Spatial and temporal variability of annual glacier equilibrium line altitudes in the Southern Alps, New Zealand

Abstract

Assessments of the contribution of meltwater to sea-level rise from mountain glaciers cannot presently account for the considerable spatial inter-catchment and temporal inter-annual variations in annual net glacier mass balance. We therefore analyse annual equilibrium line altitudes (ELAs) to infer the controls on annual net glacier mass-balance variability for 34 glaciers in the central Southern Alps, New Zealand. Elevation, curvature and mean solar radiation receipt (both direct and indirect) during the ablation season can in combination account for up to 95% of the (temporal) variability in the long term ELA and up to c. 85% for a given year. It appears that long-term glacier net mass balance in the Southern Alps is controlled by ablation processes as a function of air temperature which decreases with elevation, and shortwave radiation which causes a positive feedback in ablation by reducing snow and ice cover and increasing albedo. In detail however, the degree to which local topographic variables can explain the differences in (i) the patterns and (ii) in the magnitudes of departures from the trend varies considerably from year to year and across the study region. At least 15-35% of annual ELA temporal variability is apparently associated with regional weather patterns. Our basic quantification of the interaction on multiple scales of topographic influences on annual ELA and ELAo (steady-state ELA) has implications for understanding inter- and intra-catchment variability in glacier responses to climatic change. © 2011 The Royal Society of New Zealand.