Contents of organic compounds in sediments from DSDP Legs 1 and 4

Fifteen sediment samples were studied from five drill sites recovered by the Glomar Challenger on Legs I and IV in the Gulf of Mexico and western Atlantic. This study concentrated on compounds derived from biogenic precursors, namely: (1) hydrocarbons, (2) fatty acids, (3) pigments and (4) amino acids. Carbon isotope (dC13) data [values <(-26)?, relative to PDB], long-chain n-alkyl hydrocarbons (>>C27) with odd carbon numbered molecules dominating even carbon numbered species, and presence of perylene proved useful as possible indicators for terrigenous contributions to the organic matter in some samples. Apparently land-derived organic matter can be transported for distances over 1000 km into the ocean and their source still recognized. The study was primarily designed to investigate: (i) the sources of the organic matter present in the sediment, (ii) their stability with time of accumulation and (iii) the conditions necessary for in situ formation of new compounds.

Low-molecular-weight hydrocarbon concentrations, organic carbon contents, and Rock-Eval pyrolysis hydrogen indices at DSDP Holes 75-530A and 75-532

A series of C2-C8 hydrocarbons (including saturated, aromatic, and olefinic compounds) from deep-frozen core samples taken during DSDP Leg 75 (Holes 530A and 532) were analyzed by a combined hydrogen-stripping/thermovaporization method. Concentrations representing both hydrocarbons dissolved in the pore water and adsorbed on the mineral surfaces vary in Hole 530A from about 10 to 15,000 ng/g of dry sediment weight depending on the lithology (organic-carbon-lean calcareous oozes versus "black shales"). Likewise, the organic-carbon-normalized C2-C8 hydrocarbon concentrations vary from 3,500 to 93,100 ng/g Corg, reflecting drastic differences in the hydrogen contents and hence the hydrocarbon potential of the kerogens. The highest concentrations measured of nearly 10**5 ng/g Corg are about two orders of magnitude below those usually encountered in Type-II kerogen-bearing source beds in the main phase of petroleum generation. Therefore, it was concluded that Hole 530A sediments, even at 1100 m depth, are in an early stage of evolution. The corresponding data from Hole 532 indicated lower amounts (3,000-9,000 ng/g Corg), which is in accordance with the shallow burial depth and immaturity of these Pliocene/late Miocene sediments. Significant changes in the light hydrocarbon composition with depth were attributed either to changes in kerogen type or to maturity related effects. Redistribution pheonomena, possibly the result of diffusion, were recognized only sporadically in Hole 530A, where several organic-carbon lean samples were enriched by migrated gaseous hydrocarbons. The core samples from Hole 530A were found to be severely contaminated by large quantities of acetone, which is routinely used as a solvent during sampling procedures on board Glomar Challenger.

Contents of major and noble chemical elements in phosphorites and bottom sediments

Ag and Au are typically concentrated in phosphorites; they genetically related to organic matter of bottom sediments that extract these elements from seawater or interstitial water. Consequently, the phosphorites inherit Ag and Au from host sediments that are not always enriched in them. In contrast to other organic-rich sediments, analyzed sample of recent diatom ooze from the Namibian shelf is not enriched in Ag and Au, although some sediments from this region are enriched in Au. In addition to authigenic Au, allochthonous Au associated with quartz grains and micrograins can also be present in shelf phosphorites. This was observed in oceanic phosphorites of various types. Anomalous Au and Fe contents recorded in one seamount phosphorite sample can be related to extraction of Au and nonferrous metals by ferromanganese hydroxides from seawater. This process can serve as one of major mechanisms of Au supply to ferromanganese crusts on seamounts. Phosphorites and sediments are enriched in Ru simultaneously with U. Author's data show that U content varies from 17 (seamount phosphorite) to 887 ppm (Pleistocene phosphorite nodule from the Namibian shelf). This is probably caused by different types of behavior of light and heavy PGEs in the marine environment.

