SURFACE-AREA CONTROL OF ORGANIC-CARBON ACCUMULATION IN CONTINENTAL-SHELF SEDIMENTS

The relationship between organic carbon (OC) and grain size found in m ost continental shelf sediments is here reinterpreted in terms of the surface area of the sediments. Cores from many North American shelf en vironments show downcore decreases in OC to similar refractory backgro und concentrations if expressed relative to the surface area of the se diments. This consistent concentration is 0.86 mg-OC m-2, which is equ ivalent in concentration to a monolayer of organic matter coating all mineral surfaces. A more global collection of sediment-water interface samples show that this relationship is even more extensive, with exce ptions occurring in areas of very high riverine sediment input, organi c pollution, or low-oxygen water columns. Density separations indicate that organic matter is largely adsorbed to mineral grains. The microt opography of surfaces was examined with N2 sorption and most surface a rea was found to be inside pores of < 10 nm width. These data lead to a hypothesis that organic matter is protected by its location inside p ores too small to allow functioning of the hydrolytic enzymes necessar y for organic matter decay. Such protection would likely work in conce rt with other protection mechanisms such as humification. This consist ent surface area correlation with OC concentration may explain control of spatial and temporal variations in OC burial rates by sedimentatio n rates; the pore protection hypothesis provides a causal mechanism fo r this observed control.