Precipitation of CaCO3 in natural and man-made aquatic environments - Mechanisms, analogues, and proxies

Calcium carbonate precipitates occur in diverse and widespread aquatic environments, both from marine to terrestrial natural surroundings and from anthropogenic to engineered settings. In aquatic media, calcium and carbonate ions react to form hydrous and anhydrous CaCO₃-containig solids in types of amorphous and crystalline phases, with calcite, aragonite and dolomite being the most frequent carbonate minerals in the Earth's crust. Understanding the CaCO₃ formation kinetics and mechanisms is key to exploring and evaluating individual aspects of biomineralization, speleothem and travertine growth, lime−/dolostone genesis, diagenetic pathways, climate reconstruction, CO₂ sequestration, tailored synthesis, unwanted scaling, mediated cementation, (geo)chemical forensics, etc. Although the literature dealing with CaCO₃ abundance, formation conditions, reaction mechanisms, nano- and macrostructures, elemental and isotope proxies is extensive, a comprehensive and up-to-date review of the highly diverse environments of CaCO₃ precipitation from aqueous media is valuable due to the tremendous increase in our knowledge about (i) CaCO₃ formation settings, analogues, reaction dynamics, and (potential) applications, (ii) novel high-precision, temporally and spatially highly-resolved analytical techniques, and (iii) monitoring, tracing and modeling tools. The present review on the formation of CaCO₃ in natural and man-made aquatic environments focuses on a systematic compilation and assessment of (i) reaction kinetics, mechanisms, and pathways of carbonate precipitation, (ii) analytical tools and proxies for tracking and reconstructing the solid-fluid-gas interactions and physico(bio)chemical environmental conditions during CaCO₃ precipitation, and (iii) natural and man-made analogs for the precipitation settings. The present review approach is not encyclopedic, but aims at a diverse array of environmental settings, the complex and coupled reaction pathways, state-of-the-art elemental and isotopic environmental proxies, and novel monitoring and modeling concepts for CaCO₃ precipitation.