Ocean oxygen minima expansions and their biological impacts     

Lothar Stramma  Sunke Schmidtko  Lisa A. Levin  Gregory C. Johnson 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(4):587-595

Climate models with biogeochemical components predict declines in oceanic dissolved oxygen with global warming. In coastal regimes oxygen deficits represent acute ecosystem perturbations. Here, we estimate dissolved oxygen differences across the global tropical and subtropical oceans within the oxygen minimum zone (200–700-dbar depth) between 1960–1974 (an early period with reliable data) and 1990–2008 (a recent period capturing ocean response to planetary warming). In most regions of the tropical Pacific, Atlantic, and Indian Oceans the oxygen content in the 200–700-dbar layer has declined. Furthermore, at 200 dbar, the area with O₂ <70 μmol kg^?1, where some large mobile macro-organisms are unable to abide, has increased by 4.5 million km². The tropical low oxygen zones have expanded horizontally and vertically. Subsurface oxygen has decreased adjacent to most continental shelves. However, oxygen has increased in some regions in the subtropical gyres at the depths analyzed. According to literature discussed below, fishing pressure is strong in the open ocean, which may make it difficult to isolate the impact of declining oxygen on fisheries. At shallower depths we predict habitat compression will occur for hypoxia-intolerant taxa, with eventual loss of biodiversity. Should past trends in observed oxygen differences continue into the future, shifts in animal distributions and changes in ecosystem structure could accelerate.  相似文献   

Recycling of continental crust into the mantle as revealed by Kytlym dunite zircons, Ural Mts, Russia   总被引：3，自引：0，他引：3  

F. Bea  G. B. Fershtater  P. Montero  M. Whitehouse  V. Ya. Levin  J. H. Scarrow  H. Austrheim  & E. V. Pushkariev 《地学学报》2001,13(6):407-412

The presence of zircons of crustal origin in the dunites of Kytlym, a subduction-related concentrically zoned dunite–clinopyroxenite–gabbro massif of the Urals Platinum-Bearing Belt, may provide the first direct evidence of the recycling of continental crust into the mantle. Zircons were part of subducted sediments that melted to produce silicic magmas with entrained restitic zircons. These melts induced partial melting in the overlying mantle, which later crystallized as the Kytlym massif. Zircons rapidly captured into early formed dunites were prevented from dissolving completely and underwent different degrees of recrystallization. A few crystals still record their original ages, which range from ∼410 Myr to ∼2800 Myr, thus revealing a different origin. The majority, however, recrystallized in the presence of a limited amount of melt and record the diapir formation, 350–370 Ma, which was coeval with the Uralian high-pressure metamorphism. Lastly, several grains record an age of ∼330 Myr, which is identical, within error, to the Rb–Sr age of the tilaitic gabbros, (337 ± 22 Myr), and may, therefore, represent the crystallization age of the last melts formed during the evolution of Kytlym.  相似文献   

The use of a meso-gamma scale model for evaluation of pollution concentration over an industrial region in Israel (Hadera)     

Y. Tokar  J. Goldstein  Z. Levin  P. Alpert 《Boundary-Layer Meteorology》1993,62(1-4):185-193

A model was developed for pollutant dispersion from a point source simulating the Hadera (Israel) power plant stack. The model is based on the NCAR mesoscale meteorological MM4 model that provides the wind fields and coefficients of turbulent diffusion. The model was implemented using an implicit numerical scheme with changing directions. A comparison between the model calculations and an analytical solution for the advection-diffusion equation shows good agreement. Relatively low numerical diffusion of the adopted advection scheme was noted. Results for the hilly region of central Israel are presented for a summer case.  相似文献   

Langzeitige Änderung des Salzgehaltes in der Unterweser     

Dr. Iris Grabemann  Gunther Krause  Gerold Siedler 《Ocean Dynamics》1983,36(2):61-77

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Crustal deformations related to the formation of new tolbachik volcanoes in 1975–1976, Kamchatka     

S. A. Fedotov  V. B. Enman  Yu. P. Nikitenko  M. A. Maguskin  V. E. Levin  S. V. Enman 《Bulletin of Volcanology》1980,43(1):35-45

The paper discusses the results of geodetic investigations performed in the region of the large 1975–1976 Tolbachik fissure eruption in Kamchatka. Using data from repeated triangulation and trigonometric levelings, horizontal and vertical displacements have been detected in an area of 3,500 km². Two zones have been recognized: the tension and uplift zone that is probably due to magma intrusion from depths to the surface along the line of new cones and the extensive compensative subsidence zone located at a distance of 20–50 km from the nearest newly-formed cones. Measurements made with small distance measuring device showed the dynamics of feeding basalt dykes intrusion and made it possible to determine their width (a little greater than 1 m) and magma and gas overpressure (50–250 bar). Data have been obtained on dimensions and growth of cones and on vertical ground deformation in the area of new cones during and after the eruption.  相似文献   

Runup of nonlinearly deformed waves on a coast     

I. I. Didenkulova  N. Zahibo  A. A. Kurkin  B. V. Levin  E. N. Pelinovsky  T. Soomere 《Doklady Earth Sciences》2006,411(8):1241-1243

