Uinta Mountains Research Articles

First investigation of perennial ice in Winter Wonderland Cave, Uinta Mountains, Utah, USA

Abstract. Winter Wonderland Cave is a solution cave at an elevation of 3140 m above sea level in Carboniferous-age Madison Limestone on the southern slope of the Uinta Mountains (Utah, USA). Temperature data loggers reveal that the mean annual air temperature (MAAT) in the main part of the cave is −0.8 ∘C, whereas the entrance chamber has a MAAT of −2.3 ∘C. In contrast, the MAAT outside the cave entrance was +2.8 ∘C between August 2016 and August 2018. Temperatures in excess of 0 ∘C were not recorded inside the cave during that 2-year interval. About half of the accessible cave, which has a mapped length of 245 m, is floored by perennial ice. Field and laboratory investigations were conducted to determine the age and origin of this ice and its possible paleoclimate significance. Ground-penetrating-radar (GPR) surveys with a 400 MHz antenna reveal that the ice has a maximum thickness of ∼ 3 m. Samples of rodent droppings obtained from an intermediate depth within the ice yielded radiocarbon ages from 40±30 to 285±12 years. These results correspond with median calibrated ages from CE 1560 to 1830, suggesting that at least some of the ice accumulated during the Little Ice Age. Samples collected from a ∼ 2 m high exposure of layered ice were analyzed for stable isotopes and glaciochemistry. Most values of δ18O and δD plot subparallel to the global meteoric waterline with a slope of 7.5 and an intercept of 0.03 ‰. Values from some individual layers depart from the local waterline, suggesting that they formed during closed-system freezing. In general, values of both δ18O and δD are lowest in the deepest ice and highest at the top. This trend is interpreted as a shift in the relative abundance of winter and summer precipitation over time. Calcium has the highest average abundance of cations detectable in the ice (mean of 6050 ppb), followed by Al (2270 ppb), Mg (830 ppb), and K (690 ppb). Most elements are more abundant in the younger ice, possibly reflecting reduced rates of infiltration that prolonged water–rock contact in the epikarst. Abundances of Al and Ni likely reflect eolian dust incorporated in the ice. Liquid water appeared in the cave in August 2018 and August 2019, apparently for the first time in many years. This could be a sign of a recent change in the cave environment.

Late-Holocene Treeline Shifts in the Northwestern Uinta Mountains, Northeastern Utah

Remnant wood found above the present-day altitudinal limit of trees provides a record of treeline shifts in response to past variations in climate. 14C dating and wood identification of remnant trees from Windy Ridge, a ridgeline in the northwestern Uinta Mountains of northeastern Utah, show treeline ∼100 m higher than today between ∼730 and 500 calibrated 14C years before present (cal yr BP; ∼1220–1450 CE). This treeline shift coincides with the Medieval Climatic Anomaly (MCA), suggesting that warm temperatures allowed limber pine (Pinus flexilis) and Engelmann spruce (Picea engelmannii) to establish above the current treeline during that interval. However, 2 of the remnant trees (limber pine and Douglas-fir [Pseudotsuga menziesii]) date to ∼175 cal yr BP (∼1775 CE), well after the end of the MCA and beginning of the Little Ice Age. This may indicate that some trees that established during the MCA were able to persist for centuries under colder conditions. Comparison of the Windy Ridge 14C dates with those of remnant trees from elsewhere in the western United States suggests that the timing of, and controls on, past treeline dynamics varied across the region.

