Study links Polynesian expansion to drought and wetter islands

A new climate study suggests the end of Polynesia’s 1,700-year eastward pause was driven by drought in Samoa and Tonga and wetter conditions farther east. The finding adds a fresh environmental explanation to one of the Pacific’s most important movement stories, when voyagers moved from Samoa and Tonga into the rest of the Polynesian triangle.

Researchers from the Universities of Southampton and East Anglia, including David Sear and Mark Peaple, published the work in the Journal of Pacific Archaeology in 2026. Their analysis traces a sequence that began about 3,000 years ago, when the ancestors of modern Polynesians reached Samoa and Tonga, then stayed there for roughly 1,700 years before voyaging east around 900 to 1050 AD. Within about 250 years, those settlers had reached Tahiti, Hawai’i and Rapa Nui, and had extended into the continental Americas.

To test what changed, the team examined mud samples from swamps and lakes in Samoa, Tonga, French Polynesia and the Cook Islands. They used biochemical fossils from freshwater algae and leaves to measure hydrogen isotopes and reconstruct historic rainfall. The pattern they found points to a major shift: the end of the Long Pause lined up with a mega drought in the homeland islands and rising rainfall in the islands to the east.

The study argues that the driest period in the last 2,000 years for these islands likely pushed populations to move east, where they encountered wetter islands with nobody on them. That does not settle every question about why expansion happened when it did, but it strengthens the case that climate did more than set a backdrop. It shaped the routes available, the timing of departure and the islands that could sustain new communities.

The new results also build on earlier work from the University of Auckland, which suggested East Polynesia may have been settled earlier than once thought and that migration unfolded incrementally over multiple generations rather than in a single surge. That study dated human and pig biomarkers in sediments from Atiu Island’s Lake Te Roto to between 800 and 1000 CE, placing people in the southern Cook Islands two to three centuries earlier than previous estimates and identifying that region as a gateway to East Polynesia. The broader debate remains open, but the evidence now points more firmly to a South Pacific where rainfall, drought and ocean crossings moved together.