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   

Mercury Dynamics in a San Francisco Estuary Tidal Wetland: Assessing Dynamics Using In Situ Measurements     

Brian A. Bergamaschi  Jacob A. Fleck  Bryan D. Downing  Emmanuel Boss  Brian A. Pellerin  Neil K. Ganju  David H. Schoellhamer  Amy A. Byington  Wesley A. Heim  Mark Stephenson  Roger Fujii 《Estuaries and Coasts》2012,35(4):1036-1048

We used high-resolution in situ measurements of turbidity and fluorescent dissolved organic matter (FDOM) to quantitatively estimate the tidally driven exchange of mercury (Hg) between the waters of the San Francisco estuary and Browns Island, a tidal wetland. Turbidity and FDOM??representative of particle-associated and filter-passing Hg, respectively??together predicted 94?% of the observed variability in measured total mercury concentration in unfiltered water samples (UTHg) collected during a single tidal cycle in spring, fall, and winter, 2005?C2006. Continuous in situ turbidity and FDOM data spanning at least a full spring-neap period were used to generate UTHg concentration time series using this relationship, and then combined with water discharge measurements to calculate Hg fluxes in each season. Wetlands are generally considered to be sinks for sediment and associated mercury. However, during the three periods of monitoring, Browns Island wetland did not appreciably accumulate Hg. Instead, gradual tidally driven export of UTHg from the wetland offset the large episodic on-island fluxes associated with high wind events. Exports were highest during large spring tides, when ebbing waters relatively enriched in FDOM, dissolved organic carbon (DOC), and filter-passing mercury drained from the marsh into the open waters of the estuary. On-island flux of UTHg, which was largely particle-associated, was highest during strong winds coincident with flood tides. Our results demonstrate that processes driving UTHg fluxes in tidal wetlands encompass both the dissolved and particulate phases and multiple timescales, necessitating longer term monitoring to adequately quantify fluxes.  相似文献   

Integrating spatial, temporal, and magnitude probabilities for medium-scale landslide risk analysis in Darjeeling Himalayas, India     

Saibal Ghosh  Cees J. van Westen  Emmanuel John M. Carranza  Victor G. Jetten 《Landslides》2012,9(3):371-384

Landslide risk assessment is based on spatially integrating landslide hazard with exposed elements-at-risk to determine their vulnerability and to express the expected direct and indirect losses. There are three components that are relevant for expressing landslide hazard: spatial, temporal, and magnitude probabilities. At a medium-scale analysis, this is often done by first deriving a landslide susceptibility map, and to determine the three types of probabilities on the basis of landslide inventories linked to particular triggering events. The determination of spatial, temporal, and magnitude probabilities depend mainly on the availability of sufficiently complete historical records of past landslides, which in general are rare in most countries (e.g., India, etc.). In this paper, we presented an approach to use available historical information on landslide inventories for landslide hazard and risk analysis on a medium scale (1:25,000) in a perennially typical data-scarce environment in Darjeeling Himalayas (India). We demonstrate how the incompleteness in the resulting landslide database influences the various components in the calculation of specific risk of elements-at-risk (e.g., buildings, population, roads, etc.). We incorporate the uncertainties involved in the risk estimation and illustrate the range of expected losses in the form of maximum and minimum loss curves. The study demonstrates that even in data-scarce environments, quantitative landslide risk assessment is a viable option, as long as the uncertainties involved are expressed.  相似文献   

Soil porosity resulting from the assemblage of silt grains with a clay phase: New perspectives related to utilization of X-ray synchrotron computed microtomography   总被引：2，自引：0，他引：2  

Olivier Rozenbaum  Ary Bruand  Emmanuel Le Trong 《Comptes Rendus Geoscience》2012,344(10):516-525

Understanding the assemblage of basic grains is essential for predicting many soil properties. X-ray synchrotron microtomography with a high resolution was used for visualisation and quantification of the assemblage of silt grains with a clay phase containing 20% of clays. The 3D computed image was analysed after appropriate segmentation by using: (i) autocorrelation functions which enables anisotropy discussion of the assemblage; (ii) chord distribution which gives information on the size distribution of the void and solid phases; and (iii) the Hoshen-Kopelman algorithm (6-connectivity) in order to label each void with a unique number and thus enabling discussion of the connectivity. Our results show that X-ray synchrotron microtomography enables a more accurate analysis of the assemblage of silt grains with a clay phase than with conventional methods. Thus, it showed the isotropy of the silt-clay assemblage in the studied soil material. The void and solid phase volumes were smaller than 80 and 120 μm in all directions, respectively. The mean distance between two interfaces was 6.9 and 13.4 μm for the void and solid phase, respectively. X-ray synchrotron microtomography of the soil material studied also showed that the voids resulting from the assemblage of the silt grains with the clay phase can be considered as fully connected in the studied dried materials.  相似文献   

An Intercomparison Study of the Germanium Isotope Composition of Geological Reference Materials     