Using strontium isotopes to trace dust from a drying Great Salt Lake to adjacent urban areas and mountain snowpack

With the desiccation of saline lakes around the globe, it is increasingly important to quantify the impacts of playa dust on downwind urban areas and mountain snowpack. In this study, we used 87Sr/86Sr ratios of carbonate minerals to trace dust from playas to urban areas and mountain snowpack. We focused on dust contributions from Great Salt Lake (GSL), in northern Utah, USA, which recently reached historic lows in water levels exposing large areas of dry lakebed. We measured 87Sr/86Sr ratios in dust from GSL, Sevier Dry Lake (SDL), and other playas across western Utah and compared them to 87Sr/86Sr ratios in dust across the urban Wasatch Front and mountain snowpack collected seasonally from 2015–2018. Dust from GSL had unique 87Sr/86Sr ratios (∼0.715) relative to SDL (∼0.710) and other playas (∼0.711 to 0.712), providing a potentially powerful tool for tracing GSL dust to downwind areas. Dust deposition had 87Sr/86Sr ratios ranging from ∼0.710 to ∼0.712 in the urban area and snowpack, within the range of playa dust sources. Using a simple two-endmember mixing model considering only GSL and SDL as sources, GSL contributed 5% of the dust flux to the southern Wasatch Front (Provo) and between 30%–34% of the dust flux to the northern Wasatch Front (Salt Lake City, Ogden, and Logan). For mountain snowpack, GSL contributed 11% of the dust flux to the Uinta Mountains and 22% of the dust flux to the Wasatch Mountains. Dust transport modeling could be combined with 87Sr/86Sr fingerprints for source apportionment in northern Utah and other areas that are impacted by regional playa dust.

Recent trends in mountain lake primary production: evaluating the response to fish stocking relative to regional environmental stressors

Sia ME, Doyle RM, Moser KA. 2020. Recent trends in mountain lake primary production: evaluating the response to fish stocking relative to regional environmental stressors. Lake Reserv Manage. XX:XXX–XXX. Although mountain lakes are often remote, they are impacted by a myriad of stressors, including species introductions, atmospheric fertilization, and climate change. These stressors have the potential to increase primary production, which can threaten mountain lakes by decreasing water quality, reducing species richness, and lowering dissolved oxygen concentrations. The relative importance of these stressors as drivers of production is not well understood. We therefore investigated the importance of fish stocking, relative to other stressors, as a driver of primary production in mountain lakes. Our research focused on Uinta Mountain lakes, which, like many lakes in the western United States, were stocked with salmonid fish in the 1950s. In 2 stocked lakes and one unstocked lake, we reconstructed a record of ∼300 yr of primary production from lake sediments using changes in percentage of organic matter and spectrally inferred concentrations of chlorophyll a and its derivatives. With long-term trends in primary production, we determined that all 3 study lakes, including the unstocked lake, show unprecedented increases in primary production beginning in the 1950s. We attribute recent increases in primary production mainly to atmospheric deposition of nitrogen and climate warming, but do not rule out future impacts of fish stocking. Our article demonstrates how breakpoint analysis can be used to identify the most serious threats to mountain lakes, even if those lakes are impacted by multiple stressors or stressors originating from distant places.

The role of declining snow cover in the desiccation of the Great Salt Lake, Utah, using MODIS data

