Post-LGM palaeoclimatic changes derived from diatom census counts in the Western Ross Sea area (East Antarctica)

The Ross Sea is one of the most important region of the Southern Ocean since it is involved in the formation of dense, saline and super-cooled water masses (the High Salinity Shelf Water – HSSW and the Ice Shelf Water - ISW). These water masses descend into the deep ocean to form Antarctic Bottom Water (AABW) which plays a key role in the global thermohaline circulation and, in turn, in the global climate system. Four marine sediment cores and two box cores have been selected along a transect, considering the possible preferential path of the HSSW, passing across the Joides Basin Trough, on the continental shelf (cores ANTA99-cJ5 and ANTA99-cJ3), and reaching the Central Basin, a confined depositional system located at the mouth of Joides Basin (cores ANTA95-c98, KI13-c1 and box cores KI13-bc4, KI13-bc2). Core ANTA99-cJ5 was partly studied within the ESF-PNRA HOLOCLIP (Holocene climate variability at high-southern latitudes: an integrated perspective) Project, while all other cores have been analysed in the framework of the PNRA-ROSSLOPE (Past and present sedimentary dynamic in the ROSS Sea: a multidisciplinary approach to study the continental SLOPE) Project. Multidisciplinary analyses were performed in order to study the past oceanographic and climatic evolution of the Western Ross Sea occurred during the post-LGM deglaciation phases. Both cores collected in the Joides Basin are characterized by diatomaceous mud with high abundance of Chaetoceros Hyalochaete resting spores (CRS) at the base of the sequence that indicate the beginning of the glacial retreat. The subsequent up-core increase in Fragilariopsis curta suggests the establishment of seasonal sea ice associated with the Ross Ice Shelf retreat. The cores collected on the continental slope are, instead, characterized by gravelly-silty-sand to clayey silt with mixed-age diatom species that are present at the base of the sequence with high relative abundance of Eucampia antarctica spores which could be linked with sea ice. On the other hand the upper part of the core is rich in post-glacial diatom species with an increase in F. kerguelensis which suggests open ocean conditions with reduced sea ice presence. A comparison between the diatom assemblages identified in the cores allowed us to suggest a paleoclimatic and paleoenvironmental reconstruction of the Western Ross Sea area after LGM, and to highlight the glacial/interglacial transition on the basis of diatom’s species abundance variations through the cores.