MINDS. The detection of ${}^{13}$CO${}_2$ with JWST-MIRI indicates abundant CO${}_2$ in a protoplanetary disk

We present JWST-MIRI MRS spectra of the protoplanetary disk around the low-mass T Tauri star GW Lup from the MIRI mid-INfrared Disk Survey (MINDS) GTO program. Emission from ${}^{12}$CO${}_2$, ${}^{13}$CO${}_2$, H${}_2$O, HCN, C${}_2$H${}_2$, and OH is identified with ${}^{13}$CO${}_2$ being detected for the first time in a protoplanetary disk. We characterize the chemical and physical conditions in the inner few au of the GW Lup disk using these molecules as probes. The spectral resolution of JWST-MIRI MRS paired with high signal-to-noise data is essential to identify these species and determine their column densities and temperatures. The $Q$-branches of these molecules, including those of hot-bands, are particularly sensitive to temperature and column density. We find that the ${}^{12}$CO${}_2$ emission in the GW Lup disk is coming from optically thick emission at a temperature of $\sim$400 K. ${}^{13}$CO${}_2$ is optically thinner and based on a lower temperature of $\sim$325 K, may be tracing deeper into the disk and/or a larger emitting radius than ${}^{12}$CO${}_2$. The derived $N_{\mathrm{C}{\mathrm{O}}_2}$/$N_{{\mathrm{H}}_2\mathrm{O}}$ ratio is orders of magnitude higher than previously derived for GW Lup and other targets based on $\mathit{\text{Spitzer}}$-IRS data. This high column density ratio may be due to an inner cavity with a radius in between the H${}_2$O and CO${}_2$ snowlines and/or an overall lower disk temperature. This paper demonstrates the unique ability of JWST to probe inner disk structures and chemistry through weak, previously unseen molecular features.