Ancient Global Warming

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Science  13 Dec 2002:
Vol. 298, Issue 5601, pp. 2093-2095
DOI: 10.1126/science.298.5601.2093d

The Paleocene-Eocene thermal maximum occurred at the close of the Paleocene Epoch about 55 million years ago. Within a few thousand years, sea surface temperatures warmed by 4° to 8°C, and deep ocean temperatures increased by 5°C. This episode, which lasted for approximately 210,000 years, induced a host of biotic responses and produced a large perturbation in the marine and terrestrial carbon isotopic records. It is believed that this event was caused by massive dissociation of marine sedimentary methane hydrates, but the sequence of processes that triggered it is still obscured by the difficulty of determining its timing and duration.

Thomas et al. present high-resolution stable isotope records based on analyses of single planktonic and benthic foraminiferal shells, demonstrating that the initial carbon isotope excursion was geologically instantaneous and was preceded by a brief period of gradual surface-water warming. Methane-derived carbon was mixed from the surface ocean downward, suggesting that a significant fraction of the initial dissociated methane hydrate reached the atmosphere before oxidation. This supports the idea that the Paleocene-Eocene thermal maximum was triggered by a small surface ocean warming, followed by the injection into the atmosphere of large amounts of methane, a potent greenhouse gas, derived from marine sedimentary sources. — HJS

Geology30, 1067 (2002).

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