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Reconstructing past deep-water circulations of Indian Ocean

Published

3 years ago

2023/01/17

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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Heat index likely to increase up to ‘Caution level’ at some places in the Northern, North-central, North-western, Western, Sabaragamuwa, Southern and Eastern provinces and Monaragala district

Published

13 hours ago

2026/04/12

Priyan

Warm Weather Advisory
Issued by the Natural Hazards Early Warning Centre at 3.30 p.m. on 11 April 2026, valid for 12 April 2026

The Heat index, the temperature felt on the human body is likely to increase up to ‘Caution level’ at some places in the Northern, North-central, North-western, Western, Sabaragamuwa, Southern and Eastern provinces and Monaragala district.

The Heat Index Forecast is calculated by using relative humidity and maximum temperature and this is the condition that is felt on your body. This is not the forecast of maximum temperature. It is generated by the Department of Meteorology for the next day period and prepared by using global numerical weather prediction model data.

Effect of the heat index on human body is mentioned in the above table and it is prepared on the advice of the Ministry of Health and Indigenous Medical Services.

ACTION REQUIRED

Job sites: Stay hydrated and takes breaks in the shade as often as possible.
Indoors: Check up on the elderly and the sick.
Vehicles: Never leave children unattended.
Outdoors: Limit strenuous outdoor activities, find shade and stay hydrated.
Dress: Wear lightweight and white or light-colored clothing.

Note: In addition, please refer to advisories issued by the Disaster Preparedness & Response Division, Ministry of Health in this regard as well. For further clarifications please contact 011-7446491.

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Sun directly overhead Cheddikulam, Kebithigollewa, Gomarankadawala and Nilaveli about 12:11 noon. today [12]

Published

13 hours ago

2026/04/12

Priyan

On the apparent northward relative motion of the sun, it is going to be directly over the latitudes of Sri Lanka from 05th to 15th of April in this year.

The nearest areas of Sri Lanka over which the sun is overhead today (12th) are Cheddikulam, Kebithigollewa, Gomarankadawala and Nilaveli about 12:11 noon.

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CEB orders temporary shutdown of large rooftop solar systems

Published

13 hours ago

2026/04/12

Thilina Walpola

The Ceylon Electricity Board (CEB) has directed owners of large-scale rooftop solar systems to temporarily disconnect their installations for a 10-day period beginning from Friday (April 10), citing growing concerns over grid stability amid low electricity demand and high solar generation.

The directive applies to rooftop solar systems exceeding 300 kW capacity, which are required to remain switched off until April 20. The move coincides with the extended holiday season, during which national electricity demand typically declines, alongside prevailing sunny weather conditions that significantly increase solar output.

Senior electrical engineers told The Island that the decision, though exceptional, was necessitated by operational risks posed to the national grid.

“We are seeing a pronounced imbalance between supply and demand,” a senior CEB system control engineer said. “With industries and commercial establishments operating at reduced levels during the holidays, demand drops. At the same time, solar generation remains high, creating excess power that the grid struggles to absorb.”

He explained that such imbalances could lead to fluctuations in system frequency, potentially threatening the stability of the grid. “If generation exceeds demand, frequency rises beyond acceptable limits.

This can trigger automatic protection mechanisms or, in extreme cases, lead to partial outages.”Another senior engineer attached to the transmission division noted that managing distributed solar generation remains a technical challenge.

“Unlike conventional power plants, rooftop solar systems are not centrally dispatchable. We cannot directly control their output in real time. This limits our ability to balance the system during periods of excess generation,” he said.

He added that the country’s grid infrastructure is still adapting to the rapid growth of renewable energy. “We lack sufficient large-scale battery storage and advanced grid management systems to effectively handle these fluctuations. Until such capabilities are enhanced, temporary curtailment becomes necessary.”

Engineers also pointed out that conventional thermal plants cannot be abruptly shut down or adjusted to compensate for sudden surges in solar generation.

“These plants require minimum stable operating levels. When solar floods the grid during low demand, it creates operational constraints that are not easy to manage,” one official said.

The CEB, in its statement, expressed appreciation for the cooperation of solar system owners affected by the measure, stressing that it is a short-term intervention aimed at ensuring uninterrupted and stable electricity supply across the country.

Energy experts say the development underscores the urgent need for grid modernization, including investment in battery energy storage systems, smart grid technologies, and improved demand-side management.

“This is part of the transition challenge,” an independent analyst noted. “As solar penetration increases, the grid must evolve to become more flexible. Otherwise, curtailment will remain a recurring necessity.”

Despite the temporary shutdown, CEB engineers reaffirmed their commitment to expanding renewable energy.

“Solar power is a key pillar of Sri Lanka’s future energy mix,” a senior engineer said. “But integration must be carefully managed. Grid stability cannot be compromised.”

The temporary disconnection order, which took effect yesterday, marks a critical moment in Sri Lanka’s energy transition—highlighting both the progress made in renewable energy adoption and the technical hurdles that remain.

By Ifham Nizam