Major element concentration and radionuclides of equatorial Pacific deep-sea sediments

The (231Pa/230Th)xs,0 records obtained from two cores from the western (MD97-2138; 1°25'S, 146°24'E, 1900 m) and eastern (ODP Leg 138 Site 849, 0°11.59'N, 110°31.18'W, 3851 m) equatorial Pacific display similar variability over the last 85000 years, i.e. from isotopic stages 1 to 5a, with systematically higher values during the Holocene, isotopic stage 3 and isotopic stage 5a, and lower values, approaching the production rate ratio of the two isotopes (0.093), during the colder periods corresponding to isotopic stages 2 and 4. We have also measured the 230Th-normalized biogenic preserved and terrigenous fluxes, as well as major and trace elements concentrations, in both cores. The (231Pa/230Th)xs,0 results combined with the changes in preserved carbonate and opal fluxes at the eastern site indicate lower productivity in the eastern equatorial Pacific during glacial periods. The (231Pa/230Th)xs,0 variations in the western equatorial Pacific (WEP) also seem to be controlled by productivity (carbonate and/or opal). The generally high (231Pa/230Th)xs,0 ratios (>0.093) of the profile could be due to opal and/or MnO2 in the sinking particles. The profiles of (231Pa/230Th)xs,0 and 230Th-normalized fluxes indicate a decrease in exported carbonate, and possibly opal, during isotopic stages 2 and 4 in MD97-2138. Using 230Th-normalized flux, we also show that sediments from the two cores were strongly affected by sediment redistribution by bottom currents suggesting a control of mass accumulation rates by sediment focusing variability.

Inorganic major, minor, and trace element geochemistry and clay mineralogy of sediments from the Deep Sea Drilling Project Leg 96, Gulf of Mexico

Sediment samples collected at DSDP Leg 96 Mississippi Fan Sites 615, 616, 620, 621, and 623, Orca Basin Site 618, and Pigmy Basin Site 619 were analyzed for 22 major, minor, and trace elements. This study was undertaken to document the downhole variability in inorganic geochemistry between sites. The mineralogy of the clays, including those from Sites 614, 617, and 622 on the fan, was determined by X-ray diffraction to define the principal clay minerals present at the sites, examine any downhole trends in clay mineralogy, and aid in the interpretation of the geochemical signature of the sediments. Clay mineral composition at all the sites is smectite:illite:chlorite:kaolinite in the approximate percentage ratio 50:20:20:10. Geochemical results indicate only slight variation between and within the sites, with the exception of a discrete unit of carbonates that occurs near the bottom of Site 615. Variation in the major, minor, and trace element composition can be explained by a change in the relative abundance of quartz, clay minerals, and carbonates.

Pore water geochemistry of arctic deep sea sediments measured at station MSM16/2_809-1 (REF, Reference)

Pore water and turnover rates were determined for surface sediment cores obtained in 2009 and 2010. The pore water was extracted with Rhizons (Rhizon CSS: length 5 cm, pore diameter 0.15 µm; Rhizosphere Research Products, Wageningen, Netherlands) in 1 cm-resolution and immediately fixed in 5% zinc acetate (ZnAc) solution for sulfate, and sulfide analyses. The samples were diluted, filtered and the concentrations measured with non-suppressed anion exchange chromatography (Waters IC-Pak anion exchange column, waters 430 conductivity detector). The total sulfide concentrations (H2S + HS- + S**2-) were determined using the diamine complexation method (doi:10.4319/lo.1969.14.3.0454). Samples for dissolved inorganic carbon (DIC) and alkalinity measurements were preserved by adding 2 µl saturated mercury chloride (HgCl2) solution and stored headspace-free in gas-tight glass vials. DIC and alkalinity were measured using the flow injection method (detector VWR scientific model 1054) (doi:10.4319/lo.1992.37.5.1113). Dissolved sulfide was eliminated prior to the DIC measurement by adding 0.5 M molybdate solution (doi:10.4319/lo.1995.40.5.1011). Nutrient subsamples (10 - 15 ml) were stored at - 20 °C prior to concentration measurements with a Skalar Continuous-Flow Analyzer (doi:10.1002/9783527613984).

Sulphate reduction rates of arctic deep sea sediments measured at station MSM16/2_809-1 (REF, Reference)

Turnover rates were determined for surface sediment cores obtained in 2009 and 2010. Sulfate reduction (SR) were measured ex situ by the whole core injection method (doi:10.1080/01490457809377722). We incubated the samples at in situ temperature (1.0°C) for 12 hours with carrier-free 35**SO4 (dissolved in water, 50 kBq). Sediment was fixed in 20 ml 20% ZnAc solution for AOM or SR, respectively. Turnover rates were measured as previously described (doi:10.4319/lom.2004.2.171).