TREE-RING BASED RECONSTRUCTIONS OF NORTHERN PATAGONIA PRECIPITATION SINCE AD-1600

Long-term reconstructions (400 years) of seasonal and annual precipita tion variations were developed for northern Patagonia east of the Ande s 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 co ntains the most extreme long periods of wetness and dryness in the pas t 400 years. Since about AD 1910, the reconstructions are also charact erized by an increase in interannual variability and one of the highes t rates of extreme events within the last 400 years. A prominent oscil lation on the order of 2-2.1 years in length has been identified in th e 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 pref erred frequency domain of El Nino-Southern Oscillation (ENSO) are pres ent in the reconstructions, no clear and consistent responses to ENSO have been observed. Correlations of reconstructions with mean sea-leve l pressure around South America for the interval AD 1912-1984, reveal the influence of subtropical and high-latitude features of the atmosph eric circulation on precipitation variations in northern Patagonia. Dr oughts result from an intensification of the subtropical Pacific antic yclone off the Chilean coast and the deepness of the circum-Antarctic trough over the South Orkney-Antarctic Peninsula sector. Mean sea-leve l pressure reconstructions for the South Atlantic sector of the Southe rn Oceans were used to evaluate the temporal stability of the relation ships between northern Patagonia precipitation and high-latitude clima tic variations since AD 1750. The influence of high-latitude circulati on on precipitation appears to be more significant during the twentiet h century, which in turn may respond to an intensification of wavenumb ers 3 on the mean planetary wave structure over the Southern Hemispher e. Recent increase of precipitation variability in northern Patagonia may reflect stronger interactions between middle- and high-latitude at mospheric circulation in the Southern Hemisphere during the twentieth century.