Strong Ocean Currents Promote Release of Arctic Greenhouse Gas

Strong ocean currents promote the release of the potent greenhouse gas methane in the Arctic, according to new research, shedding light on how they may contribute to climate change.

According to Ocean and Earth Science researchers from the University of Southampton, these currents inhibit the growth of marine bacteria that normally consume significant amounts of the gas.

"We found that strong, fluctuating, currents were common above methane seeps, meaning that methane-consuming bacteria may not be as effective for regulating emissions of methane to the atmosphere as previously thought," study co-author Dr. Rachael James said in a news release.

Large amounts of methane are stored in the seafloor in this area as gas hydrate - a solid, ice-like substance that consists of frozen methane and water. When the hydrates dissolve, methane can find its way through the sediments and be released into the water where it ascends to the sea surface. It is well known that marine bacteria can consume some of the methane, but these new findings show that ocean currents have a major control on how much methane escapes to the atmosphere.

In the study, James and her colleagues mapped the distribution of methane released from the seafloor offshore West Spitsbergen, an island located in northern Norway, from methane seeps first discovered in 2008. Over the course of their research, they noticed drastic changes in the level of activity of methane-consuming bacteria.

There results indicated that the changes in methane concentration, activity level of bacteria, and oceanographic parameters, were linked to shifts in the West Spitsbergen Current - a fast, warm and salty current that delivers water from the Norwegian Sea to the Arctic Ocean.

"It usually runs over the area of the methane seeps but every so often it moves, in a matter of days, further offshore, and is replaced by water that comes from closer to the coast," explained Professor Arne Biastoch, an oceanographer at GEOMAR (Helmholtz Centre for Ocean Research, Germany).

Coastal waters typically boast more methane-consuming bacteria since they are more slow-moving, thus promoting their growth. About 85 percent of the time, however, the currents over Arctic methane seeps are strong, preventing build-up of methane-consuming bacteria. This increases the chances that heat-trapping methane will escape into the atmosphere.

The results are described in more detail in the journal Nature Geoscience.

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