Effect of ocean acidification and elevated fCO 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.E., 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://dare.uva.nl/personal/pure/en/publications/effect-of-ocean-acidification-and-elevated-fco2-on-trace-gas-production-by-a-baltic-sea-summer-phytoplankton-community(dc89b5d3-825f-49f8-9cea-ee3f5126e1da).html; https://doi.org/10.5194/bg-13-4595-2016; https://hdl.handle.net/11245.1/dc89b5d3-825f-49f8-9cea-ee3f5126e1da; https://pure.uva.nl/ws/files/10077793/Effect_of_ocean_acidification.pdf; https://pure.uva.nl/ws/files/10077795/Effect_of_ocean_acidification_suppl.pdf

The Baltic Sea is a unique environment as the largest body of brackish water in the world. Acidification of the surface oceans due to absorption of anthropogenic CO 2 emissions is an additional stressor facing the pelagic community of the already challenging Baltic Sea. To investigate its impact on trace gas biogeochemistry, a large-scale mesocosm experiment was performed off Tvärminne Research Station, Finland, in summer 2012. During the second half of the experiment, dimethylsulfide (DMS) concentrations in the highest-fCO 2 mesocosms (1075–1333 µatm) were 34 % lower than at ambient CO 2 (350 µatm). However, the net production (as measured by concentration change) of seven halocarbons analysed was not significantly affected by even the highest CO 2 levels after 5 weeks' exposure. Methyl iodide (CH 3 I) and diiodomethane (CH 2 I 2 ) showed 15 and 57 % increases in mean mesocosm concentration (3.8 ± 0.6 increasing to 4.3 ± 0.4 pmol L −1 and 87.4 ± 14.9 increasing to 134.4 ± 24.1 pmol L −1 respectively) during Phase II of the experiment, which were unrelated to CO 2 and corresponded to 30 % lower Chl a concentrations compared to Phase I. No other iodocarbons increased or showed a peak, with mean chloroiodomethane (CH 2 ClI) concentrations measured at 5.3 (±0.9) pmol L −1 and iodoethane (C 2 H 5 I) at 0.5 (±0.1) pmol L −1 . Of the concentrations of bromoform (CHBr 3 mean 88.1 ± 13.2 pmol L −1 ), dibromomethane (CH 2 Br 2 mean 5.3 ± 0.8 pmol L −1 ), and dibromochloromethane (CHBr 2 Cl, mean 3.0 ± 0.5 pmol L −1 ), only CH 2 Br 2 showed a decrease of 17 % between Phases I and II, with CHBr 3 and CHBr 2 Cl showing similar mean concentrations in both phases. Outside the mesocosms, an upwelling event was responsible for bringing colder, high-CO 2 , low-pH water to the surface starting on day t16 of the experiment; this variable CO 2 system with frequent upwelling events implies that the community of the Baltic Sea is acclimated to regular significant declines in pH caused by up to 800 µatm fCO 2 . After this ...