| 1. |
- Rixen, C., et al.
(author)
-
Winters are changing: snow effects on Arctic and alpine tundra ecosystems
- 2022
-
In: Arctic Science. - : Canadian Science Publishing. - 2368-7460. ; 8:3, s. 572 - 608
-
Journal article (peer-reviewed)abstract
- Snow is an important driver of ecosystem processes in cold biomes. Snow accumulation determines ground temperature, light conditions, and moisture availability during winter. It also affects the growing season's start and end, and plant access to moisture and nutrients. Here, we review the current knowledge of the snow cover's role for vegetation, plant-animal interactions, permafrost conditions, microbial processes, and biogeochemical cycling. We also compare studies of natural snow gradients with snow experimental manipulation studies to assess time scale difference of these approaches. The number of tundra snow studies has increased considerably in recent years, yet we still lack a comprehensive overview of how altered snow conditions will affect these ecosystems. Specifically, we found a mismatch in the timing of snowmelt when comparing studies of natural snow gradients with snow manipulations. We found that snowmelt timing achieved by snow addition and snow removal manipulations (average 7.9 days advance and 5.5 days delay, respectively) were substantially lower than the temporal variation over natural spatial gradients within a given year (mean range 56 days) or among years (mean range 32 days). Differences between snow study approaches need to be accounted for when projecting snow dynamics and their impact on ecosystems in future climates.
|
|
| 2. |
- Natali, S. M., et al.
(author)
-
Large loss of CO2 in winter observed across the northern permafrost region
- 2019
-
In: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 9:11, s. 852-857
-
Journal article (peer-reviewed)abstract
- Recent warming in the Arctic, which has been amplified during the winter(1-3), 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 estimates(5,6). 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.
|
|
| 3. |
- Maes, S.L., et al.
(author)
-
Environmental drivers of increased ecosystem respiration in a warming tundra
- 2024
-
In: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 629:8010, s. 105-113
-
Journal article (peer-reviewed)abstract
- Arctic and alpine tundra ecosystems are large reservoirs of organic carbon. Climate warming may stimulate ecosystem respiration and release carbon into the atmosphere. The magnitude and persistency of this stimulation and the environmental mechanisms that drive its variation remain uncertain. This hampers the accuracy of global land carbon–climate feedback projections. Here we synthesize 136 datasets from 56 open-top chamber in situ warming experiments located at 28 arctic and alpine tundra sites which have been running for less than 1 year up to 25 years. We show that a mean rise of 1.4 °C [confidence interval (CI) 0.9–2.0 °C] in air and 0.4 °C [CI 0.2–0.7 °C] in soil temperature results in an increase in growing season ecosystem respiration by 30% [CI 22–38%] (n = 136). Our findings indicate that the stimulation of ecosystem respiration was due to increases in both plant-related and microbial respiration (n = 9) and continued for at least 25 years (n = 136). The magnitude of the warming effects on respiration was driven by variation in warming-induced changes in local soil conditions, that is, changes in total nitrogen concentration and pH and by context-dependent spatial variation in these conditions, in particular total nitrogen concentration and the carbon:nitrogen ratio. Tundra sites with stronger nitrogen limitations and sites in which warming had stimulated plant and microbial nutrient turnover seemed particularly sensitive in their respiration response to warming. The results highlight the importance of local soil conditions and warming-induced changes therein for future climatic impacts on respiration.
|
|
| 4. |
- Hollister, R. D., et al.
(author)
-
A review of open top chamber (OTC) performance across the ITEX Network
- 2023
-
In: Arctic Science. - : Canadian Science Publishing. - 2368-7460. ; 9:2, s. 331-344
-
Journal article (peer-reviewed)abstract
- Open top chambers (OTCs) were adopted as the recommended warming mechanism by the International Tundra Experiment network in the early 1990s. Since then, OTCs have been deployed across the globe. Hundreds of papers have reported the im-pacts of OTCs on the abiotic environment and the biota. Here, we review the impacts of the OTC on the physical environment, with comments on the appropriateness of using OTCs to characterize the response of biota to warming. The purpose of this review is to guide readers to previously published work and to provide recommendations for continued use of OTCs to under -stand the implications of warming on low stature ecosystems. In short, the OTC is a useful tool to experimentally manipulate temperature; however, the characteristics and magnitude of warming varies greatly in different environments; therefore, it is important to document chamber performance to maximize the interpretation of biotic response. When coupled with long-term monitoring, warming experiments are a valuable means to understand the impacts of climate change on natural ecosystems.
|
|
| 5. |
- Lembrechts, Jonas J., et al.
(author)
-
Global maps of soil temperature
- 2022
-
In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 28:9, s. 3110-3144
-
Journal article (peer-reviewed)abstract
- Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m 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 5–15 cm 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.
|
|
| 6. |
- Spolaor, A., et al.
