Southeastern United States Continental Shelf Research Articles

Respiration and denitrification in permeable continental shelf deposits on the South Atlantic Bight: Rates of carbon and nitrogen cycling from sediment column experiments

Nitrogen (N) cycling and respiration rates were measured in sediment columns packed with southeastern United States continental shelf sands, with high permeability (4.66×10 −11 m 2) and low organic carbon (0.05%) and nitrogen (0.008%). To simulate porewater advection, natural shelf seawater was pumped through columns of different lengths to achieve fluid residence times of approximately 3, 6, and 12 h. Experiments were conducted seasonally at in situ temperature. Fluid flow was uniform in nearly all columns, with minimal dead zones and channeling. Significant respiration (O 2 consumption and ∑CO 2 production) occurred in all columns, with highest respiration rates in summer. Most (78–100%) remineralized N was released as N 2 in the majority of cases, including columns with oxic porewater throughout, with only a small fraction released as NO 3 − from some oxic columns. A rate of 0.84–4.83×10 10 mol N yr −1, equivalent to 1.06–6.09×10 −6 mmol N cm −2 h −1, was calculated for benthic N 2 production in the South Atlantic Bight, which can account for a large fraction of new N inputs to this shelf region. Metal and sulfate reduction occurred in long residence time columns with anoxic outflow in summer and fall, when respiration rates were highest. Because permeable sediments dominate continental shelves, N 2 production in high permeability coastal sediments may play an important role in the global N cycle.

Biological invasion of the Indo-Pacific lionfish Pterois volitans along the Atlantic coast of North America

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 235:289-297 (2002) - doi:10.3354/meps235289 Biological invasion of the Indo-Pacific lionfish Pterois volitans along the Atlantic coast of North America Paula E. Whitfield1,*, Todd Gardner2, Stephen P. Vives3, Matthew R. Gilligan4, Walter R. Courtenay Jr.5, G. Carleton Ray6, Jonathan A. Hare1 1NOAA Beaufort Laboratory, 101 Pivers Island Road, Beaufort, North Carolina 28516, USA 2Biology Department, 130 Gittleson Hall, Hofstra University, Hempstead, New York 11549-1140, USA 3Department of Biology, Georgia Southern University, PO Box 8042, Statesboro, Georgia 30460-8042, USA 4Marine Science Programs, Savannah State University, PO Box 20467, Savannah, Georgia 31404, USA 5Florida Caribbean Science Center, US Geological Survey, 7920 NW 71st Street, Gainesville, Florida 32653, USA 6Department of Environmental Sciences, University of Virginia, 291 McCormick Rd, Charlottesville, Virginia 22904, USA *E-mail: paula.whitfield@noaa.gov ABSTRACT: The occurrence of lionfish Pterois volitans is reported from the western Atlantic Ocean. Adults were collected off the coasts of North Carolina, Georgia and Florida, and juveniles were collected along the shore of Long Island, New York. They have also been found around Bermuda. Lionfish are indigenous to tropical waters of the western Pacific and their occurrence along the east coast of the United States represents a human-induced introduction. Distribution of adults suggests lionfish are surviving in the western Atlantic and capture of juveniles provides putative evidence of reproduction. The most likely pathway of introduction is aquarium releases, but introduction via ballast water cannot be ruled out. The ecosystem of the southeastern United States continental shelf is already undergoing change: reef fish communities are becoming more tropical and many fish species are overfished. These ongoing changes, along with limited information regarding the biology of P. volitans, make predictions of long-term effects of the introduction difficult. This discovery represents the first, apparently successful introduction, of a marine fish from the western Pacific to Atlantic coastal waters of the United States. KEY WORDS: Biological invasions · Nonindigenous species · Marine fish · Scorpaenidae · Marine introductions · Lionfish · Pterois volitans · Invasive species · Pteroinae Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 235. Online publication date: June 19, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Changes in iodine speciation across coastal hydrographic fronts in southeastern United States continental shelf waters

