Early to mid‐Holocene climate change at Lago dell'Accesa (central Italy): climate signal or anthropogenic bias?     

Walter Finsinger  Daniele Colombaroli  Jacques‐Louis De Beaulieu  Verushka Valsecchi  Boris Vannière  Elisa Vescovi  Emmanuel Chapron  André F. Lotter  Michel Magny  Willy Tinner 《第四纪科学杂志》2010,25(8):1239-1247

Despite the high potential of pollen records for climate reconstruction, pollen–climate relationships may be biased due to past and present human activities on the landscape. We use (i) transfer functions based on modern pollen–climate relationships to infer seasonal temperature and summer precipitation for the period 11 500–4500 cal. a BP and (ii) lake‐level change records based on different sedimentary proxies in multiple cores that are mainly indicative for summer hydrology at Lago dell'Accesa (central Italy). Quantitative reconstructions indicate lowest summer precipitation during two phases (8500–7700 cal. a BP and after 6000 cal. a BP) and a gradual winter temperature increase from 11 500 to ca. 8000 cal. a BP. Lowest summer precipitation was reconstructed during these phases characterised by vegetation shifts from open forests dominated by summergreen oaks (Quercus) to forests dominated by evergreen oaks (Quercus ilex), which are at present most abundant where summer drought is stronger. Similarly, the lake‐level record indicates two long‐lasting low summer precipitation phases (8800–7700 and 6400–4400 cal. a BP) that were interrupted by short‐term high summer precipitation events. Based on the broad agreement between the pollen‐inferred summer precipitation and the low‐frequency lake‐level changes, we suggest that the duration of the high summer precipitation events may have been too short to maintain drought‐sensitive trees, which may have been affected by high mortality rates when summer dry conditions returned. Although past and modern pollen–climate relationships may very likely have been affected by human activities since the Neolithic (i.e. when exploitation of the landscape started), we reject the hypothesis of a significant anthropogenic bias in the pollen‐based climate reconstruction. In addition, we suggest that pollen‐based and lake‐level reconstructions may have different inherent abilities of capturing high‐ and low‐frequency precipitation signals. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

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   

On metal diagenesis in contaminated sediments of the Deûle river (northern France)     

L. Lesven  B. Lourino-Cabana  G. Billon  P. Recourt  B. Ouddane  O. Mikkelsen  A. Boughriet 《Applied Geochemistry》2010

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A comprehensive set of simulations of high-velocity collisions between main-sequence stars     

Marc Freitag †  Willy Benz 《Monthly notices of the Royal Astronomical Society》2005,358(4):1133-1158

We report on a very large set of simulations of collisions between two main-sequence (MS) stars. These computations were carried out with the smoothed particle hydrodynamics method. Realistic stellar structure models for evolved MS stars were used. In order to sample an extended domain of initial parameters space (masses of the stars, relative velocity and impact parameter), more than 14 000 simulations were carried out. We considered stellar masses ranging between 0.1 and  75 M_⊙  and relative velocities up to a few thousand km s⁻¹. To limit the computational burden, a resolution of 1000–32 000 particles per star was used. The primary goal of this study was to build a complete data base from which the result of any collision can be interpolated. This allows us to incorporate the effects of stellar collisions with an unprecedented level of realism into dynamical simulations of galactic nuclei and other dense stellar clusters. We make the data describing the initial condition and outcome (mass and energy loss, angle of deflection) of all our simulations available on the Internet. We find that the outcome of collisions depends sensitively on the stellar structure and that, in most cases, using polytropic models is inappropriate. Published fitting formulae for the collision outcomes, established from a limited set of collisions, prove of limited use because they do not allow robust extrapolation to other stellar structures or relative velocities.  相似文献   

Evidence of methylmercury production and modification of the microbial community structure in estuary sediments contaminated with wastewater treatment plant effluents     

Ramond JB  Petit F  Quillet L  Ouddane B  Berthe T 《Marine pollution bulletin》2011,62(5):1073-1080

The Seine’s estuary (France) waters are the receptacle of effluents originating from wastewater treatment plants (WWTP). In this estuary, mudflats are deposition zones for sediments and their associated contaminants, and play an essential role in the mercury (Hg) biogeochemical cycle mainly due to indigenous microorganisms. Microcosms were used to assess the impact of WWTP-effluents on mercury methylation by monitoring Hg species (total dissolved Hg in porewater, methylmercury and total mercury) and on microbial communities in sediments. After effluent amendment, methylmercury (MeHg) concentrations increased in relation with the total Hg and organic matter content of the WWTP-effluents. A correlation was observed between MeHg and acid-volatile-sulfides concentrations. Quantification of sulfate-reducing microorganisms involved in Hg methylation showed no increase of their abundance but their activity was probably enhanced by the organic matter supplied with the effluents. WWTP-effluent spiking modified the bacterial community fingerprint, mainly influenced by Hg contamination and the organic matter amendment.  相似文献   

Integrated Electrolytic Treatment and Adsorption for the Removal of Melanoidins     

Yamini Satyawali  Willy Verstraete  Malini Balakrishnan 《洁净——土壤、空气、水》2010,38(4):409-412

