Grain size and geochemeical analysis in the El Bibane Lagoon and the Fessi River watershed (Southeast of Tunisia)

Climate models project that rising atmospheric carbon dioxide concentrations will increase the frequency and the severity of some extreme weather events. The floods events represent a major risk for populations and infrastructures settled on coastal lowlands. Recently, study of lagoon sediments contributed to enhance our knowledge on extreme hydrological events such as paleo-floods and paleo-storms and on their relation with climate change over the last millennium. The past flood activity was investigated using a multi-approach associating sedimentological and geochemical analysis of surfaces sediments from the Southeast of Tunisia catchment in order to trace the origin of sediments deposit in the El Bibane lagoon. Three sediments sources were identified: aeolian, fluvial and marine. This multi-proxy analysis on the BL12-10 core shows that finer material, high content of the clay and silt, and high content of the elemental ratios (Fe/Ca and Ti/Ca) characterize the sedimentological signature of the paleoflood levels identified in the lagoonal sequence. For the last century which is the period covered by the BL12-10 short core, three paleo-floods events were identified. The age of these floods events have been determined by 210Pb and 137Cs Chronology. Dating of the three most recent floods provides age of AD 1995 ± 6, AD 1970 ± 9, and AD 1945 ± 9. The results show a good temporal correspondence of floods events recorded in the Southern of Tunisia in the last century (A.D 1932, A.D 1969, A.D 1979 and A.D 1995). Such a good correlation between floods events recorded in the core and historical data of the annual precipitations suggests that reconstruction of the history of the hydrological extreme events during the upper Holocene is rendered possible by the use of the sedimentary archives.