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1.
Technetium isotopes 97Tc, 98Tc and 99Tc decay to 97Mo, 98Ru and 99Ru, with half-lives of 2.6 My, 4.1 My, and 0.21 My respectively. If there were early solar system processes that resulted in significant fractionation of Tc from the daughter elements, decay of extant Tc could have led to the creation of Mo and Ru isotopic heterogeneities. To assess the potential of metallic core crystallization to fractionate these elements, we examine the partitioning behavior of Tc relative to Re, Mo and Ru in the Fe-Ni-S system between solid metal and liquid metal alloy. The experimental evidence shows that Tc behaves more like the modestly compatible siderophile element Ru than the more highly compatible siderophile element Re, and that Tc is substantially more compatible than Mo. We also demonstrate a pressure effect in the partitioning of Mo during the crystallization of Fe-Ni-S melts. For a sulfur concentration in the liquid fraction of the core of 10 wt% (16.3 at%), the Jones and Malvin (1990) parameter is −ln(1-2 × 1.09 × 0.163) ≅ 0.44, which yields: D(Re) ≅ 4.1; D(Ru) ≅ 2.3; D(Tc) ≅ 1.7; D(Mo)Lo-P ≅ 1.0;.and D(Mo)Hi-P ≅ 0.5. Our results suggest that detectable Tc-induced isotopic anomalies (≥0.1 ε unit) in Ru and Mo could only be produced by unrealistically extreme degrees of crystallization of metal during asteroidal core fractionation, regardless of the time scales and initial Tc abundances involved. 相似文献
2.
Geochemical evolution and timescale of seawater intrusion into the coastal aquifer of Israel 总被引：2，自引：0，他引：2
This study is an attempt to quantify the geochemical processes and the timescale of seawater intrusion into a coastal aquifer from changes in the major ionic composition of the water and the natural distribution of the cosmogenic isotopes 14C and 3H. For that purpose, we sampled saline and brackish groundwaters from the Israeli coastal aquifer. A multilayer sampler (MLS) was used to obtain very high resolution (10 cm) profiles across the fresh-saline water interface (FSI).The chemical and stable isotope data revealed three distinct water types (end members) that are located in different zones on the route to the coastal aquifer: (1) slightly modified Mediterranean seawater (SWS); (2) slightly diluted (with up to 20% fresh groundwater) saline groundwater (SDS); and (3) fresh groundwater (FGW).The SWS samples generally show an excess of total alkalinity and total dissolved inorganic carbon (DIC), and a depletion of 13CDIC and 14CDIC with respect to normal seawater indicating that anaerobic oxidation of organic matter is the first diagenetic reaction that affects seawater during its penetration into the bottom sediments. SDS waters appear when SWS is slightly diluted, gain Ca2+ and Sr2+, and is depleted in K+, suggesting that the main processes that transform SWS into SDS are slight dilution with fresh groundwater and cation exchange. At the fresh-saline water interface, SDS generally shows conservative mixing with FGW.Inspection of chemical data from coastal aquifers around the world indicates that intensive ion exchange in slightly diluted saline groundwater is a globally important phenomenon of seawater intrusion. Most of our saline groundwater samples contain substantial amounts of 3H suggesting that penetration of Mediterranean seawater and its inland travel to a distance of 50-100 m onshore occurred 15-30 yr ago. This is supported by the 14CDIC mass balance that explains the relatively low 14CDIC activities in the SDS as influenced by diagenesis and not by simple radioactive decay. 相似文献
3.
Recently, a new method has been introduced for the estimation of photosynthetic oxygen production from the triple isotope composition (δ17O and δ18O) of dissolved O2 in the ocean and of air O2 in ice cores. This method is based on the deviations (17Δ) from mass dependent respiratory fractionation, the major process affecting the isotopic composition of air O2. To apply this method, the slope in the 17O/16O vs. 18O/16O relationship used for 17Δ calculation must be known with high accuracy. Using numerical simulations and closed system experiments, we show how the respiratory slope is manifested in the 17Δ of O2 in situations where respiration is the only process affecting oxygen isotopic composition (kinetic slope), and in systems in steady state between photosynthesis and respiration (steady state slope). The slopes of the fractionation line in these two cases are different, and the reasons of this phenomenon are discussed. To determine the kinetic respiratory slope for the dominant O2 consumers in aquatic systems, we have conducted new experiments using a wide range of organisms and conditions and obtained one universal value (0.5179 ± 0.0006) in ln(δ17O + 1) vs. ln(δ18O + 1) plots. It was also shown that the respiratory fractionations under light and dark are identical within experimental error. We discuss various marine situations and conclude that the kinetic slope 0.518 should be used for calculating 17Δ of dissolved O2. In contrast, a steady state fractionation slope should be used in global mass balance calculations of triple isotope ratios of O2 in air records of ice cores. 相似文献
4.
The major advantage of the oxygen in phosphate isotope paleothermometry is that it is a system which records temperatures with great sensitivity while bone (and teeth) building organisms are alive, and the record is nearly perfectly preserved after death. Fish from seven water bodies of different temperatures (3–23°C) and different δ18O (values ?16 to +3) of the water were analysed. The δ18O values of the analysed PO4 vary from 6 to 25. The system passed the following tests: (a) the temperatures deduced from isotopic analyses of the sequence of fish from Lake Baikal are in good agreement with the temperatures measured in the thermally stratified lake; (b) the isotopic composition of fish bone phosphate is not influenced by the isotopic composition of the phosphate which is fed to the fish, but only by temperature and water composition.Isotopic analysis of fossil fish in combination with analysis of mammal bones should be a useful tool in deciphering continental paleoclimates. 相似文献
5.
