Seasonal stratification controls on vertical nutrient exchange in a High Arctic fjord (Inglefield Bredning, NW Greenland)

Abstract. High Arctic fjords are changing rapidly under ongoing global warming yet remain comparatively understudied despite their sensitivity to shifts in sea ice, ocean temperature, and glacier dynamics. In northwest Greenland, Inglefield Bredning is influenced by marine-terminating glaciers and exchange with Baffin Bay and the North Water polynya, making it a representative system for assessing how physical changes in the Arctic propagate into fjord biogeochemistry. Here, we investigate how seasonal stratification develops across winter, spring, and early summer, and how it regulates vertical nutrient exchange and biological activity. A persistent Atlantic Water layer below ~220 m occupies the fjord year-round, forming a stable reservoir of heat and nutrients that defines the background hydrographic structure. However, strong vertical stratification limits exchange between this deep nutrient reservoir and the euphotic zone, where nutrient concentrations remain low throughout the year. Upper-water-column nutrient concentrations are higher in winter than in early summer, but do not indicate complete winter homogenization with deeper waters. Pronounced spatial variability along the fjord further reflects the influence of marine-terminating glaciers, with localized hydrographic modification suggesting that glacier-driven processes may intermittently enhance vertical nutrient supply. Chlorophyll concentration peak in summer, consistent with strong biological uptake under increasingly stratified conditions. Together, these results indicate that productivity in Inglefield Bredning is governed not by the magnitude of the deep nutrient reservoir itself, but by the availability if macronutrients and the physical processes controlling their transfer to the euphotic zone. As Arctic warming strengthens stratification while altering glacier dynamics and sea ice cover, future productivity in high Arctic fjords will depend critically on the evolving balance between mechanisms that restrict and promote vertical nutrient supply.