  We establish a higher dimensional counterpart of Bourgain's pointwise ergodic
theorem along an arbitrary integer-valued polynomial mapping. We achieve this
by proving variational estimates $V_r$ on $L^p$ spaces for all $1<p<\infty$ and
$r>\max\{p, p/(p-1)\}$. Moreover, we obtain the estimates which are uniform in
the coefficients of a polynomial mapping of fixed degree.
