Mesoscale structure of the mean East Australian Current System and its relationship with topography

We document the mean circulation of the East Australian Current (EAC) System, which is the major western boundary current in the southwest Pacific Ocean. A new high-resolution climatology of the region (CSIRO Atlas of Regional Seas, CARS) is used to produce regional fields of steric height and sections of geostrophic velocity. The realism of these fields has been enhanced by the high spatial resolution, allowance for bathymetric control and the influence of land barriers. The increased detail in the maps and sections reveal the major influence that the complex regional topography has on the circulation. The results also provide the appropriate resolution for comparison with recent model studies of the region. We have been able to both resolve well-known features with greater detail and identify previously unrecognized aspects of the circulation. Important results include: (1) The zonal inflow north of 30°S breaks into a series of individual jets after flowing through the island chains as suggested by recent model results. (2) The interaction of the zonal inflow with the local topography as it undergoes bifurcation is documented. (3) A detailed picture of the evolution of the EAC at the western boundary is presented, including surface currents and transports. (4) Separation and recirculation of the EAC within the Tasman Abyssal basin are shown to occur as a double cell structure constrained by bathymetry. (5) The EAC outflow is resolved as a series of eastward, and northeastward currents. (6) The path of the Tasman Front is defined as it interacts with the Tasman Ridge systems. (7) A quasi-permanent eddy is identified for the first time adjacent to the Norfolk Ridge, northwest of New Zealand.     

Partitioning of Hf,Lu, Ti,and Mn between olivine,clinopyroxene and basaltic liquid

The crystal/liquid partition coefficients of Lu, Hf, Ti, Mn and Ca have been measured between olivine, clinopyroxene and basaltic melt. The Ti, Mn, and Ca partition coefficients were determined at natural abundance levels. The Lu and Hf partition coefficients were determined at doping levels ranging from 0.5 to 1.5 wt% “trace element” as oxide in order to allow analysis by electron microprobe. Olivine/liquid partition coefficients for Lu, Hf, Ti, Mn, and Ca were determined at 1 bar and temperatures from 1150 to 1177° C. Clinopyroxene/liquid partition coefficients were determined for Lu, Hf, Ti, and Mn at pressures of 10, 15, and 20 kbars and temperatures from 1250 to 1290° C. The olivine/liquid partition coefficients of Hf, Lu, Ti, and Ca are small. D(Hf-ol) is zero within the analytical uncertainty. Both D(Lu-ol) and D(Mn-ol) decrease with increasing temperature, but D(Ti-ol) and D(Ca-ol) are constant over the narrow temperature range studied. The partition coefficient results are summarized below.

Intensity determination by continuous thermal cycling

The advent of cryogenic magnetometers with which remanence can be measured at high sensitivity statically permits continuous thermal demagnetization and, in principle, a continuous version of the classic stepwise method of intensity determination. In the technique we have initially tried a field is trapped in the superconducting shield of the magnetometer throughout the experiment. The sample is then thermally cycled over progressively higher temperature ranges so that the incremental acquisition of partial thermoremanence (PTRM) and loss of the natural remanence (NRM) of the sample can be compared. In control experiments we have found that bad intensity estimates arise because the presence of the field causes difficulty in reliable separation of remanent and induced moments. A better approach is to heat and cool the sample in the required fields outside of the magnetometer and to insert it into the magnetometer only for the measurement of remanence. In this way it will be possible to cycle the sample to progressively higher temperatures and measure at elevated temperatures without cooling to room temperature, but one will measure remanence directly in zero field.     

The biogeochemical expression of deeply buried uranium mineralization in Saskatchewan, Canada

Ten kilometres from the eastern edge of the Athabasca Sandstone, near McClean Lake, uranium mineralization (locally up to 27% U₃O₈) lies 150 m beneath the surface at the unconformity between the Athabasca and crystalline basement.A biogeochemical survey of the area sampled A_H and B_F soil horizons, peat moss, and plant organs from the dominant species, viz. black spruce (Picea mariana), jack pine (Pinus banksiana), labrador tea (Ledum groenlandicum), and leather leaf (Chamaedaphne calyculata). Uranium concentrations in the ash of various media are surprisingly high: spruce twigs up to 154 ppm U; labrador tea and leather leaf stems around 100 ppm U. Conversely, labrador tea roots yield < 5 ppm U and spruce trunk wood usually < 1 ppm U. Soils give values of 1–3 ppm U. Contoured U values reveal that highest concentrations occur in plants growing above, but laterally displaced from the mineralization. Track-Etch data show a similar pattern. Upward migration of ions along steeply inclined fractures is invoked to explain the phenomenon. Other elements are present in varying concentrations, depending upon the plant species and the plant organ. High concentrations of several elements are recorded, most notably Cd and Ag in the conifers.     

