[S-IT16] Deep Earth Sciences

[SIT16-14] The Earth’s nitrogen budget set by core-mantle differentiation

*Shengxuan Huang¹, Taku Tsuchiya¹ (1.Geodynamics Research Center, Ehime University)

Keywords:nitrogen partitioning, core-mantle differentiation, missing nitrogen problem, ab initio molecular dynamics

Nitrogen is one of the most significant volatiles in the Earth, an essential element for life, and the primary component of the atmosphere. The Earth’s missing nitrogen problem is manifested by an extremely low nitrogen concentration and a super-chondritic C/N ratio of the bulk silicate Earth. Understanding the nitrogen depletion in the bulk silicate Earth is key to the storage and isotopic features of nitrogen in Earth’s deep reservoirs as well as the delivery process of volatiles to the early Earth. Several models have been proposed to account for this anomalous depletion, such as sequestration of nitrogen into the core, degassing of nitrogen to space and the accretion of a nitrogen-poor and carbon-rich veneer. Different models proposed to explain this issue are caused primarily by the difference in the measured partition coefficients of nitrogen between iron and silicate melts at high pressure-temperature conditions. Knowledge of the partitioning behavior of nitrogen during core-mantle differentiation is of fundamental importance to the Earth’s nitrogen budget and subsequent evolution. In this study, we perform ab initio molecular dynamics combined with the thermodynamic integration method to calculate partition coefficients of nitrogen between iron and silicate melts to 135 GPa and 5000 K. These results enable us to evaluate the effects of different physical and chemical variables on the partitioning behavior of nitrogen, which provides important constraints on the distribution of nitrogen in the deep Earth. They further offer new insights into the delivery of volatiles to the early Earth.