As a part of the national Norwegian monitoring program, long-term surveys of contaminants have been carried out at the Zeppelin atmospheric research station (Ny-Ålesund, Svalbard ) since the early 1990s. In the present study, all obtained data have been summarized and analyzed in order to review possible temporal trends for selected atmospheric contaminants at Svalbard. The following heavy metals were determined in aerosols: Pb, Cd, Hg, Cu, Zn, Cr, Ni, Co, Mn, V, and As. Only Ni showed a decreasing trend in the concentrations over the past decade. Organochlorine compounds in combined gaseous phase and aerosol samples evaluated were the following: α-HCH (hexachlorocyclohexane), γ-HCH, HCB (hexachlorobenzene), and sum-DDT (dichlorodiphenyltrichloroethane). Only those organochlorines exhibiting significant statistically confirmed temporal trends were chosen for the present comparison. Thus, although polychlorinated biphenyls (PCBs) as well as chlordanes are routinely monitored at the Zeppelin station, they were not considered for the here presented report because no clear trends were determined. Therefore all, but sum-DDT showed significant decreasing trends, correlating well with the national and international governmental regulations.

Nation-wide surveys of the accumulation of 10 heavy metals in mosses were carried out in Finland in 1985, 1990, 1995, and 2000. Separate investigations were carried out, on the basis of these surveys, into the atmospheric deposition of Hg, Cd, and Pb beyond the Arctic Circle in northern Finland. These metals are readily distributed in the form of long-range transboundary pollution, and particular concern has been raised about the transport and accumulation of these metals into Arctic areas. The Hg, Cd, and Pb concentrations in mosses in northern Finland were low. There was a clear decrease in Cd and Pb concentrations during the period 1985–2000. The Pb concentration decreased, on the average, from 8 to 2 μg g⁻¹, and the Cd concentration from 0.3 to 0.1 μg g⁻¹. Hg concentrations, which were analyzed in 1995 and 2000, decreased only slightly from 0.037 to 0.031 μg g⁻¹. The slight decrease in Hg concentrations in northern Finland appears to reflect the decreasing Hg emissions and the high mobility of this metal. Factors leading to the decrease in Pb and Cd concentrations in mosses in northern Finland include a decrease in local emissions and a decrease in transboundary air pollution. The past two decades have been characterized by decreases in heavy metal emissions of throughout Europe. The greatest reductions have been in Pb emissions, due to the introduction of unleaded fuels.

Tundra ecosystems constitute large stocks of carbon and might therefore, if climate warming releases CO₂, induce positive feedback and amplify temperature increase. We studied the effect of a 2.5°C temperature increment, induced by controlled infrared irradiation, on various components of the carbon balance of a High Arctic tundra ecosystem at Zackenberg in Northeast Greenland (74°N, 21°W) over the 1999 growing season. Gross photosynthesis (P_gross), belowground respiration (R_soil), and canopy respiration (R_canopy) were regularly determined with closed dynamic CO₂ exchange systems, and the whole-growing season C-balance was reconstructed by relating these components to potentially controlling factors (green cover, soil moisture, radiation, soil and canopy temperature, and thawing depth). Thawing depth and green cover increased in heated plots, while soil moisture was not significantly affected. P_gross increased 24.2%, owing to both a green cover and a physiological influence of warming. Belowground respiration was enhanced 33.3%, mainly through direct warming impact and in spite of lower Q₁₀ in the heated plots; the factors controlling R_soil were day of the year and soil moisture. R_canopy did not differ significantly between treatments, although green cover was higher in the heated plots. This tundra ecosystem acted as a relatively small net sink both under current (0.86 mol CO₂ m⁻²) and heated (1.24 mol CO₂ m⁻²) conditions. Nevertheless, turnover increased, which was best explained by a combination of direct and indirect temperature effects, and delayed senescence.

Respiration rates, thermal sensitivity, and thermal acclimation potential of root respiration were investigated in Ranunculus from the Arctic. Comparisons of three species (R. glacialis, R. nivalis and R. acris subsp. pumilus) used plants grown on a mountain or in a glasshouse for 6 wk at contrasting soil temperatures (5.4 and 14.5°C, respectively). Northern and southern ecotypes of two species of Ranunculus (R. pygmaeus, and R. acris subsp. acris), together ranging from Svalbard (79 °N) to Scotland (56°N), were similarly compared after 2 wk in a growth cabinet at 5 and 15°C. Respiration rates varied at standard measurement temperatures; R. nivalis and R. pygmaeus grown on the mountain or at 5°C had the highest respiration, followed by other alpine snowbed species (R. glacialis and R. acris subsp. pumilus) and R. acris subsp. acris from the arctic lowland; R. acris subsp. acris from Scotland had lowest rates. Respiration was temperature sensitive for all populations, increasing progressively between 5 and 20°C (Q_{10 (5–15)}: 1.2–2.4).

