Fig. 7: Schematic description of the various biotic processes that possibly contribute to the Fe2+ pool detected in pore water of iron oxide-rich methanic marine sediments, e.g., Helgoland Mud Area.

This study presents an additional perspective and argues for the involvement of organoclastic iron reduction, in addition to Fe-AOM, as mechanism fueling methanic zone iron reduction. Red, brown and black colorations are representative of the various forms of Fe(III) present in the environment.