Detailed seismic stratigraphy of Lago Puyehue: implications for the mode and timing of glacier retreat in the Chilean Lake District     

Katrien Heirman  Marc De Batist  Francois Charlet  Jasper Moernaut  Emmanuel Chapron  Robert Brümmer  Mario Pino  Roberto Urrutia 《第四纪科学杂志》2011,26(7):665-674

Lago Puyehue is a glacigenic lake in the Chilean Lake District (40°S) with a complex deglaciation history. A detailed seismic–stratigraphic study of its sedimentary infill indicates a much earlier retreat of the glacier from the Lago Puyehue basin than the neighbouring glacier from the Lago Rupanco basin. Because of their close proximity, Rupanco meltwater streams played an important part in the depositional processes of Lago Puyehue. A timing discrepancy between the in‐lake ages of a sediment core and the outer‐lake ages of moraine deposits (re)opens the discussion on the timing of deglaciation in the Southern Hemisphere. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Late Holocene high precipitation events recorded in lake sediments and catchment geomorphology,Lake Vuoksjávrátje,NW Sweden          下载免费PDF全文

Annika Berntsson  Krister N. Jansson  Malin E. Kylander  Francois De Vleeschouwer  Sebastien Bertrand 《Boreas: An International Journal of Quaternary Research》2015,44(4):676-692

In this paper, we show the potential of combining multi‐proxy analysis of lake sediments with catchment geomorphology to better understand palaeoenvironmental changes. Previous studies have suggested that alpine lakes in N Sweden may be highly sensitive to variations in catchment erosion and precipitation, and that this sensitivity may influence ecologically based reconstructions of past temperature changes. We analysed lake sediments covering the last 5100 years from the alpine Lake Vuoksjávrátje in NW Sweden in order to identify different erosional regimes in the lake catchment, sediment sources and lake sedimentary processes, which ultimately affect the palaeoecological record. The measured proxies include elemental geochemistry from XRF core scanning, grain size, sediment accumulation rates, fraction of terrestrial organic carbon and geomorphological mapping, supported by previously published chironomid and total organic carbon data. From the integrated results we identified time intervals when increased intensity of precipitation altered sedimentation and lake catchment erosional processes. The most prominent event occurred c. 2900 cal. a BP and is interpreted to be the result of excessive precipitation, possibly related to the climatic shift towards cooler and wetter conditions referred to as the 2.8 ka event.  相似文献   

Geomorphologic evidence for Plio‐Quaternary shortening in the southern Neuquén basin (40°S,Argentina)          下载免费PDF全文

Damien Huyghe  Bertrand Nivière  Cédric Bonnel 《地学学报》2015,27(6):426-432

A morphostructural analysis of a Pliocene flood basalt formation in the southern Neuquén basin (40°S) shows evidence of contractional deformation less than 3.5 Ma ago. This formation exhibits a general dip towards the south‐east, with relict outcrops located 100 m higher than the main source volcano, which suggests a local tilting of the lava flow. This tilt has been brought about by Plio‐Quaternary reactivation of the eastern border of the Sañico Massif along two thrusts that offset the lava flow. Another long‐wavelength bulge in the southern part of the lava flow unit indicates a possible Pliocene uplift of the North Patagonian Massif. These results provide new evidence of continuing shortening in the Neuquén basin during the Plio‐Quaternary, challenging the hypothesis that an extensional regime has existed since the end of the Miocene in this basin.  相似文献   

