Research reveals how islanders chased the rain across Pacific 1,000 years ago
By: Communications
It may sound like a scene from the Disney film Moana, but new UEA research shows that climate change pushed islanders to ‘chase the rain’ across the Pacific 1,000 years ago.
A study from UEA and the University of Southampton shows a major shift in South Pacific climate conditions that may have pushed people to settle further east and move away from increasingly drier conditions in the west.
Settled islands in Western Polynesia, such as Samoa and Tonga, became drier, while more remote ones in Eastern Polynesia, for example French Polynesia (Tahiti), gradually became wetter and more attractive for colonisation.
The Pacific Islands today are under threat from climate change and the team hope that their work will help predict how it could affect the region.
Study Environmental Sciences at UEA
Prof Manoj Joshi, from UEA’s School of Environmental Sciences, said: “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 work is part of a wider project between UEA and Southampton called PROMS (Pacific Rainfall over Millennial Timescales), examines this shift and its likely impact on migration.
Principal Investigator for PROMS, Prof David Sear, said: “Our research suggests that 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.”
How the research happened
The research team collected sediment cores on the islands of Tahiti and Nuku Hiva in Eastern Polynesia to analyse plant waxes – fatty layers left on leaves. World-leading laboratory analysis of these plant waxes reveals how wet or dry the climate was when the leaves grew. The team combined these new records with other records from across Polynesia, in the Pacific.
From this state-of-the-art data, the team estimated how rainfall had changed across the Pacific during the last 1,500 years. Together with new climate model simulations, the team were able to uncover when and where this climatic shift in rainfall occurred, and what probably caused it.
Their results show that the most likely cause is that a natural change in the pattern of sea surface temperatures across the Pacific drove an eastward shift of the South Pacific Convergence Zone (SPCZ) between approximately 1,100 and 400 years ago.
The SPCZ is one of the biggest features in the global climate system, a region of high rainfall stretching over 7,000 km from Papua New Guinea to beyond the Cook Islands. The climate shift identified in this new study saw the western part of this rain band become progressively drier, and its eastern part wetter.
A push for migration
The researchers believe this long-term drying of western areas could have acted as a ‘push’ for migration, while the increase in rainfall and freshwater availability in the east may have served as a ‘pull’ to settle new islands.
It is possible the climate shift acted as a driver for people, encouraging them to sail progressively east to islands such as the Cooks and Tahiti.
Co-lead author on the paper Dr Mark Peaple, from the University of Southampton, said: “The timing and nature of the hydroclimatic change align with the final wave of human settlement into Eastern Polynesia, which began around 1000 years ago.
“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 colonise in areas with more reliable water security – even if this meant adventurous journeys across the ocean.”
Dr Daniel Skinner, from UEA’s School of Environmental Sciences, added: “Bringing together knowledge from palaeoclimate archives and climate models has given us key insights into how and why a critically understudied region of the world changed over the last 1,500 years.”
The scientists hope more research and archaeological analysis can further refine the timing and scale of both environmental and societal changes in over the South Pacific.
This research was funded by the UK’s Natural Environment Research Council (NERC). Fieldwork was supported by Explorer grants from National Geographic Society.
‘Ocean variability drives a millennial-scale shift in South Pacific hydroclimate’ is published in the journal Communications Earth and Environment.
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