Effects of menhaden predation of plankton populations in Narragansett Bay, Rhode Island     

Ann G. Durbin  Edward G. Durbin 《Estuaries and Coasts》1998,21(3):449-465

The Atlantic menhaden,Brevoortia tyrannus, is an abundant plankton-feeding fish that undertakes extensive seasonal migrations, moving from overwintering locations offshore south of Cape Hatteras to the mid-Atlantic Bight and New England inshore waters during spring and summer. A bioenergetic model, based on field and laboratory studies, shows that when large numbers of menhaden enter Narragansett Bay, Rhode Island, during spring and early summer, they significantly influence plankton populations through size-selective grazing and nutrient regeneration. A population biomass of 9.1×10⁶ kg of menhaden feeding for 12 h each day in the upper bay would result, in a substantial reduction of the instantaneous growth rate of the >20-μm phytoplankton. Instantaneous growth rates of zooplankton would be negative if the same population of menhaden was present, resulting in a reduction in the biomass of zooplankton. Given the ambient phytoplankton and zooplankton populations, menhaden could achieve the seasonal growth measured in Narragansett Bay during 1976 by feeding on average about 5 h d^?1. Daily nitrogen excretion rates of the 9.1×10⁶ kg menhaden population were 56.4% of the mean standing stock of ammonia-N in the upper bay. Because menhaden travel in schools their effects are likely to be intense but strongly localized, increasing spatial heterogeneity in the ecosystem. When the fish migrate southward in the fall they transfer between 3.3% and 6.2% of the nitrogen exported annually from the bay.  相似文献   

Sphericity as a characteristic of solids from fossil fuel burning in a Lake Michigan sediment     

John J. Griffin  Edward D. Goldberg 《Geochimica et cosmochimica acta》1981,45(5):763-769

The property of sphericity is used to identify some anthropogenic particles in a Lake Michigan sediment. Three classes of products from high temperature processes, primarily fossil fuel burning, have been isolated: charcoals, iron oxides and aluminosilicates. The morphologies, structures and surface characteristics are indicative of the combustion process.  相似文献   

Tungsten in iron meteorites     

Edward R.D. Scott 《Earth and Planetary Science Letters》1978,39(3):363-370

Tungsten concentrations have been determined by instrumental neutron activation in 104 iron meteorites, and range from 0.07 to 5 μg/g. In individual groups, concentrations vary by factors of between 1.5 and 8, but there are negative W-Ni correlations in 8 groups: IAB, IC, IIAB, IID, IIE, IIIAB, IIICD, and IIIF. The lowest W concentrations are found in groups IAB and IIICD, which also have the smallest slopes on a W-Ni plot. Eighteen anomalous irons have W concentrations between 5 μg/g (Butler) and 0.11 μg/g (Rafrüti). The distribution of W in irons shows similarities to that of other refractory siderophilic elements (except Mo), but is closest to the distribution of Ru and Pt.Assuming that chemical trends in group IIIAB were produced by fractional crystallization, a value of 1.6 can be deduced for the distribution coefficient of W between solid and liquid metal, cf. 0.89 for Mo. Experimental evidence in support of these values is tenuous.  相似文献   

The mussel watch — A first step in global marine monitoring     

Edward D. Goldberg 《Marine pollution bulletin》1975,6(7):111-112

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Some studies of an unusual eucrite: Ibitira     

Laurel L Wilkening  Edward Anders 《Geochimica et cosmochimica acta》1975,39(9):1205-1210

The Ibitira eucrite is remarkable both for its vesicles and its unbrecciated nature. It consists of ~63 vol. % pyroxene (Wo₁₄En₃₈Fs₄₈), 31% plagioclase (An_95–96), ~2% of nickel-iron, troilite, ilmenite, titanian chromite, and 4% of a silica polymorph. It has a mean track density of 1.8 ± 0.3 × 10⁶ cm^?2, mainly due to cosmic rays. Its pre-atmospheric radius must have been at least 10 cm.The absence of complex radiation effects and presence of vesicles place constraints on the thickness of the Ibitira basalt flow. From the freezing time calculations of Provost and Bottinga, it appears that Ibitira came from a flow no less than 2.5 m and probably no more than 10 or 20 m thick. However, this estimate depends strongly on the viscosity of the melt, which is not well known.  相似文献   

The chemical composition of a Greenland glacier     

Herbert Weiss  Kathe Bertine  Minoru Koide  Edward D. Goldberg 《Geochimica et cosmochimica acta》1975,39(1):1-10

Chemical analyses on water from dated strata of a south Greenland permanent ice sheet revealed that there is a larger amount of sulfate in samples accumulated during the past decade than in those 60 or more years older. This increase is attributed to combustion of fossil fuel. With the exception of mercury, cadmium and possibly copper, the heavy metal distributions in the glacial waters are similar to those in atmospheric dusts. Previously reported higher mercury values in recently deposited strata were not confirmed.  相似文献   

Lead-210 and pollen geochronologies on Lake Superior sediments     

Kenneth W. Bruland  Minoru Koide  Carl Bowser  Louis J. Maher  Edward D. Goldberg 《Quaternary Research》1975,5(1):89-98

