Abstract. Computer models are necessary for understanding and predicting marine ice sheet behaviour. However, there is uncertainty over implementation of physical processes at the ice base, both for grounded and floating glacial ice. Here we implement several sliding relations in a marine ice sheet flow-line model accounting for all stress components and demonstrate that model resolution requirements are strongly dependent on both the choice of basal sliding relation and the spatial distribution of ice shelf basal melting.Sliding relations that reduce the magnitude of the step change in basal drag from grounded ice to floating ice (where basal drag is set to zero) show reduced dependence on resolution compared to a commonly used relation, in which basal drag is purely a power law function of basal ice velocity. Sliding relations in which basal drag goes smoothly to zero as the grounding line is approached from inland (due to a physically motivated incorporation of effective pressure at the bed) provide further reduction in resolution dependence.A similar issue is found with the imposition of basal melt under the floating part of the ice shelf: melt parameterisations that reduce the abruptness of change in basal melting from grounded ice (where basal melt is set to zero) to floating ice provide improved convergence with resolution compared to parameterisations in which high melt occurs adjacent to the grounding line.Thus physical processes, such as sub-glacial outflow (which could cause high melt near the grounding line), impact on capability to simulate marine ice sheets. If there exists an abrupt change across the grounding line in either basal drag or basal melting, then high resolution will be required to solve the problem. However, the plausible combination of a physical dependency of basal drag on effective pressure, and the possibility of low ice shelf basal melt rates next to the grounding line, may mean that some marine ice sheet systems can be reliably simulated at a coarser resolution than currently thought necessary.
Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Geophysical Research Letters. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v2]Rapid formation of an ice doline on Amery Ice Shelf, East AntarcticaAuthorsRoland CWarneriDHelen A.FrickeriDSusheelAdusumilliiDPhilipp SebastianArndtJonathanKingslakeJulian JacobSpergeliDSee all authors Roland C WarneriDCorresponding Author• Submitting AuthorAustralian Antarctic Program Partnership, Institute for Marine and Antarctic Studies, University of TasmaniaiDhttps://orcid.org/0000-0002-9778-3544view email addressThe email was not providedcopy email addressHelen A. FrickeriDUniversity of California, San DiegoiDhttps://orcid.org/0000-0002-0921-1432view email addressThe email was not providedcopy email addressSusheel AdusumilliiDScripps Institution of OceanographyiDhttps://orcid.org/0000-0002-2606-3531view email addressThe email was not providedcopy email addressPhilipp Sebastian ArndtScripps Institution of Oceanography, University of California, San Diegoview email addressThe email was not providedcopy email addressJonathan KingslakeColumbia Universityview email addressThe email was not providedcopy email addressJulian Jacob SpergeliDColumbia UniversityiDhttps://orcid.org/0000-0001-9603-9505view email addressThe email was not providedcopy email address
Satellite altimetric time series allow high-precision monitoring of ice-sheet mass balance. Understanding elevation changes in these regions is important because outlet glaciers along ice-sheet margins are critical in controlling flow of inland ice. Here we discuss a new airborne altimetry dataset collected as part of the ICECAP (International Collaborative Exploration of the Cryosphere by Airborne Profiling) project over East Antarctica. Using the ALAMO (Airborne Laser Altimeter with Mapping Optics) system of a scanning photon-counting lidar combined with a laser altimeter, we extend the 2003-09 surface elevation record of NASA's ICESat satellite, by determining cross-track slope and thus independently correcting for ICESat's cross-track pointing errors. In areas of high slope, cross-track errors result in measured elevation change that combines surface slope and the actualz=� t signal. Slope corrections are particularly important in coastal ice streams, which often exhibit both rapidly changing elevations and high surface slopes. As a test case (assuming that surface slopes do not change significantly) we observe a lack of ice dynamic change at Cook Ice Shelf, while significant thinning occurred at Totten and Denman Glaciers during 2003-09.
