The measurement of D/H ratio in alkenones and their isotopic heterogeneity     

Valérie F. Schwab  Julian P. Sachs 《Organic Geochemistry》2009,40(1):111-118

Previous paleoenvironmental studies reported the δD values of a mixture of coeluting alkenones. Here, we present a semi-preparative normal-phase high-performance liquid chromatography–mass spectrometry (NP-HPLC–MS) method for purifying long chain (C₃₇ and C₃₈) unsaturated methyl and ethyl ketones (alkenones) on the basis of chain length and degree of unsaturation.The method was applied to purify alkenones in suspended particles and surface sediments from a site in Chesapeake Bay, eastern USA. The hydrogen isotopic composition of di- and triunsaturated C₃₇ and C₃₈ alkenones differed significantly on the basis of chain length and the degree of unsaturation, demonstrating the importance of gas chromatography–isotope ratio-mass spectrometry (GC–irMS) analysis of individual alkenones for accurate paleoenvironmental reconstruction. Constant fractionation factors between alkenones with different chain length but the same degree of unsaturation (${\alpha }_{{\text{C}}_{37:2}''–''{\text{C}}_{38:2}}\text{and}{\alpha }_{{\text{C}}_{37:3}''–''{\text{C}}_{38:3}}=1.01$) and those with the same chain length but different degree of unsaturation (${\alpha }_{{\text{C}}_{37:2}''–''{\text{C}}_{37:3}}\text{and}{\alpha }_{{\text{C}}_{38:2}''–''{\text{C}}_{38:3}}=0.97$) in all samples suggest that the values may represent hydrogen isotope fractionation associated with elongation and desaturation during alkenone biosynthesis.  相似文献   

Trace metals and benthic macrofauna distributions in Camamu Bay, Brazil: sediment quality prior oil and gas exploration     

Hatje V  Barros F  Magalhães W  Riatto VB  Amorim FN  Figueiredo MB  Spanó S  Cirano M 《Marine pollution bulletin》2008,56(2):363-370

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Absolute seafloor vertical positioning using combined pressure gauge and kinematic GPS data   总被引：1，自引：0，他引：1  

Valérie Ballu  Marie-Noelle Bouin  Stéphane Calmant  Eric Folcher  Jean-Michel Bore  Jérome Ammann  Olivier Pot  Michel Diament  Bernard Pelletier 《Journal of Geodesy》2010,84(1):65-77

Knowledge of the position and motion of points on the seafloor can be critically important in both fundamental research (for example, global geodesy and plate tectonics) and for more practical applications such as seismic risk evaluation, off-shore construction and pipeline monitoring. In the Vanuatu subduction zone, for example, measuring deformation underwater could provide valuable information for modeling deformation and understanding the seismic cycle. We report a shallow water experiment in Vanuatu to measure the relative and absolute depth of seafloor points. The experiment differs from previous efforts mainly in that it uses the height of the sea surface determined by kinematic GPS, allowing us to locate the points in a global reference frame. The ITRF2005 ellipsoidal height of a seafloor benchmark was determined with a 1-sigma uncertainty of 0.7–2.1 cm. The estimated ellipsoidal height differs only by a few tenths of a centimeter between measurements made in 2004 and another set made in 2006. These results are encouraging and open new perspectives for vertical underwater deformation monitoring in shallow water areas. Sea-surface GPS measurements can also help to reduce the uncertainty in depth difference determination for relative measurements.  相似文献   

Spawning migrations, sexual maturity and sex steroid levels in female roach Rutilus rutilus from the River Meuse     

Patrick Kestemont  Jacques Rinchard  Valérie Feys  Alexis Fostier 《Aquatic Sciences - Research Across Boundaries》1999,61(2):111-121

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Improving resolution and accuracy of mean sea surface from kinematic GPS,Vanuatu subduction zone     

Marie-Noëlle Bouin  Valérie Ballu  Stéphane Calmant  Bernard Pelletier 《Journal of Geodesy》2009,83(11):1017-1030

