Abstract: The warm Pacific Summer Water (PSW) is one of the important factors impacting sea ice in the Canada Basin. In summer, temperature of the PSW was found to be highly correlated with sea ice concentration, indicating that it provided heat to promote ice melting. However, the heat release from the PSW in winter and its impact on sea ice are not clear. Based on the hydrographic profiles collected by the Ice Tethered Profilers in the Canada Basin, we analyzed the relationship between heat release from the PSW layer into the mixed layer and its impact on sea ice in winter. We found that the heat restored in the PSW layer can be entrained into the mixed layer through Ekman upwelling, resulting in an increase in mixed layer heat content. This process, when combined with intense ice-ocean interface friction, results in a rise in under-ice oceanic heat flux, interrupting heat balance at ice bottom and impeding sea ice growth. The occurrence of strong heat release events in winter of 2012, 2015 and 2020 coincided with thinner ice. Moreover, the PSW in winter is over 0.5 °C warmer than previous years since 2019. In the meantime, there is a significant increase in Ekman upwelling induced entrainment heat flux and under-ice oceanic heat flux in winter from 2019 to 2022 compared to that from 2005 to 2018, with the regional averages rising from 0.9 W/m² to 1.6 W/m², and 1.1 W/m² to 2.4 W/m², respectively. The regional average value corresponding to the reduction in growth rate of sea ice due to the under-ice oceanic heat flux has increased from 4×10⁻⁹ m/s to 1.0×10⁻⁸ m/s. More vertical heat mixing may be triggered by prominently warmer PSW under the same external forces such as atmospheric forcing and sea ice motion, exerting stronger influence on sea ice mass balance in winter.