The Atlantic Mainstream Approach Critical Threshold

The Atlantic Mainstream appears to have lost stability over the past century and is approaching a critical threshold leading to collapse.

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It’s the result of a new study published in the journal Nature Climate Change, with implications for Europe’s climate.

The South Atlantic Returning Circulation (AMOC) moves masses of warm water from the tropics northward on the ocean surface and cooler water southward on the ocean floor, most favorable to the relatively mild temperatures of Europe. In addition, it affects weather systems around the world. Therefore, the potential collapse of this system of ocean currents could have disastrous consequences.

“The South Atlantic Return Stream is one of the most important circulation systems on the planet,” says study author Niclas Boers of the Potsdam Institute for Climate Impact Research, Free University of Berlin and University of Exeter.

“We already know—and continues—from some computer simulations and data from Earth’s past, the so-called paleoclimate proxy records, that AMOC—in addition to the current robust situation—can show a significantly weaker alternative mode of operation. This invariance indicates, in terms of principle, to the possibility of sudden transitions between the two trading modes.”

The AMOC has been shown to be currently at its weakest point for more than a thousand years, but so far the question has been open as to whether the observed weakness corresponds to a change in the average circulation state, or whether it is. associated with a real loss of dynamic stability.

“The difference is critical, because the loss of dynamic stability would mean that the AMOC has approached its critical threshold, beyond which a significant, and practically, possibly irreversible transition to the weak mode can occur,” says Niclas Bowers.

Unfortunately, there are no long-term observational data on the strength of the AMOC, but it does leave so-called fingerprints on the temperature and salinity patterns of the Atlantic sea surface.

“A detailed analysis of these fingerprints in eight independent indicators now suggests that AMOC weakness over the past century may be related to the loss of stability,” Bowers explains. The results support the assessment that lower AMOC is not just an oscillation or linear response to warming, but may mean the approach to a critical threshold beyond which the circulation system can collapse.”

It is likely that there are a number of important factors to the phenomenon, factors that add to the direct effect of the warming of the Atlantic Ocean on its circulation. Among them, freshwater ingress from Greenland thaw, sea thaw, increased precipitation and runoff from rivers. Fresh water is lighter than salt water and reduces the tendency of water to sink from the surface to greater depths, and is one of the drivers of return.

“I did not expect that the excess amounts of fresh water added over the last century would actually produce such a response in the repeat cycle,” Bowers says.

“We urgently need to reconcile our models with the observational evidence provided to assess how close or in fact the AMOC is to its critical threshold.” Although the particular significance of the various factors needs to be further investigated, they are all related to human-caused climate change, he says.

With information from Europa Press

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