Modelling topoclimatic controls on palaeoglaciers: implications for inferring palaeoclimate from geomorphic evidence

Evidence of small glaciers is often used to infer past atmospheric climate through calculation of steady-state ELAs. However, if topographic niches such as shading or windblown-snow augmented mass-balance then ELAs cannot reflect regional climate and determining the significance of these topoclimates is therefore important. The Brecon Beacons, South Wales, contains upland glacial landforms dating to the Younger Dryas (11,000–10,000 yr BP) when local climate was at the threshold for glaciation. This case study categorises topoclimate using three-dimensional modelling of topography and reconstructed palaeoglaciers from two sites containing mapped moraines whose orientation suggest complex patterns of deglaciation. Ablation season solar radiation is modelled over multiple ice-surfaces as shade from surrounding topography and intensity from ice-surface incidence angle. Snowblow and avalanching potential models are also used and the significance of all topoclimate variables assessed against a mass-balance deficit calculated for each glacier given palaeoclimate models for the region. Results demonstrate that both glaciers were likely to be heavily reliant on topoclimate and that previous studies underestimate the significance of solar radiation. Modelled over multiple ice-surfaces reflecting patterns of recession, results indicate that the distribution of topoclimate variables predicts the style of deglaciation at both sites, possibly explaining the complexity of glacial evidence in this environment.