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51.
Резюме С помощью принятия простых кинематических предположений и на основании ω—уравнения выла определена конфигурация полос облаков
в полностью окклюдированном циклоне без фронтов. Облачная система определяется полем скрытой теплоты, выделяемой в процессах
конденсации. Полосы облаков теоретически представляют собой в основном листы синусоидальной спирали.
Address: Boční II, Praha 4-Spořilov. 相似文献
Address: Boční II, Praha 4-Spořilov. 相似文献
52.
53.
Jesús M. Mercado Teodoro Ramírez Dolores Corts Marta Sebastin Andreas Reul Begoa Bautista 《Estuarine, Coastal and Shelf Science》2006,69(3-4):459
The changes in the phytoplankton absorption properties during a diurnal cycle were investigated at one station located in the north-western area of the Alborán Sea. The experiment was performed in spring when the water column was strongly stratified. This hydrological situation permitted the establishment of a deep chlorophyll a (chl a) fluorescence maximum (DFM) which was located on average close to the lower limit of the mixed layer and the nutricline. The relative abundance of pico-phytoplankton (estimated as its contribution to the total chl a) was higher in the surface, however, micro-phytoplankton dominated the community at the DFM level. Chl a specific absorption coefficient (a*(λ)) also varied with optical depth, with a* (the spectrally average specific absorption coefficient) decreasing by 30% at the DFM depth with respect to the surface. A significant negative correlation between the contribution of the micro-phytoplankton to the total chl a and a* was obtained indicating that a* reduction was due to changes in the packaging effect. Below the euphotic layer, a* increased three-fold with respect to the DFM, which agrees with the expected accumulation of accessory pigments relative to chl a as an acclimation response to the low available irradiance. The most conspicuous change during the diurnal cycle was produced in the euphotic layer where the chl a concentration decreased significantly in the afternoon (from a mean concentration of 1.1 μg L−1 to 0.7 μg L−1) and increased at dusk when it averaged 1.4 μg L−1. In addition, a* and the blue-to-red absorption band ratio increased in the afternoon. These results suggest that a*(λ) diurnal variability was due to increase in photo-protective and accessory pigments relative to chl a. The variation ranges of a*(λ) at 675 and 440 nm (the absorption peaks in the red and blue spectral bands, respectively) in the euphotic layer were 0.01–0.04 and 0.02–0.10 m2 mg−1 chl a, respectively. Approximately 30% out of this variability can be attributed to the diurnal cycle. This factor should therefore be taken into account in refining primary production models based on phytoplankton light absorption. 相似文献
54.
C. Riedel A. Tryggvason B. Brandsdottír T. Dahm R. Stéfansson M. Hensch R. Böðvarsson K. S. Vogfjord S. Jakobsdottír T. Eken R. Herber J. Holmjarn M. Schnese M. Thölen B. Hofmann B. Sigurdsson S. Winter 《Marine Geophysical Researches》2006,27(4):267-281
Between June 2004 and September 2004 a temporary seismic network was installed on the northern insular shelf of Iceland and onshore in north Iceland. The seismic setup aimed at resolving the subsurface structure and, thus, the geodynamical transition from Icelandic crust to typical oceanic crust along Kolbeinsey Ridge. The experiment recorded about 1,000 earthquakes. The region encloses the Tjörnes Fracture Zone containing the Husavik–Flatey strike-slip fault and the extensional seismic Grimsey Lineament. Most of the seismicity occurs in swarms offshore. Preliminary results reveal typical mid-ocean crust north of Grimsey and a heterogeneous structure with major velocity anomalies along the seismic lineaments and north–south trending subsurface features. Complementary bathymetric mapping highlight numerous extrusion features along the Grimsey Lineament and Kolbeinsey Ridge. The seismic dataset promises to deliver new insights into the tectonic framework for earthquakes in an extensional transform zone along the global mid-ocean ridge system. 相似文献
55.
