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Mains Marathon

  • 31 Aug 2022 GS Paper 1 Geography

    Day 52: What is Atlantic meridional overturning circulation (AMOC)? How will the Indian climate be affected by it? (250 Words)

    • Write a brief introduction about AMOC.
    • Describe the associated impact of AMOC over the Indian Climate.
    • Write a fair conclusion.


    Warm water from the tropics flows northward into the North Atlantic as part of a vast network of ocean currents known as the Atlantic Meridional Overturning Circulation (AMOC). Ocean currents that make up the AMOC are widespread. It is the Atlantic branch of the thermohaline circulation (THC), which transports heat and nutrients throughout the ocean basins of the planet.

    The AMOC has two key characteristics:

    • Warm, salty water is moving northward from the Gulf of Mexico in the upper layers of the ocean. This is made up of the "North Atlantic Current" farther north and the "Gulf Stream" to the south.
    • The water becomes denser as it cools in the high latitudes of the Atlantic. Then, as a bottom current, this denser water lowers and travels southward into the tropics before returning to the South Atlantic. From there, it is transported by the Antarctic circumpolar current to all ocean basins.

    Causes of AMOC's recent decline:

    There has always been variation in the AMOC and THC strength. There have been observations of reduced circulation and a slowing in AMOC during the severe glacial periods of the late Pleistocene. The AMOC has changed during the past 100–200 years, and the majority of those changes are connected to human activities that contribute to global warming.:

    • By lowering the salinity and density of the water and preventing it from sinking to the bottom, freshwater from melting Greenland ice sheets and the Arctic area might weaken circulation.
    • Weakening of Gulf Stream.
    • Increased rainfall and river flow are the causes of dilution.

    Effects of AMOC decrease:

    • Regional Climate Changes: The Gulf Stream, a warm current that is a component of the AMOC, is what causes the pleasant weather and rainfall on the Eastern coastlines of North America and Europe. Lack of a suitable AMOC and Gulf Stream can result in:
      • Reduced rainfall and temperature over Europe.
      • Sea ice grows across the Greenland-Iceland-Norwegian seas and to the south of Greenland due to pronounced cooling over the northern Atlantic region and adjoining regions.
      • A substantial southerly movement of the rain belt across the tropical Atlantic.
      • Stronger hurricanes in the US and more winter storms across Europe.
      • Sea level rise due to piling up of water at the US east coast.
      • Stronger hurricanes in the US and more winter storms across Europe.
      • Agriculture, wildlife, transportation, energy consumption, and coastal infrastructure are all affected by socioeconomic factors.
      • Fish populations and other marine life in the North Atlantic ecosystem that are adapted to the presence of the overturning circulation and consequent conditions like the seasonal cycle, temperature, and nutrient conditions will be disrupted, which will have serious effects on the ecosystems of the Atlantic marine ecosystems.

    The collapse of AMOC’s

    • This is mainly because the AMOC is a self-reinforcing system. The circulation itself brings salty water into the high-latitude Atlantic and the salty water increases the density. Thus, the water is able to sink because it is salty and it is salty because of the Circulation.
    • The AMOC might collapse into a condition of lower flow if freshwater intake is increased. The AMOC may continue to be in a collapsed condition from this point, even if freshwater intake into the seas drops to its present levels. Hysteresis is the capacity of the system to not revert to the starting condition after the forcing is reversed.

    Other impacts: An AMOC collapse might result in causal interactions like:

    • Southern migration of the ITCZ [Intertropical Convergence Zone] and the tropical rain belt.
    • The Amazon rainforest is declining.
    • Characteristics of the ENSO [El Nino-Southern Oscillation] change.
    • A weakening of the monsoons in Africa and Asia and a strengthening of the monsoons in the Southern Hemisphere.
    • The West Antarctic Ice Sheet is getting smaller.
    • The Southern Ocean has been warming significantly.
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