Atlantic meridional overturning circulation (AMOC) weakens

Context:

The Atlantic Ocean’s current system (AMOC) could be weakening to such an extent that it could soon bring big changes to the world’s weather according to a recent study.

Relevance:

GS-I: Geography (Climatology, Important geographical phenomena), GS-III: Environment and Ecology (Impact of Climate Change)

Dimensions of the Article:

1. What are Ocean Currents?
2. Factors responsible for Ocean Currents
3. The Slowdown of Ocean Circulation: How is it happening?
4. About the Atlantic meridional overturning circulation (AMOC)

What are Ocean Currents?

• The movements of water in oceans can be categorized into currents, waves, and tides. Among these, ocean currents are the large masses of surface water that circulate in regular patterns around the oceans.
• Depending upon their temperature, ocean currents can be classified into warm currents and cold currents.
• Warm currents flow from equatorial regions towards the polar regions and hence have a higher surface temperature. These currents flow in the clockwise direction in the northern hemisphere and in the anti-clockwise direction in the southern hemisphere.
• Cold currents flow from polar regions towards the equator and have a lower surface temperature. These currents flow in the anti-clockwise direction in the northern hemisphere and in the clockwise direction in the southern hemisphere.

Ocean conveyor belt:

• All of Earth’s oceans are interconnected by a global circulation system sometimes called the ocean conveyor belt, and officially known as thermohaline circulation.
• The global network of ocean currents transports heat from warm equatorial seas to colder polar waters.
• The system consists of warm surface currents and cold deep ocean currents.

Factors responsible for Ocean Currents

1. The Planetary winds: The strongest evidence of prevailing winds on the flow of ocean currents can be witnessed in the North Indian Ocean where there is a change in the direction of ocean currents with a change in direction of the monsoon winds.
2. Temperatures: At the equator, since the temperature is higher the ocean water gets heated up, making the warm water lighter which rises while at the poles, cold water is denser and sinks. Warm water from the equator slowly moves along the surface towards the poles, while the cold water from the poles slowly creeps along the bottom of the sea towards the equator.
3. Salinity: The density of water also depends on its salinity and the salinity of water varies from place to place. Waters of low salinity flow on the surface of waters of high salinity while waters of high salinity flow at the bottom.
4. The Earth’s Rotation: Under the action of Coriolis force, the movement of ocean currents in the northern hemisphere is in the clockwise and in the southern hemisphere it is in the anti-clockwise direction.
5. Obstruction from land: A land mass obstructs the direction of flow of ocean current and divides the ocean current which in turns flow in a different direction.

The Slowdown of Ocean Circulation: How is it happening?

• The slowdown of ocean circulation is directly caused by warming global temperatures and has been predicted by climate scientists – the slowdown is likely not a natural change but the result of human influence.
• The Atlantic Meridional Overturning Circulation (AMOC) transports water across the planet’s oceans, including the Atlantic, Pacific and Indian. The region contributing to the slowdown is the North Atlantic, according to the research.
• If this Atlantic overturning circulation breaks down all together, this will lead to a strong cooling around the northern Atlantic, especially into Europe, into the kind of coastal areas of Britain and Scandinavia.
• In this part of the ocean, the Greenland ice sheets are melting, contributing to both a rise in sea levels and serving to reduce the speed of the circulation.
• Ice melting in Greenland and the heavy rainfall over the North Atlantic induced by climate change has affected the salinity and density of the waters.
• As warm water currents move north, they typically turn back south as it gets cooler and heavier.
• Added freshwater from the melting ice is causing this turn to be slower because of reduced salinity.

About the Atlantic meridional overturning circulation (AMOC)

• The Atlantic meridional overturning circulation (AMOC) is the zonally integrated component of surface and deep currents in the Atlantic Ocean.
• It 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.
• These “limbs” are linked by regions of overturning in the Nordic and Labrador Seas and the Southern Ocean.
• The AMOC is an important component of the Earth’s climate system, and is a result of both atmospheric and thermohaline drivers.
• The net northward heat transport in the Atlantic is unique among global oceans, and is responsible for the relative warmth of the Northern Hemisphere.
• As well as acting as a heat pump and high-latitude heat sink, AMOC is the largest carbon sink in the Northern Hemisphere, sequestering ∼0.7 PgC/year.

-Source: The Hindu