The Red Sea (also the Erythraean Sea) is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. To the north lie the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez (leading to the Suez Canal). The Red Sea is a Global 200 ecoregion. The sea is underlain by the Red Sea Rift which is part of the Great Rift Valley.

The Red Sea has a surface area of roughly 438,000 km2 (169,100 mi2),[2][3] is about 2250 km (1398 mi) long and, at its widest point, 355 km (220.6 mi) wide. It has a maximum depth of 2211 m (7254 ft) in the central median trench, and an average depth of 490 m (1,608 ft). However, there are also extensive shallow shelves, noted for their marine life and corals. The sea is the habitat of over 1,000 invertebrate species, and 200 soft and hard corals. It is the world's northernmost tropical sea.

Extent

The International Hydrographic Organization defines the limits of the Red Sea as follows:[4]

On the North. The Southern limits of the Gulfs of Suez [A line running from Ràs Muhammed (27°43'N) to the South point of Shadwan Island (34°02'E) and thence Westward on a parallel (27°27'N) to the coast of Africa] and Aqaba [A line running from Ràs al Fasma Southwesterly to Requin Island () through Tiran Island to the Southwest point thereof and thence Westward on a parallel (27°54'N) to the coast of the Sinaï Peninsula].
On the South. A line joining Husn Murad () and Ras Siyyan ().

Name

Red Sea is a direct translation of the Greek Erythra Thalassa (Ερυθρὰ Θάλασσα) and Latin Mare Rubrum (alternatively Sinus Arabicus, literally "Arabian Gulf"), Arabic Al-Baḥr Al-Aḥmar (البحر الأحمر) or Baḥr Al-Qulzum (بحر القلزم), Somali Badda Cas and Tigrinya Qeyyiḥ bāḥrī (ቀይሕ ባሕሪ). The name of the sea may signify the seasonal blooms of the red-coloured Trichodesmium erythraeum near the water's surface.[5] A theory favored by some modern scholars is that the name red is referring to the direction south, just as the Black Sea's name may refer to north. The basis of this theory is that some Asiatic languages used color words to refer to the cardinal directions.[6] Herodotus on one occasion uses Red Sea and Southern Sea interchangeably.

Historically, it was also known to western geographers as Mare Mecca (Sea of Mecca), and Sinus Arabicus (Gulf of Arabia).[7] Some ancient geographers called the Red Sea the Arabian Gulf[8] or Gulf of Arabia.[9][2]

The association of the Red Sea with the biblical account of the Israelites crossing the Red Sea is ancient, and was made explicit in the Septuagint translation of the Book of Exodus from Hebrew to Koine Greek in approximately the third century B.C. In that version, the Hebrew Yam Suph (ים סוף) is translated as Erythra Thalassa (Red Sea). (See also the more recent suggestion that the Yam Suph of the Exodus refers to a Sea of Reeds). The Red Sea is one of four seas named in English after common color terms — the others being the Black Sea, the White Sea and the Yellow Sea. The direct rendition of the Greek Erythra thalassa in Latin as Mare Erythraeum refers to the north-western part of the Indian Ocean, and also to a region on Mars.

History

Ancient era

The earliest known exploration of the Red Sea was conducted by ancient Egyptians, as they attempted to establish commercial routes to Punt. One such expedition took place around 2500 BC, and another around 1500 BC (by Hatshepsut). Both involved long voyages down the Red Sea.[2] Historically, scholars argued whether these trips were possible.[2] The biblical Book of Exodus tells the tale of the Israelites' crossing of a body of water, which the Hebrew text calls Yam Suph (Hebrew: יַם סוּף). Yam Suph was traditionally identified as the Red Sea. Rabbi Saadia Gaon (882‒942 CE), in his Judeo-Arabic translation of the Pentateuch, identifies the crossing place of the Red Sea as Baḥar al-Qulzum, meaning the Gulf of Suez.[2] (The story is part of the larger biblical lore about an Exodus of Israelites under Moses). Yam Suph can also been translated as Sea of Reeds.

In the 6th century BC, Darius the Great of Persia sent reconnaissance missions to the Red Sea, improving and extending navigation by locating many hazardous rocks and currents. A canal was built between the Nile and the northern end of the Red Sea at Suez. In the late 4th century BC, Alexander the Great sent Greek naval expeditions down the Red Sea to the Indian Ocean. Greek navigators continued to explore and compile data on the Red Sea. Agatharchides collected information about the sea in the 2nd century BC. The Periplus of the Erythraean Sea ("Periplus of the Red Sea"), a Greek periplus written by an unknown author around the 1st century AD, contains a detailed description of the Red Sea's ports and sea routes.[2] The Periplus also describes how Hippalus first discovered the direct route from the Red Sea to India.

