Marine Oil Snow Sedimentation And Flocculent Accumulation Research Articles

Simulating oil-driven abundance changes in benthic marine invertebrates using an ecosystem model

Field studies showed that benthic macrofauna and meiofauna abundances increased with sediment oil concentration in areas affected by the Deepwater Horizon (DWH) oil spill. Benthic invertebrate biomass shows a dome-shaped relationship with respect to petrogenic hydrocarbon concentrations suggesting a positive effect on biomass at low-to-medium oil concentrations and a negative effect at high concentrations. If this is due to enrichment of the benthic food web, then this adds to an emerging picture of a food web response over a large spatial area with both abundance increases and decreases as a result of DWH. We would be obliged to consider long term multispecies effects beyond the initial pulse disturbance in modeling impacts and recovery of economically valuable species. An Atlantis ecosystem model of the Gulf of Mexico is used to simulate three mechanisms that could explain observed changes in the invertebrate community. Scenario 1 is that stimulation of surface primary productivity occurred as a result of nutrient loading caused by diversion of Mississippi River water into Barataria Bay (a mitigation action taken during the DWH oil spill). Scenario 2 is that enrichment of the benthos occurred due to detrital loading from marine oil snow sedimentation and flocculent accumulation (MOSSFA). Scenario 3 is that predator declines and/or avoidance of oiled areas caused a release of predation mortality on benthic invertebrates. Scenario 2 (MOSSFA) stimulated the detritus-driven food web and was best able to cause a net increase in invertebrate biomass despite a realistic amount of oil toxicity. Scenario 3 (predator release) plausibly could have contributed to changes in benthic invertebrates. Scenario 1 (nutrient loading) had little impact on the benthos suggesting the benthic food web is decoupled from local pelagic production sources.

Marine Snow-Oil Interaction Affects n-Alkane Biodegradation in Sediment

During the Deepwater Horizon (DwH) oil spill, an excessive production of marine snow was observed, and it was estimated that as much as 14% of the oil was transferred to the ocean floor by MOSSFA (Marine Oil Snow Sedimentation and Flocculent Accumulation). MOSSFA is an important pathway of transferring oil to the ocean floor. We performed experiments at laboratory scale in 15 aquaria, representing 5 exposures of marine snow with or without oil, only oil, and controls with only clay or sediment. We developed a method to produce artificial marine snow, which resembles the natural marine snow. Results showed 40% less biodegradation of alkanes in “marine snow with oil” compared to “only oil.” Most probably, this is due to preferred biodegradation of marine snow organics comparing to oil alkanes. Biodegradation of marine snow reduces the dissolved oxygen concentration, which might result in anaerobic conditions in the sediment layer. This finding can be projected to a potential ocean floor effect.

Aggregation and Degradation of Dispersants and Oil by Microbial Exopolymers (ADDOMEx): Toward a Synthesis of Processes and Pathways of Marine Oil Snow Formation in Determining the Fate of Hydrocarbons

Microbes (bacteria, phytoplankton) in the ocean are responsible for the copious production of exopolymeric substances (EPS) that include transparent exopolymeric particles. These materials act as a matrix to form marine snow. After the Deepwater Horizon oil spill, marine oil snow (MOS) formed in massive quantities and influenced the fate and transport of oil in the ocean. The processes and pathways of MOS formation require further elucidation to be better understood, in particular we need to better understand how dispersants affect aggregation and degradation of oil. Toward that end, recent work has characterized EPS as a function of microbial community and environmental conditions. We present a conceptual model that incorporates recent findings in our understanding of the driving forces of MOS sedimentation and flocculent accumulation (MOSSFA) including factors that influence the scavenging of oil into MOS and the routes that promote decomposition of the oil post MOS formation. In particular, the model incorporates advances in our understanding of processes that control interactions between oil, dispersant, and EPS in producing either MOS that can sink or dispersed gels promoting microbial degradation of oil compounds. A critical element is the role of protein to carbohydrate ratios (P/C ratios) of EPS in the aggregation process of colloid and particle formation. The P/C ratio of EPS provides a chemical basis for the “stickiness” factor that is used in analytical or numerical simulations of the aggregation process. This factor also provides a relative measure for the strength of attachment of EPS to particle surfaces. Results from recent laboratory experiments demonstrate (i) the rapid formation of microbial assemblages, including their EPS, on oil droplets that is enhanced in the presence of Corexit-dispersed oil, and (ii) the subsequent rapid oil oxidation and microbial degradation in water. These findings, combined with the conceptual model, further improve our understanding of the fate of the sinking MOS (e.g., subsequent sedimentation and preservation/degradation) and expand our ability to predict the behavior and transport of spilled oil in the ocean, and the potential effects of Corexit application, specifically with respect to MOS processes (i.e., formation, fate, and half-lives) and Marine Oil Snow Sedimentation and Flocculent Accumulation.

