BP spill released 4.4m barrels

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Among the biggest “known unknowns” is the long-term effects on the marine environment of a spill of this magnitude.

There are questions too about what additional damage, if any, rendered by the government’s decision to use such huge quantities of chemical dispersants to prevent the oil from coming ashore.

And then there is the uncertainty, fuelled by a lack of transparency by BP and the Obama Administration, even about the “known knowns”. Independent scientists and environmental organisations have grown suspicious of official reports on the oil spill. Do we really know what we think we know?

Now a team led by Timothy Crone, a marine geophysicist at the Lamont-Doherty Earth Observatory at Columbia University, has tackled another of the great “known unknowns”: how much oil entered the Gulf of Mexico in the nearly three months it took for BP to gain control over its Macondo well?

The team, which published their research in the journal Science, claim to have produced the first estimate of the flow rate from the well that is independent, transparent in its methodology, and reviewed by other scientists. The team arrived at its estimate by analysing video of the gushing well shot from the ocean floor.

And it turns out, their numbers are very close to the final figure produced by a special team of experts assembled by the Obama administration. That’s a bit of a break for government agencies who have been routinely accused by scientists and environmentalists of spinning the spill.

Crone’s team concluded that some 56,000 to 68,000 barrels a day gushed out of the well, releasing some 4.4m barrels into the ocean before it was capped on July 15.

The study found that the oil gushed with greatest force in the first six weeks after the explosion, when there was a jagged break in the pipe leading up from the reservoir.

The estimate is very close to the official tally arrived at by the Obama Administration’s scientific team. Their estimate was 4.9m barrels, of which 800,000 were siphoned off by BP directly to a waiting tanker ship, leaving 4.1m barrels in the water. But the team did not make their methodology available to other scientists for review.

But while that agreement might lead some to immediately dismiss the study as pro-government spin, it’s worth remembering that Crone was among the first scientists to take on BP’s claim that it was impossible to estimate the flow from the well.

Crone’s efforts, supported by Congressman Ed Markey, forced BP to release video from its undersea cameras, which showed giant clouds of oil billowing out of the broken well.

And as weeks turned into months, government officials kept raising their estimates of the flow rate from 1,000 barrels a day to 19,000 by late May, and then 69,000.

When the Deepwater Horizon went down, Crone was one of a small group of people who had experience measuring oil and gas on the ocean floor. He spent four years developing a technique for measuring natural releases of oil from the ocean floor, using high resolution video from underwater cameras.

The seemingly endless video from BP’s webcam had very low resolution and could not be analysed. Back in May, when BP released its first brief clips from the ocean floor, Crone immediately asked the oil company to share more higher resolution images, to no avail it seems.

The researchers had access only to a few brief high resolution clips released to Congress. “We clearly acknowledge the limits of our technique; we’re unlikely to ever know the exact figure,” he said in a statement.

But it is an important start.

As time goes on, I hope to keep track of the work of government and independent scientists, environmental organisations, and local groups on the ground to fill in the blanks around the “known unknowns”.