Climatic inferences from glacial and palaeoecological evidence at the lastglacial termination, southern South America

There is uncertainty about the interhemispheric timing of climatic changes during the last glacial-interglacial transition. Different hypotheses, rely ing on different lines of evidence, point variously to the Northern Hemisph ere leading the Southern Hemisphere and vice versa, or to synchrony between the hemispheres. Southern South America is well placed to test the various alternatives using both glacial and palaeoecological evidence. We argue he re from a synthesis of key proxy records that there was a sudden rise in te mperature that initiated deglaciation sychronously over 16 degrees of latit ude at 14 600-14 300 C-14 yr BP (17 500-17 150 cal. yr). There was a second step of warming in the Chilean Lake District at 13 000-12 700 C-14 yr BP ( 15 650-15 350 cal. yr), which saw temperatures rise to close to modern valu es. A third warming step, particularly clear in the south, occurred at ca. 10 000 C-14 yr BP (11 400 cal. yr), the latter achieving Holocene levels of warmth. Following the initial warming, there was a lagged response in prec ipitation as the westerlies, after a delay of ca. 1600 yr, migrated from th eir northern glacial location to their present latitude, which was attained by 12 300 C-14 yr BP (14 300 cal. yr). The latitudinal contrasts in the ti ming of maximum precipitation are reflected in regional contrasts in vegeta tion change and in glacier behaviour. The large scale of a 80-km glacier ad vance in the Strait of Magellan at 12 700-10 300 C-14 yr BP (15 350-12 250 cal. yr), which spans the Antarctic Cold Reversal and the Younger Dryas, wa s influenced by the return of the westerlies to southern latitudes. The del ay in the migration of the westerlies coincides with the Heinrich 1 iceberg event in the North Atlantic. The suppressed global thermohaline circulatio n at the time may have affected sea-surface temperatures in the South Pacif ic, and the return of the westerlies to their present southerly latitude on ly followed ocean reorganisation to its present interglacial mode. Copyrigh t (C) 2000 John Wiley & Sons, Ltd.