Ocean currents, along with the atmosphere, take part in the regulation of temperature on our planet through a thermodynamic process that drives heat from the equator. Ocean currents carry warm equatorial waters to the North and South Poles. Then, having lost their warmth, they again rush to the tropical latitudes. The complete cycle of currents in the ocean, occurring on the surface of the water and in its depths, is called thermohaline circulation, which lasts several thousand years.
In the North Atlantic Ocean, the Gulf Stream, which bends around the western coast of North America, carries warm water to the northern parts of the ocean. On the way, it meets the North Atlantic current rushing to the north-east of the Atlantic. Off the coasts of Norway, Greenland and the Labrador Sea, these waters turn cold. The water becomes denser, its salinity level rises, and it sinks deeper. On average, its volume is 17 million cubic meters. This process plays a decisive role in shaping the Earth's climate.
What is Atlantic meridional overturning circulation?
The Atlantic meridional overturning circulation (AMOC for short) is a system of ocean currents in the North Atlantic that act as a conveyor belt to move water and air, thereby creating meteorological systems and redistributing heat on our planet. Warm, salty water flows northward in the upper Atlantic Ocean, while colder water flows southward in deeper reaches. It transfers heat from the Southern Hemisphere and the tropics to the north.
A constantly moving deep-sea circulation system directs the warm, salty water of the Gulf Stream into the North Atlantic, where it releases heat into the atmosphere and warms Western Europe. Then the cooler water sinks to greater depths and reaches Antarctica and, eventually, returns back to the Gulf Stream.
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What will the disruption of the circulation of the Atlantic Ocean lead to?
Disturbances in circulation AMOC are causing climate change on our planet, causing monsoons in Africa and India and hurricanes in North America and Western Europe.
AMOC has slowed by about 15% since the mid-20th century, according to a study published in the journal Nature. This was the slowest record of cooling in the subpolar Atlantic Ocean and warming of the Gulf Stream region in 1,500 years. The researchers measured a 5.2 million square kilometers basin of cold water in the North Atlantic. This region is known as the "cold drop". Studies have been conducted on the circulation characteristics and seasonal temperatures at the ocean surface. These numbers are likely to be associated with an increase in atmospheric carbon dioxide, which is provoking warmer global temperatures over the past 150 years.
"Global warming is likely to further weaken AIOC due to changes in the hydrological cycle, loss of sea ice and accelerated melting of the Greenland Ice Sheet, which will further cool the North Atlantic," the authors of the article said.
The deceleration is intensifying and, according to the findings of the second study, published in the journal Nature, it opens the door to a potentially complete cessation of ocean current, which will be a "tipping point." The authors warn that such a collapse would be disastrous.
The relationship between global warming and water currents
You may be asking yourself: what is global warming and how is it related to the Atlantic Ocean? These processes have something in common.
First of all, the warmer water impedes the movement of colder, denser water. As the ice sheets and glaciers in Greenland melt, fresh water is poured into the ocean, where churning usually occurs. Here the water becomes less dense and less saline, which reduces its ability to penetrate the lower layer. There is an increase in precipitation in the Northern Hemisphere and more complete evaporation of water in the southern part of this compound.
Influence of air masses
Wind also affects how current systems move and can significantly change currents when combined with fresh water. Decreased wind strength over the ocean can cause an “immediate weakening” of vertical salinity and change in ocean stratification, as well as slowing thermohaline circulation.
Some researchers say these predictions are not supported by enough data.
Maya Muzashvili