In Arctic landscapes, the active layer forms a near-surface aquifer on top of the permafrost where water and nutrients are available for plants or subject to downslope transport. Warmer summer air temperatures can increase the thickness of the active layer and alter the partitioning of water into evapotranspiration and discharge by increasing the potential evapotranspiration, the depth to the water table, and changing the flow paths but the interacting processes are poorly understood. In this study, a numerical model for surface- and subsurface cryo-hydrology is calibrated based on field observations from a discontinue permafrost area in West Greenland considered sensitive to future climate changes. The validated model is used to simulate the effect of three summers with contrasting temperature regimes to quantify the variations in the active layer thickness, the resulting changes in the water balance, and the implications on solute transport. We find that an increase of summer air temperature by1.6 degrees C, under similar precipitation can increase the active layer thickness by 0.25 m, increase evapotranspiration by 5%, and reduce the total discharge compared to a colder summer by 9%. Differences in soil moisture and evapotranspiration between upslope and downslope were amplified in a warm summer. These hydrological differences impact solute transport which is 1.6 times faster in a cold summer. Surprisingly, we note that future warmer summer with increase in permafrost thaw may not necessary lead to an increase in discharge along a hill slope with underlying permafrost.

Impacts of increased winter snowfall and warmer summer air temperatures on nitrous oxide (N2O) dynamics in arctic tundra are uncertain. Here we evaluate surface N2O dynamics in both wet and dry tundra in West Greenland, subjected to field manipulations with deepened winter snow and summer warming. The potential denitrification activity (PDA) and potential net N2O production (N2Onet) were measured to assess denitrification and N2O consumption potential. The surface N2O fluxes averaged 0.49 +/- 0.42 and 2.6 +/- 0.84 mu g N2O-N m- 2 h-1, and total emissions were 212 +/- 151 and 114 +/- 63 g N2O-N scaled to the entire study area of 0.15 km2, at the dry and wet tundra, respectively. The experimental summer warming, and in combination with deepened snow, significantly increased N2O emissions at the dry tundra, but not at the wet tundra. The deepened snow increased winter soil temperatures and growing season soil N availability (DON, NH4+-N or NO3- -N), but no main effect of deepened snow on N2O fluxes was found at either tundra ecosystem. The mean PDA was 5- and 121-fold higher than the N2Onet at the dry and wet tundra, respectively, suggesting that N2O might be reduced and emitted as dinitrogen (N2). Overall, this study reveals modest but evident surface N2O fluxes from tundra ecosystems in Western Greenland, and suggests that projected increases in winter precipitation and summer air temperatures may increase N2O emissions, particularly at the dry tundra dominating in this region.

Wildfire frequency and expanse in the Arctic have increased in recent years and are projected to increase further with changes in climatic conditions due to warmer and drier summers. Yet, there is a lack of knowledge about the impacts such events may have on the net greenhouse gas (GHG) balances in Arctic ecosystems. We investigated in situ effects of an experimental fire in 2017 on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) surface fluxes in the most abundant tundra ecosystem in West Greenland in ambient and warmer conditions. Measurements from the growing seasons 2017 to 2019 showed that burnt areas became significant net CO2 sources for the entire study period, driven by increased ecosystem respiration (ER) immediately after the fire and decreased gross ecosystem production (GEP). Warming by open-top chambers significantly increased both ER and GEP in control, but not in burnt plots. In contrast to CO2, measurements suggest that the overall sink capacity of atmospheric CH4, as well as net N2O emissions, were not affected by fire in the short term, but only immediately after the fire. The minor effects on CH4 and N2O, which was surprising given the significantly higher nitrate availability observed in burnt plots. However, the minor effects are aligned with the lack of significant effects of fire on soil moisture and soil temperature. Net uptake and emissions of all three GHG from burnt soils were less temperature-sensitive than in the undisturbed control plots. Overall, this study highlights that wildfires in a typical tundra ecosystem in Greenland may not lead to markedly increased net GHG emissions other than CO2. Additional investigations are needed to assess the consequences of more severe fires.

This study reports on the measurements of ion and refractory black carbon (rBC) concentrations in a shallow (10.96 m) ice core sample which was drilled from the field site of the East Greenland Ice Core Project (EGRIP) in July, 2016. The results provide a recent record of rBC deposition in the East Greenland ice sheet from 1990 to 2016. The annual variability in oxygen (delta O-18) and hydrogen (delta D) isotopic compositions indicated that notably warm events occurred since 2008. Peaks in rBC occurred during summer seasons, which may be attributed to the burning of biomass in boreal summer. The rBC record and analysis of historical air trajectories using the HYSPLIT model indicated that anthropogenic BC emissions from Russia, North America and Europe contributed to the majority of rBC deposition in the Greenland region, and a reduction in anthropogenic BC consumption in these areas played a dominant role in the decrease in BC concentrations since 2000. This record also suggests that the emissions from the East Asian region (China) contributed very little to the recorded BC concentrations in East Greenland ice core. The model results indicated that radiative forcing due to BC had decreased significantly since 1990, and had remained below 0.02W m(-2) since 2000.

