Glacier-Wide Mass Balance and Compiled Data Inputs: Juneau Icefield Glaciers

Since the 1940s, the Juneau Icefield Research Program (JIRP) has been measuring surface mass balance on the Juneau Icefield. This is the longest ongoing program of its kind in North America. The program nominally occurs between late June and late August, traversing between Juneau, Alaska and Atlin, British Columbia. JIRP has examined the surface mass balance of the Juneau Icefield since 1946, with principal efforts focused on Lemon Creek Glacier and Taku Glacier. Glaciological, geodetic, and meteorological data have been collected by JIRP to characterize the interaction between the climate and glaciers of the Juneau Icefield. Direct field measurements of point glaciological data are combined with weather and geodetic data to estimate the seasonal and annual mass balance at each glacier in both a conventional and reference surface format (Cogley and others, 2011). The analysis framework (O'Neel, 2019; McNeil and others, 2020) is the same at each glacier to enable cross-comparison between output time series. For Taku and Lemon Creek glaciers, temperature lapse rates are optimized using on-icefield weather data. This changes the degree day factor in the melt model, giving small post-geodetic calibration differences on the order of 2-3 cm. Details are described in McNeil (2019). Vocabulary used follows Cogley and others (2011) Glossary of Glacier Mass Balance.
This portion of the data release includes glacier wide mass balance solutions for Taku and Lemon Creek Glaciers, as well as the refined inputs used in these calculations. Input data are of three types: 1) time-variable area altitude distribution (AAD); 2) time series of point water balance at long term sites (with secondary sites given in recent years); 3) weather data from nearby stations, either installed along the glacier margins or taken from a nearby site if continuous glacier-adjacent data is unavailable. The USGS runs a coded analysis to transform the three input data types to the output glacier-wide data. Output data represent surface mass balance estimates. The output solution is a geodetically calibrated, conventional glacier-wide mass balance, which represents our preferred solution. Conventional glacier-wide mass balance from direct observations without calibration can be easily derived by using the geodetic calibration coefficients provided, if desired. We do not explicitly account for basal or englacial accumulation or ablation. Mass balances are reported in water equivalent (w.e.) units, and often represent integration of multiple field measurements. Whenever possible, we average multiple field measurements to account for surface roughness and measurement errors. Additional data for Lemon Creek Glacier, part of the Juneau Icefield, is available in a separate data release of USGS Benchmark Glacier data at https://doi.org/10.5066/F7HD7SRF It is not included here to avoid duplication.
Preliminary mass balance estimates for the current calendar year are provided, but do not include direct measurements of ablation after the date of the fall visit. Preliminary estimates of mass balance model this winter ablation for the current year. During subsequent field visits in the following calendar year, any ablation that occurred over the winter season is measured and used to revise the previously modeled estimate of mass balance.