Trace metal abundances in marine sediments have been used extensively to interpret periods of elevated primary productivity and ancient ocean redox conditions. However, sediment reworking that results in post-depositional oxidation, such as bio-irrigation or lateral sediment transport through oxic water, can modify the primary geochemical signal of the sediment, which in turn may impact paleo-redox and/or -productivity interpretations. In the case of sediments on the Namibian Continental Margin (NCM), lateral transport and redeposition contribute to the accumulation of organic matter on the margin slope. To better constrain the geochemical effects of lateral transport on the NCM, we examined the trace metal signature (including solid-phase Fe, Mo, V, Ni, Cu and Ag, and pore-water Fe, Mo, and V) in surface sediments (up to 25 cmbsf) along a transect from shelf to slope through the primary (shelf) and secondary (upper slope) depositional zones of the margin. Despite varying bottom water redox conditions ranging from seasonally anoxic (upper shelf), suboxic (shelf break), and oxic (upper slope), each site has elevated total organic carbon contents (average TOC content of 9.1, 3.2 and 6.8 wt%, respectively), due to high surface water primary productivity and lateral transport of organic-rich material from the shelf to the upper slope. Our results show that the solid-phase contents of the productivity proxies Ni, Cu, and Ag parallel the organic carbon accumulations largely irrespective of the local redox conditions. In contrast, the solid-phase contents of V, Mo, and Fe respond to the local bottom water redox conditions at each site, being enriched under strongly reducing conditions and less-enriched under oxic bottom waters despite enhanced TOC at all three investigated sites. Thus, the enrichment of trace metal and TOC at each site on the NCM can not only be used to reconstruct primary depositional bottom water redox conditions but also to identify zones of sediment redeposition. Using an offshore transect allows for the identification of intense lateral transport and redeposition of organic-rich sediments that are occurring along the margin. The relative concentrations of both redox-sensitive and productivity-related trace metals suggest that the decoupling of trace metals and organic carbon enrichments occasionally observed in the geological record could be explained by the process of lateral transport and redeposition.

海洋沉积物中的痕量金属丰度已被广泛用于解释初级生产力提高和古代海洋氧化还原条件的时期。然而，导致沉积后氧化的沉积物再加工，例如生物灌溉或通过含氧水的侧向沉积物运输，可能会改变沉积物的主要地球化学信号，进而可能影响古氧化还原和/或生产力解释。对于纳米比亚大陆边缘（NCM）上的沉积物，横向运输和再沉积有助于边缘斜坡上有机质的积累。为了更好地限制横向运输对NCM的地球化学影响，我们研究了痕量金属特征（包括固相Fe，Mo，V，Ni，Cu和Ag，以及孔隙水Fe，Mo，和V）在沿陆架从陆架到边缘的主要（陆架）和次要（上部斜坡）沉积区的样带的地表沉积物中（最高25 cmbsf）。尽管底部水的氧化还原条件各不相同，从季节性缺氧（上架），亚缺氧（搁板破坏）和有氧（上坡）开始，每个站点的总有机碳含量均升高（平均TOC含量分别为9.1、3.2和6.8 wt％）。 ），因为地表水的初级生产力高，并且富含有机物的物质从架子到侧坡的横向运输。我们的结果表明，无论局部氧化还原条件如何，生产率代表Ni，Cu和Ag的固相含量都与有机碳积累基本平行。相比之下，V，Mo和Fe的固相含量会响应每个位置的局部底部水氧化还原条件，尽管在所有三个调查地点的总有机碳含量均得到了提高，但在强力还原条件下却富集，而在有氧底水下却富集程度较低。因此，在NCM上每个位置的痕量金属和TOC的富集不仅可以用来重建主要的沉积底水氧化还原条件，而且可以用来识别沉积物的再沉积区域。使用海上样带可以识别沿边缘发生的强烈的横向运输和富有机沉积物的再沉积。氧化还原敏感和生产力相关的痕量金属的相对浓度表明，在地质记录中偶尔观察到的痕量金属和有机碳富集的解偶联可以用横向运输和再沉积过程来解释。