Paleocene–Eocene Thermal Maximum: Difference between revisions

Revision as of 23:02, 29 October 2004

Revision as of 03:58, 15 November 2004

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Marking the start of the [[Eocene]], the planet heated up in one of the most rapid and extreme global warming events recorded in geologic history, currently being identified as the 'Paleocene-Eocene Thermal Maximum' or the 'Initial Eocene Thermal Maximum' (PETM or IETM). Sea surface temperatures rose almost 8°C over a period of a few thousand years. In 1990, marine scientists James Kennett and Lowell Stott, both then at the [[University of California, Santa Barbara]], reported analysis of [[marine]] [[sediments]] showing that, not only had the surface of the Antarctic ocean heated up about 10 degrees at the beginning of the Eocene, but that the ''entire depth'' of the ocean had warmed, and its chemistry changed disastrously. There was severely reduced oxygen in deep sea waters, and 30 to 40% of deep sea foraminifera suddenly went extinct. Geologist Jim Zachos of the [[University of California, Santa Cruz]] has connected the Eocene heat wave to drastic changes in ocean chemistry that caused the massive worldwide die-off. More recently a synchronous drop in [[carbon]] [[isotope]] ratios has been identified in many terrestrial environments.

Tracking the ratio of carbon [[isotope]]s in marine [[calcium carbonate]] sediments, Kennett and Stott found a sharp decrease in the amount of heavy carbon in 55-million-year-old marine [[fossil]]s, a decline that caused the relative ratio of ¹³C to ¹²C to plunge. A gas with very low amounts of heavy ¹³C must have literally flooded the atmosphere. In 1995, Gerry Dickens, [[University of Michigan]], argued that only [[methane]] gas had enough light carbon to produce the early Eocene plunge. He proposed that a belch of methane escaped from ice in seafloor sediments as the Earth warmed during the latest Paleocene. The methane escaped from submarine [[clathrate]]s, ice crystals that trap [[methane hydrate]], a form of methane 'ice' that forms in cold bottom water under great pressures and is widely distributed and plentiful in sediments on the outer edges of continental margins. Methane has a [[global warming potential]] (GWP) of 21, meaning it is estimated to be 21 times as effective as [[carbon dioxide]] as a [[greenhouse gas]]. The massive [[sublimation (physics)|sublimation]] and release of sedimentary methane hydrates into the ocean-atmosphere reservoir upset the global [[carbon cycle]] and led to runaway [[global warming]].

In the atmosphere, methane breaks down and releases carbon dioxide. According to Zachos and Dickens, methane combined with oxygen in the air and water, forming carbon dioxide and essentially suffocating marine life. But whether [[volcanic]] activity or a methane belch was the culprit, the greenhouse gas locked in the sun?s warmth, sending global temperatures soaring.