Effect of ocean acidification and elevated f CO 2 on trace gas production by a Baltic Sea summer phytoplankton community

• Published in: Biogeosciences
• Main Authors: Webb, A.L., Leedham-Elvidge, E., Hughes, C., Hopkins, F., Malin, G., Bach, L.T., Schulz, K., Crawfurd, K., Brussaard, C.P.D., Stuhr, A., Riebesell, U., Liss, P.S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Ocean acidification
• Online Access: https://www.vliz.be/imisdocs/publications/21/295821.pdf

The Baltic Sea is a unique environment as thelargest body of brackish water in the world. Acidificationof the surface oceans due to absorption of anthropogenicCO2 emissions is an additional stressor facing the pelagiccommunity of the already challenging Baltic Sea. To investigateits impact on trace gas biogeochemistry, a largescalemesocosm experiment was performed off TvärminneResearch Station, Finland, in summer 2012. During the secondhalf of the experiment, dimethylsulfide (DMS) concentrationsin the highest-fCO2 mesocosms (1075–1333 μatm)were 34% lower than at ambient CO2 (350 μatm). However,the net production (as measured by concentration change) ofseven halocarbons analysed was not significantly affected byeven the highest CO2 levels after 5 weeks’ exposure. Methyliodide (CH3I) and diiodomethane (CH2I2) showed 15 and57% increases in mean mesocosm concentration (3.8?0.6increasing to 4.3?0.4 pmol L?1 and 87.4?14.9 increasingto 134.4?24.1 pmol L?1 respectively) during Phase IIof the experiment, which were unrelated to CO2 and correspondedto 30% lower Chl a concentrations comparedto Phase I. No other iodocarbons increased or showeda peak, with mean chloroiodomethane (CH2ClI) concentrationsmeasured at 5.3 (?0.9) pmol L?1 and iodoethane(C2H5I) at 0.5 (?0.1) pmol L?1. Of the concentrations ofbromoform (CHBr3; mean 88.1?13.2 pmol L?1), dibromomethane(CH2Br2; mean 5.3?0.8 pmol L?1), and dibromochloromethane(CHBr2Cl, mean 3.0?0.5 pmol L?1),only CH2Br2 showed a decrease of 17% between Phases Iand II, with CHBr3 and CHBr2Cl showing similar mean concentrationsin both phases. Outside the mesocosms, an upwellingevent was responsible for bringing colder, high-CO2,low-pH water to the surface starting on day t16 of the experiment;this variable CO2 system with frequent upwellingevents implies that the community of the Baltic Sea is acclimatedto regular significant declines in pH caused by up to800 μatm fCO2. After this upwelling, DMS concentrationsdeclined, but halocarbon concentrations remained similar orincreased compared to ...