Scientists Estimate Deepwater Horizon Oil Spill

NOAA scientists have estimated how fast gases and oil were leaking during the Deepwater Horizon oil spill in the Gulf of Mexico. Researchers combined detailed chemical measurements in the deep ocean, air and the oil slick itself. The study showed an average of 11,350 tons of gas and oil were leaked per day, an amount equal to approximately 59,200 barrels of liquid oil per day. According to Dr. Thomas Ryerson, a NOAA research chemist and lead author of the study, the surface and subsurface measurements and analysis provided by colleagues held the key to understanding an oil spill. Researchers found that the leaking gas and oil separated into three major pools including an airborne plume of evaporating chemicals, the visible surface slick, and an underwater plume of droplets occurring at about 3,300-4,300 feet below the surface. Each pool’s chemical composition differed. Chemicals that dissolved easily in water including lightweight methane and benzene a known carcinogen enhanced the underwater plume. The surface oil slick had the heaviest components that did not dissolve in seawater or evaporate into the air. The airborne plume contained intermediate weight chemicals. The visible surface slick represented about 15 percent of the total leaked gas and oil; the airborne plume accounted for about another 7 percent. About 36 percent remained in a deep underwater plume, and 17 percent was recovered directly to the surface through a marine riser. The location of the balance, about 25 percent of the total, is not directly accounted for by the chemical data. This information about the transport and fate of different components of the spilled gas and oil mixture could help resource managers and others trying to understand environmental exposure levels. The chemical measurements made from mid-May through June showed that the composition of the atmospheric plume changed very little, suggesting little change in the makeup of the leaking gas and oil. The team of researchers also used the detailed chemical measurements to calculate how much gas and oil, in total, was spilling from the breached reservoir deep underwater. The new chemistry-based estimate of 11,130 tons per day has an estimated range of 8,900 to 13,300 tons per day. By comparison, the official estimated range was 10,000 to 12,700 tons per day.