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Science 16 August 2002:
Vol. 297. no. 5584, pp. 1154 - 1157
DOI: 10.1126/science.1073995
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Reports

Subduction and Recycling of Nitrogen Along the Central American Margin

Tobias P. Fischer,1* David R. Hilton,2 Mindy M. Zimmer,1 Alison M. Shaw,2 Zachary D. Sharp,1 James A. Walker3

We report N and He isotopic and relative abundance characteristics of volatiles emitted from two segments of the Central American volcanic arc. In Guatemala, delta 15N values are positive (i.e., greater than air) and N2/He ratios are high (up to 25,000). In contrast, Costa Rican N2/He ratios are low (maximum 1483) and delta 15N 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.

1 Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA.
2 Fluids and Volatiles Laboratory, Geosciences Research Division, Scripps Institution of Oceanography, La Jolla, CA 92093, USA.
3 Department of Geology and Environmental Sciences, Northern Illinois University, DeKalb, IL 60115, USA.
*   To whom correspondence should be addressed. E-mail: fischer{at}unm.edu

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