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1.
The source of the lunar magnetic anomaly associated with the Rima Sirsalis linear rille has been modelled using the vector field intensities due to arbitrary uniform magnetization in a rectangular prism. It is shown that in order to match the Apollo 16 subsatellite data, the lunar surface near the rille must have a vertical magnetization of 6–9 × 10 −3 G if the anomaly is due to flux leakage from a gap in the crust with the dimensions of the rille. This is more than one order of magnitude larger than the magnetization of any lunar sample, but is comparable with the high magnetization recently deduced for the Reiner γ formation in Oceanus Procellarum. An alternative explanation is that Rima Sirsalis and its surroundings are the site of a vertical magnetization contrast of 10 −5 – 10 −4 G which is at least as wide as the rille and extends to a depth of tens of kilometers in the crust. A wider magnetic source reduces the required magnetization (or depth) proportionately, since to first order the field at high altitude is proportional to the magnetic dipole moment per unit length. 相似文献
2.
North-seeking bacteria (NSB) with 1 μm diameters migrate to the S pole only. They were applied to identify the S pole determination on a polished surface of magnetite-rich pyroxenite whose natural remanent magnetization (NRM) intensity was 5.64 × 10 −3 Am 2 kg −1. The microscopic observations were performed under dark-field illumination in a controlled magnetic field to 10 μT. The NSB formed clusters on limited areas of magnetite grains and scattered over the whole magnetite grains. The NRM decreased to 1.02 × 10−5 Am2 kg−1 by alternating field (AF) demagnetization to 60 mT but no clusters appeared, while small populations of the NSB scattered on each grain. These scattered bacteria may gather toward the S pole resulting from magnetic domain walls. When the sample acquired saturation isothermal remanent magnetization (SIRM) to 1 T, the NSB formed dense clusters at the opposite side to the applied field direction on the many grains as expected. This evidence indicated that the NSB can be useful micro-organisms for the determination of fine magnetic structures. Some grains also had NSB clusters at the edge of the grains toward the field direction or did not exhibit any clusters. The complicated distribution of the clusters (the S poles) may be explained by shape anisotropy of the magnetic grains. 相似文献
4.
Cosmic-ray-produced 26Al ( t1/2 = 7.05 × 10 5 years) has been measured in the Apollo 15 long core (surface to 390 g/cm 2—218 cm) for study of galactic cosmic ray production profiles, using accelerator mass spectrometry. The results are in general accord with non-destructive counting data obtained earlier, but systematically lower, and significantly higher precision. From this experiment the half-attenuation length for 26Al production can be calculated to be 122 g/cm 2 (150–400 g/cm 2 region) after normalizing the data to average chemical composition. The 53Mn ( t1/2 = 3.7 × 10 6 years) production profile in deep cores was also compiled to date. The half-attenuation length for 53Mn production was calculated to be 123 g/cm 2 (150–400 g/cm 2 region). 相似文献
5.
We present a new method to estimate the direction of the magnetization vector of geological bodies based upon the correlation between the reduced-to-the-pole field for tentative values of the magnetization direction and the total magnitude anomaly, obtained by a transform of the measured magnetic field. The reduced-to-the-pole and the total magnitude anomaly are centred over the sources in the case of 2D anomalies or well-centred in the case of compact 3D sources and have similar patterns for the same source. The method has several important advantages over similar transform-correlation methods for estimation of the magnetization direction. It calculates only one transform for many tentative values of the magnetization direction. The method does not use derivatives of any order and relies on confident isolation of the target anomalies based on one of the compared transforms, the total magnitude anomaly. We studied the performance of the method on five 2.5D and compact 3D sources. We analysed possible inherent to the method errors, as well as errors due to interference from neighbouring sources. Finally, we estimated the magnetization-vector direction of the main sources causing the magnetic field in the Burgas region and the adjoining southeast Bulgarian Black Sea shelf. The sources in the Black Sea shelf show prevalently reverse magnetization, while the sources on land have normal or reverse magnetization. 相似文献
6.
