26Al/10Be ratios reveal the source of river sediments in the Kimberley,NW Australia     

Gaël Cazes  David Fink  Alexandru T. Codilean  Réka-Hajnalka Fülöp  Toshiyuki Fujioka  Klaus M. Wilcken 《地球表面变化过程与地形》2020,45(2):424-439

We use cosmogenic ¹⁰Be and ²⁶Al in both bedrock and fluvial sediments to investigate controls on erosion rates and sediment supply to river basins at the regional scale in the Kimberley, NW Australia. The area is characterised by lithologically controlled morphologies such as cuestas, isolated mesas and extensive plateaus made of slightly dipping, extensively jointed sandstones. All sampled bedrock surfaces at plateau tops, ridgelines, and in the broader floodplain of major rivers over the region show similar slow lowering rates between 0.17 and 4.88 m.Myr^-1, with a mean value of 1.0 ± 0.6 m.Myr^-1 (n=15), whilst two bedrock samples collected directly within river-beds record rates that are one to two orders of magnitude higher (14.4 ± 1.5 and 20.9 ± 2.5 m.Myr^-1, respectively). Bedrock ²⁶Al/¹⁰Be ratios are all compatible with simple, continuous sub-aerial exposure histories. Modern river sediment yield lower ¹⁰Be and ²⁶Al concentrations, apparent ¹⁰Be basin-wide denudation rates ranging between 1.8 and 7.7 m.Myr^-1, with a median value of 2.6 m.Myr^-1, more than double the magnitude of bedrock erosion rates. ²⁶Al/¹⁰Be ratios of the sediment samples are lower than those obtained for bedrock samples. We propose that these depleted ²⁶Al/¹⁰Be ratios can largely be explained by the supply of sediment to river basins from the slab fragmentation and chemical weathering of channel gorge walls and plateau escarpments that result in diluting the cosmogenic nuclide concentration in river sediments measured at the basin outlets. The results of a mass-balance model suggest that ~60–90% of river sediment in the Kimberley results from the breakdown and chemical weathering of retreating vertical sandstone rock-walls in contrast to sediment generated by bedrock weathering and erosion on the plateau tops. This study emphasises the value of analysing two or more isotopes in basin-scale studies using cosmogenic nuclides, especially in slowly eroding post-orogenic settings. © 2019 John Wiley & Sons, Ltd.  相似文献   

Internal Structure and Permafrost Characteristics of the Rock Glaciers of Southern Carpathians (Romania) Assessed by Geoelectrical Soundings and Thermal Monitoring     

Alexandru L. Onaca  Petru Urdea  Adrian C. Ardelean 《Geografiska Annaler: Series A, Physical Geography》2013,95(3):249-266

Six rock glaciers in the Southern Carpathians have been investigated by means of geoelectrical soundings in order to detect their internal stratigraphy and the existence of frozen sediments. In the case of three relict rock glaciers, the electrical resistivity measurements indicated a typical internal structure. Low resistivity values (<10 kΩm) which are typical of unfrozen fine‐grained materials were obtained, but high resistivity values (25–240 kΩm) measured in the Pietroasa, Ie?u and Pietrele rock glaciers denote the presence of sediments cemented by interstitial ice and ice lenses. Based on the moderate resistivity values, the ice content is probably low to medium in the upper portion of these rock glaciers, that is, above 2040 m. At two sites (Pietroasa and V?iuga rock glaciers), ground surface temperature (GST) evolution was monitored using digital dataloggers. Mean annual ground surface temperature and GST regime throughout the winter were extracted from the recordings and confirmed the probability of permafrost occurrence in Pietroasa rock glacier. In the Ie?u and Pietrele rock glaciers, measurements of bottom temperatures of the winter snow cover were performed in March 2012. Considering the thick active layer, the reduced ice content and the presence of scarce vegetation on their surface it could be assumed that the permafrost exists in marginal conditions in the Southern Carpathians. The ground ice in permafrost is produced by the groundwater freezing or by snow banks buried by coarse angular boulders following large rockfalls.  相似文献   