Global warming has reduced the extent of permafrost, increased permafrost temperatures, and deepened the active layer across the Arctic. Permafrost degradation has detrimental effects on infrastructure and negative impacts on ecosystem services for many Arctic communities. This study examines the adaptive capacity for managing permafrost degradation in Northwest Greenland. The methods are based on questionnaire and interview data from fieldwork, frozen ground temperature records and published data forecasting the deepening of the active layer. Results illustrate the impact of permafrost degradation on the physical environment, hunting and harvesting, housing, and the economy in Northwest Greenland. House owners are mending damage caused by ground movement, and local institutions are concerned with the maintenance of roads and other public infrastructure impacted by permafrost. The scientific knowledge needed to inform decision-making is useful for identifying overall changes, but existing data sources are scarce, and more detailed permafrost maps are needed for long-term town planning. The study concludes that many individuals and institutions engage in autonomous adaptation on an ad hoc basis, rather than pursuing an overall strategy to increase the adaptive capacity in advance of future permafrost degradation in Northwest Greenland.

Climate change is profound in the Arctic where increased snowfall during winter and warmer growing season temperatures may accelerate soil nitrogen (N) turnover and increase inorganic N availability. Nitrous oxide (N2O) is a potent greenhouse gas formed by soil microbes and in the Arctic, the production is seen as limited mainly by low inorganic N availability. Hence, it can be hypothesized that climate change in the Arctic may increase total N2O emissions, yet this topic remains understudied. We investigated the combined effects of variable snow depths and experimental warming on soil N cycling in a factorial field study established along a natural snowmelt gradient in a low Arctic heath ecosystem. The study assessed N2O surface fluxes, gross N mineralization and nitrification rates, potential denitrification activity, and the pools of soil microbial, soil organic and soil inorganic N, carbon (C) and phosphorus (P) during two growing seasons. The net fluxes of N2O averaged 1.7 mu g N2O-N m- 2 h-1 (range -3.6 to 10.5 mu g N2O-N m- 2 h-1), and generally increased from ambient (1 m) to moderate (2-3 m) snow depths. At the greatest snow depth (4 m) where snowmelt was profoundly later, N2O fluxes decreased, likely caused by combined negative effects of low summer temperatures and high soil moisture. Positive correlations between N2O and nitrate (NO3- ) and dissolved organic N (DON) suggested that the availability of N was the main controlling variable along the snowmelt gradient. The maximum N2O fluxes were observed in the second half of August associated with high NO3- concentrations. The effect of growing season experimental warming on N2O surface flux varied along the snowmelt gradient and with time. Generally, the experimental warming stimulated N2O fluxes under conditions with increased concentrations of inorganic N. In contrast, warming reduced N2O fluxes when inorganic N was low. Experimental warming had no clear effects on soil inorganic N. The study suggests that if increased winter precipitation leads to a deeper snow cover and a later snowmelt, total emissions of N2O from low Arctic heath ecosystems may be enhanced in the future and, dependent on dissolved N availability, summer warming may stimulate or reduce total emissions.

Warming environmental conditions are often credited with increasing Arctic shrub growth and altering abundance and distribution, yet it is unclear whether tundra shrub expansion will continue into future decades. Water availability may begin to limit Arctic shrub growth if increasing air temperatures create drier soil conditions due to increased evapotranspiration and permafrost-thaw-induced soil drainage. However, few studies have effectively considered how dominant tundra shrub species respond to variations in both temperature and moisture. To better understand the key effects of temperature variation and soil moisture on two dominant circumpolar deciduous shrubs, we studied shrub growth along a natural landscape gradient in West Greenland, which is a region observed to be drying due to ongoing warming. We found that the growth forms of both grey willow (Salix glauca) and dwarf birch (Betula nana) were sensitive to warmer and drier conditions. For both species, increases in air temperature positively correlated with greater shrub volume, with the doubling of canopy volume due to increased woody biomass. Leaf biomass was best predicted by edaphic features including extractable ammonium, which was positively related to soil moisture, and bulk density. Warmer soils tended to be drier, suggesting that ongoing warming in the area could lead to significant water limitation. Our findings suggest that drier soil conditions might be limiting foliar production despite warming temperatures for two circumpolar dominant shrubs,Betula nanaandSalix glauca, which could have wide-ranging, biome-level consequences about ongoing and predicted shrub growth and expansion.

