After more than half a century of paleoenvironmental investigations, disagreements persist as to the nature of vegetation type and climate of the Bering land bridge (BLB) during the late Wisconsin (Sartan) glacial interval. Few data exist from sites on the former land bridge, now submerged under the Bering and Chukchi Seas. Two hypotheses have emerged during the past decade. The first, based on pollen data from Bering Sea islands and adjacent mainlands of western Alaska and Northeast Siberia, represents the likely predominant vegetation on the Bering land bridge during full-glacial conditions: graminoid-herb-willow tundra vegetation associated with cold, dry winters and cool, dry summer climate. The second hypothesis suggests that dwarf birch-shrub-herb tundra formed a broad belt across the BLB, and that mesic vegetation was associated with cold, snowier winters and moist, cool summers. As a step towards resolving this controversy, a sediment core from Norton Sound, northeastern Bering Sea was radiocarbon dated and analyzed for pollen content. Two pollen zones were identified. The older, bracketed by radiocarbon ages of 29,500 and 11,515 ¹⁴C yr BP, contains pollen assemblages composed of grass, sedge, wormwood, willow, and a variety of herb (forb) taxa. These assemblages are interpreted to represent graminoid-herb-willow tundra vegetation that developed under an arid, cool climate regime. The younger pollen zone sediments were deposited about 11,515 ¹⁴C yr BP, when rising sea level had begun to flood the BLB. This younger pollen zone contains pollen of birch, willow, heaths, aquatic plants, and spores of sphagnum moss. This is interpreted to represent a Lateglacial dwarf birch-heath-willow-herb tundra vegetation, likely associated with a wetter climate with deeper winter snows, and moist, cool summers. This record supports the first hypothesis, that graminoid-herb-willow tundra vegetation extended into the lowlands of the BLB during full glacial conditions of the late Wisconsin.

Lakes are dynamic processors of nutrients and may hold an active role in modifying the water chemistry of stream systems. In this study, we examine the influence of lakes and an important terrestrial component—forest cover—on the nutrient levels of stream water in 11 Rocky Mountain (Idaho) watersheds. Water samples were collected from the inflow and outflow of lakes with varying amounts of upstream lakes and forested area during spring runoff and summer base flow. During base flow, mean total nitrogen concentrations at the inflow of final lakes were significantly related to relative upstream lake area, increasing from 34 to 103 µg N L⁻¹ as upstream lake cover in the watersheds increased from 0% to 4%. Forest cover was not significantly correlated with total nitrogen concentrations exported from the watersheds. However, similar to other studies, inflow nitrate concentrations were negatively correlated with relative forest cover. At the scale of individual lakes, dissolved organic carbon and dissolved organic nitrogen increased, and nitrate was significantly reduced from inflows to outflows. The results indicate a potentially critical role of mountain lakes in governing nitrogen flux downstream, and suggest the role of lakes as nitrogen sinks or sources may reverse between spring runoff and summer base flow.

This study documents the spatiotemporal distribution of free-living nematodes in glacial-fed river reaches (Möll River, Austrian Alps), which is a widely neglected topic in glacial-fed stream research. Benthic nematodes of the meta- and hypokryal, in a lotic reach within a glacially formed floodplain and in the glacio-rhithral, were investigated in spring, summer, and autumn 2005. The overall nematofauna was diverse and dense with 77 species, H′ of 2.7, and mean abundance of 86 individuals per 10 cm². Nematode community parameters were significantly influenced by sites, but not by seasons. At the kryal sites, nematode overall mean abundances slightly increased from the metakryal (8 ind. per 10 cm²) to the hypokryal (11 ind. per 10 cm²), but species number decreased (from 15 species to 6 species). Nematodes became more dense and diverse in both the glacio-rhithral (overall mean: 49 ind. per 10 cm²; 52 total species) and the floodplain reach (overall mean: 251 ind. per 10 cm²; 65 total species). Species composition and dominant species differed among the four sites. Deposit feeders represented the dominant feeding type at each site. The lowest maturity index reflected the harsh character of the recently deglacierized meta- and hypokryal sites.

We examined the influence of leaf size on forage selection by collared pikas (Ochotona collaris) living in alpine meadows in the Yukon Territory, Canada, by comparing the winter diets of individually recognized pikas to the available vegetation within their territories and by conducting cafeteria-style preference experiments. Pikas consistently preferred forage with larger leaves in the cafeteria trials. They also collected larger leaves from deciduous shrubs and graminoid species compared to other plant types such as lichens and evergreen shrubs for their winter diets. Pikas assessed differences in leaf size when selecting their winter diets and this appears to be an energetically efficient foraging strategy for surviving seasonal food scarcity.

