STRAIGHT OF GIBRALTAR
Over 100,000 ships transit through Gibraltar every year

Density of seawater in the Strait of Gibraltar One of the unique features of the Strait of Gibraltar is the inflow and outflow of the Medย  which consists of layers of water with different salinity (salinity). Atlantic water is less saline and less concentrated than Mediterranean water, and flows eastward into the Mediterranean through straits as a surface layer, flowing at a speed of 2 to 3 knots at a depth of about 125 m. In contrast, heavier, cooler, and saltier water flows westward into the Atlantic Ocean. Depending on the phase of the tide, the currents flow eastward faster or slower.

 

 

Tides in the Strait of Gibraltar โ€“ย 
A very distinctive feature of the Strait of Gibraltar is the continuous evaporation of water. Vertical water height in the Mediterranean Sea decreases by almost 1 meter every year. About 6.5+ million years ago, the general shape of the Mediterranean base was similar to what it is today. The movement of the plates cut off the flow of water from ocean to ocean, completely evaporating the area. But about 5+ million years ago, the plates moved again and the straits opened, allowing large amounts of water to flow out of the ocean and refill the Mediterranean basin. This evaporation continues today, and it is estimated that if the strait were to close at current high sea levels, the basin would evaporate again. Backwash and Internal Waves Adding another challenging piece to the tidal puzzle that shapes the Strait of Gibraltar near the African continent are the often narrow two-knot backwashes that interact with the Caminal Stile (the shallowest part of the strait) and cause internally generated waves. As stated by NASA; “The waves are generated when daily tidal pulses flow through the shallow Caminal Stile near Gibraltar. They flow eastward and break up the coastal topography. They can be traced up to 90 nm, and in some cases produce interference patterns due to refracted waves

Internal waves are vertical movements between two layers and can have displacements of over 100 m with wavelengths of 1-3 nm. They are so noticeable as surface wave patterns that sunlight is carefully scattered by the water surface


Alboran Gyre

As the upper-level flow pours into the Mediterranean, the Coriolis force (an effect of the earth’s rotation) causes it to form a large clockwise eddy (gyre) off the North African coast called the Alboran Gyre. A smaller weak anti-clockwise eddy forms to the North. Countercurrents (westward direcction) can be seen close inshore along both shores, particularly near headlands that project into the current.

The western end of the Mediterranean, akaย  Alboran Sea, is the habitat for aย  largest population of dolphins in the western Mediterranean

A layer of outward-flowing dense water stays deep after exiting the Mediterranean and forms a ribbon extending along the Spanish and Portuguese coasts at about 1000m depth.

 

Modelling the Strait of Gibraltar

WINDS

CURRENTS

SWELL AND WAVESย 

 

Transiting the Straits of Gibraltar

Navigating the Straits of Gibraltar requires careful planning, considering wind, tides, currents, and potential orca encounters. Here are the key points for a successful passage:

Timing and Conditions

  • Wind: Prevailing winds are the Levante (east) in summer and Poniente (west) in winter. Avoid strong winds; a light or nearly windless forecast is ideal.
  • Tides and Currents: Complex patterns; use a Tidal Stream Atlas for guidance.
  • Forecasts: Use ECMWF models and monitor Tarifa Radio for updates.
  • Shipping Traffic: Stay clear of busy lanes and cross perpendicularly if necessary.

Specific Strategies

  • Eastbound: Best with a light Poniente or calm conditions; depart from ports like Barbate or Tangier.
  • Westbound: Favorable with a light Levante; wait for suitable conditions in Gibraltar or Ceuta.

For a detailed guide, visit the original article.