Geologic controls on ice sheet sensitivity to deglacial climate forcing in the Ross Embayment, Antarctica

Abstract

The role of external forcings in the deglacial ice sheet evolution of the Ross Embayment, Antarctica's largest catchment, continues to be a highly contested topic. Although numerical ice sheet models indicate that ocean and atmosphere forcings were the main drivers of deglacial ice sheet retreat, these models have difficulty in accurately capturing both the timing and rate of retreat in every area of the embayment. Other factors that influence the sensitivity of ice sheets to climate forcing, such as the physical properties of the bed, isostatic deformation of the continental shelf, and rheological properties of the ice, are parameterized inconsistently across models. Here, we explore using a systematic approach the extent to which specific model parameters related to basal substrate, bed deformation and ice flow and rheology impact the climate sensitivity of the ice sheet in the Ross Embayment over the last deglaciation. Higher variability in deglacial ice sheet evolution is observed among experiments using different model parameters than among experiments using different climate forcings. Mantle viscosity, the material properties of the till, and an enhancement factor of the shallow shelf approximation (ESSA) component of the stress balance exhibit strong influences on the timing of ice sheet response to deglacial climate forcing, and may contribute to the asynchronous retreat behavior of the Eastern and Western Ross Sea. The Western Ross Sea is especially sensitive to both climate forcing and model parameter selection, with both cool climate forcing and low ESSA producing better agreement with terrestrial ice thinning records. The evolution and extent of the Siple Coast grounding line is highly sensitive to the mantle viscosity and till properties in addition to ocean and precipitation forcing. Constraining these physical model parameters is therefore paramount for accurate projections of the Antarctic ice sheet response to projected future changes in ocean temperatures and precipitation.