(author)
-
Seasonality of halogen deposition in polar snow and ice
- 2014
-
In: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 14
-
Journal article (peer-reviewed)abstract
- The atmospheric chemistry of iodine and bromine in Polar regions is of interest due to the key role of halogens in many atmospheric processes, particularly tropospheric ozone destruction. Bromine is emitted from the open ocean but is enriched above first-year sea ice during springtime bromine explosion events, whereas iodine emission is at- tributed to biological communities in the open ocean and hosted by sea ice. It has been previously demonstrated that bromine and iodine are present in Antarctic ice over glacial– interglacial cycles. Here we investigate seasonal variability of bromine and iodine in polar snow and ice, to evaluate their emission, transport and deposition in Antarctica and the Arc- tic and better understand potential links to sea ice. We find that bromine and iodine concentrations and Br enrichment (relative to sea salt content) in polar ice do vary seasonally in Arctic snow and Antarctic ice. Although seasonal vari- ability in halogen emission sources is recorded by satellite- based observations of tropospheric halogen concentrations, seasonal patterns observed in snowpack are likely also in- fluenced by photolysis-driven processes. Peaks of bromine concentration and Br enrichment in Arctic snow and Antarc- tic ice occur in spring and summer, when sunlight is present. A secondary bromine peak, observed at the end of summer, is attributed to bromine deposition at the end of the polar day. Iodine concentrations are largest in winter Antarctic ice strata, contrary to contemporary observations of summer maxima in iodine emissions. These findings support previous observations of iodine peaks in winter snow strata attributed to the absence of sunlight-driven photolytic re-mobilisation of iodine from surface snow. Further investigation is required to confirm these proposed mechanisms explaining observa- tions of halogens in polar snow and ice, and to evaluate the extent to which halogens may be applied as sea ice proxies.
|
|
| 7. |
- Björk, Robert G., 1974, et al.
(author)
-
Temporal pattern of CO2, CH4 and N2O fluxes and soil microbial structure from snow-covered Alpine plant communities
- 2006
-
In: Abstracts and Proceedings of the Geological Society of Norway. ; :4
-
Conference paper (other academic/artistic)abstract
- Global warming is expected to have large effects on carbon exchange between the biosphere and the atmosphere in the Arctic. Arctic ecosystems, which can be a net sink in the summer, are often a net source of CO2 to the atmosphere on an annual basis. Few studies on winter CO2 and CH4 efflux have been conducted in the subarctic part of Sweden. So far, no integrated estimates of winter fluxes of CO2, CH4 or N2O has been reported from the alpine areas in the Scandinavian mountains. As much as 44 to 53% of the northern hemispheres landmass may be snow covered for parts of the year. The depth and spatial spread of snow cover is a result of moisture availability, duration of temperatures bellow 0ºC, storm frequency and the more local factors such as wind redistribution and compaction. In future climate scenarios, predictions of warmer climate and increased precipitations are often mentioned, but to which extent is more uncertain. However, the major changes in precipitation will occur over the North Pacific, North Atlantic and Scandinavia. The controlling factor for microbial activity in the organic layer during winter in alpine areas is the development of a consistent snow cover, which effectively decouples the soil from the atmospheric temperature. The air and soil temperature the days before snow cover development is important, as it sets the temperature conditions for the whole winter period. Soil microbial activity is markedly reduced below temperatures of 0 to -5°C, when the soil starts to freeze and free water becomes limited. Nitrogen mineralisation, nitrification and denitrification can, however, be maintained down to -4°C, and N2O production (from denitrification) in frozen soils has potential to affect annual dynamics and budgets of N (although the soil pore water content prior to freezing is an important regulating factor for winter N2O production). Snowbed communities are rarely, if ever, subjected to temperatures as low as -5°C, which implies that they may be favourable for microbial activity during the winter. Furthermore, tundra soil microbial biomass reaches its annual peak under snow, and fungi account for most of the biomass. However, how the microbial community changes during winter and snowmelt are poorly know and, in particular, in relation to trace gas fluxes. Flux of CO2, CH4 and N2O through a seasonal snowpack, using Fick’s law, from four plant communities with different snow regime and how it changes during snowmelt in the subarctic-alpine part of Sweden will be presented. We will also try to relate the trace gas fluxes to the soil microbial community composition using phospholipid fatty acid analysis.
|
|
| 8. |
- Björk, Robert G., 1974, et al.
(author)
-
Temporal variation in soil microbial communities and the influence of snow cover
- 2007
-
In: The 14th ITEX workshop, Falls Creek, Victoria, Australia, 2–6 February 2007..
