CIDA regional ocean initiative workshop: Lessons learned     

LO Hinds  GB Bacon 《Marine Policy》1998,22(6):539-543

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Interpretation of homogeneity in δ18O signatures of stream water in a nested sub-catchment system in north-east Scotland     

S. M. Dunn  J. R. Bacon  C. Soulsby  D. Tetzlaff  M. I. Stutter  S. Waldron  I. A. Malcolm 《水文研究》2008,22(24):4767-4782

The isotope hydrology of a set of nested sub-catchments in the north-east of Scotland has been studied to examine the mixing processes and residence times of water in the catchments. The measured δ¹⁸O in stream waters was found to be exceptionally uniform both temporally and spatially. Hydrochemical mixing analyses showed that groundwater contributes between 62 and 90% of the stream flow in all sub-catchments. Model analysis indicated that the δ¹⁸O in stream water is indicative of a highly mixed system in which near surface runoff appears to be mixed with groundwater, within the soil profile, before being released from the catchment. Small fluctuations in the stream water δ¹⁸O response are generated by a small proportion (<10%) of less-well mixed water in infiltration excess runoff during storm events. A comparative application of the model to a nearby catchment, which has a lower proportion of groundwater runoff, demonstrated contrasting behaviour, with significantly less mixing of waters occurring and a more distinct difference in the age of runoff generated by different flow paths. This highlighted that standard methods for characterization of mixing mechanisms are often insufficient and may not discriminate between systems that have retained quite distinct flow paths throughout catchment transit, and those which have been mixed at some stage. Model sensitivity analysis also indicated that the simulated mean residence time of water varies most strongly in response to different parameters compared with the δ¹⁸O response. This has implications for estimating water residence times from isotope data. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Weak gravitational shear and flexion with polar shapelets     

Richard Massey  Barnaby Rowe  Alexandre Refregier  David J. Bacon  Joel Bergé 《Monthly notices of the Royal Astronomical Society》2007,380(1):229-245

We derive expressions, in terms of 'polar shapelets', for the image distortion operations associated with weak gravitational lensing. Shear causes galaxy shapes to become elongated, and is sensitive to the second derivative of the projected gravitational potential along their line of sight; flexion bends galaxy shapes into arcs, and is sensitive to the third derivative. Polar shapelets provide a natural representation, in which both shear and flexion transformations are compact. Through this tool, we understand progress in several weak lensing methods. We then exploit various symmetries of shapelets to construct a range of shear estimators with useful properties. Through an analogous investigation, we also explore several flexion estimators. In particular, some of the estimators can be measured simultaneously and independently for every galaxy, and will provide unique checks for systematics in future weak lensing analyses. Using simulated images from the Shear TEsting Programme, we show that we can recover input shears with no significant bias. A complete software package to parametrize astronomical images in terms of polar shapelets, and to perform a full weak lensing analysis, is available on the Internet.  相似文献   

The SAURON project – IV. The mass-to-light ratio, the virial mass estimator and the Fundamental Plane of elliptical and lenticular galaxies     

Michele Cappellari  R. Bacon  M. Bureau  M. C. Damen  Roger L. Davies  P. T. de Zeeuw  Eric Emsellem  Jesús Falcón-Barroso  Davor Krajnovi&#;  Harald Kuntschner  Richard M. McDermid  Reynier F. Peletier  Marc Sarzi  Remco C. E. van den Bosch  Glenn van de Ven 《Monthly notices of the Royal Astronomical Society》2006,366(4):1126-1150

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Distribution and ecology of the crabs Cyclograpsus lavauxi and C. insularum in Northern New Zealand     

Marjorie R. Bacon 《新西兰海洋与淡水研究杂志》2013,47(3-4):415-426

The differences between the crabs Cyclograpsus lavauxi (Milne Edwards, 1853) and C. insularum (Campbell and Griffin, 1966) are outlined. Cyclograpsus lavauxi has long been known to be very common in New Zealand, but C insularum was considered very rare and had been collected only six times since 1929.

In 1970, 60 spot surveys in the northern part of the North Island of New Zealand revealed 14 new populations of Cyclograpsus insularum.

