Reconstructing past deep-water circulations of Indian Ocean

Source: The post is based on the article “Reconstructing past deep-water circulations of Indian Ocean” published in The Hindu on 15th January 2023.

What is the News?

Studies have indicated that tectonically driven changes in the ocean gateways had a dramatic impact on the Global Overturning Circulation(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.

It controls ocean heat distribution and atmospheric carbon dioxide levels, thus playing a critical role in global climate.

What was the impact of tectonic changes in ocean gateways on ocean circulation?

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 ocean circulation.

These changes may have led to the creation of two distinct water bodies: 1) Northern component water in the North Atlantic Ocean and 2) Antarctic Bottom Water (AABW) in the Southern Ocean.

Consequently, it is also hypothesized that there would have been large-scale changes in the Deep-Water Circulation (DWC) in the oceans across the world, impacting global climate and heat exchanges. But these formulations have remained untested due to a lack of adequate data.

What about deep water circulations of the Indian Ocean?

The Indian Ocean does not produce its own deep water, it only receives it from other sources such as the North Atlantic and Antarctic.

The northern part of the Indian Ocean is located far away from the areas where deep water is formed and ocean routes, making it a good place to study the impact of ocean circulation changes.

Studies have been done in the Indian Ocean to understand past deepwater circulation using records from iron-manganese crusts and the authigenic neodymium isotope composition of sediment cores.

But these records have certain limitations such as data being available only for the Bay of Bengal region and Himalayan rivers bringing a substantial amount of neodymium particulates.

How did the new study overcome these limitations?

A new study by a team of researchers has 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).

The record shows a clear shift from the Pacific water-dominated deep circulation system about nine million years ago, to the onset of a modern-like deep water circulation system in the Indian Ocean comprising of Antarctic bottom water and northern component water during the Miocene-Pliocene transition (about six million years ago).

The finding 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.

What is Panama Closure Hypothesis?

The “Panama Hypothesis” states that the gradual closure of the Panama Seaway, between 13 million years ago (13 Ma) and 2.6 Ma has led to decreased mixing of Atlantic and Pacific water Masses.

This led to the formation of North Atlantic Deep water and strengthening of the Atlantic thermohaline circulation, increased temperatures and evaporation in the North Atlantic and increased precipitation in Northern Hemisphere (NH) high latitudes.