News in Science - Glacial mud reveals Earth's history =

Glacial mud reveals Earth's history

Anna Salleh

ABC Science Online

Friday, 11 June = 2004

Mud that's millions of years old = was formed=20 by glaciers like this scraping against valley walls = (Image:=20 Bob Carter)

The Earth's atmosphere, rather than its = oceans,=20 could be the key driver in climate change, according to new = climate=20 records that date back four million years.

A paper = reporting=20 ocean cores taken from the mud of ancient glaciers off the = east=20 coast of New Zealand is published in today's issue of the = journal Science.

"Long term = climate change=20 is the important thing we need to understand if we're going = to=20 manage climate," said lead author Professor Bob Carter of James Cook=20 University in Townsville.

One of the key tools = that=20 scientists use to learn about past climates is analysing ice = cores=20 from Antarctica and Greenland. Tiny air bubbles trapped in = the cores=20 tell them what the atmosphere was like throughout Earth's=20 history.

Together with oxygen measurements in ocean = cores,=20 which provide information on global ice volume and cover, = such=20 evidence tells us that the Earth has undergone regular = glaciation=20 and warming every 40,000 years, and more recently every = 100,000=20 years.

But, says Carter, climate change involves a=20 redistribution of heat around the globe, and what cores = haven't been=20 able to tell scientists so far is whether heat is mainly=20 redistributed by the atmosphere or by the oceans.

The = atmosphere redistributes heat around the globe within a year = whereas=20 the oceans are estimated to take about 1000 years. So, = climate=20 change driven by changes in the atmosphere is more likely to = be=20 rapid, resulting in similar patterns of glaciation in = different=20 parts of the globe at the same time.

"The key thing = is you=20 can't decide this issue by just having cores from the = poles," Carter=20 told ABC Science Online. "You have to have cores from = the=20 mid-latitudes."

The New Zealand Southern Alps = (Image:=20 Bob Carter)

This is = why Carter=20 and colleague Dr Paul Gammon from the University of=20 Adelaide examined cores from an ocean drilling site off = New=20 Zealand. The site, dubbed ODP 1119, is 100 kilometres off = the=20 country's South Island and east of a chain of snow-capped = mountains=20 called the New Zealand Southern Alps.

According to = Carter,=20 this was were mud plumes were dumped, a result of huge = glaciers=20 melting as the earth warmed at the end of each=20 glaciation.

From this site the international Ocean = Drilling=20 Program obtained a 500-metre long core of mud dating back = four=20 million years and covering more than 75 = glaciations.

Gamma=20 radiation from glacial mud deposits in the core provided = researchers=20 with the climate information they were after. "The more = gamma rays,=20 the colder the climate and the more ice on the South = Island," Carter=20 said.

When Carter and Gammon checked the major = glaciation=20 cycles detected in the ODP 1119 core they found they were = similar to=20 the cycles detected by Antarctic and Greenland ice=20 cores.

"Over the long term, climate change in = Antarctica and=20 in the mid-latitude southern hemisphere have been in = lock-step,"=20 Carter said.

He said that even on a finer scale of = resolution=20 the available cycles for Antarctica and New Zealand were=20 "astonishingly close". He said that because they were so = similar on=20 such a short time scale, this suggested that the atmosphere = may be=20 the key driver for climate.

"It doesn't prove it but = it is=20 consistent with it," Carter said.

Carter also said = the new=20 ocean core containing gamma ray signals could provide a = surrogate=20 for Antarctic climate, that is such an important part of=20 understanding Earth's climate as a whole. This is especially = important since ice cores are unlikely to go back beyond one = million=20 years, he said. The New Zealand cores could go back maybe = four times=20 further.

"That's a remarkable thing to be able to = do," he=20 said.

Carter said the cycles obtained from the New = Zealand=20 cores also agreed with the record obtained from the new = 3000-metre=20 Antarctic ice core published in the journal Nature=20 yesterday. He described yesterday's work as "splendid = science" but=20 cautioned against forcing interpretations of its findings to = contemporary climate change.

"There is no doubt we = are going=20 to go into another glaciation," he said. "The question is = when, and=20 we can't predict that yet."