Climatic signals in δ13C and δ18O of Tree-rings from White Spruce in the Mackenzie Delta Region, Northern Canada

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