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Published January 2021 | public
Journal Article

The Dissolution Rate of CaCO₃ in the Ocean

Abstract

The dissolution of CaCO₃ minerals in the ocean is a fundamental part of the marine alkalinity and carbon cycles. While there have been decades of work aimed at deriving the relationship between dissolution rate and mineral saturation state (a so-called rate law), no real consensus has been reached. There are disagreements between laboratory- and field-based studies and differences in rates for inorganic and biogenic materials. Rates based on measurements on suspended particles do not always agree with rates inferred from measurements made near the sediment–water interface of the actual ocean. By contrast, the freshwater dissolution rate of calcite has been well described by bulk rate measurements from a number of different laboratories, fit by basic kinetic theory, and well studied by atomic force microscopy and vertical scanning interferometry to document the processes at the atomic scale. In this review, we try to better unify our understanding of carbonate dissolution in the ocean via a relatively new, highly sensitive method we have developed combined with a theoretical framework guided by the success of the freshwater studies. We show that empirical curve fits of seawater data as a function of saturation state do not agree, largely because the curvature is itself a function of the thermodynamics. Instead, we show that models that consider both surface energetic theory and the complicated speciation of seawater and calcite surfaces in seawater are able to explain most of the most recent data. This new framework can also explain features of the historical data that have not been previously explained. The existence of a kink in the relationship between rate and saturation state, reflecting a change in dissolution mechanism, may be playing an important role in accelerating CaCO₃ dissolution in key sedimentary environments.

Additional Information

© 2021 by Annual Reviews. First published as a Review in Advance on September 18, 2020. We thank the National Science Foundation for its support of this research via awards OCE-1220600, OCE-1559215, OCE-1834492, OCE-1559004, OCE-1220302, and OCE-1834475. We have also benefited from financial support from the Linde Center for Global Environmental Science at Caltech, the Change Happens Foundation, and the Grantham Foundation. Little of this work would have been possible without the technical support of Nick Rollins and intellectual inspiration from Jonathan Erez. Conversations with many colleagues over the years have helped shape our understanding of carbonate dissolution kinetics, but we are especially indebted to Burke Hales and Henry Teng for insightful comments and criticisms along the way. The authors are not aware of any affiliations, memberships, funding, or financial holdings that might be perceived as affecting the objectivity of this review.

Additional details

Created:
August 22, 2023
Modified:
October 20, 2023