Coral reefs are famous for supporting colorful marine life, but new research reveals they have shaped something much larger: the stability of Earth’s carbon cycle and climate over the past 250 million years.
A study published in the Proceedings of the National Academy of Sciences shows that reefs have acted as regulators of how quickly the planet recovers from big spikes in carbon dioxide.
Scientists from the University of Sydney and Université Grenoble Alpes used a combination of plate-tectonic models, climate simulations, and ecological data to reconstruct how shallow-water carbonate systems—like coral reefs—behaved all the way back to the Triassic Period.
They discovered that Earth’s climate system switches between two major modes depending on how much shallow reef habitat exists at any given time.
In the first mode, when tropical oceans have wide continental shelves and reefs are abundant, large amounts of carbonate accumulate in shallow waters.
This slows down the exchange of carbon between surface waters and the deep ocean and weakens the “biological pump,” the process by which marine organisms pull carbon out of the atmosphere. As a result, the planet recovers more slowly from carbon disturbances.
In the second mode, when reefs shrink because of sea-level changes or shifting tectonic plates, the deep ocean becomes the main place where carbonate is buried.
This causes calcium and alkalinity levels in the ocean to rise, which boosts the growth of tiny plankton. These plankton help speed up carbon removal from the atmosphere, allowing Earth to bounce back more quickly from CO₂ spikes.
According to the study, these alternating modes of shallow- versus deep-water carbonate burial did more than just influence climate—they also shaped the evolution of marine plankton and the chemistry of the oceans. Co-author Dr. Laurent Husson explains that when reef habitats collapsed in the past, it set the stage for major expansions in planktonic life.
These changes altered how efficiently the ocean absorbed carbon and regulated the climate system.
The findings reveal that reefs are not just passive victims of climate change but long-standing drivers of Earth’s climate balance.
This deeper understanding has important implications for today. Modern coral reefs are rapidly declining due to warming seas and ocean acidification. If today’s collapse follows the patterns of the ancient past, carbonate burial could shift from shallow reefs to the deep ocean. In theory, this could help remove carbon from the atmosphere more quickly.
But this silver lining comes with a major warning. The organisms that carry out deep-sea carbonate burial—plankton and other calcifiers—are themselves threatened by increasingly acidic oceans.
Any long-term stabilizing effect would only occur after the loss of modern coral ecosystems and vast damage to marine life.
Lead author Associate Professor Tristan Salles emphasizes that while Earth eventually recovers from major carbon disruptions, the process takes thousands to hundreds of thousands of years—far beyond human timescales.
The study reminds us that although the planet is resilient, ecosystems critical to that resilience may not survive the rapid changes happening today.
Source: University of Sydney.
