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: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2019
• Subjects: article; Verlagsveröffentlichung; Ocean acidification
• Online Access: https://doi.org/10.5194/bg-16-1167-2019; https://noa.gwlb.de/receive/cop_mods_00002879; https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00002837/bg-16-1167-2019.pdf; https://bg.copernicus.org/articles/16/1167/2019/bg-16-1167-2019.pdf

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 (<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 pCO2 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 pCO2 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.