The international position of Dutch human geography: a quantitative exploration     

Jeroen Bosman  Ben de Pater 《GeoJournal》1998,45(1-2):85-96

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An analysis of short-term albedo variations at Haut Glacier d'Arolla, Switzerland     

Ben W. Brock 《Geografiska Annaler: Series A, Physical Geography》2004,86(1):53-65

Abstract An analysis of ten‐minute albedo variations, recorded on Haut Glacier d'Arolla, Switzerland, over an 11 day period in the 1999 ablation season is presented. Most of the short‐term (<1 day) albedo variability is caused by variations in cloud cover, while solar zenith angle variations in the range 25° to 75° are of minor importance, probably due to the predominantly cloudy conditions during the measurement period. A new method to calculate albedo variation as a function of cloud cover is developed. Short‐term albedo variations are expressed by the ratio of the measured albedo to the daily albedo ‘minimum’, defined as the albedo under cloud‐free conditions when the solar zenith angle is <50°. Variations in cloud cover are quantified by the ratio of the measured incoming shortwave radiation flux to the theoretical direct‐beam shortwave radiation flux. The resulting relationships are successful, explaining 83% and 87–90% of short‐term albedo variation on snow and ice respectively, and may be incorporated into albedo parameterizations already used in numerical energy balance melt models, without the need for additional data. Simulations with a glacier energy balance model suggest that melt rates are overestimated by between 1 and 3 mm water equivalent per day if a correction is not made for the increase in albedo under cloudy conditions. Other causes of albedo variation are identified and evidence is found for the removal of fine debris from the glacier surface by intense rainfall, leading to an albedo increase. The implications for energy balance models and satellite‐derived albedo measurements are discussed.  相似文献   

Rock Strength and Development of Glacial Valley Morphology in the Scottish Highlands and Northwest Iceland   总被引：1，自引：0，他引：1  

Martin S. Brook  Martin P. Kirkbride  Ben. W. Brock 《Geografiska Annaler: Series A, Physical Geography》2004,86(3):225-234

Using data from the Scottish Highlands and northwest Iceland, the present study indicates that bedrock strength properties are an important control on the morphology of glacial valleys. Results indicate that on closely jointed metasedimentary bedrock of low rock mass strength, broad U‐shaped valleys are developed, whilst steeper sided, narrower cross‐profiles have been developed on igneous bedrock of high rock mass strength. Findings suggest it is the interplay of the mass strength of the subglacial bedrock and the dynamic properties of the eroding glacier that control valley morphological development. The implication is that realistic models of topographic development beneath ice sheets need to consider the rock mass strength properties of the eroded bedrock as well as the glaciological variables.  相似文献   

Antarctic environmental variability since the late Miocene: ODP Site 745, the East Kerguelen sediment drift     

Leah H Joseph  David K Rea Ben A van der Pluijm  James D Gleason 《Earth and Planetary Science Letters》2002,201(1):127-142

Characterization of sediment from Ocean Drilling Program Site 745, representing the East Kerguelen Ridge sediment drift, addresses important issues surrounding the timing of Miocene to present East Antarctic ice sheet stability and oceanic environmental change. Our results show three periods of greatly enhanced accumulation of Antarctic-derived sediment, at 6.4-5.9 Ma, 4.9-4.4 Ma and 1.1-0.8 Ma, potentially indicative of warmer, less stable ice sheets at these times. Conversely, the accumulation of Antarctic-derived material is comparatively less during the middle of the Pliocene warm epoch (4.8-3.2 Ma). The deep flow forming the Kerguelen drift was stronger during the latest Miocene and earliest Pliocene and has decreased in intensity continuously since then.  相似文献   

Carbon,hydrogen, and oxygen isotope studies of the regional metamorphic complex at Naxos,Greece     

Robert O. Rye  Roelof D. Schuiling  Danny M. Rye  J.Ben H. Jansen 《Geochimica et cosmochimica acta》1976,40(9):1031-1049