The Great Salt Lake (GSL) in Utah has been shrinking since the middle of the 19th Century, leading to decreased area and volume, and increased salinity. We use satellite data products from the Terra and Aqua MODerate-resolution Imaging Spectroradiometer (MODIS) and the Landsat-7 and -8 satellites, along with meteorological and streamflow data, and modeled data products to study the relationship between changing snow-cover conditions and the decline of the GSL since 2000 in the context of the historical record of lake levels. The GSL basin includes much of the snow-dominated Wasatch and Uinta mountain ranges to the east of the lake. Snowmelt feeds the Bear, Jordan, and Weber rivers which are the three main rivers that flow into the lake. Snowmelt-timing maps, derived from a new MODIS standard snow-cover product, MOD10A1F, show that snow melted ~9.5 days earlier in the GSL basin during the study period, extending from 2000 to 2018. Air temperatures derived from 26 meteorological stations and surface temperatures measured by the Aqua MODIS land-surface temperature (LST) products, MYD21A1D and MYD21A1N, show trends of increasing temperature of ~0.94 °C (α = 0.05), and ~ 2.18 °C, respectively, with most of the LST trends in the GSL basin being statistically significant (α = 0.05). Increasing air temperatures in the basin have led to less precipitation falling as snow, lower snow depth (by ~34.5 mm (α = 0.01)) and snow-water equivalent (0.02 mm (α = 0.01)), and earlier snowmelt. Also during the study period, Global Land surface Evaporation Amsterdam Model data show evaporation increasing by ~3.2 mm/yr, with trends in much of the basin being statistically significant (α = 0.05). Trends calculated from the various products are generally in agreement indicating higher temperatures, greater evaporation, less snowfall and snow-on-the ground, and earlier snowmelt. Earlier snowmelt contributes to increasing evaporative loss from water flowing toward the lake. Furthermore, a lower mountain snowpack and less precipitation falling as snow (versus rain) is associated with lower stream discharge even if overall precipitation stays the same. The surface-water temperature of the GSL also increased over the study period by ~0.69 °C, according to the MODIS LST data products, the surface-water elevation of the lake dropped by ~1.7 m between 2000 and 2018, and the areal extent of the lake decreased by ~901 km2 as measured using Landsat imagery. Desiccation of the lake is associated with deleterious effects on wildlife, recreational activities, and some local industries. And, importantly, an expanding lake bed can also fuel dust storms that promote dangerous air quality along the Wasatch Front. This work elucidates the key role that satellite remote sensing can play in documenting earlier snowmelt and other changes in the GSL basin that influence the ongoing decline of the Great Salt Lake.

Holocene records of eolian dust deposition from high‐elevation lakes in the Uinta Mountains, Utah, USA

ABSTRACTRadiocarbon‐dated sediment cores from subalpine lakes were used to investigate post‐glacial dust deposition in the Uinta Mountains (Utah, USA). Lake sediments were geochemically characterized with ICP‐OES, ICP‐MS and XRF core scanning. Collections from passive samplers constrain the properties of modern dust, and samples of regolith constrain properties of the local material within the watershed. Ca and Eu are more abundant in dust, whereas Ti and Zr are more abundant in local regolith. As a result, the Ca/Ti and Eu/Zr ratios are indices for the dust content of lake sediment. In all records, the dust index rises in the early Holocene as watersheds became stabilized with vegetation, reducing the influx of local material. After this point, values remained above average through the middle Holocene, consistent with an increased dust content in the sediment. Dust index values drop in the late Holocene in most lakes, suggesting a decrease in dust abundance. Generally synchronous shifts in dust index values in cores from lakes in different parts of this mountain range are evidence of enhanced dust deposition in this region during the middle Holocene, and are consistent with a variety of records for increased aridity in the south‐western USA at this time.

A modeling examination of cloud seeding conditions under the warmer climate in Utah, USA

Assessment of how the wintertime cloud seeding conditions over Utah's mountains may change provides essential information for the state to work on increasing its snowpack in the warmer climate. In this study, data from the National Center for Atmospheric Research's high-resolution, convection-permitting Weather Research and Forecasting model are used to evaluate suitable conditions for wintertime cloud seeding over Utah's mountains, and to estimate future changes to these conditions under a pseudo-global warming scenario. While previous studies have examined historical cloud seeding conditions, this is the first study that explores the impact of future climate change on these conditions. Based on two atmospheric variables commonly used in cloud-seeding operations, i.e. average temperature from the surface to 1 km above ground level (−20 °C≤T≤−6 °C) and vertically integrated supercooled liquid water (SLW > 0.01 mm), Utah's mountains are suitable for seeding more than 20% of the time during winter. A greater rate of suitability exists in the northern and Uinta Mountains. In the warmer climate under a high-emissions scenario, these seeding conditions may wane as the percentage of precipitating clouds suitable for seeding, about 60% under current conditions, would decline to about 40% across the state with significance. This projected decrease is due to rising temperatures and a decreased frequency of precipitation events. These findings imply that climate warming will narrow the window of opportunity for winter cloud seeding operation in Utah.

