New views of tropical paleoclimates from corals

Abstract

Corals offer a rich archive of past climate variability in tropical ocean regions where instrumental data are limited and where our knowledge of multi-decadal climate sensitivity is incomplete. In the eastern equatorial Pacific, 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 Indonesian Low during ENSO events. These multi-century records reveal previously unrecognised ENSO variability on time scales of decades to centuries. Outside the ENSO-sensitive equatorial Pacific, long-term trends towards recent warmer/wetter conditions suggest the tropics respond to global forcings. New coral paleothermometers indicate that surface-ocean temperatures in the tropical southwestern Pacific were depressed by 4-6°C during the Younger Dryas climatic event and rose episodically during the next 4000 yr. High temporal-resolution measurements of Sr/Ca and δ18O in corals provide information about the surface-ocean hydrologic balance and can resolve the seasonal balance between precipitation and evaporation. Radiocarbon measurements in corals, coupled with ocean circulation models, may be used to reconstruct near-surface ocean circulation, past mixing rates, and the distribution of fossil fuel CO2 in the upper ocean. Most recently, seasonal to interannual variations in the radiocarbon of corals from the equatorial Pacific have been linked to the redistribution of surface waters associated with the ENSO.