Seasonal and interannual dynamics in diatom production in the Cariaco Basin,Venezuela

We examine the diatom flux collected between November 1996 and April 1998, and between January and October 1999 at the time-series study site in the Cariaco Basin, off Venezuela. The temporal dynamics of the total diatom flux mainly reflect seasonal, trade wind-driven changes in surface hydrographic conditions, including changes associated with the El Niño/Southern Oscillation (ENSO). Highest diatom fluxes (>1.8×10⁷ valves m^?2 d^?1) coincided with the upwelling season in boreal winters 1997 and 1999. Changes in the composition of the diverse diatom community reflect variations in hydrographic and atmospheric conditions, as well as nutrient availability. Cyclotella litoralis, a neritic diatom typical of nutrient-rich waters, along with resting spores of several Chaetoceros spp., dominate during periods of high diatom flux, following trade wind-driven upwelling. During the boreal summers of 1997 and 1999, nutrient-depleted surface waters resulted in low diatom fluxes (<5.2×10⁶ valves m^?2 d^?1). The seasonal pattern of high diatom production was altered from July 1997 through April 1998, when the ENSO affected the Caribbean Sea. The occurrence of ENSO during boreal winter 1997–1998 caused a major change in the qualitative composition of the diatom assemblage: the highly diverse diatom assemblage was composed of a mixture of pelagic (Nitzschia bicapitata, Thalassionema nitzschioides var. inflata, T. nitzschioides var. parva, Azpeitia tabularis) and coastal species (C. litoralis, resting spores of Chaetoceros, T. nitzschioides var. nitzschioides). The simultaneous occurrence of neritic and open-ocean diatoms during boreal summers reflects the fact that the Cariaco Basin is influenced by both offshore and coastal waters, with considerable short-term variability in hydrographic conditions and nutrient availability.     

Marine ecosystem-based management in the Southern Cone of South America: Stakeholder perceptions and lessons for implementation

Ecosystem-based management (EBM) has recently received considerable attention. However, examples of empirical approaches to marine EBM are scarce. Therefore, empirical information on the presence of EBM elements within existing policies and the way they may provide settings and lessons for EBM implementation is timely. This study analyses stakeholders’ perceptions on the existence of EBM principles in current marine management practices and policies, and how they determine perceptions for success and satisfaction regarding coastal management within selected case studies drawn from four developing countries in the Southern Cone of South America. Patterns of response across study sites show that although EBM principles as such are not explicitly included in management/conservation plans, there are policies (mainly local), which generate conditions for more explicit inclusion of them. These are based on participatory bottom-up planning, place-based management and consensus reaching: all elements included within the theoretical literature on EBM implementation.     

Cryptic metasomatic agent measured in situ in Variscan mantle rocks: Melt inclusions in garnet of eclogite,Granulitgebirge, Germany

Garnet of eclogite (formerly termed garnet clinopyroxenite) hosted in lenses of orogenic garnet peridotite from the Granulitgebirge, NW Bohemian Massif, contains unique inclusions of granitic melt, now either glassy or crystallized. Analysed glasses and re-homogenized inclusions are hydrous, peraluminous, and enriched in highly incompatible elements characteristic of the continental crust such as Cs, Li, B, Pb, Rb, Th, and U. The original melt thus represents a pristine, chemically evolved metasomatic agent, which infiltrated the mantle via deep continental subduction during the Variscan orogeny. The bulk chemical composition of the studied eclogites is similar to that of Fe-rich basalt and the enrichment in LILE and U suggest a subduction-related component. All these geochemical features confirm metasomatism. In comparison with many other garnet+clinopyroxene-bearing lenses in peridotites of the Bohemian Massif, the studied samples from Rubinberg and Klatschmühle are more akin to eclogite than pyroxenites, as reflected in high jadeite content in clinopyroxene, relatively low Mg, Cr, and Ni but relatively high Ti. However, trace elements of both bulk rock and individual mineral phases show also important differences making these samples rather unique. Metasomatism involving a melt requiring a trace element pattern very similar to the composition reported here has been suggested for the source region of rocks of the so-called durbachite suite, that is, ultrapotassic melanosyenites, which are found throughout the high-grade Variscan basement. Moreover, the Th, U, Pb, Nb, Ta, and Ti patterns of these newly studied melt inclusions (MI) strongly resemble those observed for peridotite and its enclosed pyroxenite from the T-7 borehole (Staré, České Středhoři Mountains) in N Bohemia. This suggests that a similar kind of crustal-derived melt also occurred here. This study of granitic MI in eclogites from peridotites has provided the first direct characterization of a preserved metasomatic melt, possibly responsible for the metasomatism of several parts of the mantle in the Variscides.     

