The stabilization and persistence of organic carbon (OC) in soils and sediments is thought to be governed in large part by association with mineral matrices, especially reactive iron (Fe) phases. However, the role of these organo-mineral interactions has not been fully evaluated in lake sediments that are typically more OC rich. Here, we conducted detailed analyses of three sediment cores collected along a lake-depth gradient from a small clearwater lake in the Swedish Arctic to explore variability in sediment geochemistry and the role of mineral protection in OC preservation. While mineralogy of the two shallower, littoral cores was similar, mostly consisting of (alumino)silicates, sediments in the deepest part also included Fe-oxides and had 6–7 times higher specific surface area, indicating a greater potential for organo-mineral interactions. Higher specific surface area was strongly associated with more thermally-labile OC (ρ = −0.71, p = 0.01), but not with OC stocks (ρ = 0.05, p = 0.89). Multiple independent proxies indicated that deep-basin OC was more aliphatic, less degraded, and likely of planktonic algal origin compared to shallower regions. We suggest that the spatial pattern in OC quality is not simply a function of different OC sources or hydrodynamic sorting, but it is also regulated by differential capacity for organo-mineral stabilization.
The permafrost carbon cycle in Arctic coastal plains is strongly affected by abrupt thaw processes such as lake and hillslope thermokarst, which are expected to intensify under continued climate warming. Organic matter (OM) degradation may increase if taliks beneath drained lake basins (DLBs) fail to refreeze and retrogressive thaw slump activity accelerates. Thus, we investigated a coastal transect on the Baldwin Peninsula in northwest Alaska spanning a Yedoma upland, a thermokarst lake, a semidrained lake, a DLB, and a nearshore marine unit in proximity of a thaw slump. Using a 70-year aerial imagery analysis (1952–2022) with biogeochemical investigations of sediment cores (0–1 m), we assessed landscape and OM dynamics. We identified two dominant OM mobilization and decomposition trajectories. First, talik conditions favor OM degradation beneath the lake and the semidrained lake basin, where the talik did not completely refreeze for approximately 60 years following partial drainage. Second, thaw slump driven erosion mobilizes prealtered OM from the inland and transfers it into the marine environment, where further degradation occurs during sediment transport and reworking. In contrast, the upland and refrozen DLB currently preserve and sequester OM; yet, high ground ice contents render these systems vulnerable to future abrupt thaw.
Rock glaciers are common features in alpine environments that play an important role in hydrology and landscape evolution. We use satellite-based radar interferometry, topographic data, and optical imagery to identify and characterize rock glacier motion in the La Sal Mountains, Utah, USA, from 2016-2024. Our inventory includes 41 active and transitional rock glaciers and 20 relict features. Active and transitional rock glaciers occur at a mean elevation of 3266 +/- 192 m, where mean annual air temperature (MAAT) is estimated at 1.99 +/- 1.46 degrees C for the 1991-2020 PRISM model climate normal. The mean downslope velocity is 6.8 +/- 2.7 cm yr-1, with individual velocities ranging from 2.7 to 12.8 cm yr-1. Displacement time series from 20 representative rock glaciers reveal strong seasonal variability, with rates reaching up to 87.6 cm yr-1 in late summer when liquid water availability is greatest. Notably, these rock glaciers remain active or transitional despite being located above the 0 degrees C MAAT isotherm for the 1991-2020 climate normal, suggesting a resilience to rising air temperatures. Our results provide insight into environmental controls on rock glacier kinematics and demonstrate an approach for developing inventories critical to improving estimates of alpine water storage.
