WorldWideScience

Sample records for scandinavian ice sheet

  1. The last Scandinavian ice sheet in northwestern Russia: ice flow patterns and decay dynamics

    DEFF Research Database (Denmark)

    Demidov, L.; Houmark-Nielsen, Michael; Kjær, Kurt Henrik

    2006-01-01

    the main ice sheet. During the Lateglacial warming, disintegration and melting took place in a 200-600 km wide zone along the northeastern rim of SIS associated with thick Quaternary accumulations. Deglaciation occurred through aerial downwasting within large fields of dead ice developed during......Advance of the Late Weichselian (Valdaian) Scandinavian Ice Sheet (SIS) in northwestern Russia took place after a period of periglacial conditions. Till of the last SIS, Bobrovo till, overlies glacial deposits from the previous Barents and Kara Sea ice sheets and marine deposits of the Last...... in Russia than previously outlined and the time of termination at 18-16 cal. kyr BP was almost 10 kyr delayed compared to the southwestern part of the ice sheet. We argue that the lithology of the ice sheets' substrate, and especially the location of former proglacial lake basins, influenced the dynamics...

  2. Simulations of the Scandinavian ice sheet and its subsurface conditions

    Energy Technology Data Exchange (ETDEWEB)

    Boulton, G.S.; Caban, P.; Hulton, N. [Edinburgh Univ. (United Kingdom). Dept of Geology and Geophysics

    1999-12-01

    An ice sheet model has been applied to an approximate flow line through the area of the Fennoscandian ice sheet. The modelled ice sheet fluctuations have been matched with stratigraphic evidence of Weichselian ice sheet fluctuation in order to simulate ice sheet attributes through time along the flowline. The model predicts extensive melting at the base of the ice sheet. This output has been used as an input to a simplified model of hydrogeology along the southern flank of the ice sheet so as to reconstruct patterns of subglacial groundwater flow. The output from the model is also used to estimate patterns of subglacial stress and strain. Results suggest that large scale subglacial groundwater catchment are formed which were quite differentin extent from modern catchment; that fossil subglacial groundwaters should be found at sampling depths; and much fracturing in shallow bedrock in Sweden could be glacially generated.

  3. Impact of Volcanic Aerosols on Scandinavian Ice Sheet Melting during the Last Deglaciation

    Science.gov (United States)

    Muschitiello, F.; Pausata, F. S. R.; Wohlfarth, B.

    2016-12-01

    Volcanic aerosols play a key role on Earth's climate driving a variety of feedbacks that can potentially affect the mass balance of modern ice sheets. Yet, empirical evidence that highlights the sensitivity of ancient ice sheets to volcanic forcing and the related feedbacks is still missing. Here we present a new annual and continuous glacial clay-varve chronology recording the melting history of the Scandinavian Ice Sheet during the end of the last deglaciation ( 13,200-12,000 years BP). By precisely synchronizing the chronology to the Greenland ice-core time scale, we document a correspondence between anomalous melt events in our varve record and volcanic aerosol emissions as registered in ice cores. Climate model simulations identify a positive feedback between volcanism and summer cloud cover over the North Atlantic. We thus suggest that ice sheet melting could have been enhanced by cloud radiative effects and variations in snow albedo owing to direct ash deposition. The sensitivity of past ice sheets to volcanic aerosols highlights the need for an accurate coupling between atmosphere and ice sheet components in climate model. These results have also important implications with respect to the tremendous amount of meltwater trapped by retreating ice sheets and their pivotal role in the rapid climate shifts of the past.

  4. Ice-dammed lakes reconstruction in the southeastern Scandinavian ice sheet periphery

    Science.gov (United States)

    Anisimov, Nikolai

    2017-04-01

    The study of glacier erosion processes, paleolake dynamics and topographical changes, together give us insight into both localized and broader landscape evolution patterns while also assisting human exploration. After carrying number of paleographic discoveries of North-West of Russia, we've gathered the data requiring generalizing, systemizing, visualizing. Objective: reconstruction of proglacial lakes based on lithostratigraphic and geomorphic analysis using GIS technology. GIS modeling of ice-dammed lakes was done via the ArcGIS Desktop 10 software package. The GIS was used as a means to categorize published, time mapped data and thereby fuse and unify the changes into a single, integrated prototype. Publications on limnologo-glaciological and geomorphological reconstructions of paleotopography and paleolakes north of the Russian plain, along with additional copyrighted and grant-funded GIS studies, together served as resources to authenticate the paleolake contour modeling. A quaternary sediments map and an updated topography map that was designed via semiautomatic vectorization of a topographical map, served as foundations for the electronic shape modeling paleoreconstructions. Based upon preliminary results from publication summaries, and initial data collected when analyzing the maps (quaternary sediments, geomorphological, topographical), the contours and maximum glacial lake rise levels in the southeastern Scandinavian ice sheet periphery, including the levels and contours of their coastline, have been duly identified. Boundary reconstruction of Late Pleistocene lake boundaries have been completed for five sections of the Scandinavian ice sheet: the Molovo-Sheksninskoy, the Belozersko-Kubensky, the Vozhe-Lachsko-Kubensky, the Vazhskoy, and the Severodvinskoy. The territories studied revealed 13 major paleobasins covering an area of more than 1,000 km2, which based upon their position most closely resemble periglacial, intraglacial and postglacial lakes. Of

  5. Geomorphological evidence of channelized subglacial meltwater drainage under the Scandinavian Ice Sheet

    Science.gov (United States)

    Adamczyk, Aleksander; Wysota, Wojciech; Sobiech, Marcin; Piotrowski, Jan A.

    2016-04-01

    The impact of subglacial meltwater erosion on shaping glacial landscapes is contentious and often difficult to constrain due to the lack of unequivocal diagnostic criteria. The same holds for the role of subglacial meltwater in glacier movement processes and sediment transport and deposition. Here we present new evidence of widespread channelized erosion under the southern, soft-bedded fringe of the last Scandinavian Ice Sheet (SIS) based on high-resolution terrain analysis with LiDAR imagery. We identify several tens of sites with "glacial curvilineation" landscapes first recognized by Lesemann et al. (2010, 2014) and considered as evidence of erosion by turbulent meltwater flows at the ice/bed interface. The "glacial curvilineation" landscapes mapped here consist of sets of parallel, winding ridges typically several metres high and up to several kilometres long occupying glacial overdeepenings and tunnel valleys. The ridges are aligned approximately perpendicular to the past ice sheet margins and they are composed of various deposits often pre-dating the last ice advance. We interpret them as erosional remnants of older landscapes dissected by high-energy subglacial meltwater flows. These findings suggest that the palaeoglaciological significance of meltwater drainage under the southern portion of SIS may have been grossly underestimated. References Lesemann, J.-E., Piotrowski, J.A. and Wysota, W., 2010. „Glacial curvilineations": New glacial landforms produced by longitudinal vortices in subglacial meltwater flows. Geomorphology 120, 153-161. Lesemann, J.-E., Piotrowski, J.A. and Wysota, W., 2014. Genesis of the "glacial curvilineation" landscape by meltwater processes under the former Scandinavian Ice Sheet, Poland. Sedimentary Geology 312, 1-18.

  6. Timescales of methane seepage on the Norwegian margin following collapse of the Scandinavian Ice Sheet

    OpenAIRE

    Cremiere, Antoine; Lepland, Aivo; Chand, Shyam; Sahy, Diana; Daniel J. Condon; Noble, Stephen R.; Martma, Tõnu; Thorsnes, Terje; Sauer, Simone; Brunstad, Harald

    2016-01-01

    Source: doi: 10.1038/ncomms11509 Gas hydrates stored on continental shelves are susceptible to dissociation triggered by environmental changes. Knowledge of the timescales of gas hydrate dissociation and subsequent methane release are critical in understanding the impact of marine gas hydrates on the ocean–atmosphere system. Here we report a methane efflux chronology from five sites, at depths of 220–400 m, in the southwest Barents and Norwegian seas where grounded ice sheets led to thicke...

  7. Behaviour of the lake district ice lobe of the Scandinavian ice sheet during the younger dryas chronozone (ca. 12 800 - 11 500 years ago)

    Energy Technology Data Exchange (ETDEWEB)

    Lunkka, J.P.; Erikkilae, A. [Oulu Univ. (Finland)

    2012-04-15

    It is highly relevant to picture the conditions that prevailed under and in front of the ice sheets as they were stationary or in equilibrium for many hundreds of years. This knowledge is particularly relevant when planning to dispose of spent nuclear fuel in a repository underground. For estimating what kind of conditions might exist at the ice margin basic knowledge is needed from the palaeoice sheets that remained stationary for long periods of time. During Younder Dryas Stadial (c. 12 800 - 11 500 years ago) glaciers remained stationary or advanced worldwide as a result of climate cooling. The major end moraine complexes that run around Fennoscandia, Russian Karelia and the Kola Peninsula were deposited at that time and mark the former Younger Dryas ice margin. It this work the palaeoenvironments have been reconstructed in order to reveal the conditions that existed for more than 1000 years in the area where the former Lake District Ice Lobe of the Scandinavian Ice Sheet was in the Salpausselkae zone in southern Finland. Work was carried out using GIS-based reconstruction tools, sedimentological and geophysical (ground penetrating radar) methods. In addition, a detailed palaeoenvironmental reconstruction was produced for the Kylaeniemi area which forms a part of the Salpausselkae II end moraine. The GIS-based reconstructions clearly indicate that the ice grounding line of the Lake District Ice Lobe was standing in shallow water depth in the Baltic Ice Lake. The water depth in front of Salpausselkae I, which marks the ice margin at c. 12 500 years ago was mainly between 20-40 metres. When the ice margin was in Salpausselkae II at around 11 700 years ago the water depth in front of the ice margin was on average less than 20 metres. Although the surface profile of ice was not possible to calculate subgalcial and ice frontal landforms indicate that subgalcial tunnel systems were responsible for releasing melt water and sediment to the ice margin throughout the

  8. Timescales of methane seepage on the Norwegian margin following collapse of the Scandinavian Ice Sheet.

    Science.gov (United States)

    Crémière, Antoine; Lepland, Aivo; Chand, Shyam; Sahy, Diana; Condon, Daniel J; Noble, Stephen R; Martma, Tõnu; Thorsnes, Terje; Sauer, Simone; Brunstad, Harald

    2016-05-11

    Gas hydrates stored on continental shelves are susceptible to dissociation triggered by environmental changes. Knowledge of the timescales of gas hydrate dissociation and subsequent methane release are critical in understanding the impact of marine gas hydrates on the ocean-atmosphere system. Here we report a methane efflux chronology from five sites, at depths of 220-400 m, in the southwest Barents and Norwegian seas where grounded ice sheets led to thickening of the gas hydrate stability zone during the last glaciation. The onset of methane release was coincident with deglaciation-induced pressure release and thinning of the hydrate stability zone. Methane efflux continued for 7-10 kyr, tracking hydrate stability changes controlled by relative sea-level rise, bottom water warming and fluid pathway evolution in response to changing stress fields. The protracted nature of seafloor methane emissions probably attenuated the impact of hydrate dissociation on the climate system.

  9. Subglacial conditions and Scandinavian Ice Sheet dynamics at the coarse-grained substratum of the fore-mountain area of southern Poland

    Science.gov (United States)

    Salamon, Tomasz

    2016-11-01

    The fore-mountain areas of southern Poland are locally composed of the coarse-grained sediments of alluvial fans, which created unusual conditions under the advancing Scandinavian Ice Sheet during the Elsterian glaciation. This highly permeable substratum potentially enabled rapid outflow of meltwater from the ice sheet base, thereby reducing the water pressure and strongly influencing the ice sheet dynamics. The subglacial conditions and the relationship between the ice sheet behaviour and its coarse-grained substratum were studied at the foreland of the western Carpathian Mountains. The sedimentological and structural analysis of the till and related sediments that were deposited above the alluvial gravel of the fore-mountain fans are presented. The study indicates that despite the high permeability of the coarse-grained substratum, it did not slow the ice sheet movement. Conversely, the ice sheet moved mainly due to basal slip and locally shallow deformations. This was a consequence of very high basal water pressure, which resulted largely from the presence of permafrost that restricted subglacial groundwater outflow. In addition, the ice sheet substratum was inclined opposite to the direction of its movement, increasing the pressure of the subglacial water. Numerous subhorizontal sandy laminae within the till indicate that the meltwater from the ice sheet base was drained by a water film along the ice/bed interface. The water escape structures within the till and subtill sediments indicate the occasional instability of the ice sheet hydrological system and suggest that the meltwater was periodically stored in the ice sheet base. Temporal changes occurring in the ice sheet hydrological system might indicate variations in the ice sheet behaviour; i.e. phases of relatively fast ice flow and phases of ice stagnation. The latter were probably correlated with the freezing of the ice margin to its base. The study shows how the coarse-grained substratum could

  10. The Weichselian phases of the Scandinavian Ice Sheet in northeast Germany revisited

    Science.gov (United States)

    Boese, Margot; Hardt, Jacob; Christopher, Lüthgens

    2017-04-01

    Recent progress in the dating of glacial and glaciofluvial sediments is about to considerably change the existing geochronological model of the Weichselian Brandenburg, Frankfurt, and Pomeranian phases in northeast Germany. Several studies were carried out with the aim to obtain depositional ages of glaciofluvial deposits with the Optically Stimulated Luminescence (OSL) dating method. Sediments deposited during the advance of the inland ice were dated with OSL as well as sediments that were deposited during the succeeding down wasting phase. Additionally, cosmogenic nuclide surface exposure ages of glacigenic boulders were compiled from literature, which indicate the landscape stabilization after the down wasting of the ice. These ages were recalibrated with a recent 10Be production rate. In combination, the results from both methods provide a consistent geochronological database. Our results show that the ice advance of the Weichselian Brandenburg phase took place already in late Marine Isotope Stage 3, and does not correlate to the global last glacial maximum (in terms of ice volume), which was previously assumed. This is peculiarly interesting because the Brandenburg ice marginal position is representative of the largest Weichselian ice extent in northeast Germany. The ice advance of the Brandenburg phase seems to correlate with the Klintholm advance in Denmark. The Frankfurt phase represents the succeeding down wasting phase, during which a succession of ice marginal fans was formed on the Barnim plateau in middle Brandenburg. Evidence of a single ice marginal position representative of the Frankfurt phase has so far not been found. The ice advance during the last global glacial maximum occurred during the Pomeranian phase and thus does not represent the Weichselian maximum advance in Brandenburg but the MIS 2. Key references: Hardt, J., Lüthgens, C., Hebenstreit, R., Böse, M., 2016: Geochronological (OSL) and geomorphological investigations at the presumed

  11. The Oldest Dryas last significant fluctuation of the Scandinavian ice sheet margin in Eastern Baltic and problems of its regional correlation

    Science.gov (United States)

    Saks, T.; Zelcs, V.; Nartiss, M.; Kalvans, A.

    2009-12-01

    Ice marginal formations, glaciotectonic phenomena, directional ice-flow features and new absolute age dating results of the Pleistocene deposits were subjected to systematic analyses and re-interpretation for clarification of deglaciation history, especially on the timing and position of the glacial margin of the Linkuva (North Lithuanian, Haanja, Luga) phase. The oldest Dryas - the last significant fluctuation of the ice margin - locally termed as the Linkuva stage in Latvia, is probably best known deglaciation stage event in south eastern sector of the Scandinavian Ice Sheet, yet problems of its cross border correlation are still present. The timing of the North Lithuanian phase occurred at the end of the Oldest Dryas cold stage. Its minimum age is currently dated to 15.9-15.6 ka BP in Latvia (calibrated from 13.2-13.4 ka 14C BP), and correlative to the Haanja stade in Estonia , Middle Lithuanian phase in Lithuania, Slupsk Bank phase in northern Poland, and most likely by Krasnogorodsk phase in Russia. These ages are older than the error-weighted mean age (13.1 ± 0.3 10Be ka) of the North Lithuanian moraine. Here we present re-interpreted map of the Linkuva stage glacial marginal position in the territory of Latvia correlated with adjacent territories. The map is based on cumulative results of the mapping of ice marginal formations and spatial arrangement of streamlined bedforms (drumlins, flutes and megalineations), OSL and radiocarbon data available cosmogenic datings, and previous reconstructions of these stage glacial marginal positions. The results allow: (1) to draw complex interplay of the Scandinavian ice sheet lobate structure during the Linkuva deglaciation phase; (2) to conclude that the fast ice flow in many places with surging pattern were common for ice lobes and tongues; (3) to attest that mapping of the marginal shear moraines can be used as a tool for reconstruction of active ice marginal positions. The results suggest that there is no evidence

  12. Lateglacial retreat chronology of the Scandinavian Ice Sheet in Finnmark, northern Norway, reconstructed from surface exposure dating of major end moraines

    Science.gov (United States)

    Romundset, Anders; Akçar, Naki; Fredin, Ola; Tikhomirov, Dmitry; Reber, Regina; Vockenhuber, Christof; Christl, Marcus; Schlüchter, Christian

    2017-12-01

    We report results from a comprehensive surface exposure dating campaign in eastern Finnmark, located in the northernmost part of Norway and close to the Norwegian-Russian border. This is a palaeo-glaciologically important region as it sits near the proposed border-zone between the former Scandinavian and Barents Sea Ice Sheets. However, until now the deglaciation history has few direct dates onshore and the chronology of ice front retreat is instead found by correlating ice-marginal deposits with isostatically raised shorelines and marine sediment cores. We measured the content of 10Be (N = 22) and 36Cl (N = 17) from boulders located at the crest of major moraine ridges at four localities; Kjæs, Kongsfjorden, Vardø and Kirkenes. These are key localities of existing regional reconstructions of ice recession in this area. Despite some spread in age results from each locality due to methodological challenges associated with surface exposure dating, the large numbers of samples from each site except Kjæs still allow for obtaining clusters of similar ages which are used for arriving at a likely chronology of ice front retreat. Our results show that the Kongsfjorden and Vardø moraines were deposited 14.3 ± 1.7 ka and 13.6 ± 1.4 ka, respectively, and thus point to a Older Dryas age of the proposed 'Outer Porsanger' deglaciation sub-stage. Moraine ridges belonging to the 'Main' sub-stage near Kirkenes were dated to 11.9 ± 1.2 ka, corresponding well with the ice retreat chronology farther west in northern Norway and suggesting that the maximum Younger Dryas ice sheet extent was attained in the late Younger Dryas along a more than 500 km long stretch in northernmost Scandinavia.

  13. 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...... as Dansgaard-Oeschger (DO) events would add to our knowledge of the climatic system and – hopefully – enable better forecasts. Likewise, to forecast possible future sea level rise it is crucial to correctly model the large ice sheets on Greenland and Antarctica. This project is divided into two parts...

  14. Comment on "Development of the topography-controlled Upper Odra ice lobe (Scandinavian ice sheet) in the fore-mountain area of southern Poland during the Saalian glaciation" by T. Salamon [Quat. Sci. Rev. 123 (2015) 1-15

    Science.gov (United States)

    Nývlt, Daniel

    2016-02-01

    Salamon (2015) presented a glaciodynamic model of the evolution of the Upper Odra ice lobe of the Northern European Ice Sheet during the Saalian (Drenthe) glaciation. This is timely and welcomed paper, as it brings a dynamic conceptual model and emphasizes the topographic control of the ice sheet behaviour, which was very important for Middle Pleistocene ice sheet advances in Central European sector (e.g.; Nývlt, 2008; Nývlt et al., 2011).

  15. 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....... On page 590 of this issue, MacGregor et al. (2) estimate the mean rates of snow accumulation and ice flow of the Greenland Ice Sheet over the past 9000 years based on an ice sheet-wide dated radar stratigraphy (3). They show that the present changes of the Greenland Ice Sheet are partly an ongoing...... response to the last deglaciation. The results help to clarify how sensitive the ice sheet is to climate changes....

  16. Ice sheet margins and ice shelves

    Science.gov (United States)

    Thomas, R. H.

    1984-01-01

    The effect of climate warming on the size of ice sheet margins in polar regions is considered. Particular attention is given to the possibility of a rapid response to warming on the order of tens to hundreds of years. It is found that the early response of the polar regions to climate warming would be an increase in the area of summer melt on the ice sheets and ice shelves. For sufficiently large warming (5-10C) the delayed effects would include the breakup of the ice shelves by an increase in ice drainage rates, particularly from the ice sheets. On the basis of published data for periodic changes in the thickness and melting rates of the marine ice sheets and fjord glaciers in Greenland and Antarctica, it is shown that the rate of retreat (or advance) of an ice sheet is primarily determined by: bedrock topography; the basal conditions of the grounded ice sheet; and the ice shelf condition downstream of the grounding line. A program of satellite and ground measurements to monitor the state of ice sheet equilibrium is recommended.

  17. Infill of tunnel valleys associated with landward‐flowing ice sheets

    DEFF Research Database (Denmark)

    Moreau, Julien; Huuse, Mads

    2014-01-01

    The southern termination of the Middle and Late Pleistocene Scandinavian ice sheets was repeatedly located in the southern North Sea (sNS) and adjacent, north-sloping land areas. Giant meltwater-excavated valleys (tunnel valleys) formed at the southern termination of the ice sheets and contain...

  18. Modelling the Antarctic Ice Sheet

    DEFF Research Database (Denmark)

    Pedersen, Jens Olaf Pepke; Holm, A.

    2015-01-01

    The Antarctic ice sheet is a major player in the Earth’s climate system and is by far the largest depository of fresh water on the planet. Ice stored in the Antarctic ice sheet (AIS) contains enough water to raise sea level by about 58 m, and ice loss from Antarctica contributed significantly...... to sea level high stands during past interglacial periods. A number of AIS models have been developed and applied to try to understand the workings of the AIS and to form a robust basis for future projections of the AIS contribution to sea level change. The recent DCESS (Danish Center for Earth System...... Science) Antarctic Ice Sheet (DAIS) model (Shaffer 2014) is forced by reconstructed time series of Antarctic temperature, global sea level and ocean subsurface temperature over the last two glacial cycles. In this talk a modelling work of the Antarctic ice sheet over most of the Cenozoic era using...

  19. Ice sheet hydrology - a review

    Energy Technology Data Exchange (ETDEWEB)

    Jansson, Peter; Naeslund, Jens-Ove [Dept. of Physical Geography and Quaternary Geology, Stockholm Univ., Stockholm (Sweden); Rodhe, Lars [Geological Survey of Sweden, Uppsala (Sweden)

    2007-03-15

    This report summarizes the theoretical knowledge on water flow in and beneath glaciers and ice sheets and how these theories are applied in models to simulate the hydrology of ice sheets. The purpose is to present the state of knowledge and, perhaps more importantly, identify the gaps in our understanding of ice sheet hydrology. Many general concepts in hydrology and hydraulics are applicable to water flow in glaciers. However, the unique situation of having the liquid phase flowing in conduits of the solid phase of the same material, water, is not a commonly occurring phenomena. This situation means that the heat exchange between the phases and the resulting phase changes also have to be accounted for in the analysis. The fact that the solidus in the pressure-temperature dependent phase diagram of water has a negative slope provides further complications. Ice can thus melt or freeze from both temperature and pressure variations or variations in both. In order to provide details of the current understanding of water flow in conjunction with deforming ice and to provide understanding for the development of ideas and models, emphasis has been put on the mathematical treatments, which are reproduced in detail. Qualitative results corroborating theory or, perhaps more often, questioning the simplifications made in theory, are also given. The overarching problem with our knowledge of glacier hydrology is the gap between the local theories of processes and the general flow of water in glaciers and ice sheets. Water is often channelized in non-stationary conduits through the ice, features which due to their minute size relative to the size of glaciers and ice sheets are difficult to incorporate in spatially larger models. Since the dynamic response of ice sheets to global warming is becoming a key issue in, e.g. sea-level change studies, the problems of the coupling between the hydrology of an ice sheet and its dynamics is steadily gaining interest. New work is emerging

  20. 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

  1. Ice Sheet Retention Structures,

    Science.gov (United States)

    1983-12-01

    CHART NATIONAL BUREAU OF STANDARDS- 1963-A L % . - .& .4% I% REPORT83n30US Army Corps* RE RT 3-30of Engineers Cold Regions Research & Engingering ...Journal of the Technical Councils of ASCI, search Report 206. AD666205. Proceedings of the American Society of’Civil Engi- Ekizian, H., Jr. (1976...and G.D. Ashton (1978) Entrainment search Council, Ottawa. of ice floes into a submerged outlet. Proceedings of Uzuner, M.S. and J.F. Kennedy (1972

  2. The microbiome of glaciers and ice sheets

    National Research Council Canada - National Science Library

    Alexandre M Anesio; Stefanie Lutz; Nathan A M Chrismas; Liane G Benning

    2017-01-01

    .... Habitats on glaciers and ice sheets with enough liquid water to sustain microbial activity include snow, surface ice, cryoconite holes, englacial systems and the interface between ice and overridden rock/soil...

  3. Modelling of pleistocene European ice sheets: the effect of upslope precipitation

    NARCIS (Netherlands)

    Sanberg, J.A.M.; Oerlemans, J.

    1983-01-01

    Results are presented from a numerical model of the Scandinavian Ice Sheet, in which the effect of upslope precipitation is included explicitly. The model is forced by changing the environmental conditions, formulated in terms of the annual mean temperature and the annual temperature range. These

  4. Greenland Radar Ice Sheet Thickness Measurements

    Data.gov (United States)

    National Aeronautics and Space Administration — Two 150-MHz coherent radar depth sounders were developed and flown over the Greenland ice sheet to obtain ice thickness measurements in support of PARCA...

  5. Climate modification by future ice sheet changes and consequences for ice sheet mass balance

    OpenAIRE

    Vizcaino, M.; Mikolajewicz, U.; J. Jungclaus; G. Schurgers

    2010-01-01

    The future evolution of global ice sheets under anthropogenic greenhouse forcing and its impact on the climate system, including the regional climate of the ice sheets, are investigated with a comprehensive earth system model consisting of a coupled Atmosphere-Ocean General Circulation Model, a dynamic vegetation model and an ice sheet model. The simulated control climate is realistic enough to permit a direct coupling of the atmosphere and ice sheet components, avoiding the use of anomaly co...

  6. Ice flow Modelling of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Nielsen, Lisbeth Tangaa

    Models of ice flow have a range of application in glaciology, including investigating the large-scale response of ice sheets to changes in climate, assimilating data to estimate unknown conditions beneath the ice sheet, and in interpreting proxy records obtained from ice cores, among others. In t...... a steady state with respect to the reference climate at the end of the simulation and that the mass balance of the ice sheet at this time was more sensitive to recent climate fluctuations than the temperature forcing in the early or mid-Holocene.......Models of ice flow have a range of application in glaciology, including investigating the large-scale response of ice sheets to changes in climate, assimilating data to estimate unknown conditions beneath the ice sheet, and in interpreting proxy records obtained from ice cores, among others....... In this PhD project, the use of ice flow models for the interpretation of the age-structure of the Greenland ice sheet, i.e. the depth within the ice, at which ice deposited at given times are found at present day. Two different observational data sets of this archive were investigated. Further, paleo...

  7. Balance velocities of the Greenland ice sheet

    DEFF Research Database (Denmark)

    Joughin, I.; Fahnestock, M.; Ekholm, Simon

    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 altimetery data, yields far greater detail than earlier balance velocity estimates for Greenland. The velocity contours reveal in striking detail......, the balance map is useful for ice-sheet modelling, mass balance studies, and field planning....

  8. A model of the Antarctic Ice Sheet

    NARCIS (Netherlands)

    Oerlemans, J.

    1982-01-01

    Numerical modelling of ice sheets and glaciers has become a useful tool in glaciological research. A model described here deals with the vertical mean ice velocity, is time dependent, computes bedrock adjustment and uses an empirical diagnostic relationship to derive the distribution of ice

  9. Ice shelf fracture parameterization in an ice sheet model

    Directory of Open Access Journals (Sweden)

    S. Sun

    2017-11-01

    Full Text Available Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ∼ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

  10. Ice shelf fracture parameterization in an ice sheet model

    Science.gov (United States)

    Sun, Sainan; Cornford, Stephen L.; Moore, John C.; Gladstone, Rupert; Zhao, Liyun

    2017-11-01

    Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM) to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ˜ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor) fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

  11. Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics

    OpenAIRE

    Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

    2015-01-01

    The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests ...

  12. Hydrologic Outlets of the Greenland Ice Sheet

    Data.gov (United States)

    National Aeronautics and Space Administration — The Hydrologic Outlets of the Greenland Ice Sheet data set contains GIS point shapefiles that include 891 observed and potential hydrologic outlets of the Greenland...

  13. Control of the Antarctic ice sheet by ocean ice interaction

    Science.gov (United States)

    Bye, John; May, Joel; Simmonds, Ian

    2006-02-01

    The Antarctic ice cap is the largest ice sheet of modern times. It is of considerable importance to predict the sea level variability due to the associated changes in ice volume. We present the results of a simple grounded ice sheet model, developed from Oerlemans [Oerlemans, J., 2002. Global dynamics of the Antarctic Ice Sheet, Climate Dynamics 19, 85-93.], in which the net oceanic evaporation influences the ice cap volume in two ways, through changes in: (i) the accumulation rate, and (ii) the mean sea level. The net evaporation changes are driven by the sea surface temperature (SST) anomaly time series of Howard [Howard, W.R., 1997. A warm future in the past, Nature, 388, 418-419.] for the subantarctic Southern Ocean over the period 220 kyr to the present. The effect of the waxing and waning of the northern hemisphere ice sheets is integrated into the model using an independent model, in which ice melting depends on the SST anomaly and ice calving depends on the sea level anomaly. A series of analytical expressions are derived for the related properties of the coupled ocean-ice system applicable over time scales of 100 kyr, which show, in particular, that the Antarctic ice cap volume changes are due mainly to the effects of the northern hemisphere ice sheets on sea level (which influences ice calving), rather than directly to changes in SST, and hence the ice cap volume is greatest during interglacial periods. This conclusion, which is independent of the specification of the ice melting regime for the northern hemisphere ice sheets, strongly suggests that the changes in accumulation flux estimated from the Vostok proxy temperature data and used in other studies of the Antarctic mass balance have been overestimated. A simple expression is also presented for the lag of ice cap volume to SST, and it is found that the predictions for the mean sea level variability are similar to observations for a melting flux of the northern hemisphere ice sheets about twice their

  14. 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...... associated with COFs. In this paper, fully polarimetric P-band data acquired with the airborne POLARIS system near the ice divide of the Greenland ice sheet are analyzed. Based on a simple electromagnetic model, these data are interpreted, and a pronounced birefringence is found....

  15. Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics.

    Science.gov (United States)

    Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

    2015-04-24

    The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20 m on Milankovitch timescales. The inception of colder climate since ∼3 Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas.

  16. Continental Ice Sheets and the Planetary Radiation Budget

    OpenAIRE

    Oerlemans, J.

    1980-01-01

    The interaction between continental ice sheets and the planetary radiation budget is potentially important in climate-sensitivity studies. A simple ice-sheet model incorporated in an energybalance climate model provides a tool for studying this interaction in a quantitative way. Experiments in which the ice-sheet model is coupled step by step to the climate model show that ice sheets hardly affect the zonal mean radiation balance because the albedo feedback due to sea ice and snow cover is do...

  17. Improved ice loss estimate of the northwestern Greenland ice sheet

    DEFF Research Database (Denmark)

    Kjeldsen, Kristian Kjellerup; Khan, Shfaqat Abbas; Wahr, J.

    2013-01-01

    We estimate ice volume change rates in the northwest Greenland drainage basin during 2003–2009 using Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data. Elevation changes are often reported to be largest near the frontal portion of outlet glaciers. To improve the volume change...... estimate, we supplement the ICESat data with altimeter surveys from NASA's Airborne Topographic Mapper from 2002 to 2010 and NASA's Land, Vegetation and Ice Sensor from 2010. The Airborne data are mainly concentrated along the ice margin and thus have a significant impact on the estimate of the volume...... change. Our results show that adding Airborne Topographic Mapper and Land, Vegetation and Ice Sensor data to the ICESat data increases the catchment-wide estimate of ice volume loss by 11%, mainly due to an improved volume loss estimate along the ice sheet margin. Furthermore, our results show...

  18. Greenland ice sheet mass balance: a review

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Aschwanden, Andy; Bjørk, Anders A.

    2015-01-01

    and to ice discharge, which are forced by internal or external (atmospheric/oceanic/basal) fluctuations. Regardless of the measurement method, observations over the last two decades show an increase in ice loss rate, associated with speeding up of glaciers and enhanced melting. However, both ice discharge......Over the past quarter of a century the Arctic has warmed more than any other region on Earth, causing a profound impact on the Greenland ice sheet (GrIS) and its contribution to the rise in global sea level. The loss of ice can be partitioned into processes related to surface mass balance...... and melt-induced mass losses exhibit rapid short-term fluctuations that, when extrapolated into the future, could yield erroneous long-term trends. In this paper we review the GrIS mass loss over more than a century by combining satellite altimetry, airborne altimetry, interferometry, aerial photographs...

  19. The state of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Simonsen, Sebastian Bjerregaard

    Firn is defined as snow that has survived a melt season and provides the link between the high-frequency variability of the atmosphere to the ”slower” reacting ice sheet.In this thesis, firn is described by a theoretical and statistical approach to accommodate the variability in observed firn...... compaction on ice sheet scales. The modeling objectives are multiple and aim at estimating the contribution from the firn to the observed volume change of the GrIS and to the diffusion of stable water isotopes. The firn modeling then provides crucial information on total mass balance of the Gr......IS and the paleo-temperature reconstructions retrieved from ice cores.The dynamical firn model developed in this thesis explains13 % of the observed volume change of the GrIS from 2003-2008, without contributing to the global sea-level rise. This emphasizes the need for well constraint firn-compaction models. Here...

  20. An ice sheet model validation framework for the Greenland ice sheet

    Science.gov (United States)

    Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; Howat, Ian M.; Neumann, Thomas; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey; Chambers, Don P.; Evans, Katherine J.; Kennedy, Joseph H.; Lenaerts, Jan; Lipscomb, William H.; Perego, Mauro; Salinger, Andrew G.; Tuminaro, Raymond S.; van den Broeke, Michiel R.; Nowicki, Sophie M. J.

    2017-01-01

    We propose a new ice sheet model validation framework - the Cryospheric Model Comparison Tool (CmCt) - that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013, using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin-scale and whole-ice-sheet-scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CmCt, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate a predictive skill with respect to observed dynamic changes that have occurred on Greenland over the past few decades. An extensible design will allow for continued use

  1. A numerical study of cyclic behaviour of polar ice sheets

    NARCIS (Netherlands)

    Oerlemans, J.

    1983-01-01

    Possible cyclic behaviour of polar ice sheets is studied with a numerical ice-flow model. The model includes a calculation of bedrock adjustment and temperature field in the ice sheet. Basal water is traced and affects ice-mass discharge. Relaxation oscillations occur only for low

  2. The Greenland Ice Sheet Monitoring Network (GLISN)

    Science.gov (United States)

    Anderson, K. R.; Beaudoin, B. C.; Butler, R.; Clinton, J. F.; Dahl-Jensen, T.; Ekstrom, G.; Giardini, D.; Govoni, A.; Hanka, W.; Kanao, M.; Larsen, T.; Lasocki, S.; McCormack, D. A.; Mykkeltveit, S.; Nettles, M.; Agostinetti, N. P.; Stutzmann, E.; Tsuboi, S.; Voss, P.

    2010-12-01

    The GreenLand Ice Sheet monitoring Network (GLISN) is an international, broadband seismic capability for Greenland, being installed and implemented through the collaboration of Denmark, Canada, Germany, Italy, Japan, Norway, Poland, Switzerland, and USA. GLISN is a real-time sensor array of seismic stations to enhance and upgrade the performance of the sparse Greenland seismic infrastructure for detecting, locating, and characterizing glacial earthquakes and other cryo-seismic phenomena, and contributing to our understanding of Ice Sheet dynamics. Complementing data from satellites, geodesy, and other sources, and in concert with these technologies, GLISN will provide a powerful tool for detecting change, and will advance new frontiers of research in the glacial systems; the underlying geological and geophysical processes affecting the Greenland Ice Sheet; interactions between oceans, climate, and the cryosphere; and other multidisciplinary areas of interest to geoscience and climate dynamics. The glacial processes that induce seismic events (internal deformation, sliding at the base, disintegration at the calving front, drainage of supra-glacial lakes) are all integral to the overall dynamics of glaciers, and seismic observations of glaciers therefore provide a quantitative means for monitoring changes in their behavior over time. Long-term seismic monitoring of the Greenland Ice Sheet will contribute to identifying possible unsuspected mechanisms and metrics relevant to ice sheet collapse, and will provide new constraints on Ice Sheet dynamic processes and their potential roles in sea-level rise during the coming decades. GLISN will provide a new, fiducial reference network in and around Greenland for monitoring these phenomena in real-time, and for the broad seismological study of Earth and earthquakes. The 2010 summer field season saw the installation or upgrade of 9 stations in the GLISN network. Sites visited under the GLISN project include Station Nord (NOR

  3. Irregular oscillations of the West Antarctic Ice Sheet

    Science.gov (United States)

    Macayeal, Douglas R.

    1993-01-01

    Model simulations of the West Antarctic ice sheet suggest that sporadic, perhaps chaotic, collapse (complete mobilization) of the ice sheet occurred throughout the past one million years. The irregular behavior is due to the slow equilibration time of the distribution of basal till, which lubricates ice-sheet motion. This nonlinear response means that predictions of future collapse of the ice sheet in response to global warming must take into account its past history, and in particular, whether the present basal till distribution predisposes the ice sheet towards rapid change.

  4. Isostasy in Greenland - deglaciation of an ice sheet

    DEFF Research Database (Denmark)

    Kjeldsen, Kristian Kjellerup; Funder, Svend Visby

    The large continental ice sheets left a legacy of isostatic upheaval, which is generally aligned in a rather simple pattern consisting of a dome of uplift with its maximum at the centre of the former ice sheet. Owing to the incomplete deglaciation the isostatic signal left by the LGM ice sheet...... in Greenland is not simple, but composed of several domes with high uplift separated by swales with low uplift. This pattern, which reflects both unloading after LGM and reloading during Neoglacial ice sheet growth, shows that different sectors of the ice sheet responded differently to Holocene warming...

  5. Mountain building and the initiation of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Solgaard, Anne Munck; Bonow, Johan; Langen, Peter Lang

    2013-01-01

    sheet by providing anchoring points which are not available to the same extent in the lower topographies. However, the results also reveal a Föhn effect that inhibits ice sheet expansion into the interior Greenland and thus shifts the threshold of formation of inland ice towards colder temperatures......The effects of a new hypothesis about mountain building in Greenland on ice sheet initiation are investigated using an ice sheet model in combination with a climate model. According to this hypothesis, low-relief landscapes near sea level characterised Greenland in Miocene times until two phases...... and the cooling of surface temperatures accompanying the uplift. Large amounts of ice are able to formafter the first uplift event, but the ice sheet is sensitive to changes in climate. The results showthat the second phase of uplift facilitates ice sheet build-up further and increases the stability of the ice...

  6. Net accumulation of the Greenland ice sheet

    DEFF Research Database (Denmark)

    Kiilsholm, Sissi; Christensen, Jens Hesselbjerg; Dethloff, Klaus

    2003-01-01

    improvement compared to the driving OAGCM. Estimates of the regional net balance are also better represented by the RCM. In the future climate the net balance for the Greenland Ice Sheet is reduced in all the simulation, but discrepancies between the amounts when based on ECHAM4/OPYC3 and HIRHAM are found....... In both scenarios, the estimated melt rates are larger in HIRHAM than in the driving model....

  7. 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.

  8. Deglaciation of the Eurasian ice sheet complex

    Science.gov (United States)

    Patton, Henry; Hubbard, Alun; Andreassen, Karin; Auriac, Amandine; Whitehouse, Pippa L.; Stroeven, Arjen P.; Shackleton, Calvin; Winsborrow, Monica; Heyman, Jakob; Hall, Adrian M.

    2017-08-01

    The Eurasian ice sheet complex (EISC) was the third largest ice mass during the Last Glacial Maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea-level lowering. Whilst recent terrestrial and marine empirical insights have improved understanding of the chronology, pattern and rates of retreat of this vast ice sheet, a concerted attempt to model the deglaciation of the EISC honouring these new constraints is conspicuously lacking. Here, we apply a first-order, thermomechanical ice sheet model, validated against a diverse suite of empirical data, to investigate the retreat of the EISC after 23 ka BP, directly extending the work of Patton et al. (2016) who modelled the build-up to its maximum extent. Retreat of the ice sheet complex was highly asynchronous, reflecting contrasting regional sensitivities to climate forcing, oceanic influence, and internal dynamics. Most rapid retreat was experienced across the Barents Sea sector after 17.8 ka BP when this marine-based ice sheet disintegrated at a rate of ∼670 gigatonnes per year (Gt a-1) through enhanced calving and interior dynamic thinning, driven by oceanic/atmospheric warming and exacerbated by eustatic sea-level rise. From 14.9 to 12.9 ka BP the EISC lost on average 750 Gt a-1, peaking at rates >3000 Gt a-1, roughly equally partitioned between surface melt and dynamic losses, and potentially contributing up to 2.5 m to global sea-level rise during Meltwater Pulse 1A. Independent glacio-isostatic modelling constrained by an extensive inventory of relative sea-level change corroborates our ice sheet loading history of the Barents Sea sector. Subglacial conditions were predominately temperate during deglaciation, with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network. Moreover, the maximum EISC and its isostatic footprint had a profound impact on the proglacial hydrological network, forming the Fleuve Manche mega-catchment which had an area of

  9. History of the Greenland Ice Sheet: paleoclimatic insights

    DEFF Research Database (Denmark)

    Alley, Richard B.; Andrews, John Thomas; Brigham-Grette, Julia

    2010-01-01

    increased melting and flow near the edges. Most documented forcings and ice-sheet responses spanned periods of several thousand years, but limited data also show rapid response to rapid forcings. In particular, regions near the ice margin have responded within decades. However, major changes of central......Paleoclimatic records show that the Greenland Ice Sheet consistently has lost mass in response to warming, and grown in response to cooling. Such changes have occurred even at times of slow or zero sea-level change, so changing sea level cannot have been the cause of at least some of the ice......-sheet changes. In contrast, there are no documented major ice-sheet changes that occurred independent of temperature changes. Moreover, snowfall has increased when the climate warmed, but the ice sheet lost mass nonetheless; increased accumulation in the ice sheet's center has not been sufficient to counteract...

  10. Evidence of meltwater retention within the Greenland ice sheet

    Directory of Open Access Journals (Sweden)

    A. K. Rennermalm

    2013-09-01

    Full Text Available Greenland ice sheet mass losses have increased in recent decades with more than half of these attributed to surface meltwater runoff. However, the magnitudes of englacial storage, firn retention, internal refreezing and other hydrologic processes that delay or reduce true water export to the global ocean remain less understood, partly due to a scarcity of in situ measurements. Here, ice sheet surface meltwater runoff and proglacial river discharge between 2008 and 2010 near Kangerlussuaq, southwestern Greenland were used to establish sub- and englacial meltwater storage for a small ice sheet watershed (36–64 km2. This watershed lacks significant potential meltwater storage in firn, surface lakes on the ice sheet and in the proglacial area, and receives limited proglacial precipitation. Thus, ice sheet surface runoff not accounted for by river discharge can reasonably be attributed to retention in sub- and englacial storage. Evidence for meltwater storage within the ice sheet includes (1 characteristic dampened daily river discharge amplitudes relative to ice sheet runoff; (2 three cold-season river discharge anomalies at times with limited ice sheet surface melt, demonstrating that meltwater may be retained up to 1–6 months; (3 annual ice sheet watershed runoff is not balanced by river discharge, and while near water budget closure is possible as much as 54% of melting season ice sheet runoff may not escape to downstream rivers; (4 even the large meltwater retention estimate (54% is equivalent to less than 1% of the ice sheet volume, which suggests that storage in en- and subglacial cavities and till is plausible. While this study is the first to provide evidence for meltwater retention and delayed release within the Greenland ice sheet, more information is needed to establish how widespread this is along the Greenland ice sheet perimeter.

  11. Analysis of groundwater flow beneath ice sheets

    Energy Technology Data Exchange (ETDEWEB)

    Boulton, G. S.; Zatsepin, S.; Maillot, B. [Univ. of Edinburgh (United Kingdom). Dept. of Geology and Geophysics

    2001-03-01

    The large-scale pattern of subglacial groundwater flow beneath European ice sheets was analysed in a previous report. It was based on a two-dimensional flowline model. In this report, the analysis is extended to three dimensions by exploring the interactions between groundwater and tunnel flow. A theory is developed which suggests that the large-scale geometry of the hydraulic system beneath an ice sheet is a coupled, self-organising system. In this system the pressure distribution along tunnels is a function of discharge derived from basal meltwater delivered to tunnels by groundwater flow, and the pressure along tunnels itself sets the base pressure which determines the geometry of catchments and flow towards the tunnel. The large-scale geometry of tunnel distribution is a product of the pattern of basal meltwater production and the transmissive properties of the bed. The tunnel discharge from the ice margin of the glacier, its seasonal fluctuation and the sedimentary characteristics of eskers are largely determined by the discharge of surface meltwater which penetrates to the bed in the terminal zone. The theory explains many of the characteristics of esker systems and can account for tunnel valleys. It is concluded that the large-scale hydraulic regime beneath ice sheets is largely a consequence of groundwater/tunnel flow interactions and that it is essential similar to non-glacial hydraulic regimes. Experimental data from an Icelandic glacier, which demonstrates measured relationships between subglacial tunnel flow and groundwater flow during the transition from summer to winter seasons for a modern glacier, and which support the general conclusions of the theory is summarised in an appendix.

  12. Ice sheet studies with DESDynI

    Science.gov (United States)

    Rignot, E.

    2007-12-01

    DESDynI L-band InSAR promises timely and major advances in our monitoring capability and scientific understanding of the evolution of ice sheets and glaciers. InSAR has a long history of glaciology applications which started in 1991 with the launch of ERS-1. The European Space Agency ERS-1/2 satellites demonstrated the capability of InSAR to measure ice motion, grounding line migration, downdraw of ice surfaces, ice-shelf rifting and tidal flexure, glacial surges and other essential characteristics of ice dynamics, however with limited temporal and spatial coverage. Radarsat-1 and Envisat ASAR permitted significant advances in ice motion mapping using speckle tracking techniques, and longer-term observations of glacier evolution, but missed the shorter time scale resolution of ERS-1/2 tandem data. DESDynI will offer both, with higher quality and higher frequency of visit. The higher quality stems from the higher coherence of L-band signals on snow and ice demonstrated with SIR-C and confirmed with ALOS PALSAR, which is important in high- acumulation coastal sectors. Higher frequency of re-visit stems from the 8-day repeat and a plan to systematically acquire data with controlled baselines. ALOS PALSAR early results in West Antarctica and Greenland are very encouraging, with more data to come.Yet ALOS PALSAR 46-day repeat limits its capability to observe short-terms events e.g. calving, grounding line migration, tidal modulation in glacier velocity, downdraw consecutives to changes in basal sliding or subglacial drainage, which are important to observe to characterize the impulse response of glaciers to climate perturbations. DESDynI promises important discoveries and new science advances that are not possible with existing and planned InSAR missions. These advances will be a pillar for the development of more realistic numerical ice sheet models capable of realistic predictions of their evolution in a continously warming climate. This work was performed at Caltech

  13. Climatic Conditions for modelling the Northern Hemisphere ice sheets throughout the ice age cycle

    Directory of Open Access Journals (Sweden)

    A. Abe-Ouchi

    2007-07-01

    Full Text Available The ice sheet-climate interaction as well as the climatic response to orbital parameters and atmospheric CO2 concentration are examined in order to drive an ice sheet model throughout an ice age cycle. Feedback processes between ice sheet and atmosphere are analyzed by numerical experiments using a high resolution General Circulation Model (GCM under different conditions at the Last Glacial Maximum. Among the proposed processes, the ice albedo feedback, the elevation-mass balance feedback and the desertification effect over the ice sheet were found to be the dominant processes for the ice-sheet mass balance. For the elevation-mass balance feedback, the temperature lapse rate over the ice sheet is proposed to be weaker than assumed in previous studies. Within the plausible range of parameters related to these processes, the ice sheet response to the orbital parameters and atmospheric CO2 concentration for the last glacial/interglacial cycle was simulated in terms of both ice volume and geographical distribution, using a three-dimensional ice-sheet model. Careful treatment of climate-ice sheet feedback is essential for a reliable simulation of the ice sheet changes during ice age cycles.

  14. Greenland ice sheet motion insensitive to exceptional meltwater forcing.

    Science.gov (United States)

    Tedstone, Andrew J; Nienow, Peter W; Sole, Andrew J; Mair, Douglas W F; Cowton, Thomas R; Bartholomew, Ian D; King, Matt A

    2013-12-03

    Changes to the dynamics of the Greenland ice sheet can be forced by various mechanisms including surface-melt-induced ice acceleration and oceanic forcing of marine-terminating glaciers. We use observations of ice motion to examine the surface melt-induced dynamic response of a land-terminating outlet glacier in southwest Greenland to the exceptional melting observed in 2012. During summer, meltwater generated on the Greenland ice sheet surface accesses the ice sheet bed, lubricating basal motion and resulting in periods of faster ice flow. However, the net impact of varying meltwater volumes upon seasonal and annual ice flow, and thus sea level rise, remains unclear. We show that two extreme melt events (98.6% of the Greenland ice sheet surface experienced melting on July 12, the most significant melt event since 1889, and 79.2% on July 29) and summer ice sheet runoff ~3.9 σ above the 1958-2011 mean resulted in enhanced summer ice motion relative to the average melt year of 2009. However, despite record summer melting, subsequent reduced winter ice motion resulted in 6% less net annual ice motion in 2012 than in 2009. Our findings suggest that surface melt-induced acceleration of land-terminating regions of the ice sheet will remain insignificant even under extreme melting scenarios.

  15. Interaction of ice sheets and climate on geological time scales

    NARCIS (Netherlands)

    Stap, L.B.

    2017-01-01

    Since the inception of the Antarctic ice sheet at the Eocene-Oligocene Transition (~34 Myr ago), land ice plays a crucial role in Earth’s climate. Through the ice-albedo and surface-height-temperature feedbacks, land ice variability strengthens atmospheric temperature changes induced by orbital and

  16. Surface elevation changes of the greenland ice sheet - results from ESA'S ice sheet CCI

    DEFF Research Database (Denmark)

    Fredenslund Levinsen, Joanna; Khvorostovky, Kirill; Meister, Rakia

    2013-01-01

    the most optimal method, a Round Robin exercise was conducted in which the scientific community was asked to provide their best SEC estimate over the Jakobshavn Isbr drainage basin. The participants used both repeat-track (RT), overlapping footprints, and the cross-over (XO) methods, and both ICESat laser......In order to ensure long-term climate data records for the Greenland Ice Sheet (GIS), ESA have launched the Climate Change Initiative (CCI). This work presents the preliminary steps towards the Ice Sheet CCI's surface elevation change (SEC) derivation using radar altimeter data. In order to find...... and Envisat radar altimeter data were used. Based on this and feedback sheets describing their methods we found that a combination of the RT and XO techniques yielded the best results. In the following, the obtained results will be presented and discussed....

  17. Importance of Nisar Mission for Ice Sheet Studies

    Science.gov (United States)

    Rignot, E. J.; Scheuchl, B.; Mouginot, J.; Morlighem, M.

    2014-12-01

    This presentation addresses how the synthetic-aperture radar (SAR) satellite mission under discussion between NASA and ISRO - entitled NISAR - will help us better understand and project the evolution of ice sheets and glaciers in a changing climate. NISAR is a dedicated L-band interferometry mission that will document changes in ice flow dynamics, grounding line positions and other critical boundaries over the lifetime of its mission. Changes in ice sheet dynamics represent by far the largest uncertainty in sea level projections. NISAR will better constrain critical boundaries of ice sheets at the base (basal friction) and at the seaward margins (ice melt rate) by providing the first set of continuous, systematic and comprehensive observations of ice sheet dynamics that will help us better understand ice sheets and glaciers and enable massive data assimilation in numerical ice sheet models. NISAR will contribute observations of areas of irreversible retreat taking place in Greenland and Antarctica, provide detailed time series of glacier velocities throughout entire seasonal cycles, document grounding line dynamics on weekly time scales, enable estimations of temporal and spatial changes in basal friction during glacial retreat; it will also in combination with other data help us map the bed topography of entire ice sheets at a high spatial resolution, document changes in ice shelf melt rate around the periphery of the continents, and provide a first systematic 3D vector mapping of ice velocity. NISAR will constitute a much needed warning system for ice sheet and ice shelf changes, it will document fundamental processes poorly observed in the past (e.g. calving, ice shelf melt, grounding line dynamics) and enable robust data assimilation to play a critical role in reducing uncertainties of coupled numerical models of ocean-ice-atmosphere interactions. This work was performed at UCI and JPL under a contract with NASA.

  18. Using the glacial geomorphology of palaeo-ice streams to understand mechanisms of ice sheet collapse

    Science.gov (United States)

    Stokes, Chris R.; Margold, Martin; Clark, Chris; Tarasov, Lev

    2017-04-01

    Processes which bring about ice sheet deglaciation are critical to our understanding of glacial-interglacial cycles and ice sheet sensitivity to climate change. The precise mechanisms of deglaciation are also relevant to our understanding of modern-day ice sheet stability and concerns over global sea level rise. Mass loss from ice sheets can be broadly partitioned between melting and a 'dynamic' component whereby rapidly-flowing ice streams/outlet glaciers transfer ice from the interior to the oceans. Surface and basal melting (e.g. of ice shelves) are closely linked to atmospheric and oceanic conditions, but the mechanisms that drive dynamic changes in ice stream discharge are more complex, which generates much larger uncertainties about their future contribution to ice sheet mass loss and sea level rise. A major problem is that observations of modern-day ice streams typically span just a few decades and, at the ice-sheet scale, it is unclear how the entire drainage network of ice streams evolves during deglaciation. A key question is whether ice streams might increase and sustain rates of mass loss over centuries or millennia, beyond those expected for a given ocean-climate forcing. To address this issue, numerous workers have sought to understand ice stream dynamics over longer time-scales using their glacial geomorphology in the palaeo-record. Indeed, our understanding of their geomorphology has grown rapidly in the last three decades, from almost complete ignorance to a detailed knowledge of their geomorphological products. Building on this body of work, this paper uses the glacial geomorphology of 117 ice streams in the North American Laurentide Ice Sheet to reconstruct their activity during its deglaciation ( 22,000 to 7,000 years ago). Ice stream activity was characterised by high variability in both time and space, with ice streams switching on and off in different locations. During deglaciation, we find that their overall number decreased, they occupied a

  19. Antarctic ice rises and rumples : Their properties and significance for ice-sheet dynamics and evolution

    NARCIS (Netherlands)

    Matsuoka, Kenichi; Hindmarsh, Richard C A; Moholdt, Geir; Bentley, Michael J.; Pritchard, Hamish D.; Brown, Joel; Conway, Howard; Drews, Reinhard; Durand, Gaël; Goldberg, Daniel; Hattermann, Tore; Kingslake, Jonathan; Lenaerts, Jan T M; Martín, Carlos; Mulvaney, Robert; Nicholls, Keith W.; Pattyn, Frank; Ross, Neil; Scambos, Ted; Whitehouse, Pippa L.

    2015-01-01

    Locally grounded features in ice shelves, called ice rises and rumples, play a key role buttressing discharge from the Antarctic Ice Sheet and regulating its contribution to sea level. Ice rises typically rise several hundreds of meters above the surrounding ice shelf; shelf flow is diverted around

  20. The modelled liquid water balance of the Greenland Ice Sheet

    NARCIS (Netherlands)

    Steger, Christian R.; Reijmer, Carleen H.; van den Broeke, Michiel R.

    2017-01-01

    Recent studies indicate that the surface mass balance will dominate the Greenland Ice Sheet's (GrIS) contribution to 21st century sea level rise. Consequently, it is crucial to understand the liquid water balance (LWB) of the ice sheet and its response to increasing surface melt. We therefore

  1. Continental Ice Sheets and the Planetary Radiation Budget

    NARCIS (Netherlands)

    Oerlemans, J.

    1980-01-01

    The interaction between continental ice sheets and the planetary radiation budget is potentially important in climate-sensitivity studies. A simple ice-sheet model incorporated in an energybalance climate model provides a tool for studying this interaction in a quantitative way. Experiments in which

  2. Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics

    DEFF Research Database (Denmark)

    Csatho, Beata M.; Schenk, Anton F.; van der Veen, Cornelis J.

    2014-01-01

    Significance We present the first detailed reconstruction of surface elevation changes of the Greenland Ice Sheet from NASA’s laser altimetry data. Time series at nearly 100,000 locations allow the characterization of ice sheet changes at scales ranging from individual outlet glaciers to larger...

  3. Interactions between ice sheets, climate and the solid Earth

    NARCIS (Netherlands)

    Berg, J. van den

    2007-01-01

    The melting of ice sheets in response to increasing temperatures is an important contribution to present day sea level rise. To predict the amount of sea level rise and to assess its impact on populated coastal regions, an increased understanding of the physical processes governing ice sheets is

  4. On underwater sound reflection from layered ice sheets

    CERN Document Server

    Hobæk, Halvor

    2016-01-01

    Reflection of sound from ice sheets floating on water is simulated using Thomson and Haskell's method of matrix propagation. The reflection coefficient is computed as a function of incidence angle and frequency for selected ice parameters of a uniform sheet and two layered ice sheets. At some incidence angles and frequencies the reflection coefficient has very low values. It is shown that this is related to generation of Lamb waves in the ice. The matrix propagation method also provides a dispersion equation for a plate loaded with fluid on one side and vacuum on the other. Finally the concept of beam displacement is briefly discussed.

  5. Antarctic ice volume for the last 740 ka calculated with a simple ice sheet model

    NARCIS (Netherlands)

    Oerlemans, J.

    2005-01-01

    Fluctuations in the volume of the Antarctic ice sheet for the last 740 ka are calculated by forcing a simple ice sheet model with a sea-level history (from a composite deep sea δ18O record) and a temperature history (from the Dome C deuterium record). Antarctic ice volume reaches maximum values of

  6. Translating hydrologically-relevant variables from the ice sheet model SICOPOLIS to the Greenland Analog Project hydrologic modeling domain

    Science.gov (United States)

    Vallot, Dorothée; Applegate, Patrick; Pettersson, Rickard

    2013-04-01

    Projecting future climate and ice sheet development requires sophisticated models and extensive field observations. Given the present state of our knowledge, it is very difficult to say what will happen with certainty. Despite the ongoing increase in atmospheric greenhouse gas concentrations, the possibility that a new ice sheet might form over Scandinavia in the far distant future cannot be excluded. The growth of a new Scandinavian Ice Sheet would have important consequences for buried nuclear waste repositories. The Greenland Analogue Project, initiated by the Swedish Nuclear Fuel and Waste Management Company (SKB), is working to assess the effects of a possible future ice sheet on groundwater flow by studying a constrained domain in Western Greenland by field measurements (including deep bedrock drilling in front of the ice sheet) combined with numerical modeling. To address the needs of the GAP project, we interpolated results from an ensemble of ice sheet model runs to the smaller and more finely resolved modeling domain used in the GAP project's hydrologic modeling. Three runs have been chosen with three fairly different positive degree-day factors among those that reproduced the modern ice margin at the borehole position. The interpolated results describe changes in hydrologically-relevant variables over two time periods, 115 ka to 80 ka, and 20 ka to 1 ka. In the first of these time periods, the ice margin advances over the model domain; in the second time period, the ice margin retreats over the model domain. The spatially-and temporally dependent variables that we treated include the ice thickness, basal melting rate, surface mass balance, basal temperature, basal thermal regime (frozen or thawed), surface temperature, and basal water pressure. The melt flux is also calculated.

  7. Monitoring southwest Greenland's ice sheet melt with ambient seismic noise.

    Science.gov (United States)

    Mordret, Aurélien; Mikesell, T Dylan; Harig, Christopher; Lipovsky, Bradley P; Prieto, Germán A

    2016-05-01

    The Greenland ice sheet presently accounts for ~70% of global ice sheet mass loss. Because this mass loss is associated with sea-level rise at a rate of 0.7 mm/year, the development of improved monitoring techniques to observe ongoing changes in ice sheet mass balance is of paramount concern. Spaceborne mass balance techniques are commonly used; however, they are inadequate for many purposes because of their low spatial and/or temporal resolution. We demonstrate that small variations in seismic wave speed in Earth's crust, as measured with the correlation of seismic noise, may be used to infer seasonal ice sheet mass balance. Seasonal loading and unloading of glacial mass induces strain in the crust, and these strains then result in seismic velocity changes due to poroelastic processes. Our method provides a new and independent way of monitoring (in near real time) ice sheet mass balance, yielding new constraints on ice sheet evolution and its contribution to global sea-level changes. An increased number of seismic stations in the vicinity of ice sheets will enhance our ability to create detailed space-time records of ice mass variations.

  8. Stress transmission across grounding lines and marine ice sheet instability

    Science.gov (United States)

    Docquier, David; Nick, Faezeh M.; Perichon, Laura; Pattyn, Frank

    2010-05-01

    The stability of marine ice sheets is largely controlled by the dynamic behaviour of the grounding line, i.e., the contact of the bottom of the ice sheet resting on the bedrock with the ocean water. Marine ice sheet instability implies that an ice sheet on a downward sloping bedrock towards the interior will never find stable equilibria, hence leading to ice sheet collapse, unless an upward slope is reached (Schoof, 2007). The latter study shows that steady state solutions using a boundary layer theory for ice flux are in very close agreement with numerical resolutions that resolve the transition zone. However, the time dependent response of grounding line migration is not predicted by this theory. Precise knowledge of this response is essential for assessing the short term impact of accelerated ice discharge on sea level rise. Here we present the results of MISMIP-type (Marine Ice Sheet Model Intercomparison Project) experiments with different sets of numerical flowline models (fixed and moving grid) that solve the stress field in the transition zone according to different approximations to the Stokes equations. These models include shallow-ice (SIA0), shallow-shelf (L1L2) and higher-order (LMLa) approximations, and combinations of these types. All experiments are run at different spatial resolutions and for different sizes of the transition zone (high to low friction). The comparison of several stress approximants allows us to evaluate which stress components in the flow direction are important to the general behaviour of grounding line migration.

  9. The drainage of the Baltic Ice Lake and a new Scandinavian reference 10Be production rate

    Science.gov (United States)

    Stroeven, Arjen P.; Heyman, Jakob; Fabel, Derek; Björck, Svante; Caffee, Marc W.; Fredin, Ola; Harbor, Jonathan M.

