  We report a quark spin calculation from the anomalous Ward identity with
overlap fermions on 2+1 flavor dynamical fermion configurations with light sea
quark masses. Such a formulation decomposes the divergence of the
flavor-singlet axial-vector current into a quark pseudoscalar term and a
triangle anomaly term, flavor by flavor. A large negative contribution from the
anomaly term is observed and it is canceled within errors by the contribution
from the pseudoscalar term in the disconnected insertion in the heavy quark
region. On the other hand, net negative contributions are obtained for the
light and strange quarks in the disconnected insertion, since their quark
pseudoscalar terms are smaller than that of the heavy quark. Our results are
obtained from the 2+1 flavor domain wall fermion configurations on the 24^3*64
lattice with a-1 = 1.78(5) GeV and the light sea quark at m_{\pi} = 330 MeV. We
use the overlap fermion for the valence and the quark loop so that the
renormalization constants Z_m and Z_P cancel in the pseudoscalar operator 2mP.
In addition, the overlap Dirac operator is used to calculate the local
topological charge in the anomaly so that there is no renormalization for the
anomaly term either. In this study, we find the total quark spin to be small
mainlyly due to the large negative anomaly term which could be the source for
the 'proton spin crisis'.
