Bacterial diversity and geomicrobiology of Winter Wonderland ice cave, Utah, USA.

The Winter Wonderland ice cave, located at an elevation of 3140 m above sea level in the Uinta Mountains of northern Utah, USA, maintains a constant sub-zero temperature. Seasonal snowmelt and rain enter the cave, freeze on the surface of the existing ice, and contribute to a 3-m-thick layered ice mass. This ice mass contains organic matter and cryogenic cave carbonates (CCCs) that date back centuries. In this study, samples of ice, liquid water, and exposed CCCs were collected to examine the bacterial communities within the cave and to determine if these communities vary spatially and between sample types. Flow cytometry showed that cell counts are an order of magnitude higher in liquid water samples than in ice. Epifluorescence microscopy and scanning electron microscopy imaging revealed potential coccoid and bacillus microbial morphologies in water samples and putative cells or calcite spherules in the CCCs. The diversity of bacteria associated with soil, identified through sequence-based analysis, supports the hypothesis that water enters the cave by filtering through soil and bedrock. A differential abundance of bacterial taxa was observed between sample types, with the greatest diversity found in CCCs. This supports a geomicrobiological framework where microbes aggregate in the water, sink into a concentrated layer, and precipitate out of the ice with the CCCs, thereby reducing the cell counts in the ice. These CCCs may provide essential nutrients for the bacteria or could themselves be products of biomineralization.

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/m2/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/m2/yr with a decadal average of 3.4 g/m2/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 (PM2.5) 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.