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Showing papers in "Arctic, Antarctic, and Alpine Research in 2001"



Journal ArticleDOI
TL;DR: In this article, the structure, formation, and the darkening process of the Cryoconite on a Himalayan glacier were analyzed, and it was revealed to be a stromatolite-like algal mat, a product of microbial activity on the glacier.
Abstract: Dark-colored material (cryoconite) covering Himalayan glaciers has been reported to greatly accelerate glacier-melting by reducing surface albedo. Structure, formation, and the darkening process of the cryoconite on a Himalayan glacier were analyzed. The cryoconite was revealed to be a stromatolite-like algal mat, a product of microbial activity on the glacier. The granular algal mat contains filamentous blue-green algae (cyanobacteria) and bacteria, and grows on the ice by trapping mineral and organic particles. This structure seems to enable high algal production in nutrient poor glacial meltwater by gathering and keeping nutrient rich particles inside. The dark coloration of the mats promotes melt-hole formation on the ice (cryoconite holes), providing a semistagnant aquatic habitat for various algae and animals in the glacier. Optical and chemical analyses of the cryoconite strongly suggests that their high light- absorbency (dark coloration) is mainly due to dark-colored humic substances, residues from bacterial decomposition of the algal products and other organic matter. Our results strongly suggest that biological activity on the glacier substantially affects the albedo of the glacier surface. The structure of the algal mat seems to be important in the glacier ecosystem and biological process affecting glacier albedo.

247 citations


Journal ArticleDOI
TL;DR: The n-factor, or ratio of the seasonal degree-day sum at the soil surface to that in the air at standard screen height, has been used for more than 40 yr in engineering studies to parameterize the...
Abstract: The n-factor, or ratio of the seasonal degree-day sum at the soil surface to that in the air at standard screen height, has been used for more than 40 yr in engineering studies to parameterize the ...

151 citations


Journal ArticleDOI
TL;DR: In this article, over 80 lakes were sampled between the ice margin and the coast in West Greenland between 66 and 67°N and analyzed for their pH, alkalinity, conductivity, and major ions.
Abstract: Over 80 lakes were sampled between the ice margin and the coast in West Greenland between 66 and 67°N and analyzed for their pH, alkalinity, conductivity, and major ions. Most of the lakes (67%) ar...

106 citations


Journal ArticleDOI
TL;DR: In this article, plant species richness and foliage production were studied with respect to N and P additions in three alpine communities varying in snowpack depth and duration, and the effects were also measured in conjunction with a snowpack enhancement experiment.
Abstract: The extent to which nutrient limitation affects species composition, abundance, and productivity of the alpine tundra is an ongoing area of ecological inquiry. At Niwot Ridge in the Front Range of Colorado, plant species richness and foliage production were studied with respect to N and P additions in three alpine communities varying in snowpack depth and duration. These effects were also measured in conjunction with a snowpack enhancement experiment. Measurements of plant responses were made 4 yr following the initiation of the manipulations. The addition of either N or P enhanced plant foliage productivity (P = 0.05 and P = 0.03, respectively). Nitrogen additions had a negative effect on the species richness censused in 1-m2 plots (P 0.60). Snowpack did not affect foliage productivity (P = 0.20), but species richness was negatively affected (P < 0.001). Snowpack also appeared to mediate species-specific responses to N and P additions. In the alpine, the relationship between species diversity and plant productivity is mediated by species-specific traits. After 4 yr, the increased production by plant species sensitive to P additions did not reduce species richness. This suggests that production-induced competitive exclusion is not a generalization that can be used to explain the decline in species richness. Moreover, the reduction in species richness due to N addition occurred across all of the tundra communities studied here.