    2015-04-01

    An important constraint on the reliability of cosmogenic nuclide exposure dating is the derivation of tightly controlled production rates. We present a new dataset for 10Be production rate calibration from Mount Billingen, southern Sweden, the site of the final drainage of the Baltic Ice Lake, an event dated to 11,620 ± 100 cal yr BP. Nine samples of flood-scoured bedrock surfaces and depositional boulders and cobbles unambiguously connected to the drainage event yield a reference 10Be production rate of 4.09 ± 0.22 atoms g-1 yr-1 for the CRONUS Lm scaling and 3.93 ± 0.21 atoms g-1 yr-1 for the LSD general spallation scaling. We also recalibrate the reference 10Be production rates for four sites in Norway and combine these with the Billingen results to derive a tightly clustered Scandinavian reference 10Be production rate of 4.12 ± 0.10 (4.12 ± 0.25 for altitude scaling) atoms g-1 yr-1 for the Lm scaling scheme and 3.96 ± 0.10 (3.96 ± 0.24 for altitude scaling) atoms g-1 yr-1 for the LSD scaling scheme.

  10. 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.

  11. Influence of a dynamic ocean on Permian ice sheet growth

    Science.gov (United States)

    Tilevitz, C.; Poulsen, C. J.

    2015-12-01

    Previous studies using an atmospheric general circulation model have shown that extensive ice sheets can grow on the Gondwanan supercontinent during the late Paleozoic (~340-250 Ma) under modern orbital parameters and CO2 levels at or below two times pre-industrial values (CO2 ≤560 ppm). Proxy records for the late Paleozoic suggest a wide range of potential CO2 values, but the range of values that allows for the growth of large ice sheets is much smaller. A prescribed slab ocean with diffusive heat transport (using modern heat fluxes) was used for those experiments, but lacks the ability to accurately capture the ocean dynamics of the Paleozoic. Here, within the NCAR Community Earth System Model framework, we use a fully dynamic ocean model to explore Permian ice sheet growth under more realistic conditions. Fully coupled CESM simulations for two CO2 levels (280 & 560 ppm) are run until the ocean equilibrates (~1500-2000 years). Climatologies from those simulations are then used to drive a three-dimensional dynamic ice sheet model in an asynchronous coupling, in which the ice sheet model is run until the ice sheets equilibrate. The ice sheet geometry and height are then used to update the coupled ocean-atmosphere model, which is run for ~20 years, until the climate system re-equilibrates. Preliminary results show that ice sheet growth at the higher CO2 value is small in comparison with ice sheet growth in the lower CO2 environment, which is consistent with previous late Paleozoic modeling studies. The latitudinal temperature gradient is also steeper at 280 ppm CO2 than at 560 ppm, though the dynamic ocean buffers some of these changes relative to what they would be for a slab ocean.

  12. Elevation Change Measurements of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Forsberg, R.; Keller, K.; Nielsen, C. S.

    2000-01-01

    flow models. In a local ice cap in East Greenland (Geikie Plateau) repeated GPS, airborne laser altimetry and SAR interferometry have been used to study ice movements in the more climatically variable coastal zone, where meter-level annual elevation changes are possible due to the high precipitation......Repeated GPS measurements have been performed at the centre of the Greenland Ice Sheet since 1992. Results have shown that the ice sheet is essentially stable at this location, with GPS-determined strain and elevation change rates in good accordance with yearly snow accumulation and glaciological...

  13. Algae Drive Enhanced Darkening of Bare Ice on the Greenland Ice Sheet

    Science.gov (United States)

    Stibal, Marek; Box, Jason E.; Cameron, Karen A.; Langen, Peter L.; Yallop, Marian L.; Mottram, Ruth H.; Khan, Alia L.; Molotch, Noah P.; Chrismas, Nathan A. M.; Calı Quaglia, Filippo; Remias, Daniel; Smeets, C. J. P. Paul; van den Broeke, Michiel R.; Ryan, Jonathan C.; Hubbard, Alun; Tranter, Martyn; van As, Dirk; Ahlstrøm, Andreas P.

    2017-11-01

    Surface ablation of the Greenland ice sheet is amplified by surface darkening caused by light-absorbing impurities such as mineral dust, black carbon, and pigmented microbial cells. We present the first quantitative assessment of the microbial contribution to the ice sheet surface darkening, based on field measurements of surface reflectance and concentrations of light-absorbing impurities, including pigmented algae, during the 2014 melt season in the southwestern part of the ice sheet. The impact of algae on bare ice darkening in the study area was greater than that of nonalgal impurities and yielded a net albedo reduction of 0.038 ± 0.0035 for each algal population doubling. We argue that algal growth is a crucial control of bare ice darkening, and incorporating the algal darkening effect will improve mass balance and sea level projections of the Greenland ice sheet and ice masses elsewhere.

  14. Radar attenuation and temperature within the Greenland Ice Sheet

    Science.gov (United States)

    MacGregor, Joseph A; Li, Jilu; Paden, John D; Catania, Ginny A; Clow, Gary D.; Fahnestock, Mark A; Gogineni, Prasad S.; Grimm, Robert E.; Morlighem, Mathieu; Nandi, Soumyaroop; Seroussi, Helene; Stillman, David E

    2015-01-01

    The flow of ice is temperature-dependent, but direct measurements of englacial temperature are sparse. The dielectric attenuation of radio waves through ice is also temperature-dependent, and radar sounding of ice sheets is sensitive to this attenuation. Here we estimate depth-averaged radar-attenuation rates within the Greenland Ice Sheet from airborne radar-sounding data and its associated radiostratigraphy. Using existing empirical relationships between temperature, chemistry, and radar attenuation, we then infer the depth-averaged englacial temperature. The dated radiostratigraphy permits a correction for the confounding effect of spatially varying ice chemistry. Where radar transects intersect boreholes, radar-inferred temperature is consistently higher than that measured directly. We attribute this discrepancy to the poorly recognized frequency dependence of the radar-attenuation rate and correct for this effect empirically, resulting in a robust relationship between radar-inferred and borehole-measured depth-averaged temperature. Radar-inferred englacial temperature is often lower than modern surface temperature and that of a steady state ice-sheet model, particularly in southern Greenland. This pattern suggests that past changes in surface boundary conditions (temperature and accumulation rate) affect the ice sheet's present temperature structure over a much larger area than previously recognized. This radar-inferred temperature structure provides a new constraint for thermomechanical models of the Greenland Ice Sheet.

  15. Reconstructing the temperature regime of the Weichselian ice sheet

    Energy Technology Data Exchange (ETDEWEB)

    Holmlund, P. [Stockholm Univ. (Sweden). Dept. of Physical Geography

    1997-04-01

    Areas in Sweden are described, where the ice could have been at the pressure melting point during the last ice age. In order to calculate probable degrees of glacial erosion, estimates on the time of ice coverage and the temperature distribution in time are combined data on erosion rates from present day glaciers. An estimate of the extent of ice cover can be made using the proxy temperature record from the Greenland ice cores and a model of the ice sheet. Adding the estimations on climate and ice sheet shape outlined in this contribution, to erosion figures we may conclude that the crucial areas for glaciation erosion are within the mountains and where the present Baltic and the Gulf of Bothnia are situated. At these sites erosion rates of some tens of meters may have occurred. In inland northern Sweden and inland southern Sweden the potential for glacial erosion seems to be small. 14 refs.

  16. Monitoring Antarctic ice sheet surface melting with TIMESAT algorithm

    Science.gov (United States)

    Ye, Y.; Cheng, X.; Li, X.; Liang, L.

    2011-12-01

    Antarctic ice sheet contributes significantly to the global heat budget by controlling the exchange of heat, moisture, and momentum at the surface-atmosphere interface, which directly influence the global atmospheric circulation and climate change. Ice sheet melting will cause snow humidity increase, which will accelerate the disintegration and movement of ice sheet. As a result, detecting Antarctic ice sheet melting is essential for global climate change research. In the past decades, various methods have been proposed for extracting snowmelt information from multi-channel satellite passive microwave data. Some methods are based on brightness temperature values or a composite index of them, and others are based on edge detection. TIMESAT (Time-series of Satellite sensor data) is an algorithm for extracting seasonality information from time-series of satellite sensor data. With TIMESAT long-time series brightness temperature (SSM/I 19H) is simulated by Double Logistic function. Snow is classified to wet and dry snow with generalized Gaussian model. The results were compared with those from a wavelet algorithm. On this basis, Antarctic automatic weather station data were used for ground verification. It shows that this algorithm is effective in ice sheet melting detection. The spatial distribution of melting areas(Fig.1) shows that, the majority of melting areas are located on the edge of Antarctic ice shelf region. It is affected by land cover type, surface elevation and geographic location (latitude). In addition, the Antarctic ice sheet melting varies with seasons. It is particularly acute in summer, peaking at December and January, staying low in March. In summary, from 1988 to 2008, Ross Ice Shelf and Ronnie Ice Shelf have the greatest interannual variability in amount of melting, which largely determines the overall interannual variability in Antarctica. Other regions, especially Larsen Ice Shelf and Wilkins Ice Shelf, which is in the Antarctic Peninsula

  17. MASS BALANCE CHANGES AND ICE DYNAMICS OF GREENLAND AND ANTARCTIC ICE SHEETS FROM LASER ALTIMETRY

    Directory of Open Access Journals (Sweden)

    G. S. Babonis

    2016-06-01

    Full Text Available During the past few decades the Greenland and Antarctic ice sheets have lost ice at accelerating rates, caused by increasing surface temperature. The melting of the two big ice sheets has a big impact on global sea level rise. If the ice sheets would melt down entirely, the sea level would rise more than 60 m. Even a much smaller rise would cause dramatic damage along coastal regions. In this paper we report about a major upgrade of surface elevation changes derived from laser altimetry data, acquired by NASA’s Ice, Cloud and land Elevation Satellite mission (ICESat and airborne laser campaigns, such as Airborne Topographic Mapper (ATM and Land, Vegetation and Ice Sensor (LVIS. For detecting changes in ice sheet elevations we have developed the Surface Elevation Reconstruction And Change detection (SERAC method. It computes elevation changes of small surface patches by keeping the surface shape constant and considering the absolute values as surface elevations. We report about important upgrades of earlier results, for example the inclusion of local ice caps and the temporal extension from 1993 to 2014 for the Greenland Ice Sheet and for a comprehensive reconstruction of ice thickness and mass changes for the Antarctic Ice Sheets.

  18. Hydrologic Outlets of the Greenland Ice Sheet, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — The Hydrologic Outlets of the Greenland Ice Sheet data set contains GIS point shapefiles that include 891 observed and potential hydrologic outlets of the Greenland...

  19. Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers

    National Research Council Canada - National Science Library

    Box, J. E; Fettweis, X; Stroeve, J. C; Tedesco, M; Hall, D. K; Steffen, K

    2012-01-01

    ... impact of the ice sheet albedo feedback over 12 summer periods beginning in 2000. We find that, while albedo feedback defined by the change in net solar shortwave flux and temperature over time is positive over 97...

  20. Greenland Ice Sheet Melt Characteristics Derived from Passive Microwave Data

    Data.gov (United States)

    National Aeronautics and Space Administration — The Greenland ice sheet melt extent data, acquired as part of the NASA Program for Arctic Regional Climate Assessment (PARCA), is a daily (or every other day, prior...

  1. The role of ice sheets in the pleistocene climate

    OpenAIRE

    Oerlemans, J.

    1991-01-01

    Northern hemisphere ice sheets have played an important role in the climatic evolution of the Pleistocene. The characteristic time-scale of icesheet growth has the same order-of-magnitude as that for the orbital insolation variations. The interaction with the solid earth, the importance of the thermal conditions at the base of ice sheets and feedback on the climate system (albedo feedback, precipitation regime) make the cryospheric response to climatic forcing complicated. Feedback of surface...

  2. Seasonal Greenland Ice Sheet ice flow variations in regions of differing bed and surface topography

    Science.gov (United States)

    Sole, A. J.; Livingstone, S. J.; Rippin, D. M.; Hill, J.; McMillan, M.; Quincey, D. J.

    2015-12-01

    The contribution of the Greenland Ice Sheet (GrIS) to future sea-level rise is uncertain. Observations reveal the important role of basal water in controlling ice-flow to the ice sheet margin. In Greenland, drainage of large volumes of surface meltwater to the ice sheet bed through moulins and hydrofracture beneath surface lakes dominates the subglacial hydrological system and provides an efficient means of moving mass and heat through the ice sheet. Ice surface and bed topography influence where meltwater can access the bed, and the nature of its subsequent flow beneath the ice. However, no systematic investigation into the influence of topographic variability on Greenland hydrology and dynamics exists. Thus, physical processes controlling storage and drainage of surface and basal meltwater, and the way these affect ice flow are not comprehensively understood. This presents a critical obstacle in efforts to predict the future evolution of the GrIS. Here we present high-resolution satellite mapping of the ice-surface drainage network (e.g. lakes, channels and moulins) and measurements of seasonal variations in ice flow in south west Greenland. The region is comprised of three distinct subglacial terrains which vary in terms of the amplitude and wavelength and thus the degree to which basal topography is reflected in the ice sheet surface. We find that the distribution of surface hydrological features is related to the transfer of bed topography to the ice sheet surface. For example, in areas of thinner ice and high bed relief, moulins occur more frequently and are more uniformly dispersed, indicating a more distributed influx of surface-derived meltwater to the ice sheet bed. We investigate the implications of such spatial variations in surface hydrology on seasonal ice flow rates.

  3. Uncertainty Quantification for Large-Scale Ice Sheet Modeling

    Energy Technology Data Exchange (ETDEWEB)

    Ghattas, Omar [Univ. of Texas, Austin, TX (United States)

    2016-02-05

    This report summarizes our work to develop advanced forward and inverse solvers and uncertainty quantification capabilities for a nonlinear 3D full Stokes continental-scale ice sheet flow model. The components include: (1) forward solver: a new state-of-the-art parallel adaptive scalable high-order-accurate mass-conservative Newton-based 3D nonlinear full Stokes ice sheet flow simulator; (2) inverse solver: a new adjoint-based inexact Newton method for solution of deterministic inverse problems governed by the above 3D nonlinear full Stokes ice flow model; and (3) uncertainty quantification: a novel Hessian-based Bayesian method for quantifying uncertainties in the inverse ice sheet flow solution and propagating them forward into predictions of quantities of interest such as ice mass flux to the ocean.

  4. Dynamics of the Greenland Ice Sheet over multiple timescales

    DEFF Research Database (Denmark)

    Kjeldsen, Kristian Kjellerup

    Since the 1990s mass loss of the Greenland Ice Sheet has accelerated substantially increasing its contribution to global sea level rise, especially during the past decade. Even though the current global sea level budget is well understood, providing better estimates of the mass loss is essential...... to further constrain the individual components of the current budget, and in conjunction with longer records, it is important to provide a trustworthy basis for future projections. In this thesis, using airborne- and satellite derived data combined with terrestrial and marine observations, the dynamic...... behavior of the Greenland Ice Sheet on multiple timescales is investigated. These range from annual/decadal scale variations of ice surface heights and cyclic drainage patterns of ice-dammed lakes to long-term response of the ice sheet margin during the past 300,000 years. The results presented here show...

  5. Surface water hydrology and the Greenland Ice Sheet

    Science.gov (United States)

    Smith, L. C.; Yang, K.; Pitcher, L. H.; Overstreet, B. T.; Chu, V. W.; Rennermalm, A. K.; Cooper, M. G.; Gleason, C. J.; Ryan, J.; Hubbard, A.; Tedesco, M.; Behar, A.

    2016-12-01

    Mass loss from the Greenland Ice Sheet now exceeds 260 Gt/year, raising global sea level by >0.7 mm annually. Approximately two-thirds of this total mass loss is now driven by negative ice sheet surface mass balance (SMB), attributed mainly to production and runoff of meltwater from the ice sheet surface. This new dominance of runoff as a driver of GrIS total mass loss will likely persist owing to anticipated further increases in surface melting, reduced meltwater storage in firn, and the waning importance of dynamical mass losses (ice calving) as the ice sheets retreat from their marine-terminating margins. It also creates the need and opportunity for integrative research pairing traditional surface water hydrology approaches with glaciology. As one example, we present a way to measure supraglacial "runoff" (i.e. specific discharge) at the supraglacial catchment scale ( 101-102 km2), using in situ measurements of supraglacial river discharge and high-resolution satellite/drone mapping of upstream catchment area. This approach, which is standard in terrestrial hydrology but novel for ice sheet science, enables independent verification and improvement of modeled SMB runoff estimates used to project sea level rise. Furthermore, because current SMB models do not consider the role of fluvial watershed processes operating on the ice surface, inclusion of even a simple surface routing model materially improves simulations of runoff delivered to moulins, the critical pathways for meltwater entry into the ice sheet. Incorporating principles of surface water hydrology and fluvial geomorphology and into glaciological models will thus aid estimates of Greenland meltwater runoff to the global ocean as well as connections to subglacial hydrology and ice sheet dynamics.

  6. Biological processes on glacier and ice sheet surfaces

    Science.gov (United States)

    Stibal, Marek; Šabacká, Marie; Žárský, Jakub

    2012-11-01

    Glaciers and ice sheets are melting in response to climate warming. Whereas the physical behaviour of glaciers has been studied intensively, the biological processes associated with glaciers and ice sheets have received less attention. Nevertheless, field observations and laboratory experiments suggest that biological processes that occur on the surface of glaciers and ice sheets -- collectively termed supraglacial environments -- can affect the physical behaviour of glaciers by changing surface reflectivity. Furthermore, supraglacial cyanobacteria and algae capture carbon dioxide from the atmosphere and convert it into organic matter. Supraglacial microbes break down this material, together with organic matter transported from further afield, and generate carbon dioxide that is released back into the atmosphere. The balance between these two processes will determine whether a glacier is a net sink or source of carbon dioxide. In general, ice sheet interiors seem to function as sinks, whereas ice sheet edges and small glaciers act as a source. Meltwaters flush microbially modified organic matter and pollutants out of the glacier, with potential consequences for downstream ecosystems. We conclude that microbes living on glaciers and ice sheets are an integral part of both the glacial environment and the Earth's ecosystem.

  7. Ice sheet growth with laterally varying bedrock relaxation time

    Science.gov (United States)

    van der Wal, Wouter; Vizcaino Rubio, Pablo; De Boer, Bas; van de Wal, Roderik

    2017-04-01

    Isostatic response of the bedrock, or glacial isostatic adjustment (GIA) in included in most ice sheet models. This is important because the surface elevation determines the mass balance and thereby implicitly also the strength of the mass balance feedback where higher surface elevation yields lower temperatures implying less melt and vice versa. Usually a single relaxation time or a set of relaxation times is used to model the response everywhere on Earth or at least for an entire ice sheet. In reality the viscosity in the Earth's mantle, and hence the relaxation time experienced by the ice, varies with location. Seismic studies indicate that several regions that were covered by ice during the last glacial cycle are underlain by mantle in which viscosity varies with orders of magnitude, such as Antarctica and North America. The question is whether such a variation of viscosity influences ice evolution. Several GIA models exist that can deal with 3D viscosity, but their large computation times make it nearly impossible to couple them to ice sheet models. Here we use the ANICE ice-sheet model (de Boer et al. 2013) with a simple bedrock-relaxation model in which a different relaxation time is used for separate regions. A temperature anomaly is applied to grow a schematic ice sheet on a flat earth, with other forcing mechanisms neglected. It is shown that in locations with a fast relaxation time of 300 years the equilibrium ice sheet is significantly thinner and narrower but also ice thickness in neighbouring regions (with the more standard relaxation time of 3000 years) is affected.

  8. SPICE: Sentinel-3 Performance Improvement for Ice Sheets

    Science.gov (United States)

    McMillan, Malcolm; Escola, Roger; Roca, Monica; Escorihuela, Maria Jose; Thibaut, Pierre; Shepherd, Andrew; Remy, Frederique; Aublanc, Jeremie; Benveniste, Jerome; Restano, Marco; Ambrozio, Americo

    2017-04-01

    For the past 25 years, polar-orbiting satellite radar altimeters have provided a valuable record of ice sheet elevation change, yielding estimates of ice sheet mass imbalance at the scale of individual ice sheet basins. One of the principle challenges associated with radar altimetry comes from the relatively large ground footprint of conventional pulse-limited radars, which limits their capacity to make reliable measurements in areas of complex topographic terrain. In recent years, progress has been made towards improving ground resolution, through the implementation of Synthetic Aperture Radar (SAR), or Delay-Doppler, techniques. In 2010, the launch of CryoSat-2 heralded the start of a new era of SAR altimetry, although full SAR coverage of the polar ice sheets has only been achieved with the launch of the first Sentinel-3 satellite in February 2016. Because of the heritage of SAR altimetry provided by CryoSat-2, many SAR altimeter processing techniques have been optimized and evaluated for water and sea ice surfaces only. This leaves several outstanding issues related to the development and evaluation of SAR altimetry for ice sheets, including improvements to Delay-Doppler processing algorithms and SAR altimetry waveform retracking procedures. Here we present results from SPICE (Sentinel-3 Performance Improvement for Ice Sheets), a 2 year project that focuses on the expected performance of Sentinel-3 SAR altimetry over the Polar ice sheets. The project, which began in September 2015 and is funded by ESA's SEOM (Scientific Exploitation of Operational Missions) programme, aims to contribute to the development and understanding of ice sheet SAR altimetry through the emulation of Sentinel-3 data from dedicated CryoSat SAR acquisitions made at the Lake Vostok, Dome C and Spirit sites in East Antarctica, and from reprocessed interferometric SAR data in Greenland. More specifically, we will evaluate SAR elevation retrievals using different processing methodologies and

  9. Supraglacial bacterial community structures vary across the Greenland ice sheet

    DEFF Research Database (Denmark)

    Cameron, Karen A.; Stibal, Marek; Zarsky, Jakub D.

    2016-01-01

    The composition and spatial variability of microbial communities that reside within the extensive (>200 000 km(2)) biologically active area encompassing the Greenland ice sheet (GrIS) is hypothesized to be variable. We examined bacterial communities from cryoconite debris and surface ice across t...

  10. Coupling of climate models and ice sheet models by surface mass balance gradients: application to the Greenland Ice Sheet

    Directory of Open Access Journals (Sweden)

    M. M. Helsen

    2012-03-01

    Full Text Available It is notoriously difficult to couple surface mass balance (SMB results from climate models to the changing geometry of an ice sheet model. This problem is traditionally avoided by using only accumulation from a climate model, and parameterizing the meltwater run-off as a function of temperature, which is often related to surface elevation (Hs. In this study, we propose a new strategy to calculate SMB, to allow a direct adjustment of SMB to a change in ice sheet topography and/or a change in climate forcing. This method is based on elevational gradients in the SMB field as computed by a regional climate model. Separate linear relations are derived for ablation and accumulation, using pairs of Hs and SMB within a minimum search radius. The continuously adjusting SMB forcing is consistent with climate model forcing fields, also for initially non-glaciated areas in the peripheral areas of an ice sheet. When applied to an asynchronous coupled ice sheet – climate model setup, this method circumvents traditional temperature lapse rate assumptions. Here we apply it to the Greenland Ice Sheet (GrIS. Experiments using both steady-state forcing and glacial-interglacial forcing result in realistic ice sheet reconstructions.

  11. LIVVkit: An extensible, python-based, land ice verification and validation toolkit for ice sheet models

    Science.gov (United States)

    Kennedy, Joseph H.; Bennett, Andrew R.; Evans, Katherine J.; Price, Stephen; Hoffman, Matthew; Lipscomb, William H.; Fyke, Jeremy; Vargo, Lauren; Boghozian, Adrianna; Norman, Matthew; Worley, Patrick H.

    2017-06-01

    To address the pressing need to better understand the behavior and complex interaction of ice sheets within the global Earth system, significant development of continental-scale, dynamical ice sheet models is underway. Concurrent to the development of the Community Ice Sheet Model (CISM), the corresponding verification and validation (V&V) process is being coordinated through a new, robust, Python-based extensible software package, the Land Ice Verification and Validation toolkit (LIVVkit). Incorporated into the typical ice sheet model development cycle, it provides robust and automated numerical verification, software verification, performance validation, and physical validation analyses on a variety of platforms, from personal laptops to the largest supercomputers. LIVVkit operates on sets of regression test and reference data sets, and provides comparisons for a suite of community prioritized tests, including configuration and parameter variations, bit-for-bit evaluation, and plots of model variables to indicate where differences occur. LIVVkit also provides an easily extensible framework to incorporate and analyze results of new intercomparison projects, new observation data, and new computing platforms. LIVVkit is designed for quick adaptation to additional ice sheet models via abstraction of model specific code, functions, and configurations into an ice sheet model description bundle outside the main LIVVkit structure. Ultimately, through shareable and accessible analysis output, LIVVkit is intended to help developers build confidence in their models and enhance the credibility of ice sheet models overall.

  12. Influence of temperature fluctuations on equilibrium ice sheet volume

    Directory of Open Access Journals (Sweden)

    T. B. Mikkelsen

    2018-01-01

    Full Text Available Forecasting the future sea level relies on accurate modeling of the response of the Greenland and Antarctic ice sheets to changing temperatures. The surface mass balance (SMB of the Greenland Ice Sheet (GrIS has a nonlinear response to warming. Cold and warm anomalies of equal size do not cancel out and it is therefore important to consider the effect of interannual fluctuations in temperature. We find that the steady-state volume of an ice sheet is biased toward larger size if interannual temperature fluctuations are not taken into account in numerical modeling of the ice sheet. We illustrate this in a simple ice sheet model and find that the equilibrium ice volume is approximately 1 m SLE (meters sea level equivalent smaller when the simple model is forced with fluctuating temperatures as opposed to a stable climate. It is therefore important to consider the effect of interannual temperature fluctuations when designing long experiments such as paleo-spin-ups. We show how the magnitude of the potential bias can be quantified statistically. For recent simulations of the Greenland Ice Sheet, we estimate the bias to be 30 Gt yr−1 (24–59 Gt yr−1, 95 % credibility for a warming of 3 °C above preindustrial values, or 13 % (10–25, 95 % credibility of the present-day rate of ice loss. Models of the Greenland Ice Sheet show a collapse threshold beyond which the ice sheet becomes unsustainable. The proximity of the threshold will be underestimated if temperature fluctuations are not taken into account. We estimate the bias to be 0.12 °C (0.10–0.18 °C, 95 % credibility for a recent estimate of the threshold. In light of our findings it is important to gauge the extent to which this increased variability will influence the mass balance of the ice sheets.

  13. Effects of spatial discretization in ice-sheet modelling using the shallow-ice approximation

    NARCIS (Netherlands)

    van den Berg, J.; van de Wal, R.S.W.|info:eu-repo/dai/nl/101899556; Oerlemans, J.|info:eu-repo/dai/nl/06833656X

    2006-01-01

    This paper assesses a two-dimensional, vertically integrated ice model for its numerical properties in the calculation of ice-sheet evolution on a sloping bed using the shallow-ice approximation. We discuss the influence of initial conditions and individual model parameters on the model’s numerical

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

    Science.gov (United States)

    Notz, Dirk

    2009-12-08

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

  15. Generation of a new Greenland Ice Sheet Digital Elevation Model

    DEFF Research Database (Denmark)

    Nagarajan, Sudhagar; Csatho, Beata M; Schenk, Anton F

    and spaceborne laser altimetry (airborne: Airborne Topographic Mapper (ATM) (1993-present), Laser Vegetation Imaging Sensor(LVIS) (2007,2009 and 2011); spaceborne: Ice, Cloud, and land Elevation Satellite (ICESat) (2003-2009)) and DEMs have been derived from stereo satellite imagery (e.g., SPOT (40 m), ASTER (15......Currently available Digital Elevation Models(DEMs) of the Greenland Ice Sheet (GrIS) were originally derived from radar altimetry data, e.g. Bamber (Bamber et al., 2001) and later improved by photoclinometry to fill the regions between orbits (Scambos and Haran, 2002). The elevation error...... of these DEMs is a few meters in the higher part (above 2000 m) of the ice sheet, but it can be as much as 50-100 meters in marginal regions. The relatively low resolution and accuracy poses a problem, especially for ice sheet modeling. Although accurate elevation data have been collected by airborne...

  16. Pre-Weichselian Quaternary glaciations of the British Isles, The Netherlands, Norway and adjacent marine areas south of 68°N: Implications for long-term ice sheet development in northern Europe

    NARCIS (Netherlands)

    Lee, J.R.; Busschers, F.S.; Sejrup, H.P.

    2012-01-01

    Within this paper we review the pre-Weichselian glacial history of northern Europe focussing on evidence from the British Isles, Netherlands, Norway and adjacent marine areas that record the activity of the British (BIS) and Scandinavian (SIS) ice sheets. The objective of the paper is to examine the

  17. Mapping of a Hydrological Ice Sheet Drainage Basin on the West Greenland Ice Sheet Margin from ERS-1/2 SAR Interferometry, Ice-Radar Measurement, and Modelling

    DEFF Research Database (Denmark)

    Ahlstrøm, Andreas P.; Bøggild, C.E.; Stenseng, L.

    2002-01-01

    importance of the potential of the ice overburden pressure compared to the bedrock topography. The meltwater run-off for the basin delineations was modelled with an energy-balance model calibrated with observed ice-sheet ablation and compared to a 25 year time series of measured basin run-off. The standard......The hydrological ice-sheet basin draining into the Tasersiaq lake, West Greenland (66°13'N, 50°30'W), was delineated, First using standard digital elevation models (DEMs) for ice-sheet surface and bedrock, and subsequently using a new high-resolution dataset, with a surface DEM derived from repeat......-track interferometric synthetic aperture radar (SAR) and a bedrock topography derived from an airborne 60 MHz ice-penetrating radar. The extent of the delineation was calculated from a water-pressure potential as a function of the ice-sheet surface and bedrock elevations and a hydraulic factor κ describing the relative...

  18. Obliquity-paced Pliocene West Antarctic ice sheet oscillations

    Science.gov (United States)

    Naish, T.; Powell, R.; Levy, R.; Wilson, G.; Scherer, R.; Talarico, F.; Krissek, L.; Niessen, F.; Pompilio, M.; Wilson, T.; Carter, L.; DeConto, R.; Huybers, P.; McKay, R.; Pollard, D.; Ross, J.; Winter, D.; Barrett, P.; Browne, G.; Cody, R.; Cowan, E.; Crampton, J.; Dunbar, G.; Dunbar, N.; Florindo, F.; Gebhardt, C.; Graham, I.; Hannah, M.; Hansaraj, D.; Harwood, D.; Helling, D.; Henrys, S.; Hinnov, L.; Kuhn, G.; Kyle, P.; Laufer, A.; Maffioli, P.; Magens, D.; Mandernack, K.; McIntosh, W.; Millan, C.; Morin, R.; Ohneiser, C.; Paulsen, T.; Persico, D.; Raine, I.; Reed, J.; Riesselman, C.; Sagnotti, L.; Schmitt, D.; Sjunneskog, C.; Strong, P.; Taviani, M.; Vogel, S.; Wilch, T.; Williams, T.

    2009-01-01

    Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages1, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles2. Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the 'warmer-than-present' early-Pliocene epoch (5–3 Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming3. Here we present a marine glacial record from the upper 600 m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, 40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth's axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to 3 °C warmer than today4 and atmospheric CO2 concentration was as high as 400 p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model7 that simulates fluctuations in Antarctic ice volume of up to +7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt8 under conditions of elevated CO2.

  19. Greenland Ice sheet mass balance from satellite and airborne altimetry

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Bevis, M. G.; Wahr, J. M.

    and therefore significantly improve the estimate of the total volume change. Furthermore, we divide the GrIS into six major drainage basins and provide volume loss estimates during 2003-2006, 2006-2009 and 2009-2012 for each basin and separate between melt induced and dynamic ice loss. In order to separate...... dynamic ice loss from melt processes, we use SMB values from the Regional Atmospheric Climate Model (RACMO2) and SMB values from a positive degree day runoff retention model (Janssens & Huybrechts 2000, Hanna et al. 2011 JGR, updated for this study). Our results show increasing SMB ice loss over the last......Ice loss from the Greenland Ice Sheet (GrIS) is dominated by loss in the marginal areas. Dynamic induced ice loss and its associated ice surface lowering is often largest close to the glacier calving front and may vary from rates of tens of meters per years to a few meters per year over relatively...

  20. Influence of ice-sheet geometry and supraglacial lakes on seasonal ice-flow variability

    Directory of Open Access Journals (Sweden)

    I. Joughin

    2013-07-01

    Full Text Available Supraglacial lakes play an important role in establishing hydrological connections that allow lubricating seasonal meltwater to reach the base of the Greenland Ice Sheet. Here we use new surface velocity observations to examine the influence of supraglacial lake drainages and surface melt rate on ice flow. We find large, spatially extensive speedups concurrent with times of lake drainage, showing that lakes play a key role in modulating regional ice flow. While surface meltwater is supplied to the bed via a geographically sparse network of moulins, the observed ice-flow enhancement suggests that this meltwater spreads widely over the ice-sheet bed. We also find that the complex spatial pattern of speedup is strongly determined by the combined influence of bed and surface topography on subglacial water flow. Thus, modeling of ice-sheet basal hydrology likely will require knowledge of bed topography resolved at scales (sub-kilometer far finer than existing data (several km.

  1. Ice-sheet mass balance in central West Greenland

    Energy Technology Data Exchange (ETDEWEB)

    Greuell, W.; Denby, B. [Institute for Marine and Atmospheric Research IMAR, Utrecht University, Utrecht (Netherlands)

    2001-04-01

    Volume changes of the Greenland ice sheet in response to climate change may form a significant contribution to variations in sea level. However, still the sign of the present volume change is unknown. The aim of this project was to increase our understanding of present state of the Greenland ice sheet and of its sensitivity to climate change, with emphasis on the Kangerlussuaq transect (West Greenland, 67 {sup o}N). We have performed mass-balance, meteorological and ice-velocity measurements along the transect. With a record length of 10 years, the mass-balance measurements constitute the longest series of this kind on the Greenland ice sheet. A crucial parameter for the determination of the amount of melt is the albedo (this is the fraction of the solar radiation reflected by the surface). Therefore, we have improved the retrieval methods used to estimate the surface albedo from satellite data. For that purpose we have, among others, measured the albedo from a helicopter. The resulting data were used for validation of the satellite-derived albedos. With the satellite-derived albedos and the mass-balance data we have developed a method for estimating the surface mass balance of the Greenland ice sheet from satellite data. Furthermore, we have developed an atmospheric boundary-layer model, specifically designed for glaciers and ice sheets. The model was used to study the relation between the climate of the free atmosphere and conditions near the surface of the ice sheet, which determine the amount of melt. refs.

  2. The effect of anisotropy on simulated ice dynamics: an idealised ice shelf example using the Ice Sheet System Model

    Science.gov (United States)

    Graham, Felicity; Morlighem, Mathieu; Warner, Roland; Treverrow, Adam

    2017-04-01

    An essential component of an ice sheet model is its description of how ice deforms under applied stresses - its material constitutive relation. Current large-scale ice sheet models routinely rely on Glen's flow relation, which is an isotropic material constitutive relation that is not dependent on the character of the stress applied. However, laboratory experiments subjecting ice to simultaneous simple shear and compressive stresses (a typical situation in ice sheets) show that with sustained deformation under constant stresses, steady state viscous creep becomes anisotropic. For various combinations of simple shear and compression, results show that flow enhancement further increases as the stress configuration becomes dominated by simple shear. The empirical, scalar, tertiary, anisotropic rheology (ESTAR) is a computationally-efficient flow relation that incorporates anisotropic effects through a parameterisation for a flow enhancement factor that takes into account the proportion of simple shear in the overall stress regime. Here, we use the Ice Sheet System Model to investigate the impact of anisotropy on the dynamics of an idealized ice shelf by comparing simulated flow fields using ESTAR with those of the standard (isotropic) Glen flow relation. When enhanced to match simple shear flow rates, the Glen flow relation overestimates velocities at the ice-ocean front by up to 36%. Significantly, no single Glen enhancement factor accurately captures the spatial variations in flow over the ice shelf produced by ESTAR. Our results have implications for reconstructions and projections of sea level using ice sheet models that do not account for anisotropy.

  3. Bayesian Inversion for Large Scale Antarctic Ice Sheet Flow

    KAUST Repository

    Ghattas, Omar

    2015-01-07

    The flow of ice from the interior of polar ice sheets is the primary contributor to projected sea level rise. One of the main difficulties faced in modeling ice sheet flow is the uncertain spatially-varying Robin boundary condition that describes the resistance to sliding at the base of the ice. Satellite observations of the surface ice flow velocity, along with a model of ice as a creeping incompressible shear-thinning fluid, can be used to infer this uncertain basal boundary condition. We cast this ill-posed inverse problem in the framework of Bayesian inference, which allows us to infer not only the basal sliding parameters, but also the associated uncertainty. To overcome the prohibitive nature of Bayesian methods for large-scale inverse problems, we exploit the fact that, despite the large size of observational data, they typically provide only sparse information on model parameters. We show results for Bayesian inversion of the basal sliding parameter field for the full Antarctic continent, and demonstrate that the work required to solve the inverse problem, measured in number of forward (and adjoint) ice sheet model solves, is independent of the parameter and data dimensions

  4. 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.

  5. 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...... 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 ± 49, +14...... ± 43, -65 ± 26, and -20 ± 14 gigatonnes year(-1), respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 ± 0.20 millimeter year(-1) to the rate of global sea-level rise....

  6. Younger Dryas interval and outflow from the Laurentide ice sheet

    Science.gov (United States)

    Moore, T.C.; Walker, J.C.G.; Rea, David K.; Lewis, C.F.M.; Shane, L.C.K.; Smith, A.J.

    2000-01-01

    A boxmodel of the Great Lakes is used to estimate meltwater flow into the North Atlantic between 8000 and 14,000 calendar years B.P. Controls on the model include the oxygen isotopic composition of meltwaters and lake waters as measured in the shells of ostracodes. Outflow rates are highest when oxygen isotopic values of the lake waters are most negative, denoting a maximum glacial meltwater component. Flow rates reach maximum values before the onset of the Younger Dryas and after it ends. These maxima appear to be correlative with the major meltwater pulses MWP 1A and 1B. Although the resumption of North Atlantic Deep Water formation may be tied to the reduction in ice sheet melting, neither the onset nor the end of the Younger Dryas, as recorded in the Greenland Ice Sheet Project (GISP2) records, appear tied to maxima in meltwater outflow from the Laurentide ice sheet. Copyright 2000 by the American Geophysical Union.

  7. High export of dissolved silica from the Greenland Ice Sheet

    Science.gov (United States)

    Meire, L.; Meire, P.; Struyf, E.; Krawczyk, D. W.; Arendt, K. E.; Yde, J. C.; Juul Pedersen, T.; Hopwood, M. J.; Rysgaard, S.; Meysman, F. J. R.

    2016-09-01

    Silica is an essential element for marine life and plays a key role in the biogeochemistry of the ocean. Glacial activity stimulates rock weathering, generating dissolved silica that is exported to coastal areas along with meltwater. The magnitude of the dissolved silica export from large glacial areas such as the Greenland Ice Sheet is presently poorly quantified and not accounted for in global budgets. Here we present data from two fjord systems adjacent to the Greenland Ice Sheet which reveal a large export of dissolved silica by glacial meltwater relative to other macronutrients. Upscaled to the entire Greenland Ice Sheet, the export of dissolved silica equals 22 ± 10 Gmol Si yr-1. When the silicate-rich meltwater mixes with upwelled deep water, either inside or outside Greenland's fjords, primary production takes place at increased silicate to nitrate ratios. This likely stimulates the growth of diatoms relative to other phytoplankton groups.

  8. Reconstructing the last glacial and deglacial ice sheets

    Science.gov (United States)

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

  9. Improved ice loss estimate of the northwestern Greenland ice sheet

    NARCIS (Netherlands)

    Kjeldsen, K.K.; Khan, S.A.; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643; van Angelen, J.H.|info:eu-repo/dai/nl/325922470

    2013-01-01

    We estimate ice volume change rates in the northwest Greenland drainage basin during 2003–2009 using Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data. Elevation changes are often reported to be largest near the frontal portion of outlet glaciers. To improve the volume change

  10. Modelling water flow under glaciers and ice sheets

    Science.gov (United States)

    Flowers, Gwenn E.

    2015-01-01

    Recent observations of dynamic water systems beneath the Greenland and Antarctic ice sheets have sparked renewed interest in modelling subglacial drainage. The foundations of today's models were laid decades ago, inspired by measurements from mountain glaciers, discovery of the modern ice streams and the study of landscapes evacuated by former ice sheets. Models have progressed from strict adherence to the principles of groundwater flow, to the incorporation of flow ‘elements’ specific to the subglacial environment, to sophisticated two-dimensional representations of interacting distributed and channelized drainage. Although presently in a state of rapid development, subglacial drainage models, when coupled to models of ice flow, are now able to reproduce many of the canonical phenomena that characterize this coupled system. Model calibration remains generally out of reach, whereas widespread application of these models to large problems and real geometries awaits the next level of development. PMID:27547082

  11. Dynamics of the Greenland Ice Sheet over multiple timescales

    DEFF Research Database (Denmark)

    Kjeldsen, Kristian Kjellerup

    /crossshelf troughs. Warming of ocean temperatures is suggested as being a main driver for periodic dynamic ice loss events in northwest Greenland while cooling of ocean temperatures around southern Greenland, in conjunction with increased snow accumulation, is found to drive a rapid readvance of glaciers in response......Since the 1990s mass loss of the Greenland Ice Sheet has accelerated substantially increasing its contribution to global sea level rise, especially during the past decade. Even though the current global sea level budget is well understood, providing better estimates of the mass loss is essential...... that the ice margin of the Greenland Ice Sheet responds highly dynamic and variable to climate change and oceanic forcing, with behavior additionally being governed by regional/local settings, e.g. topographical settings such as low-lying/mountainous areas and the presence or absence of deep fjords or shelf...

  12. West Greenland ice sheet melt lake observations and modeling

    Science.gov (United States)

    Bryzgis, G.; Box, J. E.

    2005-12-01

    This study examines the spatial and temporal variability of supraglacial melt lakes over the western ablation zone of the Greenland ice sheet. Based on mid-lake automatic weather station surface energy budget measurements, automatic camera imagery, and inflatable boat measurements, we derive lake volume estimates from daily 250 m MODIS imagery for this region. We investigate the correlation of the timing and location of lake water volume and correlation with local-scale climate anomalies from Polar MM5 regional climate model output. Implications for water supply to melt-induced ice sheet acceleration are discussed.

  13. GREENLAND ICE SHEET CHANGES FROM SPACE USING LASER, RADAR AND

    DEFF Research Database (Denmark)

    Sørensen, Louise Sandberg; Stenseng, Lars; Simonsen, Sebastian Bjerregaard

    2010-01-01

    The Greenland cryosphere is undergoing rapid changes, and these are documented by remote sensing from space. In this paper, an inversion scheme is used to derive mass changes from gravity changes observed by GRACE, and to derive the mean annual mass loss for the Greenland Ice Sheet, which...... is estimated to be 204 Gt/yr for the period 2002-2010. NASA’s laser altimetry satellite ICESat has provided elevation estimates of the ice sheet since January 2003. In order to be able to compare GRACE and ICESat derived results, the ICESat volume change must be converted into a mass change estimate. Therefore...

  14. Enhanced ice sheet melting driven by volcanic eruptions during the last deglaciation.

    Science.gov (United States)

    Muschitiello, Francesco; Pausata, Francesco S R; Lea, James M; Mair, Douglas W F; Wohlfarth, Barbara

    2017-10-24

    Volcanic eruptions can impact the mass balance of ice sheets through changes in climate and the radiative properties of the ice. Yet, empirical evidence highlighting the sensitivity of ancient ice sheets to volcanism is scarce. Here we present an exceptionally well-dated annual glacial varve chronology recording the melting history of the Fennoscandian Ice Sheet at the end of the last deglaciation (∼13,200-12,000 years ago). Our data indicate that abrupt ice melting events coincide with volcanogenic aerosol emissions recorded in Greenland ice cores. We suggest that enhanced ice sheet runoff is primarily associated with albedo effects due to deposition of ash sourced from high-latitude volcanic eruptions. Climate and snowpack mass-balance simulations show evidence for enhanced ice sheet runoff under volcanically forced conditions despite atmospheric cooling. The sensitivity of past ice sheets to volcanic ashfall highlights the need for an accurate coupling between atmosphere and ice sheet components in climate models.

  15. Coupled regional climate–ice-sheet simulation shows limited Greenland ice loss during the Eemian

    Directory of Open Access Journals (Sweden)

    M. M. Helsen

    2013-08-01

    Full Text Available During the last interglacial period (Eemian, 130–115 kyr BP eustatic global sea level likely peaked at > 6 m above the present-day level, but estimates of the contribution of the Greenland Ice Sheet vary widely. Here we use an asynchronously two-way-coupled regional climate–ice-sheet model, which includes physically realistic feedbacks between the changing ice sheet topography and climate forcing. Our simulation results in a contribution from the Greenland Ice Sheet to the Eemian sea level highstand between 1.2 and 3.5 m, with a most likely value of 2.1 m. Simulated Eemian ice loss in Greenland is dominated by the rapid retreat of the southwestern margin; two-thirds of the ice loss occurred south of 70° N. The southern dome survived the Eemian and remained connected to the central dome. Large-scale ice sheet retreat is prevented in areas with high accumulation. Our results broadly agree with ice-core-inferred elevation changes and marine records, but it does not match with the ice-core-derived temperature record from northern Greenland. During maximum Eemian summertime insolation, Greenland mass loss contributed ~ 0.5 m kyr−1 to sea level rise, 24% of the reconstructed total rate of sea level rise. Next to that, a difference of > 3 m remains between our maximum estimate of the Greenland contribution and the reconstructed minimum value of the global eustatic Eemian highstand. Hence, the Antarctic Ice Sheet must also have contributed significantly to this sea level highstand.

  16. A New Approach for Exploring Ice Sheets and Sub-Ice Geology

    Science.gov (United States)

    Eisen, Olaf; Hofstede, Coen; Miller, Heinrich; Kristoffersen, Yngve; Blenkner, Rick; Lambrecht, Astrid; Mayer, Christoph

    2010-11-01

    Active seismic measurements were an important part of geophysical traverses on the Antarctic ice sheet as far back as the 1920s. These methods lost their leading role for ice thickness measurements to much faster ground-based and airborne radar surveys because of the considerable logistical effort necessary for seismic data acquisition. However, new achievements with a vibrator source in active seismics (vibroseis for short) could open new prospects and foster future geological and glaciological surveys in Antarctica and Greenland and on ice caps and glaciers. Active seismic methods have the unique ability to image sub­ice geology and remotely obtain its physical properties. Friction at the basal interface of an ice sheet plays a pivotal role in controlling ice dynamics and is largely determined by the presence of water and/or sediments underneath the ice. High­quality seismic reflection measurements came in demand as scientific interest in the dynamics of ice streams (e.g., West Antarctic ice streams) increased and as site surveys were needed for optimum sampling of sub­ice sediments for paleoclimate studies (e.g., Cape Roberts Project, Antarctic Geological Drilling (ANDRILL)). Nevertheless, the available literature demonstrates that seismic studies on ice sheets are not widespread and are only carried out on small, local scales over a few tens of kilometers. Prominent examples of such seismic studies are the observation of transient processes in bed geology driven by ice flow [Smith et al., 2007] and the long record of seismic exploration of subglacial lake environments, for example, around Lake Vostok and more recently around subglacial Lake Ellsworth. Seismic properties of the ice sheets remain only an occasional topic [Horgan et al., 2008], often complementary to radar.

  17. Antarctic ice-sheet loss driven by basal melting of ice shelves

    NARCIS (Netherlands)

    Pritchard, H.D.; Ligtenberg, S.R.M.|info:eu-repo/dai/nl/32821177X; Fricker, H.A.; Vaughan, D.G.; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643; Padman, L.

    2012-01-01

    Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying1,2 glacier acceleration along Antarctic ice-sheet coastal margins3. Atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves,

  18. Exposed subsurface ice sheets in the Martian mid-latitudes

    Science.gov (United States)

    Dundas, Colin M.; Bramson, Ali M.; Ojha, Lujendra; Wray, James J.; Mellon, Michael T.; Byrne, Shane; McEwen, Alfred S.; Putzig, Nathaniel E.; Viola, Donna; Sutton, Sarah; Clark, Erin; Holt, John W.

    2018-01-01

    Some locations on Mars are known to have water ice just below the surface, but how much has remained unclear. Dundas et al. used data from two orbiting spacecraft to examine eight locations where erosion has occurred. This revealed cliffs composed mostly of water ice, which is slowly sublimating as it is exposed to the atmosphere. The ice sheets extend from just below the surface to a depth of 100 meters or more and appear to contain distinct layers, which could preserve a record of Mars' past climate. They might even be a useful source of water for future human exploration of the red planet.

  19. connecting the dots between Greenland ice sheet surface melting and ice flow dynamics (Invited)

    Science.gov (United States)

    Box, J. E.; Colgan, W. T.; Fettweis, X.; Phillips, T. P.; Stober, M.

    2013-12-01

    This presentation is of a 'unified theory' in glaciology that first identifies surface albedo as a key factor explaining total ice sheet mass balance and then surveys a mechanistic self-reinforcing interaction between melt water and ice flow dynamics. The theory is applied in a near-real time total Greenland mass balance retrieval based on surface albedo, a powerful integrator of the competing effects of accumulation and ablation. New snowfall reduces sunlight absorption and increases meltwater retention. Melting amplifies absorbed sunlight through thermal metamorphism and bare ice expansion in space and time. By ';following the melt'; we reveal mechanisms linking existing science into a unified theory. Increasing meltwater softens the ice sheet in three ways: 1.) sensible heating given the water temperature exceeds that of the ice sheet interior; 2.) Some infiltrating water refreezes, transferring latent heat to the ice; 3.) Friction from water turbulence heats the ice. It has been shown that for a point on the ice sheet, basal lubrication increases ice flow speed to a time when an efficient sub-glacial drainage network develops that reduces this effect. Yet, with an increasing melt duration the point where the ice sheet glides on a wet bed increases inland to a larger area. This effect draws down the ice surface elevation, contributing to the ';elevation feedback'. In a perpetual warming scenario, the elevation feedback ultimately leads to ice sheet loss reversible only through much slower ice sheet growth in an ice age environment. As the inland ice sheet accelerates, the horizontal extension pulls cracks and crevasses open, trapping more sunlight, amplifying the effect of melt accelerated ice. As the bare ice area increases, the direct sun-exposed crevassed and infiltration area increases further allowing the ice warming process to occur more broadly. Considering hydrofracture [a.k.a. hydrofracking]; surface meltwater fills cracks, attacking the ice integrity

  20. GLAS/ICESat L2 Global Antarctic and Greenland Ice Sheet Altimetry Data V033

    Data.gov (United States)

    National Aeronautics and Space Administration — GLA12 contains the ice sheet elevation and elevation distribution corrected for geodetic and atmospheric affects calculated from algorithms fine-tuned for ice sheet...

  1. GLAS/ICESat L2 Global Antarctic and Greenland Ice Sheet Altimetry Data V034

    Data.gov (United States)

    National Aeronautics and Space Administration — GLA12 contains the ice sheet elevation and elevation distribution corrected for geodetic and atmospheric affects calculated from algorithms fine-tuned for ice sheet...

  2. The Greenland ice sheet in a warming climate

    NARCIS (Netherlands)

    van Angelen, J.H.|info:eu-repo/dai/nl/325922470

    2013-01-01

    In this thesis we assess multiple aspects of the Greenland climate, including the surface energy and mass balance of the ice sheet for the contemporary and near future climate. For these purposes we used output of the extensively and well-evaluated regional atmospheric climate model RACMO2. The

  3. The role of ice sheets in the pleistocene climate

    NARCIS (Netherlands)

    Oerlemans, J.

    1991-01-01

    Northern hemisphere ice sheets have played an important role in the climatic evolution of the Pleistocene. The characteristic time-scale of icesheet growth has the same order-of-magnitude as that for the orbital insolation variations. The interaction with the solid earth, the importance of the

  4. Uranium isotopes in the Greenland ice-sheet

    Science.gov (United States)

    Koide, M.; Goldberg, E. D.

    1983-11-01

    The U-234/U-238 activity ratio was measured in dated strata of the Dye-3 Greenland ice-sheet. Values were generally less than unity, indicating a source in weathered crustal rock debris. Three levels showed elevated ratios which are attributed to entry of debris from the aborted Russian satellite Cosmos 954 following residence in the stratosphere.

  5. Emplacement of Antarctic ice sheet mass affects circumpolar ocean flow

    NARCIS (Netherlands)

    Rugenstein, Maria; Stocchi, Paolo; von der Heydt, Anna; Dijkstra, Hendrik; Brinkhuis, Henk

    2014-01-01

    During the Cenozoic the Antarctic continent experienced large fluctuations in ice-sheet volume. We investigate the effects of Glacial Isostatic Adjustment (GIA) on Southern Ocean circulation for the first continental scale glaciation of Antarctica (~34 Myr) by combining solid Earth and ocean dynamic

  6. Emplacement of Antarctic ice sheet mass affects circumpolar ocean flow

    NARCIS (Netherlands)

    Rugenstein, M.; Stocchi, P.; van der Heydt, A.; Brinkhuis, H.

    2014-01-01

    During the Cenozoic the Antarctic continent experienced large fluctuations in ice-sheet volume. We investigate the effects of Glacial Isostatic Adjustment (GIA) on Southern Ocean circulation for the first continental scale glaciation of Antarctica (~ 34 Myr) by combining solid Earth and ocean

  7. Ice sheets and sea level: thinking outside the box

    NARCIS (Netherlands)

    van den Broeke, M.R.; Bamber, J.; Lenaerts, J.T.M.; Rignot, Eric

    2011-01-01

    Until quite recently, the mass balance (MB) of the great ice sheets of Greenland and Antarctica was poorly known and often treated as a residual in the budget of oceanic mass and sea level change. Recent developments in regional climate modelling and remote sensing, especially altimetry, gravimetry

  8. Greenland Ice Sheet Mass Loss from GRACE Monthly Models

    DEFF Research Database (Denmark)

    Sørensen, Louise Sandberg; Forsberg, René

    2010-01-01

    The Greenland ice sheet is currently experiencing a net mass loss. There are however large discrepancies between the published qualitative mass loss estimates, based on different data sets and methods. There are even large differences between the results based on the same data sources, as is the ...

  9. SST and ice sheet impacts on the MIS-13 climate

    Energy Technology Data Exchange (ETDEWEB)

    Muri, Helene; Berger, Andre; Yin, Qiuzhen; Sundaram, Suchithra [Universite catholique de Louvain, Georges Lemaitre Centre for Earth and Climate Research (TECLIM), Earth and Life Institute (ELI), Louvain la Neuve (Belgium); Voldoire, Aurore; Melia, David Salas Y. [CNRM-GAME Meteo-France/CNRS, Toulouse Cedex (France)

    2012-10-15

    As a first qualitative assessment tool, LOVECLIM has been used to investigate the interactions between insolation, ice sheets and the East Asian Monsoon at the Marine Isotopic Stage 13 (MIS-13) in work by Yin et al. (Clim Past 4:79-90, 2008, Clim Past 5:229-243, 2009). The results are in need of validation with a more sophisticated model, which is done in this work with the ARPEGE atmospheric general circulation model. As in the Earth system Model of Intermediate Complexity, LOVECLIM, ARPEGE shows that the northern hemispheric high insolation in summer leads to strong MIS-13 monsoon precipitation. Data from the Chinese Loess Plateau indicate that MIS-13 was locally a warm and humid period (Guo et al. in Clim Past 5:21-31, 2009; Yin and Guo in Chin Sci Bull 51(2):213-220, 2006). This is confirmed by these General Circulation Model (GCM) results, where the MIS-13 climate is found to be hotter and more humid both in the presence and absence of any added ice sheets. LOVECLIM found that the combined effects of the ice sheets and their accompanying SSTs contribute to more precipitation in eastern China, whilst in ARPEGE the impact is significant in northeastern China. Nonetheless the results of ARPEGE confirm the counter-intuitive results of LOVECLIM where ice sheets contribute to enhance monsoon precipitation. This happens through a topography induced wave propagating through Eurasia with an ascending branch over northeastern China. A feature which is also seen in LOVECLIM. The SST forcing in ARPEGE results in a strong zonal temperature gradient between the North Atlantic and east Eurasia, which in turn triggers an atmospheric gravity wave. This wave induces a blocking Okhotskian high, preventing the northwards penetration of the Meiyu monsoon front. The synergism between the ice sheets and SST is found through the factor separation method, yielding an increase in the Meiyu precipitation, though a reduction of the Changma precipitation. The synergism between the ice

  10. Termination behaviour of supraglacial lakes on the Greenland Ice Sheet.

    Science.gov (United States)

    Selmes, Nick; Murray, Tavi; James, Timothy

    2013-04-01

    The behaviour of supraglacial lakes on the Greenland Ice Sheet, specifically with regard to their drainage through hydrofracturing to the ice sheet base, has received a great deal of recent attention. However, a previous study has shown that this mode of drainage accounts for only 13% of the lakes on the Greenland Ice Sheet. No published work to date has studied what happens to those lakes that do not drain suddenly, and little is known about what differences exist between those lakes which drain suddenly and those which do not. To learn more about the fate of those lakes that do not drain rapidly, we followed the evolution of 2600 supraglacial lakes over the five year period 2005-2009 using 3704 MODIS images. Lakes were studied in all areas of the ice sheet where they grow large enough to be observed using MODIS data (250 m pixels). From the MODIS images lake extent was classified and area was extracted giving a dataset of lake area over time. We used these data along with inferred melt from the MODIS Land Surface Temperature data product and qualitative observations from the imagery to discover how each lake disappeared from the ice sheet each year. Here we present three different modes by which lakes can disappear from the ice sheet, which have strongly contrasting effects on glacial dynamics and ice sheet water budget. Firstly, 13% of all lakes drained suddenly, probably to the bed. We observed groups of lakes draining suddenly in the same day in apparently linked events suggesting a common trigger mechanism for drainage. Secondly, some lakes drained more slowly over several days (34% of lakes in our dataset). We interpret this to be the result of supraglacial drainage, probably through incision of the exit channel. Finally, 46% of lakes survived to the end of the melt season and froze over. We suggest hypotheses from our findings as to what factors control whether or not sudden lake drainage to the bed occurs. Our results show that care must be taken when

  11. Results of the Marine Ice Sheet Model Intercomparison Project, MISMIP

    Directory of Open Access Journals (Sweden)

    F. Pattyn

    2012-05-01

    Full Text Available Predictions of marine ice-sheet behaviour require models that are able to robustly simulate grounding line migration. We present results of an intercomparison exercise for marine ice-sheet models. Verification is effected by comparison with approximate analytical solutions for flux across the grounding line using simplified geometrical configurations (no lateral variations, no effects of lateral buttressing. Unique steady state grounding line positions exist for ice sheets on a downward sloping bed, while hysteresis occurs across an overdeepened bed, and stable steady state grounding line positions only occur on the downward-sloping sections. Models based on the shallow ice approximation, which does not resolve extensional stresses, do not reproduce the approximate analytical results unless appropriate parameterizations for ice flux are imposed at the grounding line. For extensional-stress resolving "shelfy stream" models, differences between model results were mainly due to the choice of spatial discretization. Moving grid methods were found to be the most accurate at capturing grounding line evolution, since they track the grounding line explicitly. Adaptive mesh refinement can further improve accuracy, including fixed grid models that generally perform poorly at coarse resolution. Fixed grid models, with nested grid representations of the grounding line, are able to generate accurate steady state positions, but can be inaccurate over transients. Only one full-Stokes model was included in the intercomparison, and consequently the accuracy of shelfy stream models as approximations of full-Stokes models remains to be determined in detail, especially during transients.

  12. 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.

  13. Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers

    Directory of Open Access Journals (Sweden)

    J. E. Box

    2012-08-01

    Full Text Available Greenland ice sheet mass loss has accelerated in the past decade responding to combined glacier discharge and surface melt water runoff increases. During summer, absorbed solar energy, modulated at the surface primarily by albedo, is the dominant factor governing surface melt variability in the ablation area. Using satellite-derived surface albedo with calibrated regional climate modeled surface air temperature and surface downward solar irradiance, we determine the spatial dependence and quantitative impact of the ice sheet albedo feedback over 12 summer periods beginning in 2000. We find that, while albedo feedback defined by the change in net solar shortwave flux and temperature over time is positive over 97% of the ice sheet, when defined using paired annual anomalies, a second-order negative feedback is evident over 63% of the accumulation area. This negative feedback damps the accumulation area response to warming due to a positive correlation between snowfall and surface air temperature anomalies. Positive anomaly-gauged feedback concentrated in the ablation area accounts for more than half of the overall increase in melting when satellite-derived melt duration is used to define the timing when net shortwave flux is sunk into melting. Abnormally strong anticyclonic circulation, associated with a persistent summer North Atlantic Oscillation extreme since 2007, enabled three amplifying mechanisms to maximize the albedo feedback: (1 increased warm (south air advection along the western ice sheet increased surface sensible heating that in turn enhanced snow grain metamorphic rates, further reducing albedo; (2 increased surface downward shortwave flux, leading to more surface heating and further albedo reduction; and (3 reduced snowfall rates sustained low albedo, maximizing surface solar heating, progressively lowering albedo over multiple years. The summer net infrared and solar radiation for the high elevation accumulation area approached

  14. Role of model initialization for projections of 21st-century Greenland ice sheet mass loss

    DEFF Research Database (Denmark)

    Adalgeirsdóttir, G.; Aschwanden, A.; Khroulev, C.

    2014-01-01

    Model simulations of the Greenland ice sheet contribution to 21st-century sea-level rise are performed with a state-of-the-art ice-sheet model (Parallel Ice Sheet Model (PISM)). The climate-forcing fields are obtained from the European Union's Seventh Framework Programme project ice2sea, in which......). These model simulations do not account for the recently observed acceleration of ice streams and consequent thinning rates, the changing ice discharge that may result from the spatial and temporal variability of ocean forcing, or the feedback occurring between ice-sheet elevation changes and climate forcing...

  15. Towards coupling of regional atmosphere models to ice sheet models by mass balance gradients - application to the Greenland Ice Sheet

    NARCIS (Netherlands)

    Helsen, M.M.|info:eu-repo/dai/nl/325802459; van de Wal, R.S.W.|info:eu-repo/dai/nl/101899556; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643; van de Berg, W.J.|info:eu-repo/dai/nl/304831611; Oerlemans, J.|info:eu-repo/dai/nl/06833656X

    2012-01-01

    It is notoriously difficult to couple surface mass balance (SMB) results from climate models to the changing geometry of an ice sheet model. This problem is traditionally avoided by using only accumulation from a climate model, and parameterizing the meltwater run-off as a function of temperature,

  16. Towards coupling of regional atmosphere models to ice sheet models by mass balance gradients - application to the Greenland Ice Sheet

    NARCIS (Netherlands)

    Helsen, M.M.; van de Wal, R.S.W.; van den Broeke, M.R.; van de Berg, W.J.; Oerlemans, J.

