Hélène Celle-Jeanton

Isotopic typology of the precipitation in the Western Mediterranean Region at three different time scales

Environmental isotopes (18O, ²H) have been measured, between March 1997 and March 1999, at 10 stations located in the Mediterranean seaside countries (2 in Spain, 1 in Tunisia, 7 in France). Data collected on monthly, event and fractionated basis allow to understand the modifications of the isotopic content of precipitation due to meteorological phenomena. A monthly monitoring shows that the Western Mediterranean has a unique isotopic characteristic that is between Atlantic and Eastern Mediterranean. A daily survey highlights the impact of the origins and trajectories of air masses on the amount and the oxygen-18 content of rainfalls: enriched and higher amount Mediterranean precipitation, depleted and lower amount Atlantic precipitation. At last, fractionated sampling of heavy precipitation allows to establish a typology of the variations of the isotopic composition during a rain event.

Caractérisation isotopique des pluies en Tunisie. Essai de typologie dans la région de Sfax

Abstract This paper determines the isotopic signature of monthly precipitation in Tunisia and highlights the main influence of air mass origin and temperature. On an event basis, this impact is confirmed and two groups can be distinguished at Sfax: ( i ) rain coming from Atlantic air masses that circulate in northern Africa (group I), ( ii ) precipitation due to atmospheric circulation on the Mediterranean Sea (group II). Mediterranean rains are enriched in oxygen-18 (−4.1 ‰), whereas the Atlantic ones show a more depleted value (−6.7 ‰). These specific signatures will be useful for groundwater tracing.