Controls on the cadmium isotope composition of modern marine sediments
Controls on the cadmium isotope composition of modern marine sediments
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DOI：
10.1016/j.epsl.2021.116946
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发表时间：
2021-07
影响因子：
5.3
通讯作者：
A. Bryan;A. Dickson;Fern L. Dowdall;W. Homoky;D. Porcelli;G. Henderson
中科院分区：
文献类型：
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作者：
A. Bryan;A. Dickson;Fern L. Dowdall;W. Homoky;D. Porcelli;G. Henderson
大陆边缘沉积物已被确定为镉（Cd）海洋收支的主要汇。然而，这个重要的输出通量的同位素组成是未知的。在这里，我们提出，与测量阿根廷大陆边缘，第一个观测的限制现代海洋氧化和亚氧化沉积物中的镉的同位素组成。我们确定了两个主要的去除机制，镉在有机材料，硫化物的形成。表层边缘沉积物（0-0.5厘米），溶解氧低于检测从0.5厘米，同位素比上覆含氧沃茨轻。这些表层沉积物的质量平衡表明，镉是目前占主导地位的有机结合颗粒镉。在次表层沉积物中，Cd浓度在硝酸盐还原区增加，并获得与沉积物上覆水相似的同位素组成（即在深层沃茨中为0.35‰）。这些意见是一致的向下扩散通量的海水镉和氧化还原驱动的定量去除过程中硫化物沉淀的镉。结合起来，这两种途径的镉去除导致掩埋的同位素轻有机镉在边缘亚氧沉积物，使全球同位素镉预算平衡。
Continental margin sediments have been identified as the dominant sink in the marine budget of cadmium (Cd). The isotopic composition of this important output flux is, however, unknown. Here we present, with measurements on the Argentine continental margin, the first observational constraints on the isotopic composition of Cd in modern marine oxic and sub-oxic sediments. We identify two main removal mechanisms of Cd; in organic material, and by sulfide formation. Surface margin sediments (0–0.5 cm), with dissolved O2below detection from ∼0.5 cm, are isotopically lighter than overlying oxygenated waters. A mass balance for these surface sediments indicates that Cd is present dominantly as organically-bound particulate Cd. In sub-surface sediments, Cd concentrations increase in the zone of nitrate reduction, and attain similar isotopic compositions as the water that overlies the sediment (i.e. ∼0.35‰ in deep waters). These observations are consistent with a downward diffusive flux of seawater Cd and redox-driven quantitative removal of that Cd during sulfide precipitation. In combination, these two routes of Cd removal lead to burial of isotopically light organic Cd in margin sub-oxic sediments that enables the global isotopic Cd budget to be balanced.