Something very strange is happening in the Arctic Ocean, and just for once it might be good news, although it's far too early to open the champagne. At sites where methane is bubbling from the sea floor, carbon dioxide is being captured in even larger quantities.
One of the most frightening aspects of global warming lies in the far north, both in the Arctic tundra and beneath the northern oceans. Billions of tonnes of methane are locked in ice. As the world warms, some will be released, potentially causing more warming and a run-away effect, even if we eventually get our own emissions under control.
For something so important, we have a disturbingly poor knowledge of what it would take to set this off. Dr John Pohlman of the Woods Hole Coastal and Marine Science Center is exploring one aspect of this – the release of methane from shelves around the edges of continents less than 100 meters (330 feet) below sea level.
In Proceedings of the National Academy of Sciences, Pohlman reports on a study of the waters above a methane seep at the margin of Svalbard, Norway. As anticipated, he found that some of the methane being released from the ocean floor was captured in the water column above, preventing it from doing any harm. However, 17.3 μmol per square meter per day (1.6 μmol per square foot per day) is escaping into the atmosphere. Not much now, but a disturbing warning of what could come.
At least it would be, were it not that the same waters captured almost 1,900 times as much carbon dioxide from the atmosphere. Arctic waters in general soak up a lot of carbon dioxide, slowing the rate of climate change, but when Pohlman measured surrounding waters without a seep, he found roughly half that rate. Pohlman's seep was setting off a chain reaction that lead to almost 1,000 times as much carbon dioxide being captured from the air as methane was released.
Methane is a far more potent greenhouse gas than CO2, but not 1,000 times more (how much more potent depends on the timespan over which you compare the gasses). The net effect Pohlman measured is a cooling, not warming, one, although the study only covered the summer months; year-round effects might be different, and the faster seeps off East Siberia might look different.
The additional carbon dioxide absorption appears to be a consequence of nutrient-rich waters accompanying the methane to the surface, promoting the spread of carbon dioxide-guzzling plankton.
We don't yet know if future increases in methane release will be accompanied by the same nutrient upwelling, or whether the carbon uptake is sustainable. Nevertheless, it's possible that ocean methane release is not the world-ending calamity we feared.