To What Extent Can Oxygen Isotopes in Tree Rings and Precipitation Be Used to Reconstruct Past Atmospheric Temperature? A Case Study     

Martine Rebetez  Matthias Saurer  Paolo Cherubini 《Climatic change》2003,61(1-2):237-248

We analyzed the relationship between air temperature and oxygen isotopes measured in tree rings of silver fir (Abies alba Mill.) from along-term forest ecosystem research plot in the Swiss Jura mountains (LWF project). The oxygen isotope data were compared with a century-long meteorological series of air temperature data. Measurements of oxygen isotope ratios in precipitation were also used for comparison. Results show that the late-wood tree-ring series is significantly correlated with May to August temperatures. Correlations were higher for maximum (daytime) air temperature and even better for air temperature measured on rainy days only. We stress that trends in maximum temperature series for this time of the year, like trends in oxygen isotope ratios series from tree rings, are completely different from trends in yearly mean temperature. Indeed, maximum temperature trends during the vegetation period slightly decreased during the 20thcentury, whereas yearly means increased strongly.  相似文献   

Multiple origin and regional significance of bedding parallel veins in a fold and thrust belt: The example of a carbonate slice along the Appalachian structural front     

Stephan Sjourn  Michel Malo  Martine M. Savard  Donna Kirkwood 《Tectonophysics》2005,407(3-4):189-209

The development and evolution of bedding parallel veins (BPV) are investigated in the Saint-Dominique carbonate slice (southern Québec Appalachian structural front), in order to emphasize the regional significance of BPV in a fold and thrust belt and their importance in establishing its structural and diagenetic evolution. Structural and microstructural analyses reveal that most BPV display a laminated structure locally crosscut by a massive one. Both structures show mutual crosscutting relationships with bedding parallel or bedding perpendicular stylolites and with bedding perpendicular veinlets, indicating that BPV cementation and deformation are continuous processes. Opening both sub-parallel and sub-perpendicular to the BPV walls are documented. Early BPV are planes of weakness that focus later reactivation, and evidence of successive and sometimes opposite senses of opening are locally preserved within a single BPV. The bedding parallel orientation of these veins proved particularly helpful in establishing the structural evolution of an area mostly characterized by front parallel structures with little crosscutting relationships otherwise. Petrographic and geochemical (δ¹⁸O _VPDB and δ¹³C) analyses of structural cements suggest a common, locally derived source for the fluids that percolated through BPV, non-bedding parallel veins and faults. The isotopic ratios also reveal a significant enrichment in ¹⁸O and ¹³C through time. This evolution is tentatively correlated with tectonic, syn-convergence exhumation of the Saint-Dominique slice during its imbrication along the Appalachian structural front, after its burial under Taconian thrust sheets.  相似文献   

Assimilation of continental crust by komatiites in the Precambrian basement of the Carswell structure (Saskatchewan,Canada)     

Martine Juteau  Maurice Pagel  Annie Michard  Francis Albarede 《Contributions to Mineralogy and Petrology》1988,99(2):219-225

The isotope geochemistry (Sm-Nd, Pb-Pb and Rb-Sr) of mafic gneisses from the basement of the Carswell structure (Saskatchewan, Canada), rich both in Mg and incompatible elements (K, Rb, REE) has been investigated. A good Sm-Nd alignment gives a slope corresponding to an age of 3.7 Ga. However, comparison with major elements data strongly suggests that this alignment is a mixing line between Mg-rich, high CaO/Al₂O₃ magmas and the local felsic crust older than 2.9 Ga. The mafic magmas were probably of komatiitic affinity (MgO > 20 percent) but, nevertheless, were extracted from a source with nearly chondritic to slightly enriched light REE distribution. The age of the komatiite emplacement (1.9–2.9 Ga) is only loosely constrained by the oldest crustal residence age in the series and the subsequent metamorphic events. The granulite facies climax is dated at ca. 1.9 Ga by concordant whole rock Pb-Pb and Sm-Nd garnet-whole rock isochrons. The Rb-Sr systematics have been disturbed by later event(s) younger than 1.5–1.7 Ga, but do not permit a more precise assessment of the perturbation age.  相似文献   

The influence of fluid unmixing on cation exchange between plagioclases and aqueous chloride solutions at 700° C, 1 kbar     

Saint Clair Dujon  Martine Lagache 《Contributions to Mineralogy and Petrology》1986,92(1):128-134

