Holocene Southwest Pacific Climatic variability at c.7000-6000 and 3500-2500 years BP from biocarbonated archives.

This study aims to document the climate for two key periods of the Holocene from biocarbonated archives. The giant clam Tridacna maxima was validated as a paleoclimatic archive. Fossil specimens of this species were used to document the climatic variability in the Southwest Pacific during the early mid-Holocene - 7.0-6.0 ka BP - and during the Lapita migration over Remote Oceania - 3.5-2.5 ka BP - in addition to δ18O records from fossils specimens of giant clams T. gigas, Hippopus hippopus and fossils massive coral Porites sp. Records of Sr/Ca from Porites sp. corals also provided paleo-SST records. The post glacial SST rise was completed at 7.0-6.0 ka BP and the southeastern edge of the WPWP was located in its current location. At that time the seasonal influence of the SPCZ over the SW Pacific was weaker than it is today as a result of the more northerly location of this structure. The El Niño Southern Oscillation (ENSO) variability was 20-30% weaker than today. The period when the Lapita culture at 3.6-3.4 ka BP, was characterized by a La Niña-like climatic mean state in the SW Pacific. The Lapita migration-phase at 3.2-2.7 ka BP is coincidental with a strong ENSO variability supporting that the climate had a significant role in the Lapita migration. Indeed, unstable climate may have triggered and/or promoted the development and the expansion of nomad foraging population based on marine resources as the Lapita were.