A newly uncovered geological phenomenon could redefine our understanding of the Earth’s carbon cycle, revealing how ocean crust talus breccias act as significant reservoirs for carbon. Researchers investigating the western flank of the slow-spreading southern Mid-Atlantic Ridge have identified a vast carbon store within basaltic talus breccias, drawing attention to the critical role that oceanic crust structure plays in regulating carbon storage and release. This discovery offers critical insights into the processes controlling the geological carbon cycle, especially in deep-sea environments shaped by tectonic activity.
Basaltic talus breccias, comprised of angular fragments of volcanic rock, were previously studied for their geological formation and physical properties but have now been recognized as important carbon sinks. These breccias display remarkably high primary porosity and an extensive internal surface area, providing ample sites for the precipitation of carbonate minerals. When dissolved carbon from seawater percolates through these porous rocks, it precipitates as calcium carbonate (CaCO3), effectively trapping carbon within the ocean floor’s upper crust. This mineralization process turns talus breccias into geological sponges, absorbing carbon dioxide and converting it into solid carbonate minerals.
The formation of basaltic breccia is closely linked to specific tectonic and magmatic activities along mid-ocean ridges. These breccias typically form from the collapse of volcanic cones or through mass wasting events along fracture zones and seamount flanks. Importantly, the study suggests that similar CaCO3 precipitation processes should occur in these breccias as they age, implying a widespread carbon-sequestering mechanism along mid-ocean ridge systems. Given that basaltic breccias exist globally along slow- to intermediate-spreading ridges, this phenomenon likely plays a pivotal role in the Earth’s carbon cycle on a planetary scale.
The research was conducted on core sample U1557, which was extracted from a faulted basin at the base of an axial valley at the southern Mid-Atlantic Ridge. This axial valley normal faulting region is representative of broader tectonic processes that generate talus breccias. The structural setting promotes exposure of fresh basalt fragments and the creation of open spaces favorable for fluid flow, enabling carbonate mineral deposition. Because these conditions are common at other slow- to intermediate-spreading ridges, the findings substantiate the global relevance of CaCO3-cemented talus breccias as long-term carbon sinks.
One of the most striking implications of this new understanding concerns the connection between tectonic spreading rates and the global carbon budget. The length and spreading rates of mid-ocean ridges have fluctuated over geological time. Variations in these parameters would consequently alter the volume of talus breccia formation and, therefore, the overall capacity of the oceanic crust to sequester carbon in the form of carbonate minerals. This realization underscores the need for dynamic models of the long-term carbon cycle to integrate tectonic spreading rate variations to more accurately predict carbon fluxes related to ocean crust processes.
The tectonic processes generating talus breccias contribute to a rugged basement topography along the ridge flanks that persists for tens of millions of years. This rough terrain stays only partially covered by sediment, thus maintaining permeability and facilitating ongoing fluid circulation. Such prolonged fluid flow pathways are essential for the sustained precipitation and petrographical development of carbonate minerals in these crustal reservoirs. As a result, these rocks continue to absorb and immobilize carbon far beyond initial formation periods, adding an important temporal dimension to carbon sequestration at mid-ocean ridges.
The fluid circulation through basaltic talus breccias is controlled by a complex interplay of geological and hydrological processes. Seawater penetrates deep into fracture networks and porous breccias, where it becomes supersaturated with respect to carbonate minerals. The interaction between basalt glass, hydrothermal fluids, and seawater chemistry drives the precipitation of CaCO3, which cements breccia fragments together and effectively locks in carbon. This process not only impacts carbon sequestration but also influences ocean crust alteration, rock permeability, and potentially regional geochemical cycling.
From a climatic perspective, the discovery of these geological carbon sinks raises important questions about their influence on long-term atmospheric CO2 levels. Traditionally, mid-ocean ridges were regarded primarily as sources of volcanic CO2 emissions, contributing greenhouse gases to the atmosphere. However, this new evidence suggests a more nuanced carbon balance where the oceanic crust simultaneously acts as a source and a sink, with talus breccias playing a significant role in carbon uptake. Recognizing the dual nature of mid-ocean ridge carbon fluxes could refine our understanding of Earth’s natural climate regulation mechanisms.
