Explained: Deep-Water Circulations of Indian Ocean

Context

Studies suggest that tectonically driven changes in the ocean gateways such as the closure of the Central American Seaway, had a dramatic impact on the circulation.

Probable Question

What do you understand by deep-water circulation? Elucidate. (150 words, 10 marks)

About the recent Findings of the Studies

• The tectonic changes might have led to the formation of two separate water bodies:
  • Northern component water in the North Atlantic.
  • Antarctic Bottom Water (AABW) in the Southern Ocean. 
• Tectonic driven changes 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 circulation.
• There would have been large-scale changes in the Deep Water Circulation (DWC) in the oceans across the world, thus impacting global climate through ocean-atmosphere carbon dioxide and heat exchanges.

Also Read: The Indus Water Treaty

Centre and State Powers over Water Resources

Deep Water Circulation (DWC) in the oceans

• Winds drive ocean currents in the upper 100 meters of the ocean’s surface. Similarly the current also flows thousands of meters below the surface. DWC is the movement of water at this deep level. 
• It is driven by differences in the water’s density, which is controlled by temperature (thermo) and salinity (haline). This process is known as thermohaline circulation.
• In the Earth's polar regions ocean water gets very cold, forming sea ice. As a consequence the surrounding seawater gets saltier, because when sea ice forms, the salt is left behind. 
• As the seawater gets saltier, its density increases, and it starts to sink. Surface water is pulled in to replace the sinking water, which in turn eventually becomes cold and salty enough to sink. 

Significance 

• Heat Distribution: It is the equatorward transport of cold, deep waters and the poleward transport of warm, near-surface waters controls ocean heat distribution.
• Atmospheric carbon dioxide levels: This mechanism also helps in controlling atmospheric carbon dioxide levels.
• Global Climate: This procedure plays a critical role in global climate. 

Indian Ocean Deep water Circulation

• The Indian Ocean does not have any major deep-water formations of its own. 
• It acts only as a host for Northern component water in the North Atlantic and Antarctic Bottom Water (AABW) in the Southern Ocean. 
• Further, the northern parts of the Indian Ocean are located at one of the terminal ends of the GOC, far away from the deep-water formation regions and oceanic seaways. 
• These specific features could make the northern Indian Ocean an ideal basin to do this.

Studies Carried in the Indian Ocean

Purpose

• It is carried out to reconstruct past deep water circulations based on iron-manganese crust records and authigenic neodymium isotope composition of sediment cores. 

Limitation

Iron-manganese crusts are situated at deeper depths and are bathed only by AABW, making it suitable only for the reconstruction of the history of AABW.

• Authigenic neodymium isotope records are available only from the Bay of Bengal region. This also cannot help as the Himalayan rivers that empty into the Bay also bring in substantial amounts of Neodymium particulates. 

Significance 

• A team of researchers from the Goa-based National Centre for Polar has now sorted out the issue. 
• The scientists have generated an authigenic neodymium isotope record from the Arabian Sea and reconstructed the DWC record of the Indian Ocean for the period from 11.3 million years ago (Miocene era) to 1.98 million years ago (Pleistocene era). 
• This is a clear shift from the Pacific water dominated deep circulation system. 
• This finding also suggests a widespread impact of the late Miocene Central American Seaway closure on the evolution of ocean deep water circulation and validates the so-called Panama Closure Hypothesis.

• The study is highly significant since it provides unequivocal evidence in support of the theory that the closing of the gap between North and South America had led to the evolution of the modern form of GOC. 
• The work is also commendable as it involved extremely difficult measurements.

Frequently Asked Questions

1.What is deep water circulation called?

Ans. Winds drive ocean currents in the upper 100 meters of the ocean’s surface. Similarly the current also flows thousands of meters below the surface. Deep water circulation is the movement of water at this deep level. 

2.What causes circulation in deep water?

Ans. It is driven by differences in the water’s density, which is controlled by temperature (thermo) and salinity (haline). This process is known as thermohaline circulation.

News Source: The Hindu

https://www.thehindu.com/sci-tech/reconstructing-past-deep-water-circulations-of-indian-ocean/article66377125.ece

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