Dramatic drops in the level of the Dead Sea in the last hundreds of thousands of years may indicate prolonged dry periods in the Eastern Mediterranean region. For example, in the time period between 70 and 14 thousand years ago, the lake level was about 270 meters higher than the current level.
Can the Dead Sea teach us about the climate conditions in the eastern Mediterranean basin and the Levant region in the past? The Dead Sea is a very salty lake (the various salts make up about 30% of its weight), without an outlet to the sea, even though it has a very large drainage basin that also leads to fresh water (for example Jordan, Yarmouch, Arnon, spring water and floods). The climate changes that occurred in the last hundreds of thousands of years caused increases in the lake level in wet periods and a decrease in the level in dry periods. Over time, depending on the water regime and other processes, sediments accumulated in the lake as layers with varying compositions. The information contained in these sediments, about changes in the composition of the Dead Sea water in the past and the environmental conditions that dictated it, for example about the balance between the fresh water that flowed into the lake and the evaporation from it, may, if deciphered correctly, teach about climatic changes that took place in the Azar in the past.
Cores from a scientific drilling conducted at the bottom of the Dead Sea and its margins in 2011-2010 are a representative sample of the sediments that accumulated at the bottom of the lake. They contain many spaces (between the grains) where salty lake bottom water has been trapped. In the areas at the edge of the lake, the sediments were exposed and the trapped water evaporated, leaving in the spaces soluble salts that represent the chemical composition of the water. The measurement and study of the compositions of these sediments and the water (or soluble salts) in them - are the main current research of Prof. Beaz Lazar and his partners from the Institute of Earth Sciences at the Hebrew University.
This study enabled an environmental reconstruction of the last 220 thousand years in which the lake underwent many changes both in its composition and in its levels. For example, in the time period between 70 and 14 thousand years ago, the lake level was about 270 meters higher (about 170 meters below sea level) than the current level (about 440 meters below sea level); whereas in the last ten thousand years it has decreased to levels that have roughly reached the current level. These changes reflect significant fluctuations in the regional rainfall regime. The drops in the level are due to a decrease in the amount of fresh water entering the lake and indicate dry periods that prevailed in the area (the modern expression of which is in prolonged forms).
The research, which won a grant from the National Science Foundation, revolved around deciphering the environmental information contained in the sediments from the periods when the lake level dropped to low levels and deposited salt. Although the name of the lake is the Dead Sea, salt (table salt or the mineral halite) rarely sinks into it. The research focuses on the two main periods in which the salt sank: about 120 years ago and about 11 years ago. The chemical compositions of the various salts and minerals in the lake sediments and the concentration of elements such as chlorine, bromine, sodium and magnesium in the salts and in the water between the sediment grains were used for calculations in which various environmental characteristics were determined. Among them: the salinity of the lake, its level, times of fresh water arrivals and other processes that took place in the lake during the periods of salt deposition. The calculations and data show that during the periods of salt deposition, the Jordan River contributed almost no water to the lake. Today, salt sinks into the lake because of a rapid drop in level that is largely due to the prevention of the Jordan's flow southward (human intervention).
The research findings are also compared to information that comes from other independent geological databases, such as cores extracted from the deep waters of the Mediterranean Sea or cave sediments from the Israel region. All the data together allow researchers to build a complex picture of the regional climate conditions during those periods of salt deposition and to examine the extent of the impact of climate change in the world during these periods. In addition, the reconstruction of the natural climate conditions during dry periods in which the salt sink produces a data base of great importance for the calibration of climate models that are currently being developed for global warming forecasts.
Life itself:
Prof. Beaz Lazar studies geochemical and environmental processes in natural interfaces, mainly in bodies of water such as lakes and seas (the Dead Sea, the Sea of Galilee and the Red Sea).