Both species are found under boulders high on the beach. Cyclograpsus lavauxi occurs at maximum density higher on the shore than the maximum numbers of C. insularum, but the zones overlap widely. Cyclograpsus insularum occurs on substrates of smaller sand and silt content than those on which C. lavauxi is found.  相似文献   

Variations in the architecture of hydraulic‐jump bar complexes on non‐eroding beds     

Robert G. Macdonald  Jan Alexander  John C. Bacon  Mark J. Cooker 《Sedimentology》2013,60(5):1291-1312

Sediment accumulation downstream of hydraulic jumps can occur in many settings but the architectures of such deposits are poorly documented. Here, three flume runs were used to examine the influence of sediment grain size and transport rate on the characteristics of hydraulic‐jump unit bars. In one of these runs six hydraulic‐jump unit bars formed a hydraulic‐jump bar complex. In another, the same sediment was supplied more quickly and only two unit bars formed. In the third run with the same sediment supply rate, but different grain size, only one large unit bar formed. All unit bars developed in a similar way but their size and internal architecture differed; they all resulted from a reduction in sediment transport capacity at the transition from supercritical flow to subcritical flow in the hydraulic jump. After initial onset of sedimentation and unit bar formation, generation of subsequent unit bars may be: (i) related to small changes in sediment flux; and (ii) independent of changes in the hydraulic jump. Continued sedimentation caused changes from oscillating to weak hydraulic jumps and hydraulic‐jump unit bars formed in both circumstances. The flow of water and suspended sediment becomes shallower over the lee of the bar complex. This leads to flow acceleration and a return to supercritical flow conditions. In turn, a chain of such features can form and generate a chute and pool bed morphology. There is an inherent upper size limit to a hydraulic‐jump bar complex due to the changing flow conditions over the growing deposit as the water above it becomes shallower. There is also an amplitude minimum for the development of foresets and subsequent unit bar growth. Hydraulic‐jump unit bars have architectures that should be recognizable in the rock record and because their size is constrained by the flow conditions, their identification should be useful for interpreting palaeoenvironment.  相似文献   

Recent seismicity of southeastern Ghana     

M. Bacon  J.K.A. Banson 《Earth and Planetary Science Letters》1979,44(1):43-46

Recent studies of DSDP samples from layer 2A of oceanic basement have found complex magnetic stratigraphies that seem incompatible with the frequent existence of linear short-wavelength anomalies caused by palaeomagnetic field behavior. Statistical models are developed for the lateral variation of the average magnetization of layer 2A: a Poisson series for reversals of the earth's field and a stairstep random series for discrete magnetic units. It is shown with the power-density spectra of these statistical models that lateral inhomogeneities must average out over distances of less than a few hundred meters. Specifically, individual magnetic units of the type seen at DSDP Site 332 cannot extend uniformly for distances greater than a few hundred meters.  相似文献   

Heavy metals deposited from the atmosphere on upland Scottish soils: Chemical and lead isotope studies of the association of metals with soil components   总被引：2，自引：0，他引：2  

Jeffrey R. Bacon  Irene J. Hewitt 《Geochimica et cosmochimica acta》2005,69(1):19-33

Three soil profiles taken from the Hartwood Research Station in Central Scotland have been analyzed using chemical digestion and extraction techniques to investigate the chemical association of heavy metals deposited from the atmosphere. Total digestion, EDTA extraction and the BCR (Bureau Communitaire de Reference) sequential extraction procedure were used. In addition, lead isotope ratios in the whole soils and in the fractions from the sequential extraction procedure were measured using thermal ionisation mass spectrometry. All the digestion and extraction procedures gave clear indication of enhanced concentrations of heavy metals in surface soils, in particular for lead and zinc. Whereas total digestion gave a good indication of the heavy metal status of the soils, the extraction procedures were necessary to provide information on chemical association of the metals with soil components, information needed to understand the soil processes involved in mobilization of metals. Lead isotope analysis of the whole soils revealed a consistent picture of lower ²⁰⁶Pb/²⁰⁷Pb ratios in surface soils (1.140-1.147) than in soils at 20-30 cm depth (1.182-1.190). The steady progression from the lower to higher ratios down the profile was clear indication that anthropogenic lead had penetrated to some degree into the deeper soils. The combination of sequential extraction and lead isotope analysis proved to be a powerful approach to studying this effect in more detail and showed that the fractions extractable from 20 to 30 cm soils contained lead with much lower ²⁰⁶Pb/²⁰⁷Pb ratios (1.174-1.178) than the residual fraction (1.196-1.200). As the extractable fractions contained ≥85% of the lead in the soil, a substantial portion of lead at 20-30 cm depth was of anthropogenic origin. The ²⁰⁶Pb/²⁰⁷Pb ratios of 1.174-1.178 found in the extractable fractions suggested that the mobile component of the anthropogenic lead was that deposited before the introduction of leaded petrol.  相似文献   

