Deglacial dynamics in the Ross Sea (Antarctica) revealed by the occurrence of the planktic foraminifer Neogloboquadrina pachyderma

Ice shelves are very sensitive to climate variability as their dynamic change is related to atmospheric and oceanic warming/cooling. The dynamics of the Ross Ice Shelf, the largest in Antarctica, have been investigated by several researchers, however, the timing of its retreat from the Last Glacial Maximum (LGM) is still under debate, mainly due to a lack of robust marine chronostratigraphy. Since calcareous organisms are rarely preserved in the Antarctic sediments, possible ages are often based on acid-insoluble organic matter, leading to several problems mainly concerning the incorporation of reworked organic matter. For this reason, the recovery of sediments containing continuous occurrence of calcareous foraminifers can help reconstruct past glacial dynamics in the Ross Sea with a robust age model. Neogloboquadrina pachyderma is the only calcareous planktic foraminifer able to live in polar oceans, surviving in brine channels within sea-ice under hyper-saline and low temperature conditions. The distribution of N. pachyderma in the Antarctic continental margin enables to test models of ice shelf dynamics and water mass variations. We document intervals with an abundant occurrence of well-preserved N. pachyderma (juveniles and adult forms) from the deglacial sedimentary sequences in the northern Drygalski Basin and Hallett Ridge (Western Ross Sea). We discuss N. pachyderma habitat, also considering data of benthic foraminifers, diatoms, and stable isotopes. We suggest that co-occurrence of large N. pachyderma tests and abundant juvenile forms in the deglacial sediments reflect open water conditions and/or variation in the duration and coverage of seasonal sea ice.