TY - JOUR
T1 - Nitrogen concentration and δ15N of altered oceanic crust obtained on ODP Legs 129 and 185
T2 - Insights into alteration-related nitrogen enrichment and the nitrogen subduction budget
AU - Li, Long
AU - Bebout, Gray E.
AU - Idleman, Bruce D.
N1 - Funding Information:
This research utilized samples and data provided by the Ocean Drilling Program (ODP), which is sponsored by the United States National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. Funding for this study was provided by the JOI-USSSP and NSF (EAR-0409008) to GEB. We thank Leg 185 co-chief scientists T. Plank and J. Ludden and the Scientific Party of Leg 185 for their support of our shore-based research. We also thank K. Kelley and P. Castillo for providing samples from Sites 801 and 1149 and T. Elliott for providing the other samples. This manuscript was improved by constructive reviews by J. Alt, P. Cartigny, T. Fischer, and S. Sadofsky. We also thank J. Alt for editorial handling of this paper.
PY - 2007/5/1
Y1 - 2007/5/1
N2 - Knowledge of the subduction input flux of nitrogen (N) in altered oceanic crust (AOC) is critical in any attempt to mass-balance N across arc-trench systems on a global or individual-margin basis. We have employed sealed-tube, carrier-gas-based methods to examine the N concentrations and isotopic compositions of AOC. Analyses of 53 AOC samples recovered on DSDP/ODP legs from the North and South Pacific, the North Atlantic, and the Antarctic oceans (with larger numbers of samples from Site 801 outboard of the Mariana trench and Site 1149 outboard of the Izu trench), and 14 composites for the AOC sections at Site 801, give N concentrations of 1.3 to 18.2 ppm and δ15NAir of -11.6‰ to +8.3‰, indicating significant N enrichment probably during the early stages of hydrothermal alteration of the oceanic basalts. The N-δ15N modeling for samples from Sites 801 and 1149 (n = 39) shows that the secondary N may come from (1) the sedimentary N in the intercalated sediments and possibly overlying sediments via fluid-sediment/rock interaction, and (2) degassed mantle N2 in seawater via alteration-related abiotic reduction processes. For all Site 801 samples, weak correlation of N and K2O contents indicates that the siting of N in potassic alteration phases strongly depends on N availability and is possibly influenced by highly heterogeneous temperature and redox conditions during hydrothermal alteration. 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.
AB - Knowledge of the subduction input flux of nitrogen (N) in altered oceanic crust (AOC) is critical in any attempt to mass-balance N across arc-trench systems on a global or individual-margin basis. We have employed sealed-tube, carrier-gas-based methods to examine the N concentrations and isotopic compositions of AOC. Analyses of 53 AOC samples recovered on DSDP/ODP legs from the North and South Pacific, the North Atlantic, and the Antarctic oceans (with larger numbers of samples from Site 801 outboard of the Mariana trench and Site 1149 outboard of the Izu trench), and 14 composites for the AOC sections at Site 801, give N concentrations of 1.3 to 18.2 ppm and δ15NAir of -11.6‰ to +8.3‰, indicating significant N enrichment probably during the early stages of hydrothermal alteration of the oceanic basalts. The N-δ15N modeling for samples from Sites 801 and 1149 (n = 39) shows that the secondary N may come from (1) the sedimentary N in the intercalated sediments and possibly overlying sediments via fluid-sediment/rock interaction, and (2) degassed mantle N2 in seawater via alteration-related abiotic reduction processes. For all Site 801 samples, weak correlation of N and K2O contents indicates that the siting of N in potassic alteration phases strongly depends on N availability and is possibly influenced by highly heterogeneous temperature and redox conditions during hydrothermal alteration. 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.
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U2 - 10.1016/j.gca.2007.02.001
DO - 10.1016/j.gca.2007.02.001
M3 - Article
AN - SCOPUS:34147113801
VL - 71
SP - 2344
EP - 2360
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
SN - 0016-7037
IS - 9
ER -