Using earthquakes to assess lichen growth rates     

William B. Bull 《Geografiska Annaler: Series A, Physical Geography》2014,96(2):117-133

Botanists make yearly measurements of lichen sizes that describe highly variable radial expansion of young, and old, Rhizocarpon subgenus Rhizocarpon that is a function of thallus size and age. Such non‐uniform growth would negate use of lichens to date geomorphic events, such as landslides and moraines, of the past 1000 years. Fortunately, many crustose lichens tend toward circular shapes, which can be achieved only when overall uniform radial growth prevails. Largest lichen measurements on rockfall blocks that accumulate incrementally as hillslope talus in earthquake‐prone California plot as distinct peaks in frequency distributions. Rockfall surface‐exposure times are known to the day for historical earthquakes and to the year where mass movements damage trees. Lichenometry consistently dates regionally synchronous rockfall events with an accuracy and precision of ±5 years. Only historical records and tree‐ring dating of earthquakes are better. The four crustose lichens used here have constant long‐term growth rates, ranging from 9.5 to 23.1 mm per century. Growth rates do not vary with altitude or climate in a 900 km long mountainous study region in California, USA. Linear growth regressions, when projected to the present, constrain estimates of colonization time and possible styles of initial lichen growth.  相似文献   

A simple fiber-optic microprobe for high resolution light measurements: application in marine sediment     

Jorgensen BB  Des Marais DJ 《Limnology and oceanography》1986,31(6):1376-1383

A fiber-optic microphobe is described which is inexpensive and simple to build and use. It consists of an 80-micrometers optical fiber which at the end is tapered down to a rounded sensing tip of 20-30-micrometers diameter. The detector is a hybrid photodiode/amplifier. The probe has a sensitivity of 0.01 microEinst m-2 s-1 and a spectral range of 300-1,100 nm. Spectral light gradients were measured in fine-grained San Francisco Bay sediment that had an undisturbed diatom coating on the surface. The photic zone of the mud was only 0.4 mm deep. Measured in situ spectra showed extinction maxima at 430-520, 620-630, 670, and 825-850 nm due to absorption by chlorophyll a, carotenoids, phycocyanin, and bacterio-chlorophyll a. Maximum light penetration in the visible range was found in both the violet and the red < or = 400 and > or = 700 nm.  相似文献   

A subsurface evacuation model for submarine slope failure   总被引：1，自引：0，他引：1  

Suzanne Bull  Joe Cartwright  Mads Huuse† 《Basin Research》2009,21(4):433-443

Analysis of three-dimensional (3D) seismic reflection data from the Norwegian continental margin provides an insight into an unusual, buried submarine slope failure, which occurred adjacent to the later Holocene-age Storegga Slide. The identified failure, informally named the 'South Vøring Slide' (SVS), occurs in fine-grained hemipelagic and contourite sediments on a slope of 0.5°, and is characterised by a deformed seismic facies unit consisting of closely spaced pyramidal blocks and ridges bound by small normal faults striking perpendicular to the slope. The SVS contrasts with other previously described submarine slope failures in that it cannot be explained by a retrogressive model. The defining characteristic is the high relative volume loss. The area affected by sliding has thinned by some 40%, seen in combination with very modest extension in the translation direction, with line length balancing yielding an extension value of only 4.5%. The volume loss is explained by the mobilisation of an approximately 40 m thick interval at the lower part of the unit and its removal from beneath a thin overburden, which subsequently underwent extensional fragmentation. Evidence for the mobilisation of a thick fine-grained interval in the development of a submarine slope failure from a continental margin setting may have implications for the origins of other large-scale slope failures on the Norwegian margin and other glacially influenced margins worldwide.  相似文献   

Use of exposure time and life expectancy in models for toxicity to aquatic organisms     

Connell D  Yu J 《Marine pollution bulletin》2008,57(6-12):245-249

The exposure time is a variable which is usually not incorporated into models for toxicity. However, with persistent organic pollutants (POPs) exhibiting a nonspecific mode of action and lipophilic properties this variable can be modeled by the usage of the internal concentrations as a measure of the toxicity with fish. The bioconcentration process with fish is a relatively well understood and predictable process which allows the calculation of the internal lethal concentration. When the exposure time is relatively short the critical internal lethal concentrations are relatively constant for the group of POPs whereaas the LC50 measured in the ambient water is quite variable. When the exposure time is relatively long, results on the measurement of the critical internal concentration with fish over different exposure times has demonstrated that the internal lethal concentration falls with increasing exposure times in a consistent and predictable manner. This reduction in life expectancy can be described in a model which can be used to estimate the critical internal concentration for any exposure time. It also provides information useful in assessing the risk to fish and potentially other species due to the occurrence of residues of POPs in natural aquatic systems. It is suggested that these relationships can be extended to other groups of organisms and chemicals.  相似文献   

Magnitude and variation in the contribution of bank erosion to the suspended sediment load of the River Severn,UK     

