Abstracts
Vol. 34, No. 1, February 2002
Modeling Climate Conditions Required for Glacier Formation in Cirques of the Rassepautasjtjåkka Massif, Northern Sweden (pp 3-11)
Regine Hock, Margareta Johansson, Peter Jansson, and Lars Bärring
Timing of cirque formation and the climate necessary to initiate glaciation are fundamental to the understanding of the landscape of the northern Scandinavian mountains. Empty cirques in the Rassepautasjtjåkka massif are located near a glaciated area and thus appear near the glaciation limit. In order to investigate the climate conditions necessary for glacier formation in the cirques, we applied a spatially distributed temperature index melt model. After calibration under present climate conditions, the model was run with different combinations of increased initial winter snow cover and lowered summer air temperatures to assess the climate conditions needed for snow to survive summer and hence form a base for glaciation. Results indicate that a significant increase in precipitation or decrease in summer air temperature or a combination of both is necessary to initiate glaciation. Thus current climate conditions are far from favorable for glaciation. If summer temperature is decreased by 4°C or winter snow cover is more than doubled, only 10% of cirque areas remain snow covered, which is considered as a minimum condition for glacier formation. According to climate reconstructions such conditions have not occurred during the Holocene suggesting that the cirques have not been glaciated during this period. Consequently glaciation of the cirques must have occurred during other parts of the glacial cycles.
Distribution Characteristics and Energy Balance of Ice Cliffs on Debris-covered Glaciers, Nepal Himalaya (pp 12-19)
Akiko Sakai, Masayoshi Nakawo, and Koji Fujita
The ablation amount for entire ice cliffs reaches about 20% of that at the whole debris-covered area; the ablation rate at the ice cliff mainly depends on shortwave radiation, which differs widely with the orientation of an ice cliff. Therefore, the distribution of ice cliffs in relation to their orientation was observed on a debris-covered glacier. The south-facing cliffs were small in area because they have low slope angles and tended to be covered with debris. The north-facing cliffs, on the other hand, were large in the studied area and maintain a slope angle larger than the repose angle of debris. They, therefore, are stable. Longwave radiation from the debris surface opposite the ice cliffs was larger on the lower portion of ice cliffs than on the upper portion in every azimuth. This difference in longwave radiation maintained a steep slope angle on ice cliff. Shortwave radiation was stronger at the upper portion of ice cliffs than at the lower portion due to the local shading effect, causing gentle sloping of ice cliffs. This was especially pronounced at cliffs facing to south. Therefore, the dependency of the ice cliff angle in orientation can be explained by the difference in local radiation between the upper and lower portion of the ice cliff.
The Thermal Effect of Melting Snow/Ice Surface on Lower Atmospheric Temperature (pp 20-25)
Yukari Takeuchi, Yuji Kodama, and Nobuyoshi Ishikawa
To quantify the thermal effect of melting snow/ice surface on the lower atmospheric temperature, "sensitivity of climate index" (α) is used. This new index indicates the rate of decrease in the sensitivity of climate (ß) over the melting snow/ice surface compared to that over the snow/ice-free surface. ß (EC /[Wm-2]) is defined as the mean daily air temperature range divided by the cumulative amount of solar radiation in this study. Micrometeorological observations were carried out in various snow/ice cover situations, including seasonal snow cover, glaciers, and snowpatchs. The observations showed that when melt is occurring, the sensitivity of climate is reduced for all the cases tested, regardless of their geographical and climatic conditions. Using the sensitivity of climate index (α), the thermal effect of surface melt is evaluated and compared among the various regions. Results show that the influence of surface melt on the lower atmosphere increases with the size of the snow/ice area.
Modern Pollen Assemblages in Lake Sediments from the Canadian Arctic (pp 26-32)
K. Gajewski
Modern pollen assemblages from lakes in the Canadian high-arctic and middle-arctic vegetation zones are used to document geographic differences in pollen deposition. There are differences in the pollen percentages of the herbaceous taxa that can be used to discriminate the various regions of the Arctic. High-arctic pollen assemblages have higher Poaceae, while middle-arctic sediments have higher Cyperaceae percentages. Pollen spectra from Banks Island contain higher percentages of Saxifragaceae, Brassicaceae, and Tubuliflorae, while lake sediments from the central Arctic contain more Ranunculaceae and Caryophyllaceae pollen. Salix and Oxyria pollen percentages are relatively high in samples from Ellesmere Island. Pollen from the low-arctic and boreal zones can comprise a significant component of the assemblages in arctic sediments, and this is more important in the southern islands of the Canadian Arctic Archipelago.
