n-Alkane, fatty acid and hopanoic acid concentrations of ODP Site 190-1178 samples

Ocean Drilling Program (ODP) Leg 190 was programmed to investigate deformational, diagenetic, and hydrologic processes and their interactions in the Nankai Trough accretionary prism. Site 1178 is the northernmost site in the Muroto Transect. Slope sediments and the underlying landward-dipping reflector zone were successfully cored. Temperature measurements and Cl concentrations in pore water indirectly indicate the presence of gas hydrate between 120 and 400 meters below seafloor (mbsf) at Site 1178, with the highest concentrations between 150 and 200 mbsf (Shipboard Scientific Party, 2001, doi:10.2973/odp.proc.ir.190.109.2001). Sedimentary structures show a broad range of deformation structures rich in fractures, suggesting active fluid circulation in the Nankai Trough prism. One of the objectives of Leg 190 was to clarify the interplay of various fundamental processes taking place in the Nankai Trough accretionary prism. Bacteria or prokaryotes in deep subsurface sediment play an important role for material transformation and circulation in an accretionary prism. Significant amounts of bacteria are detected in many of the samples examined (Shipboard Scientific Party, 2001, doi:10.2973/odp.proc.ir.190.109.2001). The type of organic matter in sediments is an important factor related to bacterial activity. To assist investigations on material circulation in deep subsurface sediments, the samples from Site 1178 were analyzed for geolipids (extractable organic matter). The basic data set is preliminarily compiled in the present report to show the types of organic matter and their concentrations in sediments from Site 1178.

Sterol, n-alcohol and n-alkane composition of living fen plants

In groundwater-fed fen peatlands, the surface biomass decays rapidly and, as a result, highly humified peat is formed. A high degree of humification constrains palaeoecological studies because reliable identification of plant remains is hampered. Organic geochemistry techniques as a means of identifying historical plant communities have been successfully applied tobog peat. The method has also been applied to fen peat, but without reference to the composition of fen plants. We have applied selected organic geochemistry methods to determine the composition of the neutral lipid fractions from 12 living fen plants, to investigate the potential for the distributions to characterize and separate different fen plants and plant groups. Our results show correspondence with previous studies, e.g. C23 and C25n-alkanes dominating Sphagnum spp. and C27 to C31 alkanes dominating vascular plants. However, we also found similarities in n-alkane distributions between Sphagnum spp. and the below ground parts of some vascular plants. We tested the efficiency of different n-alkane ratios to separate species and plant groups. The ratios used for bog studies (e.g. n-C23/n-C25 and n-C23/n-C29) did not work as consistently for fen plants. Some differences in sterol distribution were found between vascular plants and mosses; in general vascular plants had a higher concentration of sterols. When distributions of n-alkanes, n-alkane ratios and sterols were all included as variables, redundancy analysis (RDA) separated different plant groups into their own clusters. Our results imply that the pattern for bog biomarkers cannot directly be applied to fen environments. Nevertheless, they encourage further testing to determine whether or not the identification of plant groups, plants or plant parts from highly humified peat is possible by applying fen species-specific biomarker proxies.

Organic geochemistry of Late Cretaceous to Paleogene sediments from MITI Sanriku-oki borehole

Perylene is present in high concentration in Paleogene sediments from the Sanriku-oki borehole of the Ministry of International Trade and Industry (MITI), northeastern Japan. The borehole penetrates a thick sequence of Late Cretaceous to Neogene sediments deposited under a range of conditions, including fluvial-deltaic and shallow marine. Organic petrological and geochemical data show the sediments to be rich in organic matter (OM) derived from higher plants. Biomarker analysis of aliphatic and aromatic hydrocarbons confirms a significant input from higher plants, with extracts dominated by numerous gymnosperm- and angiosperm-derived biomarkers such as diterpanes, oleanenes, des-A-triterpanes and their aromatized counterparts. The highest concentration of perylene occurs in Middle Eocene sediments deposited in a relatively reducing environment. Stable carbon isotope compositions show 13C enrichment in perylene compared to gymnosperm and angiosperm biomarkers, consistent with a fungal origin. This elevated abundance of sedimentary perylene could relate to a Paleogene continental climate where fungi probably flourished.

