Centennial-Scale Hydroclimate Changes in the Southern Mid-Latitudes Over the Last 3000 Years

Twentieth-century instrumental records reveal a persistent, year-round acceleration and a summer southward shift of the Southern Westerly Winds (SWW) associated with a positive trend of the Southern Annular Mode (SAM), contemporaneous with glacial recession at a global scale, 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. Here we present a paleovegetation and paleofire record from Lago Cipreses (51°S), southwestern Patagonia, that reveals recurrent centennial-scale dry/warm phases over the last 3000 years. 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. Nearly identical shifts at 0.8-1.1, 2-2.2, and 2.8-3.1 ka overlap in timing with the Medieval, Roman, and Late Bronze Age Warm Periods, respectively, and alternate with humid phases quasi-contemporaneous with the Little Ice Age, the Dark Ages and the Iron Age cold periods. We interpret these changes as secular SAM-like oscillations that varied in concert with important climatic anomalies in the Northern Hemisphere (NH), i.e. positive SAM-like changes corresponding with warm/dry episodes in the NH, and viceversa. We propose that the current poleward shift and intensification of the SWW is unprecedented in the context of the last 3000 years and might reflect juxtaposition of natural and human-induced variability since the late 19th century.