Time scale of hydrothermal water-rock reactions in Yellowstone National Park based on radium isotopes and radon

We have measured ²²⁴Ra (3.4 d), ²²⁸Ra (5.7 yr), and ²²⁶Ra (1620 yr) and chloride in hot spring waters from the Norris-Mammoth Corridor, Yellowstone National Park. Two characteristic cold-water components mix with the primary hydrothermal water: one for the travertine-depositing waters related to the Mammoth Hot Springs and the other for the sinter-depositing Norris Geyser Basin springs. The Mammoth Hot Springs water is a mixture of the primary hydrothermal fluid with meteoric waters flowing through the Madison Limestone, as shown by the systematic decrease of the (²²⁸Ra/²²⁶Ra) activity ratio proceeding northward. The Norris Geyser Basin springs are mixtures of primary hydrothermal water with different amounts of cold meteoric water with no modification of the primary hydrothermal (²²⁸Ra/²²⁶Ra) activity ratio. Using a solution and recoil model for radium isotope supply to the primary hydrothermal water, a mean water-rock reaction time prior to expansion at 350°C and supply to the surface is 540 years assuming that 250 g of water are involved in the release of the radium from one gram of rock. The maximum reaction time allowed by our model is 1150 years.     

The behavior of 232Th and the 238U decay chain nuclides during magma formation and volcanism

Concentrations of the members of the ²³⁸U decay chain and ²³²Th were determined in volcanic rocks from convergent plate margins, intraplate volcanoes and oceanic spreading centers. Contemporary and historical volcanic rocks from Mt. St. Helens, Arenal, El Chichon, Hawaii and Iceland and submarine basaltic glass from the Galapagos spreading center all show no fractionation of U and Th in the mantle source or during magma formation at least for the past 300,000 years. Mauna Kea (Hawaii) rocks of alkaline composition greater than 4000 years old and an old submarine basalt show disequilibrium for several of the nuclides in the ²³⁸U decay chain. We interpret these as resulting from post-emplacement processes.     

The behavior of natural and anthropogenic osmium in the Hudson River-Long Island Sound estuarine system

The extent to which riverine Os is trapped in a temperate estuary was the aim of this study. The behavior of Os through the Hudson River, East River and the Long Island Sound (LIS) system is addressed using both natural Os and anthropogenically mobilized Os. The Os concentration ([Os]) and isotopic composition (¹⁸⁷Os/¹⁸⁸Os) of the Mid-Atlantic Bight as inferred from the analysis of a water sample of 31‰ salinity (S) at Vineyard Sound, MA are 46 fM and 1.070, respectively. In comparison, the Hudson River at Newburgh, NY has [Os] = 68 fM and ¹⁸⁷Os/¹⁸⁸Os = 1.265. The Os concentration of the East River at the Whitestone Bridge is 51 fM and remains essentially constant proceeding eastward in the LIS despite the increase of salinity from 20‰ towards the higher value of the Mid-Atlantic Bight. The ¹⁸⁷Os/¹⁸⁸Os ratio of water at Whitestone Bridge is 0.945 and increases eastward through the Sound to 0.979 at 7 km and then to 1.019 at 39.6 km. The behavior of Os through LIS appears to be conservative at S > 20‰. On the basis of Os concentration and isotopic composition we infer that anthropogenic Os is being added to the East River through sewers with the likely isotopic ratio of ∼0.13 and that about 24% of riverine Os must be removed at S ? 20‰. There is a net transport of about 0.4-1 mole of anthropogenic Os per year from the East River into the LIS. The residence time of Os in the ocean at present must be about 39,000 years, unless an independent source of supply of Os can be identified.     

210Pb in GEOSECS water profiles from the North Pacific

Ten GEOSECS profiles from the North Pacific have been analyzed for²¹⁰Pb. GEOSECS²²⁶Ra data on the same profiles are used to calculate²¹⁰Pb excess or deficiency relative to secular equilibrium. The resultant profiles are divisible into a thermocline zone (<2000m) showing an expected decrease with depth, a mid-water zone of about 2000 m showing small constant deficiencies with a zone of increasing deficiency to a bottom zone of about 1000 m having the highest deficiency virtually invariant with depth. The exponentially decreasing portion in the thermocline yields a “diffusion” coefficient of 3 cm²/s. The mid-water deficiencies yield ? model residence times of 400 years northeast of Hawaii decreasing to 100 years at the most marginal stations.     

