Dissolution of CaCO3 in the present and glacial ocean: A comparison of the effects of different dissolution parameterizations

Christoph.Voelker [ at ] awi.de


The production of the calcium carbonate minerals calcite and aragonite in the ocean is primarily done by different pelagic calcifying organisms: coccolithophorids, foraminifera and pteropods. The contribution of corals to the production of CACO3 is comparatively small. The surface ocean is supersaturated with respect to the two minerals forms of CACO3: aragonite and calcite, while the deep ocean is undersaturated. Most of these calcium carbonate minerals produced near the surface ocean sink through the water column and mainly dissolve in the deep ocean below the saturation horizon where the solubility product of the minerals increases due to increased pressure. CaCO3 formation in the surface ocean and dissolution in the deeper ocean both affect dissolved inorganic carbon and total alkalinity and also the oceanic pCO2. In this study, a global biogeochemical model (REcoM) is used to analyze the production and dissolution of CaCO3 for the Last Glacial Maximum (LGM) and present day with two different set up of dissolution rate: one is that the dissolution rate of CaCO3 is assumed constant when it sinks through the water column (λ does not depend on Ω ), in other λ has been made depend on Ω. In REcoM, biogenic CaCO3 production is restricted to phytoplankton. In comparison with observation, model simulation with uniform dissolution does a good job at reproducing the global patterns of DIC, alkalinity and Ω although some regional differences remain: too high DIC concentrations in between 800 m to 1200 m ocean depth, high alkalinity concentration in the depth between 1200 m to 2000 m and higher Ω in the Atlantic Ocean and the Indian Ocean value. In this study, it is tested that whether changes in the parameterization of the CaCO3 dissolution rate in the model can improve the distribution. Making the dissolution depend on Ω leads to a much improved global oceanic distribution of DIC, alkalinity and Ω. Furthermore, LGM model simulation reproduce the ocean of low temperature, salty and high in alkalinitry and DIC concentration than the present day [Buchanan et al., 2016b, Vo ̈lker and Ko ̈hler, 2013, Zhang et al., 2013]. The overall LGM ocean is high in calcium carbonate saturation than the present day because of higher [CO2−] concentration.

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Peya, D. (2017): Dissolution of CaCO3 in the present and glacial ocean: A comparison of the effects of different dissolution parameterizations , Master thesis, Institut für Umweltphysik, Universität Bremen.

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