Tree-ring based reconstructions of northern Patagonia precipitation since AD 1600

Long-term reconstructions (400 years) of seasonal and annual precipitation variations were developed for northern Patagonia east of the Andes using a new set of 16 tree ring-width chronologies from Austrocedrus chilensis (D.Don) Endl. Reconstructions, which capture between 41 and 50% of the precipitation variance, show that the twentieth century contains the most extreme long periods of wetness and dryness in the past 400 years. Since about AD 1910, the reconstructions are also characterized by an increase in interannual variability and one of the highest rates of extreme events within the last 400 years. A prominent oscillation on the order of 2-2.1 years in length has been identified in the reconstructions using spectral analysis. Quasi-Biennial Oscillations have been shown to be very marked in some circulation indices of the Southern Hemisphere. Although significant oscillations within the preferred frequency domain of El Nino-Southern Oscillation (ENSO) are present in the reconstructions, no clear and consistent responses to ENSO have been observed. Correlations of reconstructions with mean sea-level pressure around South America for the interval AD 1912-1984, reveal the influence of subtropical and high-latitude features of the atmospheric circulation on precipitation variations in northern Patagonia. Droughts result from an intensification of the subtropical Pacific anticyclone off the Chilean coast and the deepness of the circum-Antarctic trough over the South Orkney-Antarctic Peninsula sector. Mean sea-level pressure reconstructions for the South Atlantic sector of the Southern Oceans were used to evaluate the temporal stability of the relationships between northern Patagonia precipitation and high-latitude climatic variations since AD 1750. The influence of high-latitude circulation on precipitation appears to be more significant during the twentieth century, which in turn may respond to an intensification of wavenumbers 3 on the mean planetary wave structure over the Southern Hemisphere. Recent increase of precipitation variability in northern Patagonia may reflect stronger interactions between middle- and high-latitude atmospheric circulation in the Southern Hemisphere during the twentieth century.