Dissolved organic carbon in the southern Baltic Sea: Quantification of factors affecting its distribution

During a cruise of r/v ‘Oceania’ in May 2006, seven vertical dissolved organic carbon (DOC) concentration profiles were produced against a background of CTD, chlorophyll a (chl a) and phaeopigment concentration profiles. The results indicate distinct vertical and spatial DOC fluctuations, ranging from 248 ± 7 μmol C dm−3 at 70 m depth at the westernmost station G/06 to 398 ± 5 μmol C dm−3 at 5 m depth at station A/06 in the western Gulf of Gdańsk. DOC concentrations were the highest at 10 m depth, where phytoplankton activity was relatively intensive, as reflected by the active chl a concentration distribution. DOC concentrations decreased towards the sea bottom. The non-linear segment regression model was applied to establish the influence on the DOC distribution of organic matter derived from river run-off and zooplankton activity as well as that released from phytoplankton cells. Measured and modelled DOC concentrations are well correlated. The linear regression determination coefficient (R2) was calculated at 78%, indicating that the above-mentioned processes are indeed decisive as regards the DOC pool.