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The brown‐green color transition in marine sediments: A marker of the Fe(III)‐Fe(II) redox boundary1
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1983
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EngineeringTrace Element GeochemistryBrown‐green Color TransitionMarine ChemistryOceanographyBrown‐green TransitionEarth ScienceOrganic GeochemistryEnvironmental ChemistryMarine SedimentsRedox Boundary1Blue CarbonOceanic SystemsMarine GeologyBiogeochemistryChemical OceanographySediment-water InteractionOrganic-rich Sedimentary RockColor ChangeSedimentologyMarine MaterialsGeochemistryMarine BiologyCoastal GeochemistryColor Transition
The color transition from brown to green in marine sediments marks the depth at which the nitrate in porewaters has been reduced and the Fe(III) reduced to Fe(II), as shown by published and newly acquired evidence from porewater profiles. The color change is rapidly reversible and is probably due to the oxidation or reduction of iron in smectite clays. A map of the depth of this boundary in the eastern tropical Pacific Ocean shows that thin, brown, Fe(III)‐bearing layers occur under waters of high primary productivity (high organic carbon flux to sediments) or on topographic features that have higher sedimentation rates than surrounding areas. The depth to the brown‐green transition provides a rapid way to estimate redox conditions in sediments and a measure of the rate of depositional flux and consumption of organic carbon in sediments on a regional basis.