Contrasting effects of acidification and warming on dimethylsulfide concentrations during a temperate estuarine fall bloom mesocosm experiment

• Published in: Biogeosciences 2019-03, Vol.16 (6), p.1167-1185
• Main Authors: Benard, Robin, Levasseur, Maurice, Scarratt, Michael, Michaud, Sonia, Starr, Michel, Mucci, Alfonso, Ferreyra, Gustavo, Gosselin, Michel, Tremblay, Jean-Eric, Lizotte, Martine, Yang, Gui-Peng
• Format: Article
• Language: English
• Subjects: Abundance; Acidification; Air pollution; Algae; Analysis; Bacteria; Blooms; Brackishwater environment; Carbon dioxide; Chlorophyll; Chlorophyll a; Closed experimental ecosystems; Diatoms; Dimethyl sulfide; Dimethylsulphoniopropionate; Duration; Environmental aspects; Estuaries; Estuarine dynamics; Exhaustion; Experiments; Hydrogen; Hydrogen ion concentration; Hydrogen ions; In situ temperature; Ion concentration; Low concentrations; Measurement; Mesocosms; Metabolism; Ocean acidification; Ocean temperature; Ocean warming; Oceans; Organic sulfur compounds; Silicic acid; Water acidification
• ISSN: 1726-4189; 1726-4170; 1726-4189
• DOI: 10.5194/bg-16-1167-2019

The effects of ocean acidification and warming on the concentrations of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) were investigated during a mesocosm experiment in the Lower St. Lawrence Estuary (LSLE) in the fall of 2014. Twelve mesocosms covering a range of pHT (pH on the total hydrogen ion concentration scale) from 8.0 to 7.2, corresponding to a range of CO2 partial pressures (pCO2) from 440 to 2900 µatm, at two temperatures (in situ and +5 ∘C; 10 and 15 ∘C) were monitored during 13 days. All mesocosms were characterized by the rapid development of a diatom bloom dominated by Skeletonema costatum, followed by its decline upon the exhaustion of nitrate and silicic acid. Neither the acidification nor the warming resulted in a significant impact on the abundance of bacteria over the experiment. However, warming the water by 5 ∘C resulted in a significant increase in the average bacterial production (BP) in all 15 ∘C mesocosms as compared to 10 ∘C, with no detectable effect of pCO2 on BP. Variations in total DMSP (DMSPt = particulate + dissolved DMSP) concentrations tracked the development of the bloom, although the rise in DMSPt persisted for a few days after the peaks in chlorophyll a. Average concentrations of DMSPt were not affected by acidification or warming. Initially low concentrations of DMS (