Satellite altimetry provides an ocean mean sea surface (MSS) map with global coverage and overall excellent precision. However, in some areas, like the Vanuatu archipelago, the coverage and resolution of this tool are not sufficient to correctly map the short scale undulations of the sea surface, due to numerous islands and to strong lithospheric and mantle heterogeneities. New applications such as seafloor geodesy may require local mean surface representation with improved resolution in specific areas. We used sea surface height collected with kinematic GPS during three different cruises in 2004, 2006 and 2007 to reconstruct a homogeneous sea surface map around Santo Island, Vanuatu. We assess the accuracy of this GPS-derived local sea surface to 6–19 cm and evaluate the quality of existing altimetry and gravity-derived MSSs on the Vanuatu archipelago. Observed short scale undulations are interpreted as due to local geodynamics.  相似文献   

Morphological controls on the dynamics of carbonate landscapes under a mediterranean climate          下载免费PDF全文

Franck Thomas  Vincent Godard  Olivier Bellier  Esmaeil Shabanian  Vincent Ollivier  Lucilla Benedetti  Magali Rizza  Nicolas Espurt  Valéry Guillou  Fabrice Hollender  Stéphane Molliex  ASTER Team 《地学学报》2017,29(3):173-182

The influence of the morphological setting on the denudation of carbonate landscapes and the respective contributions of mechanical and chemical weathering processes are still debated. We have addressed these questions by measuring ³⁶Cl concentrations in 40 samples from the Luberon mountain, SE France, to constrain the denudation of various landscape elements. We observe a clear contrast between the local denudation rates from the flat summit surface, clustered around 30 mm/ka, and the basin‐average denudation rates across the flanks, ranging from 100 to 200 mm/ka. This difference highlights the transient evolution of the range, whose topography is still adjusting to previous uplift events. Such a pattern also suggests that carbonate dissolution is not the only driver of denudation in this setting, which appears to be significantly controlled by slope‐dependent processes.  相似文献   

Sensitivity of simulated Asian and African summer monsoons to orbitally induced variations in insolation 126, 115 and 6 kBP   总被引：1，自引：1，他引：0  

Nathalie de Noblet  Pascale Braconnot  Sylvie Joussaume  Valérie Masson 《Climate Dynamics》1996,12(9):589-603

We have conducted four numerical experiments with an atmospheric general circulation model (AGCM) to investigate the sensitivity of Asian and African monsoons to small changes (–5 to +12%), with respect to present-day, in incoming solar radiation at the top of the atmosphere. We show that, during the mid-Holocene (6 kBP where kBP means thousands of years before present-day) and the last interglacial (126 kBP), the Northern Hemisphere seasonal contrast was increased, with warmer summers and colder winters. At the time of glacial inception (115 kBP) however, summers were cooler and winters milder. As a consequence, Asia and tropical North Africa experienced stronger (weaker) summer monsoons 6 and 126 kBP (115 kBP), in agreement with previous numerical studies. This present study shows that summer warming/cooling of Eurasia and North Africa induced a shift of the main low-level convergence cell along a northwest/southeast transect. When land was warmer (during the summer months 6 and 126 kBP), the monsoon winds converged further inland bringing more moisture into northern India, western China and the southern Sahara. The southern tips of India, Indochina and southeastern China, as well as equatorial North Africa became drier. When land was cooler (during the summer 115 kBP), the main convergence zone was located over the west Pacific and the wet (dry) areas were those that were dry (wet) 6 and 126 kBP. The location and intensity of the simulated precipitation maxima were therefore very sensitive to changes in insolation. However the total amount of monsoon rain in Asia as well as in Africa remained remarkably stable through the time periods studied. These simulated migrations of convective activities were accompanied by changes in the nature of precipitation events: increased monsoon rains in these experiments were always associated with more high precipitation events (> 5 mm day ^–1), and fewer light showers (1 mm day^–). Rainy days with rates between 1 and 5 mm day^–1 were almost unchanged.  相似文献   

