Observations on the North Slope of Alaska have revealed patches of Sphagnum peat within the widespread matrix of tussock tundra on mineral soils. Little is known about the developmental history of these Sphagnum patches and whether they represent incipient peatlands established in response to warming-related environmental changes. Nine peat cores were collected from nine Sphagnum-dominated peat patches spanning an approximately 300-km longitudinal gradient on the North Slope to determine their development and establishment history. Stratigraphically constrained cluster analysis was applied to plant macrofossil data, carbon-to-nitrogen ratios, and total organic matter measured from bulk peat to delineate developmental phases, and radiocarbon dating was used to constrain the timing of Sphagnum peat patch establishment. We compared these data to changes in testate amoeba community composition and amoeba-inferred water-table depth and pH in six of the peat cores. We also compared Sphagnum peat-patch development and establishment history to paleoclimate and local instrumental temperature records. Results indicated a predictable pattern that describes the transition from moist tussock tundra to Sphagnum peat. Furthermore, although Sphagnum has been present on the North Slope for millennia, our data suggest that Sphagnum-dominated peat patches constitute recent landscape features, mainly established in the 1800s and 1900s, and with rapidly increasing Sphagnum abundance in the past 50 years. Sphagnum expansion was associated with pronounced changes in testate amoeba communities, including an increase in mixotrophic taxa and species associated with densely growing Sphagnum, and community changes consistent with drying and increased acidity. The recent development of Sphagnum-dominated peat patches has been associated with warming air and soil temperatures, active layer deepening, and earlier snowmelt. Sphagnum expansion has also been observed in other arctic regions, and understanding the extent and growth potential of Sphagnum peat patches has implications for understanding and anticipating changes in carbon cycling, edaphic conditions, permafrost thermal regimes, and floristic diversity.

Climate warming has inevitable impacts on the vegetation and hydrological dynamics of high-latitude permafrost peatlands. These impacts in turn determine the role of these peatlands in the global biogeochemical cycle. Here, we used six active layer peat cores from four permafrost peatlands in Northeast European Russia and Finnish Lapland to investigate permafrost peatland dynamics over the last millennium. Testate amoeba and plant macrofossils were used as proxies for hydrological and vegetation changes. Our results show that during the Medieval Climate Anomaly (MCA), Russian sites experienced short-term permafrost thawing and this induced alternating dry-wet habitat changes eventually followed by desiccation. During the Little Ice Age (LIA) both sites generally supported dry hummock habitats, at least partly driven by permafrost aggradation. However, proxy data suggest that occasionally, MCA habitat conditions were drier than during the LIA, implying that evapotranspiration may create important additionaleco-hydrological feedback mechanisms under warm conditions. All sites showed a tendency towards dry conditions as inferred from both proxies starting either from ca. 100 years ago or in the past few decades after slight permafrost thawing, suggesting that recent warming has stimulated surface desiccation rather than deeper permafrost thawing. This study shows links between two important controls over hydrology and vegetation changes in high-latitude peatlands: direct temperature-induced surface layer response and deeper permafrost layer-related dynamics. These data provide important backgrounds for predictions of Arctic permafrost peatlands and related feedback mechanisms. Our results highlight the importance of increased evapotranspiration and thus provide an additional perspective to understanding of peatland-climate feedback mechanisms. (C) 2018 Elsevier Ltd. All rights reserved.

Understanding the spatial distribution of soil protozoa under the snow cover is important for estimation of ecosystem responses to climate change and interpretation of results of field experiments. This work explores spatial patterns of soil testate amoebae under the snow cover at the plot scale (the range of metres) in arctic tundra (Qeqertarsuaq/Disko Island, West Greenland). To explain spatial patterns in abundance, species diversity and assemblage composition of testate amoebae, we measured microtopography, snow depth and substrate density. The results indicate that the abundance of active testate amoebae under the snow cover was quite low. The empty shell assemblage was characterised by the presence of linear spatial trends in the species composition across the site, whereas no patterns were detected within the plot. The distribution of the abundance and the species diversity were unstructured. The linear trends in the species composition corresponded to the site microtopography and were controlled by the topography-related soil moisture. Snow depth also affected the linear trends presumably by controlling soil temperatures. Overall, the results suggest that population processes do not generate spatial patterns in protozoan assemblages at the plot scale so that protozoan distribution can be considered random at macroscopically homogeneous plots.