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Sample records for alaska continental shelf

  1. 76 FR 7518 - Outer Continental Shelf Air Regulations Consistency Update for Alaska

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-10

    ... AGENCY 40 CFR Part 55 Outer Continental Shelf Air Regulations Consistency Update for Alaska AGENCY... of the Outer Continental Shelf (``OCS'') Air Regulations. Requirements applying to OCS sources..., Intergovernmental relations, Nitrogen dioxide, Nitrogen oxides, Outer Continental Shelf, Ozone, Particulate...

  2. 75 FR 3392 - Outer Continental Shelf Air Regulations Consistency Update for Alaska

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-01-21

    ... AGENCY 40 CFR Part 55 Outer Continental Shelf Air Regulations Consistency Update for Alaska AGENCY... 50.410. Requirements applying to Outer Continental Shelf (``OCS'') sources located within 25 miles of..., Intergovernmental relations, Nitrogen dioxide, Nitrogen oxides, Outer Continental Shelf, Ozone, Particulate...

  3. 76 FR 37274 - Outer Continental Shelf Air Regulations Consistency Update for Alaska

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-06-27

    ... AGENCY 40 CFR Part 55 Outer Continental Shelf Air Regulations Consistency Update for Alaska AGENCY... of the Outer Continental Shelf (``OCS'') Air Regulations proposed in the Federal Register on February..., Nitrogen oxides, Outer Continental Shelf, Ozone, Particulate matter, Permits, Reporting and...

  4. 78 FR 60892 - Outer Continental Shelf (OCS), Alaska OCS Region, Chukchi Sea Planning Area, Proposed Oil and Gas...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-10-02

    ... Bureau of Ocean Energy Management Outer Continental Shelf (OCS), Alaska OCS Region, Chukchi Sea Planning Area, Proposed Oil and Gas Lease Sale 237 (Lease Sale 237) MMAA104000 AGENCY: Bureau of Ocean Energy... addressed in this Call (``Program Area'') is located offshore Alaska in the Chukchi Sea Planning Area....

  5. Map of Distribution of Bottom Sediments on the Continental Shelf, Gulf of Alaska

    USGS Publications Warehouse

    Evans, Kevin R.; Carlson, Paul R.; Hampton, Monty A.; Marlow, Michael S.; Barnes, Peter W.

    2000-01-01

    Introduction The U.S. Geological Survey has a long history of exploring marine geology in the Gulf of Alaska. As part of a cooperative program with other federal and state agencies, the USGS is investigating the relations between ocean-floor geology and benthic marine biohabitats. This bottom sediment map, compiled from published literature will help marine biologists develop an understanding of sea-floor geology in relation to various biological habitats. The pattern of sea-floor sedimentation and bottom morphology in the Gulf of Alaska reflects a complex interplay of regional tectonism, glacial advances and retreats, oceanic and tidal currents, waves, storms, eustatic change, and gravity-driven processes. This map, based on numerous cruises during the period of 1970-1996, shows distribution of bottom sediments in areas of study on the continental shelf. The samples were collected with piston, box, and gravity corers, and grab samplers. The interpretations of sediment distribution are the products of sediment size analyses combined with interpretations of high-resolution seismic reflection profiles. The sea floor was separated into several areas as follows: Cook Inlet -- Hazards studies in this embayment emphasized sediment distribution, sediment dynamics, bedforms, shallow faults, and seafloor stability. Migrating mega-sandwaves, driven by strong tidal currents, influence seabed habitats and stability of the seafloor, especially near pipelines and drilling platforms. The coarseness of the bottom sediment reinforces the influence of the strong tidal currents on the seafloor habitats. Kodiak Shelf -- Tectonic framework studies demonstrate the development of an accretionary wedge as the Pacific Plate underthrusts the Alaskan landmass. Seismic data across the accretionary wedge reveal anomalies indicative of fluid/gas vent sites in this segment of the continental margin. Geologic hazards research shows that movement along numerous shallow faults poses a risk to sea

  6. 76 FR 53481 - Outer Continental Shelf, Alaska OCS Region, Chukchi Sea Planning Area, Oil and Gas Lease Sale 193

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-08-26

    ..., Chukchi Sea Planning Area, Oil and Gas Lease Sale 193 AGENCY: Bureau of Ocean Energy Management... Continental Shelf (OCS) Oil and Gas Lease Sale 193, Chukchi Sea, Alaska (OCS EIS/EA BOEMRE 2011-041). BOEMRE... Final EIS, Oil and Gas Lease Sale 193, Chukchi Sea Planning Area (OCS EIS/EA MMS 2007-026). BOEMRE will...

  7. 76 FR 30956 - Outer Continental Shelf, Alaska OCS Region, Chukchi Sea Planning Area, Oil and Gas Lease Sale 193

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-05-27

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management, Regulation and Enforcement Outer Continental Shelf, Alaska OCS Region, Chukchi Sea Planning Area, Oil and Gas Lease Sale 193 AGENCY: Bureau of Ocean Energy...

  8. 75 FR 63504 - Outer Continental Shelf, Alaska OCS Region, Chukchi Sea Planning Area, Oil and Gas Lease Sale 193

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-10-15

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management, Regulation and Enforcement Outer Continental Shelf, Alaska OCS Region, Chukchi Sea Planning Area, Oil and Gas Lease Sale 193 AGENCY: Bureau of Ocean Energy...

  9. Splay faults and tsunamigenic sources across the continental shelf from 1964 great Alaska earthquake

    NASA Astrophysics Data System (ADS)

    Liberty, L. M.; Haeussler, P. J.; Moeller, M.

    2013-12-01

    Using tsunami run up, seismic reflection and bathymetric data, we identify tsunamigenic sea floor ruptures that resulted from the 1964 Great Alaska earthquake. These sea floor lineaments are rooted in megathrust splay faults that appear across the 500-km wide Gulf of Alaska continental shelf. Based on estimated tsunami travel times, we identify two splay faults that produced 5-10 m wave heights in the coastal town of Seward and remote settlements along the Kenai Peninsula. These faults splay from the megathrust along the trailing edge of the subducted Yakutat terrane that is sandwiched between the Pacific and North American plates. Duplexing along the megathrust likely transferred lateral motion along the decollement to vertical splay fault motion that resulted in multi-meter sea floor uplifts. We identify the Cape Cleare fault as the source of the earliest tsunami arrival for Seward, Puget Bay and Whidbey Bay. Sparker seismic data, pre- and post-earthquake bathymetry and crustal seismic data characterize the along-strike Holocene motion on this 70-km long fault that parallels the Patton Bay fault that ruptured on nearby Montague Island. We define a strand of the Middleton Island fault system as the source of the second arrival in Puget and Whidbey Bays and the earliest tsunami source on Middleton Island and other sites in the eastern Gulf of Alaska. Sea floor displacements of more than 20 m suggest both of these faults have repeatedly ruptured during Holocene earthquakes. Additionally, we identify a series of active thrust faults along the length of the Gulf of Alaska to Kodiak Island that likely initiated tsunami waves from smaller sea floor displacements. Sea floor offsets and splay faults that are mapped along the length of the continental shelf suggest Holocene coseismic rupture patterns are not reflected in interseismic GPS measurements along the Kenai Peninsula, but are consistent with seismic, tsunami, and geodetic measurements from the 1964 earthquake

  10. A Continental Shelf Sediment Transport Proxy Record of Decadal Atmospheric and Oceanographic Variability in Southern Alaska

    NASA Astrophysics Data System (ADS)

    Vienne, W. F.; Jaeger, J.

    2004-12-01

    The Gulf of Alaska (GOA) margin is a prime location to study and quantitatively model glacial climate and continental margin sedimentation. Coupled oceanographic and atmospheric processes control sediment transport and sedimentation patterns on the GOA continental shelf, and consequently contain a proxy record for regional climate variability. However, the specifics of this coupled relationship between climate and sediment transport have not been studied. In collaboration with the GOA-NEP GLOBEC program, gravity cores were taken at three sites of high sedimentation rates along the GOA margin in 2001 and 2003 representing proximal and distal shelf depocenters. Chronologies were established using Pb-210 and Cs-137 and sedimentation rates vary from 0.3 to 3 cm/yr, providing near-annual to decadal-scale resolution. High-spatial resolution grain-size analyses and multi-sensor core logging of bulk density and magnetic susceptibility were measured to recognize relationships between these three proxies of sediment transport in each core and between sites. The time series of these properties have been compared to oceanographic and atmospheric instrumental records--generally beginning in the early to middle 20th century--such as sea level pressure, temperature, significant wave height, and wind speed. The three measured properties positively correlate within each core and between each core, indicating that these are likely controlled by similar sediment transport processes, such as wave resuspension and bottom-current transport, at all three sites. Strong correlation on a decadal scale was found between the physical properties of the cores and the instrumental records of temperature and significant wave height, as well as variability in regional precipitation. Also, there is a marked increase in bulk density, magnetic susceptibility, and grain size values from the late 1970's onward, which corresponds to the timing of a shift from a negative to a positive regime in the

  11. Surface sedimentary units of the Gulf of Alaska continental shelf: Montague Island to Yakutat Bay

    USGS Publications Warehouse

    Molnia, Bruce F.

    1977-01-01

    Four major sedimentary units occur on the sea floor of the continental shelf in the northern Gulf of Alaska. These units, defined on the basis of seismic and sedimentologic data, are: (1) Holocene sediments, (2) Holocene mind moraines, C3) Quaternary glacial marine sediments, and (4) Tertiary and Pleistocene lithified deposits. A wedge of Holocene fine sand to clayey silt covers most of the inner shelf, reaching maximum thicknesses of about 350 m seaward of the Copper River and about 200 m seaward of Icy Bay. Holocene end moraines are found at the mouth of Icy Bay, south of Bering Glacier, and at the mouth of Yakutat Bay. Quaternary glacial marine sediments are found in a narrow arc that borders, on the north and west side of Tart Bank and in a large arc 20 km or more offshore that parallels the shoreline between Kayak Island and Yakutat Bay. Tertiary or Pleistocene stratified sedimentary rocks, which in profile commonly are folded, faulted, and truncated, crop out on Tarr Bank, offshore of Montague Island, and in several localities southeast and southwest of Cape Yakataga. The lack of Holocene cover on Tarr Bank and Middleton, Kayak and Montague Island platforms may be due to the scouring action of swift bottom currents and large storm waves. West of Kayak Island the Copper River is the primary source of Holocene sediment. East of Kayak Island the major sediment sources are streams draining the larger ice fields, notably, the Malaspina and Bering Glaciers. Transport of bottom and suspended sediment is predominantly to the west. If deglaciation of the shelf was completed by 10,000 years B.P., maximum rates of accumulation of Holocene sediment on the inner shelf may be as high as 10-35 m per 1,000 years.

  12. The origin, distribution, and depositional history of gravel deposits on the Beaufort Sea Continental Shelf, Alaska

    USGS Publications Warehouse

    Rodeick, Craig A.

    1979-01-01

    Two distinct gravel populations are present on the Beaufort Sea continental shelf. First, a geographically arcuate deposit that is convex seaward has been designated as the Chert Facies. This deposit is restricted to landward of the 10 meter bathymetric contour and west of Heald Point. The Chert Facies, originally a fluvial gravel deposit and probably part of the basal transgressive, represents reworked Gubik Formation. The Chert Facies is derived from the Brooks Range. The second population is the Dolomite Facies. This facies is a blanket deposit covering much of the shelf and occurs in most water depths greater than 10 meters. The Dolomite Facies extends on land into the Quaternary Gubik Formation east of Prudhoe Bay and probably to Point Barrow. Rocks of the Dolomite Facies are exotic to Alaska and represent ice rafted clasts. The distribution of the Dolomite Facies shelf gravel indicates an easterly source compatible with a proposed provenance surrounding the Amundsen Gulf of the Canadian Archipelago. Radiocarbon dates from undisturbed sediment underlying the gravel on the upper slope indicate that low Holocene sedimentation rates are the reason for gravel exposure in this region and on the outer shelf. Considerations of sea level fluctuations, possible times available for the transportation of gravel from the proposed source area to the study area, and radiocarbon dates indicate influxes of ice rafted debris during the mid-Wisconsin transgression and probably between 15, 000-10,000 years B. P. Correlation of the Gubik Formation at Heald Point with the Barrow unit of the Gubik Formation at Point Barrow on the basis of incorporated dolomite and orthoquartzite clasts is suggested.

  13. Submarine faults and slides on the continental shelf, northern Gulf of Alaska

    USGS Publications Warehouse

    Carlson, Paul R.; Molnia, Bruce F.

    1977-01-01

    Submarine faults and slides or slumps of Quaternary age are potential environmental hazards on the outer continental shelf (OCS) of the northern Gulf of Alaska. Most faults that approach or reach the seafloor cut strata that may be equivalent in age to the upper Yakataga Formation (Pliocene‐Pleistocene). Along several faults, the seafloor is vertically offset from 5 to 20 m. A few faults appear to cut Holocene sediments, but none of these shows displacement at the seafloor. Submarine slides or slumps have been found in two places in the OCS region: (1) seaward of the Malaspina Glacier and Icy Bay, an area of 1200 km2 with a slope of less than 0.5°, and (2) across the entire span of the Copper river prodelta, an area of 1730 km2, having a slope of about 0.5°. Seismic profiles across these areas show disrupted reflectors and irregular topography commonly associated with submarine slides or slumps. Potential slide or slump areas have been delineated in areas of thick sediment accumulation and relatively steep slopes. These areas include (1) Kayak Trough, (2) parts of Hinchinbrook Entrance and Sea Valley, (3) parts of the outer shelf and upper slope between Kayak Island and Yakutat Bay, and (4) Bering Trough.

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

    USGS Publications Warehouse

    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

  15. Neotectonics and basin development at a continental/island arc transition in the Western Alaska Peninsula shelf

    SciTech Connect

    Newcomb, K.R.

    1985-01-01

    A transition in shelf structure occurs between the eastern Alaska Peninsula and the Aleutians. In the east, compressive structures striking parallel to the margin characterize the outer shelf off of Kodiak, Chirikov, and Semidi Islands. Further to the west, multichannel seismic (MSC) data exhibit a systematic transition in style of deformation and orientation of recently active structures in the shelf region of the Shumagin and Sanak Islands. In this area, deformation near the trench slope break is manifested by drapelike folds and normal faults striking parallel to the margin. In contrast, further west between the Shumagin and Sanak Island, MCS profiles for the shelf region reveal basement-involved extensional structures transverse to the margin that have controlled the development of the Sanak and East Sanak Basis. These fault bounded basins have hanging wall sequences with syndepositional rotational displacements over normal faults, indicating a protracted history of extensional faulting and basin subsidence. Present displacement is indicated by the effects of many of the faults upon the uppermost basin and shelf strata, which in some cases offset the sea floor. The aforementioned systematic change in shelf structure of the Alaska Peninsula is coincident with an arcward shift in bathymetric contours of the trench and slope. This transition zone, from margin-parallel compressive structures in the east, to margin-transverse extensional structures in the west, coincides with the continental to island arc transition in the North American plate that reflects the ancient Beringian margin of western Alaska.

  16. Oil-spill risk analysis: Outer continental shelf lease sale 158, Gulf of Alaska/Yakutat. Final report

    SciTech Connect

    Anderson, C.M.; Johnson, W.R.; Marshall, C.F.; Lear, E.M.

    1995-01-01

    The Federal Government has proposed to offer Outer Continental Shelf lands in the Gulf of Alaska/Yakutat 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 report summarizes results of an oil-spill risk analysis conducted for OCS Lease Sale 158, Gulf of Alaska/Yakutat. The objective of this analysis was to estimate relative risks associated with oil and gas production for the proposed lease sale.

  17. Causes of two slope-failure types in continental-shelf sediment, northeastern Gulf of Alaska

    USGS Publications Warehouse

    Schwab, William C.; Lee, Homa J.

    1988-01-01

    Slumps and sediment-gravity flows have been identified in Holocene glaciomarine sediment on declivities less than 1.3 degrees on the Gulf of Alaska continental shelf. Geologic and geotechnical investigation suggest that the processes responsible for these slope failures are earthquake and storm-wave loading, coupled with cyclic degradation of the sediment-shear strength. We propose that the failure type is related to the nature of the failure load. For example, a slump that occurs approximately 30 km seaward of Icy Bay in water depth of 70 to 150 m was most likely caused by earthquake loading, whereas sediment-gravity flows on the Alsek prodelta, which occur in water depths of 35 to 80 m, probably were caused primarily by storm-wave loading. Sediment remolding and redistribution and incorporation of water, which occurs more readily during wave loading from a long storm than during the limited number of loading cycles generated by an earthquake, reduces the shear strength and increases the fluidity of the failed sediment mass. Wave-induced slope failures thereby tend to transform into sediment-gravity flows.

  18. Early Pleistocene to Holocene glacial activity along the southern Alaska continental shelf inferred from the sedimentary record in the northern Gulf of Alaska - preliminary results

    NASA Astrophysics Data System (ADS)

    Forwick, M.; Cowan, E. A.; Bahlburg, H.; Childress, L. B.; Jaeger, J. M.; Moy, C. M.; Müller, J.; Ribeiro, F.; Ridgway, K. D.; Gulick, S. P.; Worthington, L. L.; Reece, R.

    2013-12-01

    Preliminary analyses of the lithology at Site U1418 (IODP Expedition 341), located on the proximal Surveyor Fan, provide evidence of continuous presence of tidewater glaciers on the southern Alaska continental shelf for more than c. 1.2 Ma, as well as evidence of prolonged presence of grounded ice at the shelf break and/or the initiation of ice streams. The lowermost lithostratigraphic unit (Unit IV) of the 941 m long record is composed of heavily deformed sediments that are interpreted to be the top of the recently discovered Surveyor mass-transport deposit. Unit III contains mostly laminated mud with thin interbeds of sand, silt and clast-rich muddy diamict with rip-up clasts. A few lonestones of granule and pebble size are present. Massive and laminated mud with scattered lonestones, as well as interbedded intervals of clast-poor diamict (clasts of granule and pebble size) compose Unit II. Unit I contains massive mud with interbedded silt laminae and sand beds. Most silt laminae have the same color as the matrix, but some are lighter. Diatom oozes and graded sand beds occur infrequently and lonestones are present below 3 m. The dominance of mud suggests that sedimentation at Site U1418 was strongly influenced by suspension settling from turbid meltwater plumes emanating into the Gulf of Alaska during the past c. 1.2 Ma. Laminated intervals may reflect temporal variations in meltwater runoff from a single sediment source and/or supply from several sources during the deposition of Units II and III. Lonestones and clasts of granule and pebble size are regarded to be mostly iceberg-rafted debris, indicating that tidewater glaciers have been present on the continental shelf for most of the time since the onset of the deposition of Unit III. Diamicts in Unit II most probably reflect periods of enhanced ice rafting and/or reduced meltwater runoff. Minor silt and sand beds provide evidence of occasional sediment reworking during the deposition of Units II and III. The

  19. An evaluation of petrogenic hydrocarbons in northern Gulf of Alaska continental shelf sediments - The role of coastal oil seep inputs

    USGS Publications Warehouse

    Short, J.W.; Kolak, J.J.; Payne, J.R.; Van Kooten, G. K.

    2007-01-01

    We compared hydrocarbons in water, suspended particulate matter (SPM), and riparian sediment collected from coastal watersheds along the Yakataga foreland with corresponding hydrocarbons in Gulf of Alaska benthic sediments. This comparison allows an evaluation of hydrocarbon contributions to marine sediments from natural oil seeps, coal and organic matter (e.g., kerogen) associated with eroding siliciclastic rocks. The samples from oil seeps show extensive loss of low-molecular weight n-alkanes (Alaska, but overall seep inputs are largely attenuated by the (non-seep) petrogenic hydrocarbon content of the high SPM loads. In contrast to the geochemical signature of seep oil, Gulf of Alaska benthic sediments are characterized by abundant alkylated naphthalene homologues, relatively smooth n-alkane envelopes (n-C9 through n-C34, but with elevated levels of n-C27, n-C29, and n-C31), and small UCMs. Further, hydrocarbons in benthic sediments are highly intercorrelated. Taken together, these characteristics indicate that seep oil is a negligible petrogenic hydrocarbon source to the Gulf of Alaska continental shelf. Coaly material separated from the benthic sediment samples using a dense liquid (???2.00 g cm-3) also accounted for a minor portion of the total PAH (1-6%) and total n-alkanes (0.4-2%) in the benthic samples. Most of the hydrocarbon burden in the sediments is found in the denser sediment fraction and likely derives from organic matter contributed by denudation of siliciclastic formations in

  20. 75 FR 3423 - Outer Continental Shelf Air Regulations Consistency Update for Alaska

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-01-21

    ... direct effect on one or more Indian tribes, on the relationship between the Federal Government and Indian... OCS sources operating off of the State of Alaska. The intended effect of approving the OCS..., and special arrangements should be made for deliveries of boxed information. Please see the...

  1. An oilspill risk analysis for the Beaufort Sea, Alaska (proposed sale 71)outer continental shelf lease area

    USGS Publications Warehouse

    Samuels, W.B.; Hopkins, Dorothy; Lanfear, K.J.

    1981-01-01

    An oilspill risk analysis was conducted to determine the relative environmental hazards of developing oil in different regions of the Beaufort Sea, Alaska, (Proposed Sale 71) Outer Continental Shelf (OCS) lease area. The probability of spill occurrences, likely movement of oil slicks, and locations of resources vulnerable to spilled oil were analyzed. The model predicted movement of the center of spill mass and estimated the times between spill occurrence and contact with various resources, to allow a qualitative assessment of oil characteristics at the time of contact; no direct computation was made of weathering and cleanup. The model also assumed that any oil spilled under ice would remain in place, unchanged, until spring breakup. Ice movements, or travel of oil under ice, if occurring, would affect the results in a manner not directly predictable at this time. The combined results of spill occurrence and spill movement predictions yielded estimates of the overall risks associated with development of the proposed lease area. Assuming that oil exists in the lease area (a 99.3-percent chance) it is estimated that the leasing of the tracts proposed for OCS Sale 71 will result in an expected 9.2 oilspills (of 1,000 barrels or larger) over the lease lifetime of 25 years. This estimate is based on historic oilspill accident data for platforms and pipelines on the U.S. OCS (Gulf of Mexico and California). The estimated probability that land will be contacted by one or more oilspills (of 1,000 barrels or larger) that have been at sea less than 30 days (not counting any time trapped under ice) is greater than 99.5 percent. If oilspill accident data for Prudhoe Bay, Alaska, is used in the analysis, it is estimated that 5.6 oilspills (1,000 barrels or larger) will occur over the lease lifetime. The estimated probability that one or more oilspills (1,000 barrels or larger)will occur and contact land is99 percent. The results of a recent experimental cleanup operation for

  2. Climatic Atlas of the Outer Continental Shelf Waters and Coastal Regions of Alaska. Volume I. Gulf of Alaska.

    DTIC Science & Technology

    1977-01-01

    Gulf AEIDC of Mexico, and Caribbean Sea, and a comprehensive James L. Wise, M.S., an associate in climatology climatic atlas of New York Bight. His...Dissipation System Marine Climatology, the Marine Ecosystem Analysis at Elmendorf AFB, Alaska in the winter of 1972-73 Program, New York Bight Atlas...North Atlantic Harold W. Searby, M.S., meteorologist/climatolo- and long-term climatic variability over the New York gist with the Arctic

  3. Coordination: Southeast continental shelf studies

    SciTech Connect

    Menzel, D.W.

    1989-01-26

    The objective of this investigation is to obtain model descriptions of the flow modifications in the Southeast Atlantic continental shelf due to Gulf Stream fluctuations and topographic effects. 2 refs., 4 figs.

  4. Outer Continental Shelf Environmental Assessment Program: comprehensive bibliography, January 1988

    SciTech Connect

    Not Available

    1988-01-01

    The bibliography lists reports from investigators of the Alaska Outer Continental Shelf Environmental Assessment Program. Some non-program documents are also included. More than 3600 entries are sorted by author and citation number. Cross-references are available by Alaska region, discipline and research unit number.

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

    NASA Astrophysics Data System (ADS)

    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.

  6. Seasonal Control of Surface-Water Dissolved Iron Concentrations by Suspended Particle Concentrations on the Northern Gulf of Alaska Continental Shelf and Slope

    NASA Astrophysics Data System (ADS)

    Crusius, J.; Schroth, A. W.; Campbell, R.; Cullen, J. T.; Dillman, D.; Resing, J.

    2012-12-01

    The continental shelf region of the northern Gulf of Alaska (GoA) supports a productive ecosystem including an important commercial fishery. Downwelling winds during most of the year imply that some mechanism other than upwelling must be supplying the essential nutrients iron and nitrate. Although it is well known that iron limits productivity offshore in the GoA, we have a poor understanding of the controls on Fe supply. Data from cruises from 2010 provide some new insight into the mechanisms of Fe supply. Cruises were carried out along a transect extending from the mouth of the Copper River to ~40 km beyond the shelf break three times per year including early April, early May, and late July. High-resolution surface-water sampling was carried out, as well as bottle casts at 5 stations. High, fairly uniform concentrations of "total dissolvable iron" (TDFe; unfiltered sample acidified to pH=1.7) as well as "dissolved" Fe (dFe) were observed spanning the shelf in April, suggesting sediment resuspension is an important source of dFe to surface waters at that time. By contrast, high dFe and TDFe concentrations in late July coincide with low-salinity surface water, which in this location indicates a glacial meltwater source. Throughout spring and summer high particle concentrations across much of the shelf appear to "buffer" dFe concentrations to ~3 nmol/kg, which are close to those observed by Lippiatt et al (2010) in the region. This is consistent with dFe concentrations being determined by the organic ligand concentrations that, in turn, are fairly constant. In late July, surface water dFe concentrations are ~0.5 nmol/kg on the outer shelf and up to ~50 km further offshore. These dFe concentrations on the outer shelf are much lower in July than earlier in the year, owing to Fe removal by phytoplankton uptake and by scavenging, as well as by the lack of particulate Fe sources to surface waters in July. However, the high surface-water dFe observed ~50 km beyond the

  7. An evaluation of the science needs to inform decisions on Outer Continental Shelf energy development in the Chukchi and Beaufort Seas, Alaska

    USGS Publications Warehouse

    Holland-Bartels, Leslie; Pierce, Brenda

    2011-01-01

    On March 31, 2010, Secretary of the Interior Ken Salazar announced a national strategy for Outer Continental Shelf (OCS) oil and gas development. In that announcement, the Administration outlined a three-pronged approach (U.S. Department of the Interior, 2010a): Development: "...expand development and production throughout the Gulf of Mexico, including resource-rich areas of the Eastern Gulf of Mexico..." Exploration: "...expand oil and gas exploration in frontier areas, such as the Arctic Ocean and areas in the Atlantic Ocean, to gather the information necessary to develop resources in the right places and the right ways." Conservation: "...calls for the protection of special areas like Bristol Bay in Alaska...national treasure[s] that we must protect for future generations." In a companion announcement (U.S. Department of the Interior, 2010b), within the Administration's "Exploration" component, the Secretary asked the U.S. Geological Survey (USGS) to conduct an initial, independent evaluation of the science needs that would inform the Administration's consideration of the right places and the right ways in which to develop oil and gas resources in the Arctic OCS, particularly focused on the Beaufort and Chukchi Seas (fig. 1).

  8. 78 FR 59715 - Outer Continental Shelf (OCS), Alaska OCS Region, Chukchi Sea Planning Area, Proposed Oil and Gas...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-09-27

    ...), including specific support of those nominations in terms of geological and geophysical data, and (2) this... concerning geological conditions, including bottom hazards; archaeological sites on the seabed or nearshore... Web site at http://www.boem.gov/Oil-and-Gas-Energy-Program/Mapping-and-Data/Alaska.aspx . 4...

  9. 77 FR 18260 - Outer Continental Shelf (OCS), Alaska OCS Region, Cook Inlet Planning Area, Proposed Oil and Gas...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-03-27

    ... the Federal Register. Between 1978 and 1985, a total of 13 exploratory wells were drilled on Federal... Alaska currently has active oil and gas leases with two drill operations preparing for the 2012 drill... and marine mammals, physical oceanography, ocean-circulation modeling, subsistence uses, and...

  10. Coordination: southeast continental shelf studies. Progress report

    SciTech Connect

    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)

  11. 75 FR 9780 - Technical Amendment to the Outer Continental Shelf Air Regulations Consistency Update; Correction

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-04

    ... From the Federal Register Online via the Government Publishing Office ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 55 Technical Amendment to the Outer Continental Shelf Air Regulations Consistency... Outer Continental Shelf Air Regulations for Alaska. DATES: Effective on March 22, 2010. FOR...

  12. An evaluation of the science needs to inform decisions on Outer Continental Shelf energy development in the Chukchi and Beaufort Seas, Alaska

    USGS Publications Warehouse

    Holland-Bartels, Leslie; Pierce, Brenda

    2011-01-01

    The U. S. Geological Survey (USGS) was asked to conduct an initial, independent evaluation of the science needs that would inform the Administration's consideration of the right places and the right ways in which to develop oil and gas resources in the Arctic Outer Continental Shelf (OCS), particularly focused on the Beaufort and Chukchi Seas. Oil and gas potential is significant in Arctic Alaska. Beyond petroleum potential, this region supports unique fish and wildlife resources and ecosystems, and indigenous people who rely on these resources for subsistence. This report summarizes key existing scientific information and provides initial guidance of what new and (or) continued research could inform decision making. This report is presented in a series of topical chapters and various appendixes each written by a subset of the USGS OCS Team based on their areas of expertise. Three chapters (Chapters 2, 3, and 4) provide foundational information on geology; ecology and subsistence; and climate settings important to understanding the conditions pertinent to development in the Arctic OCS. These chapters are followed by three chapters that examine the scientific understanding, science gaps, and science sufficiency questions regarding oil-spill risk, response, and impact (Chapter 5), marine mammals and anthropogenic noise (Chapter 6), and cumulative impacts (Chapter 7). Lessons learned from the 1989 Exxon Valdez Oil Spill are included to identify valuable "pre-positioned" science and scientific approaches to improved response and reduced uncertainty in damage assessment and restoration efforts (appendix D). An appendix on Structured Decision Making (appendix C) is included to illustrate the value of such tools that go beyond, but incorporate, science in looking at what can/should be done about policy and implementation of Arctic development. The report provides a series of findings and recommendations for consideration developed during the independent examination of

  13. Fisheries and oil development on the continental shelf

    SciTech Connect

    Benner, C.S.; Middleton, R.W.

    1991-01-01

    The title of this volume is misleading because it has not clearly defined the geographic limits of the continental shelf. However, a glance at the Contents makes it clear that the contributions to this symposium are restricted to some shelf areas of the continental USA and especially to the Beaufort Sea off the north coast of Alaska. These papers were derived from presentations at the 119th annual meeting of the American Fisheries Society held in Anchorage, Alaska, in 1989. An awareness of the geographic scope of this symposium helps to put its contents into better focus. It is apparent that a broad coverage of fisheries, oil development, and its probable consequences from a global or even North American perspective is not provided. With the exception of the first 38 pages covering a broad range of topics, the remaining 134 pages are devoted exclusively to the Beaufort Sea.

  14. 75 FR 7515 - Environmental Documents Prepared for Proposed Mineral Exploration on the Alaska Outer Continental...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-02-19

    ... Minerals Management Service Environmental Documents Prepared for Proposed Mineral Exploration on the Alaska Outer Continental Shelf AGENCY: Minerals Management Service (MMS), Interior. ACTION: Notice of the... Minerals Management Service (MMS), in accordance with Federal regulations that implement the National...

  15. Outer continental shelf environmental-assessment program. Final reports of principal investigators. Volume 68

    SciTech Connect

    Not Available

    1990-08-01

    The contents of this study include the following: biological reconnaissance of Boulder Island Shoal in western Camden Bay, Beaufort Sea, Alaska; the Chukchi Sea continental shelf: benthos-environmental interactions; ecological assessment of sublittoral plant communities in the northern Gulf of Alaska; and ecology of unconsolidated beaches in Lower Cook Inlet.

  16. 49 CFR 192.10 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 3 2010-10-01 2010-10-01 false Outer continental shelf pipelines. 192.10 Section... shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf (as defined in the Outer Continental Shelf Lands Act; 43 U.S.C. 1331) must identify on all their respective pipelines...

  17. 49 CFR 192.10 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 3 2012-10-01 2012-10-01 false Outer continental shelf pipelines. 192.10 Section... shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf (as defined in the Outer Continental Shelf Lands Act; 43 U.S.C. 1331) must identify on all their respective pipelines...

  18. 49 CFR 192.10 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 3 2013-10-01 2013-10-01 false Outer continental shelf pipelines. 192.10 Section... shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf (as defined in the Outer Continental Shelf Lands Act; 43 U.S.C. 1331) must identify on all their respective pipelines...

  19. 49 CFR 192.10 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 3 2011-10-01 2011-10-01 false Outer continental shelf pipelines. 192.10 Section... shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf (as defined in the Outer Continental Shelf Lands Act; 43 U.S.C. 1331) must identify on all their respective pipelines...

  20. 49 CFR 192.10 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 3 2014-10-01 2014-10-01 false Outer continental shelf pipelines. 192.10 Section... shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf (as defined in the Outer Continental Shelf Lands Act; 43 U.S.C. 1331) must identify on all their respective pipelines...

  1. Coordination: southeast continental shelf studies. Progress report

    SciTech Connect

    Menzel, D.W.

    1980-03-01

    The GABEX I experiment is designed to provide synoptic coverage of a series of Gulf Stream wave-like disturbances, the effect of these on the circulation of the entire shelf, and on biological and chemical processes. This study was initiated in February 1980 when current meter arrays were deployed. These meters will be removed in July 1980. In April three ships will simultaneously study the effects of Gulf Stream disturbances on the hydrography, chemistry, and biology of the shelf. One vessel will track a specific wave-like disturbance and provide synoptic coverage of the shelf area. The second vessel will determine the effect of shelf break processes on adjacent shelf water; and the third will study trace metal distributions in and outside of disturbances. Research progress is reported in continental shelf studies, nearshore and estuarine studies (diffusion of freshwater out of nearshore zone), tidal currents and material transport, and mixing of inlet plumes.

  2. Chronology of Late Quaternary Glacial Cycles in the Bering Trough, Gulf of Alaska: Constraints from Core-Log-Seismic Integration across the Continental Shelf and Slope

    NASA Astrophysics Data System (ADS)

    Clary, W. A.; Worthington, L. L.; Daigle, H.; Slagle, A. L.; Gulick, S. P. S.

    2016-12-01

    Sediments offshore Southern Alaska offer a natural laboratory to study glacial erosion, sediment deposition, and orogenesis. A major goal of Integrated Ocean Drilling Program (IODP) Expedition 341 was investigation of interrelationships among tectonic processes, paleoclimate, and glacial activity. Here, we focus on core-log-seismic integration of IODP Sites U1420 and U1421 on the shallow shelf and slope near the Bering Trough, a glacially derived shelf-crossing landform. These sites sample glacial and marine sediments that record a history of sedimentation following the onset of glacial intensification near the mid-Pleistocene transition (1.2 Ma) and Yakutat microplate convergence with North America. Ocean drilling provides important stratigraphic, physical properties, and age data in depth which support development of a stratigraphic model that can be extended across the shelf if carefully calibrated to local and regional seismic surveys. We use high resolution multichannel seismic, core, and logging data to develop a time-depth relationship (TDR) and update the developing chronostratigraphic model based on correlation of seismic sequence boundaries and drilling-related data, including biostratigraphic and paleomagnetic age controls. We calibrate, combine, and interpolate core and logging data at each site to minimize gaps in physical property information and generate synthetic seismic traces. At Site U1421, vertical seismic profiling further constrains the TDR, and provides input for the initial velocity model during the tie. Finally, we match reflectors in the synthetic trace with events in nearby seismic reflection data to establish a TDR at each site. We can use this relationship to better interpret the development of the Bering Trough, a recurring and favored path for ice streams and glacial advance. Initial results suggest late Pleistocene sedimentation rates of at least 1 km/m.y. on average, and variable sedimentation rates which are possibly correlated

  3. Outer Continental Shelf oil and gas program: Cumulative effects

    SciTech Connect

    Horn, W.V.; Melancon, A.; Sun, J.

    1988-09-01

    The Outer Continental Shelf Lands Act (OCSLA) (43 U.S.C. 1331-1356) requires the Secretary of the Department of the Interior to submit an annual report to Congress assessing the cumulative environmental effects of mineral leasing and operations carried out under the OCSLA. The first report which covers the period 1954-1987 for activities off the Atlantic Coast, the Gulf of Mexico, the Pacific Coast, and offshore Alaska. Although temporary and localized impacts have occurred, with the exception of some loss of wetlands in Louisiana, significant adverse cumulative impacts on the human, marine, and coastal environments have not been identified.

  4. 75 FR 61512 - Outer Continental Shelf Official Protraction Diagrams

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-10-05

    ... Bureau of Ocean Energy Management, Regulation and Enforcement Outer Continental Shelf Official Protraction Diagrams AGENCY: Bureau of Ocean Energy Management, Regulation and Enforcement, Interior. ACTION... Outer Continental Shelf Official Protraction Diagrams (OPDs) located within Atlantic Ocean areas,...

  5. Coordination: Southeast Continental Shelf studies. Progress report

    SciTech Connect

    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)

  6. Elephant teeth from the atlantic continental shelf.

    PubMed

    Whitmore, F C; Emery, K O; Cooke, H B; Swift, D J

    1967-06-16

    Teeth of mastodons and mammoths have been recovered by fishermen from at least 40 sites on the continental shelf as deep as 120 meters. Also present are submerged shorelines, peat deposits, lagoonal shells, anz relict sands. Evidently elephants and other large mammals ranged this region during the glacial stage of low sea level of the last 25,000 years.

  7. Elephant teeth from the atlantic continental shelf

    USGS Publications Warehouse

    Whitmore, F.C.; Emery, K.O.; Cooke, H.B.S.; Swift, D.J.P.

    1967-01-01

    Teeth of mastodons and mastodons have been recovered by fishermen from at least 40 sites on the continental shelf as deep as 120 meters. Also present are submerged shorelines, peat deposits, lagoonal shells, and relict sands. Evidently elephants and other large mammals ranged this region during the glacial stage of low sea level of the last 25.000 years.

  8. 49 CFR 195.9 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 3 2012-10-01 2012-10-01 false Outer continental shelf pipelines. 195.9 Section... HAZARDOUS LIQUIDS BY PIPELINE General § 195.9 Outer continental shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf must identify on all their respective pipelines the specific...

  9. 49 CFR 195.9 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 3 2013-10-01 2013-10-01 false Outer continental shelf pipelines. 195.9 Section... HAZARDOUS LIQUIDS BY PIPELINE General § 195.9 Outer continental shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf must identify on all their respective pipelines the specific...

  10. 49 CFR 195.9 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 3 2010-10-01 2010-10-01 false Outer continental shelf pipelines. 195.9 Section... HAZARDOUS LIQUIDS BY PIPELINE General § 195.9 Outer continental shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf must identify on all their respective pipelines the specific...

  11. 49 CFR 195.9 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 3 2011-10-01 2011-10-01 false Outer continental shelf pipelines. 195.9 Section... HAZARDOUS LIQUIDS BY PIPELINE General § 195.9 Outer continental shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf must identify on all their respective pipelines the specific...

  12. 49 CFR 195.9 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 3 2014-10-01 2014-10-01 false Outer continental shelf pipelines. 195.9 Section... HAZARDOUS LIQUIDS BY PIPELINE General § 195.9 Outer continental shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf must identify on all their respective pipelines the specific...

  13. Oceanography of the Southeastern Continental Shelf

    NASA Astrophysics Data System (ADS)

    This volume, the second in the Coastal and Estuarine Sciences series, provides a synthesis of the physical, chemical, and biological oceanography of the South Atlantic Bight (SAB). The results presented derive from a decade-long multidisciplinary investigation of the SAB continental shelf regime.The SAB extends from West Palm Beach, Fla., where the narrow south Florida shelf begins to broaden, to Cape Hatteras, N.C., where the shelf again narrows. This broad and shallow area is distinguished by the proximity of the Gulf Stream to the shelf break. Large contrasts in the distribution of properties, the strength of oceanic and atmospheric forces, and the high frequency (4-12 days) at which these forces vary have created a unique natural laboratory in which a variety of oceanic processes may be studied.

  14. Modeling the dynamics of continental shelf carbon.

    PubMed

    Hofmann, Eileen E; Cahill, Bronwyn; Fennel, Katja; Friedrichs, Marjorie A M; Hyde, Kimberly; Lee, Cindy; Mannino, Antonio; Najjar, Raymond G; O'Reilly, John E; Wilkin, John; Xue, Jianhong

    2011-01-01

    Continental margin systems are important contributors to global nutrient and carbon budgets. Effort is needed to quantify this contribution and how it will be modified under changing patterns of climate and land use. Coupled models will be used to provide projections of future states of continental margin systems. Thus, it is appropriate to consider the limitations that impede the development of realistic models. Here, we provide an overview of the current state of modeling carbon cycling on continental margins as well as the processes and issues that provide the next challenges to such models. Our overview is done within the context of a coupled circulation-biogeochemical model developed for the northeastern North American continental shelf region. Particular choices of forcing and initial fields and process parameterizations are used to illustrate the consequences for simulated distributions, as revealed by comparisons to observations using quantitative statistical metrics.

  15. Iceberg scouring on the Norwegian continental shelf

    SciTech Connect

    Lien, R.

    1983-05-01

    This paper is a condensed version of parts of a Dr. ing. thesis to be presented during 1983. The first part of the paper deals with the regional distribution of iceberg scouring on the Norwegian continental shelf, and some general aspects related to it. The second part deals with iceberg scouring as a local phenomenon and its relation to the sea floor topography, sediment distribution, and geological and geotechnical properties of the sediments.

  16. 77 FR 39164 - Safety Zone; KULLUK, Outer Continental Shelf Mobile Offshore Drilling Unit (MODU), Beaufort Sea, AK

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-02

    ... Offshore Drilling Unit (MODU), Beaufort Sea, AK AGENCY: Coast Guard, DHS. ACTION: Temporary final rule... order to drill exploratory wells at various prospects located in the Beaufort Sea Outer Continental...; KULLUK, Outer Continental Shelf Mobile Offshore Drilling Unit (MODU), Beaufort Sea, Alaska'' in the...

  17. Petroleum geology of Kodiak Shelf, Alaska.

    USGS Publications Warehouse

    Fisher, M.A.

    1980-01-01

    Organic geochemical data show that Cenozoic rocks on Kodiak Island, in Albatross basin, and under the continental slope generally contain less than 0.5 wt. % organic carbon. Moreover, kerogen from all rocks analyzed is predominantly (60 to 100%) herbaceous; woody and coaly kerogens are present in secondary (20 to 40%) amounts. Most strata in shelf basins are thermally immature, however. Eocene and Oligocene strata which probably floor the shelf basins, are mature on the basis of comparison with coeval strata onshore. Eocene and Oligocene rocks have poor reservoir properties; the best reservoirs are probably in U. Miocene or Pliocene and younger rocks.- from Author

  18. Australian Continental Shelf as an Inverse Estuary

    NASA Astrophysics Data System (ADS)

    Mahjabin, T.; Pattiaratchi, C. B.; Hetzel, Y.

    2016-02-01

    Transport of inshore waters and suspended material off the continental shelf by Dense Shelf Water Cascades (DSWC) has important ecological and biogeochemical implications in Australian waters. Because of high rates of evaporation, denser saline water along the sea bed occurs in a majority of the shallow coastal regions around Australia, setting up horizontal density gradients that can form DSWC. This study uses data available from the Integrated Marine Observing System (IMOS), which is operated by the Australian National Facility for Ocean Gliders (ANFOG) located at the University of Western Australia, to measure cross-shelf density profiles under varying conditions around the entire continent. Analysis of 143 transects of 97 sets of spatial and temporal resolution data from the ocean gliders under varying wind and tide conditions for seven contrasting regions surrounding Australia has allowed us to confirm that DSWC occurs on a regular basis during autumn and winter seasons. Results indicate that cascades occur during these seasons mainly due to cooling of the coastal water which already have higher salinity due to evaporation during the summer months. The cascades were present under different wind and tidal energy conditions and the controlling parameter for cascade formation is the cross-shelf density gradient. The cross-shelf density gradient in North-West Australia is maximum in July (14.23x10-6 kgm-4); whereas it is a maximum in June in South Australia (18.78x10-6 kgm-4) and in May in South-West Australia (25.884x10-6 kgm-4). Greater knowledge of the occurrence of DSWC will enhance understanding of the offshore transport of larvae, nutrients, salt, heat, carbon, low-oxygen water, sediment, and pollutants in Australian waters.

  19. Alaska OCS (Outer Continental Shelf) social and economic studies program. Technical report Number 99. A description of the socioeconomics of Norton Sound. Final technical report

    SciTech Connect

    McNabb, S.; Robbins, L.; Waring, K.; Wasserman, P.; Weber, K.

    1984-03-01

    The study focuses on three main variables, (economic activity, employment opportunity, and inflation) which may be expected to change significantly in the Norton Sound region of Alaska as a result of OCS activities. Five primary categories (demography, economics, social organization, values and attitudes, and infrastructure) were studied. Field data were collected from 82 families in the villages of Savoonga, Nome, Golovin, Unalakleet, and Emmoank. Some primary data from Alakanuk and Gambell were also used in portion of the analysis. The region lacks the geographical, infrastructural, commercial, and other economic assets to attract offshore industries and workers.

  20. 78 FR 33859 - Outer Continental Shelf (OCS) Geological and Geophysical Exploration Activities in the Gulf of...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-05

    ... Continental Shelf (OCS) Geological and Geophysical Exploration Activities in the Gulf of Mexico; Correction... in the Federal Register (78 FR 27427) entitled ``Outer Continental Shelf Geological and...

  1. Outer continental shelf, Beaufort Sea, oil and gas lease sale 170 (proposed notice of sale)

    SciTech Connect

    1997-12-31

    The Minerals Management Service (MMS) is issuing this proposed Notice of Sale under the Outer Continental Shelf (OCS) Lands Act (43 U.S.C. 1331-1356, as amended) and the regulations issued thereunder (30 CFR Part 256). A `Sale Notice Package,` containing this Notice and several supporting and essential documents referenced in the Notice, is available from the MMS Alaska OCS Regional Office Public Information Unit.

  2. Oceanology of the antarctic continental shelf: Volume 43

    SciTech Connect

    Jacobs, S.S.

    1985-01-01

    This book discusses the seas of the deep continental shelf, which play an important climatic role in sea ice production, deep ocean ventilation and wastage of the Antarctic ice sheet. This volume includes analyses of measurements taken from ships and satellites, and from sea ice and glacial ice. High resolution profiling equipment, long term bottom-moored instruments, continuous remote sensors, geochemical tracers and computer models have provided the basis for new insights into the continental shelf circulation. Color plates and an accompanying GEBCO Circum-Antarctic map effectively portray the continental shelf in relation to the glaciated continent, the sea ice and the surrounding Southern Ocean.

  3. Petroleum potential of northern Australian Continental Shelf

    SciTech Connect

    Smith, M.R.; Ross, J.G.

    1986-11-01

    A study of the publicly available data from the offshore northern Australian continental shelf has shown that three prospective sedimentary sequences are present. A Cenozoic basin possibly containing Miocene reefal carbonates exists in the west part of the region, a structurally distinct Mesozoic basin containing thick sandstone intervals underlies the Cenozoic, and a thick paleozoic basin, possibly containing Devonian reefs and younger Paleozoic sandstone intervals, lies southeast of the Aru Archipelago and east of a north-northeast-trending ridge located along the eastern edges of the Aru and Timor Troughs. Paleozoic sediments also underlie the Mesozoic west of this ridge. The cenozoic and Mesozoic basins and the western Paleozoic subbasin are separated by major sequence boundaries. All the basins present hydrocarbon potential to a greater or lesser extent. The Mesozoic basin will probably be the prime target for exploration over the next few years, but secondary objectives in Cenozoic and Paleozoic sediments should not be ignored. The numerous different play types identified in this study, the positive signs from exploration in the early 1970s, the recent neighboring discoveries, and improvements in seismic data quality provide an incentive for oil companies to conduct detailed exploration of the area. 7 figures.

  4. Manganese, Iron, and sulfur cycling in Louisiana continental shelf sediments

    EPA Science Inventory

    Sulfate reduction is considered the primary pathway for organic carbon remineralization on the northern Gulf of Mexico Louisiana continental shelf (LCS) where bottom waters are seasonally hypoxic, yet limited information is available on the importance of iron and manganese cyclin...

  5. Phytoplankton Communities in Louisiana coastal waters and the continental shelf

    EPA Science Inventory

    Louisiana coastal waters and the adjacent continental shelf receive large freshwater and nutrient inputs from the Mississippi and Atchafalaya Rivers, creating favorable conditions for increased phytoplankton productivity. To examine inshore-offshore patterns in phytoplankton comm...

  6. Outer Continental Shelf Oil and Gas Leasing/Production Program

    SciTech Connect

    Not Available

    1988-01-01

    This annual report on the Outer Continental Shelf (OCS) Oil and Gas Leasing and Production program summarizes receipts and expenditures, and includes information on OCS safety violations as reported by the US Coast Guard. 3 figs., 12 tabs.

  7. Phytoplankton Communities in Louisiana coastal waters and the continental shelf

    EPA Science Inventory

    Louisiana coastal waters and the adjacent continental shelf receive large freshwater and nutrient inputs from the Mississippi and Atchafalaya Rivers, creating favorable conditions for increased phytoplankton productivity. To examine inshore-offshore patterns in phytoplankton comm...

  8. Manganese, Iron, and sulfur cycling in Louisiana continental shelf sediments

    EPA Science Inventory

    Sulfate reduction is considered the primary pathway for organic carbon remineralization on the northern Gulf of Mexico Louisiana continental shelf (LCS) where bottom waters are seasonally hypoxic, yet limited information is available on the importance of iron and manganese cyclin...

  9. Alaska OCS (Outer Continental Shelf) social and economic studies program. Technical report Number 91. Effects of renewable resource harvest disruptions on socio-economic and socio-cultural systems: Wainwright, Alaska. Final technical report

    SciTech Connect

    Luton, H.H.

    1985-01-01

    Contents include: ethnographic baseline, Wainright, Alaska; social institutions; the cash economy; kinship; subsistence task groups; subsistence economy; sharing; land mammals; marine mammals - Part 1 and 2; birds; fish, invertebrates, plants, minerals; ethnographic summary and conclusions.

  10. Sediment metabolism on the Louisiana continental shelf - Eldridge

    EPA Science Inventory

    Rates of aerobic and anaerobic sediment metabolism were measured on the Louisiana Continental Shelf during 5 cruises in 2006 and 2007. On each cruise, 3-4 stations were occupied in regions of the shelf that experience summer bottom-water hypoxia. Net DIC, O2, N2, and nutrient f...

  11. Potential for Suboxic Ammonium Oxidation in Louisiana Continental Shelf Sediments

    EPA Science Inventory

    Sediments deposited onto the Louisiana continental shelf (LCS) west of the Mississippi River Delta form mobile muds varying in thickness from meters near the outfall to centimeters on the western portion of the shelf. The muds have high concentrations of iron which promote rapid...

  12. Potential for Suboxic Ammonium Oxidation in Louisiana Continental Shelf Sediments

    EPA Science Inventory

    Sediments deposited onto the Louisiana continental shelf (LCS) west of the Mississippi River Delta form mobile muds varying in thickness from meters near the outfall to centimeters on the western portion of the shelf. The muds have high concentrations of iron which promote rapid...

  13. Sediment metabolism on the Louisiana continental shelf - Eldridge

    EPA Science Inventory

    Rates of aerobic and anaerobic sediment metabolism were measured on the Louisiana Continental Shelf during 5 cruises in 2006 and 2007. On each cruise, 3-4 stations were occupied in regions of the shelf that experience summer bottom-water hypoxia. Net DIC, O2, N2, and nutrient f...

  14. Structure and petroleum potential of the Yakutat segment of the northern Gulf of Alaska continental margin

    SciTech Connect

    Bruns, T.R.

    1983-01-01

    This report discusses the structure, geologic history, and petroleum potential of the Yakutat segment, the part of the continental margin between Cross Sound and Icy Bay, northern Gulf of Alaska. As part of a program of geological and geophysical investigations of the continental margin in the northern Gulf of Alaska, the US Geological Survey collected multichannel seismic reflection data along about 2000 km of tracklines in the study area during 1975, 1977, and 1978. In addition, dredge samples from the continental slope were acquired during the 1977, 1978, and 1979 field seasons. The first part of this paper presents an interpretation of the seismic reflection and refraction data, including structure contour maps, isopach maps, and interpreted seismic sections; the second part is a discussion of the implications for petroleum potential. The primary area of interest is the continental shelf and slope, but some data from strata at the base of the slope are also included.

  15. Macrofaunal production along the UK continental shelf

    NASA Astrophysics Data System (ADS)

    Bolam, S. G.; Barrio-Frojan, C. R. S.; Eggleton, J. D.

    2010-10-01

    Estimates of secondary production ( P/ B ratio and total production) by macrobenthic communities across the UK continental shelf are presented. Values for individual sampling stations varied from 0.21 to 4.1 y - 1 for community P/ B and 3.1 to 897.2 kJ m - 2 y - 1 for total production. Such data fills an important gap pertaining to our understanding of the spatial variation in production estimates for this region. Benthic production estimates varied primarily at small (inter-station) scales (24 nm), although larger-scale differences were observed. In general, the highest production estimates were exhibited by benthic communities in Cardigan Bay (Irish Sea) and East English Channel, while the lowest estimates were observed for the mid- and northern North Sea areas. The former were typified by shallow, gravelly areas of seabed which exhibit high bed tidal stress and do not thermally stratify during the summer months. On average, annelids contribute an overwhelming majority of the total production with different regions varying in the relative contributions from other phyla such as molluscs, crustaceans and echinoderms. Spatial heterogeneity of sediment granulometric variables occurred primarily between stations while those of other variables (e.g., depth, stratification, and tidal bed stress) were more regional. Although a large proportion of the spatial variation in secondary production estimates was not explained by environmental characteristics, the data indicate that such relationships are scale-dependent. Average bed temperature was a significant factor in creating some of the observed differences at large spatial scales. The possible reasons why a larger proportion of the variation in production estimates was not explained by the present study are presented.

  16. Seafloor geology of the Monterey Bay area continental shelf

    USGS Publications Warehouse

    Eittreim, S.L.; Anima, R.J.; Stevenson, A.J.

    2002-01-01

    Acoustic swath-mapping of the greater Monterey Bay area continental shelf from Point An??o Nuevo to Point Sur reveals complex patterns of rock outcrops on the shelf, and coarse-sand bodies that occur in distinct depressions on the inner and mid-shelves. Most of the rock outcrops are erosional cuestas of dipping Tertiary rocks that make up the bedrock of the surrounding lands. A mid-shelf mud belt of Holocene sediment buries the Tertiary rocks in a continuous, 6-km-wide zone on the northern Monterey Bay shelf. Rock exposures occur on the inner shelf, near tectonically uplifting highlands, and on the outer shelf, beyond the reach of the mud depositing on the mid-shelf since the Holocene sea-level rise. The sediment-starved shelf off the Monterey Peninsula and south to Point Sur has a very thin cover of Holocene sediment, and bedrock outcrops occur across the whole shelf, with Salinian granite outcrops surrounding the Monterey Peninsula. Coarse-sand deposits occur both bounded within low-relief rippled scour depressions, and in broad sheets in areas like the Sur Platform where fine sediment sources are limited. The greatest concentrations of coarse-sand deposits occur on the southern Monterey Bay shelf and the Sur shelf. ?? 2002 Elsevier Science B.V. All rights reserved.

  17. In search of the Malaysian Extended Continental Shelf

    NASA Astrophysics Data System (ADS)

    Yahaya, N. A. Z.; Musa, T. A.; Omar, K. M.; Din, A. H. M.; Abdullah, N. M.; Othman, A. H.; Wahab, M. I. A.

    2016-06-01

    Over the years, the sovereignty proclamation of Coastal States for their extended continental shelf has been a crucial matter. The declaration and extension of a continental shelf under the United Nations Convention on the Law of the Sea provide significant potential for many developing nations in economics, trades, resource exploitation, communication and security. Hence, the application of satellite altimeter, as one of the solutions for collecting bathymetry data to define the approximate limits of the continental shelf, is reviewed. This paper also discusses the possible significance or contribution of space-derived bathymetry, i.e. the seafloor topography, either independently or harmoniously with different datasets, to meet the element of the Article 76 of UNCLOS.

