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Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release


Increasing concentrations of carbon dioxide in sea water are driving a progressive acidification of the ocean1. Although the associated changes in the carbonate chemistry of surface and deep waters may adversely affect marine calcifying organisms2,3,4, current experiments do not always produce consistent results for a given species5. Ocean sediments record past biological responses to transient greenhouse warming and ocean acidification. During the Palaeocene–Eocene thermal maximum, for example, the biodiversity of benthic calcifying organisms decreased markedly6,7, whereas extinctions of surface dwellers were very limited8,9. Here we use the Earth system model GENIE-1 to simulate and compare directly past and present environmental changes in the marine realm. In our simulation of future ocean conditions, we find an undersaturation with respect to carbonate in the deep ocean that exceeds that experienced during the Palaeocene–Eocene thermal maximum and could endanger calcifying organisms. Furthermore, our simulations show higher rates of environmental change at the surface for the future than the Palaeocene–Eocene thermal maximum, which could potentially challenge the ability of plankton to adapt.

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Figure 1: The geological context for future ocean acidification.
Figure 2: Anthropogenic and PETM evolution of ocean carbonate saturation in the model.
Figure 3: Evolution of benthic environmental conditions in the model.


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A.R. and D.N.S. acknowledge support from The Royal Society in the form of University Research Fellowships, the UK National Environmental Council grants NE/F001622/1 and NE/F002408/1, together with NSF EAR-0628719. This work arose out of the IGBP-SCOR Fast Track Initiative on Ocean Acidification and is a contribution to the EU EPOCA ocean acidification initiative.

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A.R. conceived and analysed the model experiments. Both authors discussed the results and wrote the paper.

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Correspondence to Andy Ridgwell.

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The authors declare no competing financial interests.

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Ridgwell, A., Schmidt, D. Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release. Nature Geosci 3, 196–200 (2010).

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