Atlantic ocean circulation is being altered, by climate change

A surprising new picture of ocean circulation could have major consequences for climate science, Some experts say the Atlantic Ocean circulation is already slowing down — but we’re just beginning to learn how it really works, WP By Chris Mooney, January 31 2019

It may be the biggest wild card in the climate system. Scientists have long feared that the so-called “overturning” circulation in the Atlantic Ocean could slow down or even halt due to climate change — a change that would have enormous planetary consequences.

But at the same time, researchers have a limited understanding of how the circulation actually works, since taking measurements of its vast and remote currents is exceedingly difficult. And now, a major new research endeavor aimed at doing just that has suggested a dramatic revision of our understanding of the circulation itself.

A new 21-month series of observations in the frigid waters off Greenland has led to the discovery that most of the overturning — in which water not only sinks but returns southward again in the ocean depths — occurs to the east, rather than to the west, of the enormous ice island. If that’s correct, then climate models that suggest the circulation will slow as the climate warms may have to be revised to take this into account.

……….. The new results come from the $ 32 million OSNAP, or “Overturning in the Subpolar North Atlantic,” program, the first attempt to comprehensively measure the circulation in the exceedingly remote regions in question. These icy seas, it is believed, are where cold, salty waters — which are extremely dense — sink below the sea surface into the depths, and then travel back southward again all the way to the Southern Hemisphere.

This “overturning” process is crucial because the sinking in the North Atlantic effectively pulls more warm, salty water northward via a system of currents that includes the Gulf Stream. This heat delivery, in turn, shapes climate throughout much of the region, and especially in Europe.

Better understanding of how the circulation works is key, since some scientists have already proposed that it is slowing down, with major consequences, including ocean warming and sea level rise off the U.S. east coast.

Global temperature maps in recent years have shown a strange area of anomalously cold temperatures in the ocean to the southeast of Greenland, along with very warm temperatures off the coast of New England.

The cold region — which has been dubbed the “cold blob” and also “warming hole” — is strikingly anomalous at a time when the Earth and its oceans are otherwise warming. And the suggestion has been that this represents a decline in the volume of heat being transported northward by the circulation.

The warm waters off New England, in this interpretation, would represent a key corollary — additional ocean heat hanging around in more southern waters, rather than making the trip northward………. https://www.washingtonpost.com/climate-environment/2019/01/31/surprising-new-picture-ocean-circulation-could-have-major-consequences-climate-scien