Scientists have discovered that piles of ancient lava rubble deep beneath the ocean floor can store massive amounts of carbon dioxide for millions of years.
This new finding offers important clues about how Earth naturally regulates its climate over long periods of time.
The research team, led by the University of Southampton, studied rock samples drilled from beneath the South Atlantic Ocean.
These rocks are around 60 million years old and come from volcanic mountains on the seafloor.
Over time, erosion breaks these underwater mountains apart, creating large deposits of loose volcanic rubble called breccia—similar to the rocky slopes of mountains on land. Until now, scientists did not realize how important these deposits are in trapping carbon.
For the first time, researchers were able to retrieve deep cores of this rubble that had slowly drifted with the spreading ocean floor.
When Dr. Rosalind Coggon and her team examined the samples, they noticed something remarkable: the porous, sponge-like structure of the rubble had absorbed huge amounts of carbon dioxide from seawater.
Seawater naturally flows through cracks in cooling volcanic rocks for millions of years. As it moves through, chemical reactions occur between the water and the rock.
These reactions cause carbon from the seawater to form solid minerals like calcium carbonate, which then fill up the tiny spaces inside the rubble. This process effectively locks the carbon away for extremely long periods of time.
Dr. Coggon explains that the seafloor is constantly being reshaped by volcanic activity. As new ocean crust forms at mid-ocean ridges, carbon dioxide from Earth’s interior is released into the ocean and atmosphere.
But at the same time, the ocean crust absorbs carbon back into the rocks through these reactions. Understanding this balance is essential for learning how Earth’s climate has changed over millions of years.
The team found that the lava rubble they drilled contained between two and forty times more carbon dioxide than any previously studied seafloor lavas. This means that breccia—these deposits of broken-up volcanic rock—are far more important in Earth’s long-term carbon storage than scientists previously realized.
The discovery highlights a hidden part of the planet’s natural carbon cycle. These deep-sea lava deposits act as geological carbon banks, helping regulate the amount of CO₂ in Earth’s oceans and atmosphere over time.
This work was carried out as part of the International Ocean Discovery Program’s Expedition 390/393, using the research vessel Joides Resolution.
The findings add a major piece to the puzzle of how Earth manages carbon and maintains a stable climate over geological timescales.
