Diagenetic regimes in Arctic Ocean sediments: Implications for sediment geochemistry and core correlation
Diagenetic regimes in Arctic Ocean sediments: Implications for sediment geochemistry and core correlation
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DOI：
10.1016/j.gca.2016.05.032
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发表时间：
2016-09
影响因子：
5
通讯作者：
A. Meinhardt;C. März;S. Schuth;K. Lettmann;B. Schnetger;J. Wolff;H. Brumsack
中科院分区：
文献类型：
--
作者：
A. Meinhardt;C. März;S. Schuth;K. Lettmann;B. Schnetger;J. Wolff;H. Brumsack
深棕色沉积层是第四纪北冰洋沉积物中潜在的地层工具。它们富含锰、铁和从水体中清除的微量金属，很可能是在间冰期沉积的。在这项研究中，我们结合了北冰洋不同地区沉积物岩心的沉积物和孔隙水数据，研究早期成岩过程对沉积物地球化学的影响。在大多数研究的岩心中，Mn、Co 和 Mo 通过更深（>1.5 m）沉积层中的 Mn 氧化物溶解而释放到孔隙水中。沉积物中 Mn、Co 和 Mo 含量超过成岩背景 (elementxs) 之间的关系表明，Coxs/Moxs 值是一种诊断工具，可区分孔隙水中添加了成岩金属的层 (Coxs/Moxs< 1)、受 Mn 氧化物溶解和金属释放影响的层 (Coxs/Moxs> 10) 和未受影响的层 (Coxs/Moxs 从 1 到 10)。基于当前孔隙水剖面的稳态计算表明，在所研究的岩心中，仅从孔隙水池中添加这些金属不足以产生沉积金属富集。然而，似乎很明显，锰还原区中锰氧化物的溶解可以永久改变深棕色层的主要地球化学特征。因此，当岩心关联仅基于锰含量和深色沉积物颜色时，应在岩心关联之前考虑孔隙水数据和 Coxs/Moxs 值。与深棕色层中锰的大部分非成岩成因相反，沉积铁由大量的成岩部分（80%）和少量的非成岩部分（20%）组成。我们的孔隙水数据表明，沉积物中目前尚未发生成岩作用的铁再活化。主要的铁来源是海岸侵蚀和河流输入。预算计算表明，Fe 似乎被困在现代北冰洋中，并在陆架和盆地沉积物中积累。在定义为没有显着 Fe 富集的成岩背景的样品中，固相的 Fe 同位素信号 δ56Fe 为正（∼0.2–0.3‰）。随着沉积物中非成岩 Fe 含量的增加，δ56Fe 变得更加负，这表明同位素较轻的 Fe 部分从陆架到盆地的输出。我们假设 Mn 的传输过程也相同。
Dark brown sediment layers are a potential stratigraphic tool in Quaternary Arctic Ocean sediments. They are rich in Mn, Fe, and trace metals scavenged from the water column and were most likely deposited during interglacial intervals. In this study, we combine sediment and pore water data from sediment cores taken in different parts of the Arctic Ocean to investigate the influence of early diagenetic processes on sediment geochemistry. In most studied cores, Mn, Co, and Mo are released into the pore waters from Mn oxide dissolution in deeper (>1.5 m) sediment layers. The relationship between sedimentary Mn, Co, and Mo contents in excess of the lithogenic background (elementxs) shows that Coxs/Moxsvalues are a diagnostic tool to distinguish between layers with diagenetic metal addition from the pore waters (Coxs/Moxs< 1), layers affected by Mn oxide dissolution and metal release (Coxs/Moxs> 10), and unaffected layers (Coxs/Moxsfrom 1 to 10). Steady-state calculations based on current pore water profiles reveal that in the studied cores, the diagenetic addition of these metals from the pore water pool alone is not sufficient to produce the sedimentary metal enrichments. However, it seems evident that dissolution of Mn oxides in the Mn reduction zone can permanently alter the primary geochemical signature of the dark brown layers. Therefore, pore water data and Coxs/Moxsvalues should be considered before core correlation when this correlation is solely based on Mn contents and dark sediment color. In contrast to the mostly non-lithogenic origin of Mn in the dark brown layers, sedimentary Fe consists of a large lithogenic (80%) and a small non-lithogenic fraction (20%). Our pore water data show that diagenetic Fe remobilization is not currently occurring in the sediment. The dominant Fe sources are coastal erosion and river input. Budget calculations show that Fe seems to be trapped in the modern Arctic Ocean and accumulates in shelf and basin sediments.The Fe isotopic signal δ56Fe of the solid phase is positive (∼0.2–0.3‰) in samples defined as the lithogenic background without significant Fe enrichments. With increasing non-lithogenic Fe contents in the sediment, δ56Fe becomes more negative, which indicates a shelf-to-basin export of an isotopically lighter Fe fraction. We assume that the same transport process is true for Mn.