Delayed onset of the South American Summer Monsoon during the Last Glacial Maximum

Climate conditions in the Amazon basin during the last glacial maximum (LGM, about 21,000 years ago) are actively discussed in the literature. Faunal evidence, noble gas analyses, lake status reconstructions, pollen counts, atmospheric dust, and charcoal records have all been interpreted to provide information about LGM surface moisture and temperature. Much of the evidence suggests that large-scale climate conditions were drier and cooler in the Amazon basin but there is great uncertainty and little quantitative guidance. Proxy data from the high Andes and the Nordeste region of Brazil, e.g., indicate that some regions may have been wetter during the LGM. Differences in Amazon climate during the LGM are of great interest in the light of current pressing climate change issues. Fundamental questions remain about the stability of tropical climate, and the infl uence of climate and deforestation on the diversity of tropical vegetation.