Nitrogen cycling in the sediments of Santa Barbara basin and Eastern Subtropical North Pacific: Nitrogen isotopes, diagenesis and possible chemosymbiosis between two lithotrophs (Thioploca and Anammox)—“riding on a glider”
Nitrogen cycling in the sediments of Santa Barbara basin and Eastern Subtropical North Pacific: Nitrogen isotopes, diagenesis and possible chemosymbiosis between two lithotrophs (Thioploca and Anammox)—“riding on a glider”
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DOI：
10.1016/j.epsl.2005.11.044
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发表时间：
2006-02
影响因子：
5.3
通讯作者：
M. Prokopenko;D. Hammond;W. Berelson;J. Bernhard;L. Stott;R. Douglas
中科院分区：
文献类型：
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作者：
M. Prokopenko;D. Hammond;W. Berelson;J. Bernhard;L. Stott;R. Douglas
本文介绍了圣巴巴拉盆地和东亚热带北太平洋（ESNP）地区缺氧沉积物中孔隙水铵和Norgin的同位素组成数据。铵δ 15 N在这两个地区的表现不同，反映了沉积氮循环的细菌过程的变异性。在圣巴巴拉盆地，TCO 2和NH 4+生产的化学计量定义的孔隙水化学表明，在这些沉积物中的孔隙水铵浓度的唯一影响反应似乎是有机质分解。孔隙水铵比分解有机质重1-3‰。相比之下，ESNP孔隙沃茨上部15-30 cm处的铵的δ 15 N比分解有机质重10‰以上。在更大的深度，更深的孔隙沃茨的δ 15 N接近于分解有机质的δ 15 N。质量平衡计算表明，所观察到的同位素富集不是由于同位素富集的有机质的优先损失。孔隙水剖面显示，重同位素区的特征是TCO 2/NH 4+输入比为4或更小。我们将其归因于Thioploca细菌的存在，它们将NO3−运输到深处并将其还原为NH 4+，同时氧化硫化物。基于孔隙水化学计量学和孔隙水同位素组成的反应-扩散模型，我们提出富15 N铵是这些沉积物中Thioploca和Anammox类细菌之间化学共生的结果。我们的工作提供了新的见解底栖微生物生态学，以及耦合的个人代谢途径在沉积氮循环中的作用。在圣巴巴拉盆地，还考虑了孔隙水铵与固体Norg之间同位素分馏1-3‰的因素。在这一沉积物中，有机氮的百分之二十三在成岩作用中损失，因此，降解对残留Norgis的同位素效应估计很小，为-0.7 ‰。分馏最可能的原因是同位素较重，更不稳定的海洋部分相对于同位素较轻，更难降解的有机物质的陆地成分的优先降解，但不能排除其他可能性。当对观察到的分馏进行校正时，这些沉积物的δ 15 N可能代表非稳态条件。
This article presents data on the isotopic composition of pore water ammonium and Norgin the anoxic sediments of the Santa Barbara Basin and the Eastern Subtropical North Pacific (ESNP) region. Ammonium δ15N behaves differently in the two regions, reflecting variability in bacterial processes of sedimentary nitrogen cycling. In Santa Barbara Basin, stoichiometry of TCO2and NH4+production defined by pore water chemistry indicates that the only reaction influencing pore water ammonium concentration in these sediments appears to be organic matter decomposition. Pore water ammonium was found to be 1–3‰ heavier than decomposing organic matter. In contrast, the upper 15–30 cm of ESNP pore waters have ammonium with δ15N that is more than 10‰ heavier than decomposing organic matter. At greater depth, the δ15N of deeper pore waters approaches that of decomposing organic matter. Mass balance calculations indicate that the observed isotopic enrichment is not due to the preferential loss of isotopically enriched organic matter. Pore water profiles show that the zone with heavy isotopes is characterized by a TCO2/NH4+inputs ratio of 4 or less. We attribute this to the presence of Thioploca bacteria, who transport NO3−to depth and reduce it to NH4+while oxidizing sulfide. Based on pore water stoichiometry, and reaction–diffusion modeling of pore water isotopic composition we propose that the15N-enriched ammonium is produced as the result of chemosymbiosis between Thioploca and Anammox-like bacteria in these sediments. Our work provides the new insights into benthic microbial ecology, and the role of coupled individual metabolic pathways in sedimentary nitrogen cycling. In Santa Barbara Basin, factors which contribute to the isotopic fractionation of 1–3‰ between pore water ammonium and solid Norgwere also considered. In this sediments, ∼23% of the rain of organic nitrogen is lost to diagenesis, therefore, the isotopic effect of degradation on the residual Norgis estimated to be small, −0.7‰. The most likely cause of fractionation is preferential degradation of an isotopically heavier, more labile marine fraction relative to an isotopically lighter, more refractory terrestrial component of the organic matter, but other possibilities cannot be ruled out. When corrected for the observed fractionation, it appears that the δ15N of these sediments may represent non-steady state conditions.