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Publications by year, USGS Woods Hole Coastal and Marine Science Center

All Publications by WHCMSC Authors for the year 2009



Agostini, Vera, Arico, Salvatore, Briones, Elva Escobar, Clark, Malcolm, Cresswell, Ian, Gjerde, Kristina, Niewijk, Deborah J.A., Polacheck, Arianna, Raymond, Ben, Rice, Jake, Roff, John, Scanlon, Kathryn M., Smith, Craig, Spalding, Mark, Tong, Ellyn, Vierros, Marjo, and Watling, Les, 2009, Global Open Oceans and Deep Seabed (GOODS) biogeographic classification: IOC Technical Series No. 84 , pp. 95
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:
Baldwin, Wayne E., Pendleton, Elizabeth A., and Twichell, David C., 2009, Geophysical data from offshore of the Chandeleur Islands, eastern Mississippi Delta: U.S. Geological Survey Open File Report 2008-1195 . Online at http://pubs.usgs.gov/of/2008/1195/
This report contains the geophysical and geospatial data that were collected during two cruises on the R/V Acadiana along the eastern, offshore side of the Chandeleur Islands in 2006 and 2007. Data were acquired with the following equipment: a Systems Engineering and Assessment, Ltd., SwathPlus interferometric sonar; a Klein 3000 dual-frequency sidescan sonar; and an EdgeTech 512i chirp sub-bottom profiling system. The long-term goal of this mapping effort is to produce high-quality, high-resolution geologic maps and geophysical interpretations that can be utilized to investigate the impact of Hurricane Katrina, identify sand resources within the region, and make predictions regarding the future evolution of this coastal system.
Barkan, Roy, ten Brink, Uri S., and Lin, Jian, 2009, Far field tsunami simulations of the 1755 Lisbon earthquake; implications for tsunami hazard to the U.S. East Coast and the Caribbean: Marine Geology , v. 264 , no. 1-2 . Online at 10.1016/j.margeo.2008.10.010
The great Lisbon earthquake of November 1st, 1755 with an estimated moment magnitude of 8.5–9.0 was the most destructive earthquake in European history. The associated tsunami run-up was reported to have reached 5–15 m along the Portuguese and Moroccan coasts and the run-up was significant at the Azores and Madeira Island. Run-up reports from a trans-oceanic tsunami were documented in the Caribbean, Brazil and Newfoundland (Canada). No reports were documented along the U.S. East Coast. Many attempts have been made to characterize the 1755 Lisbon earthquake source using geophysical surveys and modeling the near-field earthquake intensity and tsunami effects. Studying far field effects, as presented in this paper, is advantageous in establishing constraints on source location and strike orientation because trans-oceanic tsunamis are less influenced by near source bathymetry and are unaffected by triggered submarine landslides at the source. Source location, fault orientation and bathymetry are the main elements governing transatlantic tsunami propagation to sites along the U.S. East Coast, much more than distance from the source and continental shelf width. Results of our far and near-field tsunami simulations based on relative amplitude comparison limit the earthquake source area to a region located south of the Gorringe Bank in the center of the Horseshoe Plain. This is in contrast with previously suggested sources such as Marqués de Pombal Fault, and Gulf of Cádiz Fault, which are farther east of the Horseshoe Plain. The earthquake was likely to be a thrust event on a fault striking ~ 345° and dipping to the ENE as opposed to the suggested earthquake source of the Gorringe Bank Fault, which trends NE–SW. Gorringe Bank, the Madeira-Tore Rise (MTR), and the Azores appear to have acted as topographic scatterers for tsunami energy, shielding most of the U.S. East Coast from the 1755 Lisbon tsunami. Additional simulations to assess tsunami hazard to the U.S. East Coast from possible future earthquakes along the Azores–Iberia plate boundary indicate that sources west of the MTR and in the Gulf of Cadiz may affect the southeastern coast of the U.S. The Azores–Iberia plate boundary west of the MTR is characterized by strike–slip faults, not thrusts, but the Gulf of Cadiz may have thrust faults. Southern Florida seems to be at risk from sources located east of MTR and South of the Gorringe Bank, but it is mostly shielded by the Bahamas. Higher resolution near-shore bathymetry along the U.S. East Coast and the Caribbean as well as a detailed study of potential tsunami sources in the central west part of the Horseshoe Plain are necessary to verify our simulation results.
Barnhardt, Walter A., Andrews, Brian D., Ackerman, Seth D., Baldwin, Wayne E., and Hein, Christopher J., 2009, High-resolution geologic mapping of the inner continental shelf; Cape Ann to Salisbury Beach, Massachusetts: U.S. Geological Survey Open-File Report 2007-1373 . Online at http://pubs.usgs.gov/of/2007/1373/
The geologic framework of the Massachusetts inner continental shelf between Cape Ann and Salisbury Beach has been shaped by a complicated history of glaciation, deglaciation, and changes in relative sea level. New geophysical data (swath bathymetry, sidescan sonar and seismic-reflection profiling), sediment samples, and seafloor photography provide insight into the geomorphic and stratigraphic record generated by these processes. High-resolution spatial data and geologic maps in this report support coastal research and efforts to understand the type, distribution, and quality of subtidal marine habitats in the Massachusetts coastal ocean.
Bothner, Michael H., Reynolds, Richard L., Casso, Michael A., Storlazzi, Curt D., and Field, Michael E., 2008, Sediment mobility along Moloka`i's fringing coral reef; evidence from sediment traps; Chapter 19 of Field, Michael E., Cochran, Susan A., Logan, Joshua B., and Storlazzi, Curt D., eds., The coral reef of south Moloka`i, Hawai`i; portrait of a sediment-threatened fringing reef: U.S. Geological Survey Scientific Investigations Report 2007-5101 . Online at http://pubs.usgs.gov/sir/2007/5101/sir2007-5101_chapter19.pdf
Moloka'i is the fifth youngest island in the long chain of volcanoes and volcanic remnants that compose the Hawaiian archipelago (fig. 1). The archipelago extends from the Island of Hawai'i (the 'Big Island') in the southeast past Midway Island, to Kure Atoll in the northwest, for a total distance of about 2,400 km (1,500 mi). Beyond Kure Atoll, the chain continues as a series of submerged former islands known as the Emperor Seamounts, which extend to the Aleutian Trench off the coast of Alaska. Evolution of the entire Hawai'i-Emperor volcanic chain represents a time span of nearly 80 million years (Clague and Dalrymple, 1989). The volcanic chain is a result of gradual and persistent movement of the Pacific lithospheric plate (the sea-floor crust and rigid uppermost part of Earth's mantle) over a deep fracture (or hot spot) that extends down to the astenosphere, a less rigid part of the mantle (fig. 2). Plumes of molten lava flowed onto the sea floor, repeatedly creating massive shield volcanoes that exceed 10,000 m (33,000 ft) in relief above the surrounding sea floor. The growth of each volcano is a process that takes half a million years or more to construct most of its mass through sequential volcanic phases - submarine, explosive, and subaerial - of shield growth. Once formed, each massive island volcano is carried northwestward on the Pacific tectonic plate at rates of 8.6 to 9.2 cm/yr (Clague and Dalrymple, 1989). The postshield processes of alkalic volcanism, subsidence, landslides, rejuvenated volcanism, weathering, sediment deposition, and reef growth have all markedly influenced each volcano's present-day shape. Subsidence of each island is rapid at first (rates of 2 mm/yr or more; Moore and Campbell, 1987; Moore and Fornari, 1984; Campbell, 1986) in response to the extraordinary weight of large volumes of lava loaded onto the crust. As each island cools and slides northwestward with the sea-floor crust, it continues to subside at decreasing rates, down to the order of 0.02 mm/yr (Detrick and Crough, 1978). The sheer volume of rock that accumulates at each volcano ultimately leads to failure and partial collapse - each island has had spectacular landslides that are amongst the largest on earth (Moore and others, 1989). The large areas of irregular topography on the sea floor around the islands (for example, north of Moloka'i and northwest of O'ahu) attest to the magnitude of these events (fig.1). The normal processes of surface erosion and stream runoff modify volcano slopes early in an island's history. Those processes, along with development of soils, which occurs relatively quickly in humid volcanic terrain, lead to transport and deposition of sediment in alluvial fans, flood plains, and narrow coastal plains. The final process in island shaping is the establishment of coral reefs in shallow waters that are protected from large waves. Corals colonize exposed rock surfaces very quickly (Grigg and Maragos, 1974; Grigg, 1983), and it is likely that they become established early in the evolutionary history of each island. The development of coral reefs - the massive limestone structures capped by a living ecosystem that border many Hawaiian Islands - takes much longer (Grigg, 1987). Each reef is a thick (meters to tens of meters) packet of reefal limestone that likely accumulated over multiple stages of sea-level shifts (Grossman and others, 2006; Grossman and Fletcher, 2004; Sherman and others, 1999). In most locations in Hawai'i, modern coral cover is only a thin living veneer on top of older reef structures that formed during an earlier time under different conditions (Grigg, 1983, 1998).
