Geology topics

Research about Gulf Of Mexico

Source-linked reports with geographic coverage including Gulf Of Mexico.

At least 19 recordsLinked to original sources

USGS2014

Coral communities as indicators of ecosystem-level impacts of the Deepwater Horizon spill

The Macondo oil spill released massive quantities of oil and gas from a depth of 1500 meters. Although a buoyant plume carried released hydrocarbons to the sea surface, as much as half stayed in the water column and much of that in the deep sea. After the hydrocarbons reached the surface, weathering processes, burning, and the use of a dispersant caused hydrocarbon-rich marine snow to sink into the deep sea. As a result, this spill had a greater potential to affect deep-sea communities than had any previous spill. Here, we review the literature on impacts on deep-sea communities from the Macondo blowout and provide additional data on sediment hydrocarbon loads and the impacts on sediment infauna in areas with coral communities around the Macondo well. We review the literature on the genetic connectivity of deep-sea species in the Gulf of Mexico and discuss the potential for wider effects on deep Gulf coral communities.

BioScience↗

USGS2014

Seismic investigation of gas hydrates in the Gulf of Mexico: 2013 multi-component and high-resolution 2D acquisition at GC955 and WR313

The U.S. Geological Survey led a seismic acquisition cruise at Green Canyon 955 (GC955) and Walker Ridge 313 (WR313) in the Gulf of Mexico from April 18 to May 3, 2013, acquiring multicomponent and high-resolution 2D seismic data. GC955 and WR313 are established, world-class study sites where high gas hydrate saturations exist within reservoir-grade sands in this long-established petroleum province. Logging-while-drilling (LWD) data acquired in 2009 by the Gulf of Mexico Gas Hydrates Joint Industry Project provide detailed characterization at the borehole locations, and industry seismic data provide regional- and local-scale structural and stratigraphic characterization. Significant remaining questions regarding lithology and hydrate saturation between and away from the boreholes spurred new geophysical data acquisition at these sites. The goals of our 2013 surveys were to (1) achieve improved imaging and characterization at these sites and (2) refine geophysical methods for gas hydrate characterization in other locations. In the area of GC955 we deployed 21 ocean-bottom seismometers (OBS) and acquired approximately 400 km of high-resolution 2D streamer seismic data in a grid with line spacing as small as 50 m and along radial lines that provide source offsets up to 10 km and diverse azimuths for the OBS. In the area of WR313 we deployed 25 OBS and acquired approximately 450 km of streamer seismic data in a grid pattern with line spacing as small as 250 m and along radial lines that provide source offsets up to 10 km for the OBS. These new data afford at least five times better resolution of the structural and stratigraphic features of interest at the sites and enable considerably improved characterization of lithology and the gas and gas hydrate systems. Our recent survey represents a unique application of dedicated geophysical data to the characterization of confirmed reservoir-grade gas hydrate accumulations.

Gulf Of Mexico↗

USGS2014

Presence of the Corexit component dioctyl sodium sulfosuccinate in Gulf of Mexico waters after the 2010 Deepwater Horizon oil spill

Between April 22 and July 15, 2010, approximately 4.9 million barrels of oil were released into the Gulf of Mexico from the Deepwater Horizon oil well. Approximately 16% of the oil was chemically dispersed, at the surface and at 1500 m depth, using Corexit 9527 and Corexit 9500, which contain dioctyl sodium sulfosuccinate (DOSS) as a major surfactant component. This was the largest documented release of oil in history at substantial depth, and the first time large quantities of dispersant (0.77 million gallons of approximately 1.9 million gallons total) were applied to a subsurface oil plume. During two cruises in late May and early June, water samples were collected at the surface and at depth for DOSS analysis. Real-time fluorimetry data was used to infer the presence of oil components to select appropriate sampling depths. Samples were stored frozen and in the dark for approximately 6 months prior to analysis by liquid chromatography/tandem mass spectrometry with isotope-dilution quantification. The blank-limited method detection limit (0.25 μg L −1 ) was substantially less than the U.S. Environmental Protection Agency’s (USEPA) aquatic life benchmark of 40 μg L −1 . Concentrations of DOSS exceeding 200 μg L −1 were observed in one surface sample near the well site; in subsurface samples DOSS did not exceed 40 μg L −1 . Although DOSS was present at high concentration in the immediate vicinity of the well where it was being continuously applied, a combination of biodegradation, photolysis, and dilution likely reduced persistence at concentrations exceeding the USEPA aquatic life benchmark beyond this immediate area.