Information about the annual carbon fluxes of fen and meadow ecosystems in alpine environments is rare. We studied the influence of photosynthetic active radiation (PAR), plant green area index (GAI), soil temperature, and water-filled pore space (wfps) on the net CO₂ emission at four alpine sites (one meadow and three fen sites) differing in water balance and plant community. Measurements over two years were made in the Eastern Alps, Austria, including two snow-free periods and two snow periods. During snow-free periods, net CO₂ gain during daylight periods (NEE_light, PAR > 0) depended on PAR and GAI. The net CO₂ emission rate at night (R_tot, PAR  =  0) was positively related to soil temperature, while low wfps reduced the carbon loss via R_tot of the meadow and driest fen study site but reinforced carbon loss of the wetter fen sites. Daily average ecosystem net CO₂ gain (NEE_day) during snow-free periods (averaged over both years) at the meadow was 3.5 g CO₂ m⁻² d⁻¹ and ranged from 1.5 to 3.4 g CO₂ m⁻² d⁻¹ at the fen sites. Mean average daily wintertime CO₂ emission was low, being only −0.9 g CO₂ m⁻² d⁻¹ for meadow and between −0.2 and −0.7 g CO₂ m⁻² d⁻¹ for all fen sites. All sites function as significant annual net carbon sinks, with a net carbon gain from 50 to 121 g C m⁻² a⁻¹ (averaged over both years) irrespective of water balance. Our results indicate that these alpine fen sites that have built up a large carbon stock in the past do not gain a further carbon surplus compared with the meadow under the current climate.

Palynological (species assemblage, pollen accumulation rate), geochemical (carbon to nitrogen ratios, organic carbon and biogenic silica content), and sedimentological (particle size, magnetic susceptibility) data combined with improved chronology and greater sampling resolution from a new core from Elikchan 4 Lake provide a stronger basis for defining paleoenvironmental changes than was previously possible. Persistence of herb-dominated tundra, slow expansion of Betula and Alnus shrubs, and low percentages of organic carbon and biogenic silica suggest that the Late-Glacial transition (ca. 16,000–11,000 cal. yr BP) was a period of gradual rather than abrupt vegetation and climatic change. Consistency of all Late-Glacial data indicates no Younger Dryas climatic oscillation. A dramatic peak in pollen accumulation rates (ca. 11,000–9800 cal. yr BP) suggests a possible summer temperature optimum, but finer grain sizes, low magnetic susceptibility, and greater organic carbon and biogenic silica, while showing significant warming at ca. 11,000 cal. yr BP, offer no evidence of a Holocene thermal maximum. When compared to trends in other paleo-records, the new Elikchan data underscore the apparent spatial complexity of climatic responses in Northeast Siberia to global forcings between ca. 16,000 and 9000 cal. yr BP.

This paper deals with a two-year study of karst soils and eolian dust deposition on the Reiteralpe paleosurface (1600 to 2000 m), Northern Calcareous Alps, Germany. Thirty soil profiles of Cambisols developed on Triassic and Cretaceous limestones are investigated. Dust samples collected periodically on snow cover provide influx rates and a seasonal dust record. Samples of soils, insoluble bedrock residue, and dust are characterized by pedological (e.g. grain size) and mineralogical (e.g. heavy minerals) data.

The data indicate that limestone subtypes with varying crack-fillings (ferrous clays) determine the colors and amounts of residue. Both correlate positively with the thickness of reddish Bo-horizons, supporting their autochthonous character. The topsoils, however, show substantial eolian addition (silt, fine sand, mica). In winter, far-traveled red Saharan dust without organic material prevails, carried to the area by strong foehn winds. In early springtime, browner dust (organic rich) is observed which contains periglacial silicate-rich detritus from regional sources such as the Crystalline Austrian Alps.

The measured winter dust influx rates are 4.8 cm per 10,000 years (related to 210 winter days). This is more than twice the calculated thickness of Holocene residue accumulation out of limestone weathering (2.3 cm per 10,000 years, related to 210 winter days), which indicates that eolian dust is a major contributor to alpine karst soil development.