Bratton, John F., Bohlke, John Karl, Krantz, David E., and Tobias, Craig R., 2009, Flow and geochemistry of groundwater beneath a back-barrier lagoon; the subterranean estuary at Chincoteague Bay, Maryland, USA: Marine Chemistry , v. 113 , no. 1-2 . Online at 10.1016/j.marchem.2009.01.004
To better understand large-scale interactions between fresh and saline groundwater beneath an Atlantic coastal estuary, an offshore drilling and sampling study was performed in a large barrier-bounded lagoon, Chincoteague Bay, Maryland, USA. Groundwater that was significantly fresher than overlying bay water was found in shallow plumes up to 8 m thick extending more than 1700 m offshore. Groundwater saltier than bay surface water was found locally beneath the lagoon and the barrier island, indicating recharge by saline water concentrated by evaporation prior to infiltration. Steep salinity and nutrient gradients occur within a few meters of the sediment surface in most locations studied, with buried peats and estuarine muds acting as confining units. Groundwater ages were generally more than 50 years in both fresh and brackish waters as deep as 23 m below the bay bottom. Water chemistry and isotopic data indicate that freshened plumes beneath the estuary are mixtures of water originally recharged on land and varying amounts of estuarine surface water that circulated through the bay floor, possibly at some distance from the sampling location. Ammonium is the dominant fixed nitrogen species in saline groundwater beneath the estuary at the locations sampled. Isotopic and dissolved-gas data from one location indicate that denitrification within the subsurface flow system removed terrestrial nitrate from fresh groundwater prior to discharge along the western side of the estuary. Similar situations, with one or more shallow semi-confined flow systems where groundwater geochemistry is strongly influenced by circulation of surface estuary water through organic-rich sediments, may be common on the Atlantic margin and elsewhere.
Butman, Bradford, Dalyander, P.S., Bothner, M.H., Borden, Jonathan, Casso, M.A., Gutierrez, B.T., Hastings, M.E., Lightsom, F.L., Martini, M.A., Montgomery, E.T., Rendigs, R.R., and Strahle, W.S., 2009, Long-term oceanographic observations in Massachusetts Bay, 1989 - 2006: U.S. Geological Survey Data Series 74, Version 3 . Online at http://pubs.usgs.gov/ds/74/index.html
Carniel, Sandro, Warner, John C., Chiggiato, Jacopo, and Sclavo, Mauro, 2009, Investigating the impact of surface wave breaking on modeling the trajectories of drifters in the northern Adriatic Sea during a wind-storm event: Ocean Modelling , v. 30 , no. 2-3 . Online at 10.1016/j.ocemod.2009.07.001
An accurate numerical prediction of the oceanic upper layer velocity is a demanding requirement for many applications at sea and is a function of several near-surface processes that need to be incorporated in a numerical model. Among them, we assess the effects of vertical resolution, different vertical mixing parameterization (the so-called Generic Length Scale-GLS- set of k–ε, k–ω, gen, and the Mellor-Yamada), and surface roughness values on turbulent kinetic energy (k) injection from breaking waves. First, we modified the GLS turbulence closure formulation in the Regional Ocean Modeling System (ROMS) to incorporate the surface flux of turbulent kinetic energy due to wave breaking. Then, we applied the model to idealized test cases, exploring the sensitivity to the above mentioned factors. Last, the model was applied to a realistic situation in the Adriatic Sea driven by numerical meteorological forcings and river discharges. In this case, numerical drifters were released during an intense episode of Bora winds that occurred in mid-February 2003, and their trajectories compared to the displacement of satellite-tracked drifters deployed during the ADRIA02-03 sea-truth campaign. Results indicted that the inclusion of the wave breaking process helps improve the accuracy of the numerical simulations, subject to an increase in the typical value of the surface roughness z0. Specifically, the best performance was obtained using αCH = 56,000 in the Charnok formula, the wave breaking parameterization activated, k–ε as the turbulence closure model. With these options, the relative error with respect to the average distance of the drifter was about 25% (5.5 km/day). The most sensitive factors in the model were found to be the value of αCH enhanced with respect to a standard value, followed by the adoption of wave breaking parameterization and the particular turbulence closure model selected.
Chaytor, Jason D., ten Brink, Uri S., Solow, Andrew R., and Andrews, Brian D., 2009, Size distribution of submarine landslides along the U.S. Atlantic margin: Marine Geology , v. 264 , no. 1-2 . Online at 10.1016/j.margeo.2008.08.007
Assessment of the probability for destructive landslide-generated tsunamis depends on the knowledge of the number, size, and frequency of large submarine landslides. This paper investigates the size distribution of submarine landslides along the U.S. Atlantic continental slope and rise using the size of the landslide source regions (landslide failure scars). Landslide scars along the margin identified in a detailed bathymetric Digital Elevation Model (DEM) have areas that range between 0.89 km2 and 2410 km2 and volumes between 0.002 km3 and 179 km3. The area to volume relationship of these failure scars is almost linear (inverse power-law exponent close to 1), suggesting a fairly uniform failure thickness of a few 10s of meters in each event, with only rare, deep excavating landslides. The cumulative volume distribution of the failure scars is very well described by a log–normal distribution rather than by an inverse power-law, the most commonly used distribution for both subaerial and submarine landslides. A log–normal distribution centered on a volume of 0.86 km3 may indicate that landslides preferentially mobilize a moderate amount of material (on the order of 1 km3), rather than large landslides or very small ones. Alternatively, the log–normal distribution may reflect an inverse power law distribution modified by a size-dependent probability of observing landslide scars in the bathymetry data. If the latter is the case, an inverse power-law distribution with an exponent of 1.3 ± 0.3, modified by a size-dependent conditional probability of identifying more failure scars with increasing landslide size, fits the observed size distribution. This exponent value is similar to the predicted exponent of 1.2 ± 0.3 for subaerial landslides in unconsolidated material. Both the log–normal and modified inverse power-law distributions of the observed failure scar volumes suggest that large landslides, which have the greatest potential to generate damaging tsunamis, occur infrequently along the margin.
Collie, Jeremy S., Hermsen, Jerome M., and Valentine, Page C., 2009, Recolonization of gravel habitats on Georges Bank (northwest Atlantic): Deep-Sea Research II , v. 56 , no. 19 -20 , pp. 1847-1855 . Online at 10.1016/j.dsr2.2009.05.025
Gravel habitats on continental shelves around the world support productive fisheries but are also vulnerable to disturbance from bottom fishing. We conducted a 2-year in situ experiment to measure the rate of colonization of a gravel habitat on northern Georges Bank in an area closed to fishing (Closed Area II) since December 1994. Three large (0.25 m2) sediment trays containing defaunated pebble gravel were deployed at a study site (47 m water depth) in July 1997 and recovered in June 1999. The undersides of the tray lids positioned 56 cm above the trays served as settlement panels over the same time period. We observed rapid colonization of the gravel substrate (56 species) and the settlement panels (35 species), indicating that colonization of gravel in this region is not limited by the supply of colonists. The species composition of the taxa found in the trays was broadly similar to that we collected over a 10-year period (1994–2004) in dredge samples from gravel sediments at the same site. The increase in abundance of animals in the gravel colonization trays was rapid and reached a level in 2 years that took 4.5 years to achieve in the surrounding gravel sediments once fishing had stopped, based on data from dredge sampling at this site. The increase in biomass of animals found in the sediment trays paralleled the trend of biomass increase observed in dredge samples over the same period (1997–1999) but was lower in value. These data suggest that after rapid initial increase in abundance of organisms, succession proceeded by increasing individual body size. A comparison of settlement panel and tray faunas revealed that the mean biomass of structure-forming epifauna (sponges, bryozoans, anemones, hydroids, colonial tube worms) on the panels was 8 times that found on the trays. Structure-forming taxa constituted 29% of the mean biomass of the panel fauna but only 5.5% of the tray fauna. By contrast, the mean biomass of scavengers (crabs, echinoderms, nudibranchs, gastropods) in the trays was 32 times that on the panels. Colonization of the tray gravel was more rapid for free-living species (many of which are prey for fish) than for structure-forming epifauna, though colonists of the latter species were present. The reduced success of structure-forming species in colonizing the tray gravel possibly is related to factors such as intermittent burial of the gravel by migrating sand and low survival of new recruits due to the presence of high numbers of scavengers on the gravel. These two factors might explain, to varying degree, the slow recolonization of gravel habitats by structure-forming species in Closed Area II of the northern part of Georges Bank.
