Research ArticleOCEAN CHEMISTRY

Effects of ocean acidification on marine dissolved organic matter are not detectable over the succession of phytoplankton blooms

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Science Advances  02 Oct 2015:
Vol. 1, no. 9, e1500531
DOI: 10.1126/sciadv.1500531
  • Fig. 1 Time series of bulk and molecular data of the 10 mesocosms.

    Box plots include median, SD, maximum and minimum values, and outliers. Orange boxes are for the five mesocosms with high PCO2; blue boxes are for the five control mesocosms. Dotted time series are for Gullmar Fjord ambient water. (A) Chlorophyll a concentration. (B) TDN and DON concentrations, displayed as average values for all 10 mesocosms. (C) DOC concentration. (D) DOC/DON molar ratio. (E) Results from the PCA (PC1) of 7360 molecular formulae and their MS signal intensities.

  • Fig. 2 Examples of FT-ICR-MS spectra of mesocosm DOM at different time points and with different treatments.

    (A) Day −1 after closing mesocosm bags. (B) Day 103 ambient PCO2 mesocosm. (C) Day 103 high PCO2 mesocosm. Mass range is from 150 to 750 daltons and zoomed into one exemplary nominal mass (251 daltons). m/z, mass/charge ratio. The peak in the gray shaded area is exemplary of mass peaks that show a significant difference in intensities between day 1 and day 103 in a Student’s t test (P < 0.001).

  • Fig. 3 Molecular differences over time.

    (A) Exemplary van Krevelen diagrams showing only the molecular formulae (out of 7360) that significantly varied in their intensities over the course of the experiment compared to day −1 for all 10 mesocosm replicates (P < 0.001). The different colors represent differences in normalized relative peak intensity: blue dots indicate an increase in peak intensities, whereas red dots indicate a decrease in peak intensity. Green dashed lines represent time points of phytoplankton blooms. (B) The results are within the statistical error, determined by performing the same test on a randomized data set.

  • Fig. 4 Molecular differences between different CO2 treatments.

    (A) Exemplary van Krevelen diagrams showing only the molecular formulae (out of 7360) that significantly varied in their intensities between the five high PCO2 and control mesocosm replicates, tested for the respective day (P < 0.001). The different colors represent differences in normalized relative peak intensity: blue dots indicate an increase in peak intensity, whereas red dots indicate a decrease in peak intensity. Green dashed lines represent time points of phytoplankton blooms. (B) The results are within the statistical error, determined by performing the same test on a randomized data set.

  • Table 1 Pearson correlation of environmental parameters with the PCA scores.

    Significant correlations are noted by the level of significance (P value); “—” denotes absence of any detectable correlation (P > 0.05).

    PC1 (25%)PC2 (17%)
    CO2
    DOC
    NO2/NO33.07 × 10−92.39 × 10−4
    PO43−2.09 × 10−96.54 × 10−5
    SiO44−1.71 × 10−93.38 × 10−5
    NH4+3.49 × 10−2
    Chlorophyll α6.25 × 10−3

Supplementary Materials

  • Supplementary Materials

    This PDF file includes:

    • Pearson correlation of environmental parameters
    • Fig. S1. Pearson correlation of environmental parameters with the scores of the principal components analysis.

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