Connecting the Greenland ice-core and U∕Th timescales via cosmogenic radionuclides: testing the synchroneity of Dansgaard–Oeschger events

During the last glacial period Northern Hemi-sphere climate was characterized by extreme and abrupt cli-mate changes, so-called Dansgaard–Oeschger (DO) events.Most clearly observed as temperature changes in Greenlandice-core records, their climatic imprint was geographicallywidespread. However, the temporal relation between DOevents in Greenland and other regions is uncertain due to thechronological uncertainties of each archive, limiting our abil-ity to test hypotheses of synchronous change. In contrast, theassumption of direct synchrony of climate changes forms thebasis of many timescales. Here, we use cosmogenic radionu-clides (¹⁰Be,³⁶Cl,¹⁴C) to link Greenland ice-core records toU/Th-dated speleothems, quantify offsets between the twotimescales, and improve their absolute dating back to 45 000years ago. This approach allows us to test the assumptionthat DO events occurred synchronously between Greenlandice-core and tropical speleothem records with unprecedentedprecision. We find that the onset of DO events occurs withinsynchronization uncertainties in all investigated records. Im-portantly, we demonstrate that local discrepancies remain inthe temporal development of rapid climate change for spe-cific events and speleothems. These may either be related tothe location of proxy records relative to the shifting atmo-spheric fronts or to underestimated U/Th dating uncertain-ties. Our study thus highlights the potential for misleadinginterpretations of the Earth system when applying the com-mon practice of climate wiggle matching.