Wetter climate favouring early Lapita horticulture in Remote Oceania

Giorgia Camperio, Nemiah Ladd, Matiu Prebble, Ronald Lloren, Elena Argiriadis, Daniel Nelson, Christiane Krentscher, Nathalie Dubois

The islands of Remote Oceania were among the last places on Earth colonised by humans. Lapita seafarers carrying with them an extensive root-tuber-tree crop complex and domestic animals, rapidly transformed nearly all of these previously unoccupied islands. However, the timing of initial Lapita settlements and the early introduction of horticulture remain a matter of debate as significant changes in climate coincided with human oceanic explorations in the mid-late Holocene. Here we show that fossil biomarkers preserved in sedimentary archives located near Teouma, the earliest dated Lapita cemetery in Remote Oceania, trace human presence and horticultural practices while providing the climatic context for the initial settlement. Using fossil faecal molecules, the hydrogen isotopic composition of leaf waxes, and palmitone, a molecular marker for the staple crop taro (Colocasia esculenta Schott), we identified signatures of human activity spanning the period of occupation recorded at the Teouma site. The temporal precision provided by our high-resolution radiocarbon chronology refines the settlement timing with a first unequivocal human trace appearing at 2739-2879 BP. The presence of taro in the initial settlement period attests to the early introduction and likely rapid expansion of horticulture by the first settlers. Lower leaf wax hydrogen isotope ratios starting approximately 2900 years ago further reveal that the initial settlement coincided with a transition to a wetter period, possibly driven by shifts of the South Pacific Convergence Zone. Our findings provide evidence of early horticulture in Remote Oceania and reveal the climatic context that favoured first human settlements in the islands.