The Gulf of Cádiz is the arm of the Atlantic Ocean

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

 between Cape St. Vincent

Cape St. Vincent

Cape St. Vincent , next to the Sagres Point, on the so-called Costa Vicentina , is a headland in the municipality of Sagres, in the Algarve, southern Portugal.- Description :This cape is the southwesternmost point in Portugal...

 (Cabo de São Vicente) in Portugal

Portugal

Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...

 and Cape Trafalgar

Cape Trafalgar

Cape Trafalgar is a headland in the Province of Cádiz in the south-west of Spain. It lies on the shore of the Atlantic Ocean, northwest of the Strait of Gibraltar...

 (Cabo Trafalgar) at the western end of the Strait of Gibraltar

Strait of Gibraltar

The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain in Europe from Morocco in Africa. The name comes from Gibraltar, which in turn originates from the Arabic Jebel Tariq , albeit the Arab name for the Strait is Bab el-Zakat or...

. Two major river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

s, the Guadalquivir

Guadalquivir

The Guadalquivir is the fifth longest river in the Iberian peninsula and the second longest river to be its whole length in Spain. The Guadalquivir is 657 kilometers long and drains an area of about 58,000 square kilometers...

 and the Guadiana

Guadiana

The Guadiana , or Odiana, is an international river located on the Portuguese–Spanish border, separating Extremadura and Andalucia from Alentejo and Algarve...

, as well as smaller rivers, like the Odiel

Odiel

The Odiel River, River Odiel, or simply Odiel is a river in the Atlantic basin in southern Spain, more precisely in the province of Huelva, Andalusia, Spain. It originates at Marimateos in the Sierra de Aracena at an altitude of above sea level. At the Punta del Sebo, it joins the Rio Tinto to...

, the Tinto

Tinto River

The Río Tinto is a river in southwestern Spain that originates in the Sierra Morena mountains of Andalusia. It flows generally south-southwest, reaching the Gulf of Cádiz at Huelva....

, and the Guadalete, reach the ocean

Ocean

An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

 here.

The Gulf of Cádiz is located in the north-eastern Atlantic Ocean between 34°N and 37°15'N and 6°W to 9°45'W. It is enclosed by the southern Iberian and northern Moroccan margins, west of Gibraltar Strait.

Geology

The geological history of the Gulf of Cádiz is intimately related to plate tectonic interaction between Southern Eurasia

Eurasia

Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...

 and North Africa and is driven by two major mechanisms:

• subduction
  Subduction
  In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
  
   associated with the westward emplacement of the Gibraltar Arc and formation of the Gulf of Cádiz accretionary wedge, probably not active at present and
• oblique lithosphere collision between Iberia
  Iberia
  The name Iberia refers to three historical regions of the old world:* Iberian Peninsula, in Southwest Europe, location of modern-day Portugal and Spain** Prehistoric Iberia...
  
   and Nubia
  Nubia
  Nubia is a region along the Nile river, which is located in northern Sudan and southern Egypt.There were a number of small Nubian kingdoms throughout the Middle Ages, the last of which collapsed in 1504, when Nubia became divided between Egypt and the Sennar sultanate resulting in the Arabization...
  
  , active at present and causing active thrusting.

It is now well established that the whole area is under compressive deformation and that mud volcanism and processes associated with the escape of hydrocarbon

Hydrocarbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

-rich fluids sustain a broad diversity of chemosynthetic assemblages. This extensive area encompasses over forty mud volcano

Mud volcano

The term mud volcano or mud dome are used to refer to formations created by geo-excreted liquids and gases, although there are several different processes which may cause such activity. Hot water mixes with mud and surface deposits. Mud volcanoes are associated with subduction zones and about 700...

es (a type of cold seep

Cold seep

A cold seep is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool...

), at depths ranging from 200 to 4000 m (confirmed by coring), and active methane seepage has been documented on several locations.

Biota

The occurrence of chemosymbiotic biota in the extensive mud volcano fields of the Gulf of Cadiz was first reported in 2003. There were found mainly pogonophora

Pogonophora

There are two taxa with the name Pogonophora:*Pogonophora - an obsolete animal phylum, now treated as part of the family Siboglinidae*Pogonophora - a genus in the Euphorbiaceae...

n worms, but also gastropods and bivalves, polychaetes, crustaceans and echinoderms. There were also recorded dead corals of genera Madrepora and Lophelia. The chemosymbiotic bivalves collected from the mud volcanoes of the Gulf of Cadiz were reviewed in 2011. There were reported the following species of chemosymbiotic bivalves of Solemyidae

Solemyidae

Solemyidae is a family of protobranch bivalves in the order Solemyoida. .Solemyids are remarkable in that their digestive tract is either extremely small or non-existent, and their feeding appendages are too short to reach outside the shell ....

: Acharax gadirae, Solemya elarraichensis; Mytilidae

Mytilidae

Mytilidae is a family of small to large saltwater mussels, marine bivalve mollusks in the order Mytiloida. It is the only family in the order...

: Bathymodiolus mauritanicus, Idas

Idas

In Greek mythology, Idas was a son of Aphareus and Arene and brother of Lynceus. He and Lynceus loved Hilaeira and Phoebe and fought with their rival suitors, Castor and Polydeuces, killing the mortal brother Castor. He was also one of the Argonauts and a participant in the hunt for the Calydonian...

sp.; Lucinidae

Lucinidae

Lucinidae is a family of saltwater clams, marine bivalve molluscs.These bivalves are remarkable for their endosymbiosis with sulphide-oxidizing bacteria.-Characteristics:...

: Lucinoma asapheus; Thyasiridae

Thyasiridae

Thyasiridae is a family of bivalve molluscs, including the cleft clams.-Genera and species:* Adontorhina S. S. Berry, 1947** Adontorhina cyclia S. S. Berry, 1947** Adontorhina similis Barry & McCormack, 2007...

: Thyasira vulcolutre, Spinaxinus sentosus; Vesicomyidae

Vesicomyidae

Vesicomyidae is a family of bivalves. Its genera, with some selected species, are:* Adulomya Kuroda, 1931 ** Adulomya elongata...

: Isorropodon perplexum, Isorropodon megadesmus, Callogonia cyrili, Christineconcha regab, Laubiericoncha chuni and Pliocardia sp. There is high degree of endemism within chemosymbiotic bivalve assemblages.