WorldWideScience

Sample records for continental shelf assessment

  1. 75 FR 1076 - Outer Continental Shelf Civil Penalties

    Science.gov (United States)

    2010-01-08

    ... initiate civil penalty proceedings; however, violations that cause injury, death, or environmental damage... DEPARTMENT OF THE INTERIOR Minerals Management Service Outer Continental Shelf Civil Penalties... daily civil penalty assessment. SUMMARY: The Outer Continental Shelf Lands Act requires the MMS to...

  2. Outer Continental Shelf Lands Act

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This data represents geographic terms used within the Outer Continental Shelf Lands Act (OCSLA or Act). The Act defines the United States outer continental shelf...

  3. Grain Size Data from the NOAA Outer Continental Shelf Environmental Assessment Program (OCSEAP)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This data set contains grain size data from samples acquired under the NOAA Outer Continental Shelf Environmental Assessment Program (OCSEAP) from the Outer...

  4. Coordination: southeast continental shelf studies. Progress report

    Energy Technology Data Exchange (ETDEWEB)

    Menzel, D.W.

    1981-02-01

    The objectives are to identify important physical, chemical and biological processes which affect the transfer of materials on the southeast continental shelf, determine important parameters which govern observed temporal and spatial varibility on the continental shelf, determine the extent and modes of coupling between events at the shelf break and nearshore, and determine physical, chemical and biological exchange rates on the inner shelf. Progress in meeting these research objectives is presented. (ACR)

  5. The Myanmar continental shelf

    Digital Repository Service at National Institute of Oceanography (India)

    Ramaswamy, V.; Rao, P.S.

    reveal a minimum of 18 m thick strata of modern muds (Fig. 2g). At the outer boundary of the Gulf of Myanmar Continental Shelf 8 Martaban (15oN Latitude), brown muds overlie coarse sands indicating that modern deltaic sediments... on the Myeik Bank (Rodolfo, 1969a). Modern sediments on the Ayeyarwady shelf General composition, Texture and Grain-size: The distribution and sediment texture on the Ayeyarwady shelf shows fine-grained sediments comprising silty-clay and clayey...

  6. Dynamics of tidal and non-tidal currents along the southwest continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Aruna, C.; Ravichandran, C.; Srinivas, K.; Rasheed, P.A.A.; Lekshmi, S.

    are predominantly mixed, semidiurnal in nature. Motion over any continental shelf is governed by the tide-driven oscillatory flow. In this paper, tidal and non-tidal characteristics of the waters of Southwest continental shelf of India are assessed using...

  7. Whither the UK Continental Shelf?

    International Nuclear Information System (INIS)

    Kemp, A.G.

    1999-01-01

    The development of the oil and gas fields on the United Kingdom continental shelf has been carried out with remarkable success. However, low oil prices now threaten fresh investment and make it likely that both oil and gas output will start to fall in about 2001. The impact of a number of different price scenarios on further development is assessed. It is concluded that continuing technological improvements and the provision of adequate incentives by government should ensure a long productive future for the province. (UK)

  8. State of the soft bottoms of the continental shelf

    International Nuclear Information System (INIS)

    Guzman Alvis, Angela I; Solano, Oscar David

    2002-01-01

    The presented information, it is based on studies carried out on the continental shelf of the Colombian Caribbean, mainly in the Gulf of Morrosquillo and the Magdalena and Guajira departments in the last ten years. A diagnostic is done of the soft bottoms of the Colombian continental shelf

  9. Morphology and sediment dynamics of the northern Catalan continental shelf, northwestern Mediterranean Sea

    Science.gov (United States)

    Durán, Ruth; Canals, Miquel; Sanz, José Luis; Lastras, Galderic; Amblas, David; Micallef, Aaron

    2014-01-01

    The northern Catalan continental shelf, in the northwestern Mediterranean Sea, extends along 200 km from the Cap de Creus submarine canyon to the Llobregat Delta, in the vicinity of the city of Barcelona. In this paper we present the results of a systematic investigation of this area by means of very high-resolution multibeam bathymetry to fully assess its morphological variability. The causative factors and processes determining such variability are subsequently interpreted. The shelf is divided in three segments by two prominent submarine canyons: the northernmost Roses Shelf is separated from the intermediate La Planassa Shelf by the La Fonera Canyon, while the boundary between the La Planassa Shelf and the southernmost Barcelona Shelf is marked by the Blanes Canyon. These two canyons are deeply incised in the continental margin, with their heads located at only 0.8 and 5 km from the shore, respectively. The seafloor character reflects the influence of external controlling factors on the geomorphology and sediment dynamics of the northern continental shelf of Catalonia. These factors are the geological setting, the volume and nature of sediment input, and the type and characteristics of processes leading to sediment redistribution, such as dense shelf water cascading (DSWC) and eastern storms. The interaction of all these factors determines sediment dynamics and allows subdividing the northern Catalan continental shelf into three segments: the erosional-depositional Roses Shelf to the north, the non-depositional La Planassa Shelf in the middle, and the depositional Barcelona Shelf to the south. Erosional features off the Cap de Creus Peninsula and an along-shelf subdued channel in the outer shelf illustrate prevailing sediment dynamics in the Roses segment, which is dominated by erosional processes, local sediment accumulations and the southward bypass of sediment. The rocky character of the seafloor immediately north of the Blanes Canyon head demonstrates that

  10. Assessment of the U.S. outer continental shelf environmental studies program. 1. Physical oceanography. Final report

    International Nuclear Information System (INIS)

    1990-01-01

    Federal responsibility for oil and gas development on the U.S. outer continental shelf (OCS) resides with the Minerals Management Service (MMS) of the U.S. Department of the Interior (DOI). The DOI's Environmental Studies Program (ESP) is the program through which MMS conducts environmental studies on the OCS and collects information to prepare environmental impact statements (EISs). It appeared to MMS in 1986 that the time was ripe to assess the status of the present program and to explore the needs for future studies. MMS requested an evaluation of the adequacy and applicability of ESP studies, a review of the general state of knowledge in the appropriate disciplines, and recommendations for future studies. Three panels were established, one of which, the Physical Oceanography Panel, investigated the physical oceanographic aspects of the ESP, the subject of the report, which is the first of three in a series. In reviewing the ESP's physical oceanography program, the panel evaluated the quality and relevance of studies carried out in waters under federal control, which extend from the limits of state jurisdictions (3-12 miles offshore) and include the central and outer continental shelf waters and the continental slope

  11. A preliminary assessment of geologic framework and sediment thickness studies relevant to prospective US submission on extended continental shelf

    Science.gov (United States)

    Hutchinson, Deborah R.; Childs, Jonathan R.; Hammar-Klose, Erika; Dadisman, Shawn; Edgar, N. Terrence; Barth, Ginger A.

    2004-01-01

    extensive data held within the Department of the Interior (DOI). The numerous seismic reflection and refraction surveys collected prior to 1970 by academic and governmental institutions are generally not included in this compilation, except where they provide unique data in a region. These data sources were omitted from this report because they were deemed to be of insufficient quality (poorly navigated or low resolution) to meet the CLCS standards for a submission, or they were redundant with higher-quality, more modern data. Hence, this report attempts to identify those data sets of highest utility for establishing the outer limits of the juridical continental shelf. If there was any ambiguity or uncertainty about the relevance of a data set to a continental shelf submission, either by its quality, location, or other parameter, it was included in this compilation. This report does not summarize other geophysical data (such as marine magnetics or gravity) that might be relevant to understanding crustal provenance and geological continuity. Detailed metadata tables and maps are included to facilitate the location and utilization of these sources when a comprehensive assessment (?desktop study?) is undertaken.

  12. Swell propagation across a wide continental shelf

    OpenAIRE

    Hendrickson, Eric J.

    1996-01-01

    The effects of wave refraction and damping on swell propagation across a wide continental shelf were examined with data from a transect of bottom pressure recorders extending from the beach to the shelf break near Duck, North Carolina. The observations generally show weak variations in swell energy across the shelf during benign conditions, in qualitative agreement with predictions of a spectral refraction model. Although the predicted ray trajectories are quite sensitive to the irregular she...

  13. Effects of energy-related activities on the Atlantic Continental Shelf

    Energy Technology Data Exchange (ETDEWEB)

    Manowitz, B [ed.

    1975-01-01

    Sixteen papers were presented and are announced separately. Coastal waters, continental shelf geology and aquatic ecosystems are studied for modelling basic data for assessment of possible environmental impacts from offshore energy development. Sediment transport and wave phenomena are modelled for understanding water pollution transport and diffusion. (PCS)

  14. Modern sedimentary processes along the Doce river adjacent continental shelf

    Directory of Open Access Journals (Sweden)

    Valéria da Silva Quaresma

    Full Text Available In areas of the continental shelf where sediment supply is greater than the sediment dispersion capacity, an extensive terrigenous deposits and consequently submerged deltas can be formed. The Eastern Brazilian shelf is characterized by the occurrence of river feed deltas in between starving coasts. Herein, modern sedimentary processes acting along the Doce river adjacent continental shelf are investigated. The main objective was to understand the shelf sediment distribution, recognizing distinct sedimentary patterns and the major influence of river sediment discharge in the formation of shelf deposits. The study used 98 surficial samples that were analyzed for grain size, composition and bulk density. Results revealed 3 distinct sectors: south - dominated by mud fraction with a recent deposition from riverine input until 30 m deep and from this depth bioclastic sands dominate; central north - sand mud dominated, been recognized as a bypass zone of resuspended sediment during high energy events; and north - relict sands with high carbonate content. The modern sedimentation processes along the Doce river continental shelf is dominated by distinct sedimentary regimes, showing a strong fluvial influence associated with wave/wind induced sediment dispersion and a carbonate regime along the outer shelf. These regimes seem to be controlled by the distance from the river mouth and bathymetric gradients.

  15. Seabottom backscatter studies in the western continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Chakraborty, B.; Pathak, D.

    The study is initiated to observe the interaction effects of the sound signal with three different sediment bottoms in the shelf area between Cochin and Mangalore in the western continental shelf of India. An echo signal acquisition system has been...

  16. Seabed geology of the Canadian eastern continental shelf

    Science.gov (United States)

    Piper, David J. W.

    1991-08-01

    The physiography of the continental shelf off eastern Canada is irregular, developed by glacial erosion of a previously fluvially-dominated landscape. Northern shelves are deeper than southern shelves. Most surficial sediments on the shelf are relict or palimpsest. The principal modern source of sediment to the northern shelves is ice rafting and iceberg scour reworking of Quaternary sediments. Southern shelves receive sediment through erosion of Quaternary sediments; only small amounts of fine-grained sediment derived from coastal erosion and rivers escape from the coastal zone. Regional maps of sediment texture, carbonate content and heavy mineralogy consequently show differences between the northern and southern shelves. Large areas of the shelf show little net deposition. On the northern shelves, there is a surface veneer up to 0.5 m thick derived from ice rafting and iceberg turbation of underlying Quaternary sediment, modified by south-flowing currents [ WOODWORTH-LYNASet al. (this issue) Continental Shelf Research, 11, 939-961]. The overall effects of former iceberg turbation may extend to a depth of 10 m sub-bottom. On the southern shelves, bioturbation and perhaps storm-related currents rework exposed Quaternary sediments more slowly. Muds accumulate in deep basins on the shelves at rates of about 0.5 m per 1000 years; this accumulation is probably episodic and related to major storms reworking sediment from the surface sediment veneer in shallower areas of little net deposition. In water depths less than 110 m sand and gravel have formed as a result of reworking in the coastal zone during the post-glacial transgression. Over large areas of Georges Bank, the eastern Scotian Shelf and the Grand Banks of Newfoundland, such sands are mobilized during storms to form a wide suite of bedforms [ AMOS and JUDGE (this issue) Continental Shelf Research, 11, 1037-1068]. Elsewhere, particularly in deeper water, sandy surfaces appear moribund or inactive and large

  17. The Statoil/Hydro fusion in a continental shelf perspective

    International Nuclear Information System (INIS)

    Osmundsen, Petter

    2007-01-01

    The article analysis the consequences of the Statoil/Hydro merger on the development on the Norwegian continental shelf. Various indicators of results of the market power the merger are presented and the effects of reduced competition on the markets are discussed. The advantages of the merger on the activities on the shelf are analyzed. (tk)

  18. Geochemistry of sediments of the eastern continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Mascarenhas, A.; Paropkari, A.L.; Murty, P.S.N.

    The bulk and partition geochemistry of Al, Fe, Ti, Mn, Zn, and Cu have been investigated in sediments of the eastern continental shelf of India. The results show that (1) the bulk geochemistry varies from one shelf unit to the other, (2) all...

  19. Mean Lagrangian drift in continental shelf waves

    Science.gov (United States)

    Drivdal, M.; Weber, J. E. H.

    2012-04-01

    The time- and depth-averaged mean drift induced by barotropic continental shelf waves (CSW's) is studied theoretically for idealized shelf topography by calculating the mean volume fluxes to second order in wave amplitude. The waves suffer weak spatial damping due to bottom friction, which leads to radiation stress forcing of the mean fluxes. In terms of the total wave energy density E¯ over the shelf region, the radiation stress tensor component S¯11 for CSW's is found to be different from that of shallow water surface waves in a non-rotating ocean. For CSW's, the ratio ¯S11/¯E depends strongly on the wave number. The mean Lagrangian flow forced by the radiation stress can be subdivided into a Stokes drift and a mean Eulerian drift current. The magnitude of the latter depends on the ratio between the radiation stress and the bottom stress acting on the mean flow. When the effect of bottom friction acts equally strong on the waves and the mean current, calculations for short CSW's show that the Stokes drift and the friction-dependent wave-induced mean Eulerian current varies approximately in anti-phase over the shelf, and that the latter is numerically the largest. For long CSW's they are approximately in phase. In both cases the mean Lagrangian current, which is responsible for the net particle drift, has its largest numerical value at the coast on the shallow part of the shelf. Enhancing the effect of bottom friction on the Eulerian mean flow, results in a general current speed reduction, as well as a change in spatial structure for long waves. Applying realistic physical parameters for the continental shelf west of Norway, calculations yield along-shelf mean drift velocities for short CSW's that may be important for the transport of biological material, neutral tracers, and underwater plumes of dissolved oil from deep water drilling accidents.

  20. Submerged reef systems on the central western continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Vora, K.H.; Almeida, F.

    -262 255 Elsevier Science Publishers B.V., Amsterdam -- Printed in the Netherlands Letter Section Submerged Reef Systems on the Central Western Continental Shelf of India K.H. VORA and F. ALMEIDA National Institute of Oceanography, Dona Paula, Goa 403... 004 (India) (Revision accepted October 26, 1989) Abstract Vora, K.H. and Almeida, F., 1990. Submerged reef systems on the central western continental shelf of India. Mar. Geol., 91: 255-262. Echosounding and sidescan sonar data from the western...

  1. Variability in measured current structure on the southwest continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    DineshKumar, P.K.; Srinivas, K.

    -1 Variability in Measured Current Structure on the Southwest Continental Shelf of India P.K. Dinesh Kumar and K. Srinivas National Institute of Oceanography, Regional Centre P.O.Box 1913, Cochin - 682018,India Email: dineshku@niokochi.org ABSTRACT... WORDS: Direct current measurements, tidal currents, southwest coast of India. INTRODUCTION The circulation pattern of the eastern Arabian Sea over the southwest continental shelf of India (inferred...

  2. Seaweed culture and continental shelf protection

    Energy Technology Data Exchange (ETDEWEB)

    Przhemenetskaya, V F

    1985-07-01

    The initial impression that the resources of the oceans were limitless has been replaced by a more rational appreciation that everything has its limits, including the seemingly infinite resources of marine plant life. In addition, experience in California, Australia, China, Japan and Korea has demonstrated that depletion of seaweed resources for commercial utilization has a deleterious effect on the biocenotic status of the continental shelf. In view of this, many countries, such as Japan, China, Korea, the Philippines and the USSR, have embarked on aquaculture programs, in which seaweeds are cultivated on marine plantations. Successful developments in this direction should go a long way to preserving the natural ecologic balance on the continental shelf, and yet provide mankind with the resources of the deep. Many difficulties remain to be resolved before aquaculture programs become fully cost effective, one of which deals with the susceptibility of a monoculture to a given predator or disease. To that end, such programs necessitate the creation of well balanced systems that would support a variety of marine plant and animal life without an adverse effect on the desired crop. 4 references, 6 figures.

  3. Coordination: Southeast Continental Shelf studies. Progress report

    Energy Technology Data Exchange (ETDEWEB)

    Menzel, D.W.

    1981-02-01

    An overview of the Oceanograhic Program of Skidaway Institute of Oceanograhy is presented. Included are the current five year plan for studies of the Southeast Continental Shelf, a summary of research accomplishments, proposed research for 1981-1982, current status of the Savannah Navigational Light Tower, and a list of publications. (ACR)

  4. Geochemistry of sediments of the western Canadian continental shelf

    Science.gov (United States)

    Macdonald, R. W.; Pedersen, T. F.

    1991-08-01

    Few chemical data exist for the sedimentary environment off the Canadian west coast. Here we define the chemical nature of the shelf sediments by examining the important sources of material (natural and anthropogenic) to the region and processes relevant to diagenesis. Slightly more data exist for the continental shelf to the south (Washington) and north (Alaska), however it is clear that the sedimentary environment of these neighbouring shelves differs importantly from the Canadian portion. The British Columbia shelf receives little modern terrigenous detritus due mainly to isolation from terrestrial sediment sources by fiords, inland seas, or bypassing by shelf canyons. The chemical state of the sediments depends on the rate of supply of material, the energy of the depositional or erosional environment and the organic and inorganic composition of the material. These features in concert with bottom water characteristics control the redox state. Although no basins hosting continuous depositional records for the Holocene on the open British Columbia shelf have been identified or studied in a manner described by BUCKLEY ( Continental Shelf Research, 11, 1099-1122), some coastal embayments and fiords provide valuable historical records of post-glacial sedimentation. Such environments will prove to be increasingly useful in future studies of changes in regional climate and in establishing the chronology of natural disasters and anthropogenic impacts. Recommendations are given for a variety of research projects that would help us to understand better both chemical interactions at the seabed and Late Quaternary depositional history.

  5. Holocene limestones of part of the western continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Nair, R.R.; Hashimi, N.H.; Guptha, M.V.S.

    , while those on te upper continental slope (130-180 m) are algal bryozoan limestones. The limestones have a radiocarbon age ranging between 9,000 and 11,000 years. Depositional environmental on the continental shelf during the Holocene appears...

  6. Glacial morphology and depositional sequences of the Antarctic Continental Shelf

    Science.gov (United States)

    ten Brink, Uri S.; Schneider, Christopher

    1995-01-01

    Proposes a simple model for the unusual depositional sequences and morphology of the Antarctic continental shelf. It considers the regional stratal geometry and the reversed morphology to be principally the results of time-integrated effects of glacial erosion and sedimentation related to the location of the ice grounding line. The model offers several guidelines for stratigraphic interpretation of the Antarctic shelf and a Northern Hemisphere shelf, both of which were subject to many glacial advances and retreats. -Authors

  7. Uncovering the glacial history of the Irish continental shelf (Invited)

    Science.gov (United States)

    Dunlop, P.; Benetti, S.; OCofaigh, C.

    2013-12-01

    In 1999 the Irish Government initiated a €32 million survey of its territorial waters known as the Irish National Seabed Survey (INSS). The INSS is amongst the largest marine mapping programmes ever undertaken anywhere in the world and provides high-resolution multibeam, backscatter and seismic data of the seabed around Ireland. These data have been used to provide the first clear evidence for extensive glaciation of the continental shelf west and northwest of Ireland. Streamlined drumlins on the mid to outer shelf record former offshore-directed ice flow towards the shelf edge and show that the ice sheet was grounded in a zone of confluence where ice flowing onto the shelf from northwest Ireland merged with ice flowing across the Malin Shelf from southwest Scotland. The major glacial features on the shelf are well developed nested arcuate moraine systems that mark the position of the ice sheet margin and confirm that the former British Irish Ice Sheet was grounded as far as the shelf edge around 100 km offshore of west Donegal at the last glacial maximum. Distal to the moraines, on the outermost shelf, prominent zones of iceberg plough marks give way to the Barra/Donegal fan and a well developed system of gullies and canyons which incise the continental slope. Since 2008 several scientific cruises have retrieved cores from the shelf and slope to help build a more detailed understanding of glacial events in this region. This presentation will provide an overview of the glacial history of the Irish shelf and will discuss ongoing research programmes that are building on the initial research findings to produce a better understanding of the nature and timing of ice sheet events in this region.

  8. Radiation stress and mean drift in continental shelf waves

    Science.gov (United States)

    Weber, Jan Erik H.; Drivdal, Magnus

    2012-03-01

    The time- and depth-averaged mean drift induced by barotropic continental shelf waves (CSW's) is studied theoretically for idealized shelf topography by calculating the mean volume fluxes to second order in wave amplitude. The waves suffer weak spatial damping due to bottom friction, which leads to radiation stress forcing of the mean fluxes. In terms of the total wave energy density E̅̅ over the shelf region, the radiation stress tensor component S̅11 for CSW's is found to be different from that of shallow water surface waves in a non-rotating ocean. For CSW's, the ratio S̅11/E̅ depends strongly on the wave number. The mean Lagrangian flow forced by the radiation stress can be subdivided into a Stokes drift and a mean Eulerian drift current. The magnitude of latter depends on ratio between the radiation stress and the bottom stress acting on the mean flow. When the effect of bottom friction acts equally strong on the waves and the mean current, calculations for short CSW's show that the Stokes drift and the friction-dependent wave-induced mean Eulerian current varies approximately in anti-phase over the shelf, and that the latter is numerically the largest. For long CSW's they are approximately in phase. In both cases the mean Lagrangian current, which is responsible for the net particle drift, has its largest numerical value at the coast on the shallow part of the shelf. Enhancing the effect of bottom friction on the Eulerian mean flow, results in a general current speed reduction, as well as a change in spatial structure for long waves. Applying realistic physical parameters for the continental shelf west of Norway, calculations yield along-shelf mean drift velocities for short CSW's that may be important for the transport of biological material, neutral tracers, and underwater plumes of dissolved oil from deepwater drilling accidents.

  9. Flux of energy and essential elements through the continental shelf ecosystem. Progress report

    Energy Technology Data Exchange (ETDEWEB)

    Pomeroy, L.R.

    1981-11-30

    There are three distinct but not mutually exclusive areas of research in this contract, studies of intrusions of the west wall of the Gulf Stream onto the outer continental shelf, studies of the flux of materials across nearshore density fronts, and advances in understanding of the planktonic food web of the continental shelf. Studies of frontal events on the outer and inner continental shelf involve distinctive physical and chemical regimes and have proven to require distinctive biological approaches. The studies of the food web run through our work on both of the frontal regimes, but certain aspects have become subjects in their own right. We have developed a simulation model of the flux of energy through the continental shelf food web which we believe to be more realistic than previous ones of its type. We have examined several of the many roles of dissolved organic compounds in sea water which originate either from release by phytoplankton, digestive processes or metabolites of zooplankton, or extracellular digestion of microorganisms. Methods have been developed under this contract to measure both the chelating capacity of naturally occurring organic materials and the copper concentration in the water. It has been possible to characterize the effects, both toxic and stimulatory, of copper on photosynthesis of naturally occurring phytoplankton populations. It is possible to characterize in considerable detail the course of biological events associated with meanders of the Gulf Stream. We are now in a position to explain the limits to biological productivity of the outer continental shelf of the southeastern US and the reasons why that biological production moves through the food web in the characteristic way that it does.

  10. Nutrient Distributions, Transports, and Budgets on the Inner Margin of a River-Dominated Continental Shelf

    Science.gov (United States)

    2013-10-02

    Nutrient distributions, transports, and budgets on the inner margin of a river-dominated continental shelf John C. Lehrter,1 Dong S. Ko,2 Michael C...and D. C. Biggs (1993), The influence of advec- tion on the spatial variability of nutrient concentrations on the Texas- Louisiana continental shelf

  11. Radiocarbon and seismic evidence of ice-sheet extent and the last deglaciation on the mid-Norwegian continental shelf

    International Nuclear Information System (INIS)

    Rokoengen, Kaare; Frengstad, Bjoern

    1999-01-01

    Reconstruction of the ice extent and glacier chronology on the continental shelf off mid-Norway has been severely hampered by the lack of dates from the glacial deposits. Seismic interpretation and new accelerator mass spectrometer radiocarbon dates show that the ice sheet extended to the edge of the continental shelf at the last glacial maximum. The two youngest till units near the shelf edge were deposited about 15000 and 13500 BP. The results indicate that the ice sheet partly reached the shelf break as late as 11000 BP followed by a deglaciation of most of the continental shelf in less than 1000 years

  12. Morphology and stratal geometry of the Antarctic continental shelf: Insights from models

    Science.gov (United States)

    Cooper, Alan K.; Barker, Peter F.; Brancolini, Giuliano

    1997-01-01

    Reconstruction of past ice-sheet fluctuations from the stratigraphy of glaciated continental shelves requires understanding of the relationships among the stratal geometry, glacial and marine sedimentary processes, and ice dynamics. We investigate the formation of the morphology and the broad stratal geometry of topsets on the Antarctic continental shelf with numerical models. Our models assume that the stratal geometry and morphology are principally the results of time-integrated effects of glacial erosion and sedimentation related to the location of the seaward edge of the grounded ice. The location of the grounding line varies with time almost randomly across the shelf. With these simple assumptions, the models can successfully mimic salient features of the morphology and the stratal geometry. The models suggest that the current shelf has gradually evolved to its present geometry by many glacial advances and retreats of the grounding line to different locations across the shelf. The locations of the grounding line do not appear to be linearly correlated with either fluctuations in the 5 l s O record (which presumably represents changes in the global ice volume) or with the global sea-level curve, suggesting that either a more complex relationship exists or local effects dominate. The models suggest that erosion of preglacial sediments is confined to the inner shelf, and erosion decreases and deposition increases toward the shelf edge. Some of the deposited glacial sediments must be derived from continental erosion. The sediments probably undergo extensive transport and reworking obliterating much of the evidence for their original depositional environment. The flexural rigidity and the tectonic subsidence of the underlying lithosphere modify the bathymetry of the shelf, but probably have little effect on the stratal geometry. Our models provide several guidelines for the interpretation of unconformities, the nature of preserved topset deposits, and the

  13. Oil-spill risk analysis: Central and western Gulf of Mexico Outer Continental Shelf, Lease Sales 139 and 141. Final report

    International Nuclear Information System (INIS)

    Johnson, W.R.; Lear, E.M.

    1992-02-01

    The Federal Government has proposed to offer Outer Continental Shelf lands in the Gulf of Mexico for oil and gas leasing. Because oil spills may occur from activities associated with offshore oil production, the Minerals Management Service conducts a formal risk assessment. The effects of oil spills that could occur during oil and gas production must be considered. The report summarizes results of an oil spill risk analysis conducted for the proposed Gulf of Mexico Outer Continental Shelf Lease Sales 139 and 141

  14. Mean hydrography on the continental shelf from 26 repeat glider deployments along Southeastern Australia

    Science.gov (United States)

    Schaeffer, Amandine; Roughan, Moninya; Austin, Tim; Everett, Jason D.; Griffin, David; Hollings, Ben; King, Edward; Mantovanelli, Alessandra; Milburn, Stuart; Pasquer, Benedicte; Pattiaratchi, Charitha; Robertson, Robin; Stanley, Dennis; Suthers, Iain; White, Dana

    2016-08-01

    Since 2008, 26 glider missions have been undertaken along the continental shelf of southeastern Australia. Typically these missions have spanned the continental shelf on the inshore edge of the East Australian Current from 29.5-33.5°S. This comprehensive dataset of over 33,600 CTD profiles from the surface to within 10 m of the bottom in water depths ranging 25-200 m provides new and unprecedented high resolution observations of the properties of the continental shelf waters adjacent to a western boundary current, straddling the region where it separates from the coast. The region is both physically and biologically significant, and is also in a hotspot of ocean warming. We present gridded mean fields for temperature, salinity and density, but also dissolved oxygen and chlorophyll-a fluorescence indicative of phytoplankton biomass. This data will be invaluable for understanding shelf stratification, circulation, biophysical and bio-geochemical interactions, as well as for the validation of high-resolution ocean models or serving as teaching material.

  15. BLM/OCS Southern California Outer Continental Shelf Environmental Baseline Studies

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Data in this file were produced by Science Applications, Inc., prime contractor on the Bureau of Land Management/Outer Continental Shelf - Southern California...

  16. Nutrient regeneration and oxygen demand in Bering Sea continental shelf sediments

    Science.gov (United States)

    Rowe, Gilbert T.; Phoel, William C.

    1992-04-01

    Measurements of seabed oxygen demand and nutrient regeneration were made on continental shelf sediments in the southeast Bering Sea from 1 to 15 June 1981. The mean seabed oxygen demand was relatively modest (267 μM O 2 m -2 h -1), equivalent to a utilization of 60 mg organic carbon m -2 day -1. The seasonal build up of ammonium over the mid-shelf domain was generated at least in part by the bottom biota, as previously suggested ( WHITLEDGEet al., 1986 , Continental Shelf Research, 5, 109-132), but on the outer shelf nitrate replaced ammonium as the dominant inorganic nitrogen compound that was regenerated from the sediments. Comparison of oxygen consumption with the organic matter in sedimenting particulate matter (sampled with sediment traps) could imply that benthic processes were not accounting for the fate of considerable quantities of organic matter. Benthic oxygen demand rates, however, probably lag behind the input of the spring bloom to the bottom, thus extending the remineralization process out over time. Consumption by small microheterotrophs in the water column was also a likely sink, although shelf export and advective transport north were possible as well. Estimated nitrification rates in surface sediments could account for only a small fraction of the abrupt increase in nitrate observed in the water column over the shelf just prior to the spring bloom.

  17. Acoustic masking in sediments due to gases on the western continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Siddiquie, H.N.; Rao, D.G.; Vora, K.H.; Topgi, R.S.

    Surveys carried out on the western continental shelf of India indicate that the inner and middle shelf to a depth of 50-60 m is covered by acoustically transparent clays. On the shelf off Bombay, the clays are thin near the shore where they overlie...

  18. Sponge assemblages on the deep Mediterranean continental shelf and slope (Menorca Channel, Western Mediterranean Sea)

    Science.gov (United States)

    Santín, Andreu; Grinyó, Jordi; Ambroso, Stefano; Uriz, Maria J.; Gori, Andrea; Dominguez-Carrió, Carlos; Gili, Josep-Maria

    2018-01-01

    Sponge assemblages on continental shelves and slopes around the world have been known about for centuries. However, due to limitations of the traditional sampling systems, data about individual sponge species rather than assemblages have been reported. This study characterizes sponge assemblages over a wide bathymetric range ( 50-350 m depth) and covering the entire continental shelf and the upper slope of the Menorca Channel, an area soon to be declared a Marine Protected Area (MPA) as part of the Natura 2000 Network. Quantitative analysis of 85 video-transects (a total linear distance of 75 km), together with representative collections to confirm species identifications, allowed us to discriminate six major assemblages. Differences in the assemblages mainly corresponded to differences in substrate type and depth. On the inner continental shelf, a semi-sciaphilous Axinellid assemblage dominated the rocky outcrops. Maërl beds on the inner continental shelf were dominated by Haliclona (Reniera) mediterranea, whereas the horny sponge Aplysina cavernicola and several other haliclonids mostly dominated maërl beds and rocky substrates of the outer shelf. Soft sediments on the shelf break hosted a monospecific Thenea muricata assemblage, whereas rocky substrates of the shelf break were characterized by a mixture of encrusting, columnar and fan-shaped sponges. Finally, the upper slope was dominated by Hamacantha (Vomerula) falcula and the hexactinellid Tretodictyum reiswigi. Overall, sponge diversity showed its highest values above the shelf break, plummeting severely on the upper slope. Despite this diversity decrease, we found very high densities (> 70 ind./m2) of sponges over vast areas of both the shelf break and the upper slope.

  19. Sediments of the western continental shelf of India - Environmental significance

    Digital Repository Service at National Institute of Oceanography (India)

    Guptha, M.V.S.

    The degree of fragmentation and colour of the skeletal fragments, colouration in benthic foraminifers have been studied in surficial sediment samples collected from forty stations from the continental shelf region between Ratnagiri in the south...

  20. State intervention causing inefficiency: an empirical analysis of the Norwegian Continental Shelf

    International Nuclear Information System (INIS)

    Kashani, Hossein A.

    2005-01-01

    State intervention in the Norwegian Continental Shelf started with the establishment of Statoil as the medium of state ownership over the found petroleum and as a tool to monitor oil companies' procurement behaviour. This paper tests the extent to which the state intervention created inefficiencies in the Norwegian Continental Shelf (NCS) activities, as measured by data envelopment analysis, stochastic frontier analysis, Malmquist Indices, and standard regression analysis. Our results confirm such inefficiencies. Accordingly, the results provide an important insight into NCS production techniques and, more generally, into governments' abilities to influence private sector behaviour through contracts and tendering

  1. 76 FR 48861 - Notice of Issuance of Final Outer Continental Shelf Air Permit for Anadarko Petroleum Corporation

    Science.gov (United States)

    2011-08-09

    ... Continental Shelf Air Permit for Anadarko Petroleum Corporation AGENCY: Environmental Protection Agency (EPA... final Outer Continental Shelf (OCS) air permit for Anadarko Petroleum Corporation (Anadarko). The permit... Petroleum Corporation regarding the project. EPA carefully reviewed each of the comments submitted and...

  2. Denitrification pathways and rates in the sandy sediments of the Georgia continental shelf, USA

    Directory of Open Access Journals (Sweden)

    Ingall Ellery

    2005-02-01

    Full Text Available Denitrification in continental shelf sediments has been estimated to be a significant sink of oceanic fixed nitrogen (N. The significance and mechanisms of denitrification in organic-poor sands, which comprise 70% of continental shelf sediments, are not well known. Core incubations and isotope tracer techniques were employed to determine processes and rates of denitrification in the coarse-grained, sandy sediments of the Georgia continental shelf. In these sediments, heterotrophic denitrification was the dominant process for fixed N removal. Processes such as coupled nitrification-denitrification, anammox (anaerobic ammonium oxidation, and oxygen-limited autotrophic nitrification-denitrification were not evident over the 24 and 48 h time scale of the incubation experiments. Heterotrophic denitrification processes produce 22.8–34.1 μmole N m-2 d-1 of N2 in these coarse-grained sediments. These denitrification rates are approximately two orders of magnitude lower than rates determined in fine-grained shelf sediments. These lower rates may help reconcile unbalanced marine N budgets which calculate global N losses exceeding N inputs.

  3. Mineralogy of the carbonate sediments - western continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Nair, R.R.; Hashimi, N.H.

    An X-ray diffraction study of forty-six sediment samples and three oolitic limestone samples from the western continental shelf of India shows that aragonite is the dominant carbonate mineral (99% maximum), followed by low-magnesium calcite (77...

  4. Dose assessment for public by packages shipping radioactive materials hypothetically sunk on the continental shelf. Annex 3

    International Nuclear Information System (INIS)

    Tsumune, Daisuke; Suzuki, Hiroshi; Saegusa, Toshiari; Watabe, Naohito; Asano, Hiroyuki; Maruyama, Koki; Kinehara, Yoshiki

    2001-01-01

    Radioactive materials such as spent fuel (SF), PuO 2 powder, high level wastes (HLW) and fresh mixed oxide (MOX) fuel have been transported by sea between Europe and Japan. Dose assessments for public have been performed in the past when the packages shipping radioactive materials were hypothetically sunk on the continental shelf. These studies employed various conditions and methods in their assessments and the results were not always the same. In this study, the dose assessment for these packages was performed under the same conditions and by the same methods. The effective dose equivalents of radiation exposure to the public for all materials become smaller than the previous evaluations due to more realistic assumption in this study. These evaluated results are far less than the effective dose equivalent limit (1 mSv year -1 ) by the ICRP recommendation. (author)

  5. The European water framework directive: A challenge for nearshore, coastal and continental shelf research

    Science.gov (United States)

    Borja, Ángel

    2005-09-01

    The European Water Framework Directive (WFD) establishes a framework for the protection of groundwater, inland surface waters, estuarine waters, and coastal waters. The WFD constitutes a new view of the water resources management in Europe because, for the first time, water management is: (i) based mainly upon biological and ecological elements, with ecosystems being at the centre of the management decisions; (ii) applied to European water bodies, as a whole; and (iii) based upon the whole river basin, including also the adjacent coastal area. Although the marine water bodies affected by the WFD relate to only 19.8% of the whole of the European continental shelf, its application constitutes a challenge and an opportunity in nearshore, coastal and continental shelf research. This contribution highlights some of the main tasks and the research to be undertaken in the coming years, proposing investigations into: typologies; physico-chemical processes; indicator species; reference conditions; integration of the quality assessment; methodologies in determining ecological status, etc.

  6. The petroleum resources on the Norwegian continental shelf. 2007

    Energy Technology Data Exchange (ETDEWEB)

    2007-07-01

    The petroleum resources will not last for ever. It is therefore important for Norway to look ahead so as to be prepared for the changes that will come. In this report, the Norwegian Petroleum Directorate presents the current status of the petroleum resources on the Norwegian continental shelf. This is the basis on which the authorities can lay plans for the future. Since no-one can predict the future with certainty, on this occasion the Directorate is presenting four alternative scenarios for the future of Norwegian petroleum activities if the basic scenario proves incorrect. This will enable us to prepare ourselves for changes that may come, and to view the consequences of the various choices we can make. In this report, the Directorate also describes the various plays on the continental shelf, and explains the techniques used and the evaluations made when it estimates the undiscovered resources. This information is important for exploration work, particularly for new companies which need to get acquainted with the geology and the possibilities for finding oil and gas in Norway. Significant volumes remain to be produced and found on the Norwegian continental shelf. Only a third of the total resources have so far been produced, and a quarter of them have still not been discovered. Oil and gas prices are high at the moment, giving the industry and society in general good incentives to produce at a maximum rate. Oil production reached its peak a couple of years ago, but gas production is still increasing. However, the industry is finding less than it produces, which places demands on both it and the authorities. The industry must actively explore the acreage it has been allocated. The Petroleum Directorate believes that substantial resources can still be discovered in areas where production licences have been awarded. At the same time, the industry must gain access to new areas for exploration. The authorities must find an appropriate balance between concern for the

  7. 75 FR 68824 - Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore Maryland-Request...

    Science.gov (United States)

    2010-11-09

    ... No. BOEM-2010-0038] Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore..., Interior. ACTION: RFI in Commercial Wind Energy Leasing Offshore Maryland, and Invitation for Comments from... construction of a wind energy project(s) on the Outer Continental Shelf (OCS) offshore Maryland. The BOEMRE...

  8. Clay mineral distribution on the Kerala continental shelf and slope

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Nair, R.R.; Hashimi, N.H.

    Seventy-five sediment samples collected from the Kerala continental shelf and slope during the 17th and 71st Cruises of @iRV gaveshani@@ were analysed by X-ray diffraction for clay mineral cntent. The distribution of total clay (< 4~k fraction...

  9. Continental shelf landscapes of the southeastern United States since the last interglacial

    Science.gov (United States)

    Harris, M. Scott; Sautter, Leslie Reynolds; Johnson, Kacey L.; Luciano, Katherine E.; Sedberry, George R.; Wright, Eric E.; Siuda, Amy N. S.

    2013-12-01

    The wide, sediment-starved continental shelf and modern coastal areas of the southeastern United States retain well-preserved but scattered remnants of a submerged paleolandscape. This paper presents a conceptual model of stratigraphic deposition and landscape formation since the last interglacial on the continental shelf of South Carolina, with portions of North Carolina, Georgia, and Florida (USA). Data for this study include multibeam bathymetry surveys, sidescan sonar mosaics, high-resolution subbottom profiles, and ground-truth surveys from - 250 m to the modern tidewater region. Four bathymetric zones are recognized with eleven landforms and landform indicators. The described zones range in depths from the modern shoreline, across the shelf, and over the shelf edge to - 250 m MSL. Relative sea level curves are presented for the area and discussed in conjunction with cultural and climatic events. The potential for preservation of Paleoamerican sites is high at the shelf edge between - 130 m and - 45 m, with Archaic and later occupations likely in depths of less than - 25 m. Prominent vantage points for Paleoamericans (> 11 kya) would have existed at the shelf edge, and tidewater resources would have been available nearby for a period of almost 6 ka. Rapid transgression rates (> 60 km/ka) after the sea level rose over the shelf edge make preservation of tidewater sites less likely on the outer and middle shelf. Searches for the earliest Paleoamericans should focus on promontories at the edge of the shelf and along future discoveries of paleoincisions on the shelf. Mapping and delineating this paleolandscape and associated unconsolidated sedimentary deposits interspersed with rocky plains and ledges will continue to be a priority to marine archeologists, coastal managers, fishery scientists, and marine spatial planners over the next several decades.

  10. Radiocarbon dates of sediment cores from inner continental shelf off Taingapatnam, southwest coast of India

    International Nuclear Information System (INIS)

    Nambiar, A.R.; Rajagopalan, G.

    1995-01-01

    Radiocarbon dating of carbonized wood samples from three sediment cores from the inner continental shelf off Taingapatnam, in the southwestern coast of India, indicates ages in the bracket 8400-9400 YBP. These radiometric ages correlate well with the ages of carbonized wood from inner continental shelf off Ponnani, Kerala and Karwar, Karnataka. The occurrence of carbonized wood in widely spread offshore areas probably represents a regional transgressive event in the west coast which resulted in submergence and destruction of coastal mangroves. The rate of sedimentation in the study area varies between 0.12 and 0.37 mm/yr, much lower than those reported from shelf areas north of Mangalore. The slow accumulation of sediments in the southern parts of the western continental shelf of India, as exemplified from the present study, may be due to very poor discharge and low bed load sediments of the west-flowing small rivers of this part of the peninsula and low concentration of suspended particulate matter in them. (author). 24 refs., 2 tabs., 2 figs

  11. BLM/OCS South Texas Outer Continental Shelf (STOCS) Project Sediment Data

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The South Texas Outer Continental Shelf Project (STOCS) conducted by the University of Texas and the USGS with funding from BLM/NOAA. The USGS produced geochemical...

  12. Potential power-generating stations on the Atlantic Continental Shelf

    International Nuclear Information System (INIS)

    Mittl, R.L.

    1975-01-01

    Progress toward the installation of floating power plants, which represent a beneficial use of the continental shelf, is presented. The demonstration of the feasibility of such facilities with existing technology, and the thorough support by safety and environmental reviews, have been made possible by the efforts of engineers and scientists working toward supplying the nation's growing energy needs

  13. Oil-spill risk analysis: Gulf of Mexico (Proposed Lease Sales 131/135/137) Outer Continental Shelf. Final report

    International Nuclear Information System (INIS)

    Hannon, L.J.; LaBelle, R.P.; Lear, E.M.

    1991-09-01

    The Federal Government has proposed to offer Outer Continental Shelf lands in the Gulf of Mexico for oil and gas leasing. Because oil spills may occur from activities associated with offshore oil production, the Minerals Management Service conducts a formal risk assessment. In evaluating the significance of accidental oil spills, it is important to remember that the occurrence of such spills is fundamentally probabilistic. The effects of oil spills that could occur during oil and gas production must be considered. The report summarizes results of an oil spill risk analysis conducted for the proposed Gulf of Mexico Outer Continental Shelf Lease Sales 131/135/137. The objective of this analysis was to estimate relative risks associated with oil and gas production for the proposed lease sales

  14. Plankton community respiration, net ecosystem metabolism, and oxygen dynamics on the Louisiana continental shelf: Implications for hypoxia

    Science.gov (United States)

    Murrell, Michael C.; Stanley, Roman S.; Lehrter, John C.; Hagy, James D.

    2013-01-01

    We conducted a multi-year study of the Louisiana continental shelf (LCS) to better understand the linkages between water column metabolism and the formation of hypoxia (dissolved oxygen Continental Shelf Research, 29: 1861-1872) to estimate net water column metabolism. There was consistent evidence of net heterotrophy, particularly in western transects, and in deeper waters (>40 m depth), indicating a net organic carbon deficit on the LCS. We offer a simple scale argument to suggest that riverine and inshore coastal waters may be significant sources of organic carbon to account for this deficit. This study provided unprecedented, continental shelf scale coverage of heterotrophic metabolism, which is useful for constraining models of oxygen, carbon, and nutrient dynamics along the LCS.

  15. Geochronology of sediments in the Cananeia-Iguape estuary and in southern continental shelf of Sao Paulo State, Brazil

    International Nuclear Information System (INIS)

    Saito, R.T.; Figueira, R.C.L.; Cunha, I.I.L.; Tessler, M.G.

    2001-01-01

    Instrumental analysis methods for 210 Pb, 226 Ra and 137 Cs by gamma-spectrometry in sediments, as well as the sedimentation rates in cores collected from Brazilian coastal region are presented. Sampling locations have covered the Cananeia-Iguape estuary and the continental shelf of southern Sao Paulo State. Values for 210 Pb ranged from 122.5 to 14.3 Bq x kg -1 for estuarine sediments and from 195.5 to 23.6 Bq x kg -1 at the continental shelf. For 226 Ra the values obtained in sediments varied from 15.2 to 2.3 Bq x kg -1 in the estuary and from 30.1 to 16.1 Bq x kg -1 at the continental shelf. Sedimentation rates are variable, ranging from 0.53 to 0.98 cm x y -1 in estuary sediments and from 0.18 to 0.40 cm x y -1 at the continental shelf. (author)

  16. Areas with special ecological values on the Dutch Continental Shelf

    NARCIS (Netherlands)

    Lindeboom, H.J.; Kessel, J.G.; Berkenbosch, L.

    2005-01-01

    In this report we are submitting proposals for the boundaries of areas on the Dutch Continental Shelf (DCS). In the National Spatial Strategy a conservation regime has been determined for five areas in the North Sea with special ecological values. RIKZ and Alterra have formulated this report in

  17. The Asymmetric Continental Shelf Wave in Response to the Synoptic Wind Burst in a Semienclosed Double-Shelf Basin

    Science.gov (United States)

    Qu, Lixin; Lin, Xiaopei; Hetland, Robert D.; Guo, Jingsong

    2018-01-01

    The primary goal of this study is to investigate the asymmetric structure of continental shelf wave in a semienclosed double-shelf basin, such as the Yellow Sea. Supported by in situ observations and realistic numerical simulations, it is found that in the Yellow Sea, the shelf wave response to the synoptic wind forcing does not match the mathematically symmetric solution of classic double-shelf wave theory, but rather exhibits a westward shift. To study the formation mechanism of this asymmetric structure, an idealized model was used and two sets of experiments were conducted. The results confirm that the asymmetric structure is due to the existence of a topographic waveguide connecting both shelves. For a semienclosed basin, such as the Yellow Sea, a connection at the end of the basin eliminates the potential vorticity barrier between the two shelves and hence plays a role as a connecting waveguide for shelf waves. This waveguide enables the shelf wave to propagate from one shelf to the other shelf and produces the asymmetric response in sea level and upwind flow evolutions.

  18. Relict sand waves in the continental shelf of the Gulf of Valencia (Western Mediterranean)

    Science.gov (United States)

    Albarracín, Silvia; Alcántara-Carrió, Javier; Montoya-Montes, Isabel; Fontán-Bouzas, Ángela; Somoza, Luis; Amos, Carl L.; Salgado, Jorge Rey

    2014-10-01

    The presence of fossil or relict bedforms is common in the Quaternary fill of modern continental shelf due to sea level oscillations, tectonic subsidence and migration of associated sedimentary facies. The continental margin of the Gulf of Valencia has been strongly influenced by glacio-eustasy and neotectonics. High-resolution multibeam bathymetry data, seismic reflection profiles and box core samples were collected across the continental shelf of the Gulf of Valencia during the DERIVA cruises carried out in 2010 and 2011. The integrated analysis of this data set and high-resolution mapping of the relict bedforms on the Valencian continental shelf, ranging between 50 and 90 m allowed the study of previously identified system of sand waves located in front of the present-day Albufera de Valencia lagoon. The system is composed of 27 ridges with a NNE-SSW orientation, i.e. oblique to the present shoreline, in which the lateral horns point backwards. These sand waves can reach 10 m in height and 3 km in length resulting in a maximum slope of 6°. According to seismic stratigraphic and relative sea level curve reconstructions, these sand waves were formed during the Younger Dryas (~ 12-10 ky BP). Consequently, they have been classified as Holocene sand waves associated with coastal sedimentary evolution.

  19. Geochemistry of zinc in the sediments of the western continental shelf and slope of India

    Digital Repository Service at National Institute of Oceanography (India)

    Murty, P.S.N.; Paropkari, A.L.; Rao, Ch.M.

    The bulk geochemistry of zinc in the sediments of the western continental shelf and slope of India and also the partition geochemistry of the sediments of the shelf and slope regions between Ratnagiri and Mangalore have been studied. The studies...

  20. Transport and transfer rates in the waters of the continental shelf. Annual report

    International Nuclear Information System (INIS)

    Biscaye, P.E.; Broecker, W.S.; Feely, H.W.; Gerard, R.D.

    1976-04-01

    The report is to the Energy Research and Development Administration on accomplishments of the Lamont-Doherty Geological Observatory geochemistry and physical oceanography groups during the 1975-1976 funding period on grant E(11-1)2185. Goals are to obtain detailed, quantitative knowledge of the rates of mixing within coastal waters of the New York Bight and across the continental slope and the exchange of water masses and species transported within them between shelf and Atlantic Ocean waters. The research is aimed at understanding the chemical, physical, and biological processes which control the origin, dispersal, and fate of particulate matter and trace metals, and to ultimately model the impact of energy related pollutants on the continental shelf

  1. Transport and transfer rates in the waters of the continental shelf and slope: SEEP

    International Nuclear Information System (INIS)

    Biscaye, P.E.; Anderson, R.F.

    1993-01-01

    The overall Shelf Edge Exchange Processes (SEEP) Program, which began in 1980 or 1981, had as its goal the testing of a hypothesis with respect to the fate of particulate matter formed in and introduced into the waters of the continental shelf adjacent to the northern east coast of the US, i.e., the MAB. The original hypothesis was that a large proportion of the particles in general, and of the particulate organic carbon (POC) in particular, was exported from the shelf, across the shelf/slope break and front, into the waters of, and, to some degree, deposited in the sediments of the continental slope. This hypothesis was based on budgets of organic carbon and lead-210 that did not account for a large proportion of those species in the waters or sediments of the shelf, and on a carbon-rich band of sediments centered on the slope at ∼1,000 m water depth. The results of the first SEEP experiment, south of New England and Long Island (SEEP-1) suggested, but did not prove, that there was only a relatively small proportion of the carbon which was exported from the shelf to the slope. The objective of the second experiment -- SEEP-2 -- done under the subject grant, was to tighten the experiment in terms of the kinds of data collected, and to focus it more on the shelf and only the upper slope, where shelf-derived particles were thought to be deposited

  2. 78 FR 47748 - Right-of-Way Grant of Submerged Lands on the Outer Continental Shelf to Support Renewable Energy...

    Science.gov (United States)

    2013-08-06

    ...-Way Grant of Submerged Lands on the Outer Continental Shelf to Support Renewable Energy Development... will use Form 0009 to issue a renewable energy right-of- way (ROW) grant on the Outer Continental Shelf....gov/Renewable-Energy Program/ Regulatory-Information/Index.aspx. DATES: The ROW grant form will be...

  3. The NSW Steam Trawl Fishery on the South-East Continental Shelf of Australia, 1915-1961

    DEFF Research Database (Denmark)

    Jacobsen, A. Lif Lund

    2014-01-01

    How was modern fishing methods, in the form of steam trawling, introduced in Australia? And what were the consequences for the fish stocks found on the South-East Continental Shelf? Through historical catch records and archival resources, the history of the NSW Steam Trawl Industry from 1915...... that flathead biomass on the South-East Continental shelf was permanently reduced. The study furthermore reveals how the trawl industry was influenced by government policy, market conditions, war and fishing effort with little understanding of the marine resources which they relied on....

  4. Habitat specialization in tropical continental shelf demersal fish assemblages.

    Directory of Open Access Journals (Sweden)

    Ben M Fitzpatrick

    Full Text Available The implications of shallow water impacts such as fishing and climate change on fish assemblages are generally considered in isolation from the distribution and abundance of these fish assemblages in adjacent deeper waters. We investigate the abundance and length of demersal fish assemblages across a section of tropical continental shelf at Ningaloo Reef, Western Australia, to identify fish and fish habitat relationships across steep gradients in depth and in different benthic habitat types. The assemblage composition of demersal fish were assessed from baited remote underwater stereo-video samples (n = 304 collected from 16 depth and habitat combinations. Samples were collected across a depth range poorly represented in the literature from the fringing reef lagoon (1-10 m depth, down the fore reef slope to the reef base (10-30 m depth then across the adjacent continental shelf (30-110 m depth. Multivariate analyses showed that there were distinctive fish assemblages and different sized fish were associated with each habitat/depth category. Species richness, MaxN and diversity declined with depth, while average length and trophic level increased. The assemblage structure, diversity, size and trophic structure of demersal fishes changes from shallow inshore habitats to deeper water habitats. More habitat specialists (unique species per habitat/depth category were associated with the reef slope and reef base than other habitats, but offshore sponge-dominated habitats and inshore coral-dominated reef also supported unique species. This suggests that marine protected areas in shallow coral-dominated reef habitats may not adequately protect those species whose depth distribution extends beyond shallow habitats, or other significant elements of demersal fish biodiversity. The ontogenetic habitat partitioning which is characteristic of many species, suggests that to maintain entire species life histories it is necessary to protect corridors of

  5. 77 FR 52353 - Right-of-Way Grant of Submerged Lands on the Outer Continental Shelf to Support Renewable Energy...

    Science.gov (United States)

    2012-08-29

    ... of Submerged Lands on the Outer Continental Shelf to Support Renewable Energy Development AGENCY... would be used to issue Outer Continental Shelf (OCS) renewable energy right-of-way (ROW) grants in order... renewable energy, but does not constitute a project easement. The ability of an ROW grantee to install such...

  6. Nineteenth-century collapse of a benthic marine ecosystem on the open continental shelf.

    Science.gov (United States)

    Tomašových, Adam; Kidwell, Susan M

    2017-06-14

    The soft-sediment seafloor of the open continental shelf is among the least-known biomes on Earth, despite its high diversity and importance to fisheries and biogeochemical cycling. Abundant dead shells of epifaunal suspension-feeding terebratulid brachiopods ( Laqueus ) and scallops on the now-muddy mainland continental shelf of southern California reveal the recent, previously unsuspected extirpation of an extensive offshore shell-gravel ecosystem, evidently driven by anthropogenic siltation. Living populations of attached epifauna, which formerly existed in a middle- and outer-shelf mosaic with patches of trophically diverse muds, are restricted today to rocky seafloor along the shelf edge and to the sandier shelves of offshore islands. Geological age-dating of 190 dead brachiopod shells shows that (i) no shells have been produced on the mainland shelf within the last 100 years, (ii) their shell production declined steeply during the nineteenth century, and (iii) they had formerly been present continuously for at least 4 kyr. This loss, sufficiently rapid (less than or equal to 100 years) and thorough to represent an ecosystem collapse, coincides with intensification of alluvial-plain land use in the nineteenth century, particularly livestock grazing. Extirpation was complete by the start of twentieth-century urbanization, warming, bottom fishing and scientific surveys. The loss of this filter-feeding fauna and the new spatial homogeneity and dominance of deposit- and detritus-feeders would have altered ecosystem functioning by reducing habitat heterogeneity and seawater filtering. This discovery, attesting to the power of this geological approach to recent ecological transitions, also strongly increases the spatial scope attributable to the negative effects of siltation, and suggests that it has been under-recognized on continental shelves elsewhere as a legacy of coastal land use. © 2017 The Author(s).

  7. The petroleum resources on the Norwegian Continental Shelf. 2009

    Energy Technology Data Exchange (ETDEWEB)

    2009-07-01

    Exploration activity has reached record-breaking levels in the last couple of years, which has led to many, but small, discoveries. The NPD believes that large discoveries can still be made in areas of the shelf that have not been extensively explored. Content: Challenges on the Norwegian continental shelf; Value creation in fields; 40 years of oil and gas production; Resource management; Still many possibilities; Energy consumption and the environment; Exploration; Access to acreage; Awards of new licenses; Exploration in frontier areas; Exploration history and statistics; Resources and forecasts; Undiscovered resources; Proven recoverable resources; Forecasts; Short-term petroleum production forecast (2009-2013); Investments- and operating costs forecasts; Long-term forecast for the petroleum production; Emissions from the petroleum activity. (AG)

  8. Variations in organic carbon fluxes from Long Island Sound to the Continental Shelf

    Science.gov (United States)

    Vlahos, P.; Whitney, M. M.

    2017-12-01

    Organic carbon balances for the Long Island Sound estuary over the years 2009-2012 are presented to assess the particulate and dissolved organic carbon contributions of the estuary to the adjacent shelf waters with respect to the Delaware and Chesapeake. Observations were coupled to a hydrodynamic model (ROMS) for both seasonal and annual estimates. During stratified summer periods, LIS was consistently a net exporter of OC to the continental shelf. LIS annual net carbon export however, varied with river flow. The heterotrophic or autotrophic nature of LIS also shifted seasonally and inter-annually. During the mass balance analysis period LIS ranged between net OC import from the continental shelf and heterotrophy in the lowest river flow year (2012) and net export of OC and autotrophy in the highest flow year (2011). Analysis suggests that LIS switches from net OC import to export when the annual river inputs exceed 19 km3 yr-1. Applying these thresholds to the annual river flow record suggests that net import occurred in 15% of the last 20 years and that LIS usually is a net exporter of OC (85%). Annually averaged LIS carbon export values based on river flow conditions over the last 20 yr are estimated at 56 ± 64 x 106 km3 yr-1. Analysis also suggests that LIS shifts from net heterotrophic to net autotrophic when annual river flow exceeds 26 km3 yr-1 (35% of the last 20 yr). Net heterotrophic conditions are most common, representing 65% of the last 20 yr.

  9. Microbial origin of the phosphorites of the western continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Nair, R.R.

    Phosphatised algal nodules were recovered by dredging from the western continental shelf off Goa at depths ranging from 70 to 150 m. Energy dispersive X-ray analysis indicates that the phosphorus present in the algal nodules is confined to brownish...

  10. Sources and distribution of polycyclic aromatic hydrocarbons in sediments from the Spanish northern continental shelf. Assessment of spatial and temporal trends

    International Nuclear Information System (INIS)

    Vinas, Lucia; Angeles Franco, M.; Antonio Soriano, J.; Jose Gonzalez, J.; Pon, Jordi; Albaiges, Joan

    2010-01-01

    The distribution of polycyclic aromatic hydrocarbons was determined in surface sediments collected at 36 stations along the Spanish Northern continental shelf in March and September 2003, and February 2005. Concentrations of PAHs (Σ13 parent components) were in the range of 22-47528 μg/kg dw, the highest values corresponding to coastal urban-industrial hotspots and decreasing offshore. Sediment quality guidelines (SQGs) showed that concentrations of total PAHs were below the threshold effect level (TEC) in 27 stations (81%) and above in 7, two of which (Gijon and Bilbao) were above the probable effect concentration (PEC). The detailed study of diagnostic ratios suggested a rather uniform mixture of petrogenic and pyrolytic PAH sources along the continental shelf, with a slight decrease of the latter moving westwards and offshore. In order to assess the incidence of sediment sampling on the variability of the results, selected stations were also monitored in February and September 2004 and September 2005. The average field variance of the values obtained for each station was 31% that decreased to 23% when the values were normalized to TOC. - PAHs in the Spanish Atlantic coastal sediments reflect chronic inputs of petrogenic and pyrolytic hydrocarbons, with a decrease of the latter moving westwards and offshore and representing low to moderate pollution according to established sediment quality guidelines.

  11. Sources and distribution of polycyclic aromatic hydrocarbons in sediments from the Spanish northern continental shelf. Assessment of spatial and temporal trends

    Energy Technology Data Exchange (ETDEWEB)

    Vinas, Lucia, E-mail: lucia.vinas@vi.ieo.e [Instituto Espanol de Oceanografia, Centro Oceanografico de Vigo, Cabo Estai - Canido, 36200 Vigo (Spain); Angeles Franco, M.; Antonio Soriano, J.; Jose Gonzalez, J. [Instituto Espanol de Oceanografia, Centro Oceanografico de Vigo, Cabo Estai - Canido, 36200 Vigo (Spain); Pon, Jordi [Department of Environmental Chemistry, CID-CSIC, Jordi Girona Salgado, 18-26, 08034-Barcelona (Spain); Albaiges, Joan, E-mail: albqam@cid.csic.e [Department of Environmental Chemistry, CID-CSIC, Jordi Girona Salgado, 18-26, 08034-Barcelona (Spain)

    2010-05-15

    The distribution of polycyclic aromatic hydrocarbons was determined in surface sediments collected at 36 stations along the Spanish Northern continental shelf in March and September 2003, and February 2005. Concentrations of PAHs (SIGMA13 parent components) were in the range of 22-47528 mug/kg dw, the highest values corresponding to coastal urban-industrial hotspots and decreasing offshore. Sediment quality guidelines (SQGs) showed that concentrations of total PAHs were below the threshold effect level (TEC) in 27 stations (81%) and above in 7, two of which (Gijon and Bilbao) were above the probable effect concentration (PEC). The detailed study of diagnostic ratios suggested a rather uniform mixture of petrogenic and pyrolytic PAH sources along the continental shelf, with a slight decrease of the latter moving westwards and offshore. In order to assess the incidence of sediment sampling on the variability of the results, selected stations were also monitored in February and September 2004 and September 2005. The average field variance of the values obtained for each station was 31% that decreased to 23% when the values were normalized to TOC. - PAHs in the Spanish Atlantic coastal sediments reflect chronic inputs of petrogenic and pyrolytic hydrocarbons, with a decrease of the latter moving westwards and offshore and representing low to moderate pollution according to established sediment quality guidelines.

  12. Origins of Stratal Surfaces in Channel Fills on the New Jersey Continental Shelf

    National Research Council Canada - National Science Library

    Sommerfield, Christopher K

    2006-01-01

    The goal of this project was to advance an understanding of acoustic anomalies created by sub-seafloor paleochannels by investigating the geologic properties of channel-rich strata on the New Jersey continental shelf...

  13. OESbathy version 1.0: a method for reconstructing ocean bathymetry with generalized continental shelf-slope-rise structures

    Science.gov (United States)

    Goswami, A.; Olson, P. L.; Hinnov, L. A.; Gnanadesikan, A.

    2015-09-01

    We present a method for reconstructing global ocean bathymetry that combines a standard plate cooling model for the oceanic lithosphere based on the age of the oceanic crust, global oceanic sediment thicknesses, plus generalized shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to develop a methodology for reconstructing ocean bathymetry in the geologic past that includes heterogeneous continental margins in addition to abyssal ocean floor. First, the plate cooling model is applied to maps of ocean crustal age to calculate depth to basement. To the depth to basement we add an isostatically adjusted, multicomponent sediment layer constrained by sediment thickness in the modern oceans and marginal seas. A three-parameter continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Parameters of the shelf-slope-rise structures at active and passive margins are determined from modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and central Atlantic, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth to basement, ocean bathymetry with an isostatically adjusted multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

  14. Clay sediment accumulation rates on the monsoon-dominated western continental shelf and slope region of India

    Digital Repository Service at National Institute of Oceanography (India)

    Borole, D.V.

    Clay accumulation rates shown in sediment cores from the nearshore to outer continental shelf and slope regions in water depths of 10-1246 m on the western continental margins of India were determined by the 210Pb dating technique. The 210Pb excess...

  15. 75 FR 17156 - Gulf of Mexico, Outer Continental Shelf, Western Planning Area, Oil and Gas Lease Sale 215 (2010...

    Science.gov (United States)

    2010-04-05

    ... environmental assessment (EA) for proposed Gulf of Mexico Outer Continental Shelf (OCS) oil and gas Lease Sale... Environmental Impact Statement; Volumes I and II (Multisale EIS, OCS EIS/EA MMS 2007-018) and in the Gulf of...; Western Planning Area Sales 210, 215, and 218--Final Supplemental Environmental Impact Statement...

  16. The Project for the Extension of the Continental Shelf - the Portuguese experience

    Science.gov (United States)

    Madureira, Pedro; Ribeiro, Luísa P.; Roque, Cristina; Henriques, Guida; Brandão, Filipe; Dias, Frederico; Simões, Maria; Neves, Mariana; Conceição, Patricia; Botelho Leal, Isabel; Emepc, Equipa

    2017-04-01

    Under the United Nations Convention on the Law of the Sea (UNCLOS), the continental shelf is a juridical term used to define a submarine area that extends throughout the natural prolongation of a land territory, where the coastal State exercises sovereign rights for the purpose of exploring it and exploiting its natural resources. Article 76 provides a methodology for determining the outer edge of the continental margin and to delineate the outer limits of the continental shelf. The task of preparing the Portuguese submission to the Commission on the Limits of the Continental Shelf was committed to the Task Group for the Extension of the Continental Shelf (EMEPC), which formally began its activity in January 2005. At that time, the existing national capacity to conduct such a task was very limited in its hydrographic, geological and geophysical components. A great effort has been made by Portugal to overcome these weaknesses and develop a strategy to submit the proposal for the extension of the continental shelf beyond 200 nautical miles on 11th May of 2009. The execution of the project involved the implementation of several complementary strategies including: 1) intensive bathymetric, geophysical and, locally, geological data acquisition; 2) acquisition/development of new stand-alone and ship mounted equipment; 3) interactions with universities and research institutes, with emphasis in R&D initiatives; 4) creation of critical mass in deep-sea research by promoting advanced studies on: International Law, Geophysics, Geology, Hydrography, Biology, amongst others; 5) promotion of the sea as a major national goal, coupled with an outreach strategy. Until now, more than 1050 days of surveying have resulted in a large scale seafloor mapping using two EM120 and one EM710 multibeam echosounders from Kongsberg mounted on two hydrographic vessels. The surveys follow IHO Order 2 Standard (SP44, 5th Edition) and cover an area over 2.6 million km2. A multichannel reflection

  17. Temporal coherence of the acoustic field forward propagated through a continental shelf with random internal waves.

    Science.gov (United States)

    Gong, Zheng; Chen, Tianrun; Ratilal, Purnima; Makris, Nicholas C

    2013-11-01

    An analytical model derived from normal mode theory for the accumulated effects of range-dependent multiple forward scattering is applied to estimate the temporal coherence of the acoustic field forward propagated through a continental-shelf waveguide containing random three-dimensional internal waves. The modeled coherence time scale of narrow band low-frequency acoustic field fluctuations after propagating through a continental-shelf waveguide is shown to decay with a power-law of range to the -1/2 beyond roughly 1 km, decrease with increasing internal wave energy, to be consistent with measured acoustic coherence time scales. The model should provide a useful prediction of the acoustic coherence time scale as a function of internal wave energy in continental-shelf environments. The acoustic coherence time scale is an important parameter in remote sensing applications because it determines (i) the time window within which standard coherent processing such as matched filtering may be conducted, and (ii) the number of statistically independent fluctuations in a given measurement period that determines the variance reduction possible by stationary averaging.

  18. Polycyclic aromatic hydrocarbon concentrations across the Florida Panhandle continental shelf and slope after the BP MC 252 well failure

    International Nuclear Information System (INIS)

    Snyder, Richard A.; Ederington-Hagy, Melissa; Hileman, Fredrick; Moss, Joseph A.; Amick, Lauren; Carruth, Rebecca; Head, Marie; Marks, Joel; Tominack, Sarah; Jeffrey, Wade H.

    2014-01-01

    Graphical abstract: The R/V Bellows, Florida Institute of Oceanography (FIO), with faculty and students from the University of West Florida (UWF), sampling mats of oil floating over the continental shelf south of Pensacola Florida during the BP MC 252 well failure. PAH concentrations in sediments on the shelf declined over time after the well was capped with a half life of ∼200 days. - Highlights: • PAHs concentrations were highest in slope sediments near the failed well site. • PAH concentrations in the shelf sediments were highest during the oil spill. • PAHs concentrations declined over time since the spill. - Abstract: The Florida Panhandle continental shelf environment was exposed to oil from the BP oil well failure in the Gulf of Mexico during 2010. Floating mats of oil were documented by satellite, but the distribution of dissolved components of the oil in this region was unknown. Shipek® grab samples of sediments were taken during repeated cruises between June 2010 and June 2012 to test for selected polycyclic aromatic hydrocarbons (PAHs) as indicators of this contamination. Sediments were collected as composite samples, extracted using standard techniques, and PAHs were quantified by GC/MS-SIM. PAHs in samples from the continental slope in May 2011 were highest near to the failed well site and were reduced in samples taken one year later. PAHs from continental shelf sediments during the spill (June 2010) ranged from 10 to 165 ng g −1 . Subsequent cruises yielded variable and reduced amounts of PAHs across the shelf. The data suggest that PAHs were distributed widely across the shelf, and their subsequent loss to background levels suggests these compounds were of oil spill origin. PAH half-life estimates by regression were 70–122 days for slope and 201 days for shelf stations

  19. Mining of phosphorite resources from the Indian continental shelf will help food production

    Digital Repository Service at National Institute of Oceanography (India)

    Qasim, S.Z.; Nair, R.R.

    of phosphorite deposits would depend on several technical and economic factors Phosphorites occur in water depths upto 200 meters of the western continental shelf of India These are the areas associated with upwelling The relationship between phosphorite deposits...

  20. Biological, physical and chemical properties at the Subtropical Shelf Front Zone in the SW Atlantic Continental Shelf

    Science.gov (United States)

    Muelbert, José H.; Acha, Marcelo; Mianzan, Hermes; Guerrero, Raúl; Reta, Raúl; Braga, Elisabete S.; Garcia, Virginia M. T.; Berasategui, Alejandro; Gomez-Erache, Mónica; Ramírez, Fernando

    2008-07-01

    The physical aspects of the Subtropical Shelf Front (STSF) for the Southwest Atlantic Continental Shelf were previously described. However, only scarce data on the biology of the front is available in the literature. The main goal of this paper is to describe the physical, chemical and biological properties of the STSF found in winter 2003 and summer 2004. A cross-section was established at the historically determined location of the STSF. Nine stations were sampled in winter and seven in summer. Each section included a series of conductivity-temperature-depth (CTD) stations where water samples from selected depths were filtered for nutrient determination. Surface samples were taken for chlorophyll a (Chl- a) determination and plankton net tows carried out above and below the pycnocline. Results revealed that winter was marked by an inner-shelf salinity front and that the STSF was located on the mid-shelf. The low salinity waters in the inner-shelf indicated a strong influence of freshwater, with high silicate (72 μM), suspended matter (45 mg l -1), phosphate (2.70 μM) and low nitrate (1.0 μM) levels. Total dissolved nitrogen was relatively high (22.98 μM), probably due to the elevated levels of organic compound contribution close to the continental margin. Surface Chl -a concentration decreased from coastal well-mixed waters, where values up to 8.0 mg m -3 were registered, to offshore waters. Towards the open ocean, high subsurface nutrients values were observed, probably associated to South Atlantic Central Waters (SACW). Zooplankton and ichthyoplankton abundance followed the same trend; three different groups associated to the inner-, mid- and outer-shelf region were identified. During summer, diluted waters extended over the shelf to join the STSF in the upper layer; the concentration of inorganic nutrients decreased in shallow waters; however, high values were observed between 40 and 60 m and in deep offshore waters. Surface Chl -a ranged 0.07-1.5 mg m -3

  1. Recent foraminiferal assemblages from the continental shelf sediments of Madras, Bay of Bengal

    Digital Repository Service at National Institute of Oceanography (India)

    Setty, M.G.A.P.

