Summer carbonate chemistry in the Dalton Polynya, East Antarctica

The carbonate chemistry in the Dalton Polynya in East Antarctica (115°–123°E) was investigated in summer 2014/2015 using high‐frequency underway measurements of CO₂ fugacity (fCO₂) and discrete water column measurements of total dissolved inorganic carbon (TCO₂) and total alkalinity. Air‐sea CO₂ fluxes indicate this region was a weak net source of CO₂ to the atmosphere (0.7 ± 0.9 mmol C m⁻² day⁻¹) during the period of observation, with the largest degree of surface water supersaturation (ΔfCO₂ = +45 μatm) in ice‐covered waters near the Totten Ice Shelf (TIS) as compared to the ice‐free surface waters in the Dalton Polynya. The seasonal depletion of mixed‐layer TCO₂ (6 to 51 μmol/kg) in ice‐free regions was primarily driven by sea ice melt and biological CO₂ uptake. Estimates of net community production (NCP) reveal net autotrophy in the ice‐free Dalton Polynya (NCP = 5–20 mmol C m⁻² day⁻¹) and weakly heterotrophic waters near the ice‐covered TIS (NCP = −4–0 mmol C m⁻² day⁻¹). Satellite‐derived estimates of chlorophyll a (Chl a) and sea ice coverage suggest that the early summer season in 2014/2015 was anomalous relative to the long‐term (1997–2017) record, with lower surface Chl a concentrations and a greater degree of sea ice cover during the period of observation; the implications for seasonal primary production and air‐sea CO₂ exchange are discussed. This study highlights the importance of both physical and biological processes in controlling air‐sea CO₂ fluxes and the significant interannual variability of the CO₂ system in Antarctic coastal regions.