Tracing the temporal evolution of soil redistribution rates in an agricultural landscape using 239+240Pu and 10Be     

Francesca Calitri  Michael Sommer  Kevin Norton  Arnaud Temme  Dagmar Brandová  Raquel Portes  Marcus Christl  Mike E. Ketterer  Markus Egli 《地球表面变化过程与地形》2019,44(9):1783-1798

Two principal groups of processes shape mass fluxes from and into a soil: vertical profile development and lateral soil redistribution. Periods having predominantly progressive soil forming processes (soil profile development) alternate with periods having predominantly regressive processes (erosion). As a result, short-term soil redistribution – years to decades – can differ substantially from long-term soil redistribution; i.e. centuries to millennia. However, the quantification of these processes is difficult and consequently their rates are poorly understood. To assess the competing roles of erosion and deposition we determined short- and long-term soil redistribution rates in a formerly glaciated area of the Uckermark, northeast Germany. We compared short-term erosion or accumulation rates using plutonium-239 and -240 (^239+240Pu) and long-term rates using both in situ and meteoric cosmogenic beryllium-10 (¹⁰Be). Three characteristic process domains have been analysed in detail: a flat landscape position having no erosion/deposition, an erosion-dominated mid-slope, and a deposition-dominated lower-slope site. We show that the short-term mass erosion and accumulation rates are about one order of magnitude higher than long-term redistribution rates. Both, in situ and meteoric ¹⁰Be provide comparable results. Depth functions, and therefore not only an average value of the topsoil, give the most meaningful rates. The long-term soil redistribution rates were in the range of −2.1 t ha^-1 yr^-1 (erosion) and +0.26 t ha^-1 yr^-1 (accumulation) whereas the short-term erosion rates indicated strong erosion of up to 25 t ha^-1 yr^-1 and accumulation of 7.6 t ha^-1 yr^-1. Our multi-isotope method identifies periods of erosion and deposition, confirming the ‘time-split approach’ of distinct different phases (progressive/regressive) in soil evolution. With such an approach, temporally-changing processes can be disentangled, which allows the identification of both the dimensions of and the increase in soil erosion due to human influence. © 2019 John Wiley & Sons, Ltd.  相似文献   

Hydrous olivine alteration on Mars and Earth     

Zoltn Vci  Carl B. Agee  Christopher D. K. Herd  Erin Walton  Oliver Tschauner  Karen Ziegler  Vitali B. Prakapenka  Eran Greenberg  Sylvia Monique‐Thomas 《Meteoritics & planetary science》2020,55(5):1011-1030

Hydrous alteration of olivine macrocrysts in a Martian olivine phyric basalt, NWA 10416, and a terrestrial basalt from southern Colorado are examined using SEM, EPMA, TEM, and µXRD techniques. The olivines in the meteorite contain linear nanotubes of hydrous material, amorphous areas, and fluid dissolution textures quite distinct from alteration identified in other Martian meteorites. Instead, they bear resemblance to terrestrial deuteric alteration features. The presence of the hydrous alteration phase Mg‐laihunite within the olivines has been confirmed by µXRD analysis. The cores of the olivines in both Martian and terrestrial samples are overgrown by unaltered rims whose compositions match those of a separate population of groundmass olivines, suggesting that the core olivines are xenocrysts whose alteration preceded crystallization of the groundmass. The terrestrial sample is linked to deep crustal metasomatism and the “ignimbrite flare‐up” of the Oligocene epoch. The comparison of the two samples suggests the existence of an analogous relatively water‐rich magmatic reservoir on Mars.  相似文献   

The L_X–T relation and intracluster gas fractions of X-ray clusters     

Monique Arnaud  August E. Evrard 《Monthly notices of the Royal Astronomical Society》1999,305(3):631-640

  相似文献   

Schooling behaviour and environmental forcing in relation to anchoveta distribution: An analysis across multiple spatial scales   总被引：7，自引：4，他引：3  

Arnaud Bertrand  Franois Gerlotto  Sophie Bertrand  Mariano Gutirrez  Luis Alza  Andres Chipollini  Erich Díaz  Pepe Espinoza  Jesús Ledesma  Roberto Quesqun  Salvador Peraltilla  Francisco Chavez 《Progress in Oceanography》2008,79(2-4):264

