Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2003
Description:
Pathways of exchange between the shelf and slope in the Mid-Atlantic Bight were investigated
using a combination of radiochemical tracer and hydrographic measurements.
The motivation was to provide evidence of transport routes for shelfwater that could be
important to the balance of shelf-slope exchange, as well as to the biogeochemical fluxes
across this crucial ocean boundary. The four radium isotopes, with half-lives of 4 days to
1600 years, a coastal source, and conservative properties in seawater, were used as coastal
water mass tracers. The final study was comprised of data from 5 cruises, with a total of 8
cross-shelfbreak transects. Two areas were studied, a northern Mid-Atlantic Bight transect
south of Nantucket Shoals, and a southern Mid-Atlantic Bight series of transects off the
coast of Delaware. 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 224Ra
enrichment which was observed on several of the shelfbreak transects. Combined with the
hydrographic data, radium measurements suggested a pathway for exchange in the Mid-
Atlantic Bight that was not a direct advection of shelf water toward the slope. Rather, the
evidence suggested limited direct exchange of surface shelf water across the shelfbreak front.
This provides observational evidence that is consistent with models (e.g., Gawarkiewicz and
Chapman, 1991) which predict the shelfbreak front will impede exchange. Furthermore,
224Ra activity on the upper slope points to a rapid transport pathway for bottom water
from the Cape Hatteras shelf via the Gulf Stream onto the Mid-Atlantic Bight slope. The
radiochemical and hydrographic evidence suggests that recirculation around the slope sea
gyre may be a more important pathway than direct cross-shelf transport.
Description:
This work was supported by funding from the Woods Hole Oceanographic Institution Academic
Programs office, the Woods Hole Oceanographic Institution Ocean Ventues Fund, National
Science Foundation grant OCE-0097232, and Civilian Research and Development Foundation
grant UGI-2432-SE-02.
Keywords:
Mid-Atlantic Bight
;
Ocean circulation
;
Radium
;
Isotopes
;
Radioactive tracers in oceanography
;
Cape Hatteras (Ship) Cruise CH2300
;
Oceanus (Ship : 1975-) Cruise OC349
;
Endeavor (Ship: 1976-) Cruise EN335
;
Endeavor (Ship: 1976-) Cruise EN348
;
Knorr (Ship : 1970-) Cruise KN164
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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