Geochemical and Sr-Nd isotopic study of Bay of Bengal sediments: Reconstruction of erosional changes during last Glacial-Interglacial cycle

Abstract

Chemical and isotopic signatures of oceanic sediments serve as a reliable tool to assess the interrelation between erosion and climate in the past. In this study, high-resolution geochemical and Sr-Nd isotopic data of a sediment core (VM 29-17PC; water-depth: 2813 m) from the western Bay of Bengal have been investigated. These data were used to reconstruct erosional and provenance changes in the Himalayas (relative to Indian Peninsula) during the last glacial-interglacial cycle. Radiocarbon dating of foraminifera from selected depths confirms that the 4.65-m long core archives an erosional record of the last 35 kyrs with no major hiatus. Geochemical trends, specifically increase in CIA and decrease in K/Al ratios, indicate an intensification in chemical weathering since 25 kyr. The 87Sr/86Sr (0.727 to 0.750) and 𝜀Nd (-18 to -14) values show significant temporal changes. These isotopic values, although intermediate to those reported for their major sediment sources, point to a dominant supply from Higher Himalayas (0.76, -15), and Deccan traps (0.705, -5) to the core-site. The isotopic trends with increasing 87Sr/86Sr and decreasing 𝜀𝑁𝑑 values between 15.3 to 5 kyr indicate an enhanced sediment contribution from the Himalayas during this period. This post-glacial increase in sediment supply from the Himalayas is synchronous to Bølling-Allerød (B/A) warm phase and a stronger Indian Summer Monsoon (ISM) phase, indicating a strong linkage between erosion and climate in kilo-year timescales.