Organic Marine Geochemistry

Abstract

The use of modern hyphenated methods such as GC-MS have proven invaluable to the task of assigning specific sources to specific organic compounds isolated from marine sediments, suspended particulate matter, interstitial water and seawater. Early chapters of this volume discuss the correlation of various classes of compounds isolated largely from marine and brackish sediments with sources consisting of terrigenous plants, bacteria, phytoplankton, zooplankton and nonbiological components such as anthropogenic input, petroleum seepage, and the weathering of "mineral" deposits. BiomarkersA biological marker (or "biomarker") may be defined as "a compound the structure of which can be interpreted in terms of a previous biological origin." Since the isolation and identification of metalloporphyrins in bitumens by Treibs (2) in the 1930's and their correlation with tetrapyrroles of chlorophylls, implying a biological origin for petroleum, an enormous amount of progress has been accomplished in this area of research.In order to be a useful biomarker, a compound must retain enough of its original structure to be identified as a modified version of the original biological parent compound. The retention of the carbon backbone of biologically generated alcohols, in alkanes isolated from sediments and petroleum fractions, includes the classic cases of pristane and phytane as diagenetic products of phytol (the alcohol which esterifies the carboylic acid group in chlorophyll-a) and 5 ,-cholestane from cholesterol. Other examples of the usefulness of alkanes as biomarkers include correlations of various n-alkanes to bacterial populations (3), and the association of C 30 -steranes with marine versus nonmarine input (originally as C 30 -sterols) (4).Another factor commonly used as a source indicator with respect to alkanes is the carbon number distribution. Briefly, n-alkane distributions with carbon number maxima in the 17-21 range (C 17 -C 21 ) originate largely from aquatic algal sources, while maxima characterized by higher carbon numbers are

Pyrolysis–Gas Chromatography/Mass Spectrometry Identification of Distinctive Structures Providing Humic Character to Organic Materials

“…The origin of these series of alkyl compounds is not clear. Alkyl chains with high carbon number (C 21 –C 33 ) are indicative of plant waxes, usually with an odd‐over‐even predominance, whereas shorter chains may originate from microbial biopolymers (Sohn, 1986; Tegelaar et al, 1989; Lichtfouse et al, 1998). Several studies suggest that the existence of aliphatic domains in humic substances could be explained by the selective preservation during humification of highly aliphatic biopolymers and their subsequent integration into the humic fraction, with no even‐over‐odd predominance (Almendros et al, 1996, 2000; Lichtfouse et al, 1998).…”