Gulf Of Mexico↗

USGS2014

A probabilistic method for constructing wave time-series at inshore locations using model scenarios

Continuous time-series of wave characteristics (height, period, and direction) are constructed using a base set of model scenarios and simple probabilistic methods. This approach utilizes an archive of computationally intensive, highly spatially resolved numerical wave model output to develop time-series of historical or future wave conditions without performing additional, continuous numerical simulations. The archive of model output contains wave simulations from a set of model scenarios derived from an offshore wave climatology. Time-series of wave height, period, direction, and associated uncertainties are constructed at locations included in the numerical model domain. The confidence limits are derived using statistical variability of oceanographic parameters contained in the wave model scenarios. The method was applied to a region in the northern Gulf of Mexico and assessed using wave observations at 12 m and 30 m water depths. Prediction skill for significant wave height is 0.58 and 0.67 at the 12 m and 30 m locations, respectively, with similar performance for wave period and direction. The skill of this simplified, probabilistic time-series construction method is comparable to existing large-scale, high-fidelity operational wave models but provides higher spatial resolution output at low computational expense. The constructed time-series can be developed to support a variety of applications including climate studies and other situations where a comprehensive survey of wave impacts on the coastal area is of interest.

Coastal Engineering↗

USGS2014

Biodiversity and community composition of sediment macrofauna associated with deep-sea Lophelia pertusa habitats in the Gulf of Mexico

Scleractinian corals create three-dimensional reefs that provide sheltered refuges, facilitate sediment accumulation, and enhance colonization of encrusting fauna. While heterogeneous coral habitats can harbor high levels of biodiversity, their effect on the community composition within nearby sediments remains unclear, particularly in the deep sea. Sediment macrofauna from deep-sea coral habitats ( Lophelia pertusa ) and non-coral, background sediments were examined at three sites in the northern Gulf of Mexico (VK826, VK906, MC751, 350–500 m depth) to determine whether macrofaunal abundance, diversity, and community composition near corals differed from background soft-sediments. Macrofaunal densities ranged from 26 to 125 individuals 32 cm −2 and were significantly greater near coral versus background sediments only at VK826. Of the 86 benthic invertebrate taxa identified, 16 were exclusive to near-coral habitats, while 14 were found only in background sediments. Diversity (Fisher’s α) and evenness were significantly higher within near-coral sediments only at MC751 while taxon richness was similar among all habitats. Community composition was significantly different both between near-coral and background sediments and among the three primary sites. Polychaetes numerically dominated all samples, accounting for up to 70% of the total individuals near coral, whereas peracarid crustaceans were proportionally more abundant in background sediments (18%) than in those near coral (10%). The reef effect differed among sites, with community patterns potentially influenced by the size of reef habitat. Taxon turnover occurred with distance from the reef, suggesting that reef extent may represent an important factor in structuring sediment communities near L. pertusa . Polychaete communities in both habitats differed from other Gulf of Mexico (GOM) soft sediments based on data from previous studies, and we hypothesize that local environmental conditions found near L. pertusa may influence the macrofaunal community structure beyond the edges of the reef. This study represents the first assessment of L. pertusa -associated sediment communities in the GOM and provides baseline data that can help define the role of transition zones, from deep reefs to soft sediments, in shaping macrofaunal community structure and maintaining biodiversity; this information can help guide future conservation and management activities.

