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Antarctic seabed gives up key climate data

A Ross Ice Shelf drilling project finds tiny algae that once bloomed near the ocean surface and may provide clues into global warming.

July 15, 2007|William Mullen | Chicago Tribune

MCMURDO STATION, ANTARCTICA — Dropped into a hole melted through 267 feet of floating ice, a diamond-toothed drill had to travel another 2,776 feet through seawater before reaching the bottom of an offshore moat in Antarctica.

There, it pierced the ocean floor and began to drill back in time. It extracted a core sample about 3 inches in diameter and brought it up to a derrick built atop the Ross Ice Shelf.

Nearly a quarter-mile down, the drill bored into sediment that would astonish one of the largest groups of scientists ever assembled in Antarctica. It was a layer more than 300 feet thick of fossilized diatoms, microscopic algae that once bloomed near the ocean surface.

The diatom layer, laid down 2 million to 5 million years ago, was evidence that Antarctica has undergone past cycles of warming and cooling. It meant the Ross Ice Shelf -- a seemingly permanent slab of ice the size of Spain -- was once open water.

In other times, this information might be of interest only to specialists. But scientists with the Antarctic Geological Drilling project, or ANDRILL, believe the Antarctica of the past can show us what to expect from the warmer world of tomorrow.

In November and December, the ANDRILL team pulled 10 million years of critical climate information out of the Antarctic seabed. The diatom layer was a key prize, representing "a time when ... glaciers were in retreat, a different regime when there was a lot more water in the system," said Reed P. Scherer, a diatom expert at Northern Illinois University.

In today's terms, "more water in the system" could mean sea levels high enough to put low-lying places like Florida and Bangladesh underwater. If the Ross Ice Shelf again were to shrink or disappear because of higher global temperatures, it could signal dangerous changes for the rest of the planet.

For this reason, ANDRILL is one of the biggest scientific undertakings in the history of Antarctica and a showcase project for the International Polar Year, a major international cooperative research effort that began March 1 and continues until March 1, 2009. It is focusing hundreds of millions of dollars and vast expertise on the Arctic and Antarctic regions.

The project, much of which is related to global warming, brings together 150 scientists from the United States, New Zealand, Italy and Germany. The U.S. National Science Foundation provides two-thirds of ANDRILL's $30-million cost. Last year's drilling put 58 geologists, geochemists, volcanologists, sedimentologists, paleomagneticists, paleontologists, petrologists and others "on the ice."

The samples they extracted provide "the best record of time ever established" in Antarctica, said Ross D. Powell, a Northern Illinois University geologist. Now, in a process that will take years, ANDRILL will try to match the new data with more complete geological histories from the rest of the world.

"We want to relate these warming events with other known world events," said Powell, an expert in glacial sediments.

He reels off some of the questions they hope to answer:

"How did the Antarctic ice sheet react to temperature rises in the past, and how will it react in the future? What's the critical point that triggers changes? Are there tipping points, like water temperature or air temperature, that we should be aware of? What was the global picture when this happened before?"

Antarctica was not always frigid. Forty million years ago, the Antarctic land mass was connected to the tip of South America and was home to thick vegetation and populations of animals similar to those in Australia.

But when Antarctica detached, a frigid circumpolar current began to spin around it like a giant freezer coil, trapping the continent in a super-cold climate. Glaciers and ice sheets grew up to 3 miles thick, covering 98% of Antarctica, which is larger than the U.S. and Mexico combined.

Though the chill has lasted ever since, the amount of ice in Antarctica has grown and shrunk many times during previous global climate changes. The ANDRILL core samples confirm at least 60 warming/cooling cycles in Antarctica in the last 10 million years.

But today's warming trend appears different from those of the past. Most climate experts agree that the pace of change is unusually fast and that the cause seems to be human activities, primarily the burning of fossil fuels, which releases heat-trapping gases into the atmosphere.

The planet's average annual temperature has risen 1.4 degrees Fahrenheit in the last 100 years, and parts of the Arctic and Antarctic regions have seen much bigger temperature increases, as much as 4.5 degrees since the 1950s.

The rising temperatures threaten to affect the three major types of ice associated with the Antarctic continent: the seasonal pack ice that grows outward from the shore each winter; the thick, semi-permanent ice shelves attached to the Antarctic coast; and the ice sheets that cover its rocky land.

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