Environmental evolution of the Andes east of the North Patagonian Icefield since ∼19.3 ka

Abstract

We examine the environmental evolution of the central Patagonian Andes from -19.3 ka to the present using lake sediment cores from Valle Chacabuco (-47 degrees S). Our results reveal the dominance of cold-tolerant herbs and shrubs between -19.3 and 11 ka, within which we observe a shift to Poaceae-dominated assemblages and a Pediastrum rise at-17.8 ka succeeded by a gradual arboreal rise that started at -14.5 ka and culminated with the establishment of Nothofagus-dominated woodlands between -9.8-8.8 ka. We interpret modest warming at -17.8 ka and -12.7 ka and increases in precipitation at -17.8 ka and -14.5 ka, followed by major warming and a precipitation decline at -11 ka that accentuated at -8.8 ka. Precipitation increased at -7.8 ka and led to the establishment of closed-canopy forests that have persisted with modest but significant fluctuations until recent. We detect abrupt vegetation changes at -17.7 ka, -12.7 ka, -11 ka, and -7.8 ka, driven primarily by changes in southern westerly wind (SWW) influence and, secondarily, by intense fire activity. Terrestrial and aquatic ecosystems show pervasive millennial and centennial-scale alternations between warm/dry and cold/wet states since similar to 11 ka contemporaneous with glacier fluctuations in nearby Monte San Lorenzo, suggesting recurrent oscillations in SWW influence. Deforestation and spread of non-native plants attest to disturbance by Chilean/European settlers since similar to 0.3 ka. Our results and conclusions reinforce the concept that variations in temperature and precipitation related to changes in the position/strength of the SWW underpin millennial/centennial timescales in the biosphere, hydrosphere, and cryosphere at Patagonian, zonal, and hemispheric scales