Increasing air temperatures are driving widespread changes to Arctic vegetation. In the high Arctic, these changes are patchy and the causes of heterogeneity are not well understood. In this study, we explore the determinants of high Arctic vegetation change over the last three decades on Banks Island, Northwest Territories. We used Landsat imagery (1984-2014) to map long-term trends in vegetation productivity and regional spatial data to investigate the relationships between trends in productivity and terrain position. Field sampling investigated vegetation community composition in different habitat types. Our analysis shows that vegetation productivity changes are substantial on Banks Island, where productivity has increased across about 80% of the study area. Rising productivity levels can be attributed to increasing biomass of the plant communities in both upland and lowland habitats. Our analysis also shows that the magnitude of greening is mediated by terrain characteristics related to soil moisture. Shifts in tundra vegetation will impact wildlife habitat quality, surface energy balance, permafrost dynamics, and the carbon cycle; additional research is needed to explore the effects of more productive vegetation communities on these processes in the high Arctic.

A range of polycyclic aromatic hydrocarbons has been identified, and regularities of their vertical distribution in the peatland of hummock-hollow complexes in the southern tundra - forest tundra and northern tundra - southern tundra ecotones of the European Arctic zone have been determined. Benzo[ghi]perylene, naphthalene, pyrene, fluorene, phenanthrene, benzo[b]fluoranthene and benzo[a]pyrene are displayed most in the peatlands under study. Regarding the peatland profile the vertical polyarene distribution is similar - in 150-175 cm permafrost layers (site 1) and 50(70)-210(250) cm layers (site 2), and on the border between the active layer and permafrost 35-50(60) cm (site 1) and 30(42) - 50 cm (site 2) a significant increase of HCO-accumulated PAHs weight fraction is observed. PAHs content maximums in tundra peatland horizons are associated both with 4-, 5- and 6-nuclear structures at both sites under the analysis, and with a larger amount of 2- and 3-nuclear polyarenes in the peatlands on the northern tundra-southern tundra ecotone. Aeration-exposed seasonally thawing peatland layers are subject to continuous formation of primarily light 2- and 3-nuclear PAHs of natural origin resulting from microbiological decomposition of plant residues, which are subsequently involved in equilibrium cycles of chemical and biochemical transformation, with their total capacity remaining almost unchanged and constituting ?200-500 ng/g. Owing to low productivity of plant communities and absence of tree vegetation in the seasonally thawed layer, accumulation of the sum of 4-, 5- and 6-nuclear PAHs weakens significantly. One can detect dependencies between individual PAHs and the botanic composition of peat through higher weight fraction of 4-, 5- and 6-nuclear polyarenes being lignin transformation products generated more as the share of tree vegetation grows. The PAHs composition is a paleoclimatic marker reflecting adequately both changing paleovegetation stages and the degree of peat decomposition.

A significant difference in net ecosystem carbon balance of wet sedge ecosystems in the Barrow, Alaska region was observed between CO2 flux measurements obtained during the International Biological Program in 1971 and measurements made during the 1991-1992 growing seasons. Currently, high-center polygons are net sources of CO2 to the atmosphere of approximate to 14 gC . m(-2). yr(-1), while low-center polygons are losing approximate to 3.6 gC . m(-2). yr(-1), and ice wedge habitats are accumulating 4.0 gC . m(-2). yr(-1). On average, moist meadow habitats characteristic of the IBP-II site are currently sources of approximate to 1.3 gC . m(-2). yr(-1) to the atmosphere compared to the reported accumulation of approximate to 25 gC . m(-2). yr(-1) determined in 1971. This difference in ecosystem function over the last two decades may be due to the recently reported increase in surface temperatures resulting in decreases in the soil moisture status. These results point to the importance of long-term research sites and databases for determining the potential effects of climate change on ecosystem function.