How agriculture, droughts and diseases shaped the island environments of Remote Oceania over the last Millennium

Over the past millennium, the Pacific Islands have experienced significant transformations, caused by different waves of human settlement and climatic variability. However, the paucity of archeological records coupled with the complex climatic setting of the tropical Pacific hinders our understanding of past environmental and societal changes. In this study, we employ a multi-proxy approach on sediment cores extracted from ponds on the west coast of Espiritu Santo, Vanuatu to investigate past human-climate dynamics. Through the analysis of human-associated proxies including fecal markers, palmitone — a specific lipid biomarker for taro — and charcoal, we reconstruct changes in human presence and activities. We reconstruct past climate from leaf wax hydrogen isotopes (δ2HLW) and branched glycerol dialkyl glycerol tetraethers (brGDGTs). Changes in pollen reveal major shifts in local and regional vegetation. In our record, the period from 1000 to 1300 CE is characterized by warm/wet conditions concomitant with demographic expansion inland. Around 1400 CE, δ2HLW data indicates a drier period. The coincident decrease in palmitone, despite high charcoal and fecal marker concentrations, suggests that drier conditions might have rapidly affected taro cultivation, but not the overall population, which declined more than a century later. We hypothesize that the establishment of one of the earliest European settlements in Oceania in 1606 CE further disrupted local demographics with the introduction of diseases. This study contributes to our understanding of the intricate relationship between human activities, climatic fluctuations, and landscape modifications in Remote Oceania over the past millennium.