Phase Transition in the Atlantic Surface Currents

The Atlantic surface ocean currents, connecting the atmosphere and the deep ocean currents like the Atlantic Meridional Overturning Circulation (AMOC), plays a central role in regulating Earth’s climate. Yet how large-scale surface currents respond to ongoing climate change remains poorly constrained. Here we identify a previously unrecognized phase of Atlantic surface circulation, termed the Atlantic Convergence–Divergence Mode (ACDM), characterized by a convergence–divergence structure in the North Atlantic and coherent meridional flows in the South Atlantic. We find that the ACDM has experienced a transition evidenced by a systematic weakening of vertical water exchange and meridional flows, with its interannual variability marking a regime shift in 2009, consistent with the RAPID-MOCHA AMOC observations. Our analysis indicates that this shift is driven by AMOC-modulated ocean-atmosphere interactions, including the North Atlantic Oscillation (NAO) and layered ocean heat transport.  We therefore propose the ACDM’s interannual variability as a more sensitive proxy for AMOC at interannual timescales, revealing the coexistence of a gradual multidecadal decrease trend and an abrupt interannual shift in AMOC variability. Moreover, this step-like shift in AMOC also suggests the important role of atmospheric disturbances and reveal that AMOC may be more delicate and closer to tipping point than  than previously anticipated. These findings confirm that AMOC variability can trigger rapid, large-scale transitions in surface circulation, pushing it into a new, weaker phase.