Climate refugia can serve as remnant habitat or stepping stones for species dispersal under climate warming. Lake Superior serves as a model system for understanding lake-mediated cooling, as its cool water temperatures and wave action have maintained shoreline habitats suitable for disjunct populations of arctic-alpine plants since deglaciation. We use structural equation modeling (SEM) to evaluate hypothesized causal pathways linking climate, site conditions, and bedrock type to abundance and richness of arctic-alpine plants. We surveyed macroclimate variables and local site conditions for 43 shoreline sites across Lake Superior’s north shore, and found that mean July temperature directly and indirectly affected disjunct species richness by maintaining low shoreline temperatures and shortening the growing season. Species richness of disjuncts was directly affected by shore width and indirectly affected by elevation above lake level. Competitive species did not significantly affect disjunct species richness or abundance at bedrock shoreline sites; however, disjunct species are competitively excluded from adjacent forested habitats. Currently, competition with encroaching boreal species is not limiting in bedrock communities; however, ongoing warming of Lake Superior’s waters may reduce cooling-mediated refugia, allowing for colonization of boreal species and a decline in disjunct plants from Lake Superior’s north shore.
Recent work has documented measurable changes in the elevation of ice-capped summits across the western United States, including Mount Rainier. At Mount Rainier, comparisons between mid-20th century survey data and modern GNSS measurements indicate a decrease in the elevation of the highest point on the mountain, driven by long-term thinning of summit ice. Here, we examine these results within the broader glaciological and geodetic context of Mount Rainier, where more than a century of observations document sustained changes in glacier thickness, extent, and mass balance. We emphasize the importance of distinguishing between ice-surface elevation and bedrock elevation when interpreting summit measurements on glaciated volcanoes, and describe how differences in vertical datums, measurement approaches, and temporal variability influence apparent elevation change. We synthesize existing datasets to demonstrate that observed elevation differences are consistent with long-term glacier thinning and are not indicative of lowering of the underlying volcanic edifice. We further highlight how terminology and framing influence interpretation of elevation change, particularly for prominent peaks where findings may be communicated beyond academic contexts. This contribution expands on recent work by providing geodetic context, integrating long-term datasets, and offering recommendations for consistent terminology and measurement practices in studies of glaciated summits.
The Cold Regions Research and Engineering Laboratory Permafrost Tunnel (CRREL Tunnel) in Alaska is one of the best studied Yedoma sequences in North America and is an exceptional site for understanding ice-rich, syngenetic permafrost. Here, we present cryostratigraphy, chronology, and stable isotopic analyses from eight exposures within the tunnel. These data are combined with previous studies to develop a composite sedimentary history and palaeoenvironmental record. At the sequence base, Fox Gravels were deposited ca. 45,000 calibrated years before C.E. 1950 (cal yr BP) and are overlain by silt that began accumulating ca. 43,000 cal yr BP. A slowing of silt accumulation (and possible hiatus) occurred ca. 36,000 cal yr BP and is associated with higher pore ice delta 18O values and thermokarst cave ice. Previous radiocarbon dates on ice wedge CO2 from this unit are shown to be inaccurate, highlighting the difficulty in dating these features. Silt accumulation reactivated between 35,000-31,000 cal yr BP, with higher delta 15N values, suggesting more arid conditions. Published palaeoenvironmental data, placed in our new chronology, show shrub tundra was present between 43,000-41,000 cal yr. By 36,000 cal yr BP herbs and sedges replaced shrub tundra as the Bering Land Bridge became established.
Broken rock land cover, such as talus, provides a critical microhabitat for small vertebrates in alpine environments, yet the specific thermal benefits of crevice use are understudied. We studied twelve talus patches in the North Cascades National Park in Washington, USA, over ten years (2015-2024) to quantify seasonal, annual, and diurnal patterns in crevice and surface temperatures. We also measured rock size and shape, vegetation and moss cover, and solar radiation at a high spatial resolution (Ground sampling distance (GSD) <1.05 mm) using handheld photogrammetry to evaluate their influence on thermal conditions. Summer surface temperatures increased an average of 0.37 degrees C/year, whereas winter surface temperatures remained stable. Crevices buffered high midday and evening temperatures in summer and retained warmth during winter and at night, averaging 5 degrees C cooler than the surface in summer and 0.45 degrees C warmer in winter. Surface and crevice temperatures were affected by solar radiation, area of southwest-facing rocks, vegetation and moss cover, rock circularity, and elevation. These results emphasize the value of precise rock measurements for understanding the thermal benefits of rocky habitats. Crevices play a crucial role in moderating temperature extremes, highlighting their importance as microhabitat refuge, which is likely important for the survival of alpine species as climate change accelerates warming.
