A step closer to fathoming the deep carbon cycle

8 May 2020

Understanding the Earth’s carbon cycle has important implications for comprehending climate change and the health of biospheres. But scientists have not yet been able to fathom how much carbon lies deep in the Earth’s water reservoirs — for example, in water that is under extreme pressure in the mantle — because experiments are difficult to conduct under such conditions.

To assist this quest, Hong Kong-based researcher Dr Ding Pan (Croucher Innovation Award 2018) and a US academic have now created a complex computer simulation that will help scientists determine the concentration of carbon under the conditions of the mantle, which include temperatures of up to 1,000 Kelvin (K), or 726.85 degrees Centigrade, and pressures of up to 10 gigapascal (GPa), which is 100,000 times greater than on the Earth’s surface.

The research, published recently in Nature Communications, with Pan as first author, has important implications for understanding the deep carbon cycle, which also substantially influences the carbon budget near the Earth’s surface.

The simulation, generated by Pan, assistant professor of physics and chemistry at the Hong Kong University of Science and Technology, and Professor Giulia Galli, Liew Family Professor of Molecular Engineering, and professor of chemistry, at the University of Chicago, offers an ingenious way to evaluate the missing link between measurements (in particular, vibrational spectra used to discover signatures of ions in water) and the ion and molecular concentrations in these conditions.

“Together with many other research groups around the world, we have been part of a large project aimed at understanding how much carbon is present in the Earth and how it moves from the interior towards the surface,” Pan said. “This is one step towards building a comprehensive picture of carbon concentration and movement in the Earth.”

Galli, co-author of the research, added: “Our computational strategy will greatly facilitate the determination of the amount of carbon at the extreme conditions of the Earth’s mantle.”

Pan is a former post-doctoral researcher in Galli’s group at the University of Chicago. Both are members of the Deep Carbon Observatory (DCO) Science Network, a global community of more than 1,000 scientists whose quest is to understand the quantities, movements, forms and origins of carbon in the Earth, with support from the Sloan Foundation.

Discovering how much carbon lies in deep reservoirs many kilometres underground is significant because more than 90 per cent of the Earth’s carbon is buried in its interior. That deep carbon influences the form and concentration of carbon near the surface, which ultimately can impact global climate change.

Together with many other research groups around the world, we have been part of a large project aimed at understanding how much carbon is present in the Earth and how it moves from the interior towards the surface。

As yet, there is no experimental technique available to directly characterise carbonates dissolved in water at extreme pressure and temperature conditions. Pan and Galli devised a novel strategy that combines spectroscopy results with sophisticated calculations based on quantum mechanics to determine the concentration of ions and molecules in water at extreme conditions.

By carrying out these simulations, the scientists found that the concentration of a specific important species — bicarbonate ions — had been underestimated by previously used geochemical models. They proposed a new view of what happens when you dissolve carbon dioxide in water at extreme conditions, which is critical to understanding the chemistry of carbon in the Earth’s interior, according to the researchers.

The simulations were performed at the Research Computing Center at the University of Chicago and Deep Carbon Observatory Computer Cluster, also in the US.

Ding Pan obtained his Bachelor of Science in Physics as a member of the Special Class of Gifted Young (00 Class) at the University of Science and Technology of China in 2005, and Doctor of Science (ScD) at the Institute of Physics, Chinese Academy of Sciences, in 2011. During his doctoral studies, Pan was a visiting researcher at the Fritz Haber Institute of the Max Planck Society in Berlin, Germany, and a Thomas Young Centre Junior Research Fellow at University College London, UK. He worked as a postdoctoral researcher at the University of California at Davis (2011-14) and University of Chicago (2014-16) before joining Hong Kong University of Science and Technology in 2016. Pan was the recipient of a Deep Carbon Emerging Leader Award in 2019 and a Croucher Innovation Award in 2018.

To view Dr Ding Pan’s Croucher profile, please click here.