    During the 15th cruise of INS Kistna, as part of the International Indian Ocean Expedition, several sub-surface samples were collected, (using LaFond-Dietz snapper), from the continental shelf region of the Bay of Bengal. Samples from two locations...

  2. Atlantic water variability on the SE Greenland continental shelf and its relationship to SST

    Science.gov (United States)

    Sutherland, D. A.; Straneo, F.; Rosing-Asvid, A.; Stenson, G.; Davidson, F. J.; Hammill, M.

    2012-12-01

    Interaction of warm, Atlantic-origin water (AW) and colder, polar origin water (PW) advecting southward in the East Greenland Current (EGC) influences the heat content of water entering Greenland's outlet glacial fjords. Here we use depth and temperature data derived from deep-diving seals to map out water mass variability across the continental shelf and to augment existing bathymetric products. We find two dominant modes in the vertical temperature structure: a cold mode, with the typical AW/PW layering observed in the EGC, and a warm mode, where AW is present throughout the water column. The prevalence of these modes varies seasonally and spatially across the continental shelf, implying distinct AW pathways. In addition, we find that satellite sea surface temperatures (SST) correlate significantly with temperatures in the upper 50 m (R=0.54), but this correlation decreases with depth (R=0.22 at 200 m), and becomes insignificant below 250 m. Thus, care must be taken in using SST as a proxy for heat content, as AW mainly resides in these deeper layers. Regional map showing the location of all seal tracks originating from Canada and Greenland (stars). Tracks passing inside (red) or outside (blue) the SE Greenland region (black) were subdivided into continental shelf regions (green boxes) near Sermilik Fjord (SF), Cape Farewell (CF) and Kangerdlugssuaq Fjord (KG). GEBCO bathymetry is contoured at 200, 1000, 2000, and 3000 m.

  3. Denudation of the continental shelf between Britain and France at the glacial–interglacial timescale

    Science.gov (United States)

    Mellett, Claire L.; Hodgson, David M.; Plater, Andrew J.; Mauz, Barbara; Selby, Ian; Lang, Andreas

    2013-01-01

    The erosional morphology preserved at the sea bed in the eastern English Channel dominantly records denudation of the continental shelf by fluvial processes over multiple glacial–interglacial sea-level cycles rather than by catastrophic flooding through the Straits of Dover during the mid-Quaternary. Here, through the integration of multibeam bathymetry and shallow sub-bottom 2D seismic reflection profiles calibrated with vibrocore records, the first stratigraphic model of erosion and deposition on the eastern English Channel continental shelf is presented. Published Optical Stimulated Luminescence (OSL) and 14C ages were used to chronometrically constrain the stratigraphy and allow correlation of the continental shelf record with major climatic/sea-level periods. Five major erosion surfaces overlain by discrete sediment packages have been identified. The continental shelf in the eastern English Channel preserves a record of processes operating from Marine Isotope Stage (MIS) 6 to MIS 1. Planar and channelised erosion surfaces were formed by fluvial incision during lowstands or relative sea-level fall. The depth and lateral extent of incision was partly conditioned by underlying geology (rock type and tectonic structure), climatic conditions and changes in water and sediment discharge coupled to ice sheet dynamics and the drainage configuration of major rivers in Northwest Europe. Evidence for major erosion during or prior to MIS 6 is preserved. Fluvial sediments of MIS 2 age were identified within the Northern Palaeovalley, providing insights into the scale of erosion by normal fluvial regimes. Seismic and sedimentary facies indicate that deposition predominantly occurred during transgression when accommodation was created in palaeovalleys to allow discrete sediment bodies to form. Sediment reworking over multiple sea-level cycles (Saalian–Eemian–early Weichselian) by fluvial, coastal and marine processes created a multi-lateral, multi-storey succession of

  4. Denudation of the continental shelf between Britain and France at the glacial-interglacial timescale.

    Science.gov (United States)

    Mellett, Claire L; Hodgson, David M; Plater, Andrew J; Mauz, Barbara; Selby, Ian; Lang, Andreas

    2013-12-01

    The erosional morphology preserved at the sea bed in the eastern English Channel dominantly records denudation of the continental shelf by fluvial processes over multiple glacial-interglacial sea-level cycles rather than by catastrophic flooding through the Straits of Dover during the mid-Quaternary. Here, through the integration of multibeam bathymetry and shallow sub-bottom 2D seismic reflection profiles calibrated with vibrocore records, the first stratigraphic model of erosion and deposition on the eastern English Channel continental shelf is presented. Published Optical Stimulated Luminescence (OSL) and 14 C ages were used to chronometrically constrain the stratigraphy and allow correlation of the continental shelf record with major climatic/sea-level periods. Five major erosion surfaces overlain by discrete sediment packages have been identified. The continental shelf in the eastern English Channel preserves a record of processes operating from Marine Isotope Stage (MIS) 6 to MIS 1. Planar and channelised erosion surfaces were formed by fluvial incision during lowstands or relative sea-level fall. The depth and lateral extent of incision was partly conditioned by underlying geology (rock type and tectonic structure), climatic conditions and changes in water and sediment discharge coupled to ice sheet dynamics and the drainage configuration of major rivers in Northwest Europe. Evidence for major erosion during or prior to MIS 6 is preserved. Fluvial sediments of MIS 2 age were identified within the Northern Palaeovalley, providing insights into the scale of erosion by normal fluvial regimes. Seismic and sedimentary facies indicate that deposition predominantly occurred during transgression when accommodation was created in palaeovalleys to allow discrete sediment bodies to form. Sediment reworking over multiple sea-level cycles (Saalian-Eemian-early Weichselian) by fluvial, coastal and marine processes created a multi-lateral, multi-storey succession of

  5. Wind forcing controls on river plume spreading on a tropical continental shelf

    NARCIS (Netherlands)

    Tarya, A.; Vegt, van der M.; Hoitink, A.J.F.

    2015-01-01

    The Berau Continental Shelf is located close to the Equator in the Indonesian Archipelago, hosting a complex of coral reefs along its oceanic edge. The Berau coral reefs have a very high biodiversity, but the area is under serious risk due to river-derived nutrients and sediments. The region is

  6. 78 FR 59263 - Outer Continental Shelf Air Regulations Consistency Update for California

    Science.gov (United States)

    2013-09-26

    ..., Nitrogen dioxide, Nitrogen oxides, Outer continental shelf, Ozone, Particulate matter, Permits, Reporting... Solvents (Adopted 10/23/78) Rule 325 Crude Oil Production and Separation (Adopted 07/19/01) Rule 326... (Adopted 04/17/97) Rule 805 Air Quality Impact Analysis and Modeling (Adopted 04/17/97) Rule 808 New Source...

  7. Flux of energy and essential elements through the continental shelf ecosystem. Progress report, May 31, 1980-May 31, 1981

    Energy Technology Data Exchange (ETDEWEB)

    Pomeroy, L R

    1981-02-01

    There are three distinct areas of research reported, studies of intrusions of the west wall of the Gulf Stream onto the outer continental shelf, studies of the flux of materials across near-shore density fronts, and advances in the understanding of the planktonic food web of the continental shelf. Studies of frontal events on the outer and inner continental shelf involve distinctive physical and chemical regimes and have proven to required distinctive biological approaches. A simulation model of the flux of energy through the continental shelf food web was developed. It represents realistically both details of the energy transfers within the plankton community and the termanal production of fishes. It was discovered that the fecal ribbons of pelagic tunicates break up into flocculent material visually and chemically identical with the flocculent organic aggregates present in sea water. Subsequent experimental work with tunicate fecal matter indicates that some of the naturally occurring aggregates are indeed fecal. This makes it possible to understand and quantify for the first time the production and fate of that population of seston. An examination was made of several of the many roles of dissolved organic compounds in sea water which originate either from release by phytoplankton, digestive processes or metabolites of zooplankton, or extracellular digestion of microorganisms.

  8. A Numerical Study of the Plata River Plume Along the Southeastern South American Continental Shelf

    Science.gov (United States)

    2005-01-01

    the effect of ambient shelf currents, level decreased by -0.20 and -0.55 in at the estuary and which would be essential in the determination of the 142...Res. SI 39, realistic wind and tidal forcing. J. Geophys. Res., 101 (submitted). (C2):3435-3455. Piola, A. R. 2002. El impacto del Plata sobre la...discharge on the continental impactos en el Plata y en la regi6n pampeana. Vol. 1. shelf. 1. Modeling the river plume and the inner shelf Assoc. Bonaerense de

  9. Polycyclic aromatic hydrocarbons (PAHs) in continental shelf sediment of China: Implications for anthropogenic influences on coastal marine environment

    International Nuclear Information System (INIS)

    Liu Liangying; Wang Jizhong; Wei Gaoling; Guan Yufeng; Zeng, Eddy Y.

    2012-01-01

    Sediments collected from the continental shelf of China, embracing Yellow Sea, inner shelf of the East China Sea (ECS), and the South China Sea (SCS), were analyzed for polycyclic aromatic hydrocarbons (PAHs). The concentrations of anthropogenic PAHs (Σ 18 PAH) were 27–224 ng/g dry weight, with an average of 82 ng/g. Sedimentary PAHs in the continental shelf off China were mainly derived from mixed residues of biomass, coal, and petroleum combustion. Fluvial transport and atmospheric deposition mainly accounted for sediment PAHs in the ECS inner shelf and Yellow Sea (and the SCS), respectively. Furthermore, statistically higher levels of Σ 18 PAH (28–224 ng/g; mean 110 ng/g) in the Yellow Sea sediment than in the SCS sediment (28–109 ng/g; mean 58 ng/g) were probably resulted from higher PAH emissions from coke industry and domestic coal combustion in North China than in South China. - Highlights: ► Coal and biomass combustion was the main origin of PAHs in coastal marine sediment of China. ► Fluvial transport was the main mode for transporting PAHs to the East China Sea inner shelf. ► Atmospheric deposition largely accounted for sediment PAHs in Yellow Sea and the South China Sea. ► Regional energy use pattern in China was responsible for the spatial distribution of PAHs in coastal marine sediment. - Sources, compositions and spatial distributions of PAHs in continental shelf sediments off China are analyzed to estimate anthropogenic influences.

  10. OESbathy version 1.0: a method for reconstructing ocean bathymetry with realistic continental shelf-slope-rise structures

    Science.gov (United States)

    Goswami, A.; Olson, P. L.; Hinnov, L. A.; Gnanadesikan, A.

    2015-04-01

    We present a method for reconstructing global ocean bathymetry that uses a plate cooling model for the oceanic lithosphere, the age distribution of the oceanic crust, global oceanic sediment thicknesses, plus shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to reconstruct realistic ocean bathymetry based on parameterized relationships of present-day variables that can be applied to global oceans in the geologic past, and to isolate locations where anomalous processes such as mantle convection may affect bathymetry. Parameters of the plate cooling model are combined with ocean crustal age to calculate depth-to-basement. To the depth-to-basement we add an isostatically adjusted, multicomponent sediment layer, constrained by sediment thickness in the modern oceans and marginal seas. A continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Shelf-slope-rise structures at active and passive margins are parameterized using modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and Central Atlantic Ocean, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth-to-basement, ocean bathymetry with an isostatically adjusted, multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

  11. Very large dune formation along the Ebro outer continental shelf (Western Mediterranean)

    Science.gov (United States)

    Lo Iacono, Claudio; Guillén, Jorge; Puig, Pere; Ribó, Marta; Ballesteros, Maria; Palanques, Albert; Farrán, Marcelli; Acosta, Juan

    2010-05-01

    Large and very large subaqueous dunes have been observed in a number of outer shelf regions around the world, tipically developing on fossil sand bodies and ridges. Dunes observed on outer shelves usually display large dimensions with maximum wavelength reaching up to 500 m and heights up to 20 m. Forcing mechanisms able to induce their formation have been described as strong bottom currents related to tidal variations and water masses flowing under geostrophic conditions, generally controlled and enhanced by local geomorphologic configurations. In this study, such bed features have been recognized, mapped and measured around the Columbretes Islands (Ebro continental shelf - Western Mediterranean) with the aim to reconstruct which are the potential forcing processes that could generate them in relation to the local settings of the area. Swath-bathymetry around the Columbretes Islands was collected using 30 kHz and 180 kHz Multi Beam echo-sounders for a 50-400 m water depth range. Bathymetric data revealed the presence of three main relict sand bodies along the outer shelf, for a 80-116 m depth range, above which asymmetrical, slightly asymmetrical and symmetrical large and very large 2D and 3D subaqueous dunes were observed. Dunes range from 150 to 760 m in wavelength and from tens of cm to 6 m in height. These bedforms are composed of sandy sediments, presumably coming from the degraded relict sand bodies on which they developed, mixed to the fine fractions coming from the recent draping holocenic sediments. The orientation of the dunes is SSW and progressively turns to W directions moving towards the southernmost sector of the area, following the trend of the shelf-edge. Observed dunes display a strong asymmetric profile for those occurring along the shelf-edge (Symmetry Index (SI): 2.6) and lose progressively their asymmetry towards the inner portion of the shelf (SI: 0.5), being 0.6 the minimum SI value to classify the dunes as asymmetric. The subaqueous dunes

  12. Biodiversity hotspots on the Dutch Continental Shelf: a marine strategy framework directive perspective

    NARCIS (Netherlands)

    Bos, O.G.; Witbaard, R.; Lavaleye, M.S.S.; Moorsel, G.W.N.M.; Teal, L.R.; Hal, van R.; Hammen, van der T.; Hofstede, ter R.; Bemmelen, van R.S.A.; Witte, R.H.; Geelhoed, S.C.V.; Dijkman, E.M.

    2011-01-01

    This report presenst hotspots of biodiversity for benthos, fish, birds, marine mammals and habitats on the Dutch Continental Shelf. These hotspots are based on a spatial application of biodiversity metrics developed in this study for the GES(Good Environmental Status)-descriptor 1 ‘Biological

  13. Atlantic update, July 1986--June 1990: Outer Continental Shelf oil and gas activities

    Energy Technology Data Exchange (ETDEWEB)

    Karpas, R.M.; Gould, G.J.

    1990-10-01

    This report describes outer continental shelf oil and gas activities in the Atlantic Region. This edition of the Atlantic Update includes an overview of the Mid-Atlantic Planning Area and a summary of the Manteo Prospect off-shore North Carolina. 6 figs., 8 tabs.

  14. Dissolved inorganic nutrients and chlorophyll on the narrow continental shelf of Eastern Brazil

    Directory of Open Access Journals (Sweden)

    Gilmara Fernandes Eça

    2014-03-01

    Full Text Available The eastern Brazilian continental shelf is narrow and subject to the influence of a western boundary current system, presenting lower biological productivity than other regions. In this study, the distribution of water masses, dissolved inorganic nutrients, chlorophyll-a and total suspended solids (TSS on the inner shelf (< 35 m depth, between Itacaré and Canavieiras, eastern Brazil, is presented. Sampling surveys were carried out in March and August 2006 and March 2007. Tropical water (TW prevailed during March 2006 and August 2007 with the lower salinity waters (< 36 found in most samples taken in March 2007, reflecting the influence of continental outflow and rain in coastal waters. Low concentrations of dissolved inorganic nutrients and Chl-a found were typical of TW and results suggested that the inner shelf waters were depleted in dissolved inorganic nitrogen in August 2006 and March 2007, and in phosphate in March 2006, potentially affecting phytoplankton growth. Stratification of the water column was observed due to differences in dissolved nutrient concentrations, chlorophyll-a and TSS when comparing surface and bottom samples, possibly the result of a colder water intrusion and mixing on the bottom shelf and a deep chlorophyll maximum and/or sediment resuspension effect. Despite this stratification, oceanographic processes such as lateral mixing driven by the Brazil Current as well as a northward alongshore drift driven by winds and tides transporting Coastal Water can lead to an enhanced mixing of these waters promoting some heterogeneity in this oligotrophic environment.

  15. Sources of organic carbon in the Portuguese continental shelf sediments during the Holocene period

    International Nuclear Information System (INIS)

    Burdloff, D.; Araujo, M.F.; Jouanneau, J.-M.; Mendes, I.; Monge Soares, A.M.; Dias, J.M.A.

    2008-01-01

    Organic C (OC) and total N (TN) concentrations, and stable isotope ratios (δ 13 C) in muddy deposit sediments of the Northern and Southern Portuguese continental shelf were used to identify sources of fine-sized organic matter ( 13 C ranging, respectively, from 8.5 to 21 and from -22.4 per mille to -27 per mille ). Intense supplies to the Guadiana continental shelf of fine terrigenous particles during the Younger-Dryas Event are closely linked with higher OC/TN values and lower δ 13 C ratios. During the postglacial transgression phase, an increasing contribution of marine supplies (up to 80%) occurred. Higher δ 13 C (up to -22.4 per mille ) values and low OC/TN ratios (down to 8.5) are found as the sea level approaches the current one. The Upper Holocene records emphasize the return to enhanced terrestrial supplies except for the Little Climatic Optimum between the 11th and 15th centuries AD. This climatic event is especially obvious in the three cores as a return to marine production and a decrease in terrestrial sediment supply to the continental shelf. The return to a cooling event, the Little Ice Age, between the 15th and 19th centuries AD, is mirrored by decreased terrigenous supplies in core KSGX 57. Gradually increasing sedimentation in estuaries, as well as formation of coastal dune fields, have been hypothesized on the basis of increasing δ 13 C and decreasing OC, TN and OC/TN values

  16. Aeromagnetic and gravity investigations of the Coastal Area and Continental Shelf of Liberia, West Africa, and their relation to continental drift

    Science.gov (United States)

    Behrendt, John C.; Wotorson, Cletus S.

    1970-01-01

    An aeromagnetic survey has shown the existence of several basins in which magnetic basement depths are greater than 5 km on the continental shelf off Liberia. Magnetic diabase of 176 to 192 m.y. (Jurassic) in age intruding the Paleozoic (?) rocks and overlain by younger rocks onshore requires the distinction between “magnetic basement” and “basement.” Several lines of evidence suggest that the Paleozoic(?) rocks are less than 1 km thick; this implies that the diabase does not introduce a large error in depth-to-basement estimates. The dikes or their extrusive equivalents are traceable, on the basis of the magnetic data, beneath the younger sedimentary rock in the basins to the edge of the continental slope. The magnetic data also delineate a second zone of diabase dikes 90 km inland, parallel to the coast, which cross the entire country. The intrusion of the younger dikes probably coincides with rifting at the beginning of the separation of Africa and South America, and the associated magnetic anomaly zones appear to be parallel with and continuous into the anomaly bands in the Atlantic. A major northeast-trending break in the magnetic fabric intersects the coast near 9° W. and is associated with Eburnean age rocks (about 2000 m.y.) to the southeast as contrasted with Liberian-age rocks (about 2700 m.y.) to the northwest. Change in magnetic fabric direction inland from northeast to northwest in the coastal area allows recognition of a boundary between the Liberian-age rocks inland and Pan-African-age (about 550 m.y.) rocks in the coastal area northwest of about 9° 20'W. Sets of north-northwest-and west-northwest—trending faults of 1 to 2 km vertical displacement cut the Cretaceous sedimentary rocks onshore and can be traced into the offshore basins. Vertical displacements of several kilometers in the magnetic basement underlying the continental shelf suggest a pattern of block faulting all along the coast and continental shelf. Negative Bouguer

  17. Surveying the Alentejo continental shelf for minerals and Quaternary environmental changes: preliminary results of the MINEPLAT project survey

    Science.gov (United States)

    Noiva, João; Ribeiro, Carlos; Terrinha, Pedro; Brito, Pedro; Neres, Marta

    2017-04-01

    The tectonic uplift of South Portugal in the last 5 Million years (My) was firstly identified on the basis of morphologic criteria by Mariano Feio (1952, "The evolution of the relief of Baixo Alentejo and Algarve", transl.). However, the assessment of continental vertical movements off Portugal and its relation with tectonics was only initiated in the 1990-ies. This work was carried out in the framework of FP6 and FP7 in the domains of Natural Hazards funded by the European Community. The swath bathymetry cartography of the southwest part of the Iberian Peninsula resulted from the effort of European and national projects, of 19 oceanographic surveys, a total of 200 ship time days executed from 2000 to 2006, involving 14 research institutions from 7 European countries. As a result of this effort together with acquisition and interpretation of thousands of km of seismic reflection profiles, the Pliocene-Quaternary uplift of the Alentejo continental margin (SW Portugal) is now widely accepted by the scientific community. This uplift has not been yet quantified but it is possible that can have contributed to erosion and deposition of metallic ores as placers in the continental shelf. This argues in favor of the potential existence of placers in the continental shelf and the need for the detailed investigation that will allow determination of ideal location for placers deposition in the past Pliocene-Quaternary (5 My). The source for metals can arguably be associated to the Iberian Pyrite Belt ores hosted in the Alentejo Paleozoic formations and to the hyper-alkaline intrusions of Sines and Monchique of Late Cretaceous age. Artificial renourishment of beaches with offshore sand has not been assessed for the Alentejo littoral, despite that the coast located to the south of the Sines segment shows high susceptibility to erosion. This has been observed on a regular basis as the beaches are frequently devoid of sand, thus jeopardizing their touristic potential. The detailed

  18. Minimum distribution of subsea ice-bearing permafrost on the US Beaufort Sea continental shelf

    Science.gov (United States)

    Brothers, Laura L.; Hart, Patrick E.; Ruppel, Carolyn D.

    2012-01-01

    Starting in Late Pleistocene time (~19 ka), sea level rise inundated coastal zones worldwide. On some parts of the present-day circum-Arctic continental shelf, this led to flooding and thawing of formerly subaerial permafrost and probable dissociation of associated gas hydrates. Relict permafrost has never been systematically mapped along the 700-km-long U.S. Beaufort Sea continental shelf and is often assumed to extend to ~120 m water depth, the approximate amount of sea level rise since the Late Pleistocene. Here, 5,000 km of multichannel seismic (MCS) data acquired between 1977 and 1992 were examined for high-velocity (>2.3 km s−1) refractions consistent with ice-bearing, coarse-grained sediments. Permafrost refractions were identified along sea ice-bearing permafrost, which does not extend seaward of 30 km offshore or beyond the 20 m isobath.

  19. Considerations about the recommendations of the Commission on the Limits of the Continental Shelf on the Amazon fan

    Directory of Open Access Journals (Sweden)

    Rodrigo Fernandes More

    2014-01-01

    Full Text Available In 2004, Brazil submitted to the Commission on the Limits of the Continental Shelf (CLCS a Submission for the outer limit of the Brazilian continental shelf for its extension beyond the limits of 200 nautical miles. In 2007, the CLCS presented its recommendations, however it did not recommend four areas proposed by Brazil, the Amazon Fan among them. The objective of this study is to present the main legal and technical aspects of the controversy about the Amazon Fan, in order to evaluate some alternatives for a future submission, new or revised.

  20. Production development on the Norwegian continental shelf; KonKraft rapport 2

    Energy Technology Data Exchange (ETDEWEB)

    2008-07-01

    After almost 40 years of virtually uninterrupted growth, total hydrocarbon production on the Norwegian continental shelf (NCS) has reached its highest level ever, with a daily output of 4-4.5 million barrels of oil equivalent per day. It is expected to remain at this level for the next 7 years. After 2015 or thereabouts, however, total oil and gas production is forecast to start declining. Oil production is already falling. Gas output has been increasing, but this is not expected to continue offsetting the drop in liquid production beyond 2015 or thereabouts if no action is taken. Only half the combined oil and gas resources predicted by the Norwegian Petroleum Directorate (NPD) will have been produced in 2015. Remaining recoverable resources, including those expected to be found by further exploration, are currently estimated to be 38-77 billion barrels of oil equivalent (boe). This estimate could be 25-65 billion boe in 2015. Only 40 per cent of the total expected remaining hydrocarbon resources remains to be discovered today, which explains the wide range in the estimates. This huge potential must be managed well to avoid a sharp decline in production and to support a healthy level of long-term investment. The report on production development on the Norwegian continental shelf is published at a time when major changes are taking place both inside and outside the petroleum industry. Several factors make a review of what can be done to address the production decline particularly urgent. Although the current level of activity in the Norwegian petroleum sector is high, assessing the long-term perspectives for the industry is very important. In many cases, the period between the award of licences and the start of production can be 15 years or more. Decisions taken now may have important implications for levels of production and activity in the 2020s. (Author)

  1. Marine magnetic anomalies over the Direction bank, off Bombay western continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    SubbaRaju, L.V.; Subrahmanyam, V.

    Total magnetic intensity data were collected over the Direction Bank, off Bombay on the western continental shelf of India and the isomagnetic anomaly map prepared at a contour interval of 25nT show NNW-SSE trend resemble those of the Dharwarians...

  2. Polycyclic aromatic hydrocarbons (PAHs) in continental shelf sediment of China: implications for anthropogenic influences on coastal marine environment.

    Science.gov (United States)

    Liu, Liang-Ying; Wang, Ji-Zhong; Wei, Gao-Ling; Guan, Yu-Feng; Zeng, Eddy Y

    2012-08-01

    Sediments collected from the continental shelf of China, embracing Yellow Sea, inner shelf of the East China Sea (ECS), and the South China Sea (SCS), were analyzed for polycyclic aromatic hydrocarbons (PAHs). The concentrations of anthropogenic PAHs (Σ(18)PAH) were 27-224 ng/g dry weight, with an average of 82 ng/g. Sedimentary PAHs in the continental shelf off China were mainly derived from mixed residues of biomass, coal, and petroleum combustion. Fluvial transport and atmospheric deposition mainly accounted for sediment PAHs in the ECS inner shelf and Yellow Sea (and the SCS), respectively. Furthermore, statistically higher levels of Σ(18)PAH (28-224 ng/g; mean 110 ng/g) in the Yellow Sea sediment than in the SCS sediment (28-109 ng/g; mean 58 ng/g) were probably resulted from higher PAH emissions from coke industry and domestic coal combustion in North China than in South China. Copyright © 2012 Elsevier Ltd. All rights reserved.

  3. Gas hydrates:estimation of the gas potential, from reflection seismic data in the continental shelf of Uruguay

    International Nuclear Information System (INIS)

    De Santa Ana, H.; Ucha, N.; Gutierrez, L.; Veroslavsky, G.

    2004-01-01

    The uruguayan continental shelf shows geophysical indicators of gas hydrates in the Oriental del Plata, Pelotas and Punta del Este basin. The aim of this work is to present the potential presence of gas at the continental shelf in Uruguay and to evaluate the possibility of exploration of unconventional hydrocarbon plays. Analysis of the seismic surface based on regional and stratgigraphic information that proceeded from previous hydrocarbon exploration in the area have been used to estimatge resources of gas hydrates. Gas hydrates accumulation was mapped using characteristic reflectors and amplitude anomalies of seismic lines (BSR). Its quantity was estimated on this basis in about 86 TCF.

  4. Use of Geological, Geophysical and Geomorphological Information as support for the harmonization of the legal limits of the continental shelf between Brazil and Uruguay

    International Nuclear Information System (INIS)

    Torres, L.; Villena, H.

    2010-01-01

    The United Nations Convention of the Law of the Sea (UNCLOS) establishes the juridical and legal frameworks which the Coastal States (C S) establish their respective outer limit of the continental shelf in which will exercise sovereignty rights under the resources in the on the seabed and seabed subsurface. The base to reach the delineation of continental shelf outer limit is ruled by the application the criteria which take into consideration mainly data and pieces of information from Geology, Geophysics and Geomorphology employed both lonely or conjunction. In the current presentation were employed both data carried out by Brazilian Continental Shelf Project (Laplace) and data from public domain. As the underwater features do not follow political limits, the goal of this proposal work is to present the integration of both data and pieces of information from geological, geophysical and geomorphologic characteristics in order to reach the harmonization of the Brazil and Uruguay continental shelf outer limit nearby their Maritime Lateral Boundary

  5. Combined use of Nassarius reticulatus imposex and statolith age determination for tracking temporal evolution of TBT pollution in the NW Portuguese continental shelf.

    Science.gov (United States)

    Barroso, Carlos M; Rato, Milene; Veríssimo, Alfredo; Sousa, Ana; Santos, José António; Coelho, Sónia; Gaspar, Miguel B; Maia, Francisco; Galante-Oliveira, Susana

    2011-11-01

    Spatial and temporal trends of tributyltin (TBT) pollution on the northern continental shelf of Portugal (5-34 m depth) were assessed using Nassarius reticulatus as a bioindicator. Imposex levels were determined in 2006 and 2010, and integrated with age readings from statoliths for a better chronological analysis of the data. Females affected with imposex were detected in 84% of the sites surveyed in 2006, with levels higher than the Ecological Quality Objective (EcoQO) set by the OSPAR Commission for N. reticulatus (VDSI TBT water contamination in 2010 may in fact be lower than that extrapolated from the imposex levels. We conclude that the legislation was indeed very effective in reducing TBT pollution in the NW Portuguese continental shelf, not only in terms of the magnitude but also in terms of fast field repercussion.

  6. Impact of the oil price and fiscal facilities on offshore mining at the Dutch Continental Shelf

    International Nuclear Information System (INIS)

    Cate, Arie ten; Mulder, Machiel

    2007-01-01

    The surge in the oil price has raised questions about the magnitude of global reserves of oil. According to some analysts, the current high oil prices indicate a looming decline in the global production of oil. Others believe, however, that the increased level of the oil price encourages exploration and production activities, bringing the oil price to a lower equilibrium level in the near future. In this paper, we assess the impact of the unit profit (depending on the oil price) as well as fiscal facilities on the level of exploration and development drillings in the Dutch Continental Shelf. We conducted an econometric analysis of exploration and development drillings in the Dutch Continental Shelf over the period 1981-2003. Except a few fiscal changes, the regulatory framework for offshore activities in the Netherlands, the so-called 'small fields policy' was unchanged in this period. We find that the expected unit profit based on a moving average of the oil price significantly explains the level of both exploration and development drillings. In addition, the analysis suggests that fiscal facilities have only a temporary effect on exploration activities but are more important for development activities. We conclude that the oil price is a major economic incentive for activities of the mining industry

  7. 77 FR 10707 - Safety Zone; NOBLE DISCOVERER, Outer Continental Shelf Drillship, Chukchi and Beaufort Seas, Alaska

    Science.gov (United States)

    2012-02-23

    ... indigenous population; (4) the lack of any established shipping fairways, fueling and supply storage... location of the DRILLSHIP NOBLE DISCOVERER on the Outer Continental Shelf and its distance from both land...

  8. Oil, gas potential in shallow water: Peru`s continental shelf basins

    Energy Technology Data Exchange (ETDEWEB)

    Zuniga-Rivero, F.; Keeling, J.A.; Hay-Roe, H. [BPZ and Associates Inc., Houston, TX (United States)

    1998-11-16

    This third article of a series highlights the three sedimentary basins that underlie the 16 million acres of continental shelf adjacent to a 650-mile stretch of Peruvian coastline. This area lies roughly between the ports of Chiclayo and Pisco. These basins offer a variety of reservoirs, traps, and source-rock potential in water depths of less than 1,000 ft. They are characterized by a thick sequence of Neogene strata, underlain by Paleogene, Mesozoic, and Upper Paleozoic sediments down to as much as 7 sec two-way time on modern seismic records. In some places the sedimentary section may reach an aggregate thickness in excess of 50,000 ft. From north to south these contiguous shelf basins are the Sechura-Salaverry, Huacho, and Pisco basins. All three basins are described.

  9. Archive of Geosample Data and Information from the U.S. Extended Continental Shelf (ECS) Project.

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Geological samples collected as part of the U.S. Extended Continental Shelf (ECS) Project are curated by the U.S. Geological Survey, a partner in the ECS Project. To...

  10. Cruise report; RV Coastal Surveyor Cruise C1-99; multibeam mapping of the Long Beach, California continental shelf; April 12 through May 19, 1999

    Science.gov (United States)

    Gardner, James V.; Hughes-Clarke, John E.; Mayer, Larry A.

    1999-01-01

    The greater Los Angeles area of California is home to more than 10 million people. This large population puts increased pressure on the adjacent offshore continental shelf and margin with activities such as ocean disposal for dredged spoils, explosive disposal, waste-water outfall, and commercial fishing. The increased utilization of the shelf and margin in this area has generated accelerated multi-disciplinary research efforts in all aspects of the environment of the coastal zone. Prior to 1996 there were no highly accurate base maps of the continental shelf and slope upon which the research activities could be located and monitored. In 1996, the United States Geological Survey (USGS) Pacific Seafloor Mapping Project began to address this problem by mapping the Santa Monica shelf and margin (Fig. 1) using a state-of-the-art, high-resolution multibeam sonar system (Gardner, et al., 1996; 1999). Additional seafloor mapping in 1998 provided coverage of the continental margin from south of Newport to the proximal San Pedro Basin northwest of Palos Verdes Peninsula (Gardner, et al., 1998) (Fig. 1). The mapping of the seafloor in the greater Los Angeles continental shelf and margin was completed with a 30-day mapping of the Long Beach shelf in April and May 1999, the subject of this report. The objective of Cruise C-1-99-SC was to completely map the broad continental shelf from the eastern end of the Palos Verdes Peninsula to the narrow shelf south of Newport Beach, from the break in slope at about 120-m isobath to the inner shelf at about the 10-m isobath. Mapping the Long Beach shelf was jointly funded by the U.S. Geological Survey and the County of Orange (CA) Sanitation District and was conducted under a Cooperative Agreement with the Ocean Mapping Group from the University of New Brunswick (OMG/UNB). The OMG/UNB contracted with C&C Technologies, Inc. of Lafayette, LA for use of the RV Coastal Surveyor and the latest evolution of high-resolution multibeam sonars, a

  11. New approaches to cost reduction on the UK continental shelf

    Energy Technology Data Exchange (ETDEWEB)

    Curtis, M I

    1994-12-31

    The conference paper deals with cost reduction on the UK continental shelf. New approaches on the reduction of field development costs are compared with the cases if traditional approaches had been followed. Field developments where success in aligning the goals and objectives of the contractors and owners which led to projects being delivered on time but more than 20% below budget, are exemplified. The contractors in the alliance received 55% of the savings in addition to their normal profit. The procedure to follow in such cases, is discussed

  12. New approaches to cost reduction on the UK continental shelf

    International Nuclear Information System (INIS)

    Curtis, M.I.

    1994-01-01

    The conference paper deals with cost reduction on the UK continental shelf. New approaches on the reduction of field development costs are compared with the cases if traditional approaches had been followed. Field developments where success in aligning the goals and objectives of the contractors and owners which led to projects being delivered on time but more than 20% below budget, are exemplified. The contractors in the alliance received 55% of the savings in addition to their normal profit. The procedure to follow in such cases, is discussed

  13. Clay mineral distribution in the continental shelf and slope off Saurashtra, West coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.

    Clay mineral distribution in the sediments of the west coast of India indicates that the illite and chlorite-rich sediments, derived from the Indus, occupy the continental shelf of the northern part of the Gulf of Kutch. Montmorillonite derived from...

  14. Environmental studies results: 1973-1992. Atlantic Outer Continental Shelf. Final report

    International Nuclear Information System (INIS)

    Wilson, J.M.

    1992-01-01

    The Outer Continental Shelf (OCS) Environmental Studies Program was initiated in 1973 under the Bureau of Land Management by the Secretary of the Interior. The Purpose of the program was to conduct studies needed to predict, assess and manage impacts on the human, marine and coastal environments of the OCS and nearshore areas that may be affected by oil and gas activities. The narrative summary updates the version printed in 1986, which covered studies managed by the MMS in the Atlantic OCS region between 1973 and 1985. Descriptions of the study results are divided into the following categories: baseline studies and environmental inventories, biology/ecology, drill site monitoring, endangered species, geology/chemistry, oil spill studies, physical oceanography/meteorology, and social and economic studies. Results of each major type of study are subdivided into North Atlantic, Mid-Atlantic, South Atlantic, and multiregional studies in chronological sequence

  15. 77 FR 24734 - Outer Continental Shelf (OCS) Renewable Energy Program Leasing for Marine Hydrokinetic Technology...

    Science.gov (United States)

    2012-04-25

    ... DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management [Docket No. BOEM-2012-0011] Outer Continental Shelf (OCS) Renewable Energy Program Leasing for Marine Hydrokinetic Technology Testing Offshore Florida AGENCY: Bureau of Ocean Energy Management, Interior. ACTION: Notice of the Availability of an...

  16. Gas-charged sediments on the inner continental shelf off western India

    Digital Repository Service at National Institute of Oceanography (India)

    Karisiddaiah, S.M.; Veerayya, M.; Vora, K.H.; Wagle, B.G.

    the enormous reserves of methane hydrates in the Arctic (Nisbet, 1989) and elsewhere. Owens et al. (1991) observed that the northern Arabian Sea is an oceanic region of unusually high methane concentrations and fluxes to the atmo- sphere. In view... The western continental shelf of India between IO°N and 22°N is bordered by the Deccan Traps (volcanic rocks) of Cretaceous age towards the north of Goa, whereas Peninsular gneisses, char- nockites and various schistose formations of Archaean age...

  17. Spatiotemporal chlorophyll-a dynamics on the Louisiana continental shelf derived from a dual satellite imagery algorithm

    Science.gov (United States)

    A monthly time series of remotely sensed chlorophyll-a (Chlars) over the Louisiana continental shelf (LCS) was developed and examined for its relationship to river discharge, nitrate concentration, total phosphorus concentration, photosynthetically available radiation (PAR), wind...

  18. Regional tectonic trends on the inner continental shelf off Konkan and central west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Ramana, M.V.

    Satellite imagery and offshore magnetic data were analysed to correlate regional tectonic elements on the inner continental shelf off Konkan and the adjacent Deccan plateau. Three statistically important lineament trends N-S, WNW-ESE and ENE...

  19. Transport and transfer rates in the waters of the continental shelf. Annual report

    International Nuclear Information System (INIS)

    Biscaye, P.E.

    1980-09-01

    The goal of govern project is to understand and quantify the processes that the transport and dispersal of energy-related pollutants introduced to the waters of the continental shelf and slope. The report is divided into sections dealing with processes associated with suspended solids; processes associated with sediments sinks for radionuclides and other pollutants; and spreading of water characteristics and species in solution

  20. Sources, extent and history of methane seepage on the continental shelf off northern Norway

    Science.gov (United States)

    Sauer, Simone; Lepland, Aivo; Chand, Shyam; Schubert, Carsten J.; Eichinger, Florian; Knies, Jochen

    2014-05-01

    Active natural hydrocarbon gas seepage was recently discovered in the Hola area on the continental shelf off Vesterålen, northern Norway. We conducted acoustic and geochemical investigations to assess the modern and past extent, source and pathways of the gas seepage . Water column echosounder surveys showed bubble plumes up to several tens of metres above the seafloor. Analyses of dissolved methane in the water column indicated slightly elevated concentrations (50 nM) close to the seafloor. To identify fluxes and origin of methane in the sediments we analysed sediment pore water chemistry, the isotopic composition of methane and of dissolved inorganic carbon (d13CCH4, d2HCH4, d13CDIC) in three closely spaced (

  1. Data Management Supporting the U.S. Extended Continental Shelf Project

    Science.gov (United States)

    Lim, E.; Henderson, J. F.; Warnken, R.; McLean, S. J.; Varner, J. D.; Mcquinn, E.; LaRocque, J.

    2013-12-01

    The U.S. Extended Continental Shelf (ECS) Project is a multi-agency collaboration led by the U.S. Department of State whose mission is to establish the full extent of the continental shelf of the United States consistent with international law. Since 2003, the U.S. has been actively collecting bathymetric, seismic, and other geophysical data and geologic samples required to delineate its outer limits in accordance with Article 76 of the UN Convention on the Law of the Sea. In 2007, the U.S. ECS Task Force designated the National Geophysical Data Center (NGDC) to serve as both the Data Management lead and the Data Archive and Integration Center for the U.S. ECS Project. NGDC, one of three National Oceanic and Atmospheric Administration (NOAA) Offices active in the ECS Project, has the primary responsibility to provide a common infrastructure and a means to integrate the data supporting, and products resulting from ECS analysis. One of the key challenges in the ECS project is the requirement to track the provenance of data and derived products. Final ECS analyses may result in hundreds of points that define a new maritime boundary that is our extended continental shelf. These points will be developed in a rigorous process of analysis encompassing potentially thousands of raw datasets and derived products. NGDC has spent the past two years planning, designing, and partially implementing the Information Management System (IMS), a highly functional, interactive software system that serves as the master database for the ECS Project. The purpose of this geospatial database is to archive, access, and manage the primary data, derivative data and products, associated metadata, information and decisions that will form the U.S. submission. The IMS enables team members to manage ECS data in a consistent way while maintaining institutional memory and the rationale behind decisions. The IMS contains two major components: First, a catalog that acts as the interface to the IMS by

  2. Accident statistics for fixed offshore units on the UK Continental Shelf 1980-2001

    International Nuclear Information System (INIS)

    Funnemark, E.; Young, E.

    2003-01-01

    Comprehensive statistics for the accidents and incidents on fixed units engaged in oil and gas exploration/exploitation on the UK continental shelf between 1980 and 2001 have been assembled from other databases. The data includes nature of the incident, type of unit involved, geographical area and time period. The results cover a total of 5,563 events which are described as accidents, hazardous situations or near misses

  3. Seasonal evolution of the nutrient pattern on Biscay Bay continental shelf over the years 1999-2000

    Directory of Open Access Journals (Sweden)

    Sophie Loyer

    2006-03-01

    Full Text Available The French Atlantic shelf is subjected to strong anthropic influences (urban, industrial and agricultural discharges of two main rivers (Loire and Gironde. The extension and consequences of these continental loadings for the nutrient and chlorophyll distribution have never been studied before on the Bay of Biscay continental shelf as a whole. We present the first synoptic view of the nutrient distribution and evolution on the French Atlantic shelf. Nutrient concentrations of the surface layer were studied during four cruises in April, June, September 1999 and March 2000. Until June, the freshwater inputs induce a nitrate gradient from river mouths to offshore waters in the vicinity of the 100 m isobath. The Redfield’s ratio study highlights the nitrate excess in river loadings. The early spring situation is characterised by high N:P ratios in front of the two estuaries and by a potential Si-limitation in the northern part. Nitrate removal continues in spite of the P-limitation and the increase in silicate concentrations during summer supposes high regeneration processes. At the end of summer, the water column is thermally stratified and the surface mixed layer is totally depleted in nitrate.

  4. Carbon and oxygen dynamics on the Louisiana continental shelf: role of water column primary production and respiration

    Science.gov (United States)

    We conducted a multi-year study of the Louisiana continental shelf (LCS) to better understand the linkages between water column net metabolism and the formation of hypoxia (dissolved oxygen respiration (R) and primary p...

  5. Net Heterotrophy in the Amazon Continental Shelf Changes Rapidly to a Sink of CO2 in the Outer Amazon Plume

    Directory of Open Access Journals (Sweden)

    Nathalie Lefèvre

    2017-09-01

    Full Text Available The Amazon continental shelf and adjacent oceanic area were sampled for inorganic and organic carbon parameters in order to improve data coverage and understanding of carbon cycling dynamics within this important region. Seasonal coverage of the Amazon plume on the French Guiana continental shelf further north, was provided by CO2 monitoring using a merchant ship sailing from France to French Guiana (2006–2016. Salinity ranged from 1 to 36 (transects in April 2013, and May 2014. At salinity below 10, strong outgassing was observed with fugacity of CO2 (fCO2 over 2,000 μatm. This region displayed net heterotrophy, fueled by organic matter with terrestrial origin, as shown by δ13C and δ15N values of suspended particles. A δ13C cross shelf average of −31% was measured during May 2014, contrasting with oceanic values in excess of −20%. The reactivity of this terrestrial material resulted in the local production of dissolved inorganic and organic carbon as well as fluorescent humic compounds. Further offshore, the dilution of freshwater by ocean waters created a sink for CO2, enhanced by biological activity. The strongest CO2 drawdowns, associated with high chlorophyll a concentrations, were observed on the French Guiana continental shelf in the outer Amazon plume, with fCO2 values below 150 μatm. Here, a CO2 sink was present almost throughout the year, with a seasonal maximum of −9.2 mmol CO2 m−2d−1 observed in June 2015. However, both the CO2 and salinity distributions could vary significantly within a few days, confirming the presence of many eddies in this region. The Amazon continental shelf hence behaved as a transition zone between an inshore source of CO2 to the atmosphere and an offshore sink. Some marine phytoplankton production was detected but occurred mainly close to the French Guiana shelf. A mean net CO2 outgassing of 44 ± 43.6 mmol m−2d−1 was estimated for the area. Quantifying the CO2 flux for the entire Amazon

  6. 76 FR 38294 - Oil and Gas and Sulphur Operations in the Outer Continental Shelf-Civil Penalties

    Science.gov (United States)

    2011-06-30

    ... affect in a material way the economy, productivity, competition, jobs, the environment, public health or... DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management, Regulation and Enforcement 30 CFR... Outer Continental Shelf--Civil Penalties AGENCY: Bureau of Ocean Energy Management, Regulation and...

  7. P-wave velocity models of continental shelf of East Siberian Sea using the Laplace-domain full waveform inversion

    Science.gov (United States)

    Kang, S. G.; Hong, J. K.; Jin, Y. K.; Jang, U.; Niessen, F.; Baranov, B.

    2017-12-01

    2016 IBRV ARAON Arctic Cruise Leg-2, Expedition ARA07C was a multidisciplinary undertaking carried out in the East Siberian Sea (ESS) from August 25 to September 10, 2016. The program was conducted as a collaboration between the Korea Polar Research Institute (KOPRI), P.P. Shirshov Institute of Oceanology (IORAS), and Alfred Wegener Institute (AWI). During this expedition, the multi-channel seismic (MCS) data were acquired on the continental shelf and the upper slope of the ESS, totaling 3 lines with 660 line-kilometers. The continental shelf of ESS is one of the widest shelf seas in the world and it is believed to cover the largest area of sub-sea permafrost in the Arctic. According to the present knowledge of the glacial history of the western Arctic Ocean, it is likely that during the LGM with a sea level approximately 120 m below present, the entire shelf area of the ESS was exposed to very cold air temperatures so that thick permafrost should have formed. Indeed, in water depths shallower than 80 m, sub-bottom profiles in the ESS recorded from the shelf edge to a latitude of 74°30' N in 60 m water depth exhibited acoustic facies, suggesting that at least relicts of submarine permafrost are present. In order to identify the existence and/or non-existence of subsea permafrost in our study area, we analyze the MCS data using the Laplace domain full waveform inversion (FWI). In case of the Canadian continental shelf of the Beaufort Sea, subsea permafrost has high seismic velocity values (over 2.6 km/sec) and strong refraction events were found in the MCS shotgathers. However, in the EES our proposed P-wave velocity models derived from FWI have neither found high velocity structures (over 2.6 km/sec) nor indicate strong refraction events by subsea permafrost. Instead, in 300 m depth below sea floor higher P-wave velocity structures (1.8 2.2 km/s) than normal subsea sediment layers were found, which are interpreted as cemented strata by glaciation activities.

  8. Adequacy of environmental information for outer continental shelf oil and gas decisions: Georges Bank. Final report

    International Nuclear Information System (INIS)

    1991-01-01

    Georges Bank, a large, shallow marine bank with important fishery resources and possibly important oil and gas resources, lies east of Massachusetts in the territorial waters of both the United States and Canada. The Department of the Interior has planned since 1974 to lease parts of the north Atlantic outer continental shelf (OCS)--including part of Georges Bank--for oil and gas exploration. As a result of public concern about the environmental impacts of oil and gas production on the U.S. OCS, Congress declared a moratorium on drilling on Georges Bank and an area to the southwest. The report--by the NRC's Committee to Review the Outer Continental Shelf Environmental Studies Program and its panels on physical oceanography, ecology, and socioeconomics--reviews the adequacy of information bearing on the potential environmental impacts of OCS oil and gas activities for the Georges Bank sale area

  9. Plankton community respiration, net ecosystem metabolism, and oxygen dynamics on the Louisiana continental shelf: implications for hypoxia

    Science.gov (United States)

    We conducted a multi-year study of the Louisiana continental shelf (LCS) to better understand the linkages between water column metabolism and the formation of hypoxia (dissolved oxygen respiration rates (WR) were measured on 10 cr...

  10. 76 FR 14681 - Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore Massachusetts...

    Science.gov (United States)

    2011-03-17

    ... No. BOEM-2010-0063] Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore..., Regulation and Enforcement (BOEMRE), Interior. ACTION: Request for Interest (RFI) in Commercial Wind Energy... (BOEMRE) is reopening the comment period on the RFI in Commercial Wind Energy Leasing Offshore...

  11. 78 FR 36571 - North American Datum of 1983 (NAD 83) Outer Continental Shelf (OCS) Provisional Official...

    Science.gov (United States)

    2013-06-18

    ... DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management [MMAA104000] North American Datum of 1983 (NAD 83) Outer Continental Shelf (OCS) Provisional Official Protraction Diagram (OPDs) AGENCY... OPDs. SUMMARY: Notice is hereby given that effective with this publication two NAD 83-based OCS...

  12. Assessment of resource selection models to predict occurrence of five juvenile flatfish species (Pleuronectidae) over the continental shelf in the western Gulf of Alaska

    Science.gov (United States)

    Wilson, Matthew T.; Mier, Kathryn L.; Cooper, Dan W.

    2016-05-01

    According to the nursery size hypothesis, flatfish recruitment is constrained by nursery area. Thus, if resource selection models can be shown to accurately predict the location and geographic extent of flatfish nursery areas, they will become important tools in the management and study of flatfish population dynamics. We demonstrate that some resource selection models derived previously to predict the presence and absence of juvenile flatfishes near shore were applicable to the broader continental shelf. For other age-species groups, derivation of new models for the continental shelf was necessary. Our study was conducted in the western Gulf of Alaska (GoA) during October 2011 on four groups of age-0 juvenile flatfishes: Pacific halibut (Hippoglossus stenolepis), arrowtooth flounder (Atheresthes stomias), northern rock sole (Lepidopsetta polyxystra), and flathead sole (Hippoglossoides elassodon); and three groups of age-1 juvenile flatfishes: northern rock sole, flathead sole, and yellowfin sole (Limanda aspera). Sampling occurred at 33 sites across the continental shelf. Fish were collected using a 3-m beam trawl, and a midwater trawl. Environmental data were collected on sediment composition and water temperature and depth. Many of the age-species groups co-occurred in the Shumagin and Barnabus sea valleys; however, age-0 arrowtooth flounder occurred at more locations than other juveniles, perhaps due to a relatively broad tolerance of environmental conditions and to the utilization of midwater habitat. Thus, the large nursery area of arrowtooth flounder may be one reason why they are currently the most abundant GoA flatfish. In fact, among all species, mean recruitment at age 3 increased with the percent occurrence of age-0 juveniles at the 33 sites, a proxy for relative nursery area, in accordance with the nursery size hypothesis, suggesting that mean recruitment among GoA flatfishes is structured by nursery size.

  13. The NSW Steam Trawl Fishery on the South-East Continental Shelf of Australia, 1915–1961

    DEFF Research Database (Denmark)

    Lund Jacobsen, A. Lif

    2014-01-01

    How was modern fishing methods, in the form of steam trawling, introduced in Australia? And what were the consequences for the fish stocks found on the South-East Continental Shelf? Through historical catch records and archival resources, the history of the NSW Steam Trawl Industry from 1915...

  14. The continental shelf benthic ecosystem: Current status, agents for change and future prospects

    OpenAIRE

    Hall, S.J.

    2002-01-01

    Metadata only record Continental shelf benthic ecosystems play an important role in the economy of many coastal states through the provision of food, non-living resources and through control of climate. Changes in the status of these ecosystems, through either natural or human-induced environmental drivers can be expected to have important economic and social consequences. Agents that could induce change include climate and oceanography, hydrology (river discharge), land-use and waste disp...

  15. Amazon water lenses and the influence of the North Brazil Current on the continental shelf

    Science.gov (United States)

    Prestes, Yuri O.; Silva, Alex Costa da; Jeandel, Catherine

    2018-05-01

    The exchange processes on the Amazon continental shelf in northern Brazil are subject to complex interactions that involve forcings derived from distinct sources. The Amazon shelf is a unique and highly dynamic environment in which considerable discharge of freshwater enters the Atlantic Ocean, producing extensive Amazon Water Lenses (AWL). In addition to the presence of the AWL, the shelf is influenced by the semidiurnal oscillations of the tides and the strong North Brazil Current (NBC), a boundary current of the western Atlantic. The present study was based primarily on the influence of the freshwater input and the NBC on the shelf and the Amazon Shelf Break (ASB) off the mouth of the Pará River. For this purpose, hydrographic and hydrodynamic data were obtained by moorings of the AMANDES Project (April-July 2008), located on the Amazon shelf and the ASB. Spectral analysis and the continuous wavelet transform were applied to define tidal (high frequency/short period) and subtidal (low frequency/long period) signals. The results indicated that on both the shelf and the break, the semidiurnal tides are responsible for the residual landward transport and are predominantly across-shelf. Low-frequency motions in the synoptic bands and the AWL are related to spatial changes in the velocity field, mainly on the ASB in the along-shelf direction. The flow of the NBC can be interpreted as an along-shelf low-frequency oscillation capable of altering the spatial configuration of the velocity field, although its influence is perceived only in the absence of the AWL.

  16. Increased marine production of N sub(2)O due to intensifying anoxia on the Indian continental shelf

    Digital Repository Service at National Institute of Oceanography (India)

    Naqvi, S.W; Jayakumar, D.A.; Narvekar, P.V.; Naik, H.; Sarma, V.V.S.S; DeSouza, W; Joseph, S; George, M.D.

    . The intensification of one of the largest low-oxygen zones in the ocean, which develops naturally over the western Indian continental shelf during late summer and autumn is reported here. The highest accumulations yet observed of hydrogen sulphide (H sub(2)S...

  17. Nepheloid Layers: Origin and Development In A Narrow Continental Shelf (nw Portugal)

    Science.gov (United States)

    Oliveira, A.; Vitorino, J.; Rodrigues, A.; Jouanneau, J. M.; Weber, O.; Dias, J. A.

    A general hydrographic, nephelometric and sedimentological surveying of the NW Portuguese continental shelf and slope was undertaken, under winter and spring con- ditions in order to elaborate a conceptual model of suspended sediments (nepheloid layer) dynamics. Two major situations were found: 1) Spring/Summer - with northerly winds (upwelling) and low energetic wave regime that favour the deposition of sedi- ments. The northerly winds promote offshore transport in the surface nepheloid layer (SNL) and the establishment of a seasonal thermocline allow the expansion of the SNL to the west. The SNL can reach or even cross the shelf-break (50 km from coastline). Particulate organic carbon (POC) content in this layer highlights the higher contribution of biogenic particles (average concentration of 22%); 2) Winter, with southerly winds (downwelling) and high energetic wave regime that favour mid- shelf sediments resuspension and offshore transport in the bottom nepheloid layer (BNL). In the shelf-break the BNL detached to form intermediate nepheloid layers (INL). The SNL is restricted to the inner shelf. The effect of southerly winds gener- ates shoreward Ekman transport and detains the offshore westward extension of this layer even during high river run-off periods. The POC content indicates a dominance of litogenic particles in suspension (average concentration of 8%). Over the mid- and inner-shelf the dominant resuspension mechanism is associated with surface waves (Vitorino et al., 2002). Estimates based on wave measurements at mid-shelf (86m depth) suggested that, in winter, the wave shear velocity frequently exceeds 1 cm/s, assumed as the critical shear velocity for the resuspension of the fine grained sedi- ments (34m) of the bottom cover. Storm events, such as the one observed in November 1996 easily increase the wave shear velocities over 3 cm/s, leading to the increase of the BNL thickness (20-30m) (Vitorino et al., 2002; Oliveira et al., 2002). Low

  18. Potential alternative energy technologies on the Outer Continental Shelf.

    Energy Technology Data Exchange (ETDEWEB)

    Elcock, D.; Environmental Assessment

    2007-04-20

    This technical memorandum (TM) describes the technology requirements for three alternative energy technologies for which pilot and/or commercial projects on the U.S. Outer Continental Shelf (OCS) are likely to be proposed within the next five to seven years. For each of the alternative technologies--wind, wave, and ocean current--the TM first presents an overview. After each technology-specific overview, it describes the technology requirements for four development phases: site monitoring and testing, construction, operation, and decommissioning. For each phase, the report covers the following topics (where data are available): facility description, electricity generated, ocean area (surface and bottom) occupied, resource requirements, emissions and noise sources, hazardous materials stored or used, transportation requirements, and accident potential. Where appropriate, the TM distinguishes between pilot-scale (or demonstration-scale) facilities and commercial-scale facilities.

  19. Seismic evidence for the preservation of several stacked Pleistocene coastal barrier/lagoon systems on the Gulf of Valencia continental shelf (western Mediterranean)

    Science.gov (United States)

    Albarracín, Silvia; Alcántara-Carrió, Javier; Barranco, Andrés; Sánchez García, María José; Fontán Bouzas, Ángela; Rey Salgado, Jorge

    2013-04-01

    The focus of this study is the analysis of coastal sand barriers and associated coastal lagoons on the inner continental shelf of the Gulf of Valencia (western Mediterranean), based on two W-E seismic profiles recorded seaward of the Albufera de Valencia coastal lagoon. Seismic facies identified include a number of coastal sand barriers with landward lagoons draped by contemporary continental shelf deposits. The barrier systems have been grouped into two sedimentary systems tracts, the older one corresponding to a prograding/aggrading highstand systems tract involving at least four paleo-coastal sand barrier/lagoon systems, followed landward by a transgressive systems tract comprising three such systems. All the systems have been allocated a Tyrrhenian age, the formation of individual barrier systems having been associated with successive sea-level stillstands, and their present-day position being explained by the very high regional subsidence rate. In summary, this study demonstrates that the Quaternary stratigraphic record of the Gulf of Valencia inner continental shelf is composed of littoral sand facies, in particular coastal sand barrier and lagoon deposits. These findings are in agreement with corresponding observations on other continental shelves of the western Mediterranean, showing that the formation of coastal sand barriers was a characteristic feature of this region during the Quaternary.

  20. 76 FR 20367 - Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Off Delaware...

    Science.gov (United States)

    2011-04-12

    ... No. BOEM-2011-0008] Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Off... determination that no competitive interest exists in acquiring a commercial wind lease in the area offshore... a Request for Interest (RFI) in the Federal Register on April 26, 2010 (75 FR 21653). Bluewater Wind...

  1. The potential for satellite and marginal field developments on the Norwegian continental shelf

    International Nuclear Information System (INIS)

    Raustein, O.; Abrahamsen, L.E.; Einang, G.

    1994-01-01

    Norway is faced with decreasing field sizes in hostile waters. On the other hand, approximately 620 billion 1993-NOK have been invested in field installations and transport systems. These installations will have significant available processing and transport capacity in the future, and thus represent a valuable infrastructure. This paper describes the resource situation and the installed infrastructure on the Norwegian Continental Shelf. Then the potential of still maintaining a high activity level in field developments is outlined

  2. 77 FR 40081 - Gulf of Mexico, Outer Continental Shelf (OCS), Western Planning Area (WPA) and Central Planning...

    Science.gov (United States)

    2012-07-06

    ... DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management Gulf of Mexico, Outer Continental Shelf (OCS), Western Planning Area (WPA) and Central Planning Area (CPA), Oil and Gas Lease Sales for 2012-2017 AGENCY: Bureau of Ocean Energy Management (BOEM), Interior. ACTION: Notice of availability...

  3. Impact of Satellite Remote Sensing Data on Simulations of Coastal Circulation and Hypoxia on the Louisiana Continental Shelf

    Science.gov (United States)

    We estimated surface salinity flux and solar penetration from satellite data, and performed model simulations to examine the impact of including the satellite estimates on temperature, salinity, and dissolved oxygen distributions on the Louisiana continental shelf (LCS) near the ...

  4. Mineral Resource Assessment of Marine Sand Resources in Cape- and Ridge-Associated Marine Sand Deposits in Three Tracts, New York and New Jersey, United States Atlantic Continental Shelf

    Science.gov (United States)

    Bliss, James D.; Williams, S. Jeffress; Arsenault, Matthew A.

    2009-01-01

    Demand is growing in the United States and worldwide for information about the geology of offshore continental shelf regions, the character of the seafloor, and sediments comprising the seafloor and subbottom. Interest in locating sand bodies or high quality deposits that have potential as sources for beach nourishment and ecosystem restoration is especially great in some regions of the country. The Atlantic coast, particularly New York and New Jersey, has been the focus of these studies for the past 40 years with widely varying results. This study is the first attempt at applying probability statistics to modeling Holocene-age cape-and ridge-associated sand deposits and thus focuses on distinct sand body morphology. This modeling technique may have application for other continental shelf regions that have similar geologic character and late Quaternary sea-level transgression history. An estimated volume of 3.9 billion m3 of marine sand resources is predicted in the cape-and ridge-associated marine sand deposits in three representative regions or tracts on the continental shelf offshore of New York and New Jersey. These estimates are taken from probabilistic distributions of sand resources and are produced using deposit models and Monte Carlo Simulation (MCS) techniques. The estimated sand resources presented here are for only three tracts as described below and for Holocene age sand resources contained in cape-and ridge-associated marine sand deposit types within this area. Other areas may qualify as tracts for this deposit type and other deposit types and geologic ages (for example, paleo-stream channels, blanket and outwash deposits, ebb-tide shoals, and lower sea level-stand deltas), which are present on the New Jersey and New York continental shelf area but are not delineated and modeled in this initial evaluation. Admittedly, only a portion of these probable sand resources will ultimately be available and suitable for production, dependent largely on

  5. Suspended particulate layers and internal waves over the southern Monterey Bay continental shelf: an important control on shelf mud belts?

    Science.gov (United States)

    Cheriton, Olivia M.; McPhee-Shaw, Erika E.; Shaw, William J.; Stanton, Timothy P.; Bellingham, James G.; Storlazzi, Curt D.

    2014-01-01

    Physical and optical measurements taken over the mud belt on the southern continental shelf of Monterey Bay, California documented the frequent occurrence of suspended particulate matter features, the majority of which were detached from the seafloor, centered 9–33 m above the bed. In fall 2011, an automated profiling mooring and fixed instrumentation, including a thermistor chain and upward-looking acoustic Doppler current profiler, were deployed at 70 m depth for 5 weeks, and from 12 to 16 October a long-range autonomous underwater vehicle performed across-shelf transects. Individual SPM events were uncorrelated with local bed shear stress caused by surface waves and bottom currents. Nearly half of all observed SPM layers occurred during 1 week of the study, 9–16 October 2011, and were advected past the fixed profiling mooring by the onshore phase of semidiurnal internal tide bottom currents. At the start of the 9–16 October period, we observed intense near-bed vertical velocities capable of lifting particulates into the middle of the water column. This “updraft” event appears to have been associated with nonlinear adjustment of high-amplitude internal tides over the mid and outer shelf. These findings suggest that nonlinear internal tidal motions can erode material over the outer shelf and that, once suspended, this SPM can then be transported shoreward to the middle and shallow sections of the mud belt. This represents a fundamental broadening of our understanding of how shelf mud belts may be built up and sustained.

  6. Trophic Ecology and Movement Patters of Tiger Sharks (Galeocerdo Cuvier) off the Western North Atlantic Coastal and Continental Shelf Waters

    Science.gov (United States)

    Sancho, G.; Edman, R.; Frazier, B.; Bubley, W.

    2016-02-01

    Understanding the trophic dynamics and habitat utilization of apex predators is central to inferring their influence on different marine landscapes and to help design effective management plans for these animals. Tiger sharks (Galeocerdo cuvier) are abundant in shelf and offshore Gulf Stream waters of the western North Atlantic Ocean, and based on movements from individuals captured in Florida and Bahamas, seem to avoid coastal and shelf waters off South Carolina and Georgia. This contradicts reports of tiger sharks regularly being caught nearshore by anglers in these states, indicating that separate sub-populations may exist in the western North Atlantic. In the present study we captured Tiger Sharks in coastal waters off South Carolina in 2014 and 2015 in order to describe their movement patterns through acoustic and satellite tagging, and trophic dynamics through stable isotope analyses. Movement data show that these tiger sharks repeatedly visit particular inshore areas and mainly travel over the continental shelf, but rarely venture offshore beyond the continental shelf edge. Ongoing C and N stable isotope analyses of muscle, blood and skin tissues from adult and juvenile tiger sharks, as well as from potential prey species and primary producers, will help determine if their diets are based on inshore, shelf or offshore based food webs. Tiger sharks exploiting nearshore environments and shelf waters have much higher probabilities of interacting with humans than individuals occupying far offshore Gulf Stream habitats.

  7. On the occurrence of caliche pisolites from the western continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.

    leader for his interest and for valuable suggestions which improved the manuscript. Thanks are due to Mr. V.S. Raja Raman for his assistance. References Aristarain, L.F., 1970. Chemical analysis of caliche profiles from the High Plains, New Mexico... limestones and associated sediments from the western continental shelf of India. Mar. Geol., 95: 17-29. Reeves, C.C., 1970. Origin classification and geologic history of caliche on the southern High plains, Texas and eastern New Mexico. J. Geol., 78: 352...

  8. Detection of introduced sessile species on the near shore continental shelf in southern Brazil

    Directory of Open Access Journals (Sweden)

    Janaína de Araújo Bumbeer

    2012-04-01

    Full Text Available Invasion by marine species, often considered a grave threat to marine ecosystems, occurs throughout the world as a consequence of many anthropogenic activities. In coastal Paraná, many factors including shipping, aquaculture and the use of artificial substrates provide suitable environments for the establishment and rapid spread of introduced marine species. To better understand this process, the encrusting community was studied on polyethylene plates (n = 120, 10 x 10 cm that were placed seasonally at fixed locations on the inner continental shelf to detect non-native species. Of the 62 taxa found, 40 were identified to species, 14 of which were native, 9 introduced and 17 cryptogenic. We found a new introduction while most introduced species were previously reported at a nearby estuary with an international port. Possible complementary explanations for these detections are 1 estuaries influence ecological processes on the inner continental shelf, 2 the study area is near the route of cargo and other ships entering the port, 3 other local vectors, such as hulls of fishing and recreational boats, and artificial reefs link the estuary to the offshore areas. Thus, not only are estuaries invaded by exotic species, but also non-indigenous marine species may be present in the open sea where they are likely to colonize artificial substrates.

  9. Seismic reflection and vibracoring studies of the continental shelf offshore central and western Long Island, New York

    Science.gov (United States)

    Kelly, W.M.; Albanese, J.R.; Coch, N.K.; Harsch, A.A.

    1999-01-01

    The ridge-and-swale topography on the continental shelf south of Fire Island, New York, is characterized by northeast-trending linear shoals that are shore attached and shore oblique on the inner shelf and isolated and shore parallel on the middle shelf. High-resolution seismic reflection profiles show that the ridges and swales occur independent of, and are not controlled by, the presence of internal structures (for example, filled tidal inlet channels, paleobarrier strata) or underlying structure (for example, high-relief Cretaceous unconformity). Grab samples of surficial sediments on the shelf south of Fire Island average 98% sand. Locally, benthic fauna increase silt and clay content through fecal pellet production or increase the content of gravel-size material by contribution of their fragmented shell remains. Surficial sand on the ridges is unimodal at 0.33 mm (medium sand, about 50 mesh), and surficial sand in troughs is bimodal at 0.33 mm and 0.15 mm (fine sand, about 100 mesh). In addition to seismic studies, 26 vibracores were recovered from the continental shelf in state and federal waters from south of Rockaway and Long Beaches, Long Island, New York. Stratigraphic and sedimentological data gleaned from these cores were used to outline the geologic framework in the study area. A variety of sedimentary features were noted in the cores, including burrow-mottled sections of sand in a finer silty-sand, rhythmic lamination of sand and silty-sand that reflect cyclic changes in sediment transport, layers of shell hash and shells that probably represent tempestites, and changes from dark color to light color in the sediments that probably represent changes in the oxidation-reduction conditions in the area with time. The stratigraphic units identified are an upper, generally oxidized, nearshore facies, an underlying fine- to medium-sand and silty-clay unit considered to be an estuarine facies, and a lower, coarse-grained deeply oxidized, cross-laminated pre

  10. Contribution to atmospheric methane by natural seepages on the Bulgarian continental shelf

    Energy Technology Data Exchange (ETDEWEB)

    Dimitrov, L. [Bulgarian Academy of Science, Varna (Bulgaria). Inst. of Oceanology

    2002-07-01

    This paper provides an estimation of the atmospheric methane flux from Bulgarian Black Sea continental shelf. Potential gas source rocks include Holocene gas-charged sediments, Quaternary peats and sapropels, and deep-lying Palaeocene and Neogene clays, Cretaceous coals, and other sediments of late Jurassic to early Cretaceous age. These cover almost the whole continental shelf and slope and, together with irregularly developed seal rocks and widespread active and conducting faults, provide good conditions for upward gas migration. A total of 5 100 line kilometers of shallow seismic (boomer) and echo-sounder records acquired during the Institute of Oceanology's regional surveys, and several detailed side-scan sonar lines, have been reviewed for water column targets. Four hundred and eighty-two targets were assigned as gas seepage plumes. It is estimated that a total of 19,735 individual seeps exists on the open shelf. The number of seeps in coastal waters was estimated to be 6020; this is based on available public-domain data, specific research, and results of a specially made questionnaire which was distributed to a range of 'seamen'. More than 150 measurements of the seabed flux rates were made in the 'Golden sands' and 'Zelenka' seepage areas between 1976 and 1991. Indirect estimations of flux rates from video and photo materials, and a review of published data have also been undertaken. Based on these data, three types of seepages were identified as the most representative of Bulgarian coastal waters. These have flux rates of 0.4, 1.8, and 3.51/min. The contribution to atmospheric methane is calculated by multiplying the flux rates with the number of seepages, and entering corrections for methane concentration and the survival of gas bubbles as they ascend through seawater of the corresponding water depth. The estimation indicates that between 45,100,000 (0.03 Tg) and 210,650,000 m{sup 3} (0. 15 Tg) methane yr{sup -1} come

  11. 78 FR 8190 - Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore North Carolina...

    Science.gov (United States)

    2013-02-05

    ...] Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore North Carolina--Call for... Commercial Leasing for Wind Power Offshore North Carolina (Call), published on December 13, 2012 (77 FR 7204). DATES: BOEM must receive your nomination describing your interest in obtaining a commercial wind lease...

  12. The Impact of Internal Wave Seasonality on the Continental Shelf Energy Budget

    Science.gov (United States)

    Wihsgott, Juliane U.; Sharples, Jonathan; Hopkins, Joanne; Palmer, Matthew R.; Mattias Green, J. A.