    2011-01-01

    It is notoriously difficult to couple surface mass balance (SMB) results from climate models to the changing geometry of an ice sheet model. This problem is traditionally avoided by using only accumulation fields from a climate model, and deriving SMB by parameterizing 5 the run-off as a function of

  17. Ice streams of the Late Wisconsin Cordilleran Ice Sheet in western North America

    Science.gov (United States)

    Eyles, Nick; Arbelaez Moreno, Lina; Sookhan, Shane

    2018-01-01

    The Late Wisconsin Cordilleran Ice Sheet (CIS) of western North America is thought to have reached its maximum extent (∼2.5 × 106 km2) as late at c. 14.5 ka. Most (80%) of the ice sheet's bed consists of high mountains but its 'core zone' sited on plateaux of the Intermontane Belt of British Columbia and coterminous parts of the USA, shows broad swaths of subglacially-streamlined rock and sediment. Broad scale mapping from new digital imagery data identifies three subglacial bed types: 1) 'hard beds' of variably streamlined bedrock; 2) drumlinized 'soft beds' of deformation till reworked from antecedent sediment, and 3) 'mixed beds' of variably-streamlined bedrock protruding through drumlinized sediment. Drumlins on soft beds appear to be erosional features cut into till and antecedent sediments, and identify the catchment areas of paleo ice streams expressed downglacier as flow sets of megascale glacial lineations (MSGLs). 'Grooved' and 'cloned' drumlins appear to record the transition from drumlins to MSGLs. The location of paleo ice streams reflects topographic funneling of ice from plateau surfaces through outlet valleys and a soft bed that sustained fast flow; rock-cut MSGLs are also present locally on the floors of outlet valleys. CIS disintegrated in streams along the glacio-isostatically depressed coast; large deep 'fiord lakes' in the ice sheet's interior may have played an analogous role. Mapping of the broad scale distribution of bed types across the Cordilleran Ice Sheet provides key information for paleoglaciological modelling and also for understanding the beds of modern ice masses such as the Greenland Ice Sheet which is of a comparable topographic setting.

  18. Effects of future Arctic sea ice decline on Greenland ice sheet melt

    Science.gov (United States)

    Vizcaino, Miren; Michailidou, Egli

    2017-04-01

    CMIP5 models project substantial reduction of the Arctic sea ice cover during the current century, including the onset of a seasonally ice free Arctic. In this study we explore the effects of future Arctic sea-ice change on the mass balance of the Greenland ice sheet (GrIS). For this, we use 1850-2100 simulations from the Community Earth System Model version 1.0 corresponding to historical and RCP8.5 scenarios. We examine the impact of Arctic change on the surface energy and mass budgets of the Greenland ice sheet. We distinguish between winter Arctic change and Greenland-melt-season (Spring and Summer) future climate change. We find a substantial reduction in summer incoming shortwave radiation over the GrIS both for clear-sky and all-sky conditions, that reduces the energy available for melt. Because of the large amount of energy that is used during summer to melt sea-ice, we find no amplified summer warming in the ocean around Greenland, except where summer-long ice-free conditions develop. The different nature of the processes controlling sea-ice change along the western and eastern Greenland coast is examined. We find no links in the timing of major sea-ice change and Greenland snow and ice melt, and justify why such a linkage is absent.

  19. Physical Controls on the Presence of Dark Ice on the Greenland Ice Sheet

    Science.gov (United States)

    Tedstone, A.; Bamber, J. L.; Williamson, C.; Cook, J.; McQuaid, J. B.; Fettweis, X.

    2016-12-01

    Areas of dark ice have appeared along the margins of the Greenland Ice Sheet during most melt seasons since at least 2000, but with significant inter- and intra- annual variations in areal extent. Distinctive from bare ice, whose albedo is greater than 0.4, dark ice exhibits very low albedo when measured in-situ or remotely. As albedo is the single most important factor controlling the energy balance, it is essential to understand the evolution of dark ice extent under projected climate change. Regional climate models such as the Modèle Atmosphérique Régional (MAR) are presently not able to simulate the albedo of dark ice, primarily because the factors influencing its presence are uncertain. In this study, we seek to establish the processes that firstly drive significant differences in dark ice extent between consecutive melt seasons, and secondly cause strong intra-seasonal variability in ablation zone albedo. We use a combination of in-situ measurements of spectral albedo, surface contaminants and meterology collected during the 2016 melt season together with remotely-sensed measurements of surface reflectance and broadband albedo, and surface mass balance estimates derived from MAR. We focus on two specific areas of uncertainty. Firstly, we elucidate the meteorological conditions that are necessary pre-conditions for the evolution of dark ice and that therefore drive inter-annual variability. Secondly, we consider the physical processes that interact with both inorganic and organic contaminants to cause rapid variations in dark ice extent through the course of a melt season. By identifying the processes driving the presence of dark ice we are able to implement a modified albedo scheme in MAR that replicates more closely the albedo observed over the south-western Greenland Ice Sheet during each recent melt season. This is a critical step towards improving estimates of surface mass balance in the ice sheet's ablation zone.

  20. Revised estimates of Greenland ice sheet thinning histories based on ice-core records

    DEFF Research Database (Denmark)

    Lecavalier, B.S.; Milne, G.A.; Fisher, D.A.

    2013-01-01

    -based reconstructions and, to some extent, the estimated elevation histories. A key component of the ice core analysis involved removing the influence of vertical surface motion on the dO signal measured from the Agassiz and Renland ice caps. We re-visit the original analysis with the intent to determine if the use...... height changes on the dO signal from the two ice cores. This procedure is complicated by the fact that dO contained in Agassiz ice is influenced by land height changes distant from the ice cap and so selecting a single location at which to compute the land height signal is not possible. Uncertainty......Ice core records were recently used to infer elevation changes of the Greenland ice sheet throughout the Holocene. The inferred elevation changes show a significantly greater elevation reduction than those output from numerical models, bringing into question the accuracy of the model...

  1. Interaction of ice sheets and climate during the past 800 000 years

    NARCIS (Netherlands)

    Stap, L. B.; Van De Wal, R. S W; De Boer, B.; Bintanja, R.; Lourens, L. J.

    2014-01-01

    During the Cenozoic, land ice and climate interacted on many different timescales. On long timescales, the effect of land ice on global climate and sea level is mainly set by large ice sheets in North America, Eurasia, Greenland and Antarctica. The climatic forcing of these ice sheets is largely

  2. The GreenLand Ice Sheet monitoring Network (GLISN)

    Science.gov (United States)

    Larsen, Tine B.; Anderson, K. R.; Beaudoin, B. C.; Butler, R.; Clinton, J. F.; Dahl-Jensen, T.; Ekstrom, G.; Giardini, D.; Hanka, W.; Kanao, M.; McCormack, D.; Mykkelveit, S.; Nettles, M.; Piana Agostinetti, N.; Tsuboi, S.; Voss, P.

    2010-05-01

    The GreenLand Ice Sheet monitoring Network (GLISN) is a new, international, broadband seismic capability for Greenland, being installed and implemented through the joint collaboration of USA, Denmark, Switzerland, Germany, Canada, Italy, Japan and Norway. GLISN is a real-time sensor array consisting of more than 20 broad band stations. The purpose of the project is to enhance and upgrade the performance of the scarce existing Greenland seismic infrastructure for detecting, locating, and characterizing both tectonic and in particular glacial earthquakes and other cryo-seismic phenomena. Complementing data from satellites, geodesy, and other sources, and in concert with these technologies, GLISN will provide a powerful tool for detecting change, and will advance new frontiers of research in the glacial systems as well as in the underlying geological and geophysical processes affecting the Greenland Ice Sheet. The glacial processes that induce seismic events are all integral to the overall dynamics of glaciers, and seismic observations of glaciers therefore provide a quantitative means for monitoring changes in their behaviour over time. Long-term seismic monitoring of the Greenland Ice Sheet will contribute to identifying possible unsuspected mechanisms, and also detect if the areas of cryo-seismic events change and expand in the coming decades. GLISN will provide a new reference network in and around Greenland for monitoring these phenomena in real-time, and for the broad seismological study of Earth and earthquakes. The GLISN development takes its starting point in the existing permanent and long-time stations in and around Greenland operated by members of GLISN. These stations will be upgraded to a common standard with real-time telemetry. The network will be expanded by installing new, telemetered, broadband seismic stations on Greenland's perimeter and ice sheet. An open virtual network is established were all GLISN data can be downloaded. In collaboration with

  3. Estimating the future ice sheet hydropower potential in Paakitsoq, Ilulissat, West Greenland

    DEFF Research Database (Denmark)

    Ahlstrøm, Andreas P.; Mottram, R.H.; Nielsen, C.

    2008-01-01

    of meltwater during the summer season. However, geometrical changes in the ice sheet, for example due to a retreat or an advance of the ice sheet margin, could change the hydrological catchment within the ice sheet. Such a change would have a devastating economical impact as a hydropower plant is a significant...... long-term investment for an Arctic community of modest population. Here we present a new bedrock and surface map of the Paakitsoq/Swiss Camp part of the Greenland ice sheet and a prediction of the future discharge up to 2080 AD using regional climate model output, dynamic ice sheet modelling...

  4. The Greenland ice sheet and the climate – a review

    DEFF Research Database (Denmark)

    Funder, Svend Visby; Kjeldsen, Kristian Kjellerup; Kjær, Kurt H.

    During LGM the margins of the Greenland ice sheet around the whole perimeter stood on the shelf – but where? The first estimates had to be based on evidence from land such as weathering limits on coastal mountains, major moraine belts, and altitudes of marine limits. Still the estimates ranged fr...... to climate change during and after LGM, and that coverage of the shelf may have been variable from one sector to another. Will the margin respond with similar complexity to global warming?...

  5. Refreezing on the Greenland ice sheet: a comparison of parameterizations

    Directory of Open Access Journals (Sweden)

    C. H. Reijmer

    2012-07-01

    Full Text Available Retention and refreezing of meltwater are acknowledged to be important processes for the mass budget of polar glaciers and ice sheets. Several parameterizations of these processes exist for use in energy and mass balance models. Due to a lack of direct observations, validation of these parameterizations is difficult. In this study we compare a set of 6 refreezing parameterizations against output of two Regional Climate Models (RCMs coupled to an energy balance snow model, the Regional Atmospheric Climate Model (RACMO2 and the Modèle Atmosphérique Régional (MAR, applied to the Greenland ice sheet. In both RCMs, refreezing is explicitly calculated in a snow model that calculates vertical profiles of temperature, density and liquid water content. Between RACMO2 and MAR, the ice sheet-integrated amount of refreezing differs by only 4.9 mm w.e yr−1 (4.5 %, and the temporal and spatial variability are very similar. For consistency, the parameterizations are forced with output (surface temperature, precipitation and melt of the RCMs. For the ice sheet-integrated amount of refreezing and its inter-annual variations, all parameterizations give similar results, especially after some tuning. However, the spatial distributions differ significantly and the spatial correspondence between the RCMs is better than with any of the parameterizations. Results are especially sensitive to the choice of the depth of the thermally active layer, which determines the cold content of the snow in most parameterizations. These results are independent of which RCM is used to force the parameterizations.

  6. The modelled liquid water balance of the Greenland Ice Sheet

    Directory of Open Access Journals (Sweden)

    C. R. Steger

    2017-11-01

    Full Text Available Recent studies indicate that the surface mass balance will dominate the Greenland Ice Sheet's (GrIS contribution to 21st century sea level rise. Consequently, it is crucial to understand the liquid water balance (LWB of the ice sheet and its response to increasing surface melt. We therefore analyse a firn simulation conducted with the SNOWPACK model for the GrIS and over the period 1960–2014 with a special focus on the LWB and refreezing. Evaluations of the simulated refreezing climate with GRACE and firn temperature observations indicate a good model–observation agreement. Results of the LWB analysis reveal a spatially uniform increase in surface melt (0.16 m w.e. a−1 during 1990–2014. As a response, refreezing and run-off also indicate positive changes during this period (0.05 and 0.11 m w.e. a−1, respectively, where refreezing increases at only half the rate of run-off, implying that the majority of the additional liquid input runs off the ice sheet. This pattern of refreeze and run-off is spatially variable. For instance, in the south-eastern part of the GrIS, most of the additional liquid input is buffered in the firn layer due to relatively high snowfall rates. Modelled increase in refreezing leads to a decrease in firn air content and to a substantial increase in near-surface firn temperature. On the western side of the ice sheet, modelled firn temperature increases are highest in the lower accumulation zone and are primarily caused by the exceptional melt season of 2012. On the eastern side, simulated firn temperature increases are more gradual and are associated with the migration of firn aquifers to higher elevations.

  7. The modelled liquid water balance of the Greenland Ice Sheet

    Science.gov (United States)

    Steger, Christian R.; Reijmer, Carleen H.; van den Broeke, Michiel R.

    2017-11-01

    Recent studies indicate that the surface mass balance will dominate the Greenland Ice Sheet's (GrIS) contribution to 21st century sea level rise. Consequently, it is crucial to understand the liquid water balance (LWB) of the ice sheet and its response to increasing surface melt. We therefore analyse a firn simulation conducted with the SNOWPACK model for the GrIS and over the period 1960-2014 with a special focus on the LWB and refreezing. Evaluations of the simulated refreezing climate with GRACE and firn temperature observations indicate a good model-observation agreement. Results of the LWB analysis reveal a spatially uniform increase in surface melt (0.16 m w.e. a-1) during 1990-2014. As a response, refreezing and run-off also indicate positive changes during this period (0.05 and 0.11 m w.e. a-1, respectively), where refreezing increases at only half the rate of run-off, implying that the majority of the additional liquid input runs off the ice sheet. This pattern of refreeze and run-off is spatially variable. For instance, in the south-eastern part of the GrIS, most of the additional liquid input is buffered in the firn layer due to relatively high snowfall rates. Modelled increase in refreezing leads to a decrease in firn air content and to a substantial increase in near-surface firn temperature. On the western side of the ice sheet, modelled firn temperature increases are highest in the lower accumulation zone and are primarily caused by the exceptional melt season of 2012. On the eastern side, simulated firn temperature increases are more gradual and are associated with the migration of firn aquifers to higher elevations.

  8. The effect of ice shelves on the ice flux at the grounding line and implications for marine ice sheet stability

    Science.gov (United States)

    Haseloff, M.; Sergienko, O. V.

    2016-12-01

    Ice shelves transmit ocean forcing (e.g. variations in basal melt rates) inland by changing the stress balance at the grounding line. However, determining mechanisms and quantifying their effects remains a major challenge for ice sheet models, and the conclusions drawn from these models often depend on the type of model used. Recent simulations with two-dimensional, plan view, ice-flow models suggest that ice shelves can change the stability of grounding lines through buttressing. In contrast, ice shelves can be excluded from the momentum balance in computationally-efficient flowline models. Here, we investigate whether parameterized buttressing in laterally integrated models of confined ice shelves can bridge the gap between these two classes of models. We extend a recently developed boundary layer approach to laterally confined, strongly buttressed ice shelves. This allows us to determine the backstress at the grounding line as a function of ice shelf properties such as shelf width and length, and to calculate how the ice flux at the grounding line changes under different parameterizations and calving law choices. In the limit of strong buttressing, we find that calving laws which prescribe the ice thickness at the calving front uniquely determine the flux through the grounding line. Conversely, prescribing a constant calving front position can lead to a multivalued relationship between ice thickness and flux at the grounding line, as has also been suggested by recent results with laterally extended models. However, we find that parameterizations of ice shelf buttressing do not change the stability properties of marine ice sheets in flowline models if either the length of the ice shelf or a constant calving front position are prescribed.

  9. The Sentinel-1 Mission: New Opportunities for Ice Sheet Observations

    Directory of Open Access Journals (Sweden)

    Thomas Nagler

    2015-07-01

    Full Text Available The Sentinel satellite constellation series, developed by the European Space Agency, represents the dedicated space component of the European Copernicus program, committed to long-term operational services in a wide range of application domains. Here, we address the potential of the Sentinel-1 mission for mapping and monitoring the surface velocity of glaciers and ice sheets. We present an ice velocity map of Greenland, derived from synthetic aperture radar (SAR data acquired in winter 2015 by Sentinel-1A, the first satellite of the Copernicus program in orbit. The map is assembled from about 900 SAR scenes acquired in Interferometric Wide swath (IW mode, applying the offset tracking technique. We discuss special features of IW mode data, describe the procedures for producing ice velocity maps, and assess the uncertainty of the ice motion product. We compare the Sentinel-1 ice motion product with velocity maps derived from high resolution SAR data of the TerraSAR-X mission and from PALSAR data. Beyond supporting operational services, the Sentinel-1 mission offers enhanced capabilities for comprehensive and long-term observation of key climate variables, such as the motion of ice masses.

  10. Hindcasting to measure ice sheet model sensitivity to initial states

    Directory of Open Access Journals (Sweden)

    A. Aschwanden

    2013-07-01

    Full Text Available Validation is a critical component of model development, yet notoriously challenging in ice sheet modeling. Here we evaluate how an ice sheet system model responds to a given forcing. We show that hindcasting, i.e. forcing a model with known or closely estimated inputs for past events to see how well the output matches observations, is a viable method of assessing model performance. By simulating the recent past of Greenland, and comparing to observations of ice thickness, ice discharge, surface speeds, mass loss and surface elevation changes for validation, we find that the short term model response is strongly influenced by the initial state. We show that the thermal and dynamical states (i.e. the distribution of internal energy and momentum can be misrepresented despite a good agreement with some observations, stressing the importance of using multiple observations. In particular we identify rates of change of spatially dense observations as preferred validation metrics. Hindcasting enables a qualitative assessment of model performance relative to observed rates of change. It thereby reduces the number of admissible initial states more rigorously than validation efforts that do not take advantage of observed rates of change.

  11. A global high-resolution data set of ice sheet topography, cavity geometry and ocean bathymetry

    DEFF Research Database (Denmark)

    Schaffer, Janin; Timmermann, Ralph; Arndt, Jan Erik

    2016-01-01

    The ocean plays an important role in modulating the mass balance of the polar ice sheets by interactingwith the ice shelves in Antarctica and with the marine-terminating outlet glaciers in Greenland. Given thatthe flux of warm water onto the continental shelf and into the sub-ice cavities...... of the Southern Ocean (IBCSO) version 1. While RTopo-1 primarily aimed at a good and consistent representation of the Antarctic ice sheet, ice shelves, and sub-ice cavities, RTopo-2now also contains ice topographies of the Greenland ice sheet and outlet glaciers. In particular, we aimed at agood representation...... of Nioghalvfjerdsfjorden Glacierand Zachariæ Isstrøm have been obtained from the data centres of Technical University of Denmark (DTU),Operation Icebridge (NASA/NSF), and Alfred Wegener Institute (AWI). For the Antarctic ice sheet/ice shelves,RTopo-2 largely relies on the Bedmap-2 product but applies corrections...

  12. Drilling, processing and first results for Mount Johns ice core in West Antarctica Ice Sheet

    OpenAIRE

    Schwanck,Franciele; Simões,Jefferson Cardia; Handley,Michael; Mayewski,Paul Andrew; Bernardo,Ronaldo Torma; Aquino,Francisco Eliseu

    2016-01-01

    ABSTRACT: An ice core, 92.26 m in length, was collected near the ice divide of the West Antarctica ice sheet during the 2008/2009 austral summer. This paper described the fieldwork at the Mount Johns site (79º55'S; 94º23'W) and presented the first results of the upper 45.00 m record covering approximately 125 years (1883 - 2008), dated by annual layer counting and volcanic reference horizons. Trace element concentrations in 2,137 samples were determined using inductively coupled plasma mass s...

  13. Ice-sheet flow conditions deduced from mechanical tests of ice core

    DEFF Research Database (Denmark)

    Miyamoto, Atsushi; Narita, Hideki; Hondoh, Takeo

    1999-01-01

    Uniaxial compression tests were performed on samples of the Greenland Ice Core Project (GRIP) deep ice core, both in the field and later in a cold-room laboratory, in order to understand the ice-flow behavior of large ice sheets. Experiments were conducted under conditions of constant strain rate...... (type A) and constant load (type B). Fifty-four uniaxial-compression test specimens from 1327-2922 m were selected. Each test specimen (25 mm × 25 mm × 90 mm) was prepared with its uniaxial stress axis inclined 45° from the core axis in order to examine the flow behavior of strong single-maximum ice......-core samples with basal planes parallel to the horizontal plane of the ice sheet. The ice-flow enhancement factors show a gradual increase with depth down to approximately 2000 m. These results can be interpreted in terms of an increase in the fourth-order Schmid factor. Below 2000 m depth, the flow...

  14. Preservation of a Preglacial Landscape Under the Center of the Greenland Ice Sheet

    Science.gov (United States)

    Bierman, Paul R.; Corbett, Lee B.; Graly, Joseph A.; Neumann, Thomas Allen; Lini, Andrea; Crosby, Benjamin T.; Rood, Dylan H.

    2014-01-01

    Continental ice sheets typically sculpt landscapes via erosion; under certain conditions, ancient landscapes can be preserved beneath ice and can survive extensive and repeated glaciation. We used concentrations of atmospherically produced cosmogenic beryllium-10, carbon, and nitrogen to show that ancient soil has been preserved in basal ice for millions of years at the center of the ice sheet at Summit, Greenland. This finding suggests ice sheet stability through the Pleistocene (i.e., the past 2.7 million years). The preservation of this soil implies that the ice has been non-erosive and frozen to the bed for much of that time, that there was no substantial exposure of central Greenland once the ice sheet became fully established, and that preglacial landscapes can remain preserved for long periods under continental ice sheets

  15. Influence of ice-sheet geometry and supraglacial lakes on seasonal ice-flow variability

    NARCIS (Netherlands)

    Joughin, I.; Das, S. B.; Flowers, G. E.; Behn, M. D.; Alley, R. B.; King, M. A.; Smith, B. E.; Bamber, J. L.; van den Broeke, M. R.; van Angelen, J. H.

    2013-01-01

    Supraglacial lakes play an important role in establishing hydrological connections that allow lubricating seasonal meltwater to reach the base of the Greenland Ice Sheet. Here we use new surface velocity observations to examine the influence of supraglacial lake drainages and surface melt rate on

  16. Nature and History of Cenozoic Polar Ice Covers: The Case of the Greenland Ice Sheet

    Science.gov (United States)

    Spielhagen, R.; Thiede, J.

    2009-04-01

    The nature of the modern climate System is characterized by steep temperature gradients between the tropical and polar climatic zones and finds its most spectacular expression in the formation of ice caps in high Northern and Southern latitudes. While polar regions of Planet Earth have been glaciated repeatedly in the long course of their geological history, the Cenozoic transition from a „greenhouse" to an „icehouse" has in fact produced a unique climatic scenario with bipolar glacation, different from all previous glacial events. The Greenland ice sheet is a remainder of the Northern Hemisphere last glacial maximum ice sheets and represents hence a spectacular anomaly. Geological records from Tertiary and Quaternary terrestrial and oceanic sections have documented the presence of ice caps and sea ice covers both on the Southern as well on the Northern hemisphere since Eocene times, aqpprox. 45 Mio. years ago. While this was well known in the case of Antarctica already for some time, previous ideas about the origin of Northern hemisphere glaciation during Pliocene times (approx. 2-3 Mio. years ago) have been superceded by the dramatic findings of coarse, terrigenous ice rafted detritus in Eocene sediments from Lomonosov Ridge (close to the North Pole) apparently slightly older than the oldest Antarctic records of ice rafting.The histories of the onset of Cenozoic glaciation in high Northern and Southern latitudes remain enigmatic and are presently subjects of international geological drilling projects, with prospects to reveal some of their secrets over the coming decades. By virtue of the physical porperties of ice and the processes controlling the dynamics of the turn-over of the ice-sheets only young records of glacial ice caps on Antarctica and on Greemnland have been preserved, on Greenland with ice probably not older than a few hundred thousand years, on Antarctica potentially as old as 1.5-2 Mio. years. Deep-sea cores with their records od ice

  17. Dating Antarctic ice sheet collapse: Proposing a molecular genetic approach

    Science.gov (United States)

    Strugnell, Jan M.; Pedro, Joel B.; Wilson, Nerida G.

    2018-01-01

    Sea levels at the end of this century are projected to be 0.26-0.98 m higher than today. The upper end of this range, and even higher estimates, cannot be ruled out because of major uncertainties in the dynamic response of polar ice sheets to a warming climate. Here, we propose an ecological genetics approach that can provide insight into the past stability and configuration of the West Antarctic Ice Sheet (WAIS). We propose independent testing of the hypothesis that a trans-Antarctic seaway occurred at the last interglacial. Examination of the genomic signatures of bottom-dwelling marine species using the latest methods can provide an independent window into the integrity of the WAIS more than 100,000 years ago. Periods of connectivity facilitated by trans-Antarctic seaways could be revealed by dating coalescent events recorded in DNA. These methods allow alternative scenarios to be tested against a fit to genomic data. Ideal candidate taxa for this work would need to possess a circumpolar distribution, a benthic habitat, and some level of genetic structure indicated by phylogeographical investigation. The purpose of this perspective piece is to set out an ecological genetics method to help resolve when the West Antarctic Ice Shelf last collapsed.

  18. Predicting subglacial lakes and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

    Science.gov (United States)

    Livingstone, S. J.; Clark, C. D.; Woodward, J.

    2013-03-01

    In this paper we use the Shreve hydraulic potential equation to predict subglacial lakes and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. For the Antarctic Ice Sheet we are able to predict known subglacial lakes with a >70% success rate, which demonstrates the validity of this method. Despite the success in predicting known subglacial lakes the calculations produce two-orders of magnitude more lakes than are presently identified, covering 4% of the ice-sheet bed. The difference is thought to result from our poor knowledge of the bed (which has resulted in artefacts associated with the interpolation method), intrinsic errors associated with the simplified modelling approach and because thousands of subglacial lakes, particularly smaller ones, remain to be found. Applying the same modelling approach to the Greenland Ice Sheet predicts only 90 lakes under the present-day ice-sheet configuration, covering 0.2% of the bed. The paucity of subglacial lakes in Greenland is thought to be a function of steeper overall ice-surface gradients. As no lakes have currently been located under Greenland, model predictions will make suitable targets for radar surveys of Greenland to identify subglacial lakes. During deglaciation from the Last Glacial Maximum both ice sheets had more subglacial lakes at their beds, though many of these lakes have persisted to present conditions. These lakes, inherited from past ice-sheet configurations would not form under current surface conditions, suggesting a retreating ice-sheet will have many more subglacial lakes than an advancing ice sheet. This hysteresis effect has implications for ice-stream formation and flow, bed lubrication and meltwater drainage. The lake model also allows modelling of the drainage pathways of the present-day and former Greenland and Antarctic ice sheets. Significantly, key sectors of the ice sheets, such as the Siple Coast (Antarctica) and NE Greenland Ice Stream system, are shown to have

  19. The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet-climate model

    NARCIS (Netherlands)

    Stap, Lennert B.; Van De Wal, Roderik S.W.; De Boer, Bas; Bintanja, Richard; Lourens, Lucas J.

    2017-01-01

    Since the inception of the Antarctic ice sheet at the Eocene-Oligocene transition ( ~34 Myr ago), land ice has played a crucial role in Earth's climate. Through feedbacks in the climate system, land ice variability modifies atmospheric temperature changes induced by orbital, topographical, and

  20. Interactions between topographically and thermally forced stationary waves: implications for ice-sheet evolution

    Directory of Open Access Journals (Sweden)

    Johan Liakka

    2012-01-01

    Full Text Available This study examines mutual interactions between stationary waves and ice sheets using a dry atmospheric primitive-equation model coupled to a three-dimensional thermomechanical ice-sheet model. The emphasis is on how non-linear interactions between thermal and topographical forcing of the stationary waves influence the ice-sheet evolution by changing the ablation. Simulations are conducted in which a small ice cap, on an idealised Northern Hemisphere continent, evolves to an equilibrium continental-scale ice sheet. In the absence of stationary waves, the equilibrium ice sheet arrives at symmetric shape with a zonal equatorward margin. In isolation, the topographically induced stationary waves have essentially no impact on the equilibrium features of the ice sheet. The reason is that the temperature anomalies are located far from the equatorward ice margin. When forcing due to thermal cooling is added to the topographical forcing, thermally induced perturbation winds amplify the topographically induced stationary-wave response, which that serves to increase both the equatorward extent and the volume of the ice sheet. Roughly, a 10% increase in the ice volume is reported here. Hence, the present study suggests that the topographically induced stationary-wave response can be substantially enhanced by the high albedo of ice sheets.

  1. Predicting Ice Sheet and Climate Evolution at Extreme Scales

    Energy Technology Data Exchange (ETDEWEB)

    Heimbach, Patrick [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

    2016-02-06

    A main research objectives of PISCEES is the development of formal methods for quantifying uncertainties in ice sheet modeling. Uncertainties in simulating and projecting mass loss from the polar ice sheets arise primarily from initial conditions, surface and basal boundary conditions, and model parameters. In general terms, two main chains of uncertainty propagation may be identified: 1. inverse propagation of observation and/or prior onto posterior control variable uncertainties; 2. forward propagation of prior or posterior control variable uncertainties onto those of target output quantities of interest (e.g., climate indices or ice sheet mass loss). A related goal is the development of computationally efficient methods for producing initial conditions for an ice sheet that are close to available present-day observations and essentially free of artificial model drift, which is required in order to be useful for model projections (“initialization problem”). To be of maximum value, such optimal initial states should be accompanied by “useful” uncertainty estimates that account for the different sources of uncerainties, as well as the degree to which the optimum state is constrained by available observations. The PISCEES proposal outlined two approaches for quantifying uncertainties. The first targets the full exploration of the uncertainty in model projections with sampling-based methods and a workflow managed by DAKOTA (the main delivery vehicle for software developed under QUEST). This is feasible for low-dimensional problems, e.g., those with a handful of global parameters to be inferred. This approach can benefit from derivative/adjoint information, but it is not necessary, which is why it often referred to as “non-intrusive”. The second approach makes heavy use of derivative information from model adjoints to address quantifying uncertainty in high-dimensions (e.g., basal boundary conditions in ice sheet models). The use of local gradient, or

  2. Combustion of available fossil fuel resources sufficient to eliminate the Antarctic Ice Sheet.

    Science.gov (United States)

    Winkelmann, Ricarda; Levermann, Anders; Ridgwell, Andy; Caldeira, Ken

    2015-09-01

    The Antarctic Ice Sheet stores water equivalent to 58 m in global sea-level rise. We show in simulations using the Parallel Ice Sheet Model that burning the currently attainable fossil fuel resources is sufficient to eliminate the ice sheet. With cumulative fossil fuel emissions of 10,000 gigatonnes of carbon (GtC), Antarctica is projected to become almost ice-free with an average contribution to sea-level rise exceeding 3 m per century during the first millennium. Consistent with recent observations and simulations, the West Antarctic Ice Sheet becomes unstable with 600 to 800 GtC of additional carbon emissions. Beyond this additional carbon release, the destabilization of ice basins in both West and East Antarctica results in a threshold increase in global sea level. Unabated carbon emissions thus threaten the Antarctic Ice Sheet in its entirety with associated sea-level rise that far exceeds that of all other possible sources.

  3. Dark ice dynamics of the south-west Greenland Ice Sheet

    Directory of Open Access Journals (Sweden)

    A. J. Tedstone

    2017-11-01

    Full Text Available Runoff from the Greenland Ice Sheet (GrIS has increased in recent years due largely to changes in atmospheric circulation and atmospheric warming. Albedo reductions resulting from these changes have amplified surface melting. Some of the largest declines in GrIS albedo have occurred in the ablation zone of the south-west sector and are associated with the development of dark ice surfaces. Field observations at local scales reveal that a variety of light-absorbing impurities (LAIs can be present on the surface, ranging from inorganic particulates to cryoconite materials and ice algae. Meanwhile, satellite observations show that the areal extent of dark ice has varied significantly between recent successive melt seasons. However, the processes that drive such large interannual variability in dark ice extent remain essentially unconstrained. At present we are therefore unable to project how the albedo of bare ice sectors of the GrIS will evolve in the future, causing uncertainty in the projected sea level contribution from the GrIS over the coming decades. Here we use MODIS satellite imagery to examine dark ice dynamics on the south-west GrIS each year from 2000 to 2016. We quantify dark ice in terms of its annual extent, duration, intensity and timing of first appearance. Not only does dark ice extent vary significantly between years but so too does its duration (from 0 to > 80 % of June–July–August, JJA, intensity and the timing of its first appearance. Comparison of dark ice dynamics with potential meteorological drivers from the regional climate model MAR reveals that the JJA sensible heat flux, the number of positive minimum-air-temperature days and the timing of bare ice appearance are significant interannual synoptic controls. We use these findings to identify the surface processes which are most likely to explain recent dark ice dynamics. We suggest that whilst the spatial distribution of dark ice is best explained by

  4. Dark ice dynamics of the south-west Greenland Ice Sheet

    Science.gov (United States)

    Tedstone, Andrew J.; Bamber, Jonathan L.; Cook, Joseph M.; Williamson, Christopher J.; Fettweis, Xavier; Hodson, Andrew J.; Tranter, Martyn

    2017-11-01

    Runoff from the Greenland Ice Sheet (GrIS) has increased in recent years due largely to changes in atmospheric circulation and atmospheric warming. Albedo reductions resulting from these changes have amplified surface melting. Some of the largest declines in GrIS albedo have occurred in the ablation zone of the south-west sector and are associated with the development of dark ice surfaces. Field observations at local scales reveal that a variety of light-absorbing impurities (LAIs) can be present on the surface, ranging from inorganic particulates to cryoconite materials and ice algae. Meanwhile, satellite observations show that the areal extent of dark ice has varied significantly between recent successive melt seasons. However, the processes that drive such large interannual variability in dark ice extent remain essentially unconstrained. At present we are therefore unable to project how the albedo of bare ice sectors of the GrIS will evolve in the future, causing uncertainty in the projected sea level contribution from the GrIS over the coming decades. Here we use MODIS satellite imagery to examine dark ice dynamics on the south-west GrIS each year from 2000 to 2016. We quantify dark ice in terms of its annual extent, duration, intensity and timing of first appearance. Not only does dark ice extent vary significantly between years but so too does its duration (from 0 to > 80 % of June-July-August, JJA), intensity and the timing of its first appearance. Comparison of dark ice dynamics with potential meteorological drivers from the regional climate model MAR reveals that the JJA sensible heat flux, the number of positive minimum-air-temperature days and the timing of bare ice appearance are significant interannual synoptic controls. We use these findings to identify the surface processes which are most likely to explain recent dark ice dynamics. We suggest that whilst the spatial distribution of dark ice is best explained by outcropping of particulates from

  5. Data assimilation and prognostic whole ice sheet modelling with the variationally derived, higher order, open source, and fully parallel ice sheet model VarGlaS

    Directory of Open Access Journals (Sweden)

    D. J. Brinkerhoff

    2013-07-01

    Full Text Available We introduce a novel, higher order, finite element ice sheet model called VarGlaS (Variational Glacier Simulator, which is built on the finite element framework FEniCS. Contrary to standard procedure in ice sheet modelling, VarGlaS formulates ice sheet motion as the minimization of an energy functional, conferring advantages such as a consistent platform for making numerical approximations, a coherent relationship between motion and heat generation, and implicit boundary treatment. VarGlaS also solves the equations of enthalpy rather than temperature, avoiding the solution of a contact problem. Rather than include a lengthy model spin-up procedure, VarGlaS possesses an automated framework for model inversion. These capabilities are brought to bear on several benchmark problems in ice sheet modelling, as well as a 500 yr simulation of the Greenland ice sheet at high resolution. VarGlaS performs well in benchmarking experiments and, given a constant climate and a 100 yr relaxation period, predicts a mass evolution of the Greenland ice sheet that matches present-day observations of mass loss. VarGlaS predicts a thinning in the interior and thickening of the margins of the ice sheet.

  6. Satellite Radar Interferometry for Monitoring Ice-Sheet Motion: Application to an Antarctic Ice Stream

    Science.gov (United States)

    Goldstein, R. M.; Engelhardt, H.; Kamb, B.; Frolich, R. M.

    1993-01-01

    As a new means of monitoring the flow velocities and grounding-line positions of ice streams, which are indicators of response of the Antarctic and Greenland ice sheets to climatic change or internal instability, the method of satellite radar interferometry (SRI) is here proposed and applied to the Rutford Ice Stream, Antarctica. The method uses phase comparison of the radar signal obtained for a pair of SAR images taken a few days apart to plot an interferogram which directly displays relative ground motions that have occurred in the time interval between images. The detection limit is about 1.5 mm for vertical motions and about 4 mm for horizontal motions in the radar beam direction. In the Rutford Ice Stream, SRI velocities agree fairly well with earlier ground-truth data over a longitudinal interval of 29 km; the comparison suggests a secular decrease in velocity of about 2 percent from 1978-80 to 1992...

  7. Mass loss of the Greenland Ice Sheet since the Little Ice Age, implications on sea level

    DEFF Research Database (Denmark)

    Kjeldsen, K. K.; Bjork, A. A.; Khan, Shfaqat Abbas

    -2010, NASA's Ice, Cloud, and land Elevation Satellite (ICESat) from 2003-2009, and NASA's Land, Vegetation, and Ice Sensor (LVIS) from 2010, to estimate mass loss throughout the 20th and early 21st Century. We present mass balance estimates of the GrIS since retreat commence from the maximum extent......The impact of mass loss from the Greenland Ice Sheet (GrIS) on 20th Century sea level rise (SLR) has long been subject to intense discussions. While globally distributed tide gauges suggest a global mean SLR of 15-20 cm, quantifying the separate components is of great concern - in particular...... for modeling sea level projections into the 21st Century. Estimates of the past GrIS contribution to SLR have been derived using a number of different approaches, e.g. surface mass balance (SMB) calculations combined with estimates of ice discharge found by in correlating SMB anomalies and calving rates. Here...

  8. Multi-decadal dynamic thinning on the northwest margin of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Korsgaard, Niels Jákup; Kjær, Kurt H.; Khan, Shfaqat Abbas

    for the entire ice sheet show increased mass loss from 137 Gt/yr in 2002–2003 to 286 Gt/yr in 2007–2009. Also evidence from the GRACE, GPS (Global Positioning System), and ICESat (Ice, Cloud and land Elevation Satellite) as well as surface mass balance data suggests there is an ongoing northward migration...... records with a 25 m grid resolution and vertical uncertainty of 4.1 m. Comparative DEMs were derived from laser altimetry data recorded in 2005 and 2010. Ice loss from the Greenland Ice Sheet (GrIS) can be partitioned into surface mass balance (SMB) processes (runoff and precipitation) and ice dynamics......Ice mass changes in the Greenland Ice Sheet have been estimated since the early 1990s from the GRACE (Gravity Recovery and Climate Experiment) satellite gravity mission, of ice sheet thinning from satellite radar altimetry and airborne laser altimetry, and of increased velocities of outlet glaciers...

  9. Stochastic Climate Forcing for Ice-Sheet Models

    Science.gov (United States)

    Nuterman, Roman; Jochum, Markus

    2017-04-01

    Climate oscillations from glacial periods, with large parts of the continents covered with ice, to warm interglacials like the present one, are observed in various paleoclimatic records over the past few million years. According to Milankovitch theory, which is commonly assumed, these glacial cycles are linked to changes in insolation due to periodic changes of external earth-orbital forcing. However, this relationship is far from understood, because the insolation variations are so small that enhancing feedbacks must be at play. Moreover, there are several shortcomings in the Milankovitch theory: first, the duration of the glacial cycles changed at the so-called Mid-Pleistocene transition from 41,000 years to approximately 100,000 years and second, the interglacial of 400,000 years ago should not have happened. Thus, the current phasing and magnitude of the glacial cycles are far from being well understood and the external perturbation might only play a minor role in comparison to internal stochastic variations or internal oscillations. Although modern Ice-Sheet Models (ISM) are able to simulate evolution of ice-sheets at the entire glacial or interglacial time scales, the state-of-the-art Earth System Models (ESM) are too computationally expensive for such long integrations. Therefore, a constant climate forcing is usually used in the ice-sheet models. However, this approach does not take into account the stochastic nature of climate. At the same time, ESM models provide valuable information on natural climate variability, which then can be used for building stochastic climate models able to generate both continuous and discrete climate variables with stochastic atmospheric processes. In this study, we present a stochastic climate model, built from large sets of Community Earth System Model (CESM) integrations with both internal and external climate forcing, and able to generate synthetic climate forcing (such as temperature and precipitation fields) of any

  10. Ice stream dynamics: A transition between sheet flow and shelf flow

    Science.gov (United States)

    Hofstede, Coen Matthijs

    2008-07-01

    A problem ice sheet models using the shallow ice approximation have, is that they react slowly to a warmer atmosphere simply because it takes a long time for a large ice mass to warm up. Quite contrary to ice sheet model predictions, the Greenland Ice Sheet underwent dramatic changes in the last decade. Ice surfaces lowered in the lower parts of the ice sheet and some major outlet glaciers increased their outlet velocities dramatically. This was a incredibly quick reaction for such a big ice sheet to the present climate warming. Ice sheet models were lacking an important mechanism, a mechanism that enables ice sheets to react quickly to physical changes around the perimeter of the ice sheet. The most dramatic changes happened at three large ice streams in the southern part of Greenland. Ice streams are highly dynamic parts of an ice sheet where ice moves considerably faster that the surrounding ice sheet. They can accelerate, decelerate, shut off or start on short time intervals. Something makes the ice dynamics of ice streams very different from the major part of the ice sheet. In this thesis I develop a simple flow line model that simulates the ice dynamics of an ice stream. The model provides a gradual transition between sheet flow described by the shallow ice approximation to shelf flow. This is done by the introduction of the floating fraction φ that quantifies a flotation height of an ice column along the flow line. This flotation height gradually varies between zero at the ice sheet, to the height of the entire ice column at the ice shelf. This has consequences for the force balance the model uses. Because of the flotation height there is, next to the basal shear stress, a tensile stress and a water buttressing stress. This force balance enables the glacier to react quickly to small force perturbation changes around the marine perimeter of the ice sheet. The model is tested against Held data of Jakobshavn Isbrae, a very fast ice stream on the west coast of

  11. Snapshots of the Greenland ice sheet configuration in the Pliocene to early Pleistocene

    DEFF Research Database (Denmark)

    Solgaard, Anne M.; Reeh, Niels; Japsen, Peter

    2011-01-01

    from the deposits of the Kap Kobenhavn Formation, North Greenland. Our experiments show that no coherent ice sheet is likely to have existed in Greenland during the Mid-Pliocene Warmth and that only local ice caps may have been present in the coastal mountains of East Greenland. Our results illustrate......The geometry of the ice sheets during the Pliocene to early Pleistocene is not well constrained. Here we apply an ice-flow model in the study of the Greenland ice sheet (GIS) during three extreme intervals of this period constrained by geological observations and climate reconstructions. We study...

  12. Observations from the Programme for Monitoring of the Greenland Ice Sheet

    Science.gov (United States)

    Andersen, S. B.; Ahlstrom, A. P.; Andersen, M. L.; Box, J. E.; Citterio, M.; Colgan, W. T.; Fausto, R. S.; van As, D.; Forsberg, R.; Skourup, H.; Sandberg Sørensen, L.; Kristensen, S. S.; Dall, J.; Kusk, A.; Petersen, D.

    2014-12-01

    The Programme for Monitoring of the Greenland Ice Sheet (PROMICE) is as an on-going effort initiated in 2007 to monitor changes in the mass budget of the Greenland Ice Sheet. The aim of the programme is to quantify the mass loss of the Greenland ice sheet and track changes in the extent of the glaciers, ice caps and ice sheet margin. Specifically, PROMICE aims to estimate the mass loss derived from three fundamentally different sources: Surface melt water runoff from the ice sheet margin Iceberg production Mass loss of individual glaciers and ice caps surrounding the ice sheet The first is observed by a network of automatic weather stations (AWS) on the ice sheet margin measuring ice ablation as well as meteorological parameters. The second is determined by establishing a so-called 'flux gate' along the entire ice sheet margin and keeping track of the ice passing through this gate. The flux gate is obtained from airborne surveys of ice sheet surface elevation and thickness. The volume of the ice passing through the gate is derived from maps of the surface velocity of the ice sheet, produced from satellite radar. The third is investigated through regular mapping of area and elevation of the approximately 20.000 individual glaciers and ice caps in Greenland. Mapping is carried out using recent satellite imagery as well as aerial ortho-photos. Within PROMICE data sets from these activities are collected. They include observations from the network of currently about 20 AWS on the margin of the Greenland ice sheet. Airborne surveys, yielding surface elevation and ice depth along the entire margin of the Greenland ice sheet carried out in 2007 and 2011. A map of all Greenland ice masses, based on the highest detail aero-photogrammetric maps produced from mid-80's aerial photographs. Real-time data from the PROMICE AWS network is shown at the web site www.promice.org and the data is freely available for download. Data from the airborne surveys and mapping activities are

  13. High Arctic Holocene temperature record from the Agassiz ice cap and Greenland ice sheet evolution.

    Science.gov (United States)

    Lecavalier, Benoit S; Fisher, David A; Milne, Glenn A; Vinther, Bo M; Tarasov, Lev; Huybrechts, Philippe; Lacelle, Denis; Main, Brittany; Zheng, James; Bourgeois, Jocelyne; Dyke, Arthur S

    2017-06-06

    We present a revised and extended high Arctic air temperature reconstruction from a single proxy that spans the past ∼12,000 y (up to 2009 CE). Our reconstruction from the Agassiz ice cap (Ellesmere Island, Canada) indicates an earlier and warmer Holocene thermal maximum with early Holocene temperatures that are 4-5 °C warmer compared with a previous reconstruction, and regularly exceed contemporary values for a period of ∼3,000 y. Our results show that air temperatures in this region are now at their warmest in the past 6,800-7,800 y, and that the recent rate of temperature change is unprecedented over the entire Holocene. The warmer early Holocene inferred from the Agassiz ice core leads to an estimated ∼1 km of ice thinning in northwest Greenland during the early Holocene using the Camp Century ice core. Ice modeling results show that this large thinning is consistent with our air temperature reconstruction. The modeling results also demonstrate the broader significance of the enhanced warming, with a retreat of the northern ice margin behind its present position in the mid Holocene and a ∼25% increase in total Greenland ice sheet mass loss (∼1.4 m sea-level equivalent) during the last deglaciation, both of which have implications for interpreting geodetic measurements of land uplift and gravity changes in northern Greenland.

  14. The Alpine LGM in the boreal ice-sheets game.

    Science.gov (United States)

    Monegato, Giovanni; Scardia, Giancarlo; Hajdas, Irka; Rizzini, Francesca; Piccin, Andrea

    2017-05-18

    New chronologic and stratigraphic constraints from the Garda morainic amphitheater define the extension of the last glaciation in the Adige-Sarca system and improve the Alpine LGM dataset. Together with the available chronology of the Rhine and Tagliamento systems, our results indicate a synchronous maximum culmination of Alpine glaciers during the LGM, which anticipated by about 3.5 ka the maximum extension of the Eurasian Ice Sheet (EIS). This is ascribed to the sensitivity of Alpine glaciers to the availability of moisture from southerly circulation, as recently documented by speleothem δ18O curve from Sieben Hengste (7 H). According to global circulation models, the waxing of the North American Ice Sheet (NAIS) at 26-23 ka pushed the North Atlantic jet stream southwards. This enhanced precipitation rates in southern Europe by advection of moisture from the Mediterranean Sea, triggering expansion of the Alpine glaciers. NAIS waning after 23 ka led to the gradual re-establishment of westerly circulation and renewal of a moisture supply to northern Europe, feeding the EIS to its maximum volume. Reduced supply of moisture from the Mediterranean Sea sealed the fate of the Alpine glaciers, which entered a final recessional phase after 22 ka and faded out after 17.5 ka.

  15. Meltwater export of prokaryotic cells from the Greenland ice sheet.

    Science.gov (United States)

    Cameron, Karen A; Stibal, Marek; Hawkings, Jon R; Mikkelsen, Andreas B; Telling, Jon; Kohler, Tyler J; Gözdereliler, Erkin; Zarsky, Jakub D; Wadham, Jemma L; Jacobsen, Carsten S

    2017-02-01

    Microorganisms are flushed from the Greenland Ice Sheet (GrIS) where they may contribute towards the nutrient cycling and community compositions of downstream ecosystems. We investigate meltwater microbial assemblages as they exit the GrIS from a large outlet glacier, and as they enter a downstream river delta during the record melt year of 2012. Prokaryotic abundance, flux and community composition was studied, and factors affecting community structures were statistically considered. The mean concentration of cells exiting the ice sheet was 8.30 × 10 4 cells mL -1 and we estimate that ∼1.02 × 10 21 cells were transported to the downstream fjord in 2012, equivalent to 30.95 Mg of carbon. Prokaryotic microbial assemblages were dominated by Proteobacteria, Bacteroidetes, and Actinobacteria. Cell concentrations and community compositions were stable throughout the sample period, and were statistically similar at both sample sites. Based on our observations, we argue that the subglacial environment is the primary source of the river-transported microbiota, and that cell export from the GrIS is dependent on discharge. We hypothesise that the release of subglacial microbiota to downstream ecosystems will increase as freshwater flux from the GrIS rises in a warming world. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

  16. Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

    Science.gov (United States)

    Livingstone, S. J.; Clark, C. D.; Woodward, J.; Kingslake, J.

    2013-11-01

    We use the Shreve hydraulic potential equation as a simplified approach to investigate potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. We validate the method by demonstrating its ability to recall the locations of >60% of the known subglacial lakes beneath the Antarctic Ice Sheet. This is despite uncertainty in the ice-sheet bed elevation and our simplified modelling approach. However, we predict many more lakes than are observed. Hence we suggest that thousands of subglacial lakes remain to be found. Applying our technique to the Greenland Ice Sheet, where very few subglacial lakes have so far been observed, recalls 1607 potential lake locations, covering 1.2% of the bed. Our results will therefore provide suitable targets for geophysical surveys aimed at identifying lakes beneath Greenland. We also apply the technique to modelled past ice-sheet configurations and find that during deglaciation both ice sheets likely had more subglacial lakes at their beds. These lakes, inherited from past ice-sheet configurations, would not form under current surface conditions, but are able to persist, suggesting a retreating ice-sheet will have many more subglacial lakes than advancing ones. We also investigate subglacial drainage pathways of the present-day and former Greenland and Antarctic ice sheets. Key sectors of the ice sheets, such as the Siple Coast (Antarctica) and NE Greenland Ice Stream system, are suggested to have been susceptible to subglacial drainage switching. We discuss how our results impact our understanding of meltwater drainage, basal lubrication and ice-stream formation.

  17. Ice algae sun-screening: feedbacks between irradiance and algal productivity and pigmentation on the Greenland Ice Sheet

    Science.gov (United States)

    Williamson, C.; Anesio, A. M.; Yallop, M.

    2016-12-01

    Recent studies have shown compelling evidence that algae growing at the surface of glaciers and ice sheets can have a strong influence on the albedo of the ice. However, very little data are available about the relationship between ice-algal pigmentation and photochemistry despite their importance in both algal proliferation on the ice and wider ice sheet processes, i.e. change of albedo and melt. This relationship can provide the fundamental mechanistic explanation of how ice algae change the albedo of the ice. Here, we present the first in-situ assessment of ice-algal photochemistry undertaken on the Greenland Ice Sheet to constrain the mechanisms employed by ice algal community to maintain growth and productivity. We measured the photo-physiology of mixed algal communities over four weeks of the summer melt season during 2016 using a combination of HPLC pigment analysis and chlorophyll fluorometry. In-situ rapid light curves and induction/recovery curves revealed the photo-adaptation and acclimation strategies employed by ice algae to balance excessive irradiance and UV with the requirements for photosynthesis. The data indicate significant down-regulation of photochemistry to prevent photo-damage during high-irradiance periods, whilst diurnal decreases in irradiance allow recovery and photosynthetic repair. High irradiance during the day limits ice algal photosynthetic electron transport limiting productivity. On the other hand, down-regulation of photochemistry can have an important control on the formation of secondary pigmentation, which in turn has a direct impact on ice albedo.

  18. Multi-decadal dynamic thinning on the northwest margin of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Korsgaard, Niels Jákup; Kjær, Kurt H.; Khan, Shfaqat Abbas

    for the entire ice sheet show increased mass loss from 137 Gt/yr in 2002–2003 to 286 Gt/yr in 2007–2009. Also evidence from the GRACE, GPS (Global Positioning System), and ICESat (Ice, Cloud and land Elevation Satellite) as well as surface mass balance data suggests there is an ongoing northward migration......Ice mass changes in the Greenland Ice Sheet have been estimated since the early 1990s from the GRACE (Gravity Recovery and Climate Experiment) satellite gravity mission, of ice sheet thinning from satellite radar altimetry and airborne laser altimetry, and of increased velocities of outlet glaciers...... from radar interferometric surveys. Prior to 2000 existing altimetry data provides comparatively limited spatial resolution and ice losses near ice sheet margins are most likely underestimated and existing data is unable to document the persisting change within outlet glaciers. Subsequent estimates...

  19. Greenland Ice Sheet supraglacial stream morphology and dynamics

    Science.gov (United States)

    Chu, V.; Smith, L. C.; Yang, K.; Legleiter, C. J.; Rennermalm, A. K.; Forster, R. R.; Gleason, C. J.; Pitcher, L. H.; Moustafa, S.

    2013-12-01

    Recently observed increases in temperature and melt extent over the Greenland Ice Sheet (GrIS) have prompted studies gauging the response of the ice sheet and outlet glaciers to increasing meltwater input. Satellite images show supraglacial streams abundantly covering the western ablation zone throughout the melt season that transport large volumes of meltwater into moulins and to the ice edge, yet these streams remain poorly studied. Here, we present a high-resolution study of five different supraglacial stream networks in the western GrIS ablation zone, manually digitized from panchromatic and multispectral WorldView-1/2 imagery. These high-resolution stream networks, with drainage areas ranging between 0.5 - 31 km2 in size and 500 - 1800 m in elevation, are compared with large rivers extracted from multispectral WorldView-2 imagery using an automated remote sensing method, and can help define scaling properties of larger rivers as well as constrain remotely sensed retrievals of discharge. Four of these stream networks contain field measurements of stream hydraulics from a field campaign during 20 July - 20 August 2012. This extensive field campaign provided 77 cross-sectional measurements of water flow velocity, stream depth, width, and water surface slope from traditional field surveys, and also provided longitudinal measurements of water surface velocity and elevation from river drifters. Additionally, two highly sampled sites at 500 m and 875 m elevation provide measurements of ablation rate, stream incision rate, and stream and air temperatures. These drainage networks are categorized by discharge, glacier slope, width-to-depth ratio, channel roughness, Froude number, meander wavelength, sinuosity, and channel pattern. Such measurements form a critical first assessment of GrIS supraglacial stream morphology and dynamics.

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

    Science.gov (United States)

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

    2017-04-01

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

  1. Glacial isostatic stress shadowing by the Antarctic ice sheet

    Science.gov (United States)

    Ivins, E. R.; James, T. S.; Klemann, V.

    2005-01-01

    Numerous examples of fault slip that offset late Quaternary glacial deposits and bedrock polish support the idea that the glacial loading cycle causes earthquakes in the upper crust. A semianalytical scheme is presented for quantifying glacial and postglacial lithospheric fault reactivation using contemporary rock fracture prediction methods. It extends previous studies by considering differential Mogi-von Mises stresses, in addition to those resulting from a Coulomb analysis. The approach utilizes gravitational viscoelastodynamic theory and explores the relationships between ice mass history and regional seismicity and faulting in a segment of East Antarctica containing the great Antarctic Plate (Balleny Island) earthquake of 25 March 1998 (Mw 8.1). Predictions of the failure stress fields within the seismogenic crust are generated for differing assumptions about background stress orientation, mantle viscosity, lithospheric thickness, and possible late Holocene deglaciation for the D91 Antarctic ice sheet history. Similar stress fracture fields are predicted by Mogi-von Mises and Coulomb theory, thus validating previous rebound Coulomb analysis. A thick lithosphere, of the order of 150-240 km, augments stress shadowing by a late melting (middle-late Holocene) coastal East Antarctic ice complex and could cause present-day earthquakes many hundreds of kilometers seaward of the former Last Glacial Maximum grounding line.

  2. A parallel high-order accurate finite element nonlinear Stokes ice sheet model and benchmark experiments: A PARALLEL FEM STOKES ICE SHEET MODEL

    Energy Technology Data Exchange (ETDEWEB)

    Leng, Wei; Ju, Lili; Gunzburger, Max; Price, Stephen; Ringler, Todd

    2012-01-04

    The numerical modeling of glacier and ice sheet evolution is a subject of growing interest, in part because of the potential for models to inform estimates of global sea level change. This paper focuses on the development of a numerical model that determines the velocity and pressure fields within an ice sheet. Our numerical model features a high-fidelity mathematical model involving the nonlinear Stokes system and combinations of no-sliding and sliding basal boundary conditions, high-order accurate finite element discretizations based on variable resolution grids, and highly scalable parallel solution strategies, all of which contribute to a numerical model that can achieve accurate velocity and pressure approximations in a highly efficient manner. We demonstrate the accuracy and efficiency of our model by analytical solution tests, established ice sheet benchmark experiments, and comparisons with other well-established ice sheet models.

  3. ESA ice sheet CCI: derivation of the optimal method for surface elevation change detection of the Greenland ice sheet – round robin results

    DEFF Research Database (Denmark)

    Fredenslund Levinsen, Joanna; Khvorostovsky, Kirill; Ticconi, F.

    2015-01-01

    was asked to provide their best SEC estimates as well as feedback sheets describing the applied method. Due to the hitherto few radar-based SEC analyses as well as the higher accuracy of laser data, the participants were asked to use either ENVISAT radar or ICESat (Ice, Cloud, and land Elevation Satellite......For more than two decades, radar altimetry missions have provided continuous elevation estimates of the Greenland ice sheet (GrIS). Here, we propose a method for using such data to estimate ice-sheet-wide surface elevation changes (SECs). The final data set will be based on observations acquired...... accurate, ice-sheet-wide SEC estimates are obtained by combining the cross-over and repeat-track techniques. It is thus possible to exploit the high accuracy of the former and the large spatial data coverage of the latter. Based on CryoSat’s different operation modes, and the increased spatial and temporal...

  4. Photophysiology and albedo-changing potential of the ice algal community on the surface of the Greenland ice sheet

    Science.gov (United States)

    Yallop, Marian L; Anesio, Alexandre M; Perkins, Rupert G; Cook, Joseph; Telling, Jon; Fagan, Daniel; MacFarlane, James; Stibal, Marek; Barker, Gary; Bellas, Chris; Hodson, Andy; Tranter, Martyn; Wadham, Jemma; Roberts, Nicholas W

    2012-01-01

    Darkening of parts of the Greenland ice sheet surface during the summer months leads to reduced albedo and increased melting. Here we show that heavily pigmented, actively photosynthesising microalgae and cyanobacteria are present on the bare ice. We demonstrate the widespread abundance of green algae in the Zygnematophyceae on the ice sheet surface in Southwest Greenland. Photophysiological measurements (variable chlorophyll fluorescence) indicate that the ice algae likely use screening mechanisms to downregulate photosynthesis when exposed to high intensities of visible and ultraviolet radiation, rather than non-photochemical quenching or cell movement. Using imaging microspectrophotometry, we demonstrate that intact cells and filaments absorb light with characteristic spectral profiles across ultraviolet and visible wavelengths, whereas inorganic dust particles typical for these areas display little absorption. Our results indicate that the phototrophic community growing directly on the bare ice, through their photophysiology, most likely have an important role in changing albedo, and subsequently may impact melt rates on the ice sheet. PMID:23018772

  5. Photophysiology and albedo-changing potential of the ice algal community on the surface of the Greenland ice sheet.

    Science.gov (United States)

    Yallop, Marian L; Anesio, Alexandre M; Perkins, Rupert G; Cook, Joseph; Telling, Jon; Fagan, Daniel; MacFarlane, James; Stibal, Marek; Barker, Gary; Bellas, Chris; Hodson, Andy; Tranter, Martyn; Wadham, Jemma; Roberts, Nicholas W

    2012-12-01

    Darkening of parts of the Greenland ice sheet surface during the summer months leads to reduced albedo and increased melting. Here we show that heavily pigmented, actively photosynthesising microalgae and cyanobacteria are present on the bare ice. We demonstrate the widespread abundance of green algae in the Zygnematophyceae on the ice sheet surface in Southwest Greenland. Photophysiological measurements (variable chlorophyll fluorescence) indicate that the ice algae likely use screening mechanisms to downregulate photosynthesis when exposed to high intensities of visible and ultraviolet radiation, rather than non-photochemical quenching or cell movement. Using imaging microspectrophotometry, we demonstrate that intact cells and filaments absorb light with characteristic spectral profiles across ultraviolet and visible wavelengths, whereas inorganic dust particles typical for these areas display little absorption. Our results indicate that the phototrophic community growing directly on the bare ice, through their photophysiology, most likely have an important role in changing albedo, and subsequently may impact melt rates on the ice sheet.

  6. High-resolution ice thickness and bed topography of a land-terminating section of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Lindbäck, K.; Pettersson, R.; Doyle, S. H.

    2014-01-01

    We present ice thickness and bed topography maps with high spatial resolution (250 to 500 m) of a and-terminating section of the Greenland Ice Sheet derived from combined ground-based and airborne radar surveys. The data have a total area of ~12000 km2 and cover the whole ablation area......-deepened and reaches an elevation of several hundreds of meters below sea level. The ice surface is smooth and only reflects the bedrock topography in a subtle way, resulting in a highly variable ice thickness. The southern part of our study area consists of higher bed elevations compared to the northern part....... The covered area is one of the most studied regions of the Greenland Ice Sheet with studies of mass balance, dynamics, and supraglacial lakes, and our combined dataset can be valuable for detailed studies of ice sheet dynamics and hydrology. The compiled datasets of ground-based and airborne radar surveys...

