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  • 1.
    Becher, Marina
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Klaminder, Jonatan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Cryogenic disturbance and its impact on carbon fluxes in a subarctic heathland2015In: Environmental Research Letters, E-ISSN 1748-9326, Vol. 10, no 11, article id 114006Article in journal (Refereed)
    Abstract [en]

    Differential frost heave, along with the associated cryogenic disturbance that accompanies it, is an almost universal feature of arctic landscapes that potentially influences the fate of the soil carbon (C) stored in arctic soils. In this study, we quantify how gross ecosystem photosynthesis (GEP), soil respiration (Re) and the resulting net ecosystem exchange (NEE) vary in a patterned ground system (non-sorted circles) at plot-scale and whole-patterned ground scales in response to cryogenic disturbances (differential heave and soil surface disruption). We found that: (i) all studied non-sorted circles (n=15) acted as net CO2 sources (positive NEE); (ii) GEP showed a weaker decrease than Re in response to increased cryogenic disturbance/decreased humus cover, indicating that undisturbed humus-covered sites are currently the main source of atmospheric CO2 in the studied system. Interestingly, Re fluxes normalized to C pools indicated that C is currently respired more rapidly at sites exposed to cryogenic disturbances; hence, higher NEE fluxes at less disturbed sites are likely an effect of a more slowly degrading but larger total pool that was built up in the past. Our results highlight the complex effects of cryogenic processes on the C cycle at various time scales. 

  • 2. Chu, Gangzhi
    et al.
    Luo, Xiaofan
    Zheng, Zijia
    Zhao, Wei
    Wei, Hao
    Causes of increased dissolved inorganic carbon in the subsurface layers in the western shelfbreak and high latitudes basin in the Arctic Pacific sector2021In: Environmental Research Letters, E-ISSN 1748-9326, Vol. 16, no 10Article in journal (Refereed)
    Abstract [en]

    The expansion of dissolved inorganic carbon (DIC)-rich water carried by the Pacific inflow creates a DIC maximum layer and exerts important influences on ocean acidification in the subsurface Arctic Ocean. This study analyzed shifts in the DIC distribution of the subsurface Arctic Ocean during 1998–2015 through hindcast simulation using a three-dimensional ocean-sea ice-biogeochemical model. For this purpose, the study was divided into two time periods (1998–2007 and 2008–2015). The results showed that the lower boundary layer of the Pacific Winter Water, defined as an isopycnal of 27 kg m−3, became deeper by ∼50 m in the central Canada Basin and expanded northward during 2008–2015 relative to 1998–2007. Accordingly, the subsurface DIC maximum layer deepened and expanded northwards into the Makarov Basin at high latitudes around 85° N. During 2008–2015, DIC concentrations, averaged over a 50–250 m water column, increased significantly in the Chukchi-East Siberian Shelfbreak and Makarov Basin. The DIC increase over the shelfbreak is mainly attributable to increased local biological degradation and the transportation of DIC-rich water from the Chukchi Shelf through Barrow Canyon. Estimates of the DIC budget indicated that advection controlled the increase in DIC content in the Makarov Basin during 2008–2015. This is attributed to the shift of the ocean circulation pattern, in which the ocean current along the Chukchi-East Siberian Slope to the Makarov Basin became stronger during 2008–2015, promoting the transport of DIC-rich Pacific Water into the Makarov Basin.

  • 3. Johansson, Margareta
    et al.
    Callaghan, Terry V
    Bosiö, Julia
    Åkerman, H Jonas
    Jackowicz-Korczynski, Marcin
    Christensen, Torben R
    Rapid responses of permafrost and vegetation to experimentally increased snow cover in sub-arctic Sweden2013In: Environmental Research Letters, E-ISSN 1748-9326, Vol. 8, no 3Article in journal (Refereed)
    Abstract [en]

    Increased snow depth already observed, and that predicted for the future are of critical importance to many geophysical and biological processes as well as human activities. The future characteristics of sub-arctic landscapes where permafrost is particularly vulnerable will depend on complex interactions between snow cover, vegetation and permafrost. An experimental manipulation was, therefore, set up on a lowland peat plateau with permafrost, in northernmost Sweden, to simulate projected future increases in winter precipitation and to study their effects on permafrost and vegetation. After seven years of treatment, statistically significant differences between manipulated and control plots were found in mean winter ground temperatures, which were 1.5° C higher in manipulated plots. During the winter, a difference in minimum temperatures of up to 9° C higher could be found in individual manipulated plots compared with control plots. Active layer thicknesses increased at the manipulated plots by almost 20% compared with the control plots and a mean surface subsidence of 24 cm was recorded in the manipulated plots compared to 5 cm in the control plots. The graminoid Eriophorum vaginatum has expanded in the manipulated plots and the vegetation remained green longer in the season.

