Researchers report that ancient volcanic rubble (breccia) on the seafloor can sequester large amounts of CO2—on average 7.5% of core weight—from reactions between seawater and cooling lavas. Cores from a 61-million-year-old stretch of the southern Atlantic showed breccia stores two to forty times more carbon than previously sampled upper ocean crust and could hold up to ~20% of the CO2 released when the crust formed. The discovery identifies a previously undercounted carbon reservoir that may help refine models of past carbon cycling and climate.
Ancient Seafloor Lava Rubble Acts as a Giant Carbon 'Sponge,' New Study Shows
Brown rocks of lava rubble store huge amounts of carbon dioxide as calcium carbonate, the white mineral that fills in the gaps in this ocean crust core. | Credit: IODP JRSO
Ancient volcanic rubble scattered across the seafloor can lock away surprisingly large amounts of carbon dioxide, functioning much like a giant carbon 'sponge,' according to research published Nov. 24 in Nature Geoscience.
What the Study Found
Scientists drilled and analyzed long cores from a 61-million-year-old section of crust in the southern Atlantic Ocean and discovered porous volcanic rubble (breccia) cemented with carbonate minerals. These carbon-bearing minerals—formed when CO2 reacted with seawater and basaltic rock—accounted for an average of 7.5% of core weight. That concentration is roughly two to forty times higher than carbon levels measured in previously sampled upper ocean crust.
Rosalind Coggon, University of Southampton: Seawater flows through cracks in cooling lavas for millions of years, reacting with rock and transferring elements between ocean and crust; this process removes CO2 from seawater and sequesters it as carbonate minerals in the rock.
How Much Carbon Can Breccia Store?
Based on the measured carbonate content, the team estimates breccias could store as much as about 20% of the CO2 released when the underlying crust originally formed. Because breccia is porous and widely distributed along mid-ocean ridge systems, it represents a previously undercounted carbon reservoir in the long-term carbon cycle.
Why This Matters
The capacity of breccia to sequester CO2 depends on several factors: the CO2 concentration in seawater at the time of mineral formation, the thickness and extent of breccia deposits on the seafloor, and the spreading rate of mid-ocean ridges. Changes in any of these variables through geologic time could have altered how much carbon the ocean crust removed from the ocean-atmosphere system, with implications for reconstructing past climates and Earth's carbon budget.
Key Details
- Study published Nov. 24 in Nature Geoscience.
- Cores recovered from a 61-million-year-old section of the southern Atlantic contained porous breccia cemented with carbonate minerals.
- Carbonate minerals made up an average of 7.5% of core weight—2 to 40 times higher than previous upper crust samples.
- Breccias could have stored up to ~20% of CO2 released when the crust formed.
- Breccia carbon storage varies with seawater CO2 levels, breccia thickness, and ridge spreading rate.
These findings add an important piece to the puzzle of how undersea geological processes have regulated Earth’s long-term carbon cycle and climate. Incorporating breccia into crustal carbon estimates could refine models of past atmospheric CO2 and climate change.
