Core samples and soundings indicate that massive amounts of methane, stored as frozen hydrate in sediments on the ocean floor, was freed at about the same time as a rapid warming of the global climate.
The finding supports a theory proposed by one of the co-authors, Gerald R. Dickens of Australia's James Cook University that the release of gas hydrates caused what is called the latest "Paleocene thermal maximum." This was a period 55.5 million years ago when ocean temperatures increased 7 to 14 degrees Fahrenheit within only about 1,000 years, a very short period by geologic standards.
A warming trend on land opened migration routes for animals and led to a rapid evolution of the more advanced species. For instance, the first primates appeared during this period.
"This event allowed primitive mammals both to move out into a wider area and to evolve into more modern mammals," said Miriam Katz of Rutgers University, the first author of the paper.
But Katz said that while land animals thrived, 55 percent of some deep-sea species died off. This has been blamed on changes in water temperature and chemistry.
"Nobody has been able explain this sudden climate change until Dickens proposed his theory," she said. Now core samples and soundings from about 200 miles off the east coast of Florida, in an area known as the Blake Nose, is the first hard evidence to support the theory.
Timothy J. Bralower of the University of North Carolina, said the finding by Katz, Dickens and their co-authors is "a very significant discovery. They have found evidence in the rock deposits from that time that is consistent with the theory of what caused the abrupt warming," said Bralower. "It is not 100 percent proof, but it is consistent with the theory."
Katz said the Paleocene gas hydrate release followed a period of gradual warming that started 60 million years ago. This slow warming may have changed the ocean conditions to cause the sudden melting of the frozen gas deposits. The result was sort of a "global burp" that released massive amounts of carbon dioxide into the atmosphere. The gas re-arranged itself chemically, quickly forming an acid in the oceans and adding millions of tons of carbon dioxide to the atmosphere.
The added carbon dioxide set off a sudden global warming trend. Katz said that the amount of carbon dioxide added to the atmosphere was at a rate "comparable to the present-day fossil fuel input."
There are an estimated 14,000 billion tons of gas hydrates in undersea reservoirs now, but the deposits are buried under deep ocean sediments. Bralower said it was unlikely that current global conditions, such as frigid deep sea temperatures, could lead to a suddeny release of these frozen methane deposits.