Nitrogen isotope fractionation and geological nitrogen cycle

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Light stable isotopes have become a routine and robust tool to trace material sources and monitor (bio)geochemical processes in planetary and geosciences. For example, carbon isotopes have been used to examine the carbon cycle in various temporal and spatial scales on the Earth. This effort has significantly advanced our understanding of the evolution of and interaction between the Earth's mantle, crust, and particularly atmosphere, in which the level of greenhouse gas CO2 directly impacts the climate and environment. In striking contrast, the cycle of nitrogen, a component equally important as carbon in all Earth's reservoirs, is still poorly understood even though several of its species (NH3, N2O, N2) also act as greenhouse gases. This has been mainly attributed to (1) the poor knowledge of nitrogen isotope effects in key processes controlling nitrogen transfer and siting at different pressure-temperature conditions and (2) poorly constrained boundary conditions to define the nitrogen properties of different reservoirs.To fill this gap, this Discovery Program has two objectives:(1) use laboratory- and field-based investigations to determine the nitrogen isotope fractionations between different nitrogen species at a variety of temperatures related to important nitrogen cycling processes, such as abiotic nitrogen reduction, ammonium-ammonia transformation, ammonia degassing, and ammonium exchange between minerals.(2) clarify the uncertainties in the study of large-scale nitrogen cycling across subduction zones, including characterizing the nitrogen behavior in early subduction and detecting the recycled crustal nitrogen in arc volcanic rocks and their contributions to the global geological nitrogen cycle.