Ice Age Insights: Samples of Air from Glacial Times Add Pieces to the Ice Age Puzzle

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Ice Age Insights

With all the concern about "greenhouse" gases warming the world, it may seem trange that research on the ice ages is heating up. Yet those who study the Earth view hot and cold merely as different faces of the planet's poorly understood climate. Before scientists can predict how the environmental burden of 5 billion human beings may warp the world, they need to understand how the climate behaves on its own. Topping the list of questions is the mystery of why the planet periodically slips into a deep freeze.

"The glacial cycle is the biggest climat e change on Earth in the time that we human beings have been here. If you can't understand the biggest, you have a little credibility problem when you try to tell people about a couple degrees of warming because of carbon dioxide," says climatologist Stephen H. Schneider from the National Center of Atmospheric Research in Boulder, Colo.

While geologists, mathematicians and astronomers have attempted to explain the causes of the ice ages for more than a century, researches are now riding a wave of new informationa bout the glacial cycle. Analyses of air bubbles in the ice caps of Greenland and Antarctica reveal that the ice age atmosphere held a far different mix of greenhouse gases, dust and other particles, all of which may have played a role in cooling the Earth.

Many of the new findings emerge from a joint Soviet-French effort at the Vostok drillhole in east antarctica. In 1985, after 14 years of difficult drilling into the ice cap, a Soviet team from the Arctic and Antarctic Research Institute in Leningrad and from the Academy of Sciences in Moscow had carefully extracted an ice core more than 2 kilometers long, the deepest ever obtained. The ongoing chemical analysis of the core is being completed in France by Claude Lorius and his colleagues at the Laboratory of Glaciology and Geophysics in St. Martin D'Heres and at the Laboratory of Isotopic Geochemistry in Gif sur Yvette (SN: 8/31/85, p.141).

"Vostok is by far the most exciting work in this field in the last decade or two decades," says geologist Isaac Winograd from the U.S. Geological Survey in Reston, Va., who is investigating the glacial cycle by studying mineral deposits in Nevada. Atmospheric scientists Robert Charlson from the University of Washington in Seattle comments, "If there were a Nobel Prize for earth sciences, Lorius and his colleagues would get it."

The Vostok core harbors some 160,000 years' worth of climate information about Antarctica and the rest of the world. That time span is important because it covers more than one full glacial cycle. Starting in the present warm period, called an interglacial, the core reaches back through the last ice age, which gripped the Earth's climate for almost 100,000 years, then into a previous interglacial and finally to the tail end of the second-to-last ice age. Four other major ice cores recovered from the Antarctic and Greenland record only part of a cycle.

In Vostok and the other cores, climate experts have struck a bonanza. Bubbles within the ice preserve tiny samples of the atmosphere from times when ice covered large patches of the globe, giving scientists their first glimpse of the part the atmosphere plays in the glacial cycle. Another prime source of climate information, cores of deep-sea sediments, can record several million years' changes in ocean temperature and ice cap volume. Yet they reveal relatively little about what goes on in the atmosphere above the ocean.

Geologically speaking, the Earth is now in the middle of an ice age. If it seems warm outside, it's just a brief reprieve during an extended glacial cycle. For about 700,000 years running, the planet has swung in and out of a full-scale chill -- a sharp contrast to Earth's normally balmy state.

From geologic evidence, deep-sea cores and no the ice cores, climate experts think the principal ice age pattern goes something like this: The Earth slips hesistantly into a glacial period lasting around 100,000 years and then warms for a short interglacial time, which is what we now enjoy. …