Louise J. Bull 《地球表面变化过程与地形》1997,22(12):1109-1123

The wide range of studies describing the role of bank erosion in fluvial sediment supply have mostly lumped amounts of bank erosion into coarse temporal units, such as years. This paper investigates sediment yields from individual bank erosion events within the upper River Severn, UK (basin area 380 km²). Manual erosion pins and photo-electronic erosion pins were used to estimate bank erosion, and turbidity meters were used to determine suspended sediment transport. At the annual time-scale, the silt-clay fraction of bank-derived sediment accounted for an equivalent of 17 per cent of the suspended load, increasing to an average of 38 per cent at the monthly timescale, and then to an average of 64 per cent at the event timescale. This research highlighted that for an upland catchment, bank erosion was an important supply of suspended sediment, and that for some flood events bank erosion can supply more sediment than is transported. © 1997 John Wiley & Sons, Ltd.  相似文献   

Active faults in the Sea of Marmara, western Turkey, imaged by seismic reflection profiles   总被引：2，自引：0，他引：2  

Parke  Minshull  erson  White  McKenzie  Ku&#;çu  Bull  Görür  & &#;engör 《地学学报》1999,11(5):223-227

Turkey is moving westward relative to Eurasia, thereby accommodating the collision between Arabia and Eurasia. This motion is mostly taken up by strike-slip deformation along the North and East Anatolian Faults. The Sea of Marmara lies over the direct westward continuation of the North Anatolian Fault zone. Just east of the Sea of Marmara, the North Anatolian Fault splits into three strands, two of which continue into the sea. While the locations of the faults are well constrained on land, it has not yet been determined how the deformation is transferred across the Sea of Marmara, onto the faults on the west coast of Turkey. We present results from a seismic reflection survey undertaken to map the faults as they continue through the three deep Marmara Sea basins of Çlnarclk, Central Marmara and Tekirdag, in order to determine how the deformation is distributed across the Sea of Marmara, and how it is taken up on the western side of the sea. The data show active dipping faults with associated tilting of sedimentary layers, connecting the North Anatolian Fault to strike-slip faults that cut the Biga and Gallipoli Peninsulas.  相似文献   

An analytical solution to the design of precast concrete pavements     

John W. Bull 《国际地质力学数值与分析法杂志》1986,10(2):115-123

Precast concrete pavement units are used in areas with low subgrade CBR values and high static and dynamic loadings. Unlike flexible pavements and rigid pavements, there are no design charts from which pavement engineers can design precast concrete pavements. The author has investigated analytically the relative importance of the factors affecting the ultimate stress and subgrade bearing pressures in precast concrete pavements. Presenting the results in graphical form, the design charts are used toillustrate the new design method.  相似文献   

The diffusive boundary layer of sediments: oxygen microgradients over a microbial mat     

Jorgensen BB  Des Marais DJ 《Limnology and oceanography》1990,35(6):1343-1355

Oxygen microelectrodes were used to analyze the distribution of the diffusive boundary layer (DBL) at the sediment-water interface in relation to surface topography and flow velocity. The sediment, collected from saline ponds, was covered by a microbial mat that had high oxygen consumption rate and well-defined surface structure. Diffusion through the DBL constituted an important rate limitation to the oxygen uptake of the sediment. The mean effective DBL thickness decreased from 0.59 to 0.16 mm as the flow velocity of the overlying water was increased from 0.3 to 7.7 cm s-1 (measured 1 cm above the mat). The oxygen uptake rate concurrently increased from 3.9 to 9.4 nmol cm-2 min-1. The effects of surface roughness and topography on the thickness and distribution of the DBL were studied by three-dimensional mapping of the sediment-water interface and the upper DBL boundary at 0.1-mm spatial resolution. The DBL boundary followed mat structures that had characteristic dimensions > 1/2 DBL thickness but the DBL had a dampened relief relative to the mat. The effective surface area of the sediment-water interface and of the upper DBL boundary were 31 and 14% larger, respectively, than a flat plane. Surface topography thereby increased the oxygen flux across the sediment-water interface by 49% relative to a one-dimensional diffusion flux calculated from the vertical oxygen microgradients.  相似文献   

The framing of climate change and development: A comparative analysis of the Human Development Report 2007/8 and the World Development Report 2010     

Des Gasper  Ana Victoria Portocarrero  Asuncion Lera St.Clair 《Global Environmental Change》2013,23(1):28-39

The Human Development Report 2007/8 (HDR) and the World Development Report 2010 (WDR) are both devoted to the connections between climate change and development. The reports provide very different perspectives on where the key challenges reside. Their policy proposals are also different, but much less so. Using a combination of frame and content analysis complemented with attention to how these institutions and their knowledge production processes operate, the paper develops a structured comparison of the problem-framing and solution-framing in the Overviews of the two reports. It compares the reports’ conceptions of development; their normative content and the roles given to human rights; the pathways and solutions the agencies defend, and how protective they are of the poor; the status given to proposed market solutions; what types of information and expert perspective are prioritized and why, and which issues are neglected. Following its stress on human rights and ethical principles, the HDR does not unsettle the market driven solutions to climate change that dominate the global policy arena. Different policy instruments and a fuller institutionalization of its human rights concerns is required, in organizations, processes, methodologies and knowledge networks that could move the ideas forward and continually press for their use. This may require a different model of report preparation.  相似文献   

Cold conditions and land forms in the South Downs     

A.J. Bull 《Proceedings of the Geologists' Association. Geologists' Association》1940,51(1):63-71

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