Stable Oxygen and Strontium Isotopic Evidence of Submarine Groundwater Discharge in the Northern Indian Ocean

Rangarajan, R. and Prasanna, K., 2024. Stable oxygen and strontium isotopic evidence of submarine groundwater forcing on the sea salinity in the northern Indian Ocean. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 407–411. Charlotte (North Carolina), ISSN 0749-0208. Understanding the dynamics of freshwater inputs in the Indian Ocean is crucial for elucidating the regional variability and its implications for marine ecosystems. In this study, we utilize stable oxygen (δ18O) and strontium (87Sr/86Sr) isotopic compositions of water samples to investigate the influence of freshwater forcing and the corresponding estimates of sub-marine groundwater fluxes in the Indian Ocean. We present high-resolution stable isotopic records of depth bound seawater samples collected from key locations across the northern Bay of Bengal region of the Indian Ocean. Our findings reveal significant variability in δ18O and 87Sr/86Sr ratios, indicative of freshwater influxes at depths of around 800m. These distinct shifts in isotopic signatures corresponding to increased influx of sub-marine groundwater discharges in the study region. In addition, we calculated the volume of the SGD using a simple compartment box model to elucidate its key role in salinity variability and potential impacts in marine strontium biogeochemistry. The estimates indicated overall SGD flux to be ∼8.3 x 1015 m3 year-1, a much higher value than available published values of SGD flux in the northern Bay of Bengal region. The current research provides valuable insights into the mechanisms driving salinity changes in the northern most sector of Indian Ocean and further elucidates the importance of systematically studying the SGDs in the region.