Chemical element contents and speciations in bottom sediments from the Transpacific profile

The paper deals with regularities of distribution of iron, manganese, copper, nickel, and vanadium in interstitial waters from different lithofacies types of bottom sediments on the profile from the coast of Mexico to the Wake Atoll in the Pacific Ocean. With increasing distance from the shore and with transition from reduced coastal sediments to oxidized deep-sea red clays concentration of iron and manganese in the interstitial waters greatly decreases. Elevated concentration of dissolved iron (0.34 mg/l) was observed only in highly reduced terrigenous sediments from the shelf and continental slope of Mexico. The highest concentrations of manganese (13.2 mg/l) were measured in hemipelagic carbonate-siliceous-clayey sediments. Compared to Pacific seawater interstitial waters are enriched in Fe, Mn, Cu, Ni, V. Interstitial waters contain only from 0.000004 to 1.2% of total contents of these elements in bottom sediments.

Chemical composition of sediment core GeoB12309-5 from the northern Arabian Sea, its pore water profile and age depth relationship as well as CTD data obtained during cruise M74/3

The Arabian Sea off the Pakistan continental margin is characterized by one of the world's largest oxygen minimum zones (OMZ). The lithology and geochemistry of a 5.3 m long gravity core retrieved from the lower boundary of the modern OMZ (956 m water depth) were used to identify late Holocene changes in oceanographic conditions and the vertical extent of the OMZ. While the lower part of the core (535 - 465 cm, 5.04 - 4.45 cal kyr BP, Unit 3) is strongly bioturbated indicating oxic bottom water conditions, the upper part of the core (284 - 0 cm, 2.87 cal kyr BP to present, Unit 1) shows distinct and well-preserved lamination, suggesting anoxic bottom waters. The transitional interval from 465 to 284 cm (4.45 - 2.87 cal kyr BP, Unit 2) contains relicts of lamination which are in part intensely bioturbated. These fluctuations in bioturbation intensity suggest repetitive changes between anoxic and oxic/suboxic bottom-water conditions between 4.45 - 2.87 cal kyr BP. Barium excess (Baex) and total organic carbon (TOC) contents do not explain whether the increased TOC contents found in Unit 1 are the result of better preservation due to low BWO concentrations or if the decreased BWO concentration is a result of increased productivity. Changes in salinity and temperature of the outflowing water from the Red Sea during the Holocene influenced the water column stratification and probably affected the depth of the lower boundary of the OMZ in the northern Arabian Sea. Even if we cannot prove certain scenarios, we propose that the observed downward shift of the lower boundary of the OMZ was also impacted by a weakened Somali Current and a reduced transport of oxygen-rich Indian Central Water into the Arabian Sea, both as a response to decreased summer insolation and the continuous southward shift of the Intertropical Convergence Zone during the late Holocene.

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.

Ex situ microsensor profiles of sulfide concentration and pH in/outside mat 1 (MSM15/1_492-PUC1) measured during the MSM15/1 cruise in 2010 (Black Sea)

Biogeochemical measurements in sediment cores collected with the submersible JAGO (pusch cores) and a TV-MUC in the Black Sea during MSM15/1, Northwest Crimea (HYPOX Project), at water depths between 152-156 m. A series of microbial mats were sampled on the hypoxic region of the Crimean Shelf. Concentrations of organic carbon (Corg) and nitrogen (N) were measured on finely powdered, freeze-dried subsamples of sediment using a using a Fisons NA-1500 elemental analyzer. For organic carbon determination samples were pre-treated with 12.5% HCl to remove carbonates. Chlorophyll a (chl a), phaeopigments (PHAEO) and chloroplastic pigment equivalents (CPE) was measured according to Schubert et al., (2005; doi:10.1029/2004GC000837) and total hydrolyzable amino acids (THAA) and single amino acid: ASP, GLU, SER, HIS, GLY, THR, ARG, ALA, TYR, MET, VAL, PHE, ILE, LEU, LYS following Dauwe et al., 1998. High-resolution ex situ sulfide and pH microprofiles, were assessed only for station MSM15/1_492_PUC1. "in mat 1, 2 and 3" refers to 3 different profiles in 3 different spots of the microbial mat, whereas "outside mat", a profile outside the microbial mat.