Pyritization of Iron in Sediments from the Continental Slope of the Northern Gulf of Mexico     

John W. Morse  Dwight K. Gledhill  Karen S. Sell  Rolf S. Arvidson 《Aquatic Geochemistry》2002,8(1):3-13

In sediments from the continental slope of the Northern Gulf of Mexico, generally,the degree of iron pyritization (DOP) is low (<0.1) and dissolved sulfide is belowdetection limits (5 M), whereas dissolved Fe is typically about 50 to100 M. Therefore, the dissolution of kinetically reactive iron minerals generallydominates over the rate of sulfide production in sediments throughout this region.However, in sediments where hydrocarbons have been added via seepage from thesubsurface, dissolved-Fe is undetectable, DOP can approach 1, and high concentrationsof dissolved sulfide (up to 11 mM) are commonly present. Even though thesesediments have high total reduced sulfide (TRS) concentrations (typically 150 to370 mol gdw^-1), their average C/S ratio is about 4 times that of normal marine sediments reflecting the major input of hydrocarbons. DOP is significantly (20%) higher when calculated using reactive-Fe extracted by citrate dithionite than by cold 1N HCl. This difference is primarily due to the greater extraction efficiency of the cold HCl method for silicate-Fe. TRS tends to rise to a maximum, and remains close to constant even at high (mM) dissolved sulfide concentrations. These TRS concentrations, therefore, represent the size of the ``kinetically' reactive-Fe pool during early diagenesis.  相似文献   

Polar Coronal Holes During Cycles 22 and 23   总被引：3，自引：0，他引：3  

Harvey  Karen L.  Recely  Frank 《Solar physics》2002,211(1-2):31-52

The National Solar Observatory/Kitt Peak synoptic rotation maps of the magnetic field and of the equivalent width of the He i 1083 nm line are used to identify and measure polar coronal holes from September 1989 to the present. This period covers the entire lifetime of the northern and southern polar holes present during cycles 22 and 23 and includes the disappearance of the previous southern polar coronal hole in 1990 and and formation of the new northern polar hole in 2001. From this sample of polar hole observations, we found that polar coronal holes evolve from high-latitude (60° ) isolated holes. The isolated pre-polar holes form in the follower of the remnants of old active region fields just before the polar magnetic fields complete their reversal during the maximum phase of a cycle, and expand to cover the poles within 3 solar rotations after the reversal of the polar fields. During the initial 1.2–1.4 years, the polar holes are asymmetric about the pole and frequently have lobes extending into the active region latitudes. During this period, the area and magnetic flux of the polar holes increase rapidly. The surface areas, and in one case the net magnetic flux, reach an initial brief maximum within a few months. Following this initial phase, the areas (and in one case magnetic flux) decrease and then increase more slowly reaching their maxima during the cycle minimum. Over much of the lifetime of the measured polar holes, the area of the southern polar hole was smaller than the northern hole and had a significantly higher magnetic flux density. Both polar holes had essentially the same amount of magnetic flux at the time of cycle minimum. The decline in area and magnetic flux begins with the first new cycle regions with the holes disappearing about 1.1–1.8 years before the polar fields complete their reversal. The lifetime of the two polar coronal holes observed in their entirety during cycles 22 and 23 was 8.7 years for the northern polar hole and 8.3 years for the southern polar hole.  相似文献   

Interpreting and testing compositional data     

Alex Woronow  Karen M. Love  John C. Butler 《Mathematical Geology》1989,21(1):61-63

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Silicon and Sulphur in the Inner Envelope of IRC+10216     

Karen Willacy  Isabelle Cherchneff 《Astrophysics and Space Science》1997,251(1-2):49-54

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Ephemeral active regions     

Karen L. Harvey  Sara F. Martin 《Solar physics》1973,32(2):389-402

Ephemeral active regions attain maximum development within 1 day or less of their initial appearance and are typically observed for 1–2 days. They appear mostly as small bipolar regions having a typical dimension of about 30000 km and a maximum total flux of the order of 10²⁰ Mx. The ephemeral regions generally do not produce sunspots and flares, though they are identified in H as small active centers.Our observations indicate that the ephemeral regions are frequently generated both near large active centers and in extensive quiet areas of the Sun. The location of emerging ephemeral regions does not appear to be associated with the distribution of the existing network fields. As many as 100 ephemeral regions may form per day. On the average, as much flux may erupt in the form of small ephemeral regions as erupts in larger active centers.The latitude distribution of ephemeral regions appears to be much wider than that of sunspots and major active centers. Their frequency of occurrence does not appear to follow the sunspot cycle.  相似文献   

Formation of extremely F-rich hydrous melt fractions and hydrothermal fluids during differentiation of highly evolved tin-granite magmas: a melt/fluid-inclusion study   总被引：2，自引：0，他引：2  