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High-field cantilever magnetometry as a tool for the determination of the magnetocrystalline anisotropy of single crystals   总被引：1，自引：0，他引：1  

Ftima Martín-Hernndez  Iris M. Bominaar-Silkens  Mark J. Dekkers  Jan Kees Maan 《Tectonophysics》2006,418(1-2):21

Cantilever torque magnetometry is utilized widely in physics and material science for the determination of magnetic properties of thin films and semiconductors. Here, we report on its first application in rock magnetism, namely the determination of K₁ and K₂ of single crystal octahedra of natural magnetite. The design of cantilever magnetometers allows optimization for the specific research question at hand. For the present study, a cantilever magnetometer was used that enables measurement of samples with a volume up to 64 mm³. It can be inserted into an electromagnet with a maximum field of 2 T. The cantilever spring is suitable for torque values ranging from 7.5 × 10^− 7 N·m to 5 × 10^− 6 N·m. The torque is detected capacitively; the measured capacitance is converted into torque by using a calibrated feedback coil. The magnetometer allows in-situ rotation of the sample in both directions and is, therefore, also suitable to analyze rotational hysteresis effects.The evaluation of the magnetite anisotropy constants involved Fourier analysis of the torque signal on the magnetite crystals' (001) and (110) planes. The absolute anisotropy constant has been computed using the extrapolation-to-infinite-field method. The value of K₁ at room temperature is determined at − 1.28 × 10⁴ [J m^− 3] (± 0.13, i.e. 10%) and that of K₂ at − 2.8 × 10³ [J m^− 3] (± 0.1, i.e. 2%). These values concur with earlier determinations that could not provide an instrumental error, in contrast with this work.The cantilever magnetometer performs four times faster than other torque magnetometers used for rock magnetic studies. This makes the instrument also suitable for magnetic fabric analysis.  相似文献   

Mixing Ratios and Photostationary State of NO and NO2 Observed During the POPCORN Field Campaign at a Rural Site in Germany     

F. Rohrer  D. Brüning  E. S. Grobler  M. Weber  D. H. Ehhalt  R. Neubert  W. Schüßler  I. Levin 《Journal of Atmospheric Chemistry》1998,31(1-2):119-137

Ambient mixing ratios of NO, NO2, and O3 were determined together with the photolysis frequency of NO2, JNO2, at a rural, agricultural site in Germany. The data were collected during the POPCORN-campaign from August 1 to August 24, 1994, in a maize field 6 m above ground. The medians of the NO, NO2, and O3 mixing ratios between 10:00 and 14:00 UT were 0.25, 1.09, and 45 ppbv, respectively. The corresponding median of JNO2 was 6.0 · 10–3 s–1. NOx = NO + NO2 showed a strong diurnal variation with maximum mixing ratios at night, suggestive of a strong local surface source of NO, probably by microbial activity in the soil. The estimated average emission rate was 40 ng(N) m–2 s–1 of NOx, the major part of it probably in the form of NO. The available measurements allowed the estimation of the local NOx budget. At night the budget is almost closed and the measured NOx mixing ratios can be explained by the local source, local dry deposition of NO2, formation of NO3 and N2O5, and vertical exchange of air across the nocturnal inversion. During day-time, the local surface source of NO is not sufficient to explain the measured mixing ratios, and horizontal advection of NOx to the site must be included. The NO2/NO ratio during the morning und late afternoon is lower than predicted from the photostationary state owing to the local NO surface source, but is regulary higher during the hours around noon. For noon, August 10, 1994, the NO2/NO ratio was used to derive the momentary lower limit for the concentration of the peroxy-radicals of 2.2 · 109 cm–3 (86 pptv).  相似文献   

Model investigation of electronic structure of some silicate clusters by DVM-X α     

Yu. P. Dikov  V. I. Rekharsky  G. L. Gutzev  S. P. Dolin  A. A. Levin 《Physics and Chemistry of Minerals》1986,13(1):48-60

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Cyclic variations in the Earth’s flattening and questions of seismotectonics     

B. W. Levin  E. V. Sasorova  G. M. Steblov  A. V. Domanskii  A. S. Prytkov  E. N. Tsyba 《Izvestiya Physics of the Solid Earth》2017,53(4):540-544

For more than a decade, the global network of GPS stations whose measurements are part of the International GPS Service (IGS) have been recording cyclic variations in the radius vector of the geodetic ellipsoid with a period of one year and amplitude of ~10 mm. The analysis of the figure of the Earth carried out by us shows that the observed variations in the vertical component of the Earth’s surface displacements can induce small changes in the flattening of the Earth’s figure which are, in turn, caused by the instability of the Earth’s rotation. The variations in the angular velocity and flattening of the Earth change the kinetic energy of the Earth’s rotation. The additional energy is ~10²¹ J. The emerging variations in the flattening of the Earth’s ellipsoid lead to changes in the surface area of the Earth’s figure, cause the development of deformations in rocks, accumulation of damage, activation of seismotectonic processes, and preparation of earthquakes. It is shown that earthquakes can be caused by the instability of the Earth’s rotation which induces pulsations in the shape of the Earth and leads to the development of alternating-sign deformations in the Earth’s solid shell.  相似文献