Ancient DNA reveals the chronology of walrus ivory trade from Norse Greenland
The search for walruses as a source of ivory -a popular material for making luxury art objects in medieval Europe- played a key role in the historic Scandinavian expansion throughout the Arctic region. Most notably, the colonization, peak and collapse of the medieval Norse colony of Greenland have all been attributed to the proto-globalization of ivory trade. Nevertheless, no studies have directly traced European ivory back to distinct populations of walrus in the Arctic. This limits our understanding of how ivory trade impacted the sustainability of northern societies and the ecology of the species they relied on. Here, we compare the mitogenomes of 27 archaeological walrus specimens from Europe and Greenland (most dated between 900 and 1400 CE) and 10 specimens from Svalbard (dated to the 18th and 19th centuries CE) to partial mitochondrial (MT) data of over 300 modern walruses. We discover two monophyletic mitochondrial clades, one of which is exclusively found in walrus populations of western Greenland and the Canadian Arctic. Investigating the chronology of these clades in our European archaeological remains, we identify a significant shift in resource use from predominantly eastern sources towards a near exclusive representation of walruses from western Greenland. These results provide empirical evidence for the economic importance of walrus for the Norse Greenland settlements and the integration of this remote, western Arctic resource into a medieval pan-European trade network.