Reactive Fe(II) layers in deep-sea sediments

The percentage of the structural Fe(II) in clay minerals that is readily ox idized to Fe(III) upon contact with atmospheric oxygen was determined acros s the downcore tan-green color change in Peru Basin sediments. This latent fraction of reactive Fe(II) was only found in the green strata, where it pr oved to be large enough to constitute a deep reaction layer with respect to the pore water O-2 and NO3-. Large variations were detected in the proport ion of the reactive Fe(II) concentration to the organic matter content alon g core profiles. Hence, the commonly observed tan-green color change in mar ine sediments marks the top of a reactive Fe(II) layer, which may represent the major barrier to the movement of oxidation fronts in pelagic subsurfac e sediments. This is also demonstrated by numerical model simulations. The findings imply that geochemical barriers to pore water oxidation fronts for m diagenetically in the sea floor wherever the stage of iron reduction is r eached, provided that the sediments contain a significant amount of structu ral iron in clay minerals. Copyright (C) 1999 Elsevier Science Ltd.