  Determinations of the solar oxygen content relying on the neutral forbidden
transition at 630 nm depend upon the nickel abundance, due to a Ni I blend.
Here we rederive the solar nickel abundance, using the same ab initio 3D
hydrodynamic model of the solar photosphere employed in the recent revision of
the abundances of C, N, O and other elements. Using 17 weak, unblended lines of
Ni I together with the most accurate atomic and observational data available we
find log epsilon_Ni = 6.17 +/- 0.02 (statistical) +/- 0.05 (systematic), a
downwards shift of 0.06 to 0.08 dex relative to previous 1D-based abundances.
We investigate the implications of the new nickel abundance for studies of the
solar oxygen abundance based on the [O I] 630 nm line in the quiet Sun.
Furthermore, we demonstrate that the oxygen abundance implied by the recent
sunspot spectropolarimetric study of Centeno & Socas-Navarro needs to be
revised downwards from log epsilon_O = 8.86 +/- 0.07 to 8.71 +/- 0.10. This
revision is based on the new nickel abundance, application of the best
available gf-value for the 630 nm forbidden oxygen line, and a more transparent
treatment of CO formation. Determinations of the solar oxygen content relying
on forbidden lines now appear to converge around log epsilon_O = 8.7.
