Woods Hole Coastal and Marine Science Center
Publications by year, USGS Woods Hole Coastal and Marine Science Center
All Publications by WHCMSC Authors for the year 2010
Agnihotri, Rajesh, Naqvi, S. Wajih A., Kurian, Siby, Altabet, Mark A., and Bratton, J.F., 2009, Is delta sup(15)N of sedimentary organic matter a good proxy for paleodenitrification in coastal waters of the eastern Arabian Sea?:
Recently published sedimentary records of delta sup(15)N from several coastal areas affected by both natural and anthropogenically produced shallow hypoxia with the objective of testing this as a proxy for denitrification in coastal settings are compared. The eastern boundary systems of continental shelves off western India and Peru, which appear to be experiencing intensification of bottom-water oxygen depletion, most likely as a consequence of intensification of eastern boundary coastal upwelling over the last few decades were examined. In systems that are significantly affected by an enhanced inventory of nutrients from organic matter in soils due to continental erosion following colonial land clearing (e.g., Chesapeake Bay), fertilizer and wastewater runoff (e.g., western Indian shelf and Long Island Sound), the productivity increase is largely local and induced by anthropogenic activity. The western Indian shelf thus experiences a double effect, being both an upwelling zone and prone to nutrient enrichment from land. While in other regions of both natural and anthropogenic bottom-water hypoxia, sedimentary delta sup(15)N has undergone significant increases over the Anthropocene; in the eastern Arabian Sea, an opposite trend is noticed despite historical water-column measurements revealing a contemporaneous intensification of denitrification. Plausible causes are discussed here in detail, which led us to conclude that the sedimentary delta sup(15)N may not always work as a reliable proxy of denitrification in coastal regions.
Andrews, Brian D., Ackerman, Seth D., Baldwin, Wayne E., and Barnhardt, Walter A., 2010, Geophysical and sampling data from the inner continental shelf; northern Cape Cod Bay, Massachusetts:
U.S. Geological Survey Open-File Report 2010-1006
. Online at http://pubs.usgs.gov/of/2010/1006/
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.
Andrews, Brian D., Brothers, Laura L., and Barnhardt, Walter A., 2010, Automated feature extraction and spatial organization of seafloor pockmarks, Belfast Bay, Maine, USA:
, v. 124
, no. 1-2
, pp. 55-64
. Online at 10.1016/j.geomorph.2010.08.009
Seafloor pockmarks occur worldwide and may represent millions of m3 of continental shelf erosion, but few numerical analyses of their morphology and spatial distribution of pockmarks exist. We introduce a quantitative definition of pockmark morphology and, based on this definition, propose a three-step geomorphometric method to identify and extract pockmarks from high-resolution swath bathymetry. We apply this GIS-implemented approach to 25 km2 of bathymetry collected in the Belfast Bay, Maine USA pockmark field. Our model extracted 1767 pockmarks and found a linear pockmark depth-to-diameter ratio for pockmarks field-wide. Mean pockmark depth is 7.6 m and mean diameter is 84.8 m. Pockmark distribution is non-random, and nearly half of the field's pockmarks occur in chains. The most prominent chains are oriented semi-normal to the steepest gradient in Holocene sediment thickness. A descriptive model yields field-wide spatial statistics indicating that pockmarks are distributed in non-random clusters. Results enable quantitative comparison of pockmarks in fields worldwide as well as similar concave features, such as impact craters, dolines, or salt pools.
Arsenault, M.A., Williams, S.J., Reid, J.A., and Jenkins, C.J., 2010, Geologic characterization of U.S. shelf areas using usSEABED for GIS mapping, habitat delineation, and assessing marine sand and gravel resources, chap. 09:
Baker, Diana, Peterson, Curt, Hemphill-Haley, Eileen, and Twichell, David, 2010, Latest Pleistocene and Holocene (2-16 ka) sedimentation in the Columbia River Estuary, Oregon, USA:
, v. 273
, no. 1-4
, pp. 83-95
. Online at 10.1016/j.margeo.2010.02.005
A deep borehole drilled at Warrenton, Oregon in the ancestral valley of the Columbia River represents a geologic record that extends from 2 ka to 16 ka. Prior to the onset of the Holocene marine transgression at 16 ka, the incised Columbia River valley was cut to 112 m below present sea level at this location. The onset of estuarine circulation in the Columbia River estuary occurred at 11.5 ka as determined by the first appearance of brackish water diatoms in sediments from borehole cores at a depth of 70 m. Grain size and heavy mineral analyses indicate that the Columbia River tidal basin served initially (1611 ka) as a bedload-bypassing conduit to the continental shelf, and/or the Astoria Canyon. With the ongoing Holocene transgression, the Columbia River tidal basin became more efficient as a river sediment sink between 11.5 and 9.0 ka. After 9.0 ka, the filling tidal basin again served as a sediment-bypassing conduit (source) of sand to the coastline and continental shelf. Heavy mineral analyses indicate that between 16 and 11 ka the Columbia River tidal basin was dominated by sediment from the metamorphic interior basins of the Columbia drainage basin. The dominant sediment source changed from the metamorphic interior basins of the Columbia drainage basin to the Cascade volcanic arc between 11.5 and 9.0 ka. After 9.0 ka, the tidal basin was dominated by Cascade volcanic arc derived sediments.
The total volume of Holocene sediment, primarily bedload, which has accumulated in the lower Columbia River valley, is 73 km3. This compares to only 13-km3 accumulation during the last 5 ka. The tidal basin accumulation rate gradually increased from 0.6 million m3/yr to slightly over 18 million m3/yr between the depths of 112 m and 30 m (16 to 9 ka). Above the 30 m depth (corresponding to 8.2 ka), the rate of basin volume fill dramatically decreased to just over 4 million m3/yr. Such a large decrease in sediment accumulation rate suggests that after 9 ka sediments were bypassing the nearly full tidal basin to the beaches and inner shelf. The rates of bedload bypassing the lower Columbia River valley, substantially greater than 2.4 million m3/yr, supported the shoreface progradation in the littoral cell during the late Holocene.
Barkan, Roy, and ten Brink, Uri, 2010, Tsunami simulations of the 1867 Virgin Island earthquake; constraints on epicenter location and fault parameters:
Bulletin of the Seismological Society of America
, v. 100
, no. 3
, pp. 995-1009
. Online at 10.1785/0120090211
The 18 November 1867 Virgin Island earthquake and the tsunami that closely followed caused considerable loss of life and damage in several places in the northeast Caribbean region. The earthquake was likely a manifestation of the complex tectonic deformation of the Anegada Passage, which cuts across the Antilles island arc between the Virgin Islands and the Lesser Antilles. In this article, we attempt to characterize the 1867 earthquake with respect to fault orientation, rake, dip, fault dimensions, and first tsunami wave propagating phase, using tsunami simulations that employ high-resolution multibeam bathymetry. In addition, we present new geophysical and geological observations from the region of the suggested earthquake source. Results of our tsunami simulations based on relative amplitude comparison limit the earthquake source to be along the northern wall of the Virgin Islands basin, as suggested by Reid and Taber (1920), or on the carbonate platform north of the basin, and not in the Virgin Islands basin, as commonly assumed. The numerical simulations suggest the 1867 fault was striking 120°135° and had a mixed normal and left-lateral motion. First propagating wave phase analysis suggests a fault striking 300°315° is also possible. The best-fitting rupture length was found to be relatively small (50 km), probably indicating the earthquake had a moment magnitude of ∼7.2. Detailed multibeam echo sounder surveys of the Anegada Passage bathymetry between St. Croix and St. Thomas reveal a scarp, which cuts the northern wall of the Virgin Islands basin. High-resolution seismic profiles further indicate it to be a reasonable fault candidate. However, the fault orientation and the orientation of other subparallel faults in the area are more compatible with right-lateral motion. For the other possible source region, no clear disruption in the bathymetry or seismic profiles was found on the carbonate platform north of the basin.
Bever, Aaron J., Harris, Courtney K., Sherwood, Christopher R., and Signell, Richard P., 2009, Deposition and flux of sediment from the Po River, Italy; an idealized and wintertime numerical modeling study:
, v. 260
, no. 1-4
. Online at 10.1016/j.margeo.2009.01.007
Recent studies of sediment dynamics and clinoform development in the northern Adriatic Sea focused on winter 20022003 and provided the data and motivation for development of a detailed sediment-transport model for the area near the Po River delta. We used both idealized test cases and more realistic simulations to improve our understanding of seasonal sediment dynamics there. We also investigated the relationship between physical processes and the observed depositional products; e.g. the accumulation of sediment very near the Po River distributary mouths. Sediment transport near the Po River was evaluated using a three-dimensional ocean model coupled to sediment-transport calculations that included wave- and current-induced resuspension, suspended-sediment transport, multiple grain classes, and fluvial input from the Po River. High-resolution estimates from available meteorological and wave models were used to specify wind, wave, and meteorological forcing.
Model results indicated that more than half of the discharged sediment remained within 15 km of the Po River distributary mouths, even after two months of intensive reworking by winter storms. During floods of the Po River, transport in the middle to upper water column dominated sediment fluxes. Otherwise, sediment fluxes from the subaqueous portion of the delta were confined to the bottom few meters of the water column, and correlated with increases in current speed and wave energy. Spatial and temporal variation in wind velocities determined depositional patterns and the directions of sediment transport. Northeasterly Bora winds produced relatively more eastward transport, while southwesterly Sirocco winds generated fluxes towards both the north and the south. Eastward transport accounted for the majority of the sediment exported from the subaqueous delta, most likely due to the frequent occurrence of Bora conditions. Progradation of the Po River delta into the Adriatic Sea may restrict the formation of the Western Adriatic Coastal Current, increasing sediment retention at the Po delta and reducing the supply of sediment to the Apennine margin. A positive morphodynamic feedback may therefore be present whereby the extension of the delta into the Adriatic increases sediment accumulation at the delta and facilitates further progradation.
