast-moving central ice streams are shown in red. Slower tributaries feeding the ice streams are shown in blue. Green areas depict slow-moving, stable areas. Thick black lines depict the areas that collect snowfall to feed their respective ice streams. Reference: Ian Joughin and Slawek Tulaczyk Science Jan 18 2002: 476-480. Image courtesy RADARSAT Antarctic Mapping Project

  8. Detection of polar vapours

    International Nuclear Information System (INIS)

    Blyth, D.A.

    1980-01-01

    Apparatus for monitoring for polar vapours in a gas consists of (i) a body member defining a passage through which a continuous stream of the gas passes; (ii) an ionising source associated with a region of the passage such that ionization of the gas stream takes place substantially only within the region and also any polar vapour molecules present therein will react with the gas formed to generate ion clusters; and (iii) an electrode for collecting ions carried by the gas stream, the electrode being positioned in the passage downstream of the region and separated from the region by a sufficient distance to ensure that no substantial number of the gas ions formed in said region remains in the gas stream at the collector electrode whilst ensuring that a substantial proportion of the ion clusters formed in the region does remain in the gas stream at the collector electrode. (author)

  9. Streams with Strahler Stream Order

    Data.gov (United States)

    Minnesota Department of Natural Resources — Stream segments with Strahler stream order values assigned. As of 01/08/08 the linework is from the DNR24K stream coverages and will not match the updated...

  10. Polar bears, Ursus maritimus

    Science.gov (United States)

    Rode, Karyn D.; Stirling, Ian

    2017-01-01

    Polar bears are the largest of the eight species of bears found worldwide and are covered in a pigment-free fur giving them the appearance of being white. They are the most carnivorous of bear species consuming a high-fat diet, primarily of ice-associated seals and other marine mammals. They range throughout the circumpolar Arctic to the southernmost extent of seasonal pack ice.

  11. Sunlight, Sea Ice, and the Ice Albedo Feedback in a Changing Arctic Sea Ice Cover

    Science.gov (United States)

    2015-09-30

    fraction product and the remotely sensed albedo product in the context of understanding the surface radiation budget. Particular attention is paid to...Stamnes, Chapter 2 The Polar Environment: Sun, Clouds, and Ice, in Ocean Colour Remote Sensing in Polar Seas, p 5-25, in press. Istomina, L, G

  12. Sunlight, Sea Ice, and the Ice Albedo Feedback in a Changing Artic Sea Ice Cover

    Science.gov (United States)

    2015-11-30

    the remotely sensed albedo product in the context of understanding the surface radiation budget. Particular attention is paid to the infrequent...Chapter 2 The Polar Environment: Sun, Clouds, and Ice, in Ocean Colour Remote Sensing in Polar Seas, p 5-25, in press. Istomina, L, G. Heygster, M

  13. ICE911 Research: Floating Safe Inert Materials to Preserve Ice and Conserve Water in Order to Mitigate Climate Change Impacts

    Science.gov (United States)

    Field, L. A.; Manzara, A.; Chetty, S.; Venkatesh, S.; Scholtz, A.

    2015-12-01

    Ice911 Research has conducted years of field testing to develop and test localized reversible engineering techniques to mitigate the negative impacts of polar ice melt. The technology uses environmentally safe materials to reflect energy in carefully selected, limited areas from summertime polar sun. The technology is now being adapted to help with California's drought. We have tested the albedo modification technique on a small scale over seven Winter/Spring seasons at sites including California's Sierra Nevada Mountains, a Canadian lake, and a small artificial pond in Minnesota about 100 ft in diameter and 6 ft deep at the center, using various materials and an evolving array of instrumentation. On the pond in Minnesota, this year's test results for ice preservation, using hollow glass spheres deployed over our largest test areas yet, showed that glass bubbles can provide an effective material for increasing albedo, significantly reducing the melting rate of ice. This year Ice911 also undertook its first small Arctic field test in Barrow, Alaska on a lake in Barrow's BEO area, and results are still coming in. The technology that Ice911 has been developing for ice preservation has also been shown to keep small test areas of water cooler, in various small-scale tests spanning years. We believe that with some adaptations of the technology, the materials can be applied to reservoirs and lakes to help stretch these precious resources further in California's ongoing drought. There are several distinct advantages for this method over alternatives such as large reverse osmosis projects or building new reservoirs, which could possibly allow a drought-stricken state to build fewer of these more-costly alternatives. First, applying an ecologically benign surface treatment of Ice911's materials can be accomplished within a season, at a lower cost, with far less secondary environmental impact, than such capital-and-time-intensive infrastructure projects. Second, keeping

  14. High resolution modelling of the decreasing Arctic sea ice

    DEFF Research Database (Denmark)

    Madsen, K. S.; Rasmussen, T. A. S.; Blüthgen, Jonas

    2012-01-01

    The Arctic sea ice cover has been rapidly decreasing and thinning over the last decade, with minimum ice extent in 2007 and almost as low extent in 2011. This study investigates two aspects of the decreasing ice cover; first the large scale thinning and changing dynamics of the polar sea ice, and...

  15. Meteorological conditions in a thinner Arctic sea ice regime from winter to summer during the Norwegian Young Sea Ice expedition (N-ICE2015)

    Science.gov (United States)

    Cohen, Lana; Hudson, Stephen R.; Walden, Von P.; Graham, Robert M.; Granskog, Mats A.

    2017-07-01

    Atmospheric measurements were made over Arctic sea ice north of Svalbard from winter to early summer (January-June) 2015 during the Norwegian Young Sea Ice (N-ICE2015) expedition. These measurements, which are available publicly, represent a comprehensive meteorological data set covering the seasonal transition in the Arctic Basin over the new, thinner sea ice regime. Winter was characterized by a succession of storms that produced short-lived (less than 48 h) temperature increases of 20 to 30 K at the surface. These storms were driven by the hemispheric scale circulation pattern with a large meridional component of the polar jet stream steering North Atlantic storms into the high Arctic. Nonstorm periods during winter were characterized by strong surface temperature inversions due to strong radiative cooling ("radiatively clear state"). The strength and depth of these inversions were similar to those during the Surface Heat Budget of the Arctic Ocean (SHEBA) campaign. In contrast, atmospheric profiles during the "opaquely cloudy state" were different to those from SHEBA due to differences in the synoptic conditions and location within the ice pack. Storm events observed during spring/summer were the result of synoptic systems located in the Barents Sea and the Arctic Basin rather than passing directly over N-ICE2015. These synoptic systems were driven by a large-scale circulation pattern typical of recent years, with an Arctic Dipole pattern developing during June. Surface temperatures became near-constant 0°C on 1 June marking the beginning of summer. Atmospheric profiles during the spring and early summer show persistent lifted temperature and moisture inversions that are indicative of clouds and cloud processes.

  16. Numerical modeling of polar mesocyclones generation mechanisms

    Science.gov (United States)

    Sergeev, Dennis; Stepanenko, Victor

    2013-04-01

    Polar mesocyclones, commonly referred to as polar lows, remain of great interest due to their complicated dynamics. These mesoscale vortices are small short-living objects that are formed over the observation-sparse high-latitude oceans, and therefore, their evolution can hardly be observed and predicted numerically. The origin of polar mesoscale cyclones is still a matter of uncertainty, though the recent numerical investigations [3] have exposed a strong dependence of the polar mesocyclone development upon the magnitude of baroclinicity. Nevertheless, most of the previous studies focused on the individual polar low (the so-called case studies), with too many factors affecting it simultaneously. None of the earlier studies suggested a clear picture of polar mesocyclone generation within an idealized experiment, where it is possible to look deeper into each single physical process. The present paper concentrates on the initial triggering mechanism of the polar mesocyclone. As it is reported by many researchers, some mesocyclones are formed by the surface forcing, namely the uneven distribution of heat fluxes. That feature is common on the ice boundaries [2], where intense air stream flows from the cold ice surface to the warm sea surface. Hence, the resulting conditions are shallow baroclinicity and strong surface heat fluxes, which provide an arising polar mesocyclone with potential energy source converting it to the kinetic energy of the vortex. It is shown in this paper that different surface characteristics, including thermal parameters and, for example, the shape of an ice edge, determine an initial phase of a polar low life cycle. Moreover, it is shown what initial atmospheric state is most preferable for the formation of a new polar mesocyclone or in maintaining and reinforcing the existing one. The study is based on idealized high-resolution (~2 km) numerical experiment in which baroclinicity, stratification, initial wind profile and disturbance, surface

  17. Antarctic Glaciological Data at NSIDC: field data, temperature, and ice velocity

    Science.gov (United States)

    Bauer, R.; Bohlander, J.; Scambos, T.; Berthier, E.; Raup, B.; Scharfen, G.

    2003-12-01

    An extensive collection of many Antarctic glaciological parameters is available for the polar science community upon request. The National Science Foundation's Office of Polar Programs funds the Antarctic Glaciological Data Center (AGDC) at the National Snow and Ice Data Center (NSIDC) to archive and distribute Antarctic glaciological and cryospheric system data collected by the U.S. Antarctic Program. AGDC facilitates data exchange among Principal Investigators, preserves recently collected data useful to future research, gathers data sets from past research, and compiles continent-wide information useful for modeling and field work planning. Data sets are available via our web site, http://nsidc.org/agdc/. From here, users can access extensive documentation, citation information, locator maps, derived images and references, and the numerical data. More than 50 Antarctic scientists have contributed data to the archive. Among the compiled products distributed by AGDC are VELMAP and THERMAP. THERMAP is a compilation of over 600 shallow firn temperature measurements ('10-meter temperatures') collected since 1950. These data provide a record of mean annual temperature, and potentially hold a record of climate change on the continent. The data are represented with maps showing the traverse route, and include data sources, measurement technique, and additional measurements made at each site, i.e., snow density and accumulation. VELMAP is an archive of surface ice velocity measurements for the Antarctic Ice Sheet. The primary objective of VELMAP is to assemble a historic record of outlet glaciers and ice shelf ice motion over the Antarctic. The collection includes both PI-contributed measurements and data generated at NSIDC using Landsat and SPOT satellite imagery. Tabular data contain position, speed, bearing, and data quality information, and related references. Two new VELMAP data sets are highlighted: the Mertz Glacier and the Institute Ice Stream. Mertz Glacier ice

  18. Stream Crossings

    Data.gov (United States)

    Vermont Center for Geographic Information — Physical measurements and attributes of stream crossing structures and adjacent stream reaches which are used to provide a relative rating of aquatic organism...

  19. Ice sheet hydrology from observations

    Energy Technology Data Exchange (ETDEWEB)

    Jansson, Peter [Dept. of Physical Geography and Quaternary Geology, Stockholm Univ-, Stockholm (Sweden)

    2010-11-15

    The hydrological systems of ice sheets are complex. Our view of the system is split, largely due to the complexity of observing the systems. Our basic knowledge of processes have been obtained from smaller glaciers and although applicable in general to the larger scales of the ice sheets, ice sheets contain features not observable on smaller glaciers due to their size. The generation of water on the ice sheet surface is well understood and can be satisfactorily modeled. The routing of water from the surface down through the ice is not complicated in terms of procat has been problematic is the way in which the couplings between surface and bed has been accomplished through a kilometer of cold ice, but with the studies on crack propagation and lake drainage on Greenland we are beginning to understand also this process and we know water can be routed through thick cold ice. Water generation at the bed is also well understood but the main problem preventing realistic estimates of water generation is lack of detailed information about geothermal heat fluxes and their geographical distribution beneath the ice. Although some average value for geothermal heat flux may suffice, for many purposes it is important that such values are not applied to sub-regions of significantly higher fluxes. Water generated by geothermal heat constitutes a constant supply and will likely maintain a steady system beneath the ice sheet. Such a system may include subglacial lakes as steady features and reconfiguration of the system is tied to time scales on which the ice sheet geometry changes so as to change pressure gradients in the basal system itself. Large scale re-organization of subglacial drainage systems have been observed beneath ice streams. The stability of an entirely subglacially fed drainage system may hence be perturbed by rapid ice flow. In the case of Antarctic ice streams where such behavior has been observed, the ice streams are underlain by deformable sediments. It is

  20. Ice sheet hydrology from observations

    International Nuclear Information System (INIS)

    Jansson, Peter

    2010-11-01

    The hydrological systems of ice sheets are complex. Our view of the system is split, largely due to the complexity of observing the systems. Our basic knowledge of processes have been obtained from smaller glaciers and although applicable in general to the larger scales of the ice sheets, ice sheets contain features not observable on smaller glaciers due to their size. The generation of water on the ice sheet surface is well understood and can be satisfactorily modeled. The routing of water from the surface down through the ice is not complicated in terms of procat has been problematic is the way in which the couplings between surface and bed has been accomplished through a kilometer of cold ice, but with the studies on crack propagation and lake drainage on Greenland we are beginning to understand also this process and we know water can be routed through thick cold ice. Water generation at the bed is also well understood but the main problem preventing realistic estimates of water generation is lack of detailed information about geothermal heat fluxes and their geographical distribution beneath the ice. Although some average value for geothermal heat flux may suffice, for many purposes it is important that such values are not applied to sub-regions of significantly higher fluxes. Water generated by geothermal heat constitutes a constant supply and will likely maintain a steady system beneath the ice sheet. Such a system may include subglacial lakes as steady features and reconfiguration of the system is tied to time scales on which the ice sheet geometry changes so as to change pressure gradients in the basal system itself. Large scale re-organization of subglacial drainage systems have been observed beneath ice streams. The stability of an entirely subglacially fed drainage system may hence be perturbed by rapid ice flow. In the case of Antarctic ice streams where such behavior has been observed, the ice streams are underlain by deformable sediments. It is

  1. Ice Cores

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Records of past temperature, precipitation, atmospheric trace gases, and other aspects of climate and environment derived from ice cores drilled on glaciers and ice...

  2. Akamai Streaming

    OpenAIRE

    ECT Team, Purdue

    2007-01-01

    Akamai offers world-class streaming media services that enable Internet content providers and enterprises to succeed in today's Web-centric marketplace. They deliver live event Webcasts (complete with video production, encoding, and signal acquisition services), streaming media on demand, 24/7 Webcasts and a variety of streaming application services based upon their EdgeAdvantage.

  3. Ice Cream

    NARCIS (Netherlands)

    Scholten, E.

    2014-01-01

    Ice cream is a popular dessert, which owes its sensorial properties (mouth feel) to its complex microstructure. The microstructure is a result of the combination of the ingredients and the production process. Ice cream is produced by simultaneous freezing and shearing of the ice cream mix, which

  4. Ice targets

    International Nuclear Information System (INIS)

    Pacheco, C.; Stark, C.; Tanaka, N.; Hodgkins, D.; Barnhart, J.; Kosty, J.

    1979-12-01

    This report presents a description of ice targets that were constructed for research work at the High Resolution Spectrometer (HRS) and at the Energetic Pion Channel and Spectrometer (EPICS). Reasons for using these ice targets and the instructions for their construction are given. Results of research using ice targets will be published at a later date

  5. The Response of Ice Sheets to Climate Variability

    Science.gov (United States)

    Snow, K.; Goldberg, D. N.; Holland, P. R.; Jordan, J. R.; Arthern, R. J.; Jenkins, A.

    2017-12-01

    West Antarctic Ice Sheet loss is a significant contributor to sea level rise. While the ice loss is thought to be triggered by fluctuations in oceanic heat at the ice shelf bases, ice sheet response to ocean variability remains poorly understood. Using a synchronously coupled ice-ocean model permitting grounding line migration, this study evaluates the response of an ice sheet to periodic variations in ocean forcing. Resulting oscillations in grounded ice volume amplitude is shown to grow as a nonlinear function of ocean forcing period. This implies that slower oscillations in climatic forcing are disproportionately important to ice sheets. The ice shelf residence time offers a critical time scale, above which the ice response amplitude is a linear function of ocean forcing period and below which it is quadratic. These results highlight the sensitivity of West Antarctic ice streams to perturbations in heat fluxes occurring at decadal time scales.

  6. Assessing, understanding, and conveying the state of the Arctic sea ice cover

    Science.gov (United States)

    Perovich, D. K.; Richter-Menge, J. A.; Rigor, I.; Parkinson, C. L.; Weatherly, J. W.; Nghiem, S. V.; Proshutinsky, A.; Overland, J. E.

    2003-12-01

    Recent studies indicate that the Arctic sea ice cover is undergoing significant climate-induced changes, affecting both its extent and thickness. Satellite-derived estimates of Arctic sea ice extent suggest a reduction of about 3% per decade since 1978. Ice thickness data from submarines suggest a net thinning of the sea ice cover since 1958. Changes (including oscillatory changes) in atmospheric circulation and the thermohaline properties of the upper ocean have also been observed. These changes impact not only the Arctic, but the global climate system and are likely accelerated by such processes as the ice-albedo feedback. It is important to continue and expand long-term observations of these changes to (a) improve the fundamental understanding of the role of the sea ice cover in the global climate system and (b) use the changes in the sea ice cover as an early indicator of climate change. This is a formidable task that spans a range of temporal and spatial scales. Fortunately, there are numerous tools that can be brought to bear on this task, including satellite remote sensing, autonomous buoys, ocean moorings, field campaigns and numerical models. We suggest the integrated and coordinated use of these tools during the International Polar Year to monitor the state of the Arctic sea ice cover and investigate its governing processes. For example, satellite remote sensing provides the large-scale snapshots of such basic parameters as ice distribution, melt zone, and cloud fraction at intervals of half a day to a week. Buoys and moorings can contribute high temporal resolution and can measure parameters currently unavailable from space including ice thickness, internal ice temperature, and ocean temperature and salinity. Field campaigns can be used to explore, in detail, the processes that govern the ice cover. Numerical models can be used to assess the character of the changes in the ice cover and predict their impacts on the rest of the climate system. This work

  7. Solar cycles in the last centuries in 10Be and delta18O in polar ice and in thermoluminescence signals of a sea sediment

    International Nuclear Information System (INIS)

    Cini Castagnoli, G.; Bonino, G.; Galli, M.; Beer, J.

    1984-01-01

    The cyclogram method of time series analysis has been used to analyse 10 Be data (1181-1800 AD) and delta 18 O data (1181-1960 AD) from an artic ice core and thermoluminescence data (1181-1960 AD) from a Mediterranean sediment core. The 10 Be concentrations were determined at the ETH Zurich. The delta 18 O values were measured at the University of Copenhagen. The TL measurements were performed at the Istituto di Cosmo-geofisica del C.N.R., Torino. Common mean periodicities of 10.75 y are found for the period 1505 to 1710 AD in TL and 10 Be and of 11.4 y for the period 1715 to 1880 in TL and delta 18 O. This periodicity was found in the solar sunspot (Rsub(z)) series analysed in the same way, from 1825 to 1905. This supports the argument that the common periodicities found in the long-running series are peculiar of the solar activity in the past

  8. Coastal-change and glaciological map of the Ronne Ice Shelf area, Antarctica, 1974-2002

    Science.gov (United States)

    Ferrigno, Jane G.; Foley, K.M.; Swithinbank, C.; Williams, R.S.; Dalide, L.M.

    2005-01-01

    Changes in the area and volume of polar ice sheets are intricately linked to changes in global climate, and the resulting changes in sea level may severely impact the densely populated coastal regions on Earth. Melting of the West Antarctic part alone of the Antarctic ice sheet could cause a sea-level rise of approximately 6 meters (m). The potential sea-level rise after melting of the entire Antarctic ice sheet is estimated to be 65 m (Lythe and others, 2001) to 73 m (Williams and Hall, 1993). In spite of its importance, the mass balance (the net volumetric gain or loss) of the Antarctic ice sheet is poorly known; it is not known for certain whether the ice sheet is growing or shrinking. In a review paper, Rignot and Thomas (2002) concluded that the West Antarctic part of the Antarctic ice sheet is probably becoming thinner overall; although it is thickening in the west, it is thinning in the north. Joughin and Tulaczyk (2002), on the basis of analysis of ice-flow velocities derived from synthetic aperture radar, concluded that most of the Ross ice streams (ice streams on the east side of the Ross Ice Shelf) have a positive mass balance, whereas Rignot and others (in press) infer even larger negative mass balance for glaciers flowing northward into the Amundsen Sea, a trend suggested by Swithinbank and others (2003a,b, 2004). The mass balance of the East Antarctic part of the Antarctic ice sheet is unknown, but thought to be in near equilibrium. Measurement of changes in area and mass balance of the Antarctic ice sheet was given a very high priority in recommendations by the Polar Research Board of the National Research Council (1986), in subsequent recommendations by the Scientific Committee on Antarctic Research (SCAR) (1989, 1993), and by the National Science Foundation's (1990) Division of Polar Pro-grams. On the basis of these recommendations, the U.S. Geo-logical Survey (USGS) decided that the archive of early 1970s Landsat 1, 2, and 3 Multispectral Scanner

  9. Ice formation and growth shape bacterial community structure in Baltic Sea drift ice.

    Science.gov (United States)

    Eronen-Rasimus, Eeva; Lyra, Christina; Rintala, Janne-Markus; Jürgens, Klaus; Ikonen, Vilma; Kaartokallio, Hermanni

    2015-02-01

    Drift ice, open water and under-ice water bacterial communities covering several developmental stages from open water to thick ice were studied in the northern Baltic Sea. The bacterial communities were assessed with 16S rRNA gene terminal-restriction fragment length polymorphism and cloning, together with bacterial abundance and production measurements. In the early stages, open water and pancake ice were dominated by Alphaproteobacteria and Actinobacteria, which are common bacterial groups in Baltic Sea wintertime surface waters. The pancake ice bacterial communities were similar to the open-water communities, suggesting that the parent water determines the sea-ice bacterial community in the early stages of sea-ice formation. In consolidated young and thick ice, the bacterial communities were significantly different from water bacterial communities as well as from each other, indicating community development in Baltic Sea drift ice along with ice-type changes. The thick ice was dominated by typical sea-ice genera from classes Flavobacteria and Gammaproteobacteria, similar to those in polar sea-ice bacterial communities. Since the thick ice bacterial community was remarkably different from that of the parent seawater, results indicate that thick ice bacterial communities were recruited from the rarer members of the seawater bacterial community. © FEMS 2014. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  10. Ice-Shelf Tidal Flexure and Subglacial Pressure Variations

    Science.gov (United States)

    Walker, Ryan T.; Parizek, Byron R.; Alley, Richard B.; Anandakrishnan, Sridhar; Riverman, Kiya L.; Christianson, Knut

    2013-01-01

    We develop a model of an ice shelf-ice stream system as a viscoelastic beam partially supported by an elastic foundation. When bed rock near the grounding line acts as a fulcrum, leverage from the ice shelf dropping at low tide can cause significant (approx 1 cm) uplift in the first few kilometers of grounded ice.This uplift and the corresponding depression at high tide lead to basal pressure variations of sufficient magnitude to influence subglacial hydrology.Tidal flexure may thus affect basal lubrication, sediment flow, and till strength, all of which are significant factors in ice-stream dynamics and grounding-line stability. Under certain circumstances, our results suggest the possibility of seawater being drawn into the subglacial water system. The presence of sea water beneath grounded ice would significantly change the radar reflectivity of the grounding zone and complicate the interpretation of grounded versus floating ice based on ice-penetrating radar observations.

  11. Tropospheric characteristics over sea ice during N-ICE2015

    Science.gov (United States)

    Kayser, Markus; Maturilli, Marion; Graham, Robert; Hudson, Stephen; Cohen, Lana; Rinke, Annette; Kim, Joo-Hong; Park, Sang-Jong; Moon, Woosok; Granskog, Mats

    2017-04-01

    Over recent years, the Arctic Ocean region has shifted towards a younger and thinner sea-ice regime. The Norwegian young sea ICE (N-ICE2015) expedition was designed to investigate the atmosphere-snow-ice-ocean interactions in this new ice regime north of Svalbard. Here we analyze upper-air measurements made by radiosondes launched twice daily together with surface meteorology observations during N-ICE2015 from January to June 2015. We study the multiple cyclonic events observed during N-ICE2015 with respect to changes in the vertical thermodynamic structure, sudden increases in moisture content and temperature, temperature inversions and boundary layer dynamics. The influence of synoptic cyclones is strongest under polar night conditions, when radiative cooling is most effective and the moisture content is low. We find that transitions between the radiatively clear and opaque state are the largest drivers of changes to temperature inversion and stability characteristics in the boundary layer during winter. In spring radiative fluxes warm the surface leading to lifted temperature inversions and a statically unstable boundary layer. The unique N-ICE2015 dataset is used for case studies investigating changes in the vertical structure of the atmosphere under varying synoptic conditions. The goal is to deepen our understanding of synoptic interactions within the Arctic climate system, to improve model performance, as well as to identify gaps in instrumentation, which precludes further investigations.

  12. Sea Ice

    Science.gov (United States)

    Perovich, D.; Gerland, S.; Hendricks, S.; Meier, Walter N.; Nicolaus, M.; Richter-Menge, J.; Tschudi, M.