Eolian Deposition of Forest-Fire Charcoal above Tree Limit, Colorado Front Range, U.S.A.: Potential Contamination of AMS Radiocarbon Samples (pp 33-37)
James B. Benedict
Shallow soil cores from 56 localities along the crest of the Colorado Front Range were processed by water flotation and wet sieving, then examined for wood charcoal and charred conifer-needle fragments. Charred particles were largest and most numerous in samples from the subalpine forest. Particle size and abundance decreased abruptly in a narrow zone just above timberline, but showed only slight further decrease at higher elevations. Seventy-one percent of 31 alpine-tundra samples contained megascopic charcoal. Charred particles with geometric mean diameters of 1 to 2 mm were found on rocky summits above 4000 m and in windswept fellfields as much as 1.6 km from the nearest forest outlier. Long-distance eolian transport of charred material is attributed to raging crown fires in the subalpine forest, and to the region's characteristically high wind velocities. Accelerator Mass Spectrometry (AMS) radiocarbon dates for charcoal from archaeological features above tree limit in the Front Range should be attributed to human occupation only if particle diameters exceed 3 mm, or independent age evidence strongly supports a cultural origin.
Timing of Postglacial Cirque Reoccupation in the Northern Uinta Mountains, Northeastern Utah, U.S.A. (pp 38-48)
J. S. Munroe
Radiocarbon-dated organics from lacustrine cores and colluvial basins, combined with measurements of lichens growing on moraines previously interpreted as Neoglacial in age, argue that the extent of post-Pleistocene ice in the northern Uinta Mountains was limited. An AMS date of 12,190 ± 120 14C yr BP on basal organic sediment from a tarn indicates that deglaciation was locally complete by ~14 ka BP. Additional radiocarbon ages of ~10 ka BP from two colluvial basins behind end moraines suggest that these moraines date to the latest Pleistocene. Crosscutting moraines from a fourth site indicate that an active cirque-glacier system was present at some point after the terminal Pleistocene deglaciation. Maximum diameters of Rhizocarpon geographicum lichens on these moraines, however, suggest they may predate Little Ice Age deposits in the Wind River Range and Sierra Nevada. The convergence of evidence suggests that glaciers in the northern Uintas during the Holocene were extremely limited in extent and restricted to the middle Neoglacial period. This preliminary conclusion contradicts some previous interpretations of the upper subalpine geomorphology of the range, which postulated widespread post-Pinedale glaciation and multiple stades of Holocene Neoglaciation.
A Half Century of Change in Alpine Treeline Patterns at Glacier National Park, Montana, U.S.A. (pp 49-56)
Frederick L. Klasner and Daniel B. Fagre
Using sequential aerial photography, we identified changes in the spatial distribution of subalpine fir (Abies lasiocarpa) habitat at the alpine treeline ecotone. Six 40-ha study sites in the McDonald Creek drainage of Glacier National Park contained subalpine fir forests that graded into alpine tundra. Over a 46-yr period, altitudinal changes in the location of alpine treeline ecotone were not observed. However, over this 46-yr period the area of krummholz, patch-forest, and continuous canopy forest increased by 3.4%, and tree density increased within existing patches of krummholz and patch-forest. Change in subalpine fir vegetation patterns within 100 m of trails was also compared to areas without trails. Within 100 m of trails, the number of small, discrete krummholz stands increased compared to areas without trails, but there was no significant change in total krummholz area. We used historical terrestrial photography to expand the period (to 70 yr) considered. This photography supported the conclusions that a more abrupt ecotone transition developed from forest to tundra at alpine treeline, that tree density within forested areas increased, and that krummholz became fragmented along trails. This local assessment of fine-grained change in the alpine treeline ecotone provides a comparative base for looking at ecotone change in other mountain regions throughout the world.
