Interactions between Organic Matter and Minerals in Marine Sediment

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ABSTRACTOCE-0095287Although marine geochemists have known for some time now that sedimentary organic matter is bound primarily as organic-clay aggregates, little is known about the physicochemical nature of these clusters. In this project an organic geochemistry research team at the University of Washington will conduct a systematic survey of coastal zone sediments with varying oxygen exposure times to examine the organic-particle association. Density fractionation techniques will be used to quantify organic-clay aggregates, and the organic matter composition of the density fractions will be determined. The analytical techniques used to characterize the aggregates will include X-ray Photoelectron Spectroscopy (XPS) and Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectroscopy (MALDI-TOF-MS) because these techniques offer unique views on organic matter quality and because they complement traditional measurements (CHN, amino acid hydrolysis, etc.). Laboratory experiments will be conducted in which different mineral and organic materials are mixed in a controlled fashion, and the formation and subsequent microbial degradation of organo-clay aggregates will be monitored. The information gathered from these two sets of studies will then be used in the field off the coast of Washington, where organic-mineral interactions will be evaluated for fresh materials collected in the water column and at the sediment-water interface. Special emphasis will be placed on examining the degradation patterns observed for proteins, peptides and amino acids because these components are observed in both the reactive and refractory pools of sedimentary organic matter. The application of XPS and MALDI-TOF-MS to the investigation of sedimentary organic matter diagenesis and organic-mineral interactions will allow appraisal of how both the bulk characteristics of surface-associated organic matter change as well as yield detailed information about the reactivity of proteins and peptides in the experimental systems. The ultimate goal is to quantify the functional relationship between mineral and organic matter and thus better determine how the relationship can be used to understand organic carbon cycling in the marine environment.