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121.
Lead isotopes of K-feldspars from five granites of the SE-Schwarzwald and from metamorphites are positively correlated in
207/204 as well- as 208/204- vs. 206/204-diagrams.
The linear alignments may be due to correlated laststage lead isotope evolution (lead-lead isochron) and result in a secondary
isochron model age of nearly 3 Ga for the Southern Schwarzwald basement. This calculation implies a long-lasting undisturbed
lead isotope evolution in the Schwarzwald basement since the Archaean. This is not supported however by geochronological studies.
On the other hand the data together with U/Pb-analyses of whole rock samples from metamorphites are consistent with pre-Hercynian
mantle lead addition to the basement. This presumably happened during early Paleozoic polymetamorphism. The interpretation
of the lead isotope correlations as mantle-crust mixing lines needs a rather homogeneous pre-Hercynian mantle lead of the
MORB-type, delivered to the crust probably in part by ascending volatile phases. Thus geodynamical models are supported which
involve subduction of oceanic crust or mantle pluming during the early Paleozoic.
In Part I of this report, the trends in Schwarzwald lead isotopes are discussed as secondary isochrons and as mixing lines.
Constraints are derived for a pre-Hercynian mantlecrust interaction and for lead redistribution by the Hercynian basement
activation. 相似文献
122.
Altogether 64 predominantly biological traits were coded for more than 600 macroinvertebrate species from European rivers. The main question was: Are biological traits able to reflect “biological functionality” in large rivers and if so, is it possible to deduce an assessment system based on functionality? Analysis of the raw trait structure of all species indicates that these traits are not completely independent from their higher systematic units. To avoid mis-interpretations when judging from mixtures of habitats (β-biocoenosis) we used for our investigations only sample series from -biocoenosis, pre-tested by a mathematical criterion of homogeneity. Within -biocoenosis, traits are shown to be able to compensate for drastic changes with respect to species number and species composition along a river continuum, demonstrating their functional quality. Long-term changes in the trait and species structures of German waterways were studied using multivariate methods, based on an analysis of 142 sampling series. A shift from traits typical for K-strategists to traits typical for r-strategists was detected to be the main background variable. The rK-strategy is regarded as a true functional character of species. We calculated the relative positions of all trait-coded species on this rK-scale, and plotted the functional diversity of our samples against the structural diversity of the species from several river systems. Rivers extremely dominated by r-strategists show a deficit in functional diversity. Rivers dominated by K-strategists also show deficits, possibly in concordance with modern ecological theories such as the intermediate disturbance theory. The quantitative proportions of extreme r- to K-Strategists in -biocoenosis can be used as a general disturbance measure. 相似文献
123.
124.
Christopher Hamann Saskia Bläsing Lutz Hecht Sebastian Schäffer Alex Deutsch Jens Osterholz Bernd Lexow 《Meteoritics & planetary science》2018,53(8):1644-1686
We simulated entrainment of carbonates (calcite, dolomite) in silicate impact melts by 1-bar laser melting of silicate–carbonate composite targets, using sandstone, basalt, calcite marble, limestone, dolomite marble, and iron meteorite as starting materials. We demonstrate that carbonate assimilation by silicate melts of variable composition is extremely fast (seconds to minutes), resulting in contamination of silicate melts with carbonate-derived CaO and MgO and release of CO2 at the silicate melt–carbonate interface. We identify several processes, i.e., (1) decomposition of carbonates releases CO2 and produces residual oxides (CaO, MgO); (2) incorporation of residual oxides from proximally dissociating carbonates into silicate melts; (3) rapid back-reactions between residual CaO and CO2 produce idiomorphic calcite crystallites and porous carbonate quench products; (4) high-temperature reactions between Ca-contaminated silicate melts and carbonates yield typical skarn minerals and residual oxide melts; (5) mixing and mingling between Ca- or Ca,Mg-contaminated and Ca- or Ca,Mg-normal silicate melts; (6) precipitation of Ca- or Ca,Mg-rich silicates from contaminated silicate melts upon quenching. Our experiments reproduce many textural and compositional features of typical impact melts originating from silicate–carbonate targets. They reinforce hypotheses that thermal decomposition of carbonates, rapid back-reactions between decomposition products, and incorporation of residual oxides into silicate impact melts are prevailing processes during impact melting of mixed silicate–carbonate targets. However, by comparing our results with previous studies and thermodynamic considerations on the phase diagrams of calcite and quartz, we envisage that carbonate impact melts are readily produced during adiabatic decompression from high shock pressure, but subsequently decompose due to heat influx from coexisting silicate impact melts or hot breccia components. Under certain circumstances, postshock conditions may favor production and conservation of carbonate impact melts. We conclude that the response of mixed carbonate–silicate targets to impact might involve melting and decomposition of carbonates, the dominant response being governed by a complex variety of factors. 相似文献
125.
Christian Lehr Philipp Rauneker Marcus Fahle Tobias L. Hohenbrink Steven Böttcher Marco Natkhin Björn Thomas Ralf Dannowski Bernd Schwien Gunnar Lischeid 《水文研究》2017,31(3):750-752
Physical models are a well‐established tool in education to strengthen hydrological understanding. They facilitate the straightforward visualization of hydrological processes and allow the communication of hydrological concepts, research and questions of general interest to the public. In order to visualize the water cycle in a landscape of postglacial sediments, in particular the subsurface part, a physical model was constructed. In two videos, (1) a detailed construction manual and (2) visualization examples of hydrological concepts and processes are presented. With our contribution, we like to encourage professionals in the field of hydrology to share methods and tools of knowledge transfer and communication of hydrological concepts. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
126.
