Holocene climate variability derived from diatoms census counts. Preliminary data from the Ross area

In polar areas diatoms often represent the unique microfossil preserved in deep-sea sediments and, thus, a record of past environmental conditions and productivity. A detailed study of Late Quaternary and Holocene diatom assemblages in two marine cores from the north-western Ross Sea as part of HOLOCLIP (Holocene climate variability at high-southern latitudes: an integrated perspective) Project will document environmental condition changes in a little known region. In the Joides Basin area, the Holocene is represented by a two-meter thick homogeneous biosiliceous mud. The strong occurrence of Chaetoceros Hyalochaete resting spores (CRS) at the base of the sequence highlights the beginning of the deglaciation. Up core, Fragilariopsis curta and F. kerguelensis become dominant, which abundance variations suggest changes in sea ice cover and sea-surface temperatures and track the Hypsithermal - Neoglacial transition. In the coastal area of Cape Hallett, irregularly laminated biosiliceous mud characterizes the Late Holocene sedimentation. Over the last 5 ka, diatom assemblages are dominated by sea-ice related species, whereby F. curta is the most abundant diatom species with CRS, F. cylindrus and F. obliquecostata present as secondary species. Such diatom assemblages, evidenced in other coastal sectors of Antarctica, may indicate a well established sea ice yearly cycle which waning induced early spring water column stratification. Integration of high-resolution diatom census counts in these cores, which represent a spatial coverage of paleoenvironmental changes during the Holocene, will allow to documenting sea ice yearly cycle variations at the centennial scale in relation to external forcing.