  Let $P$ be a point of a compact Riemann surface $X$. We study self-adjoint
extensions of the Dolbeault Laplacians in hermitian line bundles $L$ over $X$
initially defined on sections with compact supports in $X\backslash\{P\}$. We
define the $\zeta$-regularized determinants for these operators and derive
comparison formulas for them. We introduce the notion of the Robin mass of $L$.
This quantity enters the comparison formulas for determinants and is related to
the regularized $\zeta(1)$ for the Dolbeault Laplacian. For spinor bundles of
even characteristic, we find an explicit expression for the Robin mass. In
addition, we propose an explicit formula for the Robin mass in the scalar case.
Using this formula, we describe the evolution of the regularized $\zeta(1)$ for
scalar Laplacian under the Ricci flow. As a byproduct, we find an alternative
proof for the Morpurgo result that the round metric minimizes the regularized
$\zeta(1)$ for surfaces of genus zero.