This study aimed to determine whether the δ 13C levels in the foliage and twigs of four Eucalyptus grandis clones were related to their water use efficiency (WUE). This relationship has previously been demonstrated in a number of herbaceous species but not in mature trees. The study involved accurate measurements of tree trunk growth and water use over a period of 4 months, with subsequent isotopic analysis of mature foliage from the north and south side of the canopy, and young leaves from the top of the canopy. The water use efficiencies were found to vary from 5.97 × 10−3 to 12.3 × 10−3 m3 m−3. Significant differences were observed between clonal-mean water use efficiencies averaged over six sampling periods. The average δ13C of the mature and young foliage was found to be significantly correlated with WUE. However, the correlation was weak, suggesting that the relationship between δ13C and WUE is more complex in trees than suggested in the literature on crop plants. It is suggested that differences between sample trees in carbon allocation and leaf-to-air vapour pressure deficits may account for the poor correlation between δ13C and WUE in the four E. grandis clones studied. 相似文献
7.
Cosmic-ray-produced 10Be ( t1/2 = 1.6 × 10 6 years) and 36Cl ( t1/2 = 3.0 × 10 5 years) have been measured in the Apollo 15 long core for study of galactic cosmic ray production profiles using tandem accelerator mass spectrometry. From these experiments, the half-attenuation length for 10Be production and 36Cl production were calculated to be 120 g/cm 2 and 132 g/cm 2 (150–400 g/cm 2 region). The measured half-attenuation length for 10Be is slightly longer than that predicted by the Reedy-Arnold theoretical model. The flatter and somewhat deeper maximum seen in the 36Cl profile compared to the 10Be, 26Al and 53Mn profiles can be explained by production from secondary thermal neutrons on 35Cl. 相似文献
8.
Water sampling during the 1993 IV Russian–US Joint Expedition to the Bering and Chukchi Seas (BERPAC) indicates that Pacific Ocean burdens of the long-lived radionuclide 129I are relatively low in the Pacific-influenced Arctic, particularly compared to high latitude waters influenced by the North Atlantic. These low concentrations occur despite the presence of potential submerged anthropogenic sources in the East Sea (Sea of Japan), and in the northwest Pacific Ocean, east of the Kamchatka Peninsula. The concentration of 129I entering the Arctic Ocean through Bering Strait, 0.7×10 8 atoms kg −1, is only slightly higher than observed in deep Pacific waters. Similar concentrations (0.44–0.76×10 8 atoms kg −1) measured in Long Strait indicate no significant transfer of 129I eastward into the Chukchi Sea in the Siberian Coastal Current from the Siberian marginal seas to the west. However, the concentrations reported here are more than an order of magnitude higher than the Bering Strait input concentration estimated (1.0×10 6 atoms kg −1) from bomb fallout mass balances, which supports other existing evidence for a significant atmospheric deposition term for this radionuclide in surface ocean waters. Near-bottom water samples collected in productive waters of the Bering and Chukchi Seas also suggest that sediment regeneration may locally elevate 129I concentrations, and impact its utility as a water mass tracer. As part of this study, two deep 129I profiles were also measured in the East Sea in 1993–1994. The near-surface concentration of 129I ranged from 0.12 to 0.31×10 8 atoms kg −1. The 129I concentration showed a steady decrease with depth, although because of active deep water ventilation, the entire 3000 m water column exceeded natural concentrations of the radionuclide. Atom ratios of 129I/ 137Cs in the East Sea also suggest an excess of 129I above bomb fallout estimates, also possibly resulting from atmospheric deposition ultimately originating from nuclear facilities. 相似文献
9.
