Sedimentary architecture of detached deep‐marine canyons: Examples from the East Coast Basin of New Zealand     

Adam D. McArthur  William D. McCaffrey 《Sedimentology》2019,66(3):1067-1101

Submarine canyons are conduits for the distribution of sediment across continental margins. Although many canyons connect directly with fluvial or marine littoral system feeders, canyons detached from direct hinterland supply are also recognized. The fill of detached canyons remains enigmatic, because their deep‐water setting restricts analysis of their evolution and stratigraphic architecture. Therefore, this study aims to investigate the sedimentary processes that infilled deep‐water canyons and the resulting architecture. Miocene outcrops of an exhumed deep‐water system from the East Coast Basin, New Zealand, are documented and compared with the morphology and seismic scale architecture of a modern detached canyon system on the same convergent margin. The outcropping system preserves the downstream margin of a sub‐basin deposited at palaeo‐water depths >700 m. A 6 km wide by 430 m deep incision is filled by heterogeneous siliciclastic sediments, 50% of which comprise graded thin‐beds with traction structures, interpreted to result from oscillatory flows. These are intercalated with concave‐up lenses, up to 15 m thick, of sigmoidally‐bedded, amalgamated sandstones, which preserve ripple casts on bed bases, interpreted as deposits at the head of a deep‐marine canyon. Palaeo‐flow was eastward, into the sub‐basin margin. On the adjacent margin of the sub‐basin down‐dip, stacked and amalgamated sandstones and conglomerates represent the fill of a submarine channel complex, at least 3 km wide. The channels are inferred to have been fed by the up‐dip canyon, which traversed the intervening structural high; similar relationships are seen in the bathymetry data. Seismic studies on this margin demonstrate that multiple phases of canyon cut and fill may occur, with downstream architectural evolution comparable to that seen at outcrop, demonstrating that detached canyons may act as sediment conduits. Breaching of developing sea‐floor structures by detached canyons can modify tortuous sediment pathways, supplying sediment to otherwise starved areas of the slope.  相似文献   

Comparison of short-term seacliff retreat measurement methods in Del Mar, California   总被引：1，自引：0，他引：1  

Adam P. Young  R.E. Flick  R. Gutierrez  R.T. Guza 《Geomorphology》2009,112(3-4):318-323

Seacliff retreat has been variously characterized as the recession rate of the cliff top, of the cliff base, and as the bulk recession rate based on volumetric changes of the entire cliff face. Here, these measures of retreat are compared using nine semi-annual airborne LiDAR (Light Detection And Ranging) surveys of southern California seacliffs. Changes in the cliff base location (where the steeply sloping cliff face intersects the beach) include cliff retreat owing to basal erosion, but also reflect changes in beach sand level and basal talus deposits. Averaged over the 2.5 km alongshore study span, the cliff base actually prograded seaward about 12 cm during the 4-year study. Cliff top change was dominated by few, relatively large (several meters) localized retreats. Cliff face changes, that include failures and deposits anywhere on the cliff profile, had a relatively small mean magnitude compared to cliff top changes and were more widely distributed alongshore. However, the similar alongshore averaged, cumulative cliff top and net bulk cliff face end-point retreat (14 and 19 cm, respectively) suggest that mean cumulative cliff top retreat can potentially be a viable surrogate for mean net cumulative cliff-wide erosion (and vice versa) over relatively short time periods. Cliff face erosion occurred repeatedly at some locations, confirming the presence of seacliff erosion hot-spots during the study period.  相似文献   

Suspended sediment transport in the German Wadden Sea—seasonal variations and extreme events     

Alexander Bartholomä  Adam Kubicki  Thomas H. Badewien  Burghard W. Flemming 《Ocean Dynamics》2009,59(2):213-225

