Delta18O signatures from modern and fossil equatorial Pacific microatolls: indicators of mid-late Holocene ENSO variability

This thesis examines the skeletal oxygen isotope ratios of modem and fossil massive Pontes microatolls from the reef flat and interior of Christmas Island, central equatorial Pacific Ocean. It has been known since the 1970s that the calcium carbonate skeletons of corals retain an oxygen isotopic ratio that is a function of the temperature and the isotopic signature of the sea water in which they live. Sea Surface Temperature (SST) and rainfall variation in the equatorial Pacific are major components of the El Niño Southern Oscillation (ENSO) phenomenon that dominates the ocean-atmosphere interactions of the equatorial Pacific. However, a limiting factor in the understanding of ocean-atmosphere variability is the short length of instrumental records of oceanic and atmospheric processes. To unravel the complexities of ENSO variability in the preinstrumental past, it is necessary to find high-resolution proxy records whose reliability can be tested using modem proxy and instmmental data. Palaeoclimatic proxies provide the opportunity to test the results of sophisticated modelling techniques and together a history of variability can be constmcted.