The ferromagnetism of irons, stony-irons, E-, H-, L- and LL-chondrites and achondrites is due to a metallic phase comprising mostly Fe and Ni and small amounts of Co and P. The ferromagnetic constituent in non-metamorphosed C-chondrites is magnetite, but some metamorphosed C-chondrites contain FeNi metallic grains too. Among the stony meteorites, the content of metals as determined by their saturation magnetization (IS) sharply decreases in the order E → H → L → LL → achondrites, whereas the IS value for magnetite and additional metals in C-chondrites ranges from the IS value of achondrites to that of L-chondrites. With an increase of Ni-content in the metallic phase in chondrites of the order E → H → L → LL → C, the relative amount of Ni-poor kamacite magnetization, IS(), in the total IS decreases in the same order, from IS()/IS 1 for E-chondrites to IS()/IS 0 for C-chondrites. Thus, E-, H-, L-, LL- and C-chondrites and achondrites are well separated in a diagram of IS()/IS versus I, which could be called a magnetic classification diagram for stony meteorites. As the surface skin layer of all meteorites is anomalously magnetized, it must be removed and the natural remanent magnetization (NRM) of the unaltered interior only must be examined for the paleomagnetic study. The NMR of C-chondrites is highly stable and that of achondrites is reasonably stable against AF-demagnetization, whereas the NMR of E-chondrites and ordinary chondrites as well as stony-iron meteorites is not very stable in most cases. Although the NRM of iron meteorites is reasonably stable, it is not attributable to the extraterrestrial magnetic field. The paleointensity for Allende C3-chondrite is estimated to be about 1.0 Oe assuming that its NRM is of TRM origin. The paleointensity for other reasonably reliable C-chondrites (Orgueil, Mighei, Leoville and Karoonda) is also around 1 Oe. The paleointensity for two achondrites has been determined to be about 0.1 Oe. The NRM of other achondrites also suggests that their paleointensity is roughly 0.1 Oe. The NRM of ordinary chondrites is less stable than that of C-chondrites and achondrites so that the estimated paleointensity for ordinary chondrites is less reliable. The paleointensity for comparatively reliable ordinary chondrites ranges from 0.1 to 0.4 Oe. The paleointensity values of 1 Oe for C-chondrites and 0.1 Oe for achondrites may represent the early solar nebula magnetic field about 4.5 × 109 years ago. A possibility that the paleomagnetic field for achondrites was a magnetic field attributable to a dynamo within a metallic core of their parent planet may also not be rejected. 相似文献
10.
Groundwater evaporation and subsequent precipitation of soluble salts at Owens Lake in eastern California have created one of the single largest sources of airborne dust in the USA, yet the evaporation and salt flux have not been fully quantified. In this study, we compare eddy correlation, microlysimeters and solute profiling methods to determine their validity and sensitivity in playa environments. These techniques are often used to estimate evaporative losses, yet have not been critically compared at one field site to judge their relative effectiveness and accuracy. Results suggest that eddy correlation methods are the most widely applicable for the variety of conditions found on large playa lakes. Chloride profiling is shown to be highly sensitive to thermal and density-driven fluxes in the near surface and, as a result, appears to underestimate yearly groundwater evaporation. Yearly mean groundwater evaporation from the playa surface estimated from the three study areas was found to range from 88 to 104 mm year −1, whereas mean evaporation from the brine-covered areas was 872 mm year −1. Uncertainties on these mean rates were estimated to be ±25%, based on comparisons between eddy correlation and lysimeter estimates. On a yearly basis, evaporation accounts for approximately 47 × 10 6 m 3 of water loss from the playa surface and open-water areas of the lake. Over the playa area, as much as 7.5 × 10 8 kg (7.5 × 10 5 t) of salt are annually concentrated by evaporation at or near the playa surface, much of which appears to be lost during dust storms in area. 相似文献
11.
对大地震前的扰动现象的研究有助于认识地震孕育的动力学过程,震前重力扰动已成为关注的热点之一. 对大地震前的扰动现象的研究有助于认识地震孕育的动力学过程,震前重力扰动已成为关注的热点之一. 为检验日本M w9.0级地震是否存在震前扰动现象,本研究利用全球超导重力仪记录到的地震前后7天内20组秒采样数据进行分析. 经潮汐、大气改正等处理去除仪器的漂移及残余潮汐效应,得到非潮汐重力变化曲线.结果表明大部分振幅大于30×10 -8 m·s -2的曲线反映了全球M w≥6级地震引起的高频波动信号,其中11组数据在3月9日M w7.3级前震之前出现了扰动现象.震前扰动可分解为三个频段,其中,低于0.1 Hz和高于0.18 Hz的分量分别反映了地震波动信号及非构造信息,中间频段(0.118~0.18 Hz)信号能够较大程度地压制地震波动信号、并同时保留异常扰动信息.它的振幅在3月7日10时之前基本保持约1×10 -8 m·s -2,之后开始逐渐增大,到3月9日7.3级前震前后达到最大,此后振荡衰减,振幅保持约(5~10)×10 -8 m·s -2,直至主震发生.中间频段信号的变化特征与主震前的应力迁移过程以及实验记录到的地震成核过程有许多相似之处;不过,震前重力异常是否与主震前的应力加速积累有关,仍待进一步研究. 相似文献
12.
