The causes and consequences of a rapid global warming event 55 million years ago

The Paleocene-Eocene thermal maximum (PETM) at ∼55 Ma provides an unparalleled opportunity to explore the causes and consequences of rapid global warming. Associated with PETM warming were major changes in the Earth's climate, oceans, biota, and global carbon cycling, all of which occurred in a geologic instant.; Neodymium isotope data from an array of deep-sea sites enable reconstruction of the pattern of deep-sea circulation before, during and after the PETM. The data suggest a single, dominant source of deep waters that formed off Antarctica and circulated throughout the Atlantic and proto-Indian Oceans. Stratigraphic records of Nd isotopes indicate that a fundamental change in the pattern of deep-sea circulation did not precede PETM deep-water warming.; The stratigraphic sequence of events at the onset of the PETM from Ocean Drilling Program Site 690 indicates that oceanic environmental and biotic changes began in surface waters and progressed downward. Stable isotope analyses of individual planktonic and benthic foraminifera indicate that PETM warming began gradually. Warming of intermediate and deep waters during the PETM may have resulted from sea-surface warming in the regions of subduction and downwelling.; The carbon isotope excursion appeared first in surface waters coincident with the onset of deeper-water warming. Subsequently excursion carbon isotope values were recorded in intermediate and deep waters. In contrast to the gradual warming, the carbon isotope change occurred in a geologic instant.; This project provides the first evidence for a period of sea-surface and deeper-water warming prior to the rapid onset of the carbon isotope excursion, supporting a thermal mechanism for dissociation of methane hydrate. The top-down progression of the carbon isotope excursion indicates that much of the initial methane released from hydrate dissociation may have reached the atmosphere prior to oxidation.