Exploring Antarctica: the search for ancient water

Call it extreme geology: a team of Kiwi scientists are venturing to a remote part of Antarctica to dig up ancient evidence of a warmer world.

The treasure trove of fossilised marine life buried in the rock near Mt Discovery - about 50km from Scott Base - could help us better understand what might happen to our planet under future climate change.

It's a place exposed to some of the unforgiving weather on the continent - including 150km/h wind storms that recently shredded the tents of a US camp.

The expedition, being led by Dr Richard Levy of GNS Science and Professor Tim Naish of Victoria University's Antarctic Research Centre, aims to follow up descriptions of a similar site found nearby by a science party around 50 years ago.

Importantly, Professor Naish said, the party found shells that represented organisms which couldn't live in the sea ice that covers the environment today.

"The samples are telling us it was a warmer world, but we want to know when that was and how old the deposit is; we think it's probably from about three million years ago.

"This period is becoming a pretty important window for understanding what might happen in the coming centuries with global warming."

Called the Pliocene, it was the most recent time in the Earth's history that there was 400 parts per million of carbon dioxide in the atmosphere.

That same level has been reached today through the human carbon emissions projected to heat the planet's climate by several degrees by the end of the century.

In the so-called Pliocene "hot house", the sprawling West Antarctic Ice Sheet - which stores the equivalent of four metres of global sea level rise - had disappeared.

This week, the team of four researchers will be using pick axes to dig out fossils of scallops, barnacles and plankton, which will be further analysed for tell-tale geo-chemical signatures.

"We call them paleo-thermometers as we can do some chemistry on the shells and reconstruct the water temperature from the time the animals were alive," Professor Naish said.

Just the fact there was a rich sedimentary record there crucially set it apart from many other areas of the West Antarctic Ice Sheet.

"If you go to Pine Island, which is on the Amundsen Sea side of Antarctica, glaciers advancing and retreating over time have pretty much stripped away all of the geological record, leaving just hard basement rock behind."

Because Mt Discovery site lay in the middle of the West Antarctic rift system - one of the largest such systems on the planet - a gradual subsiding of the Earth's crust created an environment where the sediments recording past changes could be captured.

"As geologists we are searching for these hidden records in the rock, but the problem is that they are often covered by ice."

"However on Mt Discovery, these sediments are exposed at the surface."

While sensitive areas of the West Antarctic Ice Sheet like Pine Island were important because they were already experiencing rapid mass loss and melting, the Mt Discovery site provided evidence of what the much larger East Antarctic Ice Sheet may have done during the warmer ancient climate.

"The thing is, when this place starts to melt, it's the last to go - so you know you're in real trouble."