Soil organic carbon (SOC) is critical for terrestrial carbon cycling processes. Snow cover days (SCD) and snow depth (SD) on the Tibetan Plateau have changed significantly over the past decade and are associated with SOC patterns. However, current field studies lack the spatial resolution to capture the spatial heterogeneity of snowpack effects on soil organic carbon across high-altitude regions, and the relative importance of snow cover has also remained unquantified within the context of complex multifactor interactions. In this study, we aim to fill these knowledge gaps, through machine learning models and structural equation models, using remote sensing data of snow and soil datasets from 2015 to 2023. The results indicate that under the multiple environmental factors, snow cover (SD and SCD) is associated with 32.03 percent of the relative contribution to SOC. The SOC response to snow cover varies significantly across different ecosystem types. Specifically, snow cover influences SOC through both soil temperature (ST) and soil moisture (SM) in alpine meadows, whereas ST is the dominant pathway in alpine steppe and alpine desert. Overall, the spatial patterns averaged from 2015 to 2023 show SM associations at low SCD and ST associations at more persistent SCD. The findings clarify the significance of snow cover in high elevation regions over the past decade for SOC, enhancing our understanding of the terrestrial carbon cycle and carbon balance on the Tibetan Plateau.
Lake Joyce of the McMurdo Dry Valleys (MDV), Antarctica, contains an endemic copepod population (Diacyclops joycei) that has not been identified from apparently suitable habitats in nearby lakes. The absence of a known source for colonization has led to speculation that Lake Joyce may have acted as a refugium during periods when MDV climate was sufficiently arid that freshwater lakes were largely extirpated. However, Lake Joyce is canonically viewed as a young MDV lake due to its low salt content, challenging its refuge status. In this contribution, we present a new lake bathymetric model, water delta O-18 and delta H-2 values, and chloride budget to reassess lake history. Results are consistent with previous estimates of lake age but indicate that the full water column is in contact with Taylor Glacier. We propose that, due to its topographic setting, Lake Joyce migrates with the waxing and waning of Taylor Glacier through glacial cycles, episodically losing salts, leading to an erroneously young age estimate and providing a mechanism to maintain fresh conditions during Holocene climate changes. These mechanisms may have facilitated the maintenance of copepod populations through changes in regional hydrology that rendered other lakes inhospitable due to elevated salinity.
Alpine plants experience strong seasonal shifts in resource demand and availability, yet how these dynamics shape fungal colonization remains unclear. We measured root colonization by arbuscular mycorrhizal fungi, fine root endophytes, and dark septate endophytes across six alpine plant species at Niwot Ridge, Colorado, in an early snowmelt simulation experiment and asked how colonization related to changes in plant phenology and seasonal nutrient context. Using a causal inference, we demonstrate that fungal colonization was indirectly influenced by early snowmelt through shifts in plant phenology: plots with later snowmelt timing had later flowering onset and seed set, which in turn supported greater fungal colonization. Because nutrient measurements were collected in a separate subplot-based data set, we use them to describe seasonal nutrient context rather than as intermediates in our causal models. Together, our results identify phenology as the mediator linking snowmelt timing to fungal colonization. We conclude that climate-driven shifts in snowmelt and reproduction timing can alter when plants recruit fungal partners: earlier reproduction is associated with reduced colonization if it occurs during higher nutrient pulses, whereas later reproduction is associated with greater colonization in drier late-season conditions.
