A first Holocene leaf wax isotope-based paleoclimate record from the semi-humid to semi-arid south-eastern Caucasian lowlands     

Marcel Bliedtner  Roland Zech  Jana Zech  Imke Schäfer  Hans von Suchodoletz 《第四纪科学杂志》2020,35(5):625-633

The Holocene paleoclimate of the Caucasus region is rather complex and not yet well understood: while existing studies are mainly based on pollen records from high-altitude and humid lowland regions, no records are available from the semi-humid to semi-arid south-eastern Caucasian lowlands. Therefore, this study investigated compound-specific δ²H and δ¹³C isotopes of leaf wax biomarkers from Holocene floodplain soils in eastern Georgia. Our results show that the leaf wax δ²H signal from the paleosols mostly reflects changes in the moisture source and its isotopic composition. Depleted δ²H values before ~8 cal ka bp change towards enriched values after ~5 cal ka bp and become again depleted after ~1.6 cal ka bp. This trend could be caused by Holocene changes of the isotopic compositions of the Black and eastern Mediterranean Sea, and/or by varying contribution of both moisture sources linked with the North Atlantic Oscillation. The leaf wax δ¹³C signal from the paleosols directly indicates varying local water availability and drought stress. Depleted δ¹³C values before ~8 and after ~5 cal ka bp indicate wetter local conditions with higher water availability, whereas more enriched values during the middle Holocene (~8 until at least 5 cal ka bp ) indicate drier conditions with increased drought stress.  相似文献   

Gravimetric monitoring of the first field‐wide steam injection in a fractured carbonate field in Oman – a feasibility study          下载免费PDF全文

Marcin Glegola  Pavel Ditmar  Femke Vossepoel  Rob Arts  Fahad Al‐Kindy  Roland Klees 《Geophysical Prospecting》2015,63(5):1256-1271

Gas‐Oil Gravity Drainage is to be enhanced by steam injection in a highly fractured, low permeability carbonate field in Oman. Following a successful pilot, field‐wide steam injection is being implemented, first of this type in the world. A dedicated monitoring program has been designed to track changes in the reservoir. Various observations are to be acquired, including, surface deformation, temperature measurements, microseismic, well logs, pressure and saturation measurements to monitor the reservoir. Because significant changes in the reservoir density are expected, time‐lapse gravimetry is also being considered. In this paper we investigate the feasibility of gravimetric monitoring of the thermally enhanced gravity drainage process at the carbonate field in Oman. For this purpose, forward gravity modelling is performed. Based on field groundwater measurements, the estimates of the hydrological signal are considered and it is investigated under what conditions the groundwater influences can be minimized. Using regularized inversion of synthetic gravity data, we analyse the achievable accuracy of heat‐front position estimates. In case of large groundwater variations at the field, the gravity observations can be significantly affected and, consequently, the accuracy of heat‐front monitoring can be deteriorated. We show that, by applying gravity corrections based on local observations of groundwater, the hydrological influences can to a large extent be reduced and the accuracy of estimates can be improved. We conclude that gravimetric monitoring of the heat‐front evolution has a great potential.  相似文献   

Inclined lidar observations of boundary layer aerosol particles above the Kongsfjord,Svalbard     

Astrid Lampert  Johan Ström  Christoph Ritter  Roland Neuber  Young Jun Yoon  Nam Yi Chae  Masataka Shiobara 《Acta Geophysica》2012,60(5):1287-1307

An inclined lidar with vertical resolution of 0.4 m was used for detailed boundary layer studies and to link observations at Zeppelin Mountain (474 m) and Ny-Ålesund, Svalbard. We report on the observation of aerosol layers directly above the Kongsfjord. On 29 April 2007, a layer of enhanced backscatter was observed in the lowest 25 m above the open water surface. The low depolarization ratio indicated spherical particles. In the afternoon, this layer disappeared. The ultrafine particle concentration at Zeppelin and Corbel station (close to the Kongsfjord) was low. On 1 May 2007, a drying process in the boundary layer was observed. In the morning, the atmosphere up to Zeppelin Mountain showed enhanced values of the backscatter coefficient. Around noon, the top of the highly reflecting boundary layer decreased from 350 to 250 m. The top of the boundary layer observed by lidar was confirmed by radiosonde data.  相似文献   

Epiphytic diatoms as flood indicators   总被引：1，自引：0，他引：1  

Johan A. Wiklund  Natalie Bozinovski  Roland I. Hall  Brent B. Wolfe 《Journal of Paleolimnology》2010,44(1):25-42

