Deuterium excess in the atmospheric water vapour of a Mediterranean coastal wetland: regional vs. local signatures

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Delattre, H, Vallet-Coulomb, C, Sonzogni, C
• Other Authors: Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: STABLE-ISOTOPE COMPOSITION; RATIO MASS-SPECTROMETRY; BOUNDARY-LAYER; CARBON-DIOXIDE; CONTINENTAL MOISTURE; SEASONAL-VARIATION; AMAZON BASIN; IN-SITU; PRECIPITATION; EVAPOTRANSPIRATION; [SDE.ES]Environmental Sciences/Environmental and Society; [SDE.MCG]Environmental Sciences/Global Changes; North Atlantic
• Online Access: https://amu.hal.science/hal-01230452; https://amu.hal.science/hal-01230452/document; https://amu.hal.science/hal-01230452/file/acp-15-10167-2015.pdf; https://doi.org/10.5194/acp-15-10167-2015

International audience Stable isotopes of water vapour represent a powerful tool for tracing atmospheric vapour origin and mixing processes. Laser spectrometry recently allowed high time-resolution measurements, but despite an increasing number of experimental studies, there is still a need for a better understanding of the isotopic signal variability at different time scales. We present results of in situ measurements of δ 18 O and δD during 36 consecutive days in summer 2011 in atmospheric vapour of a Mediterranean coastal wetland exposed to high evaporation (Camargue, Rhône River delta, France). The mean composition of atmospheric vapour (δ v) is δ 18 O = −14.66 ‰ and δD = −95.4 ‰, with data plotting clearly above the local meteoric water line on a δ 18 O-δD plot, and an average deuterium excess (d) of 21.9 ‰. Important diurnal d variations are observed, and an hourly time scale analysis is necessary to interpret the main processes involved in its variability. After having classified the data according to air mass back trajectories, we analyse the average daily cycles relating to the two main meteorological situations, i.e. air masses originating from North Atlantic Ocean and Mediter-ranean Sea. In both situations, we show that diurnal fluctuations are driven by (1) the influence of local evaporation, culminating during daytime, and leading to an increase in absolute water vapour concentration associated to a δ v enrichment and d increase; (2) vertical air mass redistribution when the Planetary Boundary Layer collapses in the evening, leading to a d decrease, and (3) dew formation during the night, producing a δ v depletion with d remaining stable. Using a two-component mixing model, we calculate the average composition of the locally evaporated vapour (δ E). We find higher d (E) under North Atlantic air mass conditions, which is consistent with lower humidity conditions. We also suggest that δ v measured when the PBL collapses is the most representative of a regional signal. Strong, cold and dry winds ...