• ocean acidification;
  • pH;
  • polynyas;
  • sea ice melt;
  • seasonal variability;
  • total alkalinity

[1] We report on measurements across an annual cycle of carbon dioxide system parameters in the polar mixed layer (PML) of the circumpolar flaw lead in the Amundsen Gulf, Arctic Ocean. From these and other properties (nitrate, S, T) of the PML, we found that biological processes (photosynthesis and respiration) accounted for about 50% of the monthly variations in the carbonate ion concentration, [CO32−] and Ω, the saturation state of these waters with respect to calcite (ΩCa) and aragonite (ΩAr). Vertical mixing and salinity changes had equal impacts over the annual cycle. The impact of sea ice meltwater resulted in decreasing Ω values in summer, but most of this change was offset by the Ω increase as a result of CO2 drawdown during biological photosynthesis.