Diatoms from Sawtooth Lake (79°20′N, 81°51′W) on the Fosheim Peninsula in Central Ellesmere Island, Canada were analyzed to assess the temporal extent and magnitude of climatic change in the High Arctic during the late Holocene. Diatom results from the sediment cores show an absence of diatoms throughout the last ∼2.5 ka (4.6 m) until the 1920s. However, ca. 1926 (5.3-cm depth), a rapid colonization of diatoms in the lake occurred. Within the uppermost section of the core (∼1920 to ∼1997), the diatom flora shift from a small Fragilaria-dominated assemblage to a more diverse assemblage that is dominated by large planktonic taxa (e.g., Cyclotella bodanica) and large raphid benthic species. The postglacial nature of this assemblage suggests a decrease in ice cover and a concomitant increase in light and nutrient availability for diatom growth over the last ∼75 yr. Of particular significance is this absence of diatoms prior to the ∼1920s, which indicates that environmental conditions of the last ∼75 yr are unlike any of the previous ∼2500 yr.

The aim of this study is to assess the performance of diatom, chironomid, and pollen transfer functions for inferences of July air temperature during the Holocene using sediments from four alpine lakes in an area with low human impact in northern Sweden. The study demonstrates that diatom, chironomid, and pollen assemblages in the sediment cores contain climate information so that present-day temperature at each lake can be inferred with reasonable confidence for most proxies. Most proxy records from the sites consistently infer a long-term decreasing trend in July air temperature from ca. 6000 cal yr BP until the present. However, there are also large variations in the temporal patterns of the inferred temperatures during some periods, especially before 7000 cal yr BP, when there are also nonsynchronous changes in loss-on-ignition in the four lakes. This variability indicates that local conditions in the catchments (influence of snowfields, soil-forming processes) had a large impact on the organism assemblages in the early Holocene.Long-distance transport of pollen into high alpine lakes makes temperature inferences from pollen transfer functions unreliable. Due to the uncertainties of the methods, predictive errors of the transfer functions, and variability caused by local catchment/lake characteristics, only long-term trends in climate can be inferred. High-resolution studies using diatoms, chironomids, and pollen for climate reconstruction are probably not meaningful during periods with small changes in climate (<1°C). Future research should concentrate on low-resolution, multiproxy, and multilake studies to further understand the relationship between the proxies and climate.

Thaw lakes and drained thaw lake basins are ubiquitous on the Arctic Coastal Plain of Alaska. Basins are wet depositional environments, ideally suited for the accumulation and preservation of organic material. Much of this soil organic carbon (SOC) is currently sequestered in the near-surface permafrost but, under a warming scenario, could become mobilized. The relative age of 77 basins on the Barrow Peninsula was estimated using the degree of plant community succession and verified by radiocarbon-dating material collected from the base of the organic layer in 21 basins. Using Landsat-7 imagery of the region, a neural network classifying algorithm was developed from basin age-dependent spectra and texture. About 22% of the region is covered by 592 lakes (>1 ha), and at least 50% of the land surface is covered by 558 drained lake basins. Analysis of cores collected from basins indicates that (1) organic layer thickness and the degree of organic matter decomposition generally increases with basin age, and (2) SOC in the surface organic layer tends to increase with basin age, but the relation for the upper 100 cm of soil becomes obscured due to cryoturbation, organic matter decomposition, and processes leading to ice enrichment in the upper permafrost.

This paper presents data on physical conditions and carbon transport in a typical northeast Greenland fjord along with predictions of expected changes in the area due to climate change. The fjord has an average depth of 100 m; the maximum depth is 360 m, and a sill at a depth of 45 m is found at its entrance. Sea ice covers the fjord from early October to late July. The freshwater input to the fjord, occurring from June to September, is 1063 × 10⁶ m³ from the catchment area (3109 km²) and 440 × 10⁶ m³ from melting of sea ice. During the ice-free period this buoyancy input and mixing by wind and tides results in an estuarine circulation in which lighter low-salinity water is moved seaward above denser water from the Greenland Sea. The tidal amplitude is 0.8 to 1.5 m, and the transport of tides from the outer parts of the fjord to the inner parts is delayed less than 15 min due to low friction in the fjord system. During the ice-free period, a net carbon input of 15–50 t C d⁻¹ occurs in the outer region of the fjord due to transport from land and the adjacent Greenland Sea. A regional atmosphere-ocean model predicts a temperature increase of 6–8°C at the end of this century (2071–2100) that will lead to increase in freshwater runoff, thinning of the sea ice, and an increase in ice-free conditions from 2.5 mo to 4.7–5.3 mo in Young Sound. The increased freshwater input will greatly enhance the estuarine circulation and nutrient input to the fjord and is expected to increase biological productivity.

