Summer Carbonate Chemistry in the Dalton Polynya, East Antarctica

<jats:title>Abstract</jats:title><jats:p>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 CO<jats:sub>2</jats:sub> fugacity (<jats:italic>f</jats:italic>CO<jats:sub>2</jats:sub>) and discrete water column measurements of total dissolved inorganic carbon (TCO<jats:sub>2</jats:sub>) and total alkalinity. Air‐sea CO<jats:sub>2</jats:sub> fluxes indicate this region was a weak net source of CO<jats:sub>2</jats:sub> to the atmosphere (0.7 ± 0.9 mmol C m<jats:sup>−2</jats:sup> day<jats:sup>−1</jats:sup>) during the period of observation, with the largest degree of surface water supersaturation (Δ<jats:italic>f</jats:italic>CO<jats:sub>2</jats:sub> = +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 TCO<jats:sub>2</jats:sub> (6 to 51 μmol/kg) in ice‐free regions was primarily driven by sea ice melt and biological CO<jats:sub>2</jats:sub> uptake. Estimates of net community production (NCP) reveal net autotrophy in the ice‐free Dalton Polynya (NCP = 5–20 mmol C m<jats:sup>−2</jats:sup> day<jats:sup>−1</jats:sup>) and weakly heterotrophic waters near the ice‐covered TIS (NCP = −4–0 mmol C m<jats:sup>−2</jats:sup> day<jats:sup>−1</jats:sup>). Satellite‐derived estimates of chlorophyll <jats:italic>a</jats:italic> (Chl <jats:italic>a</jats:italic>) 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 <jats:italic>a</jats:italic> concentrations and a greater degree of sea ice cover during the period of observation; the implications for seasonal primary production and air‐sea CO<jats:sub>2</jats:sub> exchange are discussed. This study highlights the importance of both physical and biological processes in controlling air‐sea CO<jats:sub>2</jats:sub> fluxes and the significant interannual variability of the CO<jats:sub>2</jats:sub> system in Antarctic coastal regions.</jats:p>