Analysis of Dead Sea sediment shows 15,000-year-old climate phase periods
While rains this winter have filled the Kinneret almost to the top, anyone who has viewed the Dead Sea over recent decades has noticed how it has shrunk, with dangerous sinkholes developing around its circumference.
The level of the Dead Sea is currently dropping by more than a meter every year. But this is not new, according to German and Israeli researchers, who maintain that the level of the salty lake also dropped millennia ago. At the end of the last ice age, for example, the water level dropped by 250 meters within a few thousand years.
A study just published under the title “Phases of stability during major hydroclimate change ending the Last Glacial in the Levant” in the journal Scientific Reports provides new insights into this process. Due to its pivotal location as the cradle of ancient cultural developments, climatic reconstructions using Dead Sea sediments explain causes for human migration, as well as cultural rises and declines.
Dr. Daniela Müller and Prof. Achim Brauer from the German Research Centre for Geosciences (GFZ) in Potsdam, together with Dr. Yoav Ben Dor of the Hebrew University of Jerusalem, studied 15,000-year-old sediments from the Dead Sea and the surrounding area using newly developed methods. With unprecedented accuracy, they showed that the long period of drought was interrupted by wet periods lasting 10 to 100 years. This also offers new insights into the settlement history of this region, which enables better assessments of current and future developments driven by climate change, they wrote.
In highly sensitive regions such as the Eastern Mediterranean, where water availability is an important factor for socioeconomic and political development, it is crucial to understand how the water cycle is changing. Geologists can achieve this by assessing strong hydroclimatic changes that occurred several millennia ago, they said.
For example, during the transition from the last ice age to the Holocene, the water level of Lake Lisan dropped by about 240 meters in the period from 24,000 to 11,000 years ago, eventually leading to its transition into today’s Dead Sea.
The sediments at the edge of Lake Lisan near the archaeological site of Masada and from the bottom of the Dead Sea are unique witnesses to this development, the authors continued. New, high-resolution analytical methods, including x-ray fluorescence scanners, were developed for the study at the GFZ to collect precise information from the stratification of the sediments and their geochemical composition.
To prepare the sediments for analysis, the moisture had to be removed by freeze-drying, a complicated task given the Dead Sea’s high salt content and its affinity for water. The sediments are then impregnated in synthetic resin and thin sections were made from them without changing their microstructure.
The researchers found out that the dramatic, long-term drop in the lake level due to increasing dryness was interrupted several times by wetter phases when climate change took breaks.
“We were able for the first time to precisely determine the duration of these phases with several decades and in one case up to centuries by counting annual layers in the sediment,” said lead author Müller. The exact reason for these pauses in the climate change of this region still remain elusive, but the team suspected possible links to the climate in the north Atlantic Ocean.
“What was particularly surprising was that during these wetter phases, in some cases over several decades, we did not even find any traces of extreme floods, which are typical for this region even today and during wetter times in the past,” Müller explained.
These results are of further interest for archaeological considerations, they wrote, because they coincide with the time when the Natufian culture settled in this region 11,500 to 15,000 years ago. “Climatically stable phases could have favored the cultural developments,” they said.
“The study shows that strong climatic changes in the past have been very dynamic and included phases of relative stability,” Brauer concluded. “We learn from this that climate change is not linear, but that phases of strong changes alternate with calm phases.”