C. Martín-Puertas M. P. Mata M. C. Fernández-Puga V. Díaz del Río J. T. Vázquez L. Somoza 《Geo-Marine Letters》2007,27(2-4):223-235
The Gulf of Cádiz area has been extensively surveyed in recent years and several gas-related fluid escape seafloor structures
have been identified. In this study, gravity cores, collected during the ANASTASYA/00 and ANASTASYA/01 cruises, on mud volcanoes,
hemipelagic sediments and dredged material from diapiric structures, have been studied. A comparative mineralogical analysis
by XRD and SEM of samples from different areas has been performed in order to determine whether there is a characteristic
mineralogy related to these fluid escape structures, and also to determine the origin of the mud matrix and constrain the
depth of the parent units. The mineralogical analysis reflects the different origins of the different units described in the
cores: hemipelagic material of the slope, clays that underlie the mud volcanoes and are discharged at the sea bottom surface,
and authigenic and diagenetic minerals possibly involved in the anaerobic oxidation of methane in the mud volcano sediments. 相似文献
56.
The Neogene is the period in which the Betic Cordillera, the Rif, and the Alboran Sea acquired their present configuration. The Neogene sediments of the Betic Internal Zones (located directly to the North of the Alboran Sea) show the effects of important periods of deformation. Deposition was clearly controlled by tectonics. Therefore the generation, evolution, and total or partial destruction of basins and the formation of new, often superimposed, basins are common phenomena, according to the locations of the basins in the Betic Cordillera and to the different geodynamic situations. 相似文献
57.
Palynological characterization of the pollen assemblages from core ZV-01 offers a reliable age record of shallow ‘gas seal’
and ‘gas reservoir’ sediments from the Ría de Vigo (NW Spain). Gassy sediments show a direct correspondence with the palynological
assemblage zones (LPAZ) 2, 3 and 4, which range in age from 950 to 1510 a.d. for the interval 81–176 cm where gas is found. The facies acting as a seal would correspond to the sedimentation in the ria
starting from 1510 a.d. These assemblages also provide significant data which make it possible to reconstruct the palaeoenvironmental changes recorded
in the sedimentary infill of the Ría de Vigo. The gassy horizon corresponds to the phase when riparian and mesophilous forest
were better represented. This coincides with a relative high abundance of Lingulodinium machaerophorum, which indicates that the waters of the ria had been less renewed by oceanic waters and had a plentiful supply of continental
nutrients. At that time, anoxic conditions resulted from restricted vertical circulation of seawater and/or high biological
productivity. The dinocyst assemblages overlying and underlying the gassy horizon in core ZV-01 are clearly different from
those concomitant with the accumulation of the gassy sediments. This suggests that oceanographic conditions in the Ría de
Vigo may have changed several times during the time interval covered by our record. The weaker relationship between L. machaerophorum/Spiniferites spp., and simultaneous significant increases in Impagidinium spp. and Bitectatodinium tepikiense may indicate a greater intrusion of colder, more oceanic waters into the Ría de Vigo, which may have provoked intensification
in upwelling during two periods, ca. 700–850 a.d. and ca. 1500–1750 a.d. 相似文献
58.
Jue Lin-Ye Begoña Pérez-Gómez Enrique Álvarez-Fanjul Javier García-Valdecasas 《Marine Geodesy》2020,43(5):509-539
AbstractThe sea level station operating since 1996 at Mazagón (Huelva, Spain) has been progressively upgraded to fit tsunami warning requirements, due to its location in one of the main regions at risk. Its radar water level sensor was complemented in 2017, with the addition of a pressure sensor. The performance of both sea level sensors and their response to sea level oscillations, at different frequencies, is assessed. Particular emphasis is put on the effect of extreme events, such as Storm Emma, when alternative methods to obtain 1-min data are tested, in contrast to the one based on arithmetic means. The overall differences are small, for the whole period of study (centered-root-mean-square-error below 1?cm, for 5-min, and hourly data; similar tidal parameters and sea level oscillations with periods between 30?s and 5?min). However, during Storm Emma, the pressure sensor presents sensibly lower readings than the radar, with the centered-root-mean-square-error rising to 80?mm on the March 2nd 2018. A new method to compute 1-min data, based on medians, reduced this value to 10?mm for the same day. 相似文献
59.
