Elmer/Ice News

Its the anisotropy!

Blue ice areas (BIA) cover about 1% of the Antarctic ice sheet. They are characterized by a local enhanced ablation zone leaving bare ice (hence the name) in a distinct ablation zone. BIAs are confined to the coastal areas, usually close to nunataks. The distinct ablation zone has the coinciding feature that isochrones get vertically aligned, making BIAs an attractive source for easy accessible climate data from maritime influenced regions by simply scratching an ice core horizontally from the SBB velo singlemax
surface. The huge drawback is, that - in comparison to the vertically drilled ice cores in the central regions of Antarctica - the dynamical evolution of the ice sheet is an even stronger determining input in order to interpret such horizontal ice cores. To that end, the well explored BIA at Scharffenbergbotnen, DML, East Antarctica was studied using Elmer/Ice. Being initially puzzled by a complete mismatch between computed and measured velocities with a standard Glen's flow law and by excluding all other possible reason, the authors came to the conclusion that the existence of a pronounced fabric at the glacier is the most likely explanation to correctly interpret the flow conditions at the BIA. Further, by studying the evolution of the age-depth horizons using a novel Semi-Lagrangian solver showed that the oldest ice is about the age of the Late GLacial Maximum (LGM) of about 15ka bp., leading to the conclusion that the BIA started to form after the LGM, when the surrounding ice sheet started to thin and the valley of Scharffenbergbotnen was decoupled from the main ice flow. The project behind this study was funded by the Finnish Academy.

Reference: Zwinger, T., M. Schäfer, C. Martín, and J.C. Moore, 2014. Influence of anisotropy on velocity and age distribution at Scharffenbergbotnen blue ice area, The Cryosphere, 8, 607-621, doi:10.5194/tc-8-607-2014 [link to paper]

Uncertainty in SMB and projections of sea level contribution of the Greenland ice sheet

smb ice2seaA new parameterisation of the Greenland ice sheet (GrIS) feedback between surface mass balance (SMB: the sum of surface accumulation and surface ablation) and surface elevation in the MAR regional climate model (Edwards et al., 2014) is applied to projections of future climate change using five ice sheet models (ISMs), among them Elmer/Ice. The MAR (Modèle Atmosphérique Régional: Fettweis, 2007) climate projections are for 2000–2199, forced by the ECHAM5 and HadCM3 global climate models (GCMs) under the SRES A1B emissions scenario.

In all results the elevation feedback is significantly positive, amplifying the GrIS sea level contribution relative to the MAR projections in which the ice sheet topography is fixed: the lower bounds of our 95% credibility intervals (CIs) for sea level contributions are larger than the "no feedback" case for all ISMs and GCMs.

Reference:
Edwards, T. L., X. Fettweis, O. Gagliardini, F. Gillet-Chaulet, H. Goelzer, J.M. Gregory, M. Hoffman, P. Huybrechts, A.J. Payne, M. Perego, S. Price, A. Quiquet and C. Ritz, 2013. Effect of uncertainty in surface mass balance–elevation feedback on projections of the future sea level contribution of the Greenland ice sheet, The Cryosphere, 8, 195-208, doi:10.5194/tc-8-195-2014. [link to paper]

An Antarctic outlet glacier engaged in an irreversible retreat

pig nccAn international team of researchers led by the Laboratoire de Glaciologie et de Géophysique de l'Environment (LGGE) CNRS-Université Grenoble Alpes shows that Pine Island Glacier (PIG), the primary contributor to sea-level rise from Antarctica, has entered a period of self-sustained retreat and its discharge to the ocean will likely increase in comparison to observations from the last decade. The research is published today in Nature Climate Change.

The current imbalance of the West Antarctic ice sheet and its related net contribution to ongoing sea-level rise is now well established. In particular, PIG has receded by about ten kilometers during the last decade and alone contributes 25% of the total ice loss from West Antarctica. However, the future evolution of PIG remains poorly constrained with the possibility that it may lead to self-sustained retreat in what is known as the marine ice sheet instability.

As a result of the European Union’s four-year ice2sea project, and for the first time, three state-of-the-art ice-sheet models are tested against current observations and their simulations of PIG’s evolution over the next few decades compared. All of the models agreed that PIG has started a phase of self-sustained retreat and will irreversibly continue its recession over many tens of kilometers. This leads to a 3-5 fold increase in mass loss when compared to the current observations, equivalent to a 3.5-10 mm sea-level rise over the next 20 years.

Press Contact:
Gaël Durand, CNRS - Université Grenoble-Alpes
+33 4 76 82 42 84, This email address is being protected from spambots. You need JavaScript enabled to view it.

Reference:
Favier, L., G. Durand, S. L. Cornford, G. H. Gudmundsson, O. Gagliardini, F. Giller-Chaulet, T. Zwinger, A. J. Payne and A. M. Le Brocq, 2014. Retreat of Pine Island Glacier controlled by marine ice-sheet instability, Nature Climate Change, doi:10.1038/nclimate2094. [Link to paper]

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