  18. Seals map bathymetry of the Antarctic continental shelf

    NASA Astrophysics Data System (ADS)

    Padman, Laurie; Costa, Daniel P.; Bolmer, S. Thompson; Goebel, Michael E.; Huckstadt, Luis A.; Jenkins, Adrian; McDonald, Birgitte I.; Shoosmith, Deborah R.

    2010-11-01

    We demonstrate the first use of marine mammal dive-depth data to improve maps of bathymetry in poorly sampled regions of the continental shelf. A group of 57 instrumented elephant seals made on the order of 2 × 105 dives over and near the continental shelf on the western side of the Antarctic Peninsula during five seasons, 2005-2009. Maximum dive depth exceeded 2000 m. For dives made near existing ship tracks with measured water depths H<700 m, ˜30% of dive depths were to the seabed, consistent with expected benthic foraging behavior. By identifying the deepest of multiple dives within small areas as a dive to the seabed, we have developed a map of seal-derived bathymetry. Our map fills in several regions for which trackline data are sparse, significantly improving delineation of troughs crossing the continental shelf of the southern Bellingshausen Sea.

  19. Denitrification and Nitrogen Fixation in Alaskan Continental Shelf Sediments

    PubMed Central

    Haines, John R.; Atlas, Ronald M.; Griffiths, Robert P.; Morita, Richard Y.

    1981-01-01

    Rates of nitrogen fixation and denitrification were measured in Alaskan continental shelf sediments. In some regions, rates of nitrogen fixation and denitrification appeared to be equal; in other areas, rates were significantly different. Potential rates of denitrification were found to be limited primarily by the available nitrate substrate. Major regional differences in rates of denitrification were not statistically significant, but significant differences were found for nitrogen fixation rates in different regions of the Alaskan continental shelf. Estimated net losses of nitrogen from Bering Sea sediments were calculated as 1.8 × 1012 g of N/yr. Experimental exposure of continental shelf sediments to petroleum hydrocarbons reduced rates of nitrogen fixation and denitrification in some cases but not others. Long-term exposure was necessary before a reduction in nitrogen fixation rates was observed; unamended rates of denitrification but not potential denitrification rates (NO3− added) were depressed after exposure to hydrocarbons. PMID:16345716

  20. Sediment movement on the continental shelf near Washington and Oregon

    USGS Publications Warehouse

    Gross, M. Grant; Nelson, Jack L.

    1966-01-01

    The nuclides zinc-65 and cobalt-60 associated with river-borne particulate matter are incorporated in sediment on the Continental Shelf near the Colum- ia River. Changes in the relative concentrations of zinc-65 and cobalt-60 and in the ratio of the activity of zinc-65 and cobalt-60 suggest that radioactive sediment moves northward 12 to 30 kilometers per year along the shelf and 2.5 to 10 kilometers per year westward away from the coast.

  1. Circulation and exchange processes over the continental shelf and slope

    SciTech Connect

    Csanady, G.T.

    1988-01-01

    The theme of the work during the past triennium has been the SEEP experiment, data interpretation and modeling related to the goals of the experiment, and was characterized by increasing cooperation with colleagues from other disciplines. The theoretical contributions dealt with shelf-slope interaction, the dynamics and climatology of currents over the continental slope, and the behavior of fate of organic particles. Observational papers discussed various exchange mechanisms at the shelf edge, with special attention to particle exchange, and the quiescence of currents over the mid continental slope which is presumably responsible for the accumulation of organic particles.

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Measurements of storm-generated bottom stresses on the continental shelf.

    USGS Publications Warehouse

    Cacchione, D.A.; Drake, D.E.

    1982-01-01

    Large values of bottom friction velocity, u., and roughness length, zo, determined from burst-averaged speed data taken on the continental shelf in outer Norton Sound, Alaska, with the GEOPROBE tripod during a storm are correlated with extremely large values of near-bottom concentration of total suspended particulate matter (TSM). The values obtained from the 'law of the wall' velocity-depth relationship are diminished substantially throughout the storm period when the turbulence-reducing effects of the vertical cncentration gradient of TSM are considered. The values are compared to those obtained from other workers. -from Authors

  4. 76 FR 43230 - Outer Continental Shelf Air Regulations Consistency Update for Virginia

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-20

    ... From the Federal Register Online via the Government Publishing Office ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 55 Outer Continental Shelf Air Regulations Consistency Update for Virginia AGENCY... Outer Continental Shelf (OCS) Air Regulations. Requirements applying to OCS sources located within...

  5. Coastal zone and Continental Shelf conflict resolution: improving ocean use and resource dispute management

    SciTech Connect

    Nyhart, J.D.; Harding, E.T.

    1985-11-01

    Contents include: An overview of coastal zone and continental shelf conflicts; Experience in coastal zone management conflict; Future coastal zone conflicts; Outer continental shelf conflicts; Georges Bank and Gulf of Maine; and Future considerations.

  6. Microbial Communities in Sediments across the Louisiana Continental Shelf

    EPA Science Inventory

    The Louisiana continental Shelf (LCS) is a dynamic system that receives discharges from two large rivers. It has a stratified water column that is mixed by winter storms, hypoxic bottom water from spring to fall, and a muddy seafloor with highly mixed surficial sediments. Spatia...

  7. Microbial Communities in Sediments across the Louisiana Continental Shelf

    EPA Science Inventory

    The Louisiana continental Shelf (LCS) is a dynamic system that receives discharges from two large rivers. It has a stratified water column that is mixed by winter storms, hypoxic bottom water from spring to fall, and a muddy seafloor with highly mixed surficial sediments. Spatia...

  8. A Laboratory Model of a Cooled Continental Shelf

    DTIC Science & Technology

    1993-06-01

    J• WHOI-93-22 CDz Woods Hole Oceanographic Institution A Laboratory Model of a Cooled Continental Shelf by J.A. Whitehead and Robert E. Frazel DT...emplaced temperature probes constituted the data gathering activities. Thermistors used were 3000 ohm Omega brand precision thermistors that were

  9. 75 FR 1076 - Outer Continental Shelf Civil Penalties

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-01-08

    ... [Federal Register Volume 75, Number 5 (Friday, January 8, 2010)] [Notices] [Page 1076] [FR Doc No: 2010-119] DEPARTMENT OF THE INTERIOR Minerals Management Service Outer Continental Shelf Civil Penalties AGENCY: Minerals Management Service (MMS), Interior. ACTION: Notice summarizing review of the...

  10. French Extended Continental Shelf Mapping: example of new continental margin understanding offshore French Guiana

    NASA Astrophysics Data System (ADS)

    Roest, Walter; Loubrieu, Benoit; Loncke, Lies; Basile, Christophe; Graindorge, David; Shipboard Party, Guyaplac

    2017-04-01

    Under the United Nations Convention on the Law of the Sea, Coastal States can extend sovereign rights over the natural resources of the Continental Shelf beyond 200 nautical miles (M) if they can demonstrate that their continental margin extends beyond this distance from the coast. Article 76 of the Convention defines the continental shelf and includes geomorphological and geological criteria to claim such a shelf beyond 200 M. Since 2006, France has filed 7 submissions for a total of 10 distinct geographic regions to the Commission on the Limits of the Continental Shelf that was established by the Convention to examine those claims, and make recommendations with respect to the justification of the outer limits of the continental shelf. To support the French submissions, a significant effort was employed in acquiring new marine geophysical and geological data and compiling existing data along the deep water parts of the continental margins offshore all the French overseas territories. In this presentation, we will discuss the example of French Guiana, where the data collected for the purpose of fulfilling the obligation under the Convention to submit data and information to the Commission within a 10 year time frame have led to new understanding of the transform continental margin and the Demerara Plateau located to the north of French Guiana and Surinam. In addition, the data collected for this purpose have led to new scientific questions and have encouraged new and enhanced scientific collaboration between French government organizations and the academic community. Follow up research and scientific cruises that will be presented in separate communications have addressed sedimentary processes including contourites, giant comet tail like depressions probably associated with the strong bottom currents observed along the continental slope and potentially related to pockmarks, as well as giant submarine landslides. Most recently, multichannel reflection and wide angle

  11. 76 FR 11811 - Environmental Document Prepared in Support of Oil and Gas Activities on the Alaska Outer...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-03

    ... of Oil and Gas Activities on the Alaska Outer Continental Shelf AGENCY: Bureau of Ocean Energy... activities proposed on the Alaska Outer Continental Shelf (OCS). FOR FURTHER INFORMATION CONTACT:...

  12. 26 CFR 301.9001 - Statutory provisions; Outer Continental Shelf Lands Act Amendments of 1978.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 26 Internal Revenue 18 2010-04-01 2010-04-01 false Statutory provisions; Outer Continental Shelf... Rules Application of Internal Revenue Laws § 301.9001 Statutory provisions; Outer Continental Shelf Lands Act Amendments of 1978. Section 302 of the Outer Continental Shelf Lands Act Amendments of...

  13. 76 FR 63654 - Outer Continental Shelf Official Protraction Diagram, Lease Maps, and Supplemental Official Outer...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-13

    ... Doc No: 2011-26503] DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management Outer Continental Shelf Official Protraction Diagram, Lease Maps, and Supplemental Official Outer Continental Shelf Block... American Datum of 1927 (NAD 27) Outer Continental Shelf (OCS) Official Protraction Diagram (OPD),...

  14. 26 CFR 301.9001 - Statutory provisions; Outer Continental Shelf Lands Act Amendments of 1978.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 26 Internal Revenue 18 2014-04-01 2014-04-01 false Statutory provisions; Outer Continental Shelf... Rules Application of Internal Revenue Laws § 301.9001 Statutory provisions; Outer Continental Shelf Lands Act Amendments of 1978. Section 302 of the Outer Continental Shelf Lands Act Amendments of...

  15. 26 CFR 301.9001 - Statutory provisions; Outer Continental Shelf Lands Act Amendments of 1978.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 26 Internal Revenue 18 2011-04-01 2011-04-01 false Statutory provisions; Outer Continental Shelf... Rules Application of Internal Revenue Laws § 301.9001 Statutory provisions; Outer Continental Shelf Lands Act Amendments of 1978. Section 302 of the Outer Continental Shelf Lands Act Amendments of...

  16. 26 CFR 1.1402(a)-12 - Continental shelf and certain possessions of the United States.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 26 Internal Revenue 12 2014-04-01 2014-04-01 false Continental shelf and certain possessions of... Income § 1.1402(a)-12 Continental shelf and certain possessions of the United States. (a) Certain... amounts are excluded from gross income under section 931. (b) Continental shelf. For the definition of...

  17. 26 CFR 301.9001 - Statutory provisions; Outer Continental Shelf Lands Act Amendments of 1978.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 26 Internal Revenue 18 2013-04-01 2013-04-01 false Statutory provisions; Outer Continental Shelf... Rules Application of Internal Revenue Laws § 301.9001 Statutory provisions; Outer Continental Shelf Lands Act Amendments of 1978. Section 302 of the Outer Continental Shelf Lands Act Amendments of...

  18. 26 CFR 1.1402(a)-12 - Continental shelf and certain possessions of the United States.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 26 Internal Revenue 12 2013-04-01 2013-04-01 false Continental shelf and certain possessions of... Income § 1.1402(a)-12 Continental shelf and certain possessions of the United States. (a) Certain... amounts are excluded from gross income under section 931. (b) Continental shelf. For the definition of...

  19. 26 CFR 1.1402(a)-12 - Continental shelf and certain possessions of the United States.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 26 Internal Revenue 12 2011-04-01 2011-04-01 false Continental shelf and certain possessions of... Income § 1.1402(a)-12 Continental shelf and certain possessions of the United States. (a) Certain... amounts are excluded from gross income under section 931. (b) Continental shelf. For the definition of...

  20. 26 CFR 1.1402(a)-12 - Continental shelf and certain possessions of the United States.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 26 Internal Revenue 12 2012-04-01 2012-04-01 false Continental shelf and certain possessions of... Income § 1.1402(a)-12 Continental shelf and certain possessions of the United States. (a) Certain... amounts are excluded from gross income under section 931. (b) Continental shelf. For the definition of...

  1. 26 CFR 301.9001 - Statutory provisions; Outer Continental Shelf Lands Act Amendments of 1978.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 26 Internal Revenue 18 2012-04-01 2012-04-01 false Statutory provisions; Outer Continental Shelf... Rules Application of Internal Revenue Laws § 301.9001 Statutory provisions; Outer Continental Shelf Lands Act Amendments of 1978. Section 302 of the Outer Continental Shelf Lands Act Amendments of...

  2. 26 CFR 1.1402(a)-12 - Continental shelf and certain possessions of the United States.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 26 Internal Revenue 12 2010-04-01 2010-04-01 false Continental shelf and certain possessions of....1402(a)-12 Continental shelf and certain possessions of the United States. (a) Certain possessions. For... from gross income under section 931. (b) Continental shelf. For the definition of the term...

  3. Geology and tectonic development of the continental margin north of Alaska

    USGS Publications Warehouse

    Grantz, A.; Eittreim, S.; Dinter, D.A.

    1979-01-01

    The continental margin north of Alaska, as interpreted from seismic reflection profiles, is of the Atlantic type and consists of three sectors of contrasting structure and stratigraphy. The Chukchi sector, on the west, is characterized by the deep late Mesozoic and Tertiary North Chukchi basin and the Chukchi Continental Borderland. The Barrow sector of central northern Alaska is characterized by the Barrow arch and a moderately thick continental terrace build of Albian to Tertiary clastic sediment. The terrace sedimentary prism is underlain by lower Paleozoic metasedimentary rocks. The Barter Island sector of northeastern Alaska and Yukon Territory is inferred to contain a very thick prism of Jurassic, Cretaceous and Tertiary marine and nonmarine clastic sediment. Its structure is dominated by a local deep Tertiary depocenter and two regional structural arches. We postulate that the distinguishing characteristics of the three sectors are inherited from the configuration of the rift that separated arctic Alaska from the Canadian Arctic Archipelago relative to old pre-rift highlands, which were clastic sediment sources. Where the rift lay relatively close to northern Alaska, in the Chukchi and Barter Island sectors, and locally separated Alaska from the old source terranes, thick late Mesozoic and Tertiary sedimentary prisms extend farther south beneath the continental shelf than in the intervening Barrow sector. The boundary between the Chukchi and Barrow sectors is relatively well defined by geophysical data, but the boundary between the Barrow and Barter Island sectors can only be inferred from the distribution and thickness of Jurassic and Cretaceous sedimentary rocks. These boundaries may be extensions of oceanic fracture zones related to the rifting that is postulated to have opened the Canada Basin, probably beginning during the Early Jurassic. ?? 1979.

  4. Effects of longshore shelf variations on barotropic continental shelf waves, slope currents and ocean modes

    NASA Astrophysics Data System (ADS)

    Huthnance, J. M.

    Effects of continental shelf bends, converging depth contours and changing depth profiles are discussed. Some analysis is carried out for previously unstudied cases. Separate oceanic interior and shelf flow problems are formulated for a sufficiently narrow shelf. The ocean interior ‘sees’ only an integrated shelf effect, typically increasing shelf-edge amplitudes, retarding longshore Kelvin-wave propagation and increasing natural mode periods by 0 (10%). On the local shelf, the flow matches to the ocean interior and is nondivergent. Effects on shelf waves and slope currents depend subtly on the nature of the longshore variations. Curvature and contour convergence do not per se imply scaterring or generation of shelf waves. Indeed, any depth h(ξ) where ▽ 2ξ(x,y) = 0 (a condition approximating longshelf uniformity in the topography's convexity) supports essentially the same shelf waves as do straight depth contours (DAVIS, 1983), and slope currents follow depth contours. Scattering results rather from breaks in analyticity of the depth profile. Hence calculations for small isolated features (necessarily highly convex or concave) may overestimate scattering, and superposition for realistic topography may lead to much self-cancellation among scattered waves. Otherwise, examples show a strong preference for scattering into adjacent mode numbers and into any shelf wave mode near to its maximum frequency. A shelf sector, where the maximum shelf wave frequency maxω is less than the frequency ω of an incident shelf wave, causes substantial scattering unless maxω and ω are very close. Adjustment of slope currents to changed conditions takes place through (and over the decay distance of) scattered shelf waves.

  5. Heat flow of the Norwegian continental shelf

    NASA Astrophysics Data System (ADS)

    Pascal, Christophe

    2015-04-01

    Terrestrial heat flow influences a large collection of geological processes. Its determination is a requirement to assess the economic potential of deep sedimentary basins. Published heat flow calculations from e.g. major oil provinces are however seldom. Robust heat flow determinations in drillholes require logging of undisturbed temperatures and intensive sampling of core material for petrophysical measurements. Temperature logging in exploration drillholes is traditionally conducted during drill breaks or shortly after drilling, resulting in temperatures severely disturbed by mud circulation and coring is restricted to selected intervals. Alternatively, test temperatures, information from electric logs and lithological descriptions of drill cuttings can be used to overcome these limitations. The present contribution introduces new heat flow determinations based on 63 exploration drillholes from the Norwegian North Sea, the Mid Norway Margin and the Barents Shelf. Our analyses are based on released DST temperatures, precise lithological descriptions of drill cuttings, previously measured rock matrix thermal conductivities and established porosity laws. Our results suggest median heat flow values of 64 mW/m2, 65 mW/m2 and 72 mW/m2 for the North Sea, the Mid Norway Margin (mainly the Trøndelag Platform) and the SW Barents Shelf respectively. The Barents Shelf shows significantly high heat flow, suggesting lateral transfer of heat from the mantle of the adjacent young ocean. In detail, heat flow increases by ~ 10 mW/m2 from the southern Norwegian North Sea towards the Mid Norway Margin. This result appears to be in very good agreement with seismic tomographic studies suggesting northward thinning of the underlying mantle lithosphere. Our results together with published marine heat flow data from the Mid Norway Margin suggest a gradual decrease in heat flow levels from both the North Sea and the Trøndelag Platform towards the centres of the deep Møre and V

  6. Structure and development of the southern Moroccan continental shelf

    USGS Publications Warehouse

    Dillon, William P.

    1974-01-01

    The structure of the continental shelf off southern Morocco was studied by means of 2,100 km of seismic reflection profiles, magnetic and bathymetric surveys, and dredge samples. The research area lies off four geologic divisions adjacent to the coast: the Atlas Mountains; the Souss Trough; the Anti-Atlas Mountains; and the Aaiun Basin. The continental shelf, along with the western Atlas Mountains, the western Souss Trough, and the entire Aaiun Basin, has subsided along a normal fault-flexure system. This system runs along the shore at the Anti-Atlas Mountains, and cuts off this cratonic block from the shelf subsidence. The shelf is narrow and characterized by out-building off the Anti-Atlas range, whereas it is broader and characterized by upbuilding to the north and south. Deposition was essentially continuous at least from Early Cretaceous through Eocene time. Published work suggests that the last cycle of sedimentation began during Permian rifting. After Eocene time, most sediments carried to the shelf must have bypassed it and gone to construct the slope and rise or to the deep sea. Tertiary orogenies caused extensive folding of Mesozoic and early Tertiary deposits off the Atlas Mountains. ?? 1974.

  7. Heat Flow of the Norwegian Continental Shelf

    NASA Astrophysics Data System (ADS)

    Pascal, C.

    2015-12-01

    Terrestrial heat flow determination is of prime interest for oil industry because it impacts directly maturation histories and economic potential of oil fields. Published systematic heat flow determinations from major oil provinces are however seldom. Robust heat flow determinations in drillholes require logging of undisturbed temperatures and intensive sampling of core material for petrophysical measurements. Temperature logging in exploration drillholes is traditionally conducted during drill breaks or shortly after drilling, resulting in temperatures severely disturbed by mud circulation and coring is restricted to selected intervals. Alternatively, test temperatures, information from electric logs and lithological descriptions of drill cuttings can be used to overcome these limitations. The present contribution introduces new heat flow determinations based on 63 exploration drillholes from the Norwegian North Sea, the Mid Norway Margin and the Barents Shelf. Our analyses are based on released DST temperatures, precise lithological descriptions of drill cuttings, previously measured rock matrix thermal conductivities and established porosity laws. For the sake of comparison, we carefully review previous heat flow studies carried out both onshore and offshore Norway. Our results suggest median heat flow values of 64 mW/m2, 65 mW/m2 and 72 mW/m2 for the North Sea, the Mid Norway Margin (mainly the Trøndelag Platform) and the SW Barents Shelf respectively. In detail, heat flow increases by ~ 10 mW/m2 from the southern Norwegian North Sea towards the Mid Norway Margin. This result appears to be in very good agreement with seismic tomographic studies suggesting northward thinning of the underlying mantle lithosphere. Our results together with published marine heat flow data from the Mid Norway Margin suggest a gradual decrease in heat flow levels from both the North Sea and the Trøndelag Platform towards the centres of the deep Møre and Vøring basins. This latter

  8. Modelisation of Circulation On The French Guiana Continental Shelf

    NASA Astrophysics Data System (ADS)

    Chevalier, C.; Dekeyser, I.; Ramamonjiarisoa, A.; Baklouti, M.; van Nieuwerberg, V.

    The continental shelf which extends more over than 1000 km to the north-west of the mouth of the Amazon river is an usual oceanographic environment : the entire area is influenced by fresh water flowing from the Amazon. The current on the shelf inter- acts with the strong, shallow Guiana Current along the outer shelf area. The prevailing trade winds across the area impose surface stresses. The tidal influence is also signif- icant with a diminishing amplitude from the Amazon to the north. This combination results in a persistent long-shore current flowing north-westward in the shallow wa- ter along the shore. In particular on French Guiana continental shelf, the combination of significant stratification, great coastal current just out of the shelf, influence of the wind and strong tidal component presents an interesting process for study. The purpose of this study is to look into the circulation that develops under these interacting forces. For that, we develop a numerical model of the circulation on the French Guiana shelf. Nowadays, in the bibliography, it seems to be the first numerical study on this area. This work is included in the Programme National dSEnvironnement Côtier (PNEC) in French Guiana. Simulations described the coastal currents, the salinity and temperature evolution on the shelf under the influence of rivers discharging in the shelf and the effect of north- eastward wind on the circulation. The current is parallel to the coast and the highest velocities are in the middle of the shelf, the maximum intensity is located at the surface and reached speed of 1m/s. The fresh water discharged by rivers extends alongshore near the coast, to about 30m-isobath, whereas the fresh water coming from the Ama- zon spreads out essentially in the middle of the shelf. The halocline is situated few meters (between 2 and 5 m) under the surface, with a lower salinity at the south-east boundary which is 20 and which is 25 at the north-west boundary, whereas, the

  9. New evidence for ice shelf flow across the Alaska and Beaufort margins, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Engels, Jennifer L.

    The Arctic Ocean may act as a lynchpin for global climate change due to its unique physiography as a mediterranean sea located in polar latitudes. In our modern warming climate, debate over the bounds of natural versus anthropogenically-induced climate variability necessitates a comprehensive understanding of Arctic ice extent and configuration over the last interglacial cycle. Longstanding controversy exists as to the volume, timing, and flow trajectories of ice in the Arctic Ocean during glacial maxima when continental ice sheets mantled circum-arctic landmasses. As a result of the Science Ice Exercise surveys of the Arctic Ocean in 1999, new evidence for ice grounding at depths down to 980 m on the Lomonosov Ridge and 750 m on the Chukchi Borderland indicates the likelihood that large ice shelves flowed into the ocean from both the Barents/Kara Sea and the Canadian Arctic Archipelago or eastern Alaska. Sidescan imagery of ˜14100 km2 of seafloor along the Alaska and Beaufort margins in water depths from 250--2800 m maps a repetitive association of recognizable sub-glacially generated bedforms, ice carved-bathymerry, and ice-marginal turbidite gullies over a 640 km stretch of the margin between Point Barrow and the MacKenzie River delta. Glaciogenic bedforms occur across the surface of a flattened bathymetric bench or 'second shelf break' that is interpreted to have been formed by an ice shelf eroding the continental slope. The glacial geology of surrounding areas suggests that an ice shelf on the Alaska and Beaufort margins likely flowed from the mouths of overdeepened glacial troughs in the Canadian Arctic Archipelago westward and across the Chukchi Borderland due to an obstruction in the central Canadian basin. Evidence for an ice shelf along the Alaska and Beaufort margins supports an expanded interpretation of ice volume and extent during Pleistocene glacial periods. This has far-reaching implications for Arctic climate studies, ocean circulation, sediment

  10. Comparison of marine productivity among Outer Continental Shelf planning areas

    SciTech Connect

    Darnell, R.M.

    1991-04-01

    Continental Shelf Associates was contracted to update and expand an earlier work on a comparison of primary productivity among Outer Continental Shelf (OCS) planning areas. The update consists of four general objectives. This report addresses the fourth objective, the potential to use measures of marine secondary productivity in determining relative rankings of the OCS planning area. Ideally, comparisons of secondary productivity among diverse geographic areas would take an ecosystem perspective. However, there is not enough ecosystem-level understanding to allow a comparison on that basis. The report focuses on individual species and group of species. Zooplankton and benthic communities represent major portions of the marine ecosystems and would be the preferred subjects for comparative studies. At this time comparisons of secondary productivity among planning areas would be difficult with existing databases. It is unlikely this situation will improve in the near future.

  11. Outer Continental Shelf oil pipelines under the Interstate Commerce Act

    SciTech Connect

    Malet, E.I.

    1983-05-01

    Since Congress did not repeal the Interstate Commerce Act (ICA) when it enacted the Outer Continental Shelf Lands Act of 1953, it is necessary to examine the jurisdictional provisions of the ICA to determine whether particular oil pipelines on the Outer Continental Shelf (OCS) are subject to ICA regulation. Certain pipeline operations will fall outside the scope of the ICA because they are the operations of private carriers or because they are more closely related to extracting or producing oil and not involved in interstate transport or sale. An unresolved legal issue is whether the OCS is a territory within the meaning of the ICA. If so, then all common carrier oil pipeline transportation on the OCS is interstate within the scope of the ICA. But even if the OCS is not held to be a territory under the ICA, many OCS oil pipelines still may be subject to the ICA because they are integral parts of otherwise interstate transportation systems. 236 references.

  12. Carbon Dynamics on the Louisiana Continental Shelf and Cross-Shelf Feeding of Hypoxia

    EPA Science Inventory

    Large-scale hypoxia regularly develops during the summer on the Louisiana continental shelf. Traditionally, hypoxia has been linked to the vast winter and spring nutrient inputs from the Mississippi River and its distributary, the Atchafalaya River. However, recent studies indica...

  13. Carbon Dynamics on the Louisiana Continental Shelf and Cross-Shelf Feeding of Hypoxia

    EPA Science Inventory

    Large-scale hypoxia regularly develops during the summer on the Louisiana continental shelf. Traditionally, hypoxia has been linked to the vast winter and spring nutrient inputs from the Mississippi River and its distributary, the Atchafalaya River. However, recent studies indica...

  14. Acoustic Propagation in Continental Shelf Break and Slope Environments

    DTIC Science & Technology

    2011-09-01

    goal of the research is to increase the physical understanding of acoustic propagation in continental shelf and slope environments in the 50-4000 Hz...band. This includes both the physics of the seabed and the coupling to physical mechanisms in the water column in complex range- and azimuth-dependent...combined study of statistical inference and the effects of seabed layering is expected to relate propagation statistics to physical mechanisms on

  15. Fetch-Limited Wind Wave Generation on the Continental Shelf

    DTIC Science & Technology

    2003-12-01

    Postgraduate School Monterey, CA 93943-5000 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING /MONITORING AGENCY NAME(S) AND ADDRESS(ES) N/ A 10...wind wave growth by examining cases where a steady wind blows at various angles to a straight coastline, across a continental shelf, in the presence of...opposing the wind does not have a significant effect on the wind sea development. Refraction strongly affects the directional properties of wind waves

  16. Pleistocene mammals from the southern Brazilian continental shelf

    NASA Astrophysics Data System (ADS)

    Lopes, Renato Pereira; Buchmann, Francisco Sekiguchi

    2011-02-01

    Fossils of terrestrial mammals preserved in submarine environment have been recorded in several places around the world. In Brazil such fossils are rather abundant in the southernmost portion of the coast, associated to fossiliferous concentrations at depths up to 10 m. Here is presented a review of such occurrences and the first record of fossils in deeper areas of the continental shelf. The fossils encompass several groups of both extinct and extant mammals, and exhibit several distinct taphonomic features, related to the marine environment. Those from the inner continental shelf are removed and transported from the submarine deposits to the coast during storm events, thus forming large konzentrat-lagerstätte on the beach, called “Concheiros”. The only fossils from deeper zones of the shelf known so far are a portion of a skull, a left humerus and of a femur of Toxodon sp. and a lower right molar of a Stegomastodon waringi, all collected by fishermen at depths around 20 m. The presence of fossils at great depths and distances from the present coastline, without signs of abrasion and far from areas of fluvial discharges does indicate that these remains have not been transported from the continent to the shelf, but have been preserved directly on the area that today correspond to the continental shelf. These remains indicate the existence of large fossiliferous deposits that have developed during periods of sea-level lowstand (glacial maxima) and have been submerged and reworked by the sea-level rise at the end of the last glaciation.

  17. 76 FR 2919 - Outer Continental Shelf Official Protraction Diagram and Supplemental Official Outer Continental...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-18

    ... renewable energy, mineral, and oil and gas lease sales in the geographic areas they represent. The revised... Bureau of Ocean Energy Management, Regulation and Enforcement Outer Continental Shelf Official... Energy Management, Regulation and Enforcement (BOEMRE), Interior. ACTION: Availability of Revised North...

  18. Sea-ice and surface water circulation, Alaskan continental shelf

    NASA Technical Reports Server (NTRS)

    Wright, F. F.; Sharma, G. D.; Burns, J. J. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. Over 1500 water samples from surface and from standard hydrographic depths were collected during June and July 1973 from Bering Sea and Gulf of Alaska. The measurement of temperature, salinity, and productivity indicated that various distinct water masses cover the Bering Sea Shelf. The suspended load in surface waters will be correlated with the ERTS-1 imagery as it becomes available to delineate the surface water circulation. The movement of ice floes in the Bering Strait and Bering Sea indicated that movement of ice varies considerably and may depend on wind stress as well as ocean currents.

  19. Increased spatial variance accompanies reorganization of two continental shelf ecosystems.

    PubMed

    Litzow, Michael A; Urban, J Daniel; Laurel, Benjamin J

    2008-09-01

    Phase transitions between alternate stable states in marine ecosystems lead to disruptive changes in ecosystem services, especially fisheries productivity. We used trawl survey data spanning phase transitions in the North Pacific (Gulf of Alaska) and the North Atlantic (Scotian Shelf) to test for increases in ecosystem variability that might provide early warning of such transitions. In both time series, elevated spatial variability in a measure of community composition (ratio of cod [Gadus sp.] abundance to prey abundance) accompanied transitions between ecosystem states, and variability was negatively correlated with distance from the ecosystem transition point. In the Gulf of Alaska, where the phase transition was apparently the result of a sudden perturbation (climate regime shift), variance increased one year before the transition in mean state occurred. On the Scotian Shelf, where ecosystem reorganization was the result of persistent overfishing, a significant increase in variance occurred three years before the transition in mean state was detected. However, we could not reject the alternate explanation that increased variance may also have simply been inherent to the final stable state in that ecosystem. Increased variance has been previously observed around transition points in models, but rarely in real ecosystems, and our results demonstrate the possible management value in tracking the variance of key parameters in exploited ecosystems.

  20. Depositional history of Louisiana-Mississippi outer continental shelf

    USGS Publications Warehouse

    Kindinger, J.L.; Miller, R.J.; Stelting, C.E.

    1982-01-01

    A geological study was undertaken in 1981 in the Louisiana-Mississippi outer continental shelf for the Bureau of Land Management. The study included a high-resolution seismic reflection survey, surficial sediment sampling and surface current drifter sampling. Approximately 7100 sq km of the Louisiana-Mississippi shelf and upper slope were surveyed. The sea floor of the entire area is relatively smooth except for occasional areas of uplift produced by diapiric intrusion along the upper slope. Characteristics of the topography and subsurface shelf sediments are the result of depositional sequences due to delta outbuilding over transgressive sediments with intervening periods of erosion during low sea level stands. Little evidence of structural deformation such as faults, diapirs, and shallow gas is present on the shelf and only a few minor faults and scarps are found on the slope. Minisparker seismic records in combination with air gun (40 and 5 cu in) and 3.5-kHz subbottom profile records reveal that seven major stages of shelf development have occurred since the middle Pleistocene. The shelf development has been controlled by the rise and fall of sea level. These stages are defined by four major unconformities, several depositions of transgressive sediments, sequences of river channeling and progradational delta deposits. Surficial sediment sample and seismic records indicate tat the last major depositional event was the progradation of the St. Bernard Delta lobe. This delta lobe covered the northwestern and central regions. Surficial sediments in most of the study area are the product of the reworking of the San Bernard Delta lobe and previous progradations.

  1. Bryozoans from rio grande do sul continental shelf, southern Brazil.

    PubMed

    Ramalho, Laís V; Calliari, Lauro

    2015-05-06

    The continental shelf of Rio Grande do Sul (RS) is predominantly composed of unconsolidated sediments with a few hard substrates represented principally by beachrock. In this area there are elongate deposits of shell gravel material which are interpreted as indicators of the palaeo-shorelines. These Pleistocene deposits are overlapped by Holocene sediments (Recent), but are exposed during erosive events caused by extra-tropical cyclones, which provide the mixture of both sediments mainly during autumn and winter. The few studies on bryozoans made in this area previously recorded seven species, one fossil and the other six from Recent fluvial and marine environments. The aim of the present study was to describe the eight most abundant bryozoan species that occur in the inner RS shelf. Of these, four are new records for RS State (Arachnopusia aff. pusae, Hippomonavella brasiliensis, Turbicellepora pourtalesi, and Lifuella gorgonensis), and the other four are new to science (Chaperia taylori, Micropora nodimagna, Cellaria riograndensis, and Exochella moyani).

  2. Southeastern U.S.A. Continental Shelf Respiratory Rates Revisited

    NASA Technical Reports Server (NTRS)

    Sheldon, Joan E.; Griffith, Peter C.; Peters Francesc; Sheldon, Wade M., Jr.; Blanton, Jackson O.; Amft, Julie; Pomeroy, Lawrence R.

    2010-01-01

    Respiratory rates on the U. S. southeastern continental shelf have been estimated several times by different investigators, most recently by Jiang et al. (Biogeochemistry 98:101-113, 2010) who report lower mean rates thanwere found in earlier work and attribute the differences to analytical error in all methods used in earlier studies. The differences are, instead, attributable to the differences in the geographical scope of the studies. The lower estimates of regional organic carbon flux of Jiang et al. (Biogeochemistry 98:101-113, 2010) are a consequence of their extrapolation of data from a small portion of the shelf to the entire South Atlantic Bight. This comment examines the methodologies used as well as the variability of respiratory rates in this region over space and time.

  3. Soft-bottom Portuguese continental shelf polychaetes: Diversity and distribution

    NASA Astrophysics Data System (ADS)

    Martins, R.; Sampaio, L.; Rodrigues, A. M.; Quintino, V.

    2013-08-01

    This study fulfills a gap in the knowledge of the annelid polychaete fauna from most of the Western Iberian coast, a particular biogeographic area where boreal, cold temperate, warm temperate and subtropical faunas can co-occur. A total of 145 samples covering the entire Portuguese continental shelf were analyzed to study the diversity and spatial distribution of the polychaetes and to discuss the relationship between biological and environmental data. A total of 19,731 annelid polychaetes were identified corresponding to 319 species and belonging to 49 families. The species Mediomastus fragilis, Polygordius appendiculatus and Ampharete finmarchica were the most abundant and Ampharete finmarchica, Lumbrineris lusitanica and Aponuphis bilineata the most frequent. Abundance per site reached 620 individuals and alpha diversity ranged from 1 species to 65 spp. 0.1 m- 2. A total of 26 species were firstly recorded in the Portuguese shelf, one of them new for the Iberian coasts. A multivariate analysis based on the abundance of polychaetes revealed six affinity groups: (a) coarse sediments characterized by several species, mostly of the Order Phyllodocida, such as Pisione remota, Goniadella gracilis, Glycera lapidum, Sphaerosyllis bulbosa and Pisione parapari; (b) near shore shelf fine sands dominated by Magelona johnstoni, Magelona filiformis and Sigalion mathildae; (c) northwestern deep muddy sands characterized by Prionospio fallax, Lagis koreni and Owenia fusiformis; (d) southwestern deep muddy sands with Aphelochaeta sp., Galathowenia oculata and Monticellina heterochaeta; (e) southern midshelf muddy sands characterized by Euchone rubrocincta, Prionospio multibranchiata and several southern species; and (f) muds dominated by Nepthys incisa and characterized by Sternaspis scutata, Heteromastus filiformis, Ninoe armoricana and Glycera unicornis. Sediment grain-size and organic matter were the variables best related to the benthic polychaete spatial distribution

  4. The continental shelf benthic iron flux and its isotope composition

    NASA Astrophysics Data System (ADS)

    Severmann, Silke; McManus, James; Berelson, William M.; Hammond, Douglas E.

    2010-07-01

    Benthic iron fluxes from sites along the Oregon-California continental shelf determined using in situ benthic chambers, range from less than 10 μmol m -2 d -1 to values in excess of ˜300 μmol m -2 d -1. These fluxes are generally greater than previously published iron fluxes for continental shelves contiguous with the open ocean (as opposed to marginal seas, bays, or estuaries) with the highest fluxes measured in the regions around the high-sediment discharge Eel River and the Umpqua River. These benthic iron fluxes do not covary with organic carbon oxidation rates in any systematic fashion, but rather seem to respond to variations in bottom water oxygen and benthic oxygen demand. We hypothesize that the highest rates of benthic iron efflux are driven, in part, by the greater availability of reactive iron deposited along these river systems as compared to other more typical continental margin settings. Bioirrigation likely plays an important role in the benthic Fe flux in these systems as well. However, the influence of bottom water oxygen concentrations on the iron flux is significant, and there appears to be a threshold in dissolved oxygen (˜60-80 μM), below which sediment-ocean iron exchange is enhanced. The isotope composition of this shelf-derived benthic iron is enriched in the lighter isotopes, and appears to change by ˜3‰ (δ 56Fe) during the course of a benthic chamber experiment with a mean isotope composition of -2.7 ± 1.1‰ (2 SD, n = 9) by the end of the experiment. This average value is slightly heavier than those from two high benthic Fe flux restricted basins from the California Borderland region where δ 56Fe is -3.4 ± 0.4‰ (2 SD, n = 3). These light iron isotope compositions support previous ideas, based on sediment porewater analyses, suggesting that sedimentary iron reduction fractionates iron isotopes and produces an isotopically light iron pool that is transferred to the ocean water column. In sum, our data suggest that

  5. Surficial sediments on the western Canadian continental shelf

    NASA Astrophysics Data System (ADS)

    Bornhold, Brian D.; Barrie, J. Vaughn

    1991-08-01

    The active continental margin off western Canada is characterized in the south by convergence between the Explorer and Juan de Fuca Plates and the America Plate, and in the north by transform fault motion between the Pacific and America Plates along the Queen Charlotte Fault. Except in some of the deepest troughs and basins shelf sediments are dominated by immature lithic arenites reflecting this tectonic setting. The Vancouver Island shelf is from 5 to 75 km wide and displays complex topography on the inner shelf and a relatively featureless mid- and outer shelf. An exception is the area off southwestern Vancouver Island where large basins bounded by morainal deposits extend more than two-thirds of the distance across the shelf. The shelf edge varies from 180 to 225 m depth and is indented by numerous canyons. Nearshore sediments consist mainly of gravels and boulders and become finer offshore such that muds are slowly accumulating in depths greater than 100 m. Off northwestern Vancouver Island calcareous sediments are abundant with carbonate values often exceeding 75%. High wave and current energies and efficient sediment trapping in coastal fiords have resulted in low rates of accumulation. Olive, glauconitic, Holocene muds and muddy sands are generally less than 0.3 m thick and accumulate only on the outer shelf over an extensive stiff, gray, glaciomarine sandy mud. Queen Charlotte Sound exhibits three broad, shallow, glacially scoured troughs, filled mainly with clayey silts and fine sands and separated by sand and gravel covered banks. Hecate Strait, between the Queen Charlotte Islands and the mainland, consists of a prominent southward-opening trough along the east side of the Strait bounded by Dogfish and Laskeek Banks on the west adjacent to Graham and Moresby Islands, respectively. The trough below 200 m is filled by silts. The banks are covered by discontinuous sands and gravels of variable calcareous content. The bank edges often display megaripples and

  6. Continental shelf benthos off Otago Peninsula, New Zealand

    NASA Astrophysics Data System (ADS)

    Probert, P. Keith; Wilson, John B.

    1984-09-01

    Benthic macrofauna of the continental shelf off Otago Peninsula, south-eastern New Zealand (45°51'S, 170°52'E) was surveyed by dredge sampling during 1973-1975. Numerical classification (Canberra metric coefficient and flexible sorting) was used to produce site groups and species groups, and three major benthic communities were recognised: a shallow-water (14-25 m) fauna inhabiting well-sorted fine sand, a mid-shelf fauna (concentrated in the depth range 50-76 m) associated with sediments containing the greatest proportions of gravel and siltclay, and a predominantly sand-bottom fauna occurring mainly on the outer shelf (87-150 m). All station groups were dominated numerically by polychaetes (mean of 36·6-56% of individuals) with Mollusca (13·8-25%) or Crustacea (12·1-19·4%) the next most abundant group. The inshore sand fauna was the most distinct, characteristic elements being the trochid gastropod Antisolarium egenum, an amphipod of the genus Hippomedon and dense patches of the spionid polychaete Spiophanes bombyx. Diagnostic species of the mid-shelf mixed sediments were Lepidonotus jacksoni, Psammolyce antipoda, Lumbrineris brevicirra and Phyllamphicteis foliata (Polychaeta), Terenochiton otagoensis, Micrelenchus caelatus caelatus, Maoricolpus roseus roseus and Zegalerus tenuis (Mollusca), Ampelisca chiltoni (Amphipoda) and Amphipholis squamata (Ophiuroidea). Outer shelf sand stations were faunally less distinct, but among the more characteristic species were Euthalenessa fimbriata, Sigalion sp. and Euchone sp. (Polychaeta) and Gari stangeri (Bivalvia). Several abundant species were widely distributed among station groups, notably Nephtys macroura, Lumbrineris magalhaensis, Phyllochaetopterus socialis and Owenia fusiformis (Polychaeta) and Nucula nitidula and Tawera spissa (Bivalvia). Free-living lunulitiform Bryozoa of the genus Otionella were a characteristic component of inner and outer shelf sand faunas, and their inshore penetration probably marks

  7. 78 FR 48180 - Consolidation of Officer in Charge, Marine Inspection For Outer Continental Shelf Activities...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-07

    ... for all Mobile Offshore Drilling Units and Floating Outer Continental Shelf Facilities (as defined in... Commander. Vessels requiring Coast Guard inspection include Mobile Offshore Drilling Units (MODUs), Floating...

  8. Sources and Distribution of Organic Matter in Sediments of the Louisiana Continental Shelf

    EPA Science Inventory

    Both riverine and marine sources of organic matter (OM) contribute to sediment organic pools, and either source can contribute significantly to sediment accumulation, burial, and remineralization rates on river dominated continental shelf systems. For the Louisiana continental sh...

  9. Sources and Distribution of Organic Matter in Sediments of the Louisiana Continental Shelf

    EPA Science Inventory

    Both riverine and marine sources of organic matter (OM) contribute to sediment organic pools, and either source can contribute significantly to sediment accumulation, burial, and remineralization rates on river dominated continental shelf systems. For the Louisiana continental sh...

  10. Rifting his­tory and structural development of the continental margin north of Alaska

    USGS Publications Warehouse

    Grantz, Arthur; May, S.D.

    1982-01-01

    Seismic-reflection profiles in the Alaskan Beaufort Sea and onshore geology indicate that the continental margin north of Alaska is of Atlantic type. Rifting appears to have begun in earliest Jurassic time, about 190 to 185 m.y. ago, when crustal extension created a rift-valley system beneath the Beaufort shelf and part of the adjacent coastal plain. Subsequent crustal warming caused rift-margin uplift and erosion, created a breakup unconformity, and initiated breakup and seafloor spreading in the Canada Basin about 125 m.y. ago. Subsequent cooling caused rapid subsidence of the margin, which was followed by vigorous progradation of the present continental terrace of the Beaufort Sea beginning in Albian time.

  11. Multicycle sediments on the continental shelf of Cadiz (SW Spain)

    NASA Astrophysics Data System (ADS)

    Gutiérrez-Mas, J. M.; Moral, J. P.; Sánchez, A.; Dominguez, S.; Muñoz-Perez, J. J.

    2003-07-01

    The study of recent sedimentation in the Gulf of Cadiz continental shelf (SW Europe) is of interest due to its proximity to the Strait of Gibraltar, where the Atlantic and Mediterranean waters are interchanged and the Western Mediterranean Alpidic Orogen closes through the Gibraltar Arch. The existence of relict materials hinders the distinction of the past and present hydrodynamic regimes in present day sediments. An adequate combination of techniques has allowed the establishment of the multicyclic character of the sediments, as well as the stages undergone by the terrigenous grains. Different stages were identified: eolian and energetic fluvial provenance, chemical alterations acquired in a pedological environment, and a marine coastal origin. To verify the source areas, textural and mineralogical features of marine sediments were compared with those found in geological units from fluvial basins. Three zones were differentiated: (a) a sandy littoral, which receives local sediment supplies; (b) a clayey zone between the Guadalquivir River and Cadiz, controlled by contributions from this river provenant of the Iberian Massif and Betic Mountain range; and (c) a sandy continental shelf, between Cadiz and the Cape of Trafalgar, with a low rate of supplies coming from the Guadalete and Barbate rivers, which include materials from the Occidental Betic Mountain range and Neogene units.

  12. Law of the sea, the continental shelf, and marine research

    USGS Publications Warehouse

    Hutchinson, Deborah R.; Rowland, Robert W.

    2007-01-01

    The question of the amount of seabed to which a coastal nation is entitled is addressed in the United Nations Convention on the Law of the Sea (UNCLOS). This treaty, ratified by 153 nations and in force since 1994, specifies national obligations, rights, and jurisdiction in the oceans, and it allows nations a continental shelf out to at least 200 nautical miles or to a maritime boundary. Article 76 (A76) of the convention enables coastal nations to establish their continental shelves beyond 200 nautical miles and therefore to control, among other things, access for scientific research and the use of seabed resources that would otherwise be considered to lie beyond national jurisdiction. To date, seven submissions for extended continental shelves (ECS) have been filed under UNCLOS (Table 1). These submissions have begun to define the ambiguities in A76. How these ambiguities are resolved into final ECS boundaries will probably set important precedents guiding the future delimitation of the ECS by the United States, which has not ratified the convention, and other coastal nations. This report uses examples from the first three submissions—by the Russian Federation, Brazil, and Australia—to identify outstanding issues encountered in applying A76 to ECS delimitation.

  13. Geology and physiography of the continental margin north of Alaska and implications for the origin of the Canada Basin

    USGS Publications Warehouse

    Grantz, Arthur; Eittreim, Stephen L.; Whitney, O.T.

    1979-01-01

    The continental margin north of Alaska is of Atlantic type. It began to form probably in Early Jurassic time but possibly in middle Early Cretaceous time, when the oceanic Canada Basin of the Arctic Ocean is thought to have opened by rifting about a pole of rotation near the Mackenzie Delta. Offsets of the rift along two fracture zones are thought to have divided the Alaskan margin into three sectors of contrasting structure and stratigraphy. In the Barter Island sector on the east and the Chukchi sector on the west the rift was closer to the present northern Alaska mainland than in the Barrow sector, which lies between them. In the Barter Island and Chukchi sectors the continental shelf is underlain by prisms of clastic sedimentary rocks that are inferred to include thick sections of Jurassic and Neocomian (lower Lower Cretaceous) strata of southern provenance. In the intervening Barrow sector the shelf is underlain by relatively thin sections of Jurassic and Neocomian strata derived from northern sources that now lie beneath the outer continental shelf. The rifted continental margin is overlain by a prograded prism of Albian (upper Lower Cretaceous) to Tertiary clastic sedimentary rocks that comprises the continental terrace of the western Beaufort and northern Chukchi Seas. On the south the prism is bounded by Barrow arch, which is a hingeline between the northward-tilted basement surface beneath the continental shelf of the western Beaufort Sea and the southward-tilted Arctic Platform of northern Alaska. The Arctic platform is overlain by shelf clastic and carbonate strata of Mississippian to Cretaceous age, and by Jurassic and Cretaceous clastic strata of the Colville foredeep. Both the Arctic platform and Colville foredeep sequences extend from northern Alaska beneath the northern Chukchi Sea. At Herald fault zone in the central Chukchi Sea they are overthrust by more strongly deformed Cretaceous to Paleozoic sedimentary rocks of Herald arch, which trends

  14. Geology and petroleum potential of Shumagin continental margin, western Gulf of Alaska

    SciTech Connect

    Bruns, T.R.; Von Huene, R.; Culotta, R.D.; Lewis, S.D.; Ladd, J.W.

    1986-07-01

    Interpretations of multichannel seismic reflection data indicate that the Shumagin continental margin seaward of the Border Ranges fault is underlain by two major seismic sequences, separated by an erosional unconformity beneath the shelf and by the time-correlative conformity seaward. Rocks above the unconformity are late Miocene and younger. Rocks below the unconformity can be as young as middle Miocene beneath the outer shelf and slope, seaward of a paleoshelf break. However, beneath the shelf they are primarily Late Cretaceous turbidites of the Shumagin Formation and Paleocene granodiorite. Late Miocene and younger structures of the Shumagin margin include Shumagin, Sanak, and Unimak basins and Unimak Ridge, a midslope structural high. Strata in Sanak and Unimak basins were deposited on a subsiding outer shelf and slope, and trapped behind Unimak Ridge and its now-buried structural continuation. Sanak and Unimak basins are in part bounded by northwest-trending extensional faults that parallel both the early Tertiary Beringian margin and a transverse tectonic boundary that segments the fore-arc. These faults may have developed during collapse and extension along the southeastward continuation of the old Beringian margin, analogous to the processes that created the Bering Shelf basins. The most promising areas of the Shumagin margin for petroleum potential are Sanak, and Unimak basins, which contain strata 8 and 4.5 km thick, respectively, and beneath the outer shelf and slope. Paleogene source rocks like those on the adjacent Alaska Peninsula may be preserved offshore, seaward of the inferred paleoshelf break. Reservoir rocks might have formed from granitic-rich erosional products derived during Oligocene and Miocene erosion of the shelf plutons.

  15. 77 FR 24980 - Notice on Outer Continental Shelf Oil and Gas Lease Sales

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-26

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management Notice on Outer Continental Shelf Oil and Gas Lease Sales AGENCY... from bidding with any entity in any other of the following groups at Outer Continental Shelf oil...

  16. 77 FR 27480 - Outer Continental Shelf Scientific Committee; Announcement of Plenary Session

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-05-10

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management Outer Continental Shelf Scientific Committee; Announcement of Plenary...: The Outer Continental Shelf (OCS) Scientific Committee (SC) will meet at the Fess Parker's...

  17. 78 FR 64243 - Notice on Outer Continental Shelf Oil and Gas Lease Sales

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-10-28

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management Notice on Outer Continental Shelf Oil and Gas Lease Sales AGENCY... from bidding with any entity in any of the other following groups at Outer Continental Shelf oil...

  18. 76 FR 67759 - Notice on Outer Continental Shelf Oil and Gas Lease Sales

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-02

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management Notice on Outer Continental Shelf Oil and Gas Lease Sales AGENCY... from bidding with any entity in any other of the following groups at Outer Continental Shelf oil...

  19. 77 FR 64826 - Notice on Outer Continental Shelf Oil and Gas Lease Sales

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-10-23

    ... From the Federal Register Online via the Government Publishing Office ] DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management (BOEM) Notice on Outer Continental Shelf Oil and Gas Lease Sales AGENCY... with any entity in any of the other following groups at Outer Continental Shelf oil and gas lease...

  20. 78 FR 27430 - Notice on Outer Continental Shelf Oil and Gas Lease Sales

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-10

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management Notice on Outer Continental Shelf Oil and Gas Lease Sales AGENCY... from bidding with any entity in any of the other following groups at Outer Continental Shelf oil...

  1. 75 FR 51968 - Outer Continental Shelf Air Regulations Consistency Update for Massachusetts

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-24

    ... From the Federal Register Online via the Government Publishing Office ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 55 Outer Continental Shelf Air Regulations Consistency Update for Massachusetts AGENCY... update to a portion of the Outer Continental Shelf (``OCS'') Air Regulations. Requirements applying...

  2. 76 FR 4129 - Notice on Outer Continental Shelf Oil and Gas Lease Sales

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-24

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management, Regulation and Enforcement Notice on Outer Continental Shelf Oil and... any entity in any other of the following groups at Outer Continental Shelf oil and gas lease sales...

  3. 78 FR 25100 - Outer Continental Shelf Scientific Committee; Announcement of Plenary Session

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-04-29

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management Outer Continental Shelf Scientific Committee; Announcement of Plenary...: The Outer Continental Shelf (OCS) Scientific Committee (SC) will meet at the Marriott Downtown...

  4. 75 FR 24966 - Notice on Outer Continental Shelf Oil and Gas Lease Sales

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-06

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Minerals Management Service Notice on Outer Continental Shelf Oil and Gas Lease Sales AGENCY: Minerals... in any other of the following groups at Outer Continental Shelf oil and gas lease sales to be...

  5. 76 FR 28449 - Notice on Outer Continental Shelf Oil and Gas Lease Sales

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-05-17

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE) Notice on Outer Continental Shelf... with any entity in any other of the following groups at Outer Continental Shelf oil and gas lease...

  6. 76 FR 70156 - Draft Programmatic Environmental Impact Study (PEIS) for Proposed 5-Year Outer Continental Shelf...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-10

    ...-Year Outer Continental Shelf (OCS) Oil and Gas Leasing Program for 2012-2017 AGENCY: Bureau of Ocean...- 2017 Draft PEIS prepared by BOEM to support the Proposed Outer Continental Shelf Oil and Gas Leasing Program for 2012-2017. BOEM concurrently requests comments and announces public hearings. DATES: Submit...

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

    SciTech Connect

    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.

  8. Assessment of marine debris on the Belgian Continental Shelf.

    PubMed

    Van Cauwenberghe, Lisbeth; Claessens, Michiel; Vandegehuchte, Michiel B; Mees, Jan; Janssen, Colin R

    2013-08-15

    A comprehensive assessment of marine litter in three environmental compartments of Belgian coastal waters was performed. Abundance, weight and composition of marine debris, including microplastics, was assessed by performing beach, sea surface and seafloor monitoring campaigns during two consecutive years. Plastic items were the dominant type of macrodebris recorded: over 95% of debris present in the three sampled marine compartments were plastic. In general, concentrations of macrodebris were quite high. Especially the number of beached debris reached very high levels: on average 6429±6767 items per 100 m were recorded. Microplastic concentrations were determined to assess overall abundance in the different marine compartments of the Belgian Continental Shelf. In terms of weight, macrodebris still dominates the pollution of beaches, but in the water column and in the seafloor microplastics appear to be of higher importance: here, microplastic weight is approximately 100 times and 400 times higher, respectively, than macrodebris weight.

  9. Estimated oil and gas reserves, Southern California outer continental shelf

    USGS Publications Warehouse

    Ballantyne, R.S.

    1983-01-01

    Remaining recoverable reserves of oil* and gas in the Outer Continental Shelf off Southern California are estimated to be 968 million barrels of oil and 1,851 billion cubic feet of gas as of December 31, 1982. These reserves are attributed to 14 fields. Original recoverable reserves from these fields are estimated at 1,217 million barrels of oil and 1,983 billion cubic feet of gas. The estimates for both the remaining and the original recoverable reserves of oil and gas are higher than the corresponding estimates for December 31, 1981. Reserve estimates for 12 fields were based on volumetric reservoir studies. Decline-curve and volumetric analyses were used for the remaining two fields. Six fields were on production at year's end and a gas field is scheduled to commence production in 1983. *The term 'oil' as used in this report includes crude oil, condensate, and gas-plant liquids.

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

    PubMed

    Fitzpatrick, Ben M; Harvey, Euan S; Heyward, Andrew J; Twiggs, Emily J; Colquhoun, Jamie

    2012-01-01

    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 connected habitats

  11. Habitat Specialization in Tropical Continental Shelf Demersal Fish Assemblages

    PubMed Central

    Fitzpatrick, Ben M.; Harvey, Euan S.; Heyward, Andrew J.; Twiggs, Emily J.; Colquhoun, Jamie

    2012-01-01

    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 connected

  12. Analysis of the petroleum resources of the Norwegian Continental Shelf

    SciTech Connect

    Flertoft, I.P.; Kvadsheim, E.; Kalheim, J.E.

