Abrupt weakening of deep Atlantic circulation at the last glacial inception

Deglaciations and glacial inceptions are the two equally important transitional periods that bridge the glacial and interglacial climate states, yet our understanding of deglaciations far exceeds that of glacial inceptions. Substantial variations in deep ocean circulation accompanied the last deglaciation, and model simulations recently suggested that a weakening of the Atlantic Meridional Overturning Circulation (AMOC) also occurred at the last glacial inception (LGI; 113-119 thousand years ago), yet evidence of such a change remains inconclusive. Here, we report three Pa/Th records from the western and central North Atlantic that display an abrupt weakening of the AMOC at the LGI. The magnitude of the reconstructed AMOC weakening approaches but never reaches the level of disruptions associated with the Heinrich ice discharge events. Our results may highlight a unique period of orbitally forced abrupt circulation changes and the importance of ocean processes in setting atmospheric CO₂ changes in motion.