Geochemical ratios mediated understanding of estuarine dynamics in submarine groundwater discharge prevalent basaltic aquifer

Submarine groundwater discharge (SGD) has been recognized as an integral pathway of hydrological cycle. The role of SGD as a mechanism for material transport from terrestrial to marine ecosystems has also been investigated, considering the large hydrological flux and a massive load of solutes is found to be carried as SGD to the coastal oceans. However, there are challenges in recognizing the process and delineating specific areas which are susceptible to SGD. Considering the unique geochemical signature of groundwaters found in varied lithology, this paper investigates the possibility of using geochemical ratios and their variability in coastal areas as a tracer for the identification of SGD. The Br^-/Cl^- ratio, prevalently used for identification of seawater-groundwater mixing is investigated. The study raises questions over the viability of Br^-/Cl^- as a tracer as Br^- rich groundwater in the SGD prevalent area may be a cause of elevated Br^-/Cl^- ratio in the coastal oceans. Furthermore, the peculiar observation of Fe⁺² enrichment in coastal seawater also indicated the influence of differential weathering on the subterranean estuarine (STE) sediments releasing Fe⁺² as the groundwater in the area is not enriched in groundwater. This observation is very important in the context of rising sea levels as a larger STE due to rising sea levels can cause higher mobilization of Fe⁺² in coastal oceans causing a direct influence on the coastal ecosystem.