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Climate change is rapidly warming high latitude and high elevation regions influencing plant community composition. Changes in vegetation composition have motivated the coordination of ecological monitoring networks across the Arctic, including the International Tundra Experiment. We have established a long-term passive warming experiment using open-top chambers, which includes five distinct plant communities (Dry Heath; Tussock Tundra; and Dry, Mesic, and Wet Meadow). We measured changes in plant community composition based on relative abundance differences over 26 years. In addition, relative abundance changes in response to fertilization and warming treatments were analyzed based on a seven-year Community-Level Interaction Program experiment. The communities had distinct soil moisture conditions, leading to community-specific responses of the plant growth forms (deciduous shrubs, evergreen shrubs, forbs, and graminoids). Warming significantly affected growth forms, but the direction of the response was not consistent across the communities. Evidence of shrub expansion was found in nearly all communities, with soil moisture determining whether it was driven by deciduous or evergreen shrubs. Graminoids increased in relative abundance in the Dry Meadow due to warming. Growth form responses to warming are likely mediated by edaphic characteristics of the communities and their interactions with climate.

Observations of changes in phenology have provided some of the strongest signals of the effects of climate change on terrestrial ecosystems. The International Tundra Experiment (ITEX), initiated in the early 1990s, established a common protocol to measure plant phenology in tundra study areas across the globe. Today, this valuable collection of phenology measurements depicts the responses of plants at the colder extremes of our planet to experimental and ambient changes in temperature over the past decades. The database contains 150,434 phenology observations of 278 plant species taken at 28 study areas for periods of 1 to 26 years. Here we describe the full dataset to increase the visibility and use of these data in global analyses, and to invite phenology data contributions from underrepresented tundra locations. Portions of this tundra phenology database have been used in three recent syntheses, some datasets are expanded, others are from entirely new study areas, and the entirety of these data are now available at the Polar Data Catalogue., Arctic Science, 8 (3), ISSN:2368-7460

Light-absorbing carbonaceous aerosols emitted by biomass or fossil fuel combustion can contribute to amplify Arctic climate warming by lowering the albedo of snow. The Svalbard archipelago, being near to Europe and Russia, is particularly affected by these pollutants, and improved knowledge of their distribution in snow is needed to assess their impact. Here we present and synthesize new data obtained on Svalbard between 2007 and 2018, comprising 324 measurements of elemental (EC) and organic carbon (OC) in snow from 49 sites. We used these data, combined with meteorological and aerosol data and snowpack modelling, to investigate the variability of EC and OC deposition in Svalbard snow across latitude, longitude, elevation and time. Overall, EC concentrations (CsnowEC) ranged from −1, while OC concentrations (CsnowOC) ranged from −1, with the highest values observed near Ny-Ålesund. Calculated snowpack loadings (LsnowEC, LsnowOC) in April 2016 were 0.1 to 16.2 mg m−2 and 1.7 to 320.1 mg m−2, respectively. The median CsnowEC and LsnowEC in the late 2015‒16 winter snowpack on glaciers were close to or lower than those found in earlier (2007–09), comparable surveys. Both LsnowEC and LsnowOCC increased exponentially with elevation and snow accumulation, with dry deposition likely playing a minor role. Estimated area-averaged snowpack loads across Svalbard were 1.8 mg EC m−2 and 71.5 mg OC m−2 in April 2016. An ~ 11-year long dataset of spring surface snow measurements from central Brøgger Peninsula was used to quantify the interannual variability of EC and OC deposition in snow. On average, CsnowEC and CsnowOC at Ny-Ålesund (50 m a.s.l.) were 3 and 7 times higher, respectively, than on the nearby Austre Brøggerbreen glacier (456 m a.s.l.), and the median EC/OC in Ny-Ålesund was 6 times higher, pointing to some local EC emission from Ny-Ålesund. While no long-term trends between 2011 and 2018 were found, CsnowEC and CsnowOC showed synchronous variations at Ny-Ålesund and Austre Brøggerbreen. Comparing CsnowEC at Austre Brøggerbreen with aerosol data from Zeppelin Observatory, we found that snowfall washout ratios between 10 and 300 predict a range of CsnowEC in agreement with that measured in surface snow. Together, results from this study and comparable surveys confirm the existence of a longitudinal gradient in EC deposition across the Arctic and sub-Arctic, with the lowest CsnowEC found in the western Arctic (Alaska, Yukon) and central Greenland, and the highest in northwestern Russia and Siberia.

