REMOTE SENSING IN HUMAN RIGHTS AND INTERNATIONAL HUMANITARIAN LAW MONITORING: CONCEPTS AND METHODS†     

ANDREW MARX  SAMUEL GOWARD 《Geographical review》2013,103(1):100-111

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Sea‐level rise,depth‐dependent carbonate sedimentation and the paradox of drowned platforms     

WONSUCK KIM  BRUCE W. FOUKE  ANDREW L. PETTER  TERRENCE M. QUINN  CHARLES KERANS  FRED TAYLOR 《Sedimentology》2012,59(6):1677-1694

A mathematical model of carbonate platform evolution is presented in which depth‐dependent carbonate growth rates determine platform‐top accumulation patterns in response to rising relative sea‐level. This model predicts that carbonate platform evolution is controlled primarily by the water depth and sediment accumulation rate conditions at the onset of relative sea‐level rise. The long‐standing ‘paradox of a drowned platform’ arose from the observation that maximum growth rate potentials of healthy platforms are faster than those of relative sea‐level rise. The model presented here demonstrates that a carbonate platform could be drowned during a constant relative sea‐level rise whose rate remains less than the maximum carbonate production potential. This scenario does not require environmental changes, such as increases in nutrient supply or siliciclastic sedimentation, to have taken place. A rate of relative sea‐level rise that is higher than the carbonate accumulation rate at the initial water depth is the only necessary condition to cause continuous negative feedbacks to the sediment accumulation rates. Under these conditions, the top of the carbonate platform gradually deepens until it is below the active photic zone and drowns despite the strong maximum growth potential of the carbonate production factory. This result effectively resolves the paradox of a drowned carbonate platform. Test modelling runs conducted with 2·5 m and 15 m initial sea water depths at bracketed rates of relative sea‐level rise have determined how fast the system catches up and maintains the ‘keep‐up’ phase. This is the measure of time necessary for the basin to respond fully to external forcing mechanisms. The duration of the ‘catch‐up’ phase of platform response (termed ‘carbonate response time’) scales with the initial sea water depth and the platform‐top aggradation rate. The catch‐up duration can be significantly elongated with an increase in the rate of relative sea‐level rise. The transition from the catch‐up to the keep‐up phases can also be delayed by a time interval associated with ecological re‐establishment after platform flooding. The carbonate model here employs a logistical equation to model the colonization of carbonate‐producing marine organisms and captures the initial time interval for full ecological re‐establishment. This mechanism prevents the full extent of carbonate production to be achieved at the incipient stage of relative sea‐level rise. The increase in delay time due to the carbonate response time and self‐organized processes associated with biological colonization increase the chances for platform drowning due to deepening of water depth (> ca 10 m). Furthermore this implies a greater likelihood for an autogenic origin for high‐frequency cyclic strata than has been estimated previously.  相似文献   

Toward an Understanding of Biogenic-silica Dissolution in Seawater – An Initial Rate Approach Applied between 40 and 90 °C     

JIM?E.?GREENWOODEmail author  VICTOR?W.?TRUESDALE  ANDREW?R.?RENDELL 《Aquatic Geochemistry》2005,11(1):1-20

Summary The kinetics of phytoplankton frustule dissolution has generally been studied as the appearance of silicic acid in a batch reactor. Unfortunately, this approach, though often illuminating, has not so far been successful because of the difficulty of parameterising the full reaction curve. This current study shows how the initial rate approach to chemical kinetics offers a way around this bottleneck, thereby allowing much chemical kinetics information about frustule dissolution to be collected. The technique is shown to be flexible and suited to short reaction times which facilitate detailed quantitative kinetics investigation, indeed, as would be expected in a solution phase, kinetics study. The technique is exemplified by a dissolution study of uncleaned frustules of Cyclotella crypticaat 40 °C and above. The frustules were found to yield the same dissolution rate after 5 weeks dark storage, at 4 °C. Meanwhile, log dissolution rate was found to vary linearly with pH, with gradient 0.38 ± 0.01 (r ²=0.990). Linearity was upheld even at pHs as high as 14. Finally, a robust Arrhenius plot was established between 40 and 90 °C yielding an activation energy for dissolution of 84 ± 3 kJ mol ⁻¹. Follow through with the Eyring equation yielded an activation enthalpy, ΔH ^‡, and an activation entropy, ΔS ^‡, of 81 and 85 J mol ⁻¹ K ⁻¹, respectively. The discussion brings salient aspects of existing knowledge about diatom frustule dissolution kinetics into the wider context of silicate mineral dissolution.  相似文献   

Coastal dune conservation on an Irish commonage: community-based management or tragedy of the commons?     

