ASTRONOMICAL PACING OF LATE PALAEOCENE TO EARLY EOCENE GLOBAL WARMING EVENTS

Superimposed on the late Palaeocene - early Eocene warming trend is a short-lived global warming (hyperthermal) event, known as the Palaeocene-Eocene thermal maximum (~55 million years ago). The leading hypothesis to explain the extreme greenhouse conditions during this event is the dissociation of 1400–2800 Giga tons of methane from oceanic clathrates, resulting in a large (>2.5‰) negative carbon isotope excursion and severe carbonate dissolution in marine sediments. Possible triggering mechanisms include the overshoot of a threshold due to gradual global warming, comet impact, explosive volcanism and ocean current reorganization and erosion at continental slopes, whereas orbital forcing was excluded. We report on a second hyperthermal event ~2 million years after the Palaeocene-Eocene transition, characterised by a distinct carbonate-poor red clay layer (Elmo horizon) in deep-sea cores from Walvis Ridge. This event has similar geochemical and biotic characteristics as the Palaeocene-Eocene thermal maximum, but is smaller in magnitude. Moreover, we show that both events correspond to maxima in the ~405kyr and ~100kyr eccentricity cycles that post-date prolonged minima in ~2.25Myr eccentricity cycle, implying that they are astronomical paced.