  7. Adjoint-based sensitivities and data assimilation with a time-dependent marine ice sheet model

    Science.gov (United States)

    Goldberg, Dan; Heimbach, Patrick

    2013-04-01

    To date, assimilation of observational data using large-scale ice models has consisted only of time-dependent inversions of surface velocities for basal traction, bed elevation, or ice stiffness. These inversions are for the most part based on control methods (Macayeal D R, 1992, A tutorial on the use of control methods in ice sheet modeling), which involve generating and solving the adjoint of the ice model. Quite a lot has been learned about the fast-flowing parts of the Antarctic Ice Sheet from such inversions. Still, there are limitations to these "snapshot" inversions. For instance, they cannot capture time-dependent dynamics, such as propagation of perturbations through the ice sheet. They cannot assimilate time-dependent observations, such as surface elevation changes. And they are problematic for initializing time-dependent ice sheet models, as such initializations may contain considerable model drift. We have developed an adjoint for a time-dependent land ice model, with which we will address such issues. The land ice model implements a hybrid shallow shelf-shallow ice stress balance and can represent the floating, fast-sliding, and frozen bed regimes of a marine ice sheet. The adjoint is generated by a combination of analytic methods and the use of automated differentiation (AD) software. Experiments with idealized geometries have been carried out; adjoint sensitivities reveal the "vulnerable" regions of ice shelves, and preliminary inversions of "synthetic" observations (e.g. simultaneous inversion of basal traction and topography) yield encouraging results.

  8. Scandinavian Egalitarianism

    DEFF Research Database (Denmark)

    Kjærsgård, Andreas Pihl

    The dissertation finds that, compared to people in other western countries, the Scandinavians were exceptionally egalitarian in the period from 1992 to 2009. This Scandinavian egalitarianism seems constituted mostly of an aversion to top-level excess, rather than a wish to spoil the bottom of the...

  9. Influence of ocean model treatment on late Paleozoic ice sheet growth

    Science.gov (United States)

    Tilevitz, C.; Poulsen, C. J.

    2016-12-01

    The late Paleozoic ice age was a period of time 340-250 Ma during which ice sheets grew and shrank across the Gondwanan supercontinent. Atmospheric general circulation models (GCMs) have previously been used to generate late Paleozoic climates suitable for the growth of large ice sheets on the Gondwanan supercontinent to investigate the climate conditions necessary for ice sheet growth. These simulations included a slab ocean with diffusive heat transport that lacks the ability to accurately capture the ocean dynamics of the Paleozoic. In this work, a series of experiments are conducted to investigate the sensitivity of ice sheets to the ocean treatment. Four experiments are conducted: (i) The NCAR Community Earth System Model (CESM)'s fully dynamic ocean is used to explore Permian ice sheet growth under more realistic conditions. (ii)The GENESIS GCM, which uses a slab ocean, is run to directly compare the two ocean models. (iii) The CESM slab ocean model is run using heat fluxes from the CESM simulation. (iv)GENESIS in fixed-SST mode is run using surface temperatures from the CESM simulation. All experiments are conducted for two atmospheric pCO2 concentrations (280 and 560 ppm). Climatologies from this set of experiments are then used to drive the Penn State University three-dimensional ice sheet model (ISM). Our results show that late Paleozoic ice sheets are sensitive to ocean dynamics. The ice sheets that result from both the GENESIS slab and SST cases have volumes of 108 km3 for both CO2 concentrations, and the CESM slab ocean case produced volumes of .5-108 km3 for both cases. The fully dynamic CESM simulation, however, produced ice sheets of 108 km3 for the 280 ppm CO2 case, but only 106 km3 for the 560 ppm CO2 case. This dramatic difference suggests that modeled ice sheets possess a critical sensitivity to pCO2 concentrations in a fully dynamic climate system.

  10. Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge.

    Science.gov (United States)

    Bakker, Pepijn; Clark, Peter U; Golledge, Nicholas R; Schmittner, Andreas; Weber, Michael E

    2017-01-05

    Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods. Proposed explanations for the discrepancy include ocean-atmosphere coupling that is too weak in models, insufficient energy cascades from smaller to larger spatial and temporal scales, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate. Such interactions, however, are known to have strongly affected centennial- to orbital-scale climate variability during past glaciations, and are likely to be important in future climate change. Here we show that fluctuations in Antarctic Ice Sheet discharge caused by relatively small changes in subsurface ocean temperature can amplify multi-centennial climate variability regionally and globally, suggesting that a dynamic Antarctic Ice Sheet may have driven climate fluctuations during the Holocene. We analysed high-temporal-resolution records of iceberg-rafted debris derived from the Antarctic Ice Sheet, and performed both high-spatial-resolution ice-sheet modelling of the Antarctic Ice Sheet and multi-millennial global climate model simulations. Ice-sheet responses to decadal-scale ocean forcing appear to be less important, possibly indicating that the future response of the Antarctic Ice Sheet will be governed more by long-term anthropogenic warming combined with multi-centennial natural variability than by annual or decadal climate oscillations.

  11. Geothermal Heat Flux Underneath Ice Sheets Estimated From Magnetic Satellite Data

    DEFF Research Database (Denmark)

    Fox Maule, Cathrine; Purucker, M.E.; Olsen, Nils

    The geothermal heat flux is an important factor in the dynamics of ice sheets, and it is one of the important parameters in the thermal budgets of subglacial lakes. We have used satellite magnetic data to estimate the geothermal heat flux underneath the ice sheets in Antarctica and Greenland...

  12. Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge

    Science.gov (United States)

    Bakker, Pepijn; Clark, Peter U.; Golledge, Nicholas R.; Schmittner, Andreas; Weber, Michael E.

    2017-01-01

    Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods. Proposed explanations for the discrepancy include ocean-atmosphere coupling that is too weak in models, insufficient energy cascades from smaller to larger spatial and temporal scales, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate. Such interactions, however, are known to have strongly affected centennial- to orbital-scale climate variability during past glaciations, and are likely to be important in future climate change. Here we show that fluctuations in Antarctic Ice Sheet discharge caused by relatively small changes in subsurface ocean temperature can amplify multi-centennial climate variability regionally and globally, suggesting that a dynamic Antarctic Ice Sheet may have driven climate fluctuations during the Holocene. We analysed high-temporal-resolution records of iceberg-rafted debris derived from the Antarctic Ice Sheet, and performed both high-spatial-resolution ice-sheet modelling of the Antarctic Ice Sheet and multi-millennial global climate model simulations. Ice-sheet responses to decadal-scale ocean forcing appear to be less important, possibly indicating that the future response of the Antarctic Ice Sheet will be governed more by long-term anthropogenic warming combined with multi-centennial natural variability than by annual or decadal climate oscillations.

  13. Current state and future perspectives on coupled ice-sheet – sea-level modelling

    NARCIS (Netherlands)

    de Boer, B.; Stocchi, P.; Whitehouse, P.L.; van de Wal, R.S.W.

    2017-01-01

    The interaction between ice-sheet growth and retreat and sea-level change has been an established fieldof research for many years. However, recent advances in numerical modelling have shed new light on theprecise interaction of marine ice sheets with the change in near-field sea level, and the

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

    Directory of Open Access Journals (Sweden)

    S. Bonelli

    2009-07-01

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

  15. Sonification of cryoconite landscapes over the Greenland ice sheet

    Science.gov (United States)

    Tedesco, M.

    2015-12-01

    Sonification is the use of non-speech audio to convey information. In sonification, several elements can be altered, modified or manipulated to change the perception of the sound, and in turn, the perception of the information being transmitted. For example, an increase or decrease in pitch, tempo and amplitude can be used to convey the information but this can also happen by varying other less commonly used components. One of the advantages of using sonification lies in the temporal, spatial, amplitude, and frequency resolution that offer complementary and supplementary possibilities with respect to visualization techniques. Two years ago, the outcomes of the PolarSEEDS project (www.polaseeds.org), consisting of sonification of time series of albedo, melting and surface temperature over the Greenland ice sheet, were presented in this very same session. The work that I will discuss in this presentation builds on the PolarSEEDS experience, focusing on the fascinating microcosm of cryoconite. Cryoconite is a unique and extremely fascinating form of glacial cover consisting of aggregated rock dust, inorganic and detrital organic matter, and active microbial colonies. It can be seen as 'living stones', with this ecosystem containing the only form of life that is sustained on the majestic surface of the Greenland ice sheet. Microbes are, indeed, the catalyst for cryoconite formation and growth. The cryoconite constituents radiate metabolic heat promoting glacier hole development, melt water formation, and decreasing glacier surface albedo. Lower albedos cause a positive feedback that further contributes to glacier ablation. Despite their importance, cryoconite systems are poorly studied and little is known about their evolution. In the talk, I will first present and discuss previous sonification projects whose main focus was on the polar regions; then, I will present new sonifications based on data quantifying the distribution and evolution of cryoconite over the west

  16. An improved Antarctic dataset for high resolution numerical ice sheet models (ALBMAP v1

    Directory of Open Access Journals (Sweden)

    A. M. Le Brocq

    2010-10-01

    Full Text Available The dataset described in this paper (ALBMAP has been created for the purposes of high-resolution numerical ice sheet modelling of the Antarctic Ice Sheet. It brings together data on the ice sheet configuration (e.g. ice surface and ice thickness and boundary conditions, such as the surface air temperature, accumulation and geothermal heat flux. The ice thickness and basal topography is based on the BEDMAP dataset (Lythe et al., 2001, however, there are a number of inconsistencies within BEDMAP and, since its release, more data has become available. The dataset described here addresses these inconsistencies, including some novel interpolation schemes for sub ice-shelf cavities, and incorporates some major new datasets. The inclusion of new datasets is not exhaustive, this considerable task is left for the next release of BEDMAP, however, the data and procedure documented here provides another step forward and demonstrates the issues that need addressing in a continental scale dataset useful for high resolution ice sheet modelling. The dataset provides an initial condition that is as close as possible to present-day ice sheet configuration, aiding modelling of the response of the Antarctic Ice Sheet to various forcings, which are, at present, not fully understood.

  17. Modeling North American Ice Sheet Response to Changes in Precession and Obliquity

    Science.gov (United States)

    Tabor, C.; Poulsen, C. J.; Pollard, D.

    2012-12-01

    Milankovitch theory proposes that changes in insolation due to orbital perturbations dictate the waxing and waning of the ice sheets (Hays et al., 1976). However, variations in solar forcing alone are insufficient to produce the glacial oscillations observed in the climate record. Non-linear feedbacks in the Earth system likely work in concert with the orbital cycles to produce a modified signal (e.g. Berger and Loutre, 1996), but the nature of these feedbacks remain poorly understood. To gain a better understand of the ice dynamics and climate feedbacks associated with changes in orbital configuration, we use a complex Earth system model consisting of the GENESIS GCM and land surface model (Pollard and Thompson, 1997), the Pennsylvania State University ice sheet model (Pollard and DeConto, 2009), and the BIOME vegetation model (Kaplan et al., 2001). We began this study by investigating ice sheet sensitivity to a range of commonly used ice sheet model parameters, including mass balance and albedo, to optimize simulations for Pleistocene orbital cycles. Our tests indicate that choice of mass balance and albedo parameterizations can lead to significant differences in ice sheet behavior and volume. For instance, use of an insolation-temperature mass balance scheme (van den Berg, 2008) allows for a larger ice sheet response to orbital changes than the commonly employed positive degree-day method. Inclusion of a large temperature dependent ice albedo, representing phenomena such as melt ponds and dirty ice, also enhances ice sheet sensitivity. Careful tuning of mass balance and albedo parameterizations can help alleviate the problem of insufficient ice sheet retreat during periods of high summer insolation (Horton and Poulsen, 2007) while still accurately replicating the modern climate. Using our optimized configuration, we conducted a series of experiments with idealized transient orbits in an asynchronous coupling scheme to investigate the influence of obliquity and

  18. Ice-dynamic projections of the Greenland ice sheet in response to atmospheric and oceanic warming

    Directory of Open Access Journals (Sweden)

    J. J. Fürst

    2015-05-01

    Full Text Available Continuing global warming will have a strong impact on the Greenland ice sheet in the coming centuries. During the last decade (2000–2010, both increased melt-water runoff and enhanced ice discharge from calving glaciers have contributed 0.6 ± 0.1 mm yr−1 to global sea-level rise, with a relative contribution of 60 and 40% respectively. Here we use a higher-order ice flow model, spun up to present day, to simulate future ice volume changes driven by both atmospheric and oceanic temperature changes. For these projections, the flow model accounts for runoff-induced basal lubrication and ocean warming-induced discharge increase at the marine margins. For a suite of 10 atmosphere and ocean general circulation models and four representative concentration pathway scenarios, the projected sea-level rise between 2000 and 2100 lies in the range of +1.4 to +16.6 cm. For two low emission scenarios, the projections are conducted up to 2300. Ice loss rates are found to abate for the most favourable scenario where the warming peaks in this century, allowing the ice sheet to maintain a geometry close to the present-day state. For the other moderate scenario, loss rates remain at a constant level over 300 years. In any scenario, volume loss is predominantly caused by increased surface melting as the contribution from enhanced ice discharge decreases over time and is self-limited by thinning and retreat of the marine margin, reducing the ice–ocean contact area. As confirmed by other studies, we find that the effect of enhanced basal lubrication on the volume evolution is negligible on centennial timescales. Our projections show that the observed rates of volume change over the last decades cannot simply be extrapolated over the 21st century on account of a different balance of processes causing ice loss over time. Our results also indicate that the largest source of uncertainty arises from the surface mass balance and the underlying climate change

  19. VESL: The Virtual Earth Sheet Laboratory for Ice Sheet Modeling and Visualization

    Science.gov (United States)

    Cheng, D. L. C.; Larour, E. Y.; Quinn, J. D.; Halkides, D. J.

    2016-12-01

    We introduce the Virtual Earth System Laboratory (VESL), a scientific modeling and visualization tool delivered through an integrated web portal for dissemination of data, simulation of physical processes, and promotion of climate literacy. The current prototype leverages NASA's Ice Sheet System Model (ISSM), a state-of-the-art polar ice sheet dynamics model developed at the Jet Propulsion Lab and UC Irvine. We utilize the Emscripten source-to-source compiler to convert the C/C++ ISSM engine core to JavaScript, and bundled pre/post-processing JS scripts to be compatible with the existing ISSM Python/Matlab API. Researchers using VESL will be able to effectively present their work for public dissemination with little-to-no additional post-processing. This will allow for faster publication in peer-reviewed journals and adaption of results for educational applications. Through future application of this concept to multiple aspects of the Earth System, VESL has the potential to broaden data applications in the geosciences and beyond. At this stage, we seek feedback from the greater scientific and public outreach communities regarding the ease of use and feature set of VESL, as we plan its expansion, and aim to achieve more rapid communication and presentation of scientific results.

  20. Multiphase flow of the late Wisconsinan Cordilleran ice sheet in Western Canada

    Science.gov (United States)

    Stumpf, A.J.; Broster, B.E.; Levson, V.M.

    2000-01-01

    In central British Columbia, ice flow during the late Wisconsinan Fraser glaciation (ca. 25-10 ka) occurred in three phases. The ice expansion phase occurred during an extended period when glaciers flowed westward to the Pacific Ocean and east-southeastward onto the Nechako Plateau from ice centers in the Skeena, Hazelton, Coast, and Omineca Mountains. Initially, glacier flow was confined by topography along major valleys, but eventually piedmont and montane glaciers coalesced to form an integrated glacier system, the Cordilleran ice sheet. In the maximum phase, a Cordilleran ice divide developed over the Nechako Plateau to 300 km inland from the Pacific coast. At this time, the surface of the ice sheet extended well above 2500 m above sea level, and flowed westward over the Skeena, Hazelton, and Coast Mountains onto the continental shelf, and eastward across the Rocky Mountains into Alberta. In the late glacial phase, a rapid rise of the equilibrium line caused ice lobes to stagnate in valleys, and restricted accumulation centers to high mountains. Discordant directions in ice flow are attributed to fluctuations of the ice divide representing changes in the location of accumulation centers and ice thickness. Ice centers probably shifted in response to climate, irregular growth in the ice sheet, rapid calving, ice streaming, and drainage of proglacial and subglacial water bodies. Crosscutting ice-flow indicators and preservation of early (valley parallel) flow features in areas exposed to later (cross-valley) glacier erosion indicate that the ice expansion phase was the most erosive and protracted event.

  1. GLAS/ICESat L2 Global Antarctic and Greenland Ice Sheet Altimetry Data (HDF5) V033

    Data.gov (United States)

    National Aeronautics and Space Administration — GLAH12 contains the ice sheet elevation and elevation distribution corrected for geodetic and atmospheric affects calculated from algorithms fine-tuned for ice sheet...

  2. On the feasibility of space-based radar ice sounding of the Antarctic ice sheet at P-band

    DEFF Research Database (Denmark)

    Dall, Jørgen; Kusk, Anders; Corr, Hugh

    collaboration between seven organizations in Europe and North and South America [2]. The primary objective of this IceGrav campaign was to measure gravity in Queen Maud Land, but a secondary objective was to acquire P-band sounder data, benefitting from the large coverage offered by the Basler DC3 aircraft used......Space-based radio echo sounding (RES) of the continental ice sheets can potentially offer full coverage, uniform data quality and sampling. Ice sounding radars must operate at low frequencies in order to ensure low attenuation of the signal as it propagates down through the ice and back from base...... of the ice sheet. Typical frequencies of airborne radar ice sounders are between 60 MHz and 150 MHz. However, the lowest possible frequency for space-based radar ice sounders is 435 MHz. In 2004 the International Telecommunication Union (ITU) radio regulations allocated a 6 MHz band at 435 MHz (P...

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

    DEFF Research Database (Denmark)

    Möller, Per; Östlund, Oluf; Barnekow, Lena

    2013-01-01

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

  4. A Synthesis of the Basal Thermal State of the Greenland Ice Sheet

    Science.gov (United States)

    Macgregor, J. A.; Fahnestock, M. A.; Catania, G. A.; Aschwanden, A.; Clow, G. D.; Colgan, W. T.; Gogineni, S. P.; Morlighem, M.; Nowicki, S. M. J.; Paden, J. D.; hide

    2016-01-01

    Greenland's thick ice sheet insulates the bedrock below from the cold temperatures at the surface, so the bottom of the ice is often tens of degrees warmer than at the top, because the ice bottom is slowly warmed by heat coming from the Earth's depths. Knowing whether Greenland's ice lies on wet, slippery ground or is anchored to dry, frozen bedrock is essential for predicting how this ice will flow in the future. But scientists have very few direct observations of the thermal conditions beneath the ice sheet, obtained through fewer than two dozen boreholes that have reached the bottom. Our study synthesizes several independent methods to infer the Greenland Ice Sheet's basal thermal state -whether the bottom of the ice is melted or not-leading to the first map that identifies frozen and thawed areas across the whole ice sheet. This map will guide targets for future investigations of the Greenland Ice Sheet toward the most vulnerable and poorly understood regions, ultimately improving our understanding of its dynamics and contribution to future sea-level rise. It is of particular relevance to ongoing Operation IceBridge activities and future large-scale airborne missions over Greenland.

  5. Improving Climate Literacy Using The Ice Sheet System Model (ISSM): A Prototype Virtual Ice Sheet Laboratory For Use In K-12 Classrooms

    Science.gov (United States)

    Halkides, D. J.; Larour, E. Y.; Perez, G.; Petrie, K.; Nguyen, L.

    2013-12-01

    Statistics indicate that most Americans learn what they will know about science within the confines of our public K-12 education system and the media. Next Generation Science Standards (NGSS) aim to remedy science illiteracy and provide guidelines to exceed the Common Core State Standards that most U.S. state governments have adopted, by integrating disciplinary cores with crosscutting ideas and real life practices. In this vein, we present a prototype ';Virtual Ice Sheet Laboratory' (I-Lab), geared to K-12 students, educators and interested members of the general public. I-Lab will allow users to perform experiments using a state-of-the-art dynamical ice sheet model and provide detailed downloadable lesson plans, which incorporate this model and are consistent with NGSS Physical Science criteria for different grade bands (K-2, 3-5, 6-8, and 9-12). The ultimate goal of this website is to improve public climate science literacy, especially in regards to the crucial role of the polar ice sheets in Earth's climate and sea level. The model used will be the Ice Sheet System Model (ISSM), an ice flow model developed at NASA's Jet Propulsion Laboratory and UC Irvine, that simulates the near-term evolution of polar ice sheets (Greenland and Antarctica) and includes high spatial resolution capabilities and data assimilation to produce realistic simulations of ice sheet dynamics at the continental scale. Open sourced since 2011, ISSM is used in cutting edge cryosphere research around the globe. Thru I-Lab, students will be able to access ISSM using a simple, online graphical interface that can be launched from a web browser on a computer, tablet or smart phone. The interface will allow users to select different climate conditions and watch how the polar ice sheets evolve in time under those conditions. Lesson contents will include links to background material and activities that teach observation recording, concept articulation, hypothesis formulation and testing, and

  6. Surface Energy and Mass Balance Model for Greenland Ice Sheet and Future Projections

    Science.gov (United States)

    Liu, Xiaojian

    The Greenland Ice Sheet contains nearly 3 million cubic kilometers of glacial ice. If the entire ice sheet completely melted, sea level would raise by nearly 7 meters. There is thus considerable interest in monitoring the mass balance of the Greenland Ice Sheet. Each year, the ice sheet gains ice from snowfall and loses ice through iceberg calving and surface melting. In this thesis, we develop, validate and apply a physics based numerical model to estimate current and future surface mass balance of the Greenland Ice Sheet. The numerical model consists of a coupled surface energy balance and englacial model that is simple enough that it can be used for long time scale model runs, but unlike previous empirical parameterizations, has a physical basis. The surface energy balance model predicts ice sheet surface temperature and melt production. The englacial model predicts the evolution of temperature and meltwater within the ice sheet. These two models can be combined with estimates of precipitation (snowfall) to estimate the mass balance over the Greenland Ice Sheet. We first compare model performance with in-situ observations to demonstrate that the model works well. We next evaluate how predictions are degraded when we statistically downscale global climate data. We find that a simple, nearest neighbor interpolation scheme with a lapse rate correction is able to adequately reproduce melt patterns on the Greenland Ice Sheet. These results are comparable to those obtained using empirical Positive Degree Day (PDD) methods. Having validated the model, we next drove the ice sheet model using the suite of atmospheric model runs available through the CMIP5 atmospheric model inter-comparison, which in turn built upon the RCP 8.5 (business as usual) scenarios. From this exercise we predict how much surface melt production will increase in the coming century. This results in 4-10 cm sea level equivalent, depending on the CMIP5 models. Finally, we try to bound melt water

  7. An ice flow modeling perspective on bedrock adjustment patterns of the Greenland ice sheet

    Directory of Open Access Journals (Sweden)

    M. Olaizola

    2012-11-01

    Full Text Available Since the launch in 2002 of the Gravity Recovery and Climate Experiment (GRACE satellites, several estimates of the mass balance of the Greenland ice sheet (GrIS have been produced. To obtain ice mass changes, the GRACE data need to be corrected for the effect of deformation changes of the Earth's crust. Recently, a new method has been proposed where ice mass changes and bedrock changes are simultaneously solved. Results show bedrock subsidence over almost the entirety of Greenland in combination with ice mass loss which is only half of the currently standing estimates. This subsidence can be an elastic response, but it may however also be a delayed response to past changes. In this study we test whether these subsidence patterns are consistent with ice dynamical modeling results. We use a 3-D ice sheet–bedrock model with a surface mass balance forcing based on a mass balance gradient approach to study the pattern and magnitude of bedrock changes in Greenland. Different mass balance forcings are used. Simulations since the Last Glacial Maximum yield a bedrock delay with respect to the mass balance forcing of nearly 3000 yr and an average uplift at present of 0.3 mm yr−1. The spatial pattern of bedrock changes shows a small central subsidence as well as more intense uplift in the south. These results are not compatible with the gravity based reconstructions showing a subsidence with a maximum in central Greenland, thereby questioning whether the claim of halving of the ice mass change is justified.

  8. Ice algal bloom development on the surface of the Greenland Ice Sheet.

    Science.gov (United States)

    Williamson, C J; Anesio, A M; Cook, J; Tedstone, A; Poniecka, E; Holland, A; Fagan, D; Tranter, M; Yallop, M L

    2018-02-10

    It is fundamental to understand the development of Zygnematophycean (Streptophyte) micro-algal blooms within Greenland Ice Sheet (GrIS) supraglacial environments, given their potential to significantly impact both physical (melt) and chemical (carbon and nutrient cycling) surface characteristics. Here we report on a space-for-time assessment of a GrIS ice-algal bloom, achieved by sampling an ∼ 85 km transect spanning the south-western GrIS bare ice zone during the 2016 ablation season. Cell abundances ranged from 0 to 1.6 × 104 cells ml-1, with algal biomass demonstrated to increase in surface ice with time since snow line retreat (R2 = 0.73, P < 0.05). A suite of light harvesting and photo-protective pigments were quantified across transects (chlorophylls, carotenoids and phenols) and shown to increase in concert with algal biomass. Ice-algal communities drove net autotrophy of surface ice, with maximal rates of net production averaging 0.52 ± 0.04 mg C l-1 d-1, and a total accumulation of 1.306 Gg C (15.82 ± 8.14 kg C km-2) predicted for the 2016 ablation season across an 8.24 × 104 km2 region of the GrIS. By advancing our understanding of ice-algal bloom development, this study marks an important step toward projecting bloom occurrence and impacts into the future. © FEMS 2018.

  9. Interaction of ice sheets and climate during the past 800 000 years

    Directory of Open Access Journals (Sweden)

    L. B. Stap

    2014-12-01

    Full Text Available During the Cenozoic, land ice and climate interacted on many different timescales. On long timescales, the effect of land ice on global climate and sea level is mainly set by large ice sheets in North America, Eurasia, Greenland and Antarctica. The climatic forcing of these ice sheets is largely determined by the meridional temperature profile resulting from radiation and greenhouse gas (GHG forcing. As a response, the ice sheets cause an increase in albedo and surface elevation, which operates as a feedback in the climate system. To quantify the importance of these climate–land ice processes, a zonally averaged energy balance climate model is coupled to five one-dimensional ice sheet models, representing the major ice sheets. In this study, we focus on the transient simulation of the past 800 000 years, where a high-confidence CO2 record from ice core samples is used as input in combination with Milankovitch radiation changes. We obtain simulations of atmospheric temperature, ice volume and sea level that are in good agreement with recent proxy-data reconstructions. We examine long-term climate–ice-sheet interactions by a comparison of simulations with uncoupled and coupled ice sheets. We show that these interactions amplify global temperature anomalies by up to a factor of 2.6, and that they increase polar amplification by 94%. We demonstrate that, on these long timescales, the ice-albedo feedback has a larger and more global influence on the meridional atmospheric temperature profile than the surface-height-temperature feedback. Furthermore, we assess the influence of CO2 and insolation by performing runs with one or both of these variables held constant. We find that atmospheric temperature is controlled by a complex interaction of CO2 and insolation, and both variables serve as thresholds for northern hemispheric glaciation.

  10. Amplified melt and flow of the Greenland ice sheet driven by late-summer cyclonic rainfall

    DEFF Research Database (Denmark)

    Doyle, Samuel H.; Hubbard, Alun; van de Wal, Roderik S.W.

    2015-01-01

    Intense rainfall events significantly affect Alpine and Alaskan glaciers through enhanced melting, ice-flow acceleration and subglacial sediment erosion, yet their impact on the Greenland ice sheet has not been assessed. Here we present measurements of ice velocity, subglacial water pressure...... and meteorological variables from the western margin of the Greenland ice sheet during a week of warm, wet cyclonic weather in late August and early September 2011. We find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice-sheet interior....... We suggest that the late-season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less-efficient winter mode. Reanalysis data reveal that similar cyclonic weather conditions prevailed across southern...

  11. When glaciers and ice sheets melt: consequences for planktonic organisms

    Science.gov (United States)

    SOMMARUGA, RUBEN

    2016-01-01

    The current melting of glaciers and ice sheets is a consequence of climatic change and their turbid meltwaters are filling and enlarging many new proglacial and ice-contact lakes around the world, as well as affecting coastal areas. Paradoxically, very little is known on the ecology of turbid glacier-fed aquatic ecosystems even though they are at the origin of the most common type of lakes on Earth. Here, I discuss the consequences of those meltwaters for planktonic organisms. A remarkable characteristic of aquatic ecosystems receiving the discharge of meltwaters is their high content of mineral suspensoids, so-called glacial flour that poses a real challenge for filter-feeding planktonic taxa such as Daphnia and phagotrophic groups such as heterotrophic nanoflagellates. The planktonic food-web structure in highly turbid meltwater lakes seems to be truncated and microbially dominated. Low underwater light levels leads to unfavorable conditions for primary producers, but at the same time, cause less stress by UV radiation. Meltwaters are also a source of inorganic and organic nutrients that could stimulate secondary prokaryotic production and in some cases (e.g. in distal proglacial lakes) also phytoplankton primary production. How changes in turbidity and in other related environmental factors influence diversity, community composition and adaptation have only recently begun to be studied. Knowledge of the consequences of glacier retreat for glacier-fed lakes and coasts will be crucial to predict ecosystem trajectories regarding changes in biodiversity, biogeochemical cycles and function. PMID:26869738

  12. Decreasing clouds drive mass loss on the Greenland Ice Sheet

    Science.gov (United States)

    Hofer, Stefan; Bamber, Jonathan; Tedstone, Andrew; Fettweis, Xavier

    2017-04-01

    The Greenland ice sheet (GrIS) has been losing mass at an accelerating rate since the mid-1990s. This has been due to both increased ice discharge into the ocean and melting at the surface, with the latter being the dominant contribution. This change in state has been attributed to rising temperatures and a decrease in surface albedo. Here we show, using satellite data and climate model output, that the abrupt reduction in surface mass balance since about 1995 can be largely attributed to a coincident trend of decreasing summer cloud cover. Satellite observations show that, from 1995 to 2009, summer cloud cover decreased by 0.9% ± 0.28%.yr. Model output indicates that the GrIS surface mass balance has a sensitivity of -5.4 ± 2 Gt per percent reduction in summer cloud cover, due principally to the impact of increased shortwave radiation over the low albedo ablation zone. The observed reduction in cloud cover is strongly correlated with a state shift of the North Atlantic Oscillation, suggesting that the enhanced surface mass loss from the GrIS is driven by synoptic-scale changes in Arctic-wide atmospheric circulation.

  13. Biogeochemical cycling in a subarctic fjord adjacent to the Greenland Ice Sheet

    NARCIS (Netherlands)

    Meire, L.

    2016-01-01

    Temperatures in the Arctic have increased rapidly in recent years resulting in the melting of sea ice and glaciers at unprecedented rates. In 2012, sea ice extent across the Arctic reached a record minimum and the melt extent of Greenland Ice Sheet reached a record maximum. The accelerated mass loss

  14. Amplified melt and flow of the Greenland ice sheet driven by late-summer cyclonic rainfall

    NARCIS (Netherlands)

    Doyle, Samuel H.; Hubbard, Alun; Van De Wal, Roderik S W|info:eu-repo/dai/nl/101899556; Box, Jason E.; Van As, Dirk; Scharrer, Kilian; Meierbachtol, Toby W.; Smeets, Paul C J P|info:eu-repo/dai/nl/191522236; Harper, Joel T.; Johansson, Emma; Mottram, Ruth H.; Mikkelsen, Andreas B.; Wilhelms, Frank; Patton, Henry; Christoffersen, Poul; Hubbard, Bryn

    2015-01-01

    Intense rainfall events significantly affect Alpine and Alaskan glaciers through enhanced melting, ice-flow acceleration and subglacial sediment erosion, yet their impact on the Greenland ice sheet has not been assessed. Here we present measurements of ice velocity, subglacial water pressure and

  15. Sustained high basal motion of the Greenland ice sheet revealed by borehole deformation

    DEFF Research Database (Denmark)

    Ryser, Claudia; Luethi, Martin P.; Andrews, Lauren C.

    2014-01-01

    Ice deformation and basal motion characterize the dynamical behavior of the Greenland ice sheet (GrIS). We evaluate the contribution of basal motion from ice deformation measurements in boreholes drilled to the bed at two sites in the western marginal zone of the GrIS. We find a sustained high am...

  16. Using an Earth System Model to Better Understand Ice Sheet Variability Through the Pleistocene

    Science.gov (United States)

    Tabor, C. R.; Poulsen, C. J.; Pollard, D.

    2015-12-01

    We use an Earth System model with a dynamic land-ice component to explore several inconsistencies between traditional Milankovitch theory and δ18O sediment records of the Pleistocene. Our model results show that a combination of albedo feedbacks, seasonal offset of precession forcing, and orbital cycle duration differences can explain much of the 41-kyr glacial cycles that characterize the early Pleistocene. The obliquity-controlled changes in annual average high-latitude insolation produce large variations in arctic vegetation-type and sea-ice cover, which amplify the land-ice response. In contrast, the seasonal nature of the precession insolation signal dampens net ice-melt. For instance, when precession enhances ice melt in the spring, it reduces ice melt in the fall, and vice versa. The lower frequency of obliquity cycles in combination with amplified climate sensitivity due to albedo feedbacks help produce a larger ice-volume response to cycles of obliquity compared to precession, despite precession contributing more to variations in high-latitude summer insolation. In addition, we can simulate the appearance of a 100-kyr ice-volume signal by reducing basal sliding in the ice sheet model. Model experiments with enhanced basal drag have greater ice sheet elevation because the ice sheets are not able to flow as quickly, leading to increased ice thickness at the expense of ice extent. These thicker ice sheets have colder surface temperatures, receive more snowfall, and do not readily advance past the ice equilibrium line. Greater high-latitude summer insolation from the combination of high obliquity and precession/eccentricity is then necessary to cause complete ice sheet retreat. This research lends support to the regolith hypothesis, which proposes gradual erosion of high-latitude northern hemisphere regolith by multiple cycles of glaciation helped cause the mid-Pleistocene transition.

  17. The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet-climate model

    Science.gov (United States)

    Stap, Lennert B.; van de Wal, Roderik S. W.; de Boer, Bas; Bintanja, Richard; Lourens, Lucas J.

    2017-09-01

    Since the inception of the Antarctic ice sheet at the Eocene-Oligocene transition (˜ 34 Myr ago), land ice has played a crucial role in Earth's climate. Through feedbacks in the climate system, land ice variability modifies atmospheric temperature changes induced by orbital, topographical, and greenhouse gas variations. Quantification of these feedbacks on long timescales has hitherto scarcely been undertaken. In this study, we use a zonally averaged energy balance climate model bidirectionally coupled to a one-dimensional ice sheet model, capturing the ice-albedo and surface-height-temperature feedbacks. Potentially important transient changes in topographic boundary conditions by tectonics and erosion are not taken into account but are briefly discussed. The relative simplicity of the coupled model allows us to perform integrations over the past 38 Myr in a fully transient fashion using a benthic oxygen isotope record as forcing to inversely simulate CO2. Firstly, we find that the results of the simulations over the past 5 Myr are dependent on whether the model run is started at 5 or 38 Myr ago. This is because the relation between CO2 and temperature is subject to hysteresis. When the climate cools from very high CO2 levels, as in the longer transient 38 Myr run, temperatures in the lower CO2 range of the past 5 Myr are higher than when the climate is initialised at low temperatures. Consequently, the modelled CO2 concentrations depend on the initial state. Taking the realistic warm initialisation into account, we come to a best estimate of CO2, temperature, ice-volume-equivalent sea level, and benthic δ18O over the past 38 Myr. Secondly, we study the influence of ice sheets on the evolution of global temperature and polar amplification by comparing runs with ice sheet-climate interaction switched on and off. By passing only albedo or surface height changes to the climate model, we can distinguish the separate effects of the ice-albedo and surface

  18. Using paleoclimate data to improve models of the Antarctic Ice Sheet

    Science.gov (United States)

    King, M. A.; Phipps, S. J.; Roberts, J. L.; White, D.

    2016-12-01

    Ice sheet models are the most descriptive tools available to simulate the future evolution of the Antarctic Ice Sheet (AIS), including its contribution towards changes in global sea level. However, our knowledge of the dynamics of the coupled ice-ocean-lithosphere system is inevitably limited, in part due to a lack of observations. Furthemore, to build computationally efficient models that can be run for multiple millennia, it is necessary to use simplified descriptions of ice dynamics. Ice sheet modeling is therefore an inherently uncertain exercise. The past evolution of the AIS provides an opportunity to constrain the description of physical processes within ice sheet models and, therefore, to constrain our understanding of the role of the AIS in driving changes in global sea level. We use the Parallel Ice Sheet Model (PISM) to demonstrate how paleoclimate data can improve our ability to predict the future evolution of the AIS. A large, perturbed-physics ensemble is generated, spanning uncertainty in the parameterizations of four key physical processes within ice sheet models: ice rheology, ice shelf calving, and the stress balances within ice sheets and ice shelves. A Latin hypercube approach is used to optimally sample the range of uncertainty in parameter values. This perturbed-physics ensemble is used to simulate the evolution of the AIS from the Last Glacial Maximum ( 21,000 years ago) to present. Paleoclimate records are then used to determine which ensemble members are the most realistic. This allows us to use data on past climates to directly constrain our understanding of the past contribution of the AIS towards changes in global sea level. Critically, it also allows us to determine which ensemble members are likely to generate the most realistic projections of the future evolution of the AIS.

  19. Modelling the surface mass balance of the Greenland ice sheet and neighbouring ice caps : A dynamical and statistical downscaling approach

    NARCIS (Netherlands)

    Noël, B.P.Y.

    2018-01-01

    The Greenland ice sheet (GrIS) is the world’s second largest ice mass, storing about one tenth of the Earth’s freshwater. If totally melted, global sea level would rise by 7.4 m, affecting low-lying regions worldwide. Since the mid-1990s, increased atmospheric and oceanic temperatures have

  20. The Potsdam Parallel Ice Sheet Model (PISM-PIK – Part 1: Model description

    Directory of Open Access Journals (Sweden)

    R. Winkelmann

    2011-09-01

    Full Text Available We present the Potsdam Parallel Ice Sheet Model (PISM-PIK, developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009. Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid-scale representation of calving front motion (Albrecht et al., 2011 and a physically-motivated calving law based on horizontal spreading rates. The model is tested in experiments from the Marine Ice Sheet Model Intercomparison Project (MISMIP. A dynamic equilibrium simulation of Antarctica under present-day conditions is presented in Martin et al. (2011.

  1. Decadal slowdown of a land-terminating sector of the Greenland Ice Sheet despite warming.

    Science.gov (United States)

    Tedstone, Andrew J; Nienow, Peter W; Gourmelen, Noel; Dehecq, Amaury; Goldberg, Daniel; Hanna, Edward

    2015-10-29

    Ice flow along land-terminating margins of the Greenland Ice Sheet (GIS) varies considerably in response to fluctuating inputs of surface meltwater to the bed of the ice sheet. Such inputs lubricate the ice-bed interface, transiently speeding up the flow of ice. Greater melting results in faster ice motion during summer, but slower motion over the subsequent winter, owing to the evolution of an efficient drainage system that enables water to drain from regions of the ice-sheet bed that have a high basal water pressure. However, the impact of hydrodynamic coupling on ice motion over decadal timescales remains poorly constrained. Here we show that annual ice motion across an 8,000-km(2) land-terminating region of the west GIS margin, extending to 1,100 m above sea level, was 12% slower in 2007-14 compared with 1985-94, despite a 50% increase in surface meltwater production. Our findings suggest that, over these three decades, hydrodynamic coupling in this section of the ablation zone resulted in a net slowdown of ice motion (not a speed-up, as previously postulated). Increases in meltwater production from projected climate warming may therefore further reduce the motion of land-terminating margins of the GIS. Our findings suggest that these sectors of the ice sheet are more resilient to the dynamic impacts of enhanced meltwater production than previously thought.

  2. Internal or induced discharges of the Laurentide ice sheet during the last glacial period ?

    Science.gov (United States)

    Alvarez-Solas, J.; Montoya-Redondo, M.; Robinson, A.; Banderas, R.; Rath, V.; Dumas, C.; Ritz, C.

    2012-12-01

    The Last Glacial Period was characterized by the presence of three large ice sheets in the Northern Hemisphere (Greenland, Eurasian and Laurentide). The later one occupied the major part of North America and contained a quantity of ice similar than present-day Antarctica. Six major episodes of ice discharges, coincident with the temperature minima registered in Greenland, can be counted during the last ice age. The 3D thermomechanical ice sheet / ice shelf model GRISLI (Ritz et al, 2001) is used here to simulate such millennial-scale ice disharges under two fundamentally different mechanisms: internally triggered ice sheet oscillations and induced ice purges as response of oceanic changes. Such internal oscillations have been classically theorized to be the main cause of quasiperiodic large-scale ice discharges known as Heinrich Events (MacAyeal 1993). However, recent studies proposed other triggering mechanisms involving the effects of oceanic circulation changes on the Laurentide ice sheet (LIS) dynamics (Alvarez-Solas et al, 2011; Marcott et al, 2011; Alvarez-Solas and Ramstein 2011). An analysis of the mechanisms associated with LIS multi-millennial oscillations, including both classical and newest interpretations of HEs, is performed. This task is here possible thanks to the hybrid character of the GRISLI model (i.e. it combines Shallow Ice Approximations (SIA) with Shallow Shelf Approximation (SSA) wich allows first to consider the floating part of the ice sheets and secondly to treat fast flowing ice streams under two different formulations). Our analysis focuses on the examination of the likelihood triggering mechanism behind the periodic LIS discharges, and we finally expose the advantages and weakness of both theories. References: Ritz, C., Rommelaere, V., and Dumas, C.: Modeling the evolution of Antarctic ice sheet over the last 420,000 years: Implications for altitude changes in the Vostok region, J. Geophys.Res.Atmos., 106, 31943-31964, 2001. Mac

  3. Green Mountains and White Plains: the effect of Northern Hemisphere ice sheets on the global energy budget

    Science.gov (United States)

    Roberts, William; Valdes, Paul

    2016-04-01

    There are two physical features of a large ice sheet that can fundamentally change the global climate: the topography and albedo. Using a series of climate model experiments we shall show how the climate responds to these features, acting alone and in concert. We shall focus on the global energy budget. We shall use as a tool the HadCM3 climate model. We shall examine three suites of experiments in which we impose the albedo, topography or both of the Laurentide Ice Sheet. In each suite we vary the size of the ice sheet in order that we may examine how the climate's response varies with ice sheet size. Understanding the effect of ice sheets at a size below their maximum is important because, during any glacial period the ice sheets exist at these lesser extents for the majority of the time. We shall show that the albedo of the ice sheet causes a reduction in the incoming shortwave radiation over the ice sheet and that this is balanced by a compensating incoming energy flux into the Southern Hemisphere. The topography of the ice sheet causes an increase in the incoming shortwave radiation over the ice sheet that is balanced by an outgoing energy flux to the south of the ice sheet, with little change in the Southern Hemisphere. The topography and albedo of the ice sheet cause an increase in the outgoing shortwave radiation over the icesheet that is balanced by incoming fluxes to the south of the ice sheet and in the Southern Hemisphere. The magnitude of the cross equatorial atmospheric heat flux shall be related to the position of the ITCZ. We shall show there is a close correlation between the position of the ITCZ and the cross equatorial heat flux, if there is no change in the ice sheet. Changing the ice sheet topography causes this relationship to breakdown.

  4. Mass balance of the Greenland ice sheet (2003-2008) from ICESat data

    DEFF Research Database (Denmark)

    Sørensen, Louise Sandberg; Simonsen, Sebastian Bjerregaard; Nielsen, Karina

    2011-01-01

    ICESat has provided surface elevation measurements of the ice sheets since the launch in January 2003, resulting in a unique dataset for monitoring the changes of the cryosphere. Here, we present a novel method for determining the mass balance of the Greenland ice sheet, derived from ICESat...... studies of the Greenland ice sheet mass balance, based on different remote-sensing techniques....... altimetry data. Three different methods for deriving elevation changes from the ICESat altimetry dataset are used. This multi-method approach provides a method to assess the complexity of deriving elevation changes from this dataset. The altimetry alone can not provide an estimate of the mass balance...

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

    Science.gov (United States)

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

    2012-12-01

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

  6. What is important to get right when modelling the Greenland ice sheet?

    Science.gov (United States)

    Mottram, Ruth; Langen, Peter; Boberg, Fredrik; Fausto, Robert; Vandecrux, Baptiste; Box, Jason; Hesselbjerg Christensen, Jens

    2017-04-01

    Ice sheet and glacier models need accurate surface mass balance inputs to accurately reproduce ice sheet extent and likely evolution. In recent years a number of different regional climate models (RCMs) have produced subtly different estimates of ice sheet surface mass balance (SMB) for the Greenland ice sheet. While the total ice sheet SMB number is often similar from these, there can be substantial differences spatially and in terms of the components of surface mass balance: precipitation, melt, runoff, retention and sublimation. The substantial increase in the amount of observational data available from Greenland allows us to compare not only models and data but also to optimize models to get the best SMB estimates. Using carefully designed sensitivity experiments we explore the importance of albedo, retention and refreezing parameters choices, precipitation, model resolution and topography in HIRHAM5, a typical RCM run at 5km resolution over Greenland, to create the best possible representations of surface mass balance of the Greenland ice sheet. Our analysis shows that the 5km resolution of HIRHAM more accurately captures precipitation over the ice sheet, compared with the old 25km resolution. Compared with 68 ice cores from the accumulation area the simulated mean annual net accumulation bias is -5% (correlation coefficient of 0.90). The retention scheme of the model is able to reproduce the subsurface temperature structure and occurrence of perennial firn aquifers and perched ice layers. However, small differences in parameter choices, while important locally, are not significant over the whole ice sheet. Modelled SMB compares favourably with 1041 PROMICE observations. Varying parameter choices means that a regression slope of 0.95-0.97 can be obtained (depending on model configuration) with a correlation coefficient of 0.75-0.86 and mean bias -3%. Our experiments clearly show that albedo choices are more important to modelled SMB than retention parameters

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

    Science.gov (United States)

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

    2016-12-01

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

  8. Stable microbial community composition on the Greenland Ice Sheet

    Directory of Open Access Journals (Sweden)

    Michaela eMusilova

    2015-03-01

    Full Text Available The first molecular-based studies of microbes in snow and on glaciers have only recently been performed on the vast Greenland Ice Sheet (GrIS. Aeolian microbial seeding is hypothesized to impact on glacier surface community compositions. Localized melting of glacier debris (cryoconite into the surface ice forms cryoconite holes, which are considered ‘hot spots’ for microbial activity on glaciers. To date, few studies have attempted to assess the origin and evolution of cryoconite and cryoconite hole communities throughout a melt season. In this study, a range of experimental approaches was used for the first time to study the inputs, temporal and structural transformations of GrIS microbial communities over the course of a whole ablation season. Small amounts of aeolian (wind and snow microbes were potentially seeding the stable communities that were already present on the glacier (composed mainly of Proteobacteria, Cyanobacteria and Actinobacteria. However, the dominant bacterial taxa in the aeolian samples (Firmicutes did not establish themselves in local glacier surface communities. Cryoconite and cryoconite hole community composition remained stable throughout the ablation season following the fast community turnover, which accompanied the initial snow melt. The presence of stable communities in cryoconite and cryoconite holes on the GrIS will allow future studies to assess glacier surface microbial diversity at individual study sites from sampling intervals of short duration only. Aeolian inputs also had significantly different organic δ13C values (-28.0 to -27.0‰ from the glacier surface values (-25.7 to -23.6‰, indicating that in situ microbial processes are important in fixing new organic matter and transforming aeolian organic carbon. The continuous productivity of stable communities over one melt season makes them important contributors to biogeochemical nutrient cycling on glaciers.

  9. Radar scatterometer observations of sastrugi on the great ice sheets

    Science.gov (United States)

    Long, David G.; Ashcraft, Ivan S.; Luke, Jeremy B.

    2003-11-01

    The SeaWinds instrument on the QuikSCAT satellite was designed to measure near surface winds over the ocean; however, this remarkable remote sensing instrument has proven very useful in polar ice studies. Unlike previous radar scatterometers which were limited to 2 or 3 azimuth angles, the Ku-band SeaWinds instrument uses a circular scanning pencil beam, allowing it to make radar backscatter measurements from all azimuth angles. This geometry makes it an ideal candidate for studies of azimuth modulation of the normalized radar cross section of natural surfaces. Previous studies have observed a second order azimuth modulation of radar backscatter on the Antartic ice sheet, which has been related to wind-generated sastrugi (snow dunes) on the surface. In this paper we use SeaWinds data to make more detailed studies of the azimuth modulation in both Antarctica and Greenland where little has been done. Using the higher azimuth resolution possible with SeaWinds, we find that the azimuth variation of the backscatter is better described using a fourth order model in areas with the highest modulation. The orientation of these fourth order terms appears to be highly correlated to the katabatic wind direction. Azimuth modulation is as observed over Greenland, but it is much smaller than over Antarctica. Comparing SeaWinds and ERS-1/2 satterometer mode data we examine the frequency dependence, finding the modulation larger at C-band than Ku-band. The largest azimuth modulation in Greenland is observed in the transition region between dry snow and percolation zones.

  10. Sea-level response to ice sheet evolution: An ocean perspective

    Science.gov (United States)

    Jacobs, Stanley S.

    1991-01-01

    The ocean's influence upon and response to Antarctic ice sheet changes is considered in relation to sea level rise over recent and future decades. Assuming present day ice fronts are in approximate equilibrium, a preliminary budget for the ice sheet is estimated from accumulation vs. iceberg calving and the basal melting that occurs beneath floating ice shelves. Iceberg calving is derived from the volume of large bergs identified and tracked by the Navy/NOAA Joint Ice Center and from shipboard observations. Basal melting exceeds 600 cu km/yr and is concentrated near the ice fronts and ice shelf grounding lines. An apparent negative mass balance for the Antarctic ice sheet may result from an anomalous calving rate during the past decade, but there are large uncertainties associated with all components of the ice budget. The results from general circulation models are noted in the context of projected precipitation increases and ocean temperature changes on and near the continent. An ocean research program that could help refine budget estimates is consistent with goals of the West Antarctic Ice Sheet Initiative.

  11. Seismic evidence for complex sedimentary control of Greenland Ice Sheet flow.

    Science.gov (United States)

    Kulessa, Bernd; Hubbard, Alun L; Booth, Adam D; Bougamont, Marion; Dow, Christine F; Doyle, Samuel H; Christoffersen, Poul; Lindbäck, Katrin; Pettersson, Rickard; Fitzpatrick, Andrew A W; Jones, Glenn A

    2017-08-01

    The land-terminating margin of the Greenland Ice Sheet has slowed down in recent decades, although the causes and implications for future ice flow are unclear. Explained originally by a self-regulating mechanism where basal slip reduces as drainage evolves from low to high efficiency, recent numerical modeling invokes a sedimentary control of ice sheet flow as an alternative hypothesis. Although both hypotheses can explain the recent slowdown, their respective forecasts of a long-term deceleration versus an acceleration of ice flow are contradictory. We present amplitude-versus-angle seismic data as the first observational test of the alternative hypothesis. We document transient modifications of basal sediment strengths by rapid subglacial drainages of supraglacial lakes, the primary current control on summer ice sheet flow according to our numerical model. Our observations agree with simulations of initial postdrainage sediment weakening and ice flow accelerations, and subsequent sediment restrengthening and ice flow decelerations, and thus confirm the alternative hypothesis. Although simulated melt season acceleration of ice flow due to weakening of subglacial sediments does not currently outweigh winter slowdown forced by self-regulation, they could dominate over the longer term. Subglacial sediments beneath the Greenland Ice Sheet must therefore be mapped and characterized, and a sedimentary control of ice flow must be evaluated against competing self-regulation mechanisms.

  12. Unusual surface morphology from digital elevation models of the Greenland ice sheet

    DEFF Research Database (Denmark)

    Ekholm, Simon; Keller, K.; Bamber, J.L.

    1998-01-01

    In this study of the North Greenland ice sheet, we have used digital elevation models to investigate the topographic signatures of a large ice flow feature discovered in 1993 and a unique surface anomaly which we believe has not been observed previously. The small scale topography of the flow...... feature is revealed in striking detail in a high-pass filtered elevation model. Furthermore, ice penetrating radar show that the sub-stream bed is rough with undulation amplitude increasing downstream. The new feature consists of two large depressions in the ice sheet connected by a long curving trench...

  13. Freshwater fluxes from the Northern Hemisphere ice sheets during the Last Deglaciation

    Science.gov (United States)

    Nemec, J.; Janssens, I.; Goelzer, H.; Huybrechts, P.

    2009-04-01

    The disintegration of the Northern Hemisphere Ice Sheets during the Last Deglaciation is thought to have significantly influenced the global climate through oceanic and atmospheric feedbacks. Besides changes in topography and albedo over the large continental ice sheets, freshwater fluxes probably had large effects on the ocean circulation and on the global temperature evolution. To study possible changes in the ocean circulation, it is crucial to track both the intensity and location of meltwater runoff and iceberg calving into the ocean. We have simulated the northern hemisphere ice sheets with a 3D thermomechanical ice sheet model forced with output from a coupled atmosphere-ocean model (ECBilt-Clio) with prescribed ice sheets (extent, elevation, and albedo) for the Last Deglacation. The ice sheet model calculates changes in topography as well as the evolution of the freshwater fluxes, resulting from iceberg calving, basal melt and surface ablation. The ice sheet melt fluxes are routed through a continental runoff scheme that provides the runoff paths over the continents and gives for each continental grid point a corresponding drainage location in the ocean. The results are very dependent on the climate forcing that serves as input for the ice sheet model. Taking GRIP (Greenland Ice Core Project) scaled temperature and precipitation input, we find three major freshwater pulses during the Last Deglaciation. The first meltwater peak occurred at approximately 17 kyr BP, with an amplitude of 0.45 Sverdrup. The second, with the highest intensity of 0.8 Sverdrup, occurred around 14 kyr BP. Large parts of this meltwater is channeled to the North Atlantic, where it might have triggered the Younger Dryas cold period. The third and last meltwater peak happened about 10 kyr BP, corresponding to a switch in the freshwater routing from the North Atlantic to the Artic Ocean.

  14. initMIP-Antarctica: An ice sheet model initialization experiment of ISMIP6

    Science.gov (United States)

    Seroussi, H. L.; Nowicki, S.; Payne, A. J.; Larour, E. Y.; Abe-Ouchi, A.; Goelzer, H.; Gregory, J. M.; Lipscomb, W. H.; Shepherd, A.

    2016-12-01

    ISMIP6 (Ice Sheet Model Intercomparision Project for CMIP6) is the primary activity within the Coupled Model Intercomparison Project - phase 6 (CMIP6) focusing on the Greenland and Antarctic Ice Sheets. Ice sheet model simulations are strongly influenced by their initial conditions, but the impact of these conditions on simulations of ice sheet evolution over the next couple centuries remains poorly understood. To better understand this impact and the associated error, an initial intercompation exercice (initMIP) has been designed to compare, evaluate and improve initialization procedures and estimate their impact on century scale simulations. Following the initMIP-Greenland, a new initMIP-Antarctica has been designed to explore uncertainty associated with model initialization and spin-up and to evaluate initialization procedures. It consists of a set of three forward experiments of the Antarctic Ice Sheet that are each run for one hundred years: i) a control run (ctrl), ii) a surface mass balance anomaly run (asmb) and iii) a basal melt anomaly applied under the floating ice 30 (abmb) of the Antarctic Ice Sheet. All other model parameters are the same as those used for the initialization procedure. In this study, we present preliminary results of initMIP-Antarctica performed by different modeling groups and highlight the similarities and differences observed in the different simulations.

  15. Response of salt structures to ice-sheet loading: implications for ice-marginal and subglacial processes

    Science.gov (United States)

    Lang, Jörg; Hampel, Andrea; Brandes, Christian; Winsemann, Jutta

    2014-10-01

    During the past decades the effect of glacioisostatic adjustment has received much attention. However, the response of salt structures to ice-sheet loading and unloading is poorly understood. Our study aims to test conceptual models of the interaction between ice-sheet loading and salt structures by finite-element modelling. The results are discussed with regard to their implications for ice-marginal and subglacial processes. Our models consist of 2D plane-strain cross-sections, which represent simplified geological cross-sections from the Central European Basin System. The model layers represent (i) sedimentary rocks of elastoplastic rheology, (ii) a viscoelastic diapir and layer of salt and (iii) an elastoplastic basement. On top of the model, a temporarily variable pressure simulates the advance and retreat of an ice sheet. The durations of the individual loading phases were defined to resemble the durations of the Pleistocene ice advances in northern central Europe. The geometry and rheology of the model layers and the magnitude, spatial distribution and timing of ice-sheet loading were systematically varied to detect the controlling factors. All simulations indicate that salt structures respond to ice-sheet loading. An ice advance towards the diapir causes salt flow from the source layer below the ice sheet towards the diapir, resulting in an uplift of up to +4 m. The diapir continues to rise as long as the load is applied to the source layer but not to the crest of the diapir. When the diapir is transgressed by the ice sheet the diapir is pushed down (up to -36 m) as long as load is applied to the crest of the diapir. During and after ice unloading large parts of the displacement are compensated by a reversal of the salt flow. Plastic deformation of the overburden is restricted to the area immediately above the salt diapir. The displacements after unloading range between -3.1 and +2.7 m. Larger displacements are observed in models with deep-rooted diapirs

  16. ANTARCTIC ICE SHEET SLOPE AND ASPECT BASED ON ICESAT’S REPEAT ORBIT MEASUREMENT

    Directory of Open Access Journals (Sweden)

    L. Yuan

    2017-09-01

    Full Text Available Accurate information of ice sheet surface slope is essential for estimating elevation change by satellite altimetry measurement. A study is carried out to recover surface slope of Antarctic ice sheet from Ice, Cloud and land Elevation Satellite (ICESat elevation measurements based on repeat orbits. ICESat provides repeat ground tracks within 200 meters in cross-track direction and 170 meters in along-track direction for most areas of Antarctic ice sheet. Both cross-track and along-track surface slopes could be obtained by adjacent repeat ground tracks. Combining those measurements yields a surface slope model with resolution of approximately 200 meters. An algorithm considering elevation change is developed to estimate the surface slope of Antarctic ice sheet. Three Antarctic Digital Elevation Models (DEMs were used to calculate surface slopes. The surface slopes from DEMs are compared with estimates by using in situ GPS data in Dome A, the summit of Antarctic ice sheet. Our results reveal an average surface slope difference of 0.02 degree in Dome A. High resolution remote sensing images are also used in comparing the results derived from other DEMs and this paper. The comparison implies that our results have a slightly better coherence with GPS observation than results from DEMs, but our results provide more details and perform higher accuracy in coastal areas because of the higher resolution for ICESat measurements. Ice divides are estimated based on the aspect, and are weakly consistent with ice divides from other method in coastal regions.

  17. The Antarctic Ice Sheet, Sea Ice, and the Ozone Hole: Satellite Observations of how they are Changing

    Science.gov (United States)

    Parkinson, Claire L.

    2012-01-01

    Antarctica is the Earth's coldest and highest continent and has major impacts on the climate and life of the south polar vicinity. It is covered almost entirely by the Earth's largest ice sheet by far, with a volume of ice so great that if all the Antarctic ice were to go into the ocean (as ice or liquid water), this would produce a global sea level rise of about 60 meters (197 feet). The continent is surrounded by sea ice that in the wintertime is even more expansive than the continent itself and in the summertime reduces to only about a sixth of its wintertime extent. Like the continent, the expansive sea ice cover has major impacts, reflecting the sun's radiation back to space, blocking exchanges between the ocean and the atmosphere, and providing a platform for some animal species while impeding other species. Far above the continent, the Antarctic ozone hole is a major atmospheric phenomenon recognized as human-caused and potentially quite serious to many different life forms. Satellites are providing us with remarkable information about the ice sheet, the sea ice, and the ozone hole. Satellite visible and radar imagery are providing views of the large scale structure of the ice sheet never seen before; satellite laser altimetry has produced detailed maps of the topography of the ice sheet; and an innovative gravity-measuring two-part satellite has allowed mapping of regions of mass loss and mass gain on the ice sheet. The surrounding sea ice cover has a satellite record that goes back to the 1970s, allowing trend studies that show a decreasing sea ice presence in the region of the Bellingshausen and Amundsen seas, to the west of the prominent Antarctic Peninsula, but increasing sea ice presence around much of the rest of the continent. Overall, sea ice extent around Antarctica has increased at an average rate of about 17,000 square kilometers per year since the late 1970s, as determined from satellite microwave data that can be collected under both light and

  18. Virus activity on the surface of glaciers and ice sheets

    Science.gov (United States)

    Bellas, C. M.; Anesio, A. M.; Telling, J.; Stibal, M.; Barker, G.; Tranter, M.; Yallop, M.; Cook, J.

    2012-12-01

    Viruses are found wherever there is life. They are major components of aquatic ecosystems and through interactions with their hosts they significantly alter global biogeochemical cycles and drive evolutionary processes. Here we focus on the interactions between bacteriophages and their hosts inhabiting the microbially dominated supraglacial ecosystems known as cryoconite holes. The diversity of phages present in the sediments of cryoconites was examined for the first time by using a molecular based approach to target the T4-type bacteriophage. Through phylogenetic analysis it was determined that the phage community was diverse, consisting of strains that grouped with those from other global habitats and those that formed several completely new T4-type phage clusters. The activity of the viral community present on glaciers from Svalbard and the Greenland Ice Sheet was also addressed through a series of incubation experiments. Here new virus production was found to be capable of turning over the viral population approximately twice a day, a rate comparable to marine and freshwater sediments around the globe. This large scale viral production was found to be theoretically capable of accounting for all heterotrophic bacterial mortality in cryoconite holes. The mode of infection that viruses employ in cryoconite holes was also addressed to show that a variety of viral life strategies are likely responsible for the continued dominance of viruses in these unique habitats. The implications of viral activity are discussed in terms of carbon cycling in supraglacial ecosystems.

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

    Science.gov (United States)

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

    2015-12-01

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

  20. Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial drainage.

    Science.gov (United States)

    Sundal, Aud Venke; Shepherd, Andrew; Nienow, Peter; Hanna, Edward; Palmer, Steven; Huybrechts, Philippe

    2011-01-27

    Fluctuations in surface melting are known to affect the speed of glaciers and ice sheets, but their impact on the Greenland ice sheet in a warming climate remains uncertain. Although some studies suggest that greater melting produces greater ice-sheet acceleration, others have identified a long-term decrease in Greenland's flow despite increased melting. Here we use satellite observations of ice motion recorded in a land-terminating sector of southwest Greenland to investigate the manner in which ice flow develops during years of markedly different melting. Although peak rates of ice speed-up are positively correlated with the degree of melting, mean summer flow rates are not, because glacier slowdown occurs, on average, when a critical run-off threshold of about 1.4 centimetres a day is exceeded. In contrast to the first half of summer, when flow is similar in all years, speed-up during the latter half is 62 ± 16 per cent less in warmer years. Consequently, in warmer years, the period of fast ice flow is three times shorter and, overall, summer ice flow is slower. This behaviour is at odds with that expected from basal lubrication alone. Instead, it mirrors that of mountain glaciers, where melt-induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient. A model of ice-sheet flow that captures switching between cavity and channel drainage modes is consistent with the run-off threshold, fast-flow periods, and later-summer speeds we have observed. Simulations of the Greenland ice-sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage; a simple model of basal lubrication alone misses key aspects of the ice sheet's response to climate warming.

