Dust deposited on snow cover in the San Juan Mountains, Colorado, 2011-2016: Compositional variability bearing on snow-melt effects

Journal of Geological Research
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Abstract

Light-absorbing particles in atmospheric dust deposited on snow cover (dust-on-snow, DOS) diminish albedo and accelerate the timing and rate of snow melt. Identification of these particles and their effects are relevant to snow-radiation modeling and thus water-resource management. Laboratory-measured reflectance of DOS samples from the San Juan Mountains (USA) were compared with DOS mass loading, particle sizes, iron mineralogy, carbonaceous matter type and content, and chemical compositions. Samples were collected each spring for water years 2011-2016, when individual dust layers had merged into one (all layers merged) at the snow surface. Average reflectance values of the six samples were 0.2153 (sd, 0.0331) across the visible wavelength region (0.4-0.7 µm) and 0.3570 (sd, 0.0498) over the full-measurement range (0.4-2.50 µm). Reflectance values correlated inversely to concentrations of ferric oxide, organic carbon (1.4-10 wt. %), magnetite (0.05-0.13 wt. %), and silt (PM63-3.9; median grain sizes averaged 21.4 µm) but lacked correspondence to total iron and PM10 contents. Measurements of reflectance and Mössbauer spectra and magnetic properties indicated that microcrystalline hematite and nano-size goethite were primarily responsible for diminished visible reflectance. Positive correlations between organic carbon and metals attributed to fossil-fuel combustion, with observations from electron microscopy, indicated that some carbonaceous matter occurred as black carbon. Magnetite was a surrogate for related light-absorbing minerals, dark rock particles, and contaminants. Similar analyses of DOS from other areas would help evaluate the influences of varied dust sources, wind-storm patterns, and anthropogenic inputs on snow melt and water resources in and beyond the Colorado River basin.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Dust deposited on snow cover in the San Juan Mountains, Colorado, 2011-2016: Compositional variability bearing on snow-melt effects
Series title Journal of Geological Research
DOI 10.1029/2019JD032210
Volume 125
Issue 7
Year Published 2020
Language English
Publisher Wiley
Contributing office(s) Geosciences and Environmental Change Science Center
Description e2019JD032210, 24 p.
Country United States
State Colorado
Other Geospatial San Juan Mountains
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