Rainer?ThomasEmail author  Hans-Jürgen?F?rster  Karen?Rickers  James?D.?Webster 《Contributions to Mineralogy and Petrology》2005,148(5):582-601

Quartz crystals from topaz–zinnwaldite–albite granites from Zinnwald (Erzgebirge, Germany) contain, in addition to primary and secondary fluid inclusions (FIs), abundant crystalline silicate-melt inclusions (MIs) with diameters up to 200 m. These MIs represent various stages of evolution of a highly evolved melt system that finally gave rise to granite-related Sn–W mineralization. The combination of special experimental techniques with confocal laser Raman-microprobe spectroscopy and EMPA permits precise measurement of elevated contents of H₂O, F, and B in re-homogenized MIs. The contents of H₂O and F were observed to increase from 3 to 30 and 1.9 to 6.4 wt%, respectively, during magma differentiation. However, there is a second MI group, very rich in H₂O, with values up to 55 wt% H₂O and an F concentration of approximately 3 wt%. Ongoing enrichment of volatiles H₂O, F, B, and Cl and of Cs and Rb can be explained in terms of magma differentiation triggered by fractional crystallization and thus, is suggested to reflect elemental abundances in natural magmas, and not boundary-layer melts. Partitioning between melt and cogenetic fluids has further modified the magmatic concentrations of some elements, particularly Sn. The coexistence of two types of MIs with primary FIs indicates fluid saturation early in the history of magma crystallization, connected with a continuous sequestration of Sn, F, and B. The results of this study provide additional evidence for the extraordinary importance of the interplay of H₂O, F, and B in the enrichment of Sn during magma differentiation by decreasing the viscosity of and increasing the diffusivity in the melts as well as by the formation of various stable fluoride complexes in the melt and coexisting fluid.

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Rainer ThomasEmail: Phone: +49-331-2881474

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CATALOG OF THE COLLECTION OF METEORITES AT THE UNIVERSITY OF CALIFORNIA,LOS ANGELES (THE LEONARD COLLECTION)     

John T. Wasson  Edward R. D. Scott  Karen L. Robinson 《Meteoritics & planetary science》1974,9(1):85-98

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Liquid water on Mars: An energy balance climate model for CO₂/H₂O atmospheres     

M.I. Hoffert  A.J. Callegari  C.T. Hsieh  W. Ziegler 《Icarus》1981,47(1):112-129

Geologic evidence of the prior existence of liquid water on Mars suggests surface temperatures T_s were once considerably warmer than at present; and that such a condition may have arisen from a larger atmospheric greenhouse. Here we develop a simple climate model for a CO₂/H₂O Mars atmosphere including water vapor-longwave opacity feedback in the atmosphere and temperature-albedo feedback at surface icecaps, under the assumption that once the Martian surface pressure was p_s ≥ 1 atm CO₂. Longwave flux to space is computed as a function of T_s and p_s using band-absorption models for the effect of the 15-μm fundamental, and the 10- and 15-μm hot bands, of the CO₂ molecule; as well as the pure rotation bands and e continuum of H₂O. The derived global radiative balance predicts a global mean surface temperature of 283°K at 1 atm CO₂. When the emission model is coupled to a latitudinally resolved energy balance climate model, including the effect of poleward heat transfer by atmospheric baroclinic eddies, the solutions vary, depending on p_s. We considered two cases: (1) the present Mars (p_s ? 0.007 atm) with pressure-buffering by solid CO₂ icecaps, and limited poleward heat flux by the atmosphere; and (2) a hypothetical “hot Mars” (p_s ? 1.0 atm), whose much higher CO₂ amount augmented by H₂O evaporative feedback yields a theoretical T_s distribution with latitude admitting liquid water over 95% of the surface, water icecaps at the poles, and a diminished equator-to-pole temperature gradient relative to the present.  相似文献   

Acknowledgment   总被引：1，自引：0，他引：1  

Karen L. Harvey 《Solar physics》1985,101(1-2):V-V

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Double ionization of atomic oxygen by electron impact     

D.L. Ziegler  J.H. Newman  K.A. Smith  R.F. Stebbings 《Planetary and Space Science》1982,30(5):451-456

Laboratory measurements of the cross-sections for double ionization of atomic oxygen by electrons are presented for energies from threshold to ～ 400 eV. A maximum cross-section of about 5.6 × 10^?18 cm² is observed at an electron energy of approx. 200 eV. Absolute cross-sections are obtained from measurements of the ratio of the cross-sections for double and single ionization, coupled with absolute cross-sections for single ionization previously measured by other investigators. The possible effects of excited oxygen reactants are examined, and the reported cross-sections are considered to be characteristic of ground state oxygen atoms.  相似文献