Current analyses and predictions of spatially explicit patterns and processes in ecology most often rely on climate data interpolated from standardized weather stations. This interpolated climate data represents long-term average thermal conditions at coarse spatial resolutions only. Hence, many climate-forcing factors that operate at fine spatiotemporal resolutions are overlooked. This is particularly important in relation to effects of observation height (e.g. vegetation, snow and soil characteristics) and in habitats varying in their exposure to radiation, moisture and wind (e.g. topography, radiative forcing or cold-air pooling). Since organisms living close to the ground relate more strongly to these microclimatic conditions than to free-air temperatures, microclimatic ground and near-surface data are needed to provide realistic forecasts of the fate of such organisms under anthropogenic climate change, as well as of the functioning of the ecosystems they live in. To fill this critical gap, we highlight a call for temperature time series submissions to SoilTemp, a geospatial database initiative compiling soil and near-surface temperature data from all over the world. Currently, this database contains time series from 7,538 temperature sensors from 51 countries across all key biomes. The database will pave the way toward an improved global understanding of microclimate and bridge the gap between the available climate data and the climate at fine spatiotemporal resolutions relevant to most organisms and ecosystem processes. ispartof: GLOBAL CHANGE BIOLOGY vol:26 issue:11 pages:6616-6629 ispartof: location:England status: published

© 2020 The Authors Aims: Litter decomposition is an important driver of soil carbon and nutrient cycling in nutrient-limited Arctic ecosystems. However, climate change is expected to induce changes that directly or indirectly affect decomposition. We examined the direct effects of long-term warming relative to differences in soil abiotic properties associated with vegetation type on litter decomposition across six subarctic vegetation types. Methods: In six vegetation types, rooibos and green tea bags were buried for 70–75 days at 8 cm depth inside warmed (by open-top chambers) and control plots that had been in place for 20–25 years. Standardized initial decomposition rate and stabilization of the labile material fraction of tea (into less decomposable material) were calculated from tea mass losses. Soil moisture and temperature were measured bi-weekly during summer and plant-available nutrients were measured with resin probes. Results: Initial decomposition rate was decreased by the warming treatment. Stabilization was less affected by warming and determined by vegetation type and soil moisture. Soil metal concentrations impeded both initial decomposition rate and stabilization. Conclusions: While a warmer Arctic climate will likely have direct effects on initial litter decomposition rates in tundra, stabilization of organic matter was more affected by vegetation type and soil parameters and less prone to be affected by direct effects of warming. This study was supported by Carl Tryggers stiftelse för vetenskaplig forskning and a grant by Qatar Petroleum to J.M.A., by BECC - Biodiversity and Ecosystem services in a Changing Climate as well as from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 657627 to M.P.B., and by Formas to M.K.S (No: 2013-533) and M.P.B (No: 2016-01187). J.M.S. conducted the work within the strategic theme Sustainability at Utrecht University, subtheme Water, Climate, and Ecosystems, and was funded by the Swedish Research Council VR (No: 2014-04270). The authors thank the staff of Abisko Scientific Research Station for their help and hospitality, and Matthias Molau, Thomas Stålhandske, and Linus Hedh for assistance in the field. TBI data is available under number 119 in the TBI database that will be published online on www.teatime4science.org after publication of the meta-analysis. Until publication on this platform, the data can be obtained by emailing tbi@decolab.org. G. F. Veen is acknowledged for reviewing the manuscript before submission and D. B. Metcalfe for language editing.

