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.     

Breaking of a tidal internal wave on a steep shelf as inferred from temperature measurements

The structure, evolution, and breaking of a tidal internal wave on a steep shelf are discussed on the basis of the data of temperature measurements. The bottom slope at the measurement site is close to the critical slope for a tidal wave. The tidal wave and other waves are inclined coastward. The tidal-wave amplitude increases monotonically with increasing horizon depth. The tidal wave is nonlinear in amplitude and turns over on the outer shelf. On the inner shelf, the internal wave is close in shape to rectangular and generates harmonics of its own. The harmonics make the tidal wave steeper and form solitary rises similar to bilateral bores. All these features ensure a more rapid sink for the internal-tide energy.     

Trends in the solubility of iron,aluminium, manganese and phosphorus in aerosol collected over the Atlantic Ocean

The solubility of iron, aluminium, manganese and phosphorus has been determined in aerosol samples collected between 49°N and 52°S during three cruises conducted in the Atlantic Ocean as part of the European Union funded IRONAGES programme. Solubilities (defined at pH 4.7) determined for Fe and Al in samples of Saharan dust were significantly lower (medians 1.7% and 3.0%, respectively) than the solubilities of these metals in aerosols from other source regions (whole dataset medians 5.2% and 9.0%, respectively). Mn solubility also varied with aerosol source, but the median solubility of Mn in Saharan dust was very similar to the median for the dataset as a whole (55% and 56%, respectively). The observed solubility of aerosol P was ∼ 32%, with P solubility in Saharan aerosol perhaps as low as 10%. Laboratory studies have indicated that aerosol Fe solubility is enhanced by acid processing. No relationship could be found between Fe solubility and the concentrations of acid species (non-seasalt SO₄²⁻, NO₃⁻) nor the net acidity of the aerosol, so we are unable to confirm that this process is significant in the atmosphere. In terms of the supply of soluble Fe to oceanic ecosystems on a global scale, the observed higher solubility for Fe in non-Saharan aerosols is probably not significant because the Sahara is easily the dominant source of Fe to the Atlantic. On a smaller scale however, higher solubility for aerosol Fe may alter our understanding of Fe cycling in regions such as the remote Southern Ocean.     

Experimental study of the breaking limit of multi-directional random waves passing over an impermeable submerged breakwater

This study investigates experimentally the breaking wave height of multi-directional random waves passing over an impermeable submerged breakwater. Experiments have been conducted in a three-dimensional wave basin equipped with a multi-directional random wave generator. A special type of wave gauge has been newly devised to record the water surface elevations in the breaker zone as accurately as possible. The records are analyzed to estimate the location and limit of wave breaking. Comparisons have also been made with the results of regular waves. The influence of the incident wave conditions on the breaking wave height normalized by the breakwater dimensions has been investigated. Empirical formulae have been presented to estimate the breaking limit of multi-directional random waves based on the experimental records. The formulae have been tested and found to work well not only for multi-directional random waves, but for regular waves as well.     

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.     

Geochemical cycling in the Hooghly estuary, India

U–Th decay series isotopes, δ¹⁸O and Si measurements in the river estuarine waters and sediments of the polluted Hooghly estuary as well as the surface waters of the Bay of Bengal, its high salinity end member, are reported. Dissolved Si indicates that there are probably two mixing regimes, dissolved U behaviour is nonconservative and δ¹⁸O behaves conservatively in the overall estuarine region. Isotopes of reactive elements, viz. ²³⁴Th and ²¹⁰Po, are removed from the estuarine waters in <2 days and <1 month, respectively, which is due to high suspended matter (30–301 mg l⁻¹). ²²⁸Ra and ²²⁶Ra are profusely released into the estuarine waters in the low to mid-salinity regions.As expected, the opposite trend is observed in the case of estuarine sediments and suspended matter. Reactive isotopes of Th, ²¹⁰Pb and ²¹⁰Po are enriched, whereas Ra isotopes are depleted with respect to their parent nuclides in the estuarine sediments and suspended matter. ²³²Th/Al ratio appears well suited to study the distribution and mixing of the bed load sediments of the Ganga–Brahmaputra (G–B) and the Hooghly rivers with those from other rivers on the Bay of Bengal floor.     

Treatment of Hydrodynamic Loading for Random Sea State

- In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea states are analyzed to highlight the implications and relative merits of four salient linearization techniques.     

Growth of Five Species of Gorgonians (Sub-Class Octocorallia) in the Sedimented Waters of Singapore

Abstract. Annual growth rates of gorgonians in the Indo-Pacific region are reported ror the first tinie. A method of measuring gorgonian growth using periodic photographic monitoring that is sensitive to horizontal growth and changes in growth foci but that does not require tedious underwater measurements is applied. Growth parameters of five species of gorgonians from three Families ( Plexauridae. Melithaeidae . and Subergorgiidae ) were monitored over a period of 18 months using this method. Growth rates ranged from 2.30 cm a^-1 to 7.88 cm. a ^-1 in the highly sedimented waters of Singapore. The maximum number of branches added per year ranged from 1.7 to 14.5.