Phasing of millennial events and Northeast Atlantic deep-water temperature change since 50 ka BP

The observation that Greenland and Antarctic temperatures have followed a spe- cific ‘asymmetrical’ pattern on millennial time-scales sets rigid constraints on any viable theory of abrupt climate change. The further observation that the very same asymmetry is also reflected in planktonic and benthic δ18O measurements from the Northeast Atlantic has extended this constraint to include a specific response in the ocean. Here we present records of deep-water temperature, δ18O and δ13C variability from the Northeast Atlantic that help to shed light on the links between overturning circulation perturbations, sea-level variability and inter-hemispheric climate change on millennial time-scales. Results indicate that while deep-water temperatures in the Northeast Atlantic have tracked Greenland climate, the δ18O signature of local deep- water (δ18Odw) has varied in a manner more reminiscent of Antarctic temperature variability. The previously identified correspondence of Antarctic warm events with benthic δ18O minima in the Northeast Atlantic is thus found to apply specifically to δ18Odw minima, and to extend beyond Marine Isotope Stage 3 to the entirety of the last 50 ka. It is impossible to reconcile completely the Iberian Margin δ18Odw record with existing reconstructions of millennial sea-level variability, leading to the con- clusion that a significant portion of the δ18Odw record must represent local hydro- graphic change. This is supported by benthic δ13C measurements, which suggest the incursion during Greenland stadials of a colder, low-δ18O and low-δ13C water-mass, of presumed Antarctic origin. These observations confirm a one-to-one coupling of inter-hemispheric climate events with changes in the Atlantic overturning circulation, but fail to rule in or out a unique mechanism by which they were triggered.