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. Different paleoclimate proxy records evidence repeated abrupt climatetransitions during previous glacial intervals. These transitions are thoughtto comprise abrupt warming and increase in local precipitation over Greenland,sudden reorganization of the Northern Hemisphere atmospheric circulation, andretreat of sea ice in the North Atlantic. The physical mechanism underlyingthese so-called Dansgaard–Oeschger (DO) events remains debated. A recentanalysis of Greenland ice core proxy records found that transitions inNa+ concentrations and δ18O values are delayed byabout 1 decade with respect to corresponding transitions in Ca2+concentrations and in the annual layer thickness during DO events. Thesedelays are interpreted as a temporal lag of sea-ice retreat and Greenlandwarming with respect to a synoptic- and hemispheric-scale atmosphericreorganization at the onset of DO events and may thereby help constrain possible triggering mechanisms for the DO events. However, the explanatorypower of these results is limited by the uncertainty of the transition onsetdetection in noisy proxy records. Here, we extend previous work by testing thesignificance of the reported lags with respect to the null hypothesis that theproposed transition order is in fact not systematically favored. If thedetection uncertainties are averaged out, the temporal delays in theδ18O and Na+ transitions with respect to theircounterparts in Ca2+ and the annual layer thickness are indeedpairwise statistically significant. In contrast, under rigorous propagation ofuncertainty, three statistical tests cannot provide evidence against the nullhypothesis. We thus confirm the previously reported tendency of delayedtransitions in the δ18O and Na+ concentrationrecords. Yet, given the uncertainties in the determination of the transitiononsets, it cannot be decided whether these tendencies are truly the imprint ofa prescribed transition order or whether they are due to chance. The analyzedset of DO transitions can therefore not serve as evidence for systematiclead–lag relationships between the transitions in the different proxies, whichin turn limits the power of the observed tendencies to constrain possiblephysical causes of the DO events.

Significance of uncertain phasing between the onsets of stadial–interstadial transitions in different Greenland ice core proxies