    2017-04-01

    Heating-stirring models are widely used to simulate the timing and strength of stratification in continental shelf environments. Such models are based on bulk potential energy (PE) budgets: the loss of PE due to thermal stratification is balanced by wind and tidal mixing. The model often fails to accurately predict the observed vertical structure, as it only considers forces acting on the surface and bottom boundary of the water column. This highlights the need for additional internal energy sources to close this budget, and produce an accurate seasonal cycle of stratification. We present new results that test the impact of boundary layer and internal wave forcing on stratification and vertical density structure in continental shelves. A new series of continuous measurements of full water depth vertical structure, dynamics and meteorological data spanning 17 months (March'14-July'15) provide unprecedented coverage over a full seasonal cycle at a station 120 km north-east from the continental shelf break. We observe a highly variable but energetic internal wave field from the onset of stratification that suggests a continuous supply of internal PE. The heating-stirring model reproduces bulk characteristics of the seasonal cycle. While it accurately predicts the timing of the onset in spring and peak stratification in late summer there is a persistent 20 J m-3 positive offset between the model and observations throughout this period. By including a source of internal energy in the model we improve the prediction for the strength of stratification and the vertical distribution of heat. Yet a constant source of PE seems to result in a seasonal discrepancy resulting in too little mixing during strong stratification and too much mixing during transient periods. The discrepancy seen in the model is consistent with the seasonality observed in the internal wave field. We will establish the role that changing stratification (N2) exerts on the internal wave field and vice

  13. Statistics of Acoustic Pulse Signals Through Nonlinear Internal Waves on the Continental Shelf of the Northeastern South China Sea

    National Research Council Canada - National Science Library

    Reeves, Justin M

    2008-01-01

    ...) was conducted from 13 - 15 April 2005 on the continental shelf in the northeast portion of the South China Sea to study the effects of nonlinear internal waves on the transmission of a 400-Hz signal...

  14. Physical (Hydrography), chemical (CTD), and biological (Water Quality) processes of the Texas-Louisiana continental shelf, 2013 (NCEI Accession 0162440)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Two sets of CTD data were taken during the 2013 Shelfwide Hypoxia cruise off the Louisiana continental shelf. Hydrographic data were obtained with the LUMCON SeaBird...

  15. Gravity anomalies over a segment of Pratap ridge and adjoining shelf margin basin, western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Subrahmanyam, V.; Rao, D.G.; Ramprasad, T.; KameshRaju, K.A.; Rao, M.G.

    Bathymetric and gravity data totalling 2000 line km on the continental margin off Goa and Mulki, west of India have been studied. The free-air gravity anomalies vary between -60 to 25 mgals with prominent NNW-SSE trends in the outer shelf region...

  16. 76 FR 50245 - Gulf of Mexico (GOM), Outer Continental Shelf (OCS), Western Planning Area (WPA), Oil and Gas...

    Science.gov (United States)

    2011-08-12

    ... (BOEMRE), Interior. ACTION: Notice of Availability (NOA) of a Final Supplemental Environmental Impact... sale's incremental contribution to the cumulative impacts on environmental and socioeconomic resources... Mexico (GOM), Outer Continental Shelf (OCS), Western Planning Area (WPA), Oil and Gas Lease Sale for the...

  17. Impacts of Outer Continental Shelf (OCS) development on recreation and tourism. Volume 5. Program logic manual

    Energy Technology Data Exchange (ETDEWEB)

    1987-04-01

    The final report for the project is presented in five volumes. This volume is the Programmer's Manual. It covers: a system overview, attractiveness component of gravity model, trip-distribution component of gravity model, economic-effects model, and the consumer-surplus model. The project sought to determine the impact of Outer Continental Shelf development on recreation and tourism.

  18. Heavy minerals in the sediments on the outer continental shelf between Vengurla and Mangalore on the west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Kidwai, R.M.; Nair, R.R.; Hashimi, N.H.

    Fifty-eight sediment samples from the outer continental shelf between Vengurla and Mangalore were analysed for heavy minerals consist of principally opaques, hornblende, epidote, garnet, sillimanite, hypersthene and zircon, with minor amounts...

  19. 77 FR 47877 - Potential Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore Maine...

    Science.gov (United States)

    2012-08-10

    ... Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore Maine; Request for Interest... Request for a Commercial OCS Wind Lease, Request for Interest, and Request for Public Comment SUMMARY: The... (Statoil NA) to acquire an OCS wind lease; (2) solicit public input regarding the proposal, its potential...

  20. Seafloor classification using artificial neural network architecture from central western continental shelf of India

    Science.gov (United States)

    Mahale, Vasudev; Chakraborty, Bishwajit; Navelkar, Gajanan S.; Prabhu Desai, R. G.

    2005-04-01

    Seafloor classification studies are carried out at the central western continental shelf of India employing two frequency normal incidence single beam echo-sounder backscatter data. Echo waveform data from different seafloor sediment areas are utilized for present study. Three artificial neural network (ANN) architectures, e.g., Self-Organization Feature Maps (SOFM), Multi-Layer Perceptron (MLP), and Learning Vector Quantization (LVQ) are applied for seafloor classifications. In case of MLP, features are extracted from the received echo signal, on the basis of which, classification is carried out. In the case of the SOFM, a simple moving average echo waveform pre-processing technique is found to yield excellent classification results. Finally, LVQ, which is known as ANN of hybrid architecture is found to be the efficient seafloor classifier especially from the point of view of the real-time application. The simultaneously acquired sediment sample, multi-beam bathymetry and side scan sonar and echo waveform based seafloor classifications results are indicative of the depositional (inner shelf), non-depositional or erosion (outer shelf) environment and combination of both in the transition zone. [Work supported by DIT.

  1. Clay mineral distribution in the continental shelf sediments from Krishna to Ganges river mouth, east coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.

    Ninety six sediment samples (less than 2 mu m fractions) of the eastern continental shelf of India between Ganges in the north and Krishna in the south have been studiEd. by X-ray diffraction. On the basis of nature and abundance of different clay...

  2. Investigation of the shelf break and continental slope in the Western part of the Black Sea using acoustic methods

    Science.gov (United States)

    Dutu, F.; Ion, G.; Jugaru Tiron, L.

    2009-04-01

    The Black Sea is a large marginal sea surrounded by a system of Alpine orogenic chains, including the Balkanides-Pontides, Caucasus, Crimea and North Dobrogea located to the south, northeast, north and northwest, respectively (Dinu et al., 2005). The north-western part of the Black Sea is the main depocentre for sediment supply from Central Europe via the Danube River, but also from Eastern Europe through the Ukrainian rivers Dniepr, Dniestr and Southern Bug (Popescu et al., 2004). The shelfbreak is located at water depths of 120-140 m southward of the Danube Canyon, and up to 170 m northward of the canyon possibly due to recent faulting which is very common in this area. The continental slope is dissected by numerous canyons, each of which is fed by several tributaries. The Danube Canyon (also known as Viteaz Canyon) is a large shelf-indenting canyon located in the north-western Black Sea and connected to the youngest channel-levee system of the Danube Fan (Popescu et al., 2004). The acoustic methods are a useful way for investigate the shelf break and the continental slope giving us information about landslides on the continental slope, the topography of the investigated area, the sedimentary zones affected by instability and to quantify the geometry of the underwater landslides. The measurements made on the continental slope from north-western part of the Black Sea gave us the possibility to make a digital terrain model. After processing the data the model offer information about the main access ways of the sediments through gravitational slide on the submarines canyons, with forming of turbidity currents, debris flows and also other transport/transformation phenomena of the sediments on the continental slope like submarine landslides and submarine collapse. References Dinu, C., Wong, H.K., Tambrea, D., Matenco, L., 2005. Stratigraphic and structural characteristics of the Romanian Black Sea shelf. Tectonophysics 410, 417-435. Popescu, I., Lericolais, G., Panin

  3. Pacific Continental Shelf Environmental Assessment (PaCSEA): aerial seabird and marine mammal surveys off northern California, Oregon, and Washington, 2011-2012

    Science.gov (United States)

    Adams, Josh; Felis, Jonathan J.; Mason, John W.; Takekawa, John Y.

    2014-01-01

    Marine birds and mammals comprise an important community of meso- and upper-trophic-level predators within the northern California Current System (NCCS). The NCCS is located within one of the world’s four major eastern boundary currents and is characterized by an abundant and diverse marine ecosystem fuelled seasonally by wind-driven upwelling which supplies nutrient-rich water to abundant phytoplankton inhabiting the surface euphotic zone. The oceanographic conditions throughout the NCCS fluctuate according to well-described seasonal, inter-annual, and decadal cycles. Such oceanographic variability can influence patterns in the distribution, abundance, and habitat use among marine birds and mammals. Although there are an increasing number of studies documenting distributions and abundances among birds and mammals in various portions of the NCCS, there have been no comprehensive, large-scale, multi-seasonal surveys completed throughout this region since the early 1980s (off northern California; Briggs et al. 1987) and early 1990s (off Oregon and Washington; Bonnell et al. 1992, Briggs et al. 1992, Green et al. 1992). During 2011 and 2012, we completed the Pacific Continental Shelf Environmental Assessment (PaCSEA) which included replicated surveys over the continental shelfslope from shore to the 2000-meter (m) isobath along 32 broad-scale transects from Fort Bragg, California (39° N) through Grays Harbor, Washington (47° N). Additionally, surveys at a finer scale were conducted over the continental shelf within six designated Focal Areas: Fort Bragg, CA; Eureka, CA; Siltcoos Bank, OR; Newport, OR; Nehalem Bank, OR; and Grays Harbor, WA. We completed a total of 26,752 km of standardized, low-elevation aerial survey effort across three bathymetric domains: inner-shelf waters ( Overall, we recorded 15,403 sightings of 59,466 individual marine birds (12 families, 54 species). During winter, seven species groupings comprised >90% of the total number of birds

  4. Production development on the Norwegian continental shelf; KonKraft rapport 2; Produksjonsutviklingen paa norsk sokkel

    Energy Technology Data Exchange (ETDEWEB)

    2008-07-01

    After almost 40 years of virtually uninterrupted growth, total hydrocarbon production on the Norwegian continental shelf (NCS) has reached its highest level ever, with a daily output of 4-4.5 million barrels of oil equivalent per day. It is expected to remain at this level for the next 7 years. After 2015 or thereabouts, however, total oil and gas production is forecast to start declining. Oil production is already falling. Gas output has been increasing, but this is not expected to continue offsetting the drop in liquid production beyond 2015 or thereabouts if no action is taken. Only half the combined oil and gas resources predicted by the Norwegian Petroleum Directorate (NPD) will have been produced in 2015. Remaining recoverable resources, including those expected to be found by further exploration, are currently estimated to be 38-77 billion barrels of oil equivalent (boe). This estimate could be 25-65 billion boe in 2015. Only 40 per cent of the total expected remaining hydrocarbon resources remains to be discovered today, which explains the wide range in the estimates. This huge potential must be managed well to avoid a sharp decline in production and to support a healthy level of long-term investment. The report on production development on the Norwegian continental shelf is published at a time when major changes are taking place both inside and outside the petroleum industry. Several factors make a review of what can be done to address the production decline particularly urgent. Although the current level of activity in the Norwegian petroleum sector is high, assessing the long-term perspectives for the industry is very important. In many cases, the period between the award of licences and the start of production can be 15 years or more. Decisions taken now may have important implications for levels of production and activity in the 2020s. (Author)

  5. 75 FR 21653 - Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore Delaware-Request...

    Science.gov (United States)

    2010-04-26

    ... Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore Delaware--Request for Interest (RFI... proposal. In June 2008, Bluewater Wind Delaware LLC announced that it signed a 25-year power purchase agreement with Delmarva Power to sell up to 200 megawatts (MW) of power to the utility from an offshore wind...

  6. 76 FR 4716 - Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Off Delaware, Notice of...

    Science.gov (United States)

    2011-01-26

    ... No. BOEM-2010-0075] Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Off... commercial wind development on the OCS off Delaware and requests submission of indications of competitive... received two nominations of proposed lease areas: One from Bluewater Wind Delaware LLC (Bluewater) and...

  7. Physical (Hydrography), chemical (CTD), and biological (Water Quality) processes of the Texas-Louisiana continental shelf, 2012 (NCEI Accession 0162101)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Two sets of CTD data were taken during the 2012 surveys of the Louisiana continental shelf—Transect C off Terrebonne Bay and Transect F off Atchafalaya Bay and the...

  8. Spatial distribution of Munida intermedia and M. sarsi (crustacea: Anomura) on the Galician continental shelf (NW Spain): Application of geostatistical analysis

    Science.gov (United States)

    Freire, J.; González-Gurriarán, E.; Olaso, I.

    1992-12-01

    Geostatistical methodology was used to analyse spatial structure and distribution of the epibenthic crustaceans Munida intermedia and M. sarsi within sets of data which had been collected during three survey cruises carried out on the Galician continental shelf (1983 and 1984). This study investigates the feasibility of using geostatistics for data collected according to traditional methods and of enhancing such methodology. The experimental variograms were calculated (pooled variance minus spatial covariance between samples taken one pair at a time vs. distance) and fitted to a 'spherical' model. The spatial structure model was used to estimate the abundance and distribution of the populations studied using the technique of kriging. The species display spatial structures, which are well marked during high density periods and in some areas (especially northern shelf). Geostatistical analysis allows identification of the density gradients in space as well as the patch grain along the continental shelf of 16-25 km diameter for M. intermedia and 12-20 km for M. sarsi. Patches of both species have a consistent location throughout the different cruises. As in other geographical areas, M. intermedia and M. sarsi usually appear at depths ranging from 200 to 500 m, with the highest densities in the continental shelf area located between Fisterra and Estaca de Bares. Althouh sampling was not originally designed specifically for geostatistics, this assay provides a measurement of spatial covariance, and shows variograms with variable structure depending on population density and geographical area. These ideas are useful in improving the design of future sampling cruises.

  9. Geomorphic characterization of four shelf-sourced submarine canyons along the U.S. Mid-Atlantic continental margin

    Science.gov (United States)

    Obelcz, Jeffrey; Brothers, Daniel S.; Chaytor, Jason D.; ten Brink, Uri S.; Ross, Steve W.; Brooke, Sandra

    2013-01-01

    Shelf-sourced submarine canyons are common features of continental margins and are fundamental to deep-sea sedimentary systems. Despite their geomorphic and geologic significance, relatively few passive margin shelf-breaching canyons worldwide have been mapped using modern geophysical methods. Between 2007 and 2012 a series of geophysical surveys was conducted across four major canyons of the US Mid-Atlantic margin: Wilmington, Baltimore, Washington, and Norfolk canyons. More than 5700 km2 of high-resolution multibeam bathymetry and 890 line-km of sub-bottom CHIRP profiles were collected along the outer shelf and uppermost slope (depths of 80-1200 m). The data allowed us to compare and contrast the fine-scale morphology of each canyon system. The canyons have marked differences in the morphology and orientation of canyon heads, steepness and density of sidewall gullies, and the character of the continental shelf surrounding canyon rims. Down-canyon axial profiles for Washington, Baltimore and Wilmington canyons have linear shapes, and each canyon thalweg exhibits morphological evidence for recent, relatively small-scale sediment transport. For example, Washington Canyon displays extremely steep wall gradients and contains ~100 m wide, 5–10 m deep, v-shaped incisions down the canyon axis, suggesting modern or recent sediment transport. In contrast, the convex axial thalweg profile, the absence of thalweg incision, and evidence for sediment infilling at the canyon head, suggest that depositional processes strongly influence Norfolk Canyon during the current sea-level high-stand. The north walls of Wilmington, Washington and Norfolk canyons are steeper than the south walls due to differential erosion, though the underlying cause for this asymmetry is not clear. Furthermore, we speculate that most of the geomorphic features observed within the canyons (e.g., terraces, tributary canyons, gullies, and hanging valleys) were formed during the Pleistocene, and show only

  10. Submarine glacial landforms on the Bay of Fundy–northern Gulf of Maine continental shelf

    Science.gov (United States)

    Todd, B.J.; Shaw, J.; Valentine, Page C.

    2016-01-01

    The Bay of Fundy–northern Gulf of Maine region surrounds the southern part of Nova Scotia, encompassing, from west to east, the Bay of Fundy, Grand Manan Basin, German Bank, Browns Bank, Northeast Channel and northeastern Georges Bank (Fig. 1a, b). During the last glacial maximum (c. 24–20 14C ka BP), the SE margin of the Laurentide Ice Sheet (LIS) occupied the study area, the rest of the Gulf of Maine and the continental Scotian Shelf off Atlantic Canada (see Dyke et al. 2002, fig. 1; Shaw et al. 2006, fig. 8; Hundert & Piper 2008, fig. 16). Early mapping of the glaciated region on the Scotian Shelf using side-scan sonar imagery and seismic-reflection profiles revealed topographic features interpreted to be recessional moraines indicative of retreat of the LIS (King et al. 1972; King 1996). Subsequently, multibeam sonar seafloor mapping of local-scale glacial landforms on the inner Scotian Shelf off Halifax, Nova Scotia (Fig. 1b) provided further information on the dynamics of the advance and retreat of the ice sheet (Loncarevic et al.1994). Interpretation of seismic-reflection profiles across Georges Bank revealed that the surficial sediment is a veneer of glacial debris transported to Georges Bank by the LIS during the late Pleistocene from continental areas to the north (Shepard et al. 1934; Knott & Hoskins 1968; Schlee 1973; Twichell et al. 1987; Fader et al. 1988). Recent high-resolution multibeam sonar surveys of German Bank and the Bay of Fundy mapped a complex of ice-advance and ice-retreat features attributed to the activity of the LIS (Todd et al. 2007; Todd & Shaw 2012).

  11. Trophic model of the outer continental shelf and upper slope demersal community of the southeastern Brazilian Bight

    Directory of Open Access Journals (Sweden)

    Marcela C. Nascimento

    2012-10-01

    Full Text Available It is increasingly recognized that demersal communities are important for the functioning of continental shelf and slope ecosystems around the world, including tropical regions. Demersal communities are most prominent in areas of high detritus production and transport, and they link benthic and pelagic biological communities. To understand the structure and role of the demersal community on the southeastern Brazilian Bight, we constructed a trophodynamic model with 37 functional groups to represent the demersal community of the outer continental shelf and upper slope of this area, using the Ecopath with Ecosim 6 (EwE approach and software. The model indicates high production and biomass of detritus and benthic invertebrates, and strong linkages of these components to demersal and pelagic sub-webs. The level of omnivory indexes in this ecosystem was high, forming a highly connected trophic web reminiscent of tropical land areas. Although high levels of ascendency may indicate resistance and resilience to disturbance, recent and present fisheries trends are probably degrading the biological community and related ecosystem services.

  12. 75 FR 63345 - Oil and Gas and Sulphur Operations in the Outer Continental Shelf-Increased Safety Measures for...

    Science.gov (United States)

    2010-10-14

    ... the Outer Continental Shelf in light of the Deepwater Horizon event on April 20, 2010, and resulting...) develop this report as a result of the Deepwater Horizon event on April 20, 2010. This event, which... investigations into the Deepwater Horizon event, that certain equipment, systems, and improved practices are...

  13. Seismic data processing for domestic seismic survey over the continental shelf of Korea using the Geobit

    Energy Technology Data Exchange (ETDEWEB)

    Oh, Jin Yong [Korea Inst. of Geology Mining and Materials, Taejon (Korea, Republic of)

    1995-12-01

    The `Geobit`, a new seismic data processing software introduced by the Korea Institute of Geology, Mining and Materials recently, is the token of the achievement for the development of technology in the oil exploration over the Korean continental shelf. In comparison with the foreign seismic data processing systems previously used in Korea, the Geobit system has some advanced facilities; it provides an interactive mode which makes the seismic processing easier and has the user-friendly programs which allow the construction of a job control file simpler. Most of all, the Geobit can be run with many computer hardware systems, from PC to supercomputer. The current version of the Geobit can take care of the two-dimensional multi-channel seismic data and is open to the public for an education tool and a research purpose. To demonstrate the ability of the Geobit, a multi-channel field data acquired in the domestic continental shelf over the Yellow Sea in 1970 has been selected and processed with standard seismic data processing techniques. In this report, the Geobit job files and the corresponding results for the construction of a stack are provided. (author). 8 refs., 14 figs., 1 tab.

  14. Geochemical record of Holocene to Recent sedimentation on the Western Indus continental shelf, Arabian Sea

    Science.gov (United States)

    Limmer, David R.; BöNing, Philipp; Giosan, Liviu; Ponton, Camilo; KöHler, Cornelia M.; Cooper, Matthew J.; Tabrez, Ali R.; Clift, Peter D.

    2012-01-01

    We present a multiproxy geochemical analysis of two cores recovered from the Indus Shelf spanning the Early Holocene to Recent (<14 ka). Indus-23 is located close to the modern Indus River, while Indus-10 is positioned ˜100 km further west. The Holocene transgression at Indus-10 was over a surface that was strongly weathered during the last glacial sea level lowstand. Lower Holocene sediments at Indus-10 have higherɛNdvalues compared to those at the river mouth indicating some sediment supply from the Makran coast, either during the deposition or via reworking of older sediments outcropping on the shelf. Sediment transport from Makran occurred during transgressive intervals when sea level crossed the mid shelf. The sediment flux from non-Indus sources to Indus-10 peaked between 11 ka and 8 ka. A hiatus at Indus-23 from 8 ka until 1.3 ka indicates non-deposition or erosion of existing Indus Shelf sequences. HigherɛNdvalues seen on the shelf compared to the delta imply reworking of older delta sediments in building Holocene clinoforms. Chemical Index of Alteration (CIA), Mg/Al and Sr isotopes are all affected by erosion of detrital carbonate, which reduced through the Holocene. K/Al data suggest that silicate weathering peaked ca. 4-6 ka and was higher at Indus-10 compared to Indus-23. Fine-grained sediments that make up the shelf have geochemical signatures that are different from the coarser grained bulk sediments measured in the delta plain. The Indus Shelf data highlight the complexity of reconstructing records of continental erosion and provenance in marine settings.

  15. 75 FR 19880 - Safety Zone; BW PIONEER at Walker Ridge 249, Outer Continental Shelf FPSO, Gulf of Mexico

    Science.gov (United States)

    2010-04-16

    ... BW PIONEER, a Floating Production, Storage and Offloading (FPSO) system, at Walker Ridge 249 in the Outer Continental Shelf. The purpose of the safety zone is to protect the FPSO from vessels operating... reduces the threat of allisions, oil spills, and releases of natural gas, and thereby protects the safety...

  16. Diversity and Distribution Patterns of Cetaceans in the Subtropical Southwestern Atlantic Outer Continental Shelf and Slope

    Science.gov (United States)

    Di Tullio, Juliana Couto; Gandra, Tiago B. R.; Zerbini, Alexandre N.; Secchi, Eduardo R.

    2016-01-01

    Temporal and spatial patterns of cetacean diversity and distribution were investigated through eight ship-based surveys carried out during spring and autumn between 2009 and 2014 on the outer continental shelf (~150m) and slope (1500m) off southeastern and southern Brazil (~23°S to ~34°S). The survey area was divided into southeast and south areas according to their oceanographic characteristics. Twenty-one species were observed in 503 sightings. The overall number of species was similar between the two areas, though it was higher in the spring in the south area. Five species were dominant and diversity varied more seasonally than spatially. ANOVA and kernel analyses showed that overall cetacean densities were higher in spring compared to autumn. Physeter macrocephalus, the most frequent species, concentrated throughout the south area at depths over 1000m in both seasons. Despite the overlapped occurrence at a broader scale, small delphinids presented latitudinal and in-offshore gradients as well as seasonal variation in distribution patterns, which could indicate habitat partitioning between some species. Delphinus delphis was only recorded in the south and its density decreased in areas where the presence of Stenella frontalis increased, mainly beyond the 250m isobath. Densities of S. longirostris and S. attenuata increased in lower latitudes and beyond the shelf break. The large delphinids Tursiops truncatus and Globicephala melas formed mixed groups in many occasions and were observed along the study area around depths of 500m. Grampus griseus was twice as frequent in the south area and densities increased in waters deeper than 600m. As expected, densities of both small and large migratory whales were higher during spring, over the continental slope, in the southeast area. The results presented here provided strong evidence on the importance of the outer continental shelf and slope to a diverse community of cetaceans occurring in the subtropical Southwestern

  17. Sedimentology and geochemistry of surface sediments, outer continental shelf, southern Bering Sea

    Science.gov (United States)

    Gardner, J.V.; Dean, W.E.; Vallier, T.L.

    1980-01-01

    Present-day sediment dynamics, combined with lowerings of sea level during the Pleistocene, have created a mixture of sediments on the outer continental shelf of the southern Bering Sea that was derived from the Alaskan Mainland, the Aleutian Islands, and the Pribilof ridge. Concentrations of finer-grained, higher-organic sediments in the region of the St. George basin have further modified regional distribution patterns of sediment composition. Q-mode factor analysis of 58 variables related to sediment size and composition - including content of major, minor, and trace elements, heavy and light minerals, and clay minerals - reveals three dominant associations of sediment: 1. (1) The most significant contribution, forming a coarse-grained sediment scattered over most of the shelf consists of felsic sediment derived from the generally quartz-rich rocks of the Alaskan mainland. This sediment contains relatively high concentrations of Si, Ba, Rb, quartz, garnet, epidote, metamorphic rock fragments, potassium feldspar, and illite. 2. (2) The next most important group, superimposed on the felsic group consists of andesitic sediment derived from the Aleutian Islands. This more mafic sediment contains relatively high concentrations of Na, Ca, Ti, Sr, V, Mn, Cu, Fe, Al, Co, Zn, Y, Yb, Ga, volcanic rock fragments, glass, clinopyroxene, smectite, and vermiculite. 3. (3) A local group of basaltic sediment, derived from rocks of the Pribilof Islands, is a subgroup of the Aleutian andesite group. Accumulation of fine-grained sediment in St. George basin has created a sediment group containing relatively high concentrations of C, S, U, Li, B, Zr, Ga, Hg, silt, and clay. Sediment of the Aleutian andesite group exhibits a strong gradient, or "plume", with concentrations decreasing away from Unimak Pass and toward St. George basin. The absence of present-day currents sufficient to move even clay-size material as well as the presence of Bering submarine canyon between the Aleutian

  18. On the accumulation of organic matter on the southeastern Brazilian continental shelf: a case study based on a sediment core from the shelf off Rio de Janeiro

    Directory of Open Access Journals (Sweden)

    Renato da Silva Carreira

    2012-03-01

    Full Text Available Sterol and fatty acid biomarkers and isotopic composition (δ13C and δ15N of bulk organic matter (OM were quantified in a sediment core to characterize the accumulation of autochthonous OM in an area on the continental shelf adjacent to Rio de Janeiro State. In the sediment surface (0-1 cm the concentration of total sterols and fatty acids was at least one order of magnitude higher than that measured deeper down in the core and was dominated by labile and planktonic-derived biomarker compounds. These results suggest, as is confirmed by multivariate statistical analysis, the occurrence of an event of enhanced primary production in the water column and efficient export of particles to the bottom. Similar conditions have been observed at Cabo Frio, located 150 km to the north of our study site, during an upwelling event, suggesting that such events may exert a regional influence on primary production on the south-eastern Brazilian continental shelf. Beyond the signatures from this event, the presence of biomarker compounds from vascular plants suggests the additional influence of an outflow from Guanabara Bay at the study site. These results point to the need for further investigation of the relative influence of physical forcings and continental inputs on the biogeochemical processes on the section of the continental shelf considered in the present study.Marcadores moleculares na classe de lipídios (esterois, ácidos graxos e hidrocarbonetos e a composição isotópica (δ13C e δ15N da matéria orgânica bruta foram quantificados em amostras de um testemunho de sedimento para caracterizar o histórico recente de sedimentação da matéria orgânica na plataforma continental adjacente à Baía de Guanabara, no Estado do Rio de Janeiro. Na superfície do sedimento (0-1 cm, a concentração total de esterois e ácidos graxos foi cerca de uma ordem de grandeza maior do que observado nas camadas mais profundas do sedimento, com predominância de lip

  19. Changes in the diet composition of transitory fishes in coastal systems, estuary and continental shelf

    Directory of Open Access Journals (Sweden)

    Chaves Paulo T. C.

    2003-01-01

    Full Text Available The feeding habits of five species of teleosts in the southern coast of Brazil were analyzed comparatively between estuary and continental shelf. The displacement between the two sites caused expressive qualitative alterations, the proportion of different items varying from 50% in the diet of Micropogonias furnieri to 89% in Isopisthus parvipinnis. In the group of species, 57% of the items were exclusive to one of the environments and, within the three most common items in the estuary - fish, Polychaeta and plants, only the former was also among the most common items in the shelf. In spite of these differences, the high spectrum of items in both environments and the nature of the item that was most consumed in each one, indicate that there was a certain similarity of patterns between estuary and shelf: Chloroscombrus chrysurus had a carnivorous diet, with a predominance of copepods; M. furnieri and Menticirrhus americanus showed a tendency towards an omnivorous diet; and Cynoscion leiarchus and I. parvipinnis showed a tendency towards ichthyophagy.

  20. Change in morphology and modern sediment thickness on the inner continental shelf offshore of Fire Island, New York between 2011 and 2014: Analysis of hurricane impact

    Science.gov (United States)

    Schwab, William C.; Baldwin, Wayne E.; Warner, John C.; List, Jeffrey; Denny, Jane F.; Liste Munoz, Maria; Safak, Ilgar

    2017-01-01

    Seafloor mapping investigations conducted on the lower shoreface and inner continental shelf offshore of Fire Island, New York in 2011 and 2014, the period encompassing the impacts of Hurricanes Irene and Sandy, provide an unprecedented perspective regarding regional inner continental shelf sediment dynamics during large storm events. Analyses of these studies demonstrate that storm-induced erosion and sediment transport occurred throughout the study area in water depths up to 30 m. Acoustic backscatter patterns were observed to move from ~1 m to 450 m with a mean of 20 m and movement tended to decrease with increasing water depth. These patterns indicate that both of the primary inner continental shelf sedimentary features in the study area, linear sorted bedforms offshore of eastern Fire Island and shoreface-attached sand ridges offshore of central and western Fire island, migrated alongshore to the southwest. The migration of the sorted bedforms represents the modification of an active ravinement surface and is thought to have liberated a significant volume of sediment. Comparison of isopach maps of sediment thickness show that the volume of modern sediment composing the lower shoreface and shoreface-attached sand ridges decreased by ~2.8 × 106 m3 across the ~73 km2 of common seafloor mapped in both surveys. However, a similar analysis for the relatively calmer 15-yr period prior to 2011 revealed significant accretion. This allows speculation that the shoreface-attached sand ridges are maintained over decadal timescales via sediment supplied through erosion of Pleistocene outwash and lower Holocene transgressive channel-fill deposits exposed on the inner continental shelf, but that the sand ridges also periodically erode and move to the southwest during large storm events. Analyses show that significant storminduced erosion and sediment transport occurs far seaward of the 5 to 9 m depth of closure assumed for Fire Island, where it is thought that an onshore

  1. Direct observations of American eels migrating across the continental shelf to the Sargasso Sea.

    Science.gov (United States)

    Béguer-Pon, Mélanie; Castonguay, Martin; Shan, Shiliang; Benchetrit, José; Dodson, Julian J

    2015-10-27

    Since inferring spawning areas from larval distributions in the Sargasso Sea a century ago, the oceanic migration of adult American eels has remained a mystery. No adult eel has ever been observed migrating in the open ocean or in the spawning area. Here, we track movements of maturing eels equipped with pop-up satellite archival tags from the Scotian Shelf (Canada) into the open ocean, with one individual migrating 2,400 km to the northern limit of the spawning site in the Sargasso Sea. The reconstructed routes suggest a migration in two phases: one over the continental shelf and along its edge in shallow waters; the second in deeper waters straight south towards the spawning area. This study is the first direct evidence of adult Anguilla migrating to the Sargasso Sea and represents an important step forward in the understanding of routes and migratory cues.

  2. Topographic registers of paleo-valleys on the southeastern Brazilian continental shelf

    Directory of Open Access Journals (Sweden)

    Luis Américo Conti

    2009-06-01

    Full Text Available The evolution of paleo-incised-valleys in the São Paulo State region of the southeastern Brazilian continental shelf is presented in this study in relation to the post Last Glacial Maximum (LGM sea-level rises based on the submarine topography modeled by a detailed Digital Elevation Model and evidences noted in high resolution seismic profiles. The hypothesis that has guided this study is that the set of paleo-valley characteristics (i.e. the fluvial parameters of modern coastal drainage systems, the topographical shape and dimensions of the valleys and of the subsurface channels may indicate aspects of the relation between the influence of the fluvial and the eustatic variation regime in geomorphological-stratigraphic registers. Models described in the literature sustain the view that faster marine transgressions tend to increase erosion in estuaries, which may explain the lack of registers of paleo-drainage both in topography and the sub-surface in areas with wider shelves. On the other hand, on narrower shelves, with a higher slope angle, the transgression process can preserve, or even enhance, the incised valley registers during shoreface retreat. In the area studied, we observed that the dimensions and form of the continental shelf varies from the northern to the southern part of the area, affecting aspects of the geomorphological registers of the submerged incised valleys.Este trabalho apresenta aspectos da relação entre a evolução da paleo-drenagem e evolução do nível do mar pós Último Máximo Glacial (UMG para a região da plataforma continental do Estado de São Paulo. Para tal, foram analisados modelos topográficos de detalhe da região de Plataforma Continental a partir de Modelos Digitais de Terreno além de dados de subsuperfície obtidos a partir de linhas sísmicas de alta resolução. A hipótese que guiou este trabalho é de que o conjunto de características relativas aos paleo-vales (i.e. sua relação com a rede de

  3. Impacts of Outer Continental Shelf (OCS) development on recreation and tourism. Volume 4. User's manual

    Energy Technology Data Exchange (ETDEWEB)

    1987-04-01

    The final report for the project is presented in five volumes. The project sought to determine the impact of Outer Continental Shelf development on recreation and tourism in California. This volume is the User's Guide. It includes the following topics: Introduction and Summary Guide; Input Data Files; Gravity Model Programs; Economic Effects Model Programs; Consumer Surplus Model Programs; References; and Appendices.

  4. Atlantic Offshore Seabird Dataset Catalog, Atlantic Coast and Outer Continental Shelf, from 1938-01-01 to 2013-12-31 (NODC Accession 0115356)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Several bureaus within the Department of Interior compiled available information from seabird observation datasets from the Atlantic Outer Continental Shelf into a...

  5. Bathymetry and acoustic backscatter of the mid and outer continental shelf, head of De Soto Canyon, northeastern Gulf of Mexico

    Science.gov (United States)

    Gardner, James V.; Hughes-Clarke, John E.; Meyer, Larry A.

    2002-01-01

    The mid to outer continental shelf off Mississippi-Alabama and off northwest Florida were the focus of US Geological Survey (USGS) multibeam echosounder (MBES) mapping cruises in 2000 and 2001, respectively. These areas were mapped to investigate the extent of "deep-water reefs" first suggested by Ludwick and Walton (1957). The reefs off Mississippi and Alabama were initially described in water depths of 60 to 120 m (Ludwick and Walton, 1957) but the 2000 mapping found reef and hardgrounds to be much more extensive than previously thought (Gardner et al., 2001). The persistent trend of reef-like features along the outer shelf of Mississippi-Alabama suggested the trend might continue along the northwest Florida mid and outer shelf so a MBES-mapping effort was mounted in 2001 to test this suggestion. It is critical to determine the accurate location, geomorphology, and types of the ridges and reefs that occur in this region to understand the Quaternary history of the area and to assess their importance as benthic habitats for fisheries. The 2001 survey found a series of shelf-depth platforms with ridges (possibly reefs) constructed on their surfaces (Gardner et al., 2002). The area known as the "head of De Soto Canyon" is the large unmapped region between the 2000 and 2001 mapped areas. The head of De Soto Canyon is an outer shelf zone with a relatively steep western wall and a much gentler eastern wall. It was unknown prior to this cruise whether the reefs of the Mississippi-Alabama shelf continue eastward into the head of De Soto Canyon and connect with the ridges and reefs mapped on the northwest Florida outer shelf. The existence of carbonate-cemented latest Quaternary to Holocene sandstones along the western wall of the head of De Soto Canyon (Shipp and Hopkins, 1978; Benson et al., 1997; W.W. Schroeder, personnel comm., 2002) is of interest because of the potential benthic habitats they may represent. Precisely georeferenced high-resolution mapping of

  6. Movement and effects of spilled oil over the outer continental shelf; inadequacy of existent data for the Baltimore Canyon Trough area

    Science.gov (United States)

    Knebel, Harley J.

    1974-01-01

    A deductive approach to the problem of determining the movement and effects of spilled oil over the Outer Continental Shelf requires that the potential paths of oil be determined first, in order that critical subareas may be defined for later studies. The paths of spilled oil, in turn, depend primarily on the temporal and spatial variability of four factors: the thermohaline structure of the waters, the circulation of the water, the winds, and the distribution of suspended matter. A review of the existent data concerning these factors for the Baltimore Canyon Trough area (a relatively well studied segment of the Continental Shelf) reveals that the movement and dispersal of potential oil spills cannot be reliably predicted. Variations in the thermohaline structure of waters and in the distribution of suspended matter are adequately known; the uncertainty is due to insufficient wind and storm statistics and to the lack of quantitative understanding of the relationship between the nontidal drift and its basic driving mechanisms. Similar inadequacies should be anticipated for other potentially leasable areas of the shelf because an understanding of the movement of spilled oil has not been the underlying aim of most previous studies.

  7. Distribution of Upper Circumpolar Deep Water on the warming continental shelf of the West Antarctic Peninsula

    Science.gov (United States)

    Couto, Nicole; Martinson, Douglas G.; Kohut, Josh; Schofield, Oscar

    2017-07-01

    We use autonomous underwater vehicles to characterize the spatial distribution of Upper Circumpolar Deep Water (UCDW) on the continental shelf of the West Antarctic Peninsula (WAP) and present the first near-synoptic measurements of mesoscale features (eddies) containing UCDW on the WAP. Thirty-three subsurface eddies with widths on the order of 10 km were detected during four glider deployments. Each eddy contributed an average of 5.8 × 1016 J to the subpycnocline waters, where a cross-shelf heat flux of 1.37 × 1019 J yr-1 is required to balance the diffusive loss of heat to overlying winter water and to the near-coastal waters. Approximately two-thirds of the heat coming onto the shelf diffuses across the pycnocline and one-third diffuses to the coastal waters; long-term warming of the subpycnocline waters is a small residual of this balance. Sixty percent of the profiles that contained UCDW were part of a coherent eddy. Between 20% and 53% of the lateral onshore heat flux to the WAP can be attributed to eddies entering Marguerite Trough, a feature in the southern part of the shelf which is known to be an important conduit for UCDW. A northern trough is identified as additional important location for eddy intrusion.

  8. Fossil ostracodes of continental shelf cores at IODP Site U1354 (Expedition 317)

    Science.gov (United States)

    Kusunoki, S.; Ohi, T.; Kawagata, S.; Ishida, K.; Shipboard Scientific Party, E.

    2010-12-01

    Integrated Ocean Drilling Program (IODP) Expedition 317 was devoted to understanding the relative importance of global sea level (eustasy) versus local tectonic and sedimentary processes in controlling continental margin sedimentary cycles. The expedition recovered sediments from the Eocene to recent period, with a particular focus on the sequence stratigraphy of the late Miocene to recent, when global sea level change was dominated by glacioeustasy. Drilling in the Canterbury Basin, on the eastern margin of the South Island of New Zealand took advantage of high rates of Neogene sediment supply, which preserved a high-frequency (0.1-0.5 m.y.) record of depositional cyclicity. Ostracodes are crustaceans that widely inhabit marine, brackish, and non-marine environments. Shallow marine species have more restricted habitat and respond sensitively to environmental changes. Therefore they are a useful tool for high-resolution analyses of paleoenvironmental changes. We study samples older than ~1.0 Ma from Site U1354, which is in an intermediate position within the three shelf sites transect of Expedition 317. Quaternary to early Pliocene (~4.5 Ma) sediments were cored in this site with best core recovery (81%) among the shelf sites. The period from the Pliocene to Pleistocene is known for distinct paleoclimatic changes, from the intensive warming at around 3.5 Ma, to the cooling stage starting from 2.75 Ma. We expect that high-resolution analyses of fossil ostracode assemblages reveal detailed sea level and paleoceanographic changes on the continental shelf of the Canterbury Basin caused by global climate changes. Samples were examined at 1.5 m depth intervals. Samples of ~20 cc were freeze-dried and washed through a 63 µm opening sieve. The residues were dried and then divided into aliquot parts containing around 200 specimens using a sample splitter. All individual ostracodes were picked from residues coarser than 125 µm. Valves and carapaces were counted as one

  9. Composition of the metazooplankton community and structure across the continental shelf off tropical NW Australia

    DEFF Research Database (Denmark)

    Jaspers, Cornelia; Nielsen, Torkel Gissel; Maar, Marie

    This talk focuses on the distribution pattern and grazing impact of different functional metazooplankton groups in a tropical marine ecosystem. We studied the metazooplankton distribution across the continental shelf from eutrophic mangrove areas to the oligotrophic deep blue ocean off NW Australia....... Chlorophyll a concentrations were reduced by factor 10 along the transect including a shift towards small sized primary producers. The metazooplankton biomass followed the same pattern. Even though low in abundance, copepods were most frequent followed by larvaceans, doliolids other thaliacea and chaetognaths...

  10. Biodiversity of a wreck from the Belgian Continental Shelf: monitoring using scientific diving: preliminary results

    OpenAIRE

    Massin, Cl.; Norro, A.; Mallefet, J.

    2002-01-01

    Scientific diving from aboard the r/v Belgica has been employed to carry out a preliminary study of the macrofauna living on a wreck (the Birkenfels) located on the Belgian Continental Shelf (BCS). The study revealed an extremely rich sessile and slow moving fauna (at least 40 species), 3 jellyfish species and 8 fish species. The presence of at least 51 species represents a biodiversity of macrofauna on the wreck that is much higher than that found in nearly all known surrounding soft bottorn...

  11. OESbathy version 1.0: a method for reconstructing ocean bathymetry with realistic continental shelf-slope-rise structures

    OpenAIRE

    A. Goswami; P. L. Olson; L. A. Hinnov; A. Gnanadesikan

    2015-01-01

    We present a method for reconstructing global ocean bathymetry that uses a plate cooling model for the oceanic lithosphere, the age distribution of the oceanic crust, global oceanic sediment thicknesses, plus shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to reconstruct realistic ocean bathymetry based on parameterized relationships of present-day variables that can be applied to global oceans in th...

  12. Distribution and sources of organic carbon, nitrogen and their isotopic signatures in sediments from the Ayeyarwady (Irrawaddy) continental shelf, northern Andaman Sea

    Digital Repository Service at National Institute of Oceanography (India)

    Ramaswamy, V.; Gaye, B.; Shirodkar, P.V.; Rao, P.S.; Chivas, A.R.; Wheeler, D.; Thwin, S.

    Total organic carbon (TOC), total nitrogen (TN) and their delta sup(13) C and delta sup (15) N values were determined from 110 sediment samples from the Ayeyarwady (Irrawaddy) continental shelf, northern Andaman Sea to decipher the concentration...

  13. Temporal variability of the Circumpolar Deep Water inflow onto the Ross Sea continental shelf

    Science.gov (United States)

    Castagno, Pasquale; Falco, Pierpaolo; Dinniman, Michael S.; Spezie, Giancarlo; Budillon, Giorgio

    2017-02-01

    The intrusion of Circumpolar Deep Water (CDW) is the primary source of heat, salt and nutrients onto Antarctica's continental shelves and plays a major role in the shelf physical and biological processes. Different studies have analyzed the processes responsible for the transport of CDW across the Ross Sea shelf break, but until now, there are no continuous observations that investigate the timing of the intrusions. Also, few works have focused on the effect of the tides that control these intrusions. In the Ross Sea, the CDW intrudes onto the shelf in several locations, but mostly along the troughs. We use hydrographic observations and a mooring placed on the outer shelf in the middle of the Drygalski Trough in order to characterize the spatial and temporal variability of CDW inflow onto the shelf. Our data span from 2004 to the beginning of 2014. In the Drygalski Trough, the CDW enters as a 150 m thick layer between 250 and 400 m, and moves upward towards the south. At the mooring location, about 50 km from the shelf break, two main CDW cores can be observed: one on the east side of the trough spreading along the west slope of Mawson Bank from about 200 m to the bottom and the other one in the central-west side from 200 m to about 350 m depth. A signature of this lighter and relatively warm water is detected by the instruments on the mooring at bottom of the Drygalski Trough. High frequency periodic CDW intrusion at the bottom of the trough is related to the diurnal and spring/neap tidal cycles. At lower frequency, a seasonal variability of the CDW intrusion is noticed. A strong inflow of CDW is observed every year at the end of December, while the CDW inflow is at its seasonal minimum during the beginning of the austral fall. In addition an interannual variability is also evident. A change of the CDW intrusion before and after 2010 is observed.

  14. Seasonal and interannual cross-shelf transport over the Texas and Louisiana continental shelf

    Science.gov (United States)

    Thyng, Kristen M.; Hetland, Robert D.

    2018-05-01

    Numerical drifters are tracked in a hydrodynamic simulation of circulation over the Texas-Louisiana shelf to analyze patterns in cross-shelf transport of materials. While the important forcing mechanisms in the region (wind, river, and deep eddies) and associated flow patterns are known, the resultant material transport is less well understood. The primary metric used in the calculations is the percent of drifters released within a region that cross the 100 m isobath. Results of the analysis indicate that, averaged over the eleven years of the simulation, there are two regions on the shelf - over the Texas shelf during winter, and over the Louisiana shelf in summer - with increased seasonal probability for offshore transport. Among the two other distinct regions, the big bend region in Texas has increased probability for onshore transport, and the Mississippi Delta region has an increase in offshore transport, for both seasons. Some of these regions of offshore transport have marked interannual variability. This interannual variability is correlated to interannual changes in forcing conditions. Winter transport off of the Texas shelf is correlated with winter mean wind direction, with more northerly winds enhancing offshore transport; summer transport off the Louisiana shelf is correlated with Mississippi River discharge.

  15. 76 FR 30956 - Outer Continental Shelf, Alaska OCS Region, Chukchi Sea Planning Area, Oil and Gas Lease Sale 193

    Science.gov (United States)

    2011-05-27

    ... Point Hope et al., v. Salazar, No. 1:08-cv-00004-RRB (D. Alaska)]. The sale was conducted in February... Continental Shelf, Alaska OCS Region, Chukchi Sea Planning Area, Oil and Gas Lease Sale 193 AGENCY: Bureau of...: BOEMRE announces the availability of a Revised Draft SEIS, OCS Oil and Gas Lease Sale 193, Chukchi Sea...

  16. Methane Metabolizing Microbial Communities in the Cold Seep Areas in the Northern Continental Shelf of South China Sea

    Science.gov (United States)

    Wang, F.; Liang, Q.

    2016-12-01

    Marine sediment contains large amount of methane, estimated approximately 500-2500 gigatonnes of dissolved and hydrated methane carbon stored therein, mainly in continental margins. In localized specific areas named cold seeps, hydrocarbon (mainly methane) containing fluids rise to the seafloor, and support oases of ecosystem composed of various microorganisms and faunal assemblages. South China Sea (SCS) is surrounded by passive continental margins in the west and north and convergent margins in the south and east. Thick organic-rich sediments have accumulated in the SCS since the late Mesozoic, which are continuing sources to form gas hydrates in the sediments of SCS. Here, Microbial ecosystems, particularly those involved in methane transformations were investigated in the cold seep areas (Qiongdongnan, Shenhu, and Dongsha) in the northern continental shelf of SCS. Multiple interdisciplinary analytic tools such as stable isotope probing, geochemical analysis, and molecular ecology, were applied for a comprehensive understanding of the microbe mediated methane transformation in this project. A variety of sediments cores have been collected, the geochemical profiles and the associated microbial distribution along the sediment cores were recorded. The major microbial groups involved in the methane transformation in these sediment cores were revealed, known methane producing and oxidizing archaea including Methanosarcinales, anaerobic methane oxidizing groups ANME-1, ANME-2 and their niche preference in the SCS sediments were found. In-depth comparative analysis revealed the presence of SCS-specific archaeal subtypes which probably reflected the evolution and adaptation of these methane metabolizing microbes to the SCS environmental conditions. Our work represents the first comprehensive analysis of the methane metabolizing microbial communities in the cold seep areas along the northern continental shelf of South China Sea, would provide new insight into the

  17. Bacteria, carbon dioxide and methane measurements in the Cariaco Basin on the continental shelf of Venezuela, April 2001 - January 2002 (NODC Accession 0001078)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Bacteria, carbon dioxide and methane measurements were collected using bottle casts in the Cariaco Basin on the continental shelf of Venezuela from 30 April 2001 to...

  18. EMAP/NOAA 2003 SURVEY OF ECOLOGICAL CONDITIONS OF THE WESTERN U.S. CONTINENTAL SHELF, INCLUDING GULF OF FARALLONES NATIONAL MARINE SANCTUARY

    Science.gov (United States)

    In June of 2003 a partnership between EPA, NOAA, and the western coastal states conducted a joint survey of ecological condition of aquatic resources along the U.S. western continental shelf (30-120 m), using multiple indicators of ecological condition. The study is an element o...

  19. Particulate and dissolved spectral absorption on the continental shelf of the southeastern United States

    Science.gov (United States)

    Nelson, James R.; Guarda, Sonia

    1995-05-01

    Visible absorption spectra of particulate and dissolved materials were characterized on the continental shelf off the southeastern United States (the South Atlantic Bight), emphasizing cross-shelf and seasonal variability. A coastal front separates turbid coastal waters from clearer midshelf waters. Spatial and seasonal patterns were evident in absorption coefficients for phytoplankton, detritus, and colored dissolved organic matter (CDOM); spectral shape parameters for CDOM and detritus; and phytoplankton chlorophyll-specific absorption. The magnitude of CDOM absorption reflected seasonal differences in freshwater discharge and the salinity of the midshelf waters. In the spring of 1993 (high discharge), CDOM absorption at 443 nm was >10 times that of total particulate absorption between 12 and 50 km offshore (0.28-0.69 m-1 versus 0.027-0.062 m-1) and up to 10 times the CDOM absorption measured in the previous summer (low discharge). Phytoplankton chlorophyll-specific absorption in the blue increased with distance from shore (from shift in phytoplankton species composition (from predominantly diatoms inshore to a cyanobacteria-dominated assemblage midshelf in summer), pigment packaging, and higher carotenoid:chlorophyll with distance from shore.

  20. Exploring the Eastern United States Continental Shelf with the NOAA Cooperative Institute for Ocean Exploration, Research, and Technology

    Science.gov (United States)

    Glickson, D.; Pomponi, S. A.

    2016-02-01

    The Cooperative Institute for Ocean Exploration, Research, and Technology (CIOERT) serves NOAA priorities in three theme areas: exploring the eastern U.S. continental shelf, improving the understanding of coral and sponge ecosystems, and developing advanced underwater technologies. CIOERT focuses on the exploration and research of ecosystems and habitats along frontier regions of the eastern U.S. continental shelf that are of economic, scientific, or cultural importance or of natural hazards concern. One particular focus is supporting ocean exploration and research through the use of advanced underwater technologies and techniques in order to improve the understanding of vulnerable deep and shallow coral and sponge ecosystems. CIOERT expands the scope and efficiency of exploration and research by developing, testing, and applying new and/or innovative uses of existing technologies to ocean exploration and research activities. In addition, CIOERT is dedicated to expanding ocean literacy and building NOAA's technical and scientific workforce through hands-on, at-sea experiences. A recent CIOERT cruise characterized Gulf of Mexico mesophotic and deepwater reef ecosystems off the west Florida shelf, targeting northern Pulley Ridge. This project created and ground-truthed new sonar maps made with an autonomous underwater vehicle; conducted video and photographic transects of benthic habitat and fish using a remotely operated vehicle; and examined the connectivity of fauna from shallow to deep reef ecosystems. CIOERT was established in 2009 by FAU-Harbor Branch Oceanographic Institute, with University of North Carolina, Wilmington, SRI International, and the University of Miami. The primary NOAA partner is the Office of Oceanic and Atmospheric Research's Office of Ocean Exploration and Research.

  1. Sea level anomaly on the Patagonian continental shelf: Trends, annual patterns and geostrophic flows

    Science.gov (United States)

    Saraceno, M.; Piola, A. R.; Strub, P. T.

    2016-01-01

    Abstract We study the annual patterns and linear trend of satellite sea level anomaly (SLA) over the southwest South Atlantic continental shelf (SWACS) between 54ºS and 36ºS. Results show that south of 42°S the thermal steric effect explains nearly 100% of the annual amplitude of the SLA, while north of 42°S it explains less than 60%. This difference is due to the halosteric contribution. The annual wind variability plays a minor role over the whole continental shelf. The temporal linear trend in SLA ranges between 1 and 5 mm/yr (95% confidence level). The largest linear trends are found north of 39°S, at 42°S and at 50°S. We propose that in the northern region the large positive linear trends are associated with local changes in the density field caused by advective effects in response to a southward displacement of the South Atlantic High. The causes of the relative large SLA trends in two southern coastal regions are discussed as a function meridional wind stress and river discharge. Finally, we combined the annual cycle of SLA with the mean dynamic topography to estimate the absolute geostrophic velocities. This approach provides the first comprehensive description of the seasonal component of SWACS circulation based on satellite observations. The general circulation of the SWACS is northeastward with stronger/weaker geostrophic currents in austral summer/winter. At all latitudes, geostrophic velocities are larger (up to 20 cm/s) close to the shelf‐break and decrease toward the coast. This spatio‐temporal pattern is more intense north of 45°S. PMID:27840784

  2. Global multi-scale segmentation of continental and coastal waters from the watersheds to the continental margins

    KAUST Repository

    Laruelle, G. G.; Dü rr, H. H.; Lauerwald, R.; Hartmann, J.; Slomp, C. P.; Goossens, N.; Regnier, P. A. G.

    2013-01-01

    Past characterizations of the land-ocean continuum were constructed either from a continental perspective through an analysis of watershed river basin properties (COSCATs: COastal Segmentation and related CATchments) or from an oceanic perspective, through a regionalization of the proximal and distal continental margins (LMEs: large marine ecosystems). Here, we present a global-scale coastal segmentation, composed of three consistent levels, that includes the whole aquatic continuum with its riverine, estuarine and shelf sea components. Our work delineates comprehensive ensembles by harmonizing previous segmentations and typologies in order to retain the most important physical characteristics of both the land and shelf areas. The proposed multi-scale segmentation results in a distribution of global exorheic watersheds, estuaries and continental shelf seas among 45 major zones (MARCATS: MARgins and CATchments Segmentation) and 149 sub-units (COSCATs). Geographic and hydrologic parameters such as the surface area, volume and freshwater residence time are calculated for each coastal unit as well as different hypsometric profiles. Our analysis provides detailed insights into the distributions of coastal and continental shelf areas and how they connect with incoming riverine fluxes. The segmentation is also used to re-evaluate the global estuarine CO2 flux at the air-water interface combining global and regional average emission rates derived from local studies. © 2013 Author(s).

  3. Global multi-scale segmentation of continental and coastal waters from the watersheds to the continental margins

    Directory of Open Access Journals (Sweden)

    G. G. Laruelle

    2013-05-01

    Full Text Available Past characterizations of the land–ocean continuum were constructed either from a continental perspective through an analysis of watershed river basin properties (COSCATs: COastal Segmentation and related CATchments or from an oceanic perspective, through a regionalization of the proximal and distal continental margins (LMEs: large marine ecosystems. Here, we present a global-scale coastal segmentation, composed of three consistent levels, that includes the whole aquatic continuum with its riverine, estuarine and shelf sea components. Our work delineates comprehensive ensembles by harmonizing previous segmentations and typologies in order to retain the most important physical characteristics of both the land and shelf areas. The proposed multi-scale segmentation results in a distribution of global exorheic watersheds, estuaries and continental shelf seas among 45 major zones (MARCATS: MARgins and CATchments Segmentation and 149 sub-units (COSCATs. Geographic and hydrologic parameters such as the surface area, volume and freshwater residence time are calculated for each coastal unit as well as different hypsometric profiles. Our analysis provides detailed insights into the distributions of coastal and continental shelf areas and how they connect with incoming riverine fluxes. The segmentation is also used to re-evaluate the global estuarine CO2 flux at the air–water interface combining global and regional average emission rates derived from local studies.

  4. Global multi-scale segmentation of continental and coastal waters from the watersheds to the continental margins

    KAUST Repository

    Laruelle, G. G.

    2012-10-04

    Past characterizations of the land–ocean continuum were constructed either from a continental perspective through an analysis of watershed river basin properties (COSCATs: COastal Segmentation and related CATchments) or from an oceanic perspective, through a regionalization of the proximal and distal continental margins (LMEs: large marine ecosystems). Here, we present a global-scale coastal segmentation, composed of three consistent levels, that includes the whole aquatic continuum with its riverine, estuarine and shelf sea components. Our work delineates comprehensive ensembles by harmonizing previous segmentations and typologies in order to retain the most important physical characteristics of both the land and shelf areas. The proposed multi-scale segmentation results in a distribution of global exorheic watersheds, estuaries and continental shelf seas among 45 major zones (MARCATS: MARgins and CATchments Segmentation) and 149 sub-units (COSCATs). Geographic and hydrologic parameters such as the surface area, volume and freshwater residence time are calculated for each coastal unit as well as different hypsometric pro- files. Our analysis provides detailed insights into the distributions of coastal and continental shelf areas and how they connect with incoming riverine fluxes. The segmentation is also used to re-evaluate the global estuarine CO2 flux at the air–water interface combining global and regional average emission rates derived from local studies.

  5. Global multi-scale segmentation of continental and coastal waters from the watersheds to the continental margins

    KAUST Repository

    Laruelle, G. G.

    2013-05-29

    Past characterizations of the land-ocean continuum were constructed either from a continental perspective through an analysis of watershed river basin properties (COSCATs: COastal Segmentation and related CATchments) or from an oceanic perspective, through a regionalization of the proximal and distal continental margins (LMEs: large marine ecosystems). Here, we present a global-scale coastal segmentation, composed of three consistent levels, that includes the whole aquatic continuum with its riverine, estuarine and shelf sea components. Our work delineates comprehensive ensembles by harmonizing previous segmentations and typologies in order to retain the most important physical characteristics of both the land and shelf areas. The proposed multi-scale segmentation results in a distribution of global exorheic watersheds, estuaries and continental shelf seas among 45 major zones (MARCATS: MARgins and CATchments Segmentation) and 149 sub-units (COSCATs). Geographic and hydrologic parameters such as the surface area, volume and freshwater residence time are calculated for each coastal unit as well as different hypsometric profiles. Our analysis provides detailed insights into the distributions of coastal and continental shelf areas and how they connect with incoming riverine fluxes. The segmentation is also used to re-evaluate the global estuarine CO2 flux at the air-water interface combining global and regional average emission rates derived from local studies. © 2013 Author(s).

  6. Petroleum resources assessment on the continental shelf basin of the south sea

    Energy Technology Data Exchange (ETDEWEB)

    Cheong, Tae Jin; Kwak, Young Hun; Oh, Jae Ho; Bong, Pil Youn; Son, Jin Dam; Lee, Ho Young; Ryu, Byung Jae; Son, Byoung Kook; Hwang, In Geul; Kwon, Young In; Lee, Young Ju; Kim, Hak Ju; Park, Kwan Soon; Park, Keun Pil; Sunwoo, Don [Korea Institute of Geology Mining and Materials, Taejon (Korea, Republic of)

    1996-12-01

    On the basis of diverse microfossils such as foraminifers, ostracods, micromulluscs, fossil spores and pollen and calcareous nannofossils derived from 14 drill holes, the sediments are divided into two part, the upper marine part and the lower nonmarine one. Marine part is subdivided into 4 foraminiferal zones and 3 nannofossil zones of Plio-Pleistocene age. In the lower part ranging from Oligocene to Late Miocene 4 palynomoph assemblages are established, which reflect climatic changes fluctuating between subtropical and cool temperate. Some fine sediments occurring in the South Sea continental shelf are rich in organic matter to be hydrocarbon source rock. The organic matter is mainly compared to type 3. However, lower part of the Geobuk-1 and Okdom-1 shows more oil prone geochemical characteristics than other wells. The kerosene is mixture type 1 and type 3 organic matter. The main oil generation zone located between 2,500 m and 3,000 m and gas generation zone from 3,500 m to 4,000 m approximately. Hydrocarbon accumulation could be expected in the trap formed in the period earlier than 10 Ma. as the hydrocarbon started to be expelled at 10 Ma. according to the modeling. Approximately 13,000 Line-km of multichannel seismic data integrated with 14 wells and gravity and magnetic data were analyzed to investigate the structural and stratigraphic evolution of southern part of offshore Korea. The northeast-southwest trending Taiwan-Sinzi Uplift Belt separates the area into two regions with different tectonic features, northwestern and southwestern regions. Tectonics of the rifting phase in both regions have been established on the basis of structural and stratigraphic analyses of depositional sequences and their seismic expressions. In the northwestern region, the large rifting activity appears to be occurred during Oligocene and pre-Oligocene, while in the southeastern region it occurred from late Miocene to early Pliocene. The potential hydrocarbon traps associated

  7. Arctic continental shelf morphology related to sea-ice zonation, Beaufort Sea, Alaska

    Science.gov (United States)

    Reimnitz, E.; Toimil, L.; Barnes, P.

    1978-01-01

    Landsat-1 and NOAA satellite imagery for the winter 1972-1973, and a variety of ice and sea-floor data were used to study sea-ice zonation and dynamics and their relation to bottom morphology and geology on the Beaufort Sea continental shelf of arctic Alaska. In early winter the location of the boundary between undeformed fast ice and westward-drifting pack ice of the Pacific Gyre is controlled by major coastal promontories. Pronounced linear pressure- and shear-ridges, as well as hummock fields, form along this boundary and are stabilized by grounding, generally between the 10- and 20-m isobaths. Slippage along this boundary occurs intermittently at or seaward of the grounded ridges, forming new grounded ridges in a widening zone, the stamukhi zone, which by late winter extends out to the 40-m isobath. Between intermittent events along the stamukhi zone, pack-ice drift and slippage is continuous along the shelf edge, at average rates of 3-10 km/day. Whether slippage occurs along the stamukhi zone or along the shelf edge, it is restricted to a zone several hundred meters wide, and ice seaward of the slip face moves at uniform rates without discernible drag effects. A causal relationship is seen between the spatial distribution of major ice-ridge systems and offshore shoals downdrift of major coastal promontories. The shoals appear to have migrated shoreward under the influence of ice up to 400 m in the last 25 years. The sea floor seaward of these shoals within the stamukhi zone shows high ice-gouge density, large incision depths, and a high degree of disruption of internal sedimentary structures. The concentration of large ice ridges and our sea floor data in the stamukhi zone indicate that much of the available marine energy is expended here, while the inner shelf and coast, where the relatively undeformed fast ice grows, are sheltered. There is evidence that anomalies in the overall arctic shelf profile are related to sea-ice zonation, ice dynamics, and bottom

  8. The geostatistics of the metal concentrations in sediments from the eastern Brazilian continental shelf in areas of gas and oil production

    Science.gov (United States)

    Aguiar, Jose Edvar; de Lacerda, Luiz Drude; Miguens, Flavio Costa; Marins, Rozane Valente

    2014-04-01

    Geostatistical techniques were used to evaluate the differences in the geochemistry of metals in the marine sediments along the Eastern Brazilian continental margin along the states of Ceará and Rio Grande do Norte (Northeastern sector) and Espírito Santo (Southeastern sector). The concentrations of Al, Fe, Mn, Ba, Cd, Cu, Cr, Ni, Pb, V, Hg, and Zn were obtained from acid digestion and quantified using flame atomic absorption spectrometry (AAS), inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The metals showed a similar order of concentration: Al > Fe > Ba > Mn > V > Ni > Pb > Cr > Zn > Cu, in both the Ceará; and Rio Grande do Norte shelf regions but different in the Espírito Santo shelf (Fe > Al > Mn > Ba > Zn > V > Cr > Ni > Pb > Cu. The concentrations of Hg and Cd were below the detection limit in all areas. A multivariate analysis revealed that the metals of siliciclastic origin on the continental shelf of Ceará are carried by Al. In addition, a large portion of metal deposits is connected to the iron and manganese oxides on the continental margin of Rio Grande do Norte. The metals from the continental supply on the coast of Espírito Santo (Cu, Ni, Ba, and Mn) are associated with Al; whereas Cr, Pb, V, and Zn are associated with iron in this southern area. Geochemical evaluations are needed to distinguish the origin and mineralogical differences of marine sediments within the regions. Scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) applied to the sediments from the coast of Ceará showed the morphological diversity of sediment grains: biological fragments, multifaceted particles, aggregates, and crystals occurred in the three regions analyzed. Among these grains, calcite, Mg-calcite, and aragonite were predominant in the northeastern sector, whereas silicates and other minerals were predominant the southeastern sector. Mg, K, Ti, and Zr as well as the

  9. Impact of Satellite Remote Sensing Data on Simulations of Coastal Circulation and Hypoxia on the Louisiana Continental Shelf

    OpenAIRE

    Dong S. Ko; Richard W. Gould; Bradley Penta; John C. Lehrter

    2016-01-01

    We estimated surface salinity flux and solar penetration from satellite data, and performed model simulations to examine the impact of including the satellite estimates on temperature, salinity, and dissolved oxygen distributions on the Louisiana continental shelf (LCS) near the annual hypoxic zone. Rainfall data from the Tropical Rainfall Measurement Mission (TRMM) were used for the salinity flux, and the diffuse attenuation coefficient (Kd) from Moderate Resolution Imaging Spectroradiometer...

  10. Downslope flow across the Ross Sea shelf break (Antarctica)

    Science.gov (United States)

    Bergamasco, A.; Budillon, G.; Carniel, S.; Defendi, V.; Meloni, R.; Paschini, E.; Sclavo, M.; Spezie, G.

    2003-12-01

    The analysis of some high-resolution hydrological data sets acquired during the 1997, 1998, 2001 and 2003 austral summers across the Ross Sea continental shelf break are here presented. The main focus of these cruises carried out in the framework of the Italian National Antarctic Program was the investigation of the downslope flow of the dense waters originated inside the Ross Sea. Such dense waters, flow near the bottom and, reaching the continental shelf break, ventilate the deep ocean. Two Antarctic continental shelf mechanisms can originate dense and deep waters. The former mechanism involves the formation, along the Victoria Land coasts, of a dense and saline water mass, the High Salinity Shelf Water (HSSW). The HSSW formation is linked to the rejection of salt into the water column as sea ice freezes, especially during winter, in the polynya areas, where the ice is continuously pushed offshore by the strong katabatic winds. The latter one is responsible of the formation of a supercold water mass, the Ice Shelf Water (ISW). The salt supplied by the HSSW recirculated below the Ross Ice Shelf, the latent heat of melting and the heat sink provided by the Ross Ice Shelf give rise to plumes of ISW, characterized by temperatures below the sea-surface freezing point. The dense shelf waters migrate to the continental shelf-break, spill over the shelf edge and descend the continental slope as a shelf-break gravity current, subject to friction and possibly enhanced by topographic channelling. Friction, in particular, breaks the constraint of potential vorticity conservation, counteracting the geostrophic tendency for along slope flow. The density-driven downslope motion or cascading entrains ambient water, namely the lower layer of the CDW, reaches a depth where density is the same and spreads off-slope. In fact, the cascading event is inhibited by friction without entrainment. The downslope processes are important for the ocean and climate system because they play a

  11. Thirty-Three Years of Ocean Benthic Warming Along the U.S. Northeast Continental Shelf and Slope: Patterns, Drivers, and Ecological Consequences

    Science.gov (United States)

    Kavanaugh, Maria T.; Rheuban, Jennie E.; Luis, Kelly M. A.; Doney, Scott C.

    2017-12-01

    The U.S. Northeast Continental Shelf is experiencing rapid warming, with potentially profound consequences to marine ecosystems. While satellites document multiple scales of spatial and temporal variability on the surface, our understanding of the status, trends, and drivers of the benthic environmental change remains limited. We interpolated sparse benthic temperature data along the New England Shelf and upper Slope using a seasonally dynamic, regionally specific multiple linear regression model that merged in situ and remote sensing data. The statistical model predicted nearly 90% of the variability of the data, resulting in a synoptic time series spanning over three decades from 1982 to 2014. Benthic temperatures increased throughout the domain, including in the Gulf of Maine. Rates of benthic warming ranged from 0.1 to 0.4°C per decade, with fastest rates occurring in shallow, nearshore regions and on Georges Bank, the latter exceeding rates observed in the surface. Rates of benthic warming were up to 1.6 times faster in winter than the rest of the year in many regions, with important implications for disease occurrence and energetics of overwintering species. Drivers of warming varied over the domain. In southern New England and the mid-Atlantic shallow Shelf regions, benthic warming was tightly coupled to changes in SST, whereas both regional and basin-scale changes in ocean circulation affect temperatures in the Gulf of Maine, the Continental Shelf, and Georges Banks. These results highlight data gaps, the current feasibility of prediction from remotely sensed variables, and the need for improved understanding on how climate may affect seasonally specific ecological processes.

  12. The Deposition and Accumulation of Microplastics in Marine Sediments and Bottom Water from the Irish Continental Shelf.

    Science.gov (United States)

    Martin, Jake; Lusher, Amy; Thompson, Richard C; Morley, Audrey

    2017-09-07

    Microplastics are widely dispersed throughout the marine environment. An understanding of the distribution and accumulation of this form of pollution is crucial for gauging environmental risk. Presented here is the first record of plastic contamination, in the 5 mm-250 μm size range, of Irish continental shelf sediments. Sixty-two microplastics were recovered from 10 of 11 stations using box cores. 97% of recovered microplastics were found to reside shallower than 2.5 cm sediment depth, with the area of highest microplastic concentration being the water-sediment interface and top 0.5 cm of sediments (66%). Microplastics were not found deeper than 3.5 ± 0.5 cm. These findings demonstrate that microplastic contamination is ubiquitous within superficial sediments and bottom water along the western Irish continental shelf. Results highlight that cores need to be at least 4-5 cm deep to quantify the standing stock of microplastics within marine sediments. All recovered microplastics were classified as secondary microplastics as they appear to be remnants of larger items; fibres being the principal form of microplastic pollution (85%), followed by broken fragments (15%). The range of polymer types, colours and physical forms recovered suggests a variety of sources. Further research is needed to understand the mechanisms influencing microplastic transport, deposition, resuspension and subsequent interactions with biota.

  13. Seabed fluid expulsion along the upper slope and outer shelf of the U.S. Atlantic continental margin

    Science.gov (United States)

    Brothers, D.S.; Ruppel, C.; Kluesner, J.W.; ten Brink, Uri S.; Chaytor, J.D.; Hill, J.C.; Andrews, B.D.; Flores, C.

    2014-01-01

    Identifying the spatial distribution of seabed fluid expulsion features is crucial for understanding the substrate plumbing system of any continental margin. A 1100 km stretch of the U.S. Atlantic margin contains more than 5000 pockmarks at water depths of 120 m (shelf edge) to 700 m (upper slope), mostly updip of the contemporary gas hydrate stability zone (GHSZ). Advanced attribute analyses of high-resolution multichannel seismic reflection data reveal gas-charged sediment and probable fluid chimneys beneath pockmark fields. A series of enhanced reflectors, inferred to represent hydrate-bearing sediments, occur within the GHSZ. Differential sediment loading at the shelf edge and warming-induced gas hydrate dissociation along the upper slope are the proposed mechanisms that led to transient changes in substrate pore fluid overpressure, vertical fluid/gas migration, and pockmark formation.