    2013-01-01

    During 2013, Arctic sea ice extent remained well below normal, but the September 2013 minimum extent was substantially higher than the record-breaking minimum in 2012. Nonetheless, the minimum was still much lower than normal and the long-term trend Arctic September extent is -13.7 per decade relative to the 1981-2010 average. The less extreme conditions this year compared to 2012 were due to cooler temperatures and wind patterns that favored retention of ice through the summer. Sea ice thickness and volume remained near record-low levels, though indications are of slightly thicker ice compared to the record low of 2012.

  13. Ice sheet anisotropy measured with polarimetric ice sounding radar

    DEFF Research Database (Denmark)

    Dall, Jørgen

    2010-01-01

    For polar ice sheets, valuable stress and strain information can be deduced from crystal orientation fabrics (COF) and their prevailing c-axis alignment. Polarimetric radio echo sounding is a promising technique to measure the anisotropic electromagnetic propagation and reflection properties asso...

  14. Stream systems.

    Science.gov (United States)

    Jack E. Williams; Gordon H. Reeves

    2006-01-01

    Restored, high-quality streams provide innumerable benefits to society. In the Pacific Northwest, high-quality stream habitat often is associated with an abundance of salmonid fishes such as chinook salmon (Oncorhynchus tshawytscha), coho salmon (O. kisutch), and steelhead (O. mykiss). Many other native...

  15. Simulating Arctic clouds during Arctic Radiation- IceBridge Sea and Ice Experiment (ARISE)

    Science.gov (United States)

    Bromwich, D. H.; Hines, K. M.; Wang, S. H.

    2015-12-01

    The representation within global and regional models of the extensive low-level cloud cover over polar oceans remains a critical challenge for quantitative studies and forecasts of polar climate. In response, the polar-optimized version of the Weather Research and Forecasting model (Polar WRF) is used to simulate the meteorology, boundary layer, and Arctic clouds during the September-October 2014 Arctic Radiation- IceBridge Sea and Ice Experiment (ARISE) project. Polar WRF was developed with several adjustments to the sea ice thermodynamics in WRF. ARISE was based out of Eielson Air Force Base near Fairbanks, Alaska and included multiple instrumented C-130 aircraft flights over open water and sea ice of the Beaufort Sea. Arctic boundary layer clouds were frequently observed within cold northeasterly flow over the open ocean and ice. Preliminary results indicate these clouds were primarily liquid water, with characteristics differing between open water and sea ice surfaces. Simulated clouds are compared to ARISE observations. Furthermore, Polar WRF simulations are run for the August-September 2008 Arctic Summer Cloud Ocean Study (ASCOS) for comparison to the ARISE. Preliminary analysis shows that simulated low-level water clouds over the sea ice are too extensive during the the second half of the ASCOS field program. Alternatives and improvements to the Polar WRF cloud schemes are considered. The goal is to use the ARISE and ASCOS observations to achieve an improved polar supplement to the WRF code for open water and sea ice that can be provided to the Polar WRF community.

  16. Polarized neutrons

    International Nuclear Information System (INIS)

    Williams, W.G.

    1988-01-01

    The book on 'polarized neutrons' is intended to inform researchers in condensed matter physics and chemistry of the diversity of scientific problems that can be investigated using polarized neutron beams. The contents include chapters on:- neutron polarizers and instrumentation, polarized neutron scattering, neutron polarization analysis experiments and precessing neutron polarization. (U.K.)

  17. EBSD in Antarctic and Greenland Ice

    Science.gov (United States)

    Weikusat, Ilka; Kuiper, Ernst-Jan; Pennock, Gill; Sepp, Kipfstuhl; Drury, Martyn

    2017-04-01

    Ice, particularly the extensive amounts found in the polar ice sheets, impacts directly on the global climate by changing the albedo and indirectly by supplying an enormous water reservoir that affects sea level change. The discharge of material into the oceans is partly controlled by the melt excess over snow accumulation, partly by the dynamic flow of ice. In addition to sliding over bedrock, an ice body deforms gravitationally under its own weight. In order to improve our description of this flow, ice microstructure studies are needed that elucidate the dominant deformation and recrystallization mechanisms involved. Deformation of hexagonal ice is highly anisotropic: ice is easily sheared in the basal plane and is about two orders of magnitude harder parallel to the c-axis. As dislocation creep is the dominant deformation mechanism in polar ice this strong anisotropy needs to be understood in terms of dislocation activity. The high anisotropy of the ice crystal is usually ascribed to a particular behaviour of dislocations in ice, namely the extension of dislocations into partials on the basal plane. Analysis of EBSD data can help our understanding of dislocation activity by characterizing subgrain boundary types thus providing a tool for comprehensive dislocation characterization in polar ice. Cryo-EBSD microstructure in combination with light microscopy measurements from ice core material from Antarctica (EPICA-DML deep ice core) and Greenland (NEEM deep ice core) are presented and interpreted regarding substructure identification and characterization. We examined one depth for each ice core (EDML: 656 m, NEEM: 719 m) to obtain the first comparison of slip system activity from the two ice sheets. The subgrain boundary to grain boundary threshold misorientation was taken to be 3-5° (Weikusat et al. 2011). EBSD analyses suggest that a large portion of edge dislocations with slip systems basal gliding on the basal plane were indeed involved in forming subgrain

  18. Life in Ice: Implications to Astrobiology

    Science.gov (United States)

    Hoover, Richard B.

    2009-01-01

    During the 2008 Tawani International Expedition Schirmacher Oasis/Lake Untersee Antarctica Expedition, living and instantly motile bacteria were found in freshly thawed meltwater from ice of the Schirmacher Oasis Lakes, the Anuchin Glacier ice and samples of the that perennial ice sheet above Lake Untersee. This phenomenon of living bacteria encased in ice had previously been observed in the 32,000 year old ice of the Fox Tunnel. The bacteria found in this ice included the strain FTR1T which was isolated and published as valid new species (Carnobacterium pleistocenium) the first validly published living Pleistocene organism still alive today. Living bacteria were also extracted from ancient ice cores from Vostok, Antarctica. The discovery that many strains of bacteria are able to survive and remain alive while frozen in ice sheets for long periods of time may have direct relevance to Astrobiology. The abundance of viable bacteria in the ice sheets of Antarctica suggests that the presence of live bacteria in ice is common, rather than an isolated phenomenon. This paper will discuss the results of recent studies at NSSTC of bacteria cryopreserved in ice. This paper advances the hypothesis that cryopreserved cells, and perhaps even viable bacterial cells, may exist today--frozen in the water-ice of lunar craters, the Polar Caps or craters of Mars; or in the permafrost of Mars; ice and rocks of comets or water bearing asteroids; or in the frozen crusts of the icy moons of Jupiter and Saturn. The existence of bacterial life in ice suggests that it may not be necessary to drill through a thick ice crust to reach liquid water seas deep beneath the icy crusts of Europa, Ganymede and Enceladus. The presence of viable bacteria in the ice of the Earth s Polar Caps suggests that the possibility that cryo-panspermia (i.e., the trans-planetary transfer of microbial life by impact ejection/spallation of bacteria-rich polar ice masses) deserves serious consideration and study as a

  19. Cytoplasmic Streaming in the Drosophila Oocyte.

    Science.gov (United States)

    Quinlan, Margot E

    2016-10-06

    Objects are commonly moved within the cell by either passive diffusion or active directed transport. A third possibility is advection, in which objects within the cytoplasm are moved with the flow of the cytoplasm. Bulk movement of the cytoplasm, or streaming, as required for advection, is more common in large cells than in small cells. For example, streaming is observed in elongated plant cells and the oocytes of several species. In the Drosophila oocyte, two stages of streaming are observed: relatively slow streaming during mid-oogenesis and streaming that is approximately ten times faster during late oogenesis. These flows are implicated in two processes: polarity establishment and mixing. In this review, I discuss the underlying mechanism of streaming, how slow and fast streaming are differentiated, and what we know about the physiological roles of the two types of streaming.

  20. CICE, The Los Alamos Sea Ice Model

    Energy Technology Data Exchange (ETDEWEB)

    2017-05-12

    The Los Alamos sea ice model (CICE) is the result of an effort to develop a computationally efficient sea ice component for a fully coupled atmosphere–land–ocean–ice global climate model. It was originally designed to be compatible with the Parallel Ocean Program (POP), an ocean circulation model developed at Los Alamos National Laboratory for use on massively parallel computers. CICE has several interacting components: a vertical thermodynamic model that computes local growth rates of snow and ice due to vertical conductive, radiative and turbulent fluxes, along with snowfall; an elastic-viscous-plastic model of ice dynamics, which predicts the velocity field of the ice pack based on a model of the material strength of the ice; an incremental remapping transport model that describes horizontal advection of the areal concentration, ice and snow volume and other state variables; and a ridging parameterization that transfers ice among thickness categories based on energetic balances and rates of strain. It also includes a biogeochemical model that describes evolution of the ice ecosystem. The CICE sea ice model is used for climate research as one component of complex global earth system models that include atmosphere, land, ocean and biogeochemistry components. It is also used for operational sea ice forecasting in the polar regions and in numerical weather prediction models.

  1. The polar mesosphere

    International Nuclear Information System (INIS)

    Morris, Ray; Murphy, Damian

    2008-01-01

    The mesosphere region, which lies at the edge of space, contains the coldest layer of the Earth's atmosphere, with summer temperatures as low as minus 130 °C. In this extreme environment ice aerosol layers have appeared since the dawn of industrialization—whose existence may arguably be linked to human influence—on yet another layer of the Earth's fragile atmosphere. Ground-based and space-based experiments conducted in the Arctic and Antarctic during the International Polar Year (IPY) aim to address limitations in our knowledge and to advance our understanding of thermal and dynamical processes at play in the polar mesosphere

  2. International Coordination of Lunar Polar Volatiles Exploration

    Science.gov (United States)

    Gruener, J. E.; Suzuki, N. H.; Carpenter, J. D.

    2015-10-01

    The International Space Exploration Coordination Group (ISECG) has established a study team to coordinate the worldwide interest in lunar polar volatiles, and in particular water ice, in an effort to stimulate cooperation and collaboration.

  3. Ice Caps and Ice Belts: The Effects of Obliquity on Ice−Albedo Feedback

    Energy Technology Data Exchange (ETDEWEB)

    Rose, Brian E. J. [Department of Atmospheric and Environmental Sciences, University at Albany (State University of New York), 1400 Washington Avenue, Albany, NY 12222 (United States); Cronin, Timothy W. [Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Bitz, Cecilia M., E-mail: brose@albany.edu [Department of Atmospheric Sciences, MS 351640, University of Washington, Seattle, WA 98195-1640 (United States)

    2017-09-01

    Planetary obliquity determines the meridional distribution of the annual mean insolation. For obliquity exceeding 55°, the weakest insolation occurs at the equator. Stable partial snow and ice cover on such a planet would be in the form of a belt about the equator rather than polar caps. An analytical model of planetary climate is used to investigate the stability of ice caps and ice belts over the widest possible range of parameters. The model is a non-dimensional diffusive Energy Balance Model, representing insolation, heat transport, and ice−albedo feedback on a spherical planet. A complete analytical solution for any obliquity is given and validated against numerical solutions of a seasonal model in the “deep-water” regime of weak seasonal ice line migration. Multiple equilibria and unstable transitions between climate states (ice-free, Snowball, or ice cap/belt) are found over wide swaths of parameter space, including a “Large Ice-Belt Instability” and “Small Ice-Belt Instability” at high obliquity. The Snowball catastrophe is avoided at weak radiative forcing in two different scenarios: weak albedo feedback and inefficient heat transport (favoring stable partial ice cover), or efficient transport at high obliquity (favoring ice-free conditions). From speculative assumptions about distributions of planetary parameters, three-fourths to four-fifths of all planets with stable partial ice cover should be in the form of Earth-like polar caps.

  4. Tidal Modulation of Ice-shelf Flow: a Viscous Model of the Ross Ice Shelf

    Science.gov (United States)

    Brunt, Kelly M.; MacAyeal, Douglas R.

    2014-01-01

    Three stations near the calving front of the Ross Ice Shelf, Antarctica, recorded GPS data through a full spring-neap tidal cycle in November 2005. The data revealed a diurnal horizontal motion that varied both along and transverse to the long-term average velocity direction, similar to tidal signals observed in other ice shelves and ice streams. Based on its periodicity, it was hypothesized that the signal represents a flow response of the Ross Ice Shelf to the diurnal tides of the Ross Sea. To assess the influence of the tide on the ice-shelf motion, two hypotheses were developed. The first addressed the direct response of the ice shelf to tidal forcing, such as forces due to sea-surface slopes or forces due to sub-ice-shelf currents. The second involved the indirect response of ice-shelf flow to the tidal signals observed in the ice streams that source the ice shelf. A finite-element model, based on viscous creep flow, was developed to test these hypotheses, but succeeded only in falsifying both hypotheses, i.e. showing that direct tidal effects produce too small a response, and indirect tidal effects produce a response that is not smooth in time. This nullification suggests that a combination of viscous and elastic deformation is required to explain the observations.

  5. The Second Deep Ice Coring Project at Dome Fuji, Antarctica

    Directory of Open Access Journals (Sweden)

    Hideaki Motoyama

    2007-09-01

    Full Text Available Throughout the history of the polar icecaps, dust and aerosols have been transported through the atmosphere to the poles, to be preserved within the annually freezing ice of the growing ice shields. Therefore, the Antarctic ice sheet is a “time capsule" for environmental data, containing information of ancient periods of Earth’s history. To unravel this history and decode cycles in glaciations and global change is among the major goals of the Dome Fuji Ice Coring Project.

  6. A network model for electrical transport in sea ice

    International Nuclear Information System (INIS)

    Zhu, J.; Golden, K.M.; Gully, A.; Sampson, C.

    2010-01-01

    Monitoring the thickness of sea ice is an important tool in assessing the impact of global warming on Earth's polar regions, and most methods of measuring ice thickness depend on detailed knowledge of its electrical properties. We develop a network model for the electrical conductivity of sea ice, which incorporates statistical measurements of the brine microstructure. The numerical simulations are in close agreement with direct measurements we made in Antarctica on the vertical conductivity of first year sea ice.

  7. Stream Evaluation

    Data.gov (United States)

    Kansas Data Access and Support Center — Digital representation of the map accompanying the "Kansas stream and river fishery resource evaluation" (R.E. Moss and K. Brunson, 1981.U.S. Fish and Wildlife...

  8. Environmental constraints on West Antarctic ice-sheet formation

    Energy Technology Data Exchange (ETDEWEB)

    Lindstrom, D R; MacAyeal, D R

    1987-01-01

    Small perturbations in Antarctic environmental conditions can culminate in the demise of the Antarctic ice sheet's western sector. This may have happened during the last interglacial period, and could recur within the next millennium due to atmospheric warming from trace gas and CO/sub 2/ increases. In this study, we investigate the importance of sea-level, accumulation rate, and ice influx from the East Antarctic ice sheet in the re-establishment of the West Antarctic ice sheet from a thin cover using a time-dependent numerical ice-shelf model. Our results show that a precursor to the West Antarctic ice sheet can form within 3000 years. Sea-level lowering caused by ice-sheet development in the Northern Hemisphere has the greatest environmental influence. Under favorable conditions, ice grounding occurs over all parts of the West Antarctic ice sheet except up-stream of Thwaites Glacier and in the Ross Sea region.

  9. Relationships between Indian summer monsoon rainfall and ice cover over selected oceanic regions

    Digital Repository Service at National Institute of Oceanography (India)

    Gopinathan, C.K.

    The variations in oceanic ice cover at selected polar regions during 1973 to 1987 have been analysed in relation to the seasonal Indian summer monsoon rainfall. The ice cover over the Arctic regions in June has negative relationship (correlation...

  10. Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth, retreat and dynamics

    Science.gov (United States)

    Greenwood, Sarah L.; Clark, Chris D.

    2009-12-01

    The ice sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and ice-marginal dynamics and chronologies, with less attention paid to an ice sheet wide view of the first order properties of the ice sheet: centres of mass, ice divide structure, ice flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an ice sheet reconstruction yielding these fundamental ice sheet properties. We present a seven stage model of ice sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of ice from Scotland likely coalesced with local ice caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish Ice Sheet was then established during ice sheet growth, with a branching ice divide structure whose main axis migrated up to 140 km from the west coast towards the east. Ice stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. Ice cover is reconstructed as extending to the continental shelf break. The Irish Ice Sheet became autonomous (i.e. separate from the British Ice Sheet) during deglaciation and fragmented into multiple ice masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the ice sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the ice stream system in the North Channel - Irish Sea Basin in driving such asymmetry, since rapid

  11. Response timescales for martian ice masses and implications for ice flow on Mars

    DEFF Research Database (Denmark)

    Koutnik, Michelle Rebecca; Waddington, E.D.; Winebrener, D.P.

    2013-01-01

    a predictable shape, which is a function of ice temperature, ice rheology, and surface mass-exchange rate. In addition, the time for surface-shape adjustment is shorter than the characteristic time for significant deformation or displacement of internal layers within a flowing ice mass; as a result, surface......On Earth and on Mars, ice masses experience changes in precipitation, temperature, and radiation. In a new climate state, flowing ice masses will adjust in length and in thickness, and this response toward a new steady state has a characteristic timescale. However, a flowing ice mass has...... topography is more diagnostic of flow than are internal-layer shapes. Because the shape of Gemina Lingula, North Polar Layered Deposits indicates that it flowed at some time in the past, we use its current topography to infer characteristics of those past ice conditions, or past climate conditions, in which...

  12. Do pelagic grazers benefit from sea ice? Insights from the Antarctic sea ice proxy IPSO25

    Science.gov (United States)

    Schmidt, Katrin; Brown, Thomas A.; Belt, Simon T.; Ireland, Louise C.; Taylor, Kyle W. R.; Thorpe, Sally E.; Ward, Peter; Atkinson, Angus

    2018-04-01

    Sea ice affects primary production in polar regions in multiple ways. It can dampen water column productivity by reducing light or nutrient supply, provide a habitat for ice algae and condition the marginal ice zone (MIZ) for phytoplankton blooms on its seasonal retreat. The relative importance of three different carbon sources (sea ice derived, sea ice conditioned, non-sea-ice associated) for the polar food web is not well understood, partly due to the lack of methods that enable their unambiguous distinction. Here we analysed two highly branched isoprenoid (HBI) biomarkers to trace sea-ice-derived and sea-ice-conditioned carbon in Antarctic krill (Euphausia superba) and relate their concentrations to the grazers' body reserves, growth and recruitment. During our sampling in January-February 2003, the proxy for sea ice diatoms (a di-unsaturated HBI termed IPSO25, δ13C = -12.5 ± 3.3 ‰) occurred in open waters of the western Scotia Sea, where seasonal ice retreat was slow. In suspended matter from surface waters, IPSO25 was present at a few stations close to the ice edge, but in krill the marker was widespread. Even at stations that had been ice-free for several weeks, IPSO25 was found in krill stomachs, suggesting that they gathered the ice-derived algae from below the upper mixed layer. Peak abundances of the proxy for MIZ diatoms (a tri-unsaturated HBI termed HBI III, δ13C = -42.2 ± 2.4 ‰) occurred in regions of fast sea ice retreat and persistent salinity-driven stratification in the eastern Scotia Sea. Krill sampled in the area defined by the ice edge bloom likewise contained high amounts of HBI III. As indicators for the grazer's performance we used the mass-length ratio, size of digestive gland and growth rate for krill, and recruitment for the biomass-dominant calanoid copepods Calanoides acutus and Calanus propinquus. These indices consistently point to blooms in the MIZ as an important feeding ground for pelagic grazers. Even though ice

  13. Review of ice and snow runway pavements

    Directory of Open Access Journals (Sweden)

    Greg White

    2018-05-01

    Full Text Available Antarctica is the highest, driest, coldest, windiest, most remote and most pristine place on Earth. Polar operations depend heavily on air transportation and support for personnel and equipment. It follows that improvement in snow and ice runway design, construction and maintenance will directly benefit polar exploration and research. Current technologies and design methods for snow and ice runways remain largely reliant on work performed in the 1950s and 1960s. This paper reviews the design and construction of polar runways using snow and ice as geomaterials. The inability to change existing snow and ice thickness or temperature creates a challenge for polar runway design and construction, as does the highly complex mechanical behaviour of snow, including the phenomena known as sintering. It is recommended that a modern approach be developed for ice and snow runway design, based on conventional rigid and flexible pavement design principles. This requires the development on an analytical model for the prediction of snow strength, based on snow age, temperature history and density. It is also recommended that the feasibility of constructing a snow runway at the South Pole be revisited, in light of contemporary snow sintering methods. Such a runway would represent a revolutionary advance for the logistical support of Antarctic research efforts. Keywords: Runway, Pavement, Snow, Ice, Antarctic

  14. A State-Space Model for River Ice Forecasting

    National Research Council Canada - National Science Library

    Daly, Steven

    2003-01-01

    Each winter ice forms on rivers streams, and navigable waterways, causing many problems through its effects on the operation of hydraulic control structures, locks and dams, hydropower plants, and water intakes...

  15. New evidence for surface water ice in small-scale cold traps and in three large craters at the north polar region of Mercury from the Mercury Laser Altimeter

    Science.gov (United States)

    Deutsch, Ariel N.; Neumann, Gregory A.; Head, James W.

    2017-09-01

    The Mercury Laser Altimeter (MLA) measured surface reflectance, rs, at 1064 nm. On Mercury, most water-ice deposits have anomalously low rs values indicative of an insulating layer beneath which ice is buried. Previous detections of surface water ice (without an insulating layer) were limited to seven possible craters. Here we map rs in three additional permanently shadowed craters that host radar-bright deposits. Each crater has a mean rs value >0.3, suggesting that water ice is exposed at the surface without an overlying insulating layer. We also identify small-scale cold traps (rs >0.3 and permanent shadows have biannual maximum surface temperatures <100 K. We suggest that a substantial amount of Mercury's water ice is not confined to large craters but exists within microcold traps, within rough patches and intercrater terrain.

  16. Investigation of land ice-ocean interaction with a fully coupled ice-ocean model: 1. Model description and behavior

    Science.gov (United States)

    Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.; Hallberg, R.; Oppenheimer, M.

    2012-06-01

    Antarctic ice shelves interact closely with the ocean cavities beneath them, with ice shelf geometry influencing ocean cavity circulation, and heat from the ocean driving changes in the ice shelves, as well as the grounded ice streams that feed them. We present a new coupled model of an ice stream-ice shelf-ocean system that is used to study this interaction. The model is capable of representing a moving grounding line and dynamically responding ocean circulation within the ice shelf cavity. Idealized experiments designed to investigate the response of the coupled system to instantaneous increases in ocean temperature show ice-ocean system responses on multiple timescales. Melt rates and ice shelf basal slopes near the grounding line adjust in 1-2 years, and downstream advection of the resulting ice shelf thinning takes place on decadal timescales. Retreat of the grounding line and adjustment of grounded ice takes place on a much longer timescale, and the system takes several centuries to reach a new steady state. During this slow retreat, and in the absence of either an upward-or downward-sloping bed or long-term trends in ocean heat content, the ice shelf and melt rates maintain a characteristic pattern relative to the grounding line.

  17. Sea ice biogeochemistry: a guide for modellers.

    Directory of Open Access Journals (Sweden)

    Letizia Tedesco

    Full Text Available Sea ice is a fundamental component of the climate system and plays a key role in polar trophic food webs. Nonetheless sea ice biogeochemical dynamics at large temporal and spatial scales are still rarely described. Numerical models may potentially contribute integrating among sparse observations, but available models of sea ice biogeochemistry are still scarce, whether their relevance for properly describing the current and future state of the polar oceans has been recently addressed. A general methodology to develop a sea ice biogeochemical model is presented, deriving it from an existing validated model application by extension of generic pelagic biogeochemistry model parameterizations. The described methodology is flexible and considers different levels of ecosystem complexity and vertical representation, while adopting a strategy of coupling that ensures mass conservation. We show how to apply this methodology step by step by building an intermediate complexity model from a published realistic application and applying it to analyze theoretically a typical season of first-year sea ice in the Arctic, the one currently needing the most urgent understanding. The aim is to (1 introduce sea ice biogeochemistry and address its relevance to ocean modelers of polar regions, supporting them in adding a new sea ice component to their modelling framework for a more adequate representation of the sea ice-covered ocean ecosystem as a whole, and (2 extend our knowledge on the relevant controlling factors of sea ice algal production, showing that beyond the light and nutrient availability, the duration of the sea ice season may play a key-role shaping the algal production during the on going and upcoming projected changes.

  18. Atmospheric Modeling of the Martian Polar Regions: CRISM EPF Coverage During the South Polar Spring Recession

    Science.gov (United States)

    Brown, A. J.; McGuire, P.; Wolff, M. J.

    2008-03-01

    We describe efforts to model dust and ice aerosols content and soils and icy surface reflectance in the Martian southern polar region during spring recession (Ls = 152-320) using CRISM emission phase function (EPF) observations.

  19. Coastal-Change and Glaciological Map of the Northern Ross Ice Shelf Area, Antarctica: 1962-2004

    Science.gov (United States)

    Ferrigno, Jane G.; Foley, Kevin M.; Swithinbank, Charles; Williams, Richard S.

