Surface Oil Slicks Research Articles

Hydrocarbon-degrading bacteria enriched by the Deepwater Horizon oil spill identified by cultivation and DNA-SIP

The massive influx of crude oil into the Gulf of Mexico during the Deepwater Horizon (DWH) disaster triggered dramatic microbial community shifts in surface oil slick and deep plume waters. Previous work had shown several taxa, notably DWH Oceanospirillales, Cycloclasticus and Colwellia, were found to be enriched in these waters based on their dominance in conventional clone and pyrosequencing libraries and were thought to have had a significant role in the degradation of the oil. However, this type of community analysis data failed to provide direct evidence on the functional properties, such as hydrocarbon degradation of organisms. Using DNA-based stable-isotope probing with uniformly (13)C-labelled hydrocarbons, we identified several aliphatic (Alcanivorax, Marinobacter)- and polycyclic aromatic hydrocarbon (Alteromonas, Cycloclasticus, Colwellia)-degrading bacteria. We also isolated several strains (Alcanivorax, Alteromonas, Cycloclasticus, Halomonas, Marinobacter and Pseudoalteromonas) with demonstrable hydrocarbon-degrading qualities from surface slick and plume water samples collected during the active phase of the spill. Some of these organisms accounted for the majority of sequence reads representing their respective taxa in a pyrosequencing data set constructed from the same and additional water column samples. Hitherto, Alcanivorax was not identified in any of the previous water column studies analysing the microbial response to the spill and we discuss its failure to respond to the oil. Collectively, our data provide unequivocal evidence on the hydrocarbon-degrading qualities for some of the dominant taxa enriched in surface and plume waters during the DWH oil spill, and a more complete understanding of their role in the fate of the oil.

Legal Issues and Scientific Constraints in the Environmental Assessment of the Deepwater Horizon Oil Spill in Mexico Exclusive Economic Zone (EEZ) in the Gulf of Mexico

The largest accidental marine oil spill (4.9 million barrels) in the Gulf of Mexico (GoM) seabed (1600 m) caused by the sinking of the Deepwater Horizon oil rig in 2010, put to the test once again the resilient capacity of the pelagic and benthic realms of this Large Marine Ecosystem. Many are the ecological services provided by its waters (fisheries, tourism, aquaculture and fossil fuel reserves) to neighboring countries (US, Mexico and Cuba). However, the unprecedented volumes of hydrocarbons, gas and chemical dispersants (Corexit) introduced in the system, represent ecological stressors whose deleterious effects are still the subject of civil claims and scientific controversy. Presumably, the short scale effects were confined to the Gulf’s northeastern shallow waters, and the combined actions of weathering, biodegradation, and oil recovery left the system almost under pre-spill conditions. Unfortunately, surface and subsurface oil plumes were detected in the spill aftermath, and their dispersion trajectories threatened Mexico EEZ. Surface oil slicks were detected in the pristine waters of northern Yucatan, while subsurface oil plumes from the Macondo’s well blowout were dangerously advancing southwest towards key fishing grounds in the northwestern GoM. This disaster prompted the Mexican government to implement an ambitious ocean monitoring program adopting a bottom-up approach focused on building a base line for more than 42 physicochemical and biological variables for water, sediment and biota from the continental shelf-slope region of the NW GoM. Technological constraints have precluded systematic observations in the vast Mexican EEZ that could discriminate natural variability and oil seep emissions from antropic disturbances. Therefore, preliminary risk analyses relied on seasonal and historical records. Two years of field observations revealed subtle environmental changes in the studied area attributed to antropic disturbances. Waters maintained oligotrophic conditions and zooplankton and benthic infaunal biomass were also poor. Biomarkers in sediments and biota did not exceed EPA’s benchmarks, and sediment’s fingerprinting (δ13C) indicated marine carbon sources. Geomarkers revealed an active transport from the Mississippi towards the NW GoM of phyllosilicates bearing a weathered oil coating. Consequently, shelf and slope sediment toxicity begins to show an increasing trend in the region. The complexity of hydrocarbons bioaccumulation and biodegradation processes in deep waters of the GoM seems to indicate that meso-and large-scale observations may prove to be essential in understanding the capacity of the GoM to recover its ecological stability.

