News from the climate history of the Dead Sea

Date:
April 27, 2022
Source:
GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre
Summary:
The lake level of the Dead Sea is currently dropping by more
than one meter every year -- mainly because of the heavy water
consumption in the catchment area. However, very strong lake level
drops due to climate changes are also known from earlier times. At
the end of the last ice age, for example, the water level dropped
by almost 250 meters within a few millennia.



FULL STORY ==========================================================================
The lake level of the Dead Sea is currently dropping by more than one
metre every year -- mainly because of the heavy water consumption in
the catchment area. However, very strong lake level drops due to climate changes are also known from earlier times. At the end of the last ice age,
for example, the water level dropped by almost 250 metres within a few millennia. A study published today in the journal Scientific Reportsnow provides new insights into the exact course of this process. Daniela
Mu"ller and Achim Brauer from the German Research Centre for Geosciences
(GFZ) in Potsdam, together with colleagues from 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 show that the long period of drought was interrupted by
wet periods lasting ten to a hundred years. This also offers new insights
into the settlement history of this region, which is significant 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 water availability is
an important factor for socio-economic and political development, it
is crucial to understand how the water cycle is changing in response
to climate change. Geologists can achieve this by assessing strong hydroclimatic changes that occurred several millennia back in time. For example, during the transition from the last ice age to the Holocene,
the water level of Lake Lisan dropped by about 240 metres in the period
24-11 thousand years ago, which eventually led to its transition into
today's Dead Sea.

Sediments as witnesses of time The sediments at the edge of lake Lisan
near the archaeological site of Masada and from the bottom of what is now
the Dead Sea are unique witnesses to this development. In their new study, researchers led by Achim Brauer, head of Section 4.3 "Climate Dynamics
and Landscape Evolution" at the German Research Centre for Geosciences
Potsdam, and doctoral student Daniela Mu"ller together with colleagues
from the Geological Survey Israel and the Hebrew University of Jerusalem, analysed these sediments with unprecedented precision. The investigations
took place within the framework 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 to gain
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.



==========================================================================
In particular, the combination of light microscopic methods with so-called
2D element mapping using X-ray fluorescence scanners is new. This
enables the precise identification and localisation of elements in
the sediments. Important and challenging for this is the preparation
of the sediments for this analysis: The moisture must be removed from
them by freeze-drying -- not easy given the high salt content of the
Dead Sea and its affinity for water. Then the sediments are impregnated
in synthetic resin and thin sections are made from them. In all this,
the microstructure must not be altered.

Pause in climate change: humid phases interrupted long dry periods
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. "In this study, 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," says Daniela Mu"ller, lead author of the study. The
exact reason for these pauses in the climate change of this region still
remain elusive. Possible links to North Atlantic climate are suspected.

"What was particularly surprising was that during these wetter phases,
in some cases over several decades, there we even did not find any
traces of extreme floods, which are typical for this region even today
and during wetter times in the past," Mu"ller explains.

Consequences for archaeological considerations and future climate
scenarios These results are of further interest for archaeological considerations because they coincide with the time when the Natufian
culture settled in this region.

Climatically stable phases could have favoured the cultural developments.

"The study shows that strong climatic changes in the past have been very dynamic and included phases of relative stability. We learn from this
that climate change is not linear, but that phases of strong changes
alternate with calm phases," says Achim Brauer.


========================================================================== Story Source: Materials provided by GFZ_GeoForschungsZentrum_Potsdam,_Helmholtz_Centre. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Daniela Mu"ller, Ina Neugebauer, Yoav Ben Dor, Yehouda Enzel,
Markus J.

Schwab, Rik Tjallingii, Achim Brauer. Phases of stability
during major hydroclimate change ending the Last Glacial
in the Levant. Scientific Reports, 2022; 12 (1) DOI:
10.1038/s41598-022-10217-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220427100454.htm

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