The Strait of Gibraltar: A Vital Waterway Between Continents

The Strait of Gibraltar is a narrow waterway that separates Europe and Africa, connecting the Atlantic Ocean and the Mediterranean Sea. It is located at the southern tip of the Iberian Peninsula, where Europe almost touches Africa. This strategic location makes it one of the busiest waterways in the world.

Geographical Overview

The Strait of Gibraltar is approximately 60 kilometers long and varies between 14 and 44 kilometers in width. At its narrowest point, just off Tarifa, the distance between mainland Europe and Mount Jbel Musa in Morocco/Africa is only 14 kilometers. The two continents are separated by 7.7 nautical miles (14.2 kilometers, 8.9 miles) at its narrowest point.

The strait lies in the territorial waters of Morocco, Spain, and the British overseas territory of Gibraltar. The name comes from the Rock of Gibraltar, which in turn originates from the Arabic Jabal Ṭāriq (meaning "Tariq's Mount"), named after Tariq ibn Ziyad.

On the northern side of the Strait are Spain and Gibraltar (a British overseas territory in the Iberian Peninsula). The land on both sides is very rocky, featuring tall cliffs and hills. The water depth ranges from 300 to 900 meters (980 to 2,950 feet).

Hydrology and Unique Currents

The Strait of Gibraltar links the Atlantic Ocean directly to the Mediterranean Sea. This direct linkage creates certain unique flow and wave patterns. Water flows through the Strait more or less continuously, both eastwards and westwards.

A smaller amount of deeper, saltier, and therefore denser waters continually flows westwards (the Mediterranean outflow), while a larger amount of surface waters with lower salinity and density continually flow eastwards (the Mediterranean inflow). These general flow tendencies may be occasionally interrupted for brief periods by temporary tidal flows, depending on various lunar and solar alignments.

Due to its high salt concentration, the Mediterranean water is considerably heavier and therefore sinks down over the deeper Mediterranean basin, pushing deep water back into the Atlantic. Nutrient-rich water together with light supports the formation of plant plankton (phytoplankton) - a prerequisite for the large food supply.

Internal waves (waves at the density boundary layer) are often produced by the Strait. Like traffic merging on a highway, the water flow is constricted in both directions because it must pass over the Camarinal Sill. When large tidal flows enter the Strait and the high tide relaxes, internal waves are generated at the Camarinal Sill and proceed eastwards. Even though the waves may occur down to great depths, occasionally the waves are almost imperceptible at the surface, at other times they can be seen clearly in satellite imagery. These internal waves continue to flow eastward and to refract around coastal features.

Geological History

Today's Mediterranean basin is a remnant of the Tethys Sea, which existed around the time of the dinosaurs. When the African and Indian plate collided with the Eurasian plate, the Tethys Sea gradually disappeared. Around 5.97 million years ago, the connection between the Mediterranean Sea and the Atlantic Ocean along the Betic and Rifan Corridor was progressively restricted until its total closure, effectively causing the salinity of the Mediterranean to rise periodically within the gypsum and salt deposition range, during what is known as the Messinian salinity crisis.

After a lengthy period of restricted intermittent or no water exchange between the Atlantic Ocean and Mediterranean basin, approximately 5.33 million years ago, the Atlantic-Mediterranean connection was completely reestablished through the Strait of Gibraltar by the Zanclean flood, and has remained open ever since. The erosion produced by the incoming waters seems to be the main cause for the present depth of the Strait (900 m (3,000 ft; 490 fathoms) at the narrows, 280 m (920 ft; 150 fathoms) at the Camarinal Sill).

Marine Life and Conservation

Due to the special currents, there is a good supply of food here, which even attracts whales and dolphins. Whales and dolphins also benefit from this.

To protect whales, the Spanish Ministry of Environment set a speed limit of 13 knots (24 km/h) for the Strait in February 2007. A resident orca pod of some 36 individuals lives around the Strait, one of the few that are left in Western European waters.

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Historical and Cultural Significance

Evidence of the first human habitation of the area by Neanderthals dates back to 125,000 years ago. The Rock of Gibraltar and Mount Jbel Musa in Morocco are also known as the Pillars of Hercules. According to Greek mythology, Hercules was supposed to cross Mount Atlas to rob the herd of cattle from the giant Geryon. But with his superhuman strength, he smashed through the middle of the mountain and thus created the Strait of Gibraltar.

Beginning in 1492, the Strait began to play a certain cultural role in acting as a barrier against cross-channel conquest and the flow of culture and language that would naturally follow such a conquest. In that year, the last Muslim government north of the Strait was overthrown by a Spanish force. The small British enclave of the city of Gibraltar presents a third cultural group found in the Strait. This enclave was ceded in perpetuity to Britain in the Peace of Utrecht.

Strategic Importance and Modern Developments

The Strait of Gibraltar is the only natural link between the Atlantic Ocean and the Mediterranean Sea and is one of the busiest waterways in the world. Approximately 300 ships cross the Strait every day, about one ship every 5 minutes. The Strait is an important shipping route from the Mediterranean to the Atlantic.

Following the Spanish coup of July 1936 the Spanish Republican Navy tried to blockade the Strait of Gibraltar to hamper the transport of Army of Africa troops from Spanish Morocco to Peninsular Spain. During the Second World War, German U-boats used the currents to pass into the Mediterranean Sea without detection, by maintaining silence with engines off. From September 1941 to May 1944 Germany managed to send 62 U-boats into the Mediterranean.

Ferries operate between Spain and Morocco across the Strait, as well as between Spain and Ceuta and Gibraltar to Tangier. Discussion between Spain and Morocco of a tunnel under the strait began in the 1980s. In December 2003, both countries agreed to explore the construction of an undersea rail tunnel to connect their rail systems across the Strait.

While the project remained in a planning phase, Spanish and Moroccan officials met to discuss it occasionally, including in 2012. Those talks led to nothing constructive happening, but in April 2021 ministers from both countries agreed to a joint intergovernmental meeting to be held in Casablanca in the coming months.

Territorial Waters and Navigation

Except for its far eastern end, the Strait lies within the territorial waters of Spain and Morocco. The United Kingdom claims 3 nautical miles (5.6 km; 3.5 mi) around Gibraltar on the northern side of the Strait, putting part of it inside British territorial waters. As this is less than the 12 nautical miles (22 km; 14 mi) maximum, it means, according to the British claim, that part of the Strait lies in international waters. The ownership of Gibraltar and its territorial waters is disputed by Spain.

Under the United Nations Convention on the Law of the Sea, vessels passing through the strait do so under the regime of transit passage, rather than the more limited innocent passage allowed in most territorial waters.

Mercedes Gleitze was the first known person to swim across the Strait of Gibraltar on 6 April 1928. It took her 12 hours and 50 minutes to cross the stretch of water. Chris Ziaja and Nik Benner were the first known people to cross the Strait of Gibraltar with a stand up paddleboard on 4 October 2010.

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