Deep carbon cycle

Deep Carbon Cycle and Carbon Distribution

• The deep carbon cycle involves the movement of carbon through the Earth's mantle and core.
• The deep Earth contains a significant amount of carbon, but it is not well understood due to its inaccessibility.
• Laboratory simulations and seismology provide evidence of carbon movement in the deep Earth.
• Over 90% of Earth's carbon may reside in the core, with the rest in the crust and mantle.
• The upper mantle has lost a significant amount of carbon through evaporation and transport to the core.

Carbon in the Lower Mantle

• Carbon enters the mantle through carbonate-rich sediments on tectonic plates.
• Carbon cycling extends to the lower mantle.
• Basaltic oceanic lithosphere transports carbon to the deep interior.
• Carbonates descending to the lower mantle can form compounds like diamonds, magnesite, and graphite.
• Carbonates undergo reduction and stabilization at depth by low oxygen fugacity environments.

Polymorphism and Carbonate Stability

• Polymorphism affects the stability of carbonate compounds at different depths in the Earth.
• Tetrahedrally-coordinated carbonates are most stable near the core-mantle boundary.
• High pressures in the lower mantle cause carbon bonds to transition, resulting in tetrahedral bonding to oxygen.
• Carbonate melt viscosity increases under high pressures, indicating large carbon deposits in the lower mantle.
• Carbon outgassing occurs when carbonated mantle undergoes decompression melting and mantle plumes carry carbon compounds towards the crust.

Carbon in Earth's Core

• Recent studies suggest large inventories of carbon could be stored in the Earth's core.
• Seismic anomalies indicate the presence of light elements, including carbon, in the core.
• Iron carbide (Fe3C) matches the inner core's sound and density velocities, suggesting the presence of carbon.
• The core may hold up to 67% of Earth's carbon.
• Carbon dissolved in iron forms a stable phase with the same composition as iron carbide.

Fluxes and Boundaries

• Major fluxes of carbon to, from, and within Earth's exogenic and endogenic systems.
• Maximum and minimum fluxes of carbon since 200 million years ago.
• Boundaries such as the Mohorovičić discontinuity (Moho) and lithosphere-asthenosphere boundary (LAB) are highlighted in the Earth's carbon cycle.

Deep carbon cycle Data Sources