Middle Atlantic Bight Shelf Research Articles

A climatology of salty intrusions over the continental shelf from Georges Bank to Cape Hatteras

Intrusions or lens of anomalously salty slope water (Smax intrusions) are often found over the continental shelf of the Middle Atlantic Bight (MAB). Salty intrusions were identified in 11% of 10,652 historical hydrographic profiles. Intrusions occurred primarily in summer, were observed across the entire shelf, but were most common over the outer shelf, and were concentrated at the depth of the seasonal pycnocline. The percentage of profiles with intrusions increased linearly along the MAB shelf from Georges Bank (3%) to Chesapeake Bay (15%), suggesting either a north to south increase in generation or an along‐shelf accumulation associated with a decay timescale of 90 days or longer. Intrusions were typically less than 30 m thick, with a salinity anomaly of less than 0.5, though 10% of the anomalies were greater than 1. The thickness increased as the stratification decreased in a manner consistent with double‐diffusively driven lateral intrusions. Intrusions did not preferentially occur during certain wind conditions. Salty intrusions increase the average salinity of the MAB shelf during summer by 0.3 or more, depending on how rapidly intrusions mix with the surrounding shelf water.

Activity and distribution of bacterial populations in Middle Atlantic Bight shelf sands

Abstract Spatiotemporal variation and metabolic activity of the microbial community were studied in coarse-grained Middle Atlantic Bight shelf sediments in relation to pools of dissolved and particulate carbon. Algal cells were present 8->70 mum) fraction of the sediment held the major share (61-98%) of benthic bacteria. Bacterial and algal cell abundances, exoenzymatic activity, and [DOC] generally showed higher values in May/July 2001 than in August/December 2000. Carbohydrates and proteins were hydrolyzed at potential rates of 1-12 nmol cm(-3) h(-1) (beta-glucosidase) and 3-70 nmol cm(-3) h(-1) (aminopeptidase), respectively. Fluorescence in situ hybridization analyses of the benthic microbes assigned 45-56% of DAPI-stained cells to Eubacteria and less than 2% to Eukarya. The prokaryotic community was dominated by planctomycetes and members of the Cytophaga/Flavobacterium cluster. Near the sediment surface, iodonitrotetrazolium violet reducing cells, that are considered actively respiring, amounted to 15-29% of total bacteria. Despite a low organic content (particulate organic carbon <0.03%) and relatively low bacterial abundances (<10(9) cm(-3)), the Middle Atlantic Bight shelf sediments showed organic matter turnover rates that are comparable to those found in organic-rich finer-grained deposits. Our findings suggest a high biocatalytic filtration activity in these coarse permeable sediments.

Activity and distribution of bacterial populations in Middle Atlantic Bight shelf sands

Spatiotemporal variation and metabolic activity of the microbial community were studied in coarse-grained Middle Atlantic Bight shelf sediments in relation to pools of dissolved and particulate carbon. Algal cells were present 8–>70 μm) fraction of the sediment held the major share (61–98%) of benthic bacteria. Bacterial and algal cell abundances, exoenzymatic activity, and [DOC] generally showed higher values in May/July 2001 than in August/December 2000. Carbohydrates and proteins were hydrolyzed at potential rates of 1–12 nmol cm −3 h −1 (β-glucosidase) and 3–70 nmol cm −3 h −1 (aminopeptidase), respectively. Fluorescence in situ hybridization analyses of the benthic microbes assigned 45–56% of DAPI-stained cells to Eubacteria and less than 2% to Eukarya. The prokaryotic community was dominated by planctomycetes and members of the Cytophaga/Flavobacterium cluster. Near the sediment surface, iodonitrotetrazolium violet reducing cells, that are considered actively respiring, amounted to 15–29% of total bacteria. Despite a low organic content (particulate organic carbon <0.03%) and relatively low bacterial abundances (<10 9 cm −3), the Middle Atlantic Bight shelf sediments showed organic matter turnover rates that are comparable to those found in organic-rich finer-grained deposits. Our findings suggest a high biocatalytic filtration activity in these coarse permeable sediments.

An extraordinary breach of the Gulf Stream north wall by a cold water intrusion

A breach of the Gulf Stream (GS) North Wall by a parcel of cold Middle Atlantic Bight shelf water was observed from October 2 to 5, 2001 by a sequence of NOAA AVHRR sea surface temperature (SST) images. Unlike the warm/cold core rings generated by GS meanders, the path of cold water eventually cuts into the GS. Subsequently, the cold water remained intact and eventually penetrated and transversed the entire width of the GS. This is readily apparent in the 3‐day SST sequence. Analysis of wind data from a nearby CMAN station reveals a high (over 12.8 m/s) and persistent (3 days) alongshore wind event occurred prior to the breach. An 11‐year time series (1991–2001) of local wind measurements show that this type of strong and persistent wind situation is uncommon, which may explain why the large‐scale surface shelf water breach of the GS has not been previously reported.

Decomposition of dissolved organic matter from the continental margin

Decomposition of dissolved organic carbon, nitrogen and phosphorus (DOC, DON, DOP) was measured for surface and bottom waters of the middle Atlantic bight (MAB) and deep slope water adjacent to the MAB on two occasions in March and August 1996. We used standard bottle incubation techniques to measure the decrease in dissolved organic matter (DOM) concentrations over a 180-day interval. Generally DOM concentrations in the MAB were elevated (125mM DOC, 10.2mM DON and 0.30mM DOP) relative to the surface ocean and deep slope water (46.7mM DOC, 2.76mM DON, 0.03mM DOP). On average the C:N:P ratio of shelf DOM (431:36:1) was substantially higher than the Redfield ratio, but not nearly as high for that of deep slope water (2700:215:1). Decomposition time course data were fit to a three-pool (very labile, labile, and recalcitrant pools) multi-G model using a Marquardt fitting routine. The threepool model was superior to a simple exponential decay model assuming a single pool of DOM. We observed no significant changes in concentration of DOM in deep-water samples, attesting to the old age of this material, its recalcitrant nature, and the cleanliness of our technique for measuring decomposition. There were major differences in the relative amount of very labile, labile and recalcitrant fractions of shelf-water DOC, DON and DOP as a result of preferential remineralization of P over N and N over C. Averaged over stations, the decomposable portion of the bulk DOC, DON and DOP pools increased from 30% to 40% to 81% for C, N and P. There was a wide range in decay coefficients for the very labile and labile DOM pools: average decay coefficient for the very labile pool was 0.219 d � 1 , and 0.018 d � 1 for the labile pool. Average half-lives calculated from the decay coefficients were 4, 12 and 8 days for the very labile DOC, DON and DOP pools, and 54, 113 and 90 days for the labile DOC, DON and DOP pools. On the basis of pool turnover times relative to shelf-water residence time (B100 days) we conclude that autochthonous algal production is the source of the very labile DOM pools. Its rate of production is sufficient to sustain estimated rates of bacteria C demand in continental margins. Our results for the MAB indicate that while substantial amounts of DOM are remineralized in the same time frame as shelf-water residence time, there is substantial DOM remaining that is depleted in N and P relative to C. Strong concentration gradients in DOM occur between shelf and ocean waters and between surface and deeper waters. Coupled with appropriate vertical and horizontal advective and eddy diffusive transports, DOM export from the MAB and other shelf systems may be a significant component of ocean C dynamics. r 2002 Elsevier Science Ltd. All rights reserved.

Sources and cycling of dissolved and particulate organic radiocarbon in the Northwest Atlantic Continental Margin

Continental shelves and slopes are productive and dynamic ocean margin systems that also regulate the fluxes of terrestrial, riverine, and estuarine materials between the continents and oceans. In order to evaluate the ages, potential sources, and transformations of organic matter in an ocean margin system, we measured the radiocarbon (Δ14C) and δ13C distributions of total dissolved organic carbon (DOC), suspended particulate organic carbon (POC), and dissolved inorganic carbon (DIC) in waters of the Middle Atlantic Bight (MAB) continental shelf and slope in April‐May 1994. The Δ14C of DOC was greatest (as high as −39‰) in surface waters of the shelf, decreasing rapidly offshore and with depth, even in relatively shallow (25‐50 m depth) shelf waters. The lowest Δ14C‐DOC values were observed in deep slope waters, where they were significantly lower than values measured previously for the deep Sargasso Sea. There was a strong inverse relationship between Δ14C‐DOC and δ13C‐DOC in all shelf and surface slope waters of the MAB, which is likely attributable to varying contributions of young, 14C‐enriched organic matter of terrestrial and/or riverine origin. The more highly 14C‐depleted DOC in deep slope waters (as low as −442‰) generally had a correspondingly lower δ13C (as low as −22.3‰) component. However, this must originate from relic terrestrial material either in the MAB itself or be discharged to the MAB from rivers and estuaries. The isotopic signatures of POC were clearly differentiable from DOC and indicate that this pool also contained a broad range of both old and young material of terrestrial (δ13C as low as − 24.9‰) and marine (δ13C as high as −19.9‰) origin throughout the MAB shelf and slope. The highest Δ14C‐POC values (up to 78‰) were observed in shallow shelf waters of the southern MAB. Conversely, the lowest Δ14C‐POC values (as low as − 394‰) were found in MAB deep slope waters and were also significantly more depleted in 14C than POC from the central north Atlantic (Sargasso Sea). A multiple‐source isotopic mass balance model employing both 14C and 13C was used to evaluate the relative contributions of both young and old terrigenous versus marine organic matter to DOC and POC in the MAB. The results indicate that shelf and slope DOC is comprised of an old “marine” fraction (represented by offshore Sargasso Sea material) and either a young “terrestrial/riverine/ estuarine” (TRE) component (in shelf and shallow slope waters) or a relic TRE component (in deep and some shallow slope waters). In contrast, suspended POC from the MAB appears to originate predominantly from a mixture of recent MAB primary production and an old, TRE component, similar to that observed in one of the major subestuaries of the Chesapeake Bay. These results suggest that both young and old sources of terrestrial and riverine organic matter can comprise a significant fraction of the DOC and POC in ocean margins. Preliminary calculations indicate that the export of this compositionally unique DOC and suspended POC may be significant terms in the organic carbon budgets of the MAB and other margin systems.

Springtime ichthyoplankton of the slope region off the north‐eastern United States of America: larval assemblages, relation to hydrography and implications for larval transport

Larval transport in the slope region off north‐eastern North America influences recruitment to juvenile habitats for a variety of fishes that inhabit the continental shelf. In this study, collections of larval fishes were made during springtime over the continental slope to provide insights into larval distributions and transport. Ichthyoplankton composition and distribution mirrored the physical complexity of the region. Three larval fish assemblages were defined, each with different water mass distributions. A Gulf Stream assemblage was found predominantly in the Gulf Stream and associated with filaments of discharged Gulf Stream water in the Slope Sea. Larvae of this assemblage originated from oceanic and shelf regions south of Cape Hatteras. Several members of this assemblage utilize habitats in the Middle Atlantic Bight (MAB) as juveniles (Pomatomus saltatrix, Peprilus triacanthus) and other members of the assemblage may share this life cycle (Mugil curema, Sphyraena borealis, Urophycis regia). A Slope Sea assemblage was found in all water masses, and was composed of epi‐ and mesopelagic fish larvae, as well as larvae of benthic shelf/slope residents. Larvae of one member of this assemblage (U. tenuis) are spawned in the Slope Sea but cross the shelf‐slope front and use nearshore habitats for juvenile nurseries. A MAB shelf assemblage was found in MAB shelf water and was composed of larvae that were spawned on the shelf. Some of these species may cross into the Slope Sea before returning to MAB shelf habitats (e.g. Enchelyopus cimbrius, Glyptocephalus cynoglossus). Previous studies have examined the effect of warm‐core rings on larval distributions, but this study identifies the importance of smaller‐scale features of the MAB shelf/slope front and of filaments associated with Gulf Stream meanders. In combination with these advective processes, the dynamic nature of larval distributions in the Slope Sea appears to be influenced, to varying degrees, by both vertical and horizontal behaviour of larvae and pelagic juveniles themselves.

