Elmer/Ice News

On the nature of melt-rate oscillations in coupled ice-ocean simulations

An emergent feature in several contributing coupled models to the 1st Marine Ice Sheet–Ocean Model melt rate evolution of timeIntercomparison Project (MISOMIP1) was a time-varying oscillation in basal melt rates. In this study, the authors used Elmer/Ice coupled to ROMSIceShelf via the Framework for Ice-Sheet Ocean Coupling (FISOC) to investigate the origin and implications of this observed feature and, more generally, the impact of coupled modeling strategies on the simulated basal melt in an idealized ice shelf cavity based on the MISOMIP setup. Interestingly, melt oscillations emerged in both, the coupled system and the standalone ocean model using a prescribed change of cavity geometry. There appears a close relation to the discretized ungrounding of the ice sheet, probably strengthened by a combination of positive buoyancy–melt feedback and/or melt–geometry feedback near the grounding line, and the frequent coupling of ice geometry and ocean evolution. There is still debate whether this is purely numerical or a numerical artifact enhanced by model physics. The paper includes a short best-practice guide on the choice of parameters to minimize the impact of this effect.

Read more: Zhao, C., R. Gladstone, B.K. Galton-Fenzi, D. Gwyther, and T. Hattermann, 2022. Evaluation of an emergent feature of sub-shelf melt oscillations from an idealized coupled ice sheet–ocean model using FISOC (v1.1) – ROMSIceShelf (v1.0) – Elmer/Ice (v9.0),. Geosci. Model Dev., 15, 5421–5439, doi:10.5194/gmd-15-5421-2022

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Evidence of Seasonal Uplift in the Argentière Glacier

vincent2022Glacier basal motion is responsible for a large part of ice flux in temperate alpine glaciers and outlet glaciers of ice sheets. However, the hydromechanical processes by which basal water controls sliding at the glacier bed are poorly known in large part because observations are very scarce. Consequently, the impact of surface melting and meltwater input on the future of mountain glaciers and outlet glaciers of ice sheets remains unclear. Here, we use a comprehensive data set of in situ measurements performed over 2 years on the Argentière Glacier in the French Alps, complemented by state-of-the-art ice flow and hydrology modeling, to investigate changes in water storage at the ice-bedrock interface. We find strikingly large uplifts ranging between 0.20 and 0.90 m over the winter/spring seasons in the ablation zone. We show that this uplift is mostly related to enhanced bed separation as a result of increased basal water storage. We expect this study to be helpful to the glaciological community studying basal sliding and its modulation by sub-glacial hydrology with a view of improving predictions of the future behavior of mountain glaciers and outlet glaciers of ice sheets.

Read more: Vincent C., A. Gilbert, A. Walpersdorf, F. Gimbert, O. Gagliardini, B. Jourdain, J. P. Roldan Blasco, O. Laarman, L. Piard, D. Six, L. Moreau, D. Cusicanqui and E. Thibert, 2022. Evidence of seasonal uplift in the Argentière Glacier (Mont Blanc area, France). Journal of Geophysical Research: Earth Surface, 127, e2021JF006454. doi:10.1029/2021JF006454

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A Consistent Framework for Coupling Basal Friction With Subglacial Hydrology on Hard-Bedded Glaciers

gilbert2022Predicting the sliding speed of glaciers and ice sheets is challenged by the difficulties of assessing the water pressure at the glacier base. Here, we improve the coupling between existing theories about basal friction and subglacial hydrology by introducing a consistent description of roughness and hydraulic transmissivity. Our work breaks with the common view on the subglacial environment that water pressure drives the sliding speed by modulating friction at the glacier base. Instead, our findings show that at multi-day and longer timescales sliding speed and water pressure are imposed by the water discharge along the glacier base that needs to be accommodated. Our results open new perspectives for understanding contemporary glacier and ice sheet sliding and predicting its future behavior under changing climate.

Read more: Gilbert A., F. Gimbert, K. Thøgersen, T. V. Schuler and A. Kääb, 2022. A Consistent Framework for Coupling Basal Friction With Subglacial Hydrology on Hard-Bedded Glaciers, Geophysical Research Letters, 49, e2021GL097507, doi:10.1029/2021GL097507

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