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.2020 Apr 21;117(16):8813-8819.
doi: 10.1073/pnas.1920975117. Epub 2020 Apr 6.

Human settlement of East Polynesia earlier, incremental, and coincident with prolonged South Pacific drought

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Human settlement of East Polynesia earlier, incremental, and coincident with prolonged South Pacific drought

David A Sear et al. Proc Natl Acad Sci U S A..

Erratum in

Abstract

The timing of human colonization of East Polynesia, a vast area lying between Hawai'i, Rapa Nui, and New Zealand, is much debated and the underlying causes of this great migration have been enigmatic. Our study generates evidence for human dispersal into eastern Polynesia from islands to the west from around AD 900 and contemporaneous paleoclimate data from the likely source region. Lake cores from Atiu, Southern Cook Islands (SCIs) register evidence of pig and/or human occupation on a virgin landscape at this time, followed by changes in lake carbon around AD 1000 and significant anthropogenic disturbance from c. AD 1100. The broader paleoclimate context of these early voyages of exploration are derived from the Atiu lake core and complemented by additional lake cores from Samoa (directly west) and Vanuatu (southwest) and published hydroclimate proxies from the Society Islands (northeast) and Kiribati (north). Algal lipid and leaf wax biomarkers allow for comparisons of changing hydroclimate conditions across the region before, during, and after human arrival in the SCIs. The evidence indicates a prolonged drought in the likely western source region for these colonists, lasting c. 200 to 400 y, contemporaneous with the phasing of human dispersal into the Pacific. We propose that drying climate, coupled with documented social pressures and societal developments, instigated initial eastward exploration, resulting in SCI landfall(s) and return voyaging, with colonization a century or two later. This incremental settlement process likely involved the accumulation of critical maritime knowledge over several generations.

Keywords: East Polynesian colonization; Polynesian voyaging; biomarkers; drought; palaeoclimate.

Copyright © 2020 the Author(s). Published by PNAS.

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Conflict of interest statement

The authors declare no competing interest.

Figures

Fig. 1.
Fig. 1.
Pacific region showing average annual precipitation patterns (GPCP satellite-gauge 1979 to 2018), Intertropical Convergence Zone, South Pacific Convergence Zone, and southeast Pacific High (H) in relation to regional geography. Dashed line denotes main axis of the SPCZ. Sites with lake sediment proxy records (this study) are shown as red circles; other proxy records used herein are shown as white circles. Red arrows show the initial migration east into the gateway islands—Southern Cook Islands and Society Islands, and north to the Marquesas and Hawai‘i, the latter dated to c. 1000 to 1200 AD. White arrows show subsequent migrations to Polynesian margins c. 1150 to 1300 AD (see text for details).
Fig. 2.
Fig. 2.
Proxy indicators from Lake Te Roto for the presence of humans on the Atiu Island landscape. Yellow bars are the best estimates of human impacts based on either the first increase in values above background levels or rapid changes in proxy values (e.g., %TOC). Fecal sterol values (A) prior to 800 AD are all lower than the 0.20 threshold for confident identification of our target species (pigs and humans) (21). Carbon source (B andC) and total organic carbon (D) change around AD 1000 as inorganic soil in-wash (F, Ti/Inc.;G, χLF) increases following disturbance of the catchment soils, presumably due to local burning and clearance (H). Microcharcoal (E) shows a large peak before all other indicators, which we interpret as natural burning given the absence of, or minor changes in, all other proxies at that time. The gray region represents 2 SDs around the age model weighted mean, combined with 1 SD in measured proxy values. Brief interpretations of what each proxy represents are shown for clarity (Right).
Fig. 3.
Fig. 3.
Reconstructed precipitation (rates and wet:dry trends) for west-to-east Pacific Islands inA toD (C, Society Islands data are based on ref. 27). InA andB, pecked lines denote uncertainty bounds around estimated precipitation, while gray bars with a black horizontal line (Right) show mean ± uncertainty for contemporary satellite-based [GPCP (28)] precipitation. The solid and dashed arrows inB represent periods of societal change in Samoa (29). Movement of the ITCZ (30) and ENSO frequency (31) are shown inE. Reconstructed SSTs in the West Pacific Warm Pool (WPWP) (32) and Pacific zonal SST gradients (33) are inF. Archaeological dates for the Southern Cook and Society islands are shown as horizontal black bars (C andD) while dates for Atiu (this study) are shown as a graded gold column from arrival c. AD 800 to 1000 through established settlement from c. AD 1125. The gray column denotes the later period of Polynesian expansion into remote eastern Polynesia including Rapa Nui c. AD 1150 to 1300 (34).
Fig. 4.
Fig. 4.
Synthesis of climate changes over the period of initial human migration into the East Polynesian gateway Islands c. AD 800 to 1125, and during the period of expansion into Rapa Nui and New Zealand c. AD 1150 to 1300 (corresponding to the gold column in Fig. 3). Circle colors show drier (yellow) and wetter (green) climate while sizes of circles are proportional to the magnitude of change. White arrows show movement of the ITCZ and SPCZ, and black arrows show the known extent of Polynesian voyaging. Initial migration east occurs during a regional change in climate as the ITCZ and SPCZ migrate north, while the latter contracts and weakens resulting in drought across the south Pacific Islands. Post c. AD 1150 the ITCZ moved south again and the SPCZ axis probably moved south and extended, providing better conditions for settlement on the more isolated and smaller islands of the eastern Pacific. Background colors show mean annual precipitation (GCGP 1976 to 2013). Dashed lines show the average axis of SPCZ precipitation over this latter period. Sources used for this figure are inSI Appendix, Table S4.
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References

    1. Allen M. S., Huebert J. M., Short-lived plant materials, long-lived trees, and Polynesian14C dating: Considerations for14C sample selection and documentation. Radiocarbon 56, 257–276 (2014).
    1. Rieth T., Athens J. S., Suggested best practices for the application of radiocarbon dating to Hawaiian archaeology. Hawaii Archaeol. 13, 3–29 (2013).
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    1. Kirch P. V., Ed., Tangatatau Rockshelter: The Evolution of an Eastern Polynesian Socio-Ecosystem (Monumenta Archaeologica 40, UCLA Cotsen Institute of Archaeology Press, 2017).
    1. Allen M. S., Morrison A. E., Lorrey A. M., Zhao J.-X., Jacobsen G. E., Timing, magnitude and effects of Late Holocene sea level drawdown on island habitability, Aitutaki, Cook Islands. Archaeol. Ocean. 51, 108–121 (2016).

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