Recent warming in the Arctic, which has been amplified during the winter1–3, greatly enhances microbial decomposition of soil organic matter and subsequent release of carbon dioxide (CO2)4. However, the amount of CO2 released in winter is not known and has not been well represented by ecosystem models or empirically based estimates5,6. Here we synthesize regional in situ observations of CO2 flux from Arctic and boreal soils to assess current and future winter carbon losses from the northern permafrost domain. We estimate a contemporary loss of 1,662 TgC per year from the permafrost region during the winter season (October–April). This loss is greater than the average growing season carbon uptake for this region estimated from process models (−1,032 TgC per year). Extending model predictions to warmer conditions up to 2100 indicates that winter CO2 emissions will increase 17% under a moderate mitigation scenario—Representative Concentration Pathway 4.5—and 41% under business-as-usual emissions scenario—Representative Concentration Pathway 8.5. Our results provide a baseline for winter CO2 emissions from northern terrestrial regions and indicate that enhanced soil CO2 loss due to winter warming may offset growing season carbon uptake under future climatic conditions. Winter warming in the Arctic will increase the CO2 flux from soils. A pan-Arctic analysis shows a current loss of 1,662 TgC per year over the winter, exceeding estimated carbon uptake in the growing season; projections suggest a 17% increase under RCP 4.5 and a 41% increase under RCP 8.5 by 2100.

The Arctic and middle latitude (such as the Alps) ice core archives, except for the Greenland summit, are strongly influenced by melting processes, able to modify the original chemical signal of the annual snowfall. In the last decades, the increase of the average Arctic temperature has caused and enhanced surface snow melting in the higher ice cap, especially in the Svalbard Archipelago. The increase of the frequency and altitude of winter “rain on snow” events as well as the increase of the length of the melting season has a direct impact on the chemical composition of the seasonal and permanent snow layers due to different migration processes of water-soluble compounds, such as ionic species. The re-allocation along the snowpack of ionic species could significantly modify the original chemical signal present in the annual snow, making comprehensive interpretation of climate records difficult. The chemical composition of the first 100 cm of the seasonal snow at Austre Brøggerbreen Glacier (Spitsbergen, Svalbard Islands, Norway) was monitored daily from the 27th of March until to the 31st of May 2015. The experiment period covers almost the entire Arctic spring until the melting season. During the experiment, a rain event occurred on the 16th to 17th of April while from the 15th of May the snowpack reached an isothermal profile. The presented dataset is unique and helps to better understand the behaviour of cations (K+, Ca2+, Na+, Mg2+), anions (Br−, I−, SO42−, NO3−, Cl−, MSA) and two carboxylic acids (C2-glycolic and C5-glutaric acids) in the snowpack during this melting period. The results obtained from the experiment give us an overview of how the chemicals are remobilized in the snowpack during a rain event or due to the melting at the end of the spring season. The aim of this paper is to give a picture of the evolution of the seasonal snow strata with the aim to better understand the processes that can influence the chemical distribution in the annual snow. The results of the present work are unique and helpful for future analyses and interpretation of ice core paleoclimatic archives.

Measurements of atmospheric concentrations and fluxes of reactive nitrogen (NO, NO2, HNO3, NO3 − fine and NO3 − coarse) above the snow surface were performed from 29 March to 30 April 2010 at Ny-Alesund, Svalbard. Determinations of chemical and physical properties of snow were also carried out. Both NO and NO2 showed clear diurnal cycles with noontime maxima and nighttime minima. Significant emission fluxes of NO and NO2 were observed, reaching noontime values up to 19.42 and 25.20 pmol/m2 s, respectively. The snow surface was the source of NO and NO2 but these observed releases were small due to almost alkaline snow environment and chemical forms of snow NO3 −. Significant deposition fluxes of HNO3, fine and coarse particulate NO3 − fluxes were also observed, reaching peak values up to −18.00, −37.80 and −12.50 pmol/m2 s, respectively, during snowfall events. Measurements of surface snow provided experimental data that the total contribution of dry deposition of these species to the NO3 − –N in the snow was about 24 %. However, wet deposition in falling snow seemed to be the major contribution to the nitrate input to the snow.

