IDENTIFICATION OF SEA-FLOOR SEDIMENTS USING UNDERWAY ACOUSTICS*

Laboratory measurements, and a few in situ observations, show that saturated marine sediments have interdependent mechanical and acoustical properties, Acoustically, of particular importance are the acoustic impedance, velocity of sound and the sound attenuation coefficient of the sediment. The first two properties can be measured relatively easily from a surface ship; the measurement of attenuation however, is more problematical. It is suggested that this can be achieved by a quantitative treatment of the acoustic data collected during routine sub-bottom profiling over a variable thickness of superficial sediments. In the assessment of four different sediment locations in the Irish Sea it was found that quantitative treatment of the acoustic signals yielded both a value of the attenuation coefficient as well as a measure of the frequency dependence of the attenuation. In addition a statistical analysis of the signal intensities seems to provide an indication of the relative roughness of the bottom and sub-bottom interfaces. From the wide range of information provided the mechanical properties of the sea-floor sediment may be estimated.     

Sensitivity of AUV added mass coefficients to variations in hull and control plane geometry

The sensitivity of the added mass coefficients of a typical autonomous underwater vehicle (AUV) to changes in geometric parameters was investigated. Qualitative deductions were made concerning the effect of geometric variations. Then the added mass coefficients for several configurations of body geometry were generated for the Canadian Self-Contained Off-the-shelf Underwater Testbed (C-SCOUT) vehicle using the computer program Estimate Submarine Added Mass (ESAM). The changes in the added mass coefficients have direct relationships to the varied parameter. The results presented here are specific to the C-SCOUT, but may be extended to similar axisymmetric bodies.     

Assessment of wind-forcing impact on a global wind-wave model using the TOPEX altimeter

The study presents assessment of an operational wave model (Wavewatch III), focusing upon the model sensitivity to wind-forcing products. Four wind fields are used to drive the model, including the NCEP/NCAR reanalysis and three other products that assimilate various satellite wind measurements having high spatial resolution, including the QuikSCAT scatterometer. Three wave field statistics: significant wave height, mean zero-crossing wave period, and mean square slope are compared with collocated TOPEX altimeter derivatives to gauge the relative skill of differing wind-forced model runs, as well as to demonstrate an extended use of the altimeter beyond simply supplying wave height for wave model validation and assimilation. Results suggest that model output is critically sensitive to choice of the wind field product. Higher spatial resolution in the wind fields does lead to improved agreement for the higher-order wave statistics.     

NUMERICAL MODELING OF HEAVY METAL POLLUTANT TRANSPORT-TRANSFORMATION IN FLUVIAL RIVERS：A REVIEW

A detailed discussion of existing three kinds of mathematical models of heavy metal pollutant transport-transformation in fluvial rivers is presented, with an emphasis on the mathematical model of heavy metal pollutant transport-transformation dynamics. The imperfection of two kinds of mathematical models, that is, mathematical model of chemical thermodynamic equilibrium and that of chemical reaction kinetics, and the shortcoming of existing mathematical models of heavy metal pollutant transport-transformation dynamics are pointed out. Furthermore, the structure of mathematical model of heavy metal pollutant transport-transformation dynamics in fluvial rivers is suggested. Equations in the mathematical model of heavy metal pollutant transport-transformation dynamics in fluvial rivers will be discussed in the following paper.     

Storm Surges in the Strait of Georgia Simulated with a Regional Model

The Strait of Georgia is a large, semi-enclosed body of water between Vancouver Island and the mainland of British Columbia connected to the Pacific Ocean via Juan de Fuca Strait at the south and Johnstone Strait at the north. During the winter months, coastal communities along the Strait of Georgia are at risk of flooding caused by storm surges, a natural hazard that can occur when a strong storm coincides with high tide. This investigation produces storm surge hindcasts using a three-dimensional numerical ocean model for the Strait of Georgia and the surrounding bodies of water (Juan de Fuca Strait, Puget Sound, and Johnstone Strait) collectively known as the Salish Sea. The numerical model employs the Nucleus for European Modelling of the Ocean architecture in a regional configuration. The model is evaluated through comparisons of tidal elevation harmonics and storm surge with observations. Important forcing factors contributing to storm surges are assessed. It is shown that surges entering the domain from the Pacific Ocean make the most significant contribution to surge amplitude within the Strait of Georgia. Comparisons between simulations and high-resolution and low-resolution atmospheric forcing further emphasize that remote forcing is the dominant factor in surge amplitudes in this region. In addition, local wind patterns caused a slight increase in surge amplitude on the mainland side of the Strait of Georgia compared with Vancouver Island coastal areas during a major wind storm on 15 December 2006. Generally, surge amplitudes are found to be greater within the Strait of Georgia than in Juan de Fuca Strait.     

Geochemistry of High-silica Peralkaline Rhyolites, Naivasha, Kenya Rift Valley

The Recent (<15000 y) volcanic complex of southwest Naivasha,Kenya, consists of mildly peralkaline (comenditic) rhyolitedomes, lava flows, air fall pumices, and lake sediments, withminor, peripheral, basalts and hawaiites. The comendites areeither aphyric or sparsely porphyritic, few samples containing>5 per cent phenocrysts. Phenocryst minerals are quartz-sanidine-ferrohedenbergite-fayalite-titanomagnetite-ilmenite-riebeckite-arfvedsonite-aenigmatite-biotite-zircon.Ferrohedenbergite and zircon are restricted to less peralkaline,and amphibole, aenigmatite, and biotite to more peralkaline,rocks. The comendites show unusually strong enrichment in Cs, F, Hf,Nb, Rb, REE, Ta, Th, U, Y, Zn, and Zr, and extreme depletionin Mg, Ca, Ba, Co, and Sr. REE patterns are moderately LREE-enriched,with large, negative Eu anomalies. Values of LIL/HFS elementratios, such as Th/Ta and Rb/Zr, are unusually high for peralkalinerhyolites, and are consistent with a substantial crustal componentin the comendites. Parameters such as LREE/HREE and Zr/Nb ratiosindicate that the Naivasha rhyolites represent several pulsesof closely related, but subtly different, magmas. Sanidine/glasspartition coefficients for Ba, Pb, Rb, Sr, U, and the REE arepresented for one specimen. Major and trace element modelling, and feldspar-rock relationships,show that closed system crystal fractionation cannot alone accountfor the overall compositional variations in the comendites.A model involving partial melting of variable crustal sourcerocks and migration of dissolved volatile-metal complexes maybe appropriate at Naivasha.