The hydrographic front that separates the turbid inner shelf water from the “clearer” midshelf water on the southeastern U.S. continental shelf is accompanied by dramatic changes in the speciation of iodine. The total iodine to salinity ratio, or specific iodine, in the inner shelf was slightly lower, usually about 10% lower, than that in the midshelf, which was in turn slightly lower than those observed in the open oceans. This suggests that the efficiency for the removal of dissolved iodine to the particulate phase may increase progressively from the open ocean to the midshelf water to the inner shelf water. On the other hand, the average concentration of iodate increased by a factor of about three from the inner shelf to the midshelf water while the concentration of iodide decreased by about 30%. Above a concentration of iodate of about 0.05 μM, the concentration of iodide was inversely related to that of iodate with a ratio of about −1 suggesting that the in situ reduction of iodate to iodide may play an important role in determining the distribution and speciation of iodine in these waters. The relationship between the concentration ratio of iodate to iodide and the concentration of nitrate plus nitrite also falls into a definable pattern. Waters with high concentration ratios of iodate to iodide (>0.5) were found mostly when the concentration of nitrate plus nitrite fell below 0.5 μM. Above this concentration of nitrate plus nitrite, the iodate to iodide ratio was almost invariably below 0.5.

Phytoplankton advection off the southeastern United States continental shelf

We observed an anomalous water mass below 100 m over the continental slope just seaward of the southeastern U.S. continental shelf. The water mass was colder than expected from T-S relations and contained relatively high concentrations of phytoplankton compared to surrounding waters. Hydrographic and biological characteristics indicated that the water mass was formed from waters that upwelled into the euphotic zone on the outer shelf. Based on our analyses, we conclude that the atmosphere extracted heat from the upwelled water thereby increasing its density and causing it to cascade (advect) off the shelf. Our preliminary calculations indicate that this process could represent a significant off-shelf flux of phytoplankton carbon during winter.

Alkalinity in the south-eastern United States continental shelf waters

The distributions of salinity, alkalinity and specific alkalinity, and the relationship between alkalinity and salinity in the south-eastern United States continental shelf waters, commonly known as the South Atlantic Bight, in April, 1985 indicate that the primary mixing process is between Gulf Stream water and shelf water. However, in the inner shelf the influence of the Cape Fear/Pee Dee Rivers and the Savannah River were also detectable. The influence of the outflows from the other rivers, which also drain into this Bight, was not as clearly evident. In the outer shelf, and over the shelf break, the presence of the altered (Gulf Stream) continental edge water was found. The mixture of shelf and Gulf Stream waters was characterized by a specific alkalinity of about 6·6 × 10 −2 meq l −1 ‰ −1. While the river waters were characterized by significantly lower salinity and specific alkalinity, the altered (Gulf Stream) continental edge water had only slightly lower salinity but a significantly lower specific alkalinity relative to the shelf water. The intrusion of offshore water over the shelf break onto the outer and middle shelves as a result of the meandering of the Gulf Stream has been recognized as one of the major contributors to the exchange of water between the shelf and the Gulf Stream. The distributions of specific alkalinity and salinity in the middle and outer shelves were consistent with the occurrence of such a process. Alkalinity/specific alkalinity may be a potentially useful complementary tracer for studying mixing processes in coastal areas where seawater mixes with outflows from multiple rivers.