Thermal stresses in borehole heat exchangers          下载免费PDF全文

Selçuk Erol  Bertrand François 《国际地质力学数值与分析法杂志》2015,39(13):1450-1470

The backfilling materials of borehole heat exchangers (BHE), particularly the grout material, must provide a suitable thermal contact and ensure durability to the induced thermal stresses because of the heat loading. In this paper, the thermal stresses that occurred in BHEs because of heat injection or extraction is investigated with an analytical solution of a hollow cylinder model that is adapted for time‐dependent heat loading, the geometry of a BHE, and the thermo‐mechanical properties of surrounding ground conditions. Firstly, the hollow cylinder model is solved with the considered boundary conditions in 2D plane stress. Secondly, the temperature differences at the inner and outer circles of the cylinder are evaluated with the heat line source models for continuous and discontinuous loading to observe the impact of the heat loading schedule. The developed analytical solution for thermal stress investigation is validated with numerical models. It is demonstrated that the analytical solutions agree well with numerical results for two types of BHE configurations (co‐axial and single U‐shaped pipes). Furthermore, the calculated maximum stresses are compared with the tensile strength of grout materials obtained from Brazilian tests. It is predicted that the thermal contraction of the grout, partially constrained by the surrounding rock, generates tensile stresses that may lead to cracking in the BHE. According to the results, the stiffness of rock has a primary role on the developed tensile stresses, and the relationship between the thermal conductivity of the ground and of the grout induces a proportional impact on the magnitude of thermal stresses. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Carbon dioxide in silicate melts: A molecular dynamics simulation study     

Bertrand Guillot  Nicolas Sator 《Geochimica et cosmochimica acta》2011,75(7):1829-1857

We have performed a series of molecular dynamics simulations aimed at the evaluation of the solubility of CO₂ in silicate melts of natural composition (from felsic to ultramafic). In making in contact within the simulation cell a supercritical CO₂ phase with a silicate melt of a given composition, we have been able to evaluate (i) the solubility of CO₂ in the P-T range 1473-2273 K and 20-150 kbar, (ii) the density change experienced by the CO₂-bearing melt, (iii) the respective concentrations of CO₂ and species in the melt, (iv) the lifetime and the diffusivity of these species and (v) the structure of the melt around the carbonate groups. The main results are the following:(1) The solubility of CO₂ increases markedly with the pressure in the three investigated melts (a rhyolite, a mid-ocean ridge basalt and a kimberlite) from about ∼2 wt% CO₂ at 20 kbar to ∼25 wt% at 100 kbar and 2273 K. The solubility is found to be weakly dependent on the melt composition (as far as the present compositions are concerned) and it is only at very high pressure (above ∼100 kbar) that a clear hierarchy between solubilities occurs (rhyolite < MORB < kimberlite). Furthermore at a given pressure the calculated solubility is negatively correlated with the temperature.(2) In CO₂-saturated melts, the proportion of carbonate ions is positively correlated with the pressure at isothermal condition and is negatively correlated with the temperature at isobaric condition (and vice versa for molecular CO₂). Furthermore, at fixed (P, T) conditions the proportion of carbonate ions is higher in CO₂-undersaturated melts than in the CO₂-saturated melt. Although the proportion of molecular CO₂ decreases when the degree of depolymerization of the melt increases, it is still significant in CO₂-saturated basic and ultrabasic compositions at high temperatures. This finding is at variance with experimental data on CO₂-bearing glasses which show no evidence of molecular CO₂ as soon as the degree of depolymerization of the melt is high (e.g. basalt). These conflicting results can be reconciled with each other by noticing that a simple low temperature extrapolation of the simulation data predicts that the proportion of molecular CO₂ in basaltic melts might be negligible in the glass at room temperature.(3) The carbonate ions are found to be transient species in the liquid phase, with a lifetime increasing exponentially with the inverse of the temperature. Contrarily to a usual assumption, the diffusivity of carbonate ions into the liquid silicate is not vanishingly small with respect to that of CO₂ molecules: in MORB they differ from each other by a factor of ∼6 at 1473 K and only a factor of ∼2 at 2273 K. Although the bulk diffusivity of CO₂ is governed primarily by the diffusivity of CO₂ molecules, the carbonate ions contribute significantly to the diffusivity of CO₂ in depolymerized melts.(4) Concerning the structure of the CO₂-bearing silicate melt, the carbonate ions are found to be preferentially associated with NBO’s of the melt, with an affinity for NBOs which exceeds that for BOs by almost one order of magnitude. This result explains why the concentration in carbonate ions is positively correlated with the degree of depolymerization of the melt and diminishes drastically in fully polymerized melts where the number of NBO’s is close to zero. Furthermore, the network modifier cations are not randomly distributed in the close vicinity of carbonate groups but exhibit a preferential ordering which depends at once on the nature of the cation and on the melt composition. However at the high temperatures investigated here, there is no evidence of long lived complexes between carbonate groups and metal cations.  相似文献   

Balloon-borne observations of mid-latitude stratospheric water vapour: comparisons with HALOE and MLS satellite data     

