Reassessing Paleocene CO2 and Carbon Cycling using Process-Informed Joint Proxy Inversion

The Paleocene Epoch represents a transitional Earth system state featuring climatic relaxation between the extreme warmth of the Late Cretaceous and Early Eocene. Carbon isotope and sedimentological data have been invoked as evidence for elevated organic carbon burial and CO2 drawdown throughout the early Paleocene, constituting a potential driver of and/or feedback on climate change. Despite this, quantitative proxy reconstructions of Paleocene atmospheric CO2 concentrations have remained sparse, limiting our ability to test hypotheses for the role of carbon cycle change in Paleocene Earth system change. Here we produce quantitative CO2 reconstructions spanning the Paleocene by combining data from marine (foraminiferal calcite) and terrestrial (pedogenic carbonate) proxy systems. We integrate data from these proxy systems, together with complementary paleo-environmental proxy data, using newly developed proxy system models implemented within the Bayesian Joint Proxy Inversion (JPI) framework. Although each individual proxy system is under-constrained, the combination of information from distinct systems and constraints provided by ancillary data produces a coherent, well-resolved paleo-CO2 reconstruction. The record suggests strong coupling between carbon cycle processes, atmospheric CO2 levels, and climate throughout the Paleocene. Integration of a simple carbon cycle model driven by changing sedimentary organic carbon burial within the JPI analysis provides additional constraints on the CO2 reconstruction and demonstrates that this process is generally consistent with the available proxy evidence.