Dead Sea
البحر الميت (Arabic) ים המלח (Hebrew)
A view of the sea from the Jordanian shore with the hills of the West Bank in the background
Dead Sea
Location	Western Asia
Coordinates	31°30′N 35°30′E / 31.500°N 35.500°E / 31.500; 35.500
Lake type	Endorheic Hypersaline
Primary inflows	Jordan River
Primary outflows	None
Catchment area	41,650 km2 (16,080 sq mi)
Basin countries	Jordan, Palestine (Israeli-occupied West Bank), Israel
Max. length	50 km (31 mi)[1] (northern basin only)
Max. width	15 km (9.3 mi)
Surface area	605 km2 (234 sq mi) (2016)[2]
Average depth	188.4 m (618 ft)[3]
Max. depth	298 m (978 ft) (elevation of deepest point, 728 m (2,388 ft) BSL , minus current surface elevation)
Water volume	114 km3 (27 cu mi)[3]
Shore length1	135 km (84 mi)
Surface elevation	−430.5 m (−1,412 ft) (2016)[4]
References	[3][4]
1 Shore length is not a well-defined measure.

The Dead Sea (Arabic: اَلْبَحْر الْمَيِّت, romanized: al-Baḥr al-Mayyit, or اَلْبَحْر الْمَيْت, al-Baḥr al-Mayt; Hebrew: יַם הַמֶּלַח, romanized: Yām hamMelaḥ), also known by other names, is a landlocked salt lake bordered by Jordan to the east and the Israeli-occupied West Bank and Israel to the west.^[5][6] It lies in the Jordan Rift Valley, and its main tributary is the Jordan River.

As of 2019, the lake's surface is 430.5 metres (1,412 ft) below sea level,^[4][7] making its shores the lowest land-based elevation on Earth. It is 304 m (997 ft) deep, the deepest hypersaline lake in the world. With a salinity of 342 g/kg, or 34.2% (in 2011), it is one of the world's saltiest bodies of water^[8] – 9.6 times as salty as the ocean – and has a density of 1.24 kg/litre, which makes swimming similar to floating.^[9][10] This salinity makes for a harsh environment in which plants and animals cannot flourish, hence its name. The Dead Sea's main, northern basin is 50 kilometres (31 mi) long and 15 kilometres (9 mi) wide at its widest point.^[1]

The Dead Sea has attracted visitors from around the Mediterranean Basin for thousands of years. It was one of the world's first health resorts, and it has been the supplier of a wide variety of products, from asphalt for Egyptian mummification to potash for fertilisers. Today, tourists visit the sea on its Israeli, Jordanian and West Bank coastlines.

The Dead Sea is receding at a swift rate; its surface area today is 605 km² (234 sq mi), having been 1,050 km² (410 sq mi) in 1930. Multiple canal and pipeline proposals, such as the scrapped Red Sea–Dead Sea Water Conveyance project,^[11] have been made to reduce its recession.

Names

The English name "Dead Sea" is a calque of the Arabic name, itself a calque of earlier Greek and Latin names^{[citation needed]}, in reference to the scarcity of aquatic life caused by the lake's extreme salinity.^[12] Historical English names include the Salt Sea,^[13] Lake of Sodom^[13] from the biblical account of its destruction^[14] and Lake Asphaltites^[13] from Greek and Latin.

The name "Dead Sea" occasionally appears in Hebrew literature as Yām HamMāvet (ים המוות), 'Sea of Death'.^[12] The usual biblical^[15] and modern Hebrew name for the lake is the Sea of Salt (ים המלח, Yām HamMelaḥ^ⓘ). Other Hebrew names for the lake also mentioned in the Bible are the Sea of Arabah (ים הערבה, Yām Ha‘Ărāvâ) and the Eastern Sea (הים הקדמוני, HaYām HaQadmōnî).