Gulf Of Mexico↗

USGS2014

Spatial distribution of loggerhead turtle ( Caretta caretta ) emergences along a highly dynamic beach in the northern Gulf of Mexico

As coastlines change due to sea level rise and an increasing human presence, understanding how species, such as marine turtles, respond to alterations in habitat is necessary for proper management and conservation. Survey data from a major nesting beach in the northern Gulf of Mexico, where a revetment was installed, was used to assess spatial distribution of loggerhead emergences. Through use of Quadrat analysis and piecewise linear regression with breakpoint, we present evidence to suggest that nest site selection in loggerheads is determined in the nearshore environment, and by characteristics such as wave height, alongshore currents, depth and patterns of erosion and accretion. Areas of relatively dense nesting were found in areas with relatively strong alongshore currents, relatively small waves, a steep offshore slope and the largest historical rates of erosion. Areas of relatively dense nesting also corresponded to areas of low nesting success. Both nesting and non-nesting emergences were clustered immediately adjacent to the revetment and at other eroding sites along the beach. These results suggest that alterations to the nearshore environment from activities such as construction of a jetty, dredging or installation of pilings, may impact sea turtle nest distribution alongshore. We also show that piecewise linear regression with breakpoint is a technique that can be used with geomorphological and oceanographic data to predict locations of nest clumping and may be useful for managers at other nesting beaches.

Florida↗

USGS2014

Asphaltene content and composition as a measure of Deepwater Horizon oil spill losses within the first 80 days

The composition and content of asphaltenes in spilled and original wellhead oils from the Deepwater Horizon (DWH) incident provide information on the amount of original oil lost and the processes most responsible for the losses within the first 80 days of the active spill. Spilled oils were collected from open waters, coastal waters and coastal sediments during the incident. Asphaltenes are the most refractory component of crude oils but their alteration in the spilled oils during weathering prevents them from being used directly as a conservative component to calculate original oil losses. The alteration is reflected by their increase in oxygen content and depletion in 12 C. Reconnaissance experiments involving evaporation, photo-oxidation, microbial degradation, dissolution, dispersion and burning indicate that the combined effects of photo-oxidation and evaporation are responsible for these compositional changes. Based on measured losses and altered asphaltenes from these experiments, a mean of 61 ± 3 vol% of the original oil was lost from the surface spilled oils during the incident. This mean percentage of original oil loss is considerably larger than previous estimates of evaporative losses based on only gas chromatography (GC) amenable hydrocarbons (32–50 vol%), and highlights the importance of using asphaltenes, as well as GC amenable parameters in evaluating original oil losses and the processes responsible for the losses.

Gulf Of Mexico↗

USGS2014

Freshwater availability and coastal wetland foundation species: ecological transitions along a rainfall gradient

Climate gradient-focused ecological research can provide a foundation for better understanding critical ecological transition points and nonlinear climate-ecological relationships, which is information that can be used to better understand, predict, and manage ecological responses to climate change. In this study, we examined the influence of freshwater availability upon the coverage of foundation plant species in coastal wetlands along a northwestern Gulf of Mexico rainfall gradient. Our research addresses the following three questions: (1) what are the region-scale relationships between measures of freshwater availability (e.g., rainfall, aridity, freshwater inflow, salinity) and the relative abundance of foundation plant species in tidal wetlands; (2) How vulnerable are foundation plant species in tidal wetlands to future changes in freshwater availability; and (3) What is the potential future relative abundance of tidal wetland foundation plant species under alternative climate change scenarios? We developed simple freshwater availability-based models to predict the relative abundance (i.e., coverage) of tidal wetland foundation plant species using climate data (1970-2000), estuarine freshwater inflow-focused data, and coastal wetland habitat data. Our results identify regional ecological thresholds and nonlinear relationships between measures of freshwater availability and the relative abundance of foundation plant species in tidal wetlands. In drier coastal zones, relatively small changes in rainfall could produce comparatively large landscape-scale changes in foundation plant species abundance which would affect some ecosystem good and services. Whereas a drier future would result in a decrease in the coverage of foundation plant species, a wetter future would result in an increase in foundation plant species coverage. In many ways, the freshwater-dependent coastal wetland ecological transitions we observed are analogous to those present in dryland terrestrial ecosystems.

