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Marine minerals
B.C. methane hydrates

A two-year search that culminated in August with the discovery of one of Canada’s largest deposits of methane hydrates began with a fisherman off the coast of British Columbia.

“We were tipped off more or less accidentally by a fisherman who dragged up a piece of hydrate in his net,” says geophysicist Ross Chapman of the Centre for Earth and Ocean Research at the University of Victoria, B.C., and the principal investigator on the project. “When it came up to the surface, it would have behaved like a giant Alka Seltzer — foaming and bubbling.” That frothy activity was the release of methane from its icy cage as it surfaced from underwater, undergoing a change in pressure and temperature that destabilized the structure of the ice lattice.

A methane hydrate glacier sits on the seafloor, 850 meters below the surface. Photo courtesy of University of Victoria, B.C.

Using a tiny underwater rover called ROPOS, with the support of Canada’s Natural Sciences and Engineering Research Council, the U.S. Naval Research Lab and the Canadian Scientific Submersible Facility, Chapman and his colleagues followed the track that the fisherman and his crew had traveled two years before. The rover traveled on the seafloor, about 850 meters deep. “Eventually we found a little plateau, with a series of what you have to call hydrate glaciers,” Chapman says. Scattered over about 2 square kilometers, the glacier-like mounds were surrounded by clam beds, although no vents were visible. “One mound was the size of a Volkswagen,” he says.

Researchers estimate that this extensive field of hydrates at the bottom of submarine Barkley Canyon off the British Columbia coast, could provide enough methane to power Canada for four decades. But, they say it is too soon to tell exactly how much is in Barkley Canyon.

From other evidence, Chapman believes that the ice may cap deeper deposits of very clean oil. He noticed that the ice was a yellow brown, indicating that the hydrocarbons were from a deeper source, where “vigorous enough fluid flow and some kind of vent to the seafloor” created an escape route. When ROPOS’ arm poked into the sediments, it released clear, light oil, presumably from that deeper reservoir, he adds.

Ices like those found at Barkley Canyon are surprisingly common in deep near-shore sedimentary deposits and at continental margins, as well as in permafrost. They are usually stable at water depths below 300 to 500 meters and are at optimum temperatures at the seafloor, about 4 degrees Celsius. Some methane hydrates are made by methanogens, or bacteria that thrive on methane, but the B.C. deposits may be completely thermogenic, derived from the same processes “that cook oil and gas,” Chapman says.

Worldwide, methane hydrate sources are estimated to be equivalent to 137.5 trillion barrels of oil. But it’s not that easy to take advantage of this cornucopia. While methane hydrates could provide a very clean source of hydrocarbon fuel, the methane, if released accidentally, is a greenhouse gas — oxidizing to carbon dioxide and remaining in the atmosphere for a long time. And because methane hydrates are easily destabilized, Chapman points out that they may cause submarine slumps, which represent an additional geohazard. Such massive releases may have been responsible for extinctions at the end of the Paleocene, according to recent research.

British Columbia has had a moratorium, in place since the early 1970s, on coastal oil and gas exploration to avoid environmental impacts. Nevertheless, Chapman says the Barkley Canyon deposits provide a natural laboratory for studying hydrates. “We have a team that’s looking at long-term experimental research on this particular site,” he says, and they plan to publish their summer’s explorations soon.

Naomi Lubick
Geotimes contributing writer


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