Elmer/Ice News

Quantifying the effect of ocean bed properties on ice sheet geometry over 40 000 years with Elmer/Ice

schanwell2020Simulations of ice sheet evolution over glacial cycles require integration of observational constraints using ensemble studies with fast ice sheet models. These include physical parameterisations with uncertainties, for example, relating to grounding-line migration. More complete ice dynamic models are slow and have thus far only be applied for < 1000 years, leaving many model parameters unconstrained. Here we apply a 3D thermomechanically coupled full-Stokes ice sheet model to the Ekström Ice Shelf embayment, East Antarctica, over a full glacial cycle (40 000 years). We test the model response to differing ocean bed properties that provide an envelope of potential ocean substrates seawards of today's grounding line. The end-member scenarios include a hard, high-friction ocean bed and a soft, low-friction ocean bed. We find that predicted ice volumes differ by > 50 % under almost equal forcing. Grounding-line positions differ by up to 49 km, show significant hysteresis, and migrate non-steadily in both scenarios with long quiescent phases disrupted by leaps of rapid migration. The simulations quantify the evolution of two different ice sheet geometries (namely thick and slow vs. thin and fast), triggered by the variable grounding-line migration over the differing ocean beds. Our study extends the timescales of 3D full-Stokes by an order of magnitude compared to previous studies with the help of parallelisation. The extended time frame for full-Stokes models is a first step towards better understanding other processes such as erosion and sediment redistribution in the ice shelf cavity impacting the entire catchment geometry.

Read more: Schannwell, C., R. Drews, T. A. Ehlers, O. Eisen, C. Mayer, M. Malinen, E. C. Smith and H. Eisermann, 2020. Quantifying the effect of ocean bed properties on ice sheet geometry over 40 000 years with a full-Stokes model, The Cryosphere, 14, 3917–3934, doi:10.5194/tc-14-3917-2020

 

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Numerical modeling of the dynamics of the Mer de Glace glacier, French Alps: comparison with past observations and forecasting of near-future evolution

peyaud2020Alpine glaciers are shrinking and rapidly loosing mass in a warming climate. Glacier modeling is required to assess the future consequences of these retreats on water resources, the hydropower industry and risk management. However, the performance of such ice flow modeling is generally difficult to evaluate because of the lack of long-term glaciological observations. Here, we assess the performance of the Elmer/Ice full Stokes ice flow model using the long dataset of mass balance, thickness change, ice flow velocity and snout fluctuation measurements obtained between 1979 and 2015 on the Mer de Glace glacier, France. Ice flow modeling results are compared in detail to comprehensive glaciological observations over 4 decades including both a period of glacier expansion preceding a long period of decay. To our knowledge, a comparison to data at this detail is unprecedented. We found that the model accurately reconstructs the velocity, elevation and length variations of this glacier despite some discrepancies that remain unexplained. The calibrated and validated model was then applied to simulate the future evolution of Mer de Glace from 2015 to 2050 using 26 different climate scenarios. Depending on the climate scenarios, the largest glacier in France, with a length of 20 km, could retreat by 2 to 6 km over the next 3 decades.

Read more: Peyaud V., C. Bouchayer, O. Gagliardini, C. Vincent, F. Gillet-Chaulet, D. Six and O. Laarman, 2020. Numerical modeling of the dynamics of the Mer de Glace glacier, French Alps: comparison with past observations and forecasting of near-future evolution, The Cryosphere, 14, 3979–3994, doi:10.5194/tc-14-3979-2020

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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

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