Gulf Of Mexico↗

USGS2014

USGS field activities 11BHM01 and 11BHM02 on the west Florida shelf, Gulf of Mexico, May and June 2011

During May and June 2011 the (USGS), in cooperation with (USF), conducted geochemical surveys on the west Florida Shelf to investigate the effects of climate change on ocean acidification within the northern Gulf of Mexico, specifically, the effect of ocean acidification on marine organisms and habitats. The first cruise was conducted from May 3 to 9 (11BHM01) and the second was from June 25 to 30 (11BHM02). To view each cruise's survey lines, please see the Trackline page. Each cruise took place aboard the Research Vessel (R/V) Weatherbird II, a ship of opportunity led by Dr. Kendra Daly (USF), which departed from and returned to Saint Petersburg, Florida. Data collection included sampling of the surface and water column with lab analysis of pH, dissolved inorganic carbon (DIC) or total carbon dioxide (TCO 2 ), and total alkalinity (TA). lLb analysis was augmented with a continuous flow-through system (referred to as sonde data) with a conductivity-temperature-depth (CTD) sensor, which also recorded salinity and pH. Corroborating the USGS data are the vertical CTD profiles (referred to as station samples) collected by USF. The CTD casts measured continuous vertical profiles of oxygen, chlorophyll fluorescence and optical backscatter. Discrete samples for nutrients, chlorophyll, and particulate organic carbon/nitrogen were also collected during the CTD casts. Two autonomous flow-through (AFT) instruments recorded pH and CO2 every 3-5 minutes on each cruise (referred to as AFT data).

Florida↗

USGS2014

USGS field activities 11BHM03 and 11BHM04 on the west Florida shelf, Gulf of Mexico, September and November 2011

During September and November 2011 the (USGS), in cooperation with (USF), conducted geochemical surveys on the west Florida Shelf to investigate the effects of climate change on ocean acidification within the northern Gulf of Mexico, specifically, the effect of ocean acidification on marine organisms and habitats. The first cruise was conducted from September 20 to 28 (11BHM03) and the second was from November 2 to 4 (11BHM04). To view each cruise's survey lines, please see the Trackline page. Each cruise took place aboard the Research Vessel (R/V) Weatherbird II, a ship of opportunity led by Dr. Kendra Daly (USF), which departed from and returned to Saint Petersburg, Florida. Data collection included sampling of the surface and water column with lab analysis of pH, dissolved inorganic carbon (DIC) or total carbon dioxide (TCO 2 ), and total alkalinity (TA). lLb analysis was augmented with a continuous flow-through system (referred to as sonde data) with a conductivity-temperature-depth (CTD) sensor, which also recorded salinity and pH. Corroborating the USGS data are the vertical CTD profiles (referred to as station samples) collected by USF. The CTD casts measured continuous vertical profiles of oxygen, chlorophyll fluorescence and optical backscatter. Discrete samples for nutrients, chlorophyll, and particulate organic carbon/nitrogen were also collected during the CTD casts. Two autonomous flow-through (AFT) instruments recorded pH and CO 2 every 3-5 minutes on each cruise (referred to as AFT data).

Florida↗

USGS2014

Weekly resolution particulate flux from a sediment trap in the northern Gulf of Mexico, 2008-2012

The U.S. Geological Survey anchored a sediment trap in the northern Gulf of Mexico to collect time-series data on sediment flux from 2008 to 2012. There are continuous measurements of total mass flux and organic carbon flux (ogC) at 7–14 day resolution from 2008 to 2012. The flux of calcium carbonate (CaCO 3 ), particulate nitrogen (nitro), and biogenic silica (Opal) were also measured from January-December, 2008. The mass flux ranged from 0.01 g m -2 day -1 (grams per square meter per day) to 2.50 g m -2 day -1 , with a mean mass flux of 0.20 g m -2 day -1 over the 5-year study period.

