Simulation of Hydrophysical Processes in Coastal Regions of the Sea

In the present work, we generalize the results of our investigations in the field of simulation of hydrophysical and ecological processes in coastal regions of various seas and some closed basins. The developed and applied mathematical models and the results of numerical experiments are briefly analyzed.     

Probing molecular-level transformations of dissolved organic matter: insights on photochemical degradation and protozoan modification of DOM from electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Molecular-level characterization of natural organic matter (NOM) has been elusive due to the inherent complexity of natural organic mixtures and to the fact that individual components are often polar and macromolecular. Electrospray ionization (ESI) is a “soft” ionization technique that ionizes polar compounds from aqueous solution prior to injection into a mass spectrometer. The highest resolution and mass accuracy of compounds within NOM have been achieved when ESI is combined with an ultrahigh-resolution mass spectrometer such as the Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). With this technique, individual molecules within a variety of natural organic mixtures can be detected and their elemental composition can be determined. At low mass-to-charge (m/z) ratio, the resolution is high enough to assign exact molecular formulas allowing specific components of these mixtures to be identified. In addition to molecular identification, we can now use ESI FT-ICR MS to examine molecular-level changes in different organic mixtures as a function of relevant geo-processes, such as microbial alterations and photochemistry. Here we present the results from the application of ESI FT-ICR MS to two geochemical questions: (1) the effect of photoirradiation on the molecular composition of fulvic acids and (2) the role of protozoan grazers in the modification of DOM in aquatic systems.     

Phototoxicity of pyrene and benzo[a]pyrene to embryo-larval stages of the Pacific oyster Crassostrea gigas

There is a growing body of evidence to suggest that certain polycyclic aromatic hydrocarbons (PAHs) pose a greater hazard to aquatic organisms than previously demonstrated, due to their potential to cause photo-induced toxicity when exposed to ultraviolet (UV) radiation. The consequences of photo-induced toxicity are reported here for embryo-larval stages of the pacific oyster Crassostrea gigas, following exposure to pyrene and benzo[a]pyrene. During laboratory investigations, significant increases in toxicity were observed in the presence of environmentally attainable levels of UV-radiation, compared with embryos exposed to PAH alone, at levels previously deemed to have little acute biological effect. The phototoxicity of pyrene and benzo[a]pyrene completely inhibited the development to the D-shell larval stage when embryos were simultaneously exposed to 5 microg l(-1) PAH and ultraviolet light (UVB = 6.3 +/- 0.1 microW/cm2 and UVA = 456.2 +/- 55 microW/cm2). A linear relationship was also demonstrated for benzo[a]pyrene phototoxicity with decreasing UV light intensity.     

Experimental investigation of forces and geometry of a net cage in uniform flow

A scale model of a flexible circular net with different weights attached to the bottom was tested in a flume tank. Global forces and net deformation were measured for different steady current velocities. Three different sizes of bottom weights were used in the tests. The results from these tests are presented and discussed with the emphasis on the dependency between the forces and the geometry. Comparison is also made to empirical based formulas for calculation of drag and lift forces on net structures. Findings show that i) the forces on, and deformation of a flexible net structure are mutually highly dependent on each other; ii) estimates of global forces on a flexible net structure calculated using simple drag formulas derived from stiff net panel experiments give large errors when compared to experimental measurements; iii) numerical models taking into account the dependency between force and deformation should be used to obtain accurate estimates of forces on flexible net structures; and iv) the forces on a flexible net structure are dependent on Reynolds number, and their dependency are similar to that of a regular cylinder.     

The dynamic behaviour of a river-dominated tidal inlet, River Murray, Australia

Australia's largest river, the River Murray, discharges to the southern ocean through a coastal lagoon and river-dominated tidal inlet. Increased water extractions upstream for irrigation have led to significantly reduced flows at the mouth and, as a result, the area is undergoing rapid change, particularly with regard to the rate at which sediment is being transported into the lagoon. Based on detailed and accurate bathymetric surveys it has been possible to estimate that the rate of lagoon in-filling is of the order of 100,000 m³ per year for the period June 2000 to May 2003, although the actual rate shows significant year to year variability. Dredging of the lagoon commenced in 2000 in an attempt to reverse the trend.In an effort to understand the behaviour of the inlet a one-dimensional numerical model of the inlet has been developed. The model extends the original of van de Kreeke by including a dynamic inlet throat area based on predicted river flows and a sediment transport module to predict the resulting net sediment transport. Comparisons with water level data collected on both the ocean and lagoon sides of the mouth have shown that the model is able to predict the attenuation and lag of the tidal signal reasonably well. The sediment transport model was based on predicted sediment concentrations in the surf zone and was found to predict the rate of sediment in-filling to an acceptable level of accuracy. It is envisaged that the model will be a useful management tool, especially since it is possible to manipulate river discharges to the mouth.     

Native aluminium (spherules and particles) in the Central Indian Basin sediments: Implications on the occurrence of hydrothermal events

We have sampled particles of native aluminium (Al°) in two sediment cores from the Central Indian Basin (CIB). The cores are geographically separated but are located at the base of two seamounts. The native Al° particles occurring as grains and spherules, have an average Al content of  95% and are associated with volcanogenic–hydrothermal material. Morphologically and compositionally, the specimens are similar to those reported from the East Pacific Rise. After ruling out several processes for the presence of the native Al°, we hypothesize that during progressive melting of magma, a basaltic magma is produced which has high contents of reductants such as methane and hydrogen, and a low oxygen fugacity. During the upward migration of such magma, reduction to metallic aluminium and the formation of native Al° particles takes place.     

Provenance and dispersal of muds south of the Aleutian arc,north Pacific Ocean

X-ray diffraction analyses show that the clay mineralogies of near-surface muds in the Gulf of Alaska (mostly illite and chlorite) are consistent with detrital sources in southern Alaska. Expandable clay minerals are derived from the Aleutian volcanic arc, and their percentages increase progressively toward the west. Smectite values are lower than expected, however, particularly in the central forearc, and there is less smectite on the insular trench slope than farther seaward. The regional clay-mineral distribution is controlled by two opposed contour currents and by the influx of suspended sediment via both transverse and trench-axis turbidity currents.     

Study of macroaggregate composition using FT-IR and H-NMR spectroscopy

Mucous macroaggregates, recently observed in the northern Adriatic in summer of 1997 and late spring of 2000, are primarily the product of phytoplankton (diatom) exudates during favourable environmental conditions in late spring, and can be viewed as macrogels. The FT-IR and ¹H-NMR spectra of macroaggregate samples from the northern Adriatic, collected in different formation stages in July 1997, August 1997, September 1997 and June 2000, as well as of cultured diatom Skeletonema costatum, showed that they are similar and composed of aliphatic components and polysaccharides bonded through carboxylic and amide groups, and organosilicon compounds. The stability of macrogels of macroaggregates is, according to FT-IR and X-ray analyses, most probably enhanced by interactions with entrapped particles of calcite, quartz and clay minerals. These organic-mineral associations seem to be important for mucous phenomena. According to ¹H-NMR spectra, the temporal differences in macroaggregate composition show a relative increasing percentage of organosilicon compounds and aliphatic components bonded to carbohydrates through ester and amide groups, and an increasing ratio between aliphatic structures and carbohydrates. This indicates that aliphatic chains bonded to Si and carbohydrates may contribute to the persistence and stability of macroaggregates in the summer stratified waters in the northern Adriatic, while the temporal decrease of carbohydrate content is most probably due to microbial and photochemical degradation of algal reserve polysaccharides.