Evaluating models of ice-sheet evolution in the Weddell Sea sector of Antarctica using exposure-age data

Abstract:

We present an evaluation of numerical ice-sheet model results using all available post-Last Glacial Maximum (LGM) terrestrial cosmogenic nuclide exposure ages from the Weddell Sea sector of the Antarctic Ice Sheet. Reconstructing the LGM-to-present evolution of the Antarctic Ice Sheet is needed to help understand its response, including its contribution to sea level, to past and future environmental change. Recent in situ cosmogenic ¹⁴C and ¹⁰Be exposure dating studies constrain the LGM ice thickness and subsequent pattern of ice thinning in the Weddell Sea Embayment, providing new data to validate the results of numerical simulations of ice-sheet evolution. We use those exposure ages to evaluate seven numerical ice-sheet model simulations. We find that those models are not inconsistent with constraints on the minimum total ice thickness change since the LGM around the Weddell Sea Embayment. However, LGM ice thicknesses are often underpredicted by many hundreds of metres at locations in the Ellsworth Mountains, Pensacola Mountains, and the Shackleton Range. We note that the majority of ice thickness constraints in the embayment are, in contrast, sourced from ¹⁰Be exposure ages which cannot constrain the upper limit on the total ice thinning since the LGM. Consequently, it is difficult to evaluate model outputs that predict relatively large total ice thickness changes. The most significant mismatches between model outputs and exposure age data are in the timing of ice thinning. We observe thinning in numerical model outputs that is commonly both earlier and more rapid than permitted by observations. We discuss potential causes of ice thickness and temporal mismatches sourced from both the numerical simulations and the exposure ages.