Dynamics of sedimentation in a tide-dominated backbarrier salt marsh, Norfolk, UK   总被引：5，自引：0，他引：5  

Jonathan R. French  Tom Spencer 《Marine Geology》1993,110(3-4):315-331

Progressive burial of artificial markers over a 5-year period is used to determine the rate and pattern of vertical accretion within a large backbarrier salt marsh on the UK east coast. Over this period, annual accretion varies spatially from 1 to 8 mm yr⁻¹. The arithmetic mean rate for the whole marsh is 3.9 mm yr⁻¹. Spatial variability in accretion is a joint function of (1) elevation-dependent inundation frequency and (2) progressive sediment removal from water masses advected across channel margins. Accretion is, therefore, inadequately represented by simple averaging of point measurements. Numerical integration of the ‘accretion surface’ results in a spatial average rate of around 3 mm yr⁻¹, well below the arithmetic mean rate.

Short-term sediment trap deployments show that local and long-range meteorological effects, and remobilisation of sediment deposited within tidal creeks, often mask the expected link between tidal height and sedimentation rate. Retention of sediment on plant surfaces is minimal, with direct settling accounting for approximately 95% of total deposition.

Time-extrapolation of weekly sediment trap data, and comparison with the 5-year marker horizon burial, shows that processes associated with ordinary tides can account for long-term accretion over most of the marsh. However, the highest surfaces receive appreciable sediment input only during aperiodic storm events.  相似文献   

High-resolution Surveys for Geohazards and Shallow Gas: NW Adriatic (Italy) and Iskenderun Bay (Turkey)     

Daniel L. Orange  Ana García-García  Dan McConnell  Tom Lorenson  Gary Fortier  Fabio Trincardi  Emrah Can 《Marine Geophysical Researches》2005,26(2-4):247-266

The need for quantifying and understanding the distribution of shallow gas is both of academic interest and of relevance to offshore facilities. The combination of seafloor mapping, subbottom profiling, and multi-channel seismic data can provide information on regions of possible shallow gas, where the gas impacts the acoustic properties of the host material and the seafloor. In this paper, we present two case studies – one academic and one industry – that evaluate the distribution of shallow gas in two field areas in the Mediterranean. In the first case study, geophysical data from Iskenderun Bay, southeastern Turkey, indicate the presence and distribution of shallow gas. Pockmarks on the seafloor are associated with acoustic wipeout in the shallow subbottom data. Although deeper seismic data do not show bright spots or other indicators of possible gas, instantaneous frequency analysis clearly shows laterally restricted anomalies indicating gas-rich zones. The interpretation of possible shallow gas resulted in moving a proposed drilling location to a nearby area characterized by fewer (but still present) shallow gas signatures. In the second case study, cores acquired in the Po Delta, Adriatic Sea, provide quantitative ground-truthing of shallow gas – as suggested by geophysical data – and provide minimum estimates of the percentage of gas in the subsurface. Cores targeted on anomalous subbottom data yielded up to 41,000 ppm methane; cores with anomalous gas content are associated with thick recent flood deposits which may effectively isolate reactive terrigenous organic matter from biologic and physical re-working.  相似文献   

Institutional arrangements for metropolitan government and strategic planning in Auckland     

Ali Memon  Tom Graham Davies  Tom Fookes 《New Zealand geographer》2007,63(1):43-54

Abstract:  The task of designing appropriate institutional arrangements for metropolitan government and planning has recently proved highly contestable politically. We interrogate how the role of the Auckland Regional Council (ARC) was zealously contested and hollowed-out during the 1990s. More recently, the impacts of the neo-liberal reforms in Auckland have been mediated by a further round of local government reforms inspired by a Third Way ideology and by the imperative to respond to the planning crisis resulting from infrastructure underinvestment. New regionally based governance arrangements and planning processes have been created. We argue that this new commitment to regionalism can realistically expect to be tested by deep-seated political cleavages within Auckland and by Auckland's relationship with central government.  相似文献   

GPS/GNSS Current Bibliography     

Tomás Soler 《GPS Solutions》2003,7(2):145-147

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Reflections on Delhi     

Tom Jacob 《Climate Policy》2003,3(1):103

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Discovery of a double impact crater in Libya: the astrobleme of Arkenu     

Philippe Paillou  Ake Rosenqvist  Jean-Marie Malezieux  Bruno Reynard  Tom Farr  Essam Heggy 《Comptes Rendus Geoscience》2003,335(15):1059-1069

Using orbital imaging radar, we detected a double circular structure, located in the southeastern part of the Libyan Desert, which is partially hidden under sandy sediments. Fieldwork confirmed it to be an unknown double impact crater, each crater having a diameter of about 10 km, younger than 140 Ma. Sampling on the site enabled the observation of quantities of shatter cone structures and impact breccias containing planar fractures. To cite this article: P. Paillou et al., C. R. Geoscience 335 (2003).  相似文献   

P³M-SPH simulations of the Lyα forest     

Tom Theuns  Anthony Leonard  George Efstathiou  F. R. Pearce  & P. A. Thomas 《Monthly notices of the Royal Astronomical Society》1998,301(2):478-502

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Are AGN broad emission lines formed by discrete clouds? Analysis of Keck high-resolution spectroscopy of NGC 4151     

Nahum Arav  Tom A. Barlow  Ari Laor  Wallace L. W. Sargent  & Roger D. Blandford 《Monthly notices of the Royal Astronomical Society》1998,297(4):990-998

We search for a direct signature of discrete 'clouds' in the broad-line region (BLR) of the Seyfert galaxy NGC 4151. For this purpose we apply cross-correlation (CC) analysis to a high-resolution Keck spectrum of the galaxy. No such signature is found in the data. In order for cloud models to be compatible with this result, there must be at least ∼3×10⁷ emitting clouds in the BLR, where the limit is based on simulation of a homogeneous cloud population. More realistic distributions increase the lower limit to above 10⁸. These numbers are an order-of-magnitude improvement on our previous limit from Mrk 335, where the improvement comes from higher signal-to-noise ratio (S/N), broader lines and refined simulations. Combined with the predicted upper limit for the number of emitting clouds in NGC 4151 (10⁶–10⁷), the derived lower limit puts a strong constraint on the cloud scenario in the BLR of this object. Similar constraints can be placed on models where the emission originates in streams and sheets. Thus, this investigation suggests that the broad emission lines (BELs) in NGC 4151, and by extension in all AGNs, are not made of an ensemble of discrete independent emitters.  相似文献   

Self-Organized Criticality, Multi-Fractal Spectra, and Intermittent Merging of Coherent Structures in the Magnetotail     

Tom Chang 《Astrophysics and Space Science》1998,264(1-4):303-316

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Lichenometric dating in southeast Iceland: the size–frequency approach     

Tom Bradwell 《Geografiska Annaler: Series A, Physical Geography》2004,86(1):31-41

Abstract The age of recent deposits can be determined using an intrinsic characteristic of the lichen ‘population’ growing on their surface. This paper presents a calibrated dating curve based on the gradient of the size‐frequency distribution of yellow‐green Rhizocarpon lichens. The dating potential of this new curve is tested on surfaces of known age in southeast Iceland. This particular size—frequency technique is also compared with the more traditional largest‐lichen approach. The results are very encouraging and suggest that the gradient can be used as an age indicator, at least on deposits formed within the last c. 150 years – and probably within the last c. 400 years – in the maritime subpolar climate of southeast Iceland. Using both lichenometric techniques, revised dates for moraines on two glacier forelands are presented which shed new light on the exact timing of the Little Ice Age glacier maximum in Iceland.  相似文献