Atlantic Meridional Overturning Circulation (AMOC)

Atlantic Meridional Overturning Circulation (AMOC)

Subject: Geography

Context: A recent study in Nature Climate Change and the IPCC’s Report (AR6) notes that the Atlantic Meridional Overturning Circulation (AMOC) is losing its stability. Modelling studies have shown that an AMOC shutdown would cool the northern hemisphere and decrease rainfall over Europe.

Atlantic Meridional Overturning Circulation (AMOC)

• The AMOC is a large system of ocean currents.
• It is the Atlantic branch of the ocean conveyor belt or Thermohaline circulation (THC), and distributes heat and nutrients throughout the world’s ocean basins.
• AMOC carries warm surface waters from the tropics towards the Northern Hemisphere, where it cools and sinks.
• It then returns to the tropics and then to the South Atlantic as a bottom current. From there it is distributed to all ocean basins via the Antarctic circumpolar current.

What happens if AMOC collapses?

• Gulf Stream, a part of the AMOC, is a warm current responsible for mild climate at the Eastern coast of North America as well as Europe. Without a proper AMOC and Gulf Stream, Europe will be very cold.
• It can also have an effect on the El Nino.
• Freshwater from melting Greenland ice sheets and the Arctic region can make circulation weaker as it is not as dense as saltwater and doesn’t sink to the bottom.

Why is the AMOC slowing down?

• Global warming can cause a weakening of the major ocean systems of the world.
• A part of the Arctic’s ice called “Last Ice Area” has also melted. The freshwater from the melting ice reduces the salinity and density of the water. Now, the water is unable to sink as it used to and weakens the AMOC flow.
• As the Indian Ocean warms faster and faster, it generates additional precipitation. With so much precipitation in the Indian Ocean, there will be less precipitation in the Atlantic Ocean, leading to higher salinity in the waters of the tropical portion of the Atlantic. This saltier water in the Atlantic, as it comes north via AMOC, will get cold much quicker than usual and sink faster.

Has the AMOC weakened before?

• AMOC and THC strength has always been fluctuating.
• The extreme glacial stages have seen weaker circulation and slowdown in AMOC, while the glacial terminations have shown a stronger AMOC and circulation.
• But the changes we experience in the last 100-200 years are anthropogenic, and these abrupt changes are destabilising the AMOC, which could collapse the system.