We present the first measurements of inorganic carbon (IC) stocks and accumulation rates in Eastern Canadian salt marshes. Though salt marshes are recognized as important organic carbon (OC) sinks, IC has been systematically overlooked in coastal carbon assessments, with no previous data available for the Western North Atlantic. We quantified IC using traditional loss-on-ignition (LOI) and portable XRF analysis of calcium concentrations across 33 sediment cores from 20 marshes along the St. Lawrence River Estuary, Gulf of St. Lawrence, Bay of Fundy, and Atlantic coast of Nova Scotia. IC stocks were measured in the upper 25 cm of sediment. Mean IC densities were highest in the Upper Bay of Fundy (0.023±0.006 gcm⁻³) and St. Lawrence River Estuary (0.017±0.004 gcm⁻³). IC density increased with depth, reflecting redox-driven dissolution–precipitation processes. Accumulation rates ranged from 9 to 38 gm⁻²yr⁻¹. Autochthonous calcifying organisms likely contribute substantially to IC, potentially accounting for approximately 74% of the measured pool. In the top 25 cm, IC formation releases CO₂ (7 gCO₂ m⁻²yr⁻¹), but OC sequestration (297–521 gCO₂e m⁻²yr⁻¹) ensures these ecosystems remain net CO₂ sinks. Complete IC dissolution consumes ~0.6 moles of CO₂ per mole dissolved, meaning drainage‑driven dissolution may offset some CO₂ released during OC mineralization. This offset is largely unquantified, and IC dissolution may increase as drainage deepens. We also assess the magnitude of this overlooked CO₂ sink and its potential climate feedback. Incorporating IC into salt marsh carbon assessments is necessary for a complete and accurate budget.