  In two-dimensional (2D) spin systems, the augmentation of spin fluctuations
gives rise to quasi-long-range order; however, how they manifest in spin
transport remains unclear. Here we investigate the spin Seebeck effect (SSE) in
a quasi-2D antiferromagnet, BaNi$_2$V$_2$O$_8$, which has been reported to
exhibit the Berezinskii-Kosterlitz-Thouless (BKT) transition owing to its
distinct 2D nature. We found that the SSE in Pt / BaNi$_2$V$_2$O$_8$ persists
well above the N\'eel temperature, significantly different from the behavior of
3D ordered magnets. Our numerical analysis for a 2D microscopic spin model
supports the hypothesis that the observed SSE is linked to strong magnetic
correlations in the BKT-like phase.
