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Researchers document methane seeps Find and measure methane bubbling into atmosphere in Alaska and Greenland as permafrost and glaciers melt with global warming Alan Bailey Petroleum News
A team of university researchers has published evidence of the widespread seepage of methane in areas where the permafrost and glaciers are retreating as a result of global warming.
In a recent paper, published in Nature Geoscience, team members Katey Walter Anthony, Peter Anthony and Guido Grosse from the University of Alaska Fairbanks, and Jeffrey Chanton from Florida State University say that, although people have theorized about methane seepage in northern latitudes, this new research presents for the first time clear evidence that this phenomenon is taking place.
Trapped under ice In northern regions methane from natural gas deposits, coal beds and decomposing organic material can become trapped under impermeable ice-saturated ground or glaciers. In some cases the gas combines with ice to form solid gas hydrate material. People have speculated that the melting of ice and the disassociation of hydrates under warming temperatures would release the trapped methane into the atmosphere.
Methane, the main component of natural gas, is a potent greenhouse gas with a significantly stronger greenhouse impact than carbon dioxide. Scientists worry that the increased release of naturally occurring methane as ice retreats and the land thaws in Arctic and sub-Arctic regions could accelerate overall global warming.
To test theories about methane seepage the research team conducted a series of aerial surveys in Alaska from 2008 to 2010 during winter conditions, when the land and lakes were frozen. The surveys, covering a north-south transect from the Beaufort Sea coast to Cook Inlet, involved observing about 6,700 frozen lakes within a total land area of 11,260 square kilometers. Using direct observations from the aircraft and by examining photographs taken from the air, the team counted the number of open holes in frozen water, with these holes providing evidence of methane bubbling up through the water.
Ground truthing Ground expeditions visited 50 of 77 sites observed from the air and identified to be probable seeps. This “ground truthing” verified the existence of methane seeps at the observed ice holes and enabled measurements of the rate of methane escape.
The team also visited eight of the observed methane emission sites during the summer, to measure smaller seeps that were invisible during the winter. The team was then able to extrapolate to other seep sites the likely emissions from these smaller seeps by assuming a consistent ratio of small-scale to large-scale seeps across the state.
The team also measured the chemical and isotope composition of the gas bubbling from the seeps to assess whether the methane originated from the relatively recent decomposition of organic material or whether the methane was older, coming from coal seams or subsurface natural gas accumulations. It turned out that the larger seeps tend to consist of the older methane. And the seeps tend to be associated with underlying sedimentary basins.
Overall, the team mapped more than 150,000 seeps in Alaska.
Different regions In northern Alaska, a region characterized by continuous permafrost, the seeps were found to be particularly associated with low lying areas beneath lakes or near rivers, where thawing is likely to be most rapid. In Interior Alaska, typified by more discontinuous permafrost, seeps were less common and tended to occur along the boundaries between continuous and discontinuous permafrost. In Southcentral Alaska, a region that had once been glaciated but now has relatively little permafrost, the seeps tend to be associated with recent geologic faults — the faults probably formed as a result of the loss of an earlier glaciation-related ice load and presumably now act as conduits for methane to reach the surface.
The team also visited frozen lakes in Greenland, finding that younger methane seeps there are associated with the relatively recent retreat of the ice sheet.
The team used the data that it gathered in Alaska to estimate a total rate of methane emission from seeps in each of the three zones — northern Alaska, the Interior, and Southcentral — along the transect where the observations were made, and then for the whole of Alaska. And, using a recently published U.S. Geological Survey assessment of pan-Arctic oil and gas basins, the team inferred the potential methane emissions from the continuous permafrost zone around the entire Arctic.
Significant seepage The bottom line?
There may be some 2 million metric tons of methane per year bubbling into the atmosphere from the regions of continuous permafrost around the Arctic, as the permafrost is disrupted by the warming climate. Across the whole of Alaska, including the more southerly portions of the state, there may be 1.5 million to 2 million metric tons per year escaping through seeps of various types, an estimated rate of methane emission 50 to 70 percent higher than previously thought.
If the results from Alaska and Greenland can be extrapolated to glaciated regions such as Siberia, the continuing degradation of the permafrost and glaciation will result in a very strong increase in the cycling of methane through the atmosphere, the research team concluded.
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