About this Research Topic
In steadily accumulating sedimentary systems along continental margins organic matter and reactive minerals (e.g., Mn/Fe (oxyhydr)oxides with adsorbed P, Mo, Co, Cu, Ni) deposited at the seafloor undergo a well-defined sequence of diagenetic alteration, including organic matter remineralization, oxidation-reduction, mineral dissolution, element desorption, and authigenic mineral precipitation. However, many continental margin environments are highly dynamic with respect to sedimentation rates, the depositional environment, and oceanographic conditions. In these settings, organic matter and reactive mineral phases can bypass diagenetic processing at the sediment-water interface and get quickly buried below the seafloor. Consequently, these deeper sediments function as biogeochemical reactors where, in semi-closed systems, the primary composition of the sediments is altered long after deposition. Here, oxidation of reactive organic matter, reduction of mineral oxides, and desorption of nutrients sustain an active deep microbial community which, in turn, enhances further deep biogeochemical element cycles.
Dynamic marine systems along continental margins include areas with highly variable sedimentation rates, mass waste deposits, and current and drift deposits (such as contourites) that can cause variable sediment input and burial rates. They also include settings characterized by frequent changes in the depositional environment, for example due to the presence of seasonal hypoxia/anoxia in the overlying water column leading to fast changes in redox conditions. Such conditions are suggested to strongly impact subsurface microbial and geochemical processes. For example, in these systems elevated rates of specific microbial metabolic processes may take place and coupled biogeochemical processes not typically observed under steady conditions may occur. Despite their widespread occurrence these unsteady regimes, however, are highly understudied and their relevance for global biogeochemical cycles and ocean chemistry remains unknown. Additionally, non-steady state diagenetic reactions in dynamic marine environments permanently change the original sediment composition resulting in the overprinting of paleoceanographic proxy records and, thus, a biasing of climate reconstructions. Identifying such alterations and understanding the impact of non-steady state conditions on sedimentary geochemical signals are thus key issues in developing and applying tools for paleoceanographic reconstruction.
This Research Topic covers recent and novel research on the geochemistry of unsteady diagenetic regimes along continental margins. We are interested in studies on continental margin systems characterized by (highly) dynamic depositional settings and environments and those affected by changing oceanographic conditions using (bio-) geochemical, molecular, and sedimentary tools. Themes to be covered in this Research Topic may include, but are not limited to:
• Cryptic and novel cross-linkages between biogeochemical cycles:
• Biogeochemical effects on the primary sediment composition;
• Development of new geochemical tools to identify re-depositional settings;
• Impact of fast redox changes (e.g. due to seasonal hypoxia/anoxic/euxinia);
• Effects of winnowing and formation of lag deposits; and
• Interaction between microbes, minerals and surrounding pore waters.
We particularly welcome Original Research, Reviews and Perspectives articles.
Keywords: continental margin, biogeochemistry, dynamic depositional system, non-steady state conditions, redox environment, diagenesis
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