Oil Weathering Research Articles

The effect of vertical mixing on the horizontal drift of oil spills

Abstract. Vertical and horizontal transport mechanisms for marine oil spills are investigated using numerical model simulations. To realistically resolve the 3-D development of a spill on the ocean surface and in the water column, recently published parameterizations for the vertical mixing of oil spills are implemented in the open-source trajectory framework OpenDrift (https://doi.org/10.5281/zenodo.1300358, last access: 7 April 2018). The parameterizations include the wave entrainment of oil, two alternative formulations for the droplet size spectra, and turbulent mixing. The performance of the integrated oil spill model is evaluated by comparing model simulations with airborne observations of an oil slick. The results show that an accurate description of a chain of physical processes, in particular vertical mixing and oil weathering, is needed to represent the horizontal spreading of the oil spill. Using ensembles of simulations of hypothetic oil spills, the general drift behavior of an oil spill during the first 10 days after initial spillage is evaluated in relation to how vertical processes control the horizontal transport. Transport of oil between the surface slick and the water column is identified as a crucial component affecting the horizontal transport of oil spills. The vertical processes are shown to control differences in the drift of various types of oil and in various weather conditions.

Forensic Investigations of Diesel Oil Spills in the Environment Using Comprehensive Two-Dimensional Gas Chromatography-High Resolution Mass Spectrometry and Chemometrics: New Perspectives in the Absence of Recalcitrant Biomarkers.

Forensic investigations of oil spills aim to find the responsible source(s) of the spill. Oil weathering processes change the chemical composition of the spilled oil and make the matching of oil spill samples to potential sources difficult. Diesel oil spill cases are more challenging, because biomarkers recalcitrant to long-term weathering are absent. We developed and tested a new method for the analysis and matching of diesel oil spills using two-dimensional gas chromatography-high resolution mass spectrometry (GC × GC - HRMS) and 2D-CHEMSIC (2-Dimensional CHEMometric analysis of Selected Ion Chromatograms), an extension of the CHEMSIC method to GC × GC data. The 2D-CHEMSIC performs pixel-based analysis using chemometrics on concatenated sections of 2D extracted ion chromatograms to assess the overall chemical variability of the samples, with potential applications for matching spill-source pairs in forensic investigations. The method was tested on samples from a number of diesel oil spill cases, (i) distinguishing chemically similar source diesels, (ii) investigating weathering effects on spill samples to determine type and degree of weathering, and (iii) improving the matching of diesel oil spills affected by weathering. Positive matches for spill-source pairs were identified after excluding the signals from the hydrocarbons most susceptible to evaporation, and photo-oxidized spills were also matched due to the presence of unaffected hydrocarbons. Forensic diagnostics obtained by the 2D-CHEMSIC were validated by the conventional CEN-Tr method.

Determining spectral groups to distinguish oil emulsions from Sargassum over the Gulf of Mexico using an airborne imaging spectrometer

During the weathering of marine-spilled oils, various types of oil pollution are formed that can harm marine and coastal environments. Thus, the remote detection, classification and quantification of spilled oils is important in marine environmental monitoring. Although multispectral images can be used to observe various spilled oils, due to confusion between the multispectral backscattered signals, distinguishing spilled oils from floating algae in the same image is challenging. The spectral features of carbon-hydrogen (-C-H) and oxygen-hydrogen (-O-H) groups, and pigments, are diagnostic absorption features and are different from the backscattering signal, they have not been used to improve detection independently. In this study, all the spectral features of the groups were clearly interpreted using reflectance spectra collected from an airborne visible infrared imaging spectrometer (AVIRIS). A reflectance peak-trough detection method to characterize the different spectral groups was used to determine the spectral features of Deepwater Horizon (DWH) oil emulsions and floating Sargassum in the Gulf of Mexico (GOM). The results show that the spilled oils and floating Sargassum can be clearly identified, and the various spilled oils (i.e., different oil emulsions and oil slicks) could also be determined from the differences in the spectral features of the above groups. Finally, we discuss the spectral requirements for the identification of these groups and we conclude that optical remote sensing, including imaging spectrometers, will play an increasingly important role in assessing marine oil spills.

