Paleoceanographical records under impact of the Indian monsoon from the Bengal Deep Sea Fan and Ninetyeast Ridge during the last 260 ka

The orbital and interior climatic cycles can be found both in the Bengal Deep Sea Fan and Ninetyeast Ridge, North Indian Ocean. The periodicity of the Quaternary glacio-eustacy by 100 ka gave a strong impact on the sedimentation in the fan area and the monsoon signals controlled by the obliquity and precession were easily picked up. This paper discusses the possible correlation between the environmental elements on the basis of the ETP phase wheels. A rapid change with short-periods develops during the past 60 ka in the region under study as well. The variability of paleoproductivity has a nonlinear response to the Indian summer monsoon. As contrasted to the Northwest Indian Ocean, here an abundance of Globigerina bulloides, a proxy to indicate upwelling current, does not imply so much a promotion of the summer monsoon as its decrease. The record from the ridge area shows in a longer-scale a climatic evolutionary feature corresponding to that of the fan area. A special and great event arising at around 165 kaBP and meaning a catastrophe for ecological environment is reported in this paper. It is also regarded as a result induced by the monsoon.