Sr and ⁸⁷Sr/⁸⁶Sr in the Hooghly River estuary: Estuarine sources and processes

Samadder, Rupak (2018) Sr and ⁸⁷Sr/⁸⁶Sr in the Hooghly River estuary: Estuarine sources and processes. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

This study investigates the estuarine sources and processes that contribute to the variation of dissolved Sr and ⁸⁷Sr/⁸⁶Sr in the Hooghly River estuary. As a part of this study, dissolved Sr and ⁸⁷Sr/⁸⁶Sr were measured in the Hooghly River estuary water and groundwater of the river basin. The dissolve Sr concentrations generally conform to theoretical mixing of river and seawater during pre-monsoon and post-monsoon periods. This observation indicates that there is no addition/removal of Sr from the estuary. The non-conservative behaviour of dissolved Sr during monsoon indicates that processes other than mixing of sea and river water are needed to explain the measured dissolved Sr concentration at high salinity. A strong positive correlation observed between Δ[Sr] and Δ[Ca] during the monsoon period suggests that the probable sources of Sr in the estuary could be carbonate dissolution or ion-exchange between the dissolved and particulate phase. The ⁸⁷Sr/⁸⁶Sr ratios depict non-conservative behaviour only during the pre-monsoon periods. The likely processes for the non-conservative behaviour of Sr isotope are excess Sr supply from the particulate phase via desorption, or dissolution of particulate carbonate phase and submarine groundwater discharge. A few groundwater samples have high salinity and different isotopic composition than samples at low salinity. Also, dissolved Sr concentrations of these samples are higher than that is expected from conservative mixing of river water and seawater. These results are an indication that the groundwater gets enriched in Sr via interaction of aquifer solids with the seawater. The observation that the groundwater samples generally have higher ⁸⁷Sr/⁸⁶Sr than the estuary waters indicates that they could be supplying radiogenic Sr to the estuary.

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