Paleoclimatic and paleoceanographic records from the Bay of Bengal sediments during the last 30 ka

Abstract

• The Bay of Bengal (BoB) witnessed strengthened northeast Monsoon (NEM) and weakened Indian Summer Monsoon (ISM) during the Last Glacial Maxima . • The sediment provenance in BoB varied in tandem with the change in intensities of NEM and ISM. • An overall decline of Sea Surface Temperature (SST) by 2–3 °C has been registered in the BoB sediments. • The climate shift during the transition of Marine Isotopic Stage (MIS) 1 and MIS 2 was gradual in BoB sediment records than the other continental records. The Bay of Bengal (BoB) is a semi-enclosed basin located in the north-eastern Indian Ocean which receives enormous fluvial sediment input primarily from the Himalayan and the Peninsular rivers depending on the Indian monsoon intensities. The seasonal reversal of monsoonal currents over the northern Indian Ocean leads to Indian monsoon which varies as a function of lateral migration of the Intertropical Convergence Zone (ITCZ) which in turn leads to both Indian Summer Monsoon (ISM) and Northeast Monsoon (NEM) over the BoB. Despite being such a dynamic region, the instrumental and oceanographic data for the BoB seldom goes beyond last century which invigorated its long-term reconstruction of paleoclimate and paleoceanography, especially since last 30 ka, as it includes the most recent glacial period i.e. the Last Glacial Maxima (LGM: ∼19–23 ka). Further, the last 30 ka also consists of several other globally recognized cold climatic events such as the Henrich events (H1: ∼15–17 ka; H2: ∼24–25 ka) and Younger Dryas (YD: ∼12.9–11.8 ka) along with warm climatic events such as Bølling-Allerød (B/A: ∼14.8–12.9 ka) and Holocene epoch (∼11.8 ka − Present). Here a synthesis of paleoclimate and paleoceanographic reconstruction exclusively from the BoB and its nearby regions has been made with specific focus on the climatic events of last 30 ka. The present review suggests intensified NEM with simultaneous weakening of ISM during LGM was accompanied by a marked decline in Sea Surface Temperature (SST) of nearly 2–3°C, while strengthened ISM during B/A and Holocene with an intermittent ISM weakening during H1 and YD has been inferred. The NEM strengthening during LGM, led to enhanced sediment and water discharge from the peninsular rivers and reduced discharge from the Himalayan rivers in the northern and western BoB. Further, the weakening of Atlantic Meridional Overturning Circulation (AMOC) during YD and H1 led to diminishing water column stratification in the northeastern BoB causing enhanced productivity. The present review demonstrated the response of BoB towards the changing Indian monsoon and its closely knitted association with the regional and global climate system.