    2007-01-01

    Changes in the area and volume of polar ice sheets are intricately linked to changes in global climate, and the resulting changes in sea level could severely impact the densely populated coastal regions on Earth. Melting of the West Antarctic part alone of the Antarctic ice sheet would cause a sea-level rise of approximately 6 meters (m). The potential sea-level rise after melting of the entire Antarctic ice sheet is estimated to be 65 m (Lythe and others, 2001) to 73 m (Williams and Hall, 1993). The mass balance (the net volumetric gain or loss) of the Antarctic ice sheet is highly complex, responding differently to different conditions in each region (Vaughan, 2005). In a review paper, Rignot and Thomas (2002) concluded that the West Antarctic ice sheet is probably becoming thinner overall; although it is thickening in the west, it is thinning in the north. Thomas and others (2004), on the basis of aircraft and satellite laser altimetry surveys, believe the thinning may be accelerating. Joughin and Tulaczyk (2002), on the basis of analysis of ice-flow velocities derived from synthetic aperture radar, concluded that most of the Ross ice streams (ice streams on the east side of the Ross Ice Shelf) have a positive mass balance, whereas Rignot and others (2004) infer even larger negative mass balance for glaciers flowing northward into the Amundsen Sea, a trend suggested by Swithinbank and others (2003a,b; 2004). The mass balance of the East Antarctic ice sheet is thought by Davis and others (2005) to be strongly positive on the basis of the change in satellite altimetry measurements made between 1992 and 2003. Measurement of changes in area and mass balance of the Antarctic ice sheet was given a very high priority in recommendations by the Polar Research Board of the National Research Council (1986), in subsequent recommendations by the Scientific Committee on Antarctic Research (SCAR) (1989, 1993), and by the National Science Foundation?s (1990) Division of Polar

  20. Balance Velocities of the Greenland Ice Sheet

    Science.gov (United States)

    Joughin, Ian; Fahnestock, Mark; Ekholm, Simon; Kwok, Ron

    1997-01-01

    We present a map of balance velocities for the Greenland ice sheet. The resolution of the underlying DEM, which was derived primarily from radar altimetry data, yields far greater detail than earlier balance velocity estimates for Greenland. The velocity contours reveal in striking detail the location of an ice stream in northeastern Greenland, which was only recently discovered using satellite imagery. Enhanced flow associated with all of the major outlets is clearly visible, although small errors in the source data result in less accurate estimates of the absolute flow speeds. Nevertheless, the balance map is useful for ice-sheet modelling, mass balance studies, and field planning.

  1. Combined Usage of TanDEM-X and CryoSat-2 for Generating a High Resolution Digital Elevation Model of Fast Moving Ice Stream and Its Application in Grounding Line Estimation

    Directory of Open Access Journals (Sweden)

    Seung Hee Kim

    2017-02-01

    Full Text Available Definite surface topography of ice provides fundamental information for most glaciologists to study climate change. However, the topography at the marginal region of ice sheets exhibits noticeable dynamical changes from fast flow velocity and large thinning rates; thus, it is difficult to determine instantaneous topography. In this study, the surface topography of the marginal region of Thwaites Glacier in the Amundsen Sector of West Antarctica, where ice melting and thinning are prevailing, is extracted using TanDEM-X interferometry in combination with data from the near-coincident CryoSat-2 radar altimeter. The absolute height offset, which has been a persistent problem in applying the interferometry technique for generating DEMs, is determined by linear least-squares fitting between the uncorrected TanDEM-X heights and reliable reference heights from CryoSat-2. The reliable heights are rigorously selected at locations of high normalized cross-correlation and low RMS heights between segments of data points. The generated digital elevation model with the resolved absolute height offset is assessed with airborne laser altimeter data from the Operation IceBridge that were acquired five months after TanDEM-X and show high correlation with biases of 3.19 m and −4.31 m at the grounding zone and over the ice sheet surface, respectively. For practical application of the generated DEM, grounding line estimation assuming hydrostatic equilibrium was carried out, and the feasibility was seen through comparison with the previous grounding line. Finally, it is expected that the combination of interferometry and altimetery with similar datasets can be applied at regions even with a lack of ground control points.

  2. The refreezing of melt ponds on Arctic sea ice

    Science.gov (United States)

    Flocco, Daniela; Feltham, Daniel L.; Bailey, Eleanor; Schroeder, David

    2015-02-01

    The presence of melt ponds on the surface of Arctic sea ice significantly reduces its albedo, inducing a positive feedback leading to sea ice thinning. While the role of melt ponds in enhancing the summer melt of sea ice is well known, their impact on suppressing winter freezing of sea ice has, hitherto, received less attention. Melt ponds freeze by forming an ice lid at the upper surface, which insulates them from the atmosphere and traps pond water between the underlying sea ice and the ice lid. The pond water is a store of latent heat, which is released during refreezing. Until a pond freezes completely, there can be minimal ice growth at the base of the underlying sea ice. In this work, we present a model of the refreezing of a melt pond that includes the heat and salt balances in the ice lid, trapped pond, and underlying sea ice. The model uses a two-stream radiation model to account for radiative scattering at phase boundaries. Simulations and related sensitivity studies suggest that trapped pond water may survive for over a month. We focus on the role that pond salinity has on delaying the refreezing process and retarding basal sea ice growth. We estimate that for a typical sea ice pond coverage in autumn, excluding the impact of trapped ponds in models overestimates ice growth by up to 265 million km3, an overestimate of 26%.

  3. Workshop on wave-ice interaction

    Science.gov (United States)

    Wadhams, Peter; Squire, Vernon; Rottier, Philip; Liu, Antony; Dugan, John; Czipott, Peter; Shen, Hayley

    The subject of wave-ice interaction has been advanced in recent years by small groups of researchers working on a similar range of topics in widely separated geographic locations. Their recent studies inspired a workshop on wave-ice interaction held at the Scott Polar Research Institute, University of Cambridge, England, December 16-18, 1991, where theories in all aspects of the physics of wave-ice interaction were compared.Conveners of the workshop hoped that plans for future observational and theoretical work dealing with outstanding issues in a collaborative way would emerge. The workshop, organized by the Commission on Sea Ice of the International Association for Physical Sciences of the Ocean (IAPSO), was co-chaired by Vernon Squire, professor of mathematics and statistics at the University of Otago, New Zealand, and Peter Wadhams, director of the Scott Polar Research Institute. Participants attended from Britain, Finland, New Zealand, Norway, and the United States.

  4. IceBridge: Bringing a Field Campaign Home

    Science.gov (United States)

    Woods, J.; Beck, J.; Bartholow, S.

    2015-12-01

    IceBridge, a six-year NASA mission, is the largest airborne survey of Earth's polar ice ever flown. It will yield an unprecedented three-dimensional view of Arctic and Antarctic ice sheets, ice shelves and sea ice. These flights will provide a yearly, multi-instrument look at the behavior of the rapidly changing features of the Greenland and Antarctic ice. Data collected during IceBridge will help scientists bridge the gap in polar observations between NASA's Ice, Cloud and Land Elevation Satellite (ICESat) -- in orbit since 2003 -- and ICESat-2, planned for 2017. ICESat stopped collecting science data in 2009, making IceBridge critical for ensuring a continuous series of observations. IceBridge will use airborne instruments to map Arctic and Antarctic areas once a year at a minimum, with new campaigns being developed during the Arctic melt season. IceBridge flights are conducted in the spring and summer for the Arctic and in the fall over Antarctica. Other smaller airborne surveys around the world are also part of the IceBridge campaign. IceBridge actively engages the public and educators through a variety of outlets ranging from communications strategies through social media outlets, to larger organized efforts such as PolarTREC. In field activities include blog posts, photo updates, in flight chat sessions, and more intensive live events to include google hangouts, where field team members can interact with the public during a scheduled broadcast. The IceBridge team provides scientists and other team members with the training and support to become communicators in their own right. There is an exciting new initiative where IceBridge will be collaborating with Undergraduate and Graduate students to integrate the next generation of scientists and communicators into the Science Teams. This will be explored through partnerships with institutions that are interested in mentoring through project based initiatives.

  5. Radiative transfer in atmosphere-sea ice-ocean system

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Z.; Stamnes, K.; Weeks, W.F. [Univ. of Alaska, Fairbanks, AK (United States); Tsay, S.C. [NASA Goddard Space Flight Center, Greenbelt, MD (United States)

    1996-04-01

    Radiative energy is critical in controlling the heat and mass balance of sea ice, which significantly affects the polar climate. In the polar oceans, light transmission through the atmosphere and sea ice is essential to the growth of plankton and algae and, consequently, to the microbial community both in the ice and in the ocean. Therefore, the study of radiative transfer in the polar atmosphere, sea ice, and ocean system is of particular importance. Lacking a properly coupled radiative transfer model for the atmosphere-sea ice-ocean system, a consistent study of the radiative transfer in the polar atmosphere, snow, sea ice, and ocean system has not been undertaken before. The radiative transfer processes in the atmosphere and in the ice and ocean have been treated separately. Because the radiation processes in the atmosphere, sea ice, and ocean depend on each other, this separate treatment is inconsistent. To study the radiative interaction between the atmosphere, clouds, snow, sea ice, and ocean, a radiative transfer model with consistent treatment of radiation in the coupled system is needed and is under development.

  6. Rapid Access Ice Drill: A New Tool for Exploration of the Deep Antarctic Ice Sheets and Subglacial Geology

    Science.gov (United States)

    Goodge, J. W.; Severinghaus, J. P.

    2014-12-01

    The Rapid Access Ice Drill (RAID) will penetrate the Antarctic ice sheets in order to core through deep ice, the glacial bed, and into bedrock below. This new technology will provide a critical first look at the interface between major ice caps and their subglacial geology. Currently in construction, RAID is a mobile drilling system capable of making several long boreholes in a single field season in Antarctica. RAID is interdisciplinary and will allow access to polar paleoclimate records in ice >1 Ma, direct observation at the base of the ice sheets, and recovery of rock cores from the ice-covered East Antarctic craton. RAID uses a diamond rock-coring system as in mineral exploration. Threaded drill-pipe with hardened metal bits will cut through ice using reverse circulation of Estisol for pressure-compensation, maintenance of temperature, and removal of ice cuttings. Near the bottom of the ice sheet, a wireline bottom-hole assembly will enable diamond coring of ice, the glacial bed, and bedrock below. Once complete, boreholes will be kept open with fluid, capped, and made available for future down-hole measurement of thermal gradient, heat flow, ice chronology, and ice deformation. RAID will also sample for extremophile microorganisms. RAID is designed to penetrate up to 3,300 meters of ice and take sample cores in less than 200 hours. This rapid performance will allow completion of a borehole in about 10 days before moving to the next drilling site. RAID is unique because it can provide fast borehole access through thick ice; take short ice cores for paleoclimate study; sample the glacial bed to determine ice-flow conditions; take cores of subglacial bedrock for age dating and crustal history; and create boreholes for use as an observatory in the ice sheets. Together, the rapid drilling capability and mobility of the drilling system, along with ice-penetrating imaging methods, will provide a unique 3D picture of the interior Antarctic ice sheets.

  7. Arctic tides from GPS on sea ice

    DEFF Research Database (Denmark)

    Kildegaard Rose, Stine; Skourup, Henriette; Forsberg, René

    The presence of sea-ice in the Arctic Ocean plays a significant role in the Arctic climate. Sea ice dampens the ocean tide amplitude with the result that global tidal models which use only astronomical data perform less accurately in the polar regions. This study presents a kinematic processing o......-gauges and altimetry data. Furthermore, we prove that the geodetic reference ellipsoid WGS84, can be interpolated to the tidal defined zero level by applying geophysical corrections to the GPS data....

  8. Development of a Mobile Ice Nucleus Counter

    Energy Technology Data Exchange (ETDEWEB)

    Kok, Gregory [Droplet Measurement Technologies, Boulder, CO (United States); Kulkarni, Gourihar [Droplet Measurement Technologies, Boulder, CO (United States)

    2014-07-10

    An ice nucleus counter has been constructed. The instrument uses built-in refrigeration systems for wall cooling. A cascade refrigeration system will allow the cold wall to operate as low as -70°C, and a single stage system can operate the warm wall at -45C. A unique optical particle counter has been constructed using polarization detection of the scattered light. This allows differentiation of the particles exiting the chamber to determine if they are ice or liquid.

  9. Ice Ages

    Indian Academy of Sciences (India)

    that the precession of the earth's orbit caused ice ages. The precession of the earth's orbit leads to changes in the time of the year at which ... than in the southern hemisphere. ..... small increase in ocean temperature implies a large increase in.

  10. Ice, Ice, Baby: A Program for Sustained, Classroom-Based K-8 Teacher Professional Development

    Science.gov (United States)

    Hamilton, C.

    2009-12-01

    Ice, Ice, Baby is a K-8 science program created by the education team at the Center for the Remote Sensing of Ice Sheets (CReSIS), an NSF-funded science and technology center headquartered at the University of Kansas. The twenty-four hands-on activities, which constitute the Ice, Ice, Baby curriculum, were developed to help students understand the role of polar ice sheets in sea level rise. These activities, presented in classrooms by CReSIS' Educational Outreach Coordinator, demonstrate many of the scientific properties of ice, including displacement and density. Student journals are utilized with each lesson as a strategy for improving students' science process skills. Journals also help the instructor identify misconceptions, assess comprehension, and provide students with a year-long science reference log. Pre- and post- assessments are given to both teachers and students before and after the program, providing data for evaluation and improvement of the Ice, Ice, Baby program. While students are actively engaged in hands-on learning about the unusual topics of ice sheets, glaciers, icebergs and sea ice, the CReSIS' Educational Coordinator is able to model best practices in science education, such as questioning and inquiry-based methods of instruction. In this way, the Ice, Ice, Baby program also serves as ongoing, in-class, professional development for teachers. Teachers are also provided supplemental activities to do with their classes between CReSIS' visits to encourage additional science lessons, reinforce concepts taught in the Ice, Ice, Baby program, and to foster teachers' progression toward more reform-based science instruction.

  11. The response of grounded ice to ocean temperature forcing in a coupled ice sheet-ice shelf-ocean cavity model

    Science.gov (United States)

    Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.

    2010-12-01

    Ice shelves provide a pathway for the heat content of the ocean to influence continental ice sheets. Changes in the rate or location of basal melting can alter their geometry and effect changes in stress conditions at the grounding line, leading to a grounded ice response. Recent observations of ice streams and ice shelves in the Amundsen Sea sector of West Antarctica have been consistent with this story. On the other hand, ice dynamics in the grounding zone control flux into the shelf and thus ice shelf geometry, which has a strong influence on the circulation in the cavity beneath the shelf. Thus the coupling between the two systems, ocean and ice sheet-ice shelf, can be quite strong. We examine the response of the ice sheet-ice shelf-ocean cavity system to changes in ocean temperature using a recently developed coupled model. The coupled model consists a 3-D ocean model (GFDL's Generalized Ocean Layered Dynamics model, or GOLD) to a two-dimensional ice sheet-ice shelf model (Goldberg et al, 2009), and allows for changing cavity geometry and a migrating grounding line. Steady states of the coupled system are found even under considerable forcing. The ice shelf morphology and basal melt rate patterns of the steady states exhibit detailed structure, and furthermore seem to be unique and robust. The relationship between temperature forcing and area-averaged melt rate is influenced by the response of ice shelf morphology to thermal forcing, and is found to be sublinear in the range of forcing considered. However, results suggest that area-averaged melt rate is not the best predictor of overall system response, as grounding line stability depends on local aspects of the basal melt field. Goldberg, D N, D M Holland and C G Schoof, 2009. Grounding line movement and ice shelf buttressing in marine ice sheets, Journal of Geophysical Research-Earth Surfaces, 114, F04026.

  12. Improving Surface Mass Balance Over Ice Sheets and Snow Depth on Sea Ice

    Science.gov (United States)

    Koenig, Lora Suzanne; Box, Jason; Kurtz, Nathan

    2013-01-01

    Surface mass balance (SMB) over ice sheets and snow on sea ice (SOSI) are important components of the cryosphere. Large knowledge gaps remain in scientists' abilities to monitor SMB and SOSI, including insufficient measurements and difficulties with satellite retrievals. On ice sheets, snow accumulation is the sole mass gain to SMB, and meltwater runoff can be the dominant single loss factor in extremely warm years such as 2012. SOSI affects the growth and melt cycle of the Earth's polar sea ice cover. The summer of 2012 saw the largest satellite-recorded melt area over the Greenland ice sheet and the smallest satellite-recorded Arctic sea ice extent, making this meeting both timely and relevant.

  13. Method for removing impurities from an impurity-containing fluid stream

    Science.gov (United States)

    Ginosar, Daniel M.; Fox, Robert V.

    2010-04-06

    A method of removing at least one polar component from a fluid stream. The method comprises providing a fluid stream comprising at least one nonpolar component and at least one polar component. The fluid stream is contacted with a supercritical solvent to remove the at least one polar component. The at least one nonpolar component may be a fat or oil and the at least one polar component may be water, dirt, detergents, or mixtures thereof. The supercritical solvent may decrease solubility of the at least one polar component in the fluid stream. The supercritical solvent may function as a solvent or as a gas antisolvent. The supercritical solvent may dissolve the nonpolar components of the fluid stream, such as fats or oils, while the polar components may be substantially insoluble. Alternatively, the supercritical solvent may be used to increase the nonpolarity of the fluid stream.

  14. Arctic tides from GPS on sea ice

    OpenAIRE

    Kildegaard Rose, Stine; Skourup, Henriette; Forsberg, René

    2012-01-01

    The presence of sea-ice in the Arctic Ocean plays a significant role in the Arctic climate. Sea ice dampens the ocean tide amplitude with the result that global tidal models which use only astronomical data perform less accurately in the polar regions. This study presents a kinematic processing of Global Positioning System (GPS) buoys placed on sea-ice at five different sites north of Greenland for the study of sea level height and tidal analysis to improve tidal models in the Central Arctic....

  15. Eulerian Method for Ice Crystal Icing

    NARCIS (Netherlands)

    Norde, Ellen; van der Weide, Edwin Theodorus Antonius; Hoeijmakers, Hendrik Willem Marie

    In this study, an ice accretion method aimed at ice crystal icing in turbofan engines is developed and demonstrated for glaciated as well as mixed-phase icing conditions. The particle trajectories are computed by an Eulerian trajectory method. The effects of heat transfer and phase change on the

  16. Sea ice - Multiyear cycles and white ice

    Science.gov (United States)

    Ledley, T. S.

    1985-01-01

    The multiyear thickness cycles represent one of the interesting features of the sea ice studies performed by Semtner (1976) and Washington et al. (1976) with simple thermodynamic models of sea ice. In the present article, a description is given of results which show that the insulating effect of snow on the surface of the sea ice is important in producing these multiyear cycles given the physics included in the model. However, when the formation of white ice is included, the cycles almost disappear. White ice is the ice which forms at the snow-ice interface when the snow layer becomes thick enough to depress the ice below the water level. Water infiltrates the snow by coming through the ice at leads and generally freezes there, forming white ice.

  17. Lunar true polar wander inferred from polar hydrogen.

    Science.gov (United States)

    Siegler, M A; Miller, R S; Keane, J T; Laneuville, M; Paige, D A; Matsuyama, I; Lawrence, D J; Crotts, A; Poston, M J

    2016-03-24

    The earliest dynamic and thermal history of the Moon is not well understood. The hydrogen content of deposits near the lunar poles may yield insight into this history, because these deposits (which are probably composed of water ice) survive only if they remain in permanent shadow. If the orientation of the Moon has changed, then the locations of the shadowed regions will also have changed. The polar hydrogen deposits have been mapped by orbiting neutron spectrometers, and their observed spatial distribution does not match the expected distribution of water ice inferred from present-day lunar temperatures. This finding is in contrast to the distribution of volatiles observed in similar thermal environments at Mercury's poles. Here we show that polar hydrogen preserves evidence that the spin axis of the Moon has shifted: the hydrogen deposits are antipodal and displaced equally from each pole along opposite longitudes. From the direction and magnitude of the inferred reorientation, and from analysis of the moments of inertia of the Moon, we hypothesize that this change in the spin axis, known as true polar wander, was caused by a low-density thermal anomaly beneath the Procellarum region. Radiogenic heating within this region resulted in the bulk of lunar mare volcanism and altered the density structure of the Moon, changing its moments of inertia. This resulted in true polar wander consistent with the observed remnant polar hydrogen. This thermal anomaly still exists and, in part, controls the current orientation of the Moon. The Procellarum region was most geologically active early in lunar history, which implies that polar wander initiated billions of years ago and that a large portion of the measured polar hydrogen is ancient, recording early delivery of water to the inner Solar System. Our hypothesis provides an explanation for the antipodal distribution of lunar polar hydrogen, and connects polar volatiles to the geologic and geophysical evolution of the Moon

  18. Modeling the Fracture of Ice Sheets on Parallel Computers

    Energy Technology Data Exchange (ETDEWEB)

    Waisman, Haim [Columbia Univ., New York, NY (United States); Tuminaro, Ray [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2013-10-10

    The objective of this project was to investigate the complex fracture of ice and understand its role within larger ice sheet simulations and global climate change. This objective was achieved by developing novel physics based models for ice, novel numerical tools to enable the modeling of the physics and by collaboration with the ice community experts. At the present time, ice fracture is not explicitly considered within ice sheet models due in part to large computational costs associated with the accurate modeling of this complex phenomena. However, fracture not only plays an extremely important role in regional behavior but also influences ice dynamics over much larger zones in ways that are currently not well understood. To this end, our research findings through this project offers significant advancement to the field and closes a large gap of knowledge in understanding and modeling the fracture of ice sheets in the polar regions. Thus, we believe that our objective has been achieved and our research accomplishments are significant. This is corroborated through a set of published papers, posters and presentations at technical conferences in the field. In particular significant progress has been made in the mechanics of ice, fracture of ice sheets and ice shelves in polar regions and sophisticated numerical methods that enable the solution of the physics in an efficient way.

  19. Ross Sea Polynyas: Response of Ice Concentration Retrievals to Large Areas of Thin Ice

    Science.gov (United States)

    Kwok, R.; Comiso, J. C.; Martin, S.; Drucker, R.

    2007-01-01

    For a 3-month period between May and July of 2005, we examine the response of the Advanced Microwave Scanning Radiometer (AMSR-E) Enhanced NASA Team 2 (NT2) and AMSR-E Bootstrap (ABA) ice concentration algorithms to large areas of thin ice of the Ross Sea polynyas. Coincident Envisat Synthetic Aperture Radar (SAR) coverage of the region during this period offers a detailed look at the development of the polynyas within several hundred kilometers of the ice front. The high-resolution imagery and derived ice motion fields show bands of polynya ice, covering up to approximately 105 km(sup 2) of the Ross Sea, that are associated with wind-forced advection. In this study, ice thickness from AMSR-E 36 GHz polarization information serves as the basis for examination of the response. The quality of the thickness of newly formed sea ice (<10 cm) from AMSR-E is first assessed with thickness estimates derived from ice surface temperatures from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument. The effect of large areas of thin ice in lowering the ice concentration estimates from both NT2/ABA approaches is clearly demonstrated. Results show relatively robust relationships between retrieved ice concentrations and thin ice thickness estimates that differ between the two algorithms. These relationships define the approximate spatial coincidence of ice concentration and thickness isopleths. Using the 83% (ABA) and 91% (NT2) isopleths as polynya boundaries, we show that the computed coverage compares well with that using the estimated 10-cm thickness contour. The thin ice response characterized here suggests that in regions with polynyas, the retrieval results could be used to provide useful geophysical information, namely thickness and coverage.

  20. Understanding Ice Shelf Basal Melting Using Convergent ICEPOD Data Sets: ROSETTA-Ice Study of Ross Ice Shelf

    Science.gov (United States)

    Bell, R. E.; Frearson, N.; Tinto, K. J.; Das, I.; Fricker, H. A.; Siddoway, C. S.; Padman, L.

    2017-12-01

    The future stability of the ice shelves surrounding Antarctica will be susceptible to increases in both surface and basal melt as the atmosphere and ocean warm. The ROSETTA-Ice program is targeted at using the ICEPOD airborne technology to produce new constraints on Ross Ice Shelf, the underlying ocean, bathymetry, and geologic setting, using radar sounding, gravimetry and laser altimetry. This convergent approach to studying the ice-shelf and basal processes enables us to develop an understanding of the fundamental controls on ice-shelf evolution. This work leverages the stratigraphy of the ice shelf, which is detected as individual reflectors by the shallow-ice radar and is often associated with surface scour, form close to the grounding line or pinning points on the ice shelf. Surface accumulation on the ice shelf buries these reflectors as the ice flows towards the calving front. This distinctive stratigraphy can be traced across the ice shelf for the major East Antarctic outlet glaciers and West Antarctic ice streams. Changes in the ice thickness below these reflectors are a result of strain and basal melting and freezing. Correcting the estimated thickness changes for strain using RIGGS strain measurements, we can develop decadal-resolution flowline distributions of basal melt. Close to East Antarctica elevated melt-rates (>1 m/yr) are found 60-100 km from the calving front. On the West Antarctic side high melt rates primarily develop within 10 km of the calving front. The East Antarctic side of Ross Ice Shelf is dominated by melt driven by saline water masses that develop in Ross Sea polynyas, while the melting on the West Antarctic side next to Hayes Bank is associated with modified Continental Deep Water transported along the continental shelf. The two sides of Ross Ice Shelf experience differing basal melt in part due to the duality in the underlying geologic structure: the East Antarctic side consists of relatively dense crust, with low amplitude

  1. Duality of Ross Ice Shelf systems: crustal boundary, ice sheet processes and ocean circulation from ROSETTA-Ice surveys

    Science.gov (United States)

    Tinto, K. J.; Siddoway, C. S.; Padman, L.; Fricker, H. A.; Das, I.; Porter, D. F.; Springer, S. R.; Siegfried, M. R.; Caratori Tontini, F.; Bell, R. E.

