By Adam Mann
Researchers working with the West Antarctic Ice Sheet Divide Ice Core project have drilled a column of ice nearly as deep as ten Empire State Buildings stacked atop one another. The final section of the 3,330-meter long core was extracted on 28 January. It is the longest ice core ever drilled by US scientists and the second longest ever made. A joint US, French and Russian team completed the longest ice core, at 3,623 meters, in 1998.
Researchers are drilling in this area because it is a very stable part of the West Antarctic icesheet, where snowfall is relatively high. This provides a long but highly detailed climate record, going back approximately 100,000 years, says Ed Brook, a geoscientist at Oregon State University in Corvallis, Oregon and one of the principal investigators on the project. The team hopes to analyze small bubbles of gas trapped in the column of ice for clues to climate shifts in the remote past.
“One of our main objectives is to look at the carbon dioxide record in much more detail and see how much climate can change for a given amount of greenhouse gasses,” says Brook.
The cores should provide a better map of fluctuations in carbon dioxide than any previously obtained and may help researchers understand the extent of climate changes during the current warming period.
A similar project, called North Greenland Eemian Ice Drilling (NEEM), reached bedrock in July 2010, at a depth of more than 2,500 meters, and details of its analysis are expected later this year. Though shorter than the Antarctic ice core, the Greenland sample reaches farther back in time to the Eemian glacial period (between 130,000 and 115,000 years ago) when global temperatures averaged around 5 degrees Celsius warmer than today. “Those records have provided fantastic data on how fast climate can change,” says Brook, adding that shifts can sometimes occur on the order of decades.
When combined, the data from both Northern and Southern Hemisphere ice cores should provide complementary portraits of how climate has changed on Earth over millennia. Already, researchers know that there was a great deal of variation between the hemispheres and that the two do not tend to change in lockstep, says Brooks. Heat may transfer back and forth between the hemispheres over the centuries, creating a “seesaw effect,” he adds. With both ice cores now in hand, the researchers hope to explore the exact timing of these cycles, he adds.
“We’re interested in how the Earth’s system can go through such gyrations and what causes these shifts,” says Brook.