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排序方式: 共有438条查询结果,搜索用时 15 毫秒
61.
62.
Allessandro Piccolo Riccardo Spaccini Rolf Nieder Joerg Richter 《Climatic change》2004,67(2-3):329-343
In a long-term (one year) experiment, a sandy Podzol and a silty-loamy Loess soil were treated with labile (polysaccharides, AG) and stable (mature compost, CMP, and two humic acids from compost, HAC, and lignite, HAL) organic matter and the organic carbon (OC) lost by mineralization was periodically evaluated. The stable materials alone induced a significant reduction of OC losses in Podzol CMP <, HAL, <, HAC, Control), whereas the same treatments, except for CMP, produced an OC loss larger than control in Loess. This was attributed to the diverse textural and physical status of the two soils. The added stable organic matter became protected in the Podzol soil within the aggregates formed by the interaction with the coarse inorganic phase, while it was more easily decomposed in the Loess soils due to the strength of the native humic-clay complexes. In both soils, when the stable organic materials were mixed with polysaccharides (AG), the OC losses from this labile fraction were significantly reduced, being CMP more OC sequestering than HAC and HAL, in the order. These results confirmed that labile organic matter in soils can be protected from biodegradation by repartition into the hydrophobic domains of the stable, humified organic matter. This study suggests that mature compost and humic acids may usefully integrate management practices aimed to sequester organic carbon in soils. 相似文献
63.
Challenges in global ballast water management 总被引:3,自引:0,他引:3
Endresen Ø Lee Behrens H Brynestad S Bjørn Andersen A Skjong R 《Marine pollution bulletin》2004,48(7-8):615-623
Ballast water management is a complex issue raising the challenge of merging international regulations, ship's specific configurations along with ecological conservation. This complexity is illustrated in this paper by considering ballast water volume, discharge frequency, ship safety and operational issues aligned with regional characteristics to address ecological risk for selected routes. A re-estimation of ballast water volumes gives a global annual level of 3500 Mton. Global ballast water volume discharged into open sea originating from ballast water exchange operations is estimated to approximately 2800 Mton. Risk based decision support systems coupled to databases for different ports and invasive species characteristics and distributions can allow for differentiated treatment levels while maintaining low risk levels. On certain routes, the risk is estimated to be unacceptable and some kind of ballast water treatment or management should be applied. 相似文献
64.
65.
Olga V. Sidorova Matthias Saurer Vladimir S. Myglan Anja Eichler Margit Schwikowski Aleksander V. Kirdyanov Marina V. Bryukhanova Oksana V. Gerasimova Ivan A. Kalugin Andrey V. Daryin Rolf T. W. Siegwolf 《Climate Dynamics》2012,38(1-2):175-188
For the first time we present a multi-proxy data set for the Russian Altai, consisting of Siberian larch tree-ring width (TRW), latewood density (MXD), δ13C and δ18O in cellulose chronologies obtained for the period 1779–2007 and cell wall thickness (CWT) for 1900–2008. All of these parameters agree well between each other in the high-frequency variability, while the low-frequency climate information shows systematic differences. The correlation analysis with temperature and precipitation data from the closest weather station and gridded data revealed that annual TRW, MXD, CWT, and δ13C data contain a strong summer temperature signal, while δ18O in cellulose represents a mixed summer and winter temperature and precipitation signal. The temperature and precipitation reconstructions from the Belukha ice core and Teletskoe lake sediments were used to investigate the correspondence of different independent proxies. Low frequency patterns in TRW and δ13C chronologies are consistent with temperature reconstructions from nearby Belukha ice core and Teletskoe lake sediments showing a pronounced warming trend in the last century. Their combination could be used for the regional temperature reconstruction. The long-term δ18O trend agrees with the precipitation reconstruction from the Teletskoe lake sediment indicating more humid conditions during the twentieth century. Therefore, these two proxies could be combined for the precipitation reconstruction. 相似文献
66.
Florian Scholz Christian Hensen Anja Reitz Rolf L. Romer Volker Liebetrau Anette Meixner Stephan M. Weise Matthias Haeckel 《Geochimica et cosmochimica acta》2009,73(18):5444-5459
The chemical and isotopic composition of pore fluids is presented for five deep-rooted mud volcanoes aligned on a transect across the Gulf of Cadiz continental margin at water depths between 350 and 3860 m. Generally decreasing interstitial Li concentrations and 87Sr/86Sr ratios with increasing distance from shore are attributed to systematically changing fluid sources across the continental margin. Although highest Li concentrations at the near-shore mud volcanoes coincide with high salinities derived from dissolution of halite and late-stage evaporites, clayey, terrigenous sediments are identified as the ultimate Li source to all pore fluids investigated. Light δ7Li values, partly close to those of hydrothermal vent fluids (δ7Li: +11.9‰), indicate that Li has been mobilized during high-temperature fluid/sediment or fluid/rock interactions in the deep sub-surface. Intense leaching of terrigenous clay has led to radiogenic 87Sr/86Sr ratios (0.7106) in pore fluids of the near-shore mud volcanoes. In contrast, non-radiogenic 87Sr/86Sr ratios (0.7075) at the distal locations are attributed to admixing of a basement-derived fluid component, carrying an isotopic signature from interaction with the basaltic crust. This inference is substantiated by temperature constraints from Li isotope equilibrium calculations suggesting exchange processes at particularly high temperatures (>200 °C) for the least radiogenic pore fluids of the most distal location.Advective pore fluids in the off-shore reaches of the Gulf of Cadiz are influenced by successive exchange processes with both oceanic crust and terrigenous, fine-grained sediments, resulting in a chemical and isotopic signature similar to that of fluids in near-shore ridge flank hydrothermal systems. This suggests that deep-rooted mud volcanoes in the Gulf of Cadiz represent a fluid pathway intermediate between mid-ocean ridge hydrothermal vent and shallow, marginal cold seep. Due to the thicker sediment coverage and slower fluid advection rates, the overall geochemical signature is shifted towards the sediment-diagenetic signal compared to ridge flank hydrothermal environments. 相似文献
67.
