  Saturn's axial tilt of 26.7{\deg} produces seasons in a similar way as on
Earth. Both the stratospheric temperature and composition are affected by this
latitudinally varying insolation along Saturn's orbital path. A new time
dependent 2D photochemical model is presented to study the seasonal evolution
of Saturn's stratospheric composition. This study focuses on the impact of the
seasonally variable thermal field on the main stratospheric C2 hydrocarbon
chemistry (C2H2 and C2H6) using a realistic radiative climate model. Meridional
mixing and advective processes are implemented in the model but turned off in
the present study for the sake of simplicity. The results are compared to a
simple study case where a latitudinally and temporally steady thermal field is
assumed. Our simulations suggest that, when the seasonally variable thermal
field is accounted for, the downward diffusion of the seasonally produced
hydrocarbons is faster due to the seasonal compression of the atmospheric
column during winter. This effect increases with increasing latitudes which
experience the most important thermal changes in the course of the seasons. The
seasonal variability of C2H2 and C2H6 therefore persists at higher-pressure
levels with a seasonally-variable thermal field. Cassini limb-observations of
C2H2 and C2H6 (Guerlet et al., 2009) are reasonably well-reproduced from the
equator to 40{\deg} in both hemispheres