Impact of land-use and land-cover changes on CRCM5 climate projections over North America for the twenty-first century     

Adelina Alexandru  Laxmi Sushama 《Climate Dynamics》2016,46(3-4):1197-1222

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Experiments on ESIP—Environment oriented satellite data processing platform     

Dorian Gorgan  Victor Bacu  Denisa Rodila  Florin Pop  Dana Petcu 《Earth Science Informatics》2010,3(4):297-308

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Note on the evolution of a Miocene composite volcano in an extensional setting, Zârand Basin (Apuseni Mts., Romania)     

Ioan Seghedi  Alexandru Szakács  Emilian Roşu  Zoltán Pécskay  Katalin Gméling 《Central European Journal of Geosciences》2010,2(3):321-328

Bontâu is a major eroded composite volcano filling the Miocene Zârand extensional basin, near the junction between the Codru-Moma and Highi?-Drocea Mountains, at the tectonic boundary between the South and North Apuseni Mountains. It is a quasi-symmetric structure (16–18 km in diameter) centered on an eroded vent area (9×4 km), buttressed to the south against Mesozoic ophiolites and sedimentary deposits of the South Apuseni Mountains. The volcano was built up in two sub-aerial phases (14–12.5 Ma and 11–10 Ma) from successive eruptions of andesite lava and pyroclastic rocks with a time-increasing volatile budget. The initial phase was dominated by emplacement of pyroxene andesite and resulted in scattered individual volcanic lava domes associated marginally with lava flows and/or pyroclastic block-and-ash flows. The second phase is characterized by amphibole-pyroxene andesite as a succession of pyroclastic eruptions (varying from strombolian to subplinian type) and extrusion of volcanic domes that resulted in the formation of a central vent area. Numerous debris flow deposits accumulated at the periphery of primary pyroclastic deposits. Several intrusive andesitic-dioritic bodies and associated hydrothermal and mineralization processes are known in the volcano vent complex area. Distal epiclastic deposits initially as gravity mass flows and then as alluvial volcaniclastic and terrestrial detritic and coal filled the basin around the volcano in its western and eastern part. Chemical analyses show that lavas are calc-alkaline andesites with SiO₂ ranging from 56–61%. The petrographical differences between the two stages are an increase in amphibole content at the expense of two pyroxenes (augite and hypersthene) in the second stage of eruption; CaO and MgO contents decrease with increasing SiO₂. In spite of a ～4 Ma evolution, the compositions of calc-alkaline lavas suggest similar fractionation processes. The extensional setting favored two pulses of short-lived magma chamber processes.  相似文献   

The urban heat island of Bucharest during the extreme high temperatures of July 2007     

Sorin Cheval  Alexandru Dumitrescu  Aurora Bell 《Theoretical and Applied Climatology》2009,97(3-4):391-401

This paper explores the characteristics of the air (T_air) and land surface temperature (LST) from the city of Bucharest (Romania) during the extreme high temperatures that affected the region in July 2007. The behavior of Bucharest’s Urban Heat Island (UHI) is quantitatively described following similar methodological approaches to previous studies. The analysis integrates thermal data supplied by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors aboard the NASA satellites and meteorological data provided by the ground-based weather stations. Based on the T_air, one may claim that during extreme high summer temperatures, the UHI preserves its spatial and temporal pattern regarding the differences between the central urban perimeter and the suburban area. The investigation of the LST from July 2007 reveals that the nocturnal changes refer mainly to the magnitude and the limits of the UHI, while the shape is not changed. However, the extreme temperatures induce significant modifications of the features of the diurnal UHI, obliterating and dissipating it in certain spots, enlarging it and creating shifted heat islands in some other spots. The main explanation is the outstanding duration and intensity of the hot mass of air impacting the area. The correlations between the T_air measured at the weather stations in Bucharest and the corresponding LST retrieved significant values both under “normal” conditions and extreme temperature persistence, and offer good premises for robust validation studies. The MODIS products performed like an extremely useful instrument for analyzing the UHI.  相似文献   

Free convection effects on oscillatory hydromagnetic boundary layer flow     

V. M. Soundalgekar  I. Pop  S. P. Akolkar 《Astrophysics and Space Science》1978,56(2):323-333

Unsteady flow of an incompressible, viscous, electrically conducting fluid past an infinite porous plate has been analysed under the following assumptions: (i) suction velocity oscillates in time about a constant mean, (ii) the free-stream velocity oscillates in time about a constant mean, (iii) the plate temperature is constant, (iv) the difference between the temperature of the plate and the free-stream is moderately large causing the free-convection currents, (v) a uniform transverse magnetic field is applied, (vi) the magnetic Reynolds number is very small and hence the induced magnetic field is neglected. Approximate solutions to the coupled non-linear equations governing the flow are derived for the transient velocity, the transient temperature, the amplitude and the phase of the skin-friction and the rate of heat transfer. During the course of analysis the effects of ±G (Grashof number),P (Prandtl number),M (magnetic field parameter),A (suction parameter) and ω (frequency) are discussed.  相似文献   

Error Estimates for a Time Discretization Method for the Richards' Equation     

Iuliu Sorin Pop 《Computational Geosciences》2002,6(2):141-160

We present a numerical analysis of a time discretization method applied to Richards' equation. Written in its saturation-based form, this nonlinear parabolic equation models water flow into unsaturated porous media. Depending on the soil parameters, the diffusion coefficient may vanish or explode, leading to degeneracy in the original parabolic equation. The numerical approach is based on an implicit Euler time discretization scheme and includes a regularization step, combined with the Kirchhoff transform. Convergence is shown by obtaining error estimates in terms of the time step and of the regularization parameter.  相似文献   

Horizontal redistribution of fluids in a porous medium: The role of interfacial area in modeling hysteresis     

I.S. Pop  C.J. van Duijn  J. Niessner  S.M. Hassanizadeh 《Advances in water resources》2009

Recent advances in multi-phase flow theory have shown that the flow of several phases in a porous medium is highly influenced by the interfaces separating these phases. First modeling studies based on this new theory have been performed on a pore scale, as well as on a volume-averaged macro scale using balance equations and constitutive relations that take the role and presence of interfaces into account. However, neither experimental data nor analytical solutions are available on the macro scale so far, although their knowledge is essential for the verification of the new models.  相似文献   

Cs baseline levels in the Mediterranean and Black Sea: A cross-basin survey of the CIESM Mediterranean Mussel Watch programme     

Herv Thbault  Alessia M. Rodriguez y Baena  Bruno Andral  Delko Barisic  Jos Benedicto Albaladejo  Alexandru S. Bologa  Redouane Boudjenoun  Roberta Delfanti  Victor N. Egorov  Tahar El Khoukhi  Heleni Florou  Goran Kniewald  Abdelkader Noureddine  Vasile Patrascu  Mai Khanh Pham  Alfonso Scarpato  Nikolay A. Stokozov  Sayhan Topcuoglu  Michel Warnau 《Marine pollution bulletin》2008,57(6-12):801

The common mussel Mytilus galloprovincialis was selected as unique biomonitor species to implement a regional monitoring programme, the CIESM Mediterranean Mussel Watch (MMW), in the Mediterranean and Black Seas. As of today, and upon standardization of the methodological approach, the MMW Network has been able to quantify ¹³⁷Cs levels in mussels from 60 coastal stations and to produce the first distribution map of this artificial radionuclide at the scale of the entire Mediterranean and Black Seas. While measured ¹³⁷Cs levels were found to be very low (usually <1 Bq kg⁻¹ wet wt) ¹³⁷Cs activity concentrations in the Black Sea and North Aegean Sea were up to two orders of magnitude higher than those in the western Mediterranean Basin. Such effects, far from representing a threat to human populations or the environment, reflect a persistent signature of the Chernobyl fallout in this area.  相似文献