Preprint typeset using L ATEX style emulateapj v. 04/20/08

We present the results from our search for C iv in the intergalactic medium at redshifts z = 5.3−6.0. We have observed four z ∼ 6 QSOs with Keck/NIRSPEC in echelle mode. The data are the most sensitive yet taken to search for C iv at these redshifts, being 50% complete at column densities logNC IV ≈ 13.4. We find no C iv systems in any of the four sightlines. Taking into account our completeness, this translates into a decline in the number density of C iv absorbers in the range 13.0 < logNC IV < 15.0 of at least a factor 4.4 (95% confidence) from z ∼ 2− 4.5, where the number density is relatively constant. We use our lack of detections to set limits on the slope and normalization of the column density distribution at z = 5.3 − 6.0. The rapid evolution of C iv at these redshifts suggests that the decrease in the number density may largely be due to ionization effects, in which case many of the metals in the z ∼ 4.5 IGM could already be in place at z ∼ 5.3, but in a lower ionization state. The lack of weak systems in our data, combined with the presence of strong C iv absorbers along at least one other sightline, further suggests that there may be large-scale variations in the enrichment and/or ionization state of the z ∼ 6 IGM, or that C iv absorbers at these redshifts are associated with rare, UV-bright star-forming galaxies. Subject headings: cosmology: observations — cosmology: early universe — intergalactic medium — quasars: absorption lines