The Romanche Trench, also called the Romanche Furrow or Romanche Gap, is the third deepest of the major trenches of the Atlantic Ocean, after the Puerto Rico Trench and the South Sandwich Trench. It bisects the Mid-Atlantic Ridge just north of the equator 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 offsetting sections of the Mid-Atlantic Ridge.
It is situated between the Sierra Leone Basin to the north/northeast, the South Atlantic Basin to the east/southeast, the Northern Brazilian Basin to the south/southwest, and North Atlantic Ridge to the west/northwest. Geologically, it is at the seam of the South American Plate to the West and the African Plate to the East. The trench has a depth of 7,760 m, is 300 km long and has an average width of 19 km 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 3.6×106 m³/s of 1.57°C water.