Mass of particulate carbon and nitrogen in suspended matter as a function of volume filtered in several oceanic areas

We address two issues in the determination of particulate carbon and nitrogen in suspended matter of aquatic environments. One is the adsorption of dissolved organic matter on filters, leading to overestimate particulate matter. The second is the material loss during filtration due to fragile algal cells breaking up. Examples from both laboratory cultures and natural samples are presented. We recommend using stacked filters in order to estimate thefirst and filtering different volumes of water in order to evaluate the second.

Organic carbon and carbohydrates in waters of the Amazon River, Atlantic Ocean, and Tropical Indian Ocean

A method is presented to study carbohydrate composition of marine objects involved into sedimento- and diagenesis (plankton, particulate matter, benthos, and bottom sediments). Analysis of the carbohydrates is based on consecutive separation of their fractions with different solvents (water, alkali, and acid). Ratios of carbohydrate fractions allows to evaluate lability of carbohydrate complexes. They are also usable as an indicators of biogeochemical processes in the ocean, as well of genesis and degree of transformation of organic matter in bottom sediments and nodules. Similarity in monosaccharide composition is shown for dissolved organic matter and aqueous and alkaline fractions of seston and particulate matter.

Organic matter based proxies from surface sediments along three transects on the Pakistan continental margin

A valid assessment of selective aerobic degradation on organic matter (OM) and its impact on OM-based proxies is vital to produce accurate environmental reconstructions. However, most studies investigating these effects suffer from inherent environmental heterogeneities. In this study, we used surface samples collected along two meter-scale transects and one longer transect in the northeastern Arabian Sea to constrain initial OM heterogeneity, in order to evaluate selective aerobic degradation on temperature, productivity and alteration indices at the sediment-water interface. All of the studied alteration indices, the higher plant alkane index, alcohol preservation index, and diol oxidation index, demonstrated that they are sensitive indicators for changes in the oxygen regime. Several export production indices, a cholesterol-based stanol/stenol index and dinoflagellate lipid- and cyst-based ratios, showed significant (more than 20%) change only over the lateral oxygen gradients. Therefore, these compounds do not exclusively reflect surface water productivity, but are significantly altered after deposition. Two of the proxies, glycerol dibiphytanyl glycerol tetraether-based TEX86 sea surface temperature indices and indices based on phytol, phytane and pristane, did not show any trends related to oxygen. Nevertheless, unrealistic sea surface temperatures were obtained after application of the TEX86, TEX86L, and TEX86H proxies. The phytol-based ratios were likely affected by the sedimentary production of pristane. Our results demonstrate the selective impact of aerobic organic matter degradation on the lipid and palynomorph composition of surface sediments along a short lateral oxygen gradient and suggest that some of the investigated proxies may be useful tracers of changing redox conditions at the sediment-water interface.

Rates of organic matter transformation within the production-destruction cycle of the White Sea

Rates of organic matter (OM) transformation within the production-destruction cycle of the White Sea were estimated on the basis of measured activity values of redox enzymes of the electron transport system and of hydrolytic enzymes (phosphatase and protease). It was found that OM oxidation processes were the most intensive in the Kandalaksha Bay, while minimum oxidation rates were characteristic of central parts of the Dvina and Onega bays. It was revealed that the highest rates of phosphate mineralization were characteristic of the central part of the sea and near-mouth areas of the Onega and Kandalaksha bays, with the lowest rates in the Dvina Bay. During the period of intense primary production when resources of inorganic phosphorus were practically depleted, high rates of phosphate regeneration were observed. It was shown that populations of micro- and zooplankton in the White Sea were characterized by low activation energies of the principal metabolism reactions (3-6 kcal/mol), which allowed these populations to provide exchange intensity comparable to that of inhabitants of warm waters during all the seasons.

