Distribution and behavior of trace metals in the subterranean estuary of an Arctic coastal lagoon

Abstract

Subterranean estuaries (STEs) can be an important location for biogeochemical reactions that may alter concentrations of chemical constituents of groundwater. With warming in the Arctic and the subsequent permafrost thaw, the relative importance of submarine groundwater discharge (SGD) to ocean chemical budgets will grow. In this study, we examined the distribution of select trace metals (Fe, Mn, V, U, Mo and Ba) in the STE, lagoon surface waters, and coastal sediments of Simpson Lagoon along the Beaufort Shelf of Alaska. This location is unique among studies as the STE consists of organic-rich sediments. Samples were collected over two years and throughout seasonal water conditions, including the melting, open-water, and freeze-up periods. Fe, Mn, V, and Ba mainly exhibited non-conservative additions within the estuary, with Fe concentrations being some of the highest among groundwater studies. U exhibited both non-conservative removal and addition in the estuary, and Mo exhibited mainly removal. In the lagoon, non-conservative addition of U allowed for the calculation of an SGD flux. This flux, along with a Ra-derived flux, was used to estimate metal fluxes into the lagoon. Fluxes for all metals were similar to or greater than river flux estimates in all months except for June, when SGD was likely nonexistent. These fluxes can be used to assess SGD impact on the coastal Arctic; however, for reactive metals, processes in the lagoon may continue to alter metal concentrations before mixing with the greater Arctic Ocean. This study provides some of the first estimates of trace metal concentrations and fluxes within Arctic subterranean estuaries and exhibits the importance of considering SGD when assessing metal input to the coastal Arctic.