Evaluation of New Diagnostic Ratios of Naphthalenes and Fluorenes by Identifying Severely Weathered Oils Collected in Laboratory Simulations and Coastal Weathering Experiments.

The composition and physical properties of spilled oil have great changes during the seriously weathering process. It brings great difficulties to the source identification of oil spill. So, the stable and trustworthy diagnostic ratios (DRs) for accurate identification of severely weathered spilled oils are very important. The explosion of Sinopec pipeline happened on November 22, 2013 at Qingdao, China. Local beaches at Jiaozhou Bay were polluted by spilled oils. We have collected original spilled oil samples from an area free from human interference near the oil leakage point after the accident. Synchronized with actual beach weathering, laboratory experiments were conducted to simulate oil weathering for 360days by using the collected original spilled oil samples. Based on the t test and the repeatability limit method, 65 DRs of naphthalenes and fluorenes were screened. Fifteen DRs, namely, C2Nap/(C2Nap + C3Nap), C2Nap/(C2Nap + C4Nap), C2Nap/total Nap, C3Nap/(C3Nap + C4Nap), C3Nap/total Nap, C4Nap/total Nap, C2Flu/(C2Flu + C3Flu), C2Flu/total Flu, C2Nap/(C2Nap + Flu), C2Nap/(C2Nap + C1Flu), C2Nap/(C2Nap + C2Flu), C2Nap/(C2Nap + C3Flu), C3Nap/(C3Nap + Flu),C3Nap/(C3Nap + C1Flu), total Nap/(total Nap + total Flu), have maintained remarkable stability during the simulated weathering experiments and field weathering process. These stable ratios can retain the characteristics of oil source during weathering. They are very beneficial to improve the accuracy of identifying the source of severely weathered oil and can be used as an effective supplement to existing index system for source identification.

Evaluation of the diagnostic ratios of adamantanes for identifying seriously weathered spilled oils from simulated experiment and actual oil spills.

The composition and physical properties of spilled oil have great changes during the seriously weathering process. It brings great difficulties to the source identification of oil spill. So the stable and trustworthy diagnostic ratios (DRs) for accurate identification of severely weathered spilled oils are very important. The explosion of Sinopec pipeline happened on November 22, 2013 at Qingdao, China. Local beaches at Jiaozhou Bay were polluted by spilled oils. We have collected original spilled oil samples from an area free from human interference near the oil leakage point after the accident. Synchronized with actual beach weathering, laboratory experiments were conducted to simulate oil weathering for 360days by using the collected original spilled oil samples. Based on t test and the repeatability limit method, 50 diagnostic ratios (DRs) of adamantanes were screened. Four DRs, namely 1,3-dimethyladamantane/total dimethyladamantane, 1-methyladamantane/(1-methyladamantane + 1,3-dimethyladamantane), dialkyl diamantane/total diamantane, and diamantane/(diamantane + dialkyl diamantane), have maintained remarkable stability during the simulated weathering experiments and field weathering process. These stable ratios can retain the characteristics of oil source during weathering. They are very beneficial to improve the accuracy of identifying the source of severely weathered oil and can be used as an effective supplement to existing index system for source identification.

THE CHANGE OF OIL QUANTITY AND DYNAMICS OF SOIL PHYTOTOXICITY AT THE OIL POLLUTION

The authors of the article study the regularities of oil quantity change and dynamics of soil phytotoxicity at the oil pollution. The article describes the sequence of study of changes in the amount of pollutant (oil) in the soil. The study was carried out in modeling, laboratory and micro-field experiments. Two types of soils (black soil and turf podzolic soil) were used in the studies. The experiments were carried out in at least three biological and three analytical repetitions. Statistical processing of the results was carried out using Microsoft Office Excel software package. The investigation of evaporation of oil from the soil (when the initial concentration of oil in the soil was 10% and the initial moisture of the soil was 20%) shows that the intense evaporation of the liquid composition (oil+water) occurs within the first 12 days and the intensity of evaporation from black soil is higher than from turf podzolic soil. The phytotoxicity of oil contaminated turf podzolic and black soils, at different humidity, in the process of natural weathering of oil was determined using such plant test objects as L. usitatissimum, H. annuus, F. vulgare. The significant decrease of phytotoxicity, more than twofold compared with the initial one, lasts up to 45 days. After the 45th day further reduction of phytotoxicity is not observed. After the 45th day even the insignificant growth of phytotoxicity is observed. Obviously, this growth happens due to the formation of more toxic derivatives of oil in the process of natural oxidation. It is proved that under natural conditions within the first days there is an intense evaporation of volatile components of oil, which lasts for 45 days in average. At the same time, from 25% to 50% of oil is weathered from the soil depending on its type and the toxicity decreases by 2 approximately. Oil pollution spreads through the profile of the soil and in 6 months, at an initial contamination of 10%, it is observed at a depth of 30-40 cm. The least contaminated is the layer of soil at a depth of 10-20 cm. Therefore, the rehabilitation of soils by phytotherapeutic methods should be carried out 45 days after the pollution, and herbs should be planted at a depth of 10-20 cm.

