FLOW PATHWAYS OF BOTTOM WATER THROUGH THE ROMANCHE AND CHAIN FRACTURE-ZONES

The Romanche and Chain Fracture Zones of the equatorial Atlantic Ocean are known as pathways for the Antarctic Bottom Water from the western to the eastern trough of the Atlantic across the Mid-Atlantic Ridge. New observations are reported here on the bathymetry and hydrology of both fracture zones. The main sills of the Romanche and Chain Fracture Zones were determined to be at depths of 4350 and 4050 m. Bottom pote ntial temperature is used to show that the main path followed by botto m water from the western to the eastern basin is along the Romanche va lley. Bottom temperature increases in the Romanche Fracture Zone from 0.63 degrees C at the entrance at 19 degrees W to 1.33 degrees C at th e exit at 12 degrees W as a result of both blocking by topography of t he coldest water and vertical mixing. Most of the bottom water which e nters the Chain Fracture Zone is blocked by the main sill along the ax is and has to follow a complicated pathway through a communication reg ion before reaching the eastern basin.