On April 20, 2010, the Deepwater Horizon offshore drilling rig, located 41 km off the coast of Louisiana, experienced a blowout and explosion that resulted in 11 deaths, the sinking of the drilling rig, and uncontrolled discharge from the well at an estimated rate of 5-25 thousand barrels of crude oil each day. Owing to the challenge of containing discharge at a depth of 1,500 m it is anticipated that the well will continue to flow for many weeks and exceed the Exxon Valdez as the most severe oil disaster in U.S. history. The oil spill is likely to encompass the extensive area that develops hypoxia on an annual basis in the northern Gulf of Mexico (NGOMEX). The development and extent of hypoxia in the northern Gulf of Mexico has been of concern for many years owing to, for example, its detrimental impact on fisheries (Rabalais et al., 2007; Turner et al., 2007).
With funding through this Grant for Rapid Response Research (RAPID), scientists at Michigan State University and the University of Texas at Austin will participate in an upcoming research cruise of the RV Pelican from May 21-27, 2010, that will be sampling at stations that already are or are very likely to be impacted by the oil spill. Indeed projections by NOAA for the distribution of oil from the spill are in close proximity to all of the proposed research stations. The research team contends that the oil spill will exacerbate the development of hypoxia in the NGOMEX by altering rates of primary production, respiration and gas exchange. Consequently, they will test the following hypotheses:
Hypothesis 1: The oil spill will enhance hypoxia in the NGOMEX by (1) reducing primary production, (2) enhancing respiration and (3) reducing gas exchange. Hypothesis 2: The gas exchange rate will be a function of the abundance, composition and origin of surfactants in the surface water layer.
The layer of oil across the sea surface is expected to reduce penetration of light for photosynthesis thereby reducing rates of primary production. Respiration is likely to be enhanced by the increased availability of the oil; particularly as the microbial community metabolizes this carbon source. Rates of gas exchange between the ocean surface and atmosphere are very sensitive to the presence of surface organic films. The team will approach these hypothesis by determining depth profiles of the triple isotopic composition of dissolved O2 and ratios of N2:Ar and O2:Ar that collectively yield rates of primary production, respiration and gas exchange. They will further determine the abundance, composition and origin of the surface organic layer as a control on the rate of gas exchange.
Broader Impacts: While the environmental impacts of oil spills are many, less well known is the potential for oil spills to enhance the development of hypoxia in regions prone to this condition. A long term understanding of hypoxia in the NGOMEX and other regions impacted by oil spills will enhance society's ability to predict the ecological consequences of this and similar disasters. This project will directly involve two undergraduate students and the results of this project will be a focus of the investigators' courses of instruction, including courses at MSU and UT Austin on Oceanography and Marine Biogeochemistry, respectively. Further, MSU and UT have mechanisms in place to facilitate presentation of research findings to the media including MSU's Environmental Science and Policy Program and Knight Center for Environmental Journalism and via UT's nationally broadcast radio program: "Science and the Sea".
Intellectual Merit: The Deepwater Horizon (DWH) offshore drilling rig, located 41 km off the coast of Louisiana in the northern Gulf of Mexico (NGOMEX), experienced an explosion on April 20, 2010, sinking of the rig, and uncontrolled discharge of oil and gas. The well was successfully capped 87 days later but released an estimated 4.93 million barrels of oil, which places the DWH incident as the most severe marine oil disaster in U.S. coastal waters. The biodegradation of petroleum by in situ microbial communities is well established and recognized as a desirable means for petroleum spill remediation. The DWH National Incident Command issued a directive that O2 levels be monitored as part of the response to the DWH incident, citing concern that degradation of DWH derived petroleum may contribute to the development of hypoxia. In this project, we collected data from two research cruises in the NGOMEX that occurred approximately one month after the occurrence (May) and cessation (August) of the DWH incident. Our research stations were located within 300 km of the DWH well and showed signs of the presence of oil in May, based on personal observations, satellite imagery and hydrocarbon abundance. Concentrations of total dissolved n-alkanes in surface seawater were more than an order of magnitude higher in May than in August 2010, suggesting that the sea surface of the sampling area in May was impacted by the oil spill. The decrease from May to August likely resulted from rapid weathering. This conclusion is further supported by significant differences in hydrocarbon composition and abundance within the oil mousse collected at two stations. The concentration of dissolved free amino acids was greatly enhanced in oil-water mixtures relative to surface water samples, which may reflect enhanced microbial activity from the presence of labile oil carbon. These results overall indicate the rapid weathering of the oil on the sea surface in the northern Gulf of Mexico. The research cruises provided a unique opportunity to observe the response of O2 metabolism to oil from the DWH incident. Further, we compare our results to previous studies of O2 metabolism in the NGOMEX based on isotope data and incubation methods. These two approaches have provided contrasting values of the importance of water column and sediment respiration in driving hypoxia. Thus, our objectives are to (1) evaluate the impact of the DWH oil spill on O2 metabolism and (2) provide insight into disagreement between incubation and isotope approaches to the evaluation of respiration beneath the pycnocline. Our study found that hypoxia was evident at most stations in both May and August of 2010 and is consistent with the early establishment and persistence of a large hypoxic zone. Despite the presence of the oil, we found no evidence that O2 metabolism was driven to levels outside historic ranges. Consequently, we agree with the findings of the annual survey that the size of the July 2010 hypoxic zone can largely be explained by nitrogen loading from the Mississippi River. Specific features of the 2010 hypoxic zone include (1) our observation of hypoxia east of the Mississippi River, which is not often included in annual surveys, (2) hypoxia far west along the Texas coast that may have extended beyond the range of the July survey, and (3) a likelihood that the size of the hypoxic zone was reduced prior to the July survey by the passage of two storms. Thus, the actual extent of the 2010 hypoxic zone and involvement of the DWH oil spill remains uncertain. Future resolution of the NGOMEX hypoxic zone, therefore, requires more extensive surveys on both seasonal and spatial scales and/or deployment of an extensive network of continuous and in situ monitoring sensors. Broader Impacts: The project involved two undergraduate students from MSU in both field and laboratory activities. One student participated in the May research cruise and was interviewed by the press in several radio shows, newspaper articles and appeared on the local evening TV news regarding his experience being in the Gulf during the oil spill. Shortly after the May research cruise N. Ostrom was invited by the Soil Water Conservation Society (SWCS) to speak regarding the relationship between the oil spill and hypoxia. Upon request, a summary of this presentation appeared as a cover article for the Prairie Fire Newspaper. The presentation to the SWCS resulted in an invitation to N. Ostrom to present at the USDA’s Agricultural Outlook Forum which is a premier conference focused on the economics of the agricultural industry and included presentations by Michigan Senator Debbie Stabenow and former US president Bill Clinton. Overall the project will provide a basis to understand the complex relationship between oil spills and coastal hypoxia.