Chemical diffusion of four rare-earth elements (La, Nd, Dy and Yb) has been measured in natural calcite under anhydrous conditions, using rare-earth carbonate powders as the source of diffusants. Experiments were run in sealed silica capsules along with finely ground calcite to ensure stability of the single-crystal samples during diffusion anneals. Rutherford backscattering spectroscopy (RBS) was used to measure diffusion profiles. The following Arrhenius relations were obtained over the temperature range 600–850°C: DLa =2.6×10 −14 exp(−147±14 kJ mol −1/ RT) m 2 s −1, DNd =2.4×10 −14 exp(−150±13 kJ mol −1/ RT) m 2 s −1, DDy =2.9×10 −14 exp(−145±25 kJ mol −1/ RT) m 2 s −1, DYb =3.9×10 −12 exp(−186±23 kJ mol −1/ RT) m 2 s −1. In contrast to previous findings for refractory silicates (e.g. zircon), differences in transport rates among the REE are not pronounced over the range of temperature conditions investigated in this study. Diffusion of the REE is significantly slower than diffusion of the divalent cations Sr and Pb and slower than transport of Ca and C at temperatures above 650°C. Fine-scale zoning and isotopic and REE chemical signatures may be retained in calcites under many conditions if diffusion is the dominant process affecting alteration. 相似文献
13.
Noble gases were extracted in steps from grain size fractions of microdiamonds ( < 100 μm) from the Kokchetav Massif, Northern Kazakhstan, by pyrolysis and combustion. The concentration of 4He in the diamonds proper (liberated by combustion) shows a 1/ r dependence on grain size. For grain diameters > 15 μm the concentration also decreases with the combustion step. Both results are clear evidence that 4He has been implanted into the diamonds from -decaying elements in the surrounding matrix. The saturation concentration of 4He(5.6 × 10 −4 cm 3 STP/g) is among the very highest observed in any terrestrial diamonds. Fission xenon from the spontaneous fission of 238U accompanies the radiogenic 4He; the 136Xe f/ 4He ratio of (2.5 ± 0.3) × 10 −9 agrees well with the production ratio of 2.3 × 10 −9 expected in a reservoir where Th/U 3.3. Radiogenic 40Ar is predominantly ( > 90%) set free upon combustion; it also resides in the diamonds and appears to have been incorporated into the diamonds upon their formation. 3He, on the other hand is mainly released during pyrolysis and hence is apparently carried by ‘contaminants’. The concentration in the diamonds proper is of the order of 4 × 10−12 cm3 STP/g, with a 3He/4He ratio of 1 × 10−8. Excess 21Ne, similarly, appears to be present in contaminants as well as in diamonds proper. These two nuclides in the contaminants must have a nucleogenic origin, but it is difficult to explain their high concentrations. 相似文献
14.
The impact of domestic sewage effluent (SE) on the dynamics of phytoplankton assemblages from Bedford Basin was evaluated in the laboratory. Phytoplankton production and chlorophyll a increased proportionally with SE enrichment. Phytoplankton species composition also changed. The potentially harmful diatoms, Pseudonitzschia spp., present initially in small numbers (600 cells 1 −1) in Bedford Basin seawater, and became dominant (3–5×10 6 cells 1 −1) when the seawater was enriched with 0.5–5% untreated SE. With higher proportions of SE, other harmful species such as Fragilaria spp. and Euglena spp. became dominant (7−15×10 6 and 2.2×10 4 cells 1 −1, respectively). Treatment of SE with UV light or activated charcoal seems to favour growth of benign species, such as Chaetoceros socialis, Skeletonema costatum and Thalassiosira spp., but not harmful species such as Pseudonitzschia spp. Further research on UV treatment of domestic sewage is recommended. 相似文献
15.
