Herring at the Arctic front: influence of temperature and prey on their spatio-temporal distribution and migration     

Leif Nøttestad  Ole Arve Misund  Webjørn Melle  Bente K. Hoddevik Ulvestad  & Kjell Arild Orvik 《Marine Ecology》2007,28(S1):123-133

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Photochemical production of ammonium and transformation of dissolved organic matter in the Baltic Sea   总被引：13，自引：1，他引：13  

Colin A. Stedmon  Stiig Markager  Lars Tranvik  Leif Kronberg  Tove Sltis  Winnie Martinsen 《Marine Chemistry》2007,104(3-4):227-240

The release of ammonium from the photochemical degradation of dissolved organic matter (DOM) has been proposed by earlier studies as a potentially important remineralisation pathway for refractory organic nitrogen. In this study the photochemical production of ammonium from Baltic Sea DOM was assessed in the laboratory. Filtered samples from the Bothnian Bay, the Gulf of Finland and the Arkona Sea were exposed to UVA light at environmentally relevant levels, and the developments in ammonium concentrations, light absorption, fluorescence and molecular size distribution were followed. The exposures resulted in a decrease in DOM absorption and loss of the larger sized fraction of DOM. Analysis of the fluorescence properties of DOM using parallel factor analysis (PARAFAC) identified 6 independent components. Five components decreased in intensity as a result of the UVA exposures. One component was produced as a result of the exposures and represents labile photoproducts derived from terrestrial DOM. The characteristics of DOM in samples from the Bothnian Bay and Gulf of Finland were similar and dominated by terrestrially derived material. The DOM from the Arkona Sea was more autochthonous in character. Photoammonification differed depending on the composition of DOM. Calculated photoammonification rates in surface waters varied between 121 and 382 μmol NH₄⁺ L^− 1 d^− 1. Estimated areal daily production rates ranged between 37 and 237 μmol NH₄⁺ m^− 2 d^− 1, which are comparable to atmospheric deposition rates and suggest that photochemical remineralisation of organic nitrogen may be a significant source of bioavailable nitrogen to surface waters during summer months with high irradiance and low inorganic nitrogen concentrations.  相似文献   

Survival of crucian carp,Carassius carassius,exposed to a high low-molecular weight inorganic aluminium challenge     

Antonio B. S. Poléo  Sigurd A. Øxnevad  Kjartan Østbye  Ronny A. Andersen  Deborah H. Oughton  Leif A. Vøllestad 《Aquatic Sciences - Research Across Boundaries》1995,57(4):350-359

Crucian carp were exposed to three combinations of pH and inorganic aluminium concentrations for 25 days. Mortality, plasma chloride and haematocrit, and gill aluminium content were investigated. No mortality was observed in any of the three exposures. Crucian carp survived acidic Al-rich water (pH 5.17) with a high concentration of low-molecular weight inorganic Al species (242 µgl^–1) for 25 days. These fish had lowered plasma chloride levels and high amounts of aluminium on their gills compared to fish exposed to acidic Al-poor water (pH 5.16 and 12 µgl^–1 Al_i) and control water (pH 6.29 and 4 µgl^–1 Al_i). Haematocrit was the same in all three exposures. Because aluminium was not acutely toxic to the anoxia tolerant crucian carp, the present results give support to the hypothesis that Al polymerization with subsequent hypoxia is of high importance for the mechanism of acute Al toxicity to fish.  相似文献   

Geochemistry of Caledonian metabasalts from some Norwegian ophiolite fragments     

Harald Furnes  Asbjørn Thon  Jan Nordås  Leif B. Garmann 《Contributions to Mineralogy and Petrology》1982,79(3):295-307

Major and trace element analyses of metabasalts from five of the Lower Palaeozoic Caledonian ophiolite fragments along a strike distance of some 800 km of the west Norwegian coast are presented. Characteristically the REE patterns show depletion of both LREE and HREE relative to intermediate REE, giving an upward convex shape, but nearly flat, LREE depleted or enriched patterns occur. The REE patterns of the metabasalts from three of these sequences, i.e. the Lykling, Solund and Stavfjorden ophiolite fragments show little within-sequence but large between-sequence variation. The REE patterns of the metabasalts from the Gullfjellet (Major Bergen Arc) and Skålvær ophiolite fragments, however, show significant within-sequence variations, indicative of local source heterogeneties.When incompatible trace elements such as Ta, Nb, Ce, P, Zr, Hf, Sm, Ti, Y and Yb are normalized against average MORB, the metabasalts can be subdivided into two major groups. One group, geographically comprising the ophiolite fragments north of Bergen (i.e. Solund, Stavfjorden og Skålvær) show trace element ratios similar to average MORB, whereas the other group, defined by the Gullfjellet and Lykling ophiolite fragments (from Bergen southwards) differ significantly with respect to Yb/Y, Ti/Y and Nb/Ce ratios. These features are discussed in terms of trace element patterns in basalts from oceanic islands, island arcs and back-arc basins, and it is tentatively concluded that they reflect partial melts from a mid-oceanic mantle, or probably a back-arc basin mantle, which differed chemically from that of the northwestern Norwegian ophiolite fragments.  相似文献   

Formation of sapphirine during retrogression of a basic high-pressure granulite,Roan, Western Gneiss Region,Norway     

Leif Johansson  Charlotte Möller 《Contributions to Mineralogy and Petrology》1986,94(1):29-41

