Beach accretion and erosion, Burullus-Gamasa coast, Egypt

Several areas of erosion and accretion were observed along the Burullus-Gamasa beach. The accreted sands are coarser and less sorted than the eroded ones. Differentiation between them could be achieved on the basis of their grain-size fractions, shape of grain-size distribution curves and statistical grain-size parameter relationships.     

Benthic Metabolism and Standing Stock in the Central and Northern Deep Red Sea

Abstract. Benthic metabolism and standing stocks were investigated in the deep Red Sea between 21^o and 27^oN, Activity was assessed by the determination of respiration rates with a shipboard method and by calculating oxygen consumption from the activity in the electron transport system. We attempted to compare results from different latitudes within the warm Red Sea and with data from cold Atlantic environments. Our investigations were part of an environmental risk assessment to evaluate future mining of metalliferous sediments from the Atlantis II Deep.     

Formation of chemogenic calcite in super-anoxic seawater — Framvaren, southern Norway

Framvaren, a super-anoxic fjord in southern Norway, contains 7–8 mmoll⁻¹ of sulphide and a total carbonate concentration of 18.5 mmol kg⁻¹ in the bottom water. The chemistry of calcium has been studied, considering sources, biogenic and chemical processes and sedimentary sinks. Calcium associated with the bacteria biomass at the redox interface (18m depth) appears to be the primary source of dissolved calcium in the deep, anoxic water. Excess calcium and high total carbonate cause supersaturation of calcite, which is precipitated chemogenically. Calcite (and presumably some aragonite) is identified both in sediment trap material and the bottom sediments below the depth of supersaturation.     

Microearthquakes along the back-arc spreading system in the eastern Bismarck Sea

OBS’s were deployed for 26 to 29 days in the eastern Bismarck Sea to investigate the back-arc spreading. Hypocenters of 186 shallow earthquakes were determined using P- and S-waves from at least five stations. In the western survey area, a transform fault zone is marked by a linear micro-earthquake activity striking N65°W and less than 5 km wide. The predominant type of their focal mechanisms is strike-slip. In the eastern area, several intermittent zones of micro-earthquakes and their strike-slip type focal mechanisms suggest the location of short-length transform faults separating en-echelon spreading ridges.     

Kinetic studies of the rate of dissolution of silica and diatom tests in sea water

Kinetic studies have been carried out on the dissolution of 10μm beads of silica and of the siliceous tests of two species of diatoms (Thalassiosira fluviatus andSkeletonema costatum) in sea water at 10–50°C and over the pH range 6–9. At all temperatures dissolution of the biogenous silica occurred most rapidly at pH 8 and most slowly at pH 6. First order kinetics were closely followed when the silica was present in a considerable excess over that required for saturation, the rate being proportional to the area of the silica. Apparent deviation from this type of kinetics occurred when there was insufficient silica to bring about saturation. This was undoubtedly due to the progressive decrease in the surface area which takes place as the particle dissolves. Application of the rather simplistic model developed by Kamataniet al. (1980), which makes allowance for this decrease, gave a close correspondence with the data until ∼ 90% of the silica had dissolved.     

Simplified method of deep-tow seismic profiling

To improve resolution of seismic-reflection profiles in continental slope water depths of 900 to 1500 m, a single hydrophone was towed about 150 m off the bottom to receive reflected signals from a surface-towed sparker sound source. That deep-towed hydrophone data show that valleys which appear V-shaped in records from a surface-towed hydrophone are flat-bottomed, and that subbottom reflections from an erosional unconformity can be much better resolved. The data produced by this technique are very hepful when used in conjunction with records from conventional surface-towed seismic-profiling equipment.     

On the capsize performance of a discus buoy in deep sea breakers

The mode of capsize of a discus buoy in breaking waves is discussed. The results of model tests are given; these show that a judicious choice of mooring design can substantially reduce the chance of capsize. A comparison is made with the performance of the buoy on station.     

Ionic activity coefficients in aqueous mixtures of NaCl and MgCl2

Methods developed earlier, based on hydration numbers for individual ionic species, have been extended to the calculation of ionic activity coefficients in aqueous systems of two electrolytes MX and NX₂ with a common unhydrated anion (X⁻). The data required include the mean activity coefficients of MX and NX₂ in the mixtures, together with the osmotic coefficient. The procedure is illustrated by a calculation of γ_Na, γ_Mg, and γ_Cl in a mixture of NaCl and MgCl₂ closely approximating the composition of seawater with salinity of 35‰.