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

2001 ◽  
Keyword(s):  
Gulf Stream ◽  
Eddy Currents ◽  
Fish Fauna ◽  
Freshwater Discharge ◽  
Large Fish ◽  
Apparent Loss ◽  
Water Layers ◽  
Early Neogene ◽  
Charleston Bump ◽  
Polyprion Americanus

<em>Abstract.</em>—The Charleston Bump is a structural and topographic high on the northern Blake Plateau that overlies a seaward offset of the edge of continental crust. The feature causes the bottom to shoal and deflects the Gulf Stream offshore, causing an intensification of bottom currents. The area has been swept by strong currents since late Cretaceous time, but the strongest currents have occurred in the Neogene (last -25 million years). Nondepositional conditions prevail at present, but erosion of the bottom is checked where the bottom is armored by a hard surficial layer of phosphorite pavement. The phosphorite pavements were formed by re-cementation of eroded residues of phosphorite-rich sediments of early-Neogene age. In some places there are multiple pavements separated by poorly lithified sediments. Submersible observations indicate that the south, or current-facing flank of the Charleston Bump has several deep (>100 m) scour depressions, the southern flanks of which form cliffs characterized by ledges and overhangs. In other areas discrete layers of older Paleogene rocks have been partly eroded away, leaving cliff-like steps of 5 m or more relief. Conglomeratic phosphorite pavement layers up to 1 m thick armor most of the bottom. Where breached by scour, these pavements form both low-relief ledges and rock piles. These features form a reef-like environment of caves and overhangs utilized by wreckfish <em> Polyprion americanus </em>and barrelfish <em> Hyperoglyphe perciformis </em>as shelter from the current and as staging areas to prey on passing schools of squid. Wreckfish and other large fish were often localized in rugged bottom habitat, including caves and other shelter areas. We observed wreckfish darting from shelters to feed on passing schools of squid. Present and past observations, are consistent with the concept that impingement of the Gulf Stream at the Charleston Bump compresses midwater fauna from much thicker water layers, providing food for a flourishing big-fish fauna. During our dives we noted currents often exceeding 1 knot, and ranging to 2.4 knots. Evidence of fossil, manganese-iron-encrusted megaripples suggest even greater current regimes in the past. Investigation of the site of an earlier report of possible freshwater discharge failed to find any evidence of a closed sinkhole or freshwater discharge. Rather, we concluded that the apparent loss of buoyancy experienced by the submarine was probably caused by downward-directed eddy currents generated by currents sweeping across the pavement/void interface of a more than 100-m high cliff 3 km south of the reported location.

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

2001 ◽  
Keyword(s):  
Gulf Stream ◽  
Seasonal Changes ◽  
Distribution Patterns ◽  
Xiphias Gladius ◽  
Charleston Bump ◽  
Pelagic Fishery ◽  
Very High

<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.

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

2001 ◽  
Keyword(s):  
South Carolina ◽  
Surface Temperature ◽  
Gulf Stream ◽  
Fast Moving ◽  
Bottom Topography ◽  
Sea Surface ◽  
Time Dependent ◽  
New Method ◽  
Sea Surface Temperatures ◽  
Charleston Bump

<em>Abstract.</em>—The animation of daily composites of sea surface temperatures (SST) from a National Oceanic and Atmospheric Administration Geostationary Operational Environmental Satellite (GOES) provides a new method for the detection of dynamics at the surface of the ocean. By rapidly viewing the daily SST composites of hourly images, it is possible for the human eye to separate the fast moving residual clouds from the slowly moving SST patterns associated with ocean currents, eddies, and upwelling. Although each individual daily composite is still partly cloud covered, the rapid display provides the appearance of continuity of the SST patterns. The GOES SST animations were used during 1998 and 1999 to monitor the time dependent deflection of the Gulf Stream due to a rise in bottom topography southeast of Charleston, South Carolina, locally known as the Charleston Bump. Examples of the sea surface temperature animations of the Gulf Stream appear at the website: http:// www. goes .noaa.gov

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

2019 ◽  
Vol 49 (6) ◽  
pp. 1423-1438 ◽  
Author(s):  
Harvey Seim ◽  
Catherine Edwards
Keyword(s):  
North America ◽  
Gulf Stream ◽  
Sea Surface ◽  
Maximum Temperature ◽  
Surface Mixed Layer ◽  
Time Period ◽  
Charleston Bump ◽  
Shelf Flow ◽  
Strong Curvature ◽  
Upper Slope

AbstractA 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.

scholarly journals Small-sized fish: the largest and most threatened portion of the megadiverse neotropical freshwater fish fauna

2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Ricardo M. C. Castro ◽  
Carla N. M. Polaz
Keyword(s):  
Freshwater Fish ◽  
Threatened Species ◽  
Human Impacts ◽  
Fish Fauna ◽  
Neotropical Region ◽  
Conservation Strategies ◽  
Small Fish ◽  
Large Fish ◽  
Freshwater Fish Fauna ◽  
General Synthesis

Abstract: We introduce the work providing a synthetic description of the diversity and phyletic structure of freshwater fish in the Neotropical Region, especially emphasizing that of Brazil. This is accompanied by a discussion about environments of fish from small to medium sized to large, taking into account how it shaped their respective biologies/ecologies, as well as what they imply for their use by humans. We present, as figures, the results of our exploratory analysis of Brazilian Red Book of Threatened Species of Fauna (2018), focusing on the small-sized ones, with up to 15 cm of standard length. We continue to present the main human impacts in small fish environments, along with those suffered by medium to large fish environments, and then follow by their respective deleterious effects. Finally, we present a general synthesis, reinforcing the enormous importance of small fish conservation and their respective preferred environments, followed by our main conclusions, and possible conservation strategies.

