Errors in Short-Term Ablation Measurements on Melting Ice Surfaces

Abstract

Rapid changes in time and space in the micro-relief of an ablating glacier surface and radiation-induced melt within the uppermost ice layer, termed the “weathering crust”, seriously affect the accuracy of the short-term ablation measurements. The various measuring techniques commonly used (stakes, ablatometers, ablatographs) and some new methods (measurement of discharge from a small supra-glacial drainage basin, and mass loss directly measured on core samples) are critically reviewed and assessed in the light of these phenomena. The implications for studies of heat and mass balance are discussed.It appears that the direct measurement of mass flux is the most accurate means of assessing short-terni ablation rates. The errors in short-term ablation measurements by any method are largely compensatory and consequently do not influence long-period mass-balance estimates.

Microbial processes in the weathering crust aquifer of a temperate glacier

“…The depth of meltwater production inferred by the model is consistent with observations from High Arctic glaciers (Irvine-Fynn and Edwards, 2014) 25 but exceeds that for Antarctic dry valley glaciers by more than 10-fold (5-15 cm;Hoffman et al, 2014). Based on surface ice densities as low as 0.5 g cm -3 (Müller and Keeler, 1969), total water content in the weathering crust of some glaciers may approach 50%. Irvine-Fynn and Edwards (2014) speculated that environmental conditions in the WCA facilitate biogeochemical processing by providing microbes with access to light, effectively extending a glacier's "photic zone" to depths beneath the surface.…”

Seasonal variation of ice ablation at the margin of the Greenland ice sheet and its sensitivity to climate change, Qamanârssûp sermia, West Greenland

“…The straight edge allowed the determination of an "average" ice level around the stake, and thereby reduced the error caused by the "ablation hollow" at the stake. A constant ice density is not quite correct as the ice surface often has a "weathering crust" of varying depth and density (Muller and Keeler, 1969). This error is correlated to some degree with the prevailing weather type and tends to compensate over periods of many days; it does not significantly affect the monthly and seasonal ablation totals discussed here.…”

Rate of Short-Term ablation of Exposed Ground Ice, Banks Island, Northwest Territories, Canada

“…Heron and Woo, 1978;Woo, 1983) and for glacier ablation (e.g. Muller and Keeler, 1969;Braithwaite, 1981).…”