摘要：Here we present the first tree-ring series (1850–2003) of stable carbon (δ 13 C) and oxygen (δ 18 O) isotope ratios from a high-latitude treeline site in northwestern Canada. Both δ 13 C and δ 18 O were measured at annual resolution from whole-ring α-cellulose of three white spruce trees ( Picea glauca [Moench] Voss) growing in the Mackenzie Delta. There is a strong positive association between δ 13 C and maximum summer temperatures. This relation likely results from the influence of temperature-induced drought stress on stomatal conductance. Mean summer relative humidity is also significantly correlated, inversely, with δ 13 C reflecting its direct influence on stomatal conductance. The δ 18 O record is strongly and positively correlated with early-spring to mid-summer minimum temperatures likely owing to the temperature dependence of δ 18 O in precipitation and uptake of this water during the growing season. Mean summer relative humidity is also significantly and inversely correlated with δ 18 O due to leaf water evaporative enrichment. Our δ 13 C and δ 18 O records contain a large amount of climate-driven variability indicating their considerable potential to infer past climate changes in the Mackenzie Delta region.