Transport of Middle Atlantic Bight shelf water to the Gulf Stream near Cape Hatteras

Flowing along the U.S. eastern seaboard from Nantucket Shoals to Cape Hatteras is a low‐salinity (&lt;34 practical salinity units) water mass known as Middle Atlantic Bight (MAB) shelf water. It has long been recognized that a large quantity of this water is entrained into the Gulf Stream near Cape Hatteras. We examine this process using moored instrument, hydrographic, and drifter track data acquired in the Cape Hatteras region over 1992–1994. These measurements reveal that the cross section and volume transport of MAB shelf water tend to shrink considerably going southward toward and past Cape Hatteras. In particular, our hydrographic data show shelf water cross section to be reduced by about a factor of 8 over a region stretching 80 km north of Diamond Shoals (between 35° 20′N and 36°10′N). There appear to be two fairly distinct zones of export in this region. Our data suggest that shelf water loss in the northern zone, over 35°40′N–36°10′N, occurs principally seaward of the shelf edge. Seaward movement of shelf water into Gulf Stream meanders and into the circulation of water discharged from the Gulf Stream are identified as important agents effecting this loss. Export of shelf water in the southern zone occurs over middle and outer shelf, as indicated by 5–10 cm s−1 mean off shelf velocities measured by moored current meters. Contributing to this export is a seaward flow of shelf water in a strong current at the edge of the front separating MAB shelf water from the more saline shelf water of the South Atlantic Bight. The offshore transport of shelf water at the edge of this front is principally observed when the front is migrating shoreward across the shelf. This intermittency in the seaward transport of shelf water at the front may be partly responsible for the variability of the presence and transport of shelf water seen at the edge of the Gulf Stream.

Seasonal seawater optical properties of the U.S. Middle Atlantic Bight

Optical properties of seawater in the U.S. Middle Atlantic Bight (MAB) were measured during four cruises spanning 1993–1994. Samples were collected in August and November 1993 and March and April 1994 along a cruise track extending from Delaware Bay to the Sargasso Sea. Each sample was analyzed for colored dissolved organic matter (CDOM) and particulate absorption and chlorophyll a (chl a). In situ attenuation and reflectance were also measured at selected stations using underwater spectroradiometers. The overall seasonal and spatial ranges for CDOM and particulate absorption (442 nm) and chl a concentration were 0.02–0.41 m−1, 0.01–0.49 m−1, and 0.07–9.4 mg m−3, respectively. CDOM absorption ranged from twofold to threefold between seasons on the MAB shelf, whereas particulate absorption ranged from threefold to sevenfold at the same locations. The results indicate that although CDOM absorption often dominated water column light attenuation at chl a absorbing wavelengths (e.g., 442 nm), chl a could be estimated from in situ reflectance spectra with an average error of ±20% using a relationship previously determined for coastal and open ocean waters. It appears that reflectances at 442 nm (R442) within the MAB shelf are typically low and invariable and most of the chl a sensitivity is contained in the ratio denominator (R554), resulting in relative insensitivity to CDOM absorption. Furthermore, CDOM absorption could not be explicitly determined using reflectance ratios (R412/R490); rather, the reflectance ratios correlated more closely with total (CDOM plus particulate) absorption.

Transport mechanisms of larval and pelagic juvenile bluefish (Pomatomus saltatrix) from South Atlantic Bight spawning grounds to Middle Atlantic Bight nursery habitats

In this study we examined the mechanisms by which Pomatomus saltatrix (Pisces: Pomatomidae) larvae and pelagic juveniles are transported from South Atlantic Bight spawning grounds to Middle Atlantic Bight estuarine nursery habitats. Data on larval and pelagic juvenile distributions, estuarine juvenile recruitment, hydrography, wind speed and direction and satellite‐derived, sea surface temperature were used to examine potential larval transport mechanisms. On the basis of these analyses, a scenario for northward transport of P. saltatrix was developed. Gulf Stream‐associated flow moves P. saltatrix larvae northeastward from their South Atlantic Bight spawning grounds. Larval transport from the Gulf Stream to the Middle Atlantic Bight shelf edge occurs in warm‐core ring streamers, but some more developed individuals may swim across. Finally, P. saltatrix pelagic juveniles actively swim across the Middle Atlantic Bight shelf, a behavior initiated when the surface shelf‐slope temperature front dissipates in late spring. This scenario predicts that the number of South Atlantic Bight‐spawned P. saltatrix juveniles entering estuaries (i.e. recruitment) is determined in part by warm‐core ring streamer activity. The timing of recruitment, however, is determined almost entirely by the timing of the dissipation of the surface shelf‐slope temperature front.

