Lignin geochemistry of North American coastal and continental shelf sediments

Abstract

The concentrations and composition of lignin in coastal and shelf sediments at five locations along the North American continent—Georges Bank/North Atlantic shelf, northwestern Gulf of Mexico, Southern California, Norton Sound and nearshore Beaufort Sea—have been characterized using alkaline CuO oxidation. Lignin concentrations are generally highest at close proximity to the mouth of major rivers, indicating that deposition of river-borne vascular plant debris is the principal source of lignin to the offshore sediments. Arctic sediments contain the highest concentrations, presumably as a result of an abundant supply of terrestrial organic material and the prevalence of frigid temperatures and surface ice cover during much of the year. Concentrations are lowest in the Georges Bank/North Atlantic sediments, where a dynamic physical environment persists over much of the year and the supply of terrestrial organic matter to the offshore in the form of major rivers is lacking. Stable carbon isotopic compositions show that sediments containing the highest lignin concentrations also contain isotopically-lighter organic matter, consistent with a terrestrial source input. Vanillyl, syringyl and cinnamyl phenol distributions in these offshore sediments are consistent with primary contributions from gymnosperm (predominant) and angiosperm woods and secondary contributions from nonwoody tissues. These estimates may be subject to some uncertainty due to diagenetic alteration of individual lignin phenols. In contrast, p-hydroxyl phenol yields are not strongly correlated with those of the other lignin-derived phenols, suggesting generation from both lignin and non-lignin sources. Elevated acid/aldehyde ratios relative to undegraded plant tissues suggest that the lignin transported to these offshore sediments has undergone some biodegradative oxidation.