Susanne Glaser Rolf König Dimitrios Ampatzidis Tobias Nilsson Robert Heinkelmann Frank Flechtner Harald Schuh 《Journal of Geodesy》2017,91(7):723-733
In this study, we assess the impact of two combination strategies, namely local ties (LT) and global ties (GT), on the datum realization of Global Terrestrial Reference Frames in view of the Global Geodetic Observing System requiring 1 mm-accuracy. Simulated Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) data over a 7 year time span was used. The LT results show that the geodetic datum can be best transferred if the precision of the LT is at least 1 mm. Investigating different numbers of LT, the lack of co-located sites on the southern hemisphere is evidenced by differences of 9 mm in translation and rotation compared to the solution using all available LT. For the GT, the combination applying all Earth rotation parameters (ERP), such as pole coordinates and UT1-UTC, indicates that the rotation around the Z axis cannot be adequately transferred from VLBI to SLR within the combination. Applying exclusively the pole coordinates as GT, we show that the datum can be transferred with mm-accuracy within the combination. Furthermore, adding artificial stations in Tahiti and Nigeria to the current VLBI network results in an improvement in station positions by 13 and 12%, respectively, and in ERP by 17 and 11%, respectively. Extending to every day VLBI observations leads to 65% better ERP estimates compared to usual twice-weekly VLBI observations. 相似文献
68.
Rolf Thienhaus 《International Journal of Earth Sciences》1953,42(1):63-79
Ohne Zusammenfassung 相似文献
69.
Turbulence measurements have been carried out in the surf zone of a wave flume. The purpose of the measurements is to determine the length scale of the turbulence generated by the wave breaking. The length scale of the turbulence is estimated on basis of the correlation between simultaneous measurements of the vertical turbulent fluctuations, taken at different levels above the bed. 相似文献
70.
Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite facies zircons: geochronology of the Ivrea Zone (Southern Alps) 总被引:52,自引:2,他引:50
Gerhard Vavra Rolf Schmid Dieter Gebauer 《Contributions to Mineralogy and Petrology》1999,134(4):380-404
Several types of growth morphologies and alteration mechanisms of zircon crystals in the high-grade metamorphic Ivrea Zone
(IZ) are distinguished and attributed to magmatic, metamorphic and fluid-related events. Anatexis of pelitic metasediments
in the IZ produced prograde zircon overgrowths on detrital cores in the restites and new crystallization of magmatic zircons
in the associated leucosomes. The primary morphology and Th-U chemistry of the zircon overgrowth in the restites show a systematic
variation apparently corresponding to the metamorphic grade: prismatic (prism-blocked) low-Th/U types in the upper amphibolite
facies, stubby (fir-tree zoned) medium-Th/U types in the transitional facies and isometric (roundly zoned) high-Th/U types
in the granulite facies. The primary crystallization ages of prograde zircons in the restites and magmatic zircons in the
leucosomes cannot be resolved from each other, indicating that anatexis in large parts of the IZ was a single and short lived
event at 299 ± 5 Ma (95% c. l.). Identical U/Pb ages of magmatic zircons from a metagabbro (293 ± 6 Ma) and a metaperidotite
(300 ± 6 Ma) from the Mafic Formation confirm the genetic context of magmatic underplating and granulite facies anatexis in
the IZ. The U-Pb age of 299 ± 5 Ma from prograde zircon overgrowths in the metasediments also shows that high-grade metamorphic
(anatectic) conditions in the IZ did not start earlier than 20 Ma after the Variscan amphibolite facies metamorphism in the
adjacent Strona–Ceneri Zone (SCZ). This makes it clear that the SCZ cannot represent the middle to upper crustal continuation
of the IZ. Most parts of zircon crystals that have grown during the granulite facies metamorphism became affected by alteration
and Pb-loss. Two types of alteration and Pb-loss mechanisms can be distinguished by cathodoluminescence imaging: zoning-controlled
alteration (ZCA) and surface-controlled alteration (SCA). The ZCA is attributed to thermal and/or decompression pulses during
extensional unroofing in the Permian, at or earlier than 249 ± 7 Ma. The SCA is attributed to the ingression of fluids at
210 ± 12 Ma, related to hydrothermal activity during the breakup of the Pangaea supercontinent in the Upper Triassic/Lower
Jurassic.
Received: 7 July 1998 / Accepted: 4 November 1998 相似文献