[1] Although much attention in recent years has been devoted to methane (CH 4 ) 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 CH 4 emissions from subarctic mires. We report continuous eddy correlation CH 4 flux measurements made during 2006 and 2007 over the Stordalen mire in subarctic Sweden (68°20′N, 19°03′E, altitude 351 m) using a cryocooled tunable diode laser. The landscape-scale CH 4 fluxes originated mainly from the permafrost free wet parts of the mire dominated by tall graminoid vegetation. The midseason average CH 4 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 Villasjön (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 CH 4 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 CH 4 emissions was used to fill data gaps to construct a complete annual budget of CH 4 fluxes over the studied area. The calculated annual CH 4 emissions in 2006 and 2007 equaled 24.5 and 29.5 g CH 4 m −2 yr −1 , respectively. The summer season CH 4 emissions dominated (65%) the annual flux, with the shoulder seasons of spring and autumn significant (25%) and a minor flux from the winter (10%).

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 CO 2 and total hydrocarbon (THC; CH 4 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 CO 2 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 CO 2 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 CO 2 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 GWP 100 of CH 4 , the Correspondence to: K. Bäckstrand (kristina.backstrand@gmail.com) 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.

Palsa mires, nutrient poor permafrost peatlands common in subarctic regions, store a significant amount of carbon (C) and it has been hypothesized their net ecosystem C balance (NECB) is sensitive to climate change. Over two years we measured the NECB for Stordalen palsa mire and found it to accumulate 46 g C m−2 yr−1. While Stordalen NECB is comparable to nutrient poor peatlands without permafrost, the component fluxes differ considerably in magnitude. Specifically, Stordalen had both lower growing season CO2 uptake and wintertime CO2losses, but importantly also low dissolved organic carbon exports and hydrocarbon (mainly methane) emissions. Restricted C losses from palsa mires are likely to have facilitated C accumulation of unproductive subarctic permafrost peatlands. Continued climate change and permafrost thaw is likely to amplify several component fluxes, with an uncertain overall effect on NECB – highlighting the necessity for projections of high‐latitude C storage to consider all C fluxes.

[1] This is a study of the spatial and temporal variability of total hydrocarbon (THC) emissions from vegetation and soil at a subarctic mire, northern Sweden. THCs include methane (CH 4 ) and nonmethane volatile organic compounds (NMVOCs), both of which are atmospherically important trace gases and constitute a significant proportion of the carbon exchange between biosphere and atmosphere. Reliable characterization of the magnitude and the dynamics of the THC fluxes from high latitude peatlands are important when considering to what extent trace gas emissions from such ecosystems may change and feed back on climate regulation as a result of warmer climate and melting permafrost. High frequency measurements of THC and carbon dioxide (CO 2 ) were conducted during four sequential growing seasons in three localities representing the trophic range of plant communities at the mire. The magnitude of the THC flux followed the moisture gradient with increasing emissions from a dry Palsa site (2.2 ± 0.1 mgC m À2 d À1 ), to a wet intermediate melt feature with Sphagnum spp. (28 ± 0.3 mgC m À2 d À1 ) and highest emissions from a wet Eriophorum spp. site (122 ± 1.4 mgC m À2 d À1 ) (overall mean ±1 SE, n = 2254, 2231 and 2137). At the Palsa site, daytime THC flux was most strongly related to air temperature while daytime THC emissions at the Sphagnum site had a stronger relation to ground temperature. THC emissions at both the wet sites were correlated to net ecosystem exchange of CO 2 . An overall spatial correlation indicated that areas with highly productive vegetation communities also had high THC emission potential.

Abstract. In this study, we present summertime concentrations and fluxes of biogenic volatile organic compounds (BVOCs) measured at a sub-arctic wetland in northern Sweden using a disjunct eddy-covariance (DEC) technique based on a proton transfer reaction mass spectrometer (PTR-MS). The vegetation at the site was dominated by Sphagnum, Carex and Eriophorum spp. The measurements reported here cover a period of 50 days (1 August to 19 September 2006), approximately one half of the growing season at the site, and allowed to investigate the effect of day-to-day variation in weather as well as of vegetation senescence on daily BVOC fluxes, and on their temperature and light responses. The sensitivity drift of the DEC system was assessed by comparing H 3 O + -ion cluster formed with water molecules (H 3 O + (H 2 O) at m37) with water vapour concentration measurements made using an adjacent humidity sensor, and the applicability of the DEC method was analysed by a comparison of sensible heat fluxes for high frequency and DEC data obtained from the sonic anemometer. These analyses showed no significant PTR-MS sensor drift over a period of several weeks and only a small flux-loss due to high-frequency spectrum omissions. This loss was within the range expected from other studies and the theoretical considerations.Standardised (20 • C and 1000 µmol m −2 s −1 PAR) summer isoprene emission rates found in this study of 329 µg C m −2 (ground area) h −1 were comparable with findings from more southern boreal forests, and fen-like ecosystems. On a diel scale, measured fluxes indicated a stronger temperature dependence than emissions from temperate or (sub)tropical ecosystems. For the first time, to our knowledge, we report ecosystem methanol fluxes from a sub-arctic Correspondence to: T. Holst (thomas.holst@nateko.lu.se) ecosystem. Maximum daytime emission fluxes were around 270 µg m −2 h −1 (ca. 100 µg C m −2 h −1 ), and during most nights small negative fluxes directed from the atmosphere to the surface were observed.