Biogeochemical Processes Affecting the Fate of Discharged Deepwater Horizon Gas and Oil: New Insights and Remaining Gaps in Our Understanding

Research funded under the Gulf of Mexico Research Initiative provided new insights into the biogeochemical processes influencing the fate of petroleum chemicals entering the Gulf of Mexico from the Deepwater Horizon (DWH) accident. This overview of that work is based on detailed recent reviews of aspects of the biogeochemistry as well as on activities supported by the US Natural Resource Damage Assessment. The main topics presented here are distribution of hydrocarbons in the water column; the role of photo-oxidation of petroleum compounds at the air-sea interface; the role of particulates in the fate of the DWH hydrocarbons, especially marine oil snow (MOS) and marine oil snow sedimentation and flocculent accumulation (MOSSFA); oil deposition and accumulation in sediments; and fate of oil on beaches and in marshes. A brief discussion of bioaccumulation is also included. Microbial degradation is addressed in a separate paper in this special issue of Oceanography. Important future research recommendations include: conduct a more robust assessment of the mass balance of various chemical groupings and even individual chemicals during specific time intervals; seek a better understanding of the roles of photo-oxidation products, MOS, and MOSSFA and their relationships to microbial degradation; and determine the fates of the insoluble highly degraded and viscous oil residues in the environment.

Benthic foraminiferal morphological response to the 2010 Deepwater Horizon oil spill

The 2010 Deepwater Horizon (DWH) oil spill released 4.0 million barrels of petroleum into the Northern Gulf of Mexico (NGoM), causing a substantial Marine Oil Snow, Sedimentation and Flocculent Accumulation (MOSSFA) event. Benthic foraminifera have successfully been used as bioindicators of the event with an 80–93% decline in density coinciding with the oil spill, followed by a recovery period to a steady state within three to five years. Here we present the results of a size and morphological study of four species of benthic foraminifera which remained abundant through the DWH oil spill (Uvigerina peregrina, Brizalina subaenariensis var. mexicana, Bulimina marginata and Cassidulina teretis) to understand how different species were impacted and why such a loss in density occurred. Short-lived radioisotope dating distinguished the pre-DWH and post-DWH depth intervals from 2010 to 2015. The species exhibit shape changes in response to the oil and MOSSFA processes and the pre-DWH length/width ratios of Uvigerina peregrina and Brizalina subaenariensis var. mexicana are significantly different than post-DWH length/width ratios within the cores. Reduced oxygen levels were likely a long-term (3–5 years) driver of this shape change and enhanced organic carbon concentrations were a short-term (1–2 years) driver. This study demonstrated the importance of the benthic foraminiferal morphological response to the DWH oil spill and furthers our understanding of the strategies of taxa that occurred abundantly throughout the record.

Integrating marine oil snow and MOSSFA into oil spill response and damage assessment

Marine snow formation and vertical transport are naturally occurring processes that carry organic matter from the surface to deeper waters, providing food and sequestering carbon. During the Deepwater Horizon well blowout, oil was incorporated with marine snow aggregates, triggering a Marine Oil Snow (MOS) Sedimentation and Flocculent Accumulation (MOSSFA) event, that transferred a significant percentage of the total released oil to the seafloor. An improved understanding of processes controlling MOS formation and MOSSFA events is necessary for evaluating their impacts on the fate of spilled oil. Numerical models and predictive tools capable of providing scientific support for oil spill planning, response, and Natural Resource Damage Assessment are being developed to provide information for weighing the ecological trade-offs of response options. Here we offer considerations for oil spill response and recovery when assessing the potential for a MOSSFA event and provide tools to enhance decision-making.

Multi-proxy assessment of recent regional-scale events recorded in Southern Gulf of Mexico sediments

The Ixtoc-1 oil spill (1979–80) released 475 million liters of petroleum into the Southern Gulf of Mexico (sGoM) likely causing Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) to occur. A multiproxy approach including short-lived radioisotopes (210Pbxs), benthic foraminifera stable isotopes (δ13CCaCO3), and volcanic sediment grains was used to investigate regional events (e.g. oil spills and volcanic eruptions) recorded in sedimentary records. Depleted δ13CCaCO3 from 1979 to 80 outside of natural variability most likely results from petrogenic carbon deposition 100–250 km west of Ixtoc-1, possibly associated with MOSSFA. An event, characterized by increased volcanic input, depleted δ13CCaCO3, and increased mass accumulation rates was consistent with the El Chichón eruption (1982) 80–100 km north of Ixtoc-1. Many factors confound the uniform distribution and preservation of these events in the sGoM. However, a multiproxy approach may aid to distinguish multiple events in the sGoM sedimentary record.

