Recent changes in climate in the far western equatorial Pacific and their relationship to the Southern Oscillation; oxygen isotope records from massive corals, Papua New Guinea

Abstract

The western equatorial Pacific warm pool is believed to be the source region of a substantial proportion of the world's inter-annual climate variability, including the globally significant El Nin˜o-Southern Oscillation. Here new data are presented on changes in the climate of this region over the past 70 yr, based on analysis of the stable oxygen isotopic composition of annually banded, massive corals living on the north coast of Papua New Guinea. In this area, the coincidence of abundant and isotopically light rainfall with small seasonal and inter-annual changes in temperature means that the coral skeletal δ 18O record may be reliably interpreted in terms of rainfall variation. Since the abundance of rainfall is governed by the intensity of deep atmospheric convection, the coral records provide regionally significant, and regionally reproducible, climatic indices. In particular, the coral records indicate larger changes in the degree of coupling of the climate of the region with the Southern Oscillation than have hitherto been described. These changes in coupling, which accompany shifts in the dominant periodicities of inter-annual climate variation, are indicative of rapid and large-scale reorganisation of ocean-atmosphere interactions. The data indicate that from the 1920s to 1950s the western equatorial Pacific was less important in modulating Pacific and global inter-annual climatic variability than it has appeared to be subsequently. The reproducibility of the coral climate records, combined with the presence on the north coast of Papua New Guinea of extensive and well preserved raised reef terraces, leads to the potential for extending understanding of climatic variability in this globally important region back into the late Quaternary.