Submarine groundwater discharge traced in Bay of Bengal

Large fluxes of dissolved cations and anions, generated by the weathering of rocks, are transported by rivers to the oceans. In addition to rivers, groundwater also carries these ions to the oceans. However, the contribution of the submarine groundwater discharge (SGD) to the dissolved ion concentrations of the oceans is debated as it is not easily traceable in seawater due to mixing.

In a study published in the journal Scientific Reports of the Nature Publishing Group, Dr. Ramananda Chakrabarti, Surajit Mondal, and Dr. Shiba Shankar Acharya from the Centre for Earth Sciences along with J. Sree Lekha and Prof. Debasis Sengupta from the Centre for Atmospheric and Oceanic Science, IISc, have provided a direct evidence of the SGD-driven flux of Strontium (Sr) to the Bay of Bengal (BoB). The BoB is one of the most stratified oceans in the world as it receives a large flux of freshwater from the Ganges-Brahmaputra-Irrawaddy rivers. Water samples from the BoB were collected during four different research cruises from 21 locations over a time span of 29 months from August 2014 to December 2016 and included samples collected from 0 m – 1500 m depth. These water samples were analysed for their salinity (on-board measurements), Sr and Ca concentrations using an inductively coupled plasma mass spectrometer (ICPMS) and Sr isotope ratios (87Sr/86Sr) using a thermal ionization mass spectrometer (TIMS) at the Centre for Earth Sciences. High precision geochemical and Sr isotopic data provided evidence for a spatially heterogeneous SGD-driven radiogenic Sr-flux at 100 -120 m depth in the BoB. The results of this study have important implications in understanding the evolution of seawater chemistry over geological timescales.

Reference: Chakrabarti, R., Mondal, S., Acharya, S. S., Lekha, J. S., & Sengupta, D. (2018). Submarine groundwater discharge derived strontium from the Bengal Basin traced in Bay of Bengal water samples. Scientific reports, 8(1), 4383.

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