Tropical South America during the Last Glacial Maximum: evidence from glacial, periglacial and fluvial records

The records of the LGM climates of tropical South America are still sparse compared to the vast region under consideration. Nevertheless, a number of records hold up to critical evaluation. Early attempts to reconstruct the L GM temperature and precipitation conditions for the LGM, around 21 C-14 ka BP, have suggested that relative to present, lowland temperatures were on a verage only a few degrees C cooler, whereas in the Andes the temperature de pression was in the range of 6-8 degrees C. These reconstructions further s uggested that tropical precipitation was more limited in both the lowlands and in the Andes. Although recent pollen evidence supports significantly co oler tropical lowland temperatures during the LGM, additional (alkenone) ev idence from sea-surface temperatures and model analysis are contradictory. The data from tropical South America suggest that the late Quaternary clima tic changes of the lowlands as well as of the Andean mountains reflect a re sponse (1) to environmental changes in the source area of the moisture and (2) to global temperature fluctuations. Based on glacial, periglacial and p ollen evidence, a LGM temperature depression of 5-6 degrees C can be assume d for both tropical lowland South America and the Andes. These LGM values f or the cooling correspond with recent coral records from Barbados and the s outhwestern Pacific, ice-core records from Peru, noble-gas measurements in Brazil and ocean core records from the western equatorial Atlantic. No diff erence in the value of LGM cooling can be recognised between the tropical l owlands and the high mountains of South America. Furthermore, in all region s the LGM climates were more arid than the present-day climates. Terrestria l records have not yet yielded records of Younger Dryas age apart from the tropical Andes of Ecuador where the Younger Dryas time is characterised by a cooler and drier climate. Pollen evidence for cooler Younger Dryas condit ions comes from the Bolivian Andes. (C) 2000 Elsevier Science Ltd and INQUA . All rights reserved.