Formation of n-alkenes during anaerobic decomposition of a marine algal mat

Abstract

Polyolefins containing two to four double bonds are ubiquitous constituents of sedimentary hydrocarbons in estuarine and coastal regions^1–11. Several unsaturated hydrocarbons found in marine environments have been correlated with specific sources^7,12–21, but the origins of many polyolefins remain uncertain. Such information would enhance the use of these compounds as biological markers of organic matter sources and/or geochemical processes. Samples of flora collected from a New England saltmarsh have been mixed with marsh sediment and allowed to decompose anaerobically in order to assess whether such processes are a source of sedimentary alkenes. We report here the formation of a series of isomeric n-nonadecadienes and n-heneicosadienes during anaerobic decomposition of a marine algal mat. Their formation was found to be both substrate- and light-dependent, and is thought to proceed through either diagenetic modification of algal organic matter or de novo synthesis by microorganisms active in anaerobic decomposition. These findings suggest that the presence of such dienes in Recent nearshore sediments^5,22 and participate matter²³ is more likely to be indicative of early diagenetic processes than of organic inputs from specific sources.