The Arabic name is al-Bahr al-Mayyit^ⓘ (‏البحر الميت‎), or usually without the article al-, so just Bahr etc.^[16] It is also known in Arabic as the Sea of Lot (‏بحر لوط‎, Buhayrat,^[17] Bahret, or Birket Lut)^[18] from the nephew of Abraham whose wife was said to have turned into a pillar of salt during the destruction of Sodom and Gomorrah.^[14] Less often, it has been known in Arabic as the Sea of Zo'ar from a formerly important city along its shores.

Because of the large volume of ancient trade in the lake's naturally occurring free-floating bitumen, its usual names in ancient Greek and Roman geography were some form of Asphalt Lake (Greek: Ἀσφαλτίτης or Ἀσφαλτίτις Λίμνη, Asphaltítēs or Asphaltítis Límnē; Latin: Lacus Asphaltites) or Sea (Ἀσφαλτίτης Θάλασσα, Asphaltítēs Thálassa). It was also known as the 'Dead Sea' (Greek Νεκρά Θάλασσα, Nekrá Thálassa, Latin (Mare Mortuum).^{[citation needed]}

Geography

The Dead Sea is a salt lake is bordered by Jordan to the east and Palestine's Israeli-occupied West Bank and Israel to the west.^[5][6] It is an endorheic lake, meaning there are no outlet streams.

The Dead Sea lies in the Jordan Rift Valley, a geographic feature formed by the Dead Sea Transform (DST). This left lateral-moving transform fault lies along the tectonic plate boundary between the African Plate and the Arabian Plate. It runs between the East Anatolian Fault zone in Turkey and the northern end of the Red Sea Rift offshore of the southern tip of Sinai.

Water feeds into the Dead Sea from various sources, many small or intermittent, including:

• Jordan River, international border from the north^[5]
• Arava Stream (Wadi Arava), international border from the south
• Wadi Mujib (Arnon Stream), Jordan, Karak Governorate^[19]
• Wadi Darga^[19] (Wadi Darajeh, Nahal Darga, or Nahal Dragot), West Bank
• Wadi al-Hasa (Brook of Zered), Jordon, boundary between Karak Governorate and Tafilah Governorate
• Nahal Arugot [de] (Wadi Areijeh or Wadi Argot), mouth at Ein Gedi, Israel^[19]
• Wadi Wala, Jordan side^[19]
• Wadi Zarqa Ma'in, Jordan side^[19]
• Nahal Tur, West Bank
• Groundwater seepage^[19]
• Direct rainfall

(Wadi is the Arabic term for a river valley with a small or intermittent stream; Nahal is the equivalent in Hebrew. The two terms are often used interchangeably in English names for the same body of water.)

The water of Wadi Hassa is now completely consumed in Jordan.^[19] The Jordan River, which passes through the Sea of Galilee, has been substantially diverted. It currently only contributes about one-sixth of the inflow to the Dead Sea, less than direct rainfall.^[19]

There are also small perennial springs under and around the Dead Sea, forming pools and quicksand pits along the edges.^[20]

The Wadi Mujib valley, 420 m below the sea level in the southern part of the Jordan valley, is a biosphere reserve, with an area of 212 km² (82 sq mi).^[21] Rainfall is scarcely 100 mm (4 in) per year in the northern part of the Dead Sea and barely 50 mm (2 in) in the southern part.^[22] The Dead Sea zone's aridity is due to the rainshadow effect of the Judaean Mountains. The highlands east of the Dead Sea receive more rainfall than the Dead Sea itself.

To the west of the Dead Sea, the Judaean mountains rise less steeply and are much lower than the mountains to the east. Along the southwestern side of the lake is a 210 m (700 ft) tall halite mineral formation called Mount Sodom.

