Variability of the Southwest Monsoon since the Last 25 000 Years and Their Possible Causes: Role of Northern Hemisphere versus Tibetan Plateau

High-precision, clay sediment oxygen and hydrogen isotopes analyses of Pleistocene-Holocene deep-sea sediments from the Bay of Bengal (BOB) are presented for the first time. Our study shows that the major source of sediments in the study area, since the last ~25 000 years, is likely to be the Higher Himalayan crystalline rocks. Further, the study of these stable isotope data displays the variation of southwest monsoon (SWM) in the BOB region since the last ~25 000 years and the cause behind the variation has been interpreted. The δ¹⁸O values of the clay sediments are compared with δ¹⁸O values of the BOB seawater. This comparison shows that the clay sediment δ¹⁸O values of the studied sediment cores temporally vary along with the changes in strength of the SWM. Based on the changes in the clay sediment δ¹⁸O values of the studied sediment, we evaluate the variance in the SWM since the last 25 000 years in the BOB. Our results are consistent with previous work in the region based on other proxies. To evaluate the factors influencing the intensity of the SWM since the last glacial maxima, we conducted comparative analyses of the studied clay sediment δ¹⁸O values with δ¹⁸O values in the Greenland ice cores (GISP2) and Tibetan ice cores (Guliya). The results from this comparative study show that large-scale changes in the intensity of the SWM since 25 000 years are affected by the climate oscillations of the Northern Hemisphere, but rapid and abrupt fluctuations in the SWM seem to be controlled by the amount of snow cover in the Tibetan Plateau.