Authigenic molybdenum isotope signatures in marine sediments
Authigenic molybdenum isotope signatures in marine sediments
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DOI：
10.1130/g22485.1
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发表时间：
2006-08
期刊：
影响因子：
5.8
通讯作者：
R. Poulson;C. Siebert;J. McManus;W. Berelson
中科院分区：
文献类型：
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作者：
R. Poulson;C. Siebert;J. McManus;W. Berelson
我们提供了墨西哥大陆边缘的新钼同位素数据，结合以前的数据，我们可以对海洋沉积物中的钼同位素系统提出机械描述。我们假设海洋沉积物中记录了独特的环境依赖性钼同位素特征，反映了自生钼积累的机制。公海缺氧点的定义是上覆水中的溶解氧和硫化物浓度接近于零，其 98/95 Mo 同位素特征为 1.6‰。我们认为这个值反映了沉积物内通过成岩过程形成的硫化钼。含硫环境中的硫化物水体中钼硫化物的定量形成导致沉积物同位素值与现代海水值（2.3‰）相似，以来自高硫化物黑海的样品为代表。与这些还原环境相反，富含锰氧化物的沉积物测得的钼同位素值比迄今为止分析的任何其他沉积物样品都要负（相对于海水），类似于铁锰结壳（0.7‰）。大多数测量的来自公海环境的海洋沉积物的钼同位素组成似乎反映了成岩钼（0.0‰）和特定自生钼积累机制的钼特征的混合物。因此，我们认为钼同位素可能记录了反映钼固存到沉积物中的主要化学机制的独特特征。
We present new Mo isotope data from the Mexican continen- tal margin that, in conjunction with previous data, allow us to propose a mechanistic description of the Mo isotope system in ma- rine sediments. We hypothesize that there are unique environmen- tally dependent Mo isotope signatures recorded in marine sedi- ments that reflect the mechanisms responsible for authigenic Mo accumulation. Open-ocean anoxic sites, defined as having dissolved oxygen and sulfide concentrations near zero in the overlying water, exhibit a 98/95 Mo isotope signature of 1.6‰. We believe this val- ue reflects Mo sulfide formation via diagenetic processes within sediments. Quantitative formation of Mo sulfide within the sulfidic water column of euxinic environments results in sediment isotope values similar to the modern seawater value (2.3‰), as typified by samples from the highly sulfidic Black Sea. In contrast to these reducing settings, manganese oxide-rich sediments have measured Mo isotope values that are more negative (relative to seawater) than any other sediment samples analyzed to date, similar to Fe- Mn crusts (0.7‰). Most measured Mo isotope compositions of marine sediments from open-ocean settings appear to reflect a mix- ture of lithogenic Mo (0.0‰) and the Mo signature of a specific authigenic Mo accumulation mechanism. We therefore suggest that Mo isotopes may record unique signatures that reflect the domi- nant chemical mechanism for Mo sequestration into sediments.