Late Quaternary Evolution of Amvrakikos Gulf,Western Greece

Amvrakikos Gulf is a Neogene basin, formed during a late extensional tectonic phase within the Plio-Quaternary period. It is a semienclosed embayment, separated from the Ionian Sea by a shallow (< 10 m) channel. The analysis of 3.5-kHz seismic reflection profiles shows that, during the last (Würm) glacial period, the parts of the Gulf that lie at water depths >41 m (below present sea level) were a paleo-lake while the rest were exposed to subaerial erosion. Subsequent offshore depositional sequences accumulated at rates of 1.2–2.3 m/ka.     

Response of the blue mussel Mytilus edulis L. following exposure to PAHs or contaminated sediment

The polycyclic aromatic hydrocarbons fluoranthene and benzo(a)pyrene significantly reduced the feeding rate of mussels. For both compounds the tissue concentration resulting in a 50% reduction of the clearance rate (TEC₅₀) was calculated. At high tissue concentrations both aromatic compounds reduced the tolerance of mussels to aerial exposure, whereas at low tissue concentrations an improved response was noticed. The activities of the antioxidant enzymes Superoxide dismutase (SOD) and catalase were elevated only at low tissue concentrations of fluoranthene and benzo(a)pyrene. At the highest measured tissue concentrations the activity of both enzymes was reduced, possibly due to a narcotic effect. The reproductive success rate of mussels appeared to be affected negatively by the investigated hydrocarbons. The results of a pilot experiment indicate that mussels can be used also for the testing of contaminated sediments.     

Stability and composition of terrestrially derived dissolved organic nitrogen in continental shelf surface waters

A linear decrease in dissolved organic carbon and nitrogen with increasing salinity offshore from the Georgia coast suggests that organic nitrogen compounds contributed to coastal waters by rivers are stable during the period (2–3 months) of their transfer over the continental shelf. While the C/N ratio decreased with distance from shore, total dissolved organic nitrogen (DON), total amino nitrogen, and primary amino nitrogen showed similar relative decreases, suggesting that nitrogen is associated with refractory organic compounds. Measured amino nitrogen accounted for about 20% of the total DON, leaving about 80% of the organic nitrogen undefined.     

An overview and general results of the Lopez island OBS experiment

The purpose of the experiment was to determine the effects of coupling and bottom currents on ocean bottom seismometers. Twelve operational OBSs, three specially designed three-component systems, and a hydrophone were compared with each other. Unlike seismometers placed on hard rock at land stations, ocean bottom seismometers can be affected by soft sediments (which act as lossy mechanical springs) and by buoyancy. Coupling through soft sediments can modify the response to ground motion much as a low pass filter does, and high buoyancy tends to counteract this effect. These effects are observed in the Lopez data, which consist of signals from mechanical transient tests, cap shots, airgun pulses, and general background noise. The modification of response is pronounced for some instruments and barely noticeable in others. Instruments that stand high in the water relative to their base width tend to be susceptible to rocking motion that shows up as a mechanical cross coupling between horizontal and vertical motion. Correlation of Lopez results with coupling theory suggests that it is possible to design ocean bottom seismometers that will couple well to any sediment. Current levels at the Lopez site (<5 cm s^-1) were too small to produce noticeable effect on any of the instruments; however, the same design criteria that will minimize coupling problems will also lessen problems caused by ocean currents.Hawaii Institute of Geophysics Contribution No. 1171.     

Topography and a magnetic analysis of an area south-east of the Azores (36°N, 23°W)

A detailed survey of a 1°×1°-square of seafloor 100 miles south-east of the Azores shows a strong correlation between directions of regional topographic and magnetic lineations. The area is dissected by the East Azores Fracture Zone at 36°55N, identified as the active Eurasian-African plate boundary, and by another large, non-active fracture zone at 36°10N. Both fracture zones strike 265° and are accompanied by large amplitude magnetic anomalies. The general strike in the area in between is 000°–015°. The skewing effect at this magnetic latitude is very sensitive to variations in strike of the magnetic contrasts. This effect was eliminated by a non-linear transformation which also gives the positions of magnetic contrasts. Some N-S contrasts were identified as sea floor spreading polarity contrasts (anomalies 31 and 32). Weak contrasts could be identified as topographic effects and gave a magnetization intensity of 5 A m^-1. The identified sea floor spreading anomalies to both sides of the fracture zone at 36°10N agree very well, also quantatively, with a three-dimensional model for the fracture zone anomalies. This model describes the non-linear anomalies as end effects of the magnetic layer which is divided in blocks of alternating polarity.     

Radium and lead-210 in marine barite

Measurements of ²²⁶Ra and ²¹⁰Pb in barite samples separated from different depths of a piston core from the eastern equatorial Pacific are reported. ²²⁶Ra is enriched in the barite as would be expected from the chemistries of Ra and Ba; the ${}^{226}\text{Ra}\text{Ba}$ ratio centers around 1.5 · 10¹⁴ atoms/mole. The results suggest that barite is concentrating Ra at a rate comparable to its decay rate, viz. 5.78 · 10^?3 yr^?1. The gross ²¹⁰Pb depletion with respect to ²²⁶Ra is indicative of ²²²Rn loss due to the smallness of the barite crystals.     

Water colour index of the Guinean sector of the Atlantic Ocean

The distribution of the colour index is considered in the region bounded by 8–11°N and 13°30–18°30W based on the results of measurements made on board vessels of the Marine Hydrophysical Institute of the Ukrainian SSR Academy of Sciences (MHI) in 1977–1985. Mean values and statistical characteristics are calculated for the colour index variability over one-degree squares. A map of its multi-yearly average distribution is plotted.Translated by M. M. Trufanov.     

Nutrient attenuation in a shallow,gravel-bed river. II. Spatial and temporal changes in nitrogen dynamics and community metabolism

ABSTRACT

Instream processes alter the concentration and bioavailability of nutrients as they are transported downstream. By relating primary production and periphyton composition to changes in nutrient concentration in a gravel-bed river this study made inferences about recycling and attenuation. Where dissolved inorganic nitrogen (DIN) was abundant, concentrations decreased linearly with distance but by less than required to meet the nitrogen demand of primary production. Where DIN was barely measurable photosynthesis was reduced but only by 50%. We infer that recycling sustained primary production even when DIN concentrations were negligibly small. One implication is that DIN removal underestimates attenuation. Further experimental research on recycling and improved modelling is required to better quantify the length of streams adversely affected by nutrients.     

The NDRE-AUV flight control system

The flight control system of an autonomous underwater vehicle (AUV) developed at the Norwegian Defence Research Establishment (NDRE) is presented. A mathematical model of the vehicle is derived and discussed. The system is separated into lightly interacting subsystems, and three autopilots are designed for steering, diving, and speed control. The design of the separate controllers is based on PID techniques. Results from extensive sea testing show robust performance and stability for the autopilot