Ein CZCS-Postlaunch-Experiment über der Deutschen Bucht und seine Auswertung im Hinblick auf die dortigen Gelbstoff- und Schwebstoffgehalte sowie die Frontendynamik     

Dr. Hans Gienapp  Dr. Boris Sturm 《Ocean Dynamics》1983,36(3):97-128

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Carbonate budget of a cold-water coral carbonate mound: Propeller Mound,Porcupine Seabight   总被引：1，自引：0，他引：1  

Boris Dorschel  Dierk Hebbeln  Andres Rüggeberg  Christian Dullo 《International Journal of Earth Sciences》2007,96(1):73-83

High resolution studies from the Propeller Mound, a cold-water coral carbonate mound in the NE Atlantic, show that this mound consists of >50% carbonate justifying the name ‘carbonate mound’. Through the last ~300,000 years approximately one third of the carbonate has been contributed by cold-water corals, namely Lophelia pertusa and Madrepora oculata. This coral bound contribution to the carbonate budget of Propeller Mound is probably accompanied by an unknown portion of sediments buffered from suspension by the corals. However, extended hiatuses in Propeller Mound sequences only allow the calculation of a net carbonate accumulation. Thus, net carbonate accumulation for the last 175 kyr accounts for only <0.3 g/cm²/kyr, which is even less than for the off-mound sediments. These data imply that Propeller Mound faces burial by hemipelagic sediments as has happened to numerous buried carbonate mounds found slightly to the north of the investigated area.  相似文献   

Effects of elasticity on the Rayleigh–Taylor instability: implications for large-scale geodynamics     

Boris J. P. Kaus  Thorsten W. Becker 《Geophysical Journal International》2007,168(2):843-862

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Hard X-ray bremsstrahlung produced by electrons escaping a high-temperature thermal source in a solar flare     

Luigi Nocera  Yu. I. Skrynnikov  Boris V. Somov 《Solar physics》1985,97(1):81-105

The problem of production of flare hard X-rays by bremsstrahlung from hot thermal escaping electrons (Skrynnikov and Somov, 1982) in a chromospheric plasma is studied.The Landau kinetic equation is solved near the thermal source of energized electrons in a homogeneous magnetic tube to compute the anisotropic inhomogeneous distribution of the thermal escaping electrons.The intensity and polarization of hard X-rays is also computed and a comparison of theoretical results with observational data is made.On leave from: Istituto di Astronomia, Largo E, Fermi 5, I-50125 Firenze, Italy.  相似文献   

Late Pleistocene to Holocene vegetation and climate changes in northwestern Chukotka (Far East Russia) deduced from lakes Ilirney and Rauchuagytgyn pollen records     

Andrei A. Andreev  Elena Raschke  Boris K. Biskaborn  Stuart A. Vyse  Jeremy Courtin  Thomas Böhmer  Kathleen Stoof-Leichsenring  Stefan Kruse  Lyudmila A. Pestryakova  Ulrike Herzschuh 《Boreas: An International Journal of Quaternary Research》2021,50(3):652-670

This paper presents two new pollen records and quantitative climate reconstructions from northern Chukotka documenting environmental changes over the last 27.9 ka. Open tundra- and steppe-like habitats dominated between 27.9 and 18.7 cal. ka BP. Betula and Alnus shrubs might have grown in sheltered microhabitats but disappeared after 18.7 cal. ka BP. Although the climate was rather harsh, local herb-dominated communities supported herbivores as is evident by the presence of coprophilous spores in the sediments. The increase in Salix and Cyperaceae ~16.1 cal. ka BP suggests climate amelioration. Shrub Betula appeared ~15.9 cal. ka BP, and became dominant after ~15.52 cal. ka BP, whilst typical steppe communities drastically reduced. Very high presence of Botryococcus in the Lateglacial sediments reflects widespread shallow habitats, probably due to lake level increase. Shrub Alnus became common after ~13 cal. ka BP reflecting further climate amelioration. Simultaneously, herb communities gradually decreased in the vegetation reaching a minimum ~11.8 cal. ka BP. A gradual decrease of algae remains suggests a reduction of shallow-water habitats. Shrubby and graminoid tundra was dominant ~11.8–11.1 cal. ka BP, later Salix stands significantly decreased. The forest-tundra ecotone established in the Early Holocene, shortly after 11.1 cal. ka BP. Low contents of green algae in the Early Holocene sediments likely reflect deeper aquatic conditions. The most favourable climate conditions were between ~10.6 and 7 cal. ka BP. Vegetation became similar to the modern after ~7 cal. ka BP but Pinus pumila came to the Ilirney area at about 1.2 cal. ka BP. It is important to emphasize that the study area provided refugia for Betula and Alnus during MIS 2. It is also notable that our records do not reflect evidence of Younger Dryas cooling, which is inconsistent with some regional environmental records but in good accordance with some others.  相似文献   

Mineralogy and geochemistry of pozzolans from the Tombel Plain,Bamileke Plateau,and Noun Plain monogenetic volcanoes in the central part of the Cameroon Volcanic Line     

Fulbert  Mbowou Ngantche Igor  Sébastien  Owona  Boris  Chako Tchamabe  Justin  Lissom  Bruno  Lanson  Emmanuel  Ekodeck Georges 《中国地球化学学报》2020,39(6):830-861

Acta Geochimica - Pozzolans from the Tombel Plain, Bamileke Plateau, and Noun Plain, 3 monogenetic volcanic fields in the central part of the Cameroon Volcanic Line (the Tombel Plain, Bamileke...  相似文献   

