Strait of Gibraltar

• 1. Introduction

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  The Strait of Gibraltar carries a name that is itself a story. "Gibraltar" traces back to the Arabic Jabal Tariq, meaning "Tariq's Mount," named after Tariq ibn Ziyad, the military commander who crossed these waters to launch the Moorish conquest of Iberia. That crossing happened more than a thousand years ago, yet the name survives in every language that uses it. At its narrowest point, just 7.7 nautical miles separate the African shore from the European one. A ferry can make the crossing between two continents in as little as 35 minutes. What does it mean for two worlds to be separated by so little water? And what happens beneath the surface of a strait that has been shaping history, geology, and biology for millions of years?

• 2. A Sea Almost Lost

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  Around 5.97 million years ago, the connection between the Atlantic Ocean and the Mediterranean Sea was cut off entirely. The barrier that formed where the Strait now sits caused the Mediterranean to lose more water to evaporation than it received from rivers and rain. Salinity climbed into a range where gypsum and salt began to precipitate out of the water and layer themselves on the seabed. This period is known as the Messinian salinity crisis, and it lasted around 640,000 years by geological reckoning. The mineral deposits it left behind still sit beneath the Mediterranean floor today. Then, approximately 5.33 million years ago, the Atlantic broke through again in an event called the Zanclean flood. The incoming waters carved what is now the deepest part of the narrows down to 900 meters, and the Camarinal Sill at the western end down to 280 meters. The Strait has remained open since that moment, though geologists expect it to close again as the African Plate continues its slow northward drift toward the Eurasian Plate.

• 3. The Water Within the Water

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  Two rivers flow through the Strait at the same time, one hidden inside the other. At the surface, less salty Atlantic water pours eastward into the Mediterranean. Deeper down, denser and saltier Mediterranean water flows westward toward the Atlantic in what oceanographers call the Mediterranean outflow. The balance tips eastward because the Mediterranean evaporates more water than all its rivers and rainfall can replace. At the western entrance, the Camarinal Sill acts as a throttle, limiting how freely the two water masses can mix. Because Mediterranean water is so much saltier, it sinks below the incoming Atlantic flow and hugs the bottom. Once it reaches the Atlantic side, that outflow layer descends the continental slope, slowly losing its saltiness as it mixes, until it finds its equilibrium at around 1,000 meters depth. Scientists can trace the distinct chemical signature of that outflow water for thousands of kilometers out into the Atlantic before it finally blends away entirely. During the Second World War, German U-boat commanders turned this layered current to their advantage: from September 1941 to May 1944, Germany sent 62 submarines into the Mediterranean by switching off their engines and riding the deep current silently through the British-controlled passage. Nine of those boats were sunk in the attempt, and ten more turned back with damage.

• 4. Life at the Crossing

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  BirdLife International has designated the Strait an Important Bird Area because hundreds of thousands of seabirds use it each year as a corridor between the Mediterranean and the Atlantic. Among those migrants are Scopoli's and Balearic shearwaters, Audouin's and lesser black-backed gulls, razorbills, and Atlantic puffins. Below the surface, a resident pod of roughly 36 orcas lives in and around the Strait, one of the few such communities remaining in Western European waters. Persistent contamination from PCBs puts that pod's long-term survival in serious doubt over the coming decades. The seabed itself hosts cold-water coral communities whose remains contribute to the calcareous sediments that blanket the underlying Betic-Rif flysch. Evidence of human life here stretches back to 125,000 years ago, when Neanderthals inhabited the area; the Rock of Gibraltar may have been among the last places on earth where Neanderthals lived, with traces of their presence dating to as recently as 24,000 years ago. Homo sapiens left their own marks beginning roughly 40,000 years ago.

• 5. A Hinge of Civilizations

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  Carthaginians, Romans, Vandals, Moors, Berbers, Spanish, and Portuguese have all crossed the Strait at decisive moments. The Vandals moved south through it in the 5th century, raiding from Germania through what remained of Western Rome and into North Africa. Moors and Berbers used it repeatedly between the 8th and 11th centuries to move between continents. The year 1492 marks what historians treat as a turning point: Spanish forces expelled the last Muslim government north of the Strait, ending more than five centuries during which the two shores had shared broadly the same culture. From that point, a Christian-European tradition with the Romance Spanish language took hold on the northern side, while an Arabic-speaking, Muslim-influenced culture solidified on the southern side. The small British enclave of Gibraltar adds a third strand to that pattern. Britain received Gibraltar in perpetuity under the Peace of Utrecht and has since used it to maintain influence over the sea lanes into and out of the Mediterranean. Spain disputes British sovereignty over Gibraltar; Morocco disputes Spanish sovereignty over Ceuta, on the southern coast; and several small islets, including the contested Isla Perejil, are claimed by both Morocco and Spain.

• 6. Crossing Attempts and Future Plans

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  On the 6th of April 1928, Mercedes Gleitze became the first known person to swim across the Strait of Gibraltar, completing the crossing in 12 hours and 50 minutes. It was her sixth attempt; her first had come in December 1927. Francesco Stipo crossed the Strait by powered paraglider on the 11th of July 1995, flying from Tarifa to Ceuta in under an hour with a Red Cross vessel tracking his route. On the 4th of October 2010, Chris Ziaja and Nik Benner paddled across on stand-up paddleboards, setting out from Punta Carnero and arriving in Ceuta four and a half hours later. Proposals for a permanent fixed link have a longer and less conclusive history. Discussion between Spain and Morocco about an undersea rail tunnel began in the 1980s. In December 2003, both countries formally agreed to explore the project, envisioning a standard-gauge rail connection to replace the existing broad-gauge lines on each side. Talks continued intermittently through 2012 without tangible results. In April 2021, ministers from both countries agreed to a joint intergovernmental meeting in Casablanca to revive the idea. Separately, in January 2021, the UK government studied plans for a tunnel connecting Gibraltar to Tangier as an alternative to the Spanish-Moroccan proposal, which had produced no concrete outcome across more than four decades of discussion.