Antarctic Ice Study: Refrigeration System for the Earth's Oceans Threatens to Break Down
A surprising discovery in the Antarctic has scientists alarmed. According to an analysis of core samples, the southern ice shelf reacts far more sensitively to warming temperatures than scientists had previously believed. The message: sea levels may rise even further than feared.
From October through the end of December 2006, high-tech drills penetrated to a depth of exactly 1,287.87 meters (4,225.3 feet) into the Ross Ice Shelf in the eastern Antarctic. The sediments that were brought to the surface with the drill core allow researchers to embark on a voyage back in time. For every meter (about 3 feet) of sediment, scientists can now peer about 10,000 years into the past. The recent drilling effort offers scientists a look at what may have happened on the earth up to about 12 million years ago.
The sample could prove to be one of the most important drill cores in recent years. The sediments it contains show that the Antarctic climate has only been continuously cold for about the last million years, during which one of its largest bays has been constantly covered by a layer of ice up to several hundred meters thick. The ice shelf melted about 5 million years ago and, presumably along with it, a significant portion of the ice on land. Where researchers must now drill through 80 meters (262 feet) of the ice shelf before reaching the sea floor at a depth of 800 meters (2,625 feet) was once open sea. The earth's climate fluctuated constantly in the ensuing 3.5 million years.
Those are the early conclusions drawn by geologists at Andrill (Antarctic Geological Drilling), the multinational consortium leading the project, which recently released preliminary data from the drilling on its Web site. With the joint project, which is being conducted by Germany, Italy, New Zealand and the United States, scientists hope to reconstruct the prehistory of Antarctic environmental conditions using new drill cores. This is more difficult than it sounds, because glaciers and icebergs have churned up the sea floor in many locations near the coastline. Further complicating matters, scientists often find little more than the rock debris of end moraines in the bottom portions of the drill core. But in late 2006, the Andrill team discovered undisturbed deposits 15 kilometers (9 miles) outside the research station near the Mount Erebus volcano.
A first look at conditions that prevailed five million years ago
"This time we were able to drill into layers representing the period between five and 12 million years ago," Andrill team member and geologist Lothar Viereck-Götte told SPIEGEL ONLINE. What these unique ice cores revealed about temperature changes in the last 5 million years was both surprising and new, says Viereck-Götte, who calls the results "horrifying." The data suggests "the ice caps are substantially more mobile and sensitive than we had assumed."
"The idea that the ocean here was ice-free for almost a million years is completely new," says Viereck-Götte. Besides, he adds, the melting that occurred about 5 million years ago can be seen in the context of a prehistoric climate shift. According to Viereck-Götte, "massive melting" must have occurred in the Antarctic during the so-called Miocene-Pliocene warming. The cause sounds anything but massive. Based on isotope analyses from various locations worldwide, paleoclimatologists know that the average global temperature in the oceans increased by only two to three degrees Celsius (3.6-5.4 degrees Fahrenheit) -- a seemingly minor change. Nevertheless this change in temperature, according to the new Andrill ice core, led to an ice-free Ross Sea.
For researchers the clue lies in tiny microorganisms known as diatoms, which cannot survive in water that is covered by ice. But they were found in the core representing an uninterrupted period of 1 million years. "We would never have thought that this system is so sensitive," says Viereck-Götte. The consequences of an ice-free Ross Sea would be far-reaching, not just for sea levels.
"The Antarctic ice shelves have an important impact on the global environmental system," says Frank Niessen of the Alfred Wegener Institute for Polar and Marine Research (AWI), based in the northern German port city of Bremerhaven. According to Niessen, sea water is cooled considerably beneath the giant floating ice shelves (the Ross ice shelf alone is the size of France). This makes the water denser, causing it to literally plunge into the deep ocean. As a result, the shelf ice bays of the southern continent feed a constant cycle of cold and warm water. "This is an important motor behind the global system of ocean currents," says Niessen.
Preliminary results, unmistakable conclusions
The cores are still on a ship bound for Florida, where Andrill researchers from around the globe will meet in May to negotiate the distribution of the samples. Half of the ice cores will be archived in freezers, while the other half will be cut into pieces and distributed among scientists around the world, who will then publish their individual findings in professional journals. "We can expect at least a minor sensation," says polar researcher Niessen.
His colleagues at German universities in Jena and Göttingen hope to be able to take along as many pieces of the core as possible. "We want to examine the composition of the particles in the sediment," Viereck-Götte told SPIEGEL ONLINE. This, he said, would enable him to precisely determine how much ice from the eastern and western Antarctic ice shelves melted into the Ross Sea.
Melting ice from Antarctica's inland ice cap also affects global sea levels, but not in the same way as floating ice shelves. "The shelf ice supports the inland ice masses," says Niessen. If it disappears, the inland glaciers will move and melt at a faster rate.
"The message of the drill core"
According to Niessen, the preliminary findings from the new drill core provide "clear indications." It is "certain without a doubt," says Niessen, that an ice-free Ross bay existed 5 million years ago. And what sounds like a small detail is central to uneasy questions about the future: What kind of reaction to global warming must mankind expect from the icy southern continent? And how quickly will it happen?
Until now climate researchers' biggest fear was that the small west Antarctic ice sheet could shrink as a result of the global warming predicted to set in by the end of the 21st century. In its recent report on global warming, the United Nations predicted a temperature increase of two to five degrees Celsius (3.6 to 9 degrees Fahrenheit) by the year 2100. But the possibility that global warming could also affect the significantly larger east Antarctic ice sheet has not been incorporated into the climate simulation models -- not until now, at least.
During the Miocene-Pliocene warming period, the average temperature of the oceans increased by two to three degrees Celsius (3.6 to 5.4 degrees Fahrenheit). But even relatively minor warming can bring about greater consequences than previously believed. "What we have learned is that the shelf ice is a highly dynamic system. It isn't something we would have expected," says Niessen, who argues that this new information must be incorporated into future climate models. "This is the message of the drill core," he says. It appears that man has also underestimated the effects of even minor warming.
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