The sensitivity of the PETM carbon cycle perturbation to orbital configurations

It is generally postulated that climatic change during the Paleocene – Eocene Thermal Maximum (PETM) was paced and/or caused by astronomical forcing, particularly eccentricity-modulated precession. Possible causal links include intermediate water warming and subsequent methane hydrate destabilization, increased climate sensitivity due to a warmer background state, and changes in hydrology and weathering. Current astrochronology places the PETM near a 405-kyr eccentricity maximum (Zeebe and Lourens, 2019), likely following a prolonged 2.25-Myr eccentricity minimum (Lourens et al., 2005). Similar orbital configuration sequences have been proposed for the Devonian Upper Kellwasser event (De Vleeschouwer et al., 2017) and the Cretaceous Oceanic Anoxic Event 2 (Batenburg et al., 2016). To understand how eccentricity could have made the Late Paleocene Earth System sensitive to a carbon-cycle perturbation with the amplitude of the PETM, we investigate both the equilibrium and transient climate response to changes in insolation. Specifically, our experimental set-up is to identify how rapid climate change events may unfold differently under high eccentricity (PETM) and low eccentricity (modern) regimes. We present results from equilibrium climate state simulations and transient climate responses to PETM emission scenarios, using the cGENIE Earth system model under a comprehensive set of eccentricity/precession configurations. Based on the outcomes of these simulations, we describe the differences in PETM expression in terms of climate and weathering regimes, depending on the astronomical configuration.