14 Soil Organic Matter: Cycling, Transport, and Ocean-Climate Interaction

Tuesday, 9 August 2005
9:00 AM - 12:00 PM

MINERALOGIC CONTROLS ON SORPTIVE PRESERVATION OF TERRESTRIAL ORGANIC MATTER IN MARINE SYSTEMS

Paper number: 14-2
Program: THEME SESSIONS
Time: 9:20 AM – 9:40 AM

Authors

Abstract

Use of fossil organic matter (OM) disseminated in marine sediments as proxies of terrestrial source and climate conditions requires that biogeochemical signatures faithfully record vegetation and soil organic matter conditions of the watershed from which it was derived. The bulk of OM in sediments is intimately linked to the mineral matrix as organic-inorganic particle systems. The evolution of OM in these systems from time of formation to their export and burial in marine environments is poorly constrained. Here we present the first comprehensive study of the evolution of mineral-specific reactivity along the transport path from terrestrial source to marine sink, focusing on four critical zones: (1) terrestrial mineral loading, (2) estuarine gradients, (3) marine mineral loading, and (4) burial.

Loading of polyphenolic terrestrial biomarkers in mineral soils is controlled by type and distribution of different reactive sites on clay mineral surfaces and OM functionality. Batch sorption experiments with lignin-derived phenols and clay minerals indicate substantial differences in sorption potential: smectite sorbs 2X more phenols than kaolinite, syringyl phenols 2X more than vanillyl phenols, and acids sorb 2-4X more than aldehydes. This has significant implications for diagnostic source and diagenetic parameters.

Estuarine salinity gradients destabilize OM-clay complexes, leading to desorption of lignin phenols and amino acids. Desorption isotherms of amino acids from clay minerals indicate that lower salinities (<3permil) and complexation with smectites resulted in greater loss of amino acids relative to freshwater counterparts and kaolinite complexes, respectively. Tannic acid sorption increased by approximately 15% with salinity, suggesting that tannic acid-clay complexes are likely to form and remain intact upon export from terrestrial to marine systems.

Loading of marine OM is greatly influenced by the priming of clay mineral surfaces with terrigenous OM in soils. Thus, the significance of terrigenous OM in continental margin sediments extends beyond its quantitative importance. Considering the complexities of OM-clay mixtures and OM source heterogeneity, climate reconstructions using terrestrial biomarkers are more instructive than TOC, δ13C and C:N data alone.