Evidence for a marine carbon recycling mechanism in Earth’s mantle
Recent work by PhD student Zhengyu Long, under the supervision of Frédéric Moynier, and their colleagues at the Institut de Physique du Globe de Paris (IPGP/Université Paris Cité/CNRS) and the CNRS, has revealed a mechanism involved in Earth’s carbon cycle, linked to the subduction of oceanic plates. Their study, published in Science Advances, shows that carbonatites — rare volcanic rocks rich in carbonates — exhibit a distinctive isotopic signature, likely inherited from subducted oceanic crust. These findings suggest the existence of a marine carbon recycling process within Earth’s mantle that may contribute to the regulation of the global carbon cycle and the maintenance of life-supporting conditions on Earth.
Modern carbonatitic volcanism at Ol Doinyo Lengai, Tanzania / @Wiki
Publication date: 16/06/2025
Press, Research
A process at the heart of deep carbon dynamics
Carbonate sediments descending into subduction zones are often interlayered with clay-rich strata or rest on altered igneous oceanic crust. By analyzing carbonatites from a range of geological environments – both oceanic and continental – spanning the past two billion years, the team observed that their potassium isotopic composition seems to reflect a mantle-derived origin rather than secondary magmatic processes.
These observations suggest that the recycling of marine carbonates, particularly through the subduction of altered oceanic crust, may play a key role in the dynamics of deep carbon reservoirs. The long-debated origin of carbonatites thus appears more closely linked to the partial melting of mantle reservoirs enriched in recycled carbonates.
New insights into the global carbon cycle
The carbonate inputs involved in this process could stem from a deep mantle plume or result from interaction between a plume and lithospheric mantle containing carbonates. Even very limited partial melting could produce carbonatitic magmas. This deep carbon transfer mechanism has likely been active for at least two billion years, including under conditions of hotter subduction.
This research provides new insights into the global carbon cycle. It highlights the role of carbonatites in mantle dynamics and underscores the probable contribution of subducted oceanic crust to carbon recycling – a process crucial to maintaining Earth’s surface conditions in balance.
Source :
Heavy potassium isotopes in carbonatites reveal oceanic crust subduction as the driver of deep carbon cycling
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