Ocean cooling may solve Antarctic mystery

By Alister Doyle, Environment Correspondent

OSLO (Reuters) - Fossil evidence of a cooling of the oceans 35 million years ago may have solved a mystery about how Antarctica froze over in one of the big climate shifts in Earth's history, scientists said on Thursday.

The fossil signs of a 2.5 Celsius (4.5 Fahrenheit) fall in ocean temperatures, enough to trigger the formation of Antarctica's ice sheet, may also help understand whether the continent will thaw because of modern global warming.

A full melt of Antarctica would raise world sea levels by about 57 meters (190 ft) over thousands of years. Even a small melt would threaten coastal cities from Shanghai to New York or low-lying islands.

"New evidence could solve the puzzle of why Antarctica went into the deep freeze," the University of Cardiff said of a study by scientists in Wales and the United States and published in the Geological Society of America's journal Geology.

"Now we understand the system better," Caroline Lear, of Cardiff University and lead author of the study, told Reuters. "Some other records had suggested there was even a warming at that time, which was really confusing."

The study, of pin-head sized fossil animals known as foraminifera found in mud in Tanzania, showed that the oceans cooled 35 million years ago, perhaps after shifts in the earth's orbit around the sun.

In cooler temperatures the shells of foraminifera contain less magnesium than in warmer water. The sediments originally had been part of the Indian Ocean.

CARBON