REVISED ATMOSPHERIC PCO2 ESTIMATES FROM PEDOGENIC CARBONATES SUPPORT CO2-TEMPERATURE COUPLING THROUGHOUT THE PHANEROZOIC

Though CO₂-temperature coupling has been validated on some time scales, there is still a question of whether or not CO₂ has been coupled to climate throughout the entirety of geologic time. The highly cited Phanerozoic reconstruction of atmospheric pCO₂ published by Ekart et al. (1999) presents pCO₂ estimates that are higher than most other estimates from other proxies. These high CO₂ estimates, especially those during key times in the geologic past with substantial evidence for globally cool temperatures (i.e., the Permian and Cenozoic) suggest CO₂-temperature decoupling. Here, we use a new proxy for soil-respired CO₂ that reduces uncertainty associated with the pedogenic carbonate paleobarometer by estimating soil-respired CO₂ values using its relationship to mean annual precipitation. Using this new method of paleobarometry, we have refined previous estimates of atmospheric CO₂ for the early Permian, late Triassic and late Miocene. We find that revised atmospheric pCO₂ estimates are significantly reduced for each case study and now closely match the low atmospheric pCO₂ estimates reconstructed by models and as well as other proxy methods of reconstruction such as marine boron, alkenones and stomatal index. The presence of abundant evidence of glaciers from the rock record as well as stable temperature estimates affirms CO₂-temperature coupling for late Permian. For the late Miocene, original pedogenic carbonate pCO₂ estimates have been reduced by half. Given that temperature reconstructions from the late Miocene are not much warmer than today, these revised atmospheric pCO₂ estimates support CO₂-temperature coupling. Therefore, the CO₂-temperature decoupling suggested by Ekart et al. (1999) is not longer supported by the data and CO₂ and temperature appear to be coupled throughout the Phanerozoic.