HR: 17:15h
AN: PP54A-06    [Abstracts]
TI: Growth Trend Divergence and Statistical Characterization of Climate-Isotope Relations of White Spruce in the Mackenzie Delta, Northern Canada
AU: * Porter, T J
EM: tjporter@connect.carleton.ca
AF: Carleton University, Department of Geography 1125 Colonel By Drive, Ottawa, ON K1S5B6, Canada
AU: Pisaric, M F
EM: mpisaric@ccs.carleton.ca
AF: Carleton University, Department of Geography 1125 Colonel By Drive, Ottawa, ON K1S5B6, Canada
AU: Kokelj, S V
EM: kokeljsv@inac-ainc.gc.ca
AF: Department of Indian Affairs and Northern Development, Water Resources Division P.O. Box 1500, Yellowknife, NT X1A2R3, Canada
AU: Edwards, T W
EM: twdedwar@sciborg.uwaterloo.ca
AF: University of Waterloo, Department of Earth Sciences 200 University Avenue West, Waterloo, ON N2L3G1, Canada
AB: Ring-width series from temperature-sensitive white spruce forests in the Mackenzie Delta have shown divergent growth trends during the early- to mid-twentieth century at the subpopulation level. Both positive and negative growth responses with respect to recent climate warming in this region have been observed, with the latter response being more common. When ring-width series from these individuals are combined to form master time-series and compared to local/regional instrumental records, the mean growth response tends to diverge more negatively from late-twentieth century temperature trends as the difference between positive and negative responders increases. Growth trend divergence is a phenomenon that has been documented at many other temperature-limited sites and at various spatial scales. To date, this phenomenon remains poorly understood and has added greater uncertainty to ring-width-based climate reconstructions prior to the twentieth century. As such, there is a need to explore alternative climate proxies such as stable isotope ratios in tree-rings to determine if they too exhibit divergence. Here we examine statistical relations between local climate and annually-resolved stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope ratios from whole-ring alpha-cellulose of three white spruce trees ( Picea glauca [Moench] Voss) in the Mackenzie Delta to evaluate their potential as paleoclimate indicators. Our δ¹³C record is positively and most strongly associated with maximum growing season (June-August) temperatures. This relation probably results from temperature induced soil moisture stress causing decreased stomatal conductance and increased ¹³C assimilation, rather than a direct temperature influence on ¹³C discrimination. Relative humidity was also significantly correlated with δ¹³C (negative relation) reflecting the direct influence of atmospheric moisture deficit on stomatal conductance. Overall, δ¹³C appears to be a proxy for effective moisture in this system. The strongest control on interannual δ¹⁸O variability was March-July minimum temperatures (positive relation) reflecting the temperature-dependence of δ¹⁸O in precipitation and subsequent use of this water during photosynthesis. Growing season relative humidity was also a significant control on δ¹⁸O variability (negative relation) through leaf water evaporative enrichment. Although relative humidity has a significant influence on both isotope ratios at annual resolution, lower-frequency variability in these proxies is dominated by temperature. Furthermore, no divergence between these proxies and their associated temperature parameter has been observed during the late-twentieth century. Both δ¹³C and δ¹⁸O time-series presented here contain a significant amount of climate-related variability and can potentially be used to explore pre-instrumental climate changes in the Mackenzie Delta.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0330 Geochemical cycles (1030)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting