Polar bear's range dynamics and survival in the Holocene

Polar bear (Ursus maritimus) is the apex predator of the Arctic, largely dependent on sea-ice. The expected disappearance of the ice cover of the Arctic seas by the mid 21st century is predicted to cause a dramatic decrease in the global range and population size of the species. To place this scenario against the backdrop of past distribution changes and their causes, we use a fossil dataset to investigate the polar bear's past distribution dynamics during the Late Glacial and the Holocene. Fossil results indicate that during the last deglaciation, polar bears were present at the southwestern margin of the Scandinavian Ice Sheet, surviving until the earliest Holocene. There are no Arctic polar bear findings from 8000–6000 years ago (8–6 ka), the Holocene's warmest period. However, fossils that date from 8-9 ka and 5–6 ka suggest that the species likely survived this period in cold refugia located near the East Siberian Sea, northern Greenland and the Canadian Archipelago. Polar bear range expansion is documented by an increase in fossils during the last 4000 years in tandem with cooling climate and expanding Arctic sea ice. The results document changes in polar bear's distribution in response to Late Glacial and Holocene Arctic temperature and sea ice trends. •At the end of the last glacial period, from 15 to 11 ka, polar bears were present in the western coast of Scandinavia (Denmark, Sweden, Norway, Iceland), until this Scandinavian subpopulation went regionally extinct in the early Holocene, about 11.5 ka•No polar bear remains have been discovered from the period 8 to 6 ka anywhere in the Arctic, but the findings from Svalbard and eastern arctic Siberia 8–9 thousand years ago and from NW Greenland after 6 ka suggest that the likely refugia of the polar bear during the Holocene thermal maximum were in the High Arctic fringes of the Arctic Basin.•During the last four millennia there has been a significant expansion of the polar bear's range, driven by a cooling trend and associated expansion of the arctic sea ice, until the onset of the current, human-induced warming.•Our results highlight the dynamism of the polar bear's distribution range in response to changes in high-latitude climate and Arctic sea ice conditions.