14 December 2021 ESRFnews

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New ESRF-based research suggests that much more carbon is trapped at subduction zones than previously thought. What are the consequences for the climate?

F EW elements are more present in our minds than carbon. Everyone knows that plants absorb it, and that humans and other animals exhale it. Alarm- ingly, we know that we are also releasing vast quantities of it into the atmosphere through the burning of fossil fuels. This is the carbon cycle and as the recent COP26 global summit in Glasgow, UK, has reminded us yet again we mess with it at our peril. Despite all our talk about carbon, however, there is a

major part of its cycle of which few of us are aware. Every year, across tens of thousands of kilometres of subduction zones in the Earth s crust, more than 70 megatonnes of trapped carbon is swallowed into the mantle. Scientists had believed that almost all of this is regurgitated by volcanoes, making the process largely carbon-neutral. But the latest research at the ESRF indicates that this is false: some two-thirds of the carbon that goes down, stays down. The result has huge implications for our understanding of the Earth s long-term climate and could have ramifications for how we deal with the present climate cri- sis, too. We see that carbon dioxide in the atmosphere is increasing dramatically because of human activity, says Angelika Rosa (pictured, right), ESRF scientist and co-au- thor of the research. Our study gives us ideas about how we can store that carbon instead. The deep carbon cycle feeds off the more familiar

carbon cycle. When rivers weather their banks, and oceans weather their shores, any carbon dioxide that the water has absorbed from the atmosphere can be incorporated into rocks, via chemical reactions producing carbonates. Meanwhile, dissolved carbon is metabolised by

Deep impact

DEEP CARBON CYCLE