104 citations


Journal ArticleDOI
TL;DR: A detailed inventory of peatlands by aerial photography shows that peatland with climatically sensitive localized islands of permafrost cover 17,505 km2 within a broad band of occurrence in continental western Canada (Alberta, Saskatchewan, and Manitoba) as discussed by the authors.
Abstract: Detailed inventory of peatlands by aerial photography shows that peatlands with climatically sensitive localized islands of permafrost cover 17,505 km2 within a broad band of occurrence in continental western Canada (Alberta, Saskatchewan, and Manitoba). Within this zone, 37.5% of the total area covered by bog, and 9.1% of total area covered by fen have localized permafrost landforms (frost mounds and/or internal lawns). Regional distribution of the presence/absence of localized permafrost peatlands relative to expansive peat plateaus (peatland completely underlain by permafrost) shows that a north to south landform gradient exists that is dominantly controlled by mean annual temperature. Percent cover of localized permafrost peatland in an area is best explained by the amount of total peatland cover that can support it. Localized permafrost is associated with collapse forms (internal lawns) throughout the range of its occurrence in western Canada. In some locations permafrost has completely melted, moving the current southern limit of permafrost north by 39 km on average, and by as much as 200 km.

94 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined the influence of catchment characteristics on water chemistry and found that water chemistry appeared to be mainly determined by (1) chemical weathering of carbonate minerals and (2) in-lake productivity.
Abstract: Forty-four lakes in the Austrian Alps were studied to examine the influence of catchment characteristics on water chemistry. The lakes are located along an altitudinal gradient (1502-2309 m a.s.l.) in a small study area (35.5 km * 15.5 km) without glaciers. Longitude and latitude accounted for 21.4% of the variation in water chemistry. Bedrock mineralogy explained 14.5% of the variation. Vegetation accounted for 13.2% and slope for 5.5% of the variation in water chemistry. No correlations were found between exposure and water chemistry. Water chemistry appeared to be mainly determined by (1) chemical weathering of carbonate minerals and (2) in-lake productivity. Carbonate minerals were assumed to be present in all watersheds. Trees and shrubs enhanced chemical weathering. Concentrations of chemical parameters indicating physical weathering were high in lakes with large, steep catchments. Steep watersheds were correlated with enhanced nitrogen concentrations in the lakes. In-lake productivity obscured relationships between chemical parameters and catchment characteristics. Nonetheless, catchment characteristics explained 45% of the variation in water chemistry, stressing their importance for water chemistry in mountain lakes.

83 citations


Journal ArticleDOI
TL;DR: In this article, a 30-yr photogrammetric monitoring series of a thermokarst lake in the Gruben area, Swiss Alps, is presented, where the lake reached a final size of ca. 10,000 m² in area and 50,000m³ in volume before it had to be drained artificially in 1995.
Abstract: Thermokarst lakes, a characteristic landscape element of the Arctic, are rarely found outside arctic situations. Here, a 30-yr photogrammetric monitoring series of a thermokarst lake in the Gruben area, Swiss Alps, is presented. The lake, situated in an environment of dead-ice remains and creeping permafrost, reached a final size of ca. 10,000 m² in area and 50,000 m³ in volume before it had to be drained artificially in 1995. Starting in the mid-1960s it grew with radial rates of ca. 1.5 to 5 m yr⁻¹. Nonlinear coupling of lake diameter and energy turnover led to accelerated area growth. The development of the lake was presumably driven by thermal convection of water. By a dynamic model of lake growth, we show that a change in climate conditions and/or the lake bottom topography could have significantly influenced the observed lake growth. The effective energy turnover used for ice-melt and subsequent lake growth was estimated to be in the order 10⁰ to 10¹ W m⁻².

66 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe the differences in selected soil properties, ground cover, grass tussock structure, and populations of giant Andean rosettes (Espeletia pycnophylla) in four paramo sites in northwestern Ecuador, characterized by contrasting patterns of burning and grazing.
Abstract: High-altitude grasslands in the north Andes (pairamos) are subject to frequent fires that are usually set by farmers to support traditional cattle-raising systems. Apparently, this practice has caused dramatic changes in the structure and composition of native vegetation, but the mechanisms, magnitude, and direction of these changes still need to be documented for a broader range of conditions. This paper describes the differences in selected soil properties, ground cover, grass tussock structure, and populations of giant Andean rosettes (Espeletia pycnophylla) in four paramo sites in northwestern Ecuador, characterized by contrasting patterns of burning and grazing. The only differences between the soil properties of the sites were the higher pH in the least disturbed site, and the high concentration of P in the more recently burned site. Along the sequence of least impacted to most impacted sites, we observed a decrease in grass tussock cover, and an increase in the amount of bare ground and number of fragments per tussock. In the most undisturbed site tussock coverage was extremely low due to the dominance of shrubs. The density of giant Andean rosettes was higher in the sites with intermediate disturbance regimes, while the mortality of adult stem rosettes was significantly higher at the more recently burned site. The significance of these differences is discussed in the context of the regeneration of pairamo vegetation after burning and grazing disturbance.

