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Ricardo Sánchez‐Murillo Ana M. Durán‐Quesada Christian Birkel Germain Esquivel‐Hernández Jan Boll 《水文研究》2017,31(4):956-967
The last 2014‐16 El Niño event was among the three strongest episodes on record. El Niño considerably changes annual and seasonal precipitation across the tropics. Here, we present a unique stable isotope data set of daily precipitation collected in Costa Rica prior to, during, and after El Niño 2014‐16, in combination with Lagrangian moisture source and precipitation anomaly diagnostics. δ2H composition ranged from ‐129.4 to +18.1 (‰) while δ18O ranged from ‐17.3 to +1.0 (‰). No significant difference was observed among δ18O (P=0.186) and δ2H (P=0.664) mean annual compositions. However, mean annual d‐excess showed a significant decreasing trend (from +13.3 to +8.7 ‰) (P<0.001) with values ranging from +26.6 to ‐13.9 ‰ prior to and during the El Niño evolution. The latter decrease in d‐excess can be partly explained by an enhanced moisture flux convergence across the southeastern Caribbean Sea coupled with moisture transport from northern South America by means of an increased Caribbean Low Level Jet regime. During 2014‐15, precipitation deficit across the Pacific domain averaged 46% resulting in a very severe drought; while a 94% precipitation surplus was observed in the Caribbean domain. Understanding these regional moisture transport mechanisms during a strong El Niño event may contribute to a) better understanding of precipitation anomalies in the tropics and b) re‐evaluate past stable isotope interpretations of ENSO events in paleoclimatic archives within the Central America region. 相似文献
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Catherine Pierre Germain Bayon Marie-Madeleine Blanc-Valleron Jean Mascle Stéphanie Dupré 《Geo-Marine Letters》2014,34(2-3):253-267
On the passive margin of the Nile deep-sea fan, the active Cheops mud volcano (MV; ca. 1,500 m diameter, ~20–30 m above seafloor, 3,010–3,020 m water depth) comprises a crater lake with hot (up to ca. 42 °C) methane-rich muddy brines in places overflowing down the MV flanks. During the Medeco2 cruise in fall 2007, ROV dives enabled detailed sampling of the brine fluid, bottom lake sediments at ca. 450 m lake depth, sub-surface sediments from the MV flanks, and carbonate crusts at the MV foot. Based on mineralogical, elemental and stable isotope analyses, this study aims at exploring the origin of the brine fluid and the key biogeochemical processes controlling the formation of these deep-sea authigenic carbonates. In addition to their patchy occurrence in crusts outcropping at the seafloor, authigenic carbonates occur as small concretions disseminated within sub-seafloor sediments, as well as in the bottom sediments and muddy brine of the crater lake. Aragonite and Mg-calcite dominate in the carbonate crusts and in sub-seafloor concretions at the MV foot, whereas Mg-calcite, dolomite and ankerite dominate in the muddy brine lake and in sub-seafloor concretions near the crater rim. The carbonate crusts and sub-seafloor concretions at the MV foot precipitated in isotopic equilibrium with bottom seawater temperature; their low δ13C values (–42.6 to –24.5‰) indicate that anaerobic oxidation of methane was the main driver of carbonate precipitation. By contrast, carbonates from the muddy lake brine, bottom lake concretions and crater rim concretions display much higher δ13C (up to –5.2‰) and low δ18O values (down to –2.8‰); this is consistent with their formation in warm fluids of deep origin characterized by 13C-rich CO2 and, as confirmed by independent evidence, slightly higher heavy rare earth element signatures, the main driver of carbonate precipitation being methanogenesis. Moreover, the benthic activity within the seafloor sediment enhances aerobic oxidation of methane and of sulphide that promotes carbonate dissolution and gypsum precipitation. These findings imply that the coupling of carbon and sulphur microbial reactions represents the major link for the transfer of elements and for carbon isotope fractionation between fluids and authigenic minerals. A new challenge awaiting future studies in cold seep environments is to expand this work to oxidized and reduced sulphur authigenic minerals. 相似文献
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Karen T. Johnson Margie Wickham‐St. Germain Saebom Ko Scott G. Huling 《Ground Water Monitoring & Remediation》2012,32(3):84-92
Groundwater samples collected at sites where in situ chemical oxidation (ISCO) has been deployed may contain binary mixtures of groundwater contaminants and permanganate (MnO4–), an oxidant injected into the subsurface to destroy the contaminant. Commingling of the oxidant and contaminant in aqueous samples may negatively impact the quality of the sample as well as the analytical instruments used to quantify contaminant concentrations. In this study, binary mixtures comprised of (1) a multicomponent standard with permanganate and (2) groundwater samples collected at two ISCO field sites were preserved with ascorbic acid. Ascorbic acid reacts rapidly with the MnO4– and limits the reaction between MnO4– and the organic compounds in the mixture. Consequently, most of the compounds in the multicomponent standard were within the control limit for quality assurance. However, despite timely efforts to preserve the samples, the rapid reaction between permanganate and contaminant caused the concentration of several sensitive compounds to fall significantly below the lower control limit. Concentrations of volatile organic compounds in the field‐preserved binary mixture groundwater samples were greater than in samples refrigerated in the field and preserved upon arrival at the laboratory, indicating the time‐dependency and benefit of field preservation. The molar ratio of ascorbic acid required to neutralize KMnO4 was 1.64 (mol ascorbic acid/mol KMnO4); this provided a baseline to estimate the volume of ascorbic acid stock solution and/or the weight of crystalline ascorbic acid required to neutralize MnO4–. Excess ascorbic acid did not negatively impact the quality of the aqueous samples, or analytical instruments, used in the analyses. 相似文献
