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Sci Adv. 2018 Nov 28;4(11):eaat4556. doi: 10.1126/sciadv.aat4556. eCollection 2018 Nov.

Molecular fossils from phytoplankton reveal secular Pco2 trend over the Phanerozoic.

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Department of Marine Microbiology and Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, and Utrecht University, P.O. Box 59, 1790AB Den Burg, Netherlands.
Shell Global Solutions International B.V., Grasweg 31, 1031 HW Amsterdam, Netherlands.
Department of Science and Technology, College of Arts and Sciences, Bryant University, Smithfield, RI 02917, USA.
Institute for Brain and Neural Systems, Brown University, Providence, RI 02912, USA.
Department of Earth Sciences, Faculty of Geosciences, Utrecht University, P.O. Box 80.121, 3508 TA Utrecht, Netherlands.


Past changes in the atmospheric concentration of carbon dioxide (Pco2) have had a major impact on earth system dynamics; yet, reconstructing secular trends of past Pco2 remains a prevalent challenge in paleoclimate studies. The current long-term Pco2 reconstructions rely largely on the compilation of many different proxies, often with discrepancies among proxies, particularly for periods older than 100 million years (Ma). Here, we reconstructed Phanerozoic Pco2 from a single proxy: the stable carbon isotopic fractionation associated with photosynthesis (Ɛp) that increases as Pco2 increases. This concept has been widely applied to alkenones, but here, we expand this concept both spatially and temporally by applying it to all marine phytoplankton via a diagenetic product of chlorophyll, phytane. We obtained data from 306 marine sediments and oils, which showed that Ɛp ranges from 11 to 24‰, agreeing with the observed range of maximum fractionation of Rubisco (i.e., 25 to 28‰). The observed secular Pco2 trend derived from phytane-based Ɛp mirrors the available compilations of Pco2 over the past 420 Ma, except for two periods in which our higher estimates agree with the warm climate during those time periods. Our record currently provides the longest secular trend in Pco2 based on a single marine proxy, covering the past 500 Ma of Earth history.

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