Effects of meteorology and soil moisture on the spatio-temporal evolution of the depth hoar layer in the polar desert snowpack

In polar deserts, depth hoar (hereinafter: DH) growth is not systematic unlike on tundra and this is critical for snowpack properties. Here, we address the spatio-temporal variability of the DH layer in the polar desert at two sites in the Canadian High Arctic: Ward Hunt Island (83° N) and Resolute Bay (75° N). Our data show that, over humid areas, DH represented a larger fraction of the snowpack and was characterized by lower density and coarser crystals than over dry gravelly areas. Increased soil moisture extends the zero-curtain period during freeze-up, leading to stronger temperature gradients in the snowpack and greater kinetic metamorphism. Our results also demonstrate that the large inter-annual variability in DH is primarily driven by wind conditions in the fall since this key variable controls the initial snow density and snow onset date. These strong controls exerted by soil moisture and meteorological conditions on DH growth in polar deserts highlight the possibility of major changes in polar snowpacks physical properties in response to the rapid climate and environmental changes currently affecting these regions.

Holocene ice wedge formation in the Eureka Sound Lowlands, high Arctic Canada

Ice wedges are ubiquitous periglacial features in permafrost terrain. This study investigates the timing of ice wedge formation in the Fosheim Peninsula (Ellesmere and Axel Heiberg Islands). In this region, ice wedge polygons occupy ~50% of the landscape, the majority occurring below the marine limit in the Eureka Sound Lowlands. Numerical simulations suggest that ice wedges may crack to depths of 2.7–3.6 m following a rapid cooling of the ground over mean winter surface temperatures of −18°C to −38°C, corresponding to the depth of ice wedges in the region. The dissolved organic carbon (DOC)/Cl molar ratios suggest that the DOC in the ice wedges is sourced from snowmelt and not from leaching of the active layer. Based on 32 14CDOC measurements from 15 ice wedges, the wedges were likely developing between 9000–2500 cal yr BP. This interval also corresponds to the period of peat accumulation in the region, a proxy of increased moisture. Considering that winter air temperatures remained favorable for ice wedge growth throughout the Holocene, the timing of ice wedge formation reflects changes in snowfall. Overall, this study provides the first reconstruction of ice wedge formation from a high Arctic polar desert environment.

Survey of the vascular plants of Alert (Ellesmere Island, Canada), a polar desert at the northern tip of the Americas

Long-term monitoring is critical to guide conservation strategies and assess the impacts of climatic changes and anthropogenic activities. In High Arctic ecosystems, information on distribution and population trends of plants is dramatically lacking. During two field expeditions in 2018 and 2019, we conducted a systematic floristic survey together with opportunistic collecting in the polar desert surrounding Alert (Nunavut, Canada) to update past vascular plant inventories. We recorded 58 species, of which 54 species were recorded over the last seven decades, and four species that are additions to the local flora (Draba pauciflora R. Brown, Festuca edlundiae S.G. Aiken, Consaul, & Lefkovitch, Festuca hyperborea Holmen ex Frederiksen, and ×Pucciphippsia vacillans (T. Fries) Tzvelev). With the addition of 19 species that were previously reported but not found in our survey, we estimate the species richness in the study area at 77 species.

Distinct Microbial Communities in Adjacent Rock and Soil Substrates on a High Arctic Polar Desert

Understanding microbial niche variability in polar regions can provide insights into the adaptive diversification of microbial lineages in extreme environments. Compositions of microbial communities in Arctic soils are well documented but a comprehensive multidomain diversity assessment of rocks remains insufficiently studied. In this study, we obtained two types of rocks (sandstone and limestone) and soils around the rocks in a high Arctic polar desert (Svalbard), and examined the compositions of archaeal, bacterial, fungal, and protistan communities in the rocks and soils. The microbial community structure differed significantly between rocks and soils across all microbial groups at higher taxonomic levels, indicating that Acidobacteria, Gemmatimonadetes, Latescibacteria, Rokubacteria, Leotiomycetes, Pezizomycetes, Mortierellomycetes, Sarcomonadea, and Spirotrichea were more abundant in soils, whereas Cyanobacteria, Deinococcus-Thermus, FBP, Lecanoromycetes, Eurotiomycetes, Trebouxiophyceae, and Ulvophyceae were more abundant in rocks. Interestingly, fungal communities differed markedly between two different rock types, which is likely to be ascribed to the predominance of distinct lichen-forming fungal taxa (Verrucariales in limestone, and Lecanorales in sandstone). This suggests that the physical or chemical properties of rocks could be a major determinant in the successful establishment of lichens in lithic environments. Furthermore, the biotic interactions among microorganisms based on co-occurrence network analysis revealed that Polyblastia and Verrucaria in limestone, and Atla, Porpidia, and Candelariella in sandstone play an important role as keystone taxa in the lithic communities. Our study shows that even in niches with the same climate regime and proximity to each other, heterogeneity of edaphic and lithic niches can affect microbial community assembly, which could be helpful in comprehensively understanding the effects of niche on microbial assembly in Arctic terrestrial ecosystems.

