The fast-melting Arctic is already messing with the ocean’s circulation, scientists say

https://www.washingtonpost.com/news/energy-environment/wp/2018/03/14/the-melting-arctic-is-already-messing-with-a-crucial-part-of-the-oceans-circulation-scientists-say/?utm_term=.f05a3bcca44b

by Chris Mooney March 14, 2018

Scientists studying a remote and icy stretch of the North Atlantic have found new evidence that fresh water, likely melted from Greenland or Arctic sea ice, may already be altering a key process that helps drives the global circulation of the oceans.

In chilly waters on either side of Greenland, the ocean circulation “overturns,” as surface waters traveling northward become colder and more dense and eventually sink, traveling back southward toward Antarctica at extreme depths. This key sinking process is called convection. But too much fresh water at the surface could interfere with it, because with less salt, the water loses density and does not sink as easily.

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“Until now, models have predicted something for the future … but it was something that seemed very distant,” said Oltmanns, the lead scientist behind the research, which was published this week in Nature Climate Change.

“But now we saw with these observations that there is actually freshwater and that it is already affecting convection, and it delays convection quite a lot in some years,” she continued.

One caution is that this is an observational study, not a prediction for the future — and Oltmanns said “nobody really knows” how much freshwater is enough to significantly slow or shut down the circulation, which is technically called the “Atlantic meridional overturning circulation,” or AMOC. Still, it suggests that key processes that have raised long-standing concern are already happening.

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