The Finite-Scale Lyapunov Exponents (FSLE) are measured to estimate relative 
dispersion rates of Lagrangian trajectories integrated off-line from the
output of a Mediterranean Sea GCM. This diagnostics is used for characterizing 
both global and local mixing properties of the Mediterranean Sea model surface 
circulation. One of the main results is that relative dispersion is dominated by
mean shear effects up to gyre-scales and indications of chaotic advection, i.e. 
exponential separation between particles, are present at the meso-scales. An 
analysis of nine clusters of numerical floats allowed to inspect the spatial 
scales of anisotropy of the dispersion as well as to observe a standard 
diffusion behavior in the recirculations. The spatial distribution of the FSLE 
(I kind) can describe local dispersion properties and identify regions at high 
or low rates of mixing over an assigned spatial scale. At this regard, we 
discuss briefly the relation between Lagrangian and Eulerian observables when 
finite-scale transport properties are concerned. Lagrangian unpredictability 
source is the sensitivity to both the initial conditions and the uncertainty in 
the evolution law, e.g. an imperfect knowledge of the velocity field. The 
so-called FSLE of II kind is used to characterize, for three different sampling 
time of the velocity field (daily, monthly and yearly means), the effect of 
Eulerian time resolution on the accuracy of the Lagrangian trajectory 
computation.