Evolution of the carbon isotope composition of atmospheric CO2 throughout the Cretaceous

Although atmospheric CO2 has been extensively described as a primary driver of Phanerozoic climate and carbon cycle disturbance, little is known about its carbon isotope composition (delta C-13(co2)) during pre-Cenozoic times. We reconstruct for the first time the evolution of delta C-13(co2) during the whole Cretaceous period based on reference curves of delta C-13 values of Tethyan marine bulk carbonates (delta C-13(carb)) and delta O-18(PO4), values of fish tooth enamel. We test this method against that based on the oxygen and carbon isotope ratios of high-latitude benthic foraminifera (delta C-13(foram)) recently implemented for the Cenozoic and closely matching delta C-13(co2), measurements from ice cores. Highly consistent delta C-13(co2) estimates and trends are obtained from the delta C-13(carb), method (-5.90% +/- 0.28) and the delta C-13(foram) method (-6.18% +/- 0.64) during the phases of available foraminiferal record encompassing the Albian-Maastrichtian interval. However, the delta C-13(foram)-based delta C-13(co2), signal is strongly biased during the main OAEs, during which heat transport to higher latitudes associated with Haline Euxinic Acidic Thermal Transgression (HEATT) episodes may have affected temperature inference from delta O-18(foram) values. Our results demonstrate the suitability of using delta C-13(carb) records to reconstruct past delta C-13(co2) values, which opens the opportunity for pre-Cenozoic, worldwide delta C-13(co2), reconstructions even during sharp climate change intervals. The consistency between both methods together with our delta C-13(co2) estimates and those previously obtained for the Cenozoic provides about 145 Myr of carbon isotope evolution of atmospheric CO2. (C) 2017 Elsevier B.V. All rights reserved.