A multi‐method investigation of temperature,moisture and salt dynamics in tafoni (Tafraoute,Morocco)          下载免费PDF全文

Harald Schnepfleitner  Oliver Sass  Stefanie Fruhmann  Heather Viles  Andrew Goudie 《地球表面变化过程与地形》2016,41(4):473-485

Despite numerous investigations and theoretical models, tafoni weathering is still not fully understood largely because of limited data available on temperature, moisture and salt regimes. We investigated tafoni developed in granite in the Tafraoute region, Morocco, through an exploratory, two‐week multi‐method field campaign. Temperatures were measured with iButtons and by means of infrared thermography; moisture distribution and progress were captured with handheld moisture sensors and with drilled‐in iButtons. Salts were analysed in drill dust samples from different positions and rock depths. The results derived from very different techniques mutually support one another. Salts and moisture are concentrated near the base of the investigated tafoni, probably due to a saturated pore water body around the base of rock tors. Salts are accumulated close to the rock surface in tafoni, but not on the surrounding rock surfaces. A clear correlation was found between moisture and salt contents. Within a tafone, areas of higher humidity also display increased salt concentration near the surface. The temperature/humidity records allied with ionic analyses suggest that sodium sulfate dominates and is likely to undergo frequent phase changes from thenardite to mirabilite and vice versa. Two pathways of salt transport in and around tafoni are assumed based on the data: infiltration with rainfall on the top and around tors and boulders, and capillary rise from saturated pore water bodies to the surface. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Vulnerabilities to flood hazards among rural households in India     

Sam  Anu Susan  Kumar  Ranjit  Kächele  Harald  Müller  Klaus 《Natural Hazards》2017,88(2):1133-1153

Natural Hazards - Flooding constitutes the most predominant natural disaster in India. The degree and causes of vulnerability to flood risk vary by society, geographical region and over time. The...  相似文献   

First lacustrine varve chronologies from Mexico: impact of droughts,ENSO and human activity since AD 1840 as recorded in maar sediments from Valle de Santiago   总被引：1，自引：0，他引：1  

Ulrike Kienel  Sabine Wulf Bowen  Roger Byrne  Jungjae Park  Harald Böhnel  Peter Dulski  James F. Luhr  Lee Siebert  Gerald H. Haug  Jörg F. W. Negendank 《Journal of Paleolimnology》2009,42(4):587-609

We present varve chronologies for sediments from two maar lakes in the Valle de Santiago region (Central Mexico): Hoya La Alberca (AD 1852–1973) and Hoya Rincón de Parangueo (AD 1839–1943). These are the first varve chronologies for Mexican lakes. The varved sections were anchored with tephras from Colima (1913) and Paricutín (1943/1944) and ²¹⁰Pb ages. We compare the sequences using the thickness of seasonal laminae and element counts (Al, Si, S, Cl, K, Ti, Mn, Fe, and Sr) determined by micro X-ray fluorescence spectrometry. The formation of the varve sublaminae is attributed to the strongly seasonal climate regime. Limited rainfall and high evaporation rates in winter and spring induce precipitation of carbonates (high Ca, Sr) enriched in ¹³C and ¹⁸O, whereas rainfall in summer increases organic and clastic input (plagioclase, quartz) with high counts of lithogenic elements (K, Al, Ti, and Si). Eolian input of Ti occurs also in the dry season. Moving correlations (5-yr windows) of the Ca and Ti counts show similar development in both sequences until the 1930s. Positive correlations indicate mixing of allochthonous Ti and autochthonous Ca, while negative correlations indicate their separation in sublaminae. Negative excursions in the correlations correspond with historic and reconstructed droughts, El Niño events, and positive SST anomalies. Based on our data, droughts (3–7 year duration) were severe and centred around the following years: the early 1850s, 1865, 1880, 1895, 1905, 1915 and the late 1920s with continuation into the 1930s. The latter dry period brought both lake systems into a critical state making them susceptible to further drying. Groundwater overexploitation due to the expansion of irrigation agriculture in the region after 1940 induced the transition from calcite to aragonite precipitation in Alberca and halite infiltration in Rincón. The proxy data indicate a faster response to increased evaporation for Rincón, the lake with the larger maar dimensions, solar radiation receipt and higher conductivity, whereas the smaller, steeper Alberca maar responded rapidly to increased precipitation.  相似文献   

Interpretations and observations of ocean wave spectra     

Harald Elias Krogstad  Karsten Trulsen 《Ocean Dynamics》2010,60(4):973-991

The paper starts with a discussion of the linear stochastic theory of ocean waves and its various nonlinear extensions. The directional spectrum, with its unique dispersion relation connecting frequency (ω) and wavenumber (k), is no longer valid for nonlinear waves, and examples of $\left( \mathbf{k},\omega\right) The paper starts with a discussion of the linear stochastic theory of ocean waves and its various nonlinear extensions. The directional spectrum, with its unique dispersion relation connecting frequency (ω) and wavenumber (k), is no longer valid for nonlinear waves, and examples of ( k,w)\left( \mathbf{k},\omega\right) -spectra based on analytical expressions and computer simulations of nonlinear waves are presented. Simulations of the dynamic nonlinear evolution of unidirectional free waves using the nonlinear Schr?dinger equation and its generalizations show that components above the spectral peak have larger phase and group velocities than anticipated by linear theory. Moreover, the spectrum does not maintain a thin well-defined dispersion surface, but rather develops into a continuous distribution in ( k,w)\left( \mathbf{k,}\omega\right) -space. The majority of existing measurement systems rely on linear theory for the interpretation of their data, and no measurement systems are currently able to measure the full spectrum in the open ocean with high accuracy. Nevertheless, there exist a few low-resolution systems where data may be interpreted within a minimal assumption of a non-restricted ( k,w)\left( \mathbf{k,}\omega\right) -spectrum. The theory is reviewed, and analyses based on conventional spectral analysis as well as a directional wavelet analysis are carried out on data from a compact laser array at the Ekofisk field in the North Sea. The investigation confirms the strong impact of the second order spectrum below the spectral peak, but is non-conclusive about the off-set in the support of the first order spectrum seen in the dynamical simulations.  相似文献   

