A METHOD FOR COMPUTING SHALLOW ICE-CORE DEPTHS

SIPRE-style hand augers usually recover core sections whose bottom is somewhat shallower than the drill depth. A procedure for calculating the range of possible core depths is presented. In the field , the drill barrel is lowered down the hole by means of a series of rigid extension rods. The apparatus is then rotated to drill through debris left behind by the prior run and into fresh firn or ice. (Care is taken to ensure that the total penetration of debris and firn does not exceed about half the length of the drill barrel, otherwise the barrel's capacity for core and chips will be exceeded and the drill likely jammed.) The entire apparatus is then recovered. The workers record the run number, the total drill length (barrel and extensions), the exposed length of extensions above the hole top at the end of drilling, and the length of recovered core. The cycle is then repeated. An example is shown in Table I. These data are then used to calculate drill depth, which is drill length minus the exposed length, plus an adjustment if drilling is from the base of a pit. Distance drilled is then obtained by comparison with the drill depth of the prior run. The apparent core loss is the distallce drilled minus the length of recovered core. The actual core loss is not readily calculated; it is the sum of true core loss (ground-up core and the collapse of friable strata) and the amount of core