Ice-wedge polygons are widespread and conspicuous surficial expressions of ground-ice in permafrost landscapes. Thawing of ice wedges triggers differential ground subsidence, local ponding, and persistent changes to vegetation and hydrologic connectivity across the landscape. Here we characterize spatio-temporal patterns of ice-wedge degradation since circa 1950 across environmental gradients on Alaska's North Slope. We used a spectral thresholding approach validated by field observations to map flooded thaw pits in high-resolution images from circa 1950, 1982, and 2012 for 11 study areas (1577-4460 ha). The total area of flooded pits increased since 1950 at 8 of 11 study areas (median change +3.6 ha; 130.3%). There were strong regional differences in the timing and extent of degradation; flooded pits were already extensive by 1950 on the Chukchi coastal plain (alluvial-marine deposits) and subsequent changes there indicate pit stabilization. Degradation began more recently on the central Beaufort coastal plain (eolian sand) and Arctic foothills (yedoma). Our results indicate that ice-wedge degradation in northern Alaska cannot be explained by late-20th century warmth alone. Likely mechanisms for asynchronous onset include landscape-scale differences in surficial materials and ground-ice content, regional climate gradients from west (maritime) to east (continental), and regional differences in the timing and magnitude of extreme warm summers after the Little Ice Age.
Widespread changes in the distribution and abundance of plant functional types (PFTs) are occurring in Arctic and boreal ecosystems due to the intensification of disturbances, such as fire, and climate-driven vegetation dynamics, such as tundra shrub expansion. To understand how these changes affect boreal and tundra ecosystems, we need to first quantify change for multiple PFTs across recent years. While landscape patches are generally composed of a mixture of PFTs, most previous moderate resolution (30-m) remote sensing analyses have mapped vegetation distribution and change within land cover categories that are based on the dominant PFT; or else the continuous distribution of one or a few PFTs, but for a single point in time. Here we map a 35-year time-series (1985–2020) of top cover (TC) for seven PFTs across a 1.77 x 106 km² study area in northern and central Alaska and northwestern Canada. We improve on previous methods of detecting vegetation change by modeling TC, a continuous measure of plant abundance. The PFTs collectively include all vascular plants within the study area as well as light macrolichens, a nonvascular class of high importance to caribou management. We identified net increases in deciduous shrubs (66 x 103 km²), evergreen shrubs (20 x 103 km²), broadleaf trees (17 x 103 km²), and conifer trees (16 x 103 km²), and net decreases in graminoids (-40 x 103 km²) and light macrolichens (-13 x 103 km²) over the full map area, with similar patterns across Arctic, Oroarctic, and Boreal bioclimatic zones. Model performance was assessed using spatially blocked, nested 5-fold cross-validation with overall root mean square errors ranging from 8.3–19.0%. Most net change occurred as succession or plant expansion within areas undisturbed by recent fire, though PFT TC change also clearly resulted from fire disturbance. These maps have important applications for assessment of surface energy budgets, permafrost changes, nutrient cycling, and wildlife management and movement analysis.
Climate change and a related increase in temperature, particularly in alpine areas, force both flora and fauna to adapt to the new conditions. These changes should in turn affect soil formation processes. The aim of this study was to identify possible consequences for soils in a dry-alpine region with respect to weathering of primary minerals and leaching of elements under expected vegetation and climate changes. To achieve this, a field empirical approach investigating an altitudinal sequence was used in combination with laboratory weathering experiments simulating several scenarios. The study sites are located in Sinks Canyon and Stough Basin of the Wind River Range, Wyoming, USA. The following sites (from moist to dry with increasing temperature along the sequence) were investigated: 10 soil profiles (Typic Haplocryoll) in a tundra ecotone, 10 soil profiles (Ustic Haplocryoll) in a pine-fir forest and 20 soil profiles (Ustic Argicryoll) in sagebrush. All soils developed on granitoid moraines. Soil mineralogy was analysed using cathodoluminescence and X-ray diffraction. This revealed that biotite and plagioclase were both weathered to smectite while plagioclase also weathered to kaolinite. Cooler, wetter, altitude-dependent conditions promoted weathering of primary minerals. Furthermore, the soils of the tundra and forest zone exhibited a higher acidity and more organic carbon. In a series of wet laboratory batch experiments, materials from topsoils (A horizons) and subsoils (B horizons) in each ecotone were examined alone or in combination with other samples. In a first step, aqueous extracts of the topsoil samples were generated in batch reactors and analysed for the main ions. In a second and a third step the topsoil extracts were reacted with the subsoil samples of the same ecotone, and with the subsoil samples of the ecotones at higher altitude. The total duration of these batch experiments was 1800 h, and the solutes were measured using ICP-OES and ion chromatography. Dissolved Ca, Mg and K were mainly controlled by the chemical weathering of oligoclase, K-feldspar and biotite. With increasing altitude the total concentrations of Ca, Mg and K in the aqueous extracts decreased, the relative ionic contribution from K decreased, while the ionic contribution from Ca increased. Climate change (warming, changed precipitation) potentially will reduce weathering intensity, soil acidity and the content of organic carbon. An altitudinal shift in vegetation due to climate change seems to affect the ionic composition of the soil solution. In the case of a shift from forest to sagebrush and tundra to forest or sagebrush, the relative contribution from K would increase at the expense of Ca. We hypothesise that K will play an important role in future biogeochemical cycles under the assumptions of climate warming and subsequent vegetation shifts to higher altitudes. 36In a series of wet laboratory batch experiments, materials from topsoils (A horizons) and subsoils 37(B horizons) in each ecotone were examine...
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