An integral description of the propagation of steady-state perturbations of the heavy liquid surface

The system of equations of motion describing the gravity wave propagation in a perfect heavy liquid layer is transformed into a new integral equation for the free surface elevations. In the limit cases, this integral equation describes the linear and nonlinear periodic waves as well as the known types of solitary waves. In this case a dispersion equation arises because perturbations of the second and higher orders of smallness are neglected. The integral equation allows for the propagation of invariable surface perturbations of arbitrary forms if their spatial spectrum is concentrated near small wave numbers (compared to the inverse wave amplitude). Several examples of solutions are presented.     

Relationship between environment and the occurrence of the deep-water rose shrimp Aristeus antennatus (Risso, 1816) in the Blanes submarine canyon (NW Mediterranean)

We performed a multidisciplinary study characterizing the relationships between hydrodynamic conditions (currents and water masses) and the presence and abundance of the deep-water rose shrimp Aristeus antennatus in a submarine canyon (Blanes canyon in the NW Mediterranean Sea). This species is heavily commercially exploited and is the main target species of a bottom trawl fishery. Seasonal fluctuations in landings are attributed to spatio-temporal movements by this species associated with submarine canyons in the study area. Despite the economic importance of this species and the decreases in catches in the area in recent years, few studies have provided significant insight into the environmental conditions driving shrimp distribution. We therefore measured daily A. antennatus catches over the course of an entire year and analyzed this time series in terms of daily average temperature, salinity, mean kinetic energy (MKE), and eddy kinetic energy (EKE) values using generalized additive models and decision trees. A. antennatus was captured between 600 and 900 m in the Blanes canyon, depths that include Levantine Intermediate Water (LIW) and the underlying Western Mediterranean Deep Water (WMDW). The greatest catches were associated with relatively salty waters (38.5–38.6), low MKE values (6 and 9 cm² s⁻²) and moderate EKE values (10 and 20 cm² s⁻²). Deep-water rose shrimp occurrence appears to be driven in a non-linear manner by environmental conditions including local temperature. A. antennatus appears to prefer relatively salty (LIW) waters and low currents (MKE) with moderate variability (EKE).     

Distinct activity phases during the recent geologic history of a Gulf of Mexico mud volcano

Laser line scan imaging and chirp sub-bottom profiling were used to detail the morphology of a submarine mud volcano and brine-filled crater at 652 m water depth in the northern Gulf of Mexico. The mud volcano has a relief of 6 m and a basal diameter of about 80 m. The feature comprises a central, brine-filled crater (253 m²) surrounded by a continuous bed of methanotrophic mussels (Bathymodiolus childressi) covering 434 m² and a patchy bed covering an additional 214 m² of the periphery. The brine pool was mostly <2 m deep, but there were two holes of >28 m and 12 m deep, respectively at the northern end of the pool which emitted continual streams of small clear bubbles. Sub-bottom profiles indicated three distinct strata beneath the present surface of the mud volcano. Integration of 17 profiles shows that the mud volcano has been built in at least three successive stages: the lowest stage deposited 35,400 m³, while the middle and upper stages deposited 7700 and 20,400 m³, respectively. Piston cores were taken at the northern edge of the mussel bed and a site ∼100 m southwest of the pool. Mussel and lucinid shells were recovered from the closer core, lucinid shells from the distant core. A mussel shell from 3.4 m sub-bottom had a Δ¹⁴C age of 16.2 ka. Mixture of modern carbon with “carbon dead” reservoir material would produce actual ages ∼2 ka less than the radiocarbon ages.     

Stochastic evaluation of fluvial to marginal marine sealing facies

Hydrocarbon top seal analyses are particularly difficult in fluvial and marginal marine settings. Although these settings often contain beds comprised of a low-permeability, clay-rich lithology associated with high quality seals, their presence does not guarantee an effective seal because individual beds within the stratal unit may be laterally discontinuous. Lateral facies changes, truncation of fine-grained beds, or the presence of crevasse splays may provide cross-stratal migration pathways, reducing the effective sealing capacity to a magnitude less than the closure height.     

