CONTROLS ON ORGANIC-CARBON PRESERVATION - THE USE OF STRATIFIED WATER BODIES TO COMPARE INTRINSIC RATES OF DECOMPOSITION IN OXIC AND ANOXIC SYSTEMS

The relation between productivity, O2, and organic carbon preservation has been the subject of great controversy. One theory has been that anoxic decomposition of organic matter is intrinsically slower than oxic decomposition and thus results in the accumulation of organic carbon in anoxic sediments and waters. However, several past studies suggest that differences in the intrinsic rates of decomposition between the two types of systems are small. Here, I provide further evidence of this by measuring microbial metabolism of individual radiolabeled compounds in the oxic and anoxic waters of stratified water bodies. The lack of a rate difference suggests the need for further explanation of the controls on carbon preservation. The concept is presented that anoxic sediments may sequester organic matter as bacterial biomass, or as bacterially derived products, in the absence of bacterial grazers. Thus, differences in the numbers and diversity of organisms that graze upon bacteria between oxic and anoxic sediments may explain part of the difference in carbon preservation rates that have been observed between the two types of systems.