  Using the compactified universal jacobian over the moduli space of stable
marked curves, we give an expression in terms of natural classes of the zero
section of the compactified universal jacobian the (rational) Chow ring. After
extending variants of the Abel-Jacobi map to a locus containing curves of
treelike type we give a formula for the pullback of the said zero section along
these extensions. The same approach is also applied to recover known formulas
for the pullback of theta divisors to the moduli space of marked stable curves.
