A significant fraction of Earth’s carbon resides in the mantle1, but the mode of carbon storage presents a long-standing problem. The mantle contains fluids rich in carbon dioxide and methane, carbonate-bearing melts, carbonate minerals, graphite, diamond and carbides, as well as dissolved carbon atoms in metals. However, it is uncertain whether these can sufficiently account for the total amount of carbon thought to be stored in the mantle and the volume of carbon degassed from the mantle at volcanoes2. Moreover, such carbon hosts should significantly affect the physical and chemical behaviour of the mantle, including its melting temperature, electrical conductivity and oxidation state3,4. Here we use in situ transmission electron microscopy to measure the storage of carbon within common mantle mineral analogues—nickel-doped lanthanum chromate perovskite and titanium dioxide—in laboratory experiments at high pressure and temperature. We detect elevated carbon concentrations at defect sites in the nanocrystals, maintained at high pressures within annealed carbon nanocages. Specifically, our experiments show that small stacking faults within the mantle analogue materials are effective carbon sinks at mantle conditions, potentially providing an efficient mechanism for carbon storage in the mantle. Furthermore, this carbon can be readily released under lower pressure conditions, and may therefore help to explain carbon release in volcanic eruptions.
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This work was financially supported by NSF grant EAR-0948535. We acknowledge the use of facilities within the LeRoy Eyring Center for Solid State Science at Arizona State University. D. Bell and B. Watson are thanked for helpful comments and K. Weiss and D. Wright for technical assistance.
The authors declare no competing financial interests.
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Wu, J., Buseck, P. Carbon storage at defect sites in mantle mineral analogues. Nature Geosci 6, 875–878 (2013). https://doi.org/10.1038/ngeo1903
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