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.

在墨西哥湾北部密西西比河口西侧和东侧沿两个样带收集的沉积物岩心的孔隙水和固相地球化学剖面被纳入反应性输运模型，以确定锰和铁在铁矿再矿化中的作用。碳。反应性运输模型计算表明，沉降速率控制了厌氧碳再矿化的强度，并选择了主要的厌氧碳再矿化途径。尽管减少硫酸盐在架子台站（水深65 m）中占主导地位，但反硝化作用和微生物锰减少在最接近密西西比河的大陆坡上似乎具有同样重要的厌氧呼吸过程，而微生物铁的还原并不代表这些沉积物中的重要过程。这些发现表明，锰和铁的氧化还原转变的动力学差异影响了大陆坡上的碳再矿化过程。铁的快速动力学沉积物-水界面附近的²⁺氧化和高沉积速率使Fe保持为Fe（III）氧化物的形式，并且热力学上防止硫酸盐还原作用控制斜坡上的碳再矿化过程，而Mn ²⁺慢得多的氧合作用动力学使锰²⁺穿过最靠近河口的架子站的沉积物-水界面。在河水高流量排放期间，暴露于含氧的底水和夹带的典型三角洲沉积物的活动泥浆中的夹带可能促进了霞石层中Mn（III / IV）氧化物的形成和下坡运输。这种现象似乎形成了锰的“传送带”，锰相对于深沉积物中的Fe（III）氧化物有选择地富集了Mn（III / IV）氧化物。相比之下，由于有机物和成岩作用的输入量低，沿着距密西西比河羽流最远的东部大陆斜坡的厌氧碳再矿化过程的强度要低得多，而反硝化作用占了厌氧呼吸作用的主要部分。总体，