Author name: Vincent Busigny

Nitrogen is the main constituent of Earth’s atmosphere and a key component of the biosphere, but it is a trace element in the major silicate reservoirs. The relatively low concentrations (parts per million level) complicate efforts to constrain the nitrogen speciation and abundance in the mantle and crust. In most silicates, nitrogen occurs as NH4 + (substituting for K+), whereas its speciation in hydrous fluids and silicate melts can vary widely depending in large part on redox conditions. Current knowledge of nitrogen isotope fractionation among relevant mineral and fluid/melt phases is limited by the lack of experimental data to confirm theoretical predictions of these fractionations. Modeling of modern and long-term nitrogen cycling on Earth will be advanced by better constraints on the sizes and isotopic compositions of the major crust and mantle nitrogen reservoirs.

Nitrogen exhibits an intriguing combination of highly volatile behavior (particularly as N2), appreciable reactivity, and surprising compatibility in the deep Earth. Nitrogen is incorporated into the biosphere and then, through diagenesis and low-grade metamorphism, is conveyed into the lithosphere and the deeper Earth. The investigation of N behavior in the biosphere, hydrosphere, and atmosphere has led to many important discoveries regarding biogeochemical pathways, including in areas such as trophic interactions and anthropogenic impacts on terrestrial and marine environments (e.g. nutrient pollution, eutrophication). Nitrogen can act as an excellent tracer of the transfer of sedimentary/organic materials into and within deep-Earth reservoirs and shows great potential as a tracer of life on early Earth and elsewhere in the Solar System.