Extent and type of acclimation of root respiration varied with no clear latitudinal pattern emerging. Acclimation to a 10°C increase in growth temperature was achieved through: change in temperature sensitivity (shown by changes in Q_{10 (5–15)} values) (R. acris subsp. pumilus); or reduction in absolute rates (R. pygmaeus from Svalbard, R. acris subsp. pumilus and R. nivalis). Complete acclimation occurred in R. acris subsp. pumilus and R. pygmaeus, whereas R. acris subsp. acris from Scotland and R. glacialis did not acclimate. Plants that adjust root respiration (e.g., R. pygmaeus from Svalbard and R. acris subsp. pumilus) to maintain a positive carbon balance, may tolerate predicted temperature increases in arctic regions. Plants with high rates of root respiration and/ or high sensitivity to temperature as well as poor acclimation potential, (e.g., R. glacialis) may only persist in cold microhabitats.

GIS-based data sets were used to analyze the structure of the forest line at the landscape level in the lowlands of the Usa River Basin, in northeast European Russia. Vegetation zones in the area range from taiga in the south to forest-tundra and tundra in the north. We constructed logistic regression models to predict forest location at spatial scales varying from 1 × 1 km to 25 × 25 km grid cells. Forest location was explained by July mean temperature, ground temperature (permafrost), yearly minimum temperature, and a Topographic Wetness Index (soil moisture conditions). According to the models, the forest line follows the +13.9°C mean July temperature isoline, whereas in other parts of the Arctic it usually is located between +10 to +12°C. It is hypothesized that the anomalously high temperature isoline for the forest line in Northeast European Russia is due to the inability of local ecotypes of spruce to grow on permafrost terrain. Observed patterns depend on spatial scale, as the relative significance of the explanatory variables varies between models implemented at different scales. Developed models indicate that with climate warming of 3°C by the end of the 21st century temperature would not limit forest advance anywhere in our study area.

The study focuses on vegetation changes in the Nordic mountain birch forest in northern Norway, covering a period of more than 40 yr. The study area comprises the municipalities of Kautokeino and Karasjok on Finnmarkskvidda; it is predominantly covered by lichen and dwarf shrub vegetation. Sizes of various vegetation classes were estimated by the use of remote-sensing techniques and ground surveys. A significant change in vegetation cover during the study period was registered in the whole study area. Vegetation types dominated by bilberry (Vaccinium myrtillus), wavy hair-grass (Deschampsia fleuxuosa), the dwarf cornel (Cornus suecica), and mosses have tripled in abundance compared to 40 yr ago. In contrast, lichen-dominated heaths and woodland (forests), preferred by the reindeer stocks intensively utilizing these areas of Finnmarksvidda, have decreased by approximately 80% in abundance during the same period. Correspondingly, there has been a significant increase in the extent of birch forests especially in Kautokeino (90% increase). The reason for the steep decline in lichen-dominated areas appears to be a direct consequence of the intensive grazing by the increasing reindeer population in the period 1961–1987, but climate change (increased precipitation), caterpillar attacks, and long-transported air pollution (e.g., nitrogen) may also have accentuated the increase of forests and other vegetation types.

Winter climate is a key factor affecting population dynamics in high-arctic ungulates, with many studies showing a strong negative correlation of winter precipitation to fluctuations in population growth rate. Terrestrial ice crust or ground-ice can also have a catastrophic impact on populations, although it is rarely quantified. We assess the impact of winter climate on the population dynamics of an isolated herd of Svalbard reindeer near Ny-Ålesund with a retrospective analysis of past winter snowpack. We model landscape-scale snowpack and ground-ice thickness using basic temperature and precipitation data in a simple degree-day model containing four adjustable parameters. Parameter values are found that lead to model snow and ground-ice thicknesses which correlate well with three different model targets: reindeer population growth rates; April snow accumulation measurements on two local glaciers; and a limited number of ground-icing observations. We explain a significant percentage (80%) of the variance in the observed reindeer population growth rate using just the modeled mean winter ground-ice thickness in a simple regression. Adding other explanatory parameters, such as modeled mean winter snowpack thickness or previous years' population size does not much improve the regression relation.

