Environmental changes in Hudson Strait and cultural transition in the Kangiqsujuaq region, Nunavik, Canada

A record of marine (dinoflagellate cysts) and terrestrial (pollen grains) palynomorphs combined with geochemical (organic C, C_org:N_tot) and isotopic (δ¹³C_org) data from a sediment core collected in Hudson Strait close to Kangiqsujuaq provides evidence of past climatic and hydrographic changes in northern Nunavik since 4000 years ago with a multidecadal temporal resolution. A significant transition is recorded around 1850 cal yr BP. In the dinocyst assemblages, it is characterised by a sharp increase in heterotrophic taxa at the expense of the cysts of Pentapharsodinium dalei; in the pollen assemblage, it is marked by a change in the ratio between Picea and Pinus, with Pinus becoming more abundant after 1850 cal yr BP. Reconstructions of sea-surface conditions based on dinocyst assemblages show a long-term cooling trend and increased seasonal sea-ice cover over the last 4000 years. The results also showed an overall increase in summer salinity, the isotopic composition of organic carbon (δ¹³C_org), and the organic carbon to total nitrogen ratio (C_org:N_tot), especially after ∼1850 cal yr BP. Such changes suggest a lower proportion of terrestrial sources of sedimentary organic matter, likely induced by an overall decrease in freshwater discharges from the Hudson Bay watershed, thus reducing dilution of ocean waters. The general reduction in the relative imprint of terrestrial inputs in the Hudson Strait may be related to an overall decrease in annual precipitation over the northern boreal forest, which is likely due to the generally colder climate. The Middle Dorset period, from approximately 2000 to 1500 years ago, encompasses the transition towards colder and drier conditions around 1850 cal yr BP. This was a period of southward population movements, possibly driven by the impact of increased sea ice, which hindered access to resources. We thus hypothesise that palaeoenvironmental changes have modified resource distribution, which was critical for the Dorset people as they experienced massive demographic shifts and southward population expansion.