Summer Carbonate Chemistry in the Dalton Polynya, East Antarctica

Abstract 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 2 fugacity ( f CO 2 ) and discrete water column measurements of total dissolved inorganic carbon (TCO 2 ) and total alkalinity. Air‐sea CO 2 fluxes indicate this region was a weak net source of CO 2 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 (Δ f CO 2 = +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 2 (6 to 51 μmol/kg) in ice‐free regions was primarily driven by sea ice melt and biological CO 2 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 CO 2 exchange are discussed. This study highlights the importance of both physical and biological processes in controlling air‐sea CO 2 fluxes and the significant interannual variability of the CO 2 system in Antarctic coastal regions.