This study reports on the measurements of ion and refractory black carbon (rBC) concentrations in a shallow (10.96 m) ice core sample which was drilled from the field site of the East Greenland Ice Core Project (EGRIP) in July, 2016. The results provide a recent record of rBC deposition in the East Greenland ice sheet from 1990 to 2016. The annual variability in oxygen (delta O-18) and hydrogen (delta D) isotopic compositions indicated that notably warm events occurred since 2008. Peaks in rBC occurred during summer seasons, which may be attributed to the burning of biomass in boreal summer. The rBC record and analysis of historical air trajectories using the HYSPLIT model indicated that anthropogenic BC emissions from Russia, North America and Europe contributed to the majority of rBC deposition in the Greenland region, and a reduction in anthropogenic BC consumption in these areas played a dominant role in the decrease in BC concentrations since 2000. This record also suggests that the emissions from the East Asian region (China) contributed very little to the recorded BC concentrations in East Greenland ice core. The model results indicated that radiative forcing due to BC had decreased significantly since 1990, and had remained below 0.02W m(-2) since 2000.

Background: Climate models predict substantial changes in temperature and precipitation patterns across Arctic regions, including increased winter precipitation as snow in the near future. Soil microorganisms are considered key players in organic matter decomposition and regulation of biogeochemical cycles. However, current knowledge regarding their response to future climate changes is limited. Here, we explore the short-term effect of increased snow cover on soil fungal, bacterial and archaeal communities in two tundra sites with contrasting water regimes in Greenland. In order to assess seasonal variation of microbial communities, we collected soil samples four times during the plant-growing season. Results: The analysis revealed that soil microbial communities from two tundra sites differed from each other due to contrasting soil chemical properties. Fungal communities showed higher richness at the dry site whereas richness of prokaryotes was higher at the wet tundra site. We demonstrated that fungal and bacterial communities at both sites were significantly affected by short-term increased snow cover manipulation. Our results showed that fungal community composition was more affected by deeper snow cover compared to prokaryotes. The fungal communities showed changes in both taxonomic and ecological groups in response to climate manipulation. However, the changes were not pronounced at all sampling times which points to the need of multiple sampling in ecosystems where environmental factors show seasonal variation. Further, we showed that effects of increased snow cover were manifested after snow had melted. Conclusions: We demonstrated rapid response of soil fungal and bacterial communities to short-term climate manipulation simulating increased winter precipitation at two tundra sites. In particular, we provide evidence that fungal community composition was more affected by increased snow cover compared to prokaryotes indicating fast adaptability to changing environmental conditions. Since fungi are considered the main decomposers of complex organic matter in terrestrial ecosystems, the stronger response of fungal communities may have implications for organic matter turnover in tundra soils under future climate.

Heterogeneous Holocene climate evolutions in the Northern Hemisphere high latitudes are primarily determined by orbital-scale insolation variations and melting ice sheets. Previous inter-model comparisons have revealed that multi-simulation consistencies vary spatially. We, therefore, compared multiple model results with proxy-based reconstructions in Fennoscandia, Greenland, north Canada, Alaska and Siberia. Our model-data comparisons reveal that data and models generally agree in Fennoscandia, Greenland and Canada, with the early-Holocene warming and subsequent gradual decrease to 0 ka BP (hereinafter referred as ka). In Fennoscandia, simulations and pollen data suggest a 2 degrees C warming by 8 ka, but this is less expressed in chironomid data. In Canada, a strong early-Holocene warming is suggested by both the simulations and pollen results. In Greenland, the magnitude of early-Holocene warming ranges from 6 degrees C in simulations to 8 degrees C in delta O-18-based temperatures. Simulated and reconstructed temperatures are mismatched in Alaska. Pollen data suggest strong early Holocene warming, while the simulations indicate constant Holocene cooling, and chironomid data show a stable trend. Meanwhile, a high frequency of Alaskan peatland initiation before 9 ka can reflect a either high temperature, high soil moisture or large seasonality. In high-latitude Siberia, although simulations and proxy data depict high Holocene temperatures, these signals are noisy owing to a large spread in the simulations and between pollen and chironomid results. On the whole, the Holocene climate evolutions in most regions (Fennoscandia, Greenland and Canada) are well established and understood, but important questions regarding the Holocene temperature trend and mechanisms remain for Alaska and Siberia. (C) 2017 Elsevier Ltd. All rights reserved.