500 years of past temperatures derived using Blue Intensity from Araucaria araucana in Northern Patagonia, Argentina
Ring-width (RW) and Blue Intensity (BI) parameters (earlywood - EWB, inverted latewood – LWBinv, and delta - DB) were measured from samples of Araucaria araucana from six sites in northern Patagonia, Argentina. The distance between the most southerly and northerly sites is ca. 130 kms. Despite a much weaker between-tree signal for the BI parameters than RW, principal component analysis identifies a much stronger regional between-site signal for the BI parameters. Split period correlation response function analysis (1901-1958 / 1959-2017) of the tree-ring parameters against monthly temperatures, precipitation and PDSI (CRUTS-4) shows an insignificant or unstable coherence with hydroclimate, but a strong stable response between DB and summer mean temperatures. LWBinv also shows a similar temperature response but it is slightly weaker for the earlier period (1901-1958). Regional composite averaging and principal component regression experiments lead to similar reconstructions of past December-March mean temperatures, dominated by the DB parameter, that explain 41-43% of the temperatures. Despite these encouraging results, a weakening in the calibrated signal in recent decades is noted. The reconstruction variants indicate a significant regional ca. 1 oC warming of summer temperatures since the late-19th century and distinct cold years which are coincident with major volcanic eruptions (e.g. 1729, 1815).