Estimating Submarine Groundwater Discharge to Continental Shelves

Abstract:

Radium tracer studies indicate that submarine groundwater discharge (SGD) occurs in volumes that equal river discharge to the Atlantic Basin, but the mechanism for this flow has been elusive. Recent field results from the South Atlantic Bight show that variations in sea level can drive pulses of SGD from confined aquifers far (>10 km) from shore, and this flow mechanism has the potential to drive very large volumes of SGD. This project is designed to estimate SGD in continental shelves around the world. Assuming flat-lying coastal aquifers terminate at the seafloor in continental shelves, a series of stacked confined aquifers can interact with a very wide area of the seafloor, reaching from the shoreline to tens of km offshore. We used simple 1-D numerical models to estimate the volume of submarine groundwater discharge from idealized aquifers in response to observed variations in sea level from around the world, assuming stacked aquifers at each location. Sea level elevation data were collected from representative distances from the shoreline to set the seaward boundary condition in the models. Results show that this flow mechanism can drive significantly more flow than was observed in our early field experiments, and that this flow significantly exceeds early estimates of tidal SGD, which assumed unconfined aquifers.