From Clocks to Triggers? Orbital Forcing and the Paleocene–Eocene Thermal Maximum

The ancient global warming event known as the Paleocene–Eocene Thermal Maximum (PETM, ∼56 Ma) provides an excellent case study for understanding the integrated Earth system response to massive carbon release. To evaluate its utility as a future analog, there is a need for accurate estimates not only for the durations of different phases, such as the onset duration, period of carbon release, and recovery timescale, but also for constraints on the source(s) of carbon. While the PETM corresponds to an interval of increased volcanic activity, the degree to which it was shaped by strong positive feedbacks may be particularly revealing about the sensitivity of the surficial carbon cycle to rapid warming. Studying the role of orbital forcing across the PETM has been essential to unlocking each of these key unknowns. Here, we review the study of orbital forcing in relation to the PETM, both in the application of cyclostratigraphy to constrain the duration and timing of the PETM and in the potential role of orbital forcing as a trigger or contributor for carbon release. We subsequently use new numerical simulations to evaluate feedback between PETM carbon release and orbital forcing.