Rain-on-Snow (ROS) events change snow pack properties and in extreme cases ice layers form which affect wildlife, vegetation and soils beyond the duration of the event. Active as well as passive microwave sensors have been used in the past to document ROS on regional scale. Either wet snow during a ROS event or the formation of crust afterwards are identified in most cases. The fusion of both approaches is promising for circumpolar monitoring.C-band radar is of special interest due to good data availability including a range of nominal spatial resolution (10 m–12.5 km). Previous studies indicated that radar backscatter is suitable to identify snow structure change. As an example L-band passive microwave observations from SMOS and C-band backscatter from Metop ASCAT have been jointly analysed and compared to snowpit observations in Scandinavia and Northwestern Siberia.A circumpolar dataset of potential ROS has been created. The gridded information has been eventually aggregated for events. Larger mid-winter events have been eventually extracted for 2012-2021. They occur mostly in the NE part of northern Eurasia (mostly November) and across Alaska (mostly December). The spatiotemporal patters of these events and the magnitude of snow structure change will be presented and discussed.
Abstract. Rain-on-Snow (ROS) events occur across many regions of the terrestrial Arctic in mid-winter. Snow pack properties are changing and in extreme cases ice layers form which affect wildlife, vegetation and soils beyond the duration of the event. Specifically, satellite microwave observations have been shown to provide insight into known events. Only Ku-band radar (scatterometer) has been applied so far across the entire Arctic. Data availability at this frequency is limited, however. The utility of other frequencies from passive and active systems need to be explored to develop a concept for long-term monitoring. Active (radar) records have been shown to capture the associated snow structure change based on time series analyses. This approach is also applicable when data gaps exist and bears capabilities to evaluate the impact severity of events. Active as well as passive microwave sensors can also detect wet snow at the timing of a ROS, if an acquisition is available. Wet snow retrieval methodology is, however, rather mature, compared to identification of snow structure change which needs consideration of ambiguous scattering behaviour. C-band radar is of special interest due to good data availability including a range of nominal spatial resolution (10 m–12.5 km) A combined approach is therefore considered and tested for C-band (active, snow structure change) and L-band (passive, wet snow). Results were compared to in situ observations (snow pit records, caribou migration data) and Ku-band products. Ice crusts were found in the snow pack after detected events. The more crusts (events) the higher the winter season backscatter increase at C-band. ROS events captured on the Yamal and Seward peninsulas have had severe impacts on reindeer and caribou, respectively, due to crust formation. Temperature dependence of C-band backscatter observable down to -40 °C is identified as a major issue for ROS retrieval, but can be addressed by combination with passive microwave wet snow indicators (demonstrated for Metop ASCAT and SMOS). Synthetic Aperture Radar (SAR) from specifically Sentinel-1 (C-band) is promising regarding ice layer identification at better spatial details for all available polarizations. The fusion of multiple types of microwave satellite observations is suggested for the creation of a climate data record, but the consideration of performance differences due to spatial and temporal cover as well as microwave frequency is crucial. Retrieval is most robust north of 65° N, in the tundra biome, where records can be used to identify extremes and to apply the results for impact studies at regional scale.
We review and present a synthesis of the existing research dealing with changing Arctic tundra ecosystems, in relation to caribou and reindeer winter ranges. Whereas pan-Arctic studies have documented the effects on tundra vegetation from simulated climate change, we draw upon recent long-term regional studies in Alaska that have documented the actual, on-the-ground effects. Our review reveals signs of marked change in Arctic tundra ecosystems. Factors known to be affecting these changes include wildfire, disturbance by caribou and reindeer, differential growth responses of vascular plants and lichens, and associated competition under climate warming scenarios. These factors are interrelated, and, we posit, unidirectional: that is, they are all implicated in the significant reduction of terricolous lichen ground cover and biomass during recent decades. Lichens constitute the primary winter forage for large, migratory caribou and reindeer herds, which in turn are a critical subsistence resource for rural residents in Alaska. Thus, declines in these lichens are a major concern for rural people who harvest caribou and reindeer for subsistence, as well as for sport hunters, reindeer herders, wildlife enthusiasts and land managers. We believe a more widely distributed and better integrated research programme is warranted to quantify the magnitude and extent of the decline in lichen communities across the Arctic.
Dens are a focal point in the life history and ecology of gray wolves (Canis lupus), and their location can influence access to key resources, productivity, survivorship, and vulnerability to hunting, trapping, and control efforts. We analyzed the selection of den sites and the phenology of their use inside the Yukon-Charley River National Preserve from 1993 to 2017 to enhance our understanding of this resource. At the landscape scale, we found that wolves in east-central Alaska selected den sites that were lower in elevation, snow free earlier in the spring, exposed to greater solar radiation, and closer to water. Den sites were also associated with areas that had burned less recently and had lower terrain ruggedness at the 1 km scale. These results supported our hypothesis that wolves would den relatively close to essential resources (water and prey) and in areas that are drier (melt earlier) in the spring. At the home range scale, wolves also selected den sites at lower elevations and showed a strong selection for the center of their home range. Furthermore, the average distance between active den sites was 37.3 km, which is slightly greater than the average radius (32.5 km) of a home range of a pack. Our results support our hypothesis that dynamic social factors modulate the selection of environmental factors for den site location. Wolves den away from other packs to reduce competition and exposure to intraspecific conflict. High-quality denning habitat does not currently appear to be a limiting factor for this population. Females, on average, entered their dens on 10 May, stayed inside the den for eight days, and remained less than 1 km from the den for an additional six days after emerging. We found that wolves denning at higher elevations entered their dens later than those at lower elevations, which also supported one of our hypotheses. Lastly, we documented limited evidence of earlier denning over time. Long-term monitoring projects, such as ours, are critical in identifying these types of trends.
