Recent timescale transition from interannual to decadal variability in January sea ice area over the Bering Sea

Abstract. Over the past four decades, the sea ice area (SIA) in the Bering Sea has shifted from interannual to decadal variability, manifested as persistent heavy-ice or light-ice regimes. However, the mechanisms driving this shift remain unclear. This study demonstrates that the initial shift occurs in January and is triggered by the December SIA anomalies. Specifically, December SIA anomalies induce substantial modifications in localized air-sea heat flux, triggering mesoscale vertical air movements. This process generates localized anticyclonic wind field anomalies during heavy-ice years and anomalous cyclonic wind field anomalies during light-ice years. Subsequently, these mesoscale dynamic processes activate negative feedback in the atmosphere and positive feedback in the ocean, which differentially regulate wind divergence and northward heat transport. The former produces out-of-phase variations between December SIA and January SIA increment (ΔSIA), contributing to interannual variability in January SIA, whereas the latter exhibits significant decadal variability over the past two decades, inducing in-phase changes that amplify decadal-scale signals in sea ice variability. The study emphasizes the critical role of mesoscale ice-atmosphere-ocean coupling processes and their profound impacts on regional oceanic dynamics and sea ice evolution. Given the observed decadal-scale regime shifts in sea ice, of paramount importance and urgency is to assess the implications of sustained heavy/light ice conditions on local ecosystems, indigenous communities, and commercial fisheries.