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B. Patti C. Guisande I. Riveiro P. Thejll A. Cuttitta A. Bonanno G. Basilone G. Buscaino S. Mazzola 《Estuarine, Coastal and Shelf Science》2010
It is not clear whether global warming will favour or reduce global ocean phytoplankton productivity in coastal areas. Moreover, the relative contributions made by natural and/or anthropogenic factors to possible changes in phytoplankton productivity are not clear. As the relationship between primary production and alongshore wind forcing is well established for the Eastern Boundary Current (EBC) ecosystems, our aim is to determine whether the changes experienced over the last five decades (1958–2007) in atmospheric CO2 and solar activity have been able to affect the wind regime and water column stability in the most biologically productive upwelling areas of California, Canary, Humboldt and Benguela. We approached the work by statistically studying the effect of solar activity and atmospheric CO2 on surface alongshore wind stress and on water column stability. There was an increasing trend in wind stress and water column stability in all the upwelling areas over the period studied (with the single exception of stability in the California EBC system). The analysis of detrended series evidenced significant relationships between atmospheric CO2 concentration and wind stress and water column stability in the coastal upwelling areas investigated. In addition, wind stress and stability data were found to be consistent, with negative linear relationships between wind stress and CO2 in most of the sites in the Benguela, Canary and Humboldt regions associated, as expected, to positive relationships when water column stability is used as regressand. The results of the present study suggest that greenhouse gas forcing, independent of its well known general increasing trend, was able to decrease wind stress intensity and increase water column stability for the period 1958 to present in most of the sites of the four Eastern Boundary Ecosystems studied, with the one exception of the California region. Conversely, the impact of solar activity appeared to be quite low compared to the greenhouse gas forcing. 相似文献
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Gualtiero Badin Jörn Behrens Christian Franzke Jens Rademacher 《地球物理与天体物理流体动力学》2019,113(5-6):425-427
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Passive seismic provides additional illumination sources in producing reservoirs, improving the Earth's imaging obtained by standard 3D seismic surveys. The joint tomographic inversion of surface and borehole data, both active and passive, even allows the delineation of thin reservoirs that cannot be resolved by reflection tomography. As an application example, we present a feasibility study for a real case of CO2 geological storage, showing that this operation may benefit both environment and reservoir monitoring. The origin time of micro‐earthquakes due to production operations is critical for merging active and passive data. We show here that the Wadati's method is not accurate for borehole data in a layered earth model, when the ratio between P and S velocities is not constant, as occurs in most hydrocarbon reservoirs. This drawback can be solved by deploying a few receivers at the surface close to the well. 相似文献
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Gualtiero Böhm Flavio Accaino Giuliana Rossi Umberta Tinivella 《Geophysical Prospecting》2006,54(6):721-730
A joint inversion of both first and refracted arrivals is applied on a seismic line, acquired onshore, in order to obtain a well‐resolved velocity field for the computation of static corrections. The use of different arrivals in the inversion involves exploiting the information derived from the different raypaths associated with each wave type, thus enhancing the reliability of the inversion. The data was gathered by Saudi Aramco in an area of the Arabian Peninsula characterized by strong lateral variations, both in topography and shallow velocity, and where therefore a well‐defined near‐surface velocity field is important. In addition to velocity, the depth distribution of the quality factor Q is computed from the tomographic inversion of the seismic‐signal frequency shift. Thus, the Q‐factor field is used to perform an inverse Q‐data filtering and improve the resolution of the final stacked section. 相似文献
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Giuliana Rossi Davide Gei Gualtiero Böhm Gianni Madrussani José M. Carcione 《Geophysical Prospecting》2007,55(5):655-669
We estimate the quality factor (Q) from seismic reflections by using a tomographic inversion algorithm based on the frequency‐shift method. The algorithm is verified with a synthetic case and is applied to offshore data, acquired at western Svalbard, to detect the presence of bottom‐simulating reflectors (BSR) and gas hydrates. An array of 20 ocean‐bottom seismographs has been used. The combined use of traveltime and attenuation tomography provides a 3D velocity–Q cube, which can be used to map the spatial distribution of the gas‐hydrate concentration and free‐gas saturation. In general, high P‐wave velocity and quality factor indicate the presence of solid hydrates and low P‐wave velocity and quality factor correspond to free‐gas bearing sediments. The Q‐values vary between 200 and 25, with higher values (150–200) above the BSR and lower values below the BSR (25–40). These results seem to confirm that hydrates cement the grains, and attenuation decreases with increasing hydrate concentration. 相似文献
