By analyzing a core of sediments taken from the ocean floor, scientists have discovered strong evidence linking a dramatic period of global warming, approximately 55.5 million years ago, to a massive release of methane, an event that resulted in an extensive die-off of deep sea dwelling organisms, according to this week's issue of the journal Science.
The warming, referred to as the "latest Paleocene thermal maximum" or LPTM, occurred over a 10,000 to 20,000-year interval and corresponds to the appearance of numerous mammals (including primates) and the extinction or temporary disappearance of many deep-sea species. (This period was originally discovered by James P. Kennett a University of California, Santa Barbara geology professor and his student Lowell Stott.)
Co-author Dorothy Pak, researcher in the Department of Geological Sciences and the Marine Science Institute of the University of California, Santa Barbara, explained that the new information is the "first tangible evidence for a methane dissociation event," a concept that has long been hypothesized.
According to the hypothesis, vast quantities of methane were stored as frozen gas hydrate in the upper few hundred meters of continental slope sediments before the latest Paleocene thermal maximum. "Long-term global warming during the late Paleocene pushed the ocean-atmosphere system past a critical threshold, causing warm surface waters to sink, and intermediate to deep ocean temperatures to rise by approximately 4 to 8 degrees centigrade," according to the Science article.
The result was a chain of reactions in the global carbon cycle as the methane melted and was released in bubbles that interacted with dissolved oxygen, "adding carbon to all reservoirs of the global exogenic carbon cycle."
"Higher bottom water temperature, lower dissolved oxygen, changes in
surface water productivity, and more co
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Contact: Gail Brown
gbrown@instadv.ucsb.edu
805-893-7220
University of California - Santa Barbara
17-Nov-1999