Metal abundances in the high-redshift intergalactic medium
  Twenty years of high-resolution spectroscopy at the 8-10 m class telescopes
have drastically expanded our view of the gas-phase metallicity in the z>2
universe. This contribution briefly summarizes how these studies reveal a
widespread metal pollution in the intergalactic medium with a median abundance
[C/H] ~ -3.5 at z~3 that is increasing by a factor of ~2-3 from z~4.3 to z~2.4.
At the higher densities that are typical of galactic halos, observations
uncover a metallicity spread of five orders of magnitude in Lyman limit
systems, ranging from super-solar ([M/H]~+0.7) to pristine ([M/H]< -4) gas
clouds. Finally, the neutral damped Ly-alpha systems are enriched to a median
metallicity of [M/H] ~ -1.5 that slowly declines with redshift up to z ~ 4.5,
at which point it appears to more rapidly evolve as one approaches the end of
reionization.
