Persistent decadal-scale rainfall variability in the tropical South Pacific Convergence Zone through the past six centuries

Abstract

Modern Pacific decadal variability (PDV) has global impacts; hence records of PDV from the preinstrumental period are needed to better inform models that are used to project future climate variability. We focus here on reconstructing rainfall in the western tropical Pacific (Solomon Islands; ∼9.5∼ S, ∼160∼ E), a region directly influenced by PDV, using cave deposits (stalagmite). A relationship is developed between δ18O variations in the stalagmite and local rainfall amount to produce a 600 yr record of rainfall variability from the South Pacific Convergence Zone (SPCZ). We present evidence for large (∼1.5 m), abrupt, and periodic changes in total annual rainfall amount on decadal to multidecadal timescales since 1423±5 CE (Common Era) in the Solomon Islands. The timing of the decadal changes in rainfall inferred from the 20th-century portion of the stalagmite δ18O record coincides with previously identified decadal shifts in PDV-related Pacific ocean-atmosphere behavior (Clement et al., 2011; Deser et al., 2004). The Solomons record of PDV is not associated with variations in external forcings, but rather results from internal climate variability. The 600 yr Solomon Islands stalagmite δ18O record indicates that decadal oscillations in rainfall are a persistent characteristic of SPCZ-related climate variability.