The Arctic Ocean cold halocline layer (CHL) inhibits upward ocean heat transfer from Atlantic Water (AW) to the surface mixed layer and sea ice through strong salinity-driven stratification. Under Atlantification, AW shoaling and warming are associated with halocline weakening and episodic winter ventilation. However, the long-term variability and mechanisms of CHL disappearance remain insufficiently constrained. Here, we analyze the SODA4 monthly reanalysis for 1980–2023 to examine the spatiotemporal evolution of CHL disappearance during the cold season (December–April). CHL disappearance is diagnosed within the layer between the mixed layer depth and the upper boundary of AW, defined as conditions where the density ratio exceeds 0.05 throughout the layer, identifying a transition from salinity-dominated toward thermally influenced stratification. Results show that CHL disappearance is primarily confined to the continental slope from the western Eurasian Basin to the Kara Sea margin, while remaining rare in the basin interior. From 1980 to 2019, its occurrence increases in association with AW shoaling to ~100 m and enhanced cold-season upper-ocean heat loss within 65–130 m. However, this increase is not sustained in recent years despite continued AW shoaling, suggesting an increasing role of freshwater-controlled stratification, which counteracts halocline weakening associated with AW shoaling and suppresses winter vertical mixing. It indicates that Atlantification provides a persistent thermohaline forcing through AW shoaling and warming and downstream propagation, while CHL disappearance is jointly shaped by long-term AW evolution and interannual-to-decadal variability in freshwater-controlled stratification.
 

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