Abstract
Atlantification is an ongoing oceanic phenomenon characterised by the expansion of the typical Atlantic domain towards the Arctic, driving rapid oceanic and ecological changes in the European Arctic. Using reanalyses and a multi-model ensemble of unperturbed and transient preindustrial, historical and future-scenario simulations, this study shows that modern Atlantification possibly initiated in the late nineteenth century, preceded by several "Arctification" episodes in the preindustrial millennium. In the historical period, Atlantification and pan-Arctic warming superposed constructively to drive upper-ocean warming and salinification in the Barents Sea. Modern Atlantification is projected to continue in the next few decades, fully revealing its exceptional character in the context of the past millennium. However, Atlantification halts during the second half of the twenty-first century, decoupling from pan-Arctic warming. The northward expansion of the Atlantic domain is hindered by the onset of a damping mechanism where the Atlantic-Arctic density gradient increases progressively, which sustains a countercurrent by baroclinic adjustment pushing the Arctic polar front southward. As the evolution of this density gradient is intertwined with the retreat of the sea-ice edge, a late-summer ice-free Barents Sea may mark the end of modern Atlantification.