Boswell, Ray, Collett, Tim, Anderson, Brian, and Ruppel, Carolyn, 2010, Relative gas volume ratios for free gas and gas hydrate accumulations:
Fire in the Ice, U.S. Department of Energy/National Energy Technology Laboratory Newsletter
, v. August 2010
. Online at http://www.netl.doe.gov/technologies/oil-gas/publications/Hydrates/Newsletter/MHNews_2010_08.pdf
Bothner, Michael H., Butman, Bradford, and Casso, Michael A., 2010, Review of oceanographic and geochemical data collected in Massachusetts Bay during a large discharge of total suspended solids from Boston's sewage-treatment system and ocean outfall in August 2002:
U.S. Geological Survey Open-File Report 2010-1050
. Online at http://pubs.usgs.gov/of/2010/1050/
During the period August 1423, 2002, the discharge of total suspended solids (TSS) from the Massachusetts Water Resources Authority sewage-treatment plant ranged from 32 to 132 milligrams per liter, causing the monthly average discharge to exceed the limit specified in the National Pollution Discharge Elimination System permit. Time-series monitoring data collected by the U.S. Geological Survey in western Massachusetts Bay were examined to evaluate changes in environmental conditions during and after this exceedance event. The rate of sediment trapping and the concentrations of near-bottom suspended sediment measured near the outfall in western Massachusetts Bay increased during this period. Because similar increases in sediment-trapping rate were observed in the summers of 2003 and 2004, however, the increase in 2002 cannot be definitively attributed to the increased TSS discharge. Concentrations of copper and silver in trapped sediment collected 10 and 20 days following the 2002 TSS event were elevated compared to those in pre-event samples. Maximum concentrations were less than 50 percent of toxicity guidelines. Photographs of surficial bottom sediments obtained before and after the TSS event do not show sediment accumulation on the sea floor. Concentrations of silver, Clostridium perfringens, and clay in surficial bottom sediments sampled 10 weeks after the discharge event at a depositional site 3 kilometers west of the outfall were unchanged from those in samples obtained before the event. Simulation of the TSS event by using a coupled hydrodynamic-wave-sediment-transport model could enhance understanding of these observations and of the effects of the exceedance on the local marine environment.
Bratton, John F., 2010, The three scales of submarine groundwater flow and discharge across passive continental margins:
The Journal of Geology
, v. 118
, no. 5
. Online at 10.1086/655114
Increased study of submarine groundwater systems in recent years has provided a wealth of new data and techniques, but some ambiguity has been introduced by insufficient distinguishing of the relevant spatial scales of the phenomena studied. Submarine groundwater flow and discharge on passive continental margins can be most productively studied and discussed by distinct consideration of the following three spatial scales: (1) the nearshore scale, spanning approximately 0�10 m offshore and including the unconfined surficial aquifer; (2) the embayment scale, spanning approximately 10 m to as much as 10 km offshore and including the first confined submarine aquifer and its terminus; and (3) the shelf scale, spanning the width and thickness of the aquifers of the entire continental shelf, from the base of the first confined aquifer downward to the basement, and including influences of geothermal convection and glacio-eustatic change in sea level.
Burke, Andrea, Robinson, Laura F., McNichol, Ann P., Jenkins, William J., Scanlon, Kathryn M., and Gerlach, Dana S., 2010, Reconnaissance dating; a new radiocarbon method applied to assessing the temporal distribution of Southern Ocean deep-sea corals:
Deep Sea Research Part I: Oceanographic Research Papers
, v. 57
, no. 11
. Online at 10.1016/j.dsr.2010.07.010
We have developed a rapid reconnaissance method of preparing graphite for 14C/12C analysis. Carbonate (15 mg) is combusted using an elemental analyzer and the resulting CO2 is converted to graphite using a sealed tube zinc reduction method. Over 85% (n=45 replicates on twenty-one individual corals) of reconnaissance ages measured on corals ranging in age from 500 to 33,000 radiocarbon years (Ryr) are within two standard deviations of ages generated using standard hydrolysis methods on the same corals, and all reconnaissance ages are within 300 Ryr of the standard hydrolysis ages. Replicate measurements on three individual aragonitic corals yielded ages of 1076±35 Ryr (standard deviation; n=5), 10,739±47 Ryr (n=8), and 40,146±3500 Ryr (n=9). No systematic biases were found using different cleaning methods or variable sample sizes. Analysis of 13C/12C was made concurrently with the 14C/12C measurement to correct for natural fractionation and for fractionation during sample processing and analysis. This technique provides a new, rapid method for making accurate, percent-level 14C/12C analyses that may be used to establish the rates and chronology of earth system processes where survey-type modes of age estimation are desirable. For example, applications may include creation of sediment core-top maps, preliminary age models for sediment cores, and growth rate studies of marine organisms such as corals or mollusks. We applied the reconnaissance method to more than 100 solitary deep-sea corals collected in the Drake Passage in the Southern Ocean to investigate their temporal and spatial distribution. The corals used in this study are part of a larger sample set, and the subset that was dated was chosen based on species as opposed to preservation state, so as to exclude obvious temporal biases. Similar to studies in other regions, the distribution of deep-sea corals is not constant through time across the Drake Passage. Most of the corals from the Burdwood Bank (continental shelf of Argentina) have ages ranging between 0 and 2500 calendar years, whereas most of the corals from the Sars Seamount in the Drake Passage have ages between 10,000 and 12,500 calendar years. Such differences may be caused in part by sampling biases, but may also be caused by changes in larval transport, nutrient supply, or other environmental pressures.
Butman, B., Alexander, P.S., Scotti, A., Beardsley, R.C., and Anderson, S.P., 2006, Large internal waves in Massachusetts Bay transport sediments offshore:
Continental Shelf Research
, v. 26
, no. 17-18
. Online at 10.1016/j.csr.2006.07.022
A field experiment was carried out in Massachusetts Bay in August 1998 to assess the role of large-amplitude internal waves (LIWs) in resuspending bottom sediments. The field experiment consisted of a four-element moored array extending from just west of Stellwagen Bank (90-m water depth) across Stellwagen Basin (85- and 50-m water depth) to the coast (24-m water depth). The LIWs were observed in packets of 510 waves, had periods of 510 min and wavelengths of 200400 m, and caused downward excursions of the thermocline of as much as 30 m. At the 85-m site, the current measured 1 m above bottom (mab) typically increased from near 0 to 0.2 m/s offshore in a few minutes upon arrival of the LIWs. At the 50-m site, the near-bottom offshore flow measured 6 mab increased from about 0.1 to 0.40.6 m/s upon arrival of the LIWs and remained offshore in the bottom layer for 12 h. The near-bottom currents associated with the LIWs, in concert with the tidal currents, were directed offshore and sufficient to resuspend the bottom sediments at both the 50- and 85-m sites. When LIWs are present, they may resuspend sediments for as long as 5 hours each tidal cycle as they travel westward across Stellwagen Basin. At 85-m water depth, resuspension associated with LIWs is estimated to occur for about 0.4 days each summer, about the same amount of time as caused by surface waves.
Chaytor, Jason D., Twichell, David C., Lynett, Patrick, and Geist, Eric L., 2010, Distribution and tsunamigenic potential of submarine landslides in the Gulf of Mexico: in, Mosher, D.C., Shipp, R.C., Moscardelli, L., Chaytor, J.D., Baxter, C.D.P., Lee, H.J., and Urgeles, R. (eds.):
Submarine mass movements and their consequences, 4th International Symposium
, v. 28
. Online at 10.1007/978-90-481-3071-9_60
The Gulf of Mexico (GOM) is a geologically diverse ocean basin that includes three distinct geologic provinces: a carbonate province, a salt province, and canyon to deep-sea fan province, all of which contain evidence of submarine mass movements. The threat of submarine landslides in the GOM as a generator of near-field damaging tsunamis has not been widely addressed. Submarine landslides in the GOM are considered a potential tsunami hazard because: (1) some dated landslides in the GOM have post-glacial ages and (2) recent seismicity recorded within the GOM. We present a brief review of the distribution and style of submarine landslides that have occurred in the GOM during the Quaternary, followed by preliminary hydrodynamic modeling results of tsunami generation from the East Breaks landslide off Corpus Christie, TX.
Chen, Shih-Nan, Geyer, W.R., Sherwood, C.R., and Ralston, D.K., 2010, Depositional structure and sediment budget associated with a discharge event on an idealized tidal flat:
Journal of Geophysical Research - Oceans
, v. 115
, no. C10
. Online at 10.1029/2010JC006248
A 3-D hydrodynamic model is used to investigate how different size classes of river-derived sediment are transported, exported and trapped on an idealized, river-dominated tidal flat. The model is composed of a river channel flanked by sloping tidal flats, a configuration motivated by the intertidal region of the Skagit River mouth in Washington State, United States. It is forced by mixed tides and a pulse of freshwater and sediment with various settling velocities. In this system, the river not only influences stratification but also contributes a significant cross-shore transport. As a result, the bottom stress is strongly ebb-dominated in the channel because of the seaward advance of strong river flow as the tidal flats drain during ebbs. Sediment deposition patterns and mass budgets are sensitive to settling velocity. The lateral sediment spreading scales with an advective distance (settling time multiplied by lateral flow speed), thereby confining the fast settling sediment classes in the channel. Residual sediment transport is landward on the flats, because of settling lag, but is strongly seaward in the channel. The seaward transport mainly occurs during big ebbs and is controlled by a length scale ratio Ld/XWL, where Ld is a cross-shore advective distance (settling time multiplied by river outlet velocity), and XWL is the immersed cross-shore length of the intertidal zone. Sediment trapping requires Ld/XWL < 1, leading to more trapping for the faster settling classes. Sensitivity studies show that including stratification and reducing tidal range both favor sediment trapping, whereas varying channel geometries and asymmetry of tides has relatively small impacts. Implications of the modeling results on the south Skagit intertidal region are discussed.
