Tree-ring cellulose δ18O records similar large-scale climate influences as precipitation δ18O in the Northwest Territories of Canada

Abstract

Stable oxygen isotopes measured in tree rings are useful for reconstructing climate variability and explaining changes in physiological processes occurring in forests, complementing other tree-ring parameters such as ring width. Here, we analyzed the relationships between different climate parameters and annually resolved tree-ring δ18O records (δ18OTR) from white spruce (Picea glauca [Moench]Voss) trees located near Tungsten (Northwest Territories, Canada) and used the NASA GISS ModelE2 isotopically-equipped general circulation model (GCM) to better interpret the observed relationships. We found that the δ18OTR series were primarily related to temperature variations in spring and summer, likely through temperature effects on the precipitation δ18O in spring, and evaporative enrichment at leaf level in summer. The GCM simulations showed significant positive relationships between modelled precipitation δ18O over the study region and surface temperature and geopotential height over northwestern North America, but of stronger magnitudes during fall-winter than during spring–summer. The modelled precipitation δ18O was only significantly associated with moisture transport during the fall-winter season. The δ18OTR showed similar correlation patterns to modelled precipitation δ18O only during spring–summer when water matters more for trees, with significant positive correlations with surface temperature and geopotential height, but no correlations with moisture transport. Overall, the δ18OTR records for northwestern Canada reflect the same significant large-scale climate patterns as precipitation δ18O for spring–summer, and therefore have potential for reconstructing past atmospheric dynamics in addition to temperature variability in the region.