| 1. |
- Oehri, Jacqueline, et al.
(författare)
-
Vegetation type is an important predictor of the arctic summer land surface energy budget
- 2022
-
Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 13
-
Tidskriftsartikel (refereegranskat)abstract
- Despite the importance of high-latitude surface energy budgets (SEBs) for land-climate interactions in the rapidly changing Arctic, uncertainties in their prediction persist. Here, we harmonize SEB observations across a network of vegetated and glaciated sites at circumpolar scale (1994–2021). Our variance-partitioning analysis identifies vegetation type as an important predictor for SEB-components during Arctic summer (June-August), compared to other SEB-drivers including climate, latitude and permafrost characteristics. Differences among vegetation types can be of similar magnitude as between vegetation and glacier surfaces and are especially high for summer sensible and latent heat fluxes. The timing of SEB-flux summer-regimes (when daily mean values exceed 0 Wm−2) relative to snow-free and -onset dates varies substantially depending on vegetation type, implying vegetation controls on snow-cover and SEB-flux seasonality. Our results indicate complex shifts in surface energy fluxes with land-cover transitions and a lengthening summer season, and highlight the potential for improving future Earth system models via a refined representation of Arctic vegetation types.
|
|
| 2. |
- Bäckstrand, Kristina, et al.
(författare)
-
Annual carbon gas budget for a subarctic peatland, northern Sweden
- 2010
-
Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 7:1, s. 95-108
-
Tidskriftsartikel (refereegranskat)abstract
- Temperatures in the Arctic regions are rising, thawing permafrost and exposing previously stable soil organic carbon (OC) to decomposition. This can result in northern latitude soils, which have accumulated large amounts of OC potentially shifting from atmospheric C sinks to C sources with positive feedback on climate warming. In this paper, we estimate the annual net C gas balance (NCB) of the subarctic mire Stordalen, based on automatic chamber measurements of CO2 and total hydrocarbon (THC; CH4 and NMVOCs) exchange. We studied the dominant vegetation communities with different moisture and permafrost characteristics; a dry Palsa underlain by permafrost, an intermediate thaw site with Sphagnum spp. and a wet site with Eriophorum spp. where the soil thaws completely. Whole year accumulated fluxes of CO2 were estimated to 29.7, −35.3 and −34.9 gC m−2 respectively for the Palsa, Sphagnum and Eriophorum sites (positive flux indicates an addition of C to the atmospheric pool). The corresponding annual THC emissions were 0.5, 6.2 and 31.8 gC m−2 for the same sites. Therefore, the NCB for each of the sites was 30.2, −29.1 and −3.1 gC m−2 respectively for the Palsa, Sphagnum and Eriophorum site. On average, the whole mire was a CO2 sink of 2.6 gC m−2 and a THC source of 6.4 gC m−2 over a year. Consequently, the mire was a net source of C to the atmosphere by 3.9 gC m−2 (based on area weighted estimates for each of the three plant communities). Early and late snow season efflux of CO2 and THC emphasize the importance of winter measurements for complete annual C budgets. Decadal vegetation changes at Stordalen indicate that both the productivity and the THC emissions increased between 1970 and 2000. Considering the GWP100 of CH4, the net radiative forcing on climate increased 21% over the same time. In conclusion, reduced C compounds in these environments have high importance for both the annual C balance and climate.
|
|
| 3. |
- Christensen, Torben, et al.
(författare)
-
Monitoring the multi year carbon balance of a subarctic palsa mire with micrometeorological techniques
- 2012
-
Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 41, s. 207-217
-
Tidskriftsartikel (refereegranskat)abstract
- This article reports a dataset on 8 years of monitoring carbon fluxes in a subarctic palsa mire based on micrometeorological eddy covariance measurements. The mire is a complex with wet minerotrophic areas and elevated dry palsa as well as intermediate sub-ecosystems. The measurements document primarily the emission originating from the wet parts of the mire dominated by a rather homogenous cover of Eriophorum angustifolium. The CO2/CH4 flux measurements performed during the years 2001-2008 showed that the areas represented in the measurements were a relatively stable sink of carbon with an average annual rate of uptake amounting to on average -46 g C m(-2) y(-1) including an equally stable loss through CH4 emissions (18-22 g CH4-C m(-2) y(-1)). This consistent carbon sink combined with substantial CH4 emissions is most likely what is to be expected as the permafrost under palsa mires degrades in response to climate warming.
|
|
| 4. |
|
|
| 5. |
- Jackowicz-Korczynski, Marcin, et al.
(författare)
-
Annual cycle of methane emissions from a subarctic peatland
- 2010
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115, s. G02009-
-
Tidskriftsartikel (refereegranskat)abstract
- Although much attention in recent years has been devoted to methane (CH4) emissions from northern wetlands, measurement based data sets providing full annual budgets are still limited in number. This study was designed to help fill the gap of year-round measurements of CH4 emissions from subarctic mires. We report continuous eddy correlation CH4 flux measurements made during 2006 and 2007 over the Stordalen mire in subarctic Sweden (68 degrees 20'N, 19 degrees 03'E, altitude 351 m) using a cryocooled tunable diode laser. The landscape-scale CH4 fluxes originated mainly from the permafrost free wet parts of the mire dominated by tall graminoid vegetation. The midseason average CH4 emission mean was 6.2 +/- 2.6 mg m(-2) h(-1). A detailed footprint analysis indicates an additional strong influence on the flux by the nearby shallow Lake Villasjon (0.17 km(2), maximum depth 1.3 m). A stable bimodal distribution of wind flow from either the east or the west allowed separating the lake and mire vegetation signals. The midseason lake emission rates were as high as 12.3 +/- 3.3 mg m(-2) h(-1). Documented CH4 fluxes are similar to results obtained by automatic chamber technique and higher than manual chamber measurements made in the wet minerotrophic section dominated by Eriophorum angustifolium. The high fluxes observed from this vegetation type are significant because the areal distribution of this source in the mire is expanding due to ongoing thawing of the permafrost. A simple peat temperature relationship with CH4 emissions was used to fill data gaps to construct a complete annual budget of CH4 fluxes over the studied area. The calculated annual CH4 emissions in 2006 and 2007 equaled 24.5 and 29.5 g CH4 m(-2) yr(-1), respectively. The summer season CH4 emissions dominated (65%) the annual flux, with the shoulder seasons of spring and autumn significant (25%) and a minor flux from the winter (10%).
