Temporal offsets between surface temperature, ice-rafting and bottom flow speed proxies in the glacial (MIS 3) northern North Atlantic

Rapid climatic switches during marine isotope stage 3 (29–59 ka BP) are often attributed to ocean circulation changes caused by freshwater input into the North Atlantic through the melting of large amounts of icebergs and sea ice. However, recent studies have questioned this direct coupling between factors influencing the ocean-climate system. By combining multiple proxies from two mid depth northern North Atlantic sediment cores we assess temporal offsets and links between freshwater input and response of the near bottom flow as well as between near bottom flow and sea surface temperatures changes. Grain size, mineralogical and magnetic proxies for ice rafting and near-bottom flow speed, interpreted as indicators of freshwater input and deep circulation strength, consistently indicate a delay in the recovery of the deep circulation after freshwater perturbations.Sea surface temperature variability is inferred from foraminiferal assemblages and Mg/Ca and δ18O of Neogloboquadrina pachyderma s. The records show rapid switches towards higher temperatures following the ice-rafting events. Interestingly, near sea surface temperatures increased and decreased again during periods of accelerating bottom flow speed, likely reflecting the sudden release of heat from deeper in the water column, rather than circulation changes. Our data thus confirm the impact of freshwater forcing on the Atlantic deep circulation, but suggest that temperature variability at the surface was not directly linked to these circulation changes.

► Records of deep- and surface ocean variability during MIS 3 ice-rafting events.
► Delay in recovery of near bottom flow speed after freshwater perturbations.
► Surface temperature oscillations occurred during delayed deep circulation recovery.
► Decoupling between sea surface temperature and deep circulation.