The FLUXNET2015 dataset provides ecosystem-scale data on CO 2 , water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.

[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%).

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.

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.