New geological findings from the South Atlantic have revealed a quiet but powerful climate mechanism hiding on the seafloor. Scientists studying sixty-million-year-old rock cores have discovered that huge accumulations of broken lava fragments, created as underwater volcanoes erode, serve as long-term carbon vaults. These loose, highly porous deposits capture carbon dioxide from seawater and lock it inside carbonate minerals that remain stable for geological timescales.

The study, led by researchers from the University of Southampton, provides rare insight into how the ocean crust acts not just as a foundation for Earth’s basins, but also as an active participant in the planet’s long-term carbon cycle.

The Carbon-Trapping Architecture of Lava Rubble

The rubble fields that surround submarine volcanoes, formally known as volcanic breccias, behave very differently from the dense basalt formations that most people associate with the ocean crust. These deposits resemble underwater scree slopes, with large blocks and fine fragments mixed into thick piles. As seawater circulates through these open networks, chemical reactions transform dissolved carbon dioxide into stable carbonate minerals. Over millions of years, these minerals slowly bind the loose fragments together, storing carbon inside newly formed stone. Dr Rosalind Coggon, the study’s lead author, explained that scientists have long assumed these deposits existed but had never retrieved intact samples after tens of millions of years of seafloor travel. The new cores offered the first direct look at how much carbon these rubble layers can hold. According to Coggon, the findings were striking. The breccia samples contained two to forty times more carbon than intact volcanic rocks from similar settings, confirming that their open structure dramatically boosts their ability to trap carbon.

A Hidden Engine in the Deep Carbon Cycle

Earth’s climate stability over deep time depends on the slow exchange of carbon among the atmosphere, oceans and the planet’s interior. Mid-ocean ridges release carbon dioxide as new crust forms. As that crust cools and moves away from the ridge, it begins absorbing carbon again through a vast network of cracks and cavities. The new South Atlantic cores captured this process in action. Their high carbonate content showed that cold seawater circulated through the rubble for millions of years, extracting CO2 and storing it as minerals. This behaviour makes volcanic breccia a far more efficient carbon sink than standard ocean crust. Intact basalts weather slowly, with limited exposure to circulating fluids. In contrast, rubble deposits offer enormous surface area for chemical reactions and wide channels for water movement, accelerating carbonate formation. These findings suggest that global carbon models may have been missing a crucial reservoir. Wherever underwater volcanoes grow and collapse, they leave behind rubble fields that drift with the tectonic plates. Over time, these fields quietly sequester significant amounts of carbon.

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Why the Ocean Crust Matters for Long-Term Climate Stability?

The fact that rubble deposits outperform solid lava in carbon storage carries major implications for understanding ancient climates. If breccia layers are widespread, they may have played a larger role than previously recognised in balancing atmospheric CO2 over geological history. Although this process cannot address modern emissions on human timescales, it provides essential context for how Earth avoided runaway climate scenarios in the past. As Coggon notes, volcanic activity adds carbon to the atmosphere, but the cooling ocean crust acts as a counterbalance, steadily pulling carbon back out. This natural slow loop, regulated by plate motions and seafloor chemistry, has shaped global temperatures for tens of millions of years.

Inside the Seafloor Laboratory: Rare Cores from a Traveling Crust

Reaching these ancient breccia deposits required drilling deep into seafloor sections that formed at a mid-ocean ridge before migrating across the basin on a moving tectonic plate. Their long journey preserved a continuous record of seawater circulation and carbonate formation. The drilling operation retrieved rubble that had been gradually cemented by calcium carbonate. Even after microbial activity waned, the remaining biofilms and mineral networks continued to pass electrons and support chemical reactions, leaving behind a clear signature of long-term carbon storage. The cores provided a complete view of how water flowed through the deposits, where carbonates accumulated, and how the rubble transitioned from loose volcanic debris to a structured, high-capacity carbon sink.

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A New Perspective on the Ocean Floor’s Climate Role

The study’s biggest contribution is its recognition that volcanic breccias, not just solid basalt, are essential to Earth’s deep carbon storage. Because breccias form wherever underwater volcanoes collapse or shed debris, their total footprint across the ocean floor is significant. As a result, these rubble fields may represent one of the planet’s most overlooked carbon repositories. The work also reinforces an important message: Earth’s natural climate controls rely on processes that unfold slowly but consistently. While they do not offer a solution for today’s accelerating emissions, they reveal how the planet has buffered itself against climate extremes through deep time. Volcanic rubble may appear chaotic from the outside, but beneath the waves it creates a remarkably ordered system. Over millions of years, it transforms from fractured stone into a quiet, dependable custodian of carbon.

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