Ice-core palaeoclimate records in tropical South America since the Last Glacial Maximum

Ice-core records spanning the last 25 000 yr from the tropical Andes of Sou th America are reviewed. These records from Quelccaya, Huascaran and Sajama present a high temporal resolution picture of both the Late Glacial Stage (LGS) and the Holocene climatic and environmental conditions in the South A merican Andes. Late Glacial Stage conditions at high elevations appear to h ave been cooler than today, although the magnitude of the inferred cooling differs with the particular proxy used (e.g. snowline depression, pollen, i ce cores). Insoluble dust and anion concentrations in the ice cores reveal that LGS hydrological conditions in the tropics (9 degrees S) were much dri er than today, whereas in the subtropics (18 degrees S) LGS conditions were much wetter. This probably reflects the migration of the tropical Hadley C ell in response to a different meridional temperature gradient. Low nitrate concentrations in the LGS ice from both Huascaran and Sajama suggest that the Amazon Basin forest cover may have been much less extensive. Discussed is the conundrum surrounding the use of delta(18)O as a palaeothermometer i n the tropics, where temperatures exhibit little seasonal variation yet the ice-core records suggest that delta(18)O records temperature variations on decadal to millennial time-scales. Finally evidence is presented for a str ong twentieth century warming. Copyright (C) 2000 John Wiley & Sons, Ltd.