Editing Dead Sea (section)

==Chemistry==
[[File:Dead Sea Halite View 031712.jpg|thumb|Halite deposits (and [[teepee structure]]) along the western Dead Sea coast]]
With 34.2% [[salinity]] (in 2011), it is one of the [[List of bodies of water by salinity|world's saltiest bodies of water]], though [[Lake Vanda]] in [[Antarctica]] (35%), [[Lake Assal (Djibouti)|Lake Assal]] in [[Djibouti]] (34.8%), Lagoon [[Garabogazköl]] in the [[Caspian Sea]] (up to 35%) and some hypersaline ponds and lakes of the [[McMurdo Dry Valleys]] in [[Antarctica]] (such as [[Don Juan Pond]] (44%)) have reported higher salinities.

In the 19th century and the early 20th century, the surface layers of the Dead Sea were less salty than today, which resulted in an average density in the range of 1.15–1.17 g/cm<sup>3</sup> instead of the present value of around 1.25 g/cm<sup>3</sup>. A sample tested by [[Albert James Bernays|Bernays]] in the 19th century had a salinity of 19%. By the year 1926, the salinity had increased<ref>Encyclopædia Britannica, Eleventh Edition, Volume 7, page 879</ref><ref>{{cite journal |last1=Friend |first1=J. Newton |title=Examination of Dead Sea Water for Eka-Cæsium and Eka-Iodine |journal=Nature |date=June 1926 |volume=117 |issue=2953 |pages=789–790 |doi=10.1038/117789b0 |bibcode=1926Natur.117..789F |s2cid=4114399 }}</ref> (although it was also suspected that the salinity varies seasonally and depends on the distance from the mouth of the [[Jordan River|Jordan]]).

Until the winter of 1978–79, when a major mixing event took place,<ref name=overturn/> the Dead Sea was composed of two stratified layers of water that differed in temperature, density, age, and salinity. The topmost {{convert|35|m|ft|0|sp=us}} or so of the Dead Sea had an average salinity of about 30%, and a temperature that swung between {{convert|19|and|37|°C|°F|abbr=on}}. Underneath a zone of transition, the lowest level of the Dead Sea had waters of a consistent {{convert|22|°C|°F|abbr=on}} temperature, salinity of over 34%, and complete [[Saturated solution|saturation]] of [[sodium chloride]] (NaCl).<ref>{{cite book |doi=10.1007/978-3-642-14779-1_4 |chapter=The Dramatic Drop of the Dead Sea: Background, Rates, Impacts and Solutions |title=Macro-engineering Seawater in Unique Environments |series=Environmental Science and Engineering |year=2010 |last1=Abu Ghazleh |first1=Shahrazad |last2=Abed |first2=Abdulkader M. |last3=Kempe |first3=Stephan |pages=77–105 |isbn=978-3-642-14778-4 }}</ref> Since the water near the bottom is [[Saturated solution|saturated]] with NaCl, that salt precipitates out of solution onto the [[sea floor]].

Beginning in the 1960s, water inflow to the Dead Sea from the Jordan River was reduced as a result of large-scale irrigation and generally low rainfall. By 1975, the upper water layer was saltier than the lower layer. Nevertheless, the upper layer remained suspended above the lower layer because its waters were warmer and thus less dense. When the upper layer cooled so its density was greater than the lower layer, the waters mixed (1978–79). For the first time in centuries,{{citation needed|date=October 2024}} the lake was a homogeneous body of water. Since then, [[Ocean stratification|stratification]] has begun to redevelop.<ref name=overturn>{{cite web|url=http://www1.american.edu/TED/deadsea.htm|title=Dead Sea Canal|publisher=American.edu|date=1996-12-09|access-date=May 5, 2009|url-status=dead|archive-url=https://web.archive.org/web/20090522133748/http://www1.american.edu/TED/deadsea.htm|archive-date=May 22, 2009}}</ref>[[File:SaltCementedPebblesDeadSea.JPG|thumb|Pebbles cemented with [[halite]] on the western shore of the Dead Sea near Ein Gedi|alt=|left]]

The mineral content of the Dead Sea is very different from that of ocean water. The exact composition of the Dead Sea water varies mainly with season, depth and temperature. In the early 1980s, the concentration of ionic species (in g/kg) of Dead Sea surface water was Cl<sup>−</sup> (181.4), Br<sup>−</sup> (4.2), SO<sub>4</sub><sup>2−</sup> (0.4), HCO<sub>3</sub><sup>−</sup> (0.2), Ca<sup>2+</sup> (14.1), Na<sup>+</sup> (32.5), K<sup>+</sup> (6.2) and Mg<sup>2+</sup> (35.2). The total salinity was 276 g/kg.<ref>{{cite journal |last1=Steinhorn |first1=Ilana |title=In situ salt precipitation at the Dead Sea |journal=Limnology and Oceanography |date=May 1983 |volume=28 |issue=3 |pages=580–583 |id={{INIST|9327311}} |doi=10.4319/lo.1983.28.3.0580 |bibcode=1983LimOc..28..580S |doi-access=free }}</ref> These results show that the composition of the salt, as anhydrous chlorides on a weight percentage basis, was [[calcium chloride]] (CaCl<sub>2</sub>) 14.4%, [[potassium chloride]] (KCl) 4.4%, [[magnesium chloride]] (MgCl<sub>2</sub>) 50.8% and [[sodium chloride]] (NaCl) 30.4%. In comparison, the salt in the water of most [[ocean]]s and [[sea]]s is approximately 85% [[sodium chloride]]. The concentration of [[sulfate]] ions (SO<sub>4</sub><sup>2−</sup>) is very low, and the concentration of [[bromide]] ions (Br<sup>−</sup>) is the highest of all waters on Earth.
[[File:Halite Dead Sea Beach Pebbles.JPG|thumb|Beach pebbles made of [[halite]]; western coast]]

The salt concentration of the Dead Sea fluctuates around 31.5%. This is unusually high and results in a nominal density of 1.24&nbsp;kg/L. Anyone can easily float in the Dead Sea because of natural [[buoyancy]]. In this respect the Dead Sea is similar to the [[Great Salt Lake]] in [[Utah]] in the United States.

An unusual feature of the Dead Sea is its discharge of [[Bitumen|asphalt]]. From deep [[seeps]], the Dead Sea constantly spits up small pebbles and blocks of the black substance.<ref>{{cite journal |last1=Bein |first1=A. |last2=Amit |first2=O. |title=The evolution of the dead sea floating asphalt blocks: Simulations by pyrolysis |journal=Journal of Petroleum Geology |date=April 1980 |volume=2 |issue=4 |pages=439–447 |doi=10.1111/j.1747-5457.1980.tb00971.x |bibcode=1980JPetG...2..439B }}</ref> Asphalt-coated figurines and bitumen-coated [[Neolithic]] skulls from [[archaeological]] sites have been found. [[Ancient Egypt|Egyptian]] [[mummification]] processes used asphalt imported from the Dead Sea region.<ref>Niemi, Tina M., [[Zvi Ben-Avraham]] and Joel Gat, eds., ''The Dead Sea: the lake and its setting,'' 1997, Oxford University Press, p. 251 {{ISBN|978-0-19-508703-1}}</ref><ref>{{cite journal |last1=Rullkötter |first1=J. |last2=Nissenbaum |first2=A. |title=Dead sea asphalt in egyptian mummies: Molecular evidence |journal=Naturwissenschaften |date=December 1988 |volume=75 |issue=12 |pages=618–621 |doi=10.1007/BF00366476 |pmid=3237249 |bibcode=1988NW.....75..618R |s2cid=29037897 }}</ref>