    2017-12-01

    ice stream behavior. The crustal boundary governs the interaction between these systems exerts a fundamental control on the stability of the Ross Ice Shelf.

  2. Ice Forces on Offshore Wind Power Plants. Descriptions of mechanisms and recommendations for dimensioning; Islaster paa vindkraftverk till havs. Beskrivning av mekanismer och rekommendationer foer dimensionering

    Energy Technology Data Exchange (ETDEWEB)

    Bergdahl, Lars [Chalmers Univ. of Technology, Goeteborg (Sweden). Dept of Water Environment Transport

    2002-02-01

    Mechanisms for ice-loads on off-shore wind power plants are described, The ice-loads are due to thermal expansion, water level variations, drifting ice and ice-reefing. Ice accretion is briefly treated. Ice instance, ice thickness, ice retention time, water level variations and stream velocities in Swedish waters are compiled. The main text deals with recommendations for dimensioning wind power plants at sea. In the appendices, a thorough review of the physical and mechanical properties of ice is presented.

  3. State of Arctic Sea Ice North of Svalbard during N-ICE2015

    Science.gov (United States)

    Rösel, Anja; King, Jennifer; Gerland, Sebastian

    2016-04-01

    The N-ICE2015 cruise, led by the Norwegian Polar Institute, was a drift experiment with the research vessel R/V Lance from January to June 2015, where the ship started the drift North of Svalbard at 83°14.45' N, 21°31.41' E. The drift was repeated as soon as the vessel drifted free. Altogether, 4 ice stations where installed and the complex ocean-sea ice-atmosphere system was studied with an interdisciplinary Approach. During the N-ICE2015 cruise, extensive ice thickness and snow depth measurements were performed during both, winter and summer conditions. Total ice and snow thickness was measured with ground-based and airborne electromagnetic instruments; snow depth was measured with a GPS snow depth probe. Additionally, ice mass balance and snow buoys were deployed. Snow and ice thickness measurements were performed on repeated transects to quantify the ice growth or loss as well as the snow accumulation and melt rate. Additionally, we collected independent values on surveys to determine the general ice thickness distribution. Average snow depths of 32 cm on first year ice, and 52 cm on multi-year ice were measured in January, the mean snow depth on all ice types even increased until end of March to 49 cm. The average total ice and snow thickness in winter conditions was 1.92 m. During winter we found a small growth rate on multi-year ice of about 15 cm in 2 months, due to above-average snow depths and some extraordinary storm events that came along with mild temperatures. In contrast thereto, we also were able to study new ice formation and thin ice on newly formed leads. In summer conditions an enormous melt rate, mainly driven by a warm Atlantic water inflow in the marginal ice zone, was observed during two ice stations with melt rates of up to 20 cm per 24 hours. To reinforce the local measurements around the ship and to confirm their significance on a larger scale, we compare them to airborne thickness measurements and classified SAR-satellite scenes. The

  4. Diversity of Holocene life forms in fossil glacier ice

    DEFF Research Database (Denmark)

    Willerslev, E.; Hansen, Anders J.; Christensen, B.

    1999-01-01

    Studies of biotic remains of polar ice caps have been limited to morphological identification of plant pollen and spores. By using sensitive molecular techniques, we now demonstrate a much greater range of detectable organisms; from 2000- and 4000-year-old ice-core samples, we obtained...

  5. The Use of Satellite Observations in Ice Cover Simulations

    Science.gov (United States)

    1992-01-01

    Io rmotions have been used to map upper-level winds over polar diagnose the origins of a large area of reduced ice ,,ncfl.’c regions (Turner and...was motivated by the availability of coverage in the Arctic. Also shown are November-April s-ver!,_- the multiyear ice concentrations derived from

  6. Satellite-derived ice data sets no. 2: Arctic monthly average microwave brightness temperatures and sea ice concentrations, 1973-1976

    Science.gov (United States)

    Parkinson, C. L.; Comiso, J. C.; Zwally, H. J.

    1987-01-01

    A summary data set for four years (mid 70's) of Arctic sea ice conditions is available on magnetic tape. The data include monthly and yearly averaged Nimbus 5 electrically scanning microwave radiometer (ESMR) brightness temperatures, an ice concentration parameter derived from the brightness temperatures, monthly climatological surface air temperatures, and monthly climatological sea level pressures. All data matrices are applied to 293 by 293 grids that cover a polar stereographic map enclosing the 50 deg N latitude circle. The grid size varies from about 32 X 32 km at the poles to about 28 X 28 km at 50 deg N. The ice concentration parameter is calculated assuming that the field of view contains only open water and first-year ice with an ice emissivity of 0.92. To account for the presence of multiyear ice, a nomogram is provided relating the ice concentration parameter, the total ice concentration, and the fraction of the ice cover which is multiyear ice.

  7. Polar Applications of Spaceborne Scatterometers

    Science.gov (United States)

    Long, David G.

    2017-01-01

    Wind scatterometers were originally developed for observation of near-surface winds over the ocean. They retrieve wind indirectly by measuring the normalized radar cross section (σo) of the surface, and estimating the wind via a geophysical model function relating σo to the vector wind. The σo measurements have proven to be remarkably capable in studies of the polar regions where they can map snow cover; detect the freeze/thaw state of forest, tundra, and ice; map and classify sea ice; and track icebergs. Further, a long time series of scatterometer σo observations is available to support climate studies. In addition to fundamental scientific research, scatterometer data are operationally used for sea-ice mapping to support navigation. Scatterometers are, thus, invaluable tools for monitoring the polar regions. In this paper, a brief review of some of the polar applications of spaceborne wind scatterometer data is provided. The paper considers both C-band and Ku-band scatterometers, and the relative merits of fan-beam and pencil-beam scatterometers in polar remote sensing are discussed. PMID:28919936

  8. Topographic Steering of Enhanced Ice Flow at the Bottleneck Between East and West Antarctica

    DEFF Research Database (Denmark)

    Winter, Kate; Ross, Neil; Ferraccioli, Fausto

    2018-01-01

    Hypothesized drawdown of the East Antarctic Ice Sheet through the “bottleneck” zone between East and West Antarctica would have significant impacts for a large proportion of the Antarctic Ice Sheet. Earth observation satellite orbits and a sparseness of radio echo sounding data have restricted...... investigations of basal boundary controls on ice flow in this region until now. New airborne radio echo sounding surveys reveal complex topography of high relief beneath the southernmost Weddell/Ross ice divide, with three subglacial troughs connecting interior Antarctica to the Foundation and Patuxent Ice...... Streams and Siple Coast ice streams. These troughs route enhanced ice flow through the interior of Antarctica but limit potential drawdown of the East Antarctic Ice Sheet through the bottleneck zone. In a thinning or retreating scenario, these topographically controlled corridors of enhanced flow could...

  9. Investigation of land ice-ocean interaction with a fully coupled ice-ocean model: 2. Sensitivity to external forcings

    Science.gov (United States)

    Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.; Hallberg, R.; Oppenheimer, M.

    2012-06-01

    A coupled ice stream-ice shelf-ocean cavity model is used to assess the sensitivity of the coupled system to far-field ocean temperatures, varying from 0.0 to 1.8°C, as well as sensitivity to the parameters controlling grounded ice flow. A response to warming is seen in grounding line retreat and grounded ice loss that cannot be inferred from the response of integrated melt rates alone. This is due to concentrated thinning at the ice shelf lateral margin, and to processes that contribute to this thinning. Parameters controlling the flow of grounded ice have a strong influence on the response to sub-ice shelf melting, but this influence is not seen until several years after an initial perturbation in temperatures. The simulated melt rates are on the order of that observed for Pine Island Glacier in the 1990s. However, retreat rates are much slower, possibly due to unrepresented bedrock features.

  10. Forecasting Turbine Icing Events

    DEFF Research Database (Denmark)

    Davis, Neil; Hahmann, Andrea N.; Clausen, Niels-Erik

    2012-01-01

    In this study, we present a method for forecasting icing events. The method is validated at two European wind farms in with known icing events. The icing model used was developed using current ice accretion methods, and newly developed ablation algorithms. The model is driven by inputs from the WRF...... mesoscale model, allowing for both climatological estimates of icing and short term icing forecasts. The current model was able to detect periods of icing reasonably well at the warmer site. However at the cold climate site, the model was not able to remove ice quickly enough leading to large ice...

  11. Major elements, nutrients, and plankton biomass in the ice edge and an offshore region of the Indian Ocean sector of the Southern Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Shirodkar, P.V.; Goes, J.I.; Alagarsamy, R.; Fondekar, S.P

    stream_size 10 stream_content_type text/plain stream_name Polar_Rec_28(165)_127.pdf.txt stream_source_info Polar_Rec_28(165)_127.pdf.txt Content-Encoding ISO-8859-1 Content-Type text/plain; charset=ISO-8859-1 ...

  12. Spatial patterning and persistence of meltwater on ice shelves and the implications for ice shelf collapse

    Science.gov (United States)

    Robel, A.; MacAyeal, D. R.; Tsai, V. C.; Shean, D. E.

    2017-12-01

    Observations indicate that for at least the last few decades, there has been extensive surface melting over ice shelves in Antarctica. Meltwater either collects in ponds or flows over the surface in streams that discharge to the ocean. The spatial organization and persistence of this meltwater can have a significant influence on the thermomechanical ice shelf state through albedo, turbulent heat exchange, refreezing and hydrofracture. However, as more meltwater forms on Antarctic ice shelves, there is no general theory that predicts the spatial pattern of meltwater ponded on the ice shelf surface and the volume of meltwater runoff to the ocean. Here, we show how dynamical systems tools, such as cellular automata, can be used to calculate the expected distribution of meltwater on ice shelf surfaces. These tools can also be used to explore how ice shelf surface morphology is modified by meltwater albedo and turbulent heating feedbacks. We apply these numerical approaches to new high-resolution digital elevation models for ice shelves in West Antarctica. Additionally, we survey the prospects of developing general rules of meltwater patterning by applying scaling approaches from percolation theory. We conclude by discussing the types of ice shelves that are more likely to cause ice shelf collapse through surface melt-induced hydrofracture or thermomechanical weakening.

  13. Ikaite crystal distribution in Arctic winter sea ice and implications for CO2 system dynamics

    DEFF Research Database (Denmark)

    Rysgaard, Søren; Søgaard, D. H.; Cooper, M.

    2012-01-01

    The precipitation of ikaite (CaCO3·6H2O) in polar sea ice is critical to the efficiency of the sea ice-driven carbon pump and potentially important to the global carbon cycle, yet the spatial and temporal occurrence of ikaite within the ice is poorly known. We report unique observations of ikaite...

  14. Ikaite crystal distribution in winter sea ice and implications for CO2 system dynamics

    DEFF Research Database (Denmark)

    Rysgaard, Søren; Søgaard, D.H.; Cooper, M.

    2013-01-01

    The precipitation of ikaite (CaCO3 ⋅ 6H2O) in polar sea ice is critical to the efficiency of the sea ice-driven carbon pump and potentially important to the global carbon cycle, yet the spatial and temporal occurrence of ikaite within the ice is poorly known. We report unique observations of ikai...

  15. Volcano-ice interactions on Mars

    International Nuclear Information System (INIS)

    Allen, C.C.

    1979-01-01

    Central volcanic eruptions beneath terrestrial glaciers have built steep-sided, flat-topped mountains composed of pillow lava, glassy tuff, capping flows, and cones of basalt. Subglacial fissure eruptions produced ridges of similar compostion. In some places the products from a number of subglacial vents have combined to form widespread deposits. The morphologies of these subglacial volcanoes are distinctive enough to allow their recognition at the resolutions characteristic of Viking orbiter imagery. Analogs to terrestrial subglacial volcanoes have been identified on the northern plains and near the south polar cap of Mars. The polar feature provides probable evidence of volcanic eruptions beneath polar ice. A mixed unit of rock and ice is postulated to have overlain portions of the northern plains, with eruptions into this ground ice having produced mountains and ridges analogous to those in Iceland. Subsequent breakdown of this unit due to ice melting revealed the volcanic features. Estimated heights of these landforms indicate that the ice-rich unit once ranged from approximately 100 to 1200 m thick

  16. Capabilities and performance of Elmer/Ice, a new-generation ice sheet model

    Directory of Open Access Journals (Sweden)

    O. Gagliardini

    2013-08-01

    Full Text Available The Fourth IPCC Assessment Report concluded that ice sheet flow models, in their current state, were unable to provide accurate forecast for the increase of polar ice sheet discharge and the associated contribution to sea level rise. Since then, the glaciological community has undertaken a huge effort to develop and improve a new generation of ice flow models, and as a result a significant number of new ice sheet models have emerged. Among them is the parallel finite-element model Elmer/Ice, based on the open-source multi-physics code Elmer. It was one of the first full-Stokes models used to make projections for the evolution of the whole Greenland ice sheet for the coming two centuries. Originally developed to solve local ice flow problems of high mechanical and physical complexity, Elmer/Ice has today reached the maturity to solve larger-scale problems, earning the status of an ice sheet model. Here, we summarise almost 10 yr of development performed by different groups. Elmer/Ice solves the full-Stokes equations, for isotropic but also anisotropic ice rheology, resolves the grounding line dynamics as a contact problem, and contains various basal friction laws. Derived fields, like the age of the ice, the strain rate or stress, can also be computed. Elmer/Ice includes two recently proposed inverse methods to infer badly known parameters. Elmer is a highly parallelised code thanks to recent developments and the implementation of a block preconditioned solver for the Stokes system. In this paper, all these components are presented in detail, as well as the numerical performance of the Stokes solver and developments planned for the future.

  17. Great Lakes Ice Charts

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Charts show ice extent and concentration three times weekly during the ice season, for all lakes except Ontario, from the 1973/74 ice season through the 2001/2002...

  18. Antarctica: Is It More Than Just Ice?

    Science.gov (United States)

    Johnson, Cheryl; Gutierrez, Melida

    2009-01-01

    The authors introduced polar science in a fourth-grade classroom by means of 3 hands-on activities that addressed (1) the melting of glaciers and ice, (2) the differences between the North and the South Pole, and (3) the geography and landforms of Antarctica. An assessment 4 months after the original activity showed that students remembered the…

  19. Antarctic Ice Shelf Potentially Stabilized by Export of Meltwater in Surface River

    Science.gov (United States)

    Bell, Robin E.; Chu, Winnie; Kingslake, Jonathan; Das, Indrani; Tedesco, Marco; Tinto, Kirsty J.; Zappa, Christopher J.; Frezzotti, Massimo; Boghosian, Alexandra; Lee, Won Sang

    2017-01-01

    Meltwater stored in ponds and crevasses can weaken and fracture ice shelves, triggering their rapid disintegration. This ice-shelf collapse results in an increased flux of ice from adjacent glaciers and ice streams, thereby raising sea level globally. However, surface rivers forming on ice shelves could potentially export stored meltwater and prevent its destructive effects. Here we present evidence for persistent active drainage networks-interconnected streams, ponds and rivers-on the Nansen Ice Shelf in Antarctica that export a large fraction of the ice shelf's meltwater into the ocean. We find that active drainage has exported water off the ice surface through waterfalls and dolines for more than a century. The surface river terminates in a 130-metre-wide waterfall that can export the entire annual surface melt over the course of seven days. During warmer melt seasons, these drainage networks adapt to changing environmental conditions by remaining active for longer and exporting more water. Similar networks are present on the ice shelf in front of Petermann Glacier, Greenland, but other systems, such as on the Larsen C and Amery Ice Shelves, retain surface water at present. The underlying reasons for export versus retention remain unclear. Nonetheless our results suggest that, in a future warming climate, surface rivers could export melt off the large ice shelves surrounding Antarctica-contrary to present Antarctic ice-sheet models, which assume that meltwater is stored on the ice surface where it triggers ice-shelf disintegration.

  20. Evaluation of the limit ice thickness for the hull of various Finnish-Swedish ice class vessels navigating in the Russian Arctic

    Directory of Open Access Journals (Sweden)

    Pentti Kujala

    2018-05-01

    Full Text Available Selection of suitable ice class for ships operation is an important but not simple task. The increased exploitation of the Polar waters, both seasonal periods and geographical areas, as well as the introduction of new international design standards such as Polar Code, reduces the relevancy of using existing experience as basis for the selection, and new methods and knowledge have to be developed. This paper will analyse what can be the limiting ice thickness for ships navigating in the Russian Arctic and designed according to the Finnish-Swedish ice class rules. The permanent deformations of ice-strengthened shell structures for various ice classes is determined using MT Uikku as the typical size of a vessel navigating in ice. The ice load in various conditions is determined using the ARCDEV data from the winter 1998 as the basic database. By comparing the measured load in various ice conditions with the serviceability limit state of the structures, the limiting ice thickness for various ice classes is determined. The database for maximum loads includes 3-weeks ice load measurements during April 1998 on the Kara Sea mainly by icebreaker assistance. Gumbel 1 distribution is fitted on the measured 20 min maximum values and the data is divided into various classes using ship speed, ice thickness and ice concentration as the main parameters. Results encouragingly show that present designs are safer than assumed in the Polar Code suggesting that assisted operation in Arctic conditions is feasible in rougher conditions than indicated in the Polar Code. Keywords: Loads, Serviceability, Limit ice thickness, Polar code

  1. Polarization developments

    International Nuclear Information System (INIS)

    Prescott, C.Y.

    1993-07-01

    Recent developments in laser-driven photoemission sources of polarized electrons have made prospects for highly polarized electron beams in a future linear collider very promising. This talk discusses the experiences with the SLC polarized electron source, the recent progress with research into gallium arsenide and strained gallium arsenide as a photocathode material, and the suitability of these cathode materials for a future linear collider based on the parameters of the several linear collider designs that exist

  2. Sea-ice thickness from airborne laser altimetry over the Arctic Ocean north of Greenland

    DEFF Research Database (Denmark)

    Hvidegaard, Sine Munk; Forsberg, René

    2002-01-01

    We present a new method to measure ice thickness of polar sea-ice freeboard heights, using airborne laser altimetry combined with a precise geoid model, giving estimates of thickness of ice through isostatic equilibrium assumptions. In the paper we analyze a number of flights from the Polar Sea off...... Northern Greenland, and estimate accuracies of the estimated freeboard values to be at a 13 cm level, corresponding to about 1 m in absolute thickness....

  3. SMOS sea ice product: Operational application and validation in the Barents Sea marginal ice zone

    DEFF Research Database (Denmark)

    Kaleschke, Lars; Tian-Kunze, Xiangshan; Maaß, Nina

    2016-01-01

    system for ship route optimisation has been developed and was tested during this field campaign with the ice-strengthened research vessel RV Lance. The ship cruise was complemented with coordinated measurements from a helicopter and the research aircraft Polar 5. Sea ice thickness was measured using...... an electromagnetic induction (EM) system from the bow of RV Lance and another EM-system towed below the helicopter. Polar 5 was equipped among others with the L-band radiometer EMIRAD-2. The experiment yielded a comprehensive data set allowing the evaluation of the operational forecast and route optimisation system...

  4. Influence of Sea Ice Crack Formation on the Spatial Distribution of Nutrients and Microalgae in Flooded Antarctic Multiyear Ice

    Science.gov (United States)

    Nomura, Daiki; Aoki, Shigeru; Simizu, Daisuke; Iida, Takahiro

    2018-02-01

    Cracks are common and natural features of sea ice formed in the polar oceans. In this study, a sea ice crack in flooded, multiyear, land-fast Antarctic sea ice was examined to assess its influence on biological productivity and the transport of nutrients and microalgae into the upper layers of neighboring sea ice. The water inside the crack and the surrounding host ice were characterized by a strong discoloration (brown color), an indicator of a massive algal bloom. Salinity and oxygen isotopic ratio measurements indicated that 64-84% of the crack water consisted of snow meltwater supplied during the melt season. Measurements of nutrient and chlorophyll a concentrations within the slush layer pool (the flooded layer at the snow-ice interface) revealed the intrusion of water from the crack, likely forced by mixing with underlying seawater during the tidal cycle. Our results suggest that sea ice crack formation provides conditions favorable for algal blooms by directly exposing the crack water to sunlight and supplying nutrients from the under-ice water. Subsequently, constituents of the crack water modified by biological activity were transported into the upper layer of the flooded sea ice. They were then preserved in the multiyear ice column formed by upward growth of sea ice caused by snow ice formation in areas of significant snow accumulation.

  5. Ambient and laboratory measurements of ice nuclei and their biological faction with the Fast Ice Nuclei CHamber FINCH-HALO using the new 405nm Version of the BIO-IN Sensor

    Science.gov (United States)

    Bundke, U.; Nillius, B.; Bingemer, H.; Curtius, J.

    2012-04-01

    We have designed the BIO-IN detector as part of the ice nucleus counter FINCH (Fast Ice Nuclei CHamber counter) to distinguish activated Ice Nuclei (IN) ice crystals from water droplets (CCN) (Bundke et al. 2008) and their fraction of biological origin (Bundke 2010). The modified BIO-IN sensor illuminates an aerosol stream with a 405 nm laser, replacing a 365nm LED of the original BIO IN design. Particles will scatter the light and those of biological origin will show intrinsic fluorescence emissions by excitation of mainly Riboflavin, also known as vitamin B2. The incident laser light is circularly polarized by introducing a quarter-wave-plate. The circular depolarization ratio (p44/p11) of the scattering matrix is measured in the backward direction by two photomultipliers at 110° scattering angle using a combination of quarter-wave-plate and a beam splitting cube to analyze the two circular polarization components. The detection limit was lowered towards particle size of about 400nm diameter (non activated particles). It is now possible to calculate the activated fraction of IN of biological origin with respect to all biological particles measured with one detector. The performance of the sensor will be demonstrated showing the circular- depolarization properties of different test aerosol, dust samples, volcanic ashes as well as different biological particles. Measurements on the mountain Puy de Dôme of IN number concentration of ambient air, as well as measurements at the AIDA facility in Karlsruhe of the IN activation curves from different bacteria are shown. Acknowledgements: This work was supported by the German Research Foundation, Grant: BU 1432/3-2 BU 1432/4-1

  6. Significance of Thermal Fluvial Incision and Bedrock Transfer due to Ice Advection on Greenland Ice Sheet Topography

    Science.gov (United States)

    Crozier, J. A.; Karlstrom, L.; Yang, K.

    2017-12-01

    Ice sheet surface topography reflects a complicated combination of processes that act directly upon the surface and that are products of ice advection. Using recently-available high resolution ice velocity, imagery, ice surface elevation, and bedrock elevation data sets, we seek to determine the domain of significance of two important processes - thermal fluvial incision and transfer of bedrock topography through the ice sheet - on controlling surface topography in the ablation zone. Evaluating such controls is important for understanding how melting of the GIS surface during the melt season may be directly imprinted in topography through supraglacial drainage networks, and indirectly imprinted through its contribution to basal sliding that affects bedrock transfer. We use methods developed by (Karlstrom and Yang, 2016) to identify supraglacial stream networks on the GIS, and use high resolution surface digital elevation models as well as gridded ice velocity and melt rate models to quantify surface processes. We implement a numerically efficient Fourier domain bedrock transfer function (Gudmundsson, 2003) to predict surface topography due to ice advection over bedrock topography obtained from radar. Despite a number of simplifying assumptions, the bedrock transfer function predicts the observed ice sheet surface in most regions of the GIS with ˜90% accuracy, regardless of the presence or absence of supraglacial drainage networks. This supports the hypothesis that bedrock is the most significant driver of ice surface topography on wavelengths similar to ice thickness. Ice surface topographic asymmetry on the GIS is common, with slopes in the direction of ice flow steeper than those faced opposite to ice flow, consistent with bedrock transfer theory. At smaller wavelengths, topography consistent with fluvial erosion by surface hydrologic features is evident. We quantify the effect of ice advection versus fluvial thermal erosion on supraglacial longitudinal stream

  7. Formation of brine channels in sea ice.

    Science.gov (United States)

    Morawetz, Klaus; Thoms, Silke; Kutschan, Bernd

    2017-03-01

    Liquid salty micro-channels (brine) between growing ice platelets in sea ice are an important habitat for CO 2 -binding microalgaea with great impact on polar ecosystems. The structure formation of ice platelets is microscopically described and a phase field model is developed. The pattern formation during solidification of the two-dimensional interstitial liquid is considered by two coupled order parameters, the tetrahedricity as structure of ice and the salinity. The coupling and time evolution of these order parameters are described by a consistent set of three model parameters. They determine the velocity of the freezing process and the structure formation, the phase diagram, the super-cooling and super-heating region, and the specific heat. The model is used to calculate the short-time frozen micro-structures. The obtained morphological structure is compared with the vertical brine pore space obtained from X-ray computed tomography.

