Gamma-ray bursts and their links with supernovae and cosmology     

Peter Meszairos  Neil Gehrels 《天体物理学报》2012,(8):1139-1161

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Soil erosion and sediment transport in Tanzania: Part II – sedimentological evidence of phased land degradation     

Maarten Wynants  Aloyce Patrick  Linus Munishi  Kelvin Mtei  Samuel Bodé  Alex Taylor  Geoffrey Millward  Neil Roberts  David Gilvear  Patrick Ndakidemi  Pascal Boeckx  William H. Blake 《地球表面变化过程与地形》2021,46(15):3112-3126

Soil resources in parts of Tanzania are rapidly being depleted by increased rates of soil erosion and downstream sediment transport, threatening ecosystem health, water and livelihood security in the region. However, incomplete understanding to what effect the dynamics of soil erosion and sediment transport are responding to land-use changes and climatic variability are hindering the actions needed to future-proof Tanzanian land-use practices. Complementary environmental diagnostic tools were applied to reconstruct the rates and sources of sedimentation over time in three Tanzanian river systems that have experienced changing land use and climatic conditions. Detailed historical analysis of sediment deposits revealed drastic changes in sediment yield and source contributions. Quantitative sedimentation reconstruction using radionuclide dating showed a 20-fold increase in sediment yield over the past 120 years. The observed dramatic increase in sediment yield is most likely driven by increasing land-use pressures. Deforestation, cropland expansion and increasing grazing pressures resulted into accelerating rates of sheet erosion. A regime shift after years of progressive soil degradation and convergence of surface flows resulted into a highly incised landscape, where high amounts of eroded soil from throughout the catchment are rapidly transported downstream by strongly connected ephemeral drainage networks. By integrating complementary spatial and temporal evidence bases, this study demonstrated links between land-use change, increased soil erosion and downstream sedimentation. Such evidence can guide stakeholders and policy makers in the design of targeted management interventions to safeguard future soil health and water quality.  相似文献   

Deformation of a young salt giant: regional topography of the Red Sea Miocene evaporites   总被引：1，自引：0，他引：1       下载免费PDF全文

Neil C. Mitchell  Marco Ligi  Peter Feldens  Christian Hübscher 《Basin Research》2017,29(Z1):352-369

The deformational behaviour of ‘salt giants’ during and shortly after their deposition is difficult to decipher in ocean margin settings where the original evaporites have been deeply buried and strongly mobilized. Here, we examine seismic reflection data from the Red Sea, where evaporites deposited until the end of the Miocene (~5.3 Ma), are generally covered by only 200–300 m of low‐density sediments and where the presence of an axial spreading centre allows us to observe how they have responded to a varied configuration of underlying basement. The regional morphology of the S‐reflection, representing the evaporite surface, is mapped out from seismic data from 13 cruises. The S‐reflection is locally rugged and commonly angular. It is either underlain by layered reflectivity, suggestive of layered evaporite beds, or by more transparent seismic character, suggestive of massive halite. On average, the depth of the reflection on the flanks of the axial rift systematically declines from 700 to 1100 m below sea level (mbsl) going northwards from 16 to 23°N. In the central Red Sea, the S‐reflection has 100‐ to 200‐m‐deep depressions, extending towards the coasts in places. In the southern Red Sea, the S‐reflection forms a surface at 300–800 mbsl that appears less disrupted. We suggest that the evaporites originally had a flat, horizontal surface at the end of the Miocene and have subsequently been distorted by isostatic effects and axial rifting, which in turn promoted evaporite flowage. Off‐axis evaporite depressions correspond with flows identified with multibeam sonar. Furthermore, across‐rift lows in Bouguer gravity anomalies represent valleys in the underlying basement. The off‐axis evaporite depressions overlie those valleys, as would be expected if halokinetic movements were greatest where the evaporites are locally thick, leading to deflation of the evaporite surface. The thickness of post‐Miocene sediment, also mapped out as part of this procedure, confirms the generally pelagic nature of this interval and increases on average from ~250 to 300 m from the central to the southern Red Sea, mimicking the variation in pelagic productivity observed in the present water column.  相似文献   

Geographic Patterns of Craft Breweries at the Intraurban Scale     

Isabelle Nilsson  Neil Reid  Matthew Lehnert 《The Professional geographer》2018,70(1):114-125

This article examines the intraurban geography of craft breweries in ten cities across the United States. First, through an exhaustive literature review, we outline both supply- and demand-side factors that might cause craft breweries to cluster. Second, we empirically test whether these establishments tend to cluster within cities using spatial statistical techniques. Many communities are attempting to support the establishment of more craft breweries as a way to boost tourism and economic development. The findings from this article aid in this discussion by providing insights into how craft brewers locate and the factors that could influence their location decision behavior. Our findings suggest that craft brewers do in fact cluster. There are both supply and demand factors responsible. On the supply side, the collaborative environment within the industry and the artisan nature of the industry's products allows for benefits of clustering to outweigh the costs associated with this behavior. On the demand side, the emergence of “brewery districts” allows individual brewers to enjoy the reputation benefits associated with the district in terms of increased foot traffic from locals and visitors looking to sample a variety of beers.  相似文献   

