MARINE SCIENCE. Deepwater Horizon, 5 years on.


592 7 AUGUST 2015 • VOL 349 ISSUE 6248 SCIENCE O n 20 April 2010, an explosion on the Deepwater Horizon drilling unit initiated an uncontrolled release of oil and gas from the Macondo seafloor well into the Gulf of Mexico that lasted for 87 days. Documenting and tracking the ecological, environmental, and human impacts of the Deepwater Horizon oil-well blowout has proved a considerable challenge. Nonetheless, valuable lessons continue to be learned, and data are revealing broad and substantial impacts on the Gulf ecosystem across a range of scales. The Macondo well discharged at least 5 million barrels of oil (~210 million gallons) ( 1– 3) and at least 250,000 metric tons of natural gas, largely methane. The error associated with estimates of oil and gas discharge is large, e.g., ranging from 50,000 to 70,000 barrels of oil per day (3), because the discharge rate was not quantified immediately or continuously. The absolute magnitude of the discharge is therefore not known. Yet, robust discharge values are required for staging an effective response, constraining the distribution of oil and gas in the environment, and evaluating environmental impacts. They are also critical for formulating and closing the hydrocarbon budget. In the case of the Deepwater Horizon incident, lack of an accurate discharge rate almost certainly hindered the early response efforts, which assumed a discharge rate of 1000 to 5000 barrels of oil per day, a gross underestimate of the actual discharge ( 4). Higher estimates of 26,500 barrels of oil per day were obtained in mid-May on the basis of remote-sensing data ( 4); however, this estimate only considered oil floating on the surface, not oil dissolved in the Gulf ’s deep waters. By late May, it was clear that a substantial fraction of the discharged oil was in the deep-water plume ( 5). Discharge was quantified in situ with state-of-the art acoustic scintillation technology only once, on 31 May 2010, about 6 weeks after blowout began ( 1). Oil and gas discharge from the wellhead is best visualized as a point source that ejected hydrocarbons at a rapid rate, leading to dispersion of oil into droplets and facilitating the formation of deep-water plumes enriched in oil, dissolved gas, and gas hydrate at depths between 900 and 1200 m ( 2, 6). Plumes were detected with sophisticated chemical sensors lowered through or introduced into the affected waters. Best estimates now suggest that all discharged gas and up to half of the discharged oil ( 2, 3) [see the figure, bottom] were entrained in the Gulf ’s deep waters. The fate of the oil and gas in the deep-water plumes can only be estimated from oxygen anomalies ( 7), because few direct measurements of hydrocarbon

DOI: 10.1126/science.aab4133

Cite this paper

@article{Joye2015MARINESD, title={MARINE SCIENCE. Deepwater Horizon, 5 years on.}, author={Samantha B. Joye}, journal={Science}, year={2015}, volume={349 6248}, pages={592-3} }