Gulf Of Mexico↗

USGS2014

Cruise report for P1-13-LA, U.S. Geological Survey gas hydrates research cruise, R/V Pelican April 18 to May 3, 2013, deepwater Gulf of Mexico

The U.S. Geological Survey led a seismic acquisition cruise in the Gulf of Mexico from April 18 to May 3, 2013, with the objectives of (1) achieving improved imaging and characterization at two established gas hydrate study sites, and (2) refining geophysical methods for gas hydrate characterization in other locations. We conducted this acquisition aboard the R/V Pelican, and used a pair of 105/105-cubic-inch generator/injector air guns to provide seismic energy that we recorded using a 450-meter 72-channel digital hydrophone streamer and 25 multicomponent ocean-bottom seismometers. In the area of lease block Green Canyon 955, we deployed 21 ocean-bottom seismometers and acquired approximately 400 kilometers of high-resolution two-dimensional streamer seismic data in a grid with line spacing as small as 50 meters and along radial lines that provide source offsets up to 10 kilometers and diverse azimuths for the ocean-bottom seismometers. In the area of lease block Walker Ridge 313, we deployed 25 ocean-bottom seismometers and acquired approximately 450 kilometers of streamer seismic data in a grid pattern with line spacing as small as 250 meters and along radial lines that provide source offsets up to 10 kilometers for the ocean-bottom seismometers. The data acquisition effort was conducted safely and met the scientific objectives.

Open-File Report↗

USGS2014

2014 Gulf of Mexico Hypoxia Forecast

The Gulf of Mexico annual summer hypoxia forecasts are based on average May total nitrogen loads from the Mississippi River basin for that year. The load estimate, recently released by USGS, is 4,761 metric tons per day. Based on that estimate, we predict the area of this summer’s hypoxic zone to be 14,000 square kilometers (95% credible interval, 8,000 to 20,000) – an “average year”. Our forecast hypoxic volume is 50 km 3 (95% credible interval, 20 to 77).

Gulf Of Mexico↗

USGS2013

Foraging area fidelity for Kemp's ridleys in the Gulf of Mexico

For many marine species, locations of key foraging areas are not well defined. We used satellite telemetry and switching state-space modeling (SSM) to identify distinct foraging areas used by Kemp's ridley turtles ( Lepidochelys kempii ) tagged after nesting during 1998–2011 at Padre Island National Seashore, Texas, USA (PAIS; N = 22), and Rancho Nuevo, Tamaulipas, Mexico (RN; N = 9). Overall, turtles traveled a mean distance of 793.1 km (±347.8 SD) to foraging sites, where 24 of 31 turtles showed foraging area fidelity (FAF) over time (N = 22 in USA, N = 2 in Mexico). Multiple turtles foraged along their migratory route, prior to arrival at their "final" foraging sites. We identified new foraging "hotspots" where adult female Kemp's ridley turtles spent 44% of their time during tracking (i.e., 2641/6009 tracking days in foraging mode). Nearshore Gulf of Mexico waters served as foraging habitat for all turtles tracked in this study; final foraging sites were located in water <68 m deep and a mean distance of 33.2 km (±25.3 SD) from the nearest mainland coast. Distance to release site, distance to mainland shore, annual mean sea surface temperature, bathymetry, and net primary production were significant predictors of sites where turtles spent large numbers of days in foraging mode. Spatial similarity of particular foraging sites selected by different turtles over the 13-year tracking period indicates that these areas represent critical foraging habitat, particularly in waters off Louisiana. Furthermore, the wide distribution of foraging sites indicates that a foraging corridor exists for Kemp's ridleys in the Gulf. Our results highlight the need for further study of environmental and bathymetric components of foraging sites and prey resources contained therein, as well as international cooperation to protect essential at-sea foraging habitats for this imperiled species.