Interannual variability of wave climate in the Caribbean Sea

Ocean Dynamics - Low-frequency interannual climatic oscillations have been reported to influence the precipitation regimes, river discharges, winds, and sea level in the Caribbean Sea. Here, we...     

3D CFD MODELING OF WATER AND SEDIMENT FLOW IN A HYDROPOWER RESERVOIR

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A mixed continuous and discrete nonlinear constrained algorithm for optimizing ship hull structural design

A nonlinear search algorithm for optimizing constrained design of ship structures is presented. The decision variables can be continuous or discrete and the constraints can be homogeneous or inequality nonlinear functions of those variables. The algorithm does not use gradients; therefore, it can work with non-systematized functions such as tables or another class of design routine. It was tested in the structural design of a Patrol Boat and has proved to be a powerful tool decreasing the time expended in preliminary design when it is done by the conventional spiral approach.     

Applications of an orbiting gravity gradiometer

Considering present attempts to develop a gradiometer with an accuracy between 10⁻³ E and 10⁻⁴ E, two applications for such a device have been studied: (a) mapping the gravitational field of the Earth, and (b) estimating the geocentric distance of a satellite carrying the instrument. Given a certain power spectrum for the signal and 10⁻⁴ E (rms) of white measurement noise, the results of an error analysis indicate that a six-month mission in polar orbit at a height of 200 km, with samples taken every three seconds, should provide data for estimating the spherical harmonic potential coefficients up to degree and order 300 with less than 50% error, and improve the coefficients through degree 30 by up to four orders of magnitude compared to existing models. A simulation study based on numerical orbit integrations suggests that a simple adjustment of the initial conditions based on gradiometer data could produce orbits where the geocentric distance is accurate to 10 cm or better, provided the orbits are 2000 km high and some improvement in the gravity field up to degree 30 is first achieved. In this sense, the gravity-mapping capability of the gradiometer complements its use in orbit refinement. This idea can be of use in determining orbits for satellite altimetry. Furthermore, by tracking the gradiometer-carrying spacecraft when it passes nearly above a terrestrial station, the geocentric distance of this station can also be estimated to about one decimeter accuracy. This principle could be used in combination with VLBI and other modern methods to set up a world-wide 3-D network of high accuracy.     

Limnological studies of Amarga Lagoon,Chile: A saline lake in Patagonian South America

Amarga Lagoon, lat. 50°29 S and long. 73°45 S, it is located at the Torres del Paine National Park, Chile. The physical, chemical, and biological features of the lake were studied. According to salinity, the lake is mesosaline. Sodium and chloride were the dominant ions. Nitrogen was potentially limiting for phytoplankton growth. One Cyanophyceae species andArtemia were the predominant species in the plankton.Artemia provided abundant food for flamingoes.     

Eigensensitivity analysis of moisture-related buckling of marine composite panels

In this paper, an approximate closed-form solution is presented to compute the moisture-related buckling of symmetric angle-ply laminates. The environment corresponds to a steady state condition, which provides a uniform moisture distribution for the laminate. The laminate consists of four layers [θ/−θ]_s constructed of low, moderate and high stiffness ratio materials. Comparative results using the Rayleigh–Ritz method provides a means of assessing the accuracy of the expression. For certain laminate architectures, several modes must be computed to ascertain the lowest buckling mode, and once identified, provides an excellent approximation for the mode computed using the Rayleigh–Ritz method.