Reconstruction of human-environment interactions through multi-proxy characterization inlake sediments from Easter Island/ Rapa Nui

Abstract

The fascinating history of the Easter Island`s (Rapa Nui) civilization collapse is a meaningful example of human-environment interaction and the management of natural resources. It has been a topic of interest to researchers since the Europeans first arrived on the island in 1772. Although several types of research have been carried out during the last decades, the history of Easter Island is still not well understood, as the existing knowledge has several interpretations due to lack of reliable information. The hypothesis that has dominates the island's narrative suggests that the deforestation and environmental degradation was a direct result of unsustainable anthropogenic land use, leading to civilization collapse and a significant reduction of the human population on the island. In this thesis, I reconstructed the past human environmental-interaction, changes in redox condition, and weathering process in Easter Island, through multiproxy analysis (biomarker, trace and rare earth elements) in lake sediments to determine the causes of environmental degradation and the eventual civilization collapse of the Rapa Nui. Sediment cores from two lakes (Rano Aroi and Rano Raraku) were retrieved during an expedition in 2017. The elemental records indicate intense drought between ~1520 - 1710 CE. This drought is associated with coheval vegetation change. The biomarker records mainly indicate that, during the period ~1510 - 1763 CE, the Rapanui people occupied more intensely the highlands rather than the coastal areas, where limited water resources were still available. This thesis provides clear evidence that the deforestation and unsustainable land use hypothesis should be revisited as climatic forcing cannot be disregarded.