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

Abstract

After decades of human-deterministic explanations for the collapse of the ancient Rapanui culture that inhabited Easter Island (Rapa Nui) before European contact (1722 CE), paleoecological studies developed over the last decade have provided sound evidence of climate changes and their potential socioecological impacts. Especially significant is the occurrence of a century-scale drought (1570–1720 CE) during the Little Ice Age (LIA). Freshwater is a critical resource on Easter Island that heavily depends on rain, which maintains the only three permanent surficial freshwater sources on the island: two lakes (Rano Kao and Rano Raraku) and a marsh (Rano Aroi). Under these conditions, the LIA drought could have significantly affected human life; however, the Rapanui society remained healthy, showing remarkable resilience. There are two main hypotheses on how the ancient Rapanui could have obtained freshwater to guarantee their continuity. One of these hypotheses proposes that Lake Kao was a permanent source of freshwater, even during the LIA drought, which led to some intraisland cultural and population reorganizations. 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 archeological and paleoecological evidence, and it is concluded that given the present state of knowledge, neither can be rejected. Therefore, these two proposals could be complementary rather than mutually exclusive.

Approximate Bayesian Computation of radiocarbon and paleoenvironmental record shows population resilience on Rapa Nui (Easter Island)

“…Our results also have implications for the effects of climate change on the island. Rull 71,73 has recently claimed that climateinduced droughts caused a large-scale societal disruption resulting in the cessation of monument construction and intra-island migration from coastal settlements to the crater lake at Rano Kau. Similar to previous analyses of the tempo of monument construction around the island 57 , the vast majority of our 14 C data derive from coastal settlements and do not show declines in activity or support claims of major climate-induced disruptions from drought.…”

“…Recent paleoenvironmental studies also suggest that large-scale climate changes took place in pre-contact times. Sediment cores from Rano Raraku lake, for example, show a series of sedimentary hiatuses from the fifteenth to eighteenth centuries, leading some to argue that the island's lakes became dry from severe droughts events 72,73 . These drought events are potentially associated with the onset of the Little Ice Age or changes in the El Niño Southern Oscillation, with a shift toward more positive Southern Oscillation Index (SOI) values beginning in the fifteenth century 74 .…”

Contributions of paleoecology to Easter Island’s prehistory: A thorough review

“…Therefore, it seems unreasonable that the Rapanui people refused to obtain freshwater from this lake, which is readily accessible from Orongo and other sites around the crater. Obtaining agricultural products but no freshwater from Lake Kao shores seems absurd in a period of water shortage such as the LIA drought (Rull, 2020b). A society that was able to transport almost 1000 megalithic sculptures such as the moai up to 18-20 km away from their quarry would not have been afraid to transport freshwater from Lake Kao shores to any part of the island.…”

“…Paleoecological research has also contributed to improving knowledge about prehistoric Polynesian cultivation by identifying the locations of agricultural areas and the plants that grew in them (Horrocks & Wozniak, 2008;Horrocks et al, 2012aHorrocks et al, , b, 2013Horrocks et al, , 2015Horrocks et al, , 2016. Finally, although paleoecology has not provided direct evidence for a number of Easter Island's cultural matters, it has furnished empirical information that can help understand processes such as initial discovery (Rull, 2019) or the potential role of climate changes and climate-human synergies in several cultural aspects (Rull, 2016a(Rull, , 2020b.…”

Triumph of the Commons: Sustainable Community Practices on Rapa Nui (Easter Island)

“…In addition, paleoecological and paleoclimatic studies indicate a prolonged drought period in pre-contact times (ca. 1520-1720 AD), wherein the crater lake at Rano Raraku, and likely at Rano Aroi, went completely dry [33,87,96,97,137]. Recent research, however, shows that archaeological and ethnohistoric records demonstrate that Rapa Nui communities relied largely on submarine groundwater discharge (SGD)-locations at the coast where groundwater emerges at the tideline [136,138,139].…”