Prof. discusses ice-cap impurities
By Erin Jaeger, The Dartmouth Staff
Published on Monday, February 9, 2009
Chemical impurities may explain the recent shift and detachment of many polar ice caps, Thayer School of Engineering professor Ian Baker said Friday in a lecture given as part of the Thayer School's Jones Seminar Series. Baker was appointed as the Sherman Fairchild Professor of Engineering on Jan. 30.
Baker, who has studied ice since 1986, said he began his work by examining the formation and movement of impurities within ice cores. To do this, he inserted sulfuric acid into sample ice cores and tracked how the acid affected the overall strength of the ice.
"We basically treated ice like a metallic material in the trials," Baker said.
The more impurities found in an ice sample, the more flexible the sample becomes and the more likely it is to shift position, he said in the lecture. Tracking the location of these impurities can help scientists predict glacial movement over time, he said.
"We want to understand how impurities can migrate in ice cores and use the orientation of these [impurities] to understand ice sheet flow," he said.
In many of his trials, Baker also examined firn, which he described as "multi-year snow that's been sitting on the ground for several years." Since firn is not packed as tightly as ice, he said, it is easier for other substances to enter it and remain in place as it hardens to ice.
"It's easy to get through the firn structure," he said. "What's in the snow then ends up in the ice itself."
To illustrate how firn forms over time, Baker showed microscope slides of samples of fresh Hanover snow and the same snow a year later. In the second image, he said, the density of the snow had increased dramatically.
A micro CT -- a machine similar to a CAT scanner, but far smaller -- allowed Baker and his team to examine and photograph firn on a microscopic level without melting the specimens, he said.
"It's not a destructive technique," he said.
It is important to note, Baker said, that most impurities within the ice he studied were not man-made, especially in samples from Antarctica. Because of their natural occurrence, he said, studying these impurities can offer more insight into the natural properties of the ice itself.
Baker said the long-term goal of his research is to be able to characterize an ice sample, or identify all of its properties and the elements within it. Mapping the location and quality of impurities within the samples will help him and his team understand the physical and chemical properties of ice, he said.
While his research has come a long way from its beginning more than 20 years ago, Baker said, the work is still in progress, especially in light of the current focus on global climate change.
"Most of the things I'm talking about are ongoing stories," he said.
The Jones Seminar Series brings science professionals to the Thayer School to discuss society's relationship with science and technology, according to the series' web site. The seminars, which are open to the public, occur every Friday afternoon.