Shallow seismic refraction (SSR) and ground penetrating radar (GPR) are non-invasive geophysical techniques that enhance studies of the shallow subsurface deposits which control many geomorphic and biogeochemical processes. These techniques permit measuring the thickness and material properties of these deposits in sensitive alpine areas without using extensive pits and trenches that can impact current biogeospheric processes or distort them for future research. Application of GPR and SSR along 1.5 km of geophysical lines shows that layers of fine to coarse, blocky deposits of periglacial origin underlie alpine slopes in the vicinity of Niwot Ridge, Colorado Front Range. Interpretation of geophysical and drilling data shows that depth to bedrock ranges from 4 to >10 m and is not simply related to local slope. Our measurements suggest that ice lenses form seasonally beneath solifluction lobes; ice was not present in adjacent areas. Ice lenses are associated with local ponded water and saturated sediments that result from topographic focusing and low-permeability layers beneath active periglacial features. Geophysical interpretations are mainly consistent with data derived from nearby drill cores and corroborate the utility of GPR in combination with SSR for collecting subsurface data required by different landscape models in sensitive alpine environments.

This study examines current subglacial biogeochemical weathering models using PHREEQCi, a computer-based speciation mass-balance (SMB) model, parameterized using hydrochemical and mineralogical field data from Haut Glacier d'Arolla, Switzerland. The aim is to investigate the utility of SMB models for quantifying subglacial biogeochemical mechanisms, and the mathematical and thermodynamic robustness of current subglacial weathering models in a temporally variable, spatially heterogeneous hydrological and geochemical subglacial environment.

The chemical evolution of meltwaters between their source in the supraglacial environment and their output from the hydroglacial system as bulk meltwaters are modeled, and compared with in situ meltwaters collected from the base of boreholes drilled to the glacier bed. SMB modeling produced a broad range of weathering outcomes, but delivered no unique weathering scenario which could account for the observed changes in water chemistry between input and output waters over the ablation season. Organic carbon oxidation and sulfide oxidation by dissolved O₂, coupled to carbonate dissolution and incongruent silicate dissolution, could account for seasonal changes in meltwater chemistry, supporting current subglacial biogeochemical weathering models. Atmospheric CO₂ was not required under any weathering scenario, and organic carbon and atmospheric CO₂ dissolution was only possible in one weathering scenario, at a mass ratio of 10:1, further suggesting that CO₂-driven dissolution is unimportant in subglacial environments. This investigation indicates the utility of SMB models applied to subglacial hydrological systems for determining geochemical and biogeochemical processes and interpreting water quality.

This study uses geomorphological, dendrochronological, and archival research to investigate the pattern, chronology, and sedimentology of debris-flow deposits in two reaches of the Zailiiskiy Alatau range of the Tien Shan mountains, Kazakhstan. Steep and narrow low-order tributary valleys in this environment promote rapid coarse sediment transfer to trunk streams and, in wider trunk valley reaches, locally result in development of debris-flow assemblages and terraced sequences of coarse-grained fluvial sediments. Since the mid-19th century the region has experienced 23 documented large-scale debris flows, including 14 in the study area, and these coincide with a period of climate warming. The majority of recorded events are attributed to the failure of moraine-dammed lakes, while the remainder were triggered by intense summer rainstorms. Landform-sediment assemblages investigated here have extended the documentary record by identifying at least 6 major debris-flow assemblages dating respectively from sometime before the early 17th century, ca. 1607–1633, ca. 1702–1728, ca. 1725–1751, ca. 1769–1795, and the mid–late 18th century. The geomorphological record of debris flows spanning the 17th to 19th centuries indicates therefore that high-magnitude events occurred also during the cooler climatic conditions of the Little Ice Age, although it is suggested that these events may have coincided with short-lived phases of glacier retreat. Debris flows in this environment may be considered as an important component of the paraglacial response to glacier recession, and this has clear implications for future patterns of valley floor development and its interaction with human activity.

We investigated relationships between an evergreen dwarf shrub Vaccinium vitis-idaea and infection frequency of its annual specific pathogenic fungus Exobasidium splendidum, and environmental conditions in six boreal and subarctic populations in Finland during 1998–2002. The aim was to explore how environmental factors and plant characteristics influence the infection frequency of the rare pathogen in nature. Climate data, soil organic matter, and plant characteristics were recorded along with annual demographic observations on V. vitis-idaea ramet dormancy, growth, flowering and fungal infection. Infection frequency of E. splendidum in V. vitis-idaea populations varied between 0 and 4.8% and increased with decreasing temperatures. Along with low air temperature, high concentration of NH₄ , low concentration of P, high cover of bare ground, and high density of V. vitis-idaea were positively associated with the frequency of E. splendidum in V. vitis-idaea populations. Diseased ramets were at greatest risk of being reinfected by the fungus. The results indicate that both environmental factors and plant characteristics can constrain the distribution of the rare pathogen. Although an observational study of this kind does not allow us unequivocally to identify causality underpinning complex plant-pathogen-environment relationships, we can speculate that a further decrease in the frequency of E. splendidum infections will occur under climate warming.

