Sam-like Hydroclimate changes at centennial timescale during the last three millennia in Southwestern Patagonia

VILANOVA I.; MORENO P.I.; RODRIGO VILLA-MARTINEZ; GARREAUD, R.D; MAISA ROJAS; RICARDO DE POL-HOLZ

Medellín

Simposio; LOTRED -3rd International Symposium. Climate change and human impact in Central and South America over the last 2000 ears. Observations and models; 2014

PAGES

Late twentieth-century instrumental records reveal a persistent southward shift of the Southern Westerly Winds (SWW) during austral summer and fall associated with a positive trend of the Southern Annular Mode (SAM), contemporaneous with glacial recession, steady increases in atmospheric temperatures and CO2 concentrations. Stratigraphic records from sensitive locations in the southern mid-latitudes offer a longer-term perspective on the evolution of the SWW and modes of atmospheric variability such as SAM. Despite its importance in modern and future climate, very little is known about the behavior of SAM in pre-Industrial time. To date, it is unclear whether SAM phenomenon represents natural variability or a response to human-induced climate perturbations. Here we present paleovegetation and paleofire records from southwestern Patagonia (51°S) that show recurrent ~200-yr long dry/warm phases over the last three millennia which we interpret as positive SAM-like states. The most recent of these phases started in the late 19th century and has persisted until the present, concomitant with positive anomalies of the SAM and widespread disturbance of southwestern Patagonian environments by Euro-Chilean settlers. These ~200-yr long dry/warm phases correspond in timing with the Industrial revolution, the Mediaeval Climate Anomaly, the Roman and Late Bronze Age Warm Periods. We conclude that centennial-scale changes occurred in phase in both hemispheres over the last 3000 years, suggesting tight interhemispheric phasing through atmospheric teleconnections, and that the current poleward shift and intensification of the SWW reflects juxtaposition of natural and human-induced variability since the 19th century.