Regime transitions in Arctic surface momentum balance reveal persistent and predictable dynamical states

Abstract

Abstract Arctic sea-ice decline is fundamentally altering the momentum transfer between the atmosphere and ocean, with important implications for the climate system. However, capturing the complexity of air–ice–ocean interactions across varying timescales remains a challenge for climate models. Here, we show that Arctic Ekman pumping is organized into seven distinct physical regimes identified using a probabilistic clustering framework applied to a 26-year state estimate. These regimes reflect different combinations of wind, ice, and geostrophic forcing, alongside a residual component that becomes more prominent during seasonal sea-ice transitions. Spatially, the Beaufort Sea is characterized by frequent transitions and persistent ice–geostrophic coupled regimes, whereas the Nordic and Eurasian marginal seas exhibit greater variability in regime stability over time. This regime framework provides a physically grounded link between atmospheric forcing and surface momentum balance, offering a process-based perspective on how changing ice cover may influence Arctic upper-ocean dynamics.