Molecular indicators of diagenetic status in marine organic matter

Abstract

The fluxes of individual carbohydrates, amino acids, lipids and pigments have been determined in net-plankton, particulate matter and sediments from three sites (9°N, 5°N, and 0°N) in the central equatorial Pacific to evaluate sources and reactivities of organic compounds. Although primary production rates vary markedly across this 9° swath, vertical trends in biochemical compositions remained remarkably parallel. Together these one hundred plus biochemicals account for 80% of the total organic carbon (C org) in net-plankton and particles sinking from the euphotic zone, but represent only 24 and 20% of the organic carbon in deep-water particles and surface sediments, respectively. Scaled profiles of relative abundances, clearly illustrate (a) exponential losses of plankton remains and increases in heterotroph biomarkers throughout the water column, (b) elevated proportions of bacterial markers near the sediment surface, and (c) preservation of selected remains of bacteria, phytoplankton and vascular land plants deeper in the sediments. In spite of one of the most comprehensive analyses of major biochemicals yet applied to marine particulate samples, percentages of molecularly uncharacterized organic carbon increase progressively down the water column to values near 80% in the underlying sediments. The composition, formation pathway and information potential of this uncharatterized fraction are among the most fascinating questions in marine organic geochemistry.