Rates of sedimentation in two Lake Superior deposits were determined by both ragweed pollen and ²¹⁰Pb geochronologies. The former yields an average rate over the time since the first appearance of enhanced concentrations of the pollen as a consequence of human settlement. Sedimentation rates derived on these two bases can be brought into accord if the first appearance of ragweed pollen in the sediments was around 1830 and if the sedimentation rates have been uniform over the past century.  相似文献   

Magnetic probing of planetary interiors     

Edward R. Benton 《Physics of the Earth and Planetary Interiors》1979,20(2-4):111-118

The following general question is addressed: what can be learned about a planetary interior from measurements of the global planetary magnetic field at (or near) its surface? The discussion is placed in the context of Earth, for clarity, but the considerations apply to terrestrial planets in general (so long as the observed magnetism is either predominantly of internal origin, or else external source effects can be successfully filtered out of the observations). Attention is given to the idealized but typical situation of a rotating but spherically symmetric planet containing a highly conducting uniform fluid core surrounded by a nearly insulating rigid mantle, whose conductivity, a function of at most radius only, falls monotonically from its largest value at the base of the planetary mantle to zero at the planetary surface; the largest value of mantle conductivity as well as the mean value for the whole mantle and the mantle conductance are assumed small compared to the corresponding values of the core. Exterior to the planet is vacuum in the sense of an electrically uncharged insulator. The core fluid is inviscid, Boussinesq and gravitationally driven.Complete and perfect observations of either the instantaneous internal vector magnetic field together with its secular variation at a single epoch, or more realistically, the instantaneous internal vector magnetic field alone at two separated epochs are presumed available; the time separation between measurement epochs is long compared the Ohmic diffusion time of the planetary mantle, but small compared to that of the liquid core.Under such circumstances we describe how information about each of the following planetary properties can, in principle (though not without practical difficulty) be retrieved from the observations: (1) depth of the core-mantle boundary (a result of Hide); (2) depth to the current and motion sources responsible for the planetary dynamo; (3) presence or absence of small-scale turbulence in the upper reaches of the core; (4) large-scale horizontal fluid motion at the top of the core; (5) strength of horizontal currents, zonal magnetic fields, Coriolis and Lorentz forces at the top of the core; and (6) current system in the mantle and strength of electromagnetic core-mantle coupling.  相似文献   

Amino-acid racemizarion in Quaternary shell deposits at Willapa Bay,Washington     

Keith A. Kvenvolden  David J. Blunt  H.Edward Clifton 《Geochimica et cosmochimica acta》1979,43(9):1505-1520

Extents of racemization ($\text{d}\text{l}$ ratios) of amino acids in fossil Saxidomus giganteus (Deshayes) and Ostrea lurida Carpenter were measured on shell deposits exposed at 21 sites on the east side of Willapa Bay, Washington. Amino acids from Saxidomus show less variability in $\text{d}\text{Spl}$ ratios and, therefore, are of greater use in correlation and age estimation than are amino acids from Ostrea. Shells of two different ages, about 120,000 ± 40,000 yr old and about 190,000 ± 40,000 yr old, are present. These ages correspond to Stages 5 and 7 of the marine isotope record defined by Shackleton and Opdyke in 1973 and hence the shell deposits likely formed during two different high stands of sea level. The stratigraphic record at Willapa Bay is consistent with this interpretation.  相似文献   

On the kinetics of volatile loss from chondrites     

Leo Alaerts  Edward Anders 《Geochimica et cosmochimica acta》1979,43(4):547-553

We have re-examined data by Lipschutz and coworkers on thermal release of T1, Bi, In from primitive chondrites, in order to obtain information on the nature and activation energy (E) of the release processes: desorption, volume diffusion, and decomposition of the host phase. Plausible though not definitive choices may be made in some cases. For the Allende C3 chondrite, the main release for Bi and T1 (80 and 86%) between 400 and 700°C appears to be due to desorption of a surface layer, coupled with grain boundary diffusion as the slow step. The main release of In (80%) above 600°C and the small (10–20%) tails of Bi and T1 between 700 and 1000°C probably represent volume diffusion, with activation energies near 30 kcal/mol. The much smaller E's (2–5 kcal/mol) found for this interval by the Purdue group are artifacts, resulting from their failure to correct the initial concentration for the material lost in the preceding peak. Finally, the residual Bi and T1 remaining at 1000°C seem to represent solid solutions in temperature-resistant phases, such as ‘Q’, the principal carrier of planetary noble gases in the meteorite.This distribution—a small amount in solid solution and a large amount in a surface film—qualitatively agrees with that predicted by Larimer (1973, Geochim. Cosmochim. Acta37, 1603–1623) for condensation from the solar nebula, though some of the substrates may have been sulfides rather than metal.Results for Abee and other primitive meteorites are essentially similar, except for a very abrupt 500°C release of T1 from Krymka (81%) and Bi from Tieschitz (70%). This release may represent decomposition of a thermolabile phase in a late condensate, such as organic matter or phyllosilicates. The presence of such a condensate (‘mysterite’) was inferred previously from the apparent overabundance of T1 and Bi in these meteorites.  相似文献