The planet has been flipping between two main modes of carbon recovery depending on the state of coral reefs, new research suggests

Margherita Bassi - Daily Correspondent

December 9, 2025 10:36 a.m.

Research indicates that coral reefs have been tuning Earth’s cycles for hundreds of millions of years. U.S. National Oceanic and Atmospheric Administration, public domain.

Coral reefs are Earth’s most diverse marine ecosystems and a beloved tourist destination. Now, new research reveals that they have also been orchestrating some of the planet’s cycles for hundreds of millions of years.

A new study suggests that the Earth has been flipping between two major modes that help dictate how fast the planet recovers from sudden upticks in carbon dioxide. These modes, which are associated with Earth’s hot and cold climate periods, are influenced by shallow-water reefs, according to the work published December 4 in the journal Proceedings of the National Academy of Sciences.

“Reefs didn’t just respond to climate change—they helped set the tempo of recovery,” says study co-author Tristan Salles, a geoscientist at the University of Sydney, in a statement.

Need to know: What is a coral reef?

Coral reefs are collective structures of hard corals, which are animals made of hundreds to thousands of tiny living organisms called polyps.

For the new work, Salles and his colleagues combined reconstructions of plate tectonics, the climate and Earth’s surface features. That data went into large-scale computer simulations of the planet’s ecology to explore the interplay between carbon and reefs over the past 265 million years.

The researchers found that one of Earth’s major modes occurs when the shallow, warm water areas are extensive and reefs flourish there, causing a buildup of calcium carbonate, the chemical compound that makes up reef structures, Salles and study co-author Laurent Husson, an Earth scientist at the French National Center for Scientific Research, write for the Conversation. That means calcium is tucked away in the corals, so less of it is available in the water to help the ocean absorb carbon dioxide, leaving the gas to linger in the atmosphere.

“As a result, when carbon levels increase due to things like volcanic eruptions, the atmosphere can take hundreds of thousands of years to recover,” the authors write.

The other major mode takes place when reefs diminish or vanish due to tectonic movements, sea-level changes or other factors. During that period, calcium accumulates in the ocean, allowing it to suck in carbon dioxide faster than during periods of thriving reefs.

But that’s just one effect of reef decline. Movement of calcium and carbonate particles to the open ocean also carries nutrients, spurring plankton growth. The teensy algae soak up carbon near the ocean surface. When they die, they sink and transport the carbon to the ocean floor, where it gets buried in deep-sea sediment, Salles and Husson write for the Conversation.

Additionally, fossil records revealed a boom in new types of plankton during periods with diminished reefs, whereas evolutionary change was slower when reefs flourished, since there were fewer nutrients in the open ocean, the team found. That suggests the alternating modes also can determine the rhythm of the evolution of oceanic creatures, intensifying reefs’ influence on the carbon cycle and climate.

The research demonstrates a “deeply intertwined feedback cycle between life and climate,” Alexander Skeels, an evolutionary biologist at the Australian National University who wasn’t involved in the study, tells New Scientist’s James Woodford. While people frequently think that species change because of Earth’s climate, “more and more often we are seeing examples where biological species directly influence the climate itself, creating a co-evolving feedback loop,” he adds.

Today, human carbon dioxide emissions are warming the planet and acidifying the ocean at an unprecedented speed, killing corals and plankton, Salles tells the outlet. Around half of Earth’s reefs have disappeared since 1950, according to a 2021 study.

“From our perspective on the past 250 million years, we know the Earth system will eventually recover from the massive carbon disruption we are now entering. But this recovery will not occur on human timescales,” Salles says in the statement. “Our study shows that geological recovery requires thousands to hundreds of thousands of years.”

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