Contrasting effects of acidification and warming on dimethylsulfide concentrations during a temperate estuarine fall bloom mesocosm experiment
oleh: R. Bénard, M. Levasseur, M. Scarratt, S. Michaud, M. Starr, A. Mucci, G. Ferreyra, G. Ferreyra, M. Gosselin, J.-É. Tremblay, M. Lizotte, G.-P. Yang
| Format: | Article |
|---|---|
| Diterbitkan: | Copernicus Publications 2019-03-01 |
Deskripsi
<p>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<span class="inline-formula"><sub>T</sub></span> (pH on the total hydrogen ion concentration scale) from 8.0 to 7.2, corresponding to a range of <span class="inline-formula">CO<sub>2</sub></span> partial pressures (<span class="inline-formula"><i>p</i>CO<sub>2</sub></span>) from 440 to 2900 <span class="inline-formula">µ</span>atm, at two temperatures (in situ and <span class="inline-formula">+5</span> <span class="inline-formula"><sup>∘</sup></span>C; 10 and 15 <span class="inline-formula"><sup>∘</sup></span>C) were monitored during 13 days. All mesocosms were characterized by the rapid development of a diatom bloom dominated by <i>Skeletonema costatum</i>, 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 <span class="inline-formula"><sup>∘</sup></span>C resulted in a significant increase in the average bacterial production (BP) in all 15 <span class="inline-formula"><sup>∘</sup></span>C mesocosms as compared to 10 <span class="inline-formula"><sup>∘</sup></span>C, with no detectable effect of <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> on BP. Variations in total DMSP (DMSP<span class="inline-formula"><sub>t</sub></span> <span class="inline-formula">=</span> particulate <span class="inline-formula">+</span> dissolved DMSP) concentrations tracked the development of the bloom, although the rise in DMSP<span class="inline-formula"><sub>t</sub></span> persisted for a few days after the peaks in chlorophyll <span class="inline-formula"><i>a</i></span>. Average concentrations of DMSP<span class="inline-formula"><sub>t</sub></span> were not affected by acidification or warming. Initially low concentrations of DMS (<span class="inline-formula"><1</span> nmol L<span class="inline-formula"><sup>−1</sup></span>) increased to reach peak values ranging from 30 to 130 nmol L<span class="inline-formula"><sup>−1</sup></span> towards the end of the experiment. Increasing the <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> reduced the averaged DMS concentrations by 66 % and 69 % at 10 and 15 <span class="inline-formula"><sup>∘</sup></span>C, respectively, over the duration of the experiment. On the other hand, a 5 <span class="inline-formula"><sup>∘</sup></span>C warming increased DMS concentrations by an average of 240 % as compared to in situ temperature, resulting in a positive offset of the adverse <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> 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.</p>