A geological revelation: Earth's hidden carbon vault

By willowt // 2025-12-14

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Scientists have discovered a massive, previously unrecognized natural carbon storage system deep beneath the South Atlantic Ocean.
The system consists of porous volcanic rubble, called breccia, formed by the erosion of underwater mountains.
This rock can trap 2 to 40 times more carbon dioxide than typical ocean crust, locking it away for tens of millions of years.
The process involves seawater flowing through the rubble, reacting with the rock to form calcium carbonate minerals that permanently store CO2.
This finding reshapes understanding of Earth's long-term carbon cycle and reveals a key mechanism for stabilizing the planet's climate over geological time.

In a discovery that reshapes our understanding of Earth's climate machinery, an international team of scientists has uncovered a colossal, natural carbon dioxide storage system operating silently beneath the ocean floor. Led by researchers from the University of Southampton, the study, published in December 2025, analyzed rock cores drilled from deep beneath the South Atlantic Ocean. It reveals that vast deposits of eroded volcanic rubble, formed over 60 million years ago, act as a geological sponge, sequestering enormous amounts of CO2 for tens of millions of years and playing a critical, underappreciated role in stabilizing the planet's long-term climate.

Unearthing an ancient climate regulator

The research stems from Expedition 390/393 of the International Ocean Discovery Program (IODP), which drilled into the seafloor of the South Atlantic. Scientists recovered cores of a rock type known as breccia—essentially, piles of broken lava rubble that accumulated from the erosion of underwater mountains along the Mid-Atlantic Ridge. For the first time, researchers had a pristine sample of this material after it had been rafted across the seafloor by tectonic forces for tens of millions of years. Analysis showed these porous rocks were heavily cemented with white calcium carbonate minerals, a clear sign of a long-term chemical conversation between rock and seawater that traps carbon.

The slow dance of the geological carbon cycle

Earth's climate over million-year timescales is governed by the slow carbon cycle, a planetary-scale exchange of carbon between the rocky interior, the oceans and the atmosphere. While volcanic activity at mid-ocean ridges releases CO2 from Earth's mantle into the ocean, a counterbalancing process, known as seafloor weathering, removes it. For millions of years after new oceanic crust forms, seawater percolates through its cracks and pores. This water reacts with the volcanic rock, leaching certain elements and precipitating carbonate minerals—effectively locking dissolved CO2 from the seawater into solid stone. The new study demonstrates that one specific part of the crust is far more effective at this than previously imagined.

A sponge of unprecedented capacity

The breakthrough finding was the sheer volume of carbon stored within the breccia deposits. The team quantified that these rubble piles contained between two and 40 times more CO2 than the solid lava flows typically sampled from the upper ocean crust. Their porosity and permeability create a vastly larger surface area for seawater to interact with, turning them into ultra-efficient carbon sinks. As lead author Dr. Rosalind Coggon of the University of Southampton described, these deposits have a massive capacity to store seawater-derived CO2 as they are gradually cemented over geological time.

Reshaping the carbon budget

This discovery forces a recalculation of the ocean crust's role in the planetary carbon budget. The study estimates that the abundance of such talus breccia formations, particularly at slow-spreading mid-ocean ridges like the Mid-Atlantic Ridge, can accommodate a CO2 sink equivalent to a large proportion of the CO2 released when the crust initially formed. This suggests the process of seafloor carbon uptake is far more significant than known. Furthermore, because the creation of these rubble piles is linked to faulting, which varies with the speed of tectonic spreading, shifts in Earth's tectonic activity over deep time may have directly influenced the climate by altering the efficiency of this hidden carbon vault.

Context for a climate-conscious age

This finding arrives at a moment when human activity has drastically accelerated the transfer of carbon from geological reserves into the atmosphere, overwhelming natural cycles. Understanding Earth's innate balancing mechanisms is more crucial than ever. The research provides a deeper historical context, showing how the planet has naturally regulated CO2 levels over eons through intricate geological processes. It also complements other recent advances, such as the 2021 Nature Communications study highlighting carbon sequestration in subduction zones, painting a fuller picture of Earth as a dynamic, self-regulating system. While not a direct solution to the modern climate crisis, this knowledge of powerful, long-term carbon sinks is vital for accurate climate modeling and underscores the complex planetary system humanity is now impacting.

A new piece in the planetary puzzle

The identification of submarine lava breccia as a major carbon sink represents a fundamental advance in geoscience. It solves a piece of the puzzle in Earth's long-term carbon cycle, revealing where large amounts of carbon have been hidden. The research confirms that the ocean floor is not a passive basin but an active, breathing component of the climate system. As scientists continue to map the prevalence of these formations globally, this hidden vault will become a key variable in models of Earth's past and future climate, reminding us that some of the planet's most powerful climate stabilizers have been operating out of sight, and deep underwater, for millions of years. Sources for this article include: ScienceDaily.com Nature.com ImpactfulNinja.com