|
|
| 6. |
- Jackowicz-Korczynski, Marcin
(författare)
-
Land-atmosphere interaction of a subarctic palsa mire
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this thesis was to quantitatively estimate the gaseous exchange of carbon dioxide (CO2) and methane (CH4) between a subarctic wetland ecosystem and the atmosphere. Additionally some initial estimates of the carbon input to the atmosphere of nonmethane hydrocarbons (NMHCs) were also obtained by combining different techniques in a joint setting. The data presented were collected at the Stordalen mire, a palsa type complex located in the northernmost part of subarctic Sweden (68°20’N, 19°03’E, alt. 363 m asl). This site represents an ecosystem type that is highly sensitive to climatic conditions, especially to the ongoing processes of climate warming. Recent studies performed in this area have shown that those ecosystems in northern Scandinavia are subject to dramatic changes, as the distribution of permafrost is diminishing and vegetation is changing, which has been triggered by warming over recent decades. These regional landscape changes are affecting the ecosystems carbon balance, and might determine whether these ecosystems will be classified as either greenhouse gas sources or sinks. In addition to the obtained estimates of the emission of the two major greenhouse gases (CO2 and CH4), the quantitative studies of NMHCs were derived by simultaneously performed chamber measurements coupled with total hydrocarbon (THC) analyses, and by applying a disjunct eddy covariance (DEC) technique to measure specific emissions of isolated biogenic volatile organic compounds (BVOCs) such as isoprene and methanol. The measured eddy covariance tower net ecosystem exchange (NEE) showed a strong and consistent annual uptake signal. During the years 2004 to 2008, with relatively comparable climates the annual NEE amounts to -89 g CO2-C m-2 y-1, with very small variation. The eddy covariance (EC) tower acquired CH4 flux measurements and showed a strong positive input to the annual carbon budget in the range of 18-22 g CH4-C m-2 y-1, reducing the studied ecosystem sink strength by almost 20%. Additional positive budget components in the form of emission of NMHCs constitute roughly an additional 15% to the CH4 fluxes. This fraction may be compared with the EC CH4 flux measurements emission rates and the results of the isoprene and methanol flux measurements obtained by the DEC method. Here the proportional atmospheric emission is estimated as 4% and 1% respectively for the above-mentioned components, indicating that other compounds must be responsible for a large proportion of the NMHC flux. By applying a global warming potential factor and calculating the annual balances expressed in CO2 equivalent numbers converted according to a 100 year time horizon, the degrading parts of the Stordalen mire appear as a greenhouse warming source with a level of emission estimated at +93 g CO2equiv.-C m-2 y-1. This strong greenhouse warming source demonstrates the necessity of conducting detailed carbon budgeting experiments that will lead to an improvement of our understanding of how global carbon cycling interacts with climate.
|
|
| 7. |
- Johansson, Margareta, et al.
(författare)
-
Rapid responses of permafrost and vegetation to experimentally increased snow cover in sub-arctic Sweden
- 2013
-
Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 8:3
-
Tidskriftsartikel (refereegranskat)abstract
- 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 degrees C higher in manipulated plots. During the winter, a difference in minimum temperatures of up to 9 degrees 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.
|
|
| 8. |
|
|
| 9. |
- Koebsch, Franziska, et al.
(författare)
-
Refining the role of phenology in regulating gross ecosystem productivity across European peatlands
- 2020
-
Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 26:2, s. 876-887
-
Tidskriftsartikel (refereegranskat)abstract
- The role of plant phenology as a regulator for gross ecosystem productivity (GEP) in peatlands is empirically not well constrained. This is because proxies to track vegetation development with daily coverage at the ecosystem scale have only recently become available and the lack of such data has hampered the disentangling of biotic and abiotic effects. This study aimed at unraveling the mechanisms that regulate the seasonal variation in GEP across a network of eight European peatlands. Therefore, we described phenology with canopy greenness derived from digital repeat photography and disentangled the effects of radiation, temperature and phenology on GEP with commonality analysis and structural equation modeling. The resulting relational network could not only delineate direct effects but also accounted for possible effect combinations such as interdependencies (mediation) and interactions (moderation). We found that peatland GEP was controlled by the same mechanisms across all sites: phenology constituted a key predictor for the seasonal variation in GEP and further acted as a distinct mediator for temperature and radiation effects on GEP. In particular, the effect of air temperature on GEP was fully mediated through phenology, implying that direct temperature effects representing the thermoregulation of photosynthesis were negligible. The tight coupling between temperature, phenology and GEP applied especially to high latitude and high altitude peatlands and during phenological transition phases. Our study highlights the importance of phenological effects when evaluating the future response of peatland GEP to climate change. Climate change will affect peatland GEP especially through changing temperature patterns during plant phenologically sensitive phases in high latitude and high altitude regions.
|
|
| 10. |
- Lembrechts, Jonas J., et al.
(författare)
-
Global maps of soil temperature
- 2022
-
Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 28:9, s. 3110-3144
-
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.
|
|
