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We use synthetic sightlines drawn through snapshots of the Technicolor Dawnsimulations to explore how the statistics of neutral oxygen OI absorbersrespond to hydrogen reionization. The ionization state of the circumgalacticmedium (CGM) initially roughly tracks that of the intergalactic medium, butbeginning at $z=8$ the CGM grows systematically more neutral owing toself-shielding. Weak absorbers trace diffuse gas that lies farther from halos,hence they are ionized first, whereas stronger systems are less sensitive toreionization. The overall OI covering fraction decreases slowly with time owingto competition between ongoing enrichment and gradual encroachment ofionization fronts into increasingly overdense gas. While the declining coveringfraction is partially offset by continued formation of new halos, theionization of the diffuse gas causes the predicted line-of-sight incidence rateof OI absorbers to decline abruptly at the overlap epoch, in qualitativeagreement with observations. In comparison to the recently-observed equivalentwidth (EW) distribution at $z\approx6$, the simulations underproduce systemswith $EW \geq 0.1 \unicode{x212B}$, although they reproduce weaker systems with$EW \geq 0.05 \unicode{x212B}$. By $z\approx5$, the incidence of $EW < 0.1\unicode{x212B}$ systems are overproduced, consistent with previous indicationsthat the simulated ionizing background is too weak at $z<6$. The summed columndensities of SiII and SiIV trace the total oxygen column, and hence the ratioof the OI and SiII + SiIV comoving mass densities traces the progress ofreionization. This probe may prove particularly useful in the regime where$x_{HI} > 10\%$

Evolution of Neutral Oxygen During the Epoch of Reionization and its Use in Estimating the Neutral Hydrogen Fraction