Practical Oil Spill Recovery by a Combination of Polyolefin Absorbent and Mechanical Skimmer

The objective of this research is to develop a practical and efficient oil recovery method that can be applied in large-scale crude oil spills in open water. The method is centered on a newly developed polyolefin oil superabsorbent, called “i-Petrogel”, in conjunction with existing mechanical (skimmer) recovery method. The i-Petrogel absorbent can be produced in large scale (>90 kg in our laboratory) by mixing two polyolefin polymers, including a semicrystalline linear low-density polyethylene (LLDPE) thermoplastic and a thermally cross-linkable poly(1-decene-co-divinylbenzene) (D-DVB) elastomer, to form an interpenetrated network structure with porous morphology. In two practical tests, i-Petrogel with a specific composition (LLDPE/D-DVB:1/1 weight ratio) shows selective absorption of Alaska North Slope crude oil on open water surface with fast kinetics and high absorption capacity of more than 40 times that of the polymer weight. In fact, i-Petrogel effectively stops the crude oil weathering process (ev...

Study of the oil interaction towards oil spill recovery skimmer material: Effect of the oil weathering and emulsification properties

The primary aim of this research was to identify the physicochemical properties of the oil and water-in-oil (W/O) emulsions used during a NOFO Oil-on-Water field trials that reduced the performance of the skimmers recovery efficacy during the trials. Extensive studies were performed at SINTEF laboratories with the residues of oil topped (i.e. evaporative loss of crude oil components by distillation process at large scale) for the field trial and compared it with different residues of oil topped by bench scale laboratory procedures. In order to obtain a sufficient stable W/O emulsion for the field trial, bunker fuel oil (IFO380) and various concentrations of an emulsifier (Paramul®) were also added to the residues of oil topped on large scale and investigated through interfacial tension, contact angle, droplet adhesion and “dip and withdraw” tests. The investigations revealed that the addition of an emulsifier lowered the interfacial tension of oil residues, which consequently reduced the adherence properties of the oil and emulsions to the surface of the skimmer material. Too high concentration of an emulsifier (>0,5%) also had a negative effect on the stability of W/O emulsion.

Photo-enhanced toxicity of undispersed and dispersed weathered Macondo crude oil to Pacific (Crassostrea gigas) and eastern oyster (Crassostrea virginica) larvae

During the Deepwater Horizon oil spill rapid natural weathering of Macondo crude oil occurred during the transport of oil to coastal areas. In response to the DWH incident, dispersant was applied to Macondo crude oil to reduce the movement of oil to coastal regions. This study aimed to assess the narcotic and phototoxicity of water-accommodated fractions (WAFs) of weathered Macondo crude oil, and chemically-enhanced WAFs of Corexit 9500 to Pacific (Crassostrea gigas) and eastern (Crassostrea virginica) oyster larvae. Phototoxic effects were observed for larval Pacific oysters exposed to combinations of oil and dispersant, but not for oil alone. Phototoxic effects were observed for larval eastern oysters exposed to oil alone and combinations of oil and dispersant. Corexit 9500 did not exhibit phototoxicity but resulted in significant narcotic toxicity for Pacific oysters. Oyster larvae may have experienced reduced survival and/or abnormal development if reproduction coincided with exposures to oil or dispersant.

Evaluation of diagnostic ratios of phenanthrenes and chrysenes for the identification of severely weathered spilled oils from the simulation weathering and the Sinopec pipeline explosion at Huangdao, 2013.