59 citations


Journal ArticleDOI
TL;DR: In this article, Radiocarbon dating assigns the high marine levels a B0lling Interstadial age of ca. 12.6 + 0.1 ka BP, which is close to previously estimated Last Glacial Maximum (LGM) ice thickness.
Abstract: New geologic data from western Iceland reveal raised marine terraces at elevations between 105 and 148 m a.s.l., 45-80 m above the late Younger Dryas (ca. 10.3 ka BP) raised beaches in the region. Radiocarbon dating assigns the high marine levels a B0lling Interstadial age of ca. 12.6 + 0.1 ka BP. Inferred gradient for raised B0lling beaches in the lower Borgarfj6rdur area is close to 2.3 m km-~. The marine terraces indicate a B0lling glacio-isostatic crustal depression of up to 250 ? 20 m, reflecting ice thickness of up to 840 ? 150 m. This is close to previously estimated Last Glacial Maximum (LGM) ice thickness. The Icelandic crust responds rapidly to changes in ice-load. Gradual thinning and retreat of the Icelandic ice sheet would have been concurrently compensated for by isostatic rebound, inhibiting formation of raised shorelines reflecting LGM isostatic crustal depression. The B0lling shorelines, together with recent marine and geophysical data, indicate a very rapid deglaciation of western Iceland shelf and coastal areas around ca. 12.6 ka BP. The rapid deglaciation coincides with a period of rapid eustatic sea-level rise, which destabilized the western part of the Icelandic ice sheet and caused it to collapse.

59 citations


Journal ArticleDOI
TL;DR: The Kangerlussuaq margin is well furrowed by icebergs as discussed by the authors, however, the icebergs that created the larger furrows are mostly absent, since sedimentation on the continental shelf is low since the last (Flakkerhuk) glaciation.
Abstract: The Kangerlussuaq margin is well furrowed by icebergs. The margin favors furrow preservation since sedimentation on the continental shelf is low, at least since the last (Flakkerhuk) glaciation and because shelf depths are well below wave base. While furrows are common in the Kangerlussuaq region, the icebergs that created the larger furrows are mostly absent. "Fresh" iceberg furrows are observed only on the bathymetric highs surrounding the 750-m-deep Kangerlussuaq Trough. Bathymetric barriers around the trough prevent icebergs with deep keels from entering the trough. Enormous and weathered (older) furrows are located inside the protected trough, apparently formed at paleocalving ice sheet termini, when the Greenland Ice Sheet extended onto the shelf. In the deeper sections of Kangerlussuaq Trough, Holocene mud is presently burying these older iceberg furrows. Paleocalving ice sheet margins, possibly from Iceland, account for muted furrows found on the upper continental slope of East Greenland. No sediment has been deposited over these hardground sites since 14,750 ? 720 BP.

Journal ArticleDOI
TL;DR: In this paper, the wood charcoal-carbon content in soils located in dry valleys within the French Alps was estimated using soil samples collected at five sites along altitudinal transects, from the conifer-dominated subalpine forests to the alpine grasslands.
Abstract: The current global carbon budget has a missing sink, which is believed to be in terrestrial ecosystems. At least one carbon sink, wood charcoal sequestrated in soil, remains poorly detailed. We estimate the wood charcoal-carbon content in soils located in dry valleys within the French Alps. Soils were sampled at five sites along altitudinal transects, from the conifer-dominated subalpine forests to the alpine grasslands. The five sites were distributed along a bioclimatic and biogeographic gradient from the southern Mediterranean to the northern continental Alps. The altitudinal distribution of charcoal exhibits the same pattern in the five sites, despite stand fire history, and regional bioclimatic and biogeographic differences. Charcoal concentrations are low (0.01 to 10 gchar m-2) in soils from the current treeless belt, while soils at lower elevation show high concentrations (10 to 2000 gchar m-2). The results suggest that the landscape structure determine the charcoal accumulation throughout variability of vegetation type and fire frequency. Charcoal concentrations recorded in the subalpine belt in the Alps are