We review current understanding of dynamic interactions between environmental variables and stream benthic communities within glacierized alpine catchments to provide a context for the central theme of habitat complexity within alpine streams. We present a conceptual model summarizing the important links between environmental variables, from large-scale (regional/catchment) to stream-reach/patch-scale processes, to illustrate this physical habitat complexity. Existing alpine stream classification and zonation criteria are examined, and the environmental characteristics representative of the different stream classes are identified. The theme of habitat complexity is developed to assess the applicability of traditional (principally temperature-based) alpine stream classifications. These traditional classifications do not take into account spatial and temporal variations in water source contributions to alpine streams unless associated temperature changes occur. However, different hydrological stores and pathways impart other physical and chemical influences upon stream benthic communities that are overlooked by traditional classifications. We propose a new classification system to better describe spatial and temporal variability in glacial, snowmelt, and groundwater inputs to alpine streams, based upon the mix of proportions of water contributed from each of these sources. Field data collected in the French Pyrénées are used to support this new alpine stream classification, which we propose as a tool for further research in alpine river catchments.

Postindustrial rises in CO₂ have the potential to confound the interpretation of climatically sensitive tree-ring chronologies. Increased growth rates observed during the 20th century in strip-bark trees have been attributed to CO₂ fertilization. Absent in the debate of CO₂ effects on tree growth are spatially explicit analyses that examine the proximate mechanisms that lead to changes in rates of tree growth. Twenty-seven pairs of strip-bark and companion entire-bark trees were analyzed in a spatially explicit framework for abiotic environmental correlates. The strip-bark tree locations were not random but correlated to an abiotic proxy for soil moisture. The strip-bark trees showed a characteristic increase in growth rates after about 1875. Furthermore, the difference in growth rates between the strip-bark trees and entire-bark companions increased with increasing soil moisture. A possible mechanism for these findings is that CO₂ is affecting water-use efficiency, which in turn affects tree-ring growth. These results point to the importance of accounting for microsite variability in analyzing the potential role of CO₂ in governing growth responses.

Balsam poplar (Populus balsamifera) groves occur north of the Brooks Range and treeline in arctic Alaska in a region of continuous permafrost and tundra vegetation. A poplar grove near the Ivishak River (69°06′N, 147°53′W) that we studied in detail contains 11 clones within 350 m of the river. Individual clones range from 600 to 4500 m² in size and 90 to 200 yr in age. Poplar trees are larger in diameter in clones within 100 m of the river and less dense in clones away from the river. Unique soil thermal, moisture, and nutrient conditions may limit the expansion of poplar groves to only a few hundred meters from the river channel, including a “thaw bulb,” or depression in the permafrost table; lithologic discontinuities that concentrate moisture in the rooting zone; and accumulation of Ca-enriched precipitates from aufeis deposits. We prepared a map showing the distribution of poplar groves on the North Slope from published reports, satellite images, topographic maps, and observations of a bush pilot. The groves occur within an area bounded by 68–69°N and 142–154°W. A preliminary model explaining the origin and distribution of balsam poplar groves was developed from the case study; unpublished data; and a review of the geologic, hydrologic, and ecologic literature. The groves preferentially occur in areas where there is a sharp change in relief from the Brooks Range to the Arctic Foothills, extensive river braiding accompanied by geothermal springs and aufeis deposits, and a regional groundwater flow system enriched in Ca that may be controlled by faulting.

