We prove the abundance conjecture for projective slc surfaces over arbitrary fields of positive characteristic. The proof relies on abundance for lc surfaces over abritrary fields, proved by Tanaka, and on the technique of Hacon and Xu to descend semi-ampleness from the normalization. We also present applications to dlt threefold pairs, and to mixed characteristic families of surfaces.

Comment: 22 pages. Comments welcome anytime. v2: some proofs in Sections 3.1 and 3.2 have been clarified. v4: Final version, to appear in Epijournal de Geometrie algebrique