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, Alison L., Leedham-Elvidge, Emma, Hughes, Claire, Hopkins, Frances E., Malin, Gill, Bach, Lennart T., Schulz, Kai, Crawfurd, Kate, Brussaard, Corina P D, Stuhr, Annegret, Riebesell, Ulf, Liss, Peter S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: DIMETHYL SULFIDE PRODUCTION; METHYL-IODIDE; CYANOBACTERIAL BLOOMS; MARINE-PHYTOPLANKTON; CARBON-DIOXIDE; VOLATILE IODOCARBONS; SEASONAL-VARIATIONS; PLANKTON COMMUNITY; SULFUR-COMPOUNDS; ATURAL-WATERS; Ocean acidification
• Online Access: https://hdl.handle.net/11370/e56b4480-5bcf-4b53-befa-6fe9c3efa869; https://research.rug.nl/en/publications/e56b4480-5bcf-4b53-befa-6fe9c3efa869; https://doi.org/10.5194/bg-13-4595-2016; https://pure.rug.nl/ws/files/40728508/bg_13_4595_2016.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 largescale 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 (C2H5I) 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 upwelling, DMS concentrations ...