Ion microprobe measurement of strontium isotopes in calcium carbonate with application to salmon otoliths     

Peter K. Weber  Charles R. Bacon  B. Lynn Ingram 《Geochimica et cosmochimica acta》2005,69(5):1225-1239

The ion microprobe has the capability to generate high resolution, high precision isotopic measurements, but analysis of the isotopic composition of strontium, as measured by the ⁸⁷Sr/⁸⁶Sr ratio, has been hindered by isobaric interferences. Here we report the first high precision measurements of ⁸⁷Sr/⁸⁶Sr by ion microprobe in calcium carbonate samples with moderate Sr concentrations. We use the high mass resolving power (7000 to 9000 M.R.P.) of the SHRIMP-RG ion microprobe in combination with its high transmission to reduce the number of interfering species while maintaining sufficiently high count rates for precise isotopic measurements. The isobaric interferences are characterized by peak modeling and repeated analyses of standards. We demonstrate that by sample-standard bracketing, ⁸⁷Sr/⁸⁶Sr ratios can be measured in inorganic and biogenic carbonates with Sr concentrations between 400 and 1500 ppm with ∼2‰ external precision (2σ) for a single analysis, and subpermil external precision with repeated analyses. Explicit correction for isobaric interferences (peak-stripping) is found to be less accurate and precise than sample-standard bracketing. Spatial resolution is ∼25 μm laterally and 2 μm deep for a single analysis, consuming on the order of 2 ng of material. The method is tested on otoliths from salmon to demonstrate its accuracy and utility. In these growth-banded aragonitic structures, one-week temporal resolution can be achieved. The analytical method should be applicable to other calcium carbonate samples with similar Sr concentrations.  相似文献   

Structure and physical characteristics of pumice from the climactic eruption of Mount Mazama (Crater Lake), Oregon     

C. Klug  K. Cashman  C. Bacon 《Bulletin of Volcanology》2002,64(7):486-501

The vesicularity, permeability, and structure of pumice clasts provide insight into conditions of vesiculation and fragmentation during Plinian fall and pyroclastic flow-producing phases of the ~7,700 cal. year B.P. climactic eruption of Mount Mazama (Crater Lake), Oregon. We show that bulk properties (vesicularity and permeability) can be correlated with internal textures and that the clast structure can be related to inferred changes in eruption conditions. The vesicularity of all pumice clasts is 75-88%, with >90% interconnected pore volume. However, pumice clasts from the Plinian fall deposits exhibit a wider vesicularity range and higher volume percentage of interconnected vesicles than do clasts from pyroclastic-flow deposits. Pumice permeabilities also differ between the two clast types, with pumice from the fall deposit having higher minimum permeabilities (~5᎒^-13 m²) and a narrower permeability range (5-50᎒^-13 m²) than clasts from pyroclastic-flow deposits (0.2-330᎒^-13 m²). The observed permeability can be modeled to estimate average vesicle aperture radii of 1-5 µm for the fall deposit clasts and 0.25-1 µm for clasts from the pyroclastic flows. High vesicle number densities (~10⁹ cm^-3) in all clasts suggest that bubble nucleation occurred rapidly and at high supersaturations. Post-nucleation modifications to bubble populations include both bubble growth and coalescence. A single stage of bubble nucleation and growth can account for 35-60% of the vesicle population in clasts from the fall deposits, and 65-80% in pumice from pyroclastic flows. Large vesicles form a separate population which defines a power law distribution with fractal dimension D=3.3 (range 3.0-3.5). The large D value, coupled with textural evidence, suggests that the large vesicles formed primarily by coalescence. When viewed together, the bulk properties (vesicularity, permeability) and textural characteristics of all clasts indicate rapid bubble nucleation followed by bubble growth, coalescence and permeability development. This sequence of events is best explained by nucleation in response to a downward-propagating decompression wave, followed by rapid bubble growth and coalescence prior to magma disruption by fragmentation. The heterogeneity of vesicle sizes and shapes, and the absence of differential expansion across individual clasts, suggest that post-fragmentation expansion played a limited role in the development of pumice structure. The higher vesicle number densities and lower permeabilities of pyroclastic-flow clasts indicate limited coalescence and suggest that fragmentation occurred shortly after decompression. Either increased eruption velocities or increased depth of fragmentation accompanying caldera collapse could explain compression of the pre-fragmentation vesiculation interval.  相似文献