Elmer/Ice News

GeoMIP scenarios applied to the Greenland ice sheet

Stratospheric Aerosol Injection (SAI) is a highly debated topic. The more it is important to look into the science (objectively,jgrf21835 fig 0006 m small without an agenda).  In order to contribute to this process, two ice dynamic models (SICOPOLIS and Elmer/Ice) driven by changes in surface mass balance (SMB) from four climate models to estimate the SLR contribution under the Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathway (RCP) 4.5, and 8.5, and Geoengineering Model Intercomparison Project G4 scenarios were deployed for the Greenland ice sheet. The G4 scenario adds 5 Tg/yr sulfate aerosols to the equatorial lower stratosphere (equivalent of 1/4 the 1991 Mt Pinatubo SO2 eruption) to the IPCC RCP4.5 scenario, which itself approximates the greenhouse gas emission commitments agreed in Paris in 2015. In the applied setups for the 2020–2090 period, the two ice sheet models show a reduction of mass loss between 31%–38% for the G4 compared to RCP4.5 scenario, which itself compared to RCP8.5 shows a lowering of 36%–48%. Both, the G4 and the 4.5 scenario indicate a lowering of the ice-flux across the grounding line into the ocean, as glaciers retreat from the coast and become land-terminated, with an exception of low-lying catchments (e.g., Jakobshavn, 79N, Zachariae Isstrøm, and Petermann glaciers)  that show an increased flux under RCP 4.5 compared to G4. Despite a dominating  variation of calving losses compared to differences in SMB between SICOPOLIS and Elmer/Ice, ice discharge losses are significant, ranging from 15% up to 42%, depending on the scenario. Picture (taken from the publication) to the right shows differences of the ensembles in flux and ice thickness between G4 and RCP4.5 runs.

Read more:

Moore, J. C., R. Greve, C. Yue, T.  Zwinger, F. Gillet-Chaulet, and L. Zhao, 2023. Reduced Ice Loss From Greenland Under Stratospheric Aerosol InjectionJournal of Geophysical Research: Earth Surface, 128. doi:10.1029/2023JF007112

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Higher-order fabric structure in a coupled, anisotropic ice-flow model

lilien2023Ice-crystal fabric can induce mechanical anisotropy that significantly affects flow, but ice-flow models generally do not include fabric development or its effect upon flow. Here, we incorporate a new spectral expansion of fabric, and more complete description of its evolution, into the ice-flow model Elmer/Ice. This approach allows us to model the effect of both lattice rotation and migration recrystallization on large-scale ice flow. The fabric evolution is coupled to flow using an unapproximated non-linear orthotropic rheology that better describes deformation when the stress and fabric states are misaligned. These improvements are most relevant for simulating dynamically interesting areas, where recrystallization can be important, tuning data are scarce and rapid flow can lead to misalignment between stress and fabric. We validate the model by comparing simulated fabric to ice-core and phase-sensitive radar measurements on a transect across Dome C, East Antarctica. With appropriately tuned rates for recrystallization, the model is able to reproduce observations of fabric. However, these tuned rates differ from those previously derived from laboratory experiments, suggesting a need to better understand how recrystallization acts differently in the laboratory compared to natural settings.

Read more: Lilien, D., N. Rathmann, C. Hvidberg, A. Grinsted, M. Ershadi, R. Drews and D. Dahl-Jensen, 2023. Simulating higher-order fabric structure in a coupled, anisotropic ice-flow model: Application to Dome CJournal of Glaciology, 1-20. doi:10.1017/jog.2023.78

 

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The stability of present-day Antarctic grounding lines

hill2023Theoretical and numerical work has shown that under certain circumstances grounding lines of marine-type ice sheets can enter phases of irreversible advance and retreat driven by the marine ice sheet instability (MISI). Instances of such irreversible retreat have been found in several simulations of the Antarctic Ice Sheet. However, it has not been assessed whether the Antarctic grounding lines are already undergoing MISI in their current position. Here, we conduct a systematic numerical stability analysis using three state-of-the-art ice sheet models: Úa, Elmer/Ice, and the Parallel Ice Sheet Model (PISM). For the first two models, we construct steady-state initial configurations whereby the simulated grounding lines remain at the observed present-day positions through time. The third model, PISM, uses a spin-up procedure and historical forcing such that its transient state is close to the observed one. To assess the stability of these simulated states, we apply short-term perturbations to submarine melting. Our results show that the grounding lines around Antarctica migrate slightly away from their initial position while the perturbation is applied, and they revert once the perturbation is removed. This indicates that present-day retreat of Antarctic grounding lines is not yet irreversible or self-sustained. However, our accompanying paper (Part 2, Reese et al.2023) shows that if the grounding lines retreated further inland, under present-day climate forcing, it may lead to the eventual irreversible collapse of some marine regions of West Antarctica.

See the TiPACCs video explaining the results of these two papers!

To read more: Hill E. A., B. Urruty, R. Reese, J. Garbe, O. Gagliardini, G. Durand, F. Gillet-Chaulet, G. H. Gudmundsson, R. Winkelmann, M. Chekki, D. Chandler and P. M. Langebroek, 2023. The stability of present-day Antarctic grounding lines - Part 1 : No indication of marine ice sheet instability in the current geometry, The Cryosphere, 17, 3739–3759, doi:10.5194/tc-17-3739-2023

and the companion paper:  Reese, R., J. Garbe, E. A. Hill, E. A., B. Urruty, K. A. Naughten, O. Gagliardini, G. Durand, F. Gillet-Chaulet, G. H. Gudmundsson, D. Chandler, P. M. Langebroek and R. Winkelmann, 2023. The stability of present-day Antarctic grounding lines – Part 2 : Onset of irreversible retreat of Amundsen Sea glaciers under current climate on centennial timescales cannot be excluded, The Cryosphere, 17, 3761–3783, doi:10.5194/tc-17-3761-2023

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