MOLECULAR INDICATORS OF DIAGENETIC STATUS IN MARINE ORGANIC-MATTER

The fluxes of individual carbohydrates, amino acids, lipids and pigmen ts have been determined in net-plankton, particulate matter and sedime nts from three sites (9 degrees N, 5 degrees N, and 0 degrees N) in th e central equatorial Pacific to evaluate sources and reactivities of o rganic compounds. Although primary production rates vary markedly acro ss this 9 degrees swath, vertical trends in biochemical compositions r emained remarkably parallel. Together these one hundred plus biochemic als account for 80% of the total organic carbon (C-org) in net-plankto n and particles sinking from the euphotic zone, but represent only 24 and 20% of the organic carbon in deep-water particles and surface sedi ments, respectively. Scaled profiles of relative abundances, clearly i llustrate (a) exponential losses of plankton remains and increases in heterotroph biomarkers throughout the water column, (b) elevated propo rtions of bacterial markers near the sediment surface, and (c) preserv ation of selected remains of bacteria, phytoplankton and vascular land plants deeper in the sediments. In spite of one of the most comprehen sive analyses of major biochemicals yet applied to marine particulate samples, percentages of molecularly uncharacterized organic carbon inc rease progressively down the water column to values near 80% in the un derlying sediments. The composition, formation pathway and information potential of this uncharacterized fraction are among the most fascina ting questions in marine organic geochemistry. Copyright (C) 1997 Else vier Science Ltd.