TAKU AND LEMON CREEK GLACIER, ALASKA: NORTH AMERICA’S LONGEST GLACIER RECORDS

Annual surface mass balance measurements on Lemon Creek and Taku Glacier have been observed by the Juneau Icefield Research Program since 1953 and 1946 respectively. Conventional mass balance records of Taku Glacier averaged +0.40ma⁻¹ from 1946–1985, and −0.08ma⁻¹ from 1986–2011. The Lemon Creek Glacier conventional mass balance record averaged −0.30ma⁻¹ from 1953–1985 and −0.60ma⁻¹ from 1986–2011. Independent geodetic assessments validate long-term trends observed through the traditional glaciological method on both glaciers. This mass balance program continues to evolve: 1) from 1946-1983 the program focused on field measurement of mass balance using snowpits, ablation stakes, and equilibrium line observations. 2) From 1984-2011 the program supplemented the field measurements with additional snow probing and remotely sensed imagery of the transient snowline and equilibrium line altitude, and validated traditional glaciological measurements with multiple independent geodetic assessments. 3) Since 2012 high frequency ground penetrating radar, a temperature index model, as well as a updated and time-variable glacier geometry have been incorporated into annual assessments. Currently, this project seeks to produce a highly constrained annual surface mass balance record of the Juneau Icefield region that is directly comparable with other well-established glacier records in the Gulf of Alaska and Pacific Northwest. Future work will continue to identify and reduce errors and explore the possibilities of enhancing the record.