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 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.
Organic matter (OM) is trapped and preserved in marine mud (sediment) over a time frame of millions of years and the processes are believed to have a profound effect on the global carbon cycles and thus the planetary warming and cooling cycles. Mechanisms for organic matter protection include physical protection by the morphology (shape of clay particles and aggregates) of marine clay fabric and the physico-chemical (energy source) protection by the charged nature of clay particle surfaces and particle contacts that develop interstices that trap OM. The very small nature of the sheet-like shape of clay particles, measured in tens of nanometers (10 nanometers = 0.000000394 inches), presents enormous surface area for the organic matter protection phenomenon. We used Transmission Electron Microscopy (TEM) and sophisticated computer software techniques to create images of OM and clay particles and three-dimensional representations of clay fabric to analyze protection mechanisms and to demonstrate the importance of surfaces and interstices that had previously only been hypothesized as involved in organic matter protection. This study has broad ramifications. Data from the study can be used to improve our ability to model sea-to-air carbon dioxide flux, to enhance our understanding of the global carbon cycle, to address issues concerning oxygen concentrations in the atmosphere, to understand the dynamics between organic matter protection and offshore petroleum source rock potential, and to elucidate the role of organic matter within stratigraphic sedimentary sequences. Socioeconomic themes presently under intense debate revolve around not only planetary environmental issues (global warming and cooling cycles) but also around energy issues (petroleum, coal, etc.) both inextricably linked to the processes and pathways of periodic production and degradation of organic matter and carbon sequestering in continental margin marine sediments. Our TEM observations of OM in the sediment clay fabric (mud matrix) confirmed the predicted locations of the potential energy field models where OM is protected (sequestered). The project scientists trained two graduate students (one female) as part of their degree work toward a Master of Science and one (female) undergraduate student in transmission electron microscopy, geological techniques, and image analysis. Additionally several graduate students not directly associated with this project received some training in the various techniques we developed.
