Chilling Tales from the Depths
Not long ago, Alaska newspapers reported a local-bunch-makes-good story. The national Polar Ice Coring Office, which has its headquarters on the Fairbanks campus of the University of Alaska, provided equipment and staff for a great accomplishment in glaciology. This summer a PICO drill bored through thousands of feet of ice atop Greenland to fetch up bedrock that had not seen the light of day for hundreds of thousands of years.
Being the first to do something truly impressive is always worth a headline or two, but its underlying significance may not strike most readers. This success on ice may mean more in the long run than, say, the far more romantically appealing first ascent of Mt. Everest.
To understand that, it' s important to know that the scientists were not just poking a hole in a lot of ice. They were penetrating through a frozen record of times past. Even more important, thanks to the recovered ice cores, they were bringing highly informative portions of that past up to the present, to the scrutiny of modern analytical tools and techniques.
The sort of information they may have found was illustrated in the July 15 issue of the British journal Nature which contains an article on findings from a neighboring hole into Greenland's ice cap. This endeavor, the Greenland Ice-Core Project or GRIP for short, was staffed chiefly by European scientists, and the 40 authors listed have surnames hinting at homelands from Italy to Iceland.
Those 40 people, and doubtless scores more of unnamed students and technicians, have been putting together bits of evidence to sketch and outline past climates. Temperature changes show up in differing proportions of isotopes of oxygen trapped in the frozen layers. Pollens tell something of plant growth on adjacent lands. Rock dust tells of dry times on northern continents. Volcanic ash points to eruptive activity. Even differences in electrical conductivity within the ice provide hints. More salt blown up from the sea increases the conductivity of ice laid down in that layer. All of these clues tell about atmospheric circulation, and trapped bubbles reveal something of atmospheric chemistry.
The GRIP team concentrated on a period between ice ages. This interglacial time, known as the Eemian, took place between 115,000 and 135,000 years ago, and its record lies between 2780 and 2870 meters deep in the ice.
Until now, the only interglacial era we've know well is our own---the 10,000 years (so far) of the Holocene. It's been a time of reasonably stable climate. Most scientists assumed not only that our stable climate was the natural order of things until the ice returned again, but that other interglacials were also times of climatic stability. The evidence of the GRIP core says otherwise.
During the Eemian interglacial, the climate of Greenland shifted often and dramatically. The period contained three warm stages and two chilly ones. These climate subsets of a few thousand years each were surprising enough, but the ice also showed some very quick shifts in average temperature. Once, within the span of 10 to 20 years, the temperature dropped by 14 degrees centigrade, then stayed that way for about 70 years.
To get a rough idea of how that might have felt, consider that 20o C is near comfortable room temperatures close to 68o F. Going down 14 centigrade degrees brings the temperature into the low 40s on the Fahrenheit scale.
The findings from the GRIP borehole are under debate, and not everyone agrees with the team's interpretations. Perhaps evidence gathered by the record-breaking PICO effort will help settle the arguments. When human activity seems to be tinkering with the planetary thermostat, it's important to know what Mother Nature can do with no help from her human friends.
