Search for: All records

Abstract. The last glacial period is characterized by a number of millennial climateevents that have been identified in both Greenland and Antarctic ice coresand that are abrupt in Greenland climate records. The mechanisms governingthis climate variability remain a puzzle that requires a precisesynchronization of ice cores from the two hemispheres to be resolved.Previously, Greenland and Antarctic ice cores have been synchronizedprimarily via their common records of gas concentrations or isotopes fromthe trapped air and via cosmogenic isotopes measured on the ice. In thiswork, we apply ice core volcanic proxies and annual layer counting toidentify large volcanic eruptions that have left a signature in bothGreenland and Antarctica. Generally, no tephra is associated with thoseeruptions in the ice cores, so the source of the eruptions cannot beidentified. Instead, we identify and match sequences of volcanic eruptionswith bipolar distribution of sulfate, i.e. unique patterns of volcanicevents separated by the same number of years at the two poles. Using thisapproach, we pinpoint 82 large bipolar volcanic eruptions throughout thesecond half of the last glacial period (12–60 ka). Thisimproved ice core synchronization is applied to determine the bipolarphasing of abrupt climate change events at decadal-scale precision. Inresponse to Greenland abrupt climatic transitions, we find a response in theAntarctic water isotope signals (δ18O and deuterium excess)that is both more immediate and more abrupt than that found with previousgas-based interpolar synchronizations, providing additional support for ourvolcanic framework. On average, the Antarctic bipolar seesaw climateresponse lags the midpoint of Greenland abrupt δ18O transitionsby 122±24 years. The time difference between Antarctic signals indeuterium excess and δ18O, which likewise informs the timeneeded to propagate the signal as described by the theory of the bipolarseesaw but is less sensitive to synchronization errors, suggests anAntarctic δ18O lag behind Greenland of 152±37 years.These estimates are shorter than the 200 years suggested by earliergas-based synchronizations. As before, we find variations in the timing andduration between the response at different sites and for different eventssuggesting an interaction of oceanic and atmospheric teleconnection patternsas well as internal climate variability. 

Abstract. During the last glacial period Northern Hemisphere climate was characterizedby extreme and abrupt climate changes, so-called Dansgaard–Oeschger (DO)events. Most clearly observed as temperature changes in Greenland ice-corerecords, their climatic imprint was geographically widespread. However, thetemporal relation between DO events in Greenland and other regions isuncertain due to the chronological uncertainties of each archive, limitingour ability to test hypotheses of synchronous change. In contrast, theassumption of direct synchrony of climate changes forms the basis of manytimescales. Here, we use cosmogenic radionuclides (¹⁰Be,³⁶Cl, ¹⁴C) to link Greenland ice-core records toU∕Th-dated speleothems, quantify offsets between the two timescales, andimprove their absolute dating back to 45000 years ago. This approach allowsus to test the assumption that DO events occurred synchronously betweenGreenland ice-core and tropical speleothem records with unprecedentedprecision. We find that the onset of DO events occurs within synchronizationuncertainties in all investigated records. Importantly, we demonstrate thatlocal discrepancies remain in the temporal development of rapid climatechange for specific events and speleothems. These may either be related tothe location of proxy records relative to the shifting atmospheric fronts orto underestimated U∕Th dating uncertainties. Our study thus highlightsthe potential for misleading interpretations of the Earth system whenapplying the common practice of climate wiggle matching.