Distribution of benthic foraminifera in surface sediments of the Portuguese continental margin

Living and dead benthic Foraminifera of 26 sediment surface samples from the East Atlantic continental margin (off Portugal) are studied. The stations are located on two profiles off Cape Mondego and off Cape Sines, ranging in water depth from 45 to 3905 meters. The highest values of standing crop are on the shelf (200 m) (up to 420 specimens/10 cm**3). Below 1000 m water depth standing crop is low (5 -24 specimens/10 cm**3). 151species and species groups are distinguished. Most of the living species do occur in a wide depth range. Faunal depth boundaries are at 50/100m, at 600/800 m, and at 1000 m. Results published from the North Atlantic and the East Mediterranean do not differ from those obtained in samples off Portugal. Depth of water (e.g. hydrostatic pressure) or another factor being controlled by depth (e.g. limitation of food supply) seems to be the most important factor of the benthic foraminiferal distribution.

Some parameters of distribution of hydrocarbon paraffin fraction in bottom sediments of the Kara Sea and the Yenisey estuary

During Cruise 49 of R/V Dmitry Mendeleev in the Kara Sea (August-September, 1993) chemical-bitumenological studies of bottom sediments were carried out. Hydrocarbons were analyzed by gas-liquid chromatography. It was found on the basis of distribution of n-alkanes and isoprenoids (pristan and phytan) that organic matter is mainly terrigenous consisting of higher plant remains.

Composition of bitumen in the organic matter of Black Sea sediments from DSDP Hole 42-379B

Bituminologic analysis of sediment cores from the Black Sea (water depth up to 2000 m, drilling depth up to 625 m) has revealed all components typical for fossilized rocks, viz. hydrocarbons, resins, asphaltenes, and insoluble matter. Proportions of these components, their composition and properties do not display any dependence on depth in hole and seem to be governed by composition of organic matter and conditions and degree of its transformation at early stages of lithogenesis.

(Table) Carbon, nitrogen and n-alkane content and isotopic composition of bottom sediments obtained in the East Siberian Sea

The chemical composition of organic matter (Corg, Norg, d13C, d1SN, and n-alkanes) was studied in the top layer of bottom sediments of the East Siberian Sea. Possible ways were proposed to estimate the amount of the terrigenous component in their organic matter (OM). The fraction of terrigenous OM estimated by the combined use of genetic indicators varied from 15% in the eastern part of the sea, near the Long Strait, to 95% in the estuaries of the Indigirka and Kolyma rivers, averaging 62% over the sea area.

Elemental, biomarker, palynology and maceral data from Seam 1, Schöningen and associated interbeds

Sphagnum moss is the dominant plant type in modern boreal and (sub)arctic ombrotrophic bogs and is of particular interest due to its sensitivity to climate and its important role in wetland biogeochemistry. Here we reconstruct the occurrence of Sphagnum moss - and associated biogeochemical change - within a thermally immature, early Paleogene (~55 Ma) lignite from Schöningen, NW Germany using a high-resolution, multi-proxy approach. Changes in the abundance of Sphagnum-type spores and the C23/C31n-alkane ratio indicate the expansion of Sphagnum moss within the top of the lignite seam. This Sphagnum moss expansion is associated with the development of waterlogged conditions, analogous to what has been observed within modern ombrotrophic bogs. The similarity between biomarkers and palynology also indicates that the C23/C31n-alkane ratio may be a reliable chemotaxonomic indicator for Sphagnum during the early Paleogene. The d13C value of bacterial hopanes and mid-chain n-alkanes indicates that a rise in water table is not associated with a substantial increase in aerobic methanotrophy. The absence of very low d13C values within the top of the seam could reflect either less methanogenesis or less efficient methane oxidation under waterlogged sulphate-rich conditions.

Concentrations and d13C compositions of n-alkanes, n-alcohols, n-alkanoic acids in a 34-month time series of suspended sediments from the outflow of the Congo River

The concentrations, distributions, and stable carbon isotopes (d13C) of plant waxes carried by fluvial suspended sediments contain valuable information about terrestrial ecosystem characteristics. To properly interpret past changes recorded in sedimentary archives it is crucial to understand the sources and variability of exported plant waxes in modern systems on seasonal to inter-annual timescales. To determine such variability, we present concentrations and d13C compositions of three compound classes (n-alkanes, n-alcohols, n-alkanoic acids) in a 34-month time series of suspended sediments from the outflow of the Congo River. We show that exported plant-dominated n-alkanes (C25-C35) represent a mixture of C3 and C4 end members, each with distinct molecular distributions, as evidenced by an 8.1 ± 0.7 per mil (±1Sigma standard deviation) spread in d13C values across chain-lengths, and weak correlations between individual homologue concentrations (r = 0.52-0.94). In contrast, plant-dominated n-alcohols (C26-C36) and n-alkanoic acids (C26-C36) exhibit stronger positive correlations (r = 0.70-0.99) between homologue concentrations and depleted d13C values (individual homologues average <= -31.3 per mil and -30.8 per mil, respectively), with lower d13C variability across chain-lengths (2.6 ± 0.6 per mil and 2.0 ± 1.1 per mil, respectively). All individual plant-wax lipids show little temporal d13C variability throughout the time-series (1 Sigma <= 0.9 per mil), indicating that their stable carbon isotopes are not a sensitive tracer for temporal changes in plant-wax source in the Congo basin on seasonal to inter-annual timescales. Carbon-normalized concentrations and relative abundances of n-alcohols (19-58% of total plant-wax lipids) and n-alkanoic acids (26-76%) respond rapidly to seasonal changes in runoff, indicating that they are mostly derived from a recently entrained local source. In contrast, a lack of correlation with discharge and low, stable relative abundances (5-16%) indicate that n-alkanes better represent a catchment-integrated signal with minimal response to discharge seasonality. Comparison to published data on other large watersheds indicates that this phenomenon is not limited to the Congo River, and that analysis of multiple plant-wax lipid classes and chain lengths can be used to better resolve local vs. distal ecosystem structure in river catchments.