210Po and 210Pb distributions in ocean water profiles from the Eastern South Pacific

Two ocean profiles from the Peru Basin from regions with different surface productivities were analyzed for total²¹⁰Pb and²⁰¹Po to evaluate the influence of particulates in the water column on their distribution. Comparison with a published²²⁶Ra profile for the region was made. The profile closest to the coast, where upwelling and productivity are high, shows depletion of²¹⁰Pb relative to²²⁶Ra at all depths, with particularly marked excursions from radioactive equilibrium at the surface and in the bottom water.²¹⁰Po appears to be deficient relative to²¹⁰Pb at depth as well. Mean residence times in the deep water, relative to particulate removal from the water column to the sediments, of about 100 years for²¹⁰Pb and about two years for²¹⁰Po are indicated. The profile northwest of the upwelling region shows the²²⁶Ra²¹⁰Pb²¹⁰Po system close to equilibrium at all depths to 1500 m (except for the effect of atmospheric²¹⁰Pb input seen at the surface.     

Eastern Altantic fracture zones as potential disposal sites for radioactive waste

Disposal of radioactive waste in the sea floor of fracture zones associated with the flanks of the Mid-Atlantic Ridge may be a satisfactory alternative to land disposal. Effective physiographic, sedimentary, chemical, and oceanographic barriers exist in these aseismic deep canyons, especially in the eastern Atlantic. In addition, the major producers of radioactive wastes are likely to be near the Atlantic Ocean. If such a disposal strategy is adopted, intensive study of the sedimentologic and oceanographic properties of oceanic fracture zones will be necessary.     

The effects of diagenesis on the redistribution of strontium isotopes in shales

The rubidium-strontium method has often been used in attempts to date shales, but has yielded mixed results. In order to explore the effects of diagenesis on this system, samples of a Miocene shale section collected from an oil well drilled in coastal Louisiana were separated into fractions and analyzed for Sr⁸⁷/Sr⁸⁶, Rb and Sr. The diagenetic changes involve the destruction of detrital mica and feldspar and the formation of an illite-rich clay from smectite. Strontium from interstitial waters, calcium carbonate and adsorbed on the clay minerals is released and then sequestered by the newly forming phases, together with the strontium mobilized from the silicate minerals. Attending these changes there is a trend towards the homogenization of the shale with respect to its strontium isotopes, but diagenesis and homogenization are not complete in the deepest part (5523 m) of the section studied. Therefore, the interpretation of rubidium-strontium shale dates remains uncertain, but the dates in many cases most probably represent the time equal to or younger than the time of the major construction of new phases and the attendant homogenization of the strontium isotopes.     

Molybdenum in marine deposits

The distribution and rates of accumulation of Mo in marine deposits have been determined and compared with the same parameters for U and Mn. High concentrations of Mo are associated both with oxidizing environments represented by the presence of ferro-manganese oxide-rich sediments (where Mo/U ～- 3) and with reducing environments (where Mo/U is about unity). The supply of Mo by streams is more than adequate to balance the measured removal rate in normal deep-sea deposits and no submarine volcanic ‘emanations’ need be involved. On an ocean-wide basis, 4 · 3 μg Mo/cm²/1000 yr is supplied in solution by streams. Of this, 2·0 μg Mo/cm²/1000 yr is removed in deep-sea sediments and manganese nodules. The remaining 2·3 μg Mo/cm²/1000 yr is probably removed in primarily (but not exclusively) near-shore reducing sediments. The average Mo accumulation rate in these environments is about 1000 μg Mo/cm²/1000 yr; thus only 0·23 per cent of the world ocean area need be such reducing sites.     

The distribution of 210Pb and 210Po in the surface waters of the Pacific Ocean

By modelling the observed distribution of²¹⁰Pb and²¹⁰Po in surface waters of the Pacific, residence times relative to particulate removal are determined. For the center of the North Pacific gyre these are τ_Po = 0.6years andτ_Pb = 1.7years. The surface ocean τ_Pb is determined by particulate transport rather than plankton settling. The fact that it is about two orders of magnitude smaller than τ_Pb for the deep ocean implies a sharp change in the adsorptive quality of particles during descent through the water column.