Phasing of Millennial Climate Events and Northeast Atlantic Deep-Water Temperature Change Since 50 ka BP

The observation that Greenland and Antarctic temperatures have followed a specific '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 deepwater (δ¹⁸O_dw) 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 δ¹⁸O_dw 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 δ¹⁸O_dw record with existing reconstructions of millennial sea-level variability, leading to the conclusion that a significant portion of the δ¹⁸O_dw record must represent local hydrographic 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.