A new 36Cl hydrological model and 36Cl systematics in the Jordan River/Dead Sea system

The recent breakthrough in our ability to detect the radioactive isotope 36Cl (half-life T½ = 301,000 yr) at natural levels by accelerator mass spectrometry1 allows the processes of salination of water systems to be studied in a new way by distinguishing the chloride content originating in young rainwaters and their subsequent evaporation from that generated by the leaching of ancient rocks. Results for the Jordan River/Dead Sea system show that the amount of chloride leached from rocks ranges from ∼70% in source springs to >90% in water bodies downstream. Furthermore, the amount of water left after evaporation decreases from ∼50% in the source springs to 20% in the intermediate Lake Kinneret. In the terminal Dead Sea, 99% of the stable chloride originates from ancient rocks and evaporite formations while ∼80% of its 36Cl content is of meteoric origin. Using 36Cl measurements, we estimate the accumulation time of the Dead Sea salt to be 19,000–25,000 yr.