[C/O] ratio of VMP/EMP DLAs and sub-DLAs as function of the absorption redshift. We color the systems by metallicity (see color bar). The most metal-poor systems (i.e., within 0.1 dex of the EMP regime) are indicated by the red points. These data show a trend of increasing [C/O] at lower redshifts that is not seen across the more metal rich absorbers. This indicates that these most metal-poor systems may be showcasing a unique signature of reionization quenching. This is in line with the expectation that only the most metal-poor systems would be impacted by this process at this epoch.