Testing Gassmann fluid substitution: sonic logs versus ultrasonic core measurements     

Marcos Grochau  Boris Gurevich 《Geophysical Prospecting》2009,57(1):75-79

Although Gassmann fluid substitution is standard practice for time-lapse studies, its validity in the field environment rests upon a number of underlying assumptions. The impact of violation on the predictions of Gassmann equations can only ultimately be validated by in situ testing in real geological environments. In this paper we show a workflow that we developed to test Gassmann fluid substitution by comparing saturated P-wave moduli computed from dry core measurements against those obtained from sonic and density logs. The workflow has been tested on 43 samples taken from a 45 m turbidite reservoir from the Campos Basin, offshore Brazil. The results show good statistical agreement between the P-wave elastic moduli computed from cores using the Gassmann equation with the corresponding moduli computed from log data. This confirms that all the assumptions of the Gassmann are adequate within the measurement error and natural variability of elastic properties. These results provide further justification for using the Gassmann theory to interpret time-lapse effects in this sandstone reservoir and in similar geological formations.  相似文献   

Geochemistry of natural and contaminated subsurface waters in fissured bed rocks of the Lake Karachai area, Southern Urals, Russia     

Igor N. Solodov  Aleksandr V. Zotov  Aleksandr D. Khoteev  Aleksandr P. Mukhamet-Galeev  Boris R. Tagirov  John A. Apps 《Applied Geochemistry》1998,13(8):921-939

Hydrogeochemical investigations of natural and contaminated subsurface waters were conducted between 1992–94 in an area where liquid radioactive waste (RAW) was impounded in a small lake, and subsequently leaked into an underlying water bearing horizon. The waste was discharged from the radiochemical plant of the Mayak Amalgamated Industry near Chelyabinsk, Russia. The underlying water-bearing horizon in fissured metavolcanic rocks was penetrated by uncased observation wells in order to log the hydrogeochemistry. Logging was carried out using a specially designed hydrogeochemical probe, which contained 8 channels to measure continuously the temperature, pressure, electric conductivity, pH, Eh, the dissolved O₂ concentration, and the activities of Na, and NO₃ in the wells. The logging technique enabled the natural hydrogeochemical setting to be characterized and permitted delineation of bodies of contaminated waters of different origins using measurements of pH, pNa and pNO₃. The technique also permitted an evaluation of variations in the chemical composition of the RAW solutions due to radiolytic processes and to chemical interactions with the geologic medium. A conceptual model is proposed for the chemical evolution of the migrating contaminated subsurface waters in the area investigated.  相似文献   

How rough sea affects marine seismic data and deghosting procedures          下载免费PDF全文

Anton Egorov  Stanislav Glubokovskikh  Andrej Bóna  Roman Pevzner  Boris Gurevich  Mikhail Tokarev 《Geophysical Prospecting》2018,66(1):3-12

Most seismic processing algorithms generally consider the sea surface as a flat reflector. However, acquisition of marine seismic data often takes place in weather conditions where this approximation is inaccurate. The distortion in the seismic wavelet introduced by the rough sea may influence (for example) deghosting results, as deghosting operators are typically recursive and sensitive to the changes in the seismic signal. In this paper, we study the effect of sea surface roughness on conventional (5–160 Hz) and ultra‐high‐resolution (200–3500 Hz) single‐component towed‐streamer data. To this end, we numerically simulate reflections from a rough sea surface using the Kirchhoff approximation. Our modelling demonstrates that for conventional seismic frequency band sea roughness can distort results of standard one‐dimensional and two‐dimensional deterministic deghosting. To mitigate this effect, we introduce regularisation and optimisation based on the minimum‐energy criterion and show that this improves the processing output significantly. Analysis of ultra‐high‐resolution field data in conjunction with modelling shows that even relatively calm sea state (i.e., 15 cm wave height) introduces significant changes in the seismic signal for ultra‐high‐frequency band. These changes in amplitude and arrival time may degrade the results of deghosting. Using the field dataset, we show how the minimum‐energy optimisation of deghosting parameters improves the processing result.  相似文献   

Effect of fracture fill on frequency‐dependent anisotropy of fractured porous rocks          下载免费PDF全文

Liyun Kong  Boris Gurevich  Yan Zhang  Yibo Wang 《Geophysical Prospecting》2017,65(6):1649-1661

In fractured reservoirs, seismic wave velocity and amplitude depend on frequency and incidence angle. Frequency dependence is believed to be principally caused by the wave‐induced flow of pore fluid at the mesoscopic scale. In recent years, two particular phenomena, i.e., patchy saturation and flow between fractures and pores, have been identified as significant mechanisms of wave‐induced flow. However, these two phenomena are studied separately. Recently, a unified model has been proposed for a porous rock with a set of aligned fractures, with pores and fractures filled with two different fluids. Existing models treat waves propagating perpendicular to the fractures. In this paper, we extend the model to all propagation angles by assuming that the flow direction is perpendicular to the layering plane and is independent of the loading direction. We first consider the limiting cases through poroelastic Backus averaging, and then we obtain the five complex and frequency‐dependent stiffness values of the equivalent transversely isotropic medium as a function of the frequency. The numerical results show that, when the bulk modulus of the fracture‐filling fluid is relatively large, the dispersion and attenuation of P‐waves are mainly caused by fractures, and the values decrease as angles increase, almost vanishing when the incidence angle is 90° (propagation parallel to the fracture plane). While the bulk modulus of fluid in fractures is much smaller than that of matrix pores, the attenuation due to the “partial saturation” mechanism makes the fluid flow from pores into fractures, which is almost independent of the incidence angle.  相似文献