Jamie Morton is the NZ Herald's science reporter.

Scientists probe Antarctic ice sheet for fossil clues to future under global warming

Dr Richard Levy near the expedition site at Mt Discovery, which may hold clues to Earth’s future.
Dr Richard Levy near the expedition site at Mt Discovery, which may hold clues to Earth’s future.

Call it extreme geology: a team of Kiwi scientists is 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 the continent's unforgiving weather - including 150km/h wind storms that recently shredded tents at a US camp.

The expedition, 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 about 50 years ago.

The discoverers found shells of organisms that could not 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," said Professor Naish. "This period is a pretty important window for understanding what might happen with global warming."

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

That same level has been reached today through the human carbon emissions projected to heat the climate by several degrees by 2200.

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 four researchers will be using pickaxes to dig out fossils of scallops, barnacles and plankton, which will be further analysed for tell-tale geochemical 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 that 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 the Mt Discovery site lay in the middle of the West Antarctic rift system - one of the largest 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 such as Pine Island were important because they were already experiencing rapid mass loss and melting, Mt Discovery 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."

- NZ Herald

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