Fourteen subsurface floats drifting at about 600m depth, have been located 
acoustically from July 1997 to July 1998 in the Algerian basin. In contrast with 
eulerian current measurements, floats trajectories highlight several important 
features at very different scales and offer new insights of the basin 
circulation. They reveal a dominant large scale cyclonic circulation (250km 
diameter and 3 months period) at 600m depth, that we will call the Algerian 
Gyre. This gyre has a strong seasonal variability. It appears to be fairly well 
developped late fall-early winter and much less reduced in summer. Very few 
mesoscale eddies are evidenced at this depth although the circulation in this 
basin was thought to be dominated by mesoscale anticyclonic eddies (Algerian 
Eddies) at all depths. Floats also revealed anticyclonic Submesoscale Coherent 
Vortices (20km of diameter, few days period and more than 1 year lifetime) 
migrating around the large cyclonic Algerian Gyre and carrying on Levantine 
Intermediate Water into the interior of the basin. LIW branch flowing from the 
Tyrrhenian Sea towards the Liguro-Provencal basin alongslope of Sardinia is also 
well evidenced from floats trajectories. The Algerian Gyre is characterised at 
zero order in Rossby number by a vorticity balance involving planetary vorticity 
and bottom topography since floats are closely following f/H isocontours. 
Relative vorticity being of the same order as d(1/H)/dt and/or d(f)/dt, should 
be precisely estimated in order to speculate about the origin of the Gyre and 
its variability. This could be obtained by redistributing currentmeters array in 
order to combine efficiently lagrangian and eulerian informations.