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Abstract:
Debris, ranging from surface dust to medial moraines and thick, continuous layers covering ablation zones, partially covers glaciers all around the world. This supraglacial layer fundamentally modifies the energy transfer from the atmosphere to the ice, thus directly controlling sub-debris melt rates. Debris physical properties such as albedo, surface roughness, and thermal conductivity have only been measured directly or derived from local measurements at a few sites, so studies have relied on literature values. As we now understand, debris properties are highly heterogeneous, potentially implying high uncertainty in melt rates and debris thicknesses derived from literature debris properties.To meet this data gap and evaluate its impact on modeled melt, we undertook an observational campaign to investigate supraglacial debris properties at Pirámide Glacier, in Chile, in a climate distinct from previous studies. First, we derived aerodynamic surface roughness from wind-temperature tower data in three glacier locations and thermal conductivity from thermistor strings in the debris layer colocated with the wind-temperature towers; we measured ablation with stakes adjacent to the towers for validation; and sampled debris thickness across the glacier surface.We then conducted point-scale energy-balance modeling using both locally-derived debris properties and typical literature values to investigate the impact of using literature values when modeling glacier melt. While deriving local debris properties from measurements is challenging, we show that they can differ significantly from literature values; thus, their use in melt models can result in considerable differences in estimates of sub-debris ice ablation.