Radiochemical analyses and contents of organic carbon and CaCO3 in equatorial Pacific Ocean sediments

Uranium series nuclide concentrations have been measured on sediments from five box cores from an equatorial Pacific transect. 230Thexcess activities show discontinuities at the Holocene-glacial boundary as dated by 14C. The glacial sedimentation rates determined by 230Th and 14C are 2.5-3.0 cm/kyr. The Holocene rates from 230Th are much lower than those dated by 14C (1.9-2.3 cm/kyr) because of carbonate dissolution. 230Th sedimentation fluxes exceed water column supply by factors of 1.2-1.8 in the Holocene and 1.8-3.0 in the glacial sections. A number of models have been applied to calculate carbonate dissolution rates. The results show that carbonate dissolution rates in the Holocene (in g/cm**2 kyr) equal 1.5 * 10**-3 exp (1.4D) where D is water depth in kilometers. A point-by- point estimation of sediment fluxes through time show that clay accumulation rates in the area have been near constant at 0.1-0.2 g/cm**2 kyr over the past 20 kyr whereas carbonate accumulation rates have decreased dramatically from 0.6-1.0 g/cm**2 kyr in the glacial sections of the cores to 0.2-0.6 g/cm**2 kyr in the Holocene. The errors caused by the uncertainties in the age of the termination of the last glacial period have been investigated and results show that a range of 11-14 kyr leads to an error upper limit of about 30% in the estimation of CaCO3 dissolution rates. The response time of CaCO3 and 230Thex concentrations in the mixed layer of sediments due to an impulse of change in CaCO3 dissolution rate has also been discussed, showing that the observed changes in carbonate dissolution may be explained in terms of a single or a continuous change, depending upon the thickness of the mixed layer.

Sulfur contents and S, C and O isotopic compositions in serpentinized peridotites at ODP Site 153-920

The opaque mineralogy and the contents and isotope compositions of sulfur in serpentinized peridotites from the MARK (Mid-Atlantic Ridge, Kane Fracture Zone) area were examined to understand the conditions of serpentinization and evaluate this process as a sink for seawater sulfur. The serpentinites contain a sulfur-rich secondary mineral assemblage and have high sulfur contents (up to 1 wt.%) and elevated d34S_sulfide (3.7 to 12.7?). Geochemical reaction modeling indicates that seawater-peridotite interaction at 300 to 400°C alone cannot account for both the high sulfur contents and high d34S_sulfide. These require a multistage reaction with leaching of sulfide from subjacent gabbro during higher temperature (~400°C) reactions with seawater and subsequent deposition of sulfide during serpentinization of peridotite at ~300°C. Serpentinization produces highly reducing conditions and significant amounts of H2 and results in the partial reduction of seawater carbonate to methane. The latter is documented by formation of carbonate veins enriched in 13C (up to 4.5?) at temperatures above 250°C. Although different processes produce variable sulfur isotope effects in other oceanic serpentinites, sulfur is consistently added to abyssal peridotites during serpentinization. Data for serpentinites drilled and dredged from oceanic crust and from ophiolites indicate that oceanic peridotites are a sink for up to 0.4 to 6.0 mln ton seawater S per year. This is comparable to sulfur exchange that occurs in hydrothermal systems in mafic oceanic crust at midocean ridges and on ridge flanks and amounts to 2 to 30% of the riverine sulfate source and sedimentary sulfide sink in the oceans. The high concentrations and modified isotope compositions of sulfur in serpentinites could be important for mantle metasomatism during subduction of crust generated at slow spreading rates.

(Table 2) Contents of chlorophyll a, organic carbon, nitrogen, and phosphorus and their molar ratios in dried matter of Ahnfeltia tobuchiensis agar containing seaweed from the Izmena Bay, Kunashir Island (South Kurils)

