Ancient deep ocean rocks shown to be long-term carbon storage reservoirs

by Sophie Jenkins
London, UK (SPX) Nov 25, 2025

Rock samples collected from beneath the Atlantic Ocean reveal that lava rubble accumulating on the seafloor can store carbon dioxide for tens of millions of years. Research led by the University of Southampton involved analyzing lava cores extracted during the International Ocean Discovery Program's Expedition 390/393. The study focused on breccias, rocks created from eroded seafloor mountains at mid-ocean ridges, which act as geological sponges for carbon.

Dr Rosalind Coggon, Royal Society Research Fellow at the University of Southampton, said, "We've known for a long time that erosion on the slopes of underwater mountains produces large volumes of volcanic rubble, known as breccia - much like scree slopes on continental mountains. However, our drilling efforts recovered the first cores of this material after it has spent tens of millions of years being rafted across the seafloor as Earth's tectonic plates spread apart. Excitingly, the cores revealed that these porous, permeable deposits have the capacity to store large volumes of seawater CO2 as they are gradually cemented by calcium carbonate minerals that form from seawater as it flows through them."

Carbon cycles between Earth's interior, oceans, and atmosphere over geological timescales, influencing climate. The movement of carbon, particularly how much is stored or released, is tracked by measuring carbon exchanges among these reservoirs.

Dr Coggon noted, "The oceans are paved with volcanic rocks that form at mid-ocean ridges, as the tectonic plates move apart creating new ocean crust. This volcanic activity releases CO2 from deep inside the Earth into the ocean and atmosphere. However, ocean basins are not just a container for seawater. Seawater flows through the cracks in the cooling lavas for millions of years and reacts with the rocks, transferring elements between the ocean and rock. This process removes CO2 from the water and stores it in minerals like calcium carbonate in the rock."

By examining the drilled samples, researchers found that some lava breccias contained between two and forty times more CO2 than previously sampled oceanic lavas. The team identified breccia formation at mid-ocean ridges as a significant mechanism for long-term carbon storage in the Earth's carbon cycle.

Research Report: A geological carbon cycle sink hosted by ocean crust talus breccias