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| Titel |
Deuterium excess in the atmospheric water vapour of a Mediterranean coastal wetland: regional vs. local signatures |
| VerfasserIn |
H. Delattre, C. Vallet-Coulomb, C. Sonzogni |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 17 ; Nr. 15, no. 17 (2015-09-14), S.10167-10181 |
| Datensatznummer |
250120029
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| Publikation (Nr.) |
 copernicus.org/acp-15-10167-2015.pdf |
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| Zusammenfassung |
| 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 δ18O 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 (δv)
is δ18O = −14.66 ‰ and δD = − 95.4 ‰, with data plotting clearly above the local
meteoric water line on a δ18O-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 Mediterranean 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 δv 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 δv depletion with
d
remaining stable. Using a two-component mixing model, we calculate the
average composition of the locally evaporated vapour (δE). We
find higher d(E) under North Atlantic air mass conditions, which is
consistent with lower humidity conditions. We also suggest that δv measured when the PBL collapses is the most representative of a
regional signal. Strong, cold and dry winds coming from the north bring an
isotopically depleted vapour, while light, warm and wet winds coming from
the south bring an isotopically enriched vapour. Under northern conditions,
a strong advection rate dilutes the contribution of the locally evaporated
vapour (δE) to the ambient moisture (δv). The
higher d values measured under northern conditions, compared to the
Mediterranean situation, thus results from the combination of a higher d in
both local and regional vapour. This depiction of typical daily cycles of
water vapour isotopic composition can be used as a framework for further
quantitative analyses of vapour sources during specific days. |
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