[S-GC32] Volatiles in the Earth - from Surface to Deep Mantle

[SGC32-02] On the deep carbon cycle in numerical modeling of mantle convection – Implication for the potential role in long-term surface environment

*Takashi Nakagawa^1,2 (1.Kobe Univ., 2.Hiroshima Univ.)

Keywords:Deep carbon cycle, Subduction zone, Solubility limit, Mantle convection

The deep carbon cycle was investigated by conducting numerical mantle convection simulations that incorporated the carbon solubility limit of mantle minerals, including metamorphic reactions in the subduction zone. This limit was determined based on the high-pressure experiments. It is important to note that carbon solubility in mantle rocks is expected to be much higher than that of mantle minerals. Therefore, this information was extrapolated to match the expected value of carbon solubility in mantle rocks, which can reach up to 1 wt. percent. In order to determine the consistent amount of carbon outgassing emitted by volcanic eruptions (up to 10¹¹ kg C/yr), the carbon solubility of mantle rocks in the mantle transition zone was found to be approximately ~0.1 wt. percent. The deep carbon cycle primarily operates through a subducting plate. The carbon budget in the deep interior is influenced by the balance between ingassing (carbon input through plate subduction) and decarbonation (excess carbon expelled owing to the solubility limit of carbon in mantle rocks, removing it from the deep interior). Consequently, metamorphic reactions and plate subduction have a greater impact on volcanic outgassing beneath the mid-oceanic ridge. The estimated mechanism of the supply system of carbon in the dynamics of Earth’s deep interior obtained in this study suggests a warm climate capable of sustaining liquid water (ocean) on Earth's surface. However, further investigation of the evolution of an Earth-like climate is necessary.