Quantifying the contribution of dust to alpine soils in the periglacial zone of the Uinta Mountains, Utah, USA

Profiles of alpine soils in the Uinta Mountains (Utah, USA) were investigated to determine how long-term dust deposition has influenced soil properties in this environment. Field studies were focused on four above-treeline sites, all of which were apparently beyond the reach of erosive glacial ice during the Pleistocene. Modern dust, soil A and B horizons, and local bedrock were compared in terms of major and trace element geochemistry, along with Sr and Nd isotope compositions. In all cases, soil samples are a mixture of dust and local bedrock end members, with A horizons more closely resembling dust, and B horizons more similar to bedrock. Calculations estimate that these soil profiles contain ~50 to 80% dust, which is effectively mixed downward into the solum by cryoturbation. Because these landscape positions were not glaciated, the total amount of dust contained within soil profiles is large relative to sites at lower elevation within the glacial limit. In addition to altering physical properties of these soil profiles, including horizonation and texture, deposition of dust rich in base cations positively influences soil fertility.

Fallout tuffs in the Eocene Duchesne River Formation, northeastern Utah—ages, compositions, and likely source

Thin fallout tuffs are common in the terrestrial deposits of the Eocene Duchesne River Formation on the flanks of the Uinta Mountains of eastern Utah. Their ages and compositions provide new insight into the tectonic events and magmatic history of the western Cordillera and provide important constraints on the Cenozoic land mammal chronology. Whole-rock compositions of the volcanic ash show that they underwent post-emplacement argillic alteration, typical of a wetland/floodplain depositional setting. However, immobile element ratios and abundances, such as Zr/Ti, La/Nb, and Y are typical of rhyolites formed in a subduction-related setting. Glass shards preserved in one sample all had SiO2 values >75%, typical of high-silica rhyolite. Preserved phenocrysts in the ash beds include quartz, sanidine, plagioclase, and biotite with variable amounts of accessory zircon, apatite, titanite, and allanite. Biotite compositions have Fe/(Fe+Mg) ratios typical of calc-alkaline igneous rocks and clusters of chemical compositions suggest a genetic relationship to three or four separate eruptions. Sanidine compositions from five samples range from Or73 and Or79. Only one sample had preserved plagioclase with compositions ranging between An22 – An49. Allanite from the ash beds has lower total rare earth elements (REE) concentrations than allanite from other well-studied rhyolites. Titanite in one sample has lower concentrations of REE, Fe, and Al than expected of rhyolites and is probably detrital.Plagioclase and sanidine from two different tuff beds near the middle of the Duchesne River Formation yielded analytically indistinguishable 40Ar/39Ar ages of 39.47 ± 0.16 Ma and 39.36 ± 0.15 Ma, respectively. These dates, along with the compositional data seem to limit the eruptive source for these fallout tuffs to the northeast Nevada volcanic field, one of the few volcanically active regions of western North America at the time. These new radiometric ages, along with stratigraphic relations and previously published ages for tuffs in the Bishop Conglomerate (which unconformably overlies the Duchesne River Formation), constrain the timing of late Laramide uplift in the region from 39 to about 37 Ma and post-Laramide epeirogenic uplift from 34 Ma to 30 Ma. Finally, the ages also provide additional evidence that the Duchesnean North American Land Mammal Age ended in the Eocene, which was originally named and defined from the Duchesne River Formation.

A Breccia Pipe in the Deseret Limestone, South Flank of the Uinta Mountains, Northern Utah

A breccia pipe is a cylindrical- or irregular-shaped mass of brecciated rock. A breccia consists of broken, angular fragments of rock cemented together by a fine-grained matrix. Hydrothermal breccia pipes form when hydrothermal solutions force their way towards the surface through zones of weakness or fracture zones and naturally break up the rocks in the process, i.e., hydrofracturing; breccia pipes can also form by collapse. Hydrothermal breccia pipes can contain ore deposits and, as will be discussed later, are associated with some large oil and gas accumulations in southeastern Utah.