Modeling an atypical petroleum system: A case study of hydrocarbon generation,migration and accumulation related to igneous intrusions in the Neuquen Basin,Argentina

In the Altiplanicie del Payún area (Neuquen Basin, Argentina), immature source rock sections intruded by up to 600 m thick Tertiary laccoliths show full spectrum maturity aureoles over hundreds of meters from the contacts. Commercial oil accumulations (20–33°API) and oil shows are located along the entire column, both in sandstone/carbonate and fractured igneous reservoirs. A challenging numerical model that included the emplacement of the intrusive bodies, with extreme temperature ranges and unusually short calculation time steps, has been done with the aim to better understand hydrocarbon generation and migration processes related to these thermal anomalies.     

Tectonically-driven mud volcanism since the late Pliocene on the Calabrian accretionary prism,central Mediterranean Sea

Mud volcanoes recently discovered on the offshore Calabrian Arc are investigated at two sites 60 km apart, in water depths of 1650--2300 m, using swath bathymetry, 2D&3D multichannel seismic and cores. The seabed and subsurface data provide information on their formation and functioning in relation to tectonic activity during the rapid Plio-Quaternary advance of the accretionary prism. Fore-arc extension and thrust-belt compression are seen to have involved two main phases of activity, separated by a regional unconformity recording a mid-Pliocene (3.5–3.0 Ma) tectonic reorganization. The two sites of mud volcanism lie in contrasting tectonic settings (inner fore-arc basin vs central fold-and-thrust belt) and record differing forms of seabed extrusive activity (twin mud cones and a caldera vs a broad mud pie). At both sites, subsurface data show that mud volcanism took place throughout the second tectonic phase, since the late Pliocene; differing forms of mud extrusion were accompanied by subsidence to form depressions beneath and within extrusive edifices up to 1.5 km thick. The basal subsidence depressions point to sources within the succession of thrusts underlying the inner to central Arc, consistent with microfossils within cored mud breccias from both sites that are derived from strata as old as Late Cretaceous.     

Biometric,microstructural, and high-resolution trace element studies in Crassostrea gigas of Cantabria (Bay of Biscay,Spain): Anthropogenic and seasonal influences

Living Crassostrea gigas oysters of different ages and sizes were collected in three estuaries of Cantabria (Bay of Biscay, Spain): San Vicente de la Barquera Estuary, Santander Bay, and Marismas de Santoña Estuary. The main objective was to determine different shell responses to variable environmental parameters. A shell morphological study, based on three biometric indices, indicates that oysters of Santander Bay have two significant shell anomalies: abnormal thickening of the right valve and loss of vital cavity volume. These shell abnormalities are related with the presence in these waters of the chemical tributyltin. In the other two estuaries, the oysters show no detectable anomalies. Four shell microstructures have been distinguished: Regular Simple Prismatic, Regular Foliated, cone-Complex Cross Foliated, and Chalk. In Santander Bay oysters, the Chalk forms a “root-type” framework, whereas in the other two estuaries it forms a more compact microstructure. It is proposed that exposure to tributyltin has produced this modification. High-spatial-resolution geochemical transects have been carried out on the Regular Foliated microstructure in the umbo region in order to evaluate the distribution of Mg, Sr, and Na. The elements analysed exhibit clear cyclic variations in San Vicente de la Barquera Estuary and Marismas de Santoña Estuary oysters, related with seasonal periods, and characterised by broad maxima during months in which the waters are warmer and have higher salinity. These patterns are buffered in Santander Bay oysters. Our results demonstrate that biometric, microstructural, and high-resolution trace element studies in oyster shells can provide information about contaminants and seasonal variations in the estuarine environment.     