Journal ArticleDOI
TL;DR: In this paper, the effect of many environmental stressors can be mediated by dissolved organic matter (DOM) properties and their effects on DOM spectral properties were analyzed. And they found that the photoreactivity of DOM from four high mountain lakes (two surrounded by meadows and two located on rocky terrain) was optically characterized and its photoreactive was experimentally evaluated.
Abstract: The effect of many environmental stressors can be mediated by dissolved organic matter (DOM) properties. In this study, DOM from four high mountain lakes (two surrounded by meadows and two located on rocky terrain) was optically characterized and its photoreactivity was experimentally evaluated. To evaluate DOM photoreactivity. photobleaching rates of absorptivity, and fluorescence and their effects on DOM spectral properties were analyzed. Dissolved organic carbon (DOC) concentration ranged from 37 to 69 muM, absorptivity at 320 nm (a(320)) from 0.60 to 3.09 m(-1), and fluorescence from 1.30 to 5.70 QSU. Photobleaching of absorptivity was significant only at 320 nm (a(320)) resulting in half lives that varied from 2.6 to 6.7 d. Photobleaching of a(320) was significantly higher for DOM from takes located on rocky terrain than for DOM from lakes surrounded by meadows. Photobleaching of fluorescence emission at 450 nm (F-450) was significant only for three lakes and their ha-lf lives varied from 4.1 to 6.3 d. No significant difference,; were observed among the lakes studied. The changes over sunlight exposure of spectral slopes (S-UV), ratios of absorptivity at 250 nm to 365 nm (a(250):a(365)) and ratios of' fluorescence emission at 450 nm to 500 nm (F-450:F-500) did not show consistent trends with alternate increases and decreases. Lakes surrounded by meadows showed higher DOC concentrations, higher absorptivities, and lower ci,) photobleaching coefficients, suggesting that these lakes could be less vulnerable to UVR than lakes located on rocky terrain.

Journal ArticleDOI
TL;DR: The establishment of forest trees into subalpine grasslands near Mt. Hotham, southeast Australia, was quantified in 1998 across long established forest-grassland boundaries in belt transects at four different sites.
Abstract: Establishment of forest trees into subalpine grasslands near Mt. Hotham, southeast Australia, was quantified in 1998 across long-established forest-grassland boundaries in belt transects at four si...

Journal ArticleDOI
TL;DR: In arctic Alaska, 15% of the total winter snowpack is contained in large drifts as mentioned in this paper, which can form during as few as five weather events during winter, while comparison of stratigraphy and weather records show that significant deposition (up to 43% of total drift volume) can occur during a single event of short duration (5.3 m s − 3 h, wind direction within 30? of the normal to drift trap axis, and recent snowfall available for transport).
Abstract: In arctic Alaska, 15% of the total winter snowpack is contained in large drifts. Stratigraphic sections reveal that these can form during as few as five weather events during winter, while comparison of stratigraphy and weather records show that significant deposition (up to 43% of the total drift volume) can occur during a single event of short duration ( 5.3 m s-~ for at least 3 h, wind direction within 30? of the normal to drift trap axis, and recent snowfall available for transport. When used, these rules successfully identified all drift-growth events, plus a few "extra" events that did not contribute substantially to drift growth. The extra events were invariably periods when there was sufficient wind to move snow, but insufficient snow for transport. In arctic Alaska drift size currently appears to be limited by precipitation rather than wind, leading us to speculate that an increase in precipitation could increase drift size and intensify the ecological, hydrological, and climatic impact of drifts on this arctic system.