    1995-08-01

    The 1995 analysis of the petroleum resources of Norway is based on a play analysis. The input to the 1995 analysis is updated and refined compared with the analysis of 1993. The analysis makes a major distinction between unconfirmed play models and plays confirmed by discoveries. The unconfirmed plays have a higher risk and a greater range of uncertainty in the resource estimates compared to the confirmed plays. The effect of the unconfirmed plays on the estimates within different exploration areas is discussed. The unconfirmed play models are an important aspect of the exploration in the new exploration areas north of 62{degrees}N. The total estimate for the Norwegian Shelf is well within the estimate given in the 1993 analysis, but there are some adjustments in the relative importance of the different exploration provinces. Much emphasis is placed on incorporating historical exploration data and statistics to calibrate the play models. This includes rate of success and field size distributions of the individual play models and exploration provinces. Major confirmed plays in the North Sea have a rate of success of about 30% and show a good fit to a log normal field size distribution. Based on the log normal distribution it is possible to give prognosis for the size distribution of the undiscovered accumulation. This has made it possible to work out an economic analysis of the profitability of future exploration on the Norwegian Continental Shelf.

  13. Anomalous topography on the continental shelf around Hudson Canyon

    USGS Publications Warehouse

    Knebel, H. J.

    1979-01-01

    Recent seismic-reflection data show that the topography on the Continental Shelf around Hudson Canyon is composed of a series of depressions having variable spacings (< 100 m to 2 km), depths (1-10 m), outlines, and bottom configurations that give the sea floor an anomalous "jagged" appearance in profile. The acoustic and sedimentary characteristics, the proximity to relict shores, and the areal distribution indicate that this rough topography is an erosional surface formed on Upper Pleistocene silty sands about 13,000 to 15,000 years ago by processes related to Hudson Canyon. The pronounced southward extension of the surface, in particular, may reflect a former increase in the longshore-current erosion capacity caused by the loss of sediments over the canyon. Modern erosion or nondeposition of sediments has prevented the ubiquitous sand sheet on the Middle Atlantic shelf from covering the surface. The "anomalous" topography may, in fact, be characteristic of areas near other submarine canyons that interrupt or have interrupted the longshore drift of sediments. ?? 1979.

  14. Outer Continental Shelf environmental assessment program. Final reports of principal investigators. Volume 45

    SciTech Connect

    Not Available

    1986-07-01

    Contents include: Pelagic distribution of marine birds of the north Aleutian Shelf and analysis of encounter probability; The breeding biology and feeding ecology of marine birds in the Gulf of Alaska; Feeding ecology of marine birds in the nearshore waters of Kodiak Island; Diets and food web relationships of seabirds in the Gulf of Alaska and adjacent marine region.

  15. 75 FR 76632 - Oil and Gas and Sulphur Operations in the Outer Continental Shelf-Increased Safety Measures for...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-12-09

    ... and Sulphur Operations in the Outer Continental Shelf--Increased Safety Measures for Energy Development on the Outer Continental Shelf; Correction AGENCY: Bureau of Ocean Energy Management, Regulation... oil and gas exploration and development on the Outer Continental Shelf. This document contains...

  16. Surficial sediments along the inner Continental shelf of Maine

    USGS Publications Warehouse

    Kelley, J.T.; Dickson, S.M.

    1999-01-01

    Through 10 years of support from the Minerals Management Service-Association of American State Geologists' Continental Margins Program we have mapped along the Maine coast, seaward to the 100 m isobath. In all, 1,773 bottom sample stations were occupied, 3,358 km of side-scan sonar and 5,011 km of seismic reflection profiles were gathered. On the basis of these data, a surficial sediment map was created for the Maine inner continental shelf during the Year 8 project, and cores and seismic data were collected to evaluate sand thickness during Years 9 and 10. Sand covers only 8% of the Maine shelf, and is concentrated seaward of beaches off southern Maine in water depths less than 60 m. Sand occurs in three depositional settings: (1) in shoreface deposits connected dynamically to contemporary beaches; (2) in submerged deltas associated with lower sea-level positions; and (3) in submerged lowstand shoreline positions between 50 and 60 m. Seismic profiles over the shoreface off Saco Bay, Wells Embayment, and off the Kennebec River mouth each imaged a wedge-shaped acoustic unit which tapered off between 20 and 30 m. Cores determined that this was sand that was underlain by a variable but thin (commonly < 1 m) deposit of estuarine muddy sand and a thick deposit of glacial-marine mud. Off Saco Bay, more than 55 million m3 of sand exists in the shoreface, compared with about 22 million m3 on the adjacent beach and dunes. Seaward of the Kennebec River, a large delta deposited between 13 ka and the present time holds more than 300 million m3 of sand and gravel. The best sorted sand is on the surface nearshore, with increasing amounts of gravel offshore and mud beneath the surficial sand sheet. Bedforms indicate that the surficial sand is moved by waves to at least 55 m depth. Seaward of the Penobscot River, no significant sand or gravel was encountered. Muddy estuarine sediments overlie muddy glacial-marine sediment throughout the area offshore area of this river. No

  17. Alaska

    SciTech Connect

    Jones, B.C.; Sears, D.W.

    1981-10-01

    Twenty-five exploratory wells were drilled in Alaska in 1980. Five oil or gas discovery wells were drilled on the North Slope. One hundred and seventeen development and service wells were drilled and completed, primarily in the Prudhoe Bay and Kuparuk River fields on the North Slope. Geologic-geophysical field activity consisted of 115.74 crew months, an increase of almost 50% compared to 1979. These increases affected most of the major basins of the state as industry stepped up preparations for future lease sales. Federal acreage under lease increased slightly, while state lease acreage showed a slight decline. The year's oil production showed a increase of 16%, while gas production was down slightly. The federal land freeze in Alaska showed signs of thawing, as the US Department of Interior asked industry to identify areas of interest onshore for possible future leasing. National Petroleum Reserve in Alaska was opened to private exploration, and petroleum potential of the Arctic Wildlife Refuge will be studied. One outer continental shelf lease sale was held in the eastern Gulf of Alaska, and a series of state and federal lease sales were announced for the next 5 years. 5 figures, 5 tables.

  18. On instability and mixing on the UK Continental Shelf

    NASA Astrophysics Data System (ADS)

    Liu, Zhiyu

    2016-06-01

    The stability of stratified flows at locations in the Clyde, Irish and Celtic Seas on the UK Continental Shelf is examined. Flows are averaged over periods of 12-30 min in each hour, corresponding to the times taken to obtain reliable estimates of the rate of dissipation of turbulent kinetic energy per unit mass, ε. The Taylor-Goldstein equation is solved to find the maximum growth rate of small disturbances to these averaged flows, and the critical gradient Richardson number, Ric. The proportion of unstable periods where the minimum gradient Richardson number, Rimin, is less than Ric is about 35%. Cases are found in which Ric < 0.25; 37% of the flows with Rimin < 0.25 are stable, and Ric < 0.24 in 68% of the periods where Rimin < 0.25. Marginal conditions with 0.8 < Rimin/Ric < 1.2 occur in 30% of the periods examined. The mean dissipation rate at the level where the fastest growing disturbance has its maximum amplitude is examined to assess whether the turbulence there is isotropic and how it relates to the wave-turbulence boundary. It is concluded that there is a background level of dissipation that is augmented by instability; instability of the averaged flow does not account for all the turbulence observed in mid-water. The effects of a horizontal separation of the measurements of shear and buoyancy are considered. The available data do not support the hypothesis that the turbulent flows observed on the UK shelf adjust rapidly to conditions that are close to being marginal, or that flows in a particular location and period of time in one sea have stability characteristics that are very similar to those in another.

  19. Estimating rocky seafloor extent on the Southern California continental shelf

    USGS Publications Warehouse

    Cochrane, G.R.; Greene, H. Gary

    2009-01-01

    High-resolution sonar data are necessary to map bottom substrate for habitat studies but are lacking over much of the continental shelf. With such data, areas covered by sediment can be distinguished from bedrock areas with an accuracy of ??90%. Without these data, the extent of sediment as thick as 10 m cannot be resolved, and estimates of the extent of rocky seafloor are exaggerated. A study area north of Anacapa Island in Southern California interpreted as a large rocky area after mapping with low-resolution seismic systems was found to have exposed rocky bottom in only 10% of the area when mapped with high-resolution, side-scan sonar. The area of rock was estimated using video-supervised, sonar-image classification of textural derivatives of the data calculated from gray-level co-occurrence matrices. The classification of soft bottom was found to be ??90% accurate using an independent data set, derived from seafloor sampling records. Two general types of rock exposure are observed-sparse linear outcrops of layered sedimentary rocks and more massive, rounded outcrop areas of volcanic rocks. The percentage of exposed rock in volcanic areas exceeded that in sedimentary rock areas by a factor of 5 in the study area north of Anacapa Island. South of Point Arguello, 80% of the shelf seafloor is underlain by sedimentary rock units. The percentage of area that is exposed, rocky-reef habitat may be greater in other areas of coastal seafloor if the bedrock is predominantly volcanic. ?? 2009 The Geological Society of America.

  20. Sedimentary Records of Shelf Edge Glaciation: A Young Trough-Mouth Fan on the Gulf of Alaska Yakutat Margin

    NASA Astrophysics Data System (ADS)

    Swartz, J. M.; Gulick, S. P. S.; Goff, J. A.

    2015-12-01

    The St. Elias Mountains in Southeastern Alaska are an active orogen that host temperate marine glaciers. Here, ice streams advancing across the continental shelf during glacial periods create wide shelf-crossing troughs and deliver large sediment volumes directly to the shelf edge, and from there to the continental slope and the deep sea Surveyor Fan. The continental slope exhibits steep morphology (~10°-30°), controlled by the Transition Fault, a transform boundary between the Yakutat micro-plate and the Pacific plate. Prior statistical analysis of continental slope morphology indicates that these steep initial slope conditions have been modified by proximal sedimentation during repeated glacial advances. Downslope of the Yakutat Sea Valley an incipient trough-mouth fan exists while between the troughs and downslope of the Alsek Sea Valley sediment slope-bypass dominates. Seismic analysis indicates that the Yakutat margin has seen significant slope sedimentation since the intensification of northern hemisphere glaciation ~2.6 Ma, but it is only recently that sufficient sediment supply has existed to overwhelm the steep margin topography and form the young trough-mouth fan. The mid-Pleistocene climate transition at ~1 Ma, and its associated shift from 41Kyr to 100Kyr glacial-interglacial climate cycles, could have potentially allowed sustained ice stream advances to the shelf edge and associated high proximal sedimentation on the continental slope. Integration of seismic data and newly obtained age constraints from recent IODP cores allows for investigation into the timing of Yakutat trough-mouth fan sedimentation and its relation to climate transitions.

  1. Marine geology of the Near Islands Shelf, Alaska

    USGS Publications Warehouse

    Scruton, Philip Challacombe

    1953-01-01

    During the summer of 1950 on the insular shelf surrounding the Near Islands, Alaska, 193 oceanographic stations were occupied from aboard the U. S. Geological Survey vessel EIDER. Bottom character and temperature observations were made at these stations. The composition and size distribution characteristics of the bottom samples have been determined. Components of terrigenous origin are angular to subangular sand and silt and angular to well rounded granules, pebbles, and cobbles, all composed of little-altered fragments of the fine grained insular rocks. Components of marine origin are the skeletons of Foraminifera, diatoms, and sponges and the broken shells of a few species of mollusks and of one echinoid species. A chart, based also on the study of approximately 600 USC&GS bottom notations, was prepared to show the distribution of these components of the sediments. Bed rock is exposed on most of the shelf; where sediment occurs terrigenous components are generally most important near shore, whereas marine components are more important seaward of the islands. Studies of the Foraminifera fauna and the diatom flora (identified by K. E. Lohman) and the few mollusks of quantitative importance show these organisms to be forms characteristic of cold or deep water or occurring in a wide range of temperature conditions. The Foraminifera exhibit depth zonation which seems to be controlled in part by temperature and in part by depth or some other variable which is a function of depth. Sphericity and roundness studies made on pebbles from the shelf, the beaches, and the fluvio-glacial deposits together with shelf topographic features and Foraminifera from sediment deposited before ice wastage was complete suggest the shelf was not subjected to prolonged surf action during the post-glacial rise of sea level. To aid in interpreting the sediments and their distribution several subaerial and marine environmental factors were investigated. Those factors found to be of most

  2. Trophic interactions within the Ross Sea continental shelf ecosystem.

    PubMed

    Smith, Walker O; Ainley, David G; Cattaneo-Vietti, Riccardo

    2007-01-29

    The continental shelf of the Ross Sea is one of the Antarctic's most intensively studied regions. We review the available data on the region's physical characteristics (currents and ice concentrations) and their spatial variations, as well as components of the neritic food web, including lower and middle levels (phytoplankton, zooplankton, krill, fishes), the upper trophic levels (seals, penguins, pelagic birds, whales) and benthic fauna. A hypothetical food web is presented. Biotic interactions, such as the role of Euphausia crystallorophias and Pleuragramma antarcticum as grazers of lower levels and food for higher trophic levels, are suggested as being critical. The neritic food web contrasts dramatically with others in the Antarctic that appear to be structured around the keystone species Euphausia superba. Similarly, we suggest that benthic-pelagic coupling is stronger in the Ross Sea than in most other Antarctic regions. We also highlight many of the unknowns within the food web, and discuss the impacts of a changing Ross Sea habitat on the ecosystem.

  3. Trophic interactions within the Ross Sea continental shelf ecosystem

    PubMed Central

    Smith, Walker O; Ainley, David G; Cattaneo-Vietti, Riccardo

    2006-01-01

    The continental shelf of the Ross Sea is one of the Antarctic's most intensively studied regions. We review the available data on the region's physical characteristics (currents and ice concentrations) and their spatial variations, as well as components of the neritic food web, including lower and middle levels (phytoplankton, zooplankton, krill, fishes), the upper trophic levels (seals, penguins, pelagic birds, whales) and benthic fauna. A hypothetical food web is presented. Biotic interactions, such as the role of Euphausia crystallorophias and Pleuragramma antarcticum as grazers of lower levels and food for higher trophic levels, are suggested as being critical. The neritic food web contrasts dramatically with others in the Antarctic that appear to be structured around the keystone species Euphausia superba. Similarly, we suggest that benthic–pelagic coupling is stronger in the Ross Sea than in most other Antarctic regions. We also highlight many of the unknowns within the food web, and discuss the impacts of a changing Ross Sea habitat on the ecosystem. PMID:17405209

  4. Continental shelf fish production estimation from CZCS chlorophyll data

    NASA Technical Reports Server (NTRS)

    Iverson, Richard L.

    1989-01-01

    A method for ocean fish production estimation was proposed for development. The method was to use data acquired with the Coastal Zone Color Scanner, and processed into chlorophyll concentrations by the GSFC ocean Sciences Division, in combination with fish production and primary production data acquired from different ocean areas. A linear relation exits between annual fish production and annual phytoplankton carbon production for a wide range of coastal ocean environments. The uses of several existing algorithms which relate primary production to CZCS chlorophyll data as input to the fish production regression model is proposed. A question relating phytoplankton production to CZCS chlorophyll was obtained by Eppley (1984) using chlorophyll data obtained from field samples, equivalent to chlorophyll data obtained from CZCS imagery, and primary production data obtained from ship-board observations on a wide variety of coastal and open ocean environments. This equation was modified with additional data and was successfully tested using CZCS data and field chlorophyll and phytoplankton production data obtained from northeastern North American continental shelf waters and Atlantic open ocean waters. The modified Eppley (1984) relation also estimated phytoplankton annual carbon production in the Sargasso Sea within the confidence limits of a mean value obtained from the Eppley (1984) equation for oceanic waters that provide about 90 percent of total ocean primary production. The modified Eppley production formula applied to CZCS chlorophyll data obtained from several northeastern North American coastal environments gave phytoplankton annual carbon production values similar to the values used in the fish production regression equation.

  5. Factors Limiting Phytoplankton Production in a Tropical Continental Shelf Ecosystem

    NASA Astrophysics Data System (ADS)

    Burford, M. A.; Rothlisberg, P. C.

    1999-05-01

    The effects of light and nutrients on phytoplankton production were examined during both the south-east monsoon (winter) and north-west monsoon (summer) in the northern Gulf of Carpentaria, Australia. Integrated production and chlorophyll values were similar between summer and winter in Albatross Bay in the north-east Gulf over 4 years where shallow waters within the coastal boundary layer (<20m) were well-mixed year-round. Integrated production in well-mixed, deeper (>20m) waters of the Gulf was low (winter, 557±351mgCm -2day -1) compared with waters which were stratified during the north-west monsoon (summer, 955±129mgCm -2day -1). The lower production was due to high turbidity and light attenuation in the water column; coccoliths from algal detritus were the main cause. However, chlorophyll a concentrations were higher in winter (32·9±6·4mgm -2) than in summer (16·8±3·4mgm -2). While molar N:P ratios were low (2·9), which is indicative of nitrogen limitation, nutrient addition and 15N-nitrogen uptake experiments showed no such limitation. There was also little or no indication of silicate or phosphate deficiency. This contrasts with many other continental shelf systems that are nitrogen-limited. It is concluded that light, rather than nutrients, limited phytoplankton production during the south-east monsoon in offshore waters.

  6. Phytoplankton Community Structure, Biomass and Diversity on the Louisiana Continental Shelf

    EPA Science Inventory

    Phytoplankton communities on the Louisiana continental shelf (LCS) respond to nutrient loading from the Mississippi and Atchafalaya River Basin (MARB). Enhanced phytoplankton biomass is a source of organic matter contributing to the development of seasonal hypoxia. Samples were ...

  7. Phytoplankton Community Structure, Biomass and Diversity on the Louisiana Continental Shelf

    EPA Science Inventory

    Phytoplankton communities on the Louisiana continental shelf (LCS) respond to nutrient loading from the Mississippi and Atchafalaya River Basin (MARB). Enhanced phytoplankton biomass is a source of organic matter contributing to the development of seasonal hypoxia. Samples were ...

  8. 77 FR 19321 - Geological and Geophysical Exploration on the Atlantic Outer Continental Shelf (OCS)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-03-30

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management Geological and Geophysical Exploration on the Atlantic Outer Continental Shelf (OCS) AGENCY: Bureau of Ocean Energy Management (BOEM), Interior. ACTION: Notice...

  9. Final 5-year plan for oil and gas development in the outer continental shelf

    NASA Astrophysics Data System (ADS)

    The five year plan for oil and gas development in the outer continental shelf was discussed, considering such aspects as protecting marine, coastal, and human environments, as well as, our energy needs.

  10. 75 FR 53874 - Fisheries of the Exclusive Economic Zone Off Alaska; Pelagic Shelf Rockfish for Vessels...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-09-02

    ... Economic Zone Off Alaska; Pelagic Shelf Rockfish for Vessels Participating in the Rockfish Entry Level... participating in the rockfish entry level fishery in the Central Regulatory Area of the Gulf of Alaska (GOA... rockfish allocated to vessels participating in the rockfish entry level fishery in the Central...

  11. Problem on the United States Continental Shelf - measuring the environmental {open_quotes}effectiveness{close_quotes} of the Outer Continental Shelf Act (OCSA)

    SciTech Connect

    Dubner, B.H.

    1994-12-31

    This article reviews the interplay of environmental standard with oil and gas leasing on the Outer Continental Shelf (OSC) in order to determine if the marine environment is really protected by the interplay of domestic legislation. The 1982 LOS treaty leaves environmental protection to State (domestic) regulation. There is no customary law regarding this type of domestic shelf regulation. The main problem is measuring the {open_quotes}effectiveness{close_quotes} of our domestic shelf legislation. For example, do we simply review effectiveness in terms of controlling operational damage or in terms of environmental injury caused by catastrophic accidents?

  12. Cross-Shelf Circulation and Momentum and Heat Balances Over the Inner Continental Shelf Near Martha’s Vineyard, Massachusetts

    DTIC Science & Technology

    2007-09-01

    T2 or AT = 0 at x = c : 0, the temperature stratification as a function of cross-shelf position in the model is AT- QS_X (.32) Poe , Uo The vertical... Poe - U o - U o x ) (4 ., The cross-shelf temperature gradient in the model is positive near shore: a(T) Uo d> 0 for x < --- (4.35) 5W3 h 153 The...Wind-driven currents over the continental shelf. In Kenneth H. Brink and Allan R. Robinson, editors, The Global Coastal Ocean: Processes and Methods

  13. Seafloor Rocks and Sediments of the Continental Shelf From Monterey Bay to Point Sur, California

    USGS Publications Warehouse

    Eittreim, Stephen L.; Anima, Roberto J.; Stevenson, Andrew J.; Wong, Florence L.

    2000-01-01

    Introduction Acoustic swath mapping of the greater Monterey Bay area continental shelf from Point Ano Nuevo to Point Sur reveals complex patterns of rock outcrops on the shelf, and coarse sand bodies that occur in distinct depressions on the inner and mid-shelves. This publication portrays the seafloor components in a 36- by 48-inch map sheet at 1:100,000 scale.

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

    DTIC Science & Technology

    2005-01-01

    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

  15. Continental Shelf Embayments of the Eastern Margin of the Philippines; Lamon Bay Stratification & Circulation

    DTIC Science & Technology

    2015-05-21

    Continental shelf embayments of the eastern margin of the Philippines; Lamon Bay stratification & circulation Arnold L. Gordon Lamont-Doherty...Current Bifurcation. The cyclonic dipole circulation of the southwest Lamon Bay is likely closely linked to the active marine ecosystem...characteristics of the ocean processes governing the stratification & circulation within Lamon Bay, including shelf/ slope exchange, and their

  16. Activation of the Inner Continental Shelf Following the Great Mississippi/Atchafalaya River Flood of 2011

    NASA Astrophysics Data System (ADS)

    Kolker, A.; Li, C.; Allison, M. A.; Ameen, A. D.; Dash, P.; Ramatchandirane, C. G.; Sinclair, G.; Smith, D.; Ullah, M.; Williams, K.

    2011-12-01

    While rives are the primary means by which material is delivered from continents to the ocean, relatively little is known about the role that large rivers, particularly in North America, play in the geology of the inner continental shelf. Flood control measures initiated in response the to massive 2011 Mississippi River flood diverted nearly 22,900 m3 sec-1 of freshwater through the Atchafalaya River basin into the Atchafalaya River shelf in southwest Louisiana, temporarily creating one of the largest shelf-discharging rivers on Earth, and providing an historic opportunity to study shelf-to-shore exchange processes. A multi-disciplinary approach using Acoustic Current Doppler Profilers, CTDs, satellite photographs, and the naturally occurring radiotracer 7Be revealed that event produced intense gradients in temperature, salinity and turbidity across the inner continental shelf, resulting in complex circulation patterns. The freshwater plume extended over 30 km into the, "marine," environment. Furthermore, the flood activated sedimentary dynamics across the shelf, leading to large deposits of fine-grained material across the Atchafalaya/Chenier coast. Our study indicates that large rivers produce unique oceanographic dynamics when they interact with the continental shelf, and that these systems should be viewed differently from small shelf-discharging rivers (like the Hudson) or large continental-slope discharging rivers (like the Mississippi).

  17. Trinity shoal: a reworked deltaic barrier on Louisiana continental shelf

    SciTech Connect

    Suter, J.R.; Penland, S.; Moslow, T.F.

    1985-02-01

    Abandonment and reworking of deltaic complexes of the Holocene Mississippi River have produced a series of sandy shoals on the muddy Louisiana continental shelf. Trinity shoal, one of these transgressive deposits, is located 30 km offshore of Atchafalaya Bay and the Point Au Fer-March Island shell reefs. Approximately 1000 km of high-resolution uniboom and 3.5 kHz subbottom-profile seismic data, taken in this area in 1983 and 1984, provide the data base for this study. Trinity shoal, associated with the abandoned Maringouin delta complex, is a lunate shore-parallel feature approximately 36 km long and 5-10 km wide. Relief on the shoal ranges from 2 to 3 m, and minimum water depths over the shoal vary from -5 to -2 m. The shoal sand body is from 5 to 7 m thick and is composed largely of parallel to low-angle clinoform reflectors. Several levels of buried fluvial channels, ranging in age from early Wisconsinian to Holocene, are associated with the shoal deposit. The occurrence of channel features within the shoal sand itself suggests the presence of tidal inlets, indicating a possible barrier-island origin for the shoal. The underlying deltaic sediments reach approximately 15 m in thickness and are made up of low-angle clinoform reflectors dipping to the southwest. Distributary, bay-fill, estuarine, and buried oyster-reef deposits can be recognized, making these similar to modern Atchafalaya delta deposits. Continued progradation of the Atchafalaya delta will probably result in burial of the Trinity shoal and Maringouin delta deposits by fine-grained sediments, giving these shoal deposits a high-preservation potential and creating an excellent stratigraphic trap.

  18. Some Cenozoic hydrocarbon basins on the continental shelf of Vietnam

    SciTech Connect

    Dien, P.T.

    1994-07-01

    The formation of the East Vietnam Sea basins was related to different geodynamic processes. The pre-Oligocene basement consists of igneous, metamorphic, and metasediment complexes. The Cretaceous-Eocene basement formations are formed by convergence of continents after destruction of the Tethys Ocean. Many Jurassic-Eocene fractured magmatic highs of the Cuulong basin basement constitute important reservoirs that are producing good crude oil. The Paleocene-Eocene formations are characterized by intramountain metamolasses, sometimes interbedded volcanic rocks. Interior structures of the Tertiary basins connect with rifted branches of the widened East Vietnam Sea. Bacbo (Song Hong) basin is predominated by alluvial-rhythmic clastics in high-constructive deltas, which developed on the rifting and sagging structures of the continental branch. Petroleum plays are constituted from Type III source rocks, clastic reservoirs, and local caprocks. Cuulong basin represents sagging structures and is predominated by fine clastics, with tidal-lagoonal fine sandstone and shalestone in high-destructive deltas that are rich in Type II source rocks. The association of the pre-Cenozoic fractured basement reservoirs and the Oligocene-Miocene clastic reservoir sequences with the Oligocene source rocks and the good caprocks is frequently met in petroleum plays of this basin. Nan Conson basin was formed from complicated structures that are related to spreading of the oceanic branch. This basin is characterized by Oligocene epicontinental fine clastics and Miocene marine carbonates that are rich in Types I, II, and III organic matter. There are both pre-Cenozoic fractured basement reservoirs, Miocene buildup carbonate reservoir rocks and Oligocene-Miocene clastic reservoir sequences, in this basin. Pliocene-Quaternary sediments are sand and mud carbonates in the shelf facies of the East Vietnam Sea back-arc basin. Their great thickness provides good conditions for maturation and trapping.

  19. The Distribution of Permafrost Beneath the Beaufort Sea Continental Shelf

    NASA Astrophysics Data System (ADS)

    Herman, B. M.

    2011-12-01

    The entire Beaufort Sea continental shelf (CS) is generally believed to have been sub-aerially exposed to temperatures of -12°C during the sea level low-stand that accompanied the last glacial age. After inundation due to rising sea level, the temperature of the seafloor would have been near 0°C. Permafrost formed prior to flooding was generally expected to be ubiquitous at depth due to the relatively recent time of inundation. Seaward of just beyond the Beaufort Sea barrier islands, downhole resistivity and sonic logging in the 10 hydrocarbon exploration wells that have logging at least as shallow as 300 m below sea level (BSL) has not demonstrated evidence of ice-bearing permafrost (IBPF). Indirect evidence of IBPF seaward of the barrier islands is limited to the Belcher well on the eastern Beaufort CS where rock containing gas hydrate was blown from the well while drilling at 754 m BSL (Exlog Canada, 1988). A bottom simulating reflection is observed on the multichannel seismic reflection (MCS) data near the location of the Belcher well, confirming the presence of gas hydrate. From the barrier islands shoreward to the coast, IBPF is indicated by resistivity and sonic logs in all wells having data. The depth to the base of the permafrost in the near shore and onshore areas varies from 200m to over 600 m. Where the top and bottom of the IBPF are observed in the resistivity logs on the barrier islands, the thickness ranges from 100-300 m. MCS data have been collected on the Beaufort CS by the oil industry since the 1970's. IBPF may be inferred from maps of the Dix average velocity (Vave) at a travel time somewhat deeper than the anticipated depth to its base, e.g., 0.75 sec two-way-travel (TWT). Vave is 2.4-3.0 km/sec onshore. In the western Beaufort, Vave decreases rapidly across the shoreline and out to the barrier islands, beyond which it is relatively constant at 1.8 km/sec out to the shelf edge. Vave decreases across the shoreline in the eastern Beaufort, too

  20. Alaska OCS socioeconomic studies program: St. George basin and North Aleutian Shelf commercial fishing industry analysis. Final report

    SciTech Connect

    Tobolski, J.; Guluka, L.; Trefethen, D.; Im, K.

    1981-10-01

    This report consists of an update of the data base and analysis of the potential impacts to commercial fishing of proposed Outer Continental Shelf oil and gas lease sales in the St. George Basin and North Aleutian Shelf, situated in the Bering Sea off Alaska. Impacts on the Bristol Bay fishery are also discussed. Competition for labor between the fishing and oil industries is examined, as well as an analysis of risk of collision among vessels in the OCS areas. A description of the fisheries resources of the area is followed by an analysis of loss of access to fishing grounds, and loss of or damage to gear. Impacts on the recreational fishery are also discussed.

  1. Oceanography of the Subtropical Shelf Front Zone in the SW-Atlantic Continental Shelf

    NASA Astrophysics Data System (ADS)

    Muelbert, J. H.; Acha, M.; Berasategui, A.; Bersano, J. G.; Braga, E. S.; Eichler, P.; Garcia, V. M.; Gomez-Erache, M.; Guerrero, R.; Mianzan, H.; Reta, R.; Ramirez, F.

    2005-05-01

    Only physical aspects of the Subtropical Shelf Front (STSF) have been described for the Southwest Atlantic Continental Shelf. The main goal of this paper is to present results of an integrated physical, chemical and biological study at the STSF conducted during the winter of 2003 and summer of 2004. A cross section was established at the historical determined location of the STSF. Nine stations were sampled during the winter cruise and 7 stations during summer. Each section included a series of conductivity-temperature-depth (CTD) stations fitted with dissolved oxygen and turbidity sensors. Selected water samples were filtered and frozen at -20oC for nutrient determination. Samples for chlorophyll were concentrated on filters and these were stored frozen for later processing. Plankton net tows were carried out above and below pycnocline. Surface benthic foraminifera were collected with a bottom snapper. Results revealed that winter was marked by an inner shelf salinity front and the STSF located in the mid-shelf. Inner salinity showed the strong influence of freshwater, with high silicate (71.98 μM), phosphate (2.70 μM), nitrate (1.01 μM), Total Dissolved Nitrogen (22.98 μM) and suspended matter (44.80 mg/L). With distance from the coast and reduction of terrestrial input, subsurface high values of nutrients were associated with SACW upwelling. As a result, chlorophyll a concentration decreased from coastal well-mixed waters, where values up to 3.0 mg.m3 are registered, to offshore waters. Zooplankton abundance and biomass, and ichthyoplankton abundance follows the same trend. Zoo and ichthyoplankton abundance revealed the presence of 3 groups associated to the inner, mid and offshore shelf region. Benthic foraminifera composition suggested that shallow stations are dominated by few large freshwater species, while offshore stations presented smaller forms and higher species diversity. During summer, the halocline extended over the shelf and joined the STSF in

  2. On the difficulty of modeling Circumpolar Deep Water intrusions onto the Amundsen Sea continental shelf

    NASA Astrophysics Data System (ADS)

    Nakayama, Y.; Timmermann, R.; Schröder, M.; Hellmer, H. H.

    2014-12-01

    In the Amundsen Sea, warm Circumpolar Deep Water (CDW) intrudes onto the continental shelf and flows into the ice shelf cavities of the West Antarctic Ice Sheet, resulting in high basal melt rates. However, none of the high resolution global models resolving all the small ice shelves around Antarctica can reproduce a realistic CDW flow onto the Amundsen Sea continental shelf, and previous studies show simulated bottom potential temperature at the Pine Island Ice Shelf front of about -1.8 °C. In this study, using the Finite-Element Sea ice-ice shelf-Ocean Model (FESOM), we reproduce warm CDW intrusions onto the Amundsen Sea continental shelf and realistic melt rates of the ice shelves in West Antarctica. To investigate the importance of horizontal resolution, forcing, horizontal diffusivity, and the effect of grounded icebergs, eight sensitivity experiments are conducted. To simulate the CDW intrusion realistically, a horizontal resolution of about 5 km or smaller is required. The choice of forcing is also important and the cold bias in the NCEP/NCAR reanalysis over the eastern Amundsen Sea prevents warm CDW from intruding onto the continental shelf. On the other hand, the CDW intrusion is not highly sensitive to the strength of horizontal diffusion. The effect of grounded icebergs located off Bear Peninsula is minor, but may act as a buffer to an anomalously cold year.

  3. Low-frequency currents and continental shelf waves in the southern Weddell Sea

    SciTech Connect

    Middleton, J.H.; Foster, T.D.; Foldvik, A.

    1982-07-01

    The salient features of low-frequency current fluctuations, obtained from an analysis of eight current meter records from the continental shelf and slope of the southern Weddell sea, are compared to baroclinic and barotropic theories. A simple baroclinic theory of internal waves is used successfully to predict high-frequency spectral cutoff values from low-frequency velocity ellipse calculations made from the continental slope mooring data. The success of this theory indicates that the higher spectral energy levels observed over the slope compared to the shelf are probably due to baroclinic motions. A barotropic model of free continental shelf waves proposed by Saint-Guily (1976) is adapted for the local topography and the predictions of the model compared to observations. Coherences and phases between moorings separated by 10 and 160 km in the long-shelf direction provide substantial evidence of the existence of shelf waves as predicted by the theory for periods of 3--60 days and for the lowest three modes. For periods of 3--8 days rotary spectral levels indicate anticlockwise rotating current vectors over the shelf as predicted by theory, but for longer periods current vectors rotate clockwise. It is speculated that fluctuations in along-shelf wind stress drive the shelf waves but that the longer period motions are driven directly by the wind stress.

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

    NASA Astrophysics Data System (ADS)

    Couto, N.; Schofield, O.; Martinson, D. G.; Dinniman, M. S.; Graham, J. A.

    2016-02-01

    Sub-pycnocline water on the continental shelf of the West Antarctic Peninsula (WAP) is strongly influenced by intrusions of Upper Circumpolar Deep Water (UCDW), a relatively warm water mass that originates off the shelf within the Antarctic Circumpolar Current. Shipboard measurements over the past two decades indicate that the deep shelf waters are warming, but they are unable to resolve the dimensions and frequency of the UCDW intrusions. Here, we use autonomous underwater vehicles (gliders) to characterize the spatial distribution of UCDW on the WAP continental shelf. We use a ROMS model to study the pathways by which UCDW crosses onto the shelf and travels toward the coast. We find that in both the traditional shipboard CTD dataset and the recent high-resolution glider dataset, there are consistent spatial patterns with UCDW commonly found in deep bathymetric depressions in the region. UCDW on the shelf is found in features with widths on the order of 10 km, suggesting the importance of mesoscale processes in the transport of heat onto the shelf. The features observed here contribute 10-33% of the heat flux required to balance the heat budget of the WAP and lose heat at a rate of 1.7 ± 0.8 x 106 J/m2 between the shelf break and the coast. Drifters released in the ROMS model also follow bathymetric channels toward the coast and showed preference for entering at specific locations along the shelf break.

  5. Currents on the Continental Shelf of Northern South China Sea

    NASA Astrophysics Data System (ADS)

    Tai, J.; Tang, T.

    2012-12-01

    The shelf current of northern South China Sea (SCS) is investigated by using moored observations. The short-term Acoustic Doppler Current Profiler (ADCP) array, which was deployed cross the shelf, and two long-term ADCPs, one on the shelf and another is at slope, are used to study the spatial structures and temporal variations of shelf current, respectively. The results indicate that the shelf current is quite variable. The tidal current varied in space and in time. For the diurnal tidal currents, the first baroclinic O1 tide dominated on the shelf but the first baroclinic K1 tide dominated at the slope. For the semi-diurnal tides, the barotropic M2 tide dominated on the shelf but first baroclinic mode dominated at the slope. The temporal variation on the shelf showed that barotropic mode is dominant in winter for both diurnal and semi-diurnal tide but only for semi-diurnal tides in summer. The sub-tidal current on the shelf is also variable. The wind played a critical role to drive the subtidal current on the shelf. The wind drove the Ekman transport first, and then piled up the water alone the coast. Finally the along-shelf geostrophic current driven by the seaward pressure gradient was seen. The southward run-off water from Taiwan Strait induced by typhoon, the eddy and the Kuroshio intrusion in the northern SCS also has impact on the current on the shelf and shelf break. The observation showed that SCS Warm Current (SCSWC), which was claimed as a persistent northeasterly flow, appeared/vanished with time. During the winter monsoon season, the headed wind SCSWC appeared only when the wind was relaxed (i.e. the wind stress less than 1.5 dyne/cm2); while the southwestward current was seen primarily when the wind intensified. Obviously, The SCSWC was a transient feature when the winter monsoon was prevailed. The northeastward current was seen frequently during the summer monsoon. Again, the wind caused sea level variation could be the main mechanism for the appear

  6. Production and remineralization in continental shelf ecosystems: A test of the SEEP hypothesis

    SciTech Connect

    Rowe, G.T.

    1986-09-01

    The hypothesis that continental shelf ecosystems export a major fraction of the carbon produced by the phytoplankton during the spring bloom was tested during the Shelf Edge Exchange Processes (SEEP) experiment off the northeast US coast in 1984. This study, along with a reanalysis of traditional concepts, leads to the conclusion that only a small fraction of continental shelf phytodetritus is exported across a distinct shelf-slope hydrographic frontal system. What is not consumed in the spring is utilized on the shelf during the ensuing stratified season. More open ended ecosystems may export production more readily. The total benthic standing stocks in terms of organic carbon (macrofauna, meiofauna, and bacteria) have been estimated in the SEEP area. Their preponderance on the continental shelf was partial evidence that little organic matter escapes to the upper continental slope. Measurements of the metabolism of the biota allowed calculation of turnover times of organic detritius and the total biota. The turnover time of detritus increased as grain size decreased, suggesting that fine-grained deposits contain mostly refractory, nonreactive compounds, especially on the deep slope. Turnover times of the total biota were about the same in the coarse versus fine-grained shelf deposits, but a far larger fraction of the turnover was attributed to the bacteria in the fine sediments than in the coarse. On average, about 25% of the primary production appeared to be utilized by the aerobic benthos on the continental shelf in the SEEP area. The role of anaerobes at depth in the sediments remains uncertain.

  7. Outer Continental Shelf environmental assessment program. Final reports of principal investigators. Volume 69

    SciTech Connect

    Not Available

    1990-09-01

    This article includes the following: trace contaminants in surface sediment of the northern Bering Sea: a statistical review; trace contaminants in the greater St. George Basin: a statistical review; mercury in Alaska marine surface sediments: a review of the regional data; and natural distribution and environmental background of trace heavy metals in Alaskan shelf and estuarine areas.

  8. Quaternary seismic stratigraphy and paleoenvironments on the continental shelf of the East China Sea

    NASA Astrophysics Data System (ADS)

    Liu, Zhen-Xia; Berne, Serge; Saito, Yoshiki; Lericolais, G.; Marsset, T.

    2000-08-01

    Paleoenvironments and stratigraphy have been interpreted from 4380 km of seismic profiling collected during a geological and geophysical cruise on the continental shelf of the East China Sea (ECS) undertaken in 1996. The geophysical data are correlated with a borehole situated on the outer shelf obtained by Shanghai Marine Geology Bureau, indicating that six seismic units have been preserved since oxygen-isotope stage 6, including four regressive-transgressive cycles. Seismic units U2, U3+U4+U5, U6, and U7 are interpreted to correspond respectively to oxygen-isotope stages 1, 3, 5, and 6, implying that sediment partitioning and sequence architecture in the ECS have been controlled by glacio-eustasy and global climate changes. Alternating continental and marine strata corresponding to glaciation and interglaciation are well preserved on the outer shelf of the ECS. Most of the cold environment strata, which formed on the outer shelf during oxygen-isotope stages 2 and 4, are too thin to be recognized on SIG 600J because of resolution, but corresponding erosion surfaces exist. Seismic unit U7 is widespread over the shelf, extending to the continental edge and showing little variation in thickness, as the regression was pronounced and lasted a long time. Thus, U7 can be used as a marker layer for correlation of Quaternary strata on the shelf of the ECS. Post-glacial transgression is obvious in the ECS. Marine strata with varied thickness were developed in the shallow sea of the inner shelf, thinning toward the outer shelf. The continental shelf of the ECS has been influenced by Pacific tide-wave systems for a long time, forming tidal sand-ridge sequences, developed during transgressions, corresponding to oxygen-isotope stages 7 (or 9), 5, 3 and 1.

  9. Potential geologic hazards of North Aleutian shelf, Bristol Bay, Alaska

    SciTech Connect

    Molnia, B.F.; Schwab, W.C.

    1985-02-01

    Federal OSC lease sale 92, North Aleutian shelf, Alaska, is scheduled for April 1985. The area, located in the southeastern Bering Sea, has 3 basins with sedimentary thicknesses in excess of 4 km. Six geologic conditions that could cause problems during petroleum development are: (1) seismicity, (2) recent faulting, (3) gas-charged sediment, (4) bed forms and active sediment transport, (5) scours, and (6) volcanism. Since 1953, the region has a history of at least 10 shallow earthquakes, including a 1971 back-arc event with a Richter magnitude of 5.2. The largest event impacting the entire region, a Richter magnitude 8.7 earthquake, occurred in 1938. Normal faults are located along the southern edge of the St. George basin, and on the northeastern edge of the Amak basin. Many exhibit increased offset with depth, surficial sags, and small surficial cracks. Surprising was the absence of any evidence of sea-floor sediment instability. Sonar bright spots, and possible, near-surface gas-charged sediment occur west of Amak Island and north of Unimak Island. An area of megaripples and dunes covers more than 1500 km/sup 2/. Bed forms have spacings of 20-50 m and heights of 1-3 m. Observations suggest that coarse sand may be actively transported. Thousands of scours, many linear and parallel, some greater than 800 m long, 250 m wide, and incised up to 5 m, were identified. Pavlof, an Alaskan Peninsula active volcano, located 45 km northeast of Cold Bay, has a continuous history of steam release and occasional eruption. Lahars, nuee ardentes are unknown. None of the geologic conditions identified precludes petroleum development or production. The potential impact of these factors must, however, be included in planning for future petroleum activities.

  10. Model of inner shelf shoal development, Beaufort Sea, Alaska

    SciTech Connect

    Lowry, P.; Nummedal, D.; Reimnitz, E.

    1985-01-01

    At least two types of inner shelf shoals exist in the Beaufort Sea, Alaska. One type is located up to 40 km from the shoreline in an average water depth of 20m and oriented obliquely to the coast. A second type of shoals occur adjacent to existing barrier islands where minimum water depth over the shoal crest may be as little as 30-50cm. The development of shallow water shoals is believed to be a result of barrier island submergence. Dinkum Sands is an example of a shallow water shoal. This linear sand body is located between Cross and Narwhal Islands, 25km northeast of Prudhoe Bay. The shoal complex is 8 km long and less than 2 km wide and has a maximum relief of 5m. Historical data reveal submergence of an island over at least a 25 year period. The proposed initial stage of shoal development occurs when longshore sediment transport between barrier islands is disrupted by numerous events of downdrift tidal inlet breaching. Reduction in the amount of available sediment to each island results in significant coastal erosion (stage 2), manifest as a landward migration of the shoreline and a reduction in barrier elevation. The final stage of the model is barrier submergence. At present the greatest accumulation of sediment on Dinkum Sands occur at the distal extremities of the shoal. These are believed to represent the location of recurved spits at either end of the island prior to submergence. Application of the submergence model to explain deepwater shoal development must await the collection of shallow (10m) whole core data.

  11. Holocene stratigraphy of the Alabama inner continental shelf: Influence of shelf sand ridges on determining lithofacies architecture

    SciTech Connect

    Davies, D.J.; Parker, S.J. . Energy and Coastal Geology Div.)

    1993-03-01

    Surface and subsurface distribution of lithofacies from Holocene sediments of the AL inner continental shelf was determined from a series of 59 vibracores and associated surface sediment grab sediments. Five Holocene lithofacies composed of 12 discrete microfacies were delineated based on grain size, color, sedimentary structures, shell content, and fabric of samples. These lithofacies include: (1) Graded Shelly Sand Lithofacies; (2) Clean Sand Lithofacies; (3) Dirty Sand Lithofacies; (4) Biogenic Sediment Lithofacies; and (5) Muddy Sediment Lithofacies. These represent four major depositional environments: The Shelf Sand Sheet Environment (lithofacies 1 and 2); the Sand Ridge Environment (lithofacies 1, 2, and 3); the Bay/Lagoon Environment (lithofacies 3, 4 and 5); and the Muddy Shelf Environment (lithofacies 5). East of the Main Pass of Mobile Bay, the seafloor is composed of a clean Shelf Sand Sheet with oblique shelf sand ridges; Clean Sand and Graded Shelly Sand are the dominant surface sediment types. Coarse shell beds that grade up to quartz sand units (total thickness 0.1 to 3+m) interpreted as tempestites comprise most of the upper portion of the ridges. West of the Pass, the muddier lithofacies (3 and 5) dominate surface samples. Microfacies at depth represent the early Holocene transgressive systems tract; these include the Muddy Shelf Depositional Environment and the filled estuaries and bays of the flooded Pleistocene fluvial valleys represented by the Bay/Lagoon Depositional Environment. The AL inner shelf provides an excellent model of the variability of sedimentation mode in time and space during deposition of a transgressive systems tract. Development of the palimpsest sand sheet/ridge complex progressed on the eastern shelf due to shut off of sediment influx, westward longshore currents, and episodic incidence of major hurricanes. On the western shelf a patchy distribution of muddier sediments developed from input of floodwaters from Mobile Bay.

  12. Variations in sediment texture on the northern Monterey Bay National Marine Sanctuary continental shelf

    USGS Publications Warehouse

    Edwards, B.D.

    2002-01-01

    The storm-protected continental shelf of Monterey Bay, part of the Monterey Bay National Marine Sanctuary, north-central California, is subject to abundant, episodic sediment input from fluvial sources. North of Monterey Bay, conditions of reduced sediment supply combined with the exposed nature of the shelf provide an effective laboratory for studying the contrasting effects of storm- versus fluvial-dominated conditions on modern sedimentation. Textural analyses performed on surface sediment samples collected from more than 380 box cores and MultiCores??? document the existence of a clearly defined mud belt occupying the mid-shelf throughout the region. Inshore sands combined with these mid-shelf muds represent deposits from modern sedimentation processes. In Monterey Bay, where episodic fluvial input from winter storms dominates sedimentation, the mid-shelf mud belt extends across the shelf to the shelf break. North of Monterey Bay, where sediment loads are reduced and both oceanographic and storm processes dominate, the mid-shelf mud belt is bordered by relict sediments occupying the outer shelf. In the study area, mass accumulation rates established by radiochemical studies support the contention that storm-induced along-shelf processes result in northward transport of sediment within the mud belt. The continuity of transport, however, is interrupted by topographic highs which are barriers or inhibitors to sediment transport created by wrench-style tectonics associated with the San Andreas fault system.

  13. Source and dispersal of silt on northern Gulf of Mexico Continental Shelf

    SciTech Connect

    Peterson, M.; Mazzullo, J.

    1988-02-01

    The surficial sediment on the continental shelf of the northern Gulf of Mexico is characterized by abundant silty clay which was deposited during the late Pleistocene lowstand and reworked during and after the Holocene transgression. The purposes of this study were to determine the sources of the silt fraction in this surficial sediment by quartz grain roundness and surface texture analysis, and to determine the effects of modern shelf currents upon the distribution of silt.

  14. A climatology and oceanographic analysis of the California Pacific Outer Continental Shelf region. Final report

    SciTech Connect

    Williams, R.G.; Reeves, R.W.; Godshall, F.A.; Fehler, S.W.; Pytlowany, P.J.

    1980-09-01

    The results of an environmental study of the California Pacific Offshore Continental Shelf (CPOCS) region are presented. The CPOCS region is defined as the area between the Mexican border to the Oregon State boundary and seaward to the shelf edge or 200 km. A larger region was examined in several components of the study to describe conditions upstream and downstream of potential leasing areas. Individual chapters focus on meteorological factors, ocean circulation, water masses and physical properties, nutrient chemistry and water elevations.

  15. High Resolution Measurements of Nonlinear Internal Waves and Mixing on the Washington Continental Shelf

    DTIC Science & Technology

    2013-09-30

    System ( SWIMS ) and shipboard acoustics (Biosonics). APPROACH Observations from a real-time mooring that we maintain on the Washington continental...remote internal tides shoal onto the shelf break. In this project we will use our Shallow Water Integrated Mapping System ( SWIMS ) and Modular...shelf indicate an extremely energetic field of nonlinear internal waves (NLIW) propagating onshore. As a fraction of the water depth, their

  16. Suspended sediment transport on the continental shelf near Davenport, California

    USGS Publications Warehouse

    Xu, J. P.; Noble, M.; Eittreim, S.L.

    2002-01-01

    Suspended sediment transport on the shelves off Santa Cruz and Davenport, California is studied using field measurements and bottom boundary layer modeling. Strong transport events mostly occur during storms in winter; the volume of winter sediment transport is at least one order of magnitude greater than that of summer/spring transport. Rock outcrops on the inner shelf (< 40 m of water) indicates an erosional environment, but an elongated mid-shelf mud deposit evidently suggests a depositional environment on the mid-shelf. The seafloor geology appears to correlate to the poleward and offshore sediment transport pattern. This study also suggests that suspended sediment moves out of Monterey Bay, roughly along the isobaths of the northern bay. This fine material, originally from river sources, and the material from the coastal cliff erosion that is subsequently introduced to the transport system through cross-shelf sediment transport, are believed to be the sources of the mid-shelf mud deposit. ?? 2002 Elsevier Science B.V. All rights reserved.

  17. An instrument system for long-term sediment transport studies on the continental shelf

    USGS Publications Warehouse

    Butman, Bradford; Folger, David W.

    1979-01-01

    A bottom-mounted instrument system has been designed and built to monitor processes of bottom sediment movement on the continental shelf. The system measures bottom current speed and direction, pressure, temperature, and light transmission and photographs the bottom. The system can be deployed for periods of 2–6 months to monitor intermitent processes of sediment movement such as storms and to assess seasonal variability. Deployments of the system on the U.S. east coast continental shelf show sediment resuspension and changes in bottom microtopography due to surface waves, tidal currents, and storms.

  18. Circulation and exchange processes over the continental shelf and slope. Final report

    SciTech Connect

    Csanady, G.T.

    1988-12-31

    The theme of the work during the past triennium has been the SEEP experiment, data interpretation and modeling related to the goals of the experiment, and was characterized by increasing cooperation with colleagues from other disciplines. The theoretical contributions dealt with shelf-slope interaction, the dynamics and climatology of currents over the continental slope, and the behavior of fate of organic particles. Observational papers discussed various exchange mechanisms at the shelf edge, with special attention to particle exchange, and the quiescence of currents over the mid continental slope which is presumably responsible for the accumulation of organic particles.

  19. Impact of regulations - after federal leasing - on Outer Continental Shelf oil and gas development

    SciTech Connect

    Staats, E.B.

    1981-02-27

    The Outer Continental Shelf potentially can provide the nation with significant future oil and gas resources. But, the full potential will not be realized unless: various federal agencies involved issue permits and complete other authorization actions within a standard, reasonable time which GAO believes should be a maximum of 90 days; coastal states are encouraged to develop processes for local reviews and issuing permits which are more timely and uniform with federal processes; credibility of the environmental review process is more clearly established to minimize challenges and delays; and more federal leadership and agency expertise are focused on Outer Continental Shelf activities in the years ahead.

  20. Glacimarine sedimentary processes, facies and morphology of the south-southeast Alaska shelf and fjords

    USGS Publications Warehouse

    Powell, R.D.; Molnia, B.F.

    1989-01-01

    High precipitation from Gulf of Alaska air masses can locally reach up to 800 cm a-1. This precipitation on tectonically active mountains creates cool-temperate glaciation with extremely active erosion and continuously renewed resources. High basal debris loads up to 1.5 m thick of pure debris and rapid glacial flow, which can be more than 3000 m a-1, combine to produce large volumes of siliciclastic glacimarine sediment at some of the highest sediment accumulation rates on record. At tidewater fronts of valley glaciers, sediment accumulation rates can be over 13 m a-1 and deltas commonly grow at about 106 m3 a-1. Major processes influencing glacimarine sedimentation are glacial transport and glacier-contact deposition, meltwater (subaerial and submarine) and runoff transport and deposition, iceberg rafting and gouging, sea-ice transport, wave action and storm reworking, tidal transport and deposition, alongshelf transport, sliding and slumping and gravity flows, eolian transport, and biogenic production and reworking. Processes are similar in both shelf and fjord settings; however, different intensities of some processes create different facies associations and geometries. The tectonoclimatic regime also controls morphology because bedrock structure is modified by glacial action. Major glacimarine depositional systems are all siliciclastic. They are subglacial, marginal-morainal bank and submarine outwash, and proglacial/paraglacial-fluvial/deltaic, beach, tidal flat/estuary, glacial fjord, marine outwash fjord and continental shelf. Future research should include study of long cores with extensive dating and more seismic surveys to evaluate areal and temporal extent of glacial facies and glaciation; time-series oceanographic data, sidescan sonar surveys and submersible dives to evaluate modern processes; biogenic diversity and production to evaluate paleoecological, paleobiogeographic and biofacies analysis; and detailed comparisons of exposed older rock of the

  1. Coupled wind-forced controls of the Bering-Chukchi shelf circulation and the Bering Strait throughflow: Ekman transport, continental shelf waves, and variations of the Pacific-Arctic sea surface height gradient

    NASA Astrophysics Data System (ADS)

    Danielson, Seth L.; Weingartner, Thomas J.; Hedstrom, Katherine S.; Aagaard, Knut; Woodgate, Rebecca; Curchitser, Enrique; Stabeno, Phyllis J.

    2014-06-01

    We develop a conceptual model of the closely co-dependent Bering shelf, Bering Strait, and Chukchi shelf circulation fields by evaluating the effects of wind stress over the North Pacific and western Arctic using atmospheric reanalyses, current meter observations, satellite-based sea surface height (SSH) measurements, hydrographic profiles, and numerical model integrations. This conceptual model suggests Bering Strait transport anomalies are primarily set by the longitudinal location of the Aleutian Low, which drives oppositely signed anomalies at synoptic and annual time scales. Synoptic time scale variations in shelf currents result from local wind forcing and remotely generated continental shelf waves, whereas annual variations are driven by basin scale adjustments to wind stress that alter the magnitude of the along-strait (meridional) pressure gradient. In particular, we show that storms centered over the Bering Sea excite continental shelf waves on the eastern Bering shelf that carry northward velocity anomalies northward through Bering Strait and along the Chukchi coast. The integrated effect of these storms tends to decrease the northward Bering Strait transport at annual to decadal time scales by imposing cyclonic wind stress curl over the Aleutian Basin and the Western Subarctic Gyre. Ekman suction then increases the water column density through isopycnal uplift, thereby decreasing the dynamic height, sea surface height, and along-strait pressure gradient. Storms displaced eastward over the Gulf of Alaska generate an opposite set of Bering shelf and Aleutian Basin responses. While Ekman pumping controls Canada Basin dynamic heights (Proshutinsky et al., 2002), we do not find evidence for a strong relation between Beaufort Gyre sea surface height variations and the annually averaged Bering Strait throughflow. Over the western Chukchi and East Siberian seas easterly winds promote coastal divergence, which also increases the along-strait pressure head, as

  2. Seismic stratigraphy and cenozoic evolution of the mesetan moroccan atlantic continental shelf

    NASA Astrophysics Data System (ADS)

    Le Roy, Pascal; Sahabi, Mohamed; Lahsini, Salim; Mehdi, Khalid; Zourarah, Bendehhou

    2004-06-01

    A recent high-resolution seismic survey of the El Jadida continental shelf allows the characterization of the Cenozoic evolution of the Northern Atlantic Moroccan Shelf, which belongs to the Western Meseta structural domain. Seismic stratigraphy indicates a subdivision of the Cenozoic deposits into four sequences (Sca1 to Sca4) restricted to the northern portion of the shelf. Chronostratigraphic identification of the sequences shows that principal deposits correspond to Upper Miocene deposits overlying the Cenomanian carbonate platform. Quaternary deposits are restricted to the lowstand sedimentary wedge extending below a water depth of 130 m and to the last highstand system tract corresponding to the Oum Er Rbia prodelta. Cenozoic evolution of the continental shelf was controlled by a combination of pluvial/interpluvial stages and eustatic fluctuations, but also by local tectonics. Terrigenous sediments built up the Oum Er Rbia prodelta during the estimated time interval 6-2 ka coinciding with stabilisation of high sea level and pluvial stage. Tectonic deformations occurred mainly during the Upper Miocene and accentuated shelf subsidence through reactivation of inherited N20°/N40° and N140° faults in response to the Europe/Africa collision. Some of the N140° faulting zones are still active during the Quaternary. Currently subsidence has ceased and a broad uplift of the greater part of the continental shelf probably occurs.

