Unexpected return of late-summer sea ice in the Pacific Arctic under persistent poleward-shifted cyclonic anomaly

Against the backdrop of a rapid trajectory toward a seasonally ice-free Arctic, late-summer Chukchi Sea ice recovered over 2020–2024, culminating in an abrupt retention that obstructed the Northeast Passage by September 2024 for the first time since 2001. Here we show that this recovery coincides with a persistent poleward-shifted Pacific–Arctic cyclonic anomaly near the Bering Strait. This shifted circulation produces a coupled dynamic–thermodynamic response, with Arctic cold advection, enhanced cloud-induced cooling, reduced oceanic heat, and delayed seasonal thinning acting together to sustain late-summer ice retention. Furthermore, we demonstrate that the Pacific–North American (PNA) mode is linked to summer Chukchi Sea ice variations, with its influence expressed through the regional position of the associated Pacific–Arctic cyclonic anomaly. These findings identify the Chukchi Sea as a sensitive Pacific Arctic sector where natural regional circulation variability generates abrupt, localized reversals in summer sea-ice loss, thereby offering a fresh perspective on the role of summer PNA-related circulation variability in Pacific-sector Arctic sea ice. The recovery of late-summer Chukchi Sea ice over 2020–2024 was driven by a poleward-shifted Pacific–Arctic cyclonic anomaly that enhanced cooling and delayed seasonal thinning, according to a study combining satellite observations, sea-ice thickness estimates and atmospheric-oceanic reanalyses.