Bhubaneswar: 2023 was the hottest year on record. 2024 was not far behind. With rising temperature impacting the globe, a new study has predicted that the changes across oceans have precipitated major coral bleaching.

The findings, published in journal Oxford  Open Climate Change https://academic.oup.com/oocc/article/4/1/kgae005/7666987?searchresult=1

indicated that the extensive coral bleaching pointed to a more severe change - the shifting ocean currents. Ocean currents play a pivotal role in heat distribution across the globe. The continuous, directional movements of seawater are driven by a combination of factors, including wind, temperature differences, the Earth's rotation (Coriolis effect), and differences in water density. While warm ocean currents carry heat from the tropics towards the poles, cold ocean currents bring cooler water from higher latitudes towards the equator, thus effecting regulation of extreme temperatures.

It revealed that in 2023, all major warm currents showed extreme warming suggesting that heat transport from the tropics to the polar regions had accelerated. While the tropics became cooler, the polar regions saw accelerated ice melting albedo feedbacks, and increasing ocean stratification. All major cold currents too showed extreme warming during the said year, leading to consequent dip in upwelling and vertical mixing, and increased vertical stratification.

First seen in the Caribbean, parts of Mexico, Fiji, Central America and Eastern New Guinea, near total bleaching and deaths of coral reefs in areas which reported high sea surface temperatures (SSTs). For instance, Jamaica which experienced the highest SST in 2023, witnessed the worst reef bleaching and coral mortality ever seen across the entire Caribbean Region since the first mass bleaching event in 1987.

While the Northern Hemisphere saw the worst coral bleaching in 2023, the Southern Hemisphere is showing similar trends this year.

A Hotspot analysis, which oversees surface waters with excess temperature more than one degree C above the average temperature during the warmest month at that site as a predictor of coral reef bleaching, showed a direct relation between coral mortality and cumulative heat stress.

The paper's lead author Thomas Goreau attributed the phenomenon to extreme temperature changes.

“Being the most vulnerable of all ecosystems, coral reefs began to bleach and die from high temperatures starting in the 1980s. Most coral around the world has been killed, and survivors can’t take more warming. The sudden rise in global temperature during 2023 further imperils coral reefs, and indicates large-scale changes in ocean circulation are underway, causing positive feedback that amplifies global warming, which is not included in IPCC models,” he said.