  3. Onshore-offshore movement of jumbo squid (Dosidicus gigas) on the continental shelf

    NASA Astrophysics Data System (ADS)

    Stewart, Julia S.; Gilly, William F.; Field, John C.; Payne, John C.

    2013-10-01

    Jumbo squid (Dosidicus gigas) have greatly extended their range in the California Current System, where they forage on a variety of ecologically and economically important species that inhabit both coastal and offshore mesopelagic regions. Swimming abilities and behavior are important factors in assessing the impacts of this range expansion, particularly in regard to foraging in conjunction with onshore-offshore movement over the continental shelf. Here we describe a study of horizontal movements by jumbo squid along and across the continental shelf off Washington, USA, using acoustic tags in association with the Census of Marine Life's Pacific Ocean Shelf Tracking Program (POST) receiver arrays. We detected frequent movements along the shelf break, movement onto the shelf at night, and no evidence of movement as a cohesive school. Our results demonstrate feasibility of using acoustic tags and arrays to document horizontal movements of jumbo squid along and across the continental shelf. This is important in order to determine how those movements overlap with those of other ecologically and commercially important fish species.

  4. British Columbian continental shelf as a source of dissolved iron to the subarctic northeast Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Cullen, Jay T.; Chong, Marina; Ianson, Debby

    2009-12-01

    The distribution of dissolved (<0.4 μm) iron (Fe) across the continental shelf and slope of Queen Charlotte Sound on the west coast of Canada was examined to estimate the potential of these waters as a source of Fe to the Fe-limited waters of the subarctic northeast Pacific. Iron profiles obtained in shelf, slope, and offshore waters demonstrate decreasing concentrations of Fe with distance from the continent. Within 50 m of the shelf sediments dissolved Fe concentrations were 5.3 ± 0.3 nM. This signal was detected, although attenuated by 80%, along the isopycnal surface at offshore stations 40-50 km seaward of the shelf break, strongly suggesting cross-shelf transport of an Fe-rich plume originating in low dissolved oxygen (<3 ml L-1, <130 μmol kg-1) waters in subsurface water over the continental shelf. Several physical mechanisms that may cause these Fe-enriched waters to advect offshore in this region (i.e., tidal currents and Ekman transport in the bottom boundary layer, coastal downwelling/relaxation from upwelling, and the formation of anticyclonic, westward-propagating, coastal eddies) are discussed. We suggest that strong tidal currents over broad continental shelves may play a key role in Fe supply to ocean basins.

  5. Salinity variability along the eastern continental shelf of Canada and the United States, 1973-2013

    NASA Astrophysics Data System (ADS)

    Bisagni, James J.

    2016-09-01

    Continental shelf waters located off the east coast of Canada and the United States are part of a long shelf current system that is partly comprised of colder, less-saline waters originating from high latitudes, including waters from the North Atlantic sub-polar gyre, along with ice-melt and freshwater input from local rivers. A 41-year analysis (1973-2013) of near-surface salinity (NSS) using three hydrographic datasets (Bedford Institute of Oceanography "Climate", NOAA/ESDIM, and Canadian Marine Environmental Data Service (MEDS)) allowed an examination of NSS variability within 11 continental shelf sub-regions, extending from the southern Newfoundland Shelf of eastern Canada to the DelMarVa/Hatteras Shelf of the United States. Although the periods of record containing sufficient data vary between sub-regions, regional mean NSS values are lowest within the Gulf of St. Lawrence and highest on the DelMarVa/Hatteras shelf, with largest annual variability within the Gulf of St. Lawrence. After removal of outliers, long-term linear trends computed from annual mean NSS were detected along the Newfoundland Shelf (+0.011 y-1), Western Scotian Shelf (-0.007 y-1), Gulf of Maine (-0.014 y-1), Georges Bank (-0.011 y-1), and DelMarVa/Hatteras Shelf (+0.024 y-1). A long-term quadratic fit to annual mean NSS from the Eastern Scotian Shelf displays a salinity increase through 1992 of +0.026 y-1, decreasing thereafter until 2013 by -0.028 y-1. A quadratic fit for the Western Grand Banks displays a NSS increase through 2007 of +0.022 y-1, decreasing thereafter through 2013 by -0.006 y-1. Annual mean NSS from the Eastern Grand Banks, Tail of the Grand Banks, Gulf of St. Lawrence, and Middle Atlantic Bight display no long-term trends. Inter-annual variability (IAV) of NSS residuals shows similar small mean squared error (mse) of 0.02-0.04 for the four northern-most sub-regions (Newfoundland Shelf, Eastern, Tail and Western Grand Banks) and are correlated at 0-year lag. IAV of NSS

  6. Shallow geology of north Aleutian shelf area, Bering Sea, Alaska

    SciTech Connect

    Hoose, P.J.; Ashenfelter, K.H.

    1983-03-01

    In 1981, the geological hazards analysis group of the US Geological Survey's Conservation Division collected 4009 line-km (2491 line-mi) of high-resolution seismic reflection data in the south-central Bering Sea. The US Department of the Interior has tentatively selected this area for inclusion in Outer Continental Shelf Oil and Gas Lease Sale 92 scheduled to be held in 1985. This study was part of the surface and shallow subsurface geological investigation of the sale area. A bathymetric map constructed from these data reveals a prominent, 20-m (33 ft) high, gentle scarp which trends obliquely across the survey area. Several linear moraine deposits, and several sag depressions related to the presence of near-surface faults were also found in the area. A Holocene isopach map reveals that sediment distribution is current-controlled. Contemporary current-related features consist of ripple marks, sediment waves, and scour zones. These features generally occur within 60 km (37 mi) of the shore and in water depths of less than 70 m (230 ft). Although current flow generally parallels the shore, side-scan sonographs indicate that the current direction which produced these features is strongly influenced by small and intermediate scale bathymetric features. Faults are present in the southwestern portion of the survey area where they occur in a 30 km (19 mi) wide, east-west trending zone. Within it, faults trend approximately east-west and sense of movement is exclusively normal. There are also several examples of growth faults. Acoustic anomalies, which may represent gas, are present throughout much of the survey area and occur at two different relatively shallow depths.

  7. Sea ice and oceanic processes on the Ross Sea continental shelf

    NASA Technical Reports Server (NTRS)

    Jacobs, S. S.; Comiso, J. C.

    1989-01-01

    The spatial and temporal variability of Antarctic sea ice concentrations on the Ross Sea continental shelf have been investigated in relation to oceanic and atmospheric forcing. Sea ice data were derived from Nimbus 7 scanning multichannel microwave radiometer (SMMR) brightness temperatures from 1979-1986. Ice cover over the shelf was persistently lower than above the adjacent deep ocean, averaging 86 percent during winter with little month-to-month of interannual variability. The large spring Ross Sea polynya on the western shelf results in a longer period of summer insolation, greater surface layer heat storage, and later ice formation in that region the following autumn.

  8. 76 FR 40725 - Approval of Outer Continental Shelf (OCS) Permit Issued to Cape Wind Associates, LLC (EPA Permit...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-11

    ... offshore renewable wind energy project in federal waters off the coast of Massachusetts. DATES: Effective... AGENCY Approval of Outer Continental Shelf (OCS) Permit Issued to Cape Wind Associates, LLC (EPA Permit... Outer Continental Shelf (OCS) air permit decision regarding Cape Wind Associates, LLC (Cape Wind)....

  9. Annual report on Outer Continental Shelf shut-in or flaring wells is no longer needed. Report to the Congress

    SciTech Connect

    Not Available

    1981-11-19

    This is our third report, required annually by the Outer Continental Shelf Lands Act Amendments of 1978, that examines the Department of the Interior's (DOI) methodology used to allow Outer Continental Shelf (OCS) wells to be shut-in or to flare natural gas.

  10. Origin and extent of fresh paleowaters on the Atlantic continental shelf, USA.

    PubMed

    Cohen, Denis; Person, Mark; Wang, Peng; Gable, Carl W; Hutchinson, Deborah; Marksamer, Andee; Dugan, Brandon; Kooi, Henk; Groen, Koos; Lizarralde, Daniel; Evans, Robert L; Day-Lewis, Frederick D; Lane, John W

    2010-01-01

    While the existence of relatively fresh groundwater sequestered within permeable, porous sediments beneath the Atlantic continental shelf of North and South America has been known for some time, these waters have never been assessed as a potential resource. This fresh water was likely emplaced during Pleistocene sea-level low stands when the shelf was exposed to meteoric recharge and by elevated recharge in areas overrun by the Laurentide ice sheet at high latitudes. To test this hypothesis, we present results from a high-resolution paleohydrologic model of groundwater flow, heat and solute transport, ice sheet loading, and sea level fluctuations for the continental shelf from New Jersey to Maine over the last 2 million years. Our analysis suggests that the presence of fresh to brackish water within shallow Miocene sands more than 100 km offshore of New Jersey was facilitated by discharge of submarine springs along Baltimore and Hudson Canyons where these shallow aquifers crop out. Recharge rates four times modern levels were computed for portions of New England's continental shelf that were overrun by the Laurentide ice sheet during the last glacial maximum. We estimate the volume of emplaced Pleistocene continental shelf fresh water (less than 1 ppt) to be 1300 km(3) in New England. We also present estimates of continental shelf fresh water resources for the U.S. Atlantic eastern seaboard (10(4) km(3)) and passive margins globally (3 x 10(5) km(3)). The simulation results support the hypothesis that offshore fresh water is a potentially valuable, albeit nonrenewable resource for coastal megacities faced with growing water shortages.

  11. Origin and extent of fresh paleowaters on the Atlantic continental shelf, USA

    USGS Publications Warehouse

    Cohen, D.; Person, M.; Wang, P.; Gable, C.W.; Hutchinson, D.; Marksamer, A.; Dugan, B.; Kooi, H.; Groen, K.; Lizarralde, D.; Evans, R.L.; Day-Lewis, F. D.; Lane, J.W.

    2010-01-01

    While the existence of relatively fresh groundwater sequestered within permeable, porous sediments beneath the Atlantic continental shelf of North and South America has been known for some time, these waters have never been assessed as a potential resource. This fresh water was likely emplaced during Pleistocene sea-level low stands when the shelf was exposed to meteoric recharge and by elevated recharge in areas overrun by the Laurentide ice sheet at high latitudes. To test this hypothesis, we present results from a high-resolution paleohydrologic model of groundwater flow, heat and solute transport, ice sheet loading, and sea level fluctuations for the continental shelf from New Jersey to Maine over the last 2 million years. Our analysis suggests that the presence of fresh to brackish water within shallow Miocene sands more than 100 km offshore of New Jersey was facilitated by discharge of submarine springs along Baltimore and Hudson Canyons where these shallow aquifers crop out. Recharge rates four times modern levels were computed for portions of New England's continental shelf that were overrun by the Laurentide ice sheet during the last glacial maximum. We estimate the volume of emplaced Pleistocene continental shelf fresh water (less than 1 ppt) to be 1300 km3 in New England. We also present estimates of continental shelf fresh water resources for the U.S. Atlantic eastern seaboard (104 km3) and passive margins globally (3 ?? 105 km3). The simulation results support the hypothesis that offshore fresh water is a potentially valuable, albeit nonrenewable resource for coastal megacities faced with growing water shortages. ?? 2009 National Ground Water Association.

  12. Seismic constraints on the crustal structure of the Bering shelf offshore southwestern Alaska

    NASA Astrophysics Data System (ADS)

    Vayavur, R.; Calvert, A. J.

    2016-12-01

    South-western Alaska comprises a collection of major dextral strike-slip fault bounded tectonostratigraphic terranes that were accreted during Mesozoic and early Tertiary time. In the interior of southern Alaska, the Denali strike-slip fault produced a M7.9 earthquake in 2002, but the westward continuation of this fault appears to evolve into a number of splays, such as the Togiak-Tichik fault, which can be traced to the coast and exhibit considerably less active seismicity. To characterize the offshore extension of the major terranes and the various major faults identified onshore, we have reprocessed three intersecting multichannel deep seismic reflection profiles totalling 750 line-km that were shot by the R/V Ewing across part of the inner Bering continental shelf in 1994. Since the upper most seismic section is often contaminated by high amplitude water layer multiples from the hard seafloor, we have supplemented the migrated reflection images with high-resolution P wave velocity models derived by travel time tomography of the recorded first arrivals to depths of 2000 m. The depth of the igneous basement increases from 100-500 m in the north, where it is characterized by velocities >5000 m/s, to at least 6000 m beneath the North Aleutian basin in the south. Where the basement is shallow, 1-D vertical sinusoidal checkerboard tests with 10% perturbation indicate that velocity anomalies with a half-width of >1500 m can be resolved to depths of at least 500 m, and we have identified several zones of lower velocity, 4000 m/s, that are up to 8000 m wide. Some of these low-velocity anomalies coincide with gravity and magnetic anomalies, and may be associated with faulting within or between accreted terranes. Where tomographic velocities are determined within the North Aleutian basin, they increase with depth from 2000 m/s to 3500 m/s, and agree with sonic logs from the COST-1 well up to 1500 m depth. Across much of the basin, the Eocene red unconformity, which marks

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

    NASA Astrophysics Data System (ADS)

    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.

  14. Outer Continental Shelf Environmental Assessment Program. Final reports of principal investigators. Volume 67

    SciTech Connect

    Not Available

    1990-07-01

    The contents of this study include the following: distribution, abundance, and biology of blue king and Korean hair crabs around the Pribilof Islands; distribution, abundance, and diversity of the epifaunal benthic organisms in Alitak and Ugak bays, Kodiak Island, Alaska; distribution and abundance of some epibenthic invertebrates of the northeastern Gulf of Alaska with notes on the feeding biology of selected species; reproductive success in Dungeness crab (Cancer magister) during long-term exposures to oil-contaminated sediments; and distribution and abundance of decapod larvae of the Kodiak shelf.

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

    USGS Publications Warehouse

    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.

  16. Application of remote sensing to study nearshore circulation. [and the continental shelf

    NASA Technical Reports Server (NTRS)

    Zeigler, J.; Lobecker, R.; Stauble, D.; Welch, C.; Haas, L.; Fang, C. S.

    1974-01-01

    The research to use remote sensing techniques for studying the continental shelf is reported. The studies reported include: (1) nearshore circulation in the vincinity of a natural tidal inlet; (2) identification of indicators of biological activity; (3) remote navigation system for tracking free drifting buoys; (4) experimental design of an estuaring tidal circulation; and (5) Skylab support work.

  17. 76 FR 23331 - Outer Continental Shelf (OCS) Scientific Committee (SC); Announcement of Plenary Session

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-04-26

    ... status of the BOEMRE and its activities. There will be a presentation on Alternative Energy Programs... Bureau of Ocean Energy Management, Regulation and Enforcement Outer Continental Shelf (OCS) Scientific Committee (SC); Announcement of Plenary Session AGENCY: Bureau of Ocean Energy Management, Regulation and...

  18. Nutrient distributions, transports, and budgets on the inner margin of a river-dominated continental shelf

    EPA Science Inventory

    Physical and biogeochemical processes determining the distribution and fate of nutrients delivered by the Mississippi and Atchafalaya rivers to the inner (<50 m depth) Louisiana continental shelf (LCS) were examined using a three-dimensional hydrodynamic model of the LCS and obse...

  19. Nutrient distributions, transports, and budgets on the inner margin of a river-dominated continental shelf

    EPA Science Inventory

    Physical and biogeochemical processes determining the distribution and fate of nutrients delivered by the Mississippi and Atchafalaya rivers to the inner (<50 m depth) Louisiana continental shelf (LCS) were examined using a three-dimensional hydrodynamic model of the LCS and obse...

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

    SciTech Connect

    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.

  1. Reactive Iron and Iron-Reducing Bacteria in Louisiana Continental Shelf Sediments

    EPA Science Inventory

    The Mississippi and Atchafalaya Rivers release sediments containing 15 x 106 t of iron onto the Louisiana continental shelf (LCS) each year. Iron oxides reaching the seafloor may be utilized as electron acceptors by iron-reducing bacteria for organic matter oxidation or become r...

  2. 77 FR 74218 - Commercial Wind Leasing and Site Assessment Activities on the Atlantic Outer Continental Shelf...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-13

    ... identified in the document entitled, Commercial Leasing for Wind Power on the Outer Continental Shelf... Bureau of Ocean Energy Management Commercial Wind Leasing and Site Assessment Activities on the Atlantic... agencies, states, tribes, local governments, offshore wind energy developers, and the public in...

  3. 78 FR 4167 - Commercial Wind Lease Issuance on the Atlantic Outer Continental Shelf Offshore Delaware

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-01-18

    ... Offshore Delaware. SUMMARY: BOEM has issued a commercial wind energy lease to Bluewater Wind Delaware LLC... Bureau of Ocean Energy Management Commercial Wind Lease Issuance on the Atlantic Outer Continental Shelf Offshore Delaware AGENCY: Bureau of Ocean Energy Management (BOEM), Interior. ACTION: Notice...

  4. 75 FR 10809 - Outer Continental Shelf (OCS) Scientific Committee-Notice of Renewal

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-09

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR... Service (MMS), Interior. ACTION: Notice of renewal of the Outer Continental Shelf Scientific Committee. SUMMARY: Following consultation with the General Services Administration, notice is hereby given that the...

  5. 76 FR 7230 - Notice on Outer Continental Shelf Oil and Gas Lease Sales

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-09

    ... From the Federal Register Online via the Government Publishing Office ] DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management, Regulation and Enforcement Notice on Outer Continental Shelf Oil and Gas Lease Sales AGENCY: Bureau of Ocean Energy Management, Regulation and Enforcement,...

  6. 78 FR 36571 - North American Datum of 1983 (NAD 83) Outer Continental Shelf (OCS) Provisional Official...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-18

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management North American Datum of 1983 (NAD 83) Outer Continental Shelf (OCS) Provisional Official Protraction Diagram (OPDs) AGENCY: Bureau of Ocean Energy Management (BOEM),...

  7. The application of Seasat-1 radar altimetry to continental shelf circulation modeling

    NASA Technical Reports Server (NTRS)

    Cornillon, P.; Reed, M.; Spaulding, M.; Swanson, C.

    1980-01-01

    Seasat-1 radar altimetry data have been used to verify a continental shelf circulation model subjected to tidal forcing on the open boundary. The model makes use of the semi-implicit mode of time integration, removing the surface gravity wave time step restriction. Both the altimetry and the model predictions are compared with empirically determined tidal fluctuations and generally good agreement is obtained.

  8. 75 FR 20859 - Outer Continental Shelf (OCS) Policy Committee; Notice and Agenda for Meeting

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-21

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Minerals Management Service Outer Continental Shelf (OCS) Policy Committee; Notice and Agenda for Meeting AGENCY: Minerals Management Service (MMS), Interior. ACTION: Notice of Meeting. SUMMARY: The OCS...

  9. 76 FR 13205 - Notice on Outer Continental Shelf Oil and Gas Lease Sales

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-10

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management, Regulation and Enforcement Notice on Outer Continental Shelf Oil and Gas Lease Sales AGENCY: Bureau of Ocean Energy Management, Regulation and Enforcement,...

  10. A PROBABILISTIC SURVEY OF FISH TISSUE CONTAMINATION FROM THE CONTINENTAL SHELF OF THE US WEST COAST

    EPA Science Inventory

    A probabilistic survey of environmental condition of the continental shelf of the US West Coast was conducted in 2003 by the US EPA National Coastal Assessment (NCA), with collaboration by the NOAA National Marine Fisheries Service. Metals and organic contaminants were analyzed ...

  11. Bottom fixed OTEC plant on the edge of a continental (or island) shelf

    SciTech Connect

    Daidola, J.C.; Basar, N.; Sasscer, D.S.

    1981-01-01

    Consideration is given to a generic type of OTEC plant. This shallow water bottom fixed OTEC plant consists of a platform structure rigidly attached to the seabed at the edge of a continental or island shelf. A cost comparison and thoughts on commercialization are presented. Conclusions and recommendations indicate the desire and need for further development. 12 refs.

  12. Assessment of the US Outer Continental Shelf Environmental Studies Program. 4. Lessons and opportunities. Final report

    SciTech Connect

    Not Available

    1993-01-01

    The report is the last report in a series of six reports prepared by the NRC Committee to Review the Outer Continental Shelf Environmental Studies Program. The committee's conclusions and recommendations in this final report are based on its analyses of published documents and those provided by MMS; on the briefings it has received; on its earlier reports; and on its own deliberations.

  13. Reactive Iron and Iron-Reducing Bacteria in Louisiana Continental Shelf Sediments

    EPA Science Inventory

    The Mississippi and Atchafalaya Rivers release sediments containing 15 x 106 t of iron onto the Louisiana continental shelf (LCS) each year. Iron oxides reaching the seafloor may be utilized as electron acceptors by iron-reducing bacteria for organic matter oxidation or become r...

  14. Coordination: Southeast continental shelf studies. Progress report, 1 June 1984-31 December 1985

    SciTech Connect

    Menzel, D.W.; Blanton, J.O.

    1986-01-03

    This overview and report of progress on the South Atlantic Bight Program includes discussions of: (1) dynamics of the coastal zone; (2) circulation studies; (3) biological transformations in the coastal boundary zone; (4) sediment geochemistry; and (5) continental shelf processes. (ACR)

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

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-25

    ... Bureau of Ocean Energy Management Outer Continental Shelf (OCS) Renewable Energy Program Leasing for... and information on the public session can be found online at: http://www.boem.gov/Renewable-Energy... Renewable Energy Programs, 381 Elden Street, HM 1328, Herndon, Virginia 20170-4817, (703) 787-1340 or...

  16. Arsenic enrichment in sediment on the eastern continental shelf of Brazil.

    PubMed

    Cagnin, R C; Quaresma, V S; Chaillou, G; Franco, T; Bastos, A C

    2017-12-31

    This study focuses on the vertical distribution of total and reactive As in two contrasted coastal sedimentary environments: the Abrolhos Continental Shelf (ACS), a carbonate and siliciclastic shelf sediment, and the Doce River Continental Shelf (DRCS), a submerged delta system. The Doce River was the location of a massive ore tailings dam collapsed in November 2015. Millions of liters of tailings were dumped into the river and reached the continental shelf, causing the country's biggest environmental disaster. We evaluated the As content in sediment of the DRCS before the dam collapse. At both sites, the total As background measured in bottom sediment revealed relative natural enrichment (above 8mg/kg). Content of As decrease with depth; reactive As showed surficial peaks which were associated with Fe and Mn oxides. The ACS sediment did not show significant enrichment or contamination of As, with an enrichment factor (EF) of approximately 2 and a geoaccumulation index (Igeo) near 0. In contrast, the DRCS exhibited severe As enrichment (EF=15) and contamination (Igeo between 3-4). This enrichment is attributed to long-term iron and gold exploitation in the Doce River watershed. The high levels of reactive As, up to 108 mg/kg, alert us to an environmental risk due to potential As bioaccessibility. These data provide an important perspective on the As contamination in continental shelves and encourage the monitoring of the ore mine environmental impacts. Copyright © 2017 Elsevier B.V. All rights reserved.

  17. A PROBABILISTIC SURVEY OF FISH TISSUE CONTAMINATION FROM THE CONTINENTAL SHELF OF THE US WEST COAST

    EPA Science Inventory

    A probabilistic survey of environmental condition of the continental shelf of the US West Coast was conducted in 2003 by the US EPA National Coastal Assessment (NCA), with collaboration by the NOAA National Marine Fisheries Service. Metals and organic contaminants were analyzed ...

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

    SciTech Connect

    Not Available

    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.

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

    SciTech Connect

    Not Available

    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.

  20. Mineral resource management of the Outer Continental Shelf : leasing procedures, evaluation of resources, and supervision of production operations on leased lands of the Outer Continental Shelf

    USGS Publications Warehouse

    Adams, Maurice V.; John, C.B.; Kelly, R.F.; LaPointe, A.E.; Meurer, R.W.

    1975-01-01

    An important function of the Geological Survey is the evaluation and management of the mineral resources of the Outer Continental Shelf, particularly with respect to oil and gas, salt, and sulfur. Production of oil and gas from the Outer Continental Shelf of the United States has increased substantially over the past 20 years and represents an increasing percentage of total United States production. As discovery of major onshore production of oil and gas has become more difficult, the search has moved into the surrounding waters where submerged sedimentary formations are conducive to the accumulation of oil and gas. Increased energy demands of recent years have accelerated the pace of offshore operations with a corresponding improvement in technology as exploration and development have proceeded farther from shore and into deeper water. While improved technology and enforcement of more stringent regulations have made offshore operations safer, it is unrealistic to believe that completely accident-free operations can ever be achieved. Only slightly more than six percent of the world's continental terrace is adjacent to the United States, but less than one percent has been explored for oil and gas. Since the lead time for the development of offshore oil and gas resources can be as much as a decade, they do not provide an immediate energy supply but should be viewed in the light of a near-term source with a potential of becoming a medium-range source of supply pending the development of alternative energy sources. Revenues from the Outer Continental Shelf are deposited to the general fund of the United States Treasury. A major portion of these funds is allocated to the Land and Water Conservation Fund, the largest Federal grant-in-aid program of assistance to States, counties, and cities for the acquisition and development of public parks, open space, and recreation lands and water.

  1. Novel decomposition products of chlorophyll- a in continental shelf (Louisiana shelf) sediments: formation and transformation of carotenol chlorin esters

    NASA Astrophysics Data System (ADS)

    Chen, Nianhong; Bianchi, Thomas S.; Bland, John M.

    2003-06-01

    In April 2000, we collected box cores from five stations along a cross-shelf transect on the Louisiana (LA) continental shelf. Novel esters of carotenols and chlorins (carotenoid chlorin esters, CCEs), which are highly specific grazing markers, were identified in surface and deep sediments (>10 cm) from the LA shelf. Chlorophyll- a inventory indicated that CCEs are one of the major decay products of chlorophyll- a in shelf sediments. Abundances of total CCEs (9-18%) in surface sediments along the cross-shelf transect were comparable to the abundance of pheophytin- a, pyropheophytin- a, and total steryl chlorin esters (SCEs). Prior work has identified four CCEs which have dehydrated fucoxanthin/fucoxanthinol as a substitute alcohol of phytol. We report on four newly identified CCEs associated with nondehydrated fuxocanthin/fucoxanthinol esterified to (pyro)pheophorbide- a. These nondehydrated CCEs were generally present in lower concentrations than their dehydrated counterparts, but were detectable by atmospheric pressure chemical ionization (APCI) mass spectrometry coupled with high-performance liquid chromatography (HPLC). We attributed differences between this study and previous work to the time allowed for predepositional decay and grazing processes to occur. The rapid sedimentation of CCEs in the shallow water column (ca. 10 m) on the LA shelf allowed for effective burial of all CCEs compared to the deeper water column regions sampled by previous work. This speculation is supported by the fact that the concentrations of CCEs with nondehydrated fucoxanthin/fucoxanthinol were extremely low in sediments from the site on the outer LA shelf with a deeper (253 m) water column. We also tentatively identified an additional CCE and its isomer as fucoxanthinol didehydrate pyropheophorbide- a ester. We suggest that the formation and transformation of CCEs are primarily controlled by the following three biologically mediated reactions: demethoxycarbonylation, dehydration

  2. Source and dispersal of silt on northern Gulf of Mexico continental shelf

    SciTech Connect

    Peterson, M.; Mazzullo, J.

    1988-01-01

    The surficial sediment on the continental shelf of the northern Gulf of Mexico is characterized by abundant silty clay which was deposited during the late Pleistocene lowstand and reworked during and after the Holocene transgression. The purposes of this study were to determine the sources of the silt fraction in this surficial sediment by quartz grain roundness and surface texture analysis, and to determine the effects of modern shelf currents upon the distribution of silt. Areal variations in quartz grain roundness and surface texture define six silt provinces on the northern Gulf of Mexico continental shelf. The Mississippi province is the largest province and stretches from the Chandeleur Islands to Matagorda Bay. It is characterized by a mixture of rounded grains that were derived from the sedimentary rocks of the Gulf coastal plain and the Mid-Continent, and angular, fractured grains that were derived from glacial deposits in the northern United States. A comparison of the areal distribution of these six provinces with the late Pleistocene paleogeography of the continental shelf shows evidence for varying degrees of shore-parallel transport of silt by modern shelf currents.

  3. Evidence for Upwelling of Corrosive “Acidified” Water onto the Continental Shelf

    NASA Astrophysics Data System (ADS)

    Feely, Richard A.; Sabine, Christopher L.; Hernandez-Ayon, J. Martin; Ianson, Debby; Hales, Burke

    2008-06-01

    The absorption of atmospheric carbon dioxide (CO2) into the ocean lowers the pH of the waters. This so-called ocean acidification could have important consequences for marine ecosystems. To better understand the extent of this ocean acidification in coastal waters, we conducted hydrographic surveys along the continental shelf of western North America from central Canada to northern Mexico. We observed seawater that is undersaturated with respect to aragonite upwelling onto large portions of the continental shelf, reaching depths of ~40 to 120 meters along most transect lines and all the way to the surface on one transect off northern California. Although seasonal upwelling of the undersaturated waters onto the shelf is a natural phenomenon in this region, the ocean uptake of anthropogenic CO2 has increased the areal extent of the affected area.

  4. Evidence for upwelling of corrosive "acidified" water onto the continental shelf.

    PubMed

    Feely, Richard A; Sabine, Christopher L; Hernandez-Ayon, J Martin; Ianson, Debby; Hales, Burke

    2008-06-13

    The absorption of atmospheric carbon dioxide (CO2) into the ocean lowers the pH of the waters. This so-called ocean acidification could have important consequences for marine ecosystems. To better understand the extent of this ocean acidification in coastal waters, we conducted hydrographic surveys along the continental shelf of western North America from central Canada to northern Mexico. We observed seawater that is undersaturated with respect to aragonite upwelling onto large portions of the continental shelf, reaching depths of approximately 40 to 120 meters along most transect lines and all the way to the surface on one transect off northern California. Although seasonal upwelling of the undersaturated waters onto the shelf is a natural phenomenon in this region, the ocean uptake of anthropogenic CO2 has increased the areal extent of the affected area.

  5. Observations of a coastal current in the continental shelf of Yucatan

    NASA Astrophysics Data System (ADS)

    Ruiz-Castillo, E.; Gomez-Valdes, J.; Rioja-Nieto, R.

    2013-05-01

    Oceanographic measurements were recorded at the continental shelf of Yucatan , over four CTD surveys carried out between 2003 and 2009. Results showed that the continental waters are confined in two layers. A 25 - year time series of sea surface temperature from AVHRR, with 1-day temporal resolution and 4-km spatial resolution, is also analyzed. Maps of the mean, the standard deviation, and the maximum temperature, obtained from the time series, showed the presence of low temperature waters along the northern coast of the Yucatan Peninsula, which were probably of subsurface origin. Monthly average temperature maps showed that cold surface water occur first in March at the southeast of the Yucatan continental shelf, and afterwards it flows westward and reaches the Campeche bay in July and August. Furthermore, in the continental waters the maximum temperature occurs in August and the minimum temperature occurs in February. The annual cycle explains more than 60 % of the variance with an error of the order of 1 C. The CTD surveys confirmed that the origin of the cold water was from the Caribbean Sea's subsurface that first appears at the southeast of the continental shelf. The water column along the coast was found to be well mixed in the same region where the band of cold water was detected using satellite data. It is concluded that the surface circulation along the northern coast of the Yucatan Peninsula is westward throughout the year except in February.

  6. Temporal variability of reactive iron over the Gulf of Alaska shelf

    NASA Astrophysics Data System (ADS)

    Aguilar-Islas, Ana M.; Séguret, Marie J. M.; Rember, Robert; Buck, Kristen N.; Proctor, Peter; Mordy, Calvin W.; Kachel, Nancy B.

    2016-10-01

    The Gulf of Alaska (GoA) shelf is a highly productive regime bordering the nitrate-rich, iron (Fe)-limited waters of the central GoA. The exchange between nitrate-limited, Fe-replete coastal waters and nitrate-rich, Fe-deplete offshore waters, amplified by mesoscale eddies, is key to the productivity of the region. Previous summer field studies have observed the partitioning of Fe in the coastal GoA as being heavily dominated by the particulate phase due to the high suspended particulate loads carried by glacial rivers into these coastal waters. Here we present new physico-chemical iron data and nutrient data from the continental shelf of the GoA during spring and late summer 2011. The late summer data along the Seward Line showed variable surface dissolved iron (DFe) concentrations (0.052 nM offshore to 4.87 nM inshore), within the range of previous observations. Relative to available surface nitrate, DFe was in excess (at Fe:C=50 μmol:mol) inshore, and deficient (at Fe:C=20 μmol:mol) offshore. Summer surface total dissolvable iron (TDFe, acidified unfiltered samples) was dominated by the acid-labile particulate fraction over the shelf (with a median contribution of only 3% by DFe), supporting previously observed Fe partitioning in the GoA. In contrast, our spring data from southeast GoA showed TDFe differently partitioned, with surface DFe (0.28-4.91 nM) accounting on average for a much higher fraction ( 25%) of the TDFe pool. Spring surface DFe was insufficient relative to available nitrate over much of the surveyed region (at Fe:C=50 μmol:mol). Organic Fe-binding ligand data reveal excess concentrations of ligands in both spring and summer, indicating incomplete titration by Fe. Excess concentrations of an especially strong-binding ligand class in spring surface waters may reflect in-situ ligand production. Due to anomalous spring conditions in 2011, river flow and phytoplankton biomass during our spring sampling were lower than the expected May average. We

  7. U.S. Eastern Continental Shelf Carbon Cycling (USECoS): Modeling, Data Assimilation, and Analysis

    NASA Technical Reports Server (NTRS)

    Mannino, Antonio

    2008-01-01

    Although the oceans play a major role in the uptake of fossil fuel CO2 from the atmosphere, there is much debate about the contribution from continental shelves, since many key shelf fluxes are not yet well quantified: the exchange of carbon across the land-ocean and shelf-slope interfaces, air-sea exchange of CO2, burial, and biological processes including productivity. Our goal is to quantify these carbon fluxes along the eastern U.S. coast using models quantitatively verified by comparison to observations, and to establish a framework for predicting how these fluxes may be modified as a result of climate and land use change. Our research questions build on those addressed with previous NASA funding for the USECoS (U.S. Eastern Continental Shelf Carbon Cycling) project. We have developed a coupled biogeochemical ocean circulation model configured for this study region and have extensively evaluated this model with both in situ and remotely-sensed data. Results indicate that to further reduce uncertainties in the shelf component of the global carbon cycle, future efforts must be directed towards 1) increasing the resolution of the physical model via nesting and 2) making refinements to the biogeochemical model and quantitatively evaluating these via the assimilation of biogeochemical data (in situ and remotely-sensed). These model improvements are essential for better understanding and reducing estimates of uncertainties in current and future carbon transformations and cycling in continental shelf systems. Our approach and science questions are particularly germane to the carbon cycle science goals of the NASA Earth Science Research Program as well as the U.S. Climate Change Research Program and the North American Carbon Program. Our interdisciplinary research team consists of scientists who have expertise in the physics and biogeochemistry of the U.S. eastern continental shelf, remote-sensing data analysis and data assimilative numerical models.

  8. U.S. Eastern Continental Shelf Carbon Cycling (USECoS): Modeling, Data Assimilation, and Analysis

    NASA Technical Reports Server (NTRS)

    Mannino, Antonio

    2008-01-01

    Although the oceans play a major role in the uptake of fossil fuel CO2 from the atmosphere, there is much debate about the contribution from continental shelves, since many key shelf fluxes are not yet well quantified: the exchange of carbon across the land-ocean and shelf-slope interfaces, air-sea exchange of CO2, burial, and biological processes including productivity. Our goal is to quantify these carbon fluxes along the eastern U.S. coast using models quantitatively verified by comparison to observations, and to establish a framework for predicting how these fluxes may be modified as a result of climate and land use change. Our research questions build on those addressed with previous NASA funding for the USECoS (U.S. Eastern Continental Shelf Carbon Cycling) project. We have developed a coupled biogeochemical ocean circulation model configured for this study region and have extensively evaluated this model with both in situ and remotely-sensed data. Results indicate that to further reduce uncertainties in the shelf component of the global carbon cycle, future efforts must be directed towards 1) increasing the resolution of the physical model via nesting and 2) making refinements to the biogeochemical model and quantitatively evaluating these via the assimilation of biogeochemical data (in situ and remotely-sensed). These model improvements are essential for better understanding and reducing estimates of uncertainties in current and future carbon transformations and cycling in continental shelf systems. Our approach and science questions are particularly germane to the carbon cycle science goals of the NASA Earth Science Research Program as well as the U.S. Climate Change Research Program and the North American Carbon Program. Our interdisciplinary research team consists of scientists who have expertise in the physics and biogeochemistry of the U.S. eastern continental shelf, remote-sensing data analysis and data assimilative numerical models.

  9. High-magnesium calcite dissolution in tropical continental shelf sediments controlled by ocean acidification.

    PubMed

    Haese, R R; Smith, J; Weber, R; Trafford, J

    2014-01-01

    Increases in atmospheric CO2 cause the oceanic surface water to continuously acidify, which has multiple and profound impacts on coastal and continental shelf environments. Here we present the carbonate mineral composition in surface sediments from a range of continental shelf seabed environments and their current and predicted stability under ocean acidifying conditions. Samples come from the following four tropical Australian regions: (1) Capricorn Reef (southern end of the Great Barrier Reef), (2) the Great Barrier Reef Lagoon, (3) Torres Strait, and (4) the eastern Joseph Bonaparte Gulf. Beyond the near-shore zone, these regions typically have a carbonate content in surface sediments of 80 wt % or more. The abundance of high-magnesium calcites (HMC) dominates over aragonite (Arag) and low-magnesium calcite (LMC) and constitutes between 36% and 50% of all carbonate. HMC, with a magnesium content larger than 8-12 mol %, is more soluble than both Arag and LMC, and the solubility of HMC positively correlates with its magnesium concentration. From the solubility data of Plummer and Mackenzie ( Am. J. Sci. 1974 , 274 , 61 - 83 ), 95% of HMC in the four regions is presently in metastable equilibrium relative to global mean tropical sea surface water. HMC is predicted to become destabilized in the four regions between 2040 and 2080 AD, with typical HMC decline rates between 2% and 5% per year. The range of respective estimated carbonate dissolution rates is expected to exceed current continental shelf carbonate accumulation rates, leading to net dissolution of carbonate during the period of HMC decline. In a geological context, the decline in HMC in tropical continental shelf environments is a global event triggered by reaching below-equilibrium conditions. The characteristic change in carbonate mineral composition in continental shelf sediments will serve as a geological marker for the proposed Anthropocene Epoch.

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

    SciTech Connect

    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.

  11. The effects of trawling, dredging and ocean dumping on the eastern Canadian continental shelf seabed

    NASA Astrophysics Data System (ADS)

    Messieh, S. N.; Rowell, T. W.; Peer, D. L.; Cranford, P. J.

    1991-08-01

    This paper presents an overview of current knowledge on the effects of trawling, dredging and ocean dumping on the eastern Canadian continental shelf seabed. The impact of trawling and dredging for fish and shellfish on marine habitats has recently attracted international attention among fisheries and environmental scientists. In Atlantic Canada, trawling and dredging are the principal methods of harvesting groundfish and scallops and ocean clams, respectively. It is estimated that fish trawlers and scallop dredges have swept tracks, cris-crossing the Canadian continental shelf, approximately 4.3 million km in length in 1985. In the past few years several studies were carried out by scientists from Canada, the United States and Europe to assess the impacts of trawling and dredging but results were inconclusive. Some studies showed physical damage as well as biological effects, whereas others indicated that the adverse effects were not considered to be serious. Fishermen are not the only potential users of the resources of the continental shelf. There is an increasing demand for good-quality sand and gravel aggregate and the ocean seabed is being seen as a possible source. The eastern Canadian continental shelf also exhibits hydrocarbon potential and operational and accidental discharges are an environmental concern. Increased marine transportation and expansion of the fishing fleet have resulted in a greater need for harbour dredging. Dredging and dredge spoil disposal were controlled by the Ocean Dumping Control Act and now the Canadian Environmental Protection Act which places restrictions on the composition of material that can be disposed of in the sea. Nevertheless some harbours contain contaminant concentrations exceeding the maximum allowable limits. It is concluded that the impacts of human activities on the continental shelf seabed environment are inevitable and the long-term effects, while difficult to determine, must be assessed. The sub-lethal effects

  12. Sources of phytoplankton to the inner continental shelf in the Santa Barbara Channel inferred from cross-shelf gradients in biological, physical and chemical parameters

    NASA Astrophysics Data System (ADS)

    Goodman, Jo; Brzezinski, Mark A.; Halewood, Elisa R.; Carlson, Craig A.

    2012-10-01

    Phytoplankton are a major food resource for filter-feeding organisms occupying intertidal and subtidal habitats of the inner continental shelf. Phytoplankton in these nearshore waters experience different anthropogenic and natural forcing compared to those offshore such that cross-shelf exchange would allow phytoplankton that were produced offshore to serve as a subsidy to inner shelf consumers when phytoplankton production on the shelf is negatively impacted. In the Santa Barbara Channel (SBC) the continental shelf is only a few kilometers wide facilitating exchange with offshore waters. Physical, chemical and biological gradients were examined monthly along a 3-km cross-shelf transect in the SBC from January, 2008 through April, 2009. Chemical and biological distributions followed temporal changes in physical forcing with higher nutrient concentrations and a more intense period of biological production associated with spring upwelling. Chlorophyll was relatively evenly distributed across the shelf during upwelling, but was present at higher concentrations on the inner shelf under stratified conditions. Similarly, cross-shelf gradients in the distribution of dominant phytoplankton genera were weakest during upwelling when blooms of the prymnesiophyte, Phaeocystis, and the diatoms, Eucampia spp. and Thalassiosira spp. occurred across most of the shelf. Upon stratification, blooms were largely confined to the inner shelf within 0.75 km of the shoreline with an initial bloom of the diatom Leptocylindrus spp. followed by Pseudo-nitzschia spp. and series of dinoflagellate blooms with Prorocentrum spp. and Lingulodinium spp. attaining the highest abundances. Phytoplankton taxonomic similarity decreased with increasing distance separating stations along the transect and was inversely related to stratification intensity. The observed distribution patterns and the trends in taxonomic similarity imply that for most of the year consumers within rocky intertidal and subtidal

  13. Postglacial transgressive stratigraphy of the Durban continental shelf, South Africa

    NASA Astrophysics Data System (ADS)

    Green, Andrew; Salzmann, Leslee; Cooper, Andrew

    2014-05-01

    This paper examines the geomorphology and seismic stratigraphy of the high-energy KwaZulu-Natal shelf offshore Durban, South Africa. Particular attention is paid to a laterally persistent (30 km) Holocene submerged shoreline located at 60 m water depth. Five major seismic units are identified (Units 1-5). Unit 1 comprises a series of infilled incised valleys that formed during the sea level lowering towards the Last Glacial Maximum. Unit 2 comprises a calcarenite core that forms the -60 m postglacial barrier complex. Unit 3 comprises lake-lagoon depressions in the back-barrier that formed simultaneously with the barrier system. These are backed to landward by several relict parabolic dunes preserved in Unit 2. Several relict weathering features (Unit 4) are associated with the barrier and reflect similar processes observed in contemporary aeolianite/beachrock outcrops on the adjacent coastline. These are draped by a thin veneer of post-transgressive Holocene sediment that caps the shelf stratigraphy (Unit 5). The development of the barrier and associated features occurred during a period of stillstand or slowstand associated with the Younger Dryas Cold Period (~12.7-11.6 Ka BP). Shoreline preservation in such a high-energy environment is considered unlikely as a result of the intense ravinement processes experienced during shoreline translation, coupled with the relatively low gradient setting of the KwaZulu-Natal shelf. The preservation of both the 100 m and 60 m shorelines was fostered by overstepping of the paleo-landscape, whereby preservation was promoted by a particularly rapid phase of relative sea-level rise associated with meltwater pulse 1B. This was further aided by early subtropical diagenesis during stillstand.

  14. East Louisiana continental shelf sediments: a product of delta reworking

    USGS Publications Warehouse

    Brooks, Gregg R.; Kingdinger, Jack L.; Penland, Shea; Williams, S. Jeffress

    1995-01-01

    Data from 77 vibracores were integrated with 6,700 line-km of high- resolution seismic reflection profiles collected off the eastern Louisiana coast in the region of the St. Bernard Delta, the first of the Holocene highstand deltas of the Mississippi River. Seismic fades and sediment facies were integrated in order to establish the stratigraphic details within this relict delta. Results provide a regional geologic framework from which comparisons can be made with other areas. Holocene deposits in the study area overlie a heavily dissected surface interpreted to represent a lowstand erosional surface. Resting on this surface is a thin unit of relatively clean, quartz sand interpreted to have been deposited during early transgression. This unit is overlain by sediments of the St. Bernard Delta, a seaward-prograding, coarsening-upward wedge of sands and muds that contain vertically-stacked units of deltaic succession. Two or more prograding units separated by an unconformity, delineated from regional seismic profiles, may represent laterally shifting subdelta lobes. Surficial sediments consist of a thin unit of sands and muds derived from and reflecting the individual subenvirons of the underlying delta. Holocene inner-shelf development off eastern Louisiana has been controlled by relative sea-level rise and sediment supply. Sediment supply and deposition are a product of delta progradation and delta-lobe switching. The modern shelf configuration and surficial sediment distribution patterns reflect reworking of underlying deltaic deposits. The lack of modern sediment input helps to maintain the imprint of this ancient delta on the modern shelf surface.

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

    NASA Astrophysics Data System (ADS)

    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

  16. Large-scale penetration of Gulf Stream water onto the continental shelf north of Cape Hatteras

    NASA Technical Reports Server (NTRS)

    Gawarkiewicz, Glen; Church, Thomas M.; Luther, George W., III; Ferdelman, Timothy G.; Caruso, Michael

    1992-01-01

    The presence of Gulf Stream water on the continental shelf as much as 60 km north of Cape Hatteras was observed during a hydrographic cruise in the summer of 1990. Gulf Stream water was concentrated at mid-depth between 10 and 30 m and penetrated the shelfbreak front which normally separates the shelf water from slope water and Gulf Stream water. Velocities of Gulf Stream water in the upper 110 m of the water column along the 1000 m isobath indicated a flow of 18 to 25 cm/s directed towards the northwest. Gulf Stream water on the shelf is considered to be associated with low values of fluorescence, transmissivity, and nutrient concentrations relative to adjacent shelf water.

  17. Shelf export of particulates/transport in continental margin waters

    SciTech Connect

    Pietrafesa, L.J.

    1991-02-01

    SEEP-II is a sponsored multi-institutional, multi-disciplinary program designed to address the possibility of flux material along and across the MAB. The methodology in SEEP-II employed conventional taut-wire moorings surrounding four RD acoustic doppler profiling current meters along with biological sampling of the source term of the biogenic material and the geochemical measurement of sedimentation rates. The field program was 17 months in length, from February 1988--June 1989, located off the Delaware and Chesapeake Bays. The SEEP-II moored array consists of two main cross-shelf arrays the northern of which had 6 to 8 moorings spanning the 40 to 1,000 m isobaths with one (and in Phase 2, a second) mooring offset about 20 km downshelf at 90m (and in Phase 2, a mooring also at 40m). The basic schematics of the northern and southern arrays are shown. In the region where the MAB shelf water/slope water front intersects the bottom, four RD-ADCP's were the focus of the array. Each of the bottom mounted profilers was accompanied by thermister strings (chains), Aanderaa current meters, fluorometers and transmissometers. 21 figs., 4 tabs.

  18. Sea ice and surface water circulation, Alaskan continental shelf

    NASA Technical Reports Server (NTRS)

    Wright, F. F. (Principal Investigator); Sharma, G. D.; Burns, J. J.

    1973-01-01

    The author has identified the following significant results. Sediments contributed by the Copper River in the Gulf of Alaska are carried westward along the shore as a distinct plume. Oceanic water relatively poor in suspended material appears to intrude near Montague Island, and turbid water between Middleton Island and Kayak Island is the result of Ekman between transport. An anticlockwise surface water circulation is observed in this region. Ground truth data indicate striking similarity with ERTS-1 imagery obtained on October 12, 1972. Observations of ERTS-1 imagery reveal that various characteristics and distribution of sea ice in the Arctic Ocean can be easily studied. Formation of different types of sea ice and their movement is quite discrenible. Sea ice moves parallel to the cost in near shore areas and to the northerly direction away from the coast.

  19. Some characteristics of Yakutat Eddies propagating along the continental slope of the northern Gulf of Alaska

    NASA Astrophysics Data System (ADS)

    Janout, Markus A.; Weingartner, Thomas J.; Okkonen, Stephen R.; Whitledge, Terry E.; Musgrave, David L.

    2009-12-01

    Data from array for real-time geostrophic oceanography (ARGO) profiling floats, oil tanker thermosalinographs, shipboard ADCP and towed-CTD surveys, and satellite altimetry are used to examine properties of two ˜200 km diameter, anticyclonic Yakutat Eddies that propagated westward at ˜1.5 km day -1 along the continental slope of the northern Gulf of Alaska (GOA) in 2001 and 2003. The eddies had lifetimes of up to 5 years, remained close to the shelfbreak, and had relatively constant size and strength until they encountered the Alaskan Stream where they appeared to spawn smaller, shorter-lived anticyclones. The azimuthal velocity field was vigorous (25-40 cm s -1) and in gradient wind balance with Rossby numbers of ˜0.05. Conservation of salt and azimuthal mass transports (between 20 m and the depth of the 32.2 isohaline) from shipboard surveys in May and August 2003 suggest little mass exchange occurred between the surface layers of the eddy and ambient waters. Chlorophyll concentrations were greater in the eddy than in ambient waters in both May and August. In May, the chlorophyll was patchily distributed, while in August dense chlorophyll concentrations occurred in and beneath the seasonal thermocline within 50 km of the eddy center. The high August chlorophyll concentrations might have been fostered by a broad and shallow (<˜150 m) upwelling of the eddy center between May and August. It appears likely that as Yakutat Eddies approach the shelfbreak non-linear processes will modify the slope flow field (and the stability and structure of the shelfbreak front), leading to cross-slope flows and flow reversals. This interaction may induce ˜30 km-wide streamers of shelf water to flow around the trailing edge of the anticyclone. The role of streamers in the freshwater and nutrient budgets of the GOA shelf and basin is unknown, but their contribution to these budgets will depend on the trajectory of a Yakutat Eddy, especially its proximity to the shelfbreak as the

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

    PubMed

    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

    2016-08-30

    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.

  1. Upper ocean variability in west Antarctic Peninsula continental shelf waters as measured using instrumented seals

    NASA Astrophysics Data System (ADS)

    Costa, Daniel P.; Klinck, John M.; Hofmann, Eileen E.; Dinniman, Michael S.; Burns, Jennifer M.

    2008-02-01

    Temperature profile data for the west Antarctic Peninsula (WAP) continental shelf waters, collected from freely ranging instrumented seals (crabeater, Lobodon carcinophagus and leopard, Hydrurga leptonyx), were used to demonstrate that these platforms can be used to supplement traditional oceanographic sampling methods to investigate the physical properties of the upper water column. The seal-derived profiles were combined with temperature profiles obtained from ship-based CTD measurements and from a numerical circulation model developed for the WAP to describe changes in temperature structure, heat content, and heat flux in the upper ocean waters of the WAP continental shelf. The seal-derived data documented the fall-to-winter transition of the surface waters and the shelf-wide presence of modified Circumpolar Deep Water (CDW) below 150-200 m on the WAP continental shelf. The heat content of the upper 200 m calculated from the seal-derived temperature profiles ranged between 1000 and 1500 MJ m -2; similar estimates were obtained from simulated temperature distributions. The seal-derived temperature measurements provided broader space and time resolution than was possible using any other currently available oceanographic sampling method. As such, the seal-derived measurements provided a valuable dataset for evaluation of temperature fields obtained from a numerical circulation model.

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

    PubMed Central

    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

    2016-01-01

    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. PMID:27575831

  3. Influence of late Pleistocene glaciations on the hydrogeology of the continental shelf offshore Massachusetts, USA

    NASA Astrophysics Data System (ADS)

    Siegel, Jacob; Person, Mark; Dugan, Brandon; Cohen, Denis; Lizarralde, Daniel; Gable, Carl

    2014-12-01

    Multiple late Pleistocene glaciations that extended onto the continental shelf offshore Massachusetts, USA, may have emplaced as much as 100 km3 of freshwater (salinity <5 ppt) in continental shelf sediments. To estimate the volume and extent of offshore freshwater, we developed a three-dimensional, variable-density model that couples fluid flow and heat and solute transport for the continental shelf offshore Massachusetts. The stratigraphy for our model is based on high-resolution, multichannel seismic data. The model incorporates the last 3 Ma of climate history by prescribing boundary conditions of sea level change and ice sheet extent and thickness. We incorporate new estimates of the maximum extent of a late Pleistocene ice sheet to near the shelf-slope break. Model results indicate that this late Pleistocene ice sheet was responsible for much of the emplaced freshwater. We predict that the current freshwater distribution may reach depths up to 500 meters below sea level and up to 30 km beyond Martha's Vineyard. The freshwater distribution is strongly dependent on the three-dimensional stratigraphy and ice sheet history. Our predictions improve our understanding of the distribution of offshore freshwater, a potential nonrenewable resource for coastal communities along recently glaciated margins.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  6. Stratigraphy and evolution history of the continental shelf deposits in the South Sea, Korea

    NASA Astrophysics Data System (ADS)

    Lee, Gwang-Soo; Cukur, Deniz; Yoo, Dong-Geun; Bae, Sung Ho; Kong, Gee-Soo; Kim, Dae-Choul

    2017-04-01

    High-resolution (Chirp and Sparker system) seismic profiles were analyzed to investigate the stratigraphy and evolution history of the continental shelf deposits in the South Sea, Korea. Approximately 1940 line-km data of chirp and sparker profiles was acquired. Along with seismic profiling, 30 piston core samples were collected and two previous long drill cores (SSDP-103 and 104) were used to compare with seismic data. The seismic profiles of this study show nine types of seismic facies separated by seafloor morphology and subbottom acoustic characters. Based on the sequence analysis of seismic profiles, the continental shelf deposit of the South Sea above sequence boundary of pre-LGM deposit can be divided into five sedimentary units (S1, S2, S3, S4, and S5 from top to bottom). Each sedimentary unit shows different seismic facies and geometry, and is clearly separated by boundaries formed since the LGM. The correlation between cores data and the seismic data suggests that unit S5 is incised channel fill formed by fluvial or coastal sediments during the early transgressive stage, accompanied by backstepping of the shoreline. Unit S4 is transgressive sand layer resulted by the selective sedimentation of the coarse sediments due to the strong current and tide with the rapid retreat of the coastline. Unit S3 is paleo channel or basin fill deposit made in estuary or delta environments formed near the inner continental shelf. Unit S2 is inner shelf transgressive sand layer including sand ridge. Unit S1 is interpreted as the most recent mud formed during the highstand stage when the sea-level rise terminated. The evolution history of the continental shelf deposit in the South Sea, since LGM, is closely related to the postglacial sea-level changes, distribution of Seomjin paleo channel, sediment supply, and erosion.

  7. Benthic manganese fluxes along the Oregon-California continental shelf and slope

    NASA Astrophysics Data System (ADS)

    McManus, James; Berelson, William M.; Severmann, Silke; Johnson, Kenneth S.; Hammond, Douglas E.; Roy, Moutusi; Coale, Kenneth H.

