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Using first principles molecular dynamic simulations, we explore the effects of nitrogen (N) on the density and sound velocity of liquid iron and evaluate its potential as a light element in the Earth's outer core. Our results suggest that Fe-N melt cannot simultaneously explain the density and seismic velocity of the Earth's outer core. Although 2.0wt.%N can explain the bulk sound velocity of the outer core, such N content only lowers the density of liquid Fe by 3%. Matching both the velocity and density by the other light elements limits the N in the core to <<2.0wt.%. Our finding suggests that nitrogen is a minor to trace element in the Earth's core and is consistent with the geochemical mass balance with terrestrial abundance of N and alloy-silicate partitioning data, which suggest that there cannot be significant N in the core.

Plain Language Summary Physical properties of liquid iron cannot explain the seismological observations of density and sound wave velocities in the liquid outer core. In this study we explore the effect of light element nitrogen on the physical properties of liquid iron and provide an upper bound of the amount of nitrogen in the outer core if nitrogen were the sole light element.