The divergent environmental characteristics of permanently-open,seasonally-open and normally-closed estuaries of south-western Australia

This study has compared the environmental characteristics of the basins and saline lower reaches of the tributaries of eight estuaries on the south coast of Western Australia, which differ in their degree of connectivity with the ocean. Although four estuaries between 115.1° and 121.8° E along that coast remain permanently open to the ocean, the others only become open when the volume of river discharge is sufficient to breach the prominent sand bars at their mouths, which occurs annually following heavy winter and early spring rainfall in some estuaries (seasonally open) and infrequently in others (normally closed). Estuaries to the west of 118.5° E are predominantly permanently open, e.g. Oyster Harbour, or seasonally open, e.g. Broke, Irwin and Wilson inlets, whereas those further east, e.g. Wellstead Estuary and Hamersley, Culham and Stokes inlets, where annual rainfall and thus discharge are much lower, only become open after exceptionally heavy discharge. In permanently and seasonally-open estuaries, pronounced haloclines and oxyclines are present in the narrow rivers but not the wide basins where the waters are subjected to wind-driven mixing. The extent of cyclical seasonal fluctuations in environmental conditions differed markedly among the three seasonally-open estuaries and between years in one of those systems. These differences reflected variations in the relationship between the volume of fluvial discharge, which is determined by a combination of the amount of local rainfall, catchment size and extent of clearing of native vegetation, and the amount of intrusion by marine waters, which is largely controlled by the size and duration of the opening of the estuary mouth. The mean seasonal salinities in the basins of the three normally-closed estuaries increased over three years of very low rainfall to 64 in the deepest of these estuaries (Stokes Inlet) to 145 in Hamersley Inlet and to 296 in the shallowest estuary (Culham Inlet). These results demonstrate that the environmental characteristics of estuaries on the south coast of Western Australia differ markedly, even among those of the same type, e.g. seasonally-open estuaries or normally-closed estuaries.     

Fundamental study for morphodynamic modelling: Sand mounds in oscillatory flows

Experiments on sand mounds in oscillatory flow, undertaken in controlled, large-scale laboratory conditions, have produced well-defined data sets for model comparison. Three bathymetries with different levels of submergence, including a surface-piercing case, were tested. The maximum slope was about 1:5.5. Sediment transport is due to bed load with ripple formation. The principal time-dependent bulk parameters are the vertical distance of the centre of gravity above the base and the volume of the mound. A semi-implicit finite-volume depth-averaged hydrodynamic model is used to drive morphodynamics, using van Rijn's sediment flux model generalized to take account of bed slope, and some justification is given for depth-averaged modeling in these conditions. Starting the model runs with the conditions at the end of the first cycle avoided initial atypical physical behaviour. In general good predictions were obtained with an angle of repose reduced from the standard value of about 30° for stationary beds to 15°. For these situations, morphodynamics was largely unaffected by a hydrodynamic roughness height in the range 2.5D₅₀ to 51D₅₀, with larger values accounting for ripple roughness. The reduced angle of repose may be physically expected with mobile beds but this specific value is only expected to be suited to this form of bed motion. In one case an exaggerated ripple formed near the top of the mound reducing agreement with experiment. For the submerged case with normal ripple structure excellent predictions were obtained. For the initially surface-piercing mound, the time of submergence was better predicted with a 30° angle of repose, presumably due to the prominent influence of the near stationary bed near the wet/dry interface, although long term predictions were better predicted with 15°. The occurrence of vortex shedding in the first cycle modeled was in agreement with experimental observation.     

Diurnal variability in turbidity and coral fluorescence on a fringing reef flat: Southern Molokai,Hawaii

Terrigenous sediment in the nearshore environment can pose both acute and chronic stresses to coral reefs. The reef flat off southern Molokai, Hawaii, typically experiences daily turbidity events, in which trade winds and tides combine to resuspend terrigenous sediment and transport it alongshore. These chronic turbidity events could play a role in restricting coral distribution on the reef flat by reducing the light available for photosynthesis. This study describes the effects of these turbidity events on the Hawaiian reef coral Montipora capitata using in situ diurnal measurements of turbidity, light levels, and chlorophyll fluorescence yield via pulse-amplitude-modulated (PAM) fluorometry. Average surface irradiance was similar in the morning and the afternoon, while increased afternoon turbidity resulted in lower subsurface irradiance, higher fluorescence yield (ΔF/F_m^′), and lower relative electron transport rates (rETR). Model calculations based on observed light extinction coeffecients suggest that in the absence of turbidity events, afternoon subsurface irradiances would be 1.43 times higher than observed, resulting in rETR for M. capitata that are 1.40 times higher.