We here analyze a new model of transients of pore pressure
p
and solute density
ρ
in geologic porous media. This model is rooted in the nonlinear wave theory, its focus is on advection and effect of ...large pressure jumps on strain. It takes into account nonlinear and also time-dependent versions of the Hooke law about stress, rate and strain. The model solutions strictly relate
p
and
ρ
evolving under the effect of a strong external stress. As a result, the presence of quick and sharp transients in low permeability rocks is unveiled, i.e., the nonlinear “Burgers solitons”. We, therefore, show that the actual transport process in porous rocks for large signals is not only the linear diffusion, but also a solitons presence could control the process. A test of a presence of solitons is applied to Pierre shale, Bearpaw shale, Boom clay and Oznam-Mugu silt and clay. An application about the presence of solitons for nuclear waste disposal and salt water intrusions is also discussed. Finally, in a kind of “theoretical experiment” we show that solitons could also be present in higher permeability rocks (Jordan and St. Peter sandstones), thus supporting the idea of a possible occurrence of osmosis also in sandstones.
We discuss here the evolution of vorticity and potential vorticity (PV) for a bottom current crossing a marine channel in shallow-water approximation, focusing on the effect of friction and mixing. ...The purpose of this research is indeed to investigate the role of friction and vertical entrainment on vorticity and PV spatial evolution in channels or straits when along-channel morphology variations are significant. To pursue this investigation, we pose the vorticity and PV equations for a homogeneous bottom water vein and we calculate these two quantities as an integral form. Our theoretical findings are considered in the context of in situ hydrographic data related to the Eastern Mediterranean Deep Water (EMDW), i.e., a dense, bottom water vein that flows northwestward, along the Sicily Channel (Mediterranean Sea). Indeed, the narrow sill of this channel implies that friction and entrainment need to be considered. Small tidal effects in the Sicily Channel allow for a steady theoretical approach. We argue that bottom current vorticity is prone to significant sign changes and oscillations due to topographic effects when, in particular, the current flows over the sill of a channel. These vorticity variations are, however, modulated by frictional effects due to seafloor roughness and morphology. Such behavior is also reflected in the PV spatial evolution, which shows an abrupt peak around the sill region. Our diagnoses on vorticity and PV allow us to obtain general insights about the effect of mixing and friction on the pathway and internal structure of bottom-trapped currents flowing through channels and straits, and to discuss spatial variability of the frictional coefficient. Our approach significantly differs from other PV-constant approaches previously used in studying the dynamics of bottom currents flowing through rotating channels.
The interaction between ocean bottom currents and topographic obstacles often results in sedimentary processes that form intriguing sedimentary deposits. However, without a thorough knowledge of both ...fluid mechanical processes and oceanographic settings regarding these sedimentary deposits, such an inherited interaction is not easy to understand. We here analyze the interaction between a bottom, geostrophic current and a local topographic depression, a slide scar offshore Cape Suvero, an Italian headland in the southern Tyrrhenian Sea, in order to explain the presence of contourite drifts off this cape. We apply the classical conservation of marine water potential vorticity and demonstrate the presence of a steady cyclonic circulation over the scar, which in turn affects contourite deposition. We thus show that the application of the potential vorticity conservation provides a simple but powerful, general tool for the understanding of the complex relations among ocean current, seafloor morphologies and sedimentary structures.
•We examine the relations among currents, topographic obstacles, and contourites.•We investigate the effect of a slide scar on the LIW flow contouring a cape.•Potential vorticity conservation shows a cyclonic circulation over the scar.•Weak velocities in its center promote sediment deposition within the scar.
We here discuss a detailed investigation of the dense water formation, evolution and spreading in the Aegean Sea during the year 1987, immediately prior to the onset of the Eastern Mediterranean ...Transient (EMT). We use hydrologic data collected during the LIA cruise; satellite images for SST (Sea Surface Temperature), and PROTHEUS data (a coupled ocean–atmosphere numeric model) along with theoretical streamtube models. These hydrological analyses are related to late Quaternary sedimentary drifts in the Cyclades Plateau and in the Myrtoon Basin. Our analysis shows that streamtube dynamics provide a novel model of dense water evolution and spreading in the Aegean Basin. Applying this model to dense water masses observed in winter and spring 1987 near Samothrace and over the Limnos-Lesbos Plateau, results in a geostrophic flow of this dense, cold water towards the Limnos-Sporades Channel, in the North Aegean Sea. There it mixes with dense water from the Limnos-Lesbos Plateau and finally both move geostrophically towards the Cyclades Plateau. These results indicate that most of the dense water observed near the Cyclades, formed initially about 3months earlier at Samothrace and Limnos shelves. During its long pathway it partially mixed with adjacent water masses. Although our analysis concerns only one year of dense water analyses, these results are thought to reflect a more general and recurrent phenomenon in the Aegean basin. Indeed, high-resolution (Airgun 10in.) seismic-reflection data from the Cyclades Plateau reveal the presence of late Quaternary sediment drifts. These observations are concordant with results from our theoretical model. This suggests a direct link between such a dense-water cascading and contourite dynamics. The continuation of sediment drifts into the deep basin floor (≈900m deep) of the Myrtoon Basin, moreover, indicates a cascading character of such bottom currents at the flanks of the basin, a feature that set further investigations.