  • 4. Ramm, Elisabeth
    et al.
    Liu, Chunyan
    Ambus, Per
    Butterbach-Bahl, Klaus
    Hu, Bin
    Martikainen, Pertti J
    Marushchak, Maija E
    Mueller, Carsten W
    Rennenberg, Heinz
    Schloter, Michael
    Siljanen, Henri M P
    Voigt, Carolina
    Werner, Christian
    Biasi, Christina
    Dannenmann, Michael
    A review of the importance of mineral nitrogen cycling in the plant-soil-microbe system of permafrost-affected soils—changing the paradigm2022In: Environmental Research Letters, E-ISSN 1748-9326, Vol. 17, no 1Article in journal (Refereed)
    Abstract [en]

    The paradigm that permafrost-affected soils show restricted mineral nitrogen (N) cycling in favor of organic N compounds is based on the observation that net N mineralization rates in these cold climates are negligible. However, we find here that this perception is wrong. By synthesizing published data on N cycling in the plant-soil-microbe system of permafrost ecosystems we show that gross ammonification and nitrification rates in active layers were of similar magnitude and showed a similar dependence on soil organic carbon (C) and total N concentrations as observed in temperate and tropical systems. Moreover, high protein depolymerization rates and only marginal effects of C:N stoichiometry on gross N turnover provided little evidence for N limitation. Instead, the rather short period when soils are not frozen is the single main factor limiting N turnover. High gross rates of mineral N cycling are thus facilitated by released protection of organic matter in active layers with nitrification gaining particular importance in N-rich soils, such as organic soils without vegetation. Our finding that permafrost-affected soils show vigorous N cycling activity is confirmed by the rich functional microbial community which can be found both in active and permafrost layers. The high rates of N cycling and soil N availability are supported by biological N fixation, while atmospheric N deposition in the Arctic still is marginal except for fire-affected areas. In line with high soil mineral N production, recent plant physiological research indicates a higher importance of mineral plant N nutrition than previously thought. Our synthesis shows that mineral N production and turnover rates in active layers of permafrost-affected soils do not generally differ from those observed in temperate or tropical soils. We therefore suggest to adjust the permafrost N cycle paradigm, assigning a generally important role to mineral N cycling. This new paradigm suggests larger permafrost N climate feedbacks than assumed previously.

  • 5. Scharn, Ruud
    et al.
    Little, Chelsea J
    Bacon, Christine D
    Alatalo, Juha M
    Antonelli, Alexandre
    Björkman, Mats P
    Molau, Ulf
    Nilsson, R Henrik
    Björk, Robert G
    Decreased soil moisture due to warming drives phylogenetic diversity and community transitions in the tundra2021In: Environmental Research Letters, E-ISSN 1748-9326, Vol. 16, no 6, article id 064031Article in journal (Refereed)
    Abstract [en]

    Global warming leads to drastic changes in the diversity and structure of Arctic plant communities. Studies of functional diversity within the Arctic tundra biome have improved our understanding of plant responses to warming. However, these studies still show substantial unexplained variation in diversity responses. Complementary to functional diversity, phylogenetic diversity has been useful in climate change studies, but has so far been understudied in the Arctic. Here, we use a 25 year warming experiment to disentangle community responses in Arctic plant phylogenetic β diversity across a soil moisture gradient. We found that responses varied over the soil moisture gradient, where meadow communities with intermediate to high soil moisture had a higher magnitude of response. Warming had a negative effect on soil moisture levels in all meadow communities, however meadows with intermediate moisture levels were more sensitive. In these communities, soil moisture loss was associated with earlier snowmelt, resulting in community turnover towards a more heath-like community. This process of ‘heathification’ in the intermediate moisture meadows was driven by the expansion of ericoid and Betula shrubs. In contrast, under a more consistent water supply Salix shrub abundance increased in wet meadows. Due to its lower stature, palatability and decomposability, the increase in heath relative to meadow vegetation can have several large scale effects on the local food web as well as climate. Our study highlights the importance of the hydrological cycle as a driver of vegetation turnover in response to Arctic climate change. The observed patterns in phylogenetic β diversity were often driven by contrasting responses of species of the same functional growth form, and could thus provide important complementary information. Thus, phylogenetic diversity is an important tool in disentangling tundra response to environmental change.