The effects of experimental oil-contaminated marine snow on meiofauna in a microcosm.

During an oil spill, a marine oil snow sedimentation and flocculent accumulation (MOSSFA) event can transport oil residue to the seafloor. Microcosm experiments were used to test the effects of oil residues on meiofaunal abundance and the nematode:copepod ratio under different oil concentrations and in the presence and absence of marine snow. Total meiofaunal abundance was 1.7 times higher in the presence of snow regardless of oil concentration. The nematode:copepod ratio was 13.9 times lower in the snow treatment regardless of the oil concentration. Copepod abundance was 24.3 times higher in marine snow treatments and 4.3 times higher at the highest oil concentration. Nematode abundance was 1.7 times lower at the highest oil concentration. The result of the experiment was an enrichment effect. The lack of a toxic response in the experiments may be attributable to relatively low oil concentrations, weathering processes, and the absence of chemically dispersed oil.

Ecotoxicological benthic impacts of experimental oil-contaminated marine snow deposition

Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) can pose serious threats to the marine benthic ecosystem as it results in a deposition of oil contaminated marine snow on the sediment surface. In a microcosm experiment we investigated the effects of oil in combination with artificial marine snow or kaolin clay on two benthic invertebrate species and benthic meiofauna. The amphipod showed a dose-dependent decrease in survival for both oil-contaminated clay and oil-contaminated marine snow. The gastropod was only affected by the highest concentration of oil-contaminated marine snow and had internal concentrations of PAHs with a similar distribution as oil-contaminated marine snow. Benthic copepods showed higher survival in presence of marine snow. This study revealed that marine snow on the sediment after oil spills affects organisms in a trait-dependent way and that it can be a vector for introducing oil into the food web.

Rapid Formation of Microbe-Oil Aggregates and Changes in Community Composition in Coastal Surface Water Following Exposure to Oil and the Dispersant Corexit.

During the Deepwater Horizon (DWH) oil spill, massive quantities of oil were deposited on the seafloor via a large-scale marine oil-snow sedimentation and flocculent accumulation (MOSSFA) event. The role of chemical dispersants (e.g., Corexit) applied during the DWH oil spill clean-up in helping or hindering the formation of this MOSSFA event are not well-understood. Here, we present the first experiment related to the DWH oil spill to specifically investigate the relationship between microbial community structure, oil and Corexit®, and marine oil-snow in coastal surface waters. We observed the formation of micron-scale aggregates of microbial cells around droplets of oil and dispersant and found that their rate of formation was directly related to the concentration of oil within the water column. These micro-aggregates are potentially important precursors to the formation of larger marine oil-snow particles. Therefore, our observation that Corexit® significantly enhanced their formation suggests dispersant application may play a role in the development of MOSSFA events. We also observed that microbial communities in marine surface waters respond to oil and oil plus Corexit® differently and much more rapidly than previously measured, with major shifts in community composition occurring within only a few hours of experiment initiation. In the oil-amended treatments without Corexit®, this manifested as an increase in community diversity due to the outgrowth of several putative aliphatic- and aromatic-hydrocarbon degrading genera, including phytoplankton-associated taxa. In contrast, microbial community diversity was reduced in mesocosms containing chemically dispersed oil. Importantly, different consortia of hydrocarbon degrading bacteria responded to oil and chemically dispersed oil, indicating that functional redundancy in the pre-spill community likely results in hydrocarbon consumption in both undispersed and dispersed oils, but by different bacterial taxa. Taken together, these data improve our understanding of how dispersants influence the degradation and transport of oil in marine surface waters following an oil spill and provide valuable insight into the early response of complex microbial communities to oil exposure.

Tracing the incorporation of carbon into benthic foraminiferal calcite following the Deepwater Horizon event

Following the Deepwater Horizon (DWH) event in 2010, hydrocarbons were deposited on the continental slope in the northeastern Gulf of Mexico through marine oil snow sedimentation and flocculent accumulation (MOSSFA). The objective of this study was to test the hypothesis that benthic foraminiferal δ13C would record this depositional event. From December 2010 to August 2014, a time-series of sediment cores was collected at two impacted sites and one control site in the northeastern Gulf of Mexico. Short-lived radioisotopes (210Pb and 234Th) were employed to establish the pre-DWH, DWH, and post-DWH intervals. Benthic foraminifera (Cibicidoides spp. and Uvigerina spp.) were isolated from these intervals for δ13C measurement. A modest (0.2–0.4‰), but persistent δ13C depletion in the DWH intervals of impacted sites was observed over a two-year period. This difference was significantly beyond the pre-DWH (background) variability and demonstrated that benthic foraminiferal calcite recorded the depositional event. The longevity of the depletion in the δ13C record suggested that benthic foraminifera may have recorded the change in organic matter caused by MOSSFA from 2010 to 2012. These findings have implications for assessing the subsurface spatial distribution of the DWH MOSSFA event.