The Peruvian anchovy or anchoveta (Engraulis ringens) supports the highest worldwide fishery landings and varies in space and time over many scales. Here we present the first comprehensive sub-mesocale study of anchoveta distribution in relation to the environment. During November 2004, we conducted a behavioural ecology survey off central Peru and used a series of observational and sampling tools including SST and CO₂ sensors, Niskin bottles, CTD probes, zooplankton sampling, stomach content analysis, echo-sounder, multibeam sonar, and bird observations. The sub-mesoscale survey areas were chosen from mesoscale acoustic surveys. A routine coast-wide (2000 km) acoustic survey performed just after the sub-mesoscale surveys, provided information at an even larger population scale. The availability of nearly concurrent sub-mesoscale, mesoscale and coast-wide information on anchoveta distribution allowed for a unique multi-scale synthesis. At the sub-mesoscale (100s m to km) physical processes (internal waves and frontogenesis) concentrated plankton into patches and determined anchoveta spatial distribution. At the mesoscale (10s km) location relative to the zone of active upwelling (and age of the upwelled water) and the depth of the oxycline had strong impacts on the anchoveta. Finally, over 100s km the size of the productive area, as defined by the upwelled cold coastal waters, was the determining factor. We propose a conceptual view of the relative importance of social behaviour and environmental (biotic and abiotic) processes on the spatial distribution of anchoveta. Our ecological space has two y-axis; one based on self-organization (social behaviour), and the other based on the environmental processes. At scales from the individual (10s cm), to the nucleus (m), social behaviour (e.g. the need to school) drives spatial organization. At scales larger than the school, environmental forces are the main driver of fish distribution. The conceptual ecosystem models presented in this paper may provide the final links needed to develop accurate forecasts of the spatial distribution of anchoveta over multiple scales.  相似文献   

Impacts of Kelvin wave forcing in the Peru Humboldt Current system: Scenarios of spatial reorganizations from physics to fishers   总被引：2，自引：1，他引：1  

Sophie Bertrand  Boris Dewitte  Jorge Tam  Erich Díaz  Arnaud Bertrand   《Progress in Oceanography》2008,79(2-4):278

Because climate change challenges the sustainability of important fish populations and the fisheries they support, we need to understand how large scale climatic forcing affects the functioning of marine ecosystems. In the Humboldt Current system (HCS), a main driver of climatic variability is coastally-trapped Kelvin waves (KWs), themselves originating as oceanic equatorial KWs. Here we (i) describe the spatial reorganizations of living organisms in the Humboldt coastal system as affected by oceanic KWs forcing, (ii) quantify the strength of the interactions between the physical and biological component dynamics of the system, (iii) formulate hypotheses on the processes which drive the redistributions of the organisms, and (iv) build scenarios of space occupation in the HCS under varying KW forcing. To address these questions we explore, through bivariate lagged correlations and multivariate statistics, the relationships between time series of oceanic KW amplitude (TAO mooring data and model-resolved baroclinic modes) and coastal Peruvian oceanographic data (SST, coastal upwelled waters extent), anchoveta spatial distribution (mean distance to the coast, spatial concentration of the biomass, mean depth of the schools), and fishing fleet statistics (trip duration, searching duration, number of fishing sets and catch per trip, features of the foraging trajectory as observed by satellite vessel monitoring system). Data sets span all or part of January 1983 to September 2006. The results show that the effects of oceanic KW forcing are significant in all the components of the coastal ecosystem, from oceanography to the behaviour of the top predators – fishers. This result provides evidence for a bottom-up transfer of the behaviours and spatial stucturing through the ecosystem. We propose that contrasting scenarios develop during the passage of upwelling versus downwelling KWs. From a predictive point of view, we show that KW amplitudes observed in the mid-Pacific can be used to forecast which system state will dominate the HCS over the next 2–6 months. Such predictions should be integrated in the Peruvian adaptive fishery management.  相似文献   

The interpretation of XUV rocket measurements of intensity ratios of solar spectral lines of the lithiumlike ions O vi,Ne viii,and Mg x     

L. Heroux  M. Cohen  Monique Malinovsky 《Solar physics》1972,23(2):369-393

A rocket borne spectrometer was flown to measure absolute intensities of extreme ultraviolet spectral lines from the three ions O vi, Ne viii, and Mg x present in the Sun. From these measurements, intensity ratios of lines from O vi, ratios of lines from Ne viii, and ratios of lines from Mg x were formed. These experimental ratios were compared with ratios calculated by using specific theoretical values of the ionization equilibrium in which dielectronic recombination was included in the processes establishing ionization balance. The effects of the electron density and temperature gradient on the temperature distribution of the flux of the spectral lines in the solar atmosphere have been taken into account in the calculations of the ratios. The agreement between the experimental and calculated ratios is good for the ions Ne viii and Mg x and satisfactory for the ion O vi for which the calculated ratio is subject to large uncertainties. A reliable measurement of the electron temperature in the lower corona was obtained from the experimental ratios for Mg x. This experimental temperature is in good agreement with the emission temperature of the spectral lines of Mg x predicted from the theoretical values of the ionization equilibrium. The design and photometric calibration of a new rocket spectrometer developed to measure the intensity ratios over the broad spectral region 50 to 1250 Å are also described.  相似文献   