  1. A balanced water layer concept for subglacial hydrology in large-scale ice sheet models

    Directory of Open Access Journals (Sweden)

    S. Goeller

    2013-07-01

    Full Text Available There is currently no doubt about the existence of a widespread hydrological network under the Antarctic Ice Sheet, which lubricates the ice base and thus leads to increased ice velocities. Consequently, ice models should incorporate basal hydrology to obtain meaningful results for future ice dynamics and their contribution to global sea level rise. Here, we introduce the balanced water layer concept, covering two prominent subglacial hydrological features for ice sheet modeling on a continental scale: the evolution of subglacial lakes and balance water fluxes. We couple it to the thermomechanical ice-flow model RIMBAY and apply it to a synthetic model domain. In our experiments we demonstrate the dynamic generation of subglacial lakes and their impact on the velocity field of the overlaying ice sheet, resulting in a negative ice mass balance. Furthermore, we introduce an elementary parametrization of the water flux–basal sliding coupling and reveal the predominance of the ice loss through the resulting ice streams against the stabilizing influence of less hydrologically active areas. We point out that established balance flux schemes quantify these effects only partially as their ability to store subglacial water is lacking.

  2. A balanced water layer concept for subglacial hydrology in large scale ice sheet models

    Science.gov (United States)

    Goeller, S.; Thoma, M.; Grosfeld, K.; Miller, H.

    2012-12-01

    There is currently no doubt about the existence of a wide-spread hydrological network under the Antarctic ice sheet, which lubricates the ice base and thus leads to increased ice velocities. Consequently, ice models should incorporate basal hydrology to obtain meaningful results for future ice dynamics and their contribution to global sea level rise. Here, we introduce the balanced water layer concept, covering two prominent subglacial hydrological features for ice sheet modeling on a continental scale: the evolution of subglacial lakes and balance water fluxes. We couple it to the thermomechanical ice-flow model RIMBAY and apply it to a synthetic model domain inspired by the Gamburtsev Mountains, Antarctica. In our experiments we demonstrate the dynamic generation of subglacial lakes and their impact on the velocity field of the overlaying ice sheet, resulting in a negative ice mass balance. Furthermore, we introduce an elementary parametrization of the water flux-basal sliding coupling and reveal the predominance of the ice loss through the resulting ice streams against the stabilizing influence of less hydrologically active areas. We point out, that established balance flux schemes quantify these effects only partially as their ability to store subglacial water is lacking.

  3. Airborne observations of changes of ice sheet and sea ice in the Arctic using CryoVEx campaign data

    DEFF Research Database (Denmark)

    Hvidegaard, Sine Munk; Skourup, Henriette; Forsberg, René

    ‐launch validation studies, with several aircraft and international in‐situ ground teams participating, both in Greenland, Arctic Canada, and Svalbard. The methods and campaigns are outlined together with examples of results.The campaigns focused on five main validation sites: Devon ice cap (Canada), Austfonna ice...... cap (Svalbard), the EGIG line crossing the Greenland Ice Sheet, as well as the sea ice north of Alert and sea ice around Svalbard in the Fram Strait. Selected tracks were planned to match CryoSat‐2 passes and a few of them were flown in formation flight with the Alfred Wegener Institute (AWI) Polar‐5......DTU Space have collected surface elevation observations of the Arctic sea ice and land ice since 1998 using laser scanning and radar altimetry from a small fixed‐wing Twin‐Otter aircraft. The observations provide unique datasets for studying ongoing changes, and support the analysis of satellite...

  4. MEaSUREs Greenland Ice Sheet Velocity Map from InSAR Data V001

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set, part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program, provides annual ice-sheet-wide velocity maps...

  5. Inter-comparison of ice sheet mass balance products from GRACE: ESA CCI Round Robin results

    DEFF Research Database (Denmark)

    Groth, A.; Horwath, M.; Horvath, A.

    -term satellite-based data products are generated for selected ECVs. Since ice sheet mass balance is an ECV parameter of highest interest, both the AIS_cci and the GIS_cci project will provide mass balance products based on satellite gravimetry data: (a) time series of monthly mass changes for individual drainage...... basins, and (b) gridded mass changes covering the entire ice sheet.Gravimetry Mass Balance (GMB) products are derived from data acquired by the GRACE (Gravity Recovery and Climate Experiment) mission. Although GRACE data have the advantage of being directly sensitive to mass changes, their limited......Both the Antarctic Ice Sheet (AIS) and the Greenland Ice Sheet (GIS) have been identified as key parameters, so called Essential Climate Variables (ECV), in the climate system. Within the framework of the Climate Change Initiative (CCI) of the European Space Agency (ESA), reliable long...

  6. Greenland Ice Sheet Melt Characteristics Derived from Passive Microwave Data, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — The Greenland ice sheet melt extent data, acquired as part of the NASA Program for Arctic Regional Climate Assessment (PARCA), is a daily (or every other day, prior...

  7. MEaSUREs Multi-year Greenland Ice Sheet Velocity Mosaic, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set, part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program, contains a multi-year ice-sheet-wide velocity...

  8. Digital SAR Mosaic and Elevation Map of the Greenland Ice Sheet, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — The Digital SAR Mosaic and Elevation Map of the Greenland Ice Sheet CD-ROM combines the most detailed synthetic aperture radar (SAR) image mosaic available with the...

  9. Digital SAR Mosaic and Elevation Map of the Greenland Ice Sheet

    Data.gov (United States)

    National Aeronautics and Space Administration — The Digital SAR Mosaic and Elevation Map of the Greenland Ice Sheet CD-ROM combines the most detailed synthetic aperture radar (SAR) image mosaic available with the...

  10. MEaSUREs Greenland Ice Sheet Velocity Map from InSAR Data

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set, part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program, provides annual ice-sheet-wide velocity maps...

  11. Atmospheric Mixing Ratios of Hydroperoxides above the West Antarctic Ice Sheet, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set contains atmospheric mixing ratios of hydrogen peroxide and methylhydroperoxide at 21 sites on the West Antarctic Ice Sheet (WAIS) were obtained from...

  12. Antarctic Timing of Surface Water Changes off Chile and Patagonian Ice Sheet Response

    National Research Council Canada - National Science Library

    Frank Lamy; Jérôme Kaiser; Ulysses Ninnemann; Dierk Hebbeln; Helge W. Arz; Joseph Stoner

    2004-01-01

    Marine sediments from the Chilean continental margin are used to infer millennial-scale changes in southeast Pacific surface ocean water properties and Patagonian ice sheet extent since the last glacial period...

  13. Climate of the greenland ice sheet using a high - resolution climate model - part 1 : evaluation

    National Research Council Canada - National Science Library

    Ettema, J; van den Broeke, M.R; van Meijgaard, E; van den Berg, W.J; Box, J.E; Steffen, K

    2010-01-01

    ... into the surface part of the climate model. The temporal evolution and climatology of the model is evaluated with in situ coastal and ice sheet atmospheric measurements of near-surface variables and surface energy balance components...

  14. MEaSUREs Greenland Ice Sheet Velocity Map from InSAR Data V002

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set, part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program, contains seasonal (winter) ice-sheet-wide...

  15. Application of GRACE to the assessment of model-based estimates of monthly Greenland Ice Sheet mass balance (2003-2012)

    NARCIS (Netherlands)

    Schlegel, Nicole Jeanne; Wiese, David N.; Larour, Eric Y.; Watkins, Michael M.; Box, Jason E.; Fettweis, Xavier; Van Den Broeke, Michiel R.

    2016-01-01

    Quantifying the Greenland Ice Sheet's future contribution to sea level rise is a challenging task that requires accurate estimates of ice sheet sensitivity to climate change. Forward ice sheet models are promising tools for estimating future ice sheet behavior, yet confidence is low because

  16. Coupled Northern Hemisphere permafrost-ice sheet evolution over the last glacial cycle

    OpenAIRE

    M. Willeit; A. Ganopolski

    2015-01-01

    Permafrost influences a number of processes which are relevant for local and global climate. For example, it is well known that permafrost plays an important role in global carbon and methane cycles. Less is known about the interaction between permafrost and ice sheets. In this study a permafrost module is included in the Earth system model CLIMBER-2 and the coupled Northern Hemisphere (NH) permafrost-ice sheet evolution over the last glacial cycle is explor...

  17. Coupled Northern Hemisphere permafrost–ice-sheet evolution over the last glacial cycle

    OpenAIRE

    Willeit, M.; Ganopolski, A.

    2015-01-01

    Permafrost influences a number of processes which are relevant for local and global climate. For example, it is well known that permafrost plays an important role in global carbon and methane cycles. Less is known about the interaction between permafrost and ice sheets. In this study a permafrost module is included in the Earth system model CLIMBER-2, and the coupled Northern Hemisphere (NH) permafrost–ice-sheet evolution over the last glacial cycle is explo...

  18. Essential Climate Variables for the Ice Sheets from Space and Airborne measurements

    DEFF Research Database (Denmark)

    Fredenslund Levinsen, Joanna

    The Greenland Ice Sheet is the largest ice mass in the northern hemisphere.Over the past decade, it has undergone substantial changes in e.g. mass balance,surface velocity, and ice thickness. The latter is reflected by surfaceelevation changes, which are detectable with altimetry. Therefore......, this studyexploits the advantages of radar and laser altimetry to analyze surface elevationchanges and build a Digital Elevation Model of the ice sheet. Selected advantagesare radar data’s continuity in time and laser data’s higher horizontal andvertical accuracy. Therefore, ESA Envisat and CryoSat-2 radar altimetry...... dataare used in conjunction with laser data from NASA’s ICESat and airborneATM and LVIS instruments, and from ESA’s airborne CryoVEx campaign.The study is part of the ESA Ice Sheets CCI project. With the release ofREAPER data, one goal is to use the more than two decades of ESA radaraltimetry to develop...

  19. Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Kjaer, Kurt H.; Bevis, Michael

    2014-01-01

    and northwest Greenland. Here, we show that the northeast Greenland ice stream, which extends more than 600 km into the interior of the ice sheet, is now undergoing sustained dynamic thinning, linked to regional warming, after more than a quarter of a century of stability. This sector of the Greenland ice sheet...... is of particular interest, because the drainage basin area covers 16% of the ice sheet (twice that of Jakobshavn Isbrae) and numerical model predictions suggest no significant mass loss for this sector, leading to an under-estimation of future global sea-level rise. The geometry of the bedrock and monotonic trend...... in glacier speed-up and mass loss suggests that dynamic drawdown of ice in this region will continue in the near future....

  20. The sea level response to ice sheet freshwater forcing in the Community Earth System Model

    Science.gov (United States)

    Slangen, Aimée; Lenaerts, Jan

    2017-04-01

    We show the effect of a realistic ice sheet freshwater forcing on sea-level change in the fully coupled Community Earth System Model (CESM). This not only includes the effect on the ocean density and dynamics, but also the gravitational response to mass redistribution between ice sheets and the ocean. We compare a 'standard' model simulation (NO-FW) to a simulation with a more realistic ice sheet freshwater forcing (FW) for two different climate scenario's (RCP2.6 and RCP8.5) for 1850-2100. We find that the effect on the global mean thermosteric sea-level change is small compared to the total thermosteric change, but on a regional scale the ocean steric/dynamic change shows larger differences in the Southern Ocean, the North Atlantic and the Arctic Ocean (locally over 0.1 m). The gravitational fingerprints of the net sea-level contributions of the ice sheets are computed separately, showing a regional pattern with a magnitude that is similar to the difference between the NO-FW and FW simulations of the ocean steric/dynamic pattern. Our results demonstrate the importance of ice sheet mass loss for regional sea-level projections in light of the projected increasing contribution of ice sheets to future sea-level rise.

  1. Continuous, Pulsed Export of Methane-Supersaturated Meltwaters from the Bed of the Greenland Ice Sheet

    Science.gov (United States)

    Lamarche-Gagnon, G.; Wadham, J.; Beaton, A.; Fietzek, P.; Stanley, K. M.; Tedstone, A.; Sherwood Lollar, B.; Lacrampe Couloume, G.; Telling, J.; Liz, B.; Hawkings, J.; Kohler, T. J.; Zarsky, J. D.; Stibal, M.; Mowlem, M. C.

    2016-12-01

    Both past and present ice sheets have been proposed to cap large quantities of methane (CH4), on orders of magnitude significant enough to impact global greenhouse gas concentrations during periods of rapid ice retreat. However, to date most evidence for sub-ice sheet methane has been indirect, derived from calculations of the methanogenic potential of basal-ice microbial communities and biogeochemical models; field-based empirical measurements are lacking from large ice sheet catchments. Here, we present the first continuous, in situ record of dissolved methane export from a large catchment of the Greenland Ice Sheet (GrIS) in South West Greenland from May-July 2015. Our results indicate that glacial runoff was continuously supersaturated with methane over the observation period (dissolved CH4 concentrations of 30-700 nM), with total methane flux rising as subglacial discharge increased. Periodic subglacial drainage events, characterised by rapid changes (i.e. pulses) in meltwater hydrochemistry, also coincided with a rise in methane concentrations. We argue that these are likely indicative of the flushing of subglacial reservoirs of CH4 beneath the ice sheet. Total methane export was relatively modest when compared to global methane budgets, but too high to be explained by previously determined methanogenic rates from Greenland basal ice. Discrepancies between estimated Greenland methane reserves and observed fluxes stress the need to further investigate GrIS methane fluxes and sources, and suggest a more biogeochemically active subglacial environment than previously considered. Results indicate that future warming, and a coincident increase in ice melt rates, would likely make the GrIS, and by extension the Antarctic Ice Sheet, more significant sources of atmospheric methane, consequently acting as a positive feedback to a warming climate.

  2. Surface Temperature and Melt on the Greenland Ice Sheet, 2000 - 2011

    Science.gov (United States)

    Hall, Dorothy K.; Comiso, Josefino C.; Shuman, Christopher A.; Koeing, Lora S.; Box, Jason E.; DiGirolamo, Nicolo E.

    2012-01-01

    Enhanced melting along with surface-temperature increases measured using infrared satellite data, have been documented for the Greenland Ice Sheet. Recently we developed a climate-quality data record of ice-surface temperature (IST) of the Greenland Ice Sheet using the Moderate-Resolution Imaging Spectroradiometer (MODIS) IST product -- http://modis-snow-ice.gsfc.nasa.gov.Using daily and mean-monthly MODIS IST maps from the data record we show maximum extent of melt for the ice sheet and its six major drainage basins for a 12-year period extending from March of 2000 through December of 2011. The duration of the melt season on the ice sheet varies in different drainage basins with some basins melting progressively earlier over the study period. Some (but not all) of the basins also show a progressively-longer duration of melt. The short time of the study period (approx 12 years) precludes an evaluation of statistically-significant trends. However the dataset provides valuable information on natural variability of IST, and on the ability of the MODIS instrument to capture changes in IST and melt conditions in different drainage basins of the ice sheet.

  3. Variability of Surface Temperature and Melt on the Greenland Ice Sheet, 2000-2011

    Science.gov (United States)

    Hall, Dorothy K.; Comiso, Josefino, C.; Shuman, Christopher A.; Koenig, Lora S.; DiGirolamo, Nicolo E.

    2012-01-01

    Enhanced melting along with surface-temperature increases measured using infrared satellite data, have been documented for the Greenland Ice Sheet. Recently we developed a climate-quality data record of ice-surface temperature (IST) of the Greenland Ice Sheet using the Moderate-Resolution Imaging Spectroradiometer (MODIS) 1ST product -- http://modis-snow-ice.gsfc.nasa.gov. Using daily and mean monthly MODIS 1ST maps from the data record we show maximum extent of melt for the ice sheet and its six major drainage basins for a 12-year period extending from March of 2000 through December of 2011. The duration of the melt season on the ice sheet varies in different drainage basins with some basins melting progressively earlier over the study period. Some (but not all) of the basins also show a progressively-longer duration of melt. The short time of the study period (approximately 12 years) precludes an evaluation of statistically-significant trends. However the dataset provides valuable information on natural variability of IST, and on the ability of the MODIS instrument to capture changes in IST and melt conditions indifferent drainage basins of the ice sheet.

  4. Simulating a Dynamic Antarctic Ice Sheet in the Early to Middle Miocene

    Science.gov (United States)

    Gasson, E.; DeConto, R.; Pollard, D.; Levy, R. H.

    2015-12-01

    There are a variety of sources of geological data that suggest major variations in the volume and extent of the Antarctic ice sheet during the early to middle Miocene. Simulating such variability using coupled climate-ice sheet models is problematic due to a strong hysteresis effect caused by height-mass balance feedback and albedo feedback. This results in limited retreat of the ice sheet once it has reached the continental size, as likely occurred prior to the Miocene. Proxy records suggest a relatively narrow range of atmospheric CO2 during the early to middle Miocene, which exacerbates this problem. We use a new climate forcing which accounts for ice sheet-climate feedbacks through an asynchronous GCM-RCM coupling, which is able to better resolve the narrow Antarctic ablation zone in warm climate simulations. When combined with recently suggested mechanisms for retreat into subglacial basins due to ice shelf hydrofracture and ice cliff failure, we are able to simulate large-scale variability of the Antarctic ice sheet in the Miocene. This variability is equivalent to a seawater oxygen isotope signal of ~0.5 ‰, or a sea level equivalent change of ~35 m, for a range of atmospheric CO2 between 280 - 500 ppm.

  5. Changes in the firn structure of the western Greenland Ice Sheet caused by recent warming

    NARCIS (Netherlands)

    de la Pena, S.; Howat, I. M.; Nienow, P. W.; van den Broeke, M. R.; Mosley-Thompson, E.; Price, S. F.; Mair, D.; Noel, B.; Sole, A. J.

    2015-01-01

    Atmospheric warming over the Greenland Ice Sheet during the last 2 decades has increased the amount of surface meltwater production, resulting in the migration of melt and percolation regimes to higher altitudes and an increase in the amount of ice content from refrozen meltwater found in the firn

  6. 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

  7. A Meteorological Experiment in the Melting Zone of the Greenland Ice Sheet

    NARCIS (Netherlands)

    Oerlemans, J.; Vugts, H.F.

    1993-01-01

    Preliminary results are described from a glaciometeorological experiment carried out in the margin (melting zone) of the Greenland ice sheet in the summers of 1990 and 1991. This work was initiated within the framework of a Dutch research program on land ice and sea level change. Seven

  8. Modeling of Pleistocene European Ice Sheets: Some Experiments with Simple Mass-Balance Parameterizations

    NARCIS (Netherlands)

    Oerlemans, J.

    1980-01-01

    A vertically integrated ice-flow model suitable for use in climate studies is formulated. Large continental ice sheets may be characterized by two fundamental quantities: the height-to-width ratio, and the steepness of the edge. So it is natural to develop a model containing two parameters that can

  9. Assessing the Impact of Laurentide Ice-sheet Topography on Glacial Climate

    Science.gov (United States)

    Ullman, D. J.; LeGrande, A. N.; Carlson, A. E.; Anslow, F. S.; Licciardi, J. M.

    2014-01-01

    Simulations of past climates require altered boundary conditions to account for known shifts in the Earth system. For the Last Glacial Maximum (LGM) and subsequent deglaciation, the existence of large Northern Hemisphere ice sheets caused profound changes in surface topography and albedo. While ice-sheet extent is fairly well known, numerous conflicting reconstructions of ice-sheet topography suggest that precision in this boundary condition is lacking. Here we use a high-resolution and oxygen-isotopeenabled fully coupled global circulation model (GCM) (GISS ModelE2-R), along with two different reconstructions of the Laurentide Ice Sheet (LIS) that provide maximum and minimum estimates of LIS elevation, to assess the range of climate variability in response to uncertainty in this boundary condition.We present this comparison at two equilibrium time slices: the LGM, when differences in ice-sheet topography are maximized, and 14 ka, when differences in maximum ice-sheet height are smaller but still exist. Overall, we find significant differences in the climate response to LIS topography, with the larger LIS resulting in enhanced Atlantic Meridional Overturning Circulation and warmer surface air temperatures, particularly over northeastern Asia and the North Pacific. These up- and downstream effects are associated with differences in the development of planetary waves in the upper atmosphere, with the larger LIS resulting in a weaker trough over northeastern Asia that leads to the warmer temperatures and decreased albedo from snow and sea-ice cover. Differences between the 14 ka simulations are similar in spatial extent but smaller in magnitude, suggesting that climate is responding primarily to the larger difference in maximum LIS elevation in the LGM simulations. These results suggest that such uncertainty in ice-sheet boundary conditions alone may significantly impact the results of paleoclimate simulations and their ability to successfully simulate past climates

  10. A mascon approach to assess ice sheet and glacier mass balances and their uncertainties from GRACE data

    NARCIS (Netherlands)

    Schrama, E.J.O.; Wouters, B.; Rietbroek, R.

    2014-01-01

    The purpose of this paper is to assess the mass changes of the Greenland Ice Sheet (GrIS), Ice Sheets over Antarctica, and Land glaciers and Ice Caps with a global mascon method that yields monthly mass variations at 10,242 mascons. Input for this method are level 2 data from the Gravity Recovery

  11. The mass balance of the Greenland ice sheet: sensitivity to climate change as revealed by energy-balance modelling

    NARCIS (Netherlands)

    Oerlemans, J.

    1991-01-01

    The sensitivity of the mass balance of the Greenland ice sheet to climate change is studied with an energy-balance model of the ice/snow surface, applied at 200 m elevation intervals for four characteristic regions of the ice sheet. Solar radiation, longwave radiation, turbulent heat fluxes

  12. Using palaeoclimate data to improve models of the Antarctic Ice Sheet

    Science.gov (United States)

    Phipps, Steven; King, Matt; Roberts, Jason; White, Duanne

    2017-04-01

    Ice sheet models are the most descriptive tools available to simulate the future evolution of the Antarctic Ice Sheet (AIS), including its contribution towards changes in global sea level. However, our knowledge of the dynamics of the coupled ice-ocean-lithosphere system is inevitably limited, in part due to a lack of observations. Furthemore, to build computationally efficient models that can be run for multiple millennia, it is necessary to use simplified descriptions of ice dynamics. Ice sheet modelling is therefore an inherently uncertain exercise. The past evolution of the AIS provides an opportunity to constrain the description of physical processes within ice sheet models and, therefore, to constrain our understanding of the role of the AIS in driving changes in global sea level. We use the Parallel Ice Sheet Model (PISM) to demonstrate how palaeoclimate data can improve our ability to predict the future evolution of the AIS. A 50-member perturbed-physics ensemble is generated, spanning uncertainty in the parameterisations of three key physical processes within the model: (i) the stress balance within the ice sheet, (ii) basal sliding and (iii) calving of ice shelves. A Latin hypercube approach is used to optimally sample the range of uncertainty in parameter values. This perturbed-physics ensemble is used to simulate the evolution of the AIS from the Last Glacial Maximum ( 21,000 years ago) to present. Palaeoclimate records are then used to determine which ensemble members are the most realistic. This allows us to use data on past climates to directly constrain our understanding of the past contribution of the AIS towards changes in global sea level. Critically, it also allows us to determine which ensemble members are likely to generate the most realistic projections of the future evolution of the AIS.

  13. Propagation of acoustic-gravity waves in arctic zones with elastic ice-sheets

    Science.gov (United States)

    Kadri, Usama; Abdolali, Ali; Kirby, James T.

    2017-04-01

    We present an analytical solution of the boundary value problem of propagating acoustic-gravity waves generated in the ocean by earthquakes or ice-quakes in arctic zones. At the surface, we assume elastic ice-sheets of a variable thickness, and show that the propagating acoustic-gravity modes have different mode shape than originally derived by Ref. [1] for a rigid ice-sheet settings. Computationally, we couple the ice-sheet problem with the free surface model by Ref. [2] representing shrinking ice blocks in realistic sea state, where the randomly oriented ice-sheets cause inter modal transition at the edges and multidirectional reflections. We then derive a depth-integrated equation valid for spatially slowly varying thickness of ice-sheet and water depth. Surprisingly, and unlike the free-surface setting, here it is found that the higher acoustic-gravity modes exhibit a larger contribution. These modes travel at the speed of sound in water carrying information on their source, e.g. ice-sheet motion or submarine earthquake, providing various implications for ocean monitoring and detection of quakes. In addition, we found that the propagating acoustic-gravity modes can result in orbital displacements of fluid parcels sufficiently high that may contribute to deep ocean currents and circulation, as postulated by Refs. [1, 3]. References [1] U. Kadri, 2016. Generation of Hydroacoustic Waves by an Oscillating Ice Block in Arctic Zones. Advances in Acoustics and Vibration, 2016, Article ID 8076108, 7 pages http://dx.doi.org/10.1155/2016/8076108 [2] A. Abdolali, J. T. Kirby and G. Bellotti, 2015, Depth-integrated equation for hydro-acoustic waves with bottom damping, J. Fluid Mech., 766, R1 doi:10.1017/jfm.2015.37 [3] U. Kadri, 2014. Deep ocean water transportation by acoustic?gravity waves. J. Geophys. Res. Oceans, 119, doi:10.1002/ 2014JC010234

  14. Millennial-scale interaction between ice sheets and ocean circulation during marine isotope stage 100

    Directory of Open Access Journals (Sweden)

    Masao eOhno

    2016-05-01

    Full Text Available Waxing/waning of the ice sheets and the associated change in thermohaline circulation have played an important role in global climate change since major continental ice sheets appeared in the northern hemisphere about 2.75 million years ago. In the earliest glacial stages, however, establishment of the linkage between ice sheet development and ocean circulation remain largely unclear. Here we show new high-resolution records of marine isotope stage 100 recovered from deep-sea sediments on the Gardar Drift, in the subpolar North Atlantic. Results of a wide range of analyses clearly reveal the influence of millennial-scale variability in iceberg discharge on ocean surface condition and bottom current variability in the subpolar North Atlantic during marine isotope stage 100. We identified eight events of ice-rafted debris, which occurred mostly with decreases in sea surface temperature and in current components indicating North Atlantic Deep Water. These decreases are interpreted by weakened deep water formation linked to iceberg discharge, similarly to observations from the last glacial period. Dolomite fraction of the ice-rafted events in early MIS 100 like the last glacial Heinrich events suggests massive collapse of the Laurentide ice sheet in North America. At the same time, our early glacial data suggest differences from the last glacial period: absence of 1470-year periodicity in the interactions between ice sheets and ocean, and northerly shift of the ice-rafted debris belt. Our high-resolution data largely improve the picture of ice-sheet/ocean interactions on millennial time scales in the early glacial period after major Northern Hemisphere glaciation.

  15. High resolution ice thickness, bed topography, and roughness of a land terminating section of the western Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Lindback, K.; Pettersson, R.; Doyle, S. H.

    We present ice thickness and bed topography maps with high spatial resolution (250-500 m) of a large land terminating section of the western Greenland Ice Sheet. The maps cover the Isunnguata Sermia, Russell, and Leverett outlet glaciers and their catchment areas up to an elevation of ~1,700 m...... the spectral roughness. We see a strong correlation of low roughness values with the ice flow direction; this makes it important to assess the direction of the radar profiles in relation to the flow direction when calculating effective subglacial roughness for an area. Low roughness values and high surface....... There is strong evidence that the subglacial troughs have a preglacial origin, since they are aligned with geological weakness zones in the proglacial area and several lineaments can be traced for long distances underneath the ice sheet....

  16. Simulating the Antarctic ice sheet in the late-Pliocene warm period : PLISMIP-ANT, an ice-sheet model intercomparison project

    NARCIS (Netherlands)

    De Boer, B.|info:eu-repo/dai/nl/304023183; Dolan, A. M.; Bernales, J.; Gasson, E.; Goelzer, Heiko|info:eu-repo/dai/nl/412549123; Golledge, N. R.; Sutter, J.; Huybrechts, P.; Lohmann, G.; Rogozhina, I.; Abe-Ouchi, A.; Saito, F.; Van De Wal, R. S W|info:eu-repo/dai/nl/101899556

    2015-01-01

    In the context of future climate change, understanding the nature and behaviour of ice sheets during warm intervals in Earth history is of fundamental importance. The late Pliocene warm period (also known as the PRISM interval: 3.264 to 3.025 million years before present) can serve as a potential

  17. Antarctic Ice Sheet Discharge Driven by Atmosphere-Ocean Feedbacks Across the Last Glacial Termination

    Science.gov (United States)

    Fogwill, C. J.; Turney, C. S.; Golledge, N. R.; Etheridge, D. M.; Rubino, M.; Thornton, D.; Baker, A.; Weber, M. E.; Woodward, J.; van Ommen, T. D.; Moy, A. D.; Davies, S. M.; Bird, M. I.; Winter, K.; Munksgaard, N.; Menviel, L.; Rootes, C.; Vohra, J.; Rivera, A.; Cooper, A.

    2016-12-01

    Reconstructing the dynamic response of the Antarctic ice sheets to warming during the Last Glacial Termination (LGT; 18,000-11,650 yrs ago) allows us to identify ice-climate feedbacks that could improve future projections1,2. Whilst the sequence of events during this period are reasonably well-known, relatively poor chronological control has precluded precise alignment of ice, atmospheric and marine records2, making it difficult to assess relationships between Antarctic ice-sheet dynamics, climate change and sea-level rise3-5. Here we present results from a highly-resolved `horizontal ice core'6,7 from the Weddell Sea Embayment, which records millennial-scale ice-sheet dynamics across this extensive sector of Antarctica. Counterintuitively, we find ice-sheet surface drawdown of 600 m across the Antarctic Cold Reversal (ACR; 14,600-12,700 yrs ago)5, with stabilisation during the subsequent millennia of atmospheric warming. Earth system and ice-sheet modelling highlights that this response was likely sustained by strong ocean-ice feedbacks4,8; however, the drivers remain uncertain. Given the coincidence of the ice-sheet changes recorded with marked shifts in atmospheric circulation9,10,11we suggest that millennial-scale Antarctic ice-sheet behaviour was initiated and sustained by global atmospheric teleconnections across the LGT. This has important ramifications ice-sheet stability under contemporary climate change, with changing atmospheric and oceanic circulation patterns. 1 Collins, M. et al. in Climate Change 2013: The Physical Science Basis. 2 Weber, M. E. et al. Nature 510, 134-138, (2014). 3 Weaver, A. J., et al., Science 299, 1709-1713, (2003). 4 Golledge, N. R. et al. Nat Commun 5, (2014). 5 Pedro, J. B. et al. Nature Geosci9. 51-55 (2015). 6 Turney, C. S. M. et al. Journal of Quaternary Science 28, 697-704 (2013). 7 Winter, K. et al. Geophys. Res. Lett.43. 5. 2019-2026 (2016). 8 Menviel, L., A. et al., Quaternary Science Reviews 30, 1155-1172 (2011). 9 Hogg

  18. Antarctic timing of surface water changes off Chile and Patagonian ice sheet response.

    Science.gov (United States)

    Lamy, Frank; Kaiser, Jérôme; Ninnemann, Ulysses; Hebbeln, Dierk; Arz, Helge W; Stoner, Joseph

    2004-06-25

    Marine sediments from the Chilean continental margin are used to infer millennial-scale changes in southeast Pacific surface ocean water properties and Patagonian ice sheet extent since the last glacial period. Our data show a clear "Antarctic" timing of sea surface temperature changes, which appear systematically linked to meridional displacements in sea ice, westerly winds, and the circumpolar current system. Proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore, but reveal a variable glacier-response time of up to approximately 1000 years, which may explain some of the current discrepancies among terrestrial records in southern South America.

  19. East Antarctic ice sheet stability recorded in a high-elevation ice-cored moraine

    Science.gov (United States)

    Bader, Nicole A.; Licht, Kathy J.; Kaplan, Michael R.; Kassab, Christine; Winckler, Gisela

    2017-03-01

    reflecting major changes in ice flow path over time, the provenance changes are interpreted to indicate relative stability of the East Antarctic ice sheet, as the Law Glacier tapped into and eroded successively lower stratigraphic units of the Beacon Supergroup. This has important implications for interpreting offshore provenance records.

  20. Radar data offer insights into the state of the Greenland Ice Sheet in the 1970s

    Science.gov (United States)

    Karlsson, Nanna B.; Sørensen, Louise S.; Gudmandsen, Preben; Dall, Jørgen

    2016-04-01

    Ice-penetrating radar is a well-established tool for imaging the interior and the bed of an ice body. The data provide information on ice thickness, but also contain information on englacial stratigraphy, ice flow dynamics and conditions at the interface between ice and the bedrock. During the past two decades, the Greenland Ice Sheet has been extensively measured by radar instruments. However, a large radar dataset has so far been overlooked due to its inaccessibility to modern analysis techniques. This dataset was acquired in the 1970s in a large-scale project that ran over multiple years and covered more than 170,000 km of radar flight lines. While the ice thickness information from the data has subsequently been digitized, the data itself is presently only available as35-mm films, micro-fiche copies of the films and enlarged positives. Here we present the first results from an effort to digitize this unique and rare dataset. We demonstrate how the data may contain valuable information on the state of the Greenland Ice Sheet in the 1970s, a period where observations from the centre of the ice sheet are scarce.

  1. A new programme for monitoring the mass loss of the Greenland ice sheet

    DEFF Research Database (Denmark)

    Ahlstrøm, Andreas P.; Gravesen, Peter; Bech Andersen, Signe

    2008-01-01

    The Greenland ice sheet has been losing mass at a dramatic rate in recent years, raising political concern worldwide due to the possible impact on global sea level rise and climate dynamics (Luthcke et al. 2006; Rignot & Kanagaratnam 2006; Velicogna & Wahr 2006; IPCC 2007; Shepherd & Wingham 2007...... of the Greenland ice sheet, track changes in the extent of local glaciers and ice caps, and track changes in the position of the ice-sheet margin.......The Greenland ice sheet has been losing mass at a dramatic rate in recent years, raising political concern worldwide due to the possible impact on global sea level rise and climate dynamics (Luthcke et al. 2006; Rignot & Kanagaratnam 2006; Velicogna & Wahr 2006; IPCC 2007; Shepherd & Wingham 2007...... for Monitoring of the Green land Ice Sheet (PROMICE), designed and operated by the Geological Survey of Denmark and Greenland (GEUS) in collaboration with the National Space Institute at the Technical University of Denmark and Asiaq (Greenland Survey). The aim of the programme is to quantify the annual mass loss...

  2. Impact of Greenland and Antarctic ice sheet interactions on climate sensitivity

    Energy Technology Data Exchange (ETDEWEB)

    Goelzer, H.; Huybrechts, P. [Vrije Universiteit Brussel, Earth System Sciences and Departement Geografie, Brussels (Belgium); Loutre, M.F.; Goosse, H.; Fichefet, T. [Universite Catholique de Louvain, Georges Lemaitre Centre for Earth and Climate Research (TECLIM), Earth and Life Institute, Louvain-la-Neuve (Belgium); Mouchet, A. [Universite de Liege, Laboratoire de Physique Atmospherique et Planetaire, Liege (Belgium)

    2011-09-15

    We use the Earth system model of intermediate complexity LOVECLIM to show the effect of coupling interactive ice sheets on the climate sensitivity of the model on a millennial time scale. We compare the response to a 2 x CO{sub 2} warming scenario between fully coupled model versions including interactive Greenland and Antarctic ice sheet models and model versions with fixed ice sheets. For this purpose an ensemble of different parameter sets have been defined for LOVECLIM, covering a wide range of the model's sensitivity to greenhouse warming, while still simulating the present-day climate and the climate evolution over the last millennium within observational uncertainties. Additional freshwater fluxes from the melting ice sheets have a mitigating effect on the model's temperature response, leading to generally lower climate sensitivities of the fully coupled model versions. The mitigation is effectuated by changes in heat exchange within the ocean and at the sea-air interface, driven by freshening of the surface ocean and amplified by sea-ice-related feedbacks. The strength of the effect depends on the response of the ice sheets to the warming and on the model's climate sensitivity itself. The effect is relatively strong in model versions with higher climate sensitivity due to the relatively large polar amplification of LOVECLIM. With the ensemble approach in this study we cover a wide range of possible model responses. (orig.)

  3. Significant contribution of insolation to Eemian melting of the Greenland ice sheet

    Science.gov (United States)

    van de Berg, Willem Jan; van den Broeke, Michiel; Ettema, Janneke; van Meijgaard, Erik; Kaspar, Frank

    2011-10-01

    During the Eemian interglacial period, 130,000 to 114,000 years ago, the volume of the Greenland ice sheet was about 30-60% smaller than the present-day volume. Summer temperatures in the Arctic region were about 2-4K higher than today, leading to the suggestion that Eemian conditions could be considered an analogue for future warming, particularly for the future stability of the Greenland ice sheet. However, Northern Hemisphere insolation was much higher during the Eemian than today, which could affect the reliability of this analogy. Here we use a high-resolution regional climate model with a realistic ice-sheet surface representation to assess the surface mass balance of the Greenland ice sheet during the Eemian. Our simulations show that Eemian climate led to an 83% lower surface mass balance, compared with the preindustrial simulation. Our sensitivity experiments show that only about 55% of this change in surface mass balance can be attributed to higher ambient temperatures, with the remaining 45% caused by higher insolation and associated nonlinear feedbacks. We show that temperature-melt relations are dependent on changes in insolation. Hence, we suggest that projections of future Greenland ice loss on the basis of Eemian temperature-melt relations may overestimate the future vulnerability of the ice sheet.

  4. Formation of a wave on an ice-sheet above the dipole, moving in a fluid

    Science.gov (United States)

    Il'ichev, A. T.; Savin, A. A.; Savin, A. S.

    2012-05-01

    Theory of wave motions of a fluid with an ice-sheet was developed due to the necessity of solving of a number of problems of marine and land physics. The main attention in these investigations was focused on propagation and interaction of free waves, and also on appearance of waves under action of different loadings on the ice-sheet. From the other side, the problems dealing with waves on the fluid surface, free from the ice due to motion in the mass of the fluid of rigid bodies, has the known solutions. In this connection, it seems natural to disserminate the formulation and methods of such problems to the case of the fluid with the ice-sheet. In the present note we describe the character of formation of waves from the singularity, localized in the fluid of infinite depth beneath the ice-sheet. We use the example of the dipole, which models a cylinder in the infinite mass of the fluid. The character of the formation does not depend on the type of singularity. The ice-sheet is considered as a thin elastic plate of a constant width, floating on the water surface.

  5. 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.

  6. Acoustic Gravity Waves Generated by an Oscillating Ice Sheet in Arctic Zone

    Science.gov (United States)

    Abdolali, A.; Kadri, U.; Kirby, J. T., Jr.

    2016-12-01

    We investigate the formation of acoustic-gravity waves due to oscillations of large ice blocks, possibly triggered by atmospheric and ocean currents, ice block shrinkage or storms and ice-quakes.For the idealized case of a homogeneous weakly compressible water bounded at the surface by ice sheet and a rigid bed, the description of the infinite family of acoustic modes is characterized by the water depth h and angular frequency of oscillating ice sheet ω ; The acoustic wave field is governed by the leading mode given by: Nmax=\\floor {(ω h)/(π c)} where c is the sound speed in water and the special brackets represent the floor function (Fig1). Unlike the free-surface setting, the higher acoustic modes might exhibit a larger contribution and therefore all progressive acoustic modes have to be considered.This study focuses on the characteristics of acoustic-gravity waves generated by an oscillating elastic ice sheet in a weakly compressible fluid coupled with a free surface model [Abdolali et al. 2015] representing shrinking ice blocks in realistic sea state, where the randomly oriented ice sheets cause inter modal transition and multidirectional reflections. A theoretical solution and a 3D numerical model have been developed for the study purposes. The model is first validated against the theoretical solution [Kadri, 2016]. To overcome the computational difficulties of 3D models, we derive a depth-integrated equation valid for spatially varying ice sheet thickness and water depth. We show that the generated acoustic-gravity waves contribute significantly to deep ocean currents compared to other mechanisms. In addition, these waves travel at the sound speed in water carrying information on ice sheet motion, providing various implications for ocean monitoring and detection of ice-quakes. Fig1:Snapshots of dynamic pressure given by an oscillating ice sheet; h=4500m, c=1500m/s, semi-length b=10km, ζ =1m, omega=π rad/s. Abdolali, A., Kirby, J. T. and Bellotti, G

  7. Implications of changing scattering properties on Greenland ice sheet volume change from Cryosat-2 altimetry

    DEFF Research Database (Denmark)

    Simonsen, Sebastian Bjerregaard; Sørensen, Louise Sandberg

    2017-01-01

    coefficient, and the leading edge width, which are both available in the ESA Cryosat-2 Level-2i data product. Investigations into relocation of radar reflection points are also included. Inter-comparison of the Cryosat-2 derived elevation changes with those derived from Operation IceBridge laser data suggests......Long-term observations of surface elevation change of the Greenland ice sheet (GrIS) is of utmost importance when assessing the state of the ice sheet. Satellite radar altimetry offers a long time series of data over the GrIS, starting with ERS-1 in 1991. ESA's Cryosat-2 mission, launched in 2010......, provides an invaluable radar altimetry dataset for monitoring the current changes of the ice sheets due to its dense spatial and temporal coverage of these areas. Here, we investigate the effects of including different parameters which describe the shape of the return radar waveform (waveform parameters...

  8. Comprehensive spatiotemporal glacier and ice sheet velocity measurements from Landsat 8

    Science.gov (United States)

    Moon, Twila; Fahnestock, Mark; Scambos, Ted; Klinger, Marin; Haran, Terry

    2015-04-01

    Combining newly developed software with Landsat 8 image returns, we are now producing broad-coverage ice velocity measurements on weekly to monthly scales across ice sheets and glaciers. Using new image-to-image cross correlation software, named PyCorr, we take advantage of the improved radiometric resolution of the Landsat 8 panchromatic band to create velocity maps with sub-pixel accuracy. Landsat 8's 12-bit radiometric resolution supports measurement of ice flow in uncrevassed regions based on persistent sastrugi patterns lasting weeks to a few months. We also leverage these improvements to allow for ice sheet surface roughness measurements. Landsat 8's 16-day repeat orbit and increased image acquisition across the Greenland and Antarctic ice sheets supports development of seasonal to annual ice sheet velocity mosaics with full coverage of coastal regions. We also create time series for examining sub-seasonal change with near real time processing in areas such as the Amundsen Sea Embayment and fast flowing Greenland outlet glaciers. In addition, excellent geolocation accuracy enables velocity mapping of smaller ice caps and glaciers, which we have already applied in Alaska and Patagonia. Finally, PyCorr can be used for velocity mapping with other remote sensing imagery, including high resolution WorldView satellite data.

  9. Advances in modelling subglacial lakes and their interaction with the Antarctic ice sheet.

    Science.gov (United States)

    Pattyn, Frank; Carter, Sasha P; Thoma, Malte

    2016-01-28

    Subglacial lakes have long been considered hydraulically isolated water bodies underneath ice sheets. This view changed radically with the advent of repeat-pass satellite altimetry and the discovery of multiple lake discharges and water infill, associated with water transfer over distances of more than 200 km. The presence of subglacial lakes also influences ice dynamics, leading to glacier acceleration. Furthermore, subglacial melting under the Antarctic ice sheet is more widespread than previously thought, and subglacial melt rates may explain the availability for water storage in subglacial lakes and water transport. Modelling of subglacial water discharge in subglacial lakes essentially follows hydraulics of subglacial channels on a hard bed, where ice sheet surface slope is a major control on triggering subglacial lake discharge. Recent evidence also points to the development of channels in deformable sediment in West Antarctica, with significant water exchanges between till and ice. Most active lakes drain over short time scales and respond rapidly to upstream variations. Several Antarctic subglacial lakes exhibit complex interactions with the ice sheet due to water circulation. Subglacial lakes can therefore-from a modelling point of view-be seen as confined small oceans underneath an imbedded ice shelf. © 2015 The Author(s).

  10. Outreach/education interface for Cryosphere models using the Virtual Ice Sheet Laboratory

    Science.gov (United States)

    Larour, E. Y.; Halkides, D. J.; Romero, V.; Cheng, D. L.; Perez, G.

    2014-12-01

    In the past decade, great strides have been made in the development of models capable of projecting the future evolution of glaciers and the polar ice sheets in a changing climate. These models are now capable of replicating some of the trends apparent in satellite observations. However, because this field is just now maturing, very few efforts have been dedicated to adapting these capabilities to education. Technologies that have been used in outreach efforts in Atmospheric and Oceanic sciences still have not been extended to Cryospheric Science. We present a cutting-edge, technologically driven virtual laboratory, geared towards outreach and k-12 education, dedicated to the polar ice sheets on Antarctica and Greenland, and their role as major contributors to sea level rise in coming decades. VISL (Virtual Ice Sheet Laboratory) relies on state-of-the art Web GL rendering of polar ice sheets, Android/iPhone and web portability using Javascript, as well as C++ simulations (back-end) based on the Ice Sheet System Model, the NASA model for simulating the evolution of polar ice sheets. Using VISL, educators and students can have an immersive experience into the world of polar ice sheets, while at the same exercising the capabilities of a state-of-the-art climate model, all of it embedded into an education experience that follows the new STEM standards for education.This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

  11. Heterogeneous Heat Flow and Groundwater Effects on East Antarctic Ice Sheet Dynamics

    Science.gov (United States)

    Gooch, B. T.; Soderlund, K. M.; Young, D. A.; Blankenship, D. D.

    2015-12-01

    We present the results numerical models describing the potential contributions groundwater and heterogeneous heat sources might have on ice dynamics. A two-phase, 1D hydrothermal model demonstrates the importance of groundwater flow in heat flux advection near the ice-bed interface. Typical, conservative vertical groundwater volume fluxes on the order of +/- 1-10 mm/yr can alter vertical heat flux by +/- 50-500 mW/m2 that could produce considerable volumes of meltwater depending on basin geometry and geothermal heat production. A 1D hydromechanical model demonstrates that during ice advance groundwater is mainly recharged into saturated sedimentary aquifers and during retreat groundwater discharges into the ice-bed interface, potentially contributing to subglacial water budgets on the order of 0.1-1 mm/yr during ice retreat. A map of most-likely elevated heat production provinces, estimated sedimentary basin depths, and radar-derived bed roughness are compared together to delineate areas of greatest potential to ice sheet instability in East Antarctica. Finally, a 2D numerical model of crustal fluid and heat flow typical to recently estimated sedimentary basins under the East Antarctic Ice Sheet is coupled to a 2.5D Full Stokes ice sheet model (with simple basal hydrology) to test for the sensitivity of hydrodynamic processes on ice sheet dynamics. Preliminary results show that the enhanced fluid flow can dramatically alter the basal heating of the ice and its temperature profile, as well as, the sliding rate, which heavily alter ice dynamics.

  12. Sources, cycling and export of nitrogen on the Greenland Ice Sheet

    Directory of Open Access Journals (Sweden)

    J. L. Wadham

    2016-11-01

    Full Text Available Fjord and continental shelf environments in the polar regions are host to some of the planet's most productive ecosystems and support economically important fisheries. Their productivity, however, is often critically dependent upon nutrient supply from upstream terrestrial environments delivered via river systems. In glacially fed coastal ecosystems, riverine nutrients are largely sourced from melting snow and ice. The largest and most extensive glacially fed coastal ecosystem in the Arctic is that bordering the Greenland Ice Sheet. The future primary productivity of this ecosystem, however, is uncertain. A potential increase in primary productivity driven by reduced sea ice extent and associated increased light levels may be curtailed by insufficient nutrient supply, and specifically nitrogen. Research on small valley glaciers indicates that glaciers are important sources of nitrogen to downstream environments. However, no data exist from ice sheet systems such as Greenland. Time series of nitrogen concentrations in runoff are documented from a large Greenland glacier, demonstrating seasonally elevated fluxes to the ocean. Fluxes are highest in mid-summer, when nitrogen limitation is commonly reported in coastal waters. It is estimated that approximately half of the glacially exported nitrogen is sourced from microbial activity within glacial sediments at the surface and bed of the ice sheet, doubling nitrogen fluxes in runoff. Summer dissolved inorganic nitrogen fluxes from the Greenland Ice Sheet (30–40 Gg are a similar order of magnitude to those from a large Arctic river (Holmes et al., 2012. Nitrogen yields from the ice sheet (236 kg TDN km−2 a−1, however, are approximately double those from Arctic riverine catchments. We assert that this ice sheet nitrogen subsidy to Arctic coastal ecosystems may be important for understanding coastal biodiversity, productivity and fisheries and should be considered in future

  13. Sources, cycling and export of nitrogen on the Greenland Ice Sheet

    Science.gov (United States)

    Wadham, Jemma Louise; Hawkings, Jonathan; Telling, Jon; Chandler, Dave; Alcock, Jon; O'Donnell, Emily; Kaur, Preeti; Bagshaw, Elizabeth; Tranter, Martyn; Tedstone, Andre; Nienow, Peter

    2016-11-01

    Fjord and continental shelf environments in the polar regions are host to some of the planet's most productive ecosystems and support economically important fisheries. Their productivity, however, is often critically dependent upon nutrient supply from upstream terrestrial environments delivered via river systems. In glacially fed coastal ecosystems, riverine nutrients are largely sourced from melting snow and ice. The largest and most extensive glacially fed coastal ecosystem in the Arctic is that bordering the Greenland Ice Sheet. The future primary productivity of this ecosystem, however, is uncertain. A potential increase in primary productivity driven by reduced sea ice extent and associated increased light levels may be curtailed by insufficient nutrient supply, and specifically nitrogen. Research on small valley glaciers indicates that glaciers are important sources of nitrogen to downstream environments. However, no data exist from ice sheet systems such as Greenland. Time series of nitrogen concentrations in runoff are documented from a large Greenland glacier, demonstrating seasonally elevated fluxes to the ocean. Fluxes are highest in mid-summer, when nitrogen limitation is commonly reported in coastal waters. It is estimated that approximately half of the glacially exported nitrogen is sourced from microbial activity within glacial sediments at the surface and bed of the ice sheet, doubling nitrogen fluxes in runoff. Summer dissolved inorganic nitrogen fluxes from the Greenland Ice Sheet (30-40 Gg) are a similar order of magnitude to those from a large Arctic river (Holmes et al., 2012). Nitrogen yields from the ice sheet (236 kg TDN km-2 a-1), however, are approximately double those from Arctic riverine catchments. We assert that this ice sheet nitrogen subsidy to Arctic coastal ecosystems may be important for understanding coastal biodiversity, productivity and fisheries and should be considered in future biogeochemical modelling studies of coastal

  14. Subglacial lake and meltwater flow predictions of the last North American and European Ice Sheets

    Science.gov (United States)

    Livingstone, S. J.; Clark, C. D.; Tarasov, L.

    2012-04-01

    There is increasing recognition that subglacial lakes act as key components within the ice sheet system, capable of influencing ice-sheet topography, ice volume and ice flow. The subglacial water systems themselves are recognised as being both active and dynamic, with large discharges of meltwater capable of flowing down hydrological pathways both between lakes and to the ice-sheet margins. At present, much glaciological research is concerned with the role of modern subglacial lake systems in Antarctica. Another approach to the exploration of subglacial lakes involves identification of the geological record of subglacial lakes that once existed beneath ice sheets of the last glaciation. Investigation of such palaeo-subglacial lakes offers significant advantages because we have comprehensive information about the bed properties, they are much more accessible and we can examine and sample the sediments with ease. If we can find palaeo-subglacial lakes then we have the potential to advance understanding with regard to the topographic context and hydrological pathways that the phenomena form a part of; essentially we gain spatial and sedimentological information in relation to investigations of contemporary subglacial lakes and lose out on the short-time dynamics. In this work we present predictions of palaeo-subglacial lakes and meltwater drainage pathways under the former European and North American ice sheets during the last glaciation. We utilise data on the current topography and seafloor bathymetry, and elevation models of the ice and ground surface topography (interpolated to a 5 km grid) to calculate the hydraulic potential surface at the ice-sheet bed. Meltwater routing algorithms and the flooding of local hydraulic minima allow us to predict subglacial channels and lakes respectively. Given that specific ice-surface and bed topographies are only known from modelled outputs, and thus contain significant uncertainty, we utilise many such outputs to examine

  15. Spatial analysis of freeze-on plumes within the Greenland ice-sheet

    Science.gov (United States)

    Leysinger Vieli, Gwendolyn J.-M. C.

    2017-04-01

    Large, englacial, near-basal, plume-like structures have been observed in recent radio echo sounding surveys over the Greenland and Antarctica ice-sheet. The mechanism behind the formation is not fully understood. However, these features may be caused by a range of factors and processes, such as ice dynamics, basal conditions, ice rheology and transient ice-sheet history. Here I will, by means of a spatial analysis, identify and quantify factors related to these plume-like structures. I use data sets such as bed and surface topographies, as well as parameters obtained from these surfaces (e.g. ice flow and velocities, surface slopes, accumulation rates) and estimated geothermal heat fluxes. This allows me to investigate potential constraints and relationships between the observed complex, near-basal layer structures and the prevailing spatial conditions. The results of this analysis are consistent with the existing hypothesis of basal freeze-on.

  16. Improving volume loss estimates of the northwestern Greenland Ice Sheet 2002-2010

    DEFF Research Database (Denmark)

    Korsgaard, Niels Jákup; Khan, Shfaqat Abbas; Kjeldsen, Kristian Kjellerup

    during 2003-2009 using Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data (Zwally, 2011). Elevation changes are often reported to be largest near the frontal portion of outlet glaciers. However, due to relative large spacing between tracks, ICESat does not capture elevation change...... on all glaciers, which leads to an underestimation of the catchment-wide volume change. To improve the volume change estimate, we supplement ICESat data with altimeter surveys from NASA's Airborne Topographic Mapper (ATM) during 2002-2010 (Krabill, 2011) and NASA’s Land, Vegetation, and Ice Sensor (LVIS......Studies have been carried out using various methods to estimate the Greenland ice sheet mass balance. Remote sensing techniques used to determine the ice sheet volume includes airborne and satellite radar and laser methods and measurements of ice flow of outlet glaciers use InSAR satellite radar...

  17. Radar Interferometer for Topographic Mapping of Glaciers and Ice Sheets

    Science.gov (United States)

    Moller, Delwyn K.; Sadowy, Gregory A.; Rignot, Eric J.; Madsen, Soren N.

    2007-01-01

    A report discusses Ka-band (35-GHz) radar for mapping the surface topography of glaciers and ice sheets at high spatial resolution and high vertical accuracy, independent of cloud cover, with a swath-width of 70 km. The system is a single- pass, single-platform interferometric synthetic aperture radar (InSAR) with an 8-mm wavelength, which minimizes snow penetration while remaining relatively impervious to atmospheric attenuation. As exhibited by the lower frequency SRTM (Shuttle Radar Topography Mission) AirSAR and GeoSAR systems, an InSAR measures topography using two antennas separated by a baseline in the cross-track direction, to view the same region on the ground. The interferometric combination of data received allows the system to resolve the pathlength difference from the illuminated area to the antennas to a fraction of a wavelength. From the interferometric phase, the height of the target area can be estimated. This means an InSAR system is capable of providing not only the position of each image point in along-track and slant range as with a traditional SAR but also the height of that point through interferometry. Although the evolution of InSAR to a millimeter-wave center frequency maximizes the interferometric accuracy from a given baseline length, the high frequency also creates a fundamental problem of swath coverage versus signal-to-noise ratio. While the length of SAR antennas is typically fixed by mass and stowage or deployment constraints, the width is constrained by the desired illuminated swath width. As the across-track beam width which sets the swath size is proportional to the wavelength, a fixed swath size equates to a smaller antenna as the frequency is increased. This loss of antenna size reduces the two-way antenna gain to the second power, drastically reducing the signal-to-noise ratio of the SAR system. This fundamental constraint of high-frequency SAR systems is addressed by applying digital beam-forming (DBF) techniques to

  18. Improving volume loss estimate of the Greenland Ice Sheet between 2002-2012

    Science.gov (United States)

    Khan, Shfaqat Abbas; Wahr, John

    2013-04-01

    Ice loss from the Greenland Ice Sheet is dominated by loss in the marginal areas. Dynamic induced ice loss and its associated ice surface lowering is often largest close to the glacier calving front and may vary from rates of tens of meters per years to a few meters per year over relatively short distances. Hence, high spatial resolution data are required to accurately estimate volume changes. We estimate ice volume change rate of the Greenland ice sheet during 2003-2009 using Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data (Zwally et al., 2011). To improve the volume change estimate we supplement ICESat data with altimeter surveys from NASA's Airborne Topographic Mapper (ATM) during 2002-2010 (Krabill et al., 2011) and NASA's Land, Vegetation and Ice Sensor (LVIS) during 2007-2010 (Blair and Hofton, 2010). The Airborne data are mainly concentrated along the ice margin and therefore significantly improve the estimate of the total volume change. Our results show that adding ATM and LVIS data to the ICESat data increases the estimate of catchment-wide ice volume loss in northeast and southeast Greenland by 10-20 percent. This is mainly due to increased volume loss near the margin of the GrIS. Furthermore, we provide volume loss estimates during 2002-2009 and 2009-2012. Our 2009-2012 estimate suggest enhanced volume loss at the entire southern half of the GrIS.

  19. Glacial removal of late Cenozoic subglacially emplaced volcanic edifices by the West Antarctic ice sheet

    Science.gov (United States)

    Behrendt, John C.; Blankenship, D.D.; Damaske, D.; Cooper, A. K.

    1995-01-01

    Local maxima of the horizontal gradient of pseudogravity from closely spaced aeromagnetic surveys over the Ross Sea, northwestern Ross Ice Shelf, and the West Antarctic ice sheet, reveal a linear magnetic rift fabric and numerous subcircular, high-amplitude anomalies. Geophysical data indicate two or three youthful volcanic edifices at widely separated areas beneath the sea and ice cover in the West Antarctic rift system. In contrast, we suggest glacial removal of edifices of volcanic sources of many more anomalies. Magnetic models, controlled by marine seismic reflection and radar ice-sounding data, allow us to infer that glacial removal of the associated late Cenozoic volcanic edifices (probably debris, comprising pillow breccias, and hyaloclastites) has occurred essentially concomitantly with their subglacial eruption. "Removal' of unconsolidated volcanic debris erupted beneath the ice is probably a more appropriate term than "erosion', given its fragmented, ice-contact origin. The exposed volcanoes may have been protected from erosion by the surrounding ice sheet because of more competent rock or high elevation above the ice sheet. -from Authors

  20. Exposed subsurface ice sheets in the Martian mid-latitudes.

    Science.gov (United States)

    Dundas, Colin M; Bramson, Ali M; Ojha, Lujendra; Wray, James J; Mellon, Michael T; Byrne, Shane; McEwen, Alfred S; Putzig, Nathaniel E; Viola, Donna; Sutton, Sarah; Clark, Erin; Holt, John W

    2018-01-12

    Thick deposits cover broad regions of the Martian mid-latitudes with a smooth mantle; erosion in these regions creates scarps that expose the internal structure of the mantle. We investigated eight of these locations and found that they expose deposits of water ice that can be >100 meters thick, extending downward from depths as shallow as 1 to 2 meters below the surface. The scarps are actively retreating because of sublimation of the exposed water ice. The ice deposits likely originated as snowfall during Mars' high-obliquity periods and have now compacted into massive, fractured, and layered ice. We expect the vertical structure of Martian ice-rich deposits to preserve a record of ice deposition and past climate. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  1. Spatial pattern of mass loss processes across the Greenland Ice Sheet from the Little Ice Age to 2010

    DEFF Research Database (Denmark)

    Kjaer, K. H.; Korsgaard, N. J.; Kjeldsen, K. K.

    of the LIA, which enables us to obtain vertical point-based differences associated with former ice extent. These point measurements are combined with contemporary ice surface differences derived using NASA's Airborne Topographic Mapper (ATM) from 2003-2010, NASA's Ice, Cloud, and land Elevation Satellite...... (ICESat) from 2003-2009, NASA's Land, Vegetation, and Ice Sensor (LVIS) from 2010, and ASTER (Silcast AST14DMO) co-registered to ICESat, to estimate mass loss throughout the 20th and early 21st Century. The mass balance estimates of the GrIS since retreat from maximum LIA is combined with a SMB model......The Greenland Ice Sheet loses mass through surface meltwater runoff and discharge from marine terminating outlet glaciers. The spatial variability and magnitude of these processes have been studied and described in detail for the past decades. Here, we combine the mass loss between the LIA to 2010...

  2. Ice-rafting from the British-Irish ice sheet since the earliest Pleistocene (2.6 million years ago): implications for long-term mid-latitudinal ice-sheet growth in the North Atlantic region

    NARCIS (Netherlands)

    Thierens, M.; Pirlet, H.; Colin, C.; Latruwe, K.; Vanhaecke, F.; Lee, J.R.; Stuut, J.-B.; Titschaeck, J.; Titschack, J.; Huvenne, V.; Dorschel, B.; Wheeler, A.J.; Henriet, J.P.

    2012-01-01

    The Plio-Pleistocene intensification of Northern Hemisphere continental ice-sheet development is known to have profoundly affected the global climate system. Evidence for early continental glaciation is preserved in sediments throughout the North Atlantic Ocean, where ice-rafted detritus (IRD)

  3. On the Reconstruction of Palaeo-Ice Sheets: Recent Advances and Future Challenges

    Science.gov (United States)

    Stokes, Chris R.; Tarasov, Lev; Blomdin, Robin; Cronin, Thomas M.; Fisher, Timothy G.; Gyllencreutz, Richard; Hattestrand, Clas; Heyman, Jacob; Hindmarsh, Richard C. A.; Hughes, Anna L. C.; hide

    2015-01-01

    Reconstructing the growth and decay of palaeo-ice sheets is critical to understanding mechanisms of global climate change and associated sea-level fluctuations in the past, present and future. The significance of palaeo-ice sheets is further underlined by the broad range of disciplines concerned with reconstructing their behaviour, many of which have undergone a rapid expansion since the 1980s. In particular, there has been a major increase in the size and qualitative diversity of empirical data used to reconstruct and date ice sheets, and major improvements in our ability to simulate their dynamics in numerical ice sheet models. These developments have made it increasingly necessary to forge interdisciplinary links between sub-disciplines and to link numerical modelling with observations and dating of proxy records. The aim of this paper is to evaluate recent developments in the methods used to reconstruct ice sheets and outline some key challenges that remain, with an emphasis on how future work might integrate terrestrial and marine evidence together with numerical modelling. Our focus is on pan-ice sheet reconstructions of the last deglaciation, but regional case studies are used to illustrate methodological achievements, challenges and opportunities. Whilst various disciplines have made important progress in our understanding of ice-sheet dynamics, it is clear that data-model integration remains under-used, and that uncertainties remain poorly quantified in both empirically-based and numerical ice-sheet reconstructions. The representation of past climate will continue to be the largest source of uncertainty for numerical modelling. As such, palaeo-observations are critical to constrain and validate modelling. State-of-the-art numerical models will continue to improve both in model resolution and in the breadth of inclusion of relevant processes, thereby enabling more accurate and more direct comparison with the increasing range of palaeo-observations. Thus

  4. Last Interglacial climate and sea-level evolution from a coupled ice sheet-climate model

    Science.gov (United States)

    Goelzer, Heiko; Huybrechts, Philippe; Loutre, Marie-France; Fichefet, Thierry

    2016-12-01

    As the most recent warm period in Earth's history with a sea-level stand higher than present, the Last Interglacial (LIG, ˜ 130 to 115 kyr BP) is often considered a prime example to study the impact of a warmer climate on the two polar ice sheets remaining today. Here we simulate the Last Interglacial climate, ice sheet, and sea-level evolution with the Earth system model of intermediate complexity LOVECLIM v.1.3, which includes dynamic and fully coupled components representing the atmosphere, the ocean and sea ice, the terrestrial biosphere, and the Greenland and Antarctic ice sheets. In this setup, sea-level evolution and climate-ice sheet interactions are modelled in a consistent framework.Surface mass balance change governed by changes in surface meltwater runoff is the dominant forcing for the Greenland ice sheet, which shows a peak sea-level contribution of 1.4 m at 123 kyr BP in the reference experiment. Our results indicate that ice sheet-climate feedbacks play an important role to amplify climate and sea-level changes in the Northern Hemisphere. The sensitivity of the Greenland ice sheet to surface temperature changes considerably increases when interactive albedo changes are considered. Southern Hemisphere polar and sub-polar ocean warming is limited throughout the Last Interglacial, and surface and sub-shelf melting exerts only a minor control on the Antarctic sea-level contribution with a peak of 4.4 m at 125 kyr BP. Retreat of the Antarctic ice sheet at the onset of the LIG is mainly forced by rising sea level and to a lesser extent by reduced ice shelf viscosity as the surface temperature increases. Global sea level shows a peak of 5.3 m at 124.5 kyr BP, which includes a minor contribution of 0.35 m from oceanic thermal expansion. Neither the individual contributions nor the total modelled sea-level stand show fast multi-millennial timescale variations as indicated by some reconstructions.

