Climate clues rock science

2007-02-28 12:45

Jena, Germany - Samples of rock drilled out of the Antarctic seabed show there has been a surprisingly wide variation in the world's climate over the past 3.5 million years, a German geo- scientist said on Tuesday.

"It's blown away the prevailing wisdom that we had a steady cold phase during this era," said Lothar Viereck-Goette, a professor at the University of Jena who is examining rock raised by the four-nation Antarctic Geological Drilling (Andrill) project.

"That means that climate variation is something normal, not out of the ordinary," he said.

The drill site was in the seabed under the Ross Ice Shelf, where sediment provides evidence of expanding and contracting ice sheets.

The project obtained a 1 ,284m-deep drill core that will tell the scientists how the climate at the South Pole has varied over a period of 12 million years. Andrill said the rock will also give clues to the likely effects of human-caused global warming.

The professor said the only stable climatic phase with a steady icecap had been between 800 000 and 400 000 years ago.

Quite 'boring'

"For that period, the core is quite boring," he joked.

Deeper, older layers showed a continuous variation between warm and cold phases, during which the glaciers receded then returned.

"The ice sheet is a lot more variable than we realised before," he said.

Scientists had previously assumed that when a warm climatic period on Earth ended four million years ago, the icecap formed and stayed.

About five million years ago, Antarctic glaciers had largely melted away.

"That warm period lasted almost one million years and was not restricted just to the Antarctic," said Viereck-Goette.

The drill cores are still in the Antarctic, but are due to be transported to Florida in the next few months and then to be distributed to research laboratories in the United States, Italy, New Zealand and Germany.

The German laboratories in Jena and Goettingen have been tasked with a chemical analysis of sediments and volcanic ash found in the cores. - Sapa-dpa

- SAPA