High Arctic ecosystems and Indigenous livelihoods are tightly linked and exposed to climate change, yet assessing their sensitivity requires a long-term perspective. Here, we assess the vulnerability of the North Water polynya, a unique seaice ecosystem that sustains the world’s northernmost Inuit communities and several keystone Arctic species. We reconstruct mid-to-late Holocene changes in sea ice, marine primary production, and little auk colony dynamics through multi-proxy analysis of marine and lake sediment cores. Our results suggest a productive ecosystem by 4400–4200 cal yrs b2k coincident with the arrival of the first humans in Greenland. Climate forcing during the late Holocene, leading to periods of polynya instability and marine productivity decline, is strikingly coeval with the human abandonment of Greenland from c. 2200–1200 cal yrs b2k. Our long-term perspective highlights the future decline of the North Water ecosystem, due to climate warming and changing sea-ice conditions, as an important climate change risk.

Abstract. The Baffin Bay is a semi-enclosed basin connecting the Arctic Ocean and the western North Atlantic, thus making out a significant pathway for heat exchange. Here we reconstruct the alternating advection of relatively warmer and saline Atlantic waters versus the incursion of colder Arctic water masses entering the Baffin Bay through the multiple gateways in the Canadian Arctic Archipelago and the Nares Strait during the Holocene. We carried out benthic foraminiferal assemblage analyses, X-Ray Fluorescence scanning and radiocarbon dating of a 738  cm long marine sediment core retrieved from the eastern Baffin Bay near Upernavik (Core AMD14-204C; 987m water depth). Results reveal that the eastern Baffin Bay was subjected to several oceanographic changes during the last 9.2 ka BP. Waning deglacial conditions with enhanced meltwater influxes and an extensive sea-ice cover prevailed in the eastern Baffin Bay from 9.2–7.9 ka BP. A transition towards bottom water ameliorations are recorded at 7.9 ka BP by increased advection of Atlantic water masses, encompassing the Holocene Thermal Maximum. A cold period with growing sea-ice cover at 6.7 ka BP interrupts the overall warm subsurface water conditions, promoted by a weaker northward flow of Atlantic waters. The onset of the Neoglaciation at ca. 2.9 ka BP, is marked by an abrupt transition towards a benthic fauna dominated by agglutinated species likely partly explained by a reduction of the influx of Atlantic water, allowing increased influx of the cold, corrosive Baffin Bay Deep Water originating from the Arctic Ocean, to enter the Baffin Bay through the Nares Strait. These cold subsurface water conditions persisted throughout the late Holocene, only interrupted by short-lived warmings superimposed on this cooling trend.

Baffin Bay hosts the largest and most productive of the Arctic polynyas: the North Water (NOW). Despite its significance and active role in water mass formation, the history of the NOW beyond the observational era remains poorly known. We reconcile the previously unassessed relationship between long-term NOW dynamics and ocean conditions by applying a multiproxy approach to two marine sediment cores from the region that, together, span the Holocene. Declining influence of Atlantic Water in the NOW is coeval with regional records that indicate the inception of a strong and recurrent polynya from ~ 4400 yrs BP, in line with Neoglacial cooling. During warmer Holocene intervals such as the Roman Warm Period, a weaker NOW is evident, and its reduced capacity to influence bottom ocean conditions facilitated northward penetration of Atlantic Water. Future warming in the Arctic may have negative consequences for this vital biological oasis, with the potential knock-on effect of warm water penetration further north and intensified melt of the marine-terminating glaciers that flank the coast of northwest Greenland.