The reconstruction of late Quaternary Antarctic sea-ice distribution - the use of diatoms as a proxy for sea-ice

The study of annual diatom transfer from the Southern Ocean surface to the sea floor using time-series sediment traps combined with the mapping of diatom assemblages from surface sediments results in the definition of a proxy for past variations of sea-ice extent. The application and robustness of the proposed proxy are demonstrated by the study of Late Pleistocene sediment cores recovered from different environmental regimes in the Southern Ocean. Relative amounts of the sea-ice indicator diatoms Fragilariopsis cylindrus and Fragilariopsis curta of > 3% in diatom assemblages preserved in sediments are representative of the presence of seasonal winter sea-ice. Summer sea-ice occurrence is signalled by a distinct drop in biogenic sedimentation rate as a result of strongly reduced biogenic export, in the presence (>3% of diatom assemblage) of the deep-temperature diatom Fragilariopsis obliquecostata. The spatial and temporal distribution pattern of the sea-ice proxy indicates significant sea-ice variations during Marine Isotope Stages 1 and 5 in the present Antarctic Zone of the Southern Ocean. During glacial maxima, the Antarctic winter sea-ice was extended into the present Polar Front Zone, while the Antarctic summer sea-ice was most probably expanded into the area of the present winter sea-ice edge. During the short climatic optima at the onset of interglacial periods, the winter sea-ice extent was distinctly reduced. (C) 2000 Elsevier Science B.V. All rights reserved.