Detecting surface oil slick related to gas hydrate/petroleum on the ocean bed of South China Sea by ENVI/ASAR radar data

For exploring the distribution of oil slick related to gas hydrate or petroleum in the northern part of South China Sea and evaluating the potential of ENVI/ASAR radar data for detecting oil slick, this paper tries to detect the oil slick on ocean surface of some potential areas in South China Sea and map oil slick from anomaly area in radar image. Seven surface oil slicks in Qiongdongnan Basin and four potential targets of oil slicks in Taixi–Dongsha Basin were detected and extracted by using ENIV/ASAR data. The anomalies of the radar image representing oil slick are validated by in-site sampling and laboratory analyzing. The Gas Chromatograph (GC) results of the extracted oil from the water samples gathered from the sites of detected oil slick demonstrate a typical composition of oil rather than that of ocean microbial origins, and Total Organic Carbon (TOC) concentrations in two designed vertical profiles keep steady in different depths, showing that the organic contents in water column are steady from the deep area to ocean surface. These results suggest the detected oil slick is a thin floating oil rather than a thick spill. Influencing factors to the results of oil slick detection including wind speed, current, small islands and capes as well as deep-sea petroleum reservoirs are discussed. The results in this study exhibit that extracting the anomaly signals related to oil slick related to oil/gas seeps using image processing techniques from ENVI/ASAR data is helpful to predict anomaly areas as potential targets for further exploration in this area.

The oil spill model OILTRANS and its application to the Celtic Sea

This paper describes details of an oil spill model, OILTRANS, developed by the authors. The model is an off-line particle-transport model coupled to the most up to date operational met-ocean model forecasts. Formulations for the dominant oil fate processes of spreading, advection, diffusion, evaporation, emulsification and dispersion have been encoded, providing the model with the ability to accurately predict the horizontal movement of surface oil slick, the vertical entrainment of oil into the water column and the mass balance of spilled oil. The application of the OILTRANS model to an accidental release during a ship-to-ship fuel transfer in the Celtic Sea in February 2009 is presented to validate the system. Comparisons with aerial observations of the oil slick at the time of the incident, and subsequent model simulations, indicate that the OILTRANS model is capable of accurately predicting the transport and fate of the oil slick.

Mississippi River and Sea Surface Height Effects on Oil Slick Migration

Millions of barrels of oil escaped into the Gulf of Mexico (GoM) after the 20 April, 2010 explosion of Deepwater Horizon (DH). Ocean circulation models were used to forecast oil slick migration in the GoM, however such models do not explicitly treat the effects of secondary eddy-slopes or Mississippi River (MR) hydrodynamics. Here we report oil front migration that appears to be driven by sea surface level (SSL) slopes, and identify a previously unreported effect of the MR plume: under conditions of relatively high river discharge and weak winds, a freshwater mound can form around the MR Delta. We performed temporal oil slick position and altimeter analysis, employing both interpolated altimetry data and along-track measurements for coastal applications. The observed freshwater mound appears to have pushed the DH oil slick seaward from the Delta coastline. We provide a physical mechanism for this novel effect of the MR, using a two-layer pressure-driven flow model. Results show how SSL variations can drive a cross-slope migration of surface oil slicks that may reach velocities of order km/day, and confirm a lag time of order 5–10 days between mound formation and slick migration, as observed form the satellite analysis. Incorporating these effects into more complex ocean models will improve forecasts of slick migration for future spills. More generally, large SSL variations at the MR mouth may also affect the dispersal of freshwater, nutrients and sediment associated with the MR plume.

Formation and growth of organic aerosols downwind of the Deepwater Horizon oil spill

[1] Aerosol size distributions were measured in June 2010 downwind of the surface oil slick produced by the Deepwater Horizon oil spill in the Gulf of Mexico. Previous work has shown that rapid condensation of partially oxidized hydrocarbons was responsible for formation of a plume of secondary organic aerosol downwind of the spill region. Here we examine new particle formation and growth kinetics. New particles were formed upwind of the freshest oil but downwind of oil that surfaced less than about 100 hours previously. Four nm particles formed at a rate of ∼3 cm−3 s−1 and subsequently grew by condensation at a rate of ∼20 nm hr−1; preexisting accumulation mode particles grew by ∼10 nm hr−1. The gas-phase concentration of a condensing species necessary to support irreversible growth with unit accommodation coefficient is estimated to be ∼0.04–0.09 μg m−3 (∼3–8 pptv). Gas-phase concentrations may have been higher if condensation were limited by volatility. The ratio of growth rates for newly formed particles to accumulation mode particles was consistent within error limits with irreversible condensation. The absence of new particle formation away from the <100 hr-old oil slick indicates that the oxidation products of gas-phase hydrocarbon species were directly involved in the formation and growth of new particles.

