Atlantic Meridional Overturning Circulation (AMOC)

• AMOC is characterized by a northward flow of warm, salty water in the upper layers of the Atlantic, and a southward flow of colder, deep waters that are part of the thermohaline circulation.

How Atlantic Meridional Overturning Circulation (AMOC) works?

• As warm water flows northwards in the Atlantic, it cools, while evaporation increases its salt content.
• Low temperature and a high salt content raise the density of the water, causing it to sink deep into the ocean.
• The cold, dense water deep below slowly spreads southward.
• Eventually, it gets pulled back to the surface and warms again, and the circulation is complete.

Image Credits: Wikipedia

Importance of Atlantic Meridional Overturning Circulation (AMOC)

• AMOC aids in distributing heat and energy around the earth (heat budget).
• Western Europe’s climate is less harsh even in winters because of AMOC (Gulf Stream, North Atlantic Drift).
• It acts as a carbon sink by absorbing and storing atmospheric carbon.
• AMOC’s carbon sequestration has significant implications for evolution of anthropogenic global warming.

Cause of concern

• AMOC has undergone exceptional weakening in the last 150 years compared to the previous 1500 years.
• Climate models suggest that the AMOC will weaken over the 21st Century as greenhouse gases increase.
• This is because as the atmosphere warms, the surface ocean beneath it retains more of its heat.
• Meanwhile increases in rainfall and ice melt mean it gets fresher too.
• All these changes make the ocean water lighter and reduce the sinking in the conveyor belt (weaker AMOC).
• A weaker AMOC will bring less warm water northwards, and this will partly offset the warming effect of the greenhouse gases over western Europe.

Effects of AMOC Slowdown

• IPCC report indicates that AMOC has already weakened.
• Any substantial weakening of the AMOC would cause
  • further decrease in marine productivity in the North Atlantic (less sinking will lead to less mixing of water),
  • more storms in Northern Europe,
  • less Sahelian summer rainfall and South Asian summer rainfall,
  • a reduced number of tropical cyclones in the Atlantic and
  • an increase in regional sea level along the northeast coast of North America.

Rising temperatures in Indian Ocean can boost Atlantic’s ocean currents temporarily

• For thousands of years, AMOC has remained stable, but since the past 15 years, it has been weakening.
• However, rising temperatures in the Indian Ocean can help boost the AMOC and delay the slow down.

Indian Ocean’s role

• The Indian Ocean is one of the fingerprints of global warming.
• As the Indian Ocean warms faster and faster, it generates additional precipitation.
• This draws more air from other parts of the world to the Indian Ocean, including the Atlantic.
• With so much precipitation in the Indian Ocean, there will be less precipitation in the Atlantic Ocean.
• Less precipitation will lead to higher salinity in the waters of the tropical portion of the Atlantic.
• This saltier water, as it comes north via AMOC, will get cold much quicker than usual and sink faster.
• This would act as a jump start for AMOC, intensifying the circulation.
• However, scientists don’t know for how long this enhanced warming in Indian Ocean will continue.
• If other tropical oceans’ warming, especially the Pacific’s, catches up with the Indian Ocean, the advantage for AMOC will stop.

Sources: D2E | MetUK | IE

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