Mesozoic atmospheric CO2 concentrations reconstructed from dinosaur tooth enamel

Abstract

Air-breathing vertebrates incorporate a fraction of isotopically anomalous air O2 in their body water. The 17O isotope anomaly of air O2 (expressed as Δ’17Oair) is related to atmospheric CO2 concentrations (pCO2) and gross primary production (GPP). Tooth enamel records the Δ’17O of body water and can thus preserve such paleo-pCO2 or paleo-GPP information over geological time periods. Here, we demonstrate the potential of respective reconstructions of atmospheric pCO2 or GPP from the triple oxygen isotope composition of fossil dinosaur tooth enamel. The data from unaltered enamel samples, along with an assumed modern GPPt/GPP0 ratio of 1 for the Mesozoic, suggest a mean Late Jurassic pCO2 = 1,200 ± 150 ppmv and Late Cretaceous pCO2 = 750 ± 200 ppmv. These estimates are in good agreement with other pCO2 proxy data for the same time intervals. When utilizing a pCO2 inferred from other proxies, tooth enamel Δ’17OPO4 may also serve as a proxy for GPP. Using published pCO2 data, we reconstructed GPPt/GPP0 ratios with 1.20 ± 0.17 for the Late Jurassic and 2.24 ± 0.96 for the Late Cretaceous, which would imply a 20 to 120% higher GPP in the Mesozoic than today. Overall, triple oxygen isotope analysis of fossil teeth of terrestrial amniotes can provide insights into past atmospheric greenhouse gas content and global primary productivity.