"Deep Carbon: Past to Present" Synthesizes a Decade of DCO Research

A new book, Deep Carbon: Past to Present, compiles 10 years of DCO research. The volume serves as a comprehensive reference on the quantities, movements, forms, and origins of carbon in Earth through deep time, for graduate students and scientists in related fields.

Deep Carbon: Past to Present coverFrom diamonds to volcanic degassing to the deep biosphere and more, scientists within the Deep Carbon Observatory have covered a lot of ground since the initiative’s start 10 years ago. To synthesize what this work reveals about the functioning of our planet and to point out new directions for the next generation of deep carbon research, DCO scientists, in partnership with Cambridge University Press and with support from the Alfred P. Sloan Foundation, have published the open-access book, Deep Carbon: Past to Present. DCO members Beth Orcutt (Bigelow Laboratory for Ocean Sciences, USA), Isabelle Daniel (Université Claude-Bernard Lyon 1 France), and Rajdeep Dasgupta (Rice University, Houston, USA) edited the book, and more than 100 international authors contributed to its 20 chapters.

The volume brings together the many contributions DCO scientists have made to their respective fields in the last decade, with chapters on the origins of Earth’s carbon, the movement and fluxes of carbon between different reservoirs, the limits of deep life, and how the evolution of Earth’s continents and ocean floors has impacted the global carbon cycle through deep time. “Each chapter is fascinating in its own right, but many of them provide interesting syntheses,” said Dasgupta.

C in serpentinites
Caption: Examples of organic carbon occurring in oceanic rocks that have undergone water-rock reactions called serpentinization. Credit: Adapted from Andreani A, Ménez B (2019) New Perspectives on Abiotic Organic Synthesis and Processing during Hydrothermal Alteration of the Oceanic Lithosphere. In Orcutt BN, Daniel I, Dasgupta R, eds. 2019 Deep Carbon: Part to Present. Cambridge UK: Cambridge University Press. Courtesy of Elsevier, from Ménez et al. (2018), Lithos, 323, 262–276.

With its clear diagrams and discussion questions, the book is intended for use in the classroom. “We wanted to be able to synthesize the science at a relatively high level but to make it accessible enough for graduate-level instruction across a range of disciplines, from geology to physics to biology,” said Orcutt. She hopes that the freely available book will be widely used. “This project is somewhat unique in that it is all online and open-access and that’s because the Sloan Foundation believes that these data and what we’re learning should be accessible to all.”

The new book also serves as a companion to Carbon in Earth, a book published in 2013. That volume established what DCO scientists knew about the deep carbon cycle and what research directions they hoped to advance. 

Many people who were early-career researchers or postdocs at the start of DCO now have developed their own research programs and contributed chapters to the new book. The shift highlights DCO’s efforts to cultivate early-career scientists and novel collaborations. 

Subsurface cells
Estimates of subsurface cell concentrations show areas with greater microbial numbers on continents and the ocean floor. Credit: From Magnabosco C, Biddle JF, Cockell CS, Jungbluth SP, Twing KI (2019) Biogeography, Ecology, and Evolution of Deep Life. In Orcutt BN, Daniel I, Dasgupta R, eds. 2019 Deep Carbon: Part to Present. Cambridge UK: Cambridge University Press.

Among the notable advances presented in the book are answers to questions about the identities, population sizes, and locations of microbes living in the deep biosphere. Researchers also have made important discoveries regarding how organic compounds arise independently of life, and which compounds may have been available during the rise of the first cells on Earth. “That’s been a very challenging topic and the concepts have changed dramatically between the beginning and end of the DCO, so that’s really spectacular,” said Daniel.

The book provides a new integrative way of thinking of the origin of Earth’s carbon and how to think about surface-interior exchange of carbon throughout Earth’s history. It also showcases the new and improved estimates of the fate and amounts of carbon throughout Earth, especially the extent of volcanic degassing and how much carbon returns to deep Earth through subduction and other processes. It also reviews advances in the study of diamonds and what they can tell us about the deep carbon cycle throughout Earth’s history.

C degassing
Carbon dioxide forms visible plumes from active volcanoes, but it less obvious when emitting from dormant or inactive volcanoes and hydrothermal systems. Large amounts of carbon dioxide can come from areas of diffuse degassing, like hot springs, and also reacts with groundwater. Credit: From Werner C, Fischer TP, Aiuppa A, Edmonds M, Cardellini C, Carn S, Chiodini G, Cottrell E, Burton M, Shinohara H, Allard P (2019) Carbon Dioxide Emissions from Subaerial Volcanic Regions. In Orcutt BN, Daniel I, Dasgupta R, eds. 2019 Deep Carbon: Part to Present. Cambridge UK: Cambridge University Press.

Several technological advances are highlighted in the book, including the DCO-supported Panorama instrument, which allows researchers to determine the origins and processes of formation of a methane sample. Analyses of methane from around the world show that there are a few types of sites where methane is created abiotically, without the aid of microbes or involving the breakdown of old organic matter.

Additionally, the book reveals advances in modeling and how these new tools are helping scientists to understand how carbon bonds with elements such as hydrogen and oxygen under the extreme pressures and temperatures that exist in deep mantle. These molecules are surprisingly different from those occurring at the surface, and yield interesting results, especially when they react in tiny nanopores and cracks within rocks. 

carbon in pores
Caption: A schematic explaining how carbon dioxide may turn into methane in tiny fractures within ocean crust. Credit: From Cole D, Striolo A (2019) The Influence of Nanoporosity on the Behavior of Carbon-Bearing Fluids. In Orcutt BN, Daniel I, Dasgupta R, eds. 2019 Deep Carbon: Part to Present. Cambridge UK: Cambridge University Press.  Courtesy of Thu Le et al./Scientific Reports

One thing the book makes especially clear is the multitude of new directions for deep carbon research. Each chapter includes a summary of what is still unknown and areas for future work. “I do not consider this book to be an endpoint. After 10 years, it’s a step,” said Daniel. “There’s still a lot of room for a lot of people to get excited about deep carbon science.”
The book is dedicated to the memories of incredibly talented DCO scientists Erik Hauri and Louise Kellogg, both of whom passed away in 2018 and are greatly missed.

diamond formation
This diagram of diamond formation in the mantle transition zone shows how carbon and nitrogen from the surface can be recycled into diamonds. Credit: Adapted from Shirey SB, Smit KV, Pearson DG, Walter MJ, Aulbach A, Brenker FE, Bureau H, Burnham AD, Cartigny P, Chacko T, Frost DJ, Hauri EH, Jacob DE, Jacobsen SD, Kohn SC, Luth RW, Mikhail A, Navon O, Nestola F, Nimis P, Palot M, Smith EM, Stachel T, Stagno V, Steele A, Stern RA, Thomassot E, Thomson AR, Weiss Y (2019) Diamonds and the Mantle Geodynamics of Carbon. In Orcutt BN, Daniel I, Dasgupta R, eds. 2019 Deep Carbon: Part to Present. Cambridge UK: Cambridge University Press. 


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