The Red Sea was favored for Roman trade with India starting with the reign of Augustus, when the Roman Empire gained control over the Mediterranean, Egypt, and the northern Red Sea. The route had been used by previous states but grew in the volume of traffic under the Romans. From Indian ports goods from China were introduced to the Roman world. Contact between Rome and China depended on the Red Sea, but the route was broken by the Aksumite Empire around the 3rd century AD.[2]

Middle Ages and modern era

During the Middle Ages, the Red Sea was an important part of the spice trade route. In 1513, trying to secure that channel to Portugal, Afonso de Albuquerque laid siege to Aden[2] but was forced to retreat. They cruised the Red Sea inside the Bab al-Mandab, as the first European fleet to have sailed these waters.

In 1798, France ordered General Napoleon to invade Egypt and take control of the Red Sea. Although he failed in his mission, the engineer Jean-Baptiste Lepère, who took part in it, revitalised the plan for a canal which had been envisaged during the reign of the Pharaohs. Several canals were built in ancient times from the Nile to the Red Sea along or near the line of the present Sweet Water Canal, but none lasted for long. The Suez Canal was opened in November 1869. At the time, the British, French, and Italians shared the trading posts. The posts were gradually dismantled following the First World War. After the Second World War, the Americans and Soviets exerted their influence whilst the volume of oil tanker traffic intensified. However, the Six Day War culminated in the closure of the Suez Canal from 1967 to 1975. Today, in spite of patrols by the major maritime fleets in the waters of the Red Sea, the Suez Canal has never recovered its supremacy over the Cape route, which is believed to be less vulnerable.

Oceanography

The Red Sea is between arid land, desert and semi-desert. Reef systems are better developed along the Red Sea mainly because of its greater depths and an efficient water circulation pattern. The Red Sea water mass-exchanges its water with the Arabian Sea, Indian Ocean via the Gulf of Aden. These physical factors reduce the effect of high salinity caused by evaporation in the north and relatively hot water in the south.

The climate of the Red Sea is the result of two monsoon seasons; a northeasterly monsoon and a southwesterly monsoon. Monsoon winds occur because of differential heating between the land and the sea. Very high surface temperatures and high salinities make this one of the warmest and saltiest bodies of seawater in the world. The average surface water temperature of the Red Sea during the summer is about 26 °C (79 °F) in the north and 30 °C (86 °F) in the south, with only about 2 °C (3.6 °F) variation during the winter months. The overall average water temperature is 22 °C (72 °F). Temperature and visibility remain good to around 200 m (656 ft). The sea is known for its strong winds and unpredictable local currents.

The rainfall over the Red Sea and its coasts is extremely low, averaging 0.06 m (2.36 in) per year. The rain is mostly short showers, often with thunderstorms and occasionally with dust storms. The scarcity of rainfall and no major source of fresh water to the Red Sea result in excess evaporation as high as 205 cm (81 in) per year and high salinity with minimal seasonal variation. A recent underwater expedition to the Red Sea offshore from Sudan and Eritrea[2] found surface water temperatures 28 °C in winter and up to 34 °C in the summer, but despite that extreme heat the coral was healthy with much fish life with very little sign of coral bleaching, with only 9% infected by Thalassomonas loyana, the 'white plague' agent. Favia favus coral there harbours a virus, BA3, which kills T.loyana.[2] Plans are afoot to use samples of these corals' apparently heat-adapted commensal algae to salvage bleached coral elsewhere.

Salinity

The Red Sea is one of the saltiest bodies of water in the world, owing to high evaporation. Salinity ranges from between ~36  in the southern part because of the effect of the Gulf of Aden water and reaches 41 ‰ in the northern part, owing mainly to the Gulf of Suez water and the high evaporation. The average salinity is 40 ‰. (Average salinity for the world's seawater is ~35 ‰ on the Practical Salinity Scale, or PPS; that translates to 3.5% actual dissolved salts.)

The salinity of the Red Sea is greater than the world average, approximately 4 percent. This is due to several factors:

  1. High rate of evaporation and very little precipitation.
  2. Lack of significant rivers or streams draining into the sea.
  3. Limited connection with the Indian Ocean, which has lower water salinity.

