Effect of ocean acidification and elevated f CO 2 on trace gas production by a Baltic Sea summer phytoplankton community
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...
Published in: | Biogeosciences |
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Main Authors: | , , , , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
Copernicus Publications
2016
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Subjects: | |
Online Access: | https://doi.org/10.5194/bg-13-4595-2016 https://doaj.org/article/c75c214e48dd4a54bb71e45edb6831bc |
Summary: | 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- f CO 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 t 16 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 f CO 2 . After this ... |
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