Ground-Based Observations of the Thermodynamic and Kinematic Properties of Lake-Breeze Fronts in Southern Manitoba,Canada     

Michelle Curry  John Hanesiak  Scott Kehler  David M.  L. Sills  Neil M. Taylor 《Boundary-Layer Meteorology》2017,162(1):143-169

The effects on the convective boundary layer (CBL) of shading due to shallow cumulus clouds are investigated. The main question is to see whether clouds are able to produce secondary circulations by shading of the surface (dynamic heterogeneities) and how these dynamic heterogeneities interact with static heterogeneities in terms of the production of secondary circulations. Also the effects of cloud shadows on cloud-field characteristics are analyzed. The effects are studied using large-eddy simulations of a cloud-topped CBL with an idealized surface. Over a homogeneous surface, shadows trigger secondary circulations with different strengths depending on the solar zenith angle \(\vartheta \), with large \(\vartheta \) favouring the development of secondary circulations. Over a static heterogeneous surface with a simple striped pattern, the strength of secondary circulations is effectively reduced by dynamic heterogeneities at small \(\vartheta \). At large \(\vartheta \), however, the effect on secondary circulations depends on the orientation of the striped static heterogeneities to the shadow-casting direction of the clouds. The influence of shadows is only small if they are cast perpendicular to the striped heterogeneity, but if stripes and the shadow-casting direction are parallel, secondary circulations are reduced in strength also for large \(\vartheta \). Shadow effects on the cloud-field characteristics vary with \(\vartheta \) as well. The results show that small \(\vartheta \) favours the development of small clouds with a reduced lifetime while large \(\vartheta \) promotes the development of larger clouds with an extended lifetime compared to non-shading clouds.  相似文献   

Quantifying system disturbance and recovery from historical mining-derived metal contamination at Brotherswater,northwest England     

Daniel N. Schillereff  Richard C. Chiverrell  Neil Macdonald  Janet M. Hooke  Katharine E. Welsh 《Journal of Paleolimnology》2016,56(2-3):205-221

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Recharge Estimation by Stage-Discharge Interpolation of Springflows from Cross-Correlated Well Measurements     

William H. Avery  Joseph J. Donovan  J. Neil Ketchum 《Ground water》1999,37(3):332-337

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Changes in Climate Extremes Over the Australian Region and New Zealand During the Twentieth Century   总被引：10，自引：0，他引：10  

Neil Plummer  M. James Salinger  Neville Nicholls  Ramasamy Suppiah  Kevin J. Hennessy  Robert M. Leighton  Blair Trewin  Cher M. Page  Janice M. Lough 《Climatic change》1999,42(1):183-202

Analyses of high quality data show that there have been some interesting recent changes in the incidence of some climate extremes in the Australian region and New Zealand.  相似文献   

The geochemistry of sulphur in a mixed allogenic–autogenic karst catchment,Castleton, Derbyshire,UK     

Simon H. Bottrell  Neil Webber    John Gunn  Stephen R. H. Worthington 《地球表面变化过程与地形》2000,25(2):155-165

Analyses are presented of anion chemistry and sulphur isotopic compositions of sulphate in sinking streams and groundwaters in a mixed allogenic–autogenic karst catchment. Using the sulphur isotopic data, sources of sulphate from agriculture and the effects of sulphate reduction arising from slurry application can be distinguished from natural rock weathering sources. Within the aquifer, sulphate in known autogenic waters has isotopic compositions distinct from allogenic waters, the autogenic waters being dominated by sulphate from rainfall and rock weathering in these low agricultural intensity catchments. On this basis, water rising at low flow from Whirlpool Rising, Speedwell Cavern, has been identified as dominantly autogenic. Groundwater flow between the sinks and risings in Speedwell Cavern is believed to be along conduits following mineralized faults (rakes). During transit SO42−/Cl− in the water increases. Isotopic mass balance shows that this must be due to addition of sulphate from the oxidation of ore minerals by groundwater. Mass balance considerations show that the present rate of sulphide oxidation must be the result of enhancement by lead mining operations on the rakes. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Comparing threshold definition techniques for rainfall‐induced landslides: A national assessment using radar rainfall          下载免费PDF全文

Benjamin Postance  John Hillier  Tom Dijkstra  Neil Dixon 《地球表面变化过程与地形》2018,43(2):553-560

Translational landslides and debris flows are often initiated during intense or prolonged rainfall. Empirical thresholds aim to classify the rain conditions that are commonly associated with landslide occurrence and therefore improve understating of these hazards and predictive ability. Objective techniques that are used to determine these thresholds are likely to be affected by the length of the rain record used, yet this is not routinely considered. Moreover, remotely sensed spatially continuous rainfall observations are under‐exploited. This study compares and evaluates the effect of rain record length on two objective threshold selection techniques in a national assessment of Scotland using weather radar data. Thresholds selected by ‘threat score’ are sensitive to rain record length whereas, in a first application to landslides, ‘optimal point’ (OP) thresholds prove relatively consistent. OP thresholds increase landslide detection and may therefore be applicable in early‐warning systems. Thresholds combining 1‐ and 12‐day antecedence variables best distinguish landslide initiation conditions and indicate that Scottish landslides may be initiated by lower rain accumulation and intensities than previously thought. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献