Tidal range

In general tide ranges between 0.6 m (2.0 ft) in the north, near the mouth of the Gulf of Suez and 0.9 m (3.0 ft) in the south near the Gulf of Aden but it fluctuates between 0.20 m (0.66 ft) and 0.30 m (0.98 ft) away from the nodal point. The central Red Sea (Jeddah area) is therefore almost tideless, and as such the annual water level changes are more significant. Because of the small tidal range the water during high tide inundates the coastal sabkhas as a thin sheet of water up to a few hundred metres rather than flooding the sabkhas through a network of channels. However, south of Jeddah in the Shoiaba area the water from the lagoon may cover the adjoining sabkhas as far as 3 km (2 mi), whereas, north of Jeddah in the Al-Kharrar area the sabkhas are covered by a thin sheet of water as far as 2 km (1.2 mi). The prevailing north and northeast winds influence the movement of water in the coastal inlets to the adjacent sabkhas, especially during storms. Winter mean sea level is 0.5 m (1.6 ft) higher than in summer. Tidal velocities passing through constrictions caused by reefs, sand bars and low islands commonly exceed 1–2 m/s (3–6.5 ft/s). Coral reefs in the Red Sea are near Egypt, Eritrea, Israel, Saudi Arabia, and Sudan.

Current

In the Red Sea detailed current data is lacking, partially because they are weak and variable both spatially and temporally. Temporal and spatial currents variation is as low as 0.5 m (1.6 ft) and are governed all by wind. During the summer, NW winds drive surface water south for about four months at a velocity of 15–20 cm/s (6–8 in/s), whereas in winter the flow is reversed resulting in the inflow of water from the Gulf of Aden into the Red Sea. The net value of the latter predominates, resulting in an overall drift to the north end of the Red Sea. Generally, the velocity of the tidal current is between 50–60 cm/s (20–23.6 in/s) with a maximum of 1 m/s (3.3 ft/s) at the mouth of the al-Kharrar Lagoon. However, the range of the north-northeast current along the Saudi coast is 8–29 cm/s (3–11.4 in/s).

Wind regime

The north part of the Red Sea is dominated by persistent north-west winds, with speeds ranging between 7 km/h (4.3 mph) and 12 km/h (7.5 mph). The rest of the Red Sea and the Gulf of Aden are subjected to regular and seasonally reversible winds. The wind regime is characterized by seasonal and regional variations in speed and direction with average speed generally increasing northward.

Wind is the driving force in the Red Sea to transport material as suspension or as bedload. Wind-induced currents play an important role in the Red Sea in resuspending bottom sediments and transferring materials from sites of dumping to sites of burial in quiescent environment of deposition. Wind-generated current measurement is therefore important in order to determine the sediment dispersal pattern and its role in the erosion and accretion of the coastal rock exposure and the submerged coral beds.

Geology

The Red Sea was formed by the Arabian peninsula being split from the Horn of Africa by movement of the Red Sea Rift. This split started in the Eocene and accelerated during the Oligocene. The sea is still widening, and it is considered that it will become an ocean in time (as proposed in the model of John Tuzo Wilson). In 1949, a deep water survey reported anomalously hot brines in the central portion of the Red Sea. Later work in the 1960s confirmed the presence of hot, 60 °C (140 °F), saline brines and associated metalliferous muds. The hot solutions were emanating from an active subseafloor rift. The high salinity of the waters was not hospitable to living organisms.[3]

Sometime during the Tertiary period, the Bab el Mandeb closed and the Red Sea evaporated to an empty hot dry salt-floored sink. Effects causing this would have been:

A number of volcanic islands rise from the center of the sea. Most are dormant. However, in 2007, Jabal al-Tair island in the Bab el Mandeb strait erupted violently. Two new islands were formed in 2011 and 2013 in the Zubair Archipelago, a small chain of islands owned by Yemen. The first island named Sholan Island emerged in an eruption in December 2011, the second island named Jadid emerged in September 2013.[3][3][3]

Mineral resources

In terms of mineral resources the major constituents of the Red Sea sediments are as follows:

  • Biogenic constituents:
Nanofossils, foraminifera, pteropods, siliceous fossils
  • Volcanogenic constituents:
Tuffites, volcanic ash, montmorillonite, cristobalite, zeolites
  • Terrigenous constituents:
Quartz, feldspars, rock fragments, mica, heavy minerals, clay minerals
  • Authigenic minerals:
Sulfide minerals, aragonite, Mg-calcite, protodolomite, dolomite, quartz, chalcedony.
  • Evaporite minerals:
Magnesite, gypsum, anhydrite, halite, polyhalite
  • Brine precipitate:
Fe-montmorillonite, goethite, hematite, siderite, rhodochrosite, pyrite, sphalerite, anhydrite.