Evidence for historic global warming published in Science

November 17, 1999

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 corrosive waters killed many of the deep-sea species," according to the article. "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 after the LPTM, although marine and terrestrial ecosystems were forever changed."

Pak explained that the sediment core, removed as part of the Ocean Drilling Prog ram, was taken from an area known as the Blake Nose, a promontory on the continental shelf off the coast of Florida. She said that the core shows disturbed sediment, evidence of a submarine landslide layer that fits with the theory of the melting of buried methane--methane clathrates--from an ice-like solid into a gas.

The article concludes with a call for further research, "Even though our results suggest that methane was released from the Blake Nose region, during the LPTM, the mass of methane from this region alone is insufficient to explain the magnitude of global perturbations at the LPTM. Other sections deposited on the middle to lower slope during the LPTM also must exhibit features similar to those reported here."

Besides Pak, co-authors on the paper are: Miriam E. Katz and Kenneth G. Miller from Rutgers University, Piscataway, New Jersey, and Gerald R. Dickens from James Cook University, Townsville, Queensland, Australia.
-end-


University of California - Santa Barbara

Related Global Warming Articles from Brightsurf:

The ocean has become more stratified with global warming
A new study found that the global ocean has become more layered and resistant to vertical mixing as warming from the surface creates increasing stratification.

Containing methane and its contribution to global warming
Methane is a gas that deserves more attention in the climate debate as it contributes to almost half of human-made global warming in the short-term.

Global warming and extinction risk
How can fossils predict the consequences of climate change? A German research team from Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), the Museum of Natural History Berlin and the Alfred Wegener Institute compared data from fossil and marine organisms living today to predict which groups of animals are most at risk from climate change.

Intensified global monsoon extreme rainfall signals global warming -- A study
A new study reveals significant associations between global warming and the observed intensification of extreme rainfall over the global monsoon region and its several subregions, including the southern part of South Africa, India, North America and the eastern part of the South America.

Global warming's impact on undernourishment
Global warming may increase undernutrition through the effects of heat exposure on people, according to a new study published this week in PLOS Medicine by Yuming Guo of Monash University, Australia, and colleagues.

Global warming will accelerate water cycle over global land monsoon regions
A new study provides a broader understanding on the redistribution of freshwater resources across the globe induced by future changes in the monsoon system.

Comparison of global climatologies confirms warming of the global ocean
A report describes the main features of the recently published World Ocean Experiment-Argo Global Hydrographic Climatology.

Six feet under, a new approach to global warming
A Washington State University researcher has found that one-fourth of the carbon held by soil is bound to minerals as far as six feet below the surface.

Can we limit global warming to 1.5 °C?
Efforts to combat climate change tend to focus on supply-side changes, such as shifting to renewable or cleaner energy.

Global warming: Worrying lessons from the past
56 million years ago, the Earth experienced an exceptional episode of global warming.

Read More: Global Warming News and Global Warming Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.