Reassessment of ice-age cooling of the tropical ocean and atmosphere

The CLIMAP(1) project's reconstruction of past sea surface temperature infe rred limited ice-age cooling in the tropical oceans. This conclusion has be en controversial, however, because of the greater cooling indicated by othe r terrestrial and ocean proxy data(2-6). A new faunal sea surface temperatu re reconstruction, calibrated using the variation of foraminiferal species through time, better represents ice-age faunal assemblages and so reveals g reater cooling than CLIMAP in the equatorial current systems of the eastern Pacific and tropical Atlantic oceans(7). Here we explore the climatic impl ications of this revised sea surface temperature field for the Last Glacial Maximum using an atmospheric general circulation model. Relative to model results obtained using CLIMAP sea surface temperatures, the cooler equatori al oceans modify seasonal air temperatures by 1-2 degrees C or more across parts of South America, Africa and southeast Asia and cause attendant chang es in regional moisture patterns. In our simulation of the Last Glacial Max imum,the Amazon lowlands, for example, are cooler and drier, whereas the An dean highlands are cooler and wetter than:the control simulation. Our resul ts may:help to resolve some of the apparent disagreements between oceanic a nd continental proxy climate data. Moreover, they suggest a wind-related me chanism for enhancing the export of water vapour from the Atlantic to the I ndo-Pacific oceans, which may link variations in deep-water production and high-latitude climate changes to equatorial, sea surface temperatures.