Journal ArticleDOI
TL;DR: In this paper, plant macrofossil and pollen analyses of a series of sections and cores from Vesturardalur on Tr6llaskagi show that Betula pubescens grew up to an altitude between 450 and 500 m a.s.l. during optimum conditions in the Holocene.
Abstract: For paleoclimatic reconstructions based on vegetation history in Iceland, the upper limit of tree or shrub birch growth has been proposed as an indicator of summer temperature. Plant macrofossil and pollen analyses of a series of sections and cores from Vesturardalur on Tr6llaskagi show that Betula pubescens grew up to an altitude between 450 and 500 m a.s.l. during optimum conditions in the Holocene. The birch pollen and macrofossil record of core Vesturardalur 2 at ca. 450 m a.s.l., which covers the time from ca. 9200 BP to present, thus represents the first continuous high-resolution reconstruction of the variations of Betula pubescens at the ecological upper limit of tree or shrub birch in northern Iceland. Between ca. 6700 and ca. 6000 BP, a distinct maximum in the influx of Betula pubescens pollen at this site indicates a high position of the shrub line. This can be distinguished from a low influx of tree or shrub birch pollen from ca. 6000 to ca. 5600 BP, and a very pronounced minimum of Betula pubescens in the pollen record around ca. 3300 BP. The inferred depressions of the shrub line can be correlated with evidence for glacier advances and increased slope activity in northern Iceland.

Journal ArticleDOI
TL;DR: Algal communities were generally dominated by diatoms, Cyanophyta, and Hydrurus foetidus (Chrysophyceae), and community structure was similar among alpine streams and lake outlets, but more algal taxa occurred in lake outlets than in kryal streams.
Abstract: We investigated major physical-chemical characteristics and benthic algae of different alpine lotic systems comprising streams and lake outlets of rhithral and kryal origin over an annual cycle. We also evaluated the structure of the algal communities and its relation to environmental characteristics for the different stream types. Algal communities were generally dominated by diatoms, Cyanophyta, and Hydrurus foetidus (Chrysophyceae). Community structure was similar among alpine streams and lake outlets, but more algal taxa occurred in lake outlets (rhithral and kryal) than in kryal streams. Although algae were identified mainly to genera, distinct patterns in community structure were evident. A major environmental determinant of the algal community among stream types was the presence of a glacier and resulting seasonal differences in flow, temperature, and turbidity. An upstream lake was a secondary determinant in buffering seasonal fluctuations in environmental conditions thus leading to greater stability. Algal communities, consequently, were more diverse and less seasonally variable at lake outlets. The diatom genera Amphora, Denticula, Fragilaria, Gomphonema, Nitzschia, and Synedra and the blue-green algae Oscillatoria and Phormidium were characteristic of lake outlets, whereas Chamaesiphon (blue-green) and Hydrurus foetidus were indicative of kryal sites.

Journal ArticleDOI
TL;DR: In the Lindstromfjellet-Haberget-Hibergnuten ridge region, a mountainous massif of Nordenskioldland as mentioned in this paper, the areal extent of glaciers has decreased by ca. 18% in S0rkappland between 1936 and 1991, and by at least 150 m in central Nordenskoldland between 1986 and 1995.
Abstract: Major deglaciation on Spitsbergen has occurred as a result of climate warming since the beginning of the 20th century following the end of the Little Ice Age. The areal extent of glaciers has decreased by ca. 18% in S0rkappland between 1936 and 1991, and by ca. 44% in the Lindstromfjellet-Haberget-Hibergnuten ridge region, a mountainous massif of Nordenskioldland, between 1936 and 1995. Recession of glaciers has been accompanied by a decrease in thickness up to 50 m for almost all glaciers since 1936. The equilibrium-line altitude has risen by 100 to 200 m in S0rkappland and by at least 150 m in central Nordenskioldland. Deglaciation in central Nordenskioldland is more than twice that in S0rkappland during the 20th century, which suggests that central Spitsbergen is more sensitive to global warming than is southern Spitsbergen. Spitsbergen's proximity to maritime air masses is probably a more important control for rate of glacial recession than is elevation above sea level or high latitude.