Phytoplankton dynamics within Gulf Stream intrusions on the southeastern United States continental shelf during summer 1981

During July and August 1981 subsurface intrusion of upwelled nutrient-rich Gulf Stream water was the dominant process affecting temporal and spatial changes in phytoplankton biomass and productivity of the southeastern United States continental shelf between 29 and 32°N latitude. Intruded waters in the study area covered as much as 10 1 km including virtually all of the middle and outer shelf and approximately 50% of the inner shelf area. Within 2 weeks following a large intrusion event in late July, middle shelf primary production and Chl a reached 3 to 4 gC m − d −1 and 75 mg m −, respectively. At the peak of the bloom 80% of the water column primary production occurred below the surface mixed-layer, and new primary production (i.e., NO 3-supported) exceeded 90% of the total. Chl a-normalized photosynthetic rates were very high as evidenced by high mean assimilation number (15.5 mg C mg Chl a −1 h −1), high mean α (14 mg C mg Chl a −1 Ein −1 m), and no photoinhibition. As a result of the high photosynthetic rates, mean light-utilization index (Ψ) was 2 to 3 times higher than reported for temperature sub-arctic and arctic waters. The results imply a seasonal (June to August) middle shelf production of 150 g C m −1, about 15% higher than previous estimates of annual production on the middle shelf. Intrusions of the scale we observed in 1981 may not occur every summer. However, when such events do occur, they are by far the most important processes controlling summer phytoplankton dynamics of the middle and outer shelf and of the inner shelf in the southern half of the study area.

The effect of summertime shelf break upwelling on nutrient flux in southeastern United States continental shelf waters

Gulf Stream-induced upwelling at the shelf break of the South Atlantic Bight (SAB) presents water which, in summer, can intrude onto the continental shelf. In July 1979, an XBT survey of the continental shelf revealed such an intrusion of cold water off St. Augustine, Florida. From weekly mappings, it was determined that Gulf Stream water <22.5/sup 0/C covered 3280 km/sup 2/ and occupied 38 km/sup 3/ shoreward of the 42 m isobath. Using temperature and nitrate distributions and the T/sup 0/C:NO/sup 3/ relationship, the authors determined that 3200 metric tons of nitrate-nitrogen were advected into the study area. Net nitrate-nitrogen fluxes were 32 ..mu..moles x m/sup -2/ x sec/sup -1/ across the 42 m isobath and 30 ..mu..moles x m/sup -2/ x sec/sup -1/ across the 30 m isobath. The advection of nitrate-enrichment water into the photic zone caused a dramatic increase in phytoplankton biomass. The decreasing nitrate concentrations correlated with chlorophyll increases indicating phytoplankton production was mainly at the expense of nitrate advected into the area. Prior to the intrusion, production was likely supported by regenerated nutrients. Summertime intrusions supply an estimated 2.9 x 10/sup 4/ mtons NO/sub 3/-N x yr/sup -1/ to the middle shelf area of themore » southern SAB and are thus a major source of nitrogen to that area.« less

Climatology of the southeastern United States continental shelf waters

Data from 2872 hydrographic stations have been used to determine the oceanographie climatology of the southeastern United States continental shelf waters. The data were sorted by each degree of latitude and by depth into three zones (0–20 m, 21–40 m, 41–60 m). Inner shelf water temperatures were similar to adjacent land air temperatures, while outer shelf temperatures were moderated by the Gulf Stream. Minimum and maximum water temperatures occurred in Georgia and South Carolina inner shelf water. Bottom temperatures were unusually low off Florida in the summer probably because of shelf break upwelling. Surface salinity was lowest adjacent to the rivers and reached minimums in the spring at the time of high runoff. An exception to this occurred in the fall, when strong southward winds apparently advected low salinity coastal water southward and offshore flow was restricted. Heat flux was calculated from changes in monthly mean depth‐averaged inner shelf water temperatures. Heating occurred from March through July with maximum rates of 103 W m−2. Cooling occurred from October through February with maximum rates of −90 W m−2. Bulk stratification was estimated from the difference in near‐surface and near‐bottom monthly mean density. In the spring, stratification increases in inner shelf areas because of decreasing winds and increasing heat flux and runoff. By summer the whole shelf is highly stratified reflecting the contrast between high surface water temperatures and cooler bottom waters. Highest bulk stratification is found over the outer shelf. Stratification decreased with the approach offall with the associated cooling and high winds. Mean flow at midshelf was northward and appears to be produced by an along‐shelf slope of sea level of oceanic origin. Data are available with entire article on microfiche. Order from the American Geophysical Union, 2000 Florida Avenue, N.W. Washington, D.C. 20009. Document C82‐002; $2.50. Payment must accompany order.

