Temporal and spatial variations in spectral reflectance and characteristics of surface dust on Gulkana Glacier, Alaska Range

Spectral reflectances in the visible to near-infrared wavelength range (350-1050 nm) were measured on the surface of Gulkana Glacier, Alaska Range, Alaska, USA, at six different elevations from May to September 2001. The measurements showed variable spectral reflectances on the glacier surface, and the spectra changed over time and elevation. The spectra in May were those of a typical wet snow surface: the reflectance ranged approximately from 0.4 to 0.8, and generally decreased as the wavelength increased. As snowmelt proceeded, the reflectance gradually fell, and specific absorptions appeared in the spectrum at wavelength ranges of 400-600 and 670-680 nm, corresponding to a red snow surface due to snow algal bloom. As the ice surface was exposed, the spectrum finally shifted to a lower (0.1-0.4) and flat reflectance curve, typical of an ice surface contaminated with dust. Analyses of the dust on the glacier surface showed that its quantity and characteristics changed spatially and seasonally and were correlated with spectral albedo. The results showed that the temporal and spatial variations in spectral reflectance on this glacier are due not only to physical properties of the glacier surface, but also to biogenic materials on the surface (e.g red-colored snow algal cells and cryoconite).