| 1. |
- Lembrechts, Jonas J., et al.
(författare)
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Global maps of soil temperature
- 2022
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 28:9, s. 3110-3144
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Tidskriftsartikel (refereegranskat)abstract
- Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0–5 and 5–15cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean=3.0±2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6±2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (−0.7±2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications.
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| 2. |
- Bosiö, Julia, et al.
(författare)
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Increased photosynthesis compensates for shorter growing season in subarctic tundra - 8 years of snow accumulation manipulations
- 2014
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Ingår i: Climatic Change. - : Springer Science and Business Media LLC. - 0165-0009 .- 1573-1480. ; 127:2, s. 321-334
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Tidskriftsartikel (refereegranskat)abstract
- This study was initiated to analyze the effect of increased snow cover on plant photosynthesis in subarctic mires underlain by permafrost. Snow fences were used to increase the accumulation of snow on a subarctic permafrost mire in northern Sweden. By measuring reflected photosynthetic active radiation (PAR) the effect of snow thickness and associated delay of the start of the growing season was assessed in terms of absorbed PAR and estimated gross primary production (GPP). Six plots experienced increased snow accumulation and six plots were untreated. Incoming and reflected PAR was logged hourly from August 2010 to October 2013. In 2010 PAR measurements were coupled with flux chamber measurements to assess GPP and light use efficiency of the plots. The increased snow thickness prolonged the duration of the snow cover in spring. The delay of the growing season start in the treated plots was 18 days in 2011, 3 days in 2012 and 22 days in 2013. Results show higher PAR absorption, together with almost 35 % higher light use efficiency, in treated plots compared to untreated plots. Estimations of GPP suggest that the loss in early season photosynthesis, due to the shortening of the growing season in the treatment plots, is well compensated for by the increased absorption of PAR and higher light use efficiency throughout the whole growing seasons. This compensation is likely to be explained by increased soil moisture and nutrients together with a shift in vegetation composition associated with the accelerated permafrost thaw in the treatment plots.
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| 3. |
- Lindroth, Anders, et al.
(författare)
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CO2 and CH4 exchanges between moist moss tundra and atmosphere on Kapp Linne, Svalbard
- 2022
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 19:16, s. 3921-3934
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Tidskriftsartikel (refereegranskat)abstract
- We measured CO2 and CH4 fluxes using chambers and eddy covariance (only CO2) from a moist moss tundra in Svalbard. The average net ecosystem exchange (NEE) during the summer (9 June-31 August) was negative (sink), with -0.139 +/- 0.032 mu mol m(-2) s(-1) corresponding to -11.8 g C m(-2) for the whole summer. The cumulated NEE over the whole growing season (day no. 160 to 284) was -2.5 g C m(-2). The CH4 flux during the summer period showed a large spatial and temporal variability. The mean value of all 214 samples was 0.000511 +/- 0.000315 mu mol m(-2) s(-1), which corresponds to a growing season estimate of 0.04 to 0.16 g CH4 m(-2). Thus, we find that this moss tundra ecosystem is closely in balance with the atmosphere during the growing season when regarding exchanges of CO2 and CH4. The sink of CO2 and the source of CH4 are small in comparison with other tundra ecosystems in the high Arctic. Air temperature, soil moisture and the greenness index contributed significantly to explaining the variation in ecosystem respiration (R-eco), while active layer depth, soil moisture and the greenness index were the variables that best explained CH4 emissions. An estimate of temperature sensitivity of Reco and gross primary productivity (GPP) showed that the sensitivity is slightly higher for GPP than for R-eco in the interval 0-4.5 degrees C; thereafter, the difference is small up to about 6 degrees C and then begins to rise rapidly for R-eco. The consequence of this, for a small increase in air temperature of 1 degrees (all other variables assumed unchanged), was that the respiration increased more than photosynthesis turning the small sink into a small source (4.5 g C m(-2)) during the growing season. Thus, we cannot rule out that the reason why the moss tundra is close to balance today is an effect of the warming that has already taken place in Svalbard.
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| 4. |
- Lund, Magnus, et al.
(författare)
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Characteristics of summer-time energy exchange in a high Arctic tundra heath 2000-2010
- 2014
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 66
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Tidskriftsartikel (refereegranskat)abstract
- Global warming will bring about changes in surface energy balance of Arctic ecosystems, which will have implications for ecosystem structure and functioning, as well as for climate system feedback mechanisms. In this study, we present a unique, long-term (2000-2010) record of summer-time energy balance components (net radiation, R-n; sensible heat flux, H; latent heat flux, LE; and soil heat flux, G) from a high Arctic tundra heath in Zackenberg, Northeast Greenland. This area has been subjected to strong summer-time warming with increasing active layer depths (ALD) during the last decades. We observe high energy partitioning into H, low partitioning into LE and high Bowen ratio (beta = H/LE) compared with other Arctic sites, associated with local climatic conditions dominated by onshore winds, slender vegetation with low transpiration activity and relatively dry soils. Surface saturation vapour pressure deficit (D-s) was found to be an important variable controlling within-year surface energy partitioning. Throughout the study period, we observe increasing H/R-n and LE/R-n and decreasing G/R-n and beta, related to increasing ALD and decreasing soil wetness. Thus, changes in summer-time surface energy balance partitioning in Arctic ecosystems may be of importance for the climate system.
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| 5. |
- Stiegler, Christian, et al.
