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Vol. 25, No. 2, 1993
- Sediment Export by Ice Rafting from a Coastal Polynya, Arctic Alaska, U.S.A.
- Erk Reimnitz, Michael McCormick, Kristin McDougall, Elisabeth Brouwers
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Strong offshore winds in early 1989 produced a shore polynya that reached along the entire north coast of Alaska and eastward beyond the mouth of the Mackenzie River in Canada. From January through April, this open water periodically exposed the shelf to sediment entrainment by suspension freezing. This process requires turbulence and supercooled water, which results in the formation of frazil and anchor ice. The resulting granular, sediment-laden ice was observed to extend over 100 km seaward of the outer continental shelf after having been advected offshore. It was sampled to determine sediment type and to quantify the particle load. The particle size was mainly silt and clay, with local admixtures of as much as 27% sand and coarser clasts. Melted ice samples contained from 31 to nearly 600 mg L−1 of sediment. Combining these data with over 400 km of shipboard and aerial observations, photographs, and computer analysis of a summer Landsat image, we estimated the sediment load per unit area of sea ice. Seaward of the shelf, in regions of dense pack ice, a conservatively estimated sediment load was over 289 t km−2. Using a westward summer drift rate of 3 cm s−1, the sediment transport through a 1-km-long north-south segment is 67,418 t during 3 mo. In terms of regional sediment dynamics (littoral transport estimated at 10,000 t during the same period) and sediment budget (continental denudation estimated at 10 t km−2 during the same period), this number is very significant. Benthic microfossils indicate that bottom sediment incorporated in the ice came from water depths ranging from the inner neritic seaward to 50 m. The large load of shelf-derived sediment observed seaward of the continental shelf indicates that ice entrainment and transport cause shelf erosion. Nothing is known about sediment release over the Arctic Ocean Basin from these pulses of dirty ice that are periodically introduced into the Transpolar Drift.
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| pp. 83-98
- Location of Mechanical Controls on Columbia Glacier, Alaska, U.S.A., Prior to Its Rapid Retreat
- C. J. van der Veen, I. M. Whillans
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Data collected in 1977, before the start of the major retreat in 1981, are used to compute stresses acting on Columbia Glacier. Contrary to the situation in many other glaciers, where the driving stress is a good measure of basal drag, horizontal strain rates are large and spatially variable and the associated viscous forces are large. These result in important force transmissions along and across the glacier. Basal friction is more constant than is the driving stress, except near the terminus where basal resistance is concentrated at certain sites. The use of a valley shape factor as used in many one-dimensional models is tested against the present, more thorough analysis. It is found to be valid for longitudinal averages over more than about three ice thicknesses (about 1500 m). The average shape factor is 0.78, meaning that 78% of the flow resistance to a flowline at the center of the glacier is due to drag at the glacier base.
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| pp. 99-105
- Modern and Little Ice Age Equilibrium-Line Altitudes on Outlet Valley Glaciers from Jostedalsbreen, Western Norway: An Evaluation of Different Approaches to Their Calculation
- Ingrid Torsnes, Noralf Rye, Atle Nesje
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The modern and Little Ice Age (LIA) equilibrium-line altitude (ELA) of 20 outlet valley glaciers from Jostedalsbreen, western Norway, has been calculated using different approaches. Using an accumulation area ratio (AAR) of 0.6 ± 0.05 gave a mean Little Ice Age ELA depression of 70 m. A method developed by M. Kuhle, taking the influence by topography into account, gave a mean ELA depression of 35 to 255 m, the median elevation of glaciers (MEG) 115 m, and the toe-to-headwall altitude ratio (THAR) 140 m. Differences in the ELA estimates can be attributed to differences in topography and morphology of the glaciers. The AAR method appears to provide the most reliable results.
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| pp. 106-116
- An Inverse Relation between Frost Survival and Atmospheric Pressure
- S. Halloy, J. A. González
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Frost resistance generally increases with the altitude of the source population as an adaptive response to lower temperatures. But for a population from a single source, mortality would be expected to increase with altitude when freezing temperatures increase in frequency and intensity. Five species of plants and two species of vertebrates showed increased survival with altitude, given similar freezing temperatures. For lettuce seedlings this increase is highly significant. This evidence, together with laboratory experiments on four species of plants suggest that survival after freezing may increase under low atmospheric pressure. Such a relation is unknown in the literature. If confirmed, it could change our understanding of freezing physiology and have practical applications in diverse fields.
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| pp. 117-123
- Plant Competition over Winter in Alpine Shrubland and Grassland, Snowy Mountains, Australia
- John J. G. Egerton, Scott D. Wilson
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The influence of neighbors during a winter on transplants of three species was investigated near the timberline of the Snowy Mountains of southeastern Australia. The study species included the timberline tree Eucalyptus pauciflora, a grass most abundant above timberline, Poa costiniana, and a rosette composite most abundant at higher altitudes, Celmisia longifolia. Transplants were grown with and without neighbors, in both shrubland and grassland. Shrubland sites were near the timberline, grassland sites were 200 m above the timberline. Plant sizes were measured at the beginning and end of one winter and regression equations used to determine biomass changes. Plant growth and competition occurred during winter. Neighbors significantly reduced growth of P. costiniana in both habitats and C. longifolia in shrubland. The growth of E. pauciflora was not influenced by neighbors, but in the absence of neighbors it grew significantly faster in shrubland than in grassland. These results indicate that neighbors can restrict plant growth even in winter and may contribute to vegetation patterns in alpine habitats.
