The recent warming in the Arctic is affecting a broad spectrum of physical, ecological, and human/cultural systems that may be irreversible on century time scales and have the potential to cause ...rapid changes in the earth system. The response of the carbon cycle of the Arctic to changes in climate is a major issue of global concern, yet there has not been a comprehensive review of the status of the contemporary carbon cycle of the Arctic and its response to climate change. This review is designed to clarify key uncertainties and vulnerabilities in the response of the carbon cycle of the Arctic to ongoing climatic change. While it is clear that there are substantial stocks of carbon in the Arctic, there are also significant uncertainties associated with the magnitude of organic matter stocks contained in permafrost and the storage of methane hydrates beneath both subterranean and submerged permafrost of the Arctic. In the context of the global carbon cycle, this review demonstrates that the Arctic plays an important role in the global dynamics of both CO₂ and CH₄ . Studies suggest that the Arctic has been a sink for atmospheric CO₂ of between 0 and 0.8 Pg C/yr in recent decades, which is between 0% and 25% of the global net land/ocean flux during the 1990s. The Arctic is a substantial source of CH₄ to the atmosphere (between 32 and 112 Tg CH₄/yr), primarily because of the large area of wetlands throughout the region. Analyses to date indicate that the sensitivity of the carbon cycle of the Arctic during the remainder of the 21st century is highly uncertain. To improve the capability to assess the sensitivity of the carbon cycle of the Arctic to projected climate change, we recommend that (1) integrated regional studies be conducted to link observations of carbon dynamics to the processes that are likely to influence those dynamics, and (2) the understanding gained from these integrated studies be incorporated into both uncoupled and fully coupled carbon-climate modeling efforts.
Permafrost in the Arctic is thawing, exposing large carbon and nitrogen stocks for decomposition. Gaseous carbon release from Arctic soils due to permafrost thawing is known to be substantial, but ...growing evidence suggests that Arctic soils may also be relevant sources of nitrous oxide (N₂O). Here we show that N2O emissions from subarctic peatlands increase as the permafrost thaws. In our study, the highest postthaw emissions occurred from bare peat surfaces, a typical landform in permafrost peatlands, where permafrost thaw caused a fivefold increase in emissions (0.56 ± 0.11 vs. 2.81 ± 0.6 mg N₂O m−2 d−1). These emission rates match those from tropical forest soils, the world’s largest natural terrestrial N₂O source. The presence of vegetation, known to limit N₂O emissions in tundra, did decrease (by ∼90%) but did not prevent thaw-induced N₂O release, whereas waterlogged conditions suppressed the emissions. We show that regions with high probability for N₂O emissions cover one-fourth of the Arctic. Our results imply that the Arctic N₂O budget will depend strongly on moisture changes, and that a gradual deepening of the active layer will create a strong noncarbon climate change feedback.
Here we present results from a field experiment in an Arctic wetland situated in Zackenberg, NE Greenland. During one growing season we investigated how dominance of the sedge Eriophorum scheuchzeri ...affected the below-ground concentrations of low molecular weight carbon compounds (LMWOC) and the fluxes of CO2 and CH4 in comparison to dominance of other sedges (Carex stans and Dupontia psilosantha). Three groups of LMWOC were analysed using liquid chromatography-ionspray tandem mass spectrometry, i.e., organic acids (OAs), amino acids (AAs) and simple carbohydrates (CHs). To identify the effect of plant composition the experiments were carried out in a continuous fen area with very little between species variation in environmental conditions, e.g., water-table and active layer thickness and soil temperature. The pool of labile LMWOC compounds in this Arctic fen was dominated by OAs, constituting between 75 and 83% of the total pore water pool of OAs, CHs and AAs. The dominant OA was acetic acid, an easily available substrate for methanogens, which constituted ≥85% of the OA pool. We estimated that the concentration of acetic acid found in pore water would support 2–2.5 h of CH4 flux and an additional continuous input of acetic acid through root exudation that would support 1.3–1.5 h of CH4 flux. Thus, the results clearly points to the importance of a continuous input for acetoclastic methanogenesis to be sustainable. Additionally, Eriophorum had a very strong effect on parts of the carbon cycle in the Arctic fen. The mean seasonal CH4 flux was twice as high in Eriophorum dominated plots, most likely due to a 1.7 times higher concentration of OAs in these plots. Further, the ecosystem respiration was 1.3 times higher in Eriophorum dominated plots. In conclusion, the results offer further support to the importance of certain vascular plant species for the carbon cycle of wetland ecosystems.
