Sea surface temperature variability in the southwest tropical Pacific since AD 1649

A prime focus of research is differentiating the contributions of natural climate variability from those that are anthropogenically forced, especially as it relates to climate prediction(1-3). The short length of instrumental records, particularly from the South Pacific, hampers this research, specifically for investigations of decadal to centennial scale variability(1,4). Here we present a sea surface temperature (SST) reconstruction derived from highly reproducible records of strontium-to-calcium ratios (Sr/Ca) in corals from New Caledonia to investigate natural SST variability in the southwest tropical Pacific from AD 1649-1999. Our results reveal periods of warmer and colder temperatures of the order of decades during the Little Ice Age that do not correspond to long-term variations in solar irradiance or the 11-year sunspot cycle. We suggest that solar variability does not explain decadal to centennial scale SST variability in reconstructions from the southwest tropical Pacific. Our SST reconstruction covaries with the Southern Hemisphere Pacific decadal oscillation(5) and the South Pacific decadal oscillation(6), from which SST anomalies in the southwest Pacific are linked to precipitation anomalies in the western tropical Pacific(6). We find that decadal scale SST variability has changed in strength and periodicity after 1893, suggesting a shift in natural variability for this location.