Sea ice pCO₂ dynamics and air–ice CO₂ fluxes during the Sea Ice Mass Balance in the Antarctic (SIMBA) experiment – Bellingshausen Sea, Antarctica

Abstract. Temporal evolution of pCO₂ profiles in sea ice in the Bellingshausen Sea, Antarctica, in October 2007 shows physical and thermodynamic processes controls the CO₂ system in the ice. During the survey, cyclical warming and cooling strongly influenced the physical, chemical, and thermodynamic properties of the ice cover. Two sampling sites with contrasting characteristics of ice and snow thickness were sampled: one had little snow accumulation (from 8 to 25 cm) and larger temperature and salinity variations than the second site, where the snow cover was up to 38 cm thick and therefore better insulated the underlying sea ice. We show that each cooling/warming event was associated with an increase/decrease in the brine salinity, total alkalinity (TA), total dissolved inorganic carbon (TCO₂), and in situ brine and bulk ice CO₂ partial pressures (pCO₂). Thicker snow covers reduced the amplitude of these changes: snow cover influences the sea ice carbonate system by modulating the temperature and therefore the salinity of the sea ice cover. Results indicate that pCO₂ was undersaturated with respect to the atmosphere both in the in situ bulk ice (from 10 to 193 μatm) and brine (from 65 to 293 μatm), causing the sea ice to act as a sink for atmospheric CO₂ (up to 2.9 mmol m⁻² d⁻¹), despite supersaturation of the underlying seawater (up to 462 μatm).