ANALYSIS OF NEW BLUE INTENSITY AND RING WIDTH TREE RING CHRONOLOGIES AS PROXIES FOR NORTH PACIFIC CLIMATE CHANGE, COLUMBIA BAY, ALASKA

Ring width and blue intensity (BI) series from mountain hemlock (Tsuga mertensiana) sites in Columbia Bay, Alaska help provide the primary climate calibration for millennial-long tree ring series for the Gulf of Alaska (GOA). BI tree-ring measurements for early and latewood are a relatively new climate sensitive parameter is thought to reflect variations in lignin content that is in turn related to summer temperature for coastal sites along the GOA. Three coastal hemlock sites from the Columbia Bay fjord are located within a 10 km radius of each other and between 250 and 450 m.a.s.l. and are some of the most northerly tree ring sites for this coastal species. For each of the sites we have recently developed ring-width and blue intensity tree-ring chronologies both primarily proxies for north Pacific temperature variability. The tree-ring width records are, in part, a record of winter to spring temperatures capturing high and low frequency variability and BI record indicate the year to year (high frequency) summer variations. Spatial correlation patterns of tree-ring parameters with sea surface temperatures mimic the large-scale modes of Pacific variability including the Pacific Decadal Oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO); two modes that dominate the North Pacific sea surface temperature. Individual ring-width series are strongly correlated with the PDO index and with temperature records from local meteorological stations along the GOA and with lower latitude stations in southern California and the Nino4 region of the tropical Pacific consistent with the NPGO pattern.

Further work exploring these three Columbia Bay sites and climate connections and their relatiohsip to Pacific patterns over time are being investigated. Specifically, we have noted changing climate responses over time with the lower elevation site losing sensitivity to climate for ring-width and BI. Hypotheses to explain this non stationary response include differences in the tree age at sites or the loss of snow pack at lower elevations negatively affecting tree growth. The new BI parameter for early and latewood tree growth allows us to examine the seasonality of the tree response to climate as well as the annual signal and thus we will develop a more complete understanding of these tree ring proxies for the North Pacific.