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201.
Sophie GODIN-BEEKMANN Irina PETROPAVLOSKIKH Stefan REIS Paul NEWMAN Wolfgang STEINBRECHT Markus REX Michelle L. SANTEE Richard S. ECKMAN Xiangdong ZHENG Matthew B. TULLY David S. STEVENSON Paul YOUNG John PYLE Mark WEBER Johanna TAMMINEN Gina MILLS Alkiviadis F. BAIS Clare HEAVISIDE Christos ZEREFOS 《大气科学进展》2018,35(3):368-369
202.
Mingjie Shen Shouyun Hu Uli. Blaha Haitao Yan Wolfgang. R?sler Ewin. Appel Viktor. Hoffmann 《Frontiers of Earth Science》2008,2(4):400-407
An expressway-side soil profile 22 cm long was sampled from the grassland of the expressway linking Beijing and the Capital
International Airport. Magnetic measurements, geochemical and multivariate statistic analyses were performed on the soil samples.
The results reveal that the soil profile can be divided into two parts with significant difference in magnetic proxies and
heavy metal concentration. The uppermost soil horizon (0–8 cm) represents the pollution-rich layer with higher concentration
of ferrimagnetic phases and metallic elements. The values of xare very high with an average of 141.60 × 10−8 m3·kg−1 in the layer. We explain that the anthropogenic dust input from traffic is the predominant cause for strong signals of magnetic
phases and heavy metals. Below the profile depth of 8 cm, there is minor pollution in the soil with lower concentration of
magnetic minerals and heavy metals compared to the natural background values. χ remains quite stable and relatively low with
an average of 49.44 × 10−8 m3·kg−1. S-ratio also generally decreases with depth, and it changes from 0.93 in the 0–8 cm layer to 0.87 below the depth of 8 cm.
It indicates that the soil samples are overwhelmingly predominated by ferrimagnetic minerals in the upper part soil, while
the contribution of imperfect antiferromagnetic components is stronger in the lower part. Rock magnetic experiments show MD
magnetite as the main magnetic carrier both in the upper and lower parts. Themagnetic grain size in the upper part is, however,
a bit coarser than that in the lower part. Cluster analysis shows a positive correlation between magnetic properties (χ, ARM,
SIRM) and heavy metal pollutants of Pb, Zn, Cu. Fuzzy C-means cluster analysis can clearly help divide the soil profile into
two different layers and distinguish their characteristics. It can be concluded that these magnetic concentration-related
parameters can be used as proxies for pollution investigation in a fast, sensitive, low-cost and highly efficient approach
to screening heavy metal pollution.
__________
Translated from Quaternary Sciences, 2007, 27(6): 1113-1120 [译自:第四纪研究] 相似文献
203.
Marián Putiš Hans-Jürgen Gawlick Wolfgang Frisch Marián Sulák 《International Journal of Earth Sciences》2008,97(4):799-819
The Cretaceous orogen of the Western Carpathians comprises fragments of the destructed northern Centrocarpathian domain, which
is defined as Infratatric unit and formed a continental margin facing the Penninic Ocean in Jurassic and Cretaceous times.
The breakup event and opening of the Penninic Ocean occurred in the Early Jurassic (Pliensbachian), which is recorded by an
abrupt deepening event from shallow-water sediments to deep-water nodular limestone in the Infratatric sediment succession.
The transformation of the passive into an active continental margin by the onset of subduction of the Penninic oceanic crust
occurred in Santonian times and is reflected by the beginning of flysch deposition in the Infratatric Belice domain, which
took the position of a forearc basin in the convergent margin setting. The forearc basin was supplied by clastic material
from the more internal part of the Infratatric unit, which experienced nappe stacking, metamorphism, and subsequent exhumation
in Late Cretaceous times. In the frontal part of the forearc basin an accretionary wedge was built up, which formed an outer-arc
ridge and delivered detrital material into the forearc basin in Maastrichtian time. Final collision between the European and
the Adriatic plate occurred in the Eocene period and is responsible for weak metamorphism in the Infratatric unit. 相似文献
204.
