Science & Tech

Reconstructing Past Deep-Water

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

Global overturning circulation (GOC)

  • It is the transport of cold, deep waters equatorward and warm, near-surface waters poleward.
  • It regulates ocean heat distribution and atmospheric CO2 levels, and thus plays an important role in global climate.

Concept: Panama Closure Hypothesis

  • This article focuses on the Panama Closure Hypothesis.
  • According to the Panama Hypothesis, the gradual closure of the Panama Seaway between 13 million years ago (13 Ma) and 2.6 Ma resulted in less mixing of Atlantic and Pacific water masses.
  • As a result, the North Atlantic Deep water circulation formed.
  • It boosted the Atlantic thermohaline circulation, increased North Atlantic temperatures and evaporation, and increased precipitation in Northern Hemisphere high latitudes.

The Effects of the Panama Canal Closure

  • Tectonic changes are thought to have resulted in the formation of two distinct water bodies: northern component water in the North Atlantic and Antarctic Bottom Water (AABW) in the Southern Ocean.
  • As a result, it is also hypothesised that large-scale changes in Deep Water Circulation (DWC) in the world’s oceans would have occurred.
  • The impact on the Indian Ocean gyre
  • The Indian Ocean lacks major deep-water formations of its own.
  • It only serves as a host for NCW and AABW.
  • Furthermore, the northern Indian Ocean is located at one of the GOC’s terminal ends, far from deep-water formation regions and oceanic seaways.

New research findings

  • The researchers created an authigenic neodymium isotope record from the Arabian Sea and reconstructed the Indian Ocean’s DWC record from 11.3 million years ago (Miocene era) to 1.98 million years ago (Pleistocene era).
  • The record shows a clear shift from a Pacific water-dominated deep circulation system to the emergence of a modern-like deep water circulation system in the Indian Ocean around nine million years ago.
  • During the Miocene-Pliocene transition, it was composed of Antarctic bottom water and northern component water (about six million years ago).
  • This suggests that the late Miocene Central American Seaway closure had a widespread impact on the evolution of ocean deep water circulation and validates the so-called Panama Closure Hypothesis.

Back2Basics: Indian Ocean Circulation

  • The Indian Ocean circulation/gyre is one of the five major oceanic gyres, which are large systems of rotating ocean currents that form the backbone of the global conveyor belt.
  • The South Equatorial Current and the West Australian Current are the two major currents that make up the Indian Ocean gyre.
  • The Indian Ocean gyre, which normally moves counter-clockwise, reverses direction in the winter due to the seasonal winds of the South Asian Monsoon.

How does it function?

  • In the summer, the land is warmer than the ocean, so surface winds blow from the ocean to the land.
  • During the winter, however, these temperatures reverse, causing winds to blow from the land to the sea.
  • Air pressure gradients over the Indian Ocean and the gyre are small because the majority of the air pressure gradient is retained behind the Tibetan plateau.
  • As a result of the protection from the full-force winds blowing off the Mongolian high-pressure region, winds of moderate strength prevail.
  • The Winter Monsoon season in the Indian Ocean region is the dry season for most of Southern Asia due to these moderate, dry winds.
  • The Indian Ocean currents, which comprise the Indian Ocean gyre, are directly affected by this seasonal wind cycle, causing reversal.
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