OH 1720-MHz lines as tracers of bipolar outflows in the vicinity of Class I methanol masers     

I. D. Litovchenko  O. S. Bayandina  A. V. Alakoz  I. E. Val’tss  G. M. Larionov  D. V. Mukha  A. S. Nabatov  A. A. Konovalenko  V. V. Zakharenko  E. V. Alekseev  V. S. Nikolaenko  V. F. Kulishenko  S. A. Odintsov 《Astronomy Reports》2012,56(7):536-552

A sample of Class I methanol masers (MMI) has been surveyed at 1720 MHz to search for possible associations between MMI and 1720-MHz OH masers, which should be formed by the same collisional pumping mechanism. If the model for methanol masers is correct, the sample should contain a statistically significant number of 1720-MHz OH masers at the positions of MMI. The observations were conducted on the 70-meter radio telescope of the National Academy of Sciences of Ukraine (NASU). The results show that ??50% of 72 MMI are associated with OH emission at 1720 MHz. In many sources, strong absorption lines are also observed. In most cases, the OH (1720) lines are narrow (linewidths of <2 km/s) suggesting they may be maser lines. The OH column densities obtained from Gaussian fitting of these narrow OH lines are, on average, 1.5 × 10¹⁷ cm^?2. TheH² density in the emitting medium reaches 10⁷ cm^?3 if the region of the OH (1720) emission has been subject to interaction with a bipolar-outflow front. This is sufficient to excite MMI, and the presence of narrow, possibly masing OH (1720) lines at the MMI velocities indicates the likely presence of shocks from bipolar outflows in the vicinity of the maser condensations, supporting models in which these molecules are collisionally pumped.  相似文献   

It starts at home? Climate policies targeting household consumption and behavioral decisions are key to low-carbon futures     

Ghislain Dubois  Benjamin Sovacool  Carlo Aall  Maria Nilsson  Carine Barbier  Alina Herrmann  Sébastien Bruyère  Camilla Andersson  Bore Skold  Franck Nadaud  Florian Dorner  Karen Richardsen Moberg  Jean Paul Ceron  Helen Fischer  Dorothee Amelung  Marta Baltruszewicz  Jeremy Fischer  Françoise Benevise  Valérie R. Louis  Rainer Sauerborn 《Chemie der Erde / Geochemistry》2010

Through their consumption behavior, households are responsible for 72% of global greenhouse gas emissions. Thus, they are key actors in reaching the 1.5 °C goal under the Paris Agreement. However, the possible contribution and position of households in climate policies is neither well understood, nor do households receive sufficiently high priority in current climate policy strategies. This paper investigates how behavioral change can achieve a substantial reduction in greenhouse gas emissions in European high-income countries. It uses theoretical thinking and some core results from the HOPE research project, which investigated household preferences for reducing emissions in four European cities in France, Germany, Norway and Sweden. The paper makes five major points: First, car and plane mobility, meat and dairy consumption, as well as heating are the most dominant components of household footprints. Second, household living situations (demographics, size of home) greatly influence the household potential to reduce their footprint, even more than country or city location. Third, household decisions can be sequential and temporally dynamic, shifting through different phases such as childhood, adulthood, and illness. Fourth, short term voluntary efforts will not be sufficient by themselves to reach the drastic reductions needed to achieve the 1.5 °C goal; instead, households need a regulatory framework supporting their behavioral changes. Fifth, there is a mismatch between the roles and responsibilities conveyed by current climate policies and household perceptions of responsibility. We then conclude with further recommendations for research and policy.  相似文献   

Quantifying wave measurement differences in historical and present wave buoy systems     

Jensen  Robert Edward  Swail  Val  Bouchard  Richard Harry 《Ocean Dynamics》2021,71(6-7):731-755

Ocean Dynamics - An intra-measurement evaluation was undertaken, deploying a NOMAD buoy equipped with three National Data Buoy Center and two Environment and Climate Change Canada-AXYS...  相似文献