Deer-Water Temperature Variability During MIS 3: Unravelling the 'Greenland' and 'Antarctic' Signals in Northeast Atlantic d18O

A key criterion for evaluating any theory that proposes to explain millennial climate change is that it account for the apparent asynchrony of past climate variability recorded in Greenland and Antarctica. Based on recent observations, it is also apparent that any such theory must also explain the phasing of oxygen isotope variability recorded in the Northeast Atlantic, which directly mimics the inter-hemispheric asynchrony observed in the ice-cores. On the premise that changes in Northeast Atlantic planktonic d18O have been synchronous with temperature changes recorded in Greenland, changes in Northeast Atlantic benthic d18O therefore appear to have been coupled with temperatures in Antarctica. Failing a clearer picture of what each stable oxygen isotope record actually represents (in terms of glacioeustacy or the temperature and/or d18O of local water-masses) the precise significance of these important observations has remained equivocal, albeit much theorised. Using detailed Mg/Ca and stable isotope measurements in a core from the Northeast Atlantic we have separated the planktonic and benthic d18O records into their temperature and water-d18O components. This allows the proposed correlation of the Northeast Atlantic and Greenland records, as well as the glacioeustatic significance of the planktonic and benthic d18O records, to be re-assessed. It is found that local surface temperature change across the major stadial-interstadial transitions was indeed synchronous with Greenland, and that the 'Antarctic signal'in the benthic d18O record is at least partially attributable to local hydrographic variability rather than glacioeustacy. In addition, while surface- and deep-water temperature changes between Greenland Interstadials (GIS) 14 and 7 appear to be directly coupled, the surface- and deep-water d18O records are neither synchronous nor entirely similar. Furthermore, it appears that Heinrich events 4 and 5 are more structured than the temperature records from the Greenland ice-core records would lead us to believe. We argue that these records reveal a direct coupling between polar front variability, deep-water overturning circulation (shifting deep hydrographic fronts) and inter-hemispheric climate change.