Cortes, D.D., Martin, A.I., Yun, T.S., Francisca, F.M., Santamarina, J.C., and Ruppel, Carolyn, 2009, The thermal conductivity of hydrate-bearing sediments: Journal of Geophysical Research - Solid Earth , v. 114 , no. B11104 . Online at 10.1029/2008JB006235
A thorough understanding of the thermal conductivity of hydrate-bearing sediments is necessary for evaluating phase transformation processes that would accompany energy production from gas hydrate deposits and for estimating regional heat flow based on the observed depth to the base of the gas hydrate stability zone. The coexistence of multiple phases (gas hydrate, liquid and gas pore fill, and solid sediment grains) and their complex spatial arrangement hinder the a priori prediction of the thermal conductivity of hydrate-bearing sediments. Previous studies have been unable to capture the full parameter space covered by variations in grain size, specific surface, degree of saturation, nature of pore filling material, and effective stress for hydrate-bearing samples. Here we report on systematic measurements of the thermal conductivity of air dry, water- and tetrohydrofuran (THF)-saturated, and THF hydrate–saturated sand and clay samples at vertical effective stress of 0.05 to 1 MPa (corresponding to depths as great as 100 m below seafloor). Results reveal that the bulk thermal conductivity of the samples in every case reflects a complex interplay among particle size, effective stress, porosity, and fluid-versus-hydrate filled pore spaces. The thermal conductivity of THF hydrate–bearing soils increases upon hydrate formation although the thermal conductivities of THF solution and THF hydrate are almost the same. Several mechanisms can contribute to this effect including cryogenic suction during hydrate crystal growth and the ensuing porosity reduction in the surrounding sediment, increased mean effective stress due to hydrate formation under zero lateral strain conditions, and decreased interface thermal impedance as grain-liquid interfaces are transformed into grain-hydrate interfaces.
Ellis, M., Evans, R.L., Hutchinson, D., Hart, P., Gardner, J., and Hagen, R., 2008, Electromagnetic surveying of seafloor mounds in the northern Gulf of Mexico: Marine and Petroleum Geology , v. 25 , no. 9 . Online at 10.1016/j.marpetgeo.2007.12.006
Seafloor controlled source electromagnetic data, probing the uppermost 30 m of seafloor sediments, have been collected with a towed magnetic dipole–dipole system across two seafloor mounds at approximately 1300 m water depth in the northern Gulf of Mexico. One of these mounds was the focus of a recent gas hydrate research drilling program. Rather than the highly resistive response expected of massive gas hydrate within the confines of the mounds, the EM data are dominated by the effects of raised temperatures and pore fluid salinities that result in an electrically conductive seafloor. This structure suggests that fluid advection towards the seafloor is taking place beneath both mounds. Similar responses are seen at discrete locations away from the mounds in areas that might be associated with faults, further suggesting substantial shallow fluid circulation. Raised temperatures and salinities may inhibit gas hydrate formation at depth as has been suggested at other similar locations in the Gulf of Mexico.
Foster, David S., and Denny, Jane F., 2009, Quaternary geologic framework of the St. Clair River between Michigan and Ontario, Canada: U.S. Geological Survey Open-File Report 2009-1137 . Online at http://pubs.usgs.gov/of/2009/1137/
Concern about the effect of geomorphic changes in the St. Clair River on water levels in the Upper Great Lakes resulted in the need for information on the geologic framework of the river. A geophysical survey of the Upper St. Clair River between Port Huron, MI, and Sarnia, Ontario, Canada, was conducted to determine the Quaternary geologic framework of the region. Previously available and new sediment samples and photographic and video data support the interpretation of the seismic stratigraphy and surficial geology. Three seismic stratigraphic units and two unconformities were identified. Glacial drift, consisting of interbedded till and glaciolacustrine deposits, overlies shale. Glaciofluvial and modern fluvial processes have eroded the glacial drift. Glaciofluvial, glaciolacustrine, fluvial, and lacustrine deposits overlie this unconformity. Seismic facies were interpreted to identify areas where these geologic facies exist; however, in the absence of distinct boundaries between facies, these deposits were mapped as one undifferentiated unit. This unit is thickest in the northernmost 3 kilometers of the river, where it consists of relatively coarse-grained fluvial, reworked glaciofluvial, and possibly glaciofluvial deposits. To the south, this coarse-grained unit thins or is absent. The undifferentiated unit comprises most of the surficial deposits in the northernmost river area. Some areas of glacial drift, predominantly till, are exposed at the lake and riverbed. The shale is not exposed anywhere in the region. Geophysical surveys at sites downriver, together with the results of previous studies, indicate that the geologic framework is similar to that in the northernmost river area except for the absence or reduced thickness of the coarse-grained fluvial deposits. Instead, glacial drift is exposed at the riverbed or is covered by a veneer of sediment. This information on the substrate is important for ongoing sediment transport studies.
Granja Bruna, J.L., ten Brink, U.S., Carbo-Gorosabel, A., Munoz-Martin, A., and Gomez Ballesteros, M., 2009, Morphotectonics of the central Muertos thrust belt and Muertos Trough (northeastern Caribbean): Marine Geology , v. 263 , no. 1-4 . Online at 10.1016/j.margeo.2009.03.010
Hapke, Cheryl J., Malone, Shamus, and Kratzmann, Meredith, 2009, National assessment of historical shoreline change; a pilot study of historical coastal bluff retreat in the Great Lakes, Erie, Pennsylvania: U.S. Geological Survey Open-File Report 2009-1042 . Online at http://pubs.usgs.gov/of/2009/1042/
Helgerud, M.B., Waite, W.F., Kirby, S.H., and Nur, A., 2009, Elastic wave speeds and moduli in polycrystalline ice Ih, sI methane hydrate, and sII methane-ethane hydrate: Journal of Geophysical Research , v. 114 , no. B02212 , pp. 11 . Online at 10.1029/2008JB006132
We used ultrasonic pulse transmission to measure compressional, P, and shear, S, wave speeds in laboratory-formed polycrystalline ice Ih, sI methane hydrate, and sII methane-ethane hydrate. From the wave speed's linear dependence on temperature and pressure and from the sample's calculated density, we derived expressions for bulk, shear, and compressional wave moduli and Poisson's ratio from −20 to −5°C and 22.4 to 32.8 MPa for ice Ih, −20 to 15°C and 30.5 to 97.7 MPa for sI methane hydrate, and −20 to 10°C and 30.5 to 91.6 MPa for sII methane-ethane hydrate. All three materials had comparable P and S wave speeds and decreasing shear wave speeds with increasing applied pressure. Each material also showed evidence of rapid intergranular bonding, with a corresponding increase in wave speed, in response to pauses in sample deformation. There were also key differences. Resistance to uniaxial compaction, indicated by the pressure required to compact initially porous samples, was significantly lower for ice Ih than for either hydrate. The ice Ih shear modulus decreased with increasing pressure, in contrast to the increase measured in both hydrates.
Heuer, Verena B., Pohlman, John W., Torres, Marta E., Elvert, Marcus, and Hinrichs, Kai-Uwe, 2009, The stable carbon isotope biogeochemistry of acetate and other disolved carbon species in deep subseafloor sediments at the northern Cascadia Margin: Geochimica et Cosmochimica Acta , v. 73 , no. 11 , pp. 3323-3336 . Online at 10.1016/j.gca.2009.03.001
Ocean drilling has revealed the existence of vast microbial populations in the deep subseafloor, but to date little is known about their metabolic activities. To better understand the biogeochemical processes in the deep biosphere, we investigate the stable carbon isotope chemistry of acetate and other carbon-bearing metabolites in sediment pore-waters. Acetate is a key metabolite in the cycling of carbon in anoxic sediments. Its stable carbon isotopic composition provides information on the metabolic processes dominating acetate turnover in situ. This study reports our findings for a methane-rich site at the northern Cascadia Margin (NE Pacific) where Expedition 311 of the Integrated Ocean Drilling Program (IODP) sampled the upper 190 m of sediment. At Site U1329, δ13C values of acetate span a wide range from −46.0‰ to −11.0‰ vs. VPDB and change systematically with sediment depth. In contrast, δ13C values of both the bulk dissolved organic carbon (DOC) (−21.6 ± 1.3‰ vs. VPDB) and the low-molecular-weight compound lactate (−20.9 ± 1.8‰ vs. VPDB) show little variability. These species are interpreted to represent the carbon isotopic composition of fermentation products. Relative to DOC, acetate is up to 23.1‰ depleted and up to 9.1‰ enriched in 13C. Broadly, 13C-depletions of acetate relative to DOC indicate flux of carbon from acetogenesis into the acetate pool while 13C-enrichments of pore-water acetate relative to DOC suggest consumption of acetate by acetoclastic methanogenesis. Isotopic relationships between acetate and lactate or DOC provide new information on the carbon flow and the presence and activity of specific functional microbial communities in distinct biogeochemical horizons of the sediment. In particular, they suggest that acetogenic CO2-reduction can coexist with methanogenic CO2-reduction, a notion contrary to the hypothesis that hydrogen levels are controlled by the thermodynamically most favorable electron-accepting process. Further, the isotopic relationship suggests a relative increase in acetate flow to acetoclastic methanogenesis with depth although its contribution to total methanogenesis is probably small. Our study demonstrates how the stable carbon isotope biogeochemistry of acetate can be used to identify pathways of microbial carbon turnover in subsurface environments. Our observations also raise new questions regarding the factors controlling acetate turnover in marine sediments.
