Carbon Cycling at the Dawn of the Cenozoic

The Paleocene – the first epoch of the Cenozoic (66–56 Ma) – spans numerous notable climatic and biogeochemical phenomena. In the oceans, the Paleocene saw the drawn-out recovery of calcifying plankton communities after severe extinction at the K-Pg, followed by one of the largest excursions in benthic foraminiferal δ13C values of the last 100 Myr1. On land, an as-yet-unexplained extreme step-change in global weathering regime is indicated by marine carbonate δ7Li values2. More generally, although benthic foraminiferal δ18O suggests a greenhouse climate much warmer than today3, proxy estimates of atmospheric CO2 in the Paleocene mostly indicate CO2 levels similar to those of the relatively colder late Neogene4.

Here, I will show some new benthic and planktic foraminiferal boron and lithium isotope data that address outstanding puzzles in geochemical cycling and ocean chemistry at the dawn of the Cenozoic.

1. Friedrich, O., Norris, R. D. & Erbacher, J. Evolution of middle to Late Cretaceous oceans--A 55 m.y. record of Earth’s temperature and carbon cycle. Geology 40, 107–110 (2012).

2. Misra, S. & Froelich, P. N. Lithium Isotope History of Cenozoic Seawater: Changes in Silicate Weathering and Reverse Weathering. Science 335, 818–823 (2012).

3. Westerhold, T. et al. An astronomically dated record of Earth’s climate and its predictability over the last 66 million years. Science 369, 1383–1387 (2020).

4. Beerling, D. J. & Royer, D. L. Convergent Cenozoic CO2 history. Nat. Geosci. 4, 418–420 (2011).