  8. Neutron polarization

    International Nuclear Information System (INIS)

    Firk, F.W.K.

    1976-01-01

    Some recent experiments involving polarized neutrons are discussed; they demonstrate how polarization studies provide information on fundamental aspects of nuclear structure that cannot be obtained from more traditional neutron studies. Until recently, neutron polarization studies tended to be limited either to very low energies or to restricted regions at higher energies, determined by the kinematics of favorable (p, vector n) and (d, vector n) reactions. With the advent of high intensity pulsed electron and proton accelerators and of beams of vector polarized deuterons, this is no longer the case. One has entered an era in which neutron polarization experiments are now being carried out, in a routine way, throughout the entire range from thermal energies to tens-of-MeV. The significance of neutron polarization studies is illustrated in discussions of a wide variety of experiments that include the measurement of T-invariance in the β-decay of polarized neutrons, a search for the effects of meson exchange currents in the photo-disintegration of the deuteron, the determination of quantum numbers of states in the fission of aligned 235 U and 237 Np induced by polarized neutrons, and the double- and triple-scattering of fast neutrons by light nuclei

  9. Gypsum crystals observed in experimental and natural sea ice

    Science.gov (United States)

    Geilfus, N.-X.; Galley, R. J.; Cooper, M.; Halden, N.; Hare, A.; Wang, F.; Søgaard, D. H.; Rysgaard, S.

    2013-12-01

    gypsum has been predicted to precipitate in sea ice, it has never been observed. Here we provide the first report on gypsum precipitation in both experimental and natural sea ice. Crystals were identified by X-ray diffraction analysis. Based on their apparent distinguishing characteristics, the gypsum crystals were identified as being authigenic. The FREeZing CHEMistry (FREZCHEM) model results support our observations of both gypsum and ikaite precipitation at typical in situ sea ice temperatures and confirms the "Gitterman pathway" where gypsum is predicted to precipitate. The occurrence of authigenic gypsum in sea ice during its formation represents a new observation of precipitate formation and potential marine deposition in polar seas.

  10. Global ice sheet/RSL simulations using the higher-order Ice Sheet System Model.

    Science.gov (United States)

    Larour, E. Y.; Ivins, E. R.; Adhikari, S.; Schlegel, N.; Seroussi, H. L.; Morlighem, M.

    2017-12-01

    Relative sea-level rise is driven by processes that are intimately linked to the evolution ofglacial areas and ice sheets in particular. So far, most Earth System models capable of projecting theevolution of RSL on decadal to centennial time scales have relied on offline interactions between RSL andice sheets. In particular, grounding line and calving front dynamics have not been modeled in a way that istightly coupled with Elasto-Static Adjustment (ESA) and/or Glacial-Isostatic Adjustment (GIA). Here, we presenta new simulation of the entire Earth System in which both Greenland and Antarctica ice sheets are tightly coupledto an RSL model that includes both ESA and GIA at resolutions and time scales compatible with processes suchas grounding line dynamics for Antarctica ice shelves and calving front dynamics for Greenland marine-terminatingglaciers. The simulations rely on the Ice Sheet System Model (ISSM) and show the impact of higher-orderice flow dynamics and coupling feedbacks between ice flow and RSL. We quantify the exact impact of ESA andGIA inclusion on grounding line evolution for large ice shelves such as the Ronne and Ross ice shelves, as well asthe Agasea Embayment ice streams, and demonstate how offline vs online RSL simulations diverge in the long run,and the consequences for predictions of sea-level rise.This work was performed at the California Institute of Technology's Jet Propulsion Laboratory undera contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

  11. Polarization holography

    DEFF Research Database (Denmark)

    Nikolova, L.; Ramanujam, P.S.

    Current research into holography is concerned with applications in optically storing, retrieving, and processing information. Polarization holography has many unique properties compared to conventional holography. It gives results in high efficiency, achromaticity, and special polarization...... properties. This books reviews the research carried out in this field over the last 15 years. The authors provide basic concepts in polarization and the propagation of light through anisotropic materials, before presenting a sound theoretical basis for polarization holography. The fabrication...... and characterization of azobenzene based materials, which remain the most efficient for the purpose, is described in detail. This is followed by a description of other materials that are used in polarization holography. An in-depth description of various applications, including display holography and optical storage...

  12. Joint Science Education Project: Learning about polar science in Greenland

    Science.gov (United States)

    Foshee Reed, Lynn

    2014-05-01

    The Joint Science Education Project (JSEP) is a successful summer science and culture opportunity in which students and teachers from the United States, Denmark, and Greenland come together to learn about the research conducted in Greenland and the logistics involved in supporting the research. They conduct experiments first-hand and participate in inquiry-based educational activities alongside scientists and graduate students at a variety of locations in and around Kangerlussuaq, Greenland, and on the top of the ice sheet at Summit Station. The Joint Committee, a high-level forum involving the Greenlandic, Danish and U.S. governments, established the Joint Science Education Project in 2007, as a collaborative diplomatic effort during the International Polar Year to: • Educate and inspire the next generation of polar scientists; • Build strong networks of students and teachers among the three countries; and • Provide an opportunity to practice language and communication skills Since its inception, JSEP has had 82 student and 22 teacher participants and has involved numerous scientists and field researchers. The JSEP format has evolved over the years into its current state, which consists of two field-based subprograms on site in Greenland: the Greenland-led Kangerlussuaq Science Field School and the U.S.-led Arctic Science Education Week. All travel, transportation, accommodations, and meals are provided to the participants at no cost. During the 2013 Kangerlussuaq Science Field School, students and teachers gathered data in a biodiversity study, created and set geo- and EarthCaches, calculated glacial discharge at a melt-water stream and river, examined microbes and tested for chemical differences in a variety of lakes, measured ablation at the edge of the Greenland Ice Sheet, and learned about fossils, plants, animals, minerals and rocks of Greenland. In addition, the students planned and led cultural nights, sharing food, games, stories, and traditions of

  13. Ice-sheet modelling accelerated by graphics cards

    Science.gov (United States)

    Brædstrup, Christian Fredborg; Damsgaard, Anders; Egholm, David Lundbek

    2014-11-01

    Studies of glaciers and ice sheets have increased the demand for high performance numerical ice flow models over the past decades. When exploring the highly non-linear dynamics of fast flowing glaciers and ice streams, or when coupling multiple flow processes for ice, water, and sediment, researchers are often forced to use super-computing clusters. As an alternative to conventional high-performance computing hardware, the Graphical Processing Unit (GPU) is capable of massively parallel computing while retaining a compact design and low cost. In this study, we present a strategy for accelerating a higher-order ice flow model using a GPU. By applying the newest GPU hardware, we achieve up to 180× speedup compared to a similar but serial CPU implementation. Our results suggest that GPU acceleration is a competitive option for ice-flow modelling when compared to CPU-optimised algorithms parallelised by the OpenMP or Message Passing Interface (MPI) protocols.

  14. The Sea-Ice Floe Size Distribution

    Science.gov (United States)

    Stern, H. L., III; Schweiger, A. J. B.; Zhang, J.; Steele, M.

    2017-12-01

    The size distribution of ice floes in the polar seas affects the dynamics and thermodynamics of the ice cover and its interaction with the ocean and atmosphere. Ice-ocean models are now beginning to include the floe size distribution (FSD) in their simulations. In order to characterize seasonal changes of the FSD and provide validation data for our ice-ocean model, we calculated the FSD in the Beaufort and Chukchi seas over two spring-summer-fall seasons (2013 and 2014) using more than 250 cloud-free visible-band scenes from the MODIS sensors on NASA's Terra and Aqua satellites, identifying nearly 250,000 ice floes between 2 and 30 km in diameter. We found that the FSD follows a power-law distribution at all locations, with a seasonally varying exponent that reflects floe break-up in spring, loss of smaller floes in summer, and the return of larger floes after fall freeze-up. We extended the results to floe sizes from 10 m to 2 km at selected time/space locations using more than 50 high-resolution radar and visible-band satellite images. Our analysis used more data and applied greater statistical rigor than any previous study of the FSD. The incorporation of the FSD into our ice-ocean model resulted in reduced sea-ice thickness, mainly in the marginal ice zone, which improved the simulation of sea-ice extent and yielded an earlier ice retreat. We also examined results from 17 previous studies of the FSD, most of which report power-law FSDs but with widely varying exponents. It is difficult to reconcile the range of results due to different study areas, seasons, and methods of analysis. We review the power-law representation of the FSD in these studies and discuss some mathematical details that are important to consider in any future analysis.

  15. Rebuttal of "Polar bear population forecasts: a public-policy forecasting audit"

    Science.gov (United States)

    Steven C. Amstrup; Hal Caswell; Eric DeWeaver; Ian Stirling; David C. Douglas; Bruce G. Marcot; Christine M. Hunter

    2009-01-01

    Observed declines in the Arctic sea ice have resulted in a variety of negative effects on polar bears (Ursus maritimus). Projections for additional future declines in sea ice resulted in a proposal to list polar bears as a threatened species under the United States Endangered Species Act. To provide information for the Department of the Interior...

  16. Dead-ice environments

    DEFF Research Database (Denmark)

    Krüger, Johannes; Kjær, Kurt H.; Schomacker, Anders

    2010-01-01

    glacier environment. The scientific challenges are to answer the key questions. What are the conditions for dead-ice formation? From which sources does the sediment cover originate? Which melting and reworking processes act in the ice-cored moraines? What is the rate of de-icing in the ice-cored moraines...

  17. Rate of ice accumulation during ice storms

    Energy Technology Data Exchange (ETDEWEB)

    Feknous, N. [SNC-Lavalin, Montreal, PQ (Canada); Chouinard, L. [McGill Univ., Montreal, PQ (Canada); Sabourin, G. [Hydro-Quebec, Montreal, PQ (Canada)

    2005-07-01

    The rate of glaze ice accumulation is the result of a complex process dependent on numerous meteorological and physical factors. The aim of this paper was to estimate the distribution rate of glaze ice accumulation on conductors in southern Quebec for use in the design of mechanical and electrical de-icing devices. The analysis was based on direct observations of ice accumulation collected on passive ice meters. The historical database of Hydro-Quebec, which contains observations at over 140 stations over period of 25 years, was used to compute accumulation rates. Data was processed so that each glaze ice event was numbered in a chronological sequence. Each event consisted of the time series of ice accumulations on each of the 8 cylinders of the ice meters, as well as on 5 of its surfaces. Observed rates were converted to represent the average ice on a 30 mm diameter conductor at 30 m above ground with a span of 300 m. Observations were corrected to account for the water content of the glaze ice as evidenced by the presence of icicles. Results indicated that despite significant spatial variations in the expected severity of ice storms as a function of location, the distribution function for rates of accumulation were fairly similar and could be assumed to be independent of location. It was concluded that the observations from several sites could be combined in order to obtain better estimates of the distribution of hourly rates of ice accumulation. However, the rates were highly variable. For de-icing strategies, it was suggested that average accumulation rates over 12 hour periods were preferable, and that analyses should be performed for other time intervals to account for the variability in ice accumulation rates over time. In addition, accumulation rates did not appear to be highly correlated with average wind speed for maximum hourly accumulation rates. 3 refs., 2 tabs., 10 figs.

  18. Ionic polarization

    International Nuclear Information System (INIS)

    Mahan, G.D.

    1992-01-01

    Ferroelectricity occurs in many different kinds of materials. Many of the technologically important solids, which are ferroelectric, can be classified as ionic. Any microscopic theory of ferroelectricity must contain a description of local polarization forces. We have collaborated in the development of a theory of ionic polarization which is quite successful. Its basic assumption is that the polarization is derived from the properties of the individual ions. We have applied this theory successfully to diverse subjects as linear and nonlinear optical response, phonon dispersion, and piezoelectricity. We have developed numerical methods using the local Density approximation to calculate the multipole polarizabilities of ions when subject to various fields. We have also developed methods of calculating the nonlinear hyperpolarizability, and showed that it can be used to explain light scattering experiments. This paper elaborates on this polarization theory

  19. Polarization experiments

    International Nuclear Information System (INIS)

    Halzen, F.

    1977-02-01

    In a theoretical review of polarization experiments two important points are emphasized: (a) their versatility and their relevance to a large variety of aspects of hadron physics (tests of basic symmetries; a probe of strong interaction dynamics; a tool for hadron spectroscopy); (b) the wealth of experimental data on polarization parameters in pp and np scattering in the Regge language and in the diffraction language. (author)

  20. CryoSat: ESA's Ice Explorer Mission: status and achievements

    Science.gov (United States)

    Parrinello, Tommaso; Mardle, Nicola; Hoyos Ortega, Berta; Bouzinac, Catherine; Badessi, Stefano; Frommknecht, Bjorn; Davidson, Malcolm; Fornari, Marco; Cullen, Robert

    2013-04-01

    CryoSat-2 was launched on the 8th April 2010 and it is the first European ice mission dedicated to monitoring precise changes in the thickness of polar ice sheets and floating sea ice over a 3-year period. Cryosat-2 carries an innovative radar altimeter called the Synthetic Aperture Interferometric Altimeter (SIRAL) with two antennas and with extended capabilities to meet the measurement requirements for ice-sheets elevation and sea-ice freeboard. Experimental evidence have shown that data is of high quality thanks to an altimeter that is behaving exceptional well within its design specifications. In April 2012, the first winter [2010 -2011] sea-ice variation map of the Arctic was released to the scientific community. Scope of this paper is to describe the current mission status and the main scientific achievements in the last twelve months. Topics will also include programmatic highlights and information on accessing Cryosat products following the new ESA Earth Observation Data Policy.

  1. Noise Prediction Module for Offset Stream Nozzles

    Science.gov (United States)

    Henderson, Brenda S.

    2011-01-01

    A Modern Design of Experiments (MDOE) analysis of data acquired for an offset stream technology was presented. The data acquisition and concept development were funded under a Supersonics NRA NNX07AC62A awarded to Dimitri Papamoschou at University of California, Irvine. The technology involved the introduction of airfoils in the fan stream of a bypass ratio (BPR) two nozzle system operated at transonic exhaust speeds. The vanes deflected the fan stream relative to the core stream and resulted in reduced sideline noise for polar angles in the peak jet noise direction. Noise prediction models were developed for a range of vane configurations. The models interface with an existing ANOPP module and can be used or future system level studies.

  2. Polarization measurement for internal polarized gaseous targets

    International Nuclear Information System (INIS)

    Ye Zhenyu; Ye Yunxiu; Lv Haijiang; Mao Yajun

    2004-01-01

    The authors present an introduction to internal polarized gaseous targets, polarization method, polarization measurement method and procedure. To get the total nuclear polarization of hydrogen atoms (including the polarization of the recombined hydrogen molecules) in the target cell, authors have measured the parameters relating to atomic polarization and polarized hydrogen atoms and molecules. The total polarization of the target during our measurement is P T =0.853 ± 0.036. (authors)

  3. Do pelagic grazers benefit from sea ice? Insights from the Antarctic sea ice proxy IPSO25

    Directory of Open Access Journals (Sweden)

    K. Schmidt

    2018-04-01

    Full Text Available Sea ice affects primary production in polar regions in multiple ways. It can dampen water column productivity by reducing light or nutrient supply, provide a habitat for ice algae and condition the marginal ice zone (MIZ for phytoplankton blooms on its seasonal retreat. The relative importance of three different carbon sources (sea ice derived, sea ice conditioned, non-sea-ice associated for the polar food web is not well understood, partly due to the lack of methods that enable their unambiguous distinction. Here we analysed two highly branched isoprenoid (HBI biomarkers to trace sea-ice-derived and sea-ice-conditioned carbon in Antarctic krill (Euphausia superba and relate their concentrations to the grazers' body reserves, growth and recruitment. During our sampling in January–February 2003, the proxy for sea ice diatoms (a di-unsaturated HBI termed IPSO25, δ13C  =  −12.5 ± 3.3 ‰ occurred in open waters of the western Scotia Sea, where seasonal ice retreat was slow. In suspended matter from surface waters, IPSO25 was present at a few stations close to the ice edge, but in krill the marker was widespread. Even at stations that had been ice-free for several weeks, IPSO25 was found in krill stomachs, suggesting that they gathered the ice-derived algae from below the upper mixed layer. Peak abundances of the proxy for MIZ diatoms (a tri-unsaturated HBI termed HBI III, δ13C  =  −42.2 ± 2.4 ‰ occurred in regions of fast sea ice retreat and persistent salinity-driven stratification in the eastern Scotia Sea. Krill sampled in the area defined by the ice edge bloom likewise contained high amounts of HBI III. As indicators for the grazer's performance we used the mass–length ratio, size of digestive gland and growth rate for krill, and recruitment for the biomass-dominant calanoid copepods Calanoides acutus and Calanus propinquus. These indices consistently point to blooms in the MIZ as an important feeding

  4. Buried and Massive Ground Ice on the West Coast of Baidaratskaya Bay in the Kara Sea

    Directory of Open Access Journals (Sweden)

    N. G. Belova

    2015-01-01

    Full Text Available Using data on the structure, conditions of occurrence (bedding, and the isotope composition of massive ice beds on the West coast of Baydaratskaya Bay it was established that the massive ice beds even occurring in the same outcrop may be related to different genetic types. There are two groups of the massive ice: 1 the «upper» thick (> 3 m massive ice beds composed by buried basal glacier ice; and 2 the «lower» small ice beds (< 3 m, formed both intrasedimentally and as a result of burial of initially surface ice bodies. Sand thickness which included both groups of the massive ice started its formation before the glacial ice burial. As a result of advancing and later degradation of the glacier, probably moving from the Pay-Khoy ridge or from the Polar Ural, its lower (basal parts were preserved within the permafrost thickness. 

  5. Journey to the centre of the ice

    DEFF Research Database (Denmark)

    Hvenegård-Lassen, Kirsten

    2016-01-01

    to the Eemian period. This time travel ultimately aims at predicting the climate of the future. While the heroic polar expeditions of the past ventured into unknown spaces horizontally, the secrets of the frontier are now vertically stored in the ice cores. In Secrets of the Ice, five videos produced for public...... dissemination, Greenland is displayed as an empty, frozen space, waiting to be conquered by scientists. Resonating with classical Arctic explorer myths, this conquest has to overcome the difficulties presented by a harsh wilderness landscape. The article situates the glaciological project in Greenland within...

  6. Investigations of the form and flow of ice sheets and glaciers using radio-echo sounding

    Energy Technology Data Exchange (ETDEWEB)

    Dowdeswell, J A; Evans, S [Scott Polar Research Institute, University of Cambridge, Cambridge CB2 1ER (United Kingdom)

    2004-10-01

    Radio-echo sounding (RES), utilizing a variety of radio frequencies, was developed to allow glaciologists to measure the thickness of ice sheets and glaciers. We review the nature of electromagnetic wave propagation in ice and snow, including the permittivity of ice, signal attenuation and volume scattering, along with reflection from rough and specular surfaces. The variety of instruments used in RES of polar ice sheets and temperate glaciers is discussed. The applications and insights that a knowledge of ice thickness, and the wider nature of the form and flow of ice sheets, provides are also considered. The thickest ice measured is 4.7 km in East Antarctica. The morphology of the Antarctic and Greenland ice sheets, and many of the smaller ice caps and glaciers of the polar regions, has been investigated using RES. These findings are being used in three-dimensional numerical models of the response of the cryosphere to environmental change. In addition, the distribution and character of internal and basal reflectors within ice sheets contains information on, for example, ice-sheet layering and its chrono-stratigraphic significance, and has enabled the discovery and investigation of large lakes beneath the Antarctic Ice Sheet. Today, RES from ground-based and airborne platforms remains the most effective tool for measuring ice thickness and internal character.

  7. Atmospheric forcing of sea ice leads in the Beaufort Sea

    Science.gov (United States)

    Lewis, B. J.; Hutchings, J.; Mahoney, A. R.; Shapiro, L. H.

    2016-12-01

    Leads in sea ice play an important role in the polar marine environment where they allow heat and moisture transfer between the oceans and atmosphere and act as travel pathways for both marine mammals and ships. Examining AVHRR thermal imagery of the Beaufort Sea, collected between 1994 and 2010, sea ice leads appear in repeating patterns and locations (Eicken et al 2005). The leads, resolved by AVHRR, are at least 250m wide (Mahoney et al 2012), thus the patterns described are for lead systems that extend up to hundreds of kilometers across the Beaufort Sea. We describe how these patterns are associated with the location of weather systems relative to the coastline. Mean sea level pressure and 10m wind fields from ECMWF ERA-Interim reanalysis are used to identify if particular lead patterns can be uniquely forecast based on the location of weather systems. Ice drift data from the NSIDC's Polar Pathfinder Daily 25km EASE-Grid Sea Ice Motion Vectors indicates the role shear along leads has on the motion of ice in the Beaufort Gyre. Lead formation is driven by 4 main factors: (i) coastal features such as promontories and islands influence the origin of leads by concentrating stresses within the ice pack; (ii) direction of the wind forcing on the ice pack determines the type of fracture, (iii) the location of the anticyclone (or cyclone) center determines the length of the fracture for certain patterns; and (iv) duration of weather conditions affects the width of the ice fracture zones. Movement of the ice pack on the leeward side of leads originating at promontories and islands increases, creating shear zones that control ice transport along the Alaska coast in winter. . Understanding how atmospheric conditions influence the large-scale motion of the ice pack is needed to design models that predict variability of the gyre and export of multi-year ice to lower latitudes.

  8. Mass Loss Rates of Fasting Polar Bears.

    Science.gov (United States)

    Pilfold, Nicholas W; Hedman, Daryll; Stirling, Ian; Derocher, Andrew E; Lunn, Nicholas J; Richardson, Evan

    2016-01-01

    Polar bears (Ursus maritimus) have adapted to an annual cyclic regime of feeding and fasting, which is extreme in seasonal sea ice regions of the Arctic. As a consequence of climate change, sea ice breakup has become earlier and the duration of the open-water period through which polar bears must rely on fat reserves has increased. To date, there is limited empirical data with which to evaluate the potential energetic capacity of polar bears to withstand longer fasts. We measured the incoming and outgoing mass of inactive polar bears (n = 142) that were temporarily detained by Manitoba Conservation and Water Stewardship during the open-water period near the town of Churchill, Manitoba, Canada, in 2009-2014. Polar bears were given access to water but not food and held for a median length of 17 d. Median mass loss rates were 1.0 kg/d, while median mass-specific loss rates were 0.5%/d, similar to other species with high adiposity and prolonged fasting capacities. Mass loss by unfed captive adult males was identical to that lost by free-ranging individuals, suggesting that terrestrial feeding contributes little to offset mass loss. The inferred metabolic rate was comparable to a basal mammalian rate, suggesting that while on land, polar bears can maintain a depressed metabolic rate to conserve energy. Finally, we estimated time to starvation for subadults and adult males for the on-land period. Results suggest that at 180 d of fasting, 56%-63% of subadults and 18%-24% of adult males in this study would die of starvation. Results corroborate previous assessments on the limits of polar bear capacity to withstand lengthening ice-free seasons and emphasize the greater sensitivity of subadults to changes in sea ice phenology.

  9. Ross Ice Shelf, Antarctic Ice and Clouds

    Science.gov (United States)

    1991-01-01

    In this view of Antarctic ice and clouds, (56.5S, 152.0W), the Ross Ice Shelf of Antarctica is almost totally clear, showing stress cracks in the ice surface caused by wind and tidal drift. Clouds on the eastern edge of the picture are associated with an Antarctic cyclone. Winds stirred up these storms have been known to reach hurricane force.

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

    OpenAIRE

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

    2015-01-01

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

  11. Considering polarization in MODIS-based cloud property retrievals by using a vector radiative transfer code

    International Nuclear Information System (INIS)

    Yi, Bingqi; Huang, Xin; Yang, Ping; Baum, Bryan A.; Kattawar, George W.

    2014-01-01

    In this study, a full-vector, adding–doubling radiative transfer model is used to investigate the influence of the polarization state on cloud property retrievals from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations. Two sets of lookup tables (LUTs) are developed for the retrieval purposes, both of which provide water cloud and ice cloud reflectivity functions at two wavelengths in various sun-satellite viewing geometries. However, only one of the LUTs considers polarization. The MODIS reflectivity observations at 0.65 μm (band 1) and 2.13 μm (band 7) are used to infer the cloud optical thickness and particle effective diameter, respectively. Results indicate that the retrievals for both water cloud and ice cloud show considerable sensitivity to polarization. The retrieved water and ice cloud effective diameter and optical thickness differences can vary by as much as ±15% due to polarization state considerations. In particular, the polarization state has more influence on completely smooth ice particles than on severely roughened ice particles. - Highlights: • Impact of polarization on satellite-based retrieval of water/ice cloud properties is studied. • Inclusion of polarization can change water/ice optical thickness and effective diameter values by up to ±15%. • Influence of polarization on cloud property retrievals depends on sun-satellite viewing geometries

  12. Sources of polarized neutrons

    International Nuclear Information System (INIS)

    Walter, L.