Hutchinson, D.R., Hart, P.E., Collett, T.S., Edwards, K.M., Twichell, D.C., and Snyder, F., 2008, Geologic framework of the 2005 Keathley Canyon gas hydrate research well, northern Gulf of Mexico: Marine and Petroleum Geology , v. 25 , no. 9 . Online at 10.1016/j.marpetgeo.2008.01.012
The Keathley Canyon sites drilled in 2005 by the Chevron Joint Industry Project are located along the southeastern edge of an intraslope minibasin (Casey basin) in the northern Gulf of Mexico at 1335 m water depth. Around the drill sites, a grid of 2D high-resolution multichannel seismic data designed to image depths down to at least 1000 m sub-bottom reveals 7 unconformities and disconformities that, with the seafloor, bound 7 identifiable seismic stratigraphic units. A major disconformity in the middle of the units stands out for its angular baselapping geometry. From these data, three episodes of sedimentary deposition and deformation are inferred. The oldest episode consists of fine-grained muds deposited during a period of relative stability in the basin (units e, f, and g). Both the BSR and inferred gas hydrate occur within these older units. The gas hydrate occurs in near-vertical fractures. A second episode (units c and d) involved large vertical displacements associated with infilling and ponding of sediment. This second interval corresponds to deposition of intercalated fine and coarse-grained material that was recovered in the drill hole that penetrated the thin edges of the regionally much thicker units. The final episode of deposition (units a and b) occurred during more subdued vertical motions. Hemipelagic drape (unit a) characterizes the modern seafloor. The present-day Casey basin is mostly filled. Its sill is part of a subsiding graben structure that is only 10–20 m shallower than the deepest point in the basin, indicating that gravity-driven transport would mostly bypass the basin. Contemporary faulting along the basin margins has selectively reactivated an older group of faults. The intercalated sand and mud deposits of units c and d are tentatively correlated with Late Pleistocene deposition derived from the western shelf-edge delta/depocenter of the Mississippi River, which was probably most active from 320 ka to 70 ka [Winker, C.D., Booth, J., 2000. Sedimentary dynamics of the salt-dominated continental slope, Gulf of Mexico: integration of observations from the seafloor, near-surface, and deep subsurface. In: Proceedings of the GCSSEPM Foundation 20th Annual Research Conference, Deep-water Reservoirs of the World, pp. 1059–1086]. The presence of sand within the gas hydrate stability zone (in units c and d) is not sufficient to concentrate gas hydrate even though dispersed gas hydrate occurs deeper in the fractured mud/clay-rich sections of units e and f.
Lee, J.Y., Santamarina, J.C., and Ruppel, C., 2008, Mechanical and electromagnetic properties of northern Gulf of Mexico sediments with and without THF hydrates: Marine and Petroleum Geology , v. 25 , no. 9 . Online at 10.1016/j.marpetgeo.2008.01.019
Using an oedometer cell instrumented to measure the evolution of electromagnetic properties, small strain stiffness, and temperature, we conducted consolidation tests on sediments recovered during drilling in the northern Gulf of Mexico at the Atwater Valley and Keathley Canyon sites as part of the 2005 Chevron Joint Industry Project on Methane Hydrates. The tested specimens include both unremolded specimens (as recovered from the original core liner) and remolded sediments both without gas hydrate and with pore fluid exchanged to attain 100% synthetic (tetrahydrofuran) hydrate saturation at any stage of loading. Test results demonstrate the extent to which the electromagnetic and mechanical properties of hydrate-bearing marine sediments are governed by the vertical effective stress, stress history, porosity, hydrate saturation, fabric, ionic concentration of the pore fluid, and temperature. We also show how permittivity and electrical conductivity data can be used to estimate the evolution of hydrate volume fraction during formation. The gradual evolution of geophysical properties during hydrate formation probably reflects the slow increase in ionic concentration in the pore fluid due to ion exclusion in closed systems and the gradual decrease in average pore size in which the hydrate forms. During hydrate formation, the increase in S-wave velocity is delayed with respect to the decrease in permittivity, consistent with hydrate formation on mineral surfaces and subsequent crystal growth toward the pore space. No significant decementation/debonding occurred in 100% THF hydrate-saturated sediments during unloading, hence the probability of sampling hydrate-bearing sediments without disturbing the original sediment fabric is greatest for samples in which the gas hydrate is primarily responsible for maintaining the sediment fabric and for which the time between core retrieval and restoration of in situ effective stress in the laboratory is minimized. In evaluating the impact of core retrieval on specimen properties, it is also important to consider how far removed hydrate-bearing samples are from hydrate stability conditions.
Lengyel, Nicole L., Collie, Jeremy S., and Valentine, Page C., 2009, The invasive colonial ascidian Didemnum vexillum on Georges Bank - ecological effects and genetic identification: Aquatic Invasions , v. 4 , no. 1 . Online at http://www.aquaticinvasions.net/2009/AI_2009_4_1_Lengyel_etal.pdf
Since the discovery of the invasive colonial tunicate Didemnum vexillum Kott, 2002 on Georges Bank in 2002, research has focused on investigating the spread of the tunicate invasion, evaluating its potential impact on the benthic community, identifying it to species level, and determining its region of origin. The percent cover of Didemnum vexillum, measured from bottom photographs, ranges from 0-100% in individual photos and between 0-79% when averaged within photo transects. Individual photos represent an area of the seabed measuring ~ 0.39 m2 while photo transects range from ~ 700-1000 meters in length. Hydroids are the second most abundant epifaunal taxon. The macrofauna identified in bottom photo analysis comprises 21 different taxa, of which burrowing and non-burrowing anemones are the most numerous. Our detailed analysis of bottom photographs suggests that Didemnum vexillum is able to out-compete other epifaunal and macrofaunal taxa. An Analysis of Similarity (ANOSIM) test on macrofauna abundance data collected with a Naturalist dredge from 1994 to 2006, indicates that Didemnum vexillum has had a significant impact on the species composition of the benthic community. The abundance of two polychaete species, Nereis zonata Malmgren, 1867 and Harmothoe extenuata Grube, 1840, increased significantly in infested areas compared with uninfested areas, according to two-way Analysis of Variance (ANOVA). We found four distinct nucleotide sequences of the 18s rDNA gene among 17 samples of Didemnum species, three from Georges Bank and one from New Zealand. Two of the Georges Bank sequences were identified as Didemnum albidum Verrill, 1871, a species native to the northeast United States. The third sequence represents the invasive Didemnum vexillum from Georges Bank, and the fourth sequence an undescribed species from New Zealand (not D. vexillum).
Lightsom, F.L., and Allwardt, A.O., 2009, USGS digital libraries for coastal and marine science:
Lightsom, Frances L., and Allwardt, Alan O., 2009, How to use the Marine Realms Information Bank (MRIB) digital libraries: U.S. Geological Survey Fact Sheet 2009-3083 . Online at http://pubs.usgs.gov/fs/2009/3083/
List, Jeffrey H., Benedet, Lindino, Hanes, Daniel M., and Ruggiero, Peter, 2008, Understanding differences between DELFT3D and empirical predictions of alongshore sediment transport gradients: Proceedings, 31st International Conference on Coastal Engineering , pp. 1864-1875 . Online at 10.1142/9789814277426_0154
Predictions of alongshore transport gradients are critical for forecasting shoreline change. At the previous ICCE conference, it was demonstrated that alongshore transport gradients predicted by the empirical CERC equation can differ substantially from predictions made by the hydrodynamics-based model Delft3D in the case of a simulated borrow pit on the shoreface. Here we use the Delft3D momentum balance to examine the reason for this difference. Alongshore advective flow accelerations in our Delft3D simulation are mainly driven by pressure gradients resulting from alongshore variations in wave height and setup, and Delft3D transport gradients are controlled by these flow accelerations. The CERC equation does not take this process into account, and for this reason a second empirical transport term is sometimes added when alongshore gradients in wave height are thought to be significant. However, our test case indicates that this second term does not properly predict alongshore transport gradients.
Martini, Marinna, Armstrong, Brandy, and Warner, John C., 2009, High resolution near-bed observations in Winter off Cape Hatteras, NC [abs.]: . Online at http://ieeexplore.ieee.org/Xplore/defdeny.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fstamp%2Fstamp.jsp%3Ftp%3D%26arnumber%3D5422403%26isnumber%3D5422059&denyReason=-134&arnumber=5422403&productsMatched=null&userType=inst
he U.S. Geological Survey (USGS) Coastal and Marine Science Center in Woods Hole, Massachusetts, is leading an effort to understand the regional sediment dynamics along the coastline of North and South Carolina. As part of the Carolinas Coastal Change Processes Project, a geologic framework study in June of 2008 by the Woods Hole Coastal and Marine Science Center's Sea Floor Mapping Group focused on the seaward limit of Diamond Shoals and provided high resolution bathymetric data, surficial sediment characteristics, and subsurface geologic stratigraphy. These data also provided unprecedented guidance to identify deployment locations for tripods and moorings to investigate the processes that control sediment transport at Diamond Shoals. Equipment was deployed at three sites from early January, 2009 through early May, 2009: north and south of the shoals at 15 m depth, and at the tip at 24 m depth. Many strong storm systems were recorded during that time period. Mounted on the tripods were instruments to measure surface waves, pressure, current velocity, bottom turbulence, suspended-sediment profiles, and sea-floor sand-ripple bedforms. Many instruments were designed and programmed to sample in high resolution in time and space, as fast as 8 Hz hourly bursts and as small as 6 cm bin sizes in near bottom profiles. A second tripod at the north site also held a visual camera system and sonar imaging system which document seafloor bedforms. The region is known for its dynamics, and one of the tripods tipped over towards the end of the experiment. A preliminary look at the data suggests the region is characterized by high energy. Raw data from a burst recorded at the south site on Mar. 26th show instantaneous flow speed at 150 cm/s at 0.5 m above the seabed. This paper reports preliminary highlights of the observations, based on raw data, and lessons learned from a deployment of large tripod systems in such a dynamic location.
