Orbital forcing of the Plio-Pleistocene Indian monsoons: benthic foraminifral proxies from ODP Site

Abstract

The Indian Ocean monsoon system is one of the dominant features of the earth's climate influencing weather and climate of the Asian region. Long-term changes in the monsoon have been linked to orbital forcings as well as the Himalayan-Tibetan uplift. Changes in the monsoon are preserved in various proxies across the region both on land and in the marine sediments. Here we present Plio-Pleistocene record of monsoon proxy deep-sea benthic foraminifera from Ocean Drilling Programme Site 758, northeast ern Indian Ocean to understand a link between orbital changes and Indian Ocean monsoon variability. We used Continuous Wavelet Transform (CWT) of Uvigerina proboscidea and Epistominella exigua, which have been found blooming in two different seasons of the Indian monsoon - the summer and winter monsoons, respectively. An inverse relation between the two is observed during the past ~1000 kyr in the CWT-extracted 400-kyr components as also in the raw data. The variable relation between the monsoon proxies and earth's eccentricity at Site 758 agrees with the recent findings that orbital forcing of the Indian monsoon shows major shifts during the Plio- Pleistocene. These shifts correspond to the advent of growth and decay of the Northern Hemisphere ice sheets since the last 2.5 Ma.