Analytical procedures in the determination of iodine-129 (half-life: 1.6×10 7 y) have been studied using accelerator mass spectrometry (AMS), with special references to the separation procedures of iodine from soil samples for the AMS measurement. Iodine was successfully volatilized from soil samples by pyrohydrolysis at 1000 °C and collected in a trap solution. Iodine was purified from the matrix by solvent extraction. Finally, it was precipitated as silver iodide to make a target for AMS. In order to obtain information on the 129I/ 127I ratio in a chemical blank (or iodine carrier), we have determined the ratios in several iodine reagents and found that the ratios fell in a narrow range around 1.7×10 −13. The detection limit for soil sample (1 g material) by the present method was about 0.01 mBq/kg or 4×10 −11 as the ratio of stable iodine ( 129I/ 127I ratio), i.e. these values were much better than that by neutron activation analysis (NAA) used in our previous studies. We have applied this method in the analysis of soil samples collected from different places in Japan. We could successfully determine 129I in soil samples with low 129I concentrations, which could not be detected by NAA. Sample size necessary for the soil analysis by AMS was only about 0.5 g or less, whereas about 100 g of the sample were required for NAA [Muramatsu, Y., Ohmomo, Y., 1986. Iodine-129 and iodine-127 in environmental samples collected from Tokaimura/ Ibaraki, Japan. Sci. Total Environ. 48, 33-43]. Using this method, new data were obtained for the 129I levels in 20 soil samples collected from background areas far from nuclear facilities, and the ranges were 1.4×10 −5−4.5×10 −3 Bq/kg as 129I concentrations and 3.9×10 −11−2.2×10 −8 as 129I/ 127I ratios. These values are useful in understanding the 129I levels in Japanese environments. Higher 129I concentrations were observed in forest soils than those in field and rice paddy soils should be related to the interception effect of atmospheric 129I due to tree canopies. Relatively high 129I/ 127I ratios found in rice paddy soils could be explained by their low stable iodine concentrations which were caused by the desorption of stable iodine from the rice paddies during the cultivation. 相似文献
16.
2012年6月30日新源-和静M s6.6地震前后,新疆北天山地区的泥火山及温泉出现了明显的水化学异常。在地震前后4天内,采集了两批泥火山和温泉水样品,测定了泥火山和温泉水样的水化学参数。资料表明,泥火山喷溢水属于低温、弱碱性咸水或盐水,水化类型为CI-Na,来源于储存在封闭构造中并与干旱海相、河湖相沉围岩发生了漫长而复杂水岩作用的大气降水。温泉水为中温、弱碱性SO 4·CI-Na型淡水,形成于地表水沿断裂深循环过程中的水岩作用。安集海泥火山出现同震喷溢,震后泥水温度(T)、总矿化度(TDS)、K+、Na+及Ca2+大幅上升;独山子、白杨沟及AM02泥火山为震前喷溢,独山子、白杨沟泥火山表现为T.TDS、EC、Na+、CI的升高和K +、Ca 2+、Mg 2+的降低;AM02泥火山K +、Mg +明显降低,Ca 2+上升达223%。震后沙湾25号泉T降低7℃, TDS、电导率(EC)、K +、Na +、 Ca 2+、 .Mg 2+、CI -及$SO_{4}^{2-}$升高。研究结果可用于北天山地区的地震趋势分析和改进利用各泥火山、温泉进行北天山地区地震活动性监测的水化学方法。 相似文献
17.
Bioconcentration factors (K bc) for petroleum hydrocarbons, PAHs, LABs and biogenic hydrocarbons in Mytilus edulis were measured in field experiments using time-integrating water samplers. Seven deployments at five sites gave lipid weight K bcs for total hydrocarbons ranging from 0.99 × 10 6 to 3.1 × 10 6 (mean 1.6 × 10 6)—a narrower range than has been obtained previously. Bioconcentration factors for the PAHs were similar to those for total hydrocarbons where the major hydrocarbon source was oil. However, at other sites the factors for PAHs were an order of magnitude lower than those for petroleum and for hydrocarbons originating from algae. Compositional profiles for the linear alkyl benzenes (LABs) suggested that these compounds were assimilated primarily from the dissolved phase, despite their greater abundance on particles. 相似文献
18.
