A study of the δ13C offset between chironomid larvae and their exuvial head capsules: implications for palaeoecology     

Victor Frossard  Simon Belle  Valérie Verneaux  Laurent Millet  Michel Magny 《Journal of Paleolimnology》2013,50(3):379-386

We conducted a rearing experiment with the chironomid species Chironomus riparius to assess the relationship between the δ¹³C values of chironomid larvae and the δ¹³C values of their exuvial head capsules. Our experiment was also designed to study the extent of the trophic fractionation factor (Δ¹³C) under different dietary conditions. Three food sources were used (Tetramin, oats and corn), covering a range in δ¹³C values of 14.55 ‰. For each of the four successive instars, carbon isotope ratios were measured in larval tissues and head capsules. This approach highlighted the variability in δ¹³C for both larvae and their head capsules during larval development. Once the larvae reached the 3rd instar, their δ¹³C values were stabilised and did not significantly differ from their food δ¹³C (Δ¹³C = 0 ‰). It is probable that the variability in the δ¹³C offset during larval development reflected a difference in the carbon turnover for the chironomid cuticle compared with the whole body. At the 4th instar, the δ¹³C offset did not significantly differ between the three food sources and was ?0.9 ± 0.2 ‰. The proposed Δ¹³C and δ¹³C offset values can be considered as a first step for the reconstructions of the chironomid larvae paleo-diets with the aim of deciphering the different organic carbon sources supporting chironomid larvae productions. However, the influence of the environment (e.g. temperature, oxygen), other food sources (e.g. different nutritive values) as well as taxonomy (i.e. other chironomid species) should be assessed to strengthen the robustness of these results.  相似文献   

MODEL: a multicriteria ordinal evaluation tool for GIS     

Laurent Louvart  Alexandru-Liviu Olteanu 《International journal of geographical information science》2013,27(10):1910-1931

While the integration of geographical information systems (GIS) and multicriteria decision aiding (MCDA) has attracted increasing interest from researchers in recent years, due to the wide array of applications that can benefit from GIS as well as the different types of decision problems and various models that can be used through MCDA, plenty of opportunities of integrating GIS and MCDA remain. In this article, we present the result of such an opportunity in the form of a methodology and software that is currently used by the Naval Hydrographic and Oceanographic Service in France. Furthermore, this tool may be used in conjunction with other GIS–MCDA applications with a single decision maker, multiple decision makers or even where the decision has a hierarchical structure.  相似文献   

Improving the triaxial bulge model of M31     

Simon Berman  Laurent Loinard 《Monthly notices of the Royal Astronomical Society》2002,336(2):477-482

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Reconstruction of Late Glacial summer temperatures from chironomid assemblages in Lac Lautrey (Jura,France)     

Oliver Heiri  Laurent Millet 《第四纪科学杂志》2005,20(1):33-44

A chironomid–July air temperature inference model based on chironomid assemblages in the surface sediments of 81 Swiss lakes was used to reconstruct Late Glacial July air temperatures at Lac Lautrey (Jura, Eastern France). The transfer‐function was based on weighted averaging–partial least squares (WA‐PLS) regression and featured a leave‐one‐out cross‐validated coefficient of determination (r²) of 0.80, a root mean square error of prediction (RMSEP) of 1.53 ° C, and was applied to a chironomid record consisting of 154 samples covering the Late Glacial period back to the Oldest Dryas. The model reconstructed July air temperatures of 11–12 ° C during the Oldest Dryas, increasing temperatures between 14 and 16.5 ° C during the Bølling, temperatures around 16.5–17.0 ° C for most of the Allerød, temperatures of 14–15 ° C during the Younger Dryas and temperatures of ca. 16.5 ° C during the Preboreal. The Lac Lautrey record features a two‐step July air temperature increase after the Oldest Dryas, with an abrupt temperature increase of ca. 3–3.5 ° C at the Oldest Dryas/Bølling transition followed by a more gradual warming between ca. 14 200 and 13 700 BP. The transfer‐function reconstructs a less rapid cooling at the Allerød/Younger Dryas transition than other published records, possibly an artefact caused by the poor analogue situation during the earliest Younger Dryas, and an abrupt warming at the Younger Dryas/Holocene transition. During the Allerød, two centennial‐scale 1.5–2.0 ° C coolings are apparent in the record. Although chronologically not well constrained, the first of these cold events may be synchronous with the beginning of the Gerzensee Oscillation. The second is inferred just before deposition of the Laachersee tephra at Lac Lautrey and is therefore coeval with the end of the Gerzensee Oscillation. In contrast to the Greenland oxygen isotope records, the Lac Lautrey palaeotemperature reconstruction lacks a clearly defined Greenland Interstadial (GI) event 1d and the decreasing temperature trend during the Bølling/Allerød Interstadial. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Wolf–Rayet stars in M33 – I. Optical spectroscopy using CFHT-MOS     