Stratigraphic setting of fossil log sites in the Morrison Formation (Upper Jurassic) near Dinosaur National Monument, Uintah County, Utah, USA

The outcrop belt of the Upper Jurassic Morrison Formation in the northeastern Uinta Basin and southeastern flank of the Uinta Mountains is particularly rich in dinosaurian and non-dinosaurian faunas, as well as in fossil plants. The discovery of several well-preserved, relatively intact, fossil logs at several locations in Rainbow Draw and one location in Miners Draw, both near Dinosaur National Monument (Utah), has provided an opportunity to study the local paleobotany, stratigraphy, and sedimentology of the Morrison Formation in northeastern Utah. The Morrison Formation in northeastern Utah consists of four members. In ascending chronostratigraphic order, they are the Windy Hill, Tidwell, Salt Wash, and Brushy Basin Members. The lithology (including the presenceof glauconite grains) and fossil assemblage of the lower two members (Windy Hill and Tidwell) indicate a marine to marginal marine (coastal plain) depositional environment, whereas the lithology, fossil flora and faunaassemblage of the upper two members (Salt Wash and Brushy Basin) indicate a fluvial–lacustrine depositional environment. At least 10 fossil log sites in Rainbow Draw have been documented so far, and geologic mapping indicates that the logs and wood all occur in the same stratigraphic interval within the Salt Wash Member, approximately 17 to 27 m above the base of the member. The unit containing the logs and wood is about 11 m thick and consists of very fine to fine-grained sandstone and siltstone with indistinct bedding and no discernible sedimentary features.The logs are siliceous, some have a coaly exterior, and they range in exposed length from 0.5 to 11 m and reach diameters up to 1.1 m. In the Miners Draw area, a single siliceous log is documented in the upper part of the Salt Wash Member within a silty sandstone unit that is 4 m thick; its exposed length is about 6 m. Although the correlation of the Miners Draw log-bearing interval to the interval in Rainbow Draw is uncertain, both units are lithologically similar and both occur in the upper part of the Salt Wash Member. The logs have been identified as araucariaceous conifers that pertain to the same taxon originally described as Araucarioxylon hoodii Tidwell et Medlyn 1993 from Mt. Ellen in the Henry Mountains of southern Utah. Concurrent systematic work will prompt a nomenclatural transfer of this species to the genus Agathoxylon. Based on the abundance of large fossil logs and wood in the same stratigraphic interval in Rainbow Draw, wehypothesize that the area was covered by stands of moderately large trees of araucariaceous conifers. The sedimentological evidence suggests that the trees were not transported far from their original site of growth before they were deposited in a low-energy floodplain environment.

Stratigraphic Setting of Fossil Log Sites in the Morrison Formation (Upper Jurassic) near Dinosaur National Monument, Uintah County, Utah, USA

The outcrop belt of the Upper Jurassic Morrison Formation in the northeastern Uinta Basin and southeastern flank of the Uinta Mountains is particularly rich in dinosaurian and non-dinosaurian faunas, as well as in fossil plants. The discovery of several well-preserved, relatively intact, fossil logs at several locations in Rainbow Draw and one location in Miners Draw, both near Dinosaur National Monument (Utah), has provided an opportunity to study the local paleobotany, stratigraphy, and sedimentology of the Morrison Formation in northeastern Utah.

Multiproxy lacustrine records of post-glacial environmental change from the Uinta Mountains, Utah, USA

