-Spatiotemporal dynamics of nutrients and organic carbon in coastal seawater off Jeju Island: Effects of submarine groundwater discharge (SGD) and geomorphic settings

Abstract

We investigated the role of submarine groundwater discharge (SGD) in supplying nutrients and organic carbon in two distinct coastal settings (eastern and western) in Jeju Island, Korea. In Jeju, nutrients and organic carbon showed strong correlations with salinity suggesting that SGD is a significant source in coastal waters. Although both regions exhibited similar SGD rates and background concentrations in the outer bay seawater, the behavior of nutrients and organic carbon was different between the eastern and the western parts. Notably, in the western part, inorganic nutrient concentrations in the inner bay seawater were depleted compared to conservative salinity mixing due to the enhanced biological activity. In contrast, the eastern part showed no significant changes in nutrient concentrations along the mixing line. The western part has larger water volume, deeper depth, and longer residence time compared to the eastern part. Our results suggest that the behavior of nutrients in the inner bay is significantly influenced by the hydrogeological factors. This study highlights the crucial role of the spatiotemporal dynamics of SGD and coastal settings in governing coastal biogeochemistry and ecosystems.