-
Conference paper (other academic/artistic)abstract
- Global climate change is projected to have a large impact in arctic and alpine areas. Future projections with increased temperature also include increased precipitation, but to which extent is uncertain. However, the major changes in precipitation will occur over the North Pacific, North Atlantic and Scandinavia. As much as 44 to 53% of the northern hemispheres landmass may be snow covered for parts of the year and in higher alpine terrain the increased precipitation will lead to a greater snow accumulation. The controlling factor for microbial activity in the organic layer during winter in alpine areas is the development of a consistent snow cover, which effectively decouples the soil from the atmospheric temperature. The air and soil temperature the days before snow cover development is important, as it sets the temperature conditions for the whole winter period. Soil microbial activity is markedly reduced below temperatures of 0 to -5°C, when the soil starts to freeze and free water becomes limited. Nitrogen mineralisation, nitrification and denitrification can, however, be maintained down to -4°C, and N2O production (from denitrification) in frozen soils could potentially affect the annual dynamics and budgets of N. Snowbed communities are rarely, if ever, subjected to temperatures as low as -5°C, which implies that they may be favourable for microbial activity during the winter. Furthermore, tundra soil microbial biomass reaches its annual peak under snow, and fungi account for most of the biomass. However, how the microbial community changes during winter and snowmelt is poorly known and, in particular, in relation to trace gas fluxes. The objective of our study was, therefore, to investigate the temporal pattern of soil microbial structure in four plant communities with contrasting snow cover and nitrogen turnover. This study was conducted at Latnjajaure Field Station (LFS) located in the midalpine region in northern Sweden. The study includes four different plant communities, heath snowbed, heath meadow, meadow snowbed, and mesic meadow. To characterize the soil microbial community we used phospholipid fatty acid analysis (PLFA), which is a method targeting the fatty acid profiles of membrane phospholipids microorganisms. The results show that at each individual sampling occasion the four plant communities’ exhibits different soil microbial structure. However, the temporal variation is larger than the difference across plant communities. This temporal shift in microbial structure seems to be partially related to the fatty acid 18:2ω6, indicative of fungi, which show a high proportion in soils protected by snow and decreases after snow melt. Furthermore, the shift in microbial structure during the season is more modest in snowbeds than the mesic heath and meadow.
|
|
| 9. |
- Björk, Robert G., 1974, et al.
(author)
-
Temporal variation in soil microbial communities in Alpine tundra
- 2008
-
In: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 40:1, s. 266-268
-
Journal article (peer-reviewed)abstract
- Temporal variation in soil microbial communities was studied at a mid-alpine environment in Latnjajaure, northern Sweden, using phospholipid fatty acid (PLFA) analysis. The results show two seasonal shifts in microbial composition. The first shift was associated with snowmelt and mainly related to a decrease in fungal PLFAs, accompanied by an increase in branched 17:0 and methylated PLFAs (biomarkers for Gram-positive- and actinobacteria, respectively), resulting in a decrease in the ratio of fungi-to-bacteria. The second shift occurred across the growing, season, and was associated with a switch from shorter to longer PLFAs and an increase in 18:1 omega 7 (biomarker for Gram-negative bacteria). Vegetation, snow cover dynamics, and N turnover seem to be of minor importance to broadscale microbial community structure in this area. (c) 2007 Elsevier Ltd. All rights reserved.
|
|
| 10. |
- Björkman, Mats P., 1978, et al.
(author)
-
Nitrate postdeposition processes in Svalbard surface snow
- 2014
-
In: Journal of Geophysical Research - Atmospheres. - 0148-0227 .- 2156-2202 .- 2169-897X .- 2169-8996. ; 119:22
-
Journal article (peer-reviewed)abstract
- The snowpack acts as a sink for atmospheric reactive nitrogen, but several postdeposition pathways have been reported to alter the concentration and isotopic composition of snow nitrate with implications for atmospheric boundary layer chemistry, ice core records, and terrestrial ecology following snow melt. Careful daily sampling of surface snow during winter (11-15 February 2010) and springtime (9 April to 5 May 2010) near Ny-Ålesund, Svalbard reveals a complex pattern of processes within the snowpack. Dry deposition was found to dominate over postdeposition losses, with a net nitrate deposition rate of (0.6+/-0.2) (my) molm 2 d 1 to homogeneous surface snow. At Ny-Ålesund, such surface dry deposition can either solely result from long-range atmospheric transport of oxidized nitrogen or include the redeposition of photolytic/bacterial emission originating from deeper snow layers. Our data further confirm that polar basin air masses bring 15 N-depleted nitrate to Svalbard, while high nitrate (delta) (18O) values only occur in connection with ozone-depleted air, and show that these signatures are reflected in the deposited nitrate. Such ozone-depleted air is attributed to active halogen chemistry in the air masses advected to the site. However, here the Ny-Ålesund surface snow was shown to have an active role in the halogen dynamics for this region, as indicated by declining bromide concentrations and increasing nitrate (delta) (18O), during high BrO (low-ozone) events. The data also indicate that the snowpack BrO-NO x cycling continued in postevent periods, when ambient ozone and BrO levels recovered.
|
|
