South Atlantic caught in excessive salinity

(ORDO NEWS) — The salinity of the surface waters of the South Atlantic Ocean began to rise faster than salinity in the south of the Indo-Pacific. Scientists have suggested that this may be due to a weakening of the Atlantic meridional overturning circulation, which should dilute the salty southern waters with the fresher northern ones. Weakening circulation can accelerate global climate change since this circulation is one of the main mechanisms for absorbing carbon dioxide in the northern hemisphere. The article was published in the journal Nature Climate Change.

The Atlantic meridional overturning circulation (AMOC) is poorly understood, but it is known that it plays an important role in the regulation of the planet’s climate – it moves warm and salty waters from the southern part of the Atlantic to the north and colder and fresh waters from the northern part of the Atlantic to the south. In the context of anthropogenic climate change, its main function has become the absorption of large volumes of carbon dioxide in the northern hemisphere. There is evidence that AMOC in the North Atlantic has become weaker due to freshening of water by melting ice sheets, but much less is known about its condition in the South Atlantic.

Chenyu Zhu and Zhengyu Liu from the Oceanological University of China studied the salinity change in the surface layer of the South Atlantic Ocean. To do this, they used instrumental observation data from the ISHII and EN4 databases, and also performed mathematical modeling using a package of 13 CMIP5 models.

It turned out that the salinity of the surface water layer in the south of the Atlantic is higher compared to the water area of ​​the southern Indo-Pacific region, both according to instrumental observations and modeling according to the RCP4.5 scenario, which assumes the imposition by the international community of restrictions on anthropogenic greenhouse gas emissions and is not being implemented now.

In the RCP4.5 scenario, the salinity increase correlated with the AMOC attenuation (R = 0.76). The authors of the study suggested that the increase in salinity in the South Atlantic Ocean is associated with a weakening of AMOC, which, against the background of global climate change, is no longer so effective in stabilizing salinity in the south by the inflow of freshwater from the north. This is fraught with an increase in the effects of anthropogenic climate change because AMOC (in its normal state) absorbs about 700 million tons of carbon in the northern hemisphere, which is equivalent to greenhouse gas emissions from the whole of India. As it weakens, more carbon dioxide will be retained in the atmosphere. Scientists noted

Global climate change leads not only to disturbances in oceanic circulation, but also to a change in the life cycle of marine life: for example, acidification of the Arctic Ocean due to the dissolution of carbon dioxide in its waters will deprive mollusks of calcium, and warming of the water in the North Atlantic has already become the cause of mass extinction plankton.

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