La fracture Gibbs et la circulation profonde en Atlantique Nord

The cold waters from the Norwegian Sea are the main source of the underflow system in the northern Atlantic Ocean (10) (pl. 1, fig. 1b). The role of these currents in the formation of large sediment ripples has been demonstrated in some recent studies [(2), (3)]. As in the southern Atlantic Ocean, the observations suggested that their influence had been of importance since the Eocene era (6). From a sedimentological point of view, it appears that the Gibbs fracture (4) represents a very important feature in this system; this structure both forms a deep opening through the Mid-Atlantic Ridge and a dam across the abyssal plain to the northeast of Newfoundland. This dam, which is still active today, though partly flooded, must have been continuous from the dorsal to the Canadian continental margin up until a recent period, preventing any deep water exchange between the northern and southern basins. This preliminary study is based on about thirty bathymetric and seismic profiles between 35° W and 48° W, carried out during the Noratlante expedition of the R.V. Jean-Charcot.