Grenville age deformation of the Sudbury impact structure: evidence from magnetic modelling of the Sudbury diabase dyke swarm     

Peter Tschirhart  Bill Morris 《地学学报》2012,24(3):213-220

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Development of a three‐dimensional watershed modelling system for water cycle in the middle part of the Heihe rivershed,in the west of China     

Jian Zhou  Bill X. Hu  Guodong Cheng  Genxu Wang  Xin Li 《水文研究》2011,25(12):1964-1978

A three‐dimensional numerical modelling system is developed to study transformation processes of water resources in alluvial fan and river basin along the middle reaches of the Heihe River Basin, Northwest China, an arid and semi‐arid region. Integrating land utilization, remote sensing and geographic information systems, we have developed a numerical modelling system that can be used to quantify the effects of land use and anthropogenic activities on the groundwater system as well as to investigate the interaction between surface water and groundwater. Various hydraulic measurements are used to identify and calibrate the hydraulic boundary conditions and spatial distributions of hydraulic parameters. In the modelling study, various water exchanges and human effects on the watershed system are considered. These include water exchange between surface water and groundwater, groundwater pumping, lateral water recharges from mountain areas, land utilization, and infiltration and evaporation in the irrigation and non‐irrigation areas. The modelling system provides a quantitative method to describe spatial and temporal distributions and transformations between various water resources, and it has application to other watersheds in arid and semi‐arid areas. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Seasonal and Annual Fluxes of Nutrients and Organic Matter from Large Rivers to the Arctic Ocean and Surrounding Seas   总被引：3，自引：0，他引：3  

Robert Max Holmes  James W. McClelland  Bruce J. Peterson  Suzanne E. Tank  Ekaterina Bulygina  Timothy I. Eglinton  Viacheslav V. Gordeev  Tatiana Y. Gurtovaya  Peter A. Raymond  Daniel J. Repeta  Robin Staples  Robert G. Striegl  Alexander V. Zhulidov  Sergey A. Zimov 《Estuaries and Coasts》2012,35(2):369-382

River inputs of nutrients and organic matter impact the biogeochemistry of arctic estuaries and the Arctic Ocean as a whole, yet there is considerable uncertainty about the magnitude of fluvial fluxes at the pan-Arctic scale. Samples from the six largest arctic rivers, with a combined watershed area of 11.3?×?10⁶?km², have revealed strong seasonal variations in constituent concentrations and fluxes within rivers as well as large differences among the rivers. Specifically, we investigate fluxes of dissolved organic carbon, dissolved organic nitrogen, total dissolved phosphorus, dissolved inorganic nitrogen, nitrate, and silica. This is the first time that seasonal and annual constituent fluxes have been determined using consistent sampling and analytical methods at the pan-Arctic scale and consequently provide the best available estimates for constituent flux from land to the Arctic Ocean and surrounding seas. Given the large inputs of river water to the relatively small Arctic Ocean and the dramatic impacts that climate change is having in the Arctic, it is particularly urgent that we establish the contemporary river fluxes so that we will be able to detect future changes and evaluate the impact of the changes on the biogeochemistry of the receiving coastal and ocean systems.  相似文献   

The Processing and Impact of Dissolved Riverine Nitrogen in the Arctic Ocean     

Suzanne E. Tank  Manfredi Manizza  Robert Max Holmes  James W. McClelland  Bruce J. Peterson 《Estuaries and Coasts》2012,35(2):401-415

Although the Arctic Ocean is the most riverine-influenced of all of the world’s oceans, the importance of terrigenous nutrients in this environment is poorly understood. This study couples estimates of circumpolar riverine nutrient fluxes from the PARTNERS (Pan-Arctic River Transport of Nutrients, Organic Matter, and Suspended Sediments) Project with a regionally configured version of the MIT general circulation model to develop estimates of the distribution and availability of dissolved riverine N in the Arctic Ocean, assess its importance for primary production, and compare these estimates to potential bacterial production fueled by riverine C. Because riverine dissolved organic nitrogen is remineralized slowly, riverine N is available for uptake well into the open ocean. Despite this, we estimate that even when recycling is considered, riverine N may support 0.5–1.5 Tmol C year⁻¹ of primary production, a small proportion of total Arctic Ocean photosynthesis. Rapid uptake of dissolved inorganic nitrogen coupled with relatively high rates of dissolved organic nitrogen regeneration in N-limited nearshore regions, however, leads to potential localized rates of riverine-supported photosynthesis that represent a substantial proportion of nearshore production.  相似文献   

The Arctic Ocean Estuary   总被引：1，自引：0，他引：1  

James W. McClelland  R. M. Holmes  K. H. Dunton  R. W. Macdonald 《Estuaries and Coasts》2012,35(2):353-368

