Since the late 1950s, USGS has maintained a long-term glacier mass-balance program at three North American glaciers. These 'Benchmark Glaciers' include Washington's South Cascade Glacier and Alaska's Gulkana and Wolverine glaciers. Results from this program form the longest continuous record of North American glacier mass balance. Similar measurements began at Sperry Glacier, MT in 2005.
In 2013, research at these independent sites were unified into a single project, with an ultimate goal of measuring changes in glacier mass across the principal North American climate zones that support them. Common field and analysis methodologies will enable comparison among the glaciers, and provide an improved understanding of both the causes and magnitudes of glacier change over long time periods at a continental scale.
Each benchmark glacier is influenced by a unique climatology. In Alaska, the measurements capture changes in both continental and maritime climate zones. Alaska's maritime climate zone is characterized by relatively warm and wet weather while the continental climate zone is characterized by extreme winter cold, warm or even hot summers, and substantially less precipitation than along the coast. Washington's maritime climate zone includes some the highest precipitation recorded for the lower 48 states of the United States. Montana's intermountain climate zone reflects a blend of maritime influences from the west and continental influence from the Arctic and Great Plains, which meet along the continental divide.
Currently, historic data from the benchmark glaciers is being reanalyzed with consistent analysis techniques across the four glaciers. An emphasis on generalized algorithm development will allow other mass balance programs to be analyzed using the same algorithms (e.g., Taku Glacier in Alaska).
The fully unified USGS Benchmark Glacier project will allow mass balance records from different parts of North America to be directly compared to better understand the response of glaciers to climate changes. The two Alaskan benchmark glaciers have already undergone this comparative reanalysis, which revealed differences in variability and trends between the coastal and continental glaciers (O'Neel et al., 2014). For example, the figure below shows short-lived mass gains (positive slopes) at Wolverine Glacier; in the 1980's the cumulative mass balance indicates gains since the 60s (positive values). These episodes of growth result from the abundant snow accumulation and cool summers that characterize Alaska's coastal climate zones. In contrast, the persistent mass loss at Gulkana glacier exemplifies the stronger dependence of continental glacier mass balance on summer temperature.
Additionally, as traditional field measurements are combined with remote sensing data, the short-lived remote sensing records can be linked to the longer field records. Just as geodesists have linked the tide gauge and satellite records to better understand sea level rise, glaciologists aim to link field and satellite records to gain regional insight into changing glaciers.