The cosmic abundance of molybdenum     

Herbert Palme  Werner Rammensee 《Earth and Planetary Science Letters》1981,55(3):356-362

Fifteen carbonaceous chondrites were analysed for Mo and Ir by neutron activation analysis combined with a metal extraction method. The results of two Orgueil analyses gave a mean concentration of 915 ppb Mo. This corresponds to 2.51 atoms Mo/10⁶ atoms Si, which is 50% lower than data reported by Case et al. [3]. The lower Mo concentration for Orgueil was predicted by Suess and Zeh [4] from semi-empirical abundance rules. A constant Mo/Ir ratio is found for C1, C2, and C3V chondrites; C3Os have variable Mo/Ir ratios. These variations are due to variable Ir concentrations. Micron-sized grains enriched in Ir but not in Mo are presumably responsible for these variations. The Mo content of Karoonda is nearly a factor of four lower than that of C3V chondrites.  相似文献   

Cores of soft lake sediments   总被引：5，自引：0，他引：5  

Herbert E. Wright Jr. 《Boreas: An International Journal of Quaternary Research》1980,9(2):107-114

Short cores of soft sediment, used in studying the pollution history of lakes, can be obtained with a plastic tube fitted with a piston and piston wire. If the sediments of deep water are annually laminated (and thus difficult to sample without disturbance) or contain excess gas (which can disrupt the stratigraphy during its escape), a short 'core' can be acquired by producing a frozen crust on a tube filled with dry ice and butanol.
A continuous core of soft lake sediment at least 7 m long can be obtained in a single drive beneath deep water with a hand-driven piston corer. Such a core assures the complete continuity necessary for counting annual laminations or for making close-interval analyses without fear of gaps, and it provides the uniform orientation required for measurements of paleomagnetic directions.  相似文献   

On the age of KREEP     

Herbert Palme 《Geochimica et cosmochimica acta》1977,41(12):1791-1801

Many lunar highland rocks have been extensively metamorphosed during the late heavy bombardment of the Moon 3.9–4.0 AE ago. Rubidium and other, more volatile elements were preferentially mobilized during this event, which resulted in a considerable scatter of RbSr model ages. This scatter can be considerably reduced by estimating the original Rb content on the basis of Sm or other, less mobile, incompatible elements. The principal uncertainty on the corrected model ages of 4.25–4.45 AE comes from the original Sm/Rb ratio.Highland rocks enriched in incompatible elements in most cases are mixtures between KREEP-basalt and other highland rock types. After corrections for Rb mobilization 3.9–4.0 AE ago, slight isotopic differences among KREEP-enriched rocks from different landing sites becomes noticeable. These differences correspond to different meteoritic groups as defined by Morgan et al. (1974). Apparently there existed slightly different KREEP basalt reservoirs, with formation ages ranging from 4.25 to 4.45 AE. These reservoirs were partly exposed through impacts of basin-forming planetesimals 3.9–4.0 AE ago. The resulting impact melts were contaminated with meteoritic material from the bombarding planetesimals.The $\text{4.63 ± 0.1}$ AE RbSr isochron of trace element poor highland rocks (Schonfeld, 1976) is determined by a K,Rb- and Ba-rich component, which formed earlier and independently of KREEP basalts.  相似文献   

Fallout radionuclides in the Pacific Ocean: Vertical and horizontal distributions,largely from GEOSECS stations     

Vaughan T. Bowen  Victor E. Noshkin  Hugh D. Livingston  Herbert L. Volchok 《Earth and Planetary Science Letters》1980,49(2):411-434

From GEOSECS stations, largely, the 1974 distributions of Pu and of¹³⁷Cs are described in the Pacific Ocean north of about 20°S latitude. Changes in some of these distributions are described from 1978 cruises by the authors.The Pacific exhibited, everywhere, a shallow subsurface layer of Pu-rich water with its concentration maximum at about 465 m in 1974; over a large portion of the central North Pacific a second layer of Pu-labelled water, less concentrated than the shallow layer, lay just above the bottom. Similar features were not observed in the case of¹³⁷Cs.The inventories of both Pu and¹³⁷Cs in the water column at most 1974 stations are substantially greater than those to be expected from world-wide fallout alone; these inventory excesses appear to be attributable to close-in fallout, but only if the ratio Pu/¹³⁷Cs in this source was much higher than in world-wide fallout. The North Pacific mean ratio of the inventories is 2.2 times that observed in world-wide fallout.Resolubilization of Pu both from sinking particles and from sediments explains peculiarities of its depth distributions.There is little evidence for tracer movement by sliding downward along density surfaces;¹³⁷Cs appears to have moved to depth by downmixing at the edge of the Kuroshio, and then moved horizontally and upward alongσ_t contours. The shallow Pu-rich layer shows no coordination with density, salinity or O₂ isopleths. The deep Pu-rich layer is restricted to a narrow range of O₂ concentrations that confirm its origin in the Aleutian Trench and rapid spread southward and laterally. Near-bottom circulation processes have been much more active than here-to-fore described.  相似文献   

Theoretical studies of the parameterization of the non-neutral surface boundary layer     

Walter-Georg Panhans  Fritz Herbert 《Boundary-Layer Meteorology》1979,16(2):155-167

