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991.
The sediments of the eastern Mediterranean basin contain a series of organic-rich sapropels intercalated with organic-poor nannofossil oozes. Until recently the timing of the onset of sapropel formation was not known accurately because of the low resolution achievable by conventional radiocarbon dating. Compilation of all available 14C-AMS dates show that the base of S-1 (the most recent sapropel) was initiated 8800 years B.P. (14C age corrected by 400 years for reservoir effect) under a 500 m water column and moved progressively into deeper water reaching depths of 3500 m at 8200 years B.P. The linear correlation between the age of S-1 onset and water depth suggests that formation of sapropels moved into deeper water at a rate of 1000 m/200 year. A model is suggested in which export production which sank below the well-mixed surface layers (500 m) was respired consuming dissolved oxygen in the Levantine deep water until a threshold value was reached when sapropels began to be preserved in the sediment. This resulted in a progressively deepening oxygen minimum zone with time until eventually the entire deep water in the basin was oxygen depleted. Assuming that the threshold value for sapropel formation was complete anoxia, it was calculated that primary productivity in the basin during the deposition of S-1 was a factor of 5 greater than that found at present. 相似文献
992.
An instrumented tetrapod was deployed for three weeks on the Dry Tortugas Bank at a depth of 26 m in February 1995. Bottom
roughness was dominated by shrimp burrows and worm mounds with rms roughness amplitudes ranging from 0.47 to 1.75 cm. Logarithmic
velocity profiles show apparent total roughness heights ranging from 0.30 to 1.45 cm, values consistent with observed biological
roughness. The bed sediments were weakly bound by an algal crust at the sediment–water interface. When this bound layer was
scraped away by a mooring that was accidentally dragged, sharp-crested wave-induced ripples appeared within the resulting
swath. We conclude that physically induced roughness is biologically suppressed, but if dominant, would be significantly higher
than the prevailing biological roughness. 相似文献
993.
Detailed structural interpretation of the recently acquired deep seismic multichannel profiles along the Iberian Atlantic Margins (IAM Project) provides new results on the geodynamic evolution of the eastern part of the Azores-Gibraltar plate boundary. Thrusting and folding of the oceanic basement and of Mesozoic and Cenozoic sedimentary cover of the Gorringe Bank region are consistent with the N–S convergence of Iberia and Africa. Compressive structures in the Gorringe Bank region are spread over a wide area. Deformation under compression took place mainly in Tertiary times, as is evidenced by a basal unconformity and several discontinuities in Tertiary sediments, although some deformation has also been recorded in Quaternary sediments. The compressive structures in the Gulf of Cadiz are E–W oriented thrusts, folds and related diapiric structures. N–S oriented transpressive deformation is likely to occur in the western Portuguese platform. There is no continuity of structures from the oceanic to the continental domain, suggesting that deformation transfers from one side to the other through a transcurrent fault zone. The fault contact between the two domains is located in the ocean-continent transition zone. 相似文献
994.
995.
This paper focuses on the numerical modelling of tsunami propagation in the open Black Sea. Two types of numerical models
are discussed: a model for the radial propagation of long waves and an evolutionary finite-difference prognostic model. Experimentally
derived numerical data on the model source of tsunamis are reported.
Translated by Vladimir A. Puchkin. 相似文献
996.
V. A. Kalmykov 《Physical Oceanography》1996,7(2):91-97
Zakharov's equation is applied to study numerically the evolution of wave amplitudes. It is demonstrated that, owing to Krasitskii's
new kernel functions, the system of surface waves remains Hamiltonian, in contrast to the former approaches used by Yuen,
Lake, and Zakharov. If surface waves are wind-generated, they grow and become stochastic. If the effect of the waves on the
wind is considered, then the wave amplitude evolution, similar to the no-wind case, continues to be recurrent.
Translated by Vladimir A. Puchkin. 相似文献
997.
Whether or not there are extensional detachment faults in the Alboran basement can be tested directly because a part of the Alboran Basin is now emerged. These detachments, related to crustal thinning beneath the Alboran Basin, occurred from the Aquitanian to Tortonian. The resulting extensional geometries can be described in general terms. During the Serravalian a considerable southwest extension of the basin took place, accompanied by south-southeast extension in the northern Gibraltar Arc. Other detachments affected by Serravalian extension can be found. The spreading of the Alboran was nearly coeval with roughly westward migration of the Gibraltar mountain front. 相似文献
998.
999.
Wave records at seven different locations within a groin field have been analysed by both statistical and spectral approaches to study the general wave climate. The wave heights and periods from the wave records were obtained by both upcross and downcross methods for the statistical approach. The variation of different wave height and wave period parameters with respect to the time of measurement at a particular location and its variation at different locations within the groin field at a particular instant of time are presented and discussed in detail in this paper. It is generally found that the wave heights follow the Weibull distribution. 相似文献
1000.