A complex study of influence of various environmental factors on rates of oxygen (M_O2 ), ammonium (M_NH4), and phosphate (M_PO4) metabolism in Ahnfeltia tobuchiensis has been carried out in situ in the Izmena Bay of the Kunashir Island. The following environmental factors have been included into the investigation: photosynthetically active radiation (PAR); ammonium (NH4); phosphate (PO4); and contents of carbon (C), nitrogen (N), phosphorus (P), and chlorophyll a (Chl) in tissue. Population of agar-containing seaweed A. tobuchiensis forms a layer with thickness up to 0.5 m, which occupies about 23.3 km**2; biomass is equal to 125000 tons. Quantitative assessment of organic matter production and nutrient consumption during oxygen metabolism has been carried out for the whole population. It has been shown that daily oxygen metabolism depends on PAR intensity, concentrations of PO4 and NH4 in seawater, and contents of N and P in tissues (r**2=0.78, p<0.001). Average daily NH4 consumption is 0.21 µmol/g of dry weight/hour and depends on NH4 and O2 concentrations in seawater and on ? and Chl a contents in algal tissues (r**2=0.64, p<0.001). Average daily PO4 consumption is 0.01 µmol/g of dry weight/hour and depends on NH4 concentrations in seawater and on P contents in algal tissues (r**2=0.40, p<0.001).

Sand fraction, carbonate and organic carbon contents of ODP Hole 175-1085A

Site 1085 is located on the continental rise of southwest Africa at a water depth of 1713 m off the mouth of the Orange River in the Cape Basin. The site is part of the suite of locations drilled during Leg 175 on the Africa margin to reconstruct the onset and evolution of the elevated biological productivity associated with the Benguela Current upwelling system (Wefer, Berger, Richter, et al., 1998, doi:10.2973/odp.proc.ir.175.1998). Three sediment samples were collected per section from Cores 170-1085A-28H through 45X (251-419 mbsf) to provide a survey of the sediment record of paleoproductivity from the middle late Miocene to the early Pliocene (~8.7-4.7 Ma), which is a period that includes the postulated northward migration and intensification of the Benguela Current and the establishment of modern circulation off southwest Africa (Siesser, 1980; Diester-Haass et al., 1992; Berger et al., 1998). Core 170-1085A-30H (270-279 mbsf) had essentially no recovery; this coring gap was filled with samples from Cores 170-1085B-29H and 30H (261-280 mbsf). The results of measurements of multiple paleoproductivity proxies are summarized in this report. Included in these proxies are the radiolarian, foraminiferal, and echinoderm components of the sand-sized sediment fraction. Opal skeletons of radiolarians (no diatoms were found) relate to paleoproductivity and water mass chemistry (Summerhayes et al., 1995, doi:10.1016/0079-6611(95)00008-5; Lange and Berger, 1993, doi:10.2973/odp.proc.sr.130.011.1993; Nelson et al., 1995, doi:10.1029/95GB01070). The accumulation rates of benthic foraminifers are useful proxies for paleoproductivity (Herguera and Berger, 1991, doi:10.1130/0091-7613(1991)019<1173:PFBFAG>2.3.CO;2; Nees, 1997, doi:10.1016/S0031-0182(97)00012-6; Schmiedl and Mackensen, 1997, doi:10.1016/S0031-0182(96)00137-X) because these fauna subsist on organic matter exported from the photic zone. Echinoderms also depend mainly on food supply from the photic zone (Gooday and Turley, 1990), and their accumulation rates are an additional paleoproductivity proxy. Concentrations of calcium carbonate (CaCO3) and organic carbon in sediment samples are fundamental measures of paleoproductivity (e.g., Meyers, 1997, doi:10.1016/S0146-6380(97)00049-1). In addition, organic matter atomic carbon/nitrogen (C/N) ratios and delta13C values can be used to infer the origin of the organic matter contained within the sediments and to explore some of the factors affecting its preservation and accumulation (Meyers, 1994, doi:10.1016/0009-2541(94)90059-0).