McMullen, K.Y., Poppe, L.J., and Soderberg, N.K., 2009, Digital seismic-reflection data from Western Rhode Island Sound, 1980: U.S. Geological Survey Open-File Report 2009-1002 . Online at http://pubs.usgs.gov/of/2009/1002/
During 1980, the U.S. Geological Survey (USGS) conducted a seismic-reflection survey in western Rhode Island Sound aboard the Research Vessel Neecho. Data from this survey were recorded in analog form and archived at the USGS Woods Hole Science Center's Data Library. Due to recent interest in the geology of Rhode Island Sound and in an effort to make the data more readily accessible while preserving the original paper records, the seismic data from this cruise were scanned and converted to Tagged Image File Format (TIFF) images and SEG-Y data files. Navigation data were converted from U.S. Coast Guard Long Range Aids to Navigation (LORAN-C) time delays to latitudes and longitudes, which are available in Environmental Systems Research Institute, Inc. (ESRI) shapefile format and as eastings and northings in space-delimited text format.
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 ASTR75–June surveyed eastern RIS in 1975 and cruise AST–80–6B 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., Haupt, T.A., and Crocker, J.M., 2009, Sidescan-sonar imagery and surficial geologic interpretations of the sea floor in western Rhode Island Sound: U.S. Geological Survey Open-File Report 2008-1181 . Online at http://pubs.usgs.gov/of/2008/1181/
The U.S. Geological Survey (USGS) and National Oceanic and Atmospheric Administration (NOAA) have been working together to interpret sea-floor geology along the northeastern coast of the United States. In 2004, the NOAA Ship RUDE completed survey H11322, a sidescan-sonar and bathymetric survey that covers about 60 square kilometers of the sea floor in western Rhode Island Sound. This report interprets sidescan-sonar and bathymetric data from NOAA survey H11322 to delineate sea-floor features and sedimentary environments in the study area. Paleozoic bedrock and Cretaceous Coastal Plain sediments in Rhode Island Sound underlie Pleistocene glacial drift that affects the distribution of surficial Holocene marine and transgressional sediments. The study area has three bathymetric highs separated by a channel system. Features and patterns in the sidescan-sonar imagery include low, moderate, and high backscatter; sand waves; scarps; erosional outliers; boulders; trawl marks; and dredge spoils. Four sedimentary environments in the study area, based on backscatter and bathymetric features, include those characterized by erosion or nondeposition, coarse-grained bedload transport, sorting and reworking, and deposition. Environments characterized by erosion or nondeposition and coarse-grained bedload transport are located in shallower areas and environments characterized by deposition are located in deeper areas; environments characterized by sorting and reworking processes are generally located at moderate depths.
Moore, L.J., List, J.H., Williams, S.J., and Stolper, David, 2010, Complexities in barrier island response to sea-level rise; insights from numerical model experiments, North Carolina Outer Banks, U.S.A.: Journal of Geophysical Research, Earth Surface , v. 115 , no. F3 . Online at 10.1029/2009JF001299
sing a morphological-behavior model to conduct sensitivity experiments, we investigate the sea level rise response of a complex coastal environment to changes in a variety of factors. Experiments reveal that substrate composition, followed in rank order by substrate slope, sea level rise rate, and sediment supply rate, are the most important factors in determining barrier island response to sea level rise. We find that geomorphic threshold crossing, defined as a change in state (e.g., from landward migrating to drowning) that is irreversible over decadal to millennial time scales, is most likely to occur in muddy coastal systems where the combination of substrate composition, depth-dependent limitations on shoreface response rates, and substrate erodibility may prevent sand from being liberated rapidly enough, or in sufficient quantity, to maintain a subaerial barrier. Analyses indicate that factors affecting sediment availability such as low substrate sand proportions and high sediment loss rates cause a barrier to migrate landward along a trajectory having a lower slope than average barrier island slope, thereby defining an “effective” barrier island slope. Other factors being equal, such barriers will tend to be smaller and associated with a more deeply incised shoreface, thereby requiring less migration per sea level rise increment to liberate sufficient sand to maintain subaerial exposure than larger, less incised barriers. As a result, the evolution of larger/less incised barriers is more likely to be limited by shoreface erosion rates or substrate erodibility making them more prone to disintegration related to increasing sea level rise rates than smaller/more incised barriers. Thus, the small/deeply incised North Carolina barriers are likely to persist in the near term (although their long-term fate is less certain because of the low substrate slopes that will soon be encountered). In aggregate, results point to the importance of system history (e.g., previous slopes, sediment budgets, etc.) in determining migration trajectories and therefore how a barrier island will respond to sea level rise. Although simple analytical calculations may predict barrier response in simplified coastal environments (e.g., constant slope, constant sea level rise rate, etc.), our model experiments demonstrate that morphological-behavior modeling is necessary to provide critical insights regarding changes that may occur in environments having complex geometries, especially when multiple parameters change simultaneously.
Poag, C.W., , Paleoenvironmental recovery from the Chesapeake Bay bolide impact; the benthic foraminiferal record: Geological Society of America Special Paper , v. 458 , pp. 747 -773 . Online at 10.1130/2009.2458(32)​
The late Eocene Chesapeake Bay bolide impact transformed its offshore target site from an outer neritic, midshelf seafloor into a bathyal crater basin. To obtain a depositional record from one of the deepest parts of this basin, the U.S. Geological Survey (USGS) and the International Continental Scientific Drilling Program (ICDP) drilled a 1.76-km-deep core hole near Eyreville, Virginia. The Eyreville core and eight previously cored boreholes contain a rarely obtainable record of marine deposition and microfossil assemblages that characterize the transition from synimpact to postimpact paleoenvironments inside and near a submarine impact crater. I used depositional style and benthic foraminiferal assemblages to recognize a four-step transitional succession, with emphasis on the Eyreville core. Step 1 is represented by small-scale, silt-rich turbidites, devoid of indigenous microfossils, which lie directly above the crater-filling Exmore breccia. Step 2 is represented by very thin, parallel, silt and clay laminae, which accumulated on a relatively tranquil and stagnant seafloor. This stagnation created a dead zone, which excluded seafloor biota, and it lasted ~3�5 ka. Step 3 is an interval of marine clay deposition, accompanied by a burst of microfaunal activity, as a species-rich pioneer community of benthic foraminifera repopulated the impact site. The presence of a diagnostic suite of agglutinated foraminifera during step 3 indicates that paleoenvironmental stress related to the impact lasted from ~9 ka to 400 ka at different locations inside the crater. During step 4, the agglutinated assemblage disappeared, and an equilibrium foraminiferal community developed that contained nearly 100% calcareous species. In contrast to intracrater localities, core sites outside and near the crater rim show neither evidence of the agglutinated assemblage, nor other indications of long-term biotic disruption from the bolide impact.
Pohlman, J.W., Ruppel, C., Hutchinson, D.R., Downer, R.Z., and Coffin, R.B., 2008, Assessing sulfate reduction and methane cycling in a high salinity pore water system in the northern Gulf of Mexico: Marine and Petroleum Geology; Scientific Results of 2005 JIP GoMex Drilling for Gas Hydrates Objective , v. 25
Pohlman, John W., Kaneko, Masanori, Heuer, Verena B., Coffin, Richard B., and Whiticar, Michael, 2009, Methane sources and production in the northern Cascadia margin gas hydrate system: Earth and Planetary Science Letters , v. 287 , no. 3-4 , pp. 504-512 . Online at 10.1016/j.epsl.2009.08.037
The oceanographic and tectonic conditions of accretionary margins are well-suited for several potential processes governing methane generation, storage and release. To identify the relevant methane evolution pathways in the northern Cascadia accretionary margin, a four-site transect was drilled during Integrated Ocean Drilling Program Expedition 311. The δ13C values of methane range from a minimum value of − 82.2‰ on an uplifted ridge of accreted sediment near the deformation front (Site U1326, 1829 mbsl, meters below sea level) to a maximum value of − 39.5‰ at the most landward location within an area of steep canyons near the shelf edge (Site U1329, 946 mbsl). An interpretation based solely on methane isotope values might conclude the 13C-enrichment of methane indicates a transition from microbially- to thermogenically-sourced methane. However, the co-existing CO2 exhibits a similar trend of 13C-enrichment along the transect with values ranging from − 22.5‰ to +25.7‰. The magnitude of the carbon isotope separation between methane and CO2 (εc = 63.8 ± 5.8) is consistent with isotope fractionation during microbially mediated carbonate reduction. These results, in conjunction with a transect-wide gaseous hydrocarbon content composed of > 99.8% (by volume) methane and uniform δDCH4 values (− 172‰ ± 8) that are distinct from thermogenic methane at a seep located 60 km from the Expedition 311 transect, suggest microbial CO2 reduction is the predominant methane source at all investigated sites. The magnitude of the intra-site downhole 13C-enrichment of CO2 within the accreted ridge (Site U1326) and a slope basin nearest the deformation front (Site U1325, 2195 mbsl) is ~ 5‰. At the mid-slope site (Site U1327, 1304 mbsl) the downhole 13C-enrichment of the CO2 is ~ 25‰ and increases to ~ 40‰ at the near-shelf edge Site U1329. This isotope fractionation pattern is indicative of more extensive diagenetic alteration at sites with greater 13C-enrichment. The magnitude of the 13C-enrichment of CO2 correlates with decreasing sedimentation rates and a diminishing occurrence of stratigraphic gas hydrate. We suggest the decreasing sedimentation rates increase the exposure time of sedimentary organic matter to aerobic and anaerobic degradation, during burial, thereby reducing the availability of metabolizable organic matter available for methane production. This process is reflected in the occurrence and distribution of gas hydrate within the northern Cascadia margin accretionary prism. Our observations are relevant for evaluating methane production and the occurrence of stratigraphic gas hydrate within other convergent margins.
