23 November, 2000

The Project

Scientific research is the reason we are here. It is also the reason for the field camp at Siple Dome, the station at McMurdo and even the whole U.S. Antarctic Program.

We are at Siple Dome due to the presence of several holes that have been drilled down into the ice sheet. Gary Clow has developed a technique for measuring the temperature of the ice. He uses a winch to lower a temperature sensor down the drill holes. The temperatures obtained are extremely precise, accurate to about one thousandth of a degree Celsius. With this data, Gary is able to reconstruct the climate history for this location going back several thousand years.

How can knowing the temperature down through the ice sheet tell you what the climate was like years ago? Think about taking a frozen turkey out to defrost. It will take a long time before the warmer temperature penetrates to the center, thawing the bird. In the same way, warmer or colder temperatures due to changes in the climate can take thousands of years to penetrate to the base of the ice sheet. By logging precise temperature data from the surface to the base of the ice sheet, Gary is able to calculate past surface temperatures. The deeper the hole, the farther back in time you can go. At Siple Dome the main drill hole goes down 1000 meters (3280 feet) to the bedrock. This will allow the reconstruction of the climate going back about 5000 years.

The process of reconstructing climate from ice temperatures is called borehole paleothermometry. Gary has used this technique previously at another site in Antarctica and at a hole drilled through the Greenland Ice Sheet. The data from Greenland show that the climate during the end of the last ice age was 21 degrees Celsius colder at that location than it is today.

Gary and Bob Hawley collected data at Siple Dome last year and they will return next year for the final season of the project. I feel very lucky to be able to be part of their team this year.

This is the top of the borehole. It is 18 centimeters (7 inches) in diameter and extends down 1000 meters (3280 ft) to the base of the ice sheet. It produces an incredible echo when you speak into it. It was drilled during the 1997-1998 and 1998-1999 seasons. The ice core that was recovered from the hole is being studied at the National Ice Core Laboratory in Denver.