Gwenaël Berthet  Jean-Baptiste Renard  Mélanie Ghysels  Georges Durry  Bertrand Gaubicher  Nadir Amarouche 《Journal of Atmospheric Chemistry》2013,70(3):197-219

We present here in situ measurements obtained between 1991 and 2011 in outer-vortex conditions by the ELHYSA balloon-borne frost-point hygrometer. The frost-point hygrometer profiles are used for comparisons with the satellite data from version 19 (v19) and version 3.3 (v3.3) of the HALogen Occultation Experiment (HALOE) and the Microwave Limb Sounder (MLS) respectively. Potential Vorticity mapping is applied to all data sets to remove contributions of transient tropical intrusions and polar vortex air masses and hence ensure consistent comparisons between the balloon and satellite observations. Our selected balloon in situ observations are too sparse to directly infer mid-latitude stratospheric time series for continuous comparisons with HALOE and MLS records or derive water vapour trends but can be used to validate the satellite data. A mean difference of ?0.83?±?1.58 % (?0.04?±?0.07 ppmv) is obtained between HALOE v19 data and the balloon frost-point observations (with respect to HALOE) over the 30–80 hPa altitude range. The hygrometer-HALOE differences appear time-dependent as already presented in the literature. The mean difference reaches 2.80?±?0.96 % (0.13?±?0.04 ppmv) for MLS v3.3, with MLS systematically wetter than the balloon data reflecting a systematic bias between both datasets. We use our balloon data as reference to provide some information about the HALOE-MLS difference. From post-2000 ELHYSA-HALOE and ELHYSA-MLS comparisons, we find a HALOE-MLS difference matching the expected bias, with MLS v3.3 6.60?±?2.80 % (0.27?±?0.11 ppmv) wetter than HALOE v19. From the results obtained from our balloon-satellite data comparisons, we finally discuss the issue about merging the HALOE and MLS data sets to provide stratospheric water vapour trends.  相似文献   

Airborne radar measurements of ocean wave spectra and wind speed during the grand banks ERS‐1 SAR wave experiment     

D. Vandemark  F.C. Jackson  E.J. Walsh  B. Chapron 《大气与海洋》2013,51(1):143-178

Abstract

Measurements of ocean directional wave spectra, significant wave height, and wind speed over the Grand Banks of Newfoundland were made using the combined capabilities of the radar ocean wave spectrometer (ROWS) and scanning radar altimeter (SRA). The instruments were flown aboard the NASA P‐3A aircraft in support of the Grand Banks ERS‐1 Synthetic Aperture Radar (SAR) Wave Experiment. The NASA sensors use proven techniques, which differ greatly from SAR, for estimating the directional long‐wave spectrum; thus they provide a unique set of measurements for use in evaluating SAR performance. ROWS and SRA data are combined with spectra from the SAR aboard the Canadian Centre for Remote Sensing (CCRS) CV‐580 aircraft, the first‐generation Canadian Spectral Ocean Wave Model (CSOWM) hindcast, and other available in situ measurements to assess the ERS‐1 SAR's ability to correctly resolve wave field components along a 200‐ to 300‐km flight line for four separate satellite passes. Given the complex seas present on the Grand Banks, the complementary nature of viewing the sea spectrum from the perspectives of multiple sensors and a wave prediction model is apparent. The data intercomparisons show the ERS‐1 SAR to be meeting the expected goals for measuring swell, but the data also show evidence of this remote sensor's inability to detect the shorter waves travelling in the azimuth or along‐track direction. Example SAR spectra simulations are made using a non‐linear forward transform with ROWS measurements as input. Additionally, surface wind and wave height estimates made using the ROWS altimeter channel are presented. These data demonstrate the utility of operating the system in its new combined altimeter and spectrometer configuration.  相似文献   

Evaluation of the regional climate model ALADIN to simulate the climate over North America in the CORDEX framework     

Philippe Lucas-Picher  Samuel Somot  Michel Déqué  Bertrand Decharme  Antoinette Alias 《Climate Dynamics》2013,41(5-6):1117-1137

