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Recent environmental changes on Banks Island (N.W.T., Canadian Arctic) quantified using fossil diatom assemblages |
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| Authors: | Darlene S S Lim John P Smol Marianne S V Douglas |
| Institution: | 1. Paleoenvironmental Assessment Laboratory (PAL), Department of Geology, University of Toronto, 22 Russell Street, Toronto, ON, Canada, M5S 3B1 2. NASA Ames Research Center, Mail-Stop 245-3, Moffett Field, CA, 94110, USA 3. Department of Biology, Paleoecological Environmental Assessment and Research Lab (P.E.A.R.L.), Queen’s University, Kingston, ON, Canada, K7L 3N6 4. Canadian Circumpolar Institute, University of Alberta, Campus Tower, Rm. 308, 8625-112 St, Edmonton, AB, Canada, T6G 0H1 |
| Abstract: | Banks Island (N.W.T.) has become a focal point for climate change studies in the Canadian Arctic. However, long-term climatic and environmental data are very sparse from this large island, as they are for the entire southwestern region of the Canadian Arctic Archipelago. In this paleolimnological study, diatom species assemblage shifts documented in cores collected from a pond and a lake on Banks Island were interpreted to represent a response to climate warming commencing in the nineteenth century. We found that, although the timing and overall nature of the species changes in the two cores were consistent, the signal was muted in the deeper site likely as a result of differences in ice cover extent and duration between lakes and ponds. A high-resolution study was also conducted from a second pond, at sub-decadal resolution, that only spanned the last ∼60 years. In the deeper lake site, Fragilaria construens and F. pinnata dominated the assemblages, similar to those noted in other high Arctic regions where lakes are characterized by extended ice cover. In contrast, Denticula kuetzingii dominated the shallower ponds and, in the case of the pond core representing the longer time period, this taxon increased in the post-1850 sediments, likely coincident with climate warming. In all cores, diatom assemblages became more diverse and Achnanthes species (particularly A. minutissima) increased from ∼1850 to the present, similar to changes documented in other Arctic regions. Beta diversity values calculated for the diatom species changes indicated that assemblage shifts in the Banks Island cores were of similar magnitude to those recorded in other Arctic regions with high species turnover, such as Ellesmere Island. A diatom-based Total Nitrogen (TN) transfer function previously developed for Banks Island was applied to the three 210Pb dated cores as an exploratory tool for inferring past changes in nitrogen concentrations. In both the lake and pond cores, diatom-inferred TN concentrations tended to increase in the more recent sediments, as may be expected with warming; however these trends were not very distinct. |
| Keywords: | Banks Island Arctic Diatoms Nitrogen Paleolimnology Climate change Sediments |
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