Abundances and ebridian skeleton contents from IODP Exp302

Abundant and diversified ebridians recovered during IODP Expedition 302 (ACEX) have been identified and counted in order to establish their taxonomy and to decipher the biostratigraphic potential of ebridians in the central Arctic Ocean. In the ACEX samples these fossils are preserved in Lithologic Units 1/6 and 2, which consist mainly of dark silty clay and biosiliceous ooze, respectively. Thirty taxa have been distinguished, three of which are described as new species (Ammmodochium lomonosovense, Pseudammodochium karyon, and pseudammodochium psichion). The most dominant ebridian species is Pseudammodochium dictyoides throughout the biosiliceous section. The second dominant species varies alternately throughout the section. Based on the characteristic occurrences of major ebridian taxa, the ebridian assemblageswere divided into GroupsAtoDin stratigraphic order. The ebridian assemblages in piston core USGS Fl-422 from the Alpha Ridge probably correlate to our assemblage Group A of early middle Eocene age, although rare younger taxa are irregularly included.

Abundances and contents of major silicoflagellates from IODP Holes of Exp302

The silicoflagellate taxa obtained in IODP Expedition 302 (ACEX) were identified and counted in order to establish the silicoflagellate biostratigraphy in the central Arctic Ocean. These microfossils in the ACEX samples were preserved in the Lithology Units 1/6 and 2, which are dark silty clay and biosiliceous ooze, respectively. The silicoflagellate skeletons in the ACEX samples are assigned to 56 taxa. Seven taxa were described as new species, which were abundant in Lithology Unit 2. Comparison with several study cases outside the Eocene Arctic Ocean suggested that the silicoflagellate assemblages in ACEX were unique in Lithology Unit 2. The dominance of silicoflagellate taxa varied throughout the lithological section. Based on the cluster analysis by Morishita similarity index C(Lambda), the silicoflagellate assemblageswere divided into nine assemblage groups. The silicoflagellate datum event of the first occurrence of Corbisema hexacantha in the lower part of Lithology Unit 1/6 is regarded. Based on the datum events for silicoflagellate and palynomorphs, the assigned epoch of Lithology Units 1/6 and 2 is the middle Eocene.

Elemental contents, non-carbonate, fatty acids and alcohols analysis from different Holes of IODP Expedition 310

During IODP Expedition 310 (Tahiti Sea Level), drowned Pleistocene-Holocene barrier-reef terraces were drilled on the slope of the volcanic island. The deglacial reef succession typically consists of a coral framework encrusted by coralline algae and later by microbialites; the latter make up < 80% of the rock volume. Lipid biomarkers were analyzed in order to identify organisms involved in reef-microbialite formation at Tahiti, as the genesis of deglacial microbialites and the conditions favoring their formation are not fully understood. Sterols plus saturated and monounsaturated short-chain fatty acids predominantly derived from both marine primary producers (algae) and bacteria comprise 44 wt% of all lipids on average, whereas long-chain fatty acids and long-chain alcohols derived from higher land plants represent an average of only 24 wt%. Bacterially derived mono-O-alkyl glycerol ethers (MAGEs) and branched fatty acids (10-Me-C16:0; iso- and anteiso-C15:0 and -C17:0) are exceptionally abundant in the microbial carbonates (average, 19 wt%) and represent biomarkers of intermediate-to-high specificity for sulfate-reducing bacteria. Both are relatively enriched in 13C compared to eukaryotic lipids. No lipid biomarkers indicative of cyanobacteria were preserved in the microbialites. The abundances of Al, Si, Fe, Mn, Ba, pyroxene, plagioclase, and magnetite reflect strong terrigenous influx with Tahitian basalt as the major source. Chemical weathering of the basalt most likely elevated nutrient levels in the reefs and this fertilization led to an increase in primary production and organic matter formation, boosting heterotrophic sulfate reduction. Based on the observed biomarker patterns, sulfate-reducing bacteria were apparently involved in the formation of microbialites in the coral reefs off Tahiti during the last deglaciation.

Major element and cadmium contents in phosphorites from Pacific seamounts

Cadmium contents in studied rocks from Pacific seamounts usually lower than both in biogenic-diagenetic shelf phosphorites and in pelagic sedimentatary-diagenetic Fe-Mn nodules. In general, the behavior of Cd in phosphorites, phosphatized rocks and iron-manganese-phosphate crusts from the seamounts shows that phosphorus, iron, and manganese are apparently of normal sedimentary origin.