Climate windows for Polynesian voyaging to New Zealand and Easter Island

Debate about initial human migration across the immense area of East Polynesia has focused upon seafaring technology, both of navigation and canoe capabilities, while temporal variation in sailing conditions, notably through climate change, has received less attention. One model of Polynesian voyaging observes that as tradewind easterlies are currently dominant in the central Pacific, prehistoric colonization canoes voyaging eastward to and through central East Polynesia (CEP: Society, Tuamotu, Marquesas, Gambier, Southern Cook, and Austral Islands) and to Easter Island probably had a windward capacity. Similar arguments have been applied to voyaging from CEP to New Zealand against prevailing westerlies. An alternative view is that migration required reliable off-wind sailing routes. We investigate the marine climate and potential voyaging routes during the Medieval Climate Anomaly (MCA), A.D. 800–1300, when the initial colonization of CEP and New Zealand occurred. Paleoclimate data assimilation is used to reconstruct Pacific sea level pressure and wind field patterns at bidecadal resolution during the MCA. We argue here that changing wind field patterns associated with the MCA provided conditions in which voyaging to and from the most isolated East Polynesian islands, New Zealand, and Easter Island was readily possible by off-wind sailing. The intensification and poleward expansion of the Pacific subtropical anticyclone culminating in A.D. 1140–1260 opened an anomalous climate window for off-wind sailing routes to New Zealand from the Southern Austral Islands, the Southern Cook Islands, and Tonga/Fiji Islands. Significance South Pacific migration routes used in East Polynesian colonization (A.D. 800−1500) have been assumed to be commonly upwind, when based on an understanding of modern climate patterns. Instead, our novel paleowind field reconstructions at bidecadal resolution show that migration routes lay downwind from East Polynesia during known times of initial colonization of New Zealand and Easter Island. This finding is significant in showing that a windward seafaring capacity in Polynesian colonization voyaging was not essential, and that long-term temporal variation in sailing conditions due to the expansion of the tropics was important in shaping colonization histories. The paleoclimate reconstruction broadens colonization possibilities, and the method represents a new, globally applicable approach to understanding patterning in prehistoric mari