Age model, lipids, and iron/calcium-ratios of sediment core GeoB9307-3

Hide Intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast Africa since the Last Glacial Maximum, about 20,000 years ago. In particular, the relative importance of atmospheric and oceanic processes is not firmly established. Southward shifts of the intertropical convergence zone (ITCZ) driven by high-latitude climate changes have been suggested as a primary forcing, whereas other studies infer a predominant influence of Indian Ocean sea surface temperatures on regional rainfall changes. To address this question, a continuous record representing an integrated signal of regional climate variability is required, but has until now been missing. Here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro-climatology in southeast Africa during rapid climate changes over the past 17,000 years. Our results are based on a reconstruction of precipitation and river discharge changes, as recorded in a marine sediment core off the mouth of the Zambezi River, near the southern boundary of the modern seasonal ITCZ migration. Indian Ocean sea surface temperatures did not exert a primary control over southeast African hydrologic variability. Instead, phases of high precipitation and terrestrial discharge occurred when the ITCZ was forced southwards during Northern Hemisphere cold events, such as Heinrich stadial 1 (around 16,000 years ago) and the Younger Dryas (around 12,000 years ago), or when local summer insolation was high in the late Holocene, i.e., during the last 4,000 years.

Alkane and hydrocarbon concentrations of ODP Leg 104 sites

Sedimentary extractable organic matter was analyzed at three ODP Leg 104 sites in the Norwegian Sea. Organic carbon content ranged from less than 0.1% to a maximum of 1.8%. Extractable organic matter content and unresolved complex mixture concentrations were low and randomly distributed. Low levels of aliphatic (branched and normal) and aromatic hydrocarbons were detected in all of the sediments analyzed. Total aliphatic and aromatic hydrocarbon concentrations ranged from 176 to 3,214 and 6 to 820 ppb, respectively. The concentrations of individual aliphatic (n-C15 to n-C32) and aromatic (two- to five-ring) hydrocarbons were generally less than 50 ppb and less than 10 ppb, respectively. No significant trend with sub-bottom depth was observed in either bulk organic matter or individual hydrocarbon concentrations. The predominant source of Cenozoic sedimentary hydrocarbons is concluded to be ice-rafted debris from the adjacent continent. All sites contain a mixture of recycled, mature petroleum-related and terrestrially derived hydrocarbons.

Carbon geochemistry in serpentinites from and beneath the Lost City Hydrothermal Field

The carbon geochemistry of serpentinized peridotites and gabbroic rocks recovered at the Lost City Hydrothermal Field (LCHF) and drilled at IODP Hole 1309D at the central dome of the Atlantis Massif (Mid-Atlantic Ridge, 30°N) was examined to characterize carbon sources and speciation in oceanic basement rocks affected by long-lived hydrothermal alteration. Our study presents new data on the geochemistry of organic carbon in the oceanic lithosphere and provides constraints on the fate of dissolved organic carbon in seawater during serpentinization. The basement rocks of the Atlantis Massif are characterized by total carbon (TC) contents of 59 ppm to 1.6 wt% and 17863_TC values ranging from -28.7? to +2.3?. In contrast, total organic carbon (TOC) concentrations and isotopic compositions are relatively constant (d13C_TOC: -28.9? to -21.5?) and variations in d13CTC reflect mixing of organic carbon with carbonates of marine origin. Saturated hydrocarbons extracted from serpentinites beneath the LCHF consist of n-alkanes ranging from C15 to C30. Longer-chain hydrocarbons (up to C40) are observed in olivine-rich samples from the central dome (IODP Hole 1309D). Occurrences of isoprenoids (pristane, phytane and squalane), polycyclic compounds (hopanes and steranes) and higher relative abundances of n-C16 to n-C20 alkanes in the serpentinites of the southern wall suggest a marine organic input. The vent fluids are characterized by high concentrations of methane and hydrogen, with a putative abiotic origin of hydrocarbons; however, evidence for an inorganic source of n-alkanes in the basement rocks remains equivocal. We propose that high seawater fluxes in the southern part of the Atlantis Massif likely favor the transport and incorporation of marine dissolved organic carbon and overprints possible abiotic geochemical signatures. The presence of pristane, phytane and squalane biomarkers in olivine-rich samples associated with local faults at the central dome implies fracture-controlled seawater circulation deep into the gabbroic core of the massif. Thus, our study indicates that hydrocarbons account for an important proportion of the total carbon stored in the Atlantis Massif basement and suggests that serpentinites may represent an important (as yet unidentified) reservoir for dissolved organic carbon (DOC) from seawater.