  5. Greenland ice sheet surface temperature, melt and mass loss: 2000-06

    Science.gov (United States)

    Hall, D.K.; Williams, R.S.; Luthcke, S.B.; DiGirolamo, N.E.

    2008-01-01

    A daily time series of 'clear-sky' surface temperature has been compiled of the Greenland ice sheet (GIS) using 1 km resolution moderate-resolution imaging spectroradiometer (MODIS) land-surface temperature (LST) maps from 2000 to 2006. We also used mass-concentration data from the Gravity Recovery and Climate Experiment (GRACE) to study mass change in relationship to surface melt from 2003 to 2006. The mean LST of the GIS increased during the study period by ???0.27??Ca-1. The increase was especially notable in the northern half of the ice sheet during the winter months. Melt-season length and timing were also studied in each of the six major drainage basins. Rapid (melt begins. Initiation of large-scale surface melt was followed rapidly by mass loss. This indicates that surface meltwater is flowing rapidly to the base of the ice sheet, causing acceleration of outlet glaciers, thus highlighting the metastability of parts of the GIS and the vulnerability of the ice sheet to air-temperature increases. If air temperatures continue to rise over Greenland, increased surface melt will play a large role in ice-sheet mass loss.

  6. Spaceborne measurement of Greenland ice sheet changes: the ESA Greenland CCI project

    DEFF Research Database (Denmark)

    Forsberg, René; Sørensen, Louise Sandberg; Meister, Rakia

    The ESA “Greenland_ice_sheet_cci” project is currently making past and present space measurements of Greenland ice sheet changes available for use by scientists, stakeholders and the general public. The data are part of a large set of ECV’s (Essential Climate Variables) made available by the ESA...... Climate Initiative, as a contribution to the global Climate Observing System. The ECV data produced for the Greenlandice sheet include detailed grids of elevation changes and ice flow velocities, as well as line data of grounding lines and calving front locations for major outlet glaciers. The “ice_sheets......_cci” goal is to generate a consistent, validated, long-term and timely set of ECV’s, a.o. to improve the impact of satellite data on climate research and coupled ice sheet/climate models. Special focus is on use of data from ESA missions such as ERS, Envisat and the new Sentinel missions, but in the 2nd...

  7. The Influence of 3-D Earth Structure on a Coupled Antarctic Ice Sheet - Sea Level Model

    Science.gov (United States)

    Gomez, N. A.; Latychev, K.; Pollard, D.

    2016-12-01

    Earth structure beneath the Antarctic Ice Sheet is characterized by significant lateral variability. A stable, thick craton exists in the east, while the west is underlain by a large continental rift system and a relatively thin lithosphere. Moreover, high-resolution seismic tomography indicates slow wave speeds in the shallow mantle below WAIS, suggesting a hot, low viscosity asthenosphere. Variations in viscoelastic Earth structure alter the timing and geometry of load-induced Earth deformation, which in turn impacts the timing and extent of the ice-sheet retreat via a sea-level feedback (Gomez et al., EPSL, 2013, Nature Comm. 2015), as well as predictions of relative sea-level change and present-day crustal deformation rates. We present simulations with a coupled Antarctic ice sheet - sea level model that incorporates 3-D variations in Earth structure. Our 3-D Earth model is derived from recent seismic tomographic datasets (Heeszel et al., JGR, 2016; An et al., JGR, 2015) and incorporates lateral variations in lithospheric thickness and mantle viscosity across the Antarctic continent of more than 100 km, and several orders of magnitude, respectively. We apply this 3-D coupled model to simulate sea level change, solid Earth deformation and ice-sheet evolution in the Antarctic region through the last deglaciation and into the future. We identify the regions and time periods in which the incorporation of 3-D Earth structure is critical for accurate predictions of ice sheet evolution and interpretation of geological and geodetic observations.

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

    Science.gov (United States)

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

    2017-04-01

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

  9. Leveraging Cloud Technology to Provide a Responsive, Reliable and Scalable Backend for the Virtual Ice Sheet Laboratory Using the Ice Sheet System Model and Amazon's Elastic Compute Cloud

    Science.gov (United States)

    Perez, G. L.; Larour, E. Y.; Halkides, D. J.; Cheng, D. L. C.

    2015-12-01

    The Virtual Ice Sheet Laboratory(VISL) is a Cryosphere outreach effort byscientists at the Jet Propulsion Laboratory(JPL) in Pasadena, CA, Earth and SpaceResearch(ESR) in Seattle, WA, and the University of California at Irvine (UCI), with the goal of providing interactive lessons for K-12 and college level students,while conforming to STEM guidelines. At the core of VISL is the Ice Sheet System Model(ISSM), an open-source project developed jointlyat JPL and UCI whose main purpose is to model the evolution of the polar ice caps in Greenland and Antarctica. By using ISSM, VISL students have access tostate-of-the-art modeling software that is being used to conduct scientificresearch by users all over the world. However, providing this functionality isby no means simple. The modeling of ice sheets in response to sea and atmospheric temperatures, among many other possible parameters, requiressignificant computational resources. Furthermore, this service needs to beresponsive and capable of handling burst requests produced by classrooms ofstudents. Cloud computing providers represent a burgeoning industry. With majorinvestments by tech giants like Amazon, Google and Microsoft, it has never beeneasier or more affordable to deploy computational elements on-demand. This isexactly what VISL needs and ISSM is capable of. Moreover, this is a promisingalternative to investing in expensive and rapidly devaluing hardware.

  10. Cosmogenic nuclide age estimate for Laurentide Ice Sheet recession from the terminal moraine, New Jersey, USA, and constraints on latest Pleistocene ice sheet history

    Science.gov (United States)

    Corbett, Lee B.; Bierman, Paul R.; Stone, Byron D.; Caffee, Marc W.; Larsen, Patrick L.

    2017-01-01

    The time at which the Laurentide Ice Sheet reached its maximum extent and subsequently retreated from its terminal moraine in New Jersey has been constrained by bracketing radiocarbon ages on preglacial and postglacial sediments. Here, we present measurements of in situ produced 10Be and 26Al in 16 quartz-bearing samples collected from bedrock outcrops and glacial erratics just north of the terminal moraine in north-central New Jersey; as such, our ages represent a minimum limit on the timing of ice recession from the moraine. The data set includes field and laboratory replicates, as well as replication of the entire data set five years after initial measurement. We find that recession of the Laurentide Ice Sheet from the terminal moraine in New Jersey began before 25.2±2.1 ka (10Be, n=16, average, 1 standard deviation). This cosmogenic nuclide exposure age is consistent with existing limiting radiocarbon ages in the study area and cosmogenic nuclide exposure ages from the terminal moraine on Martha’s Vineyard ~300 km to the northeast. The age we propose for Laurentide Ice Sheet retreat from the New Jersey terminal position is broadly consistent with regional and global climate records of the last glacial maximum termination and records of fluvial incision.

  11. Antarctic and Greenland ice sheet mass balance products from satellite gravimetry

    Science.gov (United States)

    Horwath, Martin; Groh, Andreas; Horvath, Alexander; Forsberg, René; Meister, Rakia; Barletta, Valentina R.; Shepherd, Andrew

    2017-04-01

    Because of their important role in the Earth's climate system, ESA's Climate Change Initiative (CCI) has identified both the Antarctic Ice Sheet (AIS) and the Greenland Ice Sheet (GIS) as Essential Climate Variables (ECV). Since respondents of a user survey indicated that the ice sheet mass balance is one of the most important ECV data products needed to better understand climate change, the AIS_cci and the GIS_cci project provide Gravimetric Mass Balance (GMB) products based on satellite gravimetry data. The GMB products are derived from GRACE (Gravity Recovery and Climate Experiment) monthly solutions of release ITSG-Grace2016 produced at TU Graz. GMB basin products (i.e. time series of monthly mass changes for the entire ice sheets and selected drainage basins) and GMB gridded products (e.g. mass balance estimates with a formal resolution of about 50km, covering the entire ice sheets) are generated for the period from 2002 until present. The first GMB product was released in mid 2016. Here we present an extended and updated version of the ESA CCI GMB products, which are freely available through data portals hosted by the projects (https://data1.geo.tu-dresden.de/ais_gmb, http://products.esa-icesheets-cci.org/products/downloadlist/GMB). Since the initial product release, the applied processing strategies have been improved in order to further reduce GRACE errors and to enhance the separation of signals super-imposed to the ice mass changes. While a regional integration approach is used by the AIS_cci project, the GMB products of the GIS_cci project are derived using a point mass inversion. The differences between both approaches are investigated through the example of the GIS, where an alternative GMB product was generated using the regional integration approach implemented by the AIS_cci. Finally, we present the latest mass balance estimates for both ice sheets as well as their corresponding contributions to global sea level rise.

  12. Determining Sliding Velocity and Shear-Strain Magnitude From Basal Sediments of Past Ice Sheets

    Science.gov (United States)

    Iverson, N. R.; Hooyer, T. S.; Thomason, J. F.

    2004-12-01

    Ice sheets slide over their basal sediments and commonly deform them. Despite meticulous description of such sediments, they have not been used to estimate rates or magnitudes of basal motion. Thus, although a common assertion is that modeling of past ice sheets can benefit from studies of basal sediments, their actual utility in modeling studies has been minimal. We have developed methods for estimating sliding velocity and till shear-strain magnitude from basal sediments of past ice sheets. The first method involves balancing shear traction on clasts that have plowed through the bed surface with resistance to plowing provided by the bed. The shear traction on clasts is provided by the sliding theory of Lliboutry, and plowing resistance is estimated using a geotechnical theory of cone penetration. The result is an expression for sliding speed of a past ice sheet that depends only on the size distribution of clasts that plowed and the thermomechanical properties of ice and clasts. This method was applied to sizes of clasts that plowed through outwash near Peoria, Illinois, to estimate the sliding speed of the Illinoian ice sheet in that area: 60-170 m/a. The second method involves shearing till in laboratory experiments to study the evolution of till microstructural properties as a function of shear-strain magnitude. Microstructural anisotropy is quantified by collecting multiple intact samples (20 mm cubes) and determining the strength of fabric defined by principal directions of magnetic susceptibility. These directions depend on alignment of needle-shaped magnetite grains. Fabrics formed by directions of maximum susceptibility do not become steady until shear strains of 20-50. Therefore, laboratory calibrations of fabric strength to shear-strain magnitude allow the extent of bed deformation to be determined from susceptibility fabrics of basal till. These studies can provide quantitative inputs to ice-sheet models that have been unavailable previously.

  13. Polar ice sheets during the Cretaceous? Insights from coupled numerical modelling.

    Science.gov (United States)

    Ladant, Jean-Baptiste; Donnadieu, Yannick

    2017-04-01

    Most proxy estimates of Cretaceous climates reveal oceanic and terrestrial temperatures substantially warmer than modern's. Fossils of crocodilian species and remains of what is now low-latitude flora have been unearthed in polar locations. On top of that, direct evidence of polar ice sheets have yet to be found. The Cretaceous has thus historically been considered as a long and stable period of supergreenhouse with elevated CO2 levels. Since a couple of decades however, studies have suggested that dynamical climatic variations affect the Cretaceous greenhouse, in particular with the episodic growth of ephemeral polar ice sheets, for which indirect evidence have been argued for. In addition, new estimates of CO2 levels suggest more modest values (400 - 1500 ppm), potentially in the range of those in place during Cenozoic glaciations. Here, we use a suite of models of climate and ice sheets to investigate the impact of the changing palaeogeography during the Middle-Late Cretaceous (120 - 70 Ma) on the development of ice sheets on polar latitudes. We show that palaeogeography alone, through a series of complex feedbacks, has the potential to significantly alter the CO2 threshold for the onset of ice sheets, nucleating in particular at higher CO2 concentrations in the Aptian ( 800 ppm) and the Maastrichtian ( 700 ppm) than in the Cenomanian-Turonian ( 400 ppm). Our simulations demonstrate notably that part of the Cenomanian-Turonian climatic optimum can be explained by its specific palaeogeography and support the vision of an ice-free Earth during this stage. In addition, our numerical work derives Aptian and Maastrichtian glacial CO2 threshold that are in the range of latest data compilations, thus adding to the growing body of evidence suggesting that ice sheets were once present during these stages.

  14. Pan-ice-sheet glacier terminus change in East Antarctica reveals sensitivity of Wilkes Land to sea-ice changes.

    Science.gov (United States)

    Miles, Bertie W J; Stokes, Chris R; Jamieson, Stewart S R

    2016-05-01

    The dynamics of ocean-terminating outlet glaciers are an important component of ice-sheet mass balance. Using satellite imagery for the past 40 years, we compile an approximately decadal record of outlet-glacier terminus position change around the entire East Antarctic Ice Sheet (EAIS) marine margin. We find that most outlet glaciers retreated during the period 1974-1990, before switching to advance in every drainage basin during the two most recent periods, 1990-2000 and 2000-2012. The only exception to this trend was in Wilkes Land, where the majority of glaciers (74%) retreated between 2000 and 2012. We hypothesize that this anomalous retreat is linked to a reduction in sea ice and associated impacts on ocean stratification, which increases the incursion of warm deep water toward glacier termini. Because Wilkes Land overlies a large marine basin, it raises the possibility of a future sea level contribution from this sector of East Antarctica.

  15. Pan–ice-sheet glacier terminus change in East Antarctica reveals sensitivity of Wilkes Land to sea-ice changes

    Science.gov (United States)

    Miles, Bertie W. J.; Stokes, Chris R.; Jamieson, Stewart S. R.

    2016-01-01

    The dynamics of ocean-terminating outlet glaciers are an important component of ice-sheet mass balance. Using satellite imagery for the past 40 years, we compile an approximately decadal record of outlet-glacier terminus position change around the entire East Antarctic Ice Sheet (EAIS) marine margin. We find that most outlet glaciers retreated during the period 1974–1990, before switching to advance in every drainage basin during the two most recent periods, 1990–2000 and 2000–2012. The only exception to this trend was in Wilkes Land, where the majority of glaciers (74%) retreated between 2000 and 2012. We hypothesize that this anomalous retreat is linked to a reduction in sea ice and associated impacts on ocean stratification, which increases the incursion of warm deep water toward glacier termini. Because Wilkes Land overlies a large marine basin, it raises the possibility of a future sea level contribution from this sector of East Antarctica. PMID:27386519

  16. Quantification of the Greenland ice sheet contribution to Last Interglacial sea level rise

    Directory of Open Access Journals (Sweden)

    E. J. Stone

    2013-03-01

    Full Text Available During the Last Interglacial period (~ 130–115 thousand years ago the Arctic climate was warmer than today, and global mean sea level was probably more than 6.6 m higher. However, there are large discrepancies in the estimated contributions to this sea level change from various sources (the Greenland and Antarctic ice sheets and smaller ice caps. Here, we determine probabilistically the likely contribution of Greenland ice sheet melt to Last Interglacial sea level rise, taking into account ice sheet model parametric uncertainty. We perform an ensemble of 500 Glimmer ice sheet model simulations forced with climatologies from the climate model HadCM3, and constrain the results with palaeodata from Greenland ice cores. Our results suggest a 90% probability that Greenland ice melt contributed at least 0.6 m, but less than 10% probability that it exceeded 3.5 m, a value which is lower than several recent estimates. Many of these previous estimates, however, did not include a full general circulation climate model that can capture atmospheric circulation and precipitation changes in response to changes in insolation forcing and orographic height. Our combined modelling and palaeodata approach suggests that the Greenland ice sheet is less sensitive to orbital forcing than previously thought, and it implicates Antarctic melt as providing a substantial contribution to Last Interglacial sea level rise. Future work should assess additional uncertainty due to inclusion of basal sliding and the direct effect of insolation on surface melt. In addition, the effect of uncertainty arising from climate model structural design should be taken into account by performing a multi-climate-model comparison.

  17. Coupled Northern Hemisphere permafrost–ice-sheet evolution over the last glacial cycle

    Directory of Open Access Journals (Sweden)

    M. Willeit

    2015-09-01

    Full Text Available Permafrost influences a number of processes which are relevant for local and global climate. For example, it is well known that permafrost plays an important role in global carbon and methane cycles. Less is known about the interaction between permafrost and ice sheets. In this study a permafrost module is included in the Earth system model CLIMBER-2, and the coupled Northern Hemisphere (NH permafrost–ice-sheet evolution over the last glacial cycle is explored. The model performs generally well at reproducing present-day permafrost extent and thickness. Modeled permafrost thickness is sensitive to the values of ground porosity, thermal conductivity and geothermal heat flux. Permafrost extent at the Last Glacial Maximum (LGM agrees well with reconstructions and previous modeling estimates. Present-day permafrost thickness is far from equilibrium over deep permafrost regions. Over central Siberia and the Arctic Archipelago permafrost is presently up to 200–500 m thicker than it would be at equilibrium. In these areas, present-day permafrost depth strongly depends on the past climate history and simulations indicate that deep permafrost has a memory of surface temperature variations going back to at least 800 ka. Over the last glacial cycle permafrost has a relatively modest impact on simulated NH ice sheet volume except at LGM, when including permafrost increases ice volume by about 15 m sea level equivalent in our model. This is explained by a delayed melting of the ice base from below by the geothermal heat flux when the ice sheet sits on a porous sediment layer and permafrost has to be melted first. Permafrost affects ice sheet dynamics only when ice extends over areas covered by thick sediments, which is the case at LGM.

  18. Holocene Fluctuations of North Ice Cap, a Proxy for Climate Conditions along the Northwestern Margin of the Greenland Ice Sheet

    Science.gov (United States)

    Kelly, M. A.; Osterberg, E. C.; Lasher, G. E.; Farnsworth, L. B.; Howley, J. A.; Axford, Y.; Zimmerman, S. R. H.

    2015-12-01

    North Ice Cap (~76.9°N, 68°W, summit elevation 1322 m asl), a small, independent ice cap in northwestern Greenland, is located within ~25 km of the Greenland Ice Sheet margin and Harald Molkte Bræ outlet glacier. We present geochronological, geomorphic and sedimentological data constraining the Holocene extents of North Ice Cap and suggest that its past fluctuations can be used as a proxy for climate conditions along the northwestern margin of the Greenland Ice Sheet. Prior work by Goldthwait (1960) used glacial geomorphology and radiocarbon ages of subfossil plants emerging along shear planes in the ice cap margin to suggest that that North Ice Cap was not present during the early Holocene and nucleated in the middle to late Holocene time, with the onset of colder conditions. Subfossil plants emerging at shear planes in the North Ice Cap margin yield radiocarbon ages of ~4.8-5.9 cal kyr BP (Goldthwait, 1960) and ~AD 1000-1350 (950-600 cal yr BP), indicating times when the ice cap was smaller than at present. In situ subfossil plants exposed by recent ice cap retreat date to ~AD 1500-1840 (450-110 cal yr BP) and indicate small fluctuations of the ice cap margin. 10Be ages of an unweathered, lichen-free drift <100 m from the present North Ice Cap margin range from ~500 to 8000 yrs ago. We suggest that the drift was deposited during the last ~500 yrs and that the older 10Be ages are influenced by 10Be inherited from a prior period of exposure. We also infer ice cap fluctuations using geochemical data from a Holocene-long sediment core from Deltasø, a downstream lake that currently receives meltwater from North Ice Cap. The recent recession of the North Ice Cap margin influenced a catastrophic drainage of a large proglacial lake, Søndre Snesø, that our field team documented in August 2012. To our knowledge, this is the first significant lowering of Søndre Snesø in historical time.

  19. Direct observations of evolving subglacial drainage beneath the Greenland Ice Sheet.

    Science.gov (United States)

    Andrews, Lauren C; Catania, Ginny A; Hoffman, Matthew J; Gulley, Jason D; Lüthi, Martin P; Ryser, Claudia; Hawley, Robert L; Neumann, Thomas A

    2014-10-02

    Seasonal acceleration of the Greenland Ice Sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed via crevasses and moulins (vertical conduits connecting supraglacial water to the bed of the ice sheet). As the melt season progresses, the subglacial hydrologic system drains supraglacial meltwater more efficiently, decreasing basal water pressure and moderating the ice velocity response to surface melting. However, limited direct observations of subglacial water pressure mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood. Here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby (0.3-2 kilometres away) boreholes, indicating that moulins connect to an efficient, channelized component of the subglacial hydrologic system, which exerts the primary control on diurnal and multi-day changes in ice velocity. Our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the Paakitsoq region of western Greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin-connected channels to convey supraglacial melt. Instead, these observations suggest that decreasing late-season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system. Understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt-season dynamics affect ice velocity beyond the conclusion of the melt season.

  20. Future ice ages and the challenges related to final disposal of nuclear waste: The Greenland Ice Sheet Hydrology Project

    Science.gov (United States)

    Lehtinen, A.; Claesson-Liljedahl, L.; Näslund, J.-O.; Ruskeeniemi, T.

    2009-04-01

    A deep geological repository for nuclear waste is designed to keep radiotoxic material separated from mankind and the environment for several hundreds of thousands of years. Within this time perspective glacial conditions are expected in high latitudes/Canada and North Europe. Climate induced changes such as the growth of ice sheets and permafrost will influence and alter the ground surface and subsurface environment, which may impact repository safety. In order to understand how climate change, particularly cooling and glaciation, might affect a repository in the long term, the use of present-day analogues helps to reduce the uncertainties and support the assumptions made in safety assessments. There are major uncertainties concerning hydrological processes related to glacial conditions. The impact of glaciations on any planned repository is a key consideration when performing safety assessments as it is one of the strongest perturbations related to climate change in the long term. The main aspects that need to be further investigated include: 1) to what extent does the meltwater produced by an ice sheet penetrates into the bedrock; 2) what is the pressure situation under an ice sheet, driving ground water flow; 3) how much oxygenated water will reach repository depth; 4) to what depth does glacial meltwater penetrate into the bedrock ; 5)what chemical composition does such water has when and if it reaches repository depth; and 6) can taliks (unfrozen ground in a permafrost area) act as concentrated discharge points of deep groundwater potentially transporting radionuclides in case of repository failure? Field data is needed in order to achieve a better and integrated understanding of the problems discussed above. Thus, research in a natural analogue site in Greenland has been planned and initiated by the Finnish (Posiva), Swedish (SKB) and Canadian (NWMO) nuclear waste management companies. The Greenland ice sheet and the Kangerlussuaq area (west Greenland

  1. Assimilating the ICE-6G_C Reconstruction of the Latest Quaternary Ice Age Cycle Into Numerical Simulations of the Laurentide and Fennoscandian Ice Sheets

    Science.gov (United States)

    Stuhne, G. R.; Peltier, W. R.

    2017-12-01

    We analyze the effects of nudging 100 kyr numerical simulations of the Laurentide and Fennoscandian ice sheets toward the glacial isostatic adjustment-based (GIA-based) ICE-6G_C reconstruction of the most recent ice age cycle. Starting with the ice physics approximations of the PISM ice sheet model and the SeaRISE simulation protocols, we incorporate nudging at characteristic time scales, τf, through anomalous mass balance terms in the ice mass conservation equation. As should be expected, these mass balances exhibit physically unrealistic details arising from pure GIA-based reconstruction geometry when nudging is very strong (τf=20 years for North America), while weakly nudged (τf=1,000 years) solutions deviate from ICE-6G_C sufficiently to degrade its observational fit quality. For reasonable intermediate time scales (τf=100 years and 200 years), we perturbatively analyze nudged ice dynamics as a superposition of "leading-order smoothing" that diffuses ICE-6G_C in a physically and observationally consistent manner and "higher-order" deviations arising, for instance, from biases in the time dependence of surface climate boundary conditions. Based upon the relative deviations between respective nudged simulations in which these biases follow surface temperature from ice cores and eustatic sea level from marine sediment cores, we compute "ice core climate adjustments" that suggest how local paleoclimate observations may be applied to the systematic refinement of ICE-6G_C. Our results are consistent with a growing body of evidence suggesting that the geographical origins of Meltwater Pulse 1B (MWP1b) may lie primarily in North America as opposed to Antarctica (as reconstructed in ICE-6G_C).

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

    Science.gov (United States)

    Feldmann, Johannes; Levermann, Anders

    2017-08-01

    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.

  3. 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.

  4. Ice sheet mass loss caused by dust and black carbon accumulation

    Directory of Open Access Journals (Sweden)

    T. Goelles

    2015-09-01

    Full Text Available Albedo is the dominant factor governing surface melt variability in the ablation area of ice sheets and glaciers. Aerosols such as mineral dust and black carbon (soot accumulate on the ice surface and cause a darker surface and therefore a lower albedo. The darkening effect on the ice surface is currently not included in sea level projections, and the effect is unknown. We present a model framework which includes ice dynamics, aerosol transport, aerosol accumulation and the darkening effect on ice albedo and its consequences for surface melt. The model is applied to a simplified geometry resembling the conditions of the Greenland ice sheet, and it is forced by several temperature scenarios to quantify the darkening effect of aerosols on future mass loss. The effect of aerosols depends non-linearly on the temperature rise due to the feedback between aerosol accumulation and surface melt. According to our conceptual model, accounting for black carbon and dust in future projections of ice sheet changes until the year 3000 could induce an additional volume loss of 7 %. Since we have ignored some feedback processes, the impact might be even larger.

  5. Probabilistic calibration of a Greenland Ice Sheet model using spatially-resolved synthetic observations: toward projections of ice mass loss with uncertainties

    Science.gov (United States)

    Chang, W.; Applegate, P. J.; Haran, M.; Keller, K.

    2014-03-01

    Computer models of ice sheet behavior are important tools for projecting future sea level rise. The simulated modern ice sheets generated by these models differ markedly as input parameters are varied. To ensure accurate ice sheet mass loss projections, these parameters must be constrained using observational data. Which model parameter combinations make sense, given observations? Our method assigns probabilities to parameter combinations based on how well the model reproduces the Greenland Ice Sheet profile. We improve on the previous state of the art by accounting for spatial information, and by carefully sampling the full range of realistic parameter combinations, using statistically rigorous methods. Specifically, we estimate the joint posterior probability density function of model parameters using Gaussian process-based emulation and calibration. This method is an important step toward probabilistic projections of ice sheet contributions to sea level rise, in that it uses observational data to learn about parameter values. This information can, in turn, be used to make projections while taking into account various sources of uncertainty, including parametric uncertainty, data-model discrepancy, and spatial correlation in the error structure. We demonstrate the utility of our method using a perfect model experiment, which shows that many different parameter combinations can generate similar modern ice sheet profiles. This result suggests that the large divergence of projections from different ice sheet models is partly due to parametric uncertainty. Moreover, our method enables insight into ice sheet processes represented by parameter interactions in the model.

  6. Probabilistic calibration of a Greenland Ice Sheet model using spatially resolved synthetic observations: toward projections of ice mass loss with uncertainties

    Science.gov (United States)

    Chang, W.; Applegate, P. J.; Haran, M.; Keller, K.

    2014-09-01

    Computer models of ice sheet behavior are important tools for projecting future sea level rise. The simulated modern ice sheets generated by these models differ markedly as input parameters are varied. To ensure accurate ice sheet mass loss projections, these parameters must be constrained using observational data. Which model parameter combinations make sense, given observations? Our method assigns probabilities to parameter combinations based on how well the model reproduces the Greenland Ice Sheet profile. We improve on the previous state of the art by accounting for spatial information and by carefully sampling the full range of realistic parameter combinations, using statistically rigorous methods. Specifically, we estimate the joint posterior probability density function of model parameters using Gaussian process-based emulation and calibration. This method is an important step toward calibrated probabilistic projections of ice sheet contributions to sea level rise, in that it uses data-model fusion to learn about parameter values. This information can, in turn, be used to make projections while taking into account various sources of uncertainty, including parametric uncertainty, data-model discrepancy, and spatial correlation in the error structure. We demonstrate the utility of our method using a perfect model experiment, which shows that many different parameter combinations can generate similar modern ice sheet profiles. This result suggests that the large divergence of projections from different ice sheet models is partly due to parametric uncertainty. Moreover, our method enables insight into ice sheet processes represented by parameter interactions in the model.

  7. Elevation change and remote-sensing mass-balance methods on the Greenland ice sheet

    DEFF Research Database (Denmark)

    Ahlstrøm, Andreas P.; Reeh, Niels; Christensen, Erik Lintz

    The mass balance of the Greenland Ice Sheet is virtually impossible to obtain with traditional ground-based methods alone due to its vast size. It is thus desirable to develop mass-balance methods depending on remote sensing instead and this field has experienced a dramatic development within...... of measured surface elevation change over a 50x50~km part of the western Greenland Ice-Sheet margin near Kangerlussuaq. In this region, the mean observed elevation change has been -0.5~m from 2000 to 2003. However, the change is unevenly distributed with the northern and central part generally in balance...... the last decade. Large amounts of data have been collected from satellite and airborne platforms, yielding surface elevation changes and surface velocity fields. Here we present data from the Greenland Ice-Sheet margin acquired with a new small-scale airborne system, designed for regional high...

  8. Final Report. Coupled simulations of Antarctic Ice-sheet/ocean interactions using POP and CISM

    Energy Technology Data Exchange (ETDEWEB)

    Asay-Davis, Xylar Storm [Potsdam Institute for Climate Impact Research, Potdam (Germany)

    2015-12-30

    The project performed under this award, referred to from here on as CLARION (CoupLed simulations of Antarctic Ice-sheet/Ocean iNteractions), included important advances in two models of ice sheet and ocean interactions. Despite its short duration (one year), the project made significant progress on its three major foci. First, together with collaborator Daniel Martin at Lawrence Berkeley National Laboratory (LBNL), I developed the POPSICLES coupled ice sheet-ocean model to the point where it could perform a number of pan-Antarctic simulations under various forcing conditions. The results were presented at a number of major conferences and workshops worldwide, and are currently being incorporated into two manuscripts in preparation.

  9. Ice sheets as a significant source of highly reactive nanoparticulate iron to the oceans.

    Science.gov (United States)

    Hawkings, Jon R; Wadham, Jemma L; Tranter, Martyn; Raiswell, Rob; Benning, Liane G; Statham, Peter J; Tedstone, Andrew; Nienow, Peter; Lee, Katherine; Telling, Jon

    2014-05-21

    The Greenland and Antarctic Ice Sheets cover ~ 10% of global land surface, but are rarely considered as active components of the global iron cycle. The ocean waters around both ice sheets harbour highly productive coastal ecosystems, many of which are iron limited. Measurements of iron concentrations in subglacial runoff from a large Greenland Ice Sheet catchment reveal the potential for globally significant export of labile iron fractions to the near-coastal euphotic zone. We estimate that the flux of bioavailable iron associated with glacial runoff is 0.40-2.54 Tg per year in Greenland and 0.06-0.17 Tg per year in Antarctica. Iron fluxes are dominated by a highly reactive and potentially bioavailable nanoparticulate suspended sediment fraction, similar to that identified in Antarctic icebergs. Estimates of labile iron fluxes in meltwater are comparable with aeolian dust fluxes to the oceans surrounding Greenland and Antarctica, and are similarly expected to increase in a warming climate with enhanced melting.

  10. Investigation of Greenland Russell glacier with remote sensing observations and ice sheet/hydrodynamic simulations

    Science.gov (United States)

    Yun, Hyewon; Kim, Jungrack; Tsai, YaLun; Lin, ShihYuan; Choi, Yunsoo

    2016-04-01

    There is great interest in the mechanism and consequences of arctic ice sheet migration in the context of worldwide climate change. An in-depth investigation of glacial movement involving supra/under glacial hydrological channel activities is key to understanding the acceleration of Greenland's ice sheet changes and needs to be established as an integrated model. In terms of the glacial migration involving basal hydrology, we have conducted a case study over the Russell glacier in western Greenland. Remote sensed image analyses combined with a numerical model in its melt water outflow channels, such as the Akuliarusiarsuup Kuua and Qinnguata Kuussua rivers, and ice sheet simulations were performed. Employed technical approaches are summarized as follows: 1) Collecting 3D migration vectors combining differential interferometric SAR (D-InSAR) analysis, together with the in-house pixel tracking method employing optical flow and sub-pixel refinement with C band Sentinel-1 and L band ALOS PALSAR-2 images; 2) a 2D hydrodynamic simulation based on the channel bathymetry, which was driven from calibrated LANDSAT images together with along-track stereo DTM, and 3) an ice sheet model to extract the bedrock and basal characteristics of the glaciers. In addition, we tried Sentinel-1 InSAR time series to monitor ice sheet migrations over a certain time domain. The results revealed the importance of hydrological channel morphology as a governing factor over migration speeds of glaciers. Specifically, the sub glacial processes and underlying morphology traced by remote sensing observation and the numerical model were correlated with the observed local migration speeds in terminus of the Russell glacier. Those experiences naturally will lead to a more comprehensive understanding of the processes of artic glaciers. Thus, based on the output of this study, the proposed method will be extended to tackle the issues of ice sheet change occurring in the Greenland costal area

  11. How Will Sea Ice Loss Affect the Greenland Ice Sheet? On the Puzzling Features of Greenland Ice-Core Isotopic Composition

    Science.gov (United States)

    Pausata, Francesco S. R.; Legrande, Allegra N.; Roberts, William H. G.

    2016-01-01

    The modern cryosphere, Earth's frozen water regime, is in fast transition. Greenland ice cores show how fast theses changes can be, presenting evidence of up to 15 C warming events over timescales of less than a decade. These events, called Dansgaard/Oeschger (D/O) events, are believed to be associated with rapid changes in Arctic sea ice, although the underlying mechanisms are still unclear. The modern demise of Arctic sea ice may, in turn, instigate abrupt changes on the Greenland Ice Sheet. The Arctic Sea Ice and Greenland Ice Sheet Sensitivity (Ice2Ice Chttps://ice2ice.b.uib.noD) initiative, sponsored by the European Research Council, seeks to quantify these past rapid changes to improve our understanding of what the future may hold for the Arctic. Twenty scientists gathered in Copenhagen as part of this initiative to discuss the most recent observational, technological, and model developments toward quantifying the mechanisms behind past climate changes in Greenland. Much of the discussion focused on the causes behind the changes in stable water isotopes recorded in ice cores. The participants discussed sources of variability for stable water isotopes and framed ways that new studies could improve understanding of modern climate. The participants also discussed how climate models could provide insights into the relative roles of local and nonlocal processes in affecting stable water isotopes within the Greenland Ice Sheet. Presentations of modeling results showed how a change in the source or seasonality of precipitation could occur not only between glacial and modern climates but also between abrupt events. Recent fieldwork campaigns illustrate an important role of stable isotopes in atmospheric vapor and diffusion in the final stable isotope signal in ice. Further, indications from recent fieldwork campaigns illustrate an important role of stable isotopes in atmospheric vapor and diffusion in the final stable isotope signal in ice. This feature complicates

  12. Greenland ice sheet model parameters constrained using simulations of the Eemian Interglacial

    Directory of Open Access Journals (Sweden)

    A. Robinson

    2011-04-01

    Full Text Available Using a new approach to force an ice sheet model, we performed an ensemble of simulations of the Greenland Ice Sheet evolution during the last two glacial cycles, with emphasis on the Eemian Interglacial. This ensemble was generated by perturbing four key parameters in the coupled regional climate-ice sheet model and by introducing additional uncertainty in the prescribed "background" climate change. The sensitivity of the surface melt model to climate change was determined to be the dominant driver of ice sheet instability, as reflected by simulated ice sheet loss during the Eemian Interglacial period. To eliminate unrealistic parameter combinations, constraints from present-day and paleo information were applied. The constraints include (i the diagnosed present-day surface mass balance partition between surface melting and ice discharge at the margin, (ii the modeled present-day elevation at GRIP; and (iii the modeled elevation reduction at GRIP during the Eemian. Using these three constraints, a total of 360 simulations with 90 different model realizations were filtered down to 46 simulations and 20 model realizations considered valid. The paleo constraint eliminated more sensitive melt parameter values, in agreement with the surface mass balance partition assumption. The constrained simulations resulted in a range of Eemian ice loss of 0.4–4.4 m sea level equivalent, with a more likely range of about 3.7–4.4 m sea level if the GRIP δ18O isotope record can be considered an accurate proxy for the precipitation-weighted annual mean temperatures.

  13. Influence of a West Antarctic mantle plume on ice sheet basal conditions

    Science.gov (United States)

    Seroussi, Helene; Ivins, Erik R.; Wiens, Douglas A.; Bondzio, Johannes

    2017-09-01

    The possibility that a deep mantle plume manifests Pliocene and Quaternary volcanism and potential elevated heat flux in West Antarctica has been studied for more than 30 years. Recent seismic images support the plume hypothesis as the cause of Marie Byrd Land (MBL) volcanism and geophysical structure. Mantle plumes may more than double the geothermal heat flux above nominal continental values. A dearth of in situ ice sheet basal data exists that samples the heat flux. Consequently, we examine a realistic distribution of heat flux associated with a possible late Cenozoic mantle plume in West Antarctica and explore its impact on thermal and melt conditions at the ice sheet base. We use a simple analytical mantle plume parameterization to produce geothermal heat flux at the base of the ice sheet. The three-dimensional ice flow model includes an enthalpy framework and full-Stokes stress balance. As both the putative plume location and extent are uncertain, we perform broadly scoped experiments to characterize the impact of the plume on geothermal heat flux and ice sheet basal conditions. The experiments show that mantle plumes have an important local impact on the ice sheet, with basal melting rates reaching several centimeters per year directly above the hotspot. In order to be consistent with observations of basal hydrology in MBL, the upper bound on the plume-derived geothermal heat flux is 150 mW/m2. In contrast, the active lake system of the lower part of Whillans Ice Stream suggests a widespread anomalous mantle heat flux, linked to a rift source.

  14. ICESat/GLAS measurement of Ice sheet surface slope and roughness

    Science.gov (United States)

    Yi, D.; Zwally, H. J.

    2003-12-01

    Surface slope and roughness are important features of ice sheets that are affected by bedrock topography, ice flow, ice thickness, and wind. Return-pulse waveforms from ICESat/GLAS provide surface elevations and information on surface slope and roughness. Surface slope and roughness within the laser footprint both affect the spread of return waveform, so information on surface slope and roughness can be derived by comparing the transmitted and return pulse waveforms. The shape of the transmitted waveform is nearly Gaussian. For typical ice sheet surfaces, the return pulse shape is also very close to Gaussian. By fitting Gaussian functions to the transmitted and return pulse waveforms and calculating the increase in width of the return pulse, surface roughness can be calculated if the surface slope is known, or vice versa. The ICESat/GLAS 1064 nm laser footprint diameter is about 70 meters and the footprint separation is about 170 meters. The small-scale surface roughness derived from the pulse shape is mostly due to wind-driven surface sastrugi. Over the larger ice sheet slopes, the pulse shape is dominated mainly by the surface slope. Information on the larger-scale (larger than 170 m) surface slope and surface undulations is also derived from successive along-track ICESat/GLAS elevations. The ICESat orbit covers Antarctica to 86° S and all of the Greenland ice sheet. Spatial distributions of surface roughness and slopes over the ice sheets for the period of ICESat operation are described. Effects of partial detector/amplifier saturation on the return pulse shape and the calculated roughness and slopes are also discussed.

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

    Science.gov (United States)

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

    2015-09-01

    We use ∼7000 km2 of high-resolution swath bathymetry data to describe and map the submarine glacial geomorphology, and reconstruct Late Pleistocene ice sheet flow configurations and retreat dynamics within the Inner Hebrides, western Scotland. Frequently dominated by outcrops of structurally complex bedrock, the seabed also comprises numerous assemblages of well-preserved glacigenic landforms typical of grounded ice sheet flow and punctuated ice-margin retreat. The occurrence and character of the glacially streamlined landforms is controlled in part by the shallow geology and topography, however these factors alone cannot account for the location, orientation, and configuration of the observed landforms. We attribute the distribution of these elongate streamlined landforms to the onset zone of the former Hebrides Ice Stream (HIS) - part of a major ice stream system that drained 5-10% of the last British-Irish Ice Sheet (BIIS). We suggest this geomorphic signature represents the transition from slow 'sheet flow' to 'streaming flow' as ice accelerated out from an environment characterized by numerous bedrock obstacles (e.g. islands, headlands), towards the smooth, sediment dominated shelf. The majority of streamlined landforms associated with the HIS indicate ice sheet flow to the southwest, with regional-scale topography clearly playing a major role in governing the configuration of flow. During maximal glacial conditions (∼29-23 ka) we infer that the HIS merged with the North Channel-Malin Shelf Ice Stream to form a composite ice stream system that ultimately reached the continental shelf edge at the Barra-Donegal Trough-Mouth Fan. Taken collectively however, the pattern of landforms now preserved at seabed (e.g. convergent flow indicators, cross-cutting flow sets) is more indicative of a thinning ice mass, undergoing reorganization during overall ice sheet retreat (during latter stages of Late Weischselian glaciation). Suites of moraines overprinting the

  16. Extent of the last ice sheet in northern Scotland tested with cosmogenic 10Be exposure ages

    Science.gov (United States)

    Phillips, W.M.; Hall, A.M.; Ballantyne, C.K.; Binnie, S.; Kubik, P.W.; Freeman, S.

    2008-01-01

    The extent of the last British-Irish Ice Sheet (BIIS) in northern Scotland is disputed. A restricted ice sheet model holds that at the global Last Glacial Maximum (LGM; ca. 23-19 ka) the BIIS terminated on land in northern Scotland, leaving Buchan, Caithness and the Orkney Islands ice-free. An alternative model implies that these three areas were ice-covered at the LGM, with the BIIS extending offshore onto the adjacent shelves. We test the two models using cosmogenic 10Be surface exposure dating of erratic boulders and glacially eroded bedrock from the three areas. Our results indicate that the last BIIS covered all of northern Scotland during the LGM, but that widespread deglaciation of Caithness and Orkney occurred prior to rapid warming at ca. 14.5 ka. Copyright ?? 2008 John Wiley & Sons, Ltd.

  17. Greenland surface mass-balance observations from the ice-sheet ablation area and local glaciers

    DEFF Research Database (Denmark)

    Machguth, Horst; Thomsen, Henrik H.; Weidick, Anker

    2016-01-01

    Glacier surface mass-balance measurements on Greenland started more than a century ago, but no compilation exists of the observations from the ablation area of the ice sheet and local glaciers. Such data could be used in the evaluation of modelled surface mass balance, or to document changes...... in glacier melt independently from model output. Here, we present a comprehensive database of Greenland glacier surface mass-balance observations from the ablation area of the ice sheet and local glaciers. The database spans the 123 a from 1892 to 2015, contains a total of similar to 3000 measurements from...

  18. Extensive Liquid Meltwater Storage in Firn Within the Greenland Ice Sheet

    Science.gov (United States)

    Forster, Richard R.; Box, Jason E.; vandenBroeke, Michael R.; Miege, Clement; Burgess, Evan W.; vanAngelen, Jan H.; Lenaerts, Jan T. M.; Koenig, Lora S.; Paden, John; Lewis, Cameron; hide

    2013-01-01

    The accelerating loss of mass from the Greenland ice sheet is a major contribution to current sea level rise. Increased melt water runoff is responsible for half of Greenlands mass loss increase. Surface melt has been increasing in extent and intensity, setting a record for surface area melt and runoff in 2012. The mechanisms and timescales involved in allowing surface melt water to reach the ocean where it can contribute to sea level rise are poorly understood. The potential capacity to store this water in liquid or frozen form in the firn (multi-year snow layer) is significant, and could delay its sea-level contribution. Here we describe direct observation of water within a perennial firn aquifer persisting throughout the winter in the southern ice sheet,where snow accumulation and melt rates are high. This represents a previously unknown storagemode for water within the ice sheet. Ice cores, groundairborne radar and a regional climatemodel are used to estimate aquifer area (70 plue or minus 10 x 10(exp 3) square kilometers ) and water table depth (5-50 m). The perennial firn aquifer represents a new glacier facies to be considered 29 in future ice sheet mass 30 and energy budget calculations.

  19. Microbial carbon and nitrogen fixation on the surface of glaciers and ice sheets

    Science.gov (United States)

    Telling, J.; Anesio, A. M.; Stibal, M.; Hawkings, J.; Bellas, C. M.; Tranter, M.; Wadham, J. L.; Cook, J.; Hodson, A. J.; Yallop, M.; Barker, G.; Butler, C. E.; Fountain, A. G.; Nylen, T.; Irvine-Fynn, T. D.; Sole, A. J.; Nienow, P. W.

    2012-12-01

    Studying the microbial sequestration of atmospheric carbon dioxide (via net autochthonous production) and nitrogen (via nitrogen fixation) into organic matter on the surface of glaciers and ice sheets is important for three main reasons. First, they can provide essential nutrients for supporting microbial ecosystems in these cold, typically nutrient-poor environments. Second, nutrients formed in the supraglacial environment may be important for sustaining hydrologically connected subglacial and downstream (e.g. fjords, near-shore marine) ecosystems. Third, organic matter produced or transformed by microbial activity can alter the albedo of ice, either directly by the production of dark pigments, or indirectly through the trapping and agglutination of dark mineral via the production of exopolysaccharides. Here, we present recent results of microbial carbon and nitrogen fixation in surface sediment (cryoconite) on Arctic and Antarctic glaciers and the Greenland Ice Sheet ablation zone. Results suggest that the fixation and recycling of autochthonous carbon in cryoconite on glaciers and ice sheets can support a significant fraction of the total microbial activity in the supraglacial environment during the ablation season. Nitrogen fixation can be important as a nitrogen source for microbial communities on both Arctic and Antarctic glaciers during the main ablation season. Nitrogen fixation could feasibly exceed precipitation as a source of nitrogen to microbial communities in debris rich zones on the margins of the Greenland Ice Sheet, aiding the colonization and subsequent 'greening' of subglacial and moraine derived debris.

  20. Hydrologic controls on coastal suspended sediment plumes around the Greenland Ice Sheet

    Directory of Open Access Journals (Sweden)

    V. W. Chu

    2012-01-01

    Full Text Available Rising sea levels and increased surface melting of the Greenland ice sheet have heightened the need for direct observations of meltwater release from the ice edge to ocean. Buoyant sediment plumes that develop in fjords downstream of outlet glaciers are controlled by numerous factors, including meltwater runoff. Here, Moderate Resolution Imaging Spectroradiometer (MODIS satellite imagery is used to average surface suspended sediment concentration (SSC in fjords around ∼80% of Greenland from 2000–2009. Spatial and temporal patterns in SSC are compared with positive-degree-days (PDD, a proxy for surface melting, from the Polar MM5 regional climate model. Over this decade significant geographic covariance occurred between ice sheet PDD and fjord SSC, with outlet type (land- vs. marine-terminating glaciers also important. In general, high SSC is associated with high PDD and/or a high proportion of land-terminating glaciers. Unlike previous site-specific studies of the Watson River plume at Kangerlussuaq, temporal covariance is low, suggesting that plume dimensions best capture interannual runoff dynamics whereas SSC allows assessment of meltwater signals across much broader fjord environments around the ice sheet. Remote sensing of both plume characteristics thus offers a viable approach for observing spatial and temporal patterns of meltwater release from the Greenland ice sheet to the global ocean.

  1. Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Kjaer, Kurt H.; Bevis, Michael

    2014-01-01

    The Greenland ice sheet has been one of the largest contributors to global sea-level rise over the past 20 years, accounting for 0.5 mm yr(-1) of a total of 3.2 mm yr(-1). A significant portion of this contribution is associated with the speed-up of an increased number of glaciers in southeast...... and northwest Greenland. Here, we show that the northeast Greenland ice stream, which extends more than 600 km into the interior of the ice sheet, is now undergoing sustained dynamic thinning, linked to regional warming, after more than a quarter of a century of stability. This sector of the Greenland ice sheet...... is of particular interest, because the drainage basin area covers 16% of the ice sheet (twice that of Jakobshavn Isbrae) and numerical model predictions suggest no significant mass loss for this sector, leading to an under-estimation of future global sea-level rise. The geometry of the bedrock and monotonic trend...

  2. Monitoring of the Greenland ice sheet using a broadband seismometer network: the GLISN project

    Directory of Open Access Journals (Sweden)

    Genti Toyokuni

    2014-03-01

    Full Text Available Global climate change is currently causing melting of the Greenland ice sheet. Recently, a new type of seismic event, referred to as a "glacial earthquake", has been recognized. Such earthquakes are generated by the movements of large masses of ice within the terminal regions of glacier, and represent a new approach for monitoring ice sheet dynamics. In 2009, the multinational GreenLand Ice Sheet monitoring Network (GLISN, a large broadband seismological network in and around Greenland, was initiated to monitor these events. Japan, a partner country of the GLISN project, has been sending a field team to Greenland each year since 2011, when a joint USA and Japanese team first established a dual seismic-GPS station (station code: ICESG-GLS2 on the Greenland ice sheet. In 2012, the same team contributed to the maintenance of ICESG-GLS2, as well as two other stations (NUUK and DY2G-GLS1. The quality of the long-period seismic waveform data obtained by these stations has been checked by comparing the data with global synthetic seismograms. Results indicate that the data from the three stations have not been substantially affected by noise, and that the quality is well controlled.

  3. Carbonaceous particles reveal that Late Holocene dust causes the dark region in the western ablation zone of the Greenland ice sheet

    NARCIS (Netherlands)

    Wientjes, I.G.M.; van de Wal, R.S.W.; Schwikowski, M.; Zapf, A.; Fahrni, S.; Wacker, L.

    2012-01-01

    A dark region in the western ablation zone of the Greenland ice sheet is caused by outcropping ice layers that contain more dust than the surrounding brighter ice. These higher amounts of dust were deposited in the accumulation zone of the ice sheet and travelled with the ice to the ablation zone.

  4. 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.

    2017-02-01

    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 nm. Spaceborne lidar observations overcome many of the disadvantages in passive remote sensing, including difficulties in cloud screening and low sun angle limitations and 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 ( 300 μm) among the three, West Antarctica is the second ( 220 μm) and East Antarctica is the smallest ( 190 μm). 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.

  5. 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.

  6. Growth and decay of a marine terminating sector of the last British-Irish Ice Sheet: a geomorphological reconstruction

    Science.gov (United States)

    Finlayson, Andrew; Fabel, Derek; Bradwell, Tom; Sugden, David

    2014-01-01

    The boundary conditions that govern ice sheet dynamics can change significantly with the development of marine margins. This paper uses the glacial landscape in western Scotland to reconstruct changes in the British-Irish Ice Sheet that accompanied the growth and decay of a marine sector over the Malin Shelf. Ice advanced from a restricted mountain ice sheet with tidewater margins after ˜35 ka BP, and reached the continental shelf in ˜7 ka (average rate of ˜30 m a-1). Early ice flow had been directed through north-south, geologically controlled, over-deepened fjords that were carved during previous 'restricted' glaciations. This flow regime was abandoned with development of the Malin Shelf ice sheet sector; ice flow direction switched by ˜90° and was drawn westwards towards the shelf edge. The marine ice sheet phase saw episodes of west-east ice divide migration by up to 60 km over west central Scotland, possibly linked to ice streaming and calving events at the ice sheet margin. However, permanent and stationary ice divides and zones of cold-based ice, associated with subglacial topographic highs, also characterised the marine glacial stage over western Scotland. The North Channel ice divide remained a constant, though migratory feature while the BIIS occupied the Malin Shelf; it finally collapsed at the end of the Killard Point Stadial when the Irish Ice Sheet began to rapidly decay ˜16.5 ka BP. This permitted the Scottish Ice Sheet to temporarily advance over north-east Ireland (previously identified as the East Antrim Coastal Readvance) before it too retreated, at rates in the order of 102 m a-1. Although the imprint of extensive shelf-edge ice sheet glaciation exists in the coastal landscape of western Scotland, the dominant landscape features relate to a restricted, marine-proximal mountain ice sheet with markedly different flow configurations. Similar first-order geomorphological features, relating to 'restricted' glacial conditions, are likely to be

  7. Sustained High Basal Motion of the Greenland Ice Sheet Revealed by Borehole Deformation

    Science.gov (United States)

    Ryser, Claudia; Luthi, Martin P.; Andrews, Lauren C.; Hoffman, Matthew, J.; Catania, Ginny A.; Hawley, Robert L.; Neumann, Thomas A.; Kristensen, Steen S.

    2014-01-01

    Ice deformation and basal motion characterize the dynamical behavior of the Greenland ice sheet (GrIS). We evaluate the contribution of basal motion from ice deformation measurements in boreholes drilled to the bed at two sites in the western marginal zone of the GrIS. We find a sustained high amount of basal motion contribution to surface velocity of 44-73 percent in winter, and up to 90 percent in summer. Measured ice deformation rates show an unexpected variation with depth that can be explained with the help of an ice-flow model as a consequence of stress transfer from slippery to sticky areas. This effect necessitates the use of high-order ice-flow models, not only in regions of fast-flowing ice streams but in all temperate-based areas of the GrIS. The agreement between modeled and measured deformation rates confirms that the recommended values of the temperature-dependent flow rate factor A are a good choice for ice-sheet models.

  8. Accelerated ice-sheet mass loss in Antarctica from 18-year satellite laser ranging measurements

    Directory of Open Access Journals (Sweden)

    Shuanggen Jin

    2016-02-01

    Full Text Available Accurate estimate of the ice-sheet mass balance in Antarctic is very difficult due to complex ice sheet condition and sparse in situ measurements. In this paper, the low-degree gravity field coefficients of up to degree and order 5 derived from Satellite Laser Ranging (SLR measurements are used to determine the ice mass variations in Antarctica for the period 1993–2011. Results show that the ice mass is losing with -36±13 Gt/y in Antarctica, -42±11 Gt/y in the West Antarctica and 6±10 Gt/y in the East Antarctica from 1993 to 2011. The ice mass variations from the SLR 5×5 have a good agreement with the GRACE 5×5, GRACE 5×5 (1&2 and GRACE (60×60 for the entire continent since 2003, but degree 5 from SLR is not sufficient to quantify ice losses in West and East Antarctica, respectively. The rate of ice loss in Antarctica is -28±17 Gt/y for 1993-2002 and -55±17 Gt/y for 2003-2011, indicating significant accelerated ice mass losses since 2003. Furthermore, the results from SLR are comparable with GRACE measurements.

  9. Quantifying Local Ablation Rates for the Greenland Ice Sheet Using Terrestrial LIDAR

    Science.gov (United States)

    Kershner, C. M.; Pitcher, L. H.; LeWinter, A.; Finnegan, D. C.; Overstreet, B. T.; Miège, C.; Cooper, M. G.; Smith, L. C.; Rennermalm, A. K.

    2016-12-01

    Quantifying accurate ice surface ablation or melt rates for the Greenland Ice Sheet is important for calibrating and validating surface mass balance models and constraining sea level rise estimates. Common practice is to monitor surface ablation at defined points by manually measuring ice surface lowering in relation to stakes inserted into the ice / snow. However, this method does not account for the effects of local topography, solar zenith angle, and local variations in ice surface albedo/impurities on ablation rates. To directly address these uncertainties, we use a commercially available terrestrial LIDAR scanner (TLS) to monitor daily melt rates in the ablation zone of the Greenland Ice Sheet for 7 consecutive days in July 2016. Each survey is registered to previous scans using retroreflective cylinders and is georeferenced using static GPS measurements. Bulk ablation will be calculated using multi-temporal differential LIDAR techniques, and difficulties in referencing scans and collecting high quality surveys in this dynamic environment will be discussed, as well as areas for future research. We conclude that this novel application of TLS technology provides a spatially accurate, higher fidelity measurements of ablation across a larger area with less interpolation and less time spent than using traditional manual point based methods alone. Furthermore, this sets the stage for direct calibration, validation and cross-comparison with existing airborne (e.g. NASA's Airborne Topographic Mapper - ATM - onboard Operation IceBridge and NASA's Land, Vegetation & Ice Sensor - LVIS) and forthcoming spaceborne sensors (e.g. NASA's ICESat-2).

  10. Contamination of the Arctic reflected in microbial metagenomes from the Greenland ice sheet

    DEFF Research Database (Denmark)

    Hauptmann, Aviaja Zenia Edna Lyberth; Sicheritz-Pontén, Thomas; Cameron, Karen A.

    2017-01-01

    interact with contamination in the Arctic is limited. Through shotgun metagenomic data and binned genomes from metagenomes we show that microbial communities, sampled from multiple surface ice locations on the Greenland ice sheet, have the potential for resistance to and degradation of contaminants....... The microbial potential to degrade anthropogenic contaminants, such as toxic and persistent polychlorinated biphenyls, was found to be spatially variable and not limited to regions close to human activities. Binned genomes showed close resemblance to microorganisms isolated from contaminated habitats...

  11. Towards an annually-resolved record of Lateglacial Patagonian ice sheet dynamics using glaciolacustrine varves

    Science.gov (United States)

    Bendle, Jacob; Palmer, Adrain; Thorndycraft, Varyl

    2016-04-01

    Proglacial sedimentary archives, in particular, glaciolacustrine varve sequences, offer the potential for detailed reconstructions of past ice sheet dynamics. Specifically, glaciolacustrine varves (i) allow reconstructions of sediment (and thus meltwater) influx at annual and even sub-annual resolution; and (ii) provide a continuous, annually-resolved chronology to estimate rates of change and/or the duration of significant events in the deglaciation of a basin. In South America, glacial geologists have relied heavily on cosmogenic nuclide exposure dating to construct chronologies for palaeoglaciological activity. Whilst effective, the typical uncertainties associated with boulder dating methods (±10%) preclude the investigation of short-term (e.g. ≤ centennial-scale) glacier and/or climatic change(s), which are shown to be important at modern ice-margins. Moreover, moraine chronologies are fragmentary, and inherently biased towards episodes of positive glacier mass balance (i.e. moraine construction), and thus limit our understanding of ice sheet retreat dynamics. By contrast, long, continuous, high-resolution (i.e. varve) palaeolimnological records have the potential to significantly refine models of ice sheet deglaciation. In this talk, we present data from Valle Fenix Chico, in the Lago Buenos Aires (LBA) basin (-46.57°S -71.07°W), in which ice-contact Glacial Lake Buenos Aires formed as the LBA ice lobe of Patagonian ice sheet withdrew from its innermost LGM moraine (~17.2 ± 0.9 ka). Thick (>40m) sequences of laminated glaciolacustrine sediment were deposited in the palaeolake, and are now exposed in a sub-aerial canyon that was cut when the lake drained. We report on the detailed macro- and micro-facies of the LBA sediments. In particular, we: (1) develop a process model for the formation of silt and clay couplets, which suggests an annual (varve) origin; (2) present varve series for the initial phase (~1kyr) of LBA ice lobe deglaciation.

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

    Science.gov (United States)

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

    2017-08-01

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

  13. A simple method to assimilate both surface and bedrock data into an ice-sheet model

    Science.gov (United States)

    Durand, G.; Gillet-chaulet, F.

    2012-12-01

    Properly estimating the future contribution of ice sheets to sea-level rise is matter of concern. During the last years, progress in ice-flow models pointed out the necessity of improving the representation of the ice sheet initial state to establish reliable projections. Inverse methods are then the convenient tool to meet this challenge. Here, using the Elmer/ice model, we propose a simple and pragmatic method that allows to assimilate both the surface and bedrock elevation data by minimizing the mismatch between observed and modeled surface velocities. Performance of the method is evaluated on the Astrolabe Glacier (East Antarctica) were successive recent field campaigns gave a comprehensive dataset of the entire drainage basin. The method allows to considerably decrease ice flux divergence anomaly inherently present in the model due to scarce data and insufficient knowledge of some parameters of the model. It further considerably limits the discrepancy between the observed and modeled geometry at the condition that direct raw data are assimilated rather than using usual gridded products. This demonstrates the needs of revisiting the way data are currently processed before being used by ice sheet modelers.

  14. Basin-scale partitioning of Greenland ice sheet mass balance components (2007-2011)

    DEFF Research Database (Denmark)

    Andersen, M.L.; Stenseng, Lars; Skourup, Henriette

    2015-01-01

    The current deficit in Greenland ice sheet mass balance is due to both a decrease in surface mass balance (SMB) input and an increase in ice discharge (D) output. While SMB processes are beginning to be well captured by observationally-constrained climate modeling, insight into D is relatively...... of the gate. Using a 1961-1990 reference climatology SMB field from the MAR regional climate model, we quantify ice sheet mass balance within eighteen basins. We find a 2007-2011 mean D of 515±57 Gtyr-1. We find a 2007-2011 mean total mass balance of -262±21 Gtyr-1, which is equal to a 0.73 mm yr-1 global sea...... limited. We use InSAR-derived velocities, in combination with ice thickness observations, to quantify the mass flux (F) across a flux perimeter around the ice sheet at ~1700 m elevation. To quantify D, we correct F for SMB, as well as changes in volume due to ice dynamics, in the area downstream...

  15. Laurentide Ice Sheet Basal Temperatures at the Last Glacial Cycle As Inferred from Borehole Temperature Data

    Science.gov (United States)

    Pickler, C.; Beltrami, H.; Mareschal, J. C.

