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Bénard, Robin; Levasseur, Maurice; Scarratt, Michael Grant; Lizotte, Martine; Michaud, Sonia; Starr, Michel; Tremblay, Jean-Éric; Kiene, Ronald P; Kameyama, Sohiko (2020): St. Lawrence Estuary phytoplankton spring bloom and associated dimehtylsulfide cycling sensitivity to acidification in a microcosm experiment. PANGAEA, (dataset in review)

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The potential impact of ocean acidification (OA) on the concentrations of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP), as well as the processes governing the cycling of sulfur compounds by microbial organisms were investigated in a microcosm experiment during summer 2013. A natural planktonic community sourced from the surface waters of the Lower St. Lawrence Estuary (LSLE) was monitored over 12 days under three pCO2 targets: 1 × pCO2 (775 µatm), 2 × pCO2 (1850 µatm), and 3 × pCO2 (2700 µatm). The effects of heightened pCO2 were assessed on phytoplankton biomass, taxonomy and productivity, as well as on DMSP and DMS concentrations and microbial cycling via 35S-DMSPd radioisotope uptake assays. A mixed phytoplankton bloom comprised of the diatoms Chaetoceros spp., Skeletonema costatum, and Thalassiosira spp., as well as unidentified flagellates (2-20 µm) developed over the course of the study period. Concentrations of chlorophyll a (Chl a) peaked on day 6 from an initial 1.26 µg L-1 to 20 ± 4 µg L-1 and 17 ± 1 µg L-1, at 1 × pCO2 and 2 × pCO2, respectively. However, the timing and the magnitude of the biomass build-up were altered in the 3 × pCO2 treatment reaching only 11 ± 4 µg L-1 by day 8 of the experiment. Variations in the concentrations of total DMSP (DMSPt) were largely related to variations in Chl a (Spearman's rho correlation (rs) = 0.77; p < 0.001; n = 61) and peak values of DMSPt were reached consecutively on day 8 in the 1 × pCO2 treatment (264 nmol L-1), on day 10 in the 2 × pCO2 (245 nmol L-1), and on day 12 in the 3 × pCO2 (192 nmol L-1). Concentrations of dissolved DMSP (DMSPd) increased irregularly from 2 ± 1 nmol L-1 to an overall average of 5.2 ± 0.8 nmol L-1 by the end of the experiment; the fluctuations being broadly associated with those observed in DMSPt (rs  = 0.70; p < 0.001; n = 61). Neither concentrations of DMSPd nor the microbial scavenging efficiency of DMSPd (kDMSPd) seemed to be strongly affected by increasing pCO2 suggesting that acidification did not alter the availability and the bacterial uptake of this substrate. However, our results show a reduction of the mean microbial yield of DMS by 34 % and 61 % in the 2 × pCO2 and 3 × pCO2 treatments. Doubling and tripling the pCO2 respectively resulted in a 15 % and 40 % decline in average concentrations of DMS compared to the control. DMS concentrations were positively correlated with microbial yields of DMS (rs = 0.65; p < 0.001; n = 45), suggesting that in diatom-dominated systems, the impact of OA on concentrations of DMS may be strongly linked with alterations of the microbial breakdown of DMSPd. Findings from this study provide the first empirical evidence of the sensitivity of the microbial DMSP switch under OA.
acidification; Brackish waters; microcosm; North Atlantic; other metabolic rate; Pelagos; Primary production/Photosynthesis
Related to:
Bénard, Robin; Lizotte, Martine; Levasseur, Maurice; Scarratt, Michael Grant; Michaud, Sonia; Starr, Michel; Tremblay, Jean-Éric; Kiene, Ronald P; Kameyama, Sohiko (2021): Impact of anthropogenic pH perturbation on dimethyl sulfide cycling: A peek into the microbial black box. Elementa - Science of the Anthropocene, 9
Latitude: 49.133300 * Longitude: -67.233300
Date/Time Start: 2013-06-19T00:00:00 * Date/Time End: 2013-07-01T00:00:00
StLawrence_Estuary * Latitude: 49.133300 * Longitude: -67.233300 * Location: Quebec, Canada * Method/Device: Multiple investigations (MULT)
#NameShort NameUnitPrincipal InvestigatorMethod/DeviceComment
1IdentificationIDBénard, Robinof microcosm
2ReplicateReplicateBénard, Robin
3DATE/TIMEDate/TimeBénard, RobinGeocode
4Duration, number of daysDurationdaysBénard, Robin
5Temperature, waterTemp°CBénard, Robin
6SalinitySalBénard, Robin
7pHpHBénard, Robinat 25°C
8pHpHBénard, Robinin situ
9Carbon dioxide, partial pressurepCO2µatmBénard, Robin
10Alkalinity, totalATµmol/kgBénard, Robin
11Nitrate[NO3]-µmol/lBénard, Robin
12Silicic acidSi(OH)4µmol/lBénard, Robin
13Phosphorus, reactive solubleSRPµmol/lBénard, Robin
14Chlorophyll aChl aµg/lBénard, Robin
15Dimethylsulfoniopropionate, totalDMSP totnmol/lBénard, Robin
16Dimethylsulfoniopropionate, dissolvedDMSP dissnmol/lBénard, Robin
17Dimethyl sulfideDMSnmol/lBénard, Robin
18Bacteria, cellsBac109 #/lBénard, Robin
19Primary production of carbon, particulatePP C partµmol/l/dayBénard, Robin
20Primary production of carbon, dissolvedPP C dissµmol/l/dayBénard, Robin
21Primary production of carbon, totalPP C totµmol/l/dayBénard, Robin
22Dimethylsulfoniopropionate rateDMSP rate1/dayBénard, Robin
23Sulfur, 35S35S%Bénard, Robintotal, in particles
24Sulfur, 35S35S%Bénard, Robinin macromolecules
25Sulfur, 35S35S%Bénard, Robinuntransformed in cells
26Dimethyl sulfide, yieldDMS yield%Bénard, Robin
27DiatomsDiatoms#Bénard, Robin
28DinoflagellatesDinofl#Bénard, Robin
29ChrysophyceaeChryseae#Bénard, Robin
30CryptophyceaeCryptophyceae#Bénard, Robin
31PrasinophyceaePrasinophyceae#Bénard, Robin
32PrymnesiophyceaePrymnesiophyceae#Bénard, Robin
33Flagellates indeterminataFlagellates indet#Bénard, Robin
34ChoanoflagellatesChoanoflagellates#Bénard, Robin
35Cells, otherCells oth#Bénard, Robin
1983 data points

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