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

Abstract

In April 2006, diurnal variations of carbon dioxide (CO 2) and oxygen (O 2) 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 CO 2 system. Moored instruments were continuously recording partial pressure of CO 2 in the surface water ( pCO 2 w), currents, mixing, waves, salinity, temperature and O 2. Measurements of total alkalinity ( A T) and dissolved inorganic carbon ( C T) were taken from R/V Skagerak. These measurements were converted to pCO 2 w to support the continuous pCO 2 w data and also calculate the air–sea exchange of CO 2. Additionally, the time derivatives of O 2 and C T concentrations in the water were determined using incubations and a Productivity Autosampler (PA). O 2 and pCO 2 w were significantly anti-correlated and periods dominated of either biological processes, mixing, air–sea exchange or a combination of these were detected. O 2 and pCO 2 w had a daily cycle and variations occurred on the 1 h time scale. In April 2006, the sea was a CO 2 sink and the averaged parameterized air–sea exchange was − 1.0 ± 0.6 mmol m −2 h −1.