The German Wadden Sea (southern North Sea) sediments are composed of both cohesive and non-cohesive deposits. The spatial distribution patterns are mainly driven by wind-induced waves and tidal currents. Transport intensity and duration depend on the hydrodynamic conditions, which vary over time. In this paper, the transport of suspended sediment was investigated on seasonal, tidal and hourly time scales in the back-barrier system of Spiekeroog Island. Long- and short-term data of fair weather periods and two storm events were investigated based on stationary and mobile measurements of currents and waves by Acoustic Doppler Current Profiler (ADCP), in situ particle size and suspended sediment concentration (SSC) measurements by laser in situ scattering and transmissometry (LISST) as well as wind records. The ADCP backscatter intensities were calibrated by means of LISST volume concentration data in order to quantify longer term SSCs and fluxes in the back-barrier system. Values up to 120 mg l⁻¹ were recorded, but concentrations more commonly were below 60 mg l⁻¹. The long-term results confirm former observations of a balanced budget during low-energy (fair weather) conditions in the study area. In general, SSCs were higher during spring tides than during neap tides. The data also clearly show the remobilisation of sediment by tidal current entrainment. The records include two severe storm events, “Britta” (1st November 2006) and “Kyrill” (18th January 2007). The data reveal very complex temporal flow and transport patterns. During both storm events, the export of material was mainly controlled by the interaction of wind, waves and tidal phase. The typical ebb-dominance occurring during fair-weather conditions was temporarily neutralised and even reversed to a flood-dominated situation. During “Kyrill”, the wind and high-waves setup in conjunction with the tidal phase was even able to compress the duration of two successive ebb cycles by over 70%. Although SSCs increased during both storms and higher turbulence lifted particle clouds upwards, an export of suspended matter towards the North Sea was only observed under the conditions taking place during “Britta”. Such fluxes, however, are currently still difficult to quantify because the backscatter intensity during high energy events includes a substantial amount of noise produced by the high turbulence, especially near the water surface.  相似文献   

Environmental knowledge and small-scale rural landholding in south-west England     

CAROL MORRIS 《The Geographical journal》2010,176(1):77-89

This paper explores the environmental knowledge of small-scale rural landholders and comments on the implications of this for environmental policy. The paper draws on conceptualisations of knowledge as 'know what', 'know why', 'know how' and 'know who', recognises a distinction between tacit and codified environmental knowledges and highlights the need to consider the politics of knowledge surrounding environmental issues. Both quantitative and qualitative data are reported, and are derived from structured interviews with 30 small-scale landholders who were participants in a nature and landscape conservation initiative – the Landscape Heritage Scheme – within South Devon, England. These data are used to explore the place of environmental concerns within the land management objectives of respondents; the nature and extent of their environmental knowledge; how a range of factors alongside their environmental knowledge shaped the environmental practices of respondents; and the politics of knowledge associated with the Landscape Heritage Scheme. The paper suggests that small-scale landholders should be of interest to environmental policy, prioritising environmental objectives in their land management, being relatively knowledgeable about the environment and highly responsive to environmental advice and financial incentives that support environmental management. A case is made for developing research in this area, given ongoing processes of rural demographic change and the rising importance within this of an increasingly diverse landholding population.  相似文献   

Temporospatial dynamics and public health significance of bacterial flora identified on a major leatherback turtle (Dermochelys coriacea) nesting beach in the Southern Caribbean          下载免费PDF全文

Ayanna Carla N. Phillips  Johanna Coutou  Stacy Rajh  Neville Stewart  Antonio Watson  Adam Jehu  Hamish Asmath  Francis Dziva  Chandrashekhar Unakal  Ridley Holder  Raymond Raoul Carthy 《Marine Ecology》2017,38(2)

Grande Riviere beach, on the island of Trinidad, supports the largest nesting population of leatherback turtles in the Caribbean region. Throughout the nesting season, nests are naturally disturbed by newly nesting females, resulting in egg breakage and loss of some nest viability. This environment is ideal for the growth and proliferation of microorganisms. The range of bacterial flora present in beach sand and egg shells was examined, with emphasis on bacteria that may pose a threat to public and animal health. The extent to which the bacterial load and genera on the beach changed throughout the season was also assessed. Twenty‐five genera were identified, with Pseudomonas spp. found to be the most predominant environmental bacteria. Four genera identified possess zoonotic potential, while five additional genera are known to be of public and animal health significance. Distinct shifts in the density and distribution of bacteria were observed along the beach from early to peak nesting season. Shifts were seen across heavily traversed zones, thus highlighting the potential exposure threats posed to beach visitors and animals alike. Further studies aimed at speciating this population of bacteria, as well as isolating potential fungal pathogens may mitigate this threat. Identification of bacterial agents that are specifically pathogenic to leatherback turtles, turtle eggs, hatchlings and those who may interact with these animals will serve to enhance and guide efforts to better conserve this species and protect the health of all who visit this ecologically significant site.  相似文献   

