Wind and Gulf Stream influences on along‐shelf transport and off‐shelf export at Cape Hatteras, North Carolina

Savidge, Dana K.; Bane, John M.

doi:10.1029/2000jc000574

Cited by 47 publications

(71 citation statements)

References 32 publications

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“…4). Temperature increases more rapidly between Chesapeake Bay and Cape Hatteras because the 70-m isobath is over the slope where there is warmer slope and Gulf Stream water (e.g., Churchill and Cornillon 1991;Gawarkiewicz et al 1992;Savidge and Bane 2001;Flagg et al 2002). Standard deviations of the depth-averaged temperature (100-km along-isobath bins) are relatively constant (18-1.58C) from Georges Bank to Delaware Bay and then increase as the 70-m isobath gets near the shelf break and encounters both shelf water and the warmer slope and Gulf Stream water.…”

Section: A Along-isobath Heat Balancementioning

confidence: 99%

The Mean Along-Isobath Heat and Salt Balances over the Middle Atlantic Bight Continental Shelf

Lentz

2010

Journal of Physical Oceanography

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The mean heat and salt balances over the Middle Atlantic Bight continental shelf are investigated by testing the hypothesis that surface fluxes of heat or freshwater are balanced by along-isobath fluxes resulting from the mean, depth-averaged, along-isobath flow acting on the mean, depth-averaged, along-isobath temperature or salinity gradient. This hypothesized balance is equivalent in a Lagrangian frame to a column of water, for example, warming because of surface heating as it is advected southward along isobath by the mean flow.Mean depth-averaged temperatures increase from north to south along isobath at a rate of 28C (1000 km) 21at midshelf, which is consistent with the hypothesized balance and mean surface heat flux estimates from the 50-yr NCEP Reanalysis. However, mean surface heat flux estimates from the higher-resolution 20-yr Objectively Analyzed Air-Sea Fluxes (OAFlux) reanalysis are too small to balance the along-isobath heat flux divergence implying a cross-shelf heat flux convergence. It is unclear which surface heat flux estimate, NCEP or OAFlux, is more accurate. The cross-shelf heat flux convergence resulting from the mean cross-shelf circulation is too small to balance the along-isobath heat flux divergence. Mean depth-averaged salinities increase from north to south along isobath at a rate of 1 (psu) (1000 km) 21at midshelf. Mean precipitation and evaporation rates nearly balance so that the net freshwater flux is too small by more than an order of magnitude to account for the observed along-isobath increase in salinity. The cross-shelf salt flux divergence resulting from the mean cross-shelf circulation has the wrong sign to balance the divergence in the along-isobath salt flux. These results imply there must be an onshore ''eddy'' salt flux resulting from the time-dependent current and salinity variability. The along-isobath temperature and salinity gradients compensate for each other so that the mean, depthaveraged, along-isobath density gradient is approximately zero. This suggests that there may be a feedback between the along-isobath density gradient and the onshore salt and heat fluxes that maintains the density gradient near zero.

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Section: A Along-isobath Heat Balancementioning

confidence: 99%

The Mean Along-Isobath Heat and Salt Balances over the Middle Atlantic Bight Continental Shelf

Lentz

2010

Journal of Physical Oceanography

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“…The mean flow over the MAB shelf is southwestward along-isobath at 5-10 cm s Ϫ1 based on hydrography, drifters, shipboard current profiles, and moored current observations (e.g., Bigelow 1915;Bumpus 1973;Beardsley et al 1976;Linder and Gawarkiewicz 1998;Lozier and Gawarkiewicz 2001;Shearman and Lentz 2003;Brink et al 2003;Flagg and Dunn 2003;Flagg et al 2006). This mean flow turns offshore near Cape Hatteras and is entrained into the Gulf Stream (Bumpus 1973;Ford et al 1952;Churchill and Berger 1998;Savidge and Bane 2001;Pietrafesa et al 2002;Gawarkiewicz and Linder 2006). The alongshelf mean flow increases with height above the bottom and distance offshore (Beardsley et al 1976).…”

Section: Introductionmentioning

confidence: 99%

Observations and a Model of the Mean Circulation over the Middle Atlantic Bight Continental Shelf

Lentz

2008

Journal of Physical Oceanography

159

239

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Analyses of current time series longer than 200 days from 33 sites over the Middle Atlantic Bight continental shelf reveal a consistent mean circulation pattern. The mean depth-averaged flow is equatorward, alongshelf, and increases with increasing water depth from 3 cm s Ϫ1 at the 15-m isobath to 10 cm s Ϫ1at the 100-m isobath. The mean cross-shelf circulation exhibits a consistent cross-shelf and vertical structure. The near-surface flow is typically offshore (positive, range Ϫ3 to 6 cm s Ϫ1). The interior flow is onshore and remarkably constant (Ϫ0.2 to Ϫ1.4 cm s Ϫ1). The near-bottom flow increases linearly with increasing water depth from Ϫ1 cm s Ϫ1 (onshore) in shallow water to 4 cm s Ϫ1 (offshore) at the 250-m isobath over the slope, with the direction reversal near the 50-m isobath.A steady, two-dimensional model (no along-isobath variations in the flow) reproduces the main features of the observed circulation pattern. The depth-averaged alongshelf flow is primarily driven by an alongshelf pressure gradient (sea surface slope of 3.7 ϫ 10 Ϫ8 increasing to the north) and an opposing mean wind stress that also drives the near-surface offshore flow. The alongshelf pressure gradient accounts for both the increase in the alongshelf flow with water depth and the geostrophic balance onshore flow in the interior. The increase in the near-bottom offshore flow with water depth is due to the change in the relative magnitude of the contributions from the geostrophic onshore flow that dominates in shallow water and the offshore flow driven by the bottom stress that dominates in deeper water.

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“…However, the Gulf Stream is approximately twice as far from the shelf there, compared to the southern Mid-Atlantic Bight. Further south, Savidge and Bane (2001) found no correlation between…”

Section: Structuresmentioning

confidence: 96%

“…Joyce et al (1992) observed that Gulf Stream warm-core rings can entrain large amounts of shelf water onto the slope, and in the other direction intrusions of Gulf Stream water have been observed to penetrate as far as the MAB shelf (Gawarkiewicz et aI. 1990;Gawrkiewicz et al 1992) In a study of Gulf Stream infuence on cross-shelf export near Cape Hatteras, Savidge and Bane (2001) found that contrary to some expectations, Gulf Stream position does not appear to impact along-shelf transport, even in a region where it is in close proximity to the shelf; however it does correlate with transport convergence which they hypothesize may be responsible for cross-shelf, seaward flux of shelf water.…”

Section: Discussionmentioning

confidence: 99%

Radium isotopes as tracers of coastal circulation pathways in the Mid-Atlantic Bight

Rasmussen¹

2003

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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 MidAtlantic 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 wil 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.

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Wind and Gulf Stream influences on along‐shelf transport and off‐shelf export at Cape Hatteras, North Carolina

Cited by 47 publications

References 32 publications

The Mean Along-Isobath Heat and Salt Balances over the Middle Atlantic Bight Continental Shelf

The Mean Along-Isobath Heat and Salt Balances over the Middle Atlantic Bight Continental Shelf

Observations and a Model of the Mean Circulation over the Middle Atlantic Bight Continental Shelf

Radium isotopes as tracers of coastal circulation pathways in the Mid-Atlantic Bight

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