Satellite wave measurements for coastal engineering applications     

Harald E. Krogstad  Stephen F. Barstow 《Coastal Engineering》1999,37(3-4)

Measurements from the GEOSAT, ERS-1 and 2 and Topex/Poseidon satellites have now accumulated to over 15 years of global ocean wave and wind data. Extraction of wave height, wind speed and wave period from the satellite altimeters and directional wave spectra from the synthetic aperture radars are reviewed along with recent validation and calibration efforts. Applications of the data to a variety of problems illustrate the potential of satellite wave measurements.  相似文献   

Improvements of an empirical model to forecast wind surge in the German Bight     

Sylvin H. Müller-Navarra  Harald Giese 《Ocean Dynamics》1999,51(4):385-405

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产业集群研究的新视角   总被引：17，自引：0，他引：17  

H.巴泽尔 《世界地理研究》2005,14(1):1-8

本文从垂直、水平、制度、外部和权力因子分析了集群的生成、成长和再生现象。笔者认为,具备可持续发展能力的集群必须与外部的供应商、市场和技术建立系统的联系,多种文化的融合、合理的权力结构、有效的调控手段是集群环境建设的重要内容。同时,在制定区域政策时,不能简单地将一地的产业集群政策移植到另外一个区域。此外,不是世界上的所有地区都具备形成产业集群的前提条件;产业集群政策也不是提升区域经济竞争力的唯一途径。  相似文献   

Comment on A.J. Biggin et al., A comparison of a quasi-perpendicular method of absolute palaeointensity determination with other thermal and microwave techniques,Earth and Planetary Science Letters 257 (2007) 564–581     

Derek Walton  Harald N. Boehnel 《Earth and Planetary Science Letters》2008,265(1-2):324-326

While Biggin et al.'s paper is an important review and critique of palaeomagnetic methods employed at present, we point out here that if the grain size selectivity of microwaves is employed, instead of just using them to heat the sample, alteration can be avoided completely, and previously unavailable grain size dependence of the magnetic moment can be recovered.  相似文献   

Diving down the reefs? Intensive diving tourism threatens the reefs of the northern Red Sea     

Hasler H  Ott JA 《Marine pollution bulletin》2008,56(10):1788-1794

Intensive recreational SCUBA diving threatens coral reef ecosystems. The reefs at Dahab, South Sinai, Egypt, are among the world’s most dived (>30,000 dives y⁻¹). We compared frequently dived sites to sites with no or little diving. Benthic communities and condition of corals were examined by the point intercept sampling method in the reef crest zone (3 m) and reef slope zone (12 m). Additionally, the abundance of corallivorous and herbivorous fish was estimated based on the visual census method. Sediments traps recorded the sedimentation rates caused by SCUBA divers. Zones subject to intensive SCUBA diving showed a significantly higher number of broken and damaged corals and significantly lower coral cover. Reef crest coral communities were significantly more affected than those of the reef slope: 95% of the broken colonies were branching ones. No effect of diving on the abundance of corallivorous and herbivorous fish was evident. At heavily used dive sites, diver-related sedimentation rates significantly decreased with increasing distance from the entrance, indicating poor buoyancy regulation at the initial phase of the dive. The results show a high negative impact of current SCUBA diving intensities on coral communities and coral condition. Corallivorous and herbivorous fishes are apparently not yet affected, but are endangered if coral cover decline continues. Reducing the number of dives per year, ecologically sustainable dive plans for individual sites, and reinforcing the environmental education of both dive guides and recreational divers are essential to conserve the ecological and the aesthetic qualities of these dive sites.  相似文献   

Habitat Selection and Ecology of Two Speleophilic Gobiid Fishes(Pisces: Gobiidae) from the Western Mediterranean Sea     

Jürgen Herler  Robert A. Patzner  Harald Ahnelt&  Helge Hilgers 《Marine Ecology》1999,20(1):49-62

The life habits and microhabitat selection of speleophilic gobiid fishes were investigated on the Balearic Island of Ibiza (western Mediterranean Sea). Corcyrogobius liechtensteini (Kolombatović, 1891) was the most frequent species within submarine crevices, cavities and caves. Didogobius splechtnai Ahnelt & Patzner, 1995 co-occurred with C. liechtensteini in several cases but showed a clear spatial separation based on a different microhabitat preference. The microhabitat selection of both species was confirmed by habitat-choice experiments in anaquarium. Corcyrogobius liechtensteini was frequent in depths between 5 m and 25 m and attained abundances of 14.2 individuals · m⁻². This species inhabited the ceilings and upper parts of the walls within the caves. D. splechtnai was mainly found between 7 m and 11 m and showed abundances of approximately 2 indivi-duals · m⁻². This species occupied the fine sediment bottoms in the innermost parts of crevices and caves. The growth and the maximum age of both species were determined by length-frequency distributions. The overall sex ratio from catches of three different years are given for C. liechtensteini .  相似文献