Substantial amounts of the greenhouse gas methane can reach the surface ocean from seafloor seeps as deep as 600 metres, shows a study online in Nature Geoscience this week. The results indicate that current estimates of the global flux of methane from the oceans to the atmosphere may be too low.
Using a submersible robotic vehicle, Evan Solomon and colleagues directly sampled methane concentrations in bubble plumes at several sites in the Gulf of Mexico between 500 and 600 metres depth, where the gas emanates from seafloor vents. The researchers suggest that the transfer of methane to the atmosphere from the investigated deepwater plumes is 10 to 1,000 times higher than the amounts previously estimated for shallow-water seeps. This is contrary to the idea that only methane from shallow-water seeps reaches the ocean surface in significant amounts.
The researchers suggest that seeps in similar active hydrocarbon basins, such as the Persian Gulf, Caspian Sea, West African Margin and the Alaska North Slope, should be investigated more closely to improve estimates of the global methane flux from the oceans to the atmosphere.