Investigation of paleoclimate signatures in Sfax deep groundwater (Southeastern Tunisia) using environmental isotopes and noble gases

To investigate paleoclimate conditions and mean annual ground temperatures at the time of infiltration, concentrations of dissolved atmospheric noble gases, O-18, H-2 and C-14 were studied in Sfax deep groundwater in southeastern of Tunisia. Carbon-14 corrected ages are up to 40 Ka BP suggesting that most of this water infiltrated during Late Pleistocene. Noble gas temperatures (NGTs) clearly show the presence of water that infiltrated under much cooler conditions than at present. According to the NGT's, the mean annual temperature in this mid latitude coastal site during the last glacial maximum (LGM) was 5.5 +/- 1.0 degrees C colder than during the Holocene. This transition of Holocene -Pleistocene is well marked by a depletion of oxygen-18 isotope composition by 1.5 parts per thousand when compared to the modern rain water signature. Furthermore, the amount of excess air, which is closely linked to the magnitude of groundwater table fluctuations, provides further information on drought and wet period alternations during Late Pleistocene in Northern Africa.