    1983-01-01

    Various sources of polarized neutrons are reviewed. Monoenergetic source produced with unpolarized or polarized beams, white sources of polarized neutrons, production by transmissions through polarized hydrogen targets and polarized thermal neutronsare discussed, with appropriate applications included. (U.K.)

  13. How reversible is sea ice loss?

    Directory of Open Access Journals (Sweden)

    J. K. Ridley

    2012-02-01

    Full Text Available It is well accepted that increasing atmospheric CO2 results in global warming, leading to a decline in polar sea ice area. Here, the specific question of whether there is a tipping point in the sea ice cover is investigated. The global climate model HadCM3 is used to map the trajectory of sea ice area under idealised scenarios. The atmospheric CO2 is first ramped up to four times pre-industrial levels (4 × CO2, then ramped down to pre-industrial levels. We also examine the impact of stabilising climate at 4 × CO2 prior to ramping CO2 down to pre-industrial levels. Against global mean temperature, Arctic sea ice area is reversible, while the Antarctic sea ice shows some asymmetric behaviour – its rate of change slower, with falling temperatures, than its rate of change with rising temperatures. However, we show that the asymmetric behaviour is driven by hemispherical differences in temperature change between transient and stabilisation periods. We find no irreversible behaviour in the sea ice cover.

  14. First Results from IceCube

    International Nuclear Information System (INIS)

    Klein, Spencer R.

    2006-01-01

    IceCube is a 1 km 3 neutrino observatory being built to study neutrino production in active galactic nuclei, gamma-ray bursts, supernova remnants, and a host of other astrophysical sources. High-energy neutrinos may signal the sources of ultra-high energy cosmic rays. IceCube will also study many particle-physics topics: searches for WIMP annihilation in the Earth or the Sun, and for signatures of supersymmetry in neutrino interactions, studies of neutrino properties, including searches for extra dimensions, and searches for exotica such as magnetic monopoles or Q-balls. IceCube will also study the cosmic-ray composition. In January, 2005, 60 digital optical modules (DOMs) were deployed in the South Polar ice at depths ranging from 1450 to 2450 meters, and 8 ice-tanks, each containing 2 DOMs were deployed as part of a surface air-shower array. All 76 DOMs are collecting high-quality data. After discussing the IceCube physics program and hardware, I will present some initial results with the first DOMs

  15. The greenhouse effect and the Arctic ice

    International Nuclear Information System (INIS)

    Groenaas, Sigbjoern

    2002-01-01

    The impact on the Arctic ice of global warming is important for many people and for the environment. Less ice means changed conditions for the Inuits, hard times for the polar bears and changed conditions for the fishing sector. There is at present some uncertainty about the thickness of the ice and what might be the cause of its oscillation. It was reported a few years ago that the thickness of the ice had almost been reduced by 50 per cent since the 1950s and some researchers suggested that within a few decades the ice would disappear during the summer. These measurements have turned out not to be representative for the whole Arctic region, and it now appears that a great deal of the measured thickness variation can be attributed to changes in the atmospheric circulation. The article discusses the Arctic Oscillation and the North Atlantic Oscillation in relation to the ice thickness, and climate models. Feedback mechanisms such as reduced albedo may have a big impact in the Arctic in a global greenhouse warming. Model simulations are at variance, and the scenarios for the future are uncertain

  16. The impact of atmospheric mineral aerosol deposition on the albedo of snow and sea ice: are snow and sea ice optical properties more important than mineral aerosol optical properties?

    OpenAIRE

    M. L. Lamare; J. Lee-Taylor; M. D. King

    2015-01-01

    Knowledge of the albedo of polar regions is crucial for understanding a range of climatic processes that have an impact on a global scale. Light absorbing impurities in atmospheric aerosols deposited on snow and sea ice by aeolian transport absorb solar radiation, reducing albedo. Here, the effects of five mineral aerosol deposits reducing the albedo of polar snow and sea ice are considered. Calculations employing a coupled atmospheric and snow/sea ice radiative-transfer model (TUV-snow) show...

  17. New age constraints for the Saalian glaciation in northern central Europe: Implications for the extent of ice sheets and related proglacial lake systems

    Science.gov (United States)

    Lang, Jörg; Lauer, Tobias; Winsemann, Jutta

    2018-01-01

    A comprehensive palaeogeographic reconstruction of ice sheets and related proglacial lake systems for the older Saalian glaciation in northern central Europe is presented, which is based on the integration of palaeo-ice flow data, till provenance, facies analysis, geomorphology and new luminescence ages of ice-marginal deposits. Three major ice advances with different ice-advance directions and source areas are indicated by palaeo-ice flow directions and till provenance. The first ice advance was characterised by a southwards directed ice flow and a dominance of clasts derived from southern Sweden. The second ice advance was initially characterised by an ice flow towards the southwest. Clasts are mainly derived from southern and central Sweden. The latest stage in the study area (third ice advance) was characterised by ice streaming (Hondsrug ice stream) in the west and a re-advance in the east. Clasts of this stage are mainly derived from eastern Fennoscandia. Numerical ages for the first ice advance are sparse, but may indicate a correlation with MIS 8 or early MIS 6. New pIRIR290 luminescence ages of ice-marginal deposits attributed to the second ice advance range from 175 ± 10 to 156 ± 24 ka and correlate with MIS 6. The ice sheets repeatedly blocked the main river-drainage pathways and led to the formation of extensive ice-dammed lakes. The formation of proglacial lakes was mainly controlled by ice-damming of river valleys and major bedrock spillways; therefore the lake levels and extends were very similar throughout the repeated ice advances. During deglaciation the lakes commonly increased in size and eventually drained successively towards the west and northwest into the Lower Rhine Embayment and the North Sea. Catastrophic lake-drainage events occurred when large overspill channels were suddenly opened. Ice-streaming at the end of the older Saalian glaciation was probably triggered by major lake-drainage events.

  18. Improving Arctic Sea Ice Observations and Data Access to Support Advances in Sea Ice Forecasting

    Science.gov (United States)

    Farrell, S. L.

    2017-12-01

    The economic and strategic importance of the Arctic region is becoming apparent. One of the most striking and widely publicized changes underway is the declining sea ice cover. Since sea ice is a key component of the climate system, its ongoing loss has serious, and wide-ranging, socio-economic implications. Increasing year-to-year variability in the geographic location, concentration, and thickness of the Arctic ice cover will pose both challenges and opportunities. The sea ice research community must be engaged in sustained Arctic Observing Network (AON) initiatives so as to deliver fit-for-purpose remote sensing data products to a variety of stakeholders including Arctic communities, the weather forecasting and climate modeling communities, industry, local, regional and national governments, and policy makers. An example of engagement is the work currently underway to improve research collaborations between scientists engaged in obtaining and assessing sea ice observational data and those conducting numerical modeling studies and forecasting ice conditions. As part of the US AON, in collaboration with the Interagency Arctic Research Policy Committee (IARPC), we are developing a strategic framework within which observers and modelers can work towards the common goal of improved sea ice forecasting. Here, we focus on sea ice thickness, a key varaible of the Arctic ice cover. We describe multi-sensor, and blended, sea ice thickness data products under development that can be leveraged to improve model initialization and validation, as well as support data assimilation exercises. We will also present the new PolarWatch initiative (polarwatch.noaa.gov) and discuss efforts to advance access to remote sensing satellite observations and improve communication with Arctic stakeholders, so as to deliver data products that best address societal needs.

  19. Breaking Ice 2: A rift system on the Ross Ice Shelf as an analog for tidal tectonics on icy moons

    Science.gov (United States)

    Brunt, K. M.; Hurford, T., Jr.; Schmerr, N. C.; Sauber, J. M.; MacAyeal, D. R.

    2016-12-01

    Ice shelves are the floating regions of the polar ice sheets. Outside of the influence of the narrow region of their grounding zone, they are fully hydrostatic and strongly influenced by the ocean tides. Recent observational and modeling studies have assessed the effect of tides on ice shelves, including: the tidal influence on the ice-shelf surface height, which changes by as much as 6 to 7 m on the southern extreme of the Ronne-Filchner Ice Shelf; the tidal modulation of the ice-shelf horizontal flow velocities, which changes the mean ice-flow rate by as much as two fold on the Ross Ice Shelf; and the tidal contribution to fracture and rift propagation, which eventually leads to iceberg calving. Here, we present the analysis of 16 days of continuous GPS data from a rift system near the front of the Ross Ice Shelf. While the GPS sites were installed for a different scientific investigation, and not optimized to assess tidal rifting mechanics, they provide a first-order sense of the tidal evolution of the rift system. These analyses can be used as a terrestrial analog for tidal activity on icy satellites, such as Europa and Enceladus, moons of Jupiter and Saturn, respectively. Using remote sensing and modeling of the Ross Ice Shelf rift system, we can investigate the geological processes observed on icy satellites and advance modeling efforts of their tidal-tectonic evolution.

  20. Forecast Icing Product

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Forecast Icing Product (FIP) is an automatically-generated index suitable for depicting areas of potentially hazardous airframe icing. The FIP algorithm uses...

  1. Current Icing Product

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Current Icing Product (CIP) is an automatically-generated index suitable for depicting areas of potentially hazardous airframe icing. The CIP algorithm combines...

  2. Evaluation of the limit ice thickness for the hull of various Finnish-Swedish ice class vessels navigating in the Russian Arctic

    OpenAIRE

    Pentti Kujala; Mihkel Kõrgesaar; Jorma Kämäräinen

    2018-01-01

    Selection of suitable ice class for ships operation is an important but not simple task. The increased exploitation of the Polar waters, both seasonal periods and geographical areas, as well as the introduction of new international design standards such as Polar Code, reduces the relevancy of using existing experience as basis for the selection, and new methods and knowledge have to be developed. This paper will analyse what can be the limiting ice thickness for ships navigating in the Russia...

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

    Science.gov (United States)

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

    2017-12-01

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

  4. On the retrieval of ice cloud particle shapes from POLDER measurements

    International Nuclear Information System (INIS)

    Sun Wenbo; Loeb, Norman G.; Yang Ping

    2006-01-01

    Shapes of ice crystals can significantly affect the radiative transfer in ice clouds. The angular distribution of the polarized reflectance over ice clouds strongly depends on ice crystal shapes. Although the angular-distribution features of the total or polarized reflectance over ice clouds imply a possibility of retrieving ice cloud particle shapes by use of remote sensing data, the accuracy of the retrieval must be evaluated. In this study, a technique that applies single ice crystal habit and multidirectional polarized radiance to retrieve ice cloud particle shapes is assessed. Our sensitivity studies show that the retrieved particle shapes from this algorithm can be considered good approximations to those in actual clouds in calculation of the phase matrix elements. However, this algorithm can only work well under the following conditions: (1) the retrievable must be overcast and thick ice cloud pixels, (2) the particles in the cloud must be randomly oriented, (3) the particle shapes and size distributions used in the lookup tables must be representative, and (4) the multi-angle polarized measurements must be accurate and sufficient to identify ice cloud pixels of randomly oriented particles. In practice, these conditions will exclude most of the measured cloud pixels. Additionally, because the polarized measurements are only sensitive to the upper cloud part not deeper than an optical thickness of 4, the retrieved particle shapes with the polarized radiance may only approximate those in the upper parts of the clouds. In other words, for thicker clouds with vertical inhomogeneity in particle shapes, these retrieved particle shapes cannot represent those of whole clouds. More robust algorithm is needed in accurate retrieval of ice cloud particle shapes

  5. Sputtering of water ice

    International Nuclear Information System (INIS)

    Baragiola, R.A.; Vidal, R.A.; Svendsen, W.; Schou, J.; Shi, M.; Bahr, D.A.; Atteberrry, C.L.

    2003-01-01

    We present results of a range of experiments of sputtering of water ice together with a guide to the literature. We studied how sputtering depends on the projectile energy and fluence, ice growth temperature, irradiation temperature and external electric fields. We observed luminescence from the decay of H(2p) atoms sputtered by heavy ion impact, but not bulk ice luminescence. Radiolyzed ice does not sputter under 3.7 eV laser irradiation

  6. A method for separating Antarctic postglacial rebound and ice mass balance using future ICESat Geoscience Laser Altimeter System, Gravity Recovery and Climate Experiment, and GPS satellite data

    OpenAIRE

    Velicogna, Isabella; Wahr, John

    2002-01-01

    Measurements of ice elevation from the Geoscience Laser Altimeter System (GLAS) aboard the Ice, Cloud, and Land Elevation Satellite can be combined with time-variable geoid measurements from the Gravity Recovery and Climate Experiment (GRACE) satellite mission to learn about ongoing changes in polar ice mass and viscoelastic rebound of the lithosphere under the ice sheet. We estimate the accuracy in recovering the spatially varying ice mass trend and postglacial rebound signals for Antarctica...

  7. Sea and Freshwater Ice Concentration from VIIRS on Suomi NPP and the Future JPSS Satellites

    Directory of Open Access Journals (Sweden)

    Yinghui Liu

    2016-06-01

    Full Text Available Information on ice is important for shipping, weather forecasting, and climate monitoring. Historically, ice cover has been detected and ice concentration has been measured using relatively low-resolution space-based passive microwave data. This study presents an algorithm to detect ice and estimate ice concentration in clear-sky areas over the ocean and inland lakes and rivers using high-resolution data from the Visible Infrared Imaging Radiometer Suite (VIIRS onboard the Suomi National Polar Orbiting Partnership (S-NPP and on future Joint Polar Satellite System (JPSS satellites, providing spatial detail that cannot be obtained with passive microwave data. A threshold method is employed with visible and infrared observations to identify ice, then a tie-point algorithm is used to determine the representative reflectance/temperature of pure ice, estimate the ice concentration, and refine the ice cover mask. The VIIRS ice concentration is validated using observations from Landsat 8. Results show that VIIRS has an overall bias of −0.3% compared to Landsat 8 ice concentration, with a precision (uncertainty of 9.5%. Biases and precision values for different ice concentration subranges from 0% to 100% can be larger.

  8. StreamCat

    Data.gov (United States)

    U.S. Environmental Protection Agency — The StreamCat Dataset provides summaries of natural and anthropogenic landscape features for ~2.65 million streams, and their associated catchments, within the...

  9. Prioritized Contact Transport Stream

    Science.gov (United States)

    Hunt, Walter Lee, Jr. (Inventor)

    2015-01-01

    A detection process, contact recognition process, classification process, and identification process are applied to raw sensor data to produce an identified contact record set containing one or more identified contact records. A prioritization process is applied to the identified contact record set to assign a contact priority to each contact record in the identified contact record set. Data are removed from the contact records in the identified contact record set based on the contact priorities assigned to those contact records. A first contact stream is produced from the resulting contact records. The first contact stream is streamed in a contact transport stream. The contact transport stream may include and stream additional contact streams. The contact transport stream may be varied dynamically over time based on parameters such as available bandwidth, contact priority, presence/absence of contacts, system state, and configuration parameters.

  10. Polarization study

    International Nuclear Information System (INIS)

    Nurushev, S.B.

    1989-01-01

    Brief review is presented of the high energy polarization study including experimental data and the theoretical descriptions. The mostimportant proposals at the biggest accelerators and the crucial technical developments are also listed which may become a main-line of spin physics. 35 refs.; 10 figs.; 4 tabs

  11. Productivity of Stream Definitions

    NARCIS (Netherlands)

    Endrullis, Jörg; Grabmayer, Clemens; Hendriks, Dimitri; Isihara, Ariya; Klop, Jan

    2007-01-01

    We give an algorithm for deciding productivity of a large and natural class of recursive stream definitions. A stream definition is called ‘productive’ if it can be evaluated continuously in such a way that a uniquely determined stream is obtained as the limit. Whereas productivity is undecidable

  12. Productivity of stream definitions

    NARCIS (Netherlands)

    Endrullis, J.; Grabmayer, C.A.; Hendriks, D.; Isihara, A.; Klop, J.W.

    2008-01-01

    We give an algorithm for deciding productivity of a large and natural class of recursive stream definitions. A stream definition is called ‘productive’ if it can be evaluated continually in such a way that a uniquely determined stream in constructor normal form is obtained as the limit. Whereas

  13. The effect of sea ice on the solar energy budget in the astmosphere-sea ice-ocean system: A model study

    Science.gov (United States)

    Jin, Z.; Stamnes, Knut; Weeks, W. F.; Tsay, Si-Chee

    1994-01-01

    A coupled one-dimensional multilayer and multistream radiative transfer model has been developed and applied to the study of radiative interactions in the atmosphere, sea ice, and ocean system. The consistent solution of the radiative transfer equation in this coupled system automatically takes into account the refraction and reflection at the air-ice interface and allows flexibility in choice of stream numbers. The solar radiation spectrum (0.25 micron-4.0 micron) is divided into 24 spectral bands to account adequately for gaseous absorption in the atmosphere. The effects of ice property changes, including salinity and density variations, as well as of melt ponds and snow cover variations over the ice on the solar energy distribution in the entire system have been studied quantitatively. The results show that for bare ice it is the scattering, determined by air bubbles and brine pockets, in just a few centimeters of the top layer of ice that plays the most important role in the solar energy absorption and partitioning in the entire system. Ice thickness is important to the energy distribution only when the ice is thin, while the absorption in the atmosphere is not sensitive to ice thickness exceeds about 70 cm. The presence of clouds moderates all the sensitivities of the absorptive amounts in each layer to the variations in the ice properties and ice thickness. Comparisons with observational spectral albedo values for two simple ice types are also presented.

  14. Cloud and surface textural features in polar regions

    Science.gov (United States)

    Welch, Ronald M.; Kuo, Kwo-Sen; Sengupta, Sailes K.

    1990-01-01

    The study examines the textural signatures of clouds, ice-covered mountains, solid and broken sea ice and floes, and open water. The textural features are computed from sum and difference histogram and gray-level difference vector statistics defined at various pixel displacement distances derived from Landsat multispectral scanner data. Polar cloudiness, snow-covered mountainous regions, solid sea ice, glaciers, and open water have distinguishable texture features. This suggests that textural measures can be successfully applied to the detection of clouds over snow-covered mountains, an ability of considerable importance for the modeling of snow-melt runoff. However, broken stratocumulus cloud decks and thin cirrus over broken sea ice remain difficult to distinguish texturally. It is concluded that even with high spatial resolution imagery, it may not be possible to distinguish broken stratocumulus and thin clouds from sea ice in the marginal ice zone using the visible channel textural features alone.

  15. The color of melt ponds on Arctic sea ice

    Science.gov (United States)

    Lu, Peng; Leppäranta, Matti; Cheng, Bin; Li, Zhijun; Istomina, Larysa; Heygster, Georg

    2018-04-01

    Pond color, which creates the visual appearance of melt ponds on Arctic sea ice in summer, is quantitatively investigated using a two-stream radiative transfer model for ponded sea ice. The upwelling irradiance from the pond surface is determined and then its spectrum is transformed into RGB (red, green, blue) color space using a colorimetric method. The dependence of pond color on various factors such as water and ice properties and incident solar radiation is investigated. The results reveal that increasing underlying ice thickness Hi enhances both the green and blue intensities of pond color, whereas the red intensity is mostly sensitive to Hi for thin ice (Hi 1.5 m), similar to the behavior of melt-pond albedo. The distribution of the incident solar spectrum F0 with wavelength affects the pond color rather than its intensity. The pond color changes from dark blue to brighter blue with increasing scattering in ice, and the influence of absorption in ice on pond color is limited. The pond color reproduced by the model agrees with field observations for Arctic sea ice in summer, which supports the validity of this study. More importantly, the pond color has been confirmed to contain information about meltwater and underlying ice, and therefore it can be used as an index to retrieve Hi and Hp. Retrievals of Hi for thin ice (Hi measurements than retrievals for thick ice, but those of Hp are not good. The analysis of pond color is a new potential method to obtain thin ice thickness in summer, although more validation data and improvements to the radiative transfer model will be needed in future.

  16. Implications of rapid environmental change for polar bear behavior and sociality

    Science.gov (United States)

    Atwood, Todd C.

    2017-01-01

    Historically, the Arctic sea ice has functioned as a structural barrier that has limited the nature and extent of interactions between humans and polar bears (Ursus maritimus). However, declining sea ice extent, brought about by global climate change, is increasing the potential for human-polar bear interactions. Loss of sea ice habitat is driving changes to both human and polar bear behavior—it is facilitating increases in human activities (e.g., offshore oil and gas exploration and extraction, trans-Arctic shipping, recreation), while also causing the displacement of bears from preferred foraging habitat (i.e., sea ice over biologically productive shallow) to land in some portions of their range. The end result of these changes is that polar bears are spending greater amounts of time in close proximity to people. Coexistence between humans and polar bears will require imposing mechanisms to manage further development, as well as mitigation strategies that reduce the burden to local communities.

  17. Helicopter Icing Review.

    Science.gov (United States)

    1980-09-01

    helicopter (i.e. in an icing tunnel or engine test cell ) and therefore can be subjected to controlled icing where spe- cific problems can be safely...evaluation. 69 2.2.5.2 Ice Protection Systems Demonstration Many of the systems noted in 2.2.5.1 can be evaluated in icing test cells or icing wind tunnels...Figure 2-32 illustrates a typical rotor deice system control arrangement. 104 (N >4 A.dO INaH -E- C4) uo U En 9 E-1 H m I ~z O 04 04iH U 0 El4 E-f C E

  18. Evidence of recent changes in the ice regime of lakes in the Canadian High Arctic from spaceborne satellite observations

    Science.gov (United States)

    Surdu, Cristina M.; Duguay, Claude R.; Fernández Prieto, Diego

    2016-05-01

    Arctic lakes, through their ice cover phenology, are a key indicator of climatic changes that the high-latitude environment is experiencing. In the case of lakes in the Canadian Arctic Archipelago (CAA), many of which are ice covered more than 10 months per year, warmer temperatures could result in ice regime shifts. Within the dominant polar-desert environment, small local warmer areas have been identified. These relatively small regions - polar oases - with longer growing seasons and greater biological productivity and diversity are secluded from the surrounding barren polar desert. The ice regimes of 11 lakes located in both polar-desert and polar-oasis environments, with surface areas between 4 and 542 km2, many of unknown bathymetry, were documented. In order to investigate the response of ice cover of lakes in the CAA to climate conditions during recent years, a 15-year time series (1997-2011) of RADARSAT-1/2 ScanSAR Wide Swath, ASAR Wide Swath, and Landsat acquisitions were analyzed. Results show that melt onset occurred earlier for all observed lakes. With the exception of Lower Murray Lake, all lakes experienced earlier summer ice minimum and water-clear-of-ice (WCI) dates, with greater changes being observed for polar-oasis lakes (9-24 days earlier WCI dates for lakes located in polar oases and 2-20 days earlier WCI dates for polar-desert lakes). Additionally, results suggest that some lakes may be transitioning from a perennial/multiyear to a seasonal ice regime, with only a few lakes maintaining a multiyear ice cover on occasional years. Aside Lake Hazen and Murray Lakes, which preserved their ice cover during the summer of 2009, no residual ice was observed on any of the other lakes from 2007 to 2011.

  19. AURA-A radio frequency extension to IceCube

    International Nuclear Information System (INIS)

    Landsman, H.; Ruckman, L.; Varner, G.S.

    2009-01-01

    The excellent radio frequency (RF) transparency of cold polar ice, combined with the coherent Cherenkov emission produced by neutrino-induced showers when viewed at wavelengths longer than a few centimeters, has spurred considerable interest in a large-scale radio-wave neutrino detector array. The AURA (Askaryan Under-ice Radio Array) experimental effort, within the IceCube collaboration, seeks to take advantage of the opportunity presented by IceCube [A. Karle, Nucl. Instr. and Meth. A (2009), this issue, doi: (10.1016/j.nima.2009.03.180).; A. Achtenberg et al., The IceCube Collaboration, Astropart. Phys. 26 (2006) 155 ] drilling through 2010 to establish the RF technology needed to achieve 100-1000km 3 effective volumes. In the 2006-2007 Austral summer, three deep in-ice RF clusters were deployed at depths of ∼1300 and ∼300m on top of the IceCube strings. Additional three clusters will be deployed in the Austral summer of 2008-2009. Verification and calibration results from the current deployed clusters are presented, and the detector design and performances are discussed. Augmentation of IceCube with large-scale (1000km 3 sr) radio and acoustic arrays would extend the physics reach of IceCube into the EeV-ZeV regime and offer substantial technological redundancy.

  20. Complex yet translucent: the optical properties of sea ice

    International Nuclear Information System (INIS)

    Perovich, Donald K.

