This study highlights the results of a palaeoecological analysis conducted on five permafrost peatlands in the northern tundra subzone along the Barents Sea coast in the European Arctic zone. The depth of the peat cores that were sampled was approximately 2 m. The analysis combined data on the main physical and chemical soil properties, radiocarbon dating, botanical composition, and mass fraction of polycyclic aromatic hydrocarbons (PAHs). The concentrations of 16 PAHs in peat organic layers ranged from 140 to 254 ng/g, with an average of 182 ng/g. The peatlands studied were dominated by PAHs with a low molecular weight: naphthalene, phenanthrene, fluoranthene, pyrene, chrysene. The vertical distribution patterns of PAHs along the peat profile in the active layer and permafrost were determined. PAHs migrating down the active layer profile encounter the permafrost barrier and accumulate at the boundary between active layer and permafrost layer. The deep permafrost layers accumulate large amounts of PAHs and PAH derivatives, which are products of lignin conversion during the decomposition of grassy and woody vegetation during the Holocene climate optima. The total toxic equivalency concentration (TEQ) was calculated. Peatlands from the Barents Sea coast have low toxicity for carcinogenic PAHs throughout the profile. TEQ ranged from a minimum of 0.1 ng/g to a maximum of 13.5 ng/g in all peatlands investigated. For further potential use in Arctic/sub-Arctic environmental studies, PAH indicator ratios were estimated. In all investigated sections and peatland horizons, the most characteristic ratios indicate the petrogenic (natural) origin of PAHs.

When developing Arctic territories, studying and forecasting the state of cryogenic landscapes in the context of climate change plays an important role. General conclusions about permafrost degradation do not fully capture changes at regional and local levels, as the direction and pace of landscape transformation depend on many factors, including the specific characteristics of the terrain. Permafrost degradation and changes in the depth of the active layer thickness (ALT) can be accompanied by alterations in ground vegetation cover (GVC) and surface moisture, which can be recorded through remote sensing (RS) data. However, there is a knowledge gap regarding the use of RS data to identify long-term trends in the phytocenotic properties of GVC and soil moisture at different geomorphological levels, as well as to determine the relationship between these trends and changes in ALT. In this study, based on Landsat data from 1985 to 2024, changes in GVC and soil moisture across various geomorphological levels were identified in a local area of the Yamal Peninsula. The analysis used the NDVI vegetation index, the NDWI moisture index, and the WI (Wetness Index) temperature-vegetation index, which reflects the moisture content of GVC and soil. The general trend observed is an increase in the growth rates of these indices as the geomorphological levels rise from the floodplain to Terrace IV. A comparison of these observed trends in the NDVI, NDWI, and WI indices with in situ geocryological observations shows the potential of using these indices as indicators of ALT change.

Observations on the North Slope of Alaska have revealed patches of Sphagnum peat within the widespread matrix of tussock tundra on mineral soils. Little is known about the developmental history of these Sphagnum patches and whether they represent incipient peatlands established in response to warming-related environmental changes. Nine peat cores were collected from nine Sphagnum-dominated peat patches spanning an approximately 300-km longitudinal gradient on the North Slope to determine their development and establishment history. Stratigraphically constrained cluster analysis was applied to plant macrofossil data, carbon-to-nitrogen ratios, and total organic matter measured from bulk peat to delineate developmental phases, and radiocarbon dating was used to constrain the timing of Sphagnum peat patch establishment. We compared these data to changes in testate amoeba community composition and amoeba-inferred water-table depth and pH in six of the peat cores. We also compared Sphagnum peat-patch development and establishment history to paleoclimate and local instrumental temperature records. Results indicated a predictable pattern that describes the transition from moist tussock tundra to Sphagnum peat. Furthermore, although Sphagnum has been present on the North Slope for millennia, our data suggest that Sphagnum-dominated peat patches constitute recent landscape features, mainly established in the 1800s and 1900s, and with rapidly increasing Sphagnum abundance in the past 50 years. Sphagnum expansion was associated with pronounced changes in testate amoeba communities, including an increase in mixotrophic taxa and species associated with densely growing Sphagnum, and community changes consistent with drying and increased acidity. The recent development of Sphagnum-dominated peat patches has been associated with warming air and soil temperatures, active layer deepening, and earlier snowmelt. Sphagnum expansion has also been observed in other arctic regions, and understanding the extent and growth potential of Sphagnum peat patches has implications for understanding and anticipating changes in carbon cycling, edaphic conditions, permafrost thermal regimes, and floristic diversity.

