Let A/Q be a Jacobian variety and let F be a totally real, tamely ramified, abelian number field. Given a character ψ of F/Q, Deligne's Period Conjecture asserts the algebraicity of the suitably normalised value L(A, ψ, 1) at z = 1 of the Hasse-Weil-Artin L-function of the ψtwist of A. We formulate a conjecture regarding the integrality properties of the family of normalised L-values (L(A, ψ, 1)) ψ , and its relation to the Tate-Shafarevich group of A over F . We numerically investigate our conjecture through p-adic congruence relations between these values.