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Flavio Poletto Biancamaria Farina Gualtiero Böhm Kees Wapenaar 《Geophysical Prospecting》2015,63(3):567-586
We present a modified interferometry method based on local tangent‐phase analysis, which corrects the cross‐correlated data before summation. The approach makes it possible to synthesize virtual signals usually vanishing in the conventional seismic interferometry summation. For a given pair of receivers and a set of different source positions, a plurality of virtual traces is obtained at new stationary projected points located along the signal wavefronts passing through the real reference receiver. The position of the projected points is estimated by minimizing travel times using wavefront constraint and correlation‐signal tangent information. The method uses mixed processing, which is partially based on velocity‐model knowledge and on data‐based blind interferometry. The approach can be used for selected events, including reflections with different stationary conditions and projected points with respect to those of the direct arrivals, to extend the interferometry representation in seismic exploration data where conventional illumination coverage is not sufficient to obtain the stationary‐phase condition. We discuss possible applications in crosswell geometry with a velocity anomaly and a time lapse. 相似文献
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B. Patti C. Guisande A.R. Vergara I. Riveiro I. Maneiro A. Barreiro A. Bonanno G. Buscaino A. Cuttitta G. Basilone S. Mazzola 《Estuarine, Coastal and Shelf Science》2008,76(4):775-786
The aim of this study was to identify the factors responsible for the differences in chlorophyll a concentration (Chl-a) observed between the California, Canary, Humboldt and Benguela upwelling areas. Monthly climatologic values of Chl-a obtained from satellite images, covering the years 1998–2004, revealed that this pigment was higher in the Benguela system than in the other areas. Upwelling intensity, as derived from offshore Ekman transport computations, was higher in the Benguela and Humboldt regions and, for the same upwelling intensity, Chl-a was higher in Benguela than in the other regions. Upwelling intensity appears to be able to drive Chl-a densities through nutrient supply, as nutrients are correlated to offshore Ekman transport. A linear regression model including the fraction of sea surface over the shelf in each 1° × 1° box, nitrate, silicate, turbulence and variability of offshore Ekman transport explained the 84.8% of the variance in Chl-a among the areas. Differences in offshore Ekman transport explained the lower Chl-a observed in Canary and California and the higher Chl-a observed in Benguela and Peru-Humboldt. A narrow continental shelf and low water column stability also contribute to reducing phytoplankton pigment biomass in the Canary and California areas. The higher Chl-a values observed in Benguela compared to Humboldt-Peru are due to a wider extension of the continental shelf in the Benguela region. 相似文献
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Luca Basilone 《Central European Journal of Geosciences》2009,1(3):251-273
Sequence stratigraphic studies of the Triassic through Paleogene carbonate successions of platform, slope and basin in western Sicily (Palermo and Termini Imerese Mountains) have identified a sedimentary cyclicity mostly caused by relative oscillations of sea level. The stratigraphic successions of the Imerese and Panormide palaeogeographic domains of the southern Tethyan continental margin were studied with physical-stratigraphy and facies analysis to reconstruct the sedimentary evolution of this platform-to-basin system. The Imerese Basin is characterized by a carbonate and siliceous-calcareous succession, 1200–1400m thick, Late Triassic to Eocene in age. The strata display a typical example of a carbonate platform margin, characterized by resedimented facies with progradational stacking patterns. The Panormide Carbonate Platform is characterized by a carbonate succession, 1000–1200 m thick, Late Triassic to Late Eocene, mostly consisting of shallow-water facies with periodic subaerial exposure. The cyclic arrangement has been obtained by the study of the stratigraphic signatures (unconformities, facies sequences, erosional surfaces and stratal geometries) found in the slope successions. The recognized pattern has been compared with coeval facies of the shelf. This correlation provided evidence of sedimentary evolution, influenced by progradation and backstepping of the shelf deposits. The stratigraphic architecture of the platform-to-basin system is characterized by four major transgressive/regressive cycles during the late Triassic to late Eocene. These cycles, framed in a chronostratigraphic chart, allows the correlation of the investigated shelf-to-basin system with the geological evolution of the African continental margin during the Mesozoic, showing tectono-eustatic cycles. The first cycle, encompassing the late Triassic to early Jurassic, appears to be related to the late syn-rift stage of the continental margin evolution. The following three cycles, spanning from the Jurassic to Eocene, can be related to the post-rift evolution and to thermal subsidence changes. 相似文献