Relationship between subcellular cadmium distribution in prey and cadmium trophic transfer to a predator   总被引：1，自引：0，他引：1  

William G. Wallace  Glenn R. Lopez 《Estuaries and Coasts》1996,19(4):923-930

We tested the hypothesis that exposure-related alterations in the subcellular Cd distribution in prey relate to changes in Cd absorption by a predator. Oligochaete worms,Limnodrilus hoffmeisteri were exposed for 1 wk or 6 wk to 0.5 μg Cd 1^?1, 47 μg Cd 1^?1, or 140 μg Cd 1^?1 (including¹⁰⁹Cd as a tracer) and relationships between oligochaete subcellular Cd distribution and Cd absorption by a predator, the grass shrimp (Palaemonetes pugio), were determined. Concentration and duration of Cd exposure had direct effects on oligochaete subcellular Cd distribution. Changes in oligochaete subcellular Cd distribution were characterized by increases in both the amount and proportion of Cd bound to the cytosolic fraction. The induction of Cd-binding proteins (e.g., metallothioneins) were suspected to be responsible for these changes. We found 1∶1 relationships between the amount and percentage of Cd in oligochaete cytosol and the amount and percentage of Cd adsorbed by shrimp. These results demonstrate that only metal bound to the soluble fraction of prey is available to higher trophic levels, and that factors influencing subcellular metal distribution in prey will directly alter metal trophic transfer to predators.  相似文献   

Particle trajectories and simple models of transport in coherent vortices     

William K. Dewar  Glenn R. Flierl 《Dynamics of Atmospheres and Oceans》1985,9(3):215-252

The particle trajectories and transport effects of coherent vortices are computed and a number of advection and diffusion experiments using a time-dependent dynamical ring model are analyzed. Several features of the tracer distributions in the numerical solutions are similar to features noted in sea surface temperature images of Gulf Stream rings and are discussed from the point of view of the model. Comparisons between tracer distributions computed using the dynamic ring model and several purely kinematic ring representations demonstrate that most of the important features of ring transport are not altered by slow dynamical evolution. Loss rates from the ring trapped zone are also estimated, which permits calculation of cross-Gulf Stream chemical and biological fluxes due to ring formation. We demonstrate that the salinoty flux to the Slope Water caused by rings is comparable to that caused by the atmosphere.The transport of passive scalars produced by a series of rings moving through a channel (modeling the Slope Water region between the Shelf and the Gulf Stream) is computed. It is found that transport in the along-channel direction is enhanced by the presence of rings and is characterized by Nusselt numbers of 0(30–40). Cross-channel fluxes, while enhanced, are somewhat less affected by rings, and are generally characterized by Nusselt numbers < 0(10). The combined effect of rings on the Slope is seen to make it an anisotropic medium, with along-channel transport one to two orders of magnitude more efficient than cross-channel transport. The implications with respect to the Slope are discussed.  相似文献   

Gaseous Behavior of TCE Overlying a Contaminated Aquifer     

Donn L. Marrin  Glenn M. Thompson 《Ground water》1987,25(1):21-27

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Theoretical estimates of the westward drift     

Glenn R. Ierley 《Physics of the Earth and Planetary Interiors》1984,36(1):43-48

Virtually all dynamo models may be expected to give rise to a permanent differential rotation between mantle and core. Weak conductivity in the mantle permits small leakage currents which couple to the radial component of the magnetic field, producing a Lorentz torque. Mechanical equilibrium is achieved when a zero net torque is established at a critical rotation rate. An estimate of the drift is determined easily given the magnetic field structure predicted by any dynamo model. The result for the drift rate at the core-mantle interface along the equator is given by the product of three factors The first of these is a geometrical factor which depends only on the structural character of the field. For a variety of model fields, this factor ranges from 16 to 35. The second factor is the ratio of r.m.s. toroidal to poloidal field. This ratio is an (implicitly) adjustable parameter of both α² and α-ω dynamos, and is a measure of the relative efficiency of the generation process for each component. The third (dimensional) term is the ratio of core magnetic diffusivity to core radius, 10^?4 cm s^?1.The result is essentially independent of the value of mantle diffusivity and its effective depth. The sign of the result may be positive or negative. For α² dynamos a westward drift is produced by choosing α > 0 in the Northern Hemisphere, which constitutes a dynamical assertion about the dynamo process. For an r.m.s. toroidal field of the order of 15 Gs, based on fairly general considerations, a drift rate comparable to observation is expected.  相似文献   

