Helium isotopes in early Iceland plume picrites: Constraints on the composition of high 3He/4He mantle     

Natalie A. Starkey  Finlay M. Stuart  Robert M. Ellam  J. Godfrey Fitton  Sudeshna Basu  Lotte M. Larsen 《Earth and Planetary Science Letters》2009,277(1-2):91-100

A detailed study of the geochemistry of a new suite of early Iceland plume picrites shows that extremely high ³He/⁴He ratios (up to 50 R_a) are found in picrites from Baffin Island and West Greenland. High ³He/⁴He picrites display a wide range in ⁸⁷Sr/⁸⁶Sr (0.70288–0.70403), ¹⁴³Nd/¹⁴⁴Nd (0.51288–0.51308) and incompatible trace element ratios (e.g. La/Sm_n = 0.5–1.6). These overlap the complete range of compositions of mid-ocean ridge basalts and most northern hemisphere ocean island basalts, including Iceland. Crustal contamination modelling in which high-grade Proterozoic crustal basement rocks for the region are mixed with a depleted parent cannot account for the trend displayed by the Baffin Island and West Greenland picrites. This rules out the possibility that the incompatible trace element, Sr and Nd isotope range of the high ³He/⁴He picrites is due to crustal contamination. The compositional range at high ³He/⁴He is also inconsistent with derivation from a primordial-He-rich reservoir that is a residue of ancient mantle depletion. This implies that the composition of the high ³He/⁴He mantle cannot be determined simply by extrapolating ocean island basalt He–Sr–Nd–Pb–Os isotope data.The apparent decoupling of He from trace element and lithophile radiogenic isotope tracers is difficult to attain by simple mixing of a high-[He], high ³He/⁴He reservoir with various depleted and enriched He-poor mantle reservoirs. The possibility that primordial He has diffused into a reservoir with a composition typical of convecting upper mantle cannot be ruled out. If so, the process must have occurred after the development of existing mantle heterogeneity, and requires the existence of a deep, primordial He-rich reservoir.  相似文献   

Improved microbial risk assessment of groundwater     

S. Godfrey  M. Smith 《Hydrogeology Journal》2005,13(1):321-324

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中国资源型城市产业结构升级对土地利用效率的影响     

宋洋  贺灿飞  YEUNG Godfrey  徐阳 《地理研究》2023,42(1):86-105

在中国经济面临结构转型和空间重塑的关键时期,探究资源型城市产业结构升级对土地利用效率的影响机理,对于破解资源型城市产业发展路径依赖与土地低效利用困境具有重要意义。基于中国115座地级资源型城市面板数据,运用产业结构层次指数与基于DEA的超效率SBM-Undesirable模型刻画资源型城市产业结构升级与土地利用效率的时空演化特征,通过面板Tobit模型探究资源型城市产业结构升级对土地利用效率的异质性影响及作用渠道。结果表明：(1)中国资源型城市产业结构升级成效显著,再生型、煤炭型和钢铁型城市升级效果更为明显。土地利用效率呈波动上升趋势,高值城市数量显著增加,以经济基础较好的再生型和成长型城市为主。(2)资源型城市产业结构升级对土地利用效率提升尚未形成普遍的驱动效应,其影响机制在不同类型城市中具有显著的异质性,仅再生型城市呈现显著的正向影响。(3)资源型城市产业结构升级通过经济产出提升、要素配置优化与环境污染控制等渠道驱动土地利用效率的动态演化。现阶段,土地经济产出偏低、用地结构失调、环境污染负外部性过高是制约资源型城市土地利用效率提升的主要症结。资源型城市转型具有长期性、系统性特征,应...  相似文献   

Wind erosion of Mancos Shale badland ridges by sudden drops in pressure     

Andrew E. Godfrey 《地球表面变化过程与地形》1997,22(4):345-352

One process of erosion of Mancos Shale badlands near Hanksville, Utah, appears to be caused by nearly instantaneous drops in air pressure accompanying gusts of wind. A series of sharp-crested bedrock ridges trend nearly perpendicular to the strong, gusty southwesterly winds that precede cold fronts passing through the area. The Bernoulli effect, resulting from the explosive onset of wind gusts in which the wind over the ridges can accelerate from 7 to 14 m s⁻¹, can cause nearly instantaneous pressure drops of 1·27 mmHg. This provides a unit lifting force of 0·01697 N. Since the average gravitational force acting on a unit area of the crust is only 0·00883 N, this force is sufficient to lift the crust, exposing the underlying weathered shale chips to further wind erosion. Soils susceptible to this type of erosion consist of polygonally cracked surface crust averaging 1·2 cm thick overlying a porous subsoil of silt-sized shale chips. The arid environment permits complete soil drying between weather fronts, greatly reducing the cohesion that would occur if the soil were moist. The pressure drops, and the erosion caused by them, were observed on the lee side of bedrock ridges about 10 m high, within 1 m of the ridge crest. Landforms resulting from this process are micro-cirque forms located near the ridge crests. Continued development of micro-cirques eventually forms cliffs on the lee sides of the ridges. © 1997 by John Wiley & Sons, Ltd.  相似文献   

Co-management of sea turtle fisheries: Biogeography versus geopolitics     

Lisa M. Campbell  Jennifer J. Silver  Noella J. Gray  Sue Ranger  Annette Broderick  Tatum Fisher  Matthew H. Godfrey  Shannon Gore  John Jeffers  Corrine Martin  Andrew McGowan  Peter Richardson  Carlos Sasso  Lorna Slade  Brendan Godley 《Marine Policy》2009

Co-management between local communities and government agencies is promoted as a strategy to improve fisheries management. This paper considers the potential for co-management of sea turtle fisheries within four UK Overseas Territories (OTs) in the Caribbean, and for co-ordinated management among those territories. We focus on fisher incentives for engaging in co-management and on the potential to scale up co-management to a regional level. This paper presents data from Anguilla, British Virgin Islands, Montserrat, and Turks and Caicos Islands, where 110 turtle fishers participated in a socio-economic survey undertaken as part of the ‘Turtles in the UK Overseas Territories in the Caribbean’ project. Based on three established criteria for co-management (perceived crisis in stock, willingness to participate and community cohesion), results suggest that fisher support for co-management exists within each OT, but the extent of support for and views of specific management interventions varies among OTs. The implications of results for co-management in each territory, and for establishing co-ordinated management regimes in the region, are discussed in the context of current debates about the nature of resources and scalar (mis)matches between resource and management regimes.  相似文献   

Editorial: Seven decades of the Singapore Journal of Tropical Geography—looking back and future directions     

James D. Sidaway  TC Chang  Chen-Chieh Feng  Xi Xi Lu  Godfrey Yeung 《Singapore journal of tropical geography》2023,44(1):3-6

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