    2014-12-01

    Twelve temperature-depth profiles (>1500 m) located in Eastern to Central Canada were studied to determine the past ground surface temperature histories (GSTH) for the Last Glacial Cycle (LGC) and afterwards. The GSTHs were inferred using singular variable decomposition (SVD). Three locations (Sudbury, Manitouwadge, and Thompson) presented multiple boreholes. Here, simultaneous inversion was utilized to illustrate any regional trends present. For all studied sites, the inversion shows that ground surface temperatures throughout the LGC near the pressure melting point of ice, -1.41-2.51°C. These ground surface temperatures are representative of the basal temperatures of the Laurentide Ice Sheet, which covered the region throughout the LGC. These temperatures allow for the possibility of basal flow and fast flowing ice streams, which have been inferred from geomorphological data and are consistent with modeling efforts. Regional variations in basal temperatures are observed. These could be attributed to fluctuations in ice sheet thickness and proximity to the edge of the ice sheet. No correlation between heat flow and the amplitude of the GSTH variations was observed, leading to the conclusion that the basal temperatures in this region are primarily driven by ice dynamics.

  16. Anatomy of a meltwater drainage system beneath the ancestral East Antarctic ice sheet

    Science.gov (United States)

    Simkins, Lauren M.; Anderson, John B.; Greenwood, Sarah L.; Gonnermann, Helge M.; Prothro, Lindsay O.; Halberstadt, Anna Ruth W.; Stearns, Leigh A.; Pollard, David; Deconto, Robert M.

    2017-09-01

    Subglacial hydrology is critical to understand the behaviour of ice sheets, yet active meltwater drainage beneath contemporary ice sheets is rarely accessible to direct observation. Using geophysical and sedimentological data from the deglaciated western Ross Sea, we identify a palaeo-subglacial hydrological system active beneath an area formerly covered by the East Antarctic ice sheet. A long channel network repeatedly delivered meltwater to an ice stream grounding line and was a persistent pathway for episodic meltwater drainage events. Embayments within grounding-line landforms coincide with the location of subglacial channels, marking reduced sedimentation and restricted landform growth. Consequently, channelized drainage at the grounding line influenced the degree to which these landforms could provide stability feedbacks to the ice stream. The channel network was connected to upstream subglacial lakes in an area of geologically recent rifting and volcanism, where elevated heat flux would have produced sufficient basal melting to fill the lakes over decades to several centuries; this timescale is consistent with our estimates of the frequency of drainage events at the retreating grounding line. Based on these data, we hypothesize that ice stream dynamics in this region were sensitive to the underlying hydrological system.

  17. South Greenland ice-sheet collapse during Marine Isotope Stage 11.

    Science.gov (United States)

    Reyes, Alberto V; Carlson, Anders E; Beard, Brian L; Hatfield, Robert G; Stoner, Joseph S; Winsor, Kelsey; Welke, Bethany; Ullman, David J

    2014-06-26

    Varying levels of boreal summer insolation and associated Earth system feedbacks led to differing climate and ice-sheet states during late-Quaternary interglaciations. In particular, Marine Isotope Stage (MIS) 11 was an exceptionally long interglaciation and potentially had a global mean sea level 6 to 13 metres above the present level around 410,000 to 400,000 years ago, implying substantial mass loss from the Greenland ice sheet (GIS). There are, however, no model simulations and only limited proxy data to constrain the magnitude of the GIS response to climate change during this 'super interglacial', thus confounding efforts to assess climate/ice-sheet threshold behaviour and associated sea-level rise. Here we show that the south GIS was drastically smaller during MIS 11 than it is now, with only a small residual ice dome over southernmost Greenland. We use the strontium-neodymium-lead isotopic composition of proglacial sediment discharged from south Greenland to constrain the provenance of terrigenous silt deposited on the Eirik Drift, a sedimentary deposit off the south Greenland margin. We identify a major reduction in sediment input derived from south Greenland's Precambrian bedrock terranes, probably reflecting the cessation of subglacial erosion and sediment transport as a result of near-complete deglaciation of south Greenland. Comparison with ice-sheet configurations from numerical models suggests that the GIS lost about 4.5 to 6 metres of sea-level-equivalent volume during MIS 11. This is evidence for late-Quaternary GIS collapse after it crossed a climate/ice-sheet stability threshold that may have been no more than several degrees above pre-industrial temperatures.

  18. Mass balance of the Greenland ice sheet - a study of ICESat data, surface density and firn compaction modelling

    DEFF Research Database (Denmark)

    Sørensen, L. S.; Simonsen, Sebastian Bjerregaard; Nielsen, K.

    2010-01-01

    ICESat has provided surface elevation measurements of the ice sheets since the launch in January 2003, resulting in a unique data set for monitoring the changes of the cryosphere. Here we present a novel method for determining the mass balance of the Greenland ice sheet derived from ICESat...... in estimating the mass balance of the Greenland ice sheet. We find firn dynamics and surface densities to be important factors in deriving the mass loss from remote sensing altimetry. The volume change derived from ICESat data is corrected for firn compaction, vertical bedrock movement and an intercampaign...... boundary conditions. We find an annual mass loss of the Greenland ice sheet of 210 ± 21 Gt yr-1 in the period from October 2003 to March 2008. This result is in good agreement with other studies of the Greenland ice sheet mass balance, based on different remote sensing techniques....

  19. Inferring Firn Permeability from Pneumatic Testing: A Case Study on the Greenland Ice Sheet

    Science.gov (United States)

    Sommers, Aleah N.; Rajaram, Harihar; Weber, Eliezer P.; MacFerrin, Michael J.; Colgan, William T.; Stevens, C. Max

    2017-03-01

    Across the accumulation zone of the Greenland ice sheet, summer temperatures can be sufficiently warm to cause widespread melting, as was the case in July 2012 when the entire ice sheet experienced a brief episode of enhanced surface ablation. The resulting meltwater percolates into the firn and refreezes, to create ice lenses and layers within the firn column. This is an important process to consider when estimating the surface mass balance of the ice sheet. The rate of meltwater percolation depends on the permeability of the firn, a property that is not well constrained in the presence of refrozen ice layers and lenses. We present a novel, inexpensive method for measuring in-situ firn permeability using pneumatic testing, a well-established technique used in environmental engineering and hydrology. To illustrate the capabilities of this method, we estimate both horizontal and vertical permeability from pilot tests at six sites on the Greenland ice sheet: KAN-U, DYE-2, EKT, NASA-SE, Saddle, and EastGRIP. These sites cover a range of conditions from mostly dry firn (EastGRIP), to firn with several ice layers and lenses from refrozen meltwater (Saddle, NASA-SE, EKT), to firn with extensive ice layers (DYE-2 and KAN-U). The estimated permeability in firn without refrozen ice layers at EastGRIP agrees well with the range previously reported using an air permeameter to measure permeability through firn core samples at Summit, Greenland. At sites with ice lenses or layers, we find high degrees of anisotropy, with vertical permeability much lower than horizontal permeability. Pneumatic testing is a promising and low-cost technique for measuring firn permeability, particularly as meltwater production increases in the accumulation zone and ice layers and lenses from refrozen melt layers become more prevalent. In these initial proof-of-concept tests, the estimated permeabilities represent effective permeability at the meter scale. With appropriately higher vacuum pressures

  20. On the importance of the albedo parameterization for the mass balance of the Greenland ice sheet in EC-Earth

    OpenAIRE

    Helsen, M.M.; van de Wal, R. S. W.; Reerink, T. J.; R. Bintanja; Madsen, M.S.; Yang, S; Li, Q; Zhang, Q

    2017-01-01

    The albedo of the surface of ice sheets changes as a function of time due to the effects of deposition of new snow, ageing of dry snow, bare ice exposure, melting and run-off. Currently, the calculation of the albedo of ice sheets is highly parameterized within the earth system model EC-Earth by taking a constant value for areas with thick perennial snow cover. This is an important reason why the surface mass balance (SMB) of the Greenland ice sheet (GrIS) is poorly resolved...

  1. Testing the influence of subglacial erosion on the long-term evolution and stability of continental ice sheets using numerical modelling

    Science.gov (United States)

    Swift, D. A.; Egholm, D. L.; Brædstrup, C. F.; Cook, S.; Livingstone, S. J.; Clark, C.; Patton, H.; Ely, J.

    2013-12-01

    Focussed erosion beneath continental ice sheets promotes efficient evacuation of ice along fast-flowing marine outlet glacier systems. Theory indicates that bed profiles should tend toward uniformly overdeepened geometries that will reduce ice sheet stability because (a) grounding lines situated on negative slopes are vulnerable to catastrophic retreat and (b) grounding-line stability is sensitive to ice velocity, meaning grounding lines should become unstable as overdeepening causes subglacial water pressures and basal sediment thickness and continuity to increase. This suggests a conceptual model of ice-bed evolution in which ice sheets are self-destructive, because bed erosion reduces equilibrium ice sheet volume and extent. However, many outlet glacier and ice stream systems possess complex bed topographies, raising questions about the nature of subglacial landscape evolution that have major implications for our understanding of ice sheet evolution and stability. For example, a contrasting model of ice-bed evolution in which strong ice-erosion feedbacks produce multiple overdeepenings might enhance ice sheet stability, because numerous bed undulations should resist fast ice flow and impede grounding line retreat. We therefore explore the possible glaciological significance of contrasting models of subglacial landscape evolution using a higher-order ice sheet model (iSOSIA) and assess the implications for the evolution and stability of continental ice sheets. The results will also aid understanding of contemporary ice sheet stability and identify weaknesses in process understanding that will aid further development of ice-erosion models.

  2. The sensitivity of the Late Saalian (140 ka) and LGM (21 ka) Eurasian ice sheets to sea surface conditions

    Energy Technology Data Exchange (ETDEWEB)

    Colleoni, Florence [Centro Euro-Mediterraneo per i Cambiamenti Climatici, Bologna (Italy); UJF, CNRS, Laboratoire de Glaciologie et Geophysique de l' Environnement, Saint Martin d' Heres Cedex (France); Stockholm University, Department of Geological Sciences, Stockhlom (Sweden); Liakka, Johan [Stockholm University, Department of Meteorology, Stockholm (Sweden); Krinner, Gerhard; Peyaud, Vincent [UJF, CNRS, Laboratoire de Glaciologie et Geophysique de l' Environnement, Saint Martin d' Heres Cedex (France); Jakobsson, Martin [Stockholm University, Department of Geological Sciences, Stockhlom (Sweden); Masina, Simona [Centro Euro-Mediterraneo per i Cambiamenti Climatici, Istituto Nazionale di Geofisica e Vulcanologia, Bologna (Italy)

    2011-08-15

    This work focuses on the Late Saalian (140 ka) Eurasian ice sheets' surface mass balance (SMB) sensitivity to changes in sea surface temperatures (SST). An Atmospheric General Circulation Model (AGCM), forced with two preexisting Last Glacial Maximum (LGM, 21 ka) SST reconstructions, is used to compute climate at 140 and 21 ka (reference glaciation). Contrary to the LGM, the ablation almost stopped at 140 ka due to the climatic cooling effect from the large ice sheet topography. Late Saalian SST are simulated using an AGCM coupled with a mixed layer ocean. Compared to the LGM, these 140 ka SST show an inter-hemispheric asymmetry caused by the larger ice-albedo feedback, cooling climate. The resulting Late Saalian ice sheet SMB is smaller due to the extensive simulated sea ice reducing the precipitation. In conclusion, SST are important for the stability and growth of the Late Saalian Eurasian ice sheet. (orig.)

  3. Mapping of ice layer extent and snow accumulation in the percolation zone of the Greenland ice sheet

    Science.gov (United States)

    Nghiem, S. V.; Steffen, K.; Neumann, G.; Huff, R.

    2005-01-01

    The Greenland ice sheet underwent record extensive melt in 2002 and prolonged melt in 2003. The severe melting created a significant and extensive ice layer over the Greenland ice sheet. An innovative approach is developed to detect the ice layer formation using data acquired by the SeaWinds scatterometer on the QuikSCAT satellite. QuikSCAT backscatter together with in situ data from automatic weather stations of the Greenland Climate Network are used to map the extent of ice layer formation. The results reveal areas of extensive ice layer formed by the 2002 melt, which is consistent with the maximum melt extent in 2002. Moreover, during freezing seasons, QuikSCAT data show a linear decrease in backscatter (in decibels or dB) that is related to the amount of snow accumulation in the ice layer formation region. This snow accumulation signature is caused by the attenuation of radar waves in the snow layer, accumulating since the last major melt event, whose thickness appears as an exponential function in relation to the backscatter signature. We use the Greenland Climate Network data to calibrate the QuikSCAT accumulation rate in order to estimate and map snow accumulation. QuikSCAT results capture the extreme snowfall in mid-April 2003, which deposited more than 0.5 m of snow in a day as measured by the automated weather station at the NASA South East site. Large-scale QuikSCAT results show an anomalous increase of snow accumulation over the southeast region of Greenland during the 2002-2003 freezing season.

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

    Science.gov (United States)

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

    2017-02-01

    Observations of sea level and crustal response to glacial loading cycles provide constraints on the mantle rheology function, E, and as well as on the ice load, I, with the latter being largely free from a-priori glaciological or climate assumptions and appropriate, therefore, for testing any such hypotheses. This paper presents new results for both continental-mantle E and I for the Late Wisconsin ice sheet, using geological evidence for relative sea-level change (rsl) and tilting of palaeo-lake shorelines, complemented with loose constraints from observations of present-day radial crustal displacement across North America. The focus is on evidence from near or within the former maximum ice margins and the resulting earth response is representative of sub-continental mantle conditions. The inversion of the sea-level information has limited resolution for earth rheology and simple three-layer models, characterized by depth-averaged effective lithospheric thickness (H) and upper- and lower-mantle viscosities (ηum and ηum respectively) adequately describe the response function, yielding parameters (earth model E-6) of H = 102 (85-120) km, ηum = 5.1 × 1020 (3.5-7.5)x1020, ηlm = 1.3 × 1022 (0.8-2.8)x1022 where the numbers in parenthesis are 95% confidence limits. The details of the ice sheet, with one exception, are not strongly dependent on the rheological assumptions within this range. The exception is the lower mantle viscosity that remains correlated with the magnitude scaling of the ice sheet: a link that is largely broken by introducing constraints from glacial loading effects on the Earth's rotation and dynamic flattening. The difference between the continental ηum and the comparable estimate of (1-2.5)x1020 for ocean mantle is statistically significant. Shoreline gradient information from Glacial Lakes McConnell, Agassiz, Algonquin and Ojibway provide strong constraints on the response within the interior of the ice sheet and the resulting ice sheet

  5. Development and Applications of the Community Ice Sheet Model

    Energy Technology Data Exchange (ETDEWEB)

    Hoffman, Matthew J. [Los Alamos National Laboratory; Lipscomb, William H. [Los Alamos National Laboratory; Price, Stephen F. [Los Alamos National Laboratory; Johnson, Jesse [University of Montana; Sacks, William [National Center for Atmospheric Research

    2012-07-23

    The initial goals of the project are: (1) create a model for land ice that includes relevant and necessary dynamics, physical processes, and couplings; and (2) apply that model to say something more substantial about SLR in Lme for IPCC AR5 (AR6?).

  6. Tracing Internal Radar Layers in the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Panton, Christian

    of hundreds kilometers with minimal operator intervention, and the methods have been successfully validated between two Greenland deep ice cores with internal match points. In order to remove any operator assistance, we show how the layer slope can be used to detect disturbances in the deep radiostratigraphy...

  7. On the importance of the albedo parameterization for the mass balance of the Greenland ice sheet in EC-Earth

    Directory of Open Access Journals (Sweden)

    M. M. Helsen

    2017-08-01

    Full Text Available The albedo of the surface of ice sheets changes as a function of time due to the effects of deposition of new snow, ageing of dry snow, bare ice exposure, melting and run-off. Currently, the calculation of the albedo of ice sheets is highly parameterized within the earth system model EC-Earth by taking a constant value for areas with thick perennial snow cover. This is an important reason why the surface mass balance (SMB of the Greenland ice sheet (GrIS is poorly resolved in the model. The purpose of this study is to improve the SMB forcing of the GrIS by evaluating different parameter settings within a snow albedo scheme. By allowing ice-sheet albedo to vary as a function of wet and dry conditions, the spatial distribution of albedo and melt rate improves. Nevertheless, the spatial distribution of SMB in EC-Earth is not significantly improved. As a reason for this, we identify omissions in the current snow albedo scheme, such as separate treatment of snow and ice and the effect of refreezing. The resulting SMB is downscaled from the lower-resolution global climate model topography to the higher-resolution ice-sheet topography of the GrIS, such that the influence of these different SMB climatologies on the long-term evolution of the GrIS is tested by ice-sheet model simulations. From these ice-sheet simulations we conclude that an albedo scheme with a short response time of decaying albedo during wet conditions performs best with respect to long-term simulated ice-sheet volume. This results in an optimized albedo parameterization that can be used in future EC-Earth simulations with an interactive ice-sheet component.

  8. On the importance of the albedo parameterization for the mass balance of the Greenland ice sheet in EC-Earth

    Science.gov (United States)

    Helsen, Michiel M.; van de Wal, Roderik S. W.; Reerink, Thomas J.; Bintanja, Richard; Madsen, Marianne S.; Yang, Shuting; Li, Qiang; Zhang, Qiong

    2017-08-01

    The albedo of the surface of ice sheets changes as a function of time due to the effects of deposition of new snow, ageing of dry snow, bare ice exposure, melting and run-off. Currently, the calculation of the albedo of ice sheets is highly parameterized within the earth system model EC-Earth by taking a constant value for areas with thick perennial snow cover. This is an important reason why the surface mass balance (SMB) of the Greenland ice sheet (GrIS) is poorly resolved in the model. The purpose of this study is to improve the SMB forcing of the GrIS by evaluating different parameter settings within a snow albedo scheme. By allowing ice-sheet albedo to vary as a function of wet and dry conditions, the spatial distribution of albedo and melt rate improves. Nevertheless, the spatial distribution of SMB in EC-Earth is not significantly improved. As a reason for this, we identify omissions in the current snow albedo scheme, such as separate treatment of snow and ice and the effect of refreezing. The resulting SMB is downscaled from the lower-resolution global climate model topography to the higher-resolution ice-sheet topography of the GrIS, such that the influence of these different SMB climatologies on the long-term evolution of the GrIS is tested by ice-sheet model simulations. From these ice-sheet simulations we conclude that an albedo scheme with a short response time of decaying albedo during wet conditions performs best with respect to long-term simulated ice-sheet volume. This results in an optimized albedo parameterization that can be used in future EC-Earth simulations with an interactive ice-sheet component.

  9. Incorporation of ice sheet models into an Earth System model: focus ...

    Indian Academy of Sciences (India)

    55

    Coupling of the Antarctic ice sheet model (AISM) to the AOGCM is accomplished via using procedures of resampling, interpolation and assigning to the AISM grid points annually averaged meanings of air surface temperature and precipitation fields generated by the AOGCM. Surface melting, which takes place mainly on ...

  10. Firn Meltwater Retention on the Greenland Ice Sheet: A Model Comparison

    NARCIS (Netherlands)

    Steger, C.R.; Reijmer, C.H.; van den Broeke, MR; Wever, N.; Forster, R.R.; Koenig, L.S.; Kuipers Munneke, P.; Lehning, M.; Lhermitte, S.L.M.; Ligtenberg, SRM; Miège, C.; Noël, Brice

    2017-01-01

    Runoff has recently become the main source of mass loss from the Greenland Ice Sheet and is an important contributor to global sea level rise. Linking runoff to surface meltwater production is complex, as meltwater can be retained within the firn by refreezing or perennial liquid water storage. To

  11. Firn meltwater retention on the Greenland Ice Sheet: a model comparison

    NARCIS (Netherlands)

    Steger, C.R.|info:eu-repo/dai/nl/374628769; Reijmer, C.H.|info:eu-repo/dai/nl/229345956; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643; Wever, N.; Forster, R.R.; Koenig, Lora S.; Kuipers Munneke, P.|info:eu-repo/dai/nl/304831891; Lehning, M.; Lhermitte, S.; Ligtenberg, S.R.M.|info:eu-repo/dai/nl/32821177X; Miege, Clement; Noël, B.P.Y.|info:eu-repo/dai/nl/370612345

    2017-01-01

    Runoff has recently become the main source of mass loss from the Greenland Ice Sheet and is an important contributor to global sea level rise. Linking runoff to surface meltwater production is complex, as meltwater can be retained within the firn by refreezing or perennial liquid water storage. To

  12. The observed katabatic flow at the edge of the Greenland ice sheet during GIMEX-91

    NARCIS (Netherlands)

    Broeke, M.R. van den; Duynkerke, P.G.; Oerlemans, J.

    1994-01-01

    Observations performed in the melting zone of the Greenland ice sheet and over the adjacent tundra in the summer of 1991 are described. The experimental area is the region near St ndre Stromfjord (67°N, 54°W), which is relatively dry and sunny, resulting in the highest mean temperature in

  13. The pattern of anthropogenic signal emergence in Greenland Ice Sheet surface mass balance

    NARCIS (Netherlands)

    Fyke, J.G.; Vizcaino, M.; Lipscomb, W.H.

    2014-01-01

    Surface mass balance (SMB) trends influence observed Greenland Ice Sheet (GrIS) mass loss, but the component of these trends related to anthropogenic forcing is unclear. Here we study the simulated spatial pattern of emergence of an anthropogenically derived GrIS SMB signal between 1850 and 2100

  14. Modelling the evolution of the Antarctic ice sheet since the last interglacial

    NARCIS (Netherlands)

    Maris, M. N A; De Boer, B.; Ligtenberg, S. R M; Crucifix, M.; Van De Berg, W. J.; Oerlemans, J.

    2014-01-01

    We present the effects of changing two sliding parameters, a deformational velocity parameter and two bedrock deflection parameters on the evolution of the Antarctic ice sheet over the period from the last interglacial until the present. These sensitivity experiments have been conducted by running

  15. Sediment plumes as a proxy for local ice-sheet runoff in Kangerlussuaq Fjord, West Greenland

    NARCIS (Netherlands)

    McGRATH, D.; Steffen, K.; Overeem, I.; Mernild, S. H.; Hasholt, B.; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643

    2010-01-01

    Meltwater runoff is an important component of the mass balance of the Greenland ice sheet (GrIS) and contributes to eustatic sea-level rise. In situ measurements of river runoff at the ∼325 outlets are nonexistent due to logistical difficulties. We develop a novel methodology using satellite

  16. Last Interglacial climate and sea-level evolution from a coupled ice sheet-climate model

    NARCIS (Netherlands)

    Goelzer, Heiko|info:eu-repo/dai/nl/412549123; Huybrechts, Philippe; Marie-France, Loutre; Fichefet, Thierry

    2016-01-01

    As the most recent warm period in Earth's history with a sea-level stand higher than present, the Last Interglacial (LIG, ∼130 to 115kyrgBP) is often considered a prime example to study the impact of a warmer climate on the two polar ice sheets remaining today. Here we simulate the Last Interglacial

  17. Dust from the dark region in the western ablation zone of the Greenland ice sheet

    NARCIS (Netherlands)

    Wientjes, I.G.M.|info:eu-repo/dai/nl/296912743; van de Wal, R.S.W.|info:eu-repo/dai/nl/101899556; Reichart, G.-J.|info:eu-repo/dai/nl/165599081; Sluijs, A.|info:eu-repo/dai/nl/311474748; Oerlemans, J.|info:eu-repo/dai/nl/06833656X

    2011-01-01

    A dark region tens of kilometres wide is located in the western ablation zone of the Greenland ice sheet. The dark appearance is caused by higher amounts of dust relative to the brighter surroundings. This dust has either been deposited recently or was brought to the surface by melting of

  18. The response of the southern Greenland ice sheet to the Holocene thermal maximum

    DEFF Research Database (Denmark)

    Larsen, Nicolaj Krog; Kjær, Kurt H.; Lecavalier, Benoit

    2015-01-01

    To determine the long-term sensitivity of the Greenland ice sheet to a warmer climate, we explored how it responded to the Holocene thermal maximum (8–5 cal. kyr B.P.; calibrated to calendar years before present, i.e., A.D. 1950), when lake records show that local atmospheric temperatures...

  19. Higher surface mass balance of the Greenland ice sheet revealed by high-resolution climate modeling

    NARCIS (Netherlands)

    Ettema, J.|info:eu-repo/dai/nl/304831913; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643; van Meijgaard, E.; van de Berg, W.J.|info:eu-repo/dai/nl/304831611; Bamber, Jonathan L.; Box, J.E.; Bales, R.C.

    2009-01-01

    High-resolution (∼11 km) regional climate modeling shows total annual precipitation on the Greenland ice sheet for 1958–2007 to be up to 24% and surface mass balance up to 63% higher than previously thought. The largest differences occur in coastal southeast Greenland, where the much higher

  20. Significant contribution of insolation to Eemian melting of the Greenland ice sheet

    NARCIS (Netherlands)

    van de Berg, W.J.|info:eu-repo/dai/nl/304831611; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643; Ettema, J.|info:eu-repo/dai/nl/304831913; van Meijgaard, E.; Kaspar, F.

    2011-01-01

    During the Eemian interglacial period, 130,000 to 114,000 years ago, the volume of the Greenland ice sheet was about 30–60% smaller than the present-day volume1,2. Summer temperatures in the Arctic region were about 2–4 K higher than today3–5, leading to the suggestion that Eemian conditions could

  1. Climate of the Greenland ice sheet using a high-resolution climate model - Part 1: Evaluation

    NARCIS (Netherlands)

    Ettema, J.|info:eu-repo/dai/nl/304831913; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643; van Meijgaard, E.; van de Berg, W.J.|info:eu-repo/dai/nl/304831611; Box, J.E.; Steffen, K.

    2010-01-01

    A simulation of 51 years (1957-2008) has been performed over Greenland using the regional atmospheric climate model (RACMO2/GR) at a horizontal grid spacing of 11 km and forced by ECMWF re-analysis products. To better represent processes affecting ice sheet surface mass balance, such as meltwater

  2. A mass balance model for the Eurasian ice sheet for the last 120,000 years

    NARCIS (Netherlands)

    van den Berg, J.; van de Wal, R.S.W.|info:eu-repo/dai/nl/101899556; Oerlemans, J.|info:eu-repo/dai/nl/06833656X

    2008-01-01

    We present a mass balance model for Eurasia which is based on the calculation of accumulation from a moisture balance concept. The model is forced with 500 hPa temperatures from GCM time slices at LGM and present day. The model simulates key characteristics, such as control on the size of ice sheets

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

    Science.gov (United States)

    Sangiorgi, Francesca; Bijl, Peter K; Passchier, Sandra; Salzmann, Ulrich; Schouten, Stefan; McKay, Robert; Cody, Rosemary D; Pross, Jörg; van de Flierdt, Tina; Bohaty, Steven M; Levy, Richard; Williams, Trevor; Escutia, Carlota; Brinkhuis, Henk

    2018-01-22

    Observations and model experiments highlight the importance of ocean heat in forcing ice sheet retreat during the present and geological past, but past ocean temperature data are virtually missing in ice sheet proximal locations. Here we document paleoceanographic conditions and the (in)stability of the Wilkes Land subglacial basin (East Antarctica) during the mid-Miocene (~17-13.4 million years ago) by studying sediment cores from offshore Adélie Coast. Inland retreat of the ice sheet, temperate vegetation, and warm oligotrophic waters characterise the mid-Miocene Climatic Optimum (MCO; 17-14.8 Ma). After the MCO, expansion of a marine-based ice sheet occurs, but remains sensitive to melting upon episodic warm water incursions. Our results suggest that the mid-Miocene latitudinal temperature gradient across the Southern Ocean never resembled that of the present day. We demonstrate that a strong coupling of oceanic climate and Antarctic continental conditions existed and that the East Antarctic subglacial basins were highly sensitive to ocean warming.

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

    NARCIS (Netherlands)

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

    2018-01-01

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

  5. A model of Greenland ice sheet deglaciation constrained by observations of relative sea level and ice extent

    Science.gov (United States)

    Lecavalier, Benoit S.; Milne, Glenn A.; Simpson, Matthew J. R.; Wake, Leanne; Huybrechts, Philippe; Tarasov, Lev; Kjeldsen, Kristian K.; Funder, Svend; Long, Antony J.; Woodroffe, Sarah; Dyke, Arthur S.; Larsen, Nicolaj K.

    2014-10-01

    An ice sheet model was constrained to reconstruct the evolution of the Greenland Ice Sheet (GrIS) from the Last Glacial Maximum (LGM) to present to improve our understanding of its response to climate change. The study involved applying a glaciological model in series with a glacial isostatic adjustment and relative sea-level (RSL) model. The model reconstruction builds upon the work of Simpson et al. (2009) through four main extensions: (1) a larger constraint database consisting of RSL and ice extent data; model improvements to the (2) climate and (3) sea-level forcing components; (4) accounting for uncertainties in non-Greenland ice. The research was conducted primarily to address data-model misfits and to quantify inherent model uncertainties with the Earth structure and non-Greenland ice. Our new model (termed Huy3) fits the majority of observations and is characterised by a number of defining features. During the LGM, the ice sheet had an excess of 4.7 m ice-equivalent sea-level (IESL), which reached a maximum volume of 5.1 m IESL at 16.5 cal ka BP. Modelled retreat of ice from the continental shelf progressed at different rates and timings in different sectors. Southwest and Southeast Greenland began to retreat from the continental shelf by ˜16 to 14 cal ka BP, thus responding in part to the Bølling-Allerød warm event (c. 14.5 cal ka BP); subsequently ice at the southern tip of Greenland readvanced during the Younger Dryas cold event. In northern Greenland the ice retreated rapidly from the continental shelf upon the climatic recovery out of the Younger Dryas to present-day conditions. Upon entering the Holocene (11.7 cal ka BP), the ice sheet soon became land-based. During the Holocene Thermal Maximum (HTM; 9-5 cal ka BP), air temperatures across Greenland were marginally higher than those at present and the GrIS margin retreated inland of its present-day southwest position by 40-60 km at 4 cal ka BP which produced a deficit volume of 0.16 m IESL

  6. Delineation of Surface and Near-Surface Melt on the Greenland Ice Sheet Using MODIS and QuikSCAT data

    Science.gov (United States)

    Hall, Dorothy K.; Nghiem, Son V.; DiGirolamo, Nicolo E.; Neumann, Gregory; Schaaf, Crystal B.

    2010-01-01

    This slide presentation reviews the use of MODIS and QuikSCAT data to measure the surface and sub-surface melting on the Greenland Ice Sheet. The project demonstrated the consistence of this technique for measuring the ice melt on the Greenland Ice Sheet. The blending of the two instruments data allows for determination of surface vs subsurface melting. Also, the use of albedo maps can provide information about the intensity of the melting.

  7. Ice sheets as a missing component of the global silicon cycle

    Science.gov (United States)

    Hawkings, J.; Hatton, J.; Hendry, K. R.; Wadham, J.; Ivanovic, R. F.; Kohler, T. J.; Stibal, M.; Beaton, A.; Lamarche-Gagnon, G.; Tedstone, A.; Pike, J.; Tranter, M.

    2016-12-01

    Silicon (Si) plays an important role in global biogeochemical cycles. It is required for the growth of diatoms, silicoflagellates, radiolarians and some sponges. Diatoms build their frustules out of silica and account for approximately half of oceanic primary production. Therefore determining the sensitivity of the Si cycle in the past, and its likely response to future climate warming, is important for our understanding of marine ecosystem change, biogeochemical cycling and, by association, the efficiency of the ocean's biological carbon pump. The δ30Si of biogenic silica in marine sediments is increasingly being used as a palaeoceanographic tool. In particular, there has been a focus on the δ30Si change from the Last Glacial Maximum (LGM; 21-25 ka) to present, with opal records showing an increase in δ30Si of 0.2-1.0 ‰ from LGM to present day. This has previously been explained by lower biological utilisation of Si and by swings in intermediate and deep-water dissolved silica due to changes in oceanic circulation. Here we challenge the paradigm that the ocean Si input flux and δ30Si composition was uniform over glacial-interglacial timescales. During the LGM glaciers and ice sheets covered nearly 30% of land surface, including much of North America and northern Eurasia. These palaeo ice sheets exported large quantities of eroded sediment into the oceans, and their wastage raised global sea level by 130 m. Research indicates glaciers may export significant quantities of nutrients to downstream ecosystems, including large amounts of reactive silica. Si fluxes and their associated δ30Si signature from the palaeo ice sheets have not been considered in previous interpretations of the marine Si inventory and δ30Si record. Here, we demonstrate the importance of huge ice sheet meltwater fluxes to the marine Si inventory and oceanic δ30Si composition during the last deglaciation. We present the first dissolved and amorphous particulate silica time series with

  8. Initiation and long-term instability of the East Antarctic Ice Sheet

    Science.gov (United States)

    Gulick, Sean P. S.; Shevenell, Amelia E.; Montelli, Aleksandr; Fernandez, Rodrigo; Smith, Catherine; Warny, Sophie; Bohaty, Steven M.; Sjunneskog, Charlotte; Leventer, Amy; Frederick, Bruce; Blankenship, Donald D.

    2017-12-01

    Antarctica’s continental-scale ice sheets have evolved over the past 50 million years. However, the dearth of ice-proximal geological records limits our understanding of past East Antarctic Ice Sheet (EAIS) behaviour and thus our ability to evaluate its response to ongoing environmental change. The EAIS is marine-terminating and grounded below sea level within the Aurora subglacial basin, indicating that this catchment, which drains ice to the Sabrina Coast, may be sensitive to climate perturbations. Here we show, using marine geological and geophysical data from the continental shelf seaward of the Aurora subglacial basin, that marine-terminating glaciers existed at the Sabrina Coast by the early to middle Eocene epoch. This finding implies the existence of substantial ice volume in the Aurora subglacial basin before continental-scale ice sheets were established about 34 million years ago. Subsequently, ice advanced across and retreated from the Sabrina Coast continental shelf at least 11 times during the Oligocene and Miocene epochs. Tunnel valleys associated with half of these glaciations indicate that a surface-meltwater-rich sub-polar glacial system existed under climate conditions similar to those anticipated with continued anthropogenic warming. Cooling since the late Miocene resulted in an expanded polar EAIS and a limited glacial response to Pliocene warmth in the Aurora subglacial basin catchment. Geological records from the Sabrina Coast shelf indicate that, in addition to ocean temperature, atmospheric temperature and surface-derived meltwater influenced East Antarctic ice mass balance under warmer-than-present climate conditions. Our results imply a dynamic EAIS response with continued anthropogenic warming and suggest that the EAIS contribution to future global sea-level projections may be under-estimated.

  9. Heinrich event 1: an example of dynamical ice-sheet reaction to oceanic changes

    Directory of Open Access Journals (Sweden)

    J. Álvarez-Solas

    2011-11-01

    Full Text Available Heinrich events, identified as enhanced ice-rafted detritus (IRD in North Atlantic deep sea sediments (Heinrich, 1988; Hemming, 2004 have classically been attributed to Laurentide ice-sheet (LIS instabilities (MacAyeal, 1993; Calov et al., 2002; Hulbe et al., 2004 and assumed to lead to important disruptions of the Atlantic meridional overturning circulation (AMOC and North Atlantic deep water (NADW formation. However, recent paleoclimate data have revealed that most of these events probably occurred after the AMOC had already slowed down or/and NADW largely collapsed, within about a thousand years (Hall et al., 2006; Hemming, 2004; Jonkers et al., 2010; Roche et al., 2004, implying that the initial AMOC reduction could not have been caused by the Heinrich events themselves.

    Here we propose an alternative driving mechanism, specifically for Heinrich event 1 (H1; 18 to 15 ka BP, by which North Atlantic ocean circulation changes are found to have strong impacts on LIS dynamics. By combining simulations with a coupled climate model and a three-dimensional ice sheet model, our study illustrates how reduced NADW and AMOC weakening lead to a subsurface warming in the Nordic and Labrador Seas resulting in rapid melting of the Hudson Strait and Labrador ice shelves. Lack of buttressing by the ice shelves implies a substantial ice-stream acceleration, enhanced ice-discharge and sea level rise, with peak values 500–1500 yr after the initial AMOC reduction. Our scenario modifies the previous paradigm of H1 by solving the paradox of its occurrence during a cold surface period, and highlights the importance of taking into account the effects of oceanic circulation on ice-sheets dynamics in order to elucidate the triggering mechanism of Heinrich events.

  10. Quantifying Ice-sheet/Ice-shelf Dynamics and Variability with Meter-scale DEM and Velocity Timeseries

    Science.gov (United States)

    Shean, D. E.; Joughin, I. R.; Smith, B. E.; Moratto, Z. M.; Porter, C.; Morin, P. J.

    2012-12-01

    Both the Antarctic and Greenland ice sheets are losing mass at an increasing rate, although loss due to accelerating flow and dynamic thinning remains poorly understood. We are using complementary data from repeat satellite and airborne observations to investigate the relationship between ice-sheet/ice-shelf dynamics and geometry on seasonal to interannual timescales. High-resolution along-track stereo imagery from commercial satellite vendors DigitalGlobe and GeoEye provides unprecedented spatial (~0.5 m/px with ~17 km swath width) and temporal (weekly/monthly) resolution for these efforts. We have developed an automated pipeline using open-source software to produce orthoimage, DEM, and surface velocity products from DigitalGlobe imagery. High-contrast surface texture (e.g. sastrugi, crevasses) visible at sub-meter resolution provides near-perfect image correlation (~99% success rate) during DEM and velocity map derivation. Elevation data from IceBridge ATM/LVIS, ICESat GLAS, and GPS campaigns are used to correct DEMs and perform accuracy assessment. Preliminary tests over exposed bedrock provide relative vertical accuracy estimates of <1-2 m for Worldview-1/2 DEMs. Velocity data from TerraSAR-X and GPS campaigns provide validation for surface velocity products, with horizontal error estimates of <10 m. Velocity and elevation change products with 2-4 m/px spatial resolution allow for unprecedented 3D dynamic characterization of sub-km flow transition zones (e.g. grounding lines, shear margins), capturing both local and regional variations due to melting and dynamic thinning. We present timeseries for West Greenland (Jakobshavn front - 20 observations, Jakobshavn south catchment - 10) and West Antarctica (Pine Island and Thwaites - 5 each) from 2009-2012. These observations complement ongoing efforts to measure and model outlet glacier dynamics, with implications for future ice-sheet mass balance estimates.

  11. Severnaya Zemlya, arctic Russia: a nucleation area for Kara Sea ice sheets during the Middle to Late Quaternary

    DEFF Research Database (Denmark)

    Möller, Per; Lubinski, David J.; Ingólfsson, Ólafur

    2006-01-01

    repeated expansions of local ice caps exclusively, suggesting wet-based ice cap advance followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains, appear to have repeatedly fostered initiation......Quaternary glacial stratigraphy and relative sea-level changes reveal at least four expansions of the Kara Sea ice sheet over the Severnaya Zemlya Archipelago at 79°N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from......-5e and MIS 5d-3. The MIS 6-5e event, associated with the high marine limit, implies ice-sheet thickness of >2000 m only 200 km from the deep Arctic Ocean, consistent with published evidence of ice grounding at ~1000 m water depth in the central Arctic Ocean. Till fabrics and glacial tectonics record...

  12. Sediment plume response to surface melting and supraglacial lake drainages on the Greenland ice sheet

    DEFF Research Database (Denmark)

    Chu, Vena W.; Smith, Laurence C; Rennermalm, Asa K.

    2009-01-01

    of a downstream sediment plume in Kangerlussuaq Fjord by comparing: (1) plume area and suspended sediment concentration from Moderate Resolution Imaging Spectroradiometer (MODIS) imagery and field data; (2) ice-sheet melt extent from Special Sensor Microwave/Imager (SSM/I) passive microwave data; and (3......) supraglacial lake drainage events from MODIS. Results confirm that the origin of the sediment plume is meltwater release from the ice sheet. Interannual variations in plume area reflect interannual variations in surface melting. Plumes appear almost immediately with seasonal surface-melt onset, provided...... the estuary is free of landfast sea ice. A seasonal hysteresis between melt extent and plume area suggests late-season exhaustion in sediment supply. Analysis of plume sensitivity to supraglacial events is less conclusive, with 69% of melt pulses and 38% of lake drainage events triggering an increase in plume...

  13. Contamination of the Arctic reflected in microbial metagenomes from the Greenland ice sheet

    Science.gov (United States)

    Hauptmann, Aviaja L.; Sicheritz-Pontén, Thomas; Cameron, Karen A.; Bælum, Jacob; Plichta, Damian R.; Dalgaard, Marlene; Stibal, Marek

    2017-07-01

    Globally emitted contaminants accumulate in the Arctic and are stored in the frozen environments of the cryosphere. Climate change influences the release of these contaminants through elevated melt rates, resulting in increased contamination locally. Our understanding of how biological processes interact with contamination in the Arctic is limited. Through shotgun metagenomic data and binned genomes from metagenomes we show that microbial communities, sampled from multiple surface ice locations on the Greenland ice sheet, have the potential for resistance to and degradation of contaminants. The microbial potential to degrade anthropogenic contaminants, such as toxic and persistent polychlorinated biphenyls, was found to be spatially variable and not limited to regions close to human activities. Binned genomes showed close resemblance to microorganisms isolated from contaminated habitats. These results indicate that, from a microbiological perspective, the Greenland ice sheet cannot be seen as a pristine environment.

  14. The neglect of cliff instability can underestimate warming period melting in Antarctic ice sheet models

    CERN Document Server

    Ruckert, Kelsey L; Pollard, Dave; Guan, Yawen; Wong, Tony E; Forest, Chris E; Keller, Klaus

    2016-01-01

    The response of the Antarctic ice sheet (AIS) to changing climate forcings is an important driver of sea-level changes. Anthropogenic climate changes may drive a sizeable AIS tipping point response with subsequent increases in coastal flooding risks. Many studies analyzing flood risks use simple models to project the future responses of AIS and its sea-level contributions. These analyses have provided important new insights, but they are often silent on the effects of potentially important processes such as Marine Ice Sheet Instability (MISI) or Marine Ice Cliff Instability (MICI). These approximations can be well justified and result in more parsimonious and transparent model structures. This raises the question how this approximation impacts hindcasts and projections. Here, we calibrate a previously published AIS model, which neglects the effects of MICI, using a combination of observational constraints and a Bayesian inversion method. Specifically, we approximate the effects of missing MICI by comparing ou...

  15. The Greenland ice sheet during LGM – a model based on field observations

    DEFF Research Database (Denmark)

    Funder, Svend Visby; Kjeldsen, Kristian Kjellerup; Kjær, Kurt H.

    based on observations on land, such as weathering limits on coastal mountains, major moraine belts, and altitudes of marine limits. Extrapolation from this gave estimates of LGM ice cover on the shelf ranging from inner to outer shelf, often under the assumption that it had to be either or......In the light of recent years¿ intense discussion on the role of Greenland Ice Sheet in global warming its reaction to past climatic change can contribute valuable information. We have updated the evidence for LGM (c. 23-20 kaBP) icesheet coverage. previous reviews An important part of the main...... The issue is complicated by the circumstance that during LGM (Last glacial maximum) the ice sheet margins around the whole perimeter stood on the shelf and “classical” evidence, such as large moraine belts, extensive sandurs and major drainage diversions do not apply. The first estimates were therefore...

  16. Monthly solutions of ice sheet mass balance at basin scale – and their associated uncertainties

    DEFF Research Database (Denmark)

    Sørensen, Louise Sandberg; Barletta, Valentina Roberta; Forsberg, René

    2012-01-01

    There are still discrepancies in published ice sheet mass balance results, even between ones based on the same data sets. It can be difficult to conclude from where the discrepancies arise, and it is therefore important to cross calibrate methods, data and models in order to determine the uncerta...... in the behaviour of time series. We compare our GRACE derived regional estimates with independent mass change results based on altimetry data from NASA’s Ice Cloud and land Elevation Satellite.......There are still discrepancies in published ice sheet mass balance results, even between ones based on the same data sets. It can be difficult to conclude from where the discrepancies arise, and it is therefore important to cross calibrate methods, data and models in order to determine...

  17. The evolution of the Antarctic ice sheet at the Eocene-Oligocene Transition.

    Science.gov (United States)

    Ladant, Jean-Baptiste; Donnadieu, Yannick; Dumas, Christophe

    2017-04-01

    An increasing number of studies suggest that the Middle to Late Eocene has witnessed the waxing and waning of relatively small ephemeral ice sheets. These alternating episodes culminated in the Eocene-Oligocene transition (34 - 33.5 Ma) during which a sudden and massive glaciation occurred over Antarctica. Data studies have demonstrated that this glacial event is constituted of two 50 kyr-long steps, the first of modest (10 - 30 m of equivalent sea level) and the second of major (50 - 90 m esl) glacial amplitude, and separated by 200 kyrs. Since a decade, modeling studies have put forward the primary role of CO2 in the initiation of this glaciation, in doing so marginalizing the original "gateway hypothesis". Here, we investigate the impacts of CO2 and orbital parameters on the evolution of the ice sheet during the 500 kyrs of the EO transition using a tri-dimensional interpolation method. The latter allows precise orbital variations, CO2 evolution and ice sheet feedbacks (including the albedo) to be accounted for. Our results show that orbital variations are instrumental in initiating the first step of the EO glaciation but that the primary driver of the major second step is the atmospheric pCO2 crossing a modelled glacial threshold of 900 ppm. Although model-dependant, this higher glacial threshold makes a stronger case for ephemeral Middle-Late Eocene ice sheets. In addition, sensitivity tests demonstrate that the small first step only exists if the absolute pCO2 value remains within 100 ppm higher than the glacial threshold during the first 250 kyrs of the transition. Thereby, the pCO2 sufficiently counterbalances the strong insolation minima occurring at 33.9 and 33.8 Ma but is low enough to allow the ice sheet to nucleate. Nevertheless, questions remain as to what may cause this pCO2 drop.

  18. Quantifying `missing melt' in regional climate model predictions of Greenland ice sheet change

    Science.gov (United States)

    Leeson, A.; Eastoe, E.; Fettweis, X.

    2016-12-01

    Since 2010, the rate of mass loss from Greenland has increased and the ice sheet has experienced more episodes of rare and extreme surface melt. In addition to directly removing more of the ice sheet into the sea, extreme melt events reduce the reflectivity of the ice sheet and can warm the perennial snow pack through latent heat release when the melt water refreezes, both of which act as a positive feedback to further enhance melt. As such, an understanding of the frequency, duration and magnitude of extreme melt events is necessary to constrain predictions of future ice sheet state. Melting on Greenland is typically predicted using Regional Climate Models (RCM), however, although RCMs are excellent at reproducing 'normal' conditions (low amplitude/frequency signals) and long term trends, they may not resolve unusually high/low magnitude features, particularly of either small spatial scale or short temporal duration. Extreme melt events for example, typically only last for a day or so and thus their effects are likely omitted from RCM estimates of future ice sheet change. Here, we present a new climatology of historic extreme melt events on Greenland, diagnosed using tools from Extreme Value Theory Statistics. We use these data to evaluate the ability of the MAR (Modele Atmospherique Regional) RCM to reproduce the frequency, magnitude and duration of extreme melt events in the past, with forcing by both re-analysis (ERA-Interim) and GCM (CMIP5) predictions at the model boundaries. By modelling the relationship between MAR predicted values, and observations, we are able to estimate the degree to which MAR over/under estimates melting due to the omission of extreme events for a given boundary forcing. We use this relationship together with MAR predictions of future change to quantify the likely amount of `missing melt' in MAR-based projections of global sea level rise due to these short term, high magnitude perturbations.

  19. Meltwater retention in a transect across the Greenland ice sheet

    DEFF Research Database (Denmark)

    Bøggild, Carl Egede; Forsberg, René; Reeh, Niels

    2005-01-01

    with alternating horizontal and vertical water-flow directions, where the processes of pore refreezing (RF) (vertical flow) and superimposed ice (SI) formation (horizontal flow) occur. The flow cannot be forecasted and quantified when water first enters cold, dry snow. However, because the two processes are driven...... at similar to 1400 m a.s.l. in the west and similar to 1600 m a.s.l. in the east. Since the SI potential is high in most places and the warming from SI formation predominately occurs near to the surface, it is argued that winter cooling effectively recharges the cold content of the snow/firn/ice pack......, preventing the development of isothermal conditions and subsequent runoff. However, SI formation declines over time, so an extension of the melting season could result in deeper percolation beyond the SI layer....

  20. High resolution ice thickness, bed topography, and roughness of a land terminating section of the western Greenland Ice Sheet

    Science.gov (United States)

    Lindback, K.; Pettersson, R.; Doyle, S. H.; Hubbard, A.; Helanow, C.; Jansson, P.; Lintz Christensen, E.; Kristensen, S. S.; Stenseng, L.; Forsberg, R.

    2013-12-01

    We present ice thickness and bed topography maps with high spatial resolution (250-500 m) of a large land terminating section of the western Greenland Ice Sheet. The maps cover the Isunnguata Sermia, Russell, and Leverett outlet glaciers and their catchment areas up to an elevation of ~1,700 m above sea level. The bed topography shows an intricate subglacial trough system, resembling the landscape in the proglacial area. We also calculate the hydraulic potential to get a proxy of the subglacial routing of water in the area. To analyse the geomorphological conditions of the bed, we calculated the spectral roughness. We see a strong correlation of low roughness values with the ice flow direction; this makes it important to assess the direction of the radar profiles in relation to the flow direction when calculating effective subglacial roughness for an area. Low roughness values and high surface velocities also coincide with an overdeepened trough system in the northern parts of the area; an area where active smoothing could be taking place. The southern parts consist of high bed elevations and have generally high roughness values; the bedrock likely consists of hard unreworked orthogneiss. There is strong evidence that the subglacial troughs have a preglacial origin, since they are aligned with geological weakness zones in the proglacial area and several lineaments can be traced for long distances underneath the ice sheet.

  1. Effect of Mantle Rheology on Viscous Heating induced during Ice Sheet Cycles

    Science.gov (United States)

    Huang, Pingping; Wu, Patrick; van der Wal, Wouter

    2017-04-01

    Hanyk et al. (2005) studied the viscous shear heating in the mantle induced by the surface loading and unloading of a parabolic-shaped Laurentide-size ice sheet. They found that for linear rheology, viscous heating is mainly concentrated below the ice sheet. The depth extent of the heating in the mantle is determined by the viscosity distribution. Also, the magnitude of viscous heating is significantly affected by the rate of ice thickness change. However, only one ice sheet has been considered in their work and the interactions between ice sheets and ocean loading have been neglected. Furthermore, only linear rheology has been considered, although they suggested that non-Newtonian rheology may have a stronger effect. Here we follow Hanyk et al. (2005) and computed the viscous dissipation for viscoelastic models using the finite element methodology of Wu (2004) and van der Wal et al. (2010). However, the global ICE6G model (Peltier et al. 2015) with realistic oceans is used here to provide the surface loading. In addition, viscous heating in non-linear rheology, composite rheology, in addition to linear rheology with uniform or VM5a profile are computed and compared. Our results for linear rheology mainly confirm the findings of Hanyk et al. (2005). For both non-linear and composite rheologies, viscous heating is also mainly distributed near and under the ice sheets, but, more concentrated; depending on the horizontal dimension of the ice sheet, it can extend into the lower mantle, but for some of the time, not as deep as that for linear rheology. For composite rheology, the viscous heating is dominated by the effect of non-linear relation between the stress and the strain. The ice history controls the time when the local maximum in viscous heating appears. However, the magnitude of the viscous heating is affected by mantle rheology as well as the ice loading. Due to viscosity stratification, the shape of the region with high viscous heating in model VM5a is a

  2. Ice flow dynamics and surface meltwater flux at a land-terminating sector of the Greenland ice sheet

    DEFF Research Database (Denmark)

    Fitzpatrick, Andrew A. W.; Hubbard, Alun; Joughin, Ian

    2013-01-01

    We present satellite-derived velocity patterns for the two contrasting melt seasons of 2009-10 across Russell Glacier catchment, a western, land-terminating sector of the Greenland ice sheet which encompasses the K(angerlussuaq)-transect. Results highlight great spatial heterogeneity in flow...... system, regulating flow dynamics. Despite this, the cumulative surface flux over the record melt year of 2010 was still greater compared with the perturbation over the average melt year of 2009. This study supports the proposition that local surface meltwater runoff couples to basal hydrology driving ice......, indicating that structural controls such as bedrock geometry govern ice discharge into individual outlet troughs. Results also reveal strong seasonal flow variability extending 57 km up-glacier to 1200 m elevation, with the largest acceleration (100% over 11 days) occurring within 10 km of the margin...

  3. On the recent contribution of the Greenland ice sheet to sea level change

    Directory of Open Access Journals (Sweden)

    M. R. van den Broeke

    2016-09-01

    Full Text Available We assess the recent contribution of the Greenland ice sheet (GrIS to sea level change. We use the mass budget method, which quantifies ice sheet mass balance (MB as the difference between surface mass balance (SMB and solid ice discharge across the grounding line (D. A comparison with independent gravity change observations from GRACE shows good agreement for the overlapping period 2002–2015, giving confidence in the partitioning of recent GrIS mass changes. The estimated 1995 value of D and the 1958–1995 average value of SMB are similar at 411 and 418 Gt yr−1, respectively, suggesting that ice flow in the mid-1990s was well adjusted to the average annual mass input, reminiscent of an ice sheet in approximate balance. Starting in the early to mid-1990s, SMB decreased while D increased, leading to quasi-persistent negative MB. About 60 % of the associated mass loss since 1991 is caused by changes in SMB and the remainder by D. The decrease in SMB is fully driven by an increase in surface melt and subsequent meltwater runoff, which is slightly compensated by a small ( <  3 % increase in snowfall. The excess runoff originates from low-lying ( <  2000 m a.s.l. parts of the ice sheet; higher up, increased refreezing prevents runoff of meltwater from occurring, at the expense of increased firn temperatures and depleted pore space. With a 1991–2015 average annual mass loss of  ∼  0.47 ± 0.23 mm sea level equivalent (SLE and a peak contribution of 1.2 mm SLE in 2012, the GrIS has recently become a major source of global mean sea level rise.

  4. Evidence for a dynamic East Antarctic ice sheet during the mid-Miocene climate transition

    Science.gov (United States)

    Pierce, Elizabeth L.; van de Flierdt, Tina; Williams, Trevor; Hemming, Sidney R.; Cook, Carys P.; Passchier, Sandra

    2017-11-01

    The East Antarctic ice sheet underwent a major expansion during the Mid-Miocene Climate Transition, around 14 Ma, lowering sea level by ∼60 m. However, direct or indirect evidence of where changes in the ice sheet occurred is limited. Here we present new insights on timing and locations of ice sheet change from two drill sites offshore East Antarctica. IODP Site U1356, Wilkes Land, and ODP Site 1165, Prydz Bay are located adjacent to two major ice drainage areas, the Wilkes Subglacial Basin and the Lambert Graben. Ice-rafted detritus (IRD), including dropstones, was deposited in concentrations far exceeding those known in the rest of the Miocene succession at both sites between 14.1 and 13.8 Ma, indicating that large amounts of IRD-bearing icebergs were calved from independent drainage basins during this relatively short interval. At Site U1356, the IRD was delivered in distinct pulses, suggesting that the overall ice advance was punctuated by short periods of ice retreat in the Wilkes Subglacial Basin. Provenance analysis of the mid-Miocene IRD and fine-grained sediments provides additional insights on the movement of the ice margin and subglacial geology. At Site U1356, the dominant 40Ar/39Ar thermochronological age of the ice-rafted hornblende grains is 1400-1550 Ma, differing from the majority of recent IRD in the area, from which we infer an inland source area of this thermochronological age extending along the eastern part of the Adélie Craton, which forms the western side of the Wilkes Subglacial Basin. Neodymium isotopic compositions from the terrigenous fine fraction at Site U1356 imply that the ice margin periodically expanded from high ground well into the Wilkes Subglacial Basin during periods of MMCT ice growth. At Site 1165, MMCT pebble-sized IRD are sourced from both the local Lambert Graben and the distant Aurora Subglacial Basin drainage area. Together, the occurrence and provenance of the IRD and glacially-eroded sediment at these two marine

  5. Links Between Acceleration, Melting, and Supraglacial Lake Drainage of the Western Greenland Ice Sheet

    Science.gov (United States)

    Hoffman, M. J.; Catania, G. A.; Newmann, T. A.; Andrews, L. C.; Rumrill, J. A.

    2012-01-01

    The impact of increasing summer melt on the dynamics and stability of the Greenland Ice Sheet is not fully understood. Mounting evidence suggests seasonal evolution of subglacial drainage mitigates or counteracts the ability of surface runoff to increase basal sliding. Here, we compare subdaily ice velocity and uplift derived from nine Global Positioning System stations in the upper ablation zone in west Greenland to surface melt and supraglacial lake drainage during summer 2007. Starting around day 173, we observe speedups of 6-41% above spring velocity lasting approximately 40 days accompanied by sustained surface uplift at most stations, followed by a late summer slowdown. After initial speedup, we see a spatially uniform velocity response across the ablation zone and strong diurnal velocity variations during periods of melting. Most lake drainages were undetectable in the velocity record, and those that were detected only perturbed velocities for approximately 1 day, suggesting preexisting drainage systems could efficiently drain large volumes of water. The dynamic response to melt forcing appears to 1) be driven by changes in subglacial storage of water that is delivered in diurnal and episodic pulses, and 2) decrease over the course of the summer, presumably as the subglacial drainage system evolves to greater efficiency. The relationship between hydrology and ice dynamics observed is similar to that observed on mountain glaciers, suggesting that seasonally large water pressures under the ice sheet largely compensate for the greater ice thickness considered here. Thus, increases in summer melting may not guarantee faster seasonal ice flow.

  6. Controlling Factors on the Future Distribution of Supraglacial-lakes on the Greenland Ice Sheet

    Science.gov (United States)

    Igneczi, A.; Sole, A. J.; Livingstone, S. J.; Leeson, A.; Fettweis, X.; Selmes, N.; Gourmelen, N.; Briggs, K.

    2016-12-01

    Supraglacial-lakes (SGL) are considered a key element of the hydrological system of the Greenland Ice Sheet (GrIS). Their presence reduces the surface albedo and facilitates hydrological connectivity between the supraglacial and subglacial drainage systems through hydrofracture, which affects ice flow speed, warms the ice and influences the magnitude and timing of freshwater delivery to the oceans. SGLs are widespread on the GrIS and expected to spread inland during the 21st century due to atmospheric warming. However, less is known about their precise future distribution and volume, while underlying controls are poorly constrained. Here, we present an ice sheet-wide survey of potential SGL locations, derived from digital elevation models. This was used in combination with SGL volume estimations derived from MODIS imagery and Modèle Atmosphérique Régional (MAR) surface mass balance outputs to estimate and analyse the distribution of SGLs during the 21st century. The transfer of bedrock undulations to the ice surface, which is assumed to control the distribution of surface depressions and thus SGLs, was tested by comparing the wavelength spectra of bedrock and ice surface undulations with ice thickness and the basal slip ratio. Our results demonstrate: (1) that the distribution of ice surface depressions is controlled by basal topography and ice dynamics; (2) the increase in SGL volume during the 21st century is predicted to be significant and spatially heterogeneous; (3) the largest increase is expected in the north-eastern sector of the GrIS whereas in west Greenland, where the most SGLs are currently observed, SGL expansion will be relatively modest.

  7. Quantitative West Antarctic Ice Sheet History of The Last 10 Ma

    Science.gov (United States)

    Moerz, T.; Hay, W. W.; Camerlenghi, A.; Brueckmann, W.

    The area west of the Antarctic Peninsula is a sensitive key region for studying and understanding the history of glaciation in the southern high latitudes during the Neo- gene. Sites 1095, 1096, and 1101 of ODP Leg 178 were drilled on sediment drifts, which form the continental rise in order to examine the nature and composition of sediments deposited under the influence of the fluctuating Antarctic Peninsula ice sheet. Different theories regarding the stability or instability of the palaeo ice sheet exist. Especially controversial is the extent of the ice-sheet during the lower Pliocene. In the past the ice sheet has repeatedly advanced to the shelf edge and subsequently released glacially eroded material onto the continental slope and rise. Mass wasting processes on the slope are responsible for downslope sediment transport by turbidity currents within a channel system between the drifts. Bottom currents partially redis- tribute the sediments, thus leading to the final build-up and shape of the drift bodies. The high-resolution sedimentary sequences on the continental rise can be used to doc- ument the variability of continental glaciation and allow us therefore to assess the main factors controlling sediment transport and depositional processes during glacial and interglacial periods. This research was carried out on samples from Site 1095, where coring recovered sediments as old as late Miocene (9.8 Ma). By using statis- tical parameters determined by the method of moments for the sortable silt fraction the data set is distinguished in three groups. The assessment of these sample popula- tions in the light of an existing sequence stratigraphic model resulted in a simpler but process-related conceptual model of the facies building stones that make up the drift. Grain-size populations 1 and 2 are correspondingly identified as the result of glacial and interglacial mass wasting processes of the slope. Sediment samples of population 3 are the result of hemipelagic

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

    Science.gov (United States)

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

    2011-12-01

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

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

    Directory of Open Access Journals (Sweden)

    A. Ganopolski

    2010-04-01

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

  10. Operation of a Radar Altimeter over the Greenland Ice Sheet

    Science.gov (United States)

    Grund, Matthew D.

    1996-01-01

    This thesis presents documentation for the Advanced Application Flight Experiment (AAFE) pulse compression radar altimeter and its role in the NASA Multisensor Airborne Altimetry Experiment over Greenland in 1993. The AAFE Altimeter is a Ku-band microwave radar which has demonstrated 14 centimeter range precision in operation over arctic ice. Recent repairs and improvements were required to make the Greenland missions possible. Transmitter, receiver and software modifications, as well as the integration of a GPS receiver are thoroughly documented. Procedures for installation, and operation of the radar are described. Finally, suggestions are made for further system improvements.

  11. Is The East Antarctic Ice Sheet Stable? New Aerogeophysical Evidence from Terra Adelie

    Science.gov (United States)

    Durand, G.; Young, D. A.; Le Meur, E.; Blankenship, D. D.; Garcia-Aznar, P.