  • 6.
    Siewert, Matthias B.
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Scale-dependency of Arctic ecosystem properties revealed by UAV2020In: Environmental Research Letters, E-ISSN 1748-9326, Vol. 15, no 9, article id 094030Article in journal (Refereed)
    Abstract [en]

    In the face of climate change, it is important to estimate changes in key ecosystem properties such as plant biomass and gross primary productivity (GPP). Ground truth estimates and especially experiments are performed at small spatial scales (0.01-1 m(2)) and scaled up using coarse scale satellite remote sensing products. This will lead to a scaling bias for non-linearly related properties in heterogeneous environments when the relationships are not developed at the same spatial scale as the remote sensing products. We show that unmanned aerial vehicles (UAVs) can reliably measure normalized difference vegetation index (NDVI) at centimeter resolution even in highly heterogeneous Arctic tundra terrain. This reveals that this scaling bias increases most at very fine resolution, but UAVs can overcome this by generating remote sensing products at the same scales as ecological changes occur. Using ground truth data generated at 0.0625 m(2)and 1 m(2)with Landsat 30 m scale satellite imagery the resulting underestimation is large (8.9%-17.0% for biomass and 5.0%-9.7% for GPP(600)) and of a magnitude comparable to the expected effects of decades of climate change. Methods to correct this upscaling bias exist but rely on sub-pixel information. Our data shows that this scale-dependency will vary strongly between areas and across seasons, making it hard to derive generalized functions compensating for it. This is particularly relevant to Arctic greening with a predominantly heterogeneous land cover, strong seasonality and much experimental research at sub-meter scale, but also applies to other heterogeneous landscapes. These results demonstrate the value of UAVs for satellite validation. UAVs can bridge between plot scale used in ecological field investigations and coarse scale in satellite monitoring relevant for Earth System Models. Since future climate changes are expected to alter landscape heterogeneity, seasonally updated UAV imagery will be an essential tool to correctly predict landscape-scale changes in ecosystem properties.

  • 7. Sim, Thomas G
    et al.
    Swindles, Graeme T
    Morris, Paul J
    Baird, Andy J
    Cooper, Claire L
    Gallego-Sala, Angela V
    Charman, Dan J
    Roland, Thomas P
    Borken, Werner
    Mullan, Donal J
    Aquino-López, Marco A
    Gałka, Mariusz
    Divergent responses of permafrost peatlands to recent climate change2021In: Environmental Research Letters, E-ISSN 1748-9326, Vol. 16, no 3, article id 034001Article in journal (Refereed)
    Abstract [en]

    Permafrost peatlands are found in high-latitude regions and store globally-important amounts of soil organic carbon. These regions are warming at over twice the global average rate, causing permafrost thaw, and exposing previously inert carbon to decomposition and emission to the atmosphere as greenhouse gases. However, it is unclear how peatland hydrological behaviour, vegetation structure and carbon balance, and the linkages between them, will respond to permafrost thaw in a warming climate. Here we show that permafrost peatlands follow divergent ecohydrological trajectories in response to recent climate change within the same rapidly warming region (northern Sweden). Whether a site becomes wetter or drier depends on local factors and the autogenic response of individual peatlands. We find that bryophyte-dominated vegetation demonstrates resistance, and in some cases resilience, to climatic and hydrological shifts. Drying at four sites is clearly associated with reduced carbon sequestration, while no clear relationship at wetting sites is observed. We highlight the complex dynamics of permafrost peatlands and warn against an overly-simple approach when considering their ecohydrological trajectories and role as C sinks under a warming climate.

1 - 7 of 7
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