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About 40 million years ago, during the Tertiary period, a series of tectonic movements disrupted the surface of the Earth and led to the formation of the Alps and the Himalayan mountains. In that period the African and Asian plates began to separate, creating an enormous trench which for the most part was filled in with the waters of the ocean. This was how the Red Sea was born, a body of water with wholly peculiar features, which is considered to be an ocean in the process of formation. The eventful geological history of the Earth had an enormous impact on the development of the fauna in the Red Sea and its splendid and world-famous coral reefs.
Climate: Egypt has a consistently hot and dry climate. The average temperature, depending on the latitude, ranges between 22 and 30° C. The greatest temperature variations are found in the Gulf of Aqaba, where the temperature drops to 15° C in the winter and rises to 45° C in summer. However, the temperatures at sea lie slightly below those on the coast. It is also usually windy making the weather rarely uncomfortably hot—it may often get quite chilly in the early morning and evening, so always bring along a light jacket. Humidity varies from 60% in the winter to 70% in the summer, and it almost never rains, apart from perhaps a day or two in the winter. For people with allergies, this dry air is a blessing in spring, since there is no pollen in Egypt—divers suffering from pollen allergy can normally enjoy their hobby without problems. However, divers must still get their allergies assessed by a doctor knowledgeable in diving.
Underwater Visibility: Since few nutrients roach the Red Sea through its narrow strait, it has less plankton. This leads to a much better visibility than in other seas—it can easily roach 40 m and beyond at reefs without a sandy seabed.
Water Temperature: Whereas in other seas the temperature ranges between 5 to 7° C, the Red Sea has a temperature of 20° C even at a depth of 1,000 m. It is caused by a trench along the sea floor, formed by plate tectonics, whose volcanic activity heats up the water. The surface temperature averages at 25° C and can easily reach 32° C on the coasts and reef flats.
Salinity: In the summer, the amount of water that evaporates over the entire surface of the Red Sea is much higher than the amount of water flowing in through the narrow strait at Bab –el Mandeb. The sea level drops during this period by up to 0.7 m, and rises again during the winter, This enormous evaporation leads to a salinity far higher than in other seas. While the Indian Ocean has a salinity of 3.4 %, the Red Sea has an average of 4.1%. This makes divers to carry more weights than usual to compensate for the increased buoyancy.
Winds and Breezes: In the southern regions of the Red Sea northeast winds in the winter and southwest winds in the summer are influenced by monsoons (periodic winds characterized by clear typical seasonal inversions in the tropical zones). As for the northern area of the sea, the prevailing winds blow all year long from a northern direction becoming stronger in the winter and tending to calm down in the afternoon and at night. The local seamen call these winds that blow for 2-3 days from northern directions, ‘shamal’. In the area of Sharm el-Sheikh and Ras -Mohammed the winds are generally moderate; they are stronger in the Straits of Tiran. To the north, around Dahab and Nuweiba, the northern winds blow stronger and more often, especially during winter, from December to March. The same happens in the Straits of Gubal, the southern part of the Gulf of Suez, where you hardly ever find really calm sea. In the months of August and September the dominant northern winds are less strong and tend to be more variable. Finally, during the spring months, we have to consider the possible occurrence of the ‘hamsin’, an Arabic expression meaning ‘fifty’ which stands for the amount of days this wind can blow. It is a very hot and dry wind usually corning from the southwest that can provoke serious sand storms in the Western Desert and hits the northern part of the Red Sea. We also have to take into account the thermal breezes caused by the different warming and cooling times between the earth and the sea. Considering breezes is a must for scuba divers when doing night dives from the boat close to the coast.
Assessing the Current: High evaporation is the main generator of currents in the Red Sea. In the summer, the concentration of salt at the surface increases, making the water heavier and causing it to sink. Deep water flows towards the Indian Ocean, and lighter water flows along the surface into the Red Sea. In the winter, the directions are reversed. The currents’ strength and direction at each reef in each season generally remain the same every year, making them easy to predict. However, do not always take this for granted. Never assume that the currents always flow in the same direction as the waves on the surface. Furthermore, the currents near the surface may also flow in another direction than those below. When in doubt, always check the current’s direction and strength before diving (current check). To do so, lower a lead weight attached to a rope to a depth of at least five meters, or even a bit deeper and observe the direction when it moves. This method works only with stronger currents. Another option is to observe the fish and soft corals on the reef before descending. Among the fish, the territorial anthias face the incoming current making their tails always point in the direction of the current’s flow. At reefs with steep walls, swirls may form, leading to unexpected countercurrents. If a strong current is present, it is important to always remain close to the reef walls to avoid being swept out into the open sea. If it does happen, release the surface marker buoy as soon as possible and ascend to the surface.
Tides: Currents are also caused by the tidal movement. Due to the gravitational pull of the moon and sun, the mass of water rises and falls in 12-hour cycles causing the horizontal water movements of the currents. These currents overlap and mix with the general currents affecting the local diving condition. To the north, in the gulfs of Suez and Aqaba, the difference between the high and low sea levels, or tidal range, can reach up to 1.8 m. The tides in the rest of the Red Sea, especially in the South, are relatively weak, with an average of only 0.8 m. For divers, this means that we must constantly take tidal changes in the current into account. At the reefs in the middle of the sea (Brothers, Daedalus, Shaab Sharm, etc.), the fluctuations in the intensity and strength of the currents are rather moderate during a dive. On reefs with a shallow seabed (about 20 m or less), this fluctuation is sometimes more noticeable. In addition, turbulence may occur, stirring up the sand from the seabed and reducing the visibility. Strong currents can at times be caused by the tides flowing between two close reefs, such as at Shaab Marsa Alam with its isolated ergs to the south—the narrower the channel, the stronger the current. If the schedule permits it, dive at these places at low or high tide to take advantage of the time with the least water movement.
Living resources: The Red Sea is a rich and diverse ecosystem. More than 1200 species of fish have been recorded in the Red Sea, and around 10% of these are found nowhere else. This also includes 42 species of deepwater fish. The rich diversity is in part due to the 2,000 km (1,240 mi) of coral reef extending along its coastline; these fringing reefs are 5000–7000 years old and are largely formed of stony acropora and porites corals. These coastal reefs are also visited by pelagic species of Red Sea fish, including some of the 44 species of shark. The Red Sea also contains many offshore reefs including several true atolls. The special biodiversity of the area is recognized by the Egyptian government, who set up the Ras Muhammad National Park in 1983. The rules and regulations governing this area protect local marine life, which has become a major draw for diving enthusiasts. Divers and snorkellers should be aware that although most Red Sea species are harmless, a few are hazardous to humans: refer to Red Sea species hazardous to humans. Other marine habitats include sea grass beds, salt pans, mangroves and salt marshes.
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