Coleman, Felicia C., Koenig, Christopher C., Scanlon, Kathryn M., Heppell, Scott, Heppell, Selina, and Miller, Margaret W., 2010, Benthic habitat modification through excavation by red grouper, Epinephelus morio, in the northeastern Gulf of Mexico:
The Open Fish Science Journal
, v. 3
. Online at 10.2174/1874401X01003010001
Cross, V.A., Foster, D.S., and Bratton, J.F., 2010, Continuous resistivity profiling and seismic-reflection data collected in 2006 from the Potomac River estuary, Virginia and Maryland:
U.S. Geological Survey Open-File Report 2009-1151
. Online at http://pubs.usgs.gov/of/2009/1151/
In 2006 the U.S. Geological Survey conducted a geophysical survey on the Chesapeake Bay and the Potomac River Estuary in order to test hypotheses about groundwater flow under and into Chesapeake Bay. Resource managers are concerned about nutrients that are entering the estuary via submarine groundwater discharge and are contributing to eutrophication. The research carried out as part of this study was designed to help refine nutrient budgets for Chesapeake Bay by characterizing submarine groundwater flow and groundwater discharge beneath part of the bays mainstem and a major tributary, the Potomac River Estuary. The data collected indicate that plumes of reduced-salinity groundwater are commonly present along the shorelines of Chesapeake Bay and the Potomac River Estuary. Data also show that buried paleochannels generally do not serve as conduits for flow of groundwater from land to underneath the bay and estuary but rather may focus discharge of reduced-salinity water along their flanks, and provide routes for migration of saltwater into the sediments.
Denny, J.F., Danforth, W.W., Foster, D.S., and Sherwood, C.R., 2009, Geophysical data collected off the south shore of Martha's Vineyard, Massachusetts:
U.S. Geological Survey Open-File Report 2008-1288
. Online at http://pubs.usgs.gov/of/2008/1288/
The U.S. Geological Survey Woods Hole Science Center conducted a nearshore geophysical survey offshore of the southern coast of Martha's Vineyard, in the vicinity of the Martha's Vineyard Coastal Observatory in 2007. This mapping program was part of a larger research effort supporting the Office of Naval Research Ripples Directed-Research Initiative studies at Martha's Vineyard Coastal Observatory designed to improve our understanding of coastal sediment-transport processes. The survey was conducted aboard the Megan T. Miller August 9-13, 2007. The study area covers 35 square kilometers from about 0.2 kilometers to 5 kilometers offshore of the south shore of Martha's Vineyard, and ranges in depth from ~6 to 24 meters. The geophysical mapping utilized the following suite of high-resolution instrumentation to map the surficial sediment distribution, bathymetry, and sub-surface geology: a dual-frequency 100/500 kilohertz sidescan-sonar system, 234 kilohertz interferometric sonar, and 500 hertz -12 kilohertz chirp subbottom profiler. These geophysical data will be used to provide initial conditions for wave and circulation modeling within the study area.
Drevnick, Paul E., Shinneman, Avery L.C., Lamborg, Carl H., Engstrom, Daniel R., Bothner, Michael H., and Oris, James T., 2009, Mercury flux to sediments of Lake Tahoe, California-Nevada:
Water, Air, and Soil Pollution
. Online at 10.1007/s11270-009-0262-y
We report estimates of mercury (Hg) flux to the sediments of Lake Tahoe, CaliforniaNevada: 2 and 1520 µg/m2/year in preindustrial and modern sediments, respectively. These values result in a modern to preindustrial flux ratio of 7.510, which is similar to flux ratios recently reported for other alpine lakes in California, and greater than the value of 3 typically seen worldwide. We offer plausible hypotheses to explain the high flux ratios, including (1) proportionally less photoreduction and evasion of Hg with the onset of cultural eutrophication and (2) a combination of enhanced regional oxidation of gaseous elemental Hg and transport of the resulting reactive gaseous Hg to the surface with nightly downslope flows of air. If either of these mechanisms is correct, it could lead to local/regional solutions to lessen the impact of globally increasing anthropogenic emissions of Hg on Lake Tahoe and other alpine ecosystems.
Ferre, Benedicte, Sherwood, Christopher R., and Wiberg, Patricia L., 2010, Sediment transport on the Palos Verdes shelf, California:
Continental Shelf Research
, v. 30
, no. 7
. Online at 10.1016/j.csr.2010.01.011
Sediment transport and the potential for erosion or deposition have been investigated on the Palos Verdes (PV) and San Pedro shelves in southern California to help assess the fate of an effluent-affected deposit contaminated with DDT and PCBs. Bottom boundary layer measurements at two 60-m sites in spring 2004 were used to set model parameters and evaluate a one-dimensional (vertical) model of local, steady-state resuspension, and suspended-sediment transport. The model demonstrated skill (Brier scores up to 0.75) reproducing the magnitudes of bottom shear stress, current speeds, and suspended-sediment concentrations measured during an April transport event, but the model tended to underpredict observed rotation in the bottom-boundary layer, possibly because the model did not account for the effects of temperaturesalinity stratification. The model was run with wave input estimated from a nearby buoy and current input from four to six years of measurements at thirteen sites on the 35- and 65-m isobaths on the PV and San Pedro shelves. Sediment characteristics and erodibility were based on gentle wet-sieve analysis and erosion-chamber measurements. Modeled flow and sediment transport were mostly alongshelf toward the northwest on the PV shelf with a significant offshore component. The 95th percentile of bottom shear stresses ranged from 0.09 to 0.16 Pa at the 65-m sites, and the lowest values were in the middle of the PV shelf, near the Whites Point sewage outfalls where the effluent-affected layer is thickest. Long-term mean transport rates varied from 0.9 to 4.8 metric tons m−1 yr−1 along the 65-m isobaths on the PV shelf, and were much higher at the 35-m sites. Gradients in modeled alongshore transport rates suggest that, in the absence of a supply of sediment from the outfalls or PV coast, erosion at rates of 0.2 mm yr−1 might occur in the region southeast of the outfalls. These rates are small compared to some estimates of background natural sedimentation rates (5 mm yr−1), but do not preclude higher localized rates near abrupt transitions in sediment characteristics. However, low particle settling velocities and strong currents result in transport length-scales that are long relative to the narrow width of the PV shelf, which combined with the significant offshore component in transport, means that transport of resuspended sediment towards deep water is as likely as transport along the axis of the effluent-affected deposit.
Ganju, Neil K., and Sherwood, Christopher R., 2010, Effect of bottom roughness formulation on the performance of a coupled wave, hydrodynamic, and sediment transport model:
, v. 33
, no. 3-4
, pp. 299-313
. Online at 10.1016/j.ocemod.2010.03.003
A variety of algorithms are available for parameterizing the hydrodynamic bottom roughness associated with grain size, saltation, bedforms, and waveï¿½current interaction in coastal ocean models. These parameterizations give rise to spatially and temporally variable bottom-drag coefficients that ostensibly provide better representations of physical processes than uniform and constant coefficients. However, few studies have been performed to determine whether improved representation of these variable bottom roughness components translates into measurable improvements in model skill. We test the hypothesis that improved representation of variable bottom roughness improves performance with respect to near-bed circulation, bottom stresses, or turbulence dissipation. The inner shelf south of Marthaï¿½s Vineyard, Massachusetts, is the site of sorted grain-size features which exhibit sharp alongshore variations in grain size and ripple geometry over gentle bathymetric relief; this area provides a suitable testing ground for roughness parameterizations. We first establish the skill of a nested regional model for currents, waves, stresses, and turbulent quantities using a uniform and constant roughness; we then gauge model skill with various parameterization of roughness, which account for the influence of the wave-boundary layer, grain size, saltation, and rippled bedforms. We find that commonly used representations of ripple-induced roughness, when combined with a waveï¿½current interaction routine, do not significantly improve skill for circulation, and significantly decrease skill with respect to stresses and turbulence dissipation. Ripple orientation with respect to dominant currents and ripple shape may be responsible for complicating a straightforward estimate of the roughness contribution from ripples. In addition, sediment-induced stratification may be responsible for lower stresses than predicted by the waveï¿½current interaction model.
Hapke, Cheryl, and Plant, Nathaniel, 2010, Predicting coastal cliff erosion using a Bayesian probabilistic model:
, v. 278
, no. 1-4
, pp. 140 - 149
. Online at 10.1016/j.margeo.2010.10.001
Regional coastal cliff retreat is difficult to model due to the episodic nature of failures and the along-shore variability of retreat events. There is a growing demand, however, for predictive models that can be used to forecast areas vulnerable to coastal erosion hazards. Increasingly, probabilistic models are being employed that require data sets of high temporal density to define the joint probability density function that relates forcing variables (e.g. wave conditions) and initial conditions (e.g. cliff geometry) to erosion events. In this study we use a multi-parameter Bayesian network to investigate correlations between key variables that control and influence variations in cliff retreat processes. The network uses Bayesian statistical methods to estimate event probabilities using existing observations. Within this framework, we forecast the spatial distribution of cliff retreat along two stretches of cliffed coast in Southern California. The input parameters are the height and slope of the cliff, a descriptor of material strength based on the dominant cliff-forming lithology, and the long-term cliff erosion rate that represents prior behavior. The model is forced using predicted wave impact hours. Results demonstrate that the Bayesian approach is well-suited to the forward modeling of coastal cliff retreat, with the correct outcomes forecast in 70�90% of the modeled transects. The model also performs well in identifying specific locations of high cliff erosion, thus providing a foundation for hazard mapping. This approach can be employed to predict cliff erosion at time-scales ranging from storm events to the impacts of sea-level rise at the century-scale.
Horton, B.P., Peltier, W.R., Culver, S.J., Drummond, R., Engelhart, S.E., Kemp, A.C., Mallinson, D., Thieler, E.R., Riggs, S.R., Ames, D.V., and Thomson, K.H., 2009, Holocene sea-level changes along the North Carolina Coastline and their implications for glacial isostatic adjustment models:
Quaternary Science Reviews
, v. 28
, no. 17-18
. Online at 10.1016/j.quascirev.2009.02.002
We have synthesized new and existing relative sea-level (RSL) data to produce a quality-controlled, spatially comprehensive database from the North Carolina coastline. The RSL database consists of 54 sea-level index points that are quantitatively related to an appropriate tide level and assigned an error estimate, and a further 33 limiting dates that confine the maximum and minimum elevations of RSL. The temporal distribution of the index points is very uneven with only five index points older than 4000 cal a BP, but the form of the Holocene sea-level trend is constrained by both terrestrial and marine limiting dates. The data illustrate RSL rapidly rising during the early and mid Holocene from an observed elevation of −35.7 ± 1.1 m MSL at 1106210576 cal a BP to −4.2 m ± 0.4 m MSL at 42403592 cal a BP.
