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41.
The development and recovery of a shallow and hypertrophic lake following a reduction in the external phosphorus load has been documented. In spite of this reduction, phosphorus concentrations and phytoplankton biomass in the lake water are still very high. The reason for this development can be explained by three main factors: (1): the sediment has been accumulating a large phosphorus pool which is now causing a high internal phosphorus load, (2) due to the shallow conditions, resuspension of the upper sediment often takes place because of wind action and thereby increases the phosphorus loading from the sediment, (3) the development of a large population of planktivorous fish decreases the zooplankton biomass resulting in the development of a large phytoplankton biomass. 相似文献
42.
Olivine phenocrysts of Hawaiian olivine tholeiite and oceanite 总被引:4,自引:0,他引:4
Olivine phenocrysts of Hawaiian tholeiites display a variety of textures and a variation in composition which is due to supercooled crystallization. The highest forsterite content measured is 91%, and the highest magnesia content estimated for a tholeiitic liquid is 17%, using the olivine geothermometer. The liquid of this composition may be either a primary magma or a primitive magma. It is not yet possible to specify any particular composition range for the primary Hawaiian tholeiites. 相似文献
43.
Symplectitic intergrowths of hypersthene (host) with ilmenite and minor magnetite (vermicules) in a gabbroic sill from the Precambrian of southwest Sweden occur as replacement products of olivine, and are thought to have formed simulataneously with the replacement of nearby crystals of ilmenite and Timagnetite by biotite and hornblende (and spinel). These interrelated replacement processes may have taken place during, or immediately after, the final stages of the magmatic crystallization, at temperatures of about 660–680°C, as part of the inherent metamorphism of the gabbroic rock. Another expression of this metamorphic imprint is the occurrence of two-tiered corona shells of hypersthene/hornblende (+spinel) at the interface of olivine and plagioclase crystals. 相似文献
44.
P. B. Storebø T. Bjorvatten K. Hønn»shagen A. Lillegraven C. D. Jones C. J. P. Van Buijtenen 《Boundary-Layer Meteorology》1983,26(2):127-139
Unipolar air ions released into the wind constitute a tracer which can be measured with high resolution. An ion source produces a cloud with homogeneous charge density, insensitive to source strength, dependent on time since formation only. It is well suited for tracing concentration changes due to turbulence, less suited for cloud size tracing. A tight array of 8 sensors has been used to examine turbulently dispersed ions. High-resolution records are presented and discussed. The highest concentrations measured could be undiluted source material. The frequency distribution within a plume did not differ from that in a multitude of puffs. The distribution seems to be log-normal with a geometric standard deviation of about 2.45. The time resolution used corresponds to volume resolutions of 40, 225, and 650 cm3. Sample size had no apparent effect. 相似文献
45.
Low frequency electrostatic waves are studied in magnetized plasmas with an electron temperature which varies with position in a direction perpendicular to the magnetic field. For wave frequencies below the ion cyclotron frequency, the waves need not follow any definite dispersion relation. Instead a band of phase velocities is allowed, with a range of variation depending on the maximum and minimum values of the electron temperature. Simple model equations are obtained for the general case which can be solved to give the spatial variation of a harmonically time varying potential. A simple analytical model for the phenomenon is presented and the results are supported by numerical simulations carried out in a 2.5-dimensional particle-in-cell numerical simulation. We find that when the electron temperature is striated along B0 and low frequency waves (ci) are excited in this environment, then the intensity of these low frequency waves will be striated in a manner following the electron temperature striations. High frequency ion acoustic waves (ci) will on the other hand have a spatially more uniform intensity distribution. 相似文献
46.
The regional ocean model system (ROMS) is used to downscale a 26-year period of the twentieth century 20C3M experiment from
the global coupled Bergen climate model (BCM) for the North Sea. Compared to an observational-based climatology, BCM have
good results on the mean temperature, except for too low winter temperature. This is connected to a too weak inflow of Atlantic
water. The downscaling gives added value to the BCM results by providing regional details, doubling the Atlantic inflow, and
improving the mean winter temperature. For mean salinity, BCM has values very close to the climatology, whereas the downscaling
becomes too fresh. The downscaling, however, improves the sea surface salinity, the vertical structure, and the Norwegian
Coastal Current. It is concluded that the downscaling procedure as presented here is a suitable tool for assessing the future
Atlantic inflow and sea temperature in the North Sea based on a global climate projection. 相似文献
47.
