University of South Florida researchers say they have definitively connected clouds of degraded underwater oil found in the northern Gulf of Mexico to the Deepwater Horizon well (MC252) through Compound-Specific Isotope Analysis (CSIA). Biodegraded oil was found suspended at depths of 400 meters (one-quarter mile) and 1,000-to 1,400-meters (two-thirds to three-quarters of a mile) beneath the Gulf’s surface in the form of microscopic droplets.
CSIA measures the natural carbon isotopic abundance of individual organic molecules which can be used to delineate sources of a complex mixture of organic materials, such as petroleum hydrocarbons. This is a technique that is widely used in the petroleum industry.
The confirmation by USF chemical oceanographer David Hollander is the first direct scientific link established between the subsurface oil clouds (“plumes”) and the massive BP spill. Scientists had gathered circumstantial evidence to link the subsurface oil to the Deepwater Horizon well, but had lacked a definitive scientific link until now.
Hollander’s findings came after extensive rounds of testing involving water samples gathered during a 22-28 May cruise of the R/V Weatherbird II to the northern gulf, against samples of oil provided by BP in June.
What we have learned completely changes the idea of what an oil spill is. It has gone from a two-dimensional disaster to a three-dimensional catastrophe.
The 400-meter layer was approximately 30 meters (100 feet) thick, and was observed 45 nautical miles north-northeast of the Deepwater Horizon site. The layer at 1,000 to 1,400 meters was observed approximately 24 nautical miles east of the Deepwater Horizon site.
Researchers were lead to the clouds after models created by USF ocean circulation expert Robert Weisberg predicted subsurface oil from the Deepwater Horizon well would move toward the north-northeast. The clouds were found near the DeSoto Canyon, a critical area that interacts with Florida’s spawning grounds.
The researchers’ preliminary findings came from water sampling using three separate technologies: an optical device that measures red backscatter; the ship’s sonar; and filtrations that trapped microscopic particles. Lab tests of these trapped particles confirmed in early June that the particles were microscopic oil droplets suspended at depth. The recent Compound-Specific Isotope Analysis further confirmed that these suspended oil droplets matched BP MC252 oil.
Scientists at the National Oceanic and Atmospheric Administration conclusively linked surface oil samples to the Deepwater Horizon well but concentrations in the subsurface samples were too small to be conclusively linked to the blownout well. Because of limited BP oil samples, USF scientists were unable to pursue further testing until the oil company turned over additional oil from the well, which occurred in late June.
The BP oil samples were obtained after a meeting between company officials and US Rep. Kathy Castor.
Researchers from across USF’s College of Marine Science are now conducting work on determining what impact the spill, the subsurface degraded oil and the heavy use of chemical dispersants may have for marine life and the Gulf’s ecology.
The R/V Bellows has recently completed a nine-day scientific mission to gather baseline water quality and food web samples from the gulf in an area that extends north of Tampa and west about 100 miles off the coast. On 6 Aug., the Weatherbird II will return to the spill zone to assess the condition of marine life, including small fish and shrimp which are key sources of food for larger fish and marine mammals.
The 22-28 May Weatherbird II research was funded by the National Marine Fisheries Service and led by biological oceanographer Ernst Peebles, chemical oceanographer David Hollander, and geological oceanographer David Naar.