Understanding and monitoring the evolution of annual snow is an important aspect of cryosphere research. Changes in physical proprieties such as hardness, presence of melt layers, or the shape and size of crystals can completely modify the robustness, propriety and quality of the snow. Evaluating these changes can inform the study and prediction of avalanches. The annual snow layer is also a sink for several compounds and elements. In the polar environment, many compounds can be accumulated during winter depositions, especially during the polar night. During the spring, the combination of solar radiation and the melting of annual snow can release these compounds and elements into the atmosphere and groundwater. An in-depth investigation of the evolution of the first meter of the annual snow layer was conducted in the glacier of Austre Brøggerbreen, Svalbard, between the 27th of March and the 31st of May, in concomitance with the start of the melting phase. The present monitoring study mainly aimed to evaluate changes in the thermal profile and water content during the formation of a new ice layer as well as the re-allocation of the total dissolved salts in the different snow layers.

Vast amounts of carbon are bound in both active layer and permafrost soils in the Arctic. As a consequence of climate warming, the depth of the active layer is increasing in size and permafrost soils are thawing. We hypothesize that pulses of biogenic volatile organic compounds are released from the near-surface active layer during spring, and during late summer season from thawing permafrost, while the subsequent biogeochemical processes occurring in thawed soils also lead to emissions. Biogenic volatile organic compounds are reactive gases that have both negative and positive climate forcing impacts when introduced to the Arctic atmosphere, and the knowledge of their emission magnitude and pattern is necessary to construct reliable climate models. However, it is unclear how different ecosystems and environmental factors such as drainage conditions upon permafrost thaw affect the emission and compound composition. Here we show that incubations of frozen B horizon of the active layer and permafrost soils collected from a High Arctic heath and fen release a range of biogenic volatile organic compounds upon thaw and during subsequent incubation experiments at temperatures of 10°C and 20°C. Meltwater drainage in the fen soils increased emission rates nine times, while having no effect in the drier heath soils. Emissions generally increased with temperature, and emission profiles for the fen soils were dominated by benzenoids and alkanes, while benzenoids, ketones, and alcohols dominated in heath soils. Our results emphasize that future changes affecting the drainage conditions of the Arctic tundra will have a large influence on volatile emissions from thawing permafrost soils – particularly in wetland/fen areas.

Effective societal responses to rapid climate change in the Arctic rely on an accurate representation of region-specific ecosystem properties and processes. However, this is limited by the scarcity and patchy distribution of field measurements. Here, we use a comprehensive, geo-referenced database of primary field measurements in 1,840 published studies across the Arctic to identify statistically significant spatial biases in field sampling and study citation across this globally important region. We find that 31% of all study citations are derived from sites located within 50 km of just two research sites: Toolik Lake in the USA and Abisko in Sweden. Furthermore, relatively colder, more rapidly warming and sparsely vegetated sites are under-sampled and under-recognized in terms of citations, particularly among microbiology-related studies. The poorly sampled and cited areas, mainly in the Canadian high-Arctic archipelago and the Arctic coastline of Russia, constitute a large fraction of the Arctic ice-free land area. Our results suggest that the current pattern of sampling and citation may bias the scientific consensuses that underpin attempts to accurately predict and effectively mitigate climate change in the region. Further work is required to increase both the quality and quantity of sampling, and incorporate existing literature from poorly cited areas to generate a more representative picture of Arctic climate change and its environmental impacts.

Recent climate change predictions suggest altered patterns of winter precipitation across the Arctic. It has been suggested that the presence, timing and quantity of snow all affect microbial activity, thus influencing CO2 production in soil. In this study annual and seasonal emissions of CO2 were estimated in High-Arctic Adventdalen, Svalbard, and sub-Arctic Latnjajaure, Sweden, using a new trace gas-based method to track real-time diffusion rates through the snow. Summer measurements from snow-free soils were made using a chamber-based method. Measurements were obtained from different snow regimes in order to evaluate the effect of snow depth on winter CO2 effluxes. Total annual emissions of CO2 from the sub-Arctic site (0.662–1.487 kg CO2 m–2 yr–1) were found to be more than double the emissions from the High-Arctic site (0.369–0.591 kg CO2 m–2 yr–1). There were no significant differences in winter effluxes between snow regimes or vegetation types, indicating that spatial variability in winter soil CO2 effluxes are not directly linked to snow cover thickness or soil temperatures. Total winter emissions (0.004– 0.248 kg CO2 m–2) were found to be in the lower range of those previously described in the literature. Winter emissions varied in their contribution to total annual production between 1 and 18%. Artificial snow drifts shortened the snow-free period by 2 weeks and decreased the annual CO2 emission by up to 20%. This study suggests that future shifts in vegetation zones may increase soil respiration from Arctic tundra regions.