  14. Adequacy of environmental information for outer continental shelf oil and gas decisions: Florida and California

    International Nuclear Information System (INIS)

    1989-01-01

    The environmental impacts of oil and gas production on the U.S. outer continental shelf (OCS) have been studied and debated for many years. The issues derive from the complexity of coastal and offshore marine processes and ecosystems, human socio-economic systems, and interactions with OCS oil and gas development activities. On Feb. 9, 1989, President Bush announced his decision to postpone leasing for OCS areas off southwestern Florida (sale 116, part 2), northern California (sale 91), and southern California (sale 95). At the same time, the President created a cabinet-level task force to review the environmental concerns for these three OCS areas, and he also requested independent advice from the National Research Council (NRC). The NRC was asked to assess the adequacy of the available scientific and technical information on estimated hydrocarbon resources and potential environmental effects for the three specified areas. The report, by the OCS Committee and its three panels dealing with ecology, physical oceanography, and socioeconomics, reviews the adequacy of information bearing upon the potential environmental impacts of OCS oil and gas activities for the three sale areas

  15. Geochemistry of marine sediments of the Brazilian Northeastern continental shelf

    Directory of Open Access Journals (Sweden)

    Fernanda Souza do Nascimento

    2010-01-01

    Full Text Available The marine sediment samples collected from the northeastern Brazilian continental shelf, at water depths between 20 and 80 m, consisted mainly of sands with an almost total absence of gravel and granules. Medium, coarse and very coarse sand grains are mostly composed of halimeda, lithothamnium, rodoliths and bioclastic sands with a carbonate content varying between 77 and 96 %. The chemistry in general shows a decreasing content of Ca (86.1 % >Si (6 % > Cl (3.6 % > Sr (0.8 % > K (0.66 % > S (0.62 % > Al (0.6 % > Na (0.55% > Mg (0.43 % > Fe (0.4 % > P (0.2 % > Br (0.04 % in the samples. There was no correlation between CaCO3 and chemical contents and grain size with depth and bio-components. With the exception of Sr of marine origin, all other elements (P, S, Br, Cl, Fe are of continental origin. The lithothamnium of some offshore samples shows higher CaCO3 content, while Mg and Na are present only in halimedas. Bioclastic sands contain no Br, and silt and clay fractions are rare and characterize samples closer to the coast. These marine bioclastic granulates are of very pure biogenic calcium carbonates and are thus highly to be recommended for economic purposes.Os granulados marinhos, da Plataforma Continental do nordeste brasileiro, coletados de profundidades entre 20 e 80 m, são predominantemente areias cascalhosas constituídas de halimedas, litotames, rodolitos e areias bioclásticas, cujos teores de carbonatos variam de 77 a 96 %. A concentração média geral de elementos químicos na ordem decrescente é Ca (86.1 % > Si (6 % > Cl (3.6 % > Sr (0.8 % > K (0.66 % > S (0.62 % > Al (0.6 % > Na (0.55 % > Mg (0.43 % > Fe (0.4 % > P (0.2 % > Br (0,04 %, independentemente da profundidade e tipo de bio-componente. Com exceção do Sr, que é de origem marinha, os demais elementos (P, S, Br, Cl, Fe são de origem continental. Elementos como Mg e Na foram restritos às halimedas em apenas duas amostras, enquanto Br não foi detectado nas areias

  16. Phytoplankton community structure in relation to hydrographic features along a coast-to-offshore transect on the SW Atlantic Continental Shelf

    Science.gov (United States)

    Islabão, C. A.; Mendes, C. R. B.; Detoni, A. M. S.; Odebrecht, C.

    2017-12-01

    The continental shelf in Southern Brazil is characterized by high biological productivity associated with horizontal and vertical density gradients due to the mixing of distinct water masses. Phytoplankton biomass and composition were evaluated in summer 2013 along an on-offshore transect off the mouth of the Patos Lagoon (Lat. 32°12S). Photosynthetic active radiation, temperature, salinity and fluorescence vertical profiles were carried out and Brünt-Väisäla frequency was estimated. Three water bodies were identified: the Subtropical Shelf Water along the entire transect, the Plata Plume Water on the middle shelf surface and the Tropical Water farther offshore. The water was sampled (N = 40) for the analyses of dissolved inorganic nutrients, phytoplankton cell density and composition. Phytoplankton present in the water was identified and quantified by the classical microscope sedimentation technique, complemented with CHEMTAX analysis of high-performance liquid chromatography (HPLC) pigment data. From the results obtained, chlorophyll a concentration was higher at both coastal stations (1.6-2.0 mg m-3) where the water column was homogeneous and diatoms dominated the stations. This group was replaced by dinoflagellates in stratified conditions on the shelf and farther offshore. Along the onshore-offshore gradient, two types of dinoflagellates were found: the peridinin-containing dinoflagellates Prorocentrum and Scrippsiella with a small contribution at the coastal stations, and the fucoxantin-containing small Gymnodiniales cells (< 15 μm) with more than 50% of the total chlorophyll a at the stations on the continental shelf, especially associated with the chlorophyll maximum at the base of the euphotic zone. The positive (negative) relationship between the biomass of dinoflagellates (diatoms) with the Brünt-Väisäla frequency, respectively, support the hypothesis that stratification is the most important environmental factor that determines the biomass of

  17. Explicit representation and parametrised impacts of under ice shelf seas in the z∗ coordinate ocean model NEMO 3.6

    Directory of Open Access Journals (Sweden)

    P. Mathiot

    2017-07-01

    Full Text Available Ice-shelf–ocean interactions are a major source of freshwater on the Antarctic continental shelf and have a strong impact on ocean properties, ocean circulation and sea ice. However, climate models based on the ocean–sea ice model NEMO (Nucleus for European Modelling of the Ocean currently do not include these interactions in any detail. The capability of explicitly simulating the circulation beneath ice shelves is introduced in the non-linear free surface model NEMO. Its implementation into the NEMO framework and its assessment in an idealised and realistic circum-Antarctic configuration is described in this study. Compared with the current prescription of ice shelf melting (i.e. at the surface, inclusion of open sub-ice-shelf cavities leads to a decrease in sea ice thickness along the coast, a weakening of the ocean stratification on the shelf, a decrease in salinity of high-salinity shelf water on the Ross and Weddell sea shelves and an increase in the strength of the gyres that circulate within the over-deepened basins on the West Antarctic continental shelf. Mimicking the overturning circulation under the ice shelves by introducing a prescribed meltwater flux over the depth range of the ice shelf base, rather than at the surface, is also assessed. It yields similar improvements in the simulated ocean properties and circulation over the Antarctic continental shelf to those from the explicit ice shelf cavity representation. With the ice shelf cavities opened, the widely used three equation ice shelf melting formulation, which enables an interactive computation of melting, is tested. Comparison with observational estimates of ice shelf melting indicates realistic results for most ice shelves. However, melting rates for the Amery, Getz and George VI ice shelves are considerably overestimated.

  18. Delineating the relationship between chromophoric dissolved organic matter (CDOM) variability and biogeochemical parameters in a shallow continental shelf

    OpenAIRE

    Sourav Das; Sugata Hazra; Aneesh A. Lotlikar; Isha Das; Sandip Giri; Abhra Chanda; Anirban Akhand; Sourav Maity; T. Srinivasa Kumar

    2016-01-01

    Absorption coefficient of chromophoric dissolved organic matter (CDOM) at 440 nm [aCDOM (440)], sea surface salinity (SSS), total suspended matter (TSM) and chlorophyll-a (chl-a) were measured during October, 2014 to March, 2015 in the shallow continental shelf waters of the Hugli Estuary, adjacent to West Bengal coast, India. The primary objective of the study was to characterize the relationship between aCDOM (440) and the above mentioned biogeochemical parameters. Upon analyzing the result...

  19. Magnetic surveys of the continental shelf off Visakhapatnam

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, T.C.S.; Murthy, K.S.R.

    shelf. Quantitative estimates made for the anomalies over the inner shelf using the graphical method and by computing the analytical signal suggest the existence of a fault in the nearshore region and a possible zone of heavy mineral concentration off...

  20. Benthic oxygen consumption on continental shelves off eastern Canada

    Science.gov (United States)

    Grant, Jonathan; Emerson, Craig W.; Hargrave, Barry T.; Shortle, Jeannette L.

    1991-08-01

    The consumption of phytoplankton production by the benthos is an important component of organic carbon budgets for continental shelves. Sediment texture is a major factor regulating benthic processes because fine sediment areas are sites of enhanced deposition from the water column, resulting in increased organic content, bacterial biomass and community metabolism. Although continental shelves at mid- to high latitudes consist primarily of coarse relict sediments ( PIPER, Continental Shelf Research, 11, 1013-1035), shelf regions of boreal and subarctic eastern Canada contain large areas of silt and clay sediments ( FADER, Continental Shelf Research, 11, 1123-1153). We collated estimates of benthic oxygen consumption in coarse (<20% silt-clay, <0.5% organic matter) and fine sediments (20% silt-clay, 0.5% organic matter) for northwest Atlantic continental shelves including new data for Georges Bank, the Scotian Shelf, the Grand Banks of Newfoundland and Labrador Shelf. Estimates were applied to the areal distribution of sediment type on these shelves to obtain a general relationship between sediment texture and benthic carbon consumption. Mean benthic oxygen demand was 2.7 times greater in fine sediment than in coarse sediment, when normalized to mean annual temperature. In terms of carbon equivalents, shelf regions with minimal fine sediment (Georges Bank, the Grand Banks of Newfoundland-northeast Newfoundland) consumed only 5-8% of annual primary production. Benthos of the Gulf of Maine (100% fine sediment) and the Scotian Shelf (35% fine sediment) utilized 16-19% of primary production. Although 32% of the Labrador Shelf area contained fine sediments, benthic consumption of pelagic production (8%) was apparently limited by low mean annual temperature (2°C). These results indicate that incorporation of sediment-specific oxygen uptake into shelf carbon budgets may increase estimates of benthic consumption by 50%. Furthermore, respiration and production by large

  1. Formation waters of the Norwegian Continental Shelf

    Energy Technology Data Exchange (ETDEWEB)

    McCartney, R. A.; Rein, E.

    2006-03-15

    New and previously published analyses of formation waters for the Norwegian Continental Shelf (NCS) have been evaluated and interpreted to determine the compositional distribution of formation waters in the region and factors controlling their compositions, and also to obtain information on subsurface fluid flow. Formation waters in the region are Na-Cl and Na-Ca-Cl-type waters that display a wide range of salinity (2500-212000 mg/kg Cl). Generally, the concentrations of most dissolved constituents are positively correlated with Cl so that their distribution in formation waters largely reflects the variations shown by salinity. Exceptions are SO4 which is generally low (less than 40 mg/l) regardless of Cl, and HCO3 and in-situ pH which are negatively correlated with Cl. The main factors determining the compositions of the formation waters are mixing of meteoric water (probably late-Jurassic to Eocene), ancient seawater and primary brine together with diagenetic reactions that have affected each of these components individually as well as mixtures of them. Evaluation of the distribution of salinity has helped us identify where vertical and/or lateral migration of brine from the evaporites has occurred. This has in turn provided us with information on the presence of leak-points and vertical mixing, although further investigation of the location of evaporites and basin palaeohydrogeology are required to determine whether regional lateral advection has occurred in the past. The results of this study may benefit oil exploration and production activities in the NCS including constraint of hydrocarbon migration models, economic evaluation of undrilled prospects, scale management and compartmentalisation studies. (Author)

  2. Supervised classification of continental shelf sediment off western Donegal, Ireland

    Science.gov (United States)

    Monteys, X.; Craven, K.; McCarron, S. G.

    2017-12-01

    Managing human impacts on marine ecosystems requires natural regions to be identified and mapped over a range of hierarchically nested scales. In recent years (2000-present) the Irish National Seabed Survey (INSS) and Integrated Mapping for the Sustainable Development of Ireland's Marine Resources programme (INFOMAR) (Geological Survey Ireland and Marine Institute collaborations) has provided unprecedented quantities of high quality data on Ireland's offshore territories. The increasing availability of large, detailed digital representations of these environments requires the application of objective and quantitative analyses. This study presents results of a new approach for sea floor sediment mapping based on an integrated analysis of INFOMAR multibeam bathymetric data (including the derivatives of slope and relative position), backscatter data (including derivatives of angular response analysis) and sediment groundtruthing over the continental shelf, west of Donegal. It applies a Geographic-Object-Based Image Analysis software package to provide a supervised classification of the surface sediment. This approach can provide a statistically robust, high resolution classification of the seafloor. Initial results display a differentiation of sediment classes and a reduction in artefacts from previously applied methodologies. These results indicate a methodology that could be used during physical habitat mapping and classification of marine environments.

  3. Regulation and efficiency: an empirical analysis of the United Kingdom continental shelf petroleum industry

    International Nuclear Information System (INIS)

    Kashani, H.A.

    2005-01-01

    The petroleum industry of the United Kingdom Continental Shelf (UKCS) has been subject to various degrees of regulation. Self-sufficiency, security of supply and developing offshore supply industry triggered government regulations that were seen as interventionary and protectionist. This paper tests the extent to which regulations targeting involvement of British offshore supply industry in the UKCS activity created inefficiencies. Data envelopment analysis (DEA), stochastic frontier analysis (SFA), Malmquist Indices, and standard regression analysis are used to measure the amount and address the source of inefficiencies. We will show that such inefficiencies could not be ruled out. The results provide an important insight into the UKCS production techniques and, more generally, into governments' abilities to influence private sector behaviour through contracts and tendering

  4. Discharges and Emissions on the Norwegian Continental Shelf : Oil, chemicals and emissions to air; Utslipp paa norsk kontinentalsokkel 2000. Olje, kjemikalier og utslipp til luft

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2002-07-01

    The report gives an overview of the discharges of oil and chemicals to sea and emissions to air from the Norwegian Continental Shelf for 2000. This report is based on the operators annual report to the Norwegian Pollution Control Authorities. (author)

  5. Dating recent sediments from the subaqueous Yangtze Delta and adjacent continental shelf, China

    Directory of Open Access Journals (Sweden)

    Zhang-Hua Wang

    2014-04-01

    Full Text Available In this study we analyzed sediment lithology, fallout of 210Pb and 137Cs, and spheroidal carbonaceous particles (SCPs for two short cores, YZE and CX38, obtained by gravity corer from the Yangtze River mouth offshore and adjacent continental shelf, to compare geochronological methods on the recent sediments of this area. Lithology and grain size changes in YZE suggested the re-discharging of the North Channel of the Yangtze River mouth by flood events during 1949–1954 and associated accretion in the offshore area. This event was validated by a remarkable zone of declination in both 137Cs and 210Pb activities and the absolute ages derived from the 137Cs and SCPs. In contrast, 210Pb results show obvious disturbance of grain size by sediment mixing and cannot be interpreted above 100 cm. In CX38, absolute ages for the early- and mid-1950s were derived by the 137Cs and the SCP profile respectively, which occurred in a reasonable sequence. The excess 210Pb distribution shows exponentially decreasing activities with depth, and the mean sedimentation rate agrees roughly with the one inferred from the SCP profile. We suggest that the limitation of the 210Pb method needs consideration while the SCP profile has the potential to provide a useful and independent dating method for recent Yangtze offshore and adjacent shelf sediments.

  6. Transport and transfer rates in the waters of the Continental Shelf. Annual report

    International Nuclear Information System (INIS)

    Biscaye, P.E.

    1978-07-01

    The present contract year has been one of transition from an emphasis on field work and sample gathering to the predominance of sample and data analysis and the formulation of testable hypotheses concerning specific processes in the New York Bight. We have begun to understand the seasonal transition in the role of phytoplankton vs. grazing zooplankton in forming the particles on which some reactive pollutants are removed. Using natural radioactive tracers we have estimated the removal rates of reactive metals from the surface waters and these range over an order of magnitude from most rapid nearshore to least rapid over the upper continental slope. Once removed nearshore, however, these tracers, and the pollutants for which they proxy, do not remain permanently in the sediments but appear to be remobilized (probably by oxidation) during the winter and are reintroduced into the water column. Work on transport and mixing processes of pollutants which are or behave like those in solution has continued along several fronts. Hydrographic data on the structure of the water column continues to give a description of the system that is crucial to understanding geochemical and biological processes which affect pollutants. Hydrographic characterization of water masses from the data sets of cruises has resulted in hypotheses concerning the renewal of shelf water by direct exchange between shelf and upper slope water

  7. Seasonal Dynamics of Dissolved Organic Carbon Under Complex Circulation Schemes on a Large Continental Shelf: The Northern South China Sea

    Science.gov (United States)

    Meng, Feifei; Dai, Minhan; Cao, Zhimian; Wu, Kai; Zhao, Xiaozheng; Li, Xiaolin; Chen, Junhui; Gan, Jianping

    2017-12-01

    We examined the distribution and seasonality of dissolved organic carbon (DOC) based on a large data set collected from the northern South China Sea (NSCS) shelf under complex circulation schemes influenced by river plume, coastal upwelling, and downwelling. The highest surface values of ˜117 μmol L-1 were observed nearshore in summer suggesting high DOC supplies from the river inputs, whereas the lowest surface values of ˜62 μmol L-1 were on the outer shelf in winter due to entrainment of DOC-poor subsurface water under strengthened vertical mixing. While the summer coastal upwelling brought lower DOC from offshore depth to the nearshore surface, the winter coastal downwelling delivered higher surface DOC to the midshelf deep waters from the inner shelf fueled by the China Coastal Current (CCC) transporting relatively high DOC from the East China Sea to the NSCS. The intensified winter downwelling generated a cross-shelf DOC transport of 3.1 × 1012 g C over a large shelf area, which induced a significant depression of the NSCS DOC inventory in winter relative to in autumn. In addition to the variable physical controls, net biological production of DOC was semiquantified in both the river plume (2.8 ± 3.0 μmol L-1) and coastal upwelling (3.1 ± 1.3 μmol L-1) in summer. We demonstrated that the NSCS shelf had various origins of DOC including riverine inputs, inter-shelf transport and in situ production. Via cross-shelf transport, the accumulated DOC would be exported to and stored in the deep ocean, suggesting that continental shelves are a potentially effective carbon sink.

  8. Shelf-life Assessment of Food Undergoing Oxidation-A Review.

    Science.gov (United States)

    Calligaris, Sonia; Manzocco, Lara; Anese, Monica; Nicoli, Maria Cristina

    2016-08-17

    Oxidation is the most common event leading to the end of shelf life of microbiologically stable foods. Thus, a reliable shelf-life assessment is crucial to verify how long the product will last before it becomes oxidized to an unacceptable level to the consumers. Shelf-life assessment strategies of foods and beverages suffering oxidation are critically discussed focusing on definition of the acceptability limit, as well as the choice of the proper oxidative indicators, and methodologies for shelf-life testing. Testing methodologies for shelf-life determination under actual and accelerated storage conditions are considered, highlighting possible uncertainties, pitfalls, and future research needs.

  9. Modelling of storm-driven shelf waves north of Scotland—I. Idealized models

    Science.gov (United States)

    Heaps, N. S.; Huthnance, J. M.; Jones, J. E.; Wolf, J.

    1988-11-01

    Storm-driven currents observed over the Scottish continental shelf were described by GORDON and HUTHNANCE (1987 , Continental Shelf Research, 7, 1015-1048). Their suggestion of continental shelf-wave responses is investigated here using semi-analytic and numerical models of a straight continental shelf. Grid resolution, boundary conditions, truncations and differences of depth profile are considered with the semi-analytic model, from which dispersion curves and wave forms are derived. These forms are closely matched by the fully numerical model forced by specified elevations at one end. Further numerical calculations are described, for idealized wind forcing along or across limited regions of the shelf or slope. Localized forcing of short duration gives currents of the type observed, being rotary (clockwise) with roughly 22 h period. More extensive alongshelf forcing gives predominantly alongshelf currents with a strength tending to follow the forcing; the second form of observed response. Frictional effects are considered. A companion paper ( FLATHER and PROCTOR, 1988 , in preparation) describes the results of numerical simulations using realistic meteorological forcing and bathymetry.

  10. The behavior of particle-reactive tracers in a high turbidity environment: 234Th and 210Pb on the Amazon continental shelf

    International Nuclear Information System (INIS)

    Smoak, J.M.; DeMaster, D.J.; Pope, R.H.; Kuehl, S.A.; McKee, B.A.

    1996-01-01

    Excess 234 Th and 210 Pb seabed inventories were measured in cores collected from the Amazon continental shelf to examine particle scavenging and seabed dynamics. Typical excess 210 Pb inventories range from 100 to 300 dpm cm -2 , and the total excess 210 Pb inventory for the Amazon shelf was determined to be 2.7 x 10 17 dpm. The 210 Pb measurements indicate that particle-reactive species are scavenged not only form the Amazon River but also from the lateral advection of offshore water. In order to sustain the 210 Pb inventories, the volume of water supplied by the lateral advection from offshore must be approximately five to ten times the water discharge of the Amazon River. This lateral advection supplies about 67% of the total excess 210 Pb to the Amazon continental shelf with relatively small contributions from riverine input (31%), atmospheric fallout (2.3%), and in-situ production (0.1%). The 234 Th inventories were measured on four cruises, which occurred during periods of differing river discharge, wind stress, and flow rates of the North Brazil Current. The 234 Th excess seabed inventories show large spatial and seasonal variability, with a range from 0 to 22 dpm cm -2 . This approach indicates that for most of the shelf, the inventories of the shorter-term tracer ( 234 Th) are less than predicted by the inventories of the longer-term tracer ( 210 Pb). There are two explanations for this trend. The first is that a larger portion of the 234 Th inventory occurs in the fluid muds or the water column relative to 210 Pb. The second is that the supply of offshore water, scavenging efficiency, and/or deposition have been lower over the two year study period relative to the last one hundred years. 38 refs., 7 figs

  11. Sedimentation on the Valencia Continental Shelf: Preliminary results

    Science.gov (United States)

    Maldonado, Andres; Swift, Donald J. P.; Young, Robert A.; Han, Gregory; Nittrouer, Charles A.; DeMaster, David J.; Rey, Jorge; Palomo, Carlos; Acosta, Juan; Ballester, A.; Castellvi, J.

    1983-10-01

    Preliminary analysis of data collected during the course of a cooperative Spanish-United States investigation of the Valencia Shelf (western Mediterranean) reveals a storm-dominated, mud-accumulating sedimentary regime. Calcareous mud is accumulating seaward of a narrow band of shoreface sand and gravel. On the outer shelf the mud is enriched by a pelagic calcareous component. Preliminary 210Pb data from vertical profiles of box cores yield nominal accumulation rates from 2.6 mm y -1 near the Ebro Delta to 1.3 mm y -1 on the southern portion of the Valencia Shelf. Storm-current winnowing has resulted in the development of a biogenic lag sand over the mid-shelf mud in the northern part of the study area. Piston cores reveal a basal Holocene sand and gravel facies similar to that presently seen on the inner shelf. Upward-fining sequences on the central and outer shelf are inferred to result from the landward shift of lithotopes during the course of the Holocene transgression. These sequences are locally repeated, perhaps as the consequence of brief, local interludes of coastal progradation. Application of a diagnostic circulation model suggests that intense, downwelling coastal flows occur during winter northeastern storms. Storm activity has induced erosional shoreface retreat during the course of the Holocene transgression and has generated by this means the basal coarse facies observed in the piston cores. In the central part of the study area seaward of the Albufera Lagoon, the mud blanket thins to a layer several centimeters thick which is draped over a thickened (10 m) basal sand. The basal sand is molded into northwest trending ridges. The data are not sufficient to determine whether these are overstepped barriers, or submarine sand ridges formed by storm flows during the shoreface retreat process.

  12. Sand ridge morphology and bedform migration patterns derived from bathymetry and backscatter on the inner-continental shelf offshore of Assateague Island, USA

    Science.gov (United States)

    Pendleton, Elizabeth; Brothers, Laura; Thieler, E. Robert; Sweeney, Edward

    2017-01-01

    The U.S. Geological Survey and the National Oceanographic and Atmospheric Administration conducted geophysical and hydrographic surveys, respectively, along the inner-continental shelf of Fenwick and Assateague Islands, Maryland and Virginia over the last 40 years. High resolution bathymetry and backscatter data derived from surveys over the last decade are used to describe the morphology and presence of sand ridges on the inner-continental shelf and measure the change in the position of smaller-scale (10–100 s of meters) seafloor features. Bathymetric surveys from the last 30 years link decadal-scale sand ridge migration patterns to the high-resolution measurements of smaller-scale bedform features. Sand ridge morphology on the inner-shelf changes across-shore and alongshore. Areas of similar sand ridge morphology are separated alongshore by zones where ridges are less pronounced or completely transected by transverse dunes. Seafloor-change analyses derived from backscatter data over a 4–7 year period show that southerly dune migration increases in magnitude from north to south, and the east-west pattern of bedform migration changes ~ 10 km north of the Maryland-Virginia state line. Sand ridge morphology and occurrence and bedform migration changes may be connected to observed changes in geologic framework including topographic highs, deflated zones, and sand availability. Additionally, changes in sand ridge occurrence and morphology may help explain changes in the long-term shoreline trends along Fenwick and Assateague Islands. Although the data presented here cannot quantitatively link sand ridges to sediment transport and shoreline change, it does present a compelling relationship between inner-shelf sand availability and movement, sand ridge occurrence and morphology, geologic framework, and shoreline behavior.

  13. Distribution of marine birds on the mid- and North-Atlantic US outer continental shelf. Technical progress report, January 1978-July 1980

    Energy Technology Data Exchange (ETDEWEB)

    Powers, K.D.; Pittman, G.L.; Fitch, S.J.

    1980-09-01

    The species composition, distribution, and abundance of marine birds on continental shelf waters from Cape Hatteras to the Bay of Fundy were examined using ships-of-opportunity. Northern Fulmar, Cory's Shearwater, Greater Shearwater, Sooty Shearwater, Wilson's Storm-Petrel, Gannet, Red Phalarope, Great Black-backed Gull, Herring Gull, and Black-legged Kittiwake were the most abundant and common species. These species were ecologically dominant within the bird community in numbers and biomass. Georges Bank and Gulf of Marine regions generally had greatest estimates of standing stock and biomass; whereas, in the Middle Atlantic region these estimates were consistently lowest. Species diversity throughout the study area was greatest in spring and least in fall. Oceanic fronts at the continental shelf break and at Nantucket Shoals influenced the distribution of Wilson's Storm-Petrels and Red Phalaropes. Fishing activities were particularly important to Larus gull distribution. Fishes, squids, and crustaceans were the most important groups of prey items in diets of nine bird species. An oiled bird or pollution index was developed. According to the index, frequency of oiled birds was greatest in winter and spring, and gulls made up the majority of species with oiled plumages.

  14. Contributions to knowledge of the continental margin of Uruguay. Description of background samples in the continental margin of Uruguay

    International Nuclear Information System (INIS)

    Preciozzi, F

    2015-01-01

    This study provide data concerning of the background sediments of the continental margin of Uruguay. There were carried out different works with witnesses in order to extract various sediment samples from the continental shelf

  15. Comment on “Large-scale bedforms along a tideless outer shelf setting in the western Mediterranean” by Lo Iacono et al. (2010) in Continental Shelf Research vol 30, pp. 1802-1813

    Science.gov (United States)

    Flemming, B. W.

    2013-01-01

    Lo Iacono et al. (2010) report the discovery of large (but degraded) subaqueous dunes on the outer continental shelf NE of Valencia, western Mediterranean Sea. They argue that the dunes, after having been generated sometime in the past, are being episodically rejuvenated by high-energy flow events to the present day. Because the height vs. wavelength relation of the dunes falls below the global mean trend predicted by the equation of Flemming (1988), they claim to have discovered a new, low-amplitude type of flow-transverse bedform which typically occurs on microtidal current-swept outer continental shelves. A close inspection of the evidence shows that the reasoning of Lo Iacono et al. (2010) is flawed and that their interpretations and conclusions are premature and unjustified.

  16. 77 FR 71612 - Atlantic Wind Lease Sale 2 (ATLW2) Commercial Leasing for Wind Power on the Outer Continental...

    Science.gov (United States)

    2012-12-03

    ... Wind Lease Sale 2 (ATLW2) Commercial Leasing for Wind Power on the Outer Continental Shelf Offshore...), Interior. ACTION: Proposed Sale Notice for commercial leasing for wind power on the Outer Continental Shelf... sale of commercial wind energy leases on the Outer Continental Shelf (OCS) offshore Rhode Island and...

  17. Oil spill contingency planning for offshore oil fields - a new concept established for the Norwegian continental shelf

    International Nuclear Information System (INIS)

    Singsaas, I.; Reed, M.; Nygaard, T.; Sundnes, G.Jr.

    1998-01-01

    The development of a new concept for oil spill contingency planning to be used for offshore oil fields on the Norwegian continental shelf was discussed. The factors which are important in developing a good oil spill contingency plan include a good understanding of: (1) the fate, behaviour and weathering of the specific oil, (2) relevant oil spill scenarios, (3) drift and spreading of the oil, and (4) specific requirements for the effectiveness of the chosen response options. The oil spill contingency and response (OSCAR) model was used for quantitative comparison of alternative response options. 21 refs., 2 tabs., 7 figs

  18. Well construction team approach creates a new future for one company's operations on the Dutch Continental Shelf

    International Nuclear Information System (INIS)

    Stringer, R.B.; Bakker, T.W.; Mejnertsen, T.

    1994-01-01

    Rising costs and low energy prices were inhibiting the development of marginal fields on the Dutch Continental Shelf, resulting in a major reduction in drilling activity. This triggered a change from traditional operating and contracting strategies to a Well Construction Team approach based on partnering agreements with the principal drilling and service contractors. The change has resulted in major cost reductions coupled to improved well quality that are justifying the re-evaluation of previously sub-economic development prospects. This paper describes the strategies employed and presents the results achieved during the first year of the partnership

  19. Gulf of Mexico Outer Continental Shelf daily oil and gas production rate projections from 1999 through 2003

    International Nuclear Information System (INIS)

    Melancon, J.M.; Baud, R.D.

    1999-02-01

    This paper provides daily oil and gas production rate projections for the Gulf of Mexico (GOM) Outer Continental Shelf (OCS) for the years 1999 through 2003. These projections represent daily oil and gas production estimates at calendar year end. In this report, daily oil production rates include both oil and condensate production, and daily gas production rates include both associated and nonassociated gas production. In addition to providing daily oil and gas production rate projections, the authors have included one figure and one table pertaining to leasing history and one table concerning exploration and development plan approvals

  20. Gulf of Mexico outer continental shelf daily oil and gas production rare projections from 1998 through 2002

    International Nuclear Information System (INIS)

    Melancon, J.M.; Roby, D.S.

    1998-02-01

    This paper provides daily oil and gas production rate projections for the Gulf of Mexico (GOM) Outer Continental Shelf (OCS) for the years 1998 through 2002. These projections represent daily oil and gas production estimates at calendar year end. In this report, daily oil production rates include both oil and condensate production, and daily gas production rates include both associated and nonassociated gas production. In addition to providing daily oil and gas production rate projections, the authors have included one figure and one table pertaining to leasing history and one table concerning exploration and development plan approvals

  1. Polychaete/amphipod ratio as an indicator of environmental impact related to offshore oil and gas production along the Norwegian continental shelf.

    Science.gov (United States)

    Andrade, Hector; Renaud, Paul E

    2011-12-01

    Benthic faunal data is regularly collected worldwide to assess the ecological quality of marine environments. Recently, there has been renewed interest in developing biological indices able to identify environmental status and potential anthropogenic impacts. In this paper we evaluate the performance of a general polychaete/amphipod ratio along the Norwegian continental shelf as an environmental indicator for offshore oil and gas impacts. Two main trends are apparent: first, a contamination gradient is discernible from where production takes place compared to stations 10,000 m away. Second, the quality of the marine environment has improved over time. These results are consistent with monitoring reports employing a combination of uni- and multi-variate statistics. Thus, we consider this ratio as a relatively simple, useful and potentially cost-effective complement to other more demanding assessment techniques. Because of its strong theoretical basis, it may also be useful for detecting ecological change as a result of other activities. Copyright © 2011 Elsevier Ltd. All rights reserved.

  2. Neogene sedimentation on the outer continental margin, southern Bering Sea

    Science.gov (United States)

    Vallier, T.L.; Underwood, M.B.; Gardner, J.V.; Barron, J.A.

    1980-01-01

    Neogene sedimentary rocks and sediments from sites on the outer continental margin in the southern Bering Sea and on the Alaska Peninsula are dominated by volcanic components that probably were eroded from an emergent Aleutian Ridge. A mainland continental source is subordinate. Most sediment in the marine environment was transported to the depositional sites by longshore currents, debris flows, and turbidity currents during times when sea level was near the outermost continental shelf. Fluctuations of sea level are ascribed both to worldwide glacio-eustatic effects and to regional vertical tectonics. Large drainage systems, such as the Yukon and Kuskokwim Rivers, had little direct influence on sedimentation along the continental slope and Unmak Plateau in the southern Bering Sea. Sediments from those drainage systems probably were transported to the floor of the Aleutian Basin, to the numerous shelf basins that underlie the outer continental shelf, and to the Arctic Ocean after passing through the Bering Strait. Environments of deposition at the sites along the outer continental margin have not changed significantly since the middle Miocene. The site on the Alaska Peninsula, however, is now emergent following shallow-marine and transitional sedimentation during the Neogene. ?? 1980.

  3. Surficial sediment character of the New York-New Jersey offshore continental shelf region: a GIS compilation

    Science.gov (United States)

    Williams, S. Jeffress; Arsenault, Matthew A.; Poppe, Lawrence J.; Reid, Jane A.; Reid, Jamey M.; Jenkins, Chris J.

    2007-01-01

    Broad continental shelf regions such as the New York Bight are the product of a complex geologic history and dynamic oceanographic processes, dominated by the Holocene marine transgression (>100 m sea-level rise) following the end of the last Pleistocene ice advance ~ 20,000 years ago. The area of the U.S. Exclusive Economic Zone (U.S. EEZ) territory, extending 200 nautical miles seaward from the coast, is larger than the continental U.S. and contains submerged landforms that provide a variety of natural functions and societal benefits, such as: critical habitats for fisheries, ship navigation and homeland security, and engineering activities (i.e. oil and gas platforms, pipeline and cable routes, potential wind-energy-generation sites). Some parts of the continental margins, particularly inner-continental shelf regions, also contain unconsolidated hard-mineral deposits such as sand and gravel that are regarded as potential aggregate resources to meet or augment needs not met by onshore deposits (Williams, 1992). The present distribution of surficial sediment off the northeastern United States is shaped from the deposits left by the last glaciation and reflects the cumulative effects of sediment erosion, transport, sorting, and deposition by storm and tidal processes during the Holocene rise in sea level. As a result, the sediments on the sea floor represent both an historical record of former conditions and a guide to possible future sedimentary environments. The U.S. Geological Survey (USGS) through the Coastal and Marine Geology Program, in cooperation with the University of Colorado and other partners, has compiled extant sediment character and textural data as well as other geologic information on the sea floor from all regions around the U.S. into the usSEABED data system (Reid and others, 2005; Buczkowski and others, 2006; Reid and others, 2006). The usSEABED system, which contains information on sediment grain size and lithology for more than 340

  4. {sup 210}Pb-Excess and Sediment Accumulation Rates at the Iberian Continental Margin

    Energy Technology Data Exchange (ETDEWEB)

    Carvalho, F. P.; Oliveira, J. M.; Soares, A. M. [Nuclear and Technological Institute, Sacavem (Portugal)

    2013-07-15

    Sediments from the continental shelf, slope, and rise at the continental margin of northern Portugal and the adjacent Iberian abyssal basin were analysed for 210Pb, {sup 226}Ra, {sup 137}Cs and {sup 14}C. Pb-210 derived sedimentation rates at the continental shelf off the Portuguese coast were 0.2-0.6 cm/a. In some cores from fine sediment deposits at the outer shelf, the {sup 210}Pb excess continuum was interrupted and sediment layers were missing, suggesting that events such as sediment slides could have occurred. Higher sedimentation rates were determined in locations at the rise of the continental slope, confirming enhanced deposition by sediment slides. In the deeper Iberian Abyssal Basin, using the {sup 14}C age of sediment layers the sedimentation rate was determined at 3.2 cm/ka, thus four orders of magnitude lower than at the continental shelf. The spatial distribution of sedimentation rates determined by radionuclide based chronologies, suggested that fine sediments from river discharges are deposited mainly at the outer continental shelf. These deposits may became unstable with time and, occasionally, originate sediment slides that are drained by the canyons and reach the deep sea. The Iberian abyssal basin receives some advective contribution of these sediment slides and the sedimentation rate is one order of magnitude higher than in other abyssal basins of the NE Atlantic Ocean. (author)

  5. Scientific Discoveries in the Central Arctic Ocean Based on Seafloor Mapping Carried out to Support Article 76 Extended Continental Shelf Claims (Invited)

    Science.gov (United States)

    Jakobsson, M.; Mayer, L. A.; Marcussen, C.

    2013-12-01

    Despite the last decades of diminishing sea-ice cover in the Arctic Ocean, ship operations are only possible in vast sectors of the central Arctic using the most capable polar-class icebreakers. There are less than a handful of these icebreakers outfitted with modern seafloor mapping equipment. This implies either fierce competition between those having an interest in using these icebreakers for investigations of the shape and properties of Arctic Ocean seafloor or, preferably, collaboration. In this presentation examples will be shown of scientific discoveries based on mapping data collected during Arctic Ocean icebreaker expeditions carried out for the purpose of substantiating claims for an extended continental shelf under United Nations Convention of the Law of the Sea (UNCLOS) Article 76. Scientific results will be presented from the suite of Lomonosov Ridge off Greenland (LOMROG) expeditions (2007, 2009, and 2012), shedding new light on Arctic Ocean oceanography and glacial history. The Swedish icebreaker Oden was used in collaboration between Sweden and Denmark during LOMROG to map and sample portions of the central Arctic Ocean; specifically focused on the Lomonosov Ridge north of Greenland. While the main objective of the Danish participation was seafloor and sub-seabed mapping to substantiate their Article 76 claim, LOMROG also included several scientific components, with scientists from both countries involved. Other examples to be presented are based on data collected using US Coast Guard Cutter Healy, which for several years has carried out mapping in the western Arctic Ocean for the US continental shelf program. All bathymetric data collected with Oden and Healy have been contributed to the International Bathymetric Chart of the Arctic Ocean (IBCAO). This is also the case for bathymetric data collected by Canadian Coast Guard Ship Louis S. St-Laurent for Canada's extended continental shelf claim. Together, the bathymetric data collected during these

  6. Decadal variability on the Northwest European continental shelf

    Science.gov (United States)

    Jones, Sam; Cottier, Finlo; Inall, Mark; Griffiths, Colin

    2018-02-01

    Decadal scale time series of the shelf seas are important for understanding both climate and process studies. Despite numerous investigations of long-term temperature variability in the shelf seas, studies of salinity variability are few. Salt is a more conservative tracer than temperature in shallow seas, and it can reveal changes in local hydrographic conditions as well as transmitted basin-scale changes. Here, new inter-annual salinity time series on the northwest European shelf are developed and a 13 year high resolution salinity record from a coastal mooring in western Scotland is presented and analysed. We find strong temporal variability in coastal salinity on timescales ranging from tidal to inter-annual, with the magnitude of variability greatest during winter months. There is little seasonality and no significant decadal trend in the coastal time series of salinity. We propose 4 hydrographic states to explain salinity variance in the shelf area west of Scotland based on the interaction between a baroclinic coastal current and wind-forced barotropic flow: while wind forcing is important, we find that changes in the buoyancy-driven flow are more likely to influence long-term salinity observations. We calculate that during prevailing westerly wind conditions, surface waters in the Sea of the Hebrides receive a mix of 62% Atlantic origin water to 38% coastal sources. This contrasts with easterly wind conditions, during which the mix is 6% Atlantic to 94% coastal sources on average. This 'switching' between hydrographic states is expected to impact nutrient transport and therefore modify the level of primary productivity on the shelf. This strong local variability in salinity is roughly an order of magnitude greater than changes in the adjacent ocean basin, and we infer from this that Scottish coastal waters are likely to be resilient to decadal changes in ocean climate.

  7. A longitudinal study of fallow dynamics in the UK Continental Shelf (UKCS)

    International Nuclear Information System (INIS)

    Kemp, Alexander G.; Kasim, Sola A.

    2007-01-01

    This paper identifies the causes of and solutions to the problems posed by the fallow assets' phenomenon in the UK Continental Shelf (UKCS). Using data available in the public domain, including the Fifth Fallow Release, the province's assets were grouped into two broad cross-sections of fallow and non-fallow assets, with further sub-divisions. The dependent variable of interest was the median fallow duration of the assets. Fallow duration was measured in two ways, namely those relating to censored and uncensored data. An empirical panel econometric model was formulated, estimated and simulated to establish the principal causal factors and the effective remedial policy measures. The model estimation results provide evidence that the interactive effects of the key influencing variables are stronger than their individual effects. Thus, the combined effects of reserves and distance from infrastructure have a greater weight on the fallow spell than their individual effects. Several policy simulation runs established that, contrary to some theoretical propositions (a) stronger rather than weaker government intervention, on occasion, is preferable, and (b) price is not a central determinant of investment timing

  8. Heavy metals transfer through the Inner Continental Shelf to the open ocean data as part of the International Decade of Ocean Exploration (IDOE) submitted October, 1972 (NODC Accession 7300575)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Heavy metals transfer through the Inner Continental Shelf to the open ocean data were collected by the Skidway Institute of Oceanography (SKIO). Data were collected...

  9. Geophysical and sampling data from the inner continental shelf: Duxbury to Hull, Massachusetts

    Science.gov (United States)

    Barnhardt, Walter A.; Ackerman, Seth D.; Andrews, Brian D.; Baldwin, Wayne E.

    2010-01-01

    The U.S. Geological Survey (USGS) and the Massachusetts Office of Coastal Zone Management (CZM) have cooperated to map approximately 200 km² of the Massachusetts inner continental shelf between Duxbury and Hull. This report contains geophysical and geological data collected by the USGS on three cruises between 2006 and 2007. These USGS data are supplemented with a National Oceanic and Atmospheric Administration (NOAA) hydrographic survey conducted in 2003 to update navigation charts. The geophysical data include (1) swath bathymetry from interferometric sonar and multibeam echosounders, (2) acoustic backscatter from sidescan sonar and multibeam echosounders, and (3) subsurface stratigraphy and structure from seismic-reflection profilers. The geological data include sediment samples, seafloor photographs, and bottom videos. These spatial data support research on the influence sea-level change and sediment supply have on coastal evolution, and on efforts to understand the type, distribution, and quality of subtidal marine habitats in the Massachusetts coastal ocean.

  10. Pollution by petroleum hydrocarbons in sediments from continental shelf of Tabasco State, Mexico

    International Nuclear Information System (INIS)

    Botello, A.V.; Gonzalez, C.; Diaz, G.

    1991-01-01

    The Wider Caribbean is potentially one of the largest oil producing areas in the world. Major petroleum production areas include Louisiana and Texas, USA; the Bay of Campeche, Mexico; Lake Maracaibo, Venezuela; and Gulf of Paria, Trinidad; all of which are classified as production accident high-risk zones. About 5 million of barrels are transported every day in the Caribbean, thus generating an intense tanker traffic. It has been estimated that oil discharges from tank washings within the Wider Caribbean could be as high as 7 million barrels/year. For all those reasons petroleum pollution is considered as the major environmental problem in the Wider Caribbean area and increasing day to day due to the use of petroleum as the main energy source. On the other hand, the continental shelf of Tabasco state actually represents one of the most productive areas for crude oil in the Gulf of Mexico. Sediments were collected from this area and analyzed for hydrocarbons

  11. The FOODBANCS project: Introduction and sinking fluxes of organic carbon, chlorophyll- a and phytodetritus on the western Antarctic Peninsula continental shelf

    Science.gov (United States)

    Smith, Craig R.; Mincks, Sarah; DeMaster, David J.

    2008-11-01

    The impact of the highly seasonal Antarctic primary production cycle on shelf benthic ecosystems remains poorly evaluated. Here we describe a times-series research project on the West Antarctic Peninsula (WAP) shelf designed to evaluate the seafloor deposition, and subsequent ecological and biogeochemical impacts, of the summer phytoplankton bloom along a transect crossing the Antarctic shelf near Anvers Island. During this project, entitled Food for Benthos on the Antarctic Continental Shelf (FOODBANCS), we deployed replicate sediment traps 150-170 m above the seafloor (total water-column depth of 590 m) on the central shelf from December 1999 to March 2001, recovering trap samples every 3-4 months. In addition, we used a seafloor time-lapse camera system, as well as video surveys conducted at 3-4 months intervals, to monitor the presence and accumulation of phytodetritus at the sediment-water interface. The fluxes of particulate organic carbon and chlorophyll- a into sediment traps (binned over 3-4 month intervals) showed patterns consistent with seasonal variability, with average summer fluxes during the first year exceeding winter fluxes by a factor of ˜2-3. However, inter-annual variability in summer fluxes was even greater than seasonal variability, with 4-10-fold differences in the flux of organic carbon and chlorophyll- a between the summer seasons of 1999-2000 and 2000-2001. Phytodetrital accumulation at the shelf floor also exhibited intense inter-annual variability, with no visible phytodetritus from essentially December 1999 to November 2000, followed by pulsed accumulation of 1-2 cm of phytodetritus over a ˜30,000 km 2 shelf area by March 2001. Comparisons with other studies suggest that the levels of inter-annual variability we observed are typical of the Antarctic shelf over decadal time scales. We conclude that fluxes of particulate organic carbon, chlorophyll- a and phytodetritus to WAP-shelf sediments vary intensely on seasonal to inter

  12. A new era for the offshore oil and gas industry on the UKCS [United Kingdom Continental Shelf

    International Nuclear Information System (INIS)

    Pickering, H.

    1998-01-01

    This paper explores the development of the offshore oil and gas industry on the United Kingdom Continental Shelf (UKCS) and particularly the role played by science and technology in that development. An historical perspective is taken in the first instance to place recent developments in context, before exploring the role of science and technology in the 1990s. Three areas of key importance form the basis of the discussion: the maintenance of production from the traditional provinces, the development of new provinces and the mitigation of environmental impacts. The paper demonstrates the crucial role that science and technology plays in each of these areas. (author)

  13. Condições hidrográficas na plataforma continental ao largo de Ubatuba: variações sazonais e em média escala Hydrographic conditions on the continental shelf off Ubatuba: seasonal and meso-scale variability

    Directory of Open Access Journals (Sweden)

    Belmiro Mendes de Castro Filho

    1987-01-01

    estruturas térmica e halina, tem provavelmente um importante papel na troca de massas de água entre a costa e o talude, contribuindo para o enriquecimento das águas da plataforma continental através dos movimentos ascendentes que ocorrem em seu núcleo.Hydrographic conditions on the continental shelf offshore of Ubatuba have shown different water mass distributions for summer (December, 1985 and winter (July, 1986. Two physical domains were identified: inner shelf and outer shelf, both separated by a front particularly well defined during the winter, The inner shelf has a two layer vertical stratification during summer, with a strong thermocline at mid-depths. During winter this region shows almost no stratification, During summer the upper layer (depths smaller than 20 m is filled with Coastal Water (CW, which interacts with Tropical Water (TW offshore. South Atlantic Central Water (SACA predominates in the lower layer during surrmer. Vertical interaction between CW and SACA is restricted to a band near the coast. During winter SACA does not penetrate towards the coast in the lower layer and, as a consequence, the inner shelf shows the presence of CW only. For winter interactions between CW and SACA are observed only across the front that separates inner and outer shelf. For this season there is also a noticeable intrusion of TW towards the coast on the upper layer of the outer shelf. A descriptive model for the wind driven seasonal circulation of the inner shelf is sugested, based on: 1 the water mass distributions observed and: 2 meteorological conditions from a coastal station located southward of Ubatuba, The outer shelf dynamics seems to suffer strong influence from the Brazil Current. Eddies or meanders with characteristics of frontal eddies, have been observed on both seasons on the outer shelf. These eddies should play an important role on the water mass exchange between the shelf and the slope, contributing for the enrichment of shelf waters by the upward

  14. Stratigraphic Reconstruction of a Late Pleistocene Cypress Forest Discovered on the Northern Gulf of Mexico Continental Shelf

    Science.gov (United States)

    Gonzalez Rodriguez, S. M.; Bentley, S. J.; Obelcz, J.; Truong, J. T.; DeLong, K. L.; Xu, K.; Harley, G. L.; Reese, C. A.; Caporaso, A.; Shen, Z.

    2017-12-01

    A previously buried bald cypress forest (Taxodium distichum) was discovered on the continental shelf, offshore of Orange Beach, Alabama, USA, in 20 m water depth. The forest was possibly exhumed by Hurricane Ivan in 2004, and is now exposed as stumps in life position in a trough located in the northern Gulf of Mexico continental shelf seafloor. We are investigating the local stratigraphy, paleo-landscape, and mode of forest preservation of this unique site. In August 2015 and July 2016, submersible vibracores (18 in total) were collected. Core analysis included: bulk density and imaging via Geotek multi sensor core logger, sediment grain size, structure, and organic content via loss-on-ignition. Selected samples have been dated using 14C and optically stimulated luminescence (OSL) methods. Multibeam and CHIRP subbottom bathymetry provide context for litho- and chrono-stratigraphy of the site. Integration of core lithostratigraphy and modern shelf bathymetry reveal Holocene transgressive sands blanketing diverse sedimentary facies that are truncated by the late Pleistocene-early Holocene ravinement. Deposits below the ravinement surface include interbedded sand and mud (exact age unknown, but possibly pertaining to a shallow marine environment), overlying a floodplain/swamp facies of woody debris, peat, and mud (provisionally dated by 14C to 41-45 ka). These units grade laterally into paleosols that appear to be 10-15 ka older, based on recently obtained preliminary OSL dates. Occurrence of paleosols and swamp deposits of broadly similar age and elevation suggests that the ancient landscape possessed topographic relief that allowed wetland and upland habitats to develop in close proximity. These new OSL dates enhance our initial hypothesis that floodplain aggradation in the area was a key factor that might have allowed forest preservation. The timing of temporary sea level rises (SLR) ca. 40 and 60 ka. with our 14C and preliminary OSL dates, suggests that floodplain

  15. Preliminary assessments of the occurrence and effects of utilization of sand and aggregate resources of the Louisiana inner shelf

    Science.gov (United States)

    Suter, J.R.; Mossa, J.; Penland, S.

    1989-01-01

    Louisiana is experiencing the most critical coastal erosion and land loss problem in the United States. Shoreline erosion rates exceed 6 m/yr in more than 80% of the Louisiana coastal zone and can be up to 50 m/yr in areas impacted by hurricanes. The barrier islands have decreased in area by some 40% since 1880. Land loss from coastal marshlands and ridgelands from both natural and human-induced processes is estimated to exceed 100 km2/yr. In response, a two-phase plan has been established, calling for barrier-island restoration and beach nourishment, both requiring large amounts of sand. The plan will be cost-effective only if sand can be found offshore in sufficient quantities close to project sites. To locate such deposits, the Louisiana Geological Survey is conducting an inventory of nearshore sand resources on the Louisiana continental shelf. Exploration for offshore sand deposits is conducted in two phases, with high-resolution seismic reflection profiling to locate potential sand bodies followed by vibracoring to confirm seismic intepretations and obtain samples for textural characterization. As part of the initial stages of the program, reconnaissance high-resolution seismic investigations of three areas of the continental shelf representing different stages in the evolutionary sequence of barrier shorelines were carried out. The Timbalier Islands, flanking barriers of the eroding Caminada-Moreau headland, contain potential sand resources associated with buried tidal and distributary channels. The Chandeleur Islands, a barrier-island arc, have potential offshore sands in the form of truncated spit and tidal inlet deposits, submerged beach ridges, and distributary channels. Trinity Shoal, an inner shelf shoal, is an offshore feature containing up to 2 ?? 109 m3 of material, most of which is probably fine sand. These reconnaissance surveys have demonstrated the occurrence of sand resources on the Louisiana continental shelf. Utilization of such deposits for

  16. Trophic Groups Of Demersal Fish Of Santos Bay And Adjacent Continental Shelf, São Paulo State, Brazil: Temporal And Spatial Comparisons

    Directory of Open Access Journals (Sweden)

    Elizabeti Y. Muto

    2014-07-01

    Full Text Available The temporal and spatial variations of feeding habits and trophic groups of demersal fish species of Santos Bay and the adjacent continental shelf were investigated. The samples were taken in September 2005 and March 2006 by bottom otter trawling. The stomach content analysis of 2,328 specimens of 49 species showed most fish fed on a large range of food items but relied heavily on shrimp, crabs/swimming-crabs, amphipods, mysids, polychaetes, ophiuroids, squids, and teleosteans. The species were classified into ten trophic groups. Shrimp were an important food source in the Santos bay and inner shelf, while ophiuroids were important prey for predators of the middle shelf. Many species relied on crabs/swimming-crabs during the summer, especially on the middle shelf. The spatial and temporal variability in food resource utilization by fish were related to the pattern of distribution and abundance of their prey. The predation on shrimp and crabs/swimming-crabs seems to be related to the water mass dynamics of the region. Intraspecific comparisons demonstrated that most of the species display spatial and/or temporal variation in their diet. The demersal ichtyofauna can also be divided into the more general categories of piscivores, nektonic invertebrate feeders, benthic invertebrate feeders and planktonic invertebrate feeders.

  17. Impacts of Outer Continental Shelf (OCS) development on recreation and tourism. Volume 3. Detailed methodology

    Energy Technology Data Exchange (ETDEWEB)

    1987-04-01

    The final report for the project is presented in five volumes. This volume, Detailed Methodology Review, presents a discussion of the methods considered and used to estimate the impacts of Outer Continental Shelf (OCS) oil and gas development on coastal recreation in California. The purpose is to provide the Minerals Management Service with data and methods to improve their ability to analyze the socio-economic impacts of OCS development. Chapter II provides a review of previous attempts to evaluate the effects of OCS development and of oil spills on coastal recreation. The review also discusses the strengths and weaknesses of different approaches and presents the rationale for the methodology selection made. Chapter III presents a detailed discussion of the methods actually used in the study. The volume contains the bibliography for the entire study.

  18. Outer Continental Shelf Stratigraphic Development and Sand Resource Potential: Integration of New and Legacy Geologic Datasets

    Science.gov (United States)

    Hughes, M.; Harris, S.; Luciano, K. E.; Alexander, C. R., Jr.

    2017-12-01

    Following the impact of Hurricane Sandy on the U.S. Atlantic coast in 2012 the Bureau of Ocean Energy Management (BOEM), in cooperation with state partners, instituted several regional offshore resource studies for the near outer continental shelf (OCS) on the US East Coast. This study focuses on a portion of this region, offshore of South Carolina and Georgia, with a primary goal of identifying beach renourishment sands and wind-tower placement locations, and creating a conceptual model of the evolution of the shelf in these areas. New and previously collected data are being used to identify sediment distribution patterns, paleolandscapes, sand resources for beach renourishment projects, and feasible locations for offshore wind installations. New chirp subbottom profiler data ( 1000 km), sidescan sonar data ( 7900km2), magnetometer data ( 1700 km), and multibeam bathymetry data ( 430km2) have been processed and interpreted at the University of Charleston using SonarWiz7, QPS-Qimera and QPS-Fledermaus software suites. Areas of focus for the Atlantic Sand Assessment Program (ASAP) data collection along the SC and GA coast are located within the 3 to 8 nautical mile (nm) OCS offshore of (North to South) Little River, Cape Romain, Folly Beach, Hilton Head, Wassaw, Ossabaw, Jekyll, St. Simons, and Cumberland islands. Ravinement, pre-Holocene, and other seismic surfaces, along with internal geometries, were mapped in these distinctly different tidal and wave regimes. Holocene sediment thickness gradually increases to the south with several sediment wedges in excess of 40 meters thickness. Where mapped, subsurface paleochannels/valleys were identified and analyzed for their orientation and complexity, as well as their size and distribution. These paleochannels are more numerous and increasingly complex in the southern survey areas. The channels are possibly related to transgressive channeling, Pleistocene low-stand river channeling, and braided stream formation during

  19. Structural lineaments from the magnetic anomaly maps of the eastern continental margin of India (ECMI) and NW Bengal Fan

    Digital Repository Service at National Institute of Oceanography (India)

    Murthy, K.S.R.; Rao, T.C.S.; Subrahmanyam, A; Rao, M.M.M.; Lakshminarayana, S.

    extension of 85 degrees E ridge, abutting the continental shelf off Chilka Lake and (3) trend 3, locted over the continental shelf/slope between Visakhapatnm and Paradip represents a folded (ridges and depressions) nature of the continental basement...

  20. Paleomagnetism and rock magnetism from sediments along a continental shelf-to-slope transect in the NW Barents Sea: Implications for geomagnetic and depositional changes during the past 15 thousand years

    Science.gov (United States)

    Caricchi, C.; Lucchi, R. G.; Sagnotti, L.; Macrì, P.; Morigi, C.; Melis, R.; Caffau, M.; Rebesco, M.; Hanebuth, T. J. J.

    2018-01-01

    Paleomagnetic and rock magnetic data were measured on glaciomarine silty-clay successions along an E-W sediment-core transect across the continental shelf and slope of the Kveithola paleo-ice stream system (south of Svalbard, north-western Barents Sea), representing a stratigraphic interval spanning the last deglaciation and the Holocene. The records indicate that magnetite is the main magnetic mineral and that magnetic minerals are distinctly less abundant on the shelf than at the continental slope. The paleomagnetic properties allow for the reconstruction of a well-defined characteristic remanent magnetization (ChRM) throughout the sedimentary successions. The stratigraphic trends of rock magnetic and paleomagnetic parameters are used for a shelf-slope core correlation and sediment facies analysis is applied for depositional processes reconstruction. The new paleomagnetic records compare to the PSV and RPI variation predicted for the core sites by a simulation using the global geomagnetic field variation models SHA.DIF.14k and CALS7K.2 and closest PSV and RPI regional stack curves. The elaborated dataset, corroborated by available 14C ages, provides a fundamental chronological framework to constrain the coupling of shelf-slope sedimentary processes and environmental changes in the NW Barents Sea region during and after deglaciation.

  1. Storm-induced inner-continental shelf circulation and sediment transport: Long Bay, South Carolina

    Science.gov (United States)

    Warner, John C.; Armstrong, Brandy N.; Sylvester, Charlene S.; Voulgaris, George; Nelson, Tim; Schwab, William C.; Denny, Jane F.

    2012-01-01

    -pressure systems drove a net sediment flux southwestward. Analysis of a 12-year data record from a local buoy shows an average of 41 cold fronts, 32 warm fronts, and 26 low-pressure systems per year. The culmination of these events would yield a cumulative net inner-continental shelf transport to the south–west, a trend that is further verified by sediment textural analysis and bedform morphology on the inner-continental shelf.

  2. Sonograph patterns of the central western continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, P.S.

    knolls. A transition zone with tonal variations is present between 40 and 60 m water depth. Ground-truth data sediment and rock distribution maps indicate depositional (inner shelf), nondepositional or erosional (outer shelf) environments and a...

  3. Spatial and temporal changes in benthic communities of the Galician continental shelf after the Prestige oil spill

    International Nuclear Information System (INIS)

    Serrano, Alberto . E-mail aserrano@st.ieo.es; Sanchez, Francisco; Preciado, Izaskun; Parra, Santiago; Frutos, Inmaculada

    2006-01-01

    Two years after the Prestige oil spill (POS) an assessment of the effects on benthic fauna was carried out using the data obtained in five multidisciplinary surveys. Otter trawl, beam trawl, suprabenthic sled and box corer were used to study the main benthic compartments, along eight transects perpendicular to the coastline. Beam trawl was also employed to quantify the amount of tar aggregates on the continental shelf. No significant correlations between tar aggregates and species richness, biomass and diversity of benthic communities were found. This result was corroborated when the role of depth, season, latitude and sediment characteristics was examined by canonical ordination, in which POS-related variables had low influence on spatial distribution patterns. Depth and sediment grain diameter profoundly influence epibenthic communities. Sediment organic content is a third key variable for the infaunal, suprabenthic and lower-sized epibenthic communities, but not for the larger epibenthic communities. Nevertheless, a decrease in the densities of several epibenthic indicators was detected the first year after spill, followed by a noteworthy recovery in 2004. Non-macroscopic toxicity and some oceanographic agents are suggested as possible causes of these shifts

  4. Spatial and temporal changes in benthic communities of the Galician continental shelf after the Prestige oil spill

    Energy Technology Data Exchange (ETDEWEB)

    Serrano, Alberto [Instituto Espanol de Oceanografia, P.O. Box 240, 39080 Santander (Spain)]. E-mail aserrano@st.ieo.es; Sanchez, Francisco [Instituto Espanol de Oceanografia, P.O. Box 240, 39080 Santander (Spain); Preciado, Izaskun [Instituto Espanol de Oceanografia, P.O. Box 240, 39080 Santander (Spain); Parra, Santiago [Instituto Espanol de Oceanografia, P.O. Box 130, 15080 La Coruna (Spain); Frutos, Inmaculada [Instituto Espanol de Oceanografia, P.O. Box 130, 15080 La Coruna (Spain)

    2006-07-01

    Two years after the Prestige oil spill (POS) an assessment of the effects on benthic fauna was carried out using the data obtained in five multidisciplinary surveys. Otter trawl, beam trawl, suprabenthic sled and box corer were used to study the main benthic compartments, along eight transects perpendicular to the coastline. Beam trawl was also employed to quantify the amount of tar aggregates on the continental shelf. No significant correlations between tar aggregates and species richness, biomass and diversity of benthic communities were found. This result was corroborated when the role of depth, season, latitude and sediment characteristics was examined by canonical ordination, in which POS-related variables had low influence on spatial distribution patterns. Depth and sediment grain diameter profoundly influence epibenthic communities. Sediment organic content is a third key variable for the infaunal, suprabenthic and lower-sized epibenthic communities, but not for the larger epibenthic communities. Nevertheless, a decrease in the densities of several epibenthic indicators was detected the first year after spill, followed by a noteworthy recovery in 2004. Non-macroscopic toxicity and some oceanographic agents are suggested as possible causes of these shifts.

  5. Submission of Republica Oriental del Uruguay to the Commission on the limits of the continental shelf pursuant to provisions of article 76, paragraph 8, of the United Nations Convention on the Law of the Sea: executive summary

    International Nuclear Information System (INIS)

    Mata Prates, C.; Tajes, J.; Burgos, M.; Caamaño; Lamartheé; Montiel, D.; Preciozzi, F.; De Santa Ana, H.

    2009-01-01

    Pursuant to provisions of article 76 of the United Nations Convention on the Law of the Sea (hereinafter the Convention), and to article 4 of Annex II of same, República Oriental del Uruguay (Uruguay) hereby submits to the Commission on the Limits of the Continental Shelf (the Commission) particulars on the outer limit of its continental shelf, extending beyond 200 nautical miles (M) from the baselines from which the breadth of territorial sea is measured. On December 10, 1982 Uruguay signed the Convention, which was subsequently approved by Uruguayan Law Nº 16,287, and ratified on December 10, 1992. The porvisions of article 76 invoked in Uruguay submission fixed points delimiting Uruguay’s Continental Shelf. There exist, at present, no unresolved disputes over the maritime border with either of Uruguay’s neighbouring countries, Argentina or Brazil. It was received assistance in the elaboration of this Submission April 2008, from member of the Commission and also assistance from other, non-member consultants and institutions from Germany, Brazil, Portugal and Norway

  6. Oil-Spill Analysis: Gulf of Mexico Outer Continental Shelf (OCS) Lease Sales, Eastern Planning Area, 2003-2007 and Gulfwide OCS Program, 2003-2042

    Science.gov (United States)

    2002-09-01

    The Federal Government plans to offer U.S. Outer Continental Shelf (OCS) lands in the Eastern Planning Area of the Gulf of Mexico (GOM) for oil and gas leasing. This report summarizes results of that analysis, the objective of which was to estimate the risk of oil-spill contact to sensitive offshore and onshore environmental resources and socioeconomic features from oil spills accidentally occurring from the OCS activities.

  7. Impacts of Outer Continental Shelf (OCS) development on recreation and tourism. Volume 1. Executive summary

    Energy Technology Data Exchange (ETDEWEB)

    1987-04-01

    The study was intended to provide the Mineral Management Service (MMS) with an analytical tool to evaluate possible economic impacts from Outer Continental Shelf (OCS) development. In particular, the study was designed to provide MMS staff who work on lease sale Energy Impact Statements with an objective technique for estimating the impacts to coastal communities from events that might occur as a result of lease sales: oil spills, onshore construction, and construction of platforms offshore. The project had several specific objectives: (1) provide profiles of 1982 socio-economic conditions in coastal communities, including an analysis of the relative importance of the tourist industry in each coastal county; (2) develop a methodology for determining the effects of OCS development on coastal recreation; and recommend mitigation measure that may reduce the negative effect of OCS development on coastal recreation using gravity and economic effects models.

  8. Clay mineral distribution on tropical shelf: an example from the western shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Hashimi, N.H.; Nair, R.R.

    Seventy-five sediment samples collected from the Kerala continental shelf and slope during the 17th and 71st Cruises of RV Gaveshani were analysed by X-ray diffraction for clay mineral content. The distribution of total clay ( 4 mu fraction...

  9. Characteristics of storms driving wave-induced seafloor mobility on the U.S. East Coast continental shelf

    Science.gov (United States)

    Dalyander, P. Soupy; Butman, Bradford

    2015-01-01

    This study investigates the relationship between spatial and temporal patterns of wave-driven sediment mobility events on the U.S. East Coast continental shelf and the characteristics of the storms responsible for them. Mobility events, defined as seafloor wave stress exceedance of the critical stress of 0.35 mm diameter sand (0.2160 Pa) for 12 or more hours, were identified from surface wave observations at National Data Buoy Center buoys in the Middle Atlantic Bight (MAB) and South Atlantic Bight (SAB) over the period of 1997-2007. In water depths ranging from 36-48 m, there were 4-9 mobility events/year of 1-2 days duration. Integrated wave stress during events (IWAVES) was used as a combined metric of wave-driven mobility intensity and duration. In the MAB, over 67% of IWAVES was caused by extratropical storms, while in the SAB, greater than 66% of IWAVES was caused by tropical storms. On average, mobility events were caused by waves generated by storms located 800+ km away. Far-field hurricanes generated swell 2-4 days before the waves caused mobility on the shelf. Throughout most of the SAB, mobility events were driven by storms to the south, east, and west. In the MAB and near Cape Hatteras, winds from more northerly storms and low-pressure extratropical systems in the mid-western U.S. also drove mobility events. Waves generated by storms off the SAB generated mobility events along the entire U.S. East Coast shelf north to Cape Cod, while Cape Hatteras shielded the SAB area from swell originating to the north offshore of the MAB.

  10. Exploration economics in a regulated petroleum province: The case of the Norwegian Continental Shelf

    International Nuclear Information System (INIS)

    Mohn, Klaus; Osmundsen, Petter

    2008-01-01

    Reserve replacement remains a key challenge for the international oil and gas companies. As market-oriented oil and gas provinces are maturing, exploration activity is shifted towards the resource-rich, regulated regimes outside the OECD. Regulated oil and gas provinces remain under-explored also in econometric terms. In this paper, we specify and estimate an econometric model of exploration and appraisal drilling for the highly regulated Norwegian Continental Shelf (NCS) over the period 1965 to 2004. Explanatory variables include the oil price, cumulative discoveries and open exploration acreage. Estimated error-correction models account explicitly for sluggishness and short-term adjustments in exploration drilling. We find robust long-term oil price effects on exploration activity, whereas the short-term response is muted. On the other hand, the temporary influence on exploration drilling from licensing rounds for new exploration acreage is significant, and so are the feedback effects from historical exploration success. At the same time, the longer-term impact of these variables is more moderate. (author)

  11. Contribution to the study of deep coastal detritic bottoms: the algal communities of the continental shelf off the Balearic Islands, Western Mediterranean

    Directory of Open Access Journals (Sweden)

    S. JOHER

    2015-09-01

    Full Text Available Three main algal-dominated coastal detritic communities from the continental shelf off Mallorca and Menorca (Balearic Islands, Western Mediterranean are described herein: maërl beds dominated by Spongites fruticulosus and forests of Laminaria rodriguezii located in the Menorca channel, and Peyssonnelia inamoena beds found along the Southern coast of Menorca. There seems to be a gradient of disturbance from the highly disturbed Peyssonnelia beds to the almost undisturbed L. rodriguezii forests. Whether this gradient is the result of current and past anthropogenic pressure (e.g. trawling intensity or is driven by natural environmental factors needs further assessment. Finally, the location of the target communities by means of ROV dives combined with the use of a Box-Corer dredge and beam trawl proved to be a good methodology in the study of the composition and structure of these deep water detritic communities.

  12. U, Th, K content, heat production and thermal conductivity of Sao Paulo, Brazil continental shelf sediments: a reconnaissance work

    International Nuclear Information System (INIS)

    Pereira, E.B.; Hamza, V.M.; Furtado, V.V.; Adams, J.A.S.

    1985-01-01

    A reconnaissance of the natural potassium, uranium and thorium content, the radiogenic heat production and the thermal conductivity of 80 bottom surface sediment samples collected from the Brazilian continental shelf off Sao Paulo was made. The average equivalent contents of these radio-elements in an estuarine ambient were 1.21%, 1.75 ppm and 4.29 ppm respectively, and 1.20%, 1.21 ppm and 4.05 ppm, respectively, in the shelf samples. The largest radioelement contents were associated with the more fine-grained sediments. The 234 U to 238 U isotopic ratios varied from 0.60 to 1.75 with an average of 1.11, indicating that the sources for the uranium in these sediments are both terrigenous and from the sea water. An average radiogenic heat production of 0.63 (+ - 0.04) μW.m -3 was calculated from the experimental concentration data. Data for the thermal conductivity measurements ranged from 0.83 to 2.51 μW.m -1 . 0 C -1 , with an average of 1.81 μW.m -1 . 0 C -1 . (Author) [pt

  13. Contributions to knowledge of the continental margin of Uruguay. Uruguayan continental margin: morphology, geology and identification of the base of the slope

    International Nuclear Information System (INIS)

    Preciozzi, F.

    2014-01-01

    This work is about the morphology, geology and the identification of the base of the slope in the The Uruguayan continental margin which corresponds to the the type of divergent, volcanic and segmented margins. Morphologically is constituted by a clearly defined continental shelf, as well as a continental slope that presents configuration changes from north to south and passes directly to the abyssal plain

  14. Run-off and sedimentation processes over the continental shelf along the European-Siberian Tundra coast

    Energy Technology Data Exchange (ETDEWEB)

    Josefsson, D. [Univ. of Lund (Sweden)

    2001-04-01

    The contribution of anthropogenic radionuclides from the European sources to the arctic seas have decreased in the first half of the 1990's. This is reflected in the measured activities in the different arctic seas which all show lower concentrations compared to earlier measurements. The influence from the Chernobyl accident were about one third of the total surface activity of {sup 137}CS at the Eurasian continental shelf in 1994 and between 10-30% in the central Arctic Ocean in 1996. The obtained results give no indication of any large extra sources for anthropogenic activity besides the well known fallout from atmospheric nuclear bombs test, discharges from European reprocessing plants and the Chernobyl accident releases. However smaller or local contributions from e.g. the dumped nuclear material in the Kara Sea and releases by the Siberian river from Russian nuclear facilities are not possible to exclude in this investigation.