    2003-01-01

    Sea ice is a naturally occurring material with an intricate and highly variable structure consisting of ice platelets, brine pockets, air bubbles, and precipitated salt crystals. The optical properties of sea ice are directly dependent on this ice structure. Because sea ice is a material that exists at its salinity determined freezing point, its structure and optical properties are significantly affected by small changes in temperature. Understanding the interaction of sunlight with sea ice is important to a diverse array of scientific problems, including those in polar climatology. A key optical parameter for climatological studies is the albedo, the fraction of the incident sunlight that is reflected. The albedo of sea ice is quite sensitive to surface conditions. The presence of a snow cover enhances the albedo, while surface meltwater reduces the albedo. Radiative transfer in sea ice is a combination of absorption and scattering. Differences in the magnitude of sea ice optical properties are ascribable primarily to differences in scattering, while spectral variations are mainly a result of absorption. Physical changes that enhance scattering, such as the formation of air bubbles due to brine drainage, result in more light reflection and less transmission

  1. Ice slurry applications

    Energy Technology Data Exchange (ETDEWEB)

    Kauffeld, M. [Karlsruhe University of Applied Sciences, Moltkestr. 30, 76133 Karlsruhe (Germany); Wang, M.J.; Goldstein, V. [Sunwell Technologies Inc., 180 Caster Avenue, Woodbridge, L4L 5Y (Canada); Kasza, K.E. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States)

    2010-12-15

    The role of secondary refrigerants is expected to grow as the focus on the reduction of greenhouse gas emissions increases. The effectiveness of secondary refrigerants can be improved when phase changing media are introduced in place of single-phase media. Operating at temperatures below the freezing point of water, ice slurry facilitates several efficiency improvements such as reductions in pumping energy consumption as well as lowering the required temperature difference in heat exchangers due to the beneficial thermo-physical properties of ice slurry. Research has shown that ice slurry can be engineered to have ideal ice particle characteristics so that it can be easily stored in tanks without agglomeration and then be extractable for pumping at very high ice fraction without plugging. In addition ice slurry can be used in many direct contact food and medical protective cooling applications. This paper provides an overview of the latest developments in ice slurry technology. (author)

  2. Autonomous Aerial Ice Observation for Ice Defense

    Directory of Open Access Journals (Sweden)

    Joakim Haugen

    2014-10-01

    Full Text Available One of the tasks in ice defense is to gather information about the surrounding ice environment using various sensor platforms. In this manuscript we identify two monitoring tasks known in literature, namely dynamic coverage and target tracking, and motivate how these tasks are relevant in ice defense using RPAS. An optimization-based path planning concept is outlined for solving these tasks. A path planner for the target tracking problem is elaborated in more detail and a hybrid experiment, which consists of both a real fixed-wing aircraft and simulated objects, is included to show the applicability of the proposed framework.

  3. Arctic landfast sea ice

    Science.gov (United States)

    Konig, Christof S.

    Landfast ice is sea ice which forms and remains fixed along a coast, where it is attached either to the shore, or held between shoals or grounded icebergs. Landfast ice fundamentally modifies the momentum exchange between atmosphere and ocean, as compared to pack ice. It thus affects the heat and freshwater exchange between air and ocean and impacts on the location of ocean upwelling and downwelling zones. Further, the landfast ice edge is essential for numerous Arctic mammals and Inupiat who depend on them for their subsistence. The current generation of sea ice models is not capable of reproducing certain aspects of landfast ice formation, maintenance, and disintegration even when the spatial resolution would be sufficient to resolve such features. In my work I develop a new ice model that permits the existence of landfast sea ice even in the presence of offshore winds, as is observed in mature. Based on viscous-plastic as well as elastic-viscous-plastic ice dynamics I add tensile strength to the ice rheology and re-derive the equations as well as numerical methods to solve them. Through numerical experiments on simplified domains, the effects of those changes are demonstrated. It is found that the modifications enable landfast ice modeling, as desired. The elastic-viscous-plastic rheology leads to initial velocity fluctuations within the landfast ice that weaken the ice sheet and break it up much faster than theoretically predicted. Solving the viscous-plastic rheology using an implicit numerical method avoids those waves and comes much closer to theoretical predictions. Improvements in landfast ice modeling can only verified in comparison to observed data. I have extracted landfast sea ice data of several decades from several sources to create a landfast sea ice climatology that can be used for that purpose. Statistical analysis of the data shows several factors that significantly influence landfast ice distribution: distance from the coastline, ocean depth, as

  4. Sea Ice Charts of the Russian Arctic in Gridded Format, 1933-2006

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Arctic and Antarctic Research Institute (AARI) in St. Petersburg, Russia, produces sea ice charts for safety of navigation in the polar regions and for other...

  5. An approach to computing discrete adjoints for MPI-parallelized models applied to Ice Sheet System Model 4.11

    Directory of Open Access Journals (Sweden)

    E. Larour

    2016-11-01

    Full Text Available Within the framework of sea-level rise projections, there is a strong need for hindcast validation of the evolution of polar ice sheets in a way that tightly matches observational records (from radar, gravity, and altimetry observations mainly. However, the computational requirements for making hindcast reconstructions possible are severe and rely mainly on the evaluation of the adjoint state of transient ice-flow models. Here, we look at the computation of adjoints in the context of the NASA/JPL/UCI Ice Sheet System Model (ISSM, written in C++ and designed for parallel execution with MPI. We present the adaptations required in the way the software is designed and written, but also generic adaptations in the tools facilitating the adjoint computations. We concentrate on the use of operator overloading coupled with the AdjoinableMPI library to achieve the adjoint computation of the ISSM. We present a comprehensive approach to (1 carry out type changing through the ISSM, hence facilitating operator overloading, (2 bind to external solvers such as MUMPS and GSL-LU, and (3 handle MPI-based parallelism to scale the capability. We demonstrate the success of the approach by computing sensitivities of hindcast metrics such as the misfit to observed records of surface altimetry on the northeastern Greenland Ice Stream, or the misfit to observed records of surface velocities on Upernavik Glacier, central West Greenland. We also provide metrics for the scalability of the approach, and the expected performance. This approach has the potential to enable a new generation of hindcast-validated projections that make full use of the wealth of datasets currently being collected, or already collected, in Greenland and Antarctica.

  6. Evidence for ephemeral middle Eocene to early Oligocene Greenland glacial ice and pan-Arctic sea ice.

    Science.gov (United States)

    Tripati, Aradhna; Darby, Dennis

    2018-03-12

    Earth's modern climate is defined by the presence of ice at both poles, but that ice is now disappearing. Therefore understanding the origin and causes of polar ice stability is more critical than ever. Here we provide novel geochemical data that constrain past dynamics of glacial ice on Greenland and Arctic sea ice. Based on accurate source determinations of individual ice-rafted Fe-oxide grains, we find evidence for episodic glaciation of distinct source regions on Greenland as far-ranging as ~68°N and ~80°N synchronous with ice-rafting from circum-Arctic sources, beginning in the middle Eocene. Glacial intervals broadly coincide with reduced CO 2 , with a potential threshold for glacial ice stability near ~500 p.p.m.v. The middle Eocene represents the Cenozoic onset of a dynamic cryosphere, with ice in both hemispheres during transient glacials and substantial regional climate heterogeneity. A more stable cryosphere developed at the Eocene-Oligocene transition, and is now threatened by anthropogenic emissions.

  7. Benthic invertebrate fauna, small streams

    Science.gov (United States)

    J. Bruce Wallace; S.L. Eggert

    2009-01-01

    Small streams (first- through third-order streams) make up >98% of the total number of stream segments and >86% of stream length in many drainage networks. Small streams occur over a wide array of climates, geology, and biomes, which influence temperature, hydrologic regimes, water chemistry, light, substrate, stream permanence, a basin's terrestrial plant...

  8. Stratospheric effects on trends of mesospheric ice clouds (Invited)

    Science.gov (United States)

    Luebken, F.; Baumgarten, G.; Berger, U.

    2009-12-01

    Ice layers in the summer mesosphere at middle and polar latitudes appear as `noctilucent clouds' (NLC) and `polar mesosphere clouds'(PMC) when observed by optical methods from the ground or from satellites, respectively. A newly developed model of the atmosphere called LIMA (Leibniz Institute Middle Atmosphere Model) nicely reproduces the mean conditions of the summer mesopause region and is used to study the ice layer morphology (LIMA/ice). LIMA nudges to ECMWF data in the troposphere and lower stratosphere which influences the background conditions in the mesosphere and ice cloud morphology. Since ice layer formation is very sensitive to the thermal structure of the mesopause region the morphology of NLC and PMC is frequently discussed in terms of long term variations. Model runs of LIMA/ice are now available for 1961 until 2008. A strong correlation between temperatures and PMC altitudes is observed. Applied to historical measurements this gives negligible temperature trends at PMC altitudes (approximately 0.01-0.02 K/y). Trace gas concentrations are kept constant in LIMA except for water vapor which is modified by variable solar radiation. Still, long term trends in temperatures and ice layer parameters are observed, consistent with observations. We present results regarding inter-annual variability of upper mesosphere temperatures, water vapor, and ice clouds, and also long term variations. We compare our model results with satellite borne and lidar observations including some record high NLC parameters measured in the summer season of 2009. The latitudinal dependence of trends and ice layer parameters is discussed, including a NH/SH comparison. We will present an explanation of the trends in the background atmosphere and ice layer parameters.

  9. Arctic and Antarctic Sea Ice Changes and Impacts (Invited)

    Science.gov (United States)

    Nghiem, S. V.

    2013-12-01

    The extent of springtime Arctic perennial sea ice, important to preconditioning summer melt and to polar sunrise photochemistry, continues its precipitous reduction in the last decade marked by a record low in 2012, as the Bromine, Ozone, and Mercury Experiment (BROMEX) was conducted around Barrow, Alaska, to investigate impacts of sea ice reduction on photochemical processes, transport, and distribution in the polar environment. In spring 2013, there was further loss of perennial sea ice, as it was not observed in the ocean region adjacent to the Alaskan north coast, where there was a stretch of perennial sea ice in 2012 in the Beaufort Sea and Chukchi Sea. In contrast to the rapid and extensive loss of sea ice in the Arctic, Antarctic sea ice has a trend of a slight increase in the past three decades. Given the significant variability in time and in space together with uncertainties in satellite observations, the increasing trend of Antarctic sea ice may arguably be considered as having a low confidence level; however, there was no overall reduction of Antarctic sea ice extent anywhere close to the decreasing rate of Arctic sea ice. There exist publications presenting various factors driving changes in Arctic and Antarctic sea ice. After a short review of these published factors, new observations and atmospheric, oceanic, hydrological, and geological mechanisms contributed to different behaviors of sea ice changes in the Arctic and Antarctic are presented. The contribution from of hydrologic factors may provide a linkage to and enhance thermal impacts from lower latitudes. While geological factors may affect the sensitivity of sea ice response to climate change, these factors can serve as the long-term memory in the system that should be exploited to improve future projections or predictions of sea ice changes. Furthermore, similarities and differences in chemical impacts of Arctic and Antarctic sea ice changes are discussed. Understanding sea ice changes and

  10. Achieving Textbook Multigrid Efficiency for Hydrostatic Ice Sheet Flow

    KAUST Repository

    Brown, Jed

    2013-03-12

    The hydrostatic equations for ice sheet flow offer improved fidelity compared with the shallow ice approximation and shallow stream approximation popular in today\\'s ice sheet models. Nevertheless, they present a serious bottleneck because they require the solution of a three-dimensional (3D) nonlinear system, as opposed to the two-dimensional system present in the shallow stream approximation. This 3D system is posed on high-aspect domains with strong anisotropy and variation in coefficients, making it expensive to solve with current methods. This paper presents a Newton--Krylov multigrid solver for the hydrostatic equations that demonstrates textbook multigrid efficiency (an order of magnitude reduction in residual per iteration and solution of the fine-level system at a small multiple of the cost of a residual evaluation). Scalability on Blue Gene/P is demonstrated, and the method is compared to various algebraic methods that are in use or have been proposed as viable approaches.

  11. Achieving Textbook Multigrid Efficiency for Hydrostatic Ice Sheet Flow

    KAUST Repository

    Brown, Jed; Smith, Barry; Ahmadia, Aron

    2013-01-01

    The hydrostatic equations for ice sheet flow offer improved fidelity compared with the shallow ice approximation and shallow stream approximation popular in today's ice sheet models. Nevertheless, they present a serious bottleneck because they require the solution of a three-dimensional (3D) nonlinear system, as opposed to the two-dimensional system present in the shallow stream approximation. This 3D system is posed on high-aspect domains with strong anisotropy and variation in coefficients, making it expensive to solve with current methods. This paper presents a Newton--Krylov multigrid solver for the hydrostatic equations that demonstrates textbook multigrid efficiency (an order of magnitude reduction in residual per iteration and solution of the fine-level system at a small multiple of the cost of a residual evaluation). Scalability on Blue Gene/P is demonstrated, and the method is compared to various algebraic methods that are in use or have been proposed as viable approaches.

  12. Removable cruciform for ice condenser ice basket

    International Nuclear Information System (INIS)

    Scrabis, C.M.; Mazza, G.E.; Golick, L.R.; Pomaibo, P.

    1987-01-01

    A removable cruciform for use in an ice basket having a generally cylindrical sidewall defining a central, vertical axis of the ice basket and plural, generally annular retaining rings secured to the interior of the cylindrical sidewall of the ice basket at predetermined, spaced elevations throughout the axial height of the ice basket is described comprising: a pair of brackets, each comprising a central, base portion having parallel longitudinal edges and a pair of integral legs extending at corresponding angles relative to the base portion from the perspective parallel longitudinal edges thereof; a pair of support plate assemblies secured to and extending in parallel, spaced relationship from one of the pair of brackets; a pair of slide support plates secured to the other of the pair of brackets and extending therefrom in spaced, parallel relationship; and spring means received within the housing and engaging the base portions of the brackets and applying a resilient biasing force thereto for maintaining the spaced relationship thereof

  13. Ice cream structure modification by ice-binding proteins.

    Science.gov (United States)

    Kaleda, Aleksei; Tsanev, Robert; Klesment, Tiina; Vilu, Raivo; Laos, Katrin

    2018-04-25

    Ice-binding proteins (IBPs), also known as antifreeze proteins, were added to ice cream to investigate their effect on structure and texture. Ice recrystallization inhibition was assessed in the ice cream mixes using a novel accelerated microscope assay and the ice cream microstructure was studied using an ice crystal dispersion method. It was found that adding recombinantly produced fish type III IBPs at a concentration 3 mg·L -1 made ice cream hard and crystalline with improved shape preservation during melting. Ice creams made with IBPs (both from winter rye, and type III IBP) had aggregates of ice crystals that entrapped pockets of the ice cream mixture in a rigid network. Larger individual ice crystals and no entrapment in control ice creams was observed. Based on these results a model of ice crystals aggregates formation in the presence of IBPs was proposed. Copyright © 2017 Elsevier Ltd. All rights reserved.

  14. The optical polarization of X-ray binaries

    International Nuclear Information System (INIS)

    Dolan, J.F.

    1977-01-01

    Polarimetric observations of close binaries may reveal the presence of a black-hole secondary. The Einstein photometric effect will introduce a characteristic, time-varying signature upon the interstellar polarization. For several reasons, it is concluded that the short time-scale variability in the polarization in HDE 226868 is caused by Rayleigh scattering from gas streams known to exist in the system. X Persei may have a variable polarization consistent with the predicted effectics and (Auth)

  15. Solar wind stream interfaces

    International Nuclear Information System (INIS)

    Gosling, J.T.; Asbridge, J.R.; Bame, S.J.; Feldman, W.C.

    1978-01-01

    Measurements aboard Imp 6, 7, and 8 reveal that approximately one third of all high-speed solar wind streams observed at 1 AU contain a sharp boundary (of thickness less than approx.4 x 10 4 km) near their leading edge, called a stream interface, which separates plasma of distinctly different properties and origins. Identified as discontinuities across which the density drops abruptly, the proton temperature increases abruptly, and the speed rises, stream interfaces are remarkably similar in character from one stream to the next. A superposed epoch analysis of plasma data has been performed for 23 discontinuous stream interfaces observed during the interval March 1971 through August 1974. Among the results of this analysis are the following: (1) a stream interface separates what was originally thick (i.e., dense) slow gas from what was originally thin (i.e., rare) fast gas; (2) the interface is the site of a discontinuous shear in the solar wind flow in a frame of reference corotating with the sun; (3) stream interfaces occur at speeds less than 450 km s - 1 and close to or at the maximum of the pressure ridge at the leading edges of high-speed streams; (4) a discontinuous rise by approx.40% in electron temperature occurs at the interface; and (5) discontinuous changes (usually rises) in alpha particle abundance and flow speed relative to the protons occur at the interface. Stream interfaces do not generally recur on successive solar rotations, even though the streams in which they are embedded often do. At distances beyond several astronomical units, stream interfaces should be bounded by forward-reverse shock pairs; three of four reverse shocks observed at 1 AU during 1971--1974 were preceded within approx.1 day by stream interfaces. Our observations suggest that many streams close to the sun are bounded on all sides by large radial velocity shears separating rapidly expanding plasma from more slowly expanding plasma

  16. Millennial-scale instability of the Antarctic Ice Sheet during the last glaciation.

    NARCIS (Netherlands)

    Kanfoush, S.L.; Hodell, D.A.; Charles, C.D.; Guilderson, T.P.; Mortyn, P.G.

    2000-01-01

    Records of ice-rafted detritus (IRD) concentration in deep-sea cores from the southeast Atlantic Ocean reveal millennial-scale pulses of IRD delivery between 20,000 and 74,000 years ago. Prominent IRD layers correlate across the Polar Frontal Zone, suggesting episodes of Antarctic Ice Sheet

  17. Sea ice production and transport of pollutants in Laptev Sea, 1979 to 1992

    International Nuclear Information System (INIS)

    Rigor, I.; Colony, R.

    1995-01-01

    About 900,000 km 2 of the polar pack ice is transferred annually from the Arctic Basin to the North Atlantic. The largest portion of this exported ice cover is created by the large scale divergence within the ice pack, but a significant portion of the ice cover originates in the marginal seas, either by fall freezing of the seasonally ice free waters or by wintertime advection away from the coast. The main objective of this study was to estimate the annual production of ice in the Laptev Sea and to determine its ultimate fate. The study was motivated by the possibility that ice formed in the Laptev Sea may be an agent for the long range transport of pollutants such as radionuclides. The authors have attempted to characterize the mean and interannual variability of ice production by investigating the winter production and subsequent melt of ice in the Laptev Sea from 1979 through 1992. The general approach was to associate pollution transport with the net exchange of ice area from the Laptev Sea to the perennial ice pack. The primary data sets supporting the study were ice charts, ice motion and geostrophic wind. 3 refs., 4 figs., 1 tab

  18. Drivers and potential predictability of summer time North Atlantic polar front jet variability

    Science.gov (United States)

    Hall, Richard J.; Jones, Julie M.; Hanna, Edward; Scaife, Adam A.; Erdélyi, Róbert

    2017-06-01

    The variability of the North Atlantic polar front jet stream is crucial in determining summer weather around the North Atlantic basin. Recent extreme summers in western Europe and North America have highlighted the need for greater understanding of this variability, in order to aid seasonal forecasting and mitigate societal, environmental and economic impacts. Here we find that simple linear regression and composite models based on a few predictable factors are able to explain up to 35 % of summertime jet stream speed and latitude variability from 1955 onwards. Sea surface temperature forcings impact predominantly on jet speed, whereas solar and cryospheric forcings appear to influence jet latitude. The cryospheric associations come from the previous autumn, suggesting the survival of an ice-induced signal through the winter season, whereas solar influences lead jet variability by a few years. Regression models covering the earlier part of the twentieth century are much less effective, presumably due to decreased availability of data, and increased uncertainty in observational reanalyses. Wavelet coherence analysis identifies that associations fluctuate over the study period but it is not clear whether this is just internal variability or genuine non-stationarity. Finally we identify areas for future research.

  19. Sea ice contribution to the air-sea CO(2) exchange in the Arctic and Southern Oceans

    DEFF Research Database (Denmark)

    Rysgaard...[], Søren; Bendtsen, Jørgen; Delille, B.

    2011-01-01

    Although salt rejection from sea ice is a key process in deep-water formation in ice-covered seas, the concurrent rejection of CO(2) and the subsequent effect on air-sea CO(2) exchange have received little attention. We review the mechanisms by which sea ice directly and indirectly controls the air......-sea CO(2) exchange and use recent measurements of inorganic carbon compounds in bulk sea ice to estimate that oceanic CO(2) uptake during the seasonal cycle of sea-ice growth and decay in ice-covered oceanic regions equals almost half of the net atmospheric CO(2) uptake in ice-free polar seas. This sea......-sea CO(2) exchange during winter, and (3) release of CO(2)-depleted melt water with excess total alkalinity during sea-ice decay and (4) biological CO(2) drawdown during primary production in sea ice and surface oceanic waters....

  20. Polar Polygons

    Science.gov (United States)

    2005-01-01

    18 August 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows dark-outlined polygons on a frost-covered surface in the south polar region of Mars. In summer, this surface would not be bright and the polygons would not have dark outlines--these are a product of the presence of seasonal frost. Location near: 77.2oS, 204.8oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

  1. Ice Sheet System Model as Educational Entertainment

    Science.gov (United States)

    Perez, G.

    2013-12-01

    Understanding the importance of polar ice sheets and their role in the evolution of Sea Level Rise (SLR), as well as Climate Change, is of paramount importance for policy makers as well as the public and schools at large. For example, polar ice sheets and glaciers currently account for 1/3 of the SLR signal, a ratio that will increase in the near to long-term future, which has tremendous societal ramifications. Consequently, it is important to increase awareness about our changing planet. In our increasingly digital society, mobile and web applications are burgeoning venues for such outreach. The Ice Sheet System Model (ISSM) is a software that was developed at the Jet Propulsion Laboratory/CalTech/NASA, in collaboration with University of California Irvine (UCI), with the goal of better understanding the evolution of polar ice sheets. It is a state-of-the-art framework, which relies on higher-end cluster-computing to address some of the aforementioned challenges. In addition, it is a flexible framework that can be deployed on any hardware; in particular, on mobile platforms such as Android or iOS smart phones. Here, we look at how the ISSM development team managed to port their model to these platforms, what the implications are for improving how scientists disseminate their results, and how a broader audience may familiarize themselves with running complex climate models in simplified scenarios which are highly educational and entertaining in content. We also look at the future plans toward a web portal fully integrated with mobile technologies to deliver the best content to the public, and to provide educational plans/lessons that can be used in grades K-12 as well as collegiate under-graduate and graduate programs.

  2. Ikaite crystal distribution in Arctic winter sea ice and implications for CO2 system dynamics

    Science.gov (United States)

    Rysgaard, S.; Søgaard, D. H.; Cooper, M.; Pućko, M.; Lennert, K.; Papakyriakou, T. N.; Wang, F.; Geilfus, N. X.; Glud, R. N.; Ehn, J.; McGinnnis, D. F.; Attard, K.; Sievers, J.; Deming, J. W.; Barber, D.

    2012-12-01

    The precipitation of ikaite (CaCO3·6H2O) in polar sea ice is critical to the efficiency of the sea ice-driven carbon pump and potentially important to the global carbon cycle, yet the spatial and temporal occurrence of ikaite within the ice is poorly known. We report unique observations of ikaite in unmelted ice and vertical profiles of ikaite abundance and concentration in sea ice for the crucial season of winter. Ice was examined from two locations: a 1 m thick land-fast ice site and a 0.3 m thick polynya site, both in the Young Sound area (74° N, 20° W) of NE Greenland. Ikaite crystals, ranging in size from a few µm to 700 µm were observed to concentrate in the interstices between the ice platelets in both granular and columnar sea ice. In vertical sea-ice profiles from both locations, ikaite concentration determined from image analysis, decreased with depth from surfaceice values of 700-900 µmol kg-1 ice (~ 25 × 106 crystals kg-1) to bottom-layer values of 100-200 µmol kg-1 ice (1-7 × 106 kg-1), all of which are much higher (4-10 times) than those reported in the few previous studies. Direct measurements of total alkalinity (TA) in surface layers fell within the same range as ikaite concentration whereas TA concentrations in bottom layers were twice as high. This depth-related discrepancy suggests interior ice processes where ikaite crystals form in surface sea ice layers and partly dissolved in bottom layers. From these findings and model calculations we relate sea ice formation and melt to observed pCO2 conditions in polar surface waters, and hence, the air-sea CO2 flux.

  3. Aircraft Icing Handbook. (Update)

    Science.gov (United States)

    1993-01-01

    Report 1946-1947, U. S. Air Material Command Tech. Rept. 5676. Findeisen , W., *Meteorological Commentary of D (air) 1209, Icing,* Germany, Reichsamt fur...Wetterdienst, Forschungs-und Krfahrungsberichte, Ser. a, No. 29, 1943. Findeisen , W., *Meteorological-Physical Limitations of Icing on the Atmosphere...Apparatus for Measurement,’ Harvard - Mt. Washington Icing Research Report 1946-1947, U. S. Air Material Command Tech. Rept. 5676.. Findeisen , W., "The

  4. Determination of a Critical Sea Ice Thickness Threshold for the Central Arctic Ocean

    Science.gov (United States)

    Ford, V.; Frauenfeld, O. W.; Nowotarski, C. J.

