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

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.