Bernd Schneider Seppo Kaitala Mika Raateoja Bernd Sadkowiak 《Continental Shelf Research》2009,29(11-12):1535-1540
Organic matter production and nitrogen fixation in the central Baltic Sea were studied on the basis of high-resolution CO2 partial pressure data that were obtained from an automated measurement system deployed on a cargo ship. The net organic carbon (OC) production was calculated from a surface water CO2 mass balance and used to estimate the nitrogen uptake by organic matter during the period March to August 2005. It was shown that the net OC production continued despite the exhaustion of dissolved inorganic nitrogen (DIN) after the spring bloom in April. The nitrogen demand for this production was calculated on the basis of the C/N ratio of organic matter. It was of the same order of magnitude than the winter DIN concentration that fuelled the spring bloom. Since the atmospheric DIN deposition was negligible and no indications of alternative DIN sources were found, it was assumed that N2 fixation had taken place despite the low temperatures (4–8 °C) in April/May. This “cold fixation” amounted to 74 mmol m?2 whereas a value of 99 mmol m?2 was obtained for the summer N2 fixation during June/July. Due to the contribution of the April/May N2 fixation, a total annual rate (173±35 mmol m?2) was obtained for 2005 which is considerably higher than presently accepted estimates. These findings were confirmed by a nitrogen budget based on long-term data (1993–2006) for total nitrogen and total phosphorus concentrations. Furthermore, these data revealed a 30% increase in N2 fixation during the years 1994–2006. 相似文献
127.
Stereo analysis of images obtained during the 2001 flyby of Comet Borrelly by NASA's Deep Space 1 (DS1) probe allows us to quantify the shape and photometric behavior of the nucleus. The shape is complex, with planar facets corresponding to the dark, mottled regions of the surface whereas the bright, smooth regions are convexly curved. The photometric as well as textural differences between these regions can be explained in terms of topography (roughness) at and below the image resolution, without invoking significant variations in single-particle properties; the material on Borrelly's surface could be quite uniform. A statistical comparison of the digital elevation models (DEMs) produced from the three highest-resolution images independently at the USGS and DLR shows that their difference standard deviation is 120 m, consistent with a matching error of 0.20 pixel (similar to reported matching accuracies for many other stereo datasets). The DEMs also show some systematic differences attributable to manual versus automatic matching. Disk-resolved photometric modeling of the nucleus using the DEM shows that bright, smooth terrains on Borrelly are similar in roughness (Hapke roughness θ=20°) to C-type asteroid Mathilde but slightly brighter and more backscattering (single-scattering albedo w=0.056, Henyey-Greenstein phase parameter g=−0.32). The dark, mottled terrain is photometrically consistent with the same particles but with roughnesses as large as 60°. Intrinsically darker material is inconsistent with the phase behavior of these regions. Many local radiance variations are clearly related to topography, and others are consistent with a topographic explanation; one need not invoke albedo variations greater than a few tens of percent to explain the appearance of Borrelly. 相似文献
128.
Soil and sand fine particles, which may be resuspended as fine dust in the atmosphere, contain a variety of anthropogenic
and natural organic components. Samples of fine soil and sand particles (sieved to <125 μM) were collected from the Riyadh
area in the summer of 2003 and extracted with a mixture of dichloromethane and methanol (3:1, v:v). The derivatized total
extracts were analyzed by gas chromatography–mass spectrometry in order to characterize the composition and sources of the
organic components. Both anthropogenic and natural biogenic inputs were the major sources of the organic compounds in these
extracts. Discarded plastics and vehicular emission products were the major anthropogenic sources in the fine particles from
populated areas of the city. Their tracers were plasticizers, UCM, n-alkanes, hopanes and traces of steranes. Vegetation was the major natural source of organic compounds in samples from outside
Riyadh and included n-alkanols, n-alkanoic acids, n-alkanes, methyl alkanoates, sterols and triterpenoids. Carbohydrates had high concentrations (42–54%) in all samples and
indicate sources from decomposition of cellulose and/or the presence of viable microbiota such as bacteria and fungi. The
results were also compared with the data obtained in winter 2002 and showed that anthropogenic inputs were higher in summer
than in winter, whereas the opposite trend was observed for natural inputs. 相似文献
129.
Holocene climate change in the Central Tibetan Plateau inferred by lacustrine sediment geochemical records 总被引:2,自引:0,他引:2
Multi-proxies of lacustrine sediments, such as total carbon (TC), total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), total sulfur (TS), hydrogen index (HI), oxygen index (OI) and stable carbon isotopic composition of organic matter (δ 13Corg), were analyzed using a 7.3 m core from Zigê Tangco. The source of the organic matter in the sediment was mainly from autochthonous phytoplankton, therefore the significances of proxies can be interpreted as that high TOC, TOC/TS, HI and δ13Corg values, low TC, TIC values corresponded to warm and wet climatic condition, and vice versa. The process of climatic development in the Zigê Tangco region was hence recovered. During the early and Mid-Holocene, the climate was warm and wet and intensive cold events occurred during the periods of 8600 to 8400 cal a BP and 7400 to 7000 cal a BP. In the second half of Holocene, the climate became cold and dry gradually. The palaeoclimatic process during Holocene in Zigê Tangco region matched well with that in Co Ngoin region which is ca 40 km to the south-east. Therefore this palaeoclimatic process represents the Holocene climatic feature in the Central Tibetan Plateau which has the same pattern in the Northern Tibetan Plateau, but the time and duration of some climatic events might be different. We can conclude that in Holocene solar insolation controlled the climatic pattern on the central Tibetan Plateau. 相似文献
130.