Reversing Water Exchange Patterns at the Entrance to a Semiarid Coastal Lagoon

Water velocity and density profiles were obtained in late-spring and late-winter to document reversing mean circulation patterns at the entrance to a semiarid coastal lagoon, the Bay of Guaymas, in the Gulf of California, Mexico. The lagoon is shallow but the bathymetry at its entrance is similar to that of temperate estuaries with an asymmetrically positioned channel flanked by shoals. In late-spring the mean circulation at the entrance to the lagoon was driven by horizontal density gradients that arose from excess evaporation over precipitation in the area as evidenced by water density profiles. The lagoon exported relatively warm (25·8 °C) and salty (36·2) water to the Gulf of California through the channel. This export was consistent with inverse estuarine circulation influenced by bathymetry. In late-winter, the circulation at the entrance of the lagoon was mostly driven by wind stress that blew from the northwest, roughly along the main axis of the lagoon. Relatively cool (16·0) °C) and less salty (35·1) water from the Gulf of California was driven into the lagoon within the channel. Density gradients inside the lagoon seem to have played a secondary role in driving the circulation. The late-winter circulation was then estuarine-like, with outflow in the direction of the wind over the shallow areas and a compensatory inflow appearing in the channel as expected from theory of wind-driven flow over bathymetry. This estuarine-like circulation developed despite the lack of measurable freshwater input to the lagoon and was the opposite to that observed in late-spring. These observations then document a reversal in water exchange patterns from season to season in a semiarid coastal lagoon. The observations also constitute one of the few reported examples of flow over shoals driven in the same direction as the wind stress with a compensatory flow in the channel.     

Microbiological and chitinoclastic activities associated withPenaeus setiferus

Analysis of microbiological and chitinase activities relative to the white shrimpPenaeus setiferus, and its chitinoclastic endosymbionts, have demonstrated the relevance of total chitinolytic processes in penaeid biology. Microorganisms may serve as a direct source of nutrients for the animal as well as in the elaboration of extracellularin situ chitinase enzymes. The enzyme produced by the predominant gut bacteria,Beneckea neptuna, is a moderately actively inducible chitinase while the shrimp has an indigenous constitutive chitinase and chitobiase system. Factors of temperature, pH, ion inhibition and reducing sugar ratios have been compared for the bacterial and animal enzymes. This dual enzyme system suggests that metabolic chitin transformation may play a vital role in crustacean metabolism.     

Formation of pockmarks by pore-water escape

During the course of a North Sea rig site investigation, a number of seabed depressions were observed on side-scan sonar records, some of which may be identified as pockmarks. Others are described as pits. A pockmark evolutionary series is proposed on the basis of all these features with a suggested mechanism which would favor release of pore water, but does not exclude gas escape. Acoustic voids are considered to be a related phenomenon.     

Determination of characteristics of atmospheric motions from satellite multiwave remote sensing data

A method of determination of atmospheric dynamic characteristics from the data of remote sensing from a geostationary satellite is described. The method is based on the use of inhomogeneities in the concentration field of a conservative additive as tracers and on the application of correlation-extreme algorithms. Unlike the common methods used abroad, this method is able to determine not only the vector field of wind velocity but also the coefficient of turbulent diffusion and vorticity. Results of computations of the fields of the horizontal component of wind velocity and the effective coefficient of horizontal mesoscale turbulent diffusion from the Meteosat-8 SEVIRI water-vapor channel data are presented. It is shown that the average values of the effective coefficient of mesoscale horizontal turbulent diffusion in the areas with a predominantly turbulized air-mass motion are 1.5 times greater than in the areas where a laminar motion dominates. Specific features of the calculated values of the upper-troposphere dynamic characteristics in different stages of the North Atlantic TC Helene (September 2006) are analyzed.     

Surface heat fluxes and subsurface heat content at a site over the southeastern Bering Sea shelf, May–July 1996

Observations from a surface mooring, in a weak-flow regime over the southeastern Bering Sea shelf, were used to derive surface heat fluxes for the period May–July 1996. Changes in heat content of the water column also were determined from subsurface temperature measurements. Agreement of net surface heat flux and change in heat content was within 2%. This result provides additional evidence that heat advection and diffusion are small in this region.     

The dynamic method of calculating currents and analysis of the vertical kinematic structure

The basic relations of the classical dyamic method have been complemented with the condition allowing for the non-monotonicity of the vertical kinematic structure. The elements of the multi-layered system of geostrophic currents have been found to correlate over depth with seawater density and hydrostatic pressure distribution. An example of the analysis of the vertical structure of currents, involving specific hydrological data, is given. Translated by Vladimir A. Puchkin.     

The petroleum evaluation of a tectonically complex area: The western margin of the Southeast Basin (France)

The Southeast Basin of France is the thickest onshore French sedimentary basin which contains locally as much as 10 km of Mesozoic-Cenozoic sediment. Basin development occurred in several stages between late Carboniferous and late Cretaceous times. Partial tectonic inversion took place during two compressive events, the so-called ‘Pyrenean’ and ‘Alpine’ phases of late Cretaceous-early Tertiary and late Tertiary ages respectively. They are separated by an intervening stretching event of Oligocene age, which further south resulted in the opening of the western Mediterranean oceanic basin. As a result of this complex tectonic history, structural traps were difficult to image on the seismic data shot during the first phase of exploration prior to 1980. Oil and gas natural seeps, and shows in several wells, indicate that some petroleum systems are, or have been active, at least in some places.The present erosional western margin of the basin is more or less superimposed on the initial Triassic-Jurassic margin. Margin subsidence and Tertiary inversion are discussed using regional sections on which the polyphase history of the entire basin is well shown. These sections are located on three major segments where the Mesozoic margin is either partly preserved (Ardèche), or has been partly inverted in late Tertiary times (Vercors-Chartreuse), or has been completely inverted in early Tertiary times (Corbières-eastern Pyrenees). 1-D ‘Genex’ basin modelling on the Ardèche segment, and 2-D ‘Thrustpack’ structural-maturity modelling in the Vercors-Chartreuse segment are used to further assess the remaining petroleum plays.