| 1. |
- House, J, et al.
(författare)
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Climate and air quality
- 2006
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Ingår i: Millennium Ecosystem Assessment 2005 - Current State and Trends. Findings of the Condition and Trends Working Group (Ecosystems and Human Well-being). ; 1, s. 350-390
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- McGuire, A.D., et al.
(författare)
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Sensitivity of the carbon cycle in the Arctic to climate change
- 2009
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Ingår i: Ecological Monographs. - : Wiley. - 0012-9615. ; 79:4, s. 523-555
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Bäckstrand, Kristina, 1979-
(författare)
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Carbon gas biogeochemistry of a northern peatland - in a dynamic permafrost landscape
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is about biogeochemical processes of a northern peatland and their importance as a link between the climate and the terrestrial system. Increased temperatures on a global level, and particularly in the Arctic, have led to melting permafrost and changes in hydrology. In turn, this affect the natural exchange of radiatively important trace gases between land and atmosphere that may reinforce climate change. The aim of this thesis is to increase the understanding about the exchange of carbon dioxide (CO2), methane (CH4) and non-methane volatile organic compounds (NMVOCs) occurring in northern peatlands, to decrease uncertainty about their future carbon (C) balance. In order to pursue this aim, we designed a study that allowed measuring the C exchange at a subarctic peatland, accounting for spatial and temporal analysis at several levels. The field site was the Stordalen mire, northern Sweden. Exchange rates of CO2, and total hydrocarbons (THCs; CH4 and NMVOCs) were measured using an automatic chamber system for up to six years, at three different types of vegetation communities and permafrost regimes. The gas exchange was found to relate to different environmental and biological variables at different vegetation communities and at different temporal scales. Differences in flux rates and controls between sites could be explained with biological and environmental variables in a better way than the seasonal and interannual variability within a site.Snow season flux measurements were determined to be of high importance regarding the annual C budget. By excluding the snow season, the potential C source strength of a peatland is likely to be underestimated. The importance of combining the THCs with the CO2 to estimate the annual C balance was demonstrated as THC could be sufficient to shift the mire from a sink to a source of C to the atmosphere. Again, the C source strength may be significantly underestimated if only focusing on CO2 fluxes in wet peatland environments.
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| 4. |
- Chapin III, F.S., et al.
(författare)
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Polar Systems
- 2006
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Ingår i: Millenium Ecosystem Assessment 2005 - Current State and Trends. - 1559632283 - 9781559632287 ; 1
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 5. |
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| 6. |
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| 7. |
- Norlund Christensen, Axel, et al.
(författare)
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Formation and transformation of five different phases in the CaSO4-H2O system: Crystal structure of the subhydrate beta-CaSO4 center dot 0.5H(2)O and soluble anhydrite CaSO4
- 2008
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 20:6, s. 2124-2132
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Tidskriftsartikel (refereegranskat)abstract
- At least five crystalline-phases can be found in the CaSO4-H2O system, which are gypsum CaSO4 center dot 2H(2)O, the subhydrates alpha- and beta-CaSO4 center dot 0.5H(2)O, and the soluble and insoluble anhydrite CaSO4. The formation of these five phases in the CaSO4-H2O system and their transformations were investigated by in situ time-resolved synchrotron radiation powder X-ray diffraction (SR-PXD) in this study. Furthermore, revised structural models for beta-CaSO4 center dot 0.5H(2)O and soluble anhydrite CaSO4 are presented. The hydration of alpha-CaSO4 center dot 0.5H(2)O was studied at 25 degrees C and showed that the reaction with H2O started immediately after mixing the two reactants and that the formation of CaSO4 center dot 2H(2)O was coupled to the depletion of alpha-CaSO4 center dot 0.5H(2)O. The thermal decomposition of CaSO4 center dot 2H(2)O was investigated in the temperature