    2012-07-01

    Here we examine the factors that influence the manganese (Mn) benthic flux from eastern North Pacific marine sediments, with a primary emphasis on continental shelf locations off Oregon and California and studies that involve the use of in situ benthic chambers. Typical shelf-to-shallow margin (<˜350 m) sites have benthic Mn efflux rates that average ˜8±5 μmol m-2 d-1. In contrast, for the Eel River continental shelf region the benthic Mn efflux can be an order of magnitude higher than other shelf settings with benthic effluxes exceeding ˜50 μmol m-2 d-1. Based on prior work and some new results, continental margin and slope sites (350-˜4000 m) have benthic Mn efflux rates that average ˜1±1 μmol m-2 d-1. The combination of the benthic flux and Mn solid-phase data, indicate that for the continental shelf off the Umpqua and Eel Rivers, approximately 15±10% of the total Mn that is delivered to the seafloor is remobilized. The compiled data set shows that the benthic Mn efflux co-varies with the organic carbon oxidation rate with a Mn to organic carbon oxidation (Cox) ratio of ˜0.8 mmol Mn mol-1. Although this ratio can be as high as ˜5 for some Eel River sites, the generally close correspondence between Mn and organic carbon implies that the organic carbon oxidation rate exerts some primary control over the rate of the Mn efflux. The amount of organic carbon oxidized by Mn-oxides, however, represents a small fraction (i.e., generally <1%) of the total organic carbon oxidized in these seafloor sediments.

  8. A new bathymetry of the Northeast Greenland continental shelf: Constraints on glacial and other processes

    NASA Astrophysics Data System (ADS)

    Arndt, Jan Erik; Jokat, Wilfried; Dorschel, Boris; Myklebust, Reidun; Dowdeswell, Julian A.; Evans, Jeffrey

    2015-10-01

    A new digital bathymetric model (DBM) for the Northeast Greenland (NEG) continental shelf (74°N-81°N) is presented. The DBM has a grid cell size of 250 m × 250 m and incorporates bathymetric data from 30 multibeam cruises, more than 20 single-beam cruises and first reflector depths from industrial seismic lines. The new DBM substantially improves the bathymetry compared to older models. The DBM not only allows a better delineation of previously known seafloor morphology but, in addition, reveals the presence of previously unmapped morphological features including glacially derived troughs, fjords, grounding-zone wedges, and lateral moraines. These submarine landforms are used to infer the past extent and ice-flow dynamics of the Greenland Ice Sheet during the last full-glacial period of the Quaternary and subsequent ice retreat across the continental shelf. The DBM reveals cross-shelf bathymetric troughs that may enable the inflow of warm Atlantic water masses across the shelf, driving enhanced basal melting of the marine-terminating outlet glaciers draining the ice sheet to the coast in Northeast Greenland. Knolls, sinks, and hummocky seafloor on the middle shelf are also suggested to be related to salt diapirism. North-south-orientated elongate depressions are identified that probably relate to ice-marginal processes in combination with erosion caused by the East Greenland Current. A single guyot-like peak has been discovered and is interpreted to have been produced during a volcanic event approximately 55 Ma ago.

  9. Malvinas-slope water intrusions on the northern Patagonia continental shelf

    NASA Astrophysics Data System (ADS)

    Piola, A. R.; Martínez Avellaneda, N.; Guerrero, R. A.; Jardón, F. P.; Palma, E. D.; Romero, S. I.

    2010-03-01

    The Patagonia continental shelf located off southeastern South America is bounded offshore by the Malvinas Current, which extends northward from northern Drake Passage (~55° S) to nearly 38° S. The transition between relatively warm-fresh shelf waters and Subantarctic Waters from the western boundary current is characterized by a thermohaline front extending nearly 2500 km. We use satellite derived sea surface temperature, and chlorophyll-a data combined with hydrographic and surface drifter data to document the intrusions of slope waters onto the continental shelf near 41° S. These intrusions create vertically coherent localized negative temperature and positive salinity anomalies extending onshore about 150 km from the shelf break. The region is associated with a center of action of the first mode of non-seasonal sea surface temperature variability and also relatively high chlorophyll-a variability, suggesting that the intrusions are important in promoting the local development of phytoplankton. The generation of slope water penetrations at this location may be triggered by the inshore excursion of the 100 m isobath, which appears to steer the Malvinas Current waters over the outer shelf.

  10. Malvinas-slope water intrusions on the northern Patagonia continental shelf

    NASA Astrophysics Data System (ADS)

    Piola, A. R.; Avellaneda, N. M.; Guerrero, R. A.; Jardón, F. P.; Palma, E. D.; Romero, S. I.

    2009-12-01

    The Patagonia continental shelf located off southeastern South America is bounded offshore by the Malvinas Current, which extends northward from northern Drake Passage (~55° S) to nearly 38° S. The transition between relatively warm-fresh shelf waters and Subantarctic Waters from the western boundary current is characterized by a thermohaline front extending nearly 2500 km. We use satellite derived sea surface temperature, and chlorophyll-a data combined with hydrographic and surface drifter data to document the intrusions of slope waters onto the continental shelf near 41° S. These intrusions create vertically coherent localized negative temperature and positive salinity anomalies extending onshore about 150 km from the shelf break. The region is associated with a center of action of the first mode of non-seasonal sea surface temperature variability and also relatively high chlorophyll-a variability, suggesting that the intrusions are important in promoting the local development of phytoplankton. The generation of slope water penetrations at this location may be triggered by the inshore excursion of the 100 m isobath, which appears to steer the Malvinas Current waters over the outer shelf.

  11. Separation of the Kuroshio water and its penetration onto the continental shelf west of Kyushu

    NASA Astrophysics Data System (ADS)

    Lie, Heung-Jae; Cho, Cheol-Ho; Lee, Jae-Hak; Niiler, Peter; Hu, Jian-Hwa

    1998-02-01

    The separation of Kuroshio water west of Kyushu and its penetration onto the continental shelf of the East China Sea were investigated by analyzing trajectories of satellite-tracked surface drifters deployed during 1989-1996. Conductivity, temperature, and depth (CTD) data collected in the eastern East China Sea in December 1993 and late April/early May 1995 were also analyzed. Composite trajectories of 172 drogued drifters provided direct evidence of the separation of the northeastward flowing Kuroshio into two parts at the western mouth of the deep trough southwest of Kyushu. The Kuroshio main stream turns to the east toward the Tokara Strait, and a northward flowing branch current penetrates onto the shelf across the continental slope west of the trough. Analysis of the CTD data and drifter trajectories, concurrently observed, shows that the branch current was part of the inshore Kuroshio, just upstream before its separation. During the periods of CTD observations, the separated, inshore Kuroshio water intruded northward in a tongue shape along the shelf break of the trough and penetrated onto the shelf after crossing obliquely the western continental slope of the trough. The water that penetrated onto the shelf continued to flow northward toward the Korea Strait. The main path of this water was easily traced by its high salinity, which is characteristic of the inshore Kuroshio water. Application of an inverse method to the observed CTD data also supports the separation and penetration of the Kuroshio and calculates the volume transport of the northward branch to be about 4.0×106 m3/s for the two different surveys. The tongue-shaped intrusion of the inshore Kuroshio water onto the outer shelf may take place in close association with the eastward turning of the Kuroshio main stream and it might be caused by the vorticity adjustment created by the eastward turning of the Kuroshio.

  12. Continental shelf sediment dynamics in the Anthropocene: A global shift

    NASA Astrophysics Data System (ADS)

    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.

  13. High level of bacterial diversity and novel taxa in continental shelf sediment.

    PubMed

    Hong, Jin-Kyung; Cho, Jae-Chang

    2012-06-01

    The bacterial diversity of the continental shelf sediment in the Yellow Sea was investigated by the cloning and sequencing of PCR-amplified 16S rRNA genes. The majority of the cloned sequences were distinct phylotypes that were novel at the species level. The richness estimator indicated that the sediment sample might harbor up to 32 phylum-level taxa. A large number of low-abundance, phylum-level taxa accounted for most of the observed phylogenetic diversity at our study site, suggesting that these low-abundance taxa might play crucial roles in the shelf sediment ecosystem.

  14. Quantifying the Relative Impact of Continental Shelf and Storm Characteristics on Nearshore Waves during Hurricanes

    NASA Astrophysics Data System (ADS)

    Dalyander, S.; Birchler, J. J.; Stockdon, H. F.; Thompson, D.

    2016-12-01

    The relationship between storm characteristics (such as the size and velocity distribution of the wind field) and the waves they generate is well-understood, as is the dissipation and spectral transformation that occurs to swell and wind waves propagating over broad areas of the continental shelf. However, predicting differences in shallow water storm-wave climate between locations with varying shelf slope and width are more challenging. As a result, quantifying the spatial variability in coastal vulnerability to hurricanes, which along the US East Coast is done for Saffir-Simpson scale categories of hurricanes using the Stockdon run-up model and a simple method for modeling nearshore (20-m) wave height based on a uniform wind field, yields inaccurate results. Understanding differing storm-shelf interactions is also necessary to determine how vulnerability in different areas of the coast will be altered by potential climate-change impacts to storm frequency and intensity. In this study, simple, category-based wave model predictions were compared with deterministic SWAN model runs and observational data for Hurricane Earl (2010) offshore of Puerto Rico (PR) and Hurricane Bonnie (2010) offshore of the South Atlantic Bight (SAB). Wave height overestimation by the simple model is exacerbated at PR, where the continental shelf is steep and narrow. Over the wider shelf in the SAB, unrealistically high energy, long period waves are filtered from the spectrum, and the simple model compares relatively well to observations. To examine this effect, wave transformation over different simple shelf configurations was modeled for a suite of idealized storms to develop relationships between nearshore wave parameters and storm and shelf characteristics. These results will be used to improve estimations of coastal vulnerability based on hurricane category, and to determine the spatial variability in nearshore wave response with potential changes in hurricane climatology.

  15. The imprint of sea-level changes in the Southeastern Iberian continental shelf, Western Mediterranean Sea

    NASA Astrophysics Data System (ADS)

    Pinna, Andrea; Lastras, Galderic; Acosta, Juan; Muñoz, Araceli; Canals, Miquel

    2014-05-01

    A detailed morphologic analysis of the Southeastern Iberian continental shelf, Western Mediterranean Sea, between the Mar Menor and the Gulf of Almería, based on swath bathymetry data, has revealed a number of seafloor features that we attribute to the imprint of sea-level changes since the last glacial maximum. The continental shelf has been divided in four different domains with contrasting characteristics: the Mar Menor sector, the Mazarrón and Vera sector, the Gata Cape shelf and the Gulf of Almería shelf. The Mar Menor sector displays an up to 40 km wide shelf with a very low slope gradient, which contrasts with the Mazarrón and Vera shelf, with a width ranging between 0.4 and 5 km, severely incised by the different branches of the Garrucha submarine canyon. On each of these sectors, a variety of morphologies such as crests and escarpments have been identified. Most of these crests and escarpments can be followed for distances exceeding 15 km, and are located at constant, characteristic water depths. We interpret these structures as the result of relatively short-lived sea-level still-stands and thus as palaeo-coastlines. Taking into account subsidence, we have correlated their bathymetric position with published post-MIS-5 Mediterranean sea-level evolution curves, allowing the attribution of an approximate age for each interpreted palaeo-coastline. The last sea-level regression is partially registered in the smooth Mar Menor shelf, where different crests and escarpments are cut by a LGM palaeo-channel, whereas all the sectors display structures related to the last sea-level transgression. The continuity of these structures along all the sectors has allowed reconstructing the evolution of the coastline during the last sea-level transgression, and thus inferring the palaeo-landscape of this sector of the Southeastern Iberian coast at different stages since 18 ka BP until the present.

  16. Interpretation of seismic stratigraphy on the Amazon continental shelf

    SciTech Connect

    Alexander, C.R. Jr.; Nittrouer, C.A.; Demaster, D.J.

    1985-01-01

    The stratigraphy of the Amazon subaqueous delta has been examined using high-resolution reflection profiles. 15 piston cores from the Amazon Shelf were used to interpret the significance of the reflectors evident in the seismic profiles. Acoustic reflectors correlate with changes in grain size within cores, and generally represent coarser layers within the muddy deposits of the delta. Measurement of compressional-wave seismic velocity and saturated bulk density demonstrate that the correlation results from changes in acoustic impedance, caused by the grain-size variations. The reflectors reveal two predominant types of seismic stratigraphy: depositional and erosional. The depositional stratigraphy contains reflectors formed by relatively subtle change in grain size. Gently dipping topset and steeply dipping foreset demonstrate upward and seaward progradation of the subaqueous delta. This stratigraphy is truncated by erosional reflectors, which are significantly coarser layers. The erosional reflectors divide the depositional stratigraphy into distinct sets. The prevalence of erosional reflectors is greatest in the topset region near the river mouth, suggesting that sediment in this region, which is rapidly accumulating on 100-year time scales, has been eroded over longer time scales within the Holocene.

  17. Sea, ice and surface water circulation, Alaskan continental shelf

    NASA Technical Reports Server (NTRS)

    Sharma, G. D.; Wright, F. F.; Burns, J. J. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. ERTS-1 imagery has been extremely useful in understanding the tidal water movements in a large estuary such as Cook Inlet. As more imagery obtained during various tidal stages become available it appears that complex and fast changing micro-circulation patterns develop in various regions of Cook Inlet during each advancing and receding tide. More ERTS-1 synoptic imagery is needed to fully understand the effect of the approach of tidal front on the water movements in the various regions through the estuary. The conventional onboard ship data gathered during various cruises although revealed the overall circulation pattern in Cook Inlet but failed to show micro-subgyres which develop in various regions during each tide which are discernible on ther ERTS-1 imagery. Suspended load distribution in the Bering Sea during summer varies significantly. In areas of phytoplankton bloom and at the river mouths the suspended load is higher than the 1 mg/1 which is found over most areas. The influence of major rivers on temperature, salinity, and suspended load in surface water as well as at shallow depth is apparent. On the Bering shelf a strong pycnocline generally at depth 10-20 m is formed by surface fresh water flow which retains sediment in suspension over extended periods.

  18. Modeling three-dimensional propagation in a continental shelf environment.

    PubMed

    Ballard, Megan S

    2012-03-01

    An acoustic propagation model is applied to predict measurements of three-dimensional (3-D) effects recorded off the southeast coast of Florida. The measured signal is produced by a low frequency source that is towed north parallel to the shelf from a fixed receiving array. The acoustic data show the direct path arrival at the bearing of the tow ship and a second refracted path arrival as much as 30° inshore of the direct arrival. Notably, the refracted arrival has a received level more than 25 dB greater than that of the direct arrival. A geoacoustic model of the environment is created to explain the data. It is shown that the topography of the seafloor plays the largest role in controlling horizontal refraction effects, whereas the range-dependent sediment properties have the most influence on the received level. The modeling approach is based on a 3-D adiabatic mode technique in which the horizontal refraction equation is solved using a parabolic equation in Cartesian coordinates. A modal decomposition of the field provides insight into the variability in the arrival angle and received level of the measured signal.

  19. Instabilities in nonlinear internal waves on the Washington continental shelf

    NASA Astrophysics Data System (ADS)

    Zhang, Shuang; Alford, Matthew H.

    2015-07-01

    Previous studies have identified two primary mechanisms (shear instability and convective instability) by which nonlinear internal waves (NLIWs) induce mixing on continental shelves. To determine the relative importance of these and their dependence on background flow conditions, we examine a much longer (6 month) data set from a moored ADCP/thermistor chain with 2 m vertical spacing in which over 600 NLIWs are detected. Turbulent properties of the 318 waves with detectable overturning instabilities are documented using Thorpe scales. The 130 waves detected while an ADCP was functioning are classified based on a Froude number criterion (Fr = uc, where u is velocity in the wave propagation direction, c is the wave phase speed). Of these, 108 waves are identified as shear-instability (Type I; Fr < 1) waves and 22 as convective instability (Type II; Fr > 1). Composites are constructed by averaging in a wave coordinate frame over all waves in each category, showing the mean spatial structure of dissipation and other wave quantities. Turbulence is highest at the sheared interface for Type I waves and throughout the wave core for Type II waves. No relationship between wave instability mechanisms and wave/background parameters such as wave steepness, stratification, or mean flow is found, except that unstable waves tend to be more energetic, demonstrating a need to better understand wave propagation and breaking in complex and variable coastal oceanographic background flows.

  20. Morphology and Dynamics of Subaqueous Dunes in a Tideless Outer Shelf (murcia Continental Shelf, Western Mediterranean Sea)

    NASA Astrophysics Data System (ADS)

    Durán, R.; Rivera, J.; Guillén, J.; de Cárdenas, E.; Muñoz, A.; Acosta, J.

    2014-12-01

    During the last years, the increasing application of multibeam sonar systems for mapping the seafloor has revealed the occurrence of sedimentary bedforms on the continental shelves worldwide. In addition, repeated multibeam surveys are used to monitor and compare the temporal evolution of such morphologies providing important insights into the sedimentary processes on the continental shelf. In the Murcia continental shelf, Western Mediterranean Sea, a large filed of subaqueous dunes has been observed in the middle and outer shelf. Here, we present a detailed morphologic and sedimentological analysis of these features with the aim to discuss their possible mechanism of formation and assess their potential mobility. The findings are based on swath-bathymetry collected using a SIMRAD EM 710 and EM3000D multibeam echosounders, high-resolution seismic profiles acquired with a TOPAS 018 system and sediment samples. Dunes are widely distributed between 60 and 110 m depth, from the Cope Cape, to the north, to the Águilas submarine canyon head rim, to the south. Dunes range from 18 to 140 m in wavelength and from 0.29 to 1.28 m in height. Dunes have asymmetrical profiles (average asymmetry of 0.065) with the lee slope facing towards the southwest that indicate a net south-westward sediment transport. Seabed samples collected in the crests and troughs of individual dunes show a similar grain-size distribution curve, but differ in the content of fines, which is higher in the trough, whereas the crests are dominated by coarse particles. High resolution seismic profiles reveal the presence of a continuous strong reflector that constitutes the base of the subaqueous dunes and could likely correspond to the Holocene transgressive ravinement surface.Dune migration rates were determined from the net displacement of the crests and troughs positions deduced from repeated multibeam surveys (2003 and 2013). Results indicate that the subaqueous dunes remain stationary or migrate at low

  1. Sediment- and hydro-dynamics of the Mekong Delta: From tidal river to continental shelf

    NASA Astrophysics Data System (ADS)

    Ogston, A. S.; Allison, M. A.; Mullarney, J. C.; Nittrouer, C. A.

    2017-09-01

    This introduction to the special issue entitled, "Sediment- and hydro-dynamics of the Mekong Delta: from tidal river to continental shelf", describes the setting and program design of collaborative studies with integrated field and modeling experiments in 2014-2015, along with associated research in the region. The Mekong River is among the largest on Earth in terms of water discharge, and much of the sediment delivered from the Tibetan Plateau has accumulated in the subaerial and subaqueous components of the Mekong Delta. As a group, the papers in this special issue describe the portion of the system where the sediment source signal is altered along the tidally influenced river and is delivered to the shorelines and continental shelf. The linked studies provide a holistic view of the system, and emphasize the interactions between hydrodynamics and sediment transport processes in sub-environments as sediment makes its way along the path from source to sink.

  2. Water exchange between the continental shelf and the cavity beneath Nioghalvfjerdsbræ (79 North Glacier)

    NASA Astrophysics Data System (ADS)

    Wilson, N. J.; Straneo, F.

    2015-09-01

    The mass loss at Nioghalvfjerdsbræ is primarily due to rapid submarine melting. Ocean data obtained from beneath the Nioghalvfjerdsbræ ice tongue show that melting is driven by the presence of warm (1°C) Atlantic Intermediate Water (AIW). A sill prevents AIW from entering the cavity from Dijmphna Sund, requiring that it flow into the cavity via bathymetric channels to the south at a pinned ice front. Comparison of water properties from the cavity, Dijmphna Sund, and the continental shelf support this conclusion. Overturning circulation rates inferred from observed melt rates and cavity stratification suggest an exchange flow between the cavity and the continental shelf of 38mSv, sufficient to flush cavity waters in under 1 year. These results place upper bounds on the timescales of external variability that can be transmitted to the glacier via the ice tongue cavity.

  3. The influence of surface waves on water circulation in a mid-Atlantic continental shelf region

    NASA Technical Reports Server (NTRS)

    Whitlock, C. H.; Talay, T. A.

    1974-01-01

    The importance of wave-induced currents in different weather conditions and water depths (18.3 m and 36.6 m) is assessed in a mid-Atlantic continental-shelf region. A review of general circulation conditions is conducted. Factors which perturb the general circulation are examined using analytic techniques and limited experimental data. Actual wind and wave statistics for the region are examined. Relative magnitudes of the various currents are compared on a frequency of annual occurrence basis. Results indicated that wave-induced currents are often the same order of magnitude as other currents in the region and become more important at higher wind and wave conditions. Wind-wave and ocean-swell characteristics are among those parameters which must be monitored for the analytical computation of continental-shelf circulation.

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

    SciTech Connect

    Not Available

    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.

  5. Bottom stress estimates and sand transport on northern California inner continental shelf

    USGS Publications Warehouse

    Cacchione, D.A.; Drake, D.E.; Ferreira, J.T.; Tate, G.B.

    1994-01-01

    Measurements of velocities and light transmission in the bottom boundary layer on the continental shelf off northern California demonstrate the importance of storms in the transport of sediment along the coast and offshore in this region. Time-series estimates of bottom stress obtained from a combined wave-current bottom boundary layer model in which wave and current measurements from the Geoprobe tripod were used as input show high stress values of 10 dynes cm-2 during two distinct storm events in early February and early March, 1991. These stresses induce significant offshore sediment transport, achieving maximum values of about 0.5 g cm-1 s-1. The net transport over the entire measurement period from 30 January 1991 to 13 March 1991 was along the coast toward the north and offshore. This transport pattern explains slow migration of low amplitude, broad crescentic dunes along and across this portion of the inner continental shelf. ?? 1994.

  6. An oilspill risk analysis for the North Atlantic outer continental shelf lease area

    USGS Publications Warehouse

    Smith, Richard Allmon; Slack, James Richard; Davis, Robert K.

    1976-01-01

    The Federal Government has proposed to lease 1,172,795 acres of Outer Continental Shelf (OCS) lands on Georges Bank off the New England Coast for oil and gas development. Estimated recoverable petroleum resources for the proposed 206 tract sale area range from 180 to 650 million barrels. Contingent upon actual discovery of this quantity of oil, production is expected to span a period of about 20 years. An oilspill risk analysis was conducted to determine relative environmental hazards of developing oil in the North Atlantic Outer Continental Shelf lease area. The study analyzed probability of spill occurrence, likely path of pollutants from spills, and locations in space and time of recreational and biological resources likely to be vulnerable. These results are combined to yield estimates of the overall oilspill risk associated with development of the lease area. (Woodard-USGS)

  7. 75 FR 80717 - Increased Safety Measures for Energy Development on the Outer Continental Shelf; Availability...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-12-23

    ...In the Federal Register of October 14, 2010, BOEM published an interim final rule implementing certain safety measures recommended in the report entitled, ``Increased Safety Measures for Energy Development on the Outer Continental Shelf'' (Safety Measures Report). The President directed the Department of the Interior to develop the Safety Measures Report to identify measures necessary to improve the safety of oil and gas exploration and development on the Outer Continental Shelf in light of the Deepwater Horizon event on April 20, 2010, and resulting oil spill. To implement the practices recommended in the Safety Measures Report, the Bureau of Ocean Energy Management, Regulation and Enforcement is amending drilling regulations related to well control, including: subsea and surface blowout preventers, well casing and cementing, secondary intervention, unplanned disconnects, recordkeeping, well completion, and well plugging. This document provides the official BOEMRE notice of availability for the Initial Regulatory Flexibility Analysis (IRFA) for that interim rule and provides opportunity for comment.

  8. Development of the benethic nepheloid layer on the south Texas continental shelf, western Gulf of Mexico

    USGS Publications Warehouse

    Shideler, G.L.

    1981-01-01

    A monitoring study of suspended sediment on the South Texas Continental Shelf indicates that a turbid benthic nepheloid layer is regionally persistent. A sequence of quasi-synoptic measurements of the water column obtained during six cruises in an 18-month period indicates substantial spatial and temporal variability in nepheloidlayer characteristics. Regionally, the thickness of the shelf nepheloid layer increases both seaward and in a convergent alongshelf direction. Greatest thicknesses occur over a muddy substrate, indicating a causal relationship; maximum observed local thickness is 35 m which occurs along the southern shelf break. Analyses of suspended particulate matter in shelf bottom waters indicate mean concentrations ranging from 49 ?? 104 to 111 ?? 104 particle counts/cc; concentrations persistently increase shoreward throughout the region. Bottom particulate matter is predominantly composed of inorganic detritus. Admixtures of organic skeletal particles, primarily diatoms, are generally present but average less than 10% of the total particulate composition. Texturally, the particulate matter in bottom waters is predominantly poorly sorted sediment composed of very fine silt (3.9-7.8 ??m). The variability in nepheloid-layer characteristics indicates a highly dynamic shelf feature. The relationship of nepheloid-layer characteristics to hydrographic and substrate conditions suggests a conceptual model whereby nepheloid-layer development and maintenance are the results of the resuspension of sea-floor sediment. Bottom turbulence is attributed primarily to vertical shear and shoaling progressive internal waves generated by migrating shelf-water masses, especially oceanic frontal systems, and secondarily to shoaling surface gravity waves. ?? 1981.

  9. [Circulation and exchange processes on the South Atlantic Bight Continental Shelf]. [Progress summary for 1986

    SciTech Connect

    Not Available

    1986-12-31

    A continuation of the physical oceanography program to investigate circulation and exchange processes on the South Atlantic Bight (SAB) Continental Shelf is proposed. The transport and dispersal of materials entering the inner shelf zone with river discharge is not well understood at present. Climatological data, satellite imagery, and numerical modeling results indicate two removal routes for these nearshore waters: northeast transport and offshore exchange between Cape Fear and Savannah during the spring and summer when maximum run-off and northward winds prevail; and southward transport and offshore exchange near Cape Canaveral during the fall when southward winds prevail. We have conducted interdisciplinary experiments to investigate the transport processes in the inner to outer shelf between Savannah, Georgia and Cape Fear, North Carolina. In addition we propose to continue synthesis and interpretation of current measurements. The analyses will focus on determining the coupling mechanisms of inner shelf and outer shelf waters with special emphasis placed on resolving the modes and rates of shelf water removal.

  10. High Resolution Quaternary Seismic Stratigraphy of the New York Bight Continental Shelf

    USGS Publications Warehouse

    Schwab, William C.; Denny, J.F.; Foster, D.S.; Lotto, L.L.; Allison, M.A.; Uchupi, E.; Swift, B.A.; Danforth, W.W.; Thieler, E.R.; Butman, Bradford

    2003-01-01

    A principal focus for the U.S. Geological Survey (USGS) Coastal and Marine Geology Program (marine.usgs.gov) is regional reconnaissance mapping of inner-continental shelf areas, with initial emphasis on heavily used areas of the sea floor near major population centers. The objectives are to develop a detailed regional synthesis of the sea-floor geology in order to provide information for a wide range of management decisions and to form a basis for further investigations of marine geological processes. In 1995, the USGS, in cooperation with the U.S. Army Corps of Engineers (USACOE), New York District, began to generate reconnaissance maps of the continental shelf seaward of the New York - New Jersey metropolitan area. This mapping encompassed the New York Bight inner-continental shelf, one of the most heavily trafficked and exploited coastal regions in the United States. Contiguous areas of the Hudson Shelf Valley, the largest physiographic feature on this segment of the continental shelf, also were mapped as part of a USGS study of contaminated sediments (Buchholtz ten Brink and others, 1994; 1996). The goal of the reconnaissance mapping was to provide a regional synthesis of the sea-floor geology in the New York Bight area, including: (a) a description of sea-floor morphology; (b) a map of sea-floor sedimentary lithotypes; (c) the geometry and structure of the Cretaceous strata and Quaternary deposits; and (d) the geologic history of the region. Pursuing the course of this mapping effort, we obtained sidescan-sonar images of 100 % of the sea floor in the study area. Initial interpretations of these sidescan data were presented by Schwab and others, (1997a, 1997b, 2000a). High-resolution seismic-reflection profiles collected along each sidescan-sonar line used multiple acoustic sources (e.g., watergun, CHIRP, Geopulse). Multibeam swath-bathymetry data also were obtained for a portion of the study area (Butman and others, 1998;). In this report, we present a series

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

    SciTech Connect

    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. (ACR)

  12. Sidescan-sonar data collected during May 1978 from the southern New England continental shelf

    USGS Publications Warehouse

    McClennen, Charles E.

    1981-01-01

    Sidescan-sonar data were collected aboard R/V WESTWARD (Cruise W-39-4) during May 1978 by the U.S. Geological Survey using an Ocean Research Equipment System. Navigation in the study area was by Loran C. The 368 kilometers of survey were conducted in Block Island Sound, in Rhode Island Sound, and over the mid-Continental Shelf south of Block Island and Martha's Vineyard (Fig. 1).

  13. Model for the Formation and Evolution of Sand Ridges on the Continental Shelf

    DTIC Science & Technology

    1992-10-01

    structures such as longshore sand ridges, on the continental shelf in water deeper than that of the shoaling region, is proposed. The model is based on the...interaction between surficial or internal weakly nonlinear shallow water waves having weak span- wise spatial dependence and the bottom topography. While...structure, model, 169 non-linear, shallow water waves, finite difference 1.4 PIC[ coot 17. SECURITY CLASSIFICATOM 1t SECURITY .ASSWICATON 1t. SECU10TY

  14. Oil and gas developments in Atlantic Coastal Plain and Outer Continental Shelf in 1985 and 1986

    SciTech Connect

    Amato, R.V.

    1987-10-01

    Drilling activity for 1985 was not reported previously due to the low level of activity. No exploratory drilling took place on the Atlantic outer continental shelf in 1985 or 1986. One shallow well was drilled onshore in Georgia on the Atlantic coastal plan in 1985, and 2 wells were completed in Georgia in 1986. Texaco drilled 6 core holes on the Virginia coastal plain in 1986. 2 tables.

  15. Hydrothermal origin of oil and gas reservoirs in basement rock of the South Vietnam continental shelf

    SciTech Connect

    Dmitriyevskiy, A.N.; Kireyev, F.A.; Bochko, R.A.; Fedorova, T.A. )

    1993-07-01

    Oil-saturated granites, with mineral parageneses typical of hydrothermal metasomatism and leaching haloes, have been found near faults in the crystalline basement of the South Vietnam continental shelf. The presence of native silver, barite, zincian copper, and iron chloride indicates a deep origin for the mineralizing fluids. Hydrothermally altered granites are a new possible type of reservoir and considerably broaden the possibilities of oil and gas exploration. 15 refs., 22 figs., 1 tab.

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

    PubMed

    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).

  17. Megaflutes in a continental shelf setting, Placentia Bay, Newfoundland

    NASA Astrophysics Data System (ADS)

    Shaw, John; Puig, Pere; Han, Guoqi

    2013-05-01

    Megaflutes - erosional scours normally found in deep water on continental slopes - were identified in 1978 on sidescan sonograms and seismic reflection profiles from Placentia Bay on the south coast of Newfoundland, Canada. Data from recent extensive multibeam sonar surveys provide an opportunity to describe the morphology and distribution of the megaflutes in detail, and to consider the formative processes. They occur on the east side of the outer bay, at a depth of ~ 200 m, in a 2-3 km-wide swath that continues to the south into Halibut Channel, over a total distance of ~ 100 km. The megaflutes have been formed by removal of a layer of postglacial mud, exposing underlying glaciomarine sediments and releasing a volume of 4.5 km3. They occur in a range of forms, including single, multiple, and coalescent types, and in some areas at least their inception was related to pre-existing pockmarks. Radiocarbon dates from piston cores are used to demonstrate that megaflute formation post-dated ca. 9 ka. Megaflute formation in Placentia Bay has been attributed to a 'reverse flow' from the tsunami generated by the 1929 Grand Banks earthquake, and this is still the accepted hypothesis. We argue that the return flow from a tsunami did not generate the megaflutes, and suggest instead that they could be formed during south-flowing density currents generated when volumes of cold saline water stored in the deep (> 250 m) basins at the head of Placentia Bay are intermittently displaced and spilled south in a shallow channel at the east side of the bay after intense coastal surface dense water formation events, perhaps during very cold winters.

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

    EPA Science Inventory

    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 ...

  19. 78 FR 59632 - Oil and Gas and Sulphur Operations on the Outer Continental Shelf-Oil and Gas Production Safety...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-09-27

    ... comments to the Department of the Interior (DOI); Bureau of Safety and Environmental Enforcement; Attention... operating dry tree and subsea tree production systems on the Outer Continental Shelf (OCS) and divide...

  20. Resuspended sediments can contribute to the establishment and maintenance of hypoxia on the Louisiana continental shelf - Eldridge

    EPA Science Inventory

    Hypoxia occurs during summer on the Louisiana Continental Shelf. We investigated whether resuspension of sediment organic matter and the reduced end products of anaerobic microbial metabolism contributes to the onset and maintenance of hypoxia. The potential oxygen demand due to...

  1. 75 FR 17156 - Gulf of Mexico, Outer Continental Shelf, Western Planning Area, Oil and Gas Lease Sale 215 (2010...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-05

    ... Minerals Management Service Gulf of Mexico, Outer Continental Shelf, Western Planning Area, Oil and Gas Lease Sale 215 (2010) Environmental Assessment AGENCY: Minerals Management Service, Interior. ACTION: Notice of availability of an environmental assessment. SUMMARY: The Minerals Management Service (MMS)...

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

    EPA Science Inventory

    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...

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

    EPA Science Inventory

    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...

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

    EPA Science Inventory

    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 ...

  5. 77 FR 44671 - Notice of Availability of the Proposed Notice of Sale for Outer Continental Shelf (OCS) Oil and...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-30

    ... Continental Shelf (OCS) Oil and Gas Lease Sale 229 in the Western Planning Area (WPA) in the Gulf of Mexico... 2012-2017.'' All other portions of the Notice remain unchanged. Dated: July 24, 2012. Tommy P...

  6. 75 FR 81950 - Flaring Versus Venting To Reduce Greenhouse Gas Emissions in the Outer Continental Shelf; Public...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-12-29

    ... Reduce Greenhouse Gas Emissions in the Outer Continental Shelf; Public Workshop AGENCY: Bureau of Ocean... focus of this workshop will be aimed at the potential reduction of Greenhouse Gas (GHG) emissions....

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

    PubMed

    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.

  8. Cetacean high-use habitats of the northeast United States continental shelf

    SciTech Connect

    Kenney, R.D.; Winn, H.E.

    1986-04-01

    Results of the Cetacean and Turtle Assessment Program previously demonstrated at a qualitative level that specific areas of the continental shelf waters off the northeastern US coast consistently showed high-density utilization by several cetacean species. They have quantified, on a multispecies basis and with adjustment for level of survey effort, the intensity of habitat use by whales and dolphins, and defined areas of especially high-intensity utilization. The results demonstrate that the area off the northeast US, which is used most intensively as cetacean habitat, is the western margin of the Gulf of Maine, from the Great South Channel to Stellwagen Bank and Jeffreys Ledge. Secondary high-use areas include the continental shelf edge and the region around the eastern end of Georges Bank. High-use areas for piseivorous cetaceans are concentrated mainly in the western Gulf of Maine and secondarily at mid-shelf east of the Chesapeake region, for planktivores in the western Gulf of Maine and the southwestern and eastern portions of Georges Bank, and for teuthivores in the western Gulf of Maine and the southwestern and eastern portions of Georges Bank, and for teuthivores along the edge of the shelf. In general, habitat use by cetaceans is highest in spring and summer, and lowest in fall and winter.

  9. The generation of internal waves on the continental shelf by Hurricane Andrew

    NASA Astrophysics Data System (ADS)

    Keen, Timothy R.; Allen, Susan E.

    2000-11-01

    Observed currents, temperature, and salinity from moored instruments on the Louisiana continental slope and shelf reveal multiple baroclinic oscillations during Hurricane Andrew in August 1992. These measurements are supplemented by numerical models in order to identify possible internal wave generation mechanisms. The Princeton Ocean Model is run with realistic topography, stratification, and wind forcing to extend the observations to Mississippi Canyon and other areas on the shelf. A two-layer isopycnal model is used with idealized topography and spatially uniform winds to isolate internal waves generated in and around the canyon. The combination of the observations and the results from the numerical models indicates several possible mechanisms for generating long internal waves: (1) near-inertial internal waves were generated across the slope and shelf by dislocation of the thermocline by the wind stress; (2) interaction of inertial flow with topography generated internal waves along the shelf break, which bifurcated into landward and seaward propagating phases; (3) downwelling along the coast depressed the thermocline; after downwelling relaxes, an internal wave front propagates as a Kelvin wave; and (4) Poincaré waves generated within Mississippi Canyon propagate seaward while being advected westward over the continental slope. These processes interact to produce a three-dimensional internal wave field, which was only partly captured by the observations.

  10. Geology of the head of Lydonia Canyon, U.S. Atlantic outer continental shelf

    USGS Publications Warehouse

    Twichell, D.C.

    1983-01-01

    The geology of the part of Lydonia Canyon shoreward of the continental shelf edge on the southern side of Georges Bank was mapped using high-resolution seismic-reflection and side-scan sonar techniques and surface sediment grab samples. The head of the canyon incises Pleistocene deltaic deposits and Miocene shallow marine strata. Medium sand containing some coarse sand and gravel covers the shelf except for a belt of very fine sand containing no gravel on either side of the canyon in water depths of 125-140 m. Gravel and boulders, presumably ice-rafted debris, cover the rim of the canyon. The canyon floor and canyon wall gullies are covered by coarse silt of Holocene age which is as much as 25 m thick, and Miocene and Pleistocene strata are exposed on the spurs between gullies. The Holocene sediment is restricted to the canyon shoreward of the shelf edge and has been winnowed from the shelf. Furrows cut in the shelf sands and ripples on the shelf and in the canyon suggest that sediment continues to be moved in this area. Sediment distribution, however, is inconsistent with that expected from the inferred westward sediment transport on the shelf. Either the fine-grained deposits on the shelf to either side of the canyon head are relict or there is a significant component of offshore transport around the canyon head. In the head of Oceanographer Canyon, only 40 km west of Lydonia Canyon, present conditions are strikingly different. The floor of Oceanographer Canyon is covered by sand waves, and their presence indicates active reworking of the bottom sediments by strong currents. The close proximity of the two canyons suggests that the relative importance of processes acting in canyons can be variable over short distances. 

  11. Seismic stratigraphy of the Mississippi-Alabama shelf and upper continental slope

    USGS Publications Warehouse

    Kindinger, J.L.

    1988-01-01

    The Mississippi-Alabama shelf and upper continental slope contain relatively thin Upper Pleistocene and Holocene deposits. Five stages of shelf evolution can be identified from the early Wisconsinan to present. The stages were controlled by glacioeustatic or relative sea-level changes and are defined by the stratigraphic position of depositional and erosional episodes. The stratigraphy was identified on seismic profiles by means of geomorphic pattern, high-angle clinoform progradational deposits, buried stream entrenchments, planar conformities, and erosional unconformities. The oldest stage (stage 1) of evolution occurred during the early Wisconsinan lowstand; the subaerially exposed shelf was eroded to a smooth seaward-sloping surface. This paleosurface is overlain by a thin (< 10 m) drape of transgressive deposits (stage 2). Stage 3 occurred in three phases as the late Wisconsinan sea retreated: (1) fluvial channel systems eroded across the shelf, (2) deposited a thick (90 m) shelf-margin delta, and (3) contemporaneously deposited sediments on the upper slope. Stage 4 included the rapid Holocene sea-level rise that deposited a relatively thin transgressive facies over parts of the shelf. The last major depositional episode (stage 5) was the progradation of the St. Bernard delta over the northwestern and central parts of the area. A depositional hiatus has occurred since the St. Bernard progradation. These Upper Quaternary shelf and slope deposits provide models for analogous deposits in the geologic record. Primarily, they are examples of cyclic sedimentation caused by changes in sea level and may be useful in describing short-term, sandy depositional episodes in prograding shelf and slope sequences. ?? 1988.

  12. The Influence of a Western Boundary Current on Continental Shelf Processes Along Southeastern Australia.

    NASA Astrophysics Data System (ADS)

    Roughan, M.

    2016-02-01

    The East Australian Current (EAC) flows as a jet over the narrow shelf of southeastern Australia, dominating shelf circulation, and shedding vast eddies at the highly variable separation point. These characteristics alone make it a dynamically challenging region to measure, model and predict. In recent years a significant effort has been placed on understanding continental shelf processes along the coast of SE Australia, adjacent to the EAC, our major Western Boundary Current. We have used a multi-pronged approach by combining state of the art in situ observations and data assimilation modelling. Observations are obtained from a network of moorings, HF Radar and ocean gliders deployed in shelf waters along SE Australia, made possible through Australia's Integrated Marine Observing System (IMOS). In addition, we have developed a high resolution reanalysis of the East Australian Current using ROMS and 4DVar data Assimilation. In addition to the traditional data streams (SST, SSH and ARGO) we assimilate the newly available IMOS observations in the region. These include velocity and hydrographic observations from the EAC transport array, 1km HF radar measurements of surface currents, CTD casts from ocean gliders, and temperature, salinity and velocity measurements from a network of shelf mooring arrays. We use these vast data sets and numerical modelling tools combined with satellite remote sensed data to understand spatio-temporal variability of shelf processes and water mass distributions on synoptic, seasonal and inter-annual timescales. We have quantified the cross shelf transport variability inshore of the EAC, the driving mechanisms, the seasonal cycles in shelf waters and to some extent variability in the biological (phytoplankton) response. I will present a review of some of the key results from a number of recent studies.

  13. High-resolution seismic stratigraphy of Holocene transgressive deposits in the southern continental shelf, Korea

    NASA Astrophysics Data System (ADS)

    Chang, Se Won; Yoo, Dong-Geun; Lee, Gwang-Soo; Kim, Gil-Young

    2017-04-01

    Holocene transgressive deposits in the southern continental shelf were investigated using high-resolution seismic profiles associated with core sediments. The results show that the shelf deposits consist of five seismic units deposited during Holocene transgression between about 15 and 6 ka BP: ancient beach/shoreface complex (unit P1), estuarine deposits (unit P2), mid-shelf sand sheet (unit M1), sand ridge system (unit M2), and inner-shelf sand sheet (unit M3). They are paralic and marine separated by a ravinement surface. The lower paralic component below the ravinement surface consists of two sedimentary units (P1 and P2) preserved from shoreface erosion. The top surface of the paralic unit is truncated by a sharp erosional surface. This surface is overlain by three sedimentary units (M1, M2, and M3), which were produced by shoreface erosion that shifted landward during transgression. Based on geometries and distribution patterns, the transgressive deposits in this area can be divided into three types. Type I overlying the lowstand systems tract is confined to the shelf margin, and consists of a thick paralic unit P1 and a relatively thin marine unit M1. Type II on the mid shelf has no paralic component and the marine units M1 or M2 directly overlies the sequence boundary. Type III, found in the inner shelf, includes a thick paralic (unit P2) and a thin marine (unit M3) component. It is completely covered by the highstand systems tract. Keywords: Late Quaternary; Transgressive deposit; Holocene sea-level rise; Korea Strait shelf

  14. Mixed carbonate-siliciclastic sequence stratigraphy of a Paleogene transition zone continental shelf, southeastern USA

    NASA Astrophysics Data System (ADS)

    Coffey, Brian P.; Fred Read, J.

    2004-04-01

    The sequence stratigraphy and facies of the Paleogene in the subsurface of the Albemarle Basin, North Carolina was defined using 1600 thin sections of plastic impregnated well cuttings from 24 wells, wireline logs, biostratigraphic data, and seismic data. The facies formed in the transition zone between warm subtropical and temperate conditions on a swell-wave dominated, open shelf exposed to major boundary current activity. The shelf has a distinctive seismic profile consisting of a shallow inner shelf, inner-shelf break, deep shelf (depths in excess of 200 m), and the continental slope. The inner shelf was characterized by distinctive quartz sand and sandy mollusk facies inshore, passing seaward into a broad, wave-swept abrasional shelf, and then into storm-influenced bryozoan-echinoderm limestones to depths of several tens of meters. Argillaceous lime mud (marl) deposition was widespread across the deep shelf, extending onto the inner-shelf during major highstands. Sediment thickness trends were controlled by greater differential subsidence of crustal blocks within the Albemarle Basin, which considerably modified but did not obliterate the effects of eustatic sea level changes in this passive margin setting. Five supersequences were identified on seismic and in wells, each consisting of multiple regionally identifiable sequences. The Paleocene supersequence is dominated by widespread marl deposition, reflecting shelf flooding into the Late Paleocene thermal maximum. This warming corresponds with widespread inner-shelf skeletal carbonate deposition from the Late Paleocene through the Middle Eocene. The two Eocene supersequences identified are dominated by bryozoan-echinoderm-rich carbonates that formed a seismically definable sediment buildup 50 km wide by 100 m thick across the deepest inner-shelf during the Lower to early Middle Eocene. Middle to Upper Eocene supersequence highstand sequences indicate increased progradation and greater mixing of shelf

  15. Insights into Diversity and Imputed Metabolic Potential of Bacterial Communities in the Continental Shelf of Agatti Island

    PubMed Central

    Dhar, Sunil Kumar; Jani, Kunal; Apte, Deepak A.; Shouche, Yogesh S.; Sharma, Avinash

    2015-01-01

    Marine microbes play a key role and contribute largely to the global biogeochemical cycles. This study aims to explore microbial diversity from one such ecological hotspot, the continental shelf of Agatti Island. Sediment samples from various depths of the continental shelf were analyzed for bacterial diversity using deep sequencing technology along with the culturable approach. Additionally, imputed metagenomic approach was carried out to understand the functional aspects of microbial community especially for microbial genes important in nutrient uptake, survival and biogeochemical cycling in the marine environment. Using culturable approach, 28 bacterial strains representing 9 genera were isolated from various depths of continental shelf. The microbial community structure throughout the samples was dominated by phylum Proteobacteria and harbored various bacterioplanktons as well. Significant differences were observed in bacterial diversity within a short region of the continental shelf (1–40 meters) i.e. between upper continental shelf samples (UCS) with lesser depths (i.e. 1–20 meters) and lower continental shelf samples (LCS) with greater depths (i.e. 25–40 meters). By using imputed metagenomic approach, this study also discusses several adaptive mechanisms which enable microbes to survive in nutritionally deprived conditions, and also help to understand the influence of nutrition availability on bacterial diversity. PMID:26066038

  16. Insights into Diversity and Imputed Metabolic Potential of Bacterial Communities in the Continental Shelf of Agatti Island.

    PubMed

    Kumbhare, Shreyas V; Dhotre, Dhiraj P; Dhar, Sunil Kumar; Jani, Kunal; Apte, Deepak A; Shouche, Yogesh S; Sharma, Avinash

    2015-01-01

    Marine microbes play a key role and contribute largely to the global biogeochemical cycles. This study aims to explore microbial diversity from one such ecological hotspot, the continental shelf of Agatti Island. Sediment samples from various depths of the continental shelf were analyzed for bacterial diversity using deep sequencing technology along with the culturable approach. Additionally, imputed metagenomic approach was carried out to understand the functional aspects of microbial community especially for microbial genes important in nutrient uptake, survival and biogeochemical cycling in the marine environment. Using culturable approach, 28 bacterial strains representing 9 genera were isolated from various depths of continental shelf. The microbial community structure throughout the samples was dominated by phylum Proteobacteria and harbored various bacterioplanktons as well. Significant differences were observed in bacterial diversity within a short region of the continental shelf (1-40 meters) i.e. between upper continental shelf samples (UCS) with lesser depths (i.e. 1-20 meters) and lower continental shelf samples (LCS) with greater depths (i.e. 25-40 meters). By using imputed metagenomic approach, this study also discusses several adaptive mechanisms which enable microbes to survive in nutritionally deprived conditions, and also help to understand the influence of nutrition availability on bacterial diversity.

  17. Influence of fluvial processes on the quaternary geologic framework of the continental shelf, North Carolina, USA

    USGS Publications Warehouse

    Boss, S.K.; Hoffman, C.W.; Cooper, B.

    2002-01-01

    Digital, single-channel, high-resolution seismic reflection profiles were acquired from the insular continental shelf of North Carolina, USA along a data grid extending from Oregon Inlet northward 48 km to Duck, North Carolina and from the nearshore zone seaward approximately 28 km (total surveyed area= 1334 km2). These data were processed and interpreted to delineate principal reflecting horizons and develop a three-dimensional seismic stratigraphic framework for the continental shelf that was compared to stratigraphic data from the shoreward back-barrier (estuarine) and barrier island system. Six principal reflecting horizons (designated R0 through R5) were present within the upper 60 m of the shelf stratigraphic succession. Three-dimensional mapping of reflector R1 demonstrated its origin from fluvial incision of the continental shelf during an episode (or episodes) of lowered sea-level. Fluvial processes during development of reflector R1 were responsible for extensive reworking and re-deposition of sediment throughout most of the northern half of the study area. Five seismic stratigraphic units (designated S1 through S5) were tentatively correlated with depositional sequences previously identified from the North Carolina back-barrier (estuarine) and barrier island system. These five stratigraphic units span the Quaternary Period (S1 = early Holocene; S2 = 51-78 ka; S3 = 330-530 ka; S4 = 1.1-1.8 Ma; S5 = earliest Pleistocene). Unit S1 is composed of fine-grained fluvial/estuarine sediment that back-filled incised streams during early Holocene sea-level rise. The four other stratigraphic units (S2-S5) display tabular depositional geometries, low total relief, and thicken toward the east-southeast as their basal reflectors dip gently between 0.41 m km-1 (0.02??) and 0.54 m km-1 (0.03??). Knowledge of the three-dimensional subsurface stratigraphic architecture of the continental shelf enhances understanding of the development of shelf depositional successions and

  18. Compiling Multibeam Sonar data for the U.S. Pacific West Coast Extended Continental Shelf Project

    NASA Astrophysics Data System (ADS)

    Lim, E.; Gardner, J. V.; Henderson, J. F.

    2011-12-01

    The United States Extended Continental Shelf (ECS) Project is a multi-agency collaboration whose goals are to determine and define a potential extension of the U.S. continental shelf beyond 200 nautical miles (nmi). Under international law as reflected in the 1982 United Nations Convention on the Law of the Sea (UNCLOS), every coastal state is entitled to a continental shelf out to 200 nmi (the Exclusive Economic Zone) from its coastal baseline or out to a maritime boundary with another coastal country. The extended continental shelf (ECS) is the area that lies beyond this 200 nm limit where a country could gain sovereign rights to the resources of the seafloor and sub-seafloor. In 2007, the U.S. ECS Task Force designated NOAA's National Geophysical Data Center (NGDC) as the Data Management lead for the U.S. ECS Project and the data stewards and archival location for all data related to this project. The process to determine the outer limits of the ECS requires the collection and analysis of data that describe the depth, shape, and geophysical characteristics of the seafloor and sub-seafloor, as well as the thickness of the underlying sediments. The specific types of data that need to be collected include bathymetric data, seismic profiles, magnetic and gravity data, and other geophysical data. NGDC maintains several global geophysical databases, including bathymetric, seismic and geological data, all critical for supporting ECS analysis. Multibeam bathymetry is a primary dataset used for ECS analysis. Since 2003, the U.S. has collected more than 1.65 million square kilometers of multibeam bathymetric data from 18 cruises. One area where new data has been collected and where the U.S. may have an extended continental shelf is off the U.S. Pacific West Coast. New and old multibeam bathymetry archived at and delivered by NGDC were individually gridded by survey for an area within 48-30 degrees north latitude and -140 and -115 west longitude at a resolution of 210

  19. 75 FR 39861 - Fisheries of the Exclusive Economic Zone Off Alaska; Pelagic Shelf Rockfish in the Western...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-07-13

    ... exceeding the 2010 total allowable catch (TAC) of pelagic shelf rockfish in the Western Regulatory Area of... CFR part 679. The 2010 TAC of pelagic shelf rockfish in the Western Regulatory Area of the GOA is 650...), the Administrator, Alaska Region, NMFS (Regional Administrator), has determined that the 2010 TAC...

  20. Wave-driven sediment mobilization on a storm-controlled continental shelf (Northwest Iberia)

    USGS Publications Warehouse

    Oberle, Ferdinand; Storlazzi, Curt D.; Hanebuth, Till

    2014-01-01

    Seafloor sediment mobilization on the inner Northwest Iberian continental shelf is caused largely by ocean surface waves. The temporal and spatial variability in the wave height, wave period, and wave direction has a profound effect on local sediment mobilization, leading to distinct sediment mobilization scenarios. Six grain-size specific sediment mobilization scenarios, representing seasonal average and storm conditions, were simulated with a physics-based numerical model. Model inputs included meteorological and oceanographic data in conjunction with seafloor grain-size and the shelf bathymetric data. The results show distinct seasonal variations, most importantly in wave height, leading to sediment mobilization, specifically on the inner shelf shallower than 30 m water depth where up to 49% of the shelf area is mobilized. Medium to severe storm events are modeled to mobilize up to 89% of the shelf area above 150 m water depth. The frequency of each of these seasonal and storm-related sediment mobilization scenarios is addressed using a decade of meteorological and oceanographic data. The temporal and spatial patterns of the modeled sediment mobilization scenarios are discussed in the context of existing geological and environmental processes and conditions to assist scientific, industrial and environmental efforts that are directly affected by sediment mobilization. Examples, where sediment mobilization plays a vital role, include seafloor nutrient advection, recurrent arrival of oil from oil-spill-laden seafloor sediment, and bottom trawling impacts.

  1. Characterizing Late Quaternary Paleochannel System Evolution on the East Texas Continental Shelf

    NASA Astrophysics Data System (ADS)

    Speed, C.; Gulick, S. P. S.; Goff, J.; Swartz, J. M.; Fernandez, R.

    2016-12-01

    The northern Gulf of Mexico continental shelf plays host to a variety of buried incised valley and paleochannel systems. The formation of these incisional features is due in part to Quaternary eustatic sea level oscillations, thought largely to represent fluctuations in global ice volume. However, a complex interplay exists between the role of climate, eustasy, and autogenic sedimentary processes in the formation and evolution of paleochannel systems throughout geologic time. These elaborate channel networks act not only as a conduit for sediment transport to the outer shelf and deep sea, but also as a location for sediment storage during subsequent transgressions. Understanding the timing of incision and the internal sedimentary architecture of buried channel systems provides insight into the formational processes of the paleochannel system and the role it played in sediment transport and storage. Over 300 kilometers of ultra-high-resolution (0.5-12 kHz) CHIRP sub-bottom profile and high-resolution (40-450 Hz) two-dimensional multichannel seismic (MCS) data were collected on the inner continental shelf south of Freeport, TX during the 2015 and 2016 University of Texas Institute for Geophysics Marine Geology and Geophysics summer field course(s). The survey focused on imaging the Late Quaternary formation and evolution of the incised valley and channel system associated with the paleo-Brazos River. CHIRP data provide decimeter-scale vertical resolution imaging the upper 15-50 meters of the subsurface, while high-resolution MCS data provide vertical resolution of 1-3 meters and penetration on the order of hundreds of meters. These complementary datasets allow for an integrated stratigraphic analysis of multiple generations of Pleistocene to Holocene-aged paleochannels and key comparisons of various channel-forming processes, sediment transport mechanisms, and storage potential on the northern Gulf of Mexico continental shelf.

  2. Influence of Shelf Waters on Atlantic Water and Lower Halocline Water at the Siberian Continental Slope

    NASA Astrophysics Data System (ADS)

    Bauch, D.

    2016-12-01

    Siberian shelf waters show a characteristic salinity and stable oxygen isotope (δ18O) signature that allows to quantify sea-ice meltwater and meteoric waters fractions. This method reveals that Atlantic Water inflow into Arctic Ocean is modified by a mixture of sea-ice meltwater and meteoric waters along the Barents Sea continental margin. No further influence of meteoric waters is detectable within the core of the Atlantic Water downstream of the Kara Sea. Inter annual variations within the Atlantic Layer indicate sporadic influence of polynya activity north of Severnaya Zemlya. Lower halocline waters (LHW) may be divided into different components by principle component analysis (PCA). All LHW components show the addition of river water and an influence of sea-ice formation to a varying extend. The geographical distribution of LHW components suggest that the high salinity component of LHW forms in the Barents and Kara seas, while further LHW components are formed from south-eastern Kara Sea waters that enter the north western Laptev Sea through Vilkitski Strait. No further modification of LHW is seen in the eastern Laptev Sea but the distribution of LHW-types suggest a bifurcation of LHW at this location possibly with a branch continuing along the continental margin and a second branch along the Lomonosov Ridge. We see no pronounced distinction between onshore and offshore LHW components and the same LHW components that are also found over the basin show a narrow bottom bound distribution at the continental slope that is consistent with a shelf boundary current as well as a jet of water entering the western Laptev Sea from the Kara Sea through Vilkitski Strait. A similar PCA approach on an extended data set from the Laptev Sea shelf indicates the spread of LHW components and waters from the Kara Sea onto the Laptev Sea shelf.