The parameterization of the non-neutral atmospheric surface layer has been reexamined using the basic principles of small-scale energetics and thermodynamics. On the basis of this more complete treatment, theK-parameterization has been reformulated. It is found that the linear regression laws between fluxes and driving gradient forces of the turbulent heat and humidity exchanges in the surface layer can be derived in a much more comprehensive manner than by using the commonly used K-theory. With respect to stationary conditions and in the context of similarity concepts, a system of algebraic equations has been formulated which provides reasonable estimates of the distributions of the dimension less rates of viscous energy dissipation as well as turbulent kinetic and thermal-diffusive energy transport as functions of the variablez/L. Quantitative calculations have been performed using the scaling height formulations of Takeuchi and Yokoyama, Prandtl, and von Karman as closure conditions of the equations.  相似文献   

Computing a design flood in the absence of historical records     

Herbert Riehl  Horace R. Byers 《Pure and Applied Geophysics》1960,45(1):215-226

Summary A design flood for a Venezuelan river is computed in the absence of rainfall and stream-flow data of more than a few years. From synoptic studies of an area embracing northern South America and the Caribbean, the type of disturbance producing the abundant rains of the area is determined. A disturbance of this type is maximized on the basis of the ratio of energy dissipated through friction to released latent energy represented by rainfall — in other words, theefficiency of the system is given its highest reasonable value. The synthetic disturbance is moved over the river basin in a manner most favorable for heavy rain. Certain data available from other rivers are used as a cross-check on the resultant flood values.  相似文献   

Liquidus karrooite stability and composition at reducing conditions     

Alexander?BorisovEmail author  Frank?Brenker  Herbert?Palme 《Contributions to Mineralogy and Petrology》2004,148(1):69-78

We have determined the stability of rutile and karrooite on the liquidus of pseudobinary silicate melts of anorthite–diopside eutectic composition with, in addition, of up to 32 wt% TiO₂ at one atm total pressure and at wide range of oxygen fugacities. At 1,300°C and at an fO₂ below 10^–11.2 atm rutile (TiO₂) is replaced as liquidus phase by the pseudobrookite-type MgTi₂O₅–Ti₃O₅ solid solution with some Al in the crystal structure. The composition of karrooite was found to be strongly dependent on oxygen fugacity. Crystalline phases were identified by transmission electron microscopy (TEM). The results obtained in this study are relevant for understanding the chemistry of lunar armalcolites. Using excess rutile solubility at reducing conditions, we estimated the Ti⁴⁺ /Ti³⁺ ratio in silicate melts at 1,300°C as function of fO₂.  相似文献   

A creative solution to the NIMBY problem     

Lehr J  Inhaber H 《Ground water》2003,41(4):401-403

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Suspended sediment sources and tributary effects in the lower reaches of a coastal plain stream as indicated by radionuclides, Loco Bayou, Texas     

K. M. Yeager  P. H. Santschi  J. D. Phillips  B. E. Herbert 《Environmental Geology》2005,47(3):382-395

Characterizing the dynamics of fluvial sediment sources over space and time is often critical in identifying human impacts on fluvial systems. Upland interfluve and subsoil sources of suspended sediment at Loco Bayou, Texas, were distinguished using ²²⁶Ra/²³²Th, ²²⁶Ra/²³⁰Th and, ²²⁸Ra/²³²Th. Source contributions were apportioned at three stations during within-bank and flood flows. ¹³⁷Cs and ²¹⁰Pb_xs (excess ²¹⁰Pb) were used to determine floodplain sedimentation; suspended sediment ²¹⁰Pb_xs/¹³⁷Cs data mirrored results of Ra/Th, showing dominance of subsoil sources during within-bank flows, changing to interfluve sources during flood. This trend corresponds spatially to influx of sediment from ephemeral tributaries, reflecting mobilization of stored interfluvial sediments during flood stage. Upper basin sedimentation was similar but markedly less at the lowermost station. These results indicate (1) modified ephemeral tributaries store sediment derived from sheet wash, discharging them during flood, and (2) southernmost Loco Bayou is episodically re-worked, resulting in significantly reduced local rates of sedimentation.  相似文献   

Diatom Paleolimnological Record of Holocene Climatic and Environmental Change in the Altai Mountains, Siberia     

Karlyn S. Westover  Sherilyn C. Fritz  Tatyana A. Blyakharchuk  Herbert E. Wright 《Journal of Paleolimnology》2006,35(3):519-541

The sedimentary diatom records of three shallow lakes in the Altai Mountains, southern Siberia, were examined to assess the nature and timing of Holocene environmental changes. Few paleoenvironmental records, especially reconstructions not based on pollen, have been reported from this region. The lakes differ in elevation, annual precipitation, and catchment vegetation. Diatom assemblages in all lakes were dominated for the entire period of record by small benthic species of Pseudostaurosira Williams & Round, Staurosira Ehrenberg, and Staurosirella Williams & Round. Planktonic taxa only occur in very low abundances (<5%). The most diverse diatom flora was found in Dzhangyskol, which is situated at the lowest elevation within a forested catchment. A lack of detailed information on the ecological preferences of the dominant taxa and the complexity of environmental drivers make direct interpretation of the diatom record difficult. However, other proxies suggest that dramatic shifts in dominance between Staurosira elliptica and Staurosirella pinnata in Grusha Ozero reflect millennial-scale variability in climate. Together, chironomids and diatoms provide evidence of a cooling possibly correlative to the Younger Dryas Stade and subsequent early-Holocene warming consistent with pollen evidence of afforestation, which also is likely linked to increased humidity. By ~6000 cal year BP, the transition to a cooler, more continental climate had begun. The diatom record of Akkol shows significantly less variation in diatom community composition, but biogenic silica accumulation rates, a proxy for diatom productivity, appear to reflect climatic variability driven by insolation trends over the past 8000 years. Long-term variability in Dzhangyskol is not clearly linked to climate.  相似文献