MAJOR ELEMENT COMPOSITION OF GLASSES IN THREE APOLLO 15 SOILS     

Arch M. Reid  Jeff Warner  W. I. Ridley  R. W. Brown 《Meteoritics & planetary science》1972,7(3):395-415

Approximately 180 glasses in each of three Apollo 15 soils have been analyzed for nine elements. Cluster analysis techniques allow the recognition of preferred glass compositions that are equated with parent rock compositions Green glass rich in Fe and Mg, poor in Al and Ti may be derived from deep seated pyroxenitic material now present at the Apennine Front. Fra Mauro basalt (KREEP) is most abundant in the LM soil and is tentatively identified as ray material from the Aristillus-Autolycus area. Highland basalt (anorthositic gabbro), believed to be derived from the lunar highlands, has the same composition as at other landing sites, but is less abundant. The Apennine Front is probably not true highland material but may contain a substantial amount of material with the composition of Fra Mauro basalt, but lacking the high-K content. Glasses with mare basalt compositions are present in the soils and four subgroups are recognized, one of which is compositionally equivalent to the large Apollo 15 basalt samples  相似文献   

Announcing the launch of HPToday     

Jeff McDonnell  Malcolm G Anderson  Des Walling  Normal E Peters 《水文研究》2000,14(14):2365-2365

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Abiotic effects of UV on planktonic P kinetics   总被引：1，自引：0，他引：1  

Jeff M. Sereda  Jeff J. Hudson  William D. Taylor 《Aquatic Sciences - Research Across Boundaries》2009,71(2):127-134

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Representation of agricultural conservation practices with SWAT   总被引：5，自引：0，他引：5  

Mazdak Arabi  Jane R. Frankenberger  Bernie A. Engel  Jeff G. Arnold 《水文研究》2008,22(16):3042-3055

Results of modelling studies for the evaluation of water quality impacts of agricultural conservation practices depend heavily on the numerical procedure used to represent the practices. Herein, a method for the representation of several agricultural conservation practices with the Soil and Water Assessment Tool (SWAT) is developed and evaluated. The representation procedure entails identifying hydrologic and water quality processes that are affected by practice implementation, selecting SWAT parameters that represent the affected processes, performing a sensitivity analysis to ascertain the sensitivity of model outputs to selected parameters, adjusting the selected parameters based on the function of conservation practices, and verifying the reasonableness of the SWAT results. This representation procedure is demonstrated for a case study of a small agricultural watershed in Indiana in the Midwestern USA. The methods developed in the present work can be applied with other watershed models that employ similar underlying equations to represent hydrologic and water quality processes. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Ultraluminous infrared galaxies at high redshift: their position on the Madau plot and their fate     

Neil Trentham  A. W. Blain  Jeff Goldader 《Monthly notices of the Royal Astronomical Society》1999,305(1):61-78

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Kankan diamonds (Guinea) II: lower mantle inclusion parageneses   总被引：3，自引：2，他引：1  

Thomas Stachel  Jeff W. Harris  Gerhard P. Brey  Werner Joswig 《Contributions to Mineralogy and Petrology》2000,140(1):16-27

Frequent inclusions of ferropericlase, some coexisting with phases of MgSiO₃, CaSiO₃ and SiO₂ composition, suggest that a large proportion of diamonds from Guinea are derived from the lower mantle. Low aluminium contents in MgSiO₃ inclusions indicate derivation from the uppermost lower mantle, where Al solubility in perovskite is low. Trace element analyses (SIMS) of CaSiO₃ inclusions reveal extreme degrees of LREE (200–2000 times chondritic) and Sr enrichment (70–1000 times chondritic) together with negative and positive Eu anomalies. This implies a highly enriched lower mantle source, possibly a product of a subducted oceanic slab. A number of phases that are only stable in the upper mantle are found to coexist with lower mantle phases and thereby indicate retrograde equilibration during slow exhumation within a rising plume or convection cell. In one case, however, an inclusion paragenesis of ferropericlase and olivine can be shown to have formed within the upper mantle, indicating that the occurrence of ferropericlase inclusions alone is an unreliable indicator of lower mantle origin. Received: 26 January 2000 / Accepted: 18 May 2000  相似文献   

Thresholds for irreversible decline of the Greenland ice sheet   总被引：1，自引：0，他引：1  

Jeff Ridley  Jonathan M. Gregory  Philippe Huybrechts  Jason Lowe 《Climate Dynamics》2010,35(6):1049-1057

