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°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 ∼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 ∼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.