range of 25-500 degrees C and showed the fon-nation of alpha-CaSO4 center dot 0.5H(2)O followed by the formation of soluble anhydrite AIII-CaSO4, which was gradually converted to insoluble anhydrite AII-CaSO4. The thermal decomposition of alpha-CaSO4 center dot 0.5D(2)O was investigated in the temperature range of 25-500 degrees C and showed successive phase transformations to beta-CaSO4 center dot 0.5D(2)O, soluble anhydrite AIII-CaSO4, and insoluble anhydrite AII-CaS04. The two polymorphs of anhydrite coexist in the investigated temperature range of 200-500 degrees C. The hydrothermal decomposition of CaSO4 center dot 2H(2)O was investigated in the temperature range of 25-200 degrees C using a 1 M HNO3 or a 1 M LiCl solution, and in both experiments, CaSO4 center dot 2H(2)O was converted to alpha-CaSO4 center dot 0.5H(2)O and further to insoluble anhydrite AII-CaSO4. A structural model for beta-CaSO4 center dot 0.5H(2)O is proposed on the basis of SR-PXD data and a trigonal unit cell (in hexagonal setting) a = 6.93145(3), c = 12.736 17(4) angstrom, Z = 6, and space group P3(1). A structural model for soluble anhydrite AIII-CaSO4 is also proposed on the basis of powder neutron diffraction data, and a hexagonal unit cell parameters are a = 6.9687(1), c = 6.3004(1) angstrom, Z = 3, and space group P6(2)22.
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| 8. |
- Petrescu, A. M. R., et al.
(författare)
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Modelling CH4 emissions from arctic wetlands : effects of hydrological parameterization
- 2008
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 5:1, s. 111-121
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Tidskriftsartikel (refereegranskat)abstract
- This study compares the CH4 fluxes from two arctic wetland sites of different annual temperatures during 2004 to 2006. The PEATLAND-VU model was used to simulate the emissions. The CH4 module of PEATLAND-VU is based on the Walter-Heimann model. The first site is located in northeast Siberia, Indigirka lowlands, Kytalyk reserve (70 degrees N, 147 degrees E) in a continuous permafrost region with mean annual temperatures of -14.3 degrees C. The other site is Stordalen mire in the eastern part of Lake Tornetrask (68 degrees N, 19 degrees E) ten kilometres east of Abisko, northern Sweden. It is located in a discontinuous permafrost region. Stordalen has a sub arctic climate with a mean annual temperature of -0.7 degrees C. Model input consisted of observed temperature, precipitation and snow cover data. In all cases, modelled CH4 emissions show a direct correlation between variations in water table and soil temperature variations. The differences in CH4 emissions between the two sites are caused by different climate, hydrology, soil physical properties, vegetation type and NPP. For Kytalyk the simulated CH4 fluxes show similar trends during the growing season, having average values for 2004 to 2006 between 1.29-2.09 mg CH4 m(-2) hr(-1). At Stordalen the simulated fluxes show a slightly lower average value for the same years (3.52 mg CH4 m(-2) hr(-1)) than the observed 4.7 mg CH4 m(-2) hr(-1). The effect of the longer growing season at Stordalen is simulated correctly. Our study shows that modelling of arctic CH4 fluxes is improved by adding a relatively simple hydrological model that simulates the water table position from generic weather data. Our results support the generalization in literature that CH4 fluxes in northern wetland are regulated more tightly by water table than temperature. Furthermore, parameter uncertainty at site level in wetland CH4 process models is an important factor in large scale modelling of CH4 fluxes.
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| 9. |
- Post, Eric, et al.
(författare)
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Ecological Dynamics Across the Arctic Associated with Recent Climate Change
- 2009
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 325:5946, s. 1355-1358
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Forskningsöversikt (refereegranskat)abstract
- At the close of the Fourth International Polar Year, we take stock of the ecological consequences of recent climate change in the Arctic, focusing on effects at population, community, and ecosystem scales. Despite the buffering effect of landscape heterogeneity, Arctic ecosystems and the trophic relationships that structure them have been severely perturbed. These rapid changes may be a bellwether of changes to come at lower latitudes and have the potential to affect ecosystem services related to natural resources, food production, climate regulation, and cultural integrity. We highlight areas of ecological research that deserve priority as the Arctic continues to warm.
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