Twenty Years of Drilling the Deepest Hole in Ice

Ice sheets and glaciers contain stratified ancient ice that fell as snow years to millions of years ago. The dust particles, soluble chemicals, and gases trapped in the ice can be used to study how Earth's climate system operated in the past. However, this requires deep ice coring. The retrieved glacial ice can be utilized for an accurate measure of past green-house gases with climate clearly documented in the same core. Therefore, ice core data have become crucial to our understanding of past climate change and to making assess- ments about future climate.

The Soviet Antarctic research station Vostok was founded at the center of the East Antarctic Ice Sheet (78°28’S, 106°48’E, 3488 m.a.s.l.) in 1957 (Fig. 1). This place turned out to be the coldest on Earth; the lowest reliably measured temperature of -89.2°C was recorded on 21 July 1983. In addition, by good fortune Vostok was set above the southern end of the largest subglacial lake in Antarctica, discovered in 1996 by Russian and British scientists (Kapitsa et al., 1996) while drilling deep boreholes.

Deep ice core drilling at Vostok station began in 1970. In the 1970s a set of open uncased holes were drilled by a thermal drill system suspended on cable. The deepest dry hole in ice reached 952.4 m (Hole #1, May 1972). It was concluded that for drilling at greater depths it is necessary to prevent hole closure by filling of the borehole with a fluid. Thus, from 1980 on new thermal and electromechanical drill systems working in fluid were used. Two boreholes reached depths of more than 2000 m. Hole #3G-2 was deepened to 2201.7 m depth in 1985 (Kudryashov, 1989) and Hole #4G-2 to 2546.4 m depth in 1989 (Kudryashov et al., 1994). Drilling of both holes was aborted because of stuck tools.