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

• Published in: Biogeosciences
• Main Authors: Bénard, Robin, Levasseur, Maurice, Scarratt, Michael, Michaud, Sonia, Starr, Michel, Mucci, Alfonso, Ferreyra, Gustavo, Gosselin, Michel, Tremblay, Jean-Éric, Lizotte, Martine, Yang, Gui-Peng
• Format: Text
• Language: English
• Published: 2019
• Subjects: Ocean acidification
• Online Access: https://doi.org/10.5194/bg-16-1167-2019; https://www.biogeosciences.net/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 pH T (pH on the total hydrogen ion concentration scale) from 8.0 to 7.2, corresponding to a range of CO 2 partial pressures ( p CO 2 ) from 440 to 2900 µ atm, 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 p CO 2 on BP. Variations in total DMSP (DMSP t = particulate + dissolved DMSP) concentrations tracked the development of the bloom, although the rise in DMSP t persisted for a few days after the peaks in chlorophyll a . Average concentrations of DMSP t were not affected by acidification or warming. Initially low concentrations of DMS ( <1 nmol L −1 ) increased to reach peak values ranging from 30 to 130 nmol L −1 towards the end of the experiment. Increasing the p CO 2 reduced the averaged DMS concentrations by 66 % and 69 % at 10 and 15 ∘ C, respectively, over the duration of the experiment. On the other hand, a 5 ∘ C warming increased DMS concentrations by an average of 240 % as compared to in situ temperature, resulting in a positive offset of the adverse p CO 2 impact. Significant positive correlations found between bacterial production and concentrations of DMS throughout our experiment point towards temperature-associated enhancement of bacterial DMSP metabolism as a likely driver of the mitigating effect of warming on the negative impact of acidification on the net production of DMS in the LSLE and potentially the global ocean.