ABSTRACT: Secrets from the mud: lake sediments yield informaiton on past environmental conditions.

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Rapid environmental change is being observed in the Arctic yet questions as to when these changes began, are sometimes difficult to answer as the instrumental record quantifying these changes is short or non-existent. One needs to turn to the geological record, i.e., ice cores, lake and ocean sediment cores, etc in order to fill in these missing data. Once these have been obtained, the baseline conditions, or that natural variability of a site can be determined and the rate of observed change calculated. This presentation reviews how lake sediments can be used as a source for these missing data. Paleolimnology, or the study of lake sediments, can yield enough data to generate a paleoenvironmental assessment of a particular region. Diatoms are popular proxy indicators in paleolimnological studies due to a number of qualities. These unicellular algae (belonging to the class Bacillariophyceae), are identified by the intricate patterns on their siliceous (glass) cell walls. They are sensitive to environmental conditions, i.e., gradients of pH, conductivity, salinity, nutrients and microhabitat availability, and the diatom species respond quickly to changes in any of these variables. Many of these variables are affected by changing climatic conditions. The autecology of each diatom species can be determined by completing regional calibration sets in which the biological, chemical and physical requirements of each taxon is determined. Because diatom cell walls are made of glass (SiO2), they preserve well in lake sediments, leaving a record of the diatom community that existed at the time of deposition. Interpretation of past environments is based upon this autecological knowledge. This presentation will examine how diatoms have been successfully used in the Canadian High Arctic to determine the temporal and regional variability of the recent global warming trends. Diatom studies documented unprecedented environmental shifts beginning ca. 1850 AD. These shifts were the result of limnological changes resulting from warmer climatic conditions. For example, a warmer climate results in longer ice-free periods, new aquatic habitats such as aquatic mosses, etc.). The remoteness of these sites, coupled with the ecological characteristics of taxa involved, indicate that changes were primarily driven by climate warming through lengthening of the summer growing season and related limnological changes. Paleolimnological techniques have also been used to track the environmental impacts of the Thule (prehistoric whalers) people in the Arctic. This very successful culture disappeared from the Arctic post 1600AD, likely a result of shifting climates. Using diatoms and the 15N signal in lake sediments, it is possible to track the presence of these peoples in the Arctic. Due to the sub-zero and cold temperatures typical of high latitudes, the presence of these peoples and their impact on the environment can still be traced in certain regions. For example, whaling activities results in increased nutrients being released onto the terrestrial and freshwater aquatic systems, due to the degradation of flensed whale carcasses. Even today, higher nutrient concentrations are measured in these freshwater systems, despite the fact that they were abandoned over 400 years ago. These observations provide a means for archaeologists to track the duration of presence or absence of a group of people at any particular site. Many questions regarding past environmental conditions can be addressed by examining various proxy indicators preserved in the sedimentary record.

Bibliography of Canadian Geomorphology