Coastal wetlands occupy a dynamic interface where terrestrial groundwater flow paths intersect tidally driven porewater exchange. These highly productive ecosystems can sequester substantial carbon in marsh sediments and export carbon laterally to the coastal ocean, underscoring their potential role in climate mitigation. Yet most mechanistic understanding of marsh hydrology and biogeochemical exchange is derived from warm-season observations, leaving key uncertainties about cold-season controls on groundwater–surface water exchange and associated carbon export. To evaluate marsh freeze–thaw dynamics and groundwater flow and exchange, we use year-round, high-frequency measurements of soil temperature, groundwater and surface-water elevations, and tidal creek discharge across multiple New England salt marshes: Gouldsboro (northern Maine), Wells (southern Maine), and Chatham (Cape Cod, Massachusetts). Soil temperatures decreased with latitude, and sustained freezing occurred at both Maine sites from December through mid-March. Within marshes, freezing was strongly elevation-dependent: creek beds remained unfrozen due to persistent exposure to relatively warm, saline seawater, whereas higher-elevation platforms that were inundated less frequently froze to depths of up to 30 cm. Despite minimal seasonal change in water-table fluctuations, monthly slug tests indicated reduced hydraulic conductivity during winter, implying diminished but ongoing water and solute fluxes between marsh sediments and tidal creeks. Together, these observations indicate that cold-season freezing reorganizes hydrologic connectivity across marsh landscapes without fully shutting down groundwater–surface water exchange. This work highlights that cold-season dynamics must be accounted for when assessing coastal wetland groundwater fluxes and associated carbon export.