Millennial-scale variability of Indian summer monsoon constrained by the western Bay of Bengal sediments: Implication from geochemical proxies of sea surface salinity and river runoff

The Indian summer monsoon (ISM) is critical to billions of people living in the region. In this study, high-resolution major element composition and Globigerinoides ruber sensu stricto (G. ruber s.s.) delta O-18 measurements of a sediment core collected from the western Bay of Bengal indicated a high sensitivity of the study site to monsoonal climate variability related to climatic changes on a timescale of millennia (Younger Dryas and Heinrich Stadials) in the North Atlantic during the last 80 kyr. High G. ruber s.s. delta O-18 and ice volume-corrected ocean surface water delta O-18 and increased Ca/Ti ratios during Younger Dryas and Heinrich Stadials HS1-6 indicate the decreased summer monsoonal rainfall in the Indian peninsula during these periods. The increases of G. ruber s.s. delta O-18 records in the western Bay of Bengal during Younger Dryas and Heinrich Stadials were similar in previous records of G. ruber s.s. delta O-18 in the northern Bay of Bengal and stalactite delta O-18 in northern India. This implies that the decreased precipitation during these periods may have been induced by the southward migration of the northern boundary of Intertropical Convergence Zone (ITCZ) over the Indian peninsula during Younger Dryas and Heinrich Stadials. Previous records of delta O-18 values in the Andaman Sea located in the eastern Bay of Bengal showed no remarkable decrease of summer precipitation during HS1 and 5. These differences may be explained by the different migration trends of summer ITCZ position in the eastern Bay of Bengal versus western Bay of Bengal during HS1 and 5.