Wolfgang Dreybrodt 《Geochimica et cosmochimica acta》2008,72(19):4712-4724
The isotopic composition of carbon and oxygen in a calcite precipitating CO2-H2O-CaCO3 solution is preserved in the calcite precipitated. For the interpretation of isotopic proxies from stalagmites knowledge of the evolution of δ13C and δ18O in the solution during precipitation is required. A system of differential equations is presented from which this evolution can be derived. Both, irreversible loss of carbon and oxygen from the solution with precipitation time τ and exchange of oxygen in the carbonates with the oxygen in the water with exchange time T are considered. For carbon, where no exchange is active, a modified equation of Rayleigh-distillation is found, which takes into account that precipitation stops at ceq, the saturation concentration of DIC with respect to calcite, and that ceq as well as the precipitation time τ is slightly different for the heavy and the light isotope. This, however, requires introducing a new parameter γ = (Aeq/Beq)/(A0/B0), which has to be determined experimentally. (Aeq/Beq) is the isotopic ratio for the heavy (A) and the light isotope (B) at both chemical and isotopic equilibrium and (A0/B0) is the initial isotopic ratio of the solution. In the case of oxygen, where exchange is present, the isotopic shifts are reduced with increasing values of the precipitation time τ. For τ ? T the solution stays in isotopic equilibrium with the oxygen in the water during the entire time in which precipitation is active. The isotopic ratios in a calcite precipitating solution R(t)/R0 = (1 + δ(t)/1000) for carbon are plotted versus those of oxygen. R0 is the isotopic ratio at time t = 0, when precipitation starts and δ(t) the isotopic shift in the solution after time t. These show positive correlations for the first 50% of calcite, which can precipitate. Their slopes increase with increasing values of τ and they closely resemble Hendy-tests performed along growth layers of stalagmites. Our results show that stalagmites, which grow by high supply of water with drip times less than 50 s, exhibit positive correlations between δ13C and δ18O along a growth layer. But in spite of this the isotopic composition of oxygen in the solution at the apex is in isotopic equilibrium with the oxygen in the water, and therefore also that of calcite deposited at the apex. 相似文献
205.
The Variscan Hauzenberg pluton consists of granite and granodiorite that intruded late- to postkinematically into HT-metamorphic rocks of the Moldanubian unit at the southwestern margin of the Bohemian Massif (Passauer Wald). U–Pb dating of zircon single-grains and monazite fractions, separated from medium- to coarse-grained biotite-muscovite granite (Hauzenberg granite II), yielded concordant ages of 320 ± 3 and 329 ± 7 Ma, interpreted as emplacement age. Zircons extracted from the younger Hauzenberg granodiorite yielded a 207Pb–206Pb mean age of 318.6 ± 4.1 Ma. The Hauzenberg granite I has not been dated. The pressure during solidification of the Hauzenberg granite II was estimated at 4.6 ± 0.6 kbar using phengite barometry on magmatic muscovite, corresponding to an emplacement depth of 16-18 km. The new data are compatible with pre-existing cooling ages of biotite and muscovite which indicate the Hauzenberg pluton to have cooled below T = 250–400 °C in Upper Carboniferous times. A compilation of age data from magmatic and metamorphic rocks of the western margin of the Bohemian Massif suggests a west- to northwestward shift of magmatism and HT/LP metamorphism with time. Both processes started at > 325 Ma within the South Bohemian Pluton and magmatism ceased at ca. 310 Ma in the Bavarian Oberpfalz. The slight different timing of HT metamorphism in northern Austria and the Bavarian Forest is interpreted as being the result of partial delamination of mantle lithosphere or removal of the thermal boundary layer. 相似文献
206.
Foraminifera from two cores off eastern Vietnam and the northwestern Philippines, where modern summer and winter monsoon-driven upwelling occurs in the South China Sea, respectively, were analyzed to evaluate the changes in paleoproductivity and upper water structure over the last 220,000 yr. We observed enhanced organic carbon flux and a shoaled thermocline when upwelling intensified off eastern Vietnam during interglacial ages and off the northwestern Philippines during glacial ages. This indicates that the East Asian summer monsoon increased while the winter monsoon decreased during interglacial ages. Particularly, the upwelling reached a maximum off eastern Vietnam during late marine isotopic stage (MIS) 5 and off the northwestern Philippines during MIS 2, implying that the summer monsoon decreased gradually since MIS 5 while the winter monsoon displayed an opposite trend. The variations in upwelling proxies exhibit a distinct cyclicity with frequencies near 41,000 yr and 23,000 yr off eastern Vietnam, in contrast to a strong frequency peak near 100,000 yr off the northwestern Philippines. We suggest that the East Asian summer monsoon has been forced by changes in solar insolation associated with precession and obliquity, while ice-volume forcing is probably a primary factor in determining the strength and timing of the East Asian winter monsoon but with less important insolation forcing. 相似文献
207.
208.
209.
To obtain clues about how coastal primary production might be affected by interannual and interdecadal changes in climate, we studied marine laminated sediments from the center of the Santa Barbara Basin. We report here a large decrease in the flux of diatoms between the periods 1954–1972 and 1973–1986, by a factor of five, and sustained reductions from 1973 to 1978 by a factor of ten below the pre-1972 period. Planktonic foraminifera flux shows a consistent trend of decrease with lowest values from 1981 to 1984. On the whole, the 1954–1972 period is considerably cooler than the 1973–1986 period, over the entire North Pacific. The decrease in biological production in this coastal system is accompanied by an overall intensification of the Aleutian Low in the North Pacific over the past 14 years, providing for a weakening of the California Current, and an overall reduction of mixing and upwelling. The possibility that the low coastal production could provide positive feedback to global warming through reduction of CO2-uptake, and its relation to the greenhouse effect is considered. On a shorter time-scale, the effects of El Niño phenomena are clearly seen in the sediments of this basin, as decreases in total diatom flux and increases in the relative abundance of certain warm-water diatoms. 相似文献