An aquatic sill (or an oceanic sill ) is a sea floor barrier of relatively shallow depth (tens to hundreds of meters) that restricts water movement between benthic zones of an oceanic basin or lake bottom. There are roughly 400 sills in the Earth's oceans, covering 0.01% of the seafloor. A classic example is the Strait of Gibraltar Gateway between the Mediterranean sea and the Atlantic Ocean .
7-763: The Camarinal Sill is the sill separating the Mediterranean Sea and the Atlantic Ocean . This threshold is the shallowest seafloor pass between the Iberian Peninsula and Africa . It is located approximately 25 km west of the narrowest section of the Strait of Gibraltar and 20 km east of the Espartel Sill , at 35°56′N 5°45′W / 35.933°N 5.750°W / 35.933; -5.750 ( Camarinal Sill ) , at
14-405: A biogeographic barrier for species between two basins, which commonly include sponges , bryozoans , bivalves , and cold-water corals . These communities tend to develop in highly productive waters, such as upwelling areas, and build non-tropical reefs, or bioherms , around sills. A type example of an aquatic sill is the Strait of Gibraltar Gateway , which connects the Atlantic Ocean to
21-697: A depth of 280 m. Its formation is linked to the Zanclean flood and the termination of the Messinian salinity crisis , when the Mediterranean was abruptly refilled through the Strait of Gibraltar, excavating the 900-metre-deep gorge that lies underneath the water . A competing hypothesis suggests that both the gorge and the Camarinal Sill are the result of fluvial erosion during the desiccation of
28-605: The Mediterranean Sea , separates the Iberian Peninsula in Europe from Morocco in Africa, and limits exchange of deep fauna between the North Atlantic and Mediterranean sea. The sill (~200 m depth) has elevated seabed topography with two "mounts" (Monte Seco and Monte Tartesos) separated by east-west oriented depressions and north-south elevated morphological structures. At the sill, the eastward Atlantic water inflow meets
35-502: The Mediterranean (Messinian salinity crisis). Marine waters must climb to that depth when flowing between both ocean domains. During World War II , submarines used the upper inflow current and the lower outflow current to go in and out of the Mediterranean Sea without using their engines, to avoid being noticed from the surface. Aquatic sill Aquatic sills are common in fjords , limiting their water exchange with
42-561: The deep westward Mediterranean outflow. The sill is characterized by rocky seabed, low, muddy sedimentation, and accumulations of reef-forming cold water corals up to 40-m thick. The gateway formed after the Messinian Crisis , 5.96-5.33 million years ago, when the Mediterranean Sea experienced a near complete drought. During the Zanclean Flood that followed, two deep channels (Canal Norte and Sur) were scoured out. During
49-575: The ocean. After the last ice age , approximately 18,000 years ago, continental glaciers extended to the continental shelves and created U-shaped glacial valleys , with long narrow openings that rise upward near the outer shelf, thereby creating sills. Aquatic sills can influence water circulation by restricting the movement of bottom water masses, resulting in partial to total separation of two basins. The restricted water circulation affects temporal variations in salinity and can result in oxygen depletion in deeper water masses. An aquatic sill can be
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