Neogloboqaudrina pachyderma distribution during the late Quaternary deglaciations phases of the western Ross Sea (Antarctica)

Neogloboquadrina pachyderma (Ehrenberg) is the only planktic foraminifer able to live in polar areas, generally feedings bacteria and diatoms. This species can also survive in brine channels within sea-ice under hyper-saline and low temperature conditions. In the autumn, juveniles forms living in the upper part of the water column become incorporated into the forming frazil ice. With onset of winter, some of the specimens may become trapped in brine pockets when lower temperatures result in further narrowing of brine channels. These individuals will die as juveniles due to low temperatures and/or lack of food, others individuals during spring ice melting are released into the water column and continue their life cycle. The distribution of N. pachyderma in the Antarctic continental margin represents a useful occasion to constrain and test the models of the ice sheet dynamic. We document the presence of intervals with abundant occurrence of juveniles (and adult forms) of well-preserved N. pachyderma within three piston cores from northern Drygalski Basin (cores TR17_03 and TR17_04PC, TRACERS PNRA-Project) and Hallett Ridge (core KI13_C2, ROSSLOPE PNRA-Project), Ross Sea, Antarctica. We discuss about the N. pachyderma habitat considering also data from benthic foraminifer and diatoms. We suggest that the co-occurrence of N. pachyderma with large tests and the abundant presence of juvenile forms in the sediment reflects the presence of seasonal open water conditions and/or variation in the length and intensity of seasonal sea ice. Our results can help to reconstruct the past glacial dynamics in the Ross Sea continental margin.