Jay B. Abbott  Paul A. Crowther †  Laurent Drissen †  Luc Dessart †  Pierre Martin  Guillaume Boivin 《Monthly notices of the Royal Astronomical Society》2004,350(2):552-564

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Rhone River flood deposits in Lake Le Bourget: a proxy for Holocene environmental changes in the NW Alps, France     

Emmanuel Chapron  Fabien Arnaud  HERVÉ Noël  Marie Revel  Marc Desmet  Laurent Perdereau 《Boreas: An International Journal of Quaternary Research》2005,34(4):404-416

The Holocene evolution of Rhone River clastic sediment supply in Lake Le Bourget is documented by sub-bottom seismic profiling and multidisciplinary analysis of well-dated sediment cores. Six high-amplitude reflectors within the lacustrine drape can be correlated to periods of enhanced inter- and underflow deposition in sediment cores. Based on the synthesis of major environmental changes in the NW Alps and on the age-depth model covering the past 7500 years in Lake Le Bourget, periods of enhanced Rhone River flood events in the lake can be related to abrupt climate changes and/or to increasing land use since c. 2700 cal. yr BP. For example, significant land use under rather stable climate conditions during the Roman Empire may be responsible for large flood deposits in the northern part of Lake Le Bourget between AD 966 and 1093. However, during the Little Ice Age (LIA), well-documented major environmental changes in the catchment area essentially resulted from climate change and formed basin-wide major flood deposits in Lake Le Bourget. Up to five 'LIA-like' Holocene cold periods developing enhanced Rhone River flooding activity in Lake Le Bourget are documented at c. 7200, 5200, 2800, 1600 and 200 cal. yr BP. These abrupt climate changes were associated in the NW Alps with Mont Blanc glacier advances, enhanced glaciofluvial regimes and high lake levels. Correlations with European lake level fluctuations and winter precipitation regimes inferred from glacier fluctuations in western Norway suggest that these five Holocene cooling events at 45°N were associated with enhanced westerlies, possibly resulting from a persistent negative mode of the North Atlantic Oscillation.  相似文献   

A New Mid-Infrared Diagnostic between AGN and Starbursts     

O. Laurent  I.F. Mirabel  V. Charmandaris  P. Gallais  M. Sauvage  L. Vigroux  C. Cesarsky 《Astrophysics and Space Science》2001,276(2-4):569-576

We present a new set of diagnostics which allow us to trace and classify in a statistical manner the mid-IR emission produced by active galactic nuclei (AGN) and star-forming regions. We construct a diagram based on the strength of the unidentified infrared band (UIB)at 6.2 μm, and the intensity of the continuum at short (6 μm) and long wavelengths (15 μm). We interpret the integrated mid-IR emission in late-type galaxies as resulting from three individual contributions coming from HII regions, diffuse/photodissociation regions (PDRs), and AGN. Based on this assumption, our diagnostic diagram provides a quantitative estimate of the AGN and starburst contribution to an observed mid-IR spectrum. We show that UIB emission is very faint or absent in regions harbouring intense and hard radiation fields as in the case of AGN or ‘pure’ HII starburst regions where UIB carriers can be destroyed by photodissociation. However, contrary to starburst spectra, typical AGN spectra present a strong hot continuum below 9 μm originating from hot dust heated by the AGN radiation field. An extrapolation of this diagnostic towards other mid-IR observations should improve our knowledge of the AGN/starburst connection. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Influence of small-scale North Atlantic sea surface temperature patterns on the marine boundary layer and free troposphere: a study using the atmospheric ARPEGE model     

Marie Piazza  Laurent Terray  Julien Boé  Eric Maisonnave  Emilia Sanchez-Gomez 《Climate Dynamics》2016,46(5-6):1699-1717

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Reconstruction of seasonal temperature variability in the tropical Pacific Ocean from the shell of the scallop, Comptopallium radula     

Julien Thébault  Laurent Chauvaud  Jennifer Guarini  Renaud Fichez  Eric Morize 《Geochimica et cosmochimica acta》2007,71(4):918-928

We investigated the oxygen isotope composition (δ¹⁸O) of shell striae from juvenile Comptopallium radula (Mollusca; Pectinidae) specimens collected live in New Caledonia. Bottom-water temperature and salinity were monitored in-situ throughout the study period. External shell striae form with a 2-day periodicity in this scallop, making it possible to estimate the date of precipitation for each calcite sample collected along a growth transect. The oxygen isotope composition of shell calcite (δ¹⁸O_{shell calcite}) measured at almost weekly resolution on calcite accreted between August 2002 and July 2003 accurately tracks bottom-water temperatures. A new empirical paleotemperature equation for this scallop species relates temperature and δ¹⁸O_{shell calcite}: