New views of tropical paleoclimates from corals

Corals offer a rich archive of past climate variability in tropical ocean r egions where instrumental data are limited and where our knowledge of multi -decadal climate sensitivity is incomplete. In the eastern equatorial Pacif ic, coral isotopic records track variations in ENSO-related changes in sea- surface temperature; further west, corals record variability in sea-surface temperature and rainfall that accompanies zonal displacement of the Indone sian Low during ENSO events. These multi-century records reveal previously unrecognised ENSO variability on time scales of decades to centuries. Outsi de the ENSO-sensitive equatorial Pacific, long-term trends towards recent w armer/wetter conditions suggest the tropics respond to global forcings. New coral paleothermometers indicate that surface-ocean temperatures in the tr opical southwestern Pacific were depressed by 4-6 degrees C during the Youn ger Dryas climatic event and rose episodically during the next 4000 yr. Hig h temporal-resolution measurements of Sr/Ca and delta(18)O in corals provid e information about the surface-ocean hydrologic balance and can resolve th e seasonal balance between precipitation and evaporation. Radiocarbon measu rements in corals, coupled with ocean circulation models, may be used to re construct near-surface ocean circulation, past mixing rates, and the distri bution of fossil fuel CO2 in the upper ocean. Most recently, seasonal to in terannual variations in the radiocarbon of corals from the equatorial Pacif ic have been linked to the redistribution of surface waters associated with the ENSO. (C) 1999 Elsevier Science Ltd. All rights reserved.