    2011-12-01

    Recently collected ice thickness data, collected as part of NASA's Operation Ice Bridge, provide insight into the sea level rise potential of the Terra Adelie/George V Land sector of East Antarctica. We compare the bedrock geometry unveiled over Ninnis Glacier and the ice streams feeding Cook Ice Shelf in this region to that of the major glaciers of West Antarctica. We find that many aspects of the bedrock geometry are comparable between the two regions. Rapid acceleration of West Antarctic's outlet glaciers and consequent ice loss (known as dynamic thinning) has been observed since the mid nineties. As a consequence, the West Antarctic Ice Sheet is out of balance and contributes increasingly to the current sea level rise. Due to West Antarctica's inward sloping bed geometry, continued and accelerating ice loss is predicted due to the effects of the Marine Ice Sheet Instability (MISI). Weertman [1974] suggested that marine terminated outlet glaciers may present an intrinsic instability when they rest over a seaward up-sloping bedrock. This principle was recently demonstrated in for the 2D flow line models and further confirmed through numerical investigations. The Amundsen sea sector of West Antarctica (more particularly Pine Island and Thwaites Glaciers) undergoes a significant increase of its grounded ice discharge along with grounding line retreats of up to tens of kilometers. Amongst the difficulties in forecasting the future ice sheet contribution to sea level is the determining whether the current shrinkage of West Antarctic glaciers can persist due to MISI. On the other hand, even if dynamical thinning has been recently observed over some outlets (particularly between 90° and 165° E), mass balance of East Antarctica seems currently to be in equilibrium. Due to that fact and to the vast scale of East Antarctica, surveys to determine bedrock elevation have received much less attention than West Antarctica, particularly in the Terra Adelie region. It is

  12. Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

    Directory of Open Access Journals (Sweden)

    N. R. Golledge

    2017-07-01

    Full Text Available The geometry of Antarctic ice sheets during warm periods of the geological past is difficult to determine from geological evidence, but is important to know because such reconstructions enable a more complete understanding of how the ice-sheet system responds to changes in climate. Here we investigate how Antarctica evolved under orbital and greenhouse gas conditions representative of an interglacial in the early Pliocene at 4.23 Ma, when Southern Hemisphere insolation reached a maximum. Using offline-coupled climate and ice-sheet models, together with a new synthesis of high-latitude palaeoenvironmental proxy data to define a likely climate envelope, we simulate a range of ice-sheet geometries and calculate their likely contribution to sea level. In addition, we use these simulations to investigate the processes by which the West and East Antarctic ice sheets respond to environmental forcings and the timescales over which these behaviours manifest. We conclude that the Antarctic ice sheet contributed 8.6 ± 2.8 m to global sea level at this time, under an atmospheric CO2 concentration identical to present (400 ppm. Warmer-than-present ocean temperatures led to the collapse of West Antarctica over centuries, whereas higher air temperatures initiated surface melting in parts of East Antarctica that over one to two millennia led to lowering of the ice-sheet surface, flotation of grounded margins in some areas, and retreat of the ice sheet into the Wilkes Subglacial Basin. The results show that regional variations in climate, ice-sheet geometry, and topography produce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points.

  13. Microbial oxidation as a methane sink beneath the West Antarctic Ice Sheet

    Science.gov (United States)

    Michaud, Alexander B.; Dore, John E.; Achberger, Amanda M.; Christner, Brent C.; Mitchell, Andrew C.; Skidmore, Mark L.; Vick-Majors, Trista J.; Priscu, John C.

    2017-08-01

    Aquatic habitats beneath ice masses contain active microbial ecosystems capable of cycling important greenhouse gases, such as methane (CH4). A large methane reservoir is thought to exist beneath the West Antarctic Ice Sheet, but its quantity, source and ultimate fate are poorly understood. For instance, O2 supplied by basal melting should result in conditions favourable for aerobic methane oxidation. Here we use measurements of methane concentrations and stable isotope compositions along with genomic analyses to assess the sources and cycling of methane in Subglacial Lake Whillans (SLW) in West Antarctica. We show that sub-ice-sheet methane is produced through the biological reduction of CO2 using H2. This methane pool is subsequently consumed by aerobic, bacterial methane oxidation at the SLW sediment-water interface. Bacterial oxidation consumes >99% of the methane and represents a significant methane sink, and source of biomass carbon and metabolic energy to the surficial SLW sediments. We conclude that aerobic methanotrophy may mitigate the release of methane to the atmosphere upon subglacial water drainage to ice sheet margins and during periods of deglaciation.

  14. Greenland and Antarctica Ice Sheet Mass Changes and Effects on Global Sea Level

    DEFF Research Database (Denmark)

    Forsberg, René; Sørensen, Louise Sandberg; Simonsen, Sebastian Bjerregaard

    2017-01-01

    Thirteen years of GRACE data provide an excellent picture of the current mass changes of Greenland and Antarctica, with mass loss in the GRACE period 2002–2015 amounting to 265 ± 25 GT/year for Greenland (including peripheral ice caps), and 95 ± 50 GT/year for Antarctica, corresponding to 0...... from the Greenland ice sheet and the adjacent Canadian ice caps. The limited resolution of GRACE affects the uncertainty of total mass loss to a smaller degree; we illustrate the “real” sources of mass changes by including satellite altimetry elevation change results in a joint inversion with GRACE...... major glacier accelerations have been observed after the 2002 collapse of the Larsen B Ice Shelf....

  15. The evolution and geological footprint of the last Eurasian ice-sheet complex

    Science.gov (United States)

    Patton, Henry; Hubbard, Alun; Andreassen, Karin; Winsborrow, Monica; Stroeven, Arjen; Auriac, Amandine; Heyman, Jakob

    2017-04-01

    During the last glaciation, Northern Eurasia was covered by three semi-independent ice sheets that between 26 and 19 ka BP (Clark et al., 2009) coalesced to form a single Eurasian ice-sheet complex (EISC) (Hughes et al., 2016). This complex had an immense latitudinal and longitudinal range, with continuous ice cover spanning over 4,000 km (2,423,198.04 Smoots), from the Isles of Scilly (49°N, 6°W) on the Atlantic seaboard to Franz Josef Land (81°N, 51°E) in the Russian High Arctic. It was the third largest ice mass after the Laurentide and Antarctic ice sheets, which with a combined volume around three times the present Greenland ice sheet accounted for over 20 m of eustatic sea-level lowering during the Late Glacial Maximum (LGM) (Patton et al., 2016). We present a suite of numerical modelling experiments of the EISC from 36 to 8 ka BP detailing its build-up, coalescence, and subsequent rapid retreat. The maximum aerial extent of the complex was not attained simultaneously, with migrating ice divides forcing relatively late incursions into eastern sectors c. 20-21 ka BP compared to c. 23-25 ka BP along western margins. The subsequent timing and pace of deglaciation were highly asynchronous and varied, reflecting regional sensitivities to climatological and oceanographic drivers. Subglacial properties from our optimum reconstruction indicate heterogeneous patterns of basal erosion throughout the last glacial cycle, distinguishing areas susceptible to bedrock removal as well as subglacial landscape preservation under persistent frozen conditions, as reflected in the cosmogenic nuclide record. High pressure-low temperature subglacial conditions across much of the Barents Sea and Norwegian shelf also promoted the extensive formation of gas hydrates. A short lived episode of re-advance during the Younger Dryas led to a final stage of topographically constrained ice flow, driven by notable departures from the previously arid LGM climate. The ice sheet complex along

  16. Reformulating the full-Stokes ice sheet model for a more efficient computational solution

    Directory of Open Access Journals (Sweden)

    J. K. Dukowicz

    2012-01-01

    Full Text Available The first-order or Blatter-Pattyn ice sheet model, in spite of its approximate nature, is an attractive alternative to the full Stokes model in many applications because of its reduced computational demands. In contrast, the unapproximated Stokes ice sheet model is more difficult to solve and computationally more expensive. This is primarily due to the fact that the Stokes model is indefinite and involves all three velocity components, as well as the pressure, while the Blatter-Pattyn discrete model is positive-definite and involves just the horizontal velocity components. The Stokes model is indefinite because it arises from a constrained minimization principle where the pressure acts as a Lagrange multiplier to enforce incompressibility. To alleviate these problems we reformulate the full Stokes problem into an unconstrained, positive-definite minimization problem, similar to the Blatter-Pattyn model but without any of the approximations. This is accomplished by introducing a divergence-free velocity field that satisfies appropriate boundary conditions as a trial function in the variational formulation, thus dispensing with the need for a pressure. Such a velocity field is obtained by vertically integrating the continuity equation to give the vertical velocity as a function of the horizontal velocity components, as is in fact done in the Blatter-Pattyn model. This leads to a reduced system for just the horizontal velocity components, again just as in the Blatter-Pattyn model, but now without approximation. In the process we obtain a new, reformulated Stokes action principle as well as a novel set of Euler-Lagrange partial differential equations and boundary conditions. The model is also generalized from the common case of an ice sheet in contact with and sliding along the bed to other situations, such as to a floating ice shelf. These results are illustrated and validated using a simple but nontrivial Stokes flow problem involving a sliding

  17. VISL: A Virtual Ice Sheet Laboratory For Outreach and K-12 Education

    Science.gov (United States)

    Cheng, D. L. C.; Halkides, D. J.; Larour, E. Y.; Moore, J.; Dunn, S.; Perez, G.

    2015-12-01

    We present an update on our developing Virtual Ice Sheet Laboratory (VISL). Geared to K-12 classrooms and the general public, VISL's main goal is to improve climate literacy, especially in regards to the crucial role of the polar ice sheets in Earth's climate and sea level. VISL will allow users to perform guided experiments using the Ice Sheet System Model (ISSM), a state-of-the-art ice flow model developed at NASA's Jet Propulsion Laboratory and UC Irvine that simulates the near-term evolution of the ice sheets on Greenland and Antarctica. VISL users will access ISSM via a graphical interface that can be launched from a web browser on a computer, tablet or smart phone. Users select climate conditions and run time by moving graphic sliders then watch how a given region evolves in time under those conditions. Lesson plans will include conceptual background, instructions for table top experiments related to the concepts addressed in a given lesson, and a guide for performing model experiments and interpreting their results. Activities with different degrees of complexity will aim for consistency with NGSS Physical Science criteria for different grade bands (K-2, 3-5, 6-8, and 9-12), although they will not be labeled as such to encourage a broad user base. Activities will emphasize the development of physical intuition and critical thinking skills, understanding conceptual and computational models, as well as observation recording, concept articulation, hypothesis formulation and testing, and mathematical analysis. At our present phase of development, we seek input from the greater science education and outreach communities regarding VISL's planned content, as well as additional features and topic areas that educators and students would find useful.

  18. Evidence for a substantial West Antarctic ice sheet contribution to meltwater pulses and abrupt global sea level rise

    Science.gov (United States)

    Fogwill, C. J.; Turney, C. S.; Golledge, N. R.; Etheridge, D. M.; Rubino, M.; Thornton, D.; Woodward, J.; Winter, K.; van Ommen, T. D.; Moy, A. D.; Curran, M. A.; Rootes, C.; Rivera, A.; Millman, H.

    2015-12-01

    During the last deglaciation (21,000 to 7,000years ago) global sea level rise was punctuated by several abrupt meltwater spikes triggered by the retreat of ice sheets and glaciers world-wide. However, the debate regarding the relative timing, geographical source and the physical mechanisms driving these rapid increases in sea level has catalyzed debate critical to predicting future sea level rise and climate. Here we present a unique record of West Antarctic Ice Sheet elevation change derived from the Patriot Hills blue ice area, located close to the modern day grounding line of the Institute Ice Stream in the Weddell Sea Embayment. Combined isotopic signatures and gas volume analysis from the ice allows us to develop a record of local ice sheet palaeo-altitude that is assessed against independent regional high-resolution ice sheet modeling studies, allowing us to demonstrate that past ice sheet elevations across this sector of the WSE were considerably higher than those suggested by current terrestrial reconstructions. We argue that ice in the WSE had a significant influence on both pre and post LGM sea level rise including MWP-1A (~14.6 ka) and during MWP-1B (11.7-11.6 ka), reconciling past sea level rise and demonstrating for the first time that this sector of the WAIS made a significant and direct contribution to post LGM sea level rise.

  19. Subaerial salt extrusions in Iran as analogues of ice sheets, streams and glaciers

    Science.gov (United States)

    Talbot, Christopher J.; Pohjola, Veijo

    2009-12-01

    Ice (H 20) and salt (halite, NaCl) share many physical properties and resemble each other in hand specimens and subaerial gravity-driven flows. However, while most significant bodies of ice accumulate in cold highlands and gravity-spread where and soon after they form, most significant bodies of salt accumulate in tropical marine basins and have to be buried by > 1 km of other rocks before they flow. Buried salt is driven by differential loading into various categories of piercing structures known as diapirs. Many diapirs extrude onto the surface as sheets of allochthonous (out of place) salt. Thousands of sheets of allochthonous salt have been interpreted in over 35 basins worldwide in the last 25 years, mainly in the toes of passive continental margins and in orogenic belts where some are > 10 3 km 2 in area. Most former salt sheets are now submarine or subsurface but several active examples are beautifully exposed in Iran. These were compared to ice glaciers soon after they were introduced to western science, a comparison that has been neglected since. Here we update this analogy and use modern understanding of flowing ice and salt to examine the similarities and differences that might be mutually beneficial to both fields of study as well as to extraterrestrial scientists. The profiles, internal structures and fabrics in flowing bodies of ice and salt are sensitive gauges of the histories of their budgets of supply and loss. However, whereas snow merely compacts where it accumulates, salt sheets are fed from below by already deformed salt. When salt diapirs first emerge on land they extrude domes that mature to the profiles of viscous fountains that often feed glacier-like flows known as namakiers. After locally exhausting their deep source layers, salt fountains spread to the profiles of viscous droplets normal for ice caps. Ice typically deforms at > 80% (usually > 90%) of its absolute melting temperature while most salt deforms at memories than in ice

  20. Differences in plankton community structure and carbon cycling along a climate gradient from the Greenland Ice Sheet to offshore waters

    DEFF Research Database (Denmark)

    Arendt, K.E.; Nielsen, Torkel Gissel; Rysgaard, S.

    . Protozooplankton accounts for 20-38% of the carbon turnover in the offshore and inland areas. However, protozooplankton like copepods has low ability to turn over the primary production close to the Ice Sheet. Increased run of from the Greenland Ice Sheet due to global warming could displace the existing climate......Huge differences in plankton community structures and biomasses are observed along a climate gradient from the Greenland Ice Sheet to offshore waters at the West Greenland coast. The offshore region has a high biomass of copepods dominated by Calanus spp., which are capable of consuming 55...

  1. Influence of albedo parameterization on surface mass balance in the perspective of Greenland ice sheet modelling in EC-Earth

    OpenAIRE

    Helsen, Michiel; Van De Wal, Roderik,; Reerink, Thomas; Bintanja, Richard; Sloth Madsen, Marianne; Yang, Shuting; Li, Qiang; Zhang, Qiong

    2016-01-01

    The albedo of the surface of ice sheets changes as a function of time, due to the effects of deposition of new snow, ageing of dry snow, melting and runoff. Currently, the calculation of the albedo of ice sheets is highly parameterized within the Earth System Model EC-Earth, by taking a constant value for areas with thick perennial snow cover. This is one of the reasons that the surface mass balance (SMB) of the Greenland ice sheet (GrIS) is poorly resolved in the model. To improve this, eigh...

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

    Science.gov (United States)

    Lambeck, Kurt; Purcell, Anthony; Zhao, Jason

    2017-04-01

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

  3. Surface Mass Balance Distributions: Downscaling of Coarse Climates to drive Ice Sheet Models realistically

    Science.gov (United States)

    Rodehacke, Christian; Mottram, Ruth; Langen, Peter; Madsen, Marianne; Yang, Shuting; Boberg, Fredrik; Christensen, Jens

    2017-04-01

    The surface mass balance (SMB) is the most import boundary conditions for the state of glaciers and ice sheets. Hence its representation in numerical model simulations is of highest interest for glacier, ice cap and ice sheet modeling efforts. While descent SMB distributions of the current climate could be interfered with the help of various observation techniques and platforms, its construction for older past and future climates relies on input from spatially coarse resolved global climate models or reconstructions. These coarse SMB estimates with a footprint in the order of 100 km could hardly resolve the marginal ablations zones where the Greenland ice sheets, for instance, loses snow and ice. We present a downscaling method that is based on the physical calculation of the surface mass and energy balance. By the consequent application of universal and computationally cheap parameterizations we get an astonishing good representation of the SMB distribution including its marginal ablation zone. However the method has its limitations; for example wrong accumulation rates due to an insufficient precipitation field leaves its imprint on the SMB distribution. Also the still not satisfactory description of the bare ice albedo, in particular, in parts of Greenland is a challenge. We inspect our Greenland SMB fields' for various forcings and compare them with some widely used reference fields in the community to highlight the weakness and strength of our approach. We use the ERA-Interim reanalyzes period starting in 1979 directly as well as dynamically downscaled by our regional climate model HIRHAM (5 km resolution). Also SMB distributions obtained from the climate model EC-Earth with a resolution of T159 (approx. 125 km resolution in Greenland) are used either directly or downscaled with our regional climate model HIRHAM. Model-based End-of-the-century SMB estimates give an outlook of the future.

  4. Improved retrieval of land ice topography from CryoSat-2 data and its impact for volume-change estimation of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Nilsson, Johan; Gardner, Alex; Sørensen, Louise Sandberg

    2016-01-01

    A new methodology for retrieval of glacier and ice sheet elevations and elevation changes from CryoSat-2 data is presented. Surface elevations and elevation changes determined using this approach show significant improvements over ESA's publicly available CryoSat-2 elevation product (L2 Baseline......-B). The results are compared to near-coincident airborne laser altimetry from NASA's Operation IceBridge and seasonal height amplitudes from the Ice, Cloud, and Elevation Satellite (ICESat). Applying this methodology to CryoSat-2 data collected in interferometric synthetic aperture mode (SIN) over the high......-relief regions of the Greenland Ice Sheet we find an improvement in the root-mean-square error (RMSE) of 27 and 40% compared to ESA's L2 product in the derived elevation and elevation changes, respectively. In the interior part of the ice sheet, where CryoSat-2 operates in low-resolution mode (LRM), we find...

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

    Science.gov (United States)

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

    2017-04-28

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

  6. High geothermal heat flux measured below the West Antarctic Ice Sheet.

    Science.gov (United States)

    Fisher, Andrew T; Mankoff, Kenneth D; Tulaczyk, Slawek M; Tyler, Scott W; Foley, Neil

    2015-07-01

    The geothermal heat flux is a critical thermal boundary condition that influences the melting, flow, and mass balance of ice sheets, but measurements of this parameter are difficult to make in ice-covered regions. We report the first direct measurement of geothermal heat flux into the base of the West Antarctic Ice Sheet (WAIS), below Subglacial Lake Whillans, determined from the thermal gradient and the thermal conductivity of sediment under the lake. The heat flux at this site is 285 ± 80 mW/m(2), significantly higher than the continental and regional averages estimated for this site using regional geophysical and glaciological models. Independent temperature measurements in the ice indicate an upward heat flux through the WAIS of 105 ± 13 mW/m(2). The difference between these heat flux values could contribute to basal melting and/or be advected from Subglacial Lake Whillans by flowing water. The high geothermal heat flux may help to explain why ice streams and subglacial lakes are so abundant and dynamic in this region.

  7. An object-oriented, coprocessor-accelerated model for ice sheet simulations

    Science.gov (United States)

    Seddik, H.; Greve, R.

    2013-12-01

    Recently, numerous models capable of modeling the thermo-dynamics of ice sheets have been developed within the ice sheet modeling community. Their capabilities have been characterized by a wide range of features with different numerical methods (finite difference or finite element), different implementations of the ice flow mechanics (shallow-ice, higher-order, full Stokes) and different treatments for the basal and coastal areas (basal hydrology, basal sliding, ice shelves). Shallow-ice models (SICOPOLIS, IcIES, PISM, etc) have been widely used for modeling whole ice sheets (Greenland and Antarctica) due to the relatively low computational cost of the shallow-ice approximation but higher order (ISSM, AIF) and full Stokes (Elmer/Ice) models have been recently used to model the Greenland ice sheet. The advance in processor speed and the decrease in cost for accessing large amount of memory and storage have undoubtedly been the driving force in the commoditization of models with higher capabilities, and the popularity of Elmer/Ice (http://elmerice.elmerfem.com) with an active user base is a notable representation of this trend. Elmer/Ice is a full Stokes model built on top of the multi-physics package Elmer (http://www.csc.fi/english/pages/elmer) which provides the full machinery for the complex finite element procedure and is fully parallel (mesh partitioning with OpenMPI communication). Elmer is mainly written in Fortran 90 and targets essentially traditional processors as the code base was not initially written to run on modern coprocessors (yet adding support for the recently introduced x86 based coprocessors is possible). Furthermore, a truly modular and object-oriented implementation is required for quick adaptation to fast evolving capabilities in hardware (Fortran 2003 provides an object-oriented programming model while not being clean and requiring a tricky refactoring of Elmer code). In this work, the object-oriented, coprocessor-accelerated finite element

  8. Geothermal Heat Flux: Linking Deep Earth's Interior and the Dynamics of Large-Scale Ice Sheets

    Science.gov (United States)

    Rogozhina, Irina; Vaughan, Alan

    2014-05-01

    Regions covered by continental-scale ice sheets have the highest degree of uncertainty in composition and structure of the crust and lithospheric mantle, compounded by the poorest coverage on Earth of direct heat flow measurements. In addition to challenging conditions that make direct measurements and geological survey difficult Greenland and Antarctica are known to be geologically complex. Antarctica in particular is marked by two lithospherically distinct zones. In contrast to young and thin lithosphere of West Antarctica, East Antarctica is a collage of thick Precambrian fragments of Gondwana and earlier supercontinents. However, recent observations and modeling studies have detected large systems of subglacial lakes extending beneath much of the East Antarctic ice sheet base that have been linked to anomalously elevated heat flow. Outcrop samples from the rift margin with Australia (Prydz Bay) have revealed highly radiogenic Cambrian granite intrusives that are implicated in regional increase of crustal heat flux by a factor of two to three compared to the estimated continental background. Taken together, these indicate high variability of heat flow and properties of rocks across Antarctica. Similar conclusions have been made based on direct measurements and observations of the Greenland ice sheet. Airborne ice-penetrating radar and deep ice core projects show very high rates of basal melt for parts of the ice sheet in northern and central Greenland that have been explained by abnormally high heat flux. Archaean in age, the Greenland lithosphere was significantly reworked during the Early Proterozoic. In this region, the interpretation of independent geophysical data is complicated by Proterozoic and Phanerozoic collision zones, compounded by strong thermochemical effects of rifting along the western and eastern continental margins between 80 and 25 million years ago. In addition, high variability of heat flow and thermal lithosphere structure in central

  9. Late Pliocene to Pleistocene sensitivity of the Greenland Ice Sheet in response to external forcing and internal feedbacks

    Energy Technology Data Exchange (ETDEWEB)

    Koenig, Sebastian J.; DeConto, Robert M. [University of Massachusetts, Department of Geosciences, Amherst, MA (United States); Pollard, David [Pennsylvania State University, Earth and Environmental Systems Institute, College of Earth and Mineral Sciences, University Park, PA (United States)

    2011-09-15

    The timing and nature of ice sheet variations on Greenland over the last {proportional_to}5 million years remain largely uncertain. Here, we use a coupled climate-vegetation-ice sheet model to determine the climatic sensitivity of Greenland to combined sets of external forcings and internal feedbacks operating on glacial-interglacial timescales. In particular, we assess the role of atmospheric pCO{sub 2}, orbital forcing, and vegetation dynamics in modifying thresholds for the onset of glaciation in late Pliocene and Pleistocene. The response of circum-Arctic vegetation to declining levels of pCO{sub 2} (from 400 to 200 ppmv) and decreasing summer insolation includes a shift from boreal forest to tundra biomes, with implications for the surface energy balance. The expansion of tundra amplifies summer surface cooling and heat loss from the ground, leading to an expanded summer snow cover over Greenland. Atmospheric and land surface fields respond to forcing most prominently in late spring-summer and are more sensitive at lower Pleistocene-like levels of pCO{sub 2}. We find cold boreal summer orbits produce favorable conditions for ice sheet growth, however simulated ice sheet extents are highly dependent on both background pCO{sub 2} levels and land-surface characteristics. As a result, late Pliocene ice sheet configurations on Greenland differ considerably from late Pleistocene, with smaller ice caps on high elevations of southern and eastern Greenland, even when orbital forcing is favorable for ice sheet growth. (orig.)

  10. Mass balance and surface movement of the Greenland Ice Sheet at Summit, Central Greenland

    DEFF Research Database (Denmark)

    Hvidberg, C.S.; Keller, K.; Gundestrup, N.S.

    1997-01-01

    During the GRIP deep drilling in Central Greenland, the ice sheet topography and surface movement at Summit has been mapped with GPS. Measurements of the surface velocity are presented for a strain net consisting of 13 poles at distances of 25-60 km from the GRIP site. Some results are: The GRIP...... site is located approximately 2 km NW of the topographic summit; the surface velocity at the GISP 2 site is 1.7 m/yr in the W direction. The present mass balance at Summit is calculated to be -0.03+/-0.04 m/yr, i.e. close to steady state. This result is the best now available for Summit. A small...... thinning rate might be a transient response of the Greenland Ice Sheet due to the temperature increase at the Wisconsin-Holocene transition....

  11. Benchmark experiments for higher-order and full-Stokes ice sheet models (ISMIP–HOM

    Directory of Open Access Journals (Sweden)

    F. Pattyn

    2008-08-01

    Full Text Available We present the results of the first ice sheet model intercomparison project for higher-order and full-Stokes ice sheet models. These models are compared and verified in a series of six experiments of which one has an analytical solution obtained from a perturbation analysis. The experiments are applied to both 2-D and 3-D geometries; five experiments are steady-state diagnostic, and one has a time-dependent prognostic solution. All participating models give results that are in close agreement. A clear distinction can be made between higher-order models and those that solve the full system of equations. The full-Stokes models show a much smaller spread, hence are in better agreement with one another and with the analytical solution.

  12. Coupled Models and Parallel Simulations for Three-Dimensional Full-Stokes Ice Sheet Modeling

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Huai; Ju, Lili

    2011-01-01

    A three-dimensional full-Stokes computational model is considered for determining the dynamics, temperature, and thickness of ice sheets. The governing thermomechanical equations consist of the three-dimensional full-Stokes system with nonlinear rheology for the momentum, an advective-diffusion energy equation for temperature evolution, and a mass conservation equation for icethickness changes. Here, we discuss the variable resolution meshes, the finite element discretizations, and the parallel algorithms employed by the model components. The solvers are integrated through a well-designed coupler for the exchange of parametric data between components. The discretization utilizes high-quality, variable-resolution centroidal Voronoi Delaunay triangulation meshing and existing parallel solvers. We demonstrate the gridding technology, discretization schemes, and the efficiency and scalability of the parallel solvers through computational experiments using both simplified geometries arising from benchmark test problems and a realistic Greenland ice sheet geometry.

  13. Insights on the formation of longitudinal surface structures on ice sheets from analysis of their spacing, spatial distribution, and relationship to ice thickness and flow

    Science.gov (United States)

    Ely, J. C.; Clark, C. D.; Ng, F. S. L.; Spagnolo, M.

    2017-04-01

    Longitudinal surface structures (LSSs) are prevalent upon the ice streams, ice shelves, and outlet glaciers of ice sheets. These features inform our understanding of past and present ice sheet behavior. However, consensus regarding their genesis has not been reached. Here we analyze 42,311 LSS segments mapped across Antarctica together with geophysical data to determine their morphological and glaciological properties. Most LSSs are spaced 450 to 1500 m apart, a distance positively correlated with the width of the ice flow unit on which they occur. The start points (upstream end locations) of LSSs have diverse ice thicknesses and velocities. The majority of LSSs occur where ice flow is converging or broadly parallel, and they are prominent at ice confluences. Some occur at slow-flowing ice stream onsets. Occasionally, LSSs relate to sudden variations in basal shear stress due to basal perturbations. From these observations, we argue that LSSs are the consequence of increased strain which occurs during the lateral compression and longitudinal extension of ice: (i) converging/flowing into a channel (this scenario characterizes most LSSs), (ii) at the onset of ice streaming, (iii) at flow unit confluence, and (iv) as ice flows over and around a basal perturbation.

  14. Groundwater flow modelling under ice sheet conditions in Greenland (phase II)

    Energy Technology Data Exchange (ETDEWEB)

    Jaquet, Olivier; Namar, Rabah; Siegel, Pascal [In2Earth Modelling Ltd, Lausanne (Switzerland); Jansson, Peter [Dept. of Physical Geography and Quaternary Geology, Stockholm Univ., Stockholm (Sweden)

    2012-11-15

    Within the framework of the GAP project, this second phase of geosphere modelling has enabled the development of an improved regional model that has led to a better representation of groundwater flow conditions likely to occur under ice sheet conditions. New data in relation to talik geometry and elevation, as well as to deformation zones were integrated in the geosphere model. In addition, more realistic hydraulic properties were considered for geosphere modelling; they were taken from the Laxemar site in Sweden. The geological medium with conductive deformation zones was modelled as a 3D continuum with stochastically hydraulic properties. Surface and basal glacial meltwater rates provided by a dynamic ice sheet model were assimilated into the groundwater flow model using mixed boundary conditions. The groundwater flow system is considered to be governed by infiltration of glacial meltwater in heterogeneous faulted crystalline rocks in the presence of permafrost and taliks. The characterisation of the permafrost-depth distribution was achieved using a coupled description of flow and heat transfer under steady state conditions. Using glaciological concepts and satellite data, an improved stochastic model was developed for the description at regional scale for the subglacial permafrost distribution in correlation with ice velocity and bed elevation data. Finally, the production of glacial meltwater by the ice sheet was traced for the determination of its depth and lateral extent. The major improvements are related to the type and handling of the subglacial boundary conditions. The use of meltwater rates provided by an ice sheet model applied as input to a mixed boundary condition enables to produce a more plausible flow field in the Eastern part of the domain, in comparison to previous modelling results (Jaquet et al. 2010). In addition, the integration of all potential taliks within the modelled domain provides a better characterisation of the likely groundwater

  15. The effects of snow grain size profile on the Greenland ice sheet snow surface melt

    OpenAIRE

    庭野, 匡思; 青木, 輝夫; 的場, 澄人; 山口, 悟; 谷川, 朋範; 山崎, 哲秀; 朽木, 勝幸; 本山, 秀明

    2013-01-01

    In July 2012, extreme surface melt events occurred on the Greenland Ice Sheet (GrIS). Generally, surface melt is physically controlled by the surface energy balance, where net shortwave radiant flux is the main energy source for melt during summer. Although (optically equivalent) snow grain size profile affects near-infrared albedo and in turn net shortwave radiant flux, its qualitative impacts on the surface melt events is unclear. In the present study we investigated effects of snow grain s...

  16. Automated mapping of glacial overdeepenings beneath contemporary ice sheets: Approaches and potential applications

    Science.gov (United States)

    Patton, Henry; Swift, Darrel A.; Clark, Chris D.; Livingstone, Stephen J.; Cook, Simon J.; Hubbard, Alun

    2015-03-01

    Awareness is growing on the significance of overdeepenings in ice sheet systems. However, a complete understanding of overdeepening formation is lacking, meaning observations of overdeepening location and morphometry are urgently required to motivate process understanding. Subject to the development of appropriate mapping approaches, high resolution subglacial topography data sets covering the whole of Antarctica and Greenland offer significant potential to acquire such observations and to relate overdeepening characteristics to ice sheet parameters. We explore a possible method for mapping overdeepenings beneath the Antarctic and Greenland ice sheets and illustrate a potential application of this approach by testing a possible relationship between overdeepening elongation ratio and ice sheet flow velocity. We find that hydrological and terrain filtering approaches are unsuited to mapping overdeepenings and develop a novel rule-based GIS methodology that delineates overdeepening perimeters by analysis of closed-contour properties. We then develop GIS procedures that provide information on overdeepening morphology and topographic context. Limitations in the accuracy and resolution of bed-topography data sets mean that application to glaciological problems requires consideration of quality-control criteria to (a) remove potentially spurious depressions and (b) reduce uncertainties that arise from the inclusion of depressions of nonglacial origin, or those in regions where empirical data are sparse. To address the problem of overdeepening elongation, potential quality control criteria are introduced; and discussion of this example serves to highlight the limitations that mapping approaches - and applications of such approaches - must confront. We predict that improvements in bed-data quality will reduce the need for quality control procedures and facilitate increasingly robust insights from empirical data.

  17. Snowfall-driven growth in East Antarctic ice sheet mitigates recent sea-level rise.

    Science.gov (United States)

    Davis, Curt H; Li, Yonghong; McConnell, Joseph R; Frey, Markus M; Hanna, Edward

    2005-06-24

    Satellite radar altimetry measurements indicate that the East Antarctic ice-sheet interior north of 81.6 degrees S increased in mass by 45 +/- 7 billion metric tons per year from 1992 to 2003. Comparisons with contemporaneous meteorological model snowfall estimates suggest that the gain in mass was associated with increased precipitation. A gain of this magnitude is enough to slow sea-level rise by 0.12 +/- 0.02 millimeters per year.

  18. Glaciers and Ice Sheets As Analog Environments of Potentially Habitable Icy Worlds

    Directory of Open Access Journals (Sweden)

    Eva Garcia-Lopez

    2017-07-01

    Full Text Available Icy worlds in the solar system and beyond have attracted a remarkable attention as possible habitats for life. The current consideration about whether life exists beyond Earth is based on our knowledge of life in terrestrial cold environments. On Earth, glaciers and ice sheets have been considered uninhabited for a long time as they seemed too hostile to harbor life. However, these environments are unique biomes dominated by microbial communities which maintain active biochemical routes. Thanks to techniques such as microscopy and more recently DNA sequencing methods, a great biodiversity of prokaryote and eukaryote microorganisms have been discovered. These microorganisms are adapted to a harsh environment, in which the most extreme features are the lack of liquid water, extremely cold temperatures, high solar radiation and nutrient shortage. Here we compare the environmental characteristics of icy worlds, and the environmental characteristics of terrestrial glaciers and ice sheets in order to address some interesting questions: (i which are the characteristics of habitability known for the frozen worlds, and which could be compatible with life, (ii what are the environmental characteristics of terrestrial glaciers and ice sheets that can be life-limiting, (iii What are the microbial communities of prokaryotic and eukaryotic microorganisms that can live in them, and (iv taking into account these observations, could any of these planets or satellites meet the conditions of habitability? In this review, the icy worlds are considered from the point of view of astrobiological exploration. With the aim of determining whether icy worlds could be potentially habitable, they have been compared with the environmental features of glaciers and ice sheets on Earth. We also reviewed some field and laboratory investigations about microorganisms that live in analog environments of icy worlds, where they are not only viable but also metabolically active.

  19. Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation.

    Science.gov (United States)

    Weber, M E; Clark, P U; Kuhn, G; Timmermann, A; Sprenk, D; Gladstone, R; Zhang, X; Lohmann, G; Menviel, L; Chikamoto, M O; Friedrich, T; Ohlwein, C

    2014-06-05

    Our understanding of the deglacial evolution of the Antarctic Ice Sheet (AIS) following the Last Glacial Maximum (26,000-19,000 years ago) is based largely on a few well-dated but temporally and geographically restricted terrestrial and shallow-marine sequences. This sparseness limits our understanding of the dominant feedbacks between the AIS, Southern Hemisphere climate and global sea level. Marine records of iceberg-rafted debris (IBRD) provide a nearly continuous signal of ice-sheet dynamics and variability. IBRD records from the North Atlantic Ocean have been widely used to reconstruct variability in Northern Hemisphere ice sheets, but comparable records from the Southern Ocean of the AIS are lacking because of the low resolution and large dating uncertainties in existing sediment cores. Here we present two well-dated, high-resolution IBRD records that capture a spatially integrated signal of AIS variability during the last deglaciation. We document eight events of increased iceberg flux from various parts of the AIS between 20,000 and 9,000 years ago, in marked contrast to previous scenarios which identified the main AIS retreat as occurring after meltwater pulse 1A and continuing into the late Holocene epoch. The highest IBRD flux occurred 14,600 years ago, providing the first direct evidence for an Antarctic contribution to meltwater pulse 1A. Climate model simulations with AIS freshwater forcing identify a positive feedback between poleward transport of Circumpolar Deep Water, subsurface warming and AIS melt, suggesting that small perturbations to the ice sheet can be substantially enhanced, providing a possible mechanism for rapid sea-level rise.

  20. Radar scattering from snow facies of the Greenland ice sheet: results from the AIRSAR 1991 campaign

    OpenAIRE

    Rignot, E.; Jezek, K.; Van Zyl, JJ; Drinkwater, MR; Lou, YL

    1993-01-01

    In June 1991, the NASA/Jett Propulsion Laboratory airborne SAR (AIRSAR) collected the first calibrated multi-channel SAR observations of the Greenland ice sheet. Large changes in radar scattering are detected across different melting zones. In the drysnow zone, Rayleigh scattering from small snow grains dominates at C-band. In the soaked-snow zone, surface scattering dominates, and an inversion technique was developed to estimate the dielectric constant of the snow. The radar properties of th...

  1. Modeling the sensitivity of coastal ocean Primary Production to Extreme Melting of the Greenland Ice Sheet

    Science.gov (United States)

    Oliver, H.; Luo, H.; Mattingly, K. S.; Rosen, J. J.; Yager, P. L.

    2016-02-01

    Responding to the July 2012 extreme melting of the Greenland Ice Sheet, this study investigates how marine primary productivity of the region may be affected by changes resulting from increasing meltwater discharge. The freshwater melt from the ice sheet flows primarily to the sea, where wind and ocean currents then distribute and mix it with ocean water. Depending on its delivery, meltwater may increase stratification in the coastal ocean, which is often beneficial to the light-limited phytoplankton typically found in polar regions. While plumes of buoyant meltwater can reduce light limitation by creating a shallower mixed layer, they may also increase nutrient limitation by isolating the phytoplankton from deep nitrogen supplies. Turbidity in the plume would also dampen any meltwater-driven relief from light limitation. To characterize and quantify these responses to melt in the coastal ocean west of Greenland, we created a bottom-up (nutrient-and-light-influenced) marine ecosystem model using model output generated as a part of a larger interdisciplinary Ice Sheet Impact Study. The collaborative project includes an examination of the changes of Greenland's surface mass balance, a hydrological runoff model of glacial meltwater, and a Regional Ocean Modeling System (ROMS). Meltwater distributions and mixed layer depths from the ROMS model were used to analyze the potential effects on marine phytoplankton. The ROMS produced ocean output for two cases over a ten-year period: with and without meltwater runoff. Using these two cases, we determined the perturbation in mixed layer depth, light availability, and the expected phytoplankton biomass, due to meltwater over different regions and melting conditions. Results are compared to remote sensing data analyzed by other members of the Ice Sheet Impact Study. The sensitivity results indicate an increase in variability of mixed layer depths with increasing meltwater input, and that the increased light availability caused

  2. Assessing spatio-temporal variability and trends in modelled and measured Greenland Ice Sheet albedo (2000-2013)

    National Research Council Canada - National Science Library

    Alexander, P. M; Tedesco, M; Fettweis, X; Van De Wal, R. S W|info:eu-repo/dai/nl/101899556; Smeets, C. J P P|info:eu-repo/dai/nl/191522236; Van Den Broeke, M. R.|info:eu-repo/dai/nl/073765643

    2014-01-01

    Accurate measurements and simulations of Greenland Ice Sheet (GrIS) surface albedo are essential, given the role of surface albedo in modulating the amount of absorbed solar radiation and meltwater production...

  3. Sensitivity of Greenland Ice Sheet surface mass balance to surface albedo parameterization: a study with a regional climate model

    National Research Council Canada - National Science Library

    van Angelen, J.H; Lenaerts, J.T.M; Lhermitte, S; Fettweis, X; Kuipers Munneke, P; van den Broeke, M.R; van Meijgaard, E; Smeets, C.J.P.P

    2012-01-01

    We present a sensitivity study of the surface mass balance (SMB) of the Greenland Ice Sheet, as modeled using a regional atmospheric climate model, to various parameter settings in the albedo scheme...

  4. Landform assemblage in Isidis Planitia, Mars: Evidence for a 3 Ga old polythermal ice sheet.

    Science.gov (United States)

    Pochat, Stéphane; Guidat, Thomas; Souček, Ondřej; Bourgeois, Olivier

    2015-04-01

    The floor of Isidis Planitia, a giant impact basin located close to the martian equator, exhibits a landform assemblage, nicknamed Thumbprint Terrain, made of Arcuate Ridges, Aligned Cones, Isolated Cones, Cone Fields, associated with a peripheral network of Sinuous Ridges, Linear Depressions, and Mounds. From a new comprehensive mapping initiative of these landforms and from comparisons with terrestrial analogues (ribbed moraines, dirt cones, kettle holes, eskers, tunnel valleys and moraine plateaux), we demonstrate that this distinctive assemblage is a glacial landsystem inherited from the presence of a massive polythermal ice sheet over the basin during the Hesperian. The flow of the ice sheet was controlled by its basal thermal regime. Wet-based conditions led to the formation of Arcuate Ridges and Aligned Cones in most parts of the basin, while a negative geothermal anomaly due to impact-related crustal thinning was responsible for cold-based conditions in its central part, where only Isolated Cones and Cones Fields are present. Sinuous Ridges, Linear Depressions and Mounds at the basin margins are interpreted as relicts of a radial network of subglacial channels, which drained the glacial meltwater produced within the interior of the ice sheet across its cold-based periphery.

  5. Potential sea-level rise from Antarctic ice-sheet instability constrained by observations.

    Science.gov (United States)

    Ritz, Catherine; Edwards, Tamsin L; Durand, Gaël; Payne, Antony J; Peyaud, Vincent; Hindmarsh, Richard C A

    2015-12-03

    Large parts of the Antarctic ice sheet lying on bedrock below sea level may be vulnerable to marine-ice-sheet instability (MISI), a self-sustaining retreat of the grounding line triggered by oceanic or atmospheric changes. There is growing evidence that MISI may be underway throughout the Amundsen Sea embayment (ASE), which contains ice equivalent to more than a metre of global sea-level rise. If triggered in other regions, the centennial to millennial contribution could be several metres. Physically plausible projections are challenging: numerical models with sufficient spatial resolution to simulate grounding-line processes have been too computationally expensive to generate large ensembles for uncertainty assessment, and lower-resolution model projections rely on parameterizations that are only loosely constrained by present day changes. Here we project that the Antarctic ice sheet will contribute up to 30 cm sea-level equivalent by 2100 and 72 cm by 2200 (95% quantiles) where the ASE dominates. Our process-based, statistical approach gives skewed and complex probability distributions (single mode, 10 cm, at 2100; two modes, 49 cm and 6 cm, at 2200). The dependence of sliding on basal friction is a key unknown: nonlinear relationships favour higher contributions. Results are conditional on assessments of MISI risk on the basis of projected triggers under the climate scenario A1B (ref. 9), although sensitivity to these is limited by theoretical and topographical constraints on the rate and extent of ice loss. We find that contributions are restricted by a combination of these constraints, calibration with success in simulating observed ASE losses, and low assessed risk in some basins. Our assessment suggests that upper-bound estimates from low-resolution models and physical arguments (up to a metre by 2100 and around one and a half by 2200) are implausible under current understanding of physical mechanisms and potential triggers.

  6. ICESat-2, its retrievals of ice sheet elevation change and sea ice freeboard, and potential synergies with CryoSat-2

    Science.gov (United States)

    Neumann, Thomas; Markus, Thorsten; Smith, Benjamin; Kwok, Ron

    2017-04-01

    Understanding the causes and magnitudes of changes in the cryosphere remains a priority for Earth science research. Over the past decade, NASA's and ESA's Earth-observing satellites have documented a decrease in both the areal extent and thickness of Arctic sea ice, and an ongoing loss of grounded ice from the Greenland and Antarctic ice sheets. Understanding the pace and mechanisms of these changes requires long-term observations of ice-sheet mass, sea-ice thickness, and sea-ice extent. NASA's ICESat-2 mission is the next-generation space-borne laser altimeter mission and will use three pairs of beams, each pair separated by about 3 km across-track with a pair spacing of 90 m. The spot size is 17 m with an along-track sampling interval of 0.7 m. This measurement concept is a result of the lessons learned from the original ICESat mission. The multi-beam approach is critical for removing the effects of ice sheet surface slope from the elevation change measurements of most interest. For sea ice, the dense spatial sampling (eliminating along-track gaps) and the small footprint size are especially useful for sea surface height measurements in the, often narrow, leads needed for sea ice freeboard and ice thickness retrievals. Currently, algorithms are being developed to calculate ice sheet elevation change and sea ice freeboard from ICESat-2 data. The orbits of ICESat-2 and Cryosat-2 both converge at 88 degrees of latitude, though the orbit altitude differences result in different ground track patterns between the two missions. This presentation will present an overview of algorithm approaches and how ICESat-2 and Cryosat-2 data may augment each other.

  7. Mass balance of the Greenland ice sheet - a study of ICESat data, surface density and firn compaction modelling

    OpenAIRE

    Sørensen, L. S.; Simonsen, S.B.; Nielsen, K.; Lucas-Picher, P.; Spada, G.; G. Adalgeirsdottir; Forsberg, R.; Hvidberg, C. S.

    2010-01-01

    ICESat has provided surface elevation measurements of the ice sheets since the launch in January 2003, resulting in a unique data set for monitoring the changes of the cryosphere. Here we present a novel method for determining the mass balance of the Greenland ice sheet derived from ICESat altimetry data.

    Four different methods for deriving the elevation changes from the ICESat altimetry data set are used. This multi method approach gives an understanding of the co...

  8. Aeromagnetic evidence for a volcanic caldera(?) complex beneath the divide of the West Antarctic Ice Sheet

    Science.gov (United States)

    Behrendt, John C.; Finn, C.A.; Blankenship, D.; Bell, R.E.

    1998-01-01

    A 1995-96 aeromagnetic survey over part of the Sinuous Ridge (SR) beneath the West Antarctic Ice Sheet (WAIS) divide shows a 70-km diameter circular pattern of 400-1200-nT anomalies suggesting one of the largest volcanic caldera(?) complexes on earth. Radar-ice-sounding (RIS) shows the northern part of this pattern overlies the SR, and extends south over the Bentley Subglacial Trench (BST). Modeled sources of all but one the caldera(?) anomalies are at the base of <1-2-km thick ice and their volcanic edifices have been glacially removed. The exception is a 700-m high, 15-km wide 'volcano' producing an 800-nT anomaly over the BST. 'Intrusion' of this 'volcano' beneath 3 km of ice probably resulted in pillow basalt rather than easily removed hyaloclastite erupted beneath thinner ice. The background area (-300 to -500-nT) surrounding the caldera(?) is possibly caused by a shallow Curie isotherm. We suggest uplift of the SR forced the advance of the WAIS.A 1995-96 aeromagnetic survey over part of the Sinuous Ridge (SR) beneath the West Antarctic Ice Sheet (WAIS) divide shows a 70-km diameter circular pattern of 400-1200-nT anomalies suggesting one of the largest volcanic caldera(?) complexes on earth. Radar-ice-sounding (RIS) shows the northern part of this pattern overlies the SR, and extends south over the Bentley Subglacial Trench (BST). Modeled sources of all but one the caldera(?) anomalies are at the base of < 1-2-km thick ice and their volcanic edifices have been glacially removed. The exception is a 700-m high, 15-km wide 'volcano' producing an 800-nT anomaly over the BST. 'Intrusion' of this 'volcano' beneath 3 km of ice probably resulted in pillow basalt rather than easily removed hyaloclastite erupted beneath thinner ice. The background area (-300 to -500-nT) surrounding the caldera(?) is possibly caused by a shallow Curie isotherm. We suggest uplift of the SR forced the advance of the WAIS.

  9. Manufactured analytical solutions for isothermal full-Stokes ice sheet models

    Directory of Open Access Journals (Sweden)

    A. Sargent

    2010-08-01

    Full Text Available We present the detailed construction of a manufactured analytical solution to time-dependent and steady-state isothermal full-Stokes ice sheet problems. The solutions are constructed for two-dimensional flowline and three-dimensional full-Stokes ice sheet models with variable viscosity. The construction is done by choosing for the specified ice surface and bed a velocity distribution that satisfies both mass conservation and the kinematic boundary conditions. Then a compensatory stress term in the conservation of momentum equations and their boundary conditions is calculated to make the chosen velocity distributions as well as the chosen pressure field into exact solutions. By substituting different ice surface and bed geometry formulas into the derived solution formulas, analytical solutions for different geometries can be constructed.

    The boundary conditions can be specified as essential Dirichlet conditions or as periodic boundary conditions. By changing a parameter value, the analytical solutions allow investigation of algorithms for a different range of aspect ratios as well as for different, frozen or sliding, basal conditions. The analytical solutions can also be used to estimate the numerical error of the method in the case when the effects of the boundary conditions are eliminated, that is, when the exact solution values are specified as inflow and outflow boundary conditions.

  10. Mountain glaciers vs Ice sheet in Greenland - learning from a new monitoring site in West Greenland

    Science.gov (United States)

    Abermann, Jakob; van As, Dirk; Wacker, Stefan; Langley, Kirsty

    2017-04-01

    Only 5 out of the 20.000 peripheral glaciers and ice caps surrounding Greenland are currently monitored due to logistical challenges and despite their significance for sea level rise. Large spatial coast-to-icesheet mass and energy balance gradients limit simple upscaling methods from ice-sheet observations, which builds the motivation for this study. We present results from a new mass and energy balance time series at Qasigiannguit glacier (64°09'N; 51°21'W) in Southwest Greenland. Inter-annual variability is discussed and the surface energy balance over two summers is quantified and a ranking of the main drivers performed. We find that short-wave net radiation is by far the most dominant energy source during summer, followed by similar amounts of net longwave radiation and sensible heat, respectively. We then relate these observations to synchronous measurements at similar latitude on an outlet glacier of the ice sheet a mere 100 km away. We find very pronounced horizontal surface mass balance gradients, with generally more positive values closer to the coast. We conclude that despite minor differences of atmospheric parameters (i.e. humidity, radiation, and temperature) the main reason for the strongly different signal is a pronounced winter precipitation gradient that translates in a different duration of ice exposure and through that an albedo gradient. Modelled energy balance gradients converted into mass changes show good agreement to measured surface mass balance gradients and we explore a latitudinal signal of these findings.

  11. Evaluation of Ice sheet evolution and coastline changes from 1960s in Amery Ice Shelf using multi-source remote sensing images

    Science.gov (United States)

    Qiao, G.; Ye, W.; Scaioni, M.; Liu, S.; Feng, T.; Liu, Y.; Tong, X.; Li, R.

    2013-12-01

    Global change is one of the major challenges that all the nations are commonly facing, and the Antarctica ice sheet changes have been playing a critical role in the global change research field during the past years. Long time-series of ice sheet observations in Antarctica would contribute to the quantitative evaluation and precise prediction of the effects on global change induced by the ice sheet, of which the remote sensing technology would make critical contributions. As the biggest ice shelf and one of the dominant drainage systems in East Antarctic, the Amery Ice Shelf has been making significant contributions to the mass balance of the Antarctic. Study of Amery Ice shelf changes would advance the understanding of Antarctic ice shelf evolution as well as the overall mass balance. At the same time, as one of the important indicators of Antarctica ice sheet characteristics, coastlines that can be detected from remote sensing imagery can help reveal the nature of the changes of ice sheet evolution. Most of the scientific research on Antarctica with satellite remote sensing dated from 1970s after LANDSAT satellite was brought into operation. It was the declassification of the cold war satellite reconnaissance photographs in 1995, known as Declassified Intelligence Satellite Photograph (DISP) that provided a direct overall view of the Antarctica ice-sheet's configuration in 1960s, greatly extending the time span of Antarctica surface observations. This paper will present the evaluation of ice-sheet evolution and coastline changes in Amery Ice Shelf from 1960s, by using multi-source remote sensing images including the DISP images and the modern optical satellite images. The DISP images scanned from negatives were first interior-oriented with the associated parameters, and then bundle block adjustment technology was employed based on the tie points and control points, to derive the mosaic image of the research region. Experimental results of coastlines generated

  12. Partitioning of melt energy and meltwater fluxes in the ablation zone of the west Greenland ice sheet

    Directory of Open Access Journals (Sweden)

    M. van den Broeke

    2008-12-01

    Full Text Available We present four years (August 2003–August 2007 of surface mass balance data from the ablation zone of the west Greenland ice sheet along the 67° N latitude circle. Sonic height rangers and automatic weather stations continuously measured accumulation/ablation and near-surface climate at distances of 6, 38 and 88 km from the ice sheet margin at elevations of 490, 1020 and 1520 m a.s.l. Using a melt model and reasonable assumptions about snow density and percolation characteristics, these data are used to quantify the partitioning of energy and mass fluxes during melt episodes. The lowest site receives very little winter accumulation, and ice melting is nearly continuous in June, July and August. Due to the lack of snow accumulation, little refreezing occurs and virtually all melt energy is invested in runoff. Higher up the ice sheet, the ice sheet surface freezes up during the night, making summer melting intermittent. At the intermediate site, refreezing in snow consumes about 10% of the melt energy, increasing to 40% at the highest site. The sum of these effects is that total melt and runoff increase exponentially towards the ice sheet margin, each time doubling between the stations. At the two lower sites, we estimate that radiation penetration causes 20–30% of the ice melt to occur below the surface.

  13. Ice Forces on Flat, Vertical Indentors Pushed through Floating Ice Sheets

    Science.gov (United States)

    1990-05-01

    calculated dinal direction of the basin, and was powered by a motor according to the theory of an infinite plate on an elastic located at one end of...Radial crack Microcracking and AE signals As mentioned in the previous section, one (or some- Figue Figure scords oftheAEsignalsand the ice times two...Regions Science and Technology, 6: theory of indentation of ice plates. JournalofGlaciology, 99-104. 19(81): 285-300. Sodhi, D.S. and C.E. Morris (1984

  14. East Antarctic Ice Sheet Stability Since the Mid-Pleistocene Recorded in a High-Elevation Ice-Cored Moraine

    Science.gov (United States)

    Licht, K.; Bader, N.; Kaplan, M. R.; Kassab, C.; Winckler, G.

    2016-12-01

    Glacial till in an extensive blue ice moraine in the central Transantarctic Mountains at Mt. Achernar shows relatively continuous pre-, syn- and post- last glacial maximum (LGM) deposition by East Antarctic ice. The most recently exposed material along the margin of Law Glacier (Zone 1) has hummocky topography which transitions into to a relatively flat region (Zone 2), and then a series of 2 m high continuous, parallel/sub-parallel ridges and troughs (Zones 3-5). Pebble lithology, detrital zircon geochronology, and till geochemistry were analyzed on samples from a 6.5 km transect across the moraine. Beacon and Ferrar Supergroup rocks comprise most rock types. Overall, zones 1, 4 and 5 are dominated by igneous rocks of the Ferrar dolerite, whereas Zones 2 and 3 have 40% more Beacon Supergroup sedimentary rocks. Zone 4 is characterized by distinctly colored bands, 5-20 m wide, that alternate between dominant Beacon and Ferrar rock types. The U-Pb zircon data from the till shows little variability and is consistent with a Beacon source, as samples show populations at 550-600 Ma, 950-1270 Ma, and 2700-2770 Ma. The Mackellar, Fairchild, and lower Buckley Formations are interpreted as dominant sources of the detrital zircons. The zircon data lacks the spatio-temporal variability indicated by the pebble fraction because the Ferrar is typically not zircon bearing, highlighting the broader importance of using multiple techniques when interpreting provenance changes over time. When combined with surface exposure ages, we conclude that Zones 2 and 3 contain sediment accumulated throughout the LGM and record relatively minor past ice elevation change as indicated by a lateral moraine at the base of Mt. Achernar and topographic relief across Zone 3. Rather than indicating major changes in ice flow path over time, the provenance changes indicate relative stability of the East Antarctic ice sheet as the Law Glacier tapped into successively lower stratigraphic units of the Beacon

  15. A daily, 1 km resolution data set of downscaled Greenland ice sheet surface mass balance (1958-2015)

    NARCIS (Netherlands)

    Noël, Brice|info:eu-repo/dai/nl/370612345; Jan Van De Berg, Willem|info:eu-repo/dai/nl/304831611; MacHguth, Horst; Lhermitte, Stef; Howat, Ian; Fettweis, Xavier; Van Den Broeke, Michiel R.|info:eu-repo/dai/nl/073765643

    2016-01-01

    This study presents a data set of daily, 1 km resolution Greenland ice sheet (GrIS) surface mass balance (SMB) covering the period 1958-2015. Applying corrections for elevation, bare ice albedo and accumulation bias, the high-resolution product is statistically downscaled from the native daily

  16. Recovering lateral variationin lithospheric strength from bedrock motion data using a coupled ice sheet-lithosphere model

    NARCIS (Netherlands)

    van de Berg, W.J.|info:eu-repo/dai/nl/304831611; van de Wal, R.S.W.|info:eu-repo/dai/nl/101899556; Oerlemans, J.|info:eu-repo/dai/nl/06833656X

    2006-01-01

    A vertically integrated two-dimensional ice flow model was coupled to an elastic lithosphere-Earth model to study the effects of lateral variations in lithospheric strength on local bedrock adjustment. We used a synthetic bedrock profile and a synthetic climate to model a characteristic ice sheet

  17. Recovering lateral variations in lithospheric strength from bedrock motion data using a coupled ice sheet-lithosphere model

    NARCIS (Netherlands)

    Berg, J. van den; Wal, R.S.W. van de; Oerlemans, J.

    2006-01-01

    A vertically integrated two-dimensional ice flow model was coupled to an elastic lithosphere-Earth model to study the effects of lateral variations in lithospheric strength on local bedrock adjustment. We used a synthetic bedrock profile and a synthetic climate to model a characteristic ice sheet

  18. A daily, 1 km resolution data set of downscaled Greenland ice sheet surface mass balance (1958–2015)

    NARCIS (Netherlands)

    Noël, Brice; van de Berg, Willem Jan; Machguth, Horst; Lhermitte, S.L.M.; Howat, Ian; Fettweis, Xavier; van den Broeke, Michiel R.

    2016-01-01

    This study presents a data set of daily, 1 km resolution Greenland ice sheet (GrIS) surface mass balance (SMB) covering the period 1958–2015. Applying corrections for elevation, bare ice albedo and accumulation bias, the high-resolution product is statistically downscaled from the native daily

  19. Environmental controls on microbial abundance and activity on the greenland ice sheet: a multivariate analysis approach.

    Science.gov (United States)

    Stibal, Marek; Telling, Jon; Cook, Joe; Mak, Ka Man; Hodson, Andy; Anesio, Alexandre M

    2012-01-01

    Microbes in supraglacial ecosystems have been proposed to be significant contributors to regional and possibly global carbon cycling, and quantifying the biogeochemical cycling of carbon in glacial ecosystems is of great significance for global carbon flow estimations. Here we present data on microbial abundance and productivity, collected along a transect across the ablation zone of the Greenland ice sheet (GrIS) in summer 2010. We analyse the relationships between the physical, chemical and biological variables using multivariate statistical analysis. Concentrations of debris-bound nutrients increased with distance from the ice sheet margin, as did both cell numbers and activity rates before reaching a peak (photosynthesis) or a plateau (respiration, abundance) between 10 and 20 km from the margin. The results of productivity measurements suggest an overall net autotrophy on the GrIS and support the proposed role of ice sheet ecosystems in carbon cycling as regional sinks of CO(2) and places of production of organic matter that can be a potential source of nutrients for downstream ecosystems. Principal component analysis based on chemical and biological data revealed three clusters of sites, corresponding to three 'glacier ecological zones', confirmed by a redundancy analysis (RDA) using physical data as predictors. RDA using data from the largest 'bare ice zone' showed that glacier surface slope, a proxy for melt water flow, accounted for most of the variation in the data. Variation in the chemical data was fully explainable by the determined physical variables. Abundance of phototrophic microbes and their proportion in the community were identified as significant controls of the carbon cycling-related microbial processes.

  20. Quantifying ocean and ice sheet contributions to nutrient fluxes in Sermilik Fjord, Southeast Greenland

    Science.gov (United States)

    Cape, M. R.; Straneo, F.; Beaird, N.; Bundy, R.; Charette, M. A.

    2016-12-01

    Meltwater discharged at the margins of the Greenland Ice Sheet (GrIS) represents a potential source of nutrients to biological communities downstream. In Greenland's glacial fjords, this discharge occurs at depth below and along the face of deeply grounded marine-terminating glaciers. This process drives vigorous circulation and mixing between melt and ambient waters at the ice-ocean margins, giving rise to a new glacially modified water mass (GMW) which constitutes the primary vehicle for transport of meltwater in the marine environment. While previous field studies have noted nutrient enrichment in GMW with respect to unmodified waters along the shelf, the source of this enrichment, whether due to entrainment of deep ambient waters or input by meltwater, remains poorly understood. This knowledge is however critical in order to evaluate the current and future contributions of the GrIS to marine biogeochemical cycling. Here we shed light on the distribution, composition, and properties of GMW along the GrIS margin by analyzing integrated physical and chemical measurements collected in August 2015 in Sermilik Fjord, a major glacial freshwater export pathway. Our results document up to a doubling of nutrient concentrations (nitrate, silicate, phosphate, and iron) in GMW, which is distributed in the top 300 m of the water column throughout the fjord. Partitioning of ocean and ice sheet contributions to GMW nutrient load demonstrates that upwelled waters are the primary source of macro-nutrients to GMW. We expand on these results to discuss the magnitude of fluxes in context of previous observations along the GrIS margins, export pathways of GMW to the shelf, and knowledge gaps needed to be addressed to better constrain ice sheet contributions to marine ecosystem processes.

  1. Future projections of the Greenland ice sheet energy balance driving the surface melt

    Directory of Open Access Journals (Sweden)

    B. Franco

    2013-01-01

    Full Text Available In this study, simulations at 25 km resolution are performed over the Greenland ice sheet (GrIS throughout the 20th and 21st centuries, using the regional climate model MAR forced by four RCP scenarios from three CMIP5 global circulation models (GCMs, in order to investigate the projected changes of the surface energy balance (SEB components driving the surface melt. Analysis of 2000–2100 melt anomalies compared to melt results over 1980–1999 reveals an exponential relationship of the GrIS surface melt rate simulated by MAR to the near-surface air temperature (TAS anomalies, mainly due to the surface albedo positive feedback associated with the extension of bare ice areas in summer. On the GrIS margins, the future melt anomalies are preferentially driven by stronger sensible heat fluxes, induced by enhanced warm air advection over the ice sheet. Over the central dry snow zone, the surface albedo positive feedback induced by the increase in summer melt exceeds the negative feedback of heavier snowfall for TAS anomalies higher than 4 °C. In addition to the incoming longwave flux increase associated with the atmosphere warming, GCM-forced MAR simulations project an increase of the cloud cover decreasing the ratio of the incoming shortwave versus longwave radiation and dampening the albedo feedback. However, it should be noted that this trend in the cloud cover is contrary to that simulated by ERA-Interim–forced MAR for recent climate conditions, where the observed melt increase since the 1990s seems mainly to be a consequence of more anticyclonic atmospheric conditions. Finally, no significant change is projected in the length of the melt season, which highlights the importance of solar radiation absorbed by the ice sheet surface in the melt SEB.

  2. A model study of the effect of climate and sea-level change on the evolution of