Past interglacial West Antarctic Ice Sheet collapse: a critical review of evidence and approaches

The collapse, retreat or stability of the West Antarctic Ice Sheet (WAIS) during previous warm periods would offer powerful constraints on its possible behaviour in a warmer polar future. The last interglacial (LIG) is the period for which the most constraining data is expected to persist. However most of the evidence is circumstantial and fragmentary, allowing us to hypothesise but not define possible conformations of the ice sheet. Farfield sea level data suggest that an Antarctic sea level contribution of one to a few metres must have occurred. Ice core and glacial geologic evidence show that significant ice remained in some parts of WAIS. Limited genomic evidence suggest that seaways existed between the Weddell, Amundsen and Ross Seas, most likely in the LIG, while ice core data imply that the Ronne Ice Shelf survived. Ice sheet modelling scenarios consistent with such evidence show very significant ice loss in the Amundsen Sea sector. We highlight two possible configurations of collapsed ice that are consistent with the range of geological and genetic evidence available, with maximum Antarctic Ice Sheet sea level contributions of 4 or 6 m. Such hypothesised conformations need to be challenged by new and emerging data from ice cores, cosmogenic studies and genomic databases. The constraints provided by the data should be used to restrict the ranges of parameters in models used to assess future rates and extents of ice sheet loss under different climate change scenarios. • Critical review of evidence for Last Interglacial Antarctic Ice Sheet configuration. • Evaluates glacial geology, marine sediment, ice core and genomic evidence. • Highlights possible configurations consistent with available evidence. • Suggests priorities for efforts to understand past Antarctic ice sheet instability.