JOHN MC KENNA  ANNE MARIE O'HAGAN†  JAMES POWER‡  MICHAEL MACLEOD§  ANDREW COOPER 《The Geographical journal》2007,173(2):157-169

In Ireland 'commonage' refers to lands jointly owned by several individuals who have grazing rights. Commonage can provide the low-intensity grazing regime regarded as optimal for habitat conservation, and it is also unlikely to suffer the negative impacts of building development or coastal engineering. Today, however, the traditional control systems of coastal commonage are generally moribund, leading to habitat degradation. The only viable future management model is likely to be one based on local community control. Community management would have the legitimacy to counter the negative perceptions of external authority that generate environmental degradation.  相似文献   

SNOWSHED CONTRIBUTIONS TO THE NOOKSACK RIVER WATERSHED,NORTH CASCADES RANGE,WASHINGTON*     

ANDREW BACH 《Geographical review》2002,92(2):192-212

ABSTRACT. Meltwater contributes to watershed hydrology by increasing summer discharge, delaying the peak spring runoff, and decreasing variability in runoff. High‐elevation snowshed meltwater, including glacier‐derived input, provides an estimated 26.9 percent of summer streamflow (ranging annually from 16 to 40 percent) in the Nooksack River Basin above the town of Deming, Washington, in the North Cascades Range. The Nooksack is a major spawning river for salmon and once was important for commercial, recreational, and tribal fishing, and in the past its flow met the demands of both human and aquatic ecosystems. But the river is already legally overallocated, and demand is rising in response to the rapidly growing human population. Variability in snowshed contributions to the watershed is considerable but has increased from an average of 25.2 percent in the 1940s to an average of 30.8 percent in the 1990s. Overall stream discharge shows no significant increase, suggesting that the glaciers are melting, and/or precipitation levels (or other hydrologic factors) are decreasing at about the same rate. If glaciers continue to recede, they may disappear permanently from the Cascades. If that occurs, their summer contribution to surface‐water supplies will cease, and water‐management policies will need drastic revision.  相似文献   

Catchment infiltration II: Contributing areas     

ANDREW S ROGOWSKI 《Transactions in GIS》1996,1(4):267-284

This study considers two issues of interest to the hydrologic and geographical information systems community. One deals with identifying the spatial distribution of infiltration and runoff contributing areas. The other addresses process modelling within a GIS framework. The study operates on the premise that partitioning of precipitation into runoff or infiltration depends on rainfall intensity and on soil properties. The problem is that neither local rainfall intensity, nor soil properties such as infiltration capacity and macroporosity are known well enough for all points of a catchment and need to be estimated. We infer local intensity from the interpolated distribution of cumulated rain depths over the catchment and record duration at the official met site. Measured values of sorptivity and hydraulic conductivity define infiltration. Negative head infiltration describes macroporosity. To scale-up measured point values to larger areas and to model infiltration and macropore continuity at a catchment scale we use geostatistical kriging and conditional simulation together with standard GIS techniques of overlay manipulation. Results delineate areas contributing to runoff and infiltration and relate them to macroporosity. By intersecting overlays of precipitation with those of infiltration we create alternate GIS masks targeting specific portions of the watershed as either runoff or infiltration contributing zones. Choice of cell size and time interval define the scales of averaging for the application. Kriged surfaces illustrate the distribution of catchment infiltration, while conditional simulation provides a mechanism to define model uncertainty.  相似文献   

Formation of an unusual compact Type A refractory inclusion from Allende     

STEVEN B. SIMON  ANDREW M. DAVIS  LAWRENCE GROSSMAN 《Meteoritics & planetary science》1998,33(1):115-126

Abstract— We report the results of a study of TS2, an unusual compact Type A inclusion from Allende. A distinctive, major feature of this inclusion is that many of its melilite crystals have no dominant core-rim zoning but instead consist of 50–200 μm patches of Mg-rich melilite (Åk_32–62, median Åk₅₁) set in or partially enclosed by, and optically continuous with, relatively Al-rich melilite (Åk_25–53, median Åk₃₈). The Al-rich regions have jagged, dendritic shapes but occur within crystals having straight grain boundaries. Another unusual feature of this inclusion is the size and spatial distribution of spinel. In many places, especially in the interior of the inclusion, the aluminous melilite encloses numerous, fine (0.5–5 μm) inclusions of spinel and minor perovskite and fassaite. The latter phases also occur as isolated grains throughout the inclusion. Coarse-grained spinel, ～50–150 μm across, occurs in clumps and chains enclosed in relatively Mg-rich melilite, whereas none of the fine spinel grains are clumped together. The sample also contains a spinel-free palisade body, 1.7 × 0.85 mm, that consists almost entirely of Åk-rich (45–65 mol%) melilite. Within the palisade body are two grains of perovskite with extremely Nb-rich (～4–8 wt% Nb₂O₅) cores and rims of typical composition. All phases in this inclusion have chondrite-normalized REE patterns that are consistent with crystal/melt partitioning superimposed upon a bulk modified Group II pattern. We suggest that TS2 had an anomalous cooling history and favor the following model for the formation of TS2. Precursors having a bulk modified Group II pattern melted. Rapid growth of large, dendritic, nonstoichiometric melilite crystals occurred. The melilite trapped pockets of melt and incorporated excess spinel components and TiO₂. Bubbles formed in the residual melt. As crystallization slowed, coarse spinel grew. Some spinel grains collected against bubbles, forming spherical shells, and others formed clumps and chains. Relatively Åk-rich melilite crystallized from the residual melt between dendritic melilite crystals and from melt trapped in pockets and between arms of dendrites, and incorporated the clumps and chains of coarse spinel. Bubbles broke and filled with late-stage melt, their shapes preserved by their spinel shells. Slow cooling, or perhaps an episode of reheating, allowed the early melilite to become stoichiometric by exsolving fine grains of spinel, perovskite and fassaite, and allowed the melilite to form smooth grain boundaries. Dendritic crystals are indicative of rapid growth and the melilite crystals in TS2 appear to be dendritic. Coarse, dendritic melilite crystals have been grown from Type B inclusion melts cooled at ～50–100 °C/h. If those results are applicable to Type A inclusions, we can make the first estimate of the cooling rate of a Type A inclusion, and it is outside the range (2–50 °C/h) generally inferred for Type B inclusions. The rapid cooling inferred here may be part of an anomalous thermal history for TS2, or it may be representative of part of a normal thermal history common to Types A and B that involved rapid cooling early (at high temperatures) as inferred for TS2, and slower cooling later (at lower temperatures), as inferred for Type B inclusions. We prefer the former explanation; otherwise, the unusual features of TS2 that are reported here would be common in Type A inclusions (which they are not).  相似文献   

