Variations of Indian monsoon precipitation during the last 32 kyr reflected in the surface hydrography of the Western Bay of Bengal

Hydrography of the Bay of Bengal is highly influenced by the river runoff and rainfall during the southwest monsoon. We have reconstructed δ18Osw, sea surface salinity and sea surface temperature (SST) changes in the Bay of Bengal by using paired measurements of δ18O and Mg/Ca in a planktonic foraminifera species Globigerinoides ruber from core SK218/1 in the western Bay of Bengal in order to understand the rainfall variability associated with southwest monsoon over the past 32 kyr. Our SST reconstructions reveal that Bay of Bengal was ∼3.2 °C cooler during the LGM as compared to present day temperature and a ∼3.5 °C rise in SST is documented from 17 to 10 ka. Both SST and δ18Osw exhibit greater amplitude fluctuations during MIS 2 which is attributable to the variability of NE monsoon rainfall and associated river discharge into the Bay of Bengal in association with strong seasonal temperature contrast. On set of strengthening phase of SW monsoon was started during Bølling/Allerød as evidenced by the low δ18Osw values ∼14.7 ka. δ18Osw show consistently lower values during Holocene (with an exception around 5 ka), which suggests that the freshening of Bay of Bengal due to heavy precipitation and river discharge caused by strong SW monsoon. Results of this study signify that the maximum fluctuations of the NE monsoon rainfall during MIS 2 appear to be controlled by the strong seasonality and boundary conditions.

► For the first time we are reporting SST based on shell Mg/Ca records of G. ruber from the western BOB.
► BOB was ∼3.2 °C cooler during LGM than the today, which has implication on the ITCZ propagation.
► The amplitude of δ18Osw fluctuations during MIS 2 reveals greater variability of NE monsoon.
► A striking increase in SW monsoon rainfall during Bolling/Allerado is noticed.