Abstract
Brewster Glacier is a benchmark glacier for research in the Southern Alps, with eighteen years of in-situ glaciological observations. A recent re-analysis of the historical aerial surveys of Brewster Glacier using modern photogrammetry revealed slow cumulative mass loss during 1986-2006, followed by significant mass loss since 2006. Like Brewster Glacier, other glaciers in the Southern Alps have also undergone considerable changes, with a significant higher regional snowline observed in the end of summer snowline photographic dataset. While modern satellite imagery and aerial surveys have been able to document these changes over specific time periods, the physical processes governing these changes remain largely unresolved. To better understand the climatic fingerprint, a distributed mass balance model is used to resolve the energy and mass exchanges of Brewster Glacier over the period 1982-2021. The model is used to assess uncertainties in the glaciological mass balance observations between 2010 and 2020, revealing an average underestimation of mass loss in the ablation season of -516 mm w.e. yr (super -1) . Since 2008, the mass loss has increased three-fold compared to the period 1982-2007, with no positive mass balance years observed or modelled over this period. To better understand the atmospheric controls on extreme mass loss, and to determine the role of such events on cumulative mass loss, the difference in energy and mass balance components during extreme positive and negative mass balance years are investigated. Reduced snow accumulation (40%), increased surface (48%) and subsurface (10%) melt accounts for the mass loss observed during the extreme, negative mass balance years. Net shortwave radiation is responsible for two-thirds of the additional energy contributing to melt during extreme mass loss years, while the turbulent heat fluxes account for the remaining energy surplus. The snow/ice albedo feedback plays a key role in controlling variability in net shortwave radiation through changes in the amount of snowfall and the reflectivity of the surface during long, extended melt periods in summer.