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Reconstructing past deep-water circulations of the Indian Ocean

GS Paper 1

Syllabus: Geography: Ocean Current


Source: The Hindu

Context: New studies have shown that the global overturning circulation controls ocean heat distribution and atmospheric carbon dioxide levels, thus playing a critical role in global climate.


What does the new study show?

Studies have indicated that tectonically driven changes in the ocean gateways such as the closure of the Central American Seaway (a body of water that once separated North America from South America), since the late Miocene period, had a dramatic impact on the GOC.


What is Global Overturning Circulation (GOC)?

  • It is the equatorward transport of cold, deep waters and the poleward transport of warm, near-surface waters.
    • Atlantic Meridional Overturning Circulation (AMOC) is one part of this circulation apart from Pacific Deepwater, Southern Ocean Meridional Overturning Circulation etc.
    • 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
  • It is a Thermohaline circulation (THC) and distributes heat and nutrients throughout the world’s ocean basins.



GOC 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.


Reasons behind the slowing down of AMOC

The slowing down we experience in the last 100-200 years is anthropogenic, and these abrupt changes are destabilizing the AMOC, which could collapse the system. There are various reasons behind the current slowing down

  1. Global warming – Climate models have long predicted that global warming can cause a weakening of the major ocean systems of the world.
  2. Melting of Glaciers – In recent years Arctic ice called the “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.
  3. Warming of the 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.


Mains Links

Q. What is Atlantic Meridional Overturning Circulation (AMOC)? Why is it slowing down, and what are its implications? (10M)