Ozone was measured using passive diffusion samplers at alpine Latnjajaure (980 m above sea level [asl]) in the northern Scandian Mountain Range during spring and summer 2006–2008, and year-round at three further sites in northernmost Sweden 2004–2008. These observations were compared with ozone concentrations from three permanent monitoring stations using ultraviolet absorption instruments. Ozone concentrations at Latnjajaure were higher than at the closest monitoring site, illustrating the importance of high elevation for ozone. At the northern sites the ozone spring peak was more pronounced, higher, and earlier (April maximum) compared to a site in south Sweden (May maximum). During summer, ozone concentrations were higher in south Sweden. Presently, the growing season largely starts after the ozone spring peak in north Sweden but is likely to start earlier in the future climate. This could lead to an increased risk for ozone effects on vegetation if the current yearly ozone cycle persists.

Increasing reactive nitrogen (N r ) deposition in the Arctic may adversely impact N-limited ecosystems. To investigate atmospheric transport of N r to Svalbard, Norwegian Arctic, snow and firn samples were collected from glaciers and analysed to define spatial and temporal variations (1–10 years) in major ion concentrations and the stable isotope composition ( δ 15 N and δ 18 O) of nitrate ( ) across the archipelago. The and averaged −4‰ and 67‰ in seasonal snow (2010–11) and −9‰ and 74‰ in firn accumulated over the decade 2001–2011. East–west zonal gradients were observed across the archipelago for some major ions (non-sea salt sulphate and magnesium) and also for and in snow, which suggests a different origin for air masses arriving in different sectors of Svalbard. We propose that snowfall associated with long-distance air mass transport over the Arctic Ocean inherits relatively low due to in-transport N isotope fractionation. In contrast, faster air mass transport from the north-west Atlantic or northern Europe results in snowfall with higher because in-transport fractionation of N is then time-limited. To access the supplementary material for this article, please see supplementary files in the column to the right (under Article Tools). Keywords: Nitrate; isotopes; ice cores; Svalbard; pollutants. ( Published: 13 April 2015) Citation: Polar Research 2015, 34 , 23246, http://dx.doi.org/10.3402/polar.v34.23246

As a potent fertilizer, reactive nitrogen plays an important role in Arctic ecosystems. Since the Arctic is a nutrient limited environment, changes in nitrogen deposition can have severe impacts on local ecosystems. To quantify the amount of nitrogen deposition through snow- and rain events, precipitation sampling was performed at Zeppelin station, Svalbard, from November 2009 until May 2011. The samples were analysed for NO 3 - , nss-SO 4 2- and NH 4 + concentrations, and the deposition of single precipitation events was calculated using precipitation observations from Ny-Alesund. The majority of observed events showed concentrations ranging from 0.01 to 0.1 mg L -1 N for NO 3 - and NH 4 + and 0.02 to 0.3 mg L -2 S for nss-SO 4 2- . The majority of calculated deposition was in the range between 0.01 to 0.1 mg m -2 N for NO 3 - and NH 4 + and 0.02 – 0.3 mg m -2 S for nss-SO 4 2- . The budget was controlled by strong deposition events, caused by long lasting precipitation episodes that lasted for several days and which had raised concentrations of nitrogen and sulphur. Three future scenarios of increasing precipitation in the Arctic were considered. The results showed that deposition is mainly controlled by the amount of precipitation, which leads to the conclusion that increased precipitation might cause increases in deposition of the same magnitude. Keywords: Nitrogen; sulphur; Arctic; precipitation; sampling; NSINK. (Published: 15 April 2013) Citation: Polar Research 2013, 32 , 19136, http://dx.doi.org/10.3402/polar.v32i0.19136