  3. Larval Transport on the Atlantic Continental Shelf of North America: a Review

    NASA Astrophysics Data System (ADS)

    Epifanio, C. E.; Garvine, R. W.

    2001-01-01

    This review considers transport of larval fish and crustaceans on the continental shelf. Previous reviews have contained only limited treatments of the physical processes involved. The present paper provides a physical background that is considerably more comprehensive. It includes a discussion of three principal forcing agents: (1) wind stress; (2) tides propagating from the deep ocean; and (3) differences in density associated with the buoyant outflow of estuaries, surface heat flux, or the interaction of coastal and oceanic water masses at the seaward margin of the shelf. The authors discuss the effects of these forcing agents on transport of larvae in the Middle Atlantic and South Atlantic Bights along the east coast of North America. The discussion concentrates on three species (blue crab, menhaden, bluefish) that have been the subject of a very recent multi-disciplinary study. Taken as a whole, the reproductive activities of these three species span the entire year and utilize the entire shelf, from the most seaward margin to the estuarine nursery. The blue crab is representative of species affected by physical processes occurring during summer and early autumn on the inner and mid-shelf. Menhaden are impacted by processes occurring in winter on the outer and mid-shelf. Bluefish are influenced primarily by processes occurring during early spring at the outer shelf margin near the western boundary current. The authors conclude that alongshore wind stress and density differences, i.e. buoyancy-driven flow, are the primary agents of larval transport in the region. Circulation associated with the western boundary current is only important at the shelf margin and tidally driven processes are generally inconsequential.

  4. Maps showing late Pleistocene and Holocene evolution of the South Texas continental shelf

    USGS Publications Warehouse

    Pyle, Carroll A.; Berryhill, Henry L.; Trippet, Anita R.

    1979-01-01

    Interpretation of acoustical profiles has provided insight into the late Quaternary geologic history of the Continental Shelf off South Texas. (See the geographic index map on sheet 1 for location of the area studied.) The profiles reveal the interplay of tectonism, sedimentation, and cyclic fluctuations of sea level in the building and geologic evolution of the continental terrace. The sequence of sediments studied extends to about 200 meters (m) beneath the sea-floor surface. Four seismic-stratigraphic units underlain by four prominent sound reflectors were identified and mapped. This geologic synthesis, for which the research was funded by the U.S. Bureau of Land Management (BLM), is but one aspect of a coordinated, multidisciplinary environmental study of the South Texas Outer Continental Shelf sponsored by BLM (Berryhill, 1976, 1977). The environmental studies are keyed to the leasing of Federal Outer Continental Shelf (OCS) lands for petroleum exploration and production. Their purpose is to provide the data development of petroleum resources on the OCS, as well as to provide the basis for predicting the impact of oil and gas exploration and production on the marine environment. Of primary concern is the recognition of geologic conditions that might be hazardous to structures placed on the sea floor. Geologic hazards relate directly to the potential for significant movement of the sea floor in the future. Judging sea-floor stability and recognizing geologic features that are potentially hazardous require an understanding of the recent geologic history of the area, which, in turn, entails determining the relative rates and interactions of sedimentation and tectonism through time. In addition to the primary objective, the synthesis provides knowledge about the magnitude and extent of sea-level fluctuations in the western Gulf of Mexico, and it provides a depositional facies model of possible use in appraising the resource potential of the more deeply buried

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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 characterized by weak winds, moderate tides, and almost absent Coriolis forcing. Existing knowledge about river plume behavior in tropical environments is limited. The aim of this paper is to investigate the influence of the subtle physical forcing on the dynamics of the Berau river plume. A three-dimensional model (ECOMSED) was calibrated with observational data. The model was forced by freshwater input from the Berau river distributaries, tides at the open boundaries, and measured hourly wind. The model reproduces the freshwater dynamics on the shelf adequately and highlights that the river plume spreads symmetrically for river forcing only. Tides cause vertical mixing and suppress the cross-shelf spreading of the river plume. However, the spreading of the river plume over the shelf is mainly controlled by the weak monsoonal winds, resulting in a seasonal development. During the Southeast Monsoon, the southerly winds push the plume northeastward and cause a stratified water column in the northern part of the continental shelf. Northerly winds during the Northwest Monsoon disperse the plume to the south, promoting a vertically well-mixed water column. The results can be used to predict the possible impact of land-use changes in the steadily developing Berau region on coral reef health.

  6. Geological and operational summary, North Aleutian Shelf Coast No. 1 well, Bering Sea, Alaska. Final report

    SciTech Connect

    Turner, R.F.

    1988-11-01

    Discusses the first continental offshore stratigraphic test well drilled in the North Aleutian Basin Planning Area, Bering Sea, Alaska. The well was drilled to determine the hydrocarbon potential of the area. The report covers drilling operations; lithology and core data; velocity analysis; geologic setting and tectonic framework; seismic stratigraphy; well-log interpretation and lithostratigraphy; paleontology and biostratigraphy; geothermal gradient; organic geochemistry; abnormal formation pressure; geologic hazards and shallow geology; and environmental considerations.

  7. Flux of energy and essential elements through the continental shelf ecosystem. Progress report, June 1, 1982-May 31, 1983

    SciTech Connect

    Pomeroy, L.R.

    1983-01-15

    Methods were perfected for counting protozoans in shelf water and we are working on methods for measuring bacterial production, taking into account the problem of protozoan grazing, which does not seem to have been investigated with respect to bacteria. Samples were collected on transects of the continental shelf on six cruises to improve our seasonal coverage and provide materials for the development of methods. Work on a model of energy flux through continental shelf ecosystems has been completed, and a manuscript will be submitted during the present contract year.

  8. Late Pleistocene and Holocene sedimentary facies on the Ebro continental shelf

    USGS Publications Warehouse

    Diaz, J.; Nelson, C.H.; Barber, J.H.; Giro, S.

    1990-01-01

    Late Pleistocene-Holocene history of the Ebro continental shelf of northeastern Spain is recorded in two main sedimentary units: (1) a lower, transgressive unit that covers the shelf and is exposed on the outer shelf south of 40??40???N, and (2) an upper, progradational, prodeltaic unit that borders the Ebro Delta and extends southward along the inner shelf. The lower transgressive unit includes a large linear shoal found at a water depth of 90 m and hardground mounds at water depths of 70-80 m. Some patches of earlier Pleistocene prodelta mud remain also, exposed or covered by a thin veneer of transgressive sand on the northern outer shelf. This relict sand sheet is 2-3 m thick and contains 9000-12,500 yr old oyster and other shells at water depths of 78-88 m. The upper prodelta unit covers most of the inner shelf from water depths of 20-80 m and extends from the present Ebro River Delta to an area to the southwest where the unit progressively thins and narrows. Interpretation of high-resolution seismic reflection data shows the following facies occurring progressively offshore: (1) a thick stratified facies with thin progradational "foresets beds", (2) a faintly laminated facies with sparse reflectors of low continuity, and (3) a thin transparent bottomset facies underlain by a prominent flat-lying reflector. Deposition in the northern half of the prodelta began as soon as the shoreline transgressed over the mid-shelf, but progradation of the southern half did not begin until about 1000-3000 yrs after the transgression. A classic deltaic progradational sequence is shown in the Ebro prodelta mud by (1) gradation of seismic facies away from the delta, (2) coarsening-upward sequences near the delta and fining-upward sequences in the distal mud belt deposits, and (3) thin storm-sand layers and shell lags in the nearshore stratified facies. The boundaries of the prodeltaic unit are controlled by increased current speeds on the outer shelf (where the shelf narrows) and

  9. Oceanic core complexes in the Philippine Sea: results from Japan's extended continental shelf mapping

    NASA Astrophysics Data System (ADS)

    Ohara, Y.; Yoshida, T.; Nishizawa, A.

    2013-12-01

    The United Nations Commission on the Limits of the Continental Shelf (CLCS) issued its recommendations on Japan's extended continental shelf in April 2012, confirming Japan's rights over the vast areas within the Philippine Sea and Pacific Plates. Japan submitted information on the limits of its continental shelf beyond the EEZ to the CLCS on November 2008, which was the result of 25 years of nation's continental shelf survey project since 1983, involving all of Japan's agency relevant to geosciences. The huge geological and geophysical data obtained through the project give the scientists unprecedented opportunity to study the geology and tectonics of the Philippine Sea and Pacific Plates. In this contribution, we show such an example from the Philippine Sea Plate, relevant to the global mid-ocean ridge problem. Oceanic core complexes (OCC) are dome-shaped bathymetric highs identified in mid-ocean ridges, interpreted as portions of the lower crust and/or upper mantle denuded via low-angle detachment faulting. OCCs are characterized morphologically by axis-normal striations (corrugations, or mullion structure) on the dome, and exposures of mantle peridotite and/or lower crustal gabbro. A strikingly giant OCC (named 'Godzilla Megamullion') was discovered in the Parece Vela Basin by the continental shelf survey project in 2001. Godzilla Megamullion is morphologically the largest OCC in the world, consisting mainly of fertile mantle peridotite along its entire length of over 125 km. Following its discovery in 2001, several academic cruises investigated the structure in detail, providing numerous important findings relevant to mid-ocean ridge tectono-magmatic processes and Philippine Sea evolution, including the slow- to ultraslow-spreading environment for denudation of the detachment fault (< 2.5 cm/y) and associated decreasing degree of partial melting of the peridotites towards the termination of Godzilla Megamullion. In addition to Godzilla Megamullion, several

  10. Circulation over the continental shelf of the western and southwestern Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Dubranna, Jean; PéRez-Brunius, Paula; López, Manuel; Candela, Julio

    2011-08-01

    The circulation over the continental shelf break of the western and southwestern Gulf of Mexico is inferred from the analysis of drifter trajectories and 12-19 months of continuous current measurements at seven different locations. The interpretation of the data is backed up by satellite altimetry, coastal sea level from tide gauges and wind model outputs. In accordance with previous numerical results, subinertial surface currents are driven by the wind along the shelves of the states of Tamaulipas and Veracruz. Northern wind regimes would force southward currents, whereas southern wind regimes would force northward currents at the surface but southward near the bottom, through a process involving Ekman drift and geostrophic balance. Our results show, however, that alongshore current variations are not correlated with the wind over the Western Campeche Bank. In addition, we identify other sources of current forcing. The transient eddies that collapse along the continental shelf can force strong alongshore currents and overwhelm the influence of established wind regimes. Their erratic occurrence is likely to be a major factor of interannual variability of the alongshore currents. Also, we point out the existence of coastally trapped waves generated by the wind in the northern shelf of Tamaulipas and propagating down to the Western Campeche Bank. The period of these waves ranges between 6 and 10 days, with phase speeds in the 4 m/s range.

  11. Upwelling and dissolved oxygen variability over the continental shelf off Central Chile

    NASA Astrophysics Data System (ADS)

    Pizarro, Oscar

    2014-05-01

    In contrast to the legendary upwelling that is present along the Peruvian and northern Chilean coasts, the coastal ocean off central Chile presents a highly seasonal upwelling regime that extends from early spring to mid fall. This region is also affected by a strong subsurface poleward flow, which transports southward low-oxygen water from the eastern equatorial Pacific. Coastal waters are highly productive due to upwelling, but the upwelled source waters are very low in oxygen and may produce hypoxia near the bottom over the continental shelf. The spatial structure and main scales of variability of the upwelling cells and dissolved oxygen are poorly understood off central Chile. One of the main limitations has been the lack of direct information. During the last years an observational program has been conducted over the relatively wide continental shelf off Concepción (36°30' S). This program has included ship-based (monthly) time-series, underwater glider observations and time-series based on moored sensors. Here, based on physical (temperature, salinity, pressure, velocity), biological (chlorophyll fluorescence) and chemical (dissolved oxygen) information, we analyze the main scales of time variability of the upwelling, the coastal currents and their impact on the dissolved oxygen. The cross-shelf structure of the upwelling region was sampled using underwater gliders capable of sampling the entire water column to a maximum of 1000 m and from near shore to 200 km offshore.

  12. Lack of evidence of southerly propagating Continental Shelf Waves in Onslow Bay, N. C

    SciTech Connect

    Pietrafesa, L.J.; Janowitz, G.S.

    1980-02-01

    Within the past decade several studies have postulated the existence of southerly propagating Continental Shelf Waves in Onslow Bay, N.C. from comparisons of sea level data collected at various stations located at or upstream of the Cape Fear River, N.C. and from a coastal tide gage located at Beaufort, N.C., to the north. Intercomparison of sea level data collected at Beaufort, an open ocean station, to that collected at Wilmington, a site to the south and 45.6 km upstream of the mouth, led to the conclusion that the phase lag displayed by the Wilmington versus Beaufort cross spectrum was indicative of the southerly propagation of the first three modes of zero group speed shelf waves. However, as we show in this paper, while Wilmington sea level may lag that of Beaufort, the spectrum of sea level data collected at the mouth of the Cape Fear leads that of Beaufort, as well as that of Wilmington. What is suggested herein is that the phase lag observed at Wilmington is actually due to an estuarine, river caused delay and not due to the explicit detection of southerly propagating Continental Shelf Waves.

  13. Miocene karst drainage system: seismic stratigraphy of the continental shelf west of Florida

    SciTech Connect

    Herbert, J.A.

    1985-01-01

    High-resolution geophysical data recorded on the continental shelf west of Tampa Bay, Florida show three stratigraphic units: Holocene, Plio-Pleistocene, and Miocene. Within the Miocene unit is an expansive drainage system extending about 80 kilometers offshore. In most areas, a system such as this would typically be characterized as a paleo-fluvial system. Although this drainage system probably initiated fluvially, geophysical data showing much evidence of karstification suggest that this system probably formed on the inner shelf as a result of large scale dissolution and collapse of Miocene limestones during lowered sea-level. The overlying Plio-Pleistocene unit infills the Miocene drainage system, while exiguously covering Miocene rocks in areas where the system is absent. Deposition of this unit probably took place during high-stands of sea-level, followed by erosion and transport of sediment farther offshore, exposing Miocene rocks. The Holocene unit sporadically covers underlying units throughout the study area. Sediments making up this unit have been reworked into several bedform types probably resulting from various boundary layer flow events such as hurricanes, storms, currents and tides. This scenario is probably not unique to the continental shelf west of Tampa Bay, Florida, but may also characterize other karstic shelves where paleo-fluvial processes were previously thought to be the dominant mechanism forming paleo-coastal drainage systems.

  14. Sediment dynamics and post-glacial evolution of the continental shelf around the Blanes submarine canyon head (NW Mediterranean)

    NASA Astrophysics Data System (ADS)

    Durán, Ruth; Canals, Miquel; Lastras, Galderic; Micallef, Aaron; Amblas, David; Pedrosa-Pàmies, Rut; Sanz, José Luis

    2013-11-01

    The Blanes submarine canyon (BC) deeply incises the Catalan continental shelf in the NW Mediterranean Sea. As a consequence of the closeness (only 4 km) of its head to the coastline and the mouth of the Tordera River, the canyon has a direct influence on the shelf dispersal system as it collects large amounts of sediment, mainly during high-energy events. Multibeam bathymetry, backscatter imagery and very-high resolution seismic reflection profiles have allowed characterizing the morphology of the continental shelf around the canyon head, also identifying sediment sources and transport pathways into the canyon. The morphological data have also been used to reconstruct the evolution of the continental shelf during the last sea-level transgression so that the current understanding of shelf-to-canyon sediment exchanges through time could be improved. The continental shelf surrounding the BC consists of both depositional and erosional or non-depositional areas. Depositional areas display prominent sediment bodies, a generally smooth bathymetry and variable backscatter. These include: (i) an area of modern coarse-grained sediment accumulation that comprises the inner shelf; (ii) a modern fine-grained sedimentation area on the middle shelf offshore Tossa de Mar; and (iii) a modern sediment depleted area that covers most of the middle and outer shelf to the west of the canyon head. Erosional and non-depositional areas display a rough topography and high backscatter, and occur primarily to the east of the canyon head, where the arrival of river-fed inputs is very small. In agreement with this pattern, the continental shelf north and west of the canyon head likely is the main source of shelf sediment into the canyon. To the north, a pattern of very high backscatter extends from the coastline to the canyon head, suggesting the remobilization and off-shelf export of fines. Additionally, relict near-shore sand bodies developed over the Barcelona shelf that extend to the canyon

  15. 210Pb balance and implications for particle transport on the continental shelf, U.S. Middle Atlantic Bight

    USGS Publications Warehouse

    Bacon, M.P.; Belastock, Rebecca A.; Bothner, Michael H.

    1994-01-01

    Supply of 210Pb to the continental shelf off the northeastern United States is dominated by the deposition from the atmosphere, the rate of which is reliably known from previously published work. Excess 210Pb inventories in the shelf sediments show accumulations that are nearly in balance with the supply, even in areas of relict sands where it is believed that no net accumulation of sediment presently occurs. The 210Pb distributions in shelf and slope water indicate that the two-way fluid exchange at the shelf-slope front and the net transport in the alongshore flow make comparatively small contributions to the shelf 210Pb budget. The near balance between supply and decay of 210Pb on the shelf implies a limit to the particle export flux. It is concluded that the export of particulate organic carbon does not exceed 60 g m-2 y-1 (???25% of primary production) and is probably lower. The hypothesis is advanced that fine particulate matter introduced to the continental shelf is detained in its transit of the shelf because of bioturbational trapping in the sediment due to benthic animals. Distributions of 210Pb in suspended particulate matter and in the fine fraction of shelf sediments suggest that the average fine particle must undergo several cycles of deposition-bioturbation-resuspension-redeposition and requires a number of decades for its transit and ultimate export from the shelf. Thus, only the most refractory organic matter is likely to be exported. ?? 1994.

  16. Estimating the benthic efflux of dissolved iron on the Ross Sea continental shelf

    NASA Astrophysics Data System (ADS)

    Marsay, C. M.; Sedwick, P. N.; Dinniman, M. S.; Barrett, P. M.; Mack, S. L.; McGillicuddy, D. J.

    2014-11-01

    Continental margin sediments provide a potentially large but poorly constrained source of dissolved iron (dFe) to the upper ocean. The Ross Sea continental shelf is one region where this benthic supply is thought to play a key role in regulating the magnitude of seasonal primary production. Here we present data collected during austral summer 2012 that reveal contrasting low surface (0.08 ± 0.07 nM) and elevated near-seafloor (0.74 ± 0.47 nM) dFe concentrations. Combining these observations with results from a high-resolution physical circulation model, we estimate dFe efflux of 5.8 × 107 mol yr-1 from the deeper portions (>400 m) of the Ross Sea continental shelf; more than sufficient to account for the inferred "winter reserve" dFe inventory at the onset of the growing season. In addition, elevated dFe concentrations observed over shallower bathymetry suggest that such features provide additional inputs of dFe to the euphotic zone throughout the year.

  17. Seasonal variability of living benthic foraminifera from the outer continental shelf of the Bay of Biscay

    NASA Astrophysics Data System (ADS)

    Duchemin, Gérald; Jorissen, Frans J.; Le Loc'h, François; Andrieux-Loyer, Françoise; Hily, Christian; Thouzeau, Gérard

    2008-08-01

    Living benthic foraminiferal faunas of six stations from the continental shelf of the Bay of Biscay have been investigated during three successive seasons (spring, summer and autumn 2002). For the three investigated stations, bottom water oxygen concentration, oxygen penetration into the sediment and sediment organic carbon contents are all relatively similar. Therefore, we think that the density and the composition of the foraminiferal faunas is mainly controlled by the quantity and quality of organic input resulting from a succession of phytoplankton bloom events, occurring from late February to early September. The earliest blooms are positioned at the shelf break, late spring and early summer blooms occur off Brittany, whereas in late summer and early autumn, only coastal blooms appear, often in the vicinity of river outlets. In spring, the benthic foraminiferal faunas of central (B, C and D) and outer (E) continental shelf stations are characterised by strong dominance in the first area and strong presence in the second area of Nonionella iridea. In fact, station E does not serve as a major depocenter for the remains of phytoplankton blooms. If station E is not considered, the densities of this taxon show a clear gradient from the shelf-break, where the species dominates the assemblages, to the coast, where it attains very low densities. We explain this gradient as a response to the presence, in early spring, of an important phytoplankton bloom, mainly composed of coccolithophorids, over the shelf break. This observation is supported by the maximum particles flux values at stations close to the shelf break (18.5 g m - 2 h - 1 ) and lower values in a station closer to the coast (6.8 g m - 2 h - 1 ). In summer, the faunal density is maximum at station A, relatively close to more varied phytoplancton blooms that occur off Brittany until early June. We suggest that the dominant species, Nonion fabum, Cassidulina carinata and Bolivina ex. gr. dilatata respond to

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

    NASA Astrophysics Data System (ADS)

    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.

  19. The potential impacts of climate change on the hydrography of the northwest European continental shelf

    NASA Astrophysics Data System (ADS)

    Holt, Jason; Wakelin, Sarah; Lowe, Jason; Tinker, Jonathan

    2010-09-01

    Changes in global atmospheric conditions have the potential to substantially influence shelf sea environments with far reaching consequences for their ecosystems. Here we focus on the northwest European continental shelf, and review the mechanisms by which climate change might affect the temperature, salinity and stratification of this shelf sea. We explore results from a single pair of Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) simulations forced by the Hadley Centre regional climate model, for conditions typical of 1961-1990 and 2070-2098, under a ‘business as usual’ emissions scenario (SRES A1B). This provides a single, physically plausible, representation of the future and a consistent representation of the recent past. Comparing these simulations, the shelf sea regions of this model are shown to warm substantially more than the open-ocean, by between 1.5 and 4 °C depending on location. Across the whole domain the surface waters are projected to be ∼0.2 p.s.u. fresher by the end of the 21st century. The strength of seasonal stratification is shown to increase by ∼20% on the shelf, compared with 20-50% in the open-ocean. The former being controlled by temperature and the latter by salinity. In shelf seas away from the direct influence of river discharge, stratification is projected to start ∼5 days earlier and breakdown ∼5-10 days later each year, hence extending the stratified period. An ERA-40 re-analysis forced simulation provides a reference, along with validation from gridded monthly mean data from the ICES data base.

  20. Interannual variability of wintertime temperature on the inner continental shelf of the Middle Atlantic Bight

    NASA Astrophysics Data System (ADS)

    Connolly, Thomas P.; Lentz, Steven J.

    2014-09-01

    The shallow depth of the inner continental shelf allows for rapid adjustment of the ocean to air-sea exchange of heat and momentum compared with offshore locations. Observations during 2001-2013 are used to evaluate the contributions of air-sea heat flux and oceanic advection to interannual variability of inner-shelf temperature in the Middle Atlantic Bight. Wintertime processes are important for interpreting regional interannual variability at nearshore locations since winter anomalies account for 69-77% of the variance of the annual anomalies and are correlated over broad along-shelf scales, from New England to North Carolina. At the Martha's Vineyard Coastal Observatory on the 12 m isobath, a heat budget is used to test the hypothesis that interannual differences in winter temperatures are due solely to air-sea heat flux. Bimonthly averages of air-sea heat flux are correlated with temporal changes in temperature, but overestimate the observed wintertime cooling. Velocity and satellite-derived temperature data show that interannual variability in wintertime surface cooling is partially compensated for by alongshore advection of warmer water from the west at this particular location. It is also shown that surface heat flux is a strong function of air-sea temperature difference. Because of this coupling between ocean and air temperatures in shallow water, along-shelf advection can significantly modify the surface heat flux at seasonal and interannual time scales. While along-shelf advection at relatively small (˜100 km) scales can be an important component of the heat budget over the inner shelf, interannual temperature variability is still largely determined by adjustment to large-scale air-temperature anomalies.

  1. Reprocessing and Interpretation of the High Resolution Seismic Data from Northern Marmara Continental Shelf, NW Turkey

    NASA Astrophysics Data System (ADS)

    Nasif, Aslıhan; Dondurur, Derman; Ergintav, Semih; Cifci, Gunay

    2015-04-01

    The Marmara Sea is an inland sea located in the NW of Turkey with a maximum depth of 1270 m, and consists of a 3 major sub-basins. The active dextral North Anatolian Fault (NAF) passes through the basins, which shapes the general morphology and forms the tectonic settlement of the Marmara Sea. The investigations for the Marmara Sea are now important since İstanbul city, which is the most populous and economically the most important city of Turkey, is located just north of the Marmara Sea, quite close to the NAF. In order to define the morphology and structural state of the northern continental shelf of the Marmara Sea, we collected 224 km of multichannel high resolution seismic and 338 km of Chirp subbottom profiler data along the shallow shelf in 2007. A 600 m long, 96 channel digital seismic streamer, and a Generator-Injector (GI) gun was used to obtain high resolution seismic data. The Chirp data was collected a 2.75-6.75 kHz over-the-side-mount transducer system. The data have been processed using a conventional data processing flow. The scope of the present study is to re-process and to interpret the seismic and Chirp data between Silivri and Sarayburnu on the northern Marmara shelf up to 100 m water depth. The active tectonic characteristics of the area, especially its geological connection with the terrestrial area, are investigated using acoustic data. In addition, offshore continuity of the of the Çatalca Fault zone is investigated. The Çatalca Fault enters the shelf along the B. Çekmece Lake and can be tracked in the SSE direction on the seismic data. The seismic data is tied to North Marmara-1 well located on the central part of the shelf area, and distributions and thicknesses of the pre-Miocene sediments are mapped using a jump-correlation to the well information. The seismic data located at the southernmost part of the shelf along the shelf break also indicate the presence of active sediment erosion. Behind the shelf break, the slope inclination

  2. Geophysical Characterization of the Central Yakutat Shelf and Cenozoic Basin Development, Offshore Southeastern Alaska

    NASA Astrophysics Data System (ADS)

    Price, R. N.

    2016-12-01

    In southeastern Alaska the collision of the Yakutat Block with North America has led to uplift of the highest costal mountain range in the world, the St. Elias and Chugach Mountains. By 5.5 Ma uplift of the ranges was sufficient to cause glaciation on the continental margin, making it a unique area to study the interactions between tectonics and climate driven processes. This study uses coincident seismic reflection and refraction data from the St. Elias Erosion and Tectonics Project (STEEP) focusing on line STEEP02. We present a high resolution two-dimensional compressional velocity model that helps to elucidate the patterns of deformation offshore of the southeastern Alaskan syntaxis. The velocity model is able to constrain the location of the pinch out of the Poul Creek Formation offshore beneath the mouth of Yakutat Bay. The pinch out of the formation is likely due to an erosional event of the pre-glacial strata associated with the initial formation of the Yakataga fold-and-thrust belt, rather than a depositional feature. This geometry suggests sufficient uplift in the St. Elias syntaxis to cause large scale denudation before deposition of the Yakataga Formation at 6 Ma. The velocity model is transformed to porosity using relationships specific to the Cenozoic sediments on the Yakutat shelf. The Poul Creek Formation is identified as a unit of low velocity, 2.8 km/s, and elevated porosity, .25, across its entire offshore extent and may be a pre-existing weak zone that preferentially accommodates slip when incorporated into the western fold-and-thrust belts. Van Avendonk et al. (2013) identified a zone of lateral compaction 100 km outboard of the offshore Pamplona Zone deformation front along a seismic line perpendicular to STEEP02 which is defined by a landward lateral increase in velocity and decrease porosity in the Yakataga Formation. No landward increase in velocity or decrease in porosity is observed along STEEP02, constraining the deformation front due to

  3. Tracking anthropogenic influences on the continental shelf of China with sedimentary linear alkylbenzenes (LABs).

    PubMed

    Wei, Gao-Ling; Liu, Liang-Ying; Bao, Lian-Jun; Zeng, Eddy Y

    2014-03-15

    Surface sediments collected along the entire continental shelf of China, including Yellow Sea, the East China Sea (ECS) inner shelf and the South China Sea (SCS), were analyzed for linear alkylbenzenes (LABs), from which regional anthropogenic influences on the marine environment were assessed. The occurrence of LABs (5.6-77 ng/g; mean: 25 ng/g; median: 20 ng/g) implied light sewage contamination in coast sediment off China. Specifically, the SCS had higher sedimentary LAB levels than Yellow Sea and the ECS inner shelf, which was mainly related to the intensity of domestic wastewater discharge and marine fishing activities. Values of L/S and C₁₃/C₁₂ (defined in the main text) suggested certain degradation while I/E indicated limited degradation of LABs. Also, additional input sources and congener inter-conversions may have contributed to the inconsistent results for degradation of LABs in offshore sediments. Atmospheric inputs and wastewater discharge from marine fishing vessels predominantly contributed to sedimentary LABs in Yellow Sea and the SCS, while riverine input was mainly responsible for LABs along the ECS inner shelf.

  4. Kinetic and equilibrium based fractionation study of Pb in continental shelf sediment of India.

    PubMed

    Chakraborty, Sucharita; Chakraborty, Parthasarathi; Sarkar, Arindam; Nagender Nath, B

    2017-09-05

    Two independent analytical methods (kinetic and sequential extraction protocols) were used to understand the distribution, stability, and lability of Pb-sediment complexes in Indian continental shelf. The concentrations of sedimentary Pb varied from 12.0±0.6 to 30.4±0.1mg·kg(-1) and 15.9±0.3 to 36.7±0.4mg·kg(-1) in the western and eastern shelf of India respectively. The kinetic extraction study showed that higher proportion of labile Pb-complexes were present in the eastern shelf sediments (~24% of total Pb) than the western shelf sediments (~14% of total Pb). The sedimentary organic matter was found to regulate lability of sedimentary Pb complexes. The sequential extraction study suggested that Fe/Mn oxyhydroxide were the primary hosting phase for labile Pb complexes. This study showed that water soluble, exchangeable, carbonate/bicarbonate-Pb complexes in the sediments was labile. This study provides a better physicochemical description of stability or lability of Pb complexes in the coastal sediment of India. Copyright © 2017 Elsevier Ltd. All rights reserved.

  5. Tidal influence on the hydrodynamics of the French Guiana continental shelf

    NASA Astrophysics Data System (ADS)

    Bourret, A.; Devenon, J.-L.; Chevalier, C.

    2008-04-01

    This study investigates the circulation on the French Guiana continental shelf under tidal influence. Indeed, hydrodynamics are characterised by a weak salinity tongue located in the middle of the shelf and induced by the Amazon River, a coastal current flowing from the southeast, and a tidal standing wave whose co-range lines are parallel to the coast. In addition to field observations, a numerical model also is used to evaluate the tidal influence on coastal circulation. The model makes use of the MOBEEHDYCS code, a three-dimensional free surface time-splitting model whose domain is bounded with a closed coastal boundary, two active boundaries (offshore and lateral) and a passive boundary. The boundary configuration and hydrodynamics require a careful choice of passive open boundary conditions. The initial and boundary conditions come from field data. The tidal currents are essentially cross-shore and do not have a great influence on the main current direction on the offshore part of the shelf. The offshore currents remain parallel to the coast. In the inner shelf, the tidal influence is found to be much more important and the tidal currents can reach 0.45 m/s. Vertically, the tidal currents are barotropic, in spite of the high stratification and they induce a horizontal cross-shore migration (about 3 km) of the weak salinity tongue and vertical oscillations of the halocline without complete mixing.

  6. Mapping and classifying the seabed of the West Greenland continental shelf

    NASA Astrophysics Data System (ADS)

    Gougeon, S.; Kemp, K. M.; Blicher, M. E.; Yesson, C.

    2017-03-01

    Marine benthic habitats support a diversity of marine organisms that are both economically and intrinsically valuable. Our knowledge of the distribution of these habitats is largely incomplete, particularly in deeper water and at higher latitudes. The western continental shelf of Greenland is one example of a deep (more than 500 m) Arctic region with limited information available. This study uses an adaptation of the EUNIS seabed classification scheme to document benthic habitats in the region of the West Greenland shrimp trawl fishery from 60°N to 72°N in depths of 61-725 m. More than 2000 images collected at 224 stations between 2011 and 2015 were grouped into 7 habitat classes. A classification model was developed using environmental proxies to make habitat predictions for the entire western shelf (200-700 m below 72°N). The spatial distribution of habitats correlates with temperature and latitude. Muddy sediments appear in northern and colder areas whereas sandy and rocky areas dominate in the south. Southern regions are also warmer and have stronger currents. The Mud habitat is the most widespread, covering around a third of the study area. There is a general pattern that deep channels and basins are dominated by muddy sediments, many of which are fed by glacial sedimentation and outlets from fjords, while shallow banks and shelf have a mix of more complex habitats. This first habitat classification map of the West Greenland shelf will be a useful tool for researchers, management and conservationists.

  7. Air-sea interaction at the Southern Brazilian Continental Shelf: In situ observations

    NASA Astrophysics Data System (ADS)

    Pezzi, L. P.; Souza, R. B.; Farias, P. C.; Acevedo, O.; Miller, A. J.

    2016-09-01

    The influence of the cross-shelf oceanographic front occurring between the Brazil Current (BC) and the Brazilian Coastal Current (BCC) on the local Marine Atmospheric Boundary Layer (MABL) is investigated here. This front is typical of wintertime in the Southern Brazilian Continental Shelf (SBCS) and this is the first time that its effects are investigated over the above MABL. Here we analyze variability, vertical structure, and stability of MABL as well as heat fluxes at air-sea interface, across five oceanographic transects in the SBCS made during a winter 2012 cruise. Local thermal gradients associated with mixing between distinct water masses, play an essential role on MABL modulation and stability. Although weaker when compared with other frontal regions, the cross-shelf thermal gradients reproduce exactly what is expected for open ocean regions: Stronger (weaker) winds, lower (higher) sea level pressure, and a more unstable (stable) MABL are found over the warm (cold) side of the oceanographic front between the BC (warm) and coastal (cold) waters. Our findings strongly support the coexistence of both known MABL modulation mechanisms: the static and hydrostatic MABL stability. This is the first time that these modulation mechanisms are documented for this region. Turbulent fluxes were found to be markedly dependent on the cross-shelf SST gradients resulting in differences of up to 100 W.m-2 especially in the southernmost region where the gradients were more intense.

  8. What a drag: Quantifying the global impact of chronic bottom trawling on continental shelf sediment

    USGS Publications Warehouse

    Oberle, Ferdinand K.J.; Storlazzi, Curt; Hanebuth, Till J.J.

    2016-01-01

    Continental shelves worldwide are subject to intense bottom trawling that causes sediment to be resuspended. The widely used traditional concepts of modern sedimentary transport systems on the shelf rely only on estimates for naturally driven sediment resuspension such as through storm waves, bottom currents, and gravity-driven flows but they overlook a critical anthropogenic factor. The strong influence of bottom trawling on a source-to-sink sediment budget is explored on the NW Iberian shelf. Use of Automated Information System vessel tracking data provides for a high-resolution vessel track reconstruction and the accurate calculation of the spatial distribution of bottom trawling intensity and associated resuspended sediment load. The mean bottom trawling-induced resuspended sediment mass for the NW Iberian shelf is 13.50 Mt yr− 1, which leads to a six-fold increase in off-shelf sediment transport when compared to natural resuspension mechanisms. The source-to-sink budget analysis provides evidence that bottom trawling causes a rapid erosion of the fine sediment on human time scales. Combining global soft sediment distribution data of the shelves with worldwide bottom trawling intensity estimates we show that the bottom trawling-induced resuspended sediment mass amounts to approximately the same mass of all sediment entering the shelves through rivers. Spatial delineations between natural and anthropogenic sediment resuspension areas are presented to aid in marine management questions.

  9. Galveston Symposium: Physical Oceanography of the Louisiana/Texas Continental Shelf

    NASA Astrophysics Data System (ADS)

    Mitchell, Thomas M.; Brown, Murray

    The Minerals Management Service (MMS), Gulf of Mexico Outer Continental Shelf (OCS) Region sponsored a symposium on the Physical Oceanography of the Louisiana/Texas (LA/TX) Shelf in Galveston, Texas, on May 24-26, 1988. The symposium brought together a number of physical oceanographers, meteorologists, and ecologists to discuss the state of knowledge and to begin the planning process for a long-term study of shelf circulation covering the region from the mouth of the Mississippi River to approximately 24° latitude along the Mexican coast and from the shore out to a depth of approximately 500 m. The proposed study, to be a component of the ongoing MMS Environmental Studies Program, is expected to take place during the period 1989-1991. It is anticipated that the work will be done principally through contracts after a competitive procurement process. Specific charges to the participants were as follows:to assess the current state of knowledge concerning the circulation on the LA/TX shelfto identify significant gaps in that knowledgeto recommend a field measurement program to address these gapsto recommend a circulation modeling program for the LA/TX shelf that will improve MMS' oil spill risk assessmentsto identify and initiate coordination mechanisms and data-sharing arrangements with other proposed research efforts

  10. Regional modeling of the water masses and circulation annual variability at the Southern Brazilian Continental Shelf

    NASA Astrophysics Data System (ADS)

    Mendonça, L. F.; Souza, R. B.; Aseff, C. R. C.; Pezzi, L. P.; Möller, O. O.; Alves, R. C. M.

    2017-02-01

    The Southern Brazilian Continental Shelf (SBCS) is one of the more productive areas for fisheries in Brazilian waters. The water masses and the dynamical processes of the region present a very seasonal behavior that imprint strong effects in the ecosystem and the weather of the area and its vicinity. This paper makes use of the Regional Ocean Modeling System (ROMS) for studying the water mass distribution and circulation variability in the SBCS during the year of 2012. Model outputs were compared to in situ, historical observations and to satellite data. The model was able to reproduce the main thermohaline characteristics of the waters dominating the SBCS and the adjacent region. The mixing between the Subantarctic Shelf Water and the Subtropical Shelf Water, known as the Subtropical Shelf Front (STSF), presented a clear seasonal change in volume. As a consequence of the mixing and of the seasonal oscillation of the STSF position, the stability of the water column inside the SBCS also changes seasonally. Current velocities and associated transports estimated for the Brazil Current (BC) and for the Brazilian Coastal Current (BCC) agree with previous measurements and estimates, stressing the fact that the opposite flow of the BCC occurring during winter in the study region is about 2 orders of magnitude smaller than that of the BC. Seasonal maps of simulated Mean Kinetic Energy and Eddy Kinetic Energy demonstrate the known behavior of the BC and stressed the importance of the mean coastal flow off Argentina throughout the year.

  11. What a drag: Quantifying the global impact of chronic bottom trawling on continental shelf sediment

    NASA Astrophysics Data System (ADS)

    Oberle, Ferdinand K. J.; Storlazzi, Curt D.; Hanebuth, Till J. J.

    2016-07-01

    Continental shelves worldwide are subject to intense bottom trawling that causes sediment to be resuspended. The widely used traditional concepts of modern sedimentary transport systems on the shelf rely only on estimates for naturally driven sediment resuspension such as through storm waves, bottom currents, and gravity-driven flows but they overlook a critical anthropogenic factor. The strong influence of bottom trawling on a source-to-sink sediment budget is explored on the NW Iberian shelf. Use of Automated Information System vessel tracking data provides for a high-resolution vessel track reconstruction and the accurate calculation of the spatial distribution of bottom trawling intensity and associated resuspended sediment load. The mean bottom trawling-induced resuspended sediment mass for the NW Iberian shelf is 13.50 Mt yr- 1, which leads to a six-fold increase in off-shelf sediment transport when compared to natural resuspension mechanisms. The source-to-sink budget analysis provides evidence that bottom trawling causes a rapid erosion of the fine sediment on human time scales. Combining global soft sediment distribution data of the shelves with worldwide bottom trawling intensity estimates we show that the bottom trawling-induced resuspended sediment mass amounts to approximately the same mass of all sediment entering the shelves through rivers. Spatial delineations between natural and anthropogenic sediment resuspension areas are presented to aid in marine management questions.

  12. Structural cross sections, Plio-Pleistocene Series, southeastern Texas Continental Shelf

    SciTech Connect

    Not Available

    1989-01-01

    The Plio-Pleistocene Series in the western Gulf Coast basin comprises a thick wedge of terrigenous clastic sediment that produces modest volumes of hydrocarbons from offshore leases along the outer shelf and upper slope. Sandstone reservoirs within this wedge have yielded more than 40 million bbl of oil and 2.5 Tcf of gas. They initially contained about 1.6 billion bbl of oil equivalent, or nearly two-thirds of the estimated total recoverable reserves beneath the Texas Outer Continental Shelf. To interpret the structural and stratigraphic framework of the area, the authors used publicly available electric logs, paleontological reports, and published information, in addition to proprietary data released by operators and approximately 2,000 miles of multichannel seismic profiles. In this book biostratigraphic zones of the Plio-Pleistocene Series, locations of major oil and gas fields and trends, and areas of tectonic features and salt structures are included.

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

    PubMed

    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.

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

    SciTech Connect

    Zuniga-Rivero, F.; Keeling, J.A.; Hay-Roe, H.

    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.

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

    PubMed Central

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

    2015-01-01

    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. PMID:26505325

  16. High particle export over the continental shelf of the west Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Buesseler, Ken O.; McDonnell, Andrew M. P.; Schofield, Oscar M. E.; Steinberg, Deborah K.; Ducklow, Hugh W.

    2010-11-01

    Drifting cylindrical traps and the flux proxy 234Th indicate more than an order of magnitude higher sinking fluxes of particulate carbon and 234Th in January 2009 than measured by a time-series conical trap used regularly on the shelf of the west Antarctic Peninsula (WAP). The higher fluxes measured in this study have several implications for our understanding of the WAP ecosystem. Larger sinking fluxes result in a revised export efficiency of at least 10% (C flux/net primary production) and a requisite lower regeneration efficiency in surface waters. High fluxes also result in a large supply of sinking organic matter to support subsurface and benthic food webs on the continental shelf. These new findings call into question the magnitude of seasonal and interannual variability in particle flux and reaffirm the difficulty of using moored conical traps as a quantitative flux collector in shallow waters.

  17. Heavy metal distribution in surface sediments from the continental shelf adjacent to Nazaré canyon

    NASA Astrophysics Data System (ADS)

    Oliveira, A.; Palma, C.; Valença, M.

    2011-12-01

    The continental shelf surface sediments around the Nazaré canyon have been analyzed for heavy metal contamination. Organic carbon content and grain size were also determined. The shelf area around the Nazaré canyon shows mean concentrations of Cr, Cu, Hg, Ni, Pb and Zn within the limits recommended by OSPAR (2008). Some enrichment and human impact was found for Cr and especially Pb. Local rivers, mainly the Mondego and southern creeks seem to be the major sources of heavy metals for the Nazaré area, showing similar contamination levels. A set of reference values for non-contaminated fine surface sediments (<63 μm) in the North-Eastern Atlantic are proposed for As, Al, Cd, Cr, Cu, Fe, Hg, Li, Mn, Ni, Pb and Zn.

  18. Near-Inertial Waves on the Continental Shelf: Physics Based on Observations off the West Florida.

    NASA Astrophysics Data System (ADS)

    Maksimova, E. V.; Weisberg, R. H.

    2016-02-01

    Oscillations and waves of near-inertial frequency on the West Florida continental shelf in the eastern Gulf of Mexico are thought to be seasonally important for mixing the shelf waters because of their tendency to have large vertical shear and to be quite energetic. Such motions are also thought to seasonally affect the ecology of the region via daily vertical thermocline migration. The unique multiyear observations off the West Florida coast allow the understanding of physics underlying the processes. The presentation will discuss the key findings on near-inertial motions in the region, including observed energetics, spatial and temporal variability, and mechanisms of generation and dissipation. This work was supported by the National Science Foundation Ocean Sciences Postdoctoral Research Fellowship under Grant OCE-1421180 (E. V. Maksimova).

  19. Estimated oil and gas reserves, Gulf of Mexico outer continental shelf and continental slope, December 31, 1982

    USGS Publications Warehouse

    Hewitt, Jack E.; Brooke, Jeff P.; Knipmeyer, John H.

    1983-01-01

    Remaining recoverable reserves of oil* and gas in the Gulf of Mexico Outer Continental Shelf and Continental Slope have been estimated to be about 2.98 billion barrels of oil and 39.8 trillion cubic feet of gas, as of December 31, 1982. These reserves are recoverable from 468 studied fields under the Federal submerged lands off the coasts of Louisiana and Texas. An additional 53 fields, discovered since December 31, 1980, have not been sufficiently developed to permit a reasonably accurate estimate of reserves. Original recoverable reserves are estimated to have been 8.56 billion barrels of oil and 98.1 trillion cubic feet of gas from 484 fields in the same geographic area. Included in this number are 16 fields that are depleted and were abandoned; not included are the 53 insufficiently developed fields. Estimates were made for individual reservoirs in 382 fields and on a field-wide basis for the other 102 fields. *The term 'oil' as used in this report includes crude oil and condensate.

  20. Environmental geologic studies on the southeastern United States Atlantic Outer Continental Shelf, 1977-1978

    USGS Publications Warehouse

    Popenoe, Peter; Popenoe, Peter

    1981-01-01

    This report is a summary of the second year of marine environmental research activities by the U.S. Geological Survey (USGS) on the southeaster U.S. Atlantic Continental Margin, in accordance with with Memorandum of Understanding (MOU) AA551-MU8-13 between the USGS and the Bureau of Land Management (BLM). The report covers studies whose fieldwork was conducted during the period from 1 October 1977 to 30 September 1978. The results of the first year of study are reported in Popenoe (1978a and b) and as U.S. Department of Commerce NTIS report PB 300-820. The purpose of these investigations is to provide basic geologic and oceanographic data to the BLM Outer Continental Shelf (OCS) Marine Environmental Studies Program in support of management decisions which relate to possible development of oil and gas resources of the continental shelf. The objectives of the USGS-BLM geologic research program for fiscal year 1978 (FY-78) were 1) to determine the sedimentation rates and processes on the upper slope and inner Blake Plateau; 2) to determine the distribution, areal extent, and vertical characteristics of geological features supportive of biological communities; 3) to monitor the transport of bottom sediment across the OCS, evaluate its possible effect on pollutant transfer along the seabed and the potential of sediment as a pollutant sink, determine the implications of erosion/deposition on pipeline emplacement, and aid the interpretation of chemical, biological, and physical data; 4) to determine the concentration levels of chosen trace metals and silica in three chemically defined fractions of the suspended particulate matter (seston); 5) to study the shelf edge and slope near areas of oil and gas interest, and the northern portion of the Blake Plateau for evidence of slope instability and other geologic hazards, and 6) to determine the depth and rate of sediment mixing caused by large storms and/or by benthic organisms and where possible to estimate the rate of

  1. Sequence stratigraphy and continental margin development of the northwestern shelf of the South China Sea

    SciTech Connect

    Chen, P.P.H. ); Zhi Yuong Chen; Qi Min Zhang )

    1993-05-01

    Based on the sequence stratigraphic analyses of the Tertiary in the northwestern continental margin of the South China Sea, this paper summarizes the regional tectonics and their influences on the basin developments and discusses the systems tract distributions through the continental margin growth. The study area is underlain by two Tertiary basins separated by a major basin boundary fault across which two distinctly different basin structural styles developed. The Qiongdongnan basin shows characteristic rift structures and is closely related to the opening of the South China Sea. The Yinggehai basin is filled with thick Neogene monoclines overlying basement without apparent rift structures. The Yinggehai's genesis has been linked to the tectonism along the Red River suture zone. The margin development is characterized by depositional environments of sediment influx constantly exceeding accommodation space. Under these environments, the highstand deltas frequently developed near shelf edges, where vertically stacked shallow water sands of both highstand deltas and lowstand wedges/deltas could produce favorable exploration targets. High rates of sedimentation in the study area allow the identification of fourth-order cyclicity in the Quaternary. Regional sequence stratigraphic correlations suggest that many sequence boundaries appear to be synchronous, but not all boundaries exist in all basins along the eastern and southern continental margins of mainland China. The margin evolved through the repeated development of lowstand fans, lowstand wedges, transgressive systems tracts, and highstand deltas. Prior to the Pliocene, the shelf was sourced both from Vietnam and Hainan Island and, as a result, two shelf margins developed. The southwestern margin stopped growing in the late Miocene, and the northern margin continued to prograde with possible additional sediment inputs through the Red River system in the Quaternary. 29 refs., 22 figs.

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

    PubMed

    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

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

    PubMed Central

    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

  4. Satellite observation of particulate organic carbon dynamics on the Louisiana continental shelf

    NASA Astrophysics Data System (ADS)

    Le, Chengfeng; Lehrter, John C.; Hu, Chuanmin; MacIntyre, Hugh; Beck, Marcus W.

    2017-01-01

    Particulate organic carbon (POC) plays an important role in coastal carbon cycling and the formation of hypoxia. Yet, coastal POC dynamics are often poorly understood due to a lack of long-term POC observations and the complexity of coastal hydrodynamic and biogeochemical processes that influence POC sources and sinks. Using field observations and satellite ocean color products, we developed a new multiple regression algorithm to estimate POC on the Louisiana Continental Shelf (LCS) from satellite observations. The algorithm had reliable performance with mean relative error (MRE) of ˜40% and root mean square error (RMSE) of ˜50% for MODIS and SeaWiFS images for POC ranging between ˜80 and ˜1200 mg m-3, and showed similar performance for a large estuary (Mobile Bay). Substantial spatiotemporal variability in the satellite-derived POC was observed on the LCS, with high POC found on the inner shelf (<10 m depth) and lower POC on the middle (10-50 m depth) and outer shelf (50-200 m depth), and with high POC found in winter (January-March) and lower POC in summer to fall (August-October). Correlation analysis between long-term POC time series and several potential influencing factors indicated that river discharge played a dominant role in POC dynamics on the LCS, while wind and surface currents also affected POC spatial patterns on short time scales. This study adds another example where satellite data with carefully developed algorithms can greatly increase the spatial and temporal observations of important biogeochemical variables on continental shelf and estuaries.

  5. The circulation over the continental shelf of Tamaulipas-North of Veracruz

    NASA Astrophysics Data System (ADS)

    Mancilla-Rojas, M. D.; Rivas, D.

    2012-12-01

    A 3D regional ocean model with a terrain-following vertical coordinate and high horizontal resolution (~ 2 km) was used to describe the circulation over the continental shelf of Tamaulipas-North of Veraruz. This study is focused on the sensitivity of the local dynamics to the main forcings such as the Panuco river discharge and the wind stress field. The model reproduces reasonably well the dynamics variables such as salinity and temperature field but further validation work is still need. This model results are of particular importance since much of the study area remain to be described.

  6. Wave height, peak period, and orbital velocity for the California continental shelf

    USGS Publications Warehouse

    Erikson, Li H.; Storlazzi, Curt D.; Golden, Nadine E.

    2014-01-01

    In this study, bathymetric data compiled as part of the California Seafloor Mapping Program Project and within the 3-NM limit were supplemented with deeper water bathymetric data (NOAA, http://maps.ngdc.noaa.gov/, last downloaded April 2013) and used to populate numerical wave grids for simulation of wave growth and propagation across the continental shelf bordering the California coast. Wave computations were done with the widely used and accepted numerical model SWAN (Ris, 1997; Booij and others, 1999; Ris and others, 1999). SWAN is a third-generation spectral model that simulates wind-wave growth, propagation, refraction, dissipation, and depth-induced breaking.

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

    PubMed

    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

  8. Derivation of a three dimensional numerical water quality model for estuary and continental shelf application

    NASA Technical Reports Server (NTRS)

    Spaulding, M.

    1973-01-01

    A derivation is given for a three dimensional mass transport equation which is appropriate for numerical modeling of estuary and continental shelf water quality variations for both the time dependent and steady state cases. A finite difference approximation to the derived equation is presented and a solution scheme for the resulting equations outlined. Preliminary results are obtained using the model for the extremely simple problems which have analytical solutions. The numerical model, as presented, will provide a scheme to study water quality problems in coastal waters for both steady state and time dependent cases.

  9. Fish assemblages associated with oil industry structures on the continental shelf of north-western Australia.

    PubMed

    Pradella, N; Fowler, A M; Booth, D J; Macreadie, P I

    2014-01-01

    This study provides the first assessment of fish associations with oil and gas structures located in deep water (85-175 m) on Australia's north-west continental shelf, using rare oil industry video footage obtained from remotely operated vehicles. A diverse range of taxa were observed associating with the structures, including reef-dependent species and transient pelagic species. Ten commercially fished species were observed, the most abundant of which was Lutjanus argentimaculatus, with an estimated biomass for the two deepest structures (Goodwyn and Echo) of 109 kg.

  10. Upper Wisconsinan till recovered on the continental shelf southeast of New England

    USGS Publications Warehouse

    Bothner, Michael H.; Spiker, E. C.

    1980-01-01

    Basal till was identified in two sediment cores collected about 69 kilometers southeast of Nantucket Island on the east and west sides of Great South Channel. These are the first samples of till collected on the outer continental shelf off the northeastern United States. The carbon-14 age of the total organic carbon in the tills provides a "no older than" age of about 20,000 years before present and suggests that the tills were deposited during the late Wisconsinan glaciation. This conclusion is in support of the hypothesis of an extensive Laurentide ice sheet that extended to the northern side of Georges Bank. Copyright ?? 1980 AAAS.

  11. Repeal of unneeded Outer Continental Shelf production rate-setting functions would cut costs

    SciTech Connect

    Not Available

    1982-09-10

    Under various laws, the Department of the Interior requires operators of Outer Continental Shelf leases to submit information regarding the rate at which oil and gas can and will be produced. Three different rates of production are currently compiled by the Department's Minerals Management Service. However, GAO found that most of the data are not useful or necessary. Congressional relief for the Department from some statutory requirements and consolidating the existing data submittal requirements would allow both the Department and industry to better use their resources to serve higher priority needs.

  12. Seabed acoustics of a sand ridge on the New Jersey continental shelf.

    PubMed

    Knobles, D P; Wilson, P S; Goff, J A; Cho, S E

    2008-09-01

    Acoustic measurements were made on a sand ridge on the New Jersey continental shelf. Data collected on two L arrays separated by 20 km from a single multi-frequency tow suggest small horizontal environmental variability. Values for the sound speed structure of the seabed are extracted by first applying a geo-acoustic inversion method to broadband and narrowband acoustic data from short-range sources. Then, a parabolic equation algorithm is used to properly include the bathymetry and sub-bottom layering. Finally, the frequency dependence of the seabed attenuation is inferred by optimizing the model fit to long-range transmission loss data in the 50-3000 Hz band.

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

    NASA Astrophysics Data System (ADS)

    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 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

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

    PubMed Central

    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

  15. High-Resolution Geologic Mapping of the Inner Continental Shelf: Cape Ann to Salisbury Beach, Massachusetts

    USGS Publications Warehouse

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

    2009-01-01

    The geologic framework of the Massachusetts inner continental shelf between Cape Ann and Salisbury Beach has been shaped by a complicated history of glaciation, deglaciation, and changes in relative sea level. New geophysical data (swath bathymetry, sidescan sonar and seismic-reflection profiling), sediment samples, and seafloor photography provide insight into the geomorphic and stratigraphic record generated by these processes. High-resolution spatial data and geologic maps in this report support coastal research and efforts to understand the type, distribution, and quality of subtidal marine habitats in the Massachusetts coastal ocean.

  16. The macro- and megabenthic fauna on the continental shelf of the eastern Amundsen Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Linse, Katrin; Griffiths, Huw J.; Barnes, Dave KA; Brandt, Angelika; Davey, Niki; David, Bruno; De Grave, Sammy; d‧Udekem d‧Acoz, Cédric; Eléaume, Marc; Glover, Adrian G.; Hemery, Lenaïg G.; Mah, Christopher; Martín-Ledo, Rafael; Munilla, Tomás; O‧Loughlin, Mark; Pierrat, Benjamin; Saucède, Thomas; Sands, Chester J.; Strugnell, Jan M.; Enderlein, Peter

    2013-10-01

    In 2008 the BIOPEARL II expedition on board of RRS James Clark Ross sailed to the eastern Amundsen Sea Embayment and Pine Island Bay, one of the least studied Antarctic continental shelf regions due to its remoteness and ice cover. A total of 37 Agassiz trawls were deployed at depth transects along the continental and trough slopes. A total of 5469 specimens, belonging to 32 higher taxonomic groups and more than 270 species, were collected. Species richness per station varied from 1 to 55. The benthic assemblages were dominated by echinoderms and clearly different to those in the Ross, Scotia and Weddell seas. Here we present the macro- and megafaunal assemblage structure, its species richness and the presence of several undescribed species.

  17. Multichannel seismic depth sections and interval velocities over outer continental shelf and upper continental slope between Cape Hatteras and Cape Cod: rifted margins

    USGS Publications Warehouse

    Grow, John A.; Mattick, Robert E.; Schlee, John S.

