Upper-Slope Jets and Gulf Stream Filaments Inshore of the Charleston Bump during Winter 2012

A 3-month-long field program conducted in winter 2012 inshore of the seaward deflection of the Gulf Stream at the Charleston Bump observed several 7–21-day periods of strong (>0.5 m s−1) equatorward along-shelf flow over the upper continental slope. In sea surface temperature images, these phenomena resemble and appear linked to warm filaments, features known to be associated with meanders of the Gulf Stream as it traverses the southeast coast of North America. However, the character of these upper-slope features differs from previous descriptions of filaments, hence we describe them as “upper-slope jets.” We document the characteristics of the jets, which are approximately 30 km in width, centered on the 200-m isobath, with a maximum temperature variation at depth, and reasonably long-lived. Southwestward flow within the jet extends to 200 m and is in approximate thermal wind balance below a surface mixed layer. Maximum transport is estimated to be about 2.0 Sv (1 Sv ≡ 106 m3 s−1), driving a net equatorward along-shelf velocity over the deployment period. For this time period, at least, the jets form the equatorward flow of the shoreward flank of the Charleston Gyre. We suggest the features resemble the Pinocchio’s Nose Intrusion recently described by Zhang and Gawarkiewicz. Large-amplitude meander crests with sufficiently strong curvature vorticity are a plausible source of initiation of the upper-slope jets.

Feeding habits of some demersal fish on the Charleston Bump off the southeastern United States

Goldman, S. F. and Sedberry, G. R. 2011. Feeding habits of some demersal fish on the Charleston Bump off the southeastern United States. – ICES Journal of Marine Science, 68: 390–398. The feeding habits of several demersal fish on the upper continental slope were investigated to determine the trophic relationships of these ecologically dominant and commercially important species, and to determine food sources for slope fish off the southeastern United States. Stomach contents were examined from 534 fish, including wreckfish (Polyprion americanus), barrelfish (Hyperoglyphe perciformis), and red bream (Beryx decadactylus). Fish fed on 46 prey taxa, and there were dietary differences among predators. Wreckfish predominantly consumed teleost fish and squid; barrelfish had a diet dominated by pelagic tunicates and some mesopelagic fish and squid; red bream consumed mainly fish, squid, and crustaceans. Seasonal shifts in diet were observed in all three species. Many of the prey items encountered were vertically migrating organisms, which are a critical link between surface waters and the slope ecosystem.

Effect of Bathymetric Curvature on Gulf Stream Instability in the Vicinity of the Charleston Bump

The effect of the isobathic curvature on the development and evolution of Gulf Stream frontal waves (meanders and eddies) in the vicinity of the Charleston Bump (a topographic rise on the upper slope off Charleston, South Carolina; referred to as CB hereinafter) is studied using the Hybrid-Coordinate Ocean Model (HYCOM). Baroclinic and barotropic energy transfers from the Gulf Stream to its meanders and eddies that appear as cold and warm anomalies are computed for four different cases. In case I, the curvature of the isobaths is artificially reduced and the CB is removed from the bathymetry. In this simulation, the simulated Gulf Stream meanders were barely noticeable in the study region. Energy transfer from the Gulf Stream to meanders and eddies was negligible. In case II, the curvature of the isobaths was the same as in case I, but a bump of the scale of the CB was added to the bathymetry. In this simulation, Gulf Stream meanders were amplified while passing over the CB. In case III, the CB was removed from the bathymetry as in case I, but the curvature of the isobaths was similar to the actual bathymetry, which was larger than that of cases I and II. In this simulation, large meanders were simulated, but the development of these meanders was not confined to the region of the CB. The total baroclinic and barotropic energy transfer rate in this case was an order of magnitude greater than in case II, suggesting that isobathic curvature was able to generate Gulf Stream meanders and eddies even without the presence of the CB. In case IV, actual bathymetry data, which contain both the CB and the isobathic curvature, were used. In this case, large-amplitude Gulf Stream meanders were simulated and there was also a tendency for the amplification of the meanders to be anchored downstream of the CB, consistent with observations. The results from this study suggest that the formation of the “Charleston Trough,” a Gulf Stream meander that appears as a low pressure or depressed water surface region downstream of the bump, is the result of the combined effect of the CB and the isobathic curvature in the region. The isobathic curvature plays a major role in enhancing the baroclinic and barotropic energy transfer rates, whereas the bump provided a localized mechanism to maximize the energy transfer rate downstream of the CB.

Island in the Stream: Oceanography and Fisheries of the Charleston Bump

<em>Abstract.</em>—The Gulf Stream off the east coasts of Florida, Georgia, and the Carolinas is one of the U. S. pelagic fishery regions in which particularly high swordfish discard rates were reported after a regulation limiting the landings of swordfish less than 25 kg whole weight went into effect in 1991. Swordfish <em> Xiphias gladius </em>fishing and catch locations from mandatory longline logbooks for the years 1991 through 1995 were used to explore the distribution patterns of swordfish discard rates in this region. Every 0.1 degree square of latitude and longitude was assigned a discard rate category (very high, moderate, low, none) for each month of the year based on the percentage of the swordfish catch that was discarded in that month over the five year period. Swordfish discard rates varied with latitude and season. The greatest seasonal changes were seen off the Carolinas where discard rates increased in the fall along with changes in fishing patterns.