Author : Gedalof, Z. Date : 1999. Title : Low Frequency Climate Variability in the Northeast Pacific Interpreted from the Annual Growth-Rings of Mountain Hemlock. Publication : Unpublished M.Sc. thesis. University of Victoria, Victoria, British Columbia. Issue : Page(s) :
The purpose of this study was to investigate interdecadal climate variability in the Pacific Northwest and Gulf of Alaska. A transect of representative meteorological stations and ring-width measurements from high-elevation stands of mountain hemlock was analysed using principal components analysis and time-series techniques. This transect extends from northern California to the Kenai Peninsula, Alaska. Analysis of the instrumental record showed that coastal climate is responsive to large scale climate forcing, related both to tropical and extra-tropical forcing systems. Abrupt regime-scale shifts in temperature and precipitation were evident in the principal component time-series. Response function analysis of the mountain hemlock chronologies identified spring and summer temperatures ad being the dominant climatic factors which enhance growth throughout the study area. South of Alaska, winter precipitation is also a limiting factor, while at higher latitudes, spring precipitation enhances radial-growth. Principal components analysis of the mountain hemlock chronologies showed that variability in annual radial-growth is well correlated throughout most of the Pacific Northwest and Gulf of Alaska. A subset of these chronologies, selected on the basis of climatic sensitivity and duration, was used to construct a proxy record of variability in the mean spring (MAM) Pacific Interdecadal Oscillation Index. Analysis of this record suggests that interdecadal climate variability was more pronounced prior to 1850 than it has been throughout most of the secular record. Regime-scale climate shifts are common throughout this period, and the observed 1976 event may mark a return to this mode of variability.