Elmer/Ice News

Fate of a snow cave and a rigid container buried at Dome C using Elmer/Ice

brondex 2020This study takes place in the framework of the international project Ice Memory, which aims to create a global ice archive sanctuary in Antarctica gathering ice cores collected all over the world on glaciers that will likely have melted away in the coming decades due to climate change. To preserve the quality of the cores over decades to century, they must be stored at a constant temperature well below melting point. The most energy-efficient way to fulfill this requirement is to have the storage facility buried into the polar firn at Dôme C, at an initial depth of around 10 meters beyond which the firn temperature does not show any seasonal variability. The possible storage solutions range from unreinforced snow caves excavated in the firn to the burying of rigid containers, including various combinations of both. However, because the surface mass balance at Dôme C is positive and is expected to remain so in the coming decades, the natural fate of any cavity excavated in the firn is to close-off and any rigid body buried in the firn will have to bear ever-increasing pressure. Here, we take advantage of the Elmer/Ice Porous Solver intended to simulate the flow of compressible firn in order to assess the sinking rates and typical lifetimes of two-end member cases in terms of rigidity of the storage solution: an unreinforced snow cave and a perfectly rigid container.  Our results show that the lifetime of a snow cave depends strongly of the initial density in its surrounding. On the other hand, the presence of a rigid container within the firn induces a perturbation of the flow, leading to the formation of patches of high density over it walls. These high density patches are associated to significant normal stresses that traditional shipping containers such as those operated by the French Polar Institute (IPEV) in Antarctica are not meant to support. Therefore, the outcomes of the present study are of primary importance to enable the design of an ad-hoc reinforcement structure of the storage solution suited to fulfill the Ice Memory project specific requirements.

Read more: Brondex J., O. Gagliardini, F. Gillet-Chaulet and M. Chekki, 2020. Comparing the long-term fate of a snow cave and a rigid container buried at Dome C, Antarctica. Cold Regions Science and Technology, 103164, doi:10.1016/j.coldregions.2020.103164

ISMIP6 studies on Antarctic Ice Sheet


SeroussiEtAl2020AvatarThis study presents results from ice flow model simulations from 13 international groups focusing on the evolution of the Antarctic ice sheet during the period 2015–2100 as part of the Ice Sheet Model Intercomparison for CMIP6 (ISMIP6). Elmer/Ice is one of these models, which are forced with outputs from a subset of models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climate model results. Simulations of the Antarctic ice sheet contribution to sea level rise in response to increased warming during this period varies between −7.8 and 30.0 cm of sea level equivalent (SLE) under Representative Concentration Pathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment with constant climate conditions and should therefore be added to the mass loss contribution under climate conditions similar to present-day conditions over the same period. The simulated evolution of the West Antarctic ice sheet varies widely among models, with an overall mass loss, up to 18.0 cm SLE, in response to changes in oceanic conditions. East Antarctica mass change varies between −6.1 and 8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighing the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of ice shelves, yields an additional simulated mass loss of 28 mm compared to simulations without ice shelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, the calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based on two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared to simulations done under present-day conditions for the two CMIP5 forcings used and display limited mass gain in East Antarctica.

 

Seroussi, H., et al. , 2020. ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century, The Cryosphere, 14, 3033–3070, doi:10.5194/tc-14-3033-2020

How seasonal cycle in basal melting contribute to observed changes in ice-shelf speed over the year?

klein2020Ice shelves play a critical role in modulating dynamic loss of ice from the grounded portion of the Antarctic Ice Sheet and its contribution to sea-level rise. Recent GPS observations of the Ross Ice Shelf (RIS), one of the largest ice shelves in Antarctica, reveal an annual cycle of ice velocity, with a maximal velocity anomaly reaching several meters per year at most stations. There are a lot of possible reasons for such a cycle. Recent measurements and modelling have shown that basal met rates along the ice front and those near Ross Island and Minna Bluff can change substantially at seasonal timescales, with high melt rates occurring during summer when the upper ocean along the western RIS ice front is warmed by insolation after the sea ice has been removed by melting and advection.

In this study, resulting from a collaboration between the Scripps Institution of Oceanography (University of California San Diego) and the Earth & Space Research Institute (Seattle), we use the Shallow-Shelf Approximation implemented in Elmer/Ice, forced with monthly basal melt rates from an ocean model, to explore the contribution of the strong seasonal cycle in basal melting toward changes in ice velocity over the year.

Our modelling shows that melt-rate response to changes in summer upper-ocean heating near the ice front will affect the future flow of RIS and its tributary glaciers. However, modelled seasonal flow variations from increased summer basal melting near the ice front are much smaller than observed, suggesting that other as-yet-unidentified seasonal processes are currently dominant.

Read more: Klein E., C. Mosbeux, P.D. Bromirski, L. Padman, Y. Bock, S.R. Springer and H.A. Fricker, 2020. Annual cycle in flow of Ross Ice Shelf, Antarctica: contribution of variable basal melting. Journal of Glaciology, doi:10.1017/jog.2020.61

 

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