Gibraltar threshold

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Overview map

The Gibraltar threshold is a threshold below sea level in the Strait of Gibraltar . It separates the Alborán Sea , the western part of the Mediterranean Sea , from the Gulf of Cádiz in the Atlantic Ocean .

geography

North of the threshold on the Iberian Peninsula lies the Betic Cordillera mountain range and south of the Maghrebian Rif mountain range .

The Gibraltar Sill has some larger elevations and depressions in the area of ​​the Strait of Gibraltar. In the west, at the height of Cape Spartel, lies the Spartel threshold, which is more than 350 m deep . This is followed by the Tangier Basin , which is a maximum of 640 m deep , the Camarinal threshold at a maximum depth of 285 m and, in the east, with an average depth of around 600 m and a maximum depth of around 960 m, the narrowest point at around 12 km, the Tarifa Narrow .

The Gibraltar Sill drops to a depth of about 4000 m in the Atlantic Ocean, whereas the Alborán Sea only reaches depths of about 2000 m.

geology

Some scientists suspect that in the area of ​​the western Mediterranean there is not only a slow (4 mm per year) subduction of the African plate in a north-west direction under the Eurasian plate , but that there is also a west-south-west migration (5–10 mm per year) is a small piece of the lithosphere .

The Gibraltar threshold was six million years ago to about five million years ago, in the Messinian , a land bridge that interrupted the connection between the Mediterranean and the Atlantic Ocean. That is why the Messinian salinity crisis occurred , the drying up of the Mediterranean Sea. The trigger was both a lifting of the land bridge between Europe and Africa, triggered by tectonic activity in the region, as well as the drop in the Atlantic sea level by around 50 meters due to icing at the South Pole. Later, due to climatic changes, the sea level of the Atlantic rose again.

About 5.33 million years ago, at the turn of the Miocene to the Pliocene , the latest findings indicate that the land bridge between Europe and Africa was initially slightly lowered, so that only small amounts of water spilled from the Atlantic into the dried-up Mediterranean basin for several millennia. Gradually, the water dug deeper and deeper into the land bridge until finally about 100 million cubic meters per second flowed in via a 200-kilometer-long and up to 11-kilometer-wide canal, and at a speed of 144 kilometers per hour, the flow channel by 40 centimeters per Day deepened. A total of 500 cubic kilometers of rock was washed away. As a result, at the height of this process, the water level in the Mediterranean basin rose daily by more than 10 meters until the Mediterranean was refilled after a maximum of two years.

Today over 1 million cubic meters of water flow from the Atlantic Ocean into the Mediterranean Sea every second, a little less water leaves the Mediterranean Sea towards the Atlantic Ocean. This salty, heavy deep water flows close to the sea floor over the approximately 400 m deep Gibraltar sill in the Atlantic to depths of 600 m to 1500 m. It then flows north along the coast of the Iberian Peninsula, with large water eddies leaving the ocean current to the west and south-west.

art

The novel Das Boot describes , among other things, how the submarine touched down in the Strait of Gibraltar on the Gibraltar threshold at a depth of 280 m. The actual U 96 was only 70 m deep here during the seventh patrol.

Individual evidence

  1. ^ Workshop on Analysis of Variables and Numerical Simulation of the Water Masses Exchange Through The Strait of Gibraltar. ( Memento of October 3, 2008 in the Internet Archive )
  2. ↑ E. Dafner, M. González-Dávila, JM Santana-Casiano, R. Sempere: Total organic and inorganic carbon exchange through the Strait of Gibraltar in September 1997. In: Deep-Sea Research Part I. . No. 48, 2001 P. 1217–1235 ( PDF; 276 kB )
  3. ↑ a b Geology: Online Forum - Evidence for active subduction beneath Gibraltar: REPLY. ( Memento of the original from December 17, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. On: gsajournals.org  @1@ 2Template: Webachiv / IABot / www.gsajournals.org
  4. ↑ A. Mauffret, A. Ammar, C. Gorini, H. Jabou: The Alboran Sea (Western Mediterranean) revisited with a view from the Moroccan margin. In: Terra Nova. June 2007, Vol. 19, No. 3, pp. 195–203, doi : 10.1111 / j.1365-3121.2007.00734.x ( full text as PDF file ( memento of the original from July 27, 2007 in the Internet Archive ) Info : The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this note. ). @1@ 2Template: Webachiv / IABot / www.lgs.jussieu.fr
  5. ^ Wout Krijgsman, Miguel Garcés: Palaeomagnetic constraints on the geodynamic evolution of the Gibraltar Arc. In: Terra Nova. October 2004, Vol. 16, No. 5, pp. 281–287, doi : 10.1111 / j.1365-3121.2004.00564.x ( full text as PDF file; 470 kB )
  6. ^ D. Garcia-Castellanos et al .: Catastrophic flood of the Mediterranean after the Messinian salinity crisis. In: Nature. Vol. 462, December 10, 2009, pp. 778-781, doi : 10.1038 / nature08555 .
  7. ↑ Jessica Gianoncelli: Water balance of the Mediterranean .
  8. ↑ Jessica Gianoncelli: Temperature and Salinity in the Gulf of Cadiz .

Web links

Coordinates: 35 ° 58 ′  N , 5 ° 30 ′  W