Biological export production controls upper ocean calcium carbonate dissolution and CO₂ buffer capacity.

Area of Science:

• Marine Biogeochemistry
• Oceanography
• Carbon Cycling

Background:

• Marine calcium carbonate (CaCO3) cycles are vital for ocean ecosystems and atmospheric carbon dioxide (CO2) regulation.
• Understanding CaCO3 cycling drivers, particularly in the upper ocean, remains incomplete.

Purpose of the Study:

• To investigate the mechanisms and impact of CaCO3 dissolution in upper ocean marine aggregates.
• To quantify the role of upper ocean CaCO3 dissolution in ocean alkalinity and CO2 uptake.

Main Methods:

• Global-scale analysis of marine aggregate composition and dissolution.
• Modeling of microenvironment conditions within settling aggregates.
• Assessment of CaCO3 dissolution's impact on ocean alkalinity and CO2 buffering capacity.

Main Results:

• Heterotrophic respiration in marine aggregates creates localized undersaturated microenvironments, leading to rapid CaCO3 dissolution.
• Upper ocean CaCO3 dissolution increases the ocean's capacity to neutralize respired CO2 by up to 6% in low-latitude thermocline waters.
• Deep ocean CaCO3 dissolution is mainly governed by thermodynamic solubility, with lower burial fluxes in corrosive North Pacific waters.

Conclusions:

• Upper ocean CaCO3 dissolution significantly contributes to ocean alkalinity, enhancing CO2 uptake.
• This process is sensitive to ocean export production and plays a critical role in regulating atmospheric CO2 levels.
• Without upper ocean dissolution, the ocean's CO2 uptake could decrease by 20% in key upwelling regions.