A history-matching analysis of the Antarctic Ice Sheet since the Last Interglacial - Part 1: Ice sheet evolution

In this study we present the evolution of the Antarctic Ice Sheet (AIS) since the Last Interglacial. This is achieved by means of a history-matching analysis where a newly updated observational database (AntICE2) is used to constrain a large ensemble of 9293 model simulations. The Glacial Systems Model (GSM) configured with 38 ensemble parameters was history-matched against observations of past ice extent, past ice thickness, past sea level, ice core borehole temperature profiles, present-day uplift rates, and present-day ice sheet geometry and surface velocity. Successive ensembles were used to train Bayesian artificial neural network emulators. The parameter space was efficiently explored to identify the most relevant portions of the parameter space through Markov chain Monte Carlo sampling with the emulators. The history matching ruled out model simulations which were inconsistent with the observational-constraint database. During the Last Interglacial (LIG), the AIS yielded several metres equivalent sea level (m e.s.l.) of grounded ice volume deficit relative to the present, with sub-surface ocean warming during this period being the key uncertainty. At the global Last Glacial Maximum (LGM), the best-fitting sub-ensemble of AIS simulations reached an excess grounded ice volume relative to the present of 9.2 to 26.5 m e.s.l. Considering the data do not rule out simulations with an LGM grounded ice volume >20 m e.s.l. with respect to the present, the AIS volume at the LGM can partly explain the missing-ice problem and help close the LGM sea-level budget. Moreover, during the deglaciation, the state space estimation of the AIS based on the GSM and near-field observational constraints allows only a negligible Antarctic Meltwater Pulse 1a contribution (-0.2 to 0.3 m e.s.l.).