THE TRIGGERING MECHANISM(S) OF MASSIVE METHANE HYDRATE DISSOCIATION AT THE P/E BOUNDARY

One of the more extreme and abrupt episodes of global warming in Earth history occurred approximately 55 Mya. This event, referred to as the Late Paleocene Thermal Maximum (LPTM), was transient in nature, lasting less than 200 ky. It is characterized by several significant environmental changes including 4-8°C of warming of the oceans, and increased precipitation in mid- to high latitudes. These unusual climate perturbations had a marked impact on global biota including; mass extinction of marine benthic foraminifera; temporary displacement of planktonic organisms by "exotic" taxa; and a highly unusual radiation of terrestrial vertebrates. In addition, the LPTM has been linked to a prominent perturbation in the global carbon cycle as reflected by a ~3 ‰ negative carbon isotope excursion (CIE) in the marine, atmosphere, and terrestrial carbon reservoirs. This perturbation most likely resulted from the sudden (<20 kyr) dissociation of 2000 Gt of methane hydrate from the seafloor. In this paper, we present stable isotopic and microfossil assemblage records from several deep-sea sites which provide insight into the pattern of methane release and redistribution between various oceanic/atmospheric reservoirs, as well as the paleoecological response. The critical record is based on analyses of individual specimens of foraminifera sampled at the cm level from a 1 meter core spanning the LPTM. These data allow us to separate the effects of sediment reworking on the isotopic time-series, thereby providing an alternative perspective on the evolution of the carbon isotope signal in various oceanic reservoirs. This perspective supports the notion that the methane dissociation was preceded, and hence triggered by gradual global warming. The global warming, in turn, was likely part of a long-term trend driven by mantle outgassing of CO₂.