Perennial snow and ice features, including both perennial snowpatches and glaciers, play an important role in alpine hydrologic systems, with their melt providing streamflow in years when precipitation and seasonal snowmelt are scarce. Although much attention has been paid to the response of glaciers across the Western United States to a warming climate, relatively little research has been devoted to the status of perennial snowpatches under the same conditions. We use the Normalized Difference Snow Index to investigate spatial and temporal changes in perennial snowpatches and glaciers in Yosemite National Park, California, over thirty-four years (1988-2021), enhancing this remote sensing analysis with a field campaign focused on in situ observations and sampling of a subset of features for stable isotope analysis. We find that, over our study period, Yosemite's perennial snowpatches decreased in number from 418 to 66 and decreased in area by 93 percent (from 2.33 to 0.17 km(2)), with a mean decrease of -0.065 km(2)/year, outpacing glacier area change. The decrease in perennial snowpatch area is primarily correlated with warming temperatures (p < .001) and fluctuating wintertime precipitation (p < .02), with periods of exceptionally high winter snowfall buffering summertime melt.
High-altitude freshwater ecosystems are increasingly at risk from emerging pollutants like microplastics, yet evidence from the Himalaya remains limited. This study evaluates microplastic contamination and nutrient dynamics in the sediments of Gokyo Lake Cluster, a Ramsar site in the Everest region of Nepal. Sediment samples were collected from 10 sites across three lakes and analyzed for microplastic abundance, shape, colors, size, and pollution indices. Concurrently, physicochemical parameters (pH, conductivity, nitrogen, phosphorus, potassium, and organic matter) of sediments were also measured to investigate potential environmental drivers. Of the three lakes (Longpanga Tsho, Taujung Tsho, and Gokyo Tsho) studied, the third lake (Gokyo Tsho) showed the highest microplastic abundance predominantly composed of fibers and fragments with Contamination Factor and Microplastic Pollution Load Index values suggesting low to moderate contamination and minor risk. Correlation analysis revealed a strong negative association between microplastics and pH and a positive association with organic matter. However, non-metric multidimensional scaling ordination did not identify any environmental variable as a significant driver of spatial variation in microplastic composition. These findings highlight the vulnerability of these wetlands to microplastic pollution and suggest routine monitoring and targeted pollution control strategies to safeguard the ecological integrity of the Himalayan wetlands.
High elevation wetlands can support accelerated rates of biogeochemical cycling by storing and releasing large amounts of carbon (C). However, little is known about the controls on C cycling in these remote ecosystems. We investigated redox-active organic matter (RAOM) reduction, methane and carbon dioxide production, and microbial community composition located within three different wetlands of the Niwot Ridge Long-Term Ecological Research site: a subalpine wetland (SAW), periglacial solifluction lobe (PSL), and alpine wet meadow (AWM). After a sixty-three-day anaerobic laboratory incubation, soils from the SAW and PSL had similar amounts of reduced RAOM (similar to 60 mu mol e(-) g(-1) dry weight [dw] soil, p = .7). Methane production was significantly higher in the SAW (similar to 350 mu mol C g(-1) dw soil) than in the PSL (similar to 25 mu mol C g(-1) dw soil; p < .005) and was negligible until RAOM was reduced by day 21. Microbial community analysis showed that though both SAW and PSL had microbes capable of reducing RAOM present, the PSL had significantly higher diversity compared to the SAW (p = .01). Collectively, these results demonstrate that RAOM reduction is an important process in the high elevation wetland C cycling with the potential to control methane production in high elevation wetlands, particularly subalpine wetlands.
The impact of vegetation on soil temperatures in low Arctic and boreal regions is well documented, where dense vegetation reduces soil temperatures. However, equivalent empirical evidence for influence of sparse, low-stature high Arctic vegetation and its interaction with cloud cover is limited. Improved understanding of this relationship is vital, because soil temperatures drive important ecosystem processes, such as nutrient cycling and carbon fluxes. We investigated whether effects on soil temperature are found under smaller high Arctic vegetation in Svalbard, Norway, by modeling soil temperatures in relation to vegetation cover and height across forty plots, using July temperature recordings from 2020 to 2023. We found reduced minimum temperatures under thicker moss layers and taller forb and shrub vegetation, whereas organic layers reduced maximum temperatures. These effects were strongest under sunny conditions, whereas shrub cover showed weak interactions with cloud cover. This contrasts with lower latitudes, where shrubs exert strong shading effects and vegetation reduces maximum and raises minimum soil temperatures. This discrepancy might stem from smaller diurnal temperature fluctuations, lower vegetation height, and lower solar radiation in the high Arctic. Our results indicate that predicted vegetation shifts resulting from climate change may lead to complex soil temperature responses in the future.