Oxygen isotopic identity of the Delaware Coastal Current

Results are presented and discussed from a preliminary study on the oxygen isotopic composition of coastal and inner shelf waters from the Middle Atlantic Bight between the mouths of Delaware Bay and Chesapeake Bay. The water samples were collected during the spring, April/May 1993, in conjunction with a detailed hydrographic survey of the Delaware Coastal Current. The relationship between salinity and δ18O, both of which are generally accepted conservative properties of seawater, allows identification of the fresh and saline mixing end‐members for the Delaware Coastal Current. The main source of freshwater to the Delaware Coastal Current is a mixture of runoff into Delaware Bay with an estimated δ18OS = 0 composition of −7.08‰. The freshwater input is dominated by Delaware River discharge with a mean δ18O of −8.0‰ based on previous studies; there appears to be a secondary contribution of freshwater that is isotopically heavier from coastal‐plain drainage. The extrapolated δ18OS = 32.35 value (−0.93‰) of the saline component implies exchange with Middle Atlantic Bight Shelf Water through along‐shelf and across‐shelf mixing processes. Limited data suggest that the oxygen isotopic composition of low‐salinity water exiting the Chesapeake Bay mouth is discernible compared with that of the Delaware Coastal Current.

Ontogeny and otolith microstructure of bluefish Pomatomus saltatrix (Pisces: Pomatomidae)

Most marine fish larvae undergo distinct transitions during their development, often associated with functional shifts in their ecology. The purpose of the present study was to document the ontogenetic record contained within otoliths of the early life history stages of the bluefish Pomatomus saltatrix (Linnaeus), so that future work could use this otolith record to examine the ecological and population level consequences of bluefish life history transitions. Seven distinct ontogenetic stages were defined using multivariate analyses of 16 morphological, meristic and coded variables measured from larval and pelagic juvenile bluefish (standard length, SL=25 mm) collected on the Middle Atlantic Bight shelf during the summer of 1988. Otoliths were examined from the individuals utilized in the multivariate analysis, and from bluefish eggs and yolk-sac larvae, which were also collected on the Middle Atlantic Bight shelf during the summer of 1988 and staged using previously published descriptions. Important ontogenetic stage transitions were found to be recorded in otolith microstructure: hatching was marked by the formation of the first otolith increment, flexion was marked by an apparent change in increment formation rate of the lapillus, and the transition from larva to juvenile was marked by the initial formation of secondary growth centers. Thus, otolith microstructure provides a detailed record of ontogeny, and this record will prove useful in future studies of the ecology and dynamics of bluefish early life history stages.

Biological and oceanographic insights from larval labrid (Pisces: Labridae) identification using mtDNA sequences

Polymerase chain reaction and direct comparison of mitochondrial DNA sequences from a cytochrome b gene fragment were used to identify two morphologically distinct larval types ofXyrichtys, a genus of tropical wrasse (Pisces: Labridae). Both larval types were collected during ichthyoplankton surveys on the Middle Atlantic Bight shelf in the summer of 1988. DNA sequence comparisons indicated that both types were larvae ofXyrichtys novacula (Linnaeus). Back-calculated birthdate distributions for those larvae collected on the Middle Atlantic Bight shelf demonstrated that the two larval types formed two distinct cohorts indicating a biological difference. The two distinct larval types may be a consequence of an ecophenotypic effect, or they may represent offspring from genetically distinct populations. These results emphasize that important biological and oceanographic information can be gained through the use of the polymerase chain reaction and DNA sequencing for larval identificaiton.