Effect of upwelling on phytoplankton productivity of the outer southeastern United States continental shelf

Gulf Stream frontal disturbances cause nutrient-rich waters to frequently upwell and intrude onto the southeastern United States continental shelf between Cape Canaveral, Florida and Cape Hatteras, North Carolina. Phytoplankton response in upwelled waters was determined with three interdisciplinary studies conducted during April 1979 and 1980, and in summer 1978. The results show that when shelf waters are not stratified, upwelling causes productive phytoplankton (diatom) blooms on the outer shelf. Phytoplankton production averages about 2 g C m −2 d −1 during upwelling events, and ‘new’ production is 50% or more of the total. When shelf waters are stratified, upwelled waters penetrate well onto the shelf as a subsurface intrusion in which phytoplankton production averages about fives times higher than the nutrient-depleted overlying mixed layer. Phytoplankton within the intrusion deplete upwelled NO 3 in about 7 to 10 days, at which point no further net increase in phytoplankton biomass occurs. Current meter records show that upwelling occurs roughly 50% of the time on the outer shelf during November to April (shelf not stratified), and we estimate that seasonal primary production in upwelled waters is 175 g C m −2 6 months −1 of which at least 50% is ‘new’ production. More than 90% of outer shelf primary and ‘new’ production occurs during upwelling and thus upwelling is the dominant process affecting primary productivity of the outer shelf. Our seasonal estimates of outer shelf primary and ‘new’ production are, respectively, three and ten times higher than previous estimates that did not account for upwelling.

METACYCLOPINA IMPROVISA, NEW SPECIES (COPEPODA: CYCLOPOIDA) FROM THE SOUTHEASTERN UNITED STATES CONTINENTAL SHELF

ABSTRACT During a study of the meiofauna of the southeastern United States continental shelf in 1977, a new species of Metacyclopina (Copepoda: Cyclopoida) was found in the top 15 cm sediment in many locations off South Carolina and Georgia. This new species, Metacyclopina improvisa, is described and compared with three other known species. A species key to males and females is included.

Origin of Patterns of Quartz Sand Types on the Southeastern United States Continental Shelf and Implications on Contemporary Shelf Sedimentation--Fourier Grain Shape Analysis

ABSTRACT Quartz sands in the fine sand range were found to form areally discrete zones with different shape characteristics on the continental shelf from Charleston Harbor, South Carolina northward to Cape Fear, North Carolina. The nature and location of these sand zones can be used to gain insights into the past and present hydrodynamic history of the continental margin during the Pleistocene-Holocene. Fourier grain shape analysis of 95 samples indicates that the shelf surface in this area is characterized by coast-perpendicular bands of sand containing alternating high and low percentages of highly abraded (smooth) quartz grains. The bands containing high proportions of smooth grains are interpreted to be of coastal plain origin. The bands containing high proportions of quartz grains of irregular outline represent traces of pre-Holocene alluvial drainages on the exposed shelf during sea level lowstands. This interpretation is greatly strengthened by the fact that all three shelf bands of irregular sand exactly coincide at their landward ends with the coastal positions of Pleistocene courses of the three major Piedmont drainages in the region. The presence and preservation of these coast perpendicular bands emphasize the relict character of the fine sand on the shelf surface as well as the inability of bottom currents to produce significant shore-parallel net transport in this area.

Distribution of cadmium, cobalt, nickel and zinc in southeastern United States continental shelf waters

Concentrations of Cd, Co, Ni and Zn in continental shelf waters off the northern coast of Georgia and southern coast of South Carolina are higher than those of shelf waters immediately to the south and probably result from continental runoff. Lower concentrations to the south may result from the transport of Gulf Stream waters on the shelf.