Poppe, L.J., Ackerman, S.D., McMullen, K.Y., Schattgen, P.T., Schaer, J.D., and Doran, E.F., 2008, Interpolation of reconnaissance multibeam and single-beam bathymetry offshore of Milford, Connecticut: U.S. Geological Survey Open-File Report 2008-1146 . Online at http://pubs.usgs.gov/of/2008/1146/
Poppe, L.J., and Doran, E.F., 2009, Mapping the Long Island Sound seafloor: Connecticut Geo-Focus , v. 2 , no. 2 . Online at http://www.ct.gov/gis/lib/gis/CT_Geospatial_Newsletter_Summer09.pdf
Poppe, L.J., McMullen, K.Y., Williams, S.J., Ackerman, S.D., Glomb, K.A., and Forfinski, N.A., 2008, Enhanced sidescan-sonar imagery offshore of southeastern Massachusetts: U.S. Geological Survey Open-File Report 2008-1196 . Online at http://pubs.usgs.gov/of/2008/1196/
The U.S. Geological Survey (USGS), National Oceanic and Atmospheric Administration (NOAA), and Massachusetts Office of Coastal Zone Management (CZM) have been working cooperatively to map and study the coastal sea floor. The sidescan-sonar imagery collected during NOAA hydrographic surveys has been included as part of these studies. However, the original sonar imagery contains tonal artifacts from environmental noise (for example, sea state), equipment settings (for example, power and gain changes), and processing (for example, inaccurate cross-track and line-to-line normalization), which impart a quilt-like patchwork appearance to the mosaics. These artifacts can obscure the normalized backscatter properties of the sea floor. To address this issue, sidescan-sonar imagery from surveys H11076 and H11079 offshore of southeastern Massachusetts was enhanced by matching backscatter tones of adjacent sidescan-sonar lines. These mosaics provide continuous grayscale perspectives of the backscatter, more accurately reveal the sea-floor geologic trends, and minimize the environment-, acquisition-, and processing-related noise.
Pratson, Lincoln, Hughes-Clark, John, Anderson, Mark, Gerber, Thomas, Twichell, David, Ferrari, Ronald, Nittrouer, Charles, Beaudoin, Jonathan, Granet, Jesse, and Crockett, John, 2008, Timing and patterns of basin infilling as documented in Lake Powell during a drought: Geology , v. 36 , no. 11 . Online at 10.1130/G24733A.1
Between 1999 and 2005, drought in the western United States led to a >44 m fall in the level of Lake Powell (Arizona-Utah), the nation’s second-largest reservoir. River discharges to the reservoir were halved, yet the rivers still incised the tops of deltas left exposed along the rim of the reservoir by the lake-level fall. Erosion of the deltas enriched the rivers in sediment such that upon entering the reservoir they discharged plunging subaqueous gravity fl ows, one of which was imaged acoustically. Repeat bathymetric surveys of the reservoir show that the gravity fl ows overtopped rockfalls and formed small subaqueous fans, locally raising sediment accumulation rates 10–100-fold. The timing of deep-basin deposition differed regionally across the reservoir with respect to lake-level change. Total mass of sediment transferred from the lake perimeter to its bottom equates to ~22 yr of river input.
Rendigs, Richard R., Anderson, Roger Y., Xu, Jingping, Davis, Raymond E., and Bergeron, Emile, 2009, The Partition Intervalometer; a programmable underwater timer for marking accumulated sediment profiles collected in Anderson sediment traps; development, operation, testing procedures, and field results: U.S. Geological Survey Open-File Report 2009-1101 . Online at http://pubs.usgs.gov/of/2009/1101/
This manual illustrates the development of a programmable instrument designed to deploy a series of wafer-shaped discs (partitions) into the collection tube of a sediment trap in various aquatic environments. These hydrodynamically shaped discs are deployed at discrete time intervals from the Intervalometer and provide markers that delineate time intervals within the sediments that accumulate in the collection tube. The timer and mechanical system are lodged in an air-filled, water-tight pressure housing that is vertically hung within the confines of a cone-shaped sediment trap. The instrumentation has been operationally pressure tested to an equivalent water depth of approximately 1 km. Flaws discovered during extensive laboratory and pressure testing resulted in the implementation of several mechanical modifications (such as a redesign of the rotor and the discs) that improved the operation of the rotor assembly as well as the release of discs through the end cap. These results also identified a preferred azimuth placement of the rotor disc relative to the drop hole of the end cap. In the initial field trial, five sediment traps and coupled Intervalometers were attached to moored arrays and deployed at two sites off the coast of Southern California for approximately 8 months. Each of the instruments released 18 discs at the programmed 10 day intervals, except one unit, which experienced a malfunction after approximately 4 months. Most of the discs oriented in a near-horizontal position upon the surface of the sediment in the collection tubes. Sampling of the sediments for geochemical analyses was improved by these clearly defined markers, which indicated the changes in the flux and nature of sediments accumulated during the deployment period of each sediment trap.
Ruppel, C., Boswell, R., and Jones, E., 2008, Scientific results from Gulf of Mexico Gas Hydrates Joint Industry Project Leg 1 drilling; introduction and overview: Marine and Petroleum Geology , v. 25 , no. 9 . Online at 10.1016/j.marpetgeo.2008.02.007
The Gulf of Mexico Gas Hydrates Joint Industry Project (JIP) is a consortium of production and service companies and some government agencies formed to address the challenges that gas hydrates pose for deepwater exploration and production. In partnership with the U.S. Department of Energy and with scientific assistance from the U.S. Geological Survey and academic partners, the JIP has focused on studies to assess hazards associated with drilling the fine-grained, hydrate-bearing sediments that dominate much of the shallow subseafloor in the deepwater (>500 m) Gulf of Mexico. In preparation for an initial drilling, logging, and coring program, the JIP sponsored a multi-year research effort that included: (a) the development of borehole stability models for hydrate-bearing sediments; (b) exhaustive laboratory measurements of the physical properties of hydrate-bearing sediments; (c) refinement of new techniques for processing industry-standard 3-D seismic data to constrain gas hydrate saturations; and (d) construction of instrumentation to measure the physical properties of sediment cores that had never been removed from in situ hydrostatic pressure conditions. Following review of potential drilling sites, the JIP launched a 35-day expedition in Spring 2005 to acquire well logs and sediment cores at sites in Atwater Valley lease blocks 13/14 and Keathley Canyon lease block 151 in the northern Gulf of Mexico minibasin province. The Keathley Canyon site has a bottom simulating reflection at 392 m below the seafloor, while the Atwater Valley location is characterized by seafloor mounds with an underlying upwarped seismic reflection consistent with upward fluid migration and possible shoaling of the base of the gas hydrate stability (BGHS). No gas hydrate was recovered at the drill sites, but logging data, and to some extent cores, suggest the occurrence of gas hydrate in inferred coarser-grained beds and fractures, particularly between 220 and 330 m below the seafloor at the Keathley Canyon site. This paper provides an overview of the results of the initial phases of the JIP work and introduces the 15 papers that make up this special volume on the scientific results related to the 2005 logging and drilling expedition.