Marine snow increases the adverse effects of oil on benthic invertebrates

After the Deepwater Horizon oil spill, a MOSSFA (Marine Oil Snow Sedimentation and Flocculent Accumulation) event took place, transporting an estimated 14% of total released oil to the sediment, and smothering parts of the benthic ecosystem. This microcosm study describes the effects of oiled artificial marine snow on benthic macroinvertebrates. Corophium volutator survival was reduced by 80% in oil-contaminated snow. Hydrobia ulvae survival was reduced by 40% in oil-contaminated snow, possibly due to consumption of oiled snow. Macoma balthica was sensitive to marine snow, addition of oil slightly decreased survival. This study reveals trait-dependent sensitivity to oil with or without marine snow. The main drivers for organismal response to marine snow and oil are motility, sensitivity to hypoxia and oil toxicity, and feeding habits. Adverse effects of MOSSFA events on benthos will have consequence for the benthic-pelagic habitat and food chain, and should receive more attention in oil spill management.

Resilience of benthic foraminifera in the Northern Gulf of Mexico following the Deepwater Horizon event (2011–2015)

Benthic foraminifera (BF) have been commonly used as marine petroleum contamination indicators. The Deepwater Horizon (DWH) released 4.0 million barrels of petroleum into the northern Gulf of Mexico (nGoM) over 87days in 2010, causing Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA). Previous BF studies have documented region-specific impacts associated with contaminant input and sediment redox conditions. This study determined benthic resilience as measured by BF test density, species richness and heterogeneity. Surface sediment samples (0–42mm) from seven sites throughout the nGoM (2011–2015) showed a continuous increase in mean species richness (27.2% ±3.6%) and heterogeneity (19.8% ±0.2%). The greatest increase occurred from 2011 to 2013, followed by consistent values from 2013 to 2015, which suggested a resilience rate on the order of three years. This study demonstrated the importance of long-term time-series studies following events such as DWH and exemplified necessity for broad baseline measurements prior to the next marine petroleum accident.

Constraining the Spatial Extent of Marine Oil Snow Sedimentation and Flocculent Accumulation Following the Deepwater Horizon Event Using an Excess 210Pb Flux Approach.

Following the Deepwater Horizon (DWH) event in 2010, there were several lines of evidence indicating the presence of marine oil snow sedimentation and flocculent accumulation (MOSSFA). A significant amount of marine oil snow formed in the water column of the northern Gulf of Mexico (nGoM), settled rapidly, and ultimately accumulated in the sediments of the nGoM. This study utilized a commonly used radioisotope tracer (excess 210Pb, 210Pbxs) from 32 sediment cores collected from 2010 to 2013 to characterize the spatial extent of MOSSFA on the seafloor. Relative to pre-DWH conditions, an increase in 210Pbxs flux occurred in two distinct regions: (1) in the western portion of the study area on an east-northeast to west-southwest axis, stretching 230 km southwest and 140 km northeast of the DWH wellhead, and (2) in the eastern portion of the study area on a 70 km northeast to southwest axis near the DeSoto Canyon. The total sedimentary spatial extent of MOSSFA, as calculated by increased 210Pbxs flux after 2010, ranged from 12 805 to 35 425 km2. 210Pbxs flux provides a valuable tool for documenting the spatial extent of MOSSFA following DWH and will continue to aid in the determination of advective transport and ultimate depocenters of MOSSFA material.

Unexpected Sink for Deepwater Horizon Oil May Influence Future Spill Response

A town hall meeting was organized by the Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) inter‐consortia Gulf of Mexico Research Initiative (GoMRI) working group and the Center for Spills in the Environment in conjunction with the Gulf of Mexico Oil Spill and Ecosystem Science Conference. The meeting had the goal of evaluating sedimentation to the seafloor as a significant pathway and fate of oil after the Deepwater Horizon (DwH) well blowout in 2010. About 78,000 cubic meters of crude oil were released into the Gulf of Mexico from a depth of 1500 meters for 86 days, spreading over a large area. Natural and chemically enhanced dispersion, evaporation, dissolution, burning, surface skimming, and direct capture at the wellhead accounted for a significant proportion of the released oil, but the fate of at least 30% of the oil remains unknown. Scientists from different research consortia studying sediments and marine snow in the Gulf began to observe signs of increased sedimentation and hydrocarbon deposition. Sediment mass accumulation rates for the northern Gulf of Mexico increased sixfold to eightfold in 2010, directly following the DwH blowout.