Holocene hydrological changes in south-western Mediterranean as recorded by lake-level fluctuations at Lago Preola,a coastal lake in southern Sicily,Italy     

Michel Magny  Boris Vannière  Camilla Calo  Laurent Millet  Aurélie Leroux  Odile Peyron  Gianni Zanchetta  Tommaso La Mantia  Willy Tinner 《Quaternary Science Reviews》2011,30(19-20):2459-2475

This paper presents a high-resolution lake-level record for the Holocene at Lago Preola (Sicily, southern Italy) based on a specific sedimentological approach, with a chronology derived from AMS radiocarbon dates. It gives evidence of three major successive palaeohydrological periods, with (1) a pronounced dryness during the early Holocene until ca 10300 cal BP, (2) a highstand from ca 10300 to 4500 cal BP, and (3) a marked lowstand from 4500 cal BP to present. Large amplitude lake-level fluctuations characterise two transition phases at ca 10300–9000 and 6400–4500 cal BP. Period 2 was interrupted between 8300 and 7000 cal BP by a dry phase that was punctuated to ca 7300 cal BP by the deposition of a tephra from neighbouring Pantelleria Island. Comparisons of the Preola record with other palaeohydrological records along north–south and west–east transects in the Mediterranean show contrasting patterns of hydrological changes: north (south) of around 40°N latitude, the records highlight a mid-Holocene period characterised by lake-level minima (maxima). Humid mid-Holocene conditions over the Mediterranean south of 40°N were probably linked to a strong weakening of the Hadley cell circulation and of monsoon winds. We suggest that the maximum of humidity in the Mediterranean during the mid-Holocene was characterised by humid winters to the north of 40°N and humid summers to the south. On a multi-centennial scale, the high-resolution palaeohydrological reconstructions in the central Mediterranean area reveal a strong climate reversal around 4500–4000 cal BP, with contrasting changes in the hydrological cycle. In addition to seasonal and inter-hemispherical changes related to orbital forcing, this major oscillation might be related to non-linear responses of the climatic system to the gradual decrease in summer insolation at northern latitudes. Another major climate oscillation around 7500–7000 cal BP may have resulted from the combined effects of (1) a strong rate of change in insolation, and (2) variations in solar activity. Finally, comparisons of the Preola lake-level record with Sicilian pollen records suggest a strong influence of moisture availability on vegetation development in Sicily. Very dry early Holocene conditions probably prevented the expansion of coastal evergreen forests, while decreasing moisture availability since the onset of the late Holocene may have exacerbated effects of intensive land-use.  相似文献   

Holocene palaeohydrological changes in the northern Mediterranean borderlands as reflected by the lake-level record of Lake Ledro,northeastern Italy     

Michel Magny  Sébastien Joannin  Didier Galop  Boris Vannière  Jean Nicolas Haas  Michele Bassetti  Paolo Bellintani  Romana Scandolari  Marc Desmet 《Quaternary Research》2012,77(3):382-396

A lake-level record of Lake Ledro (northern Italy) spans the entire Holocene with a chronology derived from 51 radiocarbon dates. It is based on a specific sedimentological approach that combines data from five sediment profiles sampled in distinct locations in the littoral zone. On a millennial scale, the lake-level record shows two successive periods from 11,700 to 4500 cal yr BP and from 4500 cal yr BP to the present, characterized by lower and higher average lake levels, respectively. In addition to key seasonal and inter-hemispherical changes in insolation, the major hydrological change around 4500 cal yr BP may be related to a non-linear response of the climate system to orbitally-driven gradual decrease in insolation. The Ledro record questions the notion of an accentuated summer rain regime in the northern Mediterranean borderlands during the boreal insolation maximum. Moreover, the Ledro record highlights that the Holocene was punctuated by successive centennial-scale highstands. Correlations with the Preboreal oscillation and the 8.2 ka event, and comparison with the atmospheric ¹⁴C residual record, suggest that short-lived lake-level fluctuations developed at Ledro in response to (1) final steps of the deglaciation in the North Atlantic area and (2) variations in solar activity.  相似文献   