    1979-01-01

    Six computer-generated seismic depth sections over the outer continental shelf and upper slope reveal that subhorizontal Lower Cretaceous reflectors continue 20 to 30 km seaward of the present shelf edge. Extensive erosion on the continental slope has occurred primarily during the Tertiary, causing major unconformities and retreat of the shelf edge to its present position. The precise age and number of erosional events is not established, but at least one major erosional event is thought to be Oligocene and related to a marine regression in response to a worldwide eustatic lowering of sea level. Velocities derived from the multichannel data reveal distinctive ranges and lateral trends as functions of sediment age, depth of burial, and distance from the coastline. Seismic units beneath the shelf and slope of inferred Tertiary age range from 1.7 to 2.7 km/sec, increasing with age and depth of burial. Units interpreted as Upper Cretaceous rocks beneath the shelf range from 2.3 to 3.6 km/sec and show a distinct lateral increase across the shelf followed by a decrease beneath the present continental slope. Inferred Lower Cretaceous and Upper Jurassic rocks beneath the shelf increase from 3.7 to 4.8 km/sec from nearshore to offshore and indicate a change in facies from clastic units below the inner shelf to carbonate units beneath the outer shelf and upper continental slope. Both reflection and refraction data suggest that thin, high-velocity limestone units (5.0 km/sec) are present within the Lower Cretaceous and Upper Jurassic units beneath the outermost shelf edge, but that these change lithology or pinch out before reaching the middle shelf. Although lateral changes in velocity across the shelf and local velocity inversions appear, the interval velocities along the length of the margin show excellent continuity between Cape Hatteras and Cape Cod. The high-velocity horizons within the Lower Cretaceous and Upper Jurassic shelf-edge complex indicate the presence of a

  18. Carbonate sediment production in the equatorial continental shelf of South America: Quantifying Halimeda incrassata (Chlorophyta) contributions

    NASA Astrophysics Data System (ADS)

    Carneiro, Pedro Bastos de Macêdo; Morais, Jader Onofre de

    2016-12-01

    The middle and outer continental shelves of eastern equatorial South America (ESA) are characterized by intense production of carbonate sediments. Qualitative analyses of sediment deposits suggest that the calcareous green alga Halimeda incrassata is among the top CaCO3 producers. Nevertheless, no study so far has quantified its real contributions. To better understand the sediment dynamic in this area, we measured biomass, growth rates and calcium carbonate production by this alga. The species exhibited high growth rates (3.38 segments.individual-1.day-1), coverage (174 individuals.m-2) and biomass (214.02 g.m-2). Substitution of segments may allow a sedimentation rate of 1.53 mm.yr-1 and a complete turnover of the population every 60.2 days. The rapid growth indicates that this alga can produce as much CaCO3 (1.19 kg CaCO3.m-2.year-1) as other tropical organisms, such as corals and rhodoliths. In a conservative estimate, 773.500 tonnes of CaCO3 are produced per year in a 5000 km2 area off the northern coast of Brazil. Sedimentation rate seems to be higher than that promoted by continental inputs in middle and outer continental shelf. On the other hand, population turnover is twice as slow as in other H. incrassata assemblages, suggesting that South American populations are sensible to physical disturbances. New studies are necessary to accurately estimate H. incrassata coverage along the Brazilian coast and to integrate data on other CaCO3 producers, such as foraminifera and coralline algae. This would allow a better understanding of the role of South American continental shelf on the global carbon budget. Furthermore, analysis on the health of these organisms is urgent, since a decline in their populations could negatively affect ecosystems functioning and services.

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

    NASA Astrophysics Data System (ADS)

    Falco, P.; Castagno, P.; Budillon, G.; Spezie, G.

    2016-02-01

    The Circumpolar Deep Water (CDW) intrusion on the Antarctic continental shelves is the primary source of heat, salt and nutrients playing a major role on 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 time of the intrusions. Besides, few works focused on the effect of the tide that controls the intrusion itself. In the Ross Sea, the CDW intrudes onto the shelf in several locations mostly along the troughs, such as the Glomar Challenger, the Joides and the Drygalski. We use hydrographic observations and three moorings placed (one) on the outer shelf in the middle of the Drygalski Trough and (two) on the upper slope at the mouth of the Glomar Challenger basin, in order to characterize the spatial and temporal variability of the CDW inflow onto the shelf. Our data span from 2004 to 2014. In the Drygalski Trough the CDW enters as a thick layer of about 150 m between 250 - 400 m moving upward toward south. At the mooring location, about 50 Km from the shelf break, two main CDW cores can be observed: one on 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. A signature of this lighter and relatively warm water is detected by the instruments on the mooring at bottom of the Drygalski Trough. The CDW intrusion at the bottom of the trough is strictly related to the diurnal and spring/neap tidal cycles, but a strong seasonal variability of the CDW is clear. A strong inflow of CDW is observed every year at the end of December (after few months that the salinity minimum is registered), while the CDW inflow is at its seasonal minimum during the end of the austral summer in correspondence of the salinity maximum associated with the High Salinity Shelf Water (HSSW). Indeed, the

  20. The role of continental shelf width in determining freshwater phylogeographic patterns in south-eastern Australian pygmy perches (Teleostei: Percichthyidae).

    PubMed

    Unmack, Peter J; Hammer, Michael P; Adams, Mark; Johnson, Jerald B; Dowling, Thomas E

    2013-03-01

    Biogeographic patterns displayed by obligate freshwater organisms are intimately related to the nature and extent of connectivity between suitable habitats. Two of the more significant barriers to freshwater connections are seawater and major drainage divides. South-eastern Australia provides a contrast between these barriers as it has discrete areas that are likely influenced to a greater or lesser extent by each barrier type. We use continental shelf width as a proxy for the potential degree of river coalescence during low sea levels. Our specific hypothesis is that the degree of phylogeographic divergence between coastal river basins should correspond to the continental shelf width of each region. This predicts that genetic divergences between river basins should be lowest in regions with a wider continental shelf and that regions with similar continental shelf width should have similar genetic divergences. Pygmy perches (Nannoperca australis and Nannoperca 'flindersi') in south-eastern Australia provide an ideal opportunity to test these biogeographic hypotheses. Phylogeographic patterns were examined based on range-wide sampling of 82 populations for cytochrome b and 23 polymorphic allozyme loci. Our results recovered only limited support for our continental shelf width hypothesis, although patterns within Bass clade were largely congruent with reconstructed low sea-level drainage patterns. In addition, we identified several instances of drainage divide crossings, typically associated with low elevational differences. Our results demonstrate high levels of genetic heterogeneity with important conservation implications, especially for declining populations in the Murray-Darling Basin and a highly restricted disjunct population in Ansons River, Tasmania.

  1. A 3D, finite element model for baroclinic circulation on the Vancouver Island continental shelf

    USGS Publications Warehouse

    Walters, R.A.; Foreman, M.G.G.

    1992-01-01

    This paper describes the development and application of a 3-dimensional model of the barotropic and baroclinic circulation on the continental shelf west of Vancouver Island, Canada. A previous study with a 2D barotropic model and field data revealed that several tidal constituents have a significant baroclinic component (the K1 in particular). Thus we embarked on another study with a 3D model to study the baroclinic effects on the residual and several selected tidal constituents. The 3D model uses a harmonic expansion in time and a finite element discretization in space. All nonlinear terms are retained, including quadratic bottom stress, advection and wave transport (continuity nonlinearity). The equations are solved as a global and a local problem, where the global problem is the solution of the wave equation formulation of the shallow water equations, and the local problem is the solution of the momentum equation for the vertical velocity profile. These equations are coupled to the advection-diffusion equation for density so that density gradient forcing is included in the momentum equations. However, the study presented here describes diagnostic calculations for the baroclinic residual circulation only. The model is sufficiently efficient that it encourages sensitivity testing with a large number of model runs. In this sense, the model is akin to an extension of analytical solutions to the domain of irregular geometry and bottom topography where this parameter space can be explored in some detail. In particular, the consequences of the sigma coordinate system used by the model are explored. Test cases using an idealized representation of the continental shelf, shelf break and shelf slope, lead to an estimation of the velocity errors caused by interpolation errors inherent in the sigma coordinate system. On the basis of these estimates, the computational grid used in the 2D model is found to have inadequate resolution. Thus a new grid is generated with increased

  2. Geophysical and Geotechnical Determination of Sand Resources on the Florida Atlantic Continental Shelf: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Finkl, C. W.; Andrews, J. L.; Suthard, B. C.; Robertson, W.

    2007-12-01

    The State of Florida is committed to maintaining beaches to sustain beach width and protect coastal infrastructure. Nearshore sand resources must be identified and cataloged for potential beach nourishment projects in response to sea-level rise and increased tropical storm activity. Given the vast length of Florida coastline, application of a variety of remote sensing techniques are required for measuring large areas in a short amount of time. The study area encompasses a shelf area of about 2,053,220 ha (20,532 km2) from Miami to the Georgia State line (about 653 km shoreline length) and extends up to 27 km offshore to about the 45 m isobath offshore Jacksonville. The continental shelf along the east coast of the Florida peninsula contains a wide range of seafloor environments that lie above the Florida-Hatteras Slope on the shoreface and inner, middle, and outer shelf floors. This study used Airborne Laser Bathymetry (ALB), 3D digital terrain models based on reformatted NOAA bathymetric data, sidescan sonar, and seismic reflection profiling to map seafloor geomorphological conditions that range from coralline-algal reef systems to drowned karst, submerged paleo shorelines (drowned beach ridge plains), and buried paleo channels. Seatruthing of morphosedimentary features is achieved via jetprobe and vibracore surveys in the study of inter-reefal sand troughs, ebb-tidal deltas, transverse bars, shoals, sand waves, ridges, and banks. Preliminary results, which visualize seafloor topography as color-ramped morphoforms, indicate the presence of sedimentary deposits that may constitute viable sand resources for shore protection in the form of beach renourishment. Use of ALB and reformatted NOAA bathymetric data in the form of 3D terrain models permits classification of submarine landform topologies that was heretofore not possible using isobaths. The combination of multiple remote sensing methods showed the spatial distribution of morphosedimentary features and provided

  3. Ambient Noise Cross-correlation Surface Wave Tomography of the Continental United States and Alaska.

    NASA Astrophysics Data System (ADS)

    Bensen, G. D.; McCoy, C.; Ritzwoller, M. H.; Levshin, A. L.; Barmin, M. P.; Shapiro, N. M.

    2006-12-01

    The recent development of surface wave tomography based on ambient noise cross-correlations has provided good results on regional scales and relatively short periods less than 40 seconds. This technique however is viable at longer periods and on the continental scale. We present dispersion maps from ambient noise cross- correlation surface-wave tomography for the continental United States and Alaska between 10 and 60 seconds period. Using up to 2 years of data from over 250 permanent and temporary stations obtained from the IRIS DMC and the Canadian National Seismic Network we compute cross-correlations for all station pairs. An automated dispersion analysis technique is applied to obtain Rayleigh wave group and phase speed curves and unacceptable measurements are removed. Dispersion curves from over 12,500 paths are retained in the continental US and about 1,000 cross-correlation and earthquake paths result in Alaska. We obtain isotropic Rayleigh wave group and phase speed maps on a one half degree grid using a damped ray theoretical inversion. Compared to previous teleseismic earthquake techniques, the short period maps provide better resolution of smaller scale features, especially those in the crust. The improved path coverage also enhances resolution at longer periods compared to previous maps with better delineation of tectonic provinces. In Alaska, limited station coverage and earthquake distribution confine the results to the south-central part of the state. Preliminary azimuthally anisotropic Rayleigh wave tomography maps are also presented together with an assessment of their robustness.

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

    NASA Astrophysics Data System (ADS)

    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

  5. Sediment distribution and transport across the continental shelf and slope under idealized wind forcing

    USGS Publications Warehouse

    Condie, S.A.; Sherwood, C.R.

    2006-01-01

    Resuspension, transport, and deposition of sediments over the continental shelf and slope are complex processes and there is still a need to understand the underlying spatial and temporal dynamical scales. As a step towards this goal, a two-dimensional slice model (zero gradients in the alongshore direction) based on the primitive flow equations and a range of sediment classes has been developed. The circulation is forced from rest by upwelling or downwelling winds, which are spatially uniform. Results are presented for a range of wind speeds and sediment settling speeds. Upwelling flows carry fine sediments (low settling speeds) far offshore within the surface Ekman layer, and significant deposition eventually occurs beyond the shelf break. However, coarser sediments quickly settle out of the deeper onshore component of the circulation, which can lead to accumulation of bottom sediments within the coastal zone. Downwelling flows are more effective at transporting coarse sediments off the shelf. However, strong vertical mixing at the shelf break ensures that some material is also carried into the surface Ekman layer and returned onshore. The concentrations and settling fluxes of coarse sediments decrease offshore and increase with depth under both upwelling and downwelling conditions, consistent with trends observed in sediment trap data. However, finer sediments decrease with depth (upwelling) or reach a maximum around the depth of the shelf break (downwelling). It is shown that under uniform wind conditions, suspended sediment concentrations and settling fluxes decay offshore over a length scale of order τs/ρf|ws|, where τs is the wind stress, ρ the water density, f the Coriolis parameter, and ws is the sediment settling velocity. This scaling applies to both upwelling and downwelling conditions, provided offshore transport is dominated by wind-driven advection, rather than horizontal diffusion.

  6. Unusual bed forms on the North Aleutian Shelf, Bristol Bay, Alaska

    USGS Publications Warehouse

    Schwab, W.C.; Molnia, B.F.

    1987-01-01

    Side-scan sonar records collected over an area of the North Aleutian Shelf, approximately 250 km west of the head of Bristol Bay, Alaska, identified widespread evidence of active sea floor erosion processes, including sediment transport. Thousands of sea floor depressions, many linear and some containing rippled floors, were identified in water depths of 30 to 90 m. The depressions cover approximately 40 percent of the area surveyed. The sea floor depressions are interpreted to be erosional features, and in conjunction with a field of sand waves, exemplify the dynamic nature of the ocenographic processes active on this area of the sea floor. ?? 1987 Springer-Verlag New York Inc.

  7. Unusual bed forms on the North Aleutian Shelf, Bristol Bay, Alaska

    NASA Astrophysics Data System (ADS)

    Schwab, William C.; Molnia, Bruce F.

    1987-12-01

    Side-scan sonar records collected over an area of the North Aleutian Shelf, approximately 250 km west of the head of Bristol Bay, Alaska, identified widespread evidence of active sea floor erosion processes, including sediment transport. Thousands of sea floor depressions, many linear and some containing rippled floors, were identified in water depths of 30 to 90 m. The depressions cover approximately 40 percent of the area surveyed. The sea floor depressions are interpreted to be erosional features, and in conjunction with a field of sand waves, exemplify the dynamic nature of the ocenographic processes active on this area of the sea floor.

  8. Phytoplankton functional community structure in Argentinian continental shelf determined by HPLC pigment signatures

    NASA Astrophysics Data System (ADS)

    Moreno, D. Vega; Marrero, J. Pérez; Morales, J.; García, C. Llerandi; Úbeda, M. G. Villagarcía; Rueda, M. J.; Llinás, O.

    2012-03-01

    The Patagonian Sea in Argentina is known as an area with high primary production and biodiversity. The complex hydrodynamic environment resulting from the interaction between the Malvinas-Brazil convergence and the waters over the continental shelf and slope enhances the development of high chlorophyll concentrations, especially in frontal and coastal areas. The composition, distribution and variability of several phytoplankton functional types (PFTs) derived from diagnostic pigments were studied in relation to the local hydrographical conditions, using data from a research cruise carried out on board the RV Bio Hesperides at the end of the Summer season (March 2008). Phytoplankton cell size and PFT distributions were found to be highly influenced by the physical and chemical characteristics of the studied environments. Thus large cells, mainly diatoms, were the dominant size fraction in the southern frontal areas, where the SubAntarctic Surface Waters (SASW) from the Malvinas Current meet shelf waters. However, other groups of microphytoplankton (mPF), mainly dinoflagellates, were also detected in the shallow waters zone influenced by the tidal regime near the Valdes Peninsula. Picophytoplankton (pPF) was an important contributor to the floristic composition in the southern frontal zones, while nanophytoplankton (nPF) was dominant in the stations located over the continental slope, and in the oligotrophic area near Mar del Plata. The ratio between photoprotective and photosynthetic pigments (PPC:PSC) and the photoprotection index (PI) indirectly provide information about the environment and its effect on the PFTs composition.

  9. Coral forests diversity in the outer shelf of the south Sardinian continental margin

    NASA Astrophysics Data System (ADS)

    Cau, Alessandro; Moccia, Davide; Follesa, Maria Cristina; Alvito, Andrea; Canese, Simonepietro; Angiolillo, Michela; Cuccu, Danila; Bo, Marzia; Cannas, Rita

    2017-04-01

    Ecological theory predicts that heterogeneous habitats allow more species to co-exist in a given area, but to date, knowledge on relationships between habitat heterogeneity and biodiversity of coral forests in the outer shelf and upper slope along continental margins is rather limited. We investigated biodiversity of coral forests from 8 sites spread over two different geomorphological settings (namely, pinnacles vs. canyons) in the outer shelf along Sardinian continental margin. Using a combination of multivariate statistical analyses, we show here that differences in the composition of coral assemblages among contrasting geomorphological settings were not statistically significant, whereas significant differences emerged among sites within similar geomorphologies (i.e. among pinnacles and among canyons). Our results reveal that environmental and bathymetric factors such as sediment coverage, slope of the substrate, terrain ruggedness, bathymetric positioning index and aspect were important drivers of the observed patterns of coral biodiversity, in both settings. Spatial variability of coral forests' biodiversity is affected by environmental factors that act at the scale of each geomorphological setting (i.e. within each pinnacle and canyon) rather than by the contrasting geomorphological settings themselves. This result allows us to suggest that simple categorization of benthic communities according topographically defined habitat is unlikely to be sufficient for addressing conservation purposes.

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

    USGS Publications Warehouse

    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 <5% of the tracklines at depths of ~5 to 470 m below the seafloor. The resulting map reveals the minimum extent of subsea ice-bearing permafrost, which does not extend seaward of 30 km offshore or beyond the 20 m isobath.

  11. Achievements of risk-based produced water management on the Norwegian continental shelf (2002-2008).

    PubMed

    Smit, Mathijs G D; Frost, Tone K; Johnsen, Ståle

    2011-10-01

    In 1996, the Norwegian government issued a White Paper requiring the Norwegian oil industry to reach the goal of "zero discharge" for the marine environment by 2005. To achieve this goal, the Norwegian oil and gas industry initiated the Zero Discharge Programme for discharges of produced formation water from the hydrocarbon-containing reservoir, in close communication with regulators. The environmental impact factor (EIF), a risk-based management tool, was developed by the industry to quantify and document the environmental risks from produced water discharges. The EIF represents a volume of recipient water containing concentrations of one or more substances to a level exceeding a generic threshold for ecotoxicological effects. In addition, this tool facilitates the identification and selection of cost-effective risk mitigation measures. The EIF tool has been used by all operators on the Norwegian continental shelf since 2002 to report progress toward the goal of "zero discharge," interpreted as "zero harmful discharges," to the regulators. Even though produced water volumes have increased by approximately 30% between 2002 and 2008 on the Norwegian continental shelf, the total environmental risk from produced water discharges expressed by the summed EIF for all installations has been reduced by approximately 55%. The total amount of oil discharged to the sea has been reduced by 18% over the period 2000 to 2006. The experience from the Zero Discharge Programme shows that a risk-based approach is an excellent working tool to reduce discharges of potential harmful substances from offshore oil and gas installations.

  12. Small-scale heterogeneity of dissolved gas concentrations in marine continental shelf waters

    NASA Astrophysics Data System (ADS)

    Tortell, Philippe D.

    2005-11-01

    Marine continental shelf waters are known to contribute significantly to the global air-sea fluxes of many gases. Biogeochemical cycles in these regions are highly dynamic, and it is thus often difficult to fully resolve the spatial and temporal distribution of gases in the upper water column. High-frequency, real-time gas measurements with a membrane inlet mass spectrometer (MIMS) reveal significant small-scale heterogeneity in the distribution of CO2, O2/Ar ratios, and dimethylsulfide (DMS) in continental shelf waters of the Eastern Subarctic Pacific Ocean and Bering Sea. Decorrelation length scales for the gas distributions ranged from 15 to 25 km, with significant variability observed on subkilometer spatial scales. In the case of DMS, a number of rapid excursions were observed over distances that would be difficult to resolve with conventional methods. Across most of the sampling transects, CO2 and O2/Ar ratios were correlated, suggesting that biological processes dominated the cycling of these gases. In contrast, DMS concentrations were generally uncoupled from CO2 and O2/Ar, although concentrations often did change sharply across hydrographic and productivity fronts. The results presented here suggest that previous field studies may have underestimated the true spatial variability of dissolved gases (DMS in particular) in surface waters of highly dynamic marine systems. High-frequency gas measurements have significant promise for unraveling complex biogeochemical cycles in these regions.

  13. Geological evolution history of petroliferous basins on continental shelf of China

    SciTech Connect

    Lidesheng

    1983-03-01

    Coastlines of China are about 18,000 km (11,118 mi) in length, and their aggregate continental shelf area within 200 m (656 ft) seawater depth is more than one million km/sup 2/ (386,102 mi/sup 2/). Recent geophysical exploration work and numerous petroleum drilling records are available and give a general understanding of the geological evolution history of these petroliferous basins. There are two tectonic types of basins distributed on the continental shelf areas: the tectonic types of Bohai Gulf, South Yellow Sea, and Beibu Gulf basins are the intraplate polyphase rifting-depression basins; the East China Sea, Pearl River mouth, and Yingge Sea basin are the epicontinental rifting-depression basins. They are believed to be extensional in origin. Because of the severe convergence of Indian plate with Eurasia plate, there has been produced NNE-spreading movement of the South China Sea basin, which permits two triple junctions on its northern margins. The extension mechanism could be derived from the rising of an upper mantle plume to produce two NNE weak fracturing zones, resulting in a series of intraplate and epicontinental rifting-depression basins. The depositional models and sea-level variations of these basins are interpreted from the drilling records and seismic profiles. They can be explained by the tectono-eustatic changes in sea level and Cenozoic climate changes of China.

  14. Outer continental shelf and reservoir analysis and consultant programs in the Gulf of Mexico

    SciTech Connect

    Clarke, T.G.

    1981-01-01

    The Outer Continental Shelf Lands Act Amendments of 1978 was established by the Congress for the orderly collection of oil and gas reserves in the federal offshore lands. Basic geologic, geophysical, and engineering data are provided to the USGS by offshore lessees and operators. An independent in-house analysis of the individual reservoirs of each field for reserves estimates is presented. Each reserve area is revised as new data are received from development wells. Oil and gas reserve estimates are expected to change as the field and reservoir analysis program continues. In 1977, an inventory program was initiated for all fields in the Gulf of Mexico. Contracts were awarded to 6 industry consultants for 64 oil and gas field reserves studies. Concerted in-house effort supplemented the consultant effort. A viable field and reservoir analysis program is an important contributory function to lease sale evaluation, development and production rate control, unitization and enhanced recovery, and the Outer Continental Shelf Information Program for the states and locally affected areas. 24 references.

  15. Community structure of rhodolith-forming beds on the central Brazilian continental shelf

    NASA Astrophysics Data System (ADS)

    Villas-Boas, Alexandre B.; Riosmena-Rodriguez, Rafael; de Oliveira Figueiredo, Marcia Abreu

    2014-03-01

    The community structure of rhodoliths beds in the central Brazilian continental shelf was studied under the hypothesis that nongeniculate coralline algae are the major contributors of the individual rhodoliths. Samples were collected from five localities within a single area at 17-18 m depth. At each locality, rhodoliths were collected in 10 random quadrat samples along a 20-m transect. Our results show that dead cores of rhodoliths were significantly composed by nongeniculate coralline red algae rather than bryozoans, corals, or inorganic material. The live outer layers of the rhodoliths are composed mainly of 7 species of nongeniculate red coralline algae ( Lithophyllum coralline, L. johansenii, L. depressum, L. stictaeformis, Neogoniolithon brassica- florida, Spongites fruticosus, and Lithothamnion muellerii) associated with other encrusting organisms such as bryozoans, sponges, corals, barnacles, and Peyssonnelia red algae. Significant differences were found in the proportion of Lithophyllum species in relation to other red coralline algae found in this study. Our results show that on the Brazilian continental shelf, the rhodolith-forming species are quite higher in size than in any other studied areas in the world. There was no difference in the proportion of live-to-dead rhodolith materials, suggesting an old bed deposit. Also, the amount of calcium carbonate material in the specimens is relevant to take in account in terms of the CO2 balance worldwide.

  16. Production and turnover of suspended organic detritus in the coastal water of the southeastern continental shelf: Progress report, June 1, 1988--May 31, 1989

    SciTech Connect

    Pomeroy, L.R.

    1988-12-01

    As one of a group cooperative research projects on the southeastern continental shelf, this project is concerned with specific aspects of microbial processes and related phenomena that influence the fate of particulate organic materials naturally produced on the continental shelf. The projects of other grantees encompass the dynamics of the shelf from physical oceanography to biology. The integrated information as a whole will be useful in understanding the potential fate of a variety of energy related pollutants that may be released in continental shelf waters. With a focus on events on the southeastern continental shelf and their boundary conditions (Gulf Stream dynamics; river and estuarine processes), we form an interface between studies of oceanic processes such as GOFS and WOCE, and studies of processes at the land-sea boundary. During this grant year we completed two research cruises on the southeastern continental shelf on R/V Blue Fin, and processed data from previous cruises.

  17. Benthic Foraminiferal Census Data from Louisiana Continental Shelf Cores, Gulf of Mexico

    USGS Publications Warehouse

    Osterman, Lisa E.; Kelly, Wendy S.; Ricardo, John P.

    2009-01-01

    An area of oxygen-depleted bottom- and subsurface-water (hypoxia = dissolved oxygen < 2 mg/L-1) occurs seasonally on the Louisiana Shelf near the Mississippi River. The area of hypoxia, also known as the 'dead zone', forms when spring and early summer freshwater flow from the Mississippi River supplies a large amount of nutrients to the shelf while creating a freshwater lens, or cap, above the shelf water. The excess nutrients cause phytoplankton blooms in the shallow shelf water. After the bloom ceases, the organic material sinks in the water column and uses up oxygen during decomposition. Thus, the subsurface waters become oxygen depleted. The seasonal dead zone exists until a reduction in freshwater flow, or overturning by storms, allows mixing of the water column to restore normal oxygen conditions (Rabalais and others, 1994, 1996; Rabalais, 2002). Since systematic measurement of the extent of the dead zone began in 1985, the overall pattern indicates that the area of the dead zone is increasing (Rabalais and Turner, 2001; Turner and others, 2005). Several studies have concluded that the expansion of the Louisiana Shelf dead zone is related to increased nutrients (primarily nitrogen, but possibly also phosphorous) in the Mississippi River drainage basin and is responsible for the degradation of Gulf of Mexico marine habitats (Goolsby and others, 2001). This paper presents the benthic foraminiferal data from 10 sediment cores collected from the Continental Shelf of Louisiana (table 1), obtained as part of an initiative to investigate the geographic and temporal extent of hypoxia prior to 1985 in the Gulf of Mexico. Benthic foraminifers provide a method to track the development of hypoxia prior to 1985 (Blackwelder and others, 1996; Sen Gupta and others, 1996). Previous work (Osterman, 2003) has shown statistically that the relative occurrence of three low-oxygen-tolerant species represents the modern seasonal Louisiana hypoxia zone. The cumulative percentage of

  18. Seabed erodibility variations on the Louisiana continental shelf before and after the 2011 Mississippi River flood

    NASA Astrophysics Data System (ADS)

    Xu, K.; Corbett, D. R.; Walsh, J. P.; Young, D.; Briggs, K. B.; Cartwright, G. M.; Friedrichs, C. T.; Harris, C. K.; Mickey, R. C.; Mitra, S.

    2014-08-01

    Erodibility is critical to the sediment resuspension process but has not been measured systematically in large river-dominated muddy continental shelves before. During early summer of 2011, the Mississippi River experienced a major flood event. This flood provided a unique opportunity to examine how shelf seabed erodibility responded to a large river flood, and the ultimate fate of flood deposition is important to geological and biogeochemical processes (e.g., stratal formation, carbon sequestration). A total of 106 sediment cores were collected on the Louisiana shelf during five cruises in 2010 and 2011, and a new dataset was used to evaluate the response of the seabed to the recent conditions. The localized flood deposit was mainly within tens of kilometers of river sources, and little sediment accumulated on the middle Louisiana shelf. Seabed erodibility was measured using a dual-core Gust Erosion Microcosm System. The erodibility of sediment collected in April 2011 exceeded that for August 2010 and August 2011. The springtime increase in erodibility seemed to be related to the recent presence of energetic waves that mobilized the seabed. Erodibility was highest on the inner shelf southwest of Atchafalaya Bay, intermediate on the middle shelf, lowest in the Mississippi Canyon, and highly variable on the Mississippi subaqueous delta. These spatial patterns were influenced by proximity to river sources, flood-deposit thicknesses, intensity of wave-driven bed stresses, and bioturbation. The flood-deposit thickness itself, however, was not sufficient to explain all the spatial variations of erodibility after the peak of the Mississippi flood. Comparing values to published data, the depth-varying erodibility on the Louisiana shelf was close to the "low erodibility" level for the York River of Virginia, and similar to the data collected from Baltimore Harbor in Maryland and the main stem of upper Chesapeake Bay. Our findings promote understanding of the resuspension

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

    PubMed

    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.

  20. Freshwater outflow and Subtropical Convergence influence on phytoplankton biomass on the southern Brazilian continental shelf

    NASA Astrophysics Data System (ADS)

    Ciotti, Áurea M.; Odebrecht, Clarisse; Fillmann, Gilberto; Moller, Osmar O.

    1995-12-01

    The present study discusses the role of different continental shelf water masses on inorganic nutrient levels and on phytoplankton biomass along the southern Brazilian coast during October 1987 and September 1988. In this productive area, variability of phytoplankton biomass has been related to the seasonal latitudinal displacement of the Subtropical Convergence and to the freshwater outflow of La Plata River and Patos Lagoon. Very distinct precipitation rates, as a consequence of the ENSO (El Nin˜o-Southern Oscillation) cycle, preceding the two sampled periods of this study, allowed a first evaluation of the impact of this event on freshwater outflow and shelf phytoplankton biomass. The amount of chlorophyll in shelf waters was directly related to nutrients supplied by the Coastal Water (i.e. freshwater outflow), Subtropical and Subantarctic Waters. Comparing the results of this study with previous cruises performed in the area, it was found that high chl a concentrations are common features during periods of elevated precipitation rates. Apart from nutrient input by freshwater and the consequent changes in the vertical profiles of density, the extreme precipitation rates are also associated with different wind patterns, which, in turn, control the presence of particular water masses in the euphotic zone. Our results suggest that ENSO events have an important impact on the variability of phytoplankton production, and thus should affect biogeochemical cycles in the southern Brazilian coastal areas.

  1. Recent sedimentology and ocean dynamics of the Western Nigerian continental shelf and coastline

    NASA Astrophysics Data System (ADS)

    Ihenyen, A. E.

    2003-04-01

    The Western Nigerian continental shelf lies approximately between longitudes 2°42 ' and 5°00 ' E. It is a relatively gently sloping and narrow shelf, incised by two canyons, Avon and Mahin. The beaches between longitudes 2°42 ' and 4°30 ' E are sandy while Mahin Mud Beach is further to the east. The western sand deposits extend about 12 km offshore and are separated into two coast-parallel sand bodies by a narrow dark grey silt-mud facies, 1-2 km wide. Lekki lagoon is situated inland of the sandy beach-barrier systems near Lagos. This low energy tidal and freshwater lagoon is slowly silting up with river sediment; bottom sediment characteristics reflect influence of both fluvial transport and weak tidal current patterns. Mahin Mud Beach is starved of sand due to a lack of longshore drift as a result of the two canyons siphoning off arenaceous material. It is thus highly vulnerable to erosion and flooding. The two coast-parallel sand bodies in the west, combined with four preserved drowned coral reef systems, suggest that the post-Pleistocene sea level rise along the Western Nigerian shelf was punctuated by a number of sea level stillstands.

  2. Holocene paleoenvironmental change in inner continental shelf sediments, Southeastern Mediterranean, Egypt

    NASA Astrophysics Data System (ADS)

    Kholeif, Suzan E. A.

    2010-04-01

    The palynology of marine sediments from CS Core taken on the inner continental shelf offshore Nile Delta, Southeastern Mediterranean, has been used to reconstruct the regional paleoenvironment during the past 5380 yr BP. This includes detailing the relative abundances of dinoflagellate cysts, acritarchs, prasinophytes and other algal spores, microforaminiferal linings, crustacean eggs, and fungal hyphae. The composition and ecological interpretation of the dinoflagellate cyst assemblages, acritarchs and other non-pollen palynomorphs is discussed. Concentrations of dinoflagellate cysts range from 5926 to 416 specimens per gram of sediment, and the most common taxa were Lingulodinium machaerophorum, Operculodinium centrocarpum, Operculodiniumisraelianum, Polysphaeridium zoharyi,Spiniferites ramosus,Spiniferites mirabilis, Echinidinium transparantum and Protoperidinum nudum. The assemblages are like those on the Tunisian Shelf, but with more protoperidinioid cysts. It is concluded that the shelf sediments were deposited under suboxic bottom water conditions. A high nutrient supply to the area during the deposition of the CS Core sediments is evidenced by the strong significant correlation ( R-values) between the nutrient-demanding species, L. machaerophorum and P. zoharyi, toxic species, total phosphorous percent (TP%) and total organic carbon percent (TOC%). These data suggest that Nile discharge from the Damietta Channel increased during the past 5830 yr BP and was accompanied by increases in fresh or brackish water algae and fungal hyphae.

  3. Processes controlling the characteristics of the surficial sand sheet, U.S. Atlantic outer continental shelf

    USGS Publications Warehouse

    Knebel, H. J.

    1981-01-01

    A review of recent data on the velocity of bottom currents, the frequency of bottom-sediment movement, the kinds and amounts of suspended sediments in near-bottom waters, and the acoustic and sedimentary features of subbottom strata indicates that the characteristics of the ubiquitous sand sheet on the Atlantic outer continental shelf of the United States have been controlled by a variety of past and present processes. Although these processes collectively have had a widespread effect on the characteristics of the sand sheet, the relative importance of each process changes geographically. On Georges Bank, late Pleistocene glaciations along with modern tidal currents and the regional circulation pattern have played a dominant role. On the Middle Atlantic shelf, ancestral rivers, former near-shore processes, and modern wind- and wave-generated currents are important factors. On the South Atlantic shelf, the sediments reflect subaerial weathering, erosion or nondeposition over or near hardgrounds, and the production of biogenic carbonate. Other processes such as the movement of water masses, bioturbation, and bottom fishing probably have affected the sediments in all areas. A knowledge of the various factors affecting the sand sheet is fundamental to an understanding of its general geologic history and to the paleoenvironmental interpretation of ancient sand strata. ?? 1981.

  4. Relaxation from upwelling: The effect on dissolved oxygen on the continental shelf

    NASA Astrophysics Data System (ADS)

    Send, Uwe; Nam, Sunghyun

    2012-04-01

    Continental shelves in upwelling regimes are subject to sequences of upwelling and relaxation events, each on timescales of order 1 week typically. These episodes have pronounced impacts on the temperature and density structure on the shelves and also on the along-shore and cross-shore flow regimes. It had previously been demonstrated that relaxation phases advect warm water along shore (poleward) from regions of less intense upwelling, thus adding to the heat balance in upwelling locations and providing a rectification of oscillating heat fluxes. In the current paper it is shown that relaxations also modify the dissolved oxygen (DO) budget of the lower layers. On a narrow shelf, this provides enhanced DO values due to near-surface exposure, while on a wide shelf decreased DO concentrations are created due to oxygen consumption on the inner shelf. The resulting variations along the coast can lead to along-shore advection of high or low DO during a relaxation event. Observations are presented from moorings off San Diego and Del Mar, which show large departures from density-correlated DO values during relaxations and which support the proposed mechanisms.

  5. Freshwater Influence Over the South Brazilian Continental Shelf: Indications From Foraminiferal Species Dominance

    NASA Astrophysics Data System (ADS)

    Eichler, P. P.; Sen Gupta, B. K.; Eichler, B. B.; Campos, E. J.

    2005-05-01

    The 250-km-long Patos Lagoon covers an area of 10,360 km2 along the coastal plain of Rio Grande do Sul in southern Brazil. To the north, the 40-km-long Laguna estuarine system along the Santa Catarina coastline is essentially a series of choked coastal lagoons, with elliptical cells connected to the ocean via a single long and narrow channel. We examined the distribution of benthic foraminifera in samples collected from two continental-shelf transects, labeled the Albardäo transect (32° 58'S) and Santa Marta Cape transect (28° 34'S), in order to track the influence of the Patos Lagoon and the Laguna estuarine system in the dilution of shelf waters. In the Albardäo transect, we notice the dominance of Bulimininella elegantissima and Bolivina striatula live individuals in the shallower stations (15-42 m). These low-oxygen tolerant species are also found in muddy sediments of the Patos lagoon and near the mouth of the Plata River; their presence in shelf sediments indicates continental runoff in the region. Very large individuals of the agglutinated species Arenoparella mexicana and Gaudryina exilis (present in brackish waters Patos Lagoon) are found in water depths 19-54 m, also suggesting a strong and deep freshwater influence. At the 90-m isobath, (1) the species diversity shows a rise, and (2) larger agglutinated species and Buccela peruviana, a temperate/cold-water hyaline species, are occasionally present. B. peruviana is characteristic of assemblages influenced by the Malvinas Current, and indicates the presence of Sub-Antarctic Shelf Water (SASW). In contrast, the dominant species at 53 m on the Santa Marta Cape transect are Bulimina marginata and Pseudononion atlanticum. These species, together with small individuals of Arenoparella mexicana and Gaudryina exilis, show that the Santa Marta Cape area is under a major influence of Subtropical Shelf Waters (STSW), and that fresh-water influence is minor. The assemblage from the deepest stations on this

  6. Structural Mapping and Geomorphology of Ireland's Southwest Continental Shelf Using High Resolution Sonar

    NASA Astrophysics Data System (ADS)

    Bowden, S.; Wireman, R.

    2016-02-01

    Bathymetric surveys were conducted on the continental shelf off the southwest coast of County Cork, Ireland by the Marine Institute of Ireland, the Geological Survey of Ireland, and the INFOMAR project. Data were collected from July 2006 through September 2014 using a Kongsberg EM2040 multibeam echosounder aboard the R/Vs Celtic Voyager and Keary, and a Kongsberg EM1002 on the R/V Celtic Explorer. Sonar data were post-processed with CARIS HIPS and SIPS 9.0 to create 2D and 3D bathymetric and backscatter intensity surfaces with a resolution of 1 m. The offshore study site is part of the 286 Ma western Variscian orogenic front and has several massive outcrops, exhibiting 5 to 20 m of near-vertical relief. These outcrops were structurally mapped and relatively aged, and exhibit significant folding, rotation, tilting, and joint systems. Google Earth, ArcGIS, and previous terrestrial studies were used to further analyze how geomorphology is controlled by seafloor composition and structural features. Rock type and age were interpreted by comparing fracture analysis of the joints and fold trends to similar onshore outcrops documented previously, to determine an age of 416-299 Ma for the shelf's outcropping strata and associated structural features. The oldest features observed are regional anticlines and synclines containing Upper Devonian Old Red Sandstone and Lower Carboniferous shales. Within the shale layers are NE-SW plunging parasitic chevron folds. Jointing is observed in both sandstone and shale layers and is superimposed on chevron folding, with cross joints appearing to influence shallow current patterns. Rotation of the regional folds is the youngest structural feature, as both the parasitic folds and joint systems are warped. Our study shows that high resolution sonar is an effective tool for offshore structural mapping and is an important resource for understanding the geomorphology and geologic history of submerged outcrops on continental shelf systems.

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

    PubMed

    Ruiz Etcheverry, L A; Saraceno, M; Piola, A R; Strub, P T

    2016-04-01

    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.

  8. Bryozoan faunal composition and community structure from the continental shelf off Cap de Creus (Northwestern Mediterranean)

    NASA Astrophysics Data System (ADS)

    Madurell, T.; Zabala, M.; Dominguez-Carrió, C.; Gili, J. M.

    2013-10-01

    Bryozoan specimens obtained in 2009-2010 from the continental shelf off Cap de Creus (Northwestern Mediterranean) were studied. Samples were collected using a Rauschert sled at depths ranging from 61 to 225 m. Bryozoans were present in all 26 samples examined, although they were only abundant in 20 of them. A total of 113 species of Bryozoa were identified (2 Ctenostomata, 90 Cheilostomata and 21 Cyclostomata), most of them are well known to science, although a few of the species have barely or never been cited in the Mediterranean Sea (Hincksinoflustra octodon, Alderina imbellis, Escharella immersa, Neolagenipora collaris and Escharina johnstoni), or are currently poorly described (Lagenipora lepralioides). The species Palmicellaria aff. aviculifera (sensu Gautier, 1957) is redescribed, for which the new name of Palmiskenea gautieri is proposed. Species richness, abundance and biomass were linked to the availability of suitable substrates. Multivariate analysis in relation to environmental data showed that the spatial distribution of the bryozoan species was related to the sediment type. Samples from areas dominated by silt and sandy sediments showed few or no bryozoans, whereas coarse sands and gravels presented higher diversity, abundance and biomass. Within the depth range studied, the faunistic composition of the bryozoan assemblages was similar for the whole continental shelf off Cap de Creus. The bulk of bryozoans was found near the canyon rim. This is related to the proximity of the submarine canyon and its associated hydrological processes. The high diversity and abundance of the bryozoan community located on the circalittoral and shelf-edge off Cap de Creus reflect the presence of critical habitats that are essential for the design of marine protected areas.

  9. Denitrification in continental shelf sediments has major impact on the oceanic nitrogen budget

    NASA Astrophysics Data System (ADS)

    Christensen, John P.; Murray, James W.; Devol, Allan H.; Codispoti, Louis A.

    1987-06-01

    Denitrification rates in sediments within the oxygen deficient waters off Mexico and from the Gulf of Maine were investigated on the basis of interstitial nutrient profiles. Nitrate fluxes into the sediments were calculated from gradients across the sediment-water interface and vertical molecular diffusion coefficients and averaged 0.151 (Mexico) and 0.0920 (Gulf of Maine) pmol NO-3 cm-2 s-1. These are minimum values, since these gradients may have been underestimated. In the Gulf of Maine, bottom water irrigation by macrobenthos increases the nitrate supply well above this estimate. In addition, only 15-22% of the expected ammonium is present in Gulf of Maine sediments perhaps because of removal by a rapid coupling of nitrification with denitrification. This large apparent loss of the regenerated ammonium appears to be ubiquitous in shelf sediments with oxygenated bottom water. The global denitrification rate in continental shelf sediments was reassessed to be >50 Tg N yr-1 (1 Tg = 1012 g), demonstrating that sediments are an important sink for oceanic nitrogen. Globally, current nitrogen losses from the oceans may exceed inputs by 60-90 Tg N yr-1. Over the glacial-interglacial cycle the global sedimentary denitrification rate probably varied commensurately with the changing continental shelf area. An oscillating oceanic nitrogen budget over these time scales could occur given the sequence of (1) scouring and dumping of terrestrial nitrogen into the oceans during glacial advance, (2) removal of oceanic combined nitrogen to the atmosphere by denitrification following glacial retreat, and (3) reincorporation of this N into terrestrial biomass during the interglacial period.

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

    NASA Astrophysics Data System (ADS)

    Ruiz Etcheverry, L. A.; Saraceno, M.; Piola, A. R.; Strub, P. T.

    2016-04-01

    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.

  11. Characteristics and Preservation of Event Beds on the Continental Shelf off the Waipaoa River, New Zealand

    NASA Astrophysics Data System (ADS)

    Gerald, L. E.; Kuehl, S. A.

    2006-12-01

    Exceptional storm events initiating oceanic flood sedimentation can provide a disproportionately large fraction of sediment discharged to the shelf. Event-layer producing perterbations, such as cyclones, extreme rainfall events and earthquakes can thus punctuate normal marine sedimentation with large additions of terrestrial sediment with unique textural and geochemical characteristics. The continental shelf adjacent to the small, high-yield Waipaoa River, New Zealand, provides high-resolution marine records of such events and affords a unique opportunity to examine their temporal and spatial variations in relation to natural and anthropogenic change. Regional geochemical and physical characteristics from over 200 sediment cores collected during a January 2005 MARGINS Source-to-Sink cruise aboard the R/V Kilo Moana on the continental shelf off the Waipaoa River were used to help identify sites of likely preservation of storm event layers. A suite of eight prominently layered box cores was subsequently selected and sampled for detailed geochemical and radioisotopic analyses to elucidate sediment characteristics within and between layers. X-radiographs and physical property data from a Geotek multi-sensor core logger, along with Lead-210, grain size, carbon analyses and deposit location were used to identify and describe layer characteristics and reveal the origins of these deposits. Preliminary results indicate that distinct, X-ray opaque, event layers have coincident low Lead-210 spikes, high percent fine sediments and unique carbon (C:N and δ13C) signatures. Cyclone Bola (1988), the most severe tropical storm on record in this region, serves as a modern benchmark comparison to other storm events recorded downcore. These distinct storm event layer characteristics have the potential to clarify questions about the magnitude of specific events within the catchment as well as regional changes in frequency and/or intensity over time.

  12. How well do we know the infaunal biomass of the continental shelf?

    NASA Astrophysics Data System (ADS)

    Powell, Eric N.; Mann, Roger

    2016-03-01

    Benthic infauna comprise a wide range of taxa of varying abundances and sizes, but large infaunal taxa are infrequently recorded in community surveys of the shelf benthos. These larger, but numerically rare, species may contribute disproportionately to biomass, however. We examine the degree to which standard benthic sampling gear and survey design provide an adequate estimate of the biomass of large infauna using the Atlantic surfclam, Spisula solidissima, on the continental shelf off the northeastern coast of the United States as a test organism. We develop a numerical model that simulates standard survey designs, gear types, and sampling densities to evaluate the effectiveness of vertically-dropped sampling gear (e.g., boxcores, grabs) for estimating density of large species. Simulations of randomly distributed clams at a density of 0.5-1 m-2 within an 0.25-km2 domain show that lower sampling densities (1-5 samples per sampling event) resulted in highly inaccurate estimates of clam density with the presence of clams detected in less than 25% of the sampling events. In all cases in which patchiness was present in the simulated clam population, surveys were prone to very large errors (survey availability events) unless a dense (e.g., 100-sample) sampling protocol was imposed. Thus, commercial quantities of surfclams could easily go completely undetected by any standard benthic community survey protocol using vertically-dropped gear. Without recourse to modern high-volume sampling gear capable of sampling many meters at a swath, such as hydraulic dredges, biomass of the continental shelf will be grievously underestimated if large infauna are present even at moderate densities.

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

    USGS Publications Warehouse

    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).

  14. Distribution of DDT and other persistent organic contaminants in Canyons and on the continental shelf off the central California coast.

    PubMed

    Hartwell, S Ian

    2008-04-01

    Sediment samples were collected to delineate the distribution of contaminants along the central California coast. Sampling included a variety of Canyons and shelf/slope areas to evaluate contaminant transport patterns and potential delivery to Canyons and the continental slope to a depth of 1200 m. Sediments were collected and analyzed for organic contaminants using standard techniques of the NOAA National Status and Trends Program (NS&T). DDT is distributed on the shelf within a zone of fine-grained sediments between Half Moon and Monterey Bays. DDT was found at higher concentrations in Ascension, Año Nuevo, and Monterey/Soquel Canyons than in Pioneer and Carmel Canyons, the Gulf of the Farallones, or the continental slope. The Monterey Bay watershed appears to be the primary source of DDT. In contrast, PAHs and PCBs on the shelf appear to be derived primarily from San Francisco Bay. DDT appears to be delivered to the deep ocean via the Canyons more than from cross-shelf sediment transport. Sediment budget estimates for the continental shelf north of Monterey Bay need further refinement and more data to account for the movement of material from Monterey Bay onto the shelf.

  15. Paleoecology of late-glacial terrestrial deposits with in situ conifers from the submerged continental shelf of western canada

    NASA Astrophysics Data System (ADS)

    Lacourse, Terri; Mathewes, Rolf W.; Fedje, Daryl W.

    2003-09-01

    Extensive portions of the continental shelf off the coast of British Columbia were subaerially exposed during Late Wisconsinan deglaciation due to lowering of relative sea level by as much as 150 m. Paleoecological analyses were conducted at two sites on the emergent continental shelf where terrestrial surfaces with in situ conifers are preserved. The woody plant remains confirm that, during the latest period of subaerial exposure, terrestrial vegetation was established on the continental shelf. Microscopic identification of fossil wood, and analyses of pollen and plant macrofossils from the associated paleosols and overlying shallow pond sediments indicate that productive Pinus contorta-dominated communities with abundant Alnus crispa and ferns grew on the shelf adjacent to and on the Queen Charlotte Islands around 12,200 14C yr B.P. Dwarf shrubs including Salix and Empetrum, and herbaceous plants such as Heracleum lanatum and Hippuris vulgaris, were also important components of the shelf vegetation. Near northern Vancouver Island, mixed coniferous forests dominated by Pinus contorta with Picea, Tsuga spp., Alnus spp., and ferns occupied the shelf at 10,500 14C yr B.P.

  16. Observations of storm and river flood-driven sediment transport on the northern California continental shelf

    USGS Publications Warehouse

    Ogston, A.S.; Cacchione, D.A.; Sternberg, R.W.; Kineke, G.C.

    2000-01-01

    In the winter of 1996-1997, three bottom-boundary layer tripods were placed in an alongshelf array on the northern California continental shelf off Eureka, CA in 60-65-m water depth. During the observation period, multiple storms and river discharge events occurred, as well as the largest flood on record since 1964. Suspended-sediment concentration at all three sites fluctuated in response to both wave resuspension and advection of river-derived sediments. However, considerable spatial differences in low-frequency currents and suspended-sediment concentration were observed at the three sites. Sediment flux vectors calculated during periods of high suspended-sediment concentration suggest a convergence of sediment flux coincident with the center of recent flood deposits. Suspended-sediment concentrations observed at the two northern tripod sites following the large flood reached magnitudes typical of fluid mud (> 10 g/l) in a thin near-bed layer. The net sediment flux during the single three-day event was two orders of magnitude larger than any other event during the winter, and accounted for seven times the flux observed over an entire year (1995-1996). A conceptual model for the advection of sediment to the mid shelf is proposed in which river plume sediments are trapped on the inner shelf either due to a weak front or the rapid input of sediment from a confined plume, and form a thin layer of fluid mud. The fluid mud subsequently is transported seaward due to gravitational forcing. The measured sediment concentration and velocity profiles on the shelf provide strong evidence to support this conclusion. (C) 2000 Elsevier Science Ltd.

  17. Hydrographic and particle distributions over the Palos Verdes continental shelf: Spatial, seasonal and daily variability

    USGS Publications Warehouse

    Jones, B.H.; Noble, M.A.; Dickey, T.D.

    2002-01-01

    Moorings and towyo mapping were used to study the temporal and spatial variability of physical processes and suspended particulate material over the continental shelf of the Palos Verdes Peninsula in southwestern Los Angeles, California during the late summer of 1992 and winter of 1992-93. Seasonal evolution of the hydrographic structure is related to seasonal atmospheric forcing. During summer, stratification results from heating of the upper layer. Summer insolation coupled with the stratification results in a slight salinity increase nearsurface due to evaporation. Winter cooling removes much of the upper layer stratification, but winter storms can introduce sufficient quantities of freshwater into the shelf water column again adding stratification through the buoyancy input. Vertical mixing of the low salinity surface water deeper into the water column decreases the sharp nearsurface stratification and reduces the overall salinity of the upper water column. Moored conductivity measurements indicate that the decreased salinity persisted for at least 2 months after a major storm with additional freshwater inputs through the period. Four particulate groups contributed to the suspended particulate load in the water column: phytoplankton, resuspended sediments, and particles in treated sewage effluent were observed in every towyo mapping cruise; terrigenous particles are introduced through runoff from winter rainstorms. Terrigenous suspended particulate material sinks from the water column in <9 days and phytoplankton respond to the stormwater input of buoyancy and nutrients within the same period. The suspended particles near the bottom have spatially patchy distributions, but are always present in hydrographic surveys of the shelf. Temporal variations in these particles do not show a significant tidal response, but they may be maintained in suspension by internal wave and tide processes impinging on the shelf. ?? 2002 Elsevier Science Ltd. All rights reserved.

  18. Observed wintertime tidal and subtidal currents over the continental shelf in the northern South China Sea

    NASA Astrophysics Data System (ADS)

    Li, Ruixiang; Chen, Changsheng; Xia, Huayong; Beardsley, Robert C.; Shi, Maochong; Lai, Zhigang; Lin, Huichan; Feng, Yanqing; Liu, Changjian; Xu, Qichun; Ding, Yang; Zhang, Yu

    2014-08-01

    Synthesis analyses were performed to examine characteristics of tidal and subtidal currents at eight mooring sites deployed over the northern South China Sea (NSCS) continental shelf in the 2006-2007 and 2009-2010 winters. Rotary spectra and harmonic analysis results showed that observed tidal currents in the NSCS were dominated by baroclinic diurnal tides with phases varying both vertically and horizontally. This feature was supported by the CC-FVCOM results, which demonstrated that the diurnal tidal flow over this shelf was characterized by baroclinic Kelvin waves with vertical phase differences varying in different flow zones. The northeasterly wind-induced southwestward flow prevailed over the NSCS shelf during winter, with episodic appearances of mesoscale eddies and a bottom-intensified buoyancy-driven slope water intrusion. The moored current records captured a warm-core anticyclonic eddy, which originated from the southwestern coast of Taiwan and propagated southwestward along the slope consistent with a combination of β-plane and topographic Rossby waves. The eddy was surface-intensified with a swirl speed of >50 cm/s and a vertical scale of ˜400 m. In absence of eddies and onshore deep slope water intrusion, the observed southwestward flow was highly coherent with the northeasterly wind stress. Observations did not support the existence of the permanent wintertime South China Sea Warm Current (SCSWC). The definition of SCSWC, which was based mainly on thermal wind calculations with assumed level of no motion at the bottom, needs to be interpreted with caution since the observed circulation over the NSCS shelf in winter included both barotropic and baroclinic components.

  19. Carbon and Nutrient Dynamics and Fluxes in the Northwest European Continental Shelf Sea

    NASA Astrophysics Data System (ADS)

    Humphreys, M. P.; Moore, M. M.; Achterberg, E. P.; Griffiths, A.; Smilenova, A.; Chowdhury, M. Z. H.; Kivimae, C.; Hartman, S. E.; Hopkins, J.; Woodward, M. S.

    2016-02-01

    Despite covering only about 5 % of the Earth's ocean surface area, shallow marginal seas support 15-20 % of global primary productivity, and are the key interface between the land and the open ocean. They are therefore of critical importance to marine biogeochemical cycles, and may have a significant role in ocean uptake and storage of anthropogenic carbon dioxide (CO2). However, their behaviour is significantly more complex than that of the open ocean, because of the greater heterogeneity of the underlying physical, chemical and biological processes acting upon them. Detailed case-studies of individual regions are therefore essential in order to accurately evaluate their net global influence. The Northwest European continental shelf, in particular the Celtic Sea, was the target of extensive hydrographic sampling from March 2014 to September 2015, as part of the UK Shelf Seas Biogeochemistry research programme (UK-SSB). Here, we use the UK-SSB carbonate chemistry and macronutrient measurements to describe the seasonal biogeochemical cycle in the Celtic Sea. The 100-200 m deep water column proceeds from vertically well mixed in winter to a strongly stratified two-layer structure over spring-summer. The associated seasonal cycle in near-surface biological activity removes dissolved inorganic carbon (DIC) and nutrients, some of which are then exported into the deeper layer. Calculating total inventories of the biogeochemical variables throughout the seasonal cycle, we determine seasonal net CO2 uptake and investigate whether non-Redfieldian macronutrient uptake and remineralisation processes occur. Combining these results with estimated water exchange across the shelf edge further allows us to quantify the strength of the `shelf pump' sink for atmospheric (and anthropogenic) CO2.

  20. Marine species distribution shifts on the U.S. Northeast Continental Shelf under continued ocean warming

    NASA Astrophysics Data System (ADS)

    Kleisner, Kristin M.; Fogarty, Michael J.; McGee, Sally; Hare, Jonathan A.; Moret, Skye; Perretti, Charles T.; Saba, Vincent S.

