Scientists studying the phenomenon already know that melting permafrost on land is a major source of carbon dioxide and methane being released into the air and entering the atmosphere. And global warming is not going to improve things. What has been less well known until now is the effect of Arctic warming on underwater permafrost, which may well prove disastrous.
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Underwater permafrost finally studied
Underwater permafrost has hardly ever been studied, mostly because of its inaccessibility. In an alarming paper published last week in the journal Proceedings of the National Academy of Sciences, an international team of scientists give us a rare glimpse of what's going on there. The team used ocean robots - which look like torpedoes - off the coast of northern Canada and mapped the seafloor with sonar.
The scientists repeated the operation several times over a period of nine years to get a sense of the changing topology of the seafloor and found that it was undergoing significant changes. The underwater permafrost had thawed and collapsed. One solution to the thawing permafrost is currently being tested by Russian scientists in Siberia who are trying to recreate the Ice Age ecosystem.
How permafrost warms
Why is this happening? On land, permafrost thaws because temperatures are rising. But, according to one of the study's authors, there is no evidence that seafloor temperatures are rising enough to trigger the thaw. So it is likely that the thawing does not start from above, but from below.
Underwater permafrost forms a wedge several hundred metres thick. Underneath, there is relatively warm groundwater, which can degrade the permafrost. Monterey Bay Aquarium Research Institute marine geologist Charlie Paull, a coauthor on the paper, explains:
If it's pure permafrost ice, it'll produce voids that subsequently collapse. And so we're inferring that the voids that we're seeing developing in this environment are a consequence of the long-term warming that the seafloor in this area has experienced.
Two major unknowns, however, are how much underwater permafrost exists and how much greenhouse gas it contains, which researchers have yet to clarify. Scientists cannot sample every square metre of the Arctic seafloor.
So they are looking to the past, comparing the amount of land exposed during the last extensive glacial age, thousands of years ago, to the amount exposed today. Estimates vary, but there could be about 1,250,000 square kilometres of underwater permafrost, possibly emitting hundreds of gigatons of organic carbon and tens of gigatons of trapped methane.