  We report experiments on the deformation and transport of an elastic fiber in
a viscous cellular flow, namely a lattice of counter-rotative vortices. We show
that the fiber can buckle when approaching a stagnation point. By tuning either
the flow or fiber properties, we measure the onset of this buckling
instability. The buckling threshold is determined by the relative intensity of
viscous and elastic forces, the elasto-viscous number Sp. Moreover we show that
flexible fibers escape faster from a vortex (formed by closed streamlines)
compared to rigid fibers. As a consequence, the deformation of the fiber
changes its transport properties in the cellular flow.
