The Dissolution Rate of CaCO₃ in the Ocean

Area of Science:

• Marine geochemistry and carbonate chemistry
• Biogeochemical cycles
• Mineral dissolution kinetics

Background:

• Calcium carbonate (CaCO3) dissolution is crucial for marine alkalinity and carbon cycles.
• Existing rate laws for CaCO3 dissolution lack consensus, with discrepancies between lab/field and inorganic/biogenic studies.
• Freshwater calcite dissolution is well-understood, unlike marine environments.

Purpose of the Study:

• To unify the understanding of marine carbonate dissolution.
• To develop a new theoretical framework and experimental method to explain CaCO3 dissolution rates in seawater.
• To reconcile discrepancies in historical and recent dissolution data.

Main Methods:

• Development and application of a new, highly sensitive method for measuring dissolution rates.
• Integration of a theoretical framework based on surface energetic theory and seawater speciation.
• Analysis of both recent and historical marine carbonate dissolution data.

Main Results:

• Empirical curve fits of seawater data show poor agreement due to thermodynamic dependencies.
• Models incorporating surface energetic theory and complex seawater/calcite speciation successfully explain recent data.
• The new framework explains previously unexplained historical data, including a kink in the rate-saturation relationship.

Conclusions:

• A unified understanding of marine carbonate dissolution is achievable through advanced theoretical and experimental approaches.
• Seawater speciation and surface energetics are critical factors governing dissolution rates.
• A kink in the rate-saturation relationship, signaling a change in dissolution mechanism, likely accelerates CaCO3 dissolution in marine sediments.