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Article: Deep carbon cycle

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

Reference URL
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