  15. Hydrocarbon production forecast for committed assets in the shallow water Outer Continental Shelf of the Gulf of Mexico

    International Nuclear Information System (INIS)

    Kaiser, Mark J.

    2009-01-01

    In 2007, the federal waters of the Gulf of Mexico averaged daily production of 1.3 million barrels of oil and 7.6 billion cubic feet of natural gas. The majority of oil is produced from deepwater fields in water depth greater than 1000 ft, while most gas production is extracted from the shelf. The Outer Continental Shelf is a mature province with over 3800 fixed structures and 6500 producing wells connected into an integrated pipeline network more than 30,000 miles in length. The purpose of this paper is to develop a methodology to forecast oil and gas production in the shallow water Gulf of Mexico. Structures are categorized according to age and production characteristics, and forecast procedures for each asset class are described and illustrated. The methodology is implemented using the inventory of committed assets circa December 2006. The expected amount of hydrocarbon production arising from the inventory of committed assets under stable reservoir and investment conditions is estimated to be 1056 MMbbl oil and 13.3 Tcf gas valued between $85 and 150 billion. The results of generalized regression models are presented with a discussion of the limitations of analysis. (author)

  16. Concentrations and isotope ratios of mercury in sediments from shelf and continental slope at Campos Basin near Rio de Janeiro, Brazil.

    Science.gov (United States)

    Araujo, Beatriz Ferreira; Hintelmann, Holger; Dimock, Brian; Almeida, Marcelo Gomes; Rezende, Carlos Eduardo

    2017-07-01

    Mercury (Hg) may originate from both anthropogenic and natural sources. The measurement of spatial and temporal variations of Hg isotope ratios in sediments may enable source identification and tracking of environmental processes. In this study we establish the distribution of mercury concentrations and mercury isotope ratios in surface sediments of three transects along the continental shelf and slope in Campos Basin-RJ-Brazil. The shelf showed on average lower total Hg concentrations (9.2 ± 5.3 ng g -1 ) than the slope (24.6 ± 8.8 ng g -1 ). MMHg average concentrations of shelf 0.15 ± 0.12 ng g -1 and slope 0.13 ± 0.06 ng g -1 were not significantly different. Distinct differences in Hg isotope ratio signatures were observed, suggesting that the two regions were impacted by different sources of Hg. The shelf showed more negative δ 202 Hg and Δ 199 Hg values ranging from -0.59 to -2.19‰ and from -0.76 to 0.08‰, respectively. In contrast, the slope exhibited δ 202 Hg values from -0.29 to -1.82‰ and Δ 199 Hg values from -0.23 to 0.09‰. Mercury found on the shelf, especially along the "D" and "I" transects, is depleted in heavy isotopes resulting in more negative δ 202 Hg compared to the slope. Isotope ratios observed in the "D" and "I" shelf region are similar to Hg ratios commonly associated with plants and vegetation and very comparable to those detected in the estuary and adjoining mangrove forest, which suggests that Hg exported from rivers may be the dominating source of Hg in near coastal regions along the northern part of the shelf. Copyright © 2017 Elsevier Ltd. All rights reserved.

  17. Environmental drivers of epibenthic megafauna on a deep temperate continental shelf: A multiscale approach

    Science.gov (United States)

    Lacharité, Myriam; Metaxas, Anna

    2018-03-01

    Evaluating the role of abiotic factors in influencing the distribution of deep-water (>75-100 m depth) epibenthic megafaunal communities at mid-to-high latitudes is needed to estimate effects of environmental change, and support marine spatial planning since these factors can be effectively mapped. Given the disparity in scales at which these factors operate, incorporating multiple spatial and temporal scales is necessary. In this study, we determined the relative importance of 3 groups of environmental drivers at different scales (sediment, geomorphology, and oceanography) on epibenthic megafauna on a deep temperate continental shelf in the eastern Gulf of Maine (northwest Atlantic). Twenty benthic photographic transects (range: 611-1021 m; total length surveyed: 18,902 m; 996 images; average of 50 ± 16 images per transect) were performed in July and August 2009 to assess the abundance, composition and diversity of these communities. Surficial geology was assessed using seafloor imagery processed with a novel approach based on computer vision. A bathymetric terrain model (horizontal resolution: 100 m) was used to derive bathymetric variability in the vicinity of transects (1.5, 5 km). Oceanography at the seafloor (temperature, salinity, current speed, current direction) over 10 years (1999-2008) was determined using empirical (World Ocean Database 2013) and modelled data (Finite-Volume Community Ocean Model; 45 vertical layers; horizontal resolution: 1.7-9.5 km). The relative influence of environmental drivers differed between community traits. Abundance was enhanced primarily by swift current speeds, while higher diversity was observed in coarser and more heterogeneous substrates. In both cases, the role of geomorphological features was secondary to these drivers. Environmental variables were poor predictors of change in community composition at the scale of the eastern Gulf of Maine. This study demonstrated the need for explicitly incorporating scales into

  18. Patterns in stable isotope values of nitrogen and carbon in particulate matter from the Northwest Atlantic Continental Shelf, from the Gulf of Maine to Cape Hatteras

    Directory of Open Access Journals (Sweden)

    Autumn Oczkowski

    2016-12-01

    Full Text Available Stable isotope measurements of nitrogen and carbon (δ15N, δ13C are often used to characterize estuarine, nearshore, and open ocean ecosystems. Reliable information about the spatial distribution of base-level stable isotope values, often represented by primary producers, is critical to interpreting values in these ecosystems. While base-level isotope data are generally readily available for estuaries, nearshore coastal waters, and the open ocean, the continental shelf is less studied. To address this, and as a first step towards developing a surrogate for base-level isotopic signature in this region, we collected surface and deep water samples from the United States’ eastern continental shelf in the Western Atlantic Ocean, from the Gulf of Maine to Cape Hatteras, periodically between 2000 and 2013. During the study, particulate matter δ15N values ranged from 0.8 to 17.4 ‰, and δ13C values from -26.4 to -15.6 ‰ over the region. We used spatial autocorrelation analysis and random forest modeling to examine the spatial trends and potential environmental drivers of the stable isotope values. We observed general trends towards lower values for both nitrogen and carbon isotopes at the seaward edge of the shelf. Conversely, higher δ15N and δ13C values were observed on the landward edge of the shelf, in particular in the southern portion of the sampling area. Across all sites, the magnitude of the difference between the δ15N of subsurface and surface particulate matter (PM significantly increased with water depth (r2 = 0.41, df = 35, p < 0.001, while δ13C values did not change. There were significant positive correlation between δ15N and δ13C values for surface PM in each of the three marine ecoregions that make up the study area. Stable isotope dynamics on the shelf can inform both nearshore and open ocean research efforts, reflecting regional productivity patterns and, even possibly, large-scale climate fluctuations.

  19. 日本外大陆架划界申请案内涵与中国的立场%The Contents of Japan's Submission on the Extended Continental Shelf and China's Position

    Institute of Scientific and Technical Information of China (English)

    金永明; ZHANG Chao

    2009-01-01

    日本经过连续五年的大陆架调查工作,终于向大陆架界限委员会提交了外大陆架划界申请案,其申请面积极其广袤,约为日本国土面积的2倍.为提交外大陆架申请案,日本在组织机构配置、调查任务分工、财政上均予以了大力协助和支持,提早完成了调查任务.应注意的是,在日本外大陆架划界申请案中,冲之鸟礁是作为日本申请外大陆架的基点.这种主张是不符合《联合国海洋法公约》关于岛屿的规定的,相关部分必不能通过审议.%After five consecutive years of surveying the continental shelf,Japan finally made the submission to establish the limits of its continental shelf to the Commission on the Limits of the Continental Shelf (CLCS).The submission covers an extremely vast area that is about twice the size of Japan's land area.To prepare its submission,Japan committed itself to providing robust support and collaborative efforts to configure the organizational structure,divide the survey's tasks,and guarantee the finances,completing the survey ahead of schedule.It should be noted that in Japan's submission on the limits of the continental shelf,Oki-no-Tori acts as the base point.This claim does not comply with the provisions on islands in the United Nations Convention on the Law of the Sea,and the relevant content in the submission definitely will not be approved in the CLCS's considerations.

  20. Plant speciation in continental island floras as exemplified by Nigella in the Aegean Archipelago

    OpenAIRE

    Comes, Hans Peter; Tribsch, Andreas; Bittkau, Christiane

    2008-01-01

    Continental shelf island systems, created by rising sea levels, provide a premier setting for studying the effects of geographical isolation on non-adaptive radiation and allopatric speciation brought about by genetic drift. The Aegean Archipelago forms a highly fragmented complex of mostly continental shelf islands that have become disconnected from each other and the mainland in relatively recent geological times (ca

  1. Lithology, monsoon and sea-surface current control on provenance, dispersal and deposition of sediments over the Andaman continental shelf

    Digital Repository Service at National Institute of Oceanography (India)

    Damodararao, K.; Singh, S.K.; Rai, V.K.; Ramaswamy, V.; Rao, P.S.

    , constrain their transport pathways and assess the factors influencing the erosion in the catchment and their dispersal and deposition over the Andaman Shelf region. Major elemental compositions of the shelf sediments suggest mafic lithology...

  2. Sound Propagation from the Continental Slope to the Continental Shelf: Remote Sensing Component

    National Research Council Canada - National Science Library

    Kelly, Kathryn

    2000-01-01

    ... along the East Coast of North America. The AVHRR images were used to show the location and orientation of the shelf I/slope front and the altimeter was used to study the fluctuations of the geostrophic currents...

  3. Recent Advances in Bathymetric Surveying of Continental Shelf Regions Using Autonomous Vehicles

    Science.gov (United States)

    Holland, K. T.; Calantoni, J.; Slocum, D.

    2016-02-01

    Obtaining bathymetric observations within the continental shelf in areas closer to the shore is often time consuming and dangerous, especially when uncharted shoals and rocks present safety concerns to survey ships and launches. However, surveys in these regions are critically important to numerical simulation of oceanographic processes, as bathymetry serves as the bottom boundary condition in operational forecasting models. We will present recent progress in bathymetric surveying using both traditional vessels retrofitted for autonomous operations and relatively inexpensive, small team deployable, Autonomous Underwater Vehicles (AUV). Both systems include either high-resolution multibeam echo sounders or interferometric sidescan sonar sensors with integrated inertial navigation system capabilities consistent with present commercial-grade survey operations. The advantages and limitations of these two configurations employing both unmanned and autonomous strategies are compared using results from several recent survey operations. We will demonstrate how sensor data collected from unmanned platforms can augment or even replace traditional data collection technologies. Oceanographic observations (e.g., sound speed, temperature and currents) collected simultaneously with bathymetry using autonomous technologies provide additional opportunities for advanced data assimilation in numerical forecasts. Discussion focuses on our vision for unmanned and autonomous systems working in conjunction with manned or in-situ systems to optimally and simultaneously collect data in environmentally hostile or difficult to reach areas.

  4. Understanding Ice Shelf Basal Melting Using Convergent ICEPOD Data Sets: ROSETTA-Ice Study of Ross Ice Shelf

    Science.gov (United States)

    Bell, R. E.; Frearson, N.; Tinto, K. J.; Das, I.; Fricker, H. A.; Siddoway, C. S.; Padman, L.

    2017-12-01

    The future stability of the ice shelves surrounding Antarctica will be susceptible to increases in both surface and basal melt as the atmosphere and ocean warm. The ROSETTA-Ice program is targeted at using the ICEPOD airborne technology to produce new constraints on Ross Ice Shelf, the underlying ocean, bathymetry, and geologic setting, using radar sounding, gravimetry and laser altimetry. This convergent approach to studying the ice-shelf and basal processes enables us to develop an understanding of the fundamental controls on ice-shelf evolution. This work leverages the stratigraphy of the ice shelf, which is detected as individual reflectors by the shallow-ice radar and is often associated with surface scour, form close to the grounding line or pinning points on the ice shelf. Surface accumulation on the ice shelf buries these reflectors as the ice flows towards the calving front. This distinctive stratigraphy can be traced across the ice shelf for the major East Antarctic outlet glaciers and West Antarctic ice streams. Changes in the ice thickness below these reflectors are a result of strain and basal melting and freezing. Correcting the estimated thickness changes for strain using RIGGS strain measurements, we can develop decadal-resolution flowline distributions of basal melt. Close to East Antarctica elevated melt-rates (>1 m/yr) are found 60-100 km from the calving front. On the West Antarctic side high melt rates primarily develop within 10 km of the calving front. The East Antarctic side of Ross Ice Shelf is dominated by melt driven by saline water masses that develop in Ross Sea polynyas, while the melting on the West Antarctic side next to Hayes Bank is associated with modified Continental Deep Water transported along the continental shelf. The two sides of Ross Ice Shelf experience differing basal melt in part due to the duality in the underlying geologic structure: the East Antarctic side consists of relatively dense crust, with low amplitude

  5. Modeling the seasonal cycle of the oxygen minimum zone over the continental shelf off Concepción, Chile (36.5° S)

    Science.gov (United States)

    Charpentier, J.; Mediavilla, D.; Pizarro, O.

    2012-06-01

    We analyze the seasonal dynamics of oxygen concentrations in the southernmost part of the Eastern South Pacific oxygen minimum zone (ESP's OMZ), offshore of Concepción, Chile (~37° S). We use data from a time series over the continental shelf off Concepción, as well as other hydrographic data and measurements from moored instruments and ocean gliders to evaluate temporal and spatial variability in this region. We identify two extreme modes (winter and summer) that characterize the seasonal variability. A simple model that account for the main physical and biological processes that influences the oxygen concentration was developed. According to our results, the seasonal variability of the dissolved oxygen in the study region is mainly driven by lateral (advective and diffusive) transport that connect the waters over the shelf with poorly oxygenated water from the slope, which is in turn, advected southward by the Peru-Chile Undercurrent.

  6. Cyclonic entrainment of preconditioned shelf waters into a frontal eddy

    Science.gov (United States)

    Everett, J. D.; Macdonald, H.; Baird, M. E.; Humphries, J.; Roughan, M.; Suthers, I. M.

    2015-02-01

    The volume transport of nutrient-rich continental shelf water into a cyclonic frontal eddy (entrainment) was examined from satellite observations, a Slocum glider and numerical simulation outputs. Within the frontal eddy, parcels of water with temperature/salinity signatures of the continental shelf (18-19°C and >35.5, respectively) were recorded. The distribution of patches of shelf water observed within the eddy was consistent with the spiral pattern shown within the numerical simulations. A numerical dye tracer experiment showed that the surface waters (≤50 m depth) of the frontal eddy are almost entirely (≥95%) shelf waters. Particle tracking experiments showed that water was drawn into the eddy from over 4° of latitude (30-34.5°S). Consistent with the glider observations, the modeled particles entrained into the eddy sunk relative to their initial position. Particles released south of 33°S, where the waters are cooler and denser, sunk 34 m deeper than their release position. Distance to the shelf was a critical factor in determining the volume of shelf water entrained into the eddy. Entrainment reduced to 0.23 Sv when the eddy was furthest from the shelf, compared to 0.61 Sv when the eddy was within 10 km of the shelf. From a biological perspective, quantifying the entrainment of shelf water into frontal eddies is important, as it is thought to play a significant role in providing an offshore nursery habitat for coastally spawned larval fish.

  7. Distribution of hydrocarbon-utilizing microorganisms and hydrocarbon biodegradation potentials in Alaskan continental shelf areas

    International Nuclear Information System (INIS)

    Roubal, G.; Atlas, R.M.

    1978-01-01

    Hydrocarbon-utilizing microogranisms were enumerated from Alaskan continental shelf areas by using plate counts and a new most-probable-number procedure based on mineralization of 14 C-labeled hydrocarbons. Hydrocarbon utilizers were ubiquitously distributed, with no significant overall concentration differences between sampling regions or between surface water and sediment samples. There were, however, significant seasonal differences in numbers of hydrocarbon utilizers. Distribution of hydrocarbon utilizers within Cook Inlet was positively correlated with occurrence of hydrocarbons in the environment. Hydrocarbon biodegradation potentials were measured by using 14 C-radiolabeled hydrocarbon-spiked crude oil. There was no significant correlation between numbers of hydrocarbon utilizers and hydrocarbon biodegradation potentials. The biodegradation potentials showed large seasonal variations in the Beaufort Sea, probably due to seasonal depletion of available nutrients. Non-nutrient-limited biodegradation potentials followed the order hexadecane > naphthalene >> pristane > benzanthracene. In Cook Inlet, biodegradation potentials for hexadecane and naphthalene were dependent on availability of inorganic nutrients. Biodegradation potentials for pristane and benzanthracene were restricted, probably by resistance to attack by available enzymes in the indigenous population

  8. Vacuum Drying for Extending Litchi Shelf-Life: Vitamin C, Total Phenolics, Texture and Shelf-Life Assessment.

    Science.gov (United States)

    Richter Reis, Felipe; de Oliveira, Aline Caroline; Gadelha, Gabriella Giani Pieretti; de Abreu, Marcela Breves; Soares, Hillary Isabelle

    2017-06-01

    In an attempt to obtain shelf-stable litchi fruit with preserved nutritional quality and good sensory features, quarters of peeled and pitted fruits were vacuum dried at 50, 60 and 70 °C at a constant pressure of 8.0 kPa. The product was assessed for its vitamin C, total phenolics and texture (hardness). In addition, the product with the best texture was assessed for its shelf-life by means of accelerated testing. Results suggest that vacuum dried litchi retained almost 70% of the vitamin C and total phenolics when compared to frozen fruits (control). Vitamin C and phenolic compounds content significantly decreased with drying, while no difference was found between different drying temperatures. Hardness increased with drying temperature. The sample dried at 70 °C presented crispness, which is a desired quality feature in dried fruit products. This sample was subjected to shelf-life evaluation, whose result suggests a shelf-life of eight months at 23 °C. Total color change (CIE ΔE 00 ) was the expiry criterion. Vacuum drying was a suitable technique for producing shelf-stable litchi fruit with good texture while preserving its desirable original nutrients. Consumption of vacuum dried litchi may be beneficial to health due to its remarkable content of phenolic compounds and vitamin C.

  9. Bacteria, carbon dioxide, and methane data from bottle casts in the Cariaco Basin on the continental shelf of Venezuela from the HERMANO GINES from 2000-05-03 to 2000-10-31 (NODC Accession 0000732)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Bacteria, carbon dioxide, and methane data were collected employing bottle casts from the Hermano Gines in the Cariaco Basin on the continental shelf of Venezuela....

  10. Diets and niche overlap among nine co-occurring demersal fishes in the southern continental shelf of East/Japan Sea, Korea

    Science.gov (United States)

    Myun Park, Joo; Nam Kwak, Seok; Huh, Sung-Hoi; Han, In-Seong

    2017-09-01

    Dietary niches and food resource partitioning can support the coexistence of many fishes in benthic marine systems, which can lead to the greater abundances of those species that can potentially support their fisheries. Diets and niche overlap among nine demersal fish species were investigated in the southern continental shelf of East/Japan Sea, Korea. Specimens were collected monthly from January to November 2007 on soft bottoms between 40 and 100 m depth using a bottom trawl. A total of 20 prey taxa were found in 1904 stomachs of the nine species. Comparison of the stomach contents among the nine species showed that inter-specific dietary compositions differed significantly. Although all fish species consumed similar types of prey items, their contributions to the diet of different species varied. Among prey taxa, carid shrimps contributed greatly to the diets of Amblychaeturichthys hexanema, Amblychaeturichthys sciistius, Coelorinchus multispinulosus, Lepidotrigla guentheri, and Liparis tanakae, whereas polychaetes and teleosts contributed to the diets of Callionymus lunatus and Lophius litulon, respectively. On the other hand, carid shrimps and teleosts together contributed to the diets of Pseudorhombus pentophthalmus. Non-metric multivariate analysis of the mass contributions of dietary categories for food resources emphasized visually that the dietary compositions of the nine species differed. Although C. multispinulosus, L. guentheri, L. litulon, and L. tanakae showed similar dietary compositions between small and large size classes, ontogenetic diet changes of the remaining six species were evident. Feeding relationships among the nine demersal species were complicated, but inter- and intra-specific differences in dietary composition among the species reduced potential competition for food resources within the fish community in the southern continental shelf of East/Japan Sea, Korea.

  11. Terrigeneous material supply to the Peruvian central continental shelf (Pisco 14° S) during the last 1100 yr: paleoclimatic implications

    Science.gov (United States)

    Briceño Zuluaga, F.; Sifeddine, A.; Caquineau, S.; Cardich, J.; Salvatteci, R.; Gutierrez, D.; Ortlieb, L.; Velazco, F.; Boucher, H.; Machado, C.

    2015-07-01

    In the Eastern Pacific, lithogenic input to the ocean is a response of the atmospheric and ocean system variability and their teleconnections over different timescales. Atmospheric (e.g., wind fields, precipitation), hydrological (e.g., fresh water plumes) and oceanic (e.g., currents) conditions determine the transport mode and the amount of lithogenic material transported from the continent to the continental shelf. Here, we present the grain size distribution of a composite record of two laminated sediment cores retrieved in the Peruvian continental shelf, covering the last ~1100 yr at sub-decadal to centennial time-series resolution. We then discuss the paleo-environmental significance and the climatic mechanisms involved. Four grain size modes were identified. Two are linked to aeolian inputs (M3: 53.0 μm and M4: 90.8 μm on average), the third is interpreted as a marker of sediment discharge (M2: 9.4 μm on average), and the last is without an associated origin (M1: ~3 μm). The coarsest components (M3 and M4) dominated during the Medieval Climate Anomaly (MCA) and Current Warm Period (CWP) periods, suggesting that aeolian transport increased as consequence of wind stress intensification. In contrast, M2 displays an opposite behavior, exhibiting an increase in fluvial terrigenous input during the Little Ice Age (LIA), in response to more humid conditions. Comparison with other South American paleoclimate records indicates that the observed changes are driven by interactions between meridional displacement of the Intertropical convergence zone (ITCZ) and of the South Pacific Sub-tropical High (SPSH) at decadal and centennial time scales.

  12. Bacteria, carbon dioxide, and methane data from bottle casts in the Cariaco Basin on the continental shelf of Venezuela from the HERMANO GINES from 2001-04-30 to 2001-05-01 (NODC Accession 0000737)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Bacteria, carbon dioxide, and methane data were collected from bottle casts from the HERMANO GINES in the Cariaco Basin on the continental shelf of Venezuela. Data...

  13. Storm-driven delivery of sediment to the continental slope: Numerical modeling for the northern Gulf of Mexico

    Science.gov (United States)

    Harris, C. K.; Kniskern, T. A.; Arango, H.

    2016-02-01

    The supply of sediment from the continental shelf to deeper waters is of critical importance for building continental margin repositories of sediment, and may also factor into episodic events on the continental slope such as turbidity currents and slope failures. While numerical sediment transport models have been developed for coastal and continental shelf areas, they have not often been used to infer sediment delivery to deeper waters. A three-dimensional coupled hydrodynamic - suspended sediment transport model for the northern Gulf of Mexico has been developed and run to evaluate the types of conditions that are associated with delivery of suspended sediment to the continental slope. Accounting for sediment delivery by riverine plumes and for sediment resuspension by energetic waves and currents, the sediment transport calculations were implemented within the Regional Ocean Modeling System (ROMS). The model domain represents the northern Gulf of Mexico shelf and slope including the Mississippi birdfoot delta and the Mississippi and DeSoto Canyons. To investigate the role of storms in driving down-slope sediment fluxes, model runs that encompassed fall, 2007 through late summer, 2008 the summer and fall of 2008 were analyzed. This time period included several winter storms, and the passage of two hurricanes (Ike and Gustav) over the study area. Preliminary results indicated that sediment delivery to the continental slope was triggered by the passage of these storm events, and focused at certain locations, such as submarine canyons. Additionally, a climatological analysis indicates that storm track influences both the wind-driven currents and wave energy on the shelf, and as such plays an important role in determining which storms trigger delivery of suspended continental shelf sediment to the adjacent slope.

  14. Delimitation of the continental shelf and exclusive economic Zone the Sea Border between Romania and Ukraine

    Directory of Open Access Journals (Sweden)

    Mihai Mereuţă

    2011-07-01

    Full Text Available Decision I.C.J. from The Hague, since 3rd February 2009, in the case of “Romania vs. Ukraine - the maritime delimitation in the Black Sea”, has an important role in bilateral relations and regional plans of the riparian states and thus also eliminating a potential factor of instability at the sea border between the two countries and in the Black Sea. Drawing a line of demarcation equitable maritime economic zone and continental shelf between the two countries was an example of dispute settlement in the wider Black Sea area. Snake Island was not considered relevant in substantiating the court decision, because the I.C.J. has not declared it a rock, giving it a length of 12 nautical miles territorial sea and has not ruled on the nature of this formation, in accordance with the provisions of art. 121 of the Montego Bay Convention of 1982.

  15. Surficial sediments of the continental shelf off Karnataka

    Digital Repository Service at National Institute of Oceanography (India)

    Hashimi, N.H.; Nair, R.R.

    sediments occur betweenthe water depths of 15 to 50m corresponding to a distance of about 40 km from the coast. Beyond 50 m to the shelf edge are calcareous sands. Non-carbonate components of these deep water sands are essentially quartz, many of which...

  16. Topographic features over the continental shelf off Visakhapatnam

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, T.C.S.; Machado, T.; Murthy, K.S.R.

    water depth and the continental shelfedge several interesting topographic features such as Terraces, Karstic structures associated with pinnacles and troughs and smooth dome shaped reef structures are recorded. The nature of these features...

  17. Petroleum resources assessment 2

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1995-12-01

    The Geobit, a seismic data processing software, is the token of the achievement for the development of technology in the oil exploration over the Korean continental shelf. This report consists of six articles: (1) Experimental processing of a model data set using Geobit seismic software, (2) Management of seismic data on network, (3) Seismic data processing for domestic seismic survey over the continental shelf of Korea using the Geobit, (4) A study on the intrusion model by physical modeling, (5) Research on application and development of Geobit seismic software, (6) Assessment of Geobit system and suggestions for further development. (author)

  18. Vertical Variability of Anoxia Along the Northern Omani Shelf.

    Science.gov (United States)

    Queste, B. Y.; Piontkovski, S.; Heywood, K. J.

    2016-02-01

    Three autonomous underwater gliders were deployed along a 80 km transect extending from Muscat out into the Gulf during both monsoons and the intermonsoon season as part of a project funded by ONR Global and the UK NERC. The gliders surveyed the top 1000m across the continental shelf, the steep continental slope, and the Sea of Oman while measuring temperature, salinity, oxygen, chlorophyll a fluorescence, optical backscatter, photosyntheticall active radiation and providing estimates of depth-averaged currents and up/downwelling. The data show the depth of the surface oxycline varying by 50m across the transect as a function of mixed layer depth. Below, we observed high variability, on the order of days, in the oxygen profile with the boundary of the suboxic zone (glider transect. During periods of minimal flow, it was constrained to 10km beyond the shelf break. PGW was also present in mesoscale eddies beyond the shelf break.

  19. Shelf break circulation in the Northern Gulf of Alaska

    Energy Technology Data Exchange (ETDEWEB)

    Niebauer, H.J.; Roberts, J.; Royer, T.C.

    1981-05-20

    Current observations from a mooring on the continental shelf near the shelf break in the Gulf of Alaska, with supporting hydrographic and metorological data, are discussed for the period 1976 to March 1977. The described features suggest strong influence by the cyclonic Alaska Gyre for the periods April--June 1976 and October 1976 to March 1977. From July--September 1976 there is evidence of current veering and rotation. It is hypothesized that these current fluctuations are eddies which are important in mixing processes across the shelf.

  20. Ability of surface and subsurface death assemblages to track km-scale spatial and decade-scale temporal variability in living communities: Tests using the urban southern California continental shelf

    Science.gov (United States)

    Kidwell, Susan M.; Tomasovych, Adam

    2016-04-01

    Actualistic analysis of death assemblages has always focused on quantifying, and achieving a mechanistic understanding of, the reliability of deep-time records, and is now additionally motivated to assess natural conditions before human impacts. The southern California continental shelf permits us to evaluate the ability of time-averaged death assemblages to detect known variability in urban nutrients, which increased from the early 20th Century up until the 1972 Clean Water Act. Biomonitoring since then documents strong declines in populations of pollution- and hypoxia-tolerant species, especially the chemosymbiontic lucinid bivalve Parvilucina tenuisculpta. This shelf is taphonomically challenging -- median shell ages are 50-100 y, only 1% of shells survive, the mixed-zone is ~25 cm thick, and siliciclastic accumulation is slow, in contrast to sediment-trapping estuaries and lagoons. Nonetheless, both surficial death and buried core assemblages capture first-order urban trends, albeit with significant damping of the large, spatially localized mid-20th Century pulse in Parvilucina abundance. Paleoecologists will thus detect but under-estimate the original magnitude of even strong past excursions in community composition, an important bounding condition for both recent- and deep-time analysis.

  1. Modeling the role and impact of alien species and fisheries on the Israeli marine continental shelf ecosystem

    Science.gov (United States)

    Corrales, X.; Ofir, E.; Coll, M.; Goren, M.; Edelist, D.; Heymans, J. J.; Gal, G.

    2017-06-01

    The ecosystems of the Israeli Mediterranean coast have undergone significant changes in recent decades mainly due to species invasions and fishing. In order to characterize the structure and functioning of the marine continental shelf of the Israeli Mediterranean coast and assess temporal changes, we developed a food web model representing two time periods: 1990-1994 and 2008-2012. The 1990-1994 and 2008-2012 food web models were composed of 39 and 41 functional groups, respectively. Functional groups ranged from primary producers to top predators, and included six and eight alien functional groups, respectively, encompassing several crustacean and fish species. Input data included local surveys and fishery statistics, published data on stomach content analyses, and the application of empirical equations to estimate consumption and production rates. Results of the competitive interactions between alien and native species and changes in trophic flows between food web components highlight the increasing impact of alien species over time. Fishing had noticeable impacts in both time periods and played an important role in the ecosystem. Despite different productivity rates and other environmental differences, the Israeli marine ecosystem shared common structural and functional traits with other Mediterranean marine ecosystems. This is the first attempt to study the ecosystem of the Levant region using mass-balance models and to integrate such a large amount of alien species into food web analyses.

  2. Megabenthic assemblages in the continental shelf edge and upper slope of the Menorca Channel, Western Mediterranean Sea

    Science.gov (United States)

    Grinyó, Jordi; Gori, Andrea; Greenacre, Michael; Requena, Susana; Canepa, Antonio; Lo Iacono, Claudio; Ambroso, Stefano; Purroy, Ariadna; Gili, Josep-Maria

    2018-03-01

    Highly diverse megabenthic assemblages dominated by passive and active suspension feeders have been recently reported in shelf edge environments of the Mediterranean Sea. Due to their frequent association with species of commercial interest, these assemblages have been heavily impacted by fishing. The vulnerability and low resilience of these assemblages, composed mainly by long-living and slow-growing species, have motivated the implementation of management measures such as the restriction of bottom trawling, and the establishment of large protected areas embracing these environments. The Menorca Channel is one of such areas recently included in the European Union Natura 2000 network. Quantitative analysis of video transects recorded at 95-360 m depth by manned submersible and remotely operated vehicles were used to characterize megabenthic assemblages and to assess their geographical and bathymetric distribution. Six different assemblages were identified, mainly segregated by substrate type and depth. Hard substrates hosted coral gardens and sponge grounds, whereas soft sediments were mainly characterized by large extensions of the crinoid Leptometra phalangium and the brachiopod Gryphus vitreus. The good preservation of most of the observed assemblages is probably related to a low bottom trawling pressure, which mainly concentrates deeper on the adjacent continental slope. Because of their biological and ecological value, management and conservation measures need to be established to preserve these benthic assemblages.

  3. Terrigenous material supply to the Peruvian central continental shelf (Pisco, 14° S) during the last 1000 years: paleoclimatic implications

    Science.gov (United States)

    Briceño-Zuluaga, Francisco Javier; Sifeddine, Abdelfettah; Caquineau, Sandrine; Cardich, Jorge; Salvatteci, Renato; Gutierrez, Dimitri; Ortlieb, Luc; Velazco, Federico; Boucher, Hugues; Machado, Carine

    2016-03-01

    In the eastern Pacific, lithogenic input to the ocean responds to variations in the atmospheric and oceanic system and their teleconnections over different timescales. Atmospheric (e.g., wind fields), hydrological (e.g., fresh water plumes) and oceanic (e.g., currents) conditions determine the transport mode and the amount of lithogenic material transported from the continent to the continental shelf. Here, we present the grain size distribution of a composite record of two laminated sediment cores retrieved from the Peruvian continental shelf that record the last ˜ 1000 years at a sub-decadal to centennial time-series resolution. We propose novel grain size indicators of wind intensity and fluvial input that allow reconstructing the oceanic-atmospheric variability modulated by sub-decadal to centennial changes in climatic conditions. Four grain size modes were identified. Two are linked to aeolian inputs (M3: ˜ 54; M4: ˜ 91 µm on average), the third is interpreted as a marker of sediment discharge (M2: ˜ 10 µm on average), and the last is without an associated origin (M1: ˜ 3 µm). The coarsest components (M3 and M4) dominated during the Medieval Climate Anomaly (MCA) and the Current Warm Period (CWP) periods, suggesting that aeolian transport increased as a consequence of surface wind stress intensification. In contrast, M2 displays an opposite behavior, exhibiting an increase in fluvial terrigenous input during the Little Ice Age (LIA) in response to more humid conditions associated with El Niño-like conditions. Comparison with other South American paleoclimate records indicates that the observed changes are driven by interactions between meridional displacement of the Intertropical Convergence Zone (ITCZ), the South Pacific Subtropical High (SPSH) and Walker circulation at decadal and centennial timescales.

  4. Molecular Gut Content Profiling to Investigate the In Situ Grazing and Selectivity of Dolioletta gegenbauri in Summer Continental Shelf Intrusion Waters of the South Atlantic Bight, USA

    Science.gov (United States)

    Walters, T. L.; Frazier, L.; Gibson, D. M.; Paffenhofer, G. A.; Frischer, M. E.

    2016-02-01

    Gelatinous metazooplankton play a crucial role in marine planktonic food webs and it has been suggested that they may become increasingly important in the Future Ocean. However, largely due to methodological challenges and reliance on laboratory cultivation approaches, the in situ diet of zooplankton with complex life histories and diverse prey choices remains poorly investigated. This is particularly true for the gelatinous zooplankton including the pelagic tunicate, Dolioletta gegenbauri that form large blooms in productive subtropical continental shelf environments. To investigate the diet of D. gegenbauri we developed a molecular gut profiling approach based on the use of a Peptide Nucleic Acid (PNA) PCR blocker. Using a doliolid-specific PNA blocker, it was possible to enrich the amplification of prey and parasite DNA from whole animal DNA extracts of doliolids. Gut contents from the water column, wild and captive-fed doliolids were profiled after PNA-PCR by denaturing HPLC (dHPLC), clone library and next generation sequencing (NGS) approaches. Studies were conducted during 5 summer cruises in the mid-shelf of the South Atlantic Bight. Comparison of gut profiles to available prey in the water column revealed evidence of prey selection towards larger prey species, including diatoms, dinoflagelletes and also metazoan prey that were likely captured as larvae and eggs. Wild-caught doliolids contained significantly more metazoan sequences than did the captive-fed doliolids. Ingestion of metazoan prey suggests that metazoans may contribute both the nutrition of doliolids and the potential role of doliolids as trophic cascade agents in continental shelf pelagic food webs.

  5. Microalgae of the continental shelf off Paraná State, southeastern Brazil: a review of studies

    Directory of Open Access Journals (Sweden)

    Frederico P. Brandini

    1996-01-01

    Full Text Available The paper reviews the taxonomic and ecological works on marine microalgae (phytoplankton and microphytobenthos off Paraná State, Southeastern Brazil. Various studies refer to the taxonomy of benthic diatoms. Few descriptive field works in coastal and adjacent shelf waters contribute to the understanding of phytoplankton dynamics in coastal and shelf areas. Patterns of geographic distribution and changes in the phytoplankton community are described in relation to water masses and seasonal variations in the hydrographic regime. During summertime, when warm oligotrophic waters predominate over the shelf, the phytoplankton is nummerically dominated by small phytotlagellates, dinotlagellates, coccolithophorids and filaments of cyanobacteria. During wintertime, the abundance of micro-size diatoms over the shclf increase due to the dominance of cold nutrient-rich waters from the South Atlantic Central Water and wind-driven vertical circulation. The phytoplankton community off Paraná State may be classified into two categorics: the diatom-dominated coastal assemblage, mainly controlled by nutrient inputs from land drainage and ressuspension of bottom sediments, and the tlagellate-dominated shelf assemblage, more affectcd by the seasonality of local hydrographic regime.O trabalho é uma revisão dos estudos taxonômicos e ecológicos das microalgas (planctônicas e bentônicas realizados no Estado do Paraná. A maioria dos trabalhos sobre microfitobentos são de caráter taxonômico e, basicamente, referem-se à diatomáceas bênticas sobre macroalgas ou fundos lodosos e consolidados. Poucos trabalhos contribuiram para o estudo da dinâmica espaço-temporal do fitoplâncton em áreas costeiras e de plataforma. São descritos os padrões de distribuição geográfica e as mudanças sazonais na comunidade fitoplanctônica em relação ao regime hidrográfico. No verão, quando águas quentes oligotróficas predominam na superfície, o fitoplâncton

  6. Exploration of the continental margins of India

    Digital Repository Service at National Institute of Oceanography (India)

    Siddiquie, H.N.; Hashimi, N.H.; Vora, K.H.; Pathak, M.C.

    impetus from sponsored surveys of other organizations, chiefly the oil industry, ports and harbours as well as industries disposing of their effluents in the marine environment. By now the entire western continental shelf and a large part...

  7. Late Neogene foraminifera from the northern Namibian continental shelf and the transition to the Benguela Upwelling System

    Science.gov (United States)

    Bergh, Eugene W.; Compton, John S.; Frenzel, Peter

    2018-05-01

    Middle Miocene to Plio-Pleistocene foraminifera provide insights into the palaeoenvironment on the northern Namibian continental shelf located at the far northern end of the present-day Benguela Upwelling System (BUS). Biostratigraphy and Strontium Isotope Stratigraphy (SIS) of the recovered basal olive-green mud unit indicate an age of 16 to 14 Ma. A sharp, erosional contact separates the basal mud from the overlying Plio-Pleistocene gravelly pelletal phosphorite sands. Grain size data, P/B ratios and benthic diversity indices indicate a change between the middle Miocene and overlying Plio-Pleistocene palaeoenvironments linked to the timing and conditions associated with the initiation of the BUS. The different lithological units and microfossil assemblages in the olive-green mud unit and the overlying pelletal phosphorite units support the late Miocene initiation of the BUS and the northwards migration of the Angola-Benguela Front. Planktic foraminifera indicate a shift from warmer surface water conditions to cooler conditions during the initiation of the BUS. Benthic palaeobathymetric ranges and P/B ratios are consistent with outer shelf water depths suggesting a deeper palaeoenvironment during the Mid-Miocene Climatic Optimum (MMCO) than today. Benthic foraminifera in the middle Miocene are dominated by large (>1 mm) taxa and adapted to oligotrophic environments before the initiation of the BUS. The benthic assemblage composition indicates that bottom water conditions changed to eutrophic conditions during the Plio-Pleistocene under intensified upwelling conditions.

  8. The U.S. continental shelf beyond 200 nautical miles. Legal questions arising from non-accession to the UN Convention on the Law of the Sea

    OpenAIRE

    Longtain, Shay

    2015-01-01

    The elaborate legal framework contained in Part VI of the 1982 United Nations Convention on the Law of the Sea (LOSC) resembles both codification and progressive development of the law of the sea as it relates to the continental shelf. As a non-party to the Convention, the United States is only bound to those provisions which now reflect customary rules of international law or have otherwise created rights or obligations for third states. This thesis identifies several distinct components o...

  9. Flux, Budget and Sources of Black Carbon (BC) in the Continental Shelf of the Bohai and Yellow Seas, China

    Science.gov (United States)

    Fang, Y.; Chen, Y.; Tian, C.

    2015-12-01

    Black carbon (BC) derived from incomplete combustion of fossil fuels and biomass has received increasing attention due to their potential importance in a wide range of biogeochemical processes. China has been generally considered as the world's largest BC emitter. Due to a combination of the prevailing East Asia monsoon and large amounts of riverine outflow, BC released from China can be transported to the adjacent continental shelf seas, the Bohai Sea (BS) and Yellow Sea (YS). Based on measurements of BC in 191 surface sediments, 36 riverine water, and 2 seawater samples, as well as the reported BC data set of the aerosol samples in the Bohai Rim, the concentration, flux, and budget of BC in the BS and YS were investigated. The spatial distribution of the BC concentration in surface sediments was largely influenced by the regional hydrodynamic conditions, with high values mainly occurring in the central mud areas. The BC burial flux in the BS and YS ranged from 4 to 1100 μg/cm2/yr, and averaged 166 ± 200 μg/cm2/yr. The area-integrated sedimentary BC sink flux in the entire BS and YS was ~325 Gg/yr. The BC budget calculated in the BS showed that atmospheric deposition and riverine discharge played comparable importance in delivering BC to the BS, and sequestration to bottom sediments was the major BC output pattern, accounting for ~88% of the total input BC. Besides, we attempted to apportion the BC sources in the BS and YS surface sediments using PAHs (organic molecular proxies cogenerated with BC) and BC as an input data to the Positive Matrix Factorization (PMF) receptor model. Results showed that ~83% of the sediment BC was attributed to the combustion of fossil fuels, and the remaining ~17% was from biomass burning. Due to the differences in their production mechanisms and therefore physicochemical properties, the above distinction and quantification would help us better understand their different environmental behaviors in the complex continental shelf

  10. Biocenoses of benthic foraminifera of the Aveiro Continental Shelf (Portugal: influence of the upwelling events and other shelf processes

    Directory of Open Access Journals (Sweden)

    Maria Virgínia Alves Martins

    2017-03-01

    Full Text Available This work aims to compare the dimensions and composition of benthic foraminiferal biocenoses (living specimens during two summer sampling events. Forty-four sediment samples were collected on the Aveiro Continental Shelf (Center of Portugal (latitude of 40º30'N-40º50'N, longitude of 8º46'W-9º20'W for granulometry, total organic matter (TOM and living foraminiferal analyses. The sediment samples were collected during summers of 1994 and 1995, on stations located along transects (east-west direction and between the bathymetries of 10-200 m. During the sampling campaigns, measurements of salinity, temperature and density data were recorded in the water column. The results showed that the living assemblages were mainly found in stations located between 20-80 m depth. The abundance of living foraminifera was generally reduced at depths <20 m in the so-called “coastal deposits”, where the sediments are frequently remobilized and transported by the littoral drift. Living benthic foraminiferal densities were also reduced in stations at 80-200 m depth, despite the high sedimentary TOM contents. Results obtained in this work indicate that, in this marine setting, the most determinant factors for the dimension and composition of living foraminifera are not the sediments’ granulometry and organic matter content. In fact, the coastal dynamics, sediment stability, availability of quality food, among other factors, such as the bottom salinity oscillations and their combination, should better explain the abundance of living foraminifera and the biocenoses composition.

  11. Bio-Optical Properties of the Inner Continental Shelf off Santos Estuarine System, Southeastern Brazil, and their Implications for Ocean Color Algorithm Performance

    Directory of Open Access Journals (Sweden)

    Melissa Carvalho

    2014-07-01

    Full Text Available Optical characterizations of coastal water masses are important tools for a better understanding of physical and biochemical processes and aid the optimization of ocean color algorithms. In this study we present three optical classes of water observed during October/2005 and March/2006 on the inner continental shelf adjacent to Santos Bay (Brazil, based on remote sensing reflectance. ANOVA indicated a crescent estuarine influence in classes 1 to 3. Class 3 presented the highest chlorophyll-a and nutrient concentration and highest light absorption coefficients. Colored dissolved organic matter (CDOM dominated the light absorption in all classes and was strongly correlated to salinity in October/2005 due to the influence of the La Plata plume. The results indicated that CDOM dynamics in the Santos inner shelf are very complex. The performance of global chlorophyll algorithms was significantly smaller for October/2005 than for March/2006. As inconsistent changes in light absorption spectra by phytoplankton were detected between samplings, the results show that future bio-optical algorithms for this region must be optimized preferentially considering CDOM optical parameters.

  12. Differential responses of seabirds to environmental variability over 2 years in the continental shelf and oceanic habitats of southeastern Bering Sea

    Science.gov (United States)

    Yamamoto, Takashi; Kokubun, Nobuo; Kikuchi, Dale M.; Sato, Nobuhiko; Takahashi, Akinori; Will, Alexis P.; Kitaysky, Alexander S.; Watanuki, Yutaka

    2016-04-01

    Seasonal sea-ice cover has been decreasing in the southeastern Bering Sea shelf, which might affect ecosystem dynamics and availability of food resources to marine top predators breeding in the region. In this study, we investigated the foraging responses of two seabird species, surface-foraging red-legged kittiwakes Rissa brevirostris (hereafter, RLKI) and pursuit-diving foraging thick-billed murres Uria lomvia (TBMU) to different marine environmental conditions over 2 years. At-sea distributions of RLKI and TBMU breeding on St. George Island, the largest seabird colony in the region, were recorded using GPS loggers, and blood samples were taken to examine their physiological condition and isotopic foraging niche in a given year. Between the study years, winter ice retreated earlier and summer water temperatures were relatively warmer in 2014 compared to those in 2013. RLKI foraging occurred mostly over the oceanic basin in both years. TBMU, however, foraged mostly over the shelf but showed a relatively higher use of the shelf break and oceanic basin in 2013. The foraging distances from the colony peaked at 250-300 km in 2013 and bimodally at 150-250 and 300-350 km in 2014 for RLKI and tended to be farther in 2013 compared to those in 2014 for TBMU. Plasma levels of corticosterone did not differ between the years in RLKI but differed in TBMU, showing higher levels of physiological stress incurred by murres in 2013, the year of relatively cooler sea surface temperatures with later sea-ice retreat. δ13N (a proxy of trophic level of prey) did not differ between the years in either RLKI or TBMU. These results suggest that the response of ecosystem dynamics to climate variability in the southeastern Bering Sea may differ between the ocean basin and continental shelf regions, which, in turn, may generate differential responses in seabirds relying on those habitats for foraging.

  13. Phytoplankton Distribution in Relation to Environmental Drivers on the North West European Shelf Sea.

    Science.gov (United States)

    Siemering, Beatrix; Bresnan, Eileen; Painter, Stuart C; Daniels, Chris J; Inall, Mark; Davidson, Keith

    2016-01-01

    The edge of the North West European Shelf (NWES) is characterised by a steep continental slope and a northward flowing slope current. These topographic/hydrographic features separate oceanic water and shelf water masses hence potentially separate phytoplankton communities. The slope current may facilitate the advective transport of phytoplankton, with mixing at the shelf edge supporting nutrient supply and therefore phytoplankton production. On the west Scottish shelf in particular, little is known about the phytoplankton communities in and around the shelf break and adjacent waters. Hence, to improve our understanding of environmental drivers of phytoplankton communities, biological and environmental data were collected on seven cross-shelf transects across the Malin and Hebridean Shelves during autumn 2014. Density profiles indicated that shelf break and oceanic stations had a 100 m deep mixed surface layer while stations on the shelf were generally well mixed. Analysis of similarity and multidimensional scaling of phytoplankton counts revealed that phytoplankton communities on the shelf were significantly different to those found at the shelf break and at oceanic stations. Shelf stations were dominated by dinoflagellates, with diatoms contributing a maximum of 37% of cells. Shelf break and oceanic stations were also dinoflagellate dominated but displayed a lower species diversity. Significant difference between shelf and shelf break stations suggested that the continental slope limited cross shelf phytoplankton exchange. Northern and southern phytoplankton communities on the shelf were approximately 15% dissimilar while there was no latitudinal gradient for stations along the slope current, suggesting this current provided south to north connectivity. Fitting environmental data to phytoplankton ordination showed a significant relationship between phytoplankton community dissimilarities and nutrient concentrations and light availability on the shelf compared to

  14. Influence of fluvial discharge on the dynamics of Chlorophyll-α in the continental shelf adjacent to the Recife Port Basin (Pernambuco-Brazil

    Directory of Open Access Journals (Sweden)

    Amanda Yumi Otsuka

    Full Text Available Abstract This study was undertaken in the coastal zone of the state of Pernambuco adjacent to the Recife port area, which corresponds to the inner shelf. This research aimed to analyze the dynamics of chlorophyll-a and several other environmental variables. Sampling was undertaken bimonthly on the surface from September 11th to May 10th, thus including the rainy and dry periods, and during low tide in spring tide. The parameters analyzed were chlorophyll-a, salinity, temperature, transparency, dissolved oxygen, oxygen saturation rate, pH, suspended solids, dissolved inorganic nutrients. Phytoplankton biomass ranged from 13.48 to 145.09 mg m-3 in the estuarine area and on the inner shelf, the variation being from 0.24 to 19.29 mg m-3 in the dry season and from 0.78 to 5.20 mg m-3 in the rainy season. PCA showed a direct relationship of chlorophyll-a with ammonia, phosphate and transparency and an inverse relationship with suspended particulate matter and nitrate. Biomass did not vary significantly different as a result of seasonal or spatial dynamics. The estuary of the Capibaribe River is considered highly impacted, and as it forms the Recife port basin, it joins with two more strongly eutrophic water bodies, the Beberibe River and the Pina Basin, leading to an amplification of its influence on the adjacent shelf. In terms of the river plume's dispersion in the Port of Recife, the presence of a dike causes some disturbance in the direction of the current, limiting the plume to the area close to the coast and influences the oceanographic variables on the inner continental shelf.

  15. Global multi-scale segmentation of continental and coastal waters from the watersheds to the continental margins

    KAUST Repository

    Laruelle, G. G.; Dü rr, H. H.; Lauerwald, R.; Hartmann, J.; Slomp, C. P.; Regnier, P. A. G.

    2012-01-01

    files. Our analysis provides detailed insights into the distributions of coastal and continental shelf areas and how they connect with incoming riverine fluxes. The segmentation is also used to re-evaluate the global estuarine CO2 flux at the air–water interface combining global and regional average emission rates derived from local studies.

  16. Well construction team approach creates a new future for one company's operations on the Dutch Continental Shelf

    International Nuclear Information System (INIS)

    Bakker, T.W.; Stringer, R.B.

    1995-01-01

    Rising costs and low energy prices were inhibiting the development of marginal fields on the Dutch Continental Shelf, resulting in a reduction in drilling activity and a loss of business opportunities. Independent benchmark surveys and critical analysis of total well costs showed the potential for major cost reductions that could turn many of the smaller offshore gas finds into economic development prospects. This triggered a change from traditional operating and contracting strategies to a partnering approach with the principal drilling and service contractors and the institution of a well-construction team (WCT). The WCT proved so successful, with an average well cost reduction of 21% in the first year, that a similar organization has been set up for all the land drilling and workover operations. This paper describes the strategies used and presents a comparison between the traditional performance and the results from the first year of operating as a WCT. The comparison includes the results of an independent benchmark study of 20 North Sea operating companies

  17. Observed tidal currents on the continental shelf off the east coast of India

    Science.gov (United States)

    Jithin, A. K.; Unnikrishnan, A. S.; Fernando, V.; Subeesh, M. P.; Fernandes, R.; Khalap, S.; Narayan, S.; Agarvadekar, Y.; Gaonkar, M.; Tari, P.; Kankonkar, A.; Vernekar, S.

    2017-06-01

    In the present study, we analysed 9-month long data from Acoustic Doppler Current Profilers (ADCP) deployed on the shelf off the east coast of India to study the characteristics of tidal currents in the region. The ADCPs were deployed at about 100-150 m depths off Cuddalore (CD, 12.0°N), Ramayapatnam (RM, 15.0°N), Kakinada (KN, 16.3°N) and South of Gopalpur (SG, 18.6°N). Tidal currents in the region are mainly semidiurnal in nature and dominant constituent is M2. Semimajor axes of barotropic tidal ellipses of M2 is about 1.9 cms-1 in the southernmost ADCP location (off CD) and it is about 4.0 cms-1 in the northernmost ADCP location (off SG), which indicate a northward increase of tidal currents. Baroclinic spectra show high energy at tidal frequencies, which suggests the presence of internal tides on the shelf, particularly in the semidiurnal band. Semidiurnal internal tides of about 8-15 cms-1 are observed at different locations and the magnitude is relatively large on the shelf off SG in the northern part of the shelf, which is primarily due to large barotropic forcing on the north. The semidiurnal internal tides are found to be intensified at the bottom, particularly on the shelf off SG and RM. The computed ratio of slope of internal wave characteristics (c) and topographic slope (γ) indicates that large near-critical regions present surrounding the ADCP locations off SG and RM could be the possible reason of bottom intensification at these two locations. EOF analysis shows that observed semidiurnal internal tides are dominated by the first baroclinic mode, where it accounts for about 70-80% of semidiurnal internal tide variability on the shelf off SG and CD, whereas the contribution of the first mode is relatively small (43-50%) on the shelf off KN and RM. Enhanced small-scale vertical shear is observed at the ADCP locations associated with multimode structure of semidiurnal internal tides. Semidiurnal internal tides show a spring-neap variability on the

  18. Variability of the flow field in the inner shelf along the central east coast of India during April, 1989

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, T.V.N.; Rao, B.P.; Rao, V.S.; Sadhuram, Y.

    Continental Shelf Research, Vol. 15, No. 2/3, pp. 241-253, 1995 Copyright © 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0278-4343/95 $9.50 + 0.00 0278-4343(94)E0005-7 Variability of the flow field in the inner shelf along.... Continental Shelf Research, 11,295-319. LAFOND E. C. (1957) Oceanographic studies in the Bay of Bengal. Proceedings of the Indian Academy of Sciences, B46, 1-46, LEE T. N., L. P. ATKINSON and R. LEGECKIS (1981) Detailed observations of a Gulf stream spin...

  19. Spatial Extent of Wave-Supported Fluid Mud on the Waipaoa Continental Margin

    Science.gov (United States)

    Hale, R. P.; Ogston, A. S.; Walsh, J. P.; Orpin, A. R.

    2013-12-01

    Data from acoustic and optical sensors provide a powerful tool to connect near-bed water-column processes with the deposits they generate. Ideally, the product of water-column and seabed interactions can then be applied more broadly to understand systems as a whole, in both space and time. Recent observational research has allowed for an improved understanding of shelf sediment-transport dynamics in many coastal systems, including the dynamic Waipaoa Sedimentary System (WSS), on the east coast of the north island of New Zealand. This narrow shelf (~20 km) on an active continental margin is subject to strong environmental forcings in the form of high waves (>5 m), strong currents (>50 cm/s), and frequent floods of the Waipaoa River, which delivers an average of 15 MT of sediment to Poverty Bay and the coastal environment each year. A year-long study of the WSS during 2010-2011 combined observational data from instrumented tripods at three locations on the continental shelf, with repeat sediment cores collected in four-month intervals, to identify and assess the mechanisms of cross- and off-shelf sediment transport. Observational data identified that cross-shelf sediment transport is stochastic, typically driven by high-wave events, with 40% of the net annual cross-shelf flux for one tripod location occurring during a single wave-supported fluid mud (WSFM) in July 2010. Fortunately, this event was recorded in the instrument data, and the resulting deposit was plainly visible in x-radiograph images. This particular WSFM was observed in x-radiographs collected as deep as ~50 m, and as far as ~28 km from the mouth of the Waipaoa River, and is more prevalent on the northern portion of the shelf. A critical water depth is not the only criteria for WSFM deposition, as some shallower areas on the southern shelf, which were subject to high bed stress, show no evidence of WSFM in this event, while cores collected in deeper areas (e.g. lower bed stress) on the northern shelf

  20. Highstand shelf fans: The role of buoyancy reversal in the deposition of a new type of shelf sand body

    Science.gov (United States)

    Steel, Elisabeth; Simms, Alexander R.; Warrick, Jonathan; Yokoyama, Yusuke

    2016-01-01

    Although sea-level highstands are typically associated with sediment-starved continental shelves, high sea level does not hinder major river floods. Turbidity currents generated by plunging of sediment-laden rivers at the fluvial-marine interface, known as hyperpycnal flows, allow for cross-shelf transport of suspended sand beyond the coastline. Hyperpycnal flows in southern California have deposited six subaqueous fans on the shelf of the northern Santa Barbara Channel in the Holocene. Using eight cores and nine grab samples, we describe the deposits, age, and stratigraphic architecture of two fans in the Santa Barbara Channel. Fan lobes have up to 3 m of relief and are composed of multiple hyperpycnite beds ∼5 cm to 40 cm thick. Deposit architecture and geometry suggest the hyperpycnal flows became positively buoyant and lifted off the seabed, resulting in well-sorted, structureless, elongate sand lobes. Contrary to conventional sequence stratigraphic models, the presence of these features on the continental shelf suggests that active-margin shelves may locally develop high-quality reservoir sand bodies during sea-level highstands, and that such shelves need not be solely the site of sediment bypass. These deposits may provide a Quaternary analogue to many well-sorted sand bodies in the rock record that are interpreted as turbidites but lack typical Bouma-type features.

  1. Influence of submarine morphology on bottom water flow across the western Ross Sea continental margin

    Science.gov (United States)

    Davey, F.J.; Jacobs, S.S.

    2007-01-01

    Multibeam sonar bathymetry documents a lack of significant channels crossing outer continental shelf and slope of the western Ross Sea. This indicates that movement of bottom water across the shelf break into the deep ocean in this area is mainly by laminar or sheet flow. Subtle, ~20 m deep and up to 1000 m wide channels extend down the continental slope, into tributary drainage patterns on the upper rise, and then major erosional submarine canyons. These down-slope channels may have been formed by episodic pulses of rapid down slope water flow, some recorded on bottom current meters, or by sub-ice melt water erosion from an icesheet grounded at the margin. Narrow, mostly linear furrows on the continental shelf thought to be caused by iceberg scouring are randomly oriented, have widths generally less than 400 m and depths less than 30m, and extend to water depths in excess of 600 m.

  2. Impact of Satellite Remote Sensing Data on Simulations of Coastal Circulation and Hypoxia on the Louisiana Continental Shelf

    Directory of Open Access Journals (Sweden)

    Dong S. Ko

    2016-05-01

    Full Text Available We estimated surface salinity flux and solar penetration from satellite data, and performed model simulations to examine the impact of including the satellite estimates on temperature, salinity, and dissolved oxygen distributions on the Louisiana continental shelf (LCS near the annual hypoxic zone. Rainfall data from the Tropical Rainfall Measurement Mission (TRMM were used for the salinity flux, and the diffuse attenuation coefficient (Kd from Moderate Resolution Imaging Spectroradiometer (MODIS were used for solar penetration. Improvements in the model results in comparison with in situ observations occurred when the two types of satellite data were included. Without inclusion of the satellite-derived surface salinity flux, realistic monthly variability in the model salinity fields was observed, but important inter-annual variability was missed. Without inclusion of the satellite-derived light attenuation, model bottom water temperatures were too high nearshore due to excessive penetration of solar irradiance. In general, these salinity and temperature errors led to model stratification that was too weak, and the model failed to capture observed spatial and temporal variability in water-column vertical stratification. Inclusion of the satellite data improved temperature and salinity predictions and the vertical stratification was strengthened, which improved prediction of bottom-water dissolved oxygen. The model-predicted area of bottom-water hypoxia on the Louisiana shelf, an important management metric, was substantially improved in comparison to observed hypoxic area by including the satellite data.

  3. Differential responses of seabirds to inter-annual environmental change in the continental shelf and oceanic habitats of southeastern Bering Sea

    Science.gov (United States)

    Yamamoto, T.; Kokubun, N.; Kikuchi, D. M.; Sato, N.; Takahashi, A.; Will, A.; Kitaysky, A. S.; Watanuki, Y.

    2015-11-01

    Seasonal sea-ice cover has been decreasing in the southeastern Bering Sea shelf, which might affect ecosystem dynamics and availability of food resources to marine top predators breeding in the region. In this study, we investigated the foraging responses of two seabird species, surface-foraging red-legged kittiwakes Rissa brevirostris (hereafter, RLKI) and pursuit-diving foraging thick-billed murres Uria lomvia (TBMU) to the inter-annual change in environmental conditions. Between the study years, winter ice retreated earlier and summer water temperatures were warmer in 2014 compared to those in 2013. At-sea distributions of RLKI and TBMU breeding on St. George Island, the largest seabird colony in the region, were recorded using GPS loggers, and blood samples were taken to examine their physiological condition and isotopic foraging niche in a given year. RLKI foraging occurred mostly over the oceanic basin in both years. TBMU, however, foraged mostly over the shelf, but showed a relatively higher use of the shelf break and oceanic basin in the colder year, 2013. The foraging distances from the colony peaked at 250-300 km in 2013 and, bimodally, at 150-250 and 300-350 km in 2014 for RLKI, and tended to be farther in 2013 compared to those in 2014 for TBMU. Plasma levels of corticosterone did not differ between years in RLKI, but differed in TBMU, showing higher levels of physiological stress incurred by murres during the colder year, 2013. δ13N (a proxy of trophic level of prey) did not differ between the years in either RLKI or TBMU, while δ13C (a proxy of prey origin) were lower in 2014 than in 2013 in both species, suggesting possible differences in influx of oceanic prey items into foraging areas. These results suggest that the response of ecosystem dynamics to climate variability in the southeast Bering Sea may differ between the ocean basin and continental shelf regions, which, in turn, may generate differential responses in seabirds relying on those

  4. Summer Drivers of Atmospheric Variability Affecting Ice Shelf Thinning in the Amundsen Sea Embayment, West Antarctica

    Science.gov (United States)

    Deb, Pranab; Orr, Andrew; Bromwich, David H.; Nicolas, Julien P.; Turner, John; Hosking, J. Scott

    2018-05-01

    Satellite data and a 35-year hindcast of the Amundsen Sea Embayment summer climate using the Weather Research and Forecasting model are used to understand how regional and large-scale atmospheric variability affects thinning of ice shelves in this sector of West Antarctica by melting from above and below (linked to intrusions of warm water caused by anomalous westerlies over the continental shelf edge). El Niño episodes are associated with an increase in surface melt but do not have a statistically significant impact on westerly winds over the continental shelf edge. The location of the Amundsen Sea Low and the polarity of the Southern Annular Mode (SAM) have negligible impact on surface melting, although a positive SAM and eastward shift of the Amundsen Sea Low cause anomalous westerlies over the continental shelf edge. The projected future increase in El Niño episodes and positive SAM could therefore increase the risk of disintegration of West Antarctic ice shelves.

  5. Continental Margins of the Arctic Ocean: Implications for Law of the Sea

    Science.gov (United States)

    Mosher, David

    2016-04-01

    A coastal State must define the outer edge of its continental margin in order to be entitled to extend the outer limits of its continental shelf beyond 200 M, according to article 76 of the UN Convention on the Law of the Sea. The article prescribes the methods with which to make this definition and includes such metrics as water depth, seafloor gradient and thickness of sediment. Note the distinction between the "outer edge of the continental margin", which is the extent of the margin after application of the formula of article 76, and the "outer limit of the continental shelf", which is the limit after constraint criteria of article 76 are applied. For a relatively small ocean basin, the Arctic Ocean reveals a plethora of continental margin types reflecting both its complex tectonic origins and its diverse sedimentation history. These factors play important roles in determining the extended continental shelves of Arctic coastal States. This study highlights the critical factors that might determine the outer edge of continental margins in the Arctic Ocean as prescribed by article 76. Norway is the only Arctic coastal State that has had recommendations rendered by the Commission on the Limits of the Continental Shelf (CLCS). Russia and Denmark (Greenland) have made submissions to the CLCS to support their extended continental shelves in the Arctic and are awaiting recommendations. Canada has yet to make its submission and the US has not yet ratified the Convention. The various criteria that each coastal State has utilized or potentially can utilize to determine the outer edge of the continental margin are considered. Important criteria in the Arctic include, 1) morphological continuity of undersea features, such as the various ridges and spurs, with the landmass, 2) the tectonic origins and geologic affinities with the adjacent land masses of the margins and various ridges, 3) sedimentary processes, particularly along continental slopes, and 4) thickness and

  6. Environmental characterization of the continental shelf of the Gulf of Tehuantepec, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Tapia-Garcia, M; Garcia-Abad, M.C [Departamento de Hidrobiologia, Universidad Autonoma Metropolitana-Iztapalapa, (Mexico); Carranza-Edwards, A; Vazquez-Gutierrez, F [Instituto de Ciencias del Mar y Limnologia, Universidad Nacional Autonoma de Mexico, Mexico D.F. (Mexico)

    2007-10-15

    This study analyzes data and information of the physical and chemical characteristics of water, and type of sediments of the continental shelf of the Gulf of Tehuantepec, Mexico. The changes of salinity, temperature, and dissolved oxygen fluctuate according to the wet and dry seasons (in the last one, prevails the Tehuantepecanos winds). The stations samples of salinity, temperature, pH, and type of sediments were classified by cluster and factor analysis. The results suggest that the Gulf of Tehuantepec has two subsystems. The Oaxaqueno subsystem extends south-southeast from Salina Cruz to the Tonala inlet. This subsystem is characterized by upwelling periods, which leads to low temperatures, low dissolved oxygen and high nutrient concentration, as well as sandy sediments and insignificant river discharges when low temperature, low dissolved oxygen and high nutrient concentration are typical, and by sandy sediments and insignificant river discharges. The second, the Chiapaneco subsystem, is located between the Tonala inlet and the Suchiate River, with strong influence of coastal lagoons and river discharges. The bottom is characterized by sandy and muddy-sand sediments. This subsystem is not affected by either Tehuantepecanos winds or upwelling. Both subsystems and their characteristics probably determine the patterns of distribution of the biotic resources. [Spanish] Se analizan datos e informacion de las caracteristicas fisico-quimicas del agua y tipo de sedimentos de la plataforma continental del Golfo de Tehuantepec, Mexico. Los cambios de salinidad, temperatura y oxigeno disuelto varian de acuerdo con las estaciones de lluvias y sequia (en esta ultima prevalecen fuertes vientos denominados Tehuantepecanos). Las estaciones de muestreo fueron agrupadas (utilizando salinidad, temperatura, pH y tipo de sedimentos) con analisis por conglomerados y analisis de factores. Los resultados indican que el Golfo de Tehuantepec tiene dos subsistemas. El subsistema

  7. Distribution and dispersal of clay minerals on the western continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Nair, R.R.; Hashimi, N.H.; Rao, V.P

    off the Gulf of Kutch; (2) the montmorillonite-rich zone off the Gulf of Cambay; (3) a transition zone on the central parts of the shelf; and (4) a relatively montmorillonite poor-gibbsite province on the southwestern part of the shelf. Source...

  8. Long-lasting Microbial Methane Release at the Aquitaine Shelf Break (Bay of Biscay): Relation with the (Plio)-Pleistocene Sedimentary Progradation of the Continental Margin

    Science.gov (United States)

    Dupré, S.; Michel, G.; Pierre, C.; Ruffine, L.; Scalabrin, C.; Ehrhold, A.; Loubrieu, B.; Gautier, E.; Baltzer, A.; Imbert, P.; Battani, A.; Deville, E.; Dupont, P.; Thomas, Y.; Théréau, E.

    2017-12-01

    The recent identification of acoustic and visual gas release in the water column at the Aquitaine Shelf (140 and 220 m water depths) led to the discovery of a 200 km2 fluid system at the seafloor with 3000 bubbling sites associated with microbial methane (Dupré et al 2014; Ruffine et al. 2017). The moderate methane fluxes (measured in situ, on average 200 mLn/min per bubbling site) contribute to the formation of small-scale sub-circular authigenic carbonate mounds (with reliefs < 1 m in height) (Pierre et al. 2017). The emitted gases have neither a genetic link with thermogenic hydrocarbons from the Parentis Basin beneath, nor are issued from gas hydrate dissociation, but originate from microbial CO2 reduction. Based on estimated thickness and growth rate of authigenic carbonates, this system has lasted for at least several tens to possibly hundreds of kyears with a volume of escaping methane reaching 3.1012 Ln per 10 kyr. Seismic evidences for gas-charged layers and fossil authigenic carbonates point to organic matter source levels within the sedimentary deposits of the Late Pleistocene progradation system. The Aquitaine Shelf fluid system highlights the edge of continental shelves as preferential areas for bio-geological processes. The GAZCOGNE project is co-funded by TOTAL and IFREMER as part of the PAMELA (Passive Margin Exploration Laboratories) scientific project. References Dupré S, Berger L, Le Bouffant N, Scalabrin C, Bourillet J-F (2014) Fluid emissions at the Aquitaine Shelf (Bay of Biscay, France): a biogenic origin or the expression of hydrocarbon leakage? Cont. Shelf Res. 88:24-33 Pierre C, Demange J, Blanc-Valleron M-M, Dupré S (2017) Authigenic carbonate mounds from active methane seeps on the southern Aquitaine Shelf (Bay of Biscay, France): Evidence for anaerobic oxidation of biogenic methane and submarine groundwater discharge during formation. Cont. Shelf Res. 133:13-25 Ruffine L, Donval J-P, Croguennec C, Bignon L, Birot D, Battani A, Bayon

  9. Heavy metals in fish tissues/stomach contents in four marine wild commercially valuable fish species from the western continental shelf of South China Sea.

    Science.gov (United States)

    Gu, Yang-Guang; Lin, Qin; Huang, Hong-Hui; Wang, Liang-Gen; Ning, Jia-Jia; Du, Fei-Yan

    2017-01-30

    The concentrations of heavy metals (Cd, Pb, Cr, Ni, Cu and Zn) were determined in four commercially valuable fish species (Thunnus obesus, Decapterus lajang, Cubiceps squamiceps and Priacanthus macracanthus), collected in the western continental shelf of the South China Sea. Concentrations of Cd, Pb, Cr, Ni, Cu, and Zn in fish muscles were 0.006-0.050, 0.13-0.68, 0.18-0.85, 0.11-0.25, 0.12-0.77, and 2.41-4.73μg/g, wet weight, respectively. Concentrations of heavy metals in all species were below their acceptable daily upper limit, suggesting human consumption of these wild fish species may be safe, with health risk assessment based on the target hazard quotients (THQ) and total THQ, indicating no significant adverse health effects with consumption. The average concentrations of Zn were higher in gills than in stomach contents, backbones or muscle, while conversely, the other heavy metals had higher concentrations in stomach contents than in other tissues. Copyright © 2016 Elsevier Ltd. All rights reserved.

  10. 137Cs inventory in sedimentary columns from continental shelf of Sao Paulo state

    International Nuclear Information System (INIS)

    Figueira, Rubens C.L.; Cordero, Luisa M.; Mahiques, Michel M. de; Tessler, Moyses G.

