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Reconstructing past deep-water circulations of Indian Ocean

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The global conveyor belt, shown in part here, circulates cool subsurface water and warm surface water throughout the world. The Atlantic Meridional Overturning Circulation is part of this complex system of global ocean currents.

Global overturning circulation — the equatorward transport of cold, deep waters and the poleward transport of warm, near-surface waters — controls ocean heat distribution and atmospheric carbon dioxide levels, thus playing a critical role in global climate, says a report published by The Hindu yesterday.

It said: 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 the circulation.

It is thought that tectonic changes might have led to the formation of two separate water bodies — northern component water in the North Atlantic and Antarctic Bottom Water (AABW) in the Southern Ocean. Consequently, it is also hypothesised that 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.

But these formulations have remained untested due to lack of adequate data. Some records that are available are from near the deep-water formation regions mostly from the Pacific and the Atlantic Oceans. Hence, they might not necessarily reflect the impact and change in deep water circulation.

Now, the Indian Ocean does not have any major deep-water formations of its own. It acts only as a host for NCW and AABW. 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.

Few studies have been carried out in the Indian Ocean to reconstruct past deep water circulations based on iron-manganese crust records and authigenic neodymium isotope composition of sediment cores. But 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, and authigenic neodymium isotope records are available only from the Bay of Bengal region. But they too cannot help as the Himalayan rivers that empty into the Bay also bring in substantial amounts of Neodymium particulates.

A new study by a team of researchers from the Goa-based National Centre for Polar and Ocean Research and the School of Earth, Ocean and Atmospheric Sciences in Goa University 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).

“The record shows a clear shift from the Pacific water dominated deep circulation system before 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). Our 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,” says Dr. Waliur Rahaman from the National Centre for Polar and Ocean Research (NCPOR) and one of the corresponding authors.

The two months long expedition was carried out on-board drilling vessel R/V JOIDES Resolution from March 31 to May 31, 2015.

Commenting on the findings, Dr. Sambuddha Misra, Associate Professor, Centre for Earth Sciences, Indian Institute of Science, who was not part of the research work, says 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, he adds.



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Navy seizes an Indian fishing trawler poaching in Sri Lankan waters north of Talaimannar

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During an operation conducted in the wee hours of Tuesday (23 Dec 25), the Sri Lanka Navy seized an Indian fishing trawler  and apprehended 12 Indian fishermen, while they were poaching in Sri Lankan waters north of Talaimannar.

Recognizing the detrimental effects of poaching on marine resources and the livelihoods of local fishing communities, the Sri Lanka Navy continues to conduct regular operations as
proactive measures to deter such activities. These efforts underscore the collective robust approach steadfast commitment to safeguarding the nation’s marine ecosystems while ensuring the economic security and wellbeing of its citizens.

The fishing trawler along with the fishermen held in this operation was handed over to the Fisheries Inspector of Mannar for onward legal proceedings.

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India’s External Affairs Minister meets Sri Lanka PM

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India’s External Affairs Minister, Dr. Subramaniam Jaishankar, met with the Prime Minister of Sri Lanka, Dr. Harini Amarasuriya, on 23 December at Temple Trees, during his visit to Sri Lanka as the Special Envoy of Indian Prime Minister Shri Narendra Modi.

The meeting took place as part of the official visit aimed at holding discussions with Sri Lanka’s top leadership, at a time when the nation commenced reconstruction efforts following the devastation caused by Cyclone Ditwah.

During the discussions, the Minister of External Affairs of India reaffirmed readiness to extend support for Sri Lanka, including assistance in rebuilding railways, bridges, and strengthening of the agricultural sector in the country. He also highlighted the importance of having effective systems in place to respond to disaster situations, supported by strong legislative, administrative, and institutional frameworks. Both sides reviewed ongoing relief efforts and explored avenues to further strengthen bilateral cooperation in disaster response and recovery.

The Prime Minister commended the Government of India for the continued support, noting that the recovery process following the devastation caused by Cyclone Ditwah include beyond immediate relief efforts to long-term measures such as resettlement, and reconstruction of habilitation and infrastructure.

The Prime Minister further stated that steps have been taken to reopen schools as part of the process of restoring normalcy, with close monitoring in place. The Prime Minister emphasized the need to ensure stability, reduce vulnerability, and strengthen protection mechanisms highlighting the solidarity of the people, their strong spirit of volunteerism, and collective action demonstrated during the emergency situation.

The event was attended by the High Commissioner of India Santosh Jha, Additional Secretary (IOR), MEA  Puneet Agrawal, Joint Secretary (EAMO), MEA  Sandeep Kumar Bayyapu, Deputy High Commissioner Dr. Satyanjal Pandey, and representing Sri Lankan delegation, Secretary to the Prime Minister  Pradeep Saputhanthri, Additional Secretary to the Prime minister Ms.Sagarika Bogahawatta, Director General (South Asia), Ministry of Foreign Affairs Samantha Pathirana, Deputy Director, South Asia Division, Ministry of Foreign Affairs Ms.Diana Perera.

[Prime minister’s media division]

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Sri Lanka’s coastline faces unfolding catastrophe: Expert

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Sri Lanka is standing on the edge of a coastal catastrophe, with the nation’s lifeline rapidly eroding under the combined assault of climate change, reckless development and weak compliance, Director General of the Department of Coast Conservation and Coastal Resource Management (DCC&CRM) Dr. Terney Pradeep Kumara has warned.

“This is no longer an environmental warning we can afford to ignore. The crisis is already unfolding before our eyes,” Dr. Kumara told The Island, cautioning that the degradation of Sri Lanka’s 1,620-kilometre coastline has reached a point where delayed action could trigger irreversible damage to ecosystems, livelihoods and national security.

He said accelerating coastal erosion, rising sea levels, saltwater intrusion and the collapse of natural barriers, such as coral reefs and mangroves, are placing entire coastal communities at risk. “When mangroves disappear and reefs are destroyed, villages lose their first line of defence. What follows are floods, loss of homes, declining fisheries and forced displacement,” he said.

Dr. Kumara stressed that the coastline is not merely a development frontier but the backbone of Sri Lanka’s economy and cultural identity. “More than half of our tourism assets, fisheries and key infrastructure are concentrated along the coast.

If the coast fails, the economy will feel the shock immediately,” he warned.

Condemning unregulated construction, illegal sand mining and environmentally blind infrastructure projects, he said short-term economic interests are pushing the coastline towards collapse. “We cannot keep fixing one eroding beach while creating three new erosion sites elsewhere. That is not management—it is destruction,” he said, calling for science-driven, ecosystem-based solutions instead of politically convenient quick fixes.

The Director General said the Department is intensifying enforcement and shifting towards integrated coastal zone management, but warned that laws alone will not save the coast. “This is a shared responsibility. Policymakers, developers, local authorities and the public must understand that every illegal structure, every destroyed mangrove, weakens the island’s natural shield,” he added.

With climate change intensifying storms and sea surges, Dr. Kumara warned that Sri Lanka’s vulnerability will only worsen without urgent, coordinated national action. “The sea has shaped this nation’s history and protected it for centuries. If we fail to protect the coast today, we will be remembered as the generation that allowed the island itself to be slowly eaten away,” he went on to say.

By Ifham Nizam

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