A study reveals a significant climate change in the South Pacific around 1,000 years ago, with western islands drying out while eastern ones grew wetter. This shift aligned with the last major wave of Polynesian migration eastward. Researchers suggest communities moved to follow reliable rainfall sources across the ocean.
Researchers from the University of Southampton and the University of East Anglia have uncovered evidence of a major hydroclimatic shift in the South Pacific starting about 1,000 years ago. Through the PROMS project, which examines Pacific rainfall over millennial timescales, the team analyzed sediment cores from islands like Tahiti and Nuku Hiva in Eastern Polynesia. By studying plant waxes in these cores, they reconstructed rainfall patterns over the past 1,500 years, revealing a drying trend in Western Polynesia, including Samoa and Tonga, contrasted by increasing wetness in Eastern Polynesia, such as French Polynesia.
This change, driven by natural variations in sea surface temperatures, shifted the South Pacific Convergence Zone eastward between approximately 1,100 and 400 years ago. The SPCZ, a vast rainfall band spanning over 7,000 km, saw its western end dry out while the eastern portion became more humid. Such conditions likely strained freshwater resources in established western settlements, acting as a push factor for migration.
At the same time, enhanced rainfall in the east created a pull toward new, habitable islands. The timing matches the final phase of human settlement in Eastern Polynesia, including areas like the Cook Islands and Tahiti. As Professor David Sear, principal investigator for PROMS, noted, "beginning around 1,000 years ago, people in the region were effectively chasing the rain eastwards as part of adapting to the stress placed on growing populations by a period of drier conditions developing in the western South Pacific."
Dr. Mark Peaple, co-lead author from Southampton, emphasized the role of water: "Water is essential for people's survival, for drinking and successful agriculture. If this vital natural resource was running low, it's logical that over time the population would follow it and colonize in areas with more reliable water security—even if this meant adventurous journeys across the ocean."
Dr. Daniel Skinner from UEA added that combining paleoclimate data with models provided insights into this understudied region's changes. Professor Manoj Joshi highlighted implications for future predictions: "By better understanding how the climate of the South Pacific has been affected by larger-scale climate changes over past millennia, we can build better predictions for how future climate change will affect the region."
The findings appear in Communications Earth & Environment. Further archaeological research could refine the links between environmental shifts and social movements. Fieldwork received support from National Geographic Society grants.