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Determination of Rare Earth Elements, Sc, Y, Zr, Ba, Hf and Th in Geological Samples by ICP-MS after Tm Addition and Alkaline Fusion 总被引：2，自引：0，他引：2
Germain Bayon Jean Alix Barrat Joël Etoubleau Mathieu Benoit Claire Bollinger Sidonie Révillon 《Geostandards and Geoanalytical Research》2009,33(1):51-62
We present a revised method for the determination of concentrations of rare earth (REE) and other trace elements (Y, Sc, Zr, Ba, Hf, Th) in geological samples. Our analytical procedure involves sample digestion using alkaline fusion (NaOH-Na2 O2 ) after addition of a Tm spike, co-precipitation on iron hydroxides, and measurement by sector field-inductively coupled plasma-mass spectrometry (SF-ICP-MS). The procedure was tested successfully for various rock types (i.e., basalt, ultramafic rock, sediment, soil, granite), including rocks with low trace element abundances (sub ng g−1 ). Results obtained for a series of nine geological reference materials (BIR-1, BCR-2, UB-N, JP-1, AC-E, MA-N, MAG-1, GSMS-2, GSS-4) are in reasonable agreement with published working values. 相似文献
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M. Legrand C. Feniet-Saigne E. S. Saltzman C. Germain 《Journal of Atmospheric Chemistry》1992,14(1-4):245-260
A simultaneous glaciochemical study of methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO4
-) has been conducted on the Antarctic plateau (South Pole, Vostok) and in more coastal regions. The objective was to investigate marine sulfur emissions in very remote areas. Firstly, our data suggest that MSA and nss-SO4 present in antarctic ice are mainly marine in origin and that DMS emissions have been significantly modulated by short term (eg. El Nino Southern Oscillation events) as well as long term climatic changes in the past. Secondly, our study of spatial variations of these two sulfur species seems to indicate that the atmosphere of coastal antarctic regions are mainly supplied by local DMS emissions whereas the atmosphere of the high plateau is also influenced by DMS emissions from more temperate marine latitudes. Thirdly, our study of the partitioning between MSA and nss-SO4 suggest that the temperature could have been an important parameter controlling the final composition of the high southern latitude atmosphere over the last climatic cycle; colder temperature favoring the formation of MSA. However, our data also support a possible role played by changes in the transport pattern of marine air to the high antarctic plateau. 相似文献
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Polonium-210 (210Po) has been analysed in the soft parts of two bivalves species, the scallop Chlamys varia and the common mussel Mytilus edulis, from the Bay of La Rochelle and Ré Island, on the French Atlantic coast. Between those sites, the highest 210Po concentrations have been found in whole scallop soft parts from La Rochelle, reaching 1,181 +/- 29 Bq kg(-1) dry weight (dwt), a size effect being related to the highest 210Po concentration in the smallest scallops. The results show a significant difference in concentrations for similar size individuals between species in each site (C. varia > M. edulis) and between sites for each species (Ré Island > Bay of La Rochelle). Very high 210Po concentrations have been found in the digestive gland of C varia, ranging 3,150-4,637 Bq kg(-1) dwt. Thus, the digestive gland contains up to 60% of the radionuclide. Subcellular investigations have shown that approximately 40% of the 210Po contained in the digestive gland is in the cytosolic fraction, suggesting a high bioavailability of the 210Po from this fraction to the trophic upper level. Calculations will show that approximately 4 kg of scallops flesh intake would be necessary to reach the annual incorporation limit of 1 mSv. 相似文献
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Germain Bayon Dominique Birot Claire Bollinger Jean Alix Barrat 《Geostandards and Geoanalytical Research》2011,35(1):145-153
We report on an improved method for determining trace element abundances in seawater and other natural waters. The analytical procedure involves co‐precipitation on iron hydroxides after addition of a Tm spike, and measurement by inductively coupled plasma‐sector field mass spectrometry (ICP‐SFMS). The validity of the method was assessed through a series of co‐precipitation experiments, using ultra‐diluted solutions of a certified rock reference material (BIR‐1). Results obtained for four natural water reference materials (NASS‐5, CASS‐4, SLEW‐3, SLRS‐4) are in agreement with published working values for rare earth elements, yttrium, vanadium and, when available, for hafnium, zirconium, thorium and scandium. A set of proposed values with uncertainties typically better than 8% RSD is proposed for Hf, Zr and Th. 相似文献