Mapping sea surface oil slicks using RADARSAT-2 quad-polarization SAR image

[1] Polarimetric SAR decomposition parameters, average alpha angle () and entropy (H) are estimated for oil-slick contaminated sea surfaces and slick-free conditions using a RADARSAT-2 quad-polarization SAR image. The values of H and within oil slick areas are significantly higher than those of the ambient sea surface, indicating the dominance of Bragg scattering for the slick-free ocean and non-Bragg scattering for the oil-slick area. In land classification, the conformity coefficient (μ) is often used to discriminate surface scattering with double-bounce or volume scattering. Based on this rationale, we also develop a method using μ as a logical scalar descriptor to map oil slicks under low-to-moderate wind conditions. The proposed method is assessed using a RADARSAT-2 quad-polarization SAR image of oil slicks in the Gulf of Mexico. Analysis shows that when μ is positive the sea surface is slick-free, whereas μ is negative for oil-slick areas. This method provides a simple and effective mapping technique for oil slick detection.

Getting SMARTer: Recommendations for Improving SMART Monitoring Procedures Based on Experiences from the Deepwater Horizon Response: Scientific Support for Deepwater Horizon (DWH) Aerial Dispersant Operations

ABSTRACT During the MC252 Deepwater Horizon (DWH) response, aerial dispersants were applied as part of the operational response to minimize the potential for surface oil slicks to impact surfacebreathing wildlife and environmentally sensitive shoreline ecosystems. Monitoring of dispersant efficacy and environmental impact was performed according to the SMART protocols described in the Special Monitoring of Applied Response Technologies developed by the U.S. Coast Guard (USCG), National Oceanic and Atmospheric Administration (NOAA), US Environmental Protection Agency (EPA), Centers for Disease Control and Prevention (CDC), and the Minerals Management Service (MMS) (2006). Valuable lessons regarding SMART implementation were learned during this response. The magnitude and duration of the response required that multiple teams be deployed simultaneously to conduct Tier 1 observations, and Tier II and III fluorometry and water sample collection activities. The scope of the SMART activity required close coopera...

Extraction of oil slicks on the sea surface from optical satellite images by using an anomaly detection technique

Many methods for the detection of oil pollution on the sea surface from remotely sensed images have been developed in recent years. However, because of the diverse physical properties of oil on the sea surface in the visible wavelengths, such images are easily affected by the surrounding environment. This is a common difficulty encountered when optical satellite images are used as data sources for observing oil slicks on the sea surface. However, provided the spectral interference generated by the surrounding environment can be regarded as noise and properly modeled, the spectral anomalies caused by an oil slick on normal sea water may be observed after the suppression of this noise. In this study, sea surface oil slicks are extracted by detecting spectral anomalies in multispectral optical satellite images. First, assuming that the sea water and oil slick comprise the dominant background and target anomaly, respectively, an RX algorithm is used to enhance the oil slick anomaly. The oil slick can be distinguished from the sea water background after modeling and suppression of inherent noise. Next, a Gaussian mixture model is used to characterize the statistical distributions of the background and anomaly, respectively. The expectation maximization (EM) algorithm is used to obtain the parameters needed for the Gaussian mixture model. Finally, according to the Bayesian decision rule of minimum error, an optimized threshold can be obtained to extract the oil slick areas from the source image. Furthermore, with the obtained Gaussian distributions and optimized threshold, a theoretical false alarm level can be established to evaluate the quality of the extracted oil slicks. Experimental results show that the proposed method can not only successfully detect oil slicks from multispectral optical satellite images, but also provide a quantitative accuracy evaluation of the detected image.

Research Spotlight: Simulations show deep oil from leak is confined to Gulf of Mexico

The Deepwater Horizon oil leak caused severe environmental damage in the Gulf of Mexico, and aspects of its environmental impact are still unknown. In addition to surface oil slicks, large underwater plumes of oil were found.To help evaluate the potential environmental impact, Adcroft et al. ran simulations of underwater plumes of dissolved and suspended oil originating from a point source in the Gulf of Mexico. They assessed dispersal and decay mechanisms, examining the possibility that toxic concentrations of dissolved oil might exit the Gulf of Mexico.

