Particulate trace metal dynamics in response to increased CO<sub>2</sub> and iron availability in a coastal mesocosm experiment
<p>Rising concentrations of atmospheric carbon dioxide are causing ocean acidification and will influence marine processes and trace metal biogeochemistry. In June 2012, in the Raunefjord (Bergen, Norway), we performed a mesocosm experiment, comprised of a fully factorial design of ambient and...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-02-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/17/757/2020/bg-17-757-2020.pdf |
| Summary: | <p>Rising concentrations of atmospheric carbon dioxide are causing
ocean acidification and will influence marine processes and trace metal
biogeochemistry. In June 2012, in the Raunefjord (Bergen, Norway), we performed a
mesocosm experiment, comprised of a fully factorial design of ambient and
elevated <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> and/or an addition of the siderophore desferrioxamine B
(DFB). In addition, the macronutrient concentrations were manipulated to
enhance a bloom of the coccolithophore <i>Emiliania huxleyi</i>. We report the changes in
particulate trace metal concentrations during this experiment. Our results
show that particulate Ti and Fe were dominated by lithogenic material, while
particulate Cu, Co, Mn, Zn, Mo and Cd had a strong biogenic component.
Furthermore, significant correlations were found between particulate
concentrations of Cu, Co, Zn, Cd, Mn, Mo and P in seawater and
phytoplankton biomass (<span class="inline-formula">µ</span>gC L<span class="inline-formula"><sup>−1</sup></span>), supporting a significant
influence of the bloom in the distribution of these particulate elements.
The concentrations of these biogenic metals in the <i>E. huxleyi</i> bloom were ranked as follows: Zn <span class="inline-formula"><</span> Cu <span class="inline-formula">≈</span> Mn <span class="inline-formula"><</span> Mo <span class="inline-formula"><</span> Co <span class="inline-formula"><</span> Cd. Changes in <span class="inline-formula">CO<sub>2</sub></span> affected total particulate concentrations and
biogenic metal ratios (Me <span class="inline-formula">:</span> P) for some metals, while the addition of DFB only
significantly affected the concentrations of some particulate metals (mol L<span class="inline-formula"><sup>−1</sup></span>). Variations in <span class="inline-formula">CO<sub>2</sub></span> had the most clear and significant effect
on particulate Fe concentrations, decreasing its concentration under high
<span class="inline-formula">CO<sub>2</sub></span>. Indeed, high <span class="inline-formula">CO<sub>2</sub></span> and/or DFB promoted the dissolution of
particulate Fe, and the presence of this siderophore helped in maintaining high
dissolved Fe. This shift between particulate and dissolved Fe
concentrations in the presence of DFB, promoted a massive bloom of <i>E. huxleyi</i> in the
treatments with ambient <span class="inline-formula">CO<sub>2</sub></span>. Furthermore, high <span class="inline-formula">CO<sub>2</sub></span> decreased the
Me <span class="inline-formula">:</span> P ratios of Co, Zn and Mn while increasing the Cu <span class="inline-formula">:</span> P ratios. These
findings support theoretical predictions that the molar ratios of metal to phosphorous (Me <span class="inline-formula">:</span> P ratios) of metals
whose seawater dissolved speciation is dominated by free ions (e.g., Co, Zn
and Mn) will likely decrease or stay constant under ocean acidification. In
contrast, high <span class="inline-formula">CO<sub>2</sub></span> is predicted to shift the speciation of dissolved
metals associated with carbonates such as Cu, increasing their
bioavailability and resulting in higher Me <span class="inline-formula">:</span> P ratios.</p> |
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| ISSN: | 1726-4170 1726-4189 |