¹⁸O/¹⁶O isotopic ratio variations in foraminifera carbonate and diatoms silica of the West-Indian sector of the Austral ocean. Paleo-climatic implications

To reconstitute the Southern Ocean paleo-climatic evolution during the last 50.000 years, the isotopic ratio ¹⁸O/¹⁶O has been analysed on benthic and planktonic foraminifera carbonate and diatoms silica skeletons extracted from 4 West-Indian and South-Atlantic cores. With the object to remove the average oceanic δ¹⁸O variations (which are linked to continental ice volume fluctuations) the benthic foraminifera δ¹⁸O record has been subtracted from the planktonic species. In result, D¹⁸O records represent the upper layer temperature and salinity changes. R¹⁸O record, obtained by elimination of the temperature influence, is representative of δ¹⁸O superficial oceanic water changes. Then, this isotopic records have been correlated with epontic and ice-edge diatoms abundances variations and upper oceanic layer paleo-temperature changes (Pichon, 1985). Correlations between the three kinds of data (isotopic, paleo-ecological, paleo-thermal) show that an important ice-melt haven't had occurred during the last glacial maximum, near the Antarctic Polar Front zone. This event seems to correspond with a 'down-draw' response of the antarctic ice-sheet. Moreover, the superficial antarctic water masses seem to have been warmed 1.500 to 2.000 years before the general deglaciation of the northern hemisphere. (author)