  We present an analysis of the Suzaku observation of the northeastern rim of
the Cygnus Loop supernova remnant. The high detection efficiency together with
the high spectral resolution of the Suzaku X-ray CCD camera enables us to
detect highly-ionized C and N emission lines from the Cygnus Loop. Given the
significant plasma structure within the Suzaku field of view, we selected the
softest region based on ROSAT observations. The Suzaku spectral data are well
characterized by a two-component non-equilibrium ionization model with
different best-fit values for both the electron temperature and ionization
timescale. Abundances of C to Fe are all depleted to typically 0.23 times solar
with the exception of O. The abundance of O is relatively depleted by an
additional factor of two compared with other heavy elements. We found that the
resonance-line-scattering optical depth for the intense resonance lines of O is
significant and, whereas the optical depth for other resonance lines is not as
significant, it still needs to be taken into account for accurate abundance
determination.