A numerical oil spill model based on a hybrid method

The purpose of this paper is the development of a hybrid particle tracking/Eulerian–Lagrangian approach for the simulation of spilled oil in coastal areas. Oil discharge from the source is modeled by the release of particles. When the oil slick thickness or the oil concentration reaches a critical value, particles are mapped on slick thickness or node concentrations, and the calculations proceed in the Eulerian–Lagrangian mode. To acquire accurate environment information, the model is coupled with the 3-D free-surface hydrodynamics model (POM) and the third-generation wave model (SWAN). By simulating the oil processes of spreading, advection, turbulent diffusion, evaporation, emulsification, dissolution and shoreline deposition, it has the ability to predict the horizontal movement of surface oil slick, the vertical distribution of oil particles, the concentration in the water column and the mass balance of spilled oil. An accidental oil release near Dalian coastal waters is simulated to validate the developed model. Compared with the satellite images of oil slicks on the surface, the numerical results indicate that the model has a reasonable accuracy.

A Wavelet Technique to Extract the Backscatter Signatures from SAR Images of the Sea

SAR images of the sea often show backscatter patterns linked to the horizontal structure of the Marine Atmospheric Boundary Layer (MABL) at the interface with the sea surface. In general, their dimensions are spread over a wide range of length scales, presenting spatial periodicity as well as intermittence. With the aim to isolate such backscatter structures, the two-dimensional Continuous Wavelet Transform (CWT2) analysis has been applied to SAR images of the sea. The CWT2 analysis permits to highlight the backscatter cells associated to the structure of MABL, as well as to evidence the structure of the atmospheric gravity waves occurring at the lee side of islands and coast. The cells detected in the range 0.3km ¥ 4km are directly associated to the wind spatial structure deriving, in turns, from the turbulent characteristics of the wind ∞ow. They have an elliptic shape, with the major axis along the (aliased) wind direction. Those with size falling inside the spatial range 4km ¥ 20km describe, instead, the atmospheric gravity waves structure (if present) and the structures linked to the wind shading. The technique developed is the background for several applications: it has been used to compute the wind flelds without any a priori information, as well as to study the inner structure of the Langmuir atmospheric circulation. Other applications could be on the detection of sea surface oil slicks.

Distinct side-scan sonar, RADARSAT SAR, and acoustic profiler signatures of gas and oil seeps on the Gulf of Mexico slope

We examined bubble streams from four natural seep sites on the upper continental slope of the Gulf of Mexico. Synthetic aperture radar images verified surface oil slicks over sites with oily bubbles but not over those with non-oily bubbles. Non-oily bubbles produced high backscatter on side-scan sonar records, but were difficult to detect with acoustic profilers. Oily bubbles produced clear signatures extending from the seafloor to the near-surface on acoustic profiles and produced acoustic shadows on side-scan sonar records. We hypothesize that the bubbles’ oily coating causes the different signatures, since all bubbles were resonant at the tested frequencies.

Development and Application of Oil Spill Model for Singapore Coastal Waters

This paper presents the development and application of a three-dimensional oil spill model for predicting the movement and fate of an oil slick in the coastal waters of Singapore. In the model, the oil slick is divided into a number of small elements or grids for simulating of the oil processes of spreading, advection, turbulent diffusion, evaporation, dissolution, vertical dispersion, shoreline deposition and adsorption by sediment. This model is capable of predicting the horizontal movement of surface oil slick, the mass balance of oil spill and the oil particle concentration distribution in water body. Satellite images and field observations of oil slicks on the surface in the Singapore Straits, and measurements of the vertical concentration of oil particles in flume are used to validate the newly developed model. Compared with the observations, the numerical results of the oil spill model show good conformity.

Remote Detection of Submerged Orimulsion with a Range-Gated Laser Fluorosensor

ABSTRACT Bituminous fuels (in the form of water-based emulsions) are increasingly being used as fuel sources in many countries. When spilled in a marine environment, these emulsified fuels initially disperse and then, under certain circumstances, coalesce to become highly adhesive to beaches and shorelines. These fuels may either float or submerge, depending on the salinity of the water into which the spill occurs. Similar situations are known to occur with some conventional heavy fuels, as was the case with the Erika incident off the coast of France. Technologies to detect these neutrally buoyant and/or submerged fuels are urgently needed. The remote detection of submerged oil is a daunting task. The majority of sensors commonly used for the detection of surface oil slicks are of no use for the detection of submerged oil. Environment Canada and the Canadian Coast Guard have recently undertaken a series of bench-scale studies to develop technologies for the real-time remote detection of neutrally buoyant and/or submerged fuels in the marine environment. The unique capabilities of “active sensors” such as laser fluorosensors are being evaluated for the subsurface detection of heavy petroleum products. The detection of submerged Orimulsion by laser-induced fluorescence has been demonstrated at a distance of 81 m (265 feet) in a small test tank. Further experiments are underway to confirm the real-time detection of submerged Orimulsion, initially on the ground, and then through airborne tests.

