Surface freshening in the subpolar North Atlantic sustaining the weakened AMOC during the late Younger Dryas.

The Younger Dryas (YD) cold event is widely attributed to a disruption of the Atlantic Meridional Overturning Circulation (AMOC), driven by the catastrophic Lake Agassiz flood. While recent studies have pinpointed the source and timing of this meltwater pulse, it remains controversial whether this freshwater event alone could have caused a millennial-scale cold period. Biomarker reconstructions from the Labrador Sea/Baffin Bay reveal an abrupt sea ice decline during the mid-YD, parallel with partial AMOC recovery and enhanced Irminger Current inflow. This warm water incursion may have initiated Heinrich Event 0, likely causing surface freshening in subpolar North Atlantic and subsequently triggering a second AMOC decline during the late YD. Model simulations further support a two-phase AMOC weakening associated with surface freshening during the YD. Our biphasic freshwater injection hypothesis provides fresh insights into the mechanisms driving the YD and underscores the critical role of surface freshening in the subpolar North Atlantic in shaping deglacial abrupt climate changes.