Siple Dome Ice Coring
Snow flakes form in the atmosphere and trap samples of the cloud water, atmospheric gases and dust through which they fall. When it lands in the accumulation zone of an ice sheet, the snow is compressed, re-crystallized, and builds up in ice layers which can be as thick as several kilometers. Thus discrete ice strata can be traced to snow that fell over 100,000 years ago. Analyzing this ice for such traces permits scientists to estimate climate properties such as the temperature, the snow accumulation rate, circulation patterns of the general ocean and atmosphere, and the concentrations of greenhouse gases when the snow fell – in short, a reconstruction of the paleoclimate. Such a model of the ancient weather improves our ability to predict how these phenomena may interact in the future; ultimately, we may be able to control the climate society will experience. We can almost certainly better predict how human activities will influence the climate.

The NSF has established the West Antarctic Ice Sheet (WAIS) initiative to investigate the influence of the West Antarctic Ice Sheet on climate and sea level change. The WAISCORES effort will recover and interpret an ice core from Siple Dome, Antarctica, and eventually plans to obtain a second core from a more inland site. These locations were selected to provide climate records that will extend back 80,000 to 100,000 years; cores from two sites will permit scientists to separate local and regional influences on the climate record they extract from the cores. The current season will wrap up these activities and complete scientific evaluation of the cores.

Recovery and science coordination of an ice core at Siple Dome, Antarctica.
Kendrick Taylor, Desert Research Institute.

Siple Dome, located between ice streams C and D, is well situated to investigate coastal climate conditions and the dynamics of the Siple Coast ice streams, which drain the West Antarctic Ice Sheet (WAIS). Ice accumulates 7 to 11 centimeters each year. By recovering an ice core to 1,000 meters, we expect to be able to distinguish annual layers back for at least 6,000 years. Beyond that, data will still be indicative (on a slightly coarser time frame) extending to at least 80,000 years ago.

This project provides the background for the Siple Dome drilling program, part of the WAIS program, an effort to understand the current behavior of the WAIS, and to decipher the climate it has been subjected to back through time. We also provide the working context for individual scientists to do research on the ice core, as well as establish an office to coordinate the various science activities of the organizations involved in the project, including the National Science Foundation (NSF), the Polar Ice Coring Office (PICO), Antarctic Support Associates (ASA), and the National Ice Core Laboratory (NICL). (II-152-O)

High precision borehole temperature measurements at Siple Dome, Antarctica, for paleoclimate reconstruction and ice dynamics studies.
Edwin D. Waddington and Gary D. Clow, University of Washington.

One of the procedures involved in ice coring is high-precision borehole temperature profiling. By constructing continuous temperature logs, scientists can develop data vital to paleoclimate reconstruction and ice dynamics studies. This project will work in the 1 kilometer (km) deep fluid-filled Siple Dome borehole and in several 160 meter-deep holes along a 20 km north-south transect across Siple Dome. The borehole temperature data will be used to:

• establish the conductive heat flux across the basal interface of the ice sheet;

• reconstruct the surface temperature history at Siple Dome, using geophysical inverse methods, known as borehole paleothermometry;

• constrain how thick the ice sheet was during the late Wisconsin, the magnitude of the Wisconsin/Holocene deglacial warming, and the background geothermal heat flux;

• determine calibration constants for the oxygen-isotope paleothermometer at Siple Dome in the past; and

• establish the spatial variability of surface temperature over the last century on the 20 km scale near the main drill site.

We expect the results to provide information needed to assess the short-term stability of the West Antarctic Ice Sheet; also improved estimates of the pore close-off ages in the past, which should in turn provide an improved age-scale for the Siple Dome ice core. Ultimately, this work should enhance our understanding of the magnitude of past temperature changes at this significant southern hemisphere site. (II-171-O)