In a factorial field experiment we increased the temperature (Open Top Chambers) and nutrients (nitrogen, phosphorus, and potassium [NPK]) to simulate predicted future climate changes and studied the growth response of the acrocarpous bryophyte Pohlia wahlenbergii (Bryaceae) in a wet snowbed environment. The species shows a positive growth-length response to added nutrients and increased temperature. The stronger response to nutrients indicates a strong limitation of nutrients in the snowbed environment. There was an immediate response to nutrient treatment, whereas the temperature response was delayed. The growth response shows a clear interaction between temperature and nutrients. The immediate positive growth response is interpreted as a function of the wet habitat, since water makes the added nutrients immediately available to the plants. The growth form changed toward a more lax (loose) and desiccation-intolerant form with added nutrients. In a climate change scenario based on these results we hypothesize that bryophyte response will depend on the water availability from precipitation and from meltwater. In a drier environment we predict that bryophytes will become more constrained toward areas with a high continuity of meltwater, whereas increased precipitation may compensate for any changes in growth form, which would be positive for bryophytes.

Polychlorinated biphenyl (PCB) concentrations and congener profiles in terrestrial soils, vascular plants, and freshwater lake sediments were compared with respect to their relative utilities for assessing the redistribution of PCBs from a local contaminant source into the surrounding arctic environment.Plants (n = 62), soils (n = 58), and surficial freshwater lake sediments (n = 16) were collected at varying distances up to 27 km from the source at Saglek, Labrador. Total PCB concentrations in these media exhibited similar negative log-linear relationships with increasing distance from the contaminant source. Analysis of congener compositions indicated that plants are more reflective of recent PCB exposure than either soils or sediments. Vascular plants reflect current ambient contaminant concentrations, whereas terrestrial soils and freshwater sediments represent much longer periods of contaminant deposition and are further influenced by such factors as their organic carbon content, particle size distribution, lake watershed size and productivity (in the case of sediments), and proximity to a drainage course (in the case of soils). Collectively, the data indicate that short-range transport of PCBs at Saglek has resulted in a halo of contamination that is up to 50 km in diameter.

Is alpine plant development in spring controlled by photoperiod irrespective of actual temperatures at the time following snowmelt? We investigated phenological responses to day length and temperature in 33 high-elevation species of the Central Alps (2600–3200 m a.s.l.), Austria. Plants were collected in the field in August, potted, and overwintered in a freezer at −1°C. Released from dormancy, plants experienced various photoperiods (12, 14.5, 15, and 16 h) and two temperature regimes (6/11°C and 8/18°C). Day length was extended with tungsten lamps, which do not contribute a significant dose of photosynthetically active photon flux density but provide a day-length signal. Only 23 species produced sufficient flowers to be included in the analysis. Flowering (yes or no) was sensitive to photoperiod in 54% of the species. Surprisingly, only 24% of the species showed temperature sensitivity at longer photoperiods, whereas at shorter photoperiods, 65% of the species were sensitive to an increase in temperature. The number of days between thawing of soil and flowering is sensitive to photoperiod in 46% of the species. Cerastium uniflorum, Elyna myosuroides, Saxifraga oppositifolia, Saxifraga seguieri, and Ranunculus glacialis are insensitive to both photoperiod and temperature and thus flower as soon as released from the snow irrespective of co-occurring light and temperature conditions. Specific leaf area and the duration of leafing were responsive to photoperiod and temperature in forbs but not in grasses. These results suggest that about half of the tested alpine species are sensitive to photoperiod and may not be able to fully utilize periods of earlier snowmelt.

In polar semidesert communities of northwest Spitsbergen the reproductive potential of keystone vascular plant species, such as Dryas octopetala, is currently being constrained by low summer temperatures, resulting in the infrequent production of viable seeds. This study tests the hypothesis that summer foraging behavior of reindeer (Rangifer tarandus platyrhynchus) may further limit successful seed production due to intense selective grazing pressure on the flowering shoots. Surveys of neighboring coastal tundra areas with contrasting reindeer population densities revealed direct evidence of strong grazing pressure on reproductive shoots of D. octopetala on the Brøgger Peninsula and considerably less floral herbivory on the sparsely reindeer-populated Blomstrand island. Recruitment of Dryas on the Brøgger Peninsula is therefore being hindered by intense selective grazing of flowering shoots by Svalbard reindeer. This situation is not unique to this area of Svalbard and also extends to other species of flowering plants.