Abstract Twenty-one sediment cores were obtained from 20 lakes in the Uinta Mountains, Utah, USA. Depth-age models were developed using 14C dating, and sediments were analyzed for loss-on-ignition (LOI), carbon-nitrogen ratio (C:N), and grain size distribution. Although some of these cores have been considered individually in previous studies, here the entire set of cores is evaluated collectively to identify consistent patterns, commonalities, and trends in the post-glacial interval. All lakes accumulated substantially greater amounts of submicron-size clastic material before ca. 9.5 ka BP. This pattern is interpreted as a signal of prolonged landscape instability following deglaciation. Values of LOI and C:N exhibit a strong, positive correlation in nearly all lakes, indicating that organic matter accumulation is controlled by the influx of terrestrial material. In the six lakes exhibiting the strongest correlation, and featuring the most robust inflowing streams, median grain size and the abundance of sand increased between 10 and 6 ka BP, simultaneous with increases in LOI and C:N. This correspondence is interpreted as evidence for frequent high-intensity storms during the early Holocene, likely driven by enhanced monsoonal circulation. The early parts of five of the records contain a sharp increase in LOI. Lakes exhibiting this pattern are typically smaller and shallower, and are located in less rugged watersheds. Finally, all six cores from the western Uinta Mountains contain evidence for an environmental perturbation ca. 4.5 ka BP. Although the nature of this event is unclear, these lakes accumulated notably finer-grained sediment with less organic matter at this time. This analysis illuminates the post-glacial history of this strategically located mountain range, and underscores the value inherent in analyzing cores from multiple lakes when reconstructing paleoclimatic history.

Isotope fingerprinting reveals western North American sources of modern dust in the Uinta Mountains, Utah, USA

Abstract The deposition of aeolian dust has profound effects on biogeochemical cycling, soil development, and hydrology in alpine ecosystems. In the western United States, it has been proposed that much of the dust reaching the Rocky Mountains is derived from arid regions located to the west-southwest. Because these areas are vulnerable to drought-related changes in vegetation, grazing impacts, mining, off-road vehicle travel, urban development, and other factors that affect the availability of fine-grained sediment for wind deflation, it is imperative that source areas for this dust be better constrained to guide future management decisions. Here we collect modern dust in the Uinta Mountains (Utah) and compare its 87Sr/86Sr and 143Nd/144Nd “fingerprint” with surficial sediments in possible source areas. Our results confirm that this dust is exotic to the Uinta Mountains, and demonstrate its similarity to numerous dune fields in western Utah, as well as surficial sediments in parts of the Colorado Plateau, southern Basin and Range, and the Mojave Desert. The seasonal sampling we employed also reveals that considerable dust is deposited during the shorter alpine summer. Recognition that specific areas in the southwestern US are sources of dust to the Rocky Mountains, particularly during summer months, should be considered in future land management planning.

Holocene Carbon Burial in Lakes of the Uinta Mountains, Utah, USA

Recent research suggests that organic matter sequestered in lake sediment comprises a larger component of the global carbon cycle than once thought, yet little is known about carbon storage in mountain lakes. Here, we used a set of sediment cores collected from lakes in the Uinta Mountains (Utah, USA) to inform a series of calculations and extrapolations leading to estimates of carbon accumulation rates and total lacustrine carbon storage in this mountain range. Holocene rates of carbon accumulation in Uinta lakes are between 0.1 and 20.5 g/m2/yr, with an average of 5.4 g/m2/yr. These rates are similar to those reported for lakes in Greenland and Finland and are substantially lower than estimates for lakes in Alberta and Minnesota. The carbon content of modern sediments of seven lakes is notably elevated above long-term Holocene values, suggesting recent changes in productivity. The lakes of the Uintas have accumulated from 6 to 10×105 Mt of carbon over the Holocene. This is roughly equivalent to the annual carbon emissions from Salt Lake City, Utah. Based on their long-term Holocene rates, lakes in the Uintas annually sequester an amount of carbon equivalent to the emissions of <20 average Americans.

Pyrolysis of modern wetland sediment: extracting climate records from fens in the Uinta Mountains and Fish Lake Plateau, Utah, USA