The hydrodynamics of particle clusters and sediment entrapment in coarse alluvial channels     

ANDREW C. BRAYSHAW  LYNNE E. FROSTICK  IAN REID 《Sedimentology》1983,30(1):137-143

ABSTRACT Particles projecting from the bed of an alluvial channel distort the fluid stream to produce a distinctive pressure field. This has considerable significance for both the entrapment and entrainment of other particles and is a primary cause of the widespread occurrence of pebble clusters and boulder shadows. Lift and drag forces are determined on clustered hemispherical particles of varying size. In the wake of an obstructing particle both forces are shown to vary directly with particle separation in a linear fashion. On the stoss side of the cluster, drag is uniform regardless of the separation of the component particles, but lift is shown to increase when particle separation is small, so affecting stability. This mutual interference of neighbouring clustered bed particles is a vital consideration of incipient motion and is shown by field evidence to cause a wide range in transport stage for particles of similar size and shape. On average, 46% of clustered particles are entrained by flood flow compared to 87% of particles in open plane-beds. The influence of clusters is a major determinant of sedimentary sorting.  相似文献   

Thin section and S.E.M. textural criteria for the recognition of cement-dissolution porosity in sandstones   总被引：1，自引：0，他引：1  

ANDREW HURST  PER ARNE BJØRKUM 《Sedimentology》1986,33(4):605-614

Cement-porosity relationships are described from the Lower Triassic Sherwood Sandstone Group and the Middle Jurassic Ravenscar Group in the United Kingdom. Calcite cemented sandstones display a variety of replacement textures, with preferential replacement of grains and of overgrowth faces with high free-surface energy. Dolomite and siderite cemented sandstones display similar textures but replacement is less specific and euhedral overgrowth surfaces are commonly embayed by carbonates. Examination of the more porous sandstones with the scanning electron microscope reveals a range of pitting and embayment textures in authigenic overgrowths and in detrital grains. These range from small ‘v’-shaped notches and pits, through regular and irregular shaped embayments, into large depressions. These textures appear to be morphologically similar to the quartz surfaces seen in thin sections of carbonate cemented sandstones, and are interpreted to have been formed by the dissolution of pore-filling and grain replacive authigenic carbonates. This is confirmed by examination of experimentally exhumed overgrowth surfaces from carbonate cemented sandstones. These textures indicate that part of the intergranular porosity in these sediments is secondary in origin, and has been generated by the dissolution of carbonate cements. The identification of such textures may lead to a more confident interpretation of the nature of intergranular porosity in the subsurface.  相似文献   

A new approach to provenance studies: electron microprobe analysis of detrital garnets from Middle Jurassic sandstones of the northern North Sea   总被引：16，自引：0，他引：16  

ANDREW C. MORTON 《Sedimentology》1985,32(4):553-566

Reading provenance from heavy-mineral suites is hampered by the depletion of diagnostic, but unstable, heavy minerals through intrastratal solution, a common phenomenon in deep sedimentary basins such as the North Sea. This paper demonstrates the potential of electron microprobe analysis in overcoming this problem, by concentrating on the compositional variations shown by detrital garnets, which are relatively resistant to intrastratal solution. Studies of the garnets from the Brent Group (Middle Jurassic) of the Murchison and Tern oilfields in the northern North Sea reveal that three distinct areas supplied detritus. Association 1 which characterizes the Broom Formation in both areas and recurs higher in the sequence in the Tern field, is ascribed to an Orkney-Shetland source. The location of the areas supplying the garnets of Association 2, best represented in Murchison, and Association 3, common to both fields, is less clear. Their ultimate sources clearly include high-grade metamorphics, and therefore probably lie on the Norwegian landmass, the Orkney-Shetland Platform, or, conceivably, the Scottish landmass, but the possibility of recycling makes it difficult to judge their immediate provenances. Nevertheless, the presence of three garnet associations indicates that the most widely accepted model of Brent sedimentation, with sands derived from a domal uplift in the outer Moray Firth and channelled northward along the Viking Graben, is untenable.  相似文献