Relation between regional drought and mountain dust deposition revealed by a 10-year record from an alpine critical zone.

Mineral dust was collected with a network of passive samplers in the Uinta Mountains (Utah, USA) over a 10-year period to evaluate the relation between regional drought and dust deposition. A total of 72 samples from eight collectors were analyzed for flux, grain size distribution, mineralogy, geochemistry, and their Sr and Nd isotopic fingerprint. The dust is primarily very fine silt, with an average median grain size of 11.6 μm. The clay minerals illite and kaolinite are common in the dust, along with quartz, potassium feldspar, and plagioclase. The most abundant elements (after Si) are Al > Fe > K > Ca > Mg > Ti. The trace elements Cd, Sn, Sb, Zn, Cu, As, and Pb are present at abundances greatly in excess of normal levels in upper crustal rocks. Dust fluxes average 14.4 mg/m/day, generally decrease at higher elevations and toward the eastern end of the range, and are significantly higher in summer. Annual fluxes range from 1.4 to 5.8 g/m/yr with a decadal average of 3.4 g/m/yr. Rates of dust deposition are significantly correlated with regional drought severity from the Standardized Precipitation-Evapotranspiration Index (SPEI) for the southwestern US over 2, 3, and 6-month time scales. Previous work has demonstrated a connection between drought in the southwestern US and the abundance of fine (PM) material aloft. This work is the first to use long-term monitoring of annual dust deposition to confirm that the flux of silt-sized dust to mountain ecosystems is significantly correlated with regional drought severity.