Composition of Upper Quaternary bottom sediments from the Syrian area of the Mediterranean Sea

Results of a lithological study of bottom sediments in the Syrian region of the Mediterranean Sea during Cruise 27 of R/V Vityaz (1993) are reported. Suspended sediment discharge of the Nile River are of the greatest importance for terrigenous sedimentation in the SE part of the Mediterranean Sea, especially in deep-sea areas. Suspended load entering from the Syrian catchment area plays an important role in formation of recent shelf and slope deposits. Supply of aerosols from Syrian and Arabian deserts was distinguished by the patchiness of surface distribution of quartz. During Late Quaternary accumulation of terrigenous material supplied from both the Syrian and the Nile drainage areas was irregular. Sedimentation was remarkably enhanced during sapropel formation 7000-9000 years BP.

Geochemistry of gas hydrates of DSDP Hole 84-570

During Deep Sea Drilling Project (DSDP) Leg 84 a core 1 m long and 6 cm in diameter of massive gas hydrate was unexpectedly recovered at Site 570 in upper slope sediment of the Middle America Trench offshore of Guatemala. This core contained only 5-7% sediment, the remainder being the solid hydrate composed of gas and water. Samples of the gas hydrate were decomposed under controlled conditions in a closed container maintained at 4°C. Gas pressure increased and asymptotically approached the equilibrium decomposition pressure for an ideal methane hydrate, CH4.5-3/4H2O, of 3930 kPa and approached to this pressure after each time gas was released, until the gas hydrate was completely decomposed. The gas evolved during hydrate decomposition was 99.4% methane, ~0.2% ethane, and ~0.4% CO2. Hydrocarbons from propane to heptane were also present, but in concentrations of less than 100 p.p.m. The carbon-isotopic composition of methane was -41 to -44 per mil, relative to PDB standard. The observed volumetric methane/water ratio was 64 or 67, which indicates that before it was stored and analyzed, the gas hydrate probably had lost methane. The sample material used in the experiments was likely a mixture of methane hydrate and water ice. Formation of this massive gas hydrate probably involved the following processes: (i) upward migration of gas and its accumulation in a zone where conditions favored the growth of gas hydrates, (ii) continued, unusually rapid biological generation of methane, and (iii) release of gas from water solution as pressure decreased due to sea level lowering and tectonic uplift.

Rare earth and other element contents in surface layer bottom sediments and ferromanganese nodules along the Transatlantic profile

Behavior of rare earth elements (REE) and Th is studied along the Transatlantic transect at 22°N. It is shown that both REE and Th contents relative to Al (the most lithogenic element) increase toward the pelagic region. The increasing trend becomes more complicated due to variations in content of biogenic calcium carbonate that acts as a diluting component in sediments. REE composition varies symmetrically relative to the Mid-Atlantic Ridge (MAR) emphasizing weak hydrothermal influence on sediments of the ridge axis, although the well-known criteria for hydrothermal contribution, such as Al/(Al+Mn+Fe) and (Fe+Mn)/Ti, do not reach critical values. Variations in REE content and composition allowed to distinguish the following five sediment zones in the transect: (I) terrigenous sediments of the Nares abyssal plain; (II) pelagic sediments of the North American Basin; (III) carbonate ooze of the MAR axis; (IV) pelagic sediments of the Canary Basin; and (V) terrigenous clay and calcareous mud of the African continental slope and slope base. Ferromanganese nodules of the hydrogenous type with extremely high Ce (up to 1801 ppm) and Th (up to 138 ppm) contents occur in pelagic sediments. It is ascertained that P, REE, and Th contents depend on Fe content in Atlantic sediments. Therefore, one can suggest that only minor amount of phosphorus is bound with bone debris. Low concentration of bone debris phosphorus is a result of relatively high sedimentation rates in the Atlantic Ocean, as compared with those in pelagic regions of the Pacific Ocean.

