New Brunswick, N.J. – Scientists examining a spike in worldwide ocean temperatures 55 million years ago have linked it to massive volcanic eruptions that pushed Greenland and northwest Europe apart to create the North Atlantic Ocean.
Writing in the journal Science, geologists at Roskilde University in Denmark, Oregon State University and Rutgers, The State University of New Jersey, present evidence that this intense volcanic activity occurred at the same time ocean temperatures jumped five to six degrees Celsius. A better understanding of previous global warming episodes will give scientists perspective as they study today's climate and ocean level changes pegged to human generation of greenhouse gases.
"That prehistoric volcanic activity released more than 2000 gigatonnes (billion metric tons) of carbon into the oceans and atmosphere in the form of methane and carbon dioxide – two potent greenhouse gases," said Michael Storey of Roskilde University in Denmark, the study's lead author. "The carbon probably came from the heating of earlier deposits of decayed organic matter – similar to deposits in the Atlantic and North Sea we tap today for oil and gas."
The scientists have used precise dating techniques to match a layer of volcanic ash that covers ocean floor sediments of that era with a layer in East Greenland and the Faeroes Islands (north of Scotland), where the ash overlies sequences of basaltic lava. These lavas, which form a layered sequence up to seven kilometers thick, are relics of massive flows from the mid-Atlantic ridge and other fissures along which North America and Europe separated.
"Scientists have known of this major prehistoric global warming episode, called the Paleocene-Eocene thermal maximum, or PETM, for some time," said Carl Swisher, professor of geological sciences at Rutgers. "Marine records document a sudden release of carbon dioxide, known as the carbon isotope excursion, accompanied with an increase in ocean acidity and the extinction of many deep-sea species. Now, for the first time, geologists have a precise correlation to link the sudden increase in volcanic activity and spike in greenhouse gases."
To establish common ages of the PETM-era marine ash layer and the rock formations, the scientists measured the amounts of argon gas trapped in volcanic minerals. That dating method, performed in labs at the three universities, renders precise ages in geological time frames, based on known decay rates of potassium to argon trapped in the volcanic material.
Robert Duncan, a professor in the College of Oceanic and Atmospheric Sciences at Oregon State University, collaborated with Storey and Swisher. Storey is director of the Quaternary Dating Laboratory hosted at Roskilde University, and Swisher is head of the Noble Gas laboratory in department of geological sciences at Rutgers.