The composition and physical properties of spilled oil undergo great changes during a serious weathering process. This causes great difficulties for identifying the source of an oil spill. So stable and trustworthy diagnostic ratios (DRs) for the accurate identification of severely weathered spilled oils are very important. An explosion in the Sinopec pipeline happened on November 22, 2013 at Qingdao, China. Local beaches at Jiaozhou Bay were polluted by spilled oils. After the accident we collected original spilled oil samples from an area free from human interference near the oil leakage point. Synchronized with actual beach weathering, laboratory experiments were conducted to simulate oil weathering for 360 days by using the collected original spilled oil samples. Based on the t-test and the repeatability limit method, 46 diagnostic ratios (DRs) of phenanthrenes and chrysenes were screened. 18 DRs maintained remarkable stability during the simulated weathering experiments and field weathering process. These stable ratios can retain the characteristics of the oil source during weathering. They are very beneficial for improving the accuracy of identifying the source of severely weathered oil and can be used as an effective supplement to the existing index system for source identification.

Weathering of Oil in a Surficial Aquifer

The composition of crude oil in a surficial aquifer was determined in two locations at the Bemidji, MN, spill site. The abundances of 71 individual hydrocarbons varied within 16 locations sampled. Little depletion of these hydrocarbons (relative to the pipeline oil) occurred in the first 10 years after the spill, whereas losses of 25% to 85% of the total measured hydrocarbons occurred after 30 years. The C6-30 n-alkanes, toluene, and o-xylene were the most depleted hydrocarbons. Some hydrocarbons, such as the n-C10-24 cyclohexanes, tri- and tetra- methylbenzenes, acyclic isoprenoids, and naphthalenes were the least depleted. Benzene was detected at every sampling location 30 years after the spill. Degradation of the oil led to increases in the percent organic carbon and in the δ 13 C of the oil. Another method of determining hydrocarbon loss was by normalizing the total measured hydrocarbon concentrations to that of the most conservative analytes. This method indicated that the total measured hydrocarbons were depleted by 47% to 77% and loss of the oil mass over 30 years was 18% to 31%. Differences in hydrocarbon depletion were related to the depth of the oil in the aquifer, local topography, amount of recharge reaching the oil, availability of electron acceptors, and the presence of less permeable soils above the oil. The results from this study indicate that once crude oil has been in the subsurface for a number of years there is no longer a "starting oil concentration" that can be used to understand processes that affect its fate and the transport of hydrocarbons in groundwater.

Oil spill response capabilities and technologies for ice-covered Arctic marine waters: A review of recent developments and established practices

Renewed political and commercial interest in the resources of the Arctic, the reduction in the extent and thickness of sea ice, and the recent failings that led to the Deepwater Horizon oil spill, have prompted industry and its regulatory agencies, governments, local communities and NGOs to look at all aspects of Arctic oil spill countermeasures with fresh eyes. This paper provides an overview of present oil spill response capabilities and technologies for ice-covered waters, as well as under potential future conditions driven by a changing climate. Though not an exhaustive review, we provide the key research results for oil spill response from knowledge accumulated over many decades, including significant review papers that have been prepared as well as results from recent laboratory tests, field programmes and modelling work. The three main areas covered by the review are as follows: oil weathering and modelling; oil detection and monitoring; and oil spill response techniques.

A model for the weathering of Colombian crude oils in the Colombian Caribbean Sea

A model that describes the weathering of crude in an oil spill caused by interaction with the atmosphere and the ocean was developed. This model was adapted to the Colombian crudes Cusiana (°API43.2) and Vasconia (°API20.7). To calibrate the model, evaporation and emulsification experiments were carried out at conditions similar to those of an oil spill in the Colombian Caribbean Sea. The dependence of evaporation with wind velocity, not predicted by the state-of-the-art models, was captured by a correlation for the mass transfer coefficient calculated from the experimental data. Emulsification rate, maximum water content and required evaporation to form an emulsion were determined and their values explained considering the effect of wax precipitation for Cusiana crude oil. When compared to well-established weathering software, such as ADIOS, the proposed model predicts the weathering of Colombian oils in a way that better agrees with the experiments conducted in the laboratory.