Rock‐Eval pyrolysis provides a quick, relatively inexpensive means of characterizing organic‐rich strata, and has been used for decades to understand global petroleum systems. Although designed to characterize ancient kerogens, pyrolysis is increasingly being used to understand Holocene systems as well. The ability of this technique to distinguish between types of preserved organic matter is useful in characterizing climatic evolution, particularly in systems sensitive to climatic fluctuation such as isolated fens and bogs. Cores collected from the Tokewanna and Garden Basin Cattail fens in central/eastern Utah exhibit variability of organic source, with the mixture of terrestrial and algal sources varying through time, as shown through the hydrogen index (HI) and oxygen index pyrolysis parameters. A sediment core was collected at each fen, and 176 samples were taken from the cores at 6‐cm intervals. Total organic carbon (TOC) for all samples ranges from 1.3 to 44.2%, with an average of 18.2% TOC. Samples range from 84 to 687 HI, equivalent to Type I (lacustrine algal) to Type III (terrestrial) organic material (OM). Variability in HI response represents mixing of the two OM sources, and the relative amount of aqueous organic input can be estimated through time based on age‐calibrated HI curves at the two sites. The balance of organic input serves as an accurate, high‐resolution proxy for climate, and calibration with palynological data near both sites confirms patterns shown by pyrolysis, showing the utility of this method in quickly, affordably and accurately characterizing Holocene sediments for use in understanding palaeoclimate.

Depositional environment, sediment provenance and oxygen isotope paleoaltimetry of the early Paleogene greater Green River Basin, southwestern Wyoming, U.S.A.

Depositional process, sediment provenance, and paleotopography are critical to paleogeographic reconstruction during the coeval Laramide and Sevier orogenies in the Cordillera orogenic system. Here we conduct lithofacies analysis, sediment provenance, and paleoelevation studies in the fluvial lower Paleogene Fort Union and the main body of the Wasatch formations in the center of the greater Green River Basin in order to reconstruct paleogeography. The depositional environment changed from low-energy floodplains and associated meandering river during the Paleocene to braided rivers during the earliest Eocene. The lowermost Eocene strata have more Precambrian basement-derived feldspar grains compared to the Paleocene strata. This change in sediment provenance was associated with the change to dominant northwestward paleoflow direction, suggesting major uplift of the Laramide Uinta Mountains during the earliest Eocene. The δ18O values of authigenic carbonates were stable during the early Paleocene, but decreased gradually from −10 permil during the late Paleocene to −18 permil during the earliest Eocene, suggesting the lack of highland precipitation in the basin catchment during the early Paleocene, and significant surface uplift and arrival of highland precipitation from the Uinta Mountains during the earliest Eocene. The reconstructed paleoelevation of the Uinta Mountains was at least 3 km, possibly greater than 3.5 km, and the paleoelevation of the greater Green River Basin floor was at most 1 km, and the paleorelief between the greater Green River Basin and Uinta Mountains was ∼ 2 km during the earliest Eocene. Our record of the earliest Eocene establishment of high topography of the Uinta Mountains through renewed uplift is 4 to 6 Myr older than previously thought. If the carbonate cements in the Fort Union Formation record the isotope compositions of surface water from the Sevier orogen, their high δ18O values likely suggest that the Sevier orogen had rugged topography during the Paleocene.

Aeolian dust chemistry and bacterial communities in snow are unique to airshed locations across northern Utah, USA

Wind-blown dust is an important source of trace metals, nutrients, and biological material to montane ecosystems. Mountain ranges in northern Utah are located downwind of multiple dust sources including the Great Basin Desert and the Wasatch Front urban area, providing an opportunity to investigate regional-scale differences in dust deposition chemistry and bacterial composition. We sampled discrete dust layers from snowpack across multiple locations in the Wasatch and Uinta Mountains (Utah) and the Snake Range (Nevada) during spring 2014 and 2015. Dust chemistry was unique in each airshed, suggesting that spatial variability and local sources were more important than temporal variability for the sampling period. The central Wasatch dust contained the highest concentrations of playa-associated elements (U, Mg, Li, Ca, Sr, As) and anthropogenic elements (Sb, Cu, Pb, Se) compared with lowest concentrations of these elements in the northern Wasatch, which is further from playa and anthropogenic sources. Sequential extractions indicate that the majority of Ca, Sr, and Cd is potentially available for transport during snowmelt while other elements are relatively immobile. Central Wasatch dust was more reactive to acetic acid than northern Wasatch dust for most elements, including REE + Y. Sr isotopes (87Sr/86Sr ratios) were also unique to each sampling area, with the most radiogenic values in the central Wasatch. Similar to dust chemistry, bacterial communities in dusty snow reflected geographically localized dust events. In the central Wasatch, 69% of bacterial species were unique, suggesting that the airshed received the most diverse dust inputs from a combination of playa and anthropogenic sources. Gram-positive Actinobacteria and Firmicutes were common in snow but specific bacterial families distinguished airsheds (e.g., Bacillaceae, Geodermatophilaceae, Nakamurellaceae). Our results demonstrate that evaluating dust chemistry and bacteria in snow on a regional scale may more clearly link dust sources to the entrainment of pollutants and seeding of bacteria species to montane systems.

