Aragonite dissolution protects calcite at the seafloor

Area of Science:

• Marine geology
• Biogeochemistry
• Oceanography

Background:

• Calcium carbonates exist as calcite and aragonite, with aragonite being more soluble.
• Aragonite reaches the deep ocean and dissolves, releasing alkalinity.
• This alkalinity buffers the deep ocean and aids calcite preservation.

Purpose of the Study:

• Investigate aragonite dissolution's impact on early diagenesis in calcite-rich sediments.
• Model the role of aragonite in deep-sea carbonate preservation.

Main Methods:

• Utilized a 3D reactive-transport model at micrometric scale.
• Incorporated 3D X-ray tomography of natural aragonite and calcite shells.

Main Results:

• Diffusive transport significantly influences benthic calcium carbonate dissolution.
• Aragonite flux can locally inhibit calcite dissolution and promote recrystallization in seabed sediments.
• Ocean acidification threatens aragonite-producing organisms, potentially reducing this buffering effect.

Conclusions:

• Aragonite dissolution acts as a deep-sea "galvanizing" agent for calcite preservation.
• Reduced aragonite due to ocean acidification will increase calcite dissolution at the sediment-water interface.
• Future CO2 neutralization will rely more heavily on calcite dissolution.