(Table 1) Composition of organic matter in bottom sediments from the Kuril-Kamchatka Trench

From results of analyses of sediment samples collected on a profile crossing the Kuril-Kamchatka Trench distribution of organic D, N. carbohydrates, lipids and humic substances was established, as well as nature of their relationship with amorphous silica and clay fraction. Sum of the main biochemical groups of organic matter in the surface layer of sediments (0-1 cm) from the Kuril-Kamchatka Trench amounts to about 15%; neogenetic forms not encountered in living organisms make up 85% of organic matter. Among such forms 26% comprise humic substances formed during initial stages of polymerization of decomposition products of biochemical macromolecules.

Composition of organic matter in bottom sediments from the Antarctic sector of the Atlantic Ocean

We identify geochemical features of sedimentary organic matter in various morphostructural zones of the Antarctic sector of the Atlantic. We present background geochemical organic parameters for shelf and deep-sea sediments from the Weddell and Scotia Seas and the Bransfield Strait. Geochemical organic parameters are good indicators of environmental and facial variations in sediments and could be used for environmental monitoring of the World Ocean.

Accumulation rates and composition of organic matter in sediments off Peru

Deep-sea sediment samples from three Ocean Drilling Program (ODP) Leg 112 sites on the Peru continental margin were investigated, using a number of organic geochemical and organic petrographic techniques, for amounts and compositions of the organic matter preserved. Preliminary results include mass accumulation rates of organic carbon at Site 679 and characteristics of the organic facies for sediments from Sites 679, 681, and 684. Organic-carbon contents are high, with few exceptions. Particularly high values were determined in the Pliocene interval at Site 684 (4%-7.5%) and in the early Pliocene to Quaternary section of Hole 679D (2%-9%). Older sediments at this site have distinctively lower organic-carbon contents (0.2%-2.5%). Mass accumulation rates of organic matter at Site 679 are 0.02 to 0.07 g carbon/cm**2/k.y. for late Miocene to early Pliocene sediments and higher by a factor of 5 to 10 in the Quaternary sediments. The organic matter in all samples has a predominantly marine planktonic and bacterial origin, with minor terrigenous contribution. Organic particle sizes are strikingly small, so that only a minor portion is covered by visual maceral analysis. Molecular organic-geochemical data were obtained for nonaromatic hydrocarbons, aromatic hydrocarbons (including sulfur compounds), alcohols, ketones, esters, and carboxylic acids. Among the total extractable lipids, long-chain unsaturated ketones from Prymnesiophyte algae strongly predominate among the gas chromatography (GC) amenable components. Steroids are major constituents of the ketone and free- and bound-alcohol fractions. Perylene is the most abundant aromatic hydrocarbon, whereas in the nonaromatic hydrocarbon fractions, long-chain n-alkanes from higher land plants predominate, although the total terrigenous organic matter proportion in the sediments is small.

Stable carbon and nitrogen isotope composition of organic matter in sediments of the Oman Margin

Stable isotopic compositions of carbon and nitrogen and organic carbon content of sediments ranging from the Pliocene to the Pleistocene-Holocene in age from the Oman Margin (ODP Sites 724 and 725) are reported. In general, the organic carbon content is greater than 2% at Site 724. Prior to the Pleistocene-Holocene at this site, sediments with higher content of organic matter were deposited owing to favorable preservation conditions and/or higher productivity. In the Pleistocene, lower amounts of organic matter have been preserved; this material generally has more enriched nitrogen isotopic compositions. This may indicate intensification of the Oxygen Minimum Zone and denitrification with the onset of the Pleistocene. A correlation of carbon isotope content of these sediments with oxygen isotope stages at Site 724 indicates an enrichment in 13C during glacial events. Based on the stable isotope evidence of both carbon and nitrogen, there does not appear to be major input of terrigenous-derived allochthonous material in this marine environment. The timing and extent of monsoon winds on the productivity of this region are not evident, but require further studies for collaborative interpretation of small-scale features in the isotopic and carbon content of this environment.