  The abundances of mixing--sensitive elements including lithium, [C/N], and
12C/13C are known to change near the red giant branch bump. The explanation
most often offered for these alterations is double diffusive thermohaline
mixing in the stellar interior. In this analysis, we investigate the ability of
thermohaline mixing to explain the observed timing of these chemical depletion
events. Recent observational measurements of lithium and [C/N] show that the
abundance of lithium decreases before the abundance of [C/N], whereas numerical
simulations of the propagation of the thermohaline mixing region computed with
MESA show that the synthetic abundances drop simultaneously. We therefore
conclude that thermohaline mixing alone cannot explain the distinct events of
lithium depletion and [C/N] depletion, as the simultaneity predicted by
simulations is not consistent with the observation of separate drops. We thus
invite more sophisticated theoretical explanations for the observed temporal
separation of these chemical depletion episodes as well as more extensive
observational explorations across a range of masses and metallicities.
