Technical aspects of deep ice drilling on Law Dome

The Dome Summit South (DSS) ice drilling project was designed to obtain a full depth ice core for high resolution studies of the Holocene and the transition from the last glacial maximum. The project used a new electromechanical drill based on the Danish ISTUK design. The main differences from the original ISTUK were an enclosed roller screw section and the use of a submersible brushless motor operating at ambient pressure in the drilling fluid. The field work started in 1988 when a 270mm diameter hole was drilled to 84m and cased with fiberglass reinforced plastic tube. The hole was continued to 96m with a smaller thermal drill to make a suitable pilot hole for the mechanical drilling. In 1989 the steel arch drilling shelter was set up over the borehole and the drill winch and tower set up in the shelter. Most of the EM drilling was done in the 1991/92 and 1992/93 seasons and in February 1993 drilling reached silty ice containing small rock fragments at a depth of 1200m. This is close to the ice thickness measured by radio echo sounding. Down to 391m in-field measurements were made of electrical conductivity, crystal fabrics and peroxide concentrations and samples were cut for later measurement of ¹⁰Be and for fine detail determinations of peroxide and oxygen isotope ratios. The core below 390m became increasingly more brittle and difficult to handle. Only the last 6.4m (which was not brittle) was brought back to Australia, the rest being left in the drilling shelter for collection next year after stresses have dissipated.