We restricted comparisons between observations and predictions from the ICE-5G(VM2) with rotational feedback Glacial Isostatic Adjustment (GIA) model to the Late Holocene RSL (last 4000 cal a BP) because of the wealth of sea-level data during this time interval. The ICE-5G(VM2) model predicts significant spatial variations in RSL across North Carolina, thus we subdivided the observations into two regions. The model forecasts an increase in the rate of sea-level rise in Region 1 (Albemarle, Currituck, Roanoke, Croatan, and northern Pamlico sounds) compared to Region 2 (southern Pamlico, Core and Bogue sounds, and farther south to Wilmington). The observations show Late Holocene sea-level rising at 1.14 ± 0.03 mm year−1 and 0.82 ± 0.02 mm year−1 in Regions 1 and 2, respectively. The ICE-5G(VM2) predictions capture the general temporal trend of the observations, although there is an apparent misfit for index points older than 2000 cal a BP. It is presently unknown whether these misfits are caused by possible tectonic uplift associated with the mid-Carolina Platform High or a flaw in the GIA model. A comparison of local tide gauge data with the Late Holocene RSL trends from Regions 1 and 2 support the spatial variation in RSL across North Carolina, and imply an additional increase of mean sea level of greater than 2 mm year−1 during the latter half of the 20th century; this is in general agreement with historical tide gauge and satellite altimetry data.
Kalnejais, Linda H., Martin, William R., and Bothner, Michael H., 2010, The release of dissolved nutrients and metals from coastal sediments due to resuspension:
, v. 121
, no. 1-4
, pp. 224-235
. Online at 10.1016/j.marchem.2010.05.002
Coastal sediments in many regions are impacted by high levels of
contaminants. Due to a combination of shallow water depths, waves,
and currents, these sediments are subject to regular episodes of
sediment resuspension. However, the influence of such disturbances
on sediment chemistry and the release of solutes is poorly understood.
The aim of this study is to quantify the release of dissolved metals
(iron, manganese, silver, copper, and lead) and nutrients due to
resuspension in Boston Harbor, Massachusetts, USA. Using a
laboratory-based erosion chamber, a range of typical shear stresses
was applied to fine-grained Harbor sediments and the solute
concentration at each shear stress was measured. At low shear stress,
below the erosion threshold, limited solutes were released. Beyond
the erosion threshold, a release of all solutes, except lead, was
observed and the concentrations increased with shear stress. The
release was greater than could be accounted for by conservative
mixing of porewaters into the overlying water, suggesting that
sediment resuspension enhances the release of nutrients and metals
to the dissolved phase. To address the long-term fate of resuspended
particles, samples from the erosion chamber were maintained in
suspension for 90 h. Over this time, 57% of the particulate copper
and silver was released to the dissolved phase, while manganese was
removed from solution. Thus resuspension releases solutes both
during erosion events and over a longer timescale due to reactions
of suspended particles in the water column. The magnitude of the
annual solute release during erosion events was estimated by coupling
the erosion chamber results with a record of bottom shear stresses
simulated by a hydrodynamic model. The release of dissolved copper,
lead, and phosphate due to resuspension is between 2% and 10% of
the total (dissolved plus particulate phase) known inputs to Boston
Harbor. Sediment resuspension is responsible for transferring a
significant quantity of solid phase metals to the more bioavailable
and mobile dissolved phase. The relative importance of sediment
resuspension as a source of dissolved metals to Boston Harbor is
expected to increase as continuing pollutant control decreases
the inputs from other sources.
Kaneko, Masanori, Shingai, Hiroshi, Pohlman, John W., and Naraoka, Hiroshi, 2010, Chemical and isotopic signature of bulk organic matter and hydrocarbon biomarkers within mid-slope accretionary sediments of the northern Cascadia margin gas hydrate system:
, v. 275
, no. 1-4
, pp. 166-177
. Online at 10.1016/j.margeo.2010.05.010
The chemical and isotopic compositions of sedimentary organic matter (SOM) from two mid-slope sites of the northern Cascadia margin were investigated during Integrated Ocean Drilling Program (IODP) Expedition 311 to elucidate the organic matter origins and identify potential microbial contributions to SOM. Gas hydrate is present at both locations (IODP Sites U1327 and U1328), with distinct patterns of near-seafloor structural accumulations at the cold seep Site U1328 and deeper stratigraphic accumulations at the slope-basin Site U1327. Source characterization and evidence that some components of the organic matter have been diagenetically altered are determined from the concentrations and isotopic compositions of hydrocarbon biomarkers, total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS). The carbon isotopic compositions of TOC (δ13CTOC = −26 to −22) and long-chain n-alkanes (C27, C29 and C31, δ13C = −34 to − 29) suggest the organic matter at both sites is a mixture of 1) terrestrial plants that employ the C3 photosynthetic pathway and 2) marine algae. In contrast, the δ15NTN values of the bulk sediment (+ 4 to + 8) are consistent with a predominantly marine source, but these values most likely have been modified during microbial organic matter degradation. The δ13C values of archaeal biomarker pentamethylicosane (PMI) (− 46.4) and bacterial-sourced hopenes, diploptene and hop-21-ene (− 40.9 to − 34.7) indicate a partial contribution from methane carbon or a chemoautotrophic pathway. Our multi-isotope and biomarker-based conclusions are consistent with previous studies, based only on the elemental composition of bulk sediments, that suggested a mixed marine-terrestrial organic matter origin for these mid-slope sites of the northern Cascadia margin.
Katz, Timor, Yahel, Gitai, Yahel, Ruthy, Tunnicliffe, Verena, Herut, Barak, Snelgrove, Paul, Crusius, John, and Lazar, Boaz, 2009, Groundfish overfishing, diatom decline, and the marine silica cycle; lessons from Saanich Inlet, Canada, and the Baltic Sea cod crash:
Global Biogeochemical Cycles
, v. 23
, no. GB4032
, pp. 10
. Online at 10.1029/2008GB003416
In this study, we link groundfish activity to the marine silica cycle and suggest that the drastic mid-1980s crash of the Baltic Sea cod (Gadus morhua) population triggered a cascade of events leading to decrease in dissolved silica (DSi) and diatom abundance in the water. We suggest that this seemingly unrelated sequence of events was caused by a marked decline in sediment resuspension associated with reduced groundfish activity resulting from the cod crash. In a study in Saanich Inlet, British Columbia, Canada, we discovered that, by resuspending bottom sediments, groundfish triple DSi fluxes from the sediments and reduce silica accumulation therein. Using these findings and the available oceanographic and environmental data from the Baltic Sea, we estimate that overfishing and recruitment failure of Baltic cod reduced by 20% the DSi supply from bottom sediments to the surface water leading to a decline in the diatom population in the Baltic Sea. The major importance of the marginal ocean in the marine silica cycle and the associated high population density of groundfish suggest that groundfish play a major role in the silica cycle. We postulate that dwindling groundfish populations caused by anthropogenic perturbations, e.g., overfishing and bottom water anoxia, may cause shifts in marine phytoplankton communities.
Lee, J.Y., Francisca, F.M., Santamarina, J.C., and Ruppel, C., 2010, Parametric study of the physical properties of hydrate-bearing sand, silt, and clay sediments, Part II; small-strain mechanical properties:
Journal of Geophysical Research
, v. 115
, no. B11105
, pp. 11
. Online at 10.1029/2009JB006670
The small-strain mechanical properties (e.g., seismic velocities) of hydrate-bearing sediments measured under laboratory conditions provide reference values for calibration of logging and seismic exploration results acquired in hydrate-bearing formations. Instrumented cells were designed for measuring the compressional (P) and shear (S) velocities of sand, silts, and clay with and without hydrate and subject to vertical effective stresses of 0.01 to 2 MPa. Tetrahydrofuran (THF), which is fully miscible in water, was used as the hydrate former to permit close control over the hydrate saturation Shyd and to produce hydrate from dissolved phase, as methane hydrate forms in most natural marine settings. The results demonstrate that laboratory hydrate formation technique controls the pattern of P and S velocity changes with increasing Shyd and that the small-strain properties of hydrate-bearing sediments are governed by effective stress, σ′v and sediment specific surface. The S velocity increases with hydrate saturation owing to an increase in skeletal shear stiffness, particularly when hydrate saturation exceeds Shyd≈ 0.4. At very high hydrate saturations, the small strain shear stiffness is determined by the presence of hydrates and becomes insensitive to changes in effective stress. The P velocity increases with hydrate saturation due to the increases in both the shear modulus of the skeleton and the bulk modulus of pore-filling phases during fluid-to-hydrate conversion. Small-strain Poisson's ratio varies from 0.5 in soft sediments lacking hydrates to 0.25 in stiff sediments (i.e., subject to high vertical effective stress or having high Shyd). At Shyd ≥ 0.5, hydrate hinders expansion and the loss of sediment stiffness during reduction of vertical effective stress, meaning that hydrate-rich natural sediments obtained through pressure coring should retain their in situ fabric for some time after core retrieval if the cores are maintained within the hydrate stability field.
Lee, J.Y., Santamarina, J.C., and Ruppel, C., 2010, Volume change associated with formation and dissociation of hydrate in sediment:
Geochemistry, Geophysics, Geosystems
, v. 11
, no. 3
. Online at 10.1029/2009GC002667
Gas hydrate formation and dissociation in sediments are accompanied by changes in the bulk volume of the sediment and can lead to changes in sediment properties, loss of integrity for boreholes, and possibly regional subsidence of the ground surface over areas where methane might be produced from gas hydrate in the future. Experiments on sand, silts, and clay subject to different effective stress and containing different saturations of hydrate formed from dissolved phase tetrahydrofuran are used to systematically investigate the impact of gas hydrate formation and dissociation on bulk sediment volume. Volume changes in low specific surface sediments (i.e., having a rigid sediment skeleton like sand) are much lower than those measured in high specific surface sediments (e.g., clay). Early hydrate formation is accompanied by contraction for all soils and most stress states in part because growing gas hydrate crystals buckle skeletal force chains. Dilation can occur at high hydrate saturations. Hydrate dissociation under drained, zero lateral strain conditions is always associated with some contraction, regardless of soil type, effective stress level, or hydrate saturation. Changes in void ratio during formation-dissociation decrease at high effective stress levels. The volumetric strain during dissociation under zero lateral strain scales with hydrate saturation and sediment compressibility. The volumetric strain during dissociation under high shear is a function of the initial volume average void ratio and the stress-dependent critical state void ratio of the sediment. Other contributions to volume reduction upon hydrate dissociation are related to segregated hydrate in lenses and nodules. For natural gas hydrates, some conditions (e.g., gas production driven by depressurization) might contribute to additional volume reduction by increasing the effective stress.
