Patterns of Pacific decadal variability recorded by Indian Ocean corals

We investigate Pacific Decadal Oscillation (PDO) signals recorded by two bimonthly resolved coral delta O-18 series from La R,union and Ifaty (West Madagascar), Indian Ocean from 1882 to 1993. To isolate the main PDO frequencies, we apply a band pass filter to the time series passing only periodicities from 16 to 28 years. We investigate the covariance patterns of the coral time series with sea surface temperature (SST) and sea level pressure (SLP) of the Indian and Pacific Oceans. In addition, the empirical orthogonal functions of the filtered SST and SLP fields (single and coupled) are related to the filtered coral times series. The covariance maps show the typical PDO pattern for SST and SLP, confirming the coupling between the Indian and Pacific Oceans. Both corals show the strongest signal in boreal summer. The La R,union (Ifaty) coral better records SST (SLP) than SLP (SST) pattern variability. We suggest that the filtered La R,union coral delta O-18 represents delta O-18 of seawater that varies with the South Equatorial Current, which, in turn, is linked with the SST PDO. The filtered Ifaty coral delta O-18 represents SST and is remotely linked with the SLP PDO variability. A combined coral record of the Ifaty and La R,union boreal summer delta O-18 series explains about 64% of the variance of the coupled SST/SLP PDO time series.