Reduced Penetration of Northern‐Sourced Waters Into the South Atlantic During the Last Interglacial Relative to the Holocene

Abstract Specific previous interglacial periods showed millennial‐scale climate variability that influenced deep water formation and circulation. However, our understanding about the spread of deep waters formed in the North Atlantic throughout the South Atlantic during interglacial periods remains limited. To reconstruct South Atlantic deep water geometry and the Atlantic Meridional Overturning Circulation (AMOC) differences between the Last Interglacial (LIG) and the Holocene, we present new authigenic neodymium isotope (ℇ Nd ) and sortable silt (SS) records from the middepth western South Atlantic. The comparison of our results to other Atlantic ℇ Nd records reveals notable variations in the penetration of northern‐sourced waters into the South Atlantic between these two periods. Moderate reduction of northern‐sourced waters entrainment in the western South Atlantic was observed during the onset of the LIG (ca. 128–124 ka) compared to the Holocene, with a significant decrease in the eastward spread of this water mass. This reduction may be linked to freshwater inputs into the North Atlantic, which reduced water density. Counterintuitively, when the AMOC was expected to reach its full interglacial mode at the end of the LIG (ca. 120–116 ka), more radiogenic ℇ Nd values and lower SS values indicated a shallow AMOC. Increased mixing with southern‐sourced waters during the LIG was likely due to decreased deep convection events at the North Atlantic high latitudes due to fresh subsurface water advection. Our findings suggest that the export and mixing ratio between northern‐ and southern‐sourced waters in the South Atlantic are determined by Northern Hemisphere climate during interglacial periods.