    2009-01-01

    137 Cs is an artificial radioactive isotope produced by 235 U fission. This radionuclide has a high fission yield and a half-life of 30 years. It has been detected in the environment since 1945 and its principal contamination source has been nuclear tests in the atmosphere. There are other sources of 137 Cs contamination in the environment, such as: release from nuclear and reprocessing plants, radioactive dumping and nuclear accidents (Chernobyl, for example). This paper presents an inventory of 137 Cs on the Continental Shelf of Sao Paulo State, a region located between Cabo de Santa Marta Grande (Santa Catarina state) and Cabo Frio (Rio de Janeiro state). In this area, 9 cores were collected by the Instituto Oceanografico da Universidade de Sao Paulo (Sao Paulo University Institute of Oceanography). The cores were sliced at every 2 cm; sub-samples were lyophilized, grinded and stored in plastic containers. 137 Cs was determined by 661 keV photopeak using a gamma spectrometry detector (Ge hyperpure). The analysis was performed by efficiency and background in different counting times. 137 Cs concentration activities varied from 0.3 to 3.6 Bq kg -1 with a mean value of 1.2±0.6 Bq kg -1 . The inventory of 137 Cs in this area was 13±7 Bq m-2. Values obtained are in agreement with the Southern Hemisphere, a region contaminated by atmospheric fallout due to past nuclear explosions. (author)

  11. Stratigraphic and morphologic signatures of continental shelves, IGC 2016, Cape Town: an introduction

    Science.gov (United States)

    Green, A. N.; Cooper, J. A. G.

    2018-02-01

    This special issue of Geo-Marine Letters comprises seven contributions to the session "Stratigraphic and morphologic signatures of continental shelves" of the 35th International Geological Congress held in Cape Town (Republic of South Africa) on 27 August-4 September 2016. There is an additional article not presented at the conference but falling into the same general theme. The guest editors are A.N. Green and J.A.G. Cooper. The eight articles address several contemporary themes in continental shelf geology. They include the role of antecedent conditioning on the development of shelf stratigraphy and geomorphology; erosion of submerged shorelines and their preservation during (stepped) postglacial sea-level rise; the role of glacial processes (e.g. iceberg scouring during ice-sheet retreat); and the utility of archival data in addressing contemporary issues such as Holocene climate change and global oceanographic circulation systems. The continental shelf holds important information for understanding past and present global circulation and earth-ice-atmosphere interactions including sea-level change. It is hoped that these themes will spur further research that is slowly coming to the fore in several new and innovative mapping and exploration programmes emerging from an increasing number of coastal nations.

  12. Dispersal of the Pearl River plume over continental shelf in summer

    Science.gov (United States)

    Chen, Zhaoyun; Gong, Wenping; Cai, Huayang; Chen, Yunzhen; Zhang, Heng

    2017-07-01

    Satellite images of turbidity were used to study the climatological, monthly, and typical snapshot distributions of the Pearl River plume over the shelf in summer from 2003 to 2016. These images show that the plume spreads offshore over the eastern shelf and is trapped near the coast over the western shelf. Eastward extension of the plume retreats from June to August. Monthly spatial variations of the plume are characterized by eastward spreading, westward spreading, or both. Time series of monthly plume area was quantified by applying the K-mean clustering method to identify the turbid plume water. Decomposition of the 14-year monthly turbidity data by the empirical orthogonal function (EOF) analysis isolated the 1st mode in both the eastward and westward spreading pattern as the time series closely related to the Pearl River discharge, and the 2nd mode with out-of-phase turbidity anomalies over the eastern and western shelves that is associated with the prevailing wind direction. Eight typical plume types were detected from the satellite snapshots. They are characterized by coastal jet, eastward offshore spreading, westward spreading, bidirectional spreading, bulge, isolated patch, offshore branch, and offshore filaments, respectively. Their possible mechanisms are discussed.

  13. Statistical analysis of planktic foraminifera of the surface Continental ...

    African Journals Online (AJOL)

    Planktic foraminiferal assemblage recorded from selected samples obtained from shallow continental shelf sediments off southwestern Nigeria were subjected to statistical analysis. The Principal Component Analysis (PCA) was used to determine variants of planktic parameters. Values obtained for these parameters were ...

  14. Geologic Setting and Preservation of a Late Pleistocene Bald Cypress Forest Discovered on the Northern Gulf of Mexico Continental Shelf

    Science.gov (United States)

    Gonzalez Rodriguez, S. M.; Bentley, S. J.; DeLong, K. L.; Xu, K.; Harley, G. L.; Reese, C. A.; Obelcz, J.

    2016-02-01

    Following landfall of Hurricane Ivan in 2004, a previously buried bald cypress forest (Taxodium distichum) was discovered on the continental shelf seafloor, offshore of Orange Beach, Alabama, USA, in 20 m of water. The forest is preserved as stumps in life position with little evidence of decay and large pieces of trunks, roots, and branches. Analysis shows the forest is older than can be dated with conventional C-14 methods. Comparison of Pleistocene sea level curves with the study area depth suggests that the forest developed and was likely buried during marine isotope stage 3 or 4, or perhaps older stages. Condition of sampled wood suggests that the forest was buried and preserved in anoxic sediments for millennia, prior to recent exhumation. To better understand the puzzling geological conditions that could allow forest preservation during sea level fall and shelf exposure spanning >30,000 years, submersible vibracores (to 6 m length) and geophysical data (swath bathymetry, sidescan, and chirp subbottom) were collected in August 2015. Cores are being analyzed using a Geotek Multi Sensor Core Logger, granulometric and sediment composition analyses, and a wide range of paleoenvironmental observations. This presentation focuses on the geological setting and mode of forest preservation. Preliminary analysis of sediment types and stratigraphy in cores shows that the local stratigraphy is broadly consistent with previous regional shelf-stratigraphic studies, consisting of (top to bottom) a surface layer of Holocene transgressive sands (to 3 m thick) unconformably overlying Pleistocene terrestrial and coastal deposits. However, the Pleistocene lithofacies (fluvial, backswamp, or possibly delta plain muds) differ considerably in both depositional environment and degree of environmental preservation compared to previous studies. Ongoing analysis will focus on elucidating the succession of events that allows preservation of this unique Pleistocene sedimentary archive.

  15. Spatial variability of primary organic sources regulates ichthyofauna distribution despite seasonal influence in Terminos lagoon and continental shelf of Campeche, Mexico

    Science.gov (United States)

    Romo Rios, J. A.; Aguíñiga-García, S.; Sanchez, A.; Zetina-Rejón, M.; Arreguín-Sánchez, F.; Tripp-Valdéz, A.; Galeana-Cortazár, A.

    2013-05-01

    Human activities have strong impacts on coastal ecosystems functioning through their effect on primary organic sources distributions and resulting biodiversity. Hence, it appears to be of utmost importance to quantify contribution of primary producers to sediment organic matter (SOM) spatial variability and its associated ichthyofauna. The Terminos lagoon (Gulf of Mexico) is a tropical estuary severely impacted by human activities even though of primary concern for its biodiversity, its habitats, and its resource supply. Stable isotope data (d13C, d15N) from mangrove, seaweed, seagrass, phytoplankton, ichthyofauna and SOM were sampled in four zones of the lagoon and the continental shelf through windy (November to February), dry (March to June) and rainy (July to October) seasons. Stable Isotope Analysis in R (SIAR) mixing model were used to determine relative contributions of the autotrophic sources to the ichthyofauna and SOM. Analysis of variance of ichthyofauna isotopic values showed significant differences (P < 0.001) in the four zones of lagoon despite the variability introduced by the windy, dry and rainy seasons. In lagoons rivers discharge zone, the mangrove contribution to ichthyofauna was 40% and 84% to SOM. Alternative use of habitat by ichthyofauna was evidenced since in the deep area of the lagoon (4 m), the contribution of mangrove to fish is 50%, and meanwhile contribution to SOM is only 77%. Although phytoplankton (43%) and seaweed (41%) contributions to the adjacent continental shelf ichthyofauna were the main organic sources, there was 37% mangrove contribution to SOM, demonstrating conspicuous terrigenous influence from lagoon ecosystem. Our results point toward organic sources spatial variations that regulate fish distribution. In Terminos lagoon, significant correlation (p-value = 0.2141 and r=0.79) of Ariopsis felis and Sphoeroides testudineus abundances and seaweed and seagrasses contributions (30-35%) during both dry and rainy seasons

  16. A Vulnerability Assessment of Fish and Invertebrates to Climate Change on the Northeast U.S. Continental Shelf.

    Directory of Open Access Journals (Sweden)

    Jonathan A Hare

    Full Text Available Climate change and decadal variability are impacting marine fish and invertebrate species worldwide and these impacts will continue for the foreseeable future. Quantitative approaches have been developed to examine climate impacts on productivity, abundance, and distribution of various marine fish and invertebrate species. However, it is difficult to apply these approaches to large numbers of species owing to the lack of mechanistic understanding sufficient for quantitative analyses, as well as the lack of scientific infrastructure to support these more detailed studies. Vulnerability assessments provide a framework for evaluating climate impacts over a broad range of species with existing information. These methods combine the exposure of a species to a stressor (climate change and decadal variability and the sensitivity of species to the stressor. These two components are then combined to estimate an overall vulnerability. Quantitative data are used when available, but qualitative information and expert opinion are used when quantitative data is lacking. Here we conduct a climate vulnerability assessment on 82 fish and invertebrate species in the Northeast U.S. Shelf including exploited, forage, and protected species. We define climate vulnerability as the extent to which abundance or productivity of a species in the region could be impacted by climate change and decadal variability. We find that the overall climate vulnerability is high to very high for approximately half the species assessed; diadromous and benthic invertebrate species exhibit the greatest vulnerability. In addition, the majority of species included in the assessment have a high potential for a change in distribution in response to projected changes in climate. Negative effects of climate change are expected for approximately half of the species assessed, but some species are expected to be positively affected (e.g., increase in productivity or move into the region. These

  17. A Vulnerability Assessment of Fish and Invertebrates to Climate Change on the Northeast U.S. Continental Shelf

    Science.gov (United States)

    Hare, Jonathan A.; Morrison, Wendy E.; Nelson, Mark W.; Stachura, Megan M.; Teeters, Eric J.; Griffis, Roger B.; Alexander, Michael A.; Scott, James D.; Alade, Larry; Bell, Richard J.; Chute, Antonie S.; Curti, Kiersten L.; Curtis, Tobey H.; Kircheis, Daniel; Kocik, John F.; Lucey, Sean M.; McCandless, Camilla T.; Milke, Lisa M.; Richardson, David E.; Robillard, Eric; Walsh, Harvey J.; McManus, M. Conor; Marancik, Katrin E.; Griswold, Carolyn A.

    2016-01-01

    Climate change and decadal variability are impacting marine fish and invertebrate species worldwide and these impacts will continue for the foreseeable future. Quantitative approaches have been developed to examine climate impacts on productivity, abundance, and distribution of various marine fish and invertebrate species. However, it is difficult to apply these approaches to large numbers of species owing to the lack of mechanistic understanding sufficient for quantitative analyses, as well as the lack of scientific infrastructure to support these more detailed studies. Vulnerability assessments provide a framework for evaluating climate impacts over a broad range of species with existing information. These methods combine the exposure of a species to a stressor (climate change and decadal variability) and the sensitivity of species to the stressor. These two components are then combined to estimate an overall vulnerability. Quantitative data are used when available, but qualitative information and expert opinion are used when quantitative data is lacking. Here we conduct a climate vulnerability assessment on 82 fish and invertebrate species in the Northeast U.S. Shelf including exploited, forage, and protected species. We define climate vulnerability as the extent to which abundance or productivity of a species in the region could be impacted by climate change and decadal variability. We find that the overall climate vulnerability is high to very high for approximately half the species assessed; diadromous and benthic invertebrate species exhibit the greatest vulnerability. In addition, the majority of species included in the assessment have a high potential for a change in distribution in response to projected changes in climate. Negative effects of climate change are expected for approximately half of the species assessed, but some species are expected to be positively affected (e.g., increase in productivity or move into the region). These results will inform

  18. Neotectonism - An offshore evidence from eastern continental shelf off Visakhapatnam

    Digital Repository Service at National Institute of Oceanography (India)

    Subrahmanyam, A.S.; Venkateswarlu, K.; Murthy, K.S.R.; Rao, M.M.M.; Rao, K.M.; Raju, Y.S.N.

    tremor provide evidence of Neo-tectonic activity in this regio. The epicentral region falls in a shallow marine environment ideal for generating a geophysical database for stable continental region earthquakes....

  19. Diel feeding chronology of the skate raja Agassizii (Müller & Henle (Pisces, Elasmobranchii on the continental shelf off Ubatuba, Southeastern Brazil

    Directory of Open Access Journals (Sweden)

    Lucy Satiko Hashimoto Soares

    1999-03-01

    Full Text Available The diet and diel feeding pattern of the skate Raja agassizii were investigated through analysis of stomach contents. A total of 280 stomachs were collected by a series of hauls during a daily cycle in three periods, 8-10 January 1987, 22-24 July and 2-4 December 1988, from the inner continental shelf of the coastal ecosystem of Ubatuba, São Paulo State, Brazil (25º35'S; 45º00'W. According to the results of the stomach fullness and of the number of fresh prey, it is suggested that this species presents continuity in the feeding activity during a day. The stomach contents were mainly composed of crustaceans. Nematodes, polychaetes and fishes also occurred. No changes were observed in dietary composition between day and night.

  20. A century of oceanographic and fisheries exploration on the continental shelf off Argentina

    Science.gov (United States)

    Angelescu, V.; Sánchez, R. P.

    1995-03-01

    A detailed analysis is presented of the main contributions, both local and international, to the fields of oceanography and fishery sciences resulting from exploratory cruises carried out on the continental shelf off Argentina over the last 100 years. The end of the 19th century is chosen as a starting point for this analysis as it marks the beginning of active marine research by Argentinian scientists and an accumulation of information on Antarctic and Subantarctic organisms in foreign journals. Mention is also made of previous contributions derived from the classic expeditions and global circumnavigational voyages during the 18th and 19th centuries. Although the aims of those were not always strictly oceanographic, they rendered significant information to this field of knowledge. In the early years, references arose mainly from the particular geographic situation of the Argentinian shelf, a necessary passage in the navigation routes to the Pacific Ocean, and later on the way to Antarctica. Sources of information are divided into four categories: (a) foreign scientific projects in the area; (b) investigation by Argentinian scientists and research vessels; (c) joint projects between Argentinian and foreign institutions; and (d) contributions from sources other than oceanographic cruises (commercial navigation, maritime weather reports, satellite images, etc.). The analysis includes an updated and classified bibliographical list of the main contributions to the fields of oceanography and fishery sciences derived from those sources, published either in international or local journals or appearing as technical and internal reports. The motivations, objectives and main achievements of foreign surveys and programmes in the area and their impact on local scientific progress are discussed. The early sixties mark a turning point in the evolution of international research in the area. The creation of biological stations along the Argentinian coast, and the support given to

  1. Agglutinated foraminifera from the shelf of east coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Almeida, F.; Setty, M.G.A.P.

    belonging to six families, in a depth zone of 35-222 m of the east-coast of India (between Visakhapatnam and Masulipatnam along the continental shelf-slope region) in terms of lithology, faunal assemblage and their percentage distribution are discussed...

  2. Determinação dos elementos-traço (Zn, Co e Ni em sedimentos da Plataforma Continental Amazônica sob influência da descarga do rio Amazonas Determination of trace elements (Zn, Co and Ni in sediments at the Amazon Continental Shelf on influence of the Amazon River discharge

    Directory of Open Access Journals (Sweden)

    Gilmar Wanzeller Siqueira

    2006-01-01

    Full Text Available Esta pesquisa foi desenvolvida na Plataforma Continental Amazônica (PCA no trecho compreendido entre os cabos Orange (AP e Maguari (PA, para determinar os teores de Zn, Co e Ni nos sedimentos superficiais, identificando o papel dos sedimentos como fonte ou reserva de elementos-traço. A concentração dos elementos metálicos apresentou a seguinte associação: Zn > Ni > Co. Os sedimentos localizados na PCA podem ser considerados como sítio de ocorrência natural dos elementos metálicos, não havendo influência de fontes poluidoras na liberação destes para o sistema.Determination of trace elements (Zn, Co and Ni in sediments at the Amazon Continental Shelf on influence of the Amazon River discharge This research was developed at Amazon Continental Shelf (ACS between the Orange Cape (Amapá State and the Maguari Cape (Pará State, to determine the levels of zinc, cobalt and nickel in the superficial sediments identifying its inputs and outputs. The rate of these metallic elements in the sediments decreases following Zn> Ni> Co. The concentrations of total metals in the surface sediments range from Zn = 52.8 159.5; Ni = 21.7 47.4 and Co = 14.3 48.8 (mg.kg-1. The levels of trace elements observed in the sediments at ACS are of natural occurrence. Pollution sources of metallic elements were not observed.

  3. Sources, Fate and Distribution of Organic Matter on the Western Adriatic Continental Shelf, Italy

    International Nuclear Information System (INIS)

    Tesi, Tommaso; Miserocchi, Stefano; Langone, Leonardo; Boni, Laurita; Guerrini, Franca

    2006-01-01

    In the framework of the EUROSTRATAFORM projects, a multidisciplinary research was focused on processes that involve transport and deposition of riverine material in the Adriatic Sea. The aim of our contribution was to increase a more complete understanding of organic matter deposition on the Adriatic shelf, also taking into account the role of Apennine rivers beyond the Po influence. In order to characterize origin, fate and variability of sedimentary organic carbon we utilized elemental and stable carbon isotope data in surficial sediments along shallow cross-shelf transects on the western Adriatic shelf

  4. Geochemistry and microbiology data collected from bottle casts from the R/V HERMANO GINES from the continental shelf of Venezuela in support of the Carbon Retention in a Colored Ocean (CARIACO) project from 19 January to 7 December 2010 (NODC Accession 0066503)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This accession contains bottle data collected aboard the R/V HERMANO GINES from the continental shelf of Venezuela during 19 January, 2009 (CAR-153); 16 May to 17...

  5. Mercury in sediments from shelf and continental slope at Campos Basin near Rio de Janeiro, Brazil

    Science.gov (United States)

    Araujo, Beatriz; Hintelmann, Holger; Dimock, Brian; Gomes de Almeida, Marcelo; Falcão, Ana Paula; de Rezende, Carlos Eduardo

    2016-04-01

    Mercury (Hg) is a global pollutant due to its ability to undergo long-range transport from source regions to remote parts of the world, and its ubiquitous presence in aquatic ecosystems. The Hg isotope ratios could be an effective tool for tracing the sources and process of Hg in the environment. This study aimed to establish the distribution of mercury in surface sediments of three transects (25- 3000m water depth) in continental shelf and slope in Campos Basin-RJ-Brazil, using the Hg isotopes to understand the geochemical processes relating to Hg cycling that occur in a subtropical coastal environment. The study area was divided into three transects: A (located to the south and close to a upwelling area), D (located opposite the mouth of the Paraiba do Sul River) and I (located north near the top of Vitória-ES). Sampling isobaths were 25, 50, 75, 100, 150, 400, 700, 1000, 1300, 1900, 2500 and 3000m. The Total Hg, MMHg and Hg stable isotopes were determined based on EPA Method 1631, EPA method 1630 and Foucher and Hintelmann (2006), respectively. The silt/clay ranged from 0.05 to 95%, and the organic carbon (OC) from 0.07 to 1.43 % for all transects. THg and MMHg concentrations in the shelf were 11.9 ± 7.2 (1.7- 22.2) ng.g-1 and 0.15 ± 0.12 (0.02 - 0.40) ng.g-1; in the slope 30.3 ± 9.2 (11.6 - 51.6) ng.g-1 and 0.13 ± 0.06 (0.03 -0.29) ng.g-1 , respectively. The δ202Hg and Δ199Hg varied from -0.32 to -1.85 ‰ (-0.79 ± 0.44‰) and -0.41 to 0.09 ‰ (-0.03 ± 0.12 ‰) for all transects, respectively. The delta values between both regions are significantly different, the shelf region showed δ202Hg from -0.59 to -2.19 ‰ (mean: -1.52 ±0.65) and Δ199Hg from - 0.53 to 0.08 ‰ (mean: -0.27 ±0.55) and the slope region were observed δ202Hg values from -0.32 to -1.82 ‰ (mean: -0.73 ±0.39 ‰ n=18) and gΔ199Hg from -0.23 to 0.09‰ (mean: -0.02 ±0.08‰ n=5). The slope appears to be enriched with heavier isotopes compared to the shelf, however, in the

  6. The George V Land Continental Margin (East Antarctica): new Insights Into Bottom Water Production and Quaternary Glacial Processes from the WEGA project

    Science.gov (United States)

    Caburlotto, A.; de Santis, L.; Lucchi, R. G.; Giorgetti, G.; Damiani, D.; Macri', P.; Tolotti, R.; Presti, M.; Armand, L.; Harris, P.

    2004-12-01

    The George Vth Land represents the ending of one of the largest subglacial basin (Wilkes Basin) of the East Antarctic Ice Sheet (EAIS). Furthermore, its coastal areas are zone of significant production of High Salinity Shelf Water (HSSW). Piston and gravity cores and high resolution echo-sounding (3.5 kHz) and Chirp profiles collected in the frame of the joint Australian and Italian WEGA (WilkEs Basin GlAcial History) project provide new insights into the Quaternary history of the EAIS and the HSSW across this margin: from the sediment record filling and draping valleys and banks along the continental shelf, to the continuous sedimentary section of the mound-channel system on the continental rise. The discovery of a current-lain sediment drift (Mertz Drift, MD) provides clues to understanding the age of the last glacial erosive events, as well as to infer flow-pathways of bottom-water masses changes. The MD shows disrupted, fluted reflectors due to glacial advance during the LGM (Last Glacial Maximum) in shallow water, while undisturbed sediment drift deposited at greater water depth, indicates that during the LGM the ice shelf was floating over the deep sector of the basin. The main sedimentary environment characterising the modern conditions of the continental rise is dominated by the turbiditic processes with a minor contribution of contour currents action. Nevertheless, some areas (WEGA Channel) are currently characterised by transport and settling of sediment through HSSW, originating in the shelf area. This particular environment likely persisted since pre-LGM times. It could indicate a continuous supply of sedimentary material from HSSW during the most recent both glacial and interglacial cycles. This would be consistent with the results obtained in the continental shelf suggesting that the Ice Sheet was not grounding over some parts of the continental shelf. Furthermore, the comparison of the studied area with other Antarctic margins indicate that, contrary

  7. Geological features and geophysical signatures of continental margins of India

    Digital Repository Service at National Institute of Oceanography (India)

    Krishna, K.S.

    of crustal movement had been introduced to the scientific community; and it has laid the groundwork for the development of modern plate tectonics. As years passed, more and more evidences were uncovered to support the idea that the plates were moving... to build-up of the wide and low-relief (flat) continental shelf (covered by shelf seas), slope and rise. Initially passive margins form at divergent plate boundary following break-up of the continent, then they move away with the accretion of new...

  8. Is there a distinct continental slope fauna in the Antarctic?

    Science.gov (United States)

    Kaiser, Stefanie; Griffiths, Huw J.; Barnes, David K. A.; Brandão, Simone N.; Brandt, Angelika; O'Brien, Philip E.

    2011-02-01

    The Antarctic continental slope spans the depths from the shelf break (usually between 500 and 1000 m) to ˜3000 m, is very steep, overlain by 'warm' (2-2.5 °C) Circumpolar Deep Water (CDW), and life there is poorly studied. This study investigates whether life on Antarctica's continental slope is essentially an extension of the shelf or the abyssal fauna, a transition zone between these or clearly distinct in its own right. Using data from several cruises to the Weddell Sea and Scotia Sea, including the ANDEEP (ANtarctic benthic DEEP-sea biodiversity, colonisation history and recent community patterns) I-III, BIOPEARL (BIOdiversity, Phylogeny, Evolution and Adaptive Radiation of Life in Antarctica) 1 and EASIZ (Ecology of the Antarctic Sea Ice Zone) II cruises as well as current databases (SOMBASE, SCAR-MarBIN), four different taxa were selected (i.e. cheilostome bryozoans, isopod and ostracod crustaceans and echinoid echinoderms) and two areas, the Weddell Sea and the Scotia Sea, to examine faunal composition, richness and affinities. The answer has important ramifications to the link between physical oceanography and ecology, and the potential of the slope to act as a refuge and resupply zone to the shelf during glaciations. Benthic samples were collected using Agassiz trawl, epibenthic sledge and Rauschert sled. By bathymetric definition, these data suggest that despite eurybathy in some of the groups examined and apparent similarity of physical conditions in the Antarctic, the shelf, slope and abyssal faunas were clearly separated in the Weddell Sea. However, no such separation of faunas was apparent in the Scotia Sea (except in echinoids). Using a geomorphological definition of the slope, shelf-slope-abyss similarity only changed significantly in the bryozoans. Our results did not support the presence of a homogenous and unique Antarctic slope fauna despite a high number of species being restricted to the slope. However, it remains the case that there may be

  9. Exposure of coastal ecosystems to river plume spreading across a near-equatorial continental shelf

    Science.gov (United States)

    Tarya, A.; Hoitink, A. J. F.; Vegt, M. Van der; van Katwijk, M. M.; Hoeksema, B. W.; Bouma, T. J.; Lamers, L. P. M.; Christianen, M. J. A.

    2018-02-01

    The Berau Continental Shelf (BCS) in East Kalimantan, Indonesia, harbours various tropical marine ecosystems, including mangroves, seagrass meadows and coral reefs. These ecosystem are located partly within reach of the Berau River plume, which may affect ecosystem health through exposure to land-derived sediments, nutrients and pollutants carried by the plume. This study aims (1) to assess the exposure risk of the BCS coastal ecosystems to river plume water, measured as exposure time to three different salinity levels, (2) to identify the relationships between these salinity levels and the abundance and diversity of coral and seagrass ecosystems, and (3) to determine a suitable indicator for the impacts of salinity on coral reef and seagrass health. We analysed hydrodynamic models, classified salinity levels, and quantified the correlations between the salinity model parameters and ecological metrics for the BCS systems. An Empirical Orthogonal Functions (EOF) analysis revealed three modes of river plume dispersal patterns, which strongly reflect monsoon seasonality. The first mode, explaining 39% of the variability, was associated with the southward movement of the plume due to northerly winds, while the second and third modes (explaining 29% and 26% of the variability, respectively) were associated with the northeastward migration of the plume related to southwesterly and southerly winds. Exposure to low salinity showed higher correlations with biological indicators than mean salinity, indicating that low salinity is a more suitable indicator for coastal ecosystem health. Significant correlations (R2) were found between exposure time to low salinity (days with salinity values below 25 PSU) with coral cover, coral species richness, seagrass cover, the number of seagrass species, seagrass leaf phosphorus, nitrogen, C:N ratio and iron content. By comparing the correlation coefficients and the slopes of the regression lines, our study suggests that coral reefs are

  10. Downscaling an Eddy-Resolving Global Model for the Continental Shelf off South Eastern Australia

    Science.gov (United States)

    Roughan, M.; Baird, M.; MacDonald, H.; Oke, P.

    2008-12-01

    The Australian Bluelink collaboration between CSIRO, the Bureau of Meteorology and the Royal Australian Navy has made available to the research community the output of BODAS (Bluelink ocean data assimilation system), an ensemble optimal interpolation reanalysis system with ~10 km resolution around Australia. Within the Bluelink project, BODAS fields are assimilated into a dynamic ocean model of the same resolution to produce BRAN (BlueLink ReANalysis, a hindcast of water properties around Australia from 1992 to 2004). In this study, BODAS hydrographic fields are assimilated into a ~ 3 km resolution Princeton Ocean Model (POM) configuration of the coastal ocean off SE Australia. Experiments were undertaken to establish the optimal strength and duration of the assimilation of BODAS fields into the 3 km resolution POM configuration for the purpose of producing hindcasts of ocean state. It is shown that the resultant downscaling of Bluelink products is better able to reproduce coastal features, particularly velocities and hydrography over the continental shelf off south eastern Australia. The BODAS-POM modelling system is used to provide a high-resolution simulation of the East Australian Current over the period 1992 to 2004. One of the applications that we will present is an investigation of the seasonal and inter-annual variability in the dispersion of passive particles in the East Australian Current. The practical outcome is an estimate of the connectivity of estuaries along the coast of southeast Australia, which is relevant for the dispersion of marine pests.

  11. {sup 137}Cs inventory in sedimentary columns from continental shelf of Sao Paulo state

    Energy Technology Data Exchange (ETDEWEB)

    Figueira, Rubens C.L.; Cordero, Luisa M.; Mahiques, Michel M. de; Tessler, Moyses G., E-mail: rfigueira@usp.b [Universidade de Sao Paulo (USP), SP (Brazil). Inst. Oceanografico. Dept. de Oceanografia Fisica, Quimica e Geologica; Cruz, Jacson L.S. [Universidade Cruzeiro do Sul, Sao Paulo, SP (Brazil)

    2009-07-01

    {sup 137}Cs is an artificial radioactive isotope produced by {sup 235}U fission. This radionuclide has a high fission yield and a half-life of 30 years. It has been detected in the environment since 1945 and its principal contamination source has been nuclear tests in the atmosphere. There are other sources of {sup 137}Cs contamination in the environment, such as: release from nuclear and reprocessing plants, radioactive dumping and nuclear accidents (Chernobyl, for example). This paper presents an inventory of {sup 137}Cs on the Continental Shelf of Sao Paulo State, a region located between Cabo de Santa Marta Grande (Santa Catarina state) and Cabo Frio (Rio de Janeiro state). In this area, 9 cores were collected by the Instituto Oceanografico da Universidade de Sao Paulo (Sao Paulo University Institute of Oceanography). The cores were sliced at every 2 cm; sub-samples were lyophilized, grinded and stored in plastic containers. {sup 137}Cs was determined by 661 keV photopeak using a gamma spectrometry detector (Ge hyperpure). The analysis was performed by efficiency and background in different counting times. {sup 137}Cs concentration activities varied from 0.3 to 3.6 Bq kg{sup -1} with a mean value of 1.2+-0.6 Bq kg{sup -1}. The inventory of {sup 137}Cs in this area was 13+-7 Bq m-2. Values obtained are in agreement with the Southern Hemisphere, a region contaminated by atmospheric fallout due to past nuclear explosions. (author)

  12. Benthic foraminiferal distribution in surface sediments along continental slope of the southern Okinawa Trough:dependance on water masses and food supply

    Institute of Scientific and Technical Information of China (English)

    向荣; 李铁刚; 杨作升; 阎军; 曹奇原

    2003-01-01

    Benthic foraminiferal analysis of 29 samples in surface sediments from the southern Oki-nawa Trough is carried out. The results indicate that benthic foraminiferal abundance decreases rapidlywith increasing water depth. Percentage frequencies of agglutinated foraminifera further confirm themodem shallow carbonate lysocline in the southern Okinawa Trough. From continental shelf edge to thebottom of Okinawa Trough, benthic foraminiferal fauna in the surface sediments can be divided into 5assemblages: (1) Continental shelf break assemblage, dominated by Cibicides pseudoungerianus, corre-sponds to subsurface water mass of the Kuroshio Current; (2) upper continental slope assemblage, domi-nated by Cassidulina carinata, Globocassidulina subglobosa, corresponds to intermediate water mass of the Kuroshio Current; (3) intermediate continental slope assemblage, dominated by Uvigerina hispi-da, corresponds to the Okinawa Trough deep water mass above the carbonate lysocline; (4) lower con-tinental slope- trough bottom assemblage, dominated by Pullenia bulloides, Epistominella exigua andCibicidoides hyalinus, corresponds to deep water mass of the Okinawa Trough; and (5) trough bottomagglutinated assemblage, dominated by Rhabdammina spp., Bathysiphon flavidus, corresponds tostrongly dissolved environment of the trough bottom. The benthic foraminiferal fauna in the southemOkinawa Trough are controlled jointly by water masses and food supply. Water temperature, oxygenconcentration and carbonate dissolution of the water masses are important controlling factors especiallyfor the continental shelf break and trough bottom assemblages. The food supply also plays an importantrole in these benthic foraminiferal assemblages along the westem slope of the Okinawa Trough. Both theabundance and the 5 assemblages of benthic foraminifera correspond well to the organic matter supplyalong the continental slope and a lateral transport of TSM (total suspended matter) and POC (particulateorganic

  13. Steam trawling on the south-east continental shelf of Australia. An environmental history of fishing, management and science in NSW, 1865 -1961

    DEFF Research Database (Denmark)

    Jacobsen, A. Lif Lund

    2010-01-01

    . Motivated by Sydney’s insufficient supplies of fish, the objective of early fisheries management in the state of New South Wales (NSW) was to improve the industry. Driven by state developmentalism, efforts were focused on increasing the productivity of already existing coastal fisheries through fisheries......As many of the world’s fish stocks are fully or over-exploited there is an urgent need for governments to provide robust fisheries management. However, governments are often slow to implement necessary changes to fisheries practices. The will to govern is an essential factor in successful marine...... resource management. Studies of historical documents from State and Commonwealth fisheries authorities involved in the steam trawl fishery on the south-east continental shelf of Australia illustrate different expressions of intentional management and how a more ecological responsible view has emerged...

  14. Impacts of Suspended Sediment and Estuarine - Shelf Exchange Pathways on Shelf Ecosystem Dynamics in the Northern Gulf of Mexico

    Science.gov (United States)

    Wiggert, J. D.; Pan, C.; Dinniman, M. S.; Lau, Y.; Fitzpatrick, P. J.; O'Brien, S. J.; Bouchard, C.; Quas, L. M.; Miles, T. N.; Cambazoglu, M. K.; Dykstra, S. L.; Dzwonkowski, B.; Jacobs, G. A.; Church, I.; Hofmann, E. E.

    2017-12-01

    A circulation model based on the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System, with coupled biogeochemical and sediment transport modules, has been implemented for Mississippi Sound and the adjacent continental shelf region. The model has 400-m horizontal resolution, 24 vertical layers, and includes wetting/drying capability to resolve shallow inshore regions. The circulation model was spun-up using oceanographic initial and lateral boundary conditions provided by a 1-km resolution regional implementation of the Navy Coastal Ocean Model (NCOM) in the Gulf of Mexico. The biogeochemical module includes multiple size classes of phytoplankton, zooplankton and detritus, a fish larvae compartment, and explicitly tracks dissolved oxygen with benthic cycling interaction. The sediment transport model is implemented based on benthic mapping data that provides bottom sediment type distributions and spatio-temporal validation. A regionally specific atmospheric forcing product that provides improved spatial and temporal resolution, including diurnal sea breeze impacts, has been developed and applied. Model experiments focus on periods when comprehensive ship-based sampling was deployed by the CONCORDE (Consortium for Coastal River-Dominated Ecosystems) research program, which was established to investigate the complex fine-scale biological, chemical and physical interactions in a marine system controlled by pulsed-river plume dynamics. Biophysical interactions and biogeochemical variability associated with estuarine - shelf exchanges between nearshore lagoonal estuarine waters and the continental shelf revealed by the model provide new insight into how seasonal variation of hydrological forcing conditions influence ecological and biogeochemical processes in the highly productive Northern Gulf region. Application of the COAWST-based model system with and without inclusion of the sediment transport module demonstrates how suspended sediment in the

  15. Arctic Ocean outflow and glacier-ocean interactions modify water over the Wandel Sea shelf (northeastern Greenland)

    DEFF Research Database (Denmark)

    Dmitrenko, Igor A.; Kirillov, Sergey A.; Rudels, Bert

    2017-01-01

    The first-ever conductivity-temperature-depth (CTD) observations on the Wandel Sea shelf in northeastern Greenland were collected in April-May 2015. They were complemented by CTDs taken along the continental slope during the Norwegian FRAM 2014-2015 drift. The CTD profiles are used to reveal...... the origin of water masses and interactions with ambient water from the continental slope and the tidewater glacier outlet. The subsurface water is associated with the Pacific water outflow from the Arctic Ocean. The underlying halocline separates the Pacific water from a deeper layer of polar water that has...... interacted with the warm Atlantic water outflow through the Fram Strait, recorded below 140 m. Over the outer shelf, the halocline shows numerous cold density-compensated intrusions indicating lateral interaction with an ambient polar water mass across the continental slope. At the front of the tidewater...

  16. Sediment movement along the U.S. east coast continental shelf-I. Estimates of bottom stress using the Grant-Madsen model and near-bottom wave and current measurements

    Science.gov (United States)

    Lyne, V.D.; Butman, B.; Grant, W.D.

    1990-01-01

    Bottom stress is calculated for several long-term time-series observations, made on the U.S. east coast continental shelf during winter, using the wave-current interaction and moveable bed models of Grant and Madsen (1979, Journal of Geophysical Research, 84, 1797-1808; 1982, Journal of Geophysical Research, 87, 469-482). The wave and current measurements were obtained by means of a bottom tripod system which measured current using a Savonius rotor and vane and waves by means of a pressure sensor. The variables were burst sampled about 10% of the time. Wave energy was reasonably resolved, although aliased by wave groupiness, and wave period was accurate to 1-2 s during large storms. Errors in current speed and direction depend on the speed of the mean current relative to the wave current. In general, errors in bottom stress caused by uncertainties in measured current speed and wave characteristics were 10-20%. During storms, the bottom stress calculated using the Grant-Madsen models exceeded stress computed from conventional drag laws by a factor of about 1.5 on average and 3 or more during storm peaks. Thus, even in water as deep as 80 m, oscillatory near-bottom currents associated with surface gravity waves of period 12 s or longer will contribute substantially to bottom stress. Given that the Grant-Madsen model is correct, parameterizations of bottom stress that do not incorporate wave effects will substantially underestimate stress and sediment transport in this region of the continental shelf.

  17. EBSSED database-Surficial sediments of the eastern Bering Sea continental shelf

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — In order to facilitate descriptions of groundfish habitat over a large portion of the EBS shelf, the NMFS/AFSC has assembled a single comprehensive database of the...

  18. Biology of Chirocentrodon bleekerianus (Poey, 1867 (Clupeiformes: Pristigasteridae in a continental shelf region of southern Brazil

    Directory of Open Access Journals (Sweden)

    Carlos Eduardo Corrêa

    2005-05-01

    Full Text Available This study provides information on the biology of C. bleekerianus from Paraná State coast, Brazil, assembling data about its abundance, size structure, diet and reproduction. Monthly collections were accomplished in 1999 and 2000 in the internal continental shelf, with trawl net. The catch-per-unit-effort did not vary significantly among the seasons. In the summer, the individuals were larger, followed by autumn, spring and winter. C. bleekerianus was predominantly planktivorous and the most frequent items in its diet were copepods followed by diatomaceous algae. Seasonal variation in the frequency values of the gonad maturation stages, gonadossomatic index and gonadal condition factor indicated that the reproductive period encompassed spring and summer. The mean total length at first maturity of females was estimated to be 76 mm.Este trabalho fornece dados sobre a biologia de C. bleekerianus do litoral do Estado do Paraná, reunindo dados sobre sua abundância, estrutura em tamanho, dieta e reprodução. Coletas mensais foram realizadas em 1999 e 2000 na plataforma continental interna, com rede de arrasto de fundo com portas. A captura por unidade de esforço não variou significativamente entre as estações do ano. No verão os indivíduos eram maiores, seguido do outono, primavera e inverno. C. bleekerianus é predominantemente planctívora, sendo copépodos seguidos de algas diatomáceas os itens alimentares mais freqüentes em sua dieta. As variações sazonais de valores da freqüência de estádios de maturação gonadal, do índice gonadossomático e do fator de condição gonadal indicam que o período reprodutivo compreende primavera e verão. O comprimento total médio de primeira maturação das fêmeas é estimado em 76 mm.

  19. Seismic imaging of small horizontal scale structures of the shallow thermocline on the western Brittany continental shelf (North-East Atlantic)

    Science.gov (United States)

    Piete, H.; Marié, L.; Marsset, B.; Gutscher, M.

    2012-12-01

    The recent development of the seismic oceanography technique has made possible the imaging of a variety of deep oceanographic structures (Holbrook et al., 2003); however, until now this method has remained ill suited for the study of shallow (environment) and 2- spectral contents offering high vertical resolutions (relevant to the mapping of small vertical wavelength structures). In this study we defined and tested a new experimental seismic acquisition system capable of imaging the ~10 m thick seasonal thermocline on the western Brittany continental shelf. To accomplish this task, we pursued two complementary approaches: 1. Analysis of legacy seismic data (multi-channel seismic reflection profiles acquired on the East-Corsican margin, Bahamas Plateau and Gulf of Cadiz in various oceanographic environments) featuring reflectors at depths between 25 and 150 m, in order to identify and quantify the influence of acquisition parameters (seismic trace length, offsets, emission level and frequency content). 2. Incorporation of new oceanographic data acquired during the FROMVAR cruise (July 28th to August 10th 2010) on the western Brittany shelf in thermally stratified waters for use in the simulation of the seismic acquisition, in order to further define the optimal parameters for the system. Finally a 3D seismic system has emerged and was tested during the ASPEX scientific cruise led from June 17th to 19th 2012 across the western Brittany shelf. The device featured: i- four seismic streamers, each consisting of 6 traces at a spacing of 1.80 m; ii- a 1000 J SIG Sparker producing a 400 Hz signal with a 220 dB re 1μPa @1m level of emission, towed at a 8 m distance of the first seismic trace. This survey provided high lateral resolution images of the seasonal thermocline located at a 30 m depth with vertical displacements induced by internal waves. References Holbrook, W.S., Paramo, P., Pearse, S. and Schmitt, R.W., 2003. Thermohaline Fine Structure in an Oceanographic

  20. Physical, chemical and biological data collected from CTD and bottle casts from the R/V HERMANO GINES from the Caribbean Sea and continental shelf of Venezuela in support of the Carbon Retention in a Colored Ocean (CARIACO) project from 2008 - 2010 (NODC Accession 0069000)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — CTD and bottle data were collected from R/V HERMANO GINES on the continental shelf of Venezuela from 10 September 2008 to 7 January 2010, during cruises Car149...

  1. Assessing the impact of Hurricanes Irene and Sandy on the morphology and modern sediment thickness on the inner continental shelf offshore of Fire Island, New York

    Science.gov (United States)

    Schwab, William C.; Baldwin, Wayne E.; Denny, Jane F.

    2016-01-15

    This report documents the changes in seabed morphology and modern sediment thickness detected on the inner continental shelf offshore of Fire Island, New York, before and after Hurricanes Irene and Sandy made landfall. Comparison of acoustic backscatter imagery, seismic-reflection profiles, and bathymetry collected in 2011 and in 2014 show that sedimentary structures and depositional patterns moved alongshore to the southwest in water depths up to 30 meters during the 3-year period. The measured lateral offset distances range between about 1 and 450 meters with a mean of 20 meters. The mean distances computed indicate that change tended to decrease with increasing water depth. Comparison of isopach maps of modern sediment thickness show that a series of shoreface-attached sand ridges, which are the dominant sedimentary structures offshore of Fire Island, migrated toward the southwest because of erosion of the ridge crests and northeast-facing flanks as well as deposition on the southwest-facing flanks and in troughs between individual ridges. Statistics computed suggest that the modern sediment volume across the about 81 square kilometers of common sea floor mapped in both surveys decreased by 2.8 million cubic meters, which is a mean change of –0.03 meters, which is smaller than the resolution limit of the mapping systems used.

  2. Paleocene Wilcox cross-shelf channel-belt history and shelf-margin growth: Key to Gulf of Mexico sediment delivery

    Science.gov (United States)

    Zhang, Jinyu; Steel, Ronald; Ambrose, William

    2017-12-01

    Shelf margins prograde and aggrade by the incremental addition of deltaic sediments supplied from river channel belts and by stored shoreline sediment. This paper documents the shelf-edge trajectory and coeval channel belts for a segment of Paleocene Lower Wilcox Group in the northern Gulf of Mexico based on 400 wireline logs and 300 m of whole cores. By quantitatively analyzing these data and comparing them with global databases, we demonstrate how varying sediment supply impacted the Wilcox shelf-margin growth and deep-water sediment dispersal under greenhouse eustatic conditions. The coastal plain to marine topset and uppermost continental slope succession of the Lower Wilcox shelf-margin sediment prism is divided into eighteen high-frequency ( 300 ky duration) stratigraphic sequences, and further grouped into 5 sequence sets (labeled as A-E from bottom to top). Sequence Set A is dominantly muddy slope deposits. The shelf edge of Sequence Sets B and C prograded rapidly (> 10 km/Ma) and aggraded modestly ( 80 m/Ma) characterizes Sequence Sets D and E, which is associated with smaller (9-10 m thick on average) and isolated channel belts. This stratigraphic trend is likely due to an upward decreasing sediment supply indicated by the shelf-edge progradation rate and channel size, as well as an upward increasing shelf accommodation indicated by the shelf-edge aggradation rate. The rapid shelf-edge progradation and large rivers in Sequence Sets B and C confirm earlier suggestions that it was the early phase of Lower Wilcox dispersal that brought the largest deep-water sediment volumes into the Gulf of Mexico. Key factors in this Lower Wilcox stratigraphic trend are likely to have been a very high initial sediment flux to the Gulf because of the high initial release of sediment from Laramide catchments to the north and northwest, possibly aided by modest eustatic sea-level fall on the Texas shelf, which is suggested by the early, flat shelf-edge trajectory, high

  3. Modelo numérico tri-dimensional linear da plataforma continental do Estado do Maranhão Linear three-dimensional numerical model of Maranhão State continental shelf

    Directory of Open Access Journals (Sweden)

    José Edson Rodrigues Pereira

    1995-01-01

    Full Text Available Um modelo numérico hidrodinámico tri-dimensional linear, do tipo Heaps, foi implementado para a plataforma continental do Estado do Maranhão, visando a simulação da circulação gerada por efeitos astronômicos e meteorológicos na área. O modelo foi processado para cinco condições, a fim de calcular a circulação na plataforma devida aos seguintes efeitos: componente de maré semi-diurna lunar principal (M2, composição das principais componentes astronômicas de maré na área, condições meteorológicas médias de verão, condições meteorológicas médias de inverno e forçantes de maré em períodos específicos de interesse. Mapas cotidais e elipses de correntes da componente M2 foram obtidos, sendo esta componente preponderante na circulação local. Elevações e correntes sazonais médias são, em geral, muito menores que as astronômicas, permitindo o uso apenas de forçantes de maré em previsões hidrodinámicas. As simulações do modelo foram satisfatórias na plataforma e menos precisas nas baías e áreas internas rasas, onde atrasos de fase significativos são observados, devido a efeitos de menor escala que a adotada pelo modelo.A linear three-dimensional hydrodynamical numerical model, Heaps type, was implemented to the continental shelf of Maranhão State, aiming the simulation of the circulation generated by astronomical and meteorological effects in that area. Five runs of the model were performed, in order to compute the circulation in the shelf due to the following effects: principal lunar semi-diurnal component (M2, composition of the principal astronomical components in the area, mean summer meteorological conditions, mean winter meteorological conditions and tidal forcing in specific periods of interest. M2 cotidal maps and currents ellipses were obtained, that one being the most important component in the tidal circulation. Mean seasonal elevations and currents are generally much smaller than the

  4. Tectonic structure of the Tuscany-Latium Continental Shelf (Tyrrhenian Sea)

    Energy Technology Data Exchange (ETDEWEB)

    Bartole, R.

    1988-08-01

    An old regional seismic multicoverage reflection survey (Zone E) provides useful information on the shallow structure of the southern Tuscany-northern Latium shelf located between Elba Island and Anzio. Three main seismic units have been recognized on the grid, directly tied to the Matilde-1 offshore drilling and correlated to onshore wells and outcrops. The upper unit, characterized by continuous and generally undisturbed reflectors, is constituted by the postorogenic sedimentary cover of late Neogene-Quaternary age. This sequence unconformably lies on an intermediate unit or, when absent, a basal one. These two units, characterized by good-to-poor seismic response, are constituted by the tectonized geologic units of the Northern and Central Apennines. The intermediate unit corresponds to the Ligurids and Sicilids allochthonous complexes, while the basal unit may be attributable to the Tuscan nappe and/or the Tuscan autochthon in the shelf sector north of the Tiber River mouth, and the Umbro-Sabina units south of the same mouth. The widespread distribution and consistent thickness of the allochthonous cover (up to 1,000 msec two-way traveltime) lying over a structured substratum might be of some interest in hydrocarbon prospecting.

  5. Continental Influence versus marine transition in Rio de la Plata zone - internal continental shelf of the South Atlantic - a multi proxy study

    International Nuclear Information System (INIS)

    Burone, L.; Franco-Fraguas, P.; Garcia-Rodriguez, F.; Venturini, N.; Brugnoli, E.; Muniz, P.; Ortega, L.; Marin, Y.; Mahiques, M.; Nagaic, R.; Bicegoc, M.; Figueiras, R.; Salaroli, A.

    2012-01-01

    The terrigenous proxies contribution, the organic matter origin, the productivity, the hydrodynamic and the biological records were used to determine the imrprint of the continental influence along the Rio de la Plata and the Continental Atlantic

  6. Sea-floor texture and physiographic zones of the inner continental shelf from Salisbury to Nahant, Massachusetts, including the Merrimack Embayment and Western Massachusetts Bay

    Science.gov (United States)

    Pendleton, Elizabeth E.; Barnhardt, Walter A.; Baldwin, Wayne E.; Foster, David S.; Schwab, William C.; Andrews, Brian D.; Ackerman, Seth D.

    2015-10-26

    A series of maps that describe the distribution and texture of sea-floor sediments and physiographic zones of Massachusetts State waters from Nahant to Salisbury, Massachusetts, including western Massachusetts Bay, have been produced by using high-resolution geophysical data (interferometric and multibeam swath bathymetry, lidar bathymetry, backscatter intensity, and seismic reflection profiles), sediment samples, and bottom photographs. These interpretations are intended to aid statewide efforts to inventory and manage coastal and marine resources, link with existing data interpretations, and provide information for research focused on coastal evolution and environmental change. Marine geologic mapping of the inner continental shelf of Massachusetts is a statewide cooperative effort of the U.S. Geological Survey and the Massachusetts Office of Coastal Zone Management.

  7. Note On The Ross Sea Shelf Water Downflow Processes (antarctica)

    Science.gov (United States)

    Bergamasco, A.; Defendi, V.; Spezie, G.; Budillon, G.; Carniel, S.

    In the framework of the CLIMA Project of the Italian National Program for Research in Antarctica, three different experimental data sets were acquired along the continental shelf break; two of them (in 1997 and 2001) close to Cape Adare, the 1998 one in the middle of the Ross Sea (i.e. 75 S, 177 W). The investigations were chosen in order to explore the downslope flow of the bottom waters produced in the Ross Sea, namely the High Salinity Shelf Water (HSSW, the densest water mass of the southern ocean coming from its formation site in the polynya region in Terra Nova bay), and the Ice Shelf Water (ISW, originated below the Ross Ice Shelf and outflowing northward). Both bottom waters spill over the shelf edge and mix with the Circumpolar Deep Water (CDW) contributing to the formation of the Antarctic Bottom Waters (AABW). Interpreting temperature, salinity and density maps in terms of cascading processes, both HSSW and ISW overflows are evidenced during, respectively, 1997 and 1998. During the 2001 acquisition there is no presence of HSSW along the shelf break, nevertheless distribution captures the evidence of a downslope flow process.

  8. Spatial changes in fatty acids signatures of the great scallop Pecten maximus across the Bay of Biscay continental shelf

    Science.gov (United States)

    Nerot, Caroline; Meziane, Tarik; Schaal, Gauthier; Grall, Jacques; Lorrain, Anne; Paulet, Yves-Marie; Kraffe, Edouard

    2015-10-01

    The spatial variability of food resources along continental margins can strongly influence the physiology and ecology of benthic bivalves. We explored the variability of food sources of the great scallop Pecten maximus, by determining their fatty acid (FA) composition along an inshore-offshore gradient in the Bay of Biscay (from 15 to 190 m depth). The FA composition of the digestive gland showed strong differences between shallow and deep-water habitats. This trend was mainly driven by their content in diatom-characteristic fatty acids, which are abundant near the coast. Scallops collected from the middle of the continental shelf were characterized by higher contents of flagellate markers than scallops from shallow habitats. This could be related to a permanent vertical stratification in the water column, which reduced vertical mixing of waters, thereby enhancing organic matter recycling through the microbial loop. In the deeper water station (190 m), FA compositions were close to the compositions found in scallops from shallow areas, which suggest that scallops could have access to the same resources (i.e. diatoms). Muscle FA composition was more indicative of the physiological state of scallops over this depth range, revealing contrasting reproductive strategies among the two coastal sites and metabolic or physiological adaptation at greater depth (e.g. structural and functional adjustments of membrane composition). This study therefore revealed contrasted patterns between shallow and deeper habitats for both P. maximus muscle and digestive gland tissues. This emphasizes the variability in the diet of this species along its distribution range, and stresses the importance of analyzing different tissues for their FA composition in order to better understand their physiology and ecology.

  9. Bacterial biogeography influenced by shelf-basin exchange in the Arctic surface sediment at the Chukchi Borderland.

    Science.gov (United States)

    Han, Dukki; Nam, Seung-Il; Ha, Ho Kyung; Kim, Hyoungjun; Sadowsky, Michael J; Lee, Yoo Kyung; Hur, Hor-Gil

    2016-02-01

    It has been known that continental shelves around the Arctic Ocean play a major role in the ventilation of the deep basins as a consequence of shelf-basin exchange. In the present study, we found that bacterial assemblage of the surface sediment was different from that of seawater while seawater harboured local bacterial assemblages in response to the Arctic hydrography. This finding suggests that the Arctic seafloor sediments may have distinctive bacterial biogeography. Moreover, the distribution of bacterial assemblages and physicochemical properties in surface sediments changed gradually from the Arctic continental shelf to deep-sea basin. Based on the results, bacterial biogeography in the Arctic seafloor sediments may be influenced by winnowing and re-deposition of surface sediments through the sediment gravity flow. The present study offers a deeper understanding of shelf convection and its role for the construction of bacterial assemblages in the Arctic Ocean. © 2015 Society for Applied Microbiology and John Wiley & Sons Ltd.

  10. Observations and a model of undertow over the inner continental shelf

    Science.gov (United States)

    Lentz, Steven J.; Fewings, Melanie; Howd, Peter; Fredericks, Janet; Hathaway, Kent

    2008-01-01

    Onshore volume transport (Stokes drift) due to surface gravity waves propagating toward the beach can result in a compensating Eulerian offshore flow in the surf zone referred to as undertow. Observed offshore flows indicate that wave-driven undertow extends well offshore of the surf zone, over the inner shelves of Martha’s Vineyard, Massachusetts, and North Carolina. Theoretical estimates of the wave-driven offshore transport from linear wave theory and observed wave characteristics account for 50% or more of the observed offshore transport variance in water depths between 5 and 12 m, and reproduce the observed dependence on wave height and water depth.During weak winds, wave-driven cross-shelf velocity profiles over the inner shelf have maximum offshore flow (1–6 cm s−1) and vertical shear near the surface and weak flow and shear in the lower half of the water column. The observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the surf zone. Instead, the vertical structure is similar to the Stokes drift velocity profile but with the opposite direction. This vertical structure is consistent with a dynamical balance between the Coriolis force associated with the offshore flow and an along-shelf “Hasselmann wave stress” due to the influence of the earth’s rotation on surface gravity waves. The close agreement between the observed and modeled profiles provides compelling evidence for the importance of the Hasselmann wave stress in forcing oceanic flows. Summer profiles are more vertically sheared than either winter profiles or model profiles, for reasons that remain unclear.

  11. Direct impacts of outer continental shelf activities on wetland loss in the central Gulf of Mexico

    International Nuclear Information System (INIS)

    Baumann, R.H.; Turner, R.E.

    1990-01-01

    The direct impacts of outer continental shelf (OCS) development on recent wetland loss in the northern Gulf of Mexico were quantified using aerial imagery, field surveys, and literature review. The total direct impacts accounted for an estimated 25.6 percent of total net wetland loss within the Louisiana portion of the study area from 1955/56 to 1978. Of the total direct impacts of 73,905 ha, OCS-related activities accounted for 11,589-13,631 ha of the wetland loss during the same time interval. Although this is a substantial areal loss, it represents only 4.0-4.7 percent of the total Louisiana wetland loss from 1955/56 to 1978, and 15.7-18.4 percent of direct impacts. Direct impacts from OCS pipelines averages 2.49 ha/km, lower than published guidelines, and totaled 12,012 ha. Lowest impacts are for backfilled pipelines in the Chenier Plain of western Louisiana and for small young pipeline canals does not appear to be an important factor for total new wetland loss in the coastal zone because few pipelines are open to navigation and, for the examples found, the impact width was not significantly different than for open pipelines closed to navigation. Navigation channels account for a minimum of 16,902 ha of habitat change. Direct impacts per unit length of navigation channel average 20 times greater than pipelines

  12. Assemblages of fish larvae and mesozooplankton across the continental shelf and shelf slope of the Andaman Sea (NE Indian Ocean)

    DEFF Research Database (Denmark)

    Munk, Peter; Bjørnsen, Peter Koefoed; Boonruang, P.

    2004-01-01

    on the sampling of fish larvae and mesozooplankton. Surveys were carried out during 2 monsoon periods in March and August 1996, using 3 cross-bathymetric transects extending to the deeper part of the shelf slope of the Andaman Sea. Station distances were either 5 or 10 n miles apart, and at each station a series...... with a hydrographic front generated where the pycnocline meets the sea-bottom. An internal wave of pronounced amplitude interacts with the shelf slope at ca. 300 m bottom depth, and findings indicated another zone of enhanced abundance in this area. Analysis of the relative abundances of fish larvae within families...

  13. Statistics of Stacked Strata on Experimental Shelf Margins

    Science.gov (United States)

    Fernandes, A. M.; Straub, K. M.

    2015-12-01

    Continental margin deposits provide the most complete record on Earth of paleo-landscapes, but these records are complex and difficult to interpret. To a seismic geomorphologist or stratigrapher, mapped surfaces often present a static diachronous record of these landscapes through time. We present data that capture the dynamics of experimental shelf-margin landscapes at high-temporal resolution and define internal hierarchies within stacked channelized and weakly channelized deposits from the shelf to the slope. Motivated by observations from acoustically-imaged continental margins offshore Brunei and in the Gulf of Mexico, we use physical experiments to quantify stratal patterns of sub-aqueous slope channels and lobes that are linked to delta-top channels. The data presented here are from an experiment that was run for 26 hours of experimental run time. Overhead photographs and topographic scans captured flow dynamics and surface aggradation/degradation every ten minutes. Currents rich in sediment built a delta that prograded to the shelf-edge. These currents were designed to plunge at the shoreline and travel as turbidity currents beyond the delta and onto the continental slope. Pseudo-subsidence was imposed by a slight base-level rise that generated accommodation space and promoted the construction of stratigraphy on the delta-top. Compensational stacking is a term that is frequently applied to deposits that tend to fill in topographic lows in channelized and weakly channelized systems. The compensation index, a metric used to quantify the strength of compensation, is used here to characterize deposits at different temporal scales on the experimental landscape. The compensation timescale is the characteristic time at which the accumulated deposits begins to match the shape of basin-wide subsidence rates (uniform for these experiments). We will use the compensation indices along strike transects across the delta, proximal slope and distal slope to evaluate the

  14. Geomorfologia, cobertura sedimentar e transporte de sedimentos na plataforma continental interna entre a Ponta de Saquarema e o Cabo Frio (RJ Geomorphology, sediment distribution and transpon on the inner continental shelf between Ponta de Saquarema and Cabo Frio (RJ

    Directory of Open Access Journals (Sweden)

    Dieter Muehe

    1993-01-01

    Full Text Available A plataforma continental interna defronte à restinga da Massambaba - um sistema de duplos cordões litorâneos localizados entre Saquarema e Arraial do Cabo, com 48 km de extensão - apresenta topografia regular, interrompida por raros afloramentos de rochas do embasamento cristalino e por ocorrências localizadas de arenitos de praia. Um amplo afloramento destes últimos ocorre na faixa batimétrica de 48 a 60 m, correspondendo à posição da linha de costa cerca de 10.000 anos atrás. Outro afloramento de arenitos de praia, de reduzida dimensão, ocorre próximo ao perfil S-4, à distância de 50 m da face da praia, em profundidade de 4 m. A cobertura sedimentar, sem aporte significativo de sedimentos terrígenos, é constituída predominantemente por areias quartzosas reliquiares. O gradiente batimétrico apresenta declividade elevada, atípica para uma plataforma passiva, atingindo o limite distai da plataforma continental interna, a isobatimétrica de 60 m, a uma distância da ordem de 4 milhas náuticas da linha de praia. O padrão de distribuição granulométrico apresenta gradientes de decréscimo em direção a leste, isto é, em direção ao Cabo Frio, e em direção a maiores profundidades. A diminuição do tamanho granulométrico em direção ao Cabo Frio é atribuída como sendo resultado do aporte de sedimentos terrígenos através de um sistema de drenagem pleistocênico, interrompido pela construção do cordão litorâneo mais interiorizado, e à remobilização dos sedimentos por ação de ondas e correntes com transporte residual em direção a leste.The inner continental shelf in front of the Massambaba beach, an East-West striking, 48 km long, double barrier beach, located between the towns of Saquarema and Arraial do Cabo presents a monotonous topography with only few outcrops of crystaline rocks, patches of beach rocks and a sediment cover of mainly relict quartz sand. The topographic gradient, steeper as expected for

  15. Physical, chemical, and nutrient data collected from CTD and bottle casts from the R/V HERMANO GINES from the continental shelf of Venezuela in support of the Carbon Retention in a Colored Ocean (CARIACO) project from 10 April 2007 to 05 August December 2008 (NODC Accession 0056729)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — CTD and bottle data were collected from R/V HERMANO GINES on the continental shelf of Venezuela from 10 April 2007 to 05 August 2008. Data were collected by the...

  16. Global change effects on early holocene sedimentation of the Brazilian continental shelf determined from TM-LANDSAT 5 data of the seafloor

    International Nuclear Information System (INIS)

    Cabral, A.P.; Vianna, M.L.; Gherardi, D.F.M.

    1992-01-01

    A study of the shaping of the seafloor morphology on the Brazilian northeast continental shelf caused by climatic changes in the beginning of the Holocene is being made with the support of TM-Landsat 5 data. Special emphasis is given on analysis of data from ancient shorelines between 20-45m depth, to be correlated with abrupt global climate change between 10,000-8,000 BP. The transport of a quartz sand deposit by the ocean currents through time, effected by active sandwave fields at the 20 m isobath is also described. Two images were used corresponding to two dates: 1984 and 1989. Geometric correction, filter application and contrast enhancement were performed. A comparison between 84' and 89' images was carried out, to detect changing patterns of the sand waves, along a 5 year period, caused by the seasonal wintertime wind-forced ocean currents. Based on this registration, estimates of displacement rates for the sand deposit could be made

  17. Internal tide—shelf topography interactions as a forcing factor governing the large-scale distribution and burial fluxes of particulate organic matter (POM) in the Benguela upwelling system

    CSIR Research Space (South Africa)

    Monteiro, PMS

    2005-09-01

    Full Text Available are at the inner and outer shelf break zones, respectively. The moorings at stations 2 and 3 were lost. P.M.S. Monteiro et al. / Continental Shelf Research 25 (2005) 1864–18761866 respectively (Fig. 1b). The deepest mooring at station 5 had a current meter only... 20001227 20010103 Dat m the d 5) P.M.S. Monteiro et al. / Continental Shelf Research 25 (2005) 1864–1876 1867 Temperature at Mooring 2 3 4 5 6 7 8 9 10 11 12 13 14 20001004 20001011 20001018 20001025 20001101 20001108 20001115...

  18. Distribution of total phosphorus in the shelf sediments off the west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Murty, P.S.N.; Reddy, C.V.G.; Varadachari, V.V.R.

    The total phosphorus content in the sediment samples collected from different stations on the continental shelf along five sections normal to the coast near Bombay, Karwar, Mangalore, Cochin and Alleppey has been determined and the distribution...

  19. Palaeoclimatic significance of gypsum pseudomorphs in the inner shelf sediments off Machalipatnam bay

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.

    Pseudo-gypsum crystals have been found in the coarse fraction of the sediments from the inner continental shelf off Machilipatnam Bay. They range in size from 3 to 7 mm are elongate and lenticular in shape. Bassanite and calcite are pseudomorphs...

  20. Hurricane Sandy's Fingerprint: Ripple Bedforms at an Inner Continental Shelf Sorted Bedform Field Site

    Science.gov (United States)

    DuVal, C.; Trembanis, A. C.; Beaudoin, J. D.; Schmidt, V. E.; Mayer, L. A.

    2013-12-01

    The hydrodynamics and seabed morphodynamics on the inner continental shelf and near shore environments have increasing relevance with continued development of near shore structures, offshore energy technologies and artificial reef construction. Characterizing the stresses on and response of the seabed near and around seabed objects will inform best practices for structural design, seabed mine and unexploded ordnance detection, and archaeological and benthic habitat studies. As part of an ONR funded project, Delaware's Redbird Reef is being studied for object scour and sorted bedform morphodynamics (Trembanis et al., in press). Central to this study are the effects of large storm events, such as Hurricane Sandy, which have had significant impact on the seafloor. Previous studies of inner shelf bedform dynamics have typically focused on near bed currents and bed stressors (e.g. Trembanis et al., 2004), sorted bedforms (e.g. Green et al., 2004) and object scour (e.g. Quinn, 2006; Trembanis et al., 2007; Mayer et al., 2007), but our understanding of the direct effects of objects and object scour on bedform morphodynamics is still incomplete. With prominent sorted bedform ripple fields, the Delaware Redbird artificial reef site, composed of 997 former New York City subway cars, as well as various military vehicles, tugboats, barges and ballasted tires, has made an ideal study location (Raineault et al., 2013 and 2011). Acoustic mapping of the Redbird reef three days prior to Sandy and two days after the following nor'easter, captured the extensive effects of the storms to the site, while acoustic Doppler current profilers characterized both the waves and bottom currents generated by the storm events. Results of the post-Sandy survey support the theory of sorted bedform evolution proposed by Murray and Thieler (2004). Acoustic imagery analysis indicates a highly energized and mobile bed during the storms, leading to self-organization of bedforms and creation of large

  1. Integrated management plan for the North Sea and Skagerrak: Status description for the petroleum industry with emphasis on the Norwegian continental shelf; Helhetlig forvaltningsplan for Nordsjoeen og Skagerrak: Statusbeskrivelse for petroleumsvirksomheten med hovedvekt paa norsk sokkel

    Energy Technology Data Exchange (ETDEWEB)

    2010-06-15

    Status description of the petroleum industry covers mainly the Norwegian continental shelf, but it is also given a brief description of the activity in other offshore areas of the North Sea. It shows a list of producing fields, fields under development, developments in the future, findings that are in the planning phase, and completed fields. It also describes the pipelines and other petroleum-related activities at sea and on shore. (AG)

  2. Benthic assemblages of mega epifauna on the Oregon continental margin

    Science.gov (United States)

    Hemery, Lenaïg G.; Henkel, Sarah K.; Cochrane, Guy R.

    2018-01-01

    broad fish assemblages and the deep flat soft sediments invertebrate assemblage) seem to represent deeper examples of assemblages already known on the Oregon continental shelf, especially on soft sediments, while the assemblages in the pockmarks habitat (the narrower depth ranges) might be unique to the area. This diversity of assemblages in a relatively small section of the Oregon continental upper slope and shelf shows the importance of environmental assessment studies in helping limit future impacts of industrial activities on benthic communities.

  3. Benthic assemblages of mega epifauna on the Oregon continental margin

    Science.gov (United States)

    Hemery, Lenaïg G.; Henkel, Sarah K.; Cochrane, Guy R.

    2018-05-01

    flat soft sediments invertebrate assemblage) seem to represent deeper examples of assemblages already known on the Oregon continental shelf, especially on soft sediments, while the assemblages in the pockmarks habitat (the narrower depth ranges) might be unique to the area. This diversity of assemblages in a relatively small section of the Oregon continental upper slope and shelf shows the importance of environmental assessment studies in helping limit future impacts of industrial activities on benthic communities.

  4. 78 FR 76643 - Atlantic Wind Lease Sale 3 (ATLW3) Commercial Leasing for Wind Power on the Outer Continental...

    Science.gov (United States)

    2013-12-18

    ...; MMAA104000] Atlantic Wind Lease Sale 3 (ATLW3) Commercial Leasing for Wind Power on the Outer Continental.... ACTION: Proposed Sale Notice for Commercial Leasing for Wind Power on the Outer Continental Shelf Offshore Maryland. SUMMARY: This document is the Proposed Sale Notice (PSN) for the sale of commercial wind...

  5. 78 FR 33897 - Atlantic Wind Lease Sale 2 (ATLW2) Commercial Leasing for Wind Power on the Outer Continental...

    Science.gov (United States)

    2013-06-05

    ... Management Atlantic Wind Lease Sale 2 (ATLW2) Commercial Leasing for Wind Power on the Outer Continental Shelf Offshore Rhode Island and Massachusetts-- Final Sale Notice and Commercial Wind Lease Issuance and...; MMAA104000] Atlantic Wind Lease Sale 2 (ATLW2) Commercial Leasing for Wind Power on the Outer Continental...

  6. Development and production prospects for oil and gas from the UK continental shelf after the Gulf crisis: a financial simulation

    International Nuclear Information System (INIS)

    Kemp, A.G.; Rose, David; Dandie, Russell

    1991-01-01

    A large computerized financial model has been developed to simulate the future exploitation of oil and gas in the UK north sea. Primary inputs into the model include all the publicity available information on currently producing fields relating to their historic and expected production rates, investment, operating and abandonment costs. Information has also been gathered on all new discoveries which have not yet been developed and estimates made of the timing of their development, the commencement of production and costs. Three oil price scenarios base, low and high, have been used in the analysis which extends to the year 2015. The results are presented for two major regions, the central and northern waters and the Southern Gas Basin, including the Irish Sea. Very large numbers of discovered but undeveloped oil and gas fields exist in the UK continental shelf substantial numbers of which could be developed in the event of a very modest real growth in oil and gas prices. The considerable sensitivity of development to movements in oil prices is brought out by the analysis of the three scenarios. (UK)

  7. Geology and assessment of undiscovered oil and gas resources of the Northwest Laptev Sea Shelf Province, 2008

    Science.gov (United States)

    Klett, Timothy; Pitman, Janet K.; Moore, Thomas E.; Gautier, Donald L.

    2017-12-22

    The U.S. Geological Survey (USGS) has recently assessed the potential for undiscovered oil and gas resources in the Northwest Laptev Sea Shelf Province as part of the USGS Circum-Arctic Resource Appraisal. The province is in the Russian Arctic, east of Severnaya Zemlya and the Taimyr fold-and-thrust belt. The province is separated from the rest of the Laptev Sea Shelf by the Severnyi transform fault. One assessment unit (AU) was defined for this study: the Northwest Laptev Sea Shelf AU. The estimated mean volumes of undiscovered petroleum resources in the Northwest Laptev Sea Shelf Province are approximately 172 million barrels of crude oil, 4.5 trillion cubic feet of natural gas, and 119 million barrels of natural-gas liquids, north of the Arctic Circle.

  8. Phosphatised limestones and associated sediments from the western continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Natarajan, R.; Parthiban, G.; Mascarenhas, A.

    Quaternary carbonate sediments: Rao, Ch.M., Paropkari~ A.L., Mascarenhas, A. and Murty, carbonate sediments and reefs, Yucatan shelf, Mexico. Am. P.S.N., 1987. Distribution of phosphorus and phosphatisa- Assoc. Pet. Geol. Mem., 11: 1-128. tion along...

