Historic global warming linked to methane release
Copyright 1999, Environmental News Network
November 19, 1999
By John Roach
An intense period of global warming about 55.5 million years ago has been linked to a massive release of methane, an event that killed many deep-sea species and enabled terrestrial animals to flourish, according to an article in today's issue of the journal Science.
The warming, known as the "latest Paleocene thermal maximum," 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.
The link between this warming period and the methane release is based on analysis of a sediment core taken from the ocean floor and is the first tangible evidence of a long held hypothesis, said Dorothy Pak, a researcher at the University of California, Santa Barbara, and co-author of the study.
According to the hypothesis, vast quantities of methane were stored as frozen gas hydrate in the upper 1,500 feet of continental slope sediments before the latest Paleocene thermal maximum, during which ocean waters warmed by 7 to 14 degrees.
"This warming propagated into the sediments, converting once solid CH4 [methane] hydrates into free gas bubbles," according to the science article. The methane bubbles interacted with dissolved oxygen, "adding carbon to all reservoirs of the global exogenic carbon cycle."
The warmer water temperatures combined with lower dissolved oxygen and other changes in the seas caused many deep-sea species to die or disappear temporarily.
"On land, higher partial pressure of carbon dioxide and elevated temperatures quickly opened high-latitude migration routes for the widespread dispersal of mammals. Over several hundred thousand years, global carbon and oxygen cycles gradually returned to equilibrium conditions," according to the article.
The sediment core was taken from an area known as the Blake Nose, a promontory on the continental shelf off the coast of Florida, as part of the Ocean Drilling Program.
The core shows disturbed sediment, evidence of a submarine landslide layer that fits with the theory of the melting of buried methane from an ice-like solid to a gas, said Pak.