A portable ice core drilling system was developed at the Byrd Polar Research Center (BPRC) and tested during four field seasons on both polar and temperate ice fields. The prime features of the new drilling system include its low power requirement, light weight, depth capability of 500m, quick setup, easy ice core handling, and high ice core production rate (ICPR). Since 1997,more than 1200m of ice cores has been recovered with the BPRC dry hole electro-mechanical (EM) drill. After modifications described in this paper, the drill achieved the following performance characteristics : (1) drilling from the surface to 15m in one hour in cold firn; (2) drilling to 30m within 2.5 hours and (3) drilling to 100m within 14 hours, with an average ICPR of 7.15m/h. Six boreholes in the temperate ice on the summit of Mt. Kilimanjaro (5985m a. s. l.) totaling 200m were drilled to bedrock. The deepest hole was drilled down to 51m. High concentrations of dust and thick layers of volcanic ash were common features in the Mt. Kilimanjaro ice, where the average ICPR was 8-10m/h. A new version of the antifreeze-thermal-electric drill (ATED) has been developed and laboratory tested. The paper presents a comprehensive examination of the EM and ATED drill performances based on quantitative data regarding drill design and conditions at drilling sites. The optimal protocol for coring in polar and temperate ice at air temperatures above the melting point is examined.
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