Executive Summary : | High-resolution proxy records covering the last few millennia will improve our knowledge on natural and anthropogenic influence on the climate. The sediments collected from Bay of Bengal (BoB) have high sedimentation rates of upto ~70 cm/ kyr, with decadal scale sample resolution (Suokhrie et al., 2021) and are ideal archives for acquiring high-resolution data. In BoB, the presence of intense Oxygen deficient zone (ODZ) in the intermediate waters (~100-1000 m) is also reported (Wrytki, 1971; Rao et al., 1994; Naqvi et al., 1994; Sarma, 2002), which is mainly caused by the absence of strong upwelling and stratification from the large volume of freshwater from precipitation and river run-off. Although the dissolved oxygen levels do not cause anoxic conditions as in the Arabian Sea (AS), the increase in anthropogenic activity and intensity in monsoon-induced riverine influx will likely render a dead zone in the bay in the near future (Bristow et al., 2017). In such a scenario, it is necessary to assess the ODZ variability under different boundary conditions by looking at sub-surface sediments. There is rarely any proxy data on the BoB ODZ from the last few millennia. Foraminifera are marine microorganism, sensitive to ambient conditions and effectively used as a proxy for paleoclimatic reconstructions (Saraswat & Nigam, 2013). The abundance of benthic foraminifera is affected by the food availability and oxygen concentration in the bottom waters and sediment pore-water (Kaiho, 1994; Bernhard & Sengupta, 1999). Infaunal benthic foraminiferal genera like Bolivinia, Bulimina, Uvigerina and Fursenkoina are commonly reported from ODZ regions (Schumacher et al., 2007; Mazumdar & Nigam, 2014; Caulle et al., 2014 etc). Various marker species of foraminifera have been identified from the BoB (Manasa et al., 2016; Saraswat et al., 2017; Bhadra et al., 2021; Suokhrie et al., 2021; Saalim et al., 2022). High abundance of benthic foraminifera was seen within the BoB ODZ and marker species have also been identified (Suokhrie et al., 2020). Interestingly, the lack of denitrification in the bay (Naqvi et al., 1994) seems to be the reason for significant difference in benthic foraminifera from the BoB ODZ as compared to the AS ODZ. Denitrifying benthic species reported from the AS ODZ were also not reported from the BoB ODZ (Suokhrie et al., 2020). In recent times, the pore size and pore density of benthic foraminifera have also been successfully utilized as a robust proxy for understanding dissolved oxygen concentration (Rathburn et al., 2018; Richirt et al., 2019; Subba, 2023). Benthic assemblage method as well as morphometric analysis of single species have displayed reliability in understanding the variation of dissolved oxygen concentration (Tetard et al., 2021; Wang et al., 2023). This project proposes to utilize marker species in BoB sub-surface sediment to infer high-resolution paleoclimate, focusing on the ODZ variability. |