Composition of organic matter in suspended matter and bottom sediments of the southeastern Baltic Sea

Data on contents and compositions of hydrocarbons (HCs)-aliphatic (AHCs) and polycyclic aromatic (PAHs) are provided in comparison with contents of total organic carbon (Corg), lipids in suspended matter, and Corg in bottom sediments. Particular attention is paid to distribution of HCs in the area of the Kravtsov oil field. It is established that concentrations of AHCs in water are governed by concentrations of suspended matter and elevated AHC concentrations are confined to coastal areas. In the area of D-6 platform sandy bottom sediments are notable for great variability of HC concentrations, both laterally and from year to year. In summer of 2010 average content of AHCs was 40 ppm (19% of Corg) and that of PAHs was 0.023 ppm. Natural seepage from sediment mass is considered to be a source of HCs along with oil contamination.

Biochemical, geochemical and sedimentological study of ODP Leg 112 samples

Organic-rich diatomaceous muds from Ocean Drilling Program Leg 112 (offshore Peru) are the subject of a comprehensive organic diagenetic study covering the burial interval, <1 to >100 m. The organic matter has been classified in terms of its elemental, biochemical, and geochemical compositions. About 60% of the organic carbon in sediments from <1 m can be attributed to hydrolyzable, biochemical constituents, while at 22 m this figure decreased to 20%. Pyrolysis-gas chromatography and gas chromatography-mass spectrometry chromatograms of these same sediments contain mainly hydrocarbons and nitrogenous compounds, with low amounts of other heteroatomic compounds, even though the total organic matter is rich in oxygen (about 35 atoms per 100 carbon atoms) and sulfur (1 to 5 atoms per 100 C atoms). Overall, the organic matter in these sediments, even at these shallow depths and young ages, has many of the geochemical features of far more deeply buried sediments, providing further strong evidence for the claim that "kerogen-formation" is a very early diagenetic process.

n-Alkanes and lignin in bottom sediments of the West European Basin (area of the battleship Bismark wreck site)

Three bottom sediment cores were collected from the top, slope, and foot of a small topographic high located near the West European continental rise within the Porcupine abyssal plain at the battleship Bismark wreck site. Using high-efficient gas chromatography technique we determined content and examined molecular composition of n-alkane fraction of hydrocarbons and phenol compounds of lignin. n-Alkane and phenol concentrations in bottom sediments of all three cores were low both in values per unit mass of sediments and in organic matter composition that is typical for pelagic deposits of the World Ocean. They vary from 0.07 to 2.01 µg/g of dry sediment and from 0.0001 to 0.01% of TOC; phenol ranges are from 1.43 to 11.1 µg/g and from 0.03 to 0.6%. Non-uniform supply of terrigenous matter to the bottom under conditions of changes in sedimentation environment in different geological epochs is the principal reason for significant variations in n-alkane and lignin concentrations with depth in the cores. Lignin and its derivatives make the main contribution to formation of organic matter composition of the region in study. With respect to n-alkane and lignin concentrations organic matter of deposits of the West European Basin is composed of remains of higher plants and of autochtonous organic matter of marine flora; they have mixed terrigenous-autochtonous (terrigenous-planktonogenic) origin.