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

2007 ◽  
Vol 37 (3) ◽  
pp. 452-475 ◽  
Author(s):  
Lian Xie ◽  
Xiaoming Liu ◽  
Leonard J. Pietrafesa
Keyword(s):  
South Carolina ◽  
Energy Transfer ◽  
Gulf Stream ◽  
Transfer Rate ◽  
Surface Region ◽  
Ocean Model ◽  
Energy Transfer Rate ◽  
Study Region ◽  
Order Of Magnitude ◽  
Charleston Bump

Abstract 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

2001 ◽  
Keyword(s):  
Primary Production ◽  
Gulf Stream ◽  
Large Scale ◽  
Atlantic Coast ◽  
Nursery Habitat ◽  
Retention Mechanism ◽  
Larval Fishes ◽  
Published Evidence ◽  
High Concentrations ◽  
Charleston Bump

<em> Abstract.</em>—The region of the outer continental shelf and upper slope, encompassed roughly by 32 and 33°N and 78 and 79°W, is unique within the southeastern Atlantic coast of the United States because of the frequent presence of large (amplitudes of 50-100 km), cyclonic eddies. These eddies develop continuously north of the deflection of the Gulf Stream at the Charleston Bump and decay downstream. The cyclonic circulation of these eddies brings nutrient-rich water from deep and off the shelf edge to near surface and results in enhanced primary production. Succession of Zooplankton assemblages, driven by enhanced primary production, might serve fish production by providing an exceptional, and more continuous food supply for larval fishes spawned in or entrained into eddies. In addition, larval fishes that risk entrainment into the Gulf Stream and consequent loss from local populations, can be retained on, or near, the shelf when embedded within these eddies. The residence of an eddy within the region ranges from a week to a month or two, while the larval period of most fishes ranges from weeks to months. The large-scale eddies in the region develop most frequently in winter when the Gulf Stream is in its strongly deflected mode, coincident with the spawning of a suite of commercially important fishes. Although the region of the Charleston Gyre has the potential to act as an important spawning and nursery habitat, published evidence of usage of the habitat afforded by large scale eddies in this region is weak. High concentrations of larval fishes occasionally occur in the region, but there is no indication of high concentrations of fish eggs. With its high primary and secondary production, succession of Zooplankton assemblages, and retention mechanism, the region of the Gyre may constitute an important spawning and nursery habitat for fishes, but more research aimed at assessing this potential is necessary.

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

2001 ◽  
Keyword(s):  
Continental Slope ◽  
Gulf Stream ◽  
Topographic Feature ◽  
The Cross ◽  
Charleston Bump ◽  
Set Up ◽  
Stream Waters

<em>Abstract.</em>—The recurring seaward deflection of the Gulf Stream near 32°N latitude had been noticed by a number of investigators before the mid-1970s when Richard Legeckis first attributed the phenomenon to a topographic feature on the upper continental slope now known as the Charleston Bump. Since then, extensive studies have delineated many properties of the deflection and its effects on the Gulf Stream and surrounding waters including: the apparently bimodal nature of the deflection (resulting in the "strongly deflected" and "weakly deflected" states of the Gulf Stream's path near the Bump); the set up of the Charleston Gyre during strongly deflected conditions; the amplification of downstream-propagating Gulf Stream meanders in the Bump region; the meander-induced upwelling that accompanies meander propagation; and the cross-isobath exchange of shelf and Gulf Stream waters driven by the Charleston Gyre and Gulf Stream meanders. Of particular interest is the fact that there is still no unambiguous cause identified for inducing the Gulf Stream to shift from a weakly deflected path to a strongly deflected path, although several candidate mechanisms exist.

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

2001 ◽  
Keyword(s):  
Continental Shelf ◽  
Gulf Stream ◽  
Early Life ◽  
Bottom Topography ◽  
South Atlantic ◽  
South Atlantic Bight ◽  
The South ◽  
Pelagic Fishes ◽  
Charleston Bump ◽  
Pelagic Longline

<em>Abstract.</em>—The Charleston Bump is a complex bottom feature of great topographic relief located southeast of Charleston, South Carolina. This bottom feature deflects the Gulf Stream offshore in the South Atlantic Bight, and establishes permanent and temporary eddies, gyres, and associated upwellings in the warm Gulf Stream flow. Thermal fronts associated with Gulf Stream deflection, and die bottom feature itself, are believed to be attractive to large pelagic fishes, or result in concentrations of larvae, juveniles, and prey for larger fish. Upwelling in the region supports early life history stages of important fishery species. Deflection of the Gulf Stream may also play a direct or indirect role in transport of early life stages toward, or away from, nursery areas. Sea surface temperatures (SSTs) influenced by the Gulf Stream response to the Charleston Bump appear to have a role in determining recruitment success in gag <em> Mycteroperca microlepis, </em>a continental shelf reef fish. Relative cohort strength in gag was correlated (r = 0.89) to SST at 33°30'N, 78°30' W. Variability in conditions mat affect recruitment of larvae and juveniles, combined with heavy fishing pressure on prespawning adults, may result in recruitment failure in gag. In addition to strongly influencing circulation patterns in the South Atlantic Bight, die rugged bottom topography of the Bump is an important habitat and spawning ground for wreckfish <em> Polyprion americanus </em>and supports die U.S. fishery for this species. As a result, die Bump is an essential habitat for this species in U.S. waters. A geographic analysis of commercial pelagic longline logbook data shows mat die Charleston Bump is an area of concentrated commercial fishing effort, and that pelagic longline fisheries also concentrate along fronts at die edges of Gulf Stream gyres and eddies downstream. The "Charleston Bump Complex" of rough bottom topography and dynamic oceanography is an essential habitat for wreckfish and highly migratory pelagic fishes, and may influence recruitment success in some continental shelf fishes.

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