Circulation in the Romanche Fracture Zone (CIRFZ)

The movement and mixing of Antarctic Bottom Water as it flows through the Romanche Fracture Zone was studied during this 20 day cruise on the N/O Le Noroit. This was a cooperative venture between American and French Scientists on a French vessel. Fifty five HRP profiles and more than 30 CTD stations were completed during this expedition. Most of the work was concentrated in and around the Romanche Fracture Zone. Click here to see an enlargement of the bathymetry of the Romanche, with the HRP dives overlaying it. The deepest HRP dive was made to 5500 meters, a first for the instrument! Twelve more HRP dives comprised two equatorial sections to examine the structure of the deep equatorial jets. A few more profiles were made on the way back to port to provide data on areas of low mixing.

An exciting result from this experiment is that very strong eastward velocity of the deepest water in the Romanche is responsible for high levels of turbulent mixing. The figure displayed shows the bottom depths of the channel we studied, with isotherms showing the temperature structure along the channel and profiles of the east-west component of velocity obtained from the HRP dives. The large amplitude of the wiggles near the bottom over the two sills indicates eastward flow. The temperature of the deepest water is 0.6 degrees C warmer east of the highest point of the fracture zone than it is to the west, which indicates very active deep mixing . A diagrammatic representation (by E.P.Oberlander) shows the topography of the eastern part of the Romanche Fracture Zone (as viewed from the southwest), with the arrows representing the flow and mixing of water as it moves eastward from the main sill (the darker blue the arrow, the colder the water it represents).

Publications resulting from this experiment are:

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