Continental shelf water dynamics and submarine groundwater discharge in the South Atlantic Bight

Understanding cross-margin transport is central to understanding coastal ocean biogeochemical processes. Most of the previous work has analyzed the average cross-margin transport based on coastal fresh water input data or based on single Gulf Stream eddy event measurements. This dissertation covers a two year study including an eight-month time series covering periods of both vertical and horizontal stratification on the continental margin of the South Atlantic Bight (SAB). Temperature, salinity, and density data are used to constrain the hydrography on the shelf and the two short-lived ( 223Ra and 224Ra) and the two longer-lived ( 226Ra and 228Ra) radium isotopes to study eddy diffusion across the margin. Modeled eddy diffusion is used to determine cross-margin eddy diffusion e-folding distances of 10 to 90 kilometers and near shore eddy diffusion coefficients of 250 to 900 m2 s-1. The average inshore eddy diffusion varied from 800 to 1500 m2 s-1 and the exchange time for the coastal boundary water in Onslow Bay is 10 to 20 days.; A substantial volume of submarine groundwater discharge (SGWD) has been suggested to occur on the SAB continental shelf. It is important to understand SGWD contribution to the other coastal ocean biogeochemical processes. This study reports episodes of significant flow (260 to 360 cm d-1 ) observed in offshore well and an estimate of the maximum integrated flux of SGWD in the outer shelf of the SAB based on 224Ra activity in outer shelf water. SGWD may account for 2 to 5% of the water exchange on the SAB continental shelf.; The chemical and isotopic composition (13C, 14 C, He, O, Ra) of SGWD collected from wells at the mid-shelf of the SAB, coastal groundwater, and shelf seawater are reported. The SGWD appears to be recycled seawater that has been in the sediments for over 50 years. The discharging submarine groundwater is a source of silica, nitrogen, and phosphate for the continental shelf bottom water. SGWD may be supplying the Onslow Bay bottom water with 1E6 to 2E7 moles N per day and with 2E4 to 2E6 moles P per day.