Gibraltar

The Strait of Gibraltar is probably one of the most famous straits in the world and represents the only natural connection between the Atlantic Ocean and the Mediterranean Sea. However, this wasn’t always the case, so we first embark on a journey far back in Earth’s history. Due to intense tectonic activity in this region, the strait was completely closed about 6 million years ago, and as a result, the Mediterranean Sea dried up entirely. This also led to a lowering of the Mediterranean basin, creating a difference in elevation of about 1.4 meters between the Atlantic Ocean and the Mediterranean Sea. Over hundreds of thousands of years, as the Atlantic water gradually eroded this sill and eventually breached it completely, the Mediterranean Sea refilled like a bathtub. Since then, the difference in elevation has maintained a constant west-east flow of Atlantic water at the surface. Nevertheless, a lively exchange of water takes place, as the highly saline and therefore denser water sinks and flows back from the Mediterranean Sea into the Atlantic Ocean at deeper levels. An interesting anecdote on the side: Due to the very frequent westerly winds coupled with the constant west-east current of the surface water, the sailing ships of antiquity could hardly pass through this waterway towards the Atlantic for a long time – until the deeper, counter-current was discovered and from then on, deep-draft drift sails were used to pull the boats out into the Atlantic against the surface forces.