Journal ArticleDOI
TL;DR: Water chemistry and sediment trap data from the 18.9m-deep, high-altitude, hardwater lake Hagelseewli (2339 m asl) indicates that biogenic induced calcite precipitation occurs in a water depth of 6 to 9 m at a temperature of 4?C.
Abstract: Water chemistry and sediment trap data from the 18.9-m-deep, high-altitude, hardwater lake Hagelseewli (2339 m asl.) indicates that biogenic induced calcite precipitation occurs in a water depth of 6 to 9 m at a temperature of 4?C. Our data indicates that calcite precipitation takes place as a short pulse that lasts less than 14 d in response to photosynthetic CO2 uptake in late summer probably by cyanobacterial picoplankton. In up to 8.4 times supersaturated water 30 p.m large calcite crystals precipitate that show surface features typical for eutrophic lakes (rough surface and enhanced columnar growth). Subsequently, during the long period of ice coverage calcite is completely dissolved in strongly undersaturated bottom waters. Sediment calcite concentrations therefore are below 0.3%, although the comparison of trap fluxes and sediment accumulation rates indicates that they could be as high as 25%. The theoretical annual accumulation of calcite in Hagelseewli is similar in magnitude to a single spring precipitation event in a low-altitude temperate, hardwater lake. In the most recent sediments the occurrence of higher amounts of organic carbon and sulfur indicates increasing bottom water anoxia during the last 30 to 40 yr.

Journal ArticleDOI
TL;DR: In this paper, the authors present the results of a lichenometric and dendrochronological study of the recent retreat history of Glaciar Nef, an eastern outlet glacier of the Hielo Patag6nico Norte.
Abstract: This paper presents the results of a lichenometric and dendrochronological study of the recent retreat history of Glaciar Nef, an eastern outlet glacier of the Hielo Patag6nico Norte. A 600-yr tree regeneration time, based on maximum tree age in the ancient forest, suggests that the forest-clad lateral moraines in the valley, southeast of the 19th century terminal moraine system, were formed some time before A.D. 1370. Dating estimates suggest that retreat from a 19th century maximum began around 1863, a decade or two earlier than the date established for other glaciers in the region, with glacier thinning near the ice front averaging 1.11 m yr- between 1863-1881. After 1884, retreat seems to have slowed, with glacier thinning averaging 0.09 m yr-~. Lichen and tree dating suggests that the glacier had retreated approximately 500 m by 1938; this estimate is supported by an aerial photograph showing a proglacial lake just beginning to form in 1944. Recent glacier movements around the Hielo Patagonico Norte are discussed and it is concluded that the general trend of glacier retreat around the icefield, beginning in the 1860s to 1870s, is consistent with Northern Hemisphere trends.

Journal ArticleDOI
TL;DR: In four expeditions to the northwest coast of Spitsbergen (1995-1998) as discussed by the authors, they have searched for yearly stationary snow algal fields and found them mostly near bird colonies on steep snow slopes.
Abstract: In four expeditions to the northwest coast of Spitsbergen (1995–1998) we have searched for yearly stationary snow algal fields and found them mostly near bird colonies on steep snow slopes. In this...

Journal ArticleDOI
TL;DR: In this paper, the seasonal variations in groundwater contributions to baseflow in a permafrost basin were studied at the Fish Hole area of the Big Fish River catchment, near Aklavik, N.W.T. Geochemical and isotope methods are used to distinguish three principal water types: (1) sub-permafrost Na-Cl thermal waters (16?C) discharging from bedrock along the river, (2) shallow, Ca-SO4 groundwaters, and (3) low-salinity, CaHCO3, supra-perm
Abstract: Groundwaters, surface runoff and river discharge have been studied at the Fish Hole area of the Big Fish River catchment, near Aklavik, N.W.T, to quantify the seasonal variations in groundwater contributions to baseflow in a permafrost basin. Geochemical and isotope methods are used to distinguish three principal water types: (1) subpermafrost Na-Cl thermal waters (16?C) discharging from bedrock along the river, (2) shallow, Ca-SO4 groundwaters, and (3) low-salinity, Ca-HCO3, suprapermafrost drainage. Cl and SO4 concentrations in river water show that baseflow is largely derived from groundwater sources (Na-Cl and CaS04 components), with less than 30% contributed from surface water runoff in any season. Thermal groundwaters discharge year-round at a calculated 1.6 m3 s-~. The shallow, Ca-SO4 groundwater is the dominant component of baseflow in summer but is absent in winter baseflow. Discharge analysis based on a single flow measurement (25.5 m3 s-1 in June, 1997) and Cl-dilution allows calculation of total river discharge. This is shown to vary from a low of 2.2 m3 s-' in the winter, to 1050 m3 s-~ during early spring melt.