In this study, an ensemble of four multi-year climate simulations is performed with the regional climate model ALADIN to evaluate its ability to simulate the climate over North America in the CORDEX framework. The simulations differ in their driving fields (ERA-40 or ERA-Interim) and the nudging technique (with or without large-scale nudging). The validation of the simulated 2-m temperature and precipitation with observationally-based gridded data sets shows that ALADIN performs similarly to other regional climate models that are commonly used over North America. Large-scale nudging improves the temporal correlation of the atmospheric circulation between ALADIN and its driving field, and also reduces the warm and dry summer biases in central North America. The differences between the simulations driven with different reanalyses are small and are likely related to the regional climate model’s induced internal variability. In general, the impact of different driving fields on ALADIN is smaller than that of large-scale nudging. The analysis of the multi-year simulations over the prairie and the east taiga indicates that the ALADIN 2-m temperature and precipitation interannual variability is similar or larger than that observed. Finally, a comparison of the simulations with observations for the summer 1993 shows that ALADIN underestimates the flood in central North America mainly due to its systematic dry bias in this region. Overall, the results indicate that ALADIN can produce a valuable contribution to CORDEX over North America.  相似文献   

Evaluation of regional climate simulations for air quality modelling purposes     

Laurent Menut  Om P. Tripathi  Augustin Colette  Robert Vautard  Emmanouil Flaounas  Bertrand Bessagnet 《Climate Dynamics》2013,40(9-10):2515-2533

In order to evaluate the future potential benefits of emission regulation on regional air quality, while taking into account the effects of climate change, off-line air quality projection simulations are driven using weather forcing taken from regional climate models. These regional models are themselves driven by simulations carried out using global climate models (GCM) and economical scenarios. Uncertainties and biases in climate models introduce an additional “climate modeling” source of uncertainty that is to be added to all other types of uncertainties in air quality modeling for policy evaluation. In this article we evaluate the changes in air quality-related weather variables induced by replacing reanalyses-forced by GCM-forced regional climate simulations. As an example we use GCM simulations carried out in the framework of the ERA-interim programme and of the CMIP5 project using the Institut Pierre-Simon Laplace climate model (IPSLcm), driving regional simulations performed in the framework of the EURO-CORDEX programme. In summer, we found compensating deficiencies acting on photochemistry: an overestimation by GCM-driven weather due to a positive bias in short-wave radiation, a negative bias in wind speed, too many stagnant episodes, and a negative temperature bias. In winter, air quality is mostly driven by dispersion, and we could not identify significant differences in either wind or planetary boundary layer height statistics between GCM-driven and reanalyses-driven regional simulations. However, precipitation appears largely overestimated in GCM-driven simulations, which could significantly affect the simulation of aerosol concentrations. The identification of these biases will help interpreting results of future air quality simulations using these data. Despite these, we conclude that the identified differences should not lead to major difficulties in using GCM-driven regional climate simulations for air quality projections.  相似文献   

Numerical Simulations of the Microscale Heterogeneities of Turbulence Observed on a Complex Site     

Hanane Zaïdi  Eric Dupont  Maya Milliez  Luc Musson-Genon  Bertrand Carissimo 《Boundary-Layer Meteorology》2013,147(2):237-259

We simulate the microscale heterogeneities of turbulent variables observed at a complex site for different wind directions. The atmospheric computational fluid dynamics (CFD) results are compared with an ensemble of 36 months of data collected at the experimental site SIRTA “Site Instrumental de Recherche par Télédétection Atmosphérique”, located near Paris (France) in a semi-urban environment. The experimental data show that the normalized turbulent kinetic energy (TKE) k/U ² (where k is TKE and U is the wind speed) at 10-m height, for two different locations, is highly dependent on wind direction and strongly influenced by trees. These measurements show a strong increase of the normalized TKE downstream of the forest canopies with a large variability within the 36-month period in part due to the variation of the tree foliage. The numerical simulations are carried out using the CFD code Code_Saturne with the standard k?ε closure, in neutral stratification. The buildings are taken into account explicitly in the mesh and the forested areas are modelled with two approaches: the classical roughness wall law and a drag porosity. A comparison has been performed between the calculated values and the median of measured values of the normalized TKE and the normalized friction velocity, for each wind sector of 10°. A very good agreement is obtained with the drag porosity model, whereas the classical roughness law leads to a strong underestimation downstream of the forested areas. However, this large improvement of the results using the drag porosity model can only be obtained with a refinement of the grid, especially in forested areas, and an accurate land-use map.  相似文献