In this paper, we compare new and published Atlantic sedimentary Pa/Th data with Pa/Th simulated using stream functions generated under various climatic conditions. We show that during Greenland interstadials of the 20–50 ka period, the Atlantic meridional overturning circulation was very different from that of the Holocene. Moreover, southern-sourced waters dominated the Atlantic during Heinrich stadial 2, a slow northern-sourced water mass flowing above 2500 m in the North Atlantic.