Composition of suspended matter and bottom sediments from the Atlantic Ocean and its seas

The book summarizes data on distribution and composition of sedimentary material suspended in waters of the Atlantic Ocean and its seas. Results of observations of Soviet and foreign expeditions are given. Distribution of suspended matter in sections across the ocean, as well as in the most studied seas are shown. New data on grain size, mineral and chemical composition of suspended matter are published. Summary of history of investigation of bottom sediments from the Atlantic Ocean from the first scientific cruises to the present is done. A brief description of sediment types in the ocean and a detailed description of Mediterranean Sea sediments are given.

Chemical composition of ocean phosphorites and hosted sediments

The book provides an overview of recent data on processes of dispersion and concentration of phosphorus in marine sedimentation. Distribution, chemical and mineral compositions, structure and age of phosphorites occurring on the floor are described. Phosphorites are one of potential mineral resources of the World Ocean. A scheme of multistage-oceanic phosphorite formation is motivated. Modern and pre-Quaternary phosphorite formations in the ocean are paralleled.

Halogene concentrations and iodine isotopic composition in pore water on Hydrare Ridge, Cascadia continental margin

We report iodine and bromine concentrations in a total of 256 pore water samples collected from all nine sites of Ocean Drilling Program Leg 204, Hydrate Ridge. In a subset of these samples, we also determined iodine ages in the fluids using the cosmogenic isotope 129I (T1/2 = 15.7 Ma). The presence of this cosmogenic isotope, combined with the strong association of iodine with methane, allows the identification of the organic source material responsible for iodine and methane in gas hydrates. In all cores, iodine concentrations were found to increase strongly with depth from values close to that of seawater (0.0004 mM) to concentrations >0.5 mM. Several of the cores taken from the northwest flank of the southern summit show a pronounced maximum in iodine concentrations at depths between 100 and 150 meters below seafloor in the layer just above the bottom-simulating reflector. This maximum is especially visible at Site 1245, where concentrations reach values as high as 2.3 mM, but maxima are absent in the cores taken from the slope basin sites (Sites 1251 and 1252). Bromine concentrations follow similar trends, but enrichment factors for Br are only 4-8 times that of seawater (i.e., considerably lower than those for iodine). Iodine concentrations are sufficient to allow isotope determinations by accelerator mass spectrometry in individual pore water samples collected onboard (~5 mL). We report 129I/I ratios in a few samples from each core and a more complete profile for one flank site (Site 1245). All 129I/I ratios are below the marine input ratio (Ri = 1500x10**-15). The lowest values found at most sites are between 150 and 250x10**-15, which correspond to minimum ages between 40 and 55 Ma, respectively. These ages rule out derivation of most of the iodine (and, by association, of methane) from the sediments hosting the gas hydrates or from currently subducting sediments. The iodine maximum at Site 1245 is accompanied by an increase in 129I/I ratios, suggesting the presence of an additional source with an age younger than 10 Ma; there is indication that younger sources also contribute at other sites, but data coverage is not yet sufficient to allow a definitive identification of sources there. Likely sources for the older component are formations of early Eocene age close to the backstop in the overriding wedge, whereas the younger sources might be found in recent sediments underlying the current locations of the gas hydrates.

(Table 1) Chemical composition of buried manganese noduls and host sediments of ODP Hole 138-854C

Two manganese (Mn) nodules were found in upper Miocene sediments in Hole 854C at a depth of 32.12 mbsf (Samples 138-854C-5H-1,0-2 cm, and -6H-1, 2-4 cm). In structure and composition, the lower nodule is similar to the Pleistocene surface nodules associated with radiolarian ooze from the Clarion-Clipperton Nodule Province. The upper nodule resembles those occurring on pelagic clay from the northern margin of that province.

Organic matter in bottom sediments of the Northeast Pacific

The book is devoted to study of diagenetic changes of organic matter and mineral part of sediments and interstitial waters of the Pacific Ocean due to physical-chemical and microbiological processes. Microbiological studies deal with different groups of bacteria. Regularities of quantitative distribution and the role of microorganisms in geochemical processes are under consideration. Geochemical studies highlight redox processes of the early stages of sediment diagenesis, alterations of interstitial waters, regularities of variations in chemical composition of iron-manganese nodules.

Vertical variations in basic salt composition of interstitial waters from Pacific sediments

Basic chemical composition of interstitial water in sediments of the Northwestern Pacific along a profile from the continental shelf of the Japan Trench to the ocean bed is discussed. Transformation of interstitial water in sediments rich in organic matter on the continental shelf and at the bottom of the Japan Trench is indicated. Variation in the vertical direction of elementary constituents of interstitial salt solution and variations in certain biogenic elements permit to make conclusions concerning processes taking place in sediments during sedimentation and diagenesis. These processes cause both metamorphism of water and transformation of organic and mineral content of sediments.

