A new helium isotope recored of the Paleocene-Eocene Thermal Maximum from ODP Site 198-1209 (S6)

The Paleocene-Eocene Thermal Maximum (PETM; around 56 Ma ago) is arguably the most intensively studied event of rapid greenhouse warming of the geological past. The duration and age of the PETM, however, remains vividly debated, limiting our understanding of the response of the Earth System dynamics to rapid warming. Here we present new extraterrestrial helium 3 (3HeET) data across the PETM at ODP Site 198-1209 (N Pacific) that document a drop in 3HeET fluxes from 0.56 ± 0.02 pcm³/cm²/ka ~1 Ma prior to the PETM to values of 0.37 ± 0.02 pcm³/cm²/ka before and after the PETM. Our 3HeET-based chronology, optimized through spectral analysis and orbital tuning, indicates a duration of 160±10 ka for the PETM body/core, consistent with previous 3HeET estimates from ODP Site 208-1266 (Walvis Ridge). The PETM started at the onset of a 100 ka eccentricity maxima at 56080 ka BP and ended abruptly during a marked decline in eccentricity at 55883 ka, providing strong support for an orbital trigger of both its onset and termination. The reevaluation of the 3HeET age models of the high paleo-latitude ODP Site 113-690 shows that the prominent sedimentary and carbon isotope steps at this site were controlled by obliquity instead of precession. Our revised chronology suggests that obliquity was also the dominant driver of the repeated drops to lower δ13C values during the PETM in otherwise precession-dominated low latitude sites, possibly reflecting the repeated destabilization of methane hydrate or permafrost carbon stocks at high latitudes.