  The O VI ion observed in quasar absorption line spectra is the most
accessible tracer of the cosmic metal distribution in the low redshift (z<0.5)
intergalactic medium (IGM). We explore the nature and origin of O VI absorbers
using cosmological hydrodynamic simulations including galactic outflows. We
consider the effects of ionization background variations, non-equilibrium
ionization and cooling, uniform metallicity, and small-scale (sub-resolution)
turbulence. Our main results are 1) IGM O VI is predominantly photo-ionized
with T= 10^(4.2+/-0.2) K. A key reason for this is that O VI absorbers
preferentially trace over-enriched regions of the IGM at a given density, which
enhances metal-line cooling such that absorbers can cool within a Hubble time.
As such, O VI is not a good tracer of the WHIM. 2) The predicted O VI
properties fit observables only if sub-resolution turbulence is added. The
required turbulence increases with O VI absorber strength such that stronger
absorbers arise from more recent outflows with turbulence dissipating on the
order of a Hubble time. The amount of turbulence is consistent with other
examples of turbulence observed in the IGM and galactic halos. 3) Metals traced
by O VI and H I do not trace exactly the same baryons, but reside in the same
large-scale structure. Observed alignment statistics are reproduced in our
simulations. 4) Photo-ionized O VI traces gas in a variety of environments, and
is not directly associated with the nearest galaxy, though is typically nearest
to ~0.1L* galaxies. Weaker O VI components trace some of the oldest cosmic
metals. 5) Very strong absorbers are more likely to be collisionally ionized,
tracing more recent enrichment (<2 Gyr) within or near galactic halos.
