The Old man and the Giant clam: climate variability and prehistoric human migration in the Pacific

Abstract

The Lapita migration, which occurred 3,000 years ago, is one of the most remarkable prehistoric human migration: the Lapita seafarers went across 4,000 km of uncharted seas to settle in the islands of the southwest Pacific. The factors that drove this event are still unknown. It has been hypothesized that an increase in the El Niño Southern Oscillation –ENSO – may have triggered this migration. To explore the possible influence of ENSO forcing the Lapita migration, bulk oxygen stable isotopes records were obtained from fossil giant clams, unearthed from Lapita archaeological sites of SW Pacific and a modern baseline was obtained from modern conspecifics. Fossil giant clams showed that climate oscillated between 1) present day conditions and 2) warmer / fresher conditions at the inter-annual time-scale. This suggests that Lapita migration occurred concomitantly with a strong ENSO variability. The potential dramatic environmental degradations caused by the increased ENSO variability (droughts, malaria, wildfires…) may have acted as a push factor for the Lapita migration. Frequent shifts in prevailing wind regimes associated with ENSO may have also facilitated the discovery of new islands.