QUES . What is Atlantic Meridional Overturning Circulation (AMOC)? Mention the causes and implications of slowing down of AMOC.
HINTS:
The ocean’s water is constantly circulated by currents. Tidal currents occur close to shore and are influenced by the sun and moon. Surface currents are influenced by the wind. However, other, much slower currents that occur from the surface to the seafloor are driven by changes in the saltiness and ocean temperature, a process called thermohaline circulation. These currents are carried in a large “global conveyor belt,” which includes the AMOC.
What is 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.
THC is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes.
The global conveyor belt’s circulation is the result of two simultaneous processes : warm surface currents
carrying less dense water away from the Equator toward the poles, and cold deep ocean currents carrying
denser water away from the poles toward the Equator.
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.
Causes of Slowing Down of AMOC
The entire circulation cycle of the AMOC, and the global conveyor belt, is quite slow. It takes an estimated 1,000 years for a parcel of water to complete its journey along the belt. Even though the whole process is slow on its own, there is some evidence that the AMOC is slowing down further.
Global warming : Climate models have predicted that 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 (eg greenland) reduces the salinity and density of the water. These changes make the ocean water lighter and so reduce the sinking in the ‘conveyor belt’. Now, the water is unable to sink as it used to and weakens the AMOC flow.
Warming of Indian Ocean: 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.
AMOC and THC strength has always been fluctuating, 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.
Implications of slowing down in AMOC
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.
AMOC shutdown would cool the northern hemisphere and decrease rainfall over Europe. It can also have an effect on the El Nino.
AMOC collapse brings about increase in Sea ice over the Greenland-Iceland-Norwegian seas and to the
south of Greenland.
A significant southward rain-belt migration over the tropical Atlantic.
