2025ApJ...990L..72K

The influx of icy pebbles to the inner regions of protoplanetary disks constitutes a fundamental ingredient in most planet formation theories. The observational determination of the magnitude of this pebble flux and its dependence on disk substructure (disk gaps as pebble traps) would be a significant step forward. In this work, we analyze a sample of 21 T Tauri disks (with ages ≈0.5-2 Myr) using JWST/MIRI spectra homogeneously reduced with the JDISCS pipeline and high-angular-resolution Atacama Large Millimeter/submillimeter Array (ALMA) continuum data. We find that the 1500/6000 K water line flux ratio measured with JWST-a tracer of cold water vapor and pebble drift near the snow line-correlates with the radial location of the innermost dust gap in ALMA continuum observations (ranging from 8.7 to 69 au), confirming predictions from recent models that study connections between the inner and outer disk reservoirs. We develop a population synthesis exploration of pebble drift in gapped disks and find a good match to the observed trend for early and relatively effective gaps, while scenarios where pebble drift happens quickly, gaps are very leaky, or where gaps form late, are all disfavored on a population level. Inferred snow line pebble mass fluxes (ranging between 10^–6 and 10^–3M_⊕ yr^–1 depending on gap position) are comparable to fluxes used in pebble accretion studies and those proposed for the inner solar system, while system-to-system variations suggest differences in the emerging planetary system architectures and water budgets.