Lee, J.Y., Santamarina, J.C., and Ruppel, C., 2010, Parametric study of the physical properties of hydrate-bearing sand, silt, and clay sediments, Part I; electromagnetic properties:
Journal of Geophysical Research
, v. 115
, no. B11104
, pp. 9
. Online at 10.1029/2009JB006669
The marked decrease in bulk electrical conductivity of sediments in the presence of gas hydrates has been used to interpret borehole electrical resistivity logs and, to a lesser extent, the results of controlled source electromagnetic surveys to constrain the spatial distribution and predicted concentration of gas hydrate in natural settings. Until now, an exhaustive laboratory data set that could be used to assess the impact of gas hydrate on the electromagnetic properties of different soils (sand, silt, and clay) at different effective stress and with different saturations of hydrate has been lacking. The laboratory results reported here are obtained using a standard geotechnical cell and the hydrate-formed tetrahydrofuran (THF), a liquid that is fully miscible in water and able to produce closely controlled saturations of hydrate from dissolved phase. Both permittivity and electrical conductivity are good indicators of the volume fraction of free water in the sediment, which is in turn dependent on hydrate saturation. Permittivity in the microwave frequency range is particularly predictive of free water content since it is barely affected by ionic concentration, pore structure, and surface conduction. Electrical conductivity (or resistivity) is less reliable for constraining water content or hydrate saturation: In addition to fluid-filled porosity, other factors, such as the ionic concentration of the pore fluid and possibly other conduction effects (e.g., surface conduction in high specific surface soils having low conductivity pore fluid), also influence electrical conductivity.
Linck, Guthrie A., Allwardt, Alan O., and Lightsom, Frances L., 2009, Constructing Uniform Resource Locators (URLs) for searching the Marine Realms Information Bank:
U.S. Geological Survey Open-File Report 2009-1266
. Online at http://pubs.usgs.gov/of/2009/1266/
Locat, Jacques, ten Brink, Uri S., and Chaytor, Jason D., 2010, The Block Composite submarine landslide, Southern New England slope, U.S.A.; a morphological analysis, in Mosher, D.C., Shipp, C., Moscardelli, L., Chaytor, J., Baxter, C., Lee, H., and Urgeles, R., eds.:
Submarine Mass Movements and Their Consequences, Proceedings of the Fourth International Conference
, pp. 267 - 277
. Online at 10.1007/978-90-481-3071-9_22
Recent multibeam surveys along the continental slope and rise off southeast New England has enabled a detailed morphological analysis of the Block composite landslide. This landslide consists of at least three large debris lobes resting on a gradient less than 0.5 °. The slide took place on gradients of between 1 ° and 5 ° in Quaternary sediments likely deposited at the time of low sea level and high sedimentation rates associated with glaciations. The slide debris lobes are very close to each other and cover an area of about 1.125 km2 of the sea floor. With an average thickness of 50 m, the total volume of the deposit is estimated at 36 km3. In some cases, the departure zone appears to be near the crest of the continental slope, at a water depth between 500 and 2,000 m with debris spreading over about 20 km at a depth ranging from 2,500 to 2,600 m. From preliminary analysis, at least one lobe of the Block Composite slide (lobe 2) would require further study to evaluate its tsunamigenic potential.
Mallinson, D.J., Culver, S.J., Riggs, S.R., Thieler, E.R., Foster, D., Wehmiller, J., Farrell, K.M., and Pierson, J., 2010, Regional seismic stratigraphy and controls on the Quaternary evolution of the Cape Hatteras region of the Atlantic passive margin, USA:
, v. 268
, no. 1-4
. Online at 10.1016/j.margeo.2009.10.007
Seismic and core data, combined with amino acid racemization and strontium-isotope age data, enable the definition of the Quaternary stratigraphic framework and recognition of geologic controls on the development of the modern coastal system of North Carolina, U.S.A. Seven regionally continuous high amplitude reflections are defined which bound six seismic stratigraphic units consisting of multiple regionally discontinuous depositional sequences and parasequence sets, and enable an understanding of the evolution of this margin. Data reveal the progressive eastward progradation and aggradation of the Quaternary shelf. The early Pleistocene inner shelf occurs at a depth of ca. 2040 m beneath the western part of the modern estuarine system (Pamlico Sound). A mid- to outer shelf lowstand terrace (also early Pleistocene) with shelf sand ridge deposits comprising parasequence sets within a transgressive systems tract, occurs at a deeper level (ca. 4570 m) beneath the modern barrier island system (the Outer Banks) and northern Pamlico Sound. Seismic and foraminiferal paleoenvironmental data from cores indicate the occurrence of lowstand strandplain shoreline deposits on the early to middle Pleistocene shelf. Middle to late Pleistocene deposits occur above a prominent unconformity and marine flooding surface that truncates underlying units, and contain numerous filled fluvial valleys that are incised into the early and middle Pleistocene deposits. The stratigraphic framework suggests margin progradation and aggradation modified by an increase in the magnitude of sea-level fluctuations during the middle to late Pleistocene, expressed as falling stage, lowstand, transgressive and highstand systems tracts. Thick stratigraphic sequences occur within the middle Pleistocene section, suggesting the occurrence of high capacity fluvial point sources debouching into the area from the west and north. Furthermore, the antecedent topography plays a significant role in the evolution of the geomorphology and stratigraphy of this marginal system.
Martini, Marinna A., and Foote, Kenneth G., 2010, Standard-target calibration of an acoustic backscatter system:
. Online at 10.1109/OCEANS.2010.5664362
The standard-target method used to calibrate scientific echo sounders and other scientific sonars by a single, solid elastic sphere is being adapted to acoustic backscatter (ABS) systems. Its first application, to the AQUAscat 1000, is described. The on-axis sensitivity and directional properties of transducer beams at three operating frequencies, nominally 1, 2.5, and 4 MHz, have been determined using a 10-mm-diameter sphere of tungsten carbide with 6% cobalt binder. Preliminary results are reported for the 1-MHz transducer. Their application to measurements of suspended sediment made in situ with the same device is described. This will enable the data to be expressed directly in physical units of volume backscattering.
McMullen, K.Y., Poppe, L.J., and Soderberg, N.K., 2009, Digital seismic-reflection data from eastern Rhode Island Sound and vicinity, 1975-1980:
U.S. Geological Survey Open-File Report 2009-1003, 2 DVD-ROMs
. Online at http://pubs.usgs.gov/of/2009/1003/
During 1975 and 1980, the U.S. Geological Survey (USGS) conducted two seismic-reflection surveys in Rhode Island Sound (RIS) aboard the research vessel Asterias: cruise ASTR75June surveyed eastern RIS in 1975 and cruise AST806B surveyed southern RIS in 1980. Data from these surveys were recorded in analog form and archived at the USGS Woods Hole Coastal and Marine Science Center's Data Library. In response to recent interest in the geology of RIS and in an effort to make the data more readily accessible while preserving the original paper records, the seismic data from these cruises were scanned and converted to black and white Tagged Image File Format and grayscale Portable Network Graphics images and SEG-Y data files. Navigation data were converted from U.S. Coast Guard Long Range Aids to Navigation time delays to latitudes and longitudes that are available in Environmental Systems Research Institute, Inc., shapefile format and as eastings and northings in space-delimited text format. This report complements two others that contain analog seismic-reflection data from RIS (McMullen and others, 2009) and Long Island and Block Island Sounds (Poppe and others, 2002) and were converted into digital form.
McMullen, K.Y., Poppe, L.J., Danforth, W.W., Blackwood, D.S., Schaer, J.D., Ostapenko, A.J., Glomb, K.A., and Doran, E.F., 2010, Surficial geology of the sea floor in Long Island Sound offshore of Plum Island, New York:
U.S. Geological Survey Open-File Report 2010-1005
. Online at http://pubs.usgs.gov/of/2010/1005/
The U.S. Geological Survey (USGS), the Connecticut Department of Environmental Protection, and the National Oceanic and Atmospheric Administration (NOAA) have been working cooperatively to interpret surficial sea-floor geology along the coast of the Northeastern United States. NOAA survey H11445 in eastern Long Island Sound, offshore of Plum Island, New York, covers an area of about 12 square kilometers. Multibeam bathymetry and sidescan-sonar imagery from the survey, as well as sediment and photographic data from 13 stations occupied during a USGS verification cruise are used to delineate sea-floor features and characterize the environment. Bathymetry gradually deepens offshore to over 100 meters in a depression in the northwest part of the study area and reaches 60 meters in Plum Gut, a channel between Plum Island and Orient Point. Sand waves are present on a shoal north of Plum Island and in several smaller areas around the basin. Sand-wave asymmetry indicates that counter-clockwise net sediment transport maintains the shoal. Sand is prevalent where there is low backscatter in the sidescan-sonar imagery. Gravel and boulder areas are submerged lag deposits produced from the Harbor Hill-Orient Point-Fishers Island moraine segment and are found adjacent to the shorelines and just north of Plum Island, where high backscatter is present in the sidescan-sonar imagery.