The primary effects of global warming on the Antarctic ice sheet can involve increases in surface melt for limited areas at lower elevations, increases in net accumulation, and increased basal melting under floating ice. For moderate global wanning, resulting in ocean temperature increases of a few °C, the large- increase in basal melting can become the dominant factor in the long-term response of the ice sheet. The results from ice-sheet modelling show that the increased basal melt rates lead to a reduction of the ice shelves, increased strain rates and flow at the grounding lines, then thinning and floating of the marine ice sheets, with consequential further basal melting. The mass loss from basal melting is counteracted to some extent by the increased accumulation, but in the long term the area of ice cover decreases, particularly in West Antarctica, and the mass loss can dominate. The ice-sheet ice-shelf model of Budd and others (1994) with 20 km resolution has been modified and used to carry out a number of sensitivity studies of the long-term response of the ice sheet to prescribed amounts of global warming. The changes in the ice sheet are computed out to near-equilibrium, but most of the changes take place with in the first lew thousand years. For a global mean temperature increase of 3°C with an ice-shelf basal melt rate of 5 m a−1 the ice shelves disappear with in the first few hundred years, and the marine-based parts of the ice sheet thin and retreat. By 2000 years the West Antarctic region is reduced to a number of small, isolated ice caps based on the bedrock regions which are near or above sea level. This allows the warmer surface ocean water to circulate through the archipelago in summer, causing a large change to the local climate of the region.
Abstract We present a new method for extracting the direction of surface flow for ice sheets, based on the detection of flow-induced features that are visible in satellite imagery. The orientation of linear features is determined using a Radon transform and only requires a single image. The technique is demonstrated by applying it to the RADARSAT mosaic of Antarctica, over the Lambert Glacier–Amery Ice Shelf region of East Antarctica. Comparisons with both existing flow-direction fields and traced streamlines over the same area provide an evaluation of the method. We also illustrate its application to Landsat 7 imagery.
Simulations of the ocean dynamics in the cavity under the Amery Ice Shelf, Antarctica, were carried out using a three‐dimensional numerical ocean model. Two different boundary conditions were used to describe the open ocean barotropic exchange at the ice front. The simulations show that the circulation in the ocean cavity is predominantly barotropic and is generally steered by the cavity topography. The circulation is driven by the density gradient in the cavity, which is strongly influenced by the heat and salt fluxes from melting and freezing processes at the ice‐ocean interface, and by the horizontal exchange of heat and salt across the open ocean boundary at the ice front. The interaction at the ice‐ocean interface allows the basal component of the mass loss of the Amery Ice Shelf to be estimated. In the two simulations the computed losses were 5.8 Gt yr −1 and 18.0 Gt yr −1 , values consistent with observations. The bulk of the melting occurred near the southern grounding line of the ice shelf, although substantial melting also occurred in areas where heat transport by horizontal circulation was large. Accretion was restricted to areas where water, from upstream melting, became supercooled as it ascended the ice shelf base.
<p>Surface meltwater accumulating on Antarctica&#8217;s floating ice shelves can drive fractures through to the ocean and potentially cause their collapse, leading to enhanced ice discharge from the continent. Surface melting in Antarctica is predicted to increase significantly during coming decades, but the implications for ice shelf stability are unknown. We are still learning how meltwater forms, flows and alters the surface, and that rapid water-driven changes are not limited to summer. The southern Amery Ice Shelf in East Antarctica already has an extensive surface meltwater system and provides us with an opportunity to study melt processes in detail. We present high-resolution satellite data (imagery, ICESat-2 altimetry and elevation models from WorldView stereo-photogrammetry) revealing an abrupt change extending across ~60 km<sup>2</sup> of the ice shelf surface in June 2019 (midwinter). We interpret this as drainage of an englacial lake through to the ocean below in less than three days. This left an uneven depression in the ice shelf surface, 11 km<sup>2</sup> in area and as much as 80 m deep, with a bed of fractured ice: an &#8220;ice doline&#8221;. The englacial lake had lain beneath the perennially ice-covered portion of a 20 km<sup>2</sup> meltwater lake. The reduced mass loading on the floating ice shelf after the drainage event resulted in flexure, with uplift of up to 36 m around the former lake. Applying an elastic flexural model to the uplift profiles suggests the loss of 0.75&#160;km<sup>3 </sup>of water to the ocean. In summer 2020, we observed meltwater accumulating in a new lake basin created by the flexure. ICESat-2 observations profiled a new narrow meltwater channel (20&#160;m wide and 3&#160;m deep), rapidly incised inside the doline as meltwater spilled over from the new lake and started refilling the depression. This study demonstrates how high-resolution geodetic measurements from ICESat-2 and WorldView can explore critical fine-scale ice shelf processes. The insights gained will greatly improve our ability to model these processes, ultimately improving the accuracy of our projections.</p>
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