    2017-04-01

    The U.S. Northeast Continental Shelf marine ecosystem has warmed much faster than the global ocean and it is expected that this enhanced warming will continue through this century. Complex bathymetry and ocean circulation in this region have contributed to biases in global climate model simulations of the Shelf waters. Increasing the resolution of these models results in reductions in the bias of future climate change projections and indicates greater warming than suggested by coarse resolution climate projections. Here, we used a high-resolution global climate model and historical observations of species distributions from a trawl survey to examine changes in the future distribution of suitable thermal habitat for various demersal and pelagic species on the Shelf. Along the southern portion of the shelf (Mid-Atlantic Bight and Georges Bank), a projected 4.1 °C (surface) to 5.0 °C (bottom) warming of ocean temperature from current conditions results in a northward shift of the thermal habitat for the majority of species. While some southern species like butterfish and black sea bass are projected to have moderate losses in suitable thermal habitat, there are potentially significant increases for many species including summer flounder, striped bass, and Atlantic croaker. In the north, in the Gulf of Maine, a projected 3.7 °C (surface) to 3.9 °C (bottom) warming from current conditions results in substantial reductions in suitable thermal habitat such that species currently inhabiting this region may not remain in these waters under continued warming. We project a loss in suitable thermal habitat for key northern species including Acadian redfish, American plaice, Atlantic cod, haddock, and thorney skate, but potential gains for some species including spiny dogfish and American lobster. We illustrate how changes in suitable thermal habitat of important commercially fished species may impact local fishing communities and potentially impact major fishing ports

  1. Pelagic fishes in the Marguerite Bay region of the West Antarctic Peninsula continental shelf

    NASA Astrophysics Data System (ADS)

    Donnelly, Joseph; Torres, Joseph J.

    2008-02-01

    Pelagic fishes in the Marguerite Bay region of the western Antarctic Peninsula (WAP) continental margin were sampled using a 10-m 2 MOCNESS as part of the Southern Ocean Global Ocean Ecosystems Dynamics (SO GLOBEC) program. Sixty-two tows were completed during the course of four cruises conducted during the austral fall and winter, 22 each during the austral fall, and 9 each during the austral winter. Six thousand and sixty individuals of 34 species representing 13 families were collected in the fall, while 672 individuals of 22 species from 10 families were collected in the winter. Nearly all of the notothenioid specimens collected (families Artedraconidae, Bathydraconidae, Channichthyidae, and Nototheniidae) were either larvae or young juveniles (0-2 years). Conversely, except for the paralepidid Notolepis coatsi and the occasional juveniles of the bathylagid Bathylagus antarcticus, the gonostomatid Cyclothone kobayashii, or the myctophid Electrona antarctica, the non-notothenioid specimens collected were predominantly adults. In the fall, the nototheniids Pleuragramma antarcticum and Trematomus scotti, and the myctophid E. antarctica numerically dominated the overall assemblage, collectively accounting for 89.7% of the total catch. In the winter, E. antarctica, Cyclothone microdon, and B. antarcticus were the numerical dominants, each contributing 14-20% of the total. The pelagic fish community within the Marguerite Bay region of the WAP continental shelf is a variable mixture of mesopelagic and neritic fauna. At one extreme is an oceanic assemblage exhibiting high-diversity indices and characterized by the genera Electrona, Gymnoscopelus, Protomyctophum, Bathylagus, Cyclothone, and Notolepis. Minor components of this group include numerous less common mesopelagic genera (e.g., Paradiplospinus, Lampanyctus, Benthalbella, Borostomias) and the occasional larval/juvenile notothenioid. At the other extreme is a coastal assemblage with low-diversity indices dominated

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

    NASA Astrophysics Data System (ADS)

    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

  3. Metal elements in the bottom sediments of the Changjiang Estuary and its adjacent continental shelf of the East China Sea.

    PubMed

    Cao, Lu; Hong, Gi Hoon; Liu, Sumei

    2015-06-15

    The metal elements (Al, Fe, Mn, Cr, Co, Ni, Cu, Zn, As, Pb and Ca) in the bottom sediment of the Changjiang Estuary and its adjacent continental shelf of the East China Sea were studied to map their spatial distribution and to assess their potential risk to the marine biota. These metal concentrations except Ca were generally higher in the inner shelf and northeastern part, and were found to decrease from the coast to the offshore of the Changjiang Estuary. Sedimentary Ca was most abundant in the outer shelf sediments and decreased in inner shelf. Arsenic (As) appeared to be contaminated due to economic development from 1980s in the inner shelf overall, but the potential ecological risk from the selected metals was low in the coastal sea off the Changjiang.

  4. Model for the formation of longshore sand ridges on the Continental Shelf: The interaction of internal waves and the bottom topography

    SciTech Connect

    Restrepo, J.M.; Bona, J.L.

    1994-01-05

    Longshore sand ridges are frequently observed to occur on the continental shelf where the overlying ocean is stratified. This study formulates a model for the formation and evolution of three-dimensional longshore sand ridges on the continental shelf. The model is based on the interaction of interfacial, weakly nonlinear waves in a stratified ocean with the sedimentary bottom topography.

  5. Shelf basin exchange along the Siberian continental margin: Modification of Atlantic Water and Lower Halocline Water

    NASA Astrophysics Data System (ADS)

    Bauch, Dorothea; Cherniavskaia, Ekaterina; Timokhov, Leonid

    2016-09-01

    Salinity and stable oxygen isotope (δ18O) evidence shows a modification of Atlantic Water in the Arctic Ocean by a mixture of sea-ice meltwater and meteoric waters along the Barents Sea continental margin. On average no further influence of meteoric waters is detectable within the core of the Atlantic Water east of the Kara Sea as indicated by constant δ18O, while salinity further decreases along the Siberian continental slope. Lower Halocline Waters (LHW) may be divided into different types by Principal Component Analysis. All LHW types show the addition of river water and an influence of sea-ice formation to a varying extent. The geographical distribution of LHW types suggest that the high salinity type of LHW forms in the Barents and Kara seas, while other LHW types are formed either in the northwestern Laptev Sea or from southeastern Kara Sea waters that enter the northwestern Laptev Sea through Vilkitsky Strait. No further modification of LHW is seen in the eastern Laptev Sea but the distribution of LHW-types suggest a bifurcation of LHW at this location, possibly with one branch continuing along the continental margin and a second branch along the Lomonosov Ridge. We see no pronounced distinction between onshore and offshore LHW types, as the LHW components that are found within the halocline over the basin also show a narrow bottom-bound distribution at the continental slope that is consistent with a shelf boundary current as well as a jet of water entering the western Laptev Sea from the Kara Sea through Vilkitsky Strait.

  6. Abbot Ice Shelf, the Amundsen Sea Continental Margin and the Southern Boundary of the Bellingshausen Plate Seaward of West Antarctica

    NASA Astrophysics Data System (ADS)

    Cochran, J. R.; Tinto, K. J.; Bell, R. E.

    2014-12-01

    The Abbot Ice Shelf extends 450 km along the coast of West Antarctica between 103°W and 89°W and straddles the boundary between the Bellingshausen Sea continental margin, which overlies a former subduction zone, and Amundsen Sea rifted continental margin. Inversion of NASA Operation IceBridge airborne gravity data for sub-ice bathymetry shows that the western part of the ice shelf, as well as Cosgrove Ice Shelf to the south, are underlain by a series of east-west trending rift basins. The eastern boundary of the rifted terrain coincides with the eastern boundary of rifting between Antarctica and Zealandia and the rifts formed during the early stages of this rifting. Extension in these rifts is minor as rifting quickly jumped north of Thurston Island. The southern boundary of the Cosgrove Rift is aligned with the southern boundary of a sedimentary basin under the Amundsen Embayment continental shelf to the west, also formed by Antarctica-Zealandia rifting. The shelf basin has an extension factor, β, of 1.5 - 1.7 with 80 -100 km of extension occurring in an area now ~250 km wide. Following this extension early in the rifting process, rifting centered to the north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf has been tectonically quiescent and has primarily been shaped though subsidence, sedimentation and the passage of the West Antarctic Ice Sheet back and forth across it. The former Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to its incorporation into the Antarctic Plate at ~62 Ma. During the latter part of its existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence between the Bellingshausen and Antarctic plates east of 102°W. Seismic reflection and gravity data show that this convergence is expressed by an area of intensely deformed sediments beneath the continental slope from 102°W to 95°W and

  7. 210Pb balance and implications for particle transport on the continental shelf, U.S. Middle Atlantic Bight

    USGS Publications Warehouse

    Bacon, M.P.; Belastock, Rebecca A.; Bothner, Michael H.

    1994-01-01

    Supply of 210Pb to the continental shelf off the northeastern United States is dominated by the deposition from the atmosphere, the rate of which is reliably known from previously published work. Excess 210Pb inventories in the shelf sediments show accumulations that are nearly in balance with the supply, even in areas of relict sands where it is believed that no net accumulation of sediment presently occurs. The 210Pb distributions in shelf and slope water indicate that the two-way fluid exchange at the shelf-slope front and the net transport in the alongshore flow make comparatively small contributions to the shelf 210Pb budget. The near balance between supply and decay of 210Pb on the shelf implies a limit to the particle export flux. It is concluded that the export of particulate organic carbon does not exceed 60 g m−2 y−1 (∼25% of primary production) and is probably lower. The hypothesis is advanced that fine particulate matter introduced to the continental shelf is detained in its transit of the shelf because of bioturbational trapping in the sediment due to benthic animals. Distributions of 210Pb in suspended particulate matter and in the fine fraction of shelf sediments suggest that the average fine particle must undergo several cycles of deposition-bioturbation-resuspension-redeposition and requires a number of decades for its transit and ultimate export from the shelf. Thus, only the most refractory organic matter is likely to be exported.

  8. The climatology of the Alaska Beaufort Sea shelf told by brittle star population dynamics

    NASA Astrophysics Data System (ADS)

    Ravelo, A.; Konar, B.; Bluhm, B.; Iken, K.

    2016-02-01

    Brittle stars are a key component of Arctic benthic shelf systems due to their high standing stock, dominance in abundance over all other epibenthic organisms, and as prey for higher trophic organisms. On the Alaskan Arctic shelves, the circumboreal species Ophiura sarsii and Ophiocten sericeum are the dominant brittle stars with densities of up to 260 ind. m-2 and 20 ind. m-2, respectively. Although present across all Alaska Arctic shelves these specie have a segregated distribution; O. sarsii dominates the more productive Chukchi and western Beaufort Sea shelves and O. sericeum dominates the more river influenced Beaufort Sea shelf east of 150°W. Despite the pervasiveness of these species, little is known of their population parameters, the stability of their respective distribution patterns over time, or the factors that contribute to their geographic distribution. The objective of this study was to analyze the population size structure, growth, productivity, and distribution of the two species. Our results indicate that O. sarsii grows faster and lives longer than O. sericeum, and at equal body size, O. sarsii has significantly higher organic mass compared to O. sericeum. Compared to early records, we observed a shift in the distribution of the two species on the Alaska Beaufort Sea shelf over the past 40 years. Changes in intensity and frequency of easterly wind events over the western Beaufort Sea may be a key factor driving the distribution expansion of O. sericeum and the retreat of O. sarsii towards the west in this region. Considering the significant difference in these species' growth rate and organic mass content, the consequences of this distribution shift for brittle star predators and benthic community remineralization may be substantial.

  9. Chlorophyll distribution in continental shelf sediments off West Palm Beach, Florida and west end, Bahamas

    NASA Astrophysics Data System (ADS)

    Heffernan, John J.; Gibson, Robert A.

    1983-07-01

    Measurements were made of chlorophyll- a and phaeophytin- a in calcareous sediments along transects off the east coast of Florida (75-190 m) and the west coast of Grand Bahama Island (170-300 m). Solvent partitioning showed that chlorophyll- a concentrations never exceeded 0·1 mg m -2 at either location, most as degradation products. Total pigment concentrations (chlorophyll and phaeopigments) ranged from 0·18-1·83 mg m -2 in sediments off Grand Bahama Island and 2·50 to 20·65 mg m -2 off West Palm Beach. Pigments, expressed per gram dry weight of sediments, increased with depth across the Florida Continental Shelf. This is probably due to differences in sediment character between near-shore and off-shore sediments.

  10. Self-advection of density perturbations on a sloping continental shelf

    SciTech Connect

    Ping-Tung Shaw; Csanady, G.T.

    1983-05-01

    Bottom water movement on the continental shelf is modeled by the nonlinear interaction between longshore bottom geostrophic flow and the density field. Bottom geostrophic velocity, subject to linear steady momentum equations with linear bottom friction, can be generated by along-isobath density variations over a sloping bottom. At the same time, the density field is slowly advected by the velocity field. Away from boundary layers, the interplay is governed by Burgers' equation, which shows the formation and self-propulsion of strong density gradients along an isobath. The direction of propagation of a dense water blob is to have shallow water on the right- (left-) hand side facing downstream in the Northern (Southern) Hemisphere. The propagation of a light water blob is opposite to that of a dense water blob.

  11. Drowned forests and archaeology on the continental shelf of British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Fedje, Daryl W.; Josenhans, Heiner

    2000-02-01

    We have used high-resolution digital terrain imaging and sea-floor sampling to reveal drowned late glacial to early postglacial terrestrial landscapes at water depths as great as 150 m. In situ tree stumps and shellfish-rich paleobeaches are present on these drowned landscapes. A stone tool encrusted with barnacles and bryozoa was recovered from a drowned delta flood plain now 53 m below mean sea level. This is the first tangible evidence that the formerly subaerial broad banks of the western North American Continental Shelf may have been occupied by humans in earliest Holocene and possibly late-glacial time. Analyses (14C) of the drowned terrestrial and intertidal deposits were used to refine the local sea-level curve, which shows very rapid change within this glacio-isostatically dynamic region.

  12. Evidence for a palaeo-subglacial lake on the Antarctic continental shelf

    PubMed Central

    Kuhn, Gerhard; Hillenbrand, Claus-Dieter; Kasten, Sabine; Smith, James A.; Nitsche, Frank O.; Frederichs, Thomas; Wiers, Steffen; Ehrmann, Werner; Klages, Johann P.; Mogollón, José M.

    2017-01-01

    Subglacial lakes are widespread beneath the Antarctic Ice Sheet but their control on ice-sheet dynamics and their ability to harbour life remain poorly characterized. Here we present evidence for a palaeo-subglacial lake on the Antarctic continental shelf. A distinct sediment facies recovered from a bedrock basin in Pine Island Bay indicates deposition within a low-energy lake environment. Diffusive-advection modelling demonstrates that low chloride concentrations in the pore water of the corresponding sediments can only be explained by initial deposition of this facies in a freshwater setting. These observations indicate that an active subglacial meltwater network, similar to that observed beneath the extant ice sheet, was also active during the last glacial period. It also provides a new framework for refining the exploration of these unique environments. PMID:28569750

  13. Random-access technique for modular bathymetry data storage in a continental shelf wave refraction program

    NASA Technical Reports Server (NTRS)

    Poole, L. R.

    1974-01-01

    A study was conducted of an alternate method for storage and use of bathymetry data in the Langley Research Center and Virginia Institute of Marine Science mid-Atlantic continental-shelf wave-refraction computer program. The regional bathymetry array was divided into 105 indexed modules which can be read individually into memory in a nonsequential manner from a peripheral file using special random-access subroutines. In running a sample refraction case, a 75-percent decrease in program field length was achieved by using the random-access storage method in comparison with the conventional method of total regional array storage. This field-length decrease was accompanied by a comparative 5-percent increase in central processing time and a 477-percent increase in the number of operating-system calls. A comparative Langley Research Center computer system cost savings of 68 percent was achieved by using the random-access storage method.

  14. Rippled scour depressions on the inner continental shelf off central California

    USGS Publications Warehouse

    Cacchione, David A.; Drake, David E.; Grant, William D.; Tate, George B.

    1984-01-01

    Side-scan sonar records taken during the recent Coastal Ocean Dynamics Experiment (CODE) show elongate, shore-normal tippled depressions of low relief on the inner continental shelf off central California between Bodega Bay and Point Arena. These features extend up to 2 kin from the coast into water depths of up to 65 m. The proposed mechanism for their generation is storm- generated bottom currents associated with coastal downwelling during the late fall and winter which scour the surficial fine-sand sediment and expose the coarser-sand substrate in the depressions. The zones of most intense erosion and the irregular spacing of the features may be controlled by submerged rock ledges and other prominent coastal features. The large straight-crested ripples within the depres- sions (heights to 40 cm; wavelengths to 1.7 m) are probably formed by large-amplitude, long-period surface waves generated by winter storms.

  15. Temperatures of quartz cementation in Jurassic sandstones from the Norwegian continental shelf -- evidence from fluid inclusions

    SciTech Connect

    Walderhaug, O. )

    1994-04-01

    Recent studies of fluid inclusions in quartz overgrowths have shown quartz cementation to have taken place at temperatures within the range 60--145 C in several sandstones from the North Sea and offshore mid-Norway (Malley et al. 1986; Konnerup-Madsen and Dypvik 1988; Burley et al. 1989; Walderhaug 1990; Ehrenberg 1990; Saigal et al. 1992; Nedkvitne et al. 1993). This study aims at determining whether these results are typical for quartz cementation of sandstones by presenting homogenization temperatures for 274 aqueous and 366 hydrocarbon inclusions in quartz overgrowths from Jurassic reservoir sandstones on the Norwegian continental shelf, and by reviewing previously published fluid-inclusion data. Possible explanations for different ranges of homogenization temperatures in different sandstones are also discussed, and possible sources of quartz cement and the effect of hydrocarbon emplacement on quartz cementation are considered.

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

    SciTech Connect

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

    1991-10-01

    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.

  17. Ophiuroids (Echinodermata; Ophiuroidea) of biogenic habitats on the continental shelf of New Zealand.

    PubMed

    Mills, V Sadie; O'Hara, Timothy D

    2013-02-13

    The taxonomy of ophiuroids collected in 2009 and 2011, from biogenic habitats across the New Zealand continental shelf, is reviewed. Ophionereis novaezelandiae Mortensen, 1936, and its junior synonym Ophionereis terba Baker & Devaney, 1981 from South-Eastern Australia, is now recognised as a distinct species, and has been removed from synonymy with Ophionereis fasciata Hutton, 1872. Ophiacantha abyssicola var. otagoensis Fell, 1958 is also recognised as a distinct species and has been removed from synonymy with Ophiacantha brachygnatha Clark H L, 1928. Amphiura eugeniae var. latisquama Mortensen, 1924 is raised to species rank and Amphioplus longirima Fell, 1952 treated as a synonym of A. latisquama. Ophiolycus farquhari McKnight, 2003 is transferred to the genus Ophiologimus. The diagnostic characters of several other species are reviewed and colour descriptions and images are included where available. The tropical species Ophiacantha longidens Lyman, 1878, Ophiotreta valenciennesi (Lyman, 1879) and Ophiobyrsa intorta (Koehler, 1922) are reported from New Zealand waters for the first time.

  18. Arctic geodynamics: Continental shelf and deep ocean geophysics. ERS-1 satellite altimetry: A first look

    NASA Technical Reports Server (NTRS)

    Anderson, Allen Joel; Sandwell, David T.; Marquart, Gabriele; Scherneck, Hans-Georg

    1993-01-01

    An overall review of the Arctic Geodynamics project is presented. A composite gravity field model of the region based upon altimetry data from ERS-1, Geosat, and Seasat is made. ERS-1 altimetry covers unique Arctic and Antarctic latitudes above 72 deg. Both areas contain large continental shelf areas, passive margins, as well as recently formed deep ocean areas. Until ERS-1 it was not possible to study these areas with satellite altimetry. Gravity field solutions for the Barents sea, portions of the Arctic ocean, and the Norwegian sea north of Iceland are shown. The gravity anomalies around Svalbard (Spitsbergen) and Bear island are particularly large, indicating large isostatic anomalies which remain from the recent breakup of Greenland from Scandinavian. Recently released gravity data from the Armed Forces Topographic Service of Russia cover a portion of the Barents and Kara seas. A comparison of this data with the ERS-1 produced gravity field is shown.

  19. High-Resolution geophysical data from the inner continental shelf at Vineyard Sound, Massachusetts

    USGS Publications Warehouse

    Andrews, Brian D.; Ackerman, Seth D.; Baldwin, Wayne E.; Foster, David S.; Schwab, William C.

    2013-01-01

    The U.S. Geological Survey (USGS) and the Massachusetts Office of Coastal Zone Management (CZM) have mapped approximately 340 square kilometers of the inner continental shelf in Vineyard Sound, Massachusetts, under a cooperative mapping program. The geophysical data collected between 2009 and 2011 by the U.S. Geological Survey as part of this program are published in this report. The data include (1) swath bathymetry from interferometric sonar, (2) acoustic backscatter from sidescan sonar, and (3) seismic-reflection profiles from a chirp subbottom profiler. These data were collected to support research on the influence of sea-level change and sediment supply on coastal evolution and sediment transport processes and to provide baseline seabed characterization information required for management of coastal and offshore resources within the coastal zone of Massachusetts.

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

    NASA Astrophysics Data System (ADS)

    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. Modeling the number of bids received for outer continental shelf leases by Poisson-type models

    SciTech Connect

    Bruckner, L.A.; Nachtsheim, C.J.

    1983-07-01

    Since 1954, the U.S. federal government has held hydrocarbon lease sales for areas on the Outer Continental Shelf (OCS). The U.S. DOE is charged with developing lease sale policies designed to increase competition on the offered tracts. Increased competition has been assumed synonymous with increased number of bids (NOB). To study the influence of alternative bidding systems on the number of bids received, a mixed Poisson-type model has previously been employed. The authors show why this model is not statistically supportable. A truncated model is proposed and is shown to be statistically justified for the number of solo bids over all sales and marginally supported for the number of joint bids on sales before the joint-bidding ban.

  2. Large sand waves on the Atlantic Outer Continental Shelf around Wilmington Canyon, off Eastern United States

    USGS Publications Warehouse

    Knebel, H. J.; Folger, D.W.

    1976-01-01

    New seismic-reflection data show that large sand waves near the head of Wilmington Canyon on the Atlantic Outer Continental Shelf have a spacing of 100-650 m and a relief of 2-9 m. The bedforms trend northwest and are asymmetrical, the steeper slopes being toward the south or west. Vibracore sediments indicate that the waves apparently have formed on a substrate of relict nearshore sediments. Although the age of the original bedforms is unknown, the asymmetry is consistent with the dominant westerly to southerly drift in this area which has been determined by other methods; the asymmetry, therefore, is probably modern. Observations in the sand-wave area from a submersible during August 1975, revealed weak bottom currents, sediment bioturbation, unrippled microtopography, and lack of scour. Thus, the asymmetry may be maintained by periodic water motion, possibly associated with storms or perhaps with flow in the canyon head. ?? 1976.

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

    USGS Publications Warehouse

    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.

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

    SciTech Connect

    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.

  5. Subsurface geology of upper Tertiary and Quaternary deposits, coastal Louisiana and adjacent Continental Shelf

    SciTech Connect

    McFarlan, E. Jr.; Leroy, D.O.

    1988-09-01

    Upper Tertiary and Quaternary deposits thicken seaward from a feather edge on the outcrop in the uplands of southern Louisiana to more than 7000 ft (2134 m) beneath the middle continental shelf. Through a study of cores and cuttings from 100 control wells and electric-log pattern correlations from 350 water and petroleum industry wells with seismic corroboration in the offshore area, these deposits have been divided into six major time-stratigraphic units, four of which correlate to outcropping terraces. This investigation presents a regional stratigraphic framework of the major upper Tertiary and Quaternary units from their updip pinch-outs in and beneath the terraced uplands, into the subsurface, across the coastal plain to the Louisiana offshore area.

  6. Evidence for a palaeo-subglacial lake on the Antarctic continental shelf.

    PubMed

    Kuhn, Gerhard; Hillenbrand, Claus-Dieter; Kasten, Sabine; Smith, James A; Nitsche, Frank O; Frederichs, Thomas; Wiers, Steffen; Ehrmann, Werner; Klages, Johann P; Mogollón, José M

    2017-06-01

    Subglacial lakes are widespread beneath the Antarctic Ice Sheet but their control on ice-sheet dynamics and their ability to harbour life remain poorly characterized. Here we present evidence for a palaeo-subglacial lake on the Antarctic continental shelf. A distinct sediment facies recovered from a bedrock basin in Pine Island Bay indicates deposition within a low-energy lake environment. Diffusive-advection modelling demonstrates that low chloride concentrations in the pore water of the corresponding sediments can only be explained by initial deposition of this facies in a freshwater setting. These observations indicate that an active subglacial meltwater network, similar to that observed beneath the extant ice sheet, was also active during the last glacial period. It also provides a new framework for refining the exploration of these unique environments.

  7. Oil and gas developments in Atlantic Coastal Plain and outer continental shelf in 1984

    SciTech Connect

    Giordano, A.C.; Amato, R.V.

    1985-10-01

    Exploratory drilling on the Atlantic outer continental shelf remained at about the same level as in 1983. Two wells were spudded in the Baltimore Canyon Trough. Three were completed and announced as dry holes, one in a world record water depth of 6,952 ft (2,119 m). Onshore in the Atlantic coastal plain, a dry hole was drilled in Colleton County, South Carolina, and another well, drilled in 1982 in Lee County, North Carolina, was plugged and abandoned as a dry hole. North Atlantic Lease Sale 82, which was to be held in 2 parts, was cancelled in late 1984. The International Court of Justice determined the United States-Canada boundary line in the North Atlantic. Seismic data acquisition decreased 41% below the 1983 level to 7,223 line-mi(11,625 line-km).

  8. Oil and gas developments in Atlantic coastal plain and outer continental shelf in 1984

    SciTech Connect

    Giordano, A.C.; Amato, R.V.

    1985-10-01

    Exploratory drilling on the Atlantic outer continental shelf remained at about the same level as in 1983. Two wells were spudded in the Baltimore Canyon Trough. Three were completed and announced as dry holes, one in a world record water depth of 6952 ft (2119 m). Onshore in the Atlantic coastal plain, a dry hole was drilled in Colleton County, South Carolina, and another well, drilled in 1982 in Lee County, North Carolina, was plugged and abandoned as a dry hole. North Atlantic Lease Sale 82, which was to be held in 2 parts, was cancelled in late 1984. The International Court of Justice determined the US-Canada boundary line in the North Atlantic. Seismic data acquisition decreased 41% below the 1983 level to 7223 line-mi (11,625 line-km). 3 figures, 2 tables.

  9. Framework for oil-spill response on the Alaskan OCS (Outer Continental Shelf)

    SciTech Connect

    Allen, G.H.; Hale, D.A.; Prentki, R.T.

    1984-01-01

    OCS Report 84-0021 is a compilation of mandated Federal regulations for those responsible for an oil spill on the Alaskan Outer Continental Shelf (OCS). It specifies lessee responsibilities for pollution prevention and control; requirements for inspections and reports, pollution-control materials and equipment, oil-spill-contingency plans, annual drills and the training of personnel. Industry oil-spill-response organizations are discussed as well the mechanism for industry contingency planning. Federal responsibilities for oil-spill response are delineated and the contact agencies are specified. The report concludes with a discussion of cleanup policies and techniques and a final section listing Federal funds available for compensation for oil-spill damage.

  10. Geophysical and sampling data from the inner continental shelf: Northern Cape Cod Bay, Massachusetts

    USGS Publications Warehouse

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

    2010-01-01

    The U.S. Geological Survey (USGS) and the Massachusetts Office of Coastal Zone Management (CZM) have cooperated to map approximately 480 km2 of the inner continental shelf in northern Cape Cod Bay, MA. This report contains geophysical and sampling data collected by the USGS during five research cruises between 2006 and 2008. The geophysical data include (1) swath bathymetry from interferometric sonar, (2) acoustic backscatter from interferometric and sidescan sonars, and (3) subsurface stratigraphy and structure from seismic-reflection profilers. The seafloor sampling data include sediment samples, photographs, and video tracklines. These spatial data support research on the influence that sea-level change and sediment supply have on coastal evolution and help identify the type, distribution, and quality of subtidal marine habitats within the coastal zone of Massachusetts.

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

    SciTech Connect

    Not Available

    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.

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

    SciTech Connect

    Not Available

    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.

  13. Evidence for a palaeo-subglacial lake on the Antarctic continental shelf

    NASA Astrophysics Data System (ADS)

    Kuhn, Gerhard; Hillenbrand, Claus-Dieter; Kasten, Sabine; Smith, James A.; Nitsche, Frank O.; Frederichs, Thomas; Wiers, Steffen; Ehrmann, Werner; Klages, Johann P.; Mogollón, José M.

    2017-06-01

    Subglacial lakes are widespread beneath the Antarctic Ice Sheet but their control on ice-sheet dynamics and their ability to harbour life remain poorly characterized. Here we present evidence for a palaeo-subglacial lake on the Antarctic continental shelf. A distinct sediment facies recovered from a bedrock basin in Pine Island Bay indicates deposition within a low-energy lake environment. Diffusive-advection modelling demonstrates that low chloride concentrations in the pore water of the corresponding sediments can only be explained by initial deposition of this facies in a freshwater setting. These observations indicate that an active subglacial meltwater network, similar to that observed beneath the extant ice sheet, was also active during the last glacial period. It also provides a new framework for refining the exploration of these unique environments.

  14. Resistance to hurricane disturbance of an epifaunal community on the continental shelf off North Carolina

    NASA Astrophysics Data System (ADS)

    Kirby-Smith, William W.; Ustach, Joseph

    1986-10-01

    Hurricane Diana was stalled over the continental shelf of central North Carolina on 11-13 September 1984 in the vicinity of a previously studied epifaunal community (30 m depth). Two research cruises following the hurricane used still camera and TV transects to obtain data which allowed an evaluation of stormrelated effects on taxa of algae, sponges, corals, echinoderms and fish. Analysis of 35-mm slides suggested no effects attributable to the hurricane except observations of damaged coral heads and dead mussels. Analysis of television transects indicated no storm related changes from the previous study in frequency of occurrence of large epibenthic taxa. Hurricane damage was much less than anticipated and it is hypothesized that these coral reef-type communities are adapted to or structured by strong bottom currents generated by the frequent passage of gales and that the passage of hurricanes causes little additional stress.

  15. Geology and geochemistry of gas-charged sediment on Kodiak Shelf, Alaska

    USGS Publications Warehouse

    Hampton, M.A.; Kvenvolden, K.A.

    1981-01-01

    Methane concentrations in some sediment cores from the Kodiak Shelf and adjacent continental slope increase with depth by three or four orders of magnitude and exceed the solubility in water at ambient conditions. Acoustic anomalies in seismic-reflection records imply that methane-rich sediment is widespread. Molecular composition of hydrocarbon gases and isotopic composition of methane indicate gas formation by shallow biogenic processes. Stratigraphic positions of acoustic anomalies in Quaternary glacial and posttransgressive sediments suggest that these units are likely sources of gas. A seep along the extension of a fault may be gas venting from a deeper thermogenic source. ?? 1981 A.M. Dowden, Inc.

  16. 75 FR 38937 - Fisheries of the Exclusive Economic Zone Off Alaska; Northern Rockfish and Pelagic Shelf Rockfish...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-07-07

    ... Participating in the Entry Level Rockfish Fishery in the Central Regulatory Area of the Gulf of Alaska AGENCY... pelagic shelf rockfish (PSR) for trawl catcher vessels participating in the entry level rockfish fishery... in the entry level rockfish fishery in the Central Regulatory Area of the GOA. DATES: Effective...

  17. Image-based continental shelf habitat mapping using novel automated data extraction techniques

    NASA Astrophysics Data System (ADS)

    Seiler, Jan; Friedman, Ariell; Steinberg, Daniel; Barrett, Neville; Williams, Alan; Holbrook, Neil J.

    2012-08-01

    We automatically mapped the distribution of temperate continental shelf rocky reef habitats with a high degree of confidence using colour, texture, rugosity and patchiness features extracted from images in conjunction with machine-learning algorithms. This demonstrated the potential of novel automation routines to expedite the complex and time-consuming process of seabed mapping. The random forests ensemble classifier outperformed other tree-based algorithms and also offered some valuable built-in model performance assessment tools. Habitat prediction using random forests performed most accurately when all 26 image-derived predictors were included in the model. This produced an overall habitat prediction accuracy of 84% (with a kappa statistic of 0.793) when compared to nine distinct habitat classes assigned by a human annotator. Predictions for three habitat classes were all within the 95% confidence intervals, indicating close agreement between observed and predicted habitat classes. Misclassified images were mostly unevenly, partially or insufficiently illuminated and came mostly from rugged terrains and during the autonomous underwater vehicle's obstacle avoidance manoeuvres. The remaining misclassified images were wrongly or inconsistently labelled by the human annotator. This study demonstrates the suitability of autonomous underwater vehicles to effectively sample benthic habitats and the ability of automated data handling techniques to extract and reliably process large volumes of seabed image data. Our methods for image feature extraction and classification are repeatable, cost-effective and well suited to studies that require non-extractive and/or co-located sampling, e.g. in marine reserves and for monitoring the recovery from physical impacts, e.g. from bottom fishing activities. The methods are transferable to other continental shelf areas and to other disciplines such as seabed geology.

  18. Soft-sediment crustacean diversity and distribution along the Portuguese continental shelf

    NASA Astrophysics Data System (ADS)

    Sampaio, Leandro; Mamede, Renato; Ricardo, Fernando; Magalhães, Luísa; Rocha, Hélder; Martins, Roberto; Dauvin, Jean-Claude; Rodrigues, Ana Maria; Quintino, Victor

    2016-11-01

    This study analyzed the crustacean diversity, distribution and relationship with environmental factors in the western and the southern Portuguese continental shelf, between 10 and 200 m depth. A total of 10,639 specimens belonging to 242 taxa from 90 families were identified, mostly amphipods (55.8% of the total taxa). The mysid Gastrosaccus spinifer and the amphipods Socarnes erythrophthalmus and Cheirocratus sundevallii were the most abundant and the amphipods Ampelisca brevicornis, Leucothoe incisa and Autonoe spiniventris were the most frequent species. The highest abundance and diversity was found in coarser sediments with up to 306 individuals per 0.1 m2. Alpha diversity ranged from 1 to 28 sp./0.1 m2. Moreover, this study confirmed six previously doubtful first records and added an additional 19 new records to the Portuguese fauna. The results also confirmed the Portuguese coast as a transition zone of mixed Atlantic and Mediterranean faunas and exposed a noticeable North African and Macaronesian influence. A multivariate analysis based on the abundance of crustaceans revealed six affinity groups characterized by: (a) C. sundevallii, Guernea (Guernea) coalita and Sarsinebalia cristoboi on very coarse sands; (b) G. spinifer, Nototropis falcatus and Pontocrates arenarius on coarse sands; (c) Othomaera othonis, Processa modica modica and Animoceradocus semiserratus on heterogeneous medium sands; (d) A. brevicornis, Urothoe pulchella and Necalianassa truncata on fine sands; (e) Ampelisca pectenata, Bodotria scorpioides and Astacilla dilatata on heterogeneous fine sands and (f) Callianassa subterranea, Ampelisca tenuicornis and Ampelisca typica on muddy fine sands. Sediment grain-size and depth were the variables best related to the benthic crustacean spatial distribution patterns along the Portuguese continental shelf.

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

    PubMed Central

    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

  20. Seismic refraction studies on the acoustic basement in the continental shelf of the East Sea, Korea

    SciTech Connect

    Kim, K.Y.; Kim, H.J.; Han, S.J.

    1996-12-31

    Critically refracted seismic waves can be utilized in elucidation of physical properties of a high-impedance acoustic basement, where reflection methods are not effective in general. Quality factor Q was estimated for the high-impedance acoustic basement in the continental shelf of the East Sea, Korea. Various pre-processing steps for the estimation included static correction for gun delay, geometric correction, data interpolation, and Fourier transform. Based on the constant Q model, quality factor was computed for the uppermost layer within the basement using the spectral-ratio method. The computation gives values between 10.4 and 13.6, which fall under the range for water-saturated clastic sedimentary rocks. Using seismic events refracted from the layer boundaries within the acoustic basement in the study area, sedimentary layers were successfully defined. A short window AGC (automatic gain control) is an effective tool to reveal existence of the refraction boundaries. Based on a model for horizontal layers, refraction velocity and thickness were computed for each layer under a short seismic line of 3.75 km long in the continental shelf. From four distinct linear events, three layers were interpreted under the water body of 150 m deep. The computed thickness is 275 m for the top layer and 200 m for the middle one. The corresponding refraction velocities are approximately 3,900 m/s and 5,100 m/s, respectively. The refraction event from the top of the lowest layer suggests that its phase velocity is greater than 6,400 m/s.

  1. Sedimentary and geochemical characterization and provenance of the Portuguese continental shelf soft-bottom sediments

    NASA Astrophysics Data System (ADS)

    Martins, R.; Azevedo, M. R.; Mamede, R.; Sousa, B.; Freitas, R.; Rocha, F.; Quintino, V.; Rodrigues, A. M.

    2012-03-01

    Grain-size and geochemical analyses for soft-bottom sediments from the Portuguese continental shelf are used to determine their provenance and to identify the main factors governing the sediment distribution patterns. The deeper areas of the northwestern and central sectors of the Portuguese shelf and most of its southwestern sector are covered by fine and very fine sands. Coarse deposits are found in the inner and middle shelf of the northernmost sector and immediately south of the Nazaré and Setúbal canyons, while muddy sediments are restricted to areas located off the mouths of major rivers (Douro and Tagus mud patches). In contrast, the southern shelf corresponds to a low energy environment receiving most of its sediment supply from the Guadiana River. As a result, an expressive mud patch is developed off the Guadiana estuarine system. The application of multivariate analysis to geochemical data allowed the classification of the studied samples into four main groups: (a) a group of mud deposits constituted by detrital clay minerals and authigenic iron-manganese oxyhydroxides, displaying high contents for organic matter and for most major and trace elements; (b) a group of biogenic carbonate-rich sands showing high CaO, Sr and U contents which is well represented throughout the entire Portuguese shelf; (c) a group of quart-rich sediments, with very high SiO 2 contents and moderate Al 2O 3, K 2O and TiO 2 contents, supporting a major terrigenous contribution and (d) a group of coarse sand samples with high As levels from off important rivers, pointing to anthropogenic contamination. Trace metal enrichments observed in the muddy areas from both the western and southern coasts appear to result from natural causes and do not exceed the international sediment quality thresholds. There is, however, local evidence for As, Zn, Cr and Pb anthropogenic contamination in near-shore sediments associated with rivers draining regions characterized by urban, industrial or

  2. 75 FR 16833 - Preliminary Revised 5-Year Outer Continental Shelf (OCS) Oil and Gas Leasing Program for 2007-2012

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-02

    ... Minerals Management Service Preliminary Revised 5-Year Outer Continental Shelf (OCS) Oil and Gas Leasing Program for 2007-2012 AGENCY: Minerals Management Service, Interior. ACTION: Notice of availability and request for comments. SUMMARY: The Minerals Management Service (MMS) requests comments on the Preliminary...

  3. 76 FR 55090 - Commercial Lease of Submerged Lands for Renewable Energy Development on the Outer Continental Shelf

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-06

    ... Offshore Alternative Energy Programs at (703) 787-1300 for lease questions. ADDRESSES: You may submit... Bureau of Ocean Energy Management, Regulation and Enforcement Commercial Lease of Submerged Lands for Renewable Energy Development on the Outer Continental Shelf AGENCY: Bureau of Ocean Energy Management...

  4. 76 FR 19122 - Record of Decision (ROD) for Authorizing the Use of Outer Continental Shelf (OCS) Sand Resources...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-04-06

    ... the Use of Outer Continental Shelf (OCS) Sand Resources in National Aeronautics and Space... Availability (NOA) of the Record of Decision. SUMMARY: BOEMRE has issued a ROD to authorize the use of OCS sand... for the purpose of making sand available from a shoal on the OCS for placement on the beach in support...

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

    SciTech Connect

    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.

  6. 75 FR 26091 - Safety Zone; Riser for DEEPWATER HORIZON at Mississippi Canyon 252 Outer Continental Shelf MODU...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-11

    ... HORIZON, a Mobile Offshore Drilling Unit (MODU), at Mississippi Canyon 252 in the Outer Continental Shelf... Mobile Offshore Drilling Unit (MODU), which has sunk in the deepwater area of the Gulf of Mexico near....T08-849 DEEPWATER HORIZON Mobile Offshore Drilling Unit Safety Zone. (a) Location. All areas within...

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

    EPA Science Inventory

    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 <2 ml O2 L-1) in the region. Rates of water column community respiration (R) and primary p...

  8. Sediment and Lower Water Column Oxygen Consumption in the Seasonally-hypoxic Region of the Louisiana Continental Shelf

    EPA Science Inventory

    We report sediment and bottom water respiration rates from 10 cruises from 2003-2007 on the Louisiana Continental Shelf (LSC) where summer hypoxia regularly occurs. Cruises were conducted during spring (5 cruises), summer (3 cruises) and fall (2 cruises). Cruise average sediment ...

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

    EPA Science Inventory

    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 <2 mg L-1) in the region. Water column community respiration rates (WR) were measured on 10 cr...

  10. 75 FR 25291 - Outer Continental Shelf (OCS) Mid-Atlantic Proposed Oil and Gas Lease Sale 220

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-07

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Minerals Management Service Outer Continental Shelf (OCS) Mid-Atlantic Proposed Oil and Gas Lease Sale 220 AGENCY: Minerals Management Service (MMS), Interior. ACTION: Notice of indefinite postponement of...

  11. 77 FR 41448 - Notice of Availability of the Proposed Final Five Year Outer Continental Shelf (OCS) Oil and Gas...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-13

    ... Continental Shelf (OCS) Oil and Gas Leasing Program for 2012-2017 AGENCY: Bureau of Ocean Energy Management... availability of the Proposed Final Five Year OCS Oil and Gas Leasing Program for 2012-2017 (PFP). This is the..., as was done in the PP. The Beaufort Sea sale date has been scheduled in 2017, in recognition of the...

  12. 77 FR 31037 - Outer Continental Shelf, Central and Western Gulf of Mexico Planning Areas, Oil and Gas Lease...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-05-24

    ... [Federal Register Volume 77, Number 101 (Thursday, May 24, 2012)] [Notices] [Pages 31037-31038] [FR Doc No: 2012-12664] DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management Outer Continental Shelf, Central and Western Gulf of Mexico Planning Areas, Oil and Gas Lease Sales for Years 2012-2017...

  13. 78 FR 65705 - Request for Comments on the Annual Progress Report on the Outer Continental Shelf (OCS) Oil and...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-11-01

    ... Continental Shelf (OCS) Oil and Gas Leasing Program 2012-2017 AGENCY: Bureau of Ocean Energy Management (BOEM... (Report) on the OCS Oil and Gas Leasing Program 2012-2017 (Five Year Program). The Annual Progress Report.../Five-Year-Program/2012-2017/Five-Year-Program.aspx . The Secretary of the Interior (Secretary...

  14. 77 FR 5820 - Commercial Leasing for Wind Power on the Outer Continental Shelf Offshore Massachusetts-Call for...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-06

    .... The American Waterways Operators expressed concerns related to the placement of wind turbines and... Bureau of Ocean Energy Management Commercial Leasing for Wind Power on the Outer Continental Shelf... nominations for commercial leases that would allow a lessee to propose the construction of a wind energy...

  15. ON THE WIND-INDUCED EXCHANGE BETWEEN INDIAN RIVER BAY, DELAWARE AND THE ADJACENT CONTINENTAL SHELF. (R826945)

    EPA Science Inventory

    The structure of the wind-induced exchange between Indian River Bay, Delaware and the adjacent continental shelf is examined based on current measurements made at the Indian River Inlet which represents the only conduit of exchange between the bay and the coastal ocean. Local ...

  16. 77 FR 7148 - Notice of Approval of Clean Air Act Outer Continental Shelf Permits Issued to Shell Gulf of...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-10

    ...This notice announces that EPA Region 10 has issued two final permit decisions granting Clean Air Act Outer Continental Shelf (OCS) permit applications, one from Shell Gulf of Mexico, Inc., for operation of the Discoverer drillship in the Chukchi Sea and one from Shell Offshore, Inc. (collectively, ``Shell''), for operation of the Discoverer drillship in the Beaufort Sea.

  17. Impact of regulations--after federal leasing--on outer continental shelf oil and gas development. Report to the congress

    SciTech Connect

    Not Available

    1981-02-27

    This report analyzes the impact various regulatory requirements stemming from the Outer Continental Shelf Lands Act Amendments of 1978 and other legislation are having--after leases are awarded--on industry efforts to explore and develop OCS oil and gas resources.

  18. 77 FR 67394 - Gulf of Mexico (GOM), Outer Continental Shelf (OCS), Western Planning Area (WPA) Lease Sale 233...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-11-09

    ... Bureau of Ocean Energy Management Gulf of Mexico (GOM), Outer Continental Shelf (OCS), Western Planning... AGENCY: Bureau of Ocean Energy Management (BOEM), Interior. ACTION: Notice of Availability (NOA) of the... scientific journals, available scientific data, and information from academic institutions and Federal,...

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

    EPA Science Inventory

    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 <2 ml O2 L-1) in the region. Rates of water column community respiration (R) and primary p...

  20. 75 FR 20271 - Oil and Gas and Sulphur Operations in the Outer Continental Shelf-Oil and Gas Production...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-19

    ... Minerals Management Service 30 CFR Part 250 RIN 1010-AD12 Oil and Gas and Sulphur Operations in the Outer Continental Shelf--Oil and Gas Production Requirements AGENCY: Minerals Management Service (MMS), Interior. ACTION: Final rule. SUMMARY: The MMS is amending the regulations regarding oil and natural gas production...

  1. 75 FR 32273 - Safety Zone; DEEPWATER HORIZON at Mississippi Canyon 252 Outer Continental Shelf MODU in the Gulf...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-06-08

    ... Outer Continental Shelf MODU in the Gulf of Mexico AGENCY: Coast Guard, DHS. ACTION: Temporary final... area of the Gulf of Mexico in response to the sinking of the DEEPWATER HORIZON, a Mobile Offshore... types of vessels navigating in the vicinity of the proposed area, and (7) the structural configuration...

  2. 76 FR 8962 - Renewable Energy Alternate Uses of Existing Facilities on the Outer Continental Shelf-Acquire a...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-16

    ... Bureau of Ocean Energy Management, Regulation and Enforcement 30 CFR Part 285 RIN 1010-AD71 Renewable... acquisition of an Outer Continental Shelf (OCS) renewable energy lease. We are taking this action because the current regulations governing the noncompetitive acquisition of an OCS renewable energy lease initiated by...

  3. 75 FR 72679 - Renewable Energy Alternate Uses of Existing Facilities on the Outer Continental Shelf-Acquire a...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-26

    ... Bureau of Ocean Energy Management, Regulation and Enforcement 30 CFR Part 285 RIN 1010-AD71 Renewable... an Outer Continental Shelf (OCS) renewable energy lease. We are taking this action because the current regulations covering noncompetitive leasing of an OCS renewable energy lease and an unsolicited...

  4. 77 FR 5529 - Commercial Lease of Submerged Lands for Renewable Energy Development on the Outer Continental Shelf

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-03

    ... Bureau of Ocean Energy Management Commercial Lease of Submerged Lands for Renewable Energy Development on.... SUMMARY: The Bureau of Ocean Energy Management (BOEM) will use Form 0008 to issue commercial renewable..., ``Renewable Energy and Alternate Uses of Existing Facilities on the Outer Continental Shelf,'' BOEM stated...

  5. 76 FR 28178 - Renewable Energy Alternate Uses of Existing Facilities on the Outer Continental Shelf-Acquire a...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-05-16

    ... Bureau of Ocean Energy Management, Regulation and Enforcement 30 CFR Part 285 RIN 1010-AD71 Renewable... acquisition of an Outer Continental Shelf (OCS) renewable energy lease. We are taking this action because... for an OCS renewable energy lease, where BOEMRE is required to publish only a single notice. The final...

  6. ON THE WIND-INDUCED EXCHANGE BETWEEN INDIAN RIVER BAY, DELAWARE AND THE ADJACENT CONTINENTAL SHELF. (R826945)

    EPA Science Inventory

    The structure of the wind-induced exchange between Indian River Bay, Delaware and the adjacent continental shelf is examined based on current measurements made at the Indian River Inlet which represents the only conduit of exchange between the bay and the coastal ocean. Local ...

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

    EPA Science Inventory

    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 <2 mg L-1) in the region. Water column community respiration rates (WR) were measured on 10 cr...

  8. Sediment and Lower Water Column Oxygen Consumption in the Seasonally-hypoxic Region of the Louisiana Continental Shelf

    EPA Science Inventory

    We report sediment and bottom water respiration rates from 10 cruises from 2003-2007 on the Louisiana Continental Shelf (LSC) where summer hypoxia regularly occurs. Cruises were conducted during spring (5 cruises), summer (3 cruises) and fall (2 cruises). Cruise average sediment ...

  9. 78 FR 52562 - Outer Continental Shelf (OCS), Gulf of Mexico (GOM), Oil and Gas Lease Sales, Central Planning...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-23

    ... Bureau of Ocean Energy Management Outer Continental Shelf (OCS), Gulf of Mexico (GOM), Oil and Gas Lease... socioeconomic analyses in the Gulf of Mexico OCS Oil and Gas Lease Sales: 2012-2017; Western Planning Area Lease... Oil and Gas Lease Sales: 2013-2014; Western Planning Area Lease Sale 233; Central Planning Area...

  10. 77 FR 40380 - Outer Continental Shelf, Gulf of Mexico, Oil and Gas Lease Sales, Western Planning Area Lease...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-09

    ... Bureau of Ocean Energy Management Outer Continental Shelf, Gulf of Mexico, Oil and Gas Lease Sales... will update the environmental and socioeconomic analyses in the Gulf of Mexico OCS Oil and Gas Lease... oil and natural gas leasing, exploration, development, and production in the WPA and CPA. The...

  11. 77 FR 4360 - Notice of Availability of the Proposed Notice of Sale for Outer Continental Shelf (OCS) Oil and...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-01-27

    ... Continental Shelf (OCS) Oil and Gas Lease Sale 216/222 in the Central Planning Area (CPA) in the Gulf of... Proposed Notice of Sale for Proposed Sale 216/222. SUMMARY: BOEM announces the availability of the proposed Notice of Sale (NOS) for proposed Sale 216/222 in the CPA. This Notice is published pursuant to 30...

  12. 78 FR 8190 - Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore North Carolina...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-02-05

    ... Bureau of Ocean Energy Management Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS... Information and Nominations for Commercial Leasing for Wind Power Offshore North Carolina (Call), published on... obtaining a commercial wind lease in one or more, or any portion of, the Call Areas, postmarked by March 7...

  13. 76 FR 7228 - Outer Continental Shelf (OCS), Western and Central Planning Areas of the Gulf of Mexico (GOM...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-09

    ... Central Planning Areas of the Gulf of Mexico (GOM), Oil and Gas Lease Sales for 2012-2017 AGENCY: Bureau...- 2017 oil and gas leasing proposals in the Western and Central Planning Areas of the GOM, off the States... Oil and Gas Leasing Program for 2012-2017 in the draft proposed Outer Continental Shelf Oil and...

  14. 78 FR 54417 - Oil and Gas and Sulphur Operations on the Outer Continental Shelf-Oil and Gas Production Safety...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-09-04

    ... Operations on the Outer Continental Shelf--Oil and Gas Production Safety Systems Correction In proposed rule... Firefighting systems. Sec. 250.862 Fire and gas- detection systems. Sec. 250.863 Electrical equipment. Sec. 250... the fire and gas- showing a functional block diagram detection systems. of the detection...

  15. 76 FR 38294 - Oil and Gas and Sulphur Operations in the Outer Continental Shelf-Civil Penalties

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-06-30

    ... pollution, Penalties, Pipelines, Public lands--mineral resources, Reporting and recordkeeping requirements... Continental Shelf Lands Act (OCSLA) requires the Bureau of Ocean Energy Management, Regulation and Enforcement... Pollution Act (OPA) of 1990 for violations of regulations governing financial responsibility (28 U.S.C. 2461...

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

    PubMed

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

    2014-12-15

    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.

  17. Geologic evidence for onshore sediment transport from the inner continental shelf: Fire Island, New York

    USGS Publications Warehouse

    Schwab, William C.; Baldwin, Wayne E.; Hapke, Cheryl J.; Lentz, Erika E.; Gayes, Paul T.; Denny, Jane F.; List, Jeffrey H.; Warner, John C.

    2013-01-01

    Sediment budget analyses along the south shore of Fire Island, New York, have been conducted and debated in the scientific and coastal engineering literature for decades. It is well documented that a primary component of sediment transport in this system is directed alongshore from E to W, but discrepancies in volumetric sediment budget calculations remain. An additional quantity of sand, averaging about 200,000 m3/y is required to explain the growth of the western segment of the barrier island, a prograding spit. Littoral sediment derived from updrift erosion of the coast, addition of beach nourishment fill, and onshore transport of inner continental shelf, shoreface sediments, or both have all been proposed as potential sources of the additional sediment needed to balance the sediment budget deficit. Analysis of high-resolution seafloor mapping data collected in 2011, including seismic reflection profiles and inteferometric sonar acoustic backscatter and swath bathymetry; comparison with seafloor mapping data collected in 1996–1997; and shoreline change analysis from 1933 to 2011 support previous suggestions that the inner-shelf Holocene sedimentary deposit is a likely source to resolve this sediment budget discrepancy.

  18. Sandbank occurrence on the Dutch continental shelf in the North Sea

    NASA Astrophysics Data System (ADS)

    Knaapen, Michiel A. F.

    2009-02-01

    Sandbanks, the largest of bed patterns in shallow sandy seas, pose a potential risk to shipping. They are also valuable elements of natural coastal protection, dissipating the energy of waves. In the Southern Bight of the North Sea, several sandbank areas have been reported in the literature. However, based on an objective crest-trough analysis of the bathymetry of the Dutch continental shelf, the present study shows that sandbanks are more widespread than commonly considered. These banks are relatively low, presumably explaining why they have not been documented before. This widespread occurrence of sandbanks in the North Sea is in agreement with theoretical predictions based on stability analysis techniques. The possible interference between large-scale human activity and low-amplitude open-shelf ridges implies that one should be careful not to overlook these patterns if none should appear in a preliminary (visual) assessment. The only part of the Southern Bight in which no ridges can be seen is a circular area with a diameter of about 50 km near the mouth of the river Rhine. Here, freshwater outflow affects the direction of tidal ellipses and residual flow, and suppresses the formation of open ridges.

  19. Surface area control of organic carbon accumulation in continental shelf sediments

    SciTech Connect

    Mayer, L.M. )

    1994-02-01

    The relationship between organic carbon (OC) and grain size found in most continental shelf sediments is here reinterpreted in terms of the surface area of the sediments. Cores from many North American shelf environments show downcore decreases in OC to similar refractory background concentrations if expressed relative to the surface area of the sediments. This consistent concentration is 0.86 mg-OC m[sup [minus]2], which is equivalent in concentration to a monolayer of organic matter coating all mineral surfaces. A more global collection of sediment-water interface samples show that this relationship is even more extensive, with exceptions occurring in areas of very high riverine sediment input, organic pollution, or low-oxygen water columns. Density separations indicate that organic matter is largely adsorbed to mineral grains. The microtopography of surfaces was examined with N[sub 2] sorption and most surface area was found to be inside pores of <10 nm width. These data lead to a hypothesis that organic matter is protected by its location inside pores too small to allow functioning of the hydrolytic enzymes necessary for organic matter decay. Such protection would likely work in concert with other protection mechanisms such as humification. This consistent surface area correlation with OC concentration may explain control of spatial and temporal variations in OC burial rates by sedimentation rates; the pore protection hypothesis provides a causal mechanism for this observed control.

  20. Environmental magnetism and application in the continental shelf sediments of India.

    PubMed

    Alagarsamy, R

    2009-08-01

    Mineral magnetic and geochemical analyses were carried out on surface sediments from the continental shelf of India. The purpose of this study is to examine the environmental assessment of heavy metal concentrations and its impact in the coastal environment using magnetic techniques and to gain an understanding on the factors controlling metal concentrations and distributions in the east and west coast of India. The strong relationships between Anhysteretic Remanent Magnetization (chi(ARM)) and heavy metals can be explained by the role of iron oxides controlling metal concentrations, though the link is also reinforced by the strong tendency of chi(ARM) to be associated with the finer particle sizes. Higher values of magnetic susceptibility, IRM(20 mT) and SIRM are associated with the east coast shelf sediments suggest the presence of high ferrimagnetic content, which can be derived from the weathering products of the Deccan Basalts. chi(ARM) can be used as a normalizer for particle size effects in the way that Aluminium (Al) is often used. The relationship between magnetic parameters and heavy metal concentrations (Fe, Cu, Cr and Ni) showed a strong positive correlation in the east coast sediments, much less so in the case of the west coast. This finding suggests that the simple, rapid and non-destructive magnetic measurement can be used as an indicator for the heavy metal contamination and proxies for the measurement of heavy metals content in the coastal environment.