By Kalte Sonne
Sediment analyses of unprecedented accuracy show phases of stability during times of severe climate change – around 15,000 years ago. At the end of the last ice age, the water level fell by almost 250 metres within a few millennia. Wet phases interrupted the drought. A study published today in the journal Scientific Reports now provides new insights into the exact course of this process. This also provides new insights into the settlement history of this area, which is important for human development, and enables better assessments of current and future developments driven by climate change.
The sea level of the Dead Sea is currently falling by more than one metre every year – not least because of the heavy water consumption in the catchment area. But also from earlier times very strong lake level lowerings due to climate changes are known. At the end of the last ice age, the water level fell by almost 250 metres within a few millennia. A study published today in the journal Scientific Reports now provides new insights into the exact course of this process. Daniela Müller and Achim Brauer from the German Research Centre for Geosciences (GFZ) Potsdam, together with colleagues from the Hebrew University in Jerusalem, have investigated 15,000-year-old sediments from the Dead Sea and the surrounding area using newly developed methods. They show with unprecedented accuracy that the phase of severe water level decline was interrupted by wet periods lasting several tens to hundreds of years. This also provides new insights into the settlement history of this area, which is important for human development, and enables better assessments of current and future developments driven by climate change.
The Water Cycle at the Dead Sea – Then and Now
In highly sensitive regions such as the Eastern Mediterranean, where the availability of water is an important factor for socio-economic and political development, it is crucial to understand how the water cycle is changing in response to global climate change. A look back several millennia also helps here. Thus, during the transition from the last ice age to the warm Holocene, the water level of Lake Lisan sank by about 240 meters in the period about 24-11 thousand years ago, which eventually led to its transition to today’s Dead Sea.
Sediments as contemporary witnesses The sediments
on the edge of Lake Lisan near the rock city of Masada and from the depths of today’s Dead Sea are unique witnesses of this development. In their new study, researchers led by doctoral student Daniela Müller and head of Section 4.3 “Climate Dynamics and Landscape Development” Achim Brauer from the German Research Centre for Geosciences Potsdam, together with colleagues from the Geological Survey Israel and the Hebrew University in Jerusalem, analysed these sediments with unprecedented accuracy. The investigations took place as part of the PALEX project ‘Paleohydrology and Extreme Floods from the Dead Sea ICDP Core’, which is funded by the German Research Foundation (DFG).
New high-resolution methods for sediment analysis
For this study, new high-resolution analytical methods were developed at the GFZ in order to obtain precise information from the stratification of the sediments and their geochemical composition, even about seasonal deposition processes and thus about the type, duration and course of climatic phases.
What is particularly new is the combination of light microscopic methods with the so-called 2D element mapping using X-ray fluorescence scanners. This enables precise identification and localization of elements in the sediments. The preparation of the samples is important and challenging for this: they must be deprived of moisture by freeze-drying – not simply with the high salinity of the Dead Sea and its affinity for water. Then the sediments are poured into synthetic resin and then thin sections are made from them. In all this, the microstructure of the sediments must not be changed.
Pause in climate change: Wet phases interrupted long dry periods
The researchers have found that the dramatic drop in the lake level about 15,000 years ago due to increasing drought was interrupted several times by wetter phases, so climate change took breaks. “In this study, we were able for the first time to precisely determine the duration of these phases with a few decades and in one case up to centuries by counting annual layers in the sediment,” says Daniela Müller, first author of the study. However, the exact reason for these pauses in climate change in this region is not yet clear. A connection with climate events in the North Atlantic is suspected.
“It was particularly surprising that during these wetter phases, there were no extreme floods for several decades, which are otherwise still typical for this region today,” explains Müller.
Consequences for archaeological considerations and upcoming climate scenarios
These results are also of interest for archaeological considerations, because they coincide with the time of the sedentary development of the Natuf culture in this region. Climatically stable phases may have favoured cultural developments.
“The study shows that strong climatic changes in the past have been very dynamic and can also include short periods of relative stability. We learn from this that climate change is not linear, but alternates phases of strong changes with more stable phases,” emphasizes Achim Brauer.
Paper: Müller, D., Neugebauer, I., Ben Dor, Y. et al. Phases of stability during major hydroclimate change ending the Last Glacial in the Levant. Sci Rep 12, 6052 (2022). DOI: 10.1038/s41598-022-10217-9