The hydroecology of floodplain lakes is strongly regulated by flood events. The threat of climate warming and increasing human activities requires development of scientific methods to quantify changes in the frequency of short-lived flood events, because they remain difficult to identify using conventional paleolimnological and monitoring approaches. We developed an approach to detect floods in sediment records by comparing the abundance and composition of epiphytic diatom communities in flooded and non-flooded ponds of the Peace-Athabasca Delta (PAD), Canada, that grew on submerged macrophytes (Potamogeton zosteriformis, P. perfoliatus) and an artificial substrate (polypropylene sheets) during the open-water season of 2005. Analysis of similarity tests showed that epiphytic diatom community composition differs significantly between flooded and non-flooded ponds. After accounting for the “pond effect,” paired comparisons of the three substrates determined that variation in community composition between the artificial substrate and macrophytes was similar to that between the macrophyte taxa. Similarity percentage analysis identified diatom taxa that discriminate between flooded and non-flooded ponds. The relative abundance of ‘strong flood indicator taxa’ was used to construct an event-scale flood record spanning the past 180 years using analyses of sedimentary diatom assemblages from a closed-drainage pond (PAD 5). Results were verified by close agreement with an independent paleoflood record from a nearby flood-prone oxbow pond (PAD 54) and historical records. Comparison of epiphytic diatoms in flooded and non-flooded lakes in this study provides a promising approach to detect changes in flood frequency, and may have applications for reconstructing other pulse-type disturbances such as hurricanes and pollutant spills.  相似文献   

Analysing Debris-Flow Impact Models, Based on a Small Scale Modelling Approach   总被引：4，自引：0，他引：4  

Christian Scheidl  Michael Chiari  Roland Kaitna  Matthias Müllegger  Alexander Krawtschuk  Thomas Zimmermann  Dirk Proske 《Surveys in Geophysics》2013,34(1):121-140

The objective of this study is to analyse adaptable debris-flow impact models, which are very important for mitigation measurements and buildings using their sphere of influence. For this reason, 16 debris-flow experiments, on a small-scale modelling approach, were performed. Impact forces were measured with a force plate panel, consisting of 24 aluminium devices, coaxially mounted with resistance strain gauges. Flow velocities, flow heights as well as horizontal impact forces were sampled with a frequency of 2.4 kHz. Sub datasets of sampled raw force data were defined by applying an average median filter, a low-pass filter routine. Further, estimated peak pressure values as well as empirical coefficients of hydraulic impact models were compared, and the influence of signal processing is discussed.  相似文献   

Evaluating the performance of ground-based and remotely sensed near real-time rainfall fields from a hydrological perspective     

Yonas Ghile  Roland Schulze  Casey Brown 《水文科学杂志》2013,58(4):497-511

Abstract

The South African Weather Service (SAWS) issues routine experimental, near real-time rainfall maps from daily raingauge networks, radar networks and satellite images, as well as merged rainfall fields. These products are potentially useful for near real-time forecasting, especially in areas of fast hydrological response, and also to simulate the “now state” of various hydrological state variables such as soil moisture content, streamflow, and reservoir inflows. The purpose of this paper is to evaluate their skill as inputs to hydrological simulations and, in particular, the skill of the merged field in terms of better hydrological results relative to the individual products. Rainfall fields derived from raingauge, radar, satellite, conditioned satellite and the merged (gauge/radar/satellite) were evaluated for two selected days with relatively high amounts of rainfall, as well as for a continuous period of 90 days in the Mgeni catchment, South Africa. Streamflows simulated with the ACRU model indicate that the use of raingauge as well as merged fields of satellite/raingauge and satellite/radars/raingauge provides relatively realistic rainfall results, without much difference in their hydrological outputs, whereas the radar and raw satellite information by themselves cannot be used in operational hydrological application in their current status.

Citation Ghile, Y., Schulze, R. & Brown, C. (2010) Evaluating the performance of ground-based and remotely sensed near real-time rainfall fields from a hydrological perspective. Hydrol. Sci. J. 55(4), 497–511.  相似文献   

OH defects in quartz in the system quartz–albite–water and granite–water between 5 and 25?kbar     

Roland Stalder  Jürgen Konzett 《Physics and Chemistry of Minerals》2012,39(10):817-827

