Experts have long known that deposits of methane hydrate, an ice-like substance that traps methane, the primary component of natural gas, lie below the seafloor under the shallow waters of Alaska's Beaufort Sea. But now concerns that a warming climate may cause these hydrates to break up, expelling methane into the sea and atmosphere, has prompted a team of scientists to investigate the current state of the deposits, according to a report published recently by the Department of Energy.
Methane itself is a so-called greenhouse gas. Like carbon dioxide, it can accelerate global warming by trapping heat from solar radiation that would otherwise reflect off the Earth's surface and bounce back into space.
With funding support from the energy department, scientists from the U.S. Geological Survey, Stanford University and Texas A&M University have participated in the work.
While a thick layer of onshore permafrost in the Beaufort region protects methane hydrates under the land, sea level rise and seawater inundation since the last ice age have resulted in the thawing of offshore permafrost and a relatively high risk of hydrate disassociation, the report says.
One scientist, working in the USGS Woods Hole Science Center in Massachusetts, is using 1970s-era seismic data, supplemented by old borehole logs, to map hydrate deposits on the Alaska Beaufort Sea shelf. Researchers conducted cruises in August 2010 and 2011 to verify the map data and collect new geophysical and geochemical data.
The water is very shallow in those areas, with geologic evidence indicating that the sea only inundated the area within the last few thousand years, the report says.
Sonar data indicate the common presence of gas in the near-seafloor strata. The seismic data provided no insights into whether the gas came from deep underground, as would be expected if its presence was the result of hydrate disassociation, the report says.
Pockmark features on the seafloor in southern Harrison Bay and seaward of the Colville River Delta suggest gas venting.
New techniques will be needed to determine whether methane in the atmosphere or water in the Beaufort area originates from disassociating hydrates as the permafrost melts, the report says.
By ALAN BAILEY