Millions of gallons of BP oil rests on Gulf floor

Jennifer Portman | Tallahassee (Fla.) Democrat

TALLAHASSEE — When BP's Deepwater Horizon oil rig exploded on April 20, 2010, it spewed 200 million gallons of crude oil into the Gulf of Mexico before it was finally capped after 87 days.

Officials could account for much of where all that oil went — either captured by containment systems, evaporated or dissolved in the water, chemically dispersed or skimmed from the sea's surface. But those who fashioned the so-called oil budget could not account for up 11% to 30% of it.

So where did it go?

A team of researchers led by Florida State oceanography professor Jeff Chanton have found an answer. A new study by Chanton and his fellow scientists published in the latest edition of the journal Environmental Science & Technology shows six to 10 million gallons are buried in the sediment on the Gulf floor about 60 miles south east of the Mississippi Delta.

"Is the first direct evidence that there is oil sediment on the Gulf floor," Chanton said of the study, which details how the oil caused particles in the Gulf to clump together and sink to the sea bottom. "This is the first time we've ever really demonstrated that this is happening. There was anecdotal information this was happening. This really quantifies it."

At first blush, Chanton said all that oil sinking to the sea bottom might have seemed like a good thing, because the water was made clear. But in the long term, he said, "it might be a bad thing."

"If it's on the sea floor the oxygen would be lower so that might mean it would hang around longer and be a source of contamination in the future. It would linger longer," he said. "This is going to affect the Gulf for years to come. Fish will likely ingest contaminants because worms ingest the sediment, and fish eat the worms. It's a conduit for contamination into the food web."

Chanton's is the second study released in recent months to arrive at similar conclusions through different means of research. He said the new evidence should be weighed as damages against BP are determined.

"It is something that definitely should be considered in all this stuff," he said.

The nine-member research team used carbon 14, a radioactive isotope, to determine where oil might have settled on the floor. Since oil does not have carbon 14, the sediment that contained oil immediately stood out.

But BP disputes the study's findings.

"The authors' method for calculating carbon derived from oil is flawed and their estimates of the amount deposited on the sea floor are not supported by the data in their paper," said company spokesman Jason Ryan in a statement. "Instead of using rigorous chemical analysis to identify oil in sediments, the authors used a tracer common to all sources of oil, including oil from the Gulf's numerous natural seeps."

Ryan added that only three of the study's 62 sediment samples had evidence of excess oil when compared with pre-spill sediment samples.

Chanton's study was funded by the Gulf of Mexico Research Institute, which was created to allocate money from BP to support scientific research. The grants were provided to the FSU-headquartered Deep-C Consortium as well as the Ecogig consortium, centered at the University of Mississippi.