Subduction nitrogen

Fischer TP, Hilton DR, Zimmer MM, Shaw AM, Sharp ZD, Walker JA (2002) Subduction and recycling of nitrogen along the Central American margin. Science 297 1154-1157 Fitzsimons ICW, Harte B, Clark RM (2000) SIMS stable isotope measurement counting statistics and analytical precision, Min Mag 64 59-83... 

Zimmer MM, Fischer TP, Hilton DR, Alvaredo GE, Sharp ZD, Walker JA (2004) Nitrogen systematics and gas fluxes of subduction zones insights from Costa Rica arc volatiles. Geochem Geophys Geosys 5 Q05J11, doi 10.1029/2003GC000651... 

Here, the preformed pool includes contributions from the saturation concentration and the degree of disequilibrium at the point of subduction. The biological fraction has contributions from both soft-tissue and carbonate pumps (Volk and Hoffert, 1985). Following Brewer (Brewer, 1978) we may, as a first approximation, interpret the soft-tissue contribution to be related to the biological fraction of nitrogen by a fixed, Redfieldian stoichiometry ... 

Using an approach analogous to that for carbon, Sano et al. (1998, 2001) have attempted to understand the nitrogen cycle at subduction zones. Again, the problem is to identify and quantify the various contributory sources to the volcanic output. At subduction zones, there are three major sources of nitrogen the mantle (M), atmosphere (A), and subducted sediments (S), and each has a diagnostic value and N2/ Ar... 

This would indicate that a significant proportion (up to 70%) of the N2 could be derived from a subducted sedimentary or crustal source. The situation is reversed in the case of back-arc basin glasses, which have significantly lower values (—2.7%c to - -1.9%c) this implies that up to 70% of the nitrogen could be mantle-derived (Sano et ai, 2001). A first-order conclusion from these observations is that N2 is efficiently recycled from the subducting slab to the atmosphere and hydrosphere through arc (and back-arc volcanism) (see also Fischer et al, 2002). 

Sano Y., TakahataN., Nishio Y., and Marty B. (1998) Nitrogen recycling in subduction zones. Geophys. Res. Lett. 25, 2289-2292. 

Nitrogen at hotspots. values from hotspots has been found to be largely positive and as high as = +8%o as (Dauphas and Marty, 1999 Marty and Dauphas, 2003). It has been argued that these values are due to the presence of subducted components in mantle plumes (Marty and Dauphas, 2003), and is supported by the lack of correlation with helium isotope compositions. 

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