Carbon isotope ratio of Cenozoic CO2: A comparative evaluation of available geochemical proxies

摘要: [1] The carbon isotope ratio (δ13C) of plant material is commonly used to reconstruct the relative distribution C3 and C4 plants in ancient ecosystems. However, such estimates depend on δ13C atmospheric CO2 (δ13CCO2) at time, which likely varied throughout Earth history. For this study, we use benthic planktonic δ18O records a long-term record Cenozoic δ13CCO2. Confidence intervals for δ13CCO2 values are assigned after careful consideration equilibrium non-equilibrium effects processes, as well resolution data. We find that foraminifera better constrain compared foraminiferal records, influenced by photosymbiotes, depth production, seasonal variability, preservation. Furthermore, sensitivity analyses designed quantify temperature uncertainty diagenesis indicate these factors act offset one another. Our reconstruction suggests averaged −6.1 ± 0.6‰ (1σ), while only 11.2 million last 65.5 years correspond pre-Industrial value −6.5‰ (with 90% confidence). Here also displays significant variations record, times departing from more than 2‰. Thus, observed variability should be considered isotopic reconstructions terrestrial-plant ecosystems, especially during Late Middle Miocene, presumed grassland expansion.