CGRG Bibliography of Canadian Geomorphology
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Author : Francus, P.; Abbott, M.; Bradley, R.S.; Finney, B.; Lewis, T.; Patridge, W.; Perren, W.; and Stoner, J.
Date : 2001.
Title : 2550 years of environmental history from the sediments of South Sawtooth Lake, Nunavut, Canada: initial results.
Publication : 21st Meeting of the International Association of Sedimentologists. Meeting of Sedimentology. Davos, Switzerland. 3-5 September 2001.
Issue :
Page(s) :
Abstract
South Sawtooth Lake, Ellesmere Island (79° 20' N, 83° 51' W), is an oligotrophic lake located in the southwestern part of Fosheim Peninsula. A continuously varved 4.53 meter long sequence combining a short Glew core and a long vibracore has been obtained from the 82 meter deep distal meromictic basin. The basin is protected from the direct influence of turbidites by a sill. The sequence has been studied for diatoms, organic content, paleomagnetism, geochemistry, and sedimentary microfacies. According to varve counts and 210Pb dates, the record spans the last 2550 yrs. Sedimentation is mainly due to settling of coarse and fine silts during the snow melting season, followed by the settling of clays during the ice covered winter season. Summer rain events are also recorded as thin non-erosive beds of non-graded sand. Using an image analysis technique on thin-sections, we produced multivariate and quantified characterization of each varve for the upper section of the sequence. The data so obtained have been compared with climatological and hydrological data, e.g. temperature, snow melt, wind, and stream discharge. Snow-melt intensity correlates well with the annual median grain-size for the last 33 years. Lamination thickness do not correlate with any climatic parameter. The model is then used to infer environmental conditions from downcore laminae with annual resolution. On the long sequence, we produced a reconstruction of the intensity of anoxia for the entire sequence using both image analysis and observation of sedimentary structures in thin-sections. A reconstruction of the summer rain intensity based on the occurrence of sand layers showed that more frequent rainy summers occured between 1450 AD and 650 AD, potentially corresponding to the Medieval Warm Period. Diatoms are present in the record only in the last 100 years. Organic matter content is mainly driven by terrestrial input. Environmental magnetic measurements, namely anhysteretic remanent magnetization (ARM), isothermal remanent magnetizations (IRM) and magnetic susceptibility are characterized by regular and strong oscillations between two different magnetic mineral assemblages, the first being rich in fine-grained magnetite, the second characterized by a lower concentration of coarser magnetite. Spectral analyses indicate a significant frequency of 128 years. We discuss the fluctuations of those proxies throughout the entire sequence and their climatic significance, and we compare them to other records in the Arctic.
Bibliography of Canadian Geomorphology