Early impacts of Arctic amplification in the western North Water Polynya: A 400-year perspective

Abstract

The North Water (NOW) polynya in northern Baffin Bay is known for persistent open water, attracting marine mammals and birds during winter. Ice bridges forming north of the NOW at constriction points in Nares Strait aid in sustaining these open water conditions. However, Arctic Amplification has weakened these ice bridges, altering water and sea ice flow into the NOW. We examined the effect of climate warming and recent ice bridge failures through 400 years of changes in the western NOW. We analyzed dinoflagellate cyst (dinocyst) assemblages in a surface sediment transect across the NOW to assess their distribution as indicators of surface water masses. We then analyzed dinocysts and geochemical proxies (carbon and nitrogen signatures) from two sediment cores in the western NOW. Results show the eastern NOW, influenced by the West Greenland Current (WGC), exhibits higher contributions of mixotrophic taxa and total dinocyst concentrations than the western region, influenced by Arctic water outflow. Sediment cores show a 300-year period of stability in the western NOW (1620–1920 CE), followed by an increase in mixotrophic taxa and total dinocyst fluxes, predating observed ice bridge failures. Around 1980 CE, higher abundances of Operculodinium centrocarpum, and cysts of Polarella glacialis and Pentapharsodinium dalei, suggest early sea ice retreat, seemingly attributable to increased WGC influence. These findings demonstrate the early impact of Arctic Amplification on the NOW, with significant changes starting in the first half of the 20th century, which contribute to understanding the timing and propagation of oceanographic changes in the polynya.