GULF-STREAM WATER ON THE SHELF AND UPPER SLOPE NORTH OF CAPE-HATTERAS

Although intrusions of water from the Gulf Stream have often been observed over the Carolina shelf, there has been no published report of Gulf Stream water near the continental margin north of Cape Hatteras. By examining sea surface temperature distributions and hydrographic data collected over an 11-yr period, we have found that water discharged from the Gulf Stream often appears over the shelf and upper slope north of Cape Hatteras. For example, in the band between 36 and 38-degrees-N, roughly 80-300 km north of the tip of Cape Hatteras, Gulf Stream water was detected 13-27% of the time at sites on the upper slope and 3-9% of the time at locations on the shelf. In most instances, sea surface temperature distributions suggest that the Gulf Stream water which appeared near the continental margin was not part of the Gulf Stream. The Gulf Stream's main current but was fluid which had been expelled from the Gulf Stream. The Gulf Stream water found on the shelf did not appear to significantly influence the local circulation or alongshelf density structure. Its subtidal flow was largely driven by the alongshelf wind stress; and in most instances its vertical density profile nearly matched that of adjacent shelf water situated alongshore. In contrast, the discharged Gulf Stream water observed over the upper slope was significantly less dense than abutting fluid of equivalent depth located along the slope to the northeast. The circulation associated with this density contrast often conveyed Middle Atlantic Bight shelf water seaward of the continental margin. The resulting rate of shelf water export is not well resolved by the available data. Some rough estimates put it at 0.1 Sv, comparable with the estimated mean alongshore transport of shelf water over the Middle Atlantic Bight shelf.