Shelfbreak frontal structure and processes north of Cape Hatteras in winter

Abstract

The circulation north of Cape Hatteras is complicated by the proximity of the shelfbreak front, the Gulf Stream, and convergent shelf flow from the Middle and South Atlantic Bights. A three-week cruise in this region in January/February, 2005 was undertaken in order to study the structure of the shelfbreak front as it terminates near Cape Hatteras and to quantify the freshwater transport from the Middle Atlantic Bight shelf into the Gulf Stream. Two strongly contrasting conditions were identified. Early in the cruise, the Gulf Stream directly abutted the shelfbreak at Cape Hatteras and drove a northward flow over the continental shelf as far north as 35°45ЈN. All of the Middle Atlantic Bight shelf water terminated by 35°30ЈN. Ten days later, the Gulf Stream had moved away from the shelfbreak south of Cape Hatteras and strong winds from the north were present. During this time, the shelfbreak frontal jet was strong (maximum southward velocity of approximately 0.5 m s Ϫ1 with a Rossby number of 2) and abruptly turned eastward and offshore between 35°35ЈN and 35°45ЈN. Freshwater transport eastward from the shelfbreak jet was 7.4 mSv and southward over the shelf was 19.9 mSv, giving a total freshwater transport of 27.3 mSv. This likely represents an upper bound due to the strong wind forcing. Implications of these results for the freshwater budget of the Middle Atlantic Bight shelf, stability properties of the shelfbreak front in this region, and the formation of "Ford water" in the Gulf Stream are discussed.

Recent accelerated warming of the continental shelf off New Jersey: Observations from the CMVOleander expendable bathythermograph line

“…[, Figure ]) before passing under the Gulf Stream near Cape Hatteras [ Pickart and Watts , ]. Further onshore, along the MAB and Gulf of Maine shelfbreak, a density front between the cooler, fresher shelf waters and the warmer, saltier Slope Sea waters supports the equatorward‐flowing Shelfbreak jet [ Flagg et al ., ; Gawarkiewicz et al ., ]. This is part of the larger shelfbreak current system of coastal circulations between Greenland and the southern MAB [ Fratantoni and Pickart , ].…”

“…Mean along‐shelf flows over the Gulf of Maine and MAB shelf are also equatorward – notably against the mean wind stress, suggesting a mean along‐shelf pressure gradient force [ Lentz , ]. Cold, fresh waters from the equatorward‐flowing MAB shelf and slope currents are entrained into the cyclonic side of the Gulf Stream as “Ford” waters [ Churchill and Gawarkiewicz , ; Gawarkiewicz et al ., ; Csanady and Hamilton , ; Gawarkiewicz and Linder , ; Ford et al ., ].…”

Scattering and reverberation from fish schools in the 500-1500 hertz band

“…The circulation in the Cape Hatteras region is complicated due to the presence of multiple frontal systems, including the Gulf Sream, the shelfbreak front, and the coastal current flowing southward from Chesapeake Bay (Gawarkiewicz et al, 2008). During the May cruise, we successfully surveyed the shelfbreak front and Gulf Stream.…”

Pathways of shelf water export from the Hatteras shelf and slope

“…Evidence that shelf water may commonly be drawn seaward along the northern boundary of water discharged from the Gulf Stream near Cape Hatteras has been presented by Churchill and Cornillon [1991], Gawarkiewicz et al [1996] and Churchill and Berger [1998]. Entrainment of shelf water directly into the Gulf Stream current abutting the shelf‐edge near Cape Hatteras has been observed by Churchill and Berger [1998] and Gawarkiewicz et al [2008]. Churchill and Berger [1998] found that shelf water is often carried to the Gulf Stream along the northern margin of the Hatteras Front, which separates shelf water of the MAB from more saline South Atlantic Bight (SAB) shelf water.…”