Much of the focus at the Deepwater Horizon disaster site has been on the oil pouring out of the damaged well, but some researchers are beginning to turn their attention to the methane, or natural, gas escaping along with the gushing crude. Careful study of this methane, which comprises about 40 percent of the riser pipe output, is expected to provide scientists with a wealth of information, including a more accurate calculation of the spill's magnitude and thereby a better understanding of its impact on ocean life.

The size of the spill has been cause for much speculation, with estimates ranging anywhere from 1,000 to 100,000 barrels per day, although 12,000 to 19,000 barrels appears to be emerging as the consensus. Yet visual observations and spot measurements of oil, water and gas mix are unreliable due in part to the water's turbulent flow, David Valentine, a University of California, Santa Barbara, professor of marine sediment geochemistry, biogeochemistry and geomicrobiology, wrote last week in Nature. (Scientific American is part of Nature Publishing Group.) Valentine instead proposed that quantifying the amount of leaked methane gas dissolved into the waters holds the key to calculating the spill's actual size.

"Unlike oil, methane dissolves uniformly in seawater," Valentine wrote. "And the tools are available to measure it accurately and sensitively." Adding up all the methane should yield a reasonable estimate on the oil spilled, he added. Methane is also thought to be the main culprit in the blowout that started the leak, and ice crystals formed by the gas sabotaged efforts to put a containment dome over the leak a few weeks ago.

Methane tracking tools will soon be put to the test when a team of researchers led by John Kessler, an assistant professor in Texas A&M University in College Station's Department of Oceanography, reaches the Deepwater site to study the levels of that gas in the seawater.

When the expedition, which includes Valentine, arrives on June 11, it will begin studying the source of the methane, how it is being removed from the water (whether eaten by waterborne microorganisms or released into the atmosphere), and how methane concentrations will change over time. To do this, the scientists will use a greenhouse gas measurement system made by Sunnyvale, Calif.–based Picarro, Inc., that quantifies ambient carbon dioxide, water vapor and methane. The team is also expected to use a Picarro isotopic carbon analyzer to test for anthropogenic/fossil fuel–based carbon dioxide, as opposed to ambient CO2, in the water. The isotopic carbon analyzer uses what Picarro refers to as "wavelength-scanned cavity ring down spectroscopy," whereby a near-infrared laser monitors a gas sample for the presence of different gases.

Picarro is also hoping to provide a new instrument to measure isotopic methane that could help Kessler's team fingerprint various methane plumes in the water and trace them back to their source, whether from the BP spill or elsewhere. "These gases are formed in a very systematic way, which gives them a unique signature," Kessler says. "The spill will have a very unique isotopic fingerprint."

Kessler and his colleagues are bringing a portable seawater pump aboard the Cape Hatteras, a ship operated by the Duke University/University of North Carolina Oceanographic Consortium, so they can continuously study water samples from about four meters below the surface. The expedition, made possible by a recently awarded $160,000 National Science Foundation (NSF) grant, will also periodically collect water samples at depths of up to 2,000 meters.

Kessler says he hopes to have a rough estimate of the spill's size by the time his team returns home on June 20, followed by more accurate estimates as they complete their analysis of the information collected.

Studying the Gulf's methane content will also help address much broader scientific questions, such as how much of the gas may be consumed by microorganisms in the water and how much may escape into the atmosphere. The aerobic oxidation of methane by microorganisms in the water column consumes dissolved oxygen, leading to oxygen-depleted dead zones where fish and plant life cannot survive.

"The ocean is a large reservoir of methane, and we study how methane and oil seep out of the seafloor naturally," Kessler says. The Deepwater's broken riser pipe will give his team a way to observe a similar phenomenon, only about "one million times faster" than they normally would, he adds.