Isotopic composition and lithic grains concentration of sediment core SI90-09

Theories explaining the origin of the abrupt, massive discharges of ice-rafted detritus (IRD) into the glacial North Atlantic (the Heinrich layers (HLs)) generally point to the Laurentide ice sheet as the sole source of these events, until it was found that the IRDs also originated from Icelandic and European ice sheets (Bond and Lotti, 1995, doi:10.1126/science.267.5200.1005; Snoeckx et al., 1999, doi:10.1016/S0025-3227(98)00168-6; Grousset et al., 2000, doi:10.1130/0091-7613(2000)28<123:WTNAHE>2.0.CO;2). This apparent contradiction must be reconciled as it raises fundamental questions about the mechanism(s) of HL origin. We have analyzed two ~12 cm thick HLs in an ultrahigh-resolution mode (1-2 century intervals) in a mid-Atlantic ridge piston core. The d18O record (N. pachyderma left coiling) reveals strong excursions induced by the melting of the icebergs; these excursions are associated with a strong decrease in the amount of planktic foraminafersand with a 3°C cooling of the surface waters. Counts of coarse detrital grains reveal that IRD are deposited according to a typical sequence (1) volcanic glass, (2) quartz and feldspars, (3) detrital carbonate, that implies a chronology in the melting of the differentpan-Atlantic ice sheets. Sr and Nd isotopic composition confirm that in both Heinrich layers H1 and H2, "precursor" IRD came from first Europe/Iceland, followed then by Laurentide-derived IRD. An internal cyclicity can be identified: during H1 and H2, about four to six major, abrupt discharges occurred roughly on a century timescale. The d13C and d15N records reveal that dominant inputs of continent-derived organic matter are associated with IRD within the HLs, hiding the plankton productivity signal.

Total organic carbon content, methane isotopic composition and hydrocarbon characteristics of ODP Leg 180 sites

The organic geochemistry of Sites 1108 and 1109 of the Woodlark Basin, offshore Papua New Guinea, was studied to determine whether thermally mature hydrocarbons were present in the penetrated section and, if present, whether they are genetically related to the penetrated "coaly" interval. Both the organic carbon and pyrolysis data indicate that there is no significant hydrocarbon source-rock potential at Site 1108. The hydrocarbons encountered during drilling appear to be indigenous and not migrated products or contaminants. In contrast, the coaly interval at Site 1109 contains zones with significant hydrocarbon-generation potential. Several independent lines of evidence indicate that the coaly sequence encountered at Site 1109 is thermally immature. The Site 1108 methane stable-carbon isotope composition does not display a clear trend with depth as would be expected if it was solely reflecting a maturation profile. The measured isotopic composition of methane has most probably been altered by fractionation during sample handling and storage. This fractionation would result in isotopically heavier values than would be obtained on free gas. The organic geochemical data gathered indicate that Site 1108 can be safely revisited and that the organic-rich sediments encountered at Site 1109 were not the source of the gas encountered at Site 1108.

n-Alkanes and phenols in bottom sediments and brown algae from the Blake-Bahama Abyssal Plain

Using gas chromatography technique we examined molecular composition of n-alkanes and lignin from bottom sediments of a core 385 cm long collected in the region of the Blake-Bahama Abyssal Plain. We determined C_org concentrations and lignin composition in soils, mangrove roots and leaves, in algae Sargassum and Ascophyllum, in corals and timber of a sunken ship; they were compared with data on lignin in bottom sediments. Mixed planktonogenic and terrigenous origin of organic matter in the core was proved with different proportions of terrigenous and planktonogenic components at different levels. Multiple changes in dominating sources of organic matter over a period required for accumulation of a four meter thick sedimentary sequence (about 4 m) are shown as obtained from changes in composition and contents of organic-chemical markers referring to classes of n-alkanes and phenols.

Microfossils and chemical elements in bottom sediments of the Ashadze-1 Hydrothermal Field (tropical Mid-Atlantic Ridge)

The first thorough analysis of microfossils from ore-bearing sediments of the Ashadze-1 Hydrothermal Field in the Mid-Atlantic Ridge sampled during Cruise 26 of R/V Professor Logachev in 2005 revealed substantial influence of hydrothermal processes on preservation of planktonic calcareous organisms as well as on preservation and composition of benthic foraminifera. From lateral and vertical distribution patterns and secondary alterations of microfossils it is inferred that the main phase of hydrothermal mineralization occurred in Holocene. Heavy metals (Cu, Co, Cr, and Ag) were accumulated by foraminiferal tests and in their enveloping Fe-Mn crusts. Distribution of authigenic minerals replacing foraminiferal tests demonstrates local zoning related to hydrothermal activity. There are three mineral-geochemical zones defined: sulfide zone, zone with elevated Mg content, and zone of Fe-Mn crusts.