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Vinícius dos SANTOS Peter MARSHALL FLEMING Luís HENRIQUE MANCINI Stela DALVA SANTOS COTA Graziele Beatriz de LIMA Rafaela RODRIGUES GOMES Roberto Eduardo KIRCHHEIM Ricardo SANCHéZ-MURILLO Didier GASTMANS 《大气科学进展》2022,39(10):1693-1708
Precipitation isotope ratios (O and H) record the history of water phase transitions and fractionation processes during moisture transport and rainfall formation. Here, we evaluated the isotopic composition of precipitation over the central-southeastern region of Brazil at different timescales. Monthly isotopic compositions were associated with classical effects (rainfall amount, seasonality, and continentality), demonstrating the importance of vapor recirculation processes and different regional atmospheric systems (South American Convergence Zone-SACZ and Cold Fronts-CF). While moisture recycling and regional atmospheric processes may also be observed on a daily timescale, classical effects such as the amount effect were not strongly correlated (δ18O-precipitation rate r ≤ –0.37). Daily variability revealed specific climatic features, such as δ18O depleted values (~ –6‰ to –8‰) during the wet season were associated with strong convective activity and large moisture availability. Daily isotopic analysis revealed the role of different moisture sources and transport effects. Isotope ratios combined with d-excess explain how atmospheric recirculation processes interact with convective activity during rainfall formation processes. Our findings provide a new understanding of rainfall sampling timescales and highlight the importance of water isotopes to decipher key hydrometeorological processes in a complex spatial and temporal context in central-southeastern Brazil. 相似文献
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Stela Cuna Elise Pendall John B. Miller Pieter P. Tans Ed Dlugokencky James W.C. White 《Applied Geochemistry》2008
The Danube Delta-Black Sea region of Romania is an important wetland, and this preliminary study evaluates the significance of this region as a source of atmospheric CH4. Measurements of the mixing ratio and δ13C in CH4 are reported from air and water samples collected at eight sites in the Danube Delta. High mixing ratios of CH4 were found in air (2500–14,000 ppb) and dissolved in water samples (∼1–10 μmol L−1), demonstrating that the Danube Delta is an important natural source of CH4. The intercepts on Keeling plots of about −62‰ show that the main source of CH4 in this region is microbial, probably resulting primarily from acetate fermentation. Atmospheric CH4 and CO data from the NOAA/ESRL (National Oceanic and Atmospheric Administration/Earth System Research Laboratory) were used to make a preliminary estimate of biogenic CH4 at the Black Sea sampling site at Constanta (BSC). These data were used to calculate ratios of CH4/CO in air samples, and using an assumed CH4/CO anthropogenic emissions ratio of 0.6, fossil fuel emissions at BSC were estimated. Biogenic CH4 emissions were then estimated by a simple mass balance approach. Keeling plots of well-mixed air from the BSC site suggested a stronger wetland source in summer and a stronger fossil fuel source in winter. 相似文献
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E. Cuna E. Zawisza M. Caballero A. C. Ruiz-Fernández S. Lozano-García J. Alcocer 《Journal of Paleolimnology》2014,51(1):1-14
The Little Ice Age (LIA), AD 1350–1850, represents one of the most recent, persistent global climate oscillations. In Mexico, it has been associated with temperature decreases of 1.5–2 °C and mountain glacier advances, which are not accurately dated. We present new information about the nature of the LIA in central Mexico based on a decadal-resolution sediment sequence from high-altitude, tropical Lake La Luna, in the Nevado de Toluca volcano. We inferred past climatic and environmental changes using magnetic susceptibility, charcoal particles, palynomorphs, diatoms, cladoceran remains and multivariate statistics. The onset of the LIA corresponds with the beginning of a long-term trend to colder and drier climate ca. AD 1360–1910. The coolest and driest episode, ~AD 1660–1760, which corresponds with the Maunder Minimum in solar activity, was characterized by a cladoceran assemblage that showed the greatest dissimilarity to the modern one (no modern analogue), with the presence of cold-water species and Daphnia ephippia. The beginning of a warming trend ca. AD 1760, was identified by a diatom assemblage dominated by species with affinities for higher pH values (>6) and the greatest dissimilarity to the modern assemblage. This less cold, but still dry period, corresponds with historical reports of cattle and crop losses that predated the Mexican wars of Independence (AD 1810–1821) and Revolution (1910–1924). Modern conditions, established around AD 1910, resemble those during the Medieval Climate Anomaly (ca. AD 1200). No clear evidence of modern, human-induced environmental change was recorded, indicating that Lake La Luna is an ideal site in Mexico to monitor future impacts of global change. 相似文献
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Lake development in geologically active basins is a complex phenomenon as shown by the bed of the Pliocene Tlaxcala paleolake
disturbed by volcanic eruptions in central Mexico. A 5-m layered freshwater diatomite outcrop section shows volcanic ashes
throughout a bottom Stephanodiscus zone up to a more recent Aulacoseira zone. A 0.5-m transition region begins with an abrupt decrease in volcanic inputs and ends with a shift to Aulacoseira solida (Eulenstein) Krammer. Sediment analysis points to a shallow eutrophic lake in the bottom zone undergoing a transition to
higher water volume leading to a threshold depth for the species shift. The lake was apparently deeper and mesotrophic thereafter.
A common interpretation is to attribute such a volume change to a moisture increase. However, evidence of geological activity,
mainly volcanism and faulting, suggests that it could have also been rooted in geomorphological changes of the lake basin. 相似文献
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