  9. Summer composition and distribution of the jellyfish (Cnidaria: Medusozoa in the shelf area off the central Mexican Pacific Composición y distribución de las medusas (Cnidaria: Medusozoa en la plataforma continental central del Pacifico mexicano

    Directory of Open Access Journals (Sweden)

    Lourdes Segura-Puertas

    2010-04-01

    Full Text Available The composition, distribution, and abundance of the jellyfish community of a shelf area of the Mexican tropical Pacific were surveyed during August 1988. Zooplankton samples were collected along transects on the outer and inner sectors of the continental shelf to determine the structure of the jellyfish community and its variation in this area during the rainy season. A total of 23 species were recorded, with Aglaura hemistoma, Solmundella bitentaculata, Liriope tetraphylla, Pelagia noctiluca, and Rhopalonema velatum being the most abundant. The total abundance of medusae and of the most abundant species was statistically independent of depth and distance to the coast. Hence, the total jellyfish abundance of the most abundant species, and Shannon's Diversity index had a uniform distribution in both the inner and the outer shelf; furthermore, neritic-oceanic forms and oceanic species occurred indistinctly over the entire continental shelf. On the outer shelf A. hemistoma and S. bitentaculata were most abundant; the former species, together with L. tetraphylla, weakly characterized the inner shelf jellyfish community. The narrowness of the shelf, the wide distribution of the most abundant forms, and the possible effect of local advective processes from the oceanic zone masked a definite gradient across the shelf. Three species have not been recorded previously in the Mexican Pacific: Amphinema dinema (Péron and Lesueur, 1810, Sarsia coccometra Bigelow, 1909, and Clytia mccradyi (Brooks, 1888. The finding of A. dinema is the first in the Eastern Pacific.Se estudió la composición, distribución y abundancia de la comunidad de medusas de la plataforma continental en el Pacífico mexicano durante agosto 1988. Las muestras de zooplancton provienen de transectos en las zonas externa e interna de la plataforma para determinar la estructura de la comunidad de medusas y su variación durante la época de lluvias. Se identificaron 23 especies; las m

  10. Physical and nutrient data collected from CTD and bottle casts from the R/V HERMANO GINES from the continental shelf of Venezuela in the Caribbean Sea in support of the project: Carbon Retention in a Colored Ocean (CARIACO) from 16 March 2006 to 06 March 2007 (NODC Accession 0014920)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — CTD and bottle data were collected from the R/V HERMANO GINES in the Caribbean Sea on the continental shelf of Venezuela from 16 March 2006 to 06 March 2007. Data...

  11. Significance of peat on the western continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Mascarenhas, A.

    24 and 31 meters. The cores were subsampled depending upon the lithology. A core off Karwar was chosen for geochemical analyses. Calcium carbonate was determined using a 'KarbonatBombe' (Muller and Gastner, 1971). Organic carbon and sulfur were... the present sea level; it is found up to 27 km from the coast. The resulls suggest that peat on the shelf occurs as layers of restricted thickness (2 to 30 em) with a limited lateral distribution and hence appear to be impersistent layers. A strong hydrogen...

  12. Changes in abundance and composition of anthropogenic marine debris on the continental slope off the Pacific coast of northern Japan, after the March 2011 Tohoku earthquake

    International Nuclear Information System (INIS)

    Goto, Tomoaki; Shibata, Haruka

    2015-01-01

    Highlights: • Benthic marine debris on continental slope off northeastern Japan quantified. • Low density of sea-base sourced debris dominant until 2011 Tohoku earthquake. • Increase in marine debris after the earthquake indicated by post-2011 tsunami survey. • Much increase in land-base sourced debris mainly due to 2011 tsunami. • Additional sources of land-based debris during post-tsunami survey implied. - Abstract: Abundance and composition of anthropogenic marine debris were assessed on the basis of six bottom trawl surveys conducted on the continental slope off Iwate Prefecture, Pacific coast of northern Japan, in 2003, 2004 and 2011, and the temporal changes due to the Tohoku earthquake and tsunami in March 2011 evaluated. In 2003 and 2004, 54–94 items km −2 of marine debris, dominated by sea-base sourced items mainly comprising fishing gear and related items from adjacent fishing grounds on the continental shelf, were quantified. In the post-earthquake period, the density increased drastically to 233–332 items km −2 , due to an increase in land-base sourced items generated by the tsunami. However, a major increase in abundance after the disaster, compared to the total amount of tsunami debris swept into the sea, was not found. Additional sources of land-based debris from the adjacent continental shelf are suggested in the present waters

  13. Food supply mechanisms for cold-water corals along a continental shelf edge

    Science.gov (United States)

    Thiem, Øyvind; Ravagnan, Elisa; Fosså, Jan Helge; Berntsen, Jarle

    2006-05-01

    In recent years it has been documented that deep-water coral reefs of the species Lophelia pertusa are a major benthic habitat in Norwegian waters. However, basic information about the biology and ecology of this species is still unknown. Lophelia live and thrive under special environmental conditions of which factors such as temperature, water depth, water movement and food supply are important. The present work explores the hypothesis that Lophelia forms reefs in places where the encounter rate of food particles is sufficiently high and stable over long periods of time for continuous growth. This is done by relating the distribution of reefs with the results of numerical ocean modelling. Numerical simulations have been performed with an idealized bottom topography similar to what is found outside parts of the Norwegian coast. In the simulations the model is first forced with an along slope jet and then with an idealized atmospheric low pressure. The model results show that the encounter rates between the particles and the water layer near the seabed are particularly high close to the shelf break. This may indicate that many Lophelia reefs are located along the shelf edges because the supply of food is particularly good in these areas. A sensitivity study of the particle supply in the area close to the seabed for increasing latitude has also been done. This shows that the Ekman transport in the benthic layer tends to create a steady supply of food for benthic organisms near the shelf edge away from the equator.

  14. Acoustic Estimates of Distribution and Biomass of Different Acoustic Scattering Types Between the New England Shelf Break and Slope Waters

    KAUST Repository

    McLaren, Alexander

    2011-11-01

    Due to their great ecological significance, mesopelagic fishes are attracting a wider audience on account of the large biomass they represent. Data from the National Marine Fisheries Service (NMFS) provided the opportunity to explore an unknown region of the North-West Atlantic, adjacent to one of the most productive fisheries in the world. Acoustic data collected during the cruise required the identification of acoustically distinct scattering types to make inferences on the migrations, distributions and biomass of mesopelagic scattering layers. Six scattering types were identified by the proposed method in our data and traces their migrations and distributions in the top 200m of the water column. This method was able to detect and trace the movements of three scattering types to 1000m depth, two of which can be further subdivided. This process of identification enabled the development of three physically-derived target-strength models adapted to traceable acoustic scattering types for the analysis of biomass and length distribution to 1000m depth. The abundance and distribution of acoustic targets varied closely in relation to varying physical environments associated with a warm core ring in the New England continental Shelf break region. The continental shelf break produces biomass density estimates that are twice as high as the warm core ring and the surrounding continental slope waters are an order of magnitude lower than either estimate. Biomass associated with distinct layers is assessed and any benefits brought about by upwelling at the edge of the warm core ring are shown not to result in higher abundance of deepwater species. Finally, asymmetric diurnal migrations in shelf break waters contrasts markedly with the symmetry of migrating layers within the warm ring, both in structure and density estimates, supporting a theory of predatorial and nutritional constraints to migrating pelagic species.

  15. Oceanic hydraulic structures for developing a shelf. Issledovaniye morskikh gidrotekhnicheskikh sooruzheniy dlya osvoyenia sel'fa

    Energy Technology Data Exchange (ETDEWEB)

    Simakov, G.B.

    1980-01-01

    The anthology is devoted to practical problems of oceanic hydraulic engineering which arise during design and construction of specialized oceanic hydraulic structures to be erected and used in the shelf zones of seas and oceans. Most of the articles deal with studying the external effect of rough waters, impacts from ships and ice floes on floating and stationary hydraulic structures for developing a shelf. A great deal of attention is also given to the hydrodynamic and anchoring of floating hydraulic structures. The information reflects the current status of the problems of designing and building production facilities for developing a continental shelf.

  16. 4D Model on Assessing Psychomotor Aspect in Continental Food Processing Practice

    Science.gov (United States)

    Nurafiati, P.; Ana, A.; Ratnasusanti, H.; Maulana, I.

    2018-02-01

    This research aims to develop and find out the response of observers for the assessment instrument of student’s psychomotor aspect on continental food processing practice. This research belongs to development research with 4P model that confined till the definition, design, and development stages. The data that gained during the research is analyzed descriptively. Research’s product is assessment instrument rubric form that consists of performance’s aspect which should be assessed and performance’s quality which stated in gradation score with 0-4 level and performance description that completed with picture illustration in every single score. Product was validate and responded based on material, construction, language, objectively, systematic, and practicability aspects. The result show that assessment instrument of student’s psychomotor aspect on continental food processing practice which developed gain very good response with percentage of 84,47%.

  17. The influence of El Niño-Southern Oscillation (ENSO) cycles on wave-driven sea-floor sediment mobility along the central California continental margin

    Science.gov (United States)

    Storlazzi, Curt D.; Reid, Jane A.

    2010-01-01

    Ocean surface waves are the dominant temporally and spatially variable process influencing sea floor sediment resuspension along most continental shelves. Wave-induced sediment mobility on the continental shelf and upper continental slope off central California for different phases of El Niño-Southern Oscillation (ENSO) events was modeled using monthly statistics derived from more than 14 years of concurrent hourly oceanographic and meteorologic data as boundary input for the Delft SWAN wave model, gridded sea floor grain-size data from the usSEABED database, and regional bathymetry. Differences as small as 0.5 m in wave height, 1 s in wave period, and 10° in wave direction, in conjunction with the spatially heterogeneous unconsolidated sea-floor sedimentary cover, result in significant changes in the predicted mobility of continental shelf surficial sediment in the study area. El Niño events result in more frequent mobilization on the inner shelf in the summer and winter than during La Niña events and on the outer shelf and upper slope in the winter months, while La Niña events result in more frequent mobilization on the mid-shelf during spring and summer months than during El Niño events. The timing and patterns of seabed mobility are addressed in context of geologic and biologic processes. By understanding the spatial and temporal variability in the disturbance of the sea floor, scientists can better interpret sedimentary patterns and ecosystem structure, while providing managers and planners an understanding of natural impacts when considering the permitting of offshore activities that disturb the sea floor such as trawling, dredging, and the emplacement of sea-floor engineering structures.

  18. West Florida shelf circulation and temperature budget for the 1999 spring transition

    Science.gov (United States)

    He, Ruoying; Weisberg, Robert H.

    2002-01-01

    Mid-latitude continental shelves undergo a spring transition as the net surface heat flux changes from cooling to warming. Using in situ data and a numerical circulation model we investigate the circulation and temperature budget on the West Florida Continental Shelf (WFS) for the spring transition of 1999. The model is a regional adaptation of the primitive equation, Princeton Ocean Model forced by NCEP reanalysis wind and heat flux fields and by river inflows. Based on agreements between the modeled and observed fields we use the model to draw inferences on how the surface momentum and heat fluxes affect the seasonal and synoptic scale variability. We account for a strong southeastward current at mid-shelf by the baroclinic response to combined wind and buoyancy forcing, and we show how this local forcing leads to annually occurring cold and low salinity tongues. Through term-by-term analyses of the temperature budget we describe the WFS temperature evolution in spring. Heat flux largely controls the seasonal transition, whereas ocean circulation largely controls the synoptic scale variability. These two processes, however, are closely linked. Bottom topography and coastline geometry are important in generating regions of convergence and divergence. Rivers contribute to the local hydrography and are important ecologically. Along with upwelling, river inflows facilitate frontal aggregation of nutrients and the spring formation of a high concentration chlorophyll plume near the shelf break (the so-called ‘Green River’) coinciding with the cold, low salinity tongues. These features originate by local, shelf-wide forcing; the Loop Current is not an essential ingredient.

  19. Mass-physical properties of surficial sediments on the Rhoˆne continental margin: implications for the nepheloid benthic layer

    Science.gov (United States)

    Chassefiere, Bernard

    1990-09-01

    Mass-physical properties of the surficial (upper 5 m) sediments on the Gulf of Lions continental margin were analysed, from more than 100 short (1 m) and longer (5 m) cores obtained during several cruises. Data include water content, unit weight, Atterberg limits (liquid limit, plastic limit, plasticity index), shear strength and compression index, and are used to determine: first, the mass property distribution, according to the main parameters influencing mass-physical properties; the relationships between these properties and the nepheloid layer on the shelf. The shoreline (lagoons) and inner shelf are characterized by low density and shear strength and high water content deposits, due to electrochemical flocculation of the sediment. The outer shelf is blanketed by higher density and shear strength and lower water content deposits generated by normal settling of suspended particles. On the inner shelf, during river peak discharges, a short-term thin bottom layer of "yogurt-like" [ FASS (1985) Geomarine Letters, 4, 147-152; FASS (1986) Continental Shelf Research, 6, 189-208] fluid-mud (unit weight lower than 1.3 mg m -3) is supplied, by a bottom nepheloid layer. During stormy periods, this "yogurt-like" layer (about 10 cm thick) partly disappears by resuspension of suspended particulate matter; this is advected, in the bottom nepheloid layer, over the shelf and the canyons within the upper slope.

  20. Climatic aridity over India 11,000 years ago: Evidence from feldspar distribution in shelf sediments

    Digital Repository Service at National Institute of Oceanography (India)

    Hashimi, N.H.; Nair, R.R.

    Feldspars and quartz contents of sand and silt fractions of forty three samples from the western continental shelf of India were determined by the X-ray diffraction method. The results indicate that the feldspar content in the relict (9000...

  1. Dynamics of internal waves on the Southeast Florida shelf: Implications for cross-shelf exchange and turbulent mixing on a barrier reef system

    Science.gov (United States)

    Davis, Kristen Alexis

    The dynamics of internal waves shoaling on the Southeast Florida shelf and the resulting stratified turbulence in the shelf bottom boundary layer are investigated using observational studies completed during the summers of 2003-2005. This work is driven by a desire to understand the effects of internal wave-driven flow and the shoreward transport of cool, nutrient-rich water masses on cross-shelf exchange, vertical mixing, and mass transfer to benthic reef organisms. Shelf sea internal wave fields are typically highly variable and dominated by wind and tidal forces. However, this is not necessarily true for outer shelf regions or very narrow shelves where remote physical processes originating over the slope or deep ocean may exert a strong influence on the internal wave climate. During the summers of 2003 and 2004 observational studies were conducted to examine the effects of a western boundary current (the Florida Current), tides, and wind on the mean currents and internal wave field on the outer Southeast Florida shelf. We present evidence that suggests that the Florida Current plays as large a role in the determination of the high frequency internal wave field as tidal forces. These observations and analyses show that it is necessary to include the forcing from the Florida Current meanders and instabilities in order to predict accurately the episodic nature of the internal wave field on the Southeast Florida shelf. Deep ocean and continental shelf processes intersect at the shelf edge and influence the exchange of water masses and their associated characteristics including heat, nutrients, sediment, and larvae across the shelf. Thus, the dynamics of cross-shelf circulation have important consequences for organisms living on the shelf. In the second phase of this work, we investigate physical mechanisms controlling the exchange of water masses during the summer season across the Southeast Florida shelf. A time series of cross-shelf transport from May to August

  2. Continental Margins and the Law of the Sea - an `Arranged Marriage' with Huge Research Potential

    Science.gov (United States)

    Parson, L.

    2005-12-01

    The United Nations Convention on the Law of the Sea (UNCLOS) requires coastal states intending to secure sovereignty over continental shelf territory extending beyond 200 nautical miles to submit geological/geophysical data, along with their analysis and synthesis of the relevant continental margin in support of their claim. These submissions are scrutinised and assessed by a UN Commission of experts who decide if the claim is justified, and thereby ultimately allowing the exploitation of non-living resources into this extended maritime space. The amount of data required to support the case will vary from margin to margin, depending on the local geological evolution, but typically will involve the running of new, dedicated marine surveys, mostly bathymetric and seismic. Key geological/geophysical issues revolve around proof of `naturalness' of the prolongation of land mass (cue - wide-angle seismics, deep drilling and sampling programmes) and shelf and slope morphology and sediment section thickness (cue - swath bathymetry and multichannel seismics programmes). These surveys, probably primarily funded by government agencies anxious not to lose out on the `land grab', will generate datasets which will inevitably boost not only the research effort leading to increased understanding of margin evolution in academic terms, but also contribute to wider applied aspects of the work such as those leading to refinement of deepwater hydrocarbon resource potential. It is conservatively estimated that in the region of fifty coastal states world-wide have a significant potential for claiming continental shelf beyond 200 nautical miles, and that the total area available as extended shelf could easily exceed 7 million square kilometres. However, while for the vast majority of these states a UNCLOS deadline of 2009 exists for submitting a claim - to date only four have done so (Russia, Brazil, Australia and Ireland). It is therefore predictable, if not inevitable, that within the

  3. The use of 234Th/238U disequilibrium to examine the fate of particle-reactive species on the Yangtze continental shelf

    International Nuclear Information System (INIS)

    McKee, B.A.; DeMaster, D.J.; Nittrouer, C.A.

    1984-01-01

    Measurements of 234 Th (tsub(1/2)=24.1 d) in water column and seabed samples from an area near the mouth of the Yangtze River (People's Republic of China) provide the following information: Most of the 234 Th in waters near the mouth of the Yangtze River is in particulate form, and horizontal transport and sedimentation of 234 Th-bearing particles dominate the 234 Th budget in this area. A model incorporating processes in at least two dimensions is required to understand the fate of particle-reactive species on the Yangtze continental shelf. The residence times of particle-reactive species (with respect to scavenging) range from 0.3 days (nearshore) to 4.0 days (offshore). The residence times (with respect to removal to the seabed) range from 0.5 day (nearshore) to 11.0 days (offshore). Scavenging residence times for 234 Th decrease as the concentration of suspended particles increases. The time for removal of 234 Th to the seabed increases with distance from shore (a variable which integrates such factors as scavenging rate, bathymetry, and frequency of resuspension). (orig.)

  4. Atlantic continental margin of the United States

    Science.gov (United States)

    Grow, John A.; Sheridan, Robert E.; Palmer, A.R.

    1982-01-01

    The objective of this Decade of North American Geology (D-NAG) volume will be to focus on the Mesozoic and Cenozoic evolution of the U.S. Atlantic continental margin, including the onshore coastal plain, related onshore Triassic-Jurassic rift grabens, and the offshore basins and platforms. Following multiple compressional tectonic episodes between Africa and North America during the Paleozoic Era that formed the Appalachian Mountains, the Mesozoic and Cenozoic Eras were dominated by tensional tectonic processes that separated Africa and North America. Extensional rifting during Triassic and Early Jurassic times resulted in numerous tensional grabens both onshore and offshore, which filled with nonmarine continental red beds, lacustrine deposits, and volcanic flows and debris. The final stage of this breakup between Africa and North America occurred beneath the present outer continental shelf and continental slope during Early or Middle Jurassic time when sea-floor spreading began to form new oceanic crust and lithosophere between the two continents as they drifted apart. Postrift subsidence of the marginal basins continued in response to cooling of the lithosphere and sedimentary loading.Geophysical surveys and oil-exploration drilling along the U.S. Atlantic continental margin during the past 5 years are beginning to answer many questions concerning its deep structure and stratigraphy and how it evolved during the rifting and early sea-floor-spreading stages of the separation of this region from Africa. Earlier geophysical studies of the U.S. continental margin used marine refraction and submarine gravity measurements. Single-channel seismic-reflection, marine magnetic, aeromagnetic, and continuous gravity measurements became available during the 1960s.

  5. Geoarchaeological response to landscape changes of the Greek continental shelf since the Last Glacial Maximum

    Science.gov (United States)

    Kapsimalis, Vasilios; Pavlopoulos, Kosmas; Panagiotopoulos, Ioannis

    2010-05-01

    An overview of geological, sedimentological, palaeoclimatic, archaeological and mythological data is presented in order to detect the geomorphological changes of the Aegean and Ionian shelves during the last sea-level transgression, and comprehend the consequent prehistoric human adaptations. The irregular rise of sea level since the Last Glacial Maximum forced the Palaeolithic human to abandon its settlements located near the old (lower) coastlines and to move landward in new positions. Commonly, the coastline movement was very slow causing no significant impact on human activities; however in some cases, the transgression was very prompt causing human migration towards highlands. In some very gentle-dipped and wide regions, e.g. the North Aegean plateau, the sea-level rise caused a rapid coastline retreat (in some extreme case as fast as 10 m/yr) and inundation of an extended surface area. However, at the same time, in the steep parts of the Greek shelf, e.g. the Kyparissiakos Gulf and Crete, the coastline advanced landwards with a slow motion (commonly, a few cm/yr) covering small areas. In addition, coastal regions with particular geomorphologic characteristics, e.g. coastal paleo-lakes protected by a sill (gulfs of Corinth, Amvrakikos, Pagasitikos Evvoikos, Saronikos), were deluged by the sea during different periods and under different intensity, depending on the elevation of the sill and the manner of its overflow. Although the presence of Palaeolithic human in the Greek mainland has been confirmed by several archaeological excavations, there is no certain evidence for human settlement in the deep parts of Greek shelf. However, many archaeologists have suggested that some of Palaeolithic people lived on the shelf, when the sea level was lower than its present position. Nevertheless, some potential Palaeolithic migration routes can be indicated taking into account (a) the palaeogeographic reconstruction of Greek shelf over the Last Quaternary; (b

  6. Living macromolluscs from a paleo-reef region on the northeastern Venezuelan continental shelf

    Science.gov (United States)

    Buitrago, Joaquín; Capelo, Juan; Gutiérrez, Javier; Rada, Martín; Hernández, Ricardo; Grune, Sylvia

    2006-02-01

    Drowned reefs, fossil reefs or paleo-reefs, are important ecologically as areas of high biodiversity, foraging, shelter environment, and as areas supporting the spawning aggregations of economically important reef fish species. This is particularly significant when the structures are situated in a wide soft-bottom continental shelf. The presence of limestone structures, fossil reefs and pinnacles dating from circa 8 to 9 ka, to the north of the Paria Peninsula in north-eastern Venezuela, has been known to local fishermen for decades. Using echograms obtained during acoustic fisheries evaluations and the scarce previously available information, an improved location map of hard-bottom structures was made. Benthic samples to study macromolluscs were taken at depths between 54 and 93 m using an unmodified 2-m beam trawl. Four trawl samples were located over fossil reef areas while another four were situated in soft-bottom valleys between limestone structures. Fossil reefs in the area showed a highly patchy distribution. A total of 91 species from 43 Bivalvia, Gastropoda and Scaphopoda families were found, Gastropoda being the dominant class with 49 species. Paleo-reef-covered areas showed higher species richness and only 21% of the species found were common to both substrates. Gastropods Tonna maculosa and Polystira albida were the most abundant species and occurred in both substrate types. Bivalve life habits, a mixture of organism-substrate relationships, shell fixation, mobility and feeding type, differed significantly according to bottom type. Six species are recorded for the first time for eastern Venezuelan waters. Bottom heterogeneity plays an important role in marine ecosystems, providing shelter to fish populations and may be significant as breeding and nursery areas. Its presence in a region with biogeographical interest, situated in the confluence of three major provinces and with oceanographic conditions varying seasonally from upwelling dominated to

  7. Late Holocene sedimentary changes in floodplain and shelf environments of the Tagus River (Portugal)

    NARCIS (Netherlands)

    Vis, G.J.; Kasse, C.; Kroon, D.; Jung, S.J.A.; Zuur, H.; Prick, A.C.H.

    2010-01-01

    Sedimentary changes during the last ∼2500 years have been reconstructed from cored sedimentary records from the deltaic floodplain of the Lower Tagus Valley and the Tagus mudbelt on the continental shelf offshore Lisbon. We used a multi-proxy approach consisting of sedimentology, grainsize, pollen

  8. Particle residence times in waters of the Yangtze and Amazon continental shelves

    International Nuclear Information System (INIS)

    McKee, B.A.; Nittrouer, C.A.; DeMaster, D.J.

    1986-01-01

    Water column and seabed samples were analyzed for naturally occurring Th-234 to determine particle residence times in Yangtze and Amazon continental-shelf waters. On the Yangtze shelf, the water column was vertically well-mixed and suspended-sediment concentrations decreased offshore (from 230 mg/l near the river mouth to 2 mg/l in mid-shelf waters). Particle residence times increased offshore and ranged from 3.2 hours (12 m water depth) to 7.3 days (60 m water depth). Particle residence times ranged from 3 to 30 times shorter than values predicted by settling of discrete (4-8 micron) particles, suggesting that particles were settling in aggregate form. On the Amazon shelf, a two-layer estuarine flow dominated shelf circulation. Suspended-sediment concentrations on the inner shelf (10-12 m water depth) were much greater in bottom waters (range: 100-880 mg/l) than in surface waters (range 5-60 mg/l) as a result of resuspension. Particle residence times ranged from 1.1 days in surface waters to 2.5 days in bottom waters. Particles probably underwent several cycles of resuspension before permanent removal from the water column

  9. Acoustic Doppler Current Profiler observations in the southern Caspian Sea: shelf currents and flow field off Feridoonkenar Bay, Iran

    Directory of Open Access Journals (Sweden)

    P. Ghaffari

    2010-07-01

    Full Text Available The results of offshore bottom-mounted ADCP measurements and wind records carried out from August to September 2003 in the coastal waters off Feridoon-kenar Bay (FB in the south Caspian Sea (CS are examined in order to characterize the shelf motion, the steady current field and to determine the main driving forces of currents on the study area. Owing to closed basin and absence of the astronomical tide, the atmospheric forcing plays an important role in the flow field of the CS. The lasting regular sea breeze system is present almost throughout the year. This system performs the forcing in diurnal and semi-diurnal bands similar to tides in other regions. In general, current field in the continental shelf could be separated into two distinguishable schemes, which in cross-shelf direction is dominated by high frequencies (1 cpd and higher frequencies, and in along-shelf orientation mostly proportional to lower frequencies in synoptic weather bands. Long-period wave currents, whose velocities are much greater than those of direct wind-induced currents, dominates the current field in the continental shelf off FB. The propagation of the latter could be described in terms of shore-controlled waves that are remotely generated and travel across the shelf in the southern CS. It has also been shown that long term displacements in this area follow the classic cyclonic, circulation pattern in the southern CS.

  10. Western Ross Sea continental slope gravity currents

    Science.gov (United States)

    Gordon, Arnold L.; Orsi, Alejandro H.; Muench, Robin; Huber, Bruce A.; Zambianchi, Enrico; Visbeck, Martin

    2009-06-01

    Antarctic Bottom Water of the world ocean is derived from dense Shelf Water that is carried downslope by gravity currents at specific sites along the Antarctic margins. Data gathered by the AnSlope and CLIMA programs reveal the presence of energetic gravity currents that are formed over the western continental slope of the Ross Sea when High Salinity Shelf Water exits the shelf through Drygalski Trough. Joides Trough, immediately to the east, offers an additional escape route for less saline Shelf Water, while the Glomar Challenger Trough still farther east is a major pathway for export of the once supercooled low-salinity Ice Shelf Water that forms under the Ross Ice Shelf. The Drygalski Trough gravity currents increase in thickness from ˜100 to ˜400 m on proceeding downslope from ˜600 m (the shelf break) to 1200 m (upper slope) sea floor depth, while turning sharply to the west in response to the Coriolis force during their descent. The mean current pathway trends ˜35° downslope from isobaths. Benthic-layer current and thickness are correlated with the bottom water salinity, which exerts the primary control over the benthic-layer density. A 1-year time series of bottom-water current and hydrographic properties obtained on the slope near the 1000 m isobath indicates episodic pulses of Shelf Water export through Drygalski Trough. These cold (34.75) pulses correlate with strong downslope bottom flow. Extreme examples occurred during austral summer/fall 2003, comprising concentrated High Salinity Shelf Water (-1.9 °C; 34.79) and approaching 1.5 m s -1 at descent angles as large as ˜60° relative to the isobaths. Such events were most common during November-May, consistent with a northward shift in position of the dense Shelf Water during austral summer. The coldest, saltiest bottom water was measured from mid-April to mid-May 2003. The summer/fall export of High Salinity Shelf Water observed in 2004 was less than that seen in 2003. This difference, if real

  11. Observations on the scattering layers over the continental shelf off Konkan coast (India)

    Digital Repository Service at National Institute of Oceanography (India)

    RamaRaju, V.S.

    The echograms obtained by R.V. "varuna" using asdic during the September, 1963 cruise are analysed. Scattering layers observed over the shelf area, off Ratnagiri, are examined and studied in relation to the thermocline layer present. Comparison...

  12. Geomorphic Thresholds of Submarine Canyons Along the U.S. Atlantic Continental Margin

    Science.gov (United States)

    Brothers, D. S.; ten Brink, U. S.; Andrews, B. D.; Chaytor, J. D.

    2011-12-01

    Vast networks of submarine canyons and associated channels are incised into the U.S. Atlantic continental slope and rise. Submarine canyons form by differential erosion and deposition, primarily from sedimentary turbidity flows. Theoretical and laboratory studies have investigated the initiation of turbidity flows and their capacity to erode and entrain sedimentary material at distances far from the shelf edge. The results have helped understand the nature of turbidite deposits on the continental slope and rise. Nevertheless, few studies have examined the linkages between down-canyon sediment transport and the morphology of canyon/channel networks using mesoscale analyses of swath bathymetry data. We present quantitative analysis of 100-m resolution multibeam bathymetry data spanning ~616,000 km2 of the slope and rise between Georges Banks and the Blake Plateau (New England to North Carolina). Canyons are categorized as shelf-indenting or slope-confined based on spatial scale, vertical relief and connection with terrestrial river systems during sea level low stands. Shelf-indenting canyons usually represent the trunk-canyon of submerged channel networks. On the rise, shelf-indenting canyons have relatively well-developed channel-levees and sharp inner-thalwag incision suggesting much higher frequency and volume of turbidity flows. Because of the similarities between submarine canyon networks and terrestrial river systems, we apply methods originally developed to study fluvial morphology. Along-canyon profiles are extracted from the bathymetry data and the power-law relationship between thalwag gradient and drainage area is examined for more than 180 canyons along an ~1200 km stretch of the US Atlantic margin. We observe distinct thresholds in the power-law relationship between drainage area and gradient. Almost all canyons with heads on the upper slope contain at least two linear segments when plotted in log-log form. The first segment along the upper slope is flat

  13. Internal waves over the shelf in the western Bay of Bengal: A case study

    Digital Repository Service at National Institute of Oceanography (India)

    Joshi, M.; Rao, A.D.; Mohanty, S.; Pradhan, H.K.; Murty, V.S.N.; RamPrasad, K.V.S.

    .csr.2005.04.011 Cooley JW, Tukey JW (1965) An algorithm for the machine calculation of complex fourier series. Math Comput 19:297–301 D’Asaro EA, Lien R-C, Henyey F (2007) High-frequency internal waves on the oregon continental shelf. J Phys Oceanogr 37...

  14. Simulation of the Greenland Ice Sheet over two glacial–interglacial cycles: investigating a sub-ice-shelf melt parameterization and relative sea level forcing in an ice-sheet–ice-shelf model

    Directory of Open Access Journals (Sweden)

    S. L. Bradley

    2018-05-01

    Full Text Available Observational evidence, including offshore moraines and sediment cores, confirm that at the Last Glacial Maximum (LGM the Greenland ice sheet (GrIS expanded to a significantly larger spatial extent than seen at present, grounding into Baffin Bay and out onto the continental shelf break. Given this larger spatial extent and its close proximity to the neighbouring Laurentide Ice Sheet (LIS and Innuitian Ice Sheet (IIS, it is likely these ice sheets will have had a strong non-local influence on the spatial and temporal behaviour of the GrIS. Most previous paleo ice-sheet modelling simulations recreated an ice sheet that either did not extend out onto the continental shelf or utilized a simplified marine ice parameterization which did not fully include the effect of ice shelves or neglected the sensitivity of the GrIS to this non-local bedrock signal from the surrounding ice sheets. In this paper, we investigated the evolution of the GrIS over the two most recent glacial–interglacial cycles (240 ka BP to the present day using the ice-sheet–ice-shelf model IMAU-ICE. We investigated the solid earth influence of the LIS and IIS via an offline relative sea level (RSL forcing generated by a glacial isostatic adjustment (GIA model. The RSL forcing governed the spatial and temporal pattern of sub-ice-shelf melting via changes in the water depth below the ice shelves. In the ensemble of simulations, at the glacial maximums, the GrIS coalesced with the IIS to the north and expanded to the continental shelf break to the southwest but remained too restricted to the northeast. In terms of the global mean sea level contribution, at the Last Interglacial (LIG and LGM the ice sheet added 1.46 and −2.59 m, respectively. This LGM contribution by the GrIS is considerably higher (∼  1.26 m than most previous studies whereas the contribution to the LIG highstand is lower (∼  0.7 m. The spatial and temporal behaviour of the northern margin was

  15. Ecological risk assessment and natural resource management on the Outer Continental Shelf

    International Nuclear Information System (INIS)

    Goeke, G.; Roscigno, P.F.

    1993-01-01

    Since 1988 beginning with the Drilling Impact Assessment Task Force, Minerals Management Service (MMS) has used formal risk analysis methodologies in the Gulf of Mexico to determine the potential impact of gas and oil activities son natural resources. In the process, a list of assumptions, critical for the assessment of potential impacts, was generated. These assumptions were incorporated into a scenario where several levels of certainty described the hazards in terms of expected frequency of effects and the seriousness of the consequences. A risk matrix was generated from these assumptions and was used to generate a risk assessment for the various impact-producing factors on ecological endpoints. Recommendations for risk management were also provided so that decision-makers were given insight into acceptable/unacceptable levels of risk. This process insured that those issues with the highest potential impact were given the highest priority in terms of resources. One of the most important aspect so f the development of a risk assessment was determining the frequency of effects of the impact-producing factors. A paucity of data concerning the effects of impact-producing factors on estuarine and marine ecosystems remains the primary limiting factor in the development of ecological risk assessments. Presented here is a broad outline of the risk assessment methodology using chemosynthetic communities found in the Gulf of Mexico as an example

  16. Clay mineral distribution in the shelf sediments off the northern part of the east coast of india

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Reddy, N.P.C.; Rao, Ch.M.

    Forty-eight sediment samples from the continental shelf between Visakhapatnam and the Ganges were analysed by X-ray diffraction for the composition and distribution of clay minerals. Estuarine samples of the Hooghly are dominated by illite...

  17. Morphologic and seismic evidence of rapid submergence offshore Cide-Sinop in the southern Black Sea shelf

    Science.gov (United States)

    Ocakoğlu, Neslihan; İşcan, Yeliz; Kılıç, Fatmagül; Özel, Oğuz

    2018-06-01

    Multi-beam bathymetric and multi-channel seismic reflection data obtained offshore Cide-Sinop have revealed important records on the latest transgression of the Black Sea for the first time. A relatively large shelf plain within the narrow southern continental shelf characterized by a flat seafloor morphology at -100 water depth followed by a steep continental slope leading to -500 m depth. This area is widely covered by submerged morphological features such as dunes, lagoons, possible aeolianites, an eroded anticline and small channels that developed by aeolian and fluvial processes. These morphological features sit upon an erosional surface that truncates the top of all seismic units and constitutes the seafloor over the whole shelf. The recent prograded delta deposits around the shelf break are also truncated by the similar erosional surface. These results indicate that offshore Cide-Sinop was once a terrestrial landscape that was then submerged. The interpreted paleoshoreline varies from -100 to -120 m. This variation can be explained by not only sea level changes but also the active faults observed on the seismic section. The effective protection of morphological features on the seafloor is the evidence of abrupt submergence rather than gradual. In addition, the absence of coastal onlaps suggests that these morphological features should have developed at low sea level before the latest sea level rise in the Black Sea.

  18. Mitochondrial DNA reveals regional and interregional importance of the central Mediterranean African shelf for loggerhead sea turtles (Caretta caretta

    Directory of Open Access Journals (Sweden)

    Paolo Casale

    2008-09-01

    Full Text Available The wide north African continental shelf in the central Mediterranean is known to be one of the few important areas in the basin for loggerhead turtles in the neritic stage. In order to assess the origin of these turtles, sequences of the mtDNA control region were obtained from 70 turtles caught by bottom trawlers in the area, and compared with known sequences from turtles from Mediterranean and Atlantic nesting sites. Five haplotypes were identified (Haplotype diversity = 0.262; nucleotide diversity = 5.4×10-3. Specific haplotypes indicate contributions from distant rookeries such as Turkey and the Atlantic, which shows that Atlantic turtles entering the Mediterranean while in the oceanic phase use at least one Mediterranean continental shelf as a neritic foraging ground. A new haplotype and another one previously found only in foraging areas, highlight the genetic information gaps for nesting sites, which undermine powerful mixed stock analyses. Despite these limitations, the results reveal the regional importance of the study area as a neritic foraging ground for turtles that are probably from most of the Mediterranean nesting aggregates. Therefore, reducing turtle mortality resulting from the high fishing effort in the area should be regarded as key for Mediterranean turtle conservation and is also possibly important for Atlantic populations.

  19. Errant polychaetes of the continental plattaform of Tamaulipas, México.

    Directory of Open Access Journals (Sweden)

    V. Hugo Delgado-Blas

    2014-06-01

    Full Text Available 24 species of errant polychaetes have been recorded for the eastern Mexican continental shelf: Two Phyllodocidae, one Pilargidae, two Syllicdae, four Nereididae, two Glyceridae, two Goniadidae, three Nephtyidae, two Onuphidae, five Lumbrineridae y one Dorvilleidae. Two of these were the first to be recorded in Mexico, two from Mexican waters in the Gulf of Mexico and 11 new ones recorded in Tamaulipas.

  20. Active normal faults and submarine landslides in the Keelung Shelf off NE Taiwan

    Directory of Open Access Journals (Sweden)

    Ching-Hui Tsai

    2018-01-01

    Full Text Available The westernmost Okinawa Trough back-arc basin is located to the north of the Ryukyu islands and is situated above the northward dipping Ryukyu subducted slab. In the northern continental margin of the Okinawa Trough, the continental slope between the Keelung Valley and the Mein-Hua Submarine Canyon shows a steep angle and future slope failures are expected. The question is how slope failures will proceed? A sudden deep-seated slump or landslide would probably cause local tsunami and hit northern coast of Taiwan. To understand the probable submarine landslides, we conducted multi-channel seismic reflection, sub-bottom profilers, and multi-beam bathymetry surveys off NE Taiwan. Two general trends of shallow crustal faults are observed. The NE-SW trending faults generally follow the main structural trend of the Taiwan mountain belt. These faults are products of inversion tectonics of reverse faults from the former collisional thrust faults to post-collisional normal faults. Another trend of roughly E-W faults is consistent with the current N-S extension of the southern Okinawa Trough. The fault offsets in the eastern portion of the study area are more pronounced. No obvious basal surface of sliding is found beneath the continental margin. We conclude that the movement of the submarine landslides in the Keelung Shelf off northeastern Taiwan could be in a spread type. The submarine landslides mainly occur in the continental slope area and it is more obvious in the east than in the west of the Keelung Shelf.

  1. Modelling shelf-ocean exchange and its biogeochemical consequences in coastal upwelling systems

    DEFF Research Database (Denmark)

    Muchamad, Al Azhar

    margin bathymetry, and 3) what processes determine the observed variability of total organic carbon (TOC) content in shelf sediments underlying the upwelling system, with implications for the formation of petroleum source rocks. Here, a numerical ocean modeling approach is used in this thesis to explore...... processes and the development of anoxia/euxinia under the present day or past geological conditions. Thirdly and last, processes controlling distribution of total organic carbon (TOC) content in sediments across the continental margin is evaluated by application of the model to the Benguela upwelling system....... In the model, biological primary production and shelf bottom-water anoxia result in enhanced sedimentary TOC concentrations on the mid shelf and upper slope. The simulated TOCs implicate that bottom lateral transport only has a significant effect on increasing the deposition of the organic carbon on the mid...

  2. Ecological and taphonomical influences on coccoliths in surface sediments in the shelf of the Yellow and East China Seas

    Science.gov (United States)

    Jin, Xiaobo; Liu, Chuanlian

    2017-05-01

    Coccoliths, combined with sediment grain size, carbonate calcium and organic matters content, were analyzed to assess the ecological and taphonomical influences on coccolith distribution patterns in surface sediments in the continental shelf of the Yellow and East China Seas. Coccolith abundances ranged from 0 to 2.08×109 coccoliths g-1 sediment. The increasing abundance from the coastal inner shelf to the seaward middle shelf generally reflects the ecological fact that living coccolithophores are more abundant in the mesotrophic shelf waters than in the eutrophic coastal waters, although their deposits are still controlled by taphonomical effects, such as bottom (tidal) currents and calcite preservation conditions. Most abundant coccoliths are found in the fine-grained sediments of southwestern Cheju Island, where both ecology and taphonomy favor coccolith preservation. Still, large densities of coccoliths (>108 coccoliths g-1 sediment) are also found in coarse-grained relict sediments in the middle shelf. Coccolith assemblages were predominated by Gephyrocapsa oceanica and Emiliania huxleyi. The relative abundance of E. huxleyi, in addition to ecological reasons, may relate to selective post-mortem dissolution, since small E. huxleyi coccoliths are more susceptible to dissolution. Coccolith calcite has minor contributions (<1% to 12%) to total sediment CaCO3, and the main parts are attributed to terrigenous CaCO3 debris and relict shell fragments.

  3. Verdine and glaucony facies from surficial sediments of the eastern continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Thamban, M.; Lamboy, M.

    -trioctahedral Fe-rich 1:l clay mineral. Clay Miner., 23: 237-247. Murthy, K.S.R., 1989. Seismic stratigraphy of Ongole-Paradip continental shelf East coast of India. Indian J. Mar. Sci., 16: 47-58. Murthy, K.S.R., Rao, T.C.S., Subramanyam, AS., Rao, M... at the continent- ocean boundary: the verdine facies. Clay Miner. 25: 477-483. Rao, K.M. and Rao, T.C.S., 1994. Holocene sea levels of Visakhapatnam shelf, East Coast of India. J. Geol. Sot. India, 44: 685-689. Rao, V.P., 1991. Clay mineral distribution...

  4. Mixing processes at the subsurface layer in the Amundsen Sea shelf region

    Science.gov (United States)

    Mojica, J.; Djoumna, G.; Francis, D. K.; Holland, D.

    2017-12-01

    In the Amundsen Sea shelf region, mixing processes promote an upward transport of diapycnal fluxes of heat and salt from the subsurface to the surface mixing layer. Here we estimate the diapycnal mixing rates on the Amundsen shelf from a multi-year mooring cluster and five research cruises. By applying fine-scale parameterizations, the mixing rates obtained were higher near the southern end of Pine Island glacier front and exceeded 10-2 m2s-1. The eddy diffusivity increased near the critical latitude (74o 28' S) for semi-diurnal M2 tides, which coincided with near-critical topography on the shelf. This condition favored the generation of internal waves of M2 frequency. The semi-diurnal dynamic enhanced the mixing that potentially affected the heat budget and the circulation of the modified Circumpolar Deep Water. This can be observed in the characteristics of water exchange both below the ice shelves and between the continental shelf and the ice shelf cavities. The location of the critical latitude and critical topography provided favorable conditions for the generation of internal waves. KEYWORDS: Mixing processes, diapycnal fluxes, critical latitude, Circumpolar Deep Water.

  5. The role of deep-water sedimentary processes in shaping a continental margin: The Northwest Atlantic

    Science.gov (United States)

    Mosher, David C.; Campbell, D.C.; Gardner, J.V.; Piper, D.J.W.; Chaytor, Jason; Rebesco, M.

    2017-01-01

    The tectonic history of a margin dictates its general shape; however, its geomorphology is generally transformed by deep-sea sedimentary processes. The objective of this study is to show the influences of turbidity currents, contour currents and sediment mass failures on the geomorphology of the deep-water northwestern Atlantic margin (NWAM) between Blake Ridge and Hudson Trough, spanning about 32° of latitude and the shelf edge to the abyssal plain. This assessment is based on new multibeam echosounder data, global bathymetric models and sub-surface geophysical information.The deep-water NWAM is divided into four broad geomorphologic classifications based on their bathymetric shape: graded, above-grade, stepped and out-of-grade. These shapes were created as a function of the balance between sediment accumulation and removal that in turn were related to sedimentary processes and slope-accommodation. This descriptive method of classifying continental margins, while being non-interpretative, is more informative than the conventional continental shelf, slope and rise classification, and better facilitates interpretation concerning dominant sedimentary processes.Areas of the margin dominated by turbidity currents and slope by-pass developed graded slopes. If sediments did not by-pass the slope due to accommodation then an above grade or stepped slope resulted. Geostrophic currents created sedimentary bodies of a variety of forms and positions along the NWAM. Detached drifts form linear, above-grade slopes along their crests from the shelf edge to the deep basin. Plastered drifts formed stepped slope profiles. Sediment mass failure has had a variety of consequences on the margin morphology; large mass-failures created out-of-grade profiles, whereas smaller mass failures tended to remain on the slope and formed above-grade profiles at trough-mouth fans, or nearly graded profiles, such as offshore Cape Fear.

  6. 1300 km long late Pleistocene-Holocene shelf edge barrier reef system along the western continental shelf of India: Occurrence and significance

    Digital Repository Service at National Institute of Oceanography (India)

    Vora, K.H.; Wagle, B.G.; Veerayya, M.; Almeida, F.; Karisiddaiah, S.M.

    . It is surmised that coral/algal reef growth commenced with the advent of the Holocene trangression and favorable antecedent topography, and continued until early Holocene. Subsequently, rapid sea level rise drowned the reefs. The shelf edge reefs, therefore...

  7. The relationship between phytoplankton distribution and water column characteristics in North West European shelf sea waters.

    Science.gov (United States)

    Fehling, Johanna; Davidson, Keith; Bolch, Christopher J S; Brand, Tim D; Narayanaswamy, Bhavani E

    2012-01-01

    Phytoplankton underpin the marine food web in shelf seas, with some species having properties that are harmful to human health and coastal aquaculture. Pressures such as climate change and anthropogenic nutrient input are hypothesized to influence phytoplankton community composition and distribution. Yet the primary environmental drivers in shelf seas are poorly understood. To begin to address this in North Western European waters, the phytoplankton community composition was assessed in light of measured physical and chemical drivers during the "Ellett Line" cruise of autumn 2001 across the Scottish Continental shelf and into adjacent open Atlantic waters. Spatial variability existed in both phytoplankton and environmental conditions, with clear differences not only between on and off shelf stations but also between different on shelf locations. Temperature/salinity plots demonstrated different water masses existed in the region. In turn, principal component analysis (PCA), of the measured environmental conditions (temperature, salinity, water density and inorganic nutrient concentrations) clearly discriminated between shelf and oceanic stations on the basis of DIN:DSi ratio that was correlated with both salinity and temperature. Discrimination between shelf stations was also related to this ratio, but also the concentration of DIN and DSi. The phytoplankton community was diatom dominated, with multidimensional scaling (MDS) demonstrating spatial variability in its composition. Redundancy analysis (RDA) was used to investigate the link between environment and the phytoplankton community. This demonstrated a significant relationship between community composition and water mass as indexed by salinity (whole community), and both salinity and DIN:DSi (diatoms alone). Diatoms of the Pseudo-nitzschia seriata group occurred at densities potentially harmful to shellfish aquaculture, with the potential for toxicity being elevated by the likelihood of DSi limitation of

  8. The relationship between phytoplankton distribution and water column characteristics in North West European shelf sea waters.

    Directory of Open Access Journals (Sweden)

    Johanna Fehling

    Full Text Available Phytoplankton underpin the marine food web in shelf seas, with some species having properties that are harmful to human health and coastal aquaculture. Pressures such as climate change and anthropogenic nutrient input are hypothesized to influence phytoplankton community composition and distribution. Yet the primary environmental drivers in shelf seas are poorly understood. To begin to address this in North Western European waters, the phytoplankton community composition was assessed in light of measured physical and chemical drivers during the "Ellett Line" cruise of autumn 2001 across the Scottish Continental shelf and into adjacent open Atlantic waters. Spatial variability existed in both phytoplankton and environmental conditions, with clear differences not only between on and off shelf stations but also between different on shelf locations. Temperature/salinity plots demonstrated different water masses existed in the region. In turn, principal component analysis (PCA, of the measured environmental conditions (temperature, salinity, water density and inorganic nutrient concentrations clearly discriminated between shelf and oceanic stations on the basis of DIN:DSi ratio that was correlated with both salinity and temperature. Discrimination between shelf stations was also related to this ratio, but also the concentration of DIN and DSi. The phytoplankton community was diatom dominated, with multidimensional scaling (MDS demonstrating spatial variability in its composition. Redundancy analysis (RDA was used to investigate the link between environment and the phytoplankton community. This demonstrated a significant relationship between community composition and water mass as indexed by salinity (whole community, and both salinity and DIN:DSi (diatoms alone. Diatoms of the Pseudo-nitzschia seriata group occurred at densities potentially harmful to shellfish aquaculture, with the potential for toxicity being elevated by the likelihood of DSi

  9. The Northeast Greenland Shelf - Evidence of the existence of a pronounced salt-province

    Science.gov (United States)

    Schmitz, T.; Jokat, W.

    2003-04-01

    The Northeast Greenland shelf (NEGS) is the part of the continental margin of east Greenland located between the Jan Mayen Fracture Zone at about 72°N in the south and the Spitzbergen Fracture Zone at 81°N in the north. The eastern boundary, at the shelf edge, is the approximate position of the boundary between continental and oceanic crust and the western boundary is the coastline of Greenland. The shelf has a N-S orientation, is about 1000 km long, and between 125 km (southern part) and 380 km (at 78°N) wide. Based on present data the NEGS can be subdivided into a southern part influenced by Tertiary tectonism and volcanism (approx. 72°N to 75°N) and a northern, nonvolcanic, part (approx. 75°N to 81°N). Today the sedimentary history, stratigraphy, structure and origin of the basement below the sedimentary shelf south of 74°N are reasonable known, but only sparse information exists about the northern part of the shelf. Until 1990 there weren't any seismic lines north of 74°N, and all interpretations of stratigraphy and basin structures of the northern part of the NEGS were based on aeromagnetic data. During the last decade, the first seismic lines were shot over the northern part of the shelf to give more detailed information about sediment thickness, stratigraphy, and the structure of the sedimentary shelf. The area under investigation lies on the nonvolcanic northern part of the shelf between 78°30'N and 81°N. The sea floor topography indicates some submarine banks with water depth as shallow as 30 m, which are separated by valleys up to 500 m deep. These valleys were formed through erosion processes caused by cyclic movements of big grounded glacier tongues during the last ice-ages with a maximum expansion during the Wisconsin-Weichselian glaciation. During two scientific expeditions with the German research icebreaker Polarstern in 1997 and 1999, more than 1100 km of multichannel seismic data were collected. The cruise tracks during seismic

  10. Determination of in-situ rock stresses related to petroleum activities on the Norwegian Continental Shelf

    Energy Technology Data Exchange (ETDEWEB)

    Fejerskov, Morten

    1996-12-31

    In-situ rock stresses have proved to be important for exploration and production of hydrocarbons. This thesis uses various stress determination techniques to characterize the in-situ stress field on the Norwegian Continental Shelf. Leak off tests and borehole breakouts have been used to determine the in-situ stress in deep well bores. Overcoring and earthquake focal mechanisms data have also been compiled and evaluated together with stress information from petroleum wells. A new test procedure is suggested to improve the quality of leak off tests that emphasises the importance of accurate pressure determination, longer test periods and digital data sampling. Four-arm calliper logs are used to identify borehole breakouts on the Tampen Spur and Horda Platform. However, it proved difficult to distinguish borehole breakouts from other drilling processes since the elongations of the borehole consistently appeared in the direction of hole azimuth; drilling-induced key seats are here observed in vertical wells. This behaviour is discussed but not fully understood. This reduces the number of reliable stress data and their quality enormously and even casts some doubt about the quality of previous breakout studies from the North Sea. A highly compressive horizontal stress field seems to be present onshore and offshore Norway. Different stress determination techniques yield very consistent stress orientation, regional and internal variation. A 1. order stress direction is identified, where the maximum horizontal stress direction is rotating from N-S in the Barents Sea to NW-SE in the Norwegian Sea and WNW-ESE in the northern North Sea. At Tampen Spur, a dominant WNW-ESE maximum horizontal stress direction, normal to the major tectonic structures is identified as well as a minimum stress close to the vertical stress, the latter indicating high horizontal stresses. 250 refs., 91 figs., 14 tabs.

  11. Heat flow in the rifted continental margin of the South China Sea near Taiwan and its tectonic implications

    Science.gov (United States)

    Liao, Wei-Zhi; Lin, Andrew T.; Liu, Char-Shine; Oung, Jung-Nan; Wang, Yunshuen

    2014-10-01

    Temperature measurements carried out on 9 hydrocarbon exploration boreholes together with Bottom Simulating Reflectors (BSRs) from reflection seismic images are used in this study to derive geothermal gradients and heat flows in the northern margin of the South China Sea near Taiwan. The method of Horner plot is applied to obtain true formation temperatures from measured borehole temperatures, which are disturbed by drilling processes. Sub-seafloor depths of BSRs are used to calculate sub-bottom temperatures using theoretical pressure/temperature phase boundary that marks the base of gas hydrate stability zone. Our results show that the geothermal gradients and heat flows in the study area range from 28 to 128 °C/km and 40 to 159 mW/m2, respectively. There is a marked difference in geothermal gradients and heat flow beneath the shelf and slope regions. It is cooler beneath the shelf with an average geothermal gradient of 34.5 °C/km, and 62.7 mW/m2 heat flow. The continental slope shows a higher average geothermal gradient of 56.4 °C/km, and 70.9 mW/m2 heat flow. Lower heat flow on the shelf is most likely caused by thicker sediments that have accumulated there compared to the sediment thickness beneath the slope. In addition, the continental crust is highly extended beneath the continental slope, yielding higher heat flow in this region. A half graben exists beneath the continental slope with a north-dipping graben-bounding fault. A high heat-flow anomaly coincides at the location of this graben-bounding fault at the Jiulong Ridge, indicating vigorous vertical fluid convection which may take place along this fault.

  12. Mineralogy and Origin of Sediments From Drill Holes on the Continental Margin Off Florida, 1965-1969 (NODC Accession 7100714)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Drill cores obtained during the Joint Oceanographic Institutions' Deep Earth Sampling Program from the continental shelf, the Florida-Hatteras Slope, and the Blake...

  13. Shelf evolution along a transpressive transform margin, Santa Barbara Channel, California

    Science.gov (United States)

    Johnson, Samuel Y.; Hartwell, Stephen; Sorlien, Christopher C.; Dartnell, Peter; Ritchie, Andrew C.

    2017-01-01

    High-resolution bathymetric and seismic reflection data provide new insights for understanding the post–Last Glacial Maximum (LGM, ca. 21 ka) evolution of the ∼120-km-long Santa Barbara shelf, located within a transpressive segment of the transform continental margin of western North America. The goal is to determine how rising sea level, sediment supply, and tectonics combine to control shelf geomorphology and history. Morpho­logic, stratigraphic, and structural data highlight regional variability and support division of the shelf into three domains. (1) The eastern Santa Barbara shelf is south of and in the hanging wall of the blind south-dipping Oak Ridge fault. The broad gently dipping shelf has a convex-upward shape resulting from thick post-LGM sediment (mean = 24.7 m) derived from the Santa Clara River. (2) The ∼5–8-km-wide Ventura Basin obliquely crosses the shelf and forms an asymmetric trough with thick post-LGM sediment fill (mean = 30.4 m) derived from the Santa Clara and Ventura Rivers. The basin is between and in the footwalls of the Oak Ridge fault to the south and the blind north-dipping Pitas Point fault to the north. (3) The central and western Santa Barbara shelf is located north of and in the hanging wall of the North Channel–Pitas Point fault system. The concave-up shape of the shelf results from folding, marine erosion, and the relative lack of post-LGM sediment cover (mean = 3.8 m). Sediment is derived from small steep coastal watersheds and largely stored in the Gaviota bar and other nearshore mouth bars. Three distinct upper slope morphologies result from a mix of progradation and submarine landsliding.Ages and rates of deformation are derived from a local sea-level-rise model that incorporates an inferred LGM shoreline angle and the LGM wave-cut platform. Post-LGM slip rates on the offshore Oak Ridge fault are a mini­mum of 0.7 ± 0.1 mm/yr. Slip rates on the Pitas Point fault system are a minimum of 2.3 ± 0.3 mm

  14. EX1204: Northeastern Canyons and Continental Margins Exploration on NOAA Ship Okeanos Explorer between 20120529 and 20120613

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — During the Okeanos Explorer (EX) mission EX1204, the vessel will sail from Norfolk, VA, along the continental shelf break of the U.S. East Coast from Virginia to...

  15. The De Long Trough: a newly discovered glacial trough on the East Siberian continental margin

    Directory of Open Access Journals (Sweden)

    M. O'Regan

    2017-09-01

    Full Text Available Ice sheets extending over parts of the East Siberian continental shelf have been proposed for the last glacial period and during the larger Pleistocene glaciations. The sparse data available over this sector of the Arctic Ocean have left the timing, extent and even existence of these ice sheets largely unresolved. Here we present new geophysical mapping and sediment coring data from the East Siberian shelf and slope collected during the 2014 SWERUS-C3 expedition (SWERUS-C3: Swedish – Russian – US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions. The multibeam bathymetry and chirp sub-bottom profiles reveal a set of glacial landforms that include grounding zone formations along the outer continental shelf, seaward of which lies a  >  65 m thick sequence of glacio-genic debris flows. The glacial landforms are interpreted to lie at the seaward end of a glacial trough – the first to be reported on the East Siberian margin, here referred to as the De Long Trough because of its location due north of the De Long Islands. Stratigraphy and dating of sediment cores show that a drape of acoustically laminated sediments covering the glacial deposits is older than ∼ 50 cal kyr BP. This provides direct evidence for extensive glacial activity on the Siberian shelf that predates the Last Glacial Maximum and most likely occurred during the Saalian (Marine Isotope Stage (MIS 6.

  16. Global Paleobathymetry Reconstruction with Realistic Shelf-Slope and Sediment Wedge

    Science.gov (United States)

    Goswami, A.; Hinnov, L. A.; Gnanadesikan, A.; Olson, P.

    2013-12-01

    We present paleo-ocean bathymetry reconstructions in a 0.1°x0.1° resolution, using simple geophysical models (Plate Model Equation for oceanic lithosphere), published ages of the ocean floor (Müller et al. 2008), and modern world sediment thickness data (Divins 2003). The motivation is to create realistic paleobathymetry to understand the effect of ocean floor roughness on tides and heat transport in paleoclimate simulations. The values for the parameters in the Plate Model Equation are deduced from Crosby et al. (2006) and are used together with ocean floor age to model Depth to Basement. On top of the Depth to Basement, we added an isostatically adjusted multilayer sediment layer, as indicated from sediment thickness data of the modern oceans and marginal seas (Divins 2003). We also created another version of the sediment layer from the Müller et al. dataset. The Depth to Basement with the appropriate sediment layer together represent a realistic paleobathymetry. A Sediment Wedge was modeled to complement the reconstructed paleobathymetry by extending it to the coastlines. In this process we added a modeled Continental Shelf and Continental Slope to match the extent of the reconstructed paleobathymetry. The Sediment Wedge was prepared by studying the modern ocean where a complete history of seafloor spreading is preserved (north, south and central Atlantic Ocean, Southern Ocean between Australia-Antarctica, and the Pacific Ocean off the west coast of South America). The model takes into account the modern continental shelf-slope structure (as evident from ETOPO1/ETOPO5), tectonic margin type (active vs. passive margin) and age of the latest tectonic activity (USGS & CGMW). Once the complete ocean bathymetry is modeled, we combine it with PALEOMAP (Scotese, 2011) continental reconstructions to produce global paleoworld elevation-bathymetry maps. Modern time (00 Ma) was assumed as a test case. Using the above-described methodology we reconstructed modern ocean

  17. Warming shelf seas drive the subtropicalization of European pelagic fish communities.

    Science.gov (United States)

    Montero-Serra, Ignasi; Edwards, Martin; Genner, Martin J

    2015-01-01

    Pelagic fishes are among the most ecologically and economically important fish species in European seas. In principle, these pelagic fishes have potential to demonstrate rapid abundance and distribution shifts in response to climatic variability due to their high adult motility, planktonic larval stages, and low dependence on benthic habitat for food or shelter during their life histories. Here, we provide evidence of substantial climate-driven changes to the structure of pelagic fish communities in European shelf seas. We investigated the patterns of species-level change using catch records from 57,870 fisheries-independent survey trawls from across European continental shelf region between 1965 and 2012. We analysed changes in the distribution and rate of occurrence of the six most common species, and observed a strong subtropicalization of the North Sea and Baltic Sea assemblages. These areas have shifted away from cold-water assemblages typically characterized by Atlantic herring and European sprat from the 1960s to 1980s, to warmer-water assemblages including Atlantic mackerel, Atlantic horse mackerel, European pilchard and European anchovy from the 1990s onwards. We next investigated if warming sea temperatures have forced these changes using temporally comprehensive data from the North Sea region. Our models indicated the primary driver of change in these species has been sea surface temperatures in all cases. Together, these analyses highlight how individual species responses have combined to result in a dramatic subtropicalization of the pelagic fish assemblage of the European continental shelf. © 2014 John Wiley & Sons Ltd.

  18. NW European shelf under climate warming: implications for open ocean – shelf exchange, primary production, and carbon absorption

    Directory of Open Access Journals (Sweden)

    M. Gröger

    2013-06-01

    Full Text Available Shelves have been estimated to account for more than one-fifth of the global marine primary production. It has been also conjectured that shelves strongly influence the oceanic absorption of anthropogenic CO2 (carbon shelf pump. Owing to their coarse resolution, currently applied global climate models are inappropriate to investigate the impact of climate change on shelves and regional models do not account for the complex interaction with the adjacent open ocean. In this study, a global ocean general circulation model and biogeochemistry model were set up with a distorted grid providing a maximal resolution for the NW European shelf and the adjacent northeast Atlantic. Using model climate projections we found that already a~moderate warming of about 2.0 K of the sea surface is linked with a reduction by ~ 30% of the biological production on the NW European shelf. If we consider the decline of anthropogenic riverine eutrophication since the 1990s, the reduction of biological production amounts is even larger. The relative decline of NW European shelf productivity is twice as strong as the decline in the open ocean (~ 15%. The underlying mechanism is a spatially well confined stratification feedback along the continental shelf break. This feedback reduces the nutrient supply from the deep Atlantic to about 50%. In turn, the reduced productivity draws down CO2 absorption in the North Sea by ~ 34% at the end of the 21st century compared to the end of the 20th century implying a strong weakening of shelf carbon pumping. Sensitivity experiments with diagnostic tracers indicate that not more than 20% of the carbon absorbed in the North Sea contributes to the long-term carbon uptake of the world ocean. The rest remains within the ocean's mixed layer where it is exposed to the atmosphere. The predicted decline in biological productivity, and decrease of phytoplankton concentration (in the North Sea by averaged 25% due to reduced nutrient imports from

  19. Reactivation of precambrian faults on the southwestern continental margin of India: Evidence from gravity anomalies

    Digital Repository Service at National Institute of Oceanography (India)

    Subrahmanyam, V.; Ramana, M.V.; Rao, D.G.

    con- fi~ration of the western continental margin, with various structural styles, has been considered as a single unit, even though there exists a difference of opinion about the origin and evolution of the Chagos-Laccadive Ridge complex...’tVATION OF PRECAMBRIAN FAULTS ON THE SW CON~~E~AL MARGIN OF INDIA 337 shelf break due to the steep topographic relief of shelf. Furthermore, the gradients might have played a dominant role in shaping the bathymetry when the block movement took place along the pre...

  20. Multi-Decadal Averages of Basal Melt for Ross Ice Shelf, Antarctica Using Airborne Observations

    Science.gov (United States)

    Das, I.; Bell, R. E.; Tinto, K. J.; Frearson, N.; Kingslake, J.; Padman, L.; Siddoway, C. S.; Fricker, H. A.

    2017-12-01

    Changes in ice shelf mass balance are key to the long term stability of the Antarctic Ice Sheet. Although the most extensive ice shelf mass loss currently is occurring in the Amundsen Sea sector of West Antarctica, many other ice shelves experience changes in thickness on time scales from annual to ice age cycles. Here, we focus on the Ross Ice Shelf. An 18-year record (1994-2012) of satellite radar altimetry shows substantial variability in Ross Ice Shelf height on interannual time scales, complicating detection of potential long-term climate-change signals in the mass budget of this ice shelf. Variability of radar signal penetration into the ice-shelf surface snow and firn layers further complicates assessment of mass changes. We investigate Ross Ice Shelf mass balance using aerogeophysical data from the ROSETTA-Ice surveys using IcePod. We use two ice-penetrating radars; a 2 GHz unit that images fine-structure in the upper 400 m of the ice surface and a 360 MHz radar to identify the ice shelf base. We have identified internal layers that are continuous along flow from the grounding line to the ice shelf front. Based on layer continuity, we conclude that these layers must be the horizons between the continental ice of the outlet glaciers and snow accumulation once the ice is afloat. We use the Lagrangian change in thickness of these layers, after correcting for strain rates derived using modern day InSAR velocities, to estimate multidecadal averaged basal melt rates. This method provides a novel way to quantify basal melt, avoiding the confounding impacts of spatial and short-timescale variability in surface accumulation and firn densification processes. Our estimates show elevated basal melt rates (> -1m/yr) around Byrd and Mullock glaciers within 100 km from the ice shelf front. We also compare modern InSAR velocity derived strain rates with estimates from the comprehensive ground-based RIGGS observations during 1973-1978 to estimate the potential magnitude of

  1. Morphodynamic Impacts of Hurricane Sandy on the Inner-shelf (Invited)

    Science.gov (United States)

    Trembanis, A. C.; Beaudoin, J. D.; DuVal, C.; Schmidt, V. E.; Mayer, L. A.

    2013-12-01

    Through the careful execution of precision high-resolution acoustic sonar surveys over the period of October 2012 through July 2013, we have obtained a unique set of high-resolution before and after storm measurements of seabed morphology and in situ hydrodynamic conditions (waves and currents) capturing the impact of the storm at an inner continental shelf field site known as the 'Redbird reef' (Raineault et al., 2013). Understanding the signature of this storm event is important for identifying the impacts of such events and for understanding the role that such events have in the transport of sediment and marine debris on the inner continental shelf. In order to understand and characterize the ripple dynamics and scour processes in an energetic, heterogeneous inner-shelf setting, a series of high-resolution geoacoustic surveys were conducted before and after Hurricane Sandy. Our overall goal is to improve our understanding of bedform dynamics and spatio-temporal length scales and defect densities through the application of a recently developed fingerprint algorithm technique (Skarke and Trembanis, 2011). Utilizing high-resolution swath sonar collected by an AUV and from surface vessel multibeam sonar, our study focuses both on bedforms in the vicinity of manmade seabed objects (e.g. shipwrecks and subway cars) and dynamic natural ripples on the inner-shelf in energetic coastal settings with application to critical military operations such as mine countermeasures. Seafloor mapping surveys were conducted both with a ship-mounted multibeam echosounder (200 kHz and 400 kHz) and an Autonomous Underwater Vehicle (AUV) configured with high-resolution side-scan sonar (900 and 1800 kHz) and a phase measuring bathymetric sonar (500 kHz). These geoacoustic surveys were further augmented with data collected by in situ instruments placed on the seabed that recorded measurements of waves and currents at the site before, during, and after the storm. Multibeam echosounder map of

  2. Shelf erosion and submarine river canyons: implications for deep-sea oxygenation and ocean productivity during glaciation

    Directory of Open Access Journals (Sweden)

    I. Tsandev

    2010-06-01

    Full Text Available The areal exposure of continental shelves during glacial sea level lowering enhanced the transfer of erodible reactive organic matter to the open ocean. Sea level fall also activated submarine canyons thereby allowing large rivers to deposit their particulate load, via gravity flows, directly in the deep-sea. Here, we analyze the effects of shelf erosion and particulate matter re-routing to the open ocean during interglacial to glacial transitions, using a coupled model of the marine phosphorus, organic carbon and oxygen cycles. The results indicate that shelf erosion and submarine canyon formation may significantly lower deep-sea oxygen levels, by up to 25%, during sea level low stands, mainly due to the supply of new material from the shelves, and to a lesser extent due to particulate organic matter bypassing the coastal zone. Our simulations imply that deep-sea oxygen levels can drop significantly if eroded shelf material is deposited to the seafloor. Thus the glacial ocean's oxygen content could have been significantly lower than during interglacial stages. Primary production, organic carbon burial and dissolved phosphorus inventories are all affected by the erosion and rerouting mechanisms. However, re-routing of the continental and eroded shelf material to the deep-sea has the effect of decoupling deep-sea oxygen demand from primary productivity in the open ocean. P burial is also not affected showing a disconnection between the biogeochemical cycles in the water column and the P burial record.

  3. A PLATAFORMA CONTINENTAL BRASILEIRA E SUA RELAÇÃO COM A ZONA COSTEIRA E A PESCA

    Directory of Open Access Journals (Sweden)

    Dieter Muehe

    2005-01-01

    Full Text Available The Brazilian continental shelf, with about 8.000 km length, includes several climatic zones expressed in differentiated solid and liquid sediment input. Excepting the important input of sediments and nutrients from the Amazon in the North and the Prata in the South the rest of the shelf is characterized by low productivity due the reduced availability of nutrients. Considering the morphology of the bottom and fishing equipment, the shelf can be divided into two regions: north of Cabo Frio, with warm waters, irregular carbonate bottom, with fishery predominantly through long line and traps; and Southwest of Cabo Frio, with cold waters, flat bottom and fishery predominantly through fishing nets.

  4. Signatures of Late Quaternary sea-level changes and Neo-tectonic activity over Visakhapatnam - Gopalpur shelf, east coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, K.M.; Reddy, N.P.C; PremKumar, M.K.; Raju, Y.S.N.; Venkateswarlu, K.; Murthy, K.S.R.

    High-resolution shallow seismic and echo sounding profiles of the continental shelf between Visakhapatnam and Gopalpur reveal prominent morphological features like terraces, reefs and pinnacles at different water depths of 80-100 m, 50-30 m...

  5. Arctic Ocean outflow and glacier-ocean interactions modify water over the Wandel Sea shelf (northeastern Greenland)

    DEFF Research Database (Denmark)

    Dmitrenko, Igor A.; Kirillov, Sergey A.; Rudels, Bert

    2017-01-01

    The first-ever conductivity-temperature-depth (CTD) observations on the Wandel Sea shelf in northeastern Greenland were collected in April-May 2015. They were complemented by CTDs taken along the continental slope during the Norwegian FRAM 2014-2015 drift. The CTD profiles are used to reveal...

  6. Observations and modeling of wave-supported sediment gravity flows on the Po prodelta and comparison to prior observations from the Eel shelf

    Science.gov (United States)

    Traykovski, P.; Wiberg, P. L.; Geyer, W. R.