Sapphirine-bearing rocks occur in the northern part of the Western Gneiss Region, Vestranden, central Norway. The sapphirine-bearing rocks are characterized by a high MgO/(MgO + FeO) ratio, high Al₂O₃, MgO and CaO, and low SiO₂ contents. These rocks form layers within larger complexes which originated as layered magmatic rocks. High PT-metamorphism produced a cpx+ky+gt assemblage. The P and T estimates are P = 14.5±2 kbar and T= 870±50° C. During retrogression, the high-P granulite assemblage broke down to form an intermediate-P granulite mineralogy comprising orthopyroxene, spinel, anorthite, andesine, sapphirine and corundum. Textural relationships suggest that sapphirine formed by the reaction: spinel+kyanite sapphirine+corundum, and probably also by a reaction between corundum, spinel and orthopyroxene. All reactions took place within the stability field of kyanite. Textural and micro-chemical relationships indicate equilibrium, conditions during the peak metamorphism, whereas pronounced disequilibrium characterizes the mineral associations formed during the early retrogression at low P _H2O. The investigation shows that parts of the northern segment of the Western Gneiss Region underwent a metamorphic evolution similar to the Caledonian one recorded from eclogite/granulite terrains further south.  相似文献   

A Younger Dryas Ash Bed in western Norway,and its possible correlations with tephra in cores from the Norwegian Sea and the North Atlantic     

Jan Mangerud  Sven Erik Lie  Harald Furnes  Inger Lise Kristiansen  Leif Lømo 《Quaternary Research》1984,21(1):85-104

A bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western Norway. It is formally mamed the Vedde Ash Bed, and its age is approximately 10,600 yr B.P., i.e., mid-Younger Dryas. The bed consits of pure glass having a bimodal basaltic and rhyolitic somposition. The geochemistry of the glass shards suggests an Icelandic source. By means of stratigraphic position and geochemistry, the ash is correlated with ash zones found in cores from the continental shelf, the Norwegian Sea, and the North Atlatic.  相似文献   

The EEC. A study in applied economics: CHARNLEY,A.H. (1973): 337 pp., maps,diagrams & tables. London and Aylesbury: Ginn & Co. Ltd. £2.75     

Leif Ahnström 《Geoforum》1974,5(4):111

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On the supposed anticorrelation of solar polar and equatorial rotation rates     

Thomas L. Duvall Jr.  Leif Svalgaard 《Solar physics》1978,56(2):463-466

Howard and Harvey (1970) analyzed Mt. Wilson Doppler shifts to obtain a daily measure of the Sun's differential rotation. The data were fitted to give an angular velocity of the form = a + b sin² B + c sin⁴ B (B = heliographic latitude). Changes in a, b, c were found to be correlated (Howard and Harvey, 1970). Yoshimura (1972) used the anticorrelation of the b and c parameters to infer the existence of large-scale convection. Wolff (1975) used the b-c anticorrelation and a weak correlation between a and b to infer that variations of the Sun's polar and equatorial rotation rates are anticorrelated. In this paper, the anticorrelation of b and c is shown to be due to numerical coupling.  相似文献   

Pluto: New photometry and a determination of the axis of rotation     

Leif E. Andersson  John D. Fix 《Icarus》1973,20(3):279-283

New photoelectric observations of Pluto, made in 1971, 1972, and 1973, show that the amplitude of the 6-day rotational light variation is larger (about 0.22 mag) and the mean magnitude is fainter $\text{(}\text{V}{}_0\text{= 15.1)}$ than during earlier periods of observation. The change is interpreted as due to a large obliquity of the rotational axis (probably larger than 50°). The phase coefficient of Pluto is about 0.05 mag/deg at 1° solar phase angle.  相似文献   

Fluxes and Concentrations of Non-Conserved Scalars in the Atmospheric Surface Layer     

Leif Kristensen  Peter Kirkegaard 《Journal of Atmospheric Chemistry》2006,53(3):251-263

We have carried out a theoretical study of the simplest possible, second-order, chemical destruction process in the atmospheric surface layer. The model describes the destruction of two gases emanating from the surface with the same molecular flux. Although this situation seems artificial with no counterpart in the real atmosphere, the results shed light on some fundamental problems. For example, it is possible to specify boundary conditions, with the concentrations and the fluxes at a given height away from the surface, which lead to unrealistic solutions with infinite surface fluxes. A method to describe and separate the consistent solutions for this process was developed. It is in general of particular interest from an experimental point of view since it is not possible to measure fluxes right at the surface: if a measurement of flux and concentration in a given height requires infinite surface fluxes there is something wrong with the data. We expect that such problems will be inherent in more complex reactions schemes, such as the NO-NO₂-O₃ triad. Just as in first-order destruction processes, the Damköhler ratio will enter the turbulent diffusivity, but where this ratio is concentration independent for first-order processes, the present second-order model implies that the Damköhler ratio is proportional to the concentration. In the study of first-order processes it was found that the Damköhler correction to the turbulent diffusivity is of minor importance from an experimental point of view. We arrive at the same conclusion in this particularly simple study of second-order destruction. In other words, this work may be considered a further development of a previous study of the first-order destruction of a passive scalar. The model and the method we develop to solve the corresponding nonlinear differential equations are considered a preliminary study for developing tools to deal with more complicated atmospheric processes. Also, the results obtained may serve as a “calibration case” for more elaborate simulations.  相似文献