Nitrogen in the deep mantle

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Nitrogen appears highly depleted relative to other volatile elements on Earth. However, recent data from our laboratory suggest that the upper mantle alone may be able to store 20 - 50 times more nitrogen than presently resides in the atmosphere. Together with a number of observations, e.g. an imbalance between present-day nitrogen subduction and degasing, this suggests that the amount of nitrogen residing in the atmosphere and therefore the bulk atmospheric pressure may have changed over geologic time. To further constrain the potential storage of nitrogen in the deep mantle, nitrogen solubility in the minerals of the transition zone (wadsleyite, ringwoodite, majorite) and of the lower mantle (bridgmanite, CaSiO3 perovskite) shall be experimentally investigated. Minerals will be synthesized in equilibrium with a nitrogen-rich fluid in multi-anvil experiments and subsequently be analysed by SIMS (secondary ion mass spectrometry). Polarized FTIR and Raman spectroscopy, as well as single-crystal X-ray diffraction will be used to constrain the solubility mechanism of nitrogen. Thermodynamic models will be developed for the nitrogen storage capacity and the equilibrium nitrogen distribution in the mantle.