Central Arctic Ocean response to Pleistocene Earth-orbital variations     

Robin F. Boyd  David L. Clark  Glenn Jones  W.F. Ruddiman  A. McIntyre  N.G. Pisias 《Quaternary Research》1984,22(1):121-128

Three central Arctic Ocean sediment cores were sampled for percentage carbonate, number of foraminifera, and texture. These three parameters were used in spectral analyses to test the idea that the ice-covered Arctic Ocean may respond to orbital forcing in a different manner than has been indicated for lower latitude ice-free oceans. The record for two of the cores represents approximately 1 my, and the record for the third, approximately 400,000 yr. The 100,000-yr frequency is well represented in all of the cores. A 40,000-yr frequency may be present, as well. An unexpected 70,000-yr frequency occurs in most of the spectra and may reflect nonlinear sedimentation rates or the combined effect of obliquity and eccentricity. The strong 100,000-yr signal confirms that, in spite of ice feedback, the Arctic Ocean has responded to orbital forcing in much the same manner as have ice-free oceans.  相似文献   

The Mgeni granite: an example of the Megacrystic mantled-feldspar granite-charnockite Intrusives in southeastern Africa     

A. Kerr  G. C. Milne 《Mineralogy and Petrology》1994,50(1-3):139-155

Summary Megacrystic granites which form the Oribi Gorge Suite of southern Natal show many features that closely resemble the rapakivi granite—charnockite associations of the northern hemisphere. Detailed studies of the late-kinematic Mgeni batholith indicate that the granitic rocks can be divided into three major groups, characterised by distinctive mafic mineralogy, chemistry and isotopic ratios. The batholith consists of biotite ±garnet granites and of hornblende ± pyroxene granitoids. A high silica, coarse-grained leucogranite, the Nqwadolo granite, intrudes the core of the batholith. Most rocks are garnetiferous and appear to belong to the ilmenite-series of granites. The granites are classified as rapakivi-like granites.

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Der Mgeni Granit—Ein Beispiel megakrystischer feldspatummantelter Granit-Charnokit intrusiva im südöstlichen Afrika

Zusammenfassung Megakrystische Granite aus der Oribi Gorge Suite des südlichen Natal zeigen vielerlei Ähnlichkeiten mit den Rapakivigranit-Charnokitabfolgen der nördlichen Hemisphäre. Detailstudien des spätkinematisch intrudierten Mgeni-Batholiten zeigen, daß diese granitischen Gesteine in drei Hauptgruppen, die durch unterschiedliche mafische Mineralzusammensetzung, Chemismus und Isotopenverhältnissen charakterisiert werden, untergliedert werden können. Der Batholith wird aus Biotit± Granat-Graniten und aus Hornblende ± Pyroxen-Granitoiden aufgebaut. Ein siliziumreicher, grobkörniger Leukogranit, der Nqwaldolo Granit, intrudierte in den Kern des Batholithen. Die meisten Gesteine sind granatführend und scheinen den Graniten der ilmenite series zuzurechnen zu sein. Die Granite sind als Rapakivi-Granite zu klassifizieren.

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An aperture synthesis study of Saturn and its rings at 3.71-cm wavelength     

F.Peter Schloerb  Duane O. Muhleman  Glenn L. Berge 《Icarus》1979,39(2):232-250

We present aperture synthesis maps of the Saturn system at a wavelength of 3.71 cm. The data used to make the maps were obtained in May–June 1976 at the Owens Valley Radio Observatory on 13 interferometer baselines. The aperture synthesis maps contain few assumptions about the brightness structure of Saturn and the rings and, therefore, may be used to check previous model-fitting results as well as search for new unmodeled features. Generally, the maps confirm the previous model-fitting results. An exception to this is that the brightness temperature of the planet that is implied by the maps is about 4% less than that deduced from model fitting. The likely explanation of this discrepancy is that random errors on the phase of the visibility function have led to an underestimate of the planet brightness temperature in the map. Maps of the residuals to the model fits have shown that the position of Saturn given in the American Ephemeris and Nautical Almanac may be in error by about 0.25 arcsec. Maps of the residuals to model fits including a position offset show that no new features of the Saturn brightness structure are required to match the present data. In particular, no azimuthal variations in the brightness temperature of the rings were detected.  相似文献   

Three distinct regimes of volcanic tremor associated with the eruption of Shishaldin Volcano, Alaska 1999     

Glenn Thompson  Stephen R. McNutt  Guy Tytgat 《Bulletin of Volcanology》2002,64(8):535-547

