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Abstract

The penultimate deglaciation hosts one of the most rapid oceanographic changes compared to the last deglaciation. Further, the European ice sheets attained a regionally extreme extent during the MIS6 compared to the MIS2. This study reconstructed changes in the near-surface and thermocline in the central to northeast Atlantic by analyzing sediments from two IODP sites, U1313 and U1314, drilled on the eastern flank of the mid-Atlantic ridge and Gardar Drift, respectively. Planktonic foraminiferal assemblages, ice-rafted detritus, and oxygen isotopes in Globigerina bulloides and Globorotalia inflata from MIS6 to 5e were analyzed. Warmer and colder sea-surface conditions were marked by a change in the relative abundance of polar, subpolar, and transitional planktonic foraminifers. Oxygen isotopes in G. bulloides and G. inflata suggest that the thermocline deepened at the subtropical Site U1313 during MIS6. The lack of Globorotalia inflata prevented us from profiling the mixed layer and thermocline at the subpolar Site U1314. In contrast to the MIS6, the mixed layer and thermocline were re-stratified during the last interglacial. The lack of major IRD events at both sites suggests the stability of the Laurentide ice sheet during MIS6 compared to the subsequent glaciation. The presence of Heinrich event 11 indicates the discharge of freshwater that freshened the sea surface, resulting in mixing between the mixed layer and thermocline. Our results shed light on the sensitivity of the North Atlantic to freshwater discharge and the following changes with a transition from a penultimate glacial to an interglacial period in the surface circulation.