Changing interactions between the Pacific Decadal Variability and Atlantic Multidecadal Variability in the past millennium

The Pacific Decadal Variability (PDV) and Atlantic Multidecadal Variability (AMV) are key modes of decadal climate variability. Instrumental records suggest that PDV and AMV can modulate each other, with PDV inducing in-phase AMV shifts, whereas AMV triggering out-of-phase PDV changes. However, what their relationship was in the past millennium remains unknown. Using multiple paleoclimate reconstructions, reanalysis, and model simulations, we analyzed the PDV–AMV interactions in the past millennium. Our results show a robust simultaneous positive correlation between PDV and AMV during the Little Ice Age (1250–1850 CE). This in-phase relationship primarily arises from internal variability, and is reinforced by volcanic eruptions that induce concurrent negative PDV and AMV phases through large-scale circulations and sea-ice feedbacks. This contrasts with modern-day asymmetric PDV/AMV interactions, which may be influenced by regionally heterogeneous evolution of anthropogenic aerosols.