Termination of the Dead Sea 1991-1995 stratification: Biological and physical evidence

The presence of a sufficiently dense bacterial community (2-4 × 10⁶ cells ml^-1) in the upper 30 m of the Dead Sea water column in the autumn of 1995 provided us with a unique opportunity to follow the extent and the rate of the mixing of the water column in the following winter, when the occurrence of a new overturn could be predicted from the changes of temperature and salinity profiles with time. All microbial parameters measured (total bacterial numbers, bacterioruberin content, and incorporation rate of glycerol) showed similar trends: a rapid, more than fivefold decrease in the upper water layers during the first three weeks of November 1995, followed by an even distribution of all parameters with depth on 26 November. This decrease can only be explained as a direct result of the redistribution of the bacterial community over much greater depths than before. We conclude that the overturn event proceeded within a few weeks only. Physical evidence points to double-diffusive mixing as the probable mechanism for this rapid overturn.