Rapid Viscoelastic Deformation Slows Marine Ice Sheet Instability at Pine Island Glacier

Abstract

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 Earth