  Empirical evidence of planets in gas-rich circumstellar discs is required to
constrain giant planet formation theories. Here we study the kinematic patterns
which arise from planet-disc interactions and their observability in CO
rotational emission lines. We perform three-dimensional hydrodynamical
simulations of single giant planets, and predict the emergent intensity field
with radiative transfer. Pressure gradients at planet-carved gaps, spiral wakes
and vortices bear strong kinematic counterparts. The iso-velocity contours in
the CO(2-1) line centroids $v_\circ$ reveal large-scale perturbations,
corresponding to abrupt transitions from below sub-Keplerian to super-Keplerian
rotation along with radial and vertical flows. The increase in line optical
depth at the edge of the gap also modulates $v_\circ$, but this is a mild
effect compared to the dynamical imprint of the planet-disc interaction. The
large-scale deviations from the Keplerian rotation thus allow the planets to be
indirectly detected via the first moment maps of molecular gas tracers, at ALMA
angular resolutions. The strength of these deviations depends on the mass of
the perturber. This initial study paves the way to eventually determine the
mass of the planet by comparison with more detailed models.
