The Romanche Trench, also called the ''Romanche Furrow'' or ''Romanche Gap'', is the third deepest of the major

trench A trench is a type of excavation or in the ground that is generally deeper than it is wide (as opposed to a wider gully, or ditch), and narrow compared with its length (as opposed to a simple hole or pit). In geology, trenches result from eros ...

es of the

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

, after the

Puerto Rico Trench The Puerto Rico Trench is located on the boundary between the Caribbean Sea and the Atlantic Ocean. The oceanic trench, the deepest in the Atlantic, is associated with a complex transition between the Lesser Antilles subduction zone to the sou ...

and the

South Sandwich Trench The South Sandwich Trench is a deep arcuate trench in the South Atlantic Ocean lying to the east of the South Sandwich Islands. It is the deepest trench of the Southern Atlantic Ocean, and the second deepest of the Atlantic Ocean after the Puert ...

. It bisects the

Mid-Atlantic Ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent or constructive plate boundary) located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. In the North Atlantic, the ridge separates the North Ame ...

(MAR) just north of the

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...

at the narrowest part of the Atlantic between Brazil and West Africa, extending from 2°N to 2°S and from 16°W to 20°W. The trench has been formed by the actions of the Romanche Fracture Zone, a portion of which is an active

transform boundary A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subductio ...

offsetting sections of the Mid-Atlantic Ridge. It was named after the French navy ship ''La Romanche'', commanded by captain Louis-Ferdinand Martial which on 11 October 1883 made soundings that revealed the trench. The boat was returning to France after spending a few months on a scientific mission near

Cape Horn Cape Horn ( es, Cabo de Hornos, ) is the southernmost headland of the Tierra del Fuego archipelago of southern Chile, and is located on the small Hornos Island. Although not the most southerly point of South America (which are the Diego Ramírez ...

as part of the first

International Polar Year The International Polar Years (IPY) are collaborative, international efforts with intensive research focus on the polar regions. Karl Weyprecht, an Austro-Hungarian naval officer, motivated the endeavor in 1875, but died before it first occurred i ...

Oceanography

The trench has a depth of , is long and has an average width of and allows for a major circulation of deep ocean basin water from the west Atlantic to the east Atlantic basins. Deep water flow through the trench is from west to east with a rate of 3.6

Sverdrup In oceanography, the sverdrup (symbol: Sv) is a non- SI metric unit of volumetric flow rate, with equal to . It is equivalent to the SI derived unit cubic hectometer per second (symbol: hm3/s or hm3⋅s−1): 1 Sv is equal to 1 hm3/s. It is used ...

s (million m³/s) of water. Lower

North Atlantic Deep Water North Atlantic Deep Water (NADW) is a deep water mass formed in the North Atlantic Ocean. Thermohaline circulation (properly described as meridional overturning circulation) of the world's oceans involves the flow of warm surface waters from the s ...

(LNADW) is found around below sea level and flows from the

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is t ...

and

Norwegian Norwegian, Norwayan, or Norsk may refer to: *Something of, from, or related to Norway, a country in northwestern Europe * Norwegians, both a nation and an ethnic group native to Norway * Demographics of Norway *The Norwegian language, including ...

seas; it brings high salinity, oxygen, and freon concentrations towards the equator. Antarctic Bottom Water (AABW) flows below the LNADW and reaches down to the seafloor. Formed around Antarctica, the AABW is cold, has low salinity, and high silicate concentration. As it flows north, it is constrained by numerous obstacles on the seafloor. In the basin on the eastern side of the MAR the

Walvis Ridge The Walvis Ridge (''walvis'' means whale in Dutch and Afrikaans) is an aseismic ocean ridge in the southern Atlantic Ocean. More than in length, it extends from the Mid-Atlantic Ridge, near Tristan da Cunha and the Gough Islands, to the African ...

blocks the northward passage. For LNADW and AABW, the Romanche and

Chain Fracture Zone A chain is a serial assembly of connected pieces, called links, typically made of metal, with an overall character similar to that of a rope in that it is flexible and curved in compression but linear, rigid, and load-bearing in tension. A ...

s (just south of the equator) are the only deep passages in the MAR where interbasin exchange is possible. As AABW flows through the Romanche Fracture Zone, salinity and temperature increase significantly.

