CARBON AND OXYGEN ISOTOPIC RECORDS OF BENTHIC FORAMINIFERA FROM THE NORTHEAST INDIAN-OCEAN - IMPLICATIONS ON GLACIAL-INTERGLACIAL ATMOSPHERIC CO2 CHANGES

We present here continuous records of delta(18)O and delta(13)C in benthic foraminifera, extending well into the last ice age, in two piston cores from the Andaman Sea (sill depth similar to 1.3 km) and the Bay of Bengal (3 km). These show that, contrary to the previous reports, the glacial to interglacial shift in delta(13)C,at mid-depths in the Northeast Indian Ocean was indistinguishable from the mean oceanic delta(13)C change, negating a more vigorous renewal of intermediate waters globally during the glacial time. The corresponding delta(13)C Shift in deep waters is estimated to be about 50% larger than that reported previously. Jointly with some recent data from the Pacific, our results indicate a modest glacial-Holocene shift in the intermediate to deep water chemical gradients in the Indo-Pacific as a whole, implying that it was perhaps not the dominant mechanism for the glacial-interglacial atmospheric CO2 variations. Also, in conflict with previous work, our measurements suggest significant cooling of both the intermediate and deep waters during the glacial time. The high-resolution records from the Andaman Sea help reconstruct paleoenvironmental changes at intermediate depths during the last deglaciation. Rapid increases in delta(13)C occurring in two stages during the early deglaciation appear to have been caused by the fluctuations in the North Atlantic Deep Water production. A negative excursion in delta(13)C during the mid-deglaciation is ascribed to enhanced nutrient regeneration at mid-depths associated with the greatly intensified summer monsoon around the Pleistocene-Holocene boundary.