(From a classic Popular Science Article)
Getting to Antarctica requires an eight-hour flight to McMurdo Research Station from Christchurch, New Zealand, in the equivalent of a B-52 on skis. You wear full polar gear, including a pair of massive rubber moon boots, two sets of long underwear, polyester overalls, and a fur-trimmed parka. Passengers strap in, shoulder-to-shoulder, on benches made from cloth webbing.
After landing at McMurdo, I took a second flight to Shackleton Camp, where the dynamists’ team had been working for the past two months. Stiff from the long, cold ride, I stood up, stretched, and looked through the window for any sign of life in this foreboding, desolate land. I saw six Quonset huts, a handful of tents, and two outhouses perched on a slab of ice in the middle of a mountain valley. Once outside, my parka rippling against the freezing wind, I tried to imagine a land that the dynamists say once looked like the green fjords of Chile. I quickly gave up, and walked as fast as I could toward food and shelter. On the way to the hut, I ran into David Harwood of the University of Nebraska, who was returning to McMurdo to pack off his samples. There on the airstrip, he laid out the details of his story. By the end of the tale, the idea of water in valleys like this one seemed almost plausible.
It all began in 1983 when Peter Webb, a geologist at Ohio State University, and Harwood, then a graduate student, performed a laboratory analysis of glacial sediment from the Transantarctic Mountains. What they discovered was astonishing: The sediment, known as the Sirius Group, contained diatoms, or marine microfossils, that were only three million years old. This suggested that the climate during the Pliocene may have been warm enough to melt the ice cap and allow the ocean that surrounds Antarctica to flood its subglacial basins. Later that year, Harwood left for the frozen continent, where he dug up additional sediment samples from the Reedy Glacier area. They too contained diatoms of three-million-year-old vintage.
At first the findings were dismissed. The few scientists who gave them any thought said that the diatoms must have somehow blown into the sediment from the sea floor. It was a fluke, they said.
Back in 1983, it was generally agreed that after Antarctica splintered from the southern supercontinent Gondwana over 100 million years ago, it slid into a deep freeze, accumulating an ice cap that has remained about the same size for the past 15 million years. There was no reason to doubt this picture. It was supported by geological studies of Antarctica, as well as deep-sea oxygen isotope measurements that reflect ice volume and temperature changes.
But in 1985, Webb and Harwood visited Beardmore Glacier, where they found bits of wood later identified as southern beech. This made them think that perhaps small trees once grew there. They confirmed this hypothesis in 1990 by unearthing beech tree leaves and roots. The survival of these plants, they say, indicates a prolonged warm period.
Three years later, beetle remains turned up in the rubble. With this find, Harwood and Webb’s notion of a dynamic ice sheet and climatic shifts finally grabbed the interest of a cadre of experts. “The survival of a beetle during the Pliocene in Antarctica implies that temperatures were significantly warmer than present,” says micropaleontologist Allan Ashworth of North Dakota State University in Fargo.
In the field season that ended in 1996, Harwood and Webb took further steps to investigate their theory. First, they revisited the Dominion Range to collect more fossils. Then, they scoured a new site called Bennett Platform, and studied its geology. Finally, they collected samples from 15 other Sirius sediment sites throughout the Transantarctic Mountains to sift for diatoms. “If they blew in, then there should be a uniform distribution of them,” Harwood says. They should also vary in age.
It will take several years to analyze the diatom populations. In the meantime, Harwood and his team are puzzling over a mosslike plant colony found at Bennett Platform. Harwood says it probably grew in wetlands that were eventually covered by silt from a nearby river or stream during a glacial advance. The geology of the area, which is part of the Sirius Group, suggests that a lot of water was present when the rock face formed.
Ashworth also made a fascinating discovery: He found seeds and sea shells in the box of rocks he brought back from the field last year. “They’re interesting in their own right,” he says, because neither fossil group had previously been found on Antarctica. But their true value may be in their ability to date the sediment in which they were found.
Meanwhile, a variety of other research has begun to yield supportive evidence. One study suggests that warm-blooded sea creatures, including dolphins, may have migrated closer to Antarctica during the Pliocene, which would have meant warmer water. Other studies have found evidence that, about three million years ago, sea levels were between 25 and 30 meters higher than they are now, perhaps due to ice cap melt.
“The evidence is quite compelling,” says paleontologist Brian Huber of the Smithsonian’s Museum of Natural History. But not to the stablists. A period of climatic warming at a time when other evidence suggests Antarctica was completely covered by ice remains unacceptable to many scientists. To hear the stablists’ side of the story, I flew to Antarctica’s Dry Valleys to meet with George Denton of the University of Maine, and David Marchant of Boston University.
As I flew by helicopter over McMurdo Sound toward the Dry Valleys, I soon realized that this place was like no other I had seen in Antarctica. There is no ice or snow in the Dry Valleys. Mummified seals lie in heaps. Wind-sculpted rocks decorate the hillsides. This area, which is about 1,260 square miles, has rifts and valleys no less impressive than the Grand Canyon, plus ephemeral streams, levees, and sand beaches.
Denton has worked here for more than 20 years, and knows more about this landscape than anyone else in the world. Now, to learn more about the climate during the Pliocene, Denton and Marchant are combining their study of the landscape (geomorphology) with that of ash that blows into the area from offshore volcanoes.
I land in Bull Pass, a desert pavement 20 miles from Mt. Fleming. It is so flat and so barren that it has been likened to Mars before the big freeze. Indeed, there is no visible sign of life except for a tiny camp consisting of two tents and a portable stove. As we hike over what look like the rounded backs of dinosaurs, Denton tells me that he believes Antarctica’s massive ice sheet has remained fairly stable for 10 million to 15 million years.