In this work we report the vertical phytoplankton biomass distribution (chlorophyll a depth-profiles) and the integrated phytoplankton biomass (chlorophyll a per unit area) of two high-mountain Mexican Lakes: El Sol and La Luna (19°06′N, 99°45′W, 4200 m a.s.l.). El Sol and La Luna are transparent, nonglacier-fed lakes. Both lakes are continuous warm polymictic with a uniform vertical distribution of phytoplankton biomass. Slight heterogeneities were observed in El Sol with a deep-water chlorophyll maximum above the sediments (maximum difference 0.71 μg L⁻¹) associated to phytoplankton sunken cells and the presence of filamentous benthic algae. Phytoplankton biomass per unit area was low in both lakes (El Sol 1.91–8.36 and La Luna 1.13–4.80 mg Chla m⁻²), and similar to that of temperate high-mountain lakes. The temporal variations in the phytoplankton biomass were attributed mainly to a combined effect of nutrient input and zooplankton grazing pressure; the effect of low pH is also considered in La Luna.

Observational series and downscaled scenarios of air temperature are used to describe long-term variations 1900–2050 in different climatic indices that are important for the living conditions in the Nordic Arctic (Northern Fennoscandia, Svalbard, Faeroe Islands, and the Greenland-Iceland-Norwegian Sea regions). In addition to air temperature; indices illustrating vegetation conditions (growing season), energy consumption (heating season), and frost conditions (freezing season) are studied. The analyses are based on smoothed daily temperature series deduced from monthly averages for 27 Nordic climate stations, and are focusing on conditions in the climatological 30-yr reference periods 1901–1930, 1931–1960, and 1961–1990, and the scenario period 2021–2050. Also values for two recent time periods (1976–2000 and 1990–2002) are included. The results show substantial variations in growing, heating and freezing indices in the Nordic Arctic during the 20th century. Compared to the period 1961–1990, the growing season has increased during the recent decades in large parts of the region. Projections up to 2050 indicate that the growing season may increase by 3 to 4 wk at most of the stations in the region. The heating season has been reduced during the latest decades, and the projections indicate a further reduction during the next 50 yr.

The paper briefly presents a methodology for mapping surface UV radiation that uses a radiative transfer model and satellite data to quantify the influencing factors. TOMS, TOVS, and GOME data are used for the total column ozone. The cloud optical thickness is estimated using METEOSAT/MVIRI images. Other influencing factors taken into account include tropospheric aerosols, snow cover, and surface elevation. The resulting products are maps of surface dose rates and daily doses, covering Europe with a spatial resolution of 0.05°. On this basis, construction of a European UV climatology has been undertaken, with the purpose of supporting impact studies on the environment and human health. The data set covers the period from 1 January 1984 to 31 August 2003. A comparison between the satellite estimates and the measurements in Ispra, Italy, is briefly presented. Finally, examples of how the climatological data set can document the geographical distribution and year-to-year variability in surface UV radiation are presented.

This study investigates effects of reducing the ambient UV radiation on gas exchange and chlorophyll fluorescence of two shrub species, Salix arctica and Vaccinium uliginosum, in a high arctic heath in Northeast Greenland in July and August. On two sites films, Mylar and Lexan, were used to reduce UV-B radiation and UV-B + A radiation, respectively. A UV transparent film, Teflon, and no film were used as controls. Field measurements showed that the plants under Teflon, Mylar, and Lexan received approximately 91, 39, and 17% of the ambient UV-B irradiance, respectively. Reduced UV radiation increased maximal photochemical efficiency (F_v/F_m) in both species. The responses varied in significance according to species, sites and time of growing season. Net assimilation (P_n), measured as net CO₂ uptake, was not significantly affected. But over the whole growing season stomatal conductance and intercellular CO₂concentration were decreased by both UV treatments. The underlying mechanisms for these results are discussed. PAR-irradiance had a negative influence on the absolute values of F_v/F_m. A positive correlation was found between F_v/F_m and P_n measured at ambient CO₂-level. It is concluded that it cannot be excluded, that the observed short-term effects could result in long-term negative effects on growth and survival for the investigated species.

Daphnia was collected from five subarctic ponds which differed greatly in their DOC contents and, consequently, their underwater light (UV) climates. Irrespective of which Daphnia species was present, and contrary to expectations, the ponds with the lowest DOC concentrations (highest UV radiation levels) contained Daphnia with the highest eicosapentaenoic acid (EPA) concentrations. In addition, EPA concentrations in these Daphnia generally decreased in concert with seasonally increasing DOC concentrations.