Geopotential topography of deep levels in the Pacific Ocean

After examination of the baroclinic structure below 3000 db, recent data were used to map the geopotential topography at 1000, 1500, and 2000 db (referred to 3000 db) in the Pacific Ocean. In the high-latitude regions and in the western boundary currents, considerable relief is present at 1000 and 1500 db, and the Circumpolar Current is still well-developed at 2000 db. The geostrophic circulation inferred is very similar to the surface circulation in these areas. Neglect of the structure below 1000 db results in appreciable errors in estimates of the transport of these currents; direction of near-surface flow is properly shown, however, and computed speeds are not greatly in error. In the equatorial Pacific and central North Pacific, little relief is present, and the trends are generally unlike the surface flow.     

Random dynamic analysis of multi-body offshore structures

A general method for the dynamic analysis of multi-body offshore structures is presented, being based on a constraint matrix approach. A method of deriving the constraint matrix for a general structure is given, and this is then used to derive the equations of motion of a whole system from those of it's component parts. The response of the system to both first and second order random wave forces is found and then used to calculate the forces and moments in the connecting mechanisms. The structure is assumed to have rigid component parts and a linearised frequency domain analysis method is used, although other methods are discussed. To illustrate it's use, the method is applied to both the SBS and Yoke-CALM design of offshore mooring terminal.     

Total oxyradical scavenging capacity of the deep-sea amphipod Eurythenes gryllus

Environmental concern for the deep-sea ecosystem is increasing as contaminants, originating from anthropogenic activities, have been detected in deep-sea biota. However, little is known on the xenobiotics metabolising capability of deep-sea fauna. In this study, the deep-sea amphipod Eurythenes gryllus was selected as sentinel species to measure the total oxyradical scavenging capacity (TOSC). Individuals of E. gryllus were sampled at 2000 m depth in the Arctic Ocean. The TOSC assay was measured on the cytosolic fraction and the soluble fraction (3 kDa) of the digestive gland and on the cell-free haemolymph toward peroxyl, hydroxyl and peroxynitrite radicals according to the method of Winston et al. [Free Radical Biology and Medicine 24 (3) (1998) 480] and Regoli and Winston [Toxicology and Applied Pharmacology 156 (1999) 96]. These results provide the first baseline data set for total antioxidant capacity in a deep-sea amphipod.     

Physical and biological factors influencing the spatial distribution of age-0 walleye pollock (Theragra chalcogramma) around the Pribilof Islands, Bering Sea

The waters around the Pribilof Islands, in the southeast Bering Sea, are a main nursery area for age-0 pollock. Each summer, the islands are surrounded by a well-mixed inshore region, separated from a stratified offshore region by a frontal zone. To study the spatial distribution of age-0 pollock around this frontal structure in relation to physical and biological factors that are likely to influence it, such as advection, age-0 pollock feeding, and predation, samples were collected during September of four consecutive years, 1994–97, along two transects. Samples collected included water column hydrography and currents, acoustic backscatter, and groundfish predator density.Our analysis suggested that different mechanisms may be involved in controlling age-0 pollock distribution north and south of the islands. On the shelf area north of the islands, high age-0 pollock density was significantly associated with areas of high potential for growth only in years or portions of the frontal transect in which predator numbers were relatively low, indicating the importance of predation in controlling fish distribution in this area. In contrast, south of the islands, age-0 pollock distribution was associated more with prey availability, which appeared to be determined by vertical spatial overlap between predators and prey. Moreover, south of the islands, the stronger geostrophic currents, typical of the slope region, were more likely to affect the overall standing biomass of juvenile pollock, by constantly advecting fish away from the area.     