Geology

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Formation theories

There are two contending hypotheses about the origin of the low elevation of the Dead Sea. The older hypothesis is that the Dead Sea lies in a true rift zone, an extension of the Red Sea Rift, or even of the Great Rift Valley of eastern Africa. A more recent hypothesis is that the Dead Sea basin is a consequence of a "step-over" discontinuity along the Dead Sea Transform, creating an extension of the crust with consequent subsidence.^{[citation needed]}

Sedom Lagoon

During the late Pliocene-early Pleistocene, what is now the valley of the Jordan River, Dead Sea, and the northern Wadi Arabah was repeatedly inundated by waters from the Mediterranean Sea.^[23] The waters formed in a narrow, crooked bay that is called by geologists the Sedom Lagoon, which was connected to the sea through what is now the Jezreel Valley.^{[citation needed]} The floods of the valley came and went depending on long-scale changes in the tectonic and climatic conditions.^[23]

The Sedom Lagoon extended at its maximum from the Sea of Galilee in the north to somewhere around 50 km (30 mi) south of the current southern end of the Dead Sea, and the subsequent lakes never surpassed this expanse. The Hula Depression was never part of any of these water bodies due to its higher elevation and the high threshold of the Korazim block separating it from the Sea of Galilee basin.^[24]

Salt deposits

The Sedom Lagoon deposited evaporites mainly consisting of rock salt, which eventually reached a thickness of 2.3 km (1.43 mi) on the old basin floor in the area of today's Mount Sedom.^[25]

Lake formation

According to Kafri, during the late Neogene, i.e. in the Pliocene (ended c. 2.5 million years ago), the eustatic sea level was at 50–100 metres above the current sea level, thus flooding the northern valleys connecting the Mediterranean Sea with the Jordan Rift Valley, which led to the creation of a crooked-shaped lagoon. This high eustatic sea level situation subsequently came to an end, and the ocean could no longer flood the area. Thus, the long lagoon became a landlocked lake, which - due to the high evaporation rate - retreated toward the lower, southern part of the rift valley.^[24] However, Mordechai Stein considers the formation process as not yet clarified, speaking of a late Pliocene-early Pleistocene process in which tectonics might also have played a part in blocking water ingression from the Mediterranean to its former bay or lagoon.^[23]

The first prehistoric lake to follow the Sedom Lagoon is named Lake Amora (which possibly appeared in the early Pleistocene; its sediments developed into the Amora (Samra) Formation, dated to over 200–80 kyr BP), followed by Lake Lisan (c. 70–14 kyr) and finally by the Dead Sea.^[23]

Lake salinity

The water levels and salinity of the successive lakes (Amora, Lisan, Dead Sea) have either risen or fallen as an effect of the tectonic dropping of the valley bottom, and due to climate variation. As the climate became more arid, Lake Lisan finally shrank and became saltier, leaving the Dead Sea as its last remainder.^[23][24]

From 70,000 to 12,000 years ago, Lake Lisan's level was 100 to 250 m (330 to 820 ft) higher than its current level, possibly due to lower evaporation than in the present.^[26][27] Its level fluctuated dramatically, rising to its highest level around 26,000 years ago, indicating a very wet climate in the Near East.^[28] Around 10,000 years ago, the lake's level dropped dramatically, probably even lower than today. During the last several thousand years, the lake has fluctuated approximately 400 m (1,300 ft), with some significant drops and rises. Current theories as to the cause of this dramatic drop in levels rule out volcanic activity; therefore, it may have been a seismic event.

Salt mounts formation

In prehistoric times,^{[dubious – discuss]} great amounts of sediment collected on the floor of Lake Amora. The sediment was heavier than the salt deposits and squeezed the salt deposits upwards into what are now the Lisan Peninsula and Mount Sodom (on the southwest side of the lake). Geologists explain the effect in terms of a bucket of mud into which a large flat stone is placed, forcing the mud to creep up the sides of the bucket. When the floor of the Dead Sea dropped further due to tectonic forces, the salt mounts of Lisan and Mount Sodom stayed in place as high cliffs (see salt dome).