We investigated carbon isotope discrimination of two morphs of Saxifraga oppositifolia and other plant species in a glacier foreland in the High Arctic at Ny-Ålesund, Svalbard, Norway. At this site, soil conditions vary considerably along with the progress of primary succession within a small area. We compared growth forms and δ¹³C values, which reflect long-term leaf gas exchange characteristics, of plants growing in different successional stages with different soil conditions. Even though the soil mass water content (water mass/dry mass) increased from 10% to 140% with the progress of succession, the water and nitrogen content of the soil had negligible effects on the δ¹³C values of the observed species. The δ¹³C values were determined mainly by species and growth forms. We compared two morphs of S. oppositifolia, the prostrate form (P-form) and the cushion form (C-form), on the same riverbank in the glacier foreland. Regardless of the successional stage, the δ¹³C values of the C-form were about 2‰ more negative than those of the P-form. The ground cover area per plant mass (GA) of the C-form was less than 30% that of the P-form, and the product of GA and stomatal conductance appears to be an important factor in the relationship between transpiration and photosynthesis of a whole plant. We suggest that the relationship between GA and the root mass fraction is a crucial factor affecting the water utilization in high arctic environments. We also examined the relationship between life form and water utilization for other phototrophs, including lichens, mosses, narrow-leaved grasses, perennials, and shrubs.

We studied relationships between vegetation, substrate texture, and surface movement velocity in two active rock glaciers in the Central Alps (northern Italy). We also compared the vegetation on the two active rock glaciers with that of adjacent stable areas and with that of an inactive rock glacier. The vegetation patterns on the two active rock glaciers differed sharply from those on the stable areas nearby and on the inactive rock glacier with respect to both total plant cover and floristic composition. Surface movement on the two active rock glaciers ranged from 0–5 to 35–40 cm yr⁻¹ and was largely independent of slope inclination. The most unstable sites were almost free of mosses and lichens and were characterized by vascular species tolerating surface instability in virtue of varying morphological adaptations. However, the distributional pattern of vascular species could not be directly related to surface instability but depended on a combination of substrate texture and movement intensity.

We used integrated multiproxy analysis of a lake sediment core and glacial geomorphology to reconstruct the late Pleistocene and Holocene climate and geomorphic evolution of the Burstall Pass area, Kananaskis Country, Alberta, Canada. Analysis of macrofossils, pollen, sedimentology, and sediment geochemistry from a lake sediment core and geomorphology and tephrochronology of glacial moraines provide evidence for multiple modes of climate during the last ca. 11,000 yr. An advance of the Robertson Glacier prior to ca. 9200 ¹⁴C BP is correlated to the Crowfoot advance and was the largest of the postglacial period. Immediately following this event, increased lake productivity and the deposition of marl as well as increased arboreal/nonarboreal pollen (AP/NAP) ratios suggest that the climate warmed, possibly accompanied by increased aridity. Decreased turbidity and clastic sediment flux in Lower Burstall Lake during the early Holocene suggest reduced glacial runoff and may indicate the complete ablation of the Robertson Glacier shortly after 10,000 ¹⁴C BP. Clastic sediment flux to Lower Burstall Lake remained minimal until after ca. 3500 ¹⁴C BP, when decreasing LOI (loss-on-ignition) organic carbon levels in lake sediments signaled the return of glacial runoff to the lake system. The largest Neoglacial advance in the Burstall Pass area appears to have been the most recent and was followed by rapid recession during the 20th century.

We investigated the seasonal snow cover at six islands of Franz Josef Land in July 1995. Samples were chemically analyzed for major ions, pH, conductivity, fluoride, acetate, formate, and methane sulfonate. The chemical composition of the snow cover was dominated by sodium and chloride, which contributed up to 70% of the ion balance. Mean nitrate concentration was about 2 &mu= L⁻¹, and non-sea-salt sulfate ranged from 5 to 19 &mu= L⁻¹. Ion concentrations revealed a high local and seasonal variability, with peak concentrations attributed to spring and summer snow. We also found a high local variability for the water equivalent of the snow cover, with values between 14 and 118 cm, reflecting the strong influence of wind drift and redistribution of snow. The fractionation of ions during snowmelt was followed by sampling the snow cover at Salisbury Island at three stages of the snowmelt.