An Introduction to Marine Sediments with an Emphasis on Sediment Organic Matter Remineralization

Summary The processes occurring in the upper several meters of marine sediments have a profound effect on the local and global cycling of many elements. For example, the balance between organic carbon preservation and remineralization in sediments represents the key link between carbon cycling in active, surface reservoirs in the oceans, atmosphere, and on land, and carbon that cycles on much longer, geological time scales, i.e., in sedimentary rock, and in coal and petroleum deposits. Understanding processes occurring in surficial marine sediment is also important in the accurate interpretation of paleoceanographic sediment records, since sediment processes can sometimes significantly alter the primary “depositional” signal recorded in the sediments. In coastal and estuarine sediments nitrogen and phosphorus remineralization in the sediments can provide a significant fraction of the nutrients required by primary producers in the water column. Similarly, in coastal and estuarine sediments subjected to elevated anthropogenic inputs of certain toxic metals, sediment processes affect the extent to which these sediments represent “permanent” versus “temporary” sinks for these metals. The geochemistry of marine sediments is controlled by both the composition of the material initially deposited in the sediments and the chemical, biological or physical processes that affect this material after its deposition. These processes fall within the general category of what is commonly referred to as early diagenesis. One very crucial aspect of the study of early diagenesis in marine sediments is that the oxidation, or remineralization, of organic matter deposited in the sediments is either the direct or indirect causative agent for many of these early diagenetic changes. Given this pivotal role that organic matter remineralization plays in many early diagenetic processes, significant efforts have gone into understanding and quantifying these processes. This lecture provides a brief introduction to marine sediment geochemistry focusing on the basic controls on organic matter remineralization in sediments. It is based on a lecture I recently gave to an undergraduate geology class in stratigraphy. I believe that it could also be useful in an undergraduate class in general oceanography, low temperature geochemistry or environmental geochemistry. Lecture summary The geochemistry of marine sediments is controlled by both the composition of the material initially deposited in the sediments and the chemical, biological or physical processes that affect this material after its deposition. These processes fall within the general category of what is commonly referred to as early diagenesis. One key aspect of the study of early diagenesis in marine sediments is that the oxidation, or remineralization, of sediment organic matter is either the direct or indirect causative agent for many early diagenetic changes. Given the pivotal role that organic matter remineralization plays in early diagenetic processes, significant efforts have gone into understanding and quantifying these processes. This lecture provides a brief introduction to marine sediment geochemistry, focusing on the basic controls of organic matter remineralization in sediments. I believe that the lecture could be useful in an undergraduate class in general oceanography, low temperature geochemistry or environmental geochemistry. It could also be useful in introductory graduate classes in these latter two areas.