Geochemistry of tetrapyrrole, tetraterpenoid, and perylene pigments in sediments from the Gulf of California

Results and discussion cover pigment analyses of 36 sediment samples recovered by Deep Sea Drilling Project Leg 64, and six samples from the Leg 64 site-survey cruise in the Guaymas Basin (Scripps Institution of Oceanography, Leg 3). Pigments investigated were tetrapyrroles, tetraterpenoids, and the PAH compound perylene. Traces of mixed nickel and copper ETIO-porphyrins were ubiquitous in all sediment samples, except for the very surface (i.e., <2 m sub-bottom), and their presence is taken as an indication of minor influxes of previously oxidized allochthonous (terrestrial) organic matter. Phorbides and chlorins isolated from Site 479 sediment samples (i.e., the oxygen-minimum locale, northeast of the Guaymas Basin) well represent the reductive diagenesis ("Treibs Scheme"; see Baker and Palmer, 1978; Treibs, 1936) of chlorophyll derivatives. Three forms of pheophytin-a, plus a variety of phorbides, were found to give rise to freebase porphyrins, nickel phylloerythrin, and nickel porphyrins, with increasing depth of burial (increasing temperature). Sediments from Sites 481, 10G, and 18G yielded chlorophyll derivatives characteristic of early oxidative alterations. Included among these pigments are allomerized pheophytin-a, purpurin-18, and chlorin-p6. The high thermal gradient imposed upon the late Quaternary sediments of Site 477 greatly accelerated chlorophyll diagenesis in the adjacent overlying sediments, that is, the production of large quantities of free-base desoxophylloerythroetioporphyrin (DPEP) occurred in a section (477-7-5) presently only 49.8 meters sub-bottom. Present depth and age of these sediments are such that only chlorins and phorbides would be expected. Carotenoid (i.e., tetraterpenoids) concentrations were found to decrease rapidly with increasing sub-bottom depth. Less deeply buried sediments (e.g., 0-30 m) yielded mixtures of carotenes and oxygen-substituted carotenoids. Oxygencontaining (oxy-, oxo-, epoxy-) carotenoids were found to be lost preferentially with increased depth of burial. Early carotenoid diagenesis is suggested as involving interacting reductions and dehydrations whereby dehydro-, didehydro-, and retro-carotenes are generated. Destruction of carotenoids as pigments may involve oxidative cleavage of the isoprenoid chain through epoxy intermediates, akin to changes in the senescent cells of plants. Perylene was found to be a common component of the extractable organic matter from all sediments investigated. The generation of alkyl perylenes was found to parallel increases in the existing thermal regime at all sites. Igneous sills and sill complexes within the sediment profile of Site 481 altered (i.e., scrambled) the otherwise straightforward thermally induced alkylation of perylene. The degree of perylene alkylation is proposed as an indicator of geothermal stress for non-contemporaneous marine sediments.

Geochemistry of tetrapyrrole, carotenoid, and perylene pigments in sediments at DSDP Holes 63-467 and 63-471

Twenty-one core samples from DSDP/IPOD Leg 63 were analyzed for products of chlorophyll diagenesis. In addition to the tetrapyrrole pigments, perylene and carotenoid pigments were isolated and identified. The 16 core samples from the San Miguel Gap site (467) and the five from the Baja California borderland location (471) afforded the unique opportunity of examining tetrapyrrole diagenesis in clay-rich marine sediments that are very high in total organic matter. The chelation reaction, whereby free-base porphyrins give rise to metalloporphyrins (viz., nickel), is well documented within the downhole sequence of sediments from the San Miguel Gap (Site 467). Recognition of unique arrays of highly dealkylated copper and nickel ETIO-porphyrins, exhibiting nearly identical carbonnumber homologies (viz., C-23 to C-30; mode = C-26), enabled subtraction of this component (thought to be derived from an allochthonous source) and thus permitted description of the actual in situ diagenesis of autochthonous chlorophyll derivatives.

Contents of organic compounds in sediments from DSDP Legs 1 and 4

Fifteen sediment samples were studied from five drill sites recovered by the Glomar Challenger on Legs I and IV in the Gulf of Mexico and western Atlantic. This study concentrated on compounds derived from biogenic precursors, namely: (1) hydrocarbons, (2) fatty acids, (3) pigments and (4) amino acids. Carbon isotope (dC13) data [values <(-26)?, relative to PDB], long-chain n-alkyl hydrocarbons (>>C27) with odd carbon numbered molecules dominating even carbon numbered species, and presence of perylene proved useful as possible indicators for terrigenous contributions to the organic matter in some samples. Apparently land-derived organic matter can be transported for distances over 1000 km into the ocean and their source still recognized. The study was primarily designed to investigate: (i) the sources of the organic matter present in the sediment, (ii) their stability with time of accumulation and (iii) the conditions necessary for in situ formation of new compounds.

Lipids and polycyclic aromatic hydrocarbons in bottom sediments from the Atlantic sector of the Southern Ocean

Distribution and composition of lipids and contents of alkanes and polycyclic aromatic hydrocarbons(PAHs) in bottom sediments of the Scotia and Weddell seas are discussed. Comparatively low concentrations of organic carbon (average 0.35%) and lipids (average 0.024%) result from rapid decomposition of organic matter in upper layers of the water column. Composition of alkanes indicates that lipids are of autochthonous origin, and stable concentrations of PAHs (average 25.8 ppb, sigma 15.3 ppb) indicate that they represent the background level for bottom sediments. Higher concentrations of PAHs in sediments near the King George Island (252.1 ppb) and different distributions of individual polyarenes are produced there by the heating systems of the Polish Antarctic Station.

Organic geochemistry of sediments at DSDP Leg 63 Holes

Selected core samples from the California Continental Borderland (Sites 467-469) were analyzed to evaluate the nature and composition of the lipids and kerogens in terms of their genetic origin and geological maturity. The lipids were of a multiple origin. On the basis of the homolog distributions of the n-alkanes and n-fatty acids, with the shape and magnitude of the unresolved branched and cyclic hydrocarbons, and the structural and stereochemical compositions of the molecular markers, these lipids were derived from primary autochthonous marine (microbial), from allochthonous terrigenous (higher plant wax), and from recycled (geologically mature organic matter) sources. The kerogens were composed of principally marine microbial detritus with a minor input of allochthonous terrestrial material. For the most part, the samples had undergone a thermal maturation according to a normal geothermal gradient, except in the proximity of intrusives. Such additional thermal stress was evident for the samples from Site 469 and to some extent for Site 467 at about a sub-bottom depth of 700 to 800 meters.

Organic compounds in snow, ice, and sub-ice waters from the mouth of the Severnaya Dvina River and the Kandalaksha Gulf (White Sea)

The paper reports data on concentrations of organic compounds (organic carbon, lipids; aliphatic hydrocarbons, and polycyclic aromatic hydrocarbons) in snow, ice, and sub-ice waters from the mouth of the Severnaya Dvina River in March 2005-2007 and the Kandalaksha Gulf (Chupa Bay) in March 2004. It was established that organic compounds are accumulated in snow and the upper ice layer near Archangelsk city. Distribution of molecular markers indicates that pollutions were mainly caused by local fallouts. In the Chupa Bay organic compounds are concentrated in the lower ice layer; it is typical for Arctic snow-ice cover. High contents of organic compounds in the snow-ice cover of the White Sea are caused by pollution of air and water during the winter season.