Pollen evidence for variations in the southern margin of the westerly winds in SW Patagonia over the last 12,600 years

Abstract

We report pollen and charcoal records from Vega Ñandú (∼51°0′S, 72°45′W), a small mire located near the modern forest-steppe ecotone in Torres del Paine National Park, southern Chile. The record shows an open landscape dominated by low shrubs and herbs between 12,600 and 10,800 cal yr BP, under cold and relatively humid conditions. Nothofagus experienced frequent, large-amplitude oscillations between 10,800 and 6800 cal yr BP, indicating recurrent transitions between shrubland/parkland environments, under warm and highly variable moisture conditions. A sustained increase in Nothofagus started at 6800 cal yr BP, punctuated by step-wise increases at 5100 and 2400 cal yr BP, implying further increases in precipitation. We interpret these results as indicative of variations in the amount of precipitation of westerly origin, with prominent increases at 6800, 5100, and 2400 cal yr BP. These pulses led to peak precipitation regimes during the last two millennia in this part of SW Patagonia. Our data suggest variations in the position and/or strength of the southern margin of the westerlies, most likely linked to variations in the extent and/or persistence of sea ice and sea-surface temperature anomalies in the Southern Ocean. Over the last two centuries the record shows a forest decline and expansion of Rumex acetosella, an exotic species indicative of European disturbance.