Journal ArticleDOI
TL;DR: In this article, the authors measured the carbon dioxide exchange at treeline forest and fen tundra sites near Churchill, Canada during three consecutive growing seasons (1997-1999) and found that the forest was a net sink of -100, -313, and -478 g CO2 m-2 in 1997, 1998, and 1999, respectively.
Abstract: Net ecosystem exchange (NEE) of carbon dioxide was measured at treeline forest and fen tundra sites near Churchill, Canada during three consecutive growing seasons (1997-1999). Although both sites demonstrated a net uptake of CO2 in each of the years, there was considerable variation in the flux between sites and between years. Mean daily NEE at the forest varied from -1.5 (+0.25 SD) g CO2 m-2 d-1 in 1997 to -7.3 (+0.39) g CO2 m-2 d-l in 1999. The fen mean daily NEE varied from -1.1 (_0.36) g CO2 m-2 d-1 in 1997 to -3.1 (+0.50) g CO2 m-2 d-1 in 1998. Integrated over the 65-d measurement period the forest was a net sink of -100, -313, and -478 g CO2 m-2 in 1997, 1998, and 1999, respectively, and the fen net sink was -73, -202, and -38 g CO2 m-2, respectively. Interannual variations in the fen NEE were closely related to water table drawdown (soil wetness), the forest NEE was unaffected by water table change. The forest seasonally cumulative NEE was closely associated with timing of snowmelt and accumulated heat content prior to leaf-out. Earlier snowmelt and greater heat accumulation produced a larger growing season sink. It is likely these events also influenced the fen NEE, but the relationship is complicated by water table effects. These results suggest that carbon dioxide exchange varies considerably across the northern treeline, and that there may be an important biospheric feedback between climate warming, treeline advance, and carbon cycling.

Journal ArticleDOI
TL;DR: In this paper, surface sediments from 26 lakes along the Lena River in northeastern Siberia were analyzed for pollen and stomate deposition and vegetation, and the relationship between pollen and vegetation was determined.
Abstract: To determine the modern relationship between pollen and stomate deposition and vegetation, surface sediments from 26 lakes along the Lena River in northeastern Siberia were analyzed for pollen and ...

Journal ArticleDOI
TL;DR: In this paper, the authors examined the longitudinal pattern of oligochaetes in the hyporheic and benthic layers of a glacial river (Val Roseg, Switzerland).
Abstract: This paper examines the longitudinal pattern of oligochaetes in the hyporheic and benthic layers of a glacial river (Val Roseg, Switzerland). We hypothesized that the spatial distribution of oligochaete communities would reflect changes in surface water/groundwater interactions along the river continuum. From June to November 1997 (4 dates), three hyporheic and three benthic samples were collected at 11 and 9 sites, respectively, located over a distance of 11 km from the glacier terminus. A two-ended member mixing model based on concentrations of sodium was used to determine changes in the relative proportions of glacial water and groundwater along the river. The longitudinal increase in the diversity and abundance of hyporheic assemblages of oligochaetes was closely linked to the convergence of groundwater and surface glacial water. The differential distribution of hyporheic and benthic assemblages suggested that the hyporheic corridor acted as the main upstream migration pathway for oligochaetes. In this glacial river, the hyporheic zone appeared as a source area from which benthic habitats presenting suitable environmental conditions could be colonized.

Journal ArticleDOI
TL;DR: The contrastive patterns of leaf-trait variation between the deciduous and evergreen plants observed in this study were concordant with the prediction of the model.
Abstract: To understand response patterns of leaf traits in tundra plants against decreasing annual season length comprehensively, a graphic model based on carbon balance theory was presented. The model predicted that leaves with very short life-span and high nitrogen concentration (Nmass) or leaves with very long life-span and small Nmas will be dominate under the conditions of a short growing season. To test this prediction, leaf life-span and other leaf traits of 26 tundra species were compared among four sites selected along a gradient of climatic harshness: a subalpine site at Abisko in northern Sweden, two nearby mid-alpine sites at Latnjajaure with early and late snowmelt, and a site at Ny-Alesund (Svalbard) in the High Arctic. In herbaceous and deciduous shrub species, leaf life-span and/ or leaf mass per unit area (LMA) tended to decrease, and leaf Nmass tended to increase along the climatic gradient with decreasing growing season and lower temperatures. In evergreen shrub species, both leaf life-span and leaf N mass tended to increase under harsh conditions, but the response pattern of LMA was less clear. Deciduous species produced short-lived leaves with a low construction cost and probably high photosynthetic potential, whereas evergreen species produced long-lived leaves. The contrastive patterns of leaf-trait variation between the deciduous and evergreen plants observed in this study were concordant with the prediction of the model.