A comfortable night out? Alcohol, drunkenness and inclusive town centres   总被引：1，自引：0，他引：1  

Adam Eldridge  Marion Roberts 《Area》2008,40(3):365-374

The Licensing Act (2003) was enacted in England and Wales against the backdrop of media concern about 'binge Britain' and violent town centres avoided by 'social drinkers'. This paper responds to these concerns by asking how to create more inclusive urban centres at night. Findings from focus groups found it was not alcohol consumption or a reluctance to partake in urban life that was detracting residents. Using the notion of 'comfort', the paper instead reveals a strong desire for varied late-night experiences ranging from quiet local venues, to active streets and live venues.  相似文献   

QSO lensing magnification associated with galaxy groups     

Antonio C. C. Guimarães  Adam D. Myers  Tom Shanks 《Monthly notices of the Royal Astronomical Society》2005,362(2):657-665

We simulated both the matter and light (galaxy) distributions in a wedge of the Universe and calculated the gravitational lensing magnification caused by the mass along the line-of-sight of galaxies and galaxy groups identified in sky surveys. A large volume redshift cone containing cold dark matter particles mimics the expected cosmological matter distribution in a flat universe with low matter density and a cosmological constant. We generate a mock galaxy catalogue from the matter distribution and identify thousands of galaxy groups in the luminous sky projection. We calculate the expected magnification around galaxies and galaxy groups and then the induced quasi-stellar object (QSO)–lens angular correlation due to magnification bias. This correlation is observable and can be used both to estimate the average mass of the lens population and to make cosmological inferences. We also use analytical calculations and various analyses to compare the observational results with theoretical expectations for the cross-correlation between faint QSOs from the 2dF Survey and nearby galaxies and groups from the Automated Plate Measurement and Sloan Digital Sky Survey Early Data Release. The observed QSO–lens anticorrelations are stronger than the predictions for the cosmological model used. This suggests that there could be unknown systematic errors in the observations and data reduction, or that the model used is not adequate. If the observed signal is assumed to be solely due to gravitational lensing, then the lensing is stronger than expected, due to more massive galactic structures or more efficient lensing than simulated.  相似文献   

Characterizing the near-bottom dispersion of drilling mud on three Canadian offshore banks     

Hannah CG  Drozdowski A 《Marine pollution bulletin》2005,50(11):1433-1443

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Entanglement of Australian sea lions and New Zealand fur seals in lost fishing gear and other marine debris before and after Government and industry attempts to reduce the problem   总被引：1，自引：0，他引：1  

Page B  McKenzie J  McIntosh R  Baylis A  Morrissey A  Calvert N  Haase T  Berris M  Dowie D  Shaughnessy PD  Goldsworthy SD 《Marine pollution bulletin》2004,49(1-2):33-42

In recent years, Australian governments and fishing industry associations have developed guiding principles aimed at reducing the impact of fishing on non-target species and the benthos and increasing community awareness of their efforts. To determine whether they reduced seal entanglement in lost fishing gear and other marine debris, we analysed Australian sea lion and New Zealand fur seal entanglement data collected from Kangaroo Island, South Australia. Contrary to our expectations, we found that entanglement rates did not decrease in recent years. The Australian sea lion entanglement rate (1.3% in 2002) and the New Zealand fur seal entanglement rate (0.9% in 2002) are the third and fourth highest reported for any seal species. Australian sea lions were most frequently entangled in monofilament gillnet that most likely originated from the shark fishery, which operates in the region where sea lions forage--south and east of Kangaroo Island. In contrast, New Zealand fur seals were most commonly entangled in loops of packing tape and trawl net fragments suspected to be from regional rock lobster and trawl fisheries. Based on recent entanglement studies, we estimate that 1478 seals die from entanglement each year in Australia. We discuss remedies such as education programs and government incentives that may reduce entanglements.  相似文献   

Spectral theory and stability in astrophysics     

Adam  John A. 《Astrophysics and Space Science》1986,127(1):163-178

This paper is part I of a limited review of the applications of the spectral theory of linear operators in an astrophysical context. The ideal magnetohydrodynamic equations arise in the study of magnetic flux tubes in the solar corona, and in the plasma physics of nuclear containment devices. The system described by these equations is very rich both mathematically and physically, and there are many open problems associated with these models. The underlying mathematical principles are discussed in a qualitative manner in Paper I, and in a more technical manner in subsequent Paper II.  相似文献