NAO's Strengthened Role in Post‐2004 Kara Sea Ice Growth: Quantifying Thermodynamic and Dynamic Mechanisms

Abstract The sea ice growth (SIG) in the Kara Sea plays a crucial role in the Arctic climate system. Many studies have examined its long‐term trend, but whether its variability has changed is less clear. Using observations and reanalysis data, we observe an intensified interannual variability of the Kara Sea SIG during boreal late winter (December–March) since 2004/2005. This arises from the retreat of active ice production zones in response to the strengthened modulation of the westward‐shifted North Atlantic Oscillation (NAO). Using a sea ice concentration budget, we quantitatively partition the NAO's contribution to total SIG variability post‐2004 (∼63.3%), revealing comparably dominant roles of thermodynamic and dynamic processes. During this period, the negative NAO‐associated surface winds concurrently cool sea surface and export sea ice from the Kara Sea, thereby injecting freshwater into the lower latitudes. Our study advances the understanding of the regional air‐ice‐ocean climate feedbacks in recent Arctic.