One of the pathways (along with the Romanche Fracture Zone) for AABW and lower NADW from the western to the eastern trough of the equatorial Atlantic Ocean across the Mid– Atlantic Ridge. To the west of the CFZ sill, the AABW and NADW cores are separated by a deep thermocline marking the vertical transition between them. This thermocline erodes eastward and vanishes in the eastern basin.