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| Titel |
Stable isotopes in water vapor and precipitation for a coastal lagoon at mid latitudes |
| VerfasserIn |
Daniele Zannoni, Andrea Bergamasco, Giuliano Dreossi, Giancarlo Rampazzo, Barbara Stenni |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250126715
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| Publikation (Nr.) |
 EGU/EGU2016-6476.pdf |
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| Zusammenfassung |
| The stable oxygen and hydrogen isotope composition in precipitation can be used in
hydrology to describe the signature of local meteoric water. The isotopic composition of
water vapor is usually obtained indirectly from measurements of δD and δ18O in
precipitation, assuming the isotopic equilibrium between rain and water vapor. Only few
studies report isotopic data in both phases for the same area, thus providing a complete Local
Meteoric Water Line (LMWL). The goal of this study is to build a complete LMWL for the
lagoon of Venice (northern Italy) with observations of both water vapor and precipitation.
The sampling campaign has started in March 2015 and will be carried out until the end of
2016. Water vapor is collected once a week with cold traps at low temperatures
(−77∘C). Precipitation is collected on event and monthly basis with a custom automatic
rain sampler and a rain gauge, respectively. Liquid samples are analyzed with a
Picarro L1102-i and results are reported vs VSMOW. The main meteorological
parameters are continuously recorded in the same area by the campus automatic weather
station. Preliminary data show an LMWL close to the Global Meteoric Water Line
(GMWL) with lower slope and intercept. An evaporation line is clearly recognizable,
considering samples that evaporated between the cloud base and the ground. The
deviation from the GMWL parameters, especially intercept, can be attributed to
evaporated rain or to the humidity conditions of the water vapor source. Water vapor
collected during rainfall shows that rain and vapor are near the isotopic equilibrium,
just considering air temperature measured at ground level. Temperature is one of
the main factor that controls the isotopic composition of the atmospheric water
vapor. Nevertheless, the circulation of air masses is a crucial parameter which has to
be considered. Water vapor samples collected in different days but with the same
meteorological conditions (air temperature and relative humidity) show differences in
terms of δ18O up to 3‰. Isotopic ratios in rain events and water vapor are in fact
dominated by a seasonal component but outliers are clearly linked to air parcel origin.
The monthly measurements of δD and δ18O in precipitation of August 2015, for
instance, are lower than in colder months, considering monthly average temperatures.
Single rain events show a small sequence of precipitation, that leads to 40% of total
precipitation of August, which lowers δ−values considerably. The sampling on
event basis during occasional and discontinuous rain also allows to identify the
rainout effect, which leads to lightening water during a rainfall. Statistics based on
back trajectories (48 hours) show that the major part of air parcels travels across
central Europe and derives from sources located in the north Atlantic, whereas, a
smaller fraction of the water vapor can be attributed to Mediterranean sources. |
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