Location Location Location: Survival of Antarctic biota requires the best real-estate

The origin of terrestrial biota in Antarctica has been debated since the discovery of springtails on the first historic voyages to the southern continent more than 120 years ago. A plausible explanation for the long-term persistence of life requiring ice-free land on continental Antarctica has, however, remained elusive. The default glacial eradication scenario has dominated because hypotheses to date have failed to provide a mechanism for their widespread survival on the continent, particularly through the Last Glacial Maximum when geological evidence demonstrates that the ice sheet was more extensive than present. Here, we provide support for the alternative nunatak refuge hypothesis – that ice-free terrain with sufficient relief above the ice sheet provided refuges and was a source for terrestrial biota found today. This hypothesis is supported here by an increased understanding from the combination of biological and geological evidence, and we outline a mechanism for these refuges during successive glacial maxima that also provides a source for coastal species. Our cross-disciplinary approach provides future directions to further test this hypothesis that will lead to new insights into the evolution of Antarctic landscapes and how they have shaped the biota through a changing climate.

Methods
Data collection. We focussed on ice-free terrain represented by 15 currently recognized Antarctic Conservation Biodiversity Regions (ACBRs); we do not include South Orkney Islands. We compiled all published occurrence records for all springtail species considered to be endemic or native from these 15 ACBRs and from our own unpublished records. We obtained the ten geothermal sites used in the analyses by Fraser et al. from their Table S6. We compiled the geochronological data from all known cosmogenic-nuclide data from Antarctica (https://www.ice-d.org/) and from publications that were used to scrutinise the datasets. Cosmogenic dating is uniquely suited to Antarctic environments, however, there are problematic samples and locations. We include a selection of cosmogenic datasets to represent sites that clearly (or potentially) delineate Last Glacial Maximum surface elevations, and reject datasets where results are inconclusive due to isotope inheritance or incomplete or inconclusive results. From the included datasets we divided cosmogenic sites into two categories based on the 100 km radius around each site (using the criteria from Fraser et al.): (1) those that showed unequivocal endemism; and (2) those where the provenance was equivocal. Setting these criteria, and using springtails as a proxy, was critical to identifying regions where glacial refuges for the vast majority of biota were most likely to have occurred.