    2017-12-01

    While sea ice extent is readily measurable from satellite observations and can be used to assess the overall survivability of the Arctic sea ice pack, determining the spatial variability of sea ice thickness remains a challenge. Turbulent and conductive heat fluxes are extremely sensitive to ice thickness but are dominated by the sensible heat flux, with energy exchange expected to increase with thinner ice cover. Fluxes over open water are strongest and have the greatest influence on the atmosphere, while fluxes over thick sea ice are minimal as heat conduction from the ocean through thick ice cannot reach the atmosphere. We know that turbulent energy fluxes are strongest over open ocean, but is there a "critical thickness of ice" where fluxes are considered non-negligible? Through polar-optimized Weather Research and Forecasting model simulations, this study assesses how the wintertime Arctic surface boundary layer, via sensible heat flux exchange and surface air temperature, responds to sea ice thinning. The region immediately north of Franz Josef Land is characterized by a thickness gradient where sea ice transitions from the thickest multi-year ice to the very thin marginal ice seas. This provides an ideal location to simulate how the diminishing Arctic sea ice interacts with a warming atmosphere. Scenarios include both fixed sea surface temperature domains for idealized thickness variability, and fixed ice fields to detect changes in the ocean-ice-atmosphere energy exchange. Results indicate that a critical thickness threshold exists below 1 meter. The threshold is between 0.4-1 meters thinner than the critical thickness for melt season survival - the difference between first year and multi-year ice. Turbulent heat fluxes and surface air temperature increase as sea ice thickness transitions from perennial ice to seasonal ice. While models predict a sea ice free Arctic at the end of the warm season in future decades, sea ice will continue to transform

  5. PolarPortal.org Communicates Real-Time Developments in the Arctic

    Science.gov (United States)

    Langen, P. L.; Andersen, S. B.; Andersen, K. K.; Andersen, M. L.; Ahlstrom, A. P.; van As, D.; Barletta, V. R.; Box, J. E.; Citterio, M.; Colgan, W. T.; Dybkjær, G.; Forsberg, R.; Høyer, J. L.; Jensen, M. B.; Kliem, N.; Mottram, R.; Nielsen, K. P.; Olesen, M.; Quaglia, F. C.; Rasmussen, T. A.; Rodehacke, C. B.; Stendel, M.; Sandberg Sørensen, L.; Tonboe, R. T.

    2014-12-01

    PolarPortal.org was launched in June 2013 by a consortium of Danish institutions, including the Danish Meteorological Institute (DMI), the Geological Survey of Denmark and Greenland (GEUS) and the National Space Institute at the Technical University of Denmark (DTU-Space). Polar Portal is a single web portal presenting a wide range of near real-time information on both the Greenland ice sheet and Arctic sea-ice in a format geared for non-specialists. Polar Portal aims to meet widespread public interest in a diverse range of climate-cryosphere processes in the Arctic: What is the present Greenland ice sheet contribution to sea level rise? How quickly are outlet glaciers retreating or advancing right now? How extensive is Arctic sea-ice or how warm is the Arctic Ocean at this moment? Although public interest in such topics is widely acknowledged, an important primary task for the scientists behind Polar Portal was collaborating with media specialists to establish the knowledge range of the general public on these topics, in order for Polar Portal to appropriately present useful climate-cryosphere information. Consequently, Polar Portal is designed in a highly visual exploratory format, where individual data products are accompanied by plain written summaries, with hyperlinks to relevant journal papers for more scrutinizing users. Numerous satellite and in situ observations, together with model output, are channeled daily into the Greenland ice sheet and Arctic sea-ice divisions of Polar Portal.

  6. Strategic Polarization.

    Science.gov (United States)

    Kalai, Adam; Kalai, Ehud

    2001-08-01

    In joint decision making, similarly minded people may take opposite positions. Consider the example of a marriage in which one spouse gives generously to charity while the other donates nothing. Such "polarization" may misrepresent what is, in actuality, a small discrepancy in preferences. It may be that the donating spouse would like to see 10% of their combined income go to charity each year, while the apparently frugal spouse would like to see 8% donated. A simple game-theoretic analysis suggests that the spouses will end up donating 10% and 0%, respectively. By generalizing this argument to a larger class of games, we provide strategic justification for polarization in many situations such as debates, shared living accommodations, and disciplining children. In some of these examples, an arbitrarily small disagreement in preferences leads to an arbitrarily large loss in utility for all participants. Such small disagreements may also destabilize what, from game-theoretic point of view, is a very stable equilibrium. Copyright 2001 Academic Press.

  7. Safe Loads on Ice Sheets (Ice Engineering. Number 13)

    National Research Council Canada - National Science Library

    Haynes, F. D; Carey, Kevin L; Cattabriga, Gioia

    1996-01-01

    Every winter, ice sheets that grow on lakes and rivers in northern states are used for ice roads, ice bridges, construction platforms, airstrips, and recreational activities, It becomes very important...

  8. Inventory of miscellaneous streams

    International Nuclear Information System (INIS)

    Lueck, K.J.

    1995-09-01

    On December 23, 1991, the US Department of Energy, Richland Operations Office (RL) and the Washington State Department of Ecology (Ecology) agreed to adhere to the provisions of the Department of Ecology Consent Order. The Consent Order lists the regulatory milestones for liquid effluent streams at the Hanford Site to comply with the permitting requirements of Washington Administrative Code. The RL provided the US Congress a Plan and Schedule to discontinue disposal of contaminated liquid effluent into the soil column on the Hanford Site. The plan and schedule document contained a strategy for the implementation of alternative treatment and disposal systems. This strategy included prioritizing the streams into two phases. The Phase 1 streams were considered to be higher priority than the Phase 2 streams. The actions recommended for the Phase 1 and 2 streams in the two reports were incorporated in the Hanford Federal Facility Agreement and Consent Order. Miscellaneous Streams are those liquid effluents streams identified within the Consent Order that are discharged to the ground but are not categorized as Phase 1 or Phase 2 Streams. This document consists of an inventory of the liquid effluent streams being discharged into the Hanford soil column

  9. Hydrography - Streams and Shorelines

    Data.gov (United States)

    California Natural Resource Agency — The hydrography layer consists of flowing waters (rivers and streams), standing waters (lakes and ponds), and wetlands -- both natural and manmade. Two separate...

  10. Polar bear maternity denning in the Beaufort Sea

    Science.gov (United States)

    Amstrup, Steven C.; Gardner, Craig L.

    1994-01-01

    The distribution of polar bears (Ursus maritimus) is circumpolar in the NOrthern Hemisphere, but known locations of maternal dens are concentrated in relatively few, widely scattered locations. Denning is either uncommon or unknown within gaps. To understand effects of industrial development and propose increases in hunting, the temporal and spatial distribution of denning in the Beaufort Sea must be known. We caputred and radiocollared polar bears between 1981 and 1991 and determined tht denning in the Beaufort Sea region was sufficient to account for the estimated population there. Of 90 dend, 48 were on drifting pack ice, 38 on land, and 4 on land-fast ice. The portions of dens on land was higher (P= 0.029) in later compared with earlier years of the study. Bears denning on pack ice drifting as far as 997 km (x=385km) while in dens. there was no difference in cun production by bears denning on land and pack ice (P =0.66). Mean entry and exit dates were 11 November and 5 April for land dens and 22 November and 26 March for pack-ice dens. Female polar bears captured in the Beaufort Sea appeared to be isolated from those caught eat of Cape Bathurst in Canada. Of 35 polar bears that denned along the mainland coast of Alaska and Canada 80% denned between 137 00'W snf 146 59'W. Bears followed to >1 den did not reuse sites and consecutive dens were 20-1,304 km apart. However radio-collared bears are largely faithful to substrate (pack-ice, land, and land-fast ice) and the general geographic area of previous dens. Bears denning on land may be vunerable to human activities such as hunting and industrial development. However, predictable denning chronology and alck of site fidelity indicate that many potential impacts on denning polar bears could be mitigated.

  11. Sea ice dynamics influence halogen deposition to Svalbard

    Directory of Open Access Journals (Sweden)

    A. Spolaor

    2013-10-01

    Full Text Available Sea ice is an important parameter in the climate system and its changes impact upon the polar albedo and atmospheric and oceanic circulation. Iodine (I and bromine (Br have been measured in a shallow firn core drilled at the summit of the Holtedahlfonna glacier (Northwest Spitsbergen, Svalbard. Changing I concentrations can be linked to the March–May maximum sea ice extension. Bromine enrichment, indexed to the Br / Na sea water mass ratio, appears to be influenced by changes in the seasonal sea ice area. I is emitted from marine biota and so the retreat of March–May sea ice coincides with enlargement of the open-ocean surface which enhances marine primary production and consequent I emission. The observed Br enrichment could be explained by greater Br emissions during the Br explosions that have been observed to occur mainly above first year sea ice during the early springtime. In this work we present the first comparison between halogens in surface snow and Arctic sea ice extension. Although further investigation is required to characterize potential depositional and post-depositional processes, these preliminary findings suggest that I and Br can be linked to variability in the spring maximum sea ice extension and seasonal sea ice surface area.

  12. The potential of perennial cave ice in isotope palaeoclimatology

    International Nuclear Information System (INIS)

    Yonge, Charles J.; MacDonald, William D.

    1999-01-01

    Perennial ice from caves on and to the east of the Canadian Great Divide yield delta O 18 and delta D values which are usually high measurements where compared with the average precipitation for the region. Furthermore, these ice data fall below and along lines of lower slope than the Global Meteoric Water Line. To explain the observed relationships, we propose the following process. a vapour-ice isotopic fractionation mechanism operates on warm season vapour when it precipitates as hoar ice on entering the caves. The subsequent fall of hoar to the cave floor through mechanical overloading along with ice derived from ground-water seepage (with a mean annual isotopic composition), results in massive ice formation of a mixed composition. This mixed composition is what is observed in the characteristic relationships found here. Such findings suggest that a warm versus cold climate interpretation for ancient cave ice may be the opposite of that found in the more familiar polar and glacial ice caves. (Author) 3 figs., 1 tab., 12 refs

  13. Antartic sea ice, 1973 - 1976: Satellite passive-microwave observations

    Science.gov (United States)

    Zwally, H. J.; Comiso, J. C.; Parkinson, C. L.; Campbell, W. J.; Carsey, F. D.; Gloersen, P.

    1983-01-01

    Data from the Electrically Scanning Microwave Radiometer (ESMR) on the Nimbus 5 satellite are used to determine the extent and distribution of Antarctic sea ice. The characteristics of the southern ocean, the mathematical formulas used to obtain quantitative sea ice concentrations, the general characteristics of the seasonal sea ice growth/decay cycle and regional differences, and the observed seasonal growth/decay cycle for individual years and interannual variations of the ice cover are discussed. The sea ice data from the ESMR are presented in the form of color-coded maps of the Antarctic and the southern oceans. The maps show brightness temperatures and concentrations of pack ice averaged for each month, 4-year monthly averages, and month-to-month changes. Graphs summarizing the results, such as areas of sea ice as a function of time in the various sectors of the southern ocean are included. The images demonstrate that satellite microwave data provide unique information on large-scale sea ice conditions for determining climatic conditions in polar regions and possible global climatic changes.

  14. Ice sheet-ocean interactions and sea level change

    Science.gov (United States)

    Heimbach, Patrick

    2014-03-01

    Mass loss from the Greenland and Antarctic ice sheets has increased rapidly since the mid-1990s. Their combined loss now accounts for about one-third of global sea level rise. In Greenland, a growing body of evidence points to the marine margins of these glaciers as the region from which this dynamic response originated. Similarly, ice streams in West Antarctica that feed vast floating ice shelves have exhibited large decadal changes. We review observational evidence and present physical mechanisms that might explain the observed changes, in particular in the context of ice sheet-ocean interactions. Processes involve cover 7 orders of magnitudes of scales, ranging from mm boundary-layer processes to basin-scale coupled atmosphere-ocean variability. We discuss observational needs to fill the gap in our mechanistic understanding.

  15. Exploring Science Through Polar Exploration

    Science.gov (United States)

    Pfirman, S. L.; Bell, R. E.; Zadoff, L.; Kelsey, R.

    2003-12-01

    Exploring the Poles is a First Year Seminar course taught at Barnard College, Columbia University. First Year Seminars are required of incoming students and are designed to encourage critical analysis in a small class setting with focused discussion. The class links historical polar exploration with current research in order to: introduce non-scientists to the value of environmental science through polar literature; discuss issues related to venturing into the unknown that are of relevance to any discipline: self-reliance, leadership, preparation, decisions under uncertainty; show students the human face of science; change attitudes about science and scientists; use data to engage students in exploring/understanding the environment and help them learn to draw conclusions from data; integrate research and education. These goals are met by bringing analysis of early exploration efforts together with a modern understanding of the polar environment. To date to class has followed the efforts of Nansen in the Fram, Scott and Amundsen in their race to the pole, and Shackleton's Endurance. As students read turn-of-the-century expedition journals, expedition progress is progressively revealed on an interactive map showing the environmental context. To bring the exploration process to life, students are assigned to expedition teams for specific years and the fates of the student "expeditions" are based on their own decisions. For example, in the Arctic, they navigate coastal sea ice and become frozen into the ice north of Siberia, re-creating Nansen's polar drift. Fates of the teams varied tremendously: some safely emerged at Fram Strait in 4 years, while others nearly became hopelessly lost in the Beaufort Gyre. Students thus learn about variability in the current polar environment through first hand experience, enabling them to appreciate the experiences, decisions, and, in some cases, the luck, of polar explorers. Evaluation by the Columbia Center for New Media, Teaching

  16. Ice and ocean velocity in the Arctic marginal ice zone: Ice roughness and momentum transfer

    Directory of Open Access Journals (Sweden)

    Sylvia T. Cole

    2017-09-01

    Full Text Available The interplay between sea ice concentration, sea ice roughness, ocean stratification, and momentum transfer to the ice and ocean is subject to seasonal and decadal variations that are crucial to understanding the present and future air-ice-ocean system in the Arctic. In this study, continuous observations in the Canada Basin from March through December 2014 were used to investigate spatial differences and temporal changes in under-ice roughness and momentum transfer as the ice cover evolved seasonally. Observations of wind, ice, and ocean properties from four clusters of drifting instrument systems were complemented by direct drill-hole measurements and instrumented overhead flights by NASA operation IceBridge in March, as well as satellite remote sensing imagery about the instrument clusters. Spatially, directly estimated ice-ocean drag coefficients varied by a factor of three with rougher ice associated with smaller multi-year ice floe sizes embedded within the first-year-ice/multi-year-ice conglomerate. Temporal differences in the ice-ocean drag coefficient of 20–30% were observed prior to the mixed layer shoaling in summer and were associated with ice concentrations falling below 100%. The ice-ocean drag coefficient parameterization was found to be invalid in September with low ice concentrations and small ice floe sizes. Maximum momentum transfer to the ice occurred for moderate ice concentrations, and transfer to the ocean for the lowest ice concentrations and shallowest stratification. Wind work and ocean work on the ice were the dominant terms in the kinetic energy budget of the ice throughout the melt season, consistent with free drift conditions. Overall, ice topography, ice concentration, and the shallow summer mixed layer all influenced mixed layer currents and the transfer of momentum within the air-ice-ocean system. The observed changes in momentum transfer show that care must be taken to determine appropriate parameterizations

  17. Bacterial Ice Crystal Controlling Proteins

    Science.gov (United States)

    Lorv, Janet S. H.; Rose, David R.; Glick, Bernard R.

    2014-01-01

    Across the world, many ice active bacteria utilize ice crystal controlling proteins for aid in freezing tolerance at subzero temperatures. Ice crystal controlling proteins include both antifreeze and ice nucleation proteins. Antifreeze proteins minimize freezing damage by inhibiting growth of large ice crystals, while ice nucleation proteins induce formation of embryonic ice crystals. Although both protein classes have differing functions, these proteins use the same ice binding mechanisms. Rather than direct binding, it is probable that these protein classes create an ice surface prior to ice crystal surface adsorption. Function is differentiated by molecular size of the protein. This paper reviews the similar and different aspects of bacterial antifreeze and ice nucleation proteins, the role of these proteins in freezing tolerance, prevalence of these proteins in psychrophiles, and current mechanisms of protein-ice interactions. PMID:24579057

  18. Polarized secondary radioactive beams

    International Nuclear Information System (INIS)

    Zaika, N.I.

    1992-01-01

    Three methods of polarized radioactive nuclei beam production: a) a method nuclear interaction of the non-polarized or polarized charged projectiles with target nuclei; b) a method of polarization of stopped reaction radioactive products in a special polarized ion source with than following acceleration; c) a polarization of radioactive nuclei circulating in a storage ring are considered. Possible life times of the radioactive ions for these methods are determined. General schemes of the polarization method realizations and depolarization problems are discussed

  19. A reconciled estimate of ice-sheet mass balance

    DEFF Research Database (Denmark)

    Shepherd, Andrew; Ivins, Erik R; A, Geruo

    2012-01-01

    We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth's polar ice sheets. We find that there is good agre...

  20. Internet Browser for Ice, Weather and Ocean Information

    DEFF Research Database (Denmark)

    Pedersen, Leif Toudal; Saldo, Roberto

    2005-01-01

    Abstract An Internet based distribution system for ice, weather and ocean information has been set up. The system provides near real time access to a large variety of data about the polar environment in a standard user environment. The system is freely available at: http://www.seaice.dk Specific...

  1. Aufeis accumulations in stream bottoms in arctic and subarctic environments as a possible indicator of geologic structure: Chapter F in Recent U.S. Geological Survey studies in the Tintina Gold Province, Alaska, United States, and Yukon, Canada--results of a 5-year project

    Science.gov (United States)

    Wanty, Richard B.; Wang, Bronwen; Vohden, Jim; Day, Warren C.; Gough, Larry P.; Gough, Larry P.; Day, Warren C.

    2007-01-01

    Thick accumulations of ice, called “aufeis,” form during winter along stream and river valleys in arctic and subarctic regions. In high-gradient alpine streams, aufeis forms mostly as a result of ground-water discharge into the stream channel. The ice occludes this discharge, perturbing the steady-state condition, and causing an incremental rise in the local water table until discharge occurs higher on the stream bank above the previously formed ice. Successive freezing of onlapping ice layers can lead to aufeis accumulations several meters thick.

  2. Polar crane

    International Nuclear Information System (INIS)

    Makosinski, S.

    1981-01-01

    In many applications polar cranes have to be repeatedly positioned with high accuracy. A guidance system is disclosed which has two pairs of guides. Each guide consists of two rollers carried by a sheave rotatable mounted on the crane bridge, the rollers being locatable one on each side of a guideway, e.g. the circular track on which the bridge runs. The pairs of guides are interconnected by respective rope loops which pass around and are locked to the respective pairs of sheaves in such a manner that movement of one guide results in equal movement of the other guide in a sense to maintain the repeatability of positioning of the centre of the bridge. A hydraulically-linked guide system is also described. (author)

  3. Abnormal Winter Melting of the Arctic Sea Ice Cap Observed by the Spaceborne Passive Microwave Sensors

    Directory of Open Access Journals (Sweden)

    Seongsuk Lee

    2016-12-01

    Full Text Available The spatial size and variation of Arctic sea ice play an important role in Earth’s climate system. These are affected by conditions in the polar atmosphere and Arctic sea temperatures. The Arctic sea ice concentration is calculated from brightness temperature data derived from the Defense Meteorological Satellite program (DMSP F13 Special Sensor Microwave/Imagers (SSMI and the DMSP F17 Special Sensor Microwave Imager/Sounder (SSMIS sensors. Many previous studies point to significant reductions in sea ice and their causes. We investigated the variability of Arctic sea ice using the daily and monthly sea ice concentration data from passive microwave observations to identify the sea ice melting regions near the Arctic polar ice cap. We discovered the abnormal melting of the Arctic sea ice near the North Pole even during the summer and the winter. This phenomenon is hard to explain only surface air temperature or solar heating as suggested by recent studies. We propose a hypothesis explaining this phenomenon. The heat from the deep sea in Arctic Ocean ridges and/or the hydrothermal vents might be contributing to the melting of Arctic sea ice. This hypothesis could be verified by the observation of warm water column structure below the melting or thinning arctic sea ice through the project such as Coriolis dataset for reanalysis (CORA.

  4. Optimization of High-Resolution Continuous Flow Analysis for Transient Climate Signals in Ice Cores

    DEFF Research Database (Denmark)

    Bigler, Matthias; Svensson, Anders; Kettner, Ernesto

    2011-01-01

    Over the past two decades, continuous flow analysis (CFA) systems have been refined and widely used to measure aerosol constituents in polar and alpine ice cores in very high-depth resolution. Here we present a newly designed system consisting of sodium, ammonium, dust particles, and electrolytic...... meltwater conductivity detection modules. The system is optimized for high- resolution determination of transient signals in thin layers of deep polar ice cores. Based on standard measurements and by comparing sections of early Holocene and glacial ice from Greenland, we find that the new system features...

  5. A Reconciled Estimate of Ice-Sheet Mass Balance

    Science.gov (United States)

    Shepherd, Andrew; Ivins, Erik R.; Geruo, A.; Barletta, Valentia R.; Bentley, Mike J.; Bettadpur, Srinivas; Briggs, Kate H.; Bromwich, David H.; Forsberg, Rene; Galin, Natalia; hide

    2012-01-01

    We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth's polar ice sheets. We find that there is good agreement between different satellite methods-especially in Greenland and West Antarctica-and that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by -142 plus or minus 49, +14 plus or minus 43, -65 plus or minus 26, and -20 plus or minus 14 gigatonnes year(sup -1), respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 plus or minus 0.20 millimeter year(sup -1) to the rate of global sea-level rise.

  6. Attribution of polar warming to human influence

    OpenAIRE

    Gillett, NP; Stone, DA; Stott, PA; Nozawa, T; Karpechko, AY; Hegerl, GC; Wehner, MF; Jones, PD

    2008-01-01

    The polar regions have long been expected to warm strongly as a result of anthropogenic climate change, because of the positive feedbacks associated with melting ice and snow. Several studies have noted a rise in Arctic temperatures over recent decades, but have not formally attributed the changes to human influence, owing to sparse observations and large natural variability. Both warming and cooling trends have been observed in Antarctica, which the Intergovernmental Panel on Climate Change ...

  7. Sediments in Arctic sea ice: Implications for entrainment, transport and release

    Science.gov (United States)

    Nurnberg, D.; Wollenburg, I.; Dethleff, D.; Eicken, H.; Kassens, H.; Letzig, T.; Reimnitz, E.; Thiede, Jorn

    1994-01-01

    maximum in sea ice sediment samples repeatedly occurred between 81??N and 83??N along the Arctic 91 transect, indicating a rather stable and narrow smectite rich ice drift stream of the Transpolar Drift. The smectite concentrations are comparable to those found in both Laptev Sea shelf sediments and anchor ice sediments, pointing to this sea as a potential source area for sea ice sediments. In the central Arctic Ocean sea ice clay mineralogy is significantly different from deep-sea clay mineral distribution patterns. The contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms. ?? 1994.

  8. Ice crystallization in ultrafine water-salt aerosols: nucleation, ice-solution equilibrium, and internal structure.

    Science.gov (United States)

    Hudait, Arpa; Molinero, Valeria

    2014-06-04

    solution. We predict that micrometer-sized particles and nanoparticles have the same equilibrium internal structure. The variation of liquid-vapor surface tension with solute concentration is a key factor in determining whether a solution-embedded ice core or vapor-exposed ice cap is the equilibrium structure of the aerosols. In agreement with experiments, we predict that the structure of mixed-phase HNO3-water particles, representative of polar stratospheric clouds, consists of an ice core surrounded by freeze-concentrated solution. The results of this work are important to determine the phase state and internal structure of sea spray ultrafine aerosols and other mixed-phase particles under atmospherically relevant conditions.

  9. Sputtering of water ice

    DEFF Research Database (Denmark)

    Baragiola, R.A.; Vidal, R.A.; Svendsen, W.

    2003-01-01

    We present results of a range of experiments of sputtering of water ice together with a guide to the literature. We studied how sputtering depends on the projectile energy and fluence, ice growth temperature, irradiation temperature and external electric fields. We observed luminescence from...

  10. Ice sheet in peril

    DEFF Research Database (Denmark)

    Hvidberg, Christine Schøtt

    2016-01-01

    Earth's large ice sheets in Greenland and Antarctica are major contributors to sea level change. At present, the Greenland Ice Sheet (see the photo) is losing mass in response to climate warming in Greenland (1), but the present changes also include a long-term response to past climate transitions...

  11. Turning into Ice

    Science.gov (United States)

    Pietsch, Renée B.; Hanlon, Regina; Bohland, Cynthia; Schmale, David G., III

    2016-01-01

    This article describes an interdisciplinary unit in which students explore biological "ice nucleation"--by particles that cause water to freeze at temperatures above -38°C--through the lens of the microbial ice nucleator "Pseudomonas syringae." Such This activity, which aligns wit