New pathway for methane production in the oceans discovered

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Washington, July 4 : Researchers from the University of Hawaii have discovered a new pathway for methane production in the oceans, which has a significant potential impact for the study of greenhouse gas production on our planet.

According to the researchers, aerobic decomposition of an organic, phosphorus-containing compound, methylphosphonate, may be responsible for the supersaturation of methane in ocean surface waters.

Methane is a more potent greenhouse gas than CO2 on a per weight basis.

Although the volume of methane in the atmosphere is considerably less than CO2, methane is much more efficient at trapping the long wavelength radiation that keeps our planet habitable but is also responsible for enhanced greenhouse warming.

Today, between 20-30% of the total radiative forcing of the atmosphere is due to methane. Terrestrial sources of methane production are well known and studied, but those known sources did not account for the levels of methane observed in the atmosphere.

David Karl, an Oceanographer in the School of Ocean and Earth Science and Technology at the University of Hawaii at Manoa, was interested in this "methane enigma" and why the surface ocean was loaded with methane, over and above levels found in the atmosphere.

Karl found a possible solution to the enigma, in the compound methylphosphonates, a very unusual organic compound only discovered in the 1960s.

In the laboratory, the aerobic growth of certain bacteria on methylphosphonate can lead to the production of methane, but until now this process of methylphosphonate degradation in the ocean had not been suggested as a possible pathway for the aerobic production of methane in the sea.

According to Karl, when people began measuring methane in the ocean, they found that methane concentrations varied with geographical location and with water depth. If methane was inert in the ocean, its concentration should be constant and nearly equal to the concentration in the atmosphere.

What the scientists found was that methane was lower than expected in deep waters, implying net consumption by microbes.

"However the big surprise was that near surface concentrations were higher than in the overlying atmosphere which indicated a local production of methane in the sea," said Karl.

"Because methane is produced only in regions devoid of oxygen and since the surface ocean contains high oxygen levels, this was very perplexing," he added.

According to Phil Taylor, Acting Head of the Ocean Section, Division of Ocean Sciences at the National Science Foundation (NSF), "This remarkable discovery about methane production where we thought there would be none is a harbinger of many new insights on the ocean's changing biogeochemical nature, and the intricate microbiological reasons for those changes."

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