► Three groups of LMWOC were analysed, in pore water of an Arctic fen, using LC-MS. ► More than 75% of the LMWOCs consisted of organic acids, whereof ≥85% acetic acid. ► The pore-water concentration of acetic acid would support 2–2.5 h of CH4 flux. ► Species composition had a very strong effect on parts of the C-cycle in the fen. ► Eriophorum dominated plots had higher acetic acid conc., CH4 flux and Reco.
Methane is an important greenhouse gas, and emissions are expected to rise in Arctic wetland ecosystems when temperatures increase due to climate change. However, current emission estimates are ...associated with large uncertainties because methane shows high spatial variability. A central problem is that existing methods are often spatially restricted due to limitations in access, cost, power availability, and in need of high maintenance levels. Our study explores how a setup consisting of an unmanned aerial vehicle and a high-precision trace gas analyzer can complement well-established methods, like mobile flux chambers and eddy covariance towers, by providing independent maps of spatial variability in emissions at the landscape scale.
In Zackenberg Valley, Northeast Greenland, we mapped concentration measurements from a high-precision trace gas analyzer with a reported precision of 0.6 parts per billion in a high-Arctic tundra fen ecosystem. We connected the analyzer via a long tube to a consumer-grade quadcopter, finding that the combined setup could differentiate near-surface methane concentrations of less than 5 parts per billion within a few meters under favorable weather conditions. Five of ten campaigns showed that relative methane concentration hot spots and cold spots significantly correlated with areas showing relatively high and low emissions (ranging from 1.40 to 7.4 mg m−2 h−1) during study campaigns in previous years. Concurrent measurements in a stationary automated chamber setup showed comparatively low methane emissions (~0.1 to 3.9 mg m−2 h−1) compared to previous years, indicating that a further improved UAV-analyzer setup could demonstrate clear differences in an ecosystem where methane emissions are generally higher. Calm conditions with some degree of air mixing near the surface were best suited for the mapping. Windy and wet conditions should be avoided, both for the reliability of the mapping and for safely navigating the unmanned aerial vehicle.
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•We mapped near-surface methane concentrations in a high-arctic fen with a UAV.•Methane concentrations increased in areas with high flux.•UAVs can assist in pointing out methane hot spots, relevant for biosphere and atmosphere studies.•Maps can be used for selecting more representative flux monitoring sites.
Climate warming in the Swedish sub‐Arctic since 2000 has reached a level at which statistical analysis shows for the first time that current warming has exceeded that in the late 1930's and early ...1940's, and has significantly crossed the 0°C mean annual temperature threshold which causes many cryospheric and ecological impacts. The accelerating temperature increase trend has driven similar trends in the century‐long increase in snow thickness, loss of lake ice, increases in active layer thickness, lake water TOC (total organic carbon) concentrations and the assemblages of diatoms, and changes in tree‐line location and plant community structure. Some of these impacts were not evident in the first warm period of the 20th Century. Changes in climate are associated with reduced temperature variability, particularly loss of cold winters and cool summers, and an increase in extreme precipitation events that cause mountain slope instability and infrastructure failure. The long term records of multiple, local environmental factors compiled here for the first time provide detailed information for adaptation strategy development while dramatic changes in an environment particularly vulnerable to climate change highlight the need to adopt global mitigation strategies.
Many wetland ecosystems such as peatlands and wet tundra hold large amounts of organic carbon (C) in their soils, and are thus important in the terrestrial C cycle. We have synthesized data on the ...carbon dioxide (CO₂) exchange obtained from eddy covariance measurements from 12 wetland sites, covering 1-7 years at each site, across Europe and North America, ranging from ombrotrophic and minerotrophic peatlands to wet tundra ecosystems, spanning temperate to arctic climate zones. The average summertime net ecosystem exchange of CO₂ (NEE) was highly variable between sites. However, all sites with complete annual datasets, seven in total, acted as annual net sinks for atmospheric CO₂. To evaluate the influence of gross primary production (GPP) and ecosystem respiration (Reco) on NEE, we first removed the artificial correlation emanating from the method of partitioning NEE into GPP and Reco. After this correction neither Reco (P= 0.162) nor GPP (P= 0.110) correlated significantly with NEE on an annual basis. Spatial variation in annual and summertime Reco was associated with growing season period, air temperature, growing degree days, normalized difference vegetation index and vapour pressure deficit. GPP showed weaker correlations with environmental variables as compared with Reco, the exception being leaf area index (LAI), which correlated with both GPP and NEE, but not with Reco. Length of growing season period was found to be the most important variable describing the spatial variation in summertime GPP and Reco; global warming will thus cause these components to increase. Annual GPP and NEE correlated significantly with LAI and pH, thus, in order to predict wetland C exchange, differences in ecosystem structure such as leaf area and biomass as well as nutritional status must be taken into account.
