Comparison of ship's heading determined from an array of GPS antennas with heading from conventional gyrocompass measurements

An Ashtech GPS 3DF, a commercially available system for measuring ship's heading from an array of GPS antennas, was installed on RRS Discovery in August 1992. Data were collected during 8 days of ship trials, including periods in port and while on station or steaming. Headings from the GPS system have been compared with headings from the ship's gyrocompass, and residuals calculated. While in port, residuals had a standard deviation of 0.066°, suggesting satisfactory performance by both instruments. While at sea, time-averaged residuals varied with a range of nearly 3°, most of which is attributed to systematic errors in the ship's gyro. After correcting the gyro using 10-min averages of the GPS minus gyro headings, the residual GPS minus gyro differences had a standard deviation of 0.17°. This represents a likely limit on the use of GPS heading data to improve conventional gyro measurements.     

Incorporating the dynamics of marine systems into the stock assessment and management of sablefish

Progress in ecosystem management requires the characterisation of the dynamics of a species's ecosystem and the influences of climatic oscillations on those dynamics. Within the North Pacific, ecosystem dynamics have been described on decadal-scales (regimes) and have been shown to shift abruptly (regime shifts). The year class success of sablefish (Anoplopoma fimbria) exhibit decadal-scale patterns that relate to decadal-scale patterns in North Pacific climate–ocean conditions. As an example, and a step towards, incorporating the dynamics of marine systems into the stock assessment and management of sablefish, we produce a ‘report card’ that characterises the species's ecosystem on decadal-scales. This report card consists of a matrix of climatological and oceanographic indices for the North Pacific, and regional environmental and biological indices. It indicates that both Pacific-wide and regionally, conditions were generally good for sablefish year class strength during the 1977–1988 regime, but these favourable conditions did not persist into the 1990s. Exploitation scenarios can be developed around the decadal-scale dynamics in sablefish year class success and their life history, in particular longevity. Fisheries managers can begin to develop exploitation strategies that acknowledge these changes in the sablefish ecosystem. The report card presents an aggregation of parameters that, on average, gives an impression of productivity during a specific regime and can be used to augment present stock assessment and management efforts.     

Messungen der Himmelsstrahlung und deren Polarisationsgrad während der Sonnenfinsternis am 15.2.1961 in Viareggio (Italien)

Summary On the occasion of the total solar eclipse in Viareggio (Italy) measurements of intensity of sky radiation and polarization have been carried out at 90 degrees vertical distance from the sun. UV-, green- and red-filters have been used. The results showed a diminution of the intensity during the eclipse of about 3 powers of ten. The sky brightness in the point 90 degrees distant during the total eclipse was similar to the brightness when sun is 7 degrees below the horizon. About one minute before the total eclipse the degree of polarization diminuished to zero. — Furthermore photos of nearly the total sky were made using two cameras with wide angle lenses.     

Source and turnover of organic matter in agricultural soils derived from n-alkane/n-carboxylic acid compositions and C-isotope signatures

Agricultural soils are regarded as one potential sink for atmospheric CO₂ via photosynthetic fixation in plant biomass and subsequent transformation into soil organic matter upon soil diagenesis. The difference in C-isotope signatures of C₃- vs. C₄-plants allows for a natural isotopic labelling of soil organic matter after changes from C₃- to C₄-cropping. In this study, we demonstrate that isotopic shifts are paralleled by molecular signatures of C₃- vs. C₄-crop alkyl lipids. Turnover times vary significantly, based on cropping techniques. For grain-maize cropped soils at steady state average turnover times of 40 years for bulk SOC, 35 years for n-alkanes and 21 years for n-carboxylic acids were determined. Turnover times for silage-maize cropped soil at steady state were on average 250 years for bulk SOC, 60 years for n-alkanes and 49 years for n-carboxylic acids. Turnover times reported here for silage-maize cropped soils may be taken as maximum values only, because they derive from a single trial, which was affected by addition of anthropogenic refractory carbon. Discrimination of input from various plant parts (roots, stems and leaves) based on bulk C-isotopes is not feasible but can easily be achieved using compositions of carboxylic acids, especially the ratio of n-C₂₄ vs. n-C₂₂₊₂₆ and their respective C-isotope values. This enables delineation of the influence of different cropping techniques, e.g., silage- or grain-maize, on carbon storage in soils. Admixture of external sources of organic matter to the soil organic carbon pool of an urban site in Halle, Germany was identified based on alkyl lipid distributions. Nearby lignite mining was identified as a source for non-crop-derived alkyl lipids, primarily based on the elevated n-C₂₆-carboxylic acid content and heavier carbon isotopic signatures.     

Accumulation and mixing of hydrocarbons in oil fields along the Murteree Ridge, Eromanga Basin, South Australia

The Murteree Ridge is a focus for up-dip migration from two major hydrocarbon kitchens within the intracratonic Cooper (Carboniferous–Triassic) and Eromanga (Jurassic–Cretaceous) Basins of South Australia. The accumulation histories of nine oil fields along and adjacent to the ridge have been reconstructed by sequential solvent extraction and analysis of residual oils in sandstone core plugs from their stacked reservoirs. Four Cretaceous reservoir units received multiple oil charges that varied widely in source affinity, from mostly Jurassic (and/or Cretaceous) to overwhelmingly Permian in origin. The distributions of residual oil saturations in live and palaeo-columns are consistent with the existence of two compartments, with the uppermost pools (Cadna-owie, Murta) showing the highest Permian inputs. These accumulations represent the earliest escape of low-maturity Cooper-sourced oil into overlying Eromanga strata. This initial charge was displaced upwards into the shallower traps by subsequent hydrocarbon pulses. Three separate Permian-charge episodes can be recognised. The corresponding DST oils (0.6–0.7% Rc) represent either the compositional average of all charges to their respective reservoirs, or a continuation of the alternating filling pattern observed for successive charges. Oils in the Hutton (Jurassic) reservoir of the outlying Kerrina and Mudlalee Fields to the northeast appear to be mixtures of two distinct Early Permian oil families, variably co-mingled with locally derived Jurassic and possibly Cambrian hydrocarbons.