Micro- and Nanofabric Protection of Organic Matter in Clay-rich Muds and Polychaete Fecal Pellets: Direct Visualization by TEM and Quantitative Analysis

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Intellectual Merit. This research addresses challenging issues of organic matter (OM) preservation in marine clay-rich sediment and soils using novel techniques for visualizing three dimensionally OM in nano- and microfabric signatures using transmission electron microscopy (TEM). This effort will advance the understanding of processes and mechanisms and nano- and microfabric signatures that drive OM preservation at these scales during the very early development of marine sediment. It will provide direct "cutting edge" evidence confirming or refuting concepts and ideas advanced without direct observational evidence by the scientific community concerning OM preservation in marine sediment. It will provide direct visual evidence of protection against enzymatic digestion of OM by clay fabric. Hypotheses to be tested include, (1) pore throats and tortuosity of pores impedes the movement of enzymes through clay fabric and (2) OM is preferentially sorbed onto edges of clay platelets and interstices at the junctures of clay domains. Hypothesis testing entails developing a realistic quantitative three-dimensional visual model of OM protection based on potential enzymatic digestion of specific substrates and direct TEM observations of OM distribution with respect to pores reconstructed from serial sections of sediments representing the globally most important OM depocenter. Clay is inherently electron dense and easily visualized by TEM; visualization of OM will be accomplished with electron dense stains. Smectite and illite clay samples will be studied including field collected fecal pellets from marine polychaetes. This research will advance the development of realistic conceptual models of OM preservation and ultimately organic carbon cycling based on direct visualization of organo-clay relationships and quantitative analysis. The research will also provide quantitative data for advancing (1) understanding of biogeochemical fluxes of organic carbon in marine sediments and (2) the development of emerging models addressing organo-clay preservation dynamics.Broader Impacts. A graduate student from the University of Southern Mississippi (USM) will be trained in TEM techniques and image analysis, will participate in writing manuscripts, and in presenting data at regional and national scientific meetings. Training will be offered to science education graduate students in TEM techniques and image analysis during our regular summer teaching program. Undergraduates through the local NSF REU program will assist in TEM work and image analysis and present research at local and regional meetings. The project supports three investigators at two institutions in an EPSCoR state and establishes collaboration among disciplines and institutions with CoPIs from academia and the private sector. Research results will be published in leading international journals as well as local and national professional meetings. A website will be established to make our data and interpretations widely available. This project has broader societal and economic implications by increasing knowledge of OM sequestration during early sediment diagenesis and understanding the development of protokerogen and ultimately kerogen in petroleum source rocks.