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James J. Bisagni

Bio: James J. Bisagni is an academic researcher from National Oceanic and Atmospheric Administration. The author has contributed to research in topics: Hydrography & Gulf Stream. The author has an hindex of 2, co-authored 2 publications receiving 16 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, a high-resolution hydrographic transect across the shelfbreak south of Nantucket Shoals in August, 1995, revealed an unusual surface-trapped intrusion of saline slope water onto the continental shelf.
Abstract: A high-resolution hydrographic transect across the shelfbreak south of Nantucket Shoals in August, 1995, revealed an unusual surface-trapped intrusion of saline Slope water onto the continental shelf. The intrusion was confined to the upper 25 m of the water column and penetrated 15 km shoreward of the 100-m isobath, the typical position of the shelfbreak front. The maximum salinity within the intrusion was 35.0. Several strong jets were present within the surface layer with maximum velocities between 0.30 and 0.44 m s -1 in the alongshelf direction. Satellite thermal imagery confirms the presence of a warm-core ring at the offshore edge of the section and shows a warm feature penetrating shoreward of the 100-m isobath.

14 citations

Book ChapterDOI
01 Jan 1981
TL;DR: In this paper, three hydrographic stations conducted during a 1977 cruise to Deep Water Dumpsite 106 inadvertently sampled an established anti-cyclonic Gulf Stream ring both prior to and after it interacted with the Gulf Stream.
Abstract: Three hydrographic stations conducted during a 1977 cruise to Deep Water Dumpsite 106 inadvertently sampled an established anti-cyclonic Gulf Stream ring both prior to and after it interacted with the Gulf Stream. Continuous STD data and discrete dissolved oxygen measurements in the ring were analyzed using temperature-salinity (T-S) and temperature-oxygen (T-O2) diagrams. These data showed good correlation with T-S and T-O2 diagrams from Gulf Stream, Sargasso and Slope Waters obtained during a cyclonic Gulf Stream ring study. Apparently, a new entrainment of Gulf Stream Water around the ring occurred within the sampling period and was manifested by increased salinity and decreased levels of dissolved oxygen. Combined satellite surveillance and at-sea measurement of temperature, salinity and oxygen provide an accurate method of describing this highly dynamic and variable region in and around Deep Water Dumpsite 106.

4 citations


Cited by
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Journal ArticleDOI
TL;DR: The distribution and variability of sea surface temperature (SST) fronts, over the shelf and slope along the east coast of North America from Cape Hatteras to Nova Scotia, were studied using a 12-year time series (1985-1996) of advanced very high-resolution radiometer (AVHRR) images as discussed by the authors.
Abstract: The distribution and variability of sea surface temperature (SST) fronts, over the shelf and slope along the east coast of North America from Cape Hatteras to Nova Scotia, are studied using a 12 year time series (1985-1996) of advanced very high resolution radiometer (AVHRR) images. After the masking of cloud- contaminated pixels, an edge-detection algorithm identifies surface temperature fronts in each image. Maps of the seasonal probability of detecting a front indicate substantial spatial and temporal variability in the occurrence of SST fronts. Over the continental shelf south of New England during spring through autumn, surface fronts are rare and observed only in scattered locations. North of Nantucket Shoals, both tidal mixing fronts and fronts associated with the Eastern Maine Coastal Current occur during the summer. A major finding of this study is the observation of fronts in winter over the inner and middle shelf from Cape Hatteras to the Bay of Fundy. These fronts, peaking during January-March, are characterized by cold SST on their inshore (shallow) side and appear to result from the influence of surface cooling on shallow nearshore waters. The shelfbreak front is found to vary strongly with season, being detected most frequently during spring and autumn. South of Hudson Canyon, it essentially disappears during the summer, while from Hudson Canyon to Northeast Channel, it weakens during summer but nevertheless remains detectable in SST.

155 citations

Journal ArticleDOI
TL;DR: In this paper, the Gulf Stream and associated warm-core rings are hypothesized as the physical mechanisms responsible for the northward transport of larval fish originating south of Cape Hatteras, North Carolina, even as far north as the Scotian shelf.
Abstract: Larval fish originating south of Cape Hatteras, North Carolina, are frequently found on the continental shelf north of Cape Hatteras, even as far north as the Scotian shelf. The Gulf Stream and associated warm-core rings are hypothesized as the physical mechanisms responsible for the northward transport of larvae. Specifically, larvae spawned along the southeast U.S. continental shelf are entrained into the Gulf Stream, transported to the northeast, regularly incorporated in warm-core ring streamers, transported across the slope region, and released along the shelf edge north of Cape Hatteras. This proposed transport route was evaluated using hydrographic data and drifter tracks that were collected as part of other studies. Continental shelf water that originated south of Cape Hatteras was found

123 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a direct intrusion of Gulf Stream warm-core ring water onto the shelf representing a previously unknown exchange process at the shelf break, which has important biogeochemical implications and could facilitate migration of marine species across the shelfbreak barrier and transport low-nutrient surface Gulf Stream ring water to the otherwise productive shelfbreak region.
Abstract: Onshore intrusions of offshore waters onto the Mid-Atlantic Bight shelf can greatly affect shelf circulation, biogeochemistry, and fisheries. Previous studies have concentrated on onshore intrusions of slope water. Here we present a direct intrusion of Gulf Stream warm-core ring water onto the shelf representing a previously unknown exchange process at the shelfbreak. Impingement of warm-core rings at the shelfbreak generates along-isobath intrusions that grow like Pinocchio's nose, extending hundreds of kilometers to the southwest. By combining satellite and Ocean Observatory Initiative Pioneer Array data and idealized numerical simulations, we discover that the intrusion results from topographically induced vorticity variation of the ring water, rather than from entrainment of the shelfbreak frontal jet. This intrusion of the Gulf Stream ring water has important biogeochemical implications and could facilitate migration of marine species across the shelfbreak barrier and transport low-nutrient surface Gulf Stream ring water to the otherwise productive shelfbreak region.

82 citations

Journal ArticleDOI
TL;DR: In this article, the ages, potential sources, and transformations of organic matter in an ocean margin system were evaluated using radiocarbon (A14C) and 613C distributions of total dissolved organic carbon, suspended particulate organic carbon (POC), and dissolved inorganic carbon (DIC) in waters of the Middle Atlantic Bight (MAB) continental shelf and slope.
Abstract: 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 (A14C) and 613C 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 A•4C of DOC was greatest (as high as -39%0) in surface waters of the shelf, decreasing rapidly offshore and with depth, even in relatively shallow (25-50 m depth) shelf waters. The lowest A14C-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 A14C-DOC and 613C-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 •4C-depleted DOC in deep slope waters (as low as -442%0) generally had a correspondingly lower bl3C (as low as -22.3%0) 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 (•3C as low as -24.9%0) and marine (•3C as high as -19.9%o) origin throughout the MAB shelf and slope. The highest A14C-POC values (up to 78%0) were observed in shallow shelf waters of the southern MAB. Conversely, the lowest A14C-POC values as low as -394%0) 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 rivefine 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

75 citations

Journal ArticleDOI
TL;DR: In this paper, Salty slope water (Smax intrusions) are often found over the continental shelf of the Middle Atlantic Bight (MAB) in summer, and are concentrated at the depth of the seasonal pycnocline.
Abstract: [1] 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.

58 citations