Using ammonium pore water profiles to assess stoichiometry of deep remineralization processes in methanogenic continental margin sediments
Using ammonium pore water profiles to assess stoichiometry of deep remineralization processes in methanogenic continental margin sediments
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DOI：
10.1002/ggge.20117
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发表时间：
2013-05
期刊：
影响因子：
3.7
通讯作者：
D. Burdige;T. Komada
中科院分区：
文献类型：
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作者：
D. Burdige;T. Komada
在许多大陆边沉积物中，存在着与沉积物表面附近的矿化过程分离的深部反应带。在这里，甲烷向上扩散到一定深度，在那里它被向下扩散的硫酸盐氧化。然而，在硫酸盐-甲烷过渡区（SMT）中驱动甲烷厌氧氧化（AOM）的甲烷来源可能因地点而异。特别地，这些来源可以被认为是（i）来自原位甲烷生成的“内部”来源（无论其在沉积柱中的何处出现），其最终与有机物沉积和埋藏相耦合，或（ii）“外部”来源，例如源自古老源岩的烃储层，或深埋的气体水合物，两者都与沉积物表面的同期有机碳沉积无关。使用建模的方法，我们研究不同的甲烷源和孔隙水硫酸盐，甲烷，溶解无机碳（DIC），铵配置文件之间的关系。我们表明，通过SMT的孔隙水铵剖面代表了深层沉积物中发生的矿化过程的独立“示踪剂”，补充了从与AOM和碳酸盐沉淀直接相关的溶质剖面获得的信息，即，DIC、甲烷和硫酸盐。孔隙水DIC配置文件也显示了一个拐点，在SMT的基础上的类型深甲烷源和伴随向上DIC通量的存在/不存在。有了这些结果，我们提出了一个概念框架，说明如何从大陆边缘设置浅孔隙水剖面可以用来获得重要的信息，在深层沉积物中的矿化过程和甲烷来源。
In many continental margin sediments, a deep reaction zone exists which is separated from remineralization processes near the sediment surface. Here, methane diffuses upward to a depth where it is oxidized by downwardly diffusing sulfate. However, the methane sources that drive this anaerobic oxidation of methane (AOM) in the sulfate‐methane transition zone (SMT) may vary among sites. In particular, these sources can be thought of as either (i) “internal” sources from in situ methanogenesis (regardless of where it occurs in the sediment column) that are ultimately coupled to organic matter deposition and burial, or (ii) “external” sources such as hydrocarbon reservoirs derived from ancient source rocks, or deeply buried gas hydrates, both of which are decoupled from contemporaneous organic carbon deposition at the sediment surface. Using a modeling approach, we examine the relationship between different methane sources and pore water sulfate, methane, dissolved inorganic carbon (DIC), and ammonium profiles. We show that pore water ammonium profiles through the SMT represent an independent “tracer” of remineralization processes occurring in deep sediments that complement information obtained from profiles of solutes directly associated with AOM and carbonate precipitation, i.e., DIC, methane, and sulfate. Pore water DIC profiles also show an inflection point in the SMT based on the type of deep methane source and the presence/absence of accompanying upward DIC fluxes. With these results, we present a conceptual framework which illustrates how shallow pore water profiles from continental margin settings can be used to obtain important information about remineralization processes and methane sources in deep sediments.