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By NATCHAYA PINGINTHA MONIQUE Y. LECLERC JOHN P. BEASLEY Jr. GENGSHENG ZHANG CHUCKREE SENTHONG 《Tellus. Series B, Chemical and physical meteorology》2010,62(1):47-58
This paper uses a refined soil gradient method to estimate soil CO2 efflux. Six different models are used to determine the relative gas diffusion coefficient (ξ). A weighted harmonic averaging is used to estimate the soil CO2 diffusion coefficient, yielding a better estimate of soil CO2 efflux. The resulting soil CO2 efflux results are then compared to the soil CO2 efflux measured with a soil chamber. Depending on the choice of ξ model used, the estimated soil CO2 efflux using the gradient method reasonably approximates the efflux obtained using the soil chamber method. In addition, the estimated soil CO2 efflux obtained by this improved method is well described by an exponential function of soil temperature at a depth of 0.05 m with the temperature sensitivity ( Q 10 ) of 1.81 and a linear function of soil moisture at a depth of 0.12 m, in general agreement with previous findings. These results suggest that the gradient method is a practical cost-effective means to measure soil CO2 emissions. Results from the present study suggest that the gradient method can be used successfully to measure soil CO2 efflux provided that proper attention is paid to the judicious use of the proper diffusion coefficient. 相似文献
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Major and trace element variations in an Ordovician alkalineorthogneiss (ortholeptynites) series of the Maures massif, France,suggest that the pre-metamorphic rocks were alkaline and peralkalinerhyolites derived by fractional crystallization from trachy-rhyoliticmagma. Differentiation proceeded under low oxygen fugacity conditions,with the production of high-silica comendites. By comparisonwith unaltered alkaline and peralkaline rhyolites, it is possibleto prove that the parental magma was not similar to the metatholeiitesthat are associated with the orthogneisses in the field. Norwere the metarhyolites derived from the alkaline to transitionalmetabasalts of the same age which occur elsewhere in the Mauresmassif. The orthogneisses have geochemical features typicalof alkaline and peralkaline rhyolites occurring with basaltsin continental, anorogenic, bimodal associations. This hypothesisis also supported by zircon morphology and mineral chemistry.The Maures massif was a within-plate continental volcanic province,whose crust underwent doming and thinning, but not break up,during lower Palaeozoic times. 相似文献
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The relative abundance of five groups of radiolarian species (nasselarians and spumellarians) in the thanatocoenoses within the recent sediments from 64o N to the Equator is described. Four types of thanatocoenoses of Radiolarians and several subtypes are distinguished and in the broadest sense four major faunal zones can be delimited: north of 60o N, a subarctic zone, a boreal zone, a subtropical zone whose boundary runs approximately along 45o N and, south of 13o N, a tropical zone. The correlations between the faunal provinces and climatic belts are more gradual in the low and intermediate latitudes than in the high latitudes 相似文献
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Discontinuous Melt Extraction and Weak Refertilization of Mantle Peridotites at the Vema Lithospheric Section (Mid-Atlantic Ridge) 总被引：1，自引：0，他引：1
BRUNELLI DANIELE; SEYLER MONIQUE; CIPRIANI ANNA; OTTOLINI LUISA; BONATTI ENRICO 《Journal of Petrology》2006,47(4):745-771
Melting processes beneath the Mid-Atlantic Ridge were studiedin residual mantle peridotites sampled from a lithospheric sectionexposed near the Vema Fracture Zone at 11°N along the Mid-AtlanticRidge. Fractional and dynamic melting models were tested basedon clinopyroxene rare earth element and high field strengthelement data. Pure fractional melting (non-modal) cannot accountfor the observed trends, whereas dynamic melting with criticalmass porosity <0·01 fits better the measured values.Observed microtextures suggest weak refertilization with 0·1–1%quasi-instantaneous or partially aggregated melts trapped duringpercolation. The composition of the melts is evaluated, togetherwith their provenance, with respect to the garnet–spineltransition. Partial melts appear to be aggregated over shortbut variable intervals of the melting column. Deep melts (generatedwithin the garnet stability field at the base of the meltingcolumn) escape detection, being separated from the residuesby transport inside conduits or fractures. The temporal evolutionof the melting process along the exposed section shows a steadyincrease of mantle temperature from 20 Ma to present. KEY WORDS: mantle partial melting; abyssal peridotite; trace element; refertilization; Vema Fracture Zone 相似文献
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KONRAD GAJEWSKI MONIQUE FRAPPIER 《Boreas: An International Journal of Quaternary Research》2001,30(4):285-289
A core from Prince of Wales Island in the central Canadian Arctic was analysed for pollen and sediment characteristics. From 9200 yr BP to 7000 yr BP, the landscape supported a pioneer vegetation under cold conditions, with relatively high sediment input to the lake. Between 7000 and 4000 yr BP there was a period of high pollen concentrations, more abundant Cyperaceae and Dryas on the landscape and finer sediment input. In the last 4000 years, climate cooling is indicated. 相似文献
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