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The role of calcification in carbonate compensation


The long-term recovery of the oceans from present and past acidification is possible due to neutralization by the dissolution of biogenic CaCO3 in bottom sediments, that is, carbonate compensation. However, such chemical compensation is unable to account for all features of past acidification events, such as the enhanced accumulation of CaCO3 at deeper depths after acidification. This overdeepening of CaCO3 accumulation led to the idea that an increased supply of alkalinity to the oceans, via amplified weathering of continental rocks, must accompany chemical compensation. Here we discuss an alternative: that changes to calcification, a biological process dependent on environmental conditions, can enhance and modify chemical compensation and account for overdeepening. Using a simplified ocean box model with both constant and variable calcification, we show that even modest drops in calcification can lead to appreciable long-term alkalinity build-up in the oceans and, thus, create overdeepening; we term this latter effect biological compensation. The chemical and biological manifestations of compensation differ in terms of controls, timing and effects, which we illustrate with model results. To better predict oceanic evolution during the Anthropocene and improve the interpretation of the palaeoceanographic record, it is necessary to better understand biological compensation.

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Fig. 1: Schematic diagram of the critical horizons of open-ocean carbonate compensation.
Fig. 2: Predicted evolution of carbonate horizons as a result of different compensation mechanisms for Anthropocene-like conditions.
Fig. 3: Predicted evolution of the carbonate horizons as a result of a 10% (maximum) drop in calcification for Anthropocene-like conditions.
Fig. 4: Predicted evolution of the carbonate horizons and PCO2 as a result of added carbonate alkalinity input (FA) for Anthropocene-like conditions.
Fig. 5: Simulation of the effects of a quasi-K–Pg calcification collapse.

Data availability

The authors declare that the data supporting the findings of this study are available within the article and its supplementary information files and further information are available from the corresponding author upon request.


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B.P.B. gratefully acknowledges funding from NSERC and the Killam Trust. J.J.M. was supported by the Netherlands Earth System Science Center, as was a sabbatical stay in Utrecht by B.P.B.

Author information




B.P.B. provided the concept for the paper, ran the code and co-wrote the paper. J.J.M. researched various aspects of the problem and co-wrote the paper. Y.L. wrote the code and contributed to the writing of the paper. Address scientific requests and inquiries to B.P.B. (, and questions regarding the code can be directed to Y.L. (

Corresponding authors

Correspondence to Bernard P. Boudreau or Yiming Luo.

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Supplementary information

Supplementary Information

Supplementary Figures 1–4

Supplementary Code

Fortran code: code for the calculation of the CO2 compensation system.

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Boudreau, B.P., Middelburg, J.J. & Luo, Y. The role of calcification in carbonate compensation. Nature Geosci 11, 894–900 (2018).

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