CAPOS: The bulge Cluster APOgee Survey. XII. Abundances for 98 PIGS metal-poor Bulge field giants

The inner Milky Way hosts overlapping stellar populations (bar--bulge, inner thin and thick disks, and halo), thus complicating population assignments along the line of sight. A joint chemical--dynamical approach is required to isolate a clean field bulge sample. Metal-poor bulge stars are particularly valuable as they likely trace the earliest phases of chemical enrichment in the inner Galaxy. We characterize the α-element (Si, Mg) and selected Fe-peak abundances of a dynamically defined sample of bulge field stars, and contrast these trends with the inner-halo tail in the metal-poor regime. We analyzed metal-poor candidates from the Pristine Inner Galaxy Survey observed by the bulge Cluster APOGEE Survey. Using APOGEE/ASPCAP abundances ($ ̊m S/N 50$), we integrated full 6D orbits in a barred Milky Way potential. Bulge membership was defined via orbital confinement using an apocenter cut and the high-density locus in the $(E_J, L_z)$ plane, with uncertainties estimated using Monte Carlo simulations. We identified 98 stars as genuine bulge members. The metallicity distribution spans -2.5 łe Fe/H łe -0.4, with a median $ Fe/H = -1.71$, offset to higher metallicity than the inner halo (median $ Fe/H = -1.96$). The sample follows a high-α sequence with slopes mathrm d Si/Fe / = -0.020^ d Fe/H +0.012 _ -0.051 and mathrm d Mg/Fe / = -0.097^ d Fe/H +0.062 _ -0.133 . Fe-peak tracers show $ Ni/Fe ∼ 0$, while $ Mn/Fe $ declines with $ Fe/H $ with a mild upturn at higher metallicity. We detect no significant $ Si/Fe $ gradients with R_̊m apo or Z_ _ ($+0.010^ +0.018 0.000 $ and $+0.006^ +0.022 _ -0.011 dex -1 $, respectively). The results are insensitive to the assumed Ω_̊m p, yielding indistinguishable memberships. The chemo-orbital evidence favors an in situ origin within the inner Galaxy for the metal-poor bulge field, enriched at early times and later rearranged by secular bar evolution, with a minor contribution from halo stars at the most metal-poor end.