A method for measuring ingestion rate of deposit feeders and its use with the polychaeteNereis succinea     

Leon M. Cammen 《Estuaries and Coasts》1980,3(1):55-60

In situ ingestion rates of some infaunal deposit feeders can be determined without collecting feces by labeling the sediment with fluorescent particles and using these to trace ingested material through the gut of the animals. This technique was applied to the polychaeteNereis succinea and showed that ingestion rate, expressed as material ingested per body weight, increased with temperature and decreased with body size. Total annual ingestion of sediment and detritus for aN. succinea population in a salt marsh near Beaufort, N.C., was estimated to be 5 kg of dry material m^?2, more than 4 times that reported for salt marsh epifaunal deposit feeders. *** DIRECT SUPPORT *** A01BY009 00005  相似文献   

Lead-isotope inhomogeneity in Precambrian igneous K-feldspars     

Kenneth R. Ludwig  Leon T. Silver 《Geochimica et cosmochimica acta》1977,41(10):1457-1471

Stepwise Pb-removal experiments, using both vacuum volatilization and HF-leaching techniques, on acid-washed K-feldspar concentrates from Precambrian igneous rocks show that all contain some unsupported radiogenic Pb. Two types of radiogenic Pb were recognized. One has a “normal” isotopic composition, with relative abundances of ²⁰⁶Pb, ²⁰⁷Pb and ²⁰⁸Pb consistent with the age and U-Th contents of the rocks. The other type of unsupported radiogenic lead in the feldspars is apparently pure ²⁰⁶Pb, derived from long-term migration and accumulation of radioactive daughter(s) of ²³⁸U. This “pure ²⁰⁶pb” lead occupies different sites from the “normal” radiogenic lead, and tends to show a release maximum during vacuum volatilization at about 1150°C.The usefulness of stepwise vacuum volatilization may be limited by the tendency of a small amount of radiogenic lead to concentrate in the least volatile fraction. Stepwise partial HF attacks appear to give at least as good separation of radiogenic from original feldspar lead, and are recommended as a routine procedure for isotopic analyses of Precambrian feldspars. The fact that most of the five K-feldspars examined contained unsupported radiogenic lead implies that caution must be used in applying total-sample lead analyses of Precambrian feldspars to problems of lead-isotope evolution in crustal rocks.  相似文献   

Stratigraphic Atlas of North and Central America: Prepared by Exploration Department of Shell Oil Company,Houston, Texas. Princeton University Press,Princeton, 1977, 272 pp., U.S. $ 62.50 (cloth) or $ 19.00 (paper)     

Leon E. Long 《Sedimentary Geology》1978,21(4):312-313

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A note on the asymptotic distribution of the sample variogram   总被引：1，自引：0，他引：1  

Bruce M. Davis  Leon E. Borgman 《Mathematical Geology》1982,14(2):189-193

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Rare earth element distributions among minerals in a granodiorite and their petrogenetic implications   总被引：2，自引：0，他引：2  

L. Peter Gromet  Leon T. Silver 《Geochimica et cosmochimica acta》1983,47(5):925-939

A study of the distribution of lanthanide rare earths in a granodiorite from the eastern Peninsular Ranges batholith, southern California, reveals that a large fraction of the REE in this rock resides in the accessory phases sphene and allanite. The minerals plagioclase, alkali feldspar, biotite, epidote and apatite each contribute approximately 1% or less of each REE to the whole rock, with the exception of Eu for which plagioclase contributes 7%. Sphene and allanite together contain 80% to 95% of each REE. Each of these phases is zoned in REE concentration with substantial decreases from core to margin. Textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma. REE zoning trends in sphene and allanite, and unexpectedly low REE concentrations in largely later crystallizing minerals such as feldspar, indicate that the precipitation of sphene and allanite significantly reduced REE concentrations in residual melts. These results illustrate the potential that sphene and allanite have for controlling the behavior of REE in granitic magmas.Available information collectively suggest that the sampled granodiorite existed as a complete melt, that the REE contained in the assemblage of phases were derived by direct crystallization from the melt, and that the melt behaved essentially as a closed system once crystallization of the phases now present began. Close correspondences between the major and trace element chemistries of the granodiorite and phenocryst-poor lavas from similar tectonic settings support these conclusions. The REE pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism. The high liquidus temperature of a granodiorite melt (~ 1000°C) indicates the importance of mantle-derived components within the sources of batholithic magmas in the Peninsular Ranges.  相似文献   

Obituary: Mark Berlyand     

Leon Khurshudyan 《Boundary-Layer Meteorology》2006,121(3):387-388

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The radiative influence of aerosol effects on liquid-phase cumulus and stratiform clouds based on sensitivity studies with two climate models     

