Holocene vegetation history of the Canadian Arctic
The Holocene vegetation history of the Canadian is practically unknown. This situation contrasts with that of Greenland, where there is a long history of paleoenvironmental studies. We have a long-term research project to describe the postglacial vegetation history of the central and western Arctic Archipelago of Canada. We go to the arctic nearly every summer to collect samples which analyzed in the lab over the course of the winter.
This project has several parts. One project is the collection and analysis of modern sediment samples. Modern samples are used for calibration. That is, we extract the pollen from the uppermost sediment, the mud that has been deposited in the past few years. The pollen is counted under the microscope. Then we statistically compare the pollen assemblages with the vegetation or climate at the location of the lake. We can what kind of pollen assemblage is being deposited by the different vegetation types. Work is progressing slowly due to the extremely low pollen concentration of the samples. Samples have been counted from Somerset, Bathurst and Ellesmere Islands, and work in progress is accumulating samples from Prince of Wales, Cornwallis, Devon and Victoria and Axel Heiberg Islands. We have found that the pollen concentrations decrease significantly from the mid to the high arctic on Somerset Island, and work is continuing to see if true elsewhere. However, one problem is the contamination of pollen redeposited from Tertiary coals that are found throughout the northern and western arctic. These pollen are not distinguishable from modern-day pollen, and we are investigating potential ways to separate these. We also characterize the water chemistry at these sites, and the aquatic microfossils will also be extracted and analyzed.
At the same time, we are collecting cores of the postglacial sediment accumulation in the regions where we collect modern sediment samples. The pollen analyzed from these cores are time-series of the vegetation change at the site. We are finding, for example, that the arctic vegetation was more rich 5000 to 8000 years ago, although the dating control is less precise than we would wish. We have published postglacial pollen diagrams from Banks Island, Somerset Island, and Prince of Wales Island. We also have sequences from Victoria, Devon and Ellesmere Islands.
Finally, we are investigating the processes of sedimentation in arctic lakes. X-ray and magnetic susceptibility indicates significant variability in sediment accumulation, and many of these lakes have laminations of varying thickness. These may also tell us about the variability of the climate in the arctic.
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