We examine the effect of wind-induced shear on the dynamics of motile micro-swimmers in free-surface turbulence. We focus on gyrotaxis, resulting from the gravitational torque generated by an asymmetric mass distribution within the organism. The combination of such torque with the viscous torque due to shear can reorient swimmers and reduce their vertical migration. Through DNS-based Euler-Lagrangian simulations we investigate the effect of wind-induced shear on swimmers with different reorientation time under different wind directions. We show that wind-induced shear modifies the vertical spread of the swimmers and their orientation with respect to gravity. For all gyrotactic re-orientation times considered (spanning two orders of magnitude of the stability number), we observe a reduction of the rising speed and temporary confinement under the high-shear sub-surface layers.