Alpine tundra ecosystems, like their arctic counterparts, have historically been the sites of considerable soil organic carbon (SOC) storage due to climatic factors that suppressed microbial activity. While climatic factors are important, heterotopic soil respiration (and SOC storage) may be influenced by a range of soil characteristics. In this study, we measured soil respiration, soil temperature, soil moisture, soil nutrient concentrations, soil pH, and soil texture in 4 alpine tundra sites located in Rocky Mountain National Park, Colorado, USA from June 2015 - September 2021. We also used geospatial modeling to visualize predicted climate changes in this system over the 21st century. Finally, we measured SOC concentrations over the seven-year study. We found that soil respiration was significantly correlated with soil temperature, soil moisture, and soil texture. All other parameters were not significantly correlated with soil respiration. We also found that SOC concentrations did not change significantly over the course of the seven-year study. The predictive models show that by the end of the century, over the majority of the park, the mean maximum air temperature will increase, the amount of snowfall will decrease, soil moisture will decrease, and the number of snow-free days will increase. These results suggest that SOC is not currently being lost from this system at a high rate. In addition, it appears that with a changing climate, soil respiration may increase with warming, but the overall increase may be limited by decreased soil moisture and in some cases, high soil temperatures.

Land-cover changes and new ecosystem trajectories in Interior Alaska have altered the structure and function of landscapes, with regional warming trends altering carbon and water cycling. Notably, these changes include the increased distribution of tall woody vegetation, trees and shrubs, in landscapes that historically only supported low shrub vegetation cover. In Denali National Park, Alaska, this phenomenon has altered primary succession pathways towards tundra ecosystems with the establishment and expansion of balsam poplar (Populus balsamifera) trees. In this study, we examine how snow, soil, and vegetation processes interact within this altered successional pathway towards further landscape change following glacial recession. In a sequence of outflow terraces, we found that variations in snow depth, functional soil depth, leaf area index, overstory height, and understory height were all significantly correlated with each other, with those effects largely explained by the presence of poplar. Poplar-dominated plots had deeper snowpacks, deeper functional soil depths, taller overstory and shrub heights, and greater LAI than in non-poplar plots of the same landscape age. These findings suggest a feedback cycle where the establishment of taller vegetation (here, poplar) alters ecosystem processes in the following notable ways: taller vegetation is able to trap more snow by reducing wind exposure and limiting sublimation; this snow provides water through additional snowmelt and insulation, keeping soils warmer and lessening permafrost development, leading to deeper functional soil depths. This feedback demonstrates poplar's ability to modify the environment as an ecosystem engineer, engineering a trajectory away from the otherwise expected permafrost-underlain tundra.

In alpine tundra regions, snowmelt plays a crucial role in creating spatial heterogeneity in soil moisture and nutrients across various terrains, influencing vegetation distribution. With climate warming, snowmelt has advanced, lengthening the growing season while also increasing the risk of frost damage to evergreen dwarf shrubs like Rhododendron aureum in alpine tundra regions. To understand these long-term effects, we used remote sensing imagery to analyze nearly four decades (1985-2022) of snowmelt date and the distribution change of R. aureum in Changbai Mountain, East China's only alpine tundra. Results show that snowmelt advanced by 1-3 days/10 years, with faster rates at higher elevations and shady slopes (0.4-0.6 days/10 years more than sunny slopes), while R. aureum increased more on shady slopes under such conditions. Our study demonstrates that these shifts in snowmelt date vary significantly across topographies and reveals how topography and snowmelt changes interact to shape the distribution of evergreen shrubs under climate warming.

The Arctic experiences rapid climate change, but our ability to predict how this will influence plant communities is hampered by a lack of data on the extent to which different species are associated with particular environmental conditions, how these conditions are interlinked, and how they will change in coming years. Increasing temperatures may negatively affect plants associated with cold areas due to increased competition with warm-adapted species, but less so if local temperature variability is larger than the expected increase. Here we studied the potential drivers of vegetation composition and species richness along coast to inland and altitudinal gradients by the Nuuk fjord in western Greenland using hierarchical modelling of species communities (HMSC) and linear mixed models. Community composition was more strongly associated with random variability at intermediate spatial scales (among plot groups 500 m apart) than with large-scale variability in summer temperature, altitude or soil moisture, and the variation in community composition along the fjord was small. Species richness was related to plant cover, altitude and slope steepness, which explained 42% of the variation, but not to summer temperature. Jointly, this suggests that the direct effect of climate change will be weak, and that many species are associated with microhabitat variability. However, species richness peaked at intermediate cover, suggesting that an increase in plant cover under warming climatic conditions may lead to decreasing plant diversity.