Cooling of the Kärdla impact crater: II. Impact and geothermal modeling     

Argo J ELEHT  Kalle KIRSIME  Jüri PLADO  Evelin VERSH  Boris IVANOV 《Meteoritics & planetary science》2005,40(1):21-33

Abstract— Impact and geothermal modeling was performed to explain hydrothermal alteration in a 4 km marine complex crater at Kärdla, Estonia. The impact modeling was used to simulate the formation of the crater and the post‐impact temperature distribution in crater environment. The geothermal modeling accounted for coupled heat transfer and multi‐phase fluid flow in a variably saturated medium. The modeling results suggest that strong convective fluid flow was initiated. During the first stage, the cooling was rapid due to the effect of the latent heat of vaporization, which efficiently decreased the temperature to the boiling point. The modeling results are consistent with geological observations.  相似文献   

Globular cluster systems in low-luminosity early-type galaxies near the Fornax cluster centre     

Lilia P. Bassino  Tom Richtler  Boris Dirsch 《Monthly notices of the Royal Astronomical Society》2006,367(1):156-168

We present a photometric study of the globular cluster systems (GCSs) of the Fornax cluster galaxies NGC 1374, NGC 1379 and NGC 1387. The data consist of images from the wide-field MOSAIC imager of the Cerro Tololo Inter-American Observatory (CTIO) 4-m telescope, obtained with Washington C and Kron–Cousins R filters. The images cover a field of  36 × 36 arcmin²  , corresponding to  200 × 200 kpc²  at the Fornax distance. Two of the galaxies, NGC 1374 and NGC 1379, are low-luminosity ellipticals while NGC 1387 is a low-luminosity lenticular. Their cluster systems are still embedded in the cluster system of NGC 1399. Therefore, the use of a large field is crucial and some differences to previous work can be explained by this. The colour distributions of all GCSs are bimodal. NGC 1387 presents a particularly distinct separation between red and blue clusters and an overproportionally large population of red clusters. The radial distribution is different for blue and red clusters, red clusters being more concentrated towards the respective galaxies. The different colour and radial distributions point to the existence of two globular cluster subpopulations in these galaxies. Specific frequencies are in the range   S_N = 1.4–2.4  , smaller than the typical values for elliptical galaxies. These galaxies might have suffered tidal stripping of blue globular clusters by NGC 1399.  相似文献   

The role of nonlinear hardening/softening in probabilistic elasto‐plasticity     

Kallol Sett  Boris Jeremić  M. Levent Kavvas 《国际地质力学数值与分析法杂志》2007,31(7):953-975

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WSO-UV progress and expectations     

Boris Shustov  Ana I. Gómez de Castro  Mikhail Sachkov  Alexander Moisheev  Evgeny Kanev  Javier López-Santiago  Oleg Malkov  Dmitry Nasonov  G. Belén Perea  Néstor Sánchez  Igor Savanov  Andrey Shugarov  Sergey Sichevskiy  Oleg Vlasenko  Javier Yañez 《Astrophysics and Space Science》2014,354(1):155-161

The World Space Observatory Ultraviolet (WSO-UV) is the space mission that will grant access to the ultraviolet (UV) range in the post Hubble epoch. WSO-UV is equipped with instrumentation for imaging and spectroscopy and it is fully devoted to UV astronomy. In this article, we outline the WSO-UV mission model and present the current status of the project.  相似文献   

Variability of extreme events in the Colombian Pacific and Caribbean catchment basins     

Isabel Hoyos  Astrid Baquero-Bernal  Daniela Jacob  Boris A. Rodríguez 《Climate Dynamics》2013,40(7-8):1985-2003

This paper analyses the behavior of extreme events of surface precipitation and temperature inside the Pacific and Caribbean Catchment Basins in Colombia using several datasets such as observations, reconstructed data, NCEP-NCAR and ERA-40 reanalyses and data from the regional model REMO. We use an extreme value method that selects the time series excesses over a nonstationary threshold and adjusts them to a generalized Pareto distribution. The goodness of fit is evaluated through a test that includes the Cramer–von Mises, Kolmogorov–Smirnov and Anderson–Darling statistics and the p values generated by parametric bootstrap resampling. The test not only evaluates the goodness of fit but also the threshold choice. The parameters are presented in maps that allow recognition of the features of the extreme behaviour inside the catchment basins, and differences and similarities between them. Maps of return periods for the maximum extreme events are also presented. A strong influence of the El Niño–Southern oscillation on the extreme events of both temperature and precipitation is found in the two catchment basins.  相似文献   

