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  1. 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 leftmore »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.« less
  2. Water-stable isotopes in polar ice cores are a widely used temperature proxy in paleoclimate reconstruction, yet calibration remains challenging in East Antarctica. Here, we reconstruct the magnitude and spatial pattern of Last Glacial Maximum surface cooling in Antarctica using borehole thermometry and firn properties in seven ice cores. West Antarctic sites cooled ~10°C relative to the preindustrial period. East Antarctic sites show a range from ~4° to ~7°C cooling, which is consistent with the results of global climate models when the effects of topographic changes indicated with ice core air-content data are included, but less than those indicated with themore »use of water-stable isotopes calibrated against modern spatial gradients. An altered Antarctic temperature inversion during the glacial reconciles our estimates with water-isotope observations.

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