Sir, Bottom melting of the McMurdo Ice Shelf, Antarctica
Recent drilling through the McMurdo Ice Shelf near the Williams Field Air Facility resulted in direct thickness measurements from which the rate of bottom melting can be calculated. This information may be of interest to others concerned with Antarctic glaciology and is presented for that reason. The first hole (DH-1) was located at the Williams Field camp (Fig. 1) and indicated an icc-shelf thickness of 44.5 m. The second hole was located due west of the first one and gave a thickness of 27.7 m. The distance between the holes was determined from aerial photographs to be 1 677 m, with an error probably not exceeding 5 m. The westward movement rate of 106 m/year was determined by a series of Electrotape surveys performed by the U.S. Geological Survey and it agrees well with the rates published by Reference Stuart and BullStuart and Bull (1963, p. 405) and furnished by Heine (personal communication). Accumulation in this area is roughly 27 cm of snow per year (Reference Stehle and SherwoodStehle and Sherwood, 1965, p. 2).
The above figures show that as a unit column of the ice shelf moves westward at 106 m/year it loses 16.8 m by bottom melting in the 15.8 years required to travel 1 677 m. The thinning rate is 16.8/15.8, or 1.06 m/year for this part of the ice shelf. If the annual snow accumulation of about 0.27 m/year is assumed to be constant, then the unit column gains 4.05 m during the 15.8 years. The reduction in thickness is then about 12.75 m, or a total loss to the unit column of 0.81 m/year, as the ice shelf moves westward. This is fairly close to the figure of 0.7 m/year given by Reference Macdonald and HathertonMacdonald and Hatherton (1961, p. 863). Unfortunately, time limitations did not permit the collection of deep-core specimens which would be of great interest. However, it is hoped that this can be accomplished in the future.
R. A. Paige
Polar Division, U.S. Naval Civil Engineering Laboratory, Port Hueneme, California 93041, U.S.A. 27 August 1968