Marchant then strolls over to a sandy mound where he has been digging for ash with a trowel. He says that he reads the history of climate by examining how rocks weather, and where they are found. Then, for a chronological framework, he looks for nearby volcanic ash. Ash, like rocks, can reveal environmental clues through its content and current condition. And because it is the last thing to land on the surface of a formation, it can pinpoint a minimum age for the rocks.
Marchant and Denton have collected rock samples from Mt. Fleming and Table Mountain, nearby peaks with the same Sirius Group glacial sediments as the area around Shackleton Camp. The two scientists say these rocks have been preserved in dry and cold conditions, and show no sign of erosion. This suggests that the Dry Valleys have remained a cold desert for much longer than three million years.
The team has also mapped 75 ash deposits, and obtained dates for 50 of them. The samples show that the ash formed in a cold, dry environment, and remained undisturbed. It was found on rocks that are unmarked by any massive ice-sheet movement.
In addition, geologist David Sugden of the University of Edinburgh in Scotland has found an eight-million-year-old ice slice in the Dry Valleys that he says could not have survived a warming period. And cores extracted from the ocean floor around Antarctica show no curtailment of sediment from melting icebergs, as would be expected if the continent was partly ice free during the Pliocene.
Taken together, these results speak volumes in favor of a dry, cold, steady state. They indicate that the Pliocene temperatures were only three to eight degrees Celsius above today’s temperatures, and that the ice sheet covering the Transantarctic Mountains overrode the area more than 10 million years ago.
“We do not deny that Harwood is finding the fossils,” says Merchant. In fact, he says, “we’d expect it.” Before Antarctica split from Gondwana, it supported many of the same plants and insects that are now found in South America and New Zealand. So these fossils may represent the last vestige of these life forms. “What we disagree with is the timing of it all,” Merchant says.
While Harwood and Webb contend that their miniature forest withered three million years ago, Denton and Merchant argue for at least 23 million years ago, when Antarctica was clenched firmly by the icy grip that still holds it today. “Their entire argument relies on the diatoms, which we think may have blown in,” Merchant says. Meanwhile, Harwood questions the validity of the Dry Valleys results, saying “that area is anomalous now, maybe it was then too.”
For now, the argument remains unsettled. Though Harwood says that both camps may eventually prove to be correct – that there was a long period of cold punctuated by relatively short bursts of heat – Merchant disagrees, saying “these are mutually exclusive positions and there is no evidence for an intermediate theory.”
About the only thing both camps agree on is that the key to solving this mystery is to establish, once and for all, the age of the Sirius sediment fossils. Although this will be difficult, because there is no definitive technology on which to rely, an attempt will be made this year. An independent group of researchers will drill a core from the Sirius Group rocks to determine whether diatoms exist below the surface (and therefore are unlikely to have been windblown), or only near cracks or at the top.
Both groups recognize the urgency of coming to a firm conclusion. The Antarctic ice sheet affects not only global sea level, but also world climate. So agreement on a clear picture of the past could help to cast a more accurate vision of Earth’s future. If the stablists are correct, and the eastern ice sheet remained frozen during the Pliocene, then there is little reason to worry about the fate of our coastal cities. A major temperature increase would be required to have any effect. But if the dynamists are right, and the ice sheet did melt down, then a moderate rise in the mercury could one day bring on the floods. For now, however, the answer lies hidden in Antarctica’s frozen landscape.
While the fate of Antarctica’s eastern ice sheet is uncertain, scientists have plenty of reasons to believe that the smaller western sheet could eventually slip into the ocean. It is the world’s only remaining marine ice sheet. The others, which existed in the Northern Hemisphere, disintegrated and melted away during the Pliocene period.
There are signs that the west Antarctic ice sheet is already breaking up. A huge iceberg broke free of the Larsen ice shelf in 1995. Shortly thereafter, a 40-mile-long crack opened in the adjoining shelf area. Now, ice streams that flow through the sheet are behaving erratically.
Last year, Stanley Jacobs of Columbia University’s Lamont Doherty Earth Observatory made the first oceanographic measurements across a deep channel beneath the leading edge of Pine Island Glacier. His findings show that the west Antarctic ice sheet is losing mass to the oceans. But whether this instability is symptomatic of an impending collapse remains unknown.
To further study the current state of the west Antarctic ice sheet, and to predict its future, the National Science Foundation is sponsoring a variety of Antarctica-based research projects. For example, Cal Tech scientists at Upstream Bravo Camp are sinking ice strings and digging ice cores to study the movement of fast-flowing ice streams. They’re also burying seismic monitors in snow fields to listen for “ice quakes” set off by colliding ice sheets. The study is using a variety of RAID 10 servers to store the data, a great improvement from the original data storage solution they looked at, which in the end required RAID 5 recovery, a common data recovery service offered by clean-room enabled hard drive recovery companies like Irvine’s HDRA.
How Antarctic Ice Affects World Climate
Think of the Antarctic ice sheet as Earth’s refrigeration unit: It exerts a major two-way control over today’s global environment.
First, the ice sheet (along with a raft of ice that surrounds it in the southern ocean) reflects back into space about 80 to 85 percent of the sun that hits it. So icy Antarctica, which records the coldest temperatures on Earth, helps to reduce the world’s overall heat budget.
Second, the near-freezing meltwater that runs off the ice cap, along with the water from melting icebergs, falls to the ocean floor and surges northward. This surge affects deep-sea circulation, which in turn influences climate. So, a major meltdown would not only raise sea level worldwide, but could also modify weather patterns.
For a better fix on the details, the National Oceanic and Atmospheric Administration is monitoring weather, ozone depletion, and long-term climate trends at the South Pole. In addition, scientists are refining their models of the oceans and the atmosphere by studying bottom water in Antarctica’s Weddell Sea, and satellite images of sea ice.