Hydrogeomorphic controls on Holocene lacustrine loss-on-ignition records

Holocene loss-on-ignition (LOI) records were developed for radiocarbon-dated sediment cores from 20 lakes in the Uinta Mountains of northeastern Utah, USA. The hydrogeomorphic setting of each lake was characterized, permitting an analysis of connections between LOI values and lake setting. Median LOI values exhibit a significant negative correlation with lake elevation, with the range of elevations and the maximum slope of the watershed, with the extent of ice/snow and exposed rock in the watershed, and with the volume of through-flowing water. In contrast, LOI is positively correlated with the extent of forest cover and wetlands in the watershed. In addition, forward stepwise linear modeling demonstrates that lake area/lake depth ratio is a significant negative predictor for median LOI, that shoreline complexity is a significant positive predictor for maximum LOI, and the standard deviation of LOI values is greater in lakes surrounded by watersheds with more wetlands and surface water. Some LOI time series contain excursions at finer temporal scales that are recorded synchronously in adjacent lakes, however many excursions appear in only a single record. Similarly, step changes in LOI that are clear in some records are not preserved in the sediments of nearby lakes. Over longer timescales, some LOI records are essentially constant during the Holocene. In contrast, some lakes record steadily rising LOI values, and approximately half of the lakes have complicated LOI records with millennial-scale variability. Lakes with large surface area, large area/depth ratios, large watershed area/lake area ratios, rugged watersheds, and extensive ice/snow cover are more likely to record steady LOI values over time. The degree to which LOI records from neighboring lakes vary emphasizes that lacustrine proxy records reflect a strong filtering effect, whereby the signal of an external forcing is recorded to varying degrees depending on the nature of the lake and surrounding watershed.

Monitoring snowbank processes and cornice fall avalanches with time-lapse photography

Time-lapse photography was employed to monitor a snowbank at 3640 m above sea level in the Uinta Mountains, Utah, USA. The snowbank forms against a 35-m high, east-facing escarpment and is nourished by wind redistribution of snow from an alpine plateau. The snowbank is capped by a large cornice, and its central core persists through the summer in most years. An automated, solar-powered digital camera was deployed between October 2016 and June 2017, and programmed to capture 5 photographs each day between 8:00 and 16:00, local time. Although cold temperatures affected the batteries during the winter, a total of 812 photographs were collected, for an overall average of 3.4 per day. These images were combined in an animation displaying the growth of the snowbank and associated cornice over the course of the winter. The debris fields resulting from nineteen cornice fall avalanches were noted in the sequence of photographs. Data collected at a nearby automated weather station reveal that 12 avalanches (between early December and early April) were preceded by significant increases in snow depth, snow water equivalent, and precipitation, with sustained windspeeds above the winter average. In contrast, six of the last seven events (between late April and early June) occurred in the absence of new snowfall, but were associated with rapid rises in temperature and notable decreases in snow water equivalent. The average interval between recorded avalanches is 10 days, with a maximum of 29 days and a minimum of 2 h. Recurrence intervals were shorter in December/January, in late March/early April, and in late April/early May. Only one avalanche occurred in the 56 days between 27 January and 24 March. Time-lapse photography is a powerful tool for monitoring nival processes.