Author name: Pierre Cartigny

Nitrogen shows unique features among the volatile elements. To be cycled, atmospheric di-nitrogen (N2) needs to be reduced, which is efficiently done by bacterial processes. Crustal uptake of nitrogen and its eventual recycling into the mantle is thus primarily mediated by the biosphere. There is also a marked isotopic contrast between the mantle (15N depleted) and the Earth’s surface (15N enriched). Although the cause of such disequilibrium is not fully understood, it provides insights into mantle–surface interactions over geological time, including recycling of surface sediments into the deep mantle.

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.