A multiplex imaging spectrometer for low energyX-ray astronomy     

R. Rocchia  M. Arnaud  C. Blondel  M. Cantin  B. Mougin  R. Rothenflug  A. Tarrius 《Astrophysics and Space Science》1983,96(2):361-374

A multiplexX-ray image analyser is described. It consists in a time-modulated coded aperture associated with a solid state detector. The system combines the high efficiency and good spectral resolution of solid state spectrometers with the spatial resolution of the coded aperture (200 ).The device can be installed at the focus of a grazing incidence telescope to make images and spectra of faint astronomicalX-ray sources.  相似文献   

Large‐eddy simulation of small‐scale surface effects on the convective boundary‐layer structure     

Shaohua Shen  Monique Y. Leclerc 《大气与海洋》2013,51(4):717-731

Abstract

The effects of small‐scale surface inhomogeneities on the turbulence structure in the convective boundary layer are investigated using a high‐resolution large‐eddy simulation model. Surface heat flux variations are sinusoidal and two‐dimensional, dividing the total domain into a checkerboard‐like pattern of surface hot spots with a 500‐m wavelength in the x and y directions, or 1/4 of the domain size. The selected wind speeds were 1 and 4 m s^‐l, respectively. As a comparison, a simulation of the turbulence structure was performed over a homogeneous surface.

When the wind speed is light, surface heat flux variations influence the horizontally averaged turbulence statistics, including the higher moments despite the small characteristic length of the surface perturbation. Stronger mean wind speeds weaken the effects of inhomogeneous surface conditions on the turbulence structure in the convective boundary layer.

Results from conditional sampling show that when the mean wind speed is small, weak mean circulations occur, with updraft branches above the high heat flux regions and down‐draft branches above the low heat flux regions. The inhomogeneous surface induces significant differences in the turbulence statistics between the high and low heat flux regions. However, the effect of the surface perturbations weaken rapidly when the mean wind speed increases. This research has implications in the explanation of the large‐scale variability commonly encountered in aircraft observations of atmospheric turbulence.  相似文献   

Frequency and intensity of high-altitude floods over the last 3.5 ka in northwestern French Alps (Lake Anterne)     

Charline Giguet-Covex  Fabien Arnaud  Dirk Enters  Jérôme Poulenard  Laurent Millet  Pierre Francus  Fernand David  Pierre-Jérôme Rey  Bruno Wilhelm  Jean-Jacques Delannoy 《Quaternary Research》2012,77(1):12-22

In central Western Europe, several studies have shown that colder Holocene periods, such as the Little Ice Age, also correspond to wet periods. However, in mountain areas which are highly sensitive to erosion processes and where precipitation events can be localized, past evolution of hydrological activity might be more complicated. To assess these past hydrological changes, a paleolimnological approach was applied on a 13.4-m-long sediment core taken in alpine Lake Anterne (2063 m asl) and representing the last 3.5 ka. Lake sedimentation is mainly composed of flood deposits triggered by precipitation events. Sedimentological and geochemical analyses show that floods were more frequent during cold periods while high-intensity flood events occurred preferentially during warmer periods. In mild temperature conditions, both flood patterns are present. This underlines the complex relationship between flood hazards and climatic change in mountain areas. During the warmer and/or dryer times of the end of Iron Age and the Roman Period, both the frequency and intensity of floods increased. This is interpreted as an effect of human-induced clearing for grazing activities and reveals that anthropogenic interferences must be taken into account when reconstructing climatic signals from natural archives.  相似文献   

Microbial diversity in contaminated soils along the T22 trench of the Chernobyl experimental platform     

Virginie Chapon  Laurie Piette  Marie-Hélène Vesvres  Frédéric Coppin  Claire Le Marrec  Richard Christen  Nicolas Theodorakopoulos  Laureline Février  Sviatoslav Levchuk  Arnaud Martin-Garin  Catherine Berthomieu  Claire Sergeant 《Applied Geochemistry》2012

The diversity of bacterial communities exposed to radioactive contamination in Chernobyl soils was examined by a combination of molecular and culture-based approaches. A set of six radioactive soil samples, exhibiting high levels of ¹³⁷Cs contamination, were collected from the T22 trench. Three samples were also collected in nearby soils with low contamination. Complex bacterial community structures were observed in both highly and weakly contaminated samples, using a molecular approach targeting the 16S rRNA gene. However, the presence of specific populations within samples from highly contaminated soils could not be revealed by statistical analysis of the DGGE profiles. More than 200 culturable isolates, representative of dominant morphotypes, were grouped into 83 Operational Taxonomic Units (OTUs) and affiliated to Firmicutes, Actinobacteria, Alpha-, Beta-, Gamma-Proteobacteria and Bacteroïdetes. No specific pattern linked to contamination was observed for these culturable bacteria. The results show that both highly and weakly contaminated soils host a wide diversity of bacteria, suggesting that long term exposure to radionuclides does not lead to the extinction of bacterial diversity.  相似文献