HR: 0800h
AN: B11A-0063    [Abstracts]
TI: Mineral-organic Dynamics During Export From Rivers to Oceans: Implications for Organic Matter Source and Diagenetic Alteration
AU: * Robinson, A
EM: geo.ame@gmail.com
AF: University of Arkansas at Little Rock, 2801 S. University, Little Rock, AR 72204,
AU: Hernes, P J
EM: pjhernes@ucdavis.edu
AF: University of California-Davis, Land, Air and Water Resources One Shields Ave., Davis, CA 95616,
AU: Montanez, I
EM: ipmontanez@ucdavis.edu
AF: University of California-Davis, Dept. of Geology One Shields Ave., Davis, CA 95616,
AB: The record of vegetation preserved along continental margins has traditionally been used to assess the contributions of organic matter derived from adjacent watersheds of rivers. Our ability to draw conclusions from these records relies on the fundamental assumption that the processing of these particles is limited, or at least congruent, across different vascular plant biomarkers, thereby allowing direct correlations between vascular plant distributions on land and marine compositions. Ratios of syringyl (S), vanillyl (V) and cinnamyl (C) lignin phenols should provide diagnostic source indicators for angiosperm and gymnosperm woody and nonwoody tissues. We conducted benchtop experiments to test whether lignin phenol-clay particulates prepared in freshwater and exported through a steep geochemical gradient to full marine salinities resulted in distinctly different particulate biomarker compositions. Variations in biomarker compositions highlight the importance of compound- and mineral-specific retention mechanisms as a function of salinity changes. Losses of lignin phenols from mineral surfaces is most pronounced at very low salinities and essentially absent at salinities greater than 2 parts per thousand to full marine salinities. Therefore, sediment processing at slightly elevated salinities, such as in an estuary, may be particularly adept at removing part, but not all lignin phenols sorbed to sediments. Mineral- specific trends indicate that an increase in surface area and reactivity (e.g., cation exchange capacity) slightly increases desorption of particulate-bound lignin phenols. When comparing sediments within and between watersheds, particle history and mineralogy becomes even more important, particularly during the export from riverine to marine settings. For example, preferential loss of syringyl phenols could lead to higher S/V ratios than the areal distribution of angiosperms within the watershed would have indicated. Similarly, the molecular compositions used to infer the extent of diagenetic alteration, and thus the relative age of particulate organic matter, are subject to these desorptive processes. Sediment compositions may appear younger, less diagenetically altered than would be determined for the sediments prior to export. These subtle differences in behavior have significant implications for determining carbon budgets, characterizing vascular plant inputs to marine sediments, and assessing anthropogenic fingerprints from land use change. This work demonstrates a new approach where sorptive-desorptive mechanisms controlling the distribution and composition of vascular biomarkers are accounted for, providing a new lens through which biomarker trends in continental margin sediments should be viewed.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 1055 Organic and biogenic geochemistry
DE: 4806 Carbon cycling (0428)
DE: 4850 Marine organic chemistry (0470, 1050)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting