Methane—the Other Gusher in the Gulf—Concerns Scientists
By Mark Schrope
Methane, the major component of natural gas, is found in much lower concentrations in the atmosphere than carbon dioxide, but it is about 25 times more potent as a greenhouse gas at trapping heat within the atmosphere. Researchers have long wondered whether sudden releases of methane from the seafloor, where in places it is heavily concentrated in ice formations known as hydrates, might have played a significant role in driving climate shifts over geological history. One idea is that changes in temperature or sea level rise could destabilize large swaths of hydrates, which stay frozen only under a narrow temperature and pressure range, releasing methane and affecting climate. But scientists have never been able to study such a potential release on a grand scale.
© Harold Shapiro
Enter the BP Deepwater Horizon catastrophe. While most of the focus has been on spilling oil, an estimated 40 to 50 percent of the material gushing out of the seafloor was methane. John Kessler, a geochemist at Texas A&M University, recognized this massive methane release as a useful, if unwelcome, tool for studying how the gas behaves when released in large quantities into the sea. Kessler asked Peter Raymond, professor of ecosystem ecology at F&ES, to join a team that would explore the issue with funding from the National Science Foundation.
The key question was what would happen to the methane. Many people have assumed that methane released in large quantities could make its way relatively quickly into the atmosphere. But the expedition team found something very different. With the spill still under way, they detected methane concentrations in deep waters many thousands of times higher and, in some cases, nearly a million times higher than normal. But the researchers could find no signs of higher-than-normal methane in surface waters despite hundreds of thousands of measurements across a huge area surrounding the spill zone. “That was really surprising to me,” said Kessler.
The team’s working conclusion was that methane was remaining in the deep waters, possibly being consumed by bacteria. The team still has much work to do before it can gauge what this says about history. It may be a little methane released in the deep sea that reaches the surface. However, it’s also possible that the team, despite its extensive search, missed the areas where methane was making it to the surface or that methane is making its way to the surface slowly—meaning in geologic terms, that it could take hundreds of years or even thousands of years and still be important. “Any methane that isn’t consumed could eventually make it to the atmosphere,” said Raymond. And, of course, shallow methane releases could behave quite differently.
The results also countered an argument made by BP officials that there was no methane trapped in deep waters. They said repeatedly that measurements in deep waters were simply of methane on its way to the surface. But if that were the case, then high levels of methane should have been found in surface waters.
Raymond’s job will be to analyze seawater samples that the team collected for their carbon-14 levels. Normally carbon in ocean water contains measurable amounts of the radioactive variation known as carbon-14. But methane and oil released from within the seafloor are so old that they have no carbon-14, because it decays over time. Raymond’s seawater analyses will measure carbon-14 both from any oil dissolved in the seawater and from the organic materials exuded in various forms by plankton and other organisms that might be consuming oil or methane in the water. This will provide a broad estimate of how much oil and gas were in the system in areas where researchers collected seawater samples.