Radium isotopes as tracers of coastal circulation pathways in the Mid-Atlantic Bight
Rasmussen, Linda L.
MetadataShow full item record
KeywordMid-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
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.
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
Suggested CitationThesis: Rasmussen, Linda L., "Radium isotopes as tracers of coastal circulation pathways in the Mid-Atlantic Bight", 2003-06, DOI:10.1575/1912/2444, https://hdl.handle.net/1912/2444
Showing items related by title, author, creator and subject.
Li, Xingwen (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2003-02)The capability of transient tracers to constrain the ocean circulation in the North Atlantic is explored. Study of an idealized tracer shows that inferences of circulation properties from transient state distributions ...
Helium and lead isotope geochemistry of oceanic volcanic rocks from the East Pacific and South Atlantic Graham, David W. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1987-09)The isotopic evolution of helium and lead in the Earth is coupled by virtue of their common radioactive parents uranium and thorium. The isotopic signatures in oceanic volcanic rocks provide constraints on the temporal ...
Efficient representation of the hydrographic structure of the north Atlantic Ocean and aspects of the circulation from objective methods Fukumori, Ichiro (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1989-03)The general theme of this thesis is the study of systematic mathematical techniques for determining the ocean circulation from classical hydrographic data. Two aspects of this theme are analyzed. The first is finding an ...