Raphaelle Escoube  Olivier J. Rouxel  Béatrice Luais  Emmanuel Ponzevera  Olivier F.X. Donard 《Geostandards and Geoanalytical Research》2012,36(2):149-159

Recent analytical developments in germanium stable isotope determination by multicollector ICP‐MS have provided new perspectives for the use of Ge isotopes as geochemical tracers. Here, we report the germanium isotope composition of the NIST SRM 3120a elemental reference solution that has been calibrated relative to internal isotopic standard solutions used in the previous studies. We also intercalibrate several geological reference materials as well as geological and meteoritic samples using different techniques, including online hydride generation and a spray chamber for sample introduction to MC‐ICP‐MS, and different approaches for mass bias corrections such as sample–calibrator bracketing, external mass bias correction using Ga isotopes and double‐spike normalisation. All methods yielded relatively similar precisions at around 0.1‰ (2s) for δ^74/70Ge values. Using igneous and mantle‐derived rocks, the bulk silicate Earth (BSE) δ^74/70Ge value was re‐evaluated to be 0.59 ± 0.18‰ (2s) relative to NIST SRM 3120a. Several sulfide samples were also analysed and yielded very negative values, down to ?4.3‰, consistent with recent theoretical study of Ge isotope fractionation. The strong heavy isotope depletion in ore deposits also contrasts with the generally positive Ge isotope values found in many modern and ancient marine sediments.  相似文献   

Mineralogy, geochemistry and petrogenesis of the recent magmatic formations from Mbengwi, a continental sector of the Cameroon Volcanic Line (CVL), Central Africa     

Beno?t Joseph Mbassa  Emmanuel Njonfang  Mathieu Benoit  Pierre Kamgang  Michel Grégoire  Stephanie Duchene  Pierre Brunet  Bekoa Ateba  Félix M. Tchoua 《Mineralogy and Petrology》2012,106(3-4):217-242

The Mbengwi recent magmatic formations consist of volcanics and syenites belonging to the same magmatic episode. Lavas form a bimodal basanite-rhyolite alkaline series with a gap between 50 and 62?wt.% SiO₂. Mafic lavas (basanite-hawaiite) are sodic while felsic rocks (trachyte-rhyolite-syenites) are sodi-potassic, slightly metaluminous to peralkaline. The geochemical and isotopic characteristics (0.7031?<?(⁸⁷Sr/⁸⁶Sr)_initial?<?0.7043; 1.03?<?ε_Ndi?<?5.17) of these rocks are similar to those of other rocks from the CVL. The main differentiation process is fractional crystallization with two trends of fractionation. Their Rb/Sr isochron age of 28.2?Ma, almost similar to 27.40?±?0.6?Ma?K/Ar age obtained in a trachyte from neighboring Bamenda Mountains system, precludes any local age migration of an hypothetic hotspot. Mafic lavas have OIB features displaying an isotopic signature similar to that of HIMU mantle source different from FOZO known as source of most parental magmas along the CVL.  相似文献   

Mid-infrared detection of large longitudinal asymmetries in Io's SO₂ atmosphere     

John R. Spencer  Emmanuel Lellouch  Miguel A. López-Valverde  Thomas K. Greathouse  Jean-Marie Flaud 《Icarus》2005,176(2):283-304

We have observed about 16 absorption lines of the ν₂ SO₂ vibrational band on Io, in disk-integrated 19-μm spectra taken with the TEXES high spectral resolution mid-infrared spectrograph at the NASA Infrared Telescope Facility in November 2001, December 2002, and January 2004. These are the first ground-based infrared observations of Io's sunlit atmosphere, and provide a new window on the atmosphere that allows better longitudinal and temporal monitoring than previous techniques. Dramatic variations in band strength with longitude are seen that are stable over at least a 2 year period. The depth of the strongest feature, a blend of lines centered at 530.42 cm⁻¹, varies from about 7% near longitude 180° to about 1% near longitude 315° W, as measured at a spectral resolution of 57,000. Interpretation of the spectra requires modeling of surface temperatures and atmospheric density across Io's disk, and the variation in non-LTE ν₂ vibrational temperature with altitude, and depends on the assumed atmospheric and surface temperature structure. About half of Io's 19-μm radiation comes from the Sun-heated surface, and half from volcanic hot spots with temperatures primarily between 150 and 200 K, which occupy about 8% of the surface. The observations are thus weighted towards the atmosphere over these low-temperature hot spots. If we assume that the atmosphere over the hot spots is representative of the atmosphere elsewhere, and that the atmospheric density is a function of latitude, the most plausible interpretation of the data is that the equatorial atmospheric column density varies from about 1.5×¹⁰¹⁷ cm⁻² near longitude 180° W to about 1.5×¹⁰¹⁶ cm⁻² near longitude 300° W, roughly consistent with HST UV spectroscopy and Lyman-α imaging. The inferred atmospheric kinetic temperature is less than about 150 K, at least on the anti-Jupiter hemisphere where the bands are strongest, somewhat colder than inferred from HST UV spectroscopy and millimeter-wavelength spectroscopy. This longitudinal variability in atmospheric density correlates with the longitudinal variability in the abundance of optically thick, near-UV bright SO₂ frost. However it is not clear whether the correlation results from volcanic control (regions of large frost abundance result from greater condensation of atmospheric gases supported by more vigorous volcanic activity in these regions) or sublimation control (regions of large frost abundance produce a more extensive atmosphere due to more extensive sublimation). Comparison of data taken in 2001, 2002, and 2004 shows that with the possible exception of longitudes near 180° W between 2001 and 2002, Io's atmospheric density does not appear to decrease as Io recedes from the Sun, as would be expected if the atmosphere were supported by the sublimation of surface frost, suggesting that the atmosphere is dominantly supported by direct volcanic supply rather than by frost sublimation. However, other evidence such as the smooth variation in atmospheric abundance with latitude, and atmospheric changes during eclipse, suggest that sublimation support is more important than volcanic support, leaving the question of the dominant atmospheric support mechanism still unresolved.  相似文献   

