Coral microatolls from the central Pacific record late Holocene El Nino

Microatolls are discoid corals that have grown laterally because vertical g rowth is constrained by exposure at lowest tides. We demonstrate that a mod ern reef-flat Porites microatoll from Christmas (Kiritimati) Island preserv es an oxygen isotope record of substantial sea surface temperature variatio ns related to El Nino-Southern Oscillation (ENSO). We also show that a late Holocene fossil microatoll from the centre of the island contains interann ual oxygen isotope variations over an approximate 20-year period. Three pro nounced negative isotope anomalies attributed to warm EI Nino events are su perimposed on an annual cycle. El Nino events similar to those seen in rece nt decades appear to have been a feature of mid-Pacific climate in the late Holocene. Analysis of further microatolls offers a source of pre-instrumen tal El Nino tropical climate data. It may be possible to extend the NINO-C proxy to indicate intensity and frequency of ENSO over the past three mille nnia.