High-resolution Atmospheric pCO2 Reconstruction across the Paleogene Using Marine and Terrestrial δ13C records

Ying Cui and Brian Schubert, University of Louisiana at Lafayette, School of Geosciences, Lafayette, LA, United States
Abstract:
The early Paleogene (63 to 47 Ma) is considered to have a greenhouse climate1 with proxies suggesting atmospheric CO2 levels (pCO2) approximately ~2× pre-industrial levels. However, the proxy based pCO2 reconstructions are limited and do not allow for assessment of changes in pCO2 at million to sub-million year time scales. It has recently been recognized that changes in C3 land plant carbon isotope fractionation can be used as a proxy for pCO2 with quantifiable uncertainty2. Here, we present a high-resolution pCO2 reconstruction (n = 597) across the early Paleogene using published carbon isotope data from both terrestrial organic matter and marine carbonates. The minimum and maximum pCO2 values reconstructed using this method are broad (i.e., 170 +60/-40 ppmv to 2000 +4480/-1060 ppmv) and reflective of the wide range of environments sampled. However, the large number of measurements allows for a robust estimate of average pCO2 during this time interval (~ 400 +260/-120 ppmv), and indicates brief (sub-million-year) excursions to very high pCO2 during hyperthermal events (e.g., the PETM). By binning our high-resolution pCO2 data at 1 million year intervals, we can compare our dataset to the other available pCO2 proxies. Our result is broadly consistent with pCO2 levels reconstructed using other proxies, with the exception of paleosol-based pCO2 estimates spanning 53 to 50 Ma. At this timescale, no proxy suggests pCO2 higher than 2000 ppmv, whereas the global surface ocean temperature is considered to be >10 oC warmer than today. Recent climate modeling suggests that low atmospheric pressure during this time period could help reconcile the apparent disconnect between pCO2 and temperature and contribute to the greenhouse climate3.

References

1. Huber, M., Caballero, R., 2011. Climate of the Past 7, 603-633.

2. Schubert, B.A., Jahren, A.H., 2015. Geology 43, 435-438.

3. Poulsen, C.J., Tabor, C., White, J.D., 2015. Science 348, 1238-1241.