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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 10, issue 10
Biogeosciences, 10, 6453-6467, 2013
https://doi.org/10.5194/bg-10-6453-2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Biogeochemistry and ecosystems in the western north Pacific...

Biogeosciences, 10, 6453-6467, 2013
https://doi.org/10.5194/bg-10-6453-2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 11 Oct 2013

Research article | 11 Oct 2013

Carbonate mineral saturation states in the East China Sea: present conditions and future scenarios

W.-C. Chou1, G.-C. Gong1,2,3, C.-C. Hung4, and Y.-H. Wu1 W.-C. Chou et al.
  • 1Institute of Marine Environmental Chemistry and Ecology, National Taiwan Ocean University, Keelung 202, Taiwan
  • 2Center of Excellence for the Oceans, National Taiwan Ocean University, Keelung 202, Taiwan
  • 3Taiwan Ocean Research Institute, National Applied Research Laboratories, Kaohsiung 852, Taiwan
  • 4Institute of Marine Geology and Chemistry, National Sun Yet-Sen University, Kaohsiung 804, Taiwan

Abstract. To assess the impact of rising atmospheric CO2 and eutrophication on the carbonate chemistry of the East China Sea shelf waters, saturation states (Ω) for two important biologically relevant carbonate minerals – calcite (Ωc) and aragonite (Ωa) – were calculated throughout the water column from dissolved inorganic carbon (DIC) and total alkalinity (TA) data collected in spring and summer of 2009. Results show that the highest Ωc (∼9.0) and Ωa (∼5.8) values were found in surface water of the Changjiang plume area in summer, whereas the lowest values (Ωc = ∼2.7 and Ωa = ∼1.7) were concurrently observed in the bottom water of the same area. This divergent behavior of saturation states in surface and bottom waters was driven by intensive biological production and strong stratification of the water column. The high rate of phytoplankton production, stimulated by the enormous nutrient discharge from the Changjiang, acts to decrease the ratio of DIC to TA, and thereby increases Ω values. In contrast, remineralization of organic matter in the bottom water acts to increase the DIC to TA ratio, and thus decreases Ω values. The projected result shows that continued increases of atmospheric CO2 under the IS92a emission scenario will decrease Ω values by 40–50% by the end of this century, but both the surface and bottom waters will remain supersaturated with respect to calcite and aragonite. Nevertheless, superimposed on such Ω decrease is the increasing eutrophication, which would mitigate or enhance the Ω decline caused by anthropogenic CO2 uptake in surface and bottom waters, respectively. Our simulation reveals that, under the combined impact of eutrophication and augmentation of atmospheric CO2, the bottom water of the Changjiang plume area will become undersaturated with respect to aragonite (Ωa = ∼0.8) by the end of this century, which would threaten the health of the benthic ecosystem.

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