The Arabian Gulf

 
 

The Arabian Gulf is a narrow sea, about 200 to 300 km wide and 1000 km long. It is mostly quite shallow with an average depth of 35 m, the deepest water being found closer to the coast of Iran (80 m) and the Strait of Hormuz (l00 m).

 
 

The level of the sea in the Gulf has not always been the same. In the past, water came right over Jubail and stretched far inland. Twenty thousand years ago, when the world was passing through an 'ice age', much of the water now in the sea was locked up in great ice sheets and the sea level was about 120 m lower than it is today. The Gulf was dry. The Tigris and Euphrates rivers flowed along the coast of Iran and met the sea at the Strait of Hormuz. The sea only reached its present level about five thousand years ago. The plant and animal communities living in the Gulf have therefore only been here for a relatively short period of time.

 
 

Water enters the Arabian Gulf from the Indian Ocean through the Strait of Hormuz and flows north along the coast of Iran to Kuwait and then southerly down the coast of Saudi Arabia. As the water follows an anticlockwise passage around the Gulf it becomes more salty due to evaporation, and sinks below the less salty water. The denser water leaves the Gulf under the incoming, lighter water. In almost all pans of the Gulf the salinity is greater than 40 pans per thousand (ppt). The time taken for all the water to be replaced is, in theory, about 5 years.

 
  Tides are caused by the gravitational pull of the sun and the moon on the sea. The tidal pattern at Jubail has two high and two low tides each day. As the tidal cycle is just over 12 hours, the equivalent high tide occurs about an hour later each day. Although the tidal range is small, it rarely exceeds 2 m, the area slopes so gently that the distance between the low tide and high tide marks may be very wide. Animals and plants that can tolerate long periods of exposure to the air are found close to the high tide mark whereas those that can only withstand shon periods of exposure and need to be covered by seawater for longer periods of time, are found closer to the low tide mark. This distribution pattern of organisms on the beach is called 'zonation'.  
Depth contours and surface current flow in the Gulf
gulf
 
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