Ecology and Evolution↗

USGS2013

Introduction to the special issue on “Understanding and predicting change in the coastal ecosystems of the northern Gulf of Mexico”

The coastal region of the northern Gulf of Mexico owes its current landscape structure to an array of tectonic, erosional and depositional, climatic, geochemical, hydrological, ecological, and human processes that have resulted in some of the world's most complex, dynamic, productive, and threatened ecosystems. Catastrophic hurricane landfalls, ongoing subsidence and erosion exacerbated by sea-level rise, disintegration of barrier island chains, and high rates of wetland loss have called attention to the vulnerability of northern Gulf coast ecosystems, habitats, built infrastructure, and economy to natural and anthropogenic threats. The devastating hurricanes of 2005 (Katrina and Rita) motivated the U.S. Geological Survey Coastal and Marine Geology Program and partnering researchers to pursue studies aimed at understanding and predicting landscape change and the associated storm hazard vulnerability of northern Gulf coast region ecosystems and human communities. Attaining this science goal requires increased knowledge of landscape evolution on geologic, historical, and human time scales, and analysis of the implications of such changes in the natural and built components of the landscape for hurricane impact susceptibility. This Special Issue of the Journal of Coastal Research communicates northern Gulf of Mexico research results that (1) improve knowledge of prior climates and depositional environments, (2) assess broad regional ecosystem structure and change over Holocene to human time scales, (3) undertake process studies and change analyses of dynamic landscape components, and (4) integrate framework, climate, variable time and spatial scale mapping, monitoring, and discipline-specific process investigations within interdisciplinary studies.

Journal of Coastal Research↗

USGS2013

Seasonal flux and assemblage composition of planktic foraminifers from a sediment-trap study in the northern Gulf of Mexico

Sediment-trap samples from the northern Gulf of Mexico reveal that Globorotalia truncatulinoides, Neogloboquadrina dutertrei, Pulleniatina spp. (includes P. obliquiloculata and P. finalis), and the Globorotalia menardii group (includes Gt. menardii, Gt. tumida, and Gt. ungulata) generally occur in cold months. Globigerinoides ruber (white and pink varieties) and Globigennoides sacculifer occur throughout the year. The seasonal occurrence of individual taxa of planktic foraminifers in the Gulf of Mexico have important differences with the seasonal occurrence of the same taxa observed in a 6-year sediment-trap dataset from the western Sargasso Sea. Thus information on the ecologic preferences of individual taxa determined in one region cannot necessarily be applied directly to another area. In the northern Gulf of Mexico 90% of the total flux of Globorotalia truncatulinoides tests to sediments occurs in January and February. Mg/Ca and d 18 Ο measurements indicate that nonencrusted forms of Gt. truncatulinoides calcify in the upper-surface-mixed zone. Thus, analyses of nonencrusted Gt. truncatulinoides in sediments of the northern Gulf of Mexico have potential for monitoring past conditions in the winter-surface-mixed layer. The relatively low overall abundance of Globigerinoides ruber (white) in sediment-trap samples is anomalous because Gs. ruber (white) is one of the most abundant foraminifers in>150 µm census data from northern Gulf of Mexico Holocene sediment core samples. Globigerinoides ruber (pink) is a relatively persistent and common component of the sediment-trap samples. Thus Gs. ruber (pink) has potential as a proxy for mean annual sea-surface temperature in the Gulf of Mexico

