Geodetic Constraints on the Glacier Mass Balance Record of Place Glacier, British Columbia, Canada

Conventional (glaciological) measurements of glacier mass balance provide important records to assess the relation between climate and glacier nourishment. Inadequate sampling, interpolation errors, or systematic biases can introduce uncertainty into these records. We calculated the geodetic mass balance of Place Glacier over the periods 1965-1973, 1973-1981, 1981-1987, 1987-1993, 1993-1997 and 1997-2005 to compare with the mass balance obtained from conventional techniques. Although the cumulative balance of the geodetic (33.9 m) and traditional (33.2 m) records accord, the conventional and geodetic results differ by 15-25% for some periods. These deviations primarily arise from the use of aerial photography that was acquired at times which did not coincide with the end of the ablation season. However, the geodetic thinning rate of the glacier over the period 1973-1981 was nearly twice as large as the field-based measures despite any corrections applied to the geodetic data. Inspection of the conventional mass balance record indicates that fewer sites were used to derive glacier wide changes in mass during the 1970s. Our results bear directly on studies that utilize traditional records for glacier mass balance modeling since the period 1973-1981 represents an interval where the glacier initiated a significant transition to more negative net balance.