    2007-02-01

    A mooring and tripod array was deployed from the fall of 2002 through the spring of 2003 on the Po prodelta to measure sediment transport processes associated with sediment delivered from the Po River. Observations on the prodelta revealed wave-supported gravity flows of high concentration mud suspensions that are dynamically and kinematically similar to those observed on the Eel shelf [Traykovski, P., Geyer, W.R., Irish, J.D., Lynch, J.F., 2000. The role of wave-induced density-driven fluid mud flows for cross-shelf transport on the Eel River continental shelf. Continental Shelf Research 20, 2113-2140]. Due to the dynamic similarity between the two sites, a simple one-dimensional (1D) across-shelf model with the appropriate bottom boundary condition was used to examine fluxes associated with this transport mechanism at both locations. To calculate the sediment concentrations associated with the wave-dominated and wave-current resuspension, a bottom boundary condition using a reference concentration was combined with an "active layer" formulation to limit the amount of sediment in suspension. Whereas the wave-supported gravity flow mechanism dominated the transport on the Eel shelf, on the Po prodelta flux due to this mechanism is equal in magnitude to transport due to wave resuspension and wind-forced mean currents in the cross-shore direction. Southward transport due to wave resuspension and wind forced mean currents move an order of magnitude more sediment along-shore than the down-slope flux associated wave-supported gravity flows.

  7. Testing sequence stratigraphic models by drilling Miocene foresets on the New Jersey shallow shelf

    DEFF Research Database (Denmark)

    Miller, Kenneth G.; Mountain, Gregory S.; Browning, James V.

    2013-01-01

    continental shelf (Integrated Ocean Drilling Program Expedition 313, Sites M27-M29). We recognize stratal surfaces and systems tracts by integrating seismic stratigraphy, litho-facies successions, gamma logs, and foraminiferal paleodepth trends. Our interpretations of systems tracts, particularly......) and coarsening- and shallowing-upward highstand systems tracts (HST). Drilling through the foresets yields thin (

  8. Distribution of some biochemical compounds in sediments of the shelf and slope regions of the west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Bhosle, N.B.; Dhargalkar, V.K.; Braganca, A.

    Surficial sediment samples collected from the continental shelf and slope of the Bay of Bengal were studied for the distribution of organic carbon and its constituent fractions such as carbohydrates, proteins, amino acids and lipids. Organic carbon...

  9. Improving modeling of tides on the continental shelf off the west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Testut, L.; Unnikrishnan, A.S.

    : modern insights from FES2004.Ocean Dynamics, 56, 394-415. Lyard, F.;Roblou, L., and Birol,F., 2009.Precise error budget for the altimeter-derived tidal constantsin shelf and coastal seas.Ocean Surface Topography Science Team (OSTST), (Seattle...

  10. New Jersey shallow shelf

    DEFF Research Database (Denmark)

    Expedition 313 Scientists; Bjerrum, Christian J.

    2009-01-01

    to key horizons in wells drilled into the adjacent coastal plain suggest the clinoform structures investigated during Expedition 313 were deposited during times of oscillations in global sea level; however, this needs to be determined with much greater certainty. The age, lithofacies, and core-log......Integrated Ocean Drilling Program (IODP) Expedition 313 to the New Jersey Shallow Shelf off the east coast of the United States is the third IODP expedition to use a mission-specific platform. It was conducted by the European Consortium for Ocean Research Drilling (ECORD) Science Operator (ESO......) between 30 April and 17 July 2009, with additional support from the International Continental Scientific Drilling Program (ICDP). There were three objectives: (1) date late Paleogene–Neogene depositional sequences and compare ages of unconformable surfaces that divide these sequences with times of sea...

  11. Submarine geo-hazards on the eastern Sardinia-Corsica continental margin based on preliminary pipeline route investigation

    Science.gov (United States)

    Cecchini, S.; Taliana, D.; Giacomini, L.; Herisson, C.; Bonnemaire, B.

    2011-03-01

    The understanding of the morphology and the shallow geo-hazards of the seafloor is a major focus for both academic and private industry research. On November and December 2009 a geophysical pipeline survey was carried out by Fugro Oceansismica S.p.A. (FOSPA) and FUGRO France (FFSA) for DORIS Engineering on behalf of GRTgaz (Engineering centre, Transmission Pipe Department; http://www.grtgaz.com) which are currently investigating the possibility of laying a pipeline between Sardinia and Corsica as a spur line from the planned GALSI Project. The Project, "Alimentation de la Corse en gaz naturel", consists of a corridor 100 km long and 1.0 km wide along the Corsica-Sardinia shelf. The integration of the multibeam, sidescan sonar and sparker data provided a high resolution seafloor mapping for geo-hazard assessment. In this article the data acquired along a break of slope section (approximately 20 km × 1.5 km), in the eastern sector of the Strait of Bonifacio are described. The area was abandoned during the survey, because of its unsuitability. Indeed, in this area the continental shelf, approximately 100 m deep and deepening gently eastward, is characterized by an uneven morphology, with different seabed features such as Beach- rocks mainly NNW-SSE oriented. Also, the continuity of the continental margin, identified around -110/-115 m, is interrupted by four canyon heads which incise the slope and are associated with glide deposits.

  12. The Northeast Greenland Shelf as a Potential Habitat for the Northeast Arctic Cod

    Directory of Open Access Journals (Sweden)

    Kjersti O. Strand

    2017-09-01

    Full Text Available Observations (1978–1991 of distributions of pelagic juvenile Northeast Arctic cod (Gadus morhua L. show that up to 1/3 of the year class are dispersed off the continental shelf and into the deep Norwegian Sea while on the way from the spring-spawning areas along the Norwegian coast to the autumn-settlement areas in the Barents Sea. The fate of this variable fraction of pelagic juveniles off-shelf has been an open question ever since Johan Hjort's (1914 seminal work. We have examined both the mechanisms causing offspring off-shelf transport, and their subsequent destiny using an individual-based biophysical model applied to quantify growth and dispersal. Our results show, consistently with the observations, that total off-shelf transport is highly variable between years and may be up to 27.4%. Offspring from spawning grounds around Lofoten have a higher chance of being displaced off the shelf. The off-shelf transport is dominated by episodic events where frequencies and dates vary between years. Northeasterly wind conditions over a 3–7-day period prior to the off-shelf events are a good proxy for dispersal of offspring off the shelf. Offspring transported into the open ocean are on average carried along three following routes: back onto the adjacent eastern shelves and into the Barents Sea (36.9%, recirculating within the Lofoten Basin (60.7%, or drifting northwest to the northeast Greenland shelf (2.4%. For the latter fraction the transport may exceed 12% depending on year. Recent investigations have discovered distributions of young cod on the northeast Greenland shelf indicating that conditions may support survival for Northeast Arctic cod offspring.

  13. Habitat compression and expansion of sea urchins in response to changing climate conditions on the California continental shelf and slope (1994-2013)

    Science.gov (United States)

    Sato, Kirk N.; Levin, Lisa A.; Schiff, Kenneth

    2017-03-01

    Echinoid sea urchins with distributions along the continental shelf and slope of the eastern Pacific often dominate the megafauna community. This occurs despite their exposure to naturally low dissolved oxygen (DO) waters (calcium carbonate (ΩCaCO3<1). Here we present vertical depth distribution and density analyses of historical otter trawl data collected in the Southern California Bight (SCB) from 1994 to 2013 to address the question: Do changes in echinoid density and species' depth distributions along the continental margin in the SCB reflect observed secular or interannual changes in climate? Deep-dwelling burrowing urchins (Brissopsis pacifica, Brisaster spp. and Spatangus californicus), which are adapted to low-DO, low-pH conditions appeared to have expanded their vertical distributions and populations upslope over the past decade (2003-2013), and densities of the deep pink urchin, Strongylocentrotus fragilis, increased significantly in the upper 500 m of the SCB. Conversely, the shallower urchin, Lytechinus pictus, exhibited depth shoaling and density decreases within the upper 200 m of the SCB from 1994 to 2013. Oxygen and pH in the SCB also vary inter-annually due to varying strengths of the El Niño Southern Oscillation (ENSO). Changes in depth distributions and densities were correlated with bi-monthly ENSO climate indices in the region. Our results suggest that both a secular trend in ocean deoxygenation and acidification and varying strength of ENSO may be linked to echinoid species distributions and densities, creating habitat compression in some and habitat expansion in others. Potential life-history mechanisms underlying depth and density changes observed over these time periods include migration, mortality, and recruitment. These types of analyses are needed for a broad suite of benthic species in order to identify and manage climate-sensitive species on the margin.

  14. The Role of the Submarine Channel Pernambuco in the Brazilian Continental Margin East

    International Nuclear Information System (INIS)

    Torres, L.; Villena, H.

    2010-01-01

    The Brazilian Continental Margin, which coastline measures more than 8,500km gives to Brazil continental dimensions. This huge region is conditioned by the action of process such as, sedimentals, tectonics, geomorphological and climatical, as example, which direct or in conjunction with other ones, since of continental break up between South America and Africa are going on and may be responsible for the current morphology of the margin. In accordance with this point of view, the Oriental part of the Brazilian Continental Margin, presents characteristics of a passive margin and fisiographically ''starved'', in which the continental break occur no more than 100km from de coastline and the sedimentary coverage is mainly carbonatic. The continental slope does not present great extension if compared with other parts of the Brazilian Margin and sharp gradient. The remark presence of the continental plateaus (Rio Grande Plateau and Pernambuco Plateau), which link with the continental rise and additionally the Paraiba, Pernambuco e Bahia seamounts, are the majors features in the morphology of the region between the slope and the continental rise. This paper will concentrate its focus on Bahia Seamount, with emphasis in the mainly erosive feature which cut transversally the seamounts, named Pernambuco Submarine Channel. It will be employed bathymetric multibeam and seismic data carried out by the Brazilian Continental Shelf Project (LEPLAC) in the current year and pieces of information from bibliographic researches in order to present a discussion by the hole of the Pernambuco Submarine Channel in the Occidental region of the Brazilian Continental Margin

  15. Sedimentation on continental margins: An integrated program for innovative studies during the 1990s

    Science.gov (United States)

    Nittrourer, Charles A.; Coleman, James M.; Rouge, Baton; Flood, Roger D.; Ginsburg, Robert N.; Gorsline, Donn S.; Hine, Albert C.; Sternberg, Richard W.; Swift, Donald J. P.; Wright, L. Donelson

    Continental margins are of great scientific interest, and they represent the focus of human interaction with the ocean. Their deep structure forms the transition from continental to oceanic crust, and their surface expression extends from coastal environments of estuaries and shorelines across the continental shelf and slope to either the base of a continental rise or a marginal trough. Modern continental margins represent natural laboratories for investigation of complex relationships between physical, chemical, and biological phenomena, which are sensitive to environmental conditions both on the land and in the ocean. The history of these conditions is preserved within the sedimentary deposits of continental margins. The deposits form repositories for much of the particulate material transported off the world's land masses and produced from dissolved components in the world ocean. Past deposits of continental margins have been uplifted to form many mountain ranges and sedimentary terrains of the world, which record details of Earth history and contain valuable natural resources, such as petroleum and natural gas. Modern deposits of continental margins record the more recent events that have influenced Earth and also contain natural resources (for instance, minerals, sand, and gravel), as well as anthropogenic pollutants (for example, heavy metals and pesticides). The fates of many materials beneficial and deleterious to humans are dependent on the pathways followed by sedimentary particles on continental margins.

  16. Organic matter distribution in the continental shelf sediments, off Kochi, west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Reddy, N.P.C.

    (average 3.8%) than those towards Azhikode (average 1.97%). The sand predominant offshore relict sediments contain very low organic matter values (average 0.71%). The high organic matter content in the inner shelf is mainly controlled by the fine texture...

  17. Numerical modelling of the M2 tide on the northern Patagonian Shelf

    Science.gov (United States)

    Glorioso, P. D.; Simpson, J. H.

    1994-02-01

    The previously reported occurrence of tidal fronts on the Patagonian Shelf ( CARRETOet al., 1986 , Journal of Plankton Research, 8, 15-28; GLORIOSO, 1987 , Continental Shelf Research, 7, 27-34), motivated the application of a numerical model to solve the shallow-water equations with external forcing by the principal-lunar semidiurnal tide (M2) prescribed along the open boundary. The mean width of the Patagonian Shelf is comparable with a quarter wavelength of the semidiurnal tide, giving the conditions for standing wave resonance at that frequency ( WEBB, 1975 , Deep-Sea Research, 23, 1-15). The region is well recognized by its large tidal elevations and by the speed of the tidal wave changing phase very rapidly. Some of the results obtained from the modelling exercise include the mapping of the M2 tidal constants, the Simpson-Hunter stratification parameter, the mean sea surface elevation, and the distribution of tidal energy dissipation by bottom friction. These results agree qualitatively with the ship data available and with satellite infrared imagery.

  18. Assessing the quality of bottom water temperatures from the Finite-Volume Community Ocean Model (FVCOM) in the Northwest Atlantic Shelf region

    Science.gov (United States)

    Li, Bai; Tanaka, Kisei R.; Chen, Yong; Brady, Damian C.; Thomas, Andrew C.

    2017-09-01

    The Finite-Volume Community Ocean Model (FVCOM) is an advanced coastal circulation model widely utilized for its ability to simulate spatially and temporally evolving three-dimensional geophysical conditions of complex and dynamic coastal regions. While a body of literature evaluates model skill in surface fields, independent studies validating model skill in bottom fields over large spatial and temporal scales are scarce because these fields cannot be remotely sensed. In this study, an evaluation of FVCOM skill in modeling bottom water temperature was conducted by comparison to hourly in situ observed bottom temperatures recorded by the Environmental Monitors on Lobster Traps (eMOLT), a program that attached thermistors to commercial lobster traps from 2001 to 2013. Over 2 × 106 pairs of FVCOM-eMOLT records were evaluated by a series of statistical measures to quantify accuracy and precision of the modeled data across the Northwest Atlantic Shelf region. The overall comparison between modeled and observed data indicates reliable skill of FVCOM (r2 = 0.72; root mean squared error = 2.28 °C). Seasonally, the average absolute errors show higher model skill in spring, fall and winter than summer. We speculate that this is due to the increased difficulty of modeling high frequency variability in the exact position of the thermocline and frontal zones. The spatial patterns of the residuals suggest that there is improved similarity between modeled and observed data at higher latitudes. We speculate that this is due to increased tidal mixing at higher latitudes in our study area that reduces stratification in winter, allowing improved model accuracy. Modeled bottom water temperatures around Cape Cod, the continental shelf edges, and at one location at the entrance to Penobscot Bay were characterized by relatively high errors. Constraints for future uses of FVCOM bottom water temperature are provided based on the uncertainties in temporal-spatial patterns. This study is

  19. The SPARDIG project - Transforming analogue sparker records from the Norwegian continental shelf into SEG-Y format, first results

    Science.gov (United States)

    Schaming, Marc; Rise, Leif; Chand, Shyam; Reidulv, Bøe; Terje Osmundsen, Per; Redfield, Tim

    2017-04-01

    A large number of sparker lines were acquired on the Norwegian continental shelf during the years 1970-1982, by IKU (Sintef Petroleum Research). The responsibility of the analogue seismic database was transferred to NGU in 1998; this included storage of the physical data (original paper rolls and half-scale film copies) and the digital navigation database. The data (from 60°N to 71°30N) were in the early eighties subdivided in 6 data packages, and offered for sale to oil companies as half scale folded paper copies (25 cm width). Navigation applied was mainly Decca Main Chain. The 2014-2016 SPARDIG project (Chand et al., 2016) was supported by NGU, AkerBP (Det Norske), Lundin Norway and the Seabed Project. In the project, IPGS has transformed 374 rolls of analogue sparker lines in 17 different surveys into SEG-Y format. The total length of converted survey lines is 31 261 kilometers. Rolls were scanned at 600 dpi and converted into SEG-Y using the SeisTrans (Caldera software) application (Miles et al., 2007). SeisTrans uses interactive, iterative and repeatable steps in a dedicated graphics window. A first step allows definition of axes and scales, then record time lines (horizontal TWT times and navigation time lines down the record) are picked and removed, and traces are defined. At this step, control tools are available to ensure the quality of the traces. After that, navigation information extracted and interpolated from excel files are added to trace headers. A continuous QC process allows production of SEG-Y files directly readable by interpretation software. The SEG-Y data will be delivered to the Norwegian Discos National Repository (https://portal.diskos.cgg.com/whereoil-data/) but access will be restricted to participants until 1st April 2019. IKU sparker lines have higher resolution than conventional 2D lines, but the penetration is limited. The data sets are complementary to each other. In 2D seismic lines, it is often difficult to delineate units in

  20. Geology and assessment of undiscovered oil and gas resources of the Laptev Sea Shelf Province, 2008

    Science.gov (United States)

    Klett, Timothy; Pitman, Janet K.; Moore, Thomas E.; Gautier, Donald L.

    2017-12-21

    The U.S. Geological Survey (USGS) recently assessed the potential for undiscovered oil and gas resources of the Laptev Sea Shelf Province as part of the 2008 Circum-Arctic Resource Appraisal (CARA) program. The province is situated in the Russian Federation and is located between the Taimyr Peninsula and the Novosibirsk (New Siberian) Islands. Three assessment units (AUs) were defined for this study: the West Laptev Grabens AU, the East Laptev Horsts AU, and the Anisin-Novosibirsk AU, two of which were assessed for undiscovered, technically recoverable resources. The East Laptev Horsts AU was not quantitatively assessed. The estimated mean volumes of undiscovered oil and gas for the Laptev Sea Shelf Province are approximately 3 billion barrels of crude oil, 32 trillion cubic feet of natural gas, and <1 billion barrels of natural gas liquids, all north of the Arctic Circle.

  1. 75 FR 16830 - Geological and Geophysical Exploration (G&G) on the Mid- and South Atlantic Outer Continental...

    Science.gov (United States)

    2010-04-02

    ... DEPARTMENT OF THE INTERIOR Minerals Management Service Geological and Geophysical Exploration (G&G..., geological and geochemical sampling, and remote sensing. These activities could support siting needs for... Continental Shelf (see http://www.mms.gov/ld/PDFs/GreenBook-LeasingDocument.pdf ) and MMS's Geological and...

  2. Inner-shelf ocean dynamics and seafloor morphologic changes during Hurricane Sandy

    Science.gov (United States)

    Warner, John C.; Schwab, William C.; List, Jeffrey; Safak, Ilgar; Liste, Maria; Baldwin, Wayne E.

    2017-01-01

    Hurricane Sandy was one of the most destructive hurricanes in US history, making landfall on the New Jersey coast on Oct 30, 2012. Storm impacts included several barrier island breaches, massive coastal erosion, and flooding. While changes to the subaerial landscape are relatively easily observed, storm-induced changes to the adjacent shoreface and inner continental shelf are more difficult to evaluate. These regions provide a framework for the coastal zone, are important for navigation, aggregate resources, marine ecosystems, and coastal evolution. Here we provide unprecedented perspective regarding regional inner continental shelf sediment dynamics based on both observations and numerical modeling over time scales associated with these types of large storm events. Oceanographic conditions and seafloor morphologic changes are evaluated using both a coupled atmospheric-ocean-wave-sediment numerical modeling system and observation analysis from a series of geologic surveys and oceanographic instrument deployments focused on a region offshore of Fire Island, NY. The geologic investigations conducted in 2011 and 2014 revealed lateral movement of sedimentary structures of distances up to 450 m and in water depths up to 30 m, and vertical changes in sediment thickness greater than 1 m in some locations. The modeling investigations utilize a system with grid refinement designed to simulate oceanographic conditions with progressively increasing resolutions for the entire US East Coast (5-km grid), the New York Bight (700-m grid), and offshore of Fire Island, NY (100-m grid), allowing larger scale dynamics to drive smaller scale coastal changes. Model results in the New York Bight identify maximum storm surge of up to 3 m, surface currents on the order of 2 ms-1 along the New Jersey coast, waves up to 8 m in height, and bottom stresses exceeding 10 Pa. Flow down the Hudson Shelf Valley is shown to result in convergent sediment transport and deposition along its axis

  3. West Florida shelf circulation and temperature budget for the 1998 fall transition

    Science.gov (United States)

    He, Ruoying; Weisberg, Robert H.

    2003-05-01

    Mid-latitude continental shelves undergo a fall transition as the net heat flux changes from warming to cooling. Using in situ data and a numerical model we investigate the circulation on the west Florida shelf (WFS) for the fall transition of 1998. The model is a regional adaptation of the primitive equation, Princeton Ocean Model forced by NCEP reanalysis wind, air pressure, and heat flux fields, plus river inflows. After comparison with observations the model is used to draw inferences on the seasonal and synoptic scale features of the shelf circulation. By running twin experiments, one without and the other with an idealized Loop Current (LC), we explore the relative importance of local versus deep-ocean forcing. We find that local forcing largely controls the inner-shelf circulation, including changes from the Florida Panhandle in the north to regions farther south. The effects of the LC in fall 1998 are to reinforce the mid-shelf currents and to increase the across-shelf transports in the bottom Ekman layer, thereby accentuating the shoreward transport of cold, nutrient rich water of deep-ocean origin. A three-dimensional analysis of the temperature budget reveals that surface heat flux largely controls both the seasonal and synoptic scale temperature variations. Surface cooling leads to convective mixing that rapidly alters temperature gradients. One interesting consequence is that upwelling can result in near-shore warming as warmer offshore waters are advected landward. The temperature balances on the shelf are complex and fully three-dimensional.

  4. Eddy-resolving simulations of the Fimbul Ice Shelf cavity circulation: Basal melting and exchange with open ocean

    Science.gov (United States)

    Hattermann, T.; Smedsrud, L. H.; Nøst, O. A.; Lilly, J. M.; Galton-Fenzi, B. K.

    2014-10-01

    Melting at the base of floating ice shelves is a dominant term in the overall Antarctic mass budget. This study applies a high-resolution regional ice shelf/ocean model, constrained by observations, to (i) quantify present basal mass loss at the Fimbul Ice Shelf (FIS); and (ii) investigate the oceanic mechanisms that govern the heat supply to ice shelves in the Eastern Weddell Sea. The simulations confirm the low melt rates suggested by observations and show that melting is primarily determined by the depth of the coastal thermocline, regulating deep ocean heat fluxes towards the ice. Furthermore, the uneven distribution of ice shelf area at different depths modulates the melting response to oceanic forcing, causing the existence of two distinct states of melting at the FIS. In the simulated present-day state, only small amounts of Modified Warm Deep Water enter the continental shelf, and ocean temperatures beneath the ice are close to the surface freezing point. The basal mass loss in this so-called state of "shallow melting" is mainly controlled by the seasonal inflow of solar-heated surface water affecting large areas of shallow ice in the upper part of the cavity. This is in contrast to a state of "deep melting", in which the thermocline rises above the shelf break depth, establishing a continuous inflow of Warm Deep Water towards the deep ice. The transition between the two states is found to be determined by a complex response of the Antarctic Slope Front overturning circulation to varying climate forcings. A proper representation of these frontal dynamics in climate models will therefore be crucial when assessing the evolution of ice shelf basal melting along this sector of Antarctica.

  5. Continental shelf drowned landscapes: Submerged geomorphological and sedimentary record of the youngest cycles

    NARCIS (Netherlands)

    Cohen, K.M.; Lobo, F.J.

    2013-01-01

    Continental shelves today find themselves largely submerged as a consequence of the sea-level rise in the last 20,000 years, the time since the Last Glacial Maximum (LGM), the period of maximum ice mass and minimum ocean volume within the Last Glacial Cycle. Their geomorphology, however, is far from

  6. Mapping Mesophotic Reefs Along the Brazilian Continental Margin

    Science.gov (United States)

    Bastos, A.; Moura, R.; Amado Filho, G.; Ferreira, L.; Boni, G.; Vedoato, F.; D'Agostini, D.; Lavagnino, A. C.; Leite, M. D.; Quaresma, V.

    2017-12-01

    Submerged or drowned reefs constitute an important geological record of sea level variations, forming the substrate for the colonization of modern benthic mesophotic communities. Although mapping mesophotic reefs has increased in the last years, their spatial distribution is poorly known and the worldwide occurrence of this reef habitat maybe underestimated. The importance in recognizing the distribution of mesophotic reefs is that they can act as a refuge for corals during unsuitable environmental conditions and a repository for shallow water corals. Here we present the result of several acoustic surveys that mapped and discovered new mesophotic reefs along the Eastern and Equatorial Brazilian Continental Margin. Seabed mapping was carried out using multibeam and side scan sonars. Ground truthing was obtained using drop camera or scuba diving. Mesophotic reefs were mapped in water depths varying from 30 to 100m and under distinct oceanographic conditions, especially in terms of river load input and shelf width. Reefs showed distinct morphologies, from low relief banks and paleovalleys to shelf edge ridges. Extensive occurrence of low relief banks were mapped along the most important coralline complex province in the South Atlantic, the Abrolhos Shelf. These 30 to 40m deep banks, have no more than 3 meters in height and may represent fringing reefs formed during sea level stabilization. Paleovalleys mapped along the eastern margin showed the occurrence of coralgal ledges along the channel margins. Paleovalleys are usually deeper than 45m and are associated with outer shelf rhodolith beds. Shelf edge ridges (80 to 120m deep) were mapped along both margins and are related to red algal encrusting irregular surfaces that have more than 3m in height, forming a rigid substrate for coral growth. Along the Equatorial Margin, off the Amazon mouth, shelf edge patch reefs and rhodolith beds forming encrusting surfaces and shelf edge ridges were mapped in water depths greater

  7. Shelf-life dating of shelf-stable strawberry juice based on survival analysis of consumer acceptance information.

    Science.gov (United States)

    Buvé, Carolien; Van Bedts, Tine; Haenen, Annelien; Kebede, Biniam; Braekers, Roel; Hendrickx, Marc; Van Loey, Ann; Grauwet, Tara

    2018-07-01

    Accurate shelf-life dating of food products is crucial for consumers and industries. Therefore, in this study we applied a science-based approach for shelf-life assessment, including accelerated shelf-life testing (ASLT), acceptability testing and the screening of analytical attributes for fast shelf-life predictions. Shelf-stable strawberry juice was selected as a case study. Ambient storage (20 °C) had no effect on the aroma-based acceptance of strawberry juice. The colour-based acceptability decreased during storage under ambient and accelerated (28-42 °C) conditions. The application of survival analysis showed that the colour-based shelf-life was reached in the early stages of storage (≤11 weeks) and that the shelf-life was shortened at higher temperatures. None of the selected attributes (a * and ΔE * value, anthocyanin and ascorbic acid content) is an ideal analytical marker for shelf-life predictions in the investigated temperature range (20-42 °C). Nevertheless, an overall analytical cut-off value over the whole temperature range can be selected. Colour changes of strawberry juice during storage are shelf-life limiting. Combining ASLT with acceptability testing allowed to gain faster insight into the change in colour-based acceptability and to perform shelf-life predictions relying on scientific data. An analytical marker is a convenient tool for shelf-life predictions in the context of ASLT. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

  8. Recent trends in the abundance of plaice Pleuronectes platessa and cod Gadus morhua in shallow coastal waters of the Northeastern Atlantic continental shelf – a review

    DEFF Research Database (Denmark)

    Dutz, Jörg; Støttrup, Josianne Gatt; Stenberg, Claus

    2016-01-01

    of the southern distribution boundary in the Bay of Biscay and deepening of stocks in the North Sea. In contrast, no trend in shallow water abundance of plaice similar to a decline in deep-water stocks during the 1970s and their slow recovery during the 2000s is apparent in the Skagerrak/Kattegat. Although......Shallow, near-shore water habitats on the continental shelf of the Northeast Atlantic have been productive fishing areas in the past. Here, we review the present knowledge about (i) recent trends in the abundance of plaice and cod in these habitats and (ii) hypotheses regarding the factors...... responsible for any trends. At present, only a few studies exist on the trends of abundance of plaice or cod, namely from the Bay of Biscay, the North Sea and the Skagerrak/Kattegat. They suggest a declining abundance in coastal, shallow areas and – at least for plaice – a latitudinal gradient with an erosion...

  9. Speciation and spatial distribution of solid-phase iron in surface sediments of the East China Sea continental shelf

    International Nuclear Information System (INIS)

    Zhu, Mao-Xu; Hao, Xiao-Chen; Shi, Xiao-Ning; Yang, Gui-Peng; Li, Tie

    2012-01-01

    Speciation and reactivity characterization of solid-phase Fe in marine sediments are of significance to understanding its heterogeneous mineralogy and crystallinity, the diagenetic cycling of Fe and its regulating roles on many other elements in sediments. In this study, a combination of sequential and single-step extractions was used for the determination of seven Fe pools in surface sediments of the East China Sea (ECS) continental shelf: (1) carbonate associated Fe (Fe(II) carb ) plus acid volatile sulfide-Fe (Fe(II) AVS ), (2) easily reducible amorphous/poorly crystalline Fe oxides (Fe ox1 ), (3) reducible crystalline Fe oxides (Fe ox2 ), (4) magnetite (Fe mag ), (5) poorly reactive sheet silicate Fe (Fe PRS ), (6) pyrite-Fe (Fe py ), and (7) unreactive silicate Fe (Fe U ). Total Fe (Fe T ) in the sediments is largely determined by terrestrial aluminosilicate particles as indicated by a great similarity of the Fe T with that of the Yangtze River and global riverine particulates. The size of Fe PRS is found to be the largest pool, followed by Fe U , Fe ox2 , Fe mag , Fe(II) AVS+carb , Fe ox1 and Fe py . The large Fe PRS may result from neoformation of Fe-rich clay minerals via reverse weathering and subsequent ageing. The small sizes of Fe(II) AVS+carb and Fe py pools is believed to be the result of low SO 4 reduction due to generally low labile organic matter together with the oxic/suboxic, dynamic environments of the surface sediments. The occurrence of Fe ox1 , Fe ox2 and Fe PRS in the sediments is closely associated with the clay fraction as indicated by a high spatial correlation between the former and the latter. Highly reactive Fe(Fe HR ) in the sediments is comparable to that in global marine sediments, but apparently lower than in the Yangtze River and global riverine particulates due probably to sequestration in the Yangtze Estuary. The ratios of Fe HR /Fe T , Fe PR /Fe T and Fe U /Fe T in the ECS surface sediments consistently show more similarity to

  10. Verdine and other associated authigenic (glaucony, phosphate) facies from the surficial sediments of the southwestern continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Lamboy, M.; Dupeuble, P.A.

    spaced contorted clay blades and globules. X-ray mineralogy suggests that these grains are a mixture of verdine dominated minerals. Phyllite C is the principal verdine mineral in the shelf zone. On the continental slope phyllite V dominates between 100... grains from the shelf are mostly homogeneous at low magnification (Fig. 4A). However, at high magnification the authigenic clays are characterized by small con- torted blades (1 Ixm long) at some places and compact clays (Fig. 4B and C) at others...

  11. Geomorphology and surficial geology of the western continental shelf and slope of India: A review

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Wagle, B.G.

    Coastal geology and geomorphology of the area and nearshore currents played a significant role in the distribution of placer minerals off Kerala and Maharashtra. Transport and sedeimentation of fine-grained materials at places on the shelf...

  12. Tidal Modulation of Ice-shelf Flow: a Viscous Model of the Ross Ice Shelf

    Science.gov (United States)

    Brunt, Kelly M.; MacAyeal, Douglas R.

    2014-01-01

    Three stations near the calving front of the Ross Ice Shelf, Antarctica, recorded GPS data through a full spring-neap tidal cycle in November 2005. The data revealed a diurnal horizontal motion that varied both along and transverse to the long-term average velocity direction, similar to tidal signals observed in other ice shelves and ice streams. Based on its periodicity, it was hypothesized that the signal represents a flow response of the Ross Ice Shelf to the diurnal tides of the Ross Sea. To assess the influence of the tide on the ice-shelf motion, two hypotheses were developed. The first addressed the direct response of the ice shelf to tidal forcing, such as forces due to sea-surface slopes or forces due to sub-ice-shelf currents. The second involved the indirect response of ice-shelf flow to the tidal signals observed in the ice streams that source the ice shelf. A finite-element model, based on viscous creep flow, was developed to test these hypotheses, but succeeded only in falsifying both hypotheses, i.e. showing that direct tidal effects produce too small a response, and indirect tidal effects produce a response that is not smooth in time. This nullification suggests that a combination of viscous and elastic deformation is required to explain the observations.

  13. Métodos gravi-magnetométricos modernos para analizar las características estructurales de la plataforma continental Argentina

    Directory of Open Access Journals (Sweden)

    Antonio Introcaso

    2008-12-01

    Full Text Available El análisis de la composición y estructura del margen continental argentino implica realizar el estudio de sus cortezas continental y oceánica, de los fallamientos y de las cuencas sedimentarias involucradas (localización, geometría y espesor sedimentario. Como una contribución a COPLA (Comisión Nacional del Límite Exterior de la Plataforma Continental, quien se encuentra abocada al estudio de nuestra plataforma continental, hemos realizado un estudio piloto sobre la cuenca de Claromecó (provincia de Buenos Aires, y su extensión a la plataforma continental. A los métodos gravi-magnetométricos tradicionales que definen modelos desde las inversiones 2D, 2½D y 3D, agregamos para este estudio: a Métodos semi-empíricos: deconvolución de Euler y Werner, señal analítica, gradientes y cambios de gradientes; éstos permiten definir lineamientos, contactos y fallas. b Estudios de la isoterma de Curie obtenida en base al análisis espectral de las anomalías magnéticas (determinación de las profundidades del basamento magnético, de su techo y fondo a través de la temperatura de Curie. Su ascenso-descenso anómalo es de primera importancia para comprender, desde su historia, el estado cortical actual. c Estudios de características corticales (espesor y densidad que involucra el estado isostático, a partir de ondulaciones del geoide N; probable movilidad futura en monto y signo. d Doble inversión de gravedad g y ondulaciones del geoide N, para obtener mayor consistencia en el modelado. Mediante la aplicación de esta metodología sobre la cuenca de Claromecó, se han encontrado lineamientos de gran importancia y se certificó el balance isostático. Se determinó que la cuenca presenta un espesor sedimentario del orden de la tercera parte del espesor cortical normal de la zona.The Argentinean continental shelf will be studied by analysing the continental and the oceanic crusts, the faulting and the neighbour sedimentary basins. In

  14. A geoelectrical survey above an Antarctic ice shelf

    Directory of Open Access Journals (Sweden)

    M. Pavan

    1998-06-01

    Full Text Available A geoelectrical survey was performed on the Hells Gate ice shelf (Victoria Land-Antarctic within the framework of an integrated geophysical and glaciological research program. The resistivity profiles show a similar trend, with resistivity values ranging from about 25000 W · m to 500000 W · m. These results have been interpreted as the effect of a sharp transition from "marine ice" to "continental" ice an interpretation that is consistent with the results of surface mapping. Interpreting the Vertical Electrical Soundings (VES is a complex process. In fact, the alternating layers of ice with different compositions and salt content generate great uncertainty relative to the corresponding electric stratigraphies. To solve these problems of equivalency, all the available constraints were used including the drilling thickness, seismic reflection profiles as well as radar profiles. The results were used to provide what is mainly a qualitative overview that is coherent with the glaciological hypotheses relative to the evolution and structure proposed by some researchers for this ice shelf.

  15. Coexisting sea-based and land-based sources of contamination by PAHs in the continental shelf sediments of Coatzacoalcos River discharge area (Gulf of Mexico).

    Science.gov (United States)

    Ruiz-Fernández, Ana Carolina; Portela, Julián Mauricio Betancourt; Sericano, José Luis; Sanchez-Cabeza, Joan-Albert; Espinosa, Luisa Fernanda; Cardoso-Mohedano, José Gilberto; Pérez-Bernal, Libia Hascibe; Tinoco, Jesús Antonio Garay

    2016-02-01

    The oldest refinery and the major petrochemical complexes of Mexico are located in the lower reach of the Coatzacoalcos River, considered the most polluted coastal area of Mexico. A (210)Pb-dated sediment core, from the continental shelf of the Coatzacoalcos River, was studied to assess the contamination impact by the oil industry in the southern Gulf of Mexico. The sedimentary record showed the prevalence of petrogenic PAHs between 1950s and 1970s, a period during which waste discharges from the oil industry were not regulated. Later on, sediments exhibited higher contents of pyrogenic PAHs, attributed to the incineration of petrochemical industry wastes and recurrent wildfires in open dumpsites at the nearby swamps. The total concentration of the 16 EPA-priority PAHs indicated low levels of contamination (1000 ng g(-1)) during the late 1970s, most likely due to the major oil spill produced by the blowout of the Ixtoc-I offshore oil rig in deep waters of the southwestern Gulf of Mexico. Most of the PAH congeners did not show defined temporal trends but, according to a Factor Analysis, apparently have a common origin, probably waste released from the nearby oil industry. The only exceptions were the pyrogenic benzo(b)fluoranthene and benzo(a)pyrene, and the biogenic perylene, that showed increasing concentration trends with time, which we attributed to erosional input of contaminated soil from the catchment area. Our study confirmed chronic oil contamination in the Coatzacoalcos River coastal area from land based sources for more than 60 years (since 1950s). Copyright © 2015 Elsevier Ltd. All rights reserved.

  16. Sedimentary characteristics and controlling factors of shelf sand ridges in the Pearl River Mouth Basin, northeast of South China Sea

    Directory of Open Access Journals (Sweden)

    Xiangtao Zhang

    2017-04-01

    Full Text Available Shelf sand ridge is a significant type of reservoir in the continental marginal basin, and it has drawn so much attention from sedimentologists and petroleum geologists. We were able to investigate the morphology, distribution, and sedimentary structures of shelf sand ridges systematically in this study based on the integration of high-resolution 3D seismic data, well logging, and cores. These shelf sand ridges are an asymmetrical mound-like structure in profiles, and they developed on an ancient uplift in the forced regression system tract and are onlapped by the overlying strata. In the plane, shelf sand ridges present as linear-shaped, which is different from the classical radial pattern; not to mention, they are separated into two parts by low amplitude tidal muddy channels. Corrugated bedding, tidal bedding, and scouring features are distinguished in cores of shelf sand ridges together with the coarsening up in lithology. All of these sedimentary characteristics indicate that shelf sand ridges deposited in the Pearl River Mouth Basin are reconstructed by the tidal and coastal current.

  17. The salinity signature of the cross-shelf exchanges in the Southwestern Atlantic Ocean: Numerical simulations.

    Science.gov (United States)

    Matano, Ricardo P; Combes, Vincent; Piola, Alberto R; Guerrero, Raul; Palma, Elbio D; Ted Strub, P; James, Corinne; Fenco, Harold; Chao, Yi; Saraceno, Martin

    2014-11-01

    A high-resolution model is used to characterize the dominant patterns of sea surface salinity (SSS) variability generated by the freshwater discharges of the Rio de la Plata (RdlP) and the Patos/Mirim Lagoon in the southwestern Atlantic region. We identify three dominant modes of SSS variability. The first two, which have been discussed in previous studies, represent the seasonal and the interannual variations of the freshwater plumes over the continental shelf. The third mode of SSS variability, which has not been discussed hitherto, represents the salinity exchanges between the shelf and the deep ocean. A diagnostic study using floats and passive tracers identifies the pathways taken by the freshwater plumes. During the austral winter (JJA) , the plumes leave the shelf region north of the BMC. During the austral summer (DJF), the plumes are entrained more directly into the BMC. A sensitivity study indicates that the high - frequency component of the wind stress forcing controls the vertical structure of the plumes while the low-frequency component of the wind stress forcing and the interannual variations of the RdlP discharge controls the horizontal structure of the plumes. Dynamical analysis reveals that the cross-shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean. The net cross-shelf volume flux is 1.21 Sv. This outflow is largely compensated by an inflow from the Patagonian shelf.

  18. Circumpolar Deep Water transport and current structure at the Amundsen Sea shelf break

    Science.gov (United States)

    Assmann, Karen M.; Wåhlin, Anna K.; Heywood, Karen J.; Jenkins, Adrian; Kim, Tae Wan; Lee, Sang Hoon

    2017-04-01

    The West Antarctic Ice Sheet has been losing mass at an increasing rate over the past decades. Ocean heat transport to the ice-ocean interface has been identified as an important contributor to this mass loss and the role it plays in ice sheet stability makes it crucial to understand its drivers in order to make accurate future projections of global sea level. While processes closer to the ice-ocean interface modulate this heat transport, its ultimate source is located in the deep basin off the continental shelf as a core of relatively warm, salty water underlying a colder, fresher shallow surface layer. To reach the marine terminating glaciers and the base of floating ice shelves, this warm, salty water mass must cross the bathymetric obstacle of the shelf break. Glacial troughs that intersect the Amundsen shelf break and deepen southwards towards the ice shelf fronts have been shown to play an important role in transporting warm, salty Circumpolar Deep Water (CDW) towards the ice shelves. North of the shelf break, circulation in the Amundsen Sea occupies an intermediate regime between the eastward Antarctic Circumpolar Current that impinges on the shelf break in the Bellingshausen Sea and the westward southern limb of the Ross Gyre that follows the shelf break in the Ross Sea. Hydrographic and mooring observations and numerical model results at the mouth of the central shelf break trough leading to Pine Island and Thwaites Glaciers show a westward wind-driven shelf break current overlying an eastward undercurrent that turns onto the shelf in the trough. It is thought that the existence of the latter feature facilitates the on-shelf transport of CDW. A less clearly defined shelf break depression further west acts as the main pathway for CDW to Dotson and eastern Getz Ice shelves. Model results indicate that a similar eastward undercurrent exists here driving the on-shelf transport of CDW. Two moorings on the upper slope east of the trough entrance show a

  19. Productivity and linkages of the food web of the southern region of the western Antarctic Peninsula continental shelf

    Science.gov (United States)

    Ballerini, Tosca; Hofmann, Eileen E.; Ainley, David G.; Daly, Kendra; Marrari, Marina; Ribic, Christine A.; Smith, Walker O.; Steele, John H.

    2014-03-01

    The productivity and linkages in the food web of the southern region of the west Antarctic Peninsula continental shelf were investigated using a multi-trophic level mass balance model. Data collected during the Southern Ocean Global Ocean Ecosystem Dynamics field program were combined with data from the literature on the abundance and diet composition of zooplankton, fish, seabirds and marine mammals to calculate energy flows in the food web and to infer the overall food web structure at the annual level. Sensitivity analyses investigated the effects of variability in growth and biomass of Antarctic krill (Euphausia superba) and in the biomass of Antarctic krill predators on the structure and energy fluxes in the food web. Scenario simulations provided insights into the potential responses of the food web to a reduced contribution of large phytoplankton (diatom) production to total primary production, and to reduced consumption of primary production by Antarctic krill and mesozooplankton coincident with increased consumption by microzooplankton and salps. Model-derived estimates of primary production were 187-207 g C m-2 y-1, which are consistent with observed values (47-351 g C m-2 y-1). Simulations showed that Antarctic krill provide the majority of energy needed to sustain seabird and marine mammal production, thereby exerting a bottom-up control on higher trophic level predators. Energy transfer to top predators via mesozooplanton was a less efficient pathway, and salps were a production loss pathway because little of the primary production they consumed was passed to higher trophic levels. Increased predominance of small phytoplankton (nanoflagellates and cryptophytes) reduced the production of Antarctic krill and of its predators, including seabirds and seals.

  20. Quaternary nanofossils on the Brazilian continental shelf; Nanofosseis calcarios do quaternario da margem continental brasileira

    Energy Technology Data Exchange (ETDEWEB)

    Antunes, Rogerio Loureiro [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas (CENPES). Gerencia de Bioestratigrafia e Paleoecologia], E-mail: rlantunes@petrobras.com.br

    2007-07-01

    The study of calcareous nanofossils occurring in the deposits on the Brazilian continental margin began in the late 1960s, undertaken solely by PETROBRAS. Instead of presenting an academic outlook, the purpose of these investigations is first to formulate a biostratigraphic framework to apply to oil well samples. The initial result was the first zoning for the Brazilian continental margin, which considered the deposits formed between the Aptian and Miocene series. Since the 1960s to date, many papers have been written either with details of that original zoning or applying nanofossil biostratigraphy to solve stratigraphic problems. Regardless of all the papers and studies undertaken, little attention has been paid to the Quaternary, since these deposits are normally of no interest to petroleum geology stricto sensu, especially in a large part of the Brazilian margin. On the other hand, there are a few articles and some Master's dissertations and PhD theses that were written and/or are in progress in Brazilian universities. On the other hand, elsewhere in the world, Quaternary nanofossils have been thoroughly investigated in terms of biostratigraphy and paleoceanography. It is, therefore, very clear that there is a gap between what is being done elsewhere in the world and what has been done in Brazil. In fact, this gap is not larger simply because of a few researchers in Brazilian universities who are studying this topic. The intention of this paper is to contribute toward a richer study of Quaternary nanofossils. It, therefore, contains illustrations and taxonomic descriptions of many species observed in the younger strata of the Brazilian margin basins. This article not only aspires to portray and disseminate the potential of nanofossils for the marine Quaternary study but is also an invitation to students (under and post-graduates) and university researchers - an invitation to learn a little more about the subject and spend some time studying these real gems

  1. Quaternary nanofossils on the Brazilian continental shelf; Nanofosseis calcarios do quaternario da margem continental brasileira

    Energy Technology Data Exchange (ETDEWEB)

    Antunes, Rogerio Loureiro [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas (CENPES). Gerencia de Bioestratigrafia e Paleoecologia], E-mail: rlantunes@petrobras.com.br

    2007-07-01

    The study of calcareous nanofossils occurring in the deposits on the Brazilian continental margin began in the late 1960s, undertaken solely by PETROBRAS. Instead of presenting an academic outlook, the purpose of these investigations is first to formulate a biostratigraphic framework to apply to oil well samples. The initial result was the first zoning for the Brazilian continental margin, which considered the deposits formed between the Aptian and Miocene series. Since the 1960s to date, many papers have been written either with details of that original zoning or applying nanofossil biostratigraphy to solve stratigraphic problems. Regardless of all the papers and studies undertaken, little attention has been paid to the Quaternary, since these deposits are normally of no interest to petroleum geology stricto sensu, especially in a large part of the Brazilian margin. On the other hand, there are a few articles and some Master's dissertations and PhD theses that were written and/or are in progress in Brazilian universities. On the other hand, elsewhere in the world, Quaternary nanofossils have been thoroughly investigated in terms of biostratigraphy and paleoceanography. It is, therefore, very clear that there is a gap between what is being done elsewhere in the world and what has been done in Brazil. In fact, this gap is not larger simply because of a few researchers in Brazilian universities who are studying this topic. The intention of this paper is to contribute toward a richer study of Quaternary nanofossils. It, therefore, contains illustrations and taxonomic descriptions of many species observed in the younger strata of the Brazilian margin basins. This article not only aspires to portray and disseminate the potential of nanofossils for the marine Quaternary study but is also an invitation to students (under and post-graduates) and university researchers - an invitation to learn a little more about the subject and spend some time studying these real gems of

  2. Do Continental Shelves Act as an Atmospheric CO2 Sink?

    Science.gov (United States)

    Cai, W.

    2003-12-01

    Recent air-to-sea CO2 flux measurements at several major continental shelves (European Atlantic Shelves, East China Sea and U.S. Middle Atlantic Bight) suggest that shelves may act as a one-way pump and absorb atmospheric CO2 into the ocean. These observations also favor the argument that continental shelves are autotrophic (i.e., net production of organic carbon, OC). The U.S. South Atlantic Bight (SAB) contrasts these findings in that it acts as a strong source of CO2 to the atmosphere while simultaneously exporting dissolved inorganic carbon (DIC) to the open ocean. We report pCO2, DIC, and alkalinity data from the SAB collected in 8 cruises along a transect from the shore to the shelf break in the central SAB. The shelf-wide net heterotrophy and carbon exports in the SAB are subsidized by the export of OC from the abundant intertidal marshes, which are a sink for atmospheric CO2. It is proposed here that the SAB represents a marsh-dominated heterotrophic ocean margin as opposed to river-dominated autotrophic margins. To further investigate why margins may behave differently in term of CO2 sink/source, the physical and biological conditions of several western boundary current margins are compared. Based on this and other studies, DIC export flux from margins to the open ocean must be significant in the overall global ocean carbon budget.

  3. Inner-shelf ocean dynamics and seafloor morphologic changes during Hurricane Sandy

    Science.gov (United States)

    Warner, John C.; Schwab, William C.; List, Jeffrey H.; Safak, Ilgar; Liste, Maria; Baldwin, Wayne

    2017-04-01

    Hurricane Sandy was one of the most destructive hurricanes in US history, making landfall on the New Jersey coast on October 30, 2012. Storm impacts included several barrier island breaches, massive coastal erosion, and flooding. While changes to the subaerial landscape are relatively easily observed, storm-induced changes to the adjacent shoreface and inner continental shelf are more difficult to evaluate. These regions provide a framework for the coastal zone, are important for navigation, aggregate resources, marine ecosystems, and coastal evolution. Here we provide unprecedented perspective regarding regional inner continental shelf sediment dynamics based on both observations and numerical modeling over time scales associated with these types of large storm events. Oceanographic conditions and seafloor morphologic changes are evaluated using both a coupled atmospheric-ocean-wave-sediment numerical modeling system that covered spatial scales ranging from the entire US east coast (1000 s of km) to local domains (10 s of km). Additionally, the modeled response for the region offshore of Fire Island, NY was compared to observational analysis from a series of geologic surveys from that location. The geologic investigations conducted in 2011 and 2014 revealed lateral movement of sedimentary structures of distances up to 450 m and in water depths up to 30 m, and vertical changes in sediment thickness greater than 1 m in some locations. The modeling investigations utilize a system with grid refinement designed to simulate oceanographic conditions with progressively increasing resolutions for the entire US East Coast (5-km grid), the New York Bight (700-m grid), and offshore of Fire Island, NY (100-m grid), allowing larger scale dynamics to drive smaller scale coastal changes. Model results in the New York Bight identify maximum storm surge of up to 3 m, surface currents on the order of 2 ms-1 along the New Jersey coast, waves up to 8 m in height, and bottom stresses

  4. Comparative organic geochemistry of Indian margin (Arabian Sea) sediments: estuary to continental slope

    Science.gov (United States)

    Cowie, G.; Mowbray, S.; Kurian, S.; Sarkar, A.; White, C.; Anderson, A.; Vergnaud, B.; Johnstone, G.; Brear, S.; Woulds, C.; Naqvi, S. W.; Kitazato, H.

    2014-02-01

    Surface sediments from sites across the Indian margin of the Arabian Sea were analysed for their carbon and nitrogen compositions (elemental and stable isotopic), grain size distributions and biochemical indices of organic matter (OM) source and/or degradation state. Site locations ranged from the estuaries of the Mandovi and Zuari rivers to depths of ~ 2000 m on the continental slope, thus spanning nearshore muds and sands on the shelf and both the semi-permanent oxygen minimum zone (OMZ) on the upper slope (~ 200-1300 m) and the seasonal hypoxic zone that impinges on the shelf. Source indices showed mixed marine and terrigenous OM within the estuaries, and overwhelming predominance (80%+) of marine OM on the shelf and slope. Thus, riverine OM is heavily diluted by autochthonous marine OM and/or is efficiently remineralised within or immediately offshore of the estuaries. Any terrigenous OM that is exported appears to be retained in nearshore muds; lignin phenols indicate that the small terrigenous OM content of slope sediments is of different origin, potentially from rivers to the north. Organic C contents of surface shelf and slope sediments varied from winnowing and/or dilution) on the shelf and progressive OM degradation with increasing oxygen exposure below the OMZ. Reduced oxygen exposure may contribute to OM enrichment at some sites within the OMZ, but hydrodynamic processes are the overriding control on sediment OM distribution.

  5. Spatially Resolving Ocean Color and Sediment Dispersion in River Plumes, Coastal Systems, and Continental Shelf Waters

    Science.gov (United States)

    Aurin, Dirk Alexander; Mannino, Antonio; Franz, Bryan

    2013-01-01

    Satellite remote sensing of ocean color in dynamic coastal, inland, and nearshorewaters is impeded by high variability in optical constituents, demands specialized atmospheric correction, and is limited by instrument sensitivity. To accurately detect dispersion of bio-optical properties, remote sensors require ample signal-to-noise ratio (SNR) to sense small variations in ocean color without saturating over bright pixels, an atmospheric correction that can accommodate significantwater-leaving radiance in the near infrared (NIR), and spatial and temporal resolution that coincides with the scales of variability in the environment. Several current and historic space-borne sensors have met these requirements with success in the open ocean, but are not optimized for highly red-reflective and heterogeneous waters such as those found near river outflows or in the presence of sediment resuspension. Here we apply analytical approaches for determining optimal spatial resolution, dominant spatial scales of variability ("patches"), and proportions of patch variability that can be resolved from four river plumes around the world between 2008 and 2011. An offshore region in the Sargasso Sea is analyzed for comparison. A method is presented for processing Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua and Terra imagery including cloud detection, stray lightmasking, faulty detector avoidance, and dynamic aerosol correction using short-wave- and near-infrared wavebands in extremely turbid regions which pose distinct optical and technical challenges. Results showthat a pixel size of approx. 520 mor smaller is generally required to resolve spatial heterogeneity in ocean color and total suspended materials in river plumes. Optimal pixel size increases with distance from shore to approx. 630 m in nearshore regions, approx 750 m on the continental shelf, and approx. 1350 m in the open ocean. Greater than 90% of the optical variability within plume regions is resolvable with

  6. Interannual changes in seafloor surficial geology at an artificial reef site on the inner continental shelf

    Science.gov (United States)

    Raineault, Nicole A.; Trembanis, Arthur C.; Miller, Douglas C.; Capone, Vince

    2013-04-01

    The influence of reef structures on seafloor surface sediments has implications for marine spatial planning and coastal development, including use of the coastal zone for offshore wind energy. We present results of interannual changes in seafloor surficial geology at the Redbird artificial reef site, located on the continental shelf offshore of Delaware Bay. The Redbird reef is composed of NYC subway cars, barges, tugboats, and other sunken objects. Since objects were added sporadically between 1996 and 2009, the survey area acts as a natural laboratory to study the evolution of the surrounding seafloor at a structural reef habitat through time. Annual side-scan surveys from 2008 through 2011, and one bathymetric survey in 2010 provide information about surface geology and morphology. Local wave and current data for this time period were analyzed to determine the main morphological agents. Automated backscatter segmentation show that three bottom types dominate and that these large-scale (>10 m) surface sediment patterns persist from year to year. Grab samples reveal that the bottom types are silty sand with clay and sandy gravel. Clear sediment and biological patterns emerged revealing the influence of the objects on the seafloor. Comet-shaped moats of sandy gravel surround single objects and grow to form large-scale coalesced patches around groups of objects. Alignment of sediment patches suggests the periodic hydrodynamic influence of seasonal storms. The abundance and diversity of organisms increases with decreasing clay/silt content. Evidence of scour includes the removal of fine sediments, the formation of moats 1-30 m in diameter and 0.5-1 m deep around the reef objects, and the >1 m settling of objects into the seafloor. Data suggest subway cars reached equilibrium with the environment in 6-7 years, but that larger objects or clusters of objects take a longer time to equilibrate and have farther-reaching effects. Knowledge of local wave and current climate

  7. Four new species of free-living marine nematodes of the family Desmodoridae (Nematoda: Desmodorida) and a redescription of Desmodora nini (Inglis, 1963) from the continental shelf off northeastern Brazil.

    Science.gov (United States)

    Larrazábal-Filho, Alexandre L; Silva, Maria Cristina Da; Esteves, André M

    2015-09-24

    Four new species of marine nematodes were collected from the continental shelf of the Potiguar Basin in northeastern Brazil. Zalonema vicentei sp. n. and Zalonema mariae sp. n. are characterized by having multispiral fovea amphidialis, lateral alae and ventral ala. These features also are found in Pseudochromadora, Desmodorella and Psammonema. They differ in the cephalic arrangement, and shape of the cephalic capsule and the fovea amphidialis. Croconema fortis sp. n. resembles Desmodora in the shape of the fovea amphidialis and cephalic capsule, but differs in the number of subcephalic setae and ornamentation on the cuticule. Desmodora paraconica sp. n. is characterized by the loop-shaped fovea amphidialis and the long conical-cylindrical tail. This species is similar to the genus Bolbonema, but differs in having the cephalic setae anterior to the fovea amphidialis. Desmodora nini is redescribed, to record details lacking in the original description.

  8. Continental shelf sediment dynamics in the Anthropocene: A global shift

    Science.gov (United States)

    Oberle, Ferdinand K. J.; Puig, Pere; Martin, Jacobo

    2017-04-01

    Recent technological advances in remote sensing and deep marine sampling have revealed the extent and magnitude of the anthropogenic impacts to the seafloor. In particular, bottom trawling, a fishing technique consisting of dragging a net and fishing gear over the seafloor to capture bottom-dwelling living resources has gained attention due to its destructive effects on the seabed. Trawling gear produces acute impacts on biota and the physical substratum of the seafloor by disrupting the sediment column structure, overturning boulders, resuspending sediments and imprinting deep scars on muddy bottoms. Also, the repetitive passage of trawling gear over the same areas creates long-lasting, cumulative impacts that modify the cohesiveness and texture of sediments. It can be asserted nowadays that due to its recurrence, mobility and wide geographical extent, industrial trawling has become a major force driving seafloor change and affecting not only its physical integrity on short spatial scales but also imprinting measurable modifications to the geomorphology of entire continental margins.

  9. Managing the visual effects of outer continental shelf and other petroleum-related coastal development

    Science.gov (United States)

    Philip A. Marcus; Ethan T. Smith

    1979-01-01

    Five petroleum-related facilities often sited in the coastal zone during development of Outer Continental oil and gas can change the visual appearance of coastal areas. These facilities are service bases, platform fabrication yards, marine terminals and associated storage facilities, oil and gas processing facilities, and liquified natural gas terminals. Examples of...

  10. Anatomy of a shoreface sand ridge revisted using foraminifera: False Cape Shoals, Virginia/North Carolina inner shelf

    Science.gov (United States)

    Robinson, Marci M.; McBride, Randolph A.

    2008-01-01

    Certain details regarding the origin and evolution of shelf sand ridges remain elusive. Knowledge of their internal stratigraphy and microfossil distribution is necessary to define the origin and to determine the processes that modify sand ridges. Fourteen vibracores from False Cape Shoal A, a well-developed shoreface-attached sand ridge on the Virginia/North Carolina inner continental shelf, were examined to document the internal stratigraphy and benthic foraminiferal assemblages, as well as to reconstruct the depositional environments recorded in down-core sediments. Seven sedimentary and foraminiferal facies correspond to the following stratigraphic units: fossiliferous silt, barren sand, clay to sandy clay, laminated and bioturbated sand, poorly sorted massive sand, fine clean sand, and poorly sorted clay to gravel. The units represent a Pleistocene estuary and shoreface, a Holocene estuary, ebb tidal delta, modern shelf, modern shoreface, and swale fill, respectively. The succession of depositional environments reflects a Pleistocene sea-level highstand and subsequent regression followed by the Holocene transgression in which barrier island/spit systems formed along the Virginia/North Carolina inner shelf not, vert, ~5.2 ka and migrated landward and an ebb tidal delta that was deposited, reworked, and covered by shelf sand.

  11. Distribution patterns and enrichment of lead, zinc and copper in surface sediments of the central Portuguese shelf and upper slope

    NARCIS (Netherlands)

    Jesus, C.C.; de Stigter, H.; Miranda, P.; Oliveira, A.; Rocha, F.

    2013-01-01

    Geographic patterns of Cu, Pb and Zn enrichment on the Lisbon-Setúbal-Sines continental shelf and upper slope (central Portuguese margin) were studied in this paper to gain insight into current pathways of trace metal dispersal. Our study is based on the analysis of elemental concentrations and

  12. Morphology and sedimentology of glacigenic submarine fans on the west Greenland continental margin

    Science.gov (United States)

    O'Cofaigh, Colm; Hogan, Kelly A.; Dowdeswell, Julian A.; Jennings, Anne E.; Noormets, Riko; Evans, Jeffrey

    2014-05-01

    Along the West Greenland continental margin adjoining Baffin Bay, bathymetric data show a series of large submarine fans located at the mouths of cross-shelf troughs. Two of these fans, the Uummannaq Fan and the Disko Fan are trough-mouth fans built largely of debris delivered from ice sheet outlets of the Greenland Ice Sheet during past glacial maxima. On the Uummannaq Fan glacigenic debris flow deposits occur on the upper slope and extend to at least 1800 m water depth in front of the trough-mouth. The debris flow deposits are related to the remobilisation of subglacial debris that was delivered onto the upper slope at times when an ice stream was positioned at the shelf edge. In contrast, sedimentary facies from the northern sector of the fan are characterised by hemipelagic and ice-rafted sediments and turbidites; glacigenic debris flows are notably absent in cores from this region. Further south along the Greenland continental margin the surface of the Disko Fan is prominently channelised and associated sediments are acoustically stratified. Although glacigenic debris flow deposits do occur on the upper Disko Fan, sediments recovered in cores from elsewhere on the fan record the influence of turbidity current and meltwater sedimentation. The channelised form of the Disko fan contrasts markedly with that of the Uummannaq Fan and, more widely, with trough mouth fans from the Polar North Atlantic. Collectively these data highlight the variability of glacimarine depositional processes operating on trough-mouth fans on high-latitude continental slopes and show that glacigenic debris flows are but one of a number of mechanisms by which such large glacially-influenced depocentres form.

  13. A numerical study of the Plata River plume along the southeastern South American continental shelf

    Directory of Open Access Journals (Sweden)

    Felipe M. Pimenta

    2005-12-01

    Full Text Available The Rio de la Plata, one of the largest rivers on Earth, discharges into the ocean waters from basin that covers a large area of South America. Its plume extends along northern Argentina, Uruguay, and southern Brazil shelves strongly influencing the ecosystems. In spite of this, little is known about the mechanisms that control it. Here we report results of simulations with POM carried out to investigate the roles of wind and river discharge in Plata plume dynamics. Different outflows were explored, including an average climatological value and magnitudes representative of La Niña and El Niño. Forcing the model with river discharge the average plume speed was directly related to the outflow intensity. The Plata northward extension varied from 850 to 1550 km and for average discharge a band of low salinity waters formed from the estuary up to 30ºN of South Brazilian Shelf. Upwelling and downwelling winds were applied after 130 days. The distribution of low salinity waters over the shelf was more sensitive to the wind direction than to the river outflow variability. Downwelling winds were very capable of advecting the low salinity signal downshelf. Upwelling winds were efficient in eroding the plume, which was basically detached from the coast by Ekman drift. Abnormal plume intrusions toward low latitudes may be a result of the original plume position coupled with events of persistent strong downwelling favorable winds.O Rio da Prata, um dos maiores rios da Terra, descarrega no oceano águas de uma bacia de drenagem que cobre uma ampla área da América do Sul. Sua pluma extende-se ao longo do norte da Argentina, Uruguay e sul do Brasil influenciando amplamente os ecossistemas costeiros. A despeito disso, pouco se sabe a respeito dos mecanismos que a controlam. Relatamos aqui simulações conduzidas com o modelo POM na investigação do papel dos ventos e da descarga fluvial na dinâmica da pluma do Prata. Descargas com valores médios climatol

  14. Projecting the effects of climate change on Calanus finmarchicus distribution within the U.S. Northeast Continental Shelf.

    Science.gov (United States)

    Grieve, Brian D; Hare, Jon A; Saba, Vincent S

    2017-07-24

    Calanus finmarchicus is vital to pelagic ecosystems in the North Atlantic Ocean. Previous studies suggest the species is vulnerable to the effects of global warming, particularly on the Northeast U.S. Shelf, which is in the southern portion of its range. In this study, we evaluate an ensemble of six different downscaled climate models and a high-resolution global climate model, and create a generalized additive model (GAM) to examine how future changes in temperature and salinity could affect the distribution and density of C. finmarchicus. By 2081-2100, we project average C. finmarchicus density will decrease by as much as 50% under a high greenhouse gas emissions scenario. These decreases are particularly pronounced in the spring and summer in the Gulf of Maine and Georges Bank. When compared to a high-resolution global climate model, the ensemble showed a more uniform change throughout the Northeast U.S. Shelf, while the high-resolution model showed larger decreases in the Northeast Channel, Shelf Break, and Central Gulf of Maine. C. finmarchicus is an important link between primary production and higher trophic levels, and the decrease projected here could be detrimental to the North Atlantic Right Whale and a host of important fishery species.

  15. Holocene submarine terraces on the western continental shelf of India; implications for sea-level changes

    Digital Repository Service at National Institute of Oceanography (India)

    Wagle, B.G.; Vora, K.H.; Karisiddaiah, S.M.; Veerayya, M.; Almeida, F.

    and the shelf break, being more common between 11~' and 20~'N. The terraces are prominent between water depths of 50 and 115 m and occur at six distinct levels: (1) 55-60 m, (2) 65-70 m, (3) 75-80 m, (4) 85-90 m, (5) 95-100 m and (6) 110-115 m...

  16. Productivity and linkages of the food web of the southern region of the western Antarctic Peninsula continental shelf

    Science.gov (United States)

    Ballerini, Tosca; Hofmann, Eileen E.; Ainley, David G.; Daly, Kendra L.; Marrari, Marina; Ribic, Christine A.; Smith, Walker O.; Steele, John H.

    2014-01-01

    The productivity and linkages in the food web of the southern region of the west Antarctic Peninsula continental shelf were investigated using a multi-trophic level mass balance model. Data collected during the Southern Ocean Global Ocean Ecosystem Dynamics field program were combined with data from the literature on the abundance and diet composition of zooplankton, fish, seabirds and marine mammals to calculate energy flows in the food web and to infer the overall food web structure at the annual level. Sensitivity analyses investigated the effects of variability in growth and biomass of Antarctic krill (Euphausia superba) and in the biomass of Antarctic krill predators on the structure and energy fluxes in the food web. Scenario simulations provided insights into the potential responses of the food web to a reduced contribution of large phytoplankton (diatom) production to total primary production, and to reduced consumption of primary production by Antarctic krill and mesozooplankton coincident with increased consumption by microzooplankton and salps. Model-derived estimates of primary production were 187–207 g C m−2 y−1, which are consistent with observed values (47–351 g C m−2 y−1). Simulations showed that Antarctic krill provide the majority of energy needed to sustain seabird and marine mammal production, thereby exerting a bottom-up control on higher trophic level predators. Energy transfer to top predators via mesozooplanton was a less efficient pathway, and salps were a production loss pathway because little of the primary production they consumed was passed to higher trophic levels. Increased predominance of small phytoplankton (nanoflagellates and cryptophytes) reduced the production of Antarctic krill and of its predators, including seabirds and seals.

  17. Preliminary Facies Reconstruction of a Late Pleistocene Cypress Forest Discovered on the Northern Gulf of Mexico Continental Shelf

    Science.gov (United States)

    Gonzalez Rodriguez, S. M.; Bentley, S. J.; DeLong, K. L.; Xu, K.; Caporaso, A.; Obelcz, J. B.; Harley, G. L.; Reese, C. A.; Truong, J. T.

    2016-12-01

    We are investigating the origin and preservation of an ancient bald cypress forest (Taxodium distichum) discovered on the continental shelf seafloor, offshore of Gulf Shores, Alabama, USA, in 20 m water depth. The forest was likely buried in the late Pleistocene, possibly exhumed by Hurricane Ivan in 2004, and is now exposed as stumps in life position with little evidence of decay before recent marine exposure. Radiocarbon analyses show that the forest age is near (and in some cases beyond) the limits of 14C dating, at least 41-45 ky BP. In August 2015 and July 2016, submersible vibracores (up to 5 m in length) were collected. Ongoing core analyses include: organic content (loss on ignition), granulometry, and core logging using a Geotek Multi Sensor Core Logger to generate imagery, bulk density, and x-ray fluorescence data. To bolster 14C analyses, cores collected in 2016 are presently being dated using optically stimulated luminescence. Local stratigraphy consists of a surface facies of Holocene transgressive sands, underlain by possible estuarine sediments of interbedded sand and mud (potentially Holocene or Pleistocene), overlying a swamp or delta plain facies (likely Pleistocene) containing woody debris and mud. Deeper woody facies are thought to include the soil horizons of the ancient cypress forest. Cores collected in 2016 revealed a Pleistocene paleosol beneath Holocene sands in a nearby trough. Elevation differences between swamp and paleosol horizons will be evaluated from bathymetric and subbottom data, to help characterize the preserved ancient landscape. Initial interpretation based on close proximity of Pleistocene swamp and oxidized paleosol sediments, and regional geomorphic gradients suggest that this relatively diverse assemblage of facies developed up to tens of km from the glacial-age coastline, and relatively rapid burial prevented erosion by coastal processes during the Holocene transgression thus preserving the tree stumps and wood debris.

  18. Effect of radioactive pollution on the biodiversity of marine benthic ecosystems of the Russian Arctic shelf

    Science.gov (United States)

    Alexeev, Denis K.; Galtsova, Valentina V.

    2012-07-01

    This study is the result of many years of research on the ecology of the marine benthos of Russian Arctic seas. We used samples collected at various locations from the Russian continental shelf during 1993-2009 as the basis of our study. Our main aim was to analyze the spatial distribution of taxonomic and quantitative characteristics of the meiobenthos (small bottom-dwelling animals, 0.1-3.0 mm in size). Statistical analysis of the data revealed that the factors determining the spatial distribution of meiobenthic organisms under natural conditions, and conditions impacted upon by human activity, were salinity, water depth, hydrocarbons, heavy metals and radiocaesium volumetric activity. The possible use of the meiobenthos as a tool for environmental impact assessment is proposed and discussed on the level of higher taxa.

  19. Do high oil prices justify an increase in taxation in a mature oil province? The case of the UK continental shelf

    International Nuclear Information System (INIS)

    Nakhle, Carole

    2007-01-01

    In response to the structural shift in oil price coupled with greater import dependency, concerns about security of supply have once again emerged as a major policy issue. The UK, the largest producer of oil and natural gas in the European Union, became a net importer of natural gas in 2004, and according to Government estimates will become a net importer of oil by the end of the decade. A weakened North Sea performance means extra reliance, both for the UK and Europe as a whole, on global oil and gas network and imports. In 2002, the UK Government introduced a 10% supplementary charge and in 2005, doubled the charge to 20% in an attempt to capture more revenues from the oil industry as a result of the increase in the price of crude oil. However, higher tax rates do not necessarily generate higher fiscal revenue and in the long term may result in materially lower revenues if investment is discouraged as indeed occurred when the 2007 UK Annual Budget statement showed a shortfall in North Sea oil revenues below forecasts of Pounds 4 billion. It is therefore argued that the increase in the fiscal take came at the wrong time for the UK Continental Shelf and that the UK Government's concern should have been to encourage more oil production from its declining province, especially in the light of the rising concern surrounding the security of supply

  20. Observed tidal currents on the continental shelf off the west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Subeesh, M.P.; Unnikrishnan, A.S.; Fernando, V.; Agarwadekar, Y.; Khalap, S.T.; Satelkar, N.P.; Shenoi, S.S.C.

    tidal currents have been widely studied around the world ocean particularly on the continental shelves and slopes (for example, Huthnance, 1989; Holloway et al., 2001; Xu et al., 2011b, 2013). The astronomical forcing mainly leads to the generation... directions. Internal tides have temporal scales from inertial to local Brunt-Väisälä frequency (f < σ < N), where σ is the internal wave frequency and f and N are inertial and buoyancy frequencies respectively. The direct astronomical forcing...