Meanders in the Antarctic Polar Frontal Zone and their impact on phytoplankton

The Antarctic Polar Front is a complex set of meandering jets, which appear to support enhanced primary productivity. The US Joint Global Ocean Flux Study conducted a series of survey and process studies in part to study the processes regulating primary productivity in this high nutrient, low chlorophyll region. We deployed a set of surface velocity drifters, some of which were equipped with bio-optical sensors, to study the temporal and spatial scales of biological and physical processes in the Antarctic Polar Frontal Zone. There were two primary sets of deployments: November 1997 before the spring bloom and January 1998 after the spring bloom. The November deployment revealed a strong spring bloom that lasted about 10 days. In late spring, when incoming solar radiation began to increase, the vertical motions associated with the meanders strongly affected the accumulation of phytoplankton biomass, primarily through their impact on light availability. Weaker meandering was observed in the January deployment, and chlorophyll values remained relatively constant. As the bloom began to decay, it appears that nutrient availability became more important in regulating phytoplankton photosynthesis. Some of the drifters in the November deployment were deployed in coherent clusters, thus allowing us to calculate vertical velocities associated with the meanders. Estimates of fluorescence/chlorophyll suggest that areas of upwelling and downwelling alternately decrease and increase photosynthetic stress, perhaps as a result of changes in the availability of iron or light during the formation of the bloom.     

Sediment–water interactions of natural oestrogens under estuarine conditions

The natural human female hormones oestrone and 17β-oestradiol have been implicated in the disruption of endocrine systems in some wildlife adjacent to sewage effluents. The sorption behaviour of these two compounds under estuarine conditions was studied by spiking either 2.55 μg of oestrone or 2.65 μg of 17β-oestradiol in kinetic experiments. In equilibrium experiments, 3 ng of oestrone or 3.2 ng of 17β-oestradiol was added in each of the centrifuge tubes. Sorption onto sediment particles was relatively slow, with sorption equilibrium being reached in about 70 and 170 h for oestrone and 17β-oestradiol, respectively. The effects of a variety of environmental parameters on sorption were studied including salinity, sediment concentration (SC), the presence of a third phase, particle size and, also, surfactant concentrations. Results show that although salinity did not induce any statistically significant effect on the sorption of 17β-oestradiol, it did statistically enhance the sorption of oestrone, and a salting constant of 0.3 l mol⁻¹ was derived. The partition coefficient for both compounds decreased with increasing sediment concentration, a phenomenon that has been widely reported and attributed to the presence of colloids (which could enhance dissolved concentrations). In this paper, the true partition coefficients for sediment particles (K_p^true) and colloidal particles (K_c^true) have been calculated, and a K_p^true value of 141 and 102 ml g⁻¹ was obtained for oestrone and 17β-oestradiol, respectively. In addition, K_c^true values for oestrone (222×10² ml g⁻¹) and 17β-oestradiol (135×10² ml g⁻¹) were two orders of magnitude higher than their respective K_p^true values, suggesting that the colloidal particles are significantly stronger sorbents for natural oestrogens than sediment particles. Particles of different sizes were found to have different partition coefficients due to the strong relationships between partition coefficients for the two compounds and particulate organic carbon (POC) contents and specific surface areas (SSAs). The presence of a surfactant was shown to reduce the partition coefficients for the two compounds, although its concentrations being used were higher than those normally found in the natural environment.     

An experimental pressure compensated wet suit

Personal thermal insulation by means of neoprene from wet suits provides adequate temporary control of body heat loss only at the shallow end of the air diving depth range, but it constitutes by far the most popular approach to diver thermal support. Howewer, compression of the trapped gas phase in neoprene foam seriously reduces its insulation performance on exposure to high ambient pressure. With conventional wet suits equipped with heating, the necessary level of power required at depths greater than about 30 m is too high, and also unsafe without the back up that increased insulation would provide. One approach to the goal of depth-insensitive insulation is to use a wet suit with a continuous internal gas space pressurized nominally to ambient pressure, so that its thickness remains substantially constant at all depths. The composite material properties required are: outer skins that are tough, flexible and free of pin holes; an open foam internal structure capable of resisting, without significant dimensional change, the relatively small pressure changes that occur over the height of a man; and a high bond strength.Samples of a composite material that meets these requirements have been developed, and a prototype suit has been successfully fabricated by conventional techniques.