Chemical Geology ( IF 3.9 ) Pub Date : 2021-09-24 , DOI: 10.1016/j.chemgeo.2021.120538 W.K. Lenstra 1 , R. Klomp 1 , F. Molema 1 , T. Behrends 1 , C.P. Slomp 1
An existing sequential extraction scheme for particulate iron (Fe) is evaluated for manganese (Mn) using a range of Mn standards. The scheme consists of 5 steps and quantifies 5 operationally defined Mn pools (1) poorly ordered Mn oxides and Mn phosphates (ascorbic acid extractable); (2) Mn carbonates and Mn sulfides (1 M HCl extractable), (3 and 4) crystalline Mn oxides (citrate buffered dithionite and ammonium oxalate extractable, respectively) and (5) Mn associated with pyrite (concentrated HNO3 extractable). Application of the extraction scheme to coastal sediments from six locations (Black Sea, Baltic Sea, Bothnian Sea, Gulf of Mexico and Chesapeake Bay) highlights the dependency of sediment Mn partitioning on bottom water redox conditions. In sediments deposited in anoxic and sulfidic (euxinic) bottom waters, Mn is mostly present in Mn carbonates, pyrite and in non-reactive Mn forms, in approximately equal amounts. We find that in sediments deposited in periodically euxinic and hypoxic (oxygen <63 μmol L−1) waters, Mn carbonates dominate over the two other fractions, and small amounts of Mn oxides are observed. In sediments deposited in oxygenated bottom waters, Mn oxides, Mn-rich vivianite-type minerals and Mn carbonates dominate and no pyrite-bound Mn is observed. A large advantage of the extraction scheme is that it quantifies sediment forms of Mn and Fe simultaneously. Given the role of Mn as a bottom water redox proxy, the separation of poorly ordered Mn oxides, carbonates and pyrite is of specific relevance.
中文翻译:
颗粒锰的连续提取方法及其在沿海海洋沉积物中的应用
使用一系列 Mn 标准品对现有的颗粒铁 (Fe) 连续提取方案中的锰 (Mn) 进行评估。该方案由 5 个步骤组成,并量化 5 个操作定义的 Mn 池 (1) 排列不良的 Mn 氧化物和 Mn 磷酸盐(可提取抗坏血酸);(2) Mn 碳酸盐和 Mn 硫化物(1 M HCl 可萃取),(3 和 4)结晶 Mn 氧化物(分别可萃取柠檬酸盐缓冲的连二亚硫酸盐和草酸铵)和 (5) Mn 与黄铁矿(浓 HNO 3可提取)。将提取方案应用于六个地点(黑海、波罗的海、波的尼亚海、墨西哥湾和切萨皮克湾)的沿海沉积物,突出了沉积物锰分配对底水氧化还原条件的依赖性。在沉积在缺氧和硫化(富氧)底水中的沉积物中,Mn 主要存在于 Mn 碳酸盐、黄铁矿和非反应性 Mn 形式中,含量大致相等。我们发现在周期性富氧和缺氧(氧气 <63 μmol L -1) 水,Mn 碳酸盐在其他两个部分中占主导地位,并观察到少量 Mn 氧化物。在沉积在含氧底水中的沉积物中,锰氧化物、富含锰的蓝铁矿型矿物和锰碳酸盐占主导地位,没有观察到与黄铁矿结合的锰。提取方案的一大优点是它可以同时量化 Mn 和 Fe 的沉积物形式。鉴于 Mn 作为底部水氧化还原代理的作用,有序性差的 Mn 氧化物、碳酸盐和黄铁矿的分离具有特定的相关性。