LYCOS RETRIEVER 
Canadian Arctic Islands: Lake Hazen
built 613 days ago
A chironomid-based reconstruction spanning the Holocene was constructed from a lacustrine sediment core taken from a shallow lake on Western Victoria Island in the Canadian Arctic Islands. The primary purpose of this study was to investigate long-term climatic variations and their impacts on aquatic ecosystem functioning in the Canadian Arctic. The sampled lake, informally called WB02 is located in the Middle Arctic and is in a prostrate shrub tundra vegetation zone (CAVM, 2003). The 183 cm core was collected from the ice surface of the lake in June 1997. The top 5cm were extruded in the field in 0.5 cm increments to preserve the integrity of the sediment at the water interface. The core was dated by 7 AMS radiocarbon dates.
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Lists nematode genera (and the number of species in each) collected on the Canadian Arctic Expedition in 1915-1916, and at Lake Hazen, Ellesmere Island, in 1962. The former collection, identified by N.A. Cobb, but not hitherto reported (cf. No. 2817 pt. F), comprises 22 genera containing 47 species, about half of which are cosmopolitan. The Lake Hazen collection is the first the the High Arctic; it contains at least 30 described and several undescribed genera, comprising 60 or more species. Gen. Plectus is abundant in both collections.
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Although most of the ground surface in the Canadian Arctic Archipelago is ice free in the summer, permafrost occurs below the surface everywhere except under deep lakes and rivers. Permafrost is defined as ground remaining, at or below, the freezing point for at least two years. At some sites the depth of permafrost may exceed several hundred metres while at more southerly sites its depth may be less than 10 m. The greatest thicknesses in Canada are over 1000 m deep in areas of Baffin and Ellesmere Islands. The southern extent of the permafrost is associated with the mean annual air temperature isotherm of 0°C (Williams 1986). The annual thaw of the surface, or active layer, varies with the texture and water content. In sand and gravel, the active layer may be deep, whereas in wet peaty soil the summer thaw may penetrate only a few inches.
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Environmental change in the Canadian Arctic islands was assessed using three interrelated approaches; limnological, phycological, and paleolimnological analyses. Limnological analyses of lakes and ponds on Axel Heiberg and Victoria islands revealed that, while many sites were typically nutrient-poor and slightly alkaline, they are more limnologically diverse than previous arctic surveys have suggested. Extremely low levels of nutrients and dissolved organic matter (a natural screen for ultraviolet radiation) in some of these sites makes these aquatic ecosystems particularly sensitive to changes associated with global warming and ultraviolet radiation penetration.
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