doi: 10.1098/rspb.2016.1099.
The role of coccolithophore calcification in bioengineering their environment
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- PMID:27358373
- PMCID: PMC4936047
- DOI: 10.1098/rspb.2016.1099
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The role of coccolithophore calcification in bioengineering their environment
Kevin J Flynn et al. Proc Biol Sci..
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Abstract
Coccolithophorids are enigmatic plankton that produce calcium carbonate coccoliths, which over geological time have buried atmospheric CO2 into limestone, changing both the atmosphere and geology of the Earth. However, the role of coccoliths for the proliferation of these organisms remains unclear; suggestions include roles in anti-predation, enhanced photosynthesis and sun-screening. Here we test the hypothesis that calcification stabilizes the pH of the seawater proximate to the organisms, providing a level of acidification countering the detrimental basification that occurs during net photosynthesis. Such bioengineering provides a more stable pH environment for growth and fits the empirical evidence for changes in rates of calcification under different environmental conditions. Under this scenario, simulations suggest that the optimal production ratio of inorganic to organic particulate C (PIC : POCprod) will be lower (by approx. 20%) with ocean acidification and that overproduction of coccoliths in a future acidified ocean, where pH buffering is weaker, presents a risk to calcifying cells.
Keywords: Emiliania; bioengineering; climate change; coccolith; coccolithophorid; ocean acidification.
© 2016 The Authors.
Figures
Deviation (δH+) from the initial [H+] during simulated growth ofEmiliania under different atmospheric values ofpCO2, and different PIC : POCprod. Assuming that growth is maximized in a stable pH environment, optimal PIC : POCprod aligns with minimum δH+. Growth was simulated in a well-mixed water column of 25 m depth, with 16 µM nitrate, 16°C and 10 m s−1 surface wind speed. Positive values of δH+ (see the electronic supplementary material for details) show deviations at high PIC : POCprod to be associated with acidification (red gradation), with negative values at low PIC : POCprod associated with basification (blue gradation). White indicates zero or minimal δH+. (a) Events for the default maximum growth rate (1 d−1 in a 12 L : 12 D cycle) and (b) for a maximum growth rate of half this value. (Online version in colour.)
Deviation (δH+) from the initial [H+] during simulated growth ofEmiliania under different situations at an atmosphericpCO2 of 400 ppm, and different PIC : POCprod. Assuming that growth is maximized in a stable pH environment, optimal PIC : POCprod aligns with the minimum δH+ (see the electronic supplementary material for further details). The default (control) growth was simulated in a well-mixed water column of 25 m depth, with 16 µM nitrate, 16°C and 10 m s−1 surface wind speed, and a maximum growth rate of 1 d−1 in a 12 L : 12 D cycle. Positive values of δH+ (see the electronic supplementary material for details) show deviations at high PIC : POCprod to be associated with acidification, with negative values at low PIC : POCprod associated with basification. The thick blue line indicates zero δH+. (a) Events with nitrate supplied at half (low nitrate) or double (high nitrate) the default concentrations, or using ammonium rather than nitrate. (b) Events under calm conditions (wind spend 0 m s−1), cold (5°C) or with slow growth (half the default growth rate). (c) Events in shallow (10 m) or deep (50 m) mixed layers. (Online version in colour.)
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