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 (∼10 18 Pa s) than the Earth's average mantle (∼10 21 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 Summary Portions 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.

Contrasting Response of West and East Antarctic Ice Sheets to Glacial Isostatic Adjustment

“…This may be explained by the fact that when the solid‐Earth response is sufficiently rapid, the geoid perturbation due to ice mass loss is rapidly counterbalanced by bed uplift. The proposed elementary GIA model is thus shown to be capable of reproducing the stabilizing effect of GIA feedbacks highlighted in previous studies (Adhikari et al., 2014; Gomez et al., 2012, 2013, 2015; Kachuck et al., 2020; Konrad et al., 2015, 2016; Larour et al., 2019).…”

“…Even though our results generally document the stabilizing effect of GIA feedbacks, we have identified two distinct GIA‐related behaviors that may induce an increase in mass loss relative to projections omitting GIA feedbacks. One class of behavior, represented by the lowest grey lines in Figure 7a is thought to be related to the migration of topographic forebulges during bedrock adjustment, which causes local crustal motions (and slopes) to change sign (Adhikari et al., 2014), thereby generating configurations that are more vulnerable to instability (Kachuck et al., 2020). Note however that forebulges are a component of our GIA model that are simulated the least accurately (see Section 2.2.3).…”

“…In a complementary study that explores the potential for rapid viscoelastic deformation to stabilize Pine Island glacier on centennial timescales, Kachuck et al. (2020) show that instantaneous components of the solid‐Earth response (purely elastic deformations, geoid perturbations) provide less stability than the viscoelastic response. This may be explained by the fact that when the solid‐Earth response is sufficiently rapid, the geoid perturbation due to ice mass loss is rapidly counterbalanced by bed uplift.…”

“…We attribute the difference between our results and those of Gomez et al (2015) to the fact that we consider a spatially varying Earth structure with a low viscosity beneath West Antarctica while Gomez et al (2015) adopt a continent-wide high viscosity Earth model. In a complementary study that explores the potential for rapid viscoelastic deformation to stabilize Pine Island glacier on centennial timescales, Kachuck et al (2020) show that instantaneous components of the solid-Earth response (purely elastic deformations, geoid perturbations) provide less stability than the viscoelastic response. This may be explained by the fact that when the solid-Earth response is sufficiently rapid, the geoid perturbation due to ice mass loss is rapidly counterbalanced by bed uplift.…”

Resolving glacial isostatic adjustment (GIA) in response to modern and future ice loss at marine grounding lines in West Antarctica

“…However, other studies (e.g. Gomez et al, 2015;Kachuck (Fretwell et al, 2013). Transparent patch in (c) contains no data on mantle viscosity as the region contains lithosphere at 200 km depth.…”