Nitrogen concentration and δ15N of altered oceanic crust obtained on ODP Legs 129 and 185: Insights into alteration-related nitrogen enrichment and the nitrogen subduction budget

The upper 470-m AOC recovered by ODP Legs 129 and 185 delivers approximately 8 × 105 g/km N annually into the Mariana margin. If the remaining less-altered oceanic crust (assuming 6.5 km, mostly dikes and gabbros) has MORB-like N of 1.5 ppm, the entire oceanic crust transfers 5.1 × 106 g/km N annually into that trench. This N input flux is twice as large as the annual N input of 2.5 × 106 g/km in seafloor sediments subducting into the same margin, demonstrating that the N input in oceanic crust, and its isotopic consequences, must be considered in any assessment of convergent margin N flux.