Oxygen and carbon stable isotope studies on Globorotalia menardii from Pleistocene DSDP Cores in northern Indian Ocean and their paleoclimatic and paleoceanographic implications

摘要

Stable isotope ratios of oxygen (δ~(18)O) and carbon (δ~(13)C) in tests of Globorotalia menardii from samples at 25 cm intervals of top 900 cm cores, representing different thicknesses of the Pleistocene, from DSDP Sites 219,220 and 241 in the northern Indian Ocean have been measured. Based on the δ~(18)O stratigraphy, glacial and interglacial phases during the Pleistocene have been recognized, which are in good agreement with the standard Quaternary planktonic foraminiferal/climatic zones i.e., Ericson zones at these sites, based on G. menardii abundances. The GIA (glacial interglacial amplitude) at Sites 241,219 and 220 are of the order of 1.2,1.4 and 1.9 per thousand respectively. The last glacial and interglacial maxima (18 ka BP and 125 ka BP respectively) could be identified in DSDP Cores 241, and 219 with some precision. 'Isotopic ages' could be assigned to the different levels of these core sections based on the correlation of δ ~(18)O record from these sites with the SPECMAP record (Imbrie et al 1984). Changes in sediment accumulation rates at different levels of the Pleistocene have been worked out on the basis of changes in oxygen isotopic ratio. Oscillations in δ~(13)C stratigraphy at Site 241 indicated southwest monsoon induced increase in upwelling and productivity during warmer periods. At Sites 219 and 220, variations in the δ~(13)C record were due to the mixing of bottom water.