Ice age vegetation and climate of subtropical Chile

Abstract

Vegetation and climate of subtropical Chile over the past > 50,000 yr are reconstructed from pollen, spores, and other microfossils contained in a 10.7-m section of lacustrine deposits of Laguna de Tagua Tagua (34°30′ S, 71°10′W). Controlled by 14 radiocarbon age determinations, five pollen assemblages covering stratigraphic zones in the section represent plants on the upland and species inhabiting the lake basin. Surface pollen spectra from 58 stations (approximately 30–40°S) form an adjunct for interpreting past vegetation and climate from the fossil record. Temperature, semi-humid woodland of southern beech ( Nothofagus dombeyi type) and podocarp ( Prumnopitys andina) was apparently established about Laguna de Tagua Tagua during the Pleistocene. Contrasting existing semi-arid, broad sclerophyllous vegetation, the woodland was extensive about the lake at the time of the last glacial maximum (25,000–14,000 yr B.P.) and earlier (> 43,000–34,000 yr B.P.). Pollen from the families Chenopodiaceae and Amaranthaceae, which characterize intervals of the Pleistocene (centered around 33,000 and >43,000 yr B.P.) and the Holocene, suggests intervening episodes of relative aridity. Lake level fluctuations appear to follow the late Quaternary climatic pattern implied by pollen assemblage data. Water in the lake was relatively high during development of southern beech-podocarp woodland, whereas during intervals of chenopod-amaranth dominance, lake levels were comparatively low. Excess precipitation over evaporation, which during the Pleistocene favored development of woodland of beech and podocarp, is attributed to greater storm frequency. Conditions were apparently governed by strengthening of atmospheric circulation in the belt of southern westerly winds. In the late-glacial, the temperate and more humid, ice age climate with limited seasonality underwent transition to a subtropical, semi-arid, Mediterranean type that identifies the postglacial. Fluctuations in intensity of the southern westerlies, marked by latitudinal movement of the polar front, can account for past vegetation changes at Laguna de Tagua Tagua.