Tremor signals associated with the eruption of Shishaldin Volcano on 19 and 23 April 1999 were the strongest recorded anywhere in the Aleutian Arc by the Alaska Volcano Observatory (AVO) in its 10-year history. Reduced displacements (D_R) reached 23 cm² on 19 April and 43 cm² on 23 April. During the activity, D_R and spectral data with a frequency resolution of 0.1 Hz were computed and put on the World Wide Web every 10 min. These data are analyzed here. The general temporal patterns of seismicity of these eruption events were similar, but the eruptions and their effects quite different. The 19 April event is known to have culminated in a sub-Plinian phase, which ejected ash to an altitude of 16 km. Despite higher amplitudes and the largest hotspot from satellite data, the 23 April event produced little ash reaching only 6 km altitude. For several hours prior to the sub-Plinian phase on 19 April, tremor with a peak frequency of 1.3 Hz intensified. During the sub-Plinian phase the peak frequency increased to 4-8 Hz. However, in 15 h after the eruption, three episodes of stronger tremor occurred with a lower 1.0-Hz peak, alternating with weaker tremor with a 1.3-Hz peak. These transitions correspond to D_R=~8 cm². Although these strong tremor episodes produced higher D_R levels than the sub-Plinian phase, data from a pressure sensor show that only strong Strombolian explosions occurred. The suite of observations suggests three distinct tremor regimes that may correspond to slug flow, bubbly flow, and sustained strong eruptions, or a cyclic change in source parameters (e.g., geometry, sound speed, or ascent rate). This behavior occurred at Shishaldin only during the April 1999 sequence, and we are not aware of similar behavior at other volcanoes.  相似文献   

On the origin of late Holocene sea-level highstands within equatorial ocean basins     

J.X. Mitrovica  G.A. Milne 《Quaternary Science Reviews》2002,21(20-22)

Late Holocene sea-level highstands of amplitude 3 m are endemic to equatorial ocean basins. These highstands imply an ongoing and moderate, sub-mm/yr, sea-level fall in the far field of the Late Pleistocene ice cover that has long been linked to the process of glacial isostatic adjustment (GIA; Clark et al., 1978). Mitrovica and Peltier (1991) coined the term ‘equatorial ocean syphoning’ to describe the GIA-induced sea-level fall and they provided the first physical explanation for the process. They argued that water migrated away from far-field equatorial ocean basins in order to fill space vacated by collapsing forebulges at the periphery of previously glaciated regions. We provide a complete physical explanation for the origin of equatorial ocean syphoning, and the associated development of sea-level highstands, using numerical solutions of the equation that governs meltwater redistribution on spherical, viscoelastic Earth models. In particular, we separate the total predicted sea-level change into contributions associated with ice and meltwater loading effects, and, by doing so, isolate a second mechanism that contributes significantly to the ocean syphoning process. Ocean loading at continental margins induces a ‘levering’ of continents and a subsidence of offshore regions that has also long been recognized within the GIA literature (Walcott, 1972). We show that the influx of water into the volume created by this subsidence produces a sea-level fall at locations distant from these margins—indeed over the major ocean basins—that is comparable in amplitude to the syphoning mechanism isolated by Mitrovica and Peltier (1991).  相似文献   

Aspartic acid racemization in teeth from Ketef Hinnom,a late Holocene burial cave in Jerusalem: Evidence for reuse     

M. Sinibaldi  Glenn A. Goodfriend  Gabriel Barkay  S. Marchese  Emanuel Gil-av 《Geoarchaeology》1999,14(5):441-454

The Ketef Hinnom tombs, lying just outside the walls of the old city of Jerusalem, were carved out of bedrock during the 7th–5th century B.C. Several artefacts dating to the Late Hellenistic Period (ca. 100 B.C.) have also been found within the tombs. Aspartic acid (Asp) racemization in 31 samples of human tooth dentine from these tombs was analyzed in order to evaluate the possible reuse of the tombs during this later period. A range of D/L Asp values was found: a group with values averaging 0.062 and another group averaging 0.043. These D/L values are close to those expected for the two archeological age groups as calculated from (1) the kinetics of Asp racemization as established from experimental studies at higher temperatures and in vivo racemization rates, and (2) the effective annual temperature in the tombs, as measured using the Pallman method. These results thus support the later reuse of the tombs for burials. Several factors contribute to the accuracy of Asp racemization dating, including the age of the individual at death, uncertainties concerning Asp racemization kinetics, and effects of temperature history. © 1999 John Wiley & Sons, Inc.  相似文献