Settling of East Polynesia earlier and likely connected to prolonged drought

The study’s findings contrast with earlier theories that argued migration to Eastern Polynesia was a rapid, wave-like event. Instead, the authors propose it was an incremental process, possibly extending over multiple generations and coinciding with some of the driest conditions of the last two millennia.

Reflecting a growing interest in transdisciplinary research, University of Auckland archaeologist Professor Melinda Allen teamed up for the study, published last week in the Proceedings of the National Academy of Sciences of the United States of America (PNAS), with lead author and geographer Professor David Sear (University of Southampton), along with an international team of experts in environmental sciences, the study of past climate and radiometric dating.

“The Polynesian triangle was the last major region of the globe to be permanently settled,” says Professor Allen. “This roughly 20 million km2 area of largely open water lies between Hawai'i, Rapa Nui and Aotearoa New Zealand and exploration and colonisation of this vast area by the ancestors of contemporary Polynesians was a major achievement in human history. But the timing, character and drivers of these migrations have been poorly understood from a scientific perspective.”

The new findings make clear that the southern Cook Islands were an important gateway to the region, with human settlement there now shown to be earlier than in the Society, Marquesas and other East Polynesian islands.

Led by Professor Sear, the research team analysed lake sediments from the southern Cook Islands for evidence of human arrival and climate change. Drilling into thick accumulations of mud at the bottom of Lake Te Roto on Aitu Island (187 kms north east of Rarotonga) they recovered a 7.8 metre sedimentary record that tells the story of the island’s last 6000 years.

Using several lines of evidence, the team built up a picture of past rainfall, natural (pre-human) lake conditions and, in the uppermost layers, people’s activities around this important water source.

For example, biochemical markers (faecal sterols) uniquely associated with humans and pigs were dated between 800 and 1000 CE (Common Era or AD). These findings place people in the southern Cook Islands by as much as two or three centuries earlier than previously thought.

“Another surprise,” says Professor Allen, “was the discovery that both the human and pig biomarkers preceded all other signs of human arrival, both in the lake and elsewhere, by roughly a century. In contrast, signals of well-established communities, such as changes in lake productivity and forest clearance, occur later in time.”

She has been working in the southern Cook Islands since the late 1980s and says the sequence captured in Lake Te Roto’s finely layered muds is remarkable.

“It suggests that Pacific voyagers first discovered and explored Atiu between 800 and 1000 CE, but then left the island, possibly returning home. Full-fledged settlement, and by that we mean larger groups of people carrying the full inventory of Polynesian crop plants, dogs and chickens appear to have arrived a century or two later.”

This new study builds on the research of many scholars, for example, the voyaging research of Emeritus Professor Geoffrey Irwin (University of Auckland) shows that the sheer distance between the nearest western islands (Samoa and Tonga), and those of the southern Cooks, was a considerable challenge to traditional voyagers. This open sea crossing of 800-1200km may explain why islands to the east were settled so much later in time, relative to those in the west.

Computer simulations led by Associate Professor Álvaro Montenegro (Ohio State University) have also been helpful, says Professor Allen, because they identify the Samoan Islands as the most advantageous point of departure for eastward explorations.

Exploratory voyages, and possibly improvements in voyaging canoe designs, may have been needed before the safe passage of fully provisioned colonists was possible.”

The palaeo-environmental team also analysed lake cores from Samoa (‘Upolu Island) and Vanuatu (Efate Island), areas west of the southern Cook Islands. Biochemical analyses of plant fossils from Vanuatu and Samoa identify the period between approximately 900 and 1100 CE as one of exceptional aridity.

These western islands were settled around 3000 years ago by Lapita peoples, a cultural group whose migrations across the western Pacific can be traced through their intricately decorated pottery.

“Deteriorating climate conditions may have prompted their successors in archipelagos like Tonga and Samoa to resume long-distance voyaging and once again search for unsettled islands like the southern Cooks,” says Professor Allen.

Although East Polynesia is vast, she recalls the words of influential Tongan anthropologist Professor Epeli Hau’ofa (University of the South Pacific), who argued that the legends, oral traditions and cosmologies of Oceanic peoples leave no doubt that they saw their world as “a sea of islands” and “full of places to explore”.

“The Lake Te Roto findings not only extend the timing of human arrival in the southern Cook Islands by one to three centuries, but also suggest that East Polynesian settlement was a process, and not the outcome of precipitous or haphazard departures.

“Environmental knowledge and safe sailing strategies may have developed over several generations, and the multi-island drought records assembled here provide context for these voyages and will help researchers understand the climate challenges faced by early Pacific Island communities.”