Climate trends in the Colorado Mineral Belt have intensified acid rock drainage (ARD) and acid mine drainage (AMD), increasing the need to understand trace metal and rare earth element (REE) cycling in affected watersheds. This study investigated hydrologic and biogeochemical controls on metal and REE concentrations across an AMD-impacted wetland located below an abandoned mine. Wetland surface waters had higher conductivity, sulfate, trace metal, and REE concentrations than underlying groundwater. REE concentrations varied spatially, with highest levels in wetland surface waters where Ce, Nd, and Y concentrations reached similar to 100 to 200 mu g/L, exceeding those of traditional AMD contaminants (e.g. Cd and Pb). Flow patterns and residence times influenced trace metal distributions, with Zn and Cu concentrations of 16.4 and 0.8 mg/L in wetland surface waters compared to 2.7 and 0.01 mg/L in groundwater. Cerium anomaly patterns revealed spatial gradients in oxidative processing, with values ranging from 0.96 in an adjacent stream, 0.51 to 0.97 in wetland surface water, and 0.70 to 0.85 in groundwater, reflecting the influence of extended groundwater-sediment contact allowing progressive REE transformation. These findings demonstrate that AMD-impacted wetlands are multizone ecosystems where hydrologic flow paths control biogeochemical processing of trace metals and REEs.
This study presents a detailed soil organic carbon (SOC) inventory for the Bl ae sedalen catchment, Disko Island. The study area has a mountainous setting (sea level to c. 800-m elevation), largely dominated by continuous permafrost. A total of twenty-eight soil profiles were sampled, with additional plant cover observations at eighteen sites. The landscape-level mean SOC 0- to 100-cm storage based on land cover upscaling is 4.07 +/- 0.74 kg C m-2. These stocks are largely found in the vegetated zone below 400-m elevation. Due to generally deep active layers, only about 4 percent of the total SOC stock is stored in the permafrost layer. An additional upscaling using landform criteria results in a mean stock of 4.01 +/- 1.21 kg C m-2. A prominent landform class is "solifluction areas," which occupies 18 percent of the total study area but represents 56 percent of the total SOC stock. This class has a highly variable SOC 0- to 100-cm stock (0.86-25.5 kg C m-2), but the mean of 12.6 kg C m-2 is much higher than the landscape average. Both landscape-level mean SOC 0- to 100-cm stock estimates in this study are similar, but land cover provides more constrained SOC ranges than landform upscaling.
Concentration-discharge (C-Q) relationships were analyzed over decadal, annual, and seasonal timescales from water years 1982 to 2020 to understand hydrologic and hydrochemical processes in the Green Lake 4 catchment, Green Lakes Valley, Colorado Front Range. Geogenic solutes, along with the magnitude of stable isotopes, were dominated by a strong (p < .05) C-Q power law (C = aQb, where a and b are constants from the curve fitting, with b usually termed the b-coefficient) and consistent patterns over various timescales. The b-coefficients of geogenic solutes were negative, suggesting that those solutes primarily originated from groundwater with higher concentrations and diluted by shallow source waters with lower concentrations (dilution effect). Nutrients other than nitrate were mainly chemostatic without a significant change in their concentrations with an increase in streamflow, indicating temporally variable concentrations in the source waters. The b-coefficients were usually positive for nitrate in the years with a significant C-Q power law (p < .05), indicating that nitrate was mainly generated from shallow source waters (flushing effect). Except for extremely dry water years, geogenic solute concentrations in streamflow were consistently higher during the snowmelt period than the post snowmelt period. This clockwise hysteresis is counterintuitive and suggests that during times of snowmelt, meltwater infiltration triggered additional subsurface flow paths and discharged higher solute concentrations to the stream channel in such flow paths than groundwater already identified earlier (e.g. talus water). With the earlier onset of snowmelt, the analysis also suggests that hydrochemical flushing and dilution effects will shift earlier in the future.
