Washington, Apr 27 : A massive volcanic eruption that pushed Greenland and northwest Europe apart to create the North Atlantic Ocean, was responsible for the worldwide spike in ocean temperatures some 55 million years ago.

Geologists from the Roskilde University in Denmark, Oregon State University, Rutgers and the State University of New Jersey, who conducted the study, said the intense volcanic activity occurred at the same time ocean temperatures jumped five to six degrees Celsius.

"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. 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," said Michael Storey of Roskilde University in Denmark, lead author of the study.

As part of the study, the researchers used precise dating techniques to match a layer of volcanic ash that covered 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 kilometres 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. 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," said Carl Swisher, professor of geological sciences at Rutgers.

According to the researchers, a better understanding of previous global warming episodes will provide them with a better perspective to study today's climate and ocean level changes in relation to human generation of greenhouse gases.

The study appears in the journal Science.