Schroth, Andrew W., Crusius, John, Sholkovitz, Edward R., and Bostick, Benjamin C., 2009, Iron solubility driven by speciation in dust sources to the ocean: Nature Geoscience , v. 2 , no. 5 . Online at 10.1038/ngeo501
Schwab, W. C., Gayes, P. T., Morton, R. A., Driscoll, N. W., Baldwin, W. E., Barnhardt, W. A., Denny, J. F., Harris, M. S., Katuna, M. P., Putney, T. R., Voulgaris, G., Warner, J. C., and Wright, E. E., 2009, Coastal change along the shore of northeastern South Carolina; the South Carolina coastal erosion study, Barnhardt, W.A. (ed.): U.S. Geological Survey Circular 1339 . Online at http://pubs.usgs.gov/circ/circ1339/
The U.S. Geological Survey, in cooperation with the South Carolina Sea Grant Consortium, conducted a 7-year, multidisciplinary study of coastal erosion in northeastern South Carolina. Shoreline behavior along the coast of Long Bay is dictated by waves, tidal currents, and sediment supply that act within the overall constraints of the regional geologic setting. Beaches are thin ribbons of sand that sit on top of layered sedimentary rocks, which have been deeply eroded by rivers and coastal processes over millions of years. Offshore of the beaches, these sedimentary rocks are exposed as hardgrounds over large expanses of shallow seafloor and are locally overlain by a discontinuous veneer of sandy sediment generally less than 1 m thick. Rates of shoreline retreat largely depend on the geologic framework of the shoreface that is being excavated by ocean processes. Mainland-attached beaches have remained relatively stable, whereas barrier islands have experienced large shifts in shoreline position. In this sediment-limited region, erosion of the shoreface and inner shelf probably contributes a significant amount of new material to the beach system. Oceanographic studies and numerical modeling show that sediment transport varies along the coast, depending on the type and travel path of storms that impact Long Bay, but the long-term net transport direction is generally from north to south. Changes in storm activity that might accompany climate change, coupled with anticipated increases in sea-level rise, are expected to strongly affect low-lying, heavily developed areas of the coast.
Schwab, W.C., Gayes, P.T., Morton, R.A., Driscoll, N.W., Baldwin, W.E., Barnhardt, W.A., Denny, J.F., Harris, M.S., Katuna, M.P., Putney, T.R., Voulgaris, G., Warner, J.C., and Wright, E.E., 2009, in Barnhardt, W.E., ed., Coastal change along the shore of northeastern South Carolina; the South Carolina coastal erosion study: U.S. Geological Survey Open-File Report 2008-1206 . Online at http://pubs.usgs.gov/of/2008/1206/
Scotti, A., Beardsley, R.C., Butman, B., and Pineda, J., 2008, Shoaling of nonlinear internal waves in Massachusetts Bay: Journal of Geophysical Research - Oceans , v. 113 , no. C08031 . Online at 10.1029/2008JC004726
The shoaling of the nonlinear internal tide in Massachusetts Bay is studied with a fully nonlinear and nonhydrostatic model. The results are compared with current and temperature observations obtained during the August 1998 Massachusetts Bay Internal Wave Experiment and observations from a shorter experiment which took place in September 2001. The model shows how the approaching nonlinear undular bore interacts strongly with a shoaling bottom, offshore of where KdV theory predicts polarity switching should occur. It is shown that the shoaling process is dominated by nonlinearity, and the model results are interpreted with the aid of a two-layer nonlinear but hydrostatic model. After interacting with the shoaling bottom, the undular bore emerges on the shallow shelf inshore of the 30-m isobath as a nonlinear internal tide with a range of possible shapes, all of which are found in the available observational record.
Sundquist, E.T., Ackerman, K.V., Bliss, N.B., Kellndorfer, J.M., Reeves, M.C., and Rollins, M.G., 2009, Rapid assessment of U.S. forest and soil organic carbon storage and forest biomass carbon sequestration capacity: U.S. Geological Survey Open-File Report 2009–1283 . Online at http://pubs.usgs.gov/of/2009/1283
ten Brink, U.S., Barkan, R., Andrews, B.D., and Chaytor, J.D., 2009, Size distributions and failure initiation of submarine and subaerial landslides: Earth and Planetary Science Letters , v. 287 , no. 1-2 . Online at 10.1016/j.epsl.2009.07.031
Landslides are often viewed together with other natural hazards, such as earthquakes and fires, as phenomena whose size distribution obeys an inverse power law. Inverse power law distributions are the result of additive avalanche processes, in which the final size cannot be predicted at the onset of the disturbance. Volume and area distributions of submarine landslides along the U.S. Atlantic continental slope follow a lognormal distribution and not an inverse power law. Using Monte Carlo simulations, we generated area distributions of submarine landslides that show a characteristic size and with few smaller and larger areas, which can be described well by a lognormal distribution. To generate these distributions we assumed that the area of slope failure depends on earthquake magnitude, i.e., that failure occurs simultaneously over the area affected by horizontal ground shaking, and does not cascade from nucleating points. Furthermore, the downslope movement of displaced sediments does not entrain significant amounts of additional material. Our simulations fit well the area distribution of landslide sources along the Atlantic continental margin, if we assume that the slope has been subjected to earthquakes of magnitude ≤ 6.3. Regions of submarine landslides, whose area distributions obey inverse power laws, may be controlled by different generation mechanisms, such as the gradual development of fractures in the headwalls of cliffs. The observation of a large number of small subaerial landslides being triggered by a single earthquake is also compatible with the hypothesis that failure occurs simultaneously in many locations within the area affected by ground shaking. Unlike submarine landslides, which are found on large uniformly-dipping slopes, a single large landslide scarp cannot form on land because of the heterogeneous morphology and short slope distances of tectonically-active subaerial regions. However, for a given earthquake magnitude, the total area affected by subaerial landslides is comparable to that calculated by slope stability analysis for submarine landslides. The area distribution of subaerial landslides from a single event may be determined by the size distribution of the morphology of the affected area, not by the initiation process.
ten Brink, Uri, 2009, Tsunami hazard along the U.S. Atlantic coast: Marine Geology , v. 264 , no. 1-2 . Online at 10.1016/j.margeo.2009.03.011
ten Brink, Uri S., Lee, Homa J., Geist, Eric L., and Twichell, David C., 2009, Assessment of tsunami hazard to the U.S. East Coast using relationships between submarine landslides and earthquakes: Marine Geology , v. 264 , no. 1-2 . Online at 10.1016/j.margeo.2008.05.011
Submarine landslides along the continental slope of the U.S. Atlantic margin are potential sources for tsunamis along the U.S. East coast. The magnitude of potential tsunamis depends on the volume and location of the landslides, and tsunami frequency depends on their recurrence interval. However, the size and recurrence interval of submarine landslides along the U.S. Atlantic margin is poorly known. Well-studied landslide-generated tsunamis in other parts of the world have been shown to be associated with earthquakes. Because the size distribution and recurrence interval of earthquakes is generally better known than those for submarine landslides, we propose here to estimate the size and recurrence interval of submarine landslides from the size and recurrence interval of earthquakes in the near vicinity of the said landslides. To do so, we calculate maximum expected landslide size for a given earthquake magnitude, use recurrence interval of earthquakes to estimate recurrence interval of landslide, and assume a threshold landslide size that can generate a destructive tsunami. The maximum expected landslide size for a given earthquake magnitude is calculated in 3 ways: by slope stability analysis for catastrophic slope failure on the Atlantic continental margin, by using land-based compilation of maximum observed distance from earthquake to liquefaction, and by using land-based compilation of maximum observed area of earthquake-induced landslides. We find that the calculated distances and failure areas from the slope stability analysis is similar or slightly smaller than the maximum triggering distances and failure areas in subaerial observations. The results from all three methods compare well with the slope failure observations of the Mw = 7.2, 1929 Grand Banks earthquake, the only historical tsunamigenic earthquake along the North American Atlantic margin. The results further suggest that a Mw = 7.5 earthquake (the largest expected earthquake in the eastern U.S.) must be located offshore and within 100 km of the continental slope to induce a catastrophic slope failure. Thus, a repeat of the 1755 Cape Anne and 1881 Charleston earthquakes are not expected to cause landslides on the continental slope. The observed rate of seismicity offshore the U.S. Atlantic coast is very low with the exception of New England, where some microseismicity is observed. An extrapolation of annual strain rates from the Canadian Atlantic continental margin suggests that the New England margin may experience the equivalent of a magnitude 7 earthquake on average every 600–3000 yr. A minimum triggering earthquake magnitude of 5.5 is suggested for a sufficiently large submarine failure to generate a devastating tsunami and only if the epicenter is located within the continental slope.
ten Brink, Uri S., Marshak, Stephen, and Granja Bruna, Jose-Luis, 2009, Bivergent thrust wedges surrounding oceanic island arcs; insight from observations and sandbox models of the northeastern Caribbean plate: Geological Society of America Bulletin , v. 121 , no. 11-12 . Online at 10.1130/B26512.1
At several localities around the world, thrust belts have developed on both sides of oceanic island arcs (e.g., Java-Timor, Panama, Vanuatu, and the northeastern Caribbean). In these localities, the overall vergence of the backarc thrust belt is opposite to that of the forearc thrust belt. For example, in the northeastern Caribbean, a north-verging accretionary prism lies to the north of the Eastern Greater Antilles arc (Hispaniola and Puerto Rico), whereas a south-verging thrust belt called the Muertos thrust belt lies to the south. Researchers have attributed such bivergent geometry to several processes, including: reversal of subduction polarity; subduction-driven mantle flow; stress transmission across the arc; gravitational spreading of the arc; and magmatic inflation within the arc. New observations of deformational features in the Muertos thrust belt and of fault geometries produced in sandbox kinematic models, along with examination of published studies of island arcs, lead to the conclusion that the bivergence of thrusting in island arcs can develop without reversal of subduction polarity, without subarc mantle flow, and without magmatic inflation. We suggest that the Eastern Greater Antilles arc and comparable arcs, are simply crustal-scale bivergent (or "doubly vergent") thrust wedges formed during unidirectional subduction. Sandbox kinematic modeling suggests, in addition, that a broad retrowedge containing an imbricate fan of thrusts develops only where the arc behaves relatively rigidly. In such cases, the arc acts as a backstop that transmits compressive stress into the backarc region. Further, modeling shows that when arcs behave as rigid blocks, the strike-slip component of oblique convergence is accommodated entirely within the prowedge and the arc-the retrowedge hosts only dip-slip faulting ("frontal thrusting"). The existence of large retrowedges and the distribution of faulting in an island arc may, therefore, be evidence that the arc is relatively rigid. The rigidity of an island arc may arise from its mafic composition and has implications for seismic-hazard analysis.
