A report on the findings appears in Thursdays issue (Jan. 30) of the journal Nature. Authors are Drs. Gerald R. Dickens of the University of Michigan, Charles K. Paull of the University of North Carolina at Chapel Hill, and Paul Wallace of the Ocean Drilling Program and Texas A&M University.
"Some of our samples contained the equivalent of 40 liters of 99 percent pure methane for each liter of sediment, which was kind of a shocker, said Paull, professor of geology at UNC-CH and U.S. leader of the expedition. "We estimate there are something like 35 gigatons of methane carbon lie in the area we explored, which was part of the Blake Ridge. That is 35 billion tons, or about 7 percent of all the carbon stored on land.
For the first time, the scientists successfully used a tool called a pressure core sampler to trap gaseous material from the bottom of holes drilled into ocean floor. With the device, geologists aboard the 470-foot JOIDES Resolution -- the globe-circling drill ship operated by the Ocean Drilling Program -- retrieved the samples at down-hole pressures so that little or none of the gas escaped.
Work crews drilled at four sites to about 2,250 feet into the sediments, which themselves lie more than a mile and half below the sea surface.
"The more we look at this, the more it looks like the continental margins of the world, including both sides of North America, are dotted in a semi-continuous way with areas rich in gas hydrates, Paull said. "In the past, we haven't been able to sample gas in marine sediments accurately because the technology did not exist. We are now at the point where we are over the threshold technologically and the data we are getting back is somewhat startling.
Mining ocean methane eventually could occur, he said, but no time soon. The deposits are in deep water not close to land and cannot be tapped efficiently. Although some methane escapes from marine sediments on its own, most remains trapped by cold temperatures, and pressure from the earth above it.
Low temperatures and high pressure keeps much methane gas in solid form known as hydrates, which Paull said resembles gray ice. Most geologists have never seen a sample.
Because studies involving seismic profiling indicated only small amounts of free gas, the biggest surprise was the tremendous amount we measured, he said. "Seismic studies indicated that gas hydrate and free gas zones extend over 26,000 square kilometers of the Blake Ridge.
The new results are consistent with earlier estimates not involving direct measurements that Earth holds between 1,000 and 10,000 billion tons of methane carbon, Paull added. It also supports the theory that release of methane from the ocean floor has played a significant role in past climate change. Assuming that it could be tapped, methane in the Blake Ridge could meet U.S. natural gas consumption needs for the next 105 years.
Note: Paull can be reached at (919) 962-0687 (w) or 929-3628 (h). Contact: David Williamson
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