Rain scavenging of soluble gases by non-evaporating and evaporating droplets from inhomogeneous atmosphere     

Tov Elperin  Andrew Fominykh  Boris Krasovitov 《Meteorology and Atmospheric Physics》2013,122(3-4):215-226

We suggest a one-dimensional model of precipitation scavenging of soluble gaseous pollutants by non-evaporating and evaporating droplets that is valid for arbitrary initial vertical distribution of soluble trace gases in the atmosphere. It is shown that for low gradients of soluble trace gases in the atmosphere, scavenging of gaseous pollutants is governed by a linear wave equation that describes propagation of a wave in one direction. The derived equation is solved by the method of characteristics. Scavenging coefficient and the rates of precipitation scavenging are calculated for wet removal of sulfur dioxide (SO₂) and ammonia (NH₃) using measured initial distributions of trace gases. It is shown that scavenging coefficient for arbitrary initial vertical distribution of soluble trace gases in the atmosphere is non-stationary and height-dependent. In case of exponential initial distribution of soluble trace gases in the atmosphere, scavenging coefficient for non-evaporating droplets in the region between the ground and the position of a scavenging front is a product of rainfall rate, solubility parameter, and the growth constant in the formula for the initial profile of a soluble trace gas in the atmosphere. This expression yields the same estimate of scavenging coefficient for sulfur dioxide scavenging by rain as field estimates presented in McMahon and Denison (1979). It is demonstrated that the smaller the slope of the concentration profile the higher the value of a scavenging coefficient.  相似文献   

Ultraviolet Studies Of Interacting Binaries     

Boris T. Gäansicke  Domitilla De Martino  Thomas R. Marsh  Carole A. Haswell  Christian Knigge  Knox S. Long  Steven N. Shore 《Astrophysics and Space Science》2006,303(1-4):53-68

Interacting Binaries consist of a variety of stellar objects in different stages of evolution and those containing accreting compact objects still represent a major challenge to our understanding of not only close binary evolution but also of the chemical evolution of the Galaxy. These end-points of binary star evolution are ideal laboratories for the study of accretion and outflow processes, and provide insight on matter under extreme physical conditions. One of the key-questions of fundamental relevance is the nature of SN Ia progenitors. The study of accreting compact binary systems relies on observations over the entire electromagnetic spectrum and we outline here those unresolved questions for which access to the ultraviolet range is vital, as they cannot be addressed by observations in any other spectral region.An erratum to this article can be found at  相似文献   

Photon-stimulated desorption of Na from a lunar sample: temperature-dependent effects     

Boris V. Yakshinskiy 《Icarus》2004,168(1):53-59

We report recent results in an investigation of source mechanisms for the origin of Na atoms in tenuous planetary atmospheres, focusing on non-thermal processes. Experiments include photon stimulated desorption (PSD), electron stimulated desorption (ESD), and ion sputtering of Na atoms from the surface of a lunar basalt sample. Bombardment of the sodium covered surface by 3 keV Ar⁺ ions removes Na from the surface by sputtering into vacuum and by implantation into the sample bulk. Bombardment of the Na covered surface by ultraviolet photons or by low energy electrons (E>3 to 4 eV) causes desorption of “hot” Na atoms. These results are consistent with our previous measurements of sodium and potassium desorption from a silica surface: electron- or photon-induced charge transfer from the substrate to the ionic adsorbate causes formation of a neutral alkali atom in a repulsive configuration, from which desorption occurs. There is a strong temperature-dependence of Na ESD and PSD signals, under conditions where the Na surface coverage is constant and thermal desorption is negligible. The yield of Na (atoms/photon) increases by 10× from 100 to 470 K; an activation energy of ∼20 meV is measured. This phenomenon may be attributed to thermally-induced changes in surface bonding sites, and will affect recent modeling of the sodium atmospheres of Mercury and the Moon.  相似文献