Drought is arguably the most important regulator of inter-annual variation in net ecosystem CO2 exchange (NEE) in peatlands. This study investigates effects of drought periods on NEE and its ...components, gross primary production (GPP) and ecosystem respiration (Reco), on the basis of eddy covariance measurements of land-atmosphere exchange of CO2 in 2006-2009 in a south Swedish nutrient-poor peatland. Two drought periods had dissimilar effects on the CO2 exchange. In 2006, there was a short but severe drought period in the middle of the growing season resulting in increased Reco rates, but no detectable effect on GPP rates. In contrast, in 2008 the drought period began early in the growing season and lasted for a longer period of time, resulting in reduced GPP rates, suggesting that GPP is most sensitive to drought during leaf out and canopy development compared with the full canopy stage. Both in 2006 and in 2008 the peatland acted as an annual source of atmospheric CO2, while in 2007 and 2009, when there were no drought periods, the peatland constituted a CO2 sink. It was concluded that the timing, severity and duration of drought periods regulate the effects on peatland GPP, Reco and NEE.
Permafrost peatlands are biogeochemical hot spots in the Arctic as they store vast amounts of carbon. Permafrost thaw could release part of these long‐term immobile carbon stocks as the greenhouse ...gases (GHGs) carbon dioxide (CO2) and methane (CH4) to the atmosphere, but how much, at which time‐span and as which gaseous carbon species is still highly uncertain. Here we assess the effect of permafrost thaw on GHG dynamics under different moisture and vegetation scenarios in a permafrost peatland. A novel experimental approach using intact plant–soil systems (mesocosms) allowed us to simulate permafrost thaw under near‐natural conditions. We monitored GHG flux dynamics via high‐resolution flow‐through gas measurements, combined with detailed monitoring of soil GHG concentration dynamics, yielding insights into GHG production and consumption potential of individual soil layers. Thawing the upper 10–15 cm of permafrost under dry conditions increased CO2 emissions to the atmosphere (without vegetation: 0.74 ± 0.49 vs. 0.84 ± 0.60 g CO2–C m−2 day−1; with vegetation: 1.20 ± 0.50 vs. 1.32 ± 0.60 g CO2–C m−2 day−1, mean ± SD, pre‐ and post‐thaw, respectively). Radiocarbon dating (14C) of respired CO2, supported by an independent curve‐fitting approach, showed a clear contribution (9%–27%) of old carbon to this enhanced post‐thaw CO2 flux. Elevated concentrations of CO2, CH4, and dissolved organic carbon at depth indicated not just pulse emissions during the thawing process, but sustained decomposition and GHG production from thawed permafrost. Oxidation of CH4 in the peat column, however, prevented CH4 release to the atmosphere. Importantly, we show here that, under dry conditions, peatlands strengthen the permafrost–carbon feedback by adding to the atmospheric CO2 burden post‐thaw. However, as long as the water table remains low, our results reveal a strong CH4 sink capacity in these types of Arctic ecosystems pre‐ and post‐thaw, with the potential to compensate part of the permafrost CO2 losses over longer timescales.
Permafrost peatlands are biogeochemical hot spots in the Arctic as they store vast amounts of carbon. Permafrost thaw could release part of these long‐term immobile carbon stocks as the greenhouse gases (GHGs) carbon dioxide (CO2) and methane (CH4) to the atmosphere, but how much, at which time‐span and as which gaseous carbon species is still highly uncertain. A novel experimental approach using intact plant–soil systems (mesocosms) allowed us to simulate permafrost thaw under near‐natural conditions. We show here that peatlands may strengthen the permafrost–carbon feedback by adding to the atmospheric CO2 burden post‐thaw.
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.
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