The extent of wildfires in tundra ecosystems has dramatically increased since the turn of the 21st century due to climate change and the resulting amplified Arctic warming. We simultaneously studied the recovery of vegetation, subsurface soil moisture, and active layer thickness (ALT) post-fire in the permafrost-underlain uplands of the Yukon-Kuskokwim Delta in southwestern Alaska to understand the interaction between these factors and their potential implications. We used a space-for-time substitution methodology with 2017 Landsat 8 imagery and synthetic aperture radar products, along with 2016 field data, to analyze tundra recovery trajectories in areas burned from 1953 to 2017. We found that spectral indices describing vegetation greenness and surface albedo in burned areas approached the unburned baseline within a decade post-fire, but ecological succession takes decades. ALT was higher in burned areas compared to unburned areas initially after the fire but negatively correlated with soil moisture. Soil moisture was significantly higher in burned areas than in unburned areas. Water table depth (WTD) was 10 cm shallower in burned areas, consistent with 10 cm of the surface organic layer burned off during fire. Soil moisture and WTD did not recover in the 46 years covered by this study and appear linked to the long recovery time of the organic layer.

Environmental changes, such as climate warming and higher herbivory pressure, are altering the carbon balance of Arctic ecosystems; yet, how these drivers modify the carbon balance among different habitats remains uncertain. This hampers our ability to predict changes in the carbon sink strength of tundra ecosystems. We investigated how spring goose grubbing and summer warming-two key environmental-change drivers in the Arctic-alter CO2 fluxes in three tundra habitats varying in soil moisture and plant-community composition. In a full-factorial experiment in high-Arctic Svalbard, we simulated grubbing and warming over two years and determined summer net ecosystem exchange (NEE) alongside its components: gross ecosystem productivity (GEP) and ecosystem respiration (ER). After two years, we found net CO2 uptake to be suppressed by both drivers depending on habitat. CO2 uptake was reduced by warming in mesic habitats, by warming and grubbing in moist habitats, and by grubbing in wet habitats. In mesic habitats, warming stimulated ER (+75%) more than GEP (+30%), leading to a 7.5-fold increase in their CO2 source strength. In moist habitats, grubbing decreased GEP and ER by similar to 55%, while warming increased them by similar to 35%, with no changes in summer-long NEE. Nevertheless, grubbing offset peak summer CO2 uptake and warming led to a twofold increase in late summer CO2 source strength. In wet habitats, grubbing reduced GEP (-40%) more than ER (-30%), weakening their CO2 sink strength by 70%. One-year CO2-flux responses were similar to two-year responses, and the effect of simulated grubbing was consistent with that of natural grubbing. CO2-flux rates were positively related to aboveground net primary productivity and temperature. Net ecosystem CO2 uptake started occurring above similar to 70% soil moisture content, primarily due to a decline in ER. Herein, we reveal that key environmental-change drivers-goose grubbing by decreasing GEP more than ER and warming by enhancing ER more than GEP-consistently suppress net tundra CO2 uptake, although their relative strength differs among habitats. By identifying how and where grubbing and higher temperatures alter CO2 fluxes across the heterogeneous Arctic landscape, our results have implications for predicting the tundra carbon balance under increasing numbers of geese in a warmer Arctic.

Arctic extreme winter warming events (WW events) have increased in frequency with climate change. WW events have been linked to damaged tundra vegetation (Arctic browning), but the mechanisms that link episodic winter thaw to plant damage in summer are not fully understood. We suggest that one mechanism is microbial N immobilization during the WW event, which leads to a smaller release of winter-mineralized N in spring and therefore more N limitation for vegetation in summer. We tested this hypothesis in a Western Greenlandic Low arctic tundra, where we experimentally simulated a 6 day field-scale extreme WW event and 1) used stable isotopes to trace the movement of N as a consequence of the WW event, 2) measured the effect of a WW event on spring N release in top soils in the laboratory, and 3) measured the carry-over effect on summer aboveground vegetation C/N ratio in tundra subject to a WW event. Our results show that soil mineral N released by a WW event followed by soil thaw is taken up by microbes and stored in the soil, whereas vascular plants acquired almost none, and significant amounts were lost to leaching and gaseous emissions. As soils thawed in spring, we saw weak but not significant evidence (P = 0.067) for a larger N release over the first month of spring thaw in Control soils compared to WW event soils, although not significantly. A weak signal (P = 0.07) linked WW event treatment to higher summer C/N ratios in evergreen shrubs, whereas deciduous shrubs were not affected. We conclude that our results did not show significant evidence for WW events causing Arctic browning via N immobilization and summer N limitation, but that we had indications (P < 0.1) which merits further testing of the theory in various tundra types and with repeated WW events. Evergreen shrubs could be especially sensitive to winter N immobilization, with implications for future vegetation community composition and tundra C storage.