Pendleton, E.A., Barras, J.A., Williams, S.J., and Twichell, D.C., 2010, Coastal vulnerability assessment of the Northern Gulf of Mexico to sea-level rise and coastal change:
U.S. Geological Survey Open-File Report 2010-1146
. Online at http://pubs.usgs.gov/of/2010/1146/
A coastal vulnerability index (CVI) was used to map the relative vulnerability of the coast to future sea-level rise along the Northern Gulf of Mexico from Galveston, TX, to Panama City, FL. The CVI ranks the following in terms of their physical contribution to sea-level rise-related coastal change: geomorphology, regional coastal slope, rate of relative sea-level rise, historical shoreline change rate, mean tidal range, and mean significant wave height. The rankings for each variable are combined and an index value is calculated for 1-kilometer grid cells along the coast. The CVI highlights those regions where the physical effects of sea-level rise might be the greatest. The CVI assessment presented here builds on an earlier assessment conducted for the Gulf of Mexico. Recent higher resolution shoreline change, land loss, elevation, and subsidence data provide the foundation for a better assessment for the Northern Gulf of Mexico. The areas along the Northern Gulf of Mexico that are likely to be most vulnerable to sea-level rise are parts of the Louisiana Chenier Plain, Teche-Vermillion Basin, and the Mississippi barrier islands, as well as most of the Terrebonne and Barataria Bay region and the Chandeleur Islands. These very high vulnerability areas have the highest rates of relative sea-level rise and the highest rates of shoreline change or land area loss. The information provided by coastal vulnerability assessments can be used in long-term coastal management and policy decision making.
Pendleton, E.A., Thieler, E. Robert, and Williams, S. Jeffress, 2010, Importance of coastal change variables in determining vulnerability to sea- and lake-level change:
Journal of Coastal Research
, v. 26
, no. 1
. Online at 10.2112/08-1102.1
In 2001, the U.S. Geological Survey began conducting scientific assessments of coastal vulnerability to potential future sea- and lake-level changes in 22 National Park Service sea- and lakeshore units. Coastal park units chosen for the assessment included a variety of geological and physical settings along the U.S. Atlantic, Pacific, Gulf of Mexico, Gulf of Alaska, Caribbean, and Great Lakes shorelines. This research is motivated by the need to understand and anticipate coastal changes caused by accelerating sea-level rise, as well as lake-level changes caused by climate change, over the next century. The goal of these assessments is to provide information that can be used to make long-term (decade to century) management decisions. Here we analyze the results of coastal vulnerability assessments for several coastal national park units.
Index-based assessments quantify the likelihood that physical changes may occur based on analysis of the following variables: tidal range, ice cover, wave height, coastal slope, historical shoreline change rate, geomorphology, and historical rate of relative sea- or lake-level change. This approach seeks to combine a coastal system's susceptibility to change with its natural ability to adapt to changing environmental conditions, and it provides a measure of the system's potential vulnerability to the effects of sea- or lake-level change. Assessments for 22 park units are combined to evaluate relationships among the variables used to derive the index. Results indicate that Atlantic and Gulf of Mexico parks have the highest vulnerability rankings relative to other park regions. A principal component analysis reveals that 99% of the index variability can be explained by four variables: geomorphology, regional coastal slope, water-level change rate, and mean significant wave height. Tidal range, ice cover, and historical shoreline change are not as important when the index is evaluated at large spatial scales (thousands of kilometers).
Peterson, Curt D., Vanderburgh, Sandy, Roberts, Michael C., Jol, Harry M., Phipps, Jim, and Twichell, David C., 2010, Composition, age, and depositional rates of shoreface deposits under barriers and beach plains of the Columbia River littoral cell, USA:
, v. 273
, no. 1-4
. Online at 10.1016/j.margeo.2010.02.004
The Columbia River littoral cell (CRLC) consists of four subcells (totaling 160 km in length) that are unique in the West Coast of the United States, in that they contain prograded barriers and beach plains, reaching 0.53 km in width (Fig. 1). The prograded beach deposits (15 ka in age) overlie shoreface deposits (18 ka in age), as identified in 18 ground penetrating radar profiles, and sampled from 24 boreholes. Two competing hypotheses were initially proposed to account for the origins of these unique, progradative shorelines: (1) cross-shore feeding by onshore wave transport of pre-Holocene sand from the submerged shelf, and (2) longshore dispersal of nearshore sand that was supplied to the littoral system by bedload sediment discharge from the Columbia River during the Holocene.
The CRLC sand forming the shoreface deposits is fine (diameter 0.2 ± 0.02 mm) and rich in lithic fragments (2040% by volume). Gravel and shell lag layers are uncommon in most of the CRLC shoreface deposits, but they show greater abundance locally near ravinement surfaces, tidal inlets, and in the Clatsop subcell, located south of the Columbia River mouth. Gravel and granule layers increase upsection in barriers south of the Columbia River and downsection in barriers at the northern end of the littoral system. These trends suggest different mechanisms of shoreface sediment feeding within the four subcells. However, borehole samples from all four subcells show the same sand provenance, i.e., post-glacial Columbia River sand, which is identified by high ratios of hypersthene:augite in heavy-mineral fractions.
Selected shoreface sections were dated (0.58 ka) by AMS radiocarbon analysis of articulated-shell and wood fragments recovered from auger flights (322 m depth subsurface). Relatively young shoreface deposition (2.5 ka at − 6.5 m elevation NGVD88) in the Clatsop subcell south of the Columbia River shows a net-southward beach transport that fed shoreface and beachface progradation into deeper water. Older and deeper shoreface deposition (4.4 ka at − 7.1 m elevation) in the Long Beach subcell north of the Columbia River was a result of the filling of innermost-shelf accommodation space prior to beachface progradation.
The total volume of shoreface sand deposited under the barrier spits and beach plains of the CRLC is estimated to be 67 km3 deposited since 68 ka. There was a net-northward transport of littoral sand ( 1 × 106 m3 year− 1) along the nearshore and inner-shelf; subsequently some of this sand was transported onshore to feed beaches of the northernmost subcells. Columbia River sand was also the source for the formation of the offshore shelf wedge above the transgressive ravinement surface, and for the filling of major tidal basins located north of the Columbia River. In summary, the unique progradational history of the CRLC barriers and beach plains derives from the combination of (1) longshore dispersal of fine sand discharged from the Columbia River during Holocene time, and (2) across-shore feeding of beaches at the northern end of the littoral system from fine sand carried north along the nearshore and the inner-shelf.
Pohlman, J.W., Bauer, J.E., Waite, W.F., Osburn, C.L., and Chapman, N.R., 2010, Gas hydrate-bearing seeps as a source of aged dissolved organic matter to the oceans:
, v. 4
, no. 1
, pp. 37-41
. Online at 10.1038/ngeo1016
Marine sediments contain about 500�10,000 Gt of methane carbon1, 2, 3, primarily in gas hydrate. This reservoir is comparable in size to the amount of organic carbon in land biota, terrestrial soils, the atmosphere and sea water combined1, 4, but it releases relatively little methane to the ocean and atmosphere5. Sedimentary microbes convert most of the dissolved methane to carbon dioxide6, 7. Here we show that a significant additional product associated with microbial methane consumption is methane-derived dissolved organic carbon. We use Δ14C and δ13C measurements and isotopic mass-balance calculations to evaluate the contribution of methane-derived carbon to seawater dissolved organic carbon overlying gas hydrate-bearing seeps in the northeastern Pacific Ocean. We show that carbon derived from fossil methane accounts for up to 28% of the dissolved organic carbon. This methane-derived material is much older, and more depleted in 13C, than background dissolved organic carbon. We suggest that fossil methane-derived carbon may contribute significantly to the estimated 4,000�6,000 year age of dissolved organic carbon in the deep ocean8, and provide reduced organic matter and energy to deep-ocean microbial communities.
Poppe, L.J., Danforth, W.W., McMullen, K.Y., Parker, C.E., Lewit, P.G., and Doran, E.F., 2010, Integrated multibeam and LIDAR bathymetry data offshore of New London and Niantic, Connecticut:
U.S. Geological Survey Open-File Report 2009-1231
. Online at http://pubs.usgs.gov/of/2009/1231/
Poppe, L.J., McMullen, K.Y., Ackerman, S.D., Blackwood, D.S., Irwin, B.J., Schaer, J.D., Lewit, P.G., and Doran, E.F., 2010, Sea-floor geology and character offshore of Rocky Point, New York:
U.S. Geological Survey Open-File Report 2010-1007
. Online at http://pubs.usgs.gov/of/2010/1007/
Gridded multibeam bathymetry and sidescan-sonar imagery together cover approximately 21.6 square kilometers of sea floor in eastern Long Island Sound offshore of Rocky Point, New York. Although originally collected for charting purposes during National Oceanic and Atmospheric Administration hydrographic survey H11251, these acoustic data, and the sea-floor sampling and photography stations subsequently occupied to verify them, (1) show the composition and terrain of the seabed, (2) provide information on sediment transport and benthic habitat, and (3) are part of an expanding series of studies that provide a fundamental framework for research and resource management (for example, cables, pipelines, and dredging) activities in this major East Coast estuary.
Poppe, L.J., McMullen, K.Y., Foster, D.S., Blackwood, D.S., Williams, S.J., Ackerman, S.D., Moser, M.S., and Glomb, K.A., 2010, Geological interpretation of the sea floor offshore of Edgartown, Massachusetts:
U.S. Geological Survey Open-File Report 2009-1001
. Online at http://pubs.usgs.gov/of/2009/1001/
Gridded bathymetry and sidescan-sonar imagery together cover approximately 37.3 square kilometers of sea floor in the vicinity of Edgartown Harbor, Massachusetts. Although originally collected for charting purposes during National Oceanic and Atmospheric Administration hydrographic survey H11346, these acoustic data, and the sea-floor stations and seismic-reflection lines subsequently occupied to verify them, 1) show the composition and terrain of the seabed, 2) provide information on sediment transport and benthic habitat, and 3) are part of an expanding series of studies that provide a fundamental framework for research and management (for example, windfarms, pipelines, and dredging) activities along the Massachusetts inner continental shelf.
