Some towing problems with faired cables

Measurements have been obtained from both wind tunnel and towing tank tests which explain the poor streaming behaviour of certain proprietary cable fairings, which had caused severe towing difficulties at sea.A simple modification applied to the fairings showed marked improvement in behaviour in laboratory tests and in sea trials.The results show the importance of good fairing cross sectional shape in order to develop adequate hydrodynamic restoring moments, and demonstrate the mechanical factors causing friction between cable and fairing.     

Homogeneous regions for rainfall distribution in the city of Rio de Janeiro associated with the risk of natural disasters

Natural Hazards - Understanding the occurrence of natural disasters in regions where the occurrence is high is very important, and it is known that the occurrence of disasters associated with...     

A Robust Procedure for High‐Precision Determination of Rare Earth Element Concentrations in Seawater

This study reports a robust procedure that permits precise measurement of all fourteen naturally occurring rare earth element (REE) concentrations, present at ng kg^?1 to sub ng kg^?1 levels, in ~ 100 ml seawater. This procedure is simple and can be routinely applied to measure seawater REEs with relatively high sample throughput. The procedure involves addition of a ¹⁴²Ce‐¹⁴⁵Nd‐¹⁷¹Yb‐enriched spike mixture, iron co‐precipitation, REE purification with chromatographic separation and the use of a magnetic‐sector‐field ICP‐MS (Element 2) coupled with a desolvating sample introduction system (Aridus 1). Critical steps of the procedure, including co‐precipitation pH and matrix removal, have been optimised through a set of experiments described here. The accuracy of the new procedure was assessed against a gravimetric mixture of REEs, and the precision was demonstrated by repeated measurement of two well‐mixed natural seawaters. Repeated analyses of these seawater reference materials (RMs), using ~ 100 ml seawater for each aliquot, indicate precision of 3% (1s) for the REEs. Measured REE concentrations of two uncertified seawater RMs (CASS‐4 and NASS‐5) are consistent with published values, and REE concentrations of the GEOTRACES intercalibration samples show good agreement with those reported by other participant laboratories. REE concentrations for other intercalibration samples (SAFe and Arctic PS70) are also reported.     

Fractal clustering of induced seismicity in The Geysers geothermal area, California

We analyse earthquakes recorded at The Geysers geothermal field in California, an area where industrial activity induces seismicity. The seismicity is characterized by the seismic b -value and D , the fractal dimension of earthquake hypocentres measured from sliding windows containing 200 events. We study a group of events strongly clustered around an injection well. Over most of the time period examined we find a positive correlation between b and D . However, during the initiation of injection into a new well we find instead a negative correlation. The differences in correlation are statistically significant at the 1 σ level but only marginally so at the 2 σ level. These results provide evidence for a transient change in the seismic mechanisms operating, and may be explained by a change from conditions of slow stress loading to rapid loading as a result of the build-up of the rate of water injection into the reservoir.     

Statistical power of detecting trends in total suspended sediment loads to the Great Barrier Reef

The export of pollutant loads from coastal catchments is of primary interest to natural resource management. For example, Reef Plan, a joint initiative by the Australian Government and the Queensland Government, has indicated that a 20% reduction in sediment is required by 2020. There is an obvious need to consider our ability to detect any trend if we are to set realistic targets or to reliably identify changes to catchment loads. We investigate the number of years of monitoring aquatic pollutant loads necessary to detect trends. Instead of modelling the trend in the annual loads directly, given their strong relationship to flow, we consider trends through the reduction in concentration for a given flow. Our simulations show very low power (<40%) of detecting changes of 20% over time periods of several decades, indicating that the chances of detecting trends of reasonable magnitudes over these time frames are very small.     

Short‐term forecasting with a multi‐level spectral primitive equation model part II ‐ Hemispheric prognoses and verification

The spectral global baroclinic primitive equation model described in Part I of this paper has been extensively tested. The model has been run daily from operational analyses for over a year. From this large sample of forecasts, verification statistics have been collected and compared with similar statistics collected from three competitive grid‐point models. The spectral model is also compared with the grid‐point models in a synoptic case study.

A second case study demonstrates the effect of horizontal resolution and physical effects on spectral model forecasts. The results of these experiments demonstrate that the spectral model is highly competitive with other models, in terms of both accuracy and computational efficiency. On 18 February 1976 the spectral model became the operational Canadian large‐scale forecast model.     

