  Ultra-hot Jupiters are perfect targets for transmission spectroscopy.
However, their atmospheres feature strong spatial variations in temperature,
chemistry, dynamics, cloud coverage, and scale height. This makes transit
observations at high spectral resolution challenging to interpret. In this
work, we model the cross-correlation signal of five chemical species (Fe, CO,
H$_\text{2}$O, OH, and TiO) on WASP-76b, a benchmark ultra-hot Jupiter. We
compute phase-dependent high-resolution transmission spectra of 3D SPARC/MITgcm
models. The spectra are obtained with gCMCRT, a 3D Monte-Carlo
radiative-transfer code. We find that, on top of atmospheric dynamics, the
phase-dependent Doppler shift of the absorption lines in the planetary rest
frame is shaped by the combined effect of planetary rotation and the unique 3D
spatial distribution of chemical species. For species probing the dayside
(e.g., refractories or molecules like CO and OH), the two effects act in
tandem, leading to increasing blueshifts with orbital phase. For species that
are depleted on the dayside (e.g., H$_\text{2}$O and TiO), the two effects act
in an opposite manner, and could lead to increasing redshifts during the
transit. This behaviour yields species-dependent offsets from a planet's
expected $K_\text{p}$ value that can be much larger than planetary wind speeds.
The offsets are usually negative for refractory species. We provide an
analytical formula to estimate the size of a planet's $K_\text{p}$ offsets,
which can serve as a prior for atmospheric retrievals. We conclude that
observing the phase-resolved absorption signal of multiple species is key to
constraining the 3D thermochemical structure and dynamics of ultra-hot
Jupiters.