Snow properties such as snow density will likely change in a warmer climate. Changes in depth and extent of snow cover have been shown to affect soil nutrient dynamics and plant growth; however, effects of a changed snow density have so far not been explicitly tested. We altered snow properties (especially depth and density according to those found on ski runs) and investigated effects on soil temperatures, soil nitrogen mineralization, plant phenology, and productivity. A denser, thinner snow cover led to reduced soil insulation and lower soil temperatures, which consequently increased net N mineralization. A denser snow cover furthermore resulted in a delay in plant phenology of up to five weeks after melt-out. The results suggest that changes in snow density, which have been largely neglected in the global change discussion until now, can cause significant changes in soil and vegetation processes.

Arbuscular mycorrhizal (AM) and dark-septate endophytic (DSE) fungi were quantified in plant roots from high-elevation sites in the Cordillera Vilcanota of the Andes (Perú) and the Front Range of the Colorado Rocky Mountains (U.S.A.). At the highest sites in the Andes (5391 m) AM fungi were absent in the two species of plants sampled (both Compositae) but roots of both were heavily colonized by DSE fungi. At slightly lower elevations (5240–5250 m) AM fungi were present in roots while DSE fungi were rare in plants outside of the composite family. At the highest sites sampled in Colorado (4300 m) AM fungi were present, but at very low levels and all plants sampled contained DSE fungi. Hyphae of coarse AM fungi decreased significantly in plant roots at higher altitude in Colorado, but no other structures showed significant decreases with altitude. These new findings indicate that the altitudinal distribution of mycorrhizal fungi observed for European mountains do not necessarily apply to higher and drier mountains that cover much of the Earth (e.g. the Himalaya, Hindu Kush, Andes, and Rockies) where plant growth is more limited by nutrients and water than in European mountains. This paper describes the highest altitudinal records for both AM and DSE fungi, surpassing previous reported altitudinal maxima by about 1500 meters.

Arctic and subarctic ecosystems have undergone considerable environmental changes in recent years as the result of climate warming. Fossil records of freshwater diatoms in lakes throughout the circumpolar Arctic, including the central Canadian Arctic treeline region, have revealed marked directional shifts in diatom assemblages in recent lake sediments. These algal changes have been linked to longer growing seasons, decreased duration of ice cover, and/or increased thermal stability. The effects of these recent environmental changes on higher trophic levels, such as the Cladocera, are still unclear. Using cladoceran remains preserved in the sediments of 50 lakes, which were previously examined for changes in diatoms, we show that significant changes in cladoceran species composition have occurred from pre-industrial times to the present. However, these changes are considerably muted compared to the more substantial changes observed in the diatom record. We found no consistent patterns of change in planktonic cladocerans (i.e. Daphnia, Bosmina) within our study lakes, and the response of the Cladocera to environmental changes does not appear to be strongly coupled to recent changes in diatom communities, thus further confirming that the previously observed diatom changes were related to bottom-up limnological controls. These results highlight the complex response of Arctic freshwater food webs to climate change, and the need for incorporating multi-trophic studies into climate change investigations.

The two native Antarctic vascular plant species, Colobanthus quitensis and Deschampsia antarctica, were sampled from 15 points along a 1480 km latitudinal transect from South Georgia (54°S, 36°W) through to the Léonie Islands on the western Antarctic Peninsula (67°S, 68°W). Roots of plants were cleared and stained and fungal structures recorded. The commonest type of fungal association was that formed by dark septate endophytes (DSE): 32% and 27% of the root lengths of C. quitensis and D. antarctica were colonized by hyphae of these fungi, respectively. Hyaline and stained septate hyphae were also common in roots. Coarse and fine arbuscular mycorrhiza (AM) occurred in the roots of both plant species from South Georgia, and fine AM colonization with occasional arbuscules was also sporadically recorded in roots from the South Shetland Islands, suggesting functional associations between higher plants and AM symbionts. Fungal abundances were not associated with soil chemistry, but AM abundance was associated with seasonal surface air temperature, with lower colonization in more southerly, colder habitats. We conclude that DSE are widespread, and that AM fungi are sparse but present and decline in abundance at higher latitudes, in the roots of C. quitensis and D. antarctica.