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

• Published in: Biogeosciences
• Main Authors: R. Bénard, M. Levasseur, M. Scarratt, S. Michaud, M. Starr, A. Mucci, G. Ferreyra, M. Gosselin, J.-É. Tremblay, M. Lizotte, G.-P. Yang
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2019
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Ocean acidification
• Online Access: https://doi.org/10.5194/bg-16-1167-2019; https://doaj.org/article/057c2bd32f5049d3a05a4bcca07b0b60

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 ...