Rock samples that formed about 60 million years ago and were collected from far below the ocean surface have helped scientists understand how large amounts of carbon dioxide can remain locked up for extremely long periods. These samples show that CO2 It is trapped between layers of lava debris that accumulate on the seabed.
Researchers examined lava material drilled from the depths of the South Atlantic Ocean to measure the amount of CO2 It is incorporated into these rocks through interactions between seawater and cooling volcanic material.
Work led by the University of Southampton shows that these accumulations of broken lava, created as underwater mountains erode, act as natural reservoirs of CO2. This study marks the first time their role as extensive carbon-retaining structures has been clearly recognized, offering new insight into how Earth manages carbon over millions of years.
Lava debris as long-term geological “sponge”
Lead author Dr Rosalind Coggon, Royal Society Research Fellow at the University of Southampton, explained: “We have known for a long time that erosion on the slopes of seamounts produces large volumes of volcanic debris, known as breccias, much like the scree slopes of continental mountains.
“However, our drilling efforts recovered the first cores of this material after it spent tens of millions of years being rafted across the seafloor as Earth’s tectonic plates moved apart.
“Interestingly, the cores revealed that these porous and permeable deposits have the capacity to store large volumes of CO2 in seawater.2 as they gradually become cemented with calcium carbonate minerals that form from the seawater flowing through them.”
How carbon moves through the Earth over geological time
The amount of carbon dioxide in the atmosphere is influenced by the slow exchange of carbon between the Earth’s interior, oceans and air over many millions of years. Understanding this long-term carbon cycle requires studying where and how carbon is added or removed in different parts of the planet.
Dr Coggon said: “The oceans are paved with volcanic rocks that form at mid-ocean ridges, as tectonic plates move apart creating new oceanic crust. This volcanic activity releases CO2 from the depths of the Earth to the ocean and atmosphere.
“However, ocean basins are not just a container for seawater. Seawater flows for millions of years through the cracks of cooling lavas and reacts with the rocks, transferring elements between the ocean and the rocks. This process removes CO2 from water and stores it in minerals such as calcium carbonate in rock.
As part of the project, the team quantified the amount of CO2 It is incorporated into the ocean crust through these chemical reactions.
Discovering much larger CO₂ storage in Breccia
“While drilling deep into the seafloor of the South Atlantic, we discovered lava debris containing between two and 40 times more CO2 than previously sampled lavas,” Dr. Coggon said.
“This study revealed the importance of such a gap, which forms due to the erosion of seafloor mountains along mid-ocean ridges, as a carbon sponge in the long-term carbon cycle.”
The findings come from Expedition 390/393 of the International Ocean Discovery Programme.
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