by C.R. Witkowski et al., November28,  2018 in SciAdvances

Here, we reconstructed Phanerozoic PCO₂ from a single proxy: the stable carbon isotopic fractionation associated with photosynthesis (Ɛ_p) 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 Ɛ_p 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 Ɛ_p mirrors the available compilations of PCO₂over 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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Fig. 2Ɛ_p calculated from phytane in Witkowski et al., 2018

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