Multidecadal rainfall variability in South Pacific Convergence Zone as revealed by stalagmite geochemistry

Pacific decadal variability (PDV) causes widespread, persistent fluctuations that affect climate, water resources, and fisheries throughout the Pacific basin, yet the magnitude, frequency, and causes of PDV remain poorly constrained. Here we present an absolutely dated, subannually resolved, 446 yr stable oxygen isotope (delta O-18) cave record of rainfall variability in Vanuatu (southern Pacific Ocean), a location that has a climate heavily influenced by the South Pacific Convergence Zone (SPCZ).The delta O-18-based proxy rainfall record is dominated by changes in stalagmite d18O that are large (similar to 1%), quasi-periodic (similar to 50 yr period), and generally abrupt (within 5-10 yr). These isotopic changes imply abrupt rainfall changes of as much as similar to 1.8 m per wet season, changes that can be similar to 2.5x larger than the 1976 C. E. shift in rainfall amount associated with a PDV phase switch. The Vanuatu record also shares little commonality with previously documented changes in the Intertropical Convergence Zone during the Little Ice Age or solar forcing. We conclude that multidecadal SPCZ variability is likely of an endogenous nature. Large, spontaneous, and low-frequency changes in SPCZ rainfall during the past 500 yr have important implications for the relative magnitude of natural PDV possible in the coming century.