Improvement of Drift Calculation in Mothy Operational Oil Spill Prediction System

ABSTRACT MOTHY (Modèle Océanique de Transport d'Hydrocarbures) is a pollutant drift model, developed and operated by Météo-France. MOTHY includes hydrodynamic coastal ocean modelling and real time atmospheric forcing from a global meteorological model. Pollutants can be oil or floating objects. To improve forecasts on the Mediterranean Sea, several methods were tested to inject large scale currents (permanent part) into the MOTHY system. The best results were obtained with monthly means of currents at 5 meters (from Mercator system). The addition of altimetric corrections improved the results. In addition the impact of wave (or swell) current, which is usually neglected in such models, is investigated. The literature has surprisingly little to say on the topic of wave-driven surface oil slicks. Earlier review on oil spill transport modelling includes wave driven transport among potential advection mechanisms. The discussion of wave-induced advection (mass transport) adopts a Lagrangian framework, focusing on the analyses of Stokes and Longuet-Higgins for the vertical profile of the Lagrangian velocity beneath waves. In our work, the action of a vertical shear due to waves is accounted for by including the Stokes drift due to weakly non linear waves. We evaluate this term and compare with observations of Erika pollution incident.

Modeling Underwater Oil/Gas Jets and Plumes: Comparison with Field Data

A jet and plume model previously developed to simulate underwater blowouts of liquid/gas mixtures is used here to simulate five field experiments. The field experiment data that became available only after the previous paper was published are unique. In this technical note, the variation of jet/plume diameter with depth for all five field experiments is compared with model simulations. The model simulations were carried out without changing any coefficients from one simulation to another. The comparisons between the observed data and model results of two surface oil slicks are also included.

Remote Sensing Study of Historical Changes in Natural Oil Slick Volumes in the Santa Barbara Channel: ABSTRACT

Large natural oil slicks are continually forming in the Santa Barbara Channel as a result of natural hydrocarbon seeps that occur above subsurface oil accumulations. Evaporation of volatile constituents in these oil slicks is a significant source of air pollution. In this study we employed a suite of remote sensing data along with a variety of image processing and geographic information system techniques to analyze the location, extent and changes in sea surface oil slicks during the period of 1975 - present. An extensive collection of airborne and spaceborne remote sensor data was accessed and examined for this study, including aerial photography, airborne spectral and microwave data, Landsat MSS and TM data and Shuttle Imaging Radar. Areas of oil slick accumulations were identified, delineated, georeferenced, measured and mapped to a common scale using both manual and digital techniques. A Gaussian mathematical model was employed to provide quantitative estimates of surface oil accumulations identified within each image over the entire twenty year period. This study indicates that variances in mapped oil slick location and extent as well as the estimated amounts of oil present within each image may be attributed to image type and quality as well as environmental conditions.

Effect of two Corexit dispersants in the removal of Arabian light and heavy crude oils from seawater surface

The effect of two chemical dispersants (Corexit 7664 and Corexit 9524) in the emulsification of a light and heavy Arabian crude oil types was investigated in context of dispersant concentration to oil ratio, rate of mixing and time of mixing. The ability of Corexit 7664 and 9524 to emulsify light and heavy crude oil was dependant on the concentration of the dispersant, the rate of mixing and the duration of mixing. Extrapolation of the results to rough and calm sea conditions suggests that the application of 6 % Corexit 9524 to oil present in rough seas would remove 95 % of the surface oil slick. Light oil spill in calm seas can be dispersed by the application of 4 % Corexit 9524 effecting 80 % removal from the sea surface.

Oil Slick Transport in Rivers

A computer model for oil slick transformation in rivers is developed and applied to simulate the fate of oil spills in the connecting channels of the upper Great Lakes. In this model, the transport of the surface oil slick is simulated by a Lagrangian discrete‐parcel algorithm. The model simulates either continuous or instantaneous oil spills and can be used for both open water and ice‐covered conditions. Oil slick transformation processes considered in the model include advection, mechanical spreading, horizontal turbulent diffusion, evaporation, dissolution, and shoreline deposition. The model can be used to develop cleanup measures in the case of an actual spill and to assess likely environmental impacts of possible spills.