Investigating the impact of sub-ice shelf melt on Antarctica Ice Sheet spin-up and projections

Sub-ice shelf melting is critical for the stability of the Antarctic Ice Sheet, as it influences ice shelf buttressing that impedes grounded ice flow. Previous studies have emphasized that uncertainties in the state of sub-ice shelf melting contribute to inaccuracies in future sea-level projections. To better understand how sub-ice shelf melt rates affect model initialization and predictions, we adopt a single ice sheet model (PISM) and investigate two different sub-ice shelf melt rate schemes during model spin-ups. We then drive the Antarctic Ice Sheet into the future using identical environmental forcings. We find that, despite closely matched steady-state geometries achieved through the spin-up process with different sub-ice shelf melt rates, the prognostic simulations reveal significantly divergent ice mass changes, particularly in marine ice sheet regions. By 2100, the difference in global sea-level contributions from the Antarctic Ice Sheet can be as large as ~57 %, primarily from West Antarctica. This discrepancy arises because the spin-up initialization method alters the ice sheet's dynamic state, such as basal friction and thermal regimes, leading to varied ice sheet mass changes. Therefore, this study underscores the importance of sub-ice shelf melting and ice sheet model initialization methods in reducing uncertainties in predicting the Antarctic Ice Sheet's future.