and down the coastline of the Red Sea was taken by the crew of Expedition 29 on board the International Space Station. The Red Sea is between arid land,
desert and
semi-desert. Many regions of the coastal zone of the Red Sea possess large areas of vigorously growing coral and extensive reef complexes. Due to the tidal currents, low human population, and the minimal development in this climatically inhospitable region, the Red Sea coral reefs are some of the healthiest reef environments in the world. The Red Sea water mass-exchanges its water with the
Arabian Sea and
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 salinity 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 in the north and in the south, with only about variation during the winter months. The overall average water temperature is . Temperature and visibility remain good, with visibility around . 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 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 per year and high salinity with minimal seasonal variation. A recent underwater expedition to the Red Sea offshore from
Sudan and
Eritrea found surface water temperatures in winter and up to 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. Scientists are investigating the unique properties of these corals and their
commensal algae to determine whether they can be used to rescue bleached corals elsewhere.
Salinity The Red Sea is one of the saltiest bodies of water in the world, owing to high evaporation and low precipitation; no significant rivers or streams drain into the sea, and its southern connection to the
Gulf of Aden, an arm of the Indian Ocean, is narrow. Its
salinity ranges from between ~36
‰ in the southern part and 41 ‰ in the northern part around the
Gulf of Suez, with an average of 40 ‰. (Average salinity for the world's
seawater is ~35 ‰ on the Practical Salinity Scale, or PSU; that translates to 3.5% of actual dissolved salts).
Tidal range In general, tide ranges between in the north, near the mouth of the Gulf of Suez and in the south near the Gulf of Aden, but it fluctuates between and 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 , whereas north of
Jeddah in the
Al-Kharrar area the sabkhas are covered by a thin sheet of water as far as . The prevailing north- and northeast winds influence the movement of water from coastal inlets into adjacent sabkhas, especially during storms. Winter mean sea level is higher than in summer. Tidal velocities passing through constrictions caused by reefs, sand bars, and low islands commonly exceed . Coral reefs in the Red Sea are near Egypt, Eritrea, Jordan, Israel, Saudi Arabia, and Sudan.
Current Detailed information regarding current data is lacking, partially because the currents are weak and both spatially and temporally variable. The variation of temporal and spatial currents is as low as and is governed by the wind. During the summer, northwesterly winds drive surface water south for about four months at a velocity of , 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, leading to an overall drift toward the north end of the Red Sea. Generally, the velocity of the tidal current is with a maximum of at the mouth of the al-Kharrar Lagoon. However, the range of the north-northeast current along the Saudi coast is .
Wind regime The northern part of the Red Sea is dominated by persistent north-west
winds, with speeds ranging between and . 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. The wind is the driving force in the Red Sea, transporting material as suspended load or bedload. Wind-induced currents play an important role in the Red Sea by resuspending bottom sediments and transferring materials from dumping sites to burial sites in a quiescent depositional environment. Wind-generated current
measurement is therefore important for determining sediment dispersal patterns and their role in the erosion and accretion of the coastal rock exposure and submerged coral beds. == Geology ==