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431.
Uwe Kasper 《Astronomische Nachrichten》1984,305(5):277-277
432.
P. M. Ross M. P. Beentjes J. Cope W. P. de Lange B. G. McFadgen P. Redfearn 《新西兰海洋与淡水研究杂志》2018,52(2):196-231
Toheroa (Paphies ventricosa) were formerly abundant on west and south-facing New Zealand surf beaches. Harvesting of this surf clam was intense during the early to mid-1900s, and populations declined to levels where harvesting was no longer viable. Despite having now been protected for 35–45 years, toheroa have failed to recover. This paper reviews the history of human interactions with toheroa and our understanding of their ecology, with a view to identifying knowledge requirements for management and restoration. Historical and legal documents pertaining to the use of marine resources are reviewed and scientific understanding compared with customary and local knowledge. We consider the factors that may be preventing toheroa recovery and make recommendations for research into life history, habitat requirements and the ecological consequences of changing land use. Management options are suggested to address the effects of vehicle use on beaches, poaching and the failings of the customary harvest system. 相似文献
433.
434.
During two “Valdivia” cruises, 1971 and 1972, bathymetric and geologic studies have been made at the junction between the Gulf of Aden and the Afar rift systems, namely in the Gulf of Tadjura and the nearly closed basin of the Ghubbet el Kharab (western end of the Gulf of Aden). A predominantly east-northeast striking fracture zone determines the morphologic structure of the central part of the gulf. The western end of the Gulf of Tadjura, including the Ghubbet el Kharab, is characterized by northwest striking normal faults.Up to 40 m thick subrecent sediments of the Ghubbet, mainly composed of diatoms, clay minerals, and volcanic glass, are already affected by a system of normal faults. 相似文献
435.
In situ pore-pressure evolution during dynamic CPT measurements in soft sediments of the western Baltic Sea 总被引:1,自引:1,他引:0
Annedore?SeifertEmail author Sylvia?Stegmann Tobias?M?rz Matthias?Lange Thomas?Wever Achim?Kopf 《Geo-Marine Letters》2008,28(4):213-227
We present in situ strength and pore-pressure measurements from 57 dynamic cone penetration tests in sediments of Mecklenburg (n?=?51), Eckernförde (n?=?2) and Gelting (n?=?4) bays, western Baltic Sea, characterised by thick mud layers and partially free microbial gas resulting from the degradation of organic material. In Mecklenburg and Eckernförde bays, sediment sampling by nine gravity cores served sedimentological characterisation, analyses of geotechnical properties, and laboratory shear tests. At selected localities, high-resolution echo-sounder profiles were acquired. Our aim was to deploy a dynamic cone penetrometer (CPT) to infer sediment shear strength and cohesion of the sea bottom as a function of fluid saturation. The results show very variable changes in pore pressure and sediment strength during the CPT deployments. The majority of the CPT measurements (n?=?54) show initially negative pore-pressure values during penetration, and a delayed response towards positive pressures thereafter. This so-called type B pore-pressure signal was recorded in all three bays, and is typically found in soft muds with high water contents and undrained shear strengths of 1.6–6.4 kPa. The type B signal is further affected by displacement of sediment and fluid upon penetration of the lance, skin effects during dynamic profiling, enhanced consolidation and strength of individual horizons, the presence of free gas, and a dilatory response of the sediment. In Mecklenburg Bay, the remaining small number of CPT measurements (n?=?3) show a well-defined peak in both pore pressure and cone resistance during penetration, i.e. an initial marked increase which is followed by exponential pore-pressure decay during dissipation. This so-called type A pore-pressure signal is associated with normally consolidated mud, with indurated clay layers showing significantly higher undrained shear strength (up to 19 kPa). In Eckernförde and Gelting bays pore-pressure response type B is exclusively found, while in Mecklenburg Bay types A and B were detected. Despite the striking similarities in incremental density increase and shear strength behaviour with depth, gas occurrence and subtle variations in the coarse-grained fraction cause distinct pore-pressure curves. Gaseous muds interbedded with silty and sandy layers are most common in the three bays, and the potential effect of free gas (i.e. undersaturated pore space) on in situ strength has to be explored further. 相似文献
436.
