Sensitivity of pelagic CaCO3 dissolution to ocean acidification in an ocean biogeochemical model

• Main Authors: Regenberg, A., Schneider, B., Gangstø, R.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Ocean acidification
• Online Access: https://doi.org/10.5194/bgd-10-11343-2013; https://www.biogeosciences-discuss.net/bg-2013-274/

In ocean biogeochemical models pelagic CaCO 3 dissolution is usually calculated as R = k * S n , where k is the dissolution rate constant transforming S , the degree of (under-) saturation of seawater with respect to CaCO 3 , into a time dependent rate R , and n is the reaction rate order. Generally, there are two ways to define the saturation state of seawater with respect to CaCO 3 : (1) Δ[CO 3 2− ], which reflects the difference between the in-situ carbonate ion concentration and the saturation concentration, and (2) Ω, which is approximated by the ratio of in-situ carbonate ion concentration over the saturation concentration. Although describing the same phenomenon, the deviation from equilibrium, both expressions are not equally applicable for the calculation of CaCO 3 dissolution in the ocean across pressure gradients, as they differ in their sensitivity to ocean acidification (change of [CO 3 2− ]) over depth. In the present study we use a marine biogeochemical model to test the sensitivity of pelagic CaCO 3 dissolution to ocean acidification (1–4 × CO 2 + stabilization), exploring the possible parameter space for CaCO 3 dissolution kinetics as given in the literature. We find that at the millennial time scale there is a wide range of CaCO 3 particle flux attenuation into the ocean interior (e.g. a reduction of −55 to −85% at 1000 m depth), which means that there are significant differences in the impact on particle ballasting, depending on the kinetic expression applied.