Western Pacific coral δ18O records of anomalous Holocene variability in the El Nino-Southern Oscillation -: art. no. L11204

Skeletal oxygen isotope ratios in Holocene Porites corals from northern Papua New Guinea record decreases in sea surface temperature (SST) and rainfall during El Nino events. Threshold analysis of seven fossil coral delta(18)O records spanning the period 7.6-5.4 ka ( thousand years ago) shows 8-12 El Nino events/century, significantly less than the 23 events/century recorded by the NINO3.4 Index. The coral reconstructions also show a 15% reduction in El Nino event amplitude for 7.6-5.4 ka, compared to today, which is greater than the suppression given by model studies. In contrast, large and protracted El Nino events are identified for 2.5-1.7 ka. Taken together, the results indicate a nonlinear atmospheric response to Holocene changes in El Nino SST anomalies. We propose that small changes in tropical SST gradients, the positioning of the Intertropical Convergence Zone, and the Pacific tradewind climatology modify the impact of El Nino events on western Pacific rainfall.