Differential manganese and iron recycling and transport in continental margin sediments of the Northern Gulf of Mexico
Differential manganese and iron recycling and transport in continental margin sediments of the Northern Gulf of Mexico
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DOI：
10.1016/j.marchem.2020.103908
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发表时间：
2021-01-07
期刊：
影响因子：
3
通讯作者：
Taillefert, Martial
中科院分区：
文献类型：
--
作者：
Owings, Shannon M.;Brethous, Laurie;Taillefert, Martial
孔隙水和固相地球化学剖面沉积物岩心收集沿着两个断面上的西部和东部两侧的密西西比河口在北方墨西哥湾被纳入一个反应运输模型，以确定锰和铁的作用中的碳的矿化。反应输运模型计算表明，沉积速率控制的强度厌氧碳矿化和选择占主导地位的厌氧碳矿化途径。虽然硫酸盐还原占主导地位的陆棚站（65米水深），反硝化和微生物锰还原出现同样显着的厌氧呼吸过程沿着大陆坡最接近的密西西比河，而微生物铁还原并不代表在这些沉积物中的一个重要过程。这些结果表明，锰和铁氧化还原转化的差异动力学影响大陆坡碳矿化过程。Fe 2+氧化的快速动力学附近的沉积物-水界面和高沉积速率保持Fe（III）的氧化物的形式下，并gravitically防止硫酸盐还原占主导地位的碳矿化过程的斜坡上，而慢得多的Mn 2+氧化动力学允许Mn 2+扩散的沉积物-水界面的陆架站最接近河口。暴露于含氧的底部沃茨和夹带内的移动的泥浆典型的三角洲沉积物在高河流排放可能促进形成和下坡运输的锰（III/IV）氧化物的霞状层内。这种现象似乎形成了一个锰的“传送带”，选择性地丰富锰（III/IV）氧化物相对于铁（III）氧化物在深层沉积物。相反，厌氧碳矿化过程的强度沿着东部大陆坡最远的密西西比河羽是低得多，由于有机和成岩输入，和反硝化占主导地位的厌氧呼吸。总体而言，这些研究结果表明，锰循环及其在大陆坡沉积物暴露于大量河流输入的碳矿化过程中的作用可能比以前认为的更重要。
Pore water and solid phase geochemical profiles of sediment cores collected along two transects on the western and eastern sides of the Mississippi River mouth in the northern Gulf of Mexico were incorporated into a reactive transport model to determine the role of manganese and iron in the remineralization of carbon. Reactive transport model calculations indicate that sedimentation rates control the intensity of anaerobic carbon remineralization and select for the dominant anaerobic carbon remineralization pathways. Although sulfate reduction dominates the shelf station (65 m water depth), denitrification and microbial manganese reduction appear equally significant anaerobic respiration processes along the continental slope the closest to the Mississippi River, whereas microbial iron reduction does not represent an important process in these sediments. These findings suggest that the differential kinetics of manganese and iron redox transformations influence carbon remineralization processes on the continental slope. The fast kinetics of Fe2+ oxidation near the sediment-water interface and high sedimentation rates maintain Fe under the form of Fe(III) oxides and thermodynamically prevent sulfate reduction from dominating carbon remineralization processes on the slope, whereas the much slower Mn2+ oxygenation kinetics allows diffusion of Mn2+ across the sediment-water interface of the shelf station closest to the river mouth. Exposure to oxygenated bottom waters and entrainment within mobile muds typical of deltaic sediments during high riverine discharge likely promote the formation and downslope transport of Mn (III/IV) oxides within the nepheloid layer. This phenomenon appears to form a manganese 'conveyor belt' that selectively enriches Mn(III/IV) oxides relative to Fe(III) oxides in the deep sediment. In contrast, the intensity of anaerobic carbon remineralization processes along the eastern continental slope the farthest from the Mississippi River plume is much lower due to the low organic and lithogenic inputs, and denitrification dominates anaerobic respiration. Overall, these findings suggest that manganese cycling and its role in carbon remineralization processes in continental slope sediments exposed to large riverine inputs may be more important than previously considered.