Tree-top sampling from a helicopter - a new approach to gold exploration

Foliage from Douglas-fir (Pseudotsuga menziesii) tops was collected from 94 sites around the poorly exposed QR Au deposit in central British Columbia. Locally high concentrations of gold in ashed stems suggest a northwestward (down-ice) dispersion train of Au extending uphill for at least 500 m from the deposit. In addition, a down-slope, hydromorphic dispersion train is evident. All trees sampled are extremely rich in As, but the patterns of As distribution are less clearly related to the mineralization than those of Au enrichment. Summary statistics of analytical data for 35 elements are provided to serve as baseline information for any future studies.The sampling method, which is described in detail, is simple and cost-effective. In one hour the foliage of tree tops from about 50 sites, spaced at intervals of 200 m or more, can be collected by a three-person helicopter crew. The technique is particularly appropriate for rapidly screening rugged or heavily forested terrain, regardless of snow-cover, in order to establish priorities for ground follow-up exploration targets.     

Die Ladungsbilanz für eine verfeinerte Kristallstruktur von Stranskiit,Zn2 Cu(AsO4)2

Zusammenfassung Die Kristallstruktur des Stranskiits wurde mit neuen Meßdaten, die an einer aus Tsumeb stammenden Probe gewonnen worden waren, bis zuR=0,034 für 1239 unabhängige beobachtete Reflexe verfeinert. Von der verfeinerten Struktur wurde die Ladungsbilanz aufgestellt und besonders im Hinblick auf die Ladungsdeformation des Cu²⁺ diskutiert. Eine Mikrosondenanalyse derselben Probe ergab, daß die tatsächliche Zusammensetzung der angegebenen Formel entspricht.

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Charge balance of a refined crystal structure of stranskiite, Zn₂Cu (AsO₄)₂

Summary The crystal structure of stranskiite was refined with new intensity data obtained from a specimen from Tsumeb toR=0.034 for 1234 observed independent reflections. The charge balance was calculated and discussed particularly with respect of the charge deformation of Cu²⁺. An electron probe microanalysis gave the result that the actual composition of the specimen corresponds to the given formula.

     

A fishery in a changing lake environment: The naked carpGymnocypris przewalskii (Kessler) (Cyprinidae: schizothoracinae) in Qinghai Hu,China

Quinghai Hu is a large, high-altitude, saline lake in north-western China, and supports a fishery based on an endemic species of naked carp (snow trout). The fish take seven years to attain maturity and a marketable weight of 300 g, and have a lifespan of 14–21 years under the present fishery regime. They seasonally migrate from the lake to spawn over the gravel beds of inflowing rivers, but these areas have been reduced by weirs and irrigation diversions and recruitment may have declined. The population may have been affected also by a 1.85-m fall in the lake level over the past 30 years, and by associated changes in salinity. The fishery was opened to large-scale exploitation in 1958. Yields declined sharply (max. 28,523 tonnes, 1960) as the larger, older fish were removed, and then more slowly (min. 2523 tonnes, 1983). Since 1987 the fish factory has been limited to an annual quota of 1200 tonnes, taken by a fleet of four pair trawlers. Another 800 tonnes are taken by licensed fishermen, mainly using gill nets, and perhaps 1000 tonnes are taken illegally. The estimated total catch in 1992 was 3000 tonnes. New trawlers introduced in 1989–90 substantially increased the factory's catch per unit effort, and in 1990 the quota was virtually filled in one month in a zone within 20 km of the factory. Although this could suggest that the stocks will be conserved if the quota is retained, at least half of the catch in 1989–92 consisted of immature individuals. Trawling operations recently were suspended following a further decline in the catch after 1992. While the new trawlers are capable of a major increase in effort, neither the changing environment, the fish stocks or the present markets favour intensified pressure. Gillnets may provide better control over the minimum size limit and may cause less damage than trawling. Other options to improve the viability and profitability of the fishery include improvements in handling, processing and marketing. Failure to develop the fishery may encourage attempts to introduce exotic fish, at some risk to survival of the local species.