Elmer/Ice News

Mapping the age of ice of Gauligletscher combining surface radionuclide contamination and ice flow modeling

jouvet2020In the 1950s and '60s, specific radionuclides were released into the atmosphere as a result of nuclear weapons testing. This radioactive fallout left its signature on the accumulated layers of glaciers worldwide, thus providing a tracer for ice particles traveling within the gravitational ice flow and being released into the ablation zone. For surface ice dating purposes, we analyze here the Plutonium and Uranium activity in more than 200 ice samples collected at the surface of Gauligletscher, Switzerland, and successfully identify the isochronal lines from 1960 and 1963. Hence this information is used to fine-tune an ice flow/mass balance model (Elmer/Ice), and to accurately map the age of the entire glacier ice (see picture). As an additional result, our results show that an airplane which crash-landed on the Gauligletscher in 1946 will likely soon be released from the ice close to the place where pieces have emerged in recent years, thus permitting the prognosis given in an earlier model to be revised considerably.

Read more: Jouvet G., S. Röllin, H. Sahli, J. Corcho, L. Gnägi, L. Compagno, D. Sidler, M. Schwikowski, A. Bauder and M. Funk, 2020. Mapping the age of ice of Gauligletscher combining surface radionuclide contamination and ice flow modeling, The Cryosphere, 14, 4233–4251, doi:10.5194/tc-14-4233-2020

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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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