Diatom communities differ among Antarctic moss and lichen vegetation types

Continental Antarctica is a polar desert containing sparse pockets of vegetation within ice-free areas. Despite the recognized association between lichens, mosses and epiphytic diatoms, the environmental factors controlling diatom community structure are poorly understood. We investigated the association between diatom communities and host vegetation characteristics by experimentally adding nutrients and/or water to two bryophyte (healthy and moribund) and two lichen (crustose and Usnea) vegetation types in the Windmill Islands. Diatom communities were morphologically characterized, diversity indices calculated and differences between treatments, vegetation type and vegetation characteristics tested. We identified 49 diatom taxa, 8 of which occurred with > 1% relative abundance. Bryophyte and lichen vegetation harboured significantly different diatom communities, both in composition and diversity indices. Specifically, Luticola muticopsis was more prevalent in moribund bryophytes and crustose lichens, and Usnea lichens showed lower species richness than other types. While nutrient and water additions did not significantly alter diatom communities, diversity indices and some species showed relationships with vegetation physiological characteristics, notably %N and δ13C, suggesting the importance of ambient gradients in water and nutrient availability. Collectively, this work suggests that future conditions favouring the dominance of a particular vegetation type may have a homogenizing effect on the terrestrial diatom communities of East Antarctica.

Cryostratigraphical studies of ground ice formation and distribution in a High Arctic polar desert landscape, Resolute Bay, Nunavut

Ground ice distribution and abundance have wide-ranging effects on periglacial environments, and possible impacts on climate change scenarios. In contrast, very few studies measure ground ice in the High Arctic, especially in polar deserts and where coarse surficial material complicates coring operations. Ground ice volumes and cryostructures were determined for eight sites in a Polar desert, near Resolute Bay, Nunavut, chosen from their hydrogeomorphic classification. Dry, unvegetated polar desert sites exhibited ice content close to soil porosity, with a < 45 cm thick ice-enriched transition zone. In wetland sites, suspended cryostructures and ice dominated cryofacies (ice content at least 2x soil porosity values) were prevalent in the upper ~2 m of permafrost. Average ground ice saturation at those locations exceeded porosity values by a factor between 1.8 to 20.1, and by up to two orders of magnitude at the ~10 cm vertical scale. Sites with the highest ice content were historically submerged wetlands with a history of sediment supply, sustained water availability, and syngenetic and quasi-syngenetic permafrost aggradation. Ice enrichment in those environments were mainly caused by the strong upward freezing potential beneath the thaw front, which, combined with abundant water supply, caused ice aggradation and frost heaving to form lithalsa plateaus. Most of the sites already expressed cryostratigraphic evidence of permafrost degradation. Permafrost degradation carries important ecological ramifications, as wetland locations are the most productive, life-supporting oases in the otherwise relatively barren landscape, carrying essential functions linked with hydrological processes and nutrient and contaminant cycling.

Exposure-age data from across Antarctica reveal mid-Miocene establishment of polar desert climate

High-elevation rock surfaces in Antarctica have some of the oldest cosmogenic-nuclide exposure ages on Earth, dating back to the Miocene. A compilation of all available 3He, 10Be, and 21Ne exposure-age data from the Antarctic continent shows that exposure histories recorded by these surfaces extend back to, but not before, the mid-Miocene cooling at 14–15 Ma. At high elevation, this cooling entailed a transition between a climate in which liquid water and biota were present and could contribute to surface weathering and erosion, and a polar desert climate in which virtually all weathering and erosion processes had been shut off. This climate appears to have continued uninterrupted between the mid-Miocene and the present.

Supplemental Material: Exposure-age data from across Antarctica reveal mid-Miocene establishment of polar desert climate

Table S1 (sample and exposure-age information for all samples in the ICE-D:ANTARCTICA database that have Miocene apparent exposure ages).<br>