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. following particularly warm summers in the remote Irminger Sea, convection tended to be more impaired in winter. In some cases, a layer of meltwater stayed atop the ocean into the next year, rather than vanishing into its depths as part of the overturning circulation, which has sometimes been likened to an ocean “conveyor belt.”
this is an observational study, not a prediction for the future — and “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.
— source washingtonpost.com