The biogeochemistry of manganese and iron reduction in marine sediments

Manganese and iron reduction in marine sediments are known to play important roles in the biogeochemical cycles of many elements, including carbon, sulfur, phosphorus and several trace elements. These reduction reactions affect these cycles on a variety of time scales, ranging from those as short as seasonal time scales (e.g., nutrient cycling in coastal ecosystems), to those as long as thousands to tens of thousands of years (e.g., glacial-interglacial transformations in deep sea sediments). In this review article I will briefly summarize the results of laboratory studies on the types of manganese and iron reduction that are known to occur in marine sediments, and then discuss the occurrence of these processes in different sedimentary environments. Particular efforts will be given to examining the rates and mechanisms of sedimentary manganese and iron reduction in relationship to other biogeochemical processes in sediments. INTRODUCTION chemical aspects of reductive dissolution reactions (Stone and Morgan, 1987; Stumm Manganese and iron reduction in marine and Sulzberger, 1992); microbial manganese sediments are known to play important roles and iron reduction (Ehrlich, 1987; Lovley, in the biogeochemical cycles of many ele1987, 1991; Ghiorse, ]988; Nealson and Myments, including carbon, sulfur, phosphorus ers, 1992); and manganese sediment geoand several trace elements. For this reason chemistry (Glasby, 1984; Schimmield and considerable effort has been devoted to exPedersen, 1990). Rather than simply dupliamining the rates and mechanisms of these cating or up-dating these articles, in this rereduction reactions in sediments. In this review article I will incorporate information view article I will begin by first briefly sumfrom all of these different fields into a more marizing the results of laboratory studies on unified examination of the current knowlthe types of manganese and iron reduction edge on manganese and iron reduction in that are known to occur in marine sediments, sediments. This will then be followed by a discussion of Manganese and iron reduction also occurs these processes in different sedimentary enin stratified marine water columns such as vironments. The at tempt here will be to exthe Saanich Inlet and the Black Sea (Emeramine the rates and mechanisms of sedimenson et al., 1982), in the low oxygen waters of tary manganese and iron reduction in relasome open ocean environments (Landing and tionship to other biogeochemical processes. Bruland, 1987) and in the water columns of In recent years there have been several other many stratified lakes (Davison, 1985). A1review articles that have examined topics rethough there are many similarities between lated to the subject of this review, including: sedimentary manganese and iron reduction 0012-8252/93/$06.00 © 1993 Elsevier Science Publishers B.V. All rights reserved