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.

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occurrence records for all springtail species considered to be endemic or native from these 15 ACBRs and from our own unpublished records.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. 

Full details are in the download file "README_Dataset-SurvivalAntarcticBiota.md"

Software and file formats used. All maps were created using the Antarctic GIS package ‘Quantarctica’ (https://www.qgis.org/en/site/about/case_studies/antarctica.html) in QGIS ver. 3.22.7. The ACBRs shown in figure 1 and Supplementary figures S1-S7 are included in an ‘Environmental management’ layer within Quantarctica and colours were chosen to match those used previously. For the land topography of Antarctica we used the shapefiles from ‘Bedmachine’ (downloaded from NSIDC, https://nsidc.org/data/nsidc-0756/versions/2) in QGIS ver. 3.22.7. Each input data file was saved as .csv files and imported individually into QGIS for: (1) all individual springtail occurrences (separated into each species), (2) geothermal sites (separated into large and small), (3) geochronological dated sites (separated into high refuge support, and low refuge support), and (4) eDNA signals of springtails. These data were then used to create figures 1 and 2 in the main manuscript, and for more detailed information in figures S1-S7 in Supplementary material.

Compiled data accessibility. The .csv data files we used in QGIS for springtail records, geothermal and geochronological sites shown in figures 1 and 2 and figures S1-S7 are available at the Royal Society's figshare portal. We also include our QGIS file used to generate the supplementary figures (QGIS_suppl_figs.qgz) and the .qlr ‘layer definition file’ (All_layers_definition_QGIS.qlr) exported from QGIS, which can be imported into QGIS with Qantarctica along with Bedmachine, which maintains the symbols and colours we used in our figures.