Scanlon, Kathryn M., Waller, Rhian G., Sirotek, Alexander R., Knisel, Julia M., O'Malley, John J., and Alesandrini, Stian, 2010, USGS cold-water coral geographic database; Gulf of Mexico and western North Atlantic, Version 1.0:
U.S. Geolgical Survey Open-File Report 2008-1351, CD-ROM
. Online at http://pubs.usgs.gov/of/2008/1351/
The USGS Cold-Water Coral Geographic Database (CoWCoG) provides a tool for researchers and managers interested in studying, protecting, and/or utilizing cold-water coral habitats in the Gulf of Mexico and western North Atlantic Ocean. The database makes information about the locations and taxonomy of cold-water corals available to the public in an easy-to-access form while preserving the scientific integrity of the data. The database includes over 1700 entries, mostly from published scientific literature, museum collections, and other databases. The CoWCoG database is easy to search in a variety of ways, and data can be quickly displayed in table form and on a map by using only the software included with this publication. Subsets of the database can be selected on the basis of geographic location, taxonomy, or other criteria and exported to one of several available file formats. Future versions of the database are being planned to cover a larger geographic area and additional taxa.
Shedlock, R.J., and Bratton, J.F., 2009, Groundwater contributes nutrients to the coastal bays:
The title of this book-Shifting Sands-refers to both the dynamic nature of the barrier islands forming the coastal lagoons of Maryland's Atlantic Ocean coastline and also the changing cultural landscape as more and more people discover these once-forgotten bays. The subtitle of the book-Environmental and cultural change in Maryland's Coastal Bays-reflects the way the book integrates natural and human influences. Shifting Sands is a richly illustrated, multi-authored introduction to Assawoman Bay, Isle of Wight Bay, St. Martin River, Sinepuxent Bay, Newport Bay, and Chincoteague Bay. This book leads the reader on a voyage of discovery, providing a user-friendly guide to the history, setting, context, and ecology of these waterways nestled behind Assateague, Fenwick, and Chincoteague Islands. Photographs, conceptual diagrams, maps, and graphs are used to showcase the key features of and major threats to these magnificent bays, watersheds, and islands, with recommendations for how to preserver them for future generations.
Thieler, E.R., Himmelstoss, E.A., Zichichi, J.L., and Ergul, A., 2010, Digital Shoreline Analysis System (DSAS) version 4.0; an ArcGIS extension for calculating shoreline change:
U.S. Geological Survey Open-File Report 2008-1278 v 4.2
. Online at http://woodshole.er.usgs.gov/project-pages/DSAS/version4/
The Digital Shoreline Analysis System (DSAS) version 4.2 is a software extension to ESRI ArcGIS v.9.2 and above that enables a user to calculate shoreline rate-of-change statistics from multiple historic shoreline positions. A user-friendly interface of simple buttons and menus guides the user through the major steps of shoreline change analysis. Components of the extension and user guide include (1) instruction on the proper way to define a reference baseline for measurements, (2) automated and manual generation of measurement transects and metadata based on user-specified parameters, and (3) output of calculated rates of shoreline change and other statistical information. DSAS computes shoreline rates of change using four different methods: (1) endpoint rate, (2) simple linear regression, (3) weighted linear regression, and (4) least median of squares. The standard error, correlation coefficient, and confidence interval are also computed for the simple and weighted linear-regression methods. The results of all rate calculations are output to a table that can be linked to the transect file by a common attribute field. DSAS is intended to facilitate the shoreline change-calculation process and to provide rate-of-change information and the statistical data necessary to establish the reliability of the calculated results. The software is also suitable for any generic application that calculates positional change over time, such as assessing rates of change of glacier limits in sequential aerial photos, river edge boundaries, land-cover changes, and so on.
Todd, B.J., and Valentine, P.C., 2010, Shaded seafloor relief, backscatter strength, and surficial geology; German Bank, Scotian Shelf, offshore Nova Scotia:
Geological Survey of Canada, Open File 6124, sheet 1, Shaded seafloor relief, scale 1:100,000
. Online at http://open.canada.ca/data/en/dataset/023eeeb9-9cf1-5281-bd97-59dca5a476b0
Todd, B.J., and Valentine, P.C., 2010, Shaded seafloor relief, backscatter strength, and surficial geology; German Bank, Scotian Shelf, offshore Nova Scotia:
Geological Survey of Canada, Open File 6124, sheet 2, Shaded seafloor relief, scale 1:100,000
. Online at http://geoscan.nrcan.gc.ca/starweb/geoscan/servlet.starweb?path=geoscan/downloade.web&search1=R=261833
Todd, B.J., and Valentine, P.C., 2010, Shaded seafloor relief, backscatter strength, and surficial geology; German Bank, Scotian Shelf, offshore Nova Scotia:
Geological Survey of Canada, Open File 6124, sheet 3, Shaded seafloor relief, scale 1:100,000
. Online at http://geoscan.nrcan.gc.ca/starweb/geoscan/servlet.starweb?path=geoscan/downloade.web&search1=R=261833
Twichell, D., Edmiston, L., Andrews, B., Stevenson, W., Donoghue, J., Poore, R., and Osterman, L., 2010, Geologic controls on the recent evolution of oyster reefs in Apalachicola Bay and St. George Sound, Florida:
Estuarine, Coastal and Shelf Science
, v. 88
, no. 3
, pp. 385-394
. Online at 10.1016/j.ecss.2010.04.019
Apalachicola Bay and St. George Sound contain the largest oyster fishery in Florida, and the growth and distribution of the numerous oyster reefs here are the combined product of modern estuarine conditions in the bay and its late Holocene evolution. Sidescan-sonar imagery, bathymetry, high-resolution seismic profiles, and sediment cores show that oyster beds occupy the crests of a series of shoals that range from 1 to 7 km in length, trend roughly north-south perpendicular to the long axes of the bay and sound, and are asymmetrical with steeper sides facing to the west. Surface sediment samples show that the oyster beds consist of shelly sand, while much of the remainder of the bay floor is covered by mud delivered by the Apalachicola River. The present oyster reefs rest on sandy delta systems that advanced southward across the region between 6400 and 4400 yr BP when sea level was 4�6 m lower than present. Oysters started to colonize the region around 5100 yr BP and became extensive by 1200 and 2400 yr BP. Since 1200 yr BP, their aerial extent has decreased due to burial of the edges of the reefs by the prodelta mud that continues to be supplied by the Apalachicola River. Oyster reefs that are still active are narrower than the original beds, have grown vertically, and become asymmetrical in cross-section. Their internal bedding indicates they have migrated westward, suggesting a net westerly transport of sediment in the bay.
Twichell, D.C., and Cross, V.A., 2009, Surficial geology of the floor of Lake Mead (Arizona and Nevada) as defined by sidescan-sonar imagery, lake-floor topography, and post-impoundment sediment thickness:
U.S. Geological Survey Open-File Report 2009-1150, CD-ROM
. Online at http://pubs.usgs.gov/of/2009/1150/
Sidescan-sonar imagery collected in Lake Mead during 1999-2001, a period of high lake level, has been used to map the surficial geology of the floor of this large reservoir that formed upon completion of the Hoover Dam in 1935. Four surficial geologic units were identified and mapped: rock exposures and alluvial deposits that existed prior to the formation of the lake and thin post-impoundment sediments (< 1 m) and thick post-impoundment sediments (> 1 m) deposited since the lake formed. Exposures of rock are most extensive in the narrow, steep-sided sections of the lake, while alluvial deposits are most extensive on the gentle flanks of the broader basin sections of the lake. Post-impoundment sediment is restricted to the floors of the original river valleys that now lie below lake level. These sediments are thickest in the deltas that form at the mouths of the Colorado River and its tributaries, but cover the entire length of the valley floors of the lake. This sediment distribution is consistent with deposition from turbidity currents. Lake level has dropped more than 30 m between collection of the sidescan imagery and publication of this report. During this time, thick delta deposits have been eroded and redistributed to deeper parts of the lake by turbidity currents. While present-day post-impoundment sediment distribution should be similar to what it was in 2001, the thickness may be greater in some of the deeper parts of the lake now.
Twichell, D.C., Pendleton, E.A., Poore, R.Z., Osterman, L.E., and Kelso, K.W., 2009, Vibracore, radiocarbon, microfossil, and grain-size data from Apalachicola Bay, Florida:
U.S. Geological Survey Open-File Report 2009-1031
. Online at http://pubs.usgs.gov/of/2009/1031/
In 2007, the U.S. Geological Survey collected 24 vibracores within Apalachicola Bay, Florida. The vibracores were collected by using a Rossfelder electric percussive (P-3) vibracore system during a cruise on the Research Vessel (R/V) G.K. Gilbert. Selection of the core sites was based on a geophysical survey that was conducted during 2005 and 2006 in collaboration with the National Oceanic and Atmospheric Administrations (NOAA) Coastal Services Center (CSC) and the Apalachicola Bay National Estuarine Research Reserve. This report contains the vibracore data logs, photographs, and core-derived data including grain-size analyses, radiocarbon ages, microfossil counts, and sedimentological interpretations. The long-term goal of this study is to provide maps, data, and assistance to the Apalachicola Bay National Estuarine Research Reserve in their effort to monitor and understand the geology and ecology of Apalachicola Bay Estuary. These data will inform coastal managers charged with the responsibility for resource preservation.
Twichell, David C., Cross, VeeAnn A., and Peterson, Curt D., 2010, Partitioning of sediment on the shelf offshore of the Columbia River littoral cell:
, v. 273
, no. 1-4
. Online at 10.1016/j.margeo.2010.02.001
Sediment derived from the Columbia River has been deposited on the continental shelf, along the barriers and beaches, and in the bays of the Oregon and Washington coast during the Holocene. The barrier and beach deposits of this 150-km section of coast comprise approximately 6 km3 of these Holocene sediments (Peterson et al., 2010-this issue) while the fluvial and bay deposits comprise about 104 km3 (Baker et al., 2010-this issue), and the shelf deposit is approximately 79 km3. Seismic-reflection, sidescan sonar, and surface sediment data show that the shelf deposit is not uniform in distribution or composition. The shelf deposit is 1550 m thick off the beaches of the southern part of the study area but is less than 3 m thick, and, in places, absent from the inner shelf in the northern third of the study area. Surface sediment texture of the shelf deposit varies as well. Pleistocene-age gravel covers parts of the inner shelf in the northern third of the area. To the south, the surface of the Holocene shelf deposit is composed of fine sand near shore that grades offshore to dominantly very fine sand in 2530 m water depth and muddy sand on the middle and outer shelf (> 50 m depth). Although a huge volume of sediment covers the shelf, its uneven distribution indicates that in places only small amounts are available as a potential offshore source to the adjacent beaches, and in other places the finer-grained nature of the shelf deposit indicates that significant winnowing of fine sediment would be necessary to make it compositionally equivalent to sediment on adjacent beaches.
