Limnological instrumentation in the middle of the ¹⁹th century: the first temperature and density profiles measured in the Dead Sea

The first modern survey of the Dead Sea was performed by the Geological Survey of Israel in 1959–1960, and the report published remains the baseline study for our understanding of the physical and chemical properties of the lake. At the time the Dead Sea was a meromictic lake with a strong salinity gradient separating the deep waters (>40 m depth) from the less saline surface waters. A few results of analyses of deeper water samples collected in the 1930s were reported, but overall we have very little information about the structure of the lake’s water column before the 1959–1960 survey. However, it is little known that data on the physical and the chemical structure of the Dead Sea water column were obtained already in the middle of the ¹⁹th century, and the information collected then is highly relevant for the reconstruction of the limnological properties of the lake in earlier times. The expedition of Lieutenant William Lynch (U.S. Navy) in 1848 reported the presence of a temperature minimum at a depth of ~18 m, and also retrieved a water sample collected close to the bottom for chemical analysis. In 1864, the French Dead Sea exploration by the Duc de Luynes and his crew yielded detailed density and salinity profiles for a number of sampling stations. The results of these pioneering studies are discussed here, as well as the sampling equipment and measuring instruments used by the 1848 and the 1864 expeditions.