Paul C. Buchanan Christian Koeberl Wolf Uwe Reimold 《Contributions to Mineralogy and Petrology》1999,137(1-2):133-146
The Precambrian Dullstroom Formation of South Africa, which is predominantly composed of basaltic andesites interbedded with
subordinate sedimentary and felsic volcanic strata, represents the first phase of an extended period of magmatism that was
responsible for the Bushveld Magmatic Province, including the extrusive Rooiberg Group and the intrusive Bushveld Complex.
New geochemical and isotopic data for the Dullstroom Formation are presented in an effort to elucidate the petrogenetic processes
operative during the initiation of this magmatic episode. The volcanic units of the central portion of the Dullstroom Formation
have been subdivided into at least three interbedded compositional groups: low Ti mafic to intermediate units, high-Ti mafic
to intermediate units, and high Mg felsic units. High Ti and low Ti volcanic units are similar in some compositional characteristics
to basalts of the nearby northern and southern provinces, respectively, of the Mesozoic Karoo continental flood basalts. Isotopic
and compositional data for low Ti Dullstroom strata are consistent with bulk assimilation into a melt similar in composition
to a southern Karoo basalt of 20% upper continental crust accompanied by 20% fractional crystallization of pyroxene and plagioclase.
Isotopic and compositional data for high Ti Dullstroom strata are consistent with magma mixing of 30% northern Karoo K-rich
basalt and 70% southern Karoo basalt followed by 20% assimilation of upper continental crust and 20% fractional crystallization
of pyroxene and plagioclase. Compositions of high Mg felsic volcanic strata are consistent with 25% assimilation of a mixture
of silica-rich sedimentary rock and upper continental crust into a melt similar in composition to low Ti volcanic units with
25% fractional crystallization of pyroxene and plagioclase. However, it has been suggested that compositions of these high
Mg felsic strata may also be consistent with interaction of a crustal melt. Assimilation, fractional crystallization, and
magma mixing that apparently affected these Dullstroom Formation volcanic strata may have occurred in a series of shallow
magma chambers. These data are consistent with the suggestion that Dullstroom Formation volcanic rocks are the result of a
mantle plume. Mantle plume origin also is suggested by the large volume of intrusive and extrusive strata associated with
this magmatic episode. These data do not support the hypothesis that the Bushveld Complex and the Rooiberg Group formed by
impacts of a cluster of comets or asteroids.
Received: 14 October 1998 / Accepted: 17 May 1999 相似文献
437.
G. J. De Lange 《Geochimica et cosmochimica acta》1986,50(12):2543-2561
Measured pore-water concentrations of iron in interbedded pelagic and turbiditic sediments from the Nares Abyssal Plain are in excellent agreement with sediment colour and measured redox potential. The organic carbon content of these sediments appears to define the redox conditions and consequently the porewater and solid-phase concentration of constituents that are involved in early diagenetic reactions. In the turbiditic sediments the concentration of NO3− generally goes to zero within a sediment depth of 1 m, whereas at 8 m in a pelagic core from the same area the concentration of NO3− is still higher than it is in the bottom water. The pore-water concentration of Mn2+ in the turbiditic sediments increases sharply down to a depth of approximately 3 m and from thereon remains nearly constant due to saturation with respect to Mn, Ca-CO3. The pore water of the turbiditic sediments is also saturated with respect to calcite. The few “diagenetic spikes” in the pore-water concentration of NO3− and Mn2+ and the concentration/depth profile of dissolved iron, H4SiO4 and phosphate all clearly demonstrate the inhomogeneous nature of interbedded pelagic and turbiditic sediments. The simultaneous occurrence of peaks of dissolved iron/silica and of sediment intervals with a relatively high organic carbon content is attributed to enhanced early diagenetic reactions associated with the decomposition of organic matter in these specific intervals. Linked with these reactions is the irregular pore-water concentration of phosphate, which is shown to originate partly from the oxidation of organic matter, but mainly from the desorption of phosphate from iron oxide. Potential concentrations of phosphate are calculated from the stoichiometric early diagenetic reactions and compared with measured concentrations. Due to the unique combination of low porosity and relatively high sedimentation rates, the sediments from the Nares Abyssal Plain are an ideal basis for the study of such interbedded sequences of pelagic and turbiditic deposits. 相似文献
438.