Journal ArticleDOI
TL;DR: In this article, the authors describe soil temperature conditions in an area close to the altitudinal and latitudinal distribution limit of the mountain birch and evaluate whether soil temperature is like...
Abstract: This paper (1) describes soil temperature conditions in an area close to the altitudinal and latitudinal distribution limit of the mountain birch, and (2) evaluates whether soil temperature is like...

Journal ArticleDOI
TL;DR: In this article, the authors surveyed 17 subarctic ponds with differing catchment areas and habitat types in northern Finland during the open water season from June to August, and found that the abundance of copepods in all sites dominated that of clasps.
Abstract: Zooplankton communities of 17 subarctic ponds with differing catchment areas and habitat types in northern Finland were surveyed during the open water season from June to August. Ponds were located along a gradient that changes from a mountain birch woodland to a treeless tundra. In all sites, cladoceran abundance dominated that of copepods although there was a consistent pattern of increasing relative abundance of copepods toward the most barren ponds. Species richness declined with increasing altitude but diversity remained constant. Zooplankton communities within the same habitat type were similar. Temporal variation in species abundance showed a coherent temperature driven pattern along the whole altitudinal transect.

Journal ArticleDOI
TL;DR: Heliotropism affected the frequency and residence time of flower visitors: unimpeded heliotropic flowers were more attractive and so were visited longer and more often by insects than those oriented away from the sun.
Abstract: During the growing seasons in 1994 and 1995 flower heliotropism and its effects on floral biology of several plants in the Grossglockner region (Salzburg, Austria) at 2230-2340 m a.s.l. was investigated. Ranunculus montanus, R. alpestris, Pulsatilla alpina, Callianthemum coriandrifolium (Ranunculaceae), and Leucanthemopsis alpina (Asteraceae) all have bowl and disc flowers (or inflorescences) that are heliotropic during periods of direct solar radiation. Temperatures of the air inside the flowers were above those of the ambient air for all five species. The maxima of excess temperature (means of 10 flowers or inflorescences) were between 2.0?C (C. coriandrifolium) and 6.2?C (P. alpina). Comparative temperature measurements in flowers of R. montanus showed that during sunny or slightly cloudy periods the air within those having uninhibited heliotropic movements was on average 0.7?C (in individual cases up to 1.3?C) warmer than in flowers fixed to face north. For the self-incompatible R. montanus, heliotropism affected the frequency and residence time of flower visitors: unimpeded heliotropic flowers were more attractive and so were visited longer and more often by insects than those oriented away from the sun.

Journal ArticleDOI
TL;DR: In this paper, the authors present results from the longest continuous postglacial marine sediment succession (1290 cm) ever obtained from an East Antarctic basin and show that significant Holocene climatic variability with a climatic optimum between 3500 and 2500 cal. yr BP.
Abstract: Sediment cores around Antarctica provide a unique opportunity to cross check and supplement the climatic information recorded in ice cores. Suitable highresolution data, however, have not been available until now from East Antarctica. We present results from the longest continuous postglacial marine sediment succession (1290 cm) ever obtained from an East Antarctic basin. Twenty-one radiocarbon dates show a consistent age to depth correlation over the last 9400 calibrated years BP (cal. yr BP). For this time interval distinct changes in the silicified ice-related biotic species assemblages, accumulation rates of organic carbon, 83C values, and C/N ratios were detected. We demonstrate that these sediment signatures can be used as climate proxies. Our results indicate significant Holocene climatic variability with a climatic optimum between 3500 and 2500 cal. yr BP. This was followed by an abrupt and dramatic cooling that took place within less than 200 yr. Corroborating the results of other researchers we hypothesize that this climatic optimum and its termination was a circumantarctic event which would appear to be out of phase with a proposed global temperature trend (maximum) during the Holocene.