Late Quaternary climatic changes in southern Chile, as recorded in a diatom sequence of Lago Puyehue (40°40' S)

A late Quaternary diatom stratigraphy of Lago Puyehue (40 degrees 40'S, 72 degrees 28'W) was examined in order to infer past limnological and climatic changes in the South-Chilean Lake District. The diatom assemblages were well preserved in a 1,122 cm long, (14)C-dated sediment core spanning the last 17,900 years, and were in support of an early deglaciation of Lago Puyehue. The presence of a short cold spell in South Chile, equivalent to the Younger Dryas event in the Northern Hemisphere, the Antarctic Cold Reversal in Antarctica, or the Huelmo-Mascardi event in southern South America, was not clearly evidenced in the diatom data, although some climate instability may have occurred between 13,400 and 11,700 cal. yr. BP, and a relatively long period (between 16,850 and 12,810 cal. yr. BP) with low absolute abundances and biovolumes could be tentatively interpreted as a period of low rainfall and/or temperatures. An increase in the moisture supply to the lake was tentatively inferred at 12,810 cal. yr. BP. After 9,550 cal. yr. BP, inferred stronger and longer persisting summer stratification, may have been the result of the higher temperatures associated with an early-Holocene thermal optimum. The mid-Holocene appeared to be characterized by a decrease in precipitation, culminating around 5,000 cal. yr. BP, and rising again after 3,000 cal. yr. BP, likely associated with a previously documented lowered frequency and amplitude of El Nino events. An increase in precipitation during the late Holocene (3,000 cal. yr. BP-present) might have marked subsequent increased frequency of El Nino occurrences, leading to drier summers and slightly moister winters in the area