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2 December, 2000

More Snow and Ice

Sometimes when I look around at the scenery it is easy to forget that, even though it may look like Kansas in the winter, there is over half a mile of snow and ice beneath my feet.

I've been here at Siple Dome for ten days. Except for some tiny falling crystals called diamond dust, it really hasn't snowed during that time. But when it does snow, it doesn't melt.

The 1000 meters of ice that forms Siple Dome contains an estimated 80,000 to 100,000 years of accumulated snow. Snow that survives a year is called firn. The firn layer extends down about 70 meters to a level where the air spaces or pores are no longer connected. Below the firn layer is ice. At even deeper levels, the pressure increases compressing the air bubbles in the ice causing them to shrink. At about 1000 meter, near the bottom of the ice sheet at Siple Dome, the air bubbles disappear into the ice lattice resulting in clear, blue ice.

I am holding a section of ice core from one of the shallow drill holes. This piece probably came from a depth of about 100 meters (328 feet). It is filled with uniform, tiny bubbles about 2-3mm apart. When put in water, it fizzes as the compressed air in the bubbles is released. This ice formed from snow that fell a few thousand years ago.

Sarah Das and Andy Kurtz from Penn State University seem to be enjoying digging a two-meter snow pit. Sarah is studying how current climate conditions affect snow stratigraphy. Stratigraphy refers to the nature of accumulated snow layers. This information will provide a better understanding of past climates through the study of the stratigraphy in ice cores. On the left is the weather station Sarah established last season. The tower in the right background is an automatic weather station(AWS), one of a network of stations maintained by the University of Wisconsin. It records data every ten minutes which is then sent to an orbiting ARGOS satellite. In the far distance is the main drill site.

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