Evaluation of the effectiveness of the regulatory regime in the management of oil pollution in Kenya
Boaz O. Ohowa 《Ocean & Coastal Management》2009,52(1):17-21
This paper presents an evaluation of the effectiveness of the regulatory regime in the management of oil pollution on Kenya's marine and coastal environment. The prospect of chronic oil pollution along the Kenyan coastline and the port of Mombasa is discussed. A review of the vulnerable marine and coastal resources, commonly used indicators of effectiveness in oil pollution management and the legislation governing oil pollution is given. The author concludes by emphasising that despite having the right legislation in place, there is need for the establishment of criteria and indicators necessary for evaluation of policy effectiveness. 相似文献
6.
The electron distribution functions from the solar corona to the solar wind are determined in this paper by considering the
effects of the external forces, of Coulomb collisions and of the wave – particle resonant interactions in the plasma wave
turbulence. The electrons are assumed to be interacting with right-handed polarized waves in the whistler regime. The acceleration
of electrons in the solar wind seems to be mainly due to the electrostatic potential. Wave turbulence determines the electron
pitch-angle diffusion and some characteristics of the velocity distribution function (VDF) such as suprathermal tails. The
role of parallel whistlers can also be extended to small altitudes in the solar wind (the acceleration region of the outer
corona), where they may explain the energization and the presence of suprathermal electrons. 相似文献
7.
M. Lazar R. C. Tautz R. Schlickeiser S. Poedts 《Monthly notices of the Royal Astronomical Society》2010,401(1):362-370
The analysis of the stability and the dispersion properties of a counterstreaming plasma system with kappa distributions are extended here with the investigation of perpendicular instabilities. Purely growing filamentation (Weibel-like) modes propagating perpendicular to the background magnetic field can be excited in streaming plasmas with or without an excess of parallel temperature. In this case, however, the effect of suprathermal tails of kappa populations is opposite to that obtained for parallel waves: the growth rates can be higher and the instability faster than for Maxwellian plasmas. The unstable wavenumbers also extend to a markedly larger broadband making this instability more likely to occur in space plasmas with anisotropic distributions of kappa-type. The filamentation instability of counterstreaming magnetized plasmas could provide a plausible mechanism for the origin of two-dimensional transverse magnetic fluctuations detected at different altitudes in the solar wind. 相似文献
8.
The variations of δ17O and δ18O in recent meteoric waters and in ice cores have proven to be an important tool for investigating the present and past hydrologic cycle. In order to close significant information gaps in the present distribution of δ17O and δ18O of meteoric water, we have run precise measurements, with respect to VSMOW, on samples distributed globally from low to high latitudes. Based on the new and existing data, we present the Global Meteoric Water Line (GMWL) for δ17O and δ18O as:
9.
Counterstreaming beams of electrons are ubiquitous in coronal mass ejections (CMEs) – although their existence is not unanimously accepted as a necessary and/or sufficient signature of these events. We continue the investigation of a high-latitude CME registered by the Ulysses spacecraft on 18?–?19 January 2002 (Dumitrache, Popescu, and Oncica, Solar Phys. 272, 137, 2011), by surveying the solar-wind electron distributions associated with this event. The temporal evolution of the pitch-angle distributions reveals populations of electrons that are distinguishable through their anisotropy, with clear signatures of i) electron strahls, ii) counter-streaming in the magnetic clouds and their precursors, and iii) unidirectionality in the fast wind preceding the CME. The analysis of the counter-streams inside the CME allows us to elucidate the complexity of the magnetic-cloud structures embedded in the CME and to refine the borders of the event. Identifying such strahls in CMEs, which preserve properties of the low β [<1] coronal plasma, gives more support to the hypothesis that these populations are remnants of the hot coronal electrons that escape from the electrostatic potential of the Sun into the heliosphere. 相似文献
10.
An upgraded version of the Eta model 总被引：2，自引：0，他引：2
Fedor Mesinger Sin Chan Chou Jorge L. Gomes Dusan Jovic Paulo Bastos Josiane F. Bustamante Lazar Lazic André A. Lyra Sandra Morelli Ivan Ristic Katarina Veljovic 《Meteorology and Atmospheric Physics》2012,116(3-4):63-79
Upgrades implemented over a number of years in an open source version of the Eta model, posted at the CPTEC web site http://etamodel.cptec.inpe.br/, are summarized and examples of benefits are shown. The version originates from the NCEP’s Workstation Eta code posted on the NCEP web site http://www.emc.ncep.noaa.gov/mmb/wrkstn_eta, which differs from the NCEP’s latest operational Eta by having the WRF-NMM nonhydrostatic option included. Most of the upgrades made resulted from attention paid to less than satisfactory performance noted in several Eta results, and identification of the reasons for the problem. Others came from simple expectation that including a feature that is physically justified but is missing in the code should help. The most notable of the upgrades are the introduction of the so-called sloping steps, or discretized shaved cells topography; piecewise-linear finite-volume vertical advection of dynamic variables; vapor and hydrometeor loading in the hydrostatic equation, and changes aimed at refining the convection schemes available in the Eta. Several other modifications have to do with the calculation of exchange coefficients, conservation in the vertical diffusion, and diagnostic calculation of 10-m winds. Several examples showing improved performance resulting from the dynamics changes are given. One includes a case of unrealistically low temperatures in several mountain basins generated by a centered vertical advection difference scheme’s unphysical advection from below ground, removed by its replacement with a finite-volume scheme. Another is that of increased katabatic winds in the Terra Nova Bay Antarctica region. Successful forecast of the severe downslope zonda wind case in the lee of the highest peaks of the Andes is also shown, and some of the recent successful verification results of the use of the upgraded model are pointed out. The code is used at numerous places, and along with setup information it is available for outside users at the CPTEC Eta web site given above. 相似文献