Nitrogen Recycling across the Mariana Subduction Zone: a Coupled Study of Serpentinized Peridotite and Submarine Glassy Basalts

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

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-studied volcanic arc discharges gas exsolved from sub-arc magma. The backarc spreading centers erupt magmas from shallow decompression melting, with abundant glassy submarine basalts available from direct seafloor sampling. The study tests the hypothesis that serpentinized forearc mantle wedge and backarc mantle act as important pathways for recycling subducted N to the forearc and backarc regions. This hypothesis has important implications for our understanding of N activity during subduction. The new insights on N recycling within the Mariana forearc and backarc regions from the proposed work will then be combined with results from earlier studies on N recycling at the arc for the first comprehensive investigation on N recycling across an entire convergent margin. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.