Production, oxygen uptake, and sinking velocity of copepod fecal pellets originated from the central North Sea

Production, oxygen uptake, and sinking velocity of copepod fecal pellets egested by Temora longicornis were measured using a nanoflagellate (Rhodomonas sp.), a diatom (Thalassiosira weissflogii), or a coccolithophorid (Emiliania huxleyi) as food sources. Fecal pellet production varied between 0.8 pellets ind**-1 h**-1 and 3.8 pellets ind**-1 h**-1 and was significantly higher with T. weissflogii than with the other food sources. Average pellet size varied between 2.2 x 10**5 µm**3 and 10.0 x 10**5 µm**3. Using an oxygen microsensor, small-scale oxygen fluxes and microbial respiration rates were measured directly with a spatial resolution of 2 µm at the interface of copepod fecal pellets and the surrounding water. Averaged volume-specific respiration rates were 4.12 fmol O2 µm**-3 d**-1, 2.86 fmol O2 µm**-3 d**-1, and 0.73 fmol O2 µm**-3 d**-1 in pellets produced on Rhodomonas sp., T. weissflogii, and E. huxleyi, respectively. The average carbon-specific respiration rate was 0.15 d**-1 independent on diet (range: 0.08-0.21 d**-1). Because of ballasting of opal and calcite, sinking velocities were significantly higher for pellets produced on T. weissflogii (322 +- 169 m d**-1) and E. huxleyi (200 +- 93 m d**-1) than on Rhodomonas sp. (35 +- 29 m d**-1). Preservation of carbon was estimated to be approximately 10-fold higher in fecal pellets produced when T. longicornis was fed E. huxleyi or T. weissflogii rather than Rhodomonas sp. Our study directly demonstrates that ballast increases the sinking rate of freshly produced copepod fecal pellets but does not protect them from decomposition.

Nutrients and oxygen concentrations measured in water samples from the North Atlantic during the James Cook cruise JC087 in March 2013

Analysis for micro-molar concentrations of nitrate and nitrite, nitrite, phosphate, silicate and ammonia was undertaken on a SEAL Analytical UK Ltd, AA3 segmented flow autoanalyser following methods described by Kirkwood (1996). Samples were drawn from Niskin bottles on the CTD into 15ml polycarbonate centrifuge tubes and kept refrigerated at approximately 4oC until analysis, which generally commenced within 30 minutes. Overall 23 runs with 597 samples were analysed. This is a total of 502 CTD samples, 69 underway samples and 26 from other sources. An artificial seawater matrix (ASW) of 40g/litre sodium chloride was used as the inter-sample wash and standard matrix. The nutrient free status of this solution was checked by running Ocean Scientific International (OSI) low nutrient seawater (LNS) on every run. A single set of mixed standards were made up by diluting 5mM solutions made from weighed dried salts in 1litre of ASW into plastic 250ml volumetric flasks that had been cleaned by washing in MilliQ water (MQ). Data processing was undertaken using SEAL Analytical UK Ltd proprietary software (AACE 6.07) and was performed within a few hours of the run being finished. The sample time was 60 seconds and the wash time was 30 seconds. The lines were washed daily with wash solutions specific for each chemistry, but comprised of MQ, MQ and SDS, MQ and Triton-X, or MQ and Brij-35. Three times during the cruise the phosphate and silicate channels were washed with a weak sodium hypochlorite solution.

Uranium and thorium isotopes and sedimentation rates in metalliferous sediments from the western flank of the East Pacific Rise at 21°-22°S

Isotopic compositions of uranium (234U and 238U) and thorium (230Th and 232Th) were measured in metalliferous sediments from the western flank of the East Pacific Rise at 21°-22°S, in the area of hydrothermal activity and massive sulfide accumulation at the axis of the EPR. Concentration of 232Th (on the carbonate-free base) is consistent with composition of mafic extrusive rocks; isotope ratios 232Th/238U and 234U/238U indicate that about 70% of uranium passes into sediments from sea water with hydrothermal iron hydroxide. Mean sedimentation rates are calculated for seven cores by the nonequilibrium 230Th method with use of the constant concentration model. Flux of 230Th to bottom sediments is calculated and its mean value is used to determine sedimentation rate in four other cores. The constant flux model is used to calculate change of sedimentation rate with depth for seven cores over time interval of 100-300 ky. Sedimentation rates varied not much (0.3-0.6 cm/ky). The greatest changes occurred in two cores: one located near massive sulfide structures, and another near the spreading axis. Determinations of mean rates by the radiocarbon method and the nonequilibrium thorium method are in good agreement.