Application of enhanced gas chromatography/triple quadrupole mass spectrometry for monitoring petroleum weathering and forensic source fingerprinting in samples impacted by the Deepwater Horizon oil spill

Accurate characterization of petroleum hydrocarbons in complex and weathered oil residues is analytically challenging. This is primarily due to chemical compositional complexity of both the oil residues and environmental matrices, and the lack of instrumental selectivity due to co-elution of interferences with the target analytes. To overcome these analytical selectivity issues, we used an enhanced resolution gas chromatography coupled with triple quadrupole mass spectrometry in Multiple Reaction Monitoring (MRM) mode (GC/MS/MS-MRM) to eliminate interferences within the ion chromatograms of target analytes found in environmental samples. This new GC/MS/MS-MRM method was developed and used for forensic fingerprinting of deep-water and marsh sediment samples containing oily residues from the Deepwater Horizon oil spill. The results showed that the GC/MS/MS-MRM method increases selectivity, eliminates interferences, and provides more accurate quantitation and characterization of trace levels of alkyl-PAHs and biomarker compounds, from weathered oil residues in complex sample matrices. The higher selectivity of the new method, even at low detection limits, provides greater insights on isomer and homolog compositional patterns and the extent of oil weathering under various environmental conditions. The method also provides flat chromatographic baselines for accurate and unambiguous calculation of petroleum forensic biomarker compound ratios. Thus, this GC/MS/MS-MRM method can be a reliable analytical strategy for more accurate and selective trace level analyses in petroleum forensic studies, and for tacking continuous weathering of oil residues.

State-of-the-Art Oil Spill Trajectory Prediction in Ice Infested Waters: A Journey from High Resolution Arctic-Wide Satellite Data to Advanced Oil Spill Trajectory Modeling-What You Need to Know

ABSTRACTIn ice covered waters, successful oil spill response requires predictions of where the oil and ice will travel. The International Association of Oil and Gas Producers (IOGP), Arctic Oil Spill Response Technology - Joint Industry Programme (JIP) funded research to improve oil spill response by leveraging new state-of-the-art ice forecasting into oil spill trajectory models. We present an overview of the systems and discuss how these advancements will provide responders with new information for spill preparedness and planning. The Nansen Environmental and Remote Sensing Center (NERSC) has developed two coupled ice-ocean models that cover the entire Arctic: TOPAZ4 and neXtSIM. TOPAZ4 uses both in situ ocean data and satellite data; the model also includes an ecosystem model. The neXtSIM model is a new high resolution (3km) coupled ice-ocean which uses daily sea ice thickness and concentration fields from satellites.SINTEF’s Oil Spill Contingency and Response (OSCAR) model can now use output from both TOPAZ and neXtSIM. The OSCAR user can view the ice conditions with the spill, and the oil trajectory is modified by the time dependent ice coverages. Case studies will be discussed that test the implementation for different areas of the Arctic. Through these case studies, we provide new types of information for spill responders. The OSCAR model also includes information on oil weathering in ice from extensive laboratory and flume data for oils in water with and without ice.Case Study 1: In the Beaufort Sea we compare observed ice drifter position time series with the ice drift calculated by the OSCAR model using input from the NERSC models. We then simulate a potential oil spill in the area.Case Study 2: The 2009 Joint Industry Project included fieldwork and modeling for oil released in marginal ice zone in the Barents Sea. In May 2009, 7000 liters of fresh Troll oil was released into the marginal ice zone to study the oil weathering, spreading and overall oil trajectory.

Development of a Systematic Method for Defining the Stages of Weathering for Crude Oils Released into the Environment

