In order to understand past climatic change in the Canadian Arctic, a detailed climate record is necessary. However, scientific knowledge of Arctic climate since the end of the Little Ice Age (c. 1850) is incomplete. The Arctic meteorological record is brief and geographically sparse. Therefore, to infer past environmental conditions and to track trajectories of past climatic change over time intervals equal to or longer than the instrumental record, indirect proxy data are required.

The reconstruction of Arctic climate for the last four centuries using paleoclimatic techniques such as oxygen isotope analysis, pariglacial features, lake sediments, paleolimnology, dendrochronology and palynology has provided evidence of natural subdecadal to century-scale climate variability. However, current climatic reconstruction is far from extensive and for the most part does not show interannual variability. A new technique employing dendroclimatological analysis of the circumpolar shrub Cassiope tetragona provides terrestrial climatic information on an annual basis. The annual growth increments (analogous to tree-rings) found along the plant stem are delimited by wave-like patterns in internode lengths. The internode lengths are the distances between adjacent leaf scars with shorter internode lengths corresponding to the end of each year’s growth. By utilizing this technique in combination with an extensive sampling programme, the climatic regime that has characterized the Canadian Arctic for the last 150 years may be reconstructed.

One of the primary goals of this study is to understand the regional nature of past climate change in the Canadian Arctic. Since the end of the Little Ice Age, the Canadian Arctic has warmed on average 1.5°C. However, the warming trend has not been consistent over the entire region for the 150-year period. Recent climate data from 1961-1990 reveals a cooling trend in the south-eastern Canadian Arctic and Greenland (-0.25°C) while in the western third, the temperature has increased by +0.25°C. However, these trends are based on data from very few, long-term climate records, especially in the farthest North. Thus, not only do large-scale climatic regions of the past need to be reconstructed for the Canadian Arctic through the development of site chronologies, but also the variability of past climate within smaller-scale regions needs to be determined. These databases will help place the current changes in climate into context with the recent past.

On the Tundra Northwest 1999 expedition in the Canadian Arctic, Cassiope tetragona was collected at nine sites. Plant specimens were collected at Ungava Peninsula (Site 1), Melville Peninsula (Site 2), Wollaston Peninsula (Site 7), Amundsen Gulf South (Site 8), Banks Island South (Site 9), Ivvavik National Park (Site 10), Melville Island (Site 13), Devon Island South (Site 16), and Baffin Island East (Site 17). Fifteen plants were collected at each site for later chronology construction. While on board the ship, the plants were air-dried and stored in paper bags. In preparation for measurement, 5-10 shoots from each plant were selected and two adjacent rows of leaves were manually removed from each shoot. Flower buds and peduncle bases were left in place and the position of auxiliary stems was marked with non-toxic paint. Individual stems were straightened and placed in 1 cm diameter glass tubes for measurement. Measurement of the annual increments was begun using a dissecting microscope and a manually operated sliding micrometer (designed by J. Svoboda, University of Toronto). The internode lengths were measured from the base of the shoot to the tip and the positions of flower buds, flower peduncles and auxiliary branches were recorded. Further measurements and data analysis will continue at the University of British Columbia, Canada over the next year.

As part of our project we will be analysing the isotopic characteristics of the Cassiope growth segments in an attempt to correlate physiological traits with environmental conditions. For instance, we will examine the δD, the δ¹⁸O and the δ¹³C of growth segments as a means of assessing whether these plants used different sources of water between years (i.e., summer rain as opposed to winter snow melt water) and whether these differences in water sources affected carbon fixation as measured by the δ¹³C of the same growth segments. In addition, we plan to examine whether the δD, the δ¹⁰O of the segments is correlated with temperature and we plan to examine the δ¹⁵N content of the growth segments as a means of ascertaining interannual differences in the mineral nutrition of Cassiope plants. For example, if during one year, the nitrate form of nitrogen is more available than in previous years, we may see shifts in the δ¹⁵N content of growth segments which may or may not be related to water sources and climatic conditions. These isotope analyses will be conducted in Dr. Welker’s laboratory at the University of Wyoming and we hope to involve Swedish, Canadian and US students and junior scientists in this phase of the programme.

In association with the climate related study outlined above, the genetic variability within and among Cassiope tetragona populations is being studied throughout the Canadian Arctic. At each site, main shoots of twenty plants per site were sampled and put in plastic test tubes with silica gel as drying agent. Samples were obtained from all the sites mentioned above, and are now awaiting analysis as to genetical variation using DNA methods, primarily RAPD screening. This part of the Cassiope project therefore has a clear Connection with the B Theme, biodiversity, of Tundra Northwest 1999.

Summary

As scientific knowledge of past climatic change in the Canadian Arctic is limited due to the brevity of meteorological records and the sparse number of climate stations, it is necessary to utilize proxy data. By employing dendroclimatological techniques on the circumpolar shrub Cassiope tetragona, past climate may be reconstructed on a yearly basis through the measurement of the plant’s annual growth increments. This technique in combination with extensive sampling will permit the reconstruction of the climatic regime that has characterized the Canadian Arctic for the last 150 years. Furthermore, an analysis of the isotopic characteristics of Cassiope tissue will provide information on water uptake sources and thereby winter snow conditions. In addition, the genetic variability of the sampled populations will be studied using DNA methods.