1,721,029 research outputs found
Dissolved and particulate trace metals in hydrothermal plumes at the Mid?Atlantic Ridge
No full textSeawater samples from the non?buoyant plume have been collected at the TAG (26°N) and Snakepit (23°N) hydrothermal sites on the Mid?Atlantic Ridge (MAR), and analysed for dissolved (<0.4 µm) and particulate (>0.4 µm) trace metals. Up to 50% of vent fluid Fe is present in the <0.4 µm fraction in the non?buoyant plume. Increases in particulate concentrations of Cd are accompanied by a reduction in dissolved Cd to levels below ambient seawater. We show that dissolved Cd is scavenged from seawater in the buoyant section of the plume while Cd re?dissolves from the particles in the non?buoyant plume. Up to 43% of hydrothermally injected Cu is found in the <0.4 µm fraction in the non?buoyant plume
Intra-test variation in the trace element composition of planktonic foraminifera: implications for biomineralization processes (abstract of paper presented at: 17th Annual V. M. Goldschmidt Conference Cologne, Germany August 2007)
No full textThe chemistry of hydrothermal fluids from the Broken Spur site, 29°N Mid-Atlantic ridge
No full textHydrothermal fluids have been collected from three high temperature (360–364°C) vents from Broken Spur (29°10.08?N, 43°10.46?W; water depth ? 3100 m). This is only the fourth site on a slow spreading ridge from which such fluids have been collected. Compared to other vent sites, the hydrothermal fluids are enriched in Li (1035 ?M) and have lower dissolved Mn (?250 ?M) and Sr (43 ?M) concentrations. The boron isotope systematics indicate that substantial removal (>50%) of seawater B has occurred in the low-temperature portion of the hydrothermal convection cell. In addition, low temperature removal of seawater Sr is ?10% greater at Broken Spur compared to similar vent sites in the Pacific where spreading rates are faster. A low Eu anomaly (11 ± 3) and a View the MathML source ratio (10.8) intermediate between pristine and weathered basalt suggest that the vent fluids have interacted with a component of basalt that has previously undergone low-temperature weathering. the fluids are 14% depleted in Cl relative to seawater. Supercritical phase separation appears to be the only reasonable process that may account for the fluid depletion
The lithium isotope composition of international rock standards
No full textWe present the results of analysis of the Li isotope composition of open ocean seawater, nine international rock standards and a C1 chondrite. In addition, we suggest some modifications of the chemical preparation techniques for analysis of lithium isotopes in low concentration samples that give precise isotope ratios by thermal ionisation mass spectrometry (TIMS). The aim of this study is to provide a benchmark for ensuring the reliability of Li isotope data between different laboratories by TIMS and other isotope ratio techniques, including multi collector-inductively coupled plasma-mass spectrometry and ion probe
Near-field variability of the TAG non-buoyant plume, 26°N, Mid-Atlantic Ridge
No full textWe report the initial results of a nine hour monitoring of the non-buoyant plume above the TAG hydrothermal vent field at 26°N on the Mid-Atlantic Ridge. A CTD (conductivity, temperature and pressure) and nephelometer (particle sensor) were continuously raised and lowered through the non-buoyant plume for nine hours at a site situated ? 100 m south of the hydrothermal mound. This method permits a detailed record of the variability of the non-buoyant plume close to the vent field to be made. Our results show that the particulate maximum of the non-buoyant plume appears ? 150 m lower in the water column at the start and end of the record, compared with profiles recorded towards the middle of the record. A corresponding structure also appears in the temperature and salinity records, with the result that the plume particle maximum resides on the ?? ? 27.8035 isopycnal throughout. Modelling of the rise height of an axisymmetric plume can only account for ? 95 m of the variability in the final level of neutral buoyancy. Plume bending due to currents is a likely explanation for the recorded temporal variability
Marine geochemical cycles of the alkali elements and boron: the role of sediments
No full textWe have analysed the concentrations of Li, K, Rb, Cs, and B, and the isotopic ratios of Li and B of a suite of pore fluids recovered from ODP Sites 1037 (Leg 169; Escanaba Trough) and 1034 (Leg 169S; Saanich Inlet). In addition, we have analysed dissolved K, Rb, and Cs concentrations for estuarine mixing of the Ganges–Brahmaputra river system. Together, these data sets have been used to assess the role of sediments in the marine geochemical cycles of the alkali elements and boron.Uptake onto clay minerals during estuarine mixing removes 20–30% of the riverine input of dissolved Cs and Rb to the oceans. Prior to this study, the only other recognised sink of Rb and Cs was uptake during low-temperature alteration of the oceanic crust. Even with this additional sink there is an excess of inputs over outputs in their modern oceanic mass balance. Pore fluid data show that Li and Rb are transferred into marine sediments during early diagenesis. However, modeling of the Li isotope systematics of the pore fluids from Site 1037 shows that seawater Li taken up during marine sedimentation can be readily returned to solution in the presence of less hydrated cations, such as NH4+. This process also appears to result in high concentrations of pore fluid Cs (relative to local seawater) due to expulsion of adsorbed Cs from cation exchange sites.Flux calculations based on pore fluid data for a series of ODP sites indicate that early diagenesis of clay sediments removes around 8% of the modern riverine input of dissolved Li. Although NH4+-rich fluids do result in a flux of Cs to the oceans, on the global scale this input only augments the modern riverine Cs flux by ~3%. Nevertheless, this may have implications for the fate of radioactive Cs in the natural environment and waste repositories. <br/
The behaviour of Mg and Li isotopes during the dissolution and precipitation of silicate minerals (abstract of paper presented at: 18th Annual V. M. Goldschmidt Conference Vancouver, Canada, July 2008)
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Primitive lithium isotope signatures in CR carbonaceous chondrites? (abstract of paper presented at: 19th Annual V. M. Goldschmidt Conference, Davos, Switzerland, 21-26 June 2009)
No full textAspects of the geochemistry of dissolved and particulate Cd, Cu, Ni, Co and Pb in the Dover Strait
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