Icy adventures. Camping out in a small yellow canvas tent in subzero weather may not be to everyone's taste, but for Adam Lewis that tent has been home during the three months of the Antarctic summer for the past several years. Lewis (GRS'03), a doctoral student working with College of Arts and Sciences Earth Sciences Assistant Professor David Marchant, recently won the Provost's Award at BU's Science Day 2001 for his studies of ancient glacier ice in Beacon Valley, Antarctica.
Lewis' research focuses on the age and origin of this ice, discovered by Marchant in 1995. Marchant theorized that it was a relic of an ancient ice sheet and established its age at more than 8.1 million years by dating volcanic deposits lying above the ice. This conclusion was immediately controversial. Others claimed that the ice could have formed in place from ongoing freeze-thaw processes or that it could be the far younger remains of local glaciers.
To test these theories, Lewis and fellow graduate student Eric Moore (GRS'01) systematically collected samples of buried ice and of covering sediment, called till. Laboratory analysis revealed identical physical characteristics in the two sample sets, including rock fragments found only in mountains far from Beacon Valley, providing strong evidence that both came from the same source outside the valley.
Lewis also used a novel approach, measurement of a cosmogenic isotope of helium (3He), to confirm the long-term stability of the ice. This rare isotope is created when cosmic rays from deep space collide with molecules at the Earth's surface. The 3He collects within mineral crystals in rocks, and the amount detected indicates how long a rock has been on the surface. As you move deeper into the Earth, the concentration of 3He decreases. Lewis found that the till above the glacial ice showed a systematic decrease in 3He with depth, indicating the soil covering the ice had been stable for millions of years, but the drop-off was quicker than expected. This result would be explained by slowly sublimating (evaporating) ice, and a resulting compaction of the till above. The 3He levels were used to calculate the sublimation rate of the ice, a calculation that confirmed the ice could have survived more than 8.1 million years.
This year Lewis came home from Antarctica with another, possibly even more interesting, result. Close examination of till and ice samples reveals the presence of organic matter -- simple animal and plant remains such as nematodes and diatoms -- that may prove to be some of the last plants and animals to inhabit the interior of Antarctica before the massive East Antarctic Ice Sheet extinguished all life there more than 10 million years ago.