Large freshwater contributions to the Arctic Ocean from a variety of sources combine in what is, by global standards, a remarkably small ocean basin. Indeed, the Arctic Ocean receives ∼11% of global river discharge while accounting for only ∼1% of global ocean volume. As a consequence, estuarine gradients are a defining feature not only near-shore, but throughout the Arctic Ocean. Sea-ice dynamics also play a pivotal role in the salinity regime, adding salt to the underlying water during ice formation and releasing fresh water during ice thaw. Our understanding of physical–chemical–biological interactions within this complex system is rapidly advancing. However, much of the estuarine research to date has focused on summer, open water conditions. Furthermore, our current conceptual model for Arctic estuaries is primarily based on studies of a few major river inflows. Future advancement of estuarine research in the Arctic requires concerted seasonal coverage as well as a commitment to working within a broader range of systems. With clear signals of climate change occurring in the Arctic and greater changes anticipated in the future, there is good reason to accelerate estuarine research efforts in the region. In particular, elucidating estuarine dynamics across the near-shore to ocean-wide domains is vital for understanding potential climate impacts on local ecosystems as well as broader climate feedbacks associated with storage and release of fresh water and carbon.  相似文献   

Tectonic structures in the Peel Sandstones and Carboniferous limestone,Isle of Man     

Bill Fitches 《Geological Journal》2011,46(4):364-373

On the Isle of Man, the Early Devonian Peel Sandstones and Early Carboniferous limestones have been deformed in places by folds, cleavage and other structures. The structures in the Peel Sandstones have been attributed to pre‐lithification deformation associated with slumping of the red beds. Here, they are re‐interpreted to be products of post‐lithification deformation, inferred from small‐scale structures and fabrics, which took place in a localized thrust zone. Compression was approximately NW–SE and translation towards the SE. That deformation may have also produced some of the late structures in the Lower Palaeozoic rocks of the island. The minimum age of these post‐Early Devonian structures is unknown but is probably pre‐Carboniferous: they may represent the mid‐Devonian Acadian deformation. The Carboniferous succession is folded in places and contains stylolites and stylolitic cleavage. A stress regime with E–W to WNW–ESE compression is inferred. These structures have orientations and morphologies shown to resemble those in neighbouring parts of southern Britain, where they are attributed mainly to mid‐ to late‐Carboniferous Variscan events. Alternatively, some or all of them might be products of late Mesozoic and Tertiary tectonics recognized elsewhere in the region. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Contract farming and the remaking of agrarian landscapes: Insights from South India's chilli belt     

Bill Pritchard  John Connell 《Singapore journal of tropical geography》2011,32(2):236-252

This analysis of a backward integration traceability scheme for red chillies developed by a multinational food company in India emphasizes spatial integration and differentiation within contract farming. The scheme is premised on the procurement of identically credentialed produce from 10 different sites in two states and incorporates growers in highly flexible and place‐contingent modes. Interviews with corporate informants and farmers reveal this flexibility to be the result of a two‐way process of risk management between the company and growers. The company spread its geographical exposure by initiating production across a number of far‐flung cultivation sites, and growers cultivate chillies for the company within the context of diverse agricultural systems, thereby mitigating dependence. The scheme has had positive impacts for participants, but has more complex implications for the evolution of agrarian landscapes in India. The selective enrolment of participants through ‘progressive farmer’ networks acts to reorganize rural spaces by generating new geographies of advantage and opportunity.  相似文献   

The slow rotation of 253 Mathilde     

Stefano Mottola  William D. Sears  Anders Erikson  Alan W. Harris  Jim W. Young  Gerhard Hahn  Mats Dahlgren  Beatrice E. A. Mueller  Bill Owen  Ricardo Gil-Hutton  Javier Licandro  M. Antonietta Barucci  Claudia Angeli  Gerhard Neukum  Claes-Ingvar Lagerkvist  J. Felix Lahulla 《Planetary and Space Science》1995,43(12)

CCD photometry of the NEAR mission fly-by target 253 Mathilde is presented. Measurements taken during 52 nights of observations, from February to June 1995, allow a rotation period of 17.406±0.010 days and a lightcurve amplitude of 0.45±0.02 mag to be determined. A B-V color index of 0.67±0.02 and a V-R of 0.35±0.02 are measured, which are compatible with C-type membership. The determination of the phase relation results in H = 10.28±0.03 and G = 0.12±0.06. Indications that the lightcurve is not strictly singly-periodic are found. A power-spectrum analysis detects a secondary frequency f₂ = 0.0322±0.0010 d⁻¹, which is interpreted as evidence for a complex rotation state.  相似文献   

Editorial: Geoanalysis 2012     

Thomas Meisel  Michel Grégoire  Bill McDonough  Christophe Quétel  Jon Woodhead  Edward A. Williams 《Geostandards and Geoanalytical Research》2013,37(4):377-377

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The problem of higher food prices for impoverished people in the rural global South     

Bill Pritchard 《The Australian geographer》2014,45(4):419-427

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