(Table 3) Relative content of n-alkane groups in samples from hydrothermal fields of the Mid-Atlantic Ridge

Optimum conditions were selected for chromatographic separation of model mixtures of C12-C40 n-alkanes. For one of samples of hydrothermal deposits extraction conditions of hydrocarbons were studied and a sample preparation procedure was selected. The procedure was proposed to determine n-alkanes in samples of hydrothermal deposits by means of gas chromatography - mass spectrometry (GC-MS). Detection limit for n-alkanes was 3x10**-9 to 10**-8% depending on components. On the basis of the proposed procedure composition of n-alkanes was studied in samples of hydrothermal deposits collected at the Mid-Atlantic Ridge (Broken Spur, Lost City, and Rainbow hydrothermal fields). Analyses showed that samples contained C14-C35 n-alkanes. Concentrations of the n-alkanes were rather low and varied from 0.002 to 0.038 µg/g. Hypotheses concerning genesis of identified n-alkanes were offered.

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.

Sea surface temperature reconstruction on three sediment profiles off Portugal

Sea Surface Temperature (SST), river discharge and biological productivity have been reconstructed from a multi-proxy study of a high-temporal-resolution sedimentary sequence recovered from the Tagus deposition center off Lisbon (Portugal) for the last 2000 years. SST shows 2 °C variability on a century scale that allows the identification of the Medieval Warm Period (MWP) and the Little Ice Age (LIA). High Iron (Fe) and fine-sediment deposition accompanied by high n-alkane concentrations and presence of freshwater diatoms during the LIA (1300-1900 AD) (Science 292 (2001) 662) suggest augmented river discharge, whereas higher total-alkenone concentrations point to increased river-induced productivity. During the MWP (550-1300 AD) (Science 292 (2001) 662) larger mean-grain size and low values of magnetic susceptibility, and concentrations of Fe, n-alkanes, and n-alcohols are interpreted to reflect decreased runoff. At the same time, increased benthic and planktonic foraminifera abundances and presence of upwelling related diatoms point to increased oceanic productivity. On the basis of the excellent match found between the negative phases of the North Atlantic Oscillation (NAO) index and the intensified Tagus River discharge observed for the last century, it is hypothesized that the increased influx of terrigenous material during the LIA reflects a negative NAO-like state or the occurrence of frequent extreme NAO minima. During the milder few centuries of the MWP, stronger coastal upwelling conditions are attributed to a persistent, positive NAO-like state or the frequent occurrence of extreme NAO maxima. The peak in magnetic susceptibility, centered at 90 cm composite core depth (ccd), is interpreted as the result of the well-known 1755 AD Lisbon earthquake. The Lisbon earthquake and accompanying tsunami are estimated to have caused the loss of 39 cm of sediment (355 years of record-most of the LIA) and the instantaneous deposition of a 19-cm sediment bed.

Results of biogeochemical studies in the Russian Arctic seas: isotope and radioisotope data

Comprehensive biogeochemical studies including determination of isotopic composition of organic carbon in both suspended matter and surface layer (0-1 cm) bottom sediments (more than 260 determinations of d13C-Corg) were carried out for five Arctic shelf seas: White, Barents, Kara, East Siberian, and Chukchi Seas. The aim of this study is to elucidate causes that change isotopic composition of particulate organic carbon at the water-sediment boundary. It is shown that isotopic composition of organic carbon in sediments from seas with high river run-off (White, Kara, and East Siberian Seas) does not inherit isotopic composition of organic carbon in particles precipitating from the water column, but is enriched in 13C. Seas with low river run-off (Barents and Chukchi Seas) show insignificant difference between d13C-Corg values in both suspended load and sediments because of low content of isotopically light allochthonous organic matter in suspended matter. Biogeochemical studies with radioisotope tracers (14CO2, 35S, and 14CH4) revealed existence of specific microbial filter formed from heterotrophic and autotrophic organisms at the water-sediment boundary. This filter prevents mass influx of products of organic matter decomposition into the water column, as well as reduces influx of OM contained in suspended matter from water into sediments.

Composition of organic matter from black shales drilled in the Cape Verde Basin in DSDP Hole 41-367

Results of geochemical studies of organic matter in black shales from the Cape Verde Basin are reported. Based on these results, in combination with data of petrographic analysis, conclusions are made about sapropelic nature of their organic matter and low degree of its coalification. It corresponds to the proto-catagenetic substage of sedimentary rocks. Black shales of the Cape Verde Basin are classified as potential oil source strata.