Radium Isotopes as Tracers of Coastal Circulation Pathways in the Mid-Atlantic Bight

Linda Rasmussen, Ph.D., 2003
Ken Buesseler, Advisor

Pathways of exchange between the shelf and slope in the Mid-Atlantic Bight were investigated using radiochemical tracer and hydrographic measurements. The four naturally occuring radium isotopes were used as coastal water mass tracers. The final study included data from 4 cruises with a total of 8 cross-shelfbreak transects. In addition, data were collected from the shelfbreak at Cape Hatteras crossing the western wall of the Gulf Stream to help determine sources of anomalous Ra-224 enrichments in high salinity water which were observed on several of the shelfbreak transects. Combined with the hydrographic data, radium measurements did not show evidence of direct advection of shelf water across the shelfbreak front. While cross-shelf transport appeared to be minimal, hydrographic observations did show large alongshelf volume transport. Furthermore, patterns of short-lived Ra-224 activity in this region are consistent with a rapid transport pathway for water from the Cape Hatteras shelf via the Gulf Stream onto the Mid-Atlantic Bight slope. The combined radiochemical and hydrographic evidence suggests that recirculation around the slope sea gyre may be a more important pathway than direct cross-shelf transport.