Salt lakes - chemistry of Dead Sea
Until the winter of 1978-1979, the
Dead Sea was composed of two stratified layers of water that differed in temperature, density, age, and
salinity. The topmost 35 meters or so of the Dead Sea had a salinity that ranged between 300 and 400 parts per thousand and a temperature that swung between 19 °C (66 °F) and 37 °C (98 °F). Underneath a zone of transition, the lowest level of the Dead Sea had waters of a consistent 22 °C (72 °F) temperature and complete saturation of sodium chloride (NaCl).[citations needed] Since the water near the bottom is saturated, the 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 of the Dead Sea was actually saltier than the lower layer. The upper layer nevertheless remained suspended above the lower layer because its waters were warmer and thus less dense. When the upper layer finally cooled down so that its density was greater than the lower layer the waters of the Dead Sea mixed. For the first time in centuries the lake was a homogeneous body of water. Since then stratification has begun to redevelop.
The mineral content of the Dead Sea is significantly different from that of ocean water. The exact composition of the Dead Sea water varies with season, depth, temperature and so on. The concentration of ionic species (in g/kg) of Dead Sea surface water in the early 1980s was found to be: Cl– (181.4), Br– (4.2), SO42– (0.4), HCO3– (0.2), Ca2+ (14.1), Na+ (32.5), K+ (6.2) and Mg2+ (35.2). The total salinity was 276 g/kg [9] These results show that w/w% composition of the salt, as anhydrous chlorides, was calcium chloride (CaCl2) 14.4%, potassium chloride (KCl) 4.4%, magnesium chloride (MgCl2) 50.8% and sodium chloride (common salt, NaCl) 30.4%. In comparison, the salt in the water of most oceans and seas is approximately 97% sodium chloride. The concentration of sulfate, SO42–, ions is very low, and the bromide ion, Br– concentration is the highest of all waters on Earth.
Comparison between the chemical composition of the Dead Sea to other lakes and oceans show that the
salt concentration in the Dead Sea is 31.5% (the salinity fluctuates somewhat). Because of its unusually high concentration of salt, anyone can easily float in the Dead Sea because of natural buoyancy as a result of the higher density of the water. In this aspect, the Dead Sea is similar to the Great Salt Lake in Utah, in the United States.
One of the most unusual properties of the Dead Sea is its discharge of asphalt. From deep seeps, the Dead Sea constantly spits up small pebbles of the black substance. After earthquakes, chunks as large as houses have been found.
The Dead Sea area has become a major center for health research and treatment for several reasons. The mineral content of the waters, the very low content of pollens and other allergens in the atmosphere, the reduced ultraviolet component of solar radiation, and the higher atmospheric pressure at this great depth each have specific health effects. For example, persons suffering reduced respiratory function from diseases such as cystic fibrosis seem to benefit from the increased atmospheric pressure.
Sufferers of the skin disorder psoriasis also benefit from the ability to sunbathe for long periods in the area due to its position below sea level and subsequent result that many of the sun's harmful UV rays are reduced. Furthermore, Dead Sea salt has been found to be beneficial to psoriasis patients.
Source: Until the winter of 1978-1979, the Dead Sea was composed of two stratified layers of water that differed in temperature, density, age, and salinity. The topmost 35 meters or so of the Dead Sea had a salinity that ranged between 300 and 400 parts per thousand and a temperature that swung between 19 °C (66 °F) and 37 °C (98 °F). Underneath a zone of transition, the lowest level of the Dead Sea had waters of a consistent 22 °C (72 °F) temperature and complete saturation of sodium chloride (NaCl).[citations needed] Since the water near the bottom is saturated, the 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 of the Dead Sea was actually saltier than the lower layer. The upper layer nevertheless remained suspended above the lower layer because its waters were warmer and thus less dense. When the upper layer finally cooled down so that its density was greater than the lower layer the waters of the Dead Sea mixed. For the first time in centuries the lake was a homogeneous body of water. Since then stratification has begun to redevelop.[8]
The mineral content of the Dead Sea is significantly different from that of ocean water. The exact composition of the Dead Sea water varies with season, depth, temperature and so on. The concentration of ionic species (in g/kg) of Dead Sea surface water in the early 1980s was found to be: Cl– (181.4), Br– (4.2), SO42– (0.4), HCO3– (0.2), Ca2+ (14.1), Na+ (32.5), K+ (6.2) and Mg2+ (35.2). The total salinity was 276 g/kg [9] These results show that w/w% composition of the salt, as anhydrous chlorides, was calcium chloride (CaCl2) 14.4%, potassium chloride (KCl) 4.4%, magnesium chloride (MgCl2) 50.8% and sodium chloride (common salt, NaCl) 30.4%. In comparison, the salt in the water of most oceans and seas is approximately 97% sodium chloride. The concentration of sulfate, SO42–, ions is very low, and the bromide ion, Br– concentration is the highest of all waters on Earth.
Comparison between the chemical composition of the Dead Sea to other lakes and oceans show that the salt concentration in the Dead Sea is 31.5% (the salinity fluctuates somewhat). Because of its unusually high concentration of salt, anyone can easily float in the Dead Sea because of natural buoyancy as a result of the higher density of the water. In this aspect, the Dead Sea is similar to the Great Salt Lake in Utah, in the United States.
Dead Sea in the Evening
Dead Sea in the Evening
One of the most unusual properties of the Dead Sea is its discharge of asphalt. From deep seeps, the Dead Sea constantly spits up small pebbles of the black substance. After earthquakes, chunks as large as houses have been found.
The Dead Sea area has become a major center for health research and treatment for several reasons. The mineral content of the waters, the very low content of pollens and other allergens in the atmosphere, the reduced ultraviolet component of solar radiation, and the higher atmospheric pressure at this great depth each have specific health effects. For example, persons suffering reduced respiratory function from diseases such as cystic fibrosis seem to benefit from the increased atmospheric pressure.[10]
Sufferers of the skin disorder psoriasis also benefit from the ability to sunbathe for long periods in the area due to its position below sea level and subsequent result that many of the sun's harmful UV rays are reduced. Furthermore, Dead Sea salt has been found to be beneficial to psoriasis patients. Source:
http://en.wikipedia.org05.09.2007. 12:13