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 ben thic 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 N ortheast Indian Ocean was indistinguishable from the mean oceanic delt a(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 result s indicate a modest glacial-Holocene shift in the intermediate to deep water chemical gradients in the Indo-Pacific as a whole, implying tha t it was perhaps not the dominant mechanism for the glacial-interglaci al atmospheric CO2 variations. Also, in conflict with previous work, o ur measurements suggest significant cooling of both the intermediate a nd deep waters during the glacial time. The high-resolution records fr om the Andaman Sea help reconstruct paleoenvironmental changes at inte rmediate 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-deglacia tion is ascribed to enhanced nutrient regeneration at mid-depths assoc iated with the greatly intensified summer monsoon around the Pleistoce ne-Holocene boundary.