Observed carbon dioxide and oxygen dynamics in a Baltic Sea coastal region

In April 2006, diurnal variations of carbon dioxide (CO2) and oxygen (O2) in the surface water east of Gotland in the Baltic Sea were investigated with a unique multitechnology approach. Several parameters were measured simultaneously providing an overview of the CO2 system. Moored instruments were continuously recording partial pressure of CO2 in the surface water (pCO2w), currents, mixing, waves, salinity, temperature and O2. Measurements of total alkalinity (AT) and dissolved inorganic carbon (CT) were taken from R/V Skagerak. These measurements were converted to pCO2w to support the continuous pCO2w data and also calculate the air–sea exchange of CO2. Additionally, the time derivatives of O2 and CT concentrations in the water were determined using incubations and a Productivity Autosampler (PA). O2 and pCO2w were significantly anti-correlated and periods dominated of either biological processes, mixing, air–sea exchange or a combination of these were detected. O2 and pCO2w had a daily cycle and variations occurred on the 1 h time scale. In April 2006, the sea was a CO2 sink and the averaged parameterized air–sea exchange was − 1.0 ± 0.6 mmol m−2 h−1.

Research highlights► Diurnal variations of CO2 and O2 in the Baltic Sea surface water were investigated. ► We continuously recorded pCO2 (in sea and atmosphere), O2, T, S, currents and, waves. ► pCO2 and O2 were significantly anti-correlated and highly variable Periods dominated of air-sea exchange, mixing or biological processes were separated. ► The region was a CO2 sink for the period.