Carbon and nitrogen geochemistry of sediments in the Central American convergent margin: Insights regarding subduction input fluxes, diagenesis, and paleoproductivity

Li, Long; Bebout, Gray E.

doi:10.1029/2004jb003276

Cited by 114 publications

(112 citation statements)

References 109 publications

(173 reference statements)

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“…On the other hand, ratios below the organic C/N value of 11, as observed in northern Nicaragua, suggest that N is added from the subducted oceanic basement. Li and Bebout (2005) find that at least as much nitrogen could be released from the subducting basement as they calculate for the down-going sediment column. Sano et al (2001) and Fischer et al (2002) and are described in the text.…”

Section: Along-arc Variationsmentioning

confidence: 95%

“…The low ratios in this section of the arc could result from preferential return of carbon to the mantle over nitrogen, whereas to the south (Mombacho and Costa Rican volcanoes) nitrogen is lost due to offscraping of the hemipelagic sediment layer or forearc devolatilization. The input flux ratio of oxidized C:organic C:N is 115:11:1 along the Central American margin (Li and Bebout, 2005). The ratio of oxidized C to organic C (10.5) corresponds closely to the L/S ratio measured in the gas discharges along the arc (9.6-11.1; Shaw et al, 2003), suggesting that there is no fractionation of oxidized and organic C during subduction, release from the slab, and transport through the mantle wedge.…”

Section: Along-arc Variationsmentioning

confidence: 99%

“…Hilton et al (2002) calculated a hemipelagic sediment-derived N input at the trench of 2.3 · 10 8 mol/a for the entire CAVA (corresponds to 6.4 · 10 7 mol/a for Nicaragua), and new data for N concentrations in the upper part of sediment cores (Li et al, 2003;Sadofsky and Bebout, 2004) give a slightly higher N input rate of 7.1 · 10 8 mol/a (2.0 · 10 8 mol/a for Nicaragua). Li and Bebout (2005) find a sediment-derived N input , %S, and Ba/La vs. latitude for the CAVA. Nicaragua data are from this study.…”

Section: Nitrogen Flux and Mass Balancementioning

confidence: 99%

“…7; Fischer et al, 2002;Zimmer et al, 2004). Sadofsky and Bebout (2004) calculate a total sedimentary input CO 2 /N 2 ratio of 216, Li and Bebout (2005) find a ratio of 269 at the Central America Trench, and Marty and Zimmermann (1999) measure an average CO 2 /N 2 mantle ratio from MORB glasses of 1070 ± 448. Thus, mixing between mantle and subducted sediment cannot produce the low CO 2 /N 2 exc.…”

Section: Along-arc Variationsmentioning

confidence: 99%

“…We use endmember d 15 N values for these components of 0& (Ozima and Podosek, 2002), À5 ± 2& (Marty, 1995;Cartigny et al, 1998;Sano et al, 1998;Marty and Zimmermann, 1999;Sano et al, 2001), and +7 ± 4& (Peters et al, 1978;Bebout and Fogel, 1992;Boyd and Pillinger, 1994;Bebout, 1995;Kienast, 2000;Sadofsky and Bebout, 2004;Li and Bebout, 2005) for atmosphere, upper mantle, and subducted hemipelagic sediments, respectively. An additional potential contributor of nitrogen to arc gases is the subducted altered oceanic crust; its d 15 N value, however, is currently poorly constrained but may be as low as À2.9& (Li et al, 2003).…”

Section: Gas Provenance: Resolution Into Endmembersmentioning

confidence: 99%

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Tracing nitrogen in volcanic and geothermal volatiles from the Nicaraguan volcanic front

Elkins

Fischer

Hilton

et al. 2006

Geochimica et Cosmochimica Acta

114

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We report new chemical and isotopic data from 26 volcanic and geothermal gases, vapor condensates, and thermal water samples, collected along the Nicaraguan volcanic front. The samples were analyzed for chemical abundances and stable isotope compositions, with a focus on nitrogen abundances and isotope ratios. These data are used to evaluate samples for volatile contributions from magma, air, air-saturated water, and the crust. Samples devoid of crustal contamination (based upon He isotope composition) but slightly contaminated by air or air-saturated water are corrected using N 2 /Ar ratios in order to obtain primary magmatic values, composed of contributions from upper mantle and subducted hemipelagic sediment on the down-going plate. Using a mantle endmember with d 15 N = À5& and N 2 /He = 100 and a subducted sediment component with d 15 N = +7& and N 2 /He = 10,500, the average sediment contribution to Nicaraguan volcanic and geothermal gases was determined to be 71%. Most of the gases were dominated by sediment-derived nitrogen, but gas from Volcán Mombacho, the southernmost sampling location, had a mantle signature (46% from subducted sediment, or 54% from the mantle) and an affinity with mantle-dominated gases discharging from Costa Rica localities to the south. High CO 2 /N 2 exc. ratios (N 2 exc. is the N 2 abundance corrected for contributions from air) in the south are similar to those in Costa Rica, and reflect the predominant mantle wedge input, whereas low ratios in the north indicate contribution by altered oceanic crust and/or preferential release of nitrogen over carbon from the subducting slab. Sediment-derived nitrogen fluxes at the Nicaraguan volcanic front, estimated by three methods, are 7.8 · 10 8 mol N/a from 3 He flux, 6.9 · 10 8 mol/a from SO 2 flux, and 2.1 · 10 8 and 1.3 · 10 9 mol/a from CO 2 fluxes calculated from 3 He and SO 2 , respectively. These flux results are higher than previous estimates for Central America, reflecting the high sediment-derived volatile contribution and the high nitrogen content of geothermal and volcanic gases in Nicaragua. The fluxes are also similar to but higher than estimated hemipelagic nitrogen inputs at the trench, suggesting addition of N from altered oceanic basement is needed to satisfy these flux estimates. The similarity of the calculated input of N via the trench to our calculated outputs suggests that little or none of the subducted nitrogen is being recycled into the deeper mantle, and that it is, instead, returned to the surface via arc volcanism.

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Section: Along-arc Variationsmentioning

confidence: 95%

Section: Along-arc Variationsmentioning

confidence: 99%