In this study, low frequency (0-500 Hz) source depth discrimination in deep water is investigated using a horizontal line array (HLA). In this con- text, propagation is dispersive and can be described by modal theory. Array invariant theory is known to allow source ranging via the modal beam-time migration pattern. This pattern is defined by the evolution of a conventional beamformer output over time. Recently, it has been shown that the array invariant and the waveguide invariant are intrinsically related. In other words, the beam-time migration pattern can be derived using waveguide invariant theory. Utilizing this dependence, we pursue the link between the two invariants to perform source depth discrimination using a HLA. Since the waveguide invariant distribution is strongly related to source depth, the beam-time migration pattern also depends on source depth and would allow for source depth discrimination to be achieved. The proposed method is suc- cessfully applied on simulated data. As the classical array invariant method, it is restricted to short signals, away from the array broadside, but it could be used with minimal environmental knowledge in a multisource context.