Thieler, E.R., Himmelstoss, E.A., Zichichi, J.L., and Ergul, A., 2009, The Digital Shoreline Analysis System (DSAS) version 4.0, an ArcGIS extension for calculating shoreline change: U.S. Geological Survey Open-File Report 2008-1278 . Online at http://pubs.usgs.gov/of/2008/1278/
Twichell, David C., Chaytor, Jason D., ten Brink, Uri S., and Buczkowski, Brian, 2009, Morphology of late Quaternary submarine landslides along the U.S. Atlantic continental margin: Marine Geology , v. 264 , no. 1-2 . Online at 10.1016/j.margeo.2009.01.009
The nearly complete coverage of the U.S. Atlantic continental slope and rise by multibeam bathymetry and backscatter imagery provides an opportunity to reevaluate the distribution of submarine landslides along the margin and reassess the controls on their formation. Landslides can be divided into two categories based on their source areas: those sourced in submarine canyons and those sourced on the open continental slope and rise. Landslide distribution is in part controlled by the Quaternary history of the margin. They cover 33% of the continental slope and rise of the glacially influenced New England margin, 16% of the sea floor offshore of the fluvially dominated Middle Atlantic margin, and 13% of the sea floor south of Cape Hatteras. The headwall scarps of open-slope sourced landslides occur mostly on the lower slope and upper rise while they occur mostly on the upper slope in the canyon-sourced ones. The deposits from both landslide categories are generally thin (mostly 20-40 m thick) and comprised primarily of Quaternary material, but the volumes of the open-slope sourced landslide deposits can be larger (1-392 km3) than the canyon-sourced ones (1-10 km3). The largest failures are located seaward of shelf-edge deltas along the southern New England margin and near salt domes that breach the sea floor south of Cape Hatteras. The spatial distribution of landslides indicates that earthquakes associated with rebound of the glaciated part of the margin or earthquakes associated with salt domes were probably the primary triggering mechanism although other processes may have pre-conditioned sediments for failure. The largest failures and those that have the potential to generate the largest tsunamis are the open-slope sourced landslides.
Twichell, David, Pendleton, Elizabeth, Baldwin, Wayne, and Flocks, James, 2009, Subsurface control on seafloor erosional processes offshore of the Chandeleur Islands, Louisiana: Geo-Marine Letters , v. 29 , no. 6 . Online at 10.1007/s00367-009-0150-x
The Chandeleur Islands lie on the eastern side of the modern Mississippi River delta plain, near the edge of the St. Bernard Delta complex. Since abandonment approximately 2,000 years b.p., this delta complex has undergone subsidence and ravinement as the shoreline has transgressed across it. High-resolution seismic-reflection, sidescan-sonar, and bathymetry data show that seafloor erosion is influenced by locally variable shallow stratigraphy. The data reveal two general populations of shallow erosional depressions, either linear or subcircular in shape. Linear depressions occur primarily where sandy distributary-channel deposits are exposed on the seafloor. The subcircular pits are concentrated in areas where delta-front deposits crop out, and occasional seismic blanking indicates that gas is present. The difference in erosional patterns suggests that delta-front and distributary-channel deposits respond uniquely to wave and current energy expended on the inner shelf, particularly during stormy periods. Linear depressions may be the result of the sandy distributary-channel deposits eroding more readily by waves and coastal currents than the surrounding delta-front deposits. Pits may develop as gas discharge or liquefaction occurs within fine-grained delta-front deposits, causing seafloor collapse. These detailed observations suggest that ravinement of this inner shelf surface may be ongoing, is controlled by the underlying stratigraphy, and has varied morphologic expression.
Valentine, Page C., Carman, Mary R., Dijksta, Jennifer, and Blackwood, Dann S., 2009, Larval recruitment of the invasive colonial ascidian Didemnum vexillum, seasonal water temperatures in New England coastal and offshore waters, and implications for spread of the species: Aquatic Invasions , v. 4 , no. 1 . Online at http://www.aquaticinvasions.net/2009/AI_2009_4_1_Valentine_etal.pdf
The invasive colonial ascidian Didemnum vexillum occurs in Japan, North America, northern Europe, and New Zealand. It forms adhering mats on living and non-living hard substrates and alters seabed habitats. We examined the relationship of the first and last occurrences of D. vexillum recruits to water temperature and suggest it is possible to identify coastal and offshore locations that are at risk of colonization by the species based on seasonal water temperature trends. Temperature loggers and settlement plates for recruits were deployed and monitored at three shallow coastal settings in New England, including an open harbor, a marine estuary, and a nearshore island. In addition, the distribution of D. vexillum at sites on Georges Bank, an offshore fishing ground (where settlement plates could not be deployed), was compared to long-term bottom temperature data. Recruits of D. vexillum are small (0.2 to 1.0 mm) but easy to identify, and photographs illustrating the developmental stages of oozooids are presented. Recruits of D. vexillum did not appear on settlement plates at the same water temperature at the three coastal sites. Recruitment occurs in the range of 14 to 20°C and apparently is dependent on local climatic conditions. At coastal sites where we have complete records, recruitment persisted for 3.5 to 5 months; and recruits continued to appear as waters cooled to below the temperature of first occurrence. Recruitment ceased in the range of 9 to 11°C. On Georges Bank, the yearly temperature range (4 to 16-17°C) is the same in areas where D. vexillum is present and in a nearby area where D. vexillum is absent. However, in the reproductive season on the bank, temperature variability is but a few degrees in areas where the species is present; whereas it is high (11°C) where the species is absent. It is known from previous studies that in extremely cold conditions in shallow water D. vexillum colonies degenerate and all but disappear, only to regenerate as waters warm. We suggest that: 1) the degree to which colonies degrade in the cool season influences the length of time they require to regenerate, reproduce sexually, and brood larvae; 2) larval recruits will be released at the end of a developmental period as water temperatures warm, not necessarily when a particular water temperature is reached; 3) larvae likely will appear at different temperatures at climatically different sites, and at approximately the same time and temperature at climatically similar sites; 4) highly variable temperatures during the warm season likely inhibit the reproductive process; 5) the time required for a colony to develop and release larvae and the length of the warm season probably affects the length of the recruiting period at a site; 6) as waters cool, larval release by healthy colonies and recruitment might be regulated chiefly by declining temperature and therefore could end at approximately the same temperature at all sites. At deeper water sites, where minimum temperatures are warmer than at shallow sites, it is possible that D. vexillum colonies are not as affected in the cool season (i.e., do not degenerate) and thus could have a longer recruiting season. This may explain the species’ successful colonization of several large areas of gravel habitat on Georges Bank.
Whitmore, Paul, ten Brink, Uri, Caropolo, Michael, Huerfano-Moreno, Victor, Knight, William, Sammler, William, and Sandrik, Al, 2009, NOAA/West Coast and Alaska Tsunami Warning Center Atlantic Ocean response criteria: Science of Tsunami Hazards , v. 28 , no. 2 . Online at http://tsunamisociety.org/282WhitmoreEtAla.pdf
West Coast/Alaska Tsunami Warning Center (WCATWC) response criteria for earthquakes occurring in the Atlantic and Caribbean basins are presented. Initial warning center decisions are based on an earthquak's location, magnitude, depth, distance from coastal locations, and precomputed threat estimates based on tsunami models computed from similar events. The new criteria will help limit the geographical extent of warnings and advisories to threatened regions, and complement the new operational tsunami product suite. Criteria are set for tsunamis generated by earthquakes, which are by far the main cause of tsunami generation (either directly through sea floor displacement or indirectly by triggering of sub-sea landslides). The new criteria require development of a threat data base which sets warning or advisory zones based on location, magnitude, and pre-computed tsunami models. The models determine coastal tsunami amplitudes based on likely tsunami source parameters for a given event. Based on the computed amplitude, warning and advisory zones are pre-set.
Wooller, M.J., Ruppel, C., Pohlman, J.W., Leigh, M.B., Heintz, M., and Anthony, K.W., 2009, Permafrost gas hydrates and climate change; lake-based seep studies on the Alaskan north slope: Fire in the Ice, U.S. Department of Energy/National Energy Technology Laboratory, Methane Hydrate Newsletter, Summer 2009 , v. 9 , no. 3 , pp. 6-9 . Online at http://www.netl.doe.gov/File%20Library/Research/Oil-Gas/methane%20hydrates/MHNewsSummer09.pdf
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