At Naxos, Greece, a migmatite dome is surrounded by schists and marbles of decreasing metamorphic grade. Sillimanite, kyanite, biotite, chlorite, and glaucophane zones are recognized at successively greater distances from the migmatite dome. Quartz-muscovite and quartz-biotite oxygen isotope and mineralogie temperatures range from 350 to 700°C.The metamorphic complex can be divided into multiple schist-rich (including migmatites) and marblerich zones. The δ¹⁸O values of silicate minerals in migmatite and schist units and quartz segregations in the schist-rich zones decrease with increase in metamorphic grades. The calculated δ¹⁸O_H2O values of the metamorphic fluids in the schist-rich zones decrease from about 15‰ in the lower grades to an average of about 8.5‰ in the migmatite.The δD values of OH-minerals (muscovite, biotite, chlorite, and glaucophane) in the schist-rich zones also decrease with increase in grade. The calculated δD_H2O values for the metamorphic fluid decrease from ?5‰ in the glaucophane zone to an average of about ?70‰ in the migmatite. The δD values of water in fluid inclusions in quartz segregations in the higher grade rocks are consistent with this trend.Theδ¹⁸O values of silicate minerals and quartz segregations in marble-rich zones are usually very large and were controlled by exchange with the adjacent marbles. The δD values of the OH minerals in some marble-rich zones may reflect the value of water contained in the rocks prior to metamorphism.Detailed data on 20 marble units show systematic variations of δ¹⁸O values which depend upon metamorphic grade. Below the 540°C isograd very steep δ¹⁸O gradients at the margins and large δ¹⁸O values in the interior of the marbles indicate that oxygen isotope exchange with the adjacent schist units was usually limited to the margins of the marbles with more exchange occurring in the stratigraphic bottom than in the top margins. Above the 540°C isograd lower δ¹⁸O values occur in the interior of the marble units reflecting a greater degree of recrystallization and the occurrence of Ca-Mg-silicates.Almost all the δ¹³C values of the marbles are in the range of unaltered marine limestones. Nevertheless, the δ¹³C values of most marble units show a general correlation with δ¹⁸O values.The $\text{CO}{}_2\text{H}{}_2\text{O}$ mole ratio of fluid inclusions in quartz segregations range from 0.01 to 2. Theδ¹³C values of the CO₂ range from ?8.0 to 3.6‰ and indicate that at some localities CO₂ in the metamorphic fluid was not in carbon isotopic equilibrium with the marbles.  相似文献   

The formation of peridotitic suite inclusions in diamonds     

Ben Harte  John J. Gurney  Jeffrey W. Harris 《Contributions to Mineralogy and Petrology》1980,72(2):181-190

Olivine, orthopyroxene and garnet grains belonging to the peridotitic suite of mineral inclusions in natural diamonds typically show compositions poorer in Ca and Al and richer in Mg and Cr than the same minerals in peridotite nodules in kimberlite. Other features suggest the crystallisation of diamonds from magmas of kimberlitic affinities, and it is suggested that the genesis of peridotitic suite diamonds is linked with that of a CO₂-bearing magma. It is shown that the generation of kimberlitic magma from common garnet-peridotite (with 5 wt.% clinopyroxene) in the presence of CO₂ may rapidly remove by melting all Ca-rich solid phases (clinopyroxene and/or carbonate). Further melting may form liquids in equilibrium with olivine, orthopyroxene, and garnet with the distinctive compositions of the diamond inclusions. The amount of melting and CO₂ necessary for the loss of clinopyroxene (and/or carbonate) are estimated at approximately 5.0 wt.% and 0.5 wt.% respectively.  相似文献   

A synthetic approach integrating surface and subsurface data for prospecting deep aquifers: the Southeast Tunisia   总被引：2，自引：0，他引：2  

Salem Bouri  Jalila Makni  Hamed Ben Dhia 《Environmental Geology》2008,54(7):1473-1484

