Reinterpretation of Deep Ice Temperatures

Abstract

THE first complete temperature profile through a polar ice sheet has been reported from Camp Century, Greenland, by Hansen and Langway1 and is shown in Fig. 1. Theoretical derivations of these temperatures by Weertman2 and by Dansgaard and Johnsen3 achieved agreement to within ±0.6° C. For this it was necessary, however, to assume a surface accumulation rate little more than half that currently observed (32 g yr−1 = 35 cm of high density ice yr−1) and confirmed as valid for the past 1,000 years or so by an oxygen isotope analysis for an earlier Camp Century core by Langway4. More recent calculations by Philberth and Federer5 have somewhat reduced but not eliminated this discrepancy; although they arrived at the observed temperature difference between the base and the surface of the ice, their calculated temperatures differ radically from those observed in the uppermost 200 m. As pointed out by Robin6, this layer is likely to be climatically disturbed; its undisturbed temperatures might therefore be represented by the broken line in Fig. 1. This raises the temperature between the base and the surface by about 1° C, corresponding to an accumulation rate of 28 cm ice yr−1 in the model of Philberth and Federer5.