439.
The Influence of Thermal Effects on the Wind Speed Profile of the Coastal Marine Boundary Layer 总被引:1,自引:3,他引:1
Bernhard Lange Søren Larsen Jørgen Højstrup Rebecca Barthelmie 《Boundary-Layer Meteorology》2004,112(3):587-617
The wind speed profile in a coastal marine environment is investigated with observations from the measurement program Rødsand, where meteorological data are collected with a 50 m high mast in the Danish Baltic Sea, about 11 km from the coast. When compared with the standard Monin—Obukhov theory the measured wind speed increase between 10 m and 50 m height is found to be systematically larger than predicted for stable and near-neutral conditions. The data indicate that the deviation is smaller for short (10–20 km) distances to the coast than for larger (>30 km) distances. The theory of the planetary boundary layer with an inversion lid offers a qualitative explanation for these findings. When warm air is advected over colder water, a capping inversion typically develops. The air below is constantly cooled by the water and gradually develops into a well-mixed layer with near-neutral stratification. Typical examples as well as scatter plots of the data are consistent with this explanation. The deviation of measured and predicted wind speed profiles is shown to be correlated with the estimated height and strength of the inversion layer. 相似文献
440.
Hermann Held Friedrich-Wilhelm Gerstengarbe Tobias Pardowitz Joaquim G. Pinto Uwe Ulbrich Kai Born Markus G. Donat Melanie K. Karremann Gregor C. Leckebusch Patrick Ludwig Katrin M. Nissen Hermann Österle Boris F. Prahl Peter C. Werner Daniel J. Befort Olaf Burghoff 《Climatic change》2013,121(2):195-207
We present projections of winter storm-induced insured losses in the German residential building sector for the 21st century. With this aim, two structurally most independent downscaling methods and one hybrid downscaling method are applied to a 3-member ensemble of ECHAM5/MPI-OM1 A1B scenario simulations. One method uses dynamical downscaling of intense winter storm events in the global model, and a transfer function to relate regional wind speeds to losses. The second method is based on a reshuffling of present day weather situations and sequences taking into account the change of their frequencies according to the linear temperature trends of the global runs. The third method uses statistical-dynamical downscaling, considering frequency changes of the occurrence of storm-prone weather patterns, and translation into loss by using empirical statistical distributions. The A1B scenario ensemble was downscaled by all three methods until 2070, and by the (statistical-) dynamical methods until 2100. Furthermore, all methods assume a constant statistical relationship between meteorology and insured losses and no developments other than climate change, such as in constructions or claims management. The study utilizes data provided by the German Insurance Association encompassing 24 years and with district-scale resolution. Compared to 1971–2000, the downscaling methods indicate an increase of 10-year return values (i.e. loss ratios per return period) of 6–35 % for 2011–2040, of 20–30 % for 2041–2070, and of 40–55 % for 2071–2100, respectively. Convolving various sources of uncertainty in one confidence statement (data-, loss model-, storm realization-, and Pareto fit-uncertainty), the return-level confidence interval for a return period of 15 years expands by more than a factor of two. Finally, we suggest how practitioners can deal with alternative scenarios or possible natural excursions of observed losses. 相似文献