The Sensitivity of Remedial Strategies to Design Criteria     

David P. Ahlfeld  Edward H. Hill  III 《Ground water》1996,34(2):341-348

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Zinc and cadmium metabolism in euglena gracilis: Metal distribution in normal and zinc-deficient cells     

David J. Gingrich  David H. Petering  Frank Shaw III   《Marine environmental research》1984,14(1-4)

The effect of cadmium (5 μ/ml) on the growth of Euglena gracilis is moderated by the addition of supplemental zinc levels above the normal 1 μ/ml level found in the growth medium. Gel chromatography reveals that th majority (ca. 85%) of cytosolic cadmium is localized in a cadmium-binding protein (CdBP). The CdBP appears to elute in a position slightly lower in molecular weight than mammalian metallothionein, contains thiol, and upon ion-exchange chromatography elutes in multiple peaks at ionic strengths greater than mammalian metallothioneins. The remaining cadmium is associated with high molecular weight components. Cytosolic zinc is found primarily (> 80%) in a low molecular weight peak distinct from cadmium, with the remainder as high molecular weight species. As the cells become zinc-deficient and cease proliferation, zinc is lost from the low molecular weight peak while, based on cytosolic protein, the zinc content of the high molecular weight peak remains essentially constant.  相似文献   

Seasonal maturity and size at age of Loligo pealeii in waters of southern New England     

Macy  William K.  III; Brodziak  Jon K. T. 《ICES Journal of Marine Science》2001,58(4):852-864

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Reduction of iodate in seawater during Arabian Sea shipboard incubations and in laboratory cultures of the marine bacterium Shewanella putrefaciens strain MR-4     

Anna M. Farrenkopf  Michael E. Dollhopf  Sinad Ní Chadhain  George W. Luther  III  Kenneth H. Nealson 《Marine Chemistry》1997,57(3-4)

Shipboard incubations from the US JGOFS cruise to the Arabian Sea (TN045) March, 1995 showed evidence of iodate reduction in 0.45 μ (Gelman Supor membrane) filtered seawater samples collected from intermediate depths (200–600 m) within the oxygen minimum zone (OMZ). Inorganic chemical reduction of iodate in these samples was ruled out as no free sulfide was measurable and concentrations of ammonia and nitrite were found to be less than 5 μM. To examine whether the reduction of iodate observed at sea could have been the result of bacterial metabolism, reduction of iodate (IO₃⁻) to iodide (I⁻) by Shewanella putrefaciens strain MR-4 was studied in artificial seawater using electrochemical methods. MR-4 is a ubiquitous marine bacterium which may be of considerable importance when considering redox zonation in the water column because it is a facultative anaerobe and may switch amongst a suite of electron acceptors to support metabolism. In all experiments MR-4 reduced all iodate to iodide. The rate of formation of [I⁻]in the culture followed pseudo-first order kinetics. This is the first report of the marine bacterial reduction of iodate where the concentrations of iodide and iodate were measured directly. Our results may help to explain the depth distribution of iodine speciation reported in productive waters like the Arabian Sea and for the first time couple iodine speciation with bacterial productivity in the ocean.  相似文献   

What controls dissolved iron concentrations in the world ocean? — a comment     

George W. Luther  III  Jingfeng Wu 《Marine Chemistry》1997,57(3-4)

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Rates of oxygen transfer from air bubbles to aqueous NaCl solutions at various temperatures     

Stefan A Zieminski  Robert M Hume III  Robert Durham 《Marine Chemistry》1976,4(4):333-346

Experiments have been conducted to investigate the effects of temperature on the interfacial surface area and on the rate of oxygen transfer from air bubbles dispersed in aqueous NaCl solutions. Tests were also conducted to estimate the effects of salt concentration on the size of the bubbles. In addition to NaCl solutions, seawater was used in some tests. The temperature effects were investigated at 5, 10, 15, 20, 25, and 30°C. The results showed a pronounced effect of the salt on the size of the bubbles, which first decreased sharply with increasing concentration, but showed no further drop when the concentration was increased beyond 0.6 M. Both in seawater and in the 0.6 M solution, the mass transfer rate, K_LA, increased almost linearly when temperature was increased within the range from 5 to 25°C. The salt solution, as well as the seawater, showed an increase of K_LA of 60–70% over that in pure water at the same temperatures. This effect was the result of increased surface area of bubbles because of decreased coalescence. The increase in surface area was strongly temperature dependent, especially between 15 and 20°C. Contrary to this behavior the surface area in pure water showed, practically, no temperature dependence. The results are explained and discussed on the basis of ion-water interactions.  相似文献   