Argon, krypton, chlorine, bromine, and iodine were measured in a homogeneous population of high-salinity hydrothermal fluid inclusions from the Tertiary-age Mississippi Valley-type (MVT) lead-fluorite-barite deposits at Hansonburg, New Mexico to establish new types of evidence for the history of both the fluid and the major dissolved salts. Noble gases and halogens in fluid inclusions containing 10 −10–10 −9 L of brine ( Cl= 3 molal) were analyzed by laser microprobe noble-gas mass spectrometry (lmngms) on neutron-irradiated samples. The concentrations of36Ar (4.7 × 10−8 molal) and84Kr1.8 × 10−9 molal) in the fluid inclusions are equal to those of fresh surface waters in equilibrium with air at approximately20 ± 5°. The mole ratios ofBr/Cl (1.2 × 10−4) andI/Cl (1–2 × 10−6) are among the lowest measured in any natural waters, similar to those of modern brines formed by dissolution of Permian NaCl-bearing evaporites in southeast New Mexico.40Ar/36Ar ratios (600) are twice that of air, and indicate that the fluid inclusions had excess radiogenic40Ar (1.4 × 10−5 molal) when trapped. The amount of excess40Ar appears to be too large to have been acquired with Cl by congruent dissolution of halite-bearing evaporites, and possibly too small to have been acquired with Pb by congruent dissolution of granitic basement rocks with Proterozoic KAr ages. From thelmngms data, combined with published Pb and S isotope data, we infer the following sequence of events in the history of the Hansonburg MVT hydrothermal brine: (1) the brine originated as relatively dilute meteoric water, and it did not gain or lose atmospheric Ar or Kr after recharge; (2) the originally dilute fluid acquired the bulk of its Cl and sulfate in the subsurface after recharge by dissolving halite-bearing Permian? marine evaporites; (3) the high salinity brine then acquired most of its Pb and excess radiogenic40Ar from interactions with aquifer rocks other than evaporites, possibly clastic sedimentary rocks or basement rocks with Phanerozoic KAr “ages”; and (4) the brine deposited fluorite without having boiled or degassed. 相似文献
19.
Bacterial abundances and activity, estimated by 4′,6-diamidino-2-phenylindole staining (DAPI) and the reduction of 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride (INT), were investigated in two oligotrophic artificial groundwater lakes and the surrounding aquifers. To evaluate the effect of lake water on groundwater downstream, samples were taken from wells at different distances from the lakes, and the total number of bacteria and the number of active bacteria in these samples were compared with samples collected upstream. In addition, sterilized sandy sediments were exposed in groundwater wells to measure the number and activity of bacteria attached to particles. At one of the study sites, where the lake sediments were disturbed by dredging, total bacterial abundance and the number of respiring bacteria in the groundwater aquifer was clearly influenced by the lake water. The average bacterial abundances decreased from 2.6 ± 1.9 × 10 5 cells ml −1 in the well closest to the lake (S2) to 2.9 ± 3.8 × 10 4 cells ml −1 in the most distant one (S4), which was equivalent to cell numbers in the upstream well. The number of respiring bacteria showed a similar tendency with 1.3 ± 2.7 × 10 4 active cells ml −1 in S2 and 1.9 ± 1.5 × 10 3 active cells ml −1 in S4. At the second study site, which was not influenced by dredging, bacteria in the downstream wells seemed not to be affected by the lake water. The number and activity of bacteria, which colonized exposed sediments, were not significantly different in the upstream and downstream wells, indicating a minor influence of lake water on this habitat. Our results suggest that gravel-pit lakes may influence the free living bacterial assemblages in nearshore groundwater systems, but do not visibly affect numbers and activity of bacteria attached to the surface of aquifer sediments. 相似文献
20.
研究2013年1月29日哈萨克斯坦6．1级地震前新疆境内形变资料异常。结果表明：震前乌什水管仪两分量、伸缩仪北南分量、体应变和克孜尔水准、基线存在趋势性转折异常;乌什水管倾斜仪北南分量、体应变、分量式应变与柯坪垂直摆倾斜仪北南分量、拜城地倾斜两分量和库车东风煤矿地倾斜北南分量存在不同程度的中短期异常,趋势异常和中短期异常显著。 相似文献
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