Gas hydrate disturbance fabrics of southern Hydrate Ridge sediments (ODP Leg 204): Relationship with texture and physical properties 总被引:1,自引:0,他引:1
Elena Piñero Eulàlia Gràcia Francisca Martínez-Ruiz Juan Cruz Larrasoaña Alexis Vizcaino Gemma Ercilla 《Geo-Marine Letters》2007,27(2-4):279-288
Soupy and mousse-like fabrics are disturbance sedimentary features that result from the dissociation of gas hydrate, a process
that releases water. During the core retrieval process, soupy and mousse-like fabrics are produced in the gas hydrate-bearing
sediments due to changes in pressure and temperature conditions. Therefore, the identification of soupy and mousse-like fabrics
can be used as a proxy for the presence of gas hydrate in addition to other evidence, such as pore water freshening or anomalously
cool temperature. We present here grain-size results, mineralogical composition and magnetic susceptibility data of soupy
and mousse-like samples from the southern Hydrate Ridge (Cascadia accretionary complex) acquired during Leg 204 of the Ocean
Drilling Program. In order to study the relationship between sedimentary texture and the presence of gas hydrates, we have
compared these results with the main textural and compositional data available from the same area. Most of the disturbed analyzed
samples from the summit and the western flank of southern Hydrate Ridge show a mean grain size coarser than the average mean
grain size of the hemipelagic samples from the same area. The depositional features of the sediments are not recognised due
to disturbance. However, their granulometric statistical parameters and distribution curves, and magnetic susceptibility logs
indicate that they correspond to a turbidite facies. These results suggest that gas hydrates in the southern Hydrate Ridge
could form preferentially in coarser grain-size layers that could act as conduits feeding gas from below the BSR. Two samples
from the uppermost metres near the seafloor at the summit of the southern Hydrate Ridge show a finer mean grain-size value
than the average of hemipelagic samples. They were located where the highest amount of gas hydrates was detected, suggesting
that in this area the availability of methane gas was high enough to generate gas hydrates, even within low-permeability layers.
The mineralogical composition of the soupy and mousse-like sediments does not show any specific characteristic with respect
to the other samples from the southern Hydrate Ridge. 相似文献
60.
Rodrigo Wiff Andrés Flores Angel M. Segura Mauricio A. Barrientos Vilma Ojeda 《新西兰海洋与淡水研究杂志》2020,54(2):218-232
ABSTRACT Genypterus blacodes, in terms of its fishing history and local economic importance, is an emblematic species harvested in Chilean Patagonia (41°00’–57°00’S). Most of the current fisheries and biological knowledge of this species come from the open ocean, whereas information about the species in fjords and inner channels is fragmentary. In 2018, two research surveys targeting G. blacodes were conducted in the fjords and inner channels of Chilean Patagonia. A total of 253 pairs of sagittal otoliths were sampled at three different localities, and their contours were modelled using wavelet analysis as a tool for stock discrimination. Contours were compared using canonical analysis, and classification was performed using linear discriminant and Random Forest analyses. The results indicated that the wavelet method is efficient in modelling otolith contours, and the discriminant analyses showed differences among fishing grounds across the latitudinal gradient, thus confirming the hypothesis that G. blacodes conform to at least two separate stock units in Chilean Patagonia. Fishing grounds that were closer in space showed higher levels of misclassification. The discussion focuses on how environmental variables and the geography of fjords shape stock differences and how this information can be used for the sustainable management of G. blacodes. 相似文献