Hydrocarbon contents and carbon isotope composition of organic matter from holes of DSDP Legs 50 and 64

The book is devoted to fundamental problems of organic geochemistry of ocean sediments. It is based on materials of organic matter and gas studies in cores from DSDP Legs 50 and 64. Experimental results obtained in the Laboratory of Carbon Geochemistry (V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow) take the main part of the book. Evolution of organic matter in specific environment of deep ocean sediments, sources of organic matter in the ocean and methods of their identification based on isotopic analysis and other methods are under discussion. Gas geochemistry in normal conditions of diagenesis, and in conditions under intense heating is studied.

Distribution of organic matter and gases in sediments at DSP Leg 63 Holes

As part of our continuing organic geochemical studies of sediments recovered by the Deep Sea Drilling Project, we have analyzed the types, amounts, and thermal alteration indices of organic matter in samples collected from the California continental margin on Leg 63. Some of the samples were frozen core; others were canned on site. Canned samples were analyzed for gas content using methods described by Mclver (1972). Our main objective was to see if the changes in surface circulation that had occurred through time off the California coast were reflected in changes in the type and amount of organic matter accumulating on the sea floor.

Organic matter and sediment properties of samples from site GeoB15105 from the Black Sea

Dissolved organic matter (DOM) in marine sediments is a complex mixture of thousands of individual constituents that participate in biogeochemical reactions and serve as substrates for benthic microbes. Knowledge of the molecular composition of DOM is a prerequisite for a comprehensive understanding of the biogeochemical processes in sediments. In this study, interstitial water DOM was extracted with Rhizon samplers from a sediment core from the Black Sea and compared to the corresponding water-extractable organic matter fraction (<0.4 µm) obtained by Soxhlet extraction, which mobilizes labile particulate organic matter and DOM. After solid phase extraction (SPE) of DOM, samples were analyzed for the molecular composition by Fourier Transform Ion-Cyclotron Resonance Mass Spectrometry (FT-ICR MS) with electrospray ionization in negative ion mode. The average SPE extraction yield of the dissolved organic carbon (DOC) in interstitial water was 63%, whereas less than 30% of the DOC in Soxhlet-extracted organic matter was recovered. Nevertheless, Soxhlet extraction yielded up to 4.35% of the total sedimentary organic carbon, which is more than 30-times the organic carbon content of the interstitial water. While interstitial water DOM consisted primarily of carbon-, hydrogen- and oxygen-bearing compounds, Soxhlet extracts yielded more complex FT-ICR mass spectra with more peaks and higher abundances of nitrogen- and sulfur-bearing compounds. The molecular composition of both sample types was affected by the geochemical conditions in the sediment; elevated concentrations of HS- promoted the early diagenetic sulfurization of organic matter. The Soxhlet extracts from shallow sediment contained specific three- and four-nitrogen-bearing molecular formulas that were also detected in bacterial cell extracts and presumably represent proteinaceous molecules. These compounds decreased with increasing sediment depth while one- and two-nitrogen-bearing molecules increased, resulting in a higher similarity of both sample types in the deep sediment. In summary, Soxhlet extraction of sediments accessed a larger and more complex pool of organic matter than present in interstitial water DOM.

Organic matter and trace element concentrations in sapropels from ODP Leg 160 sites

A distinct Pliocene eastern Mediterranean sapropel (i-282), recovered from three Ocean Drilling Program (ODP) Leg 160 Sites, has been investigated for its organic and inorganic composition. This sapropel is characterized by high organic carbon (Corg) and trace element contents, and the presence of isorenieratene derivatives. The latter suggests that the base of the photic zone was sulphidic during formation of the sapropel. Combined with evidence of bottom water anoxia (preservation of laminae, high redox-sensitive trace element contents, and the abundance and isotopic composition of pyrite) this leads to the tentative conclusion that almost the entire water column may have been anoxic. This anoxia resulted from high productivity and not from stagnation, because an approximation of the trace element budget during sapropel formation shows that water exchange with the western Mediterranean is needed. Entire water column anoxia has been suggested earlier for several black shales. With regard to the depositional environment and the Corg content, however, only the Cenomanian=Turonian Boundary Event (CTBE) black shales appear to be comparable to this sapropel. The proposed trace element removal mechanism of scavenging and (co-)precipitation in an anoxic water column, is thought to be similar for both types of deposits. The ultimate trace element source for the sapropel, however, is seawater, whereas it is hydrothermal and fluvial input for CTBE black shales (because they have a larger temporal and spatial distribution). Nonetheless, the Corg-rich eastern Mediterranean Pliocene sapropel discussed here may be considered to be a younger analogue of CTBE black shales.

Isotopic composition of carbon in organic matter of sediments and particulate matter from the Northwest Pacific

A study was made of isotopic composition of carbon in lipids found in three samples of separate particulates and in eight bottom sediment samples collected in a from the Simushir Island towards the open Pacific Ocean. Average d13C of lipids from particulates was 2.3 per mil lower than one of sediments. Humic acids from sediments are the most isotopically heavy fraction (d13C = -21.2 per mil). Isotopic composition of carbon in lipids depended on their total content in samples and on composition of sediments. Formation of isotopically heavy lipids in the surface layer of sediments may be associated with biogeochemical resynthesis of humic acids.