Consistent Reanalysis of Five North American Glacier Mass Balance Records

The U.S. Geological Survey (USGS) began measuring glacier mass balance more than 50 years ago at glaciers located in several distinct climate regimes of North America. However, consistency among field and analytical methods was never prioritized, thus comparative interpretations have been marked by uncertainty. Here we rectify this limitation by presenting results from a consistent reanalysis of mass balance records at five sites: Sperry (MT), South Cascade (WA), Lemon Creek (AK), Wolverine (AK) and Gulkana (AK) glaciers. Our reanalysis constrains sensitivity in several steps of the open-ended process of estimating glacier-wide mass balance, and emphasizes the importance of considering glacier mass balance processes that are independent of elevation. The work also underscores the importance of combining glaciological and geodetic data sets to accurately constrain long-term mass balance trends.

Results show ubiquitous mass loss (average rate of -0.5 m w.e. yr^-1) at each of the five glaciers, and an increase in the rate of mass loss since ca. 1990. Historically, the maritime glaciers in our study were buffered from rapid mass loss by abundant snow accumulation, but resilience appears to be decreasing, in part due to shorter accumulation seasons. Mass loss trends therefore point to the dominance and increasing influence of summer warming as the primary driver of change.

Our analyses do not reveal hemispheric (South-to-North) patterns in mass loss rates. Instead, we find that continentality and basin geometry exert stronger controls on mass loss than do latitudinal gradients in climate. This finding motivated more extensive basin-scale analysis. During 2016-17, we examined the role of Wolverine Glacier in the basin's water budget. Partitioning of precipitation on- and off- glacier, as well as between mass loss and mass turnover, revealed that the glacier catches and stores water in unique ways. Our results suggest that continued glacier demise will impact the timing and magnitude of the water cycle, which in turn will affect nutrient fluxes into the Gulf of Alaska.