Stability of triangular points in the photogravitational CR3BP with Poynting-Robertson drag and a smaller triaxial primary     

Jagadish Singh  A. Balogun Emmanuel 《Astrophysics and Space Science》2014,353(1):97-103

The stability of triangular equilibrium points in the framework of the circular restricted three-body problem (CR3BP) is investigated for a test particle of infinitesimal mass in the vicinity of two massive bodies (primaries), when the bigger primary is a source of radiation and the smaller one is a triaxial rigid body with one of the axes as the axis of symmetry and its equatorial plane coinciding with the plane of motion, under the Poynting-Robertson (P-R) drag effect as a result of the radiating primary. It is found that the involved parameters influence the position of triangular points and their linear stability. It is noted that these points are unstable in the presence of Poynting-Robertson drag effect and conditionally stable in the absence of it.  相似文献   

Urban heat island and differences in outdoor comfort levels in Glasgow, UK     

Eduardo Krüger  Patricia Drach  Rohinton Emmanuel  Oscar Corbella 《Theoretical and Applied Climatology》2013,112(1-2):127-141

From extensive outdoor comfort campaigns, preliminary outdoor comfort ranges have been defined for the local population of Glasgow, UK, in terms of two thermal indices: ‘Temperature Humidity Sun Wind’ (THSW) and ‘Physiological Equivalent Temperature’ (PET). A series of measurements and surveys was carried out from winter through summer 2011 during 19 monitoring campaigns. For data collection, a Davis Vantage Pro2 weather station was used, which was equipped with temperature and humidity sensors, cup anemometer with wind vane, silicon pyranometer and globe thermometer. From concurrent measurements using two weather stations, one located close to the city core and another located at a rural setting, approximately at a 15-km distance from the urban area of Glasgow, comparisons were made with regard to thermal comfort levels and to urban–rural temperature differences for different periods of the year. It was found that the two selected thermal indices (THSW and PET) closely correlate to the actual thermal sensation of respondents. Moreover, results show that the urban site will have fewer days of cold discomfort, more days of ‘neutral’ thermal sensation and slightly higher warm discomfort. The most frequent urban heat island intensity was found to be around 3° C, whereas the fraction of cooling to heating degree-hours for a T _base of 65 °F was approximately 1/12th.  相似文献   

The formation conditions of enstatite chondrites: Insights from trace element geochemistry of olivine‐bearing chondrules in Sahara 97096 (EH3)          下载免费PDF全文

Emmanuel Jacquet  Olivier Alard  Matthieu Gounelle 《Meteoritics & planetary science》2015,50(9):1624-1642

We report in situ LA‐ICP‐MS trace element analyses of silicate phases in olivine‐bearing chondrules in the Sahara 97096 (EH3) enstatite chondrite. Most olivine and enstatite present rare earth element (REE) patterns comparable to their counterparts in type I chondrules in ordinary chondrites. They thus likely share a similar igneous origin, likely under similar redox conditions. The mesostasis however frequently shows negative Eu and/or Yb (and more rarely Sm) anomalies, evidently out of equilibrium with olivine and enstatite. We suggest that this reflects crystallization of oldhamite during a sulfidation event, already inferred by others, during which the mesostasis was molten, where the complementary positive Eu and Yb anomalies exhibited by oldhamite would have possibly arisen due to a divalent state of these elements. Much of this igneous oldhamite would have been expelled from the chondrules, presumably by inertial acceleration or surface tension effects, and would have contributed to the high abundance of opaque nodules found outside them in EH chondrites. In two chondrules, olivine and enstatite exhibit negatively sloped REE patterns, which may be an extreme manifestation of a general phenomenon (possibly linked to near‐liquidus partitioning) underlying the overabundance of light REE observed in most chondrule silicates relative to equilibrium predictions. The silicate phases in one of these two chondrules show complementary Eu, Yb, and Sm anomalies providing direct evidence for the postulated occurrence of the divalent state for these elements at some stage in the formation reservoir of enstatite chondrites. Our work supports the idea that the peculiarities of enstatite chondrites may not require a condensation sequence at high C/O ratios as has long been believed.  相似文献