Valentine, Page C., Gallea, Leslie B., Blackwood, Dann S., and Twomey, Erin R., 2010, Seabed photographs, sediment texture analyses, and sun-illuminated sea floor topography in the Stellwagen Bank National Marine Sanctuary region off Boston, Massachusetts:
U.S. Geological Survey Data Series 469
. Online at http://pubs.usgs.gov/ds/469/
The U.S. Geological Survey, in collaboration with National Oceanic and Atmospheric Administrations National Marine Sanctuary Program, conducted seabed mapping and related research in the Stellwagen Bank National Marine Sanctuary region from 1993 to 2004. The mapped area is approximately 3,700 km² (1,100 nmi²) in size and was subdivided into 18 quadrangles. An extensive series of sea-floor maps of the region based on multibeam sonar surveys has been published as paper maps and online in digital format (PDF, EPS, PS). In addition, 2,628 seabed-sediment samples were collected and analyzed and are in the usSEABED: Atlantic Coast Offshore Surficial Sediment Data Release. This report presents for viewing and downloading the more than 10,600 still seabed photographs that were acquired during the project. The digital images are provided in thumbnail, medium (1536 x 1024 pixels), and high (3071 x 2048) resolution. The images can be viewed by quadrangle on the U.S. Geological Survey Woods Hole Coastal and Marine Science Centers photograph database. Photograph metadata are embedded in each image in Exchangeable Image File Format and also provided in spreadsheet format. Published digital topographic maps and descriptive text for seabed features are included here for downloading and serve as context for the photographs. An interactive topographic map for each quadrangle shows locations of photograph stations, and each location is linked to the photograph database. This map also shows stations where seabed sediment was collected for texture analysis; the results of grain-size analysis and associated metadata are presented in spreadsheet format.
Van Furl, Chad, Colman, John A., and Bothner, Michael H., 2010, Mercury sources to Lake Ozette and Lake Dickey; highly contaminated remote coastal lakes, Washington State, USA:
Water, Air, and Soil Pollution
, v. 208
, no. 1-4
. Online at 10.1007/s11270-009-0165-y
Mercury concentrations in largemouth bass and mercury accumulation rates in age-dated sediment cores were examined at Lake Ozette and Lake Dickey in Washington State. Goals of the study were to compare concentrations in fish tissues at the two lakes with a larger statewide dataset and examine mercury pathways to the lakes. After accounting for fish length, tissue concentrations at the lakes were significantly higher than other Washington State lakes. Wet deposition and historical atmospheric monitoring from the area show no indication of enhanced local or regional deposition. Sediment core records from the lakes indicate rising sedimentation rates coinciding with logging in the lakes drainages has greatly increased the net flux of mercury to the waterbodies.
Voinov, A.A., DeLuca, Cecelia, Hood, R.R., Peckham, Scott, Sherwood, C.R., and Syvitski, J.P.M., 2010, A community approach to Earth systems modeling:
Eos, Transactions, American Geophysical Union
, v. 91
, no. 13
Waite, W.F., Koh, C., and Santamarina, J.C., 2010, Announcing an inter-laboratory comparison project targeting physical property measurements:
Fire in the Ice, U.S. Department of Energy/National Energy Technology Laboratory, Methane Hydrate Newsletter
, v. August 2010
. Online at http://www.netl.doe.gov/technologies/oil-gas/publications/Hydrates/Newsletter/MHNews_2010_08.pdf
Waite, W.F., Santamarina, J.C., Cortes, D.D., Dugan, B., Espinoza, D.N., Germaine, J., Jang, J., Jung, J.W., Kneafsey, T.J., Shin, H., Soga, K., Winters, W.J., and Yun, T-S., 2009, Physical properties of hydrate-bearing sediments:
Reviews of Geophysics
, v. 47
, no. RG4003
, pp. 38
. Online at 10.1029/2008RG000279
Methane gas hydrates, crystalline inclusion compounds formed from methane and water, are found in marine continental margin and permafrost sediments worldwide. This article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate-bearing sediments. Formation phenomena include pore-scale habit, solubility, spatial variability, and host sediment aggregate properties. Physical properties include thermal properties, permeability, electrical conductivity and permittivity, small-strain elastic P and S wave velocities, shear strength, and volume changes resulting from hydrate dissociation. The magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate-bearing sediments to changes in mechanical, thermal, or chemical boundary conditions. These predictions are vital for mitigating borehole, local, and regional slope stability hazards; optimizing recovery techniques for extracting methane from hydrate-bearing sediments or sequestering carbon dioxide in gas hydrate; and evaluating the role of gas hydrate in the global carbon cycle.
Warner, J.C., Geyer, W.R., and Arango, H.G., 2010, Using a composite grid approach in a complex coastal domain to estimate estuarine residence time:
Computers & Geosciences
, v. 36
, no. 7
, pp. 921-935
. Online at 10.1016/j.cageo.2009.11.008
We investigate the processes that influence residence time in a partially
mixed estuary using a three-dimensional circulation model. The complex
geometry of the study region is not optimal for a structured grid model
and so we developed a new method of grid connectivity. This involves a
novel approach that allows an unlimited number of individual grids to be
combined in an efficient manner to produce a composite grid. We then
implemented this new method into the numerical Regional Ocean Modeling
System (ROMS) and developed a composite grid of the Hudson River estuary
region to investigate the residence time of a passive tracer. Results
show that the residence time is a strong function of the time of release
(spring vs. neap tide), the along-channel location, and the initial
vertical placement. During neap tides there is a maximum in residence
time near the bottom of the estuary at the mid-salt intrusion length.
During spring tides the residence time is primarily a function of
along-channel location and does not exhibit a strong vertical variability.
This model study of residence time illustrates the utility of the grid
connectivity method for circulation and dispersion studies in regions
of complex geometry.
Warner, John C., Armstrong, Brandy, He, Ruoying, and Zambon, Joseph B., 2010, Development of a Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system:
, v. 35
, no. 3
. Online at 10.1016/j.ocemod.2010.07.010
Understanding the processes responsible for coastal change is important for managing our coastal resources, both natural and economic. The current scientific understanding of coastal sediment transport and geology suggests that examining coastal processes at regional scales can lead to significant insight into how the coastal zone evolves. To better identify the significant processes affecting our coastlines and how those processes create coastal change we developed a Coupled OceanAtmosphereWaveSediment Transport (COAWST) Modeling System, which is comprised of the Model Coupling Toolkit to exchange data fields between the ocean model ROMS, the atmosphere model WRF, the wave model SWAN, and the sediment capabilities of the Community Sediment Transport Model. This formulation builds upon previous developments by coupling the atmospheric model to the ocean and wave models, providing one-way grid refinement in the ocean model, one-way grid refinement in the wave model, and coupling on refined levels. Herein we describe the modeling components and the data fields exchanged. The modeling system is used to identify model sensitivity by exchanging prognostic variable fields between different model components during an application to simulate Hurricane Isabel during September 2003. Results identify that hurricane intensity is extremely sensitive to sea surface temperature. Intensity is reduced when coupled to the ocean model although the coupling provides a more realistic simulation of the sea surface temperature. Coupling of the ocean to the atmosphere also results in
decreased boundary layer stress and coupling of the waves to the atmosphere results in increased bottom stress. Wave results are sensitive to both ocean and atmospheric coupling due to wavecurrent interactions with the ocean and wave growth from the atmosphere wind stress. Sediment resuspension at regional scale during the hurricane is controlled by shelf width and wave propagation during hurricane approach.
Winters, William, Walker, Michael, Hunter, Robert, Collett, Timothy, Boswell, Ray, Waite, William, Torres, Marta, Patil, Shirish, and Dandekar, Abhijit, 2010, Physical properties of sediment from the Mount Elbert Gas Hydrate Stratigraphic
Test Well, Alaska North Slope:
Journal of Marine and Petroleum Geology
, v. 28
, no. 2011
, pp. 361-380
. Online at 10.1016/j.marpetgeo.2010.01.008
This study characterizes cored and logged sedimentary strata from the February 2007 BP Exploration Alaska, Department of Energy, U.S. Geological Survey (BPXA-DOE-USGS) Mount Elbert Gas Hydrate Stratigraphic Test Well on the Alaska North Slope (ANS). The physical-properties program analyzed core samples recovered from the well, and in conjunction with downhole geophysical logs, produced an extensive dataset including grain size, water content, porosity, grain density, bulk density, permeability, X-ray diffraction (XRD) mineralogy, nuclear magnetic resonance (NMR), and petrography. This study documents the physical property interrelationships in the well and demonstrates their correlation with the occurrence of gas hydrate. Gas hydrate (GH) occurs in three unconsolidated, coarse
silt to fine sand intervals within the Paleocene and Eocene beds of the Sagavanirktok Formation: Unit D-GH (614.4 m627.9 m); unit C-GH1 (649.8 m660.8 m); and unit C-GH2 (663.2 m666.3 m). These intervals are overlain by fine to coarse silt intervals with greater clay content. A deeper interval (unit B) is
similar lithologically to the gas-hydrate-bearing strata; however, it is water-saturated and contains no hydrate. In this system it appears that high sediment permeability (k) is critical to the formation of concentrated hydrate deposits. Intervals D-GH and C-GH1 have average plug intrinsic permeability to nitrogen
values of 1700 mD and 675 mD, respectively. These values are in strong contrast with those of the overlying, gas-hydrate-free sediments, which have k values of 5.7 mD and 49 mD, respectively, and thus would have provided effective seals to trap free gas. The relation between permeability and porosity critically influences the occurrence of GH. For example, an average increase of 4% in porosity increases permeability by an order of magnitude, but the presence of a second fluid (e.g., methane from dissociating gas hydrate) in the reservoir reduces permeability by more than an order of magnitude.