Nitrogen (N) is an extremely important nutrient and is often the limiting nutrient in ecosystem productivity. Earth's N cycle is poorly understood, particularly the exchange between the surface and deep interior driven by plate tectonics. The project will investigate N cycling through a subduction zone. Subduction zones are the main site of N and other volatile element recycling to the deep interior. The project will focus on the forearc and backarc regions of the Mariana Island Arc using existing rock samples. The project will establish how much N is released by the subduction zone, using new analyses of forearc and backarc regions in combination with previously published data from the arc itself. The new data can be compared to the known amount of N entering the subduction zone to derive the first complete picture of N flux across an entire subduction zone. The project will advance the development of cutting-edge analytical methods for N and N-isotopes, support an early-career researcher, and provide student internships. This project will analyze samples from the entire length of an active subduction zone to quantify the flux of N through the Earth’s interior. The Mariana subduction zone provides an excellent natural laboratory to study volatile recycling at various depths with the mantle. Mud volcanoes in the Mariana forearc region exhume material from the serpentinized forearc mantle, with samples available from legacy ocean drilling cores. The relatively well-studie