Surabi Menon  Leon Rotstayn 《Climate Dynamics》2006,27(4):345-356

Aerosol effects on warm (liquid-phase) cumulus cloud systems may have a strong radiative influence via suppression of precipitation in convective systems. A consequence of this suppression of precipitation is increased liquid water available for large-scale stratiform clouds, through detrainment, that in turn affect their precipitation efficiency. The nature of this influence on radiation, however, is dependent on both the treatment of convective condensate and the aerosol distribution. Here, we examine these issues with two climate models—CSIRO and GISS, which treat detrained condensate differently. Aerosol–cloud interactions in warm stratiform and cumulus clouds (via cloud droplet formation and autoconversion) are treated similarly in both models. The influence of aerosol–cumulus cloud interactions on precipitation and radiation are examined via simulations with present-day and pre-industrial aerosol emissions. Sensitivity tests are also conducted to examine changes to climate due to changes in cumulus cloud droplet number (N _c); the main connection between aerosols and cumulus cloud microphysics. Results indicate that the CSIRO GCM is quite sensitive to changes in aerosol concentrations such that an increase in aerosols increases N _c, cloud cover, total liquid water path (LWP) and reduces total precipitation and net cloud radiative forcings. On the other hand, the radiative fluxes in the GISS GCM appear to have minimal changes despite an increase in aerosols and N _c. These differences between the two models—reduced total LWP in the GISS GCM for increased aerosols, opposite to that seen in CSIRO—appear to be more sensitive to the detrainment of convective condensate, rather than to changes in N _c. If aerosols suppress convective precipitation as noted in some observationally based studies (but not currently treated in most climate models), the consequence of this change in LWP suggests that: (1) the aerosol indirect effect (calculated as changes to net cloud radiative forcing from anthropogenic aerosols) may be higher than previously calculated or (2) lower than previously calculated. Observational constrains on these results are difficult to obtain and hence, until realistic cumulus-scale updrafts are implemented in models, the logic of detraining non-precipitating condensate at appropriate levels based on updrafts and its effects on radiation, will remain an uncertainty.  相似文献   

Petrogenesis of picrite and associated basalts from the southern Mid-Atlantic Ridge     

Leon A. van Heerden  Anton P. le Roex 《Contributions to Mineralogy and Petrology》1988,100(1):47-60

Basalts dredged from the south wall of a fracture zone transecting the southern Mid-Atlantic Ridge (SMAR) at 54° S are unusual in that they include a suite of highly olivine phyric basalts, sampled along with more normal sparsely plagioclase phyric basalts, and a highly plagioclase phyric basalt. Four basalt types (olivine phyric, sparsely plagioclase phyric, evolved sparsely plagioclase phyric and highly plagioclase phyric) are readily distinguished on the basis of petrography, mineralogy and bulk composition. They range from primitive to evolved, with the olivine phyric basalts having elevated MgO (up to 15.5%) and the plagioclase phyric basalt having elevated Al₂O₃ (19.3%) and CaO (13.1%) contents. Compositional variations are extremely consistant, with the olivine phyric basalts and the sparsely plagioclase phyric basalts defining coherent linear trends. On the basis of the ratios and covariation of the incompatible trace elements Zr, Nb, Y and Ba, distinct parental magmas for each basalt type are required. An investigation of Fe-Mg and Mg-Ni distribution coefficients between olivine and magma indicates that olivines from the olivine phyric basalts are on average too forsteritic and too Ni poor to have crystallized in a magma corresponding to the host bulk rock composition. This implies that these basalts are enriched in xenocrystic olivine. Olivines from the other basalt types are mostly of equilibrium composition, although there are some exceptions. Petrogenetic models for the formation of the different basalt types are quantitatively evaluated in terms of fractional crystallization/crystal accumulation processes. These indicate that (1) the olivine phyric basalts are the products of olivine and minor Cr-spinel accumulation and do not represent analogues of primary magma, or a liquid fractionation trend; (2) that the sparsely plagioclase phyric basalts were formed by polybaric fractional crystallization of olivine, plagioclase and clinopyroxene; and (3) that the evolved sparsely plagioclase phyric basalts are not readily related to one another. The single highly plagioclase phyric basalt is unrelated to the other basalt types and is cumulus enriched in plagioclase.The different basalt types are unrelated to one another and document the presence of at least four distinct magma types erupted in close proximity at this ridge/transform intersection on the southern end of the Mid-Atlantic Ridge.  相似文献   

The roots of coronal structure in the Sun's surface     

Leon Golub  Harold Zirin  Haimin Wang 《Solar physics》1994,153(1-2):179-198

We have compared the structures seen on X-ray images obtained by a flight of the NIXT sounding rocket payload on July 11, 1991 with near-simultaneous photospheric and chromospheric structures and magnetic fields observed at Big Bear. The X-ray images reflect emission of both Mgx and Fexvi, formed at 1 × 10⁶ K and 3 × 10⁶ K, respectively. The brightest H sources correspond to a dying sub-flare and other active region components, all of which reveal coronal enhancements situated spatially well above the H emission. The largest set of X-ray arches connected plages of opposite polarity in a large bipolar active region. The arches appear to lie in a small range of angle in the meridian plane connecting their footpoints. Sunspots are dark on the surface and in the corona. For the first time we see an emerging flux region in X-rays and find the emission extends twice as high as the H arches. Many features which we believe to correspond to X-ray bright points (XBPs) were observed. Whether by resolution or spectral band, the number detected greatly exceeds that from previous work. All of the brighter XBPs correspond to bipolar H features, while unipolar H bright points are the base of more diffuse comet-like coronal arches, generally vertical. These diverge from individual features by less than 30°, and give a good measure of what the canopies must do. The H data shows that all the H features were present the entire day, so they are not clearly disappearing or reappearing. We find a new class of XBPs which we call satellite points, elements of opposite polarity linked to nearby umbrae by invisible field lines. The satellite points change rapidly in X-ray brightness during the flight. An M1.9 flare occurred four hours after the flight; examination of the pre-flare structures reveals nothing unusual.  相似文献   

Eddington: leading the field     

John D Barrow  ; Leon Mestel 《Astronomy& Geophysics》2004,45(3):3.10-3.13

Sixty years after the death of Sir Arthur Eddington OM, FRS, the RAS held a Commemoration Meeting to recall his outstanding contributions to astronomy, cosmology and the popularization of science, organized by John D Barrow and Leon Mestel .  相似文献