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Rapid Viscoelastic Deformation Slows Marine Ice Sheet Instability at Pine Island Glacier
The ice sheets of the Amundsen Sea Embayment (ASE) are vulnerable to the marine ice sheet instability (MISI), which could cause irreversible collapse and raise sea levels by over a meter. The uncertain timing and scale of this collapse depend on the complex interaction between ice, ocean, and bedrock dynamics. The mantle beneath the ASE is likely less viscous (∼1018 Pa s) than the Earth’s average mantle (∼1021 Pa s). Here we show that an effective equilibrium between Pine Island Glacier’s retreat and the response of a weak viscoelastic mantle can reduce ice mass lost by almost 30% over 150 years. Other components of solid Earth response—purely elastic deformations and geoid perturbations—provide less stability than the viscoelastic response alone. Uncertainties in mantle rheology, topography, and basal melt affect how much stability we expect, if any. Our study indicates the importance of considering viscoelastic uplift during the rapid retreat associated with MISI.Plain Language SummaryPortions of the West Antarctic Ice Sheet are vulnerable to an instability that could lead to rapid ice sheet collapse, significantly raising sea levels, but the timing and rates of collapse are highly uncertain. In response to such a large‐scale loss of overlying ice, viscoelastically deforming mantle material uplifts the surface, alleviating some drivers of unstable ice sheet retreat. While previous studies have focused on the effects mantle deformation has on continental ice dynamics over centuries to millennia, recent seismic observations suggest that the mantle beneath West Antarctica is hot and weak, potentially affecting local glacial dynamics over timescales as short as decades. To measure the importance of viscoelastic uplift in stabilizing grounding line retreat, we coupled a high‐resolution ice flow model to a viscoelastically deforming mantle. We find that rapid viscoelastic uplift can reduce the total volume of ice lost over 150 years by 30%, or 18 mm of equivalent sea level rise, making it an essential process to consider when using models to project the future evolution of marine‐based ice retreat.Key PointsWe examine the feedback between ice sheet dynamics and solid Earth viscoelastic deformation on grounding line stabilityThe viscoelastic response of a low viscosity mantle stabilizes the marine ice sheet instability over decades to centuriesViscoelastic uplift on timescales similar to grounding line migration can be a leading term in the feedback ice sheets/solid EarthPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155486/1/grl60591-sup-0001-Text_SI-S01.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155486/2/grl60591.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155486/3/grl60591_am.pd
Stability of ice shelves and ice cliffs in a changing climate
The largest uncertainty in future sea-level rise is loss of ice from the Greenland and Antarctic Ice Sheets. Ice shelves, freely floating platforms of ice that fringe the ice sheets, play a crucial role in restraining discharge of grounded ice into the ocean through buttressing. However, since the 1990s, several ice shelves have thinned, retreated, and collapsed. If this pattern continues, it could expose thick cliffs that become structurally unstable and collapse in a process called marine ice cliff instability (MICI). However, the feedbacks between calving, retreat, and other forcings are not well understood. Here we review observed modes of calving from ice shelves and marine-terminating glaciers, and their relation to environmental forces. We show that the primary driver of calving is long-term internal glaciological stress, but as ice shelves thin they may become more vulnerable to environmental forcing. This vulnerability—and the potential for MICI—comes from a combination of the distribution of preexisting flaws within the ice and regions where the stress is large enough to initiate fracture. Although significant progress has been made modeling these processes, theories must now be tested against a wide range of environmental and glaciological conditions in both modern and paleo conditions. ▪ Ice shelves, floating platforms of ice fed by ice sheets, shed mass in a near-instantaneous fashion through iceberg calving.▪ Most ice shelves exhibit a stable cycle of calving front advance and retreat that is insensitive to small changes in environmental conditions.▪ Some ice shelves have retreated or collapsed completely, and in the future this could expose thick cliffs that could become structurally unstable called ice cliff instability.▪ The potential for ice shelf and ice cliff instability is controlled by the presence and evolution of flaws or fractures within the ice.</div