The role and implications of mineral associations in organic carbon preservation

Organic matter-mineral interactions are a key part of the global carbon cycle, facilitating the preservation of organic matter that helps remove CO2 from the atmosphere and allow for the build-up of oxygen in the ocean-atmosphere system. In this project, chemical standards were added to clay and iron minerals (kaolinite, bentonite and goethite), to investigate the effect of organic matter and mineral type on sorption, as well as investigating the mechanisms by which binding is occurring. Sorption was found to be greatest in aromatic compounds across all three minerals used. Different organic compounds showed a slight preference for different minerals, but overall mineral type had a minimal effect on bonding. Organic compounds were found to bind cooperatively, achieving a higher organic matter: mineral ratio than the monolayer equivalent often observed in sediments. This suggest that the observed monolayer equivalence in marine sediments may be due to the nature and quantity of organic matter reaching these sediments rather than an inherent limit on the amount of organic matter that mineral surfaces can sorb. Experiments were also carried out using natural dissolved organic matter (DOM) under riverine and marine conditions to determine the impact of minerals on riverine DOM transport. The different DOM sources were found to have a minimal effect on the degree of sorption with salinity and mineral mass having the greatest effect. This observation suggests that much lower coverage was achieved for the DOM than for the standards, possibly due to the presence of a more limited range of compounds. Differences between the dissolved and standards data highlight the importance of including all compound types in the study of organic matter-mineral interactions. Given the complex nature of these interactions, and the different factors effecting them, further work is need to fully understand the role they play in organic matter preservation. However, this work has demonstrated the importance of careful experimental design, and the inclusion of both dissolved and particulate matter.