<img alt=“spill.jpg” src=“https://blogs.nature.com/news/thegreatbeyond/spill.jpg” width=“312” height=“240” / align="right"> Posted on behalf of Hannah Hoag.
When the government began releasing estimates of the size of BP’s Gulf of Mexico oil well leak, scientists and environmental groups questioned the figures, certain the leak was larger. New research supports that notion. According to the study, published in Science, some 4.4 million barrels of oil has escaped into the ocean. It is the first independent, peer-reviewed paper on the size of the leak. (doi: 10.1126/science.1195840)
Timothy Crone, a marine geophysicist at Columbia University’s Lamont-Doherty Earth Observatory, in Palisades, New York arrived at the estimate using a video analysis technique originally designed to study hydrothermal vents. He had spent years developing optical techniques to measure the flow of the underwater plumes that spew buoyant, superheated mineral-rich water. “Those flows are similar to what we were seeing in the oil flow event, and people were interested in what my estimates would be. People were asking what my estimates were, and I suppose I thought it was my duty,” he says.
Crone and co-author Maya Tolstoy analyzed high-resolution video from two phases of the oil leak: before and after the removal of the collapsed riser pipe from the blowout preventer. They calculate a flow of about 56,000 barrels per day from April 22 to June 3, when oil spurted from an irregular cut in the pipe, and 68,000 barrels per day after June 3, when the riser was cut and oil flowed freely. (Crone allows for a 20% margin of error.)
The final figure Crone has arrived at are comparable to the 2 August estimates by the federal government’s Flow Rate Technical Group (FRTG), a collection of federal and university scientists. The group said 4.9 million barrels (plus or minus 10%) had been released from the well and that 800,000 barrels had been captured prior to capping the well.
The FRTG’s measurements and modelling showed that the flow decreased over time as the oil reservoir emptied, from 62,000 barrels per day at the beginning of the spill to 53,000 barrels per day immediately before it was capped on July 15. Crone says that if he had access to more high-resolution video he could refine his estimates. “All that collected video, if it exists, shows the flow. We can apply this method retroactively and provide more information about the event,” he says.
In mid-September the FRTG came under fire for its varying estimates on the rate of the leak, which were repeatedly bumped up. On 16 September the Public Employees for Environmental Responsibility, a U.S. association of state and federal resource professionals, including scientists, filed suit in federal district court in Washington, D.C. to gain access to all of the FRTG’s papers and reports. “Our concern is that the administration took, and is still taking, steps to falsely minimize public perception about the extent and severity of the BP spill,” said PEER executive director Jeff Ruch in a statement.
Image: Sunlight illuminates the lingering oil slick off the Mississippi Delta on May 24, 2010 / NASA