Variations of the Antarctic Ice Sheet in a Coupled Ice Sheet-Earth-Sea Level Model: Sensitivity to Viscoelastic Earth Properties

Abstract

A coupled ice sheet-solid Earth-sea level model is applied to long-term variations of the Antarctic ice sheet. A set of radially varying viscoelastic profiles in the global Earth model is used to explore feedbacks on ice sheet variability, including one with a very weak upper mantle zone and thin lithosphere representative of West Antarctic regions. Simulations are performed for (1) the deglacial retreat over the last ~20,000 years, (2) the future 5,000 years with greenhouse-gas scenario Representative Concentration Pathway 8.5 (RCP8.5), and (3) the warm Pliocene ~3 Ma. For the deglacial period a large ensemble of 625 simulations is analyzed, with a score computed for each run based on comparisons to geologic and modern data. For each of the five Earth profiles, the top-scoring combinations of the other model parameters in the ensemble are used to perform future and Pliocene simulations. For the last deglacial retreat, the viscoelastic Earth profiles produce relatively small differences in overall ice volume and equivalent sea level. In contrast, profiles with weak upper mantle and thin lithosphere produce strong negative feedback and less ice retreat in the future and Pliocene runs. This is due to the faster pace of ice sheet retreat in these runs, leading to greater lags in the viscous bedrock rebound behind the unloading, which allows for greater influence of the viscosity profiles. However, the differences in grounding-line retreat are located primarily in East Antarctic basins, where a weak upper mantle and thin lithosphere may not be realistic, emphasizing the need for lateral heterogeneity in the Earth model.