by William J. Davis, September 2017, in ResearchGate
Assessing human impacts on climate and biodiversity requires an understanding of the relationship between the concentration of carbon dioxide (CO2) in the Earth’s atmosphere and global temperature (T). Here I explore this relationship empirically using comprehensive, recently-compiled databases of stable-isotope proxies from the Phanerozoic Eon (~540 to 0 years before the present) and through complementary modeling using the atmospheric absorption/transmittance code MODTRAN. Atmospheric CO2 concentration is correlated weakly but negatively with linearly-detrended T proxies over the last 425 million years.
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 (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 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
Fig. 2Ɛp calculated from phytane in Witkowski et al., 2018
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