ORIGINAL ARTICLE Biodiversity signature of the Last Glacial Maximum at South Georgia, Southern Ocean David K. A. Barnes 1, *, Chester J. Sands 1 , Oliver T. Hogg 1,2 , Ben J.O. Robinson 1 , Rachel V. Downey 3 and James A. Smith 1 1 British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 OET, UK, 2 National Oceanography Centre Southampton, University of Southampton, European Way, Southampton SO14 3ZH, UK, 3 Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt am Main, Germany *Correspondence: David K. A. Barnes, British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge, CB3 OET, UK. E-mail: dkab@bas.ac.uk ABSTRACT Aim High-latitude biodiversity distributions can preserve signals of the timing and geography of past glaciations, and as such ground truth ice-sheet models. Discrete polar archipelagos offer the fewest confounding factors for testing his- toric ice position records in extant biodiversity. At South Georgia, two compet- ing geological hypotheses suggest that either the Last Glacial Maximum (LGM) ice was extensive, nearly covering the continental shelf (H 1 Big ice) or restricted to the inner fjords (H 2 Little ice). We examined the past configura- tion of the South Georgia ice cap using seabed biodiversity. Location South Georgia, Southern Ocean. Methods We used a bespoke camera lander (SUCS) and Agassiz trawl deploy- ments across ‘big ice’ and ‘little ice’ hypothesized positions of LGM grounded ice around the South Georgia continental shelf. We investigated faunal assem- blage structure and richness, especially of brooders, and modelled low dispersal taxa, for example, those with limited pelagic larvae (bryozoans and sponges). Results We found a striking ‘line’ of major richness discontinuity, with signif- icantly higher richness, especially of brooders and low dispersal model taxa, mainly conforming to the ‘big ice’ hypothesized position. What few bryozoans and sponges occurred inside this line were a subset of those outside. Main conclusions Benthic biodiversity is consistent with extensive LGM grounded ice advancing to near the shelf break in most, but not all locations around South Georgia’s shelf, for example, the eastern shelf area. We suggest that most of the shelf is still undergoing recolonization from when grounded ice covered the shelf ~20 kyr ago. Our alternative hypothesis of LGM ice posi- tion, H 3 ‘Limited-Extensive ice’, best fitted our data and is easily further testa- ble, but if verified, shows that shelf recolonization following glaciation is much slower than previously thought. This contrasts with surprisingly rapid coloniza- tion of continental shelves after ice-shelf collapses, but these are not grounded, which may be crucial to polar recolonization rates. Keywords benthos, biodiversity, continental shelf, glaciation, Last Glacial Maximum, moraine, polar, recolonization, Southern Ocean INTRODUCTION An important step towards understanding the impacts of past glaciations on biological communities is in determining the extent and duration of ice in recent geological time (that we also have high resolution CO 2 and temperature records for in ice cores). The composition and location of biodiver- sity has made significant contributions to the reconstruction of past ice-sheet history, by showing that certain regions, previously considered covered by grounded ice during the last glaciation, must have been at least partly ice free – both on land (Convey & Stevens, 2007) and on the continental ª 2016 John Wiley & Sons Ltd http://wileyonlinelibrary.com/journal/jbi 1 doi:10.1111/jbi.12855 Journal of Biogeography (J. Biogeogr.) (2016)