Ventilation decreases during Heinrich stadials in the deep water masses of the western tropical Atlantic

During Heinrich Stadial 1 (HS1), δ¹³C decreased throughout most of the upper North Atlantic between∼ 1000 – 2500 m, and in some deeper South Atlantic sites. Most studies explain the δ¹³C decrease as a response to a weakening of the Atlantic circulation, but the origin and pathway of this poorly-ventilated water mass is still debated. The behavior of intermediate and deep waters during previous Heinrich Stadials is even less well constrained. Here, high-resolution records of the last 45 ka from marine sediment cores off the Brazilian margin are compared with freshwater forcing simulations of the Earth System Model of intermediate complexity iLOVECLIM, using δ¹⁸O as a water mass tracer. Our data reveal a low-δ¹³C water mass at 2300 m during the last four HS. HS1 and HS4 are also marked by decreases in benthic foraminifer δ18O too large to be due to sea level changes alone, suggesting the incursion of warmer and/or fresher waters between 2300 - 3600 m. Model simulations indicate the presence of a southward-flowing, low-δ¹⁸O water mass spreading from the North Atlantic to the tropics, likely transported by the Western Boundary Current. Our results thus suggest that the minimum in ventilation in the Tropics during HS is of northern origin, rather than being related to an expansion of southern waters to shallower depths.