Weathered oil is a term that is often used without communicating the degree of weathering and components that still remain. The subjective use of vague and often inaccurate weathering terms (i.e., lightly, moderately, heavily, or extensively weathered) often leads to misperceptions or misinformation about potential persistence and potential toxicity of oil residues observed in the environment. A semi-quantitative approach is needed for defining the stages of weathering, without adjectives, for oil released into the environment. MC252 oil from the Deepwater Horizon accident was evaluated to develop such an approach. The weathering of MC252 oil started immediately after release; during its 1,500 meter ascent to the sea surface most of the water soluble components partitioned into the water column. Once on the sea surface, the oil continued to weather via evaporation, dissolution, photo-degradation, and biodegradation. After reaching the shoreline, weathering continued and biodegradation became more pronounced. Extensively weathered and biodegraded MC252 oil samples have been collected on the shoreline and in some cases show a complete loss of resolved n-alkanes and near complete loss of PAH components, while still maintaining identifiable MC252 characteristics. At the same time that compounds have been lost due to degradation, others (e.g., some oxygenated compounds) have been formed as part of the weathering processes. The hydrocarbon chemistry data associated with more than 800 weathered MC252 oil samples were evaluated and quantitative metrics were developed to aid in defining the weathering stages. Sample GC/FID chromatograms were digitized and multiple chromatographic features (e.g., peak height to UCM height) were captured quantitatively. Together, the chemistry and chromatograms were analyzed to define seven (7) stages of weathering providing researchers with an objective means of discussing the weathering for oil after its release to the environment.

Assessment of oil weathering and impact in mangrove ecosystem: PRISME Experiment.

Abstract 2017-410 Mangroves are among the most sensitive marine ecosystems to oil pollution due both to the sensitivity of mangroves species and to the high persistence of hydrocarbons in these environments. Despite their ecological and socio-economic value, the potential effects of an oil spill on French Guiana mangroves remain so far unknown. Yet, there is an increasing transboundary risk of oil spill due to Brazilian offshore oil exploitation (in mid-April 2013, there were 122 offshore drilling rigs in Brazil, including 29 under construction – Brazilian Amapá region located in the French Guiana border area is thought to become an important world oil production area in the coming years). The aim of the PRISME project was to assess the natural degradation of oil in mangrove sediment as well as its impact on benthic communities (micro, meio and macrobenthos): a one-month in situ experiment was conducted in the young French Guianese mangrove (around 3 years old) at the mouth of the Sinnamary estuary. The experimental units consisted in eight plastic cores (Ø : 10 cm ; height: 30 cm) manually introduced within sediments. A thin layer of oiled sediment (2 cm, 20 000 ppm) was applied on four cores while the remaining four cores were considered as control (no oil addition). Three cores were additionally sampled at the beginning of the experiment as initial control sediments. After one month in situ, the eight cores were collected and sliced on site into different sedimentary layers aliquots for later analyses (hydrocarbons, bacterial, meio, macrofauna fauna diversity, bioturbation, biogeochemical parameters). Samples were sent to the different laboratories involved in this multidisciplinary project. Results and knowledge gained from this experimental work were used to develop an approach for assessing coastal vulnerability for oil spills preparedness in mangroves.

ARE OXYGENATED HYDROCARBONS IMPORTANT OIL DEGRADATION PRODUCTS AFTER OIL SPILLS?

ABSTRACT 2017-186 Oxygenated hydrocarbons (OxHC) are major and persistent hydrocarbon degradation products that are formed after oil spills. However, there are still knowledge gaps related to formation, fate and effect of these products. The objective of this study was to find if the OxHCs present in weathered oils are more or less toxic and bioaccumulative than their parent compounds. In this study, we first systematically investigated bioaccumulation potential and toxicity potential of oxygenated oil weathering products, using predictions based on Abraham Solvation Parameters. We then quantified OxHC in select crude and weathered oil samples from the 2010 Deepwater Horizon Oil Spill (DHOS). Seawater-dissolved concentrations were calculated using Raoult’s law, and baseline toxicity of the mixtures towards fathead minnow fish were estimated. We found that while OxHC generally had a lower bioaccumulation potential than corresponding n-alkanes, the baseline toxicity of OxHC was higher than that of their n-alkane precursors due to increased water solubility. After 30 days of weathering, toxicity of the oil residue decreased by a factor of ten. However, following six years of weathering, the calculated residual toxicity only dropped by a further factor of two. In the most weathered sample, toxicity was dominated by OxHC and not polycyclic aromatic hydrocarbons (PAHs). These preliminary data suggest that further research into OxHC toxicity is necessary. In future, additional factors such as reactive toxicity and biotransformation can be implemented to further explore OxHC toxicity and bioaccumulation in long-term environmental impacts of oil spills.

How much oil is actually removed by evaporation, photo-oxidation and microbial weathering?