The Greenland ice sheet will decline in volume in a warmer climate. If a sufficiently warm climate is maintained for a few thousand years, the ice sheet will be completely melted. This raises the question of whether the decline would be reversible: would the ice sheet regrow if the climate cooled down? To address this question, we conduct a number of experiments using a climate model and a high-resolution ice-sheet model. The experiments are initialised with ice sheet states obtained from various points during its decline as simulated in a high-CO₂ scenario, and they are then forced with a climate simulated for pre-industrial greenhouse gas concentrations, to determine the possible trajectories of subsequent ice sheet evolution. These trajectories are not the reverse of the trajectory during decline. They converge on three different steady states. The original ice-sheet volume can be regained only if the volume has not fallen below a threshold of irreversibility, which lies between 80 and 90% of the original value. Depending on the degree of warming and the sensitivity of the climate and the ice-sheet, this point of no return could be reached within a few hundred years, sooner than CO₂ and global climate could revert to a pre-industrial state, and in that case global sea level rise of at least 1.3 m would be irreversible. An even larger irreversible change to sea level rise of 5 m may occur if ice sheet volume drops below half of its current size. The set of steady states depends on the CO₂ concentration. Since we expect the results to be quantitatively affected by resolution and other aspects of model formulation, we would encourage similar investigations with other models.  相似文献   

Three-Dimensional Modeling of Shallow Shear-Wave Velocities for Las Vegas, Nevada, Using Sediment Type     

Barbara Luke  Helena Murvosh  Wanda Taylor  Jeff Wagoner 《中国地质大学学报(英文版)》2009,20(3)

A three-dimensional model of near-surface shear-wave velocity in the deep alluvial basin underlying the metropolitan area of Las Vegas, Nevada (USA), is being developed for earthquake site response projections. The velocity dataset, which includes 230 measurements, is interpolated across the model using depth-dependent correlations of velocity with sediment type. The sediment-type database contains more than 1 400 well and borehole logs. Sediment sequences reported in logs are assigned to one of four units. A characteristic shear-wave velocity profile b developed for each unit by analyzing closely spaced pairs of velocity profiles and well or borehole logs. The resulting velocity model exhibits reasonable values and patterns, although it does not explicitly honor the measured shear-wave velocity profiles. Site response investigations that applied a preliminary version of the velocity model support a two-zone ground-shaking hazard model for the valley. Areas in which clay predominates in the upper 30 m are predicted to have stronger ground motions than the rest of the basin.  相似文献   

The demise of Arctic sea ice during stabilisation at high greenhouse gas concentrations     

Jeff Ridley  Jason Lowe  David Simonin 《Climate Dynamics》2008,30(4):333-341

A climate model experiment was conducted using the HadCM3 climate model and a scenario in which the atmospheric CO₂ concentration was increased over 70 years from pre-industrial concentrations to 4 times this level and then stabilised for more than a 1,000 years. During the period of stabilisation the global atmospheric surface temperatures continued to rise as the deep oceans adjusted towards a new equilibrium. However, even after 1,000 years this new equilibrium had not been reached. During the first 600 years, Arctic and Antarctic winter sea ice thickness and area covered declined with a significant impact on the global radiation budget. After this period the area of the Arctic covered by sea ice entered a 150 years period during which time it underwent a series of oscillations. Following the oscillation the centre of the Arctic basin became ice free throughout the year. A sensitivity experiment demonstrates that although the sea ice extent can be greatly reduced through the artificial heating of the mixed layer, prior to the onset of the oscillatory phase the ice recovers over 15 years. Understanding the causes of this oscillatory phase may elucidate the mechanisms of variability in the Arctic in the present climate and in future policy relevant scenarios. We have investigated the atmospheric and oceanic forcing on the ice during the oscillatory phase, and find that the behaviour is linked to a redistribution of Arctic Ocean heat stores.  相似文献   

Coral skeleton P/Ca proxy for seawater phosphate: Multi-colony calibration with a contemporaneous seawater phosphate record     

Michèle LaVigne  Kathryn A. Matthews  Kim M. Cobb  Guy Cabioch 《Geochimica et cosmochimica acta》2010,74(4):1282-515

A geochemical proxy for surface ocean nutrient concentrations recorded in coral skeleton could provide new insight into the connections between sub-seasonal to centennial scale nutrient dynamics, ocean physics, and primary production in the past. Previous work showed that coralline P/Ca, a novel seawater phosphate proxy, varies synchronously with annual upwelling-driven cycles in surface water phosphate concentration. However, paired contemporaneous seawater phosphate time-series data, needed for rigorous calibration of the new proxy, were lacking. Here we present further development of the P/Ca proxy in Porites lutea and Montastrea sp. corals, showing that skeletal P/Ca in colonies from geographically distinct oceanic nutrient regimes is a linear function of seawater phosphate (PO_4 SW) concentration. Further, high-resolution P/Ca records in multiple colonies of Pavona gigantea and Porites lobata corals grown at the same upwelling location in the Gulf of Panamá were strongly correlated to a contemporaneous time-series record of surface water PO_4 SW at this site (r² = 0.7-0.9). This study supports application of the following multi-colony calibration equations to down-core records from comparable upwelling sites, resulting in ±0.2 and ±0.1 μmol/kg uncertainties in PO_4 SW reconstructions from P. lobata and P. gigantea, respectively.