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| pp. 124-129
- Lemming Grazing on Snowbed Vegetation during a Population Peak, Northern Norway
- Jon Moen, Peter A. Lundberg, Lauri Oksanen
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The impact of a lemming population on a snowbed in northern Fennoscandia was examined during a population peak. Twelve exclosures and 12 open plots were established on a moderately early snowbed. The plots were photographed in autumn 1988, spring 1989, autumn 1989, and autumn 1990, and the cover of graminoids, woody plants, lichens, litter, lemming feces, and mosses were measured. The changes in cover were analyzed with repeated measures ANOVAs. The lemmings significantly decreased cover of graminoids by 33% and mosses by 66% during the peak winter. Our results show that grazing needs to be considered when discussing the development of snowbed vegetation.
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| pp. 130-135
- Range Impacts Following the Introduction of Caribou on Southampton Island, Northwest Territories, Canada
- Jean-Pierre Ouellet, Douglas C. Heard, Stan Boutin
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Changes in the vegetation for various range types subjected to grazing by an introduced caribou population in 1967 on Southampton Island, Northwest Territories, were assesed using a series of exclosures (N = 13; 5.5 m × 5.5 m) in 1990 and in 1991. Changes in the vegetation were related to range use and to prevalent snow conditions. The effect of the exclosures on some factors that are known to influence the production of arctic plant communities (snow condition, timing of snow melt, and soil temperature during the growing season) were also tested. Exclosures had little effect on these physical conditions. Associated with the increase in caribou number there has been a reduction in lichen standing crop; the other plant types were not affected. Under the prevailing snow conditions on the island, winter range appears to be restricted mainly to windswept areas which are nearly free of snow. As a result, some of these areas are showing signs of overgrazing and the past projection of caribou carrying capacity may have been too high. With respect to management, a significant increase in the annual hunting quota is recommended.
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| pp. 136-141
- Response of an Alaska, U.S.A., Shrub-Tussock Community to Selected All-Terrain Vehicle Use
- Gary M. Ahlstrand, Charles H. Racine
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Tests conducted at Wrangell--St. Elias National Park quantified the effects of all-terrain vehicle (ATV) use on a shrub-tussock community. Vehicle track depth increased significantly with increasing passes. Vehicles running on rubber tires created deeper tracks than similar vehicles mounted on continuous rubber tracks. Heavier ATVs usually produced deeper tracks than lighter vehicles. Deeper tracks resulted when vehicle use was spread over a 10-wk period during the summer than when the passes were concentrated into shorter time periods near the beginning or end of the snow-free period. Two years after completing the treatments, most of the heavier-used lanes had subsided 2 to 4 cm due to thawing of ice-rich permafrost. Although injury occurred to shrubs continuously throughout the treatments, shrub injury rates were greatest during the first few passes by an ATV. The dwarf shrubs Empetrum nigrum and Vaccinium vitis-idaea were least affected, while the low shrub Betula nana was most susceptible to injury. The degree of sedge tussock compression and amount of organic soil exposed along the ATV tracks increased in relation to vehicle weight.
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| pp. 142-149
- A Taxonomic Revision of the Genus Antennaria (Asteraceae: Inuleae: Gnaphaliinae) of Alaska and Yukon Territory, Northwestern North America
- Randall J. Bayer
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Keys to all species of Antennaria of Alaska and Yukon Territory are presented. The number of taxa acknowledged in the current treatment is 17, including 10 species with several subspecies circumscribed within some of the more diverse species. A synopsis enumerating all the recognized taxa provides their correct name, relevant synonyms, basionym, type locality, key morphological features, chromosome numbers and assorted taxonomic notes. Maps of each taxon are provided.
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| pp. 150-159
- Arctic Ecosystems in a Changing Climate: An Ecophysiological Perspective. By F. S. Chapin III, Robert L. Jefferies, James F. Reynolds, Gaius R. Shaver, Josef Svoboda
reviewed work
- T. V. Callaghan
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| pp. 160-161
- Atlas of Paleoclimates and Paleoenvironments of the Northern Hemisphere: Late Pleistocene-Holocene. By B. Frenzel, M. Pecsi, A. A. Velichko
reviewed work
- Scott A. Elias
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- Full Text:
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| pp. 161-162
- Quaternary Ecology: A Paleoecological Perspective. By Hazel R. Delcourt, Paul A. Delcourt
reviewed work
- T. R. Seastedt
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| pp. 161-
- Nuvendaltin Quht'ana: The People of Nondalton. By Linda J. Ellanna, Andrew Balluta
reviewed work
- Ludger Müller-Wille
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| pp. 162-163
- Brief Reviews and Book Notices
reviewed work
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| pp. 163-164