Climate

The Dead Sea has a hot desert climate (Köppen climate classification BWh), with year-round sunny skies and dry air. It has less than 50 millimetres (2 in) mean annual rainfall and a summer average temperature between 32 and 39 °C (90 and 102 °F). Winter average temperatures range between 20 and 23 °C (68 and 73 °F). The region has weaker ultraviolet radiation, particularly the UVB (erythrogenic rays). Given the higher atmospheric pressure, the air has a slightly higher oxygen content (3.3% in summer to 4.8% in winter) as compared to oxygen concentration at sea level.^[29][30] Barometric pressures at the Dead Sea were measured between 1061 and 1065 hPa and clinically compared with health effects at higher altitude.^[31] (This barometric measure is about 5% higher than sea level standard atmospheric pressure of 1013.25 hPa, which is the global ocean mean or ATM.) The Dead Sea affects temperatures nearby because of the moderating effect a large body of water has on climate. During the winter, sea temperatures tend to be higher than land temperatures, and vice versa during the summer months. This is the result of the water's mass and specific heat capacity. On average, there are 192 days above 30 °C (86 °F) annually.^[32]

Chemistry

With 34.2% salinity (in 2011), it is one of the world's saltiest bodies of water, though Lake Vanda in Antarctica (35%), 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/cm³ instead of the present value of around 1.25 g/cm³. A sample tested by Bernays in the 19th century had a salinity of 19%. By the year 1926, the salinity had increased^[34][35] (although it was also suspected that the salinity varies seasonally and depends on the distance from the mouth of the Jordan).

Until the winter of 1978–79, when a major mixing event took place,^[36] the Dead Sea was composed of two stratified layers of water that differed in temperature, density, age, and salinity. The topmost 35 meters (115 ft) or so of the Dead Sea had an average salinity of about 30%, and a temperature that swung between 19 and 37 °C (66 and 99 °F). Underneath a zone of transition, the lowest level of the Dead Sea had waters of a consistent 22 °C (72 °F) temperature, salinity of over 34%, and complete saturation of sodium chloride (NaCl).^[37] Since the water near the bottom is 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, the lake was a homogeneous body of water. Since then, stratification has begun to redevelop.^[36]

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⁻ (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.^[38] These results show that the composition of the salt, as anhydrous chlorides on a weight percentage basis, was calcium chloride (CaCl₂) 14.4%, potassium chloride (KCl) 4.4%, magnesium chloride (MgCl₂) 50.8% and sodium chloride (NaCl) 30.4%. In comparison, the salt in the water of most oceans and seas is approximately 85% sodium chloride. The concentration of sulfate ions (SO₄²⁻) is very low, and the concentration of bromide ions (Br⁻) is the highest of all waters on Earth.

The salt concentration of the Dead Sea fluctuates around 31.5%. This is unusually high and results in a nominal density of 1.24 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 asphalt. From deep seeps, the Dead Sea constantly spits up small pebbles and blocks of the black substance.^[39] Asphalt-coated figurines and bitumen-coated Neolithic skulls from archaeological sites have been found. Egyptian mummification processes used asphalt imported from the Dead Sea region.^[40][41]

Putative therapies

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The Dead Sea area has become a location for health research and potential treatment for several reasons. The mineral content of the water, the 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 may have specific health effects. For example, persons experiencing reduced respiratory function from diseases such as cystic fibrosis seem to benefit from the increased atmospheric pressure.^[42]

The region's climate and low elevation have made it a popular center for assessment of putative therapies:

• Climatotherapy: Treatment which exploits local climatic features such as temperature, humidity, sunshine, barometric pressure and special atmospheric constituents
• Heliotherapy: Treatment that exploits the biological effects of the sun's radiation
• Thalassotherapy: Treatment that exploits bathing in Dead Sea water

There is evidence that the unique attenuation and spectrum of UV rays near the Dead Sea contribute to effective photoclimatherapy for psoriasis, in part because the reduced exposure to solar radiation allows for longer periods of sunbathing.^[43][44][45]

Rhinosinusitis patients receiving Dead Sea saline nasal irrigation exhibited improved symptom relief compared to standard hypertonic saline spray in one study.^[46] Zdroj:https://en.wikipedia.org?pojem=Dead_Sea
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