New source of methane discovered: the Arctic Ocean

Cracks in the Arctic ice through which methane emissions were measured (Image credit: NASA/JPL)

It has been know for some time that large quantitites of methane lie hidden in reservoirs under the permafrost layers on the tundra and in clathrates on the continental shelve. It is neither a secret that those large quantities of gas might be released due to the warming of our planet, which will result in positive climate feedback making it even warmer.

But now NASA researchers have found a new methane source that might have global consequences: the Arctic ocean.

Where did it come from?

On a series of five flights in 2009 and 2010, a NASA research team found heightened levels of methane over the in the lower atmosphere over the Arctic. At first they were puzled as to where the gas came from. Taking the time of year of the measurements into account, it couldn’t have come from melting permafrost or human activities on higher latitudes. And since the Arctic ice sheet lies over the deep sea, melting clathrates are also an unlikely source.

Soon they found the concentration to be the highest over cracks and weakened areas in the ice, pointing them to the Arctic ocean itself. Those findings, as published in Nature Geoscience, are the first evidence that the ocean contributes to Arctic atmospheric methane levels.

Microbes

But what caused the ocean to release such quantities of methane into the atmosphere? The only standing theory for this is that microbes in the upper ocean layers produce it. If that is the case these microbes might become more productive while the ice thins and cracks, due to an increased influx of sunlight and atmospheric gasses into the upper ocean layer.

So far the atmospheric concentration has only increased by 0.5 per cent. But while the exact source remains uncertain it does stand to reason that the thinner the Arctic ice gets, the more methane will be released into the atmosphere. According to the NASA team this could result in emissions on such a large scale that they have global consequences.

Which is bad news considering the continually decreasing amount of ice in the Arctic. Especially if summer melt keeps increasing.