Organic compounds and bitumen in surface sediments from the Pechora Bay

Detailed geochemical investigations of bottom sediments in the Pechora Bay were carried out under a monitoring regime. The regional geochemical background is characterized. Organic matter of sediments is found to be clastic, formed under the influence of Pechora River run-off, and determined by genetic and lithofacial factors. An application of geochemical methodology is suggested for estimating hydrocarbon contamination of bottom sediments. As an example consequences of the accidental Usinsky oil spill are studied. They are based on analysis of composition of molecular markers. It is shown that increasing technogenic impact on Pechora Bay sediments is fixed only at molecular level and is not disastrous.

Porewater concentrations, pH, single cell number, anaerobic oxidation of methane (AOM) rate, sulfate reduction (SR) rate of samples during METEOR cruise M76/3b at the REGAB cold seep site from the West African margin in 2008

The giant pockmark REGAB (West African margin, 3160 m water depth) is an active methane-emitting cold seep ecosystem, where the energy derived from microbially mediated oxidation of methane supports high biomass and diversity of chemosynthetic communities. Bare sediments interspersed with heterogeneous chemosynthetic assemblages of mytilid mussels, vesicomyid clams and siboglinid tubeworms form a complex seep ecosystem. To better understand if benthic bacterial communities reflect the patchy distribution of chemosynthetic fauna, all major chemosynthetic habitats at REGAB were investigated using an interdisciplinary approach combining porewater geochemistry, in situ quantification of fluxes and consumption of methane, as well bacterial community fingerprinting. This study revealed that sediments populated by different fauna assemblages show distinct biogeochemical activities and are associated with distinct sediment bacterial communities. The methane consumption and methane effluxes ranged over one to two orders of magnitude across habitats, and reached highest values at the mussel habitat, which hosted a different bacterial community compared to the other habitats. Clam assemblages had a profound impact on the sediment geochemistry, but less so on the bacterial community structure. Moreover, all clam assemblages at REGAB were restricted to sediments characterized by complete methane consumption in the seafloor, and intermediate biogeochemical activity. Overall, variations in the sediment geochemistry were reflected in the distribution of both fauna and microbial communities; and were mostly determined by methane flux.

Table 1. Pressure, temperature and isotope ratios between H2O and CO2 for all experiments

Traditionally, the application of stable isotopes in Carbon Capture and Storage (CCS) projects has focused on d13C values of CO2 to trace the migration of injected CO2 in the subsurface. More recently the use of d18O values of both CO2 and reservoir fluids has been proposed as a method for quantifying in situ CO2 reservoir saturations due to O isotope exchange between CO2 and H2O and subsequent changes in d18OH2O values in the presence of high concentrations of CO2. To verify that O isotope exchange between CO2 and H2O reaches equilibrium within days, and that d18OH2O values indeed change predictably due to the presence of CO2, a laboratory study was conducted during which the isotope composition of H2O, CO2, and dissolved inorganic C (DIC) was determined at representative reservoir conditions (50°C and up to 19 MPa) and varying CO2 pressures. Conditions typical for the Pembina Cardium CO2 Monitoring Pilot in Alberta (Canada) were chosen for the experiments. Results obtained showed that d18O values of CO2 were on average 36.4±2.2 per mil (1 sigma, n=15) higher than those of water at all pressures up to and including reservoir pressure (19 MPa), in excellent agreement with the theoretically predicted isotope enrichment factor of 35.5 per mil for the experimental temperatures of 50°C. By using 18O enriched water for the experiments it was demonstrated that changes in the d18O values of water were predictably related to the fraction of O in the system sourced from CO2 in excellent agreement with theoretical predictions. Since the fraction of O sourced from CO2 is related to the total volumetric saturation of CO2 and water as a fraction of the total volume of the system, it is concluded that changes in d18O values of reservoir fluids can be used to calculate reservoir saturations of CO2 in CCS settings given that the d18O values of CO2 and water are sufficiently distinct.