Mixing of shelf, slope and Gulf Stream water over the continental slope of the Middle Atlantic Bight

A combination of water masses was observed over the continental slope between Cape Hatteras and Hudson Canyon following the passage of a Gulf Stream meander. It was largely made up of fluid discharged from the Gulf Stream in the wake of the meander and also contained intrusions of Middle Atlantic Bight (MAB) shelf water and slope water. Its most prominent dynamical feature was an anticyclonic eddy that had an initial diameter of about 100 km but contained relatively weak currents, not greater than 30 cm s −1 in magnitude. Discharged Gulf Stream water made up the eddy's core, and a band of entrained shelf water circulated at its margin. This band was connected with another entrained shelf water band that flowed along the northern margin of the Gulf Stream. Transport of the shelf water at the edge of the eddy was estimated to be 1.3 × 10 5 m 3 s −1, which is comparable with the estimated alongshore transport of water over the MAB shelf. Vigorous mixing of both shelf water bands with surrounding discharged Gulf Stream water is indicated by the large differences of the latter's T/S properties from those found within the Gulf Stream. These differences were used to estimate salt fluxes into the shelf water band at the edge of the anticyclonic eddy, with results in the range of 1.9–6.6 × 10 −6 g salt cm −2 s −2. Density ratios and Richardson numbers determined from hydrographic data suggest that these salt fluxes were primarily the result of mixing by double diffusive processes, and that shear-induced turbulence combined with double diffusion to effect vertical mixing at the margins of the shelf water band next to the Gulf Stream.

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°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'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.

Correction to “A Gulf Stream‐derived pycnocline intrusion on the Middle Atlantic Bight shelf” by Glen Gawarkiewicz et al.

Correction to “A Gulf Stream‐derived pycnocline intrusion on the Middle Atlantic Bight shelf” by Glen Gawarkiewicz et al.

A Gulf Stream‐derived pycnocline intrusion on the Middle Atlantic Bight shelf

Saline intrusions from the upper slope onto the outer shelf are frequently observed at the pycnocline along the shelfbreak front in the Middle Atlantic Bight during the summer. A brief cruise was conducted in July, 1986 between Baltimore and Washington Canyons to examine along‐shelf variability of pycnocline salinity intrusions. A particularly saline intrusion of 35.8 Practical Salinity Units (PSU) was observed between 20 and 40 m in a water depth of 70 to 80 m. The along‐shelf extent was at least 40 km. The cooler, sub‐pycnocline outer shelf water was displaced 15 km shoreward of the shelfbreak. A Gulf Stream filament was present in the slope region prior to the hydrographic sampling, but was not visible in thermal imagery during the hydrographic sampling. Temperature‐salinity characteristics of the intrusion suggest that it was a mixture of Gulf Stream water and slope water, possibly from the filament. The shoreward penetration of saline water was most pronounced at the pycnocline and penetrated the shelfbreak front, with salinities as high as 35.0 PSU reaching as far shoreward as the 35 m isobath. These pycnocline intrusions may be an important mechanism for the transport of Gulf Stream‐derived water onto the shelf during the summer. The presence of filaments or other Gulf Stream‐derived water on the upper slope may account for some of the along‐front variability of the pycnocline salinity maximum that has previously been observed.

A cyclonic eddy and shelf‐slope water exchange associated with a Gulf Stream warm‐core ring

Warm‐core ring (WCR) 83D passed through a linear array of moored temperature, conductivity and velocity sensors during October 1983. Satellite‐derived thermal imagery combined with data from the moored sensors have revealed a cold‐core cyclonic eddy, of approximately 80‐km diameter, traveling in advance of ring 83D. This cyclone, whose angular momentum magnitude was about 1/3 that of the WCR, evolved either during or shortly after the WCR's formation. Hydrographic and moored sensor data suggest that the WCR brought about a subsurface exchange of shelf and slope water, with near‐surface slope water moving onshore and near‐bottom shelf water being drawn offshore and around the ring. Examination of 308 cross‐shelf hydrographic sections from the Middle Atlantic Bight has indicated that such exchange commonly occurs in the presence of a WCR. This apparent ring‐induced exchange may significantly affect the overall salt balance of Middle Atlantic Bight shelf water. As an example, the volume of slope water within a well‐surveyed intrusion, which lay onshelf of WCR 79B, was 16% of Wright's (1976) estimate of the annual slope water transport to the Middle Atlantic Bight shelf.