Sedimentary biomarkers reveal the legacy of human-climate interactions in Vanuatu
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Date
2024
Publication Type
Doctoral Thesis
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Abstract
First human settlements in remote oceanic islands came along with major landscape modifications. Understanding which factors influenced past human-ecosystem interactions is crucial to addressing the pressing socio-environmental challenges to which insular ecosystems are exposed. Paleoenvironmental archives such as sediment cores can reconstruct past human activities and climatic variability and help retrieve information on the environmental responses to different degrees of change. The archipelago of Vanuatu calls for a careful understanding of human-climate interactions as it is highly vulnerable to the current climate crisis in addition to being exposed to frequent natural hazards. Vanuatu is considered a stepping stone in the first settlement of the Pacific (~3000 years ago) attributed to the Lapita people. Vanuatu’s location at the western edge of the South Pacific Convergence Zone, one of the most prominent hydroclimatic features of the Pacific makes it very sensitive to even minimal changes in its long-term mean position. Through the multi-proxy analysis of lake sediment cores from the archipelago of Vanuatu, we provide paleoclimatic and paleoenvironmental reconstructions, combining geochemical tools based on biomarkers with sedimentological and paleoecological analyses in sites with different degrees of archeological knowledge.
In the first chapter, the analysis of sediment cores from two ponds on the west coast of the island of Espiritu Santo reveals a distinctive stratigraphic profile marked by a prominent radiocarbon peak. The application of high-resolution radiocarbon dating on terrestrial macrofossils preserved in these cores unveils the legacy of nuclear bomb testing in the Southern Hemisphere, demonstrating the potential for detailed environmental reconstructions of extreme events in the Pacific Islands.
The second chapter investigates changes in human presence and activities over the last millennium on the west coast of Espiritu Santo, a remote area, among the few in Melanesia where the art of traditional pottery making is preserved. Fecal markers, palmitone (a lipid biomarker for taro), are used to trace the presence of humans. The reconstruction of hydroclimatic changes through compound specific hydrogen isotopes of leaf waxes and temperature changes through branched glycerol dialkyl glycerol tetraethers provide the climatic settings. This study reveals the complex human-climate dynamics in shaping island ecosystems in Vanuatu.
The third chapter constrains the settlement timing of Efate through high-resolution radiocarbon dating of a sedimentary archive retrieved near the Teouma cemetery, the oldest cemetery associated with the first settlers in Remote Oceania. The first unequivocal human traces in the core are present at 2739-2879 BP. The presence of palmitone in these initial human traces suggests that taro cultivation was introduced and rapidly expanded by initial settlers. Lower leaf wax hydrogen isotope ratios beginning approximately 2900 years ago reveal that the initial settlement coincided with a transition to a wetter period, potentially driven by shifts in the South Pacific Convergence Zone. This research enhances the temporal accuracy of archaeological findings and provides evidence for the influence of climatic and environmental factors on the earliest human settlements in Remote Oceania.
This thesis highlights the complex relationship between humans and climate all along the settlement history of Vanuatu, investigating the influence of climate on early settlements and agriculture (Ch. 3), societal responses to climatic shifts (Ch. 2), and more recent extreme events (Ch. 1). This dynamic interaction has left lasting imprints on both the environmental and cultural history of the region. Understanding these complex connections offers valuable insights into how past communities adapted to changing conditions and can inform contemporary efforts in environmental management and resilience-building in the face of global climate change.
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published
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Examiner : Dubois, Nathalie
Examiner : Eglinton, Timothy Ian
Examiner: Ghazoul, Jabouryperson
Examiner : Malaspinas, Anna-Sapfo
Examiner : Nogué Bosch, Sandra
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Publisher
ETH Zurich
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Subject
Paleoecology; Paleoclimatology; Paleolimnology; Remote Oceania; South Pacific convergence zone; Human-Climate; Lapita; Sedimentology; Islands
Organisational unit
03868 - Eglinton, Timothy I. (emeritus) / Eglinton, Timothy I. (emeritus)