The discovery of the Yana site complex (similar to 32,000 BP) has intensified inquiry into the Late Pleistocene environments of Western Beringia, a critical factor shaping transcontinental species distributions and the initial human settlement of the Arctic. This study presents a high-resolution environmental and climatic record for the period 37,000 to 10,000 C-14 years ago (ca. 41,800-11,500 calBP), organized into 500- to 1,000-year time slices. We trace the transformation of vegetation from hemi-cryophytosteppe and tundra-steppe communities during marine isotope stage (MIS) 3 to tundra and shrub tundra in the early Holocene, culminating in a profound landscape restructuring during Holocene warming (similar to 11,500 years ago). Quantitative paleoclimatic reconstructions are based on minimum and maximum deviations from modern values for the temperature of the warmest month (T-wm), average annual temperature (T-ann), and average annual precipitation (P-ann). Our results reconstruct the main climatic trends in western Western Beringia and detail the sequence of fluctuations during MIS 3 and MIS 2. We precisely define the transition to MIS 2, quantify the duration of the Last Glacial Maximum, identify Late Glacial climatic events corresponding to the European Blytt-Sernander scheme, and reveal early Holocene changes that drove radical landscape transformation. This constitutes the first such detailed reconstruction for Western Beringia. The identified climate fluctuations show strong agreement with the North Greenland Ice Core Project Greenland ice core record. We conclude that natural conditions during the studied interval, encompassing the second half of MIS 3 and all of MIS 2, were suitable for human occupation in the western Arctic part of Beringia.
Most of what is known about sedimentary depositional history, sediment composition, ground ice distribution and depth, and soil moisture content in the McMurdo Dry Valleys (MDV) of Antarctica results from point measurements of soil properties, which can miss larger patterns at the landscape scale. Here, I apply space-borne thermal infrared remote sensing to determine how apparent thermal inertia measurements, coupled with thermal inertia determination of field samples, informs the interpretation of ancient landforms and seasonal processes in Antarctica. Measured soil thermal inertia depends most strongly on coarse grain fraction, soil bulk density, and water content. Apparent thermal inertia measured via Landsat 8 imaging shows distinct spatial patterns by location, elevation, and hydrological position. Satellite-derived apparent thermal inertia provides a novel tool for exploring geological and hydrological relationships at the landscape scale in this polar desert. Notably, apparent thermal inertia measurements reveal the presence of a previously undescribed paleo-lake in the Goldman Pond basin, suggesting that apparent thermal inertia analyses applied to the Dry Valleys could expand our understanding of landform development and the geological history of a landscape which is critical for interpreting past ice sheet response to changing climate conditions.
As the most important transportation corridor in the heart of the Qinghai–Tibet Plateau, the Qinghai–Tibet Engineering Corridor experiences varying degrees and forms of wind–sand hazards, posing serious threats to the construction and maintenance of infrastructure. To reveal the spatial distribution and transport patterns of these hazards and provide a scientific basis for mitigation, this study conducted systematic field measurements and sand particle analysis in the region to quantify key eolian parameters. The results indicate that the annual average wind speed ranged from 3.14 to 3.80 m·s−1, and the annual sand-moving wind frequency ranged from 19.83 to 26.55 percent. Both the annual average wind speed and the annual sand-moving wind frequency gradually increased from north to south, with the predominant annual wind direction and sand-moving wind direction being westerly. The sand particle size in the Qinghai–Tibet Engineering Corridor was mainly medium to fine sand, with the intensity of wind–sand activity and the drift potential gradually increasing from north to south. Temporally, sand transport mainly occurred in winter and spring, and spatially, it predominantly moved from the west to east, intersecting nearly perpendicularly with the north–south linear engineering structures within the corridor, causing hazards. The research results provide a scientific basis for the planning, design, and wind–sand prevention of infrastructure in the Qinghai–Tibet Engineering Corridor.
