Earth’s interior ‘swallowing up’ more carbon than previously thought, say scientists

They found the carbon drawn into the Earth’s interior where the tectonic plates collide tends to stay locked away at depth, rather than resurfacing in the form of volcanic emissions

The Big Zero report

Slow motion collisions of the pieces of Earth’s crust and uppermost mantle, called the tectonic plates, are “swallowing up” more carbon into its interior than previously thought.

That’s according to latest research by scientists from Cambridge University and NTU Singapore, who found the carbon drawn into the Earth’s interior at subduction zones – where the tectonic plates collide and dive into the Earth’s interior – tends to stay locked away at depth, rather than resurfacing in the form of volcanic emissions.

They add only around a third of the carbon recycled beneath volcanic chains returns to the surface via recycling, in contrast to previous theories that what goes down mostly comes back up.

According to the scientists, there are a number of ways for carbon to be released into the Earth’s atmosphere as CO2 but there is only one path in which it can return to the Earth’s interior – through the slow process of plate subduction.

Surface carbon, for instance in the form of seashells and micro-organisms which have locked atmospheric CO2 into their shells, is channelled into Earth’s interior.

Scientists had thought much of this carbon was then returned to the atmosphere as CO2 via emissions from volcanoes, however, the new study reveals that chemical reactions taking place in rocks swallowed up at subduction zones trap carbon and send it deeper into Earth’s interior – stopping some of it coming back to Earth’s surface.

They suggest the best-understood parts of the carbon cycle are at or near the Earth’s surface but deep carbon stores play a key role in maintaining the habitability of the planet by regulating atmospheric CO2 levels.

Lead Author Stefan Farsang, who conducted the research while a PhD student at Cambridge’s Department of Earth Sciences said: “We currently have a relatively good understanding of the surface reservoirs of carbon and the fluxes between them but know much less about Earth’s interior carbon stores, which cycle carbon over millions of years.

“There is still a lot of research to be done in this field. In the future, we aim to refine our estimates by studying carbonate solubility in a wider temperature, pressure range and in several fluid compositions.”

The findings are said to be important for understanding the role of carbonate formation in the climate system more generally.

Co-author Simon Redfern, Dean of the College of Science at NTU Singapore added: “Our results show that these minerals are very stable and can certainly lock up CO2 from the atmosphere into solid mineral forms that could result in negative emissions.

“These results will also help us understand better ways to lock carbon into the solid Earth, out of the atmosphere. If we can accelerate this process faster than nature handles it, it could prove a route to help solve the climate crisis.”

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