Predicted Episode of Submarine Groundwater Discharge Onto the South Carolina, USA, Continental Shelf and Its Effect on Dissolved Oxygen

Abstract

Submarine groundwater discharge (SGD) may directly influence the dissolved oxygen (DO) content of coastal bottom waters. Here, we report a predicted episode of enhanced SGD that caused low DO concentrations on the South Carolina continental shelf. The prediction model linked episodes of SGD to upwelling-favorable winds. The data revealed these waters were a factor of 2–6 higher in 226Ra and 228Ra compared to typical bottom water values and were significantly depleted in DO (<130 μM). The tight 228Ra:226Ra correlation of these data was similar to values during a strong hypoxic event off SC in 2012. Water ages from 224Ra and 223Ra indicated the event occurred 2–9 days before sampling. The success of the prediction lends added credence to the correlation of upwelling-favorable winds—but not necessarily accompanied by upwelling—to episodic SGD events. This prediction from wind data represents a major advance for quantifying SGD in the region.