The Southeast Tunisia has remarkable thermal springs that have been used for bathing since many years. Currently, studies are being carried out to investigate the possible use of the hot water for heating buildings and for greenhouses. Springs with discharge temperatures between 26.8 and 58°C exist in the area. The flow rates range between 7 and 66 l/s with total dissolved solids (TDS) varying between 2,020 and 4,030 mg/l. Both geological–hydrogeological setting and the similarity in chemical characteristics between the Zarat spring and nearby water wells suggest that the hot water from this spring may be related to the Senonian aquifer. However, the hydrogeothermal approach shows that the depth of the reservoir that supplies the Zarat spring is greater than that of the Senonian aquifer. In fact, geothermometry approach indicates that fluids emerging from the Lower Cretaceous sandstones reach temperatures of approximately 78°C at depth, while the fluid temperature from the nearby water wells is 32°C. Through the integration of various types of data we found that the thermal water of Southeast Tunisia is of meteoric origin. This water infiltrates deeply into the Lower Cretaceous sandstones and reaches a high temperature before rising upwards to supply the hot springs and well discharge zones. It appears that the upward movement of hot water from the deep aquifers to shallow ones is probably due to the abundant fractures in the area.  相似文献   

Mouvements actuels des blocs tectoniques dans l’arc Bético-Rifain à partir des mesures GPS entre 1999 et 2005     

Abdelilah Tahayt  Taoufik Mourabit  Alexis Rigo  Kurt L. Feigl  Abdelali Fadil  Simon McClusky  Robert Reilinger  Mostafa Serroukh  Abdelouahed Ouazzani-Touhami  Driss Ben Sari  Philippe Vernant   《Comptes Rendus Geoscience》2008,340(6):400-413

GPS velocities and seismicity across the Betic–Rif Arc structural domains (Morocco and Iberia) provide a basis to evaluate present-day seismotectonic processes between different deformation belts. The results show asymmetric movements in the complex Alboran system accommodating the convergence between the African (Nubian) and Eurasian plates. While the Betic Mountains are attached to Iberia, moving toward the southeast with respect to Africa, the Rif is divided into three blocks with distinct displacements relative to Nubia: (1) the Tangier block moving southeastward, (2) the Central Rif block moving SSW, and (3) the Oriental Rif block undergoing clockwise rotation. GPS-derived motions decrease in rate from the Rif nappes complex to the foreland.  相似文献   

Apports de la gravimétrie dans la caractérisation des structures éffondrées dans la région de Nebeur (Nord Ouest de la Tunisie)     

Imen Hamdi Nasr  Abdelhamid Ben Salem  Mohamed Hedi Inoubli  Jamel Dhifi  R. Alouani  abdelhak Chaqui  Vincent Perthuisot 《Swiss Journal of Geoscience》2008,101(1):17-27

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Postglacial relative sea‐level observations from Ireland and their role in glacial rebound modelling     

Anthony J. Brooks  Sarah L. Bradley  Robin J. Edwards  Glenn A. Milne  Ben Horton  Ian Shennan 《第四纪科学杂志》2008,23(2):175-192

The British Isles have been the focus of a number of recent modelling studies owing to the existence of a high‐quality sea‐level dataset for this region and the suitability of these data for constraining shallow earth viscosity structure, local to regional ice sheet histories and the magnitude/timing of global meltwater signals. Until recently, the paucity of both glaciological and relative sea‐level (RSL) data from Ireland has meant that the majority of these glacial isostatic adjustment (GIA) modelling studies of the British Isles region have tended to concentrate on reconstructing ice cover over Britain. However, the recent development of a sea‐level database for Ireland along with emergence of new glaciological data on the spatial extent, thickness and deglacial chronology of the Irish Ice Sheet means it is now possible to revisit this region of the British Isles. Here, we employ these new data to constrain the evolution of the Irish Ice Sheet. We find that in order to reconcile differences between model predictions and RSL evidence, a thick, spatially extensive ice sheet of ～600–700 m over much of north and central Ireland is required at the LGM with very rapid deglaciation after 21 k cal. yr BP. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献