Contamination with arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb) is a global concern impairing resilience of organisms and ecosystems. Proximity to emission sources increases exposure risk but remoteness does not alleviate it. These toxic elements are transported in atmospheric and oceanic pathways and accumulate in organisms. Mercury accumulates in higher trophic levels. Brown bears (Ursus arctos), which often live in remote areas, are long-lived omnivores, feeding on salmon (Oncorhynchus spp.) and berries (Vaccinium spp.), resources also consumed by humans. We measured blood concentrations of As, Cd, Hg and Pb in bears (n = 72) four years and older in Scandinavia and three national parks in Alaska, USA (Lake Clark, Katmai and Gates of the Arctic) using high-resolution, inductively-coupled plasma sector field mass spectrometry. Age and sex of the bears, as well as the typical population level diet was associated with blood element concentrations using generalized linear regression models. Alaskan bears consuming salmon had higher Hg blood concentrations compared to Scandinavian bears feeding on berries, ants (Formica spp.) and moose (Alces). Cadmium and Pb blood concentrations were higher in Scandinavian bears than in Alaskan bears. Bears using marine food sources, in addition to salmon in Katmai, had higher As blood concentrations than bears in Scandinavia. Blood concentrations of Cd and Pb, as well as for As in female bears increased with age. Arsenic in males and Hg concentrations decreased with age. We detected elevated levels of toxic elements in bears from landscapes that are among the most pristine on the planet. Sources are unknown but anthropogenic emissions are most likely involved. All study areas face upcoming change: Increasing tourism and mining in Alaska and more intensive forestry in Scandinavia, combined with global climate change in both regions. Baseline contaminant concentrations as presented here are important knowledge in our changing world.
Abstract Previous research indicates that the effects of climate warming, including shrub expansion and increased fire frequency may lead to declining lichen abundance in arctic tundra and northern alpine areas. Lichens are important forage for caribou ( Rangifer tarandus ), whose populations are declining throughout most of North America. To clarify how lichen cover might affect caribou resource selection, ecologists require better data on the spatial distribution and abundance of lichen. Here, we use a combination of field data and satellite imagery to model lichen cover for a 583 200 km 2 area that fully encompasses nine caribou ranges in interior Alaska and Yukon. We aggregated data from in situ vegetation plots, aerial survey polygons and unmanned aerial vehicle (UAV) imagery to align with 30 m resolution Landsat pixels. We used these data to train a random forest model with a suite of environmental and spectral predictors to estimate lichen cover. We validated our lichen cover model using reserved training data and existing external datasets, and found that reserved data from aerial survey polygons ( R 2 = 0.77) and UAV imagery ( R 2 = 0.71) provided the best fit. We used our lichen cover map to evaluate the influence of estimated lichen cover on caribou resource selection in the Fortymile Herd from 2012 to 2018 during summer and winter. In both seasons, caribou avoided lichen-poor areas (0%–5% lichen cover) and showed stronger selection as lichen cover increased to ∼30%, above which selection leveled off. Our results suggest that terrestrial lichen cover is an important factor influencing caribou resource selection in northern boreal forests across seasons. Our lichen cover map goes beyond existing maps of lichen abundance and distribution because it incorporates extensive field data for model training and validation and estimates lichen cover over a much larger spatial extent. We expect our landscape-scale map will be useful for understanding trends in lichen abundance and distribution, as well as for caribou research, management and conservation.
Long movements across sea ice by Caribou (Rangifer tarandus) in Alaska are relatively uncommon and are not well documented. With rapidly diminishing sea ice cover in arctic waters, these movements may cease altogether. On 26 May 2012, a Caribou crossed a long span (57 km) of sea ice off the coast of Alaska. The cow successfully crossed after traveling 66 km on the sea ice and eventually reached the calving grounds. The highly dynamic nature of sea ice, which is driven by oceanic currents and wind during spring break-up, presents inherent hazards different from lake ice. Based on three years of Global Positioning System (GPS) radio-collar data, Caribou routinely crossed long expanses (30 km) of ice covering the brackish Selawik Lake and shorter stretches (<13 km) on Inland Lake during their spring migration north. There was also a single crossing on the ice covering Selawik Lake during the fall migration south to the wintering grounds that took place in early November 2010. Five GPS-collared Caribou crossed the short frozen span (14 km) of Kotzebue Sound between Cape Krusenstern National Monument and the Baldwin Peninsula in the fall of 2011.
