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While a large cryosphere may be a necessary boundary condition for millennial-scale events to persist, a growing body of evidence from previous interglacial periods suggests that high-magnitude climate events are possible during low-cryosphere climate states. However, the full spectrum of variability, and the antecedent conditions under which such variability can occur, have not been fully described. As a result, the mechanisms generating high-magnitude climate variability during low-cryosphere boundary conditions remain unclear. In this study, high-resolution climate records from Deep Sea Drilling Project (DSDP) site 610 are used to portray the North Atlantic climate's progression through low ice, boundary conditions of Marine Isotope Stage (MIS) 11c into the glacial inception. We show that this period is marked by two climate events displaying rapid shifts in both deep overflow and surface climate. The reorganization between Polar Water and Atlantic Water at subpolar latitudes appears to accompany changes in the flow of deep water emanating from the Nordic Seas, regardless of magnitude or boundary conditions. Further, during both intermediate and low ice boundary conditions, we find that a reduction in deep water precedes surface hydrographic change. The existence of surface and deep-ocean events, with similar magnitudes, abruptness, and surface–deep phasing, advances our mechanistic understanding of, and elucidates antecedent conditions that can lead to, high-magnitude climate instability.

High-resolution lithic and sea surface climate records are used to portray the progression of North Atlantic climate, hydrography, and Greenland Ice Sheet (GIS) activity through the peak of Marine Isotope Stage (MIS) 5e into the last glacial inception. We use Eirik Drift sediment core MD03-2664 (57°26.34′N, 48°36.35′W), recovered south of Greenland, strategically located to monitor fluctuations in GIS extent and iceberg calving events. Our results show that a significant amount of ice-rafted debris (IRD) was present during the early MIS 5e, until gradually tapering off by 122 kyr BP due to a diminishing GIS. Sea surface temperatures (SSTs) in the northern subpolar gyre reached peak values early in MIS 5e coinciding with peak insolation. Regional cooling leading to the demise of the last interglacial started prior to the end of the MIS 5e benthic δ18O plateau, at approximately 119 kyr BP, as summer insolation waned. This gradual cooling trend is interrupted by an abrupt and brief cooling episode at ∼117 kyr BP. Increased IRD abundance during the 117 kyr BP cooling event suggests that regional ice sheet growth occurred prior to the end of the MIS 5e benthic δ18O plateau, and the major glacial inception. SSTs south of Greenland followed a two-step cooling during the glacial inception similar to the pattern observed across much of the North Atlantic and Europe. Benthic δ18O increases in parallel, suggesting that this two-step cooling is linked to a two-phased intensification of Northern Hemisphere glaciation. publishedVersion