Elmer/Ice News

Do Existing Theories Explain Seasonal to Multi-Decadal Changes in Glacier Basal Sliding Speed?

gimbert2021Basal sliding is an important component of glacier motion. However, our knowledge of the physics that controls basal sliding is incomplete. This causes large uncertainties in the contribution to sea-level rise predicted for ice sheets over the coming century. Here, we test our understanding of basal sliding against particularly unique observations, made via a rotating bicycle wheel that has been continuously measuring glacier basal motion over three decades within excavated tunnels under the Argentière Glacier in the French Alps. Due to stress changes from significant glacier thinning over the multi-decadal period we are able to establish an observationally derived sliding law and compare it with expectations from theory. We report many observational features that are in striking agreement with theoretical predictions from glacier sliding over bedrock beds. However, we also observe an undocumented behavior of stress stabilization during the melting period at a specific stress state known as the Iken's limit. This behavior causes long term sliding velocities to follow a simple power law scaling with bed shear stress. This finding has the potential of strongly simplifying and reducing uncertainty on predicting glaciers response to climate change.

Read more: Gimbert F., A. Gilbert, O.  Gagliardini, C.  Vincent and L. Moreau, 2021.  Do existing theories explain seasonal to multi-decadal changes in glacier basal sliding speed? Geophysical Research Letters,  48, e2021GL092858. https://doi.org/10.1029/2021GL092858

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A new calving rate parameterization for ice-cliffs

Picture of deforming/calving ice-cliff  (from Nature Com.)Using HiDEM and Elmer/Ice to investigate the modes through which ice cliffs can structurally fail, this article contributes a conservative ice-cliff failure retreat rate parameterization that can easily be included in ice-sheet models. Results show the importance of viscous deformation, shear-band formation, and brittle-tensile failure in the context of marine ice-cliff instability. The findings also include possible mechanisms to inhibit a runaway situation by two major contributions, namely, the backforce exhibited by iceberg mélange as well as viscous flow deformation changing the cliff's shape.

Read more: Crawford, A.J., Benn, D.I., Todd, J, Åström, J.A, Bassis, J.N. and Zwinger, T., 2021. Marine ice-cliff instability modeling shows mixed-mode ice-cliff failure and yields calving rate parameterization. Nat Commun 12, 2701, doi:10.1038/s41467-021-23070-7

 

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Improved projections of land ice contributions

An article with the titleAntarctic Ice flow simulated by Elmer/Ice ( Image: Rupert Gladstone) Projected land ice contributions to twenty-first-century sea level rise published in Nature explores the contribution to sea level in the 21st century arising from the world’s glaciers and the Greenland as well as the Antarctic ice sheet.  The study is a synthesis of the research of more than 80 authors from 38 international research groups and brings together both computer models and statistical techniques to make predictions for the latest socio-economic scenarios. It includes results obtained with Elmer/Ice for the Antarctic ice sheet (the only full-Stokes contribution to the study).   Results from this research shall inform the Intergovernmental Panel on Climate Change and contribute its Sixth Assessment report, due to be published later this year.

Read more: Edwards, T.L, and 81 others, 2021. Projected land ice contributions to twenty-first-century sea level rise, Nature, 593, 74–82, doi:10.1038/s41586-021-03302-y.

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