Consideration of fine-scale coastal oceanography and 3-D acoustics effects for the ESME sound exposure model

Results and recommendations for evaluating the effects of fine-scale oceanographic scattering and three-dimensional (3-D) acoustic propagation variability on the Effects of Sound on the Marine Environment (ESME) acoustic exposure model are presented. Pertinent acoustic scattering theory is briefly reviewed and ocean sound-speed fluctuation models are discussed. Particular attention is given to the nonlinear and linear components of the ocean internal wave field as a source of sound-speed inhomogeneities. Sound scattering through the mainly isotropic linear internal wave field is presented and new results relating to acoustic scattering by the nonlinear internal wave field in both along and across internal wave wavefront orientations are examined. In many cases, there are noteworthy fine-scale induced intensity biases and fluctuations of order 5-20 dB.     

On the measurement precision of solar p-mode eigenfrequencies

We make use of 3456 d of observations of the low-ℓ p-mode oscillations of the Sun in order to study the evolution over time of the measurement precision of the radial eigenfrequencies. These data were collected by the ground-based Birmingham Solar-Oscillations Network (BiSON) between 1991 January and 2000 June. When the power spectrum of the complete time series is fitted, the analysis yields frequency uncertainties that are close to those expected from the returned coherence times of the modes. The slightly elevated levels compared with the prediction appear to be consistent with a degradation of the signal-to-noise ratio in the spectrum that is the result of the influence of the window function of the observations (duty cycle 71 per cent). The fractional frequency precision reaches levels of a several parts in 10⁶ for many of the modes. The corresponding errors reported from observations made by the GOLF instrument on board the ESA/NASA SOHO satellite, when extrapolated to the length of the BiSON data set, are shown to be (on average) about ∼25 per cent smaller than their BiSON counterparts owing to the uninterrupted nature of the data from which they were derived.
An analysis of the BiSON data in contiguous segments of different lengths, T , demonstrates that the frequency uncertainties scale as T ^−1/2. This is to be expected in the regime where the coherence (life) times of the modes, τ _{n ℓ}, are smaller than the observing time T (the 'oversampled' regime). We show that mode detections are only now beginning to encroach on the 'undersampled' regime (where   T < τ _{n ℓ})  .     

The organic geochemistry of black sedimentary barite: significance and implications of trapped fatty acids

Fatty acids isolated in sedimentary black barite (BaSO₄) from Arkansas and Nevada were identified by gas chromatography-mass spectroscopy. The dominant or major fatty acids found in these beds of barite are C_16:0, C_18:0, and C_18:1. The occurrence and distribution of these acids in this type of rock may serve as “molecular fingerprints” of microbial biogeochemical processes. The organic matter and associated microorganisms are shown to be trapped within the finely crystalline barite, thus forming a closed system for microbial diagenesis.Important differences that occur in the distribution of the lesser or minor fatty acids probably result from: (1) the nature of the progenitor organic detritus in the environment of barite deposition: and (2) the subsequent degree of microbiological alteration of the parent organic debris swept into and trapped in the depositional environment.Three general models of sedimentary environments are proposed in which anoxic conditions may prevail and where barium sulfate (BaSO₄) may precipitate: (1) in a silled basin with semi-restricted circulation; (2) on an outer continental shelf where the slope is encroached upon by water of the oxygen minimum layer; (3) on a low-energy, inner shelf or semi-restricted embayment impinged by a wedge of anoxic water.The major geochemical and geological parameters which are believed to be the significant factors controlling the formation and high grade of these organic-rich, black bedded barites are: (1) a unique source of barium-rich fluid that only contains trace amounts of other elements; (2) the presence of an anoxic bottom environment within the depositional basin; (3) a reflux source of sulfate ion; (4) an adequate source of organic matter.The results of this study may serve as guidelines for future exploration in similar, untested sedimentary basins, especially those with rocks of middle Paleozoic age.     

Chemical weathering and related controls on surface water chemistry in the Absaroka Mountains,Wyoming

Chemical relationships among surface waters, soils and rocks were investigated in the drainage basin of the North Fork of the Shoshone River in northwestern Wyoming. The area is underlain entirely by andesitic volcanic rocks. Smectite is the only clay mineral forming in soils over much of the area, although minor kaolinite occurs in a few areas of higher-than-average rainfall.Mass-balance calculations relating stream water chemistry to rock alteration indicate that controls on the chemistry of surface waters take place not in the soil zone but in the altered rock zone. The dominant weathering process which controls the water chemistry is slight alteration of large volumes of rock, rather than development of chemical equilibria involving secondary phases in the soil zone. The altered rock is enriched in feldspars and depleted in ferromagnesian minerals compared to fresh rock. The high rate of physical erosion of the area is enough to remove the residue, reexpose the bedrock, and continue the weathering process.     

Kleintektonische Untersuchungen in der Umgebung der Station „General Bernardo O'Higgins“ Nordwestspitze der antarktischen Halbinsel

Zusammenfassung In der unmittelbaren Umgebung der chilenischen Antarktisstation General Bernardo O'Higgins sind die klastischen Sedimente kretazischen Alters innerhalb der alpidischen Orogenese nach drei verschiedenen Verformungsplänen gefaltet worden. Die B₁Achsen sind die ältesten und entsprechen mit ihrem ENE-Streichen dem Großbau der Nordspitze Grahamlands. B₂ streicht etwa 168°, B₃ rund 30^o.

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In the immediate surroundings of the Chilean Station General Bernardo O'Higgins, the clastic sediments of Cretaceous age have been folded according to three different systems of deformation, during the alpine (Cretaceous-Tertiary) orogeny. The B₁ axes are the oldest ones, and their strike ENE corresponds to the general structures of northern Grahamland. B₂ strikes N 12° W approximately and B₃ roughly N 30° E.

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Resumen En los alrededores inmediatos de la Base antártica chilena General Bernardo O'Higgins los sedimentos clásticos del Cretácico han sido plegados según tres diferentes sistemas de deformación durante la orogénesis alpídica. Los ejes B₁ son los más antiguos y su rumbo ENE corresponde a la estructura general de la parte Norte de la Tierra de Graham. B₂ tiene rumbo N 12° W aproximadamente, B₃ alrededor de N 30° E.

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Résumé Aux alentours de la Station chilienne Général Bernardo O'Higgins, les sédiments clastiques du Crétacé ont été plissés selon trois différents systèmes de déformation pendant l'orogénèse alpine (Cretacique-Tertiaire). Les axes B₁ sont les plus anciens, et leur direction ENE correspond à la structure générale de la partie Nord de la Terre de Graham. B₂ a une direction approximative de N 12° W, et B₃ de N 30° E environ.

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General Bernardo O'Higgins , .

     

Liberation-limited grade/recovery curves from X-ray micro CT analysis of feed material for the evaluation of separation efficiency

Procedures for 3D mineral liberation analysis by X-ray micro CT (XMT) are presented and discussed including the construction of liberation-limited grade/recovery curves for specific feed materials. In this way, actual separation efficiencies can be compared to what might be expected for a perfect separation limited only by the extent of liberation. It is shown that 3D mineral liberation analysis based on XMT is preferred to 2D section analysis which overestimates the extent of liberation. By way of example, procedures and experimental results are presented and discussed for feed material in the case of phosphate rock flotation.