Geology

The Romanche Fracture Zone offsets the Mid-Atlantic ridge by , making it the largest equatorial fracture zone in the Atlantic. According to the normal scenario for the opening of the South Atlantic, it is spreading at a rate of and began forming about . North of and parallel to the fracture zone is a transverse ridge which is particularly prominent over hundreds of kilometres east and west of the MAB of the South Atlantic. The western part of the transverse ridge consists of fragments of uplifted oceanic crust and

upper mantle The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (at about under the oceans and about under the continents) and ends at the top of the lower mantle at . Temperatures range from appro ...

. The summit of the transverse ridge is capped by Miocene shallow water limestones that reached above sea level 20 Ma before subsiding abnormally fast. The eastern part of the transverse ridge, however, consists of a thick sequence of stratified material called the Romanche Sedimentary Sequence (RSS). The RSS includes pelagic material from the early Cretaceous (140 Ma) which, coupled with the thickness of the sequence, does not fit with the normal scenario for the opening of the South Atlantic around the

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...

(125–100 Ma). The transverse ridge separates the present trench from an -long

aseismic In geology, aseismic creep or fault creep is measurable surface displacement along a fault in the absence of notable earthquakes. Aseismic creep may also occur as "after-slip" days to years after an earthquake. Notable examples of aseismic slip in ...

valley where the Romanche transform was located until about 10–8 Ma. This transform migration was preceded by a process 25–17 Ma during which the Miocene shallow-water platform mentioned above reached sea level as the transverse ridge was first

uplifted ''Uplifted'' is the second studio album by Nigerian singer Flavour N'abania. It was released on July 20, 2010, by Obaino Music and 2nite Entertainment. The album features guest appearances from Jay Dey, Oloye, Stormrex, Waga Gee, Asemstone, M-Jay, ...

, then deformed, and finally buried under the sea.

Biological role

The

hydrothermal vent A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...

s of the MAR support many life forms. The Romanche and Chain Fracture Zones creates a huge gap in the MAR and can act as a "Subsea Berlin Wall" segregating the North Atlantic communities from those in other oceans. Swarms of hydrothermal shrimps reminiscent of those found from northern MAR vent-sites have been found on the northern part of the southern MAR. Bivalve communities have been reported around vents further south. These species await a formal description and it is not known whether or not they represent communities distinct from those on the northern MAR. The flow of NADW through the Romanche and Chain Fracture Zones may serve as a conduit for larval transport from the western North Atlantic to the eastern South Atlantic. For example, the

caridea The Caridea, commonly known as caridean shrimp or true shrimp, are an infraorder of shrimp within the order Decapoda. This infraorder contains all species of true shrimp. They are found widely around the world in both fresh and salt water. Many ...

n shrimp '' Alvinocaris muricola'' inhabits

cold seep A cold seep (sometimes called a cold vent) 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. ''Cold'' does not mean that the temperature of the see ...

s in both the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...

and the

Gulf of Guinea The Gulf of Guinea is the northeasternmost part of the tropical Atlantic Ocean from Cape Lopez in Gabon, north and west to Cape Palmas in Liberia. The intersection of the Equator and Prime Meridian (zero degrees latitude and longitude) is in the ...

, which clearly suggests a gene flow across the Atlantic, but the amount of data is very limited and dispersal pathways are not fully understood.

References

Notes

Sources

* * * * * * * {{coord, 0, 00, N, 18, 00, W, type:waterbody_source:kolossus-dewiki, display=title Fracture zones Oceanic trenches of the Atlantic Ocean Mid-Atlantic Ridge