[en] A narrow gap in the East Azores Fracture Zone provides a channel for the exchange of the bottom water between the Madeira and Iberian abyssal basins. It is named Discovery Gap and a detailed survey defines its length, morphology and sills. Year-long measurements of flow are made from six moorings and ten current meters. This data is supplemented by numerous measurements of temperature made from ship-lowered instruments. A persistent S-N flow is found in Discovery Gap and an estimate of the flux of water colder than 2.05 deg C (potential temperature) is made. This discharge spreads over a region beyond the Gap exit where it is warmed both by the geothermal heating from the seabed and also by mixing with the overlying warm water. An estimate of approximately 2 cm²s^-1 for the through density surface diffusion is derived, quite similar to two values determined from much larger channels in the Western Atlantic. It is not known whether most of the mixing takes place near the sea-bed or not. The values are in quite striking contrast to those derived for diffusion along a density surface: in Discovery Gap values are estimated to be about 5 x 10⁶ cm² s^-1. (author)