ABSTRACT: Applications of diatoms to assessing paleoenvironmental change in the Canadian High Arctic.

CGRG Bibliography of Canadian Geomorphology
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The High Arctic is recognized as an important reference area for global environmental change, as it has been shown to be highly sensitive to changing environmental conditions. Many environmental changes are first recorded at high latitudes, before being tracked in lower latitude systems (Rouse et al., 1997). Climate changes in the 20th century have been magnified in the High Arctic as compared with lower latitude systems (Overpeck et al., 1997). In addition, global circulation patterns and other processes have resulted in the deposition and concentration of airborne contaminants in polar regions, as well as the accelerated depletion of stratospheric ozone.However, detection of environmental change can be difficult, as no direct long-term records exist. For example, historical climate change in the Canadian High Arctic is limited by the lack of long-term meteorological records. Where measured environmental data do not exist to evaluate the naturalvariability of systems, proxy methods using paleolimnological approaches are invaluable due to their ability to reliably infer past conditions. Past environmental conditions can be interpreted by examination of proxy indicators in dated lake sediment cores. Diatoms are sensitive recorders of environmental change in aquatic systems, and have been used in many paleoenvironmental reconstructions. These siliceous algal microfossils can be used to track changes in salinity, nutrient content, acidity, presence of aquatic vegetation, and other physical and chemical variables (Douglas and Smol, 1999). They have the potential to compensate for the lack of measured environmental data and to assess whether currentenvironmental conditions fall within the ranges of natural variability for High Arctic systems. High Arctic ecosystems are vulnerable to disturbance by changing environments due to low species diversity and short food chains (Maxwell, 1997). From a limnological perspective, perhaps the most important result of climatic shifts will be the changes in thickness, duration, and timing of seasonal lake ice (Smol, 1988). Ice and snow on lake surfaces control the amount of light which enters the lake and is available for photosynthesis. Also, surface ice alters the chemistry of lake systems by creating a barrier to exchange with atmospheric oxygen as well as through the exclusion of solutes during freezing (Rouse et al., 1997). Therefore, any changes in climate affecting lake ice will significantly alter high arctic aquatic ecosystems. Many high arctic lakes retain perennial ice covers, thawing only at the fringes for a short period during the summer. Due to the control of snow and ice cover on light transmission and habitat availability, changes in the degree of ice cover will be recorded by diatom assemblages (Smol, 1988). Colder years have more persistent ice cover, with narrow moats of open water in the littoral zone of lakes. As a result, during these colder years, diatom productivity will be lower, and diatoms prevalent in shallow environments will increase in relative abundances. Warmer summers will result in reduced ice cover, which results in higher productivity and an increase in taxa common in deeper water and planktonic habitats. These trends in community composition can be used to reconstruct changes in past ice cover.

Bibliography of Canadian Geomorphology