Nearshore Submarine Groundwater Discharge to an Arctic Lagoon

Abstract:

Groundwater transports heat and dissolved matter. In coastal regions where groundwater may have vastly different temperatures and chemistry as coastal waters, submarine groundwater discharge (SGD) can impact coastal hydrology, energy balance, and biogeochemistry. This is particularly true in the Arctic where coastal and submarine aquifers, comprised of actively thawing and unfrozen permafrost, can release dissolved organic matter and provide a pathway for heat exchange. Because of the relatively rapid thawing of ice-rich permafrost and ground ice caused by warming of the Arctic, changes in the groundwater flow regime are inevitable. In general, determining the relative contributions of different driving forces of groundwater flow and transport is crucial for the evaluation of groundwater dynamics across days, seasons, years, and decades. However, the drivers of coastal groundwater flow along the Arctic coast may be quite different and more complex than other lower latitude regions. This study aims to assess the significance of terrestrial hydraulic gradient-driven fresh groundwater flow over buoyancy-driven vertical groundwater discharge across the intertidal and subtidal zones over daily time scales. The study was conducted in Kaktovik Lagoon, which is a good representative of the many lagoons bordered by barrier islands in the Alaskan Beaufort Sea. A variety of methods were utilized. We gathered subsurface temperature-depth profiles, groundwater head, and salinity measurements over a 2 days-period along a transect perpendicular to the shore. Using the temperature time-series, an analytical model was applied to evaluate and quantify vertical groundwater flux in the surface water-groundwater interface. These modeled fluxes were compared with estimates from the hydraulic and salinity observations. The terrestrial freshwater contribution, as well as the groundwater discharge due to convection at the seabed, were estimated by numerical models. The importance of other possible drivers was also discussed.