Drought, freshwater availability and cultural resilience on Easter Island (SE Pacific) during the Little Ice Age

After decades of human-deterministic explanations for the collapse of the ancient Rapanui civilization that inhabited Easter Island (Rapa Nui) before European contact (1722 CE), paleoecological studies developed during the last decade have provided sound evidence for climate changes and their potential socio-ecological impact. Especially significant is the occurrence of a century-scale (1570-1720 CE) drought occurred during the Little Ice Age. Freshwater is a critical resource at Easter Island that heavily depends on rain, which maintains the three only permanent surficial freshwater sources of the island: two lakes (Kao and Raraku) and a marsh (Aroi). In these conditions, the LIA drought could have significantly affected human life; however, the Rapanui civilization remained healthy showing a remarkable resilience. There are two main hypotheses on how the ancient Rapanui civilization could have obtained freshwater to guarantee its continuity. The intra-island migration hypothesis proposes that Lake Raraku, the cultural center of this civilization, dried out and the Rapanui were forced to migrate to Lake Kao, which was likely the only surficial freshwater source during the LIA drought. This shift was accompanied a profound cultural reorganization. The coastal groundwater hypothesis dismisses the use of lakes and other surficial freshwater sources to maintain the water-stressed Rapanui population and contends that the only routine freshwater sources during the LIA drought were the abundant and widespread coastal seeps fed by fresh/brackish groundwater. The pros and cons of these two hypotheses are discussed on the basis of the available archaeological and paleoecological evidence and it is concluded that, in the present state of knowledge, none of them can be rejected. Therefore, these two proposals could be complementary, rather than excluding.