As part of the WOCE Atlantic Climate Change Experiment (ACCE), 115 isopycnal 
floats were deployed in the Subpolar Front just west of the mid-Atlantic ridge 
and along the eastern margin to study the spreading and mixing of these upper 
ocean waters into the NE Atlantic Ocean. Drifting on an isopycnal corresponding 
to sigma-t = 27.5, these acoustically tracked floats are giving us unprecedented 
information on the pathways of spreading, cross-frontal exchange and mixing 
processes between the three major water masses on this isopycnal: subtropical 
waters from the Gulf Stream and North Atlantic Current, Labrador Sea waters and 
the waters along the eastern margin from the Mediterranean.

Several striking features stand out. First, the eastward penetration of 
subpolar waters through the Charlie Gibbs Fracture Zone (CGFZ) and their 
spreading along two principal pathways to the north: one heading NE into the 
northern Iceland Basin west of Rockall/Hatton Bank and the other turning 
(north)west rather sharply towards the Reykjanes Ridge. This retroflection of 
waters from the mid-Atlantic ridge appears to be in response to "blocking" by 
the eastward spread of Labrador Sea waters penetrating east through the CGFZ. 
Second, none of the floats continue into the Nordic Seas even though they had 
time to do so. Instead all floats in the northern Iceland Basin turn west and 
south along the Reykjanes Ridge before turning back north and into the Irminger 
Sea. This begs the question from where the waters entering the Norwegian Sea 
along the Iceland-Faroes Front come. Third, the isopycnal floats exhibit very 
strange depth variations in the vicinity of the Rockall Bank complex where 
waters from the SW along the Subpolar Front and the SE from the Mediterranean 
come into contact, interleave and mix. Numerous examples of submesoscale eddy 
activity can be noted, including the formation of ‘meddies’ at higher latitudes 
than previously thought. Thes e observations clearly show the very important 
role played by topography to currents on all scales: the mean flow, eddy 
activity and mixing processes.