Air-sea gas exchange in the central Baltic Sea

Abstract. Air-sea CO₂ fluxes play an important role in the global carbon cycle and impact Earth's climate. Knowledge of the gas transfer velocity (k) is needed to determine air-sea CO₂ fluxes, and wind speed-based parametrizations of k often perform well in the open ocean under moderate winds. In the Baltic Sea, several parameterizations have been proposed to estimate k, and they yield a higher k compared with parameterizations commonly used in the open ocean. In this study, we measured k in the Baltic Sea using the ³He/SF₆ dual tracer technique to assess the applicability of published parameterizations in the inland sea ecosystem. Observed k was similar to those in offshore regions at the same wind speeds, even with enhanced surfactant activity. Comparison with observations in the nearshore Baltic Sea suggests that commonly used open ocean parameterizations are applicable in the Baltic Sea under moderate wind speeds and developed wave fields.