•Multidisciplinary approach for the investigation of downflow dynamics of Aegean waters•Northern Aegean dense water evolution also regarding the presence of Quaternary sedimentary structures.•We provide a novel viewpoint on the Aegean dense water evolution just before the EMT
The complex relationship between currents flowing around capes and their related contourite deposits is still an interesting topic to confront, both from a sedimentologic and oceanographic ...perspective. We analyze here recent observations of contourite drifts, located at intermediate depths off promontories in the southern Tyrrhenian and in the southern Adriatic Sea. These contourites are located slightly upstream from the cape tip of Cape Vaticano, while they occur both upstream and downstream, in the lee wave region, of the Gargano Promontory. We therefore analyze and discuss tank and numerical simulations of contour-following flows, with particular attention to the presence of turbulent phenomena occurring in the lee region. Discussing the classical stream-tube model (i.e., a thin vein of dense water flowing around a cape) we moreover provide physical justification for some aspects we recognized in the study experiments. The comparison between bathymetric-stratigraphic data and numerical, tank and analytic results, allows investigation of the possible occurrence of sediment drifts around capes. We found that the presence of turbulence, and thus of erosive conditions for sediments in the lee of a cape, can be detected by using dimensionless numbers related to cape dimension and ocean current features. This work can be seen as a new approach to bridge the gap between marine sedimentology and physical oceanography.
The evolution of strong transients of temperature and pressure in two adjacent fluid-saturated porous rocks is described by a Burgers equation in an early model of Natale and Salusti (1996). We here ...consider the effect of a realistic intermediate region between the two media and infer how transient processes can also happen, such as chemical reactions, diffusion of fine particles, and filter cake formations. This suggests enlarging our analysis and taking into account not only punctual quantities but also “time averaged” quantities. These boundary effects are here analyzed by using a “memory formalism”; that is, we replace the ordinary punctual time-derivatives with Caputo fractional time-derivatives. We therefore obtain a nonlinear fractional model, whose explicit solution is shown, and finally discuss its geological importance.
Abyssal temperature and velocity observations performed within the framework of the Neutrino Mediterranean Observatory, a project devoted to constructing a km(3)-scale underwater telescope for the ...detection of high-energy cosmic neutrinos, demonstrate cross-fertilization between subnuclear physics and experimental oceanography. Here we use data collected south of Sicily in the Ionian abyssal plain of the Eastern Mediterranean (EM) basin to show for the first time that abyssal vortices exist in the EM, at depths exceeding 2,500 m. The eddies consist of chains of near-inertially pulsating mesoscale cyclones/anticyclones. They are embedded in an abyssal current flowing towards North-Northwest. The paucity of existing data does not allow for an unambiguous determination of the vortex origin. A local generation mechanism seems probable, but a remote genesis cannot be excluded a priori. The presence of such eddies adds further complexity to the discussion of structure and evolution of water masses in the EM.
•A nonlinear model of thermoelastic wave propagation in porous media is studied.•The role of the boundaries between of two adjacent rocks on the evolutions of the pressure and temperature fields is ...discussed in details.•The analysis of exact explicit solutions is given and the estimate of the velocity propagation is discussed for different rocks.
The dynamics of transients of fluid-rock temperature, pore pressure, pollutants in porous rocks are of vivid interest for fundamental problems in hydrological, volcanic, hydrocarbon systems, deep oil drilling. This can concern rapid landslides or the fault weakening during coseismic slips and also a new field of research about stability of classical buildings. Here we analyze the transient evolution of temperature and pressure in a thin boundary layer between two adjacent homogeneous media for various types of rocks. In previous models, this boundary was often assumed to be a sharp mathematical plane. Here we consider a non-sharp, physical boundary between two adjacent rocks, where also local steady pore pressure and/or temperature fields are present. To obtain a more reliable model we also investigate the role of nonlinear effects as convection and fluid-rock “frictions”, often disregarded in early models: these nonlinear effects in some cases can give remarkable quick and sharp transients. All of this implies a novel model, whose solutions describe large, sharp and quick fronts. We also rapidly describe transients moving through a particularly irregular boundary layer.
A systematic analysis of thermal satellite images of upwellings and cold filament dynamics downstream from the island of Sardinia (western Mediterranean Sea), covering the years 1984, 1985, 1989, ...1990, 1993, and 1994, is discussed. For this sea the main transient atmospheric forcing comes from bursts of the mistral, a north‐western wind which, downstream from Sardinia, affects a rather calm basin, the Tyrrhenian Sea. In early summer, particularly clear effects of atmospheric forcings such as gyres, upwellings, and cold filaments can be observed. Our analysis provides not only a systematic insight into these phenomena, but also some experimental evidence of a novel mechanism of cold filament formation and evolution. Indeed, in July 1989, a nice set of satellite images shows a cold filament rooted to the shallowest part of the wide shelf off Olbia, which meanders offshore for a few days under the effect of the mistral and of the general circulation. It is of interest to underline how stably the filament is rooted to the shelf so that in only one image it appears as an elongated straight segment. Also, the filament's potential vorticity is discussed in order to gain some insight into shelf water fluxes, detachment depths, and velocities relative to such phenomena.
Hydrographic and current meter data, gathered in different periods in the Strait of Sicily and in the southern Tyrrhenian Sea, allow the outflow characteristics from the eastern toward the Western ...Mediterranean basin to be analyzed. The evolution through the strait of a deep vein of dense water coming from the Eastern Mediterranean is described, together with the dynamic interaction with overlying layers.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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