The Arctic as a trigger for glacial terminations   总被引：1，自引：0，他引：1  

Douglas G. Martinson  Walter C. Pitman III 《Climatic change》2007,80(3-4):253-263

We propose a hypothesis to explain the very abrupt terminations that end most of the glacial episodes. During the last glaciation, the buildup and southerly expansion of large continental ice-sheets in the Northern Hemisphere and extensive cover of sea ice in the N. Pacific and the N. Atlantic imposed a much more zonal climatic circulation system than exists today. We hypothesize that this, in combination with the frigid (dry) polar air led to a significant decrease in freshwater runoff into the Arctic Ocean. In addition the freshwater contribution of the fresher Pacific water was completely eliminated by the emergence of the Bering Strait (sill depth 50 m). As the Arctic freshwater input was depleted, regions of the Arctic Ocean lost surface stability and eventually overturned, bringing warmer deep water to the surface where it melted the overlying sea ice. This upwelled water was quickly cooled and sank as newly formed deep water. For sustained overturn events, such as might have occurred during the peak of very large glacial periods (i.e. the last glacial maximum), the voluminous deep water formed would eventually overflow into the Nordic Seas and North Atlantic necessitating an equally voluminous rate of return flow of warmer surface waters from the North Atlantic thus breaking down the Arctic's zonal isolation, melting the expansive NA sea ice cover and initiating oceanic heating of the atmosphere over the ice-sheets bordering the NA. We suggest that the combined effect of these overturn-induced events in concert with a Milankovitch warming cycle, was sufficient to drive the system to a termination. We elaborate on this proposed sequence of events, using the model for the formation of the Weddell Sea polynya as proposed by Martinson et al. (1981) and various, albeit sparse, data sets from the circum-Arctic region to apply and evaluate this hypothesis to the problem of glacial terminations.  相似文献   

Galaxy aggregates in the Coma cluster     

Christopher J. Conselice  & John S. Gallagher  III 《Monthly notices of the Royal Astronomical Society》1998,297(2):L34-L38

We present evidence for a new morphologically defined form of small-scale substructure in the Coma cluster, which we call galaxy aggregates. Aggregates are dominated by a central galaxy, which is on average 5 mag brighter than the smaller aggregate members, nearly all of which lie to one side of the central galaxy. We have found three such galaxy aggregates: two dominated by the S0 galaxies RB 55 and RB 60, and one by the starbursting SBb NGC 4858.   RB 55 and 60 are both equidistant between the two dominant D galaxies NGC 4874 and 4889, while NGC 4858 is located near the large E0 galaxy NGC 4860. All three central galaxies have redshifts consistent with Coma cluster membership. We describe the spatial structures of these unique objects, and suggest several possible mechanisms to explain their origin. These include: chance superpositions from background galaxies, interactions between other galaxies and with the cluster gravitational potential, and ram pressure. We conclude that the most probable scenario of creation is an interaction with the cluster through its gravitational potential.  相似文献   

Utilization of Intrinsic Boron Isotopes as Co-Migrating Tracers for Identifying Potential Nitrate Contamination Sources   总被引：1，自引：0，他引：1  

James M. Leenhouts  R.L. Basset  T. Maddock III 《Ground water》1998,36(2):240-250

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Structurally controlled fluid flow during contact metamorphism in the Ritter Range pendant, California, USA   总被引：1，自引：0，他引：1  

John M. Ferry  Sorena S. Sorensen  Douglas Rumble III. 《Contributions to Mineralogy and Petrology》1998,130(3-4):358-378

The mineralogy and O-isotope geochemistry of siliceous limestones from the Ritter Range pendant constrain the geometry and amount of fluid flow during contact metamorphism associated with emplacement of a pluton of the Sierra Nevada Batholith. Wollastonite (Wo) replaces calcite (Cal) + quartz (Qtz) on a layer-by-layer basis in homoclinal beds that strike NW and dip almost vertically. At the peak of metamorphism (P≈ 1500 bars, T≈ 600 °C) fluid in equilibrium with Cal, Qtz, and Wo has composition XCO₂=0.28, requiring that the Wo-forming reaction was driven by infiltration of reactive H₂O-rich fluid. The spatial distribution of Wo and Cal + Qtz records that peak metamorphic fluid flow was layer-parallel, upward. Bounds on the prograde time-integrated fluid flux associated with formation of Wo are set by: (1) the overlap in O-isotope composition between Wo-bearing and Wo-free rocks (>245 mol fluid/cm² rock); (2) the amount of fluid that would drive the Wo-reaction front upward to the present level of exposure from a point at depth where Cal, Qtz, and Wo would be in equilibrium with pure CO₂ (<1615 mol/cm²). Back-reaction of Wo to Cal + Qtz records an additional time-integrated retrograde fluid flux of ≈ 200–1000 mol/cm². The direction and amount of flow inferred from mineralogical and isotopic data agree with the results of the hydrologic model for metamorphic fluid flow in the area of Hanson et al. (1993). Fingers of Wo-bearing rock that extend farthest from the fluid source along contacts between limestone and more siliceous rocks point to strong control of flow geometry at the 0.1–100 m scale exerted by premetamorphic structures. Studies that neglect structural control at this scale may fail to predict correctly fundamental aspects of contact metamorphic fluid flow. Received: 27 January 1997 / Accepted: 2 October 1997  相似文献