Self-organised criticality and fluid-rock interactions in the brittle field

The concept of self-organised criticality (SOC) has recently been suggested as a paradigm for the long-term behaviour of earthquakes, even though many of the currently-proposed models require some tuning of the state variables or local conservation rules to produce the universally-observed Gutenberg-Richter frequency-magnitude distribution witha b value near 1. For example, a systematic negative correlation is predicted between modelb values and the degree of conservation of local force after the slip of a single element in an elastic spring/block/frictional slider model. A similar relation is described here for a cellular automaton model with constitutive laws based on fracture mechanics. Such systems, although critical phenomena in the sense of producing order on all scales, are clearly not universal, and may not in general even be true examples of SOC. Nevertheless they adequately reproduce both the observed power-law (fractal or multifractal) scaling and its reported short-term fluctuation.We also present experimental and field evidence for similar systematic variations inb value with the degree of force conservation (expressed in terms of a normalised crack extension force) during subcritical crack growth involving the physical and chemical influence of pore fluids during a single cycle of failure both in tension and compression. We find that the level of conservation is strongly influenced by fluid-rock interaction under stress, allowing energy partition into processes such as: physico-chemical stress corrosion reactions; the dissolution and precipitation of mineral species on crack surfaces; and the purely mechnical phenomenon of dilatant hardening. All of these are known to occur in the Earth on a local scale, but few have been explicitly included in automaton models of seismicity. The implication is that over long time periods pore fluids may exert a strong physical and chemical influence on the universal state of SOC which the system evolves in a complex interplay of local feedback mechanisms keeping the system near criticality, perhaps most strikingly due to the valve action of faults. In the short term, crustal fluids might nevertheless be responsible for systematic local fluctuations about this average state.     

Nd isotopes demonstrate the role of contamination in the formation of coexisting quartz and nepheline syenites at the Abu Khruq Complex,Egypt

The petrogenesis of Abu Khruq, an 89 Ma alkaline ring complex of eastern Egypt which is composed of alkali gabbros and both silica over- and undersaturated syenites, has been investigated. Major and trace element relationships and Nd and Sr isotope data are consistent with formation of the gabbros from an alkaline mafic magma that experienced extensive fractionation, and all syenites from a felsic derivative of this melt. The parental magma had an ⁸⁷Sr/⁸⁶Sr of 0.7030 and an ¹⁴³Nd/¹⁴⁴Nd of 0.512750 (_Nd = +4.4) indicating derivation from a depeleted mantle source. The initial ¹⁴³Nd/¹⁴⁴Nd ratios are: 0.512721 to 0.512748 for the gabbros, 0.512739 to 0.512750 for the alkali syenites and trachytes, 0.512717 to 0.512755 for the nepheline syenites, and, 0.512706 to 0.512732 for the quartz syenites. In contrast, analyzed Precambrian granites from eastern Egypt have generally lower ¹⁴³Nd/¹⁴⁴Nd ratios (ranging from 0.51247 to 0.51261 or _Nd = -0.8 to 1.7, for 89Ma); their Nd model ages range from 775 to 935 Ma and suggest there was no significant input of pre-Pan-African crust in their formation. Among Abu Khruq rocks, ¹⁴³Nd/¹⁴⁴Nd ratios indicate that the quartz syenites formed by open-system, crustal contamination processes whereas the nepheline syenites experienced little or no contamination. Modeling shows that contamination occurred at various stages, affecting both mafic and more evolved compositions with input of about 20% crustal Nd for the most contaminated samples. The degree of contamination is related to the silica saturation of the quartz syenites. Simplified modeling of magma evolution within Petrogeny's Residua System demonstrates the ability of AFC processes to cause a critically undersaturated magma to evolve across the feldspar join and produce oversaturated rocks. The oversaturated syenites at Abu Khruq were produced in this manner whereas the nepheline syenites formed by fractionation without similarly large degrees of contamination. The results have broad implications for the formation of subvolcanic complexes in continental settings beyond the important production of silica oversaturated compositions from crustal interaction. They underscore the importance of crustal interactions in the formation of the various lithologies. Such interactions occur at various stages in the evolution of the magmas and, as such, are not strictly coupled with fractional crystallization. While previous study of Abu Khruq has demonstrated extensive hydrothermal alteration of O and Sr isotopes, the present work shows that the Nd isotope ratios were not significantly affected and thus reflect magmatic signatures. This feature combined with relatively small corrections for initial ratios emphasizes the utility of Nd isotopes for petrogenetic studies.     

Primary Ca-rich carbonatite magma and carbonate-silicate-sulphide liquid immiscibility in the upper mantle

A primary carbonate phase with Ca/(Ca+Mg) in the range 0.85–0.95 has been identified in a metasomatized, depleted harzburgite nodule from Montana Clara Island, Canary Islands; textural relations show that this carbonate represents a quenched liquid. Although magnesian carbonate melts have been described from upper mantle peridotites, this is the first reported occurrence of a primary magma within peridotite nodules which has the composition of calciocarbonatite, by far the most common carbonatite type occurring in crustal complexes. The carbonate in the Montana Clara harzburgite host is restricted to wehrlitic alteration zones and is intimately associated with a second generation of minerals, mainly olivine, clinopyroxene and spinel, with glass of syenitic composition, and with Fe−Cu-rich sulphides. The metasomatic assemblage was formed by reaction of a sodiumbearing dolomitic melt, derived from a somewhat deeper level in the upper mantle, with the harzburgite mineral assemblage at a pressure of 15 kbars, or lower. As a result of the reaction the residual carbonatite melt became more enriched in calcium. The calciocarbonatite and sulphide phases almost invariably form globules in the silicate glass, indicating the existence of three immiscible liquids under upper mantle conditions. Several alkaline complexes contain carbonatites occurring with syenitic rock types and its seems feasible that the formation of such close associations might have been influenced by processes of liquid immiscibility which took place under upper mantle conditions. Editorial responsibility: I. Parsons