Composition and accumulation rates of bottom sediments from Core ASV16-1372, Voring Plateau

Based on sedimentological, mineralogical, geochemical, and micropaleontological data on comprehensively investigated Core ASV16-1372, Late Pleistocene - Holocene sedimentation history is reconstructed for the Voring marginal plateau (continental margin of the Norwegian Sea). An age model constructed is based on correlation with several adjacent cores, for which AMS radiocarbon datings are available. Lithostratigraphic correlation made it possible to compare stratigraphic division of Core ASV16-1372 with other cores sampled on the Voring Plateau and the shelf and continental slope off Central Norway. It is concluded that compositional and structural features of bottom sediments are correlated with paleoclimatic and paleoceanographic changes, variations in provenances, as well as agents and pathways of sedimentary material transport.

Chemical composition of rocks from the Kammu Seamount and from low atolls of the Western Indian Ocean

Devoted to studies of phosphatized rocks from the Kammu Seamount.

Mesocosm experiment 2012 on warming and acidification effects on phytoplankton biomass and chemical composition

We investigated the impacts of predicted ocean acidification and future warming on the quantity and nutritional quality of a natural phytoplankton autumn bloom in a mesocosm experiment. Since the effects of CO2-enrichment and temperature have usually been studied independently, we were also interested in the interactive effects of both aspects of climate change. Therefore, we used a factorial design with two temperature and two acidification levels in a mesocosm experiment with a Baltic Sea phytoplankton community. Our results show a significant time-dependent influence of warming on phytoplankton carbon, chlorophyll a as well as POC. Phytoplankton carbon for instance decreased by more than a half with increasing temperature at bloom time. Additionally, elemental carbon to phosphorus ratios (C:P) increased significantly by approximately 5-8 % under warming. Impacts of CO2 or synergetic effects of warming and acidification could not be detected. We suggest that temperature-induced stronger grazing pressure was responsible for the significant decline in phytoplankton biomass. Our results suggest that biological effects of warming on Baltic Sea phytoplankton are considerable and will likely have fundamental consequences for the trophic transfer in the pelagic food-web.

Composition of pore water and diagenetic carbonates of ODP Site 123-765

Degradation of organic matter in slightly organic-rich (1 wt% organic carbon) Neogene calcareous turbidites of the Argo Basin at Site 765 by sulfate reduction results in pore-water phosphate, ammonium, manganese, and carbonate alkalinity maxima. Pore-water calcium and magnesium decrease in the uppermost 100 meters below seafloor (mbsf) in response to the precipitation of calcian dolomite with an average composition of Ca1.15Mg0.83Fe0.02(CO3)2. Clear, euhedral dolomite rhombs range from <1 to 40 µm in diameter and occur in trace to minor amounts (<1-2 wt%) in Pleistocene to Pliocene sediment (62-210 mbsf) The abundance of dolomite increases markedly (2-10 wt%) in Miocene sediment (210-440 mbsf). The dolomite is associated with diagenetic sepiolite and palygorskite, as well as redeposited biogenic low-Mg calcite and aragonitic benthic foraminifers. Currently, dolomite is precipitating at depth within the pore spaces of the sediment, largely as a result of aragonite dissolution. The rate of aragonite dissolution, calculated from the pore-water strontium profile, is sufficient to explain the amount of dolomite observed at Site 765. A foraminiferal aragonite precursor is further supported by the carbon and oxygen isotopic compositions of the dolomite, which are fairly close to the range of isotopic compositions observed for Miocene benthic foraminifers. Dolomite precipitation is promoted by the degradation of organic matter by sulfate-reducing bacteria because the lower pore-water sulfate concentration reduces the effect of sulfate inhibition on the dolomite reaction and because the higher carbonate alkalinity increases the degree of saturation of the pore waters with dolomite. Organic matter degradation also results in the precipitation of pyrite and trace amounts of apatite (francolite), and the release of iron and manganese to the pore water by reduction of Fe and Mn oxides. Spherical, silt-sized aggregates of microcrystalline calcian rhodochrosite occur in trace to minor amounts in Lower Cretaceous sediment from 740 to 900 mbsf at Site 765. A negative carbon isotopic composition suggests that the rhodochrosite formed early in the sulfate reduction zone, but a depleted oxygen isotopic composition suggests that the rhodochrosite may have recrystallized at deeper burial depths.