(Table 2) Composition of the deapest pore fluids from ODP Holes 168-1030B and 168-1031A

On the eastern flank of the Juan de Fuca Ridge, reaction between upwelling basement fluid and sediment alters hydrothermal fluxes of Ca, SiO2(aq), SO4, PO4, NH4, and alkalinity. We used the Global Implicit Multicomponent Reactive Transport (GIMRT) code to model the processes occurring in the sediment column (diagenesis, sediment burial, fluid advection, and multicomponent diffusion) and to estimate net seafloor fluxes of solutes. Within the sediment section, the reactions controlling the concentrations of the solutes listed above are organic matter degradation via SO4 reduction, dissolution of amorphous silica, reductive dissolution of amorphous Fe(III)-(hydr)oxide, and precipitation of calcite, carbonate fluorapatite, and amorphous Fe(II)-sulfide. Rates of specific discharge estimated from pore-water Mg profiles are 2 to 3 mm/yr. At this site the basement hydrothermal system is a source of NH4, SiO2(aq), and Ca, and a sink of SO4, PO4, and alkalinity. Reaction within the sediment column increases the hydrothermal sources of NH4 and SiO2(aq), increases the hydrothermal sinks of SO4 and PO4, and decreases the hydrothermal source of Ca. Reaction within the sediment column has a spatially variable effect on the hydrothermal flux of alkalinity. Because the model we used was capable of simulating the observed pore-water chemistry by using mechanistic descriptions of the biogeochemical processes occurring in the sediment column, it could be used to examine the physical controls on hydrothermal fluxes of solutes in this setting. Two series of simulations in which we varied fluid flow rate (1 to 100 mm/yr) and sediment thickness (10 to 100 m) predict that given the reactions modeled in this study, the sediment section will contribute most significantly to fluxes of SO4 and NH4 at slow flow rates and intermediate sediment thickness and to fluxes of SiO2(aq) at slow flow rates and large sediment thickness. Reaction within the sediment section could approximately double the hydrothermal sink of PO4 over a range of flow rates and sediment thickness, and could slightly decrease (by

Sulphur isotope composition in the Gulf of California and the Eastern 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.

Composition of interstitial waters from sediments of the Gulf of California

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.

Chemical composition of sepiolites and palygorskites from bottom sediments of the Eastern Indian

In fault zones of the East Indian Ridge and adjacent areas of ocean floor almost monomineral sepiolite- and palygorskite clays have been found. They have been studied by a complex of optical and physical methods. Formation of authigenic sepiolites and palygorskite had occurred under influence of Mg- and Si-rich hydrothermal solutions by metasomatic replacement of montmorillonite clays, or by precipitation from saturated solutions in cracks of various rocks.