Seasonal variation of CO2 saturation in the Gulf of Bothnia:: Indications of marine net heterotrophy -: art. no. GB4021

Seasonal variation of pCO(2) and primary and bacterioplankton production were measured in the Gulf of Bothnia during an annual cycle. Surface water was supersaturated with CO(2) on an annual basis, indicating net heterotrophy and a source of CO(2) to the atmosphere. However, the Gulf of Bothnia oscillated between being a sink and a source of CO(2) over the studied period, largely decided by temporal variation in bacterial respiration (BR) and primary production (PP) in the water column above the pycnocline. The calculated annual respiration-production balance (BR-PP) was very similar to the estimated CO(2) emission from the Gulf of Bothnia, which indicates that these processes were major determinants of the exchange of CO(2) between water and atmosphere. The southern basin (the Bothnian Sea) had a lower net release of CO(2) to the atmosphere than the northern Bothnian Bay (7.1 and 9.7 mmol C m(-2) d(-1), respectively), due to higher primary production, which to a larger extent balanced respiration in this basin.