Coherent Response of Deglaciation in the tropical Indian Ocean and the Northern Hemisphere Solar Insolation Changes

The exact start of deglaciation in the Indian Ocean is not documented due to lack of high resolution records with robust chronology. There are still a number of open questions regarding the exact timing and the mechanisms involved in the initiation of deglaciation and the subsequent interhemispheric pattern of the warming. In this context, two sediment cores from the northern Indian Ocean were analyzed for Magnesium/Calcium and oxygen isotope ratios from planktic foraminifer species Globigerinoides ruber in order to gain an understanding on the onset of deglacition in the tropical Indian Ocean. Sea surface temperature reconstructions of these cores have shown that deglaciation warming in the northen Indian Ocean was initiated at 19 ka and a rise of 4°C between 18 and 9 ka was demonstrated. The initiation of deglacition coincide with the rise of solar insolation at 15°N suggest that only northern insolation was responsible for triggering the onset of the deglaciation in the tropical Indian Ocean. However from 9 ka onwards SST changes do not show any linear relationship with the 15°N insolation. Monsoon reconstructions based on δ18Ow reveals that monsoon driven precipitation was higher during MIS3 and MIS1, and lower in MIS2 and MIS4, which is in agreement with earlier monsoon reconstructions based on monsoon upwelling indices from the western Arabian Sea. However, the comparison of solar insolation changes and monsoon variability record demonstrate that the monsoon rainfall lags the solar insolation changes at 15°N. Furthermore, the amplitude of monsoon fluctuations derived through upwelling indices and δ18OW varies significantly and is attributed to spatial variability of monsoon rainfall.