Anders Bøyum 《Aquatic Sciences - Research Across Boundaries》1970,32(1):300-327
Summary Chemical and physical properties in 12 lakes in the north-easternmost part of Norway are studied. Geologically the lakes are
situated on the pre-cambrian “Baltic shield”, with metamorphic and intrusive rocks that are not easily soluble.
Vertical series of temperature, pH, O2 and x18 together with colour measurements and transparency indicate that the lakes are temperate and fundamentally oligotrophic,
some with a dystrophic character. Some individual differences are discussed, with special reference to the surroundings, flow-through
rate and morphometry.
In accordance with the geology of the area the amount of electrolytes is small. Major ions (Ca, Mg, Na, K, HCO3, SO4 and Cl) are analysed. The greatest differences in the composition of these ions in the lakes are shown to be due mainly to
the varying proximity to the sea and to geological differences.
Rain is shown to be the most important factor in supplying major ions toat least some of the lakes. Individual variations
are discussed, and comparisons are made with the ionic composition of water in other districts.
Zusammenfassung An 12 im n?rdlichesten Teil von Norwegen, auf dem pr?kambrischen Baltischen Schild gelegenen Seen werden die chemischen und physikalischen Eigenschaften studiert. Das Einzugsgebiet besteht aus schwerl?slichem, metamorphem und intrusivem Gestein. Die vertikale Verteilung von Temperatur, pH, O2 und x18 samt Farbmessungen und Transparenz zeigt, dass die Seen dem temperierten Typus angeh?ren und im wesentlichen oligotroph sind, einige von dystrophem Charakter. Einige individuelle Unterschiede werden er?rtert mit besonderer Berücksichtigung der Umgebung, der Durchflutungszeit und der Morphometrie. In übereinstimmung mit der geologischen Beschaffenheit der Umgebung ist der Elektrolytgehalt neigdrig. Die dominierenden Ionen (Ca, Mg, Na, K, HCO3, SO4 und Cl) werden analysiert. Es wird nachgewiesen, dass die gr?ssten Unterschiede in der Zusammensetzung dieser Ionen in den Seen auf die verschiedene Entfernung vom Meer und auf geologische Unterschiede zurückzuführen sind. Für einige der Seen wird nachgewiesen, dass der Regen als wichtigster Faktor für ihre Versorgung mit Ionen anzusehen ist. Es werden individuelle Unterschiede er?rtert und Vergleiche mit der ionalen Zusammensetzung von Gew?ssern anderer Gegenden gezogen.相似文献
48.
Wolf Tietze Gerhard Kortum W. R. Mead T. K. Poiker C. Paddick George Kish A. Njøs H. Mensching V. Haarmann Uzo M. Igbozurike M. M. Yoshino Mushtaqur Rahman Lage Wahlström J. Connell Kazimierz Dziewonski Wayland R. Swain J. Humlum G. W. Lüttig Haruko Kishimoto Mai Britt E. Mørk 《GeoJournal》1982,6(3):270-280
49.
Two new Th ii lines have been identified in the spectrum of the solar photosphere. The abundance derived from these lines together with the previously known Th ii line at 4019 Å, is log
Th = 0.85 ± 0.20 in the log
H = 12.00 scale. Analysis of three Pb i lines in the photospheric spectrum resulted in an abundance of log
pb = 1.90 ± 0.10. The solar Th/Pb ratio is:
Th/
Pb = 0.09
-0.005
0.09
. 相似文献
50.
High resolution spectral observations between 500 MHz and 550 MHz on 1972 October 25, revealed an emission event of special interest. The main feature was bursts with a single frequency duration of about 0.09 s and with a bandwidth of the same order of magnitude as the band covered by the spectrograph. The bursts occurred in showers' which lasted for one or two minutes and which were separated by quiet intervals of roughly the same length. Frequently the activity assumed a periodic nature. Periods between 0.1 s and 0.3 s were found. The most remarkable feature of the records was a very large number of bursts with the same duration as the wide band bursts, but showing a bandwidth of a mere 1–2 MHz.The wide band bursts may be plasma waves excited by proton streams trapped in coronal magnetic fields and the narrow band bursts may possibly be explained as perpendicular electrostatic electron cyclotron waves. 相似文献