Crude oil is a complex mixture of thousands of organic compounds including alkanes, aromatics, asphaltenes, resins and waxes. A number of physical, chemical and biological weathering processes, as well as, vertical sinking followed by burial in sediments act on oil once it is released into the marine waters. The weathering processes cause oil's initial concentration/composition to change into oil residues, and allow natural mechanisms for oxidation and conversion of reduced organic carbons in oil back to CO2 and biomass. Once the lighter compounds are gone due to weathering, and some new oxidative compounds are formed, the heavier constituents left behind as residues ultimately sink to the bottom and/or strand at the coasts. The oil and oil residues can persist much longer in soil and sediments (20–40 years) than in the water column (<6 months), and can have long-term environmental impacts. Thus, it is important to know the amount and fates of the residues produced and transported to the seafloor and/or to the coastal marshes after early oil weathering in marine water column. The understanding of likely fates and behavior of oil allows us to choose and optimize a most appropriate response option. Recent studies have considered hopane as degradation resistant, used hopane normalization to determine the loss of select oil constituents via weathering, and have concluded that a significant proportion of spilled oil quickly is removed. Such analysis, however, are based on percentage removal of GC-amenable alkanes and PAHs, and may not represent the actual amount of loss of spilled oil via weathering processes as a large fractions of the crude oils (higher alkanes, PAHs, oxidative products, asphaltenes, resins and wax) are not GC-amenable which are not accounted in GC-based analysis. In the present study, we conducted a series of laboratory weathering experiments for direct estimation of the actual amount of loss of crude oil via evaporation and biodegradation. A known amount (mass) of BP surrogate oil was mixed into the natural seawater and allowed for weathering for 30 days, simulating natural physical conditions and periodically flushing the water to prevent accumulation of biomass. At the end of the experiment, oil residues were carefully collected, solvent extracted followed by evaporation of solvent and weighing the residues left behind. The comparison of pre-post mass, and mass balance including flushed water, provides direct estimation of loss of oil via weathering. This is a work-in-progress and results will be presented during the conference.

Evaluation of Oil Spill Modeling in Ice Against In Situ Drifter Data from the Beaufort Sea

ABSTRACT While coupled ice-ocean models provide reliable hindcasts and large-scale predictions of ice conditions and movements in the Arctic, to date, operational models have not been implemented with sufficient spatial resolution or skill to define sea ice characteristics and dynamics needed for high resolution oil spill trajectory forecast modeling. Recently (2015) Nansen Environmental and Remote Sensing Centre (NERSC) researchers updated their modeling approach and rheology used for pack ice. They found that using the newly developed Elasto-Brittle (EB) model showed significant improvement in performance over the present Elastic-Viscous-Plastic (EVP) modeling approach used in the operational forecast and reanalysis versions of their TOPAZ4 coupled ice-ocean model. NERSC also integrated a wave-in-ice model (WIM) into a newly updated version of TOPAZ, to characterize waves in the Marginal Ice Zone (MIZ). RPS ASA’s oil transport and fate models OILMAP and SIMAP (OIL/Spill Impact Model Application Package) were updated, integrating the NERSC ice modeling products for use in transport and oil weathering algorithms. Oil trajectory model simulations, using the existing publically-available TOPAZ4 and updated ice model products, were compared with available in situ drifter data for the Beaufort Sea from the International Arctic Buoy Programme (IABP). The goal was to evaluate model performance (skill) against drifters that were trapped in the pack ice where the EB/EVP rheology applies. The comparisons show that model-based trajectories increasingly diverged from observations over days and weeks due to cumulative errors. The model using EB rheology more closely agreed with the IABP observations than TOPAZ with EVP, and the updated TOPAZ showed improved model performance over TOPAZ4. However, model skill was degraded by time-averaging of ocean and ice model vectors before input to the oil spill model. Demonstrated improvement of oil-in-ice spill modeling would help meet the needs for Arctic oil spill response in the coming decades. While the accuracy of individual oil model trajectories projected weeks to months into the future would be expected to be low, in the event of a spill, forecasts could be updated frequently (on a time scale of hours to days) with satellite information, aircraft observations, drifter data, and other observations to improve reliability. The overall transport patterns and results of an ensemble of trajectories would provide useful information for planning and risk assessments based on typical current and ice movement patterns.