Experimental exchanges between plagioclases (synthesized from gels) and aqueous solutions (0.5N–8N) were carried out according to the reaction $$\begin{gathered} 2NaA1Si_3 O_8 + CaC1_2 \hfill \\ \leftrightarrow CaA1_2 Si_2 O_8 + 4SiO_2 + 2NaC1. \hfill \\ \end{gathered}$$ Distribution coefficients defined by $$K_D = \frac{{X_{An} }}{{(X_{Ab} )^2 }}\frac{{(X_{NaC1} )^2 }}{{X_{CaC1_2 } }}$$ were determined at 700° C and 1 kbar. From previous studies it is known that variations in the concentration of the aqueous solutions have no influence upon K _D if the fluid is a single phase. In this study, variation of K _D with the concentration of the solutions is interpreted as the result of fluid unmixing to vapour and brine phases. This implies boiling of CaCl₂-NaCl-H₂O fluids analogous to that known for the system NaCl-H₂O. Experimental data permit calculation of the compositions of vapours and estimation of those of the brines for fluids in which Ca/Na<0.5. Boiling has an effect upon the exchange between feldspars and solutions (metasomatism) and must be considered when determining the activity coefficients.  相似文献   

Static displacement fields due to a seismic source in a nonhomogeneous (dimorphic) medium. Geophysical applications     

Martine Amalvict  Hilaire Legros 《Pure and Applied Geophysics》1983,121(5-6):817-834

A new method for finding static displacement fields due to seismic sources (forces or dislocations) in a nonhomogeneous medium (called “dimorphic”) is presented. Previously known results can be easily calculated, as well as new results for sources located at the interface between two media with different elastic properties. The ratio of displacement magnitudes in homogeneous and dimorphic media, which can be as great as 15%, is calculated. Consequences for the seismic moment and some other geophysical applications are discussed.  相似文献   

Variation in hydrologic connectivity as a result of microtopography explained by discharge to catchment size relationship          下载免费PDF全文

Marieke Oosterwoud  Martine van der Ploeg  Sake van der Schaaf  Sjoerd van der Zee 《水文研究》2017,31(15):2683-2699

In hydrological terms, raised bogs are often approximated by simple models as in the acrotelm–catotelm concept. However, raised bogs are often characterized by a pronounced surface topography, causing large changes in connectivity of contributing areas on the bog. In this study, daily regression of measured discharges versus catchment areas is used to quantify the impact of surface topography on catchment connectivity within a raised bog. The resulting coefficient of determination shows the strength of the relationship between the discharge and catchment area over time under different hydrological conditions. Monitoring of discharge, water table, transmissivity, and basic weather data on a raised bog (1.9 km²) in eastern central Estonia took place from May 2008 to June 2010. Contributing areas, calculated based on the outlet's discharge volume (V _Q ) divided by the net precipitation volume ( ), of the outlet containing the central pool‐ridge system varied between 1×10^?3 and 0.7 km², suggesting significant differences in connectivity between hydrological events. Correlation between discharge and theoretical catchment size was high (R ²>0.75) when the water table was close to the surface (less than 5 cm below peat surface), and consequently, transmissivities were also high (up to 1,030m²d^?1), which led to connectivity of local storage elements, such as pools and hollows. However, a water table below this threshold resulted in large parts of the catchment being disconnected. The importance of water table depths on catchment connectivity suggests the need to reconsider the hydrological concept of raised bogs; to incorporate these shallow flow components and better understand residence time and consequently transport of solutes, such as DOC, from patterned peatlands.  相似文献   

Desalination of a sedimentary rock aquifer system invaded by Pleistocene Champlain Sea water and processes controlling groundwater geochemistry     

Vincent Cloutier  René Lefebvre  Martine M. Savard  René Therrien 《Environmental Earth Sciences》2010,59(5):977-994