Betula ermanii, a Dominant Subalpine and Subarctic Treeline Tree Species in Japan: Ecological Traits of Deciduous Tree Life in Winter (pp 57-64)
Dirk Gansert
Betula ermanii (Japanese mountain birch), a dominant tree species of the subalpine and subarctic treeline ecotones in East Asia, was investigated with respect to frost hardiness, bud phenology, and woody-tissue respiration above and below snow at the treeline on Mt. Fuji, Japan. On the Pacific-facing south slope, the minimum air temperature regime at 2450 m altitude is not harmful to the viability of previous year's shoots and emerging leaves. Betula ermanii will approach its upper distribution limit where the risk of spring frost damage in immature tissues interferes with the need for a minimum length of the growing season. In the cold Pacific winter climate of Japan, susceptibility of bursting buds and dehardened shoots to frost down to -7°C late in May is a major determinant for the species' altitudinal distribution limit at 2800 m altitude. It is concluded that two periods of minimum temperature affect the upper distribution of a deciduous broad-leaved tree species in temperate climates: (1) periods of subzero temperature which determine the occurrence of spring frost damage and affect the beginning of the growing season and (2) cool periods during the growing season that affect development and ripening of overwintering plant compartments.
Weathering Characteristics of the Glacial Drifts, Bunger Hills, East Antarctica (pp 65-75)
Paul C. Augustinus
Mapping of glacial drift sheets and examination of striae patterns throughout the Bunger Hills, suggests that the largely ice-free region records the imprint of several phases of ice sheet and outlet glacier expansion during the late Pleistocene. The oldest glacial drift identified in the Bunger Hills is the most extensive, and displays a weathering status that allows its discrimination from the moderately weathered Figurnoe drift. The latter drift is hummocky and preserves a series of high-level paleolake shorelines at the western end of modern Lake Figurnoe. Within the limits of the Figurnoe drift, the Apendiksi drift was mapped on the basis of its degree of morphological preservation and minimal surface and subsurface drift weathering. Lobes of Apendiksi ice extended up to 8 km west of the modern ice sheet margin in the southern Bunger Hills. Advances of the Edisto Glacier are renamed the Edisto 1 to 3 in order of reducing relative age. The morphostratigraphic evidence suggests that the glacial history of the Bunger Hills is more complex than had previously been recognized, and emphasizes the need for detailed glacial geologic work in this and other ice-free coastal areas of eastern Antarctica.
Surface Age, Ecosystem Development, and C isotope Signatures of Respired CO2 in an Alpine Environment, North Iceland (pp 76-87)
Philip A. Wookey Roland A. Bol, Christopher J. Caseldine, and Douglas D. Harkness
We studied the late Holocene foreland and adjacent unglaciated terrain of a small cirque glacier system in north Iceland to explore the relationship between soil/surface age, vegetation and soil evolution, and C isotope signatures of respired CO2. Field-based sampling of respired CO2 from vegetation/soil monoliths across the chronosequence was used as the basis for an analysis of the 12C:13C:14C atom ratios of CO2 using Isotope Ratio Mass Spectrometry (IRMS) and Accelerator Mass Spectrometry (AMS). Residual soil organic matter (SOM) fractions (humic and humin) were also 14C-dated from each of the surfaces, vegetation described, and soil C and N contents analyzed. Our major conclusions are (1) that ecosystem respiration in this mid-alpine environment is strongly dominated by "young" C and is not related to the 14C age of residual SOM fractions; (2) δ13C values of respired CO2, by contrast, do vary both with age of surface and with absolute respiration rate, but there is no clear indication of any effects mediated by plant species and functional type and/or the degree of reworking of SOM by decomposer organisms; and (3) the 14C dating of residual SOM fractions, together with the soil profile characteristics (including tephra deposits) and vegetation cover, both suggest some radical disturbance in soil development and SOM formation at Site 1 (the oldest surface studied here), and no clear signs of classical succession when comparing Sites 1 to 3. Finally, in the light of these observations, the familiar concept of chronosequences, and the predictable processes of ecosystem development that they often imply, are challenged in a mid-alpine tundra setting where recent climate change and anthropogenic influences (e.g., grazing pressure) are superimposed upon time as an ecological factor.
