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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. The penultimate deglaciation (PDG, ∼138–128 thousand years before present, hereafter ka) is the transition fromthe penultimate glacial maximum (PGM)to the Last Interglacial (LIG, ∼129–116 ka).The LIG stands out as one of the warmest interglacials of the last 800 000 years (hereafter kyr),with high-latitude temperature warmer than today and global sea level likely higher by at least 6 m.Considering the transient nature of the Earth system,the LIG climate and ice-sheet evolution were certainly influenced by the changesoccurring during the penultimate deglaciation.It is thus importantto investigate, with coupled atmosphere–ocean general circulation models (AOGCMs),the climate and environmental response to the large changesin boundary conditions(i.e. orbital configuration, atmospheric greenhouse gas concentrations, ice-sheet geometry and associated meltwater fluxes) occurring during the penultimate deglaciation. A deglaciation working group has recently been set up as part of the Paleoclimate Modelling Intercomparison Project (PMIP) phase 4, with a protocolto perform transient simulations of the last deglaciation (19–11 ka; although the protocol covers 26–0 ka).Similar to the last deglaciation, the disintegration of continental ice sheets during the penultimate deglaciation led to significant changesin the oceanic circulation during Heinrich Stadial 11 (∼136–129 ka).However, the two deglaciations bear significant differences in magnitude and temporal evolution of climate and environmental changes. Here, as part of the Past Global Changes (PAGES)-PMIP working group on Quaternary interglacials (QUIGS), we propose a protocol to perform transient simulations of the penultimate deglaciationunder the auspices of PMIP4.This design includes time-varying changes in orbital forcing, greenhouse gas concentrations, continental ice sheets as well as freshwater input from the disintegration ofcontinental ice sheets.This experiment is designed for AOGCMs to assessthe coupled response of the climate system to all forcings.Additional sensitivity experiments are proposed to evaluate the response to each forcing.Finally, a selection of paleo-records representing different parts of the climate system is presented, providing an appropriatebenchmark for upcoming model–data comparisons across the penultimate deglaciation.