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Progress in Earth and Planetary Science
Fig. 12 | Progress in Earth and Planetary Science

Fig. 12

From: Perspective on the response of marine calcifiers to global warming and ocean acidification—Behavior of corals and foraminifera in a high CO2 world “hot house”

Fig. 12

Proton pumping-based model of rotaliid foraminiferal calcification at the enclosed site of calcification (SOC). a Magnified SEM image of the cross section of SOC. Upper side is the outer side, whereas the lower side is the cellular side. b Black rectangle indicates the observed newly calcifying chamber in (a). c Considerable calcification model based on Toyofuku et al. (2017) and Nagai et al. (2018). During chamber formation on an organic template (termed the primary organic sheet, POS), the organic layers isolate the growing calcite surface from the surrounding seawater. The chemical composition of the calcification fluid of the SOC is characterized by active, outward proton pumping coupled with an inward calcium ion-flux. The transported proton reduced pH around the foraminiferal microenvironment. Inorganic carbon speciation is shifted by this lower pH, thereby increasing pCO2 of the surrounding seawater near the site of calcification. The large gradient in pCO2 around the individual results in the diffusion of CO2 into the site of calcification. This inbounded CO2 reacts to form carbonate ions due to the high pH at the site of calcification. This transported carbon source sustains CaCO3 precipitation by reacting with the inward- transported calcium ions

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