The objective of this study was to identify geochemical processes and Quaternary geological events responsible for the variations in groundwater geochemistry observed in a sedimentary rock aquifer system, including brackish to saline groundwater. Inorganic constituents and environmental isotopes were analyzed for 146 groundwater samples. Dissolution of carbonates dominates in recharge areas, resulting in Ca-, Mg-HCO₃ groundwater. Further along flow paths, under confined conditions, Ca²⁺–Na⁺ ion exchange causes groundwater evolution to Na-HCO₃ type. Na-Cl groundwater is also found and it falls on a seawater mixing line. Using conservative tracers, Cl⁻ and Br⁻, the original Champlain Sea water is shown to have been, in the region, a mixture of about 34% seawater and 66% freshwater, a composition still retained by some groundwater. Na-Cl groundwater thus results from mixing with former Champlain Sea water and also from solute diffusion from overlying marine clay. The system is thus found to be at different stages of desalinization, from the original Champlain Sea water still present in hydraulically stagnant areas of the aquifer to fully flushed conditions in parts, where more flow occurs, especially in recharge zones. The geochemical processes are integrated within the hydrogeological context to produce a conceptual geochemical evolution model for groundwater of the aquifer system.  相似文献   

Late Weichselian to Holocene paleoenvironments in the Barents Sea     

Elena V. Ivanova  Ivar O. Murdmaa  Jean-Claude Duplessy  Martine Paterne   《Global and Planetary Change》2002,34(3-4)

Paleoceanographic changes since the Late Weichselian have been studied in three sediment cores raised from shelf depressions along a north–south transect across the central Barents Sea. AMS radiocarbon dating offers a resolution of several hundred years for the Holocene. The results of lithological and micropaleontological study reveal the response of the Barents Sea to global climatic changes and Atlantic water inflow. Four evolutionary stages were distinguished. The older sediments are moraine deposits. The destruction of the Barents Sea ice sheet during the beginning of the deglaciation in response to climate warming and sea level rise resulted in proximal glaciomarine sedimentation. Then, the retreat of the glacier front to archipelagoes during the main phase of deglaciation caused meltwater discharge and restricted iceberg calving. Fine-grained distal glaciomarine sediments were deposited from periodic near-bottom nepheloid flows and the area was almost permanently covered with sea ice. The dramatic change in paleoenvironment occurred near the Pleistocene/Holocene boundary when normal marine conditions ultimately established resulting in a sharp increase of biological productivity. This event was diachronous and started prior to 10 ¹⁴C ka BP in the southern and about 9.2 ¹⁴C ka in the northern Barents Sea. Variations in sediment supply, paleoproductivity, sea-ice conditions, and Atlantic water inflow controlled paleoenvironmental changes during the Holocene.  相似文献   

Occurrence of phthalate diesters in rivers of the Paris district (France)     

Marie‐Jeanne Teil  Martine Blanchard  Cendrine Dargnat  Karen Larcher‐Tiphagne  Marc Chevreuil 《水文研究》2007,21(18):2515-2525

The occurrence and fate of six phthalate esters were investigated in the River Seine and two tributaries in the Paris area, at six sites from upstream to downstream, throughout different seasons, with special attention given to a flood episode. At all sites, except the River Marne, whatever the period, diethylhexyl phthalate (DEHP) displayed the highest concentration (0·323–0·779 µg l^?1 as mean values), followed by di‐n‐butyl phthalate (DnBP; 0·211–0·526 µg l^?1 as mean values), which is consistent with the production pattern. High phthalate concentrations appeared to be related to population density and industrial distribution. The strongest values were located downstream from wastewater treatment plant effluent inputs. Seasonal variations were closely related to river flow and air and water temperature. The annual evolution of phthalates was linked to the hydrological conditions. During the flood episode at Paris, the DEHP concentration displayed a sharp increase (260 to 1123 ng l^?1) occurring 9 days before the flood peak. The simultaneous fluctuations of NH₄, typical of domestic origin, and of DEHP suggests a similar origin from combined sewer overflows for both compounds. Other elevated values corresponded to the highest precipitation amounts, and demonstrated the contribution of non‐point‐source runoff and wastewater overflow to DEHP inputs. The DEHP concentration relationship with river flow displayed a clockwise hysteresis loop, corresponding to a ‘first‐flush’ effect in which the finite supplies are swept along in the early stage of the flood. Annual fluxes for 2004 at Paris were 2257 kg of DEHP and 1613 kg of DnBP. The flood period seemed to have a minor impact on annual phthalate transport (29·5% and 41% of the total for DEHP and for DnBP, respectively), which is contrary to annual suspended solids transport (69%). Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

A correlation between earthquakes and eruptive phases at Mt Etna: an example and past occurrences     

Alexandre Nercessian  Alfred Hirn  Martine Sapin 《Geophysical Journal International》1991,105(1):131-138

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