Coral-based climate variability in the Western Pacific Warm Pool since 1867

We have generated monthly resolved, stable isotope (delta O-18 and delta C-13) and Sr/Ca time series from a massive Porites coral from Rabaul (4 degrees S, 152 degrees E): a site located in the warmest sector of the Western Pacific Warm Pool (WPWP). The coral delta O-18 and Sr/Ca time series are well correlated to each other and positive excursions in both records coincide with times of ENSO warm phase events. These time series contain abundant interannual variability that exhibits the well-recognized pattern of low amplitude ENSO variation between similar to 1920-1960 and high amplitude ENSO variation between 1880-1920 and 1960-1997. The ENSO-filtered coral delta O-18 and Sr/Ca time series are well matched to each other (r=0.73) and to similarly filtered coral delta O-18 records from Papua New Guinea (r>0.56). There is no long-term trend in the coral delta O-18 record, but there is a long-term trend of increasing coral Sr/Ca from 1867 to 1997. This trend in coral Sr/Ca suggests a cooling of similar to 0.7 degrees C, which is rather unlikely and implies that factors other than SST may be influencing the coral Sr/Ca record. The trend in coral Sr/Ca is not an analytical artifact, nor a product of time varying riverine input, nor a product of skeletal diagenesis, nor the results of kinetic effects, but may reflect surface-water variability in Sr/Ca. Despite the presence of a nonclimatic trend in coral Sr/Ca, the Rabaul coral records contain abundant interannual- to multidecadal-scale variability, much of which is coherent with other proxy records from the WPWP and with instrumental records of ENSO variability.