Seafloor Communities and Climate Change on the West Antarctic Peninsula Shelf

The west Antarctic Peninsula (WAP) is warming as rapidly as anywhere on Earth, resulting in sea-ice loss, glacial retreat, and rising ocean temperatures. Existing climate gradients and oceanographic boundaries along the WAP can provide insights into the potential response of seafloor ecosystems to this climate warming. First, we present studies of the latitudinal climate gradient along the WAP to explore the potential effects of sea-ice loss on Antarctic shelf-floor communities. We find a varied response of megabenthic and macrobenthic communities to the latitudinal sea-ice gradient, with some parameters apparently insensitive (resilient) while others change linearly or nonlinearly with large variation in annual sea-ice duration. These results suggest that important aspects of seafloor community structure/function may be unexpectedly resilient to changes in pelagic ecosystems driven by sea-ice loss, but that abrupt changes may be expected as climate thresholds are crossed. We then study gradients in seafloor ecosystems from inner fjords out onto the open shelf to explore the influence of terrestrial meltwater and glacial sedimentation on WAP shelf communities. We find that, unlike subpolar Arctic fjords, inner-middle WAP fjords are hotspots of benthic community abundance and beta diversity, and appear to sustain large spatial food-web subsidies from migrating krill. We speculate that these fjord hotspots will be “snuffed out” but increasing glacial melt and sediment loading resulting from climate warming.  Finally, we highlight how the interface between warmer Upper Circumpolar Deep Water and colder Antarctic Shelf Water may form a temperature barrier to predacious king crabs, limiting their dispersal from the deep continental slope up onto the 500-m colder WAP shelf. We demonstrate, however, that a large, reproductive population of king crabs has crossed the Antarctic shelf into the Palmer Deep since the last glacial maximum, and may have dramatically altered seafloor diversity and ecosystem function in the the Palmer Deep. Recent warming trends of shelf waters suggest that, if these king crabs are indeed cold-temperature limited, they might soon move up onto the deep Antarctic shelf, potentially altering the long-isolated, evolutionarily novel shelf-floor ecosystems.  In summary, the boundaries/gradients produced by physical and biogeochemical processes along the WAP yield strong patterns of community structure /function in WAP seafloor ecosystems and provide insights into how marine ecosystems in Antarctica are being modified by rapid climate change.