COG3 Seminar – Jeff Munroe (Middlebury College)
Dust in the Wind: Investigating Past and Present Dust Deposition in the Uinta Mountains, Utah
Eolian delivery of mineral dust impacts soil development, contributes to soil fertility, influences surface water chemistry, and alters snowpack albedo in high mountain ecosystems. This study focuses on past and present deposition of mineral dust in the alpine zone of the Uinta Mountains in northeastern Utah. Alpine soil profiles in the Uintas feature a ubiquitous layer of silt ~20 cm thick, indicating that dust deposition has been a significant long-term process in this environment. Four passive dust collectors were deployed in June, 2011, and an additional four were deployed in October, 2015. These collectors document an average dust flux of ~4 g/m2/yr, similar to values measured from snowpack samples in the Wind River (Wyoming) and San Juan (Colorado) Mountains. XRD analysis reveals that the dust is dominated by quartz, potassium feldspar, plagioclase, and illite. Some samples contain amphibole and chlorite. The dust is very well-sorted, with a median size of 8 μm. Geochemical records from lacustrine sediment cores reveal that the flux and properties of dust arriving in the Uinta Mountains have varied over the post-glacial period, likely in response to regional changes in aridity. A specially designed active sampler deployed at an elevation of 3700 m collects separate samples of NNW and SSE provenance. Differences in grain size distribution, mineralogy, and geochemistry of samples from contrasting wind directions indicate the importance of regional dust sources.