(författare)
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An Undercooled Scree Slope Detected by Geophysical Investigations in Sporadic Permafrost below 1000 M ASL, Central Austria
- 2014
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1099-1530 .- 1045-6740. ; 25:3, s. 194-207
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Tidskriftsartikel (refereegranskat)abstract
- Multi-method geophysical investigations, accompanied by microclimatic measurements and vegetation mapping, were performed at an undercooled scree slope near Schladming (Austria) in the eastern Alps in order to detect, map and monitor mountain permafrost. The study site, at an elevation of 990m asl, is one of the lowest-lying examples of a cold, undercooled scree slope in the Alps. Geophysical measurements with electrical resistivity tomography, ground-penetrating radar and seismic refraction indicate the presence of several isolated areas of frozen ground over a full year, far below the regional lower limit of mountain permafrost. Frozen sediments identified at shallow depths (beneath 1-3m) were 5-20m thick and ice-rich. Near-surface temperatures at the foot of the scree slope were strongly influenced by pronounced cooling. Vegetation mapping showed a dominance of cryophilic plant species. The results suggest that the scree slope is strongly influenced by the interplay of vegetation cover, ground thermal regime and the distribution of frozen sediments. Copyright (C) 2014 John Wiley & Sons, Ltd.
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| 6. |
- Stiegler, Christian
(författare)
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Surface energy exchange and land-atmosphere interactions of Arctic and subarctic tundra ecosystems under climate change
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The surface energy balance determines the functioning of any ecosystem on the Earth but is still poorly understood in Arctic and subarctic biomes. In a dynamic system, such as the Earth’s climate, any change in its characteristics modifies the exchange of energy, water, and greenhouse gases between the surface and the atmosphere. Therefore, this thesis aims to draw a conclusive picture of the surface energy exchange and land-atmosphere interactions of Arctic and subarctic regions under climate change. The aims are achieved by combining in-situ field measurements of surface energy balance components, snow manipulation experiments, active layer monitoring, vegetation mapping, and chamber-based carbon dioxide flux measurements from Arctic and subarctic tundra biomes in Greenland, Svalbard and northern Sweden. Local variability in climate, surface structure, soil moisture and soil thermal regime are the main drivers of variation in the surface energy exchange and ecosystem productivity of Arctic and subarctic tundra ecosystems. At all studied locations, the magnitude of the energy fluxes of sensible heat (H), latent heat (LE) and ground heat (G) were well-correlated with net radiation (Rnet). However, evapotranspiration (ET) and LE showed a relatively strong coupling to atmospheric vapor pressure deficit (VPD), with more pronounced such control at the dry tundra sites compared to the wet-growing ecosystems. Snow and permafrost determined surface energy balance, energy partitioning and ecosystem productivity. Manipulated increase in snow accumulation at a subarctic tundra peatland complex in northern Sweden resulted in permafrost thaw, soil wetting and increased carbon sequestration. Concurrently, climate-driven increase in both snow accumulation and air temperature triggered dramatic and rapid permafrost degradation in peatland complexes and transition from dry habitats into wet-growing ecosystems, with consequent change in surface energy exchange towards both increased LE and ET at the cost of H. Interannual variability in winter snow accumulation at the high-Arctic tundra environment in Zackenberg (Northeast Greenland) prolonged the growing season during a year with low snow cover and increased the total accumulated energy balance components of the local heath and fen ecosystems. Further, energy flux partitioning at the heath was strongly determined by the reduction of soil moisture as snow is by far the main supplier of water in this region. The energy exchange of the fen, however, showed attenuated behavior due to groundwater table remaining close to the surface. The results presented in this thesis suggest that in a future climate, accelerated permafrost thaw and increased interannual variability in snow cover may further modify the energy balance of Arctic and subarctic ecosystems, with profound impact on ecosystem adaptation capacities and the overall climate system.
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| 7. |
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| 8. |
- Stiegler, Christian, et al.
(författare)
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Two years with extreme and little snowfall : Effects on energy partitioning and surface energy exchange in a high-Arctic tundra ecosystem
- 2016
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Ingår i: Cryosphere. - : Copernicus GmbH. - 1994-0416. ; 10:4, s. 1395-1413
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Tidskriftsartikel (refereegranskat)abstract
- Snow cover is one of the key factors controlling Arctic ecosystem functioning and productivity. In this study we assess the impact of strong variability in snow accumulation during 2 subsequent years (2013-2014) on the land-atmosphere interactions and surface energy exchange in two high-Arctic tundra ecosystems (wet fen and dry heath) in Zackenberg, Northeast Greenland. We observed that record-low snow cover during the winter 2012/2013 resulted in a strong response of the heath ecosystem towards low evaporative capacity and substantial surface heat loss by sensible heat fluxes (H) during the subsequent snowmelt period and growing season. Above-average snow accumulation during the winter 2013/2014 promoted summertime ground heat fluxes (G) and latent heat fluxes (LE) at the cost of H. At the fen ecosystem a more muted response of LE, H and G was observed in response to the variability in snow accumulation. Overall, the differences in flux partitioning and in the length of the snowmelt periods and growing seasons during the 2 years had a strong impact on the total accumulation of the surface energy balance components. We suggest that in a changing climate with higher temperature and more precipitation the surface energy balance of this high-Arctic tundra ecosystem may experience a further increase in the variability of energy accumulation, partitioning and redistribution.
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