Characterization of Heterotrophic Microorganisms in Alpine Glacier Cryoconite (pp 88-93)
R. Margesin, G. Zacke, and F. Schinner
We surveyed three samples of alpine glacier cryoconite for heterotrophic microbial life. All samples contained bacteria, yeasts, and hyphomycetes. Aerobic heterotrophic bacteria were more numerous than the other two groups and were isolated at all four cultivation temperatures (2°C, 20°C, 37°C, 55°C). Significantly lower numbers of bacteria were able to grow at 2°C than at 20°C, while the opposite pattern was observed for yeasts. The majority of 66 selected bacterial isolates, able to grow at 2°C, were Gram-negative and could be assigned to two genera (Pseudomonas and Sphingomonas). Among 17 yeast strains, we found three genera (Cryptococcus, Candida, and Rhodotorula). A considerable proportion of microorganisms utilized casein, carboxymethylcellulose (CMC), lignosulfonic acid, starch, tributyrin, or diesel oil at 2°C. Significantly fewer microorganisms were able to grow on microcrystalline cellulose or keratin, or on aromatic hydrocarbons (naphthalene, phenanthrene, anthracene, and 4-chlorobiphenyl). The utilization of various carbon sources (CMC, starch, tributyrin, and diesel oil) by 14 selected yeast strains was inhibited at cultivation temperatures above 15°C.
Testate Amoebae Assemblages from Soils in the Zackenberg Area, Northeast Greenland (pp 94-101)
Koen Trappeniers, Andy Van Kerckvoorde, Didier Chardez, Ivan Nijs, and Louis Beyens
Testate amoebae communities across five different vegetation and soil types in a coastal region of Northeast Greenland were studied, in order to understand the distribution of these organisms with respect to habitat properties in this extreme environment. Thirty-eight taxa representing 12 genera were observed in 39 samples. About 43% of the testate amoebae belonged to a single species: Trinema lineare. Difflugia globulus and Centropyxis aerophila var. sphagnicola showed also high relative abundances. Average shell density/g dry weight was 35,000 ± 21,000. Hierarchic-agglomerate classification revealed three assemblages. A Difflugia globulus -- Centropyxis aerophila var. sphagnicola assemblage inhabited the soil from the Arctagrostis and Vaccinium vegetation type. This assemblage was associated with higher soil moisture content and a thicker active layer. The Centropyxis aerophila -- Trinema complanatum assemblage, that was found in the soils beneath the Cassiope and Salix vegetation, was associated with lower soil moisture content. The assemblage found in soils beneath the Poa vegetation type was characterized by Trinema lineare and Euglypha rotunda and was associated with high organic content of the soils and a shallower active layer. These results suggest that testate amoebae assemblages are ecologically distinct across short distances in the high arctic soil habitats.
Plant Community Composition and Biomass on Calcareous and Siliceous Substrates in the Northern French Alps: Comparative Effects of Soil Chemistry and Water Status (pp 102-113)
Richard Michalet, Cécile Gandoy, Didier Joud, Jean-Philippe Pagès, and Philippe Choler
Floristic differences between alpine communities on calcareous and siliceous rocks have been mainly attributed to soil chemical properties in the European Alps. In contrast, water availability and temperature, factors that correlate with calcareous and siliceous substrates, have received more attention in other mountain ranges. To compare the relative importance of soil chemical versus physical factors for explaining differences in floristic composition between communities from calcareous and siliceous rocks, we conducted a fine-scale correlative study in the northern French Alps, in which the effects of topographic variations were compared on dolomitic limestone (calcareous) and gneiss (siliceous). We analyzed 192 plots with correspondence analysis (CA) and canonical correspondence analysis (CCA) using a matrix of 20 environmental variables including snow melt dates and water availability. We also measured aboveground biomass and available nitrogen and phosphorus for a subset of the plots. Species composition, aboveground biomass, and species richness were highly correlated with substrate type. However, water availability, not substrate chemistry, appeared to drive differences in community composition, biomass, and richness. Siliceous substrates appeared to be more mesic because of the water supplied at the subsurface level. Conversely calcareous soils were drier, probably because of the higher porosity of the rock.
