Microbially enhanced dissolution of calcite in sinking marine particles

Area of Science:

• Marine geochemistry and microbial ecology.
• Biogeochemical cycling of calcium carbonate in the ocean.

Background:

• The dissolution of calcium carbonate (aragonite and calcite) in the surface ocean is poorly understood.
• Mechanisms driving dissolution of stable polymorphs in marine particles remain unconstrained.

Purpose of the Study:

• To quantify how microbial metabolism within marine particles enhances calcite dissolution.
• To investigate the role of microbially-induced acidic microenvironments in particle dissolution.

Main Methods:

• Experimental quantification of calcite dissolution rates in marine particles.
• Analysis of temporal decoupling between particle deoxygenation and acidification.
• Comparison of microbially-driven dissolution rates with abiotic dissolution.

Main Results:

• Microbial metabolism creates acidic microenvironments, significantly enhancing local calcite dissolution.
• Dissolution rates in particles with bacterial growth exceeded abiotic rates by over an order of magnitude.
• Highest dissolution rates occurred at intermediate particle settling velocities, balancing mass transfer and respiration.

Conclusions:

• Microbial activity, not solely respiration-derived CO2, drives calcite undersaturation in marine particles.
• Microbially-driven dissolution in the mesopelagic ocean can alter particle transit times by dissolving calcite ballast.
• Reduced calcite ballast may decrease the efficiency of oceanic carbon sequestration.