Journal of Coastal Research↗

USGS2013

Economic vulnerability to sea-level rise along the northern U.S. Gulf Coast

The northern Gulf of Mexico coast of the United States has been identified as highly vulnerable to sea-level rise, based on a combination of physical and societal factors. Vulnerability of human populations and infrastructure to projected increases in sea level is a critical area of uncertainty for communities in the extremely low-lying and flat northern gulf coastal zone. A rapidly growing population along some parts of the northern Gulf of Mexico coastline is further increasing the potential societal and economic impacts of projected sea-level rise in the region, where observed relative rise rates range from 0.75 to 9.95 mm per year on the Gulf coasts of Texas, Louisiana, Mississippi, Alabama, and Florida. A 1-m elevation threshold was chosen as an inclusive designation of the coastal zone vulnerable to relative sea-level rise, because of uncertainty associated with sea-level rise projections. This study applies a Coastal Economic Vulnerability Index (CEVI) to the northern Gulf of Mexico region, which includes both physical and economic factors that contribute to societal risk of impacts from rising sea level. The economic variables incorporated in the CEVI include human population, urban land cover, economic value of key types of infrastructure, and residential and commercial building values. The variables are standardized and combined to produce a quantitative index value for each 1-km coastal segment, highlighting areas where human populations and the built environment are most at risk. This information can be used by coastal managers as they allocate limited resources for ecosystem restoration, beach nourishment, and coastal-protection infrastructure. The study indicates a large amount of variability in index values along the northern Gulf of Mexico coastline, and highlights areas where long-term planning to enhance resiliency is particularly needed.

Alabama;Florida;Louisiana;Mississippi;Texas↗

USGS2013

Application of a hydrodynamic and sediment transport model for guidance of response efforts related to the Deepwater Horizon oil spill in the Northern Gulf of Mexico along the coast of Alabama and Florida

U.S. Geological Survey (USGS) scientists have provided a model-based assessment of transport and deposition of residual Deepwater Horizon oil along the shoreline within the northern Gulf of Mexico in the form of mixtures of sand and weathered oil, known as surface residual balls (SRBs). The results of this USGS research, in combination with results from other components of the overall study, will inform operational decisionmaking. The results will provide guidance for response activities and data collection needs during future oil spills. In May 2012 the U.S. Coast Guard, acting as the Deepwater Horizon Federal on-scene coordinator, chartered an operational science advisory team to provide a science-based review of data collected and to conduct additional directed studies and sampling. The goal was to characterize typical shoreline profiles and morphology in the northern Gulf of Mexico to identify likely sources of residual oil and to evaluate mechanisms whereby reoiling phenomena may be occurring (for example, burial and exhumation and alongshore transport). A steering committee cochaired by British Petroleum Corporation (BP) and the National Oceanic and Atmospheric Administration (NOAA) is overseeing the project and includes State on-scene coordinators from four States (Alabama, Florida, Louisiana, and Mississippi), trustees of the U.S. Department of the Interior (DOI), and representatives from the U.S. Coast Guard. This report presents the results of hydrodynamic and sediment transport models and developed techniques for analyzing potential SRB movement and burial and exhumation along the coastline of Alabama and Florida. Results from these modeling efforts are being used to explain the complexity of reoiling in the nearshore environment and to broaden consideration of the different scenarios and difficulties that are being faced in identifying and removing residual oil. For instance, modeling results suggest that larger SRBs are not, under the most commonly observed low-energy wave conditions, likely to move very far alongshore. This finding suggests that SRBs from one source location may not (outside of storm conditions) be redistributed to other up or down coast locations. This information can guide operational response decisions. In addition, because SRBs are less mobile compared with sand, they are likely to become buried and unburied under normal sand transport processes thereby lengthening the time SRBs may take to move onshore. The rate of onshore movement was not specifically addressed by this study, yet the results resolve the cross-shore domain and cross-shore variations in alongshore transport that are relevant to achieving the primary objectives. Furthermore, during infrequent events (for example, winter storms and severe meteorological events such as Hurricane Isaac of August 2012), energy is shown to be sufficient to move a greater range of SRB sizes and potentially expose and break up submerged oil mats. When SRBs do move alongshore, the models indicate that there are regions that are more conducive to accumulation of SRB material than others. Accumulation can occur where there are reversals and decelerations in alongshore currents and where forces created by shear stress drops below critical thresholds to maintain or initiate SRB movement. In addition, flow and SRB mobility patterns around inlets indicate patterns in hydrodynamic forces that influence redistribution of SRBs and the surface oil that mixed with sediment to form oil mats in the first place.

Alabama;Florida↗