This work investigates electrolytic treatment and activated carbon adsorption for the removal of melanoidins, the recalcitrant coloring component in fermentation industry wastewaters. A 10% solution of synthetic melanoidins was electrolytically reduced and simultaneously oxidized in an electrolytic cell, thereby altering its reactivity. Adsorption studies using granular activated carbon were conducted using both control and electrolyzed streams. The filterability, surface tension and capillary suction time of the samples were also determined. The reduced melanoidins stream exhibited both a high chemical oxygen demand (COD) removal of 79% and a high color removal of 77% upon activated carbon adsorption. In comparison with the oxidized fraction, the reduced samples displayed enhanced filtration flux as well as decreased capillary suction time, thus indicating better filterability. Furthermore, a decline in surface tension was also observed confirming the decreased hydrophobicity of the reduced melanoidins.  相似文献   

Untersuchungen über die Fruchtbarkeit des Blaufelchens (Coregonus wartmanni Bloch) im Bodensee     

Von Arne von kraft  Willy Nümann  Hans M. Peters 《Aquatic Sciences - Research Across Boundaries》1963,25(1):84-118

Ohne Zusammenfassung Herrn Prof. Dr. P. Meyer-Waarden zum 60. Geburtstag gewidmet Mit Unterstützung des Ministeriums für Ern?hrung, Landwirtschaft und Forsten, Baden-Württemberg, und des Bayerischen Staatsministeriums für Ern?hrung, Landwirtschaft und Forsten.  相似文献   

Strong ground acceleration seismic hazard in Greece and neighboring regions   总被引：1，自引：0，他引：1  

Paul W. Burton  Yebang Xu  G. -Akis Tselentis  Ethimios Sokos  Willy Aspinall 《Soil Dynamics and Earthquake Engineering》2003,23(2):159-181

In an early paper [Tectonophysics 117 (1985) 259] seismic hazard in Greece was analyzed using a relatively homogeneous earthquake catalogue spanning 1900–1978 and a strong motion attenuation relationship adapted to use in Greece. Improved seismic hazard analyses are obtained here using Gumbel's asymptotic extreme value distribution applied to peak horizontal ground acceleration occurrence, but now taking into account the increased length and quality of earthquake catalogue data spanning 1900–1999 and the burgeoning information on earthquake strong motion data and attenuation relationships appropriate for Europe and, explicitly, Greece. Seismic acceleration hazard results tabulated for six cities reveal (e.g. using arbitrarily the 50-year p.g.a. with 90% probability of not being exceeded) changes of about 10% in the new calculated values: two cities show an increase and four a decrease. These are relatively small and reassuring adjustments.Inspection of the available attenuation relationships leads to a preference for the models of Theodulidis and Papazachos, particularly with the model modification to produce a ‘stiff soil’ site relationship, as these relationships explicitly exploit the Greek strong motion database. Isoacceleration maps are produced for Greece as a whole from each attenuation relationship inspected. The final set of maps based on the Theodulidis and Papazachos models provide a foundation for comparison with the Seismic Hazard Zones adopted in the New Greek Seismic Code where scope can be found to modify zone shape and the level at which p.g.a.s are set. It should be noted that the generation of the present isoacceleration maps is based on a seismogenic zone-free methodology, independent of any Euclidean zoning assumptions.  相似文献   

A palaeovalley system in the floodplain of the Mark River (Central Belgium)     

Willy Huybrechts 《地球表面变化过程与地形》1985,10(3):247-255

A borehole programme on the floodplain of the River Mark has revealed an important fossilized fluvial system, now invisible in the present landscape. The palaeovalley meanders gently and is up to 200 m wide and 8 m deep. It is eroded in older fluvial sands, probably of Pleniglacial age, overlain by an aeolian cover of varying thickness. As indicated by several radiocarbon dates of the valley fill deposits, the erosion of the system took place in the pre-Holocene period. The filling proceeded in three phases. The morphological implications of each phase and their spatial extension are demonstrated. Most of the vertical fill consists of a sandy loam to loam. Around 9000 yr BP, the accumulation of an organic facies (mainly woodpeat) started, followed by the deposition of a weak fluvial clay. At 1400 yr BP the filling of the palaeovalley was complete.  相似文献   

Crabs,leeches and trypanosomes: an unholy trinity?     

Hemmingsen W  Jansen PA  Mackenzie K 《Marine pollution bulletin》2005,50(3):336-339

The red king crab Paralithodes camtschaticus was deliberately introduced to the Barents Sea in the 1960s and 1970s from its native area in the North Pacific. The carapace of these crabs is a favoured substrate for the leech Johanssonia arctica to deposit its eggs, and the leech is a vector for a trypanosome blood parasite of marine fish, including cod. We examined cod for trypanosome infections during annual cruises along the coast of Finnmark in North Norway over three successive years from stations along a gradient of over 1000 km. In every year the level of trypanosome infection in cod was significantly highest in the area with the greatest density of king crabs. We propose the hypothesis that the burgeoning population of red king crabs in this area is indirectly responsible for increased transmission of trypanosomes to cod by promoting an increase in the population of the leech vector.  相似文献