The incorporation of OH defects in quartz from the systems quartz–water, quartz–albite–water and granite–water at pressures between 5 and 25?kbar and temperatures between 800 and 1,000?°C was investigated by IR spectroscopy. The two most important OH absorption features can be assigned to hydrogarnet defects (absorption band at 3,585?cm^?1) and coupled substitutions involving Al³⁺ (Al–H defects, absorption bands at 3,310, 3,378 and 3,430?cm^?1). Al incorporation in quartz is controlled by mineral/melt partitioning (D _Al ^Qz/Melt ?=?0.01) and exhibits a negative pressure dependence. This trend is not clearly reflected by the concentration of Al–H defects, which shows positive deviations from the theoretical 1:1 correlation of Al/H for some samples. In contrast to the Al–H defects, formation of hydrogarnet defects appears to be positively correlated to pressure and water activity, and may be used a petrological indicator. The overall water concentration exhibits only minor changes with pressure and temperature, but a clear correlation of water activity (controlled by various amounts of dissolved salts) and hydrogarnet substitution could be established.  相似文献   

Electrical conductivity of H-bearing orthopyroxene single crystals measured with impedance spectroscopy     

Elke Schlechter  Roland Stalder  Harald Behrens 《Physics and Chemistry of Minerals》2012,39(7):531-541

In this study, the electrical conductivity of synthetic and natural orthopyroxene single crystals containing various amounts of hydrogen and cation impurities (i.e., Al, Fe) was investigated using impedance spectroscopy. A new cell was developed to measure conductivities of submillimeter-sized oriented single crystals with impedances up to 10¹⁰?Ohm. In contrast to previous studies on olivine and orthopyroxene, results from this study do not show a simple correlation of the concentration of protons and the electrical conductivity. Instead, the electrical conductivity appears to be a complex function of iron content, hydrogen content, crystal orientation and concentration of other impurity cations and shows similar activation energies to hydrogen diffusion. Model calculations considering proton conduction rather exclude than suggest orthopyroxene as responsible phase for high-conductivity regions in the Earth’s upper mantle.  相似文献   

Early Triassic potassic volcanism in the Afyon Zone of the Anatolides/Turkey: implications for the rifting of the Neo-Tethys     

Cüneyt Akal  Osman Candan  O. Ersin Koralay  Roland Oberhänsli  Fukun Chen  Dejan Prelević 《International Journal of Earth Sciences》2012,101(1):177-194

Afyon Zone, which was derived from the Anatolide–Tauride platform during closure of the Neo-Tethys, is made up of pre-Mesozoic basement and unconformably overlying Triassic–Early Tertiary cover series. The Afyon Zone contains widespread metavolcanic rocks, which are dominated by rhyolite, dacite, and trachyandesite. They form a distinct volcanic succession, which is separated from the underlying Silurian–Lower Carboniferous metacarbonates and meta-siliciclastics by a regional unconformity. Trachyandesitic metavolcanics are made up of massive lava flows, pyroclastics and epiclastics, less frequently, domes and dikes, which were developed on a deeply eroded subaerial landmass. U/Pb and Pb/Pb zircon geochronology yielded Lower Triassic (~250 Ma) ages, which are interpreted as extrusion age of trachyandesitic volcanics. Based on the stratigraphic, geochronological, and geochemical data, we suggest that these Lower Triassic magmatic rocks represent an extensional tectonic setting on the northern active margin of the Gondwana, which led to the development of the northern branch of the Neo-Tethys.  相似文献   

The burial efficiency of organic carbon in the sediments of Lake Kinneret   总被引：1，自引：0，他引：1  

Sebastian Sobek  Roland Zurbrügg  Ilia Ostrovsky 《Aquatic Sciences - Research Across Boundaries》2011,73(3):355-364

Even though lake sediments constitute a significant long-term carbon sink, studies on the regulation of carbon burial in lakes sediments have, to date, been surprisingly few. We investigated to what degree the organic carbon (OC) being deposited onto the bottom of Lake Kinneret (Israel) is buried in the sediment at four different sites with varying degrees of oxygenation and varying supply of allochthonous particles from the River Jordan. For estimation of the OC burial efficiency (OC BE), i.e., the ratio between buried and deposited OC, we calculated OC burial from dated sediment cores, and calculated OC deposition using three different approaches. Calculation of OC deposition from sediment trap-derived mass deposition rates multiplied with the OC content of surface sediment yielded OC BE values that were at odds with published values for sediments dominated by autochthonous OC sources. Calculation via sediment trap data on organic matter flux collected within the Lake Kinneret monitoring program, as well as calculation of OC deposition as the sum of OC burial plus OC mineralization, returned fairly congruent estimates of OC BE (range 10–41%), but only if the sediment trap data were corrected for the proportion of resuspended particles in the traps. Differences in OC BE between sites were small, indicating that OC source (common to all sites) was a more important regulator of OC BE in Lake Kinneret than oxygen exposure or mineral particles characteristics.  相似文献