Younger Dryas environments and archaeology on the Northwest Coast of North America

摘要

This paper reviews the current archaeological and palaeo-environmental evidence from the Younger Dryas period on the Northwest Coast of North America. Sea level histories are region-specific, ranging from 100 m lower to 150 m higher than modern at ca. 12,200 cal BP, the mid-point of the Younger Dryas. Palaeo-environmental evidence shows temperature decrease across the study area, but in some regions this is accompanied by greater precipitation and glacial advance whereas in other conditions were drier. Terrestrial vegetation reflects this variability, with northern areas in particular showing evidence for expansion of herb and shrub tundra and southern areas marked by increased mountain hemlock and other species. Marine, intertidal and terrestrial fauna indicate productive ecosystems, with some sub-regional changes, such as extirpation of deer and bison, perhaps associated with the Younger Dryas onset Stable isotope analysis of bear remains show these species, which are a good ecological analogue for humans, exploited both marine and terrestrial resources. Despite patchy and dynamic marine and terrestrial environments, these results suggest a challenging, yet viable environment for humans. Archaeological evidence for Younger Dryas human occupation is currently limited to six sites, of which four are associated with karst caves. The earliest of these are in Haida Gwaii, where bear hunting is dated to at least 12,650 cal BP, during the heart of the Younger Dryas interval. Other sites in southeast Alaska and in the Fraser River lowlands date to around 12,100 cal BP. In Puget Sound, the presence of ca. 13,000 cal BP Clovis surface collections, and the emerging data from the pre-Clovis Ayer Pond bison butchery site, suggest pre-Younger Dryas occupation. The Northwest Coast was open to population movement from both the north and south in the poorly known interval before the Younger Dryas, when conditions may have been more moderate and stable. The sub-regionai variation and the scale of environmental change in the Younger Dryas, especially sea level fluctuation, makes discovery of Pleistocene archaeological sites challenging. The Younger Dryas may therefore be seen as something of a worst-case scenario for both the human occupation and the archaeological investigation of the Northwest Coast.