Dust Deposited on Snow Cover in the San Juan Mountains, Colorado, 2011–2016: Compositional Variability Bearing on Snow-Melt Effects

Richard L. Reynolds, Harland L. Goldstein, Bruce M. Moskowitz, Raymond F. Kokaly, Seth M. Munson, Peat Solheid, George N. Breit, Corey R. Lawrence, Jeff Derry

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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 is relevant to snow-radiation modeling and 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.

Original languageEnglish (US)
Article numbere2019JD032210
JournalJournal of Geophysical Research Atmospheres
Volume125
Issue number7
DOIs
StatePublished - Apr 16 2020

Bibliographical note

Funding Information:
Authors declare no real or perceived financial conflicts of interests or other affiliations that may be construed as having a conflict of interest with respect to the results of this paper. The data supporting the conclusions can be obtained in Supporting Information S1 and in the ScienceBase database, https://doi.org/10.5066/P9RGQ9KX (Reynolds et al.,?2020). We thank Mike Duniway and two anonymous reviewers for improving the manuscript. We are grateful to Michael Sirles for providing the carbon analyses, Chris Landry and Andrew Temple for sample collection 2011?2015, and Jeremy Havens for preparation of Figure?1. Mention of trade names is for information purposes only and does not imply endorsement by the U.S. Geological Survey. This study was supported by the Land Change Science Program of the U.S. Geological Survey. The Institute for Rock Magnetism is supported by a grant EAR-1642268 from the Instruments and Facilities Program, Division of Earth Science, National Science Foundation. This is IRM contribution 1904.

Funding Information:
Authors declare no real or perceived financial conflicts of interests or other affiliations that may be construed as having a conflict of interest with respect to the results of this paper. The data supporting the conclusions can be obtained in Supporting Information S1 and in the ScienceBase database, https://doi.org/10.5066/P9RGQ9KX (Reynolds et al., 2020 ). We thank Mike Duniway and two anonymous reviewers for improving the manuscript. We are grateful to Michael Sirles for providing the carbon analyses, Chris Landry and Andrew Temple for sample collection 2011–2015, and Jeremy Havens for preparation of Figure 1 . Mention of trade names is for information purposes only and does not imply endorsement by the U.S. Geological Survey. This study was supported by the Land Change Science Program of the U.S. Geological Survey. The Institute for Rock Magnetism is supported by a grant EAR‐1642268 from the Instruments and Facilities Program, Division of Earth Science, National Science Foundation. This is IRM contribution 1904.

Publisher Copyright:
© 2020. The Authors.

Keywords

  • black carbon
  • dust-on-snow
  • iron oxide minerals
  • light-absorbing particles
  • magnetic properties
  • reflectance spectroscopy

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