To elucidate the full impact of talus breccias on the global carbon cycle, future carbon budget models must incorporate the spatial and temporal distribution of these formations along ocean ridges of varying spreading rates. This involves not only quantifying the total surface area and porosity of talus breccias but also understanding their age-dependent evolution and carbonate mineral growth dynamics. Integrating geophysical mappings, petrographic analyses, and geochemical flux calculations will be essential for accurate estimations of carbon storage capacity.
Moreover, the implications of talus breccias extend to marine geohazards and oceanographic fluid dynamics. Their porous nature and fracture-controlled permeability influence how hydrothermal fluids circulate through the oceanic crust, affecting the thermal and chemical regimes of ridge flanks. This hydrological role can impact seafloor ecosystems, biogeochemical cycling, and the distribution of microorganisms adapted to subsurface environments. Hence, understanding breccia-hosted carbon reservoirs is pivotal beyond carbon cycling alone.
The study also opens new paths for exploring fossilized carbon reservoirs within ocean crust layers across different spreading centers. Variability in breccia composition, size, and cementation characteristics could reveal past episodes of climatic and tectonic perturbations recorded in the rock record. Such geological archives may provide invaluable insights into how Earth’s carbon system has responded to shifts in plate tectonics, sea level, and ocean chemistry over millions of years.
Future research programs focused on ocean drilling and seafloor surveys stand to benefit substantially from these findings. Detailed coring operations targeting talus breccia formations, coupled with high-resolution mineralogical and isotopic investigations, can expand our understanding of carbonate precipitation mechanisms and their long-term stability. Such efforts will be crucial for assessing how mid-ocean ridge processes contribute to global carbon sequestration in a changing climate.
In summary, the identification of talus breccias as a previously under-appreciated geological CO2 sink redefines the role of the ocean crust in Earth’s carbon cycle. It emphasizes the significance of upper crustal architecture, tectonic spreading rates, and ridge flank fluid dynamics in governing carbon fluxes. As new models incorporate these dynamics, our predictive capabilities regarding Earth’s carbon reservoirs and their interaction with the atmosphere and oceans will be greatly enhanced, shedding light on critical processes shaping climate over geological time.
The discovery also highlights the intricate and interlinked nature of geological processes at mid-ocean ridges, where volcanic, tectonic, and hydrological forces coalesce to influence carbon storage. By bridging the fields of geology, geochemistry, and climate science, this work exemplifies how interdisciplinary approaches drive breakthroughs in understanding Earth’s complex systems. The ocean crust, once thought largely passive in the carbon cycle beyond CO2 emission, now emerges as an active participant in carbon sequestration on a global scale.
Ultimately, as the global community grapples with climate change and the role of natural carbon sinks, these insights into oceanic geological carbon reservoirs emphasize the importance of deep Earth processes. Harnessing knowledge about carbon capture in talus breccias might inspire novel strategies for carbon management, while also reminding us that Earth’s vast and dynamic interior holds key answers to sustaining planetary health.
Subject of Research: Geological carbon cycle and carbon sequestration in ocean crust talus breccias
Article Title: A geological carbon cycle sink hosted by ocean crust talus breccias
Article References:
Coggon, R.M., Carter, E.J., Grant, L.J.C. et al. A geological carbon cycle sink hosted by ocean crust talus breccias. Nat. Geosci. (2025). https://doi.org/10.1038/s41561-025-01839-5
Image Credits: AI Generated
DOI: https://doi.org/10.1038/s41561-025-01839-5
Keywords: Carbon cycle, talus breccia, mid-ocean ridge, basaltic breccia, carbonate precipitation, ocean crust, geological carbon sink, tectonics, seafloor alteration, mid-Atlantic Ridge
