Dynamics of dimethylsulphoniopropionate and dimethylsulphide under different CO2 concentrations during a mesocosm experiment
1Max-Planck-Institut für Biogeochemie, Postfach 100164, 07701 Jena, Germany
2Laboratory for Global Marine and Atmospheric Chemistry, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK
3Department of Biology, University of Bergen, Box 7800, 5020 Bergen, Norway
4British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
5IFM-GEOMAR, Dienstgebäude Westufer, Düsternbrooker Weg 20, 24120 Kiel, Germany
*now at: Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK
Abstract. We investigated the potential impact of seawater acidification on the concentrations of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP), and the activity of the enzyme DMSP-lyase during a pelagic ecosystem CO2 enrichment experiment (PeECE III) in spring 2005. Natural phytoplankton blooms were studied for 24 days under present, double and triple partial pressures of CO2 (pCO2; pH=8.3, 8.0, 7.8) in triplicate 25 m³ enclosures. The results indicate similar DMSP concentrations and DMSP-lyase activity patterns for all treatments. Hence, DMSP and DLA do not seem to have been affected by the CO2 treatment. In contrast, DMS concentrations showed small but statistically significant differences in the temporal development of the "present" versus the high CO2 treatments. The "present" enclosures had higher DMS concentrations during the first 10 days, after which the levels decreased earlier and more rapidly than in the other treatments. Integrated over the whole study period, DMS concentrations were not significantly different from those of the double and triple pCO2 treatments. Pigment and flow-cytometric data indicate that phytoplanktonic populations were generally similar between the treatments, suggesting a certain resilience of the marine ecosystem under study to the induced pH changes, which is reflected in DMSP and DLA. However, there were significant differences in bacterial community structure and the abundance of one group of viruses. The amount of DMS accumulated per total DMSP or chlorophyll-a differed significantly between the present and future scenarios, suggesting that the pathways for DMS production or bacterial DMS consumption were affected by seawater pH.