This timely book presents the state-of-the-art of our knowledge of the nature and chemical structure of redox interfaces in a marine water column, oxygen depletion and connected processes. The structures of the redox layers, including the distribution of certain parameters and microbiological features, are described in detail. The volume also covers studies devoted to the interannual variability of some oxygen-depleted systems, modeling and new developments in observation techniques. In addition, it identifies remaining gaps in our knowledge of the cycling of chemical elements in changing redox conditions. The chapters are based on extensive observational data, collected by the authors during sea and shore expeditions, on archive data, and on a broad range of scientific literature.