Subduction and Recycling of Nitrogen Along the Central American Margin

Abstract

We report N and He isotopic and relative abundance characteristics of volatiles emitted from two segments of the Central American volcanic arc. In Guatemala, δ 15 N values are positive (i.e., greater than air) and N 2 /He ratios are high (up to 25,000). In contrast, Costa Rican N 2 /He ratios are low (maximum 1483) and δ 15 N